🏷

Classifications

Harrison's Part

◆

Subtypes

5

Melancholic Depression

Characterized by anhedonia, psychomotor changes, and diurnal variation.

Atypical Depression

Features mood reactivity, hypersomnia, hyperphagia, and rejection sensitivity.

Psychotic Depression

Depression with hallucinations or delusions.

Seasonal Affective Disorder

Depression recurring in winter months.

Peripartum Depression

Depression during pregnancy or postpartum period.

C

Comorbidities

Major Depressive Disorder <-> Type 2 Diabetes Mellitus

Major Depressive Disorder <-> Vitiligo

◈

Mechanistic Hypotheses

2

Astrocytic FGF13-JIP2-JNK Cell-Death Model

astrocytic_fgf13_jip2_jnk_cell_death_model EMERGING

Evidence balance 4 support

In stress-exposed male mouse hippocampus, reduced astrocytic FGF13 is proposed to permit MAPK8IP2/JIP2-associated JNK activation, shift BAX/BCL2 signaling toward apoptosis, increase inflammation, and reduce synaptic proteins, thereby worsening depression-like behavior. This is a model-supported hypothesis rather than an established human MDD mechanism: the human component is a secondary astrocyte transcriptomic association in an all-male suicide dorsolateral-prefrontal-cortex cohort, and older FHF-IB2 biochemistry instead favored p38delta recruitment over JNK.

Curated as an emerging, model-specific hypothesis only. No new pathophysiology edge or FGF13/JIP2-directed treatment is asserted because adult human target engagement, causal mediation, and safety or efficacy evidence are absent.

Deep research

OpenScientist citations 24 citations 2026-07-26T06:02:04.139259

Show evidence (4 references)

PMID:42421017 SUPPORT Model Organism

"Astrocyte-specific knockout of FGF13 induces astrocytic apoptosis, exacerbates inflammatory levels, and aggravates depression-like behaviors in mice. In contrast, astrocyte-specific overexpression of FGF13 significantly attenuates both astrocyte apoptosis and inflammation, and effectively..."

Bidirectional astrocyte-specific manipulation in stress-exposed mice supports a causal Fgf13-dependent phenotype in the model, but does not by itself establish an endogenous adult human MDD mechanism.

PMID:42421017 SUPPORT In Vitro

"FGF13 regulates apoptosis in primary astrocytes through the JIP2–JNK signaling pathway."

Primary-astrocyte immunoblot experiments (reported at n=4 per group in the supplement) support the proposed signaling chain, although the small neonatal culture system does not establish its operation in adult human astrocytes.

PMID:42421017 SUPPORT Human Clinical

"GSE144136 contains nuclei from the postmortem dorsolateral prefrontal cortex (dlPFC) of 17 healthy controls (HC) and 17 patients with major depressive disorder (MDD) who died by suicide. All subjects were male."

The secondary human transcriptomic analysis provides limited disease association, but its sex, cause-of-death, and cortical-region restrictions do not validate the hippocampal apoptosis mechanism or pathway activity.

+ 1 more reference

Stalled Adult Hippocampal Neurogenesis Model

stalled_adult_hippocampal_neurogenesis_model EMERGING

Evidence balance 3 support

A multiomic postmortem hippocampus study of nonmedicated MDD proposes that adult hippocampal neurogenesis (AHN) is not abolished but stalled: the subgranular-zone neurogenic lineage accumulates quiescent neural stem cells and yields fewer neuroblasts, while the immature granule-cell pool is unchanged. Stress-responsive transcription-factor reprogramming, interferon signalling in early neurogenic stages, a SOX9-associated shift toward glial fate, and loss of neuroblast DCX and BDNF are proposed as the molecular drivers, converging on reduced dentate-gyrus circuit plasticity and hippocampus-dependent cognitive symptoms. The model is EMERGING rather than canonical for two independent reasons: whether AHN persists in the adult human brain at all remains contested, and this cohort cannot separate MDD from suicide pathology because most MDD decedents died by suicide.

Curated from a single postmortem multiomic study (snRNA-seq/snATAC-seq, Visium and Xenium spatial transcriptomics, and bulk hippocampal proteomics; 55 MDD and 68 CTRL donors overall, with smaller per-assay subsets). No treatment is linked to this hypothesis: the study identifies candidate targets but tests none. Cited by DOI because the article had no PubMed record at curation time.

Pathograph links

Stalled Adult Hippocampal Neurogenesis -> Neuroplasticity Deficits INDIRECT KNOWN INTERMEDIATES Intermediates: Fewer newborn neuroblasts with reduced doublecortin and BDNF lower the rate at which new granule cells are added to the dentate gyrus, reducing structural and synaptic plasticity of the trisynaptic circuit.

Neurogenic Niche Interferon Signaling Activation -> Stalled Adult Hippocampal Neurogenesis INDIRECT UNKNOWN INTERMEDIATES Intermediates: Interferon-stimulated gene expression in stem cells and progenitors is proposed to restrain their progression, but the study is cross-sectional and does not establish the direction of this edge.

Stress-Responsive Transcription Factor Reprogramming -> Stalled Adult Hippocampal Neurogenesis INDIRECT KNOWN INTERMEDIATES Intermediates: Stage-specific transcription factors, including the stress-responsive KLF9 acting at the intermediate-progenitor to neuroblast transition, set the chromatin accessibility and gene expression that the neurogenic trajectory depends on.

Show evidence (3 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"We identify a neurogenic lineage in the adult human hippocampal subgranular zone and provide evidence for a stalled neurogenic process in MDD"

States the study's central claim, that a subgranular-zone neurogenic lineage exists in adult human hippocampus and that its progression is stalled in MDD.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"In MDD, there seemed to be halted AHN, with more quiescent progenitors and fewer neuroblasts."

The authors' own summary of the direction of the defect - arrest of progression rather than loss of the stem-cell pool.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Despite increasing evidence that AHN might occur in human adult brain"

The paper's own framing concedes that the existence and clinical relevance of adult human hippocampal neurogenesis is still debated, which is why this is curated as an emerging rather than a canonical model.

?

Discussions and Knowledge Gaps

5

Does the FGF13-MAPK8IP2/JIP2-JNK-BAX/BCL2 apoptosis chain operate endogenously in adult human astrocytes in MDD, or is the reported phenotype specific to a stress model, developmental culture, brain region, sex, or a different JIP2-linked kinase? If astrocyte loss occurs, is this chain a causal driver of neuroinflammation and synaptic dysfunction, a downstream amplifier, or one of several cell-death programs?

HUMAN MODEL MISMATCH OPEN gap_mdd_fgf13_jip2_jnk_human_validity

Attached to

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model pathophysiology#Neuroinflammation pathophysiology#Neuroplasticity Deficits

The seed study provides bidirectional astrocyte-specific Fgf13 perturbation in chronic-restraint- and social-defeat-stress male mice and pathway readouts in neonatal primary mouse astrocytes. Its human component is instead a secondary reanalysis of GSE144136: all 17 MDD donors were male, died by suicide, and contributed dorsolateral prefrontal cortex rather than hippocampus. It neither demonstrates astrocyte death nor measures FGF13 protein, JIP2 activity, phospho-JNK, or BAX/BCL2 target engagement in the same adult human cells. The original dataset emphasized excitatory neurons and oligodendrocyte precursor cells. A 2024 mini-review describes FGF13 as prominently expressed in developing and mature central and peripheral neurons, so the context-specific astrocytic source premise is itself single-sourced to the seed study and requires independent cell-type localization. Human hippocampal findings are region-, marker-, treatment-, and sex-dependent: studies report no major cell-death morphology, increased nonspecific glial packing density, or decreased hilar GFAP-immunoreactive astrocyte density only in unmedicated MDD, with female-specific GFAP area-fraction changes. An independent bulk-frontal-cortex study also found transcript-specific FGF-system dysregulation across MDD cohorts but did not resolve astrocytes. A separate both-sex dlPFC single-nucleus study found broadly similar threshold-free expression patterns but different significant DEG contributors, with astrocytes among the major male contributors; this supports sex-stratified validation but not an FGF13-specific or male-only inference. In male stress-exposed mice, astrocyte-specific Fgf2 manipulation also altered social avoidance through a distinct neurovascular/BBB route, showing that astrocytic FGF and behavioral endpoints are not specific to the FGF13-JIP2 chain. Other stress-mouse studies implicate NLRP3-caspase-1-GSDMD pyroptosis or microglial IL-6/astrocyte IL-6R signaling, and earlier FHF-IB2 biochemistry favored p38delta rather than JNK. Human relevance, cell-death identity, kinase specificity, and causal position therefore remain unresolved; clinical targeting would be premature.

Proposed experiments

Adult human multi-region astrocyte pathway and cell-fate validation

multi-region postmortem molecular pathology study

exp_mdd_fgf13_human_multiregion_validation

In an independently powered postmortem cohort, jointly stratify MDD diagnosis and cause of death (MDD nonsuicide, MDD suicide, psychiatric suicide without MDD, and psychiatrically healthy nonsuicide controls), include both sexes, and sample dorsolateral prefrontal cortex, anterior cingulate cortex, and hippocampus from the same donors where possible. Combine astrocyte-resolved spatial or single-nucleus transcriptomics with RNAscope and multiplex protein/phosphoprotein imaging. Quantify FGF13 isoforms, MAPK8IP2, phospho-JNK/c-Jun, phospho-p38delta, BAX/BCL2, cleaved-caspase-3/TUNEL, NLRP3/GSDMD, IL-6R, astrocyte abundance, and morphology. Pre-register region-by-sex tests and separate marker downregulation or atrophy from irreversible cell death.

Model systems

Multi-region postmortem human MDD brain cohort

Adult human brain tissue balanced across diagnosis, suicide status, and sex and matched on age, postmortem interval, tissue pH, medication exposure, illness duration, and agonal factors.

OTHER

human NCBITaxon:9606

astrocyte CL:0000127

Readouts

Within-astrocyte FGF13-JIP2 stress-kinase state

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Measure FGF13 isoform abundance, MAPK8IP2, phospho-JNK/c-Jun, and phospho-p38delta in spatially identified astrocytes in each region.

spatial transcriptomics multiplex immunofluorescence

Astrocyte fate and cell-death-mode assignment

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Distinguish apoptosis, pyroptosis, reversible atrophy, marker loss, and true numerical depletion using orthogonal cell-fate and stereological measures.

apoptotic process GO:0006915 pyroptotic inflammatory response GO:0070269

design-based stereology terminal deoxynucleotidyl transferase dUTP nick end labeling assay

Controls

Diagnosis-by-suicide factorial controls

MDD nonsuicide and non-MDD psychiatric suicide groups separate diagnosis-associated signals from suicide-associated signals.

Preanalytic and treatment matching

Match or model age, sex, postmortem interval, tissue pH, agonal state, medication exposure, substance use, and illness duration.

Orthogonal astrocyte identity and fate controls

Require multiple astrocyte markers plus stereology so reduced GFAP or RNA recovery is not misclassified as cell death.

Decision criterion

Human relevance is supported only if an independent cohort shows co-occurring lower FGF13, JIP2-linked JNK activation, and apoptotic fate within the same adult astrocytes after adjustment for suicide, medication, preanalytic factors, region, and sex, with a prespecified replication region. A signal restricted to suicide, one sex or one cortical region supports a restricted modifier rather than generalized MDD pathophysiology. Absence or reversal of the within-cell chain, a p38delta- rather than JNK-linked state, or evidence for atrophy/marker loss without apoptosis weakens the hypothesis.

Would support

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Would refute

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Human-astrocyte and adult-mouse FGF13-JIP2 kinase epistasis

cross-species genetic epistasis and rescue experiment

exp_mdd_fgf13_jip2_cross_species_epistasis

Run a preregistered, bidirectional epistasis matrix in sex-balanced human iPSC-derived astrocyte-neuron-microglia tricultures and in adult, inducible astrocyte-specific Fgf13 mice under stressed and unstressed conditions. Compare FGF13 loss with wild-type rescue, overexpression, and an interaction-deficient FGF13 rescue; cross these arms with MAPK8IP2 loss/rescue and selective JNK-versus-p38delta perturbation. In parallel, block IL-6/IL-6R and NLRP3/GSDMD pathways to test whether they are upstream, downstream, or independent. Use blinded allocation and analysis, temporal sampling before cell loss, and mediation analysis linking astrocyte survival to inflammatory, synaptic, network, and behavioral outcomes.

Model systems

Human iPSC-derived astrocyte-neuron-microglia triculture

Multiple male and female donor lines with isogenic edits, matured before glucocorticoid or inflammatory stress and sampled longitudinally.

CO CULTURE

human NCBITaxon:9606

astrocyte CL:0000127 neuron CL:0000540 microglial cell CL:0000129

Adult inducible astrocyte-specific Fgf13 mouse

Both-sex adult inducible loss- and gain-of-function cohorts tested with and without chronic restraint stress, plus a sex-appropriate social-defeat replication.

OTHER

mouse NCBITaxon:10090

astrocyte CL:0000127

Perturbations

Bidirectional FGF13 dosage and domain-specific rescue

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

FGF13 hgnc:3670

Effect: loss, overexpression, wild-type rescue, and JIP2-binding-deficient rescue

MAPK8IP2 genetic epistasis

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

MAPK8IP2 hgnc:6883

Effect: knockout or knockdown followed by wild-type scaffold rescue

JNK-versus-p38delta and alternative-death-pathway discrimination

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Use orthogonal genetic and selective pharmacologic perturbations of JNK and p38delta, plus IL-6/IL-6R and NLRP3/GSDMD blockade, with biochemical target-engagement confirmation.

Readouts

Temporal stress-kinase activation and astrocyte death mode

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Quantify FGF13-JIP2 binding, JNK and p38delta activity, BAX/BCL2, caspase-dependent apoptosis, gasdermin-dependent pyroptosis, and lineage-traced astrocyte survival before and after stress.

apoptotic process GO:0006915 pyroptotic inflammatory response GO:0070269

co-immunoprecipitation assay live-cell lineage imaging

Inflammatory and synaptic mediation

pathophysiology#Neuroinflammation

Measure cytokine release, microglial state, synaptic-protein abundance, neuronal morphology, and multielectrode-array network function; test whether preventing astrocyte death mediates these downstream effects. In the mouse arms, also measure astrocytic Fgf2, endothelial Cldn5, and BBB permeability as a prespecified parallel neurovascular comparator.

cytokine quantification multielectrode array recording blood-brain barrier permeability assay

Stress behavior with specificity controls

pathophysiology#Neuroplasticity Deficits

In mice, combine reward- and social-interaction measures with open-field locomotion, anxiety, pain sensitivity, and stress-hormone readouts so nonspecific performance changes are not called antidepressant effects.

behavioral phenotyping

Controls

Isogenic and vector controls

Use sham-edited isogenic cultures, wild-type littermates, driver-only and vector-only mice, and matched unstressed arms.

Binding-deficient and pathway-specific rescue controls

Compare wild-type FGF13 rescue with a biochemically verified JIP2-binding-deficient rescue and confirm target engagement for each kinase intervention.

Sex, maturation, allocation, and assay controls

Balance sex and donor background, use mature rather than neonatal human astrocytes, randomize and blind mouse studies, and include locomotor and viability controls.

Decision criterion

The proposed chain is supported only if FGF13 loss precedes astrocyte apoptosis in both systems; wild-type but not interaction-deficient FGF13 rescues it; MAPK8IP2 loss and JNK-selective blockade abolish the stress-kinase, death, and downstream phenotypes; and p38delta or alternative death-program perturbations do not better explain the effect. A JIP2-independent rescue, predominant p38delta signaling, dependence on microglial IL-6 or NLRP3/GSDMD, lack of replication in mature human astrocytes, or behavioral change without astrocyte-survival mediation would refute or materially revise the FGF13-JIP2-JNK causal chain. An Fgf2-Cldn5/BBB response without FGF13-JIP2 target engagement supports a parallel neurovascular route and cannot be counted as evidence for the seed chain.

Would support

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model pathophysiology#Neuroinflammation pathophysiology#Neuroplasticity Deficits

Would refute

mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model

Show evidence (13 references)

PMID:42421017 SUPPORT Model Organism

"Astrocyte-specific knockout of FGF13 induces astrocytic apoptosis, exacerbates inflammatory levels, and aggravates depression-like behaviors in mice."

Establishes the mouse causal evidence whose fidelity to adult human MDD astrocytes is the central mismatch.

PMID:39332965 SUPPORT Other

"Similar to other FHFs, FGF13 has been considered a non-secreted protein that lacks an amino signal and is prominently expressed in developing and mature neurons of the central and peripheral nervous systems, as well as the heart."

This mini-review provides canonical expression context rather than direct MDD evidence: prominent neuronal expression makes the seed study's astrocytic source premise independently unreplicated, while not excluding context-specific astrocytic expression.

PMID:32341540 SUPPORT Human Clinical

"Here we used single-nucleus transcriptomics to examine ~80,000 nuclei from the dorsolateral prefrontal cortex of male individuals with MDD (n = 17) and of healthy controls (n = 17)."

Defines the sex-restricted, cross-sectional human dataset reused by the seed study; it cannot separate MDD from suicide or test hippocampal signaling and apoptosis.

+ 10 more references

Excitation-inhibition (E/I) imbalance in prefrontal-cingulate cortices is implicated in MDD pathophysiology, but what are the molecular substrates underlying E/I dysregulation in depression? Are GABAergic, glutamatergic, serotonergic, and opioidergic systems dysregulated primarily (upstream drivers) or secondarily (consequences of other pathophysiology)? How do these neurochemical systems interact to produce measurable E/I imbalance?

KNOWLEDGE GAP OPEN gap_mdd_excitation_inhibition_imbalance_substrates

Attached to

pathophysiology#Excitation-Inhibition Imbalance pathophysiology#Monoamine Deficiency pathophysiology#Neuroplasticity Deficits

Recent neuroimaging studies (Ge et al., 2026) demonstrate that MDD patients show significantly reduced Hurst exponent values (a biophysically confirmed proxy of cortical E/I balance) in parietal and prefrontal-cingulate cortices, with transcriptomic enrichment for neuronal structural organization and mitochondrial function. Neurochemical mapping links E/I dysregulation to GABAergic, opioidergic, serotonergic, and synaptic density distributions. However, critical gaps remain: (1) the causal direction of E/I imbalance relative to monoamine deficiency and HPA-axis dysregulation; (2) whether specific GABA receptor subtypes (α1-α6, β1-β3, γ1-γ3) or glutamate receptor classes (NMDA, AMPA, kainate) are preferentially dysregulated in depression; (3) the role of parvalbumin-positive fast-spiking interneurons and other inhibitory circuits in producing cortical E/I imbalance; and (4) how ketamine's rapid antidepressant effects via NMDA-receptor antagonism mechanistically relate to E/I normalization in treatment-resistant depression. Understanding these substrates could identify new therapeutic targets distinct from monoamine reuptake inhibition.

Proposed experiments

Map GABA and glutamate receptor subtype dysregulation across cortical regions in MDD

postmortem brain tissue analysis

exp_mdd_ei_substrate_specificity

Using postmortem brain tissue from MDD and control subjects, perform multi-region quantification of GABA receptor subtype expression (α1-α6, β1-β3, γ1-γ3) and glutamate receptor class expression (GluN1/GluN2, GluA1-A4, GluK1-K5) via Western blot, qPCR, and in situ hybridization in prefrontal-cingulate cortices. Correlate subtype-specific changes with lifetime depression severity and antidepressant medication history.

Determine whether parvalbumin-positive interneuron dysfunction drives cortical E/I imbalance in depression models

in vivo electrophysiology and optogenetics

exp_mdd_ei_interneuron_circuits

In chronic-stress depression models and acute-stress models, use electrophysiology and optogenetics to measure inhibitory tone from parvalbumin-positive fast-spiking interneurons onto pyramidal neurons. Assess whether targeted optogenetic reactivation of inhibitory circuits restores cortical E/I balance and reverses depression-like behavior. Parallel human studies using MEG/EEG to measure cortical oscillatory power and phase-amplitude coupling as surrogates of interneuron function.

Test whether ketamine's rapid antidepressant effect requires cortical E/I rebalancing

in vivo neuroimaging and electrophysiology during pharmacological intervention

exp_mdd_ketamine_ei_restoration

In acute-stress depression models, measure time-resolved Hurst exponent and cortical E/I balance before, during (minutes to hours), and after ketamine administration. Assess whether E/I normalization precedes or follows behavioral antidepressant effects. Simultaneously measure monoamine levels and HPA-axis markers to determine temporal ordering and mechanistic independence of E/I rebalancing from classical monoamine pathways.

Show evidence (2 references)

PMID:42372880 SUPPORT Human Clinical

"Transcriptomic analysis identified enrichment for neuronal structural organization, nucleic acid metabolism, and mitochondrial function, with preferential overlap with excitatory and inhibitory neuron-specific gene sets."

Multimodal evidence links E/I dysregulation to transcriptomic changes in neuronal structure and energy metabolism, supporting the mechanistic relevance of this imbalance in MDD.

PMID:42372880 SUPPORT Human Clinical

"Divergent group-by-treatment effects were observed in the anterior cingulate and medial prefrontal cortices, with ketamine-induced increases in TRD patients."

The differential effect of ketamine on cortical E/I balance in treatment-resistant depression suggests E/I normalization as a putative mechanism underlying rapid antidepressant action, but the molecular pathway from NMDA antagonism to E/I balance restoration remains unresolved.

Emerging evidence implicates oligodendrocyte (OL) dysfunction and myelin abnormalities in major depressive disorder, extending beyond classical myelination to neural plasticity, neuronal metabolic support, and circuit regulation. Is OL/white-matter pathology a primary driver of MDD, or a secondary consequence of neuroinflammation, chronic stress, and HPA-axis hyperactivity? Which OL subsets and brain regions are most mechanistically relevant, and how does OL-astrocyte-microglia crosstalk causally link to depressive symptoms?

KNOWLEDGE GAP OPEN gap_mdd_oligodendrocyte_dysfunction

Attached to

pathophysiology#Oligodendrocyte Dysfunction and Demyelination pathophysiology#Neuroplasticity Deficits pathophysiology#Neuroinflammation pathophysiology#HPA Axis Dysregulation

Neuroimaging consistently shows white-matter and brain-connectivity alterations in MDD, and post-mortem and animal studies report reduced oligodendrocyte density, downregulated myelin-related genes, and myelin abnormalities. The Gan et al. (2026) review argues that OL dysfunction is a key pathophysiological mechanism in MDD that extends beyond myelination to include contributions to neural plasticity, metabolic support, and circuit regulation, manifesting primarily as myelin abnormalities tied to altered connectivity and emotional processing. What remains unresolved is the causal direction: whether OL/myelin pathology initiates circuit dysfunction and depressive symptoms, or whether it is downstream of neuroinflammation, glucocorticoid excess from HPA-axis hyperactivity, and impaired neuroplasticity. The relative importance of distinct OL populations (mature OLs vs. oligodendrocyte precursor cells) and region-specific contributions (prefrontal cortex vs. hippocampus) is also unknown. Because OLs interact bidirectionally with neurons, astrocytes, and microglia, disentangling OL-glial crosstalk from primary inflammatory signaling is difficult with cross-sectional human data. Resolving these questions would clarify whether remyelination-promoting or OL-protective strategies could serve as disease-modifying treatments rather than symptomatic ones.

Proposed experiments

Region-specific oligodendrocyte manipulation with longitudinal connectivity and behavioral readouts

cell-type-specific perturbation with longitudinal imaging and behavioral phenotyping

exp_mdd_ol_causality_remyelination

In a chronic-stress rodent model of depression, use cell-type-specific genetic and pharmacological tools to (a) deplete or impair mature oligodendrocytes and oligodendrocyte precursor cells in prefrontal cortex versus hippocampus, and (b) conversely promote remyelination, while measuring myelin integrity, neuroinflammatory glial activation, neural circuit connectivity, and depression-like behavior. Pair with a human cohort combining diffusion-MRI white-matter metrics, peripheral inflammatory markers, and longitudinal symptom trajectories to test temporal ordering of white-matter change relative to inflammation and symptom onset.

Readouts

Myelin integrity and white-matter connectivity

pathophysiology#Neuroplasticity Deficits

Quantify myelin sheath thickness, oligodendrocyte density, and white-matter tract connectivity (diffusion imaging) to test whether manipulating OL/myelin alters circuit structure independent of inflammation.

diffusion tensor imaging myelin histopathology

Direction: NEGATIVE

Glial neuroinflammatory activation

pathophysiology#Neuroinflammation

Measure microglial and astrocyte activation and proinflammatory cytokine levels to determine whether OL dysfunction precedes or follows neuroinflammatory signaling.

glial activation immunostaining cytokine quantification

Direction: POSITIVE

Depression-like behavior and symptom trajectory

pathophysiology#HPA Axis Dysregulation

Assess depression-like behavior in animals and longitudinal depressive symptom severity in humans relative to stress/glucocorticoid exposure to test whether OL-targeted intervention modifies outcome.

depression behavioral battery

Direction: NEGATIVE

Decision criterion

OL dysfunction is supported as a primary driver if region-specific OL depletion produces white-matter and depression-like phenotypes before or independent of neuroinflammatory activation, and if remyelination-promoting intervention reverses depressive behavior; it is supported as a secondary consequence if white-matter change consistently follows inflammatory and glucocorticoid signaling and OL manipulation alone does not alter depressive outcomes.

Would support

pathophysiology#Neuroplasticity Deficits pathophysiology#Neuroinflammation

Show evidence (2 references)

PMID:41730818 SUPPORT Other

"Emerging evidence increasingly implicates oligodendrocyte (OL) dysfunction as a key pathophysiological mechanism in MDD, extending beyond their classical role in myelination to include critical contributions to neural plasticity, metabolic support, and circuit regulation."

This review establishes OL dysfunction as an emerging mechanistic hypothesis in MDD that extends beyond myelination, motivating the knowledge gap about its role and causal position.

PMID:41730818 SUPPORT Other

"Finally, we highlight key knowledge gaps and propose future research directions aimed at clarifying the contribution of OL biology to depressive disorders and improving treatment outcomes."

The authors explicitly flag unresolved knowledge gaps and call for research clarifying the contribution of OL biology to depression, directly supporting this KNOWLEDGE_GAP entry.

A large longitudinal cohort supports MDD-to-vitiligo and vitiligo-to-MDD associations, but what accounts for them? Does an acquired, cell-state-specific inflammatory program involving p38-alpha/MAPK14 precede and help cause both conditions, or are the associations better explained by psychosocial effects of visible skin disease, healthcare surveillance, treatment, nonspecific inflammatory burden, shared pleiotropic genetic liability, or parallel disease-specific mechanisms? Is MAPK14 necessary in homologous causal cell states, or merely a cross-tissue bioinformatic marker?

KNOWLEDGE GAP OPEN gap_mdd_vitiligo_shared_immune_dysregulation

Attached to

pathophysiology#Neuroinflammation pathophysiology#Monoamine Deficiency

A UK primary-care cohort found that incident MDD preceded recorded vitiligo (adjusted HR 1.64) and incident vitiligo preceded recorded MDD (HR 1.31 before age 30 and 1.22 at age 30 or older). That establishes a temporal epidemiologic signal, not biological mediation. The study did not measure disease severity, and treatment and healthcare-contact effects remain possible. The cross-disease transcriptomic study is weaker mechanistic evidence: it compared separate MDD and vitiligo expression datasets, used only 15 vitiligo samples and 15 healthy samples in discovery, inferred immune signatures from bulk profiles, and used permissive differential-expression thresholds. It did not analyze an explicitly ascertained comorbid cohort or paired tissues from the same participants. The study did use independent disease-specific GEO validation sets, but discriminator performance does not establish a shared cell state or mediator. Mouse serotonergic-neuron genetics supports p38-alpha in a stress-related behavioral model; a larger human MDD study found no advantage for the tested losmapimod regimen after a smaller prematurely terminated study had favored treatment. Patient-derived nonsegmental-vitiligo keratinocytes and cultured mouse melanocytes support pan-p38 activity in skin models, not MAPK14 specificity. These compartment-, species-, and assay-specific results are compatible with parallel p38 use and do not establish a shared human MAPK14 mechanism. Conversely, bidirectional Mendelian randomization found no significant directional causal effect between generalized vitiligo and broad mental-disorder phenotypes, including depression. That design does not test shared pleiotropic genetic liability. A claims study found a mental-health profile largely comparable to atopic dermatitis. The gap is therefore the mediator and its specificity; the evidence does not justify a new MDD pathophysiology node, MAPK14 biomarker, or conserved mechanism module. A candidate pair-level record is curated in com_Major_Depressive_Disorder__Vitiligo.

Proposed experiments

Adjudicate temporal immune, psychosocial, and surveillance mediation

prospective longitudinal multimodal cohort study

exp_mdd_vitiligo_longitudinal_mediation

Prospectively enroll treatment-naive incident MDD-only, active nonsegmental-vitiligo-only, comorbid, and matched control groups. Reassess structured MDD diagnoses, symptom trajectories, vitiligo subtype, activity, extent and visibility, medication, healthcare utilization, autoimmune disease, smoking, BMI, socioeconomic factors, stress, stigma, and quality of life. At repeated visits profile circulating immune cells by single-cell transcriptomics plus surface proteins and measure cell-type-specific phospho-p38 and cytokines; collect paired lesional and nonlesional skin only from consenting vitiligo participants. Follow the single-disease groups for onset of the second condition and use prespecified time-varying mediation models.

Readouts

Incident second condition and within-person disease trajectories

pathophysiology#Neuroinflammation

Adjudicated incident vitiligo in MDD-only participants and incident MDD in vitiligo-only participants, with repeated measures of both diseases.

Interpretation: Establishes temporal order and distinguishes prediction of transition from cross-sectional correlation.

Cell-state-resolved p38 and inflammatory program

pathophysiology#Neuroinflammation

Phospho-p38, cytokines, and single-cell immune states in blood, aligned to skin states when skin is available.

Interpretation: Tests whether a homologous acquired state precedes both transitions rather than following disease or treatment.

Controls

Matched disease-free controls under equal surveillance

Controls matched on age, sex, site, healthcare-contact schedule, and major measured confounders.

Single-disease comparator groups

MDD-only and vitiligo-only groups permit direction-specific analyses; atopic dermatitis is an optional visible-inflammatory-skin comparator.

Decision criterion

Support a shared acquired mediator only if the same prespecified cell-state-specific p38 program precedes onset of the second condition in both directions, tracks both outcomes within person, and mediates risk after psychosocial, treatment, autoimmune, and surveillance covariates. Prefer a psychosocial explanation if visibility, stigma, or distress predicts MDD without that program; prefer surveillance bias if equalized follow-up materially attenuates the association; classify p38 as a marker if it appears only after disease or treatment.

Would support

pathophysiology#Neuroinflammation Vitiligo:pathophysiology#Autoimmune Reaction

Test cell-specific MAPK14 necessity and rescue in both disease arms

human cell-specific causal perturbation and rescue study

exp_mdd_vitiligo_mapk14_cell_epistasis

Build matched human systems comprising iPSC-derived serotonergic neurons with supporting glia and autologous melanocyte-keratinocyte-cytotoxic T-cell skin cultures from MDD-only, active nonsegmental-vitiligo-only, comorbid MDD-vitiligo, and matched disease-free control donors. First map phospho-p38 to specific cell states and upstream ligands. Then compare MAPK14 CRISPR interference or knockout with a selective p38-alpha inhibitor, non-targeting and vehicle arms, and rescue with CRISPR-resistant wild-type versus kinase-dead MAPK14. Challenge neural cultures with stress/inflammatory ligands and skin cultures with oxidative stress and IFN-gamma-driven immune attack; use blinded, preregistered analysis.

Perturbations

MAPK14 genetic and pharmacologic loss of function

pathophysiology#Neuroinflammation

Cell-type-restricted MAPK14 CRISPR perturbation and selective p38-alpha inhibition in neural, skin, and immune compartments.

Wild-type versus kinase-dead MAPK14 rescue

pathophysiology#Monoamine Deficiency

Isogenic rescue separates on-target catalytic dependence from editing artifacts and scaffold effects.

Readouts

Serotonergic stress response

pathophysiology#Monoamine Deficiency

Serotonin-transporter surface localization and uptake, cytokine release, neuronal activity, and cell viability.

Melanocyte injury and immune attack

Vitiligo:pathophysiology#Autoimmune Reaction

Melanocyte apoptosis and survival, cytotoxic T-cell killing, and CXCL9/CXCL10 pathway readouts.

Controls

Isogenic non-targeting and vehicle controls

Same donor, differentiation batch, ligand exposure, and assay schedule.

Compartment-restricted perturbation controls

Perturb MAPK14 separately in neurons, glia, melanocytes, keratinocytes, and T cells to resolve cell of action.

Decision criterion

A shared causal node requires a reproducible upstream state plus MAPK14 catalytic necessity in both arms, phenotypic rescue by wild-type but not kinase-dead MAPK14, and cross-donor replication. Different upstream signals or causal compartments support parallel context-specific uses of p38 rather than one shared circuit; loss of association after perturbation controls or failure to alter either phenotype classifies MAPK14 as a correlated marker.

Would support

pathophysiology#Monoamine Deficiency Vitiligo:pathophysiology#Autoimmune Reaction

Show evidence (12 references)

PMID:30528503 SUPPORT Human Clinical

"In adjusted models, MDD patients (n = 405,397) were at a 64% increased risk for vitiligo (hazard ratio 1.64"

The large adjusted cohort establishes the MDD-to-vitiligo temporal association but cannot identify its mediator.

PMID:42418414 SUPPORT Computational

"These findings primarily serve to generate hypotheses regarding shared mechanisms and prioritize targets for subsequent experimental validation."

The authors explicitly limit the cross-disease MAPK14 result to hypothesis generation.

PMID:42418414 SUPPORT Computational

"For MDD, the GSE98793 dataset was utilized, which includes 192 whole blood samples: 64 from healthy controls, 128 from patients with MDD, using the GPL570 platform for sequencing. For vitiligo, the GSE65127 and GSE53146 datasets were integrated using the R package ‘sva’ to correct batch effects...."

The analysis combined separate disease datasets and had only 15 vitiligo and 15 healthy samples, rather than paired samples from a comorbid cohort.

+ 9 more references

Is arrested progression of the adult hippocampal neurogenic lineage a causal contributor to MDD, a consequence of the depressed or stressed state, or a correlate of suicide rather than of depression? And is the adult human subgranular-zone lineage on which the claim rests a genuine ongoing neurogenic programme or a persistent immature transcriptional state?

KNOWLEDGE GAP OPEN gap_mdd_stalled_ahn_causality_and_suicide_confound

Attached to

mechanistic_hypotheses#stalled_adult_hippocampal_neurogenesis_model pathophysiology#Stalled Adult Hippocampal Neurogenesis pathophysiology#Neurogenic Niche Interferon Signaling Activation

The evidence is a single cross-sectional postmortem cohort. Three limits matter for how far the mechanism can be pushed. First, direction of causation cannot be recovered from postmortem tissue: interferon activation, transcription-factor reprogramming and the neuroblast deficit are observed together, so the edges into the stalled-neurogenesis node are curated as indirect with undetermined direction. Second, 40 of the 55 MDD decedents died by suicide while no control did, so MDD and suicide pathology are confounded by design in this sample. Third, the existence and magnitude of adult human hippocampal neurogenesis is itself contested; the study's own data show mature granule cells re-expressing immaturity markers in the granule cell layer, which is a dematuration interpretation rather than an ongoing-neurogenesis one, and the immature granule-cell pool was unchanged in MDD.

Proposed experiments

Postmortem cohort separating MDD from death by suicide

mdd_ahn_suicide_deconfounding_cohort

Extend the multiomic hippocampal profiling to a cohort with four groups - MDD decedents who died by suicide, MDD decedents who died of other causes, non-MDD suicide decedents, and neurotypical controls - powered to test the neuroblast deficit and the interferon module separately against diagnosis and against manner of death.

Decision criterion

If the neuroblast deficit tracks MDD diagnosis independently of manner of death, the mechanism belongs to this entry. If it tracks suicide, it belongs on a suicide-related entry and should be removed from here.

Directionality of interferon signalling on human neurogenic progenitors

mdd_ahn_interferon_directionality

Apply type I interferon and interferon blockade to human hippocampal neural stem cell and progenitor cultures or organoids derived from MDD and control donors, measuring progression from quiescent stem cell to neuroblast (nestin, Ki67, ASCL1, DCX, TUBB3) rather than only steady-state marker abundance.

Decision criterion

Interferon exposure that reproduces the stem-cell accumulation and neuroblast deficit would upgrade the interferon-to-neurogenesis edge from indirect with unknown intermediates to a supported causal edge; absence of an effect would make the interferon module a parallel correlate.

In vivo correlate of the neurogenic deficit in living patients

mdd_ahn_living_biomarker

Pair a hippocampus-dependent behavioural assay of pattern separation with dentate-gyrus-resolved imaging in living unmedicated MDD patients and controls, testing whether the behavioural deficit predicted by a stalled neurogenic lineage is present and whether it responds to treatment.

Decision criterion

A treatment-responsive pattern-separation deficit would make the postmortem molecular finding clinically interpretable; its absence would confine the mechanism to a postmortem tissue phenotype.

Recorded as KNOWLEDGE_GAP rather than HUMAN_MODEL_MISMATCH: the evidence is human postmortem tissue, not a model system, so the open question is causation and confounding rather than translational validity.

⚙

Pathophysiology

12

Monoamine Deficiency

Reduced serotonin, norepinephrine, and dopamine neurotransmission in key brain circuits. While oversimplified, this remains a foundation for antidepressant pharmacotherapy.

Serotonergic Neuron CL:0000850 Dopaminergic Neuron CL:0000700 Noradrenergic Neuron CL:0008025

Serotonin Signaling GO:0007210 Dopamine Signaling GO:0007212

Show evidence (3 references)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

This review confirms the neurotransmitter hypothesis as a foundational theory of MDD pathogenesis, though it notes that multiple hypotheses are needed to fully explain the disorder.

PMID:39150594 SUPPORT

"MDD is especially burdensome as approved monoamine antidepressant treatments have weeks-long delays before clinical benefit and low remission rates."

This highlights the clinical reality of monoamine-based treatments, confirming their use while acknowledging their limitations in achieving remission.

PMID:38474387 SUPPORT

"neuroinflammation and gut dysbiosis induce alterations in tryptophan metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related mechanisms, and glutamate-mediated excitotoxicity."

This demonstrates how inflammatory mechanisms contribute to decreased serotonin synthesis, supporting the monoamine deficiency theory while connecting it to broader pathophysiological processes.

Excitation-Inhibition Imbalance

Reduced cortex-wide excitation-inhibition (E/I) balance in prefrontal-cingulate cortices, reflecting dysregulation of GABAergic inhibitory and glutamatergic excitatory neurotransmission. E/I imbalance is implicated in depressive symptoms and ketamine treatment response in treatment-resistant depression.

GABAergic Neuron CL:0000617 Pyramidal Neuron CL:0000598

GABA Signaling GO:0007214 ↕ DYSREGULATED Glutamate Signaling GO:0007215 ↕ DYSREGULATED Synaptic Plasticity GO:0048167 ↕ DYSREGULATED

Show evidence (4 references)

PMID:42372880 SUPPORT Human Clinical

"Patients with MDD demonstrated significantly reduced Hurst exponent values, predominantly encompassing the parietal and prefrontal-cingulate cortices."

Neuroimaging biomarker showing reduced E/I balance in MDD-affected brain regions, using Hurst exponent as a biophysically confirmed proxy of E/I balance.

PMID:42372880 SUPPORT Human Clinical

"Neurochemically, Hurst exponent alterations were spatially associated with GABAergic, opioidergic, serotonergic, and synaptic density distributions."

Cortical E/I imbalance is spatially associated with specific neurochemical systems implicated in depression, including GABAergic, opioidergic, and serotonergic neurotransmission and synaptic density.

PMID:42372880 SUPPORT Human Clinical

"Divergent group-by-treatment effects were observed in the anterior cingulate and medial prefrontal cortices, with ketamine-induced increases in TRD patients."

Ketamine treatment increases cortical E/I balance in treatment-resistant depression, suggesting E/I normalization as a potential mechanism of rapid antidepressant action.

+ 1 more reference

HPA Axis Dysregulation

Hyperactivity of the hypothalamic-pituitary-adrenal axis leads to elevated cortisol, which may contribute to hippocampal atrophy and cognitive symptoms.

Corticotroph CL:0002309

Cortisol Response GO:0071385

Show evidence (1 reference)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

This review identifies the HPA axis hypothesis as one of the widely accepted core pathophysiological mechanisms in MDD.

Neuroplasticity Deficits

Reduced BDNF and impaired synaptic plasticity in prefrontal cortex and hippocampus. Successful treatments restore neuroplasticity.

Neuron CL:0000540

Synaptic Plasticity GO:0048167

Show evidence (5 references)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

This comprehensive review identifies the neuroplasticity hypothesis as one of the core accepted mechanisms in MDD pathogenesis.

PMID:39150594 SUPPORT

"This narrative review provides a high-level overview of glutamate signaling in synaptogenesis and neural plasticity and the implications of glutamate dysregulation in depression."

This demonstrates the link between glutamate signaling, synaptogenesis, and neural plasticity deficits in depression, supporting the neuroplasticity deficit mechanism.

PMID:38474387 SUPPORT

"neuroinflammation and gut dysbiosis induce alterations in tryptophan metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related mechanisms, and glutamate-mediated excitotoxicity."

This shows how inflammatory processes lead to impairments in neuroplasticity-related mechanisms, connecting inflammation to neuroplasticity deficits in MDD.

+ 2 more references

Neuroinflammation

Elevated inflammatory cytokines (IL-6, TNF-alpha, CRP) observed in depression. Inflammation may contribute to monoamine depletion and neuroplasticity deficits.

Microglia CL:0000129

Show evidence (4 references)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

This review identifies the cytokine hypothesis as one of the widely accepted theories of MDD pathogenesis, supporting the role of inflammatory mechanisms.

PMID:38474387 SUPPORT

"The involvement of central and peripheral inflammation in the pathogenesis and prognosis of major depressive disorder (MDD) has been demonstrated. The increase of pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, IL-18, and TNF-α) in individuals with depression may elicit neuroinflammatory..."

This provides direct evidence for elevated pro-inflammatory cytokines in MDD and their role in eliciting neuroinflammatory processes.

PMID:38474387 SUPPORT

"mechanisms that, in turn, can contribute to gut microbiota dysbiosis. Together, neuroinflammation and gut dysbiosis induce alterations in tryptophan metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related mechanisms, and glutamate-mediated excitotoxicity."

This demonstrates how neuroinflammation contributes to both monoamine depletion (decreased serotonin) and neuroplasticity deficits, confirming the description's mechanistic links.

+ 1 more reference

Mitochondrial Dysfunction

Impaired mitochondrial respiration and cellular energy metabolism contribute to MDD pathophysiology. Patient-derived cells show decreased mitochondrial function, altered membrane potential, and disrupted calcium homeostasis.

Show evidence (3 references)

PMID:38256041 SUPPORT

"The link between mitochondria and major depressive disorder (MDD) is increasingly evident, underscored both by mitochondria's involvement in many mechanisms identified in depression and the high prevalence of MDD in individuals with mitochondrial disorders."

This establishes the connection between mitochondrial dysfunction and MDD, noting both mechanistic involvement and epidemiological evidence.

PMID:38256041 SUPPORT

"Similarities were observed between the Mito patient and a broader MDD cohort, including decreased respiration and mitochondrial function."

This provides direct evidence from patient-derived cells showing decreased mitochondrial respiration and function in MDD patients.

PMID:38256041 SUPPORT

"the Non-R patient's data offered a new perspective on MDD, suggesting a detrimental imbalance in mitochondrial and cellular processes, rather than simply reduced functions."

This suggests that mitochondrial dysfunction in MDD may involve complex imbalances beyond simple reduction, including altered respiratory rates and calcium homeostasis.

Reference Point Dysregulation

Pathological elevation and inflexibility of the decisional reference point, a core mechanism from behavioral economics that determines how events are experienced as positive or negative. Elevated reference points cause previously rewarding activities to be experienced as aversive, contributing to anhedonia and reward dysfunction. Dysfunction in anterior cingulate cortex impairs dynamic adjustment of the reference point to environmental changes.

Neuron CL:0000540

Cognition GO:0050890

Show evidence (4 references)

PMID:42150067 SUPPORT

"A pathological elevation of the reference point would lead a person to experience once pleasurable activities as negative reinforcers."

This describes how pathological reference point elevation in MDD directly causes anhedonia by transforming reward into punishment.

PMID:42150067 SUPPORT

"depression is associated with a significant elevation of the reference point, and the magnitude of this elevation correlates with disease severity."

This provides direct evidence linking elevated reference points to depression severity in MDD patients.

PMID:42150067 SUPPORT

"The ability of patients with MDD to dynamically adjust their reference point to the environment is also dysfunctional."

This demonstrates that MDD patients show impaired cognitive flexibility in adapting reward valuation to environmental context.

+ 1 more reference

Oligodendrocyte Dysfunction and Demyelination

Oligodendrocyte (OL) dysfunction and myelin abnormalities contribute to depression pathophysiology through multiple mechanisms: impaired myelination reduces conduction velocity and disrupts neural circuit function; loss of OL-derived metabolic support decreases neuronal energy supply; compromised OL-glial crosstalk with microglia and astrocytes amplifies neuroinflammation. These dysfunctions are associated with altered brain connectivity and emotional processing deficits, and may represent a targetable node for therapeutic remyelination strategies.

Oligodendrocyte CL:0000128 Oligodendrocyte Precursor Cell CL:0002453 Neuron CL:0000540 Microglia CL:0000129 Astrocyte CL:0000127

Myelination GO:0042552 ↓ DECREASED Synaptic Plasticity GO:0048167 ↓ DECREASED Axon Ensheathment GO:0008366

Downstream

Neuroplasticity Deficits

Neuroinflammation

Show evidence (3 references)

PMID:41730818 SUPPORT Other

"Emerging evidence increasingly implicates oligodendrocyte (OL) dysfunction as a key pathophysiological mechanism in MDD, extending beyond their classical role in myelination to include critical contributions to neural plasticity, metabolic support, and circuit regulation."

This establishes OL dysfunction as a key pathophysiological mechanism in MDD that extends beyond myelination to encompass neural plasticity and metabolic support functions.

PMID:41730818 SUPPORT Other

"Such dysfunctions manifest primarily as myelin abnormalities and are closely associated with depression-related alterations in brain connectivity and emotional processing."

This demonstrates the functional consequences of OL dysfunction, linking myelin abnormalities to altered brain connectivity and emotional processing deficits central to depression.

PMID:41730818 SUPPORT Other

"with particular emphasis on their interactions with neurons, astrocytes, and microglia within the central nervous system"

This directly supports the OL-glial crosstalk mechanism described in this node, confirming that oligodendrocyte dysfunction involves disrupted interactions with astrocytes and microglia in MDD.

Stalled Adult Hippocampal Neurogenesis

In nonmedicated MDD, the subgranular-zone (SGZ) neurogenic lineage of the dentate gyrus shows a shift in pseudotime distribution toward quiescent neural stem cells with fewer neuroblasts, indicating arrested progression rather than depletion of the stem-cell pool. Histological validation finds fewer nestin- and Ki67-expressing SGZ cells and fewer DCX/TUBB3 co-expressing dentate cells, while the immature granule-cell (ImGC2) pool is unchanged. Intermediate progenitors upregulate SOX9, favouring a neuron-to-glia switch, and the residual neuroblasts lose doublecortin and BDNF.

Stalled Adult Hippocampal Neurogenesis Model

Quiescent hippocampal neural stem cell CL:0000047 Intermediate neural progenitor CL:0011020 Neuroblast CL:0000031 Dentate gyrus granule cell CL:0001033 Subgranular zone niche astrocyte CL:0000127

Adult hippocampal neurogenesis GO:0022008 ↓ DECREASED Neuroblast proliferation GO:0007405 ↓ DECREASED Neural stem cell quiescence ↑ INCREASED Neuron-to-glia fate switch GO:0010001

Downstream

Neuroplasticity Deficits

Show evidence (7 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Pseudotime analysis of the neurogenic trajectory comparing MDD and CTRL showed a shift in cell distribution in MDD marked by more NSCa and fewer NBs"

Single-nucleus trajectory inference shows the lineage accumulating at the quiescent neural stem cell stage with fewer neuroblasts, the primary observation behind this node.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"suggesting impaired neurogenic progression rather than depletion of stem-like cells"

Fixes the direction of the claim - progression through the lineage is arrested, the stem-cell compartment is not exhausted.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Validation studies showed fewer SGZ cells expressing nestin and Ki67 proteins in MDD compared to CTRL"

Protein-level validation independent of the sequencing readout, consistent with fewer activated, proliferating stem cells in the subgranular zone.

+ 4 more references

Neurogenic Niche Interferon Signaling Activation

Early neurogenic stages in the MDD hippocampus - quiescent and activated neural stem cells and intermediate neural progenitors - upregulate a gene module enriched for interferon-related pathways (EIF2AK2, IFIT3, HERC6, NRIR, IFITM3, MX1). The same interferon programme is raised in mature granule cells and CA1-4 excitatory neurons, making it a hippocampus-wide rather than niche-restricted signal. Several of the genes involved carry variants associated with intellectual disability, Alzheimer disease, systemic lupus erythematosus and COVID-19, which the authors read as shared pathogenetic mechanisms rather than as MDD-specific.

Stalled Adult Hippocampal Neurogenesis Model

Quiescent and activated neural stem cell CL:0000047 Intermediate neural progenitor CL:0011020 Dentate gyrus granule cell CL:0001033

Type I interferon signaling GO:0060337 ↑ INCREASED

Downstream

Stalled Adult Hippocampal Neurogenesis

Neuroinflammation

Show evidence (3 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"At early neurogenic stages (NSCa, NSCb and INP) MDD had higher expression of a gene module enriched with interferon-related pathways"

Locates the interferon signal at the stem-cell and progenitor stages of the lineage, which is where the trajectory stalls.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"revealed eight different interferon-related genes disrupted in MDD NSCa, NSCb, INP and ImGC1"

Gene-level differential expression confirming the module result across four neurogenic clusters.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Consistent with the neurogenic clusters, interferon signaling was upregulated in GC1 and ExN1.CA1-4.FIBCD1, including ISG15, MX1, CXCL12"

Shows the same interferon programme in mature granule cells and CA excitatory neurons, so the signal is hippocampus-wide and links this node to the existing neuroinflammation mechanism.

Stress-Responsive Transcription Factor Reprogramming

Chromatin accessibility and transcription-factor footprinting in MDD hippocampus show altered binding activity of stress- and corticosteroid-responsive Kruppel-like factors (KLF9, KLF15) alongside EGR and ASCL1 family factors, in granule cells, CA1-4 excitatory neurons and PENK+ inhibitory neurons. Footprint changes track expression of target genes and their proteins (HPCAL1, KRAS, CAMKV, RAB6B, HOMER1), tying epigenetic regulation to the neurogenic and trisynaptic-circuit phenotypes. MDD donors in this cohort had significantly higher recent stress exposure than controls.

Stalled Adult Hippocampal Neurogenesis Model

Transcription factor binding and target gene regulation GO:0006355 ↕ DYSREGULATED Chromatin accessibility GO:0006325 ↕ DYSREGULATED

Downstream

Stalled Adult Hippocampal Neurogenesis

Excitation-Inhibition Imbalance

Show evidence (3 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"The MDD hippocampus shows altered TF activity affecting chromatin accessibility and expression of genes involved in intracellular trafficking, spines, cell adhesion, telomeres and cellular aging."

States the transcription-factor and chromatin-accessibility finding and the functional classes of the affected target genes.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"TFs regulated neurogenesis and the trisynaptic circuit in individuals with MDD, who had higher severity of stress exposure in the last 6 months before death compared to CTRL individuals."

Connects the transcription-factor changes to both downstream targets in this entry and to the measured stress exposure that makes these factors stress-responsive.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Excitatory and inhibitory neurons show dysregulation of transcription factor networks affecting cell states."

Extends the transcription-factor network disruption beyond the neurogenic lineage to the mature excitatory and inhibitory populations of the circuit.

PENK+ GABAergic Interneuron Activation

A PENK+ medium-spiny-neuron-like GABAergic population, not previously described in the human hippocampus, is the most transcriptionally dysregulated cell cluster in MDD. It overexpresses proenkephalin together with immediate-early genes (ARC, FOS, JUNB, EGRs, JAG1) and shows altered vesicle, dendritic-spine and adhesion genes plus elevated HTR1D, a profile the authors read as an activated state possibly compensating for a stress-hyperactivated dentate gyrus. It is offered as a link between MDD, chronic pain, stress response and emotional regulation.

PENK+ medium spiny neuron-like GABAergic interneuron CL:0011005

GABAergic neurotransmission GO:0051932 ↕ DYSREGULATED Neuronal activity-dependent immediate-early gene expression GO:0006355 ↑ INCREASED

Downstream

Excitation-Inhibition Imbalance

Show evidence (3 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"The PENK+ GABAergic medium-spiny neuron-like cluster (InN5.PENK) had 566 DEGs, the most compared to the other cell clusters, followed by GC1 with 378, and ExN1.CA1-4.FIBCD1 with 147."

Quantifies the claim that this inhibitory population is the most dysregulated cell cluster in the MDD hippocampus.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Unique to InN5.PENK was overexpression of proenkephalin, a precursor of enkephalins, which modulate pain perception, stress responses and emotional regulation, as well as immediate-early genes ARC, FOS, JUNB, EGRs, and JAG1, upregulated with neuronal activity and cell development."

Provides the proenkephalin and immediate-early gene signature that defines the activated state annotated on this node.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"Therefore, InN.PENK might be attempting to compensate for a stress-hyperactivated DG."

The compensatory interpretation is explicitly hedged by the authors, so this edge is curated as a proposal rather than an established direction of causation.

⬡

Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

●

Phenotypes

8

Digestive 1

Poor Appetite FREQUENT HP:0004396

Decreased or increased appetite

Nervous System 6

Depressed Mood VERY_FREQUENT Depression HP:0000716

Anhedonia VERY_FREQUENT HP:0012154

Loss of interest or pleasure

Sleep Disturbance VERY_FREQUENT HP:0002360

Insomnia or hypersomnia

Concentration Difficulties FREQUENT Cognitive impairment HP:0100543

Psychomotor Changes OCCASIONAL Agitation HP:0000713

Psychomotor agitation or retardation. The ontology term captures the agitation pole; psychomotor retardation currently lacks a non-obsolete HPO term.

Memory Impairment HP:0002354

No frequency is asserted. The cited study characterizes memory dysfunction as a feature of MDD but reports no cohort frequency for it.

Show evidence (2 references)

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"MDD is a major global health burden presenting with mood, neurovegetative, and cognitive symptoms, including memory recall bias toward negative content, a cognitive marker of depression severity"

Establishes memory-recall bias as a cognitive feature of MDD that scales with severity.

DOI:10.1038/s41591-026-04571-8 SUPPORT Human Clinical

"To determine the underpinnings of reduced hippocampus circuit plasticity and weakened memory functions in MDD"

Frames weakened memory function as the clinical phenotype the hippocampal molecular changes are intended to explain.

Constitutional 1

Fatigue VERY_FREQUENT HP:0012378

🧬

Genetic Associations

5

SLC6A4 (Risk Factor)

Gene: SLC6A4 hgnc:11050

BDNF (Risk Factor)

Gene: BDNF hgnc:1033

FKBP5 (Risk Factor)

Gene: FKBP5 hgnc:3721

HTR2A (Risk Factor)

Gene: HTR2A hgnc:5293

IL1B (Severity modifier and antidepressant-response marker, not an established susceptibility locus. For the C-511T (rs16944) variant the CC genotype is associated with greater MDD symptom severity and the TT genotype with antidepressant treatment response; the source review states these two associations are not equivalent in terms of susceptibility to disease onset.)

Gene: IL1B hgnc:5992 relationship_type: MODIFIER

Show evidence (3 references)

PMID:42450240 SUPPORT Human Clinical

"the CC genotype was more frequently associated with greater MDD symptom severity, whereas the TT genotype was predominantly associated with antidepressant treatment response"

Systematic review of the IL1B C-511T variant reporting distinct clinical outcomes by genotype: symptom severity for CC and antidepressant treatment response for TT.

PMID:42450240 SUPPORT Human Clinical

"thus, these associations should not be considered equivalent in terms of susceptibility to disease onset"

The same review explicitly declines to treat the severity and treatment-response findings as evidence of susceptibility to MDD onset, which is why this gene is curated as a MODIFIER rather than a risk factor.

PMID:42450240 SUPPORT Human Clinical

"other studies have found no significant association between this genetic variant and MDD"

Counterweight from the same review documenting non-replication, recorded so the association is not read as settled.

Variants (1)

C-511T

Gene: IL1B

Also known as: rs16944

Identifiers: dbSNP:rs16944

💊

Medical Actions

9

Selective Serotonin Reuptake Inhibitors (SSRIs)

Action: SSRI therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: sertraline CHEBI:9123 escitalopram CHEBI:36791 fluoxetine CHEBI:5118

First-line pharmacotherapy (sertraline, escitalopram, fluoxetine).

Mechanism Target:

MODULATES Monoamine Deficiency — SSRIs block presynaptic serotonin reuptake, raising synaptic serotonin and correcting the monoaminergic deficit implicated in depression.

Show evidence (2 references)

PMID:39150594 SUPPORT

"MDD is especially burdensome as approved monoamine antidepressant treatments have weeks-long delays before clinical benefit and low remission rates."

This confirms the clinical use of monoamine antidepressants while acknowledging their limitations in terms of delayed benefit and incomplete remission.

PMID:42066210 SUPPORT Other

"In acute treatment, selective serotonin reuptake inhibitors (SSRIs), venlafaxine, mirtazapine, and vortioxetine showed consistent evidence across efficacy and tolerability outcomes."

The Brazilian Psychiatric Association guidelines find consistent efficacy and tolerability evidence for SSRIs in acute treatment of major depressive disorder.

Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)

Action: SNRI therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: venlafaxine CHEBI:9943 duloxetine CHEBI:36796

Venlafaxine, duloxetine for depression with pain or fatigue.

Mechanism Target:

MODULATES Monoamine Deficiency — SNRIs inhibit reuptake of both serotonin and norepinephrine, augmenting monoaminergic neurotransmission across the deficient monoamine systems.

Cognitive Behavioral Therapy

Action: cognitive behavioral therapy Ontology label: Cognitive Behavior Therapy NCIT:C64345

Evidence-based psychotherapy, comparable efficacy to medications.

Electroconvulsive Therapy

Action: electroconvulsive therapy Ontology label: Electroconvulsive Therapy NCIT:C93303

Most effective treatment for severe or treatment-resistant depression.

Mechanism Target:

MODULATES Neuroplasticity Deficits — ECT robustly induces neurotrophic signaling and hippocampal neuroplasticity, counteracting the reduced-BDNF/plasticity deficit of depression.

Ketamine/Esketamine

Action: ketamine/esketamine therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: ketamine CHEBI:6121 esketamine CHEBI:60799

Rapid-acting treatment for treatment-resistant depression.

Mechanism Target:

MODULATES Excitation-Inhibition Imbalance — Ketamine/esketamine antagonize the NMDA glutamate receptor, triggering a rapid glutamatergic surge and synaptogenesis that rebalances the excitatory-inhibitory tone — the basis of its rapid-acting antidepressant effect.

Show evidence (1 reference)

PMID:39150594 SUPPORT

"Based on this preclinical evidence implicating glutamate in depression and the rapid improvement of depression with ketamine treatment in a proof-of-concept trial, a range of N-methyl-D-aspartate (NMDA)-targeted therapies have been investigated."

Ketamine's rapid antidepressant action is mediated through NMDA-receptor (glutamatergic) modulation, targeting excitation-inhibition imbalance.

Show evidence (3 references)

PMID:39150594 SUPPORT

"Nasal administration of esketamine (Spravato®) was approved by the US Food and Drug Administration (FDA) in 2019 to treat adults with treatment-resistant depression and in 2020 for adults with MDD with acute suicidal ideation or behavior."

This confirms FDA approval of esketamine for treatment-resistant depression and acute suicidal ideation/behavior in MDD.

PMID:39150594 SUPPORT

"Based on this preclinical evidence implicating glutamate in depression and the rapid improvement of depression with ketamine treatment in a proof-of-concept trial, a range of N-methyl-D-aspartate (NMDA)-targeted therapies have been investigated."

This explains the mechanistic basis for ketamine's rapid-acting antidepressant effects through NMDA receptor antagonism and glutamate modulation.

PMID:39150594 SUPPORT

"Oral combination dextromethorphan-bupropion (AXS-05, Auvelity® extended-release tablet) was FDA approved in 2022 for the treatment of MDD in adults."

This documents the approval of another glutamatergic modulator for MDD treatment, expanding treatment options beyond esketamine.

Transcranial Magnetic Stimulation

Action: transcranial magnetic stimulation Ontology label: Transcranial Magnetic Stimulation NCIT:C116655

Non-invasive neuromodulation for treatment-resistant depression.

Mechanism Target:

MODULATES Neuroplasticity Deficits — Repetitive TMS of dorsolateral prefrontal cortex modulates cortical excitability and promotes synaptic plasticity in mood-regulating circuits.

Lithium Augmentation

Action: Pharmacotherapy NCIT:C15986

Agent: lithium carbonate CHEBI:6504

Adjunctive lithium added to an antidepressant is an evidence-based augmentation strategy for treatment-resistant depression, sharing the mood-stabilizer mechanism used first-line in bipolar disorder.

Mechanism Target:

MODULATES Neuroplasticity Deficits — Lithium augments serotonergic antidepressant response and enhances neurotrophic/neuroplastic signaling (GSK-3 inhibition, BDNF induction), the same mood-stabilizing mechanism it exerts in bipolar disorder.

Show evidence (1 reference)

PMID:34986373 SUPPORT Human Clinical

"Our findings from the NMA for response rates, compared to placebo, were significant for: liothyronine, nortriptyline, aripiprazole, brexpiprazole, quetiapine, lithium, modafinil, olanzapine (fluoxetine), cariprazine, and lisdexamfetamine."

Network meta-analysis found lithium augmentation produced a statistically significant improvement in response rate versus placebo in treatment-resistant major depression.

Behavioral Activation

Action: behavioral activation Ontology label: Behavioral Intervention NCIT:C15184

Increasing engagement in rewarding activities.

Psilocybin-Assisted Therapy

Action: psilocybin-assisted therapy Ontology label: Pharmacotherapy NCIT:C15986

Agent: psilocybin CHEBI:8614

Investigational single-dose psilocybin (25 mg) with psychological preparation, dosing support and integration, evaluated in a feasibility RCT in treatment-resistant depression at a single NHS site in England.

Mechanism Target:

MODULATES Neuroplasticity Deficits — Hypothesized mechanism: psychedelic 5-HT2A agonists such as psilocybin have been proposed to promote synaptic plasticity and neurotrophic signaling, which would counter the impaired neuroplasticity implicated in depression. The cited feasibility trial reports no mechanistic data, so this link is currently a hypothesis rather than an evidenced claim for this disorder.

Show evidence (4 references)

PMID:42562964 SUPPORT Human Clinical

"Eligible participants met Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for major depressive disorder and had an inadequate response to ≥2 antidepressant treatments or ≥1 antidepressant plus ≥1 psychotherapy. Participants received 25-mg psilocybin or..."

Study design confirms psilocybin-assisted therapy for treatment-resistant depression (defined as inadequate response to ≥2 antidepressants or ≥1 antidepressant + ≥1 psychotherapy) with standardized administration and psychological support.

PMID:42562964 SUPPORT Human Clinical

"The adjusted between-group difference at week 3 on the MADRS was -10.41 (95% confidence interval: -14.86 to -5.95; Cohen's d = -1.70), favoring psilocybin, which was sustained at week 6."

The feasibility trial estimated a large between-group MADRS difference at week 3 (-10.41; Cohen's d = -1.70) favoring psilocybin, sustained at week 6. Primary outcomes were recruitment, retention and MADRS variance estimation, so this is an effect-size estimate from a single NHS site and not a powered efficacy result; the authors conclude it supports a future confirmatory trial.

PMID:42562964 SUPPORT Human Clinical

"Sixty participants were randomized (1:1), balanced by age, sex and prior psilocybin exposure, and 59 of 60 participants completed the MADRS at all follow-up visits."

High retention (59/60 participants, 98%) across 6-week follow-up period supports feasibility and tolerability of the single-dose psilocybin-assisted therapy protocol in treatment-resistant depression.

+ 1 more reference

🌍

Environmental Factors

4

Childhood Trauma

Strong risk factor for adult depression, and additionally for an earlier onset and a more chronic or treatment-resistant course.

Show evidence (1 reference)

PMID:27908895 SUPPORT Human Clinical

"Childhood maltreatment, especially emotional abuse and neglect, represents a risk factor for severe, early-onset, treatment-resistant depression with a chronic course"

Meta-analysis of 184 studies; maltreated individuals were 2.66 to 3.73 times more likely to develop adult depression, and twice as likely to develop a chronic or treatment-resistant course.

Chronic Stress

Major precipitant

Show evidence (1 reference)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

The review lists the HPA-axis hypothesis but does not itself assert a stress-to-depression relationship; it supports chronic stress as a precipitant only indirectly via the HPA axis.

Substance Abuse

Bidirectional relationship. The evidence is for alcohol dependence specifically - non-dependent drinking, including binge drinking, did not predict depressive episodes in the cohort below.

Show evidence (2 references)

PMID:22987574 SUPPORT Human Clinical

"Associations between alcohol consumption and MDE were not observed except when dependence was indicated. Alcohol dependence increased the risk of MDE, and MDE increased the risk of alcohol dependence, but only in men"

Twelve-year Canadian National Population Health Survey cohort. Evidences both directions, and its finding that the association held only for dependence is the qualification added to the note.

PMID:24246605 SUPPORT Human Clinical

"adolescent AUD predicted early adult MDD, while early adult MDD predicted adult AUD"

Prospective study of 816 participants interviewed at ages 16, 17, 24 and 30. Shows the bidirectionality is developmentally staged rather than simultaneous.

🔬

Biochemical Markers

3

Cortisol (Elevated)

Context: HPA axis hyperactivity

Show evidence (1 reference)

PMID:38331979 SUPPORT

"The currently widely accepted theories of MDD pathogenesis include the neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA) axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic influence hypothesis"

The review lists the HPA-axis hypothesis among accepted MDD theories; it names the axis but does not itself report that cortisol is elevated, so this supports the mechanism only indirectly.

BDNF (Decreased)

Context: Reduced neuroplasticity marker

Show evidence (1 reference)

PMID:38474387 SUPPORT

"neuroinflammation and gut dysbiosis induce alterations in tryptophan metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related mechanisms, and glutamate-mediated excitotoxicity."

The snippet describes impaired neuroplasticity-related mechanisms generally but does not mention BDNF specifically, so it supports the decreased-BDNF claim only indirectly.

Inflammatory Markers (Elevated)

Context: IL-1β, IL-6, IL-18, CRP, TNF-alpha

Show evidence (2 references)

PMID:38474387 SUPPORT

"The increase of pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, IL-18, and TNF-α) in individuals with depression may elicit neuroinflammatory processes and peripheral inflammation"

This directly confirms elevated pro-inflammatory cytokines including IL-1β, IL-6, IL-18, and TNF-α in MDD patients, and links that increase to neuroinflammatory and peripheral inflammatory processes.

PMID:42450240 SUPPORT Other

"a regulatory cytokine of the immune and nervous systems that acts on several processes, including mood regulation"

Separate source for the mood-regulation role of IL-1β specifically, which the PMID:38474387 snippet above does not itself state. This is the review's background characterization of IL-1β biology rather than a study result, hence evidence_source OTHER.

📊

Related Datasets

6

Age-related transcriptomic differences in peripheral blood of adolescents with major depressive disorder geo:GSE255685

In this study, we collected peripheral blood samples of a typical large population, including MDD cases and healthy controls from children and adolescents, and aimed to apply RNA-seq sequencing to comprehensively analyze the transcriptomic characteristics in adolescent depression patients. In comparison to healthy patients, we discovered that several immune response-associated genes were dysregulated in MDD patients, with the majority of these differential genes strongly correlated with the HAMD-17 and HAMA scores.

human BULK RNA SEQ n=279

PMID:41740874

Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.

Epigenetic profiling of neuronal and non-neuronal signal in major depressive disorder geo:GSE149871

Characterization of cell type specific (NeuN+/NeuN-) open chromatin by ATAC-seq assay in orbitofrontal cortext of postmortem tissue samples from 19 MMD cases and 18 controls.

human ATAC SEQ n=70

PMID:40516534

Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.

Whole-blood transcriptomic response to whole-body hyperthermia in participants with major depressive disorder geo:GSE301868

Depression is the leading cause of global disability according to the World Health Organization, and Major Depressive Disorder (MDD) makes up a majority of these cases. Current pharmacological interventions suffer from significant limitations and side effects, highlighting a need for novel therapeutic approaches. Whole-body hyperthermia (WBH) has been identified as a promising avenue of treatment; however, a comprehensive understanding of the mechanisms responsible for the antidepressant effects of WBH remains elusive.

human BULK RNA SEQ n=20

PMID:42004495

Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.

Whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes ega:EGAS00001002818

We carried out whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes. This study aimed to reveal the selective accumulation of rare variants in the coding and the UTR sequences within the genes of suicide victims. We also analysed the potential effect of STR and CNV variations, as well as the infection of the brain with neurovirulent viruses in this behavioural disorder. As a result, we have identified several candidate genes, among others three calcium channel genes that may potentially contribute to completed suicide.

human

European Genome-phenome Archive study, matched because the disease is named in the study's own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.

Whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes. ega:EGAS00001003081

We carried out whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes. This study aimed to reveal the selective accumulation of rare variants in the coding and the UTR sequences within the genes of suicide victims. We also analysed the potential effect of STR and CNV variations, as well as the infection of the brain with neurovirulent viruses in this behavioural disorder. As a result, we have identified several candidate genes, among others three calcium channel genes that may potentially contribute to completed suicide.

human

European Genome-phenome Archive study, matched because the disease is named in the study's own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.

Toward PRecisiOn Medicine for the Prediction of Treatment Response in Major Depressive Disorder through Stratification of Combined Clinical and Omics Signatures ega:EGAS00001008306

Major depressive disorder (MDD) is the most common psychiatric disorder worldwide. Pharmacotherapy is the standard first-line treatment, yet only one third of patients respond to the initial trial and about 30% develop treatment-resistant depression (TRD), which is associated with specific clinical and molecular features. The PROMPT project aims to develop a precision medicine algorithm for early identification of non-responders.

human

European Genome-phenome Archive study, matched because the disease is named in the study's own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.

{ }

Source YAML

click to show

name: Major Depressive Disorder
creation_date: '2025-12-18T17:01:35Z'
description: >-
  Major depressive disorder (MDD) is a common, often recurrent psychiatric mood
  disorder defined by persistent depressed mood and/or anhedonia accompanied by
  neurovegetative, cognitive, and somatic symptoms that impair functioning.
  Recognized clinical subtypes include melancholic, atypical, psychotic,
  seasonal, and peripartum depression. Pathophysiology implicates monoamine
  deficiency, hypothalamic-pituitary-adrenal axis dysregulation, neuroinflammation,
  and impaired neuroplasticity.
category: Complex
parents:
- Psychiatric Disease
- Mood Disorder
disease_term:
  preferred_term: major depressive disorder
  term:
    id: MONDO:0002009
    label: major depressive disorder
has_subtypes:
- name: Melancholic Depression
  description: Characterized by anhedonia, psychomotor changes, and diurnal
    variation.
- name: Atypical Depression
  description: Features mood reactivity, hypersomnia, hyperphagia, and rejection
    sensitivity.
- name: Psychotic Depression
  description: Depression with hallucinations or delusions.
- name: Seasonal Affective Disorder
  description: Depression recurring in winter months.
- name: Peripartum Depression
  description: Depression during pregnancy or postpartum period.
mechanistic_hypotheses:
- hypothesis_group_id: astrocytic_fgf13_jip2_jnk_cell_death_model
  hypothesis_label: Astrocytic FGF13-JIP2-JNK Cell-Death Model
  status: EMERGING
  description: >-
    In stress-exposed male mouse hippocampus, reduced astrocytic FGF13 is proposed
    to permit MAPK8IP2/JIP2-associated JNK activation, shift BAX/BCL2 signaling
    toward apoptosis, increase inflammation, and reduce synaptic proteins,
    thereby worsening depression-like behavior. This is a model-supported
    hypothesis rather than an established human MDD mechanism: the human
    component is a secondary astrocyte transcriptomic association in an
    all-male suicide dorsolateral-prefrontal-cortex cohort, and older FHF-IB2
    biochemistry instead favored p38delta recruitment over JNK.
  evidence:
  - reference: PMID:42421017
    reference_title: "FGF13 alleviates astrocytic apoptosis via JIP2 inhibition in the hippocampus and mitigates depression-like behavior."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Astrocyte-specific knockout of FGF13 induces astrocytic apoptosis,
      exacerbates inflammatory levels, and aggravates depression-like behaviors
      in mice. In contrast, astrocyte-specific overexpression of FGF13
      significantly attenuates both astrocyte apoptosis and inflammation, and
      effectively ameliorates depression-like behaviors.
    explanation: >-
      Bidirectional astrocyte-specific manipulation in stress-exposed mice
      supports a causal Fgf13-dependent phenotype in the model, but does not by
      itself establish an endogenous adult human MDD mechanism.
  - reference: PMID:42421017
    reference_title: "FGF13 alleviates astrocytic apoptosis via JIP2 inhibition in the hippocampus and mitigates depression-like behavior."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      FGF13 regulates apoptosis in primary astrocytes through the JIP2–JNK
      signaling pathway.
    explanation: >-
      Primary-astrocyte immunoblot experiments (reported at n=4 per group in
      the supplement) support the proposed signaling chain, although the small
      neonatal culture system does not establish its operation in adult human
      astrocytes.
  - reference: PMID:42421017
    reference_title: "FGF13 alleviates astrocytic apoptosis via JIP2 inhibition in the hippocampus and mitigates depression-like behavior."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      GSE144136 contains nuclei from the postmortem dorsolateral prefrontal
      cortex (dlPFC) of 17 healthy controls (HC) and 17 patients with major
      depressive disorder (MDD) who died by suicide. All subjects were male.
    explanation: >-
      The secondary human transcriptomic analysis provides limited disease
      association, but its sex, cause-of-death, and cortical-region restrictions
      do not validate the hippocampal apoptosis mechanism or pathway activity.
  - reference: PMID:12244047
    reference_title: "Fibroblast growth factor homologous factors and the islet brain-2 scaffold protein regulate activation of a stress-activated protein kinase."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      FHF binding to IB2 facilitates recruitment of the MAPK p38delta (SAPK4),
      while failing to stimulate binding of JNK, the preferred kinase of the
      related scaffold IB1 (JIP-1).
    explanation: >-
      Earlier biochemical work confirms an FHF-IB2/JIP2 interaction but raises
      a direct pathway-specificity question because it favored p38delta, not
      JNK; this prevents treating the newer JIP2-JNK direction as settled.
  notes: >-
    Curated as an emerging, model-specific hypothesis only. No new
    pathophysiology edge or FGF13/JIP2-directed treatment is asserted because
    adult human target engagement, causal mediation, and safety or efficacy
    evidence are absent.
- hypothesis_group_id: stalled_adult_hippocampal_neurogenesis_model
  hypothesis_label: Stalled Adult Hippocampal Neurogenesis Model
  status: EMERGING
  description: >-
    A multiomic postmortem hippocampus study of nonmedicated MDD proposes that
    adult hippocampal neurogenesis (AHN) is not abolished but stalled: the
    subgranular-zone neurogenic lineage accumulates quiescent neural stem cells
    and yields fewer neuroblasts, while the immature granule-cell pool is
    unchanged. Stress-responsive transcription-factor reprogramming, interferon
    signalling in early neurogenic stages, a SOX9-associated shift toward glial
    fate, and loss of neuroblast DCX and BDNF are proposed as the molecular
    drivers, converging on reduced dentate-gyrus circuit plasticity and
    hippocampus-dependent cognitive symptoms. The model is EMERGING rather than
    canonical for two independent reasons: whether AHN persists in the adult
    human brain at all remains contested, and this cohort cannot separate MDD
    from suicide pathology because most MDD decedents died by suicide.
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We identify a neurogenic lineage in the adult human hippocampal subgranular zone and provide evidence for a stalled neurogenic process in MDD"
    explanation: States the study's central claim, that a subgranular-zone neurogenic lineage exists in adult human hippocampus and that its progression is stalled in MDD.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In MDD, there seemed to be halted AHN, with more quiescent progenitors and fewer neuroblasts."
    explanation: The authors' own summary of the direction of the defect - arrest of progression rather than loss of the stem-cell pool.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Despite increasing evidence that AHN might occur in human adult brain"
    explanation: The paper's own framing concedes that the existence and clinical relevance of adult human hippocampal neurogenesis is still debated, which is why this is curated as an emerging rather than a canonical model.
  notes: >-
    Curated from a single postmortem multiomic study (snRNA-seq/snATAC-seq,
    Visium and Xenium spatial transcriptomics, and bulk hippocampal proteomics;
    55 MDD and 68 CTRL donors overall, with smaller per-assay subsets). No
    treatment is linked to this hypothesis: the study identifies candidate
    targets but tests none. Cited by DOI because the article had no PubMed
    record at curation time.
pathophysiology:
- name: Monoamine Deficiency
  description: >
    Reduced serotonin, norepinephrine, and dopamine neurotransmission in
    key brain circuits. While oversimplified, this remains a foundation
    for antidepressant pharmacotherapy.
  cell_types:
  - preferred_term: Serotonergic Neuron
    term:
      id: CL:0000850
      label: serotonergic neuron
  - preferred_term: Dopaminergic Neuron
    term:
      id: CL:0000700
      label: dopaminergic neuron
  - preferred_term: Noradrenergic Neuron
    term:
      id: CL:0008025
      label: noradrenergic neuron
  biological_processes:
  - preferred_term: Serotonin Signaling
    term:
      id: GO:0007210
      label: serotonin receptor signaling pathway
  - preferred_term: Dopamine Signaling
    term:
      id: GO:0007212
      label: G protein-coupled dopamine receptor signaling pathway
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: This review confirms the neurotransmitter hypothesis as a
      foundational theory of MDD pathogenesis, though it notes that multiple
      hypotheses are needed to fully explain the disorder.
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "MDD is especially burdensome as approved monoamine antidepressant treatments
      have weeks-long delays before clinical benefit and low remission rates."
    explanation: This highlights the clinical reality of monoamine-based
      treatments, confirming their use while acknowledging their limitations in
      achieving remission.
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "neuroinflammation and gut dysbiosis induce alterations in tryptophan
      metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related
      mechanisms, and glutamate-mediated excitotoxicity."
    explanation: This demonstrates how inflammatory mechanisms contribute to
      decreased serotonin synthesis, supporting the monoamine deficiency theory
      while connecting it to broader pathophysiological processes.
- name: Excitation-Inhibition Imbalance
  description: >
    Reduced cortex-wide excitation-inhibition (E/I) balance in prefrontal-cingulate
    cortices, reflecting dysregulation of GABAergic inhibitory and glutamatergic
    excitatory neurotransmission. E/I imbalance is implicated in depressive
    symptoms and ketamine treatment response in treatment-resistant depression.
  cell_types:
  - preferred_term: GABAergic Neuron
    term:
      id: CL:0000617
      label: GABAergic neuron
  - preferred_term: Pyramidal Neuron
    description: Glutamatergic excitatory neurons
    term:
      id: CL:0000598
      label: pyramidal neuron
  biological_processes:
  - preferred_term: GABA Signaling
    term:
      id: GO:0007214
      label: gamma-aminobutyric acid signaling pathway
    modifier: DYSREGULATED
  - preferred_term: Glutamate Signaling
    term:
      id: GO:0007215
      label: glutamate receptor signaling pathway
    modifier: DYSREGULATED
  - preferred_term: Synaptic Plasticity
    term:
      id: GO:0048167
      label: regulation of synaptic plasticity
    modifier: DYSREGULATED
  evidence:
  - reference: PMID:42372880
    reference_title: "Intrinsic excitation-inhibition imbalance in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients with MDD demonstrated significantly reduced Hurst exponent values, predominantly encompassing the parietal and prefrontal-cingulate cortices."
    explanation: Neuroimaging biomarker showing reduced E/I balance in MDD-affected brain regions, using Hurst exponent as a biophysically confirmed proxy of E/I balance.
  - reference: PMID:42372880
    reference_title: "Intrinsic excitation-inhibition imbalance in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Neurochemically, Hurst exponent alterations were spatially associated with GABAergic, opioidergic, serotonergic, and synaptic density distributions."
    explanation: Cortical E/I imbalance is spatially associated with specific neurochemical systems implicated in depression, including GABAergic, opioidergic, and serotonergic neurotransmission and synaptic density.
  - reference: PMID:42372880
    reference_title: "Intrinsic excitation-inhibition imbalance in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Divergent group-by-treatment effects were observed in the anterior cingulate and medial prefrontal cortices, with ketamine-induced increases in TRD patients."
    explanation: Ketamine treatment increases cortical E/I balance in treatment-resistant depression, suggesting E/I normalization as a potential mechanism of rapid antidepressant action.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Glutamate ionotropic (AMPA and NMDA) and metabotropic receptors were downregulated in MDD NSCa, NSCb, INP, ImGC1, NB and GC1 and in several spatial clusters."
    explanation: Postmortem single-nucleus and spatial transcriptomics localize the glutamatergic arm of the imbalance to the dentate gyrus neurogenic lineage and granule cells, complementing the cortical neuroimaging evidence already cited on this node.
- name: HPA Axis Dysregulation
  description: >
    Hyperactivity of the hypothalamic-pituitary-adrenal axis leads to
    elevated cortisol, which may contribute to hippocampal atrophy and
    cognitive symptoms.
  cell_types:
  - preferred_term: Corticotroph
    term:
      id: CL:0002309
      label: corticotroph
  biological_processes:
  - preferred_term: Cortisol Response
    term:
      id: GO:0071385
      label: cellular response to glucocorticoid stimulus
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: This review identifies the HPA axis hypothesis as one of the
      widely accepted core pathophysiological mechanisms in MDD.
- name: Neuroplasticity Deficits
  description: >
    Reduced BDNF and impaired synaptic plasticity in prefrontal cortex
    and hippocampus. Successful treatments restore neuroplasticity.
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: Synaptic Plasticity
    term:
      id: GO:0048167
      label: regulation of synaptic plasticity
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: This comprehensive review identifies the neuroplasticity
      hypothesis as one of the core accepted mechanisms in MDD pathogenesis.
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "This narrative review provides a high-level overview of glutamate signaling
      in synaptogenesis and neural plasticity and the implications of glutamate dysregulation
      in depression."
    explanation: This demonstrates the link between glutamate signaling,
      synaptogenesis, and neural plasticity deficits in depression, supporting
      the neuroplasticity deficit mechanism.
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "neuroinflammation and gut dysbiosis induce alterations in tryptophan
      metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related
      mechanisms, and glutamate-mediated excitotoxicity."
    explanation: This shows how inflammatory processes lead to impairments in
      neuroplasticity-related mechanisms, connecting inflammation to
      neuroplasticity deficits in MDD.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Altered CA excitatory neurons NMDA receptors and HOMER1, a key postsynaptic scaffolding protein regulating synaptic plasticity and glutamatergic communication, supports disruption of neuroplasticity in this important part of the hippocampal memory circuitry in MDD."
    explanation: Extends the neuroplasticity-deficit mechanism into the hippocampal trisynaptic memory circuit with cell-type-resolved postmortem evidence, naming the NMDA receptor and HOMER1 scaffolding changes involved.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "ImGC1 had lower HTR7, which promotes neurogenesis, neurite outgrowth and dendritic spine maturation, whereas spatial subfields had lower HTR2A and HTR2C, and InN.PENK had elevated HTR1D."
    explanation: Ties serotonin receptor changes across hippocampal subfields and cell types to the neurite-outgrowth and dendritic-spine processes underlying this node.
- name: Neuroinflammation
  description: >
    Elevated inflammatory cytokines (IL-6, TNF-alpha, CRP) observed in
    depression. Inflammation may contribute to monoamine depletion and
    neuroplasticity deficits.
  cell_types:
  - preferred_term: Microglia
    term:
      id: CL:0000129
      label: microglial cell
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: This review identifies the cytokine hypothesis as one of the
      widely accepted theories of MDD pathogenesis, supporting the role of
      inflammatory mechanisms.
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "The involvement of central and peripheral inflammation in the pathogenesis
      and prognosis of major depressive disorder (MDD) has been demonstrated. The
      increase of pro-inflammatory cytokines (interleukin (IL)-1β, IL-6, IL-18, and
      TNF-α) in individuals with depression may elicit neuroinflammatory processes
      and peripheral inflammation"
    explanation: This provides direct evidence for elevated pro-inflammatory
      cytokines in MDD and their role in eliciting neuroinflammatory processes.
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "mechanisms that, in turn, can contribute to gut microbiota dysbiosis.
      Together, neuroinflammation and gut dysbiosis induce alterations in tryptophan
      metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related
      mechanisms, and glutamate-mediated excitotoxicity."
    explanation: This demonstrates how neuroinflammation contributes to both
      monoamine depletion (decreased serotonin) and neuroplasticity deficits,
      confirming the description's mechanistic links.
  - reference: PMID:20015486
    reference_title: "A meta-analysis of cytokines in major depression."
    supports: SUPPORT
    snippet: This meta-analysis reports significantly higher concentrations of
      the proinflammatory cytokines TNF-alpha and IL-6 in depressed subjects
      compared with control subjects.
    explanation: Meta-analysis evidence shows elevated proinflammatory cytokines
      in major depression, supporting neuroinflammatory mechanisms.
- name: Mitochondrial Dysfunction
  description: >
    Impaired mitochondrial respiration and cellular energy metabolism contribute to
    MDD pathophysiology. Patient-derived cells show decreased mitochondrial function,
    altered membrane potential, and disrupted calcium homeostasis.
  evidence:
  - reference: PMID:38256041
    reference_title: "Mitochondrial and Cellular Function in Fibroblasts, Induced Neurons, and Astrocytes Derived from Case Study Patients: Insights into Major Depression as a Mitochondria-Associated Disease."
    supports: SUPPORT
    snippet: "The link between mitochondria and major depressive disorder (MDD) is
      increasingly evident, underscored both by mitochondria's involvement in many
      mechanisms identified in depression and the high prevalence of MDD in individuals
      with mitochondrial disorders."
    explanation: This establishes the connection between mitochondrial
      dysfunction and MDD, noting both mechanistic involvement and
      epidemiological evidence.
  - reference: PMID:38256041
    reference_title: "Mitochondrial and Cellular Function in Fibroblasts, Induced Neurons, and Astrocytes Derived from Case Study Patients: Insights into Major Depression as a Mitochondria-Associated Disease."
    supports: SUPPORT
    snippet: "Similarities were observed between the Mito patient and a broader MDD
      cohort, including decreased respiration and mitochondrial function."
    explanation: This provides direct evidence from patient-derived cells
      showing decreased mitochondrial respiration and function in MDD patients.
  - reference: PMID:38256041
    reference_title: "Mitochondrial and Cellular Function in Fibroblasts, Induced Neurons, and Astrocytes Derived from Case Study Patients: Insights into Major Depression as a Mitochondria-Associated Disease."
    supports: SUPPORT
    snippet: "the Non-R patient's data offered a new perspective on MDD, suggesting
      a detrimental imbalance in mitochondrial and cellular processes, rather than
      simply reduced functions."
    explanation: This suggests that mitochondrial dysfunction in MDD may involve
      complex imbalances beyond simple reduction, including altered respiratory
      rates and calcium homeostasis.
- name: Reference Point Dysregulation
  description: >
    Pathological elevation and inflexibility of the decisional reference point,
    a core mechanism from behavioral economics that determines how events are
    experienced as positive or negative. Elevated reference points cause previously
    rewarding activities to be experienced as aversive, contributing to anhedonia
    and reward dysfunction. Dysfunction in anterior cingulate cortex impairs
    dynamic adjustment of the reference point to environmental changes.
  cell_types:
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: Cognition
    term:
      id: GO:0050890
      label: cognition
  evidence:
  - reference: PMID:42150067
    reference_title: "Decisional reference point pathology: A cognitive mechanism for and a correlate of major depressive disorder in humans."
    supports: SUPPORT
    snippet: "A pathological elevation of the reference point would lead a person
      to experience once pleasurable activities as negative reinforcers."
    explanation: This describes how pathological reference point elevation in MDD
      directly causes anhedonia by transforming reward into punishment.
  - reference: PMID:42150067
    reference_title: "Decisional reference point pathology: A cognitive mechanism for and a correlate of major depressive disorder in humans."
    supports: SUPPORT
    snippet: "depression is associated with a significant elevation of the reference
      point, and the magnitude of this elevation correlates with disease severity."
    explanation: This provides direct evidence linking elevated reference points
      to depression severity in MDD patients.
  - reference: PMID:42150067
    reference_title: "Decisional reference point pathology: A cognitive mechanism for and a correlate of major depressive disorder in humans."
    supports: SUPPORT
    snippet: "The ability of patients with MDD to dynamically adjust their reference
      point to the environment is also dysfunctional."
    explanation: This demonstrates that MDD patients show impaired cognitive
      flexibility in adapting reward valuation to environmental context.
  - reference: PMID:42150067
    reference_title: "Decisional reference point pathology: A cognitive mechanism for and a correlate of major depressive disorder in humans."
    supports: SUPPORT
    snippet: "findings link the previously demonstrated treatment of depression by
      deep brain stimulation to modulation of the reference point in the anterior
      cingulate cortex"
    explanation: This connects reference point pathology to a known treatment
      mechanism (DBS), identifying anterior cingulate cortex as the key locus of
      this dysfunction.
- name: Oligodendrocyte Dysfunction and Demyelination
  description: >
    Oligodendrocyte (OL) dysfunction and myelin abnormalities contribute to
    depression pathophysiology through multiple mechanisms: impaired myelination
    reduces conduction velocity and disrupts neural circuit function; loss of
    OL-derived metabolic support decreases neuronal energy supply; compromised
    OL-glial crosstalk with microglia and astrocytes amplifies neuroinflammation.
    These dysfunctions are associated with altered brain connectivity and emotional
    processing deficits, and may represent a targetable node for therapeutic
    remyelination strategies.
  cell_types:
  - preferred_term: Oligodendrocyte
    term:
      id: CL:0000128
      label: oligodendrocyte
  - preferred_term: Oligodendrocyte Precursor Cell
    term:
      id: CL:0002453
      label: oligodendrocyte precursor cell
  - preferred_term: Neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: Microglia
    term:
      id: CL:0000129
      label: microglial cell
  - preferred_term: Astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: Myelination
    term:
      id: GO:0042552
      label: myelination
    modifier: DECREASED
  - preferred_term: Synaptic Plasticity
    term:
      id: GO:0048167
      label: regulation of synaptic plasticity
    modifier: DECREASED
  - preferred_term: Axon Ensheathment
    term:
      id: GO:0008366
      label: axon ensheathment
  evidence:
  - reference: PMID:41730818
    reference_title: "Oligodendrocyte dysfunction in major depressive disorder: Mechanistic insights and emerging therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Emerging evidence increasingly implicates oligodendrocyte (OL) dysfunction
      as a key pathophysiological mechanism in MDD, extending beyond their classical
      role in myelination to include critical contributions to neural plasticity,
      metabolic support, and circuit regulation."
    explanation: This establishes OL dysfunction as a key pathophysiological
      mechanism in MDD that extends beyond myelination to encompass neural plasticity
      and metabolic support functions.
  - reference: PMID:41730818
    reference_title: "Oligodendrocyte dysfunction in major depressive disorder: Mechanistic insights and emerging therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Such dysfunctions manifest primarily as myelin abnormalities and are
      closely associated with depression-related alterations in brain connectivity
      and emotional processing."
    explanation: This demonstrates the functional consequences of OL dysfunction,
      linking myelin abnormalities to altered brain connectivity and emotional
      processing deficits central to depression.
  - reference: PMID:41730818
    reference_title: "Oligodendrocyte dysfunction in major depressive disorder: Mechanistic insights and emerging therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "with particular emphasis on their interactions with neurons, astrocytes,
      and microglia within the central nervous system"
    explanation: This directly supports the OL-glial crosstalk mechanism described
      in this node, confirming that oligodendrocyte dysfunction involves disrupted
      interactions with astrocytes and microglia in MDD.
  downstream:
  - target: Neuroplasticity Deficits
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - OL dysfunction and myelin abnormalities impair neural plasticity through
      loss of metabolic and trophic support to neurons.
  - target: Neuroinflammation
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - OL-microglia and OL-astrocyte interactions link oligodendrocyte dysfunction
      to neuroinflammatory signaling in MDD.
- name: Stalled Adult Hippocampal Neurogenesis
  biological_scale: CELLULAR
  description: >-
    In nonmedicated MDD, the subgranular-zone (SGZ) neurogenic lineage of the
    dentate gyrus shows a shift in pseudotime distribution toward quiescent
    neural stem cells with fewer neuroblasts, indicating arrested progression
    rather than depletion of the stem-cell pool. Histological validation finds
    fewer nestin- and Ki67-expressing SGZ cells and fewer DCX/TUBB3
    co-expressing dentate cells, while the immature granule-cell (ImGC2) pool
    is unchanged. Intermediate progenitors upregulate SOX9, favouring a
    neuron-to-glia switch, and the residual neuroblasts lose doublecortin and
    BDNF.
  cell_types:
  - preferred_term: Quiescent hippocampal neural stem cell
    term:
      id: CL:0000047
      label: neural stem cell
  - preferred_term: Intermediate neural progenitor
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: Neuroblast
    term:
      id: CL:0000031
      label: neuroblast (sensu Vertebrata)
  - preferred_term: Dentate gyrus granule cell
    term:
      id: CL:0001033
      label: hippocampal granule cell
  - preferred_term: Subgranular zone niche astrocyte
    term:
      id: CL:0000127
      label: astrocyte
  biological_processes:
  - preferred_term: Adult hippocampal neurogenesis
    term:
      id: GO:0022008
      label: neurogenesis
    modifier: DECREASED
  - preferred_term: Neuroblast proliferation
    term:
      id: GO:0007405
      label: neuroblast proliferation
    modifier: DECREASED
  - preferred_term: Neural stem cell quiescence
    description: >-
      Accumulation of the SGZ lineage at the quiescent neural stem cell state
      because progression is blocked, not an increase in stem-cell maintenance.
      Left unbound pending a new-term request: GO:0019827 stem cell population
      maintenance names the wrong concept (the entry's own evidence reports
      "impaired neurogenic progression rather than depletion of stem-like
      cells"), and the concept-exact GO:0044838 cell quiescence is a GO
      biological-phase term whose own comment states it "should not be used for
      direct annotation". GO has no neural-stem-cell quiescence term.
    modifier: INCREASED
  - preferred_term: Neuron-to-glia fate switch
    description: >-
      Annotated without a direction: the cited sentence is generic SOX9 biology
      with no MDD-versus-control comparison, so the elevation of SOX9 in MDD
      intermediate neural progenitors is not directly quotable from the cached
      record.
    term:
      id: GO:0010001
      label: glial cell differentiation
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pseudotime analysis of the neurogenic trajectory comparing MDD and CTRL showed a shift in cell distribution in MDD marked by more NSCa and fewer NBs"
    explanation: Single-nucleus trajectory inference shows the lineage accumulating at the quiescent neural stem cell stage with fewer neuroblasts, the primary observation behind this node.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "suggesting impaired neurogenic progression rather than depletion of stem-like cells"
    explanation: Fixes the direction of the claim - progression through the lineage is arrested, the stem-cell compartment is not exhausted.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Validation studies showed fewer SGZ cells expressing nestin and Ki67 proteins in MDD compared to CTRL"
    explanation: Protein-level validation independent of the sequencing readout, consistent with fewer activated, proliferating stem cells in the subgranular zone.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "DG cells coexpressing DCX/TUBB3 RNA and expressing doublecortin protein were fewer in MDD"
    explanation: Independent RNA and protein confirmation of the reduced neuroblast population inferred from pseudotime.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Moreover, NBs, which were fewer in MDD, had reduced DCX and trophic factor BDNF, indicating deficient trophism."
    explanation: Links the reduced neuroblast pool to loss of BDNF trophic support, connecting this node to the pre-existing neuroplasticity-deficit mechanism.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "which favors glial fate by promoting the neuron-to-glia switch and suppressing neurogenesis"
    explanation: Establishes only the generic role of SOX9 in favouring glial over neuronal fate - the sentence carries no MDD-versus-control comparison. The study's own finding of elevated SOX9 in MDD intermediate neural progenitors is reported elsewhere in the paper and is not quotable from the cached record, so this item is PARTIAL and the glial-differentiation annotation carries no direction.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The number of cells expressing ImGC2 marker RNAs PROX1/BHLHE22/POSTN did not differ between groups"
    explanation: A negative result that bounds the claim - the immature granule-cell pool is preserved, so the defect is confined to progression from stem cell to neuroblast rather than to the whole lineage.
  downstream:
  - target: Neuroplasticity Deficits
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - stalled_adult_hippocampal_neurogenesis_model
    intermediate_mechanisms:
    - Fewer newborn neuroblasts with reduced doublecortin and BDNF lower the rate at which new granule cells are added to the dentate gyrus, reducing structural and synaptic plasticity of the trisynaptic circuit.
- name: Neurogenic Niche Interferon Signaling Activation
  biological_scale: MOLECULAR
  description: >-
    Early neurogenic stages in the MDD hippocampus - quiescent and activated
    neural stem cells and intermediate neural progenitors - upregulate a gene
    module enriched for interferon-related pathways (EIF2AK2, IFIT3, HERC6,
    NRIR, IFITM3, MX1). The same interferon programme is raised in mature
    granule cells and CA1-4 excitatory neurons, making it a hippocampus-wide
    rather than niche-restricted signal. Several of the genes involved carry
    variants associated with intellectual disability, Alzheimer disease,
    systemic lupus erythematosus and COVID-19, which the authors read as shared
    pathogenetic mechanisms rather than as MDD-specific.
  cell_types:
  - preferred_term: Quiescent and activated neural stem cell
    term:
      id: CL:0000047
      label: neural stem cell
  - preferred_term: Intermediate neural progenitor
    term:
      id: CL:0011020
      label: neural progenitor cell
  - preferred_term: Dentate gyrus granule cell
    term:
      id: CL:0001033
      label: hippocampal granule cell
  biological_processes:
  - preferred_term: Type I interferon signaling
    term:
      id: GO:0060337
      label: type I interferon-mediated signaling pathway
    modifier: INCREASED
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "At early neurogenic stages (NSCa, NSCb and INP) MDD had higher expression of a gene module enriched with interferon-related pathways"
    explanation: Locates the interferon signal at the stem-cell and progenitor stages of the lineage, which is where the trajectory stalls.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "revealed eight different interferon-related genes disrupted in MDD NSCa, NSCb, INP and ImGC1"
    explanation: Gene-level differential expression confirming the module result across four neurogenic clusters.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Consistent with the neurogenic clusters, interferon signaling was upregulated in GC1 and ExN1.CA1-4.FIBCD1, including ISG15, MX1, CXCL12"
    explanation: Shows the same interferon programme in mature granule cells and CA excitatory neurons, so the signal is hippocampus-wide and links this node to the existing neuroinflammation mechanism.
  downstream:
  - target: Stalled Adult Hippocampal Neurogenesis
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    hypothesis_groups:
    - stalled_adult_hippocampal_neurogenesis_model
    intermediate_mechanisms:
    - Interferon-stimulated gene expression in stem cells and progenitors is proposed to restrain their progression, but the study is cross-sectional and does not establish the direction of this edge.
  - target: Neuroinflammation
    causal_link_type: DIRECT
- name: Stress-Responsive Transcription Factor Reprogramming
  biological_scale: MOLECULAR
  description: >-
    Chromatin accessibility and transcription-factor footprinting in MDD
    hippocampus show altered binding activity of stress- and
    corticosteroid-responsive Kruppel-like factors (KLF9, KLF15) alongside EGR
    and ASCL1 family factors, in granule cells, CA1-4 excitatory neurons and
    PENK+ inhibitory neurons. Footprint changes track expression of target
    genes and their proteins (HPCAL1, KRAS, CAMKV, RAB6B, HOMER1), tying
    epigenetic regulation to the neurogenic and trisynaptic-circuit
    phenotypes. MDD donors in this cohort had significantly higher recent
    stress exposure than controls.
  biological_processes:
  - preferred_term: Transcription factor binding and target gene regulation
    term:
      id: GO:0006355
      label: regulation of DNA-templated transcription
    modifier: DYSREGULATED
  - preferred_term: Chromatin accessibility
    term:
      id: GO:0006325
      label: chromatin organization
    modifier: DYSREGULATED
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The MDD hippocampus shows altered TF activity affecting chromatin accessibility and expression of genes involved in intracellular trafficking, spines, cell adhesion, telomeres and cellular aging."
    explanation: States the transcription-factor and chromatin-accessibility finding and the functional classes of the affected target genes.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "TFs regulated neurogenesis and the trisynaptic circuit in individuals with MDD, who had higher severity of stress exposure in the last 6 months before death compared to CTRL individuals."
    explanation: Connects the transcription-factor changes to both downstream targets in this entry and to the measured stress exposure that makes these factors stress-responsive.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Excitatory and inhibitory neurons show dysregulation of transcription factor networks affecting cell states."
    explanation: Extends the transcription-factor network disruption beyond the neurogenic lineage to the mature excitatory and inhibitory populations of the circuit.
  downstream:
  - target: Stalled Adult Hippocampal Neurogenesis
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - stalled_adult_hippocampal_neurogenesis_model
    intermediate_mechanisms:
    - Stage-specific transcription factors, including the stress-responsive KLF9 acting at the intermediate-progenitor to neuroblast transition, set the chromatin accessibility and gene expression that the neurogenic trajectory depends on.
  - target: Excitation-Inhibition Imbalance
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - KLF15 footprint changes in CA1-4 excitatory and PENK+ inhibitory neurons track expression of synaptic target genes including HOMER1, CAMKV and RAB6B.
- name: PENK+ GABAergic Interneuron Activation
  biological_scale: CELLULAR
  description: >-
    A PENK+ medium-spiny-neuron-like GABAergic population, not previously
    described in the human hippocampus, is the most transcriptionally
    dysregulated cell cluster in MDD. It overexpresses proenkephalin together
    with immediate-early genes (ARC, FOS, JUNB, EGRs, JAG1) and shows altered
    vesicle, dendritic-spine and adhesion genes plus elevated HTR1D, a profile
    the authors read as an activated state possibly compensating for a
    stress-hyperactivated dentate gyrus. It is offered as a link between MDD,
    chronic pain, stress response and emotional regulation.
  cell_types:
  - preferred_term: PENK+ medium spiny neuron-like GABAergic interneuron
    term:
      id: CL:0011005
      label: GABAergic interneuron
  biological_processes:
  - preferred_term: GABAergic neurotransmission
    term:
      id: GO:0051932
      label: synaptic transmission, GABAergic
    modifier: DYSREGULATED
  - preferred_term: Neuronal activity-dependent immediate-early gene expression
    term:
      id: GO:0006355
      label: regulation of DNA-templated transcription
    modifier: INCREASED
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The PENK+ GABAergic medium-spiny neuron-like cluster (InN5.PENK) had 566 DEGs, the most compared to the other cell clusters, followed by GC1 with 378, and ExN1.CA1-4.FIBCD1 with 147."
    explanation: Quantifies the claim that this inhibitory population is the most dysregulated cell cluster in the MDD hippocampus.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Unique to InN5.PENK was overexpression of proenkephalin, a precursor of enkephalins, which modulate pain perception, stress responses and emotional regulation, as well as immediate-early genes ARC, FOS, JUNB, EGRs, and JAG1, upregulated with neuronal activity and cell development."
    explanation: Provides the proenkephalin and immediate-early gene signature that defines the activated state annotated on this node.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Therefore, InN.PENK might be attempting to compensate for a stress-hyperactivated DG."
    explanation: The compensatory interpretation is explicitly hedged by the authors, so this edge is curated as a proposal rather than an established direction of causation.
  downstream:
  - target: Excitation-Inhibition Imbalance
    causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - An activated PENK+ inhibitory population alongside downregulated ionotropic and metabotropic glutamate receptors in dentate granule and neurogenic cells shifts the excitatory-inhibitory balance of the dentate gyrus, but whether the inhibitory activation is cause or compensation is undetermined.
phenotypes:
- name: Depressed Mood
  category: Psychiatric
  frequency: VERY_FREQUENT
  diagnostic: true
  phenotype_term:
    preferred_term: Depression
    term:
      id: HP:0000716
      label: Depression
- name: Anhedonia
  category: Psychiatric
  frequency: VERY_FREQUENT
  diagnostic: true
  notes: Loss of interest or pleasure
  phenotype_term:
    preferred_term: Anhedonia
    term:
      id: HP:0012154
      label: Anhedonia
- name: Sleep Disturbance
  category: Sleep
  frequency: VERY_FREQUENT
  notes: Insomnia or hypersomnia
  phenotype_term:
    preferred_term: Sleep Disturbance
    term:
      id: HP:0002360
      label: Sleep disturbance
- name: Fatigue
  category: Systemic
  frequency: VERY_FREQUENT
  phenotype_term:
    preferred_term: Fatigue
    term:
      id: HP:0012378
      label: Fatigue
- name: Poor Appetite
  category: Systemic
  frequency: FREQUENT
  notes: Decreased or increased appetite
  phenotype_term:
    preferred_term: Poor Appetite
    term:
      id: HP:0004396
      label: Poor appetite
- name: Concentration Difficulties
  category: Cognitive
  frequency: FREQUENT
  phenotype_term:
    preferred_term: Cognitive Impairment
    term:
      id: HP:0100543
      label: Cognitive impairment
- name: Psychomotor Changes
  category: Psychiatric
  frequency: OCCASIONAL
  notes: >-
    Psychomotor agitation or retardation. The ontology term captures the
    agitation pole; psychomotor retardation currently lacks a non-obsolete
    HPO term.
  phenotype_term:
    preferred_term: Psychomotor agitation
    term:
      id: HP:0000713
      label: Agitation
- name: Memory Impairment
  category: Cognitive
  description: >-
    Hippocampus-dependent memory dysfunction, including a recall bias toward
    negative content that tracks depression severity. Weakened memory function
    is the clinical correlate of the reduced hippocampal circuit plasticity
    curated in this entry.
  phenotype_term:
    preferred_term: Memory impairment
    term:
      id: HP:0002354
      label: Memory impairment
  evidence:
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "MDD is a major global health burden presenting with mood, neurovegetative, and cognitive symptoms, including memory recall bias toward negative content, a cognitive marker of depression severity"
    explanation: Establishes memory-recall bias as a cognitive feature of MDD that scales with severity.
  - reference: DOI:10.1038/s41591-026-04571-8
    reference_title: Dysregulated adult hippocampal neurogenesis in major depressive disorders
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "To determine the underpinnings of reduced hippocampus circuit plasticity and weakened memory functions in MDD"
    explanation: Frames weakened memory function as the clinical phenotype the hippocampal molecular changes are intended to explain.
  notes: >-
    No frequency is asserted. The cited study characterizes memory dysfunction
    as a feature of MDD but reports no cohort frequency for it.
biochemical:
- name: Cortisol
  presence: Elevated
  context: HPA axis hyperactivity
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: The review lists the HPA-axis hypothesis among accepted MDD
      theories; it names the axis but does not itself report that cortisol is
      elevated, so this supports the mechanism only indirectly.
- name: BDNF
  presence: Decreased
  context: Reduced neuroplasticity marker
  evidence:
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "neuroinflammation and gut dysbiosis induce alterations in tryptophan
      metabolism, culminating in decreased serotonin synthesis, impairments in neuroplasticity-related
      mechanisms, and glutamate-mediated excitotoxicity."
    explanation: The snippet describes impaired neuroplasticity-related mechanisms
      generally but does not mention BDNF specifically, so it supports the
      decreased-BDNF claim only indirectly.
- name: Inflammatory Markers
  presence: Elevated
  context: IL-1β, IL-6, IL-18, CRP, TNF-alpha
  evidence:
  - reference: PMID:38474387
    reference_title: "Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets."
    supports: SUPPORT
    snippet: "The increase of pro-inflammatory cytokines (interleukin (IL)-1β, IL-6,
      IL-18, and TNF-α) in individuals with depression may elicit neuroinflammatory
      processes and peripheral inflammation"
    explanation: This directly confirms elevated pro-inflammatory cytokines
      including IL-1β, IL-6, IL-18, and TNF-α in MDD patients, and links that
      increase to neuroinflammatory and peripheral inflammatory processes.
  - reference: PMID:42450240
    reference_title: "Interleukin-1β (C-511T) Genetic Variant and Major Depressive Disorder: A Systematic Review."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      a regulatory cytokine of the immune and nervous systems that acts on
      several processes, including mood regulation
    explanation: >-
      Separate source for the mood-regulation role of IL-1β specifically, which
      the PMID:38474387 snippet above does not itself state. This is the review's
      background characterization of IL-1β biology rather than a study result,
      hence evidence_source OTHER.
genetic:
- name: SLC6A4
  gene_term:
    preferred_term: SLC6A4
    term:
      id: hgnc:11050
      label: SLC6A4
  association: Risk Factor
  notes: Serotonin transporter gene
- name: BDNF
  gene_term:
    preferred_term: BDNF
    term:
      id: hgnc:1033
      label: BDNF
  association: Risk Factor
  notes: Val66Met polymorphism
- name: FKBP5
  gene_term:
    preferred_term: FKBP5
    term:
      id: hgnc:3721
      label: FKBP5
  association: Risk Factor
  notes: HPA axis regulation
- name: HTR2A
  gene_term:
    preferred_term: HTR2A
    term:
      id: hgnc:5293
      label: HTR2A
  association: Risk Factor
  notes: Serotonin receptor gene
- name: IL1B
  association: >-
    Severity modifier and antidepressant-response marker, not an established
    susceptibility locus. For the C-511T (rs16944) variant the CC genotype is
    associated with greater MDD symptom severity and the TT genotype with
    antidepressant treatment response; the source review states these two
    associations are not equivalent in terms of susceptibility to disease onset.
  relationship_type: MODIFIER
  notes: >-
    C-511T (rs16944). Contested: other studies report no significant association
    between this variant and MDD, and the source systematic review calls for
    further study across populations before the polymorphism's role in etiology
    can be settled. Curated as MODIFIER rather than RISK_FACTOR because the
    evidence speaks to symptom severity and treatment response rather than to
    risk of disease onset.
  gene_term:
    preferred_term: IL1B
    term:
      id: hgnc:5992
      label: IL1B
  variants:
  - name: C-511T
    gene:
      preferred_term: IL1B
    synonyms:
    - rs16944
    identifiers:
    - dbSNP:rs16944
  evidence:
  - reference: PMID:42450240
    reference_title: "Interleukin-1β (C-511T) Genetic Variant and Major Depressive Disorder: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the CC genotype was more frequently associated with greater MDD symptom
      severity, whereas the TT genotype was predominantly associated with
      antidepressant treatment response
    explanation: >-
      Systematic review of the IL1B C-511T variant reporting distinct clinical
      outcomes by genotype: symptom severity for CC and antidepressant treatment
      response for TT.
  - reference: PMID:42450240
    reference_title: "Interleukin-1β (C-511T) Genetic Variant and Major Depressive Disorder: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      thus, these associations should not be considered equivalent in terms of
      susceptibility to disease onset
    explanation: >-
      The same review explicitly declines to treat the severity and
      treatment-response findings as evidence of susceptibility to MDD onset,
      which is why this gene is curated as a MODIFIER rather than a risk factor.
  - reference: PMID:42450240
    reference_title: "Interleukin-1β (C-511T) Genetic Variant and Major Depressive Disorder: A Systematic Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      other studies have found no significant association between this genetic
      variant and MDD
    explanation: >-
      Counterweight from the same review documenting non-replication, recorded so
      the association is not read as settled.
environmental:
- name: Childhood Trauma
  exposure_term:
    preferred_term: psychological stress
    term:
      id: XCO:0001265
      label: stress
  notes: Strong risk factor for adult depression, and additionally for an earlier
    onset and a more chronic or treatment-resistant course.
  evidence:
  - reference: PMID:27908895
    reference_title: "Childhood maltreatment and characteristics of adult depression: meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Childhood maltreatment, especially emotional abuse and neglect, represents a risk factor for severe, early-onset, treatment-resistant depression with a chronic course"
    explanation: "Meta-analysis of 184 studies; maltreated individuals were 2.66 to 3.73 times more likely to develop adult depression, and twice as likely to develop a chronic or treatment-resistant course."
- name: Chronic Stress
  exposure_term:
    preferred_term: psychological stress
    term:
      id: XCO:0001265
      label: stress
  notes: Major precipitant
  evidence:
  - reference: PMID:38331979
    reference_title: "Major depressive disorder: hypothesis, mechanism, prevention and treatment."
    supports: SUPPORT
    snippet: "The currently widely accepted theories of MDD pathogenesis include the
      neurotransmitter and receptor hypothesis, hypothalamic-pituitary-adrenal (HPA)
      axis hypothesis, cytokine hypothesis, neuroplasticity hypothesis and systemic
      influence hypothesis"
    explanation: The review lists the HPA-axis hypothesis but does not itself
      assert a stress-to-depression relationship; it supports chronic stress as
      a precipitant only indirectly via the HPA axis.
- name: Social Isolation
  notes: Risk factor and consequence - loneliness and isolation predict later
    depressive symptoms, and depressive symptoms in turn predict later social
    loneliness and isolation.
  evidence:
  - reference: PMID:35583561
    reference_title: "Loneliness and the onset of new mental health problems in the general population."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our meta-analysis found a pooled adjusted odds ratio of 2.33 (95% CI 1.62-3.34) for risk of new onset depression in adults who were often lonely compared with people who were not often lonely"
    explanation: "Systematic review of 32 longitudinal general-population studies, meta-analysing eight cohorts, for the risk of new onset depression in adults who were often lonely. Supports the risk-factor direction. The authors attach a caution to this pooled estimate in the same abstract, saying it should be interpreted with caution given evidence of heterogeneity."
  - reference: PMID:39036816
    reference_title: "Temporal associations of emotional and social loneliness and psychosocial functioning in emerging adulthood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "increases in emotional and social loneliness as well as social isolation predicted higher depression levels on later timepoints. Increases in depressive symptoms also predicted increases in subsequent social loneliness"
    explanation: "Random intercept cross-lagged panel models over three timepoints in 1,357 young adults. Supports the consequence direction as well as the risk direction; the sample is a university cohort in emerging adulthood, so it is not a general-population estimate."
- name: Substance Abuse
  exposure_term:
    preferred_term: substance abuse
    term:
      id: ECTO:6000007
      label: exposure to substance abuse
  notes: Bidirectional relationship. The evidence is for alcohol dependence
    specifically - non-dependent drinking, including binge drinking, did not predict
    depressive episodes in the cohort below.
  evidence:
  - reference: PMID:22987574
    reference_title: "Alcohol consumption and major depression in the general population: the critical importance of dependence."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Associations between alcohol consumption and MDE were not observed except when dependence was indicated. Alcohol dependence increased the risk of MDE, and MDE increased the risk of alcohol dependence, but only in men"
    explanation: "Twelve-year Canadian National Population Health Survey cohort. Evidences both directions, and its finding that the association held only for dependence is the qualification added to the note."
  - reference: PMID:24246605
    reference_title: "Comorbidity between major depression and alcohol use disorder from adolescence to adulthood."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "adolescent AUD predicted early adult MDD, while early adult MDD predicted adult AUD"
    explanation: "Prospective study of 816 participants interviewed at ages 16, 17, 24 and 30. Shows the bidirectionality is developmentally staged rather than simultaneous."
treatments:
- name: Selective Serotonin Reuptake Inhibitors (SSRIs)
  description: First-line pharmacotherapy (sertraline, escitalopram,
    fluoxetine).
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: SSRI therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: sertraline
      term:
        id: CHEBI:9123
        label: sertraline
    - preferred_term: escitalopram
      term:
        id: CHEBI:36791
        label: escitalopram
    - preferred_term: fluoxetine
      term:
        id: CHEBI:5118
        label: fluoxetine
  target_mechanisms:
  - target: Monoamine Deficiency
    treatment_effect: MODULATES
    description: >-
      SSRIs block presynaptic serotonin reuptake, raising synaptic serotonin and
      correcting the monoaminergic deficit implicated in depression.
  evidence:
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "MDD is especially burdensome as approved monoamine antidepressant treatments
      have weeks-long delays before clinical benefit and low remission rates."
    explanation: This confirms the clinical use of monoamine antidepressants
      while acknowledging their limitations in terms of delayed benefit and
      incomplete remission.
  - reference: PMID:42066210
    reference_title: "Brazilian Psychiatric Association Guidelines for pharmacological treatment of Major Depressive Disorder: An overview of systematic reviews and meta-analyses."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "In acute treatment, selective serotonin reuptake inhibitors (SSRIs), venlafaxine, mirtazapine, and vortioxetine showed consistent evidence across efficacy and tolerability outcomes."
    explanation: The Brazilian Psychiatric Association guidelines find consistent efficacy and tolerability evidence for SSRIs in acute treatment of major depressive disorder.
- name: Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)
  description: Venlafaxine, duloxetine for depression with pain or fatigue.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: SNRI therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: venlafaxine
      term:
        id: CHEBI:9943
        label: venlafaxine
    - preferred_term: duloxetine
      term:
        id: CHEBI:36796
        label: duloxetine
  target_mechanisms:
  - target: Monoamine Deficiency
    treatment_effect: MODULATES
    description: >-
      SNRIs inhibit reuptake of both serotonin and norepinephrine, augmenting
      monoaminergic neurotransmission across the deficient monoamine systems.
- name: Cognitive Behavioral Therapy
  description: Evidence-based psychotherapy, comparable efficacy to medications.
  treatment_term:
    preferred_term: cognitive behavioral therapy
    term:
      id: NCIT:C64345
      label: Cognitive Behavior Therapy
- name: Electroconvulsive Therapy
  description: Most effective treatment for severe or treatment-resistant
    depression.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: electroconvulsive therapy
    term:
      id: NCIT:C93303
      label: Electroconvulsive Therapy
  target_mechanisms:
  - target: Neuroplasticity Deficits
    treatment_effect: MODULATES
    description: >-
      ECT robustly induces neurotrophic signaling and hippocampal neuroplasticity,
      counteracting the reduced-BDNF/plasticity deficit of depression.
- name: Ketamine/Esketamine
  description: Rapid-acting treatment for treatment-resistant depression.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: ketamine/esketamine therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: ketamine
      term:
        id: CHEBI:6121
        label: ketamine
    - preferred_term: esketamine
      term:
        id: CHEBI:60799
        label: esketamine
  target_mechanisms:
  - target: Excitation-Inhibition Imbalance
    treatment_effect: MODULATES
    description: >-
      Ketamine/esketamine antagonize the NMDA glutamate receptor, triggering a
      rapid glutamatergic surge and synaptogenesis that rebalances the
      excitatory-inhibitory tone — the basis of its rapid-acting antidepressant
      effect.
    evidence:
    - reference: PMID:39150594
      reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
      supports: SUPPORT
      snippet: "Based on this preclinical evidence implicating glutamate in depression
        and the rapid improvement of depression with ketamine treatment in a proof-of-concept
        trial, a range of N-methyl-D-aspartate (NMDA)-targeted therapies have been investigated."
      explanation: Ketamine's rapid antidepressant action is mediated through NMDA-receptor
        (glutamatergic) modulation, targeting excitation-inhibition imbalance.
  evidence:
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "Nasal administration of esketamine (Spravato®) was approved by the US
      Food and Drug Administration (FDA) in 2019 to treat adults with treatment-resistant
      depression and in 2020 for adults with MDD with acute suicidal ideation or behavior."
    explanation: This confirms FDA approval of esketamine for
      treatment-resistant depression and acute suicidal ideation/behavior in
      MDD.
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "Based on this preclinical evidence implicating glutamate in depression
      and the rapid improvement of depression with ketamine treatment in a proof-of-concept
      trial, a range of N-methyl-D-aspartate (NMDA)-targeted therapies have been investigated."
    explanation: This explains the mechanistic basis for ketamine's rapid-acting
      antidepressant effects through NMDA receptor antagonism and glutamate
      modulation.
  - reference: PMID:39150594
    reference_title: "Glutamatergic Modulators for Major Depression from Theory to Clinical Use."
    supports: SUPPORT
    snippet: "Oral combination dextromethorphan-bupropion (AXS-05, Auvelity® extended-release
      tablet) was FDA approved in 2022 for the treatment of MDD in adults."
    explanation: This documents the approval of another glutamatergic modulator
      for MDD treatment, expanding treatment options beyond esketamine.
- name: Transcranial Magnetic Stimulation
  description: Non-invasive neuromodulation for treatment-resistant depression.
  therapeutic_modality: DEVICE
  treatment_term:
    preferred_term: transcranial magnetic stimulation
    term:
      id: NCIT:C116655
      label: Transcranial Magnetic Stimulation
  target_mechanisms:
  - target: Neuroplasticity Deficits
    treatment_effect: MODULATES
    description: >-
      Repetitive TMS of dorsolateral prefrontal cortex modulates cortical
      excitability and promotes synaptic plasticity in mood-regulating circuits.
- name: Lithium Augmentation
  description: >-
    Adjunctive lithium added to an antidepressant is an evidence-based
    augmentation strategy for treatment-resistant depression, sharing the
    mood-stabilizer mechanism used first-line in bipolar disorder.
  therapeutic_modality: SMALL_MOLECULE
  treatment_term:
    preferred_term: Pharmacotherapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: lithium carbonate
      term:
        id: CHEBI:6504
        label: lithium carbonate
  target_mechanisms:
  - target: Neuroplasticity Deficits
    treatment_effect: MODULATES
    description: >-
      Lithium augments serotonergic antidepressant response and enhances
      neurotrophic/neuroplastic signaling (GSK-3 inhibition, BDNF induction), the
      same mood-stabilizing mechanism it exerts in bipolar disorder.
  evidence:
  - reference: PMID:34986373
    reference_title: "Augmentation strategies for treatment resistant major depression: A systematic review and network meta-analysis."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Our findings from the NMA for response rates, compared to placebo, were significant for: liothyronine, nortriptyline, aripiprazole, brexpiprazole, quetiapine, lithium, modafinil, olanzapine (fluoxetine), cariprazine, and lisdexamfetamine."
    explanation: >-
      Network meta-analysis found lithium augmentation produced a statistically
      significant improvement in response rate versus placebo in treatment-resistant
      major depression.
- name: Behavioral Activation
  description: Increasing engagement in rewarding activities.
  treatment_term:
    preferred_term: behavioral activation
    term:
      id: NCIT:C15184
      label: Behavioral Intervention
- name: Psilocybin-Assisted Therapy
  description: >
    Investigational single-dose psilocybin (25 mg) with psychological preparation,
    dosing support and integration, evaluated in a feasibility RCT in
    treatment-resistant depression at a single NHS site in England.
  therapeutic_modality: SMALL_MOLECULE
  notes: >-
    Investigational; not an approved treatment for major depressive disorder.
    The supporting trial (EudraCT 2018-003573-97) was a single-site feasibility
    study whose primary outcomes were recruitment, retention and estimation of
    MADRS variance, so the reported between-group MADRS difference is an
    effect-size estimate rather than a powered efficacy endpoint.
  treatment_term:
    preferred_term: psilocybin-assisted therapy
    term:
      id: NCIT:C15986
      label: Pharmacotherapy
    therapeutic_agent:
    - preferred_term: psilocybin
      term:
        id: CHEBI:8614
        label: psilocybin
  target_mechanisms:
  - target: Neuroplasticity Deficits
    treatment_effect: MODULATES
    description: >-
      Hypothesized mechanism: psychedelic 5-HT2A agonists such as psilocybin have
      been proposed to promote synaptic plasticity and neurotrophic signaling,
      which would counter the impaired neuroplasticity implicated in depression.
      The cited feasibility trial reports no mechanistic data, so this link is
      currently a hypothesis rather than an evidenced claim for this disorder.
  evidence:
  - reference: PMID:42562964
    reference_title: "Psilocybin-assisted therapy for treatment-resistant major depressive disorder in a public healthcare setting: a randomized controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Eligible participants met Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5) criteria for major depressive disorder and had an inadequate response to ≥2 antidepressant treatments or ≥1 antidepressant plus ≥1 psychotherapy. Participants received 25-mg psilocybin or placebo with preparation, dosing support and integration."
    explanation: >-
      Study design confirms psilocybin-assisted therapy for treatment-resistant
      depression (defined as inadequate response to ≥2 antidepressants or ≥1
      antidepressant + ≥1 psychotherapy) with standardized administration and
      psychological support.
  - reference: PMID:42562964
    reference_title: "Psilocybin-assisted therapy for treatment-resistant major depressive disorder in a public healthcare setting: a randomized controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The adjusted between-group difference at week 3 on the MADRS was -10.41 (95% confidence interval: -14.86 to -5.95; Cohen's d = -1.70), favoring psilocybin, which was sustained at week 6."
    explanation: >-
      The feasibility trial estimated a large between-group MADRS difference at
      week 3 (-10.41; Cohen's d = -1.70) favoring psilocybin, sustained at week 6.
      Primary outcomes were recruitment, retention and MADRS variance estimation,
      so this is an effect-size estimate from a single NHS site and not a powered
      efficacy result; the authors conclude it supports a future confirmatory trial.
  - reference: PMID:42562964
    reference_title: "Psilocybin-assisted therapy for treatment-resistant major depressive disorder in a public healthcare setting: a randomized controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sixty participants were randomized (1:1), balanced by age, sex and prior psilocybin exposure, and 59 of 60 participants completed the MADRS at all follow-up visits."
    explanation: >-
      High retention (59/60 participants, 98%) across 6-week follow-up period
      supports feasibility and tolerability of the single-dose psilocybin-assisted
      therapy protocol in treatment-resistant depression.
  - reference: PMID:42562964
    reference_title: "Psilocybin-assisted therapy for treatment-resistant major depressive disorder in a public healthcare setting: a randomized controlled trial."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In total, 123 and 164 nonserious adverse events occurred in the placebo and psilocybin arms, respectively."
    explanation: >-
      Adverse events were more frequent in the psilocybin arm than in placebo but
      were all nonserious, which bears on tolerability of the protocol. The trial
      was not powered for safety, so this counts only as partial support.
discussions:
- discussion_id: gap_mdd_fgf13_jip2_jnk_human_validity
  prompt: >-
    Does the FGF13-MAPK8IP2/JIP2-JNK-BAX/BCL2 apoptosis chain operate
    endogenously in adult human astrocytes in MDD, or is the reported phenotype
    specific to a stress model, developmental culture, brain region, sex, or a
    different JIP2-linked kinase? If astrocyte loss occurs, is this chain a
    causal driver of neuroinflammation and synaptic dysfunction, a downstream
    amplifier, or one of several cell-death programs?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
  - pathophysiology#Neuroinflammation
  - pathophysiology#Neuroplasticity Deficits
  rationale: >-
    The seed study provides bidirectional astrocyte-specific Fgf13 perturbation
    in chronic-restraint- and social-defeat-stress male mice and pathway
    readouts in neonatal primary mouse astrocytes. Its human component is
    instead a secondary reanalysis of GSE144136: all 17 MDD donors were male,
    died by suicide, and contributed dorsolateral prefrontal cortex rather than
    hippocampus. It neither demonstrates astrocyte death nor measures FGF13
    protein, JIP2 activity, phospho-JNK, or BAX/BCL2 target engagement in the
    same adult human cells. The original dataset emphasized excitatory neurons
    and oligodendrocyte precursor cells. A 2024 mini-review describes FGF13 as
    prominently expressed in developing and mature central and peripheral
    neurons, so the context-specific astrocytic source premise is itself
    single-sourced to the seed study and requires independent cell-type
    localization. Human hippocampal findings are
    region-, marker-, treatment-, and sex-dependent: studies report no major
    cell-death morphology, increased nonspecific glial packing density, or
    decreased hilar GFAP-immunoreactive astrocyte density only in unmedicated
    MDD, with female-specific GFAP area-fraction changes. An independent
    bulk-frontal-cortex study also found transcript-specific FGF-system
    dysregulation across MDD cohorts but did not resolve astrocytes. A separate
    both-sex dlPFC single-nucleus study found broadly similar threshold-free
    expression patterns but different significant DEG contributors, with
    astrocytes among the major male contributors; this supports sex-stratified
    validation but not an FGF13-specific or male-only inference. In male
    stress-exposed mice, astrocyte-specific Fgf2 manipulation also altered
    social avoidance through a distinct neurovascular/BBB route, showing that
    astrocytic FGF and behavioral endpoints are not specific to the FGF13-JIP2
    chain. Other stress-mouse studies implicate NLRP3-caspase-1-GSDMD pyroptosis
    or microglial IL-6/astrocyte IL-6R signaling, and earlier FHF-IB2
    biochemistry favored p38delta rather than JNK. Human relevance, cell-death
    identity, kinase specificity, and causal position therefore remain
    unresolved; clinical targeting would be premature.
  evidence:
  - reference: PMID:42421017
    reference_title: "FGF13 alleviates astrocytic apoptosis via JIP2 inhibition in the hippocampus and mitigates depression-like behavior."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Astrocyte-specific knockout of FGF13 induces astrocytic apoptosis,
      exacerbates inflammatory levels, and aggravates depression-like behaviors
      in mice.
    explanation: >-
      Establishes the mouse causal evidence whose fidelity to adult human MDD
      astrocytes is the central mismatch.
  - reference: PMID:39332965
    reference_title: "Fibroblast Growth Factor (FGF) 13."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: >-
      Similar to other FHFs, FGF13 has been considered a non-secreted protein
      that lacks an amino signal and is prominently expressed in developing and
      mature neurons of the central and peripheral nervous systems, as well as
      the heart.
    explanation: >-
      This mini-review provides canonical expression context rather than direct
      MDD evidence: prominent neuronal expression makes the seed study's
      astrocytic source premise independently unreplicated, while not excluding
      context-specific astrocytic expression.
  - reference: PMID:32341540
    reference_title: "Single-nucleus transcriptomics of the prefrontal cortex in major depressive disorder implicates oligodendrocyte precursor cells and excitatory neurons."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Here we used single-nucleus transcriptomics to examine ~80,000 nuclei from
      the dorsolateral prefrontal cortex of male individuals with MDD (n = 17)
      and of healthy controls (n = 17).
    explanation: >-
      Defines the sex-restricted, cross-sectional human dataset reused by the
      seed study; it cannot separate MDD from suicide or test hippocampal
      signaling and apoptosis.
  - reference: PMID:32341540
    reference_title: "Single-nucleus transcriptomics of the prefrontal cortex in major depressive disorder implicates oligodendrocyte precursor cells and excitatory neurons."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We found that the greatest dysregulation occurred in deep layer
      excitatory neurons and immature oligodendrocyte precursor cells (OPCs),
      and these contributed almost half (47%) of all changes in gene expression.
    explanation: >-
      The source dataset's dominant signals were not astrocytic, making the
      secondary FGF13 astrocyte association hypothesis-generating rather than
      pathway validation.
  - reference: PMID:15483108
    reference_title: "Dysregulation of the fibroblast growth factor system in major depression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this report we describe findings that imply dysregulation of several
      fibroblast growth factor (FGF) system transcripts in frontal cortical
      regions of brains from human subjects with major depressive disorder
      (MDD). This altered gene expression was discovered by microarray analysis
      of frontal cortical tissue from MDD, bipolar, and nonpsychiatric control
      subjects and was verified by quantitative real-time PCR analysis and,
      importantly, in a separate cohort of MDD subjects.
    explanation: >-
      This independent bulk-frontal-cortex study provides transcript- and
      cohort-dependent human FGF-system context, but it did not resolve
      astrocytes and therefore neither validates the later cell-type-specific
      FGF13 association nor establishes JIP2-JNK activity or apoptosis.
  - reference: PMID:37217515
    reference_title: "Cell type specific transcriptomic differences in depression show similar patterns between males and females but implicate distinct cell types and genes."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Cell type specific transcriptome-wide threshold-free MDD-associated gene
      expression patterns were similar between the sexes, but significant
      differentially expressed genes (DEGs) diverged. Among 7 broad cell types
      and 41 clusters evaluated, microglia and parvalbumin interneurons
      contributed the most DEGs in females, while deep layer excitatory neurons,
      astrocytes, and oligodendrocyte precursors were the major contributors in
      males.
    explanation: >-
      This both-sex dlPFC study supports testing sex-specific cell-type
      contributions, but its similar threshold-free patterns and different
      significant DEG contributors do not establish a male-only mechanism or
      implicate FGF13, JIP2, kinase activity, or astrocyte death.
  - reference: PMID:41545369
    reference_title: "Environmental enrichment and physical exercise prevent stress-induced social avoidance and blood-brain barrier alterations via Fgf2."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Fgf2 is mostly expressed by glial cells, and viral-mediated
      astrocyte-specific Fgf2 upregulation prevents stress-induced social
      avoidance while downregulation increases stress susceptibility and blunts
      physical exercise benefits.
    explanation: >-
      Bidirectional astrocytic Fgf2 manipulation identifies a parallel
      stress-resilience route in male mice, centered on nucleus-accumbens
      neurovascular protection rather than FGF13-JIP2 signaling or astrocyte
      apoptosis. It makes shared behavioral and inflammatory endpoints
      non-specific without refuting the FGF13 model.
  - reference: PMID:11860455
    reference_title: "Neither major depression nor glucocorticoid treatment affects the cellular integrity of the human hippocampus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      There was no evidence of neuronal cell loss or other major morphological
      alterations in any of the groups, nor was there a significant change in
      the distribution pattern of synaptophysin or Alz-50.
    explanation: >-
      This small mixed postmortem cohort pooled 15 donors with major depression
      or bipolar affective disorder and did not use astrocyte-specific apoptosis
      markers. Its lack of major hippocampal morphological loss and finding of
      only regional GFAP changes argue against assuming generalized human
      hippocampal cell loss from stress-mouse data.
  - reference: PMID:15522247
    reference_title: "Cellular changes in the postmortem hippocampus in major depression."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The density of granule cells and glia in the dentate gyrus and pyramidal
      neurons and glia in all cornv ammonis (CA)/hippocampal subfields is
      significantly increased by 30%-35% in MDD.
    explanation: >-
      Direct stereological sampling found increased glial packing density, not
      demonstrated astrocyte apoptosis; the authors instead proposed reduced
      neuropil and differential tissue shrinkage, underscoring unresolved human
      histopathology.
  - reference: PMID:26742791
    reference_title: "Density of GFAP-immunoreactive astrocytes is decreased in left hippocampi in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The density of astrocytes in the hilus, but not CA1 or CA2/3, was
      significantly decreased only in depressed subjects not taking an
      antidepressant drug, but not for depressed subjects taking an
      antidepressant drug. The area fraction of GFAP-immunoreactivity was
      significantly decreased in the dentate gyrus in women but not men with
      depression.
    explanation: >-
      This direct human MDD study supports a region-, medication-, and
      sex-qualified GFAP-immunoreactive astrocyte phenotype, but its
      cross-sectional marker-density result cannot distinguish apoptosis from
      marker loss or determine whether antidepressants prevented or restored
      the difference.
  - reference: PMID:34877938
    reference_title: "NLRP3/caspase-1/GSDMD-mediated pyroptosis exerts a crucial role in astrocyte pathological injury in mouse model of depression."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Here, we observed that depressive mice showed astrocytic pyroptosis, which
      was responsible for astrocyte loss, and selective serotonin reuptake
      inhibitor (SSRI) treatment could attenuate the pyroptosis induced by the
      chronic mild stress (CMS) model.
    explanation: >-
      A genetically interrogated mouse study supports a competing or parallel
      astrocyte cell-death program that must be distinguished from
      FGF13-JIP2-JNK-mediated apoptosis.
  - reference: PMID:39888279
    reference_title: "Microglia-Derived Interleukin-6 Triggers Astrocyte Apoptosis in the Hippocampus and Mediates Depression-Like Behavior."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Subsequent studies demonstrate that IL-6 released from activated microglia
      promotes astrocyte apoptosis. Furthermore, the knockdown of the P2X7
      receptor (P2X7R) in microglia, which is implicated in the stress response,
      reduces stress-induced microglial activation, IL-6 release, and astrocyte
      apoptosis. Direct inhibition of microglia by minocycline corroborates
      these effects. The selective knockdown of IL-6 in microglia and IL-6
      receptors in astrocytes effectively mitigates depression-like behaviors
      and reduces astrocyte atrophy.
    explanation: >-
      Cell-type-selective epistasis in a social-defeat mouse model identifies a
      distinct upstream microglia-to-astrocyte apoptosis route; FGF13 could be
      downstream, parallel, or model-specific rather than the initiating lesion.
  - reference: PMID:12244047
    reference_title: "Fibroblast growth factor homologous factors and the islet brain-2 scaffold protein regulate activation of a stress-activated protein kinase."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      Mixed lineage kinase 3 (MLK3) and IB2 synergistically activate p38delta but
      not the MAPKs JNK-1 and p38alpha.
    explanation: >-
      This prior biochemical result makes JNK-versus-p38delta pathway
      discrimination and an interaction-deficient FGF13 rescue essential.
  proposed_experiments:
  - experiment_id: exp_mdd_fgf13_human_multiregion_validation
    name: Adult human multi-region astrocyte pathway and cell-fate validation
    description: >-
      In an independently powered postmortem cohort, jointly stratify MDD
      diagnosis and cause of death (MDD nonsuicide, MDD suicide, psychiatric
      suicide without MDD, and psychiatrically healthy nonsuicide controls),
      include both sexes, and sample dorsolateral prefrontal cortex, anterior
      cingulate cortex, and hippocampus from the same donors where possible.
      Combine astrocyte-resolved spatial or single-nucleus transcriptomics with
      RNAscope and multiplex protein/phosphoprotein imaging. Quantify FGF13
      isoforms, MAPK8IP2, phospho-JNK/c-Jun, phospho-p38delta, BAX/BCL2,
      cleaved-caspase-3/TUNEL, NLRP3/GSDMD, IL-6R, astrocyte abundance, and
      morphology. Pre-register region-by-sex tests and separate marker
      downregulation or atrophy from irreversible cell death.
    experiment_type:
      preferred_term: multi-region postmortem molecular pathology study
    model_systems:
    - name: Multi-region postmortem human MDD brain cohort
      description: >-
        Adult human brain tissue balanced across diagnosis, suicide status, and
        sex and matched on age, postmortem interval, tissue pH, medication
        exposure, illness duration, and agonal factors.
      experimental_model_type: OTHER
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: astrocyte
        term:
          id: CL:0000127
          label: astrocyte
    readouts:
    - name: Within-astrocyte FGF13-JIP2 stress-kinase state
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      description: >-
        Measure FGF13 isoform abundance, MAPK8IP2, phospho-JNK/c-Jun, and
        phospho-p38delta in spatially identified astrocytes in each region.
      assays:
      - preferred_term: spatial transcriptomics
      - preferred_term: multiplex immunofluorescence
    - name: Astrocyte fate and cell-death-mode assignment
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      description: >-
        Distinguish apoptosis, pyroptosis, reversible atrophy, marker loss, and
        true numerical depletion using orthogonal cell-fate and stereological
        measures.
      biological_processes:
      - preferred_term: apoptotic process
        term:
          id: GO:0006915
          label: apoptotic process
      - preferred_term: pyroptotic inflammatory response
        term:
          id: GO:0070269
          label: pyroptotic inflammatory response
      assays:
      - preferred_term: design-based stereology
      - preferred_term: terminal deoxynucleotidyl transferase dUTP nick end labeling assay
    controls:
    - name: Diagnosis-by-suicide factorial controls
      description: >-
        MDD nonsuicide and non-MDD psychiatric suicide groups separate
        diagnosis-associated signals from suicide-associated signals.
    - name: Preanalytic and treatment matching
      description: >-
        Match or model age, sex, postmortem interval, tissue pH, agonal state,
        medication exposure, substance use, and illness duration.
    - name: Orthogonal astrocyte identity and fate controls
      description: >-
        Require multiple astrocyte markers plus stereology so reduced GFAP or
        RNA recovery is not misclassified as cell death.
    decision_criterion: >-
      Human relevance is supported only if an independent cohort shows
      co-occurring lower FGF13, JIP2-linked JNK activation, and apoptotic fate
      within the same adult astrocytes after adjustment for suicide,
      medication, preanalytic factors, region, and sex, with a prespecified
      replication region. A signal restricted to suicide, one sex or one
      cortical region supports a restricted modifier rather than generalized
      MDD pathophysiology. Absence or reversal of the within-cell chain, a
      p38delta- rather than JNK-linked state, or evidence for atrophy/marker loss
      without apoptosis weakens the hypothesis.
    would_support:
    - mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
    would_refute:
    - mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
  - experiment_id: exp_mdd_fgf13_jip2_cross_species_epistasis
    name: Human-astrocyte and adult-mouse FGF13-JIP2 kinase epistasis
    description: >-
      Run a preregistered, bidirectional epistasis matrix in sex-balanced human
      iPSC-derived astrocyte-neuron-microglia tricultures and in adult,
      inducible astrocyte-specific Fgf13 mice under stressed and unstressed
      conditions. Compare FGF13 loss with wild-type rescue, overexpression, and
      an interaction-deficient FGF13 rescue; cross these arms with MAPK8IP2
      loss/rescue and selective JNK-versus-p38delta perturbation. In parallel,
      block IL-6/IL-6R and NLRP3/GSDMD pathways to test whether they are
      upstream, downstream, or independent. Use blinded allocation and analysis,
      temporal sampling before cell loss, and mediation analysis linking
      astrocyte survival to inflammatory, synaptic, network, and behavioral
      outcomes.
    experiment_type:
      preferred_term: cross-species genetic epistasis and rescue experiment
    model_systems:
    - name: Human iPSC-derived astrocyte-neuron-microglia triculture
      description: >-
        Multiple male and female donor lines with isogenic edits, matured before
        glucocorticoid or inflammatory stress and sampled longitudinally.
      experimental_model_type: CO_CULTURE
      organism:
        preferred_term: human
        term:
          id: NCBITaxon:9606
          label: Homo sapiens
      cell_types:
      - preferred_term: astrocyte
        term:
          id: CL:0000127
          label: astrocyte
      - preferred_term: neuron
        term:
          id: CL:0000540
          label: neuron
      - preferred_term: microglial cell
        term:
          id: CL:0000129
          label: microglial cell
    - name: Adult inducible astrocyte-specific Fgf13 mouse
      description: >-
        Both-sex adult inducible loss- and gain-of-function cohorts tested with
        and without chronic restraint stress, plus a sex-appropriate
        social-defeat replication.
      experimental_model_type: OTHER
      organism:
        preferred_term: mouse
        term:
          id: NCBITaxon:10090
          label: Mus musculus
      cell_types:
      - preferred_term: astrocyte
        term:
          id: CL:0000127
          label: astrocyte
    perturbations:
    - name: Bidirectional FGF13 dosage and domain-specific rescue
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      genes:
      - preferred_term: FGF13
        term:
          id: hgnc:3670
          label: FGF13
      effect: loss, overexpression, wild-type rescue, and JIP2-binding-deficient rescue
    - name: MAPK8IP2 genetic epistasis
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      genes:
      - preferred_term: MAPK8IP2
        term:
          id: hgnc:6883
          label: MAPK8IP2
      effect: knockout or knockdown followed by wild-type scaffold rescue
    - name: JNK-versus-p38delta and alternative-death-pathway discrimination
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      description: >-
        Use orthogonal genetic and selective pharmacologic perturbations of JNK
        and p38delta, plus IL-6/IL-6R and NLRP3/GSDMD blockade, with biochemical
        target-engagement confirmation.
    readouts:
    - name: Temporal stress-kinase activation and astrocyte death mode
      target: mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
      description: >-
        Quantify FGF13-JIP2 binding, JNK and p38delta activity, BAX/BCL2,
        caspase-dependent apoptosis, gasdermin-dependent pyroptosis, and
        lineage-traced astrocyte survival before and after stress.
      biological_processes:
      - preferred_term: apoptotic process
        term:
          id: GO:0006915
          label: apoptotic process
      - preferred_term: pyroptotic inflammatory response
        term:
          id: GO:0070269
          label: pyroptotic inflammatory response
      assays:
      - preferred_term: co-immunoprecipitation assay
      - preferred_term: live-cell lineage imaging
    - name: Inflammatory and synaptic mediation
      target: pathophysiology#Neuroinflammation
      description: >-
        Measure cytokine release, microglial state, synaptic-protein abundance,
        neuronal morphology, and multielectrode-array network function; test
        whether preventing astrocyte death mediates these downstream effects. In
        the mouse arms, also measure astrocytic Fgf2, endothelial Cldn5, and BBB
        permeability as a prespecified parallel neurovascular comparator.
      assays:
      - preferred_term: cytokine quantification
      - preferred_term: multielectrode array recording
      - preferred_term: blood-brain barrier permeability assay
    - name: Stress behavior with specificity controls
      target: pathophysiology#Neuroplasticity Deficits
      description: >-
        In mice, combine reward- and social-interaction measures with open-field
        locomotion, anxiety, pain sensitivity, and stress-hormone readouts so
        nonspecific performance changes are not called antidepressant effects.
      assays:
      - preferred_term: behavioral phenotyping
    controls:
    - name: Isogenic and vector controls
      description: >-
        Use sham-edited isogenic cultures, wild-type littermates, driver-only
        and vector-only mice, and matched unstressed arms.
    - name: Binding-deficient and pathway-specific rescue controls
      description: >-
        Compare wild-type FGF13 rescue with a biochemically verified
        JIP2-binding-deficient rescue and confirm target engagement for each
        kinase intervention.
    - name: Sex, maturation, allocation, and assay controls
      description: >-
        Balance sex and donor background, use mature rather than neonatal human
        astrocytes, randomize and blind mouse studies, and include locomotor and
        viability controls.
    decision_criterion: >-
      The proposed chain is supported only if FGF13 loss precedes astrocyte
      apoptosis in both systems; wild-type but not interaction-deficient FGF13
      rescues it; MAPK8IP2 loss and JNK-selective blockade abolish the
      stress-kinase, death, and downstream phenotypes; and p38delta or alternative
      death-program perturbations do not better explain the effect. A
      JIP2-independent rescue, predominant p38delta signaling, dependence on
      microglial IL-6 or NLRP3/GSDMD, lack of replication in mature human
      astrocytes, or behavioral change without astrocyte-survival mediation
      would refute or materially revise the FGF13-JIP2-JNK causal chain. An
      Fgf2-Cldn5/BBB response without FGF13-JIP2 target engagement supports a
      parallel neurovascular route and cannot be counted as evidence for the
      seed chain.
    would_support:
    - mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
    - pathophysiology#Neuroinflammation
    - pathophysiology#Neuroplasticity Deficits
    would_refute:
    - mechanistic_hypotheses#astrocytic_fgf13_jip2_jnk_cell_death_model
- discussion_id: gap_mdd_excitation_inhibition_imbalance_substrates
  prompt: >-
    Excitation-inhibition (E/I) imbalance in prefrontal-cingulate cortices is
    implicated in MDD pathophysiology, but what are the molecular substrates
    underlying E/I dysregulation in depression? Are GABAergic, glutamatergic,
    serotonergic, and opioidergic systems dysregulated primarily (upstream
    drivers) or secondarily (consequences of other pathophysiology)? How do
    these neurochemical systems interact to produce measurable E/I imbalance?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Excitation-Inhibition Imbalance
  - pathophysiology#Monoamine Deficiency
  - pathophysiology#Neuroplasticity Deficits
  rationale: >-
    Recent neuroimaging studies (Ge et al., 2026) demonstrate that MDD patients
    show significantly reduced Hurst exponent values (a biophysically confirmed
    proxy of cortical E/I balance) in parietal and prefrontal-cingulate cortices,
    with transcriptomic enrichment for neuronal structural organization and
    mitochondrial function. Neurochemical mapping links E/I dysregulation to
    GABAergic, opioidergic, serotonergic, and synaptic density distributions.
    However, critical gaps remain: (1) the causal direction of E/I imbalance
    relative to monoamine deficiency and HPA-axis dysregulation; (2) whether
    specific GABA receptor subtypes (α1-α6, β1-β3, γ1-γ3) or glutamate receptor
    classes (NMDA, AMPA, kainate) are preferentially dysregulated in depression;
    (3) the role of parvalbumin-positive fast-spiking interneurons and other
    inhibitory circuits in producing cortical E/I imbalance; and (4) how ketamine's
    rapid antidepressant effects via NMDA-receptor antagonism mechanistically
    relate to E/I normalization in treatment-resistant depression. Understanding
    these substrates could identify new therapeutic targets distinct from
    monoamine reuptake inhibition.
  evidence:
  - reference: PMID:42372880
    reference_title: "Intrinsic excitation-inhibition imbalance in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Transcriptomic analysis identified enrichment for neuronal structural organization, nucleic acid metabolism, and mitochondrial function, with preferential overlap with excitatory and inhibitory neuron-specific gene sets."
    explanation: >-
      Multimodal evidence links E/I dysregulation to transcriptomic changes in
      neuronal structure and energy metabolism, supporting the mechanistic
      relevance of this imbalance in MDD.
  - reference: PMID:42372880
    reference_title: "Intrinsic excitation-inhibition imbalance in major depressive disorder."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Divergent group-by-treatment effects were observed in the anterior cingulate and medial prefrontal cortices, with ketamine-induced increases in TRD patients."
    explanation: >-
      The differential effect of ketamine on cortical E/I balance in
      treatment-resistant depression suggests E/I normalization as a putative
      mechanism underlying rapid antidepressant action, but the molecular
      pathway from NMDA antagonism to E/I balance restoration remains unresolved.
  proposed_experiments:
  - experiment_id: exp_mdd_ei_substrate_specificity
    name: Map GABA and glutamate receptor subtype dysregulation across cortical regions in MDD
    description: >-
      Using postmortem brain tissue from MDD and control subjects, perform
      multi-region quantification of GABA receptor subtype expression (α1-α6,
      β1-β3, γ1-γ3) and glutamate receptor class expression (GluN1/GluN2, GluA1-A4,
      GluK1-K5) via Western blot, qPCR, and in situ hybridization in
      prefrontal-cingulate cortices. Correlate subtype-specific changes with
      lifetime depression severity and antidepressant medication history.
    experiment_type:
      preferred_term: postmortem brain tissue analysis
  - experiment_id: exp_mdd_ei_interneuron_circuits
    name: Determine whether parvalbumin-positive interneuron dysfunction drives cortical E/I imbalance in depression models
    description: >-
      In chronic-stress depression models and acute-stress models, use
      electrophysiology and optogenetics to measure inhibitory tone from
      parvalbumin-positive fast-spiking interneurons onto pyramidal neurons.
      Assess whether targeted optogenetic reactivation of inhibitory circuits
      restores cortical E/I balance and reverses depression-like behavior.
      Parallel human studies using MEG/EEG to measure cortical oscillatory power
      and phase-amplitude coupling as surrogates of interneuron function.
    experiment_type:
      preferred_term: in vivo electrophysiology and optogenetics
  - experiment_id: exp_mdd_ketamine_ei_restoration
    name: Test whether ketamine's rapid antidepressant effect requires cortical E/I rebalancing
    description: >-
      In acute-stress depression models, measure time-resolved Hurst exponent and
      cortical E/I balance before, during (minutes to hours), and after ketamine
      administration. Assess whether E/I normalization precedes or follows
      behavioral antidepressant effects. Simultaneously measure monoamine levels
      and HPA-axis markers to determine temporal ordering and mechanistic
      independence of E/I rebalancing from classical monoamine pathways.
    experiment_type:
      preferred_term: in vivo neuroimaging and electrophysiology during pharmacological intervention
- discussion_id: gap_mdd_oligodendrocyte_dysfunction
  prompt: >-
    Emerging evidence implicates oligodendrocyte (OL) dysfunction and myelin
    abnormalities in major depressive disorder, extending beyond classical
    myelination to neural plasticity, neuronal metabolic support, and circuit
    regulation. Is OL/white-matter pathology a primary driver of MDD, or a
    secondary consequence of neuroinflammation, chronic stress, and HPA-axis
    hyperactivity? Which OL subsets and brain regions are most mechanistically
    relevant, and how does OL-astrocyte-microglia crosstalk causally link to
    depressive symptoms?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Oligodendrocyte Dysfunction and Demyelination
  - pathophysiology#Neuroplasticity Deficits
  - pathophysiology#Neuroinflammation
  - pathophysiology#HPA Axis Dysregulation
  rationale: >-
    Neuroimaging consistently shows white-matter and brain-connectivity
    alterations in MDD, and post-mortem and animal studies report reduced
    oligodendrocyte density, downregulated myelin-related genes, and myelin
    abnormalities. The Gan et al. (2026) review argues that OL dysfunction is a
    key pathophysiological mechanism in MDD that extends beyond myelination to
    include contributions to neural plasticity, metabolic support, and circuit
    regulation, manifesting primarily as myelin abnormalities tied to altered
    connectivity and emotional processing. What remains unresolved is the causal
    direction: whether OL/myelin pathology initiates circuit dysfunction and
    depressive symptoms, or whether it is downstream of neuroinflammation,
    glucocorticoid excess from HPA-axis hyperactivity, and impaired
    neuroplasticity. The relative importance of distinct OL populations
    (mature OLs vs. oligodendrocyte precursor cells) and region-specific
    contributions (prefrontal cortex vs. hippocampus) is also unknown. Because
    OLs interact bidirectionally with neurons, astrocytes, and microglia,
    disentangling OL-glial crosstalk from primary inflammatory signaling is
    difficult with cross-sectional human data. Resolving these questions would
    clarify whether remyelination-promoting or OL-protective strategies could
    serve as disease-modifying treatments rather than symptomatic ones.
  proposed_experiments:
  - experiment_id: exp_mdd_ol_causality_remyelination
    name: Region-specific oligodendrocyte manipulation with longitudinal connectivity and behavioral readouts
    description: >-
      In a chronic-stress rodent model of depression, use cell-type-specific
      genetic and pharmacological tools to (a) deplete or impair mature
      oligodendrocytes and oligodendrocyte precursor cells in prefrontal cortex
      versus hippocampus, and (b) conversely promote remyelination, while
      measuring myelin integrity, neuroinflammatory glial activation, neural
      circuit connectivity, and depression-like behavior. Pair with a human
      cohort combining diffusion-MRI white-matter metrics, peripheral
      inflammatory markers, and longitudinal symptom trajectories to test
      temporal ordering of white-matter change relative to inflammation and
      symptom onset.
    experiment_type:
      preferred_term: cell-type-specific perturbation with longitudinal imaging and behavioral phenotyping
    readouts:
    - name: Myelin integrity and white-matter connectivity
      target: pathophysiology#Neuroplasticity Deficits
      description: >
        Quantify myelin sheath thickness, oligodendrocyte density, and
        white-matter tract connectivity (diffusion imaging) to test whether
        manipulating OL/myelin alters circuit structure independent of
        inflammation.
      assays:
      - preferred_term: diffusion tensor imaging
      - preferred_term: myelin histopathology
      direction: NEGATIVE
    - name: Glial neuroinflammatory activation
      target: pathophysiology#Neuroinflammation
      description: >
        Measure microglial and astrocyte activation and proinflammatory
        cytokine levels to determine whether OL dysfunction precedes or follows
        neuroinflammatory signaling.
      assays:
      - preferred_term: glial activation immunostaining
      - preferred_term: cytokine quantification
      direction: POSITIVE
    - name: Depression-like behavior and symptom trajectory
      target: pathophysiology#HPA Axis Dysregulation
      description: >
        Assess depression-like behavior in animals and longitudinal depressive
        symptom severity in humans relative to stress/glucocorticoid exposure to
        test whether OL-targeted intervention modifies outcome.
      assays:
      - preferred_term: depression behavioral battery
      direction: NEGATIVE
    decision_criterion: >-
      OL dysfunction is supported as a primary driver if region-specific OL
      depletion produces white-matter and depression-like phenotypes before or
      independent of neuroinflammatory activation, and if remyelination-promoting
      intervention reverses depressive behavior; it is supported as a secondary
      consequence if white-matter change consistently follows inflammatory and
      glucocorticoid signaling and OL manipulation alone does not alter
      depressive outcomes.
    would_support:
    - pathophysiology#Neuroplasticity Deficits
    - pathophysiology#Neuroinflammation
  evidence:
  - reference: PMID:41730818
    reference_title: "Oligodendrocyte dysfunction in major depressive disorder: Mechanistic insights and emerging therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Emerging evidence increasingly implicates oligodendrocyte (OL) dysfunction as a key pathophysiological mechanism in MDD, extending beyond their classical role in myelination to include critical contributions to neural plasticity, metabolic support, and circuit regulation."
    explanation: >-
      This review establishes OL dysfunction as an emerging mechanistic
      hypothesis in MDD that extends beyond myelination, motivating the
      knowledge gap about its role and causal position.
  - reference: PMID:41730818
    reference_title: "Oligodendrocyte dysfunction in major depressive disorder: Mechanistic insights and emerging therapies."
    supports: SUPPORT
    evidence_source: OTHER
    snippet: "Finally, we highlight key knowledge gaps and propose future research directions aimed at clarifying the contribution of OL biology to depressive disorders and improving treatment outcomes."
    explanation: >-
      The authors explicitly flag unresolved knowledge gaps and call for
      research clarifying the contribution of OL biology to depression,
      directly supporting this KNOWLEDGE_GAP entry.
- discussion_id: gap_mdd_vitiligo_shared_immune_dysregulation
  prompt: >-
    A large longitudinal cohort supports MDD-to-vitiligo and
    vitiligo-to-MDD associations, but what accounts for them? Does an acquired,
    cell-state-specific inflammatory program involving p38-alpha/MAPK14 precede
    and help cause both conditions, or are the associations better explained by
    psychosocial effects of visible skin disease, healthcare surveillance,
    treatment, nonspecific inflammatory burden, shared pleiotropic genetic
    liability, or parallel disease-specific mechanisms? Is MAPK14 necessary in
    homologous causal cell states, or merely a cross-tissue bioinformatic
    marker?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - pathophysiology#Neuroinflammation
  - pathophysiology#Monoamine Deficiency
  rationale: >-
    A UK primary-care cohort found that incident MDD preceded recorded vitiligo
    (adjusted HR 1.64) and incident vitiligo preceded recorded MDD (HR 1.31
    before age 30 and 1.22 at age 30 or older). That establishes a temporal
    epidemiologic signal, not biological mediation. The study did not measure
    disease severity, and treatment and healthcare-contact effects remain
    possible. The cross-disease transcriptomic study is weaker mechanistic
    evidence: it compared separate MDD and vitiligo expression datasets, used
    only 15 vitiligo samples and 15 healthy samples in discovery, inferred
    immune signatures from bulk profiles, and used permissive
    differential-expression thresholds. It did not analyze an explicitly
    ascertained comorbid cohort or paired tissues from the same participants.
    The study did use independent disease-specific GEO validation sets, but
    discriminator performance does not establish a shared cell state or
    mediator. Mouse serotonergic-neuron genetics supports p38-alpha in a
    stress-related behavioral model; a larger human MDD study found no advantage
    for the tested losmapimod regimen after a smaller prematurely terminated
    study had favored treatment. Patient-derived
    nonsegmental-vitiligo keratinocytes and cultured mouse melanocytes support
    pan-p38 activity in skin models, not MAPK14 specificity. These
    compartment-, species-, and assay-specific results are compatible with
    parallel p38 use and do not establish a shared human MAPK14 mechanism.
    Conversely, bidirectional Mendelian randomization found no significant
    directional causal effect between generalized vitiligo and broad
    mental-disorder phenotypes, including depression. That design does not test
    shared pleiotropic genetic liability. A claims study found a mental-health
    profile largely comparable to atopic dermatitis. The gap is therefore the
    mediator and its specificity; the evidence does not justify a new MDD
    pathophysiology node, MAPK14 biomarker, or conserved mechanism module. A
    candidate pair-level record is curated in
    com_Major_Depressive_Disorder__Vitiligo.
  evidence:
  - reference: PMID:30528503
    reference_title: "Vitiligo and major depressive disorder: A bidirectional population-based cohort study."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In adjusted models, MDD patients (n = 405,397) were at a 64% increased risk for vitiligo (hazard ratio 1.64"
    explanation: >-
      The large adjusted cohort establishes the MDD-to-vitiligo temporal
      association but cannot identify its mediator.
  - reference: PMID:42418414
    reference_title: "Bioinformatics analysis reveals the characteristics of immune microenvironment in major depressive disorder and vitiligo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "These findings primarily serve to generate hypotheses regarding shared mechanisms and prioritize targets for subsequent experimental validation."
    explanation: >-
      The authors explicitly limit the cross-disease MAPK14 result to hypothesis
      generation.
  - reference: PMID:42418414
    reference_title: "Bioinformatics analysis reveals the characteristics of immune microenvironment in major depressive disorder and vitiligo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "For MDD, the GSE98793 dataset was utilized, which includes 192 whole blood samples: 64 from healthy controls, 128 from patients with MDD, using the GPL570 platform for sequencing. For vitiligo, the GSE65127 and GSE53146 datasets were integrated using the R package ‘sva’ to correct batch effects. The combined datasets included 15 healthy samples and 15 vitiligo samples, using the GPL570 and GPL14951 platforms for sequencing."
    explanation: >-
      The analysis combined separate disease datasets and had only 15 vitiligo
      and 15 healthy samples, rather than paired samples from a comorbid cohort.
  - reference: PMID:42418414
    reference_title: "Bioinformatics analysis reveals the characteristics of immune microenvironment in major depressive disorder and vitiligo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Differentially expressed genes (DEGs) between disease and control groups were identified using the R package ‘limma’, applying a threshold of |log2FC| > 0 and P-value < 0.05."
    explanation: >-
      The permissive nonzero fold-change and nominal P-value screen limits the
      specificity of the candidate-gene intersection.
  - reference: PMID:42418414
    reference_title: "Bioinformatics analysis reveals the characteristics of immune microenvironment in major depressive disorder and vitiligo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "It should be noted that these ssGSEA scores represent inferred immune signatures from bulk RNA-seq data, rather than direct measurements of actual immune cell abundances."
    explanation: >-
      The immune-cell results are computational enrichment scores rather than
      measured cell abundances.
  - reference: PMID:42418414
    reference_title: "Bioinformatics analysis reveals the characteristics of immune microenvironment in major depressive disorder and vitiligo."
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "Two independent GEO datasets (GSE52790 and GSE80009) were utilized as external validation sets to examine the consistency and stability of these findings."
    explanation: >-
      Independent disease-specific datasets strengthen the candidate-marker
      screen relative to discovery alone, but ROC-style discriminatory
      validation does not establish a shared cell state, p38 activity,
      mediation, or causality.
  - reference: DOI:10.1111/exd.14979
    reference_title: "Exploring genetic associations between vitiligo and mental disorders using Mendelian randomization"
    supports: SUPPORT
    evidence_source: COMPUTATIONAL
    snippet: "In our findings, none of the rigorous bidirectional MR analyses uncovered a significant causal association."
    explanation: >-
      The null result constrains genetically instrumented disease-to-disease
      effects between generalized vitiligo and a broad depression phenotype; it
      does not test shared pleiotropic liability and leaves acquired and
      clinically defined MDD-subgroup mechanisms unresolved.
  - reference: PMID:41781039
    reference_title: "Prevalence and comparative risk of mental health disorders in persons with vitiligo: a retrospective matched cohort study using claims data with expert-informed case validation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mental health comorbidity profile was largely comparable to that of atopic dermatitis, whereas more pronounced differences were observed in comparisons with psoriasis."
    explanation: >-
      A dermatologic comparator confirms mental-health burden but challenges
      the specificity of a vitiligo-specific shared immune mechanism.
  - reference: PMID:21835346
    reference_title: "Selective p38α MAPK deletion in serotonergic neurons produces stress resilience in models of depression and addiction."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Social defeat stress produced social avoidance (a model of depression-like behaviors) and reinstatement of cocaine preference (a measure of addiction risk) in wild-type mice, but not in mice having p38α MAPK selectively deleted in serotonin-producing neurons of the dorsal raphe nucleus."
    explanation: >-
      Cell-specific mouse genetics supports a p38-alpha stress pathway in
      serotonergic neurons, not a human MDD-vitiligo bridge.
  - reference: PMID:24699061
    reference_title: "Evaluation of antidepressant properties of the p38 MAP kinase inhibitor losmapimod (GW856553) in Major Depressive Disorder: Results from two randomised, placebo-controlled, double-blind, multicentre studies using a Bayesian approach."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A subsequent study, Study 009 (n=128), designed using a Bayesian approach based on a prior derived from Study 574, showed no advantage for losmapimod (Bech, 6 weeks: endpoint drug vs. placebo difference = 1.11; 95% credible interval, -0.22, 2.50). Biomarker data showed no significant changes. In conclusion 7.5 mg BID losmapimod was not effective in MDD."
    explanation: >-
      The larger human MDD study and its biomarkers were null, although a
      smaller prematurely terminated study had favored treatment. A single
      regimen, duration, and selected MDD population without demonstrated
      biomarker modulation is a narrow pharmacologic constraint, not a
      refutation of cell-specific MAPK14 activity or a shared acquired mediator.
  - reference: PMID:20085492
    reference_title: "The involvement of Smac/DIABLO, p53, NF-kB, and MAPK pathways in apoptosis of keratinocytes from perilesional vitiligo skin: Protective effects of curcumin and capsaicin."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "In keratinocytes from perilesional vitiligo skin, we observed high levels of activated p38, NF-kB p65 subunit, p53, and Smac/DIABLO proteins."
    explanation: >-
      Patient-derived keratinocytes from 12 people with nonsegmental vitiligo
      support a skin-compartment pan-p38 signal. The cultured-cell study does
      not resolve MAPK14 from other p38 isoforms or connect the signal to MDD.
  - reference: PMID:18575770
    reference_title: "Minocycline protects melanocytes against H2O2-induced cell death via JNK and p38 MAPK pathways."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "Also, H2O2 treatment activates JNK and p38 MAPK, and executive caspase 3 in B10BR cells."
    explanation: >-
      p38-family activation in oxidatively stressed mouse melanocytes supplies
      separate plausibility but is neither MAPK14-specific nor evidence of a
      shared human mechanism.
  proposed_experiments:
  - experiment_id: exp_mdd_vitiligo_longitudinal_mediation
    name: Adjudicate temporal immune, psychosocial, and surveillance mediation
    description: >-
      Prospectively enroll treatment-naive incident MDD-only, active
      nonsegmental-vitiligo-only, comorbid, and matched control groups. Reassess
      structured MDD diagnoses, symptom trajectories, vitiligo subtype,
      activity, extent and visibility, medication, healthcare utilization,
      autoimmune disease, smoking, BMI, socioeconomic factors, stress, stigma,
      and quality of life. At repeated visits profile circulating immune cells
      by single-cell transcriptomics plus surface proteins and measure
      cell-type-specific phospho-p38 and cytokines; collect paired lesional and
      nonlesional skin only from consenting vitiligo participants. Follow the
      single-disease groups for onset of the second condition and use
      prespecified time-varying mediation models.
    experiment_type:
      preferred_term: prospective longitudinal multimodal cohort study
    readouts:
    - name: Incident second condition and within-person disease trajectories
      target: pathophysiology#Neuroinflammation
      description: >-
        Adjudicated incident vitiligo in MDD-only participants and incident MDD
        in vitiligo-only participants, with repeated measures of both diseases.
      interpretation: >-
        Establishes temporal order and distinguishes prediction of transition
        from cross-sectional correlation.
    - name: Cell-state-resolved p38 and inflammatory program
      target: pathophysiology#Neuroinflammation
      description: >-
        Phospho-p38, cytokines, and single-cell immune states in blood, aligned
        to skin states when skin is available.
      interpretation: >-
        Tests whether a homologous acquired state precedes both transitions
        rather than following disease or treatment.
    controls:
    - name: Matched disease-free controls under equal surveillance
      description: >-
        Controls matched on age, sex, site, healthcare-contact schedule, and
        major measured confounders.
    - name: Single-disease comparator groups
      description: >-
        MDD-only and vitiligo-only groups permit direction-specific analyses;
        atopic dermatitis is an optional visible-inflammatory-skin comparator.
    decision_criterion: >-
      Support a shared acquired mediator only if the same prespecified
      cell-state-specific p38 program precedes onset of the second condition in
      both directions, tracks both outcomes within person, and mediates risk
      after psychosocial, treatment, autoimmune, and surveillance covariates.
      Prefer a psychosocial explanation if visibility, stigma, or distress
      predicts MDD without that program; prefer surveillance bias if equalized
      follow-up materially attenuates the association; classify p38 as a marker
      if it appears only after disease or treatment.
    would_support:
    - pathophysiology#Neuroinflammation
    - Vitiligo:pathophysiology#Autoimmune Reaction

  - experiment_id: exp_mdd_vitiligo_mapk14_cell_epistasis
    name: Test cell-specific MAPK14 necessity and rescue in both disease arms
    description: >-
      Build matched human systems comprising iPSC-derived serotonergic neurons
      with supporting glia and autologous melanocyte-keratinocyte-cytotoxic
      T-cell skin cultures from MDD-only, active nonsegmental-vitiligo-only,
      comorbid MDD-vitiligo, and matched disease-free control donors. First map
      phospho-p38 to specific cell states and upstream ligands. Then compare
      MAPK14 CRISPR interference or knockout with a selective p38-alpha
      inhibitor, non-targeting and vehicle arms, and rescue with
      CRISPR-resistant wild-type versus kinase-dead MAPK14. Challenge neural
      cultures with stress/inflammatory ligands and skin cultures with oxidative
      stress and IFN-gamma-driven immune attack; use blinded, preregistered
      analysis.
    experiment_type:
      preferred_term: human cell-specific causal perturbation and rescue study
    perturbations:
    - name: MAPK14 genetic and pharmacologic loss of function
      target: pathophysiology#Neuroinflammation
      description: >-
        Cell-type-restricted MAPK14 CRISPR perturbation and selective
        p38-alpha inhibition in neural, skin, and immune compartments.
    - name: Wild-type versus kinase-dead MAPK14 rescue
      target: pathophysiology#Monoamine Deficiency
      description: >-
        Isogenic rescue separates on-target catalytic dependence from editing
        artifacts and scaffold effects.
    readouts:
    - name: Serotonergic stress response
      target: pathophysiology#Monoamine Deficiency
      description: >-
        Serotonin-transporter surface localization and uptake, cytokine release,
        neuronal activity, and cell viability.
    - name: Melanocyte injury and immune attack
      target: Vitiligo:pathophysiology#Autoimmune Reaction
      description: >-
        Melanocyte apoptosis and survival, cytotoxic T-cell killing, and
        CXCL9/CXCL10 pathway readouts.
    controls:
    - name: Isogenic non-targeting and vehicle controls
      description: >-
        Same donor, differentiation batch, ligand exposure, and assay schedule.
    - name: Compartment-restricted perturbation controls
      description: >-
        Perturb MAPK14 separately in neurons, glia, melanocytes, keratinocytes,
        and T cells to resolve cell of action.
    decision_criterion: >-
      A shared causal node requires a reproducible upstream state plus MAPK14
      catalytic necessity in both arms, phenotypic rescue by wild-type but not
      kinase-dead MAPK14, and cross-donor replication. Different upstream
      signals or causal compartments support parallel context-specific uses of
      p38 rather than one shared circuit; loss of association after perturbation
      controls or failure to alter either phenotype classifies MAPK14 as a
      correlated marker.
    would_support:
    - pathophysiology#Monoamine Deficiency
    - Vitiligo:pathophysiology#Autoimmune Reaction
- discussion_id: gap_mdd_stalled_ahn_causality_and_suicide_confound
  prompt: >-
    Is arrested progression of the adult hippocampal neurogenic lineage a
    causal contributor to MDD, a consequence of the depressed or stressed
    state, or a correlate of suicide rather than of depression? And is the
    adult human subgranular-zone lineage on which the claim rests a genuine
    ongoing neurogenic programme or a persistent immature transcriptional
    state?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - mechanistic_hypotheses#stalled_adult_hippocampal_neurogenesis_model
  - pathophysiology#Stalled Adult Hippocampal Neurogenesis
  - pathophysiology#Neurogenic Niche Interferon Signaling Activation
  rationale: >-
    The evidence is a single cross-sectional postmortem cohort. Three limits
    matter for how far the mechanism can be pushed. First, direction of
    causation cannot be recovered from postmortem tissue: interferon
    activation, transcription-factor reprogramming and the neuroblast deficit
    are observed together, so the edges into the stalled-neurogenesis node are
    curated as indirect with undetermined direction. Second, 40 of the 55 MDD
    decedents died by suicide while no control did, so MDD and suicide
    pathology are confounded by design in this sample. Third, the existence and
    magnitude of adult human hippocampal neurogenesis is itself contested; the
    study's own data show mature granule cells re-expressing immaturity markers
    in the granule cell layer, which is a dematuration interpretation rather
    than an ongoing-neurogenesis one, and the immature granule-cell pool was
    unchanged in MDD.
  proposed_experiments:
  - experiment_id: mdd_ahn_suicide_deconfounding_cohort
    name: Postmortem cohort separating MDD from death by suicide
    description: >-
      Extend the multiomic hippocampal profiling to a cohort with four groups -
      MDD decedents who died by suicide, MDD decedents who died of other
      causes, non-MDD suicide decedents, and neurotypical controls - powered to
      test the neuroblast deficit and the interferon module separately against
      diagnosis and against manner of death.
    decision_criterion: >-
      If the neuroblast deficit tracks MDD diagnosis independently of manner of
      death, the mechanism belongs to this entry. If it tracks suicide, it
      belongs on a suicide-related entry and should be removed from here.
  - experiment_id: mdd_ahn_interferon_directionality
    name: Directionality of interferon signalling on human neurogenic progenitors
    description: >-
      Apply type I interferon and interferon blockade to human hippocampal
      neural stem cell and progenitor cultures or organoids derived from MDD
      and control donors, measuring progression from quiescent stem cell to
      neuroblast (nestin, Ki67, ASCL1, DCX, TUBB3) rather than only steady-state
      marker abundance.
    decision_criterion: >-
      Interferon exposure that reproduces the stem-cell accumulation and
      neuroblast deficit would upgrade the interferon-to-neurogenesis edge from
      indirect with unknown intermediates to a supported causal edge; absence of
      an effect would make the interferon module a parallel correlate.
  - experiment_id: mdd_ahn_living_biomarker
    name: In vivo correlate of the neurogenic deficit in living patients
    description: >-
      Pair a hippocampus-dependent behavioural assay of pattern separation with
      dentate-gyrus-resolved imaging in living unmedicated MDD patients and
      controls, testing whether the behavioural deficit predicted by a stalled
      neurogenic lineage is present and whether it responds to treatment.
    decision_criterion: >-
      A treatment-responsive pattern-separation deficit would make the
      postmortem molecular finding clinically interpretable; its absence would
      confine the mechanism to a postmortem tissue phenotype.
  notes: >-
    Recorded as KNOWLEDGE_GAP rather than HUMAN_MODEL_MISMATCH: the evidence is
    human postmortem tissue, not a model system, so the open question is
    causation and confounding rather than translational validity.
classifications:
  harrisons_chapter:
  - classification_value: NEUROLOGIC
datasets:
- accession: geo:GSE255685
  title: Age-related transcriptomic differences in peripheral blood of adolescents with major depressive disorder
  description: In this study, we collected peripheral blood samples of a typical large population, including MDD cases and healthy controls from children and adolescents, and aimed to apply RNA-seq sequencing to comprehensively analyze the transcriptomic characteristics in adolescent depression patients. In comparison to healthy patients, we discovered that several immune response-associated genes were dysregulated in MDD patients, with the majority of these differential genes strongly correlated with the HAMD-17 and HAMA scores.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 279
  publication: PMID:41740874
  notes: Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE149871
  title: Epigenetic profiling of neuronal and non-neuronal signal in major depressive disorder
  description: Characterization of cell type specific (NeuN+/NeuN-) open chromatin by ATAC-seq assay in orbitofrontal cortext of postmortem tissue samples from 19 MMD cases and 18 controls.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: ATAC_SEQ
  sample_count: 70
  publication: PMID:40516534
  notes: Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.
- accession: geo:GSE301868
  title: Whole-blood transcriptomic response to whole-body hyperthermia in participants with major depressive disorder
  description: Depression is the leading cause of global disability according to the World Health Organization, and Major Depressive Disorder (MDD) makes up a majority of these cases. Current pharmacological interventions suffer from significant limitations and side effects, highlighting a need for novel therapeutic approaches. Whole-body hyperthermia (WBH) has been identified as a promising avenue of treatment; however, a comprehensive understanding of the mechanisms responsible for the antidepressant effects of WBH remains elusive.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  data_type: BULK_RNA_SEQ
  sample_count: 20
  publication: PMID:42004495
  notes: Identified by GEO DataSets index search for Major Depressive Disorder (scripts/discover_datasets.py); accession and metadata verified against NCBI E-utilities on 2026-07-31. Title, sample count, and organism are GEO's own values.
- accession: ega:EGAS00001002818
  title: Whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes
  description: We carried out whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes. This study aimed to reveal the selective accumulation of rare variants in the coding and the UTR sequences within the genes of suicide victims. We also analysed the potential effect of STR and CNV variations, as well as the infection of the brain with neurovirulent viruses in this behavioural disorder. As a result, we have identified several candidate genes, among others three calcium channel genes that may potentially contribute to completed suicide.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  notes: 'European Genome-phenome Archive study, matched because the disease is named in the study''s own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.'
- accession: ega:EGAS00001003081
  title: Whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes.
  description: We carried out whole-exome ultra-high throughput sequencing in brain samples of suicide victims who had suffered from major depressive disorder and control subjects who had died from other causes. This study aimed to reveal the selective accumulation of rare variants in the coding and the UTR sequences within the genes of suicide victims. We also analysed the potential effect of STR and CNV variations, as well as the infection of the brain with neurovirulent viruses in this behavioural disorder. As a result, we have identified several candidate genes, among others three calcium channel genes that may potentially contribute to completed suicide.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  notes: 'European Genome-phenome Archive study, matched because the disease is named in the study''s own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.'
- accession: ega:EGAS00001008306
  title: Toward PRecisiOn Medicine for the Prediction of Treatment Response in Major Depressive Disorder through Stratification of Combined Clinical and Omics Signatures
  description: Major depressive disorder (MDD) is the most common psychiatric disorder worldwide. Pharmacotherapy is the standard first-line treatment, yet only one third of patients respond to the initial trial and about 30% develop treatment-resistant depression (TRD), which is associated with specific clinical and molecular features. The PROMPT project aims to develop a precision medicine algorithm for early identification of non-responders.
  organism:
    preferred_term: human
    term:
      id: NCBITaxon:9606
      label: Homo sapiens
  notes: 'European Genome-phenome Archive study, matched because the disease is named in the study''s own title ("Major Depressive Disorder"); description-level mentions were not accepted. EGA study_type: Other. Controlled access -- data require a Data Access Agreement. EGA metadata retrieved 2026-08-01.'
references:
- reference: DOI:10.1007/s40263-024-01114-y
  title: Glutamatergic Modulators for Major Depression from Theory to Clinical
    Use
  findings: []
- reference: DOI:10.1038/s41392-024-01738-y
  title: 'Major depressive disorder: hypothesis, mechanism, prevention and treatment'
  findings: []
- reference: DOI:10.1101/2025.05.03.25326369
  title: 'Multi-omics insights in major depressive disorder: Dysfunction of Neurons'
  findings: []
- reference: DOI:10.3390/cells13050423
  title: 'Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology
    to Potential Pharmacological Targets'
  findings: []
- reference: DOI:10.3390/ijms25020963
  title: 'Mitochondrial and Cellular Function in Fibroblasts, Induced Neurons, and
    Astrocytes Derived from Case Study Patients: Insights into Major Depression as
    a Mitochondria-Associated Disease'
  findings: []
- reference: DOI:10.3390/ijtm4010010
  title: 'Advancements Exploring Major Depressive Disorder: Insights on Oxidative
    Stress, Serotonin Metabolism, BDNF, HPA Axis Dysfunction, and Pharmacotherapy
    Advances'
  findings: []

📚

References & Deep Research

References

6

DOI:10.1007/s40263-024-01114-y

Glutamatergic Modulators for Major Depression from Theory to Clinical Use

No top-level findings curated for this source.

DOI:10.1038/s41392-024-01738-y

Major depressive disorder: hypothesis, mechanism, prevention and treatment

No top-level findings curated for this source.

DOI:10.1101/2025.05.03.25326369

Multi-omics insights in major depressive disorder: Dysfunction of Neurons

No top-level findings curated for this source.

DOI:10.3390/cells13050423

Role of Inflammatory Mechanisms in Major Depressive Disorder: From Etiology to Potential Pharmacological Targets

No top-level findings curated for this source.

DOI:10.3390/ijms25020963

Mitochondrial and Cellular Function in Fibroblasts, Induced Neurons, and Astrocytes Derived from Case Study Patients: Insights into Major Depression as a Mitochondria-Associated Disease

No top-level findings curated for this source.

DOI:10.3390/ijtm4010010

Advancements Exploring Major Depressive Disorder: Insights on Oxidative Stress, Serotonin Metabolism, BDNF, HPA Axis Dysfunction, and Pharmacotherapy Advances

No top-level findings curated for this source.

Deep Research

3

Disorder ▸

Disorder

Name: Major Depressive Disorder
Category: Complex
Existing deep-research providers: falcon
Existing evidence reference count in YAML: 28

Key Pathophysiology Nodes

Monoamine Deficiency
HPA Axis Dysregulation
Neuroplasticity Deficits
Neuroinflammation
Mitochondrial Dysfunction
Deep research literature mapping

Citation Inventory (for evidence mapping)

DOI:10.1007/s40263-024-01114-y
DOI:10.1038/s41392-024-01738-y
DOI:10.1101/2025.05.03.25326369
DOI:10.3390/cells13050423
DOI:10.3390/ijms25020963
DOI:10.3390/ijtm4010010

Falcon ▸

Disease Pathophysiology Research Report

Edison Scientific Literature 19 citations 2025-12-17T18:55:49.493721

Disease Pathophysiology Research Report

Target Disease - Disease Name: Major Depressive Disorder - MONDO ID: MONDO:0009409 - Category: Complex

Pathophysiology description MDD is a heterogeneous, systems‑level brain disorder arising from convergent dysregulation of neurotransmission, stress–neuroendocrine control, immune–metabolic signaling, cellular bioenergetics, and neuroplasticity within limbic–prefrontal circuits. Contemporary models integrate: (a) monoaminergic signaling deficits (serotonin, noradrenaline, dopamine); (b) glutamate/GABA excitation–inhibition imbalance with synaptic and postsynaptic plasticity failure; (c) HPA axis hyperactivity with glucocorticoid receptor resistance; (d) innate/adaptive immune activation that biases tryptophan metabolism along the kynurenine pathway toward neurotoxic metabolites; (e) mitochondrial respiratory dysfunction, oxidative stress, and altered calcium/ATP homeostasis in neurons and glia; (f) oligodendrocyte lineage/myelination abnormalities that compromise long‑range circuit conduction; and (g) network‑scale synaptic vesicle and postsynaptic density perturbations in subgenual/anterior cingulate, prefrontal cortex, hippocampus, and amygdala (Cui 2024; McIntyre & Jain 2024; Kouba 2024; Correia & Vale 2024; Wetzel 2024; Zhang et al. 2025 preprint) (cui2024majordepressivedisorder pages 23-24, mcintyre2024glutamatergicmodulatorsfor pages 7-9, kouba2024roleofinflammatory pages 2-3, correia2024advancementsexploringmajor pages 1-2, wetzel2024mitochondrialandcellular pages 10-12, zhang2025multiomicsinsightsin pages 14-18).

Core Pathophysiology 1) Monoamine hypothesis, refined: Serotonin, noradrenaline, and dopamine pathway alterations interact with stress biology and neurotrophic signaling. Despite efficacy of monoamine reuptake inhibitors, non‑remission remains high (~30%), indicating additional pathobiology beyond monoamines (Cui 2024; Correia & Vale 2024) (cui2024majordepressivedisorder pages 23-24, correia2024advancementsexploringmajor pages 1-2). URL examples: https://doi.org/10.1038/s41392-024-01738-y (2024); https://doi.org/10.3390/ijtm4010010 (2024). 2) Glutamate/GABA and synaptic plasticity failure: Human and preclinical evidence implicates reduced GABAergic tone, altered NMDA/AMPA signaling, and impaired synaptogenesis; rapid‑acting agents (ketamine/esketamine, dextromethorphan–bupropion) exploit this pathway (McIntyre & Jain 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9). URL: https://doi.org/10.1007/s40263-024-01114-y (2024). 3) Neurotrophic/BDNF signaling: Reduced BDNF and altered TrkB signaling are linked with hippocampal atrophy and impaired synaptogenesis; stress and oxidative–HPA dysregulation suppress BDNF expression and signaling (Correia & Vale 2024; Cui 2024) (correia2024advancementsexploringmajor pages 1-2, cui2024majordepressivedisorder pages 23-24). URL: https://doi.org/10.3390/ijtm4010010 (2024); https://doi.org/10.1038/s41392-024-01738-y (2024). 4) HPA axis dysregulation: Chronic stress elevates cortisol, disrupts glucocorticoid receptor (GR) feedback, and damages hippocampal circuits. Reviews highlight patient subsets with marked HPA abnormality and propose precision testing (e.g., dex‑CRH) to match HPA‑targeted therapies (Cui 2024) (cui2024majordepressivedisorder pages 23-24). URL: https://doi.org/10.1038/s41392-024-01738-y (2024). 5) Immune–inflammation and kynurenine pathway: Elevated cytokines (IL‑6, IL‑1β, TNF‑α) and microglial–astrocytic interactions shift tryptophan metabolism via IDO1/KMO toward 3‑hydroxykynurenine and quinolinic acid (NMDA agonist), reducing serotonin bioavailability and promoting excitotoxic stress (Kouba 2024) (kouba2024roleofinflammatory pages 2-3). URL: https://doi.org/10.3390/cells13050423 (2024). 6) Mitochondrial bioenergetics and oxidative stress: Patient‑derived astrocytes and neurons show reduced basal/maximal respiration, altered mitochondrial membrane potential and calcium handling, and ATP shortfalls, consistent with oxidative–bioenergetic deficits contributing to impaired neuroplasticity (Wetzel 2024) (wetzel2024mitochondrialandcellular pages 10-12). URL: https://doi.org/10.3390/ijms25020963 (2024). 7) Myelination/oligodendrocytes: Single‑cell and multi‑omics analyses associate MDD with oligodendrocyte lineage and excitatory neuron dysfunction in prefrontal cortex, implicating myelin and axonal support in mood‑circuit dysconnectivity (Cui 2024; Zhang et al. 2025 preprint) (cui2024majordepressivedisorder pages 23-24, zhang2025multiomicsinsightsin pages 14-18). URL: https://doi.org/10.1038/s41392-024-01738-y (2024); https://doi.org/10.1101/2025.05.03.25326369 (2025 preprint). 8) Synaptic function: Transcriptomic signatures converge on synaptic vesicle cycling, postsynaptic density, and splicing programs in excitatory neurons (Zhang et al. 2025 preprint; Cui 2024) (zhang2025multiomicsinsightsin pages 14-18, cui2024majordepressivedisorder pages 23-24). URL: https://doi.org/10.1101/2025.05.03.25326369 (2025 preprint); https://doi.org/10.1038/s41392-024-01738-y (2024).

Key Molecular Players - Genes/Proteins (HGNC): BDNF; NTRK2; CREB1; GRIN1/GRIN2A (NMDA receptor subunits); GRIA1 (AMPA); GAD1; GABRA1/GABRD (GABAA subunits); SLC6A4 (SERT); IDO1; KMO; IL6; IL1B; TNF; NR3C1 (GR); FKBP5; mitochondrial bioenergetics genes (e.g., SLC25A5/ANT2, ALDH2, IMMT) (Correia 2024; Kouba 2024; Wetzel 2024; Cui 2024; McIntyre & Jain 2024) (correia2024advancementsexploringmajor pages 1-2, kouba2024roleofinflammatory pages 2-3, wetzel2024mitochondrialandcellular pages 10-12, cui2024majordepressivedisorder pages 23-24, mcintyre2024glutamatergicmodulatorsfor pages 7-9). URLs: https://doi.org/10.3390/ijtm4010010 (2024); https://doi.org/10.3390/cells13050423 (2024); https://doi.org/10.3390/ijms25020963 (2024); https://doi.org/10.1038/s41392-024-01738-y (2024); https://doi.org/10.1007/s40263-024-01114-y (2024). - Chemical Entities (CHEBI): Ketamine/esketamine; dextromethorphan; bupropion; allopregnanolone analogs (brexanolone, zuranolone); monoamine reuptake inhibitors; kynurenine pathway metabolites (kynurenine, quinolinic acid) (McIntyre & Jain 2024; Kouba 2024; Cui 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9, kouba2024roleofinflammatory pages 2-3, cui2024majordepressivedisorder pages 23-24). - Cell Types (CL): Cortical excitatory neurons; GABAergic interneurons (SST+, PVALB+); astrocytes; microglia; oligodendrocyte precursor cells and mature oligodendrocytes (Cui 2024; Kouba 2024; Wetzel 2024; Zhang et al. 2025 preprint) (cui2024majordepressivedisorder pages 23-24, kouba2024roleofinflammatory pages 2-3, wetzel2024mitochondrialandcellular pages 10-12, zhang2025multiomicsinsightsin pages 14-18). - Anatomical Locations (UBERON): Subgenual anterior cingulate cortex, dorsolateral prefrontal cortex, hippocampus, amygdala, hypothalamus–pituitary–adrenal axis structures (Cui 2024; Zhang et al. 2025 preprint) (cui2024majordepressivedisorder pages 23-24, zhang2025multiomicsinsightsin pages 14-18).

Biological Processes (GO annotations) - Synaptic transmission and plasticity: GO:0007268 (neurotransmitter receptor signaling), GO:0048167 (regulation of synaptic plasticity) (Correia 2024; McIntyre & Jain 2024) (correia2024advancementsexploringmajor pages 1-2, mcintyre2024glutamatergicmodulatorsfor pages 7-9). - Stress and HPA signaling: GO:0006950 (response to stress), GO terms related to glucocorticoid receptor signaling (Cui 2024) (cui2024majordepressivedisorder pages 23-24). - Inflammation and kynurenine metabolism: GO:0006954 (inflammatory response), GO terms for kynurenine metabolic process (Kouba 2024) (kouba2024roleofinflammatory pages 2-3). - Mitochondrial respiration/oxidative stress: GO:0006119 (oxidative phosphorylation/respiration), GO:0006979 (response to oxidative stress) (Wetzel 2024) (wetzel2024mitochondrialandcellular pages 10-12). - Myelination/oligodendrocyte differentiation: GO:0042552 (myelination), GO:0014003 (oligodendrocyte development) (Cui 2024; Zhang 2025 preprint) (cui2024majordepressivedisorder pages 23-24, zhang2025multiomicsinsightsin pages 14-18).

Cellular Components (GO CC) - Postsynaptic density; synaptic vesicle; mitochondrial inner membrane; myelin sheath; extrasynaptic GABAA receptor complexes (Cui 2024; McIntyre & Jain 2024; Wetzel 2024) (cui2024majordepressivedisorder pages 23-24, mcintyre2024glutamatergicmodulatorsfor pages 7-9, wetzel2024mitochondrialandcellular pages 10-12).

Disease Progression (sequence of events) - Stress/early adversity and genetic susceptibility activate HPA axis and peripheral immune signals → elevated cortisol and cytokines drive GR resistance, microglial activation, and IDO1/KMO upregulation → tryptophan diverted from serotonin to neurotoxic kynurenines (quinolinic acid), promoting NMDA‑mediated excitotoxicity → mitochondrial dysfunction and oxidative stress further impair synaptic plasticity and neurogenesis → network‑level deficits in glutamate/GABA balance, synaptic vesicle trafficking, and myelination in prefrontal–limbic circuits → clinical manifestations (anhedonia, low mood, cognitive dysfunction) and variable treatment response (Cui 2024; Kouba 2024; Correia & Vale 2024; Wetzel 2024) (cui2024majordepressivedisorder pages 23-24, kouba2024roleofinflammatory pages 2-3, correia2024advancementsexploringmajor pages 1-2, wetzel2024mitochondrialandcellular pages 10-12). URLs: https://doi.org/10.1038/s41392-024-01738-y (2024); https://doi.org/10.3390/cells13050423 (2024); https://doi.org/10.3390/ijtm4010010 (2024); https://doi.org/10.3390/ijms25020963 (2024).

Phenotypic Manifestations (HP terms) - Depressed mood (HP:0000716), anhedonia (HP:0034259), psychomotor changes (HP:0000752), sleep disturbance (HP:0002360), cognitive impairment (HP:0100543). Mechanistic mapping: reduced BDNF/neuroplasticity and mitochondrial ATP constrain cognitive circuits; E/I imbalance (glutamate/GABA) contributes to anhedonia and mood reactivity; HPA/immune–kynurenine perturbations align with sleep and energy dysregulation (Cui 2024; Correia & Vale 2024; Kouba 2024) (cui2024majordepressivedisorder pages 23-24, correia2024advancementsexploringmajor pages 1-2, kouba2024roleofinflammatory pages 2-3).

Current applications and real‑world implementations - Ketamine and intranasal esketamine: Rapid symptom reduction in TRD, mechanistically linked to NMDA antagonism → AMPA throughput → BDNF/mTOR synaptogenesis; considerations include dissociation, cardiovascular/urinary effects, scheduling, and supervised administration. Regulatory approvals (e.g., 2019 for esketamine) and clinical adoption are summarized (McIntyre & Jain 2024; review) (mcintyre2024glutamatergicmodulatorsfor pages 7-9). URL: https://doi.org/10.1007/s40263-024-01114-y (2024). - Dextromethorphan–bupropion (AXS‑05/Auvelity): Oral agent combining NMDA antagonism and sigma‑1 agonism with monoaminergic effects; approved for MDD and positioned as a glutamatergic modulator with favorable practicality relative to parenteral ketamine (McIntyre & Jain 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9). URL: https://doi.org/10.1007/s40263-024-01114-y (2024). - Neurosteroids (brexanolone IV; zuranolone oral): Positive allosteric modulators of GABAA receptors (including extrasynaptic δ‑subunit‑containing receptors) providing rapid relief in postpartum depression and informing GABAergic deficits in depressive pathophysiology (Correia & Vale 2024; Cui 2024) (correia2024advancementsexploringmajor pages 1-2, cui2024majordepressivedisorder pages 23-24). URLs: https://doi.org/10.3390/ijtm4010010 (2024); https://doi.org/10.1038/s41392-024-01738-y (2024).

Expert opinions and analysis from authoritative sources - Signal Transduction and Targeted Therapy (Cui 2024) synthesizes MDD as multisystem with neuroplasticity, HPA, immune and metabolic/mitochondrial axes, advocating for multi‑organ, multi‑target treatments and improved animal models (cui2024majordepressivedisorder pages 23-24). URL: https://doi.org/10.1038/s41392-024-01738-y (2024). - CNS Drugs review (McIntyre & Jain 2024) details the translational arc of glutamatergic agents, highlighting successes (esketamine, AXS‑05) and failures of several NMDA‑site modulators, underscoring synaptic plasticity’s centrality and the need for safety/access frameworks (mcintyre2024glutamatergicmodulatorsfor pages 7-9). URL: https://doi.org/10.1007/s40263-024-01114-y (2024). - Cells review (Kouba 2024) integrates immune–kynurenine mechanisms with glutamate toxicity and neuroplasticity failure, supporting immunopsychiatry approaches (kouba2024roleofinflammatory pages 2-3). URL: https://doi.org/10.3390/cells13050423 (2024). - IJMS case‑based translational work (Wetzel 2024) provides cellular bioenergetics evidence for mitochondrial involvement in MDD glia and neurons, aligning with precision‐medicine biomarker development (wetzel2024mitochondrialandcellular pages 10-12). URL: https://doi.org/10.3390/ijms25020963 (2024).

Relevant statistics and data from recent studies - Non‑remission remains substantial with current monoaminergic approaches (~30%), motivating mechanistically targeted therapies (Cui 2024) (cui2024majordepressivedisorder pages 23-24). - Translational approvals: esketamine (2019) for TRD; dextromethorphan–bupropion (2022) for MDD—illustrating the clinical impact of glutamatergic modulation (McIntyre & Jain 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9). - Cellular bioenergetics (patient‑derived astrocytes): reduced basal and maximal respiration and ATP‑related oxygen consumption; altered mitochondrial membrane potential and calcium handling, supporting bioenergetic load in symptom biology (Wetzel 2024) (wetzel2024mitochondrialandcellular pages 10-12).

Ontology‑aligned annotations - Genes/Proteins (HGNC): BDNF; NTRK2; GRIN1/2A; GRIA1; GAD1; GABRA1/GABRD; SLC6A4; IDO1; KMO; IL6; IL1B; TNF; NR3C1; FKBP5; SLC25A5; ALDH2; IMMT (correia2024advancementsexploringmajor pages 1-2, kouba2024roleofinflammatory pages 2-3, wetzel2024mitochondrialandcellular pages 10-12, cui2024majordepressivedisorder pages 23-24, mcintyre2024glutamatergicmodulatorsfor pages 7-9). - GO Biological Processes: neurotransmitter receptor signaling (GO:0007268); regulation of synaptic plasticity (GO:0048167/GO:0048168); inflammatory response (GO:0006954); response to stress (GO:0006950); mitochondrial respiration (GO:0006119); myelination (GO:0042552) (mcintyre2024glutamatergicmodulatorsfor pages 7-9, kouba2024roleofinflammatory pages 2-3, wetzel2024mitochondrialandcellular pages 10-12, cui2024majordepressivedisorder pages 23-24). - Cell Types (CL): cortical excitatory neuron; GABAergic interneuron (SST+, PVALB+); astrocyte; microglial cell; oligodendrocyte precursor cell; oligodendrocyte (cui2024majordepressivedisorder pages 23-24, kouba2024roleofinflammatory pages 2-3, wetzel2024mitochondrialandcellular pages 10-12, zhang2025multiomicsinsightsin pages 14-18). - Anatomical locations (UBERON): subgenual anterior cingulate cortex; dorsolateral prefrontal cortex; hippocampus; amygdala; hypothalamus–pituitary–adrenal axis (cui2024majordepressivedisorder pages 23-24, zhang2025multiomicsinsightsin pages 14-18). - Cellular Components (GO CC): postsynaptic density; synaptic vesicle; mitochondrial inner membrane; myelin sheath; extrasynaptic GABAA receptor complex (mcintyre2024glutamatergicmodulatorsfor pages 7-9, wetzel2024mitochondrialandcellular pages 10-12, cui2024majordepressivedisorder pages 23-24). - Chemicals (CHEBI): ketamine; esketamine; dextromethorphan; bupropion; allopregnanolone analogs (brexanolone, zuranolone); kynurenine; quinolinic acid (mcintyre2024glutamatergicmodulatorsfor pages 7-9, kouba2024roleofinflammatory pages 2-3, cui2024majordepressivedisorder pages 23-24). - Phenotypes (HP): depressed mood (HP:0000716); anhedonia (HP:0034259); psychomotor changes (HP:0000752); sleep disturbance (HP:0002360); cognitive impairment (HP:0100543) (cui2024majordepressivedisorder pages 23-24, correia2024advancementsexploringmajor pages 1-2).

Embedded Evidence Map | Domain / Pathway | Key mechanisms (1–2 sentences) | Representative genes / proteins (HGNC) | Cell types (CL) | Anatomical loci (UBERON) | GO biological processes (GO BP) | Key chemicals / drugs (CHEBI) | Recent evidence (DOI / URL / Year; brief quantitative data) | |---|---|---:|---|---|---|---|---| | Monoamine (serotonin/dopamine/noradrenaline) | Reduced monoaminergic signaling and altered transporter/receptor function impair mood regulation and reward; interacts with HPA and immune axes. | SLC6A4, TPH2, MAOA, DRD2 | Serotonergic & dopaminergic neurons; astrocytes | Raphe nuclei; ventral tegmental area; prefrontal cortex, striatum | "monoamine transport"; "neurotransmitter receptor signaling" (GO:0007268) | SSRIs (e.g., escitalopram), SNRIs (venlafaxine) | Comprehensive 2024 review summarizing monoamine + multisystem interplay: Cui et al., doi:10.1038/s41392-024-01738-y (2024) ("~30% non-remission" noted) (cui2024majordepressivedisorder pages 23-24) | | Glutamate–GABA (excitation–inhibition) | Dysregulated glutamatergic excitation and GABAergic inhibition (reduced GABA, altered NMDA/AMPA signaling) → impaired E/I balance, excitotoxic risk and rapid-acting glutamatergic therapeutics. | GRIN1/GRIN2A, GRIA1, GABRA1, GAD1 | Excitatory (glutamatergic) neurons; inhibitory interneurons (SST, PVALB); astrocytes | Prefrontal cortex (dlPFC), anterior cingulate, hippocampus | "synaptic transmission"; "regulation of membrane potential" (GO:0007269) | Ketamine, esketamine, dextromethorphan; memantine | Glutamate-targeted translational successes and trial landscape; approvals: esketamine (2019), AXS‑05 (dextromethorphan–bupropion) discussed (McIntyre & Jain, doi:10.1007/s40263-024-01114-y, 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9) | | Neuroplasticity / BDNF | Reduced BDNF expression and impaired TrkB signaling → decreased synaptogenesis, neurogenesis and structural atrophy (hippocampus) linking stress to circuit dysfunction. | BDNF, NTRK2 (TrkB), CREB1 | Neurons (excitatory), astrocytes | Hippocampus, prefrontal cortex | "synaptic plasticity" (GO:0048167); "neurotrophin signaling" | Exercise, traditional antidepressants; ketamine (indirectly increases BDNF) | BDNF–MDD mechanistic review summarizing exon/epigenetic links and clinical correlations: Correia & Vale, doi:10.3390/ijtm4010010 (2024) (correia2024advancementsexploringmajor pages 8-9, correia2024advancementsexploringmajor pages 1-2) | | HPA axis – cortisol / stress | Chronic HPA hyperactivity, glucocorticoid receptor (GR/NR3C1) resistance and elevated cortisol cause hippocampal vulnerability, reduced neurogenesis, and immune modulation. | CRH, NR3C1, FKBP5 | Hypothalamic neuroendocrine cells; hippocampal neurons; immune cells | Hypothalamus; pituitary; hippocampus | "response to stress" (GO:0006950); "glucocorticoid receptor signaling" | GR modulators (experimental) | HPA axis as precision target; reviews highlight subset HPA abnormalities and need for companion diagnostics (dex‑CRH/mDST): Menke et al. (cui2024majordepressivedisorder pages 23-24) and HPA-focused reviews (cui2024majordepressivedisorder pages 23-24, correia2024advancementsexploringmajor pages 1-2) (2024) | | Immune — inflammation & kynurenine | Peripheral/central inflammation (IL‑6, IL‑1β, TNF‑α) activates microglia, shifts tryptophan metabolism via IDO1/KMO toward neurotoxic kynurenines (3‑HK, quinolinic acid) reducing serotonin and promoting excitotoxicity. | IL6, IL1B, TNF, IDO1, KMO, KYNU | Microglia, astrocytes, peripheral monocytes | Blood–brain interface; hippocampus; PFC | "inflammatory response" (GO:0006954); "kynurenine metabolic process" | Anti‑inflammatories (investigational), kynurenine pathway modulators (experimental) | Inflammation–kynurenine mechanistic review and therapeutic implications: Kouba et al., doi:10.3390/cells13050423 (2024) (kouba2024roleofinflammatory pages 2-3) | | Mitochondria / oxidative stress & bioenergetics | Impaired mitochondrial respiration, altered membrane potential, disrupted Ca2+ homeostasis and increased ROS → reduced ATP, neuroplasticity deficits and vulnerability to stress. | SLC25A5, ALDH2, IMMT (examples); PGC1A (PPARGC1A) | Neurons, astrocytes, oligodendrocytes, peripheral immune cells | Prefrontal cortex; hippocampus; systemic (blood biomarkers) | "mitochondrial respiration" (GO:0006119); "response to oxidative stress" (GO:0006979) | CoQ10, antioxidants (nutraceuticals; investigational) | Patient‑derived cell evidence: decreased basal/maximal respiration, lower mitochondrial membrane potential in MDD astrocytes and case studies (Wetzel et al., doi:10.3390/ijms25020963, 2024) (wetzel2024mitochondrialandcellular pages 10-12) | | Circadian / sleep | Circadian clock gene dysregulation and sleep disturbance disrupts hormonal, immune and metabolic rhythms, exacerbating vulnerability to depression and impairing recovery. | CLOCK, BMAL1 (ARNTL), PER1, CRY1 | Suprachiasmatic nucleus neurons; cortical neurons; peripheral cells | Suprachiasmatic nucleus; prefrontal cortex; systemic | "circadian regulation of gene expression" (GO:0032922); "sleep regulation" | Melatonin, chronotherapies (light/behavioral) | Circadian–sleep review linking clock gene expression to depressive symptom severity and therapeutic opportunities: Gabryelska et al., doi:10.1038/s41398-024-03134-0 (2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9) | | Myelination / oligodendrocytes | Oligodendrocyte lineage dysfunction and altered myelination impair circuit conduction and metabolic support for neurons, contributing to mood circuit dysconnectivity. | MBP, OLIG2, PDGFRA, MOG | Oligodendrocyte precursor cells (OPCs), mature oligodendrocytes | Prefrontal cortex (white matter tracts), hippocampus | "myelination" (GO:0042552); "oligodendrocyte differentiation" | Remyelination strategies (emerging); indirect effect of antidepressants | Emerging evidence implicates OPCs / oligodendrocyte changes in MDD from single‑cell and translational studies (single‑cell findings summarized in Zhang preprint and reviews in 2024–25) (zhang2025multiomicsinsightsin pages 14-18, cui2024majordepressivedisorder pages 23-24) | | Synaptic function & vesicular trafficking | Altered synaptic vesicle cycling, postsynaptic density proteins and splicing lead to deficient neurotransmission and network-level dysregulation in mood circuits. | SYN1, PSD95 (DLG4), SYNAPTOTAGMINS, RAB proteins | Excitatory & inhibitory neurons; presynaptic terminals; astrocytes | Subgenual ACC, amygdala, dlPFC | "synaptic vesicle cycle" (GO:0099504); "postsynaptic density organization" | Synaptogenic agents (ketamine‑linked plasticity) | Large‑scale transcriptomic/single‑cell analyses reveal convergent dysregulation of synaptic and vesicular pathways in excitatory neurons (dlPFC/subgenual ACC): Goes et al., integrative findings summarized in multi‑omics preprints/reviews (zhang2025multiomicsinsightsin pages 14-18, cui2024majordepressivedisorder pages 23-24) (2024–2025) | | Translational — Ketamine / Esketamine | NMDA receptor antagonism → transient disinhibition of glutamate release, AMPA activation, BDNF/mTOR signaling and rapid synaptogenesis; rapid antidepressant but safety/abuse considerations limit use. | GRINs, BDNF, mTOR (FRAP1) | Cortical excitatory neurons; interneurons; microglia (immune effects) | Prefrontal cortex; limbic circuits | "regulation of synaptic plasticity" (GO:0048168) | Ketamine (R,S), Esketamine (S) | Clinical trial landscape and approvals; esketamine approved 2019; overview and trial trends (McIntyre & Jain, doi:10.1007/s40263-024-01114-y, 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9) | | Translational — Dextromethorphan–bupropion (AXS‑05) | NMDA antagonism + sigma‑1 agonism (dextromethorphan) combined with monoaminergic reuptake inhibition (bupropion) — designed for oral rapid efficacy in MDD. | SLC6A3 (bupropion target indirect), sigma‑1 receptor (SIGMAR1) | Cortical neurons; monoaminergic neurons | Prefrontal cortex | "modulation of synaptic transmission" | Dextromethorphan, bupropion (combination product Auvelity / AXS‑05) | Approved agent; cited as translational glutamatergic success in review of glutamatergic modulators (McIntyre & Jain, doi:10.1007/s40263-024-01114-y, 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9) | | Translational — Neurosteroids (brexanolone; zuranolone) | Positive allosteric modulation of synaptic and extrasynaptic GABAA receptors (including δ‑subunit‑containing receptors) producing rapid mood stabilization, esp. postpartum depression. | GABRA4, GABRD, AKR1C1/2 (steroid metabolism enzymes) | Cortical/limbic neurons; astrocytes | Limbic system; postpartum systemic context | "GABAergic synaptic transmission" (GO:0032228) | Brexanolone (IV allopregnanolone), Zuranolone (oral neurosteroid) | Neurosteroid drug reviews and clinical-update summaries (efficacy in PPD; zuranolone clinical meta‑analyses exist in 2023–24 literature); clinical trial summaries and mechanism reviews (correia2024advancementsexploringmajor pages 8-9, correia2024advancementsexploringmajor pages 1-2) (2023–2024) |

Table: Concise, citable table mapping core molecular/cellular pathways implicated in Major Depressive Disorder with representative genes, cell types, loci, GO processes, key chemicals/drugs, and recent 2023–2024 evidence (pqac citations). This aids rapid reference for mechanism-to-translation links.

Evidence items with URLs/dates (selection) - Cui L et al. Major depressive disorder: hypothesis, mechanism, prevention and treatment. Signal Transduct Target Ther. 2024; DOI: 10.1038/s41392-024-01738-y; URL: https://doi.org/10.1038/s41392-024-01738-y (Feb 2024) (cui2024majordepressivedisorder pages 23-24). - McIntyre RS, Jain R. Glutamatergic modulators for major depression from theory to clinical use. CNS Drugs. 2024; DOI: 10.1007/s40263-024-01114-y; URL: https://doi.org/10.1007/s40263-024-01114-y (Aug 2024) (mcintyre2024glutamatergicmodulatorsfor pages 7-9). - Kouba BR et al. Role of inflammatory mechanisms in major depressive disorder. Cells. 2024; DOI: 10.3390/cells13050423; URL: https://doi.org/10.3390/cells13050423 (Feb 2024) (kouba2024roleofinflammatory pages 2-3). - Correia AS, Vale N. Advancements exploring MDD: oxidative stress, serotonin, BDNF, HPA, pharmacotherapy. Int J Transl Med. 2024; DOI: 10.3390/ijtm4010010; URL: https://doi.org/10.3390/ijtm4010010 (Mar 2024) (correia2024advancementsexploringmajor pages 1-2). - Wetzel C et al. Mitochondrial and cellular function in patient‑derived cells in MDD. Int J Mol Sci. 2024; DOI: 10.3390/ijms25020963; URL: https://doi.org/10.3390/ijms25020963 (Jan 2024) (wetzel2024mitochondrialandcellular pages 10-12). - Zhang L et al. Multi‑omics insights in MDD: neuronal dysfunction (dlPFC). medRxiv. 2025; DOI: 10.1101/2025.05.03.25326369; URL: https://doi.org/10.1101/2025.05.03.25326369 (May 2025; preprint) (zhang2025multiomicsinsightsin pages 14-18).

Notes and limitations - While monoamine agents remain first‑line, recent evidence emphasizes convergent plasticity, immune, and bioenergetic mechanisms; the translational approvals of glutamatergic modulators and neurosteroids underscore the mechanistic shift (Cui 2024; McIntyre & Jain 2024) (cui2024majordepressivedisorder pages 23-24, mcintyre2024glutamatergicmodulatorsfor pages 7-9). - Quantitative effect sizes vary across agents and populations; mechanistic claims and implementation notes above derive from peer‑reviewed reviews and patient‑derived cell studies cited herein (mcintyre2024glutamatergicmodulatorsfor pages 7-9, wetzel2024mitochondrialandcellular pages 10-12).

Plan status: Completed literature identification; synthesized mechanistic domains; produced ontology mappings; summarized clinical implementations and embedded an evidence map. Further additions could include specialized biomarker prevalence estimates and circadian‑focused human studies as they emerge in 2024–2025 cohorts.

References

(cui2024majordepressivedisorder pages 23-24): Lulu Cui, Shu Li, Siman Wang, Xiafang Wu, Yingyu Liu, Weiyang Yu, Yijun Wang, Yong Tang, Maosheng Xia, and Baoman Li. Major depressive disorder: hypothesis, mechanism, prevention and treatment. Signal Transduction and Targeted Therapy, Feb 2024. URL: https://doi.org/10.1038/s41392-024-01738-y, doi:10.1038/s41392-024-01738-y. This article has 801 citations and is from a peer-reviewed journal.
(mcintyre2024glutamatergicmodulatorsfor pages 7-9): Roger S. McIntyre and Rakesh Jain. Glutamatergic modulators for major depression from theory to clinical use. CNS Drugs, 38:869-890, Aug 2024. URL: https://doi.org/10.1007/s40263-024-01114-y, doi:10.1007/s40263-024-01114-y. This article has 44 citations and is from a peer-reviewed journal.
(kouba2024roleofinflammatory pages 2-3): Bruna R. Kouba, Laura de Araujo Borba, Pedro Borges de Souza, Joana Gil-Mohapel, and Ana Lúcia S. Rodrigues. Role of inflammatory mechanisms in major depressive disorder: from etiology to potential pharmacological targets. Cells, 13:423, Feb 2024. URL: https://doi.org/10.3390/cells13050423, doi:10.3390/cells13050423. This article has 125 citations and is from a poor quality or predatory journal.
(correia2024advancementsexploringmajor pages 1-2): Ana Salomé Correia and Nuno Vale. Advancements exploring major depressive disorder: insights on oxidative stress, serotonin metabolism, bdnf, hpa axis dysfunction, and pharmacotherapy advances. International Journal of Translational Medicine, 4:176-196, Mar 2024. URL: https://doi.org/10.3390/ijtm4010010, doi:10.3390/ijtm4010010. This article has 29 citations.
(wetzel2024mitochondrialandcellular pages 10-12): Christian Wetzel, Iseline Cardon, Sonja Grobecker, Selin Kücükoktay, Stefanie Bader, Tatjana Jahner, Caroline Nothdurfter, Kevin-Thomas Koschitzki, Mark Berneburg, Heidi Stöhr, Bernhard Weber, Marcus Höring, Gerhard Liebisch, Frank Braun, Tanja Rothammer-Hampl, Markus Riemenschneider, Rainer Rupprecht, and Vladimir Milenkovic. Mitochondrial and cellular function in fibroblasts, induced neurons, and astrocytes derived from case study patients: insights into major depression as a mitochondria-associated disease. International Journal of Molecular Sciences, Jan 2024. URL: https://doi.org/10.3390/ijms25020963, doi:10.3390/ijms25020963. This article has 15 citations and is from a poor quality or predatory journal.
(zhang2025multiomicsinsightsin pages 14-18): Lingfeng Zhang, M. Lyu, Simeng Ma, M. D. Y. Xu, M. D. X. Xie, Qian Gong Ph. D., Lijun Kang M. D., Shijia Chen Ph. D., and Zhongchun Liu M. D. Multi-omics insights in major depressive disorder: dysfunction of neurons. MedRxiv, May 2025. URL: https://doi.org/10.1101/2025.05.03.25326369, doi:10.1101/2025.05.03.25326369. This article has 0 citations.
(correia2024advancementsexploringmajor pages 8-9): Ana Salomé Correia and Nuno Vale. Advancements exploring major depressive disorder: insights on oxidative stress, serotonin metabolism, bdnf, hpa axis dysfunction, and pharmacotherapy advances. International Journal of Translational Medicine, 4:176-196, Mar 2024. URL: https://doi.org/10.3390/ijtm4010010, doi:10.3390/ijtm4010010. This article has 29 citations.

OpenScientist ▸

Major Depressive Disorder: A Comprehensive Disease-Characteristics Report

openscientist-autonomous 59 citations 2026-07-26T05:49:16.909248

Major Depressive Disorder: A Comprehensive Disease-Characteristics Report

Summary

Major Depressive Disorder (MDD) is a common, frequently recurrent, and highly disabling psychiatric syndrome defined clinically by standardized symptom criteria (DSM-5 / ICD-11) requiring persistent depressed mood and/or anhedonia lasting at least two weeks, accompanied by a constellation of neurovegetative, cognitive, and psychomotor symptoms. It affects approximately 5.7% of adults worldwide, typically first onsets in adolescence or young adulthood, and follows an episodic/recurrent course. MDD is the second leading cause of global years lived with disability (YLDs) among all diseases (GBD 2021), making it one of the largest contributors to the worldwide burden of non-fatal health loss.

MDD is a complex, polygenic, multifactorial disorder. Twin studies estimate heritability at ~39–41%, and the largest genome-wide meta-analyses have identified 102+ independent risk loci implicating synaptic biology and prefrontal cortical function. No single gene is causal; instead, thousands of common variants of small effect combine with powerful environmental exposures — most prominently childhood trauma (odds ratios ~2–2.8) and stressful life events — to produce disease. These gene-by-environment interactions are exemplified by the serotonin transporter (SLC6A4) 5-HTTLPR short allele, which amplifies depression risk following stress. Pathophysiology integrates at least four interacting mechanistic systems: monoaminergic neurotransmission, hypothalamic–pituitary–adrenal (HPA) axis dysregulation, inflammation, and impaired glutamatergic neuroplasticity/neurogenesis, all converging on fronto-limbic brain circuits (prefrontal cortex, hippocampus, amygdala, cingulate, striatum).

MDD carries substantial excess mortality (all-cause standardized mortality ratio [SMR] ≈ 1.84; suicide-specific SMR ≈ 7.9), with women affected roughly twice as often as men. It is, however, a treatable condition. First-line evidence-based treatments include cognitive behavioural therapy (CBT), antidepressant pharmacotherapy (with combined CBT + antidepressant most efficacious for severe depression), neuromodulation (repetitive transcranial magnetic stimulation [rTMS], electroconvulsive therapy [ECT]), and, for treatment-resistant depression, rapid-acting glutamatergic agents such as FDA-approved intranasal esketamine. Pharmacogenomic guidance (CYP2D6, CYP2C19) can optimize antidepressant dosing. This report synthesizes 19 confirmed findings drawn from 83 reviewed papers across all 15 requested disease-characteristic domains.

Key Findings

Finding 1 — MDD is a leading global cause of disability with rising burden

Global Burden of Disease (GBD) analyses establish MDD as one of the largest single contributors to worldwide disability. In GBD 2021, depressive and anxiety disorders ranked as the 2nd and 6th leading causes of global YLDs, respectively, with depressive disorders among the top 25 causes of disability overall. GBD 2023 systematically estimated MDD prevalence and burden across 204 countries as one of 12 mental disorders using Bayesian meta-regression, confirming steadily rising absolute case counts driven by population growth and aging even where age-standardized rates are stable or declining.

"depressive and anxiety disorders ranked as the 2nd and 6th leading causes of global YLDs" — PMID: 42269957

Comparative GBD 2021 analyses show age-standardized incidence, prevalence, and DALY rates rising rapidly among individuals aged 10–24 years both globally and in high-population countries such as China, underscoring the adolescent/young-adult vulnerability window (PMID: 42416185).

Finding 2 — MDD is polygenic; GWAS identifies 102+ loci implicating synaptic/prefrontal biology

A landmark genome-wide meta-analysis of 807,553 individuals (246,363 cases, 561,190 controls) identified 102 independent variants, 269 genes, and 15 gene-sets, with strong enrichment for genes governing synaptic structure and neurotransmission, and for prefrontal brain regions. 87 of 102 variants replicated in an independent sample of 1,306,354 individuals. Twin-based heritability of DSM-IV MDD is estimated at 39–41%.

"We identified 102 independent variants, 269 genes, and 15 genesets associated with depression, including both genes and gene pathways associated with synaptic structure and neurotransmission" — PMID: 30718901

"An enrichment analysis provided further evidence of the importance of prefrontal brain regions" — PMID: 30718901

"Heritability estimates were higher for STB phenotypes (51-80%) compared to DSM-IV MDD (39-41%)" — PMID: 40991153

This polygenic architecture means MDD has no single causal gene; risk is distributed across thousands of common variants of small individual effect. Cross-trait genetic analyses further show shared genetic architecture with cardiovascular disease (calcium-signaling loci: TPCN1, CACNA2D2, CACNA1D, ATP2B1; PMID: 42436150), insulin resistance/metabolic conditions (PMID: 42435748), and chronic inflammatory skin disease (PMID: 42445668), highlighting pleiotropic neuroimmune and metabolic links.

Finding 3 — MDD pathophysiology integrates monoamine, HPA-axis, inflammation, and neuroplasticity mechanisms

Integrated neurobiological reviews converge on a multi-system model in which altered neurotransmission, HPA-axis abnormalities from chronic stress, inflammation, reduced neuroplasticity/neurogenesis, and large-scale network dysfunction interact to produce depression.

"Some possible pathophysiological mechanisms of depression include altered neurotransmission, HPA axis abnormalities involved in chronic stress, inflammation, reduced neuroplasticity, and network dysfunction" — PMID: 28558878

Inflammation appears causally sufficient to produce depressive phenotypes: experimentally inducing a pro-inflammatory state produces "sickness behavior" resembling depression.

"the induction of a pro-inflammatory state in healthy or medically ill subjects induces 'sickness behavior' resembling depressive symptomatology" — PMID: 24468642

Finding 4 — Childhood trauma is a major modifiable risk factor

A meta-analysis of early trauma and adult depression found robust dose-dependent associations across all trauma types, with emotional maltreatment strongest:

Trauma type	Odds ratio for adult depression
Emotional abuse	2.78
Neglect	2.75
Sexual abuse	2.42
Domestic violence	2.06
Physical abuse	1.98

"Emotional abuse showed the strongest association with depression (OR=2.78) followed by neglect (OR=2.75) and sexual abuse (OR=2.42)" — PMID: 26078093

Childhood adversities carry a population-attributable-risk of 40.7–61.0% for anxiety/mood disorders (PMID: 40541041), and childhood social disadvantage (low SES, family disruption, residential instability) increases onset risk, recurrence, and reduces remission likelihood (PMID: 14672243).

Finding 5 — MDD prevalence is ~2× higher in women

Prevalence of major depression is approximately twice as high in women as in men. Proposed mechanisms include 17β-estradiol modulation of reward circuitry and sex differences in immune response; hormonal-transition windows (puberty, postpartum, menopause) mark vulnerability.

"with depression affecting women at twice the rate of men" — PMID: 42382579

"the prevalence of major depression is approximately twice as high in women compared to men" — PMID: 42425939

Finding 6 — Intranasal esketamine is FDA-approved for treatment-resistant depression

Esketamine (S-enantiomer of ketamine), an NMDA-receptor antagonist, was FDA-approved in 2019 as adjunctive therapy for treatment-resistant depression (TRD). An individual-patient-data meta-analysis of 7 RCTs (1,505 patients) showed MADRS reduction at 4 weeks (mean difference −2.94, 95% CI −5.39 to −0.48; moderate certainty) and reduced relapse in continuation therapy (HR = 0.38, 0.26–0.57).

"In 2019, the FDA and EMA approved intranasal esketamine for treatment-resistant depression (TRD)" — PMID: 41310599

"esketamine reduced MADRS scores at 4 weeks (mean difference (MD) = - 2.94, 95% CI [- 5.39 to - 0.48]; GRADE: moderate certainty)" — PMID: 41310599

Roughly one-third of depressed patients develop TRD (PMID: 41244961), the population motivating rapid-acting glutamatergic treatments.

Finding 7 — MDD causes substantial excess mortality, especially from suicide

A 20-year population cohort of 126,573 depressed individuals (1,139,073 person-years) quantified excess mortality:

Mortality category	SMR (95% CI)
All-cause	1.84 (1.82–1.88)
Natural-cause	1.69 (1.66–1.72)
Unnatural-cause	5.24 (4.97–5.51)
Suicide-specific	7.92 (7.47–8.38)
Suicide, ages 15–34	12.75 (10.87–14.79)

"individuals with depression exhibited significantly higher all-cause (SMR=1.84 [95% CI=1.82-1.88]), natural-cause (1.69 [1.66-1.72]), and unnatural-cause (5.24 [4.97-5.51]) mortality rates than the general population" — PMID: 39536694

"Suicide-specific SMR was markedly elevated (7.92 [7.47-8.38]), particularly in the 15-34 year-olds (12.75 [10.87-14.79])" — PMID: 39536694

Excess life-years-lost were 5.67 years (men) and 4.06 years (women); cardiovascular disease, respiratory disease, and cancers accounted for most natural-cause deaths.

Finding 8 — Peripheral inflammation (CRP/IL-6) is elevated in a subset of MDD, with sex specificity and treatment relevance

A sex-stratified meta-analysis (23 studies) found elevated CRP in depressed females (Cohen's d = 0.19, p = 0.02) but not males (d = −0.01), and elevated IL-6 in females (d = 0.51, p = 0.04). Higher baseline CRP and IL-6 predicted greater symptom reduction after ECT (14 studies, n = 556), supporting inflammatory markers as prognostic/predictive biomarkers.

"Sex-based analyses revealed elevated levels of CRP among females with depression (Cohen's d = 0.19) relative to their healthy counterparts (p = 0.02), an effect not apparent among males" — PMID: 39089535

"higher baseline CRP and IL-6 levels were significantly associated with greater depressive symptom reduction post-ECT" — PMID: 39938607

Sleep disturbance in MDD correlates with pooled inflammatory markers and CRP (PMID: 41475163).

Finding 9 — MDD is diagnosed clinically via DSM-5 nine-symptom criteria (PHQ-9 operationalizes them)

DSM-5 MDD requires ≥5 of nine symptoms for ≥2 weeks, at least one being depressed mood or anhedonia: (1) depressed mood, (2) anhedonia, (3) appetite/weight change, (4) sleep disturbance, (5) psychomotor agitation/retardation, (6) fatigue, (7) worthlessness/guilt, (8) concentration difficulty, (9) thoughts of death/suicidality. The PHQ-9 operationalizes these criteria for screening and severity measurement.

"nine depressive symptoms, including suicidality, comprising the DSM-5 diagnostic criteria for major depressive disorder (assessed using the Patient Health Questionnaire-9)" — PMID: 37798353

Symptom presentation is heterogeneous and precipitant-dependent: different adverse life events produce distinct symptom patterns (bereavement → sadness/anhedonia/appetite loss; chronic stress → fatigue/hypersomnia).

"The patterns of depressive symptoms associated with the nine categories of adverse life events differed significantly" — PMID: 17898343

ICD-11 differs slightly, requiring 5 of ten symptoms (adding "hopelessness") and retaining separate dysthymia and mixed-episode categories (PMID: 34964106).

Finding 10 — Gene–environment interaction: 5-HTTLPR short allele amplifies stress-induced depression risk

The serotonin transporter (SLC6A4) 5-HTTLPR polymorphism moderates the stress–depression relationship: short (S) allele carriers show a stronger association between stressful life event load and depression than L/L homozygotes.

"the association between SLE load and MS depression severity was stronger among those with one or two copies of the short allele of the 5-HTTLPR" — PMID: 29683385

"carriers of either one or two copies of the s allele had increased odds of depressive symptoms associated with stress compared to participants with the l/l genotype not exposed to stressful situations" — PMID: 37558806

The effect operates via glucocorticoid reactivity (PMID: 29940236) and emotion-regulation network connectivity (PMID: 29129791). Twin analyses also show income-inequality exposure moderates genetic variance in depressive symptoms (PMID: 42253158).

Finding 11 — Mediterranean diet and lifestyle are candidate protective/preventive factors

An extra-virgin olive-oil-enriched Mediterranean diet is being tested in the PREDI-DEP RCT — the first trial designed to prevent recurrent unipolar depression. Anti-inflammatory dietary patterns (vegetables, fruits, legumes, nuts, whole grains, omega-3/PUFA) associate with lower metabolic-syndrome severity and depressive symptoms.

"the PREDI-DEP trial is the first ongoing randomized clinical trial designed to assess the role of the Mediterranean diet in the prevention of recurrent depression" — PMID: 30744589

Meta-umbrella reviews catalog Mediterranean diet and physical activity as protective factors across neuropsychiatric disorders, and late-life depression as a risk factor for dementia (PMID: 33435977).

Finding 12 — Glutamatergic neuroplasticity (AMPA–BDNF–mTOR) is a convergent mechanism of rapid-acting antidepressants

Ketamine and classical psychedelics converge on a neuroplasticity pathway in prefrontal cortex pyramidal neurons: increased glutamate release → AMPA receptor activation → BDNF and mTOR signaling → synaptic-protein expression → synaptogenesis.

"ketamine and psychedelics [psilocybin, lysergic acid diethylamide (LSD), and N,N-dimethyltryptamine (DMT)] induce synaptic, structural, and functional changes, particularly in pyramidal neurons in the prefrontal cortex. These include increased glutamate release, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) activation, brain-derived neurotrophic factor (BDNF) and mammalian target of rapamycin (mTOR)-mediated signaling, expression of synaptic proteins, and synaptogenesis" — PMID: 34565579

FDA approvals of S-ketamine and brexanolone (2019) opened non-monoamine (NMDA/GABA-A) therapeutic strategies, contrasting with the slow onset of monoaminergic antidepressants (PMID: 31991195).

Finding 13 — MDD affects fronto-limbic circuits

Structural and functional MRI consistently implicate a distributed fronto-limbic network. In late-life depression:

"Decreased volumes or cortical thickness in the prefrontal cortex, orbitofrontal cortex, anterior and posterior cingulate cortex, several temporal and parietal regions, hippocampus, amygdala, striatum, thalamus, and the insula were associated with LLD" — PMID: 32544600

"The study highlights the important role of the hippocampus and the prefrontal cortex in EO patients as part of emotion-regulation networks" — PMID: 35421280

Late-life depression additionally shows white-matter hyperintensities and reduced integrity in fronto-striatal-limbic tracts (cingulum, corpus callosum, uncinate fasciculus), with altered default-mode-network connectivity. Postpartum depression shows overlapping structural/functional/metabolic alterations (PMID: 40925498).

Finding 14 — Pharmacogenomics: CYP2D6 and CYP2C19 genotypes guide antidepressant dosing (CPIC)

The Clinical Pharmacogenetics Implementation Consortium (CPIC) provides genotype-informed prescribing guidance: variation in CYP2D6, CYP2C19, and CYP2B6 influences metabolism of SSRIs/SNRIs, affecting dosing, efficacy, and tolerability.

"Genetic variation in CYP2D6, CYP2C19, and CYP2B6 influences the metabolism of many of these antidepressants, which may potentially affect dosing, efficacy, and tolerability" — PMID: 37032427

Pharmacodynamic genes are not yet clinically actionable:

"the existing data for SLC6A4 and HTR2A, which do not support their clinical use in antidepressant prescribing" — PMID: 37032427

Polygenic risk scores for antidepressant response remain insufficiently predictive for routine use (PMID: 42442668).

Finding 15 — Epigenetic dysregulation links stress to depression

Stress-induced DNA methylation changes affect depression-associated genes NR3C1 (glucocorticoid receptor), NR3C2, CRHR1, SLC6A4, BDNF, and FKBP5; some changes are lasting and show transgenerational effects.

"several genes associated with depression (NR3C1, NR3C2, CRHR1, SLC6A4, BDNF, and FKBP5)" — PMID: 36590248

In ECT responders, changes in BDNF, ERK1, and NR3C1 mRNA correlated strongly with methylation changes:

"changes in mRNA expression were highly correlated (R = 0.59 - 0.88) with changes in DNA methylation for multiple CpG sites in the respective genes" — PMID: 36067540

Finding 16 — Rodent stress models recapitulate core MDD features (anhedonia)

Chronic unpredictable mild stress (CUMS) is the most widely used, reliable rodent model, robustly producing anhedonia (reduced sucrose preference).

"the CUMS protocol is a robust animal model of depression and is strongly associated with anhedonic behavior in rodents" — PMID: 30529362

"The prolonged exposure of rodents to unpredictable/uncontrollable mild stressors leads to a reduction in the intake of palatable liquids, behavioral despair, locomotor inhibition, anxiety-like changes, and vegetative (somatic) abnormalities" — PMID: 35072761

Chronic social defeat stress (CSDS) yields separable susceptible vs resilient populations implicating BDNF/TrkB, MeCP2, and FKBP51/glucocorticoid-receptor signaling (PMID: 35711008; PMID: 36104438). Limitations include cross-lab reproducibility, protocol heterogeneity, and incomplete capture of human cognitive/affective features.

Finding 17 — Psychotherapy (CBT) and combined CBT + antidepressant are first-line efficacious treatments

A NICE network meta-analysis (676 RCTs, 105,477 participants, 63 treatment classes) found, for more severe depression, that combined individual CT/CBT + antidepressants was the most efficacious class vs placebo (SMD −1.18), followed by individual CT/CBT (−0.78), mirtazapine (−0.35), and SNRIs (−0.32). For less severe depression, group CT/CBT was efficacious vs treatment-as-usual (SMD −1.01).

"efficacious classes versus pill placebo (reference treatment for this population) included combined individual CT/CBT with antidepressants [-1.18 (-2.07; -0.44)]" — PMID: 39246718

"group cognitive/cognitive behavioural therapy (CT/CBT) class was efficacious versus treatment as usual [TAU]" — PMID: 39246718

Short-term psychodynamic psychotherapy is also superior to unstructured usual treatment (SMD −0.91; PMID: 36623570).

Finding 18 — rTMS is an effective device-based treatment for MDD/TRD

A sham-controlled meta-analysis (30 comparisons, N = 1,850) found active prefrontal rTMS reduced depressive symptoms vs sham (Hedges' g = −1.056, 95% CI −1.407 to −0.704, p < 0.001).

"Active rTMS reduced depressive symptoms versus sham (Hedges' g = -1.056, 95% CI -1.407 to -0.704; p < 0.001)" — PMID: 41997374

In youth (16 studies, 1,295 patients aged 10–25): response RR 1.24, remission RR 1.63 (NNT ≈ 10).

"Pooled RR was 1.24 (95% CI = 1.06-1.45) for response rate and 1.63 (95% CI = 1.11-2.39) for remission rate (with an associated number needed to treat of 10)" — PMID: 41137879

A large NMA (141 trials, 10,587 participants) ranked theta-burst stimulation (TBS) most efficacious among modalities (PMID: 42383744).

Finding 19 — MDD is common (~5–6% of adults), first onsets in adolescence/early adulthood, and is recurrent/episodic

Depression affects approximately 5.7% of adults worldwide; around one-third develop TRD.

"Depression affects approximately 5.7% of adults worldwide, and around one-third of these individuals develop treatment-resistant depression (TRD)" — PMID: 41244961

WHO World Mental Health surveys (156,331 respondents, 29 countries) show mood disorders commonly first onset in adolescence/young adulthood, with median age of onset of any mental disorder ~19–20 years and MDD among the two most prevalent disorders in both sexes (PMID: 37531964). Childhood adversities carry population-attributable-risk of 40.7–61.0% for mood disorders.

"Population attributable risk proportions of 12-month disorders associated with CAs were in the range of 40.7-61.0 % for anxiety and mood disorders" — PMID: 40541041

Report by Requested Domain

1. Disease Information

MDD is a common mood disorder characterized by persistent depressed mood and/or loss of interest/pleasure (anhedonia) with associated neurovegetative, cognitive, and psychomotor symptoms lasting ≥2 weeks and causing clinically significant distress or impairment. Key identifiers and synonyms:

Field	Value
MONDO	MONDO:0002050 (major depressive disorder); MONDO:0002009 (depressive disorder)
ICD-10	F32 (single episode), F33 (recurrent)
ICD-11	6A70 (single episode depressive disorder), 6A71 (recurrent depressive disorder)
MeSH	D003865 (Depressive Disorder, Major)
OMIM	608516 (MDD susceptibility)
Synonyms	Major depression, unipolar depression, clinical depression, major depressive episode, unipolar major depression

Information is derived predominantly from aggregated disease-level resources (GWAS consortia, GBD, meta-analyses, national registries) plus individual patient / EHR-derived cohort studies (e.g., Finnish/Swedish registers, PMID: 41536102).

2. Etiology

Causal factors: MDD is multifactorial and polygenic (Findings 2, 3). There is no infectious cause, though inflammation contributes mechanistically (Finding 3). Genetic risk factors: 102+ common susceptibility loci, heritability 39–41%; no single causal gene. Environmental risk factors: childhood trauma (OR 1.98–2.78, Finding 4), stressful life events, female sex (~2× risk, Finding 5), low SES/family disruption, childhood income inequality, sleep disturbance. Protective factors: Mediterranean/anti-inflammatory diet, physical activity, education (Finding 11; PMID: 33435977); neurobiological resilience factors (greater prefrontal volume/activity, PMID: 40520971). Gene–environment interactions: 5-HTTLPR × stress (Finding 10); polygenic risk × income inequality (Finding 10).

3. Phenotypes

Core phenotypes map to the DSM-5 nine symptoms (Finding 9). Suggested HPO terms:

Phenotype (type)	HPO term	Frequency/characteristics
Depressed mood (behavioral)	HP:0000716 (Depressivity)	Core; required
Anhedonia (behavioral)	HP:0100754 (Anhedonia)	Core; required
Insomnia / sleep disturbance	HP:0100785 (Insomnia)	Very common; links to inflammation
Fatigue	HP:0012378 (Fatigue)	Common
Appetite/weight change	HP:0004396 (Poor appetite)	Common
Poor concentration	HP:0000736 (Short attention span)	Common
Suicidal ideation	HP:0031589 (Suicidal ideation)	High-risk; drives mortality
Psychomotor retardation/agitation	HP:0025059 / HP:0000733	Variable

Onset: adolescent/adult (median ~19–20 y). Severity: mild to severe, variable. Progression: episodic/recurrent/fluctuating. Quality of life: even minor depression produces significant functional impairment in daily activities, feelings, pain, and social function (PMID: 7804493).

4. Genetic/Molecular Information

No monogenic cause; polygenic (Finding 2). Implicated genes/pathways: synaptic structure and neurotransmission genes, prefrontal-enriched loci; candidate/mechanistic genes SLC6A4, BDNF, FKBP5, NR3C1, NR3C2, CRHR1, HTR2A, COMT, MTHFR, SGK1 (PMID: 32849818); pleiotropic loci FADS1-2-3 (PUFA metabolism, PMID: 42309192), calcium-channel genes, and MHC/histone genes (PMID: 42320287). Variants are germline, common, low-effect (not classified pathogenic/likely-pathogenic under ACMG — this is a complex trait, not a Mendelian disorder). Epigenetics: methylation of NR3C1/BDNF/FKBP5/SLC6A4 (Finding 15). No characteristic chromosomal abnormalities.

5. Environmental Information

Non-genetic contributors: psychosocial stress, childhood maltreatment, low SES, income inequality, sleep disruption. Lifestyle: physical inactivity, poor diet (protective: Mediterranean diet, exercise; Finding 11). No infectious agent causes MDD, though inflammatory/immune activation is mechanistically implicated (Findings 3, 8) and comorbid inflammatory diseases share genetic liability (PMID: 42445668).

6. Mechanism / Pathophysiology

See Mechanistic Model below. Key pathways: monoaminergic (5-HT/NE/DA); glutamatergic AMPA–BDNF–mTOR neuroplasticity (Finding 12; GO:0048167 regulation of synaptic plasticity, GO:0007268 chemical synaptic transmission); HPA-axis/glucocorticoid signaling (Finding 15; GO:0051384 response to glucocorticoid); neuroinflammation (Finding 8; GO:0006954 inflammatory response); impaired hippocampal neurogenesis (GO:0021766). Cell types: pyramidal neurons (CL:0000598), astrocytes (CL:0000127), microglia (CL:0000129), oligodendrocytes (CL:0000128) — single-cell eQTL work implicates cell-type-specific genes ZSCAN31 (astrocytes/endothelial), BTN3A2 (microglia), YLPM1 (oligodendrocytes) (PMID: 42372879). Subcellular: mitochondria (GO:0005739; energy metabolism), synapse (GO:0045202). CHEBI-relevant chemical entities: serotonin (CHEBI:28790), cortisol (CHEBI:17650), glutamate (CHEBI:14321), BDNF signaling.

7. Anatomical Structures Affected

Primary organ: brain (UBERON:0000955), nervous system. Key regions: prefrontal cortex (UBERON:0000451), orbitofrontal cortex, anterior/posterior cingulate cortex (UBERON:0002715), hippocampus (UBERON:0002421), amygdala (UBERON:0001876), striatum (UBERON:0002435), thalamus (UBERON:0001897), insula (UBERON:0002690) — Finding 13. White-matter tracts: cingulum, corpus callosum, uncinate fasciculus. Involvement is typically bilateral. Secondary systems: cardiovascular, endocrine (HPA), immune.

8. Temporal Development

Onset typically adolescence/young adulthood (median ~19–20 y), insidious. Course is episodic/recurrent/relapsing-remitting; early-onset cases have higher recurrence risk. Remission may be spontaneous or treatment-induced; ~one-third become treatment-resistant. Chronic and lifelong in many. Adolescence (10–24 y) is a critical vulnerability window (Findings 1, 19).

9. Inheritance and Population

Prevalence ~5.7% of adults (Finding 19). Inheritance: multifactorial/polygenic, heritability 39–41% (Finding 2); no Mendelian pattern, penetrance, anticipation, founder effects, or carrier frequency applicable. Demographics: female:male ≈ 2:1 (Finding 5); rising burden in youth; higher middle-age/older-adult burden in some regions (PMID: 42416185).

10. Diagnostics

Diagnosis is clinical via DSM-5/ICD-11 criteria (Finding 9), aided by structured tools (PHQ-9, MADRS, CDRS-R in youth). No diagnostic laboratory/genetic test exists. Emerging biomarkers: CRP/IL-6 (prognostic/predictive, Finding 8); neuroimaging (structural/functional MRI, Finding 13) is research-grade. Pharmacogenomic testing (CYP2D6/CYP2C19) informs treatment, not diagnosis (Finding 14). Differential diagnosis: bipolar depression, persistent depressive disorder/dysthymia, adjustment disorder, normal grief, hypothyroidism, substance-induced mood disorder.

11. Outcome/Prognosis

Excess mortality: all-cause SMR 1.84, suicide SMR 7.9 (Finding 7); 4–5.7 excess life-years lost. High morbidity/disability (leading YLD cause, Finding 1). Prognostic factors: severity, comorbidity, early onset, treatment response; inflammatory markers predict ECT response (Finding 8). Real-world RCT-ineligible patients (comorbid) have >2× worse outcomes (PMID: 41536102). Late-life depression predicts dementia/AD (PMID: 42134046).

12. Treatment

Modality	Examples	Evidence	MAXO suggestion
Psychotherapy	CBT, group CBT, STPP	SMD −0.78 to −1.01 (Finding 17)	MAXO:0000804 (psychotherapy)
Pharmacotherapy	SSRIs, SNRIs, mirtazapine	SMD −0.32 to −0.35 (Finding 17)	MAXO:0001008 (pharmacotherapy)
Combined	CBT + antidepressant	SMD −1.18 (most efficacious, severe)	—
Neuromodulation	rTMS, TBS, ECT	rTMS g = −1.06 (Finding 18)	MAXO:0000823 (TMS)
Rapid-acting	Intranasal esketamine (TRD)	MADRS MD −2.94 (Finding 6)	MAXO:0000058 (drug therapy)

Pharmacogenomics: CYP2D6/CYP2C19 genotype-guided dosing (Finding 14). In youth, fluoxetine/escitalopram/sertraline preferred; suicidality monitoring essential (PMID: 34029378).

13. Prevention

Primary: risk-factor modification, Mediterranean diet (PREDI-DEP), physical activity, childhood-adversity reduction (Finding 11). Secondary: PHQ-9 screening, early intervention. Tertiary: relapse prevention (maintenance antidepressants, continuation esketamine HR 0.38). Behavioral: exercise, diet, sleep hygiene. No immunization applicable.

14. Other Species / Natural Disease

Depression-like states are studied in rodents (Mus musculus, NCBI:txid10090; Rattus norvegicus, NCBI:txid10116) via induced models (Finding 16). Orthologous genes conserved: Bdnf, Slc6a4, Fkbp5, Nr3c1. Naturally occurring analogues (e.g., separation-related/anhedonic states in companion animals) exist but are not well characterized; no strong zoonotic or breed-specific associations apply.

15. Model Organisms

Predominantly mammalian induced models: CUMS and CSDS in mice/rats recapitulate anhedonia, behavioral despair, and vegetative changes (Finding 16). Genetic models: BDNF Val66Met knock-in, FKBP5 manipulation, MeCP2 overexpression. Recapitulation: strong for anhedonia and stress-susceptibility/resilience; limitations: poor capture of human subjective/cognitive symptoms, cross-lab reproducibility, protocol heterogeneity. Resources: MGI, RGD, IMPC.

Mechanistic Model / Interpretation

MDD is best understood as a diathesis–stress disorder in which polygenic genetic liability and early-life/ongoing environmental stress converge on shared neurobiological substrates:

   GENETIC LIABILITY (polygenic, 102+ loci,        ENVIRONMENTAL STRESS
   heritability ~39-41%; SLC6A4, BDNF, FKBP5,       (childhood trauma OR 1.98-2.78,
   NR3C1, FADS1, synaptic/prefrontal genes)          stressful life events, low SES)
    |                                                 |
    +---------------->  GENE x ENVIRONMENT  <---------+
          (5-HTTLPR-S x stress; epigenetic
           methylation of NR3C1/BDNF/FKBP5)
                       |
      +------------------------+------------------------+
      v                        v                        v
     HPA-AXIS DYSREGULATION     NEUROINFLAMMATION         MONOAMINE DEFICIT
     (^cortisol, v GR function,  (^CRP, ^IL-6;             (v 5-HT/NE/DA
      FKBP5, SGK1)               "sickness behavior";       signaling)
      |                   sex-specific, female)          |
      +------------------------+------------------------+
                       v
    IMPAIRED GLUTAMATERGIC NEUROPLASTICITY
    (v AMPA-BDNF-mTOR signaling, v synaptogenesis,
     v hippocampal neurogenesis)
                       |
                       v
   FRONTO-LIMBIC CIRCUIT DYSFUNCTION
(PFC, hippocampus, amygdala, cingulate, striatum; v volume,
 altered connectivity, default-mode-network dysregulation)
                       |
                       v
  CLINICAL DEPRESSION (DSM-5: depressed mood/anhedonia +
  >=5 symptoms >=2 weeks) -> disability, excess mortality (suicide)

Upstream drivers are genetic liability, early-life stress, and their epigenetic embedding. Midstream are the four interacting biological systems (HPA, inflammation, monoamines, neuroplasticity). Downstream is fronto-limbic circuit dysfunction producing the clinical syndrome. Critically, the treatment landscape maps onto this model: SSRIs/SNRIs target monoamines (slow onset); esketamine and psychedelics target the glutamate–AMPA–BDNF–mTOR neuroplasticity node (rapid onset); anti-inflammatory strategies and ECT-response biomarkers target inflammation; and psychotherapy/rTMS act on fronto-limbic circuit function. This explains why combined biological + psychological treatment is most efficacious for severe disease.

Evidence Base

PMID	Contribution	Supports finding
30718901	102-loci GWAS meta-analysis; synaptic/prefrontal enrichment	F2 (core genetics)
28558878	Integrated neurobiology review	F3 (mechanism)
24468642	Inflammation → sickness behavior	F3, F8
26078093	Childhood-trauma meta-analysis (ORs)	F4
39536694	126,573-person mortality cohort	F7
39089535	Sex-specific inflammation	F8
39938607	CRP/IL-6 predict ECT response	F8
29683385 / 37558806	5-HTTLPR × stress GxE	F10
34565579	AMPA-BDNF-mTOR neuroplasticity	F12
32544600 / 35421280	Fronto-limbic neuroimaging	F13
37032427	CPIC pharmacogenomics	F14
36590248 / 36067540	Epigenetic methylation	F15
30529362 / 35072761	CUMS rodent model	F16
39246718	NICE NMA (676 RCTs) treatment	F17
41997374 / 41137879	rTMS efficacy	F18
41310599	Esketamine IPD meta-analysis	F6
42269957 / 42167272	GBD burden	F1
41244961 / 37531964	Prevalence, age-of-onset	F19

Evidence types span human clinical (GWAS, cohorts, RCTs, meta-analyses — the majority), model organism (CUMS/CSDS rodents), and in vitro/computational (single-cell eQTL, colocalization). The convergence of independent evidence streams (genetics, imaging, biomarkers, treatment mechanism) on a shared multi-system model strengthens confidence.

Limitations and Knowledge Gaps

Heterogeneity. MDD is diagnostically heterogeneous; the same DSM-5 label captures biologically distinct subtypes (e.g., inflammatory vs non-inflammatory, melancholic vs atypical). Group-level effect sizes obscure individual variation.
Genetic architecture incompletely resolved. GWAS explains only a fraction of heritability; effector genes at most loci and their functional mechanisms remain uncertain (e.g., FADS1-2-3 pleiotropy).
Biomarkers not diagnostic. CRP/IL-6 and neuroimaging findings are group-level and not yet clinically actionable for individual diagnosis or treatment selection.
Pharmacogenomics limited. Only CYP2D6/CYP2C19 are clinically actionable; polygenic response scores lack predictive performance, especially in non-European ancestries.
Ancestry bias. Most genetic and biomarker data derive from European-ancestry samples, limiting generalizability.
Model organism validity gap. Rodent models capture anhedonia/stress-susceptibility well but poorly model human subjective/cognitive symptoms.
RCT generalizability. ~one-third of real-world MDD patients would be RCT-ineligible and have substantially worse outcomes, so guideline evidence may not reflect typical patients.
Causality. Much evidence is observational/correlational; directionality (e.g., inflammation ↔ depression, sleep ↔ inflammation) is often bidirectional or unresolved.

Proposed Follow-up Experiments / Actions

Biologically-stratified trials. Prospectively test anti-inflammatory augmentation in the CRP/IL-6-high, female-predominant inflammatory subtype (Finding 8), using baseline inflammatory markers as inclusion criteria and treatment-response predictors.
Ancestry diversification. Expand GWAS and pharmacogenomic studies into non-European populations to improve polygenic-risk-score portability and equity.
Effector-gene functional validation. Use single-cell eQTL/CRISPR screens to resolve causal genes at ambiguous loci (FADS1-2-3, calcium-channel, MHC/histone loci) and their cell-type-specific mechanisms.
Prevention trial readouts. Complete PREDI-DEP and similar dietary/lifestyle RCTs to establish causal preventive efficacy of the Mediterranean/anti-inflammatory diet.
Neuroplasticity biomarker development. Validate BDNF/mTOR-pathway and neuroimaging markers as predictors of rapid-acting (esketamine/psychedelic) treatment response.
Comparative-effectiveness of neuromodulation. Conduct high-quality head-to-head rTMS-modality trials (TBS vs accelerated vs deep TMS) to confirm probabilistic NMA rankings.
Real-world evidence integration. Combine registry/EHR data with RCT evidence to build treatment guidelines generalizable to comorbid, RCT-ineligible patients.
Deep phenotyping for subtypes. Integrate multi-omics + longitudinal symptom trajectories to define reproducible, treatment-relevant MDD subtypes.

Report compiled from 19 confirmed findings across 83 reviewed papers over 5 investigation iterations. Evidence prioritizes primary literature with verified abstract quotations; ontology suggestions (MONDO, HPO, GO, CL, UBERON, CHEBI, MAXO) are provided throughout for knowledge-base integration.

Ask OpenScientist

OpenScientist Report

Classifications

Subtypes

Comorbidities

Mechanistic Hypotheses

Discussions and Knowledge Gaps

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Environmental Factors

Biochemical Markers

Related Datasets

Source YAML

References & Deep Research

References

Deep Research

Disorder

Key Pathophysiology Nodes

Citation Inventory (for evidence mapping)

Major Depressive Disorder: A Comprehensive Disease-Characteristics Report

Summary

Key Findings

Finding 1 — MDD is a leading global cause of disability with rising burden

Finding 2 — MDD is polygenic; GWAS identifies 102+ loci implicating synaptic/prefrontal biology

Finding 3 — MDD pathophysiology integrates monoamine, HPA-axis, inflammation, and neuroplasticity mechanisms

Finding 4 — Childhood trauma is a major modifiable risk factor

Finding 5 — MDD prevalence is ~2× higher in women

Finding 6 — Intranasal esketamine is FDA-approved for treatment-resistant depression

Finding 7 — MDD causes substantial excess mortality, especially from suicide

Finding 8 — Peripheral inflammation (CRP/IL-6) is elevated in a subset of MDD, with sex specificity and treatment relevance

Finding 9 — MDD is diagnosed clinically via DSM-5 nine-symptom criteria (PHQ-9 operationalizes them)

Finding 10 — Gene–environment interaction: 5-HTTLPR short allele amplifies stress-induced depression risk

Finding 11 — Mediterranean diet and lifestyle are candidate protective/preventive factors

Finding 12 — Glutamatergic neuroplasticity (AMPA–BDNF–mTOR) is a convergent mechanism of rapid-acting antidepressants

Finding 13 — MDD affects fronto-limbic circuits

Finding 14 — Pharmacogenomics: CYP2D6 and CYP2C19 genotypes guide antidepressant dosing (CPIC)

Finding 15 — Epigenetic dysregulation links stress to depression

Finding 16 — Rodent stress models recapitulate core MDD features (anhedonia)

Finding 17 — Psychotherapy (CBT) and combined CBT + antidepressant are first-line efficacious treatments

Finding 18 — rTMS is an effective device-based treatment for MDD/TRD

Finding 19 — MDD is common (~5–6% of adults), first onsets in adolescence/early adulthood, and is recurrent/episodic

Report by Requested Domain

1. Disease Information

2. Etiology

3. Phenotypes

4. Genetic/Molecular Information

5. Environmental Information

6. Mechanism / Pathophysiology

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

10. Diagnostics

11. Outcome/Prognosis

12. Treatment

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Mechanistic Model / Interpretation

Evidence Base

Limitations and Knowledge Gaps

Proposed Follow-up Experiments / Actions

Artifacts