This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "deregulated_nutrient_sensing#mTORC1 Hyperactivation"). Conforming nodes in disorder files should include the corresponding biological processes and causal edges, specialized to their disease context. The module is intentionally kept lean: it captures the conserved anabolic-vs-catabolic nutrient-sensing imbalance, its convergence on autophagy suppression, and the geroprotector drug-target pattern (rapamycin and metformin both restrain the anabolic mTORC1 node via target_mechanisms; dietary protein/amino-acid restriction is the non-pharmacological arm of the same pattern), but deliberately does NOT embed disease-specific or contested downstream theories (e.g. tissue-specific mTOR-driven pathologies, or the antagonistic-pleiotropy debate on whether mTOR inhibition trades growth for longevity). Such specific or context-dependent claims belong on the relevant disorder or comorbidity/trajectory entry, which may conforms_to or reference this module. Complements the cellular_senescence module (another antagonistic hallmark of aging): deregulated nutrient sensing is one of several senescence-inducing stresses, and both converge on age-related tissue dysfunction. Key conformance target: "deregulated_nutrient_sensing#mTORC1 Hyperactivation". The module models TWO catabolic sensing arms that nutrient surplus leaves attenuated, and they are not interchangeable: AMPK/sirtuins sense energy (low ATP/high AMP, NAD+), while GCN2 senses amino-acid scarcity via uncharged tRNAs. The distinction matters because dietary protein and amino-acid restriction acts through the GCN2 arm - and its FGF21 endocrine output - rather than through energy restriction, which is why protein restriction extends lifespan without reducing calorie intake. A disorder conforming only to the mTORC1 node should not be assumed to engage the GCN2/FGF21 arm. Two cautions on the amino-acid arm, both carried as open discussions rather than settled model content. First, individual amino acids are NOT interchangeable: isoleucine or valine restriction each extends mouse lifespan on its own, while leucine restriction - the strongest mTORC1 activator of the three branched-chain amino acids - does not improve metabolic health, so a conforming entry should name the amino acid it means. Second, the evidence is split across the chain: the proximal FGF21/energy-expenditure response is now shown directly in humans, but the lifespan benefit is rodent-only and repeatedly male-biased, and no long-term human data exist in the older adults for whom higher protein intake is clinically recommended.
Pharmacokinetic (Drug-Exposure) Model of Sex-Dimorphic Geroprotector Response
sex_dimorphic_geroprotector_exposure
EMERGING
Evidence: 3
Evidence balance
2 support
1 refute
The most reproducible single finding of the NIA Interventions Testing Program across two decades is that most lifespan-extending compounds work preferentially in one sex, usually males. This hypothesis holds that the dimorphism is pharmacokinetic - that males and females achieve different effective drug exposures, so the aging substrate itself responds equally and the apparent sex difference is a dosing artifact. The competing reading, which this module does not currently model as a separate group, is pharmacodynamic: that the nutrient-sensing network is differently wired or differently rate-limiting for lifespan in the two sexes, so matched exposure would still produce divergent outcomes. The two make an experimentally separable prediction - under the pharmacokinetic model, dose-matching to equal blood levels should abolish the sex difference.
Scope caveat a curator must carry forward: this module is an imperfect home for the hypothesis. The ITP male bias spans compounds that act well outside nutrient sensing (17-alpha-estradiol, nordihydroguaiaretic acid), so the phenomenon is broader than the mechanism modeled here; the hypothesis is filed on this module because rapamycin, acarbose, canagliflozin and metformin are the compounds it can be tested against structurally. Note also that the SUPPORT and REFUTE evidence come from the same program and are genuinely in tension - the pharmacokinetic model may hold for some compounds (canagliflozin, rapamycin) and fail for others (NDGA), in which case the single-model framing is itself wrong and should be split.
Rapamycin Extends Lifespan by a Route Distinct from Dietary Restriction
rapamycin_distinct_from_dietary_restriction
EMERGING
Evidence: 9
Evidence balance
7 support
2 refute
Rapamycin is routinely described as a dietary-restriction mimetic, on the reasoning that both down-shift anabolic nutrient signaling and both extend lifespan. This hypothesis holds that the shared endpoint conceals distinct routes - that pharmacologic mTORC1 inhibition and dietary restriction produce materially different endocrine, metabolic, proteostatic and hepatic transcriptional states, and therefore converge on longevity without being the same intervention. The claim as curated is "distinct but partially overlapping", not "fully distinct", because the same body of evidence that shows the divergence also locates genuine convergence: both interventions enter at mTORC1, both suppress translation and relieve the block on autophagy, and both leave overlapping hepatic gene-body hypermethylation. Where they part is downstream and endocrine - most sharply on insulin sensitivity, which dietary restriction improves and rapamycin degrades, and on protein turnover, where the two move canonical pathways in opposite directions. That insulin-sensitivity divergence is not by itself proof that the longevity routes differ: the improvement dietary restriction produces is dispensable for its own lifespan benefit, so the most-cited divergence sits on an axis at least partly off the longevity path. The distinction matters for this module because it determines whether mTORC1 hyperactivation is the single hub through which the whole hallmark acts, or one of several partly independent routes to the same consequence node.
Assessed against the openscientist run under kb/hypotheses/deregulated_nutrient_sensing/rapamycin_distinct_from_dietary_restriction/. That assessment's verdict (PARTIALLY_SUPPORTED) stays in its sidecar and is deliberately not written here: MechanisticHypothesisStatusEnum records where a hypothesis sits among competing accounts of a mechanism, not how one provider run read the evidence on one date, so the status remains EMERGING. What the added evidence changes is the shape of the claim rather than its standing. The divergence now rests on four modalities - endocrine and metabolic, hepatic xenobiotic-metabolism expression, liver proteome turnover and polysome loading, and cross-model lifespan responses - instead of on the single study the hypothesis was seeded with; but the same corpus establishes convergence at the mTORC1 entry point and in part of the hepatic methylome, which is why the shared-signature result is carried as REFUTE rather than left out. Three limits to carry forward. The additivity result that most directly discriminates the two models is in Drosophila, not mice. The insulin-sensitivity divergence, which is the one most often cited and the only one with human grounding, is weaker support than it looks: dietary restriction extends lifespan just as far in mice that cannot sensitize to insulin, so that axis is at least partly off the longevity path, and the REFUTE item recording this is a check on the hypothesis's own best-known argument rather than on its conclusion. And the decisive experiment - one lifespan-matched cohort comparing dietary restriction, rapamycin and the combination on a common readout - was not located, which is recorded as discussions#knowledge_gap_head_to_head_rapamycin_versus_dietary_restriction rather than resolved here. The module's own framing tension noted at seeding is unchanged: the mTORC1 node describes rapamycin as targeting the anabolic hub without asserting equivalence to dietary restriction, while the AMPK node cites a review that groups caloric restriction, sirtuin activation and rapamycin together as one longevity-promoting arm.
Which dietary amino acid restriction actually drives the benefit, and by what sensor - is the GCN2/FGF21 arm modelled here the route for all of them, or does each amino acid act through a partly distinct mechanism?
KNOWLEDGE GAP
OPEN
knowledge_gap_which_amino_acid_is_the_signal
Attached to:
GCN2 Amino-Acid-Scarcity Sensing Attenuation
Attenuated FGF21 Endocrine Starvation Response
This module's treatment node names "dietary protein and amino-acid restriction" as one intervention acting on one sensing arm, and that framing is now known to be under-specified. Restriction of isoleucine alone, or of valine alone, is each sufficient to extend mouse lifespan, yet restricting leucine - the strongest mTORC1 activator of the three branched-chain amino acids, and therefore the one the anabolic-signalling model predicts should matter most - did not improve metabolic health. Methionine restriction is a third, chemically unrelated route. If a single upstream sensor explained all of these, the amino acids should be broadly substitutable, and they are not. The unresolved question is whether GCN2/FGF21 is the common trunk with amino-acid-specific branches downstream, or whether isoleucine, valine and methionine each engage largely separate mechanisms that this module currently collapses into one node. Until that is settled, a conforming entry should name the specific amino acid it means rather than asserting generic amino-acid restriction.
Proposed experiments:
GCN2-dependence of single-amino-acid restriction benefits
FGF21-dependence of single-amino-acid restriction benefits
Human evidence now supports the proximal FGF21 and energy-expenditure response to protein restriction, but does the mouse lifespan benefit - which is largely male-specific - translate to humans at all?
HUMAN MODEL MISMATCH
OPEN
human_model_mismatch_amino_acid_restriction_lifespan
Attached to:
Attenuated FGF21 Endocrine Starvation Response
Accelerated Cellular Aging and Age-Related Tissue Decline
The two ends of this chain are not equally evidenced in humans, and the gap between them is where over-claiming happens. The proximal end now has direct human support: a controlled eucaloric intervention in healthy lean men raised fasting FGF21 and the energy intake needed to hold weight steady, and improved insulin sensitivity. The distal end - that this delays ageing - rests entirely on rodents, and there the benefit is repeatedly sex-dimorphic: isoleucine restriction extends lifespan more in males, and valine restriction raises median male lifespan by 23% without a female lifespan benefit. Three things therefore do not follow from the human data and must not be curated as if they did: that protein restriction extends human lifespan; that a benefit shown in young lean men generalises to older adults, women, or people with metabolic disease; or that a 5-week study speaks to lifelong exposure. The countervailing clinical concern - that reduced protein intake accelerates sarcopenia and frailty in the elderly, which is why higher intakes are recommended above age 65 - is exactly the population in which no long-term human data exist. Note the human study preserved lean body mass over 5 weeks, but only in young men, and only when energy intake was raised to hold weight constant.
Proposed experiments:
Protein restriction in older adults with body-composition endpoints
Sex-stratified single-amino-acid restriction in humans
Has anyone run the decisive comparison - dietary restriction, rapamycin, and the two combined, in one lifespan-matched mouse cohort on a common multi-omic readout - or is the "distinct routes" reading still assembled from separately designed studies?
KNOWLEDGE GAP
OPEN
knowledge_gap_head_to_head_rapamycin_versus_dietary_restriction
Attached to:
rapamycin_distinct_from_dietary_restriction
mTORC1 Hyperactivation
Rapamycin (mTOR Inhibition)
The evidence that rapamycin and dietary restriction reach longevity by partly separate routes is real but it is assembled, not designed. Each study behind it compares the two interventions on one modality in one tissue - hepatic xenobiotic-metabolism expression in one, liver proteome turnover and polysome loading in another, hepatic methylation in a third - at doses and durations chosen for that study rather than matched for equivalent lifespan effect. Differences read off such a set are confounded with dose and with exposure duration, and the confound runs both ways: a divergence may be a dose artifact, and a convergence may be the coincidence of two interventions happening to sit at comparable points on different curves. The experiment that would settle it is a single cohort in which dietary restriction and rapamycin are titrated to comparable lifespan extension and profiled on one platform, with a combination arm. The combination arm is what makes the question tractable rather than merely tidier: full additivity would be strong evidence for separate routes, and no additivity for a shared one, and the review that concludes rapamycin is not a true dietary-restriction mimetic predicts additivity explicitly. No such study was located by the provider run assessed for this hypothesis, which is a claim about that search and not about the literature; a curator who finds one should retire this gap rather than treat the absence as established.
Proposed experiments:
Lifespan-matched dietary restriction versus rapamycin, one cohort, one platform
Combination arm testing additivity of dietary restriction and rapamycin
Nutrient Surplus and Anabolic Signaling
trigger
A sustained state of nutrient and growth-factor abundance keeps the anabolic arm of the nutrient-sensing network engaged: the somatotroph GH/IGF-1 axis and amino-acid/nutrient sensing upstream of mTORC1. Because reducing the activity of these nutrient-sensing pathways (by dietary restriction, mutation, or chemical inhibitors) extends lifespan and lowers age-related disease, their chronic engagement is the initiating driver of the deregulated-nutrient-sensing hallmark.
Downstream
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mTORC1 Hyperactivation
-
AMPK and Sirtuin Catabolic-Sensing Attenuation
-
GCN2 Amino-Acid-Scarcity Sensing Attenuation
mTORC1 Hyperactivation
central effector
Persistent nutrient and growth-factor input drives chronic activation of mTOR complex 1 (mTORC1), the master anabolic sensor that couples nutrient availability to cell growth, protein translation, and biosynthesis. Because inhibition of the mTOR pathway extends lifespan across model organisms and protects against a growing list of age-related pathologies, its age-associated hyperactivation is the central effector of this hallmark and the node targeted by rapamycin and (indirectly, via AMPK) metformin. This is the conserved central node that disease-specific mTOR-activating lesions converge upon.
Downstream
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Autophagy Suppression and Anabolic Bias
-
Accelerated Cellular Aging and Age-Related Tissue Decline
AMPK and Sirtuin Catabolic-Sensing Attenuation
effector
In parallel with anabolic hyperactivation, the catabolic low-energy sensors that oppose mTORC1 - AMP-activated protein kinase (AMPK, which senses a low energy/high-AMP state) and the NAD+-dependent sirtuins - are relatively attenuated in the nutrient-replete aging state. These sensors normally drive the protective, pro-longevity response to nutrient scarcity (the mechanism engaged by dietary restriction, Sirtuin 1 activation, and metformin), so their reduced activity reinforces the anabolic bias and its downstream consequences.
Downstream
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Autophagy Suppression and Anabolic Bias
-
Accelerated Cellular Aging and Age-Related Tissue Decline
GCN2 Amino-Acid-Scarcity Sensing Attenuation
effector
The second catabolic sensing arm, sensing amino-acid rather than energy scarcity. GCN2 (general control nonderepressible 2) is the conserved stress-responsive kinase activated by the uncharged tRNAs that accumulate when amino acids are limiting; activated GCN2 phosphorylates eIF2-alpha, repressing global translation while selectively increasing translation of ATF4, and it additionally restrains TORC1 directly. Because this sensor is engaged only by amino-acid scarcity, a protein- and amino-acid-replete state leaves the GCN2-eIF2-alpha-ATF4 integrated stress response unmobilized: translation is not restrained, ATF4 target genes are not induced, and the GCN2-mediated brake on TORC1 is absent. Engaging this arm is what dietary protein and amino-acid restriction does, and GCN2 is required for the lifespan extension those diets produce - so its quiescence in nutrient surplus is the amino-acid-sensing counterpart of AMPK/sirtuin attenuation.
Downstream
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mTORC1 Hyperactivation
-
Attenuated FGF21 Endocrine Starvation Response
-
Autophagy Suppression and Anabolic Bias
Attenuated FGF21 Endocrine Starvation Response
effector
The organism-level endocrine output of the amino-acid-sensing arm. FGF21 is a hepatokine induced by amino-acid scarcity downstream of GCN2/ATF4 acting on amino-acid response elements in the FGF21 promoter; once secreted it drives the systemic adaptive starvation response (increased energy expenditure, improved insulin sensitivity, restrained somatic growth via the GH/IGF-1 axis). In a protein-replete state this signal stays low. The node is included because FGF21 is not merely correlative: it is required for dietary protein restriction to extend lifespan, and raising it alone is sufficient to extend lifespan - making the attenuated FGF21 signal an independent endocrine route from deregulated amino-acid sensing to age-related decline, parallel to the cell-autonomous mTORC1/autophagy route. The dependence on GCN2 is partial and time-limited rather than absolute: Gcn2-null mice recover low-protein-induced FGF21 after roughly two weeks on diet, so GCN2-independent routes to FGF21 induction operate on longer timescales and this node should not be curated as strictly GCN2-gated.
Downstream
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Accelerated Cellular Aging and Age-Related Tissue Decline
Autophagy Suppression and Anabolic Bias
amplifier
Active mTORC1 suppresses macroautophagy, while attenuated AMPK/sirtuin signaling fails to induce it. Autophagy is the cytoplasmic recycling process that clears damaged organelles and proteins; its induction by starvation or genetic inactivation of nutrient signaling counteracts the age-associated accumulation of cellular damage. When nutrient signaling holds autophagy suppressed, this quality-control capacity is lost and damaged components accumulate - the amplifying step that links deregulated nutrient sensing to tissue decline.
Downstream
-
Accelerated Cellular Aging and Age-Related Tissue Decline