This is a mechanism module, not a specific disease. Disorder entries reference individual nodes via conforms_to (e.g., "nlrp3_inflammasome_activation#NLRP3 Inflammasome Assembly and Caspase-1 Activation"). The module was created because the inflammasome was the one major innate-immune convergence point with no reusable module: 66 disorder entries mention the inflammasome in prose and about 20 carry a dedicated inflammasome pathophysiology node, but the only inflammasome node anywhere in kb/modules/ sat inside gout_urate_crystal_inflammation, where it is scoped to monosodium urate crystal arthropathy and is not reusable by a silicosis, atherosclerosis, or neuroinflammation entry.
Relationship to gout_urate_crystal_inflammation. That module is deliberately left untouched by this one. Its "NLRP3 Inflammasome Activation" node remains the crystal-arthropathy-specific step, and no existing conformance to it has been retargeted here. Whether the gout module should instead declare conformance to this module, or keep its own node, is a governance question recorded as an OPEN discussion below rather than decided unilaterally.
Scope. This module models the canonical, NLRP3-specific, two-signal pathway. It does not model the other inflammasome sensors (NLRP1, NLRC4, AIM2, pyrin), which have distinct ligands and priming requirements; an entry whose evidence identifies a non-NLRP3 sensor should curate its own node rather than conform here. The non-canonical caspase-4/5/11 route to cytosolic-LPS sensing feeds gasdermin D cleavage and, through the resulting potassium efflux, the canonical NLRP3 step; it is described in prose at the activating-signal node rather than given its own branch, because the evidence assembled here does not separate its contribution in any conforming disorder.
Relationship to other modules. The mitochondrial arm of the activating signal overlaps mitochondrial_dysfunction (which owns impaired mitophagy and quality control) and disabled_macroautophagy; this module does not re-derive those, and a conforming entry whose claim is about clearance capacity rather than inflammasome output should attach there instead. cellular_senescence and inflammaging describe sterile inflammation downstream of senescence without owning an inflammasome node, so they are complementary rather than overlapping.
Two conformance patterns are worth stating, because both came out of wiring the first conformers and neither is obvious from the chain alone.
First, a conforming entry may legitimately split the activating signal across several atomic nodes that each conform to the single "Activating Danger Signal" node. That node is explicitly a union of non-exclusive routes, so Silicosis, which curates phagolysosomal rupture with cathepsin B release and reactive oxygen species generation as two separate nodes both feeding assembly, conforms twice rather than being forced to bundle two mechanistic claims into one node.
Second, a gain-of-function NLRP3 variant enters this module at the central effector and legitimately bypasses the trigger and amplifier nodes. In the cryopyrin-associated periodic syndromes the mutant sensor assembles with a reduced or absent requirement for a second signal, so a conforming node there should attach at "NLRP3 Inflammasome Assembly and Caspase-1 Activation" and must not be wired to "Activating Danger Signal" — the whole point of the genetic lesion is that the second signal is not needed. Worked conformers: Silicosis (particulate route, conforming at the activating-signal and assembly nodes) and Familial_Cold_Autoinflammatory_Syndrome (constitutive variant route, conforming at the assembly and cytokine-output nodes).
Modules bind GO and CL terms only; drug chemistry is carried by the treatments block per the treatment schema, and cytokine and crystal chemistry is described in prose.
Which of the proposed activating signals for NLRP3 (potassium efflux, lysosomal rupture, mitochondrial reactive oxygen species and mitochondrial DNA release) is the proximal event NLRP3 actually senses, and are they a single convergent pathway or genuinely independent routes?
KNOWLEDGE GAP
OPEN
gap_nlrp3_no_consensus_activating_signal
Attached to:
Activating Danger Signal
The three routes curated at the activating-signal node are supported by strong primary evidence individually but conflict with one another when tested as unifying models. Munoz-Planillo et al. (PMID:23809161) found that every NLRP3 agonist they tested induced potassium efflux, that lowering cytosolic potassium alone was sufficient, and explicitly that mitochondrial perturbation and reactive oxygen species generation were not required. Zhou et al. (PMID:21124315) reached the opposite emphasis, showing that blocking mitophagy accumulates ROS-generating mitochondria and that this activates the inflammasome. Hornung et al. (PMID:18604214) place the proximal event at the lysosome for particulate stimuli. Much of the supporting evidence rests on pharmacological inhibitors with known off-target effects rather than genetic ablation, so the discrepancy may be methodological. Until this is resolved, a conforming disorder entry should curate the specific activating route its own evidence establishes and must not assert one of these as the general mechanism of NLRP3 activation.
Proposed experiments:
Genetic rather than pharmacological dissection of the three activating routes
Should gout_urate_crystal_inflammation declare conformance to this module's assembly node and retire its own "NLRP3 Inflammasome Activation" node, or should the two coexist as a crystal-specific node and a generic one?
OPEN QUESTION
OPEN
open_nlrp3_module_relationship_to_gout_module
Attached to:
NLRP3 Inflammasome Assembly and Caspase-1 Activation
Before this module existed, gout_urate_crystal_inflammation carried the only inflammasome pathophysiology node in kb/modules/. That node is scoped to monosodium urate crystal arthropathy: its description, cell types, and evidence are crystal-specific, and disorder entries already declare conforms_to against it. Retargeting those conformances is a governance decision with consequences beyond this module, and modules are a consistency check rather than an inheritance mechanism, so duplication between a disease-family module and a generic mechanism module is not automatically an error. This module therefore leaves the gout module untouched and records the question. The same question will recur for the roughly twenty disorder entries that carry their own inflammasome node; none has been rewired here.
Priming Signal and NLRP3 Transcriptional Upregulation
trigger
Signal 1. Engagement of a pattern-recognition receptor (Toll-like receptors, NOD2) by a pathogen-associated or damage-associated molecular pattern, or of a cytokine receptor by TNF or IL-1 beta, activates NF-kappaB and transcriptionally upregulates NLRP3 itself along with pro-IL-1 beta. NLRP3 expression is the rate-limiting checkpoint: resting cells express too little NLRP3 to assemble an inflammasome, so priming licenses the cell to respond to a subsequent danger signal without itself activating the complex. Priming additionally imposes post-translational modifications that hold NLRP3 in an inactive but signal-competent state. Conforming disorder nodes substitute the disorder-specific priming stimulus (microbial ligand, sterile DAMP, or an ambient inflammatory cytokine milieu).
Show evidence (3 references)
"cell priming through multiple signaling receptors induces NLRP3 expression, which we identified to be a critical checkpoint for NLRP3 activation"
Identifies priming-induced NLRP3 expression as the critical checkpoint, which is what makes this a distinct upstream node rather than part of assembly. Evidence source is IN_VITRO because the genetic dissection used cultured mouse macrophages and human monocytes.
"Signals provided by NF-kappaB activators are necessary but not sufficient for NLRP3 activation, and a second stimulus such as ATP or crystal-induced damage is required for NLRP3 activation."
Establishes the two-signal architecture this module is built on: the priming node is necessary but not sufficient, so it is typed as the trigger and the activating signal is modelled as a separate downstream node. Evidence source is IN_VITRO for the same reason.
"NLRP3 (NOD-, LRR- and pyrin domain-containing protein 3) is an intracellular sensor that detects a broad range of microbial motifs, endogenous danger signals and environmental irritants, resulting in the formation and activation of the NLRP3 inflammasome."
Establishes the breadth of stimuli that converge on NLRP3, which is the property that makes this a reusable module across infectious, crystal, metabolic, and neurodegenerative disorders. Evidence source is OTHER because this is a narrative review.
Activating Danger Signal
amplifier
Signal 2. A primed cell is converted to an assembling one by a cellular stress that NLRP3 senses indirectly. Three routes are established and are not mutually exclusive: efflux of potassium from the cytosol, driven by pore-forming toxins, ATP acting through P2X7, or particulate stimuli; lysosomal destabilization and rupture following phagocytosis of crystalline or fibrous material; and mitochondrial damage with release of reactive oxygen species and oxidized mitochondrial DNA, which accumulates when mitophagy is blocked. Cytosolic LPS sensed by caspase-4/5 additionally reaches this node indirectly, because the resulting gasdermin D pores themselves cause potassium efflux. Conforming disorder nodes substitute the disorder-specific danger signal; which route dominates is disease-specific and, as recorded in the open discussion below, there is no consensus unifying model.
Used by disorders
Silicosis
as Phagolysosomal Membrane Rupture and Cathepsin B Release
Silicosis
as Reactive Oxygen Species Generation
Downstream
-
NLRP3 Inflammasome Assembly and Caspase-1 Activation
Show evidence (4 references)
"Notably, reduction of the intracellular K⁺ concentration was sufficient to activate NLRP3, whereas an increase in intracellular Na⁺ modulated but was not strictly required for inflammasome activation."
Establishes falling cytosolic potassium as sufficient for NLRP3 activation, the best-supported of the three activating routes at this node. Evidence source is IN_VITRO because the ion-substitution experiments were done in cultured macrophages.
"We show that NLRP3 activators including bacterial pore-forming toxins, nigericin, ATP, and particulate matter caused mitochondrial perturbation or the opening of a large membrane pore, but this was not required for NLRP3 activation."
Refutes the mitochondrial arm of this node as a required activating route: these authors found mitochondrial perturbation dispensable for NLRP3 activation. This is why the mitochondrial route is curated as one of several non-exclusive routes rather than as the mechanism, and why the conflict is carried as an open discussion. The same paper's supporting result for the potassium-efflux route is carried as a separate SUPPORT item above, quoting the sentence that reports it.
"NALP3 activation required phagocytosis of crystals, and this uptake subsequently led to lysosomal damage and rupture."
Supports the lysosomal-rupture route, the one that conforming particulate-exposure disorders (silicosis, asbestosis, gout, atherosclerosis) substitute into this node. Evidence source is IN_VITRO because the phagocytosis and cathepsin experiments used cultured macrophages.
+ 1 more reference
NLRP3 Inflammasome Assembly and Caspase-1 Activation
central effector
The rate-limiting, disorder-agnostic step and the key conformance target of this module. Activated NLRP3 oligomerizes and recruits the adaptor ASC through pyrin-domain interactions, nucleating ASC filaments that coalesce into a single macromolecular speck. Assembled ASC recruits pro-caspase-1 through CARD-CARD interactions, and the resulting proximity drives autoproteolytic cleavage and activation of caspase-1. Every route through the module funnels through this complex: whatever the priming stimulus and whatever the danger signal, an entry conforms here if the evidence places an assembled, caspase-1-activating NLRP3 complex in the causal chain. An entry that evidences only elevated IL-1 beta, or only NLRP3 transcript upregulation, does not satisfy this node.
Used by disorders
Ischemic Stroke
as Microglial NLRP3 Inflammasome Activation in the Ischemic Penumbra
Downstream
-
IL-1 Family Cytokine Maturation and Gasdermin D-Mediated Pyroptosis
Show evidence (3 references)
"Here we report the identification of a caspase-activating complex that we call the inflammasome."
The founding identification of the inflammasome as a caspase-activating complex, which is the claim this node makes. Evidence source is IN_VITRO because the complex was defined in a cell-free system and in THP-1 cells.
"Moreover, expression of a dominant-negative form of Pycard in differentiated THP-1 cells blocks proIL-1beta maturation and activation of inflammatory caspases induced by LPS in vivo."
Shows the ASC/Pycard adaptor is required for caspase activation and pro-IL-1 beta maturation, supporting assembly as the necessary step upstream of cytokine output rather than a parallel event.
"Once activated, NLRP3 nucleates the assembly of an inflammasome, leading to caspase 1-mediated proteolytic activation of the interleukin-1β (IL-1β) family of cytokines, and induces an inflammatory, pyroptotic cell death."
States the assembly-to-caspase-1-to-cytokine-and-pyroptosis sequence that defines this node and the edge into the effector node. Evidence source is OTHER because this is a narrative review.
Sterile Inflammatory Tissue Injury
consequence
Released IL-1 beta and IL-18, together with the intracellular contents spilled by pyroptotic cells, drive a self-amplifying inflammatory response: IL-1 beta acts on IL-1 receptors to upregulate adhesion molecules and chemokines and recruit neutrophils, and because IL-1 beta is itself a priming stimulus it feeds back onto the trigger node in neighbouring cells. Sustained or repeated cycles produce the tissue injury, fibrosis, and clinical inflammation attributed to inflammasome-driven disease. This is the node conforming disorders specialize to their affected tissue, and it is where the therapeutic argument is anchored: blocking IL-1 beta reduces clinical events in humans.
Show evidence (3 references)
"Danger signals are a hallmark of many common inflammatory diseases, and these stimuli can function to activate the cytosolic innate immune signalling receptor NLRP3 (NOD-, LRR- and pyrin domain-containing 3)."
Establishes that this chain is a recurrent feature of common inflammatory disease rather than a single-disorder mechanism, which is the justification for modelling it as a module. Evidence source is OTHER because this is a review.
"Pharmacological inhibition of NLRP3 activation results in potent therapeutic effects in a wide variety of rodent models of inflammatory diseases, effects that are mirrored by genetic ablation of NLRP3."
Supports the causal direction of the whole chain: removing NLRP3 pharmacologically or genetically removes the downstream tissue injury. Evidence source is MODEL_ORGANISM because the summarized experiments are rodent disease models.
"Antiinflammatory therapy targeting the interleukin-1β innate immunity pathway with canakinumab at a dose of 150 mg every 3 months led to a significantly lower rate of recurrent cardiovascular events than placebo, independent of lipid-level lowering."
The strongest human evidence that the IL-1 beta output of this pathway causes tissue-level disease: a randomized trial in 10,061 patients in which neutralizing IL-1 beta reduced cardiovascular events without changing lipids.
IL-1 beta Neutralizing Antibody (Canakinumab)
Platform:
Monoclonal antibody
A monoclonal antibody that binds IL-1 beta and prevents it from engaging the IL-1 receptor, neutralizing the principal secreted output of the pathway without touching the sensor. This is the output-blockade arm of the inflammasome drug-target pattern: it is agnostic to which danger signal activated NLRP3, which is why the same agent is used in the cryopyrin-associated periodic syndromes, gout, and atherosclerotic disease. Its limitation is the mirror image of its breadth: blocking IL-1 beta also removes a defence cytokine, and the CANTOS trial recorded more fatal infections on canakinumab than on placebo. Conforming disorders should curate their own indication and outcome evidence rather than inheriting a recommendation from this module.
Evidence: 2
Direct NLRP3 Inhibitor (MCC950)
Platform:
Small molecule
A small-molecule inhibitor that binds NLRP3 itself and blocks inflammasome assembly, the sensor-blockade arm of the drug-target pattern. Unlike IL-1 beta neutralization it is selective for the NLRP3 sensor and spares the NLRP1, NLRC4, and AIM2 inflammasomes, so it removes only this pathway's output. It is curated here as a mechanistic tool and design pattern, not as an available therapy: MCC950 is investigational, and a phase II trial in rheumatoid arthritis was suspended for hepatic toxicity. A conforming disorder should not curate MCC950 as a treatment on the strength of this module.
Evidence: 2