CASP1 (Caspase 1) is a key inflammatory caspase that serves as the central protease of the inflammasome complex. Originally discovered for its role in processing pro-inflammatory cytokines IL-1β and IL-18, caspase-1 has since been recognized as the executor of pyroptosis—a highly inflammatory form of programmed cell death. In the central nervous system, caspase-1 plays critical roles in neuroinflammation, neuronal death, and the progression of neurodegenerative diseases including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, multiple sclerosis, and stroke.
The enzymatic activity of caspase-1 is tightly regulated at multiple levels: gene expression, protein activation through inflammasome assembly, and inhibition by endogenous regulators. Dysregulation of caspase-1 activity contributes to chronic neuroinflammation and excessive neuronal loss, making it an attractive therapeutic target.
| Property | Value |
|---|---|
| Gene Symbol | CASP1 |
| Gene Name | Caspase 1 |
| NCBI Gene ID | 842 |
| UniProt ID | P29465 |
| Aliases | Caspase-1, ICE, IL-1β converting enzyme |
| Chromosomal Location | 11q22.3 |
| Protein Length | 404 amino acids |
| Protein Mass | ~45 kDa (pro-enzyme) |
The CASP1 gene spans approximately 30 kb and contains 11 exons. It encodes a cysteine-aspartic protease synthesized as an inactive zymogen (pro-caspase-1) that undergoes autocatalytic processing to form the active enzyme.
Caspase-1 contains several distinct structural domains:
N-terminal CARD Domain (~90 aa): Caspase Recruitment Domain that enables interaction with adaptor proteins containing CARD domains, including ASC (PYCARD) and RIPK2.
Linker Region: Contains autocleavage sites that are critical for activation.
Large Subunit (p20, ~20 kDa): Contains the catalytic cysteine residue (Cys285) and substrate binding pocket.
Small Subunit (p10, ~10 kDa): Completes the active site formation.
Caspase-1 has relatively broad substrate specificity compared to other caspases:
Pro-caspase-1 activation requires inflammasome assembly:
Caspase-1 is activated by multiple inflammasome complexes:
NLRP1 Inflammasome:
NLRC4 Inflammasome:
AIM2 Inflammasome:
Pyrin Inflammasome:
In mice and humans, caspase-11 (caspase-4/5 in humans) responds to cytosolic LPS, but CASP1 can still integrate these signals through cross-talk mechanisms.
Caspase-1 cleaves pro-inflammatory cytokines:
| Substrate | Cleavage Product | Function |
|---|---|---|
| Pro-IL-1β (31 kDa) | IL-1β (17 kDa) | Potent inflammatory cytokine |
| Pro-IL-18 (24 kDa) | IL-18 (18 kDa) | IFN-γ inducing factor |
| Pro-IL-33 (31 kDa) | IL-33 (25 kDa) | Alarmin, Th2 responses |
| Pro-IL-37 (25 kDa) | IL-37 (17 kDa) | Anti-inflammatory cytokine |
Caspase-1 triggers pyroptosis through gasdermin D cleavage:
Caspase-1 cleaves other substrates:
| Cell Type | Expression Level | Notes |
|---|---|---|
| Microglia | High | Constitutive, increases with activation |
| Astrocytes | Low-Moderate | Inducible upon inflammatory signals |
| Neurons | Moderate | Increases in disease states |
| Oligodendrocytes | Low | Increases in demyelinating conditions |
| Endothelial Cells | Moderate | Blood-brain barrier function |
Caspase-1 expression is regulated by:
Caspase-1 plays multiple roles in AD pathogenesis:
NLRP3 Inflammasome Activation: NLRP3 inflammasome is activated by amyloid-beta aggregates in microglia[1]. This activation triggers caspase-1 activation and subsequent IL-1β and IL-18 production, creating a chronic neuroinflammatory environment.
Tau Pathology: Caspase-1 cleaves tau protein, generating neurotoxic fragments that propagate tau pathology[2]. Caspase-1 deficiency reduces tau pathology and cognitive decline in animal models.
Synaptic Dysfunction: IL-1β and IL-18 released following caspase-1 activation contribute to synaptic impairment and memory deficits.
Microglial Pyroptosis: Caspase-1-mediated pyroptosis in microglia releases ASC specks that can seed amyloid-β aggregation, creating a feed-forward pathological loop.
Therapeutic Implications: NLRP3 inhibitors and caspase-1 blockers show promise in AD models, reducing neuroinflammation and improving cognitive function[3].
In Parkinson's disease, caspase-1 contributes to dopaminergic neuron loss:
α-Synuclein-Induced Activation: α-Synuclein aggregates activate NLRP3 inflammasome in microglia and neurons[4]. Caspase-1 activation leads to pyroptotic cell death of dopaminergic neurons.
Dopaminergic Neuron Pyroptosis: Caspase-1-mediated pyroptosis has been demonstrated in PD models[5]. The release of intracellular contents amplifies neuroinflammation in the substantia nigra.
Microglial Activation: Chronic activation of caspase-1 in microglia creates a persistent pro-inflammatory environment that contributes to progressive neuronal loss.
Therapeutic Potential: Caspase-1 inhibitors protect dopaminergic neurons and reduce neuroinflammation in PD models.
Caspase-1 contributes to motor neuron degeneration:
TDP-43 and SOD1 Activation: Pathological protein aggregates (TDP-43, mutant SOD1) activate inflammasomes in motor neurons and glia. Caspase-1 activation drives inflammation and pyroptosis.
Peripheral Blood Cell Activation: Elevated caspase-1 activity in peripheral blood cells predicts disease progression in ALS patients[6].
Therapeutic Targeting: Caspase-1 inhibitors reduce disease severity in ALS animal models.
Caspase-1 plays important roles in demyelination:
Demyelination: Caspase-1 contributes to oligodendrocyte death in demyelinating conditions. Inhibition reduces demyelination in EAE models.
T Cell Differentiation: IL-1β (produced by caspase-1) promotes Th17 differentiation, driving autoimmune responses[7].
Microglial Activation: NLRP3/caspase-1 axis in microglia drives chronic neuroinflammation characteristic of MS.
Caspase-1 is rapidly activated following brain injury:
Ischemic Stroke: NLRP3 inflammasome is activated within hours of ischemia. Caspase-1 contributes to neuronal death through pyroptosis and amplifies inflammatory damage.
Traumatic Brain Injury: Caspase-1 activation following TBI contributes to secondary injury through neuroinflammation and cell death[8].
Therapeutic Potential: VX-765 and other caspase-1 inhibitors show neuroprotective effects in stroke models.
| Compound | Mechanism | Development Stage | Disease Focus |
|---|---|---|---|
| VX-765 (Belnacasan) | Pro-drug of P10/P20 inhibitor | Phase II (psoriasis) | Psoriasis, AD, PD |
| Pralnacasan (VX-740) | P1 pocket inhibitor | Phase II (withdrawn) | Rheumatoid arthritis |
| Emricasan | Pan-caspase inhibitor | Clinical trials | Liver disease, PD |
| MCC950 | NLRP3-specific inhibitor | Preclinical | Multiple |
| Ac-YVAD-CMK | Caspase-1 tetrapeptide inhibitor | Research | Various |
NLRP3-Specific Inhibitors: Target upstream activation, potentially fewer side effects
IL-1 Receptor Antagonists: Block downstream effects (Anakinra, Canakinumab)
Gasdermin D Inhibitors: Block pyroptotic cell death
ASC Specks Inhibitors: Prevent inflammasome assembly
| Interacting Protein | Interaction Type | Functional Consequence |
|---|---|---|
| NLRP3 | Inflammasome sensor | Activation |
| ASC (PYCARD) | Adaptor protein | Inflammasome assembly |
| Pro-IL-1β | Substrate | Cytokine maturation |
| Pro-IL-18 | Substrate | Cytokine maturation |
| Gasdermin D | Substrate | Pyroptosis execution |
| NLRP1 | Inflammasome sensor | Activation |
| NLRC4 | Inflammasome sensor | Activation |
| AIM2 | Inflammasome sensor | Activation |
While germline mutations in CASP1 are rare, polymorphisms have been associated with:
Most variants affect:
Key questions remain:
Heneka MT, Kummer MP, Stutz A, et al. NLRP3 is activated in Alzheimer's disease and contributes to amyloid-β pathology. Nature. 2013. ↩︎
Jiang M, Liu X, Zhang D, et al. Caspase-1 deficiency attenuates tau pathology and cognitive decline. Journal of Neuroinflammation. 2022. ↩︎
Daniels MJ, Fleshner M, Watowich MM. Therapeutic targeting of NLRP3 inflammasome in Alzheimer's disease. Pharmacology & Therapeutics. 2022. ↩︎
Liu Z, Wang C, Yang J, et al. NLRP3 inflammasome activation by α-synuclein in Parkinson's disease. Cellular & Molecular Neurobiology. 2023. ↩︎
Wang W, Zhang L, Liu M, et al. Caspase-1-mediated pyroptosis in dopaminergic neurons of Parkinson's disease model. Cell Death & Disease. 2021. ↩︎
Shen H, Wu N, Liu Z, et al. Caspase-1-dependent pyroptosis of peripheral blood cells predicts disease progression in ALS. Brain. 2021. ↩︎
Yang Y, Wang H, Kou M, et al. Targeting NLRP3 inflammasome in multiple sclerosis: therapeutic potential. Frontiers in Immunology. 2022. ↩︎
Meng L, Huang J, Sun W, et al. Caspase-1 inhibitor VX-765 attenuates traumatic brain injury via inhibiting neuroinflammation and apoptosis. Cellular and Molecular Neurobiology. 2023. ↩︎