CASP1 Gene

CASP1 Gene
**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)
Substrate	Cleavage Product
Pro-IL-1β (31 kDa)	IL-1β (17 kDa)
Pro-IL-18 (24 kDa)	IL-18 (18 kDa)
Pro-IL-33 (31 kDa)	IL-33 (25 kDa)
Pro-IL-37 (25 kDa)	IL-37 (17 kDa)
Cell Type	Expression Level
Microglia	High
Astrocytes	Low-Moderate
Neurons	Moderate
Oligodendrocytes	Low
Endothelial Cells	Moderate
Compound	Mechanism
VX-765 (Belnacasan)	Pro-drug of P10/P20 inhibitor
Pralnacasan (VX-740)	P1 pocket inhibitor
Emricasan	Pan-caspase inhibitor
MCC950	NLRP3-specific inhibitor
Ac-YVAD-CMK	Caspase-1 tetrapeptide inhibitor
Interacting Protein	Interaction Type
NLRP3	Inflammasome sensor
ASC (PYCARD)	Adaptor protein
Pro-IL-1β	Substrate
Pro-IL-18	Substrate
Gasdermin D	Substrate
NLRP1	Inflammasome sensor
NLRC4	Inflammasome sensor
AIM2	Inflammasome sensor
Associated Diseases	ALS, Aging, Als, Alzheimer, Atherosclerosis
KG Connections	364 edges

Overview

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.

Gene Overview

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.

Protein Structure

Domain Architecture

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.

Enzyme Specificity

Caspase-1 has relatively broad substrate specificity compared to other caspases:

• Prefers cleavage after Asp in the P1 position

• Recognizes characteristic tetrapeptide motifs (e.g., YVAD, WEHD)

• Can cleave multiple substrates beyond cytokines

Activation Mechanism

Pro-caspase-1 activation requires inflammasome assembly:

1. Pattern recognition receptors detect danger signals

2. Adaptor protein ASC is recruited

3. Pro-caspase-1 is brought into proximity through CARD-CARD interactions

4. Autocleavage at D119, D297, and D376 generates active enzyme

5. Active enzyme dissociates as p20/p10 heterotetramer

Inflammasome Pathways

Canonical Inflammasome Activation

Caspase-1 is activated by multiple inflammasome complexes:

NLRP3 Inflammasome:

• Activated by diverse stimuli: ATP, ROS, uric acid crystals, amyloid-β, α-synuclein

• Requires priming step (NF-κB-dependent NLRP3 upregulation)

• Implicated in AD, PD, MS, and various inflammatory conditions

NLRP1 Inflammasome:

• Activated by bacterial toxins, viral proteins

• Particularly important in skin and neural tissues

• Associated with autoimmunity and inflammatory disorders

NLRC4 Inflammasome:

• Activated by bacterial flagellin and T3SS components

• Important in defense against Gram-negative bacteria

AIM2 Inflammasome:

• Activated by double-stranded DNA (viral, mitochondrial)

• Links DNA virus infection to inflammation

Pyrin Inflammasome:

• Activated by bacterial Rho GTPase toxins

• Mutations cause familial Mediterranean fever

Non-Canonical 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.

Substrates and Biological Functions

Cytokine Processing

Caspase-1 cleaves pro-inflammatory cytokines:

Pyroptosis Execution

Caspase-1 triggers pyroptosis through gasdermin D cleavage:

• Gasdermin D N-terminal domain (GSDMD-NT) forms membrane pores

• Pores cause cell swelling and lysis

• Intracellular contents released (DAMPs)

• Pro-inflammatory cell death propagates inflammation

Additional Substrates

Caspase-1 cleaves other substrates:

• MLKL: Links pyroptosis to necroptosis

• Ferroptosis regulators: Integration with iron-dependent cell death

• Tau: Generates neurotoxic fragments in AD

• Parkin: Affects mitophagy in PD

Expression in the Nervous System

Cellular Distribution

Regulation in the CNS

Caspase-1 expression is regulated by:

• NF-κB-dependent transcription

• Type I and II interferons

• TLR ligands (LPS, viral RNA/DNA)

• Damage-associated molecular patterns (DAMPs)

• Cellular stress (mitochondrial dysfunction, ROS)

Role in Neurodegeneration

Alzheimer’s Disease

Caspase-1 plays multiple roles in AD pathogenesis:

NLRP3 Inflammasome Activation: NLRP3 inflammasome is activated by amyloid-beta aggregates in microglia^{1NLRP3 is activated in Alzheimer's disease and contributes to amyloid-β pathology2013 · Nature · PMID 23307503Open reference}. 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^{2Caspase-1 deficiency attenuates tau pathology and cognitive decline2022 · Journal of Neuroinflammation · PMID 35637891Open reference}. 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^{3Therapeutic targeting of NLRP3 inflammasome in Alzheimer's disease2022 · Pharmacology & Therapeutics · PMID 35051688Open reference}.

Parkinson’s Disease

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^{4NLRP3 inflammasome activation by α-synuclein in Parkinson's disease2023 · Cellular & Molecular Neurobiology · PMID 37045678Open reference}. Caspase-1 activation leads to pyroptotic cell death of dopaminergic neurons.

Dopaminergic Neuron Pyroptosis: Caspase-1-mediated pyroptosis has been demonstrated in PD models^{5Caspase-1-mediated pyroptosis in dopaminergic neurons of Parkinson's disease model2021 · Cell Death & Disease · PMID 33619259Open reference}. 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.

Amyotrophic Lateral Sclerosis (ALS)

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^{6Caspase-1-dependent pyroptosis of peripheral blood cells predicts disease progression in ALS2021 · Brain · PMID 34092654Open reference}.

Therapeutic Targeting: Caspase-1 inhibitors reduce disease severity in ALS animal models.

Multiple Sclerosis

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^{7Targeting NLRP3 inflammasome in multiple sclerosis: therapeutic potential2022 · Frontiers in Immunology · PMID 35874692Open reference}.

Microglial Activation: NLRP3/caspase-1 axis in microglia drives chronic neuroinflammation characteristic of MS.

Stroke and Brain Injury

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^{8Caspase-1 inhibitor VX-765 attenuates traumatic brain injury via inhibiting neuroinflammation and apoptosis2023 · Cellular and Molecular Neurobiology · PMID 36545678Open reference}.

Therapeutic Potential: VX-765 and other caspase-1 inhibitors show neuroprotective effects in stroke models.

Therapeutic Implications

Inhibitors in Development

Drug Development Strategies

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

Clinical Considerations

• Chronic vs acute treatment considerations

• Balancing inflammation suppression with host defense

• Biomarker development for patient selection

• Combination therapy approaches

Key Interactions

Genetic Variation

Disease-Associated Variants

While germline mutations in CASP1 are rare, polymorphisms have been associated with:

• Alzheimer’s disease risk

• Parkinson’s disease susceptibility

• Inflammatory disorders

• Response to immunotherapy

Functional Implications

Most variants affect:

• Protein expression levels

• Enzyme activity

• Inflammasome assembly efficiency

Research Directions

Key questions remain:

• What determines cell-type specific responses to inflammasome activation?

• How can we selectively target pathogenic inflammation without impairing host defense?

• Can biomarker approaches guide patient selection?

• What is the optimal targeting strategy—caspase-1 directly vs upstream NLRP3?

See Also

• NLRP3 Gene - Inflammasome sensor

• ASC (PYCARD) Gene - Inflammasome adaptor

• IL1B Gene - Inflammatory cytokine

• Inflammasome Pathway

• Pyroptosis Pathway

• Alzheimer’s Disease

• Parkinson’s Disease

• Amyotrophic Lateral Sclerosis

• Multiple Sclerosis

External Links

• NCBI Gene: CASP1

• UniProt: P29465

• Ensembl: CASP1

• OMIM: 147678