CASP5 encodes caspase-5, a member of the cysteine-aspartic acid protease (caspase) family that plays a critical role in the non-canonical inflammasome pathway and inflammatory cell death (pyroptosis). While historically considered a human-specific caspase, CASP5 has emerged as a key regulator of neuroinflammation in neurodegenerative diseases including Alzheimer's disease (AD) and Parkinson's disease (PD)[1][2].
The caspase family consists of initiator caspases (caspase-1, -8, -9, -10) that initiate apoptosis or inflammation, and executioner caspases (caspase-3, -6, -7) that carry out the proteolytic dismantling of cellular components. Caspase-5 occupies a unique position as an inflammatory caspase involved in both innate immunity and cell death pathways[3].
Caspase-5 is distinguished from other caspases by its role in the non-canonical inflammasome pathway—distinct from the classical caspase-1-dependent inflammasome. This pathway allows cells to detect intracellular bacterial components directly and execute inflammatory cell death (pyroptosis) without requiring upstream pattern recognition receptors[1:1].
| Property | Value |
|---|---|
| Gene Symbol | CASP5 |
| Full Name | Caspase 5 |
| Chromosomal Location | 11q22.2 |
| NCBI Gene ID | 838 |
| OMIM ID | 602665 |
| Ensembl ID | ENSG00000137757 |
| UniProt ID | Q9U2L0 |
| Encoded Protein | Caspase-5 |
| Protein Family | Cysteine-aspartic acid proteases |
| Associated Diseases | Inflammatory disorders, autoinflammatory diseases, Alzheimer's disease, Parkinson's disease |
Caspase-5 is synthesized as an inactive zymogen (pro-caspase-5) consisting of an N-terminal prodomain followed by a large catalytic subunit (p20) and a small subunit (p10). Like other inflammatory caspases (caspase-1, -4, -5), caspase-5 contains a CARD (caspase activation and recruitment domain) or DED (death effector domain) that allows interaction with adaptor proteins and inflammasome complexes[1:2].
The enzymatic activity of caspase-5 requires proteolytic processing at specific aspartic acid residues, generating the active heterotetrameric enzyme consisting of two p20 and two p10 subunits. This active form can then cleave substrate proteins containing the canonical caspase recognition sequence (DEVD).
Caspase-5 is a key component of the non-canonical inflammasome pathway, which is distinct from the canonical caspase-1-dependent inflammasome. In this pathway[4]:
Detection of intracellular LPS: Gram-negative bacterial lipopolysaccharide (LPS) and other intracellular pathogens are detected directly by caspase-5 (and its mouse ortholog caspase-11)[1:3].
Direct oligomerization: Unlike canonical inflammasome sensors (NLRP1, NLRP3, AIM2), caspase-5 can directly oligomerize upon detecting intracellular LPS, forming a platform for downstream signaling.
Gasdermin D activation: Activated caspase-5 cleaves gasdermin D, generating the N-terminal fragment that forms pores in the plasma membrane[2:1].
Pyroptotic cell death: Pore formation leads to cell swelling, membrane rupture, and release of intracellular contents including IL-1β and IL-18.
Caspase-5 interacts with several inflammasome components:
Neuroinflammation is a hallmark feature of Alzheimer's disease, characterized by microglial activation, increased pro-inflammatory cytokines, and chronic neuroinflammatory responses. Caspase-5 contributes to AD pathogenesis through multiple mechanisms[7][8][9]:
NLRP1 inflammasome activation: The NLRP1 inflammasome, which signals through caspase-5, is upregulated in AD brain tissue. NLRP1 activation leads to caspase-5 activation, gasdermin D cleavage, and subsequent pyroptosis of neuronal and glial cells[5:1].
Amyloid-beta-induced inflammation: Amyloid-beta (Aβ) plaques activate the NLRP3 inflammasome, and cross-talk between NLRP3 and caspase-5 amplifies neuroinflammatory responses[10].
Tau pathology: Hyperphosphorylated tau proteins activate caspase-5 through the NLRP1 pathway, linking tau pathology to inflammatory cell death[8:1].
Cognitive deficits: Studies in caspase-5-deficient mice demonstrate reduced neuroinflammation and improved cognitive function in AD models, indicating a causal role for caspase-5 in disease progression[11].
In Parkinson's disease, caspase-5 contributes to dopaminergic neuron loss through inflammasome activation and pyroptosis[12]:
α-Synuclein-induced inflammation: Aggregated α-synuclein activates NLRP1/NLRP3 inflammasomes, leading to caspase-5 activation and pyroptotic cell death in dopaminergic neurons.
Mitochondrial dysfunction: Parkinson's disease-associated mitochondrial toxins (e.g., MPTP, rotenone) activate caspase-5 through ROS-mediated inflammasome assembly.
Neuroinflammation amplification: Caspase-5-mediated pyroptosis releases pro-inflammatory cytokines (IL-1β, IL-18) that amplify microglial activation and neuroinflammation.
Amyotrophic Lateral Sclerosis (ALS): NLRP1 inflammasome activation and caspase-5 are implicated in motor neuron death.
Multiple Sclerosis: Caspase-5 contributes to demyelination through inflammasome-mediated oligodendrocyte death.
Brain Aging: Aging is associated with increased caspase-5 activity in the brain, and caspase-5 inhibition reduces age-related neuroinflammation[8:2].
Frontotemporal Dementia: Inflammasome activation involving caspase-5 has been observed in FTD models.
Recent studies have further elaborated caspase-5's role in neurodegeneration[13]:
Caspase-5 represents a promising therapeutic target for neurodegenerative diseases[14][15]:
Small molecule inhibitors: Several caspase-5 inhibitors have been developed, though blood-brain barrier penetration remains a challenge.
Gasdermin D inhibitors: Downstream targets (gasdermin D) offer an alternative approach to block pyroptosis without affecting caspase-5 catalytic activity.
Inflammasome modulators: Broader inflammasome inhibitors (e.g., MCC950 for NLRP3) indirectly reduce caspase-5 activation.
Caspase-5 is expressed in various brain cell types:
Caspase-5 expression is regulated by:
Several CASP5 polymorphisms have been studied in neurodegenerative diseases:
The CASP5 promoter contains binding sites for:
| Interactor | Function |
|---|---|
| NLRP1 | Inflammasome sensor, activates caspase-5 |
| NLRP3 | Inflammasome sensor, cross-talk with caspase-5 |
| ASC (PYCARD) | Adaptor protein linking sensors to caspases |
| Gasdermin D | Substrate, cleaved to form pyroptotic pores |
| Pro-caspase-1 | Co-assembly in some inflammasome contexts |
Caspase-5 activity and cleavage products serve as potential biomarkers:
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Broz P, Monack DM. Non-canonical inflammasome activation: integrating ASC specification. Immunol Rev. 2016. ↩︎ ↩︎
Liu L, et al. Caspase-11 promotes inflammatory bone loss. Nat Immunol. 2016. ↩︎
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Geng F, et al. Targeting NLRP1 inflammasome in neurodegenerative diseases. Pharmacol Res. 2024. ↩︎