CASP5 Gene

CASP5 (Caspase 5)

Overview

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)[@Shi2014][@Broz2016].

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[@Liu2016].

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[@Shi2014].

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CASP5 (Caspase 5)

Overview

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)[@Shi2014][@Broz2016].

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[@Liu2016].

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[@Shi2014].

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| 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 |

</div>

Structure and Function

Protein Structure

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[@Shi2014].

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).

Role in Non-Canonical Inflammasome

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[@Kayagaki2015]:

Inflammasome Complex Formation

Caspase-5 interacts with several inflammasome components:

• NLRP1: Human NLRP1 directly interacts with and activates caspase-5, forming the NLRP1 inflammasome[@Xia2019][@Tan2020].
• ASC adaptor: Caspase-5 can recruit ASC (PYCARD) to form inflammasome complexes.
• Gasdermin D: Primary substrate for caspase-5-mediated cleavage.

Role in Neurodegeneration

Neuroinflammation in Alzheimer's Disease

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[@Hou2021][@Wang2023][@Burger2018]:

Parkinson's Disease and Related Disorders

In Parkinson's disease, caspase-5 contributes to dopaminergic neuron loss through inflammasome activation and pyroptosis[@Kotsafti2022]:

Other Neurodegenerative Conditions

Evidence from Recent Research

Recent studies have further elaborated caspase-5's role in neurodegeneration[@Bjorgaard2023]:

• Microglial pyroptosis: Caspase-5 in microglia drives chronic neuroinflammation
• Neuronal vulnerability: Caspase-5 activation makes neurons more susceptible to toxic insults
• Therapeutic targeting: Caspase-5 inhibition shows promise in preclinical models

Therapeutic Implications

Caspase-5 as Drug Target

Caspase-5 represents a promising therapeutic target for neurodegenerative diseases[@Wu2020][@Geng2024]:

Preclinical Evidence

• Caspase-5 knockout mice: Show reduced neuroinflammation, improved neuronal survival, and better cognitive performance in AD models[@Li2022].
• Pharmacological inhibition: Caspase-5 inhibitors reduce markers of pyroptosis and improve behavioral outcomes in animal models.
• Combination therapy: Targeting multiple caspases (caspase-1, -5, -11) may provide additive benefits.

Expression Patterns

Brain Expression

Caspase-5 is expressed in various brain cell types:

• Neurons: Express low basal levels of caspase-5; expression increases in neurodegenerative conditions.
• Microglia: Primary immune cells in the brain show caspase-5 activation in response to inflammatory stimuli.
• Astrocytes: Reactive astrocytes exhibit NLRP1/caspase-5 inflammasome activation.
• Oligodendrocytes: Vulnerable to caspase-5-mediated pyroptosis in demyelinating diseases.

Regulation

Caspase-5 expression is regulated by:

• Pro-inflammatory cytokines: TNF-α, IL-1β, and IFN-γ upregulate CASP5 gene expression.
• NF-κB signaling: Canonical NF-κB pathways drive transcription of CASP5.
• Oxidative stress: ROS accumulation activates inflammasomes leading to caspase-5 processing.

Genetic Associations

Polymorphisms

Several CASP5 polymorphisms have been studied in neurodegenerative diseases:

• rs2010963: Associated with altered caspase-5 expression and inflammasome activity.
• rs2709327: Potential link to Alzheimer's disease susceptibility in some populations.

Gene Regulation

The CASP5 promoter contains binding sites for:

• NF-κB (p65/p50)
• AP-1
• STAT1
• C/EBP family transcription factors

Interactions and Pathways

Key Protein Interactions

| 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 |

Signaling Pathways

Clinical and Research Significance

Biomarker Potential

Caspase-5 activity and cleavage products serve as potential biomarkers:

• CSF caspase-5: Elevated in AD and PD patients.
• Soluble gasdermin D: Marker of pyroptosis in neurodegenerative diseases.
• Inflammasome components: NLRP1/caspase-5 complex as diagnostic marker.

Research Tools

• Knockout mice: Casp5-/- mice available for study.
• Inhibitors: Chemical inhibitors (z-VAD-fmk, VX-740) for experimental use.
• Activity assays: Fluorometric caspase-5 activity kits.

See Also

• [Apoptosis](/entities/apoptosis)
• [Pyroptosis](/entities/pyroptosis)
• [Neuroinflammation](/mechanisms/neuroinflammation-mechanisms)
• [Inflammasome](/entities/inflammasome)
• [Alzheimer's Disease](/diseases/alzheimers-disease)
• [Parkinson's Disease](/diseases/parkinsons-disease)
• [Caspases](/entities/caspases)
• [NLRP1 Inflammasome](/entities/nlrp1-inflammasome)
• [Gasdermin D](/entities/gasdermin-d)

External Links

• [Ensembl: ENSG00000137757](https://www.ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000137757)
• [NCBI Gene: CASP5](https://www.ncbi.nlm.nih.gov/gene/838)
• [GeneCards: CASP5](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CASP5)
• [OMIM: CASP5](https://omim.org/search?search=CASP5)
• [UniProt: Q9U2L0](https://www.uniprot.org/uniprot/Q9U2L0)
• [PubMed: CASP5 Research](https://pubmed.ncbi.nlm.nih.gov/?term=CASP5+inflammasome+neurodegeneration)

References