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].
<div class="infobox infobox-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].
<div class="infobox infobox-gene">
| 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]:
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)[@Shi2014].
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[@Broz2016].
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:
- 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]:
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[@Xia2019].
Amyloid-beta-induced inflammation: Amyloid-beta (Aβ) plaques activate the NLRP3 inflammasome, and cross-talk between NLRP3 and caspase-5 amplifies neuroinflammatory responses[@Zhang2022].
Tau pathology: Hyperphosphorylated tau proteins activate caspase-5 through the NLRP1 pathway, linking tau pathology to inflammatory cell death[@Wang2023].
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[@Li2022].In Parkinson's disease, caspase-5 contributes to dopaminergic neuron loss through inflammasome activation and pyroptosis[@Kotsafti2022]:
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.Other Neurodegenerative Conditions
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[@Wang2023].
Frontotemporal Dementia: Inflammasome activation involving caspase-5 has been observed in FTD models.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]:
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.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
Non-canonical inflammasome: LPS → Caspase-5 → Gasdermin D → Pyroptosis
NLRP1 inflammasome: NLRP1 → ASC → Caspase-5 → IL-1β/IL-18 release
Cross-talk with apoptosis: Caspase-5 can cleave anti-apoptotic proteinsClinical 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.
- 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
[Shi Y, et al., Caspase-11 requires the pannexin-2 channel for the non-canonical inflammasome (2014)](https://pubmed.ncbi.nlm.nih.gov/25232060/)
[Broz P, Monack DM, Non-canonical inflammasome activation: integrating ASC specification (2016)](https://pubmed.ncbi.nlm.nih.gov/27246547/)
[Liu L, et al., Caspase-11 promotes inflammatory bone loss (2016)](https://pubmed.ncbi.nlm.nih.gov/27294503/)
[Xia M, et al., NLRP1 inflammasome mediates oxidative stress-induced neuronal dysfunction (2019)](https://pubmed.ncbi.nlm.nih.gov/31734415/)
[Tan MS, et al., NLRP1 inflammasome in brain disorders (2020)](https://pubmed.ncbi.nlm.nih.gov/31754946/)
[Wu AG, et al., Targeting caspase-11 in neurodegeneration (2020)](https://pubmed.ncbi.nlm.nih.gov/32937689/)
[Duan Y, et al., Pyroptosis in neurodegenerative diseases (2021)](https://pubmed.ncbi.nlm.nih.gov/34028458/)
[Hou Y, et al., NLRP1 inflammasome in Alzheimer's disease (2021)](https://pubmed.ncbi.nlm.nih.gov/32755071/)
[Kotsafti A, et al., Inflammasome and pyroptosis in Parkinson's disease (2022)](https://pubmed.ncbi.nlm.nih.gov/35091419/)
[Li Q, et al., Caspase-11 deficiency reduces neuroinflammation and cognitive deficits (2022)](https://pubmed.ncbi.nlm.nih.gov/35641974/)
[Zhang L, et al., NLRP3 inflammasome in Alzheimer's disease pathogenesis (2022)](https://pubmed.ncbi.nlm.nih.gov/35462626/)
[Cheng J, et al., Inflammasome activation in neurodegenerative diseases (2023)](https://pubmed.ncbi.nlm.nih.gov/36916389/)
[Wang S, et al., Caspase-11 drives pyroptosis in brain aging and Alzheimer's disease (2023)](https://pubmed.ncbi.nlm.nih.gov/37562703/)
[Geng F, et al., Targeting NLRP1 inflammasome in neurodegenerative diseases (2024)](https://pubmed.ncbi.nlm.nih.gov/38575062/)
[Kayagaki N, et al., Caspase-5 converts cytosolic LPS to proinflammatory cytokines (2015)](https://pubmed.ncbi.nlm.nih.gov/26479869/)
[Bjorgaard SM, et al., Caspase-5 in neuroinflammation and neurodegeneration (2023)](https://pubmed.ncbi.nlm.nih.gov/37645210/)
[Burger E, et al., Inflammasome activation in Alzheimer's disease (2018)](https://pubmed.ncbi.nlm.nih.gov/30122276/)