CASP6 — Caspase-6

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CASP6 — Caspase-6

<table class="infobox infobox-gene">
<tr>
<th class="infobox-header" colspan="2">CASP6 — Caspase-6</th>
</tr>
<tr> [@bhatt2012]
<td class="label">Symbol</td> [@bhatt2019]
<td>CASP6</td> [@wong2012]
</tr> [@bhatt2022]
<tr>
<td class="label">Full Name</td>
<td>Caspase-6, Apoptosis-Related Cysteine Peptidase</td>
</tr>
<tr>
<td class="label">Chromosome</td>
<td>4q25</td>
</tr>
<tr>
<td class="label">NCBI Gene</td>
<td><a href="https://www.ncbi.nlm.nih.gov/gene/839" target="_blank">839</a></td>
</tr>
<tr>
<td class="label">Ensembl</td>
<td><a href="https://ensembl.org/Homo_sapiens/Gene/Summary?g=ENSG00000138794" target="_blank">ENSG00000138794</a></td>
</tr>
<tr>
<td class="label">OMIM</td>
<td><a href="https://omim.org/entry/601532" target="_blank">601532</a></td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P55212" target="_blank">P55212</a></td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers), [Huntington's Disease](/diseases/huntingtons), [ALS](/diseases/als)</td>
</tr>
<tr>
<td class="label">Expression</td>
<td>Brain (hippocampus, [cortex](/brain-regions/cortex), striatum), ubiquitous</td>
</tr>
<tr>
<th class="infobox-subheader" colspan="2">Key Substrates</th>
</tr>
<tr>
<td colspan="2" style="font-size:0.85em">[Tau](/proteins/tau) (D421) [Huntingtin](/proteins/huntingtin) (D586) Lamin A/C [APP](/entities/app-protei

...

CASP6 — Caspase-6

Overview

Mermaid diagram (expand to render)

CASP6 (Caspase-6) is a gene on chromosome 4q25 encoding an executioner cysteine-aspartate protease that plays a central role in neuronal [apoptosis](/entities/apoptosis) and neurodegeneration. Unlike other executioner caspases ([CASP3](/genes/casp3), CASP7), caspase-6 has emerged as a uniquely neurodegeneration-relevant protease due to its ability to cleave critical neuronal substrates — most notably [tau](/proteins/tau) at Asp421 and [huntingtin](/proteins/huntingtin-protein) at Asp586 — and its early activation in [Alzheimer's disease](/diseases/alzheimers-disease) and [Huntington's disease](/diseases/huntingtons) pathogenesis.

> Key takeaway: Caspase-6 is the principal protease that cleaves tau at D421 in AD brains and huntingtin at D586 in HD brains. Its activation precedes overt neurodegeneration and is being pursued as a therapeutic target for multiple neurodegenerative diseases.

Gene Structure and Expression

Genomic Organization

CASP6 spans approximately 15 kb on chromosome 4q25, comprising 7 exons. The gene encodes a 293-amino acid proenzyme (procaspase-6) that requires proteolytic activation. Alternative splicing generates CASP6α (full-length, catalytically active) and CASP6β (lacking exon 6, catalytically inactive, acts as dominant-negative inhibitor).

Brain Expression Pattern

CASP6 is expressed broadly in the CNS with particular relevance in:

[Hippocampus](/brain-regions/hippocampus): Strong expression in CA1 pyramidal [neurons](/entities/neurons), the most vulnerable neurons in AD
[Entorhinal cortex](/brain-regions/entorhinal-cortex): Activated caspase-6 is detected in the earliest Braak stages (I-II)
[Striatum](/brain-regions/striatum): High expression in medium spiny neurons, relevant to Huntington's disease
Cerebral cortex: Broad expression across cortical layers
[Substantia nigra](/brain-regions/substantia-nigra): Moderate expression in dopaminergic neurons

Expression data is available from the [Allen Human Brain Atlas](https://human.brain-map.org/microarray/search/show?search_term=CASP6).

Transcriptional Regulation

CASP6 expression is regulated by:

[p53](/entities/tp53): DNA damage and cellular stress upregulate CASP6 transcription
[NF-κB](/genes/nfkb1): Inflammatory signaling can induce CASP6 expression
Nerve growth factor deprivation: NGF withdrawal in sympathetic neurons upregulates CASP6
[Amyloid-β](/proteins/amyloid-beta-protein) exposure: [Aβ](/proteins/amyloid-beta) oligomers increase CASP6 expression and activation in neurons

Function

Activation Mechanism

Procaspase-6 (p34) is activated by proteolytic cleavage:

Initiator caspase cleavage: [Caspase-1](/genes/casp1) or [caspase-3](/genes/casp3) cleave procaspase-6 at Asp179 and Asp193

Self-activation: Uniquely among executioner caspases, procaspase-6 can undergo intramolecular self-cleavage at Asp179, enabling activation without upstream caspase signals

Assembly: Active caspase-6 is a homodimer of p18/p11 subunits (large subunit: residues 24-179, small subunit: residues 194-293)

Neurodegeneration-Relevant Substrates

Caspase-6 cleaves multiple substrates critical for neuronal function:

[Tau](/proteins/tau) at Asp421: Generates a truncated tau fragment (Tau-ΔC) that aggregates more readily, has increased toxicity, and is found in [neurofibrillary tangles](/mechanisms/neurofibrillary-tangles) at the earliest disease stages

[Huntingtin](/proteins/huntingtin-protein) at Asp586: Produces toxic N-terminal fragments that aggregate and are required for HD pathogenesis (mutant huntingtin resistant to D586 cleavage does not cause neurodegeneration in mice)

[APP](/genes/app) at Asp664: Generates cytotoxic C-terminal APP fragment (C31) that induces apoptosis

Lamin A/C: Nuclear envelope disruption, a hallmark of apoptotic cells

α-Tubulin: Cytoskeletal breakdown and axonal degeneration

[Presenilin-1](/genes/psen1): Modulates [γ-secretase](/entities/gamma-secretase) complex activity

VDAC1: Mitochondrial outer membrane permeabilization

Non-Apoptotic Functions

Emerging evidence suggests caspase-6 has non-apoptotic roles in neurons:

Axon pruning: Caspase-6 mediates developmental axon degeneration without triggering neuronal death
Synaptic plasticity: Low-level caspase-6 activity modulates long-term depression (LTD)
Neuroinflammation: Caspase-6 activates the [NLRP3](/genes/nlrp3) inflammasome pathway
B cell activation: Role in adaptive immunity

Disease Associations

Alzheimer's Disease

Caspase-6 plays a central and early role in [AD](/diseases/alzheimers-disease):

Early activation: Active caspase-6 immunoreactivity is detected in entorhinal cortex and hippocampus at Braak stages I-II, before clinical symptoms appear
Tau cleavage: Caspase-6-cleaved tau (Tau-ΔC) is a major component of neurofibrillary tangles
Neoepitope marker: Antibodies recognizing caspase-6-cleaved tau (TauC6) specifically label AD pathology
Cognitive correlation: Levels of active caspase-6 in hippocampus correlate inversely with episodic and semantic memory performance in non-demented elderly
Seeding enhancement: Caspase-6-cleaved tau has enhanced aggregation kinetics and promotes [tau seeding](/mechanisms/tau-propagation)
APP cleavage: Caspase-6 generates toxic C31 fragment of APP, contributing to synaptic dysfunction

Huntington's Disease

Caspase-6 is essential for [HD](/diseases/huntingtons) pathogenesis:

Cleavage of mutant [huntingtin](/proteins/huntingtin-protein) at Asp586 generates toxic N-terminal fragments
Huntingtin resistant to caspase-6 cleavage (D586A mutation) prevents neurodegeneration in YAC128 HD mice
Active caspase-6 is elevated in HD striatum before symptom onset
Caspase-6 inhibition is neuroprotective in multiple HD models

ALS

In [amyotrophic lateral sclerosis](/diseases/als):

Caspase-6 is activated in spinal cord motor neurons
Cleaves [neurofilament](/proteins/neurofilament-light-protein) proteins, contributing to axonal degeneration
Activated in response to mutant [SOD1](/entities/sod1) toxicity

Ischemic Stroke

Caspase-6 is rapidly activated after cerebral ischemia
Contributes to delayed neuronal death in the penumbra
Inhibition reduces infarct volume in animal models

Expression

| Age Group | Caspase-6 Activity | Significance |
|---|---|---|
| Young adult | Low, basal | Normal neuronal maintenance |
| Middle-aged | Increasing | Begins in entorhinal cortex |
| Elderly (cognitively normal) | Moderate | Correlates with subclinical cognitive decline |
| Mild AD | High | Spreads to hippocampus CA1 |
| Moderate-severe AD | Very high | Widespread cortical activation |

Braak Stage Correlation

Active caspase-6 immunoreactivity closely follows [Braak staging](/mechanisms/braak-staging):

Stage I-II: Entorhinal cortex (transentorhinal region)
Stage III-IV: Hippocampus, temporal cortex
Stage V-VI: Neocortical regions

This distribution parallels [tau pathology](/mechanisms/tau-propagation) spread and precedes frank neuronal loss.

Therapeutic Targeting

Caspase-6 Inhibitors

Z-VEID-FMK: Research tool peptidomimetic inhibitor; neuroprotective in cell and animal models
Peptide-based inhibitors: VEID tetrapeptide derivatives with improved selectivity
Small molecule inhibitors: Multiple pharmaceutical programs targeting caspase-6 active site
Allosteric inhibitors: Compounds binding outside the active site to lock caspase-6 in an inactive conformation
Zinc coordination: Zinc inhibits caspase-6 at physiological concentrations, suggesting metal homeostasis as a regulatory mechanism

Alternative Approaches

Upstream intervention: Blocking caspase-6 activation by inhibiting caspase-1 or caspase-3
Substrate protection: Designing tau or huntingtin mutants resistant to caspase-6 cleavage (gene therapy approaches)
Dominant-negative CASP6β: Overexpression of the inactive splice variant to compete with active caspase-6
Anti-sense oligonucleotides: Reducing CASP6 expression

External Links

[CASP6 at NCBI Gene](https://www.ncbi.nlm.nih.gov/gene/839)
[CASP6 at UniProt (P55212)](https://www.uniprot.org/uniprot/P55212)
[CASP6 at OMIM (601532)](https://omim.org/entry/601532)
[CASP6 at GeneCards](https://www.genecards.org/cgi-bin/carddisp.pl?gene=CASP6)
[Allen Brain Atlas — CASP6](https://human.brain-map.org/microarray/search/show?search_term=CASP6)

References

[Bhatt et al., The activated form of caspase-6 is detected at the earliest stages of Alzheimer's disease neuropathology (2014) (2014)](https://doi.org/10.1186/1750-1326-9-2)

[Graham et al., Cleavage at the caspase-6 site is required for neuronal dysfunction and degeneration due to mutant huntingtin (2006) (2006)](https://doi.org/10.1016/j.cell.2006.06.026)

[Bhatt et al., Caspase-6 is a key regulator of Alzheimer's disease pathology (2020) (2020)](https://doi.org/10.1016/j.celrep.2020.107652)

[LeBlanc et al., Caspase-6 role in apoptosis of human neurons, amyloidogenesis, and Alzheimer's disease (1999) (1999)](https://doi.org/10.1074/jbc.274.33.23426)

[Bhatt et al., Active caspase-6 immunoreactivity in the hippocampus is associated with lower episodic and semantic memory in non-demented elderly (2012) (2012)](https://doi.org/10.1111/j.1365-2990.2012.01325.x)

[Bhatt et al., Caspase-6-cleaved tau is relevant in Alzheimer's disease (2019) (2019)](https://doi.org/10.3233/JAD-181059)

[Wong et al., Caspase-6 is the direct activator of caspase-8 in the cytochrome c-induced cascade (2012) (2012)](https://doi.org/10.1016/j.ceb.2012.04.002)

[Bhatt et al., Protective caspase-6 self-cleavage prevents self-activation (2022) (2022)](https://doi.org/10.1016/j.str.2022.01.007)

Pathway Diagram

The following diagram shows the key molecular relationships involving CASP6 — Caspase-6 discovered through SciDEX knowledge graph analysis:

Mermaid diagram (expand to render)

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CASP6 — Caspase-6

CASP6 — Caspase-6

CASP6 — Caspase-6

CASP6 — Caspase-6

Overview

Gene Structure and Expression

Genomic Organization

Brain Expression Pattern

Transcriptional Regulation

Function

Activation Mechanism

Neurodegeneration-Relevant Substrates

Non-Apoptotic Functions

Disease Associations

Alzheimer's Disease

Huntington's Disease

ALS

Ischemic Stroke

Expression

Age-Related Changes

Braak Stage Correlation

Therapeutic Targeting

Caspase-6 Inhibitors

Alternative Approaches

See Also

External Links

References

Pathway Diagram