| Caspase-3 (CASP3) | |
|---|---|
| Gene | CASP3 |
| UniProt | P42574 |
| PDB Structures | 2J30, 1CP3, 3EDQ |
| Molecular Weight | 32 kDa (zymogen); 17 + 12 kDa (active heterodimer) |
| Localization | Cytoplasm, mitochondria (activated) |
| Protein Family | Cysteine-aspartate protease (caspase) family |
| Diseases | Alzheimer's Disease, Parkinson's Disease, Huntington's Disease, ALS, FTD |
Caspase 3 (Casp3) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Caspase-3 (also known as CPP32, apopain, or YAMA) is a 32 kDa cysteine-aspartate protease encoded by the CASP3 gene on chromosome 4q35.1. [It is the principal executioner caspase of apoptosis — the major downstream effector protease that cleaves the majority of cellular substrates during programmed cell death. Caspase-3 is activated by initiator caspases (caspase-8 and [caspase-9[/proteins/caspase-9 and cleaves over 600 cellular substrates at specific aspartate residues, dismantling the cell in an orderly fashion ([Asadi et al., 2022]https://doi.org/10.1002/bab.2233)).
In the nervous system, caspase-3 plays dual roles: it is essential for normal brain development (mediating synaptic pruning, axon guidance, and neurogenesis) and is pathologically activated in virtually all neurodegenerative diseases. In [Alzheimer's disease[/diseases/alzheimers, caspase-3-mediated cleavage of tau]/proteins/tau generates toxic truncated fragments that accelerate neurofibrillary tangle formation and [synaptic dysfunction[/mechanisms/synaptic-dysfunction. In [Huntington's disease[/mechanisms/huntington-pathway, caspase cleavage of [huntingtin/proteins/[huntingtin) produces N-terminal fragments with enhanced aggregation propensity. The growing appreciation that caspase-3 can operate at sub-lethal levels to drive synaptic damage and protein toxicity — without full apoptosis — has repositioned it from a simple cell death executor to a central mediator of neurodegeneration (D'Amelio et al., 2010; Bhatt et al., 2023).
Caspase-3 is synthesized as an inactive 32 kDa zymogen (procaspase-3) comprising:
The active enzyme functions as a homodimer of heterodimers — a p17/p12 heterodimer pair forming a tetramer (p17₂p12₂) with two active sites. Each active site features:
Caspase-3 activation occurs through two principal pathways:
| Pathway | Initiator | Mechanism |
|---|---|---|
| Intrinsic (mitochondrial) | [Caspase-9[/proteins/caspase-9 | Cytochrome c release → apoptosome formation → caspase-9 activation → caspase-3 cleavage at Asp-175 |
| Extrinsic (death receptor) | Caspase-8 | Death ligand (FasL, TRAIL, TNF) → DISC formation → caspase-8 → direct or BID-mediated caspase-3 activation |
Both pathways converge on the cleavage of procaspase-3 at Asp-175 (between the large and small subunits), followed by autocatalytic removal of the prodomain at Asp-28. The activated enzyme then processes a cascade of downstream substrates.
Caspase-3 is essential for normal brain development, acting at sub-lethal levels to shape neural circuits:
Caspase-3 knockout mice are viable but display marked brain overgrowth (exencephaly) and disorganized neural architecture, confirming its developmental requirement (Bhatt et al., 2023).
At sub-apoptotic levels, caspase-3 participates in:
Caspase-3 cleaves tau[/proteins/tau at Asp-421, generating a C-terminally truncated fragment (Δ[tau](/proteins/tau at Asp-421, generating a C-terminally truncated fragment (Δtau) that:
Caspase-cleaved tau (detected by the TauC3 antibody at D421) is found in AD brains at early [Braak stages], suggesting it is an early event in tangle pathology that precedes full-length tau aggregation (Rissman et al., 2004).
Caspase-3 cleaves [APP[/proteins/app-protein at Asp-664 (in the cytoplasmic domain), releasing:
[Aβ[/proteins/Amyloid-Beta-induced synapse loss in [hippocampal CA1 neurons[/cell-types/hippocampal-ca1 correlates with localized caspase-3 activation and [APP[/genes/app cleavage at D664 (Bhatt et al., 2020).
Caspase-3 cleaves [huntingtin[/proteins/huntingtin at Asp-513 and Asp-530, generating N-terminal fragments that:
| Substrate | Cleavage Site | Consequence |
|---|---|---|
| PARP-1 | Asp-214 | Inactivation of DNA repair — hallmark of apoptosis |
| ICAD/DFF45 | Asp-117 | Release of CAD endonuclease → DNA fragmentation |
| Lamin A/C | Asp-230 | Nuclear envelope breakdown |
| Beclin-1 | Asp-149 | Switches from [autophagy[/entities/autophagy to apoptosis |
| Actin | Asp-11 | Cytoskeletal collapse, membrane blebbing |
| [GFAP[/entities/glial-fibrillary-acidic-protein | Multiple | [Astrocyte[/cell-types/astrocytes activation and intermediate filament reorganization |
Caspase-3 activation is a consistent finding in AD brain tissue and models:
Several caspase-3 inhibitors have been explored in preclinical neurodegenerative disease models:
Blocking caspase-3-mediated tau cleavage at D421 is being explored as a disease-modifying strategy:
The study of Caspase 3 (Casp3) has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.