HDAC5 (histone deacetylase 5, encoded by the HDAC5 gene) is a class IIa histone deacetylase that regulates gene expression through chromatin modification and transcription factor interaction. It is highly expressed in the brain, where it plays critical roles in synaptic plasticity, memory formation, stress responses, and neuronal survival. HDAC5 is implicated in Alzheimer's disease, Parkinson's disease, depression, and stroke, making it a potential therapeutic target.
¶ Gene and Protein Structure
| Property |
Value |
| Gene Symbol |
HDAC5 |
| Chromosomal Location |
17q21.31 |
| UniProt ID |
Q9UQL6 |
| Protein Length |
1112 amino acids |
| Molecular Weight |
~112 kDa |
| Protein Family |
Class IIa histone deacetylases |
| Subcellular Localization |
Nucleus (basal) and cytoplasm (signal-dependent) |
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- N-terminal regulatory domain: Contains binding sites for transcription factors (MEF2, HIC1, CtBP) and importin-alpha binding sites for nuclear-cytoplasmic shuttling. This region contains serine residues (Ser259, Ser498) that are phosphorylated by kinases such as CaMK and PKD
- Catalytic deacetylase domain: Located in the C-terminal portion; retains the HD domain but has reduced catalytic activity compared to class I HDACs. The catalytic domain interacts with the N-terminal repressor domain to regulate gene expression
- Nuclear localization signal (NLS): Situated near the N-terminus
- Nuclear export signal (NES): Located in the C-terminal region
Class IIa HDACs (HDAC4, HDAC5, HDAC7, HDAC9) differ from class I HDACs (HDAC1-3, 8) in several ways:
- They have low intrinsic deacetylase activity and function primarily as transcriptional corepressors through recruitment of other proteins (e.g., NCoR/SMRT complexes, Sin3A)
- They shuttle between nucleus and cytoplasm in response to cellular signals (particularly calcium and cAMP)
- They have tissue-enriched expression patterns (HDAC5 is enriched in brain, heart, and skeletal muscle)
¶ Chromatin Modification and Gene Regulation
HDAC5 exerts its transcriptional repression effects through multiple mechanisms:
- Histone deacetylation: HDAC5 deacetylates histone H3 and H4 tails, creating a chromatin environment that suppresses transcription
- Non-histone protein deacetylation: HDAC5 can deacetylate transcription factors (MEF2, p53, NF-κB) and other regulatory proteins
- Corepressor complex recruitment: HDAC5 recruits NCoR/SMRT complexes and Sin3A to specific gene promoters
- Interaction with HDAC3: HDAC5 forms complexes with class I HDAC3, which provides the actual deacetylase activity
| Target |
Interaction |
Biological Effect |
| MEF2 (myocyte enhancer factor 2) |
Direct binding and repression |
Suppression of MEF2-dependent gene programs (including neuronal survival genes) |
| CREB |
Co-repressor recruitment |
Modulation of cAMP-responsive gene expression |
| NF-κB |
Deacetylation |
Repression of inflammatory gene expression |
| HIF-1α |
Interaction |
Regulation of hypoxic response genes |
| ERα |
Interaction |
Modulation of estrogen receptor signaling |
HDAC5 is a central node in calcium and cAMP signaling to the nucleus:
- Activation of CaMK: Synaptic activity and neurotransmitter signaling activate calcium/calmodulin-dependent kinase (CaMK)
- Phosphorylation: CaMK (and PKD) phosphorylates HDAC5 at Ser259 and Ser498
- 14-3-3 binding: Phosphorylated HDAC5 binds 14-3-3 proteins, which mask the NLS and expose the NES
- Nuclear export: Exportin CRM1 binds the exposed NES and shuttles HDAC5 to the cytoplasm
- Gene derepression: Removal of HDAC5 from chromatin allows activation of HDAC5-repressed genes
In the healthy brain, HDAC5 regulates:
- Synaptic plasticity: Activity-dependent chromatin remodeling at synaptic plasticity genes (c-Fos, BDNF, Arc)
- Memory formation: Consolidation of long-term memory through epigenetic regulation of memory-related genes
- Neuronal development: Differentiation of neural progenitors and maturation of neurons
- Stress responses: Modulation of HPA axis activity and stress resilience
- Neurogenesis: Regulation of hippocampal neurogenesis
HDAC5 is dysregulated in Alzheimer's disease, with altered expression and localization in affected brains.
- HDAC5 mRNA and protein levels are altered in AD brain tissue, particularly in the hippocampus and prefrontal cortex
- Altered subcellular localization (changes in nuclear/cytoplasmic ratio) have been reported in AD neurons
- The changes suggest both dysregulation of HDAC5 itself and disruption of the signaling pathways that control its localization
HDAC5 contributes to synaptic dysfunction in AD through:
- Activity-dependent gene dysregulation: Aβ oligomers disrupt calcium signaling, leading to abnormal HDAC5 nuclear export/retention and altered synaptic plasticity gene expression
- Memory consolidation deficits: HDAC5-mediated chromatin changes impair the formation of long-term memories
- Dendritic spine alterations: HDAC5 dysregulation affects spine morphology and density
¶ Neuroprotection and Therapeutic Potential
- HDAC5 modulation: Altering HDAC5 activity or localization can protect neurons from Aβ toxicity
- Epigenetic therapy: HDAC5 is a target for HDAC inhibitor approaches in AD; Class I-selective HDAC inhibitors (entinostat) may spare HDAC5's beneficial effects while achieving therapeutic benefit
- Interaction with tau: Some evidence suggests HDAC5 may interact with tau pathology pathways
¶ Role in Depression and Psychiatric Disorders
HDAC5 is a key regulator of mood and stress responses.
- Stress regulation: Chronic stress increases HDAC5 nuclear levels in the hippocampus; antidepressant treatments (SSRIs, ECT) promote HDAC5 phosphorylation and nuclear export, allowing derepression of antidepressant-responsive genes
- HPA axis modulation: HDAC5 regulates genes involved in the hypothalamic-pituitary-adrenal (HPA) axis
- Synaptic plasticity in depression: HDAC5-mediated chromatin remodeling affects synaptic plasticity genes that are dysregulated in depression
- HDAC5 knockout mice show altered stress responses and antidepressant-like phenotypes
- Viral-mediated HDAC5 overexpression in the hippocampus produces antidepressant effects
- Class IIa HDAC-selective compounds have been explored as potential antidepressants
¶ Role in Stroke and Brain Injury
HDAC5 is implicated in neuronal damage following stroke and ischemia.
- HDAC5 and HDAC4 form a complex with DREAM (downstream regulatory element antagonist modulator) that binds to the NCX3 gene promoter and epigenetically suppresses NCX3 (sodium-calcium exchanger 3) expression
- NCX3 is neuroprotective during ischemia; suppression of its expression by HDAC4/5-DREAM complexes exacerbates neuronal damage
- Pharmacological inhibition of this HDAC4/5-DREAM complex restores NCX3 expression and reduces stroke damage
- HDAC4/5-DREAM complex inhibitors: Small molecules targeting this repressive complex could restore neuroprotective gene expression
- Nuclear export-promoting agents: Compounds that promote HDAC5 phosphorylation and nuclear export could derepress protective genes
In Parkinson's disease, HDAC5 may contribute to:
- Dysregulation of dopaminergic neuron survival pathways
- Alterations in stress response gene programs
- Potential cross-talk with alpha-synuclein pathology
HDAC inhibitors broadly target multiple HDAC enzymes. Key considerations for HDAC5:
| Compound |
Class Selectivity |
CNS Penetration |
Notes |
| Vorinostat (SAHA) |
Pan-HDAC (class I > IIa) |
Limited |
FDA-approved for CTCL; not suitable for neurodegeneration |
| Entinostat (MS-275) |
Class I selective (HDAC1-3) |
Moderate |
Spares class IIa; explored for AD and depression |
| TSA (Trichostatin A) |
Pan-HDAC |
Limited |
Preclinical tool compound |
| MC1568 |
Class IIa selective |
Unknown |
Preclinical |
- Developing selective HDAC5 modulators is challenging due to the structural similarity among class IIa HDACs
- Targeting HDAC5's signal-dependent regulation (e.g., CaMK activators) may be more selective
- Protein-protein interaction disruptors targeting HDAC5's repressor complexes
- Isoform selectivity: Achieving selectivity for HDAC5 over HDAC4 and HDAC9 is difficult
- Brain penetration: Many HDAC inhibitors have limited CNS penetration
- Biphasic effects: HDAC5 has both protective and potentially harmful roles depending on context
- Nuclear vs. cytoplasmic function: Selective targeting of specific HDAC5 compartments may be needed
| Partner |
Interaction Type |
Function |
| MEF2 (MEF2C) |
Transcription factor binding |
Corepressor; HDAC5-MEF2 interaction regulates neuronal survival |
| 14-3-3 proteins |
Phosphorylation-dependent binding |
Cytoplasmic sequestration after nuclear export |
| CaMK |
Phosphorylation |
Kinase that phosphorylates Ser259/Ser498 to trigger nuclear export |
| PKD |
Phosphorylation |
Kinase that phosphorylates HDAC5 in response to DAG/PKC signaling |
| NCoR/SMRT |
Corepressor complex |
Recruitment of HDAC3 and chromatin remodeling machinery |
| Sin3A |
Corepressor complex |
Transcriptional repression |
| DREAM |
Transcription factor complex |
HDAC4/5-DREAM complex regulates NCX3 in stroke |
| CRM1/Exportin |
Nuclear export |
Mediates nuclear export of phosphorylated HDAC5 |
| HDAC3 |
Enzymatic partner |
Class I partner providing deacetylase activity |