HDAC2 (Histone Deacetylase 2 Class I Synaptic Plasticity Brake & Glucocorticoid Co-Repressor Gene)
HDAC2 (histone deacetylase 2; HGNC:4853, NCBI Gene ID 3066) is a human locus mapped to chromosome band 6q21 that encodes zn2+-dependent Class I nuclear histone deacetylase 2 (488 aa; 55 kDa; EC 3.5.1.98). HDAC2 acts in co-repressor of BDNF/EGR1/Synapsin synaptic memory genes & glucocorticoid receptor (NR3C1) transrepression of NF-kappaB in airways, together with HDAC1 (Close Class I Paralog Gene), BDNF (Hippocampal Promoter Repressed by HDAC2), and CREB1 (Synaptic Memory Factor Opposed by HDAC2). Encodes Class I histone deacetylase 2, which restrains hippocampal synaptic plasticity and mediates glucocorticoid receptor anti-inflammatory transrepression.
Approved Symbol
HDAC2
Chromosomal Locus
6q21
Encoded Product
Zn2+-dependent Class I nuclear histone deacetylase 2 (488 aa; 55 kDa; EC 3.5.1.98)
Primary Pathway
Co-repressor of BDNF/EGR1/Synapsin synaptic memory genes & glucocorticoid receptor (NR3C1) transrepression of NF-kappaB in airways
Clinical / Therapeutic Role
Acts as the molecular brake on hippocampal long-term memory & synaptic density; oxidative loss in COPD macrophages causes corticosteroid resistance
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 14-exon gene on chromosome 6q21 sharing 83% sequence identity with HDAC1, containing a coding microsatellite tract of 9 adenines in exon 1 that is somatically frameshift-mutated in ~20–30% of microsatellite-unstable colorectal and endometrial cancers.
Cellular & Tissue Expression Profile: Co-expressed with HDAC1 in proliferating cells inside Sin3, NuRD, and CoREST complexes, but upon neuronal differentiation switches to become the predominant Class I HDAC expressed in mature post-mitotic cortical and hippocampal neurons.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Performs two high-impact physiological functions: (1) in hippocampal CA1 pyramidal neurons, HDAC2 (unlike HDAC1) binds the promoters of activity-dependent synaptic plasticity and memory genes—including BDNF, EGR1, CREB1, Camk2a, Synapsin-1, and NMDA receptor subunits—deacetylating H4K12ac and H3K9ac to act as a negative constraint on dendritic spine formation and long-term potentiation (LTP); and (2) in alveolar macrophages and airway epithelium, ligand-bound glucocorticoid receptor (GR / NR3C1) recruits HDAC2 to deacetylate NF-kappaB-activated inflammatory cytokine promoters (IL-8, TNF-alpha, GM-CSF).
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Landmark studies by Li-Huei Tsai demonstrated that neuron-specific overexpression of Hdac2 (but not Hdac1) abolishes hippocampal LTP and spatial memory, whereas Hdac2 knockout increases dendritic spine density and enhances memory formation; in Alzheimer disease and aging brains, stress-activated glucocorticoid/Sp3 signaling pathologically up-regulates HDAC2 to create an epigenetic blockade of memory genes.
Therapeutic & Clinical Pharmacology: In chronic obstructive pulmonary disease (COPD) and severe smoking-related asthma, peroxynitrite oxidative stress nitrates and degrades macrophage HDAC2—causing clinical corticosteroid resistance that can be reversed by low-dose theophylline (which activates PI3K-delta to restore HDAC2); in neurology, isoform-selective HDAC2 inhibition and endogenous exercise ketone body beta-hydroxybutyrate (an endogenous Class I HDAC inhibitor) restore BDNF transcription and synaptic resilience.