Epigenetic Control of Stress-Induced Depression: Emerging Roles of HDAC3 and HDAC6.

Major depressive disorder (MDD) is a heterogeneous psychiatric disorder characterized by impaired mood, neuroplasticity, neuroinflammation, and dysregulated stress response systems. Chronic stress can induce epigenetic changes leading to depression. Evidence suggests that histone acetylation and deacetylation are epigenetic processes involved in changes in gene expression. Histone deacetylases (HDACs) modulate chromatin structure and transcription, and their dysregulation is associated with stress susceptibility, decreased brain-derived neurotrophic factor (BDNF) signaling, impaired synaptic plasticity, and inflammatory activation. HDAC isoforms HDAC3 and HDAC6 have emerged as epigenetic regulators in stress-induced depression. HDAC3 is a transcriptional regulator involved in neuroplasticity-related gene expression, inflammatory signaling, and glucocorticoid receptor-mediated stress responses. In contrast, HDAC6 is cytoplasmic and regulates non-histone substrates involved in microtubule dynamics, synaptic function, protein trafficking, and the regulation of the hypothalamic-pituitary-adrenal axis (HPA axis). Preclinical studies show that HDAC3 or HDAC6 inhibition can exert antidepressant-like effects by promoting neuroplasticity, reducing neuroinflammation, and restoring stress-related signaling. Dual targeting is an interesting therapeutic approach because both regulate complementary mechanisms. However, clinical translation is limited by poor blood-brain barrier penetration, systemic toxicity, insufficient isoform selectivity, and a lack of clinical evidence. This review summarizes the roles and mechanisms of HDAC3 and HDAC6, the rationale for dual targeting, translational limitations, and future therapeutic perspectives.