Epigenetic mechanisms in stress and the hypothalamic-pituitary-adrenal axis.

The hypothalamic-pituitary-adrenal (HPA) axis is central to regulating the body's stress response. While HPA axis function enables physiologic and behavioral adaptation to stress, dysregulation of its feedback mechanisms - driven by early-life adversity, chronic stress, trauma, or illness - contributes to the pathophysiology of various physical and neuropsychiatric disorders. Gene expression is controlled by chromatin plasticity, which involves epigenetic mechanisms such as DNA methylation, histone modifications, and noncoding RNA regulation. Animal models demonstrate that early-life stressors, including maternal deprivation or chronic social stress, induce stable epigenetic changes in key genes, primarily through DNA methylation and histone acetylation. These modifications result in persistent alterations in gene expression, affecting HPA regulation and behavioral phenotypes. Human studies confirm similar epigenetic signatures associated with stress-related learning, memory, and neuropsychiatric conditions. Epigenome-wide association studies have identified stress-related DNA methylation and histone modification profiles linked to both resilience and susceptibility to stress-induced pathologies. Emerging research highlights the role of noncoding RNAs and chromatin remodeling in fine-tuning HPA function, revealing the complex interplay between genetic risk and environmental modulation. These findings suggest promising therapeutic avenues, including pharmacologic agents targeting epigenetic modifiers, psychosocial interventions, and dietary strategies aimed at restoring HPA axis equilibrium to mitigate stress-related disorders.