Epigenetic, neuroplasticity, and adrenergic targets associated with major depression in immune cells

Major depression (MD) has been linked to both neuroinflammation and impaired synaptic plasticity. Furthermore, epigenetic mechanisms involving certain histone deacetylases (HDACs) may initiate these changes. Specifically, altered expression of particular HDACs, including HDAC5, HDAC2, SIRT1, and SIRT2, has been associated with depressive-like behavior, suppressed levels of brain-derived neurotrophic factor (BDNF), and the promotion of neuroinflammation. Additionally, changes in these HDACs within peripheral blood mononuclear cells might contribute to peripheral low-grade inflammation. Here, we investigated the influence of MD on the regulation of specific epigenetic targets, alongside the expression of genes involved in neuroplasticity and inflammation. We analyzed fluorescence-activated cell sorting (FACS)-isolated monocytes (classic, intermediate, and non-classic) and T-cells (CD3+) from fifty-six patients with moderate-to-severe MD and age- and sex-matched healthy controls. Decreased HDAC5 cytoplasm/nucleus ratio in MD monocytes were observed. Moreover, decreased HDAC5 cytoplasm/nucleus ratio negatively correlated with illness severity in MD monocyte subsets and T-cells. In addition, decreased SIRT2 cytoplasm/nucleus ratio in monocytes and T-cells were observed. Gene expression studies showed an increase in HDAC5 mRNA both in intermediate monocytes and T-cells as well as an increase of SIRT2 in intermediate monocytes. Moreover, decreased expression of the neuroplasticity biomarker BDNF, known to be regulated by these two epigenetic enzymes was observed in intermediate monocytes and T-cells. Moreover, an increase of ADRB2 mRNA, encoding the β2 adrenoceptor was observed in classic monocytes. Furthermore, in these cells, both ADRB2 and IL-6 mRNA showed a negative correlation with the HDAC5 cytoplasm/nucleus ratio. Importantly, logistic regression analysis revealed that changes observed with ADRB2 in classic monocytes, SIRT2 in intermediate monocytes and HDAC5 in T-cells were associated to MD with a moderate discriminatory accuracy. These studies suggest that MD promotes nuclear enrichment of the epigenetic enzymes HDAC5 and SIRT2 in monocytes and T-cells of MD patients. These epigenetic changes could potentially contribute to the observed adrenergic and neuroplasticity markers alterations in monocytes and T-cells respectively. Further, some of the targets studied were associated to MD with an acceptable diagnostic value, suggesting the need to enlarge the cohort in order to identify whether they are biomarkers for MD.