Differential phosphoproteome regulation of nucleus accumbens in environmentally enriched and isolated rats in response to acute stress.

Increasing evidence shows that stress contributes to the pathogenesis of major depressive disorder which is a severe neuropsychiatric disorder and influences over 10% of the world's population. Our previous studies revealed that rats reared in an enriched environment display less depression-related behavior compared to rats raised in an isolated environment, which implies that environmental enrichment produces an antidepressant-like behavioral phenotype. However, the molecular mechanisms are not fully understood. Protein phosphorylation rapidly changes signaling pathway function and alters the function of proteins associated with the stress-induced depressive disorder. Thus, in this study, a phosphoproteomic approach was used to uncover differential phosphoprotein regulation in rat nucleus accumbens between isolated (IC) and enriched environmental conditions (EC) under basal conditions, and in response to acute stress. We found 23 phosphoproteins were regulated in EC vs. IC rats under basal conditions; 10 phosphoproteins regulated by stress in IC rats; and 15 regulated by stress in EC rats. Among all significantly regulated phosphoproteins, 11 of them were represented in at least two conditions. The regulated phosphoproteins represent signaling pathway proteins (including ERK2), enzymes, transcriptional regulators, protein translation regulators, transporters, chaperones and cytoskeletal proteins. These findings provide a global view for further understanding the contribution of protein phosphorylation in depression pathogenesis and antidepressant action.