The Impact of Chronic Mild Stress and Agomelatine Treatment on the Expression Level and Methylation Status of Genes Involved in Tryptophan Catabolic Pathway in PBMCs and Brain Structures

Depression is the serious mental disorder. Previous studies suggest that the development mechanism of depression may be associated with disorders of the tryptophan catabolic pathway (TRYCAT). Thus, this study investigates the effect of agomelatine treatment on the expression and methylation status of genes involved in TRYCAT in the brain and blood of rats exposed to a chronic mild stress (CMS). Separate groups of rats were exposed to CMS for two or seven weeks; the second group received vehicle or agomelatine for five weeks. After completion of both stress conditions and treatment, the expression levels of messenger RNA (mRNA) and protein, as well as the methylation status of promoters, were measured in peripheral blood mononuclear cells (PBMCs) and in brain structures with the use of TaqMan Gene Expression Assay, Western blot, and methylation-sensitive high-resolution melting techniques. In PBMCs, Kmo mRNA expression increased in the group after CMS, while this effect was normalized by agomelatine therapy. In brain, KatI and KatII expression changed following CMS exposure. Moreover, CMS decreased the methylation status of the second Tdo2 promoter in the amygdala. Protein expression of Tph1, Tph2, Ido1, and KatII changed in the group after CMS and agomelatine administration, most prominently in the basal ganglia, cerebral cortex, hippocampus, and amygdala. The results indicate that CMS and agomelatine affect the mRNA and protein expression, as well as the methylation of promoters of genes involved in the tryptophan catabolic pathway.