Paulina Wigner

The journal retracts the article titled, “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”

Previous studies suggest that depression may be associated with reactive oxygen species overproduction and disorders of the tryptophan catabolites pathway. Moreover, one-third of patients do not respond to conventional pharmacotherapy. Therefore, the study investigates the molecular effect of escitalopram on the expression of Cat, Gpx1/4, Nos1/2, Tph1/2, Ido1, Kmo, and Kynu and promoter methylation in the hippocampus, amygdala, cerebral cortex, and blood of rats exposed to CMS (chronic mild stress). The animals were exposed to CMS for two or seven weeks followed by escitalopram treatment for five weeks. The mRNA and protein expression of the genes were analysed using the TaqMan Gene Expression Assay and Western blotting, while the methylation was determined using methylation-sensitive high-resolution melting. The CMS caused an increase of Gpx1 and Nos1 mRNA expression in the hippocampus, which was normalised by escitalopram administration. Moreover, Tph1 and Tph2 mRNA expression in the cerebral cortex was increased in stressed rats after escitalopram therapy. The methylation status of the Cat promoter was decreased in the hippocampus and cerebral cortex of the rats after escitalopram therapy. The Gpx4 protein levels were decreased following escitalopram compared to the stressed/saline group. It appears that CMS and escitalopram influence the expression and methylation of the studied genes.

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.

Preclinical studies conducted so far suggest that oxidative stress processes may be associated with the mechanism of depression development. This study shows the effects of chronic administration of agomelatine on expression and the methylation status of Sod1, Sod2, Gpx1, Gpx4, Cat, Nos1, and Nos2 in the brain stricture and blood in the chronic mild stress (CMS) animal model of depression. The animals were exposed to the CMS procedure and treatment with agomelatine (10 mg/kg/day, IP) for five weeks and then were sacrificed. TaqMan Gene Expression Assay, Western blot, and methylation-sensitive high-resolution melting techniques were used to evaluate mRNA and protein expression of the genes, and the methylation status of their promoters. Gpx1, Gpx4, and Sod2 expression in the PBMCs and Sod1 and Sod2 expression in the brain were reduced in the stressed group after agomelatine administration. CMS caused an increase in the methylation of the third Gpx4 promoter in peripheral blood mononuclear cells and Gpx1 promoter in the cerebral cortex. Additionally, stressed rats treated with agomelatine displayed a significantly lower Gpx4 level in the hypothalamus. The results confirm the hypothesis that the CMS procedure and agomelatine administration change the expression level and methylation status of the promoter region of genes involved in oxidative and nitrosative stress.