Nrf2 activation rescues stress-induced depression-like behaviour and inflammatory responses in male but not female rats

Major depressive disorder is two times more prevalent in females than males. Further, immune system dysfunction has been shown to contribute to the development of depression, with previous studies consistently reporting chronic low-grade inflammation in depressed individuals. Not surprisingly, the immune system dysfunction associated with depression appears to be sex specific. As such, while anti-inflammatory drugs have shown antidepressant effects in preclinical studies, the sex differences in these effects are seldomly investigated. Thus, this study sought to determine the sex-specific antidepressant and immune modulatory effects of dimethyl fumarate (DMF) treatment. DMF is a drug that activates the protein nuclear factor erythroid 2-related factor 2 to initiate anti-inflammatory signaling pathways. Here, male and female rats were exposed to 8 weeks of chronic stress while receiving daily DMF treatment. Subsequently, their expression of depression- and anxiety-like behaviours, as well as learning and memory deficits were assessed. Changes in the levels of an inflammatory marker in the brain and alterations in gene expression were also evaluated. DMF treatment had antidepressant effects in male rats only but did not have anti-anxiety effects in either sex. The learning and memory deficits in both sexes were rescued with DMF treatment. Notably, chronic stress only increased inflammatory marker levels in male rats, which was prevented by DMF treatment. Additionally, DMF normalized several of the sex-specific gene alterations induced by chronic stress, with many of the male-specific genes relating to inflammatory processes. These data suggest that anti-inflammatory drugs may be an effective antidepressant treatment in males.