Depression and neuroprogression: Sirtuins and mitochondria as crucial hubs

Neuroprogressive processes in major depressive disorder (MDD) can occur in association with recurrent episodes. The primary biological underpinnings are mediated by increases in the levels of immune-inflammation, tryptophan catabolites, mitochondrial dysfunction, and oxidative and nitrosative stress. Such biochemical alterations may be driven by changes in many peripheral and central sites, including in the gut, as well as by early developmental priming, such as prenatal stressors and breastfeeding consequences. As such, the conceptualization of MDD is shifted from simple psychological and central biochemical models to one that includes whole body processes over a developmental timescale. This provides a model that better integrates wider bodies of data relevant to the aetiology and course of MDD, and which therefore underpins the neuroprogressive processes that can occur over the course of MDD. This also significantly challenges current MDD (and wider psychiatric) classification by shifting classification to one based on biological processes rather than one based on subjective phenomenology.