FNDC5 and major depressive disorder: Further, associations between AD neuropathology and depression remain controversial (Li et al., 2017; Babulal et al., 2020; Saldanha et al., 2021; Pomara et al., 2022).The links between AD and depression (Ledo et al., 2016, 2013; Dafsari and Jessen, 2020) and previous findings of the association between exercise and antidepressant activity prompted us to investigate whether fndc5 expression could be dysregulated in depression.