SIK2 and major depressive disorder: In addition to PPARα, there are a lot of other proteins that not only control BDNF biosynthesis and neuroplasticity but also are implicated in depression, such as salt-inducible kinase 2, glycogen synthase kinase 3β and mammalian target of rapamycin (Zhou et al., 2014; Peng et al., 2018; Jiang et al., 2019).