The serotonergic system, classically involved in the depression/anxiety mechanisms, is now proposed to regulate Aβ precursor protein (APP) activity and metabolism (Shen et al., 2011), while Brain Derived Neurotrophic Factor (BDNF) has a relevance not only in MD, but also in depression-associated cognitive decline (Diniz et al., 2014). Here, APP is linked to major depressive disorder.