Functionally, ATP6AP2 plays important roles in multiple organs and cell types; and dysregulation of ATP6AP2 is implicated in the pathogenesis of numerous diseases, such as hypertension, pre-eclampsia, diabetic microangiopathy, acute kidney injury, cardiovascular disease, cancer, obesity, mental disorders (e.g., depression and post-traumatic stress disorder), and neurodegenerative diseases (e.g., Parkinson disease and Alzheimer disease).9,19–31 Notice that ATP6AP2 is abundantly expressed in bone cells, including OBs and OCs. This evidence concerns the gene ATP6AP2 and major depressive disorder.