MTOR and major depressive disorder: In addition, some scholars compared the expression profile of various microRNA in patients with depression with that in normal subjects, from the results of their comparison, the expression of the microRNA let-7b and let-7c was significantly down-regulated in patients with depression, and let-7c and let-7b participate in regulation for the expression of 27 genes which involved in the PI3k-Akt-mTOR signaling pathway (51, 52).