ACE and major depressive disorder: Besides, we have shown that LQYY increased the content of ACE levels in CUMS-induced depression with constipation mice, and to further verify the effect of LQYY on FFAR2 signaling in vivo, we detected the levels of FFAR2, IBA-1, IL-6 and TNF-α, and found that LQYY increased the expression of FFAR2 and decreased the expression of IBA-1, IL-6 and TNF-α.