Gut microbiota modified by mulberry leaf water extract improves T2DM through browning of WAT/BAT activation mediated by SCFAs-AMPK/SIRT1/PGC-1α signaling pathway
Description
Background: SCFAs, the principal metabolites produced by gut microbiota, are pivotal regulators of glucose and lipid metabolism and energy metabolism. Mulberry leaf water extract (MLE) improves type 2 diabetes mellitus (T2DM) by modulating gut microbiota, increasing short chain fatty acids (SCFAs), and promoting the browning of white adipose tissue (WAT) and activation of brown adipose tissue (BAT). The causal relationship between the regulation of gut microbiota homeostasis and SCFAs level by MLE and the improvement of T2DM and the exact mechanism remain to be confirmed. Objective: This study aims to investigate whether the hypoglycemic effect of gut microbiota regulated by MLE is related to browning of WAT/BAT activation mediated by SCFAs-AMP-activated protein kinase (AMPK) signaling pathway. Design: db/db mice treated with and without MLE were used as fecal donors. In addition, db/db mice were administrated with antibiotics to clear gut microbiota, and then received fecal microbiota transplantation (FMT) and supplementation of exogenous SCFAs. Gut microbiota and its metabolite SCFAs were analyzed by 16s rRNA and GC/MS. In addition, gene and protein expressions were verified by qRT-PCR and Western blotting, and insulin (INS) were measured by ELISA. Biochemical Kit measured the concentrations of serum total cholesterol (TC), triglycerides (TG), low-density lipoprotein-cholesterol (LDL-C), high-density lipoprotein-cholesterol (HDL-C), etc. Results: SCFAs and gut microbiota of mice treated with MLE promoted SCFAs production by increasing the abundance of SCFAs-producing bacteria such as norank_f__Muribaculaceae, Muribaculum, Parabacteroides and Dubosiella. SCFAs and gut microbiota of mice treated with MLE improved glucose and lipid metabolism disorders and alleviated insulin resistance (IR). Moreover, SCFAs activated BAT and induced the browning of inguinal white adipose tissue (IWAT) by increasing the expressions of brown adipocyte marker genes and proteins such as uncoupling protein 1 (UCP1) and beige adipocyte marker genes such as tumor necrosis factor receptor superfamily member 9 (Tnfrsf9/Cd137), thereby promoting mitochondrial biogenesis. Mechanistically, MLE facilitated the activation of BAT and the induction of WAT browning to ameliorate T2DM primarily through the activation of AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor-gamma coactivator 1α (PGC-1α) signaling pathway. Conclusion: MLE can regulate gut microbiota homeostasis and SCFAs levels, restore SCFAs and mediate AMPK signaling pathway to normal, promote browning of WAT/BAT activation, improve glucose and lipid metabolism, and exert hypoglycemic, lipid-lowering effects and improve IR. The mechanism is related to browning of WAT/BAT activation mediated by SCFAs-AMPK/SIRT1/PGC-1α signaling pathway.