Imbalance of Bile Acids Metabolism Mediated by Gut Microbiota Contributed to Metabolic Disorders in Diabetic Model Mice

Type 2 diabetes (T2D) is a chronic disease prevalent in the world, accompanied by a variety of diseases, endangering human health and safety. Bile acids (BAs) play an important role in the regulation of host glucose and lipid metabolism homeostasis, and are strictly regulated by gut microbiota. However, the relationship between key BAs, BAs transporters and signaling, as well as gut microbiota, and host metabolism in T2D remains elusive. In this study, 9-week-old db/db mice were used as diabetes model (db/db group, <i>n</i> = 10), and their wild-type (wt) littermates of same age were used as the healthy control (CON group, <i>n</i> = 10). After 8 weeks of feeding, the BA profiles and microbial composition in the colon, and gene expression level of BA regulatory factors were analyzed in the db/db and CON groups to explore the underlying mechanisms of T2D. Compared with healthy mice, the body weight, blood glucose and lipid levels of db/db mice were significantly increased. The concentrations of total BAs, primary BAs, conjugated BAs and non-12α-hydroxylated BAs (non-12-OH BAs) were significantly decreased, while Deoxycholic acid (DCA) in secondary BAs was increased in db/db group. Compared with wt mice, the synthesis of BAs in the liver was transformed from the alternative pathway to the classical pathway, and hepatic BAs transporters (NTCP, BSEP, MRP2, OATP-1 and OSTβ) and receptors (FXR and TGR5) were significantly down-regulated in the db/db mice. In the colon, the mRNA level of FXR was up-regulated, while TGR5 was down-regulated. The diabetic (db/db) mice presented a changed gut microbiota composition, including an increased abundance of secondary BAs-producing bacteria, <i>Escherichia-Shigella</i>, and a decreased the abundance of <i>Akkermansia</i>, which are involved in the synthesis of non-12-OH BAs. We further found that the reduced BA types in db/db mice were negatively correlated with metabolic-disorder-related indicators, while an increased DCA level had the opposite correlation. Our results shed light into how the imbalance of BAs' metabolism mediated by intestinal flora may be potential mechanisms of T2D.