Bisphenol A induced hepatic steatosis by disturbing bile acid metabolism and FXR/TGR5 signaling pathways via remodeling the gut microbiota in CD-1 mice

Abstract

Dysregulation of gut microbiota-mediated bile acid (BA) metabolism plays an important role in the pathogenesis of hepatic steatosis and nonalcoholic fatty liver disease (NAFLD). Our previous studies found that bisphenol A (BPA) exposure induced hepatic steatosis and gut microbiota dysbiosis. However, whether the gut microbiota-dependent BA metabolism alterations were involved in BPA-induced hepatic steatosis remains unclear. Therefore, we explored the gut microbiota-related metabolic mechanisms of hepatic steatosis induced by BPA. Male CD-1 mice were exposed to low-dose BPA (50 μg/kg/day) for 6 months. Fecal microbiota transplantation (FMT) and broad-spectrum antibiotic cocktail (ABX) treatment were further adopted to test the role of gut microbiota in the adverse effects of BPA. We found that BPA induced hepatic steatosis in mice. Additionally, 16S rRNA gene sequencing showed that BPA reduced the relative abundance of Bacteroides, Parabacteroides and Akkermansia, which are associated with BA metabolism. Metabolomic analyses demonstrated that BPA significantly altered the ratio of conjugated to unconjugated BAs and increased the total level of taurine-α/β-muricholic acid while decreasing the level of chenodeoxycholic acid, thus inhibiting the activation of special receptors, including farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5), in the ileum and liver. The inhibition of FXR reduced short heterodimer partner and subsequently induced cholesterol 7α-hydroxylase and sterol regulatory element-binding protein-1c expression, which is related to hepatic BA synthesis and lipogenesis, eventually leading to liver cholestasis and steatosis. Furthermore, we found that mice that received FMT from BPA-exposed mice developed hepatic steatosis, and the influences of BPA on hepatic steatosis and FXR/TGR5 signaling pathways could be eliminated by ABX treatment, confirming the role of gut microbiota in BPA effects. Collectively, our study illustrates that suppressed microbiota-BA-FXR/TGR signaling pathways may be a potential mechanism for hepatic steatosis induced by BPA, providing a new target for the prevention of BPA-induced NAFLD.

Keywords: Bile acid; Bisphenol A; Farnesoid X receptor; Gut microbiota; Hepatic steatosis; Takeda G protein-coupled receptor 5.