The Bile Acid Metabolism And Signaling In Diabetic Encephalopathy Mice

Purposes Bile acid(BA)metabolism and signaling have been suggested to play a critical role in the pathogenesis of various metabolic diseases,such as diabetes,obesity,and cholelithiasis.Diabetic encephalopathy is a complicated metabolic disease with central neuropathy and functional cerebral impairment.However,whether BA metabolism and signaling are altered in this disease remains unknown.The purpose of the present project was to evaluate the BA metabolism and signaling during the development of diabetic encephalopathy.Moreover,there were reports indicating that diabetes could impair the vagal nerve.Thus,we also tried to identify the role of the vagal nerve in BA metabolism and signaling for exploring the potential therapeutic target of diabetic encephalopathy.Methods A simple and valid LC-MS method was established to quantify BAs in biological tissues and fluids.The animal model of diabetic encephalopathy was achieved by feeding a high-fat diet with a single intraperitoneal injection of streptozotocin.Based on the serum glucose levels and behavior test results,the mice were divided into four groups representing different disease stages,namely normal control(NC),high-fat diet(HFD),diabetes without cognitive dysfunction(unDCD),and diabetes with cognitive dysfunction(DCD).The BA concentrations in liver and intestine,the cecal microbiota,as well as the expression of genes involved in BA homeostasis were systematically evaluated.To further evaluate how the brain regulates BA metabolism,subdiaphragmatic vagotomy(SDV)was performed in rats and the BA homeostasis was investigated.Results Total BAs in liver and intestine were both increased in unDCD and DCD(with statistically significance)groups compared with NC group.In contrast,the BA levels of HFD group remained unchanged in both liver and intestine compared with NC group.BA efflux transporters(Ost?,Ost?,and Mrp4)in livers of DCD mice were increased due to the feedback regulation of the increased BA concentrations in the liver.BA synthetic enzymes(Cyp7a1,Cyp8b1,Cyp7b1 and Cyp27a1)were all decreased in livers of DCD mice.Fxr-Fgf15 signaling was activated in the intestine of DCD mice,which might contribute to the suppression of Cyp7a1 in the liver.The total bacterial content in cecal contents were significantly reduced in DCD mice.Thecompositions of Bacteroidetes,Tenericutes,and ?-Proteobacteria were markedly decreased in DCD mice.The mRNA expressions of Asbt,Ost? and Ost? in the intestine were significantly increased.The decrease of Bacteroidetes and up-regulation of BA transporters in the enterocyte might be the reason why the conjugated BAs(C-BAs)were significantly increased in the liver.Interestingly,tetra-hydroxyl BAs in the liver were almost diminished in unDCA and DCD groups compared with NC mice,which was associated with the down-regulation of Cyp3a11 expression.Sult2a1 mRNA was markedly increased in unDCD and DCD mice,suggesting that BA sulfation may become a major pathway to detoxify BAs during the development of DCD.SDV increased both the unconjugated and secondary BAs in bile,serum and livers of rats,leading to an increase in hydrophobicity.SDV also caused the increased bile flow in rats.The gene expressions of synthetic enzymes Cyp7a1 and Cyp8b1 were decreased in SDV rats.Intestinal Fxr-Fgf15 signaling was activated in SDV rats.Moreover,intestinal BA transporter Asbt was suppressed due to the activated Fxr-Shp signaling.In addition,the tight junction proteins Claudin-5 and Occludin were decreased in the intestine membrane,suggesting that the increased unconjugated BAs(U-BAs)in blood and bile might be due to the increased intestinal permeability.Conclusions Our study demonstrates that intestinal bacteria were altered in DCD mice,leading to increased BA absorption from intestine to liver and activated Fxr-Fgf15 signaling in the intestine.The vagal nerve participates in the regulation of BA metabolism and signaling.The current findings on BA metabolism and signaling in DCD mice and vagotomy rats provide new insights into the pathogenesis and therapeutic treatments of diabetic encephalopathy.