The Expression of Bile Acid Receptor TGR5 in Adipose Tissue in Diet-Induced Obese Mice

Abstract

Bile acids are significant physiological factors for digestion, solubilization, absorption, toxic metabolites and xenobiotics. In addition, bile acids are responsible of signal transduction as well as metabolic regulation that activate several receptors such as farnesoid X receptor (FXR) and the membrane G-protein receptor 5 (TGR5). Activation of TGR5 by bile acids is associated with prevention of obesity as well as ameliorating the resistance to insulin via increasing energy expenditure. The objective of this research is to investigate TGR5 gene expression level in different fat depots including visceral or epididymal adipose tissue (eWAT), brown adipose tissue and inguinal adipose tissue (iWAT) and to study the response of TGR5 gene expression to the antiobesity treatment (SFN). Three groups of male CD1 mice were used in this study; lean group fed with SCD, DIO mice on HFD and DIO obese mice treated with anti-obesity treatment. Body weight (BW) and phenotype data were evaluated by weekly including blood samples for analysis of glucose, insulin, leptin, triglycerides (TG). Total RNA was extracted from different fat depots and RT-PCR profiler array technology was used to in order to assess the mRNA expression of TGR5 and leptin. There was significant downregulation of TGR5 gene expression level in obese (DIO) mice and remarkable upregulation of TGR5 gene expression after successful weight loss in DIO mice treated with SFN in time dependent manner at 1 weeks and 4 weeks of ip applications. In conclusion, obesity is associated with decrease in expression of TGR5 in different fat depots and treatment with anti-obesity drug (Sulforaphane) causes stepwise upregulation of TGR5 gene expression in epididymal white adipose tissue parallel stepwise decrease in body weight. Increase of expression of TGR5 in DIO mice in eWAT is accompanied by improvement in glucose homeostasis and insulin action.