int-777 and Diabetes-Mellitus--Type-2

Bile acids are ligands for the nuclear hormone receptor farnesoid X receptor (FXR) and the G protein-coupled receptor TGR5. We have shown that FXR and TGR5 have renoprotective roles in diabetes- and obesity-related kidney disease. Here, we determined whether these effects are mediated through differential or synergistic signaling pathways. We administered the FXR/TGR5 dual agonist INT-767 to DBA/2J mice with streptozotocin-induced diabetes, db/db mice with type 2 diabetes, and C57BL/6J mice with high-fat diet-induced obesity. We also examined the individual effects of the selective FXR agonist obeticholic acid (OCA) and the TGR5 agonist INT-777 in diabetic mice. The FXR agonist OCA and the TGR5 agonist INT-777 modulated distinct renal signaling pathways involved in the pathogenesis and treatment of diabetic nephropathy. Treatment of diabetic DBA/2J and db/db mice with the dual FXR/TGR5 agonist INT-767 improved proteinuria and prevented podocyte injury, mesangial expansion, and tubulointerstitial fibrosis. INT-767 exerted coordinated effects on multiple pathways, including stimulation of a signaling cascade involving AMP-activated protein kinase, sirtuin 1, PGC-1

Topics: Albuminuria; Animals; Bile Acids and Salts; Chenodeoxycholic Acid; Cholesterol; Cholic Acids; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Diabetic Nephropathies; Disease Progression; Endoplasmic Reticulum Stress; Fibrosis; Glomerular Mesangium; Humans; Kidney Tubules; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mitochondria; Obesity; Oxidative Stress; Podocytes; Receptors, Cytoplasmic and Nuclear; Receptors, G-Protein-Coupled; RNA, Messenger; Signal Transduction; Triglycerides

The physiological role of the TGR5 receptor in the pancreas is not fully understood. We previously showed that activation of TGR5 in pancreatic β cells by bile acids induces insulin secretion. Glucagon released from pancreatic α cells and glucagon-like peptide 1 (GLP-1) released from intestinal L cells regulate insulin secretion. Both glucagon and GLP-1 are derived from alternate splicing of a common precursor, proglucagon by PC2 and PC1, respectively. We investigated whether TGR5 activation in pancreatic α cells enhances hyperglycemia-induced PC1 expression thereby releasing GLP-1, which in turn increases β cell mass and function in a paracrine manner. TGR5 activation augmented a hyperglycemia-induced switch from glucagon to GLP-1 synthesis in human and mouse islet α cells by GS/cAMP/PKA/cAMP-response element-binding protein-dependent activation of PC1. Furthermore, TGR5-induced GLP-1 release from α cells was via an Epac-mediated PKA-independent mechanism. Administration of the TGR5 agonist, INT-777, to db/db mice attenuated the increase in body weight and improved glucose tolerance and insulin sensitivity. INT-777 augmented PC1 expression in α cells and stimulated GLP-1 release from islets of db/db mice compared with control. INT-777 also increased pancreatic β cell proliferation and insulin synthesis. The effect of TGR5-mediated GLP-1 from α cells on insulin release from islets could be blocked by GLP-1 receptor antagonist. These results suggest that TGR5 activation mediates cross-talk between α and β cells by switching from glucagon to GLP-1 to restore β cell mass and function under hyperglycemic conditions. Thus, INT-777-mediated TGR5 activation could be leveraged as a novel way to treat type 2 diabetes mellitus.

Topics: Animals; Benzene Derivatives; Benzenesulfonates; Cell Line; Cholic Acids; Cyclic AMP-Dependent Protein Kinases; Diabetes Mellitus, Experimental; Diabetes Mellitus, Type 2; Estrenes; Gene Expression Regulation; Glucagon-Like Peptide 1; Glucagon-Secreting Cells; Glucose; Homeostasis; Humans; Insulin Resistance; Insulin-Secreting Cells; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Paracrine Communication; Proprotein Convertase 1; Proprotein Convertase 2; Pyrrolidinones; Receptors, G-Protein-Coupled; Signal Transduction; Sulfones