Activation of transmembrane bile acid receptor TGR5 stimulates insulin secretion in pancreatic β cells

DP Kumar, S Rajagopal, S Mahavadi, F Mirshahi… - Biochemical and …, 2012 - Elsevier
DP Kumar, S Rajagopal, S Mahavadi, F Mirshahi, JR Grider, KS Murthy, AJ Sanyal
Biochemical and biophysical research communications, 2012Elsevier
Bile acids act as signaling molecules and stimulate the G protein coupled receptor, TGR5, in
addition to nuclear farnesoid X receptor to regulate lipid, glucose and energy metabolism.
Bile acid induced activation of TGR5 in the enteroendocrine cells promotes glucagon like
peptide-1 (GLP-1) release, which has insulinotropic effect in the pancreatic β cells. In the
present study, we have identified the expression of TGR5 in pancreatic β cell line MIN6 and
also in mouse and human pancreatic islets. TGR5 selective ligands, oleanolic acid (OA) and …
Bile acids act as signaling molecules and stimulate the G protein coupled receptor, TGR5, in addition to nuclear farnesoid X receptor to regulate lipid, glucose and energy metabolism. Bile acid induced activation of TGR5 in the enteroendocrine cells promotes glucagon like peptide-1 (GLP-1) release, which has insulinotropic effect in the pancreatic β cells. In the present study, we have identified the expression of TGR5 in pancreatic β cell line MIN6 and also in mouse and human pancreatic islets. TGR5 selective ligands, oleanolic acid (OA) and INT-777 selectively activated Gαs and caused an increase in intracellular cAMP and Ca2+. OA and INT-777 also increased phosphoinositide (PI) hydrolysis and the increase was blocked by NF449 (a selective Gαs inhibitor) or U73122 (PI hydrolysis inhibitor). OA, INT-777 and lithocholic acid increased insulin release in MIN6 and human islets and the increase was inhibited by treatment with NF449, U73122 or BAPTA-AM (chelator of calcium), but not with myristoylated PKI (PKA inhibitor), suggesting that the release is dependent on Gs/cAMP/Ca2+ pathway. 8-pCPT-2′-O-Me-cAMP, a cAMP analog, which activates Epac, but not PKA also stimulated PI hydrolysis. In conclusion, our study demonstrates that the TGR5 expressed in the pancreatic β cells regulates insulin secretion and highlights the importance of ongoing therapeutic strategies targeting TGR5 in the control of glucose homeostasis.
Elsevier