Pancreatic islets were isolated from 90-day-old male mice. Insulin secretion was measured by radioimmunoassay, protein phosphorylation by western blot, Ca2 + signals by fluorescence microscopy and ATP-dependent K+ (KATP) channels by electrophysiology.
TUDCA dose-dependently increased GSIS in fresh islets at stimulatory glucose concentrations but remained without effect at low glucose levels. This effect was not associated with changes in glucose metabolism, Ca2 + signals or KATP channel activity; however, it was lost in the presence of a cAMP competitor or a PKA inhibitor. Additionally, PKA and CREB phosphorylation were observed after 1-hour incubation with TUDCA. The potentiation of GSIS was blunted by the Gα stimulatory, G protein subunit-specific inhibitor NF449 and mimicked by the specific TGR5 agonist INT-777, pointing to the involvement of the bile acid G protein-coupled receptor TGR5.
Our data indicate that TUDCA potentiates GSIS through the cAMP/PKA pathway.