TGR5 (Gpbar–1) is expressed in cholangiocarcinomas and confers apopotosis resistance in isolated cholangiocytes

Cholangiocarcinomas (CCA) are malignancies of the biliary tract with limited treatment options. The molecular mechanisms leading to the development of CCA are unknown, however, chronic inflammation and elevated bile acid levels have been implicated in the pathogenesis of CCA. TGR5 is a membrane-bound bile acid receptor, which is expressed in cholangiocytes. Aim of the present study was to analyze the expression of TGR5 in CCA and to determine the role of TGR5 for cholangiocyte proliferation and apoptosis. Results: Liver tissue was collected from 18 patients undergoing liver resection for CCA (3 PSC patients). If possible two samples were taken from each liver: one within the macroscopically visible tumor (CCA) and one from the resection margin (control). TGR5 mRNA and protein expression were significantly higher in CCA as compared to control tissue. Impaired function of the CD95 receptor (CD95R) is one of the mechanisms by which CCA evade CD95-induced apoptosis. Phosphorylation of the CD95R at serine residues prevents apoptosis through intracellular retention of the receptor. CD95R serine phosphorylation was significantly higher in the CCA samples as compared to the control samples. To analyze if activation of TGR5 may induce CD95R serine phosphorylation, we stimulated mouse cholangiocytes with a TGR5 agonist (25µM), taurolithocholic acid (TLC, 25µM) or DMSO for 30 min. A significant increase in CD95R serine phosphorylation after bile acid/TGR5 agonist treatment was observed. Furthermore, incubation of murine cholangiocytes with TLC (25µM) led to a significantly higher BrDU incorporation in wildtype as compared to TGR5 knockout cells. Discussion / Conclusion: These findings suggest that activation of TGR5 may prevent CD95 ligand-mediated apoptosis through serine phosphorylation of the CD95 receptor, thereby promoting apoptosis resistance in CCA. Furthermore, the receptor may play a role in bile acid-dependent cholangiocyte proliferation.

Cholangiozyten - TGR5