Z Gastroenterol 2014; 52 - P_1_39
DOI: 10.1055/s-0033-1360883

TGR5 (Gpbar-1) mediates cholangiocyte proliferation via ROS-Src-EGFR-ERK1/2 signaling

M Reich 1, A Sommerfeld 1, D Häussinger 1, V Keitel 1
  • 1Heinrich-Heine-University, Clinic for Gastroenterology, Hepatology and Infectious Diseases, Düsseldorf, Germany

Introduction: TGR5 (Gpbar-1) is a membrane-bound bile acid receptor, which is expressed in cholangiocytes. In biliary epithelial cells the activation of TGR5 via bile acids promotes chloride secretion, proliferation and protects the cells from apoptosis (Xia et al., WJG 2006; 12:3553 – 3563). Aim of this study was to determine the role of TGR5 for cholangiocyte proliferation and to elucidate the underlying signalling mechanisms.

Methods: Cholangiocytes were isolated from TGR5 knockout and wildtype mice. Cell proliferation was measured using a BrdU incorporation assay. Protein expression was investigated by western blotting. Reactive oxygen species (ROS) were measured using the cell permeant reagent 2', 7'-dichlorofluorescein diacetate (DCFDA).

Results: Activation of TGR5 by taurolithocholic acid or a TGR5 specific agonist increases cell proliferation in wildtype but not in knockout derived cholangiocytes. The TGR5-dependent cholangiocyte proliferation is accompanied by activation of ERK1/2 and sensitive towards the inhibition of MEK1/2. Furthermore, activation of TGR5 induces EGF shedding and subsequent tyrosin-phosphorylation of the EGFR at tyrosine residues 845 and 1045. In line with these findings, the TGR5 mediated cholangiocyte proliferation is sensitive to inhibition of matrix metalloproteinases, EGF receptor tyrosine kinases, as well as Src family kinases. Moreover, treatment of cholangiocytes with the Src-kinase inhibitor SU6656 reduces the TGR5-mediated phosphorylation of ERK1/2. ROS formation was observed in cholangiocytes after stimulation with different concentrations of bile acids and inhibition of ROS formation significantly reduced BrDU incorporation.

Discussion: The present study demonstrates that bile acids induce cholangiocyte proliferation in a TGR5 dependent manner. The TGR5-dependent proliferation is mediated by ROS formation which leads to cSrc-kinase mediated EGFR transactivation and subsequent ERK1/2 activation.