TGR5 (Gpbar-1) expression is downregulated in biliary epithelial cells in livers of PSC patients and in Abcb4-/- mice

Introduction Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease characterized by progressive inflammatory and fibrotic injury to the biliary tree. The localization of TGR5 in cholangiocytes and immune cells, the choleretic, and anti-inflammatory functions of the receptor suggest that TGR5 is important for the pathogenesis of biliary diseases. Aim of this study was to evaluate changes in TGR5 expression and localization in livers from PSC patients as well as from Abcb4-/- mice, which serve as an animal model for sclerosing cholangitis.

Methods TGR5 expression and localization in livers from PSC patients and Abcb4-/- animals were evaluated using immunofluorescence staining. TGR5 mRNA expression was analyzed in isolated intrahepatic and extrahepatic bile ducts from Abcb4-/- mice and WT controls by real-time PCR in relation to an endogenous housekeeping control. BECs (biliary epithelial cells) were isolated by microdissection or by FACS using positive selection for EpCAM from livers of 6-8 weeks-old animals. Abcb4-/- mice with genetic overexpression of TGR5 (Abcb4-/-/Tgr5-Tg) were generated and serum biochemistry as well as liver histology and immunohistochemistry were assessed.

Results Reduced TGR5 staining intensity was detected in BECs from liver tissue of PSC patients as well as in BECs of Abcb4-/- mice. This downregulation was not observed in BECs in liver tissue from PBC, NAFLD or viral hepatitis patients. No downregulation in TGR5 fluorescence intensity was observed in F4/80- and CD68-positive intrahepatic macrophages in Abcb4-/- livers. Analysis of isolated intrahepatic and extrahepatic bile ducts as well as in EpCAM+-enriched cells showed a significant decrease in TGR5 mRNA in Abcb4-/- mice as compared to the controls. Genetic overexpression of TGR5 in livers from Abcb4-/-/Tgr5-Tg mice improved serum liver enzymes and biliary fibrosis compared to Abcb4-/- mice.

Conclusion TGR5 levels were significantly and specifically downregulated in bile ducts from PSC livers. Moreover, a significant reduction of TGR5 mRNA was detected in intrahepatic and extrahepatic bile ducts as well as in isolated BECs from Abcb4-/- mice livers. Genetic overexpression of TGR5 ameliorates the biliary fibrosis phenotype of Abcb4-/- mice.

Publication History

Article published online:
04 January 2021