TGR5 knockout mice are highly susceptible to LCA induced liver damage

Introduction:

TGR5 (Gpbar-1) is a G-Protein-coupled membrane-bound cell surface-receptor for bile acids associated not only with the regulation of bile acid homeostasis, but also with the suppression of macrophage activity (1,2). It is expressed in several different organs and cell types, e.g. nonparenchymal liver cells and monocytes/macrophages. Thereby, TGR5 can function as a mediator for bile acids in modulating different pathologies of the liver distinguished by inflammatory processes (1,2). Lithocholic acid (LCA) is a hydrophobic bile acid with toxic properties produced by intestinal bacteria. Feeding of a diet containing 1% LCA leads to intrahepatic cholestasis, inflammation and toxic liver damage in mice (3,4). The role of TGR5 during this process is yet to be determined.

Methods:

8 – 12 week old mice with a TGR5 KO and WT genotype were sacrificed after feeding with a diet containing 1% LCA (lithocholic acid) for 4 days. Bile acid composition and concentration in serum and bile was determined. Serum analysis of liver enzymes and bilirubin was done using the Spotchem-biochemical analyzer. Depiction of the liver was performed utilising HE (hematoxylin-eosin) as well as immunohistochemical staining for proliferation and inflammatory markers. The mRNA levels of proinflammatory cytokines in the liver were determined by realtime-PCR.

Results:

As indicated by the sizes of necrotic areas in HE-staining and significantly higher elevated serum AST and bilirubin-levels, TGR5 KO mice were suffering from a more severe liver damage as compared to their wildtype littermates after being fed a diet containing 1% LCA for 4 days. The observed liver necrosis triggered by LCA was accompanied by an increase in mRNA of cytokines and chemokines. Furthermore, the TGR5 KO mice had a considerably enlarged bile acid pool with an altered serum bile acid composition. Proliferation of hepatocytes and cholangiocytes was significantly reduced in absence of TGR5 as determined by immunohistochemical staining for PCNA and Ki67.

Conclusion:

In conclusion TGR5 knockout mice suffer from more severe liver damage and also show reduced proliferative response after liver injury. This demonstrates a protective role of TGR5 in LCA-induced intrahepatic cholestasis.

References:

[1] Kawamata Y, Fujii R, Hosoya M, Harada M, Yoshida H, Miwa M, et al. A G protein-coupled receptor responsive to bile acids. J Biol Chem 2003;278:9435 – 9440.

[2] Duboc H, Taché Y, Hofmann AF. The bile acid TGR5 membrane receptor: From basic research to clinical application. Digestive and Liver Disease 2014, Pages 302 – 312

[3] Woolbright BL, Li F, Xie Y, Farhood A, Fickert P, Trauner M, Jaeschke H. Lithocholic acid feeding results in direct hepato-toxicity independent of neutrophil function in mice. Toxicol Lett. 2014 Jul 3;228(1):56 – 66.

[4] Fickert P, Fuchsbichler A, Marschall HU, Wagner M, Zollner G, Krause R, Zatloukal K, Jaeschke H, Denk H, Trauner M. Lithocholic acid feeding induces segmental bile duct obstruction and destructive cholangitis in mice. Am J Pathol. 2006 Feb;168(2):410 – 22

Corresponding author: Klindt, Caroline

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