Epithelial Transforming Growth Factor-β Signaling Does Not Contribute to Liver Fibrosis but Protects Mice From Cholangiocarcinoma

Abstract

Background & aims: Transforming growth factor-β (TGFβ) exerts key functions in fibrogenic cells, promoting fibrosis development in the liver and other organs. In contrast, the functions of TGFβ in liver epithelial cells are not well understood, despite their high level of responsiveness to TGFβ. We sought to determine the contribution of epithelial TGFβ signaling to hepatic fibrogenesis and carcinogenesis.

Methods: TGFβ signaling in liver epithelial cells was inhibited by albumin-Cre-, K19-CreERT-, Prom1-CreERT2-, or AAV8-TBG-Cre-mediated deletion of the floxed TGFβ receptor II gene (Tgfbr2). Liver fibrosis was induced by carbon tetrachloride, bile duct ligation, or disruption of the multidrug-resistance transporter 2 gene (Mdr2). Hepatocarcinogenesis was induced by diethylnitrosamine or hepatic deletion of PTEN.

Results: Deletion of Tgfbr2 from liver epithelial cells did not alter liver injury, toxin-induced or biliary fibrosis, or diethylnitrosamine-induced hepatocarcinogenesis. In contrast, epithelial deletion of Tgfbr2 promoted tumorigenesis and reduced survival of mice with concomitant hepatic deletion of Pten, accompanied by an increase in tumor number and a shift from hepatocellular carcinoma to cholangiocarcinoma. Surprisingly, both hepatocyte- and cholangiocyte-specific deletion of Pten and Tgfbr2 promoted the development of cholangiocarcinoma, but with different latencies. The prolonged latency and the presence of hepatocyte-derived cholangiocytes after AAV8-TBG-Cre-mediated deletion of Tgfbr2 and Pten indicated that cholangiocarcinoma might arise from hepatocyte-derived cholangiocytes in this model. Pten deletion resulted in up-regulation of Tgfbr2, and deletion of Tgfbr2 increased cholangiocyte but not hepatocyte proliferation, indicating that the main function of epithelial TGFBR2 is to restrict cholangiocyte proliferation.

Conclusions: Epithelial TGFβ signaling does not contribute to the development of liver fibrosis or formation of hepatocellular carcinomas in mice, but restricts cholangiocyte proliferation to prevent cholangiocarcinoma development, regardless of its cellular origin.

Keywords: Liver Cancer; Mouse Model; Signal Transduction; TGFβ.