Differential responses of receptor tyrosine kinases C‐Met and EGFR in mice

Abstract

In previous studies, we have demonstrated the critical roles of EGFR and HGFR (c‐Met) for liver regeneration and for conversion of hepatocytes to cholangiocytes by a “clean” partial hepatectomy model, in which hepatocytes and cholangiocytes grow rapidly and synchronously. In contrast, the vast majority of liver diseases involve a prolonged pathologic duration, therefore multiple types of cells participate and play different roles in the variant stages. However, it is not fully understood how EGFR and Met play their roles in this complicated setting. In this study, we explore the role of MET and EGFR signaling pathways in biliary injury after common bile duct ligation. Mice with inhibition of EGFR signaling alone (EGFRi) showed abolished hepatocyte proliferation and biliary duct cell proliferation (Ki67 immunochemistry staining) at 2, 5, and 7 days after BDL. However, Met knockout mice (KO) showed increased proliferation of cholangiocytes at 2, 5, and 7 days. Met KO mice subjected to BDL surgery had an increase of the CK19‐ marked ductular reaction at 2, 5, and 7 days. In contrast, EGFRi mice showed a reduced ductular reaction at the same time point. There was enhanced immunohistochemistry for Sox9 in EGFRi mice, but absence of its expression in Met KO mice at 7 days post‐BDL. From western blot results of total liver tissue lysate, we found increased EpCAM expression after BDL at 7 days in Met KO but not in EGFRi mice. In addition, we also observed that both p‐Merlin and cleaved p‐Mst1, components of the Hippo pathway, decreased only in Met knockout mice. Mice with combined disruption of Met and EGFR signaling became very ill by 24 hours and died at 1 to 2 days after bile duct ligation. From Kaplan‐Meier analysis, both EGFR inhibition and Met knockout mice had decreased survival rates starting at 11 days, though the survival rate of Met KO mice was overall much better than EGFRi mice by around 40%. We also observed that p‐Ezrin (Thr567) was downregulated in either Met KO or EGFRi mice, while the total Ezrin expression did not change.ConclusionsOur study demonstrates that both c‐Met and EGFR control biliary response to bile duct ligation. The cholangiocyte responses, however, were very different between these two receptors. Their combined disruption led to acute liver failure and early death following bile duct ligation. The receptor tyrosine kinases c‐Met and EGFR may play different roles in the biliary injury‐repair responses, including proliferation, trans‐differentiation, and bi‐potential progenitor cells activation.