Hepatocyte Nuclear Factor 4 alpha (HNF4α) Activation is Essential for Termination of Liver Regeneration
Hepatocyte Nuclear Factor 4 alpha (HNF4) is critical for hepatic differentiation. Recent studies have highlighted its role in inhibition of hepatocyte proliferation and tumor suppression. However, the role of HNF4 in liver regeneration is not known. We hypothesized that hepatocytes modulate HNF4 activity when navigating between differentiated and proliferative states during liver regeneration. Western blot analysis revealed a rapid decline in nuclear and cytoplasmic HNF4 protein levels accompanied with decreased target gene expression within 1 hour after 2/3 partial hepatectomy (post-PH) in C57BL/6J mice. HNF4 protein expression did not recover to the pre-PH levels until day 3. Hepatocyte-specific deletion of HNF4 (HNF4-KO) in mice resulted in 100% mortality post-PH despite increased proliferative marker expression throughout regeneration. Sustained loss of HNF4 target gene expression throughout regeneration indicated HNF4-KO mice were unable to compensate for loss of HNF4 transcriptional activity. Deletion of HNF4 resulted in sustained proliferation accompanied by c-myc and cyclin D1 over expression and a complete deficiency of hepatocyte function after PH. Interestingly, overexpression of degradation-resistant HNF4 in hepatocytes did not prevent initiation of regeneration after PH. Finally, AAV8-mediated reexpression of HNF4 in hepatocytes of HNF4-KO mice post-PH restored HNF4 protein levels, induced target gene expression and improved survival of HNF4-KO mice post-PH. In conclusion, these data indicate that HNF4 reexpression following initial decrease is critical for hepatocytes to exit from cell cycle and resume function during the termination phase of liver regeneration. These results reveal the role of HNF4 in liver regeneration and have implications for therapy of liver failure.