Ian Huck1, Sumedha Gunewardena2, Regina Espanol-Suner3, Holger Willenbring3,4,5, Udayan Apte1. 1. Department of Pharmacology, Toxicology and Therapeutics, University of Kansas Medical Center, Kansas City, KS. 2. Department of Biostatistics, University of Kansas Medical Center, Kansas City, KS. 3. Eli and Edythe Broad Center of Regeneration Medicine and Stem Cell Research, University of California San Francisco, San Francisco, CA. 4. Liver Center, University of California San Francisco, San Francisco, CA. 5. Department of Surgery, Division of Transplantation, University of California San Francisco, San Francisco, CA.
Abstract
Hepatocyte nuclear factor 4 alpha (HNF4α) is critical for hepatic differentiation. Recent studies have highlighted its role in inhibition of hepatocyte proliferation and tumor suppression. However, the role of HNF4α in liver regeneration (LR) is not known. We hypothesized that hepatocytes modulate HNF4α activity when navigating between differentiated and proliferative states during LR. Western blotting analysis revealed a rapid decline in nuclear and cytoplasmic HNF4α protein levels, accompanied with decreased target gene expression, within 1 hour after two-thirds partial hepatectomy (post-PH) in C57BL/6J mice. HNF4α protein expression did not recover to pre-PH levels until day 3. Hepatocyte-specific deletion of HNF4α (HNF4α-KO [knockout]) in mice resulted in 100% mortality post-PH, despite increased proliferative marker expression throughout regeneration. Sustained loss of HNF4α target gene expression throughout regeneration indicated that HNF4α-KO mice were unable to compensate for loss of HNF4α transcriptional activity. Deletion of HNF4α resulted in sustained proliferation accompanied by c-Myc and cyclin D1 overexpression and a complete deficiency of hepatocyte function after PH. Interestingly, overexpression of degradation-resistant HNF4α in hepatocytes delayed, but did not prevent, initiation of regeneration after PH. Finally, adeno-associated virus serotype 8 (AAV8)-mediated reexpression of HNF4α in hepatocytes of HNF4α-KO mice post-PH restored HNF4α protein levels, induced target gene expression, and improved survival of HNF4α-KO mice post-PH. Conclusion: In conclusion, these data indicate that HNF4α reexpression following initial decrease is critical for hepatocytes to exit from cell cycle and resume function during the termination phase of LR. These results indicate the role of HNF4α in LR and have implications for therapy of liver failure.
Hepatocyte nuclear factor 4 alpha (HNF4α) is critical for hepatic differentiation. Recent studies have highlighted its role in inhibition of hepatocyte proliferation and tumor suppression. However, the role of HNF4α in liver regeneration (LR) is not known. We hypothesized that hepatocytes modulate HNF4α activity when navigating between differentiated and proliferative states during LR. Western blotting analysis revealed a rapid decline in nuclear and cytoplasmic HNF4α protein levels, accompanied with decreased target gene expression, within 1 hour after two-thirds partial hepatectomy (post-PH) in C57BL/6J mice. HNF4α protein expression did not recover to pre-PH levels until day 3. Hepatocyte-specific deletion of HNF4α (HNF4α-KO [knockout]) in mice resulted in 100% mortality post-PH, despite increased proliferative marker expression throughout regeneration. Sustained loss of HNF4α target gene expression throughout regeneration indicated that HNF4α-KO mice were unable to compensate for loss of HNF4α transcriptional activity. Deletion of HNF4α resulted in sustained proliferation accompanied by c-Myc and cyclin D1 overexpression and a complete deficiency of hepatocyte function after PH. Interestingly, overexpression of degradation-resistant HNF4α in hepatocytes delayed, but did not prevent, initiation of regeneration after PH. Finally, adeno-associated virus serotype 8 (AAV8)-mediated reexpression of HNF4α in hepatocytes of HNF4α-KO mice post-PH restored HNF4α protein levels, induced target gene expression, and improved survival of HNF4α-KO mice post-PH. Conclusion: In conclusion, these data indicate that HNF4α reexpression following initial decrease is critical for hepatocytes to exit from cell cycle and resume function during the termination phase of LR. These results indicate the role of HNF4α in LR and have implications for therapy of liver failure.
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