Role of HNF4alpha-cMyc Interaction in CDE-diet Induced Liver Injury and Regeneration
BackgroundHepatocyte nuclear factor 4 alpha (HNF4) is a nuclear factor essential for liver function and regeneration. HNF4 negatively regulates the expression of cMyc, which plays an important role in proliferation and differentiation during liver regeneration. This study investigated the role of HNF4-cMyc interaction in regulating liver injury and regeneration using the choline-deficient and ethionine-supplemented (0.15%) (CDE) diet feeding model, which exhibits characteristics of chronic liver diseases including liver injury, inflammation, early fibrotic changes along with hepatocyte and biliary epithelial cell regeneration, and activation of hepatic progenitor cells (HPC). MethodsWild-type (WT), hepatocyte-specific knockout of HNF4 (HNF4-KO), cMyc (cMyc-KO), and HNF4-cMyc double knockout (DKO) mice were fed a CDE diet for one week to induce subacute liver injury. To study regeneration and recovery, mice were fed a one-week CDE diet followed by a one-week recovery period on a normal chow diet. ResultsWT mice showed significant liver injury and decreased HNF4 mRNA and protein expression after one week of a CDE diet. WT mice also showed an increase in markers of proliferation and HPC activation, but no major change in markers of inflammation or fibrosis. The HNF4-KO mice exhibited baseline hepatomegaly, which significantly declined during the recovery period. HNF4 deletion resulted in significantly higher injury compared to WT mice after one week of CDE diet feeding but similar recovery. Markers of inflammation, fibrosis, proliferation, and HPC activation were significantly higher in HNF4-KO mice during the injury period but declined during the recovery period. The cMyc-KO mice showed increased injury after one week of the CDE diet, but it was substantially lower than the WT and HNF4-KO mice. Deletion of cMyc resulted in a significant activation of inflammatory genes higher than in the WT and HNF4-KO mice. Whereas fibrosis and proliferation markers increased in cMyc-KO mice, they were substantially lower than in HNF4-KO mice and similar to WT mice. cMyc-KO also showed an increase in HPC markers following one week of CDE-induced injury. Deletion of both HNF4 and cMyc in DKO mice resulted in significant liver injury comparable to the HNF4-KO mice after one week of CDE diet feeding, but led to complete recovery. Markers of inflammation, fibrosis, and proliferation increased after CDE diet feeding, were higher than WT mice, and comparable to HNF4-KO mice. Interestingly, DKO mice showed a significant increase in HPC markers both following one week of CDE-induced injury and after one week of recovery. ConclusionsThese data indicate that deletion of HNF4 increases and deletion of cMyc decreases subacute liver injury induced by a one week CDE diet feeding. Deletion of HNF4 results in increased inflammation, fibrosis, proliferation, and HPC activation, all of which except inflammation are reduced following cMyc deletion. Simultaneous deletion of HNF4 and cMyc results in a phenotype similar to HNF4 deletion but with higher HPC activation. Taken together, these data show that HNF4 protects against inflammatory and fibrotic change following CDE diet-induced injury, which is driven by cMyc.