Hepatic Regenerative Medicine Exploiting the Liver's Will to Live

This Guest Editorial introduces this month's special Liver Pathobiology Theme Issue, a series of reviews that encompass the discipline of hepatic regenerative medicine

γ-Catenin at Adherens Junctions: Mechanism and Biologic Implications in Hepatocellular Cancer after β-Catenin Knockdown

Abstractβ-Catenin is important in liver homeostasis as a part of Wnt signaling and adherens junctions (AJs), while its aberrant activation is observed in hepatocellular carcinoma (HCC). We have reported hepatocyte-specific β-catenin knockout (KO) mice to lack adhesive defects as γ-catenin compensated at AJ. Because γ-catenin is a desmosomal protein, we asked if its increase in KO might deregulate desmosomes. No changes in desmosomal proteins or ultrastructure other than increased plakophilin-3 were observed. To further elucidate the role and regulation of γ-catenin, we contemplate an in vitro model and show γ-catenin increase in HCC cells upon β-catenin knockdown (KD). Here, γ-catenin is unable to rescue β-catenin/T cell factor (TCF) reporter activity; however, it sufficiently compensates at AJs as assessed by scratch wound assay, centrifugal assay for cell adhesion (CAFCA), and hanging drop assays. γ-Catenin increase is observed only after β-catenin protein decrease and not after blockade of its transactivation. γ-Catenin increase is associated with enhanced serine/threonine phosphorylation and abrogated by protein kinase A (PKA) inhibition. In fact, several PKA-binding sites were detected in γ-catenin by in silico analysis. Intriguingly γ-catenin KD led to increased β-catenin levels and transactivation. Thus, γ-catenin compensates for β-catenin loss at AJ without affecting desmosomes but is unable to fulfill functions in Wnt signaling. γ-Catenin stabilization after β-catenin loss is brought about by PKA. Catenin-sensing mechanism may depend on absolute β-catenin levels and not its activity. Anti-β-catenin therapies for HCC affecting total β-catenin may target aberrant Wnt signaling without negatively impacting intercellular adhesion, provided mechanisms leading to γ-catenin stabilization are spared

Disparate Cellular Basis of Improved Liver Repair in β-Catenin-Overexpressing Mice After Long-Term Exposure to 3,5-Diethoxycarbonyl-1,4-Dihydrocollidine

Administration of a hepatotoxic diet containing 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) induces biliary damage followed by hepatocyte injury, which is repaired through atypical ductular proliferation and oval cells and their subsequent differentiation to bile duct cells and hepatocytes. In this study, we examine whether excess β-catenin in transgenic (TG) mice would provide any reparative advantage in response to DDC. No differences in appearance or numbers of total A6-positive oval cells were observed after DDC administration. However, an increase in A6-positive “atypical hepatocytes” in the TG livers was observed after 14 and 28 days, coinciding with an increase in proliferating cell nuclear antigen-positive hepatocytes. Intriguingly, after chronic DDC administration for 150 days, a further increase in atypical hepatocytes was evident in TG mice, with higher numbers of proliferating cell nuclear antigen-positive hepatocytes exhibiting cytoplasmic/nuclear β-catenin and α-fetoprotein but not CK19, HNF1β, or Trop-2. Coincidently, we observed an improvement in intrahepatic cholestasis as seen by decreases in both serum bilirubin and alkaline phosphatase levels in TG mice, indicating an overall improvement in hepatic repair. TG mice exposed to DDC for 4 weeks followed by 2 days of normal chow showed decreases in alkaline phosphatase, atypical ductular proliferation, and periportal inflammation compared with wild-type animals, verifying improved biliary repair in TG livers. Thus, we report a potential role of β-catenin in liver repair, especially in enhancing the resolution of intrahepatic cholestasis after DDC injury