Although the role of Wnt/beta-catenin signaling in liver growth and development is well established, its contribution in non-neoplastic hepatic pathologies has not been investigated. Here, we examine the role of beta-catenin in a murine model of diet-induced liver injury. Mice with hepatocyte-specific beta-catenin deletion (KO) and littermate controls were fed the steatogenic methionine and choline-deficient (MCD) diet or the corresponding control diet for 2 weeks and characterized for histological, biochemical, and molecular changes. KO mice developed significantly higher steatohepatitis and fibrosis on the MCD diet compared with wild-type mice. Both wild-type and KO livers accumulated triglyceride on the MCD diet but, unexpectedly, higher hepatic cholesterol levels were observed in KO livers on both control and MCD diets. Gene expression analysis showed that hepatic cholesterol accumulation in KO livers was not attributable to increased synthesis or uptake. KO mice had lower expression of bile acid synthetic enzymes but exhibited higher hepatic bile acid and serum bilirubin levels, suggesting defects in bile export. Therefore, loss of beta-catenin in the liver leads to defective cholesterol and bile acid metabolism in the liver and increased susceptibility to developing steatohepatitis in the face of metabolic stress.

Beta-catenin plays important roles in liver physiology and hepatocarcinogenesis. While studying the role of b-catenin in diet-induced steatohepatitis, we recently found that liverspecific b-catenin knockout (KO) mice exhibit intrahepatic cholestasis. This study was undertaken to further characterize the role of b-catenin in biliary physiology. KO mice and wild-type (WT) littermates were fed standard chow or a diet supplemented with 0.5% cholic acid for 2 weeks. Chow-fed KO mice had higher serum and hepatic total bile acid levels and lower bile flow rate than WT mice. Expression levels of bile acid biosynthetic genes were lower and levels of major bile acid exporters were similar, which therefore could not explain the KO phenotype. Despite loss of the tight junction protein claudin-2, KO mice had preserved functional integrity of tight junctions. KO mice had bile canalicular morphologic abnormalities as evidenced by staining for F-actin and zona occludens 1. Electron microscopy revealed dilated and tortuous bile canaliculi in KO livers along with decreased canalicular and sinusoidal microvilli. KO mice on a cholic acid diet had higher hepatic and serum bile acid levels, bile ductular reaction, increased pericellular fibrosis, and dilated, misshapen bile canaliculi. Compensatory changes in expression levels of several bile acid transporters and regulatory genes were found in KO livers. Conclusion: Liver-specific loss of b-catenin leads to defective bile canalicular morphology, bile secretory defect, and intrahepatic cholestasis. Thus, our results establish a critical role for b-catenin in biliary physiology. (HEPATOLOGY 2010;52:1410-1419 B eta-catenin, the primary effector of the canonical Wnt signaling pathway, plays critical roles in hepatocarcinogenesis and liver development. [1][2][3][4][5][6] However, its role in adult liver physiology is not well understood. Cytoplasmic levels and localization of bcatenin are tightly regulated (reviewed in MacDonald et al. 7 ). In the absence of Wnt signaling, b-catenin is bound in the cytoplasm by a multiprotein complex. Phosphorylation via the action of glycogen synthase kinase 3b and casein kinase 1 targets b-catenin for proteasomal degradation. In the presence of Wnt ligands, bcatenin remains unphosphorylated, translocates to the nucleus, and activates transcription of its target genes by binding to T cell factor/lymphoid-enhancing factor family of transcriptional activators. Through its association with E-cadherin at the cell membrane, where it links cadherins to the actin cytoskeleton, b-catenin also plays an important role in the formation of adherens junctions (reviewed in Hartsock and Nelson 8 ).We recently showed that liver-specific b-catenin knockout (KO) mice have increased susceptibility to developing

The liver plays a central role in ethanol metabolism and oxidative stress is implicated in alcohol-mediated liver injury. β-Catenin regulates hepatic metabolic zonation and adaptive response to oxidative stress. We hypothesized that β-catenin regulates the hepatic response to ethanol ingestion. Female liver-specific β-catenin knockout (KO) mice and wild type (WT) littermates were fed the Lieber-Decarli liquid diet (5% ethanol) in a pair-wise fashion. Liver histology, biochemistry, and gene expression studies were performed. Plasma alcohol and ammonia levels were measured using standard assays. Ethanol-fed KO mice exhibited systemic toxicity and early mortality. KO mice exhibited severe macrovesicular steatosis and five to six-fold higher serum ALT and AST levels. KO mice had modest increase in hepatic oxidative stress, lower expression of mitochondrial superoxide dismutase (SOD-2), and lower citrate synthase activity, the first step in the tricarboxylic acid cycle. N-Acetyl cysteine (NAC) did not prevent ethanol-induced mortality in KO mice. In WT livers, β-catenin was found to co-precipitate with FoxO3, the upstream regulator of SOD-2. Hepatic alcohol dehydrogenase and aldehyde dehydrogenase activities and expression were lower in KO mice. Hepatic cytochrome P450 2E1 protein levels were upregulated in ethanol-fed WT mice but were nearly undetectable in KO mice. These changes in ethanol-metabolizing enzymes were associated with 30-fold higher blood alcohol levels in KO mice. Conclusion β-catenin is essential for hepatic ethanol metabolism and plays a protective role in alcohol-mediated liver steatosis. Our results strongly suggest that integration of these functions by β-catenin is critical for adaptation to ethanol ingestion in vivo.