Wnt/β-Catenin Signaling Protects Mouse Liver against Oxidative Stress-induced Apoptosis through the Inhibition of Forkhead Transcription Factor FoxO3

Numerous liver diseases are associated with extensive oxidative tissue damage. It is well established that Wnt/beta-catenin signaling directs multiple hepatocellular processes, including development, proliferation, regeneration, nutrient homeostasis, and carcinogenesis. It remains unexplored whether Wnt/beta-catenin signaling provides hepatocyte protection against hepatotoxin-induced apoptosis. Conditional, liver-specific beta-catenin knockdown (KD) mice and their wild-type littermates were challenged by feeding with a hepatotoxin 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet to induce chronic oxidative liver injury. Following the DDC diet, mice with beta-catenin-deficient hepatocytes demonstrate increased liver injury, indicating an important role of beta-catenin signaling for liver protection against oxidative stress. This finding was further confirmed in AML12 hepatocytes with beta-catenin signaling manipulation in vitro using paraquat, a known oxidative stress inducer. Immunofluorescence staining revealed an intense nuclear FoxO3 staining in beta-catenin-deficient livers, suggesting active FoxO3 signaling in response to DDC-induced liver injury when compared with wild-type controls. Consistently, FoxO3 target genes p27 and Bim were significantly induced in beta-catenin KD livers. Conversely, SGK1, a beta-catenin target gene, was significantly impaired in beta-catenin KD hepatocytes that failed to inactivate FoxO3. Furthermore, shRNA-mediated deletion of FoxO3 increased hepatocyte resistance to oxidative stress-induced apoptosis, confirming a proapoptotic role of FoxO3 in the stressed liver. Our findings suggest that Wnt/beta-catenin signaling is required for hepatocyte protection against oxidative stress-induced apoptosis. The inhibition of FoxO through its phosphorylation by beta-catenin-induced SGK1 expression reduces the apoptotic function of FoxO3, resulting in increased hepatocyte survival. These findings have relevance for future therapies directed at hepatocyte protection, regeneration, and anti-cancer treatment.