Dual catenin loss in murine liver causes tight junctional deregulation and progressive intrahepatic cholestasis

ABSTRACT

β-Catenin, the downstream effector of the Wnt signaling, plays important roles in hepatic development, regeneration and tumorigenesis. However, its role at hepatocyte adherens junctions (AJ) is relatively poorly understood, chiefly due to spontaneous compensation by γ-catenin. Here, we simultaneously ablate β- and γ-catenin expression in mouse liver by interbreeding β-catenin-γ-catenin double-floxed mice and albumin-cre transgenic mice. Double knockout mice (DKO) show failure to thrive, impaired hepatocyte differentiation, cholemia, ductular reaction, progressive cholestasis, inflammation, fibrosis and tumorigenesis, which was associated with deregulation of tight junctions (TJ) and bile acid transporters, leading to early morbidity and mortality, a phenotype reminiscent of Progressive Familial Intrahepatic Cholestasis (PFIC). To address the mechanism, we specifically and temporally eliminated both catenins from hepatocytes using adeno-associated virus-8 carrying cre-recombinase under the thyroid-binding globulin promoter (AAV8-TBG-Cre). This led to a time-dependent breach of blood bile barrier associated with sequential disruption of AJ and TJ verified by ultrastructural imaging and intravital microscopy, which revealed unique para-cellular leaks around individual hepatocytes allowing mixing of blood and bile, and leakage of blood from one sinusoid to another. Molecular analysis identified sequential losses of E-cadherin, occludin, claudin-3 and claudin-5 due to enhanced proteasomal degradation, and of claudin-2, a β-catenin transcriptional target, which was also validated in vitro. In conclusion, we report partially redundant function of catenins at AJ in regulating TJ and contributing to blood bile barrier. Furthermore, concomitant hepatic loss of β- and γ-catenin disrupts structural and functional integrity of AJ and TJ via transcriptional and posttranslational mechanisms. Mice with dual catenin loss develop progressive intrahepatic cholestasis, and hence provides a unique model to study diseases like PFIC. This article is protected by copyright. All rights reserved.

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