Cardiomyocyte-targeted overexpression of the coxsackie–adenovirus receptor causes a cardiomyopathy in association with β-catenin signaling

Abstract 

The coxsackie–adenovirus receptor (CAR) is an adhesion molecule found at the intercalated disc of cardiomyocytes in association with other adherens and tight junction proteins. CAR expression is increased at cardiomyocyte junctions in patients with heart failure. It is not known what contribution elevated CAR expression makes to cardiac pathology. We generated a binary transgenic mouse enabling cardiac-restricted doxycycline-regulated expression of Flag-tagged murine CAR (mCAR⁺/αMtTA⁺ mice). Myocardial CAR levels were increased 6-fold in mCAR⁺/αMtTA⁺ mice, localizing to intercalated discs and sarcolemma. Well at birth, mCAR⁺/αMtTA⁺ mice developed a severe cardiomyopathy and died by 4weeks. Cardiomyocyte hypertrophy was evident at 1week, with increased heart:body weight ratios by 3weeks. Disorganization and degeneration of cardiomyocytes were evident with disrupted adherens junctions. Doxycycline administration turned off transgene expression and rescued mice from the development of the cardiomyopathic phenotype. In CAR-overexpressing mCAR⁺/αMtTA⁺ mice, adherens junction proteins were abnormally expressed. N-cadherin protein levels were 83% lower in mCAR⁺/αMtTA⁺ hearts vs controls at 1week, with levels subsequently increased above controls at 3weeks. β-catenin expression was 90% and 135% above controls at 1 and 3weeks, respectively. Nuclear translocation of β-catenin in cardiomyocytes of mCAR⁺/αMtTA⁺ mice was associated with increased c-myc RNA, a target of active β-catenin known to be associated with cardiac hypertrophy. Our study is the first to demonstrate that increased CAR expression can induce a cardiomyopathy and supports a model whereby the pathogenesis is determined by CAR stimulated β-catenin signaling, and/or disruption of the adherens junction.

Abbreviations: CAR, coxsackie–adenovirus receptor, DCM, dilated cardiomyopathy, CVB, coxsackievirus group B, mCAR, murine CAR, β-gal, β-galactosidase, tTA, tetracycline transactivator, PBS, phosphate buffered saline, αMHC, α-myosin heavy chain, αMtTa, α-myosin heavy chain (αMHC) promoter-driven tTA, CSA, cardiomyocyte cross-sectional area, Ab(s), antibody (antibodies), MDTF, Mus dunni tail fibroblast, ZO-1, zona occludens-1, GSK3β, glycogen synthase kinase-3β, Tcf/Lef, T cell-factor/lymphoid-enhancer-factor.

Keywords: Cardiomyopathy, Coxsackie–adenovirus receptor, Beta-catenin, Cadherin, Akt