Coxsackievirus and adenovirus receptor (CAR) mediates atrioventricular-node function and connexin 45 localization in the murine heart
Byung-Kwan Lim, Dingding Xiong, Andrea Dorner, Tae-Jin Youn, Aaron Yung, Taylor I. Liu, Yusu Gu, Nancy D. Dalton, Adam T. Wright, Sylvia M. Evans, Ju Chen, Kirk L. Peterson, Andrew D. McCulloch, Toshitaka Yajima, Kirk U. Knowlton
Byung-Kwan Lim, Dingding Xiong, Andrea Dorner, Tae-Jin Youn, Aaron Yung, Taylor I. Liu, Yusu Gu, Nancy D. Dalton, Adam T. Wright, Sylvia M. Evans, Ju Chen, Kirk L. Peterson, Andrew D. McCulloch, Toshitaka Yajima, Kirk U. Knowlton
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Research Article Cardiology

Coxsackievirus and adenovirus receptor (CAR) mediates atrioventricular-node function and connexin 45 localization in the murine heart

Abstract

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that belongs to the family of adhesion molecules. In the postnatal heart, it is localized predominantly at the intercalated disc, where its function is not known. Here, we demonstrate that a first degree or complete block of atrioventricular (AV) conduction developed in the absence of CAR in the adult mouse heart and that prolongation of AV conduction occurred in the embryonic heart of the global CAR-KO mouse. In the cardiac-specific CAR-KO (CAR-cKO) mouse, we observed the loss of connexin 45 localization to the cell-cell junctions of the AV node but preservation of connexin 40 and 43 in contracting myocardial cells and connexin 30.2 in the AV node. There was also a marked decrease in β-catenin and zonula occludens-1 (ZO-1) localization to the intercalated discs of CAR-cKO mouse hearts at 8 weeks before the mice developed cardiomyopathy at 21 weeks of age. We also found that CAR formed a complex with connexin 45 via its PSD-95/DigA/ZO-1–binding (PDZ-binding) motifs. We conclude that CAR expression is required for normal AV-node conduction and cardiac function. Furthermore, localization of connexin 45 at the AV-node cell-cell junction and of β-catenin and ZO-1 at the ventricular intercalated disc are dependent on CAR.

Authors

Byung-Kwan Lim, Dingding Xiong, Andrea Dorner, Tae-Jin Youn, Aaron Yung, Taylor I. Liu, Yusu Gu, Nancy D. Dalton, Adam T. Wright, Sylvia M. Evans, Ju Chen, Kirk L. Peterson, Andrew D. McCulloch, Toshitaka Yajima, Kirk U. Knowlton

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Figure 5

Protein expression in AV node of WT and CAR-cKO mice.

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Protein expression in AV node of WT and CAR-cKO mice. (A) Immunoblot for...
(A) Immunoblot for HCN4, connexin 45 (Cx45), connexin 30.2, and connexin 40, and GAPDH demonstrate that the levels of connexin 45 are markedly decreased whereas levels of connexins 30.2 and 40 are somewhat increased. (B–CC) Immunofluorescent staining of the AV node in WT (B–O) and CAR-cKO (P–CC) mice. HCN4 stain in the area of the AV node identified the conduction tissue (B and P). Higher magnification of the area of the AV node (rectangles) stained with HCN4 and CAR (D–F and R–T). An adjacent section of the AV-nodal tissue that stained positive for HCN4 was costained for connexin 45 and CAR (G–I and U–W). As a control for AV-node, cell-cell junction adjacent sections were costained for γ-catenin and CAR (J–L and X–Z). The AV nodes of WT and CAR-cKO mice were then costained for CAR and connexin 45 and imaged at high magnification using deconvolution microscopy (M–O and AA–CC). Scale bars are measured in micrometers. Arrows indicate staining of cell-cell junctions.