ZO-1 Regulates Intercalated Disc Composition and Atrioventricular Node Conduction.

Abstract

ZO-1 (Zona occludens 1), encoded by the tight junction protein 1 (<i>TJP1</i>) gene, is a regulator of paracellular permeability in epithelia and endothelia. ZO-1 interacts with the actin cytoskeleton, gap, and adherens junction proteins and localizes to intercalated discs in cardiomyocytes. However, the contribution of ZO-1 to cardiac physiology remains poorly defined. We aim to determine the role of ZO-1 in cardiac function. Inducible cardiomyocyte-specific <i>Tjp1</i> deletion mice (<i>Tjp1</i>^<i>fl/fl</i>; <i>Myh6</i>^{<i>Cre/Esr1*</i>}) were generated by crossing the <i>Tjp1</i> floxed mice and <i>Myh6</i>^{<i>Cre/Esr1*</i>} transgenic mice. Tamoxifen-induced loss of ZO-1 led to atrioventricular (AV) block without changes in heart rate, as measured by ECG and ex vivo optical mapping. Mice with tamoxifen-induced conduction system-specific deletion of <i>Tjp1</i> (<i>Tjp1</i>^<i>fl/fl</i><i>; Hcn4</i>^{<i>CreERt2</i>}) developed AV block while tamoxifen-induced conduction system deletion of <i>Tjp1</i> distal to the AV node (<i>Tjp1</i>^<i>fl/fl</i><i>; Kcne1</i>^{<i>CreERt2</i>}) did not demonstrate conduction defects. Western blot and immunostaining analyses of AV nodes showed that ZO-1 loss decreased Cx (connexin) 40 expression and intercalated disc localization. Consistent with the mouse model study, immunohistochemical staining showed that ZO-1 is abundantly expressed in the human AV node and colocalizes with Cx40. Ventricular conduction was not altered despite decreased localization of ZO-1 and Cx43 at the ventricular intercalated disc and modestly decreased left ventricular ejection fraction, suggesting ZO-1 is differentially required for AV node and ventricular conduction. ZO-1 is a key protein responsible for maintaining appropriate AV node conduction through maintaining gap junction protein localization.