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

Rationale: Zona occludens 1 (ZO-1), encoded by the Tight Junction Protein 1 (TJP1) 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. Objective: We aim to determine the role of ZO-1 in cardiac function. Methods and Results: Inducible cardiomyocyte-specific Tjp1 deletion mice (Tjp1(fl/fl); Myh6(Cre/Esr1*)) were generated by crossing the Tjp1 floxed mice and Myh6(Cre/Esr1*) transgenic mice. Tamoxifen-induced loss of ZO-1 led to atrioventricular (AV) block without changes in heart rate, as measured by electrocardiogram (ECG) and ex vivo optical mapping. Mice with tamoxifen-induced conduction system specific deletion of Tjp1 (Tjp1(fl/fl); Hcn4(CreERt2)) developed AV block while tamoxifen-induced conduction system deletion of Tjp1 distal to the AV node (Tjp1(fl/fl); Kcne1(CreERt2)) did not demonstrate conduction defects. Western blot and immunostaining analyses of AV nodes showed that ZO-1 loss decreased connexin (Cx) 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 slightly decreased left ventricular ejection fraction, suggesting ZO-1 is differentially required for AV node and ventricular conduction. Conclusions: ZO-1 is a key protein responsible for maintaining appropriate AV node conduction through maintaining gap junction protein localization.