Cardiomyocyte ZO-1 Regulates Intercalated Disc Organization and Whole Heart Physiology

Abstract

Intercalated discs (IDs) in the heart provide both electrical and mechanical coupling between cells. Abnormalities in ID proteins are associated with arrhythmogenic cardiomyopathy, however the regulation of the ID and the role of ID proteins in heart physiology is still poorly understood. Tight junction proteins such as ZO-1 (Tjp1) are present and can bind to multiple ID proteins. However, its contributions to ID organization and heart function remain largely undefined. We aim to understand if and how the tight junction protein ZO-1 contributes to ID structure and heart physiology. We find ZO-1 expression was decreased in patients with paroxysmal atrial fibrillation (81±9% of control, P=0.03) by qPCR, suggesting ZO-1 expression change is associated with human disease. We then generated an inducible cardiomyocyte specific ZO-1 knockout mouse (ZO-1 KO) was by crossing Tjp1 floxed mice with myosin heavy chain 6-CreERT2 mice. 8-12 week old mice were injected with tamoxifen to induce Tjp1 gene deletion. Immunofluorescent staining showed decreased Coxsackie and adenovirus receptor (CAR) (56±2% decrease), and connexin 43 (67±3% decrease) distribution at IDs but no decrease of desmosome and adherens junction proteins was observed. Transmission and immunogold electron microscopy showed loss of gap junction structures. Surface ECG showed ZO-1 KO caused increased PR interval (28.0 vs. 45.3 ms) and intra-cardiac electrogram showed increased atrial-His interval (24.5±1.1 vs. 69.5±3.0 ms) and Wenckebach time (68.9±20.1 vs. 131.4±15.1 ms), without affecting His-ventricular interval. ZO-1 KO mice developed 3rd degree heart block 2 weeks after ZO-1 deletion. Loss of ZO-1 in adult heart results in altered ID protein composition, heart block, and heart failure. We propose a model in which ZO-1 stabilizes connexins and CAR to allow efficient cell-cell communication, and loss of ZO-1 contributes to the pathogenesis of heart disease.