Altered Expression of Zonula occludens-1 Affects Cardiac Na+ Channels and Increases Susceptibility to Ventricular Arrhythmias

Mona El Refaey,Michel Skaf,Michael J Wallace,Mei Han,Heather R Manring,Crystal F Kline,Nathaniel P Murphy,Hassan Musa,Peter J Mohler,Steve Antwi-Boasiako,Tyler L Stevens,Paul M L Janssen,Lindsay J Young,Maegen A Borzok,Sara Coles,Federica Accornero,Sara N Koenig,Michael Makara ,Kelli M Sas ,James F Curran

doi:10.3390/cells11040665

Abstract

Zonula occludens-1 (ZO-1) is an intracellular scaffolding protein that orchestrates the anchoring of membrane proteins to the cytoskeleton in epithelial and specialized tissue including the heart. There is clear evidence to support the central role of intracellular auxiliary proteins in arrhythmogenesis and previous studies have found altered ZO-1 expression associated with atrioventricular conduction abnormalities. Here, using human cardiac tissues, we identified all three isoforms of ZO-1, canonical (Transcript Variant 1, TV1), CRA_e (Transcript Variant 4, TV4), and an additionally expressed (Transcript Variant 3, TV3) in non-failing myocardium. To investigate the role of ZO-1 on ventricular arrhythmogenesis, we generated a haploinsufficient ZO-1 mouse model (ZO-1+/−). ZO-1+/− mice exhibited dysregulated connexin-43 protein expression and localization at the intercalated disc. While ZO-1+/− mice did not display abnormal cardiac function at baseline, adrenergic challenge resulted in rhythm abnormalities, including premature ventricular contractions and bigeminy. At baseline, ventricular myocytes from the ZO-1+/− mice displayed prolonged action potential duration and spontaneous depolarizations, with ZO-1+/− cells displaying frequent unsolicited (non-paced) diastolic depolarizations leading to spontaneous activity with multiple early afterdepolarizations (EADs). Mechanistically, ZO-1 deficient myocytes displayed a reduction in sodium current density (INa) and an increased sensitivity to isoproterenol stimulation. Further, ZO-1 deficient myocytes displayed remodeling in ICa current, likely a compensatory change. Taken together, our data suggest that ZO-1 deficiency results in myocardial substrate susceptible to triggered arrhythmias.

Highlights

Zonula occludens-1 (ZO-1) is a large scaffolding protein located at the gap junctions (GJ) and adherens junctions (AJ) of cardiomyocytes [1]
ZO-1 is known to play a role in the regulation of heart disease and several studies have reported the levels of ZO-1 in patients with end-stage heart failure
While Laing and colleagues reported a reduction in ZO-1 and connexin-43 expression (Cx43) levels in the intercalated disc (ID) of patients with heart failure [1], Bruce et al found an increase in ZO-1 levels associated with a significant decrease in Cx43 in the ventricular tissues of patients with end-stage heart failure [12,30]

Summary

Introduction

Zonula occludens-1 (ZO-1) is a large scaffolding protein located at the gap junctions (GJ) and adherens junctions (AJ) of cardiomyocytes [1]. ZO-1 localizes at the AJ as a binding partner of occludin to maintain cell-cell adhesion and at the GJ as a binding partner of connexin-43 (Cx43) for regulating cell-cell communication [2,3,4,5,6]. ZO-1 expression is altered in heart failure, albeit in a contradictory manner. While several studies have identified a decrease in ZO-1 expression in the ventricular myocardium of patients with diverse etiologies of heart failure [1,11], others have found ZO-1 expression to be increased [12]

Methods

Results

Conclusion