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

Abstract

Zonula occludens-1 (ZO-1) is an intracellular scaffolding protein that orchestrates the an-choring 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 ar-rhythmogenesis and previous studies have found altered ZO-1 expression associated with atrioven-tricular 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, ad-renergic 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 unsolic-ited (non-paced) diastolic depolarizations leading to spontaneous activity with multiple early af-terdepolarizations (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 to-gether, our data suggest that ZO-1 deficiency results in myocardial substrate susceptible to triggered arrhythmias.