Cardiomyocyte SNAP29 Insulates Desmosomes from Targeted Protein Degradation by Selective Autophagy to Restrict Arrhythmias

Abstract

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a fatal and untreatable inherited cardiomyopathy associated with ventricular dysfunction and cardiac arrhythmias leading to sudden cardiac death in the young. Early detection is hindered as people present with complex disease patterns and harbors a “concealed phase”, where lethal arrhythmias are observed in the absence of overt structural changes to the heart. Mutations and loss of components of the desmosome, a cardiac mechanical cell‐cell junction, have been linked to the development of ARVC through human and mouse genetic studies. However, limited information exists on how desmosomal protein dysregulation/loss can trigger the complex features of ARVC, especially the asymptomatic “concealed phase”. Using a yeast two‐hybrid screen we identified Synaptoso‐malassociated protein 29 (SNAP29) as a novel desmosomal (desmoplakin, DSP)‐interacting protein. Traditional functions of SNAP29 are to regulate membrane fusion and play a role in autophagy in non‐cardiomyocytes; however, its role at the desmosome and/or heart is undefined. We hypothesize that SNAP29 may play a critical role in maintaining desmosomal protein homeostasis and have direct relevance to ARVC disease features, as it is a disease associated with desmosomal protein dissolution. We show that SNAP29 co‐localizes with DSP in both the adult mouse and human heart. Cardiac‐specific SNAP29‐deficient mice (SNAP29‐cKO) displayed baseline and pacing‐ induced ventricular arrhythmias in an age‐dependent manner in the absence of cardiac structural and functional deficits. Furthermore, molecular analyses revealed that the arrhythmias found in SNAP29‐cKO hearts and cardiomyocytes were associated with a molecular loss of a subset of desmosomal proteins (DSP and plakophilin‐2) and the gap junction protein, connexin43. Furthermore, an accumulation of autophagic markers (p62 and LC3BII), as well as machinery, was observed at the cardiac cell‐cell junction in SNAP29 deficient cardiomyocytes. Acute blockade of autophagy using specific inhibitors (chloroquine and bafilomycin A1) was sufficient to rescue levels of desmosomal and gap junction proteins as well as arrhythmias in SNAP29 deficient cardiomyocytes. Our data suggest that SNAP29 insulates a subset of desmosomal proteins from selective autophagy‐mediated degradation to restrict cardiac arrhythmias. Thus, SNAP29 loss may directly contribute to the “concealed phase” of ARVC. Our results further identify autophagy defects as an underlying mechanism in desmosomal disease pathogenesis and highlight new potential therapeutic targets for ARVC.Support or Funding InformationNIH/NHLBI (HL09780)