Abstract 15271: Modification of Cardiomyocyte Lateral Membrane Composition Promotes Cardiac Function by Regulating Connexome Organization

Abstract

Introduction: Loss of contacts between adjacent cardiomyocytes is detrimental to proper electromechanical function. For instance, connexome remodeling is a common feature of both acquired and inherited cardiac arrhythmias. We have shown that the lateral membrane-specific scaffolding protein CASK regulates the trafficking and targeting of certain connexome components, notably the sodium channel. Question: Does compartmentalization of the cardiomyocyte membrane involves lateral membrane proteins? Our hypothesis is that CASK, due to its association with costamere and its developmental expression gradient, may be involved in a more global control of connexome organization. Aims: To demonstrate that CASK, a lateral membrane-specific protein, is crucial for the development and maintenance of connexome integrity. Method: Viral constructs were designed to inhibit the expression of CASK in vivo (AAV-shCASK) and in vitro (Ad-shCASK) both in murine and human cardiomyocytes. Results: In vivo, echocardiography phenotyping of CASK invalidated rats at the neonatal stage revealed, at the adult stage, eccentric ventricular remodeling associated with increased stroke volume and increased cardiac output suggestive of athlete’s heart phenotype. Hemodynamic measurements (pressure-volume loops) confirmed that CASK invalidation increases both myocardium contractility and compliance. Proteomic analysis showed that CASK invalidation in vitro strongly modify immature cardiomyocyte proteome, notably junction signaling. Immunostaining experiments on cultured neonatal rat cardiomyocytes and adult rat hearts confirmed that CASK is required for the correct organization of myofibrils and favors connexome organization. Remarkably, CASK invalidation in a human in vitro model of arrhythmogenic cardiomyopathy (hiPSC-CM PKP2 +/- ) rescues desmosome assembly. Conclusion: CASK regulates the organization of myofibrils and connexome, with major functional consequences for cardiac performance. Our results suggest for the first time the existence of a crosstalk between lateral membrane and connexome proteins. Therefore, targeting CASK to promote electromechanical coupling of cardiomyocytes could be promising in the context of cardiac remodeling.