CASK Silencing Favors Systolic Function by Regulating Junction's Signaling

Although the organization of the cardiomyocyte (CM) membrane into functional microdomains directly influences the anisotropic propagation of the AP, the mechanisms underlying the rod-like structural organization of CMs during post-natal development are poorly understood. We have previously shown in the adult CM that CASK regulates sodium channel expression at the lateral membrane in interaction with focal adhesion complexes. In addition, preliminary results have shown that the expression level of CASK evolves during postnatal development and is altered during post-infarction myocardial remodeling in rat. To unravel the implication of CASK in postnatal cardiomyocyte differentiation and in the acquisition of structural and electrical function. CASK viral constructs were designed to inhibit the expression of CASK in neonatal cardiomyocytes, both in vitro (Ad-shCASK) and in vivo (AAV-shCASK). Western blots on human heart samples of arrythmogenic cardiomyopathy, dilated cardiomyopathy and atrial fibrilation patients revealed strong decrease of CASK expression. Proteomic analysis showed that CASK invalidation strongly modify immature CM proteome, notably junction signaling. Immunostaining experiments on neonatal CMs confirmed that CASK is required for the correct organization of the cytoskeleton and differentially regulates both mechanical and electrical junction formation of the intercalated disc. Neonatal CMs invalidated for CASK displayed abnormal contractility and cell adhesion fragility. Stiffness measurements using SICM shows increased stiffness at the junction site, validating the modification of the cell-cell contacts' physical properties. Echocardiography phenotyping of CASK-invalidated rats at the neonatal stage reveals eccentric ventricular remodeling, decreased systolic performance but a preserved contractile reserve. Pressure-volume measurements confirmed that CASK invalidation increased myocardium contractility and compliance. In addition, CASK silencing does not trigger electrical remodeling or spontaneous arrhythmias, despite the reduced Nav1.5/Kir2.1 expression level. This study demonstrates that CASK confers the ability to orchestrate both CM molecular organization and tissue cohesion. As the decrease of CASK expression appears to be a marker of cardiac remodeling, CASK overexpression therapy could be promising regarding hereditary cardiomyopathies.