Depleting trafficking regulator CASK promotes intercalated disc organization and ventricular function
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Background
The intercalated disc (ID) electromechanically couples adjacent cardiomyocytes. Alteration of this structure plays a central role in cardiac arrhythmias, notably arrhythmogenic cardiomyopathy (ACM), an inherited genetic disorder of desmosomes. Calcium/Calmodulin-Dependent Serine Protein Kinase (CASK), a costameric component of the lateral membrane, regulates cardiomyocyte protein trafficking. Here, we investigated CASK regulation of the organization of ID components in normal and pathological contexts. Here, we investigated CASK regulation of the organization of ID components in normal and pathological contexts.
Methods
We studied the outcomes of CASK depletion in neonatal rat hearts using a cardiac-specific adeno-associated virus strategy. We used conventional and strain echocardiography, hemodynamics, electrocardiography, histology, and gene and protein expression studies to characterize adult rat hearts. We also studied the effects of CASK depletion in neonatal rat ventricular cardiomyocytes (NRVM), and control and ACM ( PKP2 +/- ) IPS cell-derived CM (hIPS-CM) using proteomics, electron microscopy, high-resolution imaging, mechano-scanning ion conductance microscopy (mechano-SICM), and stress resistance tests. We studied cardiac CASK expression and localization in human ACM and non-transplantable control hearts.
Results
Depletion of CASK in our multiple experimental models revealed that CASK regulates cardiomyocyte IDs. In rats, CASK depletion improved contractile reserve and compliance. In cultured rat cardiomyocytes, CASK knockdown increased localization of connexin 43 (Cx43) and PKP2 at IDs, resulting in increased contact stiffness. In PKP2 +/- hIPS-CMs, CASK expression was increased. CASK depletion in these cells promoted PKP2 accumulation at cell contacts, formation of desmosome-like structures, and stress resistance. In the right ventricles of ACM patients, CASK protein level was also increased and CASK abnormally localized at the ID.
Conclusion
CASK functions as a repressor of ID organization and tissue cohesion, suggesting novel mechanisms for regulating ID structure and function. These observations, along with CASK upregulation and mislocalization in ACM, open up new perspectives on understanding the pathophysiology of ACM and suggest innovative strategies for its treatment.
