Abstract 4369381: Regulation of Nav1.5 Channel Surface Expression and Function by Sorbs2 in Atrial Cardiomyocytes

Background: Voltage-gated Nav1.5 channel, encoded by SCN5A , is essential for initiation and propagation of action potentials (AP) in atria. Nav1.5 channelopathy is strongly associated with arrhythmogenesis, including atrial fibrillation. Sorbin and SH3 domain-containing protein 2 (Sorbs2), encoded by SORBS2 , is an important cytoskeletal protein for maintaining atrial structural and electrical integrity. However, the specific mechanisms through which Sorbs2 modulates Nav1.5 function in atria is unknown. Hypothesis: Sorbs2 modulates atrial Nav1.5 expression and function through direct protein-protein interaction. Methods: We created the cardiac-specific Sorbs2 knockout ( c-Sorbs2 KO) mice. We determined the mechanisms by which Sorbs2 regulates Nav1.5 channel expression and function by performing electrophysiological experiments using atrial cells and tissues from control and c-Sorbs2 KO mice, in conjunction with molecular biological studies and in silico analysis. Results: c-Sorbs2 KO mice at 8-10 months showed marked left atrial (LA) enlargement, and ECG showed significantly prolonged P-R durations. Compared to wild-type controls, intracellular recordings in LA tissues isolated from c-Sorbs2 KO mice showed reduced AP amplitude, decreased upstroke velocity, prolonged AP duration at 90% repolarization and effective refractory period, spontaneous atrial tachycardias and triggered activity. Patch-clamp recordings in freshly isolated atrial cardiomyocytes showed a significantly reduced peak sodium current density in c-Sorbs2 KO mice (-12.0 ± 1.6 pA/pF at -45 mV, n = 10), compared to controls (-21.3 ± 4.0 pA/pF at -45 mV, n = 12, p < 0.05). Also, the steady-state activation and inactivation curves of Nav1.5 channel were rightward shifted in c-Sorbs2 KO atrial cardiomyocytes. Molecular docking analysis showed that the Sorbs2 SH3 domain interacts directly with the voltage-sensing domain of Nav1.5. Co-immunoprecipitation assays confirmed the physical interactions between Nav1.5 and the C-terminal SH3 domain of Sorbs2. Furthermore, results from membrane biotinylation study demonstrated that deletion of the SH3 domains of Sorbs2 significantly reduced Nav1.5 surface expression in HEK293 cells. Sorbs2 interacts directly with Nav1.5 through its SH3 domain, playing a key role in regulating Nav1.5 channel gating kinetics and surface expression in atrial cardiomyocytes. Loss of Sorbs2 results in Nav1.5 channelopathy and contributes to atrial electrical remodeling.