Electrophysiological remodeling in the hypertrophic cardiomyopathy MYBPC3 R943X mutant in human iPSC-derived cardiomyocytes and modulation by IKto-targeting drugs.

Hypertrophic cardiomyopathy is a leading cause of sudden cardiac death, often driven by pathogenic variants in sarcomeric genes such as MYBPC3. The precise electrophysiological mechanisms underlying arrhythmogenesis in HCM, particularly in the context of MYBPC3 truncating mutations, remain incompletely defined, hindering the development of targeted therapies. Here, we leveraged human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the MYBPC3 p.R943X mutation to systematically characterize action potential remodeling and evaluate the efficacy of ion-channel-modulating drugs.High-throughput optical AP assays revealed that R943X mutant hiPSC-CMs exhibit profound baseline electrophysiological disruption, with a marked reduction in normal AP profiles and increased incidence of pro-arrhythmic morphologies, including AP prolongation, early afterdepolarizations, and delayed afterdepolarizations, compared to isogenic non-diseased controls. Pharmacological profiling demonstrated that NS-5806, a Kv4 channel modulator, exerts a biphasic, dose-dependent effect in non-diseased isogenic control cells and partially restores normal AP morphology in R943X mutants by enhancing repolarizing current and suppressing AP prolongation. In contrast, Acacetin, an ITo and late Na+ current inhibitor, preserved electrical stability in non-diseased isogenic control cells but conferred limited and dose-sensitive rescue in mutants, with higher concentrations exacerbating arrhythmic features. These findings provide direct evidence that targeted augmentation of transient outward K+ current can selectively mitigate mutation-induced arrhythmogenic remodeling in hiPSC-CMs modeling HCM. Our study highlights the therapeutic promise, and challenges, of precision ion-channel modulation in genetic cardiomyopathy and establishes a scalable platform for genotype-guided drug discovery.