Pioner, J. M. | bioRxiv Science

bioRxiv2025

Long-term mavacamten exposure reduces force and sarcomere density in a hiPSC model of hypertrophic cardiomyopathy

BackgroundMavacamten, a first-in-class allosteric myosin inhibitor, has demonstrated efficacy and safety in obstructive hypertrophic cardiomyopathy (oHCM), notably reducing symptoms, left ventricular outflow obstruction, and wall thickness over 30 weeks. We recently reported that the MYBPC3:c.772G>A variant causes HCM through cMyBP-C haploinsufficiency, leading to accelerated sarcomere kinetics and higher energy consumption in patient myocardium and hiPSC- derived cardiomyocytes (hiPSC-CMs). These effects are counterbalanced by prolonged action potentials and slower Ca{superscript 2} transients, which preserve twitch duration but may increase arrhythmic risk. Mavacamten may reduce myocardial energetic defects in HCM. ObjectivesTo investigate the long-term effects of Mavacamten on sarcomere structure, contractility, and transcriptional remodeling using patient-specific and CRISPR-corrected isogenic hiPSC-derived cardiomyocyte models of HCM. MethodsHiPSC-CMs and engineered heart tissues (EHTs) derived from a MYBPC3:c.772G>A patient and its CRISPR-corrected line were first exposed to increasing concentrations of Mavacamten to assess acute dose-response relationships and determine IC50 values. Based on these data, chronic treatments (0.3- 0.75 M for 20 days) were performed mechanical, structural, electrophysiological, and transcriptomic adaptations. ResultsAcute exposure produced a rapid and fully reversible reduction in active force, while chronic treatment for 20 days induced a sustained decrease in contractility with incomplete recovery after 4 days of washout, indicating a two-phase mechanism of action. Long-term force reduction was paralleled by decreased cell area and sarcomere density, indicating that structural disassembly contributes to sustained functional depression and re-assembly after washout. Electrophysiological analysis confirmed the specific alterations of the MYBPC3:c.772G>A mutation previously observed, with no detectable effects following treatment with Mavacamten. In addition, transcriptome analysis was used to study the molecular mechanisms underlying the long-term effect. ConclusionsMavacamten induces a biphasic, persistent-to-reversible, reduction of sarcomeric force associated with structural remodeling, providing mechanistic insight into its capacity to promote favorable cardiac remodeling in oHCM.

physiology↗

bioRxiv2025

Molecular mechanisms of altered contraction with the β-myosin R403Q mutation in porcine ventricular muscle and a human stem cell-derived cardiomyocyte model.

I.The R403Q mutation in the sarcomere protein beta-myosin heavy chain ({beta}-MHC) is a known genetic cause of hypertrophic cardiomyopathy (HCM), associated with ventricular hypercontractility, impaired relaxation, and cardiac arrhythmias. Despite extensive research, the mutations impact on myosin contractile properties remains unclear, likely due, at least in part, to discrepancies cross different model systems. In this study, we used a multidisciplinary approach to explore mutational effects using two distinct heterozygous R403Q systems: a Yucatan minipig model and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). X-ray diffraction of R403Q minipig ventricular muscle demonstrated reduced order of the thick filament, suggesting destabilization of the inhibited OFF (vs. ON) state of myosin in relaxed muscle, which correlated with elevated force at submaximal calcium. Super-resolution, single-molecule fluorescence microscopy indicated elevated ATPase activity in thick filament zones lacking cMyBP-C. Furthermore, R403Q myofibrils exhibited slower activation and relaxation kinetics, with reduced sensitivity to ADP. Molecular dynamics simulations suggested that altered interactions at the actomyosin interface contribute to these effects, rather than changes at the nucleotide binding pocket, typically associated with ADP release. Human engineered heterozygous R403Q hiPSC-CMs exhibited reduced maximal myofibril force, slowed contractile kinetics, and hypercontraction in engineered heart tissue constructs-consistent with HCM phenotypes observed in the heterozygous porcine model. Our results demonstrate that the R403Q mutation induces early and persistent contractile dysfunction, and that hypercontractility and slower contractile kinetics may result from a combination of an increased population of activated (ON) myosin heads and delayed detachment during cross-bridge cycling, respectively.

biophysics↗