Variable cMyBP-C expression from cell to cell in a MYBPC3^c.927-2 A>G hiPSC-CM model recapitulates HCM patient...

Hypertrophic cardiomyopathy (HCM) is frequently associated with mutations in cardiac myosin binding protein C (cMyBP-C; MYBPC3) and cMyBP-C haploinsufficiency. Previously we discovered burst-like transcription of MYBPC3 and unequal amounts of wild type cMyBP-C from cardiomyocyte to cardiomyocyte in HCM-patient's myocardium. The present study introduces human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the patient-specific heterozygous MYBPC3 c.927-2 A > G mutation and the respective isogenic control to examine in long-term culture whether comparable pathophysiological features exist in vitro.

We generated a human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model harboring the patient-specific MYBPC3 c.927-2 A > G splice-site mutation. An isogenic control line was used for direct comparison. We assessed cMyBP-C protein expression, transcriptional dynamics, contractile function, and calcium handling, and compared the cellular phenotype to heart tissue from the HCM patient with the same mutation.

cMyBP-C haploinsufficiency in MYBPC3^{c.927-2 A> G}-hiPSC-CMs was confirmed by Western blot. Immunostaining showed myofibrillar disarray and an increasing proportion of cMyBP-C-negative CMs over time for mutant hiPSC-CMs, closely mirrored the variable cMyBP-C protein expression observed in HCM-patient's myocardium. RNA-FISH revealed variable MYBPC3 transcription from cell to cell, likely contributing to cMyBP-C expression heterogeneity. Twitch shortening velocity slowed over time while Ca²⁺ transient kinetics accelerated in mutant hiPSC-CMs. Transcriptomic analysis revealed dysregulation of pathways associated with contraction, calcium handling, and HCM.

This study presents a validated hiPSC-based model of MYBPC3-associated HCM that captures the variability in protein expression and functional phenotype observed in patient heart tissue. Our findings support the relevance of single-cell transcriptional variability in HCM pathogenesis and highlight the utility of this model for future studies.