Modelling diastolic dysfunction in induced pluripotent stem cell-derived cardiomyocytes from hypertrophic cardiomyopathy patients

Aims Diastolic dysfunction (DD) is common among hypertrophic cardiomyopathy (HCM) patients, causing major morbidity and mortality. However, its cellular mechanisms are not fully understood, and presently there is no effective treatment. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold great potential for investigating the mechanisms underlying DD in HCM and as a platform for drug discovery. Methods and results In the present study, beating iPSC-CMs were generated from healthy controls and HCM patients with DD. Micropatterned iPSC-CMs from HCM patients showed impaired diastolic function, as evidenced by prolonged relaxation time, decreased relaxation rate, and shortened diastolic sarcomere length. Ratiometric Ca2+ imaging indicated elevated diastolic [Ca2+](i) and abnormal Ca2+ handling in HCM iPSC-CMs, which were exacerbated by beta-adrenergic challenge. Combining Ca2+ imaging and traction force microscopy, we observed enhanced myofilament Ca2+ sensitivity (measured as dF/Delta[Ca2+](i)) in HCM iPSC-CMs. These results were confirmed with genome-edited isogenic iPSC lines that carry HCM mutations, indicating that cytosolic diastolic Ca2+ overload, slowed [Ca2+](i) recycling, and increased myofilament Ca2+ sensitivity, collectively impairing the relaxation of HCM iPSC-CMs. Treatment with partial blockade of Ca2+ or late Na+ current reset diastolic Ca2+ homeostasis, restored diastolic function, and improved long-term survival, suggesting that disturbed Ca2+ signalling is an important cellular pathological mechanism of DD. Further investigation showed increased expression of L-type Ca(2+)channel (LTCC) and transient receptor potential cation channels (TRPC) in HCM iPSC-CMs compared with control iPSC-CMs, which likely contributed to diastolic [Ca2+](i) overload. Conclusion In summary, this study recapitulated DD in HCM at the single-cell level, and revealed novel cellular mechanisms and potential therapeutic targets of DD using iPSC-CMs.