Action potential heterogeneity in the myosin binding protein C3 mutant, R943x.

Abstract

Hypertrophic cardiomyopathy (HCM) can be caused by a truncation mutant, p.R943X, in the Myosin Binding Protein C3 (MYBPC3). Early and delayed afterdepolarizations are common action potential (AP) features seen in early stages of HCM; however, the myofibrillar disarray and calcium dysfunction may induce other channelopathies and AP morphologies. The presence of an AP notch also predisposes to lethal forms of arrhythmias, culminating in sudden cardiac arrest. Using human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), we characterized baseline arrhythmia type and incidence in hiPSC-CMs carrying the MYBPC3 p.R943x and its isogenic control. AP metrics were measured using the voltage probe, Fluovolt, from spontaneously beating and electrically paced cells. Acacetin, NS-5806, nifedipine, and GS-967 were administered to probe the channelopathies underlying the AP types recorded. We evaluated whether a dysregulated Ca2+-CaMKIId-INaL circuit is a cellular mechanism that predisposes HCM cardiomyocytes to arrhythmias. We established a high throughput, 384-well optical physiological system revealing baseline arrhythmogenic APs characterized in HCM hiPSC-CMs carrying MYBPC3 p.R943X. The APs clearly show a marked increase in early afterdepolarizations, non-sustained ventricular tachycardia, sustained ventricular tachycardia, and AP notches compared to isogenic control hiPSC-CMs.Understanding the mechanisms underlying heightened AP heterogeneity in HCM hiPSC-CMs is pivotal in administering or discovering precise therapy. This study is the first to characterize cellular inputs into an array of AP phenotypes in MYBPC3 p.R943X. The use of hiPSC-CMs lines unambiguously associates the signaling pathways and intracellular circuitries involved in sustaining arrhythmogenesis. Results may incentivize the discovery of antiarrhythmics with pleiotropic profiles suited to target multiple ion channel dysfunctions. This comprehensive approach will establish many novel molecular mechanisms and reveal points of therapeutic intervention.