PO-01-175 HEIGHTENED ACTION POTENTIAL HETEROGENEITY IN THE HYPERTROPHIC CARDIOMYOPATHY MYBPC3 MUTANT, P.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. We plan to characterize baseline cellular AP types and incidence in human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) carrying the HCM MYBPC3 p.R943X mutation along with their CRISPR-corrected isogenic controls. We established a high throughput, 384-well optical physiological system revealing baseline arrhythmogenic APs characterized in HCM hiPSC-CMs carrying MYBPC3 p.R943X. 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. The APs in HCM MYBPC3 p.R943X hiPSC-CMs clearly show a marked increase in early afterdepolarizations, non-sustained ventricular tachycardia, sustained ventricular tachycardia, and AP notches compared to their isogenic controls. AP notches were significantly augmented by NS-5806 and suppressed by Acacetin in MYBPC3 p.R943X hiPSC-CMs. GS-967 administration also significantly reduced the occurrence of EADs. This study is the first to characterize cellular inputs into an array of AP phenotypes in MYBPC3 p.R943X. Using 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.