Search

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited cardiac arrhythmia condition, triggered by physical or acute emotional stress, that predominantly expresses early in life. Gain-of-function mutations in the cardiac ryanodine receptor gene (RYR2) account for the majority of CPVT cases, causing substantial disruption of intracellular calcium (Ca) homeostasis particularly during the periods of β-adrenergic receptor stimulation. However, the highly variable penetrance, patient outcomes, and drug responses observed in clinical practice remain unexplained, even for patients with well-established founder RyR2 mutations. Therefore, investigation of the electrophysiological consequences of CPVT-causing RyR2 mutations is crucial to better understand the pathophysiology of the disease. The development of strategies for reprogramming human somatic cells to human induced pluripotent stem cells (hiPSCs) has provided a unique opportunity to study inherited arrhythmias, due to the ability of hiPSCs to differentiate down a cardiac lineage. Employment of genome editing enables generation of disease-specific cell lines from healthy and diseased patient-derived hiPSCs, which subsequently can be differentiated into cardiomyocytes. This paper describes the means for establishing an hiPSC-based model of CPVT in order to recapitulate the disease phenotype in vitro and investigate underlying pathophysiological mechanisms. The framework of this approach has the potential to contribute to disease modeling and personalized medicine using hiPSC-derived cardiomyocytes. © 2021 Wiley Periodicals LLC. The authors gratefully acknowledge financial support from the Stem Cell Network(FY21/ACCT2-13 to GFT); the Canadian Institutes of Health Research Institute of Circulatory and Respiratory Health (GR020601 toGFT and FVP); and the Mining for Miraclesfund raising on behalf of the BC Children’s Hospital Foundation (to G.F.T., S.S., and F.L.).

hERG K+ channels are important in cardiac repolarization and their dysfunction causes prolongation of the ventricular action potential, Long QT Syndrome, and arrhythmia. As such, approaches to augment hERG channel function, such as activator compounds, have been of significant interest due to their marked therapeutic potential. Activator compounds that hinder channel inactivation abbreviate action potential duration (APD), but carry risk of over-correction leading to Short QT Syndrome. Enhanced risk by over-correction of the APD may be tempered by activator-induced increased refractoriness, however investigation of the cumulative effect of hERG activator compounds on the balance of these effects in whole organ systems is lacking. Here, we have investigate the antiarrhythmic capability of a hERG activator, RPR260243, which augments channel function by slowing deactivation kinetics, in ex vivo zebrafish whole hearts. We show that 30 mM RPR260243 abbreviates the ventricular APD, reduces triangulation, and steepens the slope of the electrical restitution curve. In addition, RPR260243 increases the post-repolarization refractory period. We provide evidence that this latter effect arises from RPR260243-induced enhancement of hERG channel protective currents flowing early in refractory. Finally, the cumulative effect of RPR260243 on arrhythmogenicity in whole organ zebrafish hearts is demonstrated by the restoration of normal rhythm in hearts presenting dofetilide-induced arrhythmia. These findings in a whole organ model demonstrate the antiarrhythmic benefit of hERG activator compounds that modify both APD and refractoriness. Furthermore, our results demonstrate that targeted slowing of hERG channel deactivation and enhancement of protective currents may provide an effective antiarrhythmic approach.

hERG K+ channels are important in cardiac repolarization and their dysfunction causes prolongation of the ventricular action potential, Long QT Syndrome, and arrhythmia. As such, approaches to augment hERG channel function, such as activator compounds, have been of significant interest due to their marked therapeutic potential. Activator compounds that hinder channel inactivation abbreviate action potential duration (APD), but carry risk of over-correction leading to Short QT Syndrome. Enhanced risk by over-correction of the APD may be tempered by activator-induced increased refractoriness, however investigation of the cumulative effect of hERG activator compounds on the balance of these effects in whole organ systems is lacking. Here, we have investigate the antiarrhythmic capability of a hERG activator, RPR260243, which augments channel function by slowing deactivation kinetics, in ex vivo zebrafish whole hearts. We show that 30 mM RPR260243 abbreviates the ventricular APD, reduces triangulation, and steepens the slope of the electrical restitution curve. In addition, RPR260243 increases the post-repolarization refractory period. We provide evidence that this latter effect arises from RPR260243-induced enhancement of hERG channel protective currents flowing early in refractory. Finally, the cumulative effect of RPR260243 on arrhythmogenicity in whole organ zebrafish hearts is demonstrated by the restoration of normal rhythm in hearts presenting dofetilide-induced arrhythmia. These findings in a whole organ model demonstrate the antiarrhythmic benefit of hERG activator compounds that modify both APD and refractoriness. Furthermore, our results demonstrate that targeted slowing of hERG channel deactivation and enhancement of protective currents may provide an effective antiarrhythmic approach.

hERG K+ channels are important in cardiac repolarization and their dysfunction causes prolongation of the ventricular action potential, Long QT Syndrome, and arrhythmia. As such, approaches to augment hERG channel function, such as activator compounds, have been of significant interest due to their marked therapeutic potential. Activator compounds that hinder channel inactivation abbreviate action potential duration (APD), but carry risk of over-correction leading to Short QT Syndrome. Enhanced risk by over-correction of the APD may be tempered by activator-induced increased refractoriness, however investigation of the cumulative effect of hERG activator compounds on the balance of these effects in whole organ systems is lacking. Here, we have investigate the antiarrhythmic capability of a hERG activator, RPR260243, which augments channel function by slowing deactivation kinetics, in ex vivo zebrafish whole hearts. We show that 30 mM RPR260243 abbreviates the ventricular APD, reduces triangulation, and steepens the slope of the electrical restitution curve. In addition, RPR260243 increases the post-repolarization refractory period. We provide evidence that this latter effect arises from RPR260243-induced enhancement of hERG channel protective currents flowing early in refractory. Finally, the cumulative effect of RPR260243 on arrhythmogenicity in whole organ zebrafish hearts is demonstrated by the restoration of normal rhythm in hearts presenting dofetilide-induced arrhythmia. These findings in a whole organ model demonstrate the antiarrhythmic benefit of hERG activator compounds that modify both APD and refractoriness. Furthermore, our results demonstrate that targeted slowing of hERG channel deactivation and enhancement of protective currents may provide an effective antiarrhythmic approach.