Gene Transfer of Engineered Calmodulin Alleviates Ventricular Arrhythmias in a Calsequestrin-Associated Mouse Model of Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a familial arrhythmogenic syndrome characterized by sudden death. There are several genetic forms of CPVT associated with mutations in genes encoding the cardiac ryanodine receptor (RyR2) and its auxiliary proteins including calsequestrin (CASQ2) and calmodulin (CaM). It has been suggested that impairment of the ability of RyR2 to stay closed (ie, refractory) during diastole may be a common mechanism for these diseases. Here, we explore the possibility of engineering CaM variants that normalize abbreviated RyR2 refractoriness for subsequent viral-mediated delivery to alleviate arrhythmias in non-CaM-related CPVT. METHODS AND RESULTS: To that end, we have designed a CaM protein (GSH-M37Q; dubbed as therapeutic CaM or T-CaM) that exhibited a slowed N-terminal Ca dissociation rate and prolonged RyR2 refractoriness in permeabilized myocytes derived from CPVT mice carrying the CASQ2 mutation R33Q. This T-CaM was introduced to the heart of R33Q mice through recombinant adeno-associated viral vector serotype 9. Eight weeks postinfection, we performed confocal microscopy to assess Ca handling and recorded surface ECGs to assess susceptibility to arrhythmias in vivo. During catecholamine stimulation with isoproterenol, T-CaM reduced isoproterenol-promoted diastolic Ca waves in isolated CPVT cardiomyocytes. Importantly, T-CaM exposure abolished ventricular tachycardia in CPVT mice challenged with catecholamines. CONCLUSIONS: Our results suggest that gene transfer of T-CaM by adeno-associated viral vector serotype 9 improves myocyte Ca handling and alleviates arrhythmias in a calsequestrin-associated CPVT model, thus supporting the potential of a CaM-based antiarrhythmic approach as a therapeutic avenue for genetically distinct forms of CPV

Cardiac Sodium Channel (Dys)Function and Inherited Arrhythmia Syndromes

Normal cardiac sodium channel function is essential for ensuring excitability of myocardial cells and proper conduction of the electrical impulse within the heart. Cardiac sodium channel dysfunction is associated with an increased risk of arrhythmias and sudden cardiac death. Over the last 20 years, (combined) genetic, electrophysiological, and molecular studies have provided insight into the (dys)function and (dys)regulation of the cardiac sodium channel under physiological circumstances and in the setting of SCN5A mutations identified in patients with inherited arrhythmia syndromes. Although our understanding of these sodium channelopathies has increased substantially, important issues remain incompletely understood. It has become increasingly clear that sodium channel distribution, function, and regulation are more complicated than traditionally assumed. Moreover, recent evidence suggests that the sodium channel may play additional, as of yet unrecognized, roles in cardiomyocyte function, which in turn may ultimately also impact on arrhythmogenesis. In this chapter, an overview is provided of the structure and function of the cardiac sodium channel and the clinical and biophysical characteristics of inherited sodium channel dysfunction. In addition, more recent insights into the electrophysiological and molecular aspects of sodium channel dysregulation and dysfunction in the setting of SCN5A mutations are discussed