Single Delivery of an Adeno-Associated Viral Construct to Transfer the CASQ2 Gene to Knock-In Mice Affected by Catecholaminergic Polymorphic Ventricular Tachycardia Is Able to Cure the Disease From Birth to Advanced Age

Abstract

C atecholaminergic polymorphic ventricular tachycardia (CPVT) is a life-threatening familial disorder characterized by adrenergically mediated arrhythmias in a structurally normal heart that may lead to sudden death.1 Two genetic forms of CPVT have been identified: the autosomal-dominant variant caused by mutations in the cardiac ryanodine receptor type 2 (RyR2) gene 2 and the autosomal-recessive variantBackground-Catecholaminergic polymorphic ventricular tachycardia is an inherited arrhythmogenic disorder characterized by sudden cardiac death in children. Drug therapy is still insufficient to provide full protection against cardiac arrest, and the use of implantable defibrillators in the pediatric population is limited by side effects. There is therefore a need to explore the curative potential of gene therapy for this disease. We investigated the efficacy and durability of viral gene transfer of the calsequestrin 2 (CASQ2) wild-type gene in a catecholaminergic polymorphic ventricular tachycardia knock-in mouse model carrying the CASQ2 R33Q/R33Q (R33Q) mutation. Methods and Results-We engineered an adeno-associated viral vector serotype 9 (AAV9) containing cDNA of CASQ2 wild-type (AAV9-CASQ2) plus the green fluorescent protein (GFP) gene to infect newborn R33Q mice studied by in vivo and in vitro protocols at 6, 9, and 12 months to investigate the ability of the infection to prevent the disease and adult R33Q mice studied after 2 months to assess whether the AAV9-CASQ2 delivery could revert the catecholaminergic polymorphic ventricular tachycardia phenotype. In both protocols, we observed the restoration of physiological expression and interaction of CASQ2, junctin, and triadin; the rescue of electrophysiological and ultrastructural abnormalities in calcium release units present in R33Q mice; and the lack of life-threatening arrhythmias. Conclusions-Our data demonstrate that viral gene transfer of wild-type CASQ2 into the heart of R33Q mice prevents and reverts severe manifestations of catecholaminergic polymorphic ventricular tachycardia and that this curative effect lasts for 1 year after a single injection of the vector, thus posing the rationale for the design of a clinical trial. caused by mutations in the cardiac calsequestrin 2 (CASQ2) gene. 3 Additionally, 4 other genes have been associated with a clinical spectrum of manifestations consistent with the diagnosis of CPVT or with its phenocopies. [4][5][6] Interestingly, RyR2 and CASQ2 mutations induce diastolic Ca 2+ release from the sarcoplasmic reticulum (SR), leading to the development of delayed afterdepolarizations (DADs) and triggered activity (TA), which may precipitate life-threatening arrhythmias.7-10 This arrhythmogenic mechanism has been confirmed in patients during monophasic action potential recordings that documented the presence of adrenergically mediated DADs and TA in patients with CPVT. 11CPVT, unless promptly diagnosed and treated, may be lethal, as documented by the fact that up to 30% of untreated individuals die suddenly before the ...

Catecholaminergic Polymorphic Ventricular Tachycardia

“…Using a knock-in mouse model harboring the CASQ2 R33Q/R33Q mutation, an adeno-associated viral vector with the wild-type CASQ2 gene was injected into newborn CPVT mice. 68 This intervention reversed the CPVT phenotype of these mice and was still successful in reversing the phenotype after 1 year of follow-up. These first results seem encouraging and point toward potential future gene therapies.…”

Gene Therapy for the Treatment of Catecholaminergic Polymorphic Ventricular Tachycardia

“…In this issue of Circulation, Denegri and colleagues 11 report a novel approach with cardiac gene transfer to treat a transgenic murine model of CPVT. In their study, the investigators used knock-in model of calsequestrin CASQ/33Q as their disease model.…”

“…In summary Denegri and colleagues 11 present a rodent study which opens up the exciting prospect of cardiac gene therapy as a potential novel therapeutic option for this malignant inherited arrhythmogenic syndrome. However a number of challenges remain before this can be effectively studied in man.…”

Genetics of Sudden Cardiac Death

“…Data showed that a mere 30% of reduction of the mutant allele was able to abrogate cardiac hypertrophy. These data opened the concept that, in analogy with what has been described for recessive CPVT, 121 gene therapy may become a promising therapeutic approach for inherited cardiomyopathies.…”

“…The authors have used an adenoassociated viral vector to replace wild-type-Casq2 leading to the abolishment of life-threatening arrhythmias and on several disease markers including ultrastructural abnormalities. 121 As we will also see in the section dedicated to hypertrophic cardiomyopathies, the in vivo modification of the genetic defect for therapeutic purposes is a novel and fascinating development in the field.…”