Viral delivered gene therapy to treat catecholaminergic polymorphic ventricular tachycardia (CPVT2) in mouse models

Background: The recessive form of catecholaminergic polymorphic ventricular tachycardia 2 (CPVT2) is caused by mutations in cardiac calsequestrin (CASQ2), leading to protein deficiency.

Objectives: The aims of this study were to develop a viral-delivered gene therapy for CPVT2 and to determine the relationship between CASQ2 expression and antiarrhythmic efficacy in a murine model.

Methods: We used a murine model of CPVT2 caused by the D307H human mutation (CASQ2^D307H) or CASQ2 knockout (CASQ2^Δ/Δ). Adeno-associated virus (AAV) particles containing the CASQ2 gene (AAV_CASQ2) were injected into the heart or intraperitoneally to 12-week-old mice. A telemetry device was implanted, and mice underwent provocation testing 7-8 weeks after gene therapy.

Results: CASQ2^Δ/Δ mice injected intracardiacally with AAV_CASQ2 expressed 40% ± 25% of the normal CASQ2 protein level, which was increased compared to untreated CASQ2^Δ/Δ mice (n = 10; P < .05). Intraperitoneal therapy led to a significantly elevated expression of the CASQ2 protein, which was comparable in CASQ2^D307H (n = 12) and CASQ2^Δ/Δ (n = 4) mice. All control mice with CPVT2 had nonsustained ventricular tachycardia (VT) and 8 of 13 had sustained VT on provocation. Expressing ≥33% of the normal CASQ2 level was needed to protect from nonsustained VT as well as stress-induced premature ventricular contractions. Lower levels of expression prevented sustained VT in AAV_CASQ2-treated mice (0 of 26; P < .001 vs controls).

Conclusion: AAV_CASQ2 displays a long-lasting capacity to attenuate and potentially cure CPVT2. Systemic delivery is feasible and convenient, reproducibly providing adequate levels of transgene expression. Antiarrhythmic efficacy depends on the CASQ2 level: ≥33% of the normal CASQ2 level is needed to prevent arrhythmia. However, even lower levels of protein protect from sustained VT, thereby potentially reducing the risk of sudden death.