In Vivo Dissection Of CaMKII-Mediated Arrhythmias In CPVT

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome of the structurally intact heart manifesting life-threatening bursts of ventricular tachycardias due to dominant gain-of-function mutations in the ryanodine receptor type 2 (RyR2) and β-adrenergic (β-AR) stimulation. Both protein kinase A (PKA) and Ca 2+ - calmodulin-dependent protein kinase II (CaMKII) can phosphorylate RyR2 channels, but only the latter can initiate the arrhythmogenic phenotype in CPVT. Whether through L-type Ca 2+ channel (LTCC)-mediated Ca 2+ increase or the Epac2-nitric oxide pathway, the exact mechanism by which β-AR-mediated CaMKII activation unmasks lethal arrhythmias in CPVT remains unresolved. Aim: To gain mechanistic insight and ablate ventricular arrhythmias in a mouse model of CPVT by selectively disrupting integral components of β-AR signaling. Methods: By utilizing either direct adeno-associated virus (AAV) delivery or the CRISPR/Cas9-AAV-based somatic mutagenesis (CASAAV) system, we selectively expressed a mutant LTCC β 2 -subunit, ablated the small GTPase Rad, or disrupted other components of the β-AR pathway in the hearts of mice with the pathogenic RyR2 mutation R4650I as a model of CPVT. The effects of disruption of LTCC regulation were determined by high-speed Ca 2+ imaging of isolated ventricular cardiomyocytes or whole animal electrophysiological (EP) testing for ventricular arrhythmia incidence in vivo . Results & Conclusions: Our data demonstrate that abnormal RyR2-mediated calcium release events are induced by hyperactivated LTCCs in vitro , even in the absence of adrenergic stimulation, with increased arrhythmia incidence in vivo . These results suggest that β-AR stimulation leads to pathogenic RyR2 Ca 2+ leak through LTCC-mediated contribution to CaMKII hyperactivity. Alternative mechanisms of CaMKII activation that mediate arrhythmia induction in CPVT require additional future investigation.