Inhibition of CaMKII phosphorylation of RyR2 prevents inducible ventricular arrhythmias in mice with Duchenne muscular dystrophy

Background: Ventricular tachycardia (VT) is the second most common cause of death in patients with Duchenne muscular dystrophy (DMD). Recent studies have implicated enhanced sarcoplasmic reticulum (SR) Ca²⁺ leak via type 2 ryanodine receptor (RyR2) as a cause of VT in the mdx mouse model of DMD. However, the signaling mechanisms underlying induction of SR Ca²⁺ leak and VT are poorly understood. Objective: To test whether enhanced Ca ²⁺/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of RyR2 underlies SR Ca²⁺ leak and induction of VT in mdx mice. Methods: Programmed electrical stimulation was performed on anesthetized mice and confocal imaging of Ca²⁺ release events in isolated ventricular myocytes. Results: Programmed electrical stimulation revealed inducible VT in mdx mice, which was inhibited by CaMKII inhibition or mutation S2814A in RyR2. Myocytes from mdx mice exhibited more Ca²⁺ sparks and Ca²⁺ waves compared with wild-type mice, in particular at faster pacing rates. Arrhythmogenic Ca²⁺ waves were inhibited by CaMKII but not by protein kinase A inhibition. Moreover, mutation S2814A but not S2808A in RyR2 suppressed spontaneous Ca²⁺ waves in myocytes from mdx mice. Conclusions: CaMKII blockade and genetic inhibition of RyR2-S2814 phosphorylation prevent VT induction in a mouse model of DMD. In ventricular myocytes from mdx mice, spontaneous Ca²⁺ sparks and Ca²⁺ waves can be suppressed by CaMKII inhibition or mutation S2814A in RyR2. Thus, the inhibition of CaMKII-induced SR Ca²⁺ leak might be a new strategy to prevent arrhythmias in patients with DMD without heart failure.