Abstract 13197: Inhibition of CaMKII Phosphorylation of RyR2 Prevents Ventricular Tachycardia in Duchenne Muscular Dystrophy
Background: Cardiomyopathy and ventricular tachycardia (VT) are the second most common cause of death in patients with Duchenne Muscular Dystrophy (DMD), which is the most common form of muscular dystrophy. Previous studies have shown increased cystolic Ca2+ levels and enhanced sarcoplasmic reticulum (SR) Ca2+ leak via ryanodine receptors (RyR2) in ventricular myocytes from mdx mice, a model of DMD. RyR2 is activated by Ca2+/calmodulin-dependent protein kinase II (CaMKII), which itself is activated by high cytosolic Ca2+. However, it is unclear whether, in mdx mice, increased cytosolic Ca2+ leads to CaMKII activation and phosphorylation of RyR2 causing SR Ca2+ leak and VT.
Hypothesis: Inhibition of CaMKII phosphorylation of RyR2 prevents VT in mdx mice by inhibiting spontaneous Ca2+ release (SCR) events from SR.
Methods: To evaluate the role of CaMKII phosphorylation of RyR2 in DMD, 4 groups were evaluated: wild type (WT), mdx , mdx :S2814A (Genetically inhibited CaMKII phosphorylation site on RyR2 in mdx mice) and mdx :S2808A (Genetically inhibited PKA phosphorylation site on RyR2 in mdx mice) mice. Intracardiac programmed electrical stimulation along with caffeine (120mg/kg) and epinephrine (2mg/kg) was used to evaluate incidence of inducible VT in all the 4 groups (defined as 10 beats). SR Ca2+ leak was assessed by measuring SCR events during 1 minute following burst pacing at 3 Hz in Fluo4 loaded ventricular myocytes.
Results: Following cardiac pacing, mdx mice had a higher incidence of VT (6/12) compared with WT (0/7; p<0.05). mdx :S2814A mice were protected (0/7, P<0.05 vs. mdx ), whereas mdx :S2808A mice did not show a reduction in VT (6/10). The incidence of SCR events was higher in mdx ventricular myocytes, compared with WT mice (6.95 vs. 1.0 events/min, p<0.001, n=18 and 6, respectively). CaMKII inhibitor, KN93, inhibited SCR in mdx cardiomyocytes (1.15 events/min, p<0.001, n=6).
Conclusions: Inhibition of RyR2 phosphorylation by CaMKII, but not PKA, prevents VT in a mouse model of DMD. mdx mice have elevated SR Ca2+ leak, which is reversed by inhibition of CaMKII. Thus, CaMKII-induced Ca2+ leak from the SR may trigger VT in patients with DMD.
- © 2010 by American Heart Association, Inc.