Abstract 13635: Heterozygous Ablation of Ryanodine Receptor Phosphorylation at Ser2808 Exacerbates Disease in a Genetic Model of Ca-Dependent Heart Failure
RyR2 dysfunction (i.e. “leaky” RyRs) due to hyperphosphorylation at Ser-2808 by PKA has been implicated in the pathophysiology of heart failure (HF), although this remains uncertain. We recently generated a model of Ca leak-dependent HF by ablation of CASQ2, a stabilizer of RyR2 function, with upregulation of SR Ca uptake by overexpression of SERCA1a (SERCA1aOX). The HF phenotype was more severe in double mutant (DM) mice homozygous for CASQ2 ablation (CASQ2-/- X SERCA1aOX) than in DM mice heterozygous for CASQ2 ablation (CASQ2+/- X SERCA1aOX). To examine the role of RyR2 phosphorylation at Ser 2808 in the settings of Ca-dependent HF we generated triple mutant (TM) mice that combined CASQ2 ablation and SERCA1a overexpression with the RyR2 mutation S2808A that prevents RyR2 phosphorylation by PKA. The RyR2 mutation did not affect the survival of the TM mice homozygous for CASQ2 ablation, with a 12 week mortality of ∼60% in all groups. However, in the milder disease setting of heterozygous CASQ2 ablation, triple mutant mice heterozygous for RyR2 S2808A (TM-S2808A+/-) had a significantly higher percentage of premature deaths compared with their counterparts either homozygous for this mutation (TM-S2808A+/+) or normal for RyR2. Consistent with the survival data, in vivo cardiac function of TM-S2808A+/- mice was significantly worse than in the two other groups. TM-S2808A+/- mice also had the greatest extent of ultrastructural remodeling indicated by myofibril disarray and abnormal mitochondria morphology. Additionally, confocal microscope imaging of cardiomyocytes isolated from TM-S2808A+/- mice revealed increased predisposition to spontaneous Ca oscillations and pacing-induced alternans associated with Ca release heterogeneities. Thus, the RyR2 S2808A mutation exacerbated Ca-dependent HF in a heterozygote disadvantage manner (i.e. the heterozygote is more harmful than the homozygote). Considering the tetrameric composition of the RyR2 with each channel assembled randomly from WT and mutated monomers, these results suggest that partial disruption of RyR2 phosphorylation by PKA plays a detrimental role in the settings of abnormal Ca cycling, possibly through disrupting spatial heterogeneity of Ca signaling in cardiac myocytes.
- © 2012 by American Heart Association, Inc.