Ablation of PLN rescues reperfusion arrhythmias but exacerbates myocardium infarction in hearts with Ca2+/calmodulin kinase II constitutive phosphorylation of ryanodine receptors.

UNASSIGNED

Abnormal Ca2+ release from the sarcoplasmic reticulum (SR), associated with CaMKII-dependent phosphorylation of RyR2 at Ser2814, has consistently been linked to arrhythmogenesis and ischemia/reperfusion-induced cell death. In contrast, the role played by SR Ca2+ uptake under these stress conditions remains controversial. We tested the hypothesis that an increase in SR Ca2+ uptake is able to attenuate reperfusion arrhythmias and cardiac injury elicited by increased RyR2-Ser2814 phosphorylation.

UNASSIGNED

We used WT mice, which have been previously shown to exhibit a transient increase in RyR2-Ser2814 phosphorylation at the onset of reperfusion; mice with constitutive pseudo-phosphorylation of RyR2 at Ser2814 (S2814D) to exacerbate CaMKII-dependent reperfusion arrhythmias and cardiac damage, and PLN-deficient-S2814D knock-in mice (SDKO) resulting from crossbreeding S2814D with PLN deficient mice (PLNKO). At baseline, S2814D and SDKO mice had structurally normal hearts. Moreover none of the strains were arrhythmic before ischemia. Upon cardiac ischemia/reperfusion (I/R), WT and S2814 hearts exhibited abundant arrhythmias that were prevented by PLN ablation. In contrast, PLN ablation increased infarct size compared to WT and S2814D hearts. Mechanistically, the enhanced SR Ca2+ sequestration evoked by PLN ablation in SDKO hearts prevented arrhythmogenic events upon reperfusion by fragmenting SR Ca2+ waves into non-propagated, non-arrhythmogenic events (mini-waves). Conversely, the increase in SR Ca2+ sequestration did not reduce but rather exacerbated I/R induced SR Ca2+ leak, as well as mitochondrial alterations, which were greatly avoided by inhibition of RyR2. These results indicate that the increase in SR Ca2+ uptake is ineffective in preventing the enhanced SR Ca2+ leak of PLN ablated myocytes from either entering into nearby mitochondria and/or activating additional CaMKII pathways, contributing to cardiac damage.

UNASSIGNED

Our results demonstrate that increasing SR Ca2+ uptake by PLN ablation can prevent the arrhythmic events triggered by CaMKII-dependent phosphorylation of RyR2-induced-SR Ca2+ leak. These findings underscore the benefits of increasing SERCA2a activity in the face of SR Ca2+ triggered arrhythmias. However, enhanced SERCA2a cannot prevent but rather exacerbates I/R cardiac injury.