Abstract 16335: S100A1 Prevents SR Ca2+ Leak and Protects Against Arrhythmias in Ventricular Cardiomyocytes
Purpose: S100A1 exerts its inotropic and therapeutic actions in normal (NCM) and failing (FCM) cardiomyocytes in part through improved sarcoplasmic reticulum (SR) calcium (Ca2+) resequestration. The goal of this study was to determine whether S100A1-mediated SR Ca2+ content enhancement entails pro-arrhythmogenic diastolic SR Ca2+ leakage in vitro and in vivo.
Methods and Results: Adenoviral-mediated S100A1 overexpression (3-4 fold vs. GFP-control) in quiescent NCMs and FCMs decreased SR Ca2+-frequency (-50 and -40%) and prevented β-AR-triggered compound Ca2+-sparks and Ca2+ waves (-32% in FCMs) as assessed by epifluorescent and confocal Ca2+ imaging. Under electrical stimulation (2Hz), S100A1 protected NCMs and FCMs from β-AR-triggered diastolic Ca2+ waves (-62 and -58%). In multicellular rat engineered heart tissue (EHT), S100A1-overexpression (6-8 fold vs. GFP-control) protected from Ca2+- and β-AR-triggered after-contractions (ACs) vs. GFP-control (-50%) with preserved enhancement of isometric twitch force (+40%) at 2Hz and 1.6 mM Ca2+extra. S100A1-mediated rescue of contractile failure of endothelin-1-treated EHT (-50% decrease in TF) was associated with protection from Ca2+- and β-AR-triggered ACs. Mechanistically, confocal immunofluorescence and co-immunoprecipitation reveals that S100A1 interacts with RyR2 in intact normal myocardium and S100A1/RyR2 binding is decreased in failing hearts (-50%). Enhanced S100A1/ryanodine receptor (RyR2) stoichiometry by S100A1-overexpression changed neither PKA nor CaMKII RyR2 phosphorylation pattern. AAV9/S100A1-mediated cardiac S100A1 restoration eventually protected post-MI failing wild-type as well as S100A1 knock-out mice from epinephrine-induced lethal ventricular fibrillations in vivo.
Conclusion: Our data disclose that the cardiac inotropic factor S100A1 exerts profound antiarrhythmic potency in vitro and in vivo. Enhanced binding of S100A1 to RyR2 seems to improve diastolic closure but future work is needed to decipher mutual binding sites and RyR2 conformational changes.
- © 2012 by American Heart Association, Inc.