Abstract 37: The Positive Inotropic S100a1 Prevents Arrhythmogenic Sarcoplasmic Reticulum Ca2+ Leak And Ventricular Arrhythmias

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S100A1 has emerged as a key factor in the control of cardiomyocyte (CM) contractile performance. Improved sarcoplasmic reticulum (SR) function with enhanced Ca2+ resequestration appears critical for its cAMP-independent inotropic effects but raises concerns about potential diastolic SR Ca2+ leakage that might trigger fatal arrhythmias. Thus, the goal of this study was to determine the impact of S100A1 on ryanodine receptor 2 (RyR2)-mediated SR Ca2+ leakage in vitro and in vivo.

S100A1 association with the RyR2 was significantly diminished (-50%) in failing cardiomyocytes and hearts with S100A1 downregulation, as shown by co-immunofluorescence, co-immunoprecipitation and proximity ligation assay. Adenoviral-mediated S100A1 overexpression (3-4 fold vs. GFP-control) in quiescent NCs (normal CMs) and FCs (failing CMs) decreased SR Ca2+-frequency (-50 and −40% respectively) and protected from β-AR-triggered diastolic Ca2+-waves (-62 and −58% respectively) in electrically stimulated (2Hz) CMs as assessed by epifluorescent and confocal Ca2+ imaging. In multicellular rat engineered heart tissue (EHT), S100A1-overexpression (6-8 fold vs. GFP-control) protected from Ca2+-triggered after-contractions (ACs) (-50%) with preserved enhancement of isometric twitch force (TF, +40%) at 2Hz. S100A1-mediated rescue of contractile failure of endothelin-1-treated EHT (-50% decrease in TF) was associated with protection from Ca2+-triggered ACs. In mice with post-ischemic heart failure, AAV9-mediated therapeutic administration of S100A1 enhanced S100A1/RyR2 association and prevented epinephrine-induced VTs (70% in MI group vs. 30% in MI-S100A1 group). Mechanistically, S100A1-overexpression changed neither PKA/CaMKII RyR2 phosphorylation pattern nor binding of accessory proteins like FKBP12.6, calmodulin or sorcin to RyR2 but enhanced S100A1/RyR2 stoichiometry.

Our data provide evidence that S100A1 interaction with the RyR2 can beneficially modulate and reverse diastolic RyR2 function dysfunction. S100A1 appears to convey a rather unique molecular profile combining cAMP-independent inotropy with protection against Ca2+-triggered arrhythmias.

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