S100A1 DNA-based Inotropic Therapy Protects Against Proarrhythmogenic Ryanodine Receptor 2 Dysfunction

Abstract

Restoring expression levels of the EF-hand calcium (Ca(2+)) sensor protein S100A1 has emerged as a key factor in reconstituting normal Ca(2+) handling in failing myocardium. Improved sarcoplasmic reticulum (SR) function with enhanced Ca(2+) resequestration appears critical for S100A1's cyclic adenosine monophosphate-independent inotropic effects but raises concerns about potential diastolic SR Ca(2+) leakage that might trigger fatal arrhythmias. This study shows for the first time a diminished interaction between S100A1 and ryanodine receptors (RyR2s) in experimental HF. Restoring this link in failing cardiomyocytes, engineered heart tissue and mouse hearts, respectively, by means of adenoviral and adeno-associated viral S100A1 cDNA delivery normalizes diastolic RyR2 function and protects against Ca(2+)- and β-adrenergic receptor-triggered proarrhythmogenic SR Ca(2+) leakage in vitro and in vivo. S100A1 inhibits diastolic SR Ca(2+) leakage despite aberrant RyR2 phosphorylation via protein kinase A and calmodulin-dependent kinase II and stoichiometry with accessory modulators such as calmodulin, FKBP12.6 or sorcin. Our findings demonstrate that S100A1 is a regulator of diastolic RyR2 activity and beneficially modulates diastolic RyR2 dysfunction. S100A1 interaction with the RyR2 is sufficient to protect against basal and catecholamine-triggered arrhythmic SR Ca(2+) leak in HF, combining antiarrhythmic potency with chronic inotropic actions.

S100A1 Protein Does Not Compete with Calmodulin for Ryanodine Receptor Binding but Structurally Alters the Ryanodine Receptor·Calmodulin Complex

“…2A). In addition, further evidence of a physical interaction between RyR2 and S100A1 has been recently provided via proximity ligation assays and immunoprecipitation (6).…”

“…Either way, these results require both S100A1 and CaM to concurrently bind to RyR2. Numerous studies in electrically stimulated and quiescent cardiomyocytes have indicated that S100A1 indeed has a dual effect on the activity of the macromolecular RyR2 complex by improving both systolic opening and diastolic closure of the channel when intracellular S100A1 protein levels are elevated above normal (4,6,25). Increasing the amount of S100A1 bound to the RyR2 significantly reduced the calcium spark rate in normal cardiomyocytes and rescued the arrhythmogenic diastolic RyR2 dysfunction in failing cells.…”

“…1). Our FRET toolkit is uniquely capable of resolving RyR-specific readouts from SR samples, in which RyRs are known to only be a small fraction (ϳ25%) of the S100A1 targets in resting cardiomyocytes (6). Results largely contradict the tested hypothesis and show that S100A1 and CaM can concurrently bind to and regulate RyR1 and RyR2.…”

“…Thus, S100A1 and CaM might appear to exert similar effects on the RyR2 channel activity because CaM is well characterized to decrease RyR2 activity at both submicromolar and high micromolar Ca 2ϩ (14,15). However, measurements of [ 3 H]ryanodine binding to isolated cardiac SR membranes, a convenient index of the open RyR, show activation of RyR2 at both nano-and micromolar calcium (4), which appears inconsistent with some of the channel and myocyte measurements (5,6,13). This discrepancy indicates that the in vivo effect of S100A1 on RyR activity depends on interactions with intracellular partners or conditions that are insufficiently understood.…”

“…S100A1 has also been shown to interact with and functionally modulate RyR1 and RyR2 (3)(4)(5). As a modulator of RyR2 activity, CaM is widely considered to be an effective inhibitor of Ca 2ϩ leak through RyR2 (6,7), and S100A1 is thought to exert a similar effect. Moreover, S100A1-based gene therapy shows promising effectiveness to correct abnormal Ca 2ϩ cycling in heart failure (8,9).…”