Cardiac ryanodine receptor and oxidative stress

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PROJECT SUMMARY Abnormal activity of the cardiac ryanodine receptor (RyR2) leads to increased and untimely release of Ca2+ from the sarcoplasmic reticulum (SR), driving Ca2+-dependent arrhythmogenesis that can lead to sudden death in many cardiac disorders. Oxidative modification of RyR2 by reactive oxygen species (ROS) has long been established to enhance the sensitivity of the channels to Ca2+ within the SR (intraluminal Ca2+) in the failing heart. However, both the intracellular source of ROS, as well as the specific redox-sensitive residues of RyR2 which control intraluminal Ca2+ sensitivity, remain elusive. Our initial studies implicate the role of the SR oxidoreductase system in this control, whereby molecular chaperones and enzymes that facilitate protein folding also modulate activity of RyR2. We have identified intraluminal cysteines of RyR2 that elicit functional effects on the channel, as well as an oxidoreductase chaperone that associates with the channel in a redox-dependent manner. Moreover, we found upregulation of oxidoreductase enzyme in rodent models of cardiac disease, and observed RyR2 activity stabilization with pharmacological inhibition of this enzyme. We therefore hypothesize that dysregulation of the SR oxidoreductase system impairs luminal Ca2+ regulation of RyR2 via an ‘intraluminal SR redox sensor’ and promotes arrhythmogenesis. We will test our hypothesis by 1) defining the molecular components of the SR redox sensor that control luminal Ca2+ sensitivity of RyR2, and 2) determining the role of dysregulated SR redox homeostasis in Ca2+-dependent arrhythmogenesis. To address these aims, we will employ a multilevel experimental approach, investigating at the molecular, cellular, and whole heart level. We propose to use heterologous systems, biochemical approaches and human induced pluripotent stem cell cardiomyocyte (hiPSC-CM) technology to identify the RyR2 redox sensor. We also propose to study disease- associated perturbations of the SR oxidoreductase system in rodent models of inherited and acquired Ca2+- dependent arrhythmia, utilizing novel genetic biosensors, as well as adenoviral (AV) and adeno-associated viral (AAV) gain- and loss- of function approaches. With renowned experts in cardiac EC coupling, protein biochemistry and hiPSC-CM technology, The Ohio State University offers an exceptional training environment for the mentored phase of the award to reach these goals. Furthermore, building on my strong background in molecular biology, I will collaborate with an expert in CRISPR-mediated gene editing of hiPSC-CMs to study these mechanisms in a relevant human model. The achievement of the proposed aims will uncover novel regulatory mechanisms of RyR2 regulation, with potential to be therapeutically exploited. This proposal therefore addresses a fruitful and unexplored research area, relevant to a spectrum of cardiovascular diseases, which will lay strong foundations for an independent research career in cardiovascular physiology.