Calsequestrin in Ventricular Arrhythmia and Sudden Death

描述（由申请人提供）：心脏钙螯合蛋白（CASQ 2）及其结合伴侣连接蛋白和三聚体蛋白-1（TRDN）是肌浆网（SR）钙储存和释放的关键调节因子。在人类中，CASQ 2突变导致儿茶酚胺能多态性室性心动过速（CPVT）和心源性猝死综合征。在之前的资助期间，我们已经产生并研究了Casq 2 null（Casq 2-/-）小鼠，以确定CASQ 2突变导致电生理不稳定的机制。我们发现，尽管缺乏Casq 2蛋白，这些小鼠仍保持接近正常的SR Ca储存、Ca释放和收缩功能，这可能是由于SR体积的扩大和Casq 2结合蛋白triadin-1和junctin的急剧减少。Casq 2-/-小鼠表现出CPVT表型，即它们在儿茶酚胺输注或运动的情况下发展多形室性心动过速。我们目前的概念是，在高SR Ca负荷条件下，Ca释放不应性的丧失和SR Ca过早释放，导致延迟后除极、触发搏动和多形性室性心动过速。然而，如果触发源来自心室肌细胞或来自传导系统的专门细胞，浦肯野细胞，是无法解决的。来自RyR 2突变小鼠模型的实验数据和理论考虑支持浦肯野网络。此外，生物化学，电子显微镜和共聚焦研究表明，Casq 2只发现在终端池的交界SR密切接触RyR 2钙释放通道。因此，我们假设，在心室肌细胞和/或浦肯野细胞中RyR 2附近Casq 2的存在减少是导致SR Ca过早释放并增加心律失常易感性的基本缺陷。这适用于遗传综合征（例如，Casq 2连锁的CPVT;目的1+2）和由于RyR 2附近的Casq 2运输和/或保留缺陷而导致的潜在获得性心脏病（目的3）。目的1：检验Casq 2的恢复挽救Casq 2-/-小鼠的CPVT表型的假设。目标二：目的3：检验心肌梗死后存活的心肌中Casq 2在RyR 2 Ca释放通道附近减少的假设。 公共卫生相关性：拟议的工作将研究某些遗传性心脏病的原因，这些心脏病与心律失常（不规则心跳）以及猝死和过早死亡的高风险有关。这些研究还将在动物模型中检查基因治疗的益处，这将为遗传性心律失常患者的新疗法提供重要信息。

DESCRIPTION (provided by applicant): Cardiac calsequestrin (CASQ2), and its binding partners junction and triadin-1 (TRDN), are key regulators of sarcoplasmic reticulum (SR) Ca storage and release. In humans, CASQ2 mutations cause the syndrome of catecholaminergic polymorphic ventricular tachycardia (CPVT) and sudden cardiac death. During the previous funding period, we have generated and studied Casq2 null (Casq2-/-) mice to determine the mechanisms whereby CASQ2 mutations cause electrophysiological instability. We found that despite a lack of Casq2 protein, these mice maintain near normal SR Ca storage, Ca release and contractile function, likely as a result of an expansion of SR volume and drastic reductions in the Casq2 binding proteins triadin-1 and junctin. Casq2-/- mice exhibit the CPVT phenotype, i.e. they develop polymorphic ventricular tachycardia with catecholamine infusion or exercise. Our current concept is that the loss of Ca release refractoriness and premature SR Ca release under conditions of high SR Ca load, results in delayed after-depolarizations, triggered beats and polymorphic ventricular tachycardia. However, if the trigger originates from ventricular myocytes or from specialized cells of the conduction system, the Purkinje cells, is unresolved. Experimental data from a RyR2 mutant mouse model and theoretical considerations favor the Purkinje network. Furthermore, biochemical, electron microscopy and confocal studies show that Casq2 is only found in the terminal cisternae of the junctional SR in close contact with RyR2 Ca release channels. Thus, we hypothesize that the reduced presence of Casq2 near the RyR2 in ventricular myocytes and/or Purkinje cells is a fundamental defect that causes premature SR Ca release and increases arrhythmia susceptibility. This is applicable to inherited syndromes (e.g., Casq2-linked CPVT; Aims 1+2) and potentially acquired heart disease due to defects in the trafficking to and/or retention of Casq2 near the RyR2 (Aim 3). Aim 1: To test the hypothesis that restoration of Casq2 rescues the CPVT phenotype of Casq2-/- mice. Aim 2: To test the hypothesis that loss of Casq2 in Purkinje cells is both necessary and sufficient to cause CPVT Aim 3: To test the hypothesis that Casq2 is reduced near RyR2 Ca release channels in cardiac muscle surviving after myocardial infarction. PUBLIC HEALTH RELEVANCE: The proposed work will study the causes for certain inherited heart diseases associated with arrhythmia (irregular heartbeats) and a high risk for sudden and premature deaths. The studies will also examine the benefit of gene therapy in an animal model, which will provide important information for new therapies for patients with inherited arrhythmia disorders.