Calsequestrin in Ventricular Arrhythmia and Sudden Death

摘要 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）是心脏钙螯合蛋白的关键调节因子。 肌浆网（SR）钙的储存和释放。在人类中，CASQ 2突变导致 儿茶酚胺能性多形性室性心动过速（CPVT）和心源性猝死。前一 在资助期间，我们已经产生并研究了Casq 2 null（Casq 2-/-）小鼠，以确定其机制 由此CASQ 2突变引起电生理不稳定性。我们发现，尽管缺乏Casq 2蛋白， 这些小鼠保持接近正常的SR钙储存，钙释放和收缩功能，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。Casq2-/- 小鼠表现出CPVT表型，即它们发展为具有儿茶酚胺的多形性室性心动过速 输液或锻炼。我们目前的概念是，钙的损失释放不应性和过早的SR钙 在高SR Ca负荷条件下释放，导致延迟的后去极化、触发性搏动和 多形性室性心动过速然而，如果触发源来自心室肌细胞或 传导系统的专门细胞，浦肯野细胞，尚未解决。来自RyR 2的实验数据 突变小鼠模型和理论考虑有利于浦肯野网络。此外，生物化学， 电子显微镜和共聚焦研究表明，Casq 2只存在于终末脑池中， 连接SR与RyR 2 Ca释放通道紧密接触。因此，我们假设， 在心室肌细胞和/或浦肯野细胞中RyR 2附近存在Casq 2是一个基本缺陷 导致SR Ca过早释放并增加心律失常易感性。这适用于 遗传综合征（例如，Casq 2连锁CPVT;目的1+2）和由于 在RyR 2附近运输和/或保留Casq 2的缺陷（Aim 3）。 目标1.为了检验Casq 2的恢复挽救Casq 2-/-小鼠的CPVT表型的假设。 目标2.为了检验浦肯野细胞中Casq 2的缺失对于以下假设是必要的和充分的： 引起CPVT 目标3.为了检验Casq 2在心肌中RyR 2 Ca释放通道附近减少的假设， 心肌梗死后存活

ABSTRACT Cardiac calsequestrin (CASQ2), and its binding partners junctin 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