Arrhythmia Mechanisms in Sarcomeric Cardiomyopathies

描述（由申请人提供）：肌丝钙敏感性增加是引起家族性肥厚性心肌病（HCM）的肌瘤突变的共同特征，心肌梗死（MI）后也描述了同样的钙敏感性增加。这两种疾病都与室性心律失常和猝死的高风险相关，但肌丝钙敏感性和心律失常易感性之间的机制尚不清楚。这项更新应用将研究肌丝钙敏感性与诱发心律失常之间的机制联系。在上一个资助周期中，我们发现两个钙致敏肌钙蛋白T （TnT）突变（I79N, F110I）和钙致敏化合物EMD57033都显著增加了细胞质的钙结合亲和力（即表观Kd），但对最大细胞质缓冲能力（即Bmax）没有影响。这些数据首次证实了TnT突变对细胞质钙缓冲性能的直接影响。在生理心率下肌丝钙结合亲和力增加的主要结果是舒张末期细胞质中钙的增加。令人惊讶的是，与先前的预测相反，肌浆网（SR）中的钙含量没有降低。相反，肌丝钙结合增加的净效应是在心率加快期间，钙在细胞质中积累，在短暂的暂停后，导致SR钙过载，动作电位（AP）延长和早期后去极化。再加上我们在HCM和心肌梗死后小鼠模型中发现暂停依赖性触发严重室性心律失常，这些令人兴奋的新结果使我们提出以下假设：肌丝Ca结合亲和力增加是导致暂停依赖性SR Ca过载的根本缺陷，从而增加诱发心律失常的易感性。Aim 1中的实验将检验我们的假设是否可以推广到导致遗传性心肌病（即家族性HCM或扩张型心肌病[DCM]）的其他肌瘤突变。目的2将确定不同物种肌丝钙结合增加如何改变钙处理和AP调节。目的3将测试肌丝钙结合增加是否会导致获得性心脏病（即缺血性心肌病）的心律失常风险。目的1。为了验证改变肌丝钙敏感性的肉瘤突变引起肌丝钙结合亲和力和细胞质钙缓冲的一致变化的假设。目的：探讨肌丝钙结合亲和力增加对不同物种肌细胞钙稳态和动作电位调节的影响。验证肌纤丝钙结合增加导致慢性心肌梗死后心律失常的假说

DESCRIPTION (provided by applicant): Increased myofilament Ca sensitivity is a common feature of sarcomeric mutations that cause familial hypertrophic cardiomyopathy (HCM) and the same Ca sensitivity increase has also been described after myocardial infarction (MI). Both diseases are associated with a high risk for ventricular arrhythmia and sudden death, but the mechanisms linking myofilament Ca sensitivity and arrhythmia susceptibility remain poorly understood. This renewal application will investigate the mechanistic link between myofilament Ca sensitivity and triggered arrhythmia. During the last funding cycle, we discovered that two Ca-sensitizing Troponin T (TnT) mutations (I79N, F110I) and the Ca sensitizing compound EMD57033 both significantly increase the Ca binding affinity of the cytosol (i.e., apparent Kd), but have no effect on the maximal cytosolic buffering capacity (i.e., Bmax). These data establish for the first time a direct effect of the TnT mutations on cytosolic Ca buffering properties. The main consequence of the increased myofilament Ca binding affinity at physiological heart rates was an increase in end-diastolic Ca in the cytosol. Surprisingly, and in contrast to previous predictions, Ca content in the sarcoplasmic reticulum (SR) was NOT reduced. Rather, the net effect of increased myofilament Ca binding was the accumulation of Ca in the cytosol during periods of rapid heart rates, which after brief pauses then led to SR Ca overload, action potential (AP) prolongation and early afterdepolarizations. Together with our finding of pause-dependent triggering of serious ventricular arrhythmia both in HCM and post-MI mouse models, these provocative new results have led us to formulate the following hypothesis: Increased myofilament Ca binding affinity is a fundamental defect that causes pause-dependent SR Ca overload and thereby increases triggered arrhythmia susceptibility. Experiments in Aim 1 will test whether our hypothesis can be generalized to other sarcomeric mutations that cause inherited cardiomyopathies (i.e., familial HCM or dilated cardiomyopathy [DCM]). Aim 2 will determine how increased myofilament Ca binding alters Ca handling and AP regulation in different species. Aim 3 will test whether increased myofilament Ca binding causes arrhythmia risk in acquired heart disease (i.e., ischemic cardiomyopathy). Aim 1. To test the hypothesis that sarcomeric mutations that change myofilament Ca sensitivity cause concordant changes in myofilament Ca binding affinity and cytosolic Ca buffering Aim 2. To determine the effect of increased myofilament Ca binding affinity on myocyte Ca homeostasis and action potential regulation in different species Aim 3. To test the hypothesis that increased myofilament Ca binding contributes to triggered arrhythmia after chronic MI