Troponin T mutations and Sudden Cardiac Death

描述（由申请人提供）：家族性肥厚性心肌病（FHC）是一种常染色体显性遗传疾病，由编码心脏收缩蛋白的基因突变引起，是心脏性猝死（SCD）的重要原因。基因型/表型相关性研究表明，大多数突变的预后意义与心脏肥大和纤维化的程度有关。 肌钙蛋白T（TnT）突变是一个例外，即使没有明显的心肌肥厚和纤维化，也会增加SCD的风险，体外研究表明这些TnT突变都增加了肌丝Ca 2+敏感性。 为了研究Ca 2+敏感性增加本身是否可能是促肾上腺皮质激素的，理想的是没有混杂纤维化和/或肥大的动物模型。 我们最近通过转基因表达突变型人TnT（179 N）建立了这样一个模型，该突变型人TnT（179 N）导致肌丝Ca 2+敏感性增加，而心肌肥厚和纤维化消失。 我们对单个细胞的初步实验显示，β-肾上腺素能受体激动剂可降低Ca 2+瞬变，衰减速率较慢，并升高舒张期（Ca 2+）i。 离体心脏灌注显示室性心律失常的高发生率，特别是在高（Ca）o时，与后除极和心室动作电位波形改变有关。 因此，我们推测肌丝Ca 2+敏感性的增加改变了细胞内Ca 2+信号传导，并独立地促进了后除极和室性心律失常的发展，导致心源性猝死。 另一种假设是，除了肌丝Ca 2+敏感性（即，Ca 2 +信号传导的改变而不改变肌丝Ca 2+敏感性）导致与TnT突变相关的心律失常。 为了解决替代假设，我们将检查一个转基因模型，表达一个TnT突变（R278 C），这不会改变肌丝Ca 2+敏感性。 我们将使用Tg-179 N和Tg-R278 C转基因模型从分子到器官水平来检验这些假设。每个特定的目的将独立地检验肌丝Ca 2+敏感性、细胞Ca 2+信号传导和可能导致室性心律失常的整个心脏电生理学变化之间的潜在机制联系。 如果这项研究得到证实，所提出的发病机制可能适用于其他FHC突变和疾病，增加肌丝钙敏感性。

DESCRIPTION (provided by applicant): Familial Hypertrophic Cardiomyopathy (FHC) is an autosomal-dominant disease resulting from mutations in genes encoding cardiac contractile proteins, and an important cause of Sudden Cardiac Death (SCD). Genotype/phenotype correlation studies suggest that the prognostic significance of most mutations is related to the degree of cardiac hypertrophy and fibrosis. An exception are several Troponin T (TnT) mutations, which confer a high risk of SCD even in absence of significant cardiac hypertrophy and fibrosis.In vitro studies suggest that these TnT mutations all increase myofilament Ca 2+ sensitivity. To investigate if an increased Ca 2+ sensitivity itself could be pro-arrhythmic, an animal model without the confounding fibrosis and/or hypertrophy would be ideal. We recently generated such a model by transgenic expression of mutant human TnT (179N), which resulted in increased myofilament Ca 2+ sensitivity and lack of cardiac hypertrophy and fibrosis. Our preliminary experiments on single cells show decreased Ca 2+ transients with slower decay rates, and elevated diastolic (Ca2+)i in response to beta-adrenergic receptor agonists. Isolated perfused hearts show a high incidence of ventricular arrhythmias, particularly at higher (Ca)o, associated with afterdepolarizations and altered ventricular action potential waveform. Thus we hypothesize that increased myofilament Ca 2+ sensitivity changes intracellular Ca 2+ signaling and contributes independently to development of afterdepolarizations and ventricular arrhythmias, leading to sudden cardiac death. The alternate hypothesis is that other factors than myofilament Ca 2+ sensitivity (i.e., alterations of Ca 2 + signaling without changes in myofilament Ca 2+ sensitivity) contribute to arrhythmias related to TnT mutations. To address the alternate hypothesis, we will examine a transgenic model that expresses a TnT mutation (R278C), which does NOT change myofilament Ca 2+ sensitivity. We will use the Tg-179N and Tg-R278C transgenic models to test these hypotheses from the molecular to the organ level, Each SPECIFIC AIM will independently test potential mechanistic links between changes in myofilament Ca 2+ sensitivity, in cellular Ca 2+ signaling, and in whole heart electrophysiology that may lead to ventricular arrhythmias. If validated by this research, the proposed mechanism of arrhythmogenesis may be applicable to other FHC mutations and diseases that increase myofilament Ca 2+ sensitivity.