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/表型相关研究表明，大多数突变的预后意义与心脏肥大和纤维化程度有关。一个例外是几种肌钙蛋白T （TnT）突变，即使没有明显的心脏肥大和纤维化，也会导致SCD的高风险。体外研究表明，这些TnT突变都增加了肌丝ca2 +的敏感性。为了研究ca2 +敏感性增加本身是否可能导致心律失常，理想的动物模型是没有混杂的纤维化和/或肥大。我们最近通过转基因表达突变的人TnT （179N）建立了这样一个模型，该模型导致肌丝ca2 +敏感性增加，心脏肥厚和纤维化减少。我们对单细胞的初步实验表明，β -肾上腺素能受体激动剂会降低Ca2+瞬态，降低衰减速率，并升高舒张（Ca2+）i。离体灌注心脏显示室性心律失常的高发生率，特别是在高（Ca）o时，与后去极化和心室动作电位波形改变有关。因此，我们假设肌丝ca2 +敏感性的增加改变了细胞内ca2 +信号，并独立地促进了去极化后和室性心律失常的发展，从而导致心源性猝死。另一种假设是肌丝ca2 +敏感性以外的其他因素（即ca2 +信号的改变而不改变肌丝ca2 +敏感性）导致了与TnT突变相关的心律失常。为了解决另一种假设，我们将研究表达TnT突变（R278C）的转基因模型，该模型不会改变肌丝ca2 +的敏感性。我们将使用Tg-179N和Tg-R278C转基因模型从分子到器官水平验证这些假设，每个SPECIFIC AIM将独立测试肌丝ca2 +敏感性变化、细胞ca2 +信号传导和可能导致室性心律失常的全心电生理之间的潜在机制联系。如果本研究得到证实，所提出的心律失常机制可能适用于其他FHC突变和肌丝ca2 +敏感性增加的疾病。

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.