Regulation and role of the cardiac sodium channel Nav1.5 in heart failure

项目概要/摘要 心力衰竭（HF）和相关的心脏性猝死（SCD）是发病的主要原因 和死亡率，这使得进一步研究危险因素和致病机制成为可能。精确 控制心率和节律的心脏离子通道的调节是至关重要的， 电导会引发心律失常，增加SCD的风险。心脏动作电位是由 钠电流通过心脏的主要电压门控钠通道Nav1.5，由SCN 5A编码。 改变Nav1.5功能的突变会导致糖尿病综合征（Brugada、长QT、遗传性传导）， 扩张型心肌病（DCM）和SCN 5A基因座内的常见遗传变异已与微妙的 心电图测量的变化。然而，SCN 5A表达的改变对临床的影响， HF的病程和相关的非中毒性死亡仍有待彻底研究。 先前的研究表明，SCN 5A +/-单倍型不足的小鼠发生与衰老相关的不良心肌梗死。 重塑，伴随纤维化增加和传导减慢。我们最近发现，这些发现可能 转化到临床上。具体来说，我们发现了一种常见的遗传变异，它支持了一种 SCN 5A的末端编码序列（CDS）内的微小RNA（miR）结合位点。我们发现这种变异 与人心脏中SCN 5A mRNA水平降低（10-20%）有关， HF患者死亡。我们意外发现SCN 5A +/-小鼠 心脏表现出氧化应激和脂肪酸氧化的增加（FAO）。这些综合的初步数据 为我们的核心假设提供了坚实的基础，即心脏SCN 5A表达减少会提高一个人的 对亚临床心脏病的易感性，在HF的情况下转化为重大风险。与 核心概念是低Nav1.5对你的心脏不好，我们现在的首要目标是1）定义新的 控制Nav1.5水平的途径，2）描述较低的Nav1.5如何不利地影响心肌细胞，以及3） 经验性检验是否降低Nav1.5 μ s HF结局。在目标1中，我们将描述新的途径， 通过其CDS调节SCN 5A mRNA的稳定性和翻译，这是一个广泛的区域， 对RNA调控功能的探索不足。在目标2中，我们将定义还原的SCN 5A 在心肌细胞中的表达导致氧化应激和FAO升高。在目标3中，我们将确定是否减少 SCN 5A表达足以增加SCN 5A +/-单倍体不足小鼠的HF相关发病率和死亡率 有心肌病的病人总的来说，这项工作有很强的潜力，1）填补重要的知识 关于SCN 5A在RNA水平上的调控的差距，2）改变我们对Nav1.5的理解 功能超出了心脏传导中公认的作用，3）加强了减少的SCN 5A之间的联系， 表达和更差的HF，从关联观察到经验证据，以及4）提示未来 旨在将这些发现转化为改善高危HF患者的识别和护理的研究。

PROJECT SUMMARY / ABSTRACT Heart failure (HF) and associated arrhythmic sudden cardiac death (SCD) are primary causes of morbidity and mortality worldwide, warranting further investigation of risk factors and pathogenic mechanisms. Precise regulation of cardiac ion channels governing heart rate and rhythm is vital, since slight changes in ion conductance can trigger arrhythmia, elevating one’s risk for SCD. The cardiac action potential is initiated by sodium current through the heart’s primary voltage-gated sodium channel, Nav1.5, encoded by SCN5A. Mutations that alter Nav1.5 function cause arrhythmic syndromes (Brugada, long QT, inherited conduction) and dilated cardiomyopathy (DCM), and common genetic variants within the SCN5A locus have been linked to subtle changes in electrocardiographic measures. However, the impact of altered SCN5A expression on the clinical course of HF and associated non-arrhythmic deaths remains to be thoroughly investigated. Prior studies have shown that SCN5A+/- haploinsufficient mice develop aging-related adverse myocardial remodeling, with increased fibrosis and conduction slowing. We recently discovered that these findings may translate to the clinical setting. Specifically, we identified a common genetic variant that bolsters the activity of a microRNA (miR) binding site within the terminal coding sequence (CDS) of SCN5A. We found that this variant is linked to reduced SCN5A mRNA levels (10-20%) in human hearts, and surprisingly, increased non-arrhythmic death in HF patients. A potential basis for this was identified upon our unexpected finding that SCN5A+/- mouse hearts exhibit increases in oxidative stress and fatty acid oxidation (FAO). These combined preliminary data provide a solid foundation for our central hypothesis that reduced cardiac SCN5A expression elevates one’s susceptibility to subclinical cardiac pathologies that transform into significant risk in the setting of HF. With the core concept being that low Nav1.5 is bad for your heart, our overarching goals are now to 1) define new pathways controlling Nav1.5 levels, 2) delineate how lower Nav1.5 adversely impacts cardiomyocytes, and 3) empirically test if reduced Nav1.5 worsens HF outcomes. In Aim 1, we will characterize novel pathways that regulate SCN5A mRNA stability and translation via its CDS, an expansive region that remains largely underexplored for RNA regulatory functions. In Aim 2, we will define the pathways by which reduced SCN5A expression in cardiomyocytes leads to elevated oxidative stress and FAO. In Aim 3, we will determine if reduced SCN5A expression is sufficient to increase HF-related morbidity and mortality in SCN5A+/- haploinsufficient mice with surgically-induced cardiomyopathy. Overall, this work has strong potential to 1) fill significant knowledge gaps regarding the regulatory control of SCN5A at the RNA level, 2) transform our understanding of Nav1.5 functions beyond well-established roles in cardiac conduction, 3) reinforce the link between reduced SCN5A expression and worse HF, advancing from associative observations to empirical evidence, and 4) prompt future studies aimed at translating these findings towards improved identification and care of high-risk HF patients.