Cardiomyocyte-mediated mechanisms of ischemia

 描述(申请人提供)：室性快速性心律失常导致的心脏性猝死(SCD)是成人死亡的主要原因，仅在美国每年就有30多万人丧生，其中心肌缺血是最常见的原因。在这里，我们提供的数据有力地支持了这一新的假设，即使肌丝对钙(心肌细胞)敏感会损害局部冠状动脉灌注(血管系统)，从而产生心律失常易感性心脏。肌丝钙敏化发生在缺血性(ICM)和家族性肥厚型心肌病(HCM)中。我们发现，由于HCM连锁突变(TNT-I79N)引起的钙敏化或钙增敏剂EMD57033治疗，增加了应激性室性心动过速的易感性。心律失常是导致心律失常的区域缝隙连接解偶联和传导速度减慢的结果，与局灶性能量剥夺有关。更具体地说，钙致敏的心脏表现出P0连接蛋白43磷酸异构体(Cx43-P0)和磷酸化AMP-激酶的局灶性积累，这两个指标都是细胞能量剥夺的标志。然而，尚不清楚肌丝钙敏化是如何导致心肌能量剥夺的，以及为什么这种情况发生在某些区域而不是其他区域。我们的初步数据表明，缺血至少是局灶性能量剥夺的部分原因。Cx43-P0升高的区域在应激期间会变得低氧，这与与非低氧区域相比冠状动脉灌注量显著减少有关。我们的初步数据还表明，pannin(Px)通道在肌丝钙敏化和局灶性能量剥夺之间起着关键作用。PX1通道形成大孔，释放旁分泌信号分子，如ATP，并参与不同细胞类型之间的远程信号传递。缺血后PX1表达增加，并在TNT-I79N脑室异质性增加。引人注目的是，整体PX1消融抑制了TNT-I79N小鼠的局灶性能量剥夺和心律失常。我们的主要假设是，肌丝钙敏化损害局部冠脉血流，并在应激时导致局部缺血，部分由PX1介导。我们将通过直接量化能量赤字来检验这一假设，b确定结构属性是否使某些区域易于能量匮乏(目标1)，以及肌丝钙敏化如何损害冠状动脉灌注(目标2)。我们将通过PX1测试旁分泌信号在局灶性脑缺血发生中的作用(目标3)。这些实验将描绘出一种新的机械途径，将心肌细胞的特性与改变的局部血流联系起来，以产生易发生心律失常的心脏。这些结果将推动了解SCD的机制、定义预防策略和确定新的治疗靶点的长期目标。

 DESCRIPTION (provided by applicant): Sudden cardiac death (SCD) from ventricular tachyarrhythmia's is a leading cause of death in adults and costs more than 300,000 lives annually in the US alone, with myocardial ischemia being the most common cause. Here we present data that strongly support the novel hypothesis that sensitizing the myofilaments to Ca (cardiomyocyte) impairs local coronary perfusion (vasculature) to generate an arrhythmia-susceptible heart. Myofilament Ca sensitization occurs in ischemic (ICM) and familial hypertrophic cardiomyopathy (HCM). We found that Ca sensitization, due to a HCM-linked mutation (TnT-I79N) or treatment with the Ca sensitizer EMD57033, increases the susceptibility to ventricular tachycardia during stress. The arrhythmias are the result of arrhythmogenic regional gap junctional uncoupling and conduction velocity slowing linked to focal energy deprivation. More specifically, Ca sensitized hearts showed focal accumulation of the P0 connexin 43 phospho-isoform (Cx43-P0) and phosphorylated AMP-kinase, both markers for cellular energy deprivation. Unknown is though how myofilament Ca sensitization causes myocardial energy deprivation and why this occurs in some regions and not others. Our preliminary data indicate that ischemia is at least in part responsible for the focal energy deprivation. Regions with increased Cx43-P0 become hypoxic during stress and this is associated with drastically reduced coronary perfusion compared to non-hypoxic regions. Our preliminary data also suggest that pannexin (Px) channels provide a critical link between myofilament Ca sensitization and focal energy deprivation. Px1 channels form large pores, release paracrine signaling molecules like ATP and are implicated in long-range signaling between different cell types. Expression of Px1 increases post-ischemia and is heterogeneously increased in TnT-I79N ventricle. Strikingly, global Px1 ablation suppressed focal energy deprivation and arrhythmias in TnT-I79N mice. Our overarching hypothesis is that myofilament Ca sensitization impairs local coronary perfusion and leads to focal ischemia during stress, mediated in part by Px1. We will test this hypothesis by quantifying the energy deficit directly, b determining if structural properties predispose certain regions to energy deprivation (Aim 1) and how myofilament Ca sensitization impairs coronary perfusion (Aim 2). We will test the contribution of paracrine signaling via Px1 for the generation of focal ischemia (Aim 3). These experiments will delineate a novel mechanistic pathway linking myocyte properties to altered local blood flow to generate an arrhythmia- prone heart. The results will advance the long-term goals of understanding mechanisms of SCD, defining strategies to prevent it and identifying novel therapeutic targets.