Modeling the spatiotemporal properties of crosstalk between RYR-mediated and IP3R-mediated calcium signaling in cardiac myocytes

项目总结 据估计，全球每年有400-500万人死于心脏性猝死。在心脏病患者中 失败，SCD是头号死亡原因，并与室性心律失常的发生有关。 因此，了解心力衰竭患者的室性心律失常是如何发生的，这对于设计 预防心力衰竭和延长心力衰竭患者生存时间的有效药物。在脑室 心肌细胞兴奋收缩偶联的基础是细胞内钙信号。具体来说， 激活电压门控的钙通道导致SR通过钙释放通道释放钙，从而 在局部胞浆内的[钙离子]增加被称为“火花”。然后，火花加在一起，产生全球增长 整个细胞的胞质内的[钙]称为钙瞬变。在正常情况下，这是一个紧密的 控制和协调的过程，导致脑室的同步收缩。当受到干扰时， 然而，整个细胞内不同步的钙释放，即所谓的钙波，可能会导致不协调 室性收缩，即心律失常。 在研究技术上具有挑战性的条件时--例如形象化个人的安排 SR上的Ca2+释放通道-或调查无法轻松操作的条件-例如 研究改变排列方式如何影响致心律失常波的形成概率--计算 建模变得非常有用。这样的变量可以很容易地被操纵来预测可通过实验测量的 结果。虽然以前已经使用建模来研究钙火花和波，但目前的数学模型 模型对钙离子释放单位的亚细胞性质做出了几个假设。更确切地说， 他们认为只有兰尼定受体负责SR钙离子的释放，而忽略了IP3受体。 它们在健康的心肌细胞中低表达，在衰竭的心肌细胞中表达增加。 它们还假定释放点之间的通道的同质并矢几何和空间排列。 虽然已知诸如释放单元中的释放通道的数量之类的属性在 健康的心肌细胞，这些影响以及二元构型的改变在衰竭时变得尤为突出。 已经发生重构的心室肌细胞，因此应该包括在模型中。 鉴于临床上需要了解心力衰竭时心室肌细胞的变化 易发生心律失常和SCD，但在实验中操作重要的空间和 在衰竭的心肌细胞中发现几何变化，显然需要准确的数学模型 与健康心肌细胞相比，细胞内钙信号失灵。我计划通过开发 更准确的钙电火花和钙波模型，可解释(1)钙释放单位的异质性 (2)IP3受体在正常和病变心肌细胞中的表达。然后我会改进的 这些模型基于体外实验结果。

PROJECT SUMMARY Sudden cardiac death (SCD) is estimated to cause 4-5 million deaths per year worldwide. In patients with heart failure, SCD is the number one leading cause of death and is linked to the onset of ventricular arrhythmias. Understanding how ventricular arrhythmias arise in patients with heart failure is thus critical to designing effective drugs that prevent SCD and prolong survival in patients with heart failure. In ventricular cardiomyocytes, the foundation of excitation-contraction coupling is intracellular Ca2+ signaling. Specifically, activation of voltage-gated Ca2+ channels cause Ca2+ release from the SR via Ca2+ release channels resulting in local increases in cytoplasmic [Ca2+] known as “sparks.” Sparks then sum to generate global increases in cytoplasmic [Ca2+] across the cell called Ca2+ transients. Under normal circumstances, this is a tightly controlled and coordinated process that leads to synchronous contraction of the ventricles. When disturbed, however, dyssynchronous Ca2+ release across the cell, known as Ca2+ waves, can lead to uncoordinated ventricular contraction i.e. arrhythmia. When studying conditions that are technically challenging—such as visualizing the arrangement of individual Ca2+ release channels on the SR—or investigating conditions that cannot be easily manipulated—such as studying how changing that arrangement affects probability of arrhythmogenic wave formation—computational modeling becomes very useful. Such variables can be easily manipulated to predict experimentally measurable outcomes. While modeling has been used to study Ca2+ sparks and waves previously, current mathematical models make several assumptions about the subcellular properties of Ca2+ release units. More specifically, they assume that only ryanodine receptors are responsible for SR Ca2+ release while ignoring IP3 receptors, which are lowly expressed in healthy ventricular myocytes and show increased expression in failing myocytes. They also assume homogeneous dyadic geometry and spatial arrangement of channels between release sites. While it is known that properties such as the number of release channels in a release unit are variable in healthy myocytes, these effects as well as changes to dyadic geometry become especially prominent in failing ventricular myocytes in which remodeling has occurred, and should thus be included in models. Given the immense clinical need to understand how changes to ventricular myocytes in heart failure predisposes to arrhythmia and SCD yet the difficulty in experimentally manipulating important spatial and geometric changes found in failing myocytes, there is a clear need for accurate mathematical models of intracellular Ca2+ signaling in failing compared to healthy myocytes. I plan to address this need by developing more accurate models of Ca2+ sparks and Ca2+ waves that account for (1) heterogeneity in Ca2+ release units and (2) the expression of IP3 receptors in both healthy and diseased ventricular myocytes. I will then refine these models based on in vitro experimental findings.