Sarcomere Length Shortening and the Destabilization of the Ca2+ Control System in

描述（由申请人提供）：Ca2+依赖性心律失常是心源性猝死的主要原因，常意外发生于心肌。提出的工作旨在检查假设，即关键细胞内Ca2+信号蛋白的空间重塑可能是这种功能障碍的基础。他们最近在初步工作中发现，即使这些蛋白质的空间分布发生很小（~10%）的变化，也会极大地改变Ca2+控制系统的稳定性；当蛋白质簇靠近时，剧烈的不稳定性产生，并将正常的细胞稳定性改变为致心律失常的底物。提出的工作将结合心脏Ca2+信号的数学建模与单细胞、小梁和整个心脏的关键实验研究，以确定异常Ca2+信号如何在细胞水平上产生并影响心脏的电活动。Ryanodine受体（RyRs）在连接肌浆网中形成簇状，并构成心脏的Ca2+释放单元（CRU）。cru靠近附近含有l型Ca2+通道（LTCC）的肌层或横管膜。在去极化时，LTCC触发CRU产生Ca2+火花，当同步时，产生[Ca2+]i瞬态。当它们不同步时，罕见的自发Ca2+火花通常不会触发附近的CRU，因为局部[Ca2+]i升高不足以激活CRU中的ryr。然而，在特定疾病状态下，cru空间分布的重塑可能会改变这种安全系数，从而导致cru的异常触发。如果这种情况频繁发生，否则正常的Ca2+火花将在细胞水平上触发升高的Ca2+的致心律失常传播波。这种升高的Ca2+波传播波可以激活向内电流，产生心动过速和心律失常。使用两种容易发生意外Ca2+依赖性心律失常的动物模型，PI将研究CRU空间重塑是心律失常功能障碍的基础或促成的核心假设。小鼠表达基因定义熟悉肥厚性心肌病（FHC）和自发性高血压大鼠将进行检查。将解决三个问题：(1)根据新的，最先进的数学模型，肌节缩短是否会破坏Ca2+控制系统的稳定性？(2)如果是这样，缩短CRU间距的药理学手段是否也会产生Ca2+不稳定性？(3)最后，具有无法解释的Ca2+依赖性心律失常的动物模型是否显示其心律失常对CRU间距的依赖性相同？总之，计划中的工作将提供心脏Ca2+信号传导和心律失常的新信息，并为治疗困惑和迄今无法解释的Ca2+依赖性心律失常的新方法奠定基础。公共卫生相关性：钙依赖性心律失常是心源性猝死的主要原因，经常意外地出现在心肌中。本研究旨在验证以下假设：在某些心脏疾病的发展过程中，关键细胞内钙信号蛋白的空间重塑可能是这种功能障碍的基础。这些研究将数学建模、超级计算机模拟、最先进的成像和心脏病模型结合起来，研究这些关键分子空间分布的细微变化如何引发心律失常和心源性猝死。这些研究将为治疗复杂和迄今无法解释的钙依赖性心律失常的新方法奠定基础。

DESCRIPTION (provided by applicant): Ca2+ dependent arrhythmias, a leading cause of sudden cardiac death, often arises unexpectedly in heart muscle. The proposed work seeks to examine the hypothesis that spatial remodeling of key intracellular Ca2+ signaling proteins may underlie this dysfunction. The has recently discovered in preliminary work that even a small (~10%) change in the spatial distribution of these proteins can dramatically alter the stability of the Ca2+ control system; as clusters of the proteins get closer together, dramatic instability arises and changes normal cellular stability into an arrhythmogenic substrate. The proposed work will combine mathematical modeling of cardiac Ca2+ signaling with critical experimental investigations in single cells, trabeculae, and whole heart to determine how abnormal Ca2+ signals arise at the cellular level and affect electrical activity in the heart. Ryanodine receptors (RyRs) form clusters in the junctional sarcoplasmic reticulum and constitute the Ca2+ release unit (CRU) of the heart. The CRUs are apposed to nearby sarcolemmal or transverse tubular membranes containing L-type Ca2+ channels (LTCC). On depolarization, the LTCC trigger the CRU to produce Ca2+ sparks which, when synchronized, produce a [Ca2+]i transient. When they are not synchronized, rare spontaneous Ca2+ sparks do not normally trigger nearby CRUs because local [Ca2+]i is insufficiently elevated to activate the RyRs in the CRU. Remodeling of the spatial distribution of the CRUs in specific disease state, however, may change that safety factor and contribute to the aberrant triggering of CRUs. Should this occur with great frequency, an otherwise normal Ca2+ spark will trigger an arrhythmogenic propagating wave of elevated Ca2+ at the cellular level. This propagating wave of elevated Ca2+ wave can activate inward current to produce extrasystoles and arrhythmias. Using two animal models prone to unexpected Ca2+ dependent arrhythmogenesis, the PI will investigate the core hypothesis that CRU spatial remodeling underlies or contributes to arrhythmic dysfunction. Mice expressing genetically defined familiar hypertrophic cardiomyopathy (FHC) and spontaneous hypertensive rats will be examined. Three questions will be addressed: (1) Does sarcomere shortening destabilize Ca2+ control system according to new, state- of-the-art mathematical models? (2) If so, can pharmacological means of shortening CRU spacing also produce Ca2+ instability? (3) Finally, do the animal models that have unexplained Ca2+ dependent arrhythmogenesis reveal the same dependence of their arrhythmias on CRU spacing? Taken together, the planned work will provide new information of cardiac Ca2+ signaling and arrhythmogenesis and lay the foundation for new approaches to treating perplexing and heretofore unexplained Ca2+ dependent arrhythmia PUBLIC HEALTH RELEVANCE: Calcium dependent arrhythmias, a leading cause of sudden cardiac death, often arises unexpectedly in heart muscle. The proposed work seeks to test the hypothesis that spatial remodeling of key intracellular calcium signaling proteins during the development of some heart diseases may underlie this dysfunction. These studies bring together mathematical modeling, supercomputer simulations, state-of-the-art imaging, and heart disease models to examine how even subtle changes in the spatial distribution of these key molecules can trigger arrhythmias and sudden cardiac death. These studies will lay the foundation for new approaches to treating perplexing and heretofore unexplained calcium dependent cardiac arrhythmias.