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

描述（由申请人提供）：Ca 2+依赖性心律失常是心源性猝死的主要原因，通常在心肌中意外发生。拟议的工作旨在研究关键细胞内Ca 2+信号蛋白的空间重构可能是这种功能障碍的基础这一假设。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（约10%）的变化，也会显著改变Ca 2+控制系统的稳定性;随着蛋白质簇靠得更近，会出现显著的不稳定性，并将正常的细胞稳定性改变为促细胞增殖底物。拟议的工作将结合联合收割机的数学模型的心脏钙+信号与关键的实验研究在单细胞，小梁，和整个心脏，以确定如何异常钙2+信号出现在细胞水平上，并影响电活动的心脏。Ryanodine受体（RyRs）在连接肌浆网中形成簇，并构成心脏的Ca 2+释放单位（CRU）。CRU与附近含有L型Ca 2+通道（LTCC）的肌膜或横管膜并列。在去极化时，LTCC触发CRU产生Ca 2+火花，当同步时，产生[Ca 2 +]i瞬变。当它们不同步时，罕见的自发Ca 2+火花通常不会触发附近的CRU，因为局部[Ca 2 +]i不足以升高以激活CRU中的RyR。然而，特定疾病状态下CRU空间分布的重塑可能会改变该安全系数，并导致CRU的异常触发。如果这以很高的频率发生，否则正常的Ca 2+火花将在细胞水平上触发升高的Ca 2+的致瘤传播波。这种升高的Ca 2+波的传播波可以激活内向电流，从而产生期外收缩和心律失常。PI将使用两种易发生非预期Ca 2+依赖性血管生成的动物模型，研究CRU空间重构是血管功能障碍的基础或促成血管功能障碍的核心假设。将检查表达遗传定义的家族性肥厚性心肌病（FHC）的小鼠和自发性高血压大鼠。三个问题将得到解决：（1）根据新的，最先进的数学模型，肌节缩短是否会使Ca 2+控制系统不稳定？(2)如果是这样，缩短CRU间距的药理学手段是否也会产生Ca 2+不稳定性？(3)最后，具有原因不明的Ca 2+依赖性心律失常发生的动物模型是否揭示了心律失常对CRU间距的相同依赖性？总的来说，计划的工作将提供心脏Ca 2+信号传导和血管生成的新信息，并为治疗令人困惑的和迄今无法解释的Ca 2+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脏性猝死的主要原因，经常在心肌中意外发生。拟议的工作旨在验证这一假设，即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构可能是这种功能障碍的基础。这些研究汇集了数学建模，超级计算机模拟，最先进的成像和心脏病模型，以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脏性猝死。这些研究将为治疗复杂的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.