T-tubule remodeling and Ca2+-dependent arrhythmogenesis in cardiomyopathies.

心力衰竭(HF)是美国增长最快的心脏病类型，是心脏无法泵送足够的血液来满足身体需求的一种病理生理状态。在动物模型和人类患者衰竭的心室肌细胞中，我们和其他人已经证明了广泛分布和高度组织的心肌细胞横跨(T)-小管系统的破坏。这些有序的表面膜内陷进入细胞内部，对于快速电刺激、启动和同步触发肌浆网(SR)钙释放，从而在整个肌细胞中协调收缩每个收缩单位至关重要。由于细胞内钙离子释放异常和收缩功能减退，T-小管的丢失和紊乱会导致心力衰竭的发生。然而，对调节T小管完整性或参与破坏性T小管重塑的分子机制和途径的了解有限。我们的初步数据表明，连接蛋白-2(JP2)是一种横跨T小管和SR膜的结构蛋白，对正常的T小管组织至关重要。我们在心脏应激动物模型中的数据显示，JP2的下调与T小管的破坏和心衰的发生有关。此外，我们的初步结果表明，JP2的下调是由钙离子依赖的蛋白酶CalPain的激活驱动的，尽管导致Calain介导的JP2在HF中降解的上游事件尚不清楚。该项目的目标是明确心脏疾病中JP2调节失调和T-小管重构的机制。我们将结合原位共聚焦成像、电生理学、分子生物学、病理小鼠模型和新型转基因小鼠模型等多学科方法，测试两个特定的目标。目的1.明确心力衰竭时JP2下调的分子机制。目的2.确定重组JP2表达是否以及如何减轻应激诱导的T小管重塑和防止心衰进展。由于心力衰竭是65岁以上患者住院的最常见原因，并给我们的卫生保健系统带来了巨大的负担，因此仍然迫切需要新的治疗方法。这些研究的潜在积极影响是，预防T管功能障碍可能代表了一种新的基于机制的方法，以改善与心力衰竭相关的医疗保健结果。了解这些分子机制将为T小管靶向治疗提供一个新的平台，以防止心衰的发生和进展。

Heart failure (HF), the fastest-growing type of cardiac disease in the U.S., is a pathophysiologic state in which the heart fails to pump sufficient blood to meet the needs of the body. In failing ventricular myocytes from animal models and human patients, we and others have demonstrated disruption of the widely distributed and highly organized cardiomyocyte traverse (T)-tubule system. These orderly invaginations of surface membrane into the cell interior are critical for rapid electric excitation, initiation and synchronous triggering of sarcoplasmic reticulum (SR) Ca2+ release, and, therefore, coordinated contraction of each contractile unit throughout the entire myocyte. T-tubule loss and disorganization instigate development of HF due to aberrant intracellular Ca2+ release and blunted contractile function. However, there is a limited understanding of the molecular mechanisms and pathways that regulate T-tubular integrity or that participate in destructive T-tubule remodeling. Our preliminary data indicate that junctophilin-2 (JP2), a structural protein spanning T-tubules and the SR membrane, is crucial for normal T-tubule organization. Our data in animal models of cardiac stress show that downregulation of the JP2 is associated with T-tubule disorganization and HF development. Furthermore, our preliminary results indicate that JP2 downregulation is driven by activation of the Ca2+- dependent protease, calpain, though the upstream events that result in calpain-mediated degradation of JP2 in HF remain unclear. The goal of this project is to define the mechanisms of JP2 dysregulation and T-tubule remodeling in cardiac disease. We will combine multidisciplinary approaches including in situ confocal imaging, electrophysiology, molecular biology, pathological mouse models and novel transgenic mouse models, to test two specific aims. Aim 1. To define the molecular mechanisms underlying JP2 downregulation in heart failure. Aim 2. To determine if and how recombinant JP2 expression can attenuate stress-induced T-tubule remodeling and protect against HF progression. As HF is the most common cause of hospitalization in patients over 65 and causes an enormous burden on our health care system, new therapeutic approaches for HF are still critically needed. The potential positive impact of these studies is that preventing T-tubule dysfunction may represent a novel mechanism-based approach to improve health care outcomes related to HF. Understanding these molecular mechanisms will provide a novel platform for T-tubule-targeted therapies that prevent HF development and progression.