Junctophilin-2 dysregulation and T-tubule remodeling in heart failure

描述（由申请人提供）：心力衰竭（HF）是美国增长最快的心脏病类型，是一种心脏不能泵出足够的血液来满足身体需要的病理生理状态。在动物模型和人类患者的衰竭心室肌细胞中，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穿越(T)-小管系统的破坏。这些表面膜有序内陷到细胞内部对于快速电兴奋、肌浆网（SR） Ca2+释放的启动和同步触发至关重要，因此，整个肌细胞中每个收缩单元的协调收缩。由于细胞内Ca2+释放异常和收缩功能减弱，t小管的丢失和紊乱引发了HF的发展。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 （junctophilin-2, JP2）是一种跨越t小管和SR膜的结构蛋白，对t小管的正常组织至关重要。我们在心脏应激动物模型中的数据显示，JP2的下调与t小管紊乱和HF的发生有关。此外，我们的初步结果表明，JP2下调是由Ca2+依赖性蛋白酶calpain的激活驱动的，尽管在HF中导致calpain介导的JP2降解的上游事件尚不清楚。该项目的目的是明确心肌疾病中JP2失调和t小管重构的机制。我们将结合多学科方法，包括原位共聚焦成像、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，来测试两个特定的目标。目的1。明确心衰中JP2下调的分子机制。目标2。目的：确定重组JP2表达是否以及如何减弱应力诱导的t小管重塑和防止HF进展。由于心衰是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心衰治疗方法。这些研究的潜在积极影响是，预防t小管功能障碍可能是一种基于机制的新方法，可以改善与心衰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HF的发生和进展。

DESCRIPTION (provided by applicant): 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 synchronus 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.