The role of thrombospondin-4 in the secretory pathway, extracellular matrix produ

描述（由申请人提供）：心血管疾病是美国死亡的主要原因，相关医疗费用每年超过2000亿美元。心血管疾病，包括心脏病，通常以心力衰竭为高潮，心脏不能向周围组织和器官输送足够的血液。事实上，心力衰竭的5年生存率为50%，是最常见的出院诊断。目前的治疗标准包括靶向与心脏病进展相关的途径的药物，如神经内分泌刺激和高血压，导致心力衰竭和死亡率的延迟进展，但不影响疾病的根本原因或实质性改变最终的疾病结局。因此，更好地了解直接参与心脏病发病机制或介导心脏保护免受疾病诱发刺激（即心肌梗死）的分子途径将有助于开发新的、有效的治疗心脏病的治疗策略。为此，赞助商的实验室一直在研究血栓反应蛋白（一种钙结合糖蛋白家族，在伤口愈合和组织修复中起着重要作用）在预防心脏病方面的作用。血栓反应蛋白在心脏病状态下被诱导，血栓反应蛋白-4的过度表达保护心脏免受压力过载肥厚（PO）和心肌梗死损伤（MI），而缺乏血栓反应蛋白-1、2或4的小鼠在心脏应激后死亡率大大增加。申办者的实验室最近在心肌细胞中发现了一种由thbrobrospondin -4 （Thbs4）激活的心脏保护性适应性内质网（ER）应激途径。Thbs4的过表达还会导致心脏和骨骼肌的囊泡扩张和分泌增强，这表明血栓反应蛋白通过分泌途径调节通量的组织自主作用。此外，蛋白质相互作用研究表明，Thbs-4与细胞内底物运输或细胞外基质（ECM）或细胞膜的许多蛋白质相互作用。这些发现表明Thbs4在将底物运送到最终目的地以维持心肌细胞稳态和/或ECM产生方面具有关键作用。因此，Thbs4激活的分泌途径可能对维持心肌细胞内蛋白质的正常转换和定位以及心脏应激条件下（如PO或MI）的适应性至关重要。因此，本提案将研究1)Thbs4的结构域介导其在内质网应激感知、运输或ECM产生/稳态调节中的功能，以及2)Thbs4在将蛋白质运输到细胞内、膜内和细胞外目的地中的作用。这些研究将阐明细胞运输和调控的机制

DESCRIPTION (provided by applicant): Cardiovascular disease is the leading cause of mortality in the United States, with associated healthcare costs exceeding $200 billion per year. Cardiovascular diseases, including heart disease, commonly culminate in heart failure, in which the heart is incapable of pumping a sufficient supply of blood to the peripheral tissues and organs. Indeed, heart failure has a 50% 5 year survival rate and is the most common hospital discharge diagnosis. Current standards of care include drugs that target pathways involved in the progression of heart disease, such as neuroendocrine stimulation and hypertension, resulting in delayed progression of heart failure and mortality but not affecting the underlying cause of the disease or substantially altering ultimate disease outcomes. Therefore, a better understanding of the molecular pathways directly involved in the pathogenesis of heart disease or that mediate cardioprotection from disease-inducing stimuli (i.e. myocardial infarction) will ai in the development of novel, efficacious therapeutic strategies to treat heart disease. To that end, the sponsor's laboratory has been investigating the role of thrombospondins, a family of calcium-binding glycoproteins with fundamental roles in wound healing and tissue repair, in protection from heart disease. Thrombospondins are induced in cardiac disease states and overexpression of thrombospondin-4 protects the heart from pressure overload hypertrophy (PO) and myocardial infarction injury (MI), while mice lacking thrombospondin-1, 2, or 4 exhibit greatly increased mortality after cardiac stress. The sponsor's laboratory has recently identified a cardioprotective adaptive endoplasmic reticulum (ER) stress pathway that is activated by thbrombospondin-4 (Thbs4) in cardiomyocytes. Overexpression of Thbs4 also results in vesicular expansion and enhanced secretion in the heart and skeletal muscle, suggesting a tissue autonomous role for thrombospondins in regulating flux through the secretory pathway. Moreover, protein interaction studies reveal that Thbs-4 interacts with a number of proteins involved in trafficking of substrates within the cell or to the extracelluar matrix (ECM) or cell membrane. These findings suggest that Thbs4 has critical roles in trafficking substrates to their ultimate destinations to maintain cardiomyocyte homeostasis and/or ECM production. Thus, Thbs4 activates a secretory pathway that may be critical in maintaining normal turnover and localization of proteins within cardiomyocytes and adaptive under cardiac stress conditions, such as PO or MI. Therefore, this proposal will examine 1) the domains of Thbs4 that mediate its functions in ER stress sensing, trafficking, or regulation of ECM production/homeostasis and 2) the roles of Thbs4 in trafficking proteins to intracellular, membranous, and extracellular destinations. These studies will elucidate mechanisms of cellular trafficking and regulation of the ER stress response and provide insight into molecular pathways involved in protection from cardiac disease, thereby aiding in the development of novel therapeutic strategies to treat heart disease and other diseases associated with protein quality control and ECM remodeling.