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，每年相关的医疗费用超过2000亿美元。心血管疾病，包括心脏病，通常以心力衰竭而告终，在心力衰竭中，心脏不能向外周组织和器官泵送足够的血液供应。事实上，心力衰竭具有50%的5年存活率，并且是最常见的出院诊断。目前的护理标准包括靶向参与心脏病进展的途径的药物，如神经内分泌刺激和高血压，导致心力衰竭和死亡的延迟进展，但不影响疾病的根本原因或实质上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导刺激（即心肌梗死）的分子途径将有助于开发治疗心脏病的新的有效治疗策略。为此，申办方的实验室一直在研究血小板反应蛋白（一种钙结合糖蛋白家族，在伤口愈合和组织修复中发挥重要作用）在预防心脏病中的作用。血小板反应蛋白在心脏疾病状态中被诱导，并且血小板反应蛋白-4的过表达保护心脏免受压力超负荷肥大（PO）和心肌梗死损伤（MI），而缺乏血小板反应蛋白-1，2或4的小鼠在心脏应激后表现出大大增加的死亡率。申办方的实验室最近确定了一种心脏保护性适应性内质网（ER）应激途径，该途径由心肌细胞中的thbrombospondin-4（Thbs 4）激活。Thbs 4的过表达还导致心脏和骨骼肌中的囊泡扩张和分泌增强，表明血小板反应蛋白在调节通过分泌途径的流量中的组织自主作用。此外，蛋白质相互作用研究揭示，Thbs-4与参与细胞内底物运输或运输至细胞外基质（ECM）或细胞膜的许多蛋白质相互作用。这些发现表明Thbs 4在将底物运输至其最终目的地以维持心肌细胞稳态和/或ECM产生中具有关键作用。因此，Thbs 4激活分泌途径，其在维持心肌细胞内的蛋白质的正常周转和定位以及在心脏应激条件下（例如PO或MI）的适应性中可能是关键的。因此，本提案将检查1）Thbs 4的结构域，其介导其在ER应激传感、运输或ECM产生/稳态调节中的功能，以及2）Thbs 4在将蛋白运输至细胞内、膜和细胞外目的地中的作用。这些研究将阐明细胞运输和调节的机制， ER应激反应，并提供深入了解参与心脏病保护的分子途径，从而有助于开发新的治疗策略，以治疗心脏病和其他与蛋白质质量控制和ECM重塑相关的疾病。

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.