Thrombospondin 4 Regulates Adaptive ER Stress Response

摘要 与骨骼肌肌纤维类似，心脏中的心肌细胞似乎特别 容易受到膜不稳定和破裂的最轻微的扰动，部分原因是 它们的收缩状态产生持续的机械变形。的基因突变 破坏或削弱肌营养不良蛋白-糖蛋白复合物的膜锚定蛋白 (DGC)或整联蛋白粘附网络引起广泛的肌营养不良， 引起心肌病。我们最近的研究表明，thromobospondin基因家族（Thbs 1- 5)通过对ER应激反应的影响， 分泌途径，以及控制存在于肌膜上的整联蛋白复合物。在 我们上一轮的资助表明，心脏中选择性Thbs蛋白的过度表达 或骨骼肌对心脏和骨骼肌肌膜稳定性有显著影响， 肌肉细胞，而相同Thbs基因的KO小鼠具有互补效应， 正是过度表达效应。因此，在此更新应用程序中，我们将尝试揭示 Thbs蛋白调节肌膜稳定性的分子机制 内质网应激和愈合，部分通过编码细胞表面的选择整合素异源二聚体 的心肌细胞。我们提出了一个统一的假设，即Thbs蛋白是应激诱导的 ER驻留因子，其通过充当囊内 用于通过分泌途径将整联蛋白递送到肌膜的分子伴侣。为了解决这个 假设我们提出了三个具体目标。目标1将比较Thbs 3与Thbs 4在调节 心脏肌膜稳定性与阿霉素诱导的心肌病和肌肉疾病 营养不良（膜不稳定模型）。目标#2我们将尝试拯救增强的 整合素介导的Thbs 3 TG和Thbs 4-/-小鼠心脏病表型和肌膜不稳定性 体内过表达。目标#3我们将研究Thbs 3 降低膜稳定性，而Thbs 4通过细胞内的整合素加工增加膜稳定性。 定义起作用的分子机制以及选择性整合素分选如何通过 THBS蛋白在应激刺激和愈合过程中的作用将为治疗 MI损伤和缺血后心力衰竭。

Abstract Similar to skeletal muscle myofibers, cardiomyocytes in the heart appear to be particularly susceptible to membrane instability and rupture with the slightest perturbation, in part because of their contractile status that produces ongoing mechanical deformation. Mutations in genes that disrupt or weaken the membrane anchoring proteins of the dystrophin-glycoprotein complex (DGC) or the integrin adhesion network causes a wide range of muscular dystrophies that also cause cardiomyopathy. We have recently shown that the thromobospondin gene family (Thbs1- 5) plays a critical role in membrane stability through both effects on the ER stress response and secretory pathways, as well as controlling the integrin complexes present on the sarcolemma. In our previous cycle of funding we showed that overexpression of select Thbs proteins in the heart or skeletal muscle can have remarkable effects on sarcolemma stability in heart and skeletal muscle cells, while KO mice for the same Thbs genes have reciprocal effects that complement exactly the overexpression effect. Thus, in this renewal application we will attempt to uncover the molecular mechanisms whereby the Thbs proteins serve to regulate sarcolemmal stability during ER stress and healing, in part, through coding for select integrin heterodimers on the cell surface of cardiomyocytes. We propose the unifying hypothesis that the Thbs proteins are stress-induced ER resident factors that facilitate healing after injury or with stress by serving as intra-vesicular chaperones for sarcolemmal delivery of integrins through the secretory pathway. To address this hypothesis we propose 3 specific aims. Aim #1 will compare Thbs3 versus Thbs4 in regulating cardiac sarcolemma stability and disease with doxorubicin induced cardiomyopathy and muscular dystrophy (models of membrane instability). Aim #2 we will attempt to rescue the enhanced cardiac disease phenotype and sarcolemmal instability of Thbs3 TG and Thbs4-/- mice by integrin overexpression in vivo. Aim #3 we will examine the molecular mechanisms whereby Thbs3 reduces membrane stability and Thbs4 increases it through integrin processing within the cell. Defining the molecular mechanisms in play and how selective integrin sorting is achieved by the Thbs proteins during stress stimulation and healing will suggest novel treatment approaches for MI injury and post-ischemic heart failure.