Thrombospondin 4 regulates adaptive ER stress response

摘要 心肌细胞中的ER/SR区室高度专门用于控制兴奋中的钙流动- 收缩偶联（ECC），以及调节蛋白质合成和对未折叠的应激反应 proteins.传统的内质网应激反应涉及钙和未折叠或受损的蛋白质的传感， ER通过3种不同途径启动信号级联以改变蛋白质合成和其他 细胞适应压力的特征。我们最近发现血小板反应蛋白4（TSP 4）是一种应激诱导的 在分泌到细胞外基质（ECM）之前在ER/SR中驻留一段时间的因子， 改变了内质网的应激反应心脏表达TSP 1、TSP 2和TSP 4，每一种都是 在受伤或应激刺激后显著上调。有趣的是，TSP 4仅在心脏中表达， 和骨骼肌，它似乎是一个完全不同的功能亚类从TSP 1和TSP 2。我们 已经确定了TSP 4作为心脏诱导蛋白的一种新功能， ER/SR的功能导致更大的收缩性，增加适应性ER应激的活性 反应，并保护心脏衰竭诱导的刺激。因此，我们假设TSP 4是一种新的 适应性应激反应因子，有利于ER/SR功能提供心脏保护。在这个项目中，我们将： 1)确定TSP 4是否通过适应性ER应激反应途径保护心脏免于衰竭 2）研究介导TSP 4依赖性心脏保护的ER应激反应因子， 以及3）确定TSP 4如何以及在何处发出适应性ER应激反应的信号。我们将使用TSP 4转基因 和基因靶向小鼠来研究这3个具体目标，以及许多转基因模型， 改变的ER应激信号传导或基于蛋白质聚集的心肌病。广泛的体外分子 还提出了确定TSP 4协调保护性ER应激的机制的方法 对心脏有益。最后，与Kranias和Robbins实验室的许多合作是 提出确定TSP 4如何影响钙处理和未折叠蛋白质反应。

ABSTRACT The ER/SR compartment in a cardiomyocyte is highly specialized for controlling calcium fluxing in excitation- contraction coupling (ECC), as well as for regulating protein synthesis and stress responsiveness to unfolded proteins. The traditional ER stress response involves sensing of calcium and unfolded or damaged proteins in the ER through 3 distinct pathways that initiate a cascade of signaling to alter protein synthesis and other features of cellular adaptation to stress. We recently identified thrombospondin 4 (TSP4) as a stress-inducible factor that resides for a period of time in the ER/SR before being secreted to the extracellular matrix (ECM), where it alters the ER stress response. The heart expresses TSP1, TSP2, and TSP4, each of which is dramatically up-regulated following injury or stress stimulation. Interestingly, TSP4 is only expressed in heart and skeletal muscle, and it appears to be of an entirely different functional subclass from TSP1 and TSP2. We have identified a novel function for TSP4 as a cardiac inducible protein that dramatically enhances the content and function of the ER/SR resulting in greater contractility, increased activity of the adaptive ER stress response, and protection from heart failure-inducing stimuli. Thus, we hypothesize that TSP4 is a novel adaptive stress-response factor that benefits ER/SR function to provide cardioprotection. In this project we will: 1) determine if TSP4 protects the heart from failure through adaptive ER stress response pathway engagement, 2) investigate the ER stress response factors that mediate TSP4-dependent cardio-protection, and 3) determine how and where TSP4 signals the adaptive ER stress response. We will use TSP4 transgenic and gene-targeted mice to investigate these 3 specific aims, as well as numerous transgenic models with altered ER stress signaling or protein aggregation-based cardiomyopathy. Extensive in vitro molecular approaches are also proposed to identify the mechanism whereby TSP4 coordinates the protective ER stress response and benefits the heart. Finally, numerous collaborations with the Kranias and Robbins lab's are proposed to determine how TSP4 affects calcium handling and the unfolded proteins response.