Thrombospondin 4 regulates adaptive ER stress response

描述（由申请人提供）：心肌细胞中的ER/SR室高度专门化，用于控制兴奋-收缩偶联（ECC）中的钙通量，以及调节蛋白质合成和对未折叠蛋白质的应激反应。传统的内质网应激反应包括通过3种不同的途径感知内质网中的钙和未折叠或受损的蛋白质，这些途径启动一系列信号传导，改变蛋白质合成和细胞适应应激的其他特征。我们最近发现血栓反应蛋白4 （TSP4）是一种应激诱导因子，在分泌到细胞外基质（ECM）之前，它在内质网/SR中存在一段时间，在那里它改变内质网应激反应。心脏表达TSP1、TSP2和TSP4，它们在损伤或应激刺激后均显著上调。有趣的是，TSP4仅在心脏和骨骼肌中表达，它似乎是与TSP1和TSP2完全不同的功能亚类。我们已经确定了TSP4作为心脏诱导蛋白的一种新功能，它可以显著增强ER/SR的含量和功能，从而增强收缩性，增加适应性ER应激反应的活性，并保护心脏免受心力衰竭诱导的刺激。因此，我们假设TSP4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。在本项目中，我们将：1)确定TSP4是否通过参与适应性内质网应激反应途径保护心脏免于衰竭；2)研究介导TSP4依赖性心脏保护的内质网应激反应因子；3)确定TSP4如何以及在何处发出适应性内质网应激反应的信号。我们将使用TSP4转基因和基因靶向小鼠来研究这3种特异性目的，以及许多具有改变内质网应激信号或蛋白质聚集性心肌病的转基因模型。还提出了广泛的体外分子方法来确定TSP4协调保护性内质网应激反应并有益于心脏的机制。最后，我们与Kranias和Robbins实验室进行了多次合作，以确定TSP4如何影响钙处理和未折叠蛋白的反应。

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: The ER stress response appears to be a universal feature of all cardiomyopathies. However, there are very little data that directly examine if the ER stress response is beneficial or detrimental to the heart. We have identified a novel regulator of the ER stress response, TSP4, which appears to only engage the protective ER stress response. Understanding how and why TSP4 does this is of great medical relevance.