Role of co-chaperone, BAG3, in muscle degeneration under physiological stress

描述（由申请人提供）：项目概述。BAG3是co-chaperones的一员，结合并调节hsp70家族分子伴侣。BAG3在肌肉中表达，据报道具有抗凋亡作用。已经产生了bag基因纯合破坏的小鼠，揭示了一种惊人的产后表型，即动物在2周龄后停止生长，并在4周龄时均匀死亡。这些缺乏bag3的动物出现肌原纤维变性并伴有凋亡特征。膈肌和比目鱼肌的肌肉退行性变尤其严重，这表明在缺乏BAG3的情况下，生理使用更容易导致肌肉退行性变。在bag3缺乏的肌肉中，观察到泛素化蛋白的积累，蛋白酶体亚基的上调和肌钙蛋白T的降解。环指型泛素连接酶，Siah家族蛋白直接与BAG3蛋白相互作用。此外，一些证据表明，bagS抑制泛素蛋白酶体系统。C2C12成肌细胞中bag3基因敲低表明细胞凋亡和泛素化蛋白的积累增加。综上所述，BAG3似乎是通过抑制细胞凋亡和泛素蛋白酶体蛋白水解来保护肌肉的关键。为探索细胞凋亡及泛素蛋白酶体抑制的分子机制，拟开展以下实验：(1)研究bag -deficiency导致细胞凋亡的分子机制；(2)确定BAG3在骨骼肌中调控泛素蛋白酶体和相互作用蛋白的功能；(3)通过病理生理模型和交叉交配实验，通过Cre-lox系统或体内骨骼肌特异性过表达BAG3来产生和分析骨骼肌中BAG3耗损的影响。相关性：这些研究将揭示BAG3在生理应激下肌肉细胞存活中的作用，并可能为我们理解肌原纤维变性的分子机制和探索人类肌肉退行性疾病治疗的新靶点提供线索

DESCRIPTION (provided by applicant): Project Summary. BAG3 is a member of co-chaperones that binds to and regulates Hsp70-family molecular chaperones. BAG3 is expressed in muscle and has been reported to possess anti-apoptotic. Mice with homozygous disruption of their bagS genes have been generated, revealing a striking post-natal phenotype whereby animals stop growing after 2 weeks of age, and uniformly die by 4 weeks. These bag3-deficient animals develop myofibrillar degeneration with apoptotic feature. The muscle degeneration is especially severe in the diaphragm and soleus muscles, suggesting that physiological use predisposes to muscle degeneration in the absence of BAG3. In bag3 deficient muscle, accumulation of ubiquitinated protein, upregulation of proteasome subunit and degradation of troponin T has been observed. Ring finger type ubiquitin ligase, Siah family protein directly interact to BAG3 protein. Additionally, several lines of evidence indicate that bagS inhibits the ubiquitin proteasome system. Gene knockdown of bag3 in C2C12 myoblast indicates increased apoptosis and accumulation of ubiquitinated proteins. Taken together, BAG3 appears to be critical for protection of muscle through inhibition of apoptosis and ubiquitin proteasome proteolysis. Experiments are proposed to explore the molecular mechanism of inhibition of apoptosis and ubiquitin proteasome including: (1) Studying the molecular mechanisms of apoptosis caused by bagS-deficiency; (2) To determine the function of BAG3 in regulation of ubiquitin proteasome and interacting protein in skeletal muscle and (3) Generation and Analyzing the effects of bag3 depletion in skeletal muscle by Cre-lox system or skeletal muscle specific over-expression of bag3 in vivo using pathophysiological model and cross mating experiments. Relevance: These studies will provide insights about the roles of BAG3 in muscle cell survival under physiological stress, and may provide us clues for understanding molecular mechanisms of myofibrillar degeneration and for investigating the new target for therapy of muscular degenerative human diseases