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

描述（由申请人提供）：项目摘要。BAG 3是与Hsp 70家族分子伴侣结合并调节Hsp 70家族分子伴侣的共伴侣成员。BAG 3在肌肉中表达，并且已经报道具有抗凋亡作用。已经产生了具有其bagS基因的纯合破坏的小鼠，揭示了惊人的出生后表型，其中动物在2周龄后停止生长，并且均匀地在4周龄时死亡。这些bag 3缺陷的动物发生具有凋亡特征的肌原纤维变性。肌肉变性在横膈膜和比目鱼肌中尤其严重，这表明生理用途在BAG 3不存在的情况下易发生肌肉变性。在bag 3缺陷的肌肉中，已经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（Ring finger type ubiquitin ligase）是Siah家族蛋白，与BAG 3蛋白直接相互作用。此外，一些证据表明，bagS抑制泛素蛋白酶体系统。在C2 C12成肌细胞中bag 3基因敲低表明细胞凋亡和泛素化蛋白积累增加。综上所述，BAG 3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。本研究拟从分子水平探讨泛素蛋白酶体抑制细胞凋亡的机制，包括：（1）研究bagS缺陷导致细胞凋亡的分子机制;（2）确定BAG 3在骨骼肌中对泛素蛋白酶体和相互作用蛋白的调节中的功能。使用病理生理学模型和交叉交配实验在体内检测Bag 3的LOX系统或骨骼肌特异性过表达。相关性：这些研究将为了解BAG 3在生理应激下肌细胞存活中的作用提供新的思路，并为了解肌原纤维变性的分子机制和探索治疗肌肉退行性疾病的新靶点提供线索

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