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

描述(申请人提供)：项目摘要。BAG3是与Hsp70家族分子伴侣结合并调控的辅伴分子。BAG3在肌肉中表达，已被报道具有抗细胞凋亡作用。已经产生了Baks基因纯合破坏的小鼠，显示出一种显著的出生后表型，动物在2周后停止生长，并在4周前一致死亡。这些bag3基因缺陷的动物发生了具有细胞凋亡特征的肌原纤维变性。肌肉退行性变在隔肌和比目鱼肌中尤为严重，这表明在缺乏BAG3的情况下，生理性使用容易导致肌肉退变。在Bag3缺陷的肌肉中，观察到泛素化蛋白的积累，蛋白酶体亚单位的上调和肌钙蛋白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，有几条证据表明，袋子抑制泛素蛋白酶体系统。C2C12成肌细胞中bag3的基因敲除表明细胞凋亡增加，泛素化蛋白积累增加。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分解来保护肌肉的关键。本实验从以下几个方面探讨了抑制细胞凋亡和泛素蛋白酶体的分子机制：(1)研究BAG缺乏引起细胞凋亡的分子机制；(2)确定Bag3在调节骨骼肌泛素蛋白酶体和相互作用蛋白中的作用；(3)通过Cre-lox系统或骨骼肌特异性过表达Bag3的病理生理学模型和杂交实验，在体内产生并分析Bag3缺失对骨骼肌的影响。相关性：这些研究将提供关于BAG3在生理应激下肌肉细胞存活中的作用的见解，并可能为我们理解肌纤维变性的分子机制和探索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