Costamere Defects in Muscular Dystrophies

描述（由申请人提供）：肌原体是横纹肌细胞中的肌鞘下蛋白质组装体，其与周围肌原纤维的Z盘呈周向排列，并将产生力的肌节与肌膜物理偶联。由于一些组成蛋白是人类肌营养不良症和扩张型心肌病的主要缺陷部位，因此Costameres对正常肌肉功能显然是重要的。我们之前已经证明，在杜氏肌营养不良症和贝克尔肌营养不良症中，由基因缺陷产生的肌营养不良蛋白，在肌动蛋白丝和肌膜之间形成了重要的机械联系。我们的初步数据表明，在肌营养不良蛋白缺乏的肌肉中，y-肌动蛋白水平显著升高。虽然y-肌动蛋白单体池的增加可能通过大量作用稳定了肋肌细丝，但过量的肌浆y-肌动蛋白可能对肌肉细胞功能产生不利影响。本项目的主要目的是阐明肌营养不良基因缺陷与肌营养不良表型之间的致病机制。在这个提议中，我们将测试新的假设，即增加的y-肌动蛋白可能直接改变参与信号传导、基因表达或收缩性的其他肌肉细胞成分的活性。我们将对新的转基因小鼠品系进行表征，以确定在没有肌层损伤的情况下，哪些营养不良表型可能是由肌浆性肌动蛋白浓度增加引起的。最后，我们将通过在横纹肌中特异性消融y-肌动蛋白的新小鼠系来评估y-肌动蛋白在costamer组装和机械功能中的作用。拟议的研究将直接解决y-肌动蛋白表达增加和肋突不稳定在引起与肌营养不良病相关的骨骼肌病理中的作用。

DESCRIPTION (provided by applicant): Costameres are subsarcolemmal protein assemblies in striated muscle cells that circumferentially align in register with the Z disk of peripheral myofibrils and physically couple force-generating sarcomeres with the sarcolemma. Costameres are clearly important for normal muscle function because several constituent proteins are the primary sites of defect in human muscular dystrophies and dilated cardiomyopathies. We previously demonstrated that dystrophin, the product of the gene defective in Duchenne and Becker muscular dystrophies, forms an important mechanical link between costameric y-actin filaments and the sarcolemma. Our preliminary data indicates that y-actin protein levels are dramatically increased in dystrophin-deficient muscle. While an increase in the y-actin monomer pool likely stabilizes costameric filaments by mass action, excess myoplasmic y-actin may have adverse consequences for muscle cell function. The major objective of this project is to elucidate the pathogenic mechanisms linking dystrophin gene defects to muscular dystrophy phenotypes. In this proposal, we will test the novel hypotheses that increased y-actin may directly alter the activity of other muscle cell constituents involved in signaling, gene expression, or contractility. We will characterize new transgenic mouse lines to determine which dystrophy phenotypes may be caused by increased myoplasmic y-actin concentration in the absence of sarcolemmal damage. Finally, we will assess the role of y-actin in costamere assembly and mechanical function by characterizing new lines of mice where it is specifically ablated in striated muscle. The proposed research will directly address the role of increased y-actin expression and costamere instability in causing the skeletal muscle pathologies associated with dystrophinopathy.