Costamere Defects in Muscular Dystrophies

描述（由申请人提供）：肋节是横纹肌细胞中的肌膜下蛋白质组装体，其与外周肌原纤维的Z盘配准地周向对齐，并将产生力的肌节与肌膜物理偶联。Costameres对于正常的肌肉功能显然是重要的，因为几种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。我们以前证明，dystrophin，在杜氏和贝克肌营养不良症的基因缺陷的产品，形成一个重要的机械联系costameric y-肌动蛋白丝和肌膜。我们的初步数据表明，y-肌动蛋白蛋白水平显着增加，肌营养不良蛋白缺乏的肌肉。虽然y-肌动蛋白单体库的增加可能通过质量作用稳定了肋丝，但过量的肌浆y-肌动蛋白可能对肌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蛋白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，增加y-肌动蛋白可能直接改变其他肌肉细胞成分参与信号，基因表达，或收缩性的活动。我们将描述新的转基因小鼠品系，以确定哪些营养不良表型可能是由肌膜损伤的情况下肌浆γ-肌动蛋白浓度增加引起的。最后，我们将评估y-肌动蛋白在肋节组装和机械功能的作用，通过表征新的小鼠品系，它是专门消融在横纹肌。拟议的研究将直接解决增加的y-肌动蛋白表达和肋节不稳定性在引起与肌营养不良蛋白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.