Costamere Defects in Muscular Dystrophies

描述(申请人提供)：肋骨是横纹肌肉细胞中的肌膜下蛋白集合，它与周围肌原纤维的Z盘周向对齐，并在物理上将产生力量的肌节与肌膜偶联。由于在人类肌肉营养不良和扩张型心肌病中，几种组成蛋白是主要的缺陷部位，因此，衣壳对于正常的肌肉功能是很重要的。我们先前已经证明，Duchenne和Becker肌营养不良症基因缺陷的产物--dystrophin，在胞核的y-肌动蛋白细丝和肌膜之间形成了一个重要的机械连接。我们的初步数据表明，在肌营养不良蛋白缺乏的肌肉中，y-肌动蛋白水平显著增加。虽然y-肌动蛋白单体池的增加可能通过质量作用来稳定胞囊细丝，但过量的肌浆y-肌动蛋白可能会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蛋白基因缺陷与肌营养不良表型之间的致病机制。在这项提案中，我们将测试新的假设，即增加的y-肌动蛋白可能直接改变与信号、基因表达或收缩有关的其他肌肉细胞成分的活性。我们将鉴定新的转基因小鼠品系，以确定在没有肌膜损伤的情况下，哪些营养不良表型可能是由于肌浆Y-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地消融y-肌动蛋白的小鼠新品系的特征来评估y-肌动蛋白在胞囊组装和机械功能中的作用。这项拟议的研究将直接解决y-肌动蛋白表达增加和胞膜不稳定在导致与营养不良症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.