SARCOGLYCAN IN MYOPATHY AND MUSCLE MEMBRANE STABILITY

肌营养不良蛋白的缺陷被认为破坏了肌肉细胞的细胞骨架、膜和细胞外基质之间的机械连接，导致肌营养不良和心肌病。 肌营养不良蛋白结合蛋白质复合物，该蛋白质复合物锚其与肌膜的附着，并进而结合细胞外基质蛋白，层粘连蛋白。 层粘连蛋白突变也会导致肌病，但层粘连蛋白缺乏的肌肉中的膜似乎不像肌营养不良蛋白缺乏的膜那样被物理破坏，这意味着一种独特的分子机制。 在肌营养不良蛋白-糖蛋白复合物中是一种多亚基蛋白，肌聚糖，当肌营养不良蛋白突变时，肌聚糖会继发性减少。 最近，发现肌聚糖基因突变是人类肌病的主要原因。 肌聚糖的功能是未知的，其预测的结构表明细胞表面受体。 为了研究缺乏肌聚糖的肌肉中的膜缺陷，我们使用胚胎干细胞中的同源重组来产生缺乏肌聚糖不同亚基的小鼠。γ-肌聚糖和δ-肌聚糖是通常在心肌和骨骼肌中表达的相关的35 kDa糖基化跨膜蛋白。 我们已经产生了缺乏γ-肌聚糖的小鼠和异源缺乏δ-肌聚糖的胚胎干细胞。 初步数据表明，缺乏γ-肌聚糖的小鼠表现出严重的营养不良模式，类似于由肌聚糖突变引起的人类肌病。将使用多种免疫细胞化学方法表征肌聚糖缺陷小鼠。 将研究肌聚糖缺乏引起的基因表达变化。最后，我们将进行旨在破坏多种膜-细胞外基质连接的遗传实验，以评估这些不同附件的相对贡献及其在正常和异常心脏和肌肉功能中的作用。

Defects in dystrophin are thought to disrupt a mechanical link between the cytoskeleton, the membrane and the extracellular matrix of muscle cells resulting in muscular dystrophy and cardiomyopathy. Dystrophin binds a complex of proteins that anchor its attachment to the muscle membrane and in turn, bind the extracellular matrix protein, laminin. Laminin mutations also result in myopathy, but the membrane in laminin-deficient muscle does not seem to be as physically disrupted as dystrophin-deficient membranes implying a distinct molecular mechanism. Within the dystrophin-glycoprotein complex is a multisubunit protein, sarcoglycan, that is secondarily decreased when dystrophin is mutated. Recently, it was discovered that mutations in sarcoglycan genes are a primary cause of human myopathy. The function of sarcoglycan is unknown and its predicted structure suggests a cell surface receptor. To investigate membrane defects in muscle lacking sarcoglycan, we are using homologous recombination in embryonic stem cells to generate mice lacking different subunits of sarcoglycan. gamma-sarcoglycan and delta-sarcoglycan are related 35 kDa glycosylated, transmembrane proteins normally expressed in cardiac and skeletal muscle. We have generated mice lacking gamma-sarcoglycan and embryonic stem cells heterozygously lacking delta-sarcoglycan. Preliminary data indicate mice lacking gamma-sarcoglycan show a severe dystrophic pattern that resembles human myopathy arising from sarcoglycan mutations. Sarcoglycan-deficient mice will be characterized using a variety of immunocytochemical approaches. Changes in gene expression that result from sarcoglycan deficiency will be investigated. Lastly, we will perform genetic experiments aimed at disrupting multiple membrane-extracellular matrix connections to assess the relative contribution of these different attachments and their role in normal and abnormal heart and muscle function.