Molecular pathogenesis of congenital muscular dystrophies and development of new therapeutic measures

营养不良多糖(DG)将细胞外基质与细胞骨架连接起来。最近，在几种先天性肌营养不良症中发现了编码糖基转移酶的基因突变，α-DG的异常糖基化与它们的发病机制(α-血糖营养不良症)有关。在这项研究中，我们获得了一些关于α-营养不良糖病分子发病机制的新发现：(1)我们发现了特异性地降解β-DG胞外区的蛋白酶活性。这种活性被基质金属蛋白酶-2和基质金属蛋白酶-9的抑制剂抑制。培养细胞向培养液中分泌基质金属蛋白酶-2和基质金属蛋白酶-9。活性的MMP2和MMP9酶可降解β-DG。在Duchenne肌营养不良症和肌糖症及其模型动物中，MMP2和MMP9被激活。这些结果表明，基质金属蛋白酶-2和基质金属蛋白酶-9的抑制剂对这些疾病可能是有效的。(2)FUKUTIN缺陷嵌合小鼠的周围神经髓鞘形成缺陷，这是一种小鼠…更多的福山型先天性肌营养不良模型。有髓神经纤维密度明显降低，大量异常大的无髓轴突被单个雪旺细胞包裹。α-DG的糖链部分和层粘连蛋白结合活性在嵌合小鼠的周围神经中严重降低。这些小鼠的乙酰胆碱受体聚集性有缺陷，神经肌肉接头出现碎片化。这些结果表明，先天性肌营养不良时应注意周围神经髓鞘损伤。(3)我们发现了α-DG的N-末端结构域(α-DG-N)的裂解和分泌。分泌的α-DG-N既是N-糖基化的，也是0-糖基化的，在人血清和脑脊液中都能检测到α-DG-N。这些观察结果表明，α-DG-N的裂解是一种广泛的事件，提示分泌的α-DG-N可能通过体循环运输，α-DG-N的水平在α-糖代谢不良症中可能发生改变。较少

Dystroglycan (DG) links the extracellular matrix with cytoskeleton. Recently, mutations of the genes encoding putative glycosyltransferases were identified in several congenital muscular dystrophies and aberrant glycosylation of α-DG has been implicated in their pathogeneses (α-dystroglycanopathy). In this study, we have obtained several novel findings concerning the molecular pathogenesis of a-dystroglycanopathy.(1) We found the protease activity that degrades the extracellular domain of β-DG specifically. This activity was suppressed by the inhibitor of MMP-2 and MMP-9. Cultured cells secreted MMP-2 and MMP-9 into the culture medium. Active MMP-2 and MMP-9 enzymes degraded the β-DG. MMP-2 and MMP-9 were activated in Duchenne muscular dystrophy and sarcoglycanopathyas well as in their model animals. These results indicate that inhibitors of MMP-2 and MMP-9 may be effective for these diseases.(2) Peripheral nerve myelination was defective in the fukutin-deficient chimeric mice, a mouse … More model of Fukuyama-type congenital muscular dystrophy. The density of myelinated nerve fibers was significantly decreased and clusters of abnormally large non-myelinated axons were ensheathed by a single Schwann cell. The sugar chain moiety and laminin-binding activity of α-DG were severely reduced in the peripheral nerve of the chimeric mice. The clustering of acetylcholine receptor was defective and neuromuscular junctions are fragmented in appearance in these mice. These results demonstrate that dysmyelination of peripheral nerve should be carefully watched in congenital muscular dystrophies.(3) We found the cleavage and secretion of the N-terminal domain of α-DG (α-DG-N). Secreted α-DG-N was both N- and 0-glycosylated.α-DG-N was detectable in the human serum and cerebrospinal fluid. These observations indicate that the cleavage of α-DG-N is a widespread event and suggest that the secreted α-DG-N might be transported via systemic circulation and that the level of α-DG-N may be altered in α-dystroglycanopathies. Less