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

糖酐（DG）连接细胞外基质和细胞骨架。最近，在一些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-糖营养不良症）有关。在这项研究中，我们获得了一些关于a-糖营养不良的分子发病机制的新发现。(1)发现了特异性降解β-DG胞外结构域的蛋白酶活性。这种活性被MMP-2和MMP-9抑制剂抑制。培养细胞向培养基中分泌MMP-2和MMP-9。活性MMP-2和MMP-9酶降解β-DG。MMP-2和MMP-9在杜氏肌营养不良症和肌糖病变及其模型动物中被激活。这些结果表明，MMP-2和MMP-9抑制剂可能对这些疾病有效。(2)福山型先天性肌营养不良小鼠（Fukuyama-type congenital muscular dystrophy， fufutin -deficient嵌合小鼠）周围神经髓鞘形成缺陷。有髓神经纤维密度明显降低，单个雪旺细胞包裹异常大的非有髓神经轴突。嵌合小鼠周围神经中α-DG糖链片段和层粘连蛋白结合活性严重降低。这些小鼠乙酰胆碱受体的聚类有缺陷，神经肌肉连接在外观上呈碎片化。提示先天性肌营养不良患者应密切注意周围神经的髓鞘发育异常。(3)发现α-DG （α-DG- n）的n端结构域被切割和分泌。分泌的α-DG-N同时被N-和0-糖基化。人血清和脑脊液中均检测到α-DG-N。这些观察结果表明α-DG-N的裂解是一个广泛的事件，提示分泌的α-DG-N可能通过体循环运输，α-DG-N的水平可能在α-糖营养不良病中发生改变。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