Banks Glen B, Chamberlain Jeffrey S, Froehner Stanley C
Department of Neurology, Senator Paul D Wellstone Muscular Dystrophy Cooperative Research Center, University of Washington, Seattle, Washington 98195, USA.
Mol Cell Neurosci. 2009 Apr;40(4):433-41. doi: 10.1016/j.mcn.2008.12.011. Epub 2009 Jan 8.
Duchenne muscular dystrophy (DMD) is characterized by muscle degeneration and structural defects in the neuromuscular synapse that are caused by mutations in dystrophin. Whether aberrant neuromuscular synapse structure is an indirect consequence of muscle degeneration or a direct result of loss of dystrophin function is not known. Rational design of truncated dystrophins has enabled the design of expression cassettes highly effective at preventing muscle degeneration in mouse models of DMD using gene therapy. Here we examined the functional capacity of a minidystrophin (minidysGFP) and a microdystrophin (microdystrophin(DeltaR4-R23)) transgene on the maturation and maintenance of neuromuscular junctions (NMJ) in mdx mice. We found that minidysGFP prevents fragmentation and the loss of postsynaptic folds at the NMJ. In contrast, microdystrophin (DeltaR4-R23) was unable to prevent synapse fragmentation in the limb muscles despite preventing muscle degeneration, although fragmentation was observed to temporally correlate with the formation of ringed fibers. Surprisingly, microdystrophin(DeltaR4-R23) increased the length of synaptic folds in the diaphragm muscles of mdx mice independent of muscle degeneration or the formation of ringed fibers. We also demonstrate that the number and depth of synaptic folds influences the density of voltage-gated sodium channels at the neuromuscular synapse in mdx, microdystrophin(DeltaR4-R23)/mdx and mdx:utrophin double knockout mice. Together, these data suggest that maintenance of the neuromuscular synapse is governed through its lateral association with the muscle cytoskeleton, and that dystrophin has a direct role in promoting the maturation of synaptic folds to allow more sodium channels into the junction.
杜兴氏肌肉营养不良症（DMD）的特征是肌肉退化以及由肌营养不良蛋白突变导致的神经肌肉突触结构缺陷。目前尚不清楚异常的神经肌肉突触结构是肌肉退化的间接后果还是肌营养不良蛋白功能丧失的直接结果。截短型肌营养不良蛋白的合理设计使得能够设计出在DMD小鼠模型中通过基因治疗有效预防肌肉退化的表达盒。在此，我们研究了微型肌营养不良蛋白（minidysGFP）和微小型肌营养不良蛋白（microdystrophin(DeltaR4-R23)）转基因对mdx小鼠神经肌肉接头（NMJ）成熟和维持的功能能力。我们发现minidysGFP可防止NMJ处突触后褶皱的断裂和丧失。相比之下，微小型肌营养不良蛋白（DeltaR4-R23）尽管能预防肌肉退化，但无法预防肢体肌肉中的突触断裂，不过观察到断裂与环状纤维的形成在时间上相关。令人惊讶的是，微小型肌营养不良蛋白（DeltaR4-R23）增加了mdx小鼠膈肌中突触褶皱的长度，这与肌肉退化或环状纤维的形成无关。我们还证明，突触褶皱的数量和深度会影响mdx、微小型肌营养不良蛋白（DeltaR4-R23）/mdx和mdx:utrophin双敲除小鼠神经肌肉突触处电压门控钠通道的密度。总之，这些数据表明神经肌肉突触的维持是通过其与肌肉细胞骨架的侧向关联来调控 的，并且肌营养不良蛋白在促进突触褶皱成熟以允许更多钠通道进入接头方面具有直接作用。
