Elucidation of Molecular Mechanism of Muscle Regeneration of Dystrophin-dificient Duchenne Muscular Dystorophy

我们之前在α1-syntrophin敲除小鼠中发现了异常的肌肉再生（J.Cell Biol 158:1097-1107, 2002）。这些发现可能代表在肌营养不良蛋白缺乏的杜氏肌营养不良症中发现的异常肌肉再生，因为肌营养不良蛋白结合蛋白之一α1-突触蛋白的表达在肌营养不良蛋白缺乏的肌膜中也不存在。在本研究中，我们试图进一步阐明肌肉再生的分子机制。我们特别关注了尾部悬架模型，其中骨骼肌由于微重力而遭受肌肉萎缩。非常有趣的是，那些萎缩的肌肉在地面上重新加载后显示出迅速恢复。我们深入分析了模型中肌营养不良蛋白-糖蛋白复合物（DGC）成分的表达。我们发现，在尾部悬浮期间，神经元一氧化氮合酶（nNOS）的表达减少。nNOS是一种功能分子，通过DGC α1-syntrophin锚定在肌膜上。因此，我们研究了nNOS和α1-syntrophin敲除小鼠的尾巴悬浮过程。非常有趣的是，nNOS敲除小鼠在悬尾过程中表现出肌肉萎缩的抵抗性，而α1-综合征敲除小鼠则没有。此外，nNOS敲除小鼠在重新加载过程中肌肉再生困难。在肌肉再生过程中，卫星细胞的增殖最为重要。我们最后检测了nNOS敲除小鼠肌肉卫星细胞的增殖能力，发现这些细胞的增殖能力受损。因此，我们认为nNOS的表达在悬吊期间的肌肉萎缩和地面重装后肌肉再生期间的卫星细胞增殖中都起着重要作用。

We previously identified abnormal muscle regeneration in α1-syntrophin knock-out mice (J.Cell Biol 158:1097-1107, 2002). These findings may represent abnormal muscle regeneration found in dystrophin-deficient Duchenne muscular dystrophy, since expression of α1-syntorophin, one of dystrophin-binding proteins, was also absent from the dystrophin-deficient sarcolemma. In this study, we further tried to elucidate molecular mechanism of muscle regeneration. We paticulaly paid attention on tail suspension model, where skeletal muscle was suffered from muscle atroply due to micro-gravity. Very interestingly those atrophied muscle revealed prompt recovery after re-loading on the ground. We intensively analyzed expression of constituents of dystrophin-glycoprotein complex (DGC) on the model. We found a decrease of expression of neuronal Nitric Oxide synthase (nNOS) from the sarcolemma during the tail suspension. nNOS is one of functional molecules, which is anchored to the sarcolemma through α1-syntrophin of DGC. Therefore, we examined process of tail suspension of both nNOS and α1-syntrophin knock out mice. Very interestingly, nNOS knock-out mice revealed resistency in muscle atrophy during tail suspension process, but α1-syntorophim knock-out mice did not. Moreover, nNOS knock-out mice showed difficulty in muscle regrowth in re-loading process. In muscle regrowth process, proliferation of satellite cells were most important, as found in muscle regeneration. We finally examined proliferation capacity of muscle satellite cells of nNOS knock out mice and revealed impaired proliferation capacity of these cells. Therefore, we concluded the expression of nNOS is very important both in muscle atrophy during tail suspension and in proliferation of satellite cells during muscle re-growth after reloading on the ground.