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

我们以前发现了α1-合成素基因敲除小鼠的异常肌肉再生(J.Cell Biol158：1097-1107,2002)。这些发现可能代表了Duchenne型肌营养不良症的肌肉再生异常，因为Duchenne肌营养不良症的肌膜中也缺乏α1-Syntoropin的表达，这是一种Duchenne肌营养不良蛋白结合蛋白。在本研究中，我们进一步试图阐明肌肉再生的分子机制。我们特别关注了尾部悬吊模型，在该模型中，骨骼肌由于微重力而出现肌肉萎缩。非常有趣的是，这些萎缩的肌肉在重新加载到地面后很快就恢复了。我们深入分析了营养不良蛋白-糖蛋白复合体(DGC)的成分在该模型上的表达。我们发现在尾部悬吊过程中，肌膜神经元型一氧化氮合酶(NNOS)的表达减少。一氧化氮合酶是一种功能分子，通过α-1-合成素与肌膜结合。因此，我们研究了nNOS和α1-合成素基因敲除小鼠的尾部悬吊过程。非常有趣的是，nNOS基因敲除的小鼠在尾部悬吊过程中表现出对肌肉萎缩的抵抗，而α1-syntorophim基因敲除的小鼠则没有。此外，nNOS基因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，卫星细胞的增殖是最重要的，在肌肉再生中也是如此。最后，我们检测了nNOS基因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，我们得出结论，nNOS的表达在尾部悬吊时肌肉萎缩和地面上重负荷后肌肉重新生长过程中卫星细胞的增殖过程中都是非常重要的。

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.