Musde Passive Stretch-Induced Activation of Skeletal Muscle Satellite Cells

卫星细胞在成人肌肉中通常是静止的，但它们可以负责肌肉纤维的再生和工作诱导的肥大。到目前为止，在所有的生长因子研究中，只有肝细胞生长因子（HGF）被证明可以刺激静止的卫星细胞进入细胞周期（Alien et al., 1995; Tatsumi et al., 1998）。HGF蛋白定位于未受伤的骨骼肌纤维的细胞外基质中，并在粉碎的肌肉提取物中显示为活性剂。HGF的信号受体是c-met原癌基因，在静止的卫星细胞中发现了它的信息和蛋白（Alien et al., 1995; Cornelison & Wold, 1997; Tatsumi et al., 1998）。因此，静止卫星细胞激活的一个关键方面可能是活性HGF从其隔离和提交到c- met中释放出来。本研究的目的是确定卫星细胞是否可以在体内被机械拉伸激活，并进一步探讨HGF在激活机制中的可能作用。活体拉伸实验采用我们的悬吊模型，利用9月龄sd大鼠后肢的重量对悬吊的左后肢内侧的内收肌和股薄肌进行拉伸，拉伸时间0.5 ~ 2.0 hr。在拉伸期结束时，大鼠接受ip注射BrdU；16小时后制备卫星细胞（> 97% desmin阳性），然后在镀后30小时进行BrdU免疫细胞化学。根据拉伸时间的不同，brdu标记和细胞产量分别比未拉伸大鼠的对侧腿或对照肌肉增加2倍和4倍。拉伸肌肉提取物（SME）在PBS中培养2小时后，免疫印迹显示HGF活性，并能以剂量依赖性方式激活培养中的卫星细胞；0.5 mg SME/ml的活性与外源HGF相当，可被抗HGF抗体中和。未拉伸的肌肉提取物没有显示出激活活性。这些实验提供了骨骼肌的机械扰动和导致卫星细胞进入细胞周期的生化信号之间的关键联系。目前，肌纤维中HGF释放的机制尚未确定，有待进一步研究。少

Satellite cells are normally quiescent in adult muscle, but they can be responsible for regeneration and work-induced hypertrophy of muscle fibers. Of all the growth factors studies thus far, only hepatocyte growth factor (HGF) has been shown to stimulate quiescent satellite cells to enter the cell cycle (Alien et al., 1995; Tatsumi et al., 1998). HGF protein was localized in the extracellular matrix of uninjured skeletal muscle fibers and shown to be the active agent in a crushed muscle extract. The signaling receptor for HGF is the c-met proto-oncogene, and its message and protein have been found in quiescent satellite cells (Alien et al., 1995; Cornelison ＆ Wold, 1997; Tatsumi et al., 1998). Therefore, a critical aspect of the activation of quiescent satellite cells may be the release of active HGF from its sequestration and presentation to the c- met. The purpose of this study was to determine whether satellite cells could be activated by mechanical stretch in vivo, and to explore … More the possible role of HGF in the activation mechanism.Stretch experiments were conducted in the living animal using our suspension model, which used the weight of the hind portion of 9-month-old S. D. rats to stretch the adductor and gracilis muscles on the inside of the left hind limb suspended for a period of 0.5-2.0 hr. At the end of the stretch period, rats received an ip-injection of BrdU; 16 hr later satellite cells were prepared (>97 % desmin-positive) followed by immunocytochemistry for BrdU at 30 hr post-plating. Depending on the period of stretch, BrdU-labeling and cell yield were increased two and four-fold, respectively, over the contralateral un-stretched leg or control muscle from untreated rats. Also, stretched muscle extract (SME), which was prepared from the 2 hr-stretched tissue by incubating it in PBS, showed active HGF as revealed by immunoblotting, and could activate satellite cells in culture in a dose-dependent manner; the activity of 0.5 mg SME/ml was comparable to that of exogenous HGF and could be neutralized by anti-HGF antibody. Un-stretched muscle extract did not show activating activity. These experiments provide a critical link between mechanical perturbation of skeletal muscle and biochemical signals that result in entry of satellite cells into the cell cycle. At this time, the mechanism of HGF release from muscle fibers has not been established, awaiting further studies. Less