Musde Passive Stretch-Induced Activation of Skeletal Muscle Satellite Cells

卫星细胞在成年肌肉中通常是静止的，但它们可以负责肌纤维的再生和工作诱导的肥大。在迄今为止的所有生长因子研究中，仅肝细胞生长因子（HGF）已显示刺激静止卫星细胞进入细胞周期（Alien等人，1995; Tatsumi等人，1998年）。肝细胞生长因子蛋白定位于未受伤的骨骼肌纤维的细胞外基质中，并显示为粉碎的肌肉提取物中的活性剂。HGF的信号传导受体是c-met原癌基因，并且其信息和蛋白质已在静止卫星细胞中发现（Alien et al.，1995; Cornelison & Wold，1997; Tatsumi等人，1998年）。因此，静止卫星细胞活化的一个关键方面可能是活性HGF从其隔离中释放并呈递给c-met.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，并探索 ...更多信息 采用9月龄SD大鼠后肢重量的悬吊模型，在活体动物上进行牵拉实验。D.使大鼠牵拉悬挂的左后肢内侧的内收肌和股薄肌0.5 - 2.0小时。在牵拉期结束时，大鼠接受BrdU的ip注射; 16小时后制备卫星细胞（> 97%结蛋白阳性），随后在铺板后30小时进行BrdU的免疫细胞化学。根据拉伸的时间，BrdU标记和细胞产量分别增加了2倍和4倍，超过对侧未拉伸的腿或未处理大鼠的对照肌肉。此外，拉伸的肌肉提取物（SME），这是从2小时拉伸的组织，通过在PBS中孵育它制备，显示活性HGF所揭示的免疫印迹，并能激活卫星细胞在培养中的剂量依赖性的方式，0.5毫克SME/毫升的活性是可比的外源性HGF，并可以被抗HGF抗体中和。未拉伸的肌肉提取物没有显示出活化活性。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。此时，肌纤维释放HGF的机制尚未建立，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