St Pierre B A, Tidball J G
School of Nursing, University of California, Los Angeles 90024-1527.
Am J Pathol. 1994 Dec;145(6):1463-71.
Modifications in muscle loading have been reported previously to result in increased numbers of mononucleated cells and changes in myofibril organization at myotendinous junctions (MTJs). The goals of this study were to determine the identity of those mononucleated cells and to examine the relationships between changes in their structure, location, and number with structural aspects of remodeling at MTJs experiencing modified loading. Soleus muscles from rats subjected to 10 days of hindlimb suspension were analyzed 0, 2, 4, and 7 days after return to weight bearing. Immunohistochemistry showed that ED1+, ED2+ and Ia+ macrophages were present at the MTJ and microtendon of control muscle. After reloading, ED2+ macrophages increased in number and size at MTJs and microtendons, indicating their activation. ED1+ cells showed no change in size or number whereas Ia+ cells were increased in size at day 7 of reloading. Electron microscopic observations showed that mononucleated cells near MTJs of control or suspended muscle were not highly active in protein synthesis or secretion. However, in reloaded muscle, mononucleated cells were found to be in close proximity to MTJs and to contain a high concentration of organelles associated with protein secretion. During these stages of reloading, extensive remodeling of myofibril-membrane associations occurred and nascent sarcomeres appeared in the MTJ regions of muscle fibers. Immunohistochemistry showed that during these stages of nascent sarcomere formation, there was renewed expression of developmental myosin heavy chain at MTJs, with this heavy chain appearing most prominently at the MTJ at day 7 of reloading. The activation and increased numbers of macrophages at MTJs and the close apposition of secretory cells to the MTJ membrane during remodeling lead us to propose that macrophage-derived factors may influence remodeling of MTJs in muscles experiencing modified loading.
先前已有报道称，肌肉负荷的改变会导致单核细胞数量增加以及肌腱结合处（MTJ）肌原纤维组织的变化。本研究的目的是确定这些单核细胞的身份，并研究它们的结构、位置和数量变化与经历负荷改变的MTJ重塑结构方面之间的关系。对经历10天后肢悬吊的大鼠比目鱼肌在恢复负重后的0、2、4和7天进行分析。免疫组织化学显示，ED1 +、ED2 +和Ia +巨噬细胞存在于对照肌肉的MTJ和微肌腱处。重新加载后，ED2 +巨噬细胞在MTJ和微肌腱处的数量和大小增加，表明它们被激活。ED1 +细胞的大小和数量没有变化，而Ia +细胞在重新加载第7天时大小增加。电子显微镜观察显示，对照或悬吊肌肉的MTJ附近的单核细胞在蛋白质合成或分泌方面活性不高。然而，在重新加载的肌肉中，发现单核细胞靠近MTJ，并且含有高浓度的与蛋白质分泌相关的细胞器。在重新加载的这些阶段，肌原纤维-膜结合发生了广泛的重塑，并且新生肌节出现在肌纤维的MTJ区域。免疫组织化学显示，在新生肌节形成的这些阶段，MTJ处出现了发育性肌球蛋白重链的重新表达，这种重链在重新加载第7天时在MTJ处最为明显。MTJ处巨噬细胞的激活和数量增加以及重塑过程中分泌细胞与MTJ膜的紧密相邻，使我们提出巨噬细胞衍生因子可能影响经历负荷改变的肌肉中MTJ的重塑。
