Macrophage activation and muscle remodeling at myotendinous junctions after modifications in muscle loading

Document Type

Article

Publication Date

12-1994

Publication Title

American Journal of Pathology

Volume

145

Issue

6

First page number:

1463

Last page number:

1471

Abstract

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.

Keywords

Animals; Female; Immunohistochemistry; Isoenzymes; Isoenzymes/metabolism; Macrophages; Macrophages/cytology; Macrophages/physiology; Microscopy; Electron; Muscles – Regeneration; Muscles – Wounds and injuries; Muscles/cytology; Muscles/physiology; Myosin; Myosins/metabolism; Rats; Rats – Wounds and injuries; Rats; Wistar; Tendons/cytology; Tendons/physiology; Time Factors; Weight-Bearing/physiology

Disciplines

Medicine and Health Sciences | Nursing | Pathology

Language

English

Permissions

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