THE IDENTIFICATION AND QUANTIFICATION OF MACROPHAGE SUBPOPULATIONS AND THE EXPRESSION OF DEVELOPMENTAL MYOSIN HEAVY CHAIN IN RAT SOLEUS MUSCLE DURING HINDLIMB SUSPENSION AND RECOVERY (MYOSIN).
Contributors: University of California, Los Angeles.
Published: 1993
Number of pages: 173
Subjects: Health Sciences, Nursing.; Biology, Cell.; Health Sciences, Immunology.
Description: Macrophage subpopulations were identified and quantified and the renewed expression of developmental myosin heavy chain (dMHC) was examined in rat soleus muscle following hindlimb suspension and 2, 4, and 7 days of reloading after suspension. Additionally, the number of necrosis was evaluated. In the midportion of the muscle, after 2 days of reloading, the incidence of necrotic fibers in the soleus muscle was 15-fold greater than in control. These myofibers were invaded by ED1$\sp+$ and Ia$\sp+$ macrophages but not ED2$\sp+$ cells. There was also an accumulation of ED1$\sp+$ and Ia$\sp+$ cells in the interstitial space. ED2$\sp+$ macrophages demonstrated changes in size and shape, but did not increase in number until after 4 days of reloading. dMHC was detected in structures resembling myotubes, cytoplasm of small myofibers, and subsarcolemmal region of larger myofibers at this time point also. By 7 days of reloading, mean fiber cross-sectional area returned to control values; however, the number of macrophages remained elevated.

The presence of macrophages and dMHC expression were examined also at the proximal end of the muscle. ED2$\sp+$, Ia$\sp+$, and ED1$\sp+$ macrophages were distributed near the myotendinous junction (MTJ) in control soleus muscles. No change in phenotype, number, or localization occurred with suspension or after 2 days of recovery. After 4 and 7 days of reloading, ED2$\sp+$ and Ia$\sp+$ cells accumulated in this region of the muscle. The dMHC expression was detected at the MTJ after 7 days of recovery. Vinculin concentration at the MTJ was evaluated by immunoblots and immunolocalization. While no difference in vinculin expression was observed in the immunoblots at any of the recovery time points studied, anti-vinculin labeling at the MTJ in many myofibers appeared more intense after 4 and 7 days of reloading compared to controls.

Findings in the midportion and proximal end of the muscle show that the resumption of weight-bearing after a period of unloading activates macrophage subpopulations and the renewed dMHC expression. The stimulation of nonphagocytic ED2$\sp+$ macrophages during periods in which dMHC is present in myogenic cells suggest that ED2$\sp+$ macrophages may be involved in the reactivation of myogenic genes.
Notes: Source: Dissertation Abstracts International, Volume: 54-06, Section: B, page: 2999.

Thesis (D.N.SC.)--UNIVERSITY OF CALIFORNIA, LOS ANGELES, 1993.

School code: 0031.