Abstract
Role of macrophage in the regulation of soleus muscle fibers in response to gravitational unloading followed by reloading was investigated in adult op/op (-/-) mice with deficient macrophage colony-stimulating factor, as well as heterozygous (+/-) and wild type (+/+) mice. They were separated into cage control and unloaded groups. The sampling of soleus muscle was performed before suspension, immediately after 10 days of hindlimb suspension, and 10 days after recovery. The fiber cross-sectional area (CSA), myonuclear number, and the number of quiescent and mitotic active satellite cells were measured in the single muscle fibers of soleus, which were isolated from tendon to tendon by collagen digestion. The mean length of muscle fibers and tibia of -/- mice was shorter than +/+ and +/- mice in both cage control and suspension groups, suggesting that the inhibition of longitudinal muscle growth in -/- mice was closely associated with the shorter bone length. The fiber CSA was decreased by unloading in all mice. However, the fiber CSA in -/- mice did not recover following 10 days of reloading, whereas the CSAs in +/+ and +/- mice were increased to the control level. Such irreversible effects were also observed in the myonuclear number and the number of quiescent and mitotic active satellite cells in -/- mice. It is suggested that the macrophages play one of the key roles during the recovery from muscular atrophy. [J Physiol Sci. 2007;57 Suppl:S95]
