Satellite Cells Are Not Required For Longitudinal Muscle Growth

Abstract

1822 Muscle hypertrophy is dependent on a population of myogenic stem cells termed satellite cells. Inhibiting proliferation of satellite cells by irradiation of muscle prevents hypertrophy. It is not known whether satellite cells are obligatory for longitudinal muscle growth as well. PURPOSE: To evaluate the role of satellite cells during longitudinal muscle growth. METHODS: Rats underwent bone lengthening procedures that lengthen their tibia by 0.5 mm/day for 30 days. A control group (CON), a bone distraction group (DIS), and a bone distraction plus irradiation group (DI) were evaluated. At the conclusion of the treatment soleus muscles were removed, fixed in 4% paraformaldahyde and single muscle fibers were extracted. The cytoskeleton and myonuclei of the muscle fibers were fluorescently labeled, analyzed by confocal scanning microscopy, and subsequently measured for fiber volume and myonuclear number. RESULTS: The number of myonuclei per mm was significantly (p<0.05) less in the DIS group (145.5 ± 7.1) (mean ± SE) compared to the CON group (196.4 ± 6.2), and the DI group (89.8 ± 3.5) also had significantly (p<0.05) less myonuclei per mm than the DIS group. The fiber volume (cubic 7μm) to myonuclei ratio was significantly (p<0.05) greater in the DI group (16,016 ± 1202) than the DIS group (11,896 ± 481). This indicates that there are relatively less myonuclei in the DI muscle, attributed to the prevention of satellite cell proliferation. CONCLUSION: Muscle lengthening occurred without the contribution of satellite cells, suggesting that satellite cells are not necessary to support longitudinal muscle growth. This study was supported in part by NIH AR44743 (VJC) and NIH AR46856 (VJC).