Satellite cell proliferation: Two models and two anabolic stimuli.

摘要

Skeletal muscle is a dynamic tissue. It can respond rapidly to abrupt changes in use and hormone levels. The plasticity of muscle is attributed to some extent to a muscle precursor cell called the satellite cell. Satellites cells provide myoblasts necessary for repair and hypertrophy of skeletal muscle. In response to anabolic stimuli, increased loading or injury satellite cells divide and become myoblasts, ultimately forming new myonuclei. Diminished satellite cell contribution of myoblasts has been proposed as a potential source of the age-related blunting of the regenerative process and the reduced hypertrophic response to anabolic stimuli.;Studies have demonstrated that anabolic-androgenic steroids increase satellite cell numbers in both rat and human skeletal muscles. Study one of this dissertation sought to determine the time-course of satellite cell activation in the rat model utilizing the diaphragm muscle to control for activation history. Serum testosterone levels were elevated to approximately 6.5x physiologic levels for zero (sham-control), seven, 14, and 28 days in gonadally intact adult male rats. We showed significant increases in average number of satellite cell number per diaphragm muscle fiber after seven and 14-days of testosterone propionate treatment. These data suggest a temporal response of satellite cell proliferation to chronic testosterone propionate treatment. Additionally, increases in satellite cells were observed without concomitant increases in myonuclear number or fiber cross-sectional area, suggesting that testosterone may increase satellite cell proliferation without activating their myogenic potential.;The second study of this dissertation tested the hypothesis that older human muscle would respond with less satellite cell activation 24 hours after a single bout of maximal-eccentric exercise compared to young muscle. We obtained muscle biopsies from ten young (23--35 years) and nine older (60--75 years) men, 12.5 days apart. The post-exercise biopsy was performed 24 hours after a single bout of maximal-eccentric exercise and the pre-exercise biopsy served as control. Twenty-four hours after exercise, we observed a significant increase in the number of satellite cells/muscle fiber in both age groups. However, the magnitude of change was significantly greater in younger muscle. These data demonstrate greater satellite cell proliferation from young muscle.