Effects of endurance training on satellite cell frequency in skeletal muscle of old men

Muscle tissue changes with aging

PURPOSE OF REVIEW

This review article focuses on the changes that occur in muscle with age, specifically the involuntary loss of muscle mass, strength and function, termed sarcopenia. Particular emphasis is given to the metabolic alterations that characterize sarcopenia, and to the potentially treatable causes of this condition, including age-related endocrine and nutritional changes, and inactivity.

RECENT FINDINGS

Recent data reported include those regarding the potential role of insulin resistance in the development of sarcopenia, the potential role of androgens and growth hormone in the treatment of this condition, the usefulness of exercise including both resistance and aerobic training to improve muscle growth and function, and, finally, the possible use of nutritional manipulations to improve muscle mass.

SUMMARY

Sarcopenia is likely a multifactorial condition that impairs physical function and predisposes to disability. It may be prevented or treated with lifestyle interventions and pharmacological treatment. Further long-term investigations are needed, however, to ascertain what type and combinations of interventions are the most efficacious in improving muscle mass and function in older people.

The effects of heavy resistance training and detraining on satellite cells in human skeletal muscles

The aim of this study was to investigate the modulation of satellite cell content and myonuclear number following 30 and 90 days of resistance training and 3, 10, 30, 60 and 90 days of detraining. Muscle biopsies were obtained from the vastus lateralis of 15 young men (mean age: 24 years; range: 20-32 years). Satellite cells and myonuclei were studied on muscle cross-sections stained with a monoclonal antibody against CD56 and counterstained with Mayer's haematoxylin. Cell cycle markers CyclinD1 and p21 mRNA levels were determined by Northern blotting. Satellite cell content increased by 19% (P= 0.02) at 30 days and by 31% (P= 0.0003) at 90 days of training. Compared to pre-training values, the number of satellite cells remained significantly elevated at 3, 10 and 60 days but not at 90 days of detraining. The two cell cycle markers CyclinD1 and p21 mRNA significantly increased at 30 days of training. At 90 days of training, p21 was still elevated whereas CyclinD1 returned to pre-training values. In the detraining period, p21 and CyclinD1 levels were similar to the pre-training values. There were no significant alterations in the number of myonuclei following the training and the detraining periods. The fibre area controlled by each myonucleus gradually increased throughout the training period and returned to pre-training values during detraining. In conclusion, these results demonstrate the high plasticity of satellite cells in response to training and detraining stimuli and clearly show that moderate changes in the size of skeletal muscle fibres can be achieved without the addition of new myonuclei.

Effects of one bout of endurance exercise on the expression of myogenin in human quadriceps muscle

The objective of this study was to investigate the cellular localisation of MyoD and myogenin in human skeletal muscle fibres as well as the possible alterations in the expression of MyoD and myogenin in response to a single bout of endurance exercise at 40% and 75% of maximum oxygen uptake (VO(2) max). Twenty-five biopsies (5 per subject) from the vastus lateralis muscle were obtained before exercise, from the exercising leg at 40% and 75% of VO(2) max and from the resting leg following these exercise bouts. The tyramide signal amplification-direct and the Vectastain ABC methods using specific monoclonal antibodies were used to determine the exact location of myogenin and MyoD, to identify muscle satellite cells and to determine myosin heavy chain (MyHC) composition. At rest, myonuclei did not express MyoD or myogenin. Following a single bout of exercise at 40% and 75% of VO(2) max, an accumulation of myogenin in myonuclei and not in satellite cells was observed in biopsies from the exercised leg but not in biopsies before exercise and from the resting leg. The number of myogenin-positive myonuclei varied among individuals indicating differences in the response to a single exercise bout. In conclusion, this immunohistochemical study showed that a rapid rearrangement of myogenin expression occurs in exercised human skeletal muscles in response to a single bout of exercise.

Satellite cells and myonuclei in young and elderly women and men

The overall aim of this study was to assess the effects of aging on the satellite cell population. Muscle biopsies were taken from the tibialis anterior muscle of healthy, moderately active young (age range, 20-32 years; n = 31) and elderly (age range, 70-83 years; n = 27) women and men with comparable physical activity pattern. Satellite cells and myonuclei were visualized using a monoclonal antibody against neural cell adhesion molecule and counterstained with Mayer's hematoxylin. An average of 211 (range, 192-241) muscle fibers were examined for each individual. Compared with the young women and men, the elderly subjects had a significantly lower (P < 0.011) number of satellite cells per muscle fiber but a significantly higher (P < 0.004) number of myonuclei per muscle fiber. The number of satellite cells relative to the total number of nuclei [satellite cells/(myonuclei + satellite cells)] was significantly lower in the elderly than in the young women and men. These results imply that a reduction in the satellite cell population occurs as a result of increasing age in healthy men and women.

Skeletal muscle stem cells

Satellite cells are myogenic stem cells responsible for the post-natal growth, repair and maintenance of skeletal muscle. This review focuses on the basic biology of the satellite cell with emphasis on its role in muscle repair and parallels between embryonic myogenesis and muscle regeneration. Recent advances have altered the long-standing view of the satellite cell as a committed myogenic stem cell derived directly from the fetal myoblast. The experimental basis for this evolving perspective will be highlighted as will the relationship between the satellite cell and other newly discovered muscle stem cell populations. Finally, advances and prospects for cell-based therapies for muscular dystrophies will be addressed.