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

Abstract

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.

Figure 1. Identification of satellite cells and myonuclei

Muscle cross-section stained with the antibody against CD56 (brown colour) and counterstained with Mayer's haematoxylin. Myonuclei are blue, and satellite cells are surrounded by a brown rim. The arrowhead indicates a satellite cell and arrows show myonuclei.

Figure 2. Satellite cell number

The number of satellite cells per muscle fibre before training (Pre), after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining. * Significantly different from Pre; # significantly different from T90.

Figure 3. Northern blot of p21 and CyclinD1

A, Northern example for one subject before training (Pre), after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining. B, staining of the ribosomal RNA with SYBR green before blotting is shown below.

Figure 4. Quantification of p21 and CyclinD1 mRNA

mRNA for the cell-cycle markers p21 (A) and CyclinD1 (B) and the 28S rRNA (C) after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining. The RNA levels are normalized to GAPDH mRNA and are relative to the pre-training value for each subject. * Significantly different from pre-training value (pre-training value = 1); # significantly different from T90.

Figure 5. Myonuclear number

The mean number of myonuclei per muscle fibre before training (Pre), after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining.

Figure 6. Fibre area

Mean cross-sectional area of muscle fibres before training (Pre), after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining. * Significantly different from Pre; # significantly different from T90.

Figure 7. Myonuclear domain

Myonuclear domain before training (Pre), after 30 (T30) and 90 (T90) days of training and following 3 (D3), 10 (D10), 30 (D30), 60 (D60) and 90 (D90) days of detraining. * Significantly different from Pre; # significantly different from T90.