The expression of a set of 588 widely expressed genes coding for proteins involved in a wide variety of cellular functions was studied on biopsies from m. vastus lateralis of seven highly endurance trained males (professional cyclists) and seven untrained males. Their average ÎO2,max was 78 ml O2 min-1 kg-1 (S.D. = 8.8) and 35 ml O2 min-1 kg-1 (S.D. = 6.6), respectively. Biopsies were obtained from m. vastus lateralis using the Bergström technique (Bergström, 1962) with permission from the Ethical Committee of the University of Bern. Total RNA (0.7-2 mg) was obtained from cryostat sections (10-25 mg) of the biopsies and used to probe Clontech Atlas Human 588 arrays with 32P labelling (Wittwer et al. 2002).
A comparison of the array scans with the ones from rat m. soleus (Wittwer et al. 2002) showed considerably greater inter-individual variability in the human samples (R 2 for trained vs. untrained human samples 0.41-0.81, compared with 0.72-0.92 for atrophied vs. normal rat m. solei). Statistical analysis was done with the non-parametric Mann-Whitney U test. Fifteen of 408 detected transcripts were significantly different (P < 0.05) between the cyclists and the untrained samples, differing between 25 % and 4-fold. They included indicators of enhanced cell destruction and replacement (e.g. the mRNAs of cyclin B1 or inhibitor of apoptosis protein 1). This is compatible with enhanced degeneration/regeneration due to greater wear and tear in the cyclists. The increased prohibitin mRNA corresponds to their enhanced mitochondrial volume. Other changed mRNAs coded for immune status indicators (e.g. CD 33, leukaemia inhibitory factor and interleukin-3 receptor) and signal transduction proteins (protein kinase C α and tie-1). Despite the low number of differing transcripts (well within the range of false positives), their nature and direction of change fits structural and biochemical adaptations of highly endurance trained muscles, where known.
In conclusion, the expression of these widely expressed mRNAs was remarkably similar between the muscles of highly trained athletes and untrained males. The statistical parameters (correlation coefficients and median absolute deviations, which were similar for cyclists and untrained) suggest a considerable individual component in a human muscle’s adaptation to a given level of activity.
This work was supported by the Swiss National Foundation and by the Swiss Foundation for Research on Muscle Diseases.
All procedures accord with current local guidelines and the Declaration of Helsinki.