Expression patterns of atrogenic and ubiquitin proteasome component genes with exercise: Effect of different loading patterns and repeated exercise bouts Authors

Unaccustomed exercise is known to produce strength loss, soreness, and myocellular disruption. With repeated application of exercise stimuli, the appearance of these indices of muscle damage is attenuated, the so-called “repeated bout effect”. No direct connection have been established between this repeated bout effect and exercise-induced increases in protein turnover, but it appears that a degree of tolerance is developed towards exercise for both. The present study sought to investigate markers of protein degradation by determining the expression of components related to the ubiquitin-proteasome system with repeated exercise bouts. Healthy males carried out 30 min of bench stepping, performing eccentric work with one and concentric work with the other leg (n=14), performing a duplicate exercise bout 8 weeks later. A non-exercising control group was included (n=6). RNA was extracted from muscle biopsies representing time points PRE, +3 hours, +24 hours and +7 days, and selected mRNA species were quantified using Northern blotting. The exercise model proved sufficient to produce a repeated bout effect in terms of strength and soreness. For FOXO1 and MURF1, strong upregulations were seen exclusively with concentric loading (p<0.001), while Atrogin-1 displayed a strong downregulation exclusively in response to eccentric exercise (p<0.001). For MURF1 transcription, the first bout produced a downregulation that persisted until the second bout (p<0.01). In conclusion, the ubiquitin-proteasome system (UPS) is modulated differentially in response to varying loading modalities and with different time frames in a way that to some extent reflects changes in protein metabolism known to take place with exercise.