Molecular adaptations in mouse skeletal muscle following eccentrically versus concentrically biased training

Introduction

The molecular adaptations specifically induced by different muscle contraction types have only been partially elucidated. We previously demonstrated that eccentric contractions in human quadriceps elicited proteome modifications that suggest a muscle fiber typology adaptation (Hody et al. 2011). We address this question in a more systematic way by examining the effects of different running modes on the mouse muscle proteome and the muscle fiber typology on the whole quadriceps.

Methods

Male adult mice (C57BL6) were randomly divided into downhill running (DHR, quadricipital eccentrically biased contractions), uphill running (UHR, quadricipital concentrically biased contractions) and untrained control (CONT) groups. Running groups performed five training sessions on an inclined treadmill for 75 to 135 min/day and the quadriceps muscles were dissected 96 hours after the last session. Muscle protein extracts of DHR and UHR groups (n=4/group) were subjected to a 2D-DIGE analysis coupled with mass spectrometry. The assessment of fiber type, size and number was performed on the rectus femoris of the three groups (n=6/group) using myosin heavy chain (MHC) immunofluorescence.

Results

In the proteomic analysis, eight spots identified as the fast MHC isoforms exhibited a lower abundance in DHR compared to UHR (p<0.05, t-test). In contrast, ATP synthase subunit a and tubulin ß were more expressed in DHR (p<0.05). Immunohistological analysis revealed a significant higher proportion of type I and IIa fibers for DHR compared to UHR or CONT groups (p<0.05, one-way ANOVA).

Discussion

Our data demonstrate that the eccentrically biased contractions in mice induced specific adaptations in protein expression as well as in muscle fiber type and size which may reflect a more oxidative muscle phenotype. The differences in stress placed on the muscle between both trainings may be responsible for some unique adaptations resulting from the eccentrically biased training. Eccentric training is known to protect skeletal muscles against exercise-induced muscle damage (EIMD) which may occur after intense eccentric contractions (Chen et al. 2010; Hody et al. 2011). It is also suggested that fast glycolytic muscle fibers are more vulnerable to EIMD than oxidative fibers (Lieber and Friden, 1988). Therefore, it would be interesting to investigate whether the molecular changes induced by an eccentrically biased training are involved in protection against EIMD.

References

Chen TC, Chen HL, Lin MJ, Wu CJ, Nosaka K. (2010). Med Sci Sports Exerc 42, 1004-1012.

Hody S, Leprince P, Sergeant K, Renaut J, Croisier JL, Wang F, Rogister B. (2011). Med Sci Sports Exerc 43, 2281-2296.

Lieber RL, Friden J. (1988). Acta Physiol Scand 133, 587-588.