Skeletal muscle HSP72 response to mechanical unloading: influence of endurance training.
OBJECTIVE
It has been shown that increased contractile activity results in heat shock protein 72 (HSP72) accumulation in various skeletal muscles. By contrast, there is no consensus for muscle HSP72 response to muscle disuse for short duration (5-8 days). On the basis of a greater constitutive HSP72 expression in slow-twitch muscles we tested the hypothesis that mechanical unloading for a longer period (2 weeks) would affect this phenotype to a greater extent. Secondly, we evaluated the effects of a physiological muscle heat shock protein (HSP) enhancer (endurance training) on HSP response to unloading and muscle remodelling.


METHODS
Adult male Wistar rats were assigned randomly to four groups: (1) sedentary weight-bearing; (2) hindlimb-unloaded (HU) via tail suspension for 2 week; (3) trained on a treadmill (6 week) and (4) trained 6 week and then HU for 2 week.


RESULTS
Unloading resulted in a preferential atrophy of slow muscles [soleus (SOL), adductor longus (AL)] and a slow-to-fast fibre transition with no change in HSP72 level. HSP72 levels were significantly lower in fast muscles [extensor digitorum longus (EDL) and plantaris (PLA)], and did not change with mechanical unloading. Endurance training was accompanied by a small (SOL) or a large (EDL, PLA) increase in HSP72 level with no change in AL. Training-induced accumulation of HSP72 disappeared with subsequent unloading in the SOL and PLA whereas HSP72 content remained elevated in EDL.


CONCLUSIONS
The results of this study indicate that (1) after 2 weeks of unloading no change occurred in HSP72 protein levels of slow-twitch muscles despite a slow-to-fast fibre transition; and (2) the training-induced increase of HSP72 content in skeletal muscles did not attenuate fibre transition.
Desplanches
D
D
Unité Mixte de Recherche 5123 Centre National de la Recherche Scientifique, Laboratoire de Physiologie, Université Claude Bernard, Lyon Cedex 08, France.
Ecochard
L
L
Sempore
B
B
Mayet-Sornay
M-H
MH
Favier
R
R
D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D050884:HSP72 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006614:Hindlimb; D008297:Male; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D009124:Muscle Proteins / Q000032:analysis; D018482:Muscle, Skeletal / Q000378:metabolism*; D009133:Muscular Atrophy / Q000503:physiopathology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010807:Physical Endurance; D051381:Rats; D017208:Rats, Wistar; D013314:Stress, Mechanical
D050884:HSP72 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D009124:Muscle Proteins; D002950:Citrate (si)-Synthase