Heat stress inhibits skeletal muscle hypertrophy.
Heat shock proteins (Hsps) are molecular chaperones that aid in protein synthesis and trafficking and have been shown to protect cells/tissues from various protein damaging stressors. To determine the extent to which a single heat stress and the concurrent accumulation of Hsps influences the early events of skeletal muscle hypertrophy, Sprague-Dawley rats were heat stressed (42 degrees C, 15 minutes) 24 hours prior to overloading 1 plantaris muscle by surgical removal of the gastrocnemius muscle. The contralateral plantaris muscles served as controls. Heat-stressed and/or overloaded plantaris muscles were assessed for muscle mass, total muscle protein, muscle protein concentration, Type I myosin heavy chain (Type I MHC) content, as well as Hsp72 and Hsp25 content over the course of 7 days following removal of the gastrocnemius muscle. As expected, in non-heat-stressed animals, muscle mass, total muscle protein and MHC I content were significantly increased (P < 0.05) following overload. In addition, Hsp25 and Hsp72 increased significantly after 2 and 3 days of overload, respectively. A prior heat stress-elevated Hsp25 content to levels similar to those measured following overload alone, but heat stress-induced Hsp72 content was increased significantly greater than was elicited by overload alone. Moreover, overloaded muscles from animals that experienced a prior heat stress showed a lower muscle mass increase at 5 and 7 days; a reduced total muscle protein elevation at 3, 5, and 7 days; reduced protein concentration; and a diminished Type I MHC content accumulation at 3, 5, and 7 days relative to nonheat-stressed animals. These data suggest that a prior heat stress and/or the consequent accumulation of Hsps may inhibit increases in muscle mass, total muscle protein content, and Type I MHC in muscles undergoing hypertrophy.
Frier
Bruce C
BC
Faculty of Physical Education and Health, University of Toronto, 55 Harbord Street, Toronto, Ontario M5S 2W6, Canada.
Locke
Marius
M
D000818:Animals; D001831:Body Temperature; D001835:Body Weight; D055551:HSP27 Heat-Shock Proteins; D050884:HSP72 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000378:metabolism; D006979:Hyperthermia, Induced; D006984:Hypertrophy; D008297:Male; D018482:Muscle, Skeletal / Q000473:pathology*; D009363:Neoplasm Proteins / Q000378:metabolism; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley
D055551:HSP27 Heat-Shock Proteins; D050884:HSP72 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D015395:Histocompatibility Antigens Class I; C486114:Hspb1 protein, rat; D009363:Neoplasm Proteins
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