Heat shock protein accumulation and heat shock transcription factor activation in rat skeletal muscle during compensatory hypertrophy.
OBJECTIVE
To assess the stress/heat shock protein (HSP) and heat shock factor activation response in overloaded (hypertrophied) plantaris muscles.


METHODS
Male Sprague-Dawley rats (n = 5 per time point) underwent unilateral removal of the left gastrocnemius muscle. After 1, 2, 3, 5, 7, 14 and 28 days, plantaris muscles were removed, weighted rapidly frozen in liquid nitrogen. Total protein content was determined and HSP 25 and HSP 72 contents were assessed by Western blotting. Heat shock transcription factor (HSF) activation was assessed by electrophoretic mobility shift assay (EMSA).


RESULTS
While plantaris muscle mass was significantly increased 3 days after the imposition of overload and remained elevated thereafter confirming muscle hypertrophy, muscle protein content was not increased until 7 days after the imposition of overload. HSP 72 content was significantly increased at 3 days, while HSP 25 content was not significantly increased until 7 days after synergistic muscle removal. HSF activation was detected at 1, 2 and 3 days of overload but undetectable thereafter. The addition of HSF1- and HSF2-specific antibodies to extracts prior to EMSA failed to supershift the HSF-heat shock element complex.


CONCLUSIONS
The temporal pattern of both HSF activation and HSP expression in skeletal muscle undergoing hypertrophy suggests the increased level of the observed HSPs may be both a consequence of both the immediate stress of overload and the hypertrophic process. The inability of HSF1- and HSF2-specific antibodies to cause supershifts suggests the HSF detected during overload may not be HSF1 or HSF2.
Locke
M
M
Faculty of Physical Education and Health, University of Toronto, Toronto, ON, Canada. marius.locke@utoronto.ca
D000818:Animals; D019138:Antibodies, Blocking / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000096:biosynthesis* / Q000187:drug effects; D055551:HSP27 Heat-Shock Proteins; D050884:HSP72 Heat-Shock Proteins / Q000276:immunology / Q000378:metabolism*; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins / Q000276:immunology / Q000378:metabolism*; D006984:Hypertrophy / Q000378:metabolism* / Q000473:pathology; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000276:immunology / Q000378:metabolism*; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000096:biosynthesis* / Q000187:drug effects; D016474:Weight-Bearing
D019138:Antibodies, Blocking; D004268:DNA-Binding Proteins; D055551:HSP27 Heat-Shock Proteins; D050884:HSP72 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; D006360:Heat-Shock Proteins; C000619709:Hsf1 protein, rat; C486114:Hspb1 protein, rat; D009124:Muscle Proteins; D009363:Neoplasm Proteins; D014157:Transcription Factors