Temperature- and exercise-induced gene expression and metabolic enzyme changes in skeletal muscle of adult zebrafish (Danio rerio).
Both exercise training and cold acclimatization induce muscle remodelling in vertebrates, producing a more aerobic phenotype. In ectothermic species exercise training and cold-acclimatization represent distinct stimuli. It is currently unclear if these stimuli act through a common mechanism or if different mechanisms lead to a common phenotype. The goal of this study was to survey responses that represent potential mechanisms responsible for contraction- and temperature-induced muscle remodelling, using an ectothermic vertebrate. Separate groups of adult zebrafish (Danio rerio) were either swim trained or cold acclimatized for 4 weeks. We found that the mitochondrial marker enzyme citrate synthase ( CS) was increased by 1.5x in cold and by 1.3x with exercise (P < 0.05). Cytochrome c oxidase (COx) was increased by 1.2x following exercise training (P < 0.05) and 1.2x (P = 0.07) with cold acclimatization. However, only cold acclimatization increased beta-hydroxyacyl-CoA dehydrogenase (HOAD) compared to exercise-trained (by 1.3x) and pyruvate kinase (PK) relative to control zebrafish. We assessed the whole-animal performance outcomes of these treatments. Maximum absolute sustained swimming speed (U(crit)) was increased in the exercise trained group but not in the cold acclimatized group. Real-time PCR analysis indicated that increases in CS are primarily transcriptionally regulated with exercise but not with cold treatments. Both treatments showed increases in nuclear respiratory factor (NRF)-1 mRNA which was increased by 2.3x in cold-acclimatized and 4x in exercise-trained zebrafish above controls. In contrast, peroxisome proliferator-activated receptor (PPAR)-alpha mRNA levels were decreased in both experimental groups while PPAR-beta(1) declined in exercise training only. Moreover, PPAR-gamma coactivator (PGC)-1alpha mRNA was not changed by either treatment. In zebrafish, both temperature and exercise produce a more aerobic phenotype, but there are stimulus-dependent responses (i.e. HOAD and PK activities). While similar changes in NRF-1 mRNA suggest that common responses might underlie aerobic muscle remodelling there are distinct changes (i.e. CS and PPAR-beta(1) mRNA) that contribute to specific temperature- and exercise-induced phenotypes.[1]References
- Temperature- and exercise-induced gene expression and metabolic enzyme changes in skeletal muscle of adult zebrafish (Danio rerio). McClelland, G.B., Craig, P.M., Dhekney, K., Dipardo, S. J. Physiol. (Lond.) (2006) [Pubmed]
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