Temperature‐ and exercise‐induced gene expression and metabolic enzyme changes in skeletal muscle of adult zebrafish (Danio rerio)
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abstract
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 1.5× in cold and by 1.3× with exercise (P < 0.05). Cytochrome c oxidase (COx) was increased by 1.2× following exercise training (P < 0.05) and 1.2× (P= 0.07) with cold acclimatization. However, only cold acclimatization increased β‐hydroxyacyl‐CoA dehydrogenase (HOAD) compared to exercise‐trained (by 1.3×) and pyruvate kinase (PK) relative to control zebrafish. We assessed the whole‐animal performance outcomes of these treatments. Maximum absolute sustained swimming speed (Ucrit) 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 2.3× in cold‐acclimatized and 4× in exercise‐trained zebrafish above controls. In contrast, peroxisome proliferator‐activated receptor (PPAR)‐α mRNA levels were decreased in both experimental groups while PPAR‐β1 declined in exercise training only. Moreover, PPAR‐γ coactivator (PGC)‐1α 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‐β1 mRNA) that contribute to specific temperature‐ and exercise‐induced phenotypes.
