title: Exercise influences circadian gene expression in equine skeletal muscle.
abstract: Circadian rhythms are endogenously generated 24-h oscillations that coordinate numerous aspects of mammalian physiology, metabolism and behaviour. The existence of a molecular circadian clock in equine skeletal muscle has previously been demonstrated. This study investigates how the circadian 24-h expression of exercise-relevant genes in skeletal muscle is influenced by a regular exercise regime. Mid-gluteal, percutaneous muscle biopsies were obtained over a 24-h period from six Thoroughbred mares before and after an 8-week exercise programme. Real-time qPCR assays were used to assess the expression patterns of core clock genes ARNTL, PER2, NR1D1, clock-controlled gene DBP, and muscle genes MYF6, UCP3, VEGFA, FOXO1, MYOD1, PPARGC1A, PPARGC1B, FBXO32 and PDK4. Two-way repeated measures ANOVA revealed a significant interaction between circadian time and exercise for muscle genes MYF6, UCP3, MYOD1 and PDK4. A significant effect of time was observed for all genes with the exception of VEGFA, where a main effect of exercise was observed. By cosinor analysis, the core clock genes, ARNTL (P <0.01) and NR1D1 (P <0.05), showed 24-h rhythmicity both pre- and post-exercise, while PER2 expression was rhythmic post-exercise (P <0.05) but not pre-exercise. The expression profiles of muscle genes MYOD1 and MYF6 showed significant fits to a 24-h cosine waveform indicative of circadian rhythmicity post-exercise only (P <0.01). This study suggests that the metabolic capacity of muscle is influenced by scheduled exercise and that optimal athletic performance may be achieved when exercise times and competition times coincide.
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland. Electronic address: Barbara.murphy@ucd.ie.
authors.forename: B A
authors.initials: BA
authors.lastname: Murphy
authors.affiliation: Center of Muscle Biology, Department of Physiology, University of Kentucky, Lexington, KY 40536, USA.
authors.forename: A L
authors.initials: AL
authors.lastname: Wagner
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: O F
authors.initials: OF
authors.lastname: McGlynn
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: F
authors.initials: F
authors.lastname: Kharazyan
authors.affiliation: School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4, Ireland.
authors.forename: J A
authors.initials: JA
authors.lastname: Browne
authors.affiliation: Center for Chronobiology, Departments of Psychiatry and Psychology, University of California, La Jolla, San Diego, CA 92093-0109, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Elliott
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D005786:Gene Expression Regulation; D006736:Horses / Q000235:genetics / Q000293:injuries / Q000502:physiology*; D018482:Muscle, Skeletal / Q000293:injuries / Q000502:physiology*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction / Q000662:veterinary; D013045:Species Specificity
keywords: Circadian; Equine; Exercise; Gene expression; Skeletal muscle