title: Muscle satellite cells are activated after exercise to exhaustion in Thoroughbred horses.
abstract: BACKGROUND
  Although satellite cells are well known as muscle stem cells capable of adding myonuclei during muscle repair and hypertrophy, the response of satellite cells in horse muscles to a run to exhaustion is still unknown.
  
  
  OBJECTIVE
  To investigate the time course of satellite cell activation in Thoroughbred horse muscle after running to exhaustion. We hypothesised that this type of intense exercise would induce satellite cell activation in skeletal muscle similar to a resistance exercise.
  
  
  METHODS
  Nine de-trained Thoroughbred horses (6 geldings and 3 mares) aged 3-6 years were studied. Biopsy samples were taken from the gluteus medius muscle of the horses before and 1 min, 3 h, 1 day, 3 days, 1 week and 2 weeks after a treadmill run to exhaustion. The numbers of satellite cells for each fibre type were determined by using immunofluorescence staining. Total RNA was extracted from these samples, and the expressions of interleukin (IL)-6, paired box transcriptional factor (Pax) 7, myogenic differentiation 1 (MyoD), myogenin, proliferating cell nuclear antigen (PCNA), insulin-like growth factor (IGF)-I and hepatocyte growth factor (HGF) mRNA were analysed using real-time reverse transcription-PCR.
  
  
  RESULTS
  The numbers of satellite cells were significantly increased in type I and IIa fibres at 1 week and in type IIa/x fibre at 2 weeks post exercise. The expression of IL-6 mRNA increased significantly by 3 h post exercise. The expression of PCNA mRNA also increased by 1 day after running, indicating that running can initiate satellite cell proliferation. The expression of Pax7, MyoD, myogenin, IGF-I and HGF mRNA peaked at 1 week post exercise.
  
  
  CONCLUSIONS
  Satellite cell activation and proliferation could be enhanced after a run to exhaustion without detectable injury as assessed by the histochemical analysis. Understanding the response of satellite cell activation to running exercise provides fundamental information about the skeletal muscle adaptation in Thoroughbred horses.
authors.affiliation: Biological Sciences, Graduate School of Medicine, Yamaguchi University, Yamaguchi, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kawai
authors.forename: H
authors.initials: H
authors.lastname: Aida
authors.forename: A
authors.initials: A
authors.lastname: Hiraga
authors.forename: H
authors.initials: H
authors.lastname: Miyata
mesh_terms: D000818:Animals; D005260:Female; D005786:Gene Expression Regulation; D006736:Horses / Q000502:physiology*; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000166:cytology; D010805:Physical Conditioning, Animal / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000502:physiology*
chemical_list: D012333:RNA, Messenger