title: Androgens affect myogenesis in vitro and increase local IGF-1 expression.
abstract: OBJECTIVE
  The mechanism whereby anabolic androgens are associated with hypertrophy of skeletal muscle is incompletely understood but may involve an interaction with locally generated insulin-like growth factor (IGF) 1. The present investigation utilized a cell culture model of human skeletal muscle-derived cell maturation to test the hypothesis that androgens increase differentiation of human muscle precursor cells in vitro and to assess effects of androgen with or without IGF-1 on IGF-1 messenger RNA (mRNA) expression in human muscle precursor cells.
  
  
  METHODS
  Differentiation of muscle-derived cells was induced under standard low-serum conditions. Cultures were then exposed to androgen (testosterone (T)) at 50, 100, and 500 nM or IGF-1 (10-50 ng·mL⁻¹). Immunocytochemistry and real-time polymerase chain reaction (RT-PCR) were used to assess effects of androgens and IGF-1 after 3- (early) or 7-d (late) muscle differentiation, respectively; RT-PCR was used to quantify the effects on androgen receptor expression.
  
  
  RESULTS
  Under low-serum conditions, 3-d exposure to androgens or IGF-1 or both resulted in no significant increase in cellular myogenic commitment. After 7-d exposure, however, T and IGF-1 were both found to increase fusion index with no observable synergistic effect. T also increased IGF-1 mRNA generation (P < 0.0001), whereas exogenous IGF-1 (P < 0.001) reduced IGF-1 mRNA transcription relative to control. The T effect was reversible after treatment with flutamide, an androgen receptor antagonist.
  
  
  CONCLUSIONS
  Both T and IGF-1 increase myogenic commitment after 7-d exposure to a differentiation medium. With T causing a concomitant increase in IGF-1 mRNA underpinning IGF-1 as a central mediator in the cellular pathways associated with muscle hypertrophy, including those affected by androgens. The novel system described has the potential for elucidating the pattern of growth factor effects associated with androgens in skeletal muscle.
authors.affiliation: Muscle Cellular and Molecular Physiology Research Group, Institute for Sport and Physical Activity Research, University of Bedfordshire, Bedford, United Kingdom. nick.sculthorpe@beds.ac.uk
authors.forename: Nick
authors.initials: N
authors.lastname: Sculthorpe
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Solomon
authors.forename: Andrea C M
authors.initials: AC
authors.lastname: Sinanan
authors.forename: Pierre-Marc G
authors.initials: PM
authors.lastname: Bouloux
authors.forename: Fergal
authors.initials: F
authors.lastname: Grace
authors.forename: Mark P
authors.initials: MP
authors.lastname: Lewis
mesh_terms: D000293:Adolescent; D000328:Adult; D059002:Androgen Receptor Antagonists / Q000494:pharmacology; D002478:Cells, Cultured; D005485:Flutamide / Q000494:pharmacology; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis*; D008297:Male; D024510:Muscle Development / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology; D011944:Receptors, Androgen / Q000096:biosynthesis; D013739:Testosterone / Q000494:pharmacology*; D055815:Young Adult
chemical_list: C410798:AR protein, human; D059002:Androgen Receptor Antagonists; D011944:Receptors, Androgen; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D005485:Flutamide