Purpose: 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.
1Muscle Cellular and Molecular Physiology Research Group, Institute for Sport and Physical Activity Research, University of Bedfordshire, Bedford, UNITED KINGDOM; 2Eastman Dental Institute, University College London, London, UNITED KINGDOM; 3Department of Endocrinology, Royal Free and University College Medical School, London, UNITED KINGDOM; 4Department of Sport Science, University of Kingston, Kingston, UNITED KINGDOM; and 5School of Sport, Exercise and Health Sciences, Loughborough University, UNITED KINGDOM
Address for correspondence: Nick Sculthorpe, Ph.D., Department of Sport and Exercise Sciences, University of Bedfordshire, Polhill Avenue, Bedford MK41 9EA, United Kingdom; E-mail: email@example.com.
Submitted for publication July 2011.
Accepted for publication September 2011.
Nick Sculthorpe and Andrew M. Solomon are considered joint primary authors of this article.