Testosterone up-regulates androgen receptors and decreases differentiation of porcine myogenic satellite cells in vitro

Accumulation of DNA is essential for muscle growth, yet mechanisms of androgen-induced DNA accretion in skeletal muscle are unclear. The purpose of this study was to determine whether androgen receptors (AR) are present in cultured skeletal muscle satellite cells and myotubes and examine the effects of testosterone on satellite cell proliferation and differentiation. Immunoblot analysis using polyclonal AR antibodies (PG-21) revealed an immunoreactive AR protein of approximately 107 kDa in porcine satellite cells and myotubes. Immunocytochemical AR staining was confined to the nuclei of satellite cells, myotubes, and muscle-derived fibroblasts. Administration of 10(-7) M testosterone to satellite cells, myotubes, and muscle-derived fibroblasts increased immunoreactive AR. In satellite cells and myotubes, AR increased incrementally after 6, 12, and 24 h of exposure to testosterone. Testosterone (10(-10)-10(-6) M), alone or in combination with insulin-like growth factor I, basic fibroblast growth factor, or platelet-derived growth factor-BB, had no effect (P > 0.1) on porcine satellite cell proliferation, and testosterone pretreatment for 24 h did not alter the subsequent responsiveness of cells to these growth factors. Satellite cell differentiation was depressed (20-30%) on days 2-4 of treatment with 10(-7) M testosterone. This effect was not reversible within 48 h after treatment withdrawal and replacement with control medium. These data indicate that satellite cells are direct targets for androgen action, and testosterone administration increases immunoreactive AR protein and reduces differentiation of porcine satellite cells in vitro.