Expression of Myogenic Regulatory Factors in Normal and Dystrophic Mice: Effects of IGF-1 Treatment

Myogenic regulatory factors (MRFs) promote differentiation of muscle cells from fibroblasts and are induced by insulin-like growth factor I (IGF-1). Prior studies have shown synthesis of new muscle protein and improved muscle morphology when maturedymice with muscular dystrophy are treated with IGF-1. We investigated whether these salutary effects of IGF-1 might be attributable to stimulation of MRFs. Maledy(129ReJ) mice and controls (129J) were assigned to IGF-1 treatment (10 μg twice daily) or nontreatment at about 5 weeks of life and sacrificed 6 weeks later. RNA was extracted from skeletal muscles, reverse transcribed, and amplified by polymerase chain reaction (PCR) using primers specific for each MRF. Competitive PCR was performed to quantifyMyoDexpression in response to IGF-1 treatment. Transcripts formyf-5, MRF4,and myogenin were detected in both control anddymouse muscles; no apparent differences were observed between treatment groups. Quantitative analysis of transcripts forMyoDindicated no significant basal differences between control anddymice. There was, however, significantly higherMyoDexpression in thedygroup, and a trend toward significance in the control group, following IGF-1 treatment. These data suggest that IGF-1 exerts itsin vivoeffects in postembryonal muscle by stimulating MRFs.