Résumé :
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Communication n° 716. Insulin-like Growth Factor 1 is a major factor for the regulation of the proliferation and the differentiation of satellite cells. It has been shown to enhance the replicative life span of satellite cells isolated from transgenic mice that overexpress IGF-1 in muscle (chakravarthy, 2000). In mice, IGF-1 has also been shown to induce hypertrophy and to be able to prevent loss of muscle mass with aging but few data are available in human. In a previous study we showed that in contrast to mouse model, IGF-1 has little effect on the lifespan of human satellite cells in vitro. According to previous findings in mouse models, we investigated whether IGF-1 could induce hypertrophy of human myotubes. Hypertrophy was estimated by counting the mean number of nuclei per myotube, the percentage of fusion and the myosine content related to the number of nuclei. We showed that IGF-1 induces a dose dependant increase in the mean number of nuclei per myotube when added at day 0 of differentiation. We also showed that IGF-1 induces an increase in proliferation at early steps of differentiation. However hypertrophy can also be induced independently of proliferation by adding IGF-1 at day 3 of differentiation, when no more BrdU incorporation is detected. In these conditions, an increase in the ratio MyHC/ nuclei was also observed. We also showed that IGF-1 induces hypertrophy mainly by increasing cell recruitment, thus potentially depleting the reserve cell compartment and by stimulating protein synthesis. This model is now used to determine signaling pathways involved in IGF-1 induced hypertrophy.
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