Résumé :
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Communication n° 377 A soluble and membrane-bound metallo-endopeptidase activity has been shown to be involved in myoblast fusion (Couch and Stritmatter 1983, and 1984). Furthermore, MMP-2 and MMP-9 activation and regulation during skeletal muscle remodelling suggested they could play a role in myogenic cell migration and/or fusion (Kherif, S, et al. 1998, and 1999). To clarify MMPs involvement in both phenomena, we have used C2C12 murine cell line and a variant, C2F, isolated for its different fusion capacity, to correlate MMP-2 and MMP-9 regulation during myogenesis, in vitro and in vivo, with migratory and fusion capacities. Concomitantly, we investigated TIMP-1 and TIMP-2 regulation to detect an imbalance between MMPs and their inhibitors. MMPs and TIMPs expression was carried out by zymography and western blotting of conditioned medium. Quantitative RT-PCR of MMP-2, MMP-9, TIMP-1 and TIMP-2 was performed using light-Cycler (Roche). Migration on matrigel was quantified using the two chamber assay. Myotube formation was studied 3 weeks after the injection of 5x105 C2C12 and C2F cells into irradiated and non-irradiated mdx nu/nu mouse muscles. Myotube formation were examined on HE stained transverse sections. We show that, in comparison to C2F, 1) C2C12 cells produce higher amounts of MMP-9 and exhibit higher overall gelatinolytic activity that correlated with higher migratory and fusion capacities, 2) C2C12 cell grafting into nude mdx muscles resulted in a significant increase of muscle weight, number of dystrophin-positive fibers and cell incorporation into myofibers. In both cell lines, no regulation of TIMP-1 and TIMP- 2 with fusion could be evidenced. Our findings strongly indicate that MMP-9 and higher overall gelatinolytic activity account for the increased incorporation of myogenic cells upon cell grafting and, hence, contribute to increase cell migration Acknowledgement: The authors wish to thank the Association Française contre les Myopathies, the Medical Research Council and INSERM for financial support.
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