Résumé :
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Communication n° 301 Introduction : Transplantation of myogenic cells is the only treatment that could reconstitute the satellite cell population of the muscle and introduce normal genes in pre-existing myofibers. One major problem that contributes to the low degree of success in clinical trials is a poor migration and fusion of myoblasts outside the injected site. Objectives : The present study aims to corroborate the theory suggesting that myotubes secrete IL-4 to recruit additional myoblast fusion during the second phase of their maturation. We therefore hypothesized that IL-4 treatment could be a pharmacological approach to improve human myoblast migration and potentially be helpful for the treatment of Duchenne Muscular Dystrophy (DMD). Methods : In vitro evaluation of human myoblast invasion capacity was assessed using an Invasion Chamber Assay. Chemokinetic and chemoattractant potential were evaluated by adding IL-4 to the upper or to the lower chamber of the assay. For in vitro study of pro-migratory component, myoblasts were co-incubated with different concentrations of IL-4. Zymography and western blot analysis were made to determine the cytokine effects on proteolytic systems and on integrins. In vivo, intra-muscular migration capacity following IL-4 co-injection with cells was assessed using the microtube technique in SCID mice. Results : In vitro studies showed that Il-4 is a strong chemokinetic and chemoattractant factor for human myoblasts. The presence of 10 ng/ml with the cells improved their migration by 1.8-fold and the presence of IL-4 in the lower chamber of the assay improved the migration rate by 2.57-fold. The chemokinetic potential of IL-4 had also been demonstrated in vivo. Although other pro-migratory components remain to be investigated, our current results suggest that an up-regulation of the urokinase plasminogen activator receptor is implicated in the migration improvement following IL-4 treatment. Conclusions : As it been suggested for mouse myoblasts (Horsley, 2003), our in vitro and in vivo studies showed that IL-4 is a potent recruitment factor for human skeletal myoblasts. Consequently, IL-4 treatment of transplanted myoblasts could potentially reduce the number of injection sites and enhance the graft success for the treatment of DMD patients.
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