Résumé :
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Communication n° 331. Background : During skeletal muscle regeneration, myogenic precursor cells (mpc) attract monocyte/macrophages (MP) to set up their own stromal support necessary to a good regeneration. We previously shown that human mpc firstly initiate monocyte recruitment and interplay with MP to amplify chemotaxis. Then, MP exert a supportive role toward human mpc through both the delivery of soluble mitogenic factors and the establishment of cell:cell contacts that rescue myogenic cells from apoptosis. We aimed at identify the nature of these contacts. Methods : We used human mpc and human monocyte-derived MP, in direct cocultures at various ratio. Apoptosis was evaluated in vitro by annexin-V labelling and DiOC6(3) uptake analyzed by cytofluometry, and by caspase 3 activity measurement. A DNA macroarray-based strategy helped at select antiapoptotic molecular candidates that were: 1) involved in cell:cell contacts; 2) shown to be involved in antiapoptotic pathways; 3) expressed by mpc and MP. Results : We firstly showed that mpc apoptosis occurred during post-lesional skeletal muscle regeneration in vivo. We then showed in vitro that MP inhibited both natural and staurosporine-induced mpc apoptosis in a dose-dependent way. The DNA array identified four candidates and their counter receptors: fractalkine/CX3CR1, VCAM-1/VLA4, ICAM-1/LFA1, and PECAM-1/PECAM-1. All receptors at the myogenic cell surface were functional in adhesion assays. Antibodies neutralizing each molecular interactions inhibited the beneficial effect of macrophages on mpc in cocultures. The protective effect of MP was also observed on differentiated mpc, the multinucleated myotubes, and involved the same couple of molecules. In conclusion, our results show that MP play a cytoprotective role on both undifferentiated and differentiated mpc through cell adhesion molecule interactions. These results suggest that during muscle regeneration, the massive MP infiltrate protects myogenic cells from excessive apoptosis to ensure a good repair of muscle tissue.
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