Résumé :
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Muscle satellite cells play central roles in postnatal muscle growth and regeneration, and therefore, are the most promising tool for cell therapy for Duchenne muscular dystrophy. It is now feasible to directly purify satellite cells in a quiescent state (G0) from mouse skeletal muscle using a cell sorter and a monoclonal antibody, SM/C-2.6. Genome-wide gene expression analysis of quiescent and activated and cycling satellite cells identified several candidate genes that regulate quiescence in satellite cells. In addition, gene set enrichment analysis (GSEA) revealed that quiescent satellite cells preferentially express genes involved in cell-cell adhesion, regulation of cell growth, formation of extracellular matrix, copper and iron homeostasis, and lipid transportation. To determine the usefulness of fresh satellite cells for cell therapy, we injected fresh satellite cells and satellite cells expanded in vitro into TA muscle of C57BL/6 and dystrophin-deficient mdx mice. Importantly, fresh satellite cells participated in muscle repair more effectively than cultured satellite cells. A lentiviral vector efficiently introduced a micro-dystrophin gene into mdx satellite cells ex vivo and restored dystrophin expression in mdx muscle. CD31-negative, CD45-negative SP cells (DN-SP cells) are a minor SP subpopulation which differentiate into adipocytes or osteogenic or myogenic cells in vitro. Interestingly, DN-SP cells expand upon muscle injury. Co-transplantation of DN-SP cells and myoblasts into mdx or NOD/scid mice increased the efficiency of transplantation, compared with transplantation of myoblasts alone. Further experiments suggested that DN-SP cells promote both proliferation and migration of myoblasts. Microarray analysis revealed that DN-SP cells express numerous extracellular matrix proteins, cytokines, and matrix metalloproteinases (MMPs). Co-transplantation of MMP-2-null DN-SP cells demonstated that DN-SP cells stimulate migration of myoblasts mainly via activation of MMP-2. Elucidation of the mechanisms by which DN-SP cells improve the efficiency of transplantation would facilitate the development of cell therapy for muscular dystrophy.
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