Résumé :
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Evelyne Gicquel, Karine Charton, Nathalie Dani and Isabelle Richard.Gthon, 1 bis rue de l'Internationale, 91000 Evry, France.Limb Girdle Muscular Dystrophies (LGMD) constitute a group of myopathies affecting muscles of shoulder and pelvic girdles. Among them, LGMD2I, a recessive autosomal muscular dystrophy, is caused by mutations in the Fukutin Related Protein (FKRP) gene. The function of FKRP still remains unclear, but it is supposed to participate in alpha-dystroglycan glycosylation. Alpha-dystroglycan is a membrane protein containing many glycosylated residues that mediate the link to laminin in the extracellular matrix. This connection provides the cell / matrix anchor which protects the muscle fibers from damages related to contraction.We generated a knock-in mouse model of LGMD2I, carrying the most frequent mutation (L276I) encountered in LGMD2I patients. Molecular characterization of this mouse model showed that the introduction of the mutation did not alter the expression of FKRP, neither at transcriptional or translational level. However, the protein appears to have altered function since abnormal glycosylation of alphadystroglycan was observed. Histologically, the muscles of this model show a moderate dystrophic pattern starting from 6 months of age, consisting mainly in the presence of central nuclei. The functional impairment is also moderate. In parallel, we cloned the FKRP cDNA in an expression cassette of a rAAV9 vector under the control of muscle-specific desmin promoter. To evaluate the therapeutic approach for gene transfer, the rAAV vector was injected intramuscularly in the model. A strong expression of the transgene FKRP was obtained, both at RNA and protein levels. The therapeutic efficacy of this vector is under evaluation after systemic injection in KI-FKRP mice.
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