Résumé :
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Objective: Dysferlin is a transmembrane protein implicated in surface membrane repair of muscle cells. Mutations in dysferlin cause the progressive muscular dystrophies Miyoshi Myopathy, Limb Girdle Muscular Dystrophy 2B, and distal anterior compartment myopathy. Dysferlinopathies are inherited in an autosomal recessive manner, and many patients with this disease harbor mis-sense mutations in at least one of their two pathogenic DYSF alleles. These patients have significantly reduced dysferlin levels or lack the protein in skeletal muscle, suggesting that dysferlin encoded by mis-sense alleles is rapidly degraded by the cell's quality-control system. We reasoned that mis-sense mutated dysferlin, if salvaged from degradation, might be biologically functional.Methods: We used a dysferlin deficient human myoblast culture harboring the common Arg555Trp mis-sense allele and a DYSF non-sense allele, as well as control human myoblast cultures harboring either two wild-type or two non-sense alleles. We measured dysferlin protein levels, resealing kinetics of laser-induced plasmalemmal wounds, myotube formation, and cellular viability after treatment of the human myoblast cultures with the proteasome inhibitors Lactacystin or Velcade (Bortezomib).Results: We show that endogenous Arg555Trp mis-sense mutated dysferlin is degraded by the proteasomal system. Inhibition of the proteasome by Lactacystin or Velcade rescues Arg555Trp mis-sense mutated dysferlin from degradation. This salvaged protein is functional as it restores plasma membrane resealing in patient derived myoblasts, and reverses their deficit in myotube formation. Velcade and Lactacystin did not cause cellular toxicity at the regimen used.Interpretation: Our results indicate that proteasomal inhibition may provide a viable therapeutic strategy for patients harboring certain dysferlin mis-sense mutations.
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