Résumé :
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Deficiencies in dysferlin (DYSF) are responsible for two main progressive muscular dystrophies: limb-girdle muscular dystrophy type 2B (LGMD2B) and Miyoshi myopathy (MM). This transmembrane protein was shown to play a role in the repair of the plasma membrane by vesicle fusion, providing a possible hypothesis for the pathophysiology of these diseases. We previously demonstrated that a strategy relying on the concatemerization property of the AAV vector to transfer the dysferlin gene by means of two Adeno-Associated Viral vectors (AAV) was efficient to obtain full-length dysferlin expression in muscle. In addition, expression of the transgene was associated with restoration of the membrane repair potential and recovery of locomotor activity of the mice.The aim of the study was to determine whether this therapeutic strategy was efficient to protect the muscle from eccentric exercise. For this purpose, we undertook a comparison in wild-type and dysferlin deficient mice (B6.A/J-Dysfprmd) of different assays, including running protocols in treadmill and the large-strain injury (LSI) assay involving 15 repetitive lengthening contractions (Roche et al. 2008). All these tests were associated with Evans Blue injection to evaluate the muscle impairment. The difference in the number of Evans Blue positive cells obtained with the LSI was more significant than with the running protocol. Therefore, LSI was applied to dysferlin deficient mice that were injected by the two AAV vectors to investigate whether a restoration to the normal phenotype could be obtained. The results showed that expression of dysferlin was associated with an improved phenotype after LSI, indicating that the AAV-mediated transfer of the dysferlin gene has protected the muscle from damage resulting from eccentric contraction. These results validate the suitability of this test to discriminate between treated and untreated animals. A dose effect study with this test is on-going to define the minimum level of dysferlin required for reversal of the pathology.
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