Micro-dystrophin cDNA ameliorates dystrophic phenotypes when introduced into mdx mice as a transgene

The adeno-associated virus vector is a good tool for gene transfer into skeletal muscle, but the length of a gene that can be incorporated is limited. To develop a gene therapy for Duchenne muscular dystrophy, we generated a series of rod-truncated micro-dystrophin cDNAs: M3 (one rod repeat, 3.9 kb), AX11 (three rod repeats, 4.4 kb), and CS1 (four rod repeats, 4.9 kb). These micro-dystrophins, driven by a CAG promoter, were used to produce transgenic (Tg) mdx mice and all three micro-dystrophins were shown to localize at the sarcolemma together with the expression of dystrophin-associated proteins. Among them, CS1 greatly improved dystrophic phenotypes of mdx mice and contractile force of the diaphragm in particular was restored to the level of normal C57BL/10 mice. AX11 modestly ameliorated the dystrophic pathology, but, importantly, M3-Tg mdx mice still showed severe dystrophic phenotypes. These data suggest that the rod structure, and its length in particular, is crucial for the function of micro-dystrophin.