[Current status and perspective of gene therapy on dystrophic animal model]

Duchenne muscular dystrophy (DMD) is an X-linked, lethal muscle disorder caused by mutations in the dystrophin gene. An adeno-associated virus (AAV) vector-mediated gene transfer is one of attractive approaches to the treatment of DMD, though it has a limitation in insertion size up to 4.9 kb. Therefore, a full-length dystrophin cDNA (14 kb) cannot be incorporated into an AAV vector. We previously generated micro-dystrophin transgenic dystrophin-deficient mdx mice. Micro-dystrophin CS1 transgenic mdx mice showed almost complete amelioration of dystrophic phenotypes. We, therefore, constructed an AAV vector expressing micro-dystrophin deltaCS1, a modified version of CS1, driven by skeletal muscle-specific MCK promoter, since the MCK promoter in AAV vector drives longer expression of the LacZ gene than the CMV promoter in skeletal muscle. We injected the AAV-MCK deltaCS1 into anterior tibial (TA) muscles of 5-week-old or 10-day-old mdx mice. Dystrophic phenotypes were largely improved in both injections. Especially in the latter occasion, less than 20% of muscle fibers were microdystrophin positive at 24 weeks after the injection, but specific tetanic force of the injected muscle was not statistically different from that of control normal muscle. In conclusion, deltaCS1 micro-dystrophin introduced by an AAV vector could be a powerful tool for the gene therapy of DMD. A bigger animal model, canine X-linked muscular dystrophy will contribute to pre-clinical study of gene therapy.