Electrotransfer of Naked DNA in the Skeletal Muscles of Animal Models of Muscular Dystrophies

The electrotransfer of naked DNA has recently been adapted to the transduction of skeletal muscle fibers. We investigated the short- and long-term efficacy of this methodology in wild-type animals and in mouse models of congenital muscular dystrophy (dy/dy, dy(2J)/dy(2J)), or Duchenne muscular dystrophy (mdx/mdx). Using a reporter construct, the short-term efficacy of fiber transduction reached 40% and was similar in wild-type, dy/dy and dy(2J)/dy(2J) animals, indicating that ongoing muscle fibrosis was not a major obstacle to the electrotransfer-mediated gene transfer. Although the complete rejection of transduced fibers was observed within 3 weeks in the absence of immunosuppression, the persistency was prolonged over 10 weeks when transient or continuous immunosuppressive regimens were used. Using therapeutic plasmids, we demonstrated that electrotransfer also allowed the transduction of large constructs encoding the laminin alpha2 chain in dy/dy mouse, or a chimeric dystrophin-EGFP protein in mdx/mdx mouse. The correct sarcolemmal localization of these structural proteins demonstrated the functional relevance of their expression in vivo, with a diffusion domain estimated to be 300 to 500 microm. However, degeneration-regeneration events hampered the long-term stability of transduced fibers. Given its efficacy for naked DNA transfer in these models of muscular dystrophies, and despite some limitations, gene electrotransfer methodology should be further explored as a potential avenue for treatment of muscular dystrophies.