Adenovirus-mediated utrophin gene transfer mitigates the dystrophic phenotype of mdx mouse muscles

Utrophin is a close homolog of dystrophin, the protein whose mutations caus e Duchenne muscular dystrophy (DMD), Utrophin is present at low levels in n ormal and dystrophic muscle, whereas dystrophin is largely absent in DMD. I n such cases, the replacement of dystrophin using a utrophin gene transfer strategy could be more advantageous because utrophin would not be a neoanti gen, To establish if adenovirus (AV)-mediated utrophin gene transfer is a p ossible option for the treatment of DMD, an AV vector expressing a shortene d version of utrophin (AdCMV-Utr) was constructed, The effect of utrophin o verexpression was investigated following intramuscular injection of this AV into mdx mice, the mouse model of DMD. When the tibialis anterior (TA) mus cles of 3- to 5-day-old animals were injected with 5 mu l of AdCMV-Utr (7.0 x 10(11) virus/ml), an average of 32% of fibers were transduced and the tr ansduction level remained stable for at least 60 days, The presence of utro phin restored the normal histochemical pattern of the dystrophin-associated protein complex at the cell surface and resulted in a reduction in the num ber of centrally nucleated fibers, The transduced fibers were largely imper meable to the tracer dye Evans blue, suggesting that utrophin protects the surface membrane from breakage, In vitro measurements of the force decline in response to high-stress eccentric contractions demonstrated that the mus cles overexpressing utrophin were more resistant to mechanical stress-induc ed injury, Taken together, these data indicate that AV-mediated utrophin ge ne transfer can correct various aspects of the dystrophic phenotype, Howeve r, a progressive reduction in the number of transduced fibers was observed when the TA muscles of 30- to 45-day-old mice were injected with 25 mu l of AdCMV-Utr, This reduction coincides with a humoral response to the AV and transgene, which consists of a hybrid mouse-human cDNA.