Background: Efficient adenovirus (AdV)-mediated gene transfer is possible only in immature muscle or regenerating muscle, suggesting that a developmentally regulated event plays a major role in limiting AdV uptake in mature skeletal muscle. Previously, we showed that the expression of the primary coxsackie and adenovirus receptor (CAR) is severely down-regulated during muscle maturation and that, in muscle-specific CAR transgenic mice, there is significant enhancement of AdV-mediated gene transfer to mature skeletal muscle.
Methods: To evaluate whether increasing CAR expression can also augment gene transfer to dystrophic muscle that has many regenerating fibers, we crossed CAR transgenics with dystrophin-deficient mice (mdx/CAR). We also tested a two-step protocol in which CAR levels were increased in the target muscle, prior to administration of AdV, through the use of recombinant adeno-associated virus (AAV2) expressing CAR. Lastly, we assessed the effect of histone deacetylase inhibitors on CAR and AdV transduction efficiency in myoblasts and mdx muscle.
Results: Although somewhat higher rates of transduction can be achieved in adult mdx mice than in normal mice as a result of ongoing muscle regeneration in these animals, CAR expression in the mdx background (mdx/CAR transgenics) still markedly improved the susceptibility of mature muscle to AdV-mediated gene transfer of dystrophin. Prior administration of AAV2-CAR to normal muscle led to significantly increased transduction by subsequent injection of AdV. The histone deacetylase inhibitor valproate increased CAR transcript and protein levels in myoblasts and mdx muscle, and also increased AdV-mediated gene transfer.
Conclusions: We have developed a method of increasing CAR levels in both normal and regenerating muscle.