Mini- and full-length dystrophin gene transfer induces the recovery of nitric oxide synthase at the sarcolemma of mdx4cv skeletal muscle fibers

In normal skeletal muscle fibers, dystrophin accumulates at the cytoplasmic face of the sarcolemma where it associates with dystrophin-associated proteins (DAPs). Several studies have recently shown that neuronal isoform of nitric oxide synthase (nNOS) is also located at the sarcolemma, and that this membrane localization is mediated through interactions of nNOS with one of the DAPS, namely alpha 1-syntrophin. Since the lack of dystrophin in muscle fibers from Duchenne muscular dystrophy patients and mdx mice is accompanied by an absence of sarcolemmal nNOS, we examined in the present study, whether dystrophin gene replacement would lead to the restoration of nNOS at its appropriate subcellular location. To this end, tibialis anterior muscles from mdx4(cv) mice were directly injected with plasmid DNA encoding either full-length (pRSV-dys) or mini- (pRSV-dyB; lacking exons 17-48) dystrophin. For these experiments, we chose to study 10-week-old mdx4(cv) mice since at this developmental stage, muscles from these mice have already undergone several cycles of degeneration-regeneration. Immunofluorescence experiments performed on serial cross-sections revealed that approximately 50% of the dystrophin-positive fibers also exhibited significant levels of nNOS at their sarcolemma 2 weeks following gene transfer with pRSV-dys. Similar results were obtained with pRSV-dyB indicated that exons 17-48 of the dystrophin gene are not essential for the correct localization of nNOS in skeletal muscle fibers. Taken together with the recent demonstration that dystrophin gene transfer leads to significant physiological benefits our results suggest that dystrophin gene therapy using full-length or truncated dystrophin, also induces a rapid recovery of biochemical functions.