Dystrophic phenotype of canine X-linked muscular dystrophy is mitigated by adenovirus-mediated utrophin gene transfer.

Utrophin is highly homologous and structurally similar to dystrophin, and in gene delivery experiments in mdx mice was able to functionally replace dystrophin. We performed mini-utrophin gene transfer in Golden Retriever dogs with canine muscular dystrophy (CXMD). Unlike the mouse model, the clinicopathological phenotype of CXMD is similar to that of Duchenne muscular dystrophy (DMD). We injected an adenoviral vector expressing a synthetic utrophin into tibialis anterior muscles of newborn dogs affected with CXMD and examined transgene expression by RNA and protein analysis at 10, 30 and 60 days postinjection in cyclosporin-treated and -untreated animals. Immunosuppression by cyclosporin was required to mitigate the immune response to viral and transgene antigens. RT-PCR analysis showed the presence of the exogenous transcript in the muscle of cyclosporin-treated and -untreated animals. The transgenic utrophin was efficiently expressed at the extrajunctional membrane in immunosuppressed dogs and this expression was stable for at least 60 days. We found reduced fibrosis and increased expression of dystrophin-associated proteins (DAPs) in association with muscle areas expressing the utrophin minigene, indicating that mini-utrophin can functionally compensate for lack of dystrophin in injected muscles. For this reason, utrophin transfer to dystrophin-deficient muscle appears as a promising therapeutic approach to DMD.

Development of muscle pathology in canine X-linked muscular dystrophy. II. Quantitative characterization of histopathological progression during postnatal skeletal muscle development.

We have characterized the time course of muscle pathology development during the postnatal maturation of quadriceps and tibialis anterior muscle in dystrophic golden retriever dogs. We determined the percentages of degenerating, regenerating, calcium-positive, hypercontracted, albumin-positive, and C3 complement fraction-positive muscle fibers and the extent of connective tissue proliferation in animals from neonate to adult. Necrotic fibers increased from days 2 to 30, decreased at 60 days (to 0.8%) and increased in older animals to a stable level of around 2%. Hypercontracted fibers peaked at 15 days (19.1%) and declined to 3.7% in adults. Regenerating fibers were numerous at 15 and 30 days (10%), declined at 60 days to 4.7% and declined further in adults. Calcium- and albumin-positive fibers peaked at 30 days (6.5% and 13.8%, respectively) and then declined to around 3% and 5%, respectively, in older dogs. In dystrophic dogs, the extent of fibrosis was significantly greater on 15 days than in controls, but did not then increase with age. In carriers, calcium- and albumin-positive fibers always expressed dystrophin abnormally. Muscle damage occurs before completion of muscle maturation in dystrophic dogs. While necrosis and hypercontraction remain stable in adults, fiber regeneration declines to very low levels. In contrast to Duchenne muscular dystrophy, muscle fibrosis in the muscle studied does not increase with age.

Development of muscle pathology in canine X-linked muscular dystrophy. I. Delayed postnatal maturation of affected and normal muscle as revealed by myosin isoform analysis and utrophin expression.

Canine X-linked muscular dystrophy (CXMD) is genetically homologous to Duchenne muscular dystrophy and shares the severe myopathy and lethal clinical development of the human disease. We used immunohistochemistry to characterize the time course of postnatal expression of adult fast, adult slow and developmental myosin in the muscle of CXMD dogs, carriers and healthy controls. We also characterized the expression of utrophin and dystrophin. This detailed immunolocalization study confirmed that postnatal muscle maturation is delayed in normal dogs compared to other animals and humans, and is only achieved at around 60 days. In CXMD dogs major derangement of myosin expression became evident from about 15 days; there was a selective loss of fibers expressing fast myosin and persistence of developmental fibers compared to controls. In carriers, the proportion of dystrophin-deficient fibers, which mainly expressed fast myosin, decreased with age. In controls and carriers utrophin was absent from muscle fiber surfaces in 2-day-old animals but present between 15 and 30 days, to mostly disappear by 60 days. In dystrophic animals, sarcolemmal expression of utrophin was more marked and persistent. That immature neonatal muscle from control dogs normally contains sarcolemmal utrophin may have implications for the success of utrophin up-regulation therapy to correct the dystrophic phenotype. The data of this study provide important baseline information for further studies on the development and progression of pathological changes in the muscle of CXMD dogs.