Canine X-linked Muscular Dystrophy Research Articles

Canine X-linked muscular dystrophy in Japan (CXMDJ).

The purpose of this study was to develop a strain of canine X-linked muscular dystrophy (CXMD), a model of Duchenne muscular dystrophy, in Japan. A female beagle was artificially inseminated with frozen-thawed spermatozoa derived from an affected golden retriever. Subsequently, two carrier female dogs (G1 carriers) and four normal male littermates were produced. Thereafter, the two G1 carriers were mated with beagle sires. As a result, each bitch whelped three times, and out of 54 pups, 17 affected male descendants, and 11 carrier female descendants (G2 carriers) were detected. One G2 carrier was then mated with a beagle sire and 15 pups in two whelpings were produced, including five affected males and four carrier females (G3 carriers). A total of 10 female beagles were artificially inseminated to evaluate the fertility of the frozen-thawed spermatozoa from the two affected dogs. The whelping rates of the two affected dogs were 4/5 and the litter sizes were 5.0 +/- 1.41 and 6.0 +/- 0.82, respectively. These results indicate that a canine X-linked muscular dystrophy colony has been established in Japan. We called them CXMDJ.

Transplanted fetal cardiomyocytes as cardiac pacemaker.

While morphologic integration of transplanted fetal cardiomyocytes into the ventricular myocardium is a well-known fact, no studies have yet shown transplanted cells to coherently contribute to contraction and electrical excitation of the host myocardium. The aim of this study was to prove the hypothesis that by transplanting cardiomyocytes with a higher intrinsic rhythmic rate into the myocardium of the left ventricle, these cells could act as an ectopic pacemaker by functional coupling with host cardiomyocytes. Dissociated fetal canine atrial cardiomyocytes including sinus nodal cells were delivered into the free wall of the left ventricle of adult canine X-linked muscular dystrophy dogs (n=2). These dogs fail to express Dystrophin in both cardiac and skeletal muscle. In the control group (n=2) fetal skin fibroblasts were used for grafting. A total of 3-4 weeks after transplantation the dogs underwent catheter ablation of the atrioventricular node (AV-node) and subsequent electrophysiological mapping studies. Transplanted cells were identified by Dystrophin immunoreactivity, indicating survival and morphological integration in the recipient heart. The expression of Connexin 43 between donor and recipient cells suggested formation of gap junctions between injected and host cardiomyocytes. After catheter ablation of the AV-node, a ventricular escape rhythm emerged driving the pace of the heart and originating from the labeled transplantation site. This effect could not be observed in the control group (n=2). The results constitute the first observation of phenomena indicating electrical and mechanical coupling between allogeneic donor cardiomyocytes and recipient myocardium in-vivo. Further experiments are necessary to evaluate the technique as a potential therapy for atrioventricular block.

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.

Stable fetal cardiomyocyte grafts in the hearts of dystrophic mice and dogs.

This report documents the formation of stable fetal cardiomyocyte grafts in the myocardium of dystrophic dogs. Preliminary experiments established that the dystrophin gene product could be used to follow the fate of engrafted cardiomyocytes in dystrophic mdx mice. Importantly, ultrastructural analyses revealed the presence of intercalated discs consisting of fascia adherens, desmosomes, and gap junctions at the donor-host cardiomyocyte border. To determine if isolated cardiomyocytes could form stable intracardiac grafts in a larger species, preparations of dissociated fetal canine cardiomyocytes were delivered into the hearts of adult CXMD (canine X-linked muscular dystrophy) dogs. CXMD dogs, like Duchenne muscular dystrophy patients and mdx mice, fail to express dystrophin in both cardiac and skeletal muscle. Engrafted fetal cardiomyocytes, identified by virtue of dystrophin immunoreactivity, were observed to be tightly juxtaposed with host cardiomyocytes as long as 10 wk after engraftment, the latest date analyzed. Confocal laser scanning microscopy revealed the presence of connexin43, a major constituent of the gap junction, at the donor-host cardiomyocyte border. The presence of intracardiac grafts was not associated with arrhythmogenesis in the CXMD model. These results indicate that fetal cardiomyocyte grafting can successfully augment cardiomyocyte number in larger animals.

P-399 Preservation and transportation of graft for cadaveric liver transplant in Japan

Recombinant adeno-associated virus (rAAV)-mediated gene transfer is an attractive approach to the treatment of Duchenne muscular dystrophy (DMD). We investigated the muscle transduction profiles and immune responses associated with the administration of rAAV2 and rAAV8 in normal and canine X-linked muscular dystrophy in Japan (CXMDJ) dogs. rAAV2 or rAAV8 encoding the lacZ gene was injected into the skeletal muscles of normal dogs. Two weeks after the injection, we detected a larger number of β-galactosidase-positive fibers in rAAV8-transduced canine skeletal muscle than in rAAV2-transduced muscle. Although immunohistochemical analysis using anti-CD4 and anti-CD8 antibodies revealed less T-cell response to rAAV8 than to rAAV2, β-galactosidase expression in rAAV8-injected muscle lasted for <4 weeks with intramuscular transduction. Canine bone marrow-derived dendritic cells (DCs) were activated by both rAAV2 and rAAV8, implying that innate immunity might be involved in both cases. Intravenous administration of rAAV8-lacZ into the hind limb in normal dogs and rAAV8-microdystrophin into the hind limb in CXMDJ dogs resulted in improved transgene expression in the skeletal muscles lasting over a period of 8 weeks, but with a declining trend. The limb perfusion transduction protocol with adequate immune modulation would further enhance the rAAV8-mediated transduction strategy and lead to therapeutic benefits in DMD gene therapy.

Reduction of the transient outward potassium current in canine X-linked muscular dystrophy.

The xmd dog develops a cardiomyopathy similar to that seen in Duchenne muscular dystrophy patients. In both the canine and human diseases, ECG abnormalities may precede the development of overt cardiac pathological lesions. The purpose of this study was to determine whether specific cellular electrical abnormalities occur in dystrophic ventricular tissue. Action potentials were recorded in epicardial tissue strips obtained from normal and xmd dogs. Phase 1 amplitude was increased from 86.8 +/- 2.7 mV in normal dogs to 94.3 +/- 1.8 mV in xmd dogs (mean +/- SEM; P < .05). The 4-aminopyridine-sensitive transient outward potassium current (Ito), as recorded in isolated epicardial myocytes using the whole-cell patch-clamp technique, was reduced in xmd dogs compared with age-matched normal dogs. Cell capacitance also was reduced significantly in xmd compared with normal cells, as was the current density (3.6 +/- 0.3 versus 5.4 +/- 0.8 pA/pF, respectively). No differences were observed in the time constants of current decay or in the kinetics of recovery from inactivation between groups. The slope factor (k) of steady-state inactivation was significantly greater in xmd compared with normal cells (7.2 +/- 0.9 versus 5.4 +/- 0.5, respectively), whereas the V1/2 of inactivation did not differ (-38.2 +/- 2.4 versus -36.8 +/- 1.6 mV, respectively). These data indicate that the magnitude of Ito is reduced in dystrophic epicardial myocytes, resulting in an increase in phase 1 amplitude. The reduction of Ito may alter the balance of inward and outward currents in dystrophic myocardium and thereby contribute to the development of cardiac pathology.

Canine X‐linked muscular dystrophy as an animal model of Duchenne muscular dystrophy: A review

Canine X-linked muscular dystrophy is a spontaneously occurring, progressive, degenerative myopathy of dogs that is clinically and pathologically similar to Duchenne muscular dystrophy in man. The molecular basis for the disease has been shown to be a lack of dystrophin, the protein product of the Duchenne muscular dystrophy gene. Breeding colonies of dystrophic dogs have been established. This report reviews the findings of genetic, clinical, pathologic, molecular biologic, and immunocytochemical studies of the canine model, and compares the features of the canine disease to those of Duchenne dystrophy in man.

Canine X-linked muscular dystrophy: Selective involvement of muscles in neonatal dogs

The development of lesions in dogs with canine X-linked muscular dystrophy (CXMD) was studied in dogs from birth to 8 weeks of age. Selective involvement of muscles was noted in dogs up to 4 weeks of age, after which lesions were noted in all muscles examined. Marked fiber hypertrophy was a consequence of the dystrophic process. Severe degenerative lesions were first detected in the tongue, diaphragm, trapezius, deltoideus, extensor carpi radialis, sartorius, and cranial tibial muscles, with relative sparing of the triceps, biceps femoris, and quadriceps muscles. Fiber necrosis and regeneration were present in the tongue muscle at birth, indicating onset of degeneration in utero. The propensity for early development of lesions in certain muscles could not be attributed to larger fiber diameter or to fiber maturity. It is suggested that early development of lesions in these muscles may be related to the activity of these muscles in neonatal dogs.

Canine X-linked muscular dystrophy: Morphologic lesions

Gross pathologic lesions and light microscopic and ultrastructural features of skeletal muscle lesions in canine X-linked muscular dystrophy (CXMD) were studied in dogs from 3 months to 6 years of age. Necrosis and regeneration were present at all ages, but were most prominent in the youngest dogs studied. Increased intracytoplasmic calcium, as evidenced by positive alizarin red S staining, was associated with fiber necrosis, but was also seen in small numbers of otherwise normal fibers. Progressive changes included development of severe fiber size variation, endomysial and perimysial fibrosis, prominent cytoplasmic disorganization, internalization of myonuclei, mitochondrial proliferation, mild fat infiltration, and alterations in the fiber-type pattern. The most consistent early ultrastructural changes were dilatation of the sarcoplasmic reticulum and focal subsarcolemmal areas of degeneration. Convincing sarcolemmal defects were not found. Z-band streaming was present at all ages, and Z-band duplication and nemaline rods were seen in older dogs. Evidence for abnormal regeneration was found in the oldest dog, and was associated with extensive fibrosis. These findings document the progression of lesions in CXMD, and illustrate the profound alterations in fiber organization and fiber type that may occur in late stages of dystrophin-deficient muscular dystrophy.

Increased Serum Alanine Aminotransferase Activity Associated With Muscle Necrosis in the Dog

Serum activity of alanine aminotransferase (ALT) was consistently increased in dogs with canine X-linked muscular dystrophy (CXMD), a primary myopathy characterized by profound and on-going skeletal muscle necrosis. In order to determine whether the ALT was of liver origin, serum activity of creatine kinase (CK), aspartate aminotransferase (AST), ALT, and sorbitol dehydrogenase (SDH) obtained from dystrophic dogs was compared with enzyme activity present in clinically normal dogs. In dystrophic dogs at all ages tested, serum activity of CK, AST, and ALT was increased, and significant increases were present in dogs four weeks or older. In contrast, SDH activity in dystrophic dogs was not statistically different from values in clinically normal dogs. Ultrastructural examination of liver tissue revealed no evidence of hepatic degeneration in dystrophic dogs. It was concluded that increased serum activity of ALT in the dog may be associated with severe skeletal muscle degeneration, without concurrent hepatocellular necrosis.

Canine X-linked muscular dystrophy: An animal model of Duchenne muscular dystrophy: Clinical studies

The progression of clinical disease and serum creatine kinase (CK) levels in canine X-linked muscular dystrophy (CXMD) was studied in 7 dogs from birth to 12–14 months and in 18 dogs at varying intervals from birth to 8 weeks. One affected male was studied from age 3.5 to 6 years, and all pups were descendants of this dog. A lethal neonatal form was recognized in some pups. In the more typical form, clinical signs of stunting, weakness and gait abnormalities were evident by 6–9 weeks and were progressive, leading to marked muscle atrophy, fibrosis and contractures by 6 months. Serum CK levels were markedly elevated, such that affected pups could be identified by 1 week. CK values increased until 6–8 weeks, then plateaued at approx. 100 times normal. Affected females and beagle-cross dogs were less severely affected than large breed-cross dogs. In the 2 adult dogs with cardiac insufficiency CK levels had decreased to 5–15 times normal. These studies show that CXMD and Duchenne muscular dystrophy have striking phenotypic as well as genotypic similarities. In addition, these studies of CXMD suggest that in females and in smaller dogs the same genetic defect results in a less severe clinical disease.