Search

Highlights • Normalized muscle volumes distinguish between wild type and DE50-MD dogs. • Global muscle T2 signal intensities discriminate between wild type and DE50-MD dogs. • Musculoskeletal changes detected by MRI reflect those seen in human DMD patients. • Musculoskeletal MRI in this model will be useful to assess treatment efficacy., The DE50-MD canine model of Duchenne muscular dystrophy (DMD) has a dystrophin gene splice site mutation causing deletion of exon 50, an out-of-frame transcript and absence of dystrophin expression in striated muscles. We hypothesized that the musculoskeletal phenotype of DE50-MD dogs could be detected using Magnetic Resonance Imaging (MRI), that it would progress with age and that it would reflect those in other canine models and DMD patients. 15 DE50-MD and 10 age-matched littermate wild type (WT) male dogs underwent MRI every 3 months from 3 to 18 months of age. Normalized muscle volumes, global muscle T2 and ratio of post- to pre-gadolinium T1-weighted SI were evaluated in 7 pelvic limb and 4 lumbar muscles bilaterally. DE50-MD dogs, compared to WT, had smaller volumes in all muscles, except the cranial sartorius; global muscle T2 was significantly higher in DE50-MD dogs compared to WT. Muscle volumes plateaued and global muscle T2 decreased with age. Normalized muscle volumes and global muscle T2 revealed significant differences between groups longitudinally and should be useful to determine efficacy of therapeutics in this model with suitable power and low sample sizes. Musculoskeletal changes reflect those of DMD patients and other dog models.

Several human and animal myopathies, such as malignant hyperthermia (MH), central core disease and equine recurrent exertional rhabdomyolysis (RER) are confirmed or thought to be associated with dysfunction of skeletal muscle calcium regulation. For some patients in whom the genetic cause is unknown, or when mutational analysis reveals genetic variants with unclear pathogenicity, defects are further studied through use of muscle histopathology and in vitro contraction tests, the latter in particular, when assessing responses to ryanodine receptor agonists, such as caffeine. However, since muscle biopsy is not always suitable, researchers have used cultured cells to model these diseases, by examining calcium regulation in myotubes derived from skin, following forced expression of muscle-specific transcription factors. Here we describe a novel adenoviral vector that we used to express equine MyoD in dermal fibroblasts. In permissive conditions, transduced equine and human fibroblasts differentiated into multinucleated myotubes. We demonstrate that these cells have a functional excitation-calcium release mechanism and, similarly to primary muscle-derived myotubes, respond in a dose-dependent manner to increasing concentrations of caffeine. MyoD-induced conversion of equine skin-derived fibroblasts offers an attractive method for evaluating calcium homeostasis defects in vitro without the need for invasive muscle biopsy.

Autosomal dominant Emery-Dreifuss muscular dystrophy (AD-EDMD) is one of a number of allelic disorders caused by mutations in the nuclear lamina proteins, lamins A and C. The disorder is characterised by the early onset of skeletal muscle weakness and joint contractures and later, by dilated cardiomyopathy and cardiac arrythmias. Although the pathophysiology is not understood, one theory suggests that disordered structural organisation at weakened nuclei in contractile cells may underlie the disease. Previous work shows that mice deficient in lamin A/C develop similar skeletal and cardiac muscle signs to patients with AD-EDMD and ultrastructural examination of muscle from these mice shows abnormal localisation of desmin. We hypothesised therefore that desmin localisation may be abnormal in muscle or cells from patients with AD-EDMD and/or in cells expressing mutant lamins. In order to evaluate this, desmin immunolocalisation was determined in skeletal muscle biopsy sections from patients with AD-EDMD and cell lines including MyoD-transfected fibroblast-derived myotubes from AD-EDMD patients and murine embryonic stem cell-derived cardiomyocytes stably transfected with mutant human lamin A. Ultrastructural examination of patient muscle was also performed. Desmin was expressed and localised normally in patient muscle and cell lines and ultrastructural examination was similar to controls. These results fail to provide any evidence that dominant mutations in lamin A/C lead to a disorganisation of the desmin associated cytoskeleton.

Exertional rhabdomyolysis (ER) is common in sled dogs, animals with high energy expenditures that consume high fat (60% of ingested calories) diets. Associations between pre-race plasma [vitamin E] and total antioxidant status (TAS) and risk of developing ER were examined in dogs competing in the 1998 Iditarod race. Pre-race blood samples were collected from 750 dogs and a second sample was collected from 158 dogs withdrawn from the race at various times. Plasma creatine kinase activity was used to identify withdrawn dogs with ER. There was no association between pre-race plasma [vitamin E] and risk of development of ER. Dogs that developed ER started the race with higher TAS, but when withdrawn, had lower TAS than unaffected dogs and had similar pre-race [vitamin E] but higher [vitamin E] at time of withdrawal. Hence, the risk of ER in sled dogs is not affected by plasma [vitamin E] before the race.