Dystrophin deficiency in canine X-linked muscular dystrophy in Japan (CXMDJ) alters myosin heavy chain expression profiles in the diaphragm more markedly than in the tibialis cranialis muscle

<p>Abstract</p> <p>Background</p> <p>Skeletal muscles are composed of heterogeneous collections of muscle fiber types, the arrangement of which contributes to a variety of functional capabilities in many muscle types. Furthermore, skeletal muscles can adapt individual myofibers under various circumstances, such as disease and exercise, by changing fiber types. This study was performed to examine the influence of dystrophin deficiency on fiber type composition of skeletal muscles in canine X-linked muscular dystrophy in Japan (CXMD_J), a large animal model for Duchenne muscular dystrophy.</p> <p>Methods</p> <p>We used tibialis cranialis (TC) muscles and diaphragms of normal dogs and those with CXMD_Jat various ages from 1 month to 3 years old. For classification of fiber types, muscle sections were immunostained with antibodies against fast, slow, or developmental myosin heavy chain (MHC), and the number and size of these fibers were analyzed. In addition, MHC isoforms were detected by gel electrophoresis.</p> <p>Results</p> <p>In comparison with TC muscles of CXMD_J, the number of fibers expressing slow MHC increased markedly and the number of fibers expressing fast MHC decreased with growth in the affected diaphragm. In populations of muscle fibers expressing fast and/or slow MHC(s) but not developmental MHC of CXMD_Jmuscles, slow MHC fibers were predominant in number and showed selective enlargement. Especially, in CXMD_Jdiaphragms, the proportions of slow MHC fibers were significantly larger in populations of myofibers with non-expression of developmental MHC. Analyses of MHC isoforms also indicated a marked increase of type I and decrease of type IIA isoforms in the affected diaphragm at ages over 6 months. In addition, expression of developmental (embryonic and/or neonatal) MHC decreased in the CXMD_Jdiaphragm in adults, in contrast to continuous high-level expression in affected TC muscle.</p> <p>Conclusion</p> <p>The CXMD_Jdiaphragm showed marked changes in fiber type composition unlike TC muscles, suggesting that the affected diaphragm may be effectively adapted toward dystrophic stress by switching to predominantly slow fibers. Furthermore, the MHC expression profile in the CXMD_Jdiaphragm was markedly different from that in <it>mdx </it>mice, indicating that the dystrophic dog is a more appropriate model than a murine one, to investigate the mechanisms of respiratory failure in DMD.</p

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

Initial Pulmonary Respiration Causes Massive Diaphragm Damage and Hyper-CKemia in Duchenne Muscular Dystrophy Dog

The molecular mechanism of muscle degeneration in a lethal muscle disorder Duchene muscular dystrophy (DMD) has not been fully elucidated. The dystrophic dog, a model of DMD, shows a high mortality rate with a marked increase in serum creatine kinase (CK) levels in the neonatal period. By measuring serum CK levels in cord and venous blood, we found initial pulmonary respiration resulted in massive diaphragm damage in the neonates and thereby lead to the high serum CK levels. Furthermore, molecular biological techniques revealed that osteopontin was prominently upregulated in the dystrophic diaphragm prior to the respiration, and that immediate-early genes (c-fos and egr-1) and inflammation/immune response genes (IL-6, IL-8, COX-2, and selectin E) were distinctly overexpressed after the damage by the respiration. Hence, we segregated dystrophic phases at the molecular level before and after mechanical damage. These molecules could be biomarkers of muscle damage and potential targets in pharmaceutical therapies