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Mechanisms of resistance to pathogenesis in muscular dystrophies
1Institute for Theoretical Biochemistry and Molecular Biology, Ithaca, NY 14852-4512, USA.
Abstract:
A mechanistic definition of the dystrophic process is proposed, and the effects of growth factors vs. down-regulation of growth are critically analyzed. A conceptual scheme is presented to illustrate the steps leading to pathology, and various compensatory systems which ameliorate the pathology are examined, particularly in regards to the mdv mouse which is resistant to the deficiency of dystrophin, the main protein product of the Duchenne and Becker muscular dystrophy (DMD/BMD) gene. These compensatory systems are analyzed in terms of the differential resistance of fiber types to pathogenesis. The generation of a stable population of maturationally arrested centronucleated fibers which express the mature adult myosin isoforms is proposed to be the main strategy of mdx muscle to minimize apoptosis. Physiological properties of these fibers, such as utrophin expression, and high mitochondrial and endoplasmic reticulum content, together with probable increased glycerophosphorylcholine concentrations and facile access to the vascular system, are hypothesized to be instrumental in their resistance to pathogenesis. It is proposed that the major element that determines the susceptibility of most human muscles to the dystrophic process is their inability to arrest the maturation of regenerated fibers at the centronucleated stage with a concomitant expression of the adult myosins.
Insights
Duchenne and Becker muscular dystrophy (DMD/BMD) pathology involves growth dysregulation. Resistant mdx mice minimize apoptosis via arrested, centronucleated fibers expressing adult myosins, a strategy lacking in human muscles.
Area of Science:
- Muscle physiology and pathology
- Molecular biology of dystrophinopathies
Background:
- Duchenne and Becker muscular dystrophy (DMD/BMD) are genetic disorders characterized by progressive muscle degeneration.
- The primary cause is mutations in the dystrophin gene, leading to a deficiency of the dystrophin protein.
- Understanding the mechanistic basis of the dystrophic process and compensatory mechanisms is crucial for therapeutic development.
Purpose of the Study:
- To propose a mechanistic definition of the dystrophic process.
- To analyze the roles of growth factors and growth downregulation in muscular dystrophy.
- To examine compensatory systems, particularly in the dystrophin-deficient (mdx) mouse model, that ameliorate pathology.
Main Methods:
- Conceptual scheme development to illustrate pathological steps.
- Analysis of compensatory systems and fiber-type resistance to pathogenesis.
- Examination of physiological properties of centronucleated fibers in mdx mice.
Main Results:
- A conceptual framework for dystrophic pathology and compensatory mechanisms is presented.
- The mdx mouse exhibits resistance to dystrophin deficiency, attributed to compensatory systems.
- Maturationally arrested centronucleated fibers expressing adult myosin isoforms are identified as a key anti-apoptotic strategy in mdx muscle.
Conclusions:
- Physiological traits of arrested centronucleated fibers (utrophin expression, high mitochondrial/ER content) contribute to resistance.
- The inability of human muscles to arrest regenerated fiber maturation at the centronucleated stage with adult myosins is a key factor in susceptibility to dystrophic processes.
- This study provides insights into differential fiber resistance and potential therapeutic targets for DMD/BMD.