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Adaptations in myosin heavy chain expression and contractile function in dystrophic mouse diaphragm
B J Petrof1, H H Stedman, J B Shrager
1Department of Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104.
The American Journal of Physiology
|September 1, 1993
Summary
The mdx mouse model of Duchenne muscular dystrophy shows diaphragm muscle changes. Progressive degeneration leads to a slower muscle fiber type, reducing power but increasing endurance.
Area of Science:
- Muscle physiology
- Genetics
- Biochemistry
Background:
- The X chromosome-linked muscular dystrophic (mdx) mouse is a model for Duchenne muscular dystrophy, lacking dystrophin.
- Progressive muscle degeneration impacts diaphragm function.
Purpose of the Study:
- To investigate diaphragm contractile properties and myosin heavy chain (MHC) expression in young and old mdx mice.
- To understand adaptive changes in muscle fiber type during degeneration.
Main Methods:
- Comparative analysis of diaphragm contractile function (maximum isometric tension, twitch kinetics, endurance) in control and mdx mice at different ages.
- Assessment of myosin heavy chain (MHC) isoform expression in diaphragm muscle fibers using immunohistochemistry.
Main Results:
- Young mdx mice exhibited reduced maximum tension and altered MHC expression, with increased slow (Type I) and embryonic MHC fibers, and decreased Type IIx/b fibers.
- Old mdx mice showed further tension reduction, slower twitch kinetics, and significantly increased diaphragm endurance.
- In old mdx mice, there was a substantial increase in Type I MHC fibers and near absence of Type IIx/b fibers, with no embryonic MHC detected.
Conclusions:
- The mdx diaphragm adapts to progressive degeneration by shifting towards a slower muscle phenotype.
- This phenotypic shift is associated with decreased force production but enhanced endurance, potentially preserving muscle function and fiber survival by lowering energy demands.