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Postnatal changes in sarcolemmal organization in the mdx mouse
1Department of Physiology, School of Medicine, University of Maryland, 655 W. Baltimore Steet, Baltimore, MD 21201, USA.
Abstract:
The tibialis anterior muscles of mdx mice degenerate between 3 and 4 weeks after birth and then partially recover. We show that the membrane cytoskeleton at the mdx sarcolemma is disorganized at 18-days postnatal, and becomes more disorganized at 4 weeks compared to earlier or later times. Mdx muscle at 18 days have few central nuclei, suggesting that it has not yet sustained significant damage. The variance of myofiber diameter confirms that the mdx pathology is greatest at 4 weeks, when the sarcolemma is most disorganized. Sarcolemmal disorganization in the mdx does not involve contractile structures, nor is it seen in age-matched controls. In revertant mdx fibers expressing dystrophin, sarcolemmal organization is similar to controls. Our results suggest that the absence of dystrophin results in the disorganization of the sarcolemma, even in 18-day-old mice, and that the extent of disorganization is greater when the myopathy is most severe.
Insights
The absence of dystrophin causes sarcolemmal disorganization in mdx mice, even before severe muscle damage occurs. This disorganization worsens as the muscular dystrophy progresses.
Area of Science:
- Muscle Biology
- Biochemistry
- Genetics
Background:
- Muscular dystrophy in mdx mice involves tibialis anterior muscle degeneration and partial recovery.
- Sarcolemmal integrity is crucial for muscle function and is compromised in muscular dystrophies.
Purpose of the Study:
- To investigate the early changes in sarcolemmal organization in mdx mice.
- To correlate sarcolemmal disorganization with the severity of muscular dystrophy in mdx mice.
Main Methods:
- Microscopic examination of tibialis anterior muscle sarcolemma in mdx mice at different postnatal ages (18 days, 4 weeks).
- Assessment of myofiber diameter variance and central nuclei presence.
- Analysis of sarcolemmal organization in control mice and dystrophin-expressing revertant mdx fibers.
Main Results:
- Sarcolemmal cytoskeleton disorganization was observed in mdx mice as early as 18 days postnatal.
- The disorganization increased by 4 weeks, coinciding with the peak of myopathy and myofiber diameter variance.
- Sarcolemmal disorganization was not linked to contractile structures and was absent in controls.
- Revertant mdx fibers expressing dystrophin showed normal sarcolemmal organization.
Conclusions:
- The absence of dystrophin leads to early sarcolemmal disorganization in mdx mice.
- Sarcolemmal disorganization is a sensitive indicator of muscular dystrophy severity.
- Restoration of dystrophin expression normalizes sarcolemmal organization.
