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Aquaporin 4 Expression in the mdx Mouse Diaphragm
Hajime Hara1, Yoshihiro Wakayama, Hiroko Kojima
1Department of Neurology, Showa University Fujigaoka Hospital, 1-30 Fujigaoka, Aoba-ku, Yokohama 227-8501, Japan.
Abstract:
Expression of aquaporin (AQP) 4 in the surface membranes of skeletal myofibers is well established; however, its functional significance is still unknown. The alterations of AQP4 expressions in dystrophic muscles at RNA and protein levels have been reported in various dystrophic muscles such as dystrophinopathy, dysferlinopathy, and sarcoglycanopathy. We are interested in the relationship between the severity of dystrophic muscle degeneration and the expression of AQP4. Here we compared the AQP4 expression of the limb muscles with that of diaphragms in both mdx and control mice. The dystrophic muscle degeneration, such as rounding profile of cross sectional myofiber shape, dense eosin staining, central nuclei, and endomysial fibrosis in mdx mice, were more marked in diaphragms than in limb muscles. The decrease of AQP4 expression at protein level was more marked in diaphragms than in the limb muscles of mdx mice. However, the expression of AQP4 mRNA in the diaphragms of mdx mice was not reduced in comparison with limb muscles of mdx mice. The present study revealed that AQP4 expression at protein level was correlated with the severity of dystrophic changes in muscle tissues of mdx mice.
Insights
Aquaporin-4 protein levels decrease more in diaphragm muscles than limb muscles of mdx mice, correlating with disease severity. This suggests a link between aquaporin-4 protein expression and muscular dystrophy progression.
Area of Science:
- Muscle physiology
- Molecular biology
- Biochemistry
Background:
- Aquaporin-4 (AQP4) is present in skeletal myofibers, but its function in muscle is unclear.
- AQP4 expression changes are noted in various muscular dystrophies at RNA and protein levels.
- The relationship between AQP4 expression and the severity of muscle degeneration requires further investigation.
Purpose of the Study:
- To compare AQP4 expression in limb and diaphragm muscles of mdx mice (a model for muscular dystrophy) and control mice.
- To investigate the correlation between the severity of dystrophic muscle degeneration and AQP4 expression levels.
Main Methods:
- Comparative analysis of AQP4 expression (mRNA and protein) in limb and diaphragm muscles of mdx and control mice.
- Assessment of dystrophic muscle degeneration characteristics (myofiber shape, eosin staining, central nuclei, fibrosis).
Main Results:
- Dystrophic changes were more severe in the diaphragms of mdx mice compared to their limb muscles.
- A more significant decrease in AQP4 protein expression was observed in the diaphragms of mdx mice relative to limb muscles.
- AQP4 mRNA levels did not show a similar reduction in diaphragms compared to limb muscles in mdx mice.
Conclusions:
- Muscle AQP4 protein expression is correlated with the severity of dystrophic changes.
- Diaphragm muscles exhibit more pronounced AQP4 protein reduction in mdx mice, aligning with greater degeneration.
- Post-transcriptional regulation may influence AQP4 protein levels in dystrophic muscle.
