Accumulation of collagen and altered fiber-type ratios as indicators of abnormal muscle gene expression in the mdx dystrophic mouse.

The growth and development of the X-linked muscular dystrophy mutant mouse (mdx) was compared with a control group from 3 weeks to 1 year old. Quantitative cytological analysis of the soleus muscle revealed cycles of degeneration, regeneration, and hypertrophy, and at any one time it was difficult to assess the extent of the disease based on muscle fiber size. One noticeable difference even in the youngest muscles studied was the reduced numbers of slow oxidative fibers and the increased number of fast glycolytic fibers in the mdx soleus muscles. The collagen of the connective tissue components of selectively stained sections was determined by computerized image analysis. Marked accumulation of collagen was found in both the endomysium and perimysium of the dystrophic muscles as compared with age-matched controls. Since the mdx mouse is a result of the same type of genetic defect as in human Duchenne muscular dystrophy, this model could thus be used to assess the effectiveness of various therapeutic approaches, including gene therapy using muscle fibrosis and fiber type proportions as the indicators.