Comparison of skeletal muscle pathology and motor function of dystrophin and utrophin deficient mouse strains

The genetic defect of mdx mice resembles that of Duchenne muscular dystrophy, although their functional performance and life expectancy is nearly normal. By contrast, mice lacking utrophin and dystrophin (mdx/utrn −/−) are severely affected and die prematurely. Mice with one utrophin allele (mdx/utrn +/−) are more severely affected than mdx mice, but outlive mdx/utrn −/− mice. We subjected mdx/utrn +/+, +/−, −/− and wild type males to a 12 week functional test regime of four different functional tests. Mdx/utrn +/+ and +/− mice completed the regime, while mdx/utrn −/− mice died prematurely. Mdx/utrn +/− mice performed significantly worse compared to mdx/utrn +/+ mice in functional tests. Creatine kinase levels, percentage of fibrotic/necrotic tissue, morphology of neuromuscular synapses and expression of biomarker genes were comparable, whereas mdx/utrn +/− and −/− mice had increased levels of regenerating fibers. This makes mdx/utrn +/− mice valuable for testing the benefit of potential therapies on muscle function parameters.