Early Inflammation in Muscular Dystrophy Differs Between Limb and Respiratory Muscles and Increases with Dystrophic Severity.

Abstract Duchenne muscular dystrophy (DMD) is a genetic, degenerative striated muscle disease exacerbated by chronic inflammation. Mdx mice, the genotypic DMD model, poorly represent immune-mediated pathology observed in patients, but improved understanding of innate immunity in dystrophic muscles is required to develop specific anti-inflammatory treatments. We comprehensively investigated inflammation in mdx mice and the more fibrotic utrn+/-;mdx “Het” model. Unbiased analysis shows that mdx and Het mice contain increased levels of numerous chemokines and cytokines with further increases in Het mice. Chemokine and chemokine receptor gene expression is dramatically increased in 4 week-old dystrophic quadriceps muscles, and to a lower extent in diaphragm during the early injury phase and increases persist at lower levels at 8 and 20 weeks. We optimized a direct immune cell isolation method, preventing loss of up to 90% of macrophages with density-dependent centrifugation previously used for mdx flow cytometry. Het quadriceps contain higher proportions of neutrophils and infiltrating monocytes than mdx. Het quadriceps contain higher percentages of F4/80Hi, but lower percentages of F4/80Lo cells and patrolling monocytes compared to Het diaphragms. These differences may restrict regenerative potential of dystrophic diaphragms, increasing pathological severity. Fibrotic and inflammatory gene expression is higher in myeloid cells isolated from Het compared to mdx quadriceps, supporting Het mice may represent an improved model for testing therapeutic manipulation of inflammation in DMD.