Increased collagen cross‐linking is a signature of dystrophin‐deficient muscle

INTRODUCTION: Collagen cross‐linking is a key parameter in extracellular matrix (ECM) maturation, turnover, and stiffness. We examined aspects of collagen cross‐linking in dystrophin‐deficient murine, canine, and human skeletal muscle. METHODS: DMD patient biopsies and samples from mdx mice and golden retriever muscular dystrophy dog samples (with appropriate controls) were analyzed. Collagen cross‐linking was evaluated using solubility and hydroxyproline assays. Expression of the cross‐linking enzyme lysyl oxidase (LOX) was determined by real‐time polymerase chain reaction, immunoblotting, and immunofluorescence. RESULTS: LOX protein levels are increased in dystrophic muscle from all species evaluated. Dystrophic mice and dogs had significantly higher cross‐linked collagen than controls, especially in the diaphragm. Distribution of intramuscular LOX was heterogeneous in all samples, but it increased in frequency and intensity in dystrophic muscle. CONCLUSION: These findings implicate elevated collagen cross‐linking as an important component of the disrupted ECM in dystrophic muscles, and heightened cross‐linking is evident in mouse, dog, and man. Muscle Nerve 54: 71–78, 2016