Embryonic myosin is a regeneration marker to monitor utrophin based therapies for DMD

Duchenne muscular dystrophy (DMD) is a lethal, X-linked muscle-wasting disease caused by lack of the cytoskeletal protein dystrophin. Constitutive utrophin expression, a structural and functional paralogue of dystrophin, can successfully prevent the dystrophic pathology in the dystrophin-deficient mdx mouse model. In dystrophic muscles, utrophin is increased as part of the repair process and localised at the sarcolemma of regenerating myofibers. The presence of developmental myosin such as embryonic myosin (MyHC-emb) and neonatal (MyHC-neo) represents a useful marker of muscle regeneration and a meaningful indicator of muscle damage which correlates with the clinical severity of milder Becker Muscular dystrophy (BMD) and DMD patients. In the present study, we demonstrate that MyHC-emb is a robust marker of regeneration at different ages and in different skeletal muscles. We also evaluate the correlation between utrophin, dystrophin and MyHC-emb in wild-type and regenerating dystrophic muscles. Restoration of dystrophin significantly reduced MyHC-emb levels. Similarly, overexpression of utrophin in the transgenic mdx-Fiona mice reduced the number of MyHC-emb positive fibres to wild-type level, prevented the regenerative process and rescued the muscle function. In contrast, the absence of utrophin in the dystrophin deficient double knock out (dko) mice resulted in a higher MyHC-emb content and in a more severe dystrophic pathophysiology than in mdx mice. These data illustrate the importance of monitoring utrophin and MyHC-emb levels in the pre-clinical evaluation of therapies and provide translational support for the use of developmental myosin as a disease biomarker in DMD clinical trials.