Exercise improves the success of myoblast transplantation in mdx mice

Transplantation of normal muscle precursor cells is a potential approach to restore dystrophin expression within dystrophin [deficient] mdx mice, a model of Duchenne Muscular Dystrophy. This study aims to evaluate whether exercise could improve graft success and hybrid fiber distribution within mdx muscle. eGFP(+) Muscle precursor cells were transplanted into tibialis anterior muscles of mdx mice using a single injection trajectory. During the following weeks, muscle fiber breaks were induced by making mdx mice swim. To evaluate fiber damage, Evans blue solution was injected intraperitoneally to mice 16h before their sacrifice. Tibialis anterior muscles were then harvested and eGFP, dystrophin and Evans blue labeling were analyzed by fluorescent microscopy. Twenty minutes of exercise (i.e., swimming) were used to induce damage in about 30% of TA muscle fibers. Graft success, evaluated as the percentage of hybrid fibers which are eGFP(+), was improved by 1.9-fold after swimming 3 times per week during 4 weeks and by 1.8-fold after daily swimming. Hybrid muscle fiber transversal and longitudinal distribution were also increased after repeated physical efforts. Exercise induced fiber breaks, which improved MPC recruitment and fusion and increased long-term graft success and also transverse and longitudinal distribution of hybrid fibers.