Myoblast survival enhancement and transplantation success improvement by heat-shock treatment in MDX mice

Background. Duchenne muscular dystrophy is a disease caused by the incapacity to synthesize dystrophin, which is implicated in the maintenance of the sarcolemma integrity. Myoblast transplantation is a potential treatment of this disease. However, most of the transplanted cells die very rapidly after their injection. Heat-shock proteins (HSPs) are over-expressed when cells undergo various types of stresses. Our goal was thus to investigate whether the expression of HSPs (HSP70 in particular) could protect myoblasts from death after intramuscular injection. Methods. HSP70 expression was induced by warming the cells at 42degreesC for 60 minutes. HSP70 over-expression was quantified by Western blot analysis. The in vitro effect of HSPs on cell survival was evaluated by fluorescence-activated cell sorter analysis using the Hoescht/propidium iodide-labeling technique, and their in vivo effects were investigated by transplanting TnI-LacZ myoblasts labeled with [methyl-C-14] thymidine. Results. Western blots indicated a sevenfold overexpression of the HSP70 after the heat-shock treatment. In vitro, the heat-shock treatment protected 18% of the cells from staurosporine- (1 muM) induced apoptosis. HSPs also protected 10% of the cells from death induced by either tumor necrosis factor-a (30 ng/mL) or glucose oxydase (0.1 U/mL). In vivo, the treatment improved the cell survival by twofold 5 days after the graft and increased by fourfold the long-term graft success. Conclusions. The heat-shock treatment is a practical approach for improving the success of myoblast transplantation; in fact, using this kind of treatment, there is no need to genetically modify the cells before their transplantation.