Improved success of myoblast transplantation in mdx mice by blocking the myostatin signal.

BACKGROUND: : Duchenne muscular dystrophy (DMD) is caused by a dystrophin gene mutation. Transplantation of normal myoblasts results in long-term restoration of dystrophin. However, the success of this approach is compromised by the limited time of regeneration following muscle damage. Myostatin is known to be responsible for limiting skeletal muscle regeneration. Our purpose is to verify whether blocking the myostatin signal in mdx host mice or in normal myoblasts transplanted in mdx host mice would increase the extent of muscle repair and thus allow the formation of more dystrophin-positive fibers.

METHODS: : Transgenic mdx mice carrying a dominant negative form of myostatin receptor (dnActRIIB) were used to test the fiber resistance to damage and to act as a host for normal myoblast transplantation. Myoblasts obtained from nondystrophic transgenic mice carrying the dominant negative myostatin receptor were also transplanted in nontransgenic mdx mice.

RESULTS: : Transgenic mdx mice carrying the dnActRIIB gene have bigger muscles than mdx mice with the normal gene of ActRIIB. Their fiber resistance to exercise-induced damage was also greatly improved. Moreover, the success of normal myoblast transplantation was significantly enhanced in mdx/dnActRIIB mice. Finally, nondystrophic dnActRIIB myoblasts formed more abundant and bigger dystrophin positive fibers when transplanted in mdx mice.

CONCLUSIONS: : Blocking the myostatin signal in mdx mice allowed the size of muscle fibers to increase, the fiber resistance to damage induced by exercise to increase, and the success of normal myoblast transplantation to improve. The transplantation in mdx mice of dnActRIIB myoblasts formed more abundant and larger dystrophin positive fibers.