Administration of a Soluble Activin Type IIB Receptor Promotes the Transplantation of Human Myoblasts in Dystrophic Mice

Duchenne muscular dystrophy (DMD) is a recessive disease caused by a dystrophin gene mutation. Myoblast transplantation permits the introduction of the dystrophin gene into dystrophic muscle fibers. However, this strategy has so far produced limited results. Modulation of transforming growth factor-beta (TGF-beta) superfamily signaling promotes skeletal muscle differentiation and growth and myogenic regeneration. We investigated the possibility that the combination of TGF-beta superfamily signaling inhibition with myoblast transplantation might be an effective therapeutic approach in dystrophin-deficient patients. In vitro, blocking myostatin and other ligands with a soluble form of the extracellular domain of the activin IIB receptor (ActRIIB/Fc) upregulated the expression of myogenic differentiation factors and increased human myoblast fusion. In vivo, systemic inhibition of activin IIB receptor signaling by delivery of ActRIIB/Fc increased the success of the myoblast transplantation. This effect was further increased by forcing the mice to swim weekly to induce cycles of muscle degeneration and regeneration. Treatment of dystrophic mice with ActRIIB/Fc led to increased body weight, increased skeletal muscle mass, and improved myoblast transplantation. Thus, ActRIIB/Fc represents an effective therapeutic strategy for muscular dystrophies, and its effects are enhanced when combined with muscle exercise.