Top of pageAbstract Vascular endothelial growth factor (VEGF) is a major regulator of blood vessel formation during development and in the adult organism. Recent evidence indicates that this factor also plays an important role in sustaining the proliferation and differentiation of progenitor cells of different tissues, including bone marrow, bone, and the central nervous system. Here we show that the delivery of the 165 aa isoform of VEGF-A cDNA using an adeno-associated virus (AAV) vector exerts a powerful effect on the promotion of myogenic precursor cells differentiation to form multinucleated myotubes in vitro, as well as in the enhancement of muscle regeneration in vivo. By immunofluorescence staining, we observerved that both VEGFR-1 and VEGFR1-2 are highly expressed during myofiber formation in vitro, and that their expression persists until the late stages of the differentiation process. Receptor expression was concomitant with a pro-fusogenic effect of recombinant VEGF and with the protection of myogenic cells from apoptosis. These activities were most likely mediated by VEGFR-2, since the drug SU-1498, a specific inhibitor of this receptor, completely abolished the effects of VEGF. Following different types of skeletal muscle damage in mice (resection of the femoral artery or injection of glycerol or cardiotoxin), the delivery of AAV-VEGF markedly improved muscle fiber reconstitution in a dose-dependent manner. This activity was better exerted when the vector was administered 5 days after damage, rather than before, thus clearly indicating that the activity of VEGF most likely exerted on the muscle fibers independently of its well-known pro-angiogenic effects. In a consistent manner, the expression of both VEGFR-1 and VEGFR-2 was found up-regulated in the satellite cells of the muscles regenerating after damage. The effect of VEGF in vivo appeared to be mediated by VEGFR-2, since the transfer of PlGF, a VEGF family member selectively interacting with VEGFR-1, was ineffective. These results are consistent with the observation that VEGF promotes the growth of myogenic fibers and protects myogenic cells from apoptosis in vitro, and prompt a therapeutic use of VEGF gene transfer in a variety of muscular disorders.