The critical role of VEGF in skeletal muscle angiogenesis and blood flow.

VEGF (vascular endothelial growth factor) is well known as an important molecule in angiogenesis. Its inhibition is pursued as an anticancer therapy; its enhancement as therapy for tissue ischaemia. In the present paper, its role in skeletal muscle is explored, both at rest and after exercise. Muscle VEGF mRNA and protein are increased severalfold after heavy exercise. Whereas global VEGF knockout is embryonically lethal, muscle-specific knockout is not, providing models for studying its functional significance. Its deletion in adult mouse skeletal muscle: (i) reduces muscle capillarity by more than 50%, (ii) decreases exercise endurance time by approximately 80%, and (iii) abolishes the angiogenic response to exercise training. What causes VEGF to increase with exercise is not clear. Despite regulation by HIF (hypoxia-inducible factor), increased HIF on exercise, and PO2 falling to single digit values during exercise, muscle-specific HIF knockout does not impair performance or capillarity, leaving many unanswered questions.