KDR and disease of the tendon: As for the mechanism of action of VEGF in tendinopathy, some studies have shown that VEGF activates the binding of VEGF and its receptor VEGFR-2 to promote angiogenesis in tendon tissue by up-regulating the expression of matrix metalloproteinases (MMPs) and down-regulating the expression of metalloproteinase-3 (TIMP-3) in tendon cells [74–77].