Vascular endothelial growth factor and basic fibroblast growth factor induce expression of CXCR4 on human endothelial cells - In vivo neovascularization induced by stromal-derived factor-1 alpha

Furthermore, subcutaneous SDF-1 alpha injections into mice induced formatio n of local small blood vessels that was accompanied by leukocytic infiltrat es. To test whether these effects were dependent on circulating leukocytes, we successfully obtained SDF-1 alpha-induced neovascularization from cross sections of leukocyte-free rat aorta. Taken together, our data indicate th at SDF-1 alpha acts as a potent chemoattractant for endothelial cells of di fferent origins bearing CXCR4 and is a participant in angiogenesis that is regulated at the receptor level by VEGF and bFGF, The contribution of chemo kines toward angiogenesis is currently a focus of intensive investigation. Certain members of the CXC chemokine family can induce bovine capillary end othelial cell migration in vitro and corneal angiogenesis in vivo, and appa rently act via binding to their receptors CXCR1 and CXCR2, We used an RNAse protection assay that permitted the simultaneous detection of mRNA for var ious CXC chemokine receptors in resting human umbilical vein endothelial ce lls (HUVECs) and detected low levels of only CXCR4 mRNA, Stimulation of HUV ECs with vascular endothelial growth factor (VEGF) or basic fibroblast grow th factor (bFGF) up-regulated levels of only CXCR4 mRNA, CXCR4 specifically binds the chemokine stromal-derived factor-1 alpha (SDF-1 alpha), Competit ive binding studies using I-125-labeled SDF-1 alpha with Scatchard analysis indicated that VEGF or bFGF induced an average number of approximately 16, 600 CXCR4 molecules per endothelial cell, with a K-d = 1.23 x 10(-9) mol/L, These receptors were functional as HUVECs and human aorta endothelial cell s (HAECs) migrated toward SDF-1 alpha. Although SDF-1 alpha-induced chemota xis was inhibited by the addition of a neutralizing monoclonal CXCR4 antibo dy, endothelial chemotaxis toward VEGF was not altered; therefore, the angi ogenic effect of VEGF is independent of SDF-1 alpha.