PDGF-BB increases endothelial migration on cord movements during angiogenesis in vitro

To explore direct effects of platelet-derived growth factor (PDGF) on endothelial cells during angiogenesis in vitro, we have used cloned bovine aortic endothelial cells that spontaneously form cord structures. Recently we have shown that cells forming these endothelial cords express PDGF beta-receptors and that PDGF-BB can contribute to cellular proliferation and cord formation. In this study we investigated whether PDGF-induced cellular migration might also contribute to endothelial repair and angiogenesis in vitro. Ten individual endothelial cells in cords were tracked at an early stage of cord formation by video-timelapse microscopy. PDGF-BB (100 ng/ml) induced an increase in endothelial cell movement of 67 +/- 15% as compared with diluent control. Interestingly, PDGF-BB also increased movements of entire cord structures, followed at branching points, by 53 +/- 12% over diluent control. Taken together, these video-timelapse experiments suggested that the apparent movements of single endothelial cord cells might also be due to the motion of entire underlying cord structures in response to PDGF. To analyze the response of single endothelial cord cells we therefore examined whether PDGF-induced migration contributes to endothelial repair. Abrasions were applied with a razor blade to confluent monolayers of endothelial cells at an intermediate stage of cord formation. PDGF-BB concentration-dependently increased the distance to which cord-forming endothelial cells migrated into the abrasion. An increased number of elongated, i.e., probably migrating, endothelial cells was found in the abrasion in response to PDGF-BB. However, there was no effect of PDGF-BB on the total number of endothelial cells found in the abrasion. PDGF-AA affected neither the distance to which the cells migrated nor the number of elongated cells. Actin and tubulin stainings revealed that these cytoskeletal structures were not appreciably altered by PDGF-BB. Furthermore, urokinase-type plasminogen activator transcripts were not modulated in response to PDGF-BB. We conclude that in this model of angiogenesis in vitro PDGF-BB can elicit the movement of entire cord structures, possibly via u-PA-independent mechanisms. PDGF-BB also controls the migration of single cord-forming endothelial cells. Thus, PDGF-BB possibly contributes to endothelial repair and angiogenesis by direct effects on proliferation and composite movements of PDGF beta-receptor-expressing endothelial cells and cords.