PDGF-BB Modulates Endothelial Proliferation and Angiogenesis in Vitro via PDGF β-Receptors

To delineate potential angiogenic roles of platelet-derived growth factor (PDGF), we have investigated PDGF and its receptors on bovine aortic endothelial cells that exhibit spontaneous angiogenesis in vitro (angiogenic endothelial cells). Initiation of cord/tube formation by angiogenic endothelial cells required bovine or human serum. Neutralization of PDGF-BB in human serum with a monoclonal anti-PDGF-BB antibody reduced cord/tube formation by 37 ± 10%, whereas neutralizing anti-PDGF-AA and an IgG isotype-matched control antibody had no effect. DNA synthesis in response to PDGF-BB increased as the cords and tubes developed; furthermore, PDGF-BB induced the incorporation of BrdU in the nuclei of cells associated with these structures. PDGF β-receptor (PDGFR-β) mRNA increased concomitantly with cord/tube formation, and PDGFR-β were specifically localized by immunocytochemistry to developing and mature cords and tubes. However, PDGFR-β transcripts and protein were undetectable in nonangiogenic endothelial cells, and PDGF α-receptor mRNA was not expressed in either endothelial cell strain. In contrast to nonangiogenic endothelial cells, angiogenic endothelial cells did not express the PDGF B-chain, the required ligand for the PDGFR-β. We conclude that (a) PDGF-BB can contribute to angiogenesis in vitro, (b) PDGFR-β are specific for cord/tube-forming endothelial cells and mediate endothelial proliferation and cord/tube formation, and (c) in angiogenic and nonangiogenic endothelial cells, the expression of PDGFR-β and PDGF B-chain is inversely correlated. We therefore suggest that paracrine PDGF might amplify angiogenesis via direct action on endothelially expressed PDGFR-β.