ENDOTHELIAL-CELLS EXHIBITING ANGIOGENESIS IN-VITRO PROLIFERATE IN RESPONSE TO TGF-BETA-1

Transforming growth factor-beta1 (TGF-beta1) has been implicated in th e positive regulation of angiogenesis in vivo, whereas it inhibits the proliferation of endothelial cells in vitro. To reconcile these appar ently contradictory effects, we have investigated the effect of TGF-be ta1 on bovine aortic endothelial cells that exhibit spontaneous angiog enesis in vitro. We show that concentrations of TGF-beta1 which stimul ate proliferation of cells that form endothelial cords and/or tubes in hibit proliferation of the same cells grown at subconfluent densities. An increase in cell number of 35% over control cultures was achieved with 0.5 ng TGF-beta1/ml. The proliferative effect was blocked by anti bodies against TGF-beta. Immunological detection of BrdU-labeled nucle i revealed an increase greater than 220% in cells treated with TGF-bet a1. Moreover, a population of cells within the cords appeared to be a selective target for this cytokine. The stimulatory effect was not res tricted to bovine aortic endothelial cells, as similar results were ob tained with endothelial cells derived from rat microvessels. Significa nt levels of active TGF-beta1 were detected in cultures containing cor ds/tubes, whereas only latent TGF-beta1 was detected in subconfluent c ultures. We show further that endothelial cells exhibiting angiogenesi s in vitro secrete plasminogen activator, an enzyme that regulates act ivation of TGF-beta. The major increases in mRNA transcripts for extra cellular matrix proteins that are typically associated with TGF-beta1 were not seen in cells exhibiting angiogenesis in vitro. Since the for mation of tubular networks requires both invasion and proliferation, w e propose that TGF-beta1 is a major morphoregulatory factor in angioge nesis that specifically controls endothelial cell proliferation and ex tracellular matrix turnover. (C) 1993 Wiley-Liss, Inc.