ENDOTHELIAL-CELLS MODULATE SMOOTH-MUSCLE CELL MORPHOLOGY BY INHIBITION OF TRANSFORMING GROWTH FACTOR-BETA(1) ACTIVATION

Background. We have previously demonstrated in a coculture model that endothelial cells (ECs) exert regulatory control over smooth muscle ce ll (SMC) morphology. This study was preformed to test the hypothesis t hat ECs inhibit transforming growth factor-beta(2) (TGF-beta(1)) activ ation through the release of plasminogen activator inhibitor (PAI-1). Methods. Bovine SMCs were cultured on a thin, semipermeable membrane, either alone or opposite ECs in coculture (SMC/EC). Conditioned media and cell lysates at 1, 5, and 21 days were assayed for TGF-beta(1) and PAI-1 by enzyme-linked immunoabsorbent assay. Cell proliferation rate s, protein, and DNA content were measured and compared with SMC morpho logy. Results. Activation of TGF-beta(1) was significantly decreased ( 1.2% versus 18.9% active TGF-beta(1), p < 0.05) and PAI-1 was increase d (659 pg/ml versus 343 pg/ml, p < 0.05) in SMC/EC medium on day 1, co mpared with the medium of SMC alone. Significantly higher levels of PA I-1 were measured in cell lysates of cocultured ECs (128 pg/mu g DNA) than in cocultured SMCs (5.8 pg/mu g DNA, p < 0.05). SMC/EC coculture prevented the SMC hill-and-valley growth morphology seen in SMCs cultu red alone. Conclusion. In a model designed to study SMC/EC interaction s, it was seen that ECs can alter growth characteristics of SMCs by pr oducing PAI-1, which interferes with the plasminogen pathway of TGF-be ta(1) activation. This suggests that reduced EC PAI-1 production could play a role in alternation of SMC phenotype in vivo.