Endothelial cells modulate smooth muscle cell morphology by inhibition of transforming growth factor-beta 1...

We have previously demonstrated in a coculture model that endothelial cells (ECs) exert regulatory control over smooth muscle cell (SMC) morphology. This study was performed to test the hypothesis that ECs inhibit transforming growth factor-beta 2 (TGF-beta 1) activation through the release of plasminogen activator inhibitor (PAI-1).

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 rates, protein, and DNA content were measured and compared with SMC morphology.

Activation of TGF-beta 1 was significantly decreased (1.2% versus 18.9% active TGF-beta 1 p < 0.05) and PAI-1 was increased (659 pg/ml versus 343 pg/ml p < 0.05) in SMC/EC medium on day 1, compared with the medium of SMC alone. Significantly higher levels of PAI-1 were measured in cell lysates of cocultured ECs (128 pg/micrograms DNA) than in cocultured SMCs (5.8 pg/micrograms DNA, p < 0.05). SMC/EC coculture prevented the SMC hill-and-valley growth morphology seen in SMCs cultured alone.

In a model designed to study SMC/EC interactions, it was seen that ECs can alter growth characteristics of SMCs by producing PAI-1, which interferes with the plasminogen pathway of TGF-beta 1 activation. This suggests that reduced EC PAI-1 production could play a role in alteration of SMC phenotype in vivo.