Growth Factor Expression of Human Arterial Smooth Muscle Cells and Endothelial Cells in a Transfilter Coculture System

By releasing growth factors, vascular cells can modulate proliferation and migration of neighboring cells in the arterial wall. Previous histological studies in transfilter cocultures, a culture model aimed to simulate vessel wall architecture, indicated that human arterial endothelial cells (haEC) can influence human arterial smooth muscle cell (haSMC) growth significantly. The aim of this study was to investigate the expression and secretion of various growth factors in order to better define the functional interactions between haEC and haSMC. Protein levels of platelet-derived-growth factor-AB (PDGF-AB), transforming-growth factor-β1 (TGF-β1), and tumor-necrosis factor-α(TNF-α) in mono- and cocultures were determined by ELISA 6, 12, 24, 48, 72 h after serum reduction. Highest PDGF-AB levels were found in monocultures with proliferative haEC, showing a peak after 24 h. In cocultures of haEC and haSMC, PDGF-AB levels were significantly lower. In contrast, neither proliferative, nor confluent haSMC released PDGF-AB significantly. Highest TGF-β1 concentrations were detected in cocultures, followed by monocultures of haSMC and monocultures of haEC. In all cultures, TGF-β1 levels increased in parallel with cultivation time and cell numbers, showing a maximum after 72 h. TNF-αcould not be detected in any culture. Northern blots demonstrated a strong expression of PDGF-B chain-mRNA in haEC, but not in haSMC. PDGF-A chain and TGF-β1-mRNA were expressed by haSMC and haEC. Addition of PDGF-AB to haSMC resulted in a potent growth stimulation, whereas TGF-β1 and TNF-αexerted only moderate, divergent effects on haSMC. Histological observations in transfilter cocultures demonstrated that proliferative haEC induce the formation of fibromuscular plaques. These results suggest that proliferative haEC act as potent growth stimulators for haSMC, predominantly by PDGF-AB or -BB release.