In vitro studies on the expansion of endothelial cell monolayers on components of the basement membrane.

The purpose of the present study was to observe the expansion of a monolayer of endothelial cells over specific components of the basement membrane. This was performed in vitro in a monolayer expansion assay over 5 days. The control surface was uncoated glass in the form of coverslips. Test substances were coated at a concentration of 10 micrograms/ml. The highest expansion was obtained with a high molecular weight fragment mixture of collagen type IV (IV-F, consisting of 75, 120 and 140 KD fragments), followed by fibronectin. Collagens type I, III and IV tetramer gave similar results, less than fibronectin or collagen type IV-F, although all of the above basement membrane coatings promoted expansion significantly above that of the control (P less than 0.01). The poorest expansion was obtained with laminin, which was significantly less than the control. The pentapeptide GRGDS, related to the fibronectin cell binding region, gave expansion significantly below that of the intact fibronectin molecule, as did the intact collagen type IV molecule compared with type IV-F (P less than 0.025). This indicates that sequences of the fibronectin molecule other than the cell binding sequence may be involved in promoting endothelial cell expansion. In addition, the integrity of the collagen type IV molecule does not appear necessary for this effect. On the contrary, the higher movement on IV-F may represent an inherent repair mechanism in damaged endothelium. Autoradiographic studies show that endothelial cell proliferation at the expanding front is involved in the migration assay.