Hyaluronan Oligosaccharides Induce Tube Formation of a Brain Endothelial Cell Line in Vitro

In remodeling tissues the formation of new blood vessels is an essential process which is regulated by different factors. During such processes an increase in hyaluronan synthesis and turnover is often seen and recent observations have suggested that hyaluronan can both promote and inhibit neovascularization depending on its molecular mass. In this work we show that a brain capillary endothelial cell line forms tubes in a collagen gel after stimulation by hyaluronan oligosaccharides. Ultrastructural examination of the tubes by transmission electron microscopy revealed that the cord-like outgrowths consisted of 2–10 tightly packed cells containing a continuous lumen. The tube formation in response to hyaluronan oligosaccharide was not mediated by activation of receptors for fibroblast growth factor. The endothelial cell line, which does not synthesize hyaluronan, exhibited specific hyaluronan-binding sites, with about 3000 hyaluronan molecules ( M r3.85 × 10 6) bound per cell at saturation and K d was 0.05 × 10 −9M. Furthermore, the cell line was stained with mAb IVd4 that recognizes a novel class of hyaluronan-binding proteins and mAb IM7 which recognizes CD44 molecules.