Mannose dependent tightening of the rat ependymal cell barrier. In vivo and in vitro study using neoglycoproteins

The possible role of carbohydrate binding proteins (lectins) and glycoconjugates in the formation of junctions ensuring tightening between ependymal cells was studied using synthetic glycoconjugates, the neoglycoproteins. These compounds are prepared by substituting bovine serum albumin with sugar residues and additional labelling (or not) with fluorescein or biotin. Injections of these components into the cerebral ventricles of adult rats resulted in a binding pattern which could be related to their carbohydrate composition. Mannose-containing neoglycoproteins were bound to ependymal cell cilia and penetrated rapidly the brain tissue. Such phenomenon was not seen with glucose- or galactose-containing neoglycoprotein molecules. In contrast, mannose-, galactose- and glucose-containing neoglycoproteins bound strongly to some endothelial cells around blood vessels. Fluorescent unglycosylated serum albumin did not bind to any brain structures. In contrast, co-injection of mannose-containing non-fluorescent neoglycoproteins with the other fluorescent compounds (including fluorescent sugar-free BSA) resulted in the penetration of the fluorescent compounds into the brain tissue. This internalization into brain was attributed to disaggregation of junctions between ependymal cells. Cultured ependymal cells behaved likewise. In short term experiments (5 min-1 h), only the mannose-containing neoglycoproteins bound strongly to the ependymal cells, particularly to the cilia. In long term experiments (1-9 days), mannose-containing neoglycoproteins specifically induced the disappearance of junctions between the cultured cells. These results emphasize the importance of mannose-dependent recognition system in the maintenance of junctions between ependymal cells, where a mannose-binding lectin has been previously detected.