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 glyco conjugates in the formation of junctions ensuring tightening between e pendymal cells was studied using synthetic glycoconjugates, the neogly coproteins. These compounds are prepared by substituting bovine serum albumin with sugar residues and additional labelling (or not) with flu orescein or biotin. Injections of these components into the cerebral v entricles of adult rats resulted in a binding pattern which could be r elated to their carbohydrate composition. Mannose-containing neoglycop roteins 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 endo thelial cells around blood vessels. Fluorescent unglycosylated serum a lbumin 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 li kewise. In short term experiments (5 min-1 h), only the mannose-contai ning neoglycoproteins bound strongly to the ependymal cells, particula rly to the cilia. In long term experiments (1-9 days), mannose-contain ing neoglycoproteins specifically induced the disappearance of junctio ns between the cultured cells. These results emphasize the importance of mannose-dependent recognition system in the maintenance of junction s between ependymal cells, where a mannose-binding lectin has been pre viously detected.