Endothelial glycoconjugates: a comparative lectin study of the brain, retina and myocardium

Abstract

There is evidence that the endothelial cell (EC) glycocalyx is a significant determinant of vascular permeability, acting as a charge-size filter to permeant molecules. We have therefore examined its oligosaccharide composition in 3 classes of microvessel with differing permeabilities. EC in rat brain, retina and myocardium were labelled with a panel of lectins and subjected to a semiquantitative analysis. Surprisingly, no substantial differences were evident for any lectin labelling between the 3 microvessel types despite their marked morphophysiological diversity. In particular, all showed substantial sialic acid expression, with Maackia amurensis (MAA) labelling sialic acid in an α2–3 linkage to β-galactose and Sambucus nigra (SNA) recognising sialic acid in an α2–6 linkage to β-galactose. Arachis hypogaea (PNA) binding after neuraminidase digestion indicated the presence of Gal β1–3GalNAc attached to terminal sialic acid. The results therefore show that the sequences NeuNAc α2–3Gal β1–3GalNAc and NeuNAc α2–6Gal β1–3GalNAc are strongly expressed in the 3 microvessel types irrespective of their permeability properties. This homogeneity suggests that these lectin ligands may be involved in a common set of EC functions, e.g. cell[ratio ]cell and cell[ratio ]matrix interactions. However, we cannot rule out the possibility that glycocalyx differences may exist between vessels in the paracellular cleft which may alter its filtration properties.