Alterations of heparan sulfate moieties in cultured endothelial cells exposed to endotoxin

In previous studies, we observed that exposure to endotoxin markedly reduces the level of heparan sulfate proteoglycans in the extracellular matrix of cultured endothelial cells and at the same time causes the accumulation of proteoglycans bearing glycosaminoglycan chains of reduced size in the conditioned medium (P. Colburn, E. Kobayashi, and V. Buonassisi, 1994, J. Cell. Physiol. 159, 121-130). We have now investigated the structural and ligand-binding features which distinguish the matrix glycosaminoglycan moiety and the nature of the alterations of the truncated glycosaminoglycans. The matrix glycosaminoglycans are less sulfated than those of other cellular compartments and are more extensively degraded by heparitinase I, yielding a larger proportion of smaller oligosaccharides. In the binding assays, matrix glycosaminoglycans had greater specificity than those of the cell surface for a synthetic peptide patterned on the carboxyl-terminal sequence of an N-glycan sulfated protein synthesized by the endothelial cell. The nature of the alteration caused by exposure to endotoxin consists in the loss of a region rich in sulfate, located at the nonreducing end of the glycosaminoglycan chain. We also determined that only proteoglycans with intact chains are found in the extracellular matrix of endotoxin-treated cells.