N-Unsubstituted Glucosamine Residues in Heparan Sulfate and Their Potential Relation to Alzheimer's Disease

Sammanfattning: Heparan sulfate (HS) is a linear polysaccharide, located on the surface and in the extracellular matrix of most cells, that regulates functions of numerous proteins. HS-protein interaction is mainly mediated by sulfate groups found in N-sulfated (NS) regions of the HS, but may also involve rare HS substituents such as N-unsubstituted glucosamine (GlcNH2) residues. The location of GlcNH2 in an HS-epitope recognized by the monoclonal antibody 10E4, that specifically stains the prion lesions in scrapie-infected murine brain, suggests an involvement of GlcNH2 in prion disease and other amyloid-related disorders. HS in general is strongly associated with amyloidosis, including Alzheimer’s disease (AD). Therefore, the aims of this thesis were to structurally characterize GlcNH2-containing HS sequences found in native tissues, to further study HS epitopes recognized by 10E4, and to investigate the possible role(s) of GlcNH2 and other HS structures in binding to amyloid ? peptide (A?) (core material in AD plaque lesions, also stained by 10E4).The GlcNH2 content (0.7-4% of total disaccharide units) varied between HS from different tissues. Most GlcNH2 units were found in poorly modified N-acetylated (NA-) or NA/NS-domains, located toward the polysaccharide-protein linkage region.Binding of human cerebral cortex HS to A?(1–40) monomers requires N-, 2- and 6-O-sulfation of HS, while binding to A? fibrils requires N- and 2-O-sulfation only. GlcNH2 units do not appreciably contribute to interaction with A?. A? fibril-binding HS domains also bind to fibroblast growth factor 2 (FGF-2), indicating that A? (neurotoxic) and FGF-2 (neuroprotective) may compete for common binding sites in HS. However, A? had no effect on FGF-2-induced MAPK signaling in NIH 3T3 fibroblasts.Continued studies on 10E4-antigenic HS epitope(s) showed that binding of 10E4 to the previously identified antigenic tetrasaccharide, ?UA-GlcNH2-GlcA-GlcNAc, requires the nonreducing hexuronic acid (?UA) to be 4,5 unsaturated (induced by lyase cleavage), and thus is artificial. Further studies are needed to clarify the potential involvement of GlcNH2 in 10E4-recognition of the native HS epitope(s).