Appican, the Proteoglycan Form of the Amyloid Precursor Protein, Contains Chondroitin Sulfate E in the Repeating Disaccharide Region and 4-O-Sulfated Galactose in the Linkage Region

Chondroitin sulfate (CS)-D and CS-E, which are characterized by oversulfated disaccharide units, have been shown to regulate neuronal adhesion, cell migration, and neurite outgrowth. CS proteoglycans (CSPGs) consist of a core protein to which one or more CS chains are attached via a serine residue. Although several brain CSPGs, including mouse DSD-1-PG/phosphacan, have been found to contain the oversulfated D disaccharide motif, no brain CSPG has been reported to contain the oversulfated E motif. Here we analyzed the CS chain of appican, the CSPG form of the Alzheimer's amyloid precursor protein. Appican is expressed almost exclusively by astrocytes and has been reported to have brain- and astrocyte-specific functions including stimulation of both neural cell adhesion and neurite outgrowth. The present findings show that the CS chain of appican has a molecular mass of 25–50 kDa. This chain contains a significant fraction (14.3%) of the oversulfated E motif GlcUAβ1–3GalNAc(4,6-O-disulfate). The rest of the chain consists of GlcUAβ1–3GalNAc(4-O-sulfate) (81.2%) and minor fractions of GlcUAβ1–3GalNAc and GlcUAβ1–3GalNAc(6-O-sulfate). We also show that the CS chain of appican contains in its linkage region the 4-O-sulfated Gal structure. Thus, appican is the first example of a specific brain CSPG that contains the E disaccharide unit in its sugar backbone and the 4-O-sulfated Gal residue in its linkage region. The presence of the E unit is consistent with and may explain the neurotrophic activities of appican.