Demonstration of the hepatocyte growth factor signaling pathway in the in vitro neuritogenic activity of chondroitin sulfate from ray fish cartilage

Chondroitin sulfate (CS) was isolated from ray fish cartilage, an industrial waste, after protease digestion, and its structure and neurite outgrowth-promoting (NOP) activity were analyzed to investigate a potential application to nerve regeneration. A disaccharide analysis using chondroitinase ABC revealed that the major unit in the CS preparation was GlcUA-GalNAc(6-O-sulfate) (63%), where GlcUA and GalNAc represent D-glucuronic acid and N-acetyl-D-galactosamine, respectively. Small proportions of other disaccharide units, GlcUA-GalNAc(4-O-sulfate) (25%), GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate) (7%), and GlcUA-GalNAc (5%), were also detected. The average molecular mass of CS was estimated to be 142 kDa by gel-filtration chromatography. The prepration showed NOP activity in vitro, which was eliminated by digestion with chondroitinase ABC, suggesting that a polymeric structure is required for the activity. Antibodies against hepatocyte growth factor (HGF) and its receptor c-Met suppressed the NOP activity, suggesting the involvement of the HGF signaling pathway in the in vitro NOP activity of the CS preparation. Since the specific binding of HGF to the CS preparation was also demonstrated by surface plasmon resonance spectroscopy, the CS chains were fractionated using an HGF-immobilized column into unbound and bound fractions accounting for 44 and 56% of the total yield, respectively. The latter contained a higher proportion of the GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate) unit, and showed greater NOP activity than the former, indicating that the HGF-binding domain contains GlcUA(2-O-sulfate)-GalNAc(6-O-sulfate) and is involved in the NOP activity. CS from ray cartilage may have potential pharmaceutical applications

Development of a mouse monoclonal antibody against the chondroitin sulfate-protein linkage region derived from shark cartilage

Glycosaminoglycans (GAGs) like chondroitin sulfate (CS) and heparan sulfate (HS) are synthesized on the tetrasaccharide linkage region, GlcAβ1-3Galβ1-3Galβ1-4Xylβ1-O-Ser, of proteoglycans. The Xyl can be modified by 2-O-phosphate in both CS and HS, whereas the Gal residues can be sulfated at C-4 and/or C-6 in CS but not in HS. To study the roles of these modifications, monoclonal antibodies were developed against linkage glycopeptides of shark cartilage CS proteoglycans, and one was characterized in detail. This antibody bound hexa- and pentasaccharide-peptides more strongly than tetrasaccharide-peptides, suggesting the importance of GalNAc. It did not react to the CS linkage region modified by 4-O-sulfation. Its reactivity was not affected by treatment with chondro-4-sulfatase or alkaline phosphatase. The results of an ELISA using various proteoglycans and glycopeptides with different modifications suggested the recognition of 6-O-sulfate on the GalNAc and/or Gal residues. Treatments with exopeptidases did not affect the reactivity of the hexasaccharide-peptide fraction, whereas weak alkali to cleave the Xyl-Ser linkage completely abolished the binding activity, suggesting the importance of the Xy-Ser linkage for the binding. Furthermore, the antibody stained wild-type CHO cells, but not mutant cells deficient in xylosyltransferase required for the synthesis of the linkage region. These results suggest that the antibody recognizes the structure GalNAc-GlcA-Gal-Gal-Xyl-Ser that is modified by 6-O-sulfation on GalNAc and/or Gal. The antibody will be a useful tool for investigating the significance of the linkage region in the biosynthesis and/or intracellular transport of different GAG chains