Different subsets of CNS neurons express different glycosaminoglycan epitopes on large perineuronal proteoglycans

Proteoglycans are known to occur in the central nervous tissue, but their function is not well understood. We made a biochemical study of four perineuronal antigens on different subsets of rat brain neurons and found that three antigens recognized by antibodies against glycosaminoglycan epitopes were large proteoglycans. Molecular masses estimated by immunoblotting were 700 kDa for 473, 376 and 1B5 antigens and 600 kDa for the 374 antigen. Reactivities of the antigens on immunoblots to monoclonal antibodies (MAbs) 473 and 376 were lost, and that to MAb 1B5 uncovered, after chondroitinase ABC treatment as in the brain sections. The elution profiles from ion-exchange and gel-filtration column chromatography of 473, 376 and 1B5 antigens were quite similar, but those of 374 antigen were slightly different. The immunoaffinity-purified 473 antigen migrated at 700 kDa on sodium dodecylsulfate gel electrophoresis, and chondroitinase ABC treatment decreased the molecular mass to 600 kDa. The 473 antigen was recognized by MAbs 376 and 1B5 although these MAbs also reacted with 473-negative 700 kDa molecules. These results suggest that neuronal subset-specific glycosylation may occur on the 700 kDa proteoglycans, and that the glycosaminoglycan structures may be involved in the pericellular diversity of CNS neurons.