A comparison of the proteoglycans produced by rabbit articular chondrocytes in monolayer and spinner culture and those of bovine nasal cartilage

Abstract

The structural and immunological properties of the glycosaminoglycans and the core proteins of bovine nasal cartilage proteoglycan and the proteoglycans produced by rabbit articular chondrocytes in spinner and monolayer culture were compared. Culture medium with 35SO4- or 3H-serine-labeled proteoglycan was mixed with bovine nasal cartilage 4M guanidine-HCl extract and digested with trypsin. The proteoglycan fragments were then isolated by DEAE-cellulose chromatography and fractionated by dissociative CsCl density gradient centrifugation. Approximately 90% of the 35SO4 incorporated into proteoglycan by the cultured chondrocytes was in chondroitin sulfates and about 5% in keratan sulfate. Although there was considerable overlap in the Sepharose 4B elution of the tryptic proteoglycan fragments of highest buoyant density, some monolayer-produced proteoglycan fragments eluted earlier and some spinner-produced proteoglycan fragments eluted later than the proteoglycan fragments from bovine nasal cartilage. These differences in apparent fragment size could relate to differences in glycosaminoglycan chain length, since the glycosaminoglycans released by treatment with alkali from monolayer-produced proteoglycan in part eluted from Sepharose 4B earlier and those from spinner-produced proteoglycan in part eluted later than the chondroitin sulfate chains released from bovine cartilage proteoglycan. After digestion with chondroitinase ABC, 3H-serine-labeled high density tryptic proteoglycan fragments from monolayer and spinner culture yielded Sepharose 6B elution profiles which were similar to each other but did not coincide with the peaks of carbazole reactivity found with similarly treated fragments of bovine nasal cartilage proteoglycan. Cross-reactivity was demonstrated by radioimmunoautography between bovine cartilage and rabbit chondrocyte proteoglycan fragments restricted to gradient fractions of low buoyant density, but immunological cross-reactivity was not found for the antigens associated with the keratan sulfate-rich and chondroitin sulfate-bearing tryptic fragments of bovine nasal cartilage proteoglycan. These studies indicate that the proteoglycan core proteins produced by rabbit articular chondrocytes in monolayer and spinner culture are, in part, different from the core protein of bovine nasal cartilage proteoglycan and that the three proteoglycans differ in the length of some of their chondroitin sulfate chains.