Aggregation of cartilage proteoglycans. Ii. Evidence for the presence of a hyaluronate‐binding region on proteoglycans from osteoarthritic cartilage

Abstract

Proteoglycan aggregates isolated from normal bovine knee cartilage were larger than those from osteoarthritic cartilage of the same joints and appeared relatively more resistant to digestion with leech hyaluronidase. Incubation of proteoglycan subunits from the arthritic cartilage with hyaluronic acid resulted in marked aggregation, comparable in magnitude to that shown by subunits from normal cartilage. The results indicate that the hyaluronate-binding region of these proteoglycans was functionally intact and suggest that diminished aggregation of proteoglycans in osteoarthritic cartilage may be due to an abnormality in some other constituent of the aggregates.Cartilage matrix consists to a considerable extent of large proteoglycan aggregates, in which many proteoglycan molecules are noncovalently linked to highly polymerized hyaluronic acid (1). At least one tissue glycoprotein (2) is also present in these macromolecular complexes, and appears to stalbilize the proteoglycan-hyaluronic acid interaction (3). The complexes, which have a sedimentation coefficient (So20,w) of 60-70 S (4), by virtue of their size alone must exercise a significant effect on the physical integrity and biomechanical properties of the tissue.In osteoarthritis, softening and ultimate loss of cartilage matrix are apparent, although the basis for these morphologic changes is not clear. Recent studies have indicated that a proportion of the proteoglycans of osteoarthritic cartilage are much more readily extracted than normal by brief agitation of the tissue in iso-osmotic neutral salt ( 5 ) . Because this extraction procedure does not dissociate large aggregates, the results imply that in osteoarthritis some proteoglycans are less aggregated than normal. Furthermore, aggregates obtained after extraction of bovine osteoarthritic cartilage with 4.0 M guanidinium chloride were smaller in hydrodynamic size than aggregates from normal cartilage of the same joints (6).Proteoglycans of osteoarthritic cartilage have been shown to contain less chondroitin sulfate (7) and keratan sulfate (8) and shorter chains of chondroitin sulfate (9,lO) than normal, but whether these differences in structure relate to differences in proteoglycan aggregation is not known. In the current view, proteoglycans consist of a ) an inhomogeneous protein core, on which are situated a polysaccharide attachment region, to which most of the chondroitin sulfate and keratan sul-

Effects of diphosphonates on glycosaminoglycan synthesis and proteoglycan aggregation in normal adult articular cartilage

“…To assess the ability of proteoglycans to undergo aggregation in vitro, fraction Do, was incubated with a sample of hyaluronic acid from umbilical cord (Sigma Chemical Co., St. Louis, Missouri) which was large enough to elute wholly in the void volume of a Sepharose 2B column (13). The hyaluronic acid was dissolved (100 pg/ml) in 0.5 M sodium acetate, pH 6.5, and was added to a solution of fraction D,, in the same acetate buffer, so that the ratio of hyaluronic acid to proteoglycan was 1 : 38 (uronic acid).…”

Immobilization of the knee prevents osteoarthritis after anterior cruciate ligament transection

“…35S-proteoglycans in did not exist in aggregates because none of the fraction was excluded by Sepharose 2B and the K,, of the material that was retarded by the gel was approximately 0.70, indicating that its average hydrodynamic size was only slightly greater than that of purified 35S-labeled glycosaminoglycans (Kav = 0.90) (14).…”

Glycosaminoglycans from growing antlers of wapiti (Cervus elaphus)

“…Digestion with Streptomyces hyaluronidase (CalbiochemNova Biochem) was carried out as described (Brandt et al 1976). The hyaluronidase cleaves N-acetylglucosamidic linkages in hyaluronic acid (Kresse and Glössl 1987).…”