Large and small proteoglycans of osteoarthritic and rheumatoid articular cartilage

To identify characteristic changes in large aggregating (aggrecan) and small proteoglycan (PG) populations in articular cartilages during osteoarthritis (OA) and rheumatoid arthritis (RA).

Aggrecan populations in guanidine extracts of femoral condylar cartilages of 46 OA and 8 RA patients who underwent total knee arthroplasty, as well as of 2 fetuses and 6 normal adults, were separated in agarose-polyacrylamide composite gels. Small PGs (biglycan, decorin, and fibromodulin) in the same extracts were analyzed in 12% polyacrylamide gels. Gels were stained or electrophoretically transferred and probed with antibodies to aggrecan epitopes and to small PGs. Epitope contents of the samples were also compared by inhibition radioimmunoassay.

There were significant differences found among normal and diseased samples in their electrophoretic mobilities, band distributions, and antibody staining. OA and especially RA samples were heavily degraded, lacked certain aggrecan populations, and contained fewer keratan sulfate and chondroitin-6-sulfate epitopes compared with normal samples. Levels of chondroitin-4-sulfate and "fetal-type" epitopes were elevated in the OA samples compared with the normal ones. More core proteins of small PGs were found in diseased than in normal cartilages, but they were more heterogeneous in size and glycosaminoglycan substitution.

There is extensive degradation of both large and small PGs in diseased cartilages, but a repair process does exist, especially in OA cartilages. Chondrocytes of diseased cartilages are able to synthesize fetal-type aggrecans. Small PGs are glycosylated differently in diseased cartilages than in normal ones.