CONTENTS AND DISTRIBUTIONS OF THE PROTEOGLYCANS DECORIN AND BIGLYCAN IN NORMAL AND OSTEOARTHRITIC HUMAN ARTICULAR-CARTILAGE

The study was designed to determine the contents and distributions of the proteoglycans decorin and biglycan in adult human femoral condylar cartilage and whether these may change in osteoarthritis. New radioim munoassays were established using peptides representing the amino-term inal 21 amino acid sequence of each proteoglycan (to which a tyrosine was added for radioiodination) and antibodies in a rabbit antiserum ra ised to both these molecules. Cartilage was extracted with 4 M guanidi ne HCl to determine total content, and extracts were analyzed by chrom atography to determine molecular sizes. Frozen sections were cut paral lel to the articular surface and were extracted to determine distribut ion within the tissue. Gel chromatography on Sepharose CL-2B under dis sociative conditions revealed molecules with a partition coefficient o f 0.7-0.75 in both normal and osteoarthritic cartilage. In normal adul t cartilage, the mean contents of the core proteins of biglycan and de corin were calculated to be approximately 0.34 and 0.48 mg per gram we t weight, respectively. These represented molar contents similar to th at of aggrecan. In osteoarthritic cartilage, there were no overall sig nificant changes in the content and distribution of these molecules. T here was, however, considerable individual variation in both distribut ion and content. Analyses indicated that there was a trend in osteoart hritic cartilage toward a loss of biglycan and decorin from the more s uperficial layers of intact cartilage, where both these molecules are normally more concentrated. This was accompanied by maintenance of pro teoglycan content deeper in the cartilage, regardless of the degree of degeneration.