Human cartilage gp-39, a major secretory product of articular chondrocytes and synovial cells, is a mammalian member of a chitinase protein family

One of the major secreted proteins of human articular chondrocytes in monolayer or explant culture and of synovial fibroblasts is a glycoprotein with an apparent molecular weight of approximately 39,000, referred to as human cartilage glycoprotein-39 (HC gp-39). The protein was purified, and its complete cDNA sequence was determined. It contained an open reading frame coding for a 383-amino acid long peptide. Comparison of the deduced amino acid sequence with known sequences revealed that HC gp-39 contained regions displaying significant homology with a group of bacterial and fungal chitinases and a similar enzyme found in the nematode, Brugia malayi. In addition significant homologies were observed with three mammalian secretory proteins of as yet unknown function, suggesting that a related protein family exists in mammals. The human protein does not possess any glycosidic activity against chitinase substrates, arguing against any function as an endoglycosidase with specificity for N-acetylglucosamine. Analysis by Northern blotting and by reverse transcription/polymerase chain reaction showed mRNA for HC gp-39 to be present in human articular chondrocytes as well is in liver, while mRNA was undetectable in muscle tissues, lung, pancreas, mononuclear cells, or fibroblasts. Neither the protein nor mRNA for HC gp-39 was detectable in normal newborn or adult human articular cartilage obtained at surgery, while mRNA for HC gp-39 was detectable both in synovial specimens and in cartilage obtained from patients with rheumatoid arthritis. These observations suggest that the expression of HC gp-39 may be related to a response of these cells to an altered tissue environment.

A new biochemical marker for joint injury. Analysis of YKL-40 in serum and synovial fluid

We report the development of the first radioimmunoassay for YKL-40, a M(r) = 40 kDa protein which is secreted at high levels by human synovial cells and articular cartilage chondrocytes, and by the human osteosarcoma cell line MG63. This assay uses YKL-40 purified from the conditioned medium of MG63 cells as standard and tracer, and as antigen for immunizing rabbits. With this assay we have discovered high levels of YKL-40 antigen in serum and SF. The molecular weight of serum and SF YKL-40 is identical to purified YKL-40. To evaluate the possible utility of YKL-40 in the assessment of joint disease, we measured YKL-40 in serum and SF of 49 patients with various forms of inflammatory and degenerative joint disease and in the serum of 50 normal adults. The YKL-40 level in serum was significantly higher (P < 0.001) in the patients compared to the normal adults, but there was no difference in serum YKL-40 between the patients with inflammatory joint diseases and OA. The SF levels of YKL-40 were 15-fold higher than serum levels and there was a significant correlation (r = 0.55, P < 0.001) between YKL-40 concentration in SF and serum. Although the tissue distribution of YKL-40 secretion is presently unknown, these observations suggest that a major portion of serum YKL-40 in fact arises from the joint.(ABSTRACT TRUNCATED AT 250 WORDS)