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Ann Rheum Dis. 2003 Oct; 62(10): 995–998.
PMCID: PMC1754335

YKL-39 (chitinase 3-like protein 2), but not YKL-40 (chitinase 3-like protein 1), is up regulated in osteoarthritic chondrocytes


Methods: cDNA array and online quantitative polymerase chain reaction (PCR) were used to measure mRNA expression levels of YKL-39 and YKL-40 in chondrocytes in normal, early degenerative, and late stage osteoarthritic cartilage samples.

Results: Expression analysis showed high levels of both proteins in normal articular chondrocytes, with lower levels of YKL-39 than YKL-40. Whereas YKL-40 was significantly down regulated in late stage osteoarthritic chondrocytes, YKL-39 was significantly up regulated. In vitro both YKLs were down regulated by interleukin 1ß.

Conclusions: The up regulation of YKL-39 in osteoarthritic cartilage suggests that YKL-39 may be a more accurate marker of chondrocyte activation than YKL-40, although it has yet to be established as a suitable marker in synovial fluid and serum. The decreased expression of YKL-40 by osteoarthritic chondrocytes is surprising as increased levels have been reported in rheumatoid and osteoarthritic synovial fluid, where it may derive from activated synovial cells or osteophytic tissue or by increased matrix destruction in the osteoarthritic joint. YKL-39 and YKL-40 are potentially interesting marker molecules for arthritic joint disease because they are abundantly expressed by both normal and osteoarthritic chondrocytes.

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Figures and Tables

Figure 1
Demonstration of YKL-39, YKL-40, and ß-actin in normal (n=5: lanes 1–5) and osteoarthritic (n=5: lanes 6–10) articular cartilage by conventional PCR. Lane M, 100 bp DNA ladder (MBI Fermentas, FRG); lane 11, negative (water) control. ...
Figure 2
(A) cDNA array analysis of mRNA expression levels in chondrocytes in normal ("no"; n=20), early degenerative ("edeg"; n=21), and late stage osteoarthritic ("lOA"; n=20) articular cartilage for YKL-39 and YKL-40. Results are shown as ratios to normal ...
Figure 3
Quantitative TAQMAN analysis for mRNA expression levels of YKL-39 and YKL-40 in isolated normal articular chondrocytes after stimulation with 1 ng and 10 ng IL1ß. The ratios of IL1ß stimulated to non-IL1ß stimulated samples in ...

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