title: YKL-39 (chitinase 3-like protein 2), but not YKL-40 (chitinase 3-like protein 1), is up regulated in osteoarthritic chondrocytes.
abstract: OBJECTIVE
  To investigate quantitatively the mRNA expression levels of YKL-40, an established marker of rheumatoid and osteoarthritic cartilage degeneration in synovial fluid and serum, and a closely related molecule YKL-39, in articular 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 1beta.
  
  
  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.
authors.affiliation: Cartilage Research, Department of Pathology, University of Erlangen-Nürnberg, FRG.
authors.forename: T
authors.initials: T
authors.lastname: Knorr
authors.forename: F
authors.initials: F
authors.lastname: Obermayr
authors.forename: E
authors.initials: E
authors.lastname: Bartnik
authors.forename: A
authors.initials: A
authors.lastname: Zien
authors.forename: T
authors.initials: T
authors.lastname: Aigner
mesh_terms: D054392:Adipokines; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002358:Cartilage, Articular / Q000187:drug effects / Q000378:metabolism*; D016022:Case-Control Studies; D000071451:Chitinase-3-Like Protein 1; D019902:Chondrocytes / Q000187:drug effects / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006023:Glycoproteins / Q000235:genetics*; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D037102:Lectins; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D010003:Osteoarthritis / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis*; D015854:Up-Regulation
chemical_list: D054392:Adipokines; C084533:CHI3L1 protein, human; D000071451:Chitinase-3-Like Protein 1; D006023:Glycoproteins; D007375:Interleukin-1; D037102:Lectins; D012333:RNA, Messenger