Regulation of MMP-13 expression by RUNX2 and FGF2 in osteoarthritic cartilage.
OBJECTIVE
To understand the molecular mechanisms that lead to increased MMP-13 expression and cartilage degeneration during the progression of osteoarthritis (OA), we have investigated the expression of the transcription factor RUNX2 in OA cartilage and the regulation of MMP-13 expression by RUNX2 and FGF2 in articular chondrocytes.


METHODS
RUNX2 and MMP-13 expression in human OA and control cartilage was analyzed by immunohistochemistry. The effects of RUNX2 over-expression, with or without FGF2 treatment, on MMP-13 promoter activity and enzyme accumulation were measured in articular chondrocytes. Inhibitors of MEK/ERK were assayed for their ability to block FGF2 and RUNX2 up-regulation of the MMP-13 promoter. We analyzed RUNX2 phosphorylation in response to FGF2.


RESULTS
Fibrillated OA cartilage exhibited increased RUNX2 immunoreactivity when compared to control cartilage. RUNX2 co-localized with MMP-13 in clusters of chondrocytes in fibrillated OA cartilage. RUNX2 over-expression in cultured chondrocytes increased their responsiveness to FGF2 treatment, which led to increased MMP-13 expression. Inhibitors of MEK/ERK signaling blocked up-regulation of the MMP-13 promoter by RUNX2 and FGF2, and also blocked the activation of RUNX2 by FGF2. FGF2 treatment of articular chondrocytes increased RUNX2 phosphorylation approximately 2-fold.


CONCLUSIONS
Increased expression of RUNX2 in OA cartilage may contribute to increased expression of MMP-13. FGF2, which is present in OA synovial fluid, activated RUNX2 via the MEK/ERK pathway and increased MMP-13 expression. However, it is unlikely that RUNX2 is a substrate of ERK1/2. RUNX2 expression and activation may be a significant step in the progression of OA by promoting changes in gene expression and chondrocyte differentiation.
Wang
Xibin
X
Cartilage Biology and Orthopaedics Branch, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892-4872, USA.
Manner
Paul A
PA
Horner
Alan
A
Shum
Lillian
L
Tuan
Rocky S
RS
Nuckolls
Glen H
GH
D000818:Animals; D015153:Blotting, Western / Q000379:methods; D002070:Butadienes / Q000494:pharmacology; D002358:Cartilage, Articular / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D016022:Case-Control Studies; D002417:Cattle; D002478:Cells, Cultured; D019902:Chondrocytes / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D017364:Collagenases / Q000032:analysis / Q000378:metabolism*; D050659:Core Binding Factor Alpha 1 Subunit; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D053509:Matrix Metalloproteinase 13; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D009281:Naphthalenes / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000032:analysis / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D020370:Osteoarthritis, Knee / Q000378:metabolism*; D010766:Phosphorylation; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015398:Signal Transduction / Q000187:drug effects; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism*
D002070:Butadienes; D050659:Core Binding Factor Alpha 1 Subunit; D005419:Flavonoids; D009281:Naphthalenes; D009363:Neoplasm Proteins; D009570:Nitriles; D014157:Transcription Factors; C113580:U 0126; D016222:Fibroblast Growth Factor 2; D011493:Protein Kinase C; D020929:Mitogen-Activated Protein Kinase Kinases; D017364:Collagenases; C507079:MMP13 protein, human; D053509:Matrix Metalloproteinase 13; C058819:calphostin C; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one