title: Involvement of SOX-9 and FGF-23 in RUNX-2 regulation in osteoarthritic chondrocytes.
abstract: Chondrocytes' hypertrophy includes metabolic changes, matrix remodelling, proliferation and apoptosis, characteristics associated with the progression of osteoarthritis. We investigated a possible association among Runt-related transcription factor 2 (RUNX-2), SOX-9 and fibroblast growth factor (FGF)-23 mRNA expressions in articular chondrocytes in order to elucidate their contribution in the osteoarthritic hypertrophic cartilage. SOX-9, FGF-23, RUNX-2 and matrix metalloproteinase (MMP)-13 mRNA expressions were evaluated in osteoarthritic and normal chondrocytes by real-time PCR whereas MMP-13 protein expression by immunofluorescense. RUNX-2, FGF-23 and SOX-9 were down-regulated using small interfering RNA technology and transfection with liposomes. The effect of human recombinant FGF-23 (hrFGF-23) on SOX-9 and RUNX-2 expression was tested in normal chondrocytes. We found higher expression of RUNX-2 and FGF-23 and a decreased expression of SOX-9 mRNA in osteoarthritic chondrocytes compared to normal (P < 0.0001). RUNX-2 down-regulation resulted in reduced MMP-13 expression in osteoarthritic chondrocytes and inhibition of SOX-9 in increased RUNX-2 and MMP-13 mRNA expression in normal chondrocytes, whereas inhibition of FGF-23 resulted in reduced RUNX-2 mRNA expression in osteoarthritic chondrocytes (all P < 0.0001). Silencing of RUNX-2 or FGF-23 did not affect SOX-9 mRNA levels in osteoarthritic chondrocytes. Moreover simultaneous down-regulation of SOX-9 and up-regulation of FGF-23 mRNA expressions in normal chondrocytes resulted in additive up-regulation of RUNX-2 mRNA expression. Treatment of normal chondrocytes with hrFGF-23 resulted in increased RUNX-2 mRNA expression, whereas it had no effect on SOX-9 mRNA expression. We demonstrated convincing associations among RUNX-2, SOX-9 and FGF-23 in relation to MMP-13 expression in osteoarthritic chondrocytes, contributing to a better understanding of the abnormal gene expression and cartilage degeneration processes associated with osteoarthritis.
authors.affiliation: Laboratory of Cytogenetics and Medical Genetics, University of Thessaly, Medical School, Larissa, Greece.
authors.forename: Timoklia
authors.initials: T
authors.lastname: Orfanidou
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Iliopoulos
authors.forename: Konstantinos N
authors.initials: KN
authors.lastname: Malizos
authors.forename: Aspasia
authors.initials: A
authors.lastname: Tsezou
mesh_terms: D000368:Aged; D002356:Cartilage / Q000166:cytology; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism; D050659:Core Binding Factor Alpha 1 Subunit / Q000378:metabolism*; D005260:Female; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D053509:Matrix Metalloproteinase 13 / Q000378:metabolism*; D008856:Microscopy, Fluorescence / Q000379:methods; D008875:Middle Aged; D008954:Models, Biological; D010003:Osteoarthritis / Q000378:metabolism*; D055758:SOX9 Transcription Factor / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; C000717427:FGF23 protein, human; C493709:RUNX2 protein, human; D055758:SOX9 Transcription Factor; C527932:SOX9 protein, human; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D053509:Matrix Metalloproteinase 13