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 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 Ͻ 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 Ͻ 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.