Low oxygen tension modulates the effects of TNFα and fibronectin fragments in compressed chondrocytes

Abstract

Oxygen tension and biomechanical signals are factors that regulate inflammatory mechanisms in chondrocytes. We examined whether low oxygen tension influenced the cells response to TNFα and dynamic compression.

Chondrocyte/agarose constructs were treated with varying concentrations of TNFα (0.1 to 100 ng/ml) and cultured at 5% and 21% oxygen tension for 48 hours. In separate experiments, constructs were subjected to dynamic compression (15%) and treated with TNFα (10 ng/ml) and/or L-NIO (1 mM) at 5% and 21% oxygen tension using an ex-vivo bioreactor for 48 hours. Markers for catabolic activity (NO, PGE2) and tissue remodelling (GAG, MMPs) were quantified by biochemical assay. ADAMTS-5 and MMP-13 expression were examined by real-time qPCR. 2-way ANOVA and a post hoc Bonferroni-corrected t-test were used to analyse data.

TNFα dose-dependently increased NO, PGE2 and MMP activity (all p<0.001) and induced MMP-13 (p<0.05) and ADAMTS-5 gene expression (p<0.01) with values greater at 5% oxygen tension than 21%. The induction of catabolic mediators by TNFα was reduced by dynamic compression and/or L-NIO (all p<0.001), with a greater inhibition observed at 5% than 21%. The stimulation of GAG synthesis by dynamic compression was greater at 21% than 5% oxygen tension and this response was reduced with TNFα or reversed with L-NIO.

The present findings revealed that TNFα has dose-dependent catabolic activities and increased production of inflammatory mediators at low oxygen tension. Dynamic compression or the NOS inhibitor downregulated the inflammatory effects induced by TNFα, linking both types of stimuli to reparative activities. Future therapeutics should develop oxygen-sensitive antagonists which are directed to interfering with the TNFα induced pathways.