Oxygen tension modulates the effects of TNFa in compressed chondrocytes

Abstract

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

Materials and methods: Chondrocyte/agarose constructs were treated with varying concentrations of TNF? (0.1–100 ng/ml) and cultured at 5 and 21 % oxygen tension for 48 h. In separate experiments, constructs were subjected to dynamic compression (15 %) and treated with TNF? (10 ng/ml) and/or L-NIO (1 mM) at 5 and 21 % oxygen tension using an ex vivo bioreactor for 48 h. 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.

Results: TNF? dose-dependently increased NO, PGE2 and MMP activity (all p < 0.001) and induced MMP-13 (p < 0.05) and ADAMTS-5 gene expression (pp < 0.01) with values greater at 5 % oxygen tension than 21 %. The induction of catabolic mediators by TNF? 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 TNF? or reversed with L-NIO.

Conclusions: The present findings revealed that TNF? increased production of NO, PGE2 and MMP activity at 5 % oxygen tension. The effects induced by TNF? were reduced by dynamic compression and/or the NOS inhibitor, linking both types of stimuli to reparative activities. Future therapeutics should develop oxygen-sensitive antagonists which are directed to interfering with the TNF?-induced pathways.

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Identifiers

ORCID for D.L. Bader: orcid.org/0000-0002-1208-3507

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