Tumor necrosis factor α-dependent proinflammatory gene induction is inhibited by cyclic tensile strain in articular chondrocytes in vitro

Abstract

Objective. To understand the intracellular mechanisms of the action of mechanical strain on articular chondrocytes during inflammation. Methods. One of the major mediators responsible for cartilage destruction in inflamed articular joints is tumor necrosis factor α (TNFα). Therefore, in this study we examined the intracellular mechanisms of actions of cyclic tensile strain (CTS) on the recombinant human TNFα (rHuTNFα)-induced proinflammatory pathways in primary cultures of chondrocytes. The expression of messenger RNA (mRNA) for TNFα-dependent proinflammatory proteins was examined by semiquantitative reverse transcriptase-polymerase chain reaction. The synthesis of proinflammatory proteins was examined by Western blot analysis in cell extracts, followed by semiquantitative measurement of bands using densitometric analysis. Nitric oxide production was measured by Griess reaction, and prostaglandin E2 production was assessed by radioimmunoassays. The proteoglycan synthesis in chondrocytes was assessed by incorporation of Na235SO4 in chondroitin sulfate proteoglycans. Results. By exposing chondrocytes to CTS in the presence of TNFα in vitro, we showed that CTS is an effective antagonist of TNFα actions and acts as both an antiinflammatory signal and a reparative signal. CTS of low magnitude suppresses TNFα-induced mRNA expression of multiple proinflammatory proteins involved in catabolic responses, such as inducible nitric oxide synthase, cyclooxygenase 2, and collagenase. CTS also counteracts cartilage degradation by augmenting induction of tissue inhibitor of metalloproteinase 2. Additionally, CTS augments the reparative process via abrogation of TNFα-induced suppression of proteoglycan synthesis. Nonetheless, CTS acts on chondrocytes in a TNFα-dependent manner, since exposure of chondrocytes to CTS alone had no effect on these parameters. Conclusion. CTS of low magnitude acts as an effective antagonist of TNFα not only by inhibiting the TNFα-dependent induction of proinflammatory proteins upstream of mRNA transcription, but also by augmenting the proteoglycan synthesis that is inhibited by TNFα.