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

Objective. To understand the intracellular mechanisms of the action of mech anical strain on articular chondrocytes during inflammation. Methods. One of the major mediators responsible for cartilage destruction i n inflamed articular joints is tumor necrosis factor alpha (TNF alpha). The refore, in this study we examined the intracellular mechanisms of actions o f cyclic tensile strain (CTS) on the recombinant human TNF alpha (rHuTNF al pha)-induced proinflammatory pathways in primary cultures of chondrocytes. The expression of messenger RNA (mRNA) for TNF alpha -dependent proinflamma tory proteins was examined by semiquantitative reverse transcriptase-polyme rase chain reaction. The synthesis of proinflammatory proteins was examined by Western blot analysis in cell extracts, followed by semiquantitative me asurement of bands using densitometric analysis. Nitric oxide production wa s measured by Griess reaction, and prostaglandin E-2 production was assesse d by radioimmunoassays. The proteoglycan synthesis in chondrocytes was asse ssed by incorporation of (Na2SO4)-S-35 in chondroitin sulfate proteoglycans . Results. By exposing chondrocytes to CTS in the presence of TNF alpha in vi tro, we showed that CTS is an effective antagonist of TNF alpha actions and acts as both an antiinflammatory signal and a reparative signal. CTS of lo w magnitude suppresses TNF alpha -induced mRNA expression of multiple proin flammatory proteins involved in catabolic responses, such as inducible nitr ic oxide synthase, cyclooxygenase 2, and collagenase. CTS also counteracts cartilage degradation by augmenting induction of tissue inhibitor of metall oproteinase 2. Additionally, CTS augments the reparative process via abroga tion of TNF alpha -induced suppression of proteoglycan synthesis. Nonethele ss, CTS acts on chondrocytes in a TNF alpha -dependent manner, since exposu re of chondrocytes to CTS alone had no effect on these parameters. Conclusion. CTS of low magnitude acts as an effective antagonist of TNF alp ha not only by inhibiting the TNF alpha -dependent induction of proinflamma tory proteins upstream of mRNA transcription, but also by augmenting the pr oteoglycan synthesis that is inhibited by TNF alpha.