The role of IL-4 in the control of mechanical stress-induced inflammatory mediators by rat chondrocytes

A complex environment controls the metabolism of chondrocytes in the inflammatory joint. Although mechanical stimuli are essential for the chondrocyte metabolism, excessive mechanical force contributes to the release of inflammatory mediators leading the cartilage destruction under the arthritic condition. IL-4 is a chondroprotective cytokine, which is also involved in the integrin-mediated chondrocyte mechano-transduction. We examined the effects of cyclic mechanical stress on the gene expression profile of rat chondrocytes, and tested the in vitro effects of recombinant IL-4. Chondrocytes were obtained from the knee joints of 7-day-old Wister rats. Cyclic mechanical stress was applied on the cultured chondrocytes for 24 hours using Flexercell strain unit (Flexcell International Co., Hillsboro, NC, USA) with 0.5 Hz, 7% elongation, with or without treatment by recombinant IL-4. The cDNA microarray analysis revealed that, of 1080 genes, 37 genes were upregulated and 46 genes were downregulated after mechanical stress. RT-PCR and real-time PCR analysis confirmed that treatment by IL-4 resulted in the significant downregulation of mRNA expression of cysteine proteinase cathepsin B, and the inducible form of nitric oxide synthase. Next, an osteoarthritis model was created in the knee joints of Wistar rats (200 g) with anterior cruciate ligament and medial collateral ligament transection. The rats were killed 2, 4, or 6 weeks after the surgery, and the gross morphology and histology of the knee joint cartilage were examined. The preliminary results showed that intra-articular administration of IL-4 exerted a protective effect on the development of osteophytes, and cartilage lesions in this model of osteoarthritis. These results suggested the possible role of IL-4 in the control of mechanical stress-induced inflammatory mediators in vitro and in vivo.