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Logo of annrheumdAnnals of the Rheumatic DiseasesCurrent TOCInstructions for authors
 
Ann Rheum Dis. May 2005; 64(5): 735–742.
PMCID: PMC1755478

Implication of interleukin 18 in production of matrix metalloproteinases in articular chondrocytes in arthritis: direct effect on chondrocytes may not be pivotal

Abstract

Objective: To clarify the effect of interleukin (IL) 18 on cartilage degeneration by studying the profile of IL18 receptor (IL18R) on chondrocytes and the direct effect of IL18 on production of matrix metalloproteinases (MMPs), aggrecanases, and tissue inhibitors of metalloproteinases (TIMPs) in articular chondrocytes.

Methods: Monolayer cultured human articular chondrocytes were isolated from non-arthritic subjects and patients with rheumatoid arthritis or osteoarthritis. Gene expression of IL18, IL18Rα, IL18Rß, MMPs, and aggrecanases was detected by RT-PCR. Protein levels of IL18Rα were analysed by flow cytometry. Protein levels of IL18, MMPs, and TIMPs were measured by ELISA. Aggrecanase-2 mRNA expression was quantitatively analysed by real time RT-PCR. Protein levels of signalling molecules were assayed by western blotting.

Results: IL18 mRNA was constitutively expressed in chondrocytes, and was enhanced by IL1ß stimulation. Flow cytometric analysis showed that IL1ß, tumour necrosis factor α, and IL18 up regulated IL18Rα expression levels. The level of IL18Rß mRNA was much lower than that of IL18Rα, and was slightly up regulated by IL1ß. In chondrocytes responding to IL18, IL18 (1–100 ng/ml) slightly increased the production of MMP-1, MMP-3, and MMP-13, which was blocked by NF-κB inhibitor and p38 mitogen activated protein kinase inhibitor. IL18 up regulated mRNA expression of aggrecanase-2, but not aggrecanase-1. IL18 also slightly stimulated TIMP-1 production?through extracellular signal regulated kinase activation.

Conclusion: IL18 induces production of MMPs from chondrocytes in inflammatory arthritis. Although the direct effect of IL18 on chondrocytes may not be pivotal for the induction of cartilage degeneration, IL18 seems to play some part in the degradation of articular cartilage in arthritis.

Figure 1
 Production of type II collagen and proteoglycan during the continuous culture of chondrocytes. The levels of production of type II collagen and proteoglycan released by cultured chondrocytes were analysed by an ELISA.
Figure 2
 Expression of mRNA for IL18, IL18Rα, and IL18Rß by cultured chondrocytes. The chondrocytes were isolated from normal human joint cartilage, OA and RA cartilage, and mRNA expression was detected by RT-PCR. PCR products were stained ...
Figure 3
 Flow cytometric analysis of IL18Rα expression on the surface of cultured OA chondrocytes. (A) Representative dot plots of cells incubated with or without IL1ß (5 ng/ml), TNFα (10 ng/ml), or IL18 (10 ng/ml) for 12 hours. ...
Figure 4
 Time course of IL18 effects on gene expression of MMP-1, MMP-3, MMP-13, and aggrecanase-2 in OA chondrocytes. (A) Representative results from chondrocytes that responded to IL18 by RT-PCR. (B) Expression level of aggrecanase-2 analysed by quantitative ...
Figure 5
 Dose-response of IL18 effects on MMP-1, MMP-3, MMP-13, and TIMP-1 production in chondrocytes. After a 48 hour incubation with indicated concentrations of IL18, the supernatants were harvested. The levels of MMPs and TIMP-1 in the supernatants ...
Figure 6
 Effect of specific inhibitors on IL18 enhanced production of MMP-1, MMP-3, MMP-13, and TIMP-1 in OA chondrocytes. In IL18 responsive chondrocytes, specific inhibitor of NF-κB (20 µM Bay11-7085), PI3K (10 µM LY294002), ...
Figure 7
 Phosphorylation of IκB, p38 MAPK, and Erk1/2 induced by IL18 in responsive OA chondrocytes. Chondrocyte lysates were prepared at the indicated times after stimulation with 100 ng/ml IL18. Whole cell lysates were subjected to western ...

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