Interleukin-18 promotes joint inflammation and induces interleukin-1-driven cartilage destruction - PubMed (original) (raw)

Comparative Study

Interleukin-18 promotes joint inflammation and induces interleukin-1-driven cartilage destruction

Leo A B Joosten et al. Am J Pathol. 2004 Sep.

Abstract

Interleukin (IL)-18 is a member of the IL-1 family of proteins that exerts proinflammatory effects and is a pivotal cytokine for the development of Th1 responses. The goal of the present study was to investigate whether IL-18 induces joint inflammation and joint destruction directly or via induction of other cytokines such as IL-1 and tumor necrosis factor (TNF). To this end we performed both in vitro and in vivo kinetic studies. For in vivo IL-18 exposure studies C57BL/6, TNF-deficient, and IL-1-deficient mice were injected intra-articularly with 1.10(7) pfu mIL-18 adenovirus followed by histopathological examination. Local overexpression of IL-18 resulted in pronounced joint inflammation and cartilage proteoglycan loss in control mice. Of high interest, IL-18 gene transfer in IL-1-deficient mice did not show cartilage damage, although joint inflammation was similar to that in wild-type animals. Overexpression of IL-18 in TNF-deficient mice showed that TNF was partly involved in IL-18-induced joint swelling and influx of inflammatory cells, but cartilage proteoglycan loss occurred independent of TNF. In vitro cartilage degradation by IL-18 was found after a 72-hour culture period. Blocking of IL-1 with IL-1Ra or an ICE-inhibitor resulted in complete protection against IL-18-mediated cartilage degradation. The present study demonstrated that IL-18 induces joint inflammation independently of IL-1. In addition, we showed that IL-1beta generation, because of IL-18 exposure, was essential for marked cartilage degradation both in vitro and in vivo. These findings implicate that IL-18, in contrast to TNF, contributes through separate pathways to joint inflammation and cartilage destruction.

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Figures

Figure 1

Figure 1

IL-18-driven joint inflammation in wild-type, IL-1−/−, and TNF−/− mice. IL-18 was overexpressed in the right knee of C57/BL6 mice by intra-articular injection of 1.107 pfu of AdmIL-18. A: At several time points both joint swelling (99mTc-uptake) and chondrocyte proteoglycan synthesis (35S-sulfate incorporation) were assessed. B: To examine the role of either IL-1 or TNF, IL-18 was overexpressed in IL-1- or TNF-deficient mice. Data expressed the mean ± SD of at least eight mice per group. The experiment was repeated once with approximately the same outcome. *, P < 0.01, Mann-Whitney _U_-test compared to C57/BL6 wild-type mice control group.

Figure 2

Figure 2

Joint inflammation induced by prolonged IL-18 overexpression. At day 0 1.107 pfu of control virus (Ad5del70-3) or 1.107 pfu of AdmIL-18 was intra-articularly injected in wild-type, IL-1-deficient, or TNF-deficient mice. At day 7 knee joints were removed and processed for histological analysis. A: Inflammation found after injection of Ad5del70-3 control virus. B: IL-18-induced joint inflammation in a wild-type mouse. C: IL-18-induced joint inflammation in IL-1 gene-deficient mouse. D: IL-18-induced joint inflammation in TNF knockout mouse. P, patella; F, femur; JC, joint cavity; and C, cartilage. H&E staining. Original magnifications, ×200.

Figure 3

Figure 3

Cartilage degradation after IL-18 gene transfer in wild-type, IL-1-deficient, or TNF-deficient mice. IL-18-driven cartilage proteoglycan loss was analyzed on day 14 after intra-articular injection of 1.107 pfu of Ad5del70-3 or AdmIL-18. A: Wild-type mouse injected with control virus. B: AdmIL-18 injection in a wild-type mouse. C: IL-18 overexpression in a IL-1α,β-deficient mouse. D: IL-18 overexpression in a TNF-deficient mouse. For details see Figure 2. Note the enhanced cartilage proteoglycan loss in wild-type and TNF-deficient mice (arrows). Safranin O staining. Original magnifications, ×400.

Figure 4

Figure 4

Prolonged exposure to IL-18 induced cartilage degradation in vitro. A: Patellar cartilage explants were isolated from naïve knee joints of C57/BL6 mice and cultured for 24 to 72 hours in RPMI 1640 medium supplemented with recombinant hIGF-1 (250 ng/ml) with or without mIL-18. Thereafter chondrocyte proteoglycan synthesis was determined by 35S-sulfate incorporation. For details see Materials and Methods. B: For cartilage degradation studies cartilage explants were prelabeled with 35S-sulfate. Data expressed the mean ± SD of six patellae per group. The experiments were repeated twice with similar outcome. *, P < 0.01, Mann-Whitney _U_-test compared to IGF-1 control group.

Figure 5

Figure 5

In vitro cartilage degradation by IL-18 is mediated by IL-1. Patellar cartilage explants were prelabeled as indicated in Materials and Methods. Thereafter, cartilage explants were cultured for 72 hours with IGF-1-containing medium with either IL-18 (10 or 100 ng/ml) or IL-1β (10 ng/ml). To block IL-1 we added either recombinant mIL-1Ra (A, 10 μg/ml) or ICE-inhibitor (B, 2.5 μmol/L) to the culture medium. C: To confirm the ICE data and examine the role of TNF in IL-18-driven proteoglycan loss we use patellar explants from both IL-1β- and TNF-α-deficient mice. For details see Figure 4. *, P < 0.01, Mann-Whitney _U_-test compared to C57/BL6 × 129Sv wild-type mice control group.

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