No abstract

Oncostatin M (OSM), a member of the IL-6 superfamily of cytokines, is elevated in patients with rheumatoid arthritis and, in synergy with IL-1, promotes cartilage degeneration by matrix metalloproteinases (MMPs). We have previously shown that OSM induces MMP and tissue inhibitor of metalloproteinase-3 (TIMP-3) gene expression in chondrocytes by protein tyrosine kinase-dependent mechanisms. In the present study, we investigated signaling pathways regulating the induction of MMP and TIMP-3 genes by OSM. We demonstrate that OSM rapidly stimulated phosphorylation of Janus kinase (JAK) 1, JAK2, JAK3, and STAT1 as well as extracellular signal-regulated kinase (ERK) 1/2, p38, and c-Jun N-terminal kinase 1/2 mitogen-activated protein kinases in primary bovine and human chondrocytes. A JAK3-specific inhibitor blocked OSM-stimulated STAT1 tyrosine phosphorylation, DNA-binding activity of STAT1 as well as collagenase-1 (MMP-1), stromelysin-1 (MMP-3), collagenase-3 (MMP-13), and TIMP-3 RNA expression. In contrast, a JAK2-specific inhibitor, AG490, had no impact on these events. OSM-induced ERK1/2 activation was also not affected by these inhibitors. Similarly, curcumin (diferuloylmethane), an anti-inflammatory agent, suppressed OSM-stimulated STAT1 phosphorylation, DNA-binding activity of STAT1, and c-Jun N-terminal kinase activation without affecting JAK1, JAK2, JAK3, ERK1/2, and p38 phosphorylation. Curcumin also inhibited OSM-induced MMP-1, MMP-3, MMP-13, and TIMP-3 gene expression. Thus, OSM induces MMP and TIMP-3 genes in chondrocytes by activating JAK/STAT and mitogen-activated protein kinase signaling cascades, and interference with these pathways may be a useful approach to block the catabolic actions of OSM.

The major pathologic manifestations of rheumatoid arthritis (RA) and osteoarthritis (OA) are joint inflammation and articular cartilage resorption by proinflammatory cytokine-stimulated matrix metalloproteinases (MMPs) and aggrecanases. The Chinese herbal remedy Tripterygium wilfordii Hook F (TWHF) is effective for treatment of various types of arthritis. However, mechanisms and targets of its actions are poorly understood. Anti-inflammatory activities of the extracts of this plant were previously attributed to inhibition of cyclooxygenase-2 mRNA and prostaglandin E(2) synthesis. Here, we show that in primary human femoral head osteoarthritic and normal bovine chondrocytes, TWHF partially or completely inhibited mRNA and protein expression of tumor necrosis factor-alpha, interleukin (IL)-1, and IL-17-inducible MMP-3 and MMP-13. This agent also inhibited cytokine-stimulated MMP-3 protein expression in human synovial fibroblasts. A dose range of 2.5 to 10 ng/ml of TWHF was effectively inhibitory for IL-1. Pretreatment for 30 min or 1 h (but not 2-10 h) after IL-1 treatment with TWHF inhibited MMP-3 RNA induction. The inhibitory doses had no adverse effect on the viability of chondrocytes. Mechanistic studies revealed no impact on the activation of extracellular signal-regulated kinase, p38, and c-Jun N-terminal kinase mitogen-activated protein kinases. Instead, TWHF partially inhibited DNA binding capacity of cytokine-stimulated activating protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB) transcription factors. Therefore, besides its anti-inflammatory activity, this agent may also be effective in blocking cartilage matrix resorption by MMPs by impairing AP-1 and NF-kappaB binding activities. Thus, TWHF extract contains novel inhibitors of MMP expression that may be of therapeutic potential in arthritis and other conditions associated with increased MMPs.