Abstract

Tumor necrosis factor alpha (TNF-alpha), a major proinflammatory cytokine, induces arthritic joint inflammation and resorption of cartilage by matrix metalloproteinase-13 (MMP-13). RNA for MMP-13 is increased in human arthritic femoral cartilage. Mechanisms of this induction were investigated by pretreating primary human osteoarthritic (OA) femoral head chondrocytes or chondrosarcoma cells with the potential inhibitors of TNF-alpha signal transduction and downstream target transcription factors followed by stimulation with TNF-alpha and analysis of MMP-13 RNA/protein. TNF-alpha rapidly activated phosphorylation of extracellular signal-regulated kinases (ERKs), p38, and c-jun N-terminal kinase (JNK) mitogen-activated protein (MAP) kinases in human chondrocytes. Inhibitors of ERK (U0126, PD98059, and ERK1/2 antisense phosphorothioate oligonucleotide), JNK (SB203580, SP600125, and curcumin), and p38 (SB203580 and SB202190) pathways down-regulated the TNF-stimulated expression of MMP-13. Inhibitors of the transcription factors AP-1 (nordihydroguaiaretic acid, NDGA) and NF-kappaB (curcumin, proteasome inhibitors, and Bay-11-7085) suppressed TNF-alpha-induced MMP-13 expression in primary chondrocytes and SW1353 cells. These results suggest that induction of the MMP-13 gene by TNF-alpha is mediated by ERK, p38, and JNK MAP kinases as well as AP-1 and NF-kappaB transcription factors. Blockade of TNF-alpha signaling and its target transcription factors by the approaches tested here may be beneficial for reducing cartilage breakdown by MMP-13 in arthritis.