Matrix Metalloproteinase-9 Production by Immortalized Human Chondrocyte Lines.

We reported at the Keynote Forum of Immunology Summit-2015 that recombinant human (rh) TNF-α or rhIL-6 stimulated production of matrix metalloproteinase-9 (MMP-9) in the T/C28a2 and C-28/I2 human immortalized chondrocyte cell lines. Furthermore, we reported that tocilizumab (TCZ), a fully humanized monoclonal antibody which neutralizes IL-6-mediated signaling, inhibited the rhIL-6-mediated increase in the production of MMP-9. IL-6 is also a known activator of the JAK/STAT signaling pathway. In that regard, we evaluated the effect of rhIL-6 on total and phosphorylated Signal Transducer and Activator of Transcription by these chondrocyte lines which showed that whereas STAT3 was constitutively phosphorylated in T/C28a2 chondrocytes, rhIL-6 activated STAT3 in C-28/I2 chondrocytes. The finding that rhIL-6 increased the production of MMP-9 by human immortalized chondrocyte cell lines may have important implications with respect to the destruction of articular cartilage in rheumatoid arthritis and osteoarthritis. Thus, the markedly elevated level of IL-6 in rheumatoid arthritis and osteoarthritis sera and synovial fluid would be expected to generate significant MMP-9 to cause the degradation of articular cartilage extracellular matrix proteins. The finding that TCZ suppressed rhIL-6-mediated MMP-9 production suggests that TCZ, currently employed in the medical therapy of rheumatoid arthritis, could be considered as a drug for osteoarthritis.