MMP1 and rheumatoid arthritis: Moreover, RA synovial fibroblasts can spontaneously secrete numerous proinflammatory cytokines such as interleukin-6 (IL-6) and IL-8 and matrix metalloproteinases (MMPs) including MMP-1 and MMP-3, which plays an important role in progressive destruction of articular cartilage and bone [6–9].