MMP13 and osteoarthritis: Hamada et al. showed that insulin inhibits the expression of ADAMTS4, matrix metalloproteinase 1 (MMP1), matrix metalloproteinase 13 (MMP13), and IL6 in fibroblast-like synoviocytes (FLS) in patients with osteoarthritis (6) These genes depend on tumor necrosis factor (TNF), which can damage cartilage, and insulin may protect cartilage by inhibiting TNF.