Matrilin-3 MATN3) inhibits the expression of several osteoarthritis (OA)-associated proteases. Recombinant human (rh) MATN3 protein inhibits the gene expression of metalloproteinase (MMP)-13 in a dose-dependent manner in the presence and absence of IL-1β in C28/I2 cells (A). MATN3 inhibits IL-1β-induced MMP-13 mRNA levels (B) and protein levels in primary human chondrocyte (PHC)-conditioned media (C). MATN3 inhibits the mRNA expression of OA-associated proteases ADAMTS-4 and ADAMTS-5 in C28/I2 cells (D) and PHCs (E). MMP-13 mRNA and protein analysis were conducted after MATN3 treatment for 24 hours. In these experiments, rh MATN3 protein is used at one of two concentrations: lower dose (+) of 100 ng/ml, or higher dose (++) of 200 ng/ml. Rh IL-1β protein treatment is always 5.0 ng/ml. *P ≤ 0.05, **P ≤ 0.01, for statistically significant differences from the untreated control group; #P ≤ 0.05, ##P ≤ 0.01 for statistically significant differences from the IL-1β only treated group. Data are representative of three individual experiments.