IL-1β-mediated increase in MMP-3 in cultured articular chondrocytes is enhanced in absence of FrzB. Primary chondrocytes were treated for 24 hours with interleukin (IL)-1β (10, 100 or 1,000 pg/ml). (A) Real-time polymerase chain reaction analysis of Mmp-3 gene expression. Results from the treated chondrocytes were normalized to those from nontreated samples (Ctrl), so that the graphs represent the fold-induction in response to IL-1β. The IL-1β-induced Mmp-3 gene expression tends to be enhanced in FrzB−/− chondrocytes compared with wild-type (WT) chondrocytes, especially with 1,000 pg/ml (P = 0.10, n = 3). (B) Culture media were analyzed for total MMP-3 by enzyme-linked immunosorbent assay. MMP-3 protein release in response to 100 pg/ml IL-1β tends to be enhanced in FrzB−/− chondrocytes compared with WT chondrocytes (P = 0.10, n = 3). Bars represent the mean ± standard error of the mean. *P ≤ 0.05 versus Ctrl, #P ≤ 0.10 between FrzB−/− and WT. FrzB, frizzled-related protein B; KO, knockout; MMP, matrix metalloproteinase; ND, not detected.