Upregulation of LRP5 in interleukin 1β-treated mouse articular chondrocytes. (A) Mesenchymal cells from mouse embryos were maintained as micromass cultures for 12 days, and the expression levels of Col2a1, Mmp13, Lrp5, Lrp6 and Gapdh were detected by RT-PCR. LRP5 expression was confirmed by Western blot analysis. (B) and (C) Primary cultured mouse articular chondrocytes were treated with the indicated concentrations of interleukin 1β (IL-1β) for 24 hours (B) or with 1 ng/ml IL-1β for the indicated periods (C), and RT-PCR, quantitative RT-PCR and Western blot analysis were carried out. Values are presented as means ± SEM (*P < 0.001, **P < 0.0001; n = 6 independent experiments). (D) through (G) RT-PCR and Western blot analysis were performed on chondrocytes treated with IL-1β (1 ng/ml) for 24 hours in the presence of the indicated inhibitors (micromolar concentrations): PD98059, an extracellular signal-regulated kinase (ERK) inhibitor (D); SB203580, a p38 mitogen-activated protein (MAP) kinase inhibitor (E); SP600125, a c-Jun N-terminal kinase (JNK) inhibitor (F); and (2E)-3-[[4-(1,1-dimethylethyl)phenyl]sulfonyl]-2-propenenitrile (BAY11-7085), an inhibitor of nuclear factor κB α (IκBα) (G).