Fig. 4. OSCAR–collagen binding co-stimulates IL-1β-induced apoptotic signaling in articular chondrocytes.

a Caspase activity in mouse articular chondrocytes treated with IL-1β (5 ng mL⁻¹) and collagenase (Coll, 50 U mL⁻¹). b, c qRT-PCR analysis (b) and western blotting (c) in mouse articular chondrocytes. Chondrocytes were either untreated or transfected with control siRNA (C-siRNA) (100 nM) or siRNAs specific for mouse Oscar and exposed to IL-1β (5 ng mL⁻¹) and collagenase (50 U mL⁻¹) for 48 h. d Articular chondrocyte viability was quantified by MTT assay. Error bars represent mean ± S.E.M. of n = 5 wells. e Caspase-8 and caspase-3 activity was measured using the respective assay kits. f, g qRT-PCR analysis (f) and western blotting (g) in mouse articular chondrocytes. Chondrocytes were treated with hIgG or hOSCAR-Fc (10 μg ml⁻¹) with collagenase and exposed to IL-1β for 48 h. h Apoptotic articular chondrocytes were detected and quantified by TUNEL assay. Scale bar = 100 μm. i, j qRT-PCR analysis (i) and western blotting (j) in mouse articular chondrocytes treated with 10 μΜ OSCAR-binding triple-helical peptide before IL-1β treatment. Articular chondrocytes were treated with hOSCAR-Fc for 48 h. Error bars shown in a, b, e, f, h and i are mean ± S.E.M. for n = 4 independent experiments. One-way ANOVA was performed followed by Dunnett’s Multiple Comparison’s test (a, i) and Tukey’s Multiple Comparison’s test (b, d, e, f, h), with p values indicated in figure.