Figure 3. Knockdown of RIPK1 inhibits interleukin (IL)-1β–induced production of catabolic enzymes and proinflammatory cytokines in vitro. (A, B) Representative western blots and quantitative data of RIPK1 and p-RIPK1 in chondrocytes transfected with Ad-shRIPK1 and Ad-RIPK1. (C, D) Knockdown of RIPK1 reduced the IL-β–induced expression of MMPs in chondrocytes. (E, F) Overexpression of RIPK1 promoted the IL-β–induced expression of MMPs in chondrocytes. (G) Enzyme-linked immunosorbent assay (ELISA) of the tumor necrosis factor (TNF)-α level in culture supernatants. (H, I) Western blots and quantitative data of p-RIPK1 in chondrocytes treated with IL-1β. The experiments were repeated three times independently. Columns represent means ± SD. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.