Effect of interleukin 1β on the recruitment of lysine-specific demethylase 1 to the microsomal prostaglandin E synthase 1. A, nuclear extracts (20 μg) from four different osteoarthritis (OA) chondrocyte populations obtained from four different donors were studied by Western blot analysis and hybridized to antibodies specific to LSD1/KDM1, JMJD1A/JHDM2A/KDM3A, KIAA1718/JHDM1D/KDM7A, PHF8/JHDM1F/KDM7B and PHF2/JHDM1E/KDM7C. (B) Confluent OA chondrocytes were treated with 100 pg/ml interleukin 1β (IL-1β) for the indicated time periods, and chromatin immunoprecipitation (ChIP) assays were performed using a specific antibody against lysine-specific demethylase 1 (LSD1). The results are expressed as fold changes of LSD1 binding to the microsomal prostaglandin E synthase 1 (mPGES-1) or matrix metalloproteinase 13 (MMP-13) promoter relative to untreated cells and represent the mean ± SD of four independent experiments. *P < 0.05 compared with unstimulated cells. (C) Confluent OA chondrocytes were treated as described in part (B), and cell lysates were prepared and analyzed for LSD1 protein expression by Western blotting. In the lower panels, the blots were stripped and reprobed with a specific anti-β-actin antibody. The blots are representative of similar results obtained from four independent experiments using cells from four separate donors.