Effects of IL-1β-mediated signaling on mRNA expression of GREM1 , FRZB and DKK1 . Chondrocytes received a single dose of 10 or 100 ng/ml IL-1β, or a daily medium refreshment containing 10 ng/ml IL-1β. Chondrocytes were stimulated up to 96 hours and mRNA expression was analyzed by quantitative PCR at the indicated time points for GREM1 (A), FRZB (B), and DKK1 (C). Data expressed as fold-change relative to untreated time point-matched control and represent the mean of three donors ± standard deviation. *P <0.05 compared with unstimulated cells. DKK1, dickkopf 1 homolog (Xenopus laevis); FRZB, frizzled-related protein; GADPH, glyceraldehyde 3-phosphate dehydrogenase; GREM1, Gremlin 1.