Effects of physiological factor-mediated signaling on mRNA expression of GREM1 , FRZB and DKK1 . Effects of mechanical loading, oxygen level and medium tonicity mediated signaling on mRNA expression of GREM1, FRZB and DKK1. Chondrocytes encapsulated in a hydrogel received no, intermittent or constant cyclical mechanical loading of 0.5 MPa with a frequency of 0.33 Hz and a loading phase of 50% (A). Chondrocytes were exposed to normoxic or hypoxic culture conditions (B), or were cultured in media with different tonicity with or without FK506 (C). All conditions were analyzed for the mRNA expression of GREM1, FRZB and DKK1 by quantitative PCR after 48 hours. Data expressed as fold-change relative to control and represent the mean of three donors ± standard deviation. *P <0.05 compared with unloaded samples or samples containing medium of 280 mOsm. DKK1, dickkopf 1 homolog (Xenopus laevis); FRZB, frizzled-related protein; GADPH, glyceraldehyde 3-phosphate dehydrogenase; GREM1, Gremlin 1.