BEAS-2B (a,c,e) and HPMEC (b,d,f) cells exposed to room air (room air-5% CO2) and 24, 48, or 72 h of hyperoxia (95% O2-5% CO2). GDF15 siRNA or negative control siRNA were transfected into BEAS-2B and HPMEC cells. Expression of GDF-15 was measured at the mRNA (a-d) and protein level (e,f) by ELISA. Values are means ± SEM of 3 independent biological replicates. Significant differences between GDF15 siRNA and negative control siRNA groups are indicated by *P <0.05, **P<0.01 and ***P <0.001.