Effect of Naproxen on phosphorylation of MAPKs in OA hMSCs. OA hMSCs were cultured to near confluence in complete DMEM. Then, the cells were serum starved for 24 h and were treated without (CTL) or with Naproxen (100 μg/mL) for up to 6 h. Protein expression and phosphorylation of ERK 1/2, JNK, and p38 were determined by immunoblotting and protein bands were quantified using Image J (NIH) software. Total ERK 1/2, JNK, and p38 were used to normalize corresponding phosphorylated forms. Values represent the mean±SE of four donors. (A) Effect of Naproxen on phosphorylation of ERK. Naproxen had significantly increased the phosphorylation of ERK by 0.5 h (294±24, ***p<0.001) and reached to nonsignificant levels only after 6 h. (B) Effects of Naproxen on phosphorylation of JNK. Naproxen did not change the phosphorylation of JNK as compared with control. (C) Effects of Naproxen on phosphorylation of p38. The phosphorylation of p38 increased by 0.5 h and this increase was statistically significant at 1 h (170±32, *p<0.05) and 6 h (195±39, *p<0.05).