Thrombin induced Nrf2 activation in synovial fibroblasts. (A) Osteoarthritis synovial fibroblasts (OASFs; six OA lines) were transfected with Nrf2 siRNA for 24 hours, and HO-1 expression was examined with qPCR. (B) OASFs (six OA lines) were incubated with thrombin for indicated time intervals, and Nrf2 phosphorylation was examined with Western blotting. (C) Cells (five OA lines) were pretreated 30 minutes with PPACK, rottlerin, or PP2 followed by stimulation with thrombin for 30 minutes, and Nrf2 phosphorylation was examined with Western blotting. Results are expressed as the mean ± SEM. *P < 0.05 as compared with basal level. #P < 0.05 as compared with thrombin-treated group.