Fig. 2

Basal activation status of the ER stress sensors in osteoarthritic (OA) chondrocytes. a The phosphorylation of PERK was determined by immunohistochemistry (IHC) in normal (n = 7) and OA (n = 7) cartilage. Illustrated are representative images of cartilage IHC and a graph of the data expressed as mean ± SEM. Statistical significance assessed by the unpaired t test comparing OA to normal chondrocytes showed no difference. Magnification × 63 (a, b) and × 250 (c and d, upper cartilage zone; e and f, lower zone); boxes indicate where the magnifications were taken, and arrows, the positively stained chondrocytes. b The uncleaved form (approximately 75 kDa) of ATF6B in OA chondrocytes (n = 6) treated or not (control) for 20 minutes with thapsigargin (Tg; 50 nM) and tunicamycin (Tm; 500 ng/ml) assessed by Western blot using an antibody that recognizes the C-terminus of the protein. Illustrated are representative Western blots with GAPDH as loading control and a graph of the densitometry analysis of the uncleaved ATF6B. Data are expressed as mean ± SEM, and p values assessed by the unpaired t test comparing OA to normal chondrocytes. c The presence of the spliced form of XBP1 mRNA was determined by PCR followed by gel electrophoresis (n = 8). In addition, OA chondrocyte sample #8 treated for 20 minutes with Tg (50 nM) and Tm (500 ng/ml) is shown as control for the ER stress activation