Fig. 3.

PLR enzyme expression is suppressed in human OA subchondral bone. a–d Immunohistochemical analysis of MMP13 (a) and Cathepsin K (CatK, c) levels and localization in subchondral bone from control and OA tibial plateau specimens was performed at low (4x, top, scale bars: 200 μm) and high (40x, bottom, scale bars: 100 μm) magnification. Qualitative and quantitative analyses show diminished MMP13 and CatK expression in the OA tibial plateau, with a significant reduction in the percentage of osteocytes stained positively for MMP13 (b, control n = 4, OA n = 5) and CatK (d, control n = 4, OA n = 5) in both regions. e No differences in negative control staining were observed. f–g Furthermore, Pearson’s product–moment correlation indicates that percent of MMP13-positive osteocytes is strongly correlated with lacunocanalicular area (f, r = 0.79, P < 0.000 1) and canalicular length (g, r = 0.82, P < 0.000 1). Graphs show mean ± SEM. *P < 0.05 compared with respective regions of control specimens, ^⋄P < 0.05 between regions by Holm–Sidak post hoc tests