Fig. 1

Characterization of human monocyte-derived osteoclasts secreted protease activity. a Bright field image of monocytes and differentiated osteoclasts stained for TRAP. Scale bar 10 µm. b qRT-PCR of freshly isolated CD14⁺ monocytes and differentiated osteoclasts. Values were first normalized to RRN18S and then to the gene expression levels in monocytes. Data is presented as the mean ± SD, n = 3. c CM from freshly isolated CD14⁺ monocytes and differentiated osteoclasts were analyzed for the presence of active CTSK. Data is presented as the mean ± SD, n = 3. d CM from Ocs were subjected to Western blot analysis and probed with an antibody against proMMP-9. 20 ng of rhproMMP-9 was used as a positive control. e Gelatin zymography of Oc CM. The pH of the CMs was maintained at 7.4 or lowered to 5.0 and incubated for 1 h at 37°C with or without a CTSK inhibitor. Afterwards, the samples were analyzed by gelatin zymography. *P < 0.05 and ***P < 0.005.