Production of collagenase by human osteoblasts and osteoclasts in vivo

Studies in some animal species have demonstrated the production of metalloproteinases by bone cells, suggesting that they may play a role in bone modeling and remodeling. The aim of the present study was to investigate the expression of collagenase in human bone in situ, using heterotopic and osteophytic bone. Immunohistochemistry was performed on chilled sections of bone, using well characterized polyclonal antibodies to human collagenase. The heterotopic and osteophytic bone exhibited high turnover and both bone modeling and remodeling were evident. Collagenase expression by osteoblasts was demonstrated in cells synthesising matrix and in lining cells; the strongest signal was seen in areas of de novo matrix formation, where bridges of woven bone were being formed between areas of mineralized bone. Collagenase was also present in some osteoclasts associated with eroded bone surfaces and in some mononuclear cells that were present in resorption cavities and in the bone marrow. Our results provide the first demonstration, in situ, of collagenase in human bone and suggest that it may play a role in human bone modeling and remodeling. Production of collagenase by active osteoblasts and lining cells suggest that it may be involved both in matrix formation and activation of bone remodeling. The presence of collagenase in osteoclasts provides further evidence that metalloproteinases may play a role in bone resorption.