Osteoclast formation is related to bone matrix age

Little is known about the relationship between the age of the skeleton and the development of multinucleated bone-resorbing cells, osteoclasts. It has been shown that mineralized bone implanted onto the chick chorioallantoic membrane (CAM) is effective in the recruitment and differentiation of osteoclast precursors. In studies reported here we used the CAM system to examine the influence of bone matrix age on osteoclast formation. Devitalized mineralized bone particles (75-250 microns) were prepared from rats of various ages (2, 4, 9, 12, and 16 months). The particles were implanted onto the chick chorioallantoic membrane and 8 days later implants were harvested and processed for morphometric or immunohistochemical analysis. Osteoclast number, cell area, nucleocytoplasmic ratio, and the presence of a distinctive osteoclast antigen, defined by the 121F monoclonal antibody, were determined. Bone particles of each age group resulted in the formation of osteoclast-like giant cells. Compared with multinucleated cells that formed in response to bone particles obtained from 2-month-old rats, matrix from the oldest age group (16 months) elicited significantly fewer and smaller cells which contained a smaller number of nuclei. These data suggest that with aging, bone undergoes qualitative and/or quantitative changes that affect the recruitment and differentiation of osteoclast precursor cells.