IMPLANTED BONE PARTICLES INDUCE OSTEOCLAST DEVELOPMENT IN THE PRESENCE OF OSTEOBLAST LINEAGE CELLS

We implanted mineral-containing bone particles (BPs) in rats to invest igate the involvement of osteoblast lineage cells in osteoclast develo pment in vivo. BPs were implanted in subcutaneous regions on calvaria or artificial defects of calvaria, with or without adjacent parathyroi d glands prepared from other rats. The structural characteristics of m ultinucleated giant cells (MGCs) induced by the BPs were investigated. The MGCs induced by subcutaneously implanted BPs showed membrane ruff ling at the basolateral site, but not at the apical site, regardless o f whether parathyroid glands were also implanted. In contrast, the MGC s induced by intraosseously implanted BPs showed the characteristics o f osteoclasts, i.e., ruffled borders at the apical sites, clear zone, vacuoles, many mitochondria, and scattered rough endoplasmic reticulum . When BPs and parathyroid glands were implanted in bone defects, the number of MGCs was increased compared to that induced by BPs only. The se MGCs showed the typical characteristics of active osteoclasts, incl uding developed ruffled borders and stacks of Golgi succules. The numb er of osteoclasts was also investigated quantitatively by counting the numbers of MGCs positive and negative for tartrate-resistant acid pho sphatase. In intraosseous implantation, MGCs with the characteristics of osteoclasts were observed close to osteoblastic cells characterized by developed rough endoplasmic reticulum. These results indicate that the osteoclasts were not induced solely by the subcutaneously implant BPs, but required osteoblast lineage cells for development.