Expression of RANKL and OPG in the Developing Teeth of the Postnatal Rat

Kim, Min Seok; Kim, Hyun Jin; Kim, Il Sup; Kim, Sun Hun

Abstract

Differentiation and activation of osteoclasts are crucial in bone resorption. RANKL released from osteoblasts, also known as ODF, and proteins such as OPG/OCIF, decoy receptor of RANKL for inhibition of osteoclast formation play an important role. Teeth exhibit various movement patterns in mandible before eruption, inevitably accompaning peripheral bone resorption. Therefore, it is very meaningful to study osteoclasts differentiation and activation-related various factors near developing teeth for prediction of tooth movement patterns and understanding of mechanism of pre-and post-eruptive movement. This study examined distribution of RANKL and OPG in the mandible of postnatal 1~24 day rats containing developing teeth using immunohistochemical methods. After birth, the mandibular pre-eruptive first and second molars showed tooth germ morphology from bell stage to crown stage. In postnatal day 17, the mandibular first molar crown was completed and continuous eruption was in process along with root formation. On the twenty fourth day after birth, it was exposed to the oral cavity. RANKL exhibited strong positive immunohistochemical reactions in dental follicles and stromal cells around the mandibular first molar. On the third day after birth, strong positive reaction to RANKL was observed in the alvelolar bone above the mandibular first molar along with appearance of numerous osteoclasts. The reactivity was slightly attenuated on the seventh day and increased again on the tenth day after birth. The positive immunoreactivities were found not only in alveolar bone above the developing first molar, but also in stromal cells of the cervical area in contact with HERS. The alveolar bone below developing roots was also strongly stained. OPG displayed a similar patterns in the RANKL expression and locations of posively reacting cells, but relatively weakly stained on the third and tenth day after birth, when numerous osteoclasts made their appearnace. Above results suggest that RANKL and OPG have a close relation to the teeth movement in mandible such as eruption during teeth developing process. They also imply that RANKL and OPG play an important role in osteoclasts formation after synthesized in dental follicular cells and alveolar stromal cells.