Periodontal ligament-associated protein-1 gets involved in the development of osseous eruption canal.

Osseous eruption is an important stage of tooth eruption process. The role of periodontal ligament-associated protein-1 (PLAP-1/asporin) in the development of osseous eruption canal remain undefined and were the focus of this study. C57BL/6 mice at postnatal days P11-13 and P 15-16 were chosen. The development of osseous eruption canal of lower first molar was observed and osteoclasts were detected by staining for tartrate-resistant acid phosphatase (TRAP). PLAP-1 expression in the process of osseous eruption (OE, P11-13) and post- osseous eruption (P-OE, P15-16) was assessed by immunohistochemistry, immunofluorescence and western blotting. Receptor activator of NF-κB ligand (RANKL) distribution in the process was also assessed by immunohistochemistry. A double immunofluorescence stain was used to reveal PLAP-1 in association with CD68 (osteoclast maker). Fresh occlusal tissues of erupting lower first molars at OE and P-OE were separated to detected RANKL/OPG ratio by western blotting to elucidate related mechanisms. At osseous eruption (OE), osseous and mucosal tissues could be observed on the occlusal side of lower first molar. Osseous eruption canal was developing. Many osteoclasts were found around occlusal alveolar bone in the development of osseous eruption canal. At post- osseous eruption (P-OE), osseous eruption canal had been built, only mucosal tissues were observed, and few osteoclasts were detected. More PLAP-1 expression was detected at OE, compared with that at P-OE. Similar distributions of PLAP-1 and RANKL in occlusal bone tissues of erupting lower first molars were detected at OE. Colocalization of PLAP-1 and CD68 revealed the positive relationship between PLAP-1 and osteoclasts in the development of osseous eruption canal. PLAP-1 positively correlated with RANKL and CD68+ osteoclasts, and areas of bone resorption. Higher RANKL/OPG ratio was detected at OE, compared with that at P-OE. PLAP-1 gets involved in the development of osseous eruption canal.