Asporin in compressed periodontal ligament cells inhibits bone formation

• Periodontal ligament (PDL) cells and bone metabolism are greatly related.
• PDL cells inhibit of bone formation by secreting anti-osteogenic factors.
• PDL cells subjected to an optimal compressive force induce asporin (ASPN).
• PDL cells subjected to an optimal compressive force downregulate SOST/sclerostin.
• ASPN inhibits bone formation during orthodontic treatment on the compressed side.

ObjectiveDuring orthodontic tooth movement, bone resorption and inhibition of bone formation occur on the compressed side, thereby preventing ankylosis. Periodontal ligament (PDL) cells control bone metabolism and inhibition of bone formation on the compressed side by secreting bone-formation inhibitory factors such as asporin (ASPN) or sclerostin (encoded by SOST). The aim of this study was to identify the inhibitory factors of bone formation in PDL cells.DesignIn vitro, the changes in expression of ASPN and SOST and subsequent protein release in human PDL (hPDL) cells were assessed by semi-quantitative polymerase chain reaction (PCR), real-time PCR, and immunofluorescence in hPDL cells subjected to centrifugal force using a centrifuge (45, 90, 135, and 160 × g). In vivo, we applied a compressive force using the Waldo method in rats, and examined the distribution of ASPN or sclerostin by immunohistochemistry.ResultsIn vitro, hPDL cells subjected to 90 × g for 24 h demonstrated upregulated ASPN and downregulated SOST expressions, which were confirmed by immunofluorescent staining. In addition, the formation of mineralized tissue by human osteoblasts was significantly inhibited by the addition of medium from hPDL cells cultured during compressive force as well as the addition of equivalent amounts of ASPN peptide. In vivo, asporin-positive immunoreactive PDL cells and osteoclasts were found on the compressed side, whereas few sclerostin-positive PDL cells were observed.ConclusionsPDL cells subjected to an optimal compressive force induce the expression and release of ASPN, which inhibits bone formation during orthodontic tooth movement on the compressed side.