The function of periostin during periodontal tissue remodeling caused by mechanical stress.

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The periodontal ligament (PDL) plays an important role in the remodeling of the periodontal tissues during orthodontic tooth movement. Many factors are involved in the mechanisms of response to an orthodontic force. One of these factors might be periostin, which has a specific expression in the PDL and the periosteum. Therefore, the aim of this study was to elucidate the role of periostin in the PDL during tooth movement and its effect on osteoclasts. In this study, periostin mRNA expression was investigated using experimental tooth movement model in rats in vivo and the effect of uni-axial mechanical stress was examined on human periodontal ligament fibroblastic cells (hPDLF) in vitro. Also the effect of periostin on osteoclasts was analyzed. In situhybridization assay revealed that periostin mRNA was expressed in the PDL in controls stained with antisense probes. This expression appeared to be stronger in the compression sites compared with the tension sites after 3 hours of starting tooth movement. At 24 hours periostin mRNA showed the highest levels and returned to levels similar to controls after 168 hours. In vitro experiments showed that periostin mRNA expression detected by RT-PCR increased after uni-axial mechanical stress was applied for 24 hours in hPDLF cultures. We also found that periostin had an inhibitory effect on osteoclast differentiation and activation when conditioned medium from mechanically stressed hPDLF was added to human osteoclast culture system. These data was confirmed when similar results were observed in mouse unfractionated bone cell cultures treated with mouse recombinant periostin to a final concentration of 600 ng/ml. In this study, we demonstrated that periostin mRNA expression increased in the PDL during experimental tooth movement in vivo, especially in the compression sites, and was induced by uni-axial mechanical stress in vitro. Furthermore, periostin may inhibit osteoclast differentiation and activation.