MicroRNA 21 and PLAP-1 regulate periodontal ligament remodeling during tooth movement of rats

Periodontal ligament associated protein-1 (PLAP-1), a newly discovered extracellular matrix protein in periodontal ligament (PDL), plays a unique biological role in periodontal ligament mineralization. MicroRNA 21 (miR-21) is one of the endogenous small noncoding RNAs which is involved in osteogenic differentiation of PDLCs by targeting PLAP-1 in vitro. Our study was to investigate the specific expression and function of PLAP-1 and miR-21 in PDL during orthodontic tooth movement and attempt to study on whether miR-21 modulated PDL remodeling by targeting PLAP-1 in vivo. We detected the expression of PLAP-1 and miR-21 in rat PDL during experimental tooth movement by in situ hybridization and immunohistochemical staining. The results showed that both PLAP-1 and miR-21 specifically expressed in PDL. The expression of PLAP-1 on the pressure side increased to the peak in 7 days (7d-) group and decreased in 14d-and 21d-groups, while its expression on tension side decreased in 3d- and 5d-groups and increased later. MiR-21 expression on both pressure side and tension side exhibited a trend of increasing firstly and decreasing later. But the peak of expression appeared at different time on the two sides (7 days for pressure side and 3 days for tension side). Our study suggests that both miR-21 and PLAP-1 were involved in the reconstruction of periodontal tissue under the orthodontic force in rats. MiR-21 probably targeted PLAP-1 to implicate in the periodontal bone remodeling in the late period of tooth movement on tension side.