Effects of IL-17 and the expression of RANKL and OPG on orthodontic tooth resorption

Abstract

Objective The objectives of this study were (1) to investigate the expressions of interleukin (IL)-17 and receptor activator for nuclear factor-κB ligand(RANKL)in root resorption areas during experimental tooth movement in rats, and (2)to investigate the effect of IL-17 on the expressions of RANKL and osteoprotegerin (OPG) in human periodontal ligament fibroblasts. Methods Male SD rats were subjected to an orthodontic force of 60 g to induce a mesially tipping movement of the maxillary first molars for 1, 3 and 5 days, with 3 rats in force group and 2 rats in control group at each time point. The morphology changes in periodontal tissues were analyzed and the expression levels of interleukin (IL)-17, RANKL were determined by immunohistochemical analysis. Furthermore, human periodontal ligament fibroblasts cell line were cultured and were treated with IL-17 (20 ng/ml) with different time(0、12、24、48、72 h) in vitro, and then the expression of RANKL and OPG were respectively detected. Results In the force group, hematoxylin-eosin staining showed that there were alveolar bone absorption, root resorption and compression of periodontal ligament in the pressure side. IL-17 and RANKL were detected in the pressure area. The expression of IL-17 and RANKL were hightest at 5 d. Moreover, the expressions of RANKL were significantly up-regulated by IL-17 in vitro. It reached its peak value at 48 h(P<0.05). However IL-17 negatively regulated OPG in HPDLF. The expressions of mRNA of OPG decreased in time-dependent manner. And its protein level was minimum at 48 h(P<0.05). Conclusions IL-17 may be involved in the process of orthodontically induced inflammatory root resorption by up-regulated RANKL expression and inhibit OPG expression. Key words: interleukin-17; RANKL; OPG; orthodontically induced inflammatory root resorption