Immunohistochemical Localization of T-helper 17 Cells, IL-17, and RANKL during Root Resorption Induced by Excessive Orthodontic Force in the Mouse Model of T Cell-mediated Autoimmune Disease

Involvement of interleukins-17 and -34 in exacerbated orthodontic root resorption by jiggling force during rat experimental tooth movement

BACKGROUND

Orthodontically induced root resorption (OIRR) is considered as an undesirable and unpredictable sequel of orthodontic treatment. Recent reports demonstrated that interleukin (IL)-17/IL-34, and T cells secrete inflammatory/osteoclastogenic cytokines, which might stimulate osteoclastogenesis/bone resorption. However, little is known about the role played by IL-17/IL-34 in OIRR. The present study was aimed at investigating the odontoclastic expression pattern of IL-17 and IL-34 in resorbed cementum during different experimental tooth movements in vivo.

METHODS

Twenty-four 8-week-old male Wistar rats were divided into four groups: control group, optimal force group (10 g), heavy force group (50 g), and jiggling force group (compression and tension, repetition; 10 g). After 7, 14, and 21 days, the expression levels of IL-17 and IL-34 protein in the resorbed cementum were analyzed using immunohistochemical methods.

RESULTS

On day 21, the immunoreactivity for IL-17 and IL-34 in resorbed roots in the jiggling force group was stronger than that in the heavy force and optimal force groups. Moreover, the number of IL-17-positive and IL-34-positive odontoclasts was significantly increased in the jiggling force group compared with those in the other groups on day 21.

CONCLUSIONS

These results suggest that jiggling forces might exacerbate OIRR compared with heavy forces, as evidenced by the increased expression of IL-17 and IL-34 in odontoclasts obtained from resorbed roots.

Odontoclastogenesis of mouse papilla-derived MDPC-23 cells induced by lipopolysaccharide

AIM

To investigate the role of Lipopolysaccharide (LPS) in the odontoclast differentiation of MDPC-23 cells. It was hypothesized that MDPC-23 odontoblast-like cells may function as odontoclasts under the influence of LPS.

METHODOLOGY

MDPC-23 cells were cultured in the presence of 0.1 or 1 μg mL^-1 LPS for 6 days. Cell viability was determined using the CCK8 assay. TRAP staining, dentine resorption assay and ROS detection by confocal laser scanning microscope were used to test the odontoclast-like function of the induced cells. In additional, the related protein expression was confirmed by Western blotting and ELISA. An unpaired Student's t-test and one-way anova were used in statistical analysis.

RESULTS

TRAP-positive cells, which are multinucleated, on the dentine slice were significantly increased in 1 μg mL^-1 LPS-induced cells (P < 0.05). Osteoclast-specific proteins such as TRAP cathepsin K and Rac1 were upregulated in the 1 μg mL^-1 LPS-treated cells (P < 0.05), whilst the expression of marker proteins of the RANKL-RANK signalling pathway (RANKL, RANK and TRAF6) in the induced cells was not significantly changed (P > 0.05). ROS production was observed in the 1 μg mL^-1 LPS treatment group (P < 0.05), but no significant differences were observed in the level of RANKL in the cell supernatant between the LPS-treated group and the control group (P > 0.05).

CONCLUSIONS

A known value of 1 μg mL^-1 LPS might induce odontoblast-like MDPC-23 cells to generate odontoclast-like cells or to function as odontoclasts. The data might provide a new explanation for the precursors of odontoclasts and root resorption.