Melatonin inhibits orthodontically induced root resorption through YAP/P65/IL-6 signaling pathway

Background: To explore the effects and mechanisms of melatonin on orthodontically induced root resorption (OIIRR) by focusing its role on IL-6 secretion in human periodontal ligament cells (hPDLCs).

Methods: Cytokine array was used to identify the key inflammatory cytokine secreted by hPDLCs under excessive compressive force. Western blot analysis and immunohistochemistry staining (IHC) were conducted to examine the key proteins in the YAP/P65/IL-6 signaling pathway both in in vitro and in vivo experiments. Verteporfin, a YAP Inhibitor, was used to confirm the involvement of p-YAP and its downstream signaling factor p-P65. Root resorption volume was assessed using micro-computed tomography (micro-CT).

Results: Cytokine array revealed that excessive compressive force significantly elevated interleukin-6 (IL-6) levels in hPDLCs. IHC indicated that both IL-6 and Melatonin Receptor 1 (MT1) were highly expressed in hPDLCs on the compressive side in the mouse OIIRR model. in vitro experiments demonstrated that the levels of p-YAP and p-P65 significantly increased when compressive force was applied to hPDLCs, and melatonin reversed this effect. Furthermore, Verteporfin produced effects similar to melatonin on IL-6 expression and the YAP/P65 signaling pathway. Micro-CT analysis showed noticeable root resorption in the mouse OIIRR model, which was significantly reduced following intraperitoneal injection of melatonin. IHC staining further confirmed that the YAP/P65/IL-6 signaling pathway was inhibited on the compressive side of the mouse OIIRR model after melatonin injection.

Conclusions: Melatonin was able to inhibit root resorption in the mouse OIIRR model and reduced IL-6 secretion in hPDLCs under compressive force by suppressing the YAP/P65 signaling pathway.

Plain language summary: This study explored how melatonin, a natural hormone, protects against root resorption during orthodontic treatment. Specifically, we focused on how excessive compressive force induces IL-6 production and root resorption in both in vitro and in vivo experiments. in vitro, we found that applying compressive force to hPDLCs increased the release of IL-6, a molecule that promotes inflammation and bone resorption. Melatonin, however, reduced IL-6 levels by blocking the YAP/P65 signaling pathway. In vivo, we developed a mouse model of orthodontically induced root resorption, in which melatonin was injected intraperitoneally. Results showed that melatonin reduced root resorption and decreased IL-6 secretion in the periodontal tissues. Additionally, proteins of the YAP/P65 signaling pathway and the RANKL/OPG system were involved in vivo. Our findings suggest that melatonin could be a promising preventive approach to protect against root resorption during orthodontic treatment.

IL‐6; YAP; compressive force; inflammatory response; melatonin; periodontal ligament cells; root resorption.