NELL1 Growth Factor Suppresses the NF-κB Signaling Pathway During Orthodontic Tooth Movement and Attenuates the Inflammatory Response

Abstract

Background: Exogenous Nel-like molecule type 1 (NELL1) is a viable alternative in orthodontics and other fields due to its osteogenic and angiogenic properties. This study aimed to elucidate the role of NELL1 in the inflammatory response elicited by orthodontic tooth movement (OTM), providing insights into the mechanisms behind this response and establishing a theoretical foundation for the utilizing NELL1 as a therapeutic option. Methods: Human periodontal ligament (hPDL) cells obtained from clinical samples were divided into three groups: control, compressive forces (CF), and CF+ NELL1. Inflammatory factors (cyclooxygenase 2 (COX2), interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS) and interleukin-1β (IL-1β)) were measured using real-time quantitative PCR (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA). Culture supernatants were co-cultured with THP-1 cells to assess macrophage differentiation. Immunoblotting and Co-Immunoprecipitation (Co-IP) assays were employed to investigate the molecular mechanism of NELL1 in hPDL cells. Results: In comparison to the CF group, the CF+ NELL1 group exhibited reduced mRNA levels and production of inflammatory factors, including COX2, IL-6, IL-8, TNF-α, iNOS, and IL-1β (p < 0.05, p < 0.01, p < 0.001, and p < 0.0001) and reduced macrophage activation (p < 0.05). Immunoblotting assays showed that NELL1 could inhibit the activation of the nuclear factor-kappa B (NF-κB) signaling pathway, consequently regulating the expression of inflammatory factors (p < 0.0001, p < 0.05, p < 0.05, and p < 0.01). Co-Immunoprecipitation (Co-IP) results confirmed the intermolecular interaction between NELL1 and inhibitor of kappa B kinase (IKK), and overexpression of IKK in hPDL cells could reduce the anti-inflammatory effect of NELL1 following CF treatment (p < 0.01, p < 0.001, and p < 0.0001). Conclusions: NELL1 presents a promising therapeutic option to inhibit the activation of the NF-κB signaling pathway by preventing phosphorylation and reducing the inflammatory response during the orthodontic tooth movement.