Interleukin‐12 Induces Receptor Activator of Nuclear Factor‐Kappa B Ligand Expression by Human Periodontal Ligament Cells

Background: Increased level of proinflammatory cytokine interleukin (IL)‐12 correlates with the severity of periodontitis. Yet, a possible role of IL‐12 in periodontal disease has not been clarified. The aim of this study is to investigate whether IL‐12 affects expression of receptor activator of nuclear factor‐kappa B (NF‐κB) ligand (RANKL), a potent osteoclast‐stimulating factor, by human periodontal ligament (hPDL) cells. Methods: To determine the effect of IL‐12, hPDL cells were incubated with recombinant human IL‐12 (p70) in a dose‐ (0 to 10 ng/mL) and time‐dependent manner. Expression of RANKL was evaluated at mRNA and protein levels. Underlying signaling pathways of IL‐12 were determined by using specific inhibitors. Results: Under the influence of IL‐12, hPDL cells expressed significantly higher levels of RANKL. Expression was mediated by signal transducer and activator of transcription 4 and NF‐κB signaling pathways. Conditioned medium of IL‐12–incubated cells proved to contain molecule(s) that induced RANKL expression. Addition of suramin (G protein–coupled receptor inhibitor) and ethylene glycol tetraacetic acid (calcium chelator) suggested existence of intermediate molecule(s) that could activate heterotrimeric G protein signaling in a calcium‐dependent pathway. Conclusions: Expression of RANKL by hPDL cells significantly increased after IL‐12 treatment. Therefore, this study supports a close interrelationship between immune and skeletal systems and suggests an osteolytic role of IL‐12 in pathogenesis of periodontal disease.