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.