Lymphocyte-derived microparticles stimulate osteoclastogenesis by inducing RANKL in fibroblasts of odontogenic keratocysts

Abstract

Leukocyte-derived microparticles (LMPs) include neutrophil-, lymphocyte-and monocyte-derived MPs. LMPs act as proinflammatory mediators in autoimmune diseases, infectious diseases and vascular diseases. The present study examined the hypothesis that the percentage of LMPs was increased in patients with inflamed odontogenic keratocysts (OKCs), and investigated the biological effects of Jurkat cell-derived MPs on the fibroblasts of OKCs in vitro. Cyst fluid MPs, obtained by centrifugation of samples from 20 patients with inflamed OKCs, 3 patients with uninflamed OKCs, 15 patients with radicular cysts (RCs) and 12 patients with inflamed dentigerous cysts (DCs), were analyzed by transmission electron microscopy, dynamic light scattering and immunofluorescence staining. The percentages and concentrations of cyst fluid LMPs were further determined by flow cytometry. The cytokine levels of apoptotic Jurkat cell-derived MPs and Jurkat cell supernatants were compared by cytokine antibody arrays. Fibroblasts were isolated from 3 patients with OKC and co.cultured with apoptotic Jurkat cell.derived MPs with or without interleukin (IL)-15Rα to detect the levels of matrix metallopeptidase 9 (MMP.9) and receptor activator of nuclear factor-κB ligand (RANKL) by reverse transcription.quantitative polymerase chain reaction and enzyme-linked immunosorbent assay. The supernatant from Jurkat MPs-treated fibroblasts was collected to make conditioned medium in which the osteoclastogenesis of Raw264.7 cells was determined. Antibodies against human soluble (s)RANKL were added to the conditioned medium to investigate the inhibitory effects. Mean percentages of lymphocyte. and neutrophil-derived MPs were significantly higher in inflamed OKCs than in DCs. Significant elevations in IL-15 were detected in apoptotic Jurkat cell-derived MPs compared with that in Jurkat cell supernatant. Furthermore, higher levels of MMP-9 and RANKL were detected in Jurkat cell MP-treated OKC fibroblasts, and this was partially blocked by IL-15Rα. Increased osteoclast-like cell formation was observed in the Jurkat MPs-treated fibroblast supernatant and Raw264.7 co-culture groups. The anti-human sRANKL antibody in the Jurkat MPs-treated fibroblast supernatant group decreased the osteoclastogenesis of the Raw264.7 cells. These results indicate that LMPs serve as novel communication tools that contribute toward the bone resorption of inflamed OKCs by inducing RANKL of OKC fibroblasts via IL-15.