The upregulation of receptor activator NF-κB ligand expression by interleukin-1α and Porphyromonas endodontalis in human osteoblastic cells

To investigate the receptor activator of nuclear factor-kappa B (NF-kappa B) ligand (RANKL) in osteoblastic cells stimulated with inflammatory mediators. The expression of RANKL in human osteoblastic cell line U2OS stimulated by pro-inflammatory cytokine interleukin (IL)-1 alpha and black-pigmented bacteria Porphyromonas endodontalis was investigated by Western blot and enzyme-linked immunosorbent assay (ELISA). The significance of the results obtained from control and treated groups was statistically analysed by the paired Student's t-test. IL-1 alpha was found to upregulate RANKL production in U2OS cells (P < 0.05). Investigations of the time dependence of RANKL expression in IL-1 alpha-treated cells revealed a rapid accumulation of RANKL protein after 1 h of exposure; it remained elevated throughout the 24-h incubation period shown by Western blot and ELISA. In addition, P. endodontalis also increased RANKL expression in U2OS cells after 4-h incubation period demonstrated by Western blot and ELISA (P < 0.05). IL-1 alpha and P. endodontalis may be involved in developing apical periodontitis through the stimulation of RANKL production.