Effects of Enterococcus faecalis lipoteichoic acid on receptor activator of nuclear factor‐κB ligand and osteoprotegerin expression in periodontal ligament fibroblasts

Abstract

To investigate the influence of Enterococcus faecalis lipoteichoic acid (LTA) on the key bone resorption-regulating proteins, receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) in human periodontal ligament fibroblasts (PDL cells). Periodontal ligament cells were subjected to various concentrations of LTA. Cell viability was then determined by methyl thiazolyl tetrazolium (MTT) assay, whilst the expression levels of RANKL and OPG were investigated by enzyme-linked immunosorbent assay (ELISA) and Western blotting. The effect of the inhibitors [IL-1 receptor-associated kinase (IRAK)-1/4, p38 mitogen-activated protein kinase (MAPK) (SB203580)] on LTA-stimulated RANKL/OPG activation was examined. Cell viability and RANKL/OPG ratio in PDL cells were also analysed by MTT assay and Western blotting. Data were analysed using one-way anova or t-test at a significance level of P = 0.05. Cell viability was reduced significantly in the LTA group in a dose-dependent fashion (P < 0.05). In addition, LTA was found to upregulate the protein expression of RANKL, OPG and their relative ratio in PDL cells (P < 0.05). The optimal concentration of LTA used in PDL cells was determined to be 10 μg mL(-1) . Following IRAK1/4 and p38MAPK inhibition, LTA-stimulated increases of RANKL/OPG ratio were significantly reduced (P < 0.05). Enterococcus faecalis LTA could upregulate the expression of RANKL and OPG at different rates, suggesting a potential role for LTA in the bone resorption process of refractory apical periodontitis through the regulation of RANKL and OPG. In addition, IRAK1/4 and p38MAPK signalling involving RANKL/OPG may contribute to inflammatory responses from PDL cells.