Aim: To investigate the involvement of the phosphatidylinositol-3-kinase (PI3K) in interleukin-6 (IL-6) and interleukin-8 (IL-8) gene expression in odontoblast-like cells when exposed to heat-killed Streptococcus mutans.
Methodology: Cultured human odontoblast-like cells (Dulbecco's modified Eagle's medium) were pre-treated with a specific inhibitor for PI3K (LY 294002) and subsequently stimulated with heat-killed S. mutans for 6 and 24 h. After stimulation, RNA was extracted from the cells and cDNA synthesis was performed. Gene expression of IL-6 and IL-8 was analysed by real-time polymerase chain reaction and normalized to the gene expression of beta-actin. Cell survival was determined for stimulation experiments.
Results: The gene expression of IL-6 and IL-8 was significantly increased in response to heat-killed S. mutans (P = 0.002 and P < 0.001, respectively). After 6 h, the mRNA expression of IL-6 and IL-8 was significantly higher than after 24 h of stimulation (P = 0.019 and P < 0.001, respectively). Pre-treatment with the inhibitor LY 294002 blocked the induced gene expression of IL-6 and IL-8 (P = 0.002 and P < 0.001, respectively). No differences in viable cell counts were found after stimulation with heat-killed S. mutans and/or pre-treatment with LY 294002 compared with the unstimulated control.
Conclusion: Gene expression of IL-6 and IL-8 was induced by heat-killed S. mutans via signalling pathways mediated by PI3K. These findings indicate that odontoblasts respond to cariogenic bacteria with increased gene expression of pro-inflammatory mediators and hence participate in immune processes.