Hydrostatic Pressure Up-regulate IL-6 Expression Via P2Y6 Receptor In HDPCs

During pulpal inflammation, an increase of intrapulpal hydrostatic pressure (HP) has been reported. However, the role of HP on human dental pulp cells (HDPCs) with special reference to inflammatory cytokines production has not been elucidated. Objectives: In this study, we examined the effect of simulated HP on interleukin-6 (IL-6) expression in cultured HDPCs. Methods: The cells were subjected to various HP (0-1.4 g/cm2) for 16 h. The cell viability was observed by MTT and the production of IL-6 was examined by RT-PCR and ELISA. Results: HP up-regulated IL-6 at both mRNA and protein levels in a time and dose-dependent manner. In addition, the conditioned medium collected from the culture after application of HP for 2 h could induce IL-6 expression. The induction of IL-6 either by HP and conditioned medium was significantly inhibited by suramin, an antagonist for the non-specific purineric receptor family, suggesting the role of nucleotides in the HP-induced IL-6 expression in HDPCs. We next confirmed by using specific antagonist for P2Y receptor. The results showed that HP-induced IL-6 was inhibited by using MRS2578 (specific P2Y6 receptor antagonist) and P2Y6R small interfering RNA, whereas MRS2179 (specific P2Y1 receptor antagonist) had no effect. Finally, we demonstrated that UDP, a selective agonist of P2Y6 receptor, could up-regulate IL-6 expression in HDPCs. Conclusion: These results indicate that HP could induce IL-6 expression through P2Y6 receptor in HDPCs, which provide the new insight into the role of pressure on cytokine release during pulpal inflammation.