Signaling mechanisms of PGF2alpha-induced Interleukin-8 Production in dental pulp cells

Objectives: PGF2alpha and interleukin-1beta (IL-1beta) levels are elevated in inflamed dental pulp tissues. The roles of PGF2alpha and IL-1beta in the pathogenesis of pulpal inflammation await investigation. Methods: Primary human dental pulp cells were exposed to IL-1beta or PGF2alpha. PGF2alpha and IL-8 levels in the culture medium were determined by enzyme linked immunosorbant assay (ELISA). Prostaglandin FP receptor and IL-8 mRNA expression was evaluated by reverse transcriptase polymerase chain reaction. Protein levels and the phosphorylation of extracellular regulated protein kinase (ERK) and cAMP response-element-binding protein (CREB) in dental pulp cells was detected by western blotting. Results: IL-1beta stimulated PGF2alpha production of pulp cells. IL-1beta and PGF2alpha (0.5-10 uM) also induced IL-8 production and mRNA expression in pulp cells. Aspirin inhibited the IL-1beta-induced PGF2alpha production, but not the IL-8 production. Dental pulp cells expressed FP receptor and exposure of pulp cells to PGF2alpha stimulated the phosphorylation of ERK1/ERK2 and CREB within 60 min of exposure. PGF2alpha-induced IL-8 production can be inhibited by U0126 (1 and 10 uM, a MEK inhibitor), whereas SQ22536 (100 and 250 uM, an adenylate cyclase inhibitor) and U73122 (an inhibitor of phospholipase C - PLC) enhanced IL-8 production. Conclusion: These results indicate that IL-1beta-induced IL-8 production in dental pulp cells is not via direct activation of cyclooxygenase and PGF2alpha generation. PGF2alpha-induced IL-8 production is possibly mediated by FP receptor activation and MEK/ERK/CREB signaling, but not adenylate cyclase and PLC activation. IL-1beta and PGF2alpha are important in the pathogenesis of pulpal inflammation via induction of IL-8 production. (This study is supported by a grant from National Science Council, Taiwan)