Sphingosine1-phosphate Elicits Proinflammatory Responses In RPE Cells

Purpose: To investigate the effects of Sphingosine-1-phosphate （S1P）on the production of inflammatory mediators and the signaling pathwaysinvolved in S1P mediated production of cytokines by ARPE-19cells.Methods: Expression of S1P receptors was examined using RT-PCRand real time PCR. ARPE-19cells were stimulated with S1P or TNF-α, andby coculturing with S1P in the presence or absence of pertussis toxin （PTX）or a series of kinase inhibitors. The induction of inflammatory cytokinesproduction was determined by ELISA. Western blot analysis was used todetect the activation of signaling mediators and S1P3receptor.Results: ARPE-19cells express all the known receptors for S1P.Moreover, exogenously applied S1P induces ARPE-19cell secretion ofinterleukin-8（IL-8） in a dose-and time-dependent manner, but not IL-6and monocyte chemotactic protein-1（MCP-1）. S1P-mediated IL-8secretion is regulated by PTX, ERK1/2and p38mitogen-activated proteinkinase （MAPK）. Interestingly, treatment of ARPE-19cells with tumornecrosis factor-α （TNF-α） increases S1P₃expression and correlates with theenhancement of S1P-induced IL-8and IL-6production. Conclusions: This study demonstrates that S1P significantlypromoted ARPE-19cells to secrete inflammatory mediators. ERk1/2, p38MAPK and Gi-dependent pathways are important signaling components inS1P-mediated IL-8secretion by ARPE-19cells. Moreover, these resultsprovide evidence that S1P stimulation of RPE cells may play a role inregulating leukocyte function during ocular inflammation.