Sphingosine 1-phosphate receptor 3 is highly upregulated on human neutrophils upon migration to the airways

Objective Migration of polymorphonuclear neutrophils (PMNs) from blood into the airway lumen is accompanied by changes in surface receptors and responsiveness to environmental cues, such as sphingolipids. In particular, signaling via extracellular ceramide/sphingosine 1 phosphate (S1P) was suggested to contribute to human airway disease, such as cystic fibrosis (CF). We hypothesized that airway PMNs would alter expression of the S1P receptor, S1PR3, which was recently implicated in lung inflammation and fibrosis. Methods We collected blood and sputum from healthy control (HC) and CF subjects and analyzed S1PR3 expression in live PMNs gated by flow cytometry. In addition, we used a novel in vitro model to study the effect of transepithelial migration of blood PMNs on S1PR3 expression. Results We observed a 10-fold upregulation of surface S1PR3 expression on HC and CF airway PMNs, in vivo, compared to their blood counterparts. This major increase was recapitulated in vitro, when naive blood PMNs were induced to transmigrate through an airway epithelial layer upon exposure to apical CF airway fluid. S1PR3 expression increased over time, by 10-fold after 10 hours, and up to 20-fold at 18 hours. Conclusion Modulation of S1PR3 expression follows PMN migration to both HC and CF airways. Further studies will determine the importance of this receptor in mediating responses to ceramide/S1P signaling in these cells, including PMN migration, apoptosis and activation.