Differential expression of the S1P transporter, Spinster homologue 2 (Spns2), in airway epithelial cells and macrophages may drive defective macrophage function in COPD

Abstract

We previously established a link between impaired phagocytosis and deregulated S1P signaling in alveolar macrophages in COPD. We hypothesized that this may result from disrupted epithelial-macrophage crosstalk via Spns2-mediated intercellular S1P signaling. Alveolar macrophages and bronchial epithelial cells from COPD subjects and controls, cigarette smoke (CS)-exposed mice, and CS-exposed cell lines were studied. Spns2 expression and subcellular localization was studied by immunofluorescence, confocal microscopy and RT-PCR. Phagocytosis was assessed by flow-cytometry. Levels of intra- and extracellular S1P were measured by S1P [3H]-labeling. In both macrophage and epithelial cells, Spns2 was localized to cytoplasm and nucleus, consistent with predicted bipartile Nuclear Localization Signal at the position aa282 of the human Spns2 sequence. In alveolar macrophages from 4 current-smoker COPD patients, Spns2 expression was significantly increased compared to 7 non-smoker controls. Spns2 was also increased in both human alveolar and THP-1 macrophages exposed to CS. In contrast, a remarkable Spns2 down-regulation was noted in CS-exposed 16HBE epithelial cells (p