Disrupted epithelial/macrophage crosstalk via Spinster homologue 2-mediated S1P signaling may drive defective macrophage phagocytic function in COPD

Abstract

IntroductionWe have previously established a link between impaired phagocytic capacity and deregulated S1P signaling in alveolar macrophages from COPD subjects. We hypothesize that this defect may include a disruption of epithelial-macrophage crosstalk via Spns2-mediated intercellular S1P signaling.MethodsPrimary alveolar macrophages and bronchial epithelial cells from COPD subjects and controls, cell lines, and a mouse model of chronic cigarette smoke exposure were studied. Cells were exposed to 10% cigarette smoke extract, or vehicle control. 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.ResultsSpns2 expression was significantly increased (p<0.05) in alveolar macrophages from current-smokers/COPD patients (n = 5) compared to healthy nonsmokers (n = 8) and non-smoker lung transplant patients (n = 4). Consistent with this finding, cigarette smoke induced a significant increase in Spns2 expression in both human alveolar and THP-1 macrophages. In contrast, a remarkable Spns2 down-regulation was noted in response to cigarette smoke in 16HBE14o- cell line (p<0.001 in 3 experiments), primary nasal epithelial cells (p<0.01 in 2 experiments), and in smoke-exposed mice (p<0.001, n = 6 animals per group). Spns2 was localized to cilia in primary bronchial epithelial cells. In both macrophage and epithelial cell types, Spns2 was also found localized to cytoplasm and the nucleus, in line with a predicted bipartile Nuclear Localization Signal at the position aa282 of the human Spns2 sequence. In smoke-exposed mice, alveolar macrophage phagocytic function positively correlated with Spns2 protein expression in bronchial epithelial cells.ConclusionOur data suggest that the epithelium may be the major source for extracellular S1P in the airway and that there is a possible disruption of epithelial/macrophage cross talk via Spns2-mediated S1P signaling in COPD and in response to cigarette smoke exposure.

Functional contribution of sphingosine‐1‐phosphate to airway pathology in cigarette smoke‐exposed mice

“…Indeed, in the lungs of mice exposed for 11 months at CS exposure, there was an increased expression of Sph‐K 2 , mainly localised in the airway epithelium and pulmonary macrophages. The strong positivity found in the airway epithelium well fits with previous evidence showing epithelium as the major source for S1P in the airways (Tran et al, ). Recent clinical data also suggest a potential link between the S1P pathway and the defective macrophage phagocytic function in COPD patients (Barnawi et al, ).…”

Enhanced inflammasome activation and reduced sphingosine-1 phosphate S1P signalling in a respiratory mucoobstructive disease model

“…Consistent with our findings in the lungs of mice chronically exposed to cigarette smoke [15], the mouse model of βENaC overexpression revealed bronchiolar epithelial SPNS2 downregulation, with the notable Fig. 9 Hypothetical model of NLRP3 inflammasome activation and S1P signalling dysregulation in mucus-obstructed bronchioles.…”

“…Less is known on the alteration of S1P signalling and its role in mucoobstructive diseases. Previous studies by us and others indicated complex dysregulation of the S1P signalling system in COPD (and in response to cigarette smoke) involving several components and various cell types [14][15][16]. Large gaps in this field remain, especially whether and how individual components of the S1P signalling system are dysregulated in diseases such as CF, COPD, non-CF bronchiectasis, and whether mucus obstruction directly contributes to this dysregulation.…”

Tobacco Smoke Induces and Alters Immune Responses in the Lung Triggering Inflammation, Allergy, Asthma and Other Lung Diseases: A Mechanistic Review

“…Impaired efferocytosis by alveolar macrophages appears to be an important contributor to the exacerbated cellular inflammation not only in COPD, but also in asthma, bronchiolitis obliterans, protracted bacterial bronchitis and bronchiectasis in children [ 216 , 218 , 219 , 220 , 221 ]. Recently, considerable emphasis has been placed on the role of sphingolipid metabolites in cigarette induced-efferocytosis impairment with sphingosine 1-phosphate (S1P) signaling garnering especially great attention [ 222 , 223 , 224 , 225 ]. S1P downstream signaling pathways participate in innate and adaptive immune responses, in particular in leukocyte trafficking and differentiation.…”