Potential Link between the Sphingosine-1-Phosphate (S1P) System and Defective Alveolar Macrophage Phagocytic Function in Chronic Obstructive Pulmonary Disease (COPD)

Abstract

IntroductionWe previously reported that alveolar macrophages from patients with chronic obstructive pulmonary disease (COPD) are defective in their ability to phagocytose apoptotic cells, with a similar defect in response to cigarette smoke. The exact mechanisms for this defect are unknown. Sphingolipids including ceramide, sphingosine and sphingosine-1-phosphate (S1P) are involved in diverse cellular processes and we hypothesised that a comprehensive analysis of this system in alveolar macrophages in COPD may help to delineate the reasons for defective phagocytic function.MethodsWe compared mRNA expression of sphingosine kinases (SPHK1/2), S1P receptors (S1PR1-5) and S1P-degrading enzymes (SGPP1, SGPP2, SGPL1) in bronchoalveolar lavage-derived alveolar macrophages from 10 healthy controls, 7 healthy smokers and 20 COPD patients (10 current- and 10 ex-smokers) using Real-Time PCR. Phagocytosis of apoptotic cells was investigated using flow cytometry. Functional associations were assessed between sphingosine signalling system components and alveolar macrophage phagocytic ability in COPD. To elucidate functional effects of increased S1PR5 on macrophage phagocytic ability, we performed the phagocytosis assay in the presence of varying concentrations of suramin, an antagonist of S1PR3 and S1PR5. The effects of cigarette smoking on the S1P system were investigated using a THP-1 macrophage cell line model.ResultsWe found significant increases in SPHK1/2 (3.4- and 2.1-fold increases respectively), S1PR2 and 5 (4.3- and 14.6-fold increases respectively), and SGPL1 (4.5-fold increase) in COPD vs. controls. S1PR5 and SGPL1 expression was unaffected by smoking status, suggesting a COPD “disease effect” rather than smoke effect per se. Significant associations were noted between S1PR5 and both lung function and phagocytosis. Cigarette smoke extract significantly increased mRNA expression of SPHK1, SPHK2, S1PR2 and S1PR5 by THP-1 macrophages, confirming the results in patient-derived macrophages. Antagonising SIPR5 significantly improved phagocytosis.ConclusionOur results suggest a potential link between the S1P signalling system and defective macrophage phagocytic function in COPD and advise therapeutic targets.

Targeting sphingosine-1-phosphate signaling in lung diseases

“…Further, significant associations were noted between S1P 5 and both lung function and phagocytosis. Cigarette smoke extract significantly increased mRNA expression of SphK1, SphK2, S1P 2 , and S1P 5 in THP-1 macrophages, confirming the results from patient-derived macrophages, and antagonizing SIP 5 significantly improved phagocytosis of the macrophages (Barnawi et al, 2015). …”

“…S1PR profiling in the lungs of COPD patients showed significant down regulation S1P 5 , which could be a possible target for COPD pharmacotherapy (Cordts et al, 2011). A potential link between S1P 5 and S1P metabolizing enzymes and defective alveolar macrophage function in COPD has been reported (Barnawi et al, 2015). A significant increase in mRNA levels of SphK1/2, S1P 2 , and S1PL in alveolar macrophages from COPD patients compared to control subjects was observed while S1P 5 and SGPL1 expression was unaffected by smoking status, suggesting a COPD “disease effect” rather than smoke effect per se (Barnawi et al, 2015).…”

“…A potential link between S1P 5 and S1P metabolizing enzymes and defective alveolar macrophage function in COPD has been reported (Barnawi et al, 2015). A significant increase in mRNA levels of SphK1/2, S1P 2 , and S1PL in alveolar macrophages from COPD patients compared to control subjects was observed while S1P 5 and SGPL1 expression was unaffected by smoking status, suggesting a COPD “disease effect” rather than smoke effect per se (Barnawi et al, 2015). Further, significant associations were noted between S1P 5 and both lung function and phagocytosis.…”

Reduced DNA methylation of sphingosine‐1 phosphate receptor 5 in alveolar macrophages in COPD: A potential link to failed efferocytosis

“…The sphingolipid signalling pathway involving sphingosine kinase (SPHK) and its product sphingosine‐1 phosphate (S1P) is required for effective macrophage function by promoting maturation and phagocytosis . Recently, we identified dysregulation of the S1P signalling system as a potential cause of defective efferocytosis in alveolar macrophages in COPD . Relative mRNA expression levels of several S1P system genes were increased in alveolar macrophages from COPD patients, as well as in current smokers compared with healthy non‐smokers.…”

“…Relative mRNA expression levels of several S1P system genes were increased in alveolar macrophages from COPD patients, as well as in current smokers compared with healthy non‐smokers. In particular, sphingosine‐1 phosphate receptor 5 (S1PR5) expression levels were significantly increased in alveolar macrophages of COPD patients independent of smoking status . These findings suggested a possible link between COPD and S1PR5 function.…”