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


METHODS
We 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.


RESULTS
We 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.


CONCLUSIONS
Our results suggest a potential link between the S1P signalling system and defective macrophage phagocytic function in COPD and advise therapeutic targets.
Lung Research, Hanson Institute, Adelaide, Australia; Dept of Medicine, University of Adelaide, Adelaide, Australia; Dept Medical Laboratory Technology, University of Tabuk, Tabuk, Saudi Arabia.
Jameel
J
Barnawi
Lung Research, Hanson Institute, Adelaide, Australia.
Hai
H
Tran
Lung Research, Hanson Institute, Adelaide, Australia; Dept of Medicine, University of Adelaide, Adelaide, Australia.
Hubertus
H
Jersmann
Dept of Medicine, University of Adelaide, Adelaide, Australia; Centre for Cancer Biology, University of South Australia, Adelaide, Australia and SA Pathology, Adelaide, Australia.
Stuart
S
Pitson
Lung Research, Hanson Institute, Adelaide, Australia.
Eugene
E
Roscioli
Lung Research, Hanson Institute, Adelaide, Australia; Dept of Medicine, University of Adelaide, Adelaide, Australia.
Greg
G
Hodge
Department of Clinical Pharmacology, Flinders University, Adelaide, Australia.
Robyn
R
Meech
Centre for Neuroscience, Anatomy & Histology, Flinders University, Adelaide, Australia.
Rainer
R
Haberberger
Lung Research, Hanson Institute, Adelaide, Australia; Dept of Medicine, University of Adelaide, Adelaide, Australia.
Sandra
S
Hodge
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008246:Lysophospholipids / Q000235:genetics / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D010587:Phagocytosis / Q000502:physiology*; D010744:Phosphoric Monoester Hydrolases / Q000235:genetics / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism*; D029424:Pulmonary Disease, Chronic Obstructive / Q000235:genetics / Q000378:metabolism*; D049349:Receptors, Lysosphingolipid / Q000235:genetics / Q000378:metabolism*; D012907:Smoking / Q000235:genetics / Q000378:metabolism*; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000235:genetics / Q000378:metabolism; D000099157:Sphingosine Kinase
D008246:Lysophospholipids; D008565:Membrane Proteins; D010744:Phosphoric Monoester Hydrolases; D017853:Phosphotransferases (Alcohol Group Acceptor); D049349:Receptors, Lysosphingolipid; D013110:Sphingosine; D000099157:Sphingosine Kinase; C060506:sphingosine 1-phosphate; C498527:SGPP1 protein, human