Increased expression of sphingosine-1-phosphate and S1PR2 are associated with attenuated macrophage phagocytosis in COPD

Sphingosine-1-phosphate (S1P) is a lipid mediator that may alter macrophage polarisation and function. S1P is synthesised by SPHK1 and SPHK2 and acts via S1P receptors. Its role in COPD is unclear and so this study examined S1P levels in induced sputum and its role using monocyte-derived macrophages (MDM). Induced sputum was collected from non-smokers (NS), smokers (S) and COPD patients. MDM were generated from monocytes. S1P was measured by ELISA and gene expression of SPHK1-2 and S1PR1-5 measured by qPCR and Western blotting. MDM phagocytosis of Haemophilus influenzae (HI) or Streptococcus pneumoniae (SP) was assessed by fluorimetry. S1P was elevated in induced sputum from COPD patients compared with NS (NS 6.2±2μM; S 11.1±2μM; COPD 15.4±3μM; n=8-9, p<0.05). There was no difference in expression of SPHK1 or SPHK2 between the groups (Table 1). However, expression of only one receptor (S1PR2) was significantly increased in COPD MDM (Table 1). Inhibition of SPHK increased phagocytosis of HI and SP by COPD MDM (138±11% and 122±4% respectively) as did a selective S1PR2 antagonist, JTE-013 (144±7% and 137±7% respectively). Exogenous addition of S1P suppressed phagocytosis of HI by NS MDM by 19±7%. These data suggest that S1P may suppress phagocytosis and inhibition of synthesis or blockade of S1PR2 might improve bacterial clearance in COPD. Enzyme and S1P receptor gene expression levels. NS n=13 S n=12 COPD n=23 SPHK1 1172±426 2253±854 1317±445 SPHK2 352±88 51±122 2808±1155 S1PR1 16±12 51±19 56±40 S1PR2 526±118 1463±268* 1545±320* S1PR3 86±69 21±15 216±180 S1PR4 251±83 186±48 393±80 S1PR5 1±0 3±2 6±2 Table 1: Data are mean±SEM of % ratio gene:HPRT1; *p<0.05