Base-modified UDP-sugars reduce cell surface levels of P-selectin glycoprotein 1 (PSGL-1) on IL-1β-stimulated human monocytes

Abstract

P-selectin glycoprotein ligand-1 (PSGL-1, CD162) is a cell-surface glycoprotein that is expressed, either constitutively or inducibly, on all myeloid and lymphoid cell lineages. PSGL-1 is implicated in cell–cell interactions between platelets, leukocytes and endothelial cells, and a key mediator of inflammatory cell recruitment and transmigration into tissues. Here, we have investigated the effects of the β-1,4-galactosyltransferase inhibitor 5-(5-formylthien-2-yl) UDP-Gal (5-FT UDP-Gal, compound 1) and two close derivatives on the cell surface levels of PSGL-1 on human peripheral blood mononuclear cells (hPBMCs). PSGL-1 levels were studied both under basal conditions, and upon stimulation of hPBMCs with interleukin-1β (IL-1β). Between 1 and 24 hours after IL-1β stimulation, we observed initial PSGL-1 shedding, followed by an increase in PSGL-1 levels on the cell surface, with a maximal window between IL-1β-induced and basal levels after 72 h. All three inhibitors reduce PSGL-1 levels on IL-1β-stimulated cells in a concentration-dependent manner, but show no such effect in resting cells. Compound 1 also affects the cell surface levels of adhesion molecule CD11b in IL-1β-stimulated hPBMCs, but not of glycoproteins CD14 and CCR2. This activity profile may be linked to the inhibition of global Sialyl Lewis presentation on hPBMCs by compound 1, which we have also observed. Although this mechanistic explanation remains hypothetical at present, our results show, for the first time, that small molecules can discriminate between IL-1β-induced and basal levels of cell surface PSGL-1. These findings open new avenues for intervention with PSGL-1 presentation on the cell surface of primed hPBMCs and may have implications for anti-inflammatory drug development.

Platelet–Eosinophil Interactions As a Potential Therapeutic Target in Allergic Inflammation and Asthma

“…Selectins are difficult structures to create effective small molecule antagonists against. Consequently, several drugs that inhibit the synthesis of PSGL-1 and therefore have the potential to suppress P-selectin-dependent eosinophil recruitment are being examined ( 98 ). These compounds have been reported to inhibit the synthesis of PSGL-1 under inflammatory conditions, rather than affecting expression at resting state, and might therefore provide an important safety benefit of not affecting the necessary immunosurveillance of the host ( 98 ).…”

“…Consequently, several drugs that inhibit the synthesis of PSGL-1 and therefore have the potential to suppress P-selectin-dependent eosinophil recruitment are being examined ( 98 ). These compounds have been reported to inhibit the synthesis of PSGL-1 under inflammatory conditions, rather than affecting expression at resting state, and might therefore provide an important safety benefit of not affecting the necessary immunosurveillance of the host ( 98 ). Heparin is known to inhibit P-selectin-dependent events, and a non-anticoagulant form of heparin ( N -acetyl-de- O -sulfated-heparin), has recently been reported to disrupt platelet-dependent eosinophil recruitment in animal models ( 93 ).…”

A Peptide Analogue of Selectin Ligands Attenuated Atherosclerosis by Inhibiting Monocyte Activation

“…Thus, an alternative approach is to reduce the cell surface of functional PSGL-1, in particular sLeX. To date, attempts to inhibit the biosynthesis of sLeX have been accomplished by interfering with functional glycosylation sites of sLeX to inhibit galactosylation [34], sialylation [35], and fucosylation [36]. IELLQAR, a peptide analogue of selectin ligands, potently blocks binding to the natural selectin ligand sLeX with substantially high affinity, with an IC 50 value of 10 −5 M [13].…”

The Role of Platelets in Allergic Inflammation and Asthma

“…A recent study reported that platelet aggregation was inhibited by the eosinophil cationic protein (ECP) and eosinophil supernatant [55]. The role of eosinophils in platelet aggregation and thrombosis is not yet clear [56]. Certainly there is a therapeutic potential in disrupting eosinophil-platelet interactions in asthmatic patients inhibiting platelet activation and release of platelet cytokines or platelet interaction with other inflammatory cells such as eosinophils.…”