Dynamic adhesion of eryptotic erythrocytes to endothelial cells via CXCL16/SR-PSOX

Suicidal death of erythrocytes, or eryptosis, is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine exposure at the cell surface. Eryptosis is triggered by increase of cytosolic Ca2+ activity, which may result from treatment with the Ca2+ ionophore ionomycin or from energy depletion by removal of glucose. The present study tested the hypothesis that phosphatidylserine exposure at the erythrocyte surface fosters adherence to endothelial cells of the vascular wall under flow conditions at arterial shear rates and that binding of eryptotic cells to endothelial cells is mediated by the transmembrane CXC chemokine ligand 16 (CXCL16). To this end, human erythrocytes were exposed to energy depletion (for 48 h) or treated with the Ca2+ ionophore ionomycin (1 μM for 30 min). Phosphatidylserine exposure was quantified utilizing annexin-V binding, cell volume was estimated from forward scatter in FACS analysis, and erythrocyte adhesion to human vascular endothelial cells (HUVEC) was determined in a flow chamber model. As a result, both, ionomycin and glucose depletion, triggered eryptosis and enhanced the percentage of erythrocytes adhering to HUVEC under flow conditions at arterial shear rates. The adhesion was significantly blunted in the presence of erythrocyte phosphatidylserine-coating annexin-V (5 μl/ml), of a neutralizing antibody against endothelial CXCL16 (4 μg/ml), and following silencing of endothelial CXCL16 with small interfering RNA. The present observations demonstrate that eryptotic erythrocytes adhere to endothelial cells of the vascular wall in part by interaction of phosphatidylserine exposed at the erythrocyte surface with endothelial CXCL16.