Protease activation of calcium-independent phospholipase A2 leads to neutrophil recruitment to coronary artery endothelial cells

Introduction: Thrombin or tryptase cleavage of protease-activated receptors (PAR) on human coronary artery endothelial cells (HCAEC) results in activation of a membrane-associated, calcium-independent phospholipase A(2) (iPLA(2)) that selectively hydrolyzes plasmalogen phospholipids: Atherosclerotic plaque rupture results in a coronary ischemic event in which HCAEC in the ischemic area would be exposed to increased thrombin concentrations in addition to tryptase released by activated mast cells present in the plaque. Materials and methods: HCAEC were stimulated with thrombin or tryptase in the absence or presence of bromoenol lactone (BEL), a selective iPLA2 inhibitor, and iPLA2 activation, accumulation of biologically active membrane phospholipid-derived metabolites, upregulation of cell surface P-selectin expression and neutrophil adherence were measured. Results: HCAEC exposed to thrombin or tryptase stimulation demonstrated an increase in iPLA2 activity and arachidonic acid release. Additionally, stimulated HCAEC demonstrated increased platelet-activating factor (PAF).production and cell surface P-selectin expression, resulting in increased adhesion of neutrophils to HCAEC monolayers. Pretreatment with bromoenol lactone to inhibit iPLA(2), blocked membrane phospholipid-derived metabolite production, increased cell surface P-selectin expression and neutrophil adherence.