Protease activation of calcium-independent phospholipase A2 leads to neutrophil recruitment to coronary artery endothelial cells.
BACKGROUND
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 A2 (iPLA2) 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.


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 iPLA2, blocked membrane phospholipid-derived metabolite production, increased cell surface P-selectin expression and neutrophil adherence.


CONCLUSIONS
The similar biochemical and cellular responses in HCAEC exposed to thrombin or tryptase stimulation suggest that the cleavage of two separate PAR serve to extend the range of proteases to which the cells respond rather than resulting in separate intracellular events. This suggests that in conditions such as thrombosis and atherosclerosis that multiple mechanisms can activate the inflammatory response.
White
Maureen C
MC
Saint Louis University School of Medicine, Department of Pathology, 1402 S. Grand, St. Louis, MO 63104, United States. meyerm3@slu.edu
McHowat
Jane
J
D016718:Arachidonic Acid / Q000378:metabolism; D002448:Cell Adhesion; D002478:Cells, Cultured; D003331:Coronary Vessels / Q000166:cytology*; D042783:Endothelial Cells / Q000166:cytology; D004730:Endothelium, Vascular / Q000166:cytology; D054522:Group VI Phospholipases A2; D006801:Humans; D020556:Neutrophil Infiltration; D009504:Neutrophils / Q000166:cytology; D010447:Peptide Hydrolases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism* / Q000502:physiology; D054467:Phospholipases A2; D044462:Receptors, Proteinase-Activated; D013917:Thrombin / Q000494:pharmacology; D053802:Tryptases / Q000494:pharmacology
D044462:Receptors, Proteinase-Activated; D016718:Arachidonic Acid; D010741:Phospholipases A; D054522:Group VI Phospholipases A2; C516475:PLA2G6 protein, human; D054467:Phospholipases A2; D010447:Peptide Hydrolases; D013917:Thrombin; D053802:Tryptases