Potential role for mast cell tryptase in recruitment of inflammatory cells to endothelium

Department of Pathology, Saint Louis University School of Medicine, St. Louis, Missouri Submitted 4 May 2005 ; accepted in final form 28 July 2005 Recent research suggests that activation of protease-activated receptors (PARs) on the surface of endothelial and epithelial cells may play a role in general mechanisms of inflammation. We hypothesized that mast cell tryptase activation of endothelial cell PAR-2 is coupled to increased calcium-independent PLA 2 (iPLA 2 ) activity and increased platelet-activating factor (PAF) production that may play a role in inflammatory cell recruitment at sites of vascular injury. Stimulation of human coronary artery endothelial cells (HCAEC) with 20 ng/ml tryptase increased iPLA 2 activity, arachidonic acid release, and PAF production. These tryptase-stimulated responses were inhibited by pretreatment with the iPLA 2 -selective inhibitor bromoenol lactone (BEL; 5 µM, 10 min). Similar patterns of increased iPLA 2 activity and PAF production were also seen when HCAEC were treated with SLIGKV, which represents the tethered ligand sequence for the human PAR-2 once the receptor is cleaved by tryptase. Tryptase stimulation also increased cell surface expression of P-selectin, decreased electrical resistance, and increased neutrophil adherence to the endothelial cell monolayer. The tryptase-stimulated increases in both cell surface P-selectin expression and neutrophil adhesion were also inhibited with BEL pretreatment. We conclude that tryptase stimulation of HCAEC contributes importantly to early inflammatory events after vascular injury by activation of iPLA 2 , leading to arachidonic acid release, PAF production, cell surface P-selectin expression, and increased neutrophil adherence. atherosclerosis; endothelial cells Address for reprint requests and other correspondence: J. McHowat, Dept. of Pathology, Saint Louis Univ. School of Medicine, 1402 S. Grand Blvd., St. Louis, MO 63104 (e-mail: jane.mchowat{at}tenethealth.com )