Summary
During systemic inflammation, neutrophil activation is accompanied by endothelial
cell damage and hypercoagulability. Activated neutrophils release serine proteases
that participate in tissue injury.We sought to investigate the effects of neutrophil
proteases on proinflammatory and procoagulant changes in endothelial cells.The effects
of elastase (HNE), cathepsin G (CG), and proteinase 3 (PR3) on expression of tissue
factor (TF) and tissue factor pathway inhibitor-1 (TFPI) were examined in human umbilical
vein endothelial cells. Flow cytometry demonstrated that these proteases proteolytically
degraded endothelial cell-bound TFPI. TFPI mRNA expression was reduced by HNE and
CG. PR3, but not HNE or CG, increased surface expression of TF and TF mRNA.Yet, increased
TF expression did not enhance TF activity suggesting induction of encrypted TF. Using
antibodies and siRNA to inhibit and silence PAR-1 and PAR-2, we observed that PR3
upregulation of TF is at least in part mediated by PAR-1.Although CG and HNE cleaved
PAR-1, antibody reactivity to the PAR-1 hirudin-like sequence demonstrated inactivating
cleavage, accounting for the selective ability of PR3 to induce PAR-1-mediated procoagulant
effects.This was supported by induction of p42/44 MAPK by PR3. In conclusion, PR3
degradation of TFPI increases the procoagulant activity of endothelial cells. Release
of PR3 after neutrophil activation may represent an important step in neutrophil-mediated
vascular injury.
Keywords
Tissue factor (TF) - tissue factor pathway inhibitor (TFPI) - proteinase 3 - cathepsin
G - human neutrophil elastase