The mechanisms linking prothrombotic changes to endothelial dysfunction and accelerated atheroma formation have yet to be fully defined. Expression of TF (tissue factor) on the endothelium is potentially an initiating event as binding and activation of FVII (factor VII) can result in thrombosis. Although PAR2 (protease-activated receptor-2) is expressed on vascular endothelium, its precise physiological significance and mechanism of activation have yet to be defined. In the present study, we investigated whether PAR2 can be activated by FVIIa (activated FVII) and induce ET-1 (endothelin-1) synthesis. In bovine aortic endothelial cells pretreated with TNF (tumour necrosis factor-α) to increase TF expression, FVIIa stimulated ET-1 synthesis via activation of PAR2. Although FX (factor X) alone was inactive, this response was enhanced by using FVII and FX in combination. Inhibition of the proteolytic activity of FVIIa abolished the response. The PAR2 agonist peptide SLIGKV also enhanced ET-1 release on TNF-pretreated cells. The response to FVIIa was inhibited by a PAR2 antagonist peptide FSLLRY. Inhibition of the p38 MAPK (mitogen-activated protein kinase) reduced PAR2 expression and the ET-1 response. In summary, FVIIa can stimulate ET-1 synthesis in endothelial cells by activating PAR2, demonstrating a potential link between thrombotic processes and endothelial cell dysfunction.

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