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Inflammatory cytokines alter the hemostatic balance of endothelial cells (ECs). Alternatively spliced human tissue factor (asHTF), a soluble isoform of tissue factor (TF), has recently been detected in ECs, possibly contributing to procoagulability. Agonists regulating asHTF expression and release are yet unknown. This study examines the effect of TNF-alpha and IL-6 on the endothelial expression of both TF variants and delineates the impact of asHTF on the procoagulability of extracellular fluids. asHTF and TF mRNA were assessed by real-time PCR, and asHTF, TF, and tissue factor pathway inhibitor (TFPI) proteins by Western blot and fluorescence microscopy before and after stimulation with TNF-alpha (10 ng/mL) or IL-6 (10 ng/L). The procoagulability of cell supernatant was analyzed by a chromogenic assay with or without phospholipid vesicles. We found asHTF mRNA to be maximally increased 10 minutes after TNF-alpha and 40 minutes after IL-6 treatment (asHTF/GAPDH ratio 0.0223+/-0.0069 versus 0.0012+/-0.0006 for control, P<0.001 and 0.0022+/-0.0004 versus 0.0012+/-0.0007, P<0.05, respectively). Not only was asHTF increased, but also TFPI decreased after cytokine treatment. asHTF was found in the supernatant as early as 5 hours after TNF-alpha stimulation, supporting factor Xa generation after relipidation (6.55+/-1.13 U versus 2.99+/-0.59 U in control supernatant, P<0.00001). Removal of asHTF from supernatants by immunoprecipitation diminished its procoagulability to baseline. The soluble TF isoform expressed and released from ECs in response to inflammatory cytokines becomes procoagulant in the presence of phospholipids. Thus, asHTF released from ECs is a marker for and a contributor to imbalanced hemostasis.
Szotowski et al. (Fri,) studied this question.