Background: Interleukin (IL)-33 is a member of the IL-1 cytokine family. IL-33 was previously shown to induce angiogenesis and the expression of inflammatory cytokines and adhesion molecules in endothelial cells. Tissue factor (TF) is a primary trigger of coagulation. Elevated levels of TF are found in atherosclerotic plaques, and TF leads to thrombus formation, when released upon plaque rupture.
Aim: Here we investigated the impact of IL-33 on TF expression in human endothelial cells, as a new possible mechanism for IL-33 to regulate their thrombotic potential.
Methods and Results: Human umbilical vein endothelial cells (HUVEC) and human coronary artery endothelial cells (HCAEC) were treated with 100, 10 and 1ng/ml recombinant human IL-33. Expression of mRNA specific for TF was determined by RT-PCR. TF protein levels were measured by specific enzyme-linked immunosorbent assays (ELISAs). We found that IL-33 significantly induced TF mRNA up to 200-fold and protein expression up to 145-fold in a time- and concentration-dependent manner in HUVEC and HCAEC. ST2-siRNA-mediated gene knockdown inhibited IL-33-induced TF expression, suggesting that this effect of IL-33 is facilitated through its receptor ST2. Preincubation of HUVEC with 100μM of the NFkB-inhibitor dimethyl-fumarate abrogated IL-33-induced TF protein synthesis. IL-1 receptor antagonist had no effect on IL-33-induced increase of TF expression. In human carotid atherosclerotic plaques (n=16), TF mRNA positively correlated with IL-33 mRNA expression (r=0.86, p<0.001).
Conclusion: Our results showed that IL-33 increases TF expression in human endothelial cells, and that this effect is ST2/NFkB-dependent, but IL-1-independent. Furthermore, we supported our in vitro data in human atherosclerotic tissue where we found a strong positive correlation of IL-33 and TF expression. Thus, IL-33-induced changes in TF expression could affect the thrombotic potential of endothelial cells, as well as potentiate thrombotic events in the setting of ruptured human atherosclerotic plaques.