Urokinase-type plasminogen activator (u-PA) and its inhibitor, PA inhibitor type-1 (PAI-1) by regulating extracellular proteolysis are involved among other pathophysiological events in vascular remodeling and in plaque angiogenesis and stability in atherosclerosis. IL-33 is a novel member of the IL-1 cytokine family and is a ligand of the ST2 receptor. IL-33 has recently been implicated in the pathogenesis of atherosclerosis. It was shown to induce vascular permeability and angiogenesis and the production of inflammatory cytokines in endothelial cells. Here we aimed to study a possible regulation of u-PA and PAI-1 by IL-33 in human endothelial cells (EC).Methods
Human umbilical vein EC (HUVEC) and human coronary artery EC (HCAEC) were treated with IL-33 alone or together with soluble ST2 fusion-protein (sST2 Fc) or together with simvastatin. Specific mRNA levels for u-PA and PAI-1 were determined by RT-PCR and u-PA and PAI-1 antigen and activity were measured by specific ELISAs.Results
u-PA mRNA was up-regulated up to 5-fold in HUVEC and up to 2.4-fold in HCAEC when these cells were treated with 100 ng/ml IL-33 for 9h whereas PAI-1 mRNA increased up to 2.5-fold and up to 2-fold, respectively. IL-1 receptor antagonist had no effect on IL-33-induced increase in u-PA and PAI-1, which suggests that these effects are IL-1-independent. u-PA antigen increased up to 30-fold and PAI-1 antigen increased up to 2-fold after 48h of incubation with 100 ng/ml IL-33 in HUVEC. In HCAEC u-PA increased up to 10-fold after 4h and PAI-1 increased up to 3.5 fold after 24h of incubation with 100 ng/ml IL-33. PAI-1 activity increased up to 4.5-fold after 4h of incubation with 100 ng/ml IL-33 in HUVEC and up to 5-fold after 6h of incubation in HCAEC. The increase in u-PA and PAI-1 antigen was concentration-dependent when the cells were incubated with IL-33 at concentrations ranging from 1 to 100 ng/ml. sST2 Fc abrogated the IL-33-induced increase in u-PA and PAI-1 antigen suggesting that these effects of IL-33 are ST2 receptor-mediated. Simvastatin at concentrations ranging from 0.5-2.5 μM also abrogated IL-33-induced increase of u-PA and PAI-1 antigen, thus providing further evidence that statins have effects beyond reduction of cholesterol.Conclusion
Via induction of u-PA and PAI-1 in endothelial cells, IL-33 could contribute to the modulation of endothelial cell-mediated extravascular proteolysis in processes such as neovascularization and vascular remodeling. By modulating these processes IL-33 could affect plaque angiogenesis thereby impacting on the stability of these vascular lesions in atherosclerosis.