Role of the renin angiotensin system in TNF-α and Shiga-toxin-induced tissue factor expression

Current evidence implicates a prothrombotic state in the development of Shiga-toxin (Stx)-mediated hemolytic uremic syndrome (HUS). We recently reported that Stx modulates procoagulant activity by enhancing functional tissue factor (TF) activity on cytokine-activated human glomerular endothelial cells (HGECs). Since angiotensin II (Ang II), the key effector of the renin angiotensin system (RAS), has been shown to increase TF expression in vascular tissue, we examined the possible involvement of Ang II in TF expression in HGECs. HGECs were exposed to tumor necrosis factor (TNF)-α ± Stx-1 ± Ang II. Exogenous Ang II significantly increased TF activity and TF mRNA in TNF-α- ± Stx-1-activated HGECs. This increase was mediated via Ang II type I receptor (AT₁R), as losartan, an AT₁R inhibitor, attenuated Ang-II-induced TF activity. To study the effect of endogenous Ang II in TF expression by TNF-α ± Stx-1, HGECs were incubated with losartan or an AT₂R inhibitor (PD 123319) or an angiotensin-converting enzyme inhibitor (enalapril). Losartan but not PD 123319 decreased TF activity induced by TNF-α ± Stx-1 (P < 0.05). Enalapril, also, dose dependently, downregulated TF expression in HGECs exposed to TNF-α ± Stx-1 (P < 0.05). AT₁R mRNA was upregulated in TNF-α- ± Stx-1-activated HGECs (P < 0.05). These data indicate that TF expression in TNF-α- and Stx-1-activated HGECs is enhanced by exogenous Ang II and that endogenous Ang II production may be upregulated by TNF-α ± Stx-1. Hence, local RAS activation may be important in the development of the thrombotic microangiopathy observed in HUS.