Angiotensin II induces the expression of tissue factor and its mechanism in human monocytes.

The renin–angiotensin system (RAS) is linked with the vascular motion and the secretion of aldosterone. The purpose of the present study was to elucidate whether angiotensin II (Ang II) induces monocytes (Mo) to express tissue factor (TF) and if Ang II subtype 1 receptor (AT1R) antagonists inhibit the effect of Ang II. The roles of different intracellular signal transduction pathways and IκB/NF-κB in Ang II-induced TF expression of Mo were also studied to explore the mechanisms involved. Mo were isolated from heparinized human blood by a two-step gradient centrifugation, cultured in RPMI-1640 and exposed to Ang II and other test reagents. Mo TF activity and TF antigen were determined with a one-stage clotting method and ELISA, respectively, after the culture. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the TF mRNA levels in Mo. The level of IκBα in Mo was detected by Western blot analysis. Electrophoresis mobility shift assay (EMSA) was performed to evaluate the binding activity of NF-κB in Mo. The experiment results are as follows: (1) Ang II (10−10–10−7 M) induced Mo to express TF activity but had no marked effect on other mononuclear cells. Ang II 10−10–10−7 M) also caused increased TF mRNA expression and TF antigen from Mo in a dose-dependent manner. The TF antigen of Mo was elevated at 4 h after Mo was exposed to Ang II (10−7 M) in culture, reached the peak at 6 h, and then declined from 12 h. The changes of TF activity were positively correlated with those of TF antigen. TF mRNA expression was elevated at 1 h, peaked at 3 h, and declined after 8 h. (2) Losartan (10−6–10−5 M) significantly inhibited the stimulative effects of Ang II on TF activity, TF antigen and TF mRNA in Mo in a dose-dependent manner. (3) The protein kinase C (PKC) inhibitor, staurosporine, and the protein tyrosine kinase (PTK) inhibitor, genistein, both lowered TF levels in Mo, but the inhibitory effect of staurosporine was stronger than that of genistein. The effect of mitogen-activated protein kinase (MAPK) inhibitor, U0126, on monocytic TF expression was not significant. (4) Western blot analysis revealed that after Ang II (10−7 M)exposure, levels of IκBα began to decrease at 15 min, reached a nadir at 60 min (P<.01), and recovered at 180 min. (5) EMSA showed that NF-κB binding activity started to increase at 15 min, reached a peak at 60 min, and returned to baseline at 180 min. The present data suggest that Ang II can directly induce TF expression in human Mo and this effect is mediated by AT1R. PKC may play the most important role in Ang II-induced TF expression among the three signal pathways detected. In addition, activation of NF-κB is also involved in the TF expression of Mo induced by Ang II.