AT ₁ Receptor Agonistic Antibodies From Preeclamptic Patients Cause Vascular Cells to Express Tissue Factor

Abstract

Background-We recently described autoantibodies (angiotensin-1 receptor autoantibodies, AT 1 -AA) directed at the AT 1 receptor in the serum of preeclamptic patients, whose placentas are commonly infarcted and express tissue factor (TF). Mechanisms of how AT 1 -AA might contribute to preeclampsia are unknown. We tested the hypothesis that AT 1 -AA cause vascular smooth muscle cells (VSMC) to express TF. Methods and Results-IgG from preeclamptic patients containing AT 1 -AA was purified with anti-human IgG columns.AT 1 -AA were separated from the IgG by ammonium sulfate precipitation. We transfected Chinese hamster ovary cells overexpressing the AT 1 receptor with TF promoter constructs coupled to a luciferase reporter gene. VSMC were obtained from human coronary arteries. Extracellular signal-related kinase activation was detected by an in-gel kinase assay. AP-1 activation was determined by electromobility shift assay. TF was measured by ELISA and detected by immunohistochemistry. Placentas from preeclamptic women stained strongly for TF, whereas control placentas showed far less staining. We proved AT 1 -AA specificity by coimmunoprecipitating the AT 1 receptor with AT 1 -AA but not with nonspecific IgG. Angiotensin (Ang) II and AT 1 -AA both activated extracellular signal-related kinase, AP-1, and the TF promoter transfected VSMC and Chinese hamster ovary cells, but only when the AP-1 binding site was present. We then demonstrated TF expression in VSMC exposed to either Ang II or AT 1 -AA. All these effects were blocked by losartan. Nonspecific IgG or IgG from nonpreeclamptic pregnant women had a negligible effect. Conclusions-We conclude that AT 1 -AA and Ang II both stimulate the AT 1 receptor and initiate a signaling cascade resulting in TF expression. These results show an action of AT 1 -AA on human cells that could contribute to the pathogenesis of preeclampsia.

Agonistic AT1 Receptor Autoantibody Increases in Serum of Patients with Refractory Hypertension and Improves Ca2+ Mobilization in Cultured Rat Vascular Smooth Muscle Cells

“…According to present data, AT 1 -AAs were suggested to have similar effects. Dechend et al reported that AT 1 -AAs induced signaling in vascular cells including AP-1 and NF-κB activation (10,11). Both of these nuclear factors participate in inflammation (23,24).…”

“…AT 1 -AAs induced signaling in vascular cells and trophoblasts including activator protein-1 (AP-1) and nuclear factorkappa B (NF-κB) (10,11), and activated calcineurin-NFAT (nuclear factor of activated T cells) through increased intracellular Ca 2+ mobilization in Chinese hamster ovary cells transferred with the rat AT 1A receptor (12). However, there were limited data related to the role of AT 1 -AAs in pathogenesis of hypertension.…”

Vasoreactivity of Chorionic Plate Arteries in Response to Vasoconstrictors Produced by Preeclamptic Placentas

“…The placenta is a key component in the pathophysiology of PE particularly those with reduced placental perfusion. Many investigators believe that preeclampsia is the result of vasoactive and inflammatory mediators secreted by the placenta acting on the vascular endothelium leading to vasoconstriction of the smooth muscle [1,2]. These mediators are likely secreted from trophoblast cells (TCs) in response to placental hypoxia/ischemia and shallow cytotrophoblast invasion acting on vascular endothelium [3].…”

“…It has been demonstrated that multiple mechanisms contribute to the increased vascular resistance during PE, including increased vascular sensitivity to angiotensin II (ANG II) [4,5], the presence of angiotensin II receptor-1 (AT 1 ) autoantibody [2,6], an imbalance between the vasoconstrictor thromboxane (TX) and decreased vasodilator prostacyclin (PGI2) [7,8], and altered endothelin (ET) [9,10] and nitric oxide (NO) [11] levels in both the maternal circulation and in the placenta in women with PE. These alterations may result in a detrimental positive feedback system that promotes inflammation and further vasoconstriction.…”

“…Receptors for ANG II [2,6,[22][23][24][25], TX [26,27], and ET [28] are present in placental trophoblasts and vasculature. However, the differential effects of each vasoconstrictor in the regulation of placental vasomotor tone have not been simultaneously studied.…”