Neutrophil activation by the tissue factor/Factor VIIa/PAR2 axis mediates fetal death in a mouse model of antiphospholipid syndrome

Abstract

Women with antiphospholipid syndrome (APS), a condition characterized by the presence of antiphospholipid antibodies (aPL), often suffer pregnancy-related complications, including miscarriage. We have previously shown that C5a induction of tissue factor (TF) expression in neutrophils contributes to respiratory burst, trophoblast injury, and pregnancy loss in mice treated with aPL. Here we analyzed how TF contributes to neutrophil activation and trophoblast injury in this model. Neutrophils from aPL-treated mice expressed protease-activated receptor 2 (PAR2), and stimulation of this receptor led to neutrophil activation, trophoblast injury, and fetal death. An antibody specific for human TF that has little impact on coagulation, but potently inhibits TF/Factor VIIa (FVIIa) signaling through PAR2, inhibited aPL-induced neutrophil activation in mice that expressed human TF. Genetic deletion of the TF cytoplasmic domain, which allows interaction between TF and PAR2, reduced aPL-induced neutrophil activation in aPL-treated mice. Par2 -/-mice treated with aPL exhibited reduced neutrophil activation and normal pregnancies, which indicates that PAR2 plays an important role in the pathogenesis of aPL-induced fetal injury. We also demonstrated that simvastatin and pravastatin decreased TF and PAR2 expression on neutrophils and prevented pregnancy loss. Our results suggest that TF/FVIIa/PAR2 signaling mediates neutrophil activation and fetal death in APS and that statins may be a good treatment for women with aPL-induced pregnancy complications.

Pravastatin prevents miscarriages in mice: role of tissue factor in placental and fetal injury

“…40,41 We previously demonstrated that pregnancy loss induced by antiphospholipid antibodies in mice is associated with increased TF expression. 16,20 In this study, we found increased TF expression and activity in placentas from CBA/J ϫ DBA/2 matings compared with control matings with normal pregnancies. Interestingly, we were able to translate the results obtained in mice in humans.…”

“…16,20 Day-15 placentas were frozen in OCT compound, cut into 10-m sections, and incubated with DHE (10 M) for 30 minutes at 37°C. Subsequently, the sections were washed and fluorescence images were obtained (Ex: 520, Em: 605 nm).…”

“…Statins are postulated to inhibit inflammation and coagulation 31,32 and to reduce TF expression and activity in blood monocytes and neutrophils. 20,33,34 Knowing that TF is a crucial mediator in pregnancy complications observed in CBA/J ϫ DBA/2 mice, we sought to investigate whether pravastatin can prevent pregnancy loss in this model of spontaneous miscarriages. In accordance with our hypothesis, pravastatin prevented fetal loss ( Figure 4A) and IUGR ( Figure 4B) in DBA/2-mated CBA/J mice at day 15 of pregnancy.…”

The role of TLR4 in pathophysiology of antiphospholipid syndrome‐associated thrombosis and pregnancy morbidity

“…It is a specific, high-affinity receptor for factor (F)VII/VIIa and functions as a co-factor for FVIIa enzymatic activity. Activation of FVIIa triggers physiological blood coagulation and thrombosis, activates neutrophils through TF/FVIIa/proteinase-activated receptor-2 (PAR2) signalling and functions as an important mediator of C5a-induced oxidative burst in neutrophils in aPL-induced fetal injury (Redecha et al, 2007(Redecha et al, , 2008Boles & Mackman, 2010;Owens & Mackman, 2010).…”

“…A high prospective fetal loss rate was observed in untreated pregnancies of aPL-positive women with recurrent miscarriage, among whom the most common type of miscarriage is the first trimester loss of embryonic pregnancies (Rai et al, 1995). Both clinical and experimental observations suggest that pregnancy loss in these patients may involve an inflammatory response at the maternal-fetal interface, as well as disruption of normal trophoblast survival and function (Sebire et al, 2002;Bose et al, 2006;Redecha et al, 2007Redecha et al, , 2008. Mulla et al (2009) demonstrated for the first time that anti-b2GPI antibodies elicit a dose-dependent response in human first trimester trophoblast cells.…”