Induction of Neutrophil Extracellular DNA Lattices by Placental Microparticles and IL-8 and Their Presence in Preeclampsia
Introduction
Preeclampsia is a significant cause of fetal and maternal mortality worldwide [1, 2, 3]. This disorder, which is peculiar to human pregnancy, is typically characterized by elevated blood pressure and proteinuria in previously normotensive pregnant women [1, 2, 3]. Although the etiology of this enigmatic disorder is likely to be multifactorial, the placenta has been proposed to play a key role. This is largely thought to result from superficial placentation associated with a condition of oxidative stress [4, 5], which leads to the elevated release of inflammatory placentally derived microparticles and cytokines, [6] as well as an imbalance of angiogenic factors [7, 8]. Although it is likely that the latter represent a key event in the development of maternal hypertensive symptoms [7], the elevated shedding of syncytiotrophoblast microparticles (frequently termed STBM) in the maternal circulation during preeclampsia has been proposed to be instrumental in eliciting an overt activation of the innate arm of the maternal immune system, in particular of circulatory neutrophils [9, 10].
In addition, we and others have previously shown that preeclampsia is associated with increased transplacental trafficking of fetal cells [11], as well as elevated concentrations of cell-free fetal DNA [12, 13, 14], which may occur before onset of symptoms [15, 16, 17]. These studies, however, also indicated that cell-free DNA levels of maternal origin were also significantly elevated in preeclampsia, and that these levels correlated well with severity of the disorder [13]. While the results concerning fetal cells and cell-free fetal nucleic acids have been interpreted as further evidence of an underlying placental dysfunction in preeclampsia, those concerning the elevated presence of circulatory DNA of maternal origin have been more difficult to explain, because the source of this material is unclear [18].
For this reason, we were intrigued by the recent observation that, on activation by inflammatory signals, peripheral neutrophils generate extracellular DNA containing fibrous lattices, termed NETs (neutrophil extracellular traps) [19]. In this seminal report, the extracellular lattices exuded by activated peripheral neutrophils were found to trap bacteria and to possess bactericidal activities. Furthermore, it has also been demonstrated that interferon-γ priming and subsequent C5a stimulation resulted in NETs formation in mature but not in immature neutrophils [20]. This observation suggests that the NETs generation is a characteristic feature of mature neutrophils [20].
Because this feature may therefore link the independent observations concerning the activation of peripheral neutrophils and the elevated presence of maternal circulatory DNA during preeclampsia, we examined whether placentally derived inflammatory factors can trigger peripheral neutrophils to generate NETs. We also examined for the presence of such NETs in preeclamptic placentae.
Section snippets
Collection of Samples
The Cantonal Institutional Review Board of Basel, Switzerland, and Department of Obstetrics and Gynecology, University of Stellenbosch, South Africa, approved this study. Written informed consent was requested in all instances. Blood samples (20 ml each) for the isolation of peripheral neutrophils were obtained from healthy donors at the blood donation center of the Swiss Red Cross, University Hospital, Basel. Placentae were obtained from normal and preeclamptic pregnancies at the University
Placentally Derived IL-8 and STBM-Activated Neutrophils in Independent Manner
Although placentally derived microparticles can be detected in maternal blood samples, they cannot be reliably isolated for in vitro experiments [6]. For this reason, we made use of STBM generated from placental villous explants in vitro as described previously [21]. Because the placenta also produces a variety of inflammatory cytokines, we also prepared culture supernatants that had been extensively cleared of any microparticulate matter.
To assess the activation of isolated peripheral
Discussion
In this study we expand on the recent observations that, on activation with PMA, IL-8 and IFN γ neutrophils generated extracellular DNA containing NETs [19, 20], by demonstrating that these NETs can be induced by physiological signals, such as placentally derived inflammatory debris (STBM) and IL-8. Therefore, this phenomenon is not solely mediated by foreign objects, such as bacteria, but may be a part of normal physiology. Our observations further suggest that NETs formation may be a general
Acknowledgments
We would like to thank Mr. Daniel Mathys (ZMB, University of Basel) for his excellent technical assistance with the scanning electron microscopy and Mrs. Vivian Kiefer-Vargas and Mrs. Lisbeth Dudler for their kind help in the preparation of specimens for microscopic analysis. We would also like to thank Drs. Susanne Mergenthaler for her help with fluorescence microscopy and Carolyn Troeger for placentae collection. We thank Drs. Berthold Huppertz and Corinne Rusterholz for constructive
References (25)
- et al.
Pre-eclampsiamore than pregnancy-induced hypertension
Lancet
(1993) - et al.
Pre-eclampsia
Lancet
(2005) - et al.
Neutrophils are stimulated by syncytiotrophoblast microvillous membranes to generate superoxide radicals in women with preeclampsia
Am J Obstet Gynecol
(2004) - et al.
Placental debris, oxidative stress and pre-eclampsia
Placenta
(2000) - et al.
Disturbed feto-maternal cell traffic in preeclampsia
Obstet Gynecol
(1998) - et al.
Elevation of both maternal and fetal extracellular circulating deoxyribonucleic acid concentrations in the plasma of pregnant women with preeclampsia
Am J Obstet Gynecol
(2001) - et al.
Two-stage elevation of cell-free fetal DNA in maternal sera before onset of preeclampsia
Am J Obstet Gynecol
(2004) - et al.
Induction of genes mediating interferon-dependent extracellular trap formation during neutrophil differentiation
J Biol Chem
(2004) - et al.
A comparative study of the effect of three different syncytiotrophoblast micro-particles preparations on endothelial cells
Placenta
(2005) - et al.
Hypoxia favours necrotic versus apoptotic shedding of placental syncytiotrophoblast into the maternal circulation
Placenta
(2003)