Increased expression of high mobility group box 1 (HMGB1) in the cytoplasm of placental syncytiotrophoblast from preeclamptic placentae.

BACKGROUND: Preeclampsia is a pregnancy-specific disorder characterised by an inappropriate maternal inflammatory response during pregnancy. High mobility group box 1 (HMGB1) was originally characterised as a nuclear protein but when released into the extracellular environment following necrotic cell death, it is proinflammatory. HMGB1 is expressed in the syncytiotrophoblast of human placenta. Higher levels of uric acid are reported in preeclampsia. The aim of this study was to investigate whether the expression of HMGB1differed between early onset and late onset preeclampsia or severe and mild preeclampsia and whether its expression correlated with the levels of uric acid. METHODS: 74 preeclamptic placentae and 110 normotensive placentae were included in this study. The levels of uric acid in women with preeclampsia were measured. The expression of HMGB1 in preeclamptic placentae or in first trimester and term placentae that had been treated with uric acid was measured. RESULTS: HMGB1 was expressed predominantly in the syncytiotrophoblast of the placenta and the expression of HMGB1 in the cytoplasm of the syncytiotrophoblast was significantly increased in both severe preeclampsia and early onset preeclampsia compared to normotensive pregnancies. The circulating levels of uric acid were significantly increased in preeclampsia and correlated with the expression of HMGB1. Increased levels of HMGB1 were significantly correlated with the severity and the time of onset of preeclampsia, but pathologic levels of uric acid did not increase the expression of HMGB1. CONCLUSION: Our data provides a better understanding of the function of HMGB1, a danger molecule in the pathogenesis of preeclampsia.

Enoxaparin for the prevention of preeclampsia and intrauterine growth restriction in women with a prior history - an open-label randomised trial (the EPPI trial): study protocol.

BACKGROUND: Preeclampsia and intrauterine fetal growth restriction (IUGR) are two of the most common causes of maternal and perinatal morbidity and mortality. Current methods of predicting those at most risk of these conditions remain relatively poor, and in clinical practice past obstetric history remains the most commonly used tool. Aspirin and, in women at risk of preeclampsia only, calcium have been demonstrated to have a modest effect on risk reduction. Several observational studies and randomised trials suggest that low molecular weight heparin (LMWH) therapy may confer some benefit. METHODS/DESIGN: This is a multicentre open label randomised controlled trial to determine the effect of the LMWH, enoxaparin, on the prevention of recurrence of preeclampsia and/or IUGR in women at high risk due to their past obstetric history in addition to standard high risk care for all participants. INCLUSION CRITERIA: A singleton pregnancy >6+0 and <16+0 weeks gestation with most recent prior pregnancy with duration >12 weeks having; (1) preeclampsia delivered <36+0 weeks, (2) Small for gestational age (SGA) infant <10th customised birthweight centile delivered <36+0 weeks or, (3) SGA infant ≤3rd customised birthweight centile delivered at any gestation. Randomisation is stratified for maternal thrombophilia status and women are randomly assigned to 'standard high risk care' or 'standard high risk care' plus enoxaparin 40 mg from recruitment until 36+0 weeks or delivery, whichever occurs sooner. Standard high risk care includes the use of aspirin 100 mg daily and calcium 1000-1500 mg daily (unless only had previous SGA with no preeclampsia). The primary outcome is preeclampsia and/or SGA <5th customised birthweight centile. Analysis will be by intention to treat. DISCUSSION: The EPPI trial has more focussed and clinically relevant inclusion criteria than other randomised trials with a more restricted composite primary outcome. The inclusion of standard use of aspirin (and calcium) for all participants will help to ensure that any differences observed in outcome are likely to be related to enoxaparin use. These data will make a significant contribution to future meta-analyses and systematic reviews on the use of LMWH for the prevention of placental mediated conditions. TRIAL REGISTRATION: ACTRN12609000699268 Australian New Zealand Clinical Trials Registry. Date registered 13/Aug/2009 (prospective registration).

Isolation and characterisation of a novel trophoblast side-population from first trimester placentae.

The placenta is responsible for all nutrient and gas exchange between mother and baby during pregnancy. The differentiation of specialised placental epithelial cells called trophoblasts is essential for placental function, but we understand little about how these populations arise. Mouse trophoblast stem cells have allowed us to understand many of the factors that regulate murine trophoblast lineage development, but the human placenta is anatomically very different from the mouse, and it is imperative to isolate a human trophoblast stem cell to understand human placental development. Here we have developed a novel methodology to isolate a Hoechst side-population of trophoblasts from early gestation placentae and compared their transcriptome to differentiated trophoblast populations (cytotrophoblasts and extravillous trophoblasts) using microarray technology. Side-population trophoblasts clustered as a transcriptomically distinct population but were more closely related to cytotrophoblasts than extravillous trophoblasts. Side-population trophoblasts up-regulated a number of genes characteristic of trophectoderm and murine trophoblast stem cells in comparison to cytotrophoblasts or extravillous trophoblasts and could be distinguished from both of these more mature populations by a unique set of 22 up-regulated genes, which were enriched for morphogenesis and organ development and the regulation of growth functions. Cells expressing two of these genes (LAMA2 and COL6A3) were distributed throughout the cytotrophoblast layer at the trophoblast/mesenchymal interface. Comparisons to previously published trophoblast progenitor populations suggest that the side-population trophoblasts isolated in this work are a novel human trophoblast population. Future work will determine whether these cells exhibit functional progenitor/stem cell attributes.

The relationship between TGFß, low oxygen and the outgrowth of extravillous trophoblasts from anchoring villi during the first trimester of pregnancy.

BACKGROUND: During the first trimester of human pregnancy, specialised placental cells called extravillous trophoblasts (EVTs) grow out from anchoring villi, invade the maternal decidua and remodel the uterine spiral arteries. Inadequate EVT invasion is associated with pregnancy complications including intrauterine growth restriction (IUGR) and pre-eclampsia. During early pregnancy, the placenta exists in a physiologically normal low oxygen environment, which may regulate EVT outgrowth. One potential oxygen responsive regulator of EVTs is the transforming growth factor-beta (TGFß) family of cytokines. This work aimed to determine the role of TGFß1, ß2 and ß3 in regulating EVT outgrowth in the low oxygen environment of early pregnancy. RESULTS: Using a quantitative high-throughput first trimester villous explant model of EVT outgrowth we demonstrated no significant difference in the frequency of EVT outgrowth between explants treated with TGFß1, ß2 or ß3. However, explants treated with TGFß2, but not ß1 or ß3, produced EVT outgrowths with a significantly smaller area in comparison to untreated controls (p=0.03). When explants were cultured in 1.5% oxygen, TGFß2, but not ß1 or ß3, in the conditioned medium of explants that produced EVT outgrowth was significantly reduced in comparison to 8% oxygen (p<0.05). There was no significant difference in the concentration of TGFß2 or TGFß3 from isolated primary EVTs cultured in 1.5% or 8% oxygen. CONCLUSIONS: TGFß2 inhibits EVT outgrowth expansion from first trimester anchoring villi. As TGFß2 secretion from anchoring villi is down-regulated in low oxygen, these findings suggest that the low oxygen environment in early pregnancy may be important to allow EVT outgrowth expansion and promote adequate placentation.

Use of equine embryo -derived mesenchymal stromal cells and their extracellular vesicles as a treatment for persistent breeding-induced endometritis in susceptible mares.

Persistent breeding induced endometritis (PBIE) is a significant cause of infertility in mares. The development of a safe, universal, readily available therapeutic to manage PBIE and facilitate an optimal uterine environment for embryo development may improve pregnancy rates in susceptible mares. Mesenchymal stromal cells (MSCs) are being used increasingly as a therapeutic mediator for inflammatory conditions such as endometritis, and early gestational tissue provides a unique source of multipotent stem cells for creating MSCs. Extracellular vesicles (EVs) are mediators of cell communication produced by many different cell types. This study utilized embryo-derived mesenchymal stromal cells (EDMSCs) and their EVs as a potential therapeutic modality for PBIE in two groups: a) PBIE-susceptible mares challenged with pooled dead sperm (n=5); and b) client-owned mares diagnosed as susceptible to PBIE (n=37 mares and 40 estrous cycles). Mares pre-treated with intrauterine EDMSCs or their EVs resulted in a significant reduction in the accumulation of intrauterine fluid post-breeding. Nine of 19 (47 %) mares treated with EDMSCs prior to natural breeding and 13 of 20 (65 %) mares treated with EDMSC derived EVs were pregnant after the first cycle and 12 of 18 (67 %) mares treated with EDMSCs, and 15 of 19 (79 %) mares treated with EVs conceived by the end of the breeding season. These preliminary clinical studies are the first reports of the use of EDMSCs or their EVs as a potential intrauterine therapy for the management of PBIE susceptible mares.

A simple method to isolate term trophoblasts and maintain them in extended culture.

INTRODUCTION: Primary trophoblast cultures obtained from term placentae are an important research tool. Term trophoblasts, while isolated as mononuclear cells, spontaneously fuse to form multinucleated syncytial clusters. Since term trophoblast cells do not replicate in vitro, contaminating cells can overgrow the culture limiting the lifespan of primary trophoblast cultures to about seven days. We aimed to develop a method that would allow the prolonged culture of term trophoblasts. METHODS: Trophoblasts were isolated from term placentae, following vaginal or cesarean section delivery, using either trypsin/DNase or dispase/DNase to digest the tissue. Purity of the trophoblasts was confirmed using flow cytometry prior to plating and during culture using immunocytochemistry. Cell death was examined with propidium iodide and trophoblast fusion monitored using PKH67 membrane stain. RESULTS: Digestion of term villous tissue with dispase/DNase resulted in the release of significantly more trophoblasts than digestion with trypsin/DNase (n = 8, p = 0.0051). Viability of the trophoblasts was unaffected by enzyme choice. The use of Advanced DMEM/F12 supplemented with 2% fetal bovine serum allowed culture of the trophoblasts with minimal cell death or contamination for 30 days. Despite prolonged culture over half of the trophoblasts remained mononuclear. DISCUSSION: We report a simple, optimized method to isolate and culture trophoblasts from term placentae for prolonged periods without substantial contamination with other cell types. Consistent with previous findings, trophoblasts cultured using our method were able to syncytialise, forming multi-nucleated syncytia. This extended growth time allows long term in vitro experimentation to further understand the nature of trophoblasts.

A role for interleukin-6 in spreading endothelial cell activation after phagocytosis of necrotic trophoblastic material: implications for the pathogenesis of pre-eclampsia.

Pre-eclampsia is characterized by systemic maternal endothelial dysfunction that precedes the onset of clinical symptoms. The cause of the dysfunction is not clear but the number and the nature of trophoblasts shed from the placenta may be altered in pre-eclamptic pregnancies. These dead trophoblasts become trapped in the pulmonary capillaries and may then be phagocytosed by endothelial cells. Phagocytosis of necrotic, but not apoptotic, trophoblasts results in endothelial cell activation. We have explored the hypothesis that activation can subsequently spread to other endothelial cells via soluble factors without the need for direct contact with shed trophoblasts. Conditioned medium from endothelial cells that had phagocytosed necrotic, but not apoptotic, trophoblasts was shown to activate fresh endothelial cells due, in large part, to IL-6 secreted into the conditioned medium. The amount of IL-6 secreted in response to phagocytosis of necrotic trophoblasts was similar to the levels of IL-6 found by others in the blood of pre-eclamptic women and was substantially more than the level of IL-6 which has been reported to induce symptoms of pre-eclampsia in pregnant rats. We demonstrated that phagocytosis of both a trophoblast cell line as well as trophoblasts shed from human placentae, had this effect on two different types of endothelial cells. The role of IL-6 in endothelial cell activation was confirmed using recombinant IL-6 and neutralizing antibodies against IL-6 and the IL-6 receptor. Thus, IL-6 secreted by pulmonary endothelial cells after they have phagocytosed necrotic trophoblasts that are trapped in the pulmonary capillaries could activate endothelial cells in other remote vascular beds, contributing to the systemic activation of the endothelium that is a hallmark of pre-eclampsia.

Vitamin C enhances phagocytosis of necrotic trophoblasts by endothelial cells and protects the phagocytosing endothelial cells from activation.

Preeclampsia is a pregnancy-specific disease characterised by maternal hypertension that is preceded by endothelial cell activation and an inappropriate inflammatory response. The exact cause of preeclampsia is unclear but this disease is known to be induced by a placental factor and it is hypothesised that oxidative stress may also contribute to its pathogenesis. We have shown that dead trophoblasts shed from the placenta can be phagocytosed by endothelial cells and that phagocytosis of necrotic, but not apoptotic, trophoblasts leads to endothelial cells activation. Since phagocytosis may be accompanied by an oxidative burst which may lead to damage/activation of the phagocyte, in this study we have investigated whether the antioxidant vitamin C can protect endothelial cells that phagocytose necrotic trophoblasts from activation. We demonstrate that treatment of phagocytosing endothelial cells with vitamin C induced an increase in the phagocytosis of necrotic trophoblasts but that activation of the phagocytosing endothelial cells was prevented. Treatment of phagocytosing endothelial cells with vitamin C also prevented the increase in IL-6 secretion that normally accompanies phagocytosis of necrotic trophoblasts. Thus treatment of endothelial cells with vitamin C appears to modify both the phagocytosis of necrotic trophoblasts and the response of the endothelial cells to the necrotic trophoblastic material.

IFPA meeting 2008 workshops report.

Workshops are an important part of the IFPA annual meeting. At the IFPA meeting 2008 diverse topics were discussed in 12 themed workshops. Topics covered included: immunology of placentation; galectins and trophoblast invasion; signaling in implantation and invasion; markers to identify trophoblast subpopulations; placental pathology; placental toxicology; stereology; placental transport of fatty acids; placental mesenchymal stem cells; comparative placentation; trophoblast and neoplasia; trophoblast differentiation. This report is a summary of the various topics covered.

Cryptic natural autoantibodies and co-potentiators.

Natural autoantibodies are normal components of the humoral arm of the immune system found in clinically healthy individuals. There are two subpopulations of natural antibodies, including an overt group of antibodies that are readily detected in unfractionated normal human sera. The other natural antibody subgroup is revealed by physico or biochemical treatment of normal human sera in vitro. Unmasking of this latter cryptic natural autoantibodies (cNA) may occur in vivo by local factors in the tissue environment of disease states. The masking cryptic factors may be immunoglobulin (Ig) or non-Ig in nature. These factors may either be co-inhibitors or co-enhancers of cNA. In the heat-potentiated binding of natural anti-phospholipid antibodies, apolipoprotein H (beta 2-glycoprotein I) appears to act as a co-enhancer. The immuno-relationship between the in vitro and in vivo cNA phenomenon remains to be elucidated.

Nuclear localisation of the endocannabinoid metabolizing enzyme fatty acid amide hydrolase (FAAH) in invasive trophoblasts and an association with recurrent miscarriage.

Endocannabinoids are lipid signalling molecules that are related to the major psychoactive component in marijuana, delta-9-tetrahydrocannabinol and are increasingly recognized as being important in implantation and development of early embryos. The endocannabinoid anandamide, is metabolized by the enzyme fatty acid amide hydrolase (FAAH), and insufficient levels of this enzyme have been implicated in spontaneous miscarriage in women and implantation failure in mice. We screened placental bed biopsies and placental tissue from 45 women with recurrent miscarriage and 17 gestation-matched women with normal pregnancies for the expression of FAAH by immunohistochemistry. Unexpectedly, the enzyme appeared to be localised to the nucleus of trophoblasts and this was confirmed by western blotting of sub-cellular fractions and confocal microscopy. FAAH was expressed in the cytoplasm of large decidual stromal cells and significantly more women with recurrent miscarriage (73%) expressed FAAH in these cells than women with normal pregnancy (31%). FAAH was also expressed in the nucleus of extravillous trophoblasts that had invaded the decidua from 67% of women with recurrent miscarriage but was not expressed by these cells in any women with normal pregnancies. In contrast, FAAH was expressed in extravillous trophoblasts that had migrated out of the villi but that had not yet invaded the decidua in both normal pregnancies and in cases of recurrent miscarriage. FAAH was also present in the nucleus of a small number of villous trophoblasts in some specimens. FAAH appears to be over expressed in trophoblasts that have invaded the decidua, as well as in large decidual stromal cells in many cases of recurrent miscarriage. This may reflect inadequate control of the cannabinoid system in the uterus of women who experience recurrent miscarriages. The functional significance of the unexpected nuclear localisation of FAAH in trophoblasts is not yet clear.

Activated endothelial cells resist displacement by trophoblast in vitro.

BACKGROUND: Transformation of the spiral arteries by invading trophoblasts is an essential prerequisite to the development of a healthy fully grown fetus. Reduced transformation of the spiral arteries is a characteristic feature of pregnancies complicated by several diseases of pregnancy including preeclampsia. The aim of this study was to investigate further the hypothesis that spiral artery endothelial cells can contribute to the mechanism of shallow trophoblast invasion. METHOD: Fluorescently labeled Jar cells were added to monolayers of fluorescently-labeled endothelial cells that had been activated by treatment with TNFalpha, INF gamma or necrotic cell bodies. The ability of the Jars to displace endothelial cells from the monolayers was quantified by measuring the area of Jar cells "islands" formed in the endothelial cell monolayers by confocal microscopy and digital image. RESULTS: The area of Jar cell islands formed in monolayers of activated endothelial cells was significantly smaller that the area of islands formed in control resting/non-activated endothelial cell monolayers regardless of the activator. DISCUSSION: This work demonstrates that activated endothelial cells are more resistant to trophoblast displacement than resting endothelial cells and adds weight to the suggestion that endothelial cells could contribute to shallow invasion of the spiral arteries by trophoblasts in diseases such as preeclampsia.

The effects of apoptotic, deported human placental trophoblast on macrophages: possible consequences for pregnancy.

During pregnancy, trophoblasts are shed into maternal blood from the placenta as they die. Trophoblasts are fetal cells and are therefore immunologically foreign to the maternal immune system, but the effects of shed trophoblasts on the maternal immune system are poorly characterized. We have used an in vitro villous explant model to harvest shed trophoblasts. These shed trophoblasts consist of multinucleated syncytial knots as well as mononuclear cells, and approximately 90% are apoptotic as determined by immunostaining with antibodies recognizing activated caspase-3 and the M30 cytokeratin neoepitope. U937 cells phagocytosed the shed apoptotic trophoblasts and, subsequently, secretion of the anti-inflammatory cytokine IL-10 was increased. In contrast, secretion of the proinflammatory cytokine Il-1beta by U937 cells was decreased after phagocytosis of apoptotic trophoblasts and the changes in both IL-10 and IL-1beta secretion were blocked by co-incubation with the phagocytosis inhibitor cytochalasin B. Shed trophoblasts caused a significant increase also in expression of the, immunosuppressive, tryptophan-metabolizing enzyme indoleamine 2,3-dioxygenase. We speculate that the shedding of trophoblasts may not be simply a mechanism the fetus uses to dispose of aged trophoblasts but rather shed apoptotic trophoblasts may provide a chronic source of tolerizing paternally derived antigens to regulate maternal immune responses to the fetus.

Reduction in the severity of early onset severe preeclampsia during gestation may be associated with changes in endothelial cell activation: A pathological case report.

Early severe preeclampsia with changes consistent with the Hemolysis elevated liver enzymes low platelet count (HELLP) variant and severe fetal growth restriction rarely resolves prior to delivery. Established clinical disease is preceded by endothelial dysfunction and inflammation. Endothelial activation is reported in vitro to be raised in the presence of necrotic trophoblastic debris which is deported into the maternal circulation in preeclampsia. We report on an early severe preeclamptic patient admitted at 24 weeks gestation. Maternal serum was taken at day 2, 16, 30 of admission and 45 days postpartum. 20% maternal serum or trophoblastic debris from first trimester placental explants that had been cultured with 10% maternal serum was exposed to endothelial cells. Endothelial cell activation was quantified by the cell surface ICAM-1 expression and U937 monocyte adhesion assay. The clinical condition of this patient improved including the blood pressure, liver function, and platelet count by the 3rd day after antihypertensive treatment and remained normal until delivery at 37 weeks. ICAM-1 expression and U937 moncyte adhesion assay of endothelial cells was significantly increased following exposure of the endothelial cells to the maternal serum or trophoblastic debris from placentae treated with maternal serum drawn on day 2. However, ICAM-1 expression and the monocyte adhesion assay were significantly reduced following exposure of endothelial cells to maternal serum or trophoblastic debris from placenta treated with maternal serum drawn on day 16 or 30. Our data suggest unknown factor(s) in the maternal serum triggered endothelial cell activation when the clinical symptoms were present. The improvement in the clinical condition occurred along with the changes in endothelial cell activation.

The anti-inflammatory effect of calcium for preventing endothelial cell activation in preeclampsia.

Preeclampsia is a disorder of pregnancy characterized by endothelial activation. It is believed to be a response to a 'toxin(s)' from the placenta including trophoblastic debris and inflammatory cytokines. Calcium is known to reduce the risk of preeclampsia but the mechanism of its protective effect remains unknown. In this study, we investigated the potential mechanism(s) of calcium supplementation for preventing endothelial activation induced by trophoblastic debris. Trophoblastic debris was harvested from preeclamptic placentae and also from first-trimester placentae, which had been treated with preeclamptic sera. Endothelial cells were then cultured with trophoblastic debris in the presence of calcium. Endothelial activation was measured by quantifying endothelial cell-surface intercellular adhesion molecule-1 (ICAM-1) and by U937 monocyte adhesion to endothelial cells. The expression of ICAM-1 and U937 adhesion to endothelial cells were significantly reduced following exposure of endothelial cells to trophoblastic debris from preeclamptic placenta or from first-trimester placentae treated with preeclamptic sera in the presence of calcium compared with treatment without calcium. The expression of ICAM-1 was also significantly reduced following exposure of endothelial cells to trophoblastic debris with the nitric oxide donor or following treatment of endothelial cells with interleukin (IL)-1ß in the presence of calcium. Our study demonstrated that calcium supplementation prevented endothelial cell activation induced by trophoblastic debris from preeclamptic placentae. The nitric oxide synthase (NOS) pathway and anti-inflammatory effects are involved in the action of calcium on endothelial cell activation. These findings may suggest, at least in part, the protective mechanism of calcium supplementation on preeclampsia.

Flow speed alters the apparent size and concentration of particles measured using NanoSight nanoparticle tracking analysis.

Nanoparticle tracking analysis (NTA) is commonly used to count and size nano-sized particles. A sample loading pump can be used to analyse a larger sample volume, but it is unclear whether accuracy is affected. Using a NanoSight NS300 with the manufacturer-supplied pump, we examined synthetic silica and latex microspheres, liposomes and placental extracellular vesicles at different flow speeds. Analysis at flow speeds of 20 or 50 significantly reduced the measured concentration and mean/modal size of particles, particularly for mono-dispersed samples. We identify sample flow speed as a crucial instrument setting which should be reported in all studies that use NTA.

Trophoblastic debris modifies endothelial cell transcriptome in vitro: a mechanism by which fetal cells might control maternal responses to pregnancy.

The mechanisms by which the fetus induces maternal physiological adaptations to pregnancy are unclear. Cellular debris, shed from the placental syncytiotrophoblast into the maternal blood and phagocytosed by maternal endothelial and immune cells, may be one of these mechanisms. Here we show that trophoblastic debris from normal first trimester placentae induces changes in the transcriptome and proteome of endothelial cells in vitro, which might contribute to the adaptation of the maternal cardiovascular system to pregnancy. Trophoblastic debris also induced endothelial cells to transcribe placenta-specific genes, including the vasodilator hormone CSH1, thereby expanding the effective functional size of the placenta. Our data suggest that the deportation of trophoblastic debris is an important part of the complex network of feto-maternal communication.

IFPA meeting 2015 workshop report I: placental mitochondrial function, transport systems and epigenetics.

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialized topics. At IFPA meeting 2015 there were twelve themed workshops, three of which are summarized in this report. These workshops covered areas of placental regulation and nutrient handling: 1) placental epigenetics; 2) placental mitochondrial function; 3) placental transport systems.

IFPA meeting 2015 workshop report IV: placenta and obesity; stem cells of the feto-maternal interface; placental immunobiology and infection.

Workshops are an important part of the IFPA annual meeting as they allow for discussion of specialised topics. At the 2015 IFPA annual meeting there were 12 themed workshops, three of which are summarized in this report. These workshops related to various aspects of placental biology and collectively covered areas of obesity and the placenta, stem cells of the feto-maternal interface, and placental immunobiology and infection.

Interaction of Jar choriocarcinoma cells with endothelial cell monolayers.

During human pregnancy the uterine spiral arteries are invaded by placental trophoblasts which replace the endothelial cells that line the non-pregnant spiral arteries and transform these vessels into large-bore conduits enabling adequate perfusion of the placenta with maternal blood. Failure of this process may predispose to preeclampsia and fetal growth restriction [Brosens I, Robertson WB, Dixon HG. The physiological response of the vessels of the placental bed to normal pregnancy. Journal of Pathology and Bacteriology 1967;93:569-79; Khong TY, De Wolf F, Robertson WB, Brosens I. Inadequate maternal vascular response to placentation in pregnancies complicated by pre-eclampsia and by small-for-gestational age infants. British Journal of Obstetrics and Gynaecology 1986;93:1049-59]. There is a paucity of data on the role of maternal endothelial cells in this process. In this study we investigated the cellular interactions between trophoblast-derived Jar cells and endothelial cells (HUVECs and HMEC-1). The effect of coculturing Jar cells with endothelial cell monolayers was determined by confocal microscopy, DNA fragmentation assay and flow cytometry. We demonstrated that Jar cells migrate into focal areas in endothelial cell monolayers, where they induce endothelial cell death and, then phagocytose the dead endothelial cells. Our results suggest that endothelial cells may not simply be passive targets for invading trophoblasts during the remodeling of the spiral arteries.