Spreading endothelial cell dysfunction in response to necrotic trophoblasts. Soluble factors released from endothelial cells that have phagocytosed necrotic shed trophoblasts reduce the proliferation of additional endothelial cells

Investigation of Beclin 1 and TNF-α expressions in preeclampsia placentas: Immunohistochemical study

BACKGROUND

Preeclampsia is a pregnancy complication Aim of this study was to investigate expression of Beclin1 and tumor necrosis factor (TNF)-α in normotensive and preeclamptic placentas of pregnant women patients.

METHODS

Twenty normotensive and 20 preeclamptic patients placentas were dissected for paraffin- wax processing. Placental samples were embedded in parafin blocks. Sections were stained with Hematoxylin-Eosin staining and TNF-α and Beclin1 immunostaining.

RESULTS

In control group, root and floating villi were normal in histological perspectives, syncytial node number was low, vessels were normal with connective tissue. No hemorrhage was observed in the intervillous area. In preeclampsia group, decidual cell degeneration and fibrinoid accumulation increased. Vascular dilatation and congestion with mononuclear cell infiltration were observed. Beclin1 reaction was generally negative in control group. In preeclampsia group, Beclin1 reaction was increased in decidual cells, syncytial nodes and bridges and in chorionic villi and in some Hoffbauer cells. In control group, TNF-α expression was mainly negative but only in some decidual cells. In preeclampsia, TNF-α reaction was observed in degenerated decidua cells, in leukocytes and in villi.

CONCLUSION

In preeclampsia placentas, degenerated decidua cells and inflammation increased. It was thought that Beclin1 and TNF-α signals could be used as a marker in affecting the fetal structure of blood flow in preeclamptic placentas.

Preeclampsia link to gestational hypoxia

Complications of pregnancy remain key drivers of morbidity and mortality, affecting the health of both the mother and her offspring in the short and long term. There is lack of detailed understanding of the pathways involved in the pathology and pathogenesis of compromised pregnancy, as well as a shortfall of effective prognostic, diagnostic and treatment options. In many complications of pregnancy, such as in preeclampsia, there is an increase in uteroplacental vascular resistance. However, the cause and effect relationship between placental dysfunction and adverse outcomes in the mother and her offspring remains uncertain. In this review, we aim to highlight the value of gestational hypoxia-induced complications of pregnancy in elucidating underlying molecular pathways and in assessing candidate therapeutic options for these complex disorders. Chronic maternal hypoxia not only mimics the placental pathology associated with obstetric syndromes like gestational hypertension at morphological, molecular and functional levels, but also recapitulates key symptoms that occur as maternal and fetal clinical manifestations of these pregnancy disorders. We propose that gestational hypoxia provides a useful model to study the inter-relationship between placental dysfunction and adverse outcomes in the mother and her offspring in a wide array of examples of complicated pregnancy, such as in preeclampsia.

Phagocytosis of Extracellular Vesicles Extruded From the Placenta by Ovarian Cancer Cells Inhibits Growth of the Cancer Cells

OBJECTIVE

Ovarian cancer is a common gynecological cancer, and parity is negatively associated with the incidence of this disease. This negative association is hypothesized to be due in part to shifting the balance of estrogen and progesterone toward more progesterone and reduced ovulation during pregnancy. However, studies suggested that parity is also associated with estrogen-independent gynecological cancers suggesting balance of hormones may not be the only protective factor. Extracellular vesicles (EVs) play an important role in cell-to-cell communication in physiological and pathological conditions. During pregnancy, large amounts of EVs are extruded from the placenta, and they seem to be involved in the remarkable adaptation of a woman's body to normal pregnancy. We hypothesized that EVs extruded from the placenta play a role in this protective effect.

METHODS

Placental EVs were collected from first-trimester placentae, and cancer cell EVs were isolated from ovarian cancer cells. The EVs were exposed to ovarian cancer cells for 48 hours. The proliferation of cancer cells and the cell cycle were measured. In addition, phagocytosis of deported placental EVs by cancer cells was also measured.

RESULTS

The proliferation of cancer cells was significantly reduced by treatment with placental EVs (P = 0.001, analysis of variance), but not EVs from monocytes (P = 0.195), compared with untreated cancer cells. Furthermore, placental EVs also prevented the proliferation of cancer cells induced by cancer cell-derived EVs (P = 0.001). This inhibition of proliferation of ovarian cancer cells was partially due to phagocytosis of placental EVs by cancer cells. Phagocytosis of placental EVs delayed progression through the cell cycle. Calreticulin, a phagocytic "eat me" signal carried by placental EVs significantly inhibited ovarian cancer growth (P = 0.001).

CONCLUSIONS

Our data demonstrated that EVs extruded from the placenta prevented ovarian cancer cell growth by a mechanism that involved delaying progression of the cell cycle after phagocytosis of the EVs.

Various levels of circulating exosomal total-miRNA and miR-210 hypoxamiR in different forms of pregnancy hypertension

INTRODUCTION

Hypertension is a common complication during pregnancy, affecting 10% of pregnant women worldwide. Several microRNA (miRNA) were shown to be involved in hypertensive disorders of pregnancy. In preeclampsia (PE), placental dysfunction causes the enhanced release of extracellular vesicle-derived miRNAs. The hypoxia-sensitive hsa-mir-210 is the most common PE-associated miRNA, but its exosomal profile has not been investigated.

OBJECTIVES

Our aims were to measure exosomal total-miRNA concentration and to perform expression analysis of circulating exosomal hsa-miR-210 in women affected by chronic hypertension (CHT) gestational hypertension (GHT) or PE.

MATERIALS AND METHODS

We collected plasma samples from women with CHT, GHT, PE (moderate: mPE and severe: sPE) and from normotensive pregnancies. Exosomal miRNAs were extracted and miRNA concentration was measured. RT-PCR was carried out with hsa-miR-210-3p-specific primers and relative expression was calculated using the comparative Ct method.

RESULTS

The total-miRNA concentration was different in the disease subgroups, and was significantly higher in mPE and sPE compared to the other groups. We found a significant difference in the relative exosomal hsa-miR-210-3p expression between all hypertensive groups compared to the normotensive samples, but significant upregulation was only observed in case of mPE and sPE patients. Both the level of total-miRNA and hsa-miR-210 expression was higher in case of severe PE.

CONCLUSIONS

The level of circulating exosomal total-miRNA and hsa-miR-210 was elevated in women with PE, and it was higher in the severe form. We showed that hsa-miR-210 is secreted via exosomes, which may have a role in the pathomechanism of the disease.

Melatonin prevents preeclamptic sera and antiphospholipid antibodies inducing the production of reactive nitrogen species and extrusion of toxic trophoblastic debris from first trimester placentae

BACKGROUND

The exact cause of preeclampsia is unknown. However a "toxin" from the placenta triggers the condition via activation of the maternal endothelium. Extracellular vesicles (EVs) from the syncytiotrophoblast, may be an endothelial-activating toxin. Antiphospholipid antibodies (aPL) and preeclamptic sera both induce the production of endothelial cell-activating EVs by mechanisms which may produce excess free-radicals in the placenta. Melatonin is produced by the human placenta and has both direct and indirect anti-free-radical properties and may therefore counter the effects of aPL and preeclamptic sera.

METHODS

First trimester placental explants were exposed to preeclamptic sera or aPL in the presence or absence of melatonin. Nitrosylative damage was assessed in the explants by immunohistochemistry and the effect of EVs from these explants on endothelial cell activation determined by ICAM-1. Release of nitrosylated proteins from the explants was also measured.

RESULTS

Placental explants showed reduced secretion of melatonin after treatment with preeclamptic sera. Nitrosylated proteins were more abundant in placentae that had been treated with aPL or preeclamptic sera and EVs from such placentae induced endothelial cell activation. Adding melatonin to the aPL or preeclamptic sera reversed the protein nitrosylation and production of endothelial-activating EVs.

DISCUSSION

Our data are consistent with reports that the levels of circulating melatonin are reduced in preeclampsia and suggest that aPL and factors in preeclamptic sera induce free-radical-mediated damage in the placenta leading to the production of endothelial-activating EVs. Melatonin reversing production of endothelial-activating EVs indicates that melatonin may have therapeutic benefits in women with preeclampsia and/or aPL.

In vivo targets of human placental micro-vesicles vary with exposure time and pregnancy

Throughout human gestation, the placenta extrudes vast quantities of extracellular vesicles (EVs) of different sizes into the maternal circulation. Although multinucleated macro-vesicles are known to become trapped in the maternal lungs and do not enter the peripheral circulation, the maternal organs and cells that smaller placental micro-vesicles interact with in vivo remain unknown. This study aimed to characterise the interaction between placental micro-vesicles and endothelial cells in vitro and to elucidate which organs placental micro-vesicles localise to in vivo Placental macro- and micro-vesicles were isolated from cultured human first trimester placental explants by sequential centrifugation and exposed to human microvascular endothelial cells for up to 72 h. In vivo, placental macro- and micro-vesicles were administered to both non-pregnant and pregnant CD1 mice, and after two or 30 min or 24 h, organs were imaged on an IVIS Kinetic Imager. Placental EVs rapidly interacted with endothelial cells via phagocytic and clathrin-mediated endocytic processes in vitro, with over 60% of maximal interaction being achieved by 30 min of exposure. In vivo, placental macro-vesicles were localised exclusively to the lungs regardless of time of exposure, whereas micro-vesicles were localised to the lungs, liver and kidneys, with different distribution patterns depending on the length of exposure and whether the mouse was pregnant or not. The fact that placental EVs can rapidly interact with endothelial cells and localise to different organs in vivo supports that different size fractions of placental EVs are likely to have different downstream effects on foeto-maternal communication.

Micro- and Nano-vesicles from First Trimester Human Placentae Carry Flt-1 and Levels Are Increased in Severe Preeclampsia

BACKGROUND/OBJECTIVES

Preeclampsia is a life-threatening hypertensive disease affecting 3-5% of pregnancies. While the pathogenesis of preeclampsia remains unclear, it is known that placenta-derived factors trigger the disease by activating maternal endothelial cells prior to the onset of clinical symptoms. Extracellular vesicles (EVs) of different sizes extruded by the placenta may be one factor. The truncated/secreted form of Flt-1 (sFlt-1) has also been implicated in the pathogenesis of preeclampsia. We investigated whether placental EV production is altered in preeclampsia such that they induce endothelial cell activation, and whether (s)Flt-1 is involved.

METHODS

Macro-, micro-, and nano-vesicles were collected from normal and preeclamptic (PE) placental explants, and separated by differential centrifugation. The number and size of micro- and nano-vesicles was measured by nanoparticle tracking analysis and their ability to activate endothelial cells was quantified by endothelial cell intercellular adhesion molecule 1 expression and monocyte adhesion. The levels of Flt-1 were measured by western blots and ELISA.

RESULTS

PE placentae extruded significantly more micro- and nano-vesicles than control placentae and the extruded micro-vesicles were larger than those from control placentae. Micro- and nano-vesicles from both first trimester and term human placentae carried Flt-1 and levels were significantly increased in EVs from severe, but not mild, PE compared to normotensive placentae. All fractions of EVs from PE placentae activated endothelial cells, and for micro- and nano-vesicles, activation was reduced in the presence of exogenous vascular endothelial growth factor (VEGF), a Flt-1 neutralizing antibody, or by pre-treatment with VEGF. While EV-bound VEGF constituted over 20% of the total detected VEGF secreted by PE and normotensive placentae, EV-bound Flt-1 did not significantly contribute to the total level of sFlt-1/Flt-1 released by human third trimester placentae.

DISCUSSION

Micro- and nano-vesicles extruded by human placentae carry Flt-1 across gestation and in severe preeclampsia, the levels of vesicle-bound Flt-1 are upregulated. All fractions of PE placental EVs activated endothelial cells and for micro- and nano-vesicles, this was in part due to the ability of EV-bound Flt-1 to sequester VEGF. That placental EVs can activate endothelial cells supports the contention that EVs are one placental toxin contributing to the pathogenesis of preeclampsia.

Increased levels of HMGB1 in trophoblastic debris may contribute to preeclampsia

Preeclampsia is triggered by an as yet unknown toxin from the placenta. Antiphospholipid antibodies (aPL), a strong risk factor for preeclampsia, have been shown to induce the production of toxic trophoblastic debris from the placenta. High mobility group box 1 (HMGB1) is a proinflammatory danger signal, and the expression of it has been reported to be increased in preeclampsia. This study examined whether aPL or preeclamptic sera increase the expression of HMGB1 in the syncytiotrophoblast or trophoblastic debris. Trophoblastic debris from normal placental explants that had been cultured with aPL or preeclamptic sera was exposed to endothelial cells. Endothelial cell activation was quantified by cell-surface ICAM-1 expression and U937 monocyte adhesion. The expression of HMGB1 in placental explants and trophoblastic debris that had been treated with aPL or preeclamptic sera was measured by immunohistochemistry and western blotting. The expression of the receptor for advanced glycation end products (RAGE) in endothelial cells was quantified by western blotting. Compared with controls, the expression of HMGB1 in the cytoplasm of the syncytiotrophoblast and trophoblastic debris was increased by treating placental explants with aPL or preeclamptic sera. The increased levels of HMGB1 contributed to endothelial cell activation, mediated in part by the RAGE. Preeclamptic sera and aPL both induced an increase in the cytoplasmic levels of the danger signal HMGB1 in trophoblastic debris. This increased HMGB1 in trophoblastic debris may be one of the toxic factors released from the placenta in preeclampsia.

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)-1β 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.

Placental extracellular vesicles and feto-maternal communication

The human placenta is an anatomically unique structure that extrudes a variety of extracellular vesicles into the maternal blood (including syncytial nuclear aggregates, microvesicles, and nanovesicles). Large quantities of extracellular vesicles are produced by the placenta in both healthy and diseased pregnancies. Since their first description more than 120 years ago, placental extracellular vesicles are only now being recognized as important carriers for proteins, lipids, and nucleic acids, which may play a crucial role in feto-maternal communication. Here, we summarize the current literature on the cargos of placental extracellular vesicles and the known effects of such vesicles on maternal cells/systems, especially those of the maternal immune and vascular systems.

Human placental microRNAs and preeclampsia

MicroRNAs are a class of noncoding small RNAs that regulate the expression of nearly 30% of all the human genes and participate in all fundamental cell processes. Genome-wide analysis has revealed that human placenta expresses more than 600 miRNA species, including placenta-specific ones with high levels of expression. Comparative analysis also has revealed many differentially expressed miRNAs with either high or low levels of expression in human placentas from normal versus preeclamptic pregnancies, indicating an important role of miRNAs in normal and pathological placental physiology. Although limited information is currently available as to how miRNA regulates human placental development and function, there are studies suggesting that preeclampsia-associated differentially expressed miRNAs possess critical roles in regulating placental development and function via targeting specific genes with diverse known functions. Herein we summarize the current findings regarding the expression of placental miRNAs and their function, especially in the trophoblast cells. We have recently found that the angiogenesis-associated miR-17-family miRNAs are upregulated in preeclamptic compared with normotensive placentas and they target the ephrin-B2/Eph receptor B4 (EPHB4) system. Because ephrin-B2 and EPHB4 has been previously shown to play a crucial role in trophoblast invasion into maternal spiral artery and vascular patterning during early human placental development, the miR-17-ephrin-B2/EPHB4 pathway seems to be a novel miRNA pathway for regulating normal and aberrant placental development during preeclampsia.

[Immunological aspect of pregnancy]

Pregnancy is a temporary semi-allograft that survives for nine months. The importance of this event for the survival of the species justifies several tolerance mechanisms that are put into place at the beginning of pregnancy, some of which occur even at the time of implantation. The presence of multiple tolerance mechanisms and the richness of the means employed underline the central importance of the trophoblast. Understanding these mechanisms, and in particular, their integration into an overall scheme, enables the anomalies encountered in certain pathologies of pregnancy to be placed into context. Understanding these mechanisms and their interruption at the end of pregnancy should improve our understanding of disappointing results from current immunological treatments facilitate the implementation of new prophylactic and therapeutic strategies.

Human placental expression of SLIT/ROBO signaling cues: effects of preeclampsia and hypoxia

Preeclampsia is characterized by dysfunctional endothelium and impaired angiogenesis. Recent studies suggest that the neuronal guidance SLIT/ROBO system regulates tumor angiogenesis. This study investigated if SLIT and ROBO are differentially expressed in healthy term and preeclamptic placentas and if hypoxia regulates SLIT and ROBO expression in placental trophoblast and endothelial cells. Total RNA and protein were extracted from placental tissues of healthy term (n = 5) and preeclamptic (n = 6) pregnancies and used for SLIT/ROBO expression analyses with reverse transcription-polymerase chain reaction (RT-PCR), real-time quantitative-PCR, and immunoblotting. Paraffin-embedded tissues were processed to localize SLIT/ROBO proteins in placental villi by immunohistochemistry. BeWo choriocarcinoma cells and human umbilical vein endothelial cells (HUVEC) were treated with 2% or 10% oxygen or the hypoxia mimetic deferoxamine mesylate (100 μM) to test if hypoxia regulates SLIT/ROBO expression. SLIT2, SLIT3, ROBO1, and ROBO4 mRNA and proteins were detected in the placenta. SLIT2 and ROBO1 proteins localized in the syncytiotrophoblast, and SLIT3, ROBO1, and ROBO4 in capillary endothelium of the placental villi. Levels of ROBO1 and ROBO4 as well as sFLT1 (soluble fms-like tyrosine kinase-1) proteins were significantly greater in preeclamptic placentas compared to normal controls. Hypoxia significantly increased both mRNA and protein levels of SLIT2 in BeWo cells and of SLIT3, ROBO1, and ROBB4 in HUVEC. Thus, trophoblast and endothelial coexpression of SLIT/ROBO suggests an autocrine/paracrine regulatory system for regulating placental function. Differential expression of SLITs and ROBOs in healthy term and preeclamptic placentas and hypoxia regulation of their expressions in placental cells implicate a potential pathophysiological role for this system in preeclampsia.

The placenta in preeclampsia

The root cause of preeclampsia is the placenta. Preeclampsia begins to abate with the delivery of the placenta and can occur in the absence of a fetus but with the presence of trophoblast tissue with hydatidiform moles. In view of this, study of the placenta should provide insight into the pathophysiology of preeclampsia. In this presentation we examine placental pathological and pathophysiological changes with preeclampsia and fetal growth restriction (FGR). It would seem that this comparison should be illuminating as both conditions are associated with similarly abnormal placentation yet only in preeclampsia is there a maternal pathophysiological syndrome. Similar insights about early and late onset preeclampsia should also be provided by such information.We report that the placental abnormalities in preeclampsia are what would be predicted in a setting of reduced perfusion and oxidative stress. However, the differences from FGR are inconsistent. The most striking differences between the two conditions are found in areas that have been the least studied. There are differences between the placental findings in early and late onset preeclampsia but whether these are qualitative, indicating different diseases, or simply quantitative differences within the same disease is difficult to determine.We attempt to decipher the true differences, seek an explanation for the disparate results and provide recommendations that we hope may help resolve these issues in future studies.

Trophoblast deportation: just a waste disposal system or antigen sharing?

Trophoblast deportation, the removal of trophoblastic debris from the placenta via the maternal blood, was first described over 100 years ago. Deported trophoblastic debris ranges in size from nano-meter scale subcellular particles to large multinucleated syncytial knots. Whether trophoblast deportation has any biological significance remains unclear. However, the (semi) allogeneic fetus must induce maternal tolerance to paternally inherited placental antigens. We propose that the clearance of deported trophoblasts may be a mechanism by which the maternal immune system is maintained in a state of tolerance towards paternal antigens. Using an in vitro model, we have shown that when syncytial knots are shed by an apoptosis-like programmed cell death process, then phagocytosed by macrophages, the macrophages produce a tolerogenic response. However, necrotic syncytial knots, when phagocytosed, appear to be immunostimulatory. We have also shown that endothelial cells are likely to be involved in the clearance of syncytial knots from the pulmonary vessels. Phagocytosis of apoptotic syncytial knots by endothelial cells is silent while phagocytosis of necrotic syncytial knots leads to endothelial cell activation characterised by increased endothelial cell-surface adhesion molecule expression and secretion of IL-6 and TGFβ1. All of these molecules may interact with the maternal immune system to exacerbate any adverse maternal response. We propose that in normal pregnancy clearance of apoptotic syncytial knots is important to maintain maternal immune tolerance to the fetus and that in abnormal pregnancies, especially preeclampsia, clearance of necrotic syncytial knots may contribute to the pathogenesis of that condition.