Adriana and Luisa Castellucci award lecture 1999: role of oxygen in the regulation of trophoblast gene expression and invasion

Human placental development and function

The placenta is a transient fetal organ that plays a critical role in the health and wellbeing of both the fetus and its mother. Functionally, the placenta sustains the growth of the fetus as it facilitates delivery of oxygen and nutrients and removal of waste products. Not surprisingly, defective early placental development is the primary cause of common disorders of pregnancy, including recurrent miscarriage, fetal growth restriction, pre-eclampsia and stillbirth. Adverse pregnancy conditions will also affect the life-long health of the fetus via developmental programming[1]. Despite its critical importance in reproductive success and life-long health, our understanding of placental development is not extensive, largely due to ethical limitations to studying early or chronological placental development, lack of long-term in vitro models, or comparative animal models. In this review, we examine current knowledge of early human placental development, discuss the critical role of the maternal endometrium and of the fetal-maternal dialogue in pregnancy success, and we explore the latest models of trophoblast and endometrial stem cells. In addition, we discuss the role of oxygen in placental formation and function, how nutrient delivery is mediated during the periods of histotrophic nutrition (uptake of uterine secretions) and haemotrophic nutrition (exchange between the maternal and fetal circulations), and how placental endocrine function facilitates fetal growth and development.

RNA-Seq reveals changes in human placental metabolism, transport and endocrinology across the first-second trimester transition

The human placenta is exposed to major environmental changes towards the end of the first trimester associated with full onset of the maternal arterial placental circulation. Changes include a switch from histotrophic to hemotrophic nutrition, and a threefold rise in the intraplacental oxygen concentration. We evaluated their impact on trophoblast development and function using RNA-sequencing (RNA-Seq) and DNA-methylation analyses performed on the same chorionic villous samples at 7-8 (n=8) and 13-14 (n=6) weeks of gestation. Reads were adjusted for fetal sex. Most DEGs were associated with protein processing in the endoplasmic reticulum (ER), hormone secretion, transport, extracellular matrix, vasculogenesis, and reactive oxygen species metabolism. Transcripts higher in the first trimester were associated with synthesis and ER processing of peptide hormones, and glycolytic pathways. Transcripts encoding proteins mediating transport of oxygen, lipids, protein, glucose, and ions were significantly increased in the second trimester. The motifs of CBX3 and BCL6 were significantly overrepresented, indicating the involvement of these transcription factor networks in the regulation of trophoblast migration, proliferation and fusion. These findings are consistent with a high level of cell proliferation and hormone secretion by the early placenta to secure implantation in a physiological low-oxygen environment.

Downregulation of fascin in the first trimester placental villi is associated with early recurrent miscarriage

Inadequate trophoblast proliferation, shallow invasion and exaggerated rate of trophoblast apoptosis are implicated in early recurrent miscarriage (ERM). However, the mechanistic bases of this association have not been fully established. We aimed at investigating the involvement of fascin, an actin-bundling protein, in trophoblast activities and ERM. We found that fascin was downregulated in the cytotrophoblasts (CTBs) and distal cytotrophoblasts (DCTs) of ERM placentae. Knockdown of fascin altered cellular and nucleolar morphology, and inhibited the proliferation but increased apoptosis of trophoblastic HTR8/SVneo cells. Furthermore, fascin knockdown decreased the expression of transcription factors such as Snail1/2, Twist and Zeb1/2, mesenchymal molecules such as Vimentin and N-cadherin, and the protein expression of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphorylates signal transducer and activator of transcript 3 (STAT3). Exposure of HTR-8/SVneo cells to hypoxia reoxygenation (H/R) decreased fascin expression to affect the cells' invasion. Our results indicate for the first time that the downregulation of fascin is involved in the pathogenesis of early recurrent miscarriage; and hence a potential therapeutic target against the disease.

Endovascular trophoblast and spiral artery remodeling

Spiral artery remodeling, which is indispensable for successful pregnancy, is accomplished by endovascular trophoblasts that move upstream along the arterial wall, replace the endothelium, and disrupt the muscular lining. This review outlines the possible factors that could regulate endovascular trophoblast differentiation and invasion. First, high oxygen tension in the spiral artery could initiate endovascular trophoblast invasion. Second, activation of maternal decidual natural killer (dNK) cells could support perivascular invasion of interstitial trophoblasts and consequently could facilitate the endovascular trophoblast invasion. Third, maternal platelets trapped by the endovascular trophoblasts could enhance endovascular trophoblast invasion, which is in part mediated by chemokine CCL5 (C-C motif ligand 5) released from the activated platelets and chemokine receptor CCR1 (C-C chemokine receptor type 1) expressed specifically on the endovascular trophoblasts. The rat, in which trophoblast cells exhibit extensive interstitial and endovascular invasion, could be a suitable model animal for the study of human spiral artery remodeling. Apparently paradoxical results came from the rat study, i.e., exposure to hypoxia or depletion of dNK cells resulted in acceleration of the endovascular trophoblast invasion. This implies the presence of as-yet-undetermined regulator(s) whose effects on endovascular trophoblast invasion surpass the effects of surrounding oxygen tension or maternal dNK cells. In the future, clarification of the molecular differences between human interstitial and endovascular trophoblasts as well as establishment of the pregnant rat model exhibiting shallow endovascular trophoblast invasion and preeclamptic symptoms will contribute to elucidating the mechanism of spiral artery remodeling.

Hypoxia and Placental Development

Hemochorial placentation is orchestrated through highly regulated temporal and spatial decisions governing the fate of trophoblast stem/progenitor cells. Trophoblast cell acquisition of specializations facilitating invasion and uterine spiral artery remodeling is a labile process, sensitive to the environment, and represents a process that is vulnerable to dysmorphogenesis in pathologic states. Hypoxia is a signal guiding placental development, and molecular mechanisms directing cellular adaptations to low oxygen tension are integral to trophoblast cell differentiation and placentation. Hypoxia can also be used as an experimental tool to investigate regulatory processes controlling hemochorial placentation. These developmental processes are conserved in mouse, rat, and human placentation. Consequently, elements of these developmental events can be modeled and hypotheses tested in trophoblast stem cells and in genetically manipulated rodents. Hypoxia is also a consequence of a failed placenta, yielding pathologies that can adversely affect maternal adjustments to pregnancy, fetal health, and susceptibility to adult disease. The capacity of the placenta for adaptation to environmental challenges highlights the importance of its plasticity in safeguarding a healthy pregnancy. Birth Defects Research 109:1309-1329, 2017.© 2017 Wiley Periodicals, Inc.

Reduced FOXM1 Expression Limits Trophoblast Migration and Angiogenesis and Is Associated With Preeclampsia

Trophoblast cells are often compared to highly invasive carcinoma cells due to their capacity to proliferate in hypoxic conditions and to exhibit analogous vascular, proliferative, migratory, and invasive capacities. Thus, genes that are important for tumorigenesis, such as forkhead box M1 ( FOXM1) may also be involved in processes of trophoblast invasion. Indeed, we found Foxm1 protein and messenger RNA (mRNA) levels decreased as gestational age increased in rat's placentae. Accordingly, when mimicking early placental events in vitro, protein and mRNA expression of FOXM1 increased from 21% to 8% O₂, reaching its highest expression at 3% oxygen tension, which reflects early implantation environment, and dropping to very low levels at 1% O₂. Remarkably, FOXM1 silencing in JEG-3 cells was able to significantly decrease migration by 27.9%, in comparison with those cells transfected with control siRNA. Moreover, angiogenesis was compromised when conditioned media (CM) from FOXM1-siRNA -JEG-3 (3% O₂) was added to human umbilical vein endothelial cells (HUVEC) cells; however, when CM of JEG-3 cells overexpressing FOXM1 at 1% O₂ was added, the ability of HUVEC to form tubule networks was restored. Additionally, quantitative real-time polymerase chain reaction (PCR) assays of FOXM1 knockdown and overexpression experiments in JEG-3 cells revealed that the depletion of FOXM1 at 3% O₂ and overexpression of FOXM1 at 1% O₂ led to downregulation and upregulation of vascular endothelial growth factor transcriptional (VEGF) levels, respectively. Conversely, we also observed deregulation of FOXM1 in placentae derived from pregnancies complicated by preeclampsia (PE). Therefore, we demonstrate that FOXM1 may be a new regulatory protein of early placentation processes and that under chronic hypoxic conditions (1% O₂) and in patients with severe PE, its levels decrease.

Placental Hypoxia During Early Pregnancy Causes Maternal Hypertension and Placental Insufficiency in the Hypoxic Guinea Pig Model

Chronic placental hypoxia is one of the root causes of placental insufficiencies that result in pre-eclampsia and maternal hypertension. Chronic hypoxia causes disruption of trophoblast (TB) development, invasion into maternal decidua, and remodeling of maternal spiral arteries. The pregnant guinea pig shares several characteristics with humans such as hemomonochorial placenta, villous subplacenta, deep TB invasion, and remodeling of maternal arteries, and is an ideal animal model to study placental development. We hypothesized that chronic placental hypoxia of the pregnant guinea pig inhibits TB invasion and alters spiral artery remodeling. Time-mated pregnant guinea pigs were exposed to either normoxia (NMX) or three levels of hypoxia (HPX: 16%, 12%, or 10.5% O2) from 20 day gestation until midterm (39-40 days) or term (60-65 days). At term, HPX (10.5% O2) increased maternal arterial blood pressure (HPX 57.9 ± 2.3 vs. NMX 40.4 ± 2.3, P < 0.001), decreased fetal weight by 16.1% (P < 0.05), and increased both absolute and relative placenta weights by 10.1% and 31.8%, respectively (P < 0.05). At midterm, there was a significant increase in TB proliferation in HPX placentas as confirmed by increased PCNA and KRT7 staining and elevated ESX1 (TB marker) gene expression (P < 0.05). Additionally, quantitative image analysis revealed decreased invasion of maternal blood vessels by TB cells. In summary, this animal model of placental HPX identifies several aspects of abnormal placental development, including increased TB proliferation and decreased migration and invasion of TBs into the spiral arteries, the consequences of which are associated with maternal hypertension and fetal growth restriction.

Mesenteric Vascular Responsiveness in a Rat Model of Pregnancy-Induced Hypertension

Reduced perfusion to the placenta in early pregnancy is believed to be the initiating factor in the development of preeclampsia, triggering local ischemia and systemic vascular hyperresponsiveness. This sequence of events creates a predisposition to the development of altered vascular function and hypertension. This study was designed to determine the influence of placental insufficiency on the responsiveness of mesenteric resistance arteries in an animal model of preeclampsia. Placental insufficiency was induced by reduction in uteroplacental perfusion pressure (RUPP) in experimental Sprague-Dawley rat dams. The uterine branches of the ovarian arteries and the abdominal aortae of pregnant rats were surgically constricted on gestational Day 14. Dams in the control group underwent a sham procedure. Rats were euthanized on gestational Day 20, followed by removal of the small intestine and adjacent mesentery. First-order mesenteric resistance arteries were mounted on a small vessel wire myograph and challenged with incremental concentrations of vasoconstrictors and vasorelaxants. Mesenteric arteries in dams with placental insufficiency demonstrated an increased maximal tension to phenylephrine (7.15 ± 0.15 vs. 5.4 ± 0.27 mN/mm, P < 0.001); potassium chloride at 60 mM (3.43 ± 0.11 vs. 2.77 ± 0.14 mN/mm, P < 0.01) and 120 mM (3.92 ± 0.18 vs. 2.97 ± 0.16 mN/mm, P < 0.01); and angiotensin II (2.59 ± 0.42 vs. 1.51 ± 0.22 mN/mm, P < 0.05). Maximal relaxation to endothelium-dependent relaxants acetylcholine and calcium lonophore (A23187) was not significantly reduced. Data suggest that placental insufficiency leads to hyperresponsiveness to vasoconstrictor stimuli in mesenteric arteries.

Placental Oxidative Stress: From Miscarriage to Preeclampsia

OBJECTIVE

To review the role of oxidative stress in two common placental-related disorders of pregnancy, miscarriage and preeclampsia.

METHODS

Review of published literature.

RESULTS

Miscarriage and preeclampsia manifest at contrasting stages of pregnancy, yet both have their roots in deficient trophoblast invasion during early gestation. Early after implantation, endovascular trophoblast cells migrate down the lumens of spiral arteries, and are associated with their physiological conversion into flaccid conduits. Initially these cells occlude the arteries, limiting maternal blood flow into the placenta. The embryo therefore develops in a low oxygen environment, protecting differentiating cells from damaging free radicals. Once embryogenesis is complete, the maternal intervillous circulation becomes fully established, and intraplacental oxygen concentration rises threefold. Onset of the circulation is normally a progressive periphery-center phenomenon, and high levels of oxidative stress in the periphery may induce formation of the chorion laeve. If trophoblast invasion is severely impaired, plugging of the spiral arteries is incomplete, and onset of the maternal intervillous circulation is premature and widespread throughout the placenta. Syncytiotrophoblastic oxidative damage is extensive, and likely a major contributory factor to miscarriage. Between these two extremes will be found differing degrees of trophoblast invasion compatible with ongoing pregnancy but resulting in deficient conversion of the spiral arteries and an ischemia-reperfusion-type phenomenon. Placental perfusion will be impaired to a greater or lesser extent, generating commensurate placental oxidative stress that is a major contributory factor to preeclampsia.

CONCLUSION

Miscarriage, missed miscarriage, and early- and late-onset preeclampsia represent a spectrum of disorders secondary to deficient trophoblast invasion.

The role of VEGF-A165b in trophoblast survival

Background

Pre-eclampsia remains a dominant cause of maternal and fetal mortality in developed countries. In a previous prospective study we identified a fall in the VEGF-A isoform VEGF-A₁₆₅b in the plasma of patients in the first trimester to be a predictor of later pre-eclampsia. VEGF-A₁₆₅b has been shown to have potent cytoprotective properties in many cell types. We therefore tested the hypothesis that VEGF-A₁₆₅b may be cytoprotective for placental trophoblasts.

Methods

We used an immortalised first trimester trophoblast cell line exposed to chemical toxicity, and physiological (<2% O₂) and atmospheric oxygen (21% O₂) in the presence or absence of VEGF-A₁₆₅b, angiogenic VEGF-A₁₆₅a, a non-specific anti-VEGF-A blocking antibody (bevacizumab), or a specific anti-VEGF-A₁₆₅b antibody. Cell viability and cytotoxicity were measured by trypan blue and LDH assay respectively.

Results

Under high (21%) levels of oxygen, trophoblast viability was increased, and cytotoxicity reduced by exogenous recombinant VEGF-A₁₆₅b (p < 0.05, n = 10) or VEGF-A₁₆₅a. The cytoprotective effect was not seen under lower (<2%) oxygen conditions, where VEGF-A₁₆₅b was upregulated. However inhibition of VEGF-A with blocking antibodies (bevacizumab or anti-VEGF-A₁₆₅b) had marked cytotoxic effects under low oxygen conditions presumably through the blockade of autocrine survival pathways.

Conclusions

These results show that when trophoblasts are exposed to lower oxygen tensions (as they are early in the 1^st trimester) endogenous VEGF-A₁₆₅b contributes to their survival through an autocrine pathway. In contrast in high oxygen conditions exogenous VEGF-A isoforms have a greater effect on trophoblast survival.

CNN3 regulates trophoblast invasion and is upregulated by hypoxia in BeWo cells

CNN3 is an ubiquitously expressed F-actin binding protein, shown to regulate trophoblast fusion and hence seems to play a role in the placentation process. In this study we demonstrate that CNN3 levels are upregulated under low oxygen conditions in the trophoblast cell line BeWo. Since hypoxia is discussed to be a pro-migratory stimulus for placental cells, we examined if CNN3 is involved in trophoblast invasion. Indeed, when performing a matrigel invasion assay we were able to show that CNN3 promotes BeWo cell invasion. Moreover, CNN3 activates the MAPKs ERK1/2 and p38 in trophoblast cells and interestingly, both kinases are involved in BeWo invasion. However, when we repeated the experiments under hypoxic conditions, CNN3 did neither promote cell invasion nor MAPK activation. These results indicate that CNN3 promotes invasive processes by the stimulation of ERK1/2 and/or p38 under normoxic conditions in BeWo cells, but seems to have different functions at low oxygen levels. We further speculated that CNN3 expression might be altered in human placentas derived from pregnancies complicated by IUGR and preeclampsia, since these placental disorders have been described to go along with impaired trophoblast invasion. Our studies show that, at least in our set of placenta samples, CNN3 expression is neither deregulated in IUGR nor in preeclampsia. In summary, we identified CNN3 as a new pro-invasive protein in trophoblast cells that is induced under low oxygen conditions.

The timing and duration of hypoxia determine gene expression patterns in cultured human trophoblasts

OBJECTIVE

Exposure of cultured trophoblasts to hypoxia is commonly used to interrogate the molecular mechanisms underlying placental hypoxic injury. We examined the effect of levels, durations, and patterns of hypoxia on gene expression patterns in primary human trophoblasts.

STUDY DESIGN

We exposed primary term human trophoblasts to either standard culture conditions (O(2) = 20%) or to static or alternating levels of oxygen (O(2) = 8%, or O(2) = 0%) either early or late in culture, and analyzed the expression of 34 genes that are known to be regulated in placentas from pregnancies complicated by fetal growth restriction (FGR).

RESULTS

Using multidimensional scale analysis, Euclidean distance, and hierarchical clustering, we found that gene expression patterns in cells exposed to O(2) = 8% were similar to patterns observed in O(2) = 20%, but more distant from patterns in O(2) = 0%. Alternating atmospheric oxygen (8% vs. 0%) yielded intermediate results. Changes in oxygen levels over a longer period had a greater effect on gene expression than short-term changes. Gene expression patterns in cultured trophoblasts did not fully capture expression patterns observed in biopsies from FGR placentas vs. control.

CONCLUSIONS

The level, duration, and patterns of hypoxia are critical in determining trophoblast gene expression, and therefore germane for analysis of trophoblast hypoxic injury.

Vascular, renal and placental effects on pregnant offspring of protein-restricted rat dams

AIM

Our previous study showed that a maternal low-protein diet induced hypertension and vascular dysfunction in rat offspring after day 175. In the present study, we hypothesized that these female offspring would develop hypertension in their own pregnancies even at ages less than 175 days because potential vascular dysfunction is exacerbated by the circulatory demands of pregnancy.

MATERIAL AND METHODS

Wistar rats were fed an isocaloric diet containing either 18% (control group) or 9% (low-protein group) casein throughout pregnancy. The female offspring were fed standard chow and mated between days 70 and 125. At the end of pregnancy, blood pressure was measured, and the uterine arteries were dissected and investigated with a wire myograph.

RESULTS

Placental weights were significantly lower in offspring of the low-protein group versus control. There were no significant differences in blood pressure. Renal expression of AT1 receptor mRNA was greater, and of AT2 receptor was less, in the low-protein group versus control. Vasoconstriction of uterine arteries to phenylephrine and U46619 was increased in the low-protein group, and vasodilatation to sodium nitroprusside was also increased.

CONCLUSION

Low-protein diet induces vascular effects on female offspring in their pregnancy, in terms of increased uterine artery vasoconstriction. This may be compensated for by increased sensitivity to nitric oxide (NO), maintaining blood pressure normal in the face of the demands of pregnancy. Such renal and vascular effects, combined with placental size, may transmit risk of vascular dysfunction to subsequent generations.

A critical role of interleukin-10 in modulating hypoxia-induced preeclampsia-like disease in mice

Hypoxia has been implicated in the pathogenesis of preeclampsia, a hypertensive disorder of pregnancy. However, in vivo evidence and mechanistic understanding remain elusive. Preeclampsia is associated with impaired placental angiogenesis. We have recently shown that interleukin (IL)-10 can support trophoblast-driven endovascular crosstalk. Accordingly, we hypothesize that pathological levels of oxygen coupled with IL-10 deficiency induce severe preeclampsia-like features coupled with elevated production of antiangiogenic factors, apoptotic pathways, and placental injury. Exposure of pregnant wild-type and IL-10(-/-) mice to 9.5% oxygen resulted in graded placental injury and systemic symptoms of renal pathology, proteinuria (wild-type 645.15 ± 115.73 versus 198.09 ± 93.45; IL-10(-/-) 819.31 ± 127.85 versus 221.45 ± 82.73 μg/mg/24 hours) and hypertension (wild-type 118.37 ± 14.45 versus 78.67 ± 14.07; IL-10(-/-) 136.03 ± 22.59 versus 83.97 ± 18.25 mm Hg). Recombinant IL-10 reversed hypoxia-induced features in pregnant IL-10(-/-) mice confirming the protective role of IL-10 in preeclampsia. Hypoxic exposure caused marked elevation of soluble fms-like tyrosine kinase 1 (110.8 ± 20.1 versus 44.7 ± 11.9 ng/mL) in IL-10(-/-) mice compared with their wild-type counterparts (81.6 ± 13.1 versus 41.2 ± 8.9 ng/mL), whereas soluble endoglin was induced to similar levels in both strains (approximately 380 ± 50 versus 180 ± 31 ng/mL). Hypoxia-induced elevation of p53 was associated with marked induction of proapoptotic protein Bax, downregulation of Bcl-2, and trophoblast-specific apoptosis in utero-placental tissue. Collectively, we conclude that severe preeclampsia pathology could be triggered under certain threshold oxygen levels coupled with intrinsic IL-10 deficiency, which lead to excessive activation of antiangiogenic and apoptotic pathways.

Regulation of the matricellular proteins CYR61 (CCN1) and NOV (CCN3) by hypoxia-inducible factor-1{alpha} and transforming-growth factor-{beta}3 in the human trophoblast

It is known that a hypoxic environment is critical for trophoblast migration and invasion and is fundamental for appropriate placental perfusion. Because cysteine-rich 61 (CYR61, CCN1) and nephroblastoma overexpressed (NOV, CCN3) are expressed in the extravillous trophoblast and expression levels are deregulated in preeclampsia, we investigated their regulation properties in first-trimester placental explants and in JEG3 choriocarcinoma cells upon a physiological low oxygen tension of 1-3%. In placental explants, both proteins were expressed in the extravillous trophoblast cells and were increased upon hypoxia. JEG3 cells revealed a significant up-regulation of CYR61 and NOV intracellular as well as secreted protein upon hypoxic treatment accompanied by the stabilization of the hypoxia-inducible factor-1alpha (HIF-1alpha). Treatment with dimethyloxalylglycine to mimic hypoxia and silencing of HIF-1alpha using small interfering RNA revealed that only the increase in intracellular protein expression seems to be dependent on HIF-1alpha but obviously not the secretion process. Moreover, recombinant TGF-beta3 was able to further enhance the amount of intracellular CCN proteins as well as secreted CYR61 levels under hypoxia. These results indicate that low oxygen levels trigger elevation of intracellular as well as secreted CYR61 and NOV protein probably in two independent pathways. Addition of recombinant CYR61 and NOV proteins increases migration as well as invasion properties of JEG3 trophoblast cells, which strengthen their role in supporting trophoblast migration invasion properties. In summary, CYR61 and NOV are regulated by HIF-1alpha and TGF-beta3 in the trophoblast cell line JEG3, and their enhanced secretion could be implicated in appropriate placental invasion.

An imbalance between angiogenic and anti-angiogenic factors precedes fetal death in a subset of patients: results of a longitudinal study

OBJECTIVE

Women with a fetal death at the time of diagnosis have higher maternal plasma concentrations of the anti-angiogenic factor, soluble vascular endothelial growth factor receptor (sVEGFR)-1, than women with a normal pregnancy. An important question is whether these changes are the cause or consequence of fetal death. To address this issue, we conducted a longitudinal study and measured the maternal plasma concentrations of selective angiogenic and anti-angiogenic factors before the diagnosis of a fetal death. The anti-angiogenic factors studied were sVEGFR-1 and soluble endoglin (sEng), and the angiogenic factor, placental growth factor (PlGF).

METHODS

This retrospective longitudinal nested case-control study included 143 singleton pregnancies in the following groups: (1) patients with uncomplicated pregnancies who delivered a term infant with an appropriate weight for gestational age (n=124); and (2) patients who had a fetal death (n=19). Blood samples were collected at each prenatal visit, scheduled at 4-week intervals from the first trimester until delivery. Plasma concentrations of sVEGFR-1, sEng, and PlGF were determined by specific and sensitive ELISA. A linear mixed-effects model was used for analysis.

RESULTS

(1) The average profiles of analyte concentrations as a function of gestational age for sVEGFR-1, sEng and PlGF were different between women destined to have a fetal death and those with a normal pregnancy after adjusting for covariates (p<0.05); (2) Plasma sVEGFR-1 concentrations in patients destined to have a fetal death were significantly lower between 7 and 11 weeks of gestation and became significantly higher than those of women with a normal pregnancy between 20 and 37 weeks of gestation (p<0.05); (3) Similarly, plasma sEng concentrations of women destined to have a fetal death were lower at 7 weeks of gestation (p=0.04) and became higher than those of controls between 20 and 40 weeks of gestation (p<0.05); (4) In contrast, plasma PlGF concentrations were higher among patients destined to develop a fetal death between 7 and 14 weeks of gestation and became significantly lower than those in the control group between 22 and 39 weeks of gestation (p<0.05); (5) The ratio of PlGF/(sVEGFR-1 × sEng) was significantly higher in women destined to have a fetal death between 7 and 13 weeks of gestation (94-781%) and significantly lower (44-75%) than those in normal pregnant women between 20 and 40 weeks of gestation (p<0.05); (6) Similar results were obtained when patients with a fetal death were stratified into those who were diagnosed before or after 37 weeks of gestation.

CONCLUSIONS

Fetal death is characterised by higher maternal plasma concentrations of PlGF during the first trimester compared to normal pregnancy. This profile changes into an anti-angiogenic one during the second and third trimesters.

The origin of pre-eclampsia: from decidual "hyperoxia" to late hypoxia

Normal gestation implants on a relatively hypoxic deciduas so that trophoblast deeply invades endometrium and angiogenesis seeks for oxygen supply. If implantation occurs before those hypoxic conditions occur, trophoblast invasion is defective, due to the relatively high oxygen tension in the decidual environment, laying the foundations for subsequent pre-eclampsia.

Preeclampsia: 2-methoxyestradiol induces cytotrophoblast invasion and vascular development specifically under hypoxic conditions

Inadequate invasion of the uterus by cytotrophoblasts is speculated to result in pregnancy-induced disorders such as preeclampsia. However, the molecular mechanisms that govern appropriate invasion of cytotrophoblasts are unknown. Here, we demonstrate that under low-oxygen conditions (2.5% oxygen), 2-methoxyestradiol (2-ME), which is a metabolite of estradiol and is generated by catechol-o-methyltransferase (COMT), induces invasion of cytotrophoblasts into a naturally-derived, extracellular matrix. Neither low-oxygen conditions nor 2-ME alone induces the invasion of cytotrophoblasts in this system; however, low-oxygen conditions combined with 2-ME result in the appropriate invasion of cytotrophoblasts into the extracellular matrix. Cytotrophoblast invasion under these conditions is also associated with a decrease in the expression of hypoxia-inducible factor-1alpha (HIF-1alpha), transforming growth factor-beta3 (TGF-beta3), and tissue inhibitor of metalloproteinases-2 (TIMP-2). Pregnant COMT-deficient mice with hypoxic placentas and preeclampsia-like features demonstrate an up-regulation of HIF-1alpha, TGF-beta3, and TIMP-2 when compared with wild-type mice; normal levels are restored on administration of 2-ME, which also results in the resolution of preeclampsia-like features in these mice. Indeed, placentas from patients with preeclampsia reveal lower levels of COMT and higher levels of HIF-1alpha, TGF-beta3, and TIMP-2 when compared with those from normal pregnant women. We demonstrate that low-oxygen conditions of the placenta are a critical co-stimulator along with 2-ME for the proper invasion of cytotrophoblasts to facilitate appropriate vascular development and oxygenation during pregnancy.

Mitochondrial manganese superoxide dismutase mRNA expression in human chorioamniotic membranes and its association with labor, inflammation, and infection

OBJECTIVE

Human parturition is characterized by the activation of genes involved in acute inflammatory responses in the fetal membranes. Manganese superoxide dismutase (Mn SOD) is a mitochondrial enzyme that scavenges reactive oxygen species (ROS). Mn SOD is up-regulated in sites of inflammation and has an important role in the down-regulation of acute inflammatory processes. Therefore, the aim of this study was to determine the differences in Mn SOD mRNA expression in the fetal membranes in patients with term and preterm labor (PTL) as well as in acute chorioamnionitis.

STUDY DESIGN

Fetal membranes were obtained from patients in the following groups: (1) term not in labor (n = 29); (2) term in labor (n = 29); (3) spontaneous PTL with intact mebranes (n = 16); (4) PTL with histological chorioamnionitis (n = 12); (5) preterm prelabor rupture of the membranes (PPROM; n = 17); and (6) PPROM with histological chorioamnionitis (n = 21). Mn SOD mRNA expression in the membranes was determined by quantitative real-time reverse transcription-polymerase chain reaction.

RESULTS

(1) Mn SOD mRNA expression was higher in the fetal membranes of patients at term in labor than those not in labor (2.4-fold; p = 0.02); (2) the amount of Mn SOD mRNA in the fetal membranes was higher in PTL than in term labor or in PPROM (7.2-fold, p = 0.03; 3.2-fold, p = 0.03, respectively); (3) Mn SOD mRNA expression was higher when histological chorioamnionitis was present both among patients with PPROM (3.8-fold, p = 0.02) and with PTL (5.4-fold, p = 0.02) than in patients with these conditions without histological chorioamnionitis; (4) expression of Mn SOD mRNA was higher in PTL with chorioamnionitis than in PPROM with chorioamnionitis (4.3-fold, p = 0.03).

CONCLUSION

The increase in Mn SOD mRNA expression by fetal membranes in term labor and in histological chorioamnionitis in PTL and PPROM suggests that the fetus deploys anti-oxidant mechanisms to constrain the inflammatory processes in the chorioamniotic membranes.

Respiratory response of malignant and placental cells to changes in oxygen concentration

Malignant cells and foetal tissues are exposed to low oxygen partial pressure (pO2) in situ due to the limited supply of oxygenated blood. Whether these cells have adapted to low pO2 or live under constant constraint is not clear. Herein, we compared the respiratory responses of different malignant cell types, maternal and foetal placental leucocytes, and benign cells by incubating them under a gradient of pO2, from saturation to hypoxia, in a high resolution respirometer. The malignant cells and foetal leucocytes showed higher rates of mitochondrial oxygen uptake compared to the benign cells and maternal leucocytes, respectively. On the other hand, the mitochondrial oxygen uptake rates of the hypoxia adapted cells declined faster than the other cell types during the onset of hypoxia, probably suggesting conformance of aerobic metabolism to the local oxygen concentration. The O2 consumption rate per million cells (JO2) of the malignant cells declined only when the O2 concentration ([O2]) decreased to values<or=10 microM. On the other hand, the JO2 of the benign cells declined with the decrease in [O2] from 200 to 40 microM and <or=10 microM. In the [O2] ranges outside these values the JO2 remained constant regardless of the decline of [O2] in the medium. The JO2 of foetal leucocytes and malignant cells responded to the change in [O2] in a similar manner, and may indicate comparable mechanisms of adaptation to hypoxia.

A randomized double blind comparison of real and placebo acupuncture in IVF treatment

BACKGROUND

Acupuncture has been used during IVF treatment as it may improve outcome, however, there are concerns about the true efficacy of this approach. This randomized double blind study aimed to compare real acupuncture with placebo acupuncture in patients undergoing IVF treatment.

METHODS

On the day of embryo transfer (ET), 370 patients were randomly allocated to either real or placebo acupuncture according to a computer-generated randomization list in sealed opaque envelopes. They received 25 min of real or placebo acupuncture before and after ET. The endometrial and subendometrial vascularity, serum cortisol concentration and the anxiety level were evaluated before and after real and placebo acupuncture.

RESULTS

The overall pregnancy rate was significantly higher in the placebo acupuncture group than that in the real acupuncture group (55.1 versus 43.8%, respectively, P = 0.038; Common odds ratio 1.578 95% confidence interval 1.047-2.378). No significant differences were found in rates of ongoing pregnancy and live birth between the two groups. Reduction of endometrial and subendometrial vascularity, serum cortisol concentration and the anxiety level were observed following both real and placebo acupuncture, although there were no significant differences in the changes in all these indices between the two groups.

CONCLUSIONS

Placebo acupuncture was associated with a significantly higher overall pregnancy rate when compared with real acupuncture. Placebo acupuncture may not be inert. Trial registered with HKClinicalTrials.com: number HKCTR-236.

Oxygen, the Janus gas; its effects on human placental development and function

The accumulation of oxygen in the earth's atmosphere enabled metabolic pathways based on high-energy electron transfers that were capable of sustaining complex multicellular organisms to evolve. This advance came at a price, however, for the high reactivity of oxygen posed a major challenge as biological molecules became susceptible to oxidative damage, resulting in potential loss of function. Many extant physiological systems are therefore adapted, and homeostatically regulated, to supply sufficient oxygen to meet energy demands whilst also protecting cells, and mitochondria in particular, from excessive concentrations that could lead to oxidative damage. The invasive form of implantation displayed by the human conceptus presents particular challenges in this respect. During the first trimester, the conceptus develops in a low oxygen environment that favours organogenesis in the embryo, and cell proliferation and angiogenesis in the placenta. Later in pregnancy, higher oxygen concentrations are required to support the rapid growth of the fetus. This transition, which appears unique to the human placenta, must be negotiated safely for a successful pregnancy. Normally, onset of the maternal placental circulation is a progressive periphery-centre phenomenon, and is associated with extensive villous regression to form the chorion laeve. In cases of miscarriage, onset of the circulation is both precocious and disorganized, and excessive placental oxidative stress and villous regression undoubtedly contribute to loss of the pregnancy. Comparison of experimental and in vivo data indicates that fluctuations in placental oxygen concentration are a more powerful stimulus for the generation of oxidative stress than chronic hypoxia alone. Placental oxidative and endoplasmic reticulum stress appear to play key roles in the pathophysiology of complications of pregnancy, such as intrauterine growth restriction and preeclampsia, through their adverse impacts on placental function and growth. Establishing an inviolable maternal blood supply for the second and third trimesters is therefore one of the most crucial aspects of human placentation.

Tumor necrosis factor-alpha converting enzyme in the human placenta throughout gestation

Ectodomain shedding of epidermal growth factor receptor ligands such as transforming growth factor- alpha (TGF-alpha), heparin-binding epidermal growth factor-like growth factor (HBEGF), and amphiregulin (AREG) is considered to be important during implantation. Tumor necrosis factor-alpha converting enzyme (TACE) has been suggested as the major sheddase for these molecules. The objectives of this study are (1) to characterize the expression of TACE in the human placenta throughout gestation; (2) to determine the association between the expression of TACE with TGF-alpha, HBEGF, and AREG; (3) to ascertain whether TACE mediates TGF-alpha, HBEGF, and AREG shedding; and (4) to examine the effect of hypoxia on the expression of TACE. By analyzing a total of 55 villous samples representing different gestational ages, the authors found that TACE was continuously expressed in the placentas throughout gestation and that the levels of TACE were positively correlated with the levels of TGF-alpha, HBEGF, and AREG. Preadministration of a TACE inhibitor in villous explant cultures or transfection of cytotrophoblastic cells with TACE-specific small interference RNA decreased the shedding of HBEGF and AREG. Moreover, hypoxia (2% O(2)) caused an increase in the levels of TACE mRNA and protein in villous explants and primary cytotrophoblastic cells in vitro. These results indicate that oxygen regulates the expression of TACE and that TACE may be important for placental development during human pregnancy.

Maternal hypoxia activates endovascular trophoblast cell invasion

Oxygen is a critical regulator of placentation. Early placental development occurs in a predominantly low oxygen environment and is, at least partially, under the control of hypoxia signaling pathways. In the present study, in vivo hypobaric hypoxia was used as an experimental tool to delineate hypoxia-sensitive events during placentation. Pregnant rats were exposed to the equivalent of 11% oxygen between days 6.5 and 13.5 of gestation. Pair-fed pregnant animals exposed to ambient conditions were included as a control group. Uterine mesometrial blood vessels in the hypoxia-exposed animals were greatly expanded and some contained large cuboidal cells that were positive for cytokeratin and other markers characteristic of invasive trophoblast cells. Unlike later in gestation, the route of trophoblast cell invasion in the hypoxia-exposed animals was restricted to endovascular, with no interstitial invasion observed. Hypoxia-activated endovascular trophoblast invasion required exposure to hypoxia from gestation day 8.5 to day 9.5. Activation of the invasive trophoblast lineage was also associated with an enlargement of the junctional zone of the chorioallantoic placenta, a source of invasive trophoblast cell progenitors. In summary, maternal hypoxia during early stages of placentation activates the invasive endovascular trophoblast cell lineage and promotes uterine vascular remodeling.

The role of endometrial blood flow measured by three-dimensional power Doppler ultrasound in the prediction of pregnancy during in vitro fertilization treatment

Ultrasound examination of the endometrium is a commonly used non-invasive method to assess endometrial receptivity during in vitro fertilization (IVF) treatment. A good blood supply towards the endometrium is usually considered to be an essential requirement for implantation and therefore assessment of endometrial blood flow in IVF treatment has attracted a lot of attention in recent years. Doppler study of uterine arteries does not reflect the actual blood flow to the endometrium. Endometrial and subendometrial blood flows can be more objectively and reliably measured with three-dimensional power Doppler ultrasound. However, conflicting results are reported with regard to their role in the prediction of pregnancy in IVF treatment. Relevant studies in the literature differed in patients' characteristics, the day of ultrasound examination and the selection of the subendometrial region. As the degree of change in endometrial perfusion from the late follicular phase to the early luteal phase may be a more important determinant of endometrial receptivity, further studies should be conducted to determine the change in endometrial and subendometrial blood flows from late follicular phase to early luteal phase in order to delineate the role of endometrial and subendometrial blood flows in predicting IVF outcome.

New approaches to pathogenesis of malaria in pregnancy

Malaria infection during pregnancy is associated with poor maternal and foetal outcomes including low birth weight. In malaria-endemic areas, low birth weight is primarily a consequence of foetal growth restriction. Little is known on the pathogenesis of foetal growth restriction and our understanding of the relationship between epidemiological observations and the pathogenesis or consequences of disease is incomplete. In this review, we describe these gaps in our knowledge and also try to identify goals for future research into malaria in pregnancy. Foetal growth restriction results from a complex four-dimensional interaction between the foetus, the mother and the malaria parasite over gestation, and research into its pathogenesis may be advanced by combining longitudinal studies with techniques and approaches new to the field of malaria in pregnancy. Such approaches would greatly increase our knowledge on the pathogenesis of this disease and may provide new avenues for intervention strategies.

The role of oxidative stress in spontaneous abortion and recurrent pregnancy loss: a systematic review

Human reproduction is not considered a highly efficient biological process. Before the end of the first trimester, 30%-50% of conceptions end in spontaneous abortion. Most losses occur at the time of implantation. 15%-20% of clinical pregnancies end in spontaneous abortions. Recurrent pregnancy loss is a frustrating clinical problem both for clinicians and patients. Recurrent pregnancy loss affects 0.5%-3% of women in the reproductive age group, and between 50%-60% of recurrent pregnancy losses are idiopathic. Oxidative stress-induced damage has been hypothesized to play a role in spontaneous abortion, idiopathic recurrent pregnancy loss, hydatidiform mole, defective embryogenesis, and drug-induced teratogenicity. Some studies implicate systemic and placental oxidative stress in the pathophysiology of abortion and recurrent pregnancy loss. Oxidant-induced endothelial damage, impaired placental vascularization and immune malfunction have all been proposed to play a role in the pathophysiology of idiopathic recurrent pregnancy loss. Oxidative stress-induced placental dysfunction may be a common cause of the multifactorial and polygenic etiologies of abortion, recurrent pregnancy loss, defective embryogenesis, hydatidiform mole, and drug-induced teratogenic effects. Oxidative stress-induced modification of phospholipids has been linked to the formation of antiphospholipid antibodies in the antiphospholipid syndrome. The objective of this review was to examine the association between oxidative stress, spontaneous abortion and recurrent pregnancy loss, based on the published literature. We conducted an extensive literature search utilizing the databases of Medline, CINAHL, and Cochrane from 1986 to 2005. The following keywords were used: oxidative stress, abortion, recurrent pregnancy loss, reactive oxygen species, antioxidants, fetal development, and embryopathies. We conducted an electronic search, as well as a manual search of cross-references. We have included all studies in the English language found in the literature focusing on oxidative stress and its association with abortions, recurrent pregnancy loss and drug-induced teratogenicity. The role of antioxidant vitamins for primary prevention of oxidative stress-induced pathologies needs to be investigated further.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians.

LEARNING OBJECTIVES

After completion of this article, the reader should be able to state that the causes of spontaneous and recurrent abortion are multifaceted, however, some of the causes may be preventable and also explain that the role of oxidative stress during pregnancy and adverse pregnancy outcomes has a basis in pathophysiology, although the role of oxidative stress and the treatment of oxidative stress during or before pregnancy remains speculative.

Preeclampsia: new insights

PURPOSE OF REVIEW

Preeclampsia is a disorder of gestation characterized by hypertension and proteinuria and can be complicated by eclamptic seizures. This review describes recent advances in the role of the renin-angiotensin system and angiogenic and anti-angiogenic factors of placental origin in its pathogenesis.

RECENT FINDINGS

Deficient uteroplacental perfusion has been recognized to be a feature in all preeclampsia syndromes. Increased renin expression observed in humans and animal models supports the concept that activation of the decidual renin-angiotensin system may mediate the pathogenesis of preeclampsia. Novel angiotensin II-related biomolecular mechanisms, angiotensin II type 1-B2 receptor heterodimerization and autoantibody against angiotensin II type 1 have recently been described in preeclampsia. New evidence suggests that vascular endothelial growth factor and its receptors, antagonists, and reduced placental growth factor may play a role in the development of proteinuria and other renal injury-mediated manifestations in preeclampsia.

SUMMARY

Vascular maladaptation, with increased vasomotor tone, endothelial dysfunction, increased sensitivity to angiotensin II and norepinephrine, and multiorgan dysfunction seen in preeclampsia, may be explained by angiotensin II-mediated mechanisms. Future investigations need to define the mechanism of activation of the decidual renin-angiotensin system and the release of placental factors in the pathogenesis of preeclampsia.

Hypoxia and placental remodelling

In the first trimester of pregnancy fetal trophoblast cells invade the maternal uterine spiral arteries leading to loss of the vascular cells from the vessel wall and remodelling of the extracellular matrix. This is crucial to ensure that sufficient blood can reach the developing fetus. Impaired arterial remodelling is a feature of the major pregnancy pathologies pre-eclampsia and fetal growth restriction. Despite its importance, little is known about the regulation of this process. We have shown, using in vitro culture models and ex vivo explant models, that trophoblast cells play an active role in remodelling spiral arteries, and have implicated apoptotic events in this process. Further we have shown that trophoblast-derived factors such as Fas-ligand, tumor necrosis factor-related apoptosis inducing ligand (TRAIL) are important regulators of this process. The oxygen tension within the uteroplacental environment will vary with gestational age and will depend on the extent of trophoblast invasion and artery remodelling. Fluctuations in oxygen tension may be an important determinant of cellular events both during invasion towards uterine vessels and during the remodelling process. The components of this process known to be regulated by oxygen are reviewed, including lessons that can be learned from pregnancies at high altitude. In addition, data on the effect of varying oxygen tension on trophoblast production of pro-apoptotic factors and susceptibility of vascular smooth muscle cells to induction of apoptosis are described.

Coordinated regulation of human trophoblast invasiveness by macrophages and interleukin 10

Trophoblast invasion and modification of the spiral arterioles are essential for the establishment of adequate uteroplacental blood flow during pregnancy. However, such vascular remodeling is deficient in preeclampsia. This disease is also associated with increased maternal levels of circulating proinflammatory cytokines such as tumor necrosis factor (TNF) and reduced levels of immunoregulatory cytokines such as interleukin 10 (IL10). We have previously shown that activated macrophages inhibit trophoblast invasiveness in vitro. The present study demonstrates that IL10 interferes with the invasion-inhibitory effect that activated macrophages exert on trophoblast cells. Co-culture experiments revealed that human lipopolysaccharide (LPS)-activated macrophages inhibited the ability of immortalized HTR-8/SVneo human trophoblast cells to invade through reconstituted extracellular matrix. This effect of activated macrophages on trophoblast invasiveness was paralleled by decreased expression of urokinase plasminogen activator receptor (PLAUR) on the surface of trophoblast cells, and by increased secretion of plasminogen activator inhibitor type 1 (SERPINE1). Exposure of LPS-treated macrophages to IL10 prior to co-culture prevented their ability to inhibit trophoblast invasion, PLAUR expression, and to stimulate SERPINE1 secretion. Interleukin 10 prevented macrophage activation by LPS as determined by the lack of secretion of TNF in the culture medium, and a neutralizing TNF antibody completely blocked the effect of macrophages on trophoblast invasion. These results indicate that decreased circulating levels of IL10 associated with preeclampsia may contribute to inadequate trophoblast invasion and remodeling of the uterine spiral arterioles.

Complex congenital malformations and the impact of the plasminogen activator system and beta-hCG in amniotic fluid

OBJECTIVE

The plasminogen activator system and beta-hCG may affect neural crest cells and angiogenesis, and thereby embryogenesis. Therefore, we investigated these parameters in amniotic fluids of pregnancies with a complex congenital malformation.

STUDY DESIGN

In a case-control study amniotic fluid samples were collected from 62 pregnancies with a complex congenital malformation and from 110 healthy control pregnancies at an obstetric department of a large university hospital in the Netherlands. We determined concentrations of tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA), plasminogen activator inhibitors (PAI-1, PAI-2), tPA approximately PAI-1 and uPA approximately PAI-1 complexes, and beta-hCG with enzyme-linked immunosorbent assays. Mann-Whitney U-tests and analysis of covariance, adjusting for gestational and maternal age, were performed for data comparisons.

RESULTS

Compared with controls, cases demonstrated significantly lower adjusted geometric mean levels of uPA (24%), tPA (> or =19%) and tPA approximately PAI-1 (35%). Cases showed significantly higher adjusted mean levels of beta-hCG (> or =48%) and PAI-2 (10 ng/mL) than controls. Mean PAI-1 and uPA approximately PAI-1 levels were comparable between both groups.

CONCLUSIONS

Disturbances in the plasminogen activator system and beta-hCG levels are suggested to be involved in the pathogenesis of complex congenital malformations by affecting neural crest cell migration and angiogenesis.

Hypoxia regulates the expression of PHLDA2 in primary term human trophoblasts

Hypoxia influences gene expression in placental trophoblasts. We sought to examine the effect of hypoxia on trophoblast expression of human PHLDA2 (also termed IPL, TSSC3 or BWR-1C), a product of an imprinted gene on human chromosome 11p15.5 whose murine ortholog plays a pivotal role in placental development. We initially confirmed that PHLDA2 was expressed in term placental villi, primarily in the trophoblast layer. Using quantitative PCR we found that the expression of PHLDA2 gradually declined during differentiation of primary term human trophoblasts. A similar expression pattern was seen for p57(Kip2) and IGF-II, both products of imprinted genes on chromosome 11p15.5. Exposure of trophoblasts to hypoxia in vitro (O(2)<or=2%) markedly reduced the expression of PHLDA2 mRNA and protein. This effect was not consistent among other chromosome 11p15.5 genes products, as the expression of p57(Kip2) decreased, but that of IGF-II increased in hypoxic trophoblasts. PHLDA2 expression in trophoblasts exposed to TGFbeta1, -beta2 or -beta3 was unchanged. We conclude that hypoxia down-regulates the expression of PHLDA2 in human term placental trophoblasts. As murine PHLDA2 limits placental growth, our results suggest that down-regulation of PHLDA2 attenuates the impact of hypoxia on placental growth.

First-trimester trophoblast cell model gene response to hypoxia

OBJECTIVE

Trophoblast invasion, which sets the stage for placentation and pregnancy outcome, likely occurs in a hypoxic environment. We used microarray technology in a trophoblast cell line to identify hypoxia-responsive genes that may impact placentation.

STUDY DESIGN

An immortalized extravillous cytotrophoblast cell line, HTR-8/SVneo, was exposed to normoxia (20% oxygen) or hypoxia (1% oxygen) for 6 hours. Total RNA was harvested and prepared for microarray study. Quantitative reverse transcriptase polymerase chain reaction was performed for array confirmation.

RESULTS

We confirmed the up- and down-regulation of 10 hypoxia-responsive genes using quantitative reverse transcriptase polymerase chain reaction. Ontologic gene categories that were found to be hypoxia-responsive included motility/migration, angiogenesis, and apoptosis.

CONCLUSION

Specific genes that were found to be up-regulated in this first-trimester array (such as plasminogen activator inhibitor-1 and tissue inhibitor of metalloproteinase 3) have been described in preeclampsia. The hypoxia-responsive genes that we identified may be physiologic in early pregnancy. However, up-regulation of these same genes in later pregnancy augurs poorly.

N-Myc Down-regulated Gene 1 Modulates the Response of Term Human Trophoblasts to Hypoxic Injury

The placenta is susceptible to diverse insults during human pregnancy. The expression of the protein N-myc down-regulated gene 1 (NDRG1) is regulated during cell proliferation, differentiation, and in response to stress. Nevertheless, the function of this protein in humans remains unknown. We tested the hypothesis that NDRG1 is up-regulated in hypoxic primary human trophoblasts and that NDRG1 modulates trophoblast response to hypoxia. We initially demonstrated that the expression of NDRG1 is enhanced in primary human trophoblasts exposed to hypoxia. Importantly, we found a similar increase in NDRG1 expression in placental samples derived from either singleton gestations complicated by intrauterine growth restriction or from dizygotic twin gestation where one twin exhibited growth restriction. Having established efficient lentivirus-mediated transfection of primary human trophoblasts, we overexpressed NDRG1 in trophoblasts, which resulted in enhanced trophoblast differentiation. In contrast, lentivirus-driven short interfering RNA-mediated silencing of NDRG1 diminished trophoblast viability and differentiation. Consistent with these results, NDRG1 reduced the expression level of p53 in trophoblasts cultured in standard or hypoxic conditions. Furthermore, NDRG1 expression was regulated by the activity of SIRT1 (Sir2-like protein 1), which promotes cell survival. Together, our data indicate that NDRG1 interacts with SIRT1/p53 signaling to attenuate hypoxic injury in human trophoblasts.

The role of endometrial and subendometrial vascularity measured by three-dimensional power Doppler ultrasound in the prediction of pregnancy during frozen–thawed embryo transfer cycles

BACKGROUND

A good blood supply to the endometrium is usually considered as an essential requirement for implantation.

OBJECTIVE

The aim of this study was to evaluate the role of endometrial and subendometrial vascularity in the prediction of pregnancy during frozen-thawed embryo transfer (FET) cycles.

METHODS

Women undergoing FET in natural or clomiphene-induced cycles after the first stimulated IVF treatment were recruited. A three-dimensional (3D) ultrasound examination with power Doppler was performed 1 day after the LH surge to determine endometrial thickness, endometrial pattern, pulsatility index (PI) and resistance index (RI) of uterine vessels, endometrial volume, vascularization index, flow index and vascularization flow index of endometrial and subendometrial regions.

RESULTS

Women in the pregnant group were significantly younger and used less gonadotrophins in their stimulated cycle. Endometrial thickness, endometrial volume, endometrial pattern, uterine PI, uterine RI, endometrial and subendometrial 3D power Doppler flow indices were similar between the nonpregnant and the pregnant groups. The age of women was the only predictive factor for pregnancy. Receiver operating characteristic curve analysis revealed that the area under the curve was around 0.5 for all ultrasound parameters for endometrial receptivity.

CONCLUSION

Vascularity of endometrial and subendometrial layers measured by 3D power Doppler ultrasound is not a good predictor of pregnancy in FET cycles if measured at one time point only.

The regulation of trophoblast differentiation by oxygen in the first trimester of pregnancy

In the first trimester of human pregnancy villous cytotrophoblasts are able to differentiate to form either the overlying syncytiotrophoblast layer or, in anchoring villi, extravillous trophoblasts which grow out from the villi and invade into the maternal decidua, acting to both physically attach the placenta to the decidua, and modify the maternal spiral arteries to sustain pregnancy. During the first 10-12 weeks of gestation, extravillous trophoblast plugs block the spiral arteries and prevent maternal blood flow entering the intervillous space, thereby creating an environment of physiological hypoxia in which placental and fetal development occur. As extravillous trophoblasts migrate away from the villus they differentiate from a proliferative to an invasive phenotype. The hypoxic environment of the first trimester is believed to play an important role in the regulation of trophoblast differentiation. However, there is currently a large body of conflicting experimental evidence concerning this topic. This review examines the experimental evidence to date on the role of oxygen in trophoblast differentiation.

The role of endometrial and subendometrial blood flows measured by three-dimensional power Doppler ultrasound in the prediction of pregnancy during IVF treatment

BACKGROUND

A good blood supply towards the endometrium is usually considered to be an essential requirement for implantation. We aimed to evaluate the role of endometrial and subendometrial blood flows in the prediction of pregnancy during IVF treatment.

METHODS

Patients undergoing the first IVF cycle were recruited. A three-dimensional (3D) ultrasound examination with power Doppler was performed on the day of oocyte retrieval to determine endometrial thickness, endometrial pattern, pulsatility index (PI) and resistance index (RI) of uterine vessels, endometrial volume, vascularization index (VI), flow index (FI) and vascularization flow index (VFI) of endometrial and subendometrial regions.

RESULTS

Uterine RI, endometrial VI and VFI were significantly lower in the pregnant group than the non-pregnant group. There was a non-significant trend of higher implantation and pregnancy rates in patients with absent endometrial or subendometrial blood flow. The number of embryos replaced and endometrial VI were the only two predictive factors for pregnancy. Receiver operator characteristic curve analysis revealed that the area under the curve was approximately 0.5 for all ultrasound parameters for endometrial receptivity.

CONCLUSION

Endometrial and subendometrial blood flows measured by 3D power Doppler ultrasound were not good predictors of pregnancy if they were measured at one time-point during IVF treatment.

Platelet-derived soluble factors induce human extravillous trophoblast migration and differentiation: platelets are a possible regulator of trophoblast infiltration into maternal spiral arteries

In early pregnancy, human extravillous trophoblasts (EVTs) invade and remodel maternal arteries. We have previously demonstrated that CCR1 is expressed on perivascular/endovascular trophoblasts and that CCR1 ligands promote EVT migration. In this study, we examined the physiologic roles of platelet-derived chemoattractants on EVT invasion. By immunohistochemistry, maternal platelets were localized among endovascular trophoblasts within the lumen of spiral arteries. Extracellular matrices (ECMs) were also detected among endovascular trophoblasts and platelets, suggesting that the platelets in these arteries were activated by ECMs. In vitro, platelets attached to EVTs isolated from human villous explant cultures and expressed P-selectin on the cell surface. Platelets significantly enhanced migration of EVTs without affecting proliferation of EVTs or secretion of MMP-2 or MMP-9. The invasion-enhancing effect of platelet-derived culture medium on EVTs was neutralized by anti-CCR1 antibody. Heat treatment completely abrogated the invasion-promoting effects of platelet-derived culture medium, but charcoal stripping did not. Platelets also induced endovascular trophoblast-like morphologic changes and integrin alpha1 expression in EVTs during 48-hour culture. These findings suggest that maternal platelets activated in the spiral arteries can regulate trophoblastic vascular infiltration and differentiation by releasing various soluble factors.

Direct placental effects of cigarette smoke protect women from pre-eclampsia: the specific roles of carbon monoxide and antioxidant systems in the placenta

Pre-eclampsia is a hypertensive disorder of pregnancy characterized by shallow placentation, inadequate placental perfusion, localized placental oxidative stress, a heightened maternal inflammatory response and subsequent maternal endothelial dysfunction. This pathophysiology leads to an increase in maternal blood pressure, edema and proteinurea. Interestingly, women who smoke cigarettes throughout pregnancy are at a 33% reduced risk of developing this disorder. The exact mechanisms through which cigarette smoke reduces the risk of pre-eclampsia are not yet understood. We propose that cigarette smoke reduces the risk of developing pre-eclampsia via direct placental effects. In this review we will address, and provide evidence for, our specific hypotheses that: (a) CO increases trophoblast invasion and spiral arteriole remodeling; (b) CO decreases a localized inflammatory response at the level of the decidua; (c) CO increases utero-placental, intra-placental and feto-placental blood flow; (d) CO decreases hypoxia-induced apoptosis of the syncitiotrophoblast layer; (e) CO activates hemoproteins involved in normal endothelial functioning normally acted upon by NO; (f) compound(s) within cigarette smoke result in upregulation of antioxidant systems within the placenta. These various mechanisms of action must be further examined as they may provide valuable keys to novel therapeutic design in the realm of pre-eclampsia research.

A novel role for vascular endothelial growth factor as an autocrine survival factor for embryonic stem cells during hypoxia

Vascular endothelial growth factor (VEGF) is best known for its angiogenic activity on endothelial cells, but it also affects neurons, pneumocytes, and other mature cell types as well as endothelial, neural, and hematopoietic progenitors. Here, we examined its effect on pluripotential embryonic stem (ES) cells under hypoxic stress. ES cells were found to produce VEGF and to express VEGF receptor-2 and neuropilin-1 (Nrp-1), a VEGF165 isoform-specific receptor. During hypoxia, expression levels of VEGF, Flk-1, and Nrp-1 were elevated. Inhibition or targeted gene inactivation of VEGF increased ES cell apoptosis during prolonged hypoxia (48 h) by about 10-fold. The survival activity of VEGF was specific since inhibition of other growth factors (including basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor, platelet-derived growth factor, and placental growth factor) had no effect. Neuropilin-1 was involved in the VEGF-survival activity since overexpression of Nrp-1 decreased hypoxia-induced apoptosis about 3-fold. The hypoxia-response element, via which hypoxia-inducible transcription factors up-regulate VEGF expression under hypoxic conditions, was critical since targeted deletion of this element in the VEGF promoter enhanced hypoxia-induced ES cell apoptosis to the same extent as VEGF inhibition or gene inactivation. Thus, VEGF plays a critical role in survival of ES cells during prolonged hypoxia.

Endometrial and subendometrial perfusion are impaired in women with unexplained subfertility

BACKGROUND

We used three-dimensional power Doppler angiography (3D-PDA) to examine the periodic changes in endometrial development and subendometrial vascularity during the normal menstrual cycle in 29 women with unexplained subfertility and 19 controls.

METHODS

3D-PDA was performed on alternate days from day 3 of the cycle until ovulation and then every 4 days until menses. VOCAL (Virtual Organ Computer-aided AnaLysis) and shell-imaging were used to define and to quantify the power Doppler signal within the endometrial and subendometrial regions producing indices of their relative vascularity.

RESULTS

Women with unexplained subfertility demonstrated significant changes with time (P<0.001) in the indices of vascularity within the endometrium and subendometrium during the menstrual cycle characterized by a pre-ovulatory peak and post-ovulatory fall. These changes mirrored those observed in the control group but were significantly reduced in the endometrium and subendometrium during the mid-late follicular phase and early luteal phase. There were no differences in endometrial thickness or volume between the groups or in the plasma concentrations of estradiol or progesterone.

CONCLUSIONS

Endometrial and subendometrial vascularity are significantly reduced in women with unexplained subfertility during the mid-late follicular phase irrespective of estradiol or progesterone concentrations and endometrial morphometry.