Influence of hypoxia on vascular endothelial growth factor and chorionic gonadotrophin production in the trophoblast-derived cell lines: JEG, JAr and BeWo

Trophoblast-derived factors drive human mesenchymal stem cell differentiation along an endothelial lineage: A model of early placental vasculogenesis

Mechanisms controlling the process and patterning of blood vessel development in the placenta remain largely unknown. The close physical proximity of early blood vessels observed in the placenta and the cytotrophoblast, as well as the reported production of vasculogenic growth factors by the latter, suggests that signalling between these two niches may be important. Here, we have developed an in vitro model to address the hypothesis that the cytotrophoblast, by the secretion of soluble factors, drives differentiation of resident sub-trophoblastic mesenchymal stem cells (MSCs) along a vascular lineage, thereby establishing feto-placental circulation. BM-MSCs (a readily available model for placental stem cells) were treated with conditioned medium containing the secretome from human BeWo trophoblast cells, or endothelial growth medium (EGM2) supplemented with exogenous growth factors (VEGF, IGF1 and EGF) for 10-12 days. Trophoblast-conditioned media, found to contain detectable concentrations of cytokines including VEGF, uPAR, TIMP-1, TIMP-2, IL6 and placental growth factor, induced the expression of the endothelial genes CD31, von Willibrand factor (vWF), FLT-1, VEGFR2 and VE-Cadherin. Upregulation of vWF protein was also detected following growth in trophoblast-conditioned media, using immunocytochemistry. Wound healing (migration assay) and Matrigel-tube formation assays confirmed that the BM-MSCs cultured in trophoblast-conditioned media exhibited functional measures of endothelial cells in addition to expressing relevant markers. Identification of key trophoblast-secreted factors and their promotion of endothelial differentiation in BM-MSCs helps advance our theories regarding the close relationship of the mesenchymal stem cell-cytotrophoblast niche in coordinating the complex angiogenic events that occur in the placenta. The in vitro model presented here provides an accessible and reproducible tool for further investigations into placental development.

Histopathological study with immunohistochemical expression of vascular endothelial growth factor in placentas of hyperglycemic and diabetic women

AIMS AND OBJECTIVES

Spectrum of hyperglycemia in pregnancy includes gestational diabetes mellitus (GDM), mild hyperglycemia, and overt diabetes. Many authors have worked on morphological changes of the placenta in diabetes, but few studies have correlated histopathological changes with vascular endothelial growth factor (VEGF) immunoexpression. The aim of this study was to detect different histopathological changes in various groups of diabetic placentas and to correlate with VEGF immunoexpression.

MATERIALS AND METHODS

Pregnant women were screened for diabetes. They were subsequently divided into normoglycemic (12 cases), GDM (33 cases), mild hyperglycemic (13 cases), and overt diabetes (18 cases). Placentas collected were subjected to histopathological examination. VEGF expressions were studied by immunohistochemistry.

RESULTS

Overt diabetic placenta displayed villous immaturity (44.4%), villous edema (38.9%), chorangiosis (61.1%), fibrinoid substance deposition (38.9%), and Hofbauer cell hyperplasia in 44.4% cases. GDM placentas displayed villous immaturity (45.5%), villous edema (45.5%), chorangiosis (42.4%), and fibrinoid substance deposition in 75.6% cases. Mild hyperglycemic placentas displayed villous immaturity (38.5%), chorangiosis (61.5%), and fibrinoid substance deposition in 61.5% cases. VEGF immunoexpression in GDM placentas was absent in all placental components except syncytiotrophoblast. VEGF expression in overt diabetic placentas was increased in syncytiotrophoblast and capillary endothelium compared to normoglycemic placentas. Mild hyperglycemic placentas expressed similar VEGF expression in all components when compared to normoglycemic controls. However, it displayed weak expression in vessel endothelium.

CONCLUSION

Histopathological changes in diabetic placentas might be a consequence of altered or abnormal VEGF expression in diabetic placentas. Pathogenesis and VEGF expression in GDM placentas are significantly different from overt diabetic placentas.

Altered maternal immune networks are associated with adverse child neurodevelopment: Impact of alcohol consumption during pregnancy

Cytokines and chemokines are potent modulators of brain development and as such, dysregulation of the maternal immune system can result in deviations in the fetal cytokine balance, altering the course of typical brain development, and putting the individual on a "pathway to pathology". In the current study, we used a multi-variate approach to evaluate networks of interacting cytokines and investigated whether alterations in the maternal immune milieu could be linked to alcohol-related and alcohol-independent child neurodevelopmental delay. This was achieved through the measurement of 40 cytokines/chemokines from maternal blood samples collected during the second and third trimesters of pregnancy. Importantly, during the second trimester we identified network enrichment in levels of cytokines including IFN-ɣ, IL-10, TNF-β, TNF-α, and CRP associated with offspring neurodevelopmental delay. However, as elevations in levels of these cytokines have previously been reported in a wide range of neurodevelopmental disorders including autism spectrum disorder and schizophrenia, we suggest that this cytokine profile is likely not disorder specific, but rather may be an indicator of neurodevelopmental delay in general. By contrast, distinct clusters of activated/inhibited cytokines were identified based on maternal alcohol consumption and child neurodevelopmental outcome. Specifically, cytokines including IL-15, IL-10, MDC, and members of the VEGF sub-family were highest in alcohol-consuming mothers of children with neurodevelopmental delay and were identified in both network analyses and examination of individual cytokines, whereas a differential and unique cytokine profile was identified in the case of alcohol-independent child neurodevelopmental delay. We propose that the current findings could provide a critical step towards the development of early biomarkers and possibly interventions for alcohol-related neurodevelopmental delay. Importantly, the current approach could be informative for understanding mechanisms linking maternal immune system dysfunction and adverse child outcomes in a range of other neurodevelopmental disorders.

Decreased PGF may contribute to trophoblast dysfunction in fetal growth restriction

Fetal growth restriction (FGR) threatens perinatal health and is correlated with increased incidence of fetal original adult diseases. Most cases of FGR were idiopathic, which were supposed to be associated with placental abnormality. Decreased circulating placental growth factor (PGF) was recognized as an indication of placental deficiency in FGR. In this study, the epigenetic regulation of PGF in FGR placentas and the involvement of PGF in modulation of trophoblast activity were investigated. The expression level of PGF in placental tissues was determined by RT-qPCR, immunohistochemistry and ELISA. DNA methylation profile of PGF gene was analyzed by bisulfite sequencing. Trophoblastic cell lines were treated with ZM-306416, an inhibitor of PGF receptor FLT1, to observe the effect of PGF/FLT1 signaling on cell proliferation and migration. We demonstrated that PGF was downregulated in placentas from FGR pregnancies compared with normal controls. The villous expression of PGF was positively correlated with placental and fetal weight. The CpG island inside PGF promoter was hypomethylated without obvious difference in both normal and FGR placentas. However, the higher DNA methylation at another CpG island downstream exon 7 of PGF was demonstrated in FGR placentas. Additionally, we found FLT1 was expressed in trophoblast cells. Inhibition of PGF/FLT1 signaling by a selective inhibitor impaired trophoblast proliferation and migration. In conclusion, our data suggested that the PGF expression was dysregulated, and disrupted PGF/FLT1 signaling in trophoblast might contribute to placenta dysfunction in FGR. Thus, our results support the significant role of PGF in the pathogenesis of FGR.

Systematic Review of Micro-RNA Expression in Pre-Eclampsia Identifies a Number of Common Pathways Associated with the Disease

Background

Pre-eclampsia (PE) is a complex, multi-systemic condition of pregnancy which greatly impacts maternal and perinatal morbidity and mortality. MicroRNAs (miRs) are differentially expressed in PE and may be important in helping to understand the condition and its pathogenesis.

Methods

Case-control studies investigating expression of miRs in PE were collected through a systematic literature search. Data was extracted and compared from 58 studies to identify the most promising miRs associated with PE pathogenesis and identify areas of methodology which could account for often conflicting results.

Results

Some of the most frequently differentially expressed miRs in PE include miR-210, miR-223 and miR-126/126* which associate strongly with the etiological domains of hypoxia, immunology and angiogenesis. Members of the miR-515 family belonging to the imprinted chromosome 19 miR cluster with putative roles in trophoblast invasion were also found to be differentially expressed. Certain miRs appear to associate with more severe forms of PE such as miR-210 and the immune-related miR-181a and miR-15 families. Patterns of miR expression may help pinpoint key pathways (e.g. IL-6/miR-223/STAT3) and aid in untangling the heterogeneous nature of PE. The detectable presence of many PE-associated miRs in antenatal circulatory samples suggests their usefulness as predictive biomarkers. Further progress in ascertaining the clinical value of miRs and in understanding how they might contribute to pathogenesis is predicated upon resolving current methodological challenges in studies. These include differences in diagnostic criteria, cohort characteristics, sampling technique, RNA isolation and platform-dependent variation in miR profiling.

Conclusion

Reviewing studies of PE-associated miRs has revealed their potential as informants of underlying target genes and pathways relating to PE pathogenesis. However, the incongruity in results across current studies hampers their capacity to be useful biomarkers of the condition.

Ketoconazole-induced estrogen deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats

This study investigated the relationship among estrogen, placental blood flow and placental weight gain in rats treated with ketoconazole. Oral administration of ketoconazole (25mg/kg/day) on Days 12-14 of pregnancy induced reduction of plasma estradiol-17β (E2) concentration, transient decrease in placental blood flow and increased intensity of a hypoxia-related marker in the placenta on Day 14 of pregnancy. On Day 20 of pregnancy, placental weights of ketoconazole-treated rats increased when compared to controls. Histologically, maternal sinusoidal area of the placenta decreased on Day 14 of pregnancy and the total area of maternal and fetal sinusoids increased on Day 20. All the changes disappeared by concomitant subcutaneous infusion of E2. These results indicate that ketoconazole-induced E2 deficiency causes transient decrease in placental blood flow associated with hypoxia and later placental weight gain in rats.

A Unique Expression of Keratin 14 in a Subset of Trophoblast Cells

The placenta, a transient organ in human, is essential for pregnancy maintenance and for fetal growth and development. Trophoblast and stromal cells are the main cell types present in human placenta. Trophoblast cells are present in different subtypes depending on their differentiation state and their temporal and spatial location during pregnancy. The stromal cells are of extraembryonic mesenchymal origin and are important for villous formation and maintenance. Interestingly, many pregnancy-related diseases are associated with defect in trophoblast differentiation and villous integrity. Therefore, it's crucial to specifically identify each type of placental cells using specific markers. Keratins (CK) are widely used as marker of epithelial cells, cancer origin identification and in some cases as marker of stem/progenitor cells. Vimentin is widely used as marker of mesenchymal cells. The aim of this study is to characterize the presence of different keratins in human trophoblast cells and vimentin in stromal cells. Using immunohistochemistry on term placental sections, our results show that vimentin is solely expressed in stromal-mesenchymal cells while keratins 5, 7, 8, 14 and 19 are expressed in trophoblast cells. Interestingly, all keratins tested, except for keratin 14, were evenly expressed in all trophoblast cells. Keratin 14 was expressed in a subset of CK7 positive cells. Moreover, the same results were obtained when using freshly isolated cytotrophoblast cells or BeWo cells. In conclusion, this study is a crucial step in the advancement of our knowledge in placental cell type identification and characterization.

Vascular endothelial growth factor and endothelin-1 levels in normal pregnant women and pregnant women with pre-eclampsia

The aim of the study was to estimate the levels of vascular endothelial growth factor (VEGF) and endothelin-1 (ET-1) in maternal serum from normal pregnant women and women with pre-eclampsia. Serum concentrations of VEGF and ET-1 were measured in maternal blood in control group (n = 40) and in pregnancies complicated by pre-eclampsia (n = 40). Results showed that maternal VEGF levels were significantly raised in women with pre-eclampsia (p < 0.001). ET-1 concentration was not significantly different among women with pre-eclampsia compared with that in the control group. It was concluded that an increase in serum VEGF level was demonstrated in pre-eclampsia, suggesting that VEGF is involved in pathogenesis of pre-eclampsia. Further studies are needed to determine the serum concentrations of VEGF in pregnant women before the development of pre-eclampsia.

Maternal and fetoplacental hypoxia do not alter circulating angiogenic growth effectors during human pregnancy

One causal model of preeclampsia (PE) postulates that placental hypoxia alters the production of angiogenic growth effectors (AGEs), causing an imbalance leading to maternal endothelial cell dysfunction. We tested this model using the natural experiment of high-altitude (HA) residence. We hypothesized that in HA pregnancies 1) circulating soluble fms-like tyrosine kinase 1 (sFlt-1) is increased and placental growth factor (PlGF) decreased, and 2) AGE concentrations correlate with measures of hypoxia. A cross-sectional study of healthy pregnancies at low altitude (LA) (400 m) versus HA (3600 m) compared normal (n = 80 at HA, n = 90 at LA) and PE pregnancies (n = 20 PE at HA, n = 19 PE at LA). Blood was collected using standard serum separation and, in parallel, by a method designed to inhibit platelet activation. AGEs were measured by enzyme-linked immunosorbent assays. AGEs did not differ between altitudes in normal or PE pregnancies. AGE concentrations were unrelated to measures of maternal or fetal hypoxia. PlGF was lower and sFlt-1 higher in PE, but overlapped considerably with the range observed in normal samples. PlGF correlated with placental mass in both normal and PE pregnancies. The contribution of peripheral cells to the values measured for AGEs was similar at LA and HA, but was greater in PE than in normotensive women. Hypoxia, across a wide physiological range in pregnancy, does not alter levels of circulating AGEs in otherwise normal pregnancies. Peripheral cell release of AGEs with the hemostasis characteristic of standard blood collection is highly variable and contributes to a doubling of the amount of sFlt-1 measured in PE as compared to normal pregnancies.

Effect of oxygen on multidrug resistance in the first trimester human placenta

INTRODUCTION

The multidrug resistance proteins, P-glycoprotein (P-gp, encoded by the ABCB1 gene) and breast cancer resistance protein (BCRP, encoded by ABCG2) are highly expressed in the first trimester placenta. These transporters protect the fetus from exposure to maternally derived toxins and xenobiotics. Since oxygen is a regulator of multidrug resistance in various tissues, we hypothesized that changes in oxygen tension alter placental ABCB1/P-gp and ABCG2/BCRP expression in the first trimester.

METHODS

Placental specimens were collected from first (n = 7), second (n = 5) and term pregnancies (n = 5). First trimester placental villous explants were incubated (24 or 48 h) in different oxygen tension (3-20%). ABCB1, ABCG2 and VEGFA mRNA expression levels were assessed by RT-PCR and protein was localized by IHC.

RESULTS

ABCB1 is expressed most highly in the first trimester placenta (p < 0.05), whereas ABCG2 expression does not change significantly over pregnancy. P-gp and BCRP staining is present in the syncytiotrophoblast and in cytotrophoblasts. ABCG2 mRNA is increased in hyperoxic (20%) conditions after 48 h (p < 0.05). In contrast, hypoxia (3%) did not change ABCB1 mRNA expression but significantly increased VEGFA mRNA (p < 0.05). Hypoxia resulted in increased BCRP staining in cytotrophoblasts and in the microvillous membrane of the syncytium. Whereas, hypoxia resulted in increased P-gp staining in proliferating cytotrophoblasts.

CONCLUSION

We conclude that placental multidrug resistance expression, specifically ABCG2, is regulated by oxygen tension in the first trimester. It is possible that changes in placental oxygen supply are capable of altering fetal drug exposure especially during early pregnancy.

Anti-human vascular endothelial growth factor (VEGF) antibody selection for immunohistochemical staining of proliferating blood vessels

Nine commercially available vascular endothelial growth factor (VEGF) antibodies were investigated for their ability to immunostain vascular malformations (VMs) with or without immature capillary proliferation. First, all antibodies were optimized for their performance in IHC, with placenta and colon adenocarcinoma as positive control tissues. Five antibodies were regarded as unfit for VEGF immunostaining based on poor immunostaining criteria. Subsequently, Western blot analysis using VEGF rabbit polyclonal antibody (Thermo RB-9031) revealed a clear 45-kDa band in tissue extracts from VMs with immature capillary proliferation and a high Ki67-labeling index, whereas tissue extracts from mature VMs without microvascular proliferation and no Ki67-labeling index demonstrated only a very weak 45-kDa band. In contrast, two VEGF antibodies, including the popular Santa Cruz A-20, revealed bands at 45 kDa of similar intensity in tissue extracts from both types of VMs. Staining characteristics of the 45-kDa band were reflected in the results obtained in IHC.

Placental growth factor (PlGF): a key to optimizing fetal growth

The needs of the uterus and the fetus for the provision of nutrients and oxygen, supplied by the blood flow, are understandably extremely high, with the circulatory system playing the most important role in this action. Abnormal vascular growth and transformation that create a high vessel resistance network have been associated with various pregnancy pathologies, including miscarriage, small for gestational age (SGA) fetuses with or without preeclampsia and intrauterine growth restriction (IUGR). Placental growth factor (PlGF) has a major role in vasculogenesis and angiogenesis in human placenta. Low concentrations of PlGF and high concentrations of its inhibitor-soluble Fms-like tyrosine kinase-1 (sFlt-1) are linked with impaired angiogenesis and placental development, leading to the above pregnancy complications. The activity of vascular endothelial growth factor (VEGF), which is the most potent of all angiogenic mediators, is partly modulated by PlGF. Although the mechanisms via which PlGF exerts its various effects are still under investigation, we herein discuss the known actions exerted by this major mediator together with its results on fetal growth.

Vascular endothelial growth factor in neonates with perinatal asphyxia

BACKGROUND

Vascular endothelial growth factor (VEGF) is a polypeptide growth factor that is activated by tissue hypoxia. The role of VEGF in perinatal asphyxia in human neonates is yet to be clarified. In infants who develop moderate to severe acute hypoxic ischemic encephalopathy (HIE) it is crucial to clearly understand physiologic and biochemical changes that accompany HIE before a novel treatment can be developed.

OBJECTIVES

To assess VEGF in cord blood of infants suffering from perinatal asphyxia, and to determine whether an association exists between increased concentrations of VEGF and the risk for development of encephalopathy.

STUDY DESIGN

We prospectively studied 40 full term infants; of them 20 infants suffered from perinatal asphyxia, and 20 control infants of comparable age and sex. We obtained cord blood samples from all subjects immediately after delivery. Neurological examination and grading of HIE were performed during the first day of life.

RESULTS

Birth weight, gestational age and gender did not differ between the control (n=20) and asphyxia (n=20) groups. Within the asphyxia group four infants developed HIE; one with severe encephalopathy who died shortly after birth, while the other three infants had moderate HIE. Concentrations of VEGF were increased in infants with asphyxia when compared to controls (P0.001). Within the asphyxia group, infants with HIE had significantly increased concentrations of VEGF when compared to non-HIE asphyxiated infants (P=0.008). In the logistic regression model, VEGF inversely correlated with pH and PO(2) in cord blood, and Apgar scores at 1min, while it did not associate with gestational age and birth weight.

CONCLUSIONS

This study indicates that VEGF is increased in cord blood of neonates following birth asphyxia, and that VEGF is specifically most increased in infants who later developed encephalopathy. Further studies are required to determine the role of VEGF in brain insult. Such studies will help determine whether a therapeutic role for VEGF or VEGF inhibitors can exist for HIE infants.

Antiangiogenic Effect of Soluble Vascular Endothelial Growth Factor Receptor-1 in Placental Angiogenesis

Differential splicing of the flt-1 mRNA generates soluble variant of vascular endothelial growth factor (VEGF) receptor-1 (sVEGFR-1, also known as sFlt-1). The action of VEGF is antagonized by sVEGFR-1. Soluble VEGFR-1 binds to VEGF with a high affinity and therefore works to modulate VEGF and VEGF signaling pathway. In this study, the authors tested the hypothesis that VEGF-mediated endothelial cell angiogenesis is tightly modulated by the release of sVEGFR-1 and placental expression of sVEGFR-1 is upregulated by hypoxia. Immunolocalization studies showed progressively intense staining for sVEGFR-1 and VEGF in the trophoblast of placental villous explants throughout gestation. Endothelial cell migration studies using a modified Boyden's chamber showed a significant increase in cell migration in response to VEGF that was significantly attenuated in the presence of exogenous sVEGFR-1. Furthermore, stimulation of endothelial cells with VEGF led to a dose-dependent increase in the release of sVEGFR-1 as determined by enzyme-linked immunosorbent assay (ELISA). Exposure of normal placental villous explants to hypoxia (1% pO2) increased trophoblast expression of sVEGFR-1 when compared with tissue normoxia (5% pO2). In addition, conditioned media from hypoxia treated placental villous explants induced a significant increase in endothelial cell migration that was significantly reduced in presence of sVEGFR-1. Our study demonstrates that hypoxia positively regulates sVEGFR-1 protein expression in ex vivo trophoblasts, which control VEGF-driven angiogenesis.

Effect of impaired glucose tolerance during pregnancy on the expression of VEGF receptors in human placenta

The aim of the present study was to determine the expression of vascular endothelial growth factor (VEGF) receptors VEGFR-1, VEGFR-2 and VEGFR-3 in placentas from pregnancies complicated by altered glycaemia. Placentas from women with physiological pregnancies (Group 1), pregnancies complicated by minor degree of glucose intolerance (MDGI, Group 2) and by gestational diabetes mellitus (GDM) treated with insulin (Group 3) were collected. Immunohistochemistry, RT-PCR and western blot were employed to evaluate receptor expression. In the three study groups, VEGFR-1 immunoreactivity was detected in all the placental components. VEGFR-2 immunoreactivity was observed in the vessels of all the placentas from Groups 1 and 2, but only in some placentas of Group 3. VEGFR-3 reactivity was observed in all the components of Group 1; in Groups 2 and 3 reactivity was observed in some portions of the trophoblast or the whole trophoblast, and in the stroma. VEGFR-1 and VEGFR-2 mRNA levels in Groups 2 and 3 were significantly higher compared with Group 1, whereas those of VEGFR-3 were significantly lower. Receptor protein levels were significantly lower in Groups 2 and 3 compared with Group 1. These findings demonstrated dysregulation of expression of the three placental receptors, both in GDM and in MDGI.

Vascular endothelial growth factor levels in newborns with meconium stained amniotic fluid

OBJECTIVE

The effects of meconium-stained amniotic fluid (MSAF) on cord blood vascular endothelial growth factor (VEGF) levels have not been explored. The aim of this study was to verify whether MSAF influences cord blood VEGF levels in healthy term neonates and we can use cord blood VEGF levels in infants with MSAF as an indicator of fetal distress.

METHODS

Using an enzyme-linked immunosorbent assay double sandwich method, plasma VEGF levels were determined in 18 healthy term neonates with MSAF and in 16 healthy term neonates without MSAF.

RESULTS

VEGF plasma levels were not significantly different between healthy term neonates with or without MSAF.

CONCLUSION

Intrauterine meconium passage could not affect VEGF levels on cord blood in term newborn infants and VEGF level may not be used as an indicator of fetal distress in infants with MSAF.

Placental hypoxia during placental malaria

BACKGROUND

Placental malaria causes fetal growth retardation (FGR), which has been linked epidemiologically to placental monocyte infiltrates. We investigated whether parasite or monocyte infiltrates were associated with placental hypoxia, as a potential mechanism underlying malarial FGR.

METHODS

We studied the hypoxia markers hypoxia inducible factor (HIF)-1alpha, vascular endothelial growth factor (VEGF), placental growth factor, VEGF receptor 1 and its soluble form, and VEGF receptor 2. We used real-time polymerase chain reaction (in 59 women) to examine gene transcription, immunohistochemistry (in 30 women) to describe protein expression, and laser-capture microdissection (in 23 women) to examine syncytiotrophoblast-specific changes in gene expression. We compared gene and protein expression in relation to malaria infection, monocyte infiltrates, and birth weight.

RESULTS

We could not associate any hallmark of placental malaria with a transcription, expression, or tissue-distribution profile characteristic of a response to hypoxia, but we found higher HIF-1alpha levels (P= .0005) and lower VEGF levels (P= .0026) in the syncytiotrophoblasts of cases of malaria than in those of asymptomatic control placentas.

CONCLUSIONS

Our data are inconsistent with a role for placental hypoxia in the pathogenesis of malaria-associated FGR. The laser-capture microdissection study was small, but its results suggest (1) that malaria affects syncytiotrophoblast-gene transcription and (2) novel potential mechanisms for placental malaria-associated FGR.

Evaluation of physiological alterations of the placenta through analysis of cell-free messenger ribonucleic acid concentrations of angiogenic factors

OBJECTIVE

Placental messenger ribonucleic acid (mRNA) has been shown to circulate in maternal plasma. We investigated concentrations of vascular endothelial growth factor (VEGF), VEGF receptor-1 (VEGFR-1), and endoglin in subjects with preeclampsia, compared with normal pregnancies.

STUDY DESIGN

Peripheral blood samples were obtained from preeclampsia (n = 43) and control subjects (n = 41). Plasma ribonucleic acid was subjected to analysis by reverse transcription-polymerase chain reaction assay to examine the mRNA distribution among women with preeclampsia and control subjects during weeks 35-41 of gestation.

RESULTS

Concentrations of VEGF, VEGFR-1, and endoglin mRNA of women with preeclampsia were significantly increased. The mRNA values were observed to correlate directly with the severity of hypertension and proteinuria. VEGFR-1 mRNA was markedly elevated in women with preeclampsia and hemolysis, elevated liver enzymes, and low platelet syndrome.

CONCLUSION

The mRNA concentrations of VEGF, VEGFR-1, and endoglin were observed to correlate directly with the severity of preeclampsia.

Expression of vascular endothelial growth factor receptor types 1, 2 and 3 in placenta from pregnancies complicated by hypertensive disorders

The aim of the present study was to determine the expression of vascular endothelial growth factor (VEGF) family receptors (VEGFR) in placentas from pregnancies complicated by hypertensive disorders of different clinical severity. Placental tissue from women with gestational hypertension, pre-eclampsia, pre-eclampsia with haemolysis, elevated liver enzymes and low platelets (HELLP syndrome) and normotensive women, as a control group, was examined. Immunohistochemical techniques, reverse transcription–polymerase chain reaction and western blot were used to evaluate receptor expression. In cases with gestational hypertension, as well as in control cases, VEGFR-1 and VEGFR-3 immunoreactivity was detected in all placental components, whereas in placentas from the pre-eclampsia and pre-eclampsia with HELLP syndrome groups, VEGFR-1 and VEGFR-3 immunoreactivity was detected only in some portions of trophoblast and/or some vessels and/or clusters of stromal cells. In the control group, VEGFR-2 immunoreactivity was observed only in the vessels, whereas the hypertensive groups showed VEGF-2 immunoreactivity also in trophoblast and stromal cells. The mRNA levels of the three receptors in the group with gestational hypertension were higher with respect to those in the control group. Placentas from pregnancies with pre-eclampsia showed lowest mRNA expression levels, whereas placentas from women with pre-eclampsia plus HELLP syndrome showed higher mRNA expression levels with respect to the three other groups. Receptor protein levels were lower in pathological cases compared with levles in the control group. These findings demonstrate a dysregulation of placental expression of VEGF family receptors related to the degree of clinical severity of the hypertensive disorder.

Mechanisms regulating cytotrophoblast invasion in normal pregnancy and pre-eclampsia

The placental bed underlies the placenta and includes the decidua basalis and underlying myometrium containing the uterine spiral arteries. For successful human haemochorial placentation, the placental bed spiral arteries must undergo considerable alterations. These physiological modifications are thought to be brought about by the interaction of invasive cytotrophoblast with the spiral artery vessel wall. Failure of spiral artery transformation is thought to play an important role in the sequence of events that gives rise to pre-eclampsia. The mechanisms that control human trophoblast invasion in normal, let alone abnormal pregnancy, are still poorly understood. Much of the information on the early physiological changes within the placental bed comes from studies on intact hysterectomy specimens.(1) Details of such events in late pregnancy and in pregnancies complicated by pre-eclampsia and fetal growth restriction are principally derived from the study of placental bed biopsies taken at Caesarean section. The methods of sampling the placental bed have been reviewed elsewhere.(2) Many investigators have relied on in vitro models of trophoblast invasion. In vitro models can be extremely useful in dissecting out some of these processes but may be open to artefacts. The mechanisms underlying normal and failed trophoblast invasion appear to be complex. In this manuscript the mechanisms that control the invasion of trophoblast into the decidua and myometrium are reviewed. Along with this is a review of the purported mechanisms underlying failed spiral artery transformation. Particular emphasis has been placed on topics that have been best studied.

Vascular endothelial growth factor and placenta growth factor in intrauterine growth-restricted fetuses and neonates

The angiogenic factors vascular endothelial growth factor (VEGF) and placenta growth factor (PlGF) are respectively up- and downregulated by hypoxia. We aimed to study circulating levels of the above factors in intrauterine growth restriction (IUGR) and to correlate their levels with the customized centiles of the infants. The study included 25 IUGR and 25 appropriate for gestational age (AGA) full-term, singleton infants and their mothers. Maternal (MS), fetal (UC), and neonatal day 1 (N1) and 4 (N4) blood was examined. MS and N1 PlGF, as well as UC VEGF levels correlated with the customized centiles of the infants (r = 0.39, P = .007, r = 0.34, P = .01, and r = −0.41, P = .004, resp). Furthermore, UC, N1, and N4 VEGF levels were higher in girls (r = 0.36, P = .01, r = 0.33, P = .02, and r = 0.41, P = .005 resp). In conclusion, positive and negative correlations of examined factors with the customized centiles of the infant could rely on placental function and intrauterine oxygen concentrations—both being usually lower in IUGR cases—while higher VEGF levels in girls should possibly be attributed to the stimulating action of estrogens.

Maternal medicine: Morphometric placental villous and vascular abnormalities in early- and late-onset pre-eclampsia with and without fetal growth restriction

OBJECTIVE

To evaluate placental morphology in pregnancies complicated by early- and late-onset pre-eclampsia (PET) with and without fetal growth restriction (FGR) using stereological techniques.

DESIGN

A total of 69 pregnant women were studied. Twenty women had pregnancies complicated by PET, 17 by FGR and 16 by both PET and FUR; the remaining 16 were from gestational-age-matched controls. Each group was further classified into early onset (<34 weeks) and late onsets (>34 weeks) based on gestational ages.

SETTING

NPIMR at Northwick Park and St Marks Hospital.

POPULATION

placentae from pregnant women.

METHODS

Formalin-fixed, wax-embedded sections stained with anti-CD34 antibodies and counterstained with haematoxylin.

MAIN OUTCOME MEASURES

Volumes, surface areas, lengths, diameters and shape factors of the villous tissues and fetal vasculature in the intermediate and terminal villi of all the groups studied.

RESULTS

Terminal villi volume and surface area were compromised in early-onset PET cases, late-onset PET had no impact on peripheral villi or vasculature features. The morphology of the vascular and villous subcomponents in the intermediate and terminal villi was significantly influenced by late-onset FGR, whereas early-onset FGR caused a reduction in placental weight. Length estimates were not influenced by PET, FGR or age of onset. Intermediate arteriole shape factor was significantly reduced in late-onset FGR.

CONCLUSIONS

Isolated early-onset PET was associated with abnormal placental morphology, but placentas from late-onset PET were morphologically similar to placentas from gestational-age-matched controls, confirming the existence of two subsets of this condition and supporting the hypothesis that late-onset PET is a maternal disorder and not a placental disease.

Hypoxia up-regulated angiogenin and down-regulated vascular cell adhesion molecule-1 expression and secretion in human placental trophoblasts

OBJECTIVE

Many processes that are involved in cellular invasion, including blastocyst implantation, placental development, and rapidly growing tumors, occur in reduced oxygen environments. It has been surmised that oxygen tension could regulate the cytotrophoblast ability to differentiate and, as a consequence, to express proteins that are critical for placentation. The objective of the current investigation was therefore to test the hypothesis that placental tissues and trophoblast cells in culture, under low oxygen tension, release angiogenic factors that could affect vascular behavior and invasive potential, thus providing a link between abnormal placentation and maternal vascular abnormality.

METHODS

Functionally active term placental explant culture and trophoblast cultures were used to demonstrate the secretion profiles of angiogenin and vascular cell adhesion molecule-1 (VCAM-1), and the real-time quantitative reverse transcriptase polymerase chain reaction (RT-PCR) technique was employed to demonstrate the mRNA expression under both normoxic and hypoxic conditions.

RESULTS

A significant increase in the secretion (P <.01) and mRNA expression (P <.01) of angiogenin and a significant decrease in the secretion (P <.04) and mRNA expression (P <.03) of VCAM-1 from both term placental explants and trophoblast cultures subjected to hypoxia in vitro were observed.

CONCLUSION

Because the primary defect in uteroplacental insufficiency is placental maldevelopment probably associated with hypoxia in situ, this study provides molecular evidence to indicate that the differential expression and secretion of angiogenic factors may play an important role in these pathologic conditions.

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 correlation between sampling site and gene expression in the term human placenta

Using oligonucleotide microarrays we recently identified a set of transcripts that were up-regulated in hypoxic human trophoblasts. To test the hypothesis that expression of hypoxia-related placental transcripts depends on sampling site we analyzed nine different sites from term human placentas (n=6), obtained after uncomplicated pregnancies. These sites spanned the placental center to the lateral border and the basal to the chorionic plate. Relative gene expression at each site, determined using quantitative PCR, was correlated with villous histology. The expression of vascular endothelial growth factor (VEGF) and connective tissue growth factor (CTGF), the cytoskeleton proteins lamininA3 and alpha-tubulin, and the signal transduction protein Rad was enhanced in the subchorionic lateral border compared to medial basal site (1.6-2.9 fold, p<0.05). In contrast, the expression of NDRG1, adipophilin and human placental lactogen was unchanged. Enhanced villous maturation, syncytial knots and fibrin deposits were more frequent in the subchorionic placental lateral border, and correlated with up-regulation of hypoxia-related transcripts (p<0.05). The association between sample site and expression level was not observed in placentas with marginal cord insertion. The expression of hypoxia-related genes in the term human placenta is dependent on sampling site within the placental disk, likely reflecting local differences in villous perfusion.

Endocrine cell lines from the placenta

Cell-lines derived from human placenta and chorion have been used extensively to model the endocrine functions of human trophoblast. In general terms, the endocrine functions of the primary cells and tissues are at least partially replicated within the cell-lines, suggesting that they may be used as appropriate models. There are, however, two major provisos that compromise this generalisation. Firstly, the endocrine function of placenta represents a complex interaction between cytotrophoblast, syncytiotrophoblast and multiple regulators, so a single cell population digested from the normal environment is unlikely to represent this. Secondly, the characterisation of primary trophoblast populations and of cell-lines is incomplete, complicating the assignment of functions to trophoblast populations. Despite these difficulties, useful information has been obtained from the available cell-lines, regardless of whether they have arisen spontaneously, been transformed in vitro, or derived from cancers in vivo.

Angiogenin and vascular endothelial growth factor in pregnancies complicated by preeclampsia

OBJECTIVE

To investigate the role of the angiogenic factors, vascular endothelial growth factor (VEGF) and angiogenin in the pathophysiology of preeclampsia and how their concentrations correlate with the severity of the disease and fetal outcome.

PATIENTS AND METHODS

A prospective study was carried out on 71 pregnant patients with preeclampsia and 20 pregnant normotensive controls. Maternal serum levels of VEGF and angiogenin were determined in all cases by enzyme immunoassay. Assessment of fetal well-being using the Biophysical Profile Score (BPS), umbilical and uterine artery Doppler velocimetry, and infant birthweight were carried out.

RESULTS

Maternal serum VEGF and angiogenin levels were significantly increased in cases of mild and severe preeclampsia compared to controls. Their increase was positively correlated with elevated systolic and diastolic blood pressure, as well as poor BPS, abnormal Doppler velocimetry, and low birthweight.

CONCLUSION

Elevated levels of both VEGF and angiogenin could confirm the existence of vascular reactivity and endothelial disturbance in preeclampsia. Measurement of these angiogenic factors in maternal serum may be a useful as biomarkers for the assessment of the severity of the disease and of fetal outcome.

Human chorionic gonadotrophin beta expression in malignant Barrett's oesophagus

BACKGROUND

Human chorionic gonadotrophin beta (hCGbeta) is expressed in several non-trophoblastic tumours, and this is usually associated with aggressive behaviour. Little is known about hCGbeta expression in Barrett's adenocarcinoma.

MATERIALS AND METHODS

We determined the hCGbeta profile in a large series of surgically resected Barrett's adenocarcinoma (a) at mRNA level using real-time quantitative reverse-transcription polymerase chain reaction analysis and (b) at protein level using immunohistochemistry with a polyclonal antibody and with a monoclonal antibody specific for free hCGbeta. We then sought links between the hCGbeta protein expression pattern and clinical and pathological parameters, including patient outcome as well as vascular endothelial growth factor (VEGF) expression.

RESULTS

hCGbeta protein expression was observed in 43 of 76 (57%) Barrett's adenocarcinomas. We showed a strong correlation between hCGbeta protein abundance and CGB mRNA level. We observed a statistical link between hCGbeta protein expression and infiltrative tumour type ( P=0.023), perineural neoplastic invasion ( P=0.007) and VEGF protein expression ( P=0.016). hCGbeta expression tended to be associated with a poor outcome (16% versus 36% survival 8 years after resection).

CONCLUSION

Expression of hCGbeta correlates with specific infiltrative characteristics and is associated with higher VEGF expression. Both molecules may play a co-ordinated role in the development of Barrett's adenocarcinomas.

Oxidative stress in the placenta

Pregnancy is a state of oxidative stress arising from increased placental mitochondrial activity and production of reactive oxygen species (ROS), mainly superoxide anion. The placenta also produces other ROS including nitric oxide, carbon monoxide, and peroxynitrite which have pronounced effects on placental function including trophoblast proliferation and differentiation and vascular reactivity. Excessive production of ROS may occur at certain windows in placental development and in pathologic pregnancies, such as those complicated by preeclampsia and/or IUGR, overpowering antioxidant defenses with deleterious outcome. In the first trimester, establishment of blood flow into the intervillous space is associated with a burst of oxidative stress. The inability to mount an effective antioxidant defense against this results in early pregnancy loss. In late gestation increased oxidative stress is seen in pregnancies complicated by diabetes, IUGR, and preeclampsia in association with increased trophoblast apoptosis and deportation and altered placental vascular reactivity. Evidence for this oxidative stress includes increased lipid peroxides and isoprostanes and decreased expression and activity of antioxidants. The interaction of nitric oxide and superoxide produces peroxynitrite, a powerful prooxidant with diverse deleterious effects including nitration of tyrosine residues on proteins thus altering function. Nitrative stress, subsequent to oxidative stress is seen in the placenta in preeclampsia and diabetes in association with altered placental function.

VEGF expression in the placenta from pregnancies complicated by hypertensive disorders

OBJECTIVE

To determine the expression of VEGF in the placental tissue from pregnancies complicated by hypertension disorders of different clinical severity.

DESIGN

Prospective cohort study.

SETTING

Polyclinic of Careggi, University of Florence, Italy.

SAMPLE

Placentas from women with gestational hypertension (n= 20), pre-eclampsia (n= 20) and pre-eclampsia with HELLP syndrome (n= 20) and from normotensive women (n= 20), as control group (gestational age comprised between 35 and 38 weeks).

METHODS

An immunohistochemical technique and a quantitative analysis to measure mRNA levels (RT-PCR) were employed.

MAIN OUTCOME MEASURES

Intensity of immunoreactivity and mRNA levels in the placental components. Differences between the data.

RESULTS

VEGF immunoreactivity was observable in all the placental components in the gestational hypertension cases as in the control ones. In the cases with pre-eclampsia and pre-eclampsia with HELLP syndrome, some placental components were not immunoreactive. However, the VEGF positive components of all the pathological groups showed a higher intensity of reactivity with respect to that of the control group. The levels of VEGF mRNA were higher in the gestational hypertension cases and lower in the cases of pre-eclampsia with HELLP syndrome with respect to the control ones; in the cases of pre-eclampsia, the levels were the same as the control ones.

CONCLUSION

The different expression of VEGF in the placenta of the pathological cases is probably related to haemodynamic changes that take place in these disorders, in order to attempt restoration of a normal uteroplacental flow.

Intrauterine infection/inflammation during pregnancy and offspring brain damages: possible mechanisms involved

Intrauterine infection is considered as one of the major maternal insults during pregnancy. Intrauterine infection during pregnancy could lead to brain damage of the developmental fetus and offspring. Effects on the fetal, newborn, and adult central nervous system (CNS) may include signs of neurological problems, developmental abnormalities and delays, and intellectual deficits. However, the mechanisms or pathophysiology that leads to permanent brain damage during development are complex and not fully understood. This damage may affect morphogenic and behavioral phenotypes of the developed offspring, and that mice brain damage could be mediated through a final common pathway, which includes over-stimulation of excitatory amino acid receptor, over-production of vascularization/angiogenesis, pro-inflammatory cytokines, neurotrophic factors and apoptotic-inducing factors.

Novel placental and nonplacental serum markers in ectopic versus normal intrauterine pregnancy

OBJECTIVE

To evaluate whether the serum concentrations of novel placental markers and nonplacental markers differ in ectopic pregnancy when compared with normal intrauterine pregnancy.

DESIGN

Prospective clinical study.

SETTING

University hospital.

PATIENT(S)

Patients with confirmed ectopic pregnancy (EP) and control population with normal intrauterine pregnancy (IUP).

INTERVENTION(S)

Laparoscopy.

MAIN OUTCOME MEASURE(S)

Serum concentrations of placental markers: pregnancy-associated plasma protein A (PAPP-A), pregnancy-specific beta(1)-glycoprotein (SP1), human placental lactogen (HPL), and HCG; and nonplacental markers: glycodelin, vascular endothelial growth factor (VEGF), and P.

RESULT(S)

The multiples of median of all markers (except VEGF) were decreased in EP when compared with the control group. Conversely, the serum values of VEGF were significantly increased in EP. VEGF showed a negative correlation with HCG and SP1, but not with PAPP-A, P, or the nonplacental markers. HCG, PAPP-A, SP1, and HPL strongly correlated with each other. But, in contrast to the above, P only correlated with HCG and, in contrast to the controls, with glycodelin. The combination of three independent markers in the formula VEGF/(PAPP-A x P) was found to be largely superior to the measure of any single marker.

CONCLUSION(S)

The "triple marker analysis" [VEGF/(PAPP-A x P] allows a clear discrimination between normal IUP and EP.

[The human placenta and its pathologies: focus on oxygen]

At the time of placentation, the conceptus surrounds itself with a trophoblastic layer where the villous tree develops and the uteroplacental circulation takes place. Analysis of the modalities of maternal blood entrance demonstrated a physiological hypoxia ending with the first trimester of pregnancy. Moreover, cultures of first trimester villous explants have shown the role of oxygen in extravillous cytotrophoblast proliferation, decidual invasion and spiral artery remodeling. Oxygen appears to be a key factor controlling the mechanism of placentation by regulating the transcription of several genes, such as VEGF (vascular endothelial growth factor), leptin, etc. These genes are turned on or off as a function of oxygen partial pressure via an oxygen sensor. Oxygen is now considered to be implicated in the development of several pathologies of pregnancy. It is involved at different steps in the cascade of events leading to preeclampsia. Positive correlations have been observed between oxygen partial pressure and abnormal development of the villous tree in intrauterine growth retardation, and in maternal anemia or pregnancy in altitude.

The placenta at high altitude

The influence of oxygen pressure on placental and villous vascular development is reviewed and considered relative to the natural experiment afforded by residence at high altitude. Data obtained from normal high altitude pregnancies are compared with those from IUGR and preeclampsia, conditions believed to be caused by placental hypoxia. High altitude placentas are characterized by increased villous vascularization, thinning of the villous membranes, proliferation of the villous cytotrophoblast, and reduced perisyncytial fibrin deposition relative to low altitude placentas. The significance of reduced fibrin deposition is unknown; it could be explained by less apoptosis along the barrier membrane, less syncytiotrophoblast turnover, or altered ratios of local proversus anticoagulant production. Increased villous capillary density and thinning of the villous membranes increases oxygen diffusion capacity and is generally considered a beneficial adaptation. Nonetheless, there is evidence that hypoxia and/or reduced blood flow reduce placental nutrient transporter densities, and this may act in additive or synergistic fashion to reduce birth weight at high altitude. The available literature on high altitude placentas derives from less than 100 pregnancies from three different continents and six different ethnic groups, and were acquired in pregnancies ranging from 2500 to 4300 m in altitude. Thus differences between studies are likely to be due to variation in altitude and/or to ethnic variation, which in turn may be due to differences in population history of residence at high altitude (e.g., Andeans vs. Europeans). Nonetheless, systematic examination of human placental development under conditions of lowered maternal arterial oxygen pressure (high altitude > 2700 m) may provide useful insights into the etiology of pathological conditions believed to be associated with placental hypoxia.

The relationship between transplacental O2 diffusion and placental expression of PlGF, VEGF and their receptors in a placental insufficiency model of fetal growth restriction

Placental growth factor (PlGF) and vascular endothelial growth factor (VEGF) are involved in placental angiogenesis through interactions with the VEGFR-1 and VEGFR-2 receptors. The placenta of pregnancies whose outcome is fetal growth restriction (FGR) are characterized by abnormal angiogenic development, classically associated with hypoxia. The present study evaluated the near-term expression of this growth factor family in an ovine model of placental insufficiency-FGR, in relationship to uteroplacental oxygenation. Compared to controls, FGR pregnancies demonstrated a 37% increase in uterine blood flow (FGR vs. control, 610.86+/-48.48 vs. 443.17+/-37.39 ml min(-1) (kg fetus)(-1); P<0.04), which was associated with an increased maternal uterine venous PO2 (58.13+/-1.00 vs. 52.89+/-1.26 mmHg; P<0.02), increased umbilical artery systolic/diastolic ratio (3.90+/-0.33 vs. 2.12+/-0.26, P<0.05), and fetal hypoxia (arterial PO2; 12.79+/-0.97 vs. 18.65+/-1.6 mmHg, P<0.005). Maternal caruncle PlGF mRNA was increased in FGR (P<0.02), while fetal cotyledon VEGF mRNA was reduced (P<0.02). VEGFR-1 mRNA was also reduced in FGR fetal cotyledon (P<0.001) but was not altered in caruncle tissue. Immunoblot analysis of PlGF and VEGF demonstrated single bands at 19,000 and 18,600 Mr, respectively. Caruncle PlGF concentration was increased (P<0.04), while cotyledon VEGF was decreased (P<0.05) in FGR placentae. The data establish that uterine blood flow is not reduced in relationship to metabolic demands in this FGR model and that the transplacental PO2 gradient is increased, maintaining umbilical oxygen uptake per unit of tissue. Furthermore, these data suggest that an increased transplacental gradient of oxygen generates changes in angiogenic growth factors, which may underline the pathophysiology of the post-placental hypoxic FGR.

Hypoxia activates the human placental vascular endothelial growth factor system in vitro and in vivo: up-regulation of vascular endothelial growth factor in clinically relevant hypoxic ischemia in birth asphyxia

OBJECTIVE

We investigated the influence of acute hypoxia on the placental vascular endothelial growth factor system in vitro and in vivo in acute birth asphyxia compared with pregnancies that were complicated by preeclampsia and with healthy control subjects.

STUDY DESIGN

Messenger RNA levels for vascular endothelial growth factor, flt-1, and KDR were measured by TaqMan real-time polymerase chain reaction in human placental choriocarcinoma cells (BeWo) that were exposed to hypoxia (1% oxygen, 5% carbon dioxide, 94% nitrogen) and in placental tissue of neonates with birth asphyxia (n = 20), newborn infants of mothers with preeclampsia (n = 20), and gestational age-matched control subjects. Immunhistologically, placental vascular endothelial growth factor protein expression was compared among the groups.

RESULTS

In BeWo cells, vascular endothelial growth factor, flt-1 and KDR messenger RNA increased in a time-dependent manner in response to hypoxia. In vivo, vascular endothelial growth factor/beta-actin and KDR/beta-actin messenger RNA were significantly higher in placental tissue of newborn infants with severe hypoxic-ischemic encephalopathy than with newborn infants with mild or no hypoxic-ischemic encephalopathy and control subjects. In chronic placental hypoxia (preeclampsia), vascular endothelial growth factor and both receptors were found to be up-regulated. Increased placental vascular endothelial growth factor expression was confirmed by immunohistologic examination.

CONCLUSION

The vascular endothelial growth factor system is up-regulated in response to placental hypoxia and is assumed to be a potential early indicator of severe birth asphyxia.

Impaired oxygen-dependent reduction of HIF-1alpha and -2alpha proteins in pre-eclamptic placentae

Pre-eclamptic (PE) placentae overexpress hypoxia inducible transcription factors-1alpha and -2alpha proteins (Biol. Repro. 64: 499-506, 2001; Ibid 1019-1020). Possible explanations include (a) impaired oxygen-dependent reduction, and/or (b) enhanced sensitivity to reduced oxygen. After 18 h equilibration under 21 per cent O(2) atmosphere, we subjected villous explants prepared from placentae of normal pregnant (NP) and pre-eclamptic (PE) women (n=8 each) to 4h of hypoxia (2 per cent oxygen), and then studied the disappearance of HIF-1alpha and -2alpha proteins during subsequent oxygenation over 90 min (21 per cent oxygen). The disappearance of these HIF proteins as assessed by Western analysis was significantly impaired in the pre-eclamptic tissues. Even after 18h equilibration under a 21 per cent O(2) atmosphere, and then a further 4h at 21 per cent O(2), HIF-1alpha and -2alpha protein expression remained increased in villous explants from PE women (both P< 0.04 vs NP). To address whether chronic hypoxia per se (which is believed to exist in the pre-eclamptic placenta) might contribute to these findings, we subjected villous explants from normal placentae (n=6) to 18 h preincubation under 2 per cent or 21 per cent oxygen prior to subsequent incubation for 4h at 2 per cent oxygen and then 90 min at 21 per cent oxygen. The time course of disappearance of HIF proteins during oxygenation was similar irrespective of the 2 per cent or 21 per cent preconditioning. To evaluate oxygen sensitivity, we exposed villous explants from NP and PE women (n=6 each) to different oxygen atmospheres for 4h and measured HIF protein induction. Although the data showed a significant inverse relationship between HIF expression and oxygen concentration, there was no significant difference between the slopes of this relationship for the two groups of women. We conclude that villous explants from PE placentae fail to adequately downregulate HIF protein expression upon oxygenation. This abnormality may contribute to their overexpression in vivo.

Cytokines of the placenta and extra-placental membranes: biosynthesis, secretion and roles in establishment of pregnancy in women

Virtually all known cytokines have been demonstrated to be expressed in the placenta and associated fetal and maternal membranes during normal gestation. In addition to playing their traditional roles as modulators of immunological function, cytokines derived from the placenta and extraplacental membranes, together with other locally-derived growth factors, appear to be implicated in various aspects of implantation and placental development. Imbalances in the intrauterine cytokine milieu around the time of implantation and invasion may play a causative role in disorders associated with early pregnancy failure, and are also associated with the abnormal trophoblast development seen in gestational trophoblastic disease. Cytokines thus appear to be an important component of a paracrine/autocrine communication network operating within the feto-maternal interface to ensure the successful establishment of pregnancy.

Placental expression of VEGF, PlGF and their receptors in a model of placental insufficiency-intrauterine growth restriction (PI-IUGR)

Placental development requires adequate and organized interaction of vascular growth factors and their receptors, including vascular endothelial growth factor (VEGF) and placental growth factor (PlGF). Both VEGF and PlGF, acting through the tyrosine kinase receptors VEGFR-1 and VEGFR-2, have been implicated in playing a role in ovine placental vascular development. The present studies describe the placental expression of components of the VEGF family at two maturational time points (55 and 90 days post coitus, dpc) in a hyperthermic-induced ovine model of placental insufficiency-intrauterine growth restriction (PI-IUGR). Both caruncular and cotyledonary VEGF and PlGF mRNA concentration increased with gestational age (P< 0.05), whereas only cotyledonary VEGF and PlGF protein concentration increased over gestation (P< 0.002). At 55 dpc, VEGF mRNA concentration was elevated in hyperthermic (HT) ewes, compared to control thermoneutral (TN) animals (TN; 0.52+/-0.08 vs HT; 1.27+/-0.17 VEGF/GAPDH, P< 0.001). At 90 dpc, expression of PlGF and VEGF mRNA was not altered by the HT treatment. Both TN cotyledonary VEGFR-1 and VEGFR-2 mRNA expression levels rose significantly over the period studied (P< 0.05 and P< 0.01 respectively). Receptor mRNA concentration in HT cotyledonary tissue was significantly reduced at 90 dpc (VEGFR-1; TN 0.21+/-0.02 vs HT 0.11+/-0.01 VEGFR-1/actin, P< 0.05, VEGFR-2; TN 0.18+/-0.05 vs HT 0.07+/-0.01 VEGFR-2/actin, P< 0.01). Soluble VEGFR-1 (sVEGFR-1) mRNA was not detected in these tissues. These alterations in growth factor and growth factor receptor mRNA expression, as a result of environmental heat stress early in placental development, could impair normal placental vascular development. Furthermore, alterations in VEGF, VEGFR-1 and VEGFR-2 mRNA expression, during the period of maximal placental growth, may contribute to the development of placental insufficiency, and ultimately intrauterine growth restriction.

Transcriptional effect of hypoxia on placental leptin

We observed recentlyl that placental leptin is markedly increased in preeclampsia. Since this disorder is associated with vascular disorders, we have tested the hypothesis that hypoxia regulates leptin expression. We show that hypoxia increased leptin mRNA and secretion in trophoblast-derived BeWo cells. This effect was mediated through leptin promoter activation. 5' deletion analysis allowed us to delineate two regions containing 1.87 kb and 1.20 kb of the promoter which conferred respectively high and low responsiveness to hypoxia. These data indicate that leptin is up-regulated by hypoxia through a transcriptional mechanism likely to involve distinct hypoxia-responsive cis-acting sequences on the promoter.

Hypoxia attenuates PGE(2)but increases prostacyclin and thromboxane production in human term villous trophoblast

Prostanoids have been proposed to play a major role in the regulation of uteroplacental blood flow. We examined the effect of hypoxia on the production of prostaglandin E(2)(PGE(2)) thromboxane B(2)(TXB(2)), and prostacyclin (measured as 6-keto-PGF(1alpha)) by human term trophoblast cells and villous placental explants. Explants (n=8) and purified trophoblast cells (n=5) were incubated for 24-72 h under either normoxic (21 per cent O(2)) or hypoxic (2 per cent O(2)) conditions. In trophoblast monolayer cultures, hypoxia attentuated PGE(2)production rates to 52+/-9.4 per cent (mean+/-sem, P< 0.05) but recovered to control rates within 48 h. In villous explants, PGE(2)production was significantly decreased after 48 and 72 h of hypoxia versus the normoxic control, accompanied by increased production of 6-keto-PGF(1alpha)to 173.9+/-26.7 per cent after 48 h. TXB(2)production was increased to 172.3+/-25.9 per cent and 653.2+/-135.7 per cent (P< 0.05) control after 48 and 72 h of hypoxia, respectively. These results were confirmed in villous explants (n=3) cultured in the presence of exogenous 10 microm arachidonic acid. Hypoxia had no significant effect on TXB(2)and 6-keto-PGF(1alpha)in trophoblast cells. In summary, our findings suggest that hypoxia could be responsible for abnormal profiles of prostanoid production commonly observed in women with pre-eclampsia. These results indicate a putative link between hypoxia and compromised placental perfusion.

Maternal plasma vascular endothelial growth factor concentrations in normal and hypertensive pregnancies and their relationship to peripheral vascular resistance

OBJECTIVE

The aim of this study was to measure maternal plasma vascular endothelial growth factor concentrations during normal and hypertensive pregnancies and examine their relationship with maternal total peripheral resistance values.

STUDY DESIGN

Plasma concentrations of total immunoreactive vascular endothelial growth factor and total peripheral resistances were measured serially throughout pregnancy in 20 women with preeclampsia, 24 women with gestational hypertension, and 26 normotensive control women. One-way analysis of variance and a regression model were used to analyze the vascular endothelial growth factor levels in the groups and the relationship between vascular endothelial growth factor concentration and total peripheral resistance.

RESULTS

At 10 to 14 weeks' gestation plasma vascular endothelial growth factor concentrations in all subjects were 4 to 5 times greater than the levels measured post partum (P <.0001). Mean vascular endothelial growth factor concentrations were similar in the control and gestational hypertension groups; in both groups levels remained stable until 34 to 36 weeks' gestation, when levels increased a further 1.3-fold (P <.01). In comparison, vascular endothelial growth factor concentrations in subjects in the preeclampsia group were greater at 28 to 32 weeks' gestation (P =.002) and at 34 to 36 weeks' gestation (P <.001). Vascular endothelial growth factor concentrations were also increased during the 4 weeks that preceded the diagnosis of preeclampsia (P <.05). Vascular endothelial growth factor concentrations were associated with the elevated total peripheral resistance observed during the clinical disorder in the preeclampsia group but not in the other groups.

CONCLUSION

Maternal plasma vascular endothelial growth factor concentrations increased before the clinical onset of preeclampsia and were further elevated during the vasoconstricted state observed in this disorder. We speculate that the hyperdynamic circulation that characterizes the latent phase of preeclampsia causes vascular shear stress, which in turn increases the levels of circulating vascular endothelial growth factor. Because vascular endothelial growth factor normally acts as a vasodilator, its increase may represent an unsuccessful vascular rescue response.

Uteroplacental blood flow and placental vascular endothelial growth factor in normotensive and pre-eclamptic pregnancy

OBJECTIVE

To determine whether placental vascular endothelial growth factor (VEGF) is increased in pre-eclampsia.

DESIGN

Prospective cohort study.

SETTING

Royal Prince Alfred Hospital, Sydney, Australia.

SAMPLE

Eleven normotensive women and eight women with pre-eclampsia matched for age and gestation.

METHODS

Uterine artery Doppler ultrasound flow velocity profiles were recorded in the third trimester and resistance index calculated as (Vs-Vd)/Vs (Vs = peak systolic flow velocity, Vd = end diastolic flow velocity). Placental tissue at delivery was examined for VEGF distribution with avidin-biotin-peroxidase immunohistochemistry.

RESULTS

Uterine resistance index [median (range)] was significantly increased in pre-eclamptic women (normotensive: 0.42 (0.36-0.51); pre-eclampsia: 0.59 (0.40-0.75); P = 0.005). Notching of the uterine artery waveform, consistent with a high resistance circulation, was evident in early diastole in five women with pre-eclampsia but only one normotensive woman (P = 0.013). Placental VEGF was increased in women with pre-eclampsia in the decidual trophoblast (normotensive: 34% (4-59) cells stained for VEGF; pre-eclampsia: 58% (15-95); P = 0.033) and in the villous syncytiotrophoblast (normotensive: VEGF count 1.4 arbitrary units (1.1-2.1); pre-eclampsia: 1.8 arbitrary units (1.4-2.2); P = 0.041). Analysis indicated that uterine artery resistance index was directly correlated with placental VEGF staining, mean arterial pressure and birthweight.

CONCLUSIONS

Abnormal uterine artery Doppler ultrasound flow velocity profiles in pre-eclampsia indicate increased uteroplacental resistance. The associated increase in placental VEGF may represent a compensatory mechanism attempting to restore blood flow towards normal.

Hypoxia-inducible factor-1 mediates the biological effects of oxygen on human trophoblast differentiation through TGFbeta(3)

During early pregnancy, placentation occurs in a relatively hypoxic environment that is essential for appropriate embryonic development. Intervillous blood flow increases around 10 to 12 weeks of gestation and results in exposure of trophoblast cells to increased oxygen tension. Before this time, low oxygen appears to prevent trophoblast differentiation toward an invasive phenotype. Using human villous explants of 5-8 weeks' gestation, we found that low oxygen tension triggered trophoblast proliferation, fibronectin synthesis, alpha(5) integrin expression, and gelatinase A activity. These biochemical markers were barely detectable under oxic conditions. We therefore examined the placental expression of hypoxia-inducible factor-1 (HIF-1), a master regulator of oxygen homeostasis, and determined that expression of HIF-1alpha subunit during the first trimester of gestation parallels that of TGFbeta(3), an inhibitor of extravillous trophoblast differentiation. Expression of both molecules is high in early pregnancy and falls around 9 weeks of gestation, when placental pO(2) levels are believed to increase. Increasing oxygen tension induced a similar decrease in expression in cultured explants. Moreover, antisense inhibition of HIF-1alpha expression in hypoxic explants inhibited expression of TGFbeta(3), arrested cell proliferation, decreased alpha(5) expression and gelatinase A activity, and triggered biochemical markers of an invasive trophoblast phenotype such as alpha(1) integrin and gelatinase B expression. These data suggest that the oxygen-regulated early events of trophoblast differentiation are in part mediated by TGFbeta(3) through HIF-1 transcription factors.

Oxygen and placental vascular development

Human embryogenesis takes place in a hypoxic environment because the trophoblast shell excludes entry of maternal blood. The first fetal-placental villi develop as trophoblast sprouts. These are invaded by allantoic mesoderm to form secondary villi and are transformed, by vasculogenesis, into tertiary villi. The placental barrier to maternal blood is gradually breached between 8-12 weeks of gestation, due to invasion of placental-bed uteroplacental spiral arteries by the extravillous trophoblast (EVT). Placental oxygen tension thus rises and a phase of branching angiogenesis continues until 24 weeks. Thereafter a gradual shift takes place favoring non-branching angiogenesis. Gas-exchanging terminal villi thus form which are essential for rapid fetal growth and development of a high-flow, low-resistance fetal-placental circulation. Inadequate invasion of the uteroplacental spiral arteries by EVT results in placental ischemia and the development of obstetrical complications--preeclampsia and/or intrauterine growth restriction (IUGR). Placental villi often show evidence of continued branching angiogenesis, as is the case with anemic pregnancy, and pregnancy at high altitude. These structural alterations may reflect continued hypoxia-driven activity of vascular endothelial growth factor (VEGF). By contrast, a minority of severe early-onset IUGR pregnancies exhibit reduced fetal-placental blood flow with elongated maldeveloped villous capillaries. Placenta-like growth factor (PIGF) expression is increased while trophoblast proliferation is reduced, suggesting "hyperoxia" in the placental villous tree. IUGR may thus have two phenotypes--a more common hypoxic and a rarer hyperoxic type. While this concept is gaining acceptance, we have no insight as to the initiating mechanism(s).