Vascular endothelial growth factor and placental growth factor release in cultured trophoblast cells under different oxygen tensions

(Dis)similarities between the Decidual and Tumor Microenvironment

Placenta-specific trophoblast and tumor cells exhibit many common characteristics. Trophoblast cells invade maternal tissues while being tolerated by the maternal immune system. Similarly, tumor cells can invade surrounding tissues and escape the immune system. Importantly, both trophoblast and tumor cells are supported by an abetting microenvironment, which influences invasion, angiogenesis, and immune tolerance/evasion, among others. However, in contrast to tumor cells, the metabolic, proliferative, migrative, and invasive states of trophoblast cells are under tight regulatory control. In this review, we provide an overview of similarities and dissimilarities in regulatory processes that drive trophoblast and tumor cell fate, particularly focusing on the role of the abetting microenvironments.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

Impaired vascular endothelial growth factor expression and secretion during in vitro differentiation of human primary term cytotrophoblasts

Vascular endothelial growth factor A (VEGF-A) is one of the main growth factors involved in placental vasculogenesis and angiogenesis, but its placental expression is still ambiguous. During in vitro cultures of primary term cytotrophoblasts, VEGF could not be detected in the supernatants by enzyme-linked immunosorbent assays (ELISA). One hypothesis is that VEGF is immediately and completely bound to its soluble receptor after secretion, and cannot be recognized by the antibodies used in the commercial ELISA kits. We decided to verify this hypothesis by measuring VEGF-A expression during in vitro cultures of primary term cytotrophoblasts. Term cytotrophoblasts were cultured under 21% and 2.5% O₂ for 4 days. VEGF-A transcripts were quantified by real-time polymerase chain reaction. The proteins from cell lysates and concentrated media were separated by polyacrylamide gel electrophoresis (PAGE) under denaturing and reducing conditions, and VEGF-A immunodetected by western blotting. VEGF mRNA expression did not increase during in vitro cell differentiation under 21% O₂, but slightly increased under 2.5% O₂ only at 24 h. VEGF-A monomer was not detected in the cell lysates and in the concentrated supernatants, while a ~ 42 KDa band corresponding to the precursor L-VEGF was detected in all the cellular extracts. Isolated term villous cytotrophoblasts produce the L-VEGF precursor but they do not secrete VEGF-A even under low-oxygen tension. The question remains about the origin of VEGF in pregnancy but also about the biological role of L-VEGF, which can represent a form of storage for rapid VEGF secretion when needed.

In vitro fertilization is associated with the onset and progression of preeclampsia

OBJECTIVE

We aimed to estimate the risk of preeclampsia (PE) associated with in vitro fertilization (IVF) and potential predisposing factors responsible for the observed association.

METHODS

This retrospective cohort study included 114485 pregnant women who delivered at the Nanjing Maternity and Child Health Care Hospital between 2013 and 2018. Of the 114485 women, 4601 (4%) conceived through IVF (IVF group) and 109884 (96%) conceived spontaneously (SC group). We performed logistic regression analysis to evaluate the risk of PE following IVF compared to spontaneous conception (SC). Then, we used propensity score matching analysis to compare the clinical characteristics and pregnancy outcomes between IVF patients with and without PE.

RESULT

There were 1339 PE cases in the total study population, with a significantly higher incidence of PE in IVF relative to spontaneous pregnancies (6.1% vs. 1.0%, p < 0.01). Severe PE was more prevalent in singleton IVF-PE group than in singleton SC-PE group (40% vs. 24.1%, p = 0.025). Placenta accreta was more common in singleton preeclamptic patients with IVF than without IVF (12.5vs.2.6%, p = 0.003). Placental hypoxia was more prevalent in twin IVF pregnancies with PE than without PE (6% vs. 12.2%, p = 0.045). Moreover, the IVF-PE group showed more frequent first-trimester bleeding (31.6% vs. 10.5%, p = 0.024) compared to the control group.

CONCLUSION

IVF is associated with the onset and progression of PE. Defective placentation and placental insufficiency may predispose IVF patients to PE and may manifest as first-trimester bleeding.

Oxygen-dependent regulation of tumor growth and metastasis in human breast cancer xenografts

Background

Tumor hypoxia is relevant for tumor growth, metabolism, resistance to chemotherapy and metastasis. We have previously shown that hyperoxia, using hyperbaric oxygen treatment (HBOT), attenuates tumor growth and shifts the phenotype from mesenchymal to epithelial (MET) in the DMBA-induced mammary tumor model. This study describes the effect of HBOT on tumor growth, angiogenesis, chemotherapy efficacy and metastasis in a triple negative MDA-MB-231 breast cancer model, and evaluates tumor growth using a triple positive BT-474 breast cancer model.

Materials and methods

5 x 10⁵ cancer cells were injected s.c. in the groin area of NOD/SCID female mice. The BT-474 group was supplied with Progesterone and Estradiol pellets 2-days prior to tumor cell injection. Mice were divided into controls (1 bar, pO₂ = 0.2 bar) or HBOT (2.5 bar, pO₂ = 2.5 bar, 90 min, every third day until termination of the experiments). Treatment effects were determined by assessment of tumor growth, proliferation (Ki67-staining), angiogenesis (CD31-staining), metastasis (immunostaining), EMT markers (western blot), stromal components collagen type I, Itgb1 and FSP1 (immunostaining) and chemotherapeutic efficacy (5FU).

Results

HBOT significantly suppressed tumor growth in both the triple positive and negative tumors, and both MDA-MB-231 and BT-474 showed a decrease in proliferation after HBOT. No differences were found in angiogenesis or 5FU efficacy between HBOT and controls. Nevertheless, HBOT significantly reduced both numbers and total area of the metastastatic lesions, as well as reduced expression of N-cadherin, Axl and collagen type I measured in the MDA-MB-231 model. No change in stromal Itgb1 and FSP1 was found in either tumor model.

Conclusion

Despite the fact that behavior and prognosis of the triple positive and negative subtypes of cancer are different, the HBOT had a similar suppressive effect on tumor growth, indicating that they share a common oxygen dependent anti-tumor mechanism. Furthermore, HBOT significantly reduced the number and area of metastatic lesions in the triple negative model as well as a significant reduction in the EMT markers N-cadherin, Axl and density of collagen type I.

Mild anemia during pregnancy upregulates placental vascularity development

The connection between maternal hematological status and pregnancy outcome has been shown by many independent researchers. Attention was initially focused on the adverse effects of moderate and severe anemia. Interestingly, some studies revealed that mild anemia was associated with optimal fetal development and was not affecting pregnancy outcome. The explanation for this phenomenon became a target for scientists. Hemodilution, physiologic anemia and relative decrease in hemoglobin concentration are the changes observed during pregnancy but they do not explain the reasons for the positive influence of mild anemia on a fetomaternal unit. It is hypothesized that hemodilution facilitates placental perfusion because blood viscosity is reduced. Subsequently, it may lead to a decline in hemoglobin concentration. Anemia from its definition implies decreased oxygen carrying capacity of the blood and can result in hypoxemia and even hypoxia, which is a common factor inducing new blood vessels formation. Therefore, we raised the hypothesis that the lowered hemoglobin concentration during pregnancy may upregulate vascular growth factor receptors expression such as VEGFR-1 (Flt-1) and VEGFR-2 (FLK-1/KDR). Consecutively, increased fetoplacental vasculogenesis and angiogenesis provide further expansion of vascular network development, better placental perfusion and hence neither fetus nor the mother are affected.

Predisposing Factors to Abnormal First Trimester Placentation and the Impact on Fetal Outcomes

Normal placentation during the first trimester sets the stage for the rest of pregnancy and involves a finely orchestrated cellular and molecular interplay of maternal and fetal tissues. The resulting intrauterine environment plays an important role in fetal programming and the future health of the fetus, and is impacted by multiple genetic and epigenetic factors. Abnormalities in placentation and spiral artery invasion can lead to ischemia, placental disease, and adverse obstetrical outcomes including preeclampsia, intrauterine growth restriction, and placental abruption. Although first trimester placentation is affected by multiple factors, preconception environmental influences such as mode of conception, including assisted reproductive technologies which result in fertilization in vitro and intrauterine influences due to sex differences, are emerging as potential significant factors impacting first trimester placentation.

Nanoadduct relieves: Alleviation of developmental toxicity of Cr(VI) due to its spontaneous adsorption to Mg(OH)2 nanoflakes

During pregnancy, both the mother and fetus are vulnerable to environmental pollution by particulate matters and chemicals. Although the toxicity of free pollutants has been frequently reported, the impact of nanoparticle/pollutant adducts on the vulnerable pregnant population remains unclear. In this study, pregnant mice were orally exposed to Mg(OH)2 nanoflakes and nanoflakes adsorbed with Cr(VI) anions during the peri-implantation and organogenesis stages of pregnancy at doses that did not induce systemic toxicity or pregnancy complications. The nano-Mg(OH)2/Cr(VI) adducts formation reduced fetal developmental toxicity compared with the toxicity induced by the same concentration of free Cr(VI) anions.

TCDD induces the hypoxia-inducible factor (HIF)-1α regulatory pathway in human trophoblastic JAR cells

The exposure to dioxin can compromise pregnancy outcomes and increase the risk of preterm births. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) has been demonstrated to induce placental hypoxia at the end of pregnancy in a rat model, and hypoxia has been suggested to be the cause of abnormal trophoblast differentiation and placental insufficiency syndromes. In this study, we demonstrate that the non-hypoxic stimulation of human trophoblastic cells by TCDD strongly increased hypoxia inducible factor-1 alpha (HIF-1α) stabilization. TCDD exposure induced the generation of reactive oxygen species (ROS) and nitric oxide. TCDD-induced HIF-1α stabilization and Akt phosphorylation was inhibited by pretreatment with wortmannin (a phosphatidylinositol 3-kinase (PI3K) inhibitor) or N-acetylcysteine (a ROS scavenger). The augmented HIF-1α stabilization by TCDD occurred via the ROS-dependent activation of the PI3K/Akt pathway. Additionally, a significant increase in invasion and metallomatrix protease-9 activity was found in TCDD-treated cells. The gene expression of vascular endothelial growth factor and placental growth factor was induced upon TCDD stimulation, whereas the protein levels of peroxisome proliferator-activated receptor γ (PPARγ), PPARγ coactivator-1α, mitochondrial transcription factor, and uncoupling protein 2 were decreased. Our results indicate that an activated HIF-1α pathway, elicited oxidative stress, and induced metabolic stress contribute to TCDD-induced trophoblastic toxicity. These findings may provide molecular insight into the TCDD-induced impairment of trophoblast function and placental development.

Evidence for extraplacental sources of circulating angiogenic growth effectors in human pregnancy

Pregnancy complications such as preeclampsia (PE) and intrauterine growth restriction (IUGR) are associated with reduced blood flow, contributing to placental and fetal hypoxia. Placental hypoxia is thought to cause altered production of angiogenic growth effectors (AGEs), reflected in the circulation of mother and fetus. Vascular endothelial growth factor (VEGF), placental growth factor (PlGF) and their soluble binding protein (sFlt-1) are, in turn, postulated as being causally involved in PE via induction of systemic endothelial cell dysfunction. To dissect the role of AGEs, accurate measurement is of great importance. However, the values of AGEs are highly variable, contributing to heterogeneity in their association (or lack thereof) with preeclampsia. To test the hypothesis that variability may be due to peripheral cell release of AGEs we obtained blood samples from normal healthy pregnant women (n = 90) and the cord blood of a subset of their neonates using standard serum separation and compared results obtained in parallel samples collected into reagents designed to inhibit peripheral cell activation (sodium citrate, theophylline, adenosine and dipyridamole-CTAD). AGEs were measured by ELISA. CTAD collection reduced maternal and fetal free VEGF by 83%, and 98%, respectively. Free PlGF was decreased by 29%, maternal sFlt-1 by >20% and fetal sFlt-1 by 59% in the CTAD-treated vs. serum sample (p < 0.0001). In summary blood collection techniques can profoundly alter measured concentrations of AGEs in mother and fetus. This process is highly variable, contributes to variation reported in the literature, and renders questionable the true impact of alteration in AGEs on pregnancy pathologies.

Global protein synthesis in human trophoblast is resistant to inhibition by hypoxia

Placental growth and function depend on syncytial cell processes which require the continuing synthesis of cellular proteins. The substantial energy demands of protein synthesis are met primarily from oxidative metabolism. Although the responses of individual proteins produced by the syncytiotrophoblast to oxygen deprivation have been investigated previously, there is no information available on global protein synthesis in syncytiotrophoblast under conditions of hypoxia. These studies were designed to test the hypothesis that syncytial protein synthesis is decreased in a dose-dependent manner by hypoxia. Experiments were performed to measure amino acid incorporation into proteins in primary syncytiotrophoblast cells exposed to oxygen concentrations ranging from 0 to 10%. Compared to cells exposed to normoxia (10% O₂), no changes were observed following exposure to 5% or 3% O₂, but after exposure to 1% O₂, protein synthesis after 24 and 48 h decreased by 24% and 23% and with exposure to 0% O₂, by 65% and 50%. As a consequence of these results, we hypothesized that global protein synthesis in conditions of severe hypoxia was being supported by glucose metabolism. Additional experiments were performed therefore to examine the role of glucose in supporting protein synthesis. These demonstrated that at each oxygen concentration there was a significant, decreasing linear trend in protein synthesis as glucose concentration was reduced. Under conditions of near-anoxia and in the absence of glucose, protein synthesis was reduced by >85%. Even under normoxic conditions (defined as 10% O₂) and in the presence of oxidative substrates, reductions in glucose were accompanied by decreases in protein synthesis. These experiments demonstrate that syncytiotrophoblast cells are resistant to reductions in protein synthesis at O₂ concentrations greater than 1%. This could be explained by our finding that a significant fraction of protein synthesis in the syncytiotrophoblast is sustained by glycolytic metabolism. This suggests that with increasing degrees of chronic hypoxia there is a shift from oxidative to glycolytic pathways, allowing a substantial degree of protein synthesis to be maintained.

High altitude during pregnancy

One of the greatest physiologic challenges during pregnancy is to maintain an adequate supply of oxygenated blood to the uteroplacental circulation for fetal development. This challenge is magnified under conditions of limited oxygen availability. High altitude impairs fetal growth, increases the incidence of preeclampsia, and, as a result, significantly increases the risk of perinatal and/or maternal morbidity and mortality. This review summarizes the clinical consequences and physiologic challenges that emerge when pregnancy and high altitude coincide and highlights the adaptations that serve to protect oxygenation and fetal growth under conditions of chronic hypoxia.

Do anti-angiogenic or angiogenic factors contribute to the protection of birth weight at high altitude afforded by Andean ancestry?

OBJECTIVE

This prospective study was designed to determine whether variation in angiogenic (placental growth factor [PlGF]) and/or anti-angiogenic (soluble fms-like tyrosine kinase [sFlt-1]) factors contribute to the protective effect of highland ancestry (Andean) from altitude-associated reductions in fetal growth.

STUDY DESIGN

Plasma sFlt-1 and PlGF levels, uterine artery (UA) blood flow, and fetal biometry were determined in low-altitude (400 m; Andean n = 27, European n = 28) and high-altitude (3600 m; Andean n = 51, European n = 44) residents during pregnancy (20 and 36 weeks) and 4 months postpartum.

RESULTS

High-altitude decreased sFlt-1 levels in both groups, Andeans had lower sFlt-1, comparable PlGF, lower sFlt-1/PlGF ratios, and higher UA blood flow throughout pregnancy relative to Europeans. Altitude decreased birth weight in Europeans but not Andeans. In high-altitude Europeans sFlt-1/PlGF and sFlt-1 levels were negatively associated with UA diameter and birth weight, respectively.

CONCLUSIONS

Lower sFlt-1 and sFlt-1/PLGF ratio may contribute to or result from variations in maternal vascular adaptation to pregnancy between Andean and Europeans at high altitude. Subsequently, these effects could potentially influence ancestry-associated differences in birth weight.

Plasma soluble vascular endothelial growth factor receptor-1 concentration is elevated prior to the clinical diagnosis of pre-eclampsia

OBJECTIVE

Accumulating evidence suggests that the balance between vascular endothelial growth factor (VEGF), placental growth factor (PIGF), and their receptors is important for effective vasculogenesis, angiogenesis, and placental development. Recently, the soluble form of VEGFR-1 (sVEGFR-1), an antagonist to VEGF and PIGF, has been implicated in the pathophysiology of pre-eclampsia. Plasma sVEGFR-1 concentration is elevated in pre-eclampsia at the time of clinical diagnosis and correlates with the severity of the disease. The purpose of this study was to determine whether the concentrations of sVEGFR-1 in plasma of pre-eclamptic patients change prior to the clinical manifestations of the disease.

METHODS

A longitudinal case-control study was conducted in normal pregnant women (n = 44) and patients with pre-eclampsia (n = 44). Blood sampling was performed at six intervals: (1) 7-16 weeks; (2) 16-24 weeks; (3) 24-28 weeks; (4)28-32 weeks; (5) 32-36 weeks; and (6) more than 37 weeks of gestation. To examine the relationship between plasmasVEGFR-1 concentration and interval to clinical diagnosis of pre-eclampsia, plasma samples of pre-eclamptic patients at different gestational ages were stratified according to the interval from blood sampling to clinical development of the disease into five groups: (1) at clinical manifestation; (2) 2-5 weeks; (3) 6-10 weeks; (4) 11-16 weeks; and (5) 17-25 weeks before clinical manifestations. Plasma concentrations of sVEGFR-1 were determined by enzyme-linked immunoassay. Parametric statistics and repeated measure procedures were used for the analysis.

RESULTS

The mean plasma sVEGFR-1 concentration in pre-eclamptic patients before the clinical manifestation of the disease was significantly higher than in normal pregnant women at 24-28, 28-32, and 32-37 weeks of gestation (p = 0.02,p < 0.001, and p < 0.001, respectively). In contrast, no significant differences in the mean plasma sVEGFR-1 concentration between patients with pre-eclampsia and normal pregnant women were observed both at 7-16 weeks and 16-24 weeks of gestation (p= 0.1 and p= 0.9). Similarly, the mean plasma sVEGFR-1 concentration was significantly higher in pre-eclamptic patients than in normal pregnant women at clinical manifestation, at 2-5 weeks (mean 3.8 weeks), and at 6-10 weeks (mean 8.2 weeks) prior to the development of clinical pre-eclampsia (p < 0.001, p < 0.001, and p = 0.002,respectively). Among patients with early-onset pre-eclampsia (defined as gestational age of 34 weeks or less), the mean plasma sVEGFR-1 concentration was significantly higher in pre-eclampsia (before clinical diagnosis) than in normal pregnant women at 24-28 (mean 26.4) weeks of gestation (p = 0.008). In contrast, among patients with the late-onset disease(defined as gestational age of more than 34 weeks), plasma sVEGFR-1 concentration in pre-clinical pre-eclampsia was significantly higher than in normal pregnant women at 28-32 (mean 30.2) weeks of gestation (p < 0.001).

CONCLUSIONS

Plasma sVEGFR-1 concentration is elevated in pre-eclampsia prior to the clinical diagnosis of the disease. This elevation began 6-10 weeks prior to the clinical manifestations, and the increase was more pronounced at 2-5 weeks before the diagnosis, as well as at clinical presentation. Furthermore, in early-onset pre-eclampsia, plasma concentration ofsVEGFR-1 is elevated earlier than the late-onset disease.

Metal transcription factor-1 is involved in hypoxia-dependent regulation of placenta growth factor in trophoblast-derived cells

Placenta growth factor (PlGF) is a placental angiogenic factor. Metal-responsive transcription factor (MTF)-1 was reported to take part in the hypoxic induction of PlGF in RAS-transformed mouse fibroblasts. We contrarily showed that PlGF mRNA and protein levels decreased under hypoxia in a choriocarcinoma BeWo cell line derived from trophoblast. In this report, we examined whether hypoxia-dependent regulation of the PlGF gene in these cells also depends on MTF-1. We analyzed the effect of hypoxia on MTF-1 expression, and it was revealed to be decreased. Moreover, MTF-1 small interfering RNA treatment decreased PlGF mRNA level. To investigate the transcription of PlGF under hypoxia, we cloned promoter region of the human PlGF. Promoter deletion analysis suggested that triple repeats of metal-responsive element located between -511 and -468 bp in the promoter are important for the hypoxic regulation of PlGF. Treatment with MTF-1 small interfering RNA resulted in the significant decreased luciferase activity in PlGF reporter constructs. Chromatin immunoprecipitation showed the binding of the MTF-1 protein to the promoter region. We examined MTF-1 immunoreactivity in trophoblasts of term placental tissue from patients with normal pregnancies and preeclampsia, which represents a condition of placental hypoxia. Immunoreactivity of the MTF-1 protein was decreased in placentas from pregnant women with preeclampsia when compared with those from normal pregnant women. Taken together, these findings suggest that MTF-1 is involved in hypoxia-dependent regulation of PlGF in trophoblast-derived cells.

Vasoactivity to and endogenous release of vascular endothelial growth factor in the in vitro perfused human placental lobule from pregnancies complicated by preeclampsia

Vascular endothelial growth factor (VEGF) is a potent, physiologically relevant, vasodilator of the human term fetoplacental vasculature of placental lobules from normal pregnancy. There is evidence that VEGF and its receptors are dysregulated in preeclampsia (PE). Here, we used dual perfusion of the human placental lobule to test the hypothesis that the VEGF vasodilatory effect on the fetoplacental circulation is altered in PE and examined how vascular responsiveness relates to circulating levels of free VEGF in fetal sera in this disease. Umbilical cord sera and fetal venous perfusate concentrations of free VEGF from pregnancies complicated with PE were significantly lower compared to the normal group (P<0.05 and P<0.01, respectively). There was elevated in vitro placental release of the sequestrating soluble receptor, sVEGFR-1, into the fetal-side perfusate with PE compared to the normal group (P<0.05). The umbilical sera PlGF-1 level was higher by an order of magnitude in the fetal circulation in PE compared to normal pregnancy (P<0.0001), with the placenta appearing to contribute appreciably to these levels. Placental net contribution to maternal systemic free VEGF levels appeared to be negligible in both groups. sVEGFR-1 levels were elevated in the maternal-side venous perfusate with PE compared to the normal pregnancy (P<0.01). Perfused lobules from PE pregnancy exhibited an enhanced fetoplacental vasodilatory response to exogenous VEGF (P<0.001), with a longer recovery time (P<0.05), compared to the normal control group. Extrapolation of our combined functional and biochemical data suggests that a decrease in the in vivo circulating levels of free VEGF in PE is likely to contribute to compromised fetoplacental vascular patency in this disease.

The functional role of the renin-angiotensin system in pregnancy and preeclampsia

During normal pregnancy, the renin-angiotensin system (RAS) plays a vitally important role in salt balance and subsequent well-being of mother and fetus. In this balance, one must consider not only the classical renal RAS but also that of the uteroplacental unit, where both maternal and fetal tissues contribute to the signaling cascade. Many studies have shown that in normal pregnancy there is an increase in almost all of the components of the RAS. In derangements of pregnancy this delicate equilibrium can become unbalanced. Preeclampsia is one such case. It is a disorder of pregnancy characterized by hypertension, proteinuria and placental abnormalities associated with shallow trophoblast invasion and impaired spiral artery remodeling. Despite being a leading cause of maternal death and a major contributor to maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of preeclampsia are poorly understood. Immunological mechanisms and the RAS have been long considered to be involved in the development of preeclampsia. Numerous recent studies demonstrate the presence of the angiotensin II type I receptor agonistic autoantibody (AT1-AA). This autoantibody can induce many key features of the disorder and upregulate molecules involved in the pathogenesis of preeclampsia. Here we review the functional role of the RAS during pregnancy and the impact of AT1-AA on preeclampsia.

The maternal plasma soluble vascular endothelial growth factor receptor-1 concentration is elevated in SGA and the magnitude of the increase relates to Doppler abnormalities in the maternal and fetal circulation

OBJECTIVES

The soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1), an antagonist to vascular endothelial growth factor and placental growth factor, has been implicated in the pathophysiology of preeclampsia. Preeclampsia and pregnancy complicated with small for gestational age (SGA) fetuses share some pathophysiologic derangements, such as failure of physiologic transformation of the spiral arteries, endothelial cell dysfunction, and leukocyte activation. The objectives of this study were to: (1) determine whether plasma concentrations of sVEGFR-1 in mothers with SGA fetuses without preeclampsia at the time of diagnosis are different from those in patients with preeclampsia or normal pregnant women, and (2) examine the relationship between plasma concentrations of sVEGFR-1 and Doppler velocimetry in uterine and umbilical arteries in patients with preeclampsia and those with SGA.

STUDY DESIGN

A cross-sectional study was conducted to determine the concentrations of the soluble form of VEGFR-1 in plasma obtained from normal pregnant women (n = 135), women with SGA fetuses (n = 53), and patients with preeclampsia (n = 112). Patients with SGA fetuses and those with preeclampsia were sub-classified according to the results of uterine and umbilical artery Doppler velocimetry examinations. Plasma concentrations of sVEGFR-1 were determined by an ELISA. Since these concentrations change with gestational age, differences among various subgroups were statistically estimated with the delta value, defined as the difference between the observed and expected plasma sVEGFR-1 concentration. The expected values were derived from regression analysis of plasma sVEGFR-1 concentrations in normal pregnancy. Regression analysis and univariate and multivariate analysis were employed.

RESULTS

(1) Mothers with SGA fetuses had a mean plasma concentration of sVEGFR-1 higher than normal pregnant women (p < 0.001), but lower than patients with preeclampsia (p < 0.001). (2) Among patients with SGA fetuses, only those with abnormal uterine artery Doppler velocimetry had a mean plasma sVEGFR-1 concentration significantly higher than normal pregnant women (p < 0.001). (3) Among mothers with SGA fetuses in whom Doppler velocimetry was performed (n = 41), those with abnormalities in both the uterine and umbilical artery velocimetry had the highest mean delta of sVEGFR-1 plasma concentration (mean +/- standard deviation (SD): 0.69 +/- 0.29). Conversely, patients who had normal Doppler velocimetry in both uterine and umbilical arteries had the lowest mean delta (mean +/- SD: 0.09 +/- 0.29) of sVEGFR-1 plasma concentrations (ANOVA; p < 0.001). (4) Among patients with preeclampsia in whom Doppler velocimetry was performed (n = 69), those with abnormalities in both the uterine and umbilical artery velocimetry had the highest mean delta sVEGFR-1 plasma concentration (mean +/- SD: 1.01 +/- 0.22) among all groups classified (ANOVA; p < 0.001). (5) Among patients with SGA and those with preeclampsia, there was a relationship (Chi-square for trend p < 0.001 for both) between the severity of Doppler velocimetry abnormalities and the proportion of patients who had high delta sVEGFR-1 plasma concentrations (defined as a concentration two standard deviations (2SD) above the mean delta of normal pregnant women). (6) Multiple regression analysis suggested that the diagnostic category (e.g., SGA or preeclampsia), Doppler abnormalities, and gestational age at blood sampling were associated with an increase in plasma sVEGFR-1 concentrations (p < 0.001).

CONCLUSIONS

These observations provide support for the participation of the soluble receptor of vascular endothelial growth factor in the pathophysiology of SGA with abnormal uterine artery Doppler velocimetry and preeclampsia. An excess of sVEGFR-1 is released into the maternal circulation of patients with preeclampsia and those with SGA fetuses, as abnormalities of impedance to blood flow involve uterine and umbilical circulation.

Medically indicated preterm birth: recognizing the importance of the problem

Preterm birth complicates over 500,000 births annually, affecting 12.5% of pregnancies in the United States. Much of the temporal increase in preterm birth (<37 weeks) over the past decade is largely driven by a concurrent temporal increase in medically indicated preterm birth. Maternal and fetal indications that prompt an intervention at preterm gestational ages include preeclampsia, intrauterine growth restriction, and placental abruption-conditions that constitute "ischemic placental disease." Ischemic placental disease is implicated in over one of every two indicated preterm births compared with less than one in five births at term. Comprehensive evaluation of risk factors, with careful consideration of heterogeneity in the syndrome of medically indicated preterm birth and ischemic placental disease may provide important clues to predict and consequently prevent preterm birth.

Vasoactive and permeability effects of vascular endothelial growth factor-165 in the term in vitro dually perfused human placental lobule

Vascular endothelial growth factor (VEGF) is an important vasodilator and effector of permeability in systemic blood vessels. Molecular and tissue culture techniques have provided evidence for its placental synthesis and release. Using an in vitro dual-perfusion model of the term placental lobule from normal pregnancy, we report here the relative secretion of total VEGF, soluble VEGF receptor (VEGFR)-1, and free VEGF into the maternal and fetoplacental circulations of the placenta. We tested the hypothesis that VEGF has vasomotor and permeability effects in the fetoplacental circulation of the human placenta, and we examined the broad intracellular pathways involved in the vasodilatory effect that we found. We show that total VEGF is released into the fetal and maternal circulations in a bipolar fashion, with a bias toward maternal side output. Soluble VEGFR-1 was also secreted into both circulations with bias toward the maternal side. Consequently, free VEGF (12.8 +/- 2.4 pg/ml, mean +/- se) was found only in the fetoplacental circulation. VEGF-165 was found to be a potent vasodilator of the fetoplacental circulation (maximum response: 77% of previous steady-state fetal-side inflow hydrostatic pressure after preconstriction with U46619; EC(50) = 71 pm). This vasodilatory effect was mediated by the VEGFR-2 receptor and nitric oxide in a manner-independent of the involvement of prostacyclin and the src-family tyrosine kinases. However, nitric oxide could explain only 50% of the vasodilatory effect. Finally, we measured the permeability of the perfused placenta to inert hydrophilic tracers and found no difference in the presence and absence of VEGF.

Down-regulation of placenta growth factor by promoter hypermethylation in human lung and colon carcinoma

Two recent clinical trials have shown that the placenta growth factor (PlGF) is up-regulated after bevacizumab treatment in colorectal cancer and after SU11248 treatment in metastatic renal cell carcinoma. The regulation of expression for the vascular endothelial growth factor (VEGF) has been well documented in human tumors; however, the data for PlGF are lacking. We investigated the epigenetic regulation of PlGF and correlated the results with clinicopathologic features. We used plgf promoter analysis, cDNA microarray, immunohistochemistry, and Northern blot analysis to determine the expression level of PlGF in 22 human lung carcinoma and 11 colorectal tumors and in 12 cell lines. Sodium bisulfite modification of genomic DNA followed by methylation-specific PCR (MSP) and sequencing were used to determine the methylation status of the PlGF promoter. Treatments with 5-aza-2'-deoxycytidine and trichostatin A (TSA) were used to reactivate PlGF expression. Significance analysis showed that PlGF expression level was low in human lung and colorectal tumor tissues and in cell lines. PlGF gene promoter was hypermethylated. Treatment with the demethylating agent 5-Aza-dC restored PlGF transcript expression in the lung and colon carcinoma cell lines. By combining the results from cDNA microarray, immunohistochemistry, and MSP, we report, for the first time, that the PlGF gene promoter is methylated, and methylation may be one of the mechanisms that contributes to the low PlGF expression level in human lung and colorectal tumor tissues and cell lines.

Hypoxia and Lactate Production in Trophoblast Cells

The etiology of preeclampsia is unknown but is thought to be related to hypoxia in the placenta. We previously reported that the enzyme lactate dehydrogenase (LDH) has increased activity and gene expression in placentas from preeclamptic pregnancies [Tsoi SCM, Zheng J, Xu F, Kay HH. Differential expression of lactate dehydrogenase isozymes (LDH) in human placenta with high expression of LDH-A(4) isozyme in the endothelial cells of pre-eclampsia villi. Placenta 2001;22:317-22]. LDH is responsible for pyruvate conversion to lactate through glycolysis. In this study, we further investigated the role of hypoxia in primary trophoblast cells and a cultured cell line, JEG3 cells, to obtain a better understanding of how it affects the activities of lactate dehydrogenase, lactate production and regulatory genes, as a possible model for preeclampsia. Primary trophoblast cells and JEG3 cells were cultured under 1% oxygen. At 6, 12 and 24h, cells were analyzed for LDHA and LDHB isozyme activities, mRNA and protein expression compared to standard culture conditions. Lactate was measured from cell medium. The hypoxia inducible transcription factor (HIF-1alpha) protein expression was confirmed by western blot. Two lactate transporters (MCT1 and MCT4) mRNA and protein expression were also studied under hypoxia. Finally, lactate was measured in plasma obtained from patients with severe preeclampsia. Under hypoxic conditions, LDHA mRNA is increased in primary trophoblast cells and JEG3 cells. The HIF-1alpha protein expression is higher in hypoxia-treated JEG3 cells than control. LDHA isozyme activity and its protein expression are increased most significantly at 24h of culture under hypoxia. However, LDHB protein is unchanged while its mRNA is decreased. Lactate secretion from JEG3 cells under hypoxia is increased, as is the lactate levels in the plasma from preeclampsia patients. Of the two lactate transporters studied, MCT4 mRNA and protein level are increased under hypoxia. Our findings support the role of hypoxia in inducing HIF-1alpha activity in trophoblasts and increasing LDH transcription as well as its activity. Higher levels of lactate are produced and secreted which may contribute to the higher lactate levels in plasma of preeclamptic patients. These mechanisms may be important in the pathophysiology of preeclampsia.

Alterations in placental growth factor levels before and after the onset of preeclampsia are more pronounced in women with early onset severe preeclampsia

It has been established that the serum placental growth factor (PlGF) decreases and the soluble fms-like tyrosine kinase-1 (sFlt-1) increases in women with preeclampsia. However, there have been no studies on the relation between preeclampsia onset time and the changes in PlGF and sFlt-1. Furthermore, the PlGF and sFlt-1 levels have not been evaluated using their reference values specific to each gestational age. In this study we reevaluated the serum PlGF and sFlt-1 levels before and after the clinical manifestation of early and late onset severe preeclampsia using the new reference values developed in our recent longitudinal study. Blood specimens were obtained immediately after the clinical manifestation of severe preeclampsia in 34 referred women, and both before and after the clinical manifestation in 8 women receiving a routine checkup at our institute. Both women with early and those with late preeclampsia showed decreased PlGF and increased sFlt-1 levels compared to normotensive controls at 28 and 37 weeks (n=68). However, those with early onset preeclampsia had a higher incidence of low PlGF (<5th percentile on the reference values) and high sFlt-1 (>or=95th percentile) than those with late onset (low PlGF: 93% vs. 55%; high sFlt-1: 100% vs. 60%). log10PlGF (r=0.574, p<0.001) and log10(sFlt-1/PlGF) (r=-0.556, p<0.001) were correlated with the week of onset of preeclampsia. Before the onset of preeclampsia, the incidence rate of low PlGF in the women with early onset preeclampsia was 100% (5/5), whereas that in the women with late onset preeclampsia was 0% (0/2) (p=0.048). Therefore, alterations in the PlGF levels both before and after the onset of preeclampsia may be more pronounced in women with early onset than those with late onset severe preeclampsia.

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.

Thrombin regulates soluble fms-like tyrosine kinase-1 (sFlt-1) expression in first trimester decidua: implications for preeclampsia

The primary placental defect in preeclampsia is shallow trophoblast invasion of the decidua leading to incomplete vascular transformation and inadequate uteroplacental perfusion. Soluble fms-like tyrosine kinase-1 (sFlt-1) seems to interfere with these events by inhibiting local angiogenesis and/or by impeding trophoblast invasion. Preeclampsia is also associated with maternal thrombophilias and decidual hemorrhage, which form thrombin from decidual cell-expressed tissue factor. Although sFlt-1 is highly expressed by trophoblasts, sFlt-1 expression has not been studied in decidual cells, which are the predominant cell type encountered by invading trophoblasts. Here, we demonstrate that isolated decidual cells express sFlt-1 mRNA, suggesting that they can synthesize sFlt-1. Moreover, in first trimester decidual cells, thrombin enhanced sFlt-1 mRNA levels, as measured by quantitative reverse transcriptase-polymerase chain reaction, and levels of secreted sFlt-1 protein, as measured by enzyme-linked immunosorbent assay. The thrombin antagonist hirudin blocked this effect, demonstrating that active thrombin is required. Emphasizing the specificity of the thrombin response, neither interleukin-1beta nor tumor necrosis factor-alpha affected sFlt-1 expression in the decidual cells. In contrast to first trimester decidual cells, thrombin did not affect sFlt-1 levels in cultured term decidual cells. In early pregnancy, thrombin may act as an autocrine/paracrine enhancer of sFlt-1 expression by decidual cells to promote pre-eclampsia by interfering with local vascular transformation.

Effect of low oxygen concentrations on trophoblast-like cell line invasion

The applicability of trophoblast-like cell lines to the study of trophoblast function has been widely debated. The present study investigated the effect of oxygen on the invasiveness, apoptosis, proliferation and secreted proteases of four different trophoblast cell lines; HTR-8/SVneo, SGHPL-4, JEG3 and JAR. All experiments were performed at 20% and 3% oxygen for 24, 48 and 72h. Immunostaining for integrins alpha1, alpha6 and beta3, cytokeratin 7 and HLA-G was used to determine the phenotype of the different cell lines. Invasion was assessed using the Matrigel invasion assay. Immunostaining for M30 and Ki67 determined levels of apoptosis and proliferation, respectively. Gelatin and casein/plasminogen zymography were performed on conditioned media to determine levels of secreted matrix metalloproteinase (MMP) 2 and MMP9 and urokinase plasminogen activator (uPA), respectively. None of the cell lines immunostained for all markers normally expressed by extravillous trophoblast cells. Invasiveness of HTR-8/SVneo and JEG3 cells cultured in 3% oxygen was increased after 24h but was inhibited by 72h in culture. Invasion of SGHPL-4 cells was inhibited after culture in 3% oxygen for 24h. Invasion by JAR cells was not affected by changes in oxygen concentration. The different cell lines also displayed different responses to culture period in 3% oxygen with respect to apoptosis, proliferation and secreted proteases. Care should be taken before results obtained using cell lines as a model for EVT are extrapolated to extravillous trophoblast cell behaviour in vivo.

Shared and disparate components of the pathophysiologies of fetal growth restriction and preeclampsia

Intrauterine growth restriction (IUGR) and preeclampsia differ in their association with maternal disease but share a similar placental pathology. Moreover, mothers who have had pregnancies complicated by preeclampsia or IUGR are at elevated later-life cardiovascular risk. Why, then, do some women develop IUGR and others develop preeclampsia? In this clinical opinion, based on a review of the literature, we hypothesize that both women experiencing preeclampsia and IUGR enter pregnancy with some degree of endothelial dysfunction, a lesion that predisposes to shallow placentation. In our opinion, preeclampsia develops when abnormal placentation, through the mediator of elevated circulating cytokines, interacts with maternal metabolic syndrome, comprised of adiposity, insulin resistance/hyperglycemia, hyperlipidemia, and coagulopathy. IUGR develops in the absence of antenatal metabolic syndrome. Among these women, the baby is affected by shallow placentation but the mother does not develop clinically apparent disease. This conceptualization provides a testable framework for future etiologic studies of preeclampsia and IUGR.

Evidence supporting that the excess of the sVEGFR-1 concentration in maternal plasma in preeclampsia has a uterine origin

BACKGROUND

Preeclampsia has been considered an anti-angiogenic state. Two factors have been implicated in the genesis of this state: soluble vascular endothelial growth factor receptor-1 (sVEGFR-1) and placental growth factor (PlGF). Indeed, the concentrations of PlGF, an angiogenic factor, are lower in preeclampsia than in normal pregnancy, while the opposite is the case for the anti-angiogenic factor, sVEGFR-1. The source of the excess sVEGFR-1 has not yet been determined. Since the placenta could be a source of sVEGFR-1, we conducted a study to determine whether there is a gradient in the plasma concentration of sVEGFR-1 and PlGF between the uterine vein and the antecubital vein in both patients with preeclampsia and normal pregnant women.

METHODS

A cross-sectional study was performed to determine the plasma concentrations of sVEGFR-1 and PlGF in the uterine and antecubital vein of patients with preeclampsia (n = 9) and normal pregnant women at term (n = 9). Plasma samples were collected from antecubital and uterine veins at the time of cesarean section. The concentrations of sVEGFR-1 and PlGF were determined using specific enzyme-linked immunoassays. The differences of plasma concentrations of sVEGFR-1 and PlGF between uterine and antecubital veins in both groups were compared by paired t-tests.

RESULTS

Patients with preeclampsia had a significantly higher mean plasma concentration of sVEGFR-1 in the uterine vein than in the antecubital vein (uterine vein: mean 13,675 +/- 5,684 pg/ml vs. antecubital vein: mean 10,234 +/- 4,700 pg/ml; paired t-tests, p = 0.04). In contrast, among normal pregnant women at term, there was no significant difference in plasma concentrations of sVEGFR-1 between the uterine and antecubital veins (uterine vein: mean 1,918 +/- 665 pg/ml vs. antecubital vein: mean 1,750 +/- 475 pg/ml; paired t-tests, p = 0.1). The mean plasma concentration of sVEGFR-1, either in the antecubital or uterine vein, was significantly higher in preeclampsia than in normal pregnancy (unpaired t-tests; both p < 0.001). There was no significant difference in the mean plasma concentration of PlGF between the uterine and the antecubital veins in both the preeclamptic (uterine vein, mean +/- SD: 129 +/- 106 pg/ml vs. antecubital vein, mean +/- SD: 82 +/- 43 pg/ml; paired t-tests, p = 0.2) and normal pregnancy groups (uterine vein, mean +/- SD: 331 +/- 254 pg/ml vs. antecubital vein, mean +/- SD: 319 +/- 259 pg/ml; paired t-tests, p = 0.4). The mean plasma concentration of PlGF, either in the uterine or antecubital vein, was lower in preeclampsia than in normal pregnancy (unpaired t-tests; p = 0.008 and 0.02 respectively).

CONCLUSIONS

Plasma concentration of sVEGFR-1 was higher in the uterine vein than in the antecubital vein in women with preeclampsia. This provides evidence supporting the concept that the uterus is a potential source of the excess circulating sVEGFR-1 concentration in preeclamptic women.

Dynamic changes in expression of heme oxygenases in mouse heart and liver during hypoxia

Heme oxygenase cleaves heme to form biliverdin, carbon monoxide (CO), and iron, and consists of two structurally related isozymes, HO-1 and HO-2. HO-2 is also known as a potential oxygen sensor. Here we show that the relative CO content in arterial blood, which reflects the total amount of endogenous heme degradation, dynamically changes in mice during acclimatization to normobaric hypoxia (10% O2), with the two peaks at 1 day and 21 days of hypoxia. The expression levels of HO-1 and HO-2 proteins were decreased by 20% and 40%, respectively, in the mouse liver at 7 days of hypoxia, which returned to the basal levels at 14 days. On the other hand, HO-1 and HO-2 proteins were increased 2-fold and 1.3-fold, respectively, in the heart at 28 days of hypoxia. Thus, hypoxia induces or represses the expression of HO-1 and HO-2 in vivo, depending on cellular microenvironments.

An imbalance between vascular endothelial growth factor and its soluble receptor in placental villous explants of intrauterine growth-restricted pregnancies

OBJECTIVES

Human umbilical vascular endothelial cells (HUVECs), seeded on Matrigel (BD Biosciences, Bedford, UK), undergo an angiogenic-like process. We hypothesized that placental explants from normal pregnancies, maintained in cultures of different oxygen, would liberate factors that could be measured in this system. We further tested the angiogenic potential of placentae from intrauterine growth-restricted (IUGR) pregnancies and the effects of vascular endothelial growth factor (VEGF) blockade.

METHODS

Placental villous explants were maintained in culture at 3% and 20% O2. The resultant media was added to HUVECs seeded on 80% Matrigel. Cells were incubated at 6% O2 in accordance with the natural placental environment. After 6 hours, cells were fixed and stained and the length and number of tubules measured by morphometric imaging. Finally, VEGF and soluble VEGF receptor (sVEGFR-1) were recorded in the explant conditioned media.

RESULTS

Within the angiogenic assay, recombinant human VEGF significantly enhanced tubule outgrowth (branching and elongation) and this effect was blocked with neutralising antibody. Compared to 20% O2, media of placental explants conditioned at 3% O2 significantly encouraged tubule length and numbers. Again this affect was ablated by VEGF blockade. In cases of IUGR, conditioned media at 3% O2 showed a significant reduction in tubule growth. This was paralleled by a decline in available VEGF brought about an exaggeration in liberated sVEGFR-1. Notably, venous cord serum from IUGR pregnancies showed a similar elevation in sVEGFR-1.

CONCLUSION

Under restricted oxygen, placental angiogenic potential is suppressed in IUGR pregnancies through the overproduction of placental sVEGFR-1. This reduction may discourage normal placental vascularization and impact on fetal development.

Soluble fms-like tyrosine kinase 1 is increased in preeclampsia but not in normotensive pregnancies with small-for-gestational-age neonates: relationship to circulating placental growth factor

CONTEXT

An excess of the soluble receptor, fms-like tyrosine kinase 1 (sFlt-1) may contribute to maternal vascular dysfunction in women with preeclampsia by binding and thereby reducing concentrations of free vascular endothelial growth factor and placental growth factor (PlGF) in the circulation. The putative stimulus for increased sFlt-1 during preeclampsia, placental hypoxia due to poor perfusion, is common to both preeclampsia and idiopathic intrauterine growth restriction. However, the latter condition occurs without maternal vascular disease.

OBJECTIVE

We asked whether, as with preeclampsia, sFlt-1 is increased and free PlGF is decreased in villous placenta and maternal serum of normotensive women with small-for-gestational-age (SGA) neonates.

STUDY DESIGN

This was a case-control study using banked samples. Groups of women with SGA neonates (birth weight centile < 10th) and women with preeclampsia were matched to separate sets of normal pregnancy controls based on gestational age at blood sampling (serum) or gestational age at delivery (placenta).

RESULTS

sFlt-1 levels were higher in preeclamptics than controls (serum, P < 0.0001; placental protein, P = 0.03; placental mRNA, P = 0.007) but not increased in SGA pregnancies. PlGF was lower in both preeclampsia (serum, P < 0.0001; placental protein, P = 0.05) and SGA (serum, P = 0.0008; placental protein, P = 0.03) compared with their controls. PlGF in preeclampsia and SGA groups did not differ.

CONCLUSIONS

These data are consistent with a role for sFlt-1 in the maternal manifestations of preeclampsia. In contrast to preeclampsia, sFlt-1 does not appear to contribute substantially to decreased circulating free PlGF in SGA pregnancies in the absence of a maternal syndrome.

Aspects of human fetoplacental vasculogenesis and angiogenesis. III. Changes in complicated pregnancies

Patterns of fetoplacental angiogenesis vary not only during the course of a normal pregnancy but also in certain pregnancy pathologies. Here, we review some of the molecular and morphological events which occur in complicated pregnancies. The pregnancy complications are chosen in an attempt to represent the possible different origins (preplacental, uteroplacental, postplacental) of fetal hypoxia. Molecular events focus on reported changes in hypoxia-inducible factors, angiopoietins and the vascular endothelial, basic fibroblast and placenta growth factors and their receptors. Morphological changes focus on patterns of angiogenesis (branching and non-branching) and a consistent set of morphometric descriptors (covering measures of total capillary growth, villous capillarization and capillary size and shape in transverse section). Apart from some uncertainties due to lack of information, or failure to resolve fully the effects of intrauterine growth restriction and pre-eclampsia, alterations in the angiogenic growth factors and morphologies of capillaries and villi in different complicated pregnancies seem to conform reasonably well to those predicted by the fetal hypoxia paradigm. However, it is clear that future studies on the effects of different origins of fetal hypoxia should exercise more care in the choice and interpretation of relevant descriptors and take more account of the parallel effects of possible confounders. In addition, rather than comparing uncomplicated and complicated pregnancies only at term, more information about molecular and morphological events that occur throughout gestation would be extremely valuable. This includes further studies on changes in growth factor receptors, the less-well-documented angiogenic factors (e.g. angiogenin, angiostatin, endostatin) and the associations between endothelial cells and pericytes. A more integrated approach involving also parallel analysis of the effects of erythropoietin and other potential vasoactive factors on the behaviour and morphology of fetal vessels would be beneficial.

Determinants of Placental Vascularity

PROBLEM

Vascular growth during implantation and placentation is critical for successful gestation and it is thought that vascular insufficiencies during placentation contribute to a number of obstetrical complications. However, relatively little is known regarding the regulation of angiogenesis in the placenta.

METHOD OF STUDY

We review literature concerning the potential significance of inadequate placental vascularity as a contributor to the obstetrical complications of spontaneous abortion, fetal growth restriction and preeclampsia. Gene expression assays were used to compare fluctuations of placenta growth factor (PlGF) and PlGF receptor expression in normal and preeclamptic trophoblast in vitro.

RESULTS

Studies have shown that common obstetrical complications manifest altered placental vascularity. Both intrinsic defects (gene knockouts) and extrinsic factors (O(2) tension, cytokines, etc) may be responsible for the defects. Some of these factors have been shown to influence trophoblast vascular endothelial growth factor (VEGF)/PlGF expression suggesting this particular family of angiogenic proteins play an important role in placental angiogenesis.

CONCLUSION

Placental vascularization reflects a complex interaction of regulatory factors. Understanding the regulation of vascular growth in the placenta will provide much needed insight into placenta-related vascular insufficiencies.

Confocal laser scanning microscope study of cytokeratin immunofluorescence differences between villous and extravillous trophoblast: Cytokeratin downregulation in pre-eclampsia

Pre-eclampsia is a disease characterized by failures in interstitial implantation. One product of the implantation process is the basal plate; a structure whose complexity makes it hard to fully appreciate the pathological changes in significant diseases of pregnancy. This article describes our use of CLSM immunofluorescence to examine the cytokeratin composition of the cells of trophoblastic origin in the term placental basal plate. Large differences in the content of the structural polymeric protein were compared using analysis of digital images. We show that greater pancytokeratin immunofluorescence is observed in extravillous cytotrophoblast cells as compared with villous trophoblast. There is a >30-fold difference in the mean area percent of the most intensely immunofluorescent pixels in the tissue containing these cells. This is a very high, statistically significant difference as defined by the Wilcoxon Signed Ranks Test Asym. Sig. (two-tailed): P < 0.001. The most invasive population of cells of the trophoblast lineage (the extravillous trophoblast) exhibits a significant reduction in cytokeratin immunofluorescence when comparisons of healthy and pre-eclamptic pregnancies are made. This ratio was 2.4:1. It was tested using the Mann-Whitney U-test. From healthy to pre-eclamptic the reduction was from mean rank 83.42((healthy)) to 51.13((pre-eclamptic)). The difference was very highly statistically significant (n = 53 + 75 = 128; U = 984.500; Z = -4.852; P < 0.001). There was also less cytokeratin-related immunofluorescence in villous trophoblast when healthy villi were compared with pre-eclamptic villi. The observed alterations in trophoblastic cytoskeletal components are expected to damage the anchorage and motility of cells. The extravillous trophoblast is known to be necessary for implantation. This leads to a cellular hypothesis of the failure of implantation resulting in reduced depth of uterine invasion and failure to adapt the spiral arterioles for low-pressure perfusion of the intervillus space, two well-known features of pre-eclampsia. The reduction in cytokeratin-related immunofluorescence in the villus trophoblast seen on comparing healthy term placentae with those from pre-eclamptics implies that the trophoblast is a weaker epithelial layer in the hypertensive pregnancy. This could account for the rise in deported trophoblast associated with pre-eclampsia. Deported trophoblast has been invoked as the systemic messenger that leads to generalized maternal hypertension seen in this condition.