Proteasomal Activity in Placentas from Women with Preeclampsia and Intrauterine Growth Restriction: Implications for Expression of HIF-α Proteins

Controlling Trophoblast Cell Fusion in the Human Placenta-Transcriptional Regulation of Suppressyn, an Endogenous Inhibitor of Syncytin-1

Cell fusion in the placenta is tightly regulated. Suppressyn is a human placental endogenous retroviral protein that inhibits the profusogenic activities of another well-described endogenous retroviral protein, syncytin-1. In this study, we aimed to elucidate the mechanisms underlying suppressyn's placenta-specific expression. We identified the promoter region and a novel enhancer region for the gene encoding suppressyn, ERVH48-1, and examined their regulation via DNA methylation and their responses to changes in the oxygen concentration. Like other endogenous retroviral genes, the ERVH48-1 promoter sequence is found within a characteristic retroviral 5' LTR sequence. The novel enhancer sequence we describe here is downstream of this LTR sequence (designated EIEs: ERV internal enhancer sequence) and governs placental expression. The placenta-specific expression of ERVH48-1 is tightly controlled by DNA methylation and further regulated by oxygen concentration-dependent, hypoxia-induced transcription factors (HIF1α and HIF2α). Our findings highlight the involvement of (1) tissue specificity through DNA methylation, (2) expression specificity through placenta-specific enhancer regions, and (3) the regulation of suppressyn expression in differing oxygen conditions by HIF1α and HIF2α. We suggest that these regulatory mechanisms are central to normal and abnormal placental development, including the development of disorders of pregnancy involving altered oxygenation, such as preeclampsia, pregnancy-induced hypertension, and fetal growth restriction.

Hypoxia Inducible Factors (HIF1α and HIF3α) are differentially methylated in preeclampsia placentae and are associated with birth outcomes

Preeclampsia is a placental vascular pathology and hypoxia is known to influence placental angiogenesis. Hypoxia Inducible Factors (HIF1α and HIF3α) mediate the response to cellular oxygen concentration and bind to hypoxia response element of target genes. However the mechanism regulating above activity is not well-understood. We investigated if placental DNA methylation (DNAm) and expression of HIF1α and 3α genes are altered and associated with pre-eclampsia, placental weight and birth outcomes. Using a cohort comprising women with preeclampsia [N = 100, delivering at term (N = 43) and preterm (N = 57)] and normotensive controls (N = 100), we analysed DNAm in HIF1α and 3α, and their mRNA expression in placentae, employing pyrosequencing and quantitative real-time PCR, respectively. We observed significant hypermethylation at cg22891070 of HIF3α in preeclampsia placentae compared to controls (β = 1.5%, p = 0.04). CpG8 in the promoter region of HIF1α, showed marginally significant hypomethylation in preterm preeclampsia compared to controls (β = - 0.15%, p = 0.055). HIF1α expression was significantly lower in preterm preeclampsia compared to controls (mean ± SE = 10.16 ± 2.00 vs 4.25 ± 0.90, p = 0.04). Further, DNAm in HIF1α promoter region was negatively associated with its expression levels (β =  - 0.165, p = 0.024). Several CpGs in HIF1α were negatively associated with placental weight and birth outcomes including birth weight (β range =  - 0.224-0.300) and birth length [β range =  - 0.248 to - 0.301 (p < 0.05 for all)]. Overall, we demonstrate altered DNAm in HIF1α and HIF3α in preeclampsia placentae, also associated with various birth outcomes. Correlation of DNAm in HIF1α and its expression suggests a possible role in the pathogenesis of pre-eclampsia. Further investigations on interactions between HIF1α and HIF3α in preeclampsia would be interesting.

Nitroxide-HMP-Protects Human Trophoblast HTR-8/SVneo Cells from H2O2-Induced Oxidative Stress by Reducing the HIF1A Signaling Pathway

Preeclampsia (PE) is a pregnancy-specific syndrome affecting 5-7% of patients. There is no effective treatment available. Early abnormal placental development is associated with oxidative stress (OS) and a release of reactive oxygen species (ROS) in the placenta. This phenomenon leads to downstream signaling, Hypoxia Inducible Factor 1A (HIF1A) stabilization and transcription of the anti-angiogenic factors soluble fms-like tyrosine kinase 1 (sFLT1) and soluble endoglin (sEng), which are known to cause endothelial and trophoblast dysfunction and cardinal features of PE: hypertension, proteinuria and, in severe cases, eclampsia. We tested whether 3-(Hydroxymethyl)-1-oxy-2,2,5,5-tetramethylpyrrolidine (HMP)-a nitroxide-type antioxidant molecule-can reduce placental OS and mitigate PE symptoms in vitro. We induced OS in human trophoblast (HTR-8/SVneo) cells with hydrogen peroxide (H2O2) and assessed whether modulating cell redox function with HMP reduces cell injury, mitochondrial stress and HIF1A and sFLT1 production. Pre-treatment with HMP reduced mitochondrial-derived ROS production, restored LC3B expression and reduced HIF1A and sFLT1 expression in H2O2-exposed HTR-8/SVneo trophoblast cells. HMP improved the mitochondrial electron chain enzyme activity, indicating that a reduction in OS alleviates mitochondrial stress and also reduces anti-angiogenic responses. In reducing placental trophoblast OS, HMP presents a potential novel therapeutic approach for the treatment of PE. Future investigation is warranted regarding the in vivo use of HMP.

Genome-Wide Analysis of Hypoxia-Inducible Factor Binding Reveals Targets Implicated in Impaired Human Placental Syncytiotrophoblast Formation under Low Oxygen

Preeclampsia (PE) is a common and serious complication of pregnancy with no cure except premature delivery. The root cause of PE is improper development of the placenta-the temporary organ supporting fetal growth and development. Continuous formation of the multinucleated syncytiotrophoblast (STB) layer via differentiation and fusion of cytotrophoblasts (CTBs) is vital for healthy placentation and is impaired in preeclamptic pregnancies. In PE, there is reduced/intermittent placental perfusion, likely resulting in a persistently low O2 environment. Low O2 inhibits differentiation and fusion of CTBs into STB and may thus contribute to PE pathogenesis; however, the underlying mechanisms are unknown. Because low O2 activates a transcription factor complex in cells known as the hypoxia-inducible factor (HIF), the objective of this study was to investigate whether HIF signaling inhibits STB formation by regulating genes required for this process. Culture of primary CTBs, the CTB-like cell line BeWo, and human trophoblast stem cells under low O2 reduced cell fusion and differentiation into STB. Knockdown of aryl hydrocarbon receptor nuclear translocator (a key component of the HIF complex) in BeWo cells restored syncytialization and expression of STB-associated genes under different O2 levels. Chromatin immunoprecipitation sequencing facilitated the identification of global aryl hydrocarbon receptor nuclear translocator/HIF binding sites, including several near genes implicated in STB development, such as ERVH48-1 and BHLHE40, providing new insights into mechanisms underlying pregnancy diseases linked to poor placental O2 supply.

Dysregulation of Oxygen Sensing/Response Pathways in Pregnancies Complicated by Idiopathic Intrauterine Growth Restriction and Early-Onset Preeclampsia

Preeclampsia (PE) and intrauterine growth restriction (IUGR) are the leading causes of maternal and fetal morbidity/mortality. The central deficit in both conditions is impaired placentation due to poor trophoblast invasion, resulting in a hypoxic milieu in which oxidative stress contributes to the pathology. We examine the factors driving the hypoxic response in severely preterm PE (n = 19) and IUGR (n = 16) placentae compared to the spontaneous preterm (SPT) controls (n = 13) using immunoblotting, RT-PCR, immunohistochemistry, proximity ligation assays, and Co-IP. Both hypoxia-inducible factor (HIF)-1α and HIF-2α are increased at the protein level and functional in pathological placentae, as target genes prolyl hydroxylase domain (PHD)2, PHD3, and soluble fms-like tyrosine kinase-1 (sFlt-1) are increased. Accumulation of HIF-α-subunits occurs in the presence of accessory molecules required for their degradation (PHD1, PHD2, and PHD3 and the E3 ligase von Hippel–Lindau (VHL)), which were equally expressed or elevated in the placental lysates of PE and IUGR. However, complex formation between VHL and HIF-α-subunits is defective. This is associated with enhanced VHL/DJ1 complex formation in both PE and IUGR. In conclusion, we establish a significant mechanism driving the maladaptive responses to hypoxia in the placentae from severe PE and IUGR, which is central to the pathogenesis of both diseases.

ceRNA Network and Functional Enrichment Analysis of Preeclampsia by Weighted Gene Coexpression Network Analysis

BACKGROUND

Preeclampsia (PE) is a multisystemic syndrome which has short- and long-term risk to mothers and children and has pluralistic etiology.

OBJECTIVE

This study is aimed at constructing a competitive endogenous RNA (ceRNA) network for pathways most related to PE using a data mining strategy based on weighted gene coexpression network analysis (WGCNA).

METHODS

We focused on pathways involving hypoxia, angiogenesis, and epithelial mesenchymal transition according to the gene set variation analysis (GSVA) scores. The gene sets of these three pathways were enriched by gene set enrichment analysis (GSEA). WGCNA was used to study the underlying molecular mechanisms of the three pathways in the pathogenesis of PE by analyzing the relationship among pathways and genes. The soft threshold power (β) and topological overlap matrix allowed us to obtain 15 modules, among which the red module was chosen for the downstream analysis. We chose 10 hub genes that satisfied ∣log2Fold Change | >2 and had a higher degree of connectivity within the module. These candidate genes were subsequently confirmed to have higher gene significance and module membership in the red module. Coexpression networks were established for the hub genes to unfold the connection between the genes in the red module and PE. Finally, ceRNA networks were constructed to further clarify the underlying molecular mechanism involved in the occurrence of PE. 56 circRNAs, 17 lncRNAs, and 20 miRNAs participated in the regulation of the hub genes. Coagulation factor II thrombin receptor (F2R) and lumican (LUM) were considered the most relevant genes, and ceRNA networks of them were constructed.

CONCLUSION

The microarray data mining process based on bioinformatics methods constructed lncRNA and miRNA networks for ten hub genes that were closely related to PE and focused on ceRNAs of F2R and LUM finally. The results of our study may provide insight into the mechanisms underlying PE occurrence.

Paeoniflorin alleviates endothelial dysfunction caused by overexpression of soluble fms-like tyrosine kinase 1 and soluble endoglin in preeclampsia via VEGFA upregulation

This study assessed the protective effects of paeoniflorin against preeclampsia-related endothelial damage (ED). Human umbilical vein endothelial cells (HUVECs) isolated from healthy puerperae were identified by immunofluorescence assay. After paeoniflorin treatment, HUVECs were induced by soluble fms-like tyrosine kinase 1 (sFlt-1) and soluble endoglin (sEng) to establish ED. Cell viability, migration, invasion, tube formation, and apoptosis were assessed by (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) tetrazolium MTT assay, Scratch assay, Transwell assay, tube formation assay, and flow cytometry. VEGFA expression in HUVECs was analyzed by Western blot. HUVECs were successfully isolated and identified as Von Willebrand factor (vWF) positive. Individual treatment or cotreatment of sFlt-1 and sEng inhibited migration, invasion and tube formation, enhanced apoptosis, and decreased VEGFA expression in HUVECs. Paeoniflorin pretreatment partially reversed the effects delivered by cotreatment of sFlt-1 and sEng in HUVECs. Paeoniflorin alleviated preeclampsia-related ED caused by overexpression of sFlt-1 and sEng by upregulating VEGFA.

Current State of Preeclampsia Mouse Models: Approaches, Relevance, and Standardization

Preeclampsia (PE) is a multisystemic, pregnancy-specific disorder and a leading cause of maternal and fetal death. PE is also associated with an increased risk for chronic morbidities later in life for mother and offspring. Abnormal placentation or placental function has been well-established as central to the genesis of PE; yet much remains to be determined about the factors involved in the development of this condition. Despite decades of investigation and many clinical trials, the only definitive treatment is parturition. To better understand the condition and identify potential targets preclinically, many approaches to simulate PE in mice have been developed and include mixed mouse strain crosses, genetic overexpression and knockout, exogenous agent administration, surgical manipulation, systemic adenoviral infection, and trophoblast-specific gene transfer. These models have been useful to investigate how biological perturbations identified in human PE are involved in the generation of PE-like symptoms and have improved the understanding of the molecular mechanisms underpinning the human condition. However, these approaches were characterized by a wide variety of physiological endpoints, which can make it difficult to compare effects across models and many of these approaches have aspects that lack physiological relevance to this human disorder and may interfere with therapeutic development. This report provides a comprehensive review of mouse models that exhibit PE-like symptoms and a proposed standardization of physiological characteristics for analysis in murine models of PE.

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.

Vitamin D₃ levels in the maternal serum, cord blood, and placenta of preeclamptic pregnant women

BACKGROUND Preeclampsia is affected by oxidative stress, a free-radical produced as a by-product of endothelial damage, and antioxidant imbalance, such as vitamin D₃. This study was aimed to compare the vitamin D₃ levels in the placenta, cord blood, and maternal serum between patients with and without preeclampsia.  METHODS This cross-sectional study included 86 patients from Cipto Mangunkusumo Hospital and Tangerang District Hospital, in which 47 had preeclampsia (13 early-onset and 16 late-onset preeclampsia cases) and 39 had no preeclampsia. The placenta, cord blood, and maternal serum were taken after labor, then were analyzed according to preeclampsia and non-preeclampsia; furthermore, the preeclampsia group was analyzed in a subgroup of early- and late-onset preeclampsia. This is analyzed with either unpaired t-test, Mann–Whitney U test, or Kruskal–Wallis test.  RESULTS The maternal serum, cord blood, and placental tissue vitamin D₃ levels (16.30 [6.20–49.00], 11.80 [3.50–38.60], and 49.00 [22.00–411.00] ng/ml, respectively) of the preeclampsia group were similar to those of the non-preeclampsia group (13.50 [4.80– 29.20], 11.70 [1.00–28.80], and 43.40 [11.80–153.00] ng/ml, respectively) (p = 0.459, 0.964, and 0.354, respectively). However, the placental tissue vitamin D₃ levels in early-onset preeclampsia (79.00 [36.00–411.00] ng/ml) were higher than those in late-onset preeclampsia (40.00 [22.00–171.00] ng/ml) (p = 0.006).  CONCLUSIONS The vitamin D₃ levels between patients with and without preeclampsia were similar. However, the placental tissue vitamin D₃ levels in early-onset preeclampsia were higher than those in late-onset preeclampsia, possibly because of the different pathophysiology between early- and late-onset preeclampsia. 

Proteasome Levels and Activity in Pregnancies Complicated by Severe Preeclampsia and Hemolysis, Elevated Liver Enzymes, and Thrombocytopenia (HELLP) Syndrome

Excessive accumulation of misfolded proteins was recently demonstrated in preeclampsia. We examined levels and activity of circulatory proteasome and immunoproteasome (inflammatory subtype) in preeclampsia and hemolysis, elevated liver enzymes, and thrombocytopenia (HELLP) syndrome. We analyzed samples from women with hypertensive pregnancy disorders (n=115), including preeclampsia with severe features (sPE) and HELLP syndrome, and normotensive controls (n=45). Plasma proteasome and immunoproteasome immunoreactivity were determined by quantifying the α-subunit of the 20S core and β5i (proteasome subunit beta 8 [PSMB8]), respectively. Plasma proteasome activity was analyzed with fluorogenic substrates. MG132, lactacystin, and ONX0914 were used to inhibit the circulating proteasome and immunoproteasome, respectively. Plasma cytokine profiles were evaluated by multiplex immunoassay. Placental expression of β5 (constitutive proteasome) and β5i (immunoproteasome) was interrogated by immunohistochemistry. Women with sPE had increased plasma 20S levels ( P<0.001) and elevated lytic activities (chymotrypsin-like 7-fold, caspase-like 4.2-fold, trypsin-like 2.2-fold; P <0.001 for all) compared with pregnant controls. Women with features of HELLP displayed the highest plasma proteasome levels and activity, which correlated with decreased IFN-γ (interferon-γ), and increased IL (interleukin)-8 and IL-10. In sPE and HELLP, chymotrypsin-like activity was suppressed by proteasome inhibitors including ONX0914. Compared with gestational age-matched controls, sPE placentas harbored increased β5 and β5i immunostaining in trophoblasts. β5i signal was elevated in HELLP with predominant staining in villous core, extravillous trophoblasts in placental islands, and extracellular vesicles in intervillous spaces. Pregnancy represents a state of increased proteostatic stress. sPE and HELLP were characterized by significant upregulation in circulating levels and lytic activity of the proteasome that was partially explained by placental immunoproteasome upregulation.

AP39, a Modulator of Mitochondrial Bioenergetics, Reduces Antiangiogenic Response and Oxidative Stress in Hypoxia-Exposed Trophoblasts: Relevance for Preeclampsia Pathogenesis

Although the cause of preeclampsia, a pregnancy complication with significant maternal and neonatal morbidity, has not been fully characterized, placental ischemia attributable to impaired spiral artery remodeling and abnormal secretion of antiangiogenic factors are thought to be important in the pathogenesis of the disease. Placental ischemia could impair trophoblast mitochondrial function and energy production, leading to the release of reactive oxygen species (ROS). ROS have been shown to stabilize hypoxia-inducible factor (HIF)-1α, which, in turn, may induce transcription of antiangiogenic factors, soluble fms-like tyrosine kinase 1 (sFLT1), and soluble endoglin in trophoblasts. Herein, we tested whether the angiogenic imbalance and oxidative stress in the preeclamptic placenta may be prevented by improving mitochondrial function. First, to evaluate the cause-effect relationship between mitochondrial function and sFLT1 production, a human trophoblast primary cell culture model was established in which hypoxia induced mitochondrial ROS production and concurrent sFLT1 increase. Second, treatment with AP39, a novel mitochondria-targeted hydrogen sulfide donor, prevented ROS production, reduced HIF-1α protein levels, and diminished sFLT1 production. Finally, AP39, a modulator of mitochondrial bioenergetics enhanced cytochrome c oxidase activity, reversed oxidative stress and antiangiogenic response in hypoxic trophoblasts. These results suggest that placental hypoxia induces ROS production, HIF-1α stabilization, and sFLT1 up-regulation; these pathophysiological alterations can be attenuated by mitochondrial-targeted antioxidants.

Hypoxia and Placental Development

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

The association of the placental Hypoxia-inducible factor1-α polymorphisms and HIF1-α mRNA expression with preeclampsia

INTRODUCTION

Evidence has confirmed that placental/fetal hypoxia plays a key role in both endothelial cell dysfunction and PE pathogenesis. The aim of the present study was to investigate whether maternal/placental hypoxia-inducible factor1-α (HIF1-α) C1772T (rs11549465) and/or G1790A (rs11549467) polymorphisms and HIF1-α mRNA expression are associated with PE development.

METHODS

The blood samples of 203 PE and 202 control women and the placenta of 86 PE and 84 control women were collected after delivery. The HIF1-α polymorphisms were genotyped using PCR- RFLP method. The mRNA expression levels were measured by Quantitative Real -Time PCR.

RESULTS

The present study found no association between maternal HIF1-α rs11549465 and rs11549467 and placental rs11549467 polymorphisms and PE. However, the placental rs11549465 polymorphism was associated with PE in the dominant model. The CT/GG combined genotypes and TG haplotype of placental rs11549465 and rs11549467 polymorphisms were associated with higher risk of PE. The HIF1-α mRNA expression was 3-fold higher in the PE women. The rs11549465 TT genotype was associated with higher HIF1-α mRNA expression in PE women and in total population and rs11549467 GA genotype was associated with higher mRNA expression in total population. The relative mRNA expression of HIF1-α gene was higher in presence of CC/GA, TT/GG and TT/GA combined genotypes.

CONCLUSION

This study found an association between placental but not maternal HIF1-α rs11549465 polymorphism and PE in the dominant model. The HIF1-α mRNA expression was higher in the placenta of PE women and was associated with rs11549465 and rs11549467 polymorphisms.

Placental Origins of Chronic Disease

Epidemiological evidence links an individual's susceptibility to chronic disease in adult life to events during their intrauterine phase of development. Biologically this should not be unexpected, for organ systems are at their most plastic when progenitor cells are proliferating and differentiating. Influences operating at this time can permanently affect their structure and functional capacity, and the activity of enzyme systems and endocrine axes. It is now appreciated that such effects lay the foundations for a diverse array of diseases that become manifest many years later, often in response to secondary environmental stressors. Fetal development is underpinned by the placenta, the organ that forms the interface between the fetus and its mother. All nutrients and oxygen reaching the fetus must pass through this organ. The placenta also has major endocrine functions, orchestrating maternal adaptations to pregnancy and mobilizing resources for fetal use. In addition, it acts as a selective barrier, creating a protective milieu by minimizing exposure of the fetus to maternal hormones, such as glucocorticoids, xenobiotics, pathogens, and parasites. The placenta shows a remarkable capacity to adapt to adverse environmental cues and lessen their impact on the fetus. However, if placental function is impaired, or its capacity to adapt is exceeded, then fetal development may be compromised. Here, we explore the complex relationships between the placental phenotype and developmental programming of chronic disease in the offspring. Ensuring optimal placentation offers a new approach to the prevention of disorders such as cardiovascular disease, diabetes, and obesity, which are reaching epidemic proportions.

Inflammation-induced fetal growth restriction in rats is associated with increased placental HIF-1α accumulation

Introduction

Hypoxia-inducible factor 1-alpha (HIF-1α) is the oxygen-sensitive subunit of the transcription factor HIF-1, and its expression is increased in placentas from pregnancies complicated by pre-eclampsia (PE). Fetal growth restriction (FGR) and PE often share a common pathophysiology; however, it is unknown whether increased placental HIF-1α occurs in FGR. We previously demonstrated that aberrant maternal inflammation in rats resulted in altered utero-placental perfusion and FGR, both of which were prevented by administration of the nitric oxide mimetic glyceryl trinitrate (GTN). Our aim here was to determine whether abnormal maternal inflammation causing FGR is linked to placental HIF-1α accumulation and whether GTN administration could prevent increases in placental HIF-1α.

Methods

Levels of inflammatory factors in maternal plasma were measured using a multiplex assay after an injection of low-dose lipopolysaccharide (LPS) to rats on gestational day (GD) 13.5. Following three additional daily LPS injections from GD14.5–16.5, GD17.5 placentas were harvested for HIF-1α immunolocalisation; serial sections were also stained for the hypoxia marker pimonidazole. A subset of rats received LPS injections along with GTN delivered continuously (25 μg/h via a transdermal patch) on GD12.5-GD17.5.

Results

Within two hours of LPS administration, levels of maternal pro-inflammatory cytokines were increased compared with saline-treated controls. GD17.5 placentas of growth-restricted fetuses exhibited increased HIF-1α accumulation; however, this did not correlate with pimonidazole staining for which no differences were observed between groups. Furthermore, the LPS-mediated increases in maternal inflammatory cytokine levels and placental HIF-1α accumulation did not occur in rats treated with GTN.

Discussion

Our results demonstrate that inflammation-induced FGR is associated with increased placental HIF-1α accumulation; however, expression of this transcription factor may not correlate with regions of hypoxia in late-gestation placentas. The GTN-mediated attenuation of placental HIF-1α accumulation in LPS-treated rats provides insight into the mechanism by which GTN improves inflammation-induced complications of pregnancy.

Human placental renin-angiotensin system in normotensive and pre-eclamptic pregnancies at high altitude and after acute hypoxia-reoxygenation insult

A functioning placental renin-angiotensin system (RAS) appears necessary for uncomplicated pregnancy and is present during placentation, which occurs under low oxygen tensions. Placental RAS is increased in pre-eclampsia (PE), characterised by placental dysfunction and elevated oxidative stress. We investigated the effect of high altitude hypoxia on the RAS and hypoxia-inducible factors (HIFs) by measuring mRNA and protein expression in term placentae from normotensive (NT) and PE women who delivered at sea level or above 3100 m, using an explant model of hypoxia-reoxygenation to assess the impact of acute oxidative stress on the RAS and HIFs. Protein levels of prorenin (P = 0.049), prorenin receptor (PRR; P = 0.0004), and angiotensin type 1 receptor (AT1R, P = 0.006) and type 2 receptor (AT2R, P = 0.002) were all significantly higher in placentae from NT women at altitude, despite mRNA expression being unaffected. However, mRNA expression of all RAS components was significantly lower in PE at altitude than at sea level, yet PRR, angiotensinogen (AGT) and AT1R proteins were all increased. The increase in transcript and protein expression of all the HIFs and NADPH oxidase 4 seen in PE compared to NT at sea level was blunted at high altitude. Experimentally induced oxidative stress stimulated AGT mRNA (P = 0.04) and protein (P = 0.025). AT1R (r = 0.77, P < 0.001) and AT2R (r = 0.81, P < 0.001) mRNA both significantly correlated with HIF-1β, whilst AT2R also correlated with HIF-1α (r = 0.512, P < 0.013). Our observations suggest that the placental RAS is responsive to changes in tissue oxygenation: this could be important in the interplay between reactive oxygen species as cell-signalling molecules for angiogenesis and hence placental development and function.

Genetic, immune and vasoactive factors in the vascular dysfunction associated with hypertension in pregnancy

INTRODUCTION

Preeclampsia (PE) is a major complication of pregnancy that could lead to maternal and fetal morbidity and mortality. The pathophysiological mechanisms of PE are not completely understood, but recent research has begun to unravel some of the potential mechanisms.

AREAS COVERED

Genetic polymorphisms and altered maternal immune response may cause impaired remodeling of the spiral arteries; a potential early defect in PE. Inadequate invasion of cytotrophoblasts into the decidua leads to reduced uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia. Placental ischemia causes the release of biologically active factors such as anti-angiogenic factors, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and angiotensin II receptor autoantibodies. These vasoactive factors could cause systemic vascular endotheliosis and consequent increase in vascular resistance and blood pressure, glomerular endotheliosis causing proteinuria, cerebrovascular endotheliosis causing cerebral edema, seizures and visual disturbances, and hepatic endotheliosis, which may contribute to the manifestations of HELLP syndrome. PE-associated vascular endotheliosis causes a decrease in vasodilator mediators such as nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor, an increase in vasoconstrictors such as endothelin-1, angiotensin II and thromboxane A2, and enhanced mechanisms of vascular smooth muscle contraction such as intracellular Ca(2+), protein kinase C and Rho-kinase. Changes in matrix metalloproteinase activity and extracellular matrix cause vascular remodeling and further vasoconstriction.

EXPERT OPINION

Some of the genetic, immune and vasoactive factors involved in vascular endotheliosis could be used as biomarkers for early detection, and as potential targets for prevention and treatment of PE.

Bioactive factors in uteroplacental and systemic circulation link placental ischemia to generalized vascular dysfunction in hypertensive pregnancy and preeclampsia

Preeclampsia is a pregnancy-associated disorder characterized by hypertension, and could lead to maternal and fetal morbidity and mortality; however, the pathophysiological mechanisms involved are unclear. Predisposing demographic, genetic and environmental risk factors could cause localized abnormalities in uteroplacental cytoactive factors such as integrins, matrix metalloproteinases, cytokines and major histocompatibility complex molecules leading to decreased vascular remodeling, uteroplacental vasoconstriction, trophoblast cells apoptosis, and abnormal development of the placenta. Defective placentation and decreased trophoblast invasion of the myometrium cause reduction in uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia, an important event in preeclampsia. RUPP could stimulate the release of circulating bioactive factors such as the anti-angiogenic factors soluble fms-like tyrosine kinase-1 and soluble endoglin that cause imbalance with the pro-angiogenic factors vascular endothelial growth factor and placental growth factor, or cause the release of inflammatory cytokines, reactive oxygen species, hypoxia-induced factor-1 and AT1 angiotensin receptor agonistic autoantibodies. The circulating bioactive factors target endothelial cells causing generalized endotheliosis, endothelial dysfunction, decreased vasodilators such as nitric oxide and prostacyclin and increased vasoconstrictors such as endothelin-1 and thromboxane A2, leading to increased vasoconstriction. The bioactive factors also stimulate the mechanisms of VSM contraction including Ca(2+), protein kinase C, and Rho-kinase and induce extracellular matrix remodeling leading to further vasoconstriction and hypertension. While therapeutic options are currently limited, understanding the underlying mechanisms could help design new interventions for management of preeclampsia.

Placental expression of adenosine A(2A) receptor and hypoxia inducible factor-1 alpha in early pregnancy, term and pre-eclamptic pregnancies: interactions with placental renin-angiotensin system

Hypoxia-inducible factors (HIFs), adenosine and tissue renin-angiotensin-system (RAS) promote angiogenesis and vascularisation. We investigated the temporal expression placental adenosine A2AR receptor and HIF-1α in early pregnancy and at delivery in normotensive (NT) and pre-eclamptic (PE) women. Results were compared to our previously reported angiotensin receptor data. Expression of A2AR and HIF-1α was highest at ≤10 weeks, positively correlated through pregnancy and was higher in PE than NT at delivery. The A2AR associated with the AT4R only in early pregnancy. We suggest adenosine and RAS may interact to promote placentation with a potential adaptation to poor placental perfusion in PE.

Dynamic proteomic profiles of in vivo- and in vitro-produced mouse postimplantation extraembryonic tissues and placentas

As the interface between the mother and the developing fetus, the placenta is believed to play an important role in assisted reproductive technology (ART)-induced aberrant intrauterine and postnatal development. However, the mechanisms underlying aberrant placentation remain unclear, especially during extraembryonic tissue development and early stages of placental formation. Using a mouse model, this investigation provides the first comparative proteomic analysis of in vivo (IVO) and in vitro-produced (IVP) extraembryonic tissues and placentas after IVO fertilization and development, or in vitro fertilization and culture, respectively. We identified 165 and 178 differentially expressed proteins (DEPs) between IVO and IVP extraembryonic tissues and placentas on Embryonic Day 7.5 (E7.5) and E10.5, respectively. Many DEPs were functionally associated with genetic information processing, such as impaired de novo DNA methylation, as well as posttranscriptional, translational and posttranslational dysregulation. These novel findings were further confirmed by global hypomethylation, and a lower level of correlation was found between the transcriptome and proteome in the IVP groups. In addition, numerous DEPs were involved in energy and amino acid metabolism, cytoskeleton organization and transport, and vasculogenesis and angiogenesis. These disturbed processes and pathways are likely to be associated with embryonic intrauterine growth restriction, an enlarged placenta, and impaired labyrinth morphogenesis. This study provides a direct and comprehensive reference for the further exploration of the placental mechanisms that underlie ART-induced developmental aberrations.

Genome-wide hypermethylation coupled with promoter hypomethylation in the chorioamniotic membranes of early onset pre-eclampsia

Pre-eclampsia is the leading cause of fetal and maternal morbidity and mortality. Early onset pre-eclampsia (EOPE) is a disorder that has severe maternal and fetal outcomes, whilst its etiology is poorly understood. We hypothesize that epigenetics plays an important role to mediate the development of EOPE and conducted a case-control study to compare the genome-wide methylome difference between chorioamniotic membranes from 30 EOPE and 17 full-term pregnancies using the Infinium Human Methylation 450 BeadChip arrays. Bioinformatics analysis tested differential methylation (DM) at CpG site level, gene level, and pathway and network level. A striking genome-wide hypermethylation pattern coupled with hypomethylation in promoters was observed. Out of 385 184 CpG sites, 9995 showed DM (2.6%). Of those DM sites, 91.9% showed hypermethylation (9186 of 9995). Over 900 genes had DM associated with promoters. Promoter-based DM analysis revealed that genes in canonical cancer-related pathways such as Rac, Ras, PI3K/Akt, NFκB and ErBB4 were enriched, and represented biological functional alterations that involve cell cycle, apoptosis, cancer signaling and inflammation. A group of genes previously found to be up-regulated in pre-eclampsia, including GRB2, ATF3, NFKB2, as well as genes in proteasome subunits (PSMA1, PMSE1, PSMD1 and PMSD8), harbored hypomethylated promoters. Contrarily, a cluster of microRNAs, including mir-519a1, mir-301a, mir-487a, mir-185, mir-329, mir-194, mir-376a1, mir-486 and mir-744 were all hypermethylated in their promoters in the EOPE samples. These findings collectively reveal new avenues of research regarding the vast epigenetic modifications in EOPE.

Proteasome inhibition augments cigarette smoke-induced GM-CSF expression in trophoblast cells via the epidermal growth factor receptor

Maternal cigarette smoking has adverse effects on pregnancy outcomes. The granulocyte-macrophage colony-stimulating factor (GM-CSF) is an essential cytokine for a normal pregnancy. We investigated the impact of cigarette smoke extract (CSE) on GM-CSF expression in human cytotrophoblast cells and suggested a cellular mechanism underlying the CSE-induced GM-CSF expression. An immortalized normal human trophoblast cell line (B6Tert-1) was treated with CSE. The viability and proliferation of the CSE-treated B6Tert-1 cells were evaluated, and the expression of GM-CSF in these cells was quantified at the mRNA and the protein levels by means of reverse-transcription and quantitative polymerase chain reaction (RT-qPCR); and enzyme-linked immunosorbent assay (ELISA), respectively. Human trophoblast cells treated with CSE had an increased expression of GM-CSF at both the mRNA and the protein levels. The CSE-induced GM-CSF expression was synergistically enhanced by the addition of the proteasome inhibitor MG-132, but inhibited by AG-1478, an inhibitor of the epidermal growth factor receptor (EGFR) kinase. Furthermore, CSE treatment increased the phosphorylation of the extracellular-signal regulated kinases (ERK1/2) in the trophoblast cells. The expression of other growth factors such as heparin-binding epidermal growth factor-like growth factor (HB-EGF) and vascular endothelial growth factor (VEGF) was also evaluated. Our data suggested that cigarette smoking and proteasome inhibition synergistically up-regulate GM-CSF cytokine expression by activating the EGFR signaling pathway.

Altered expression of COP9 signalosome proteins in preeclampsia

OBJECTIVE

The presumptive factors that are released by the preeclamptic placenta to cause maternal disease are less well known. The constitutive photomorphogenic-9 (COP9) signalosome (CSN) complex, a multifunctional protein complex involved in modulating signal transduction, gene transcription, and protein stability in cells. Although the roles of most CSN components in early embryonic development have been studied, their role in preeclamptic human placentas is not known. Thus, this study was aimed to show the localization and the protein expression of CSN1 and CSN5 in normal and preeclamptic placenta.

STUDY DESIGN

The distribution and the protein expression of CSN1 and CSN5 were analyzed in normal (n: 15) and preeclamptic (n: 15) human placenta by using immunohistochemistry (IHC) and Western blotting.

RESULTS

CSN1 and CSN5 were mainly localized in the vascular endothelium, syncytiotrophoblast, stromal and Hofbauer cells in normal and preeclamptic placentas. However, a stronger immunoreactivity and protein expression for CSN1 and CSN5 were observed in preeclamptic placentas compared to normal term placentas. Western blotting of the tissue extracts confirmed the IHC results.

CONCLUSIONS

Our results suggest that an increased level of CSN1 and CSN5 as an important part of the ubiquitin proteasome system (UPS) might be associated with the pathophysiology of preeclampsia.

Down-regulation of the transcription factor snail in the placentas of patients with preeclampsia and in a rat model of preeclampsia

BACKGROUND

Placental malfunction in preeclampsia is believed to be a consequence of aberrant differentiation of trophoblast lineages and changes in utero-placental oxygenation. The transcription factor Snail, a master regulator molecule of epithelial-mesenchymal transition in embryonic development and in cancer, is shown to be involved in trophoblast differentiation as well. Moreover, Snail can be controlled by oxidative stress and hypoxia. Therefore, we examined the expression of Snail and its downstream target, e-cadherin, in human normal term, preterm and preeclamptic placentas, and in pregnant rats that developed preeclampsia-like symptoms in the response to a 20-fold increase in sodium intake.

METHODS

Western blotting analysis was used for comparative expression of Snail and e- cadherin in total protein extracts. Placental cells expressing Snail and e-cadherin were identified by immunohistochemical double-labeling technique.

RESULTS

The levels of Snail protein were decreased in human preeclamptic placentas by 30% (p < 0.01) compared to normal term, and in the rat model by 40% (p < 0.001) compared to control placentas. In preterm placentas, the levels of Snail expression varied, yet there was a strong trend toward statistical significance between preterm and preeclamptic placentas. In humans, e-cadherin protein level was 30% higher in preeclamptic (p < 0.05) placentas and similarly, but not significantly (p = 0.1), high in the preterm placentas compared to normal term. In the rat model of preeclampsia, e-cadherin was increased by 60% (p < 0.01). Immunohistochemical examination of human placentas demonstrated Snail-positive staining in the nuclei of the villous trophoblasts and mesenchymal cells and in the invasive trophoblasts of the decidua. In the rat placenta, the majority of Snail positive cells were spongiotrophoblasts of the junctional zone, while in the labyrinth, Snail-positive sinusoidal giant trophoblasts cells were found in some focal areas located close to the junctional zone.

CONCLUSION

We demonstrated that human preeclampsia and the salt-induced rat model of preeclampsia are associated with the reduced levels of Snail protein in placenta. Down-regulation of the transcription factor Snail in placental progenitor cell lineages, either by intrinsic defects and/or by extrinsic and maternal factors, may affect normal placenta development and function and thus contribute to the pathology of preeclampsia.

Preeclampsia leads to dysregulation of various signaling pathways in placenta

OBJECTIVES

To compare gene expression profiles of placentas from preeclamptic and normal pregnancies.

STUDY DESIGN

We performed microarray experiments to analyze genome-wide expression profiling for 10 placentas from pregnant women with preeclampsia and 10 placentas from women who experienced noncomplicated pregnancies (CON), and to identify dysregulated signaling pathways as well as genes in preeclampsia. RT-PCR, real-time RT-PCR and/or immunofluorescence analyses were performed to validate the data obtained from microarray experiments.

RESULTS

Unsupervised hierarchical clustering showed heterogeneity of preeclampsia at the molecular levels, whereas expression profiles of preeclampsia are distinctly different from those of CON. A list of genes which are differentially expressed between preeclampsia and CON included well known preeclampsia markers, such as Flt-1, leptin, HTRA1 and SIGLEC6. Gene Set Enrichment Analysis, a pathway-oriented analysis method for expression profiles, provided evidence that a number of biological activities including pathways that regulate actin cytoskeleton, TGFβ signaling, oxidative phosphorylation, and proteasome activity were aberrantly either up-regulated or down-regulated in preeclampsia. RT-PCR and real-time-RT-PCR for genes contributing these biological pathways (gene sets) enriched in either CON or preeclampsia reinforced that these biological processes were systemically dysregulated in preeclampsia.

CONCLUSIONS

Genome-wide expression profiles of preeclampsia showed heterogeneous characteristics of preeclampsia at the molecular levels. Dysregulation of genes and biological pathways could contribute to abnormal behavior of preeclmapsia. Our results will help further understand underlying mechanisms by which preeclampsia affects placental physiology.

Angiotensin II type 1 receptor antibodies and increased angiotensin II sensitivity in pregnant rats

Pregnant women who subsequently develop preeclampsia are highly sensitive to infused angiotensin (Ang) II; the sensitivity persists postpartum. Activating autoantibodies against the Ang II type 1 (AT(1)) receptor are present in preeclampsia. In vitro and in vivo data suggest that they could be involved in the disease process. We generated and purified activating antibodies against the AT(1) receptor (AT(1)-AB) by immunizing rabbits against the AFHYESQ epitope of the second extracellular loop, which is the binding epitope of endogenous activating autoantibodies against AT(1) from patients with preeclampsia. We then purified AT(1)-AB using affinity chromatography with the AFHYESQ peptide. We were able to detect AT(1)-AB both by ELISA and a functional bioassay. We then passively transferred AT(1)-AB into pregnant rats, alone or combined with Ang II. AT(1)-AB activated protein kinase C-α and extracellular-related kinase 1/2. Passive transfer of AT(1)-AB alone or Ang II (435 ng/kg per minute) infused alone did not induce a preeclampsia-like syndrome in pregnant rats. However, the combination (AT(1)-AB plus Ang II) induced hypertension, proteinuria, intrauterine growth retardation, and arteriolosclerosis in the uteroplacental unit. We next performed gene-array profiling of the uteroplacental unit and found that hypoxia-inducible factor 1α was upregulated by Ang II plus AT(1)-AB, which we then confirmed by Western blotting in villous explants. Furthermore, endothelin 1 was upregulated in endothelial cells by Ang II plus AT(1)-AB. We show that AT(1)-AB induces Ang II sensitivity. Our mechanistic study supports the existence of an "autoimmune-activating receptor" that could contribute to Ang II sensitivity and possible to preeclampsia.

Molecular and vascular targets in the pathogenesis and management of the hypertension associated with preeclampsia

Normal pregnancy is associated with significant hemodynamic changes and vasodilation of the uterine and systemic circulation in order to meet the metabolic demands of the mother and developing fetus. Preeclampsia (PE) is one of the foremost complications of pregnancy and a major cause of maternal and fetal mortality. The pathophysiological mechanisms of PE have been elusive, but some parts of the puzzle have begun to unravel. Genetic factors such as leptin gene polymorphism, environmental and dietary factors such as Ca(2+) and vitamin D deficiency, and co-morbidities such as obesity and diabetes may increase the susceptibility of pregnant women to develop PE. An altered maternal immune response may also play a role in the development of PE. Although the pathophysiology of PE is unclear, most studies have implicated inadequate invasion of cytotrophoblasts into the uterine artery, leading to reduced uteroplacental perfusion pressure (RUPP) and placental ischemia/hypoxia. Placental ischemia induces the release of biologically active factors such as growth factor inhibitors, anti-angiogenic factors, inflammatory cytokines, reactive oxygen species, hypoxia-inducible factors, and antibodies to vascular angiotensin II (AngII) receptor. These bioactive factors could cause vascular endotheliosis and consequent increase in vascular resistance and blood pressure, as well as glomerular endotheliosis with consequent proteinuria. The PE-associated vascular endotheliosis could be manifested as decreased vasodilator mediators such as nitric oxide, prostacyclin and hyperpolarizing factor and increased vasoconstrictor mediators such as endothelin-1, AngII and thromboxane A₂. PE could also involve enhanced mechanisms of vascular smooth muscle contraction including intracellular Ca(2+), and Ca(2+) sensitization pathways such as protein kinase C and Rho-kinase. PE-associated changes in the extracellular matrix composition and matrix metalloproteinases activity also promote vascular remodeling and further vasoconstriction in the uterine and systemic circulation. Some of these biologically active factors and vascular mediators have been proposed as biomarkers for early prediction or diagnosis of PE, and as potential targets for prevention or treatment of the disease.

Reduced placental prolyl hydroxylase 3 mRNA expression in pregnancies affected by fetal growth restriction

OBJECTIVE

To investigate the role of the hypoxia-inducible factor (HIF) pathway in fetal growth restriction (FGR).

DESIGN

A case-control study.

SETTING

Research laboratory and gynaecology clinic.

SAMPLE

Twenty placentas from normal pregnancies and 20 from FGR pregnancies.

METHODS

RNA extraction, cDNA synthesis, quantitative real-time polymerase chain reaction (qRT-PCR) assay, statistical analysis.

MAIN OUTCOME MEASURES

mRNA expression of HIF-1α, HIF-2α and HIF-β (ARNT), along with prolyl hydroxylase domain 3 (PHD3), which leads to proteasomal degradation of HIF-α subunits.

RESULTS

No statistically significant differences in the transcription levels of ARNT and HIF-2α were found between FGR and normal placentas. By contrast, PHD3 and HIF-1α mRNA were downregulated in FGR placentas. PHD3 mRNA expression was associated with gestational age at delivery (P = 0.008), birthweight centile (P = 0.029) and abnormal umbilical artery (UA) Doppler measurements (P = 0.034).

CONCLUSIONS

As PHD3 regulates the HIF-mediated hypoxic response in FGR, we deduce that fetal adaptation to hypoxia ranges from impaired to adequate, as observed by the gradient of PHD3 downregulation in relation to the severity of FGR.

Fbxw8 is involved in the proliferation of human choriocarcinoma JEG-3 cells

Fbxw8 is the F-box component of a SCF-like E3 ubiquitin ligase complex. Mice lacking Fbxw8 exhibit pathological defects in placenta and embryo similar to fetal growth retardation, suggesting a role of Fbxw8 in placentation. Proliferative capacity of trophoblast cells is very important in placental development. In this context, we revealed that Fbxw8 was expressed in four different human trophoblast cell lines. Silencing of Fbxw8 expression by siRNA inhibited the growth of choriocarcinoma JEG-3 cells. By Western blotting, cell cycle analysis, we showed that down-regulation of Fbxw8 by RNAi induced cell-growth arrest at G2/M phase through decreasing the levels of CDK1, CDK2, cyclin A and cyclin B1 and up-regulation of p27 at protein level. Conversely, over-expression of Fbxw8 led to the opposite effect. These results suggest that Fbxw8 plays an essential role in the proliferation of human trophoblast cells, especially JEG-3 cells, via G2/M phase transition in association with regulation of CDK1, CDK2, cyclin A, cyclin B1 and p27 expression.

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

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

Beyond oxygen: complex regulation and activity of hypoxia inducible factors in pregnancy

In the first trimester the extravillous cytotrophoblast cells occlude the uterine spiral arterioles creating a low oxygen environment early in pregnancy, which is essential for pregnancy success. Paradoxically, shallow trophoblast invasion and defective vascular remodelling of the uterine spiral arteries in the first trimester may result in impaired placental perfusion and chronic placental ischemia and hypoxia later in gestation leading to adverse pregnancy outcomes. The hypoxia inducible factors (HIFs) are key mediators of the response to low oxygen. We aimed to elucidate mechanisms of regulation of HIFs and the role these may play in the control of placental differentiation, growth and function in both normal and pathological pregnancies. The Pubmed database was consulted for identification of the most relevant published articles. Search terms used were oxygen, placenta, trophoblast, pregnancy, HIF and hypoxia. The HIFs are able to function throughout all aspects of normal and abnormal placental differentiation, growth and function; during the first trimester (physiologically low oxygen), during mid-late gestation (where there is adequate supply of blood and oxygen to the placenta) and in pathological pregnancies complicated by placental hypoxia/ischemia. During normal pregnancy HIFs may respond to complex alterations in oxygen, hormones, cytokines and growth factors to regulate placental invasion, differentiation, transport and vascularization. In the ever-changing environment created during pregnancy, the HIFs appear to act as key mediators of placental development and function and thereby are likely to be important contributors to both normal and adverse pregnancy outcomes.

Non-synonymous sequence variants within the oxygen-dependent degradation domain of the HIF1A gene are not associated with pre-eclampsia in the Finnish population

Background

Reduced placental perfusion predisposes to the maternal syndrome pre-eclampsia characterized by systemically reduced perfusion. Considerable data support the role of angiogenic factors in the development of the maternal syndrome. Hypoxia-inducible factor (HIF-1) mediates the cellular responses to hypoxia e.g. by promoting angiogenesis.

Methods

Here we studied whether two single nucleotide sequence variants, c.1744 C>T that changes residue 582 of HIF-1α from proline to serine (P582S) and c.1762 G>A that changes residue 588 of HIF-1α from alanine to threonine (A588T) in the exon 12 of the HIF1A gene, are associated with pre-eclampsia. We studied 108 women with pre-eclampsia in their first pregnancy, and 101 controls with normotensive pregnancies. Pre-eclampsia was defined as a blood pressure level of at least 140/90 mmHg in a woman who was normotensive before 20 weeks of gestation, and proteinuria at least of 0.3 g per 24-hour urine collection. The patients and controls were genotyped for variations in the exon 12 of HIF1A gene by sequencing

Results

The frequencies of the c.1744 C>T and c.1762G>A sequence variants were not significantly different between women with pre-eclamptic first pregnancies and women with normotensive pregnancies. In addition, two synonymous variants (c.1740G>A and c.1800A>T) were detected at comparable levels in the two groups. All variants were identified in the heterozygous form.

Conclusion

The sequence variants in the exon 12 of the HIF1A gene were not associated with pre-eclampsia in the Finnish population.