STOX1 is not imprinted and is not likely to be involved in preeclampsia

STOX1 promotor region -922 T > C polymorphism is associated with Early-Onset preeclampsia

Preeclampsia (PE), affecting 5-8% of pregnancies, is a common pregnancy disease that has harmful effects on mother and foetus. It has been found that the STOX1 (Storkhead Box 1), which is a transcription factor, carries variants associated with PE. Previous studies showed that, there was a strong relationship between PE and STOX1 variants. Therefore, we hypothesised that variants in the promoter region of the gene may be related to the onset of PE. The aim of this study is to investigate the contribution of STOX1 gene promoter region variants to PE. The blood samples taken from 118 PE patients and 96 healthy pregnant women were analysed by Sanger sequencing method. Sequence analysis results showed that, there is a-922 T > C polymorphism (rs884181) in the promoter region of the STOX1 gene. This polymorphism was found to be statistically significant in individuals with early onset PE (p = 0.02) and in PE (p = 0.014) compared to the control group.IMPACT STATEMENTWhat is already known on this subject? As a result of whole-exon studies on the STOX1 gene, polymorphisms were found to disrupt the structure/expression/function of the gene and strengthen its relationship with PE and HELLP syndrome. A previous study by our team found an association between Y153H, the most common polymorphism of STOX1, and early onset PE.What do the results of this study add? In our study, it was aimed to investigate the effect of genetic modifications in STOX1 gene promoter region on PE through the maternal genotype. Because any change in the promoter region affects the expression level of the gene. Also, for the first time, sequence analysis of the promoter region of STOX1 is investigated in PE. The variations in STOX1 appear to be important in PE especially in Early Onset PE.What are the implications of these findings for clinical practice and/or further research? Although PE is a disease that occurs with pregnancy and shows its effects most during this period, women and children with a history of PE are more prone to various disorders, especially cardiovascular diseases in the following years. Therefore, understanding the pathogenesis of the disease is important for both prevention and treatment process. Variations on STOX1 appear to be important in terms of disease risk.

Animal Models of Cardiovascular Complications of Pregnancy

Cardiovascular complications of pregnancy have risen substantially over the past decades, and now account for the majority of pregnancy-induced maternal deaths, as well as having substantial long-term consequences on maternal cardiovascular health. The causes and pathophysiology of these complications remain poorly understood, and therapeutic options are limited. Preclinical models represent a crucial tool for understanding human disease. We review here advances made in preclinical models of cardiovascular complications of pregnancy, including preeclampsia and peripartum cardiomyopathy, with a focus on pathological mechanisms elicited by the models and on relevance to human disease.

Preeclampsia, Natural History, Genes, and miRNAs Associated with the Syndrome

Preeclampsia (PE) is a hypertensive disease that affects pregnant women after 20 weeks of gestation. This disease is associated with an important risk of maternal and fetal mortality. PE is described as a placental pathology because, after delivery, most women recover normal arterial pressure. Poor invasion of the spiral arteries is a phenomenon well described in PE; this leads to a hypoxic uterine bed and imbalance of antiangiogenic and proangiogenic factors in the uteroplacental region, which in turn triggers the disease phenotype. The causes of the pathology are unclear; nevertheless, numerous approaches, including next-generation sequencing, association, and case control and miRNA studies, have shed light on the genetic/molecular basis of PE. These studies help us better understand the disease to advance new treatment strategies.

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.

STOX1 deficiency is associated with renin-mediated gestational hypertension and placental defects

The pathogenesis of preeclampsia and other hypertensive disorders of pregnancy remains poorly defined despite the substantial burden of maternal and neonatal morbidity associated with these conditions. In particular, the role of genetic variants as determinants of disease susceptibility is understudied. Storkhead-box protein 1 (STOX1) was first identified as a preeclampsia risk gene through family-based genetic linkage studies in which loss-of-function variants were proposed to underlie increased preeclampsia susceptibility. We generated a genetic Stox1 loss-of-function mouse model (Stox1 KO) to evaluate whether STOX1 regulates blood pressure in pregnancy. Pregnant Stox1-KO mice developed gestational hypertension evidenced by a significant increase in blood pressure compared with WT by E17.5. While severe renal, placental, or fetal growth abnormalities were not observed, the Stox1-KO phenotype was associated with placental vascular and extracellular matrix abnormalities. Mechanistically, we found that gestational hypertension in Stox1-KO mice resulted from activation of the uteroplacental renin-angiotensin system. This mechanism was supported by showing that treatment of pregnant Stox1-KO mice with an angiotensin II receptor blocker rescued the phenotype. Our study demonstrates the utility of genetic mouse models for uncovering links between genetic variants and effector pathways implicated in the pathogenesis of hypertensive disorders of pregnancy.

Functional Evaluation of STOX1 (STORKHEAD-BOX PROTEIN 1) in Placentation, Preeclampsia, and Preterm Birth

Revaluation of the association of the STOX1 (STORKHEAD_BOX1 PROTEIN 1) transcription factor mutation (Y153H, C allele) with the early utero-vascular origins of placental pathology is warranted. To investigate if placental STOX1 Y153H genotype affects utero-vascular remodeling-compromised in both preterm birth and preeclampsia-we utilized extravillous trophoblast (EVT) explant and placental decidual coculture models, transfection of STOX1 wild-type and mutant plasmids into EVT-like trophoblast cell lines, and a cohort of 75 placentas from obstetric pathologies. Primary EVT and HTR8/SVneo cells carrying STOX1 Y153H secreted lower levels of IL (interleukin) 6, and IL-8, and higher CXCL16 (chemokine [C-X-C motif] ligand 16) and TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) than wild-type EVT and Swan71 cells. Media from wild-type EVT or Swan71 cells transfected with wild-type STOX1 stimulated: endothelial chemokine expression, angiogenesis, and decidual natural killer cell and monocyte migration. In contrast, Y153H EVT conditioned medium, Swan71 transfected with the Y153H plasmid, or HTR8/SVneo media had no effect. Genotyping of placental decidual cocultures demonstrated association of the placental STOX1 CC allele with failed vascular remodeling. Decidual GG NODAL R165H increased in failed cocultures carrying the placental CC alleles of STOX1. Multivariate analysis of the placental cohort showed that the STOX1 C allele correlated with premature birth, with or without severe early-onset preeclampsia, and small for gestational age babies. In conclusion, placental STOX1 Y153H is a precipitating factor in preterm birth and placental preeclampsia due to defects in early utero-placental development.

STOX1 gene Y153H polymorphism is associated with early-onset preeclampsia in Turkish population

Preeclampsia (PE) is a disease of pregnancy that causes of maternal and prenatal morbidity worldwide. Studies indicate that variations in STOX1 gene may be a direct risk factor to PE but controversial results regarding the relationship of Y153H variation in the second exon of STOX1 gene with PE have been ongoing since 2005. The aim of this study was to identify if there is any correlation between Y153H polymorphisms and PE in Turkish preeclampsia patients. We performed polymerase chain reaction- restriction fragment lengthpolymorphism(PCR-RFLP) analysis in 500 pregnant women, of whom 373 pregnant women with early onset PE (EOPE) and 500 normal pregnant women. The relationship between STOX1 Y153H polymorphism and EOPE/LOPE was evaluated by statistical analysis. We found that STOX1 Y153H polymorphism is a risk factor for EOPE (p = 0.03). The odds ratio was 1,45 (CI 95% = 1,03-2,05). No relationship between STOX1 Y153H polymorphisms and LOPE (p = 0.13) was found. STOX1 gene Y153H polymorphism is associated with the risk ofearly onset of pre-eclampsiain a Turkish population. The results provide further evidence of the role of STOX1 in the pathophysiology of this disease.

Aspirin modulates STOX1 expression and reverses STOX1-induced insufficient proliferation and migration of trophoblast cells

BACKGROUND

A major cause of preeclampsia is the placental ischemia caused by insufficient trophoblast cells, invading into the spiral artery. Storkhead-box protein 1 (STOX1) is highly associated with preeclampsia. Meanwhile, low-dose aspirin for patients with preeclampsia is effective in reducing the incidence of preeclampsia. The aim of the present study was to explore the underlying mechanism, and the relationship between STOX1 and aspirin in preeclampsia.

METHODS

The human choriocarcinoma cell line JEG-3 was employed to mimic trophoblast cells and establish a model for trophoblast cells overexpressing STOX1 and knockdown of JEG cell lines, which were treated with aspirin afterwards. Cell counting kit-8 (CCK-8) assay was utilized to estimate cell proliferation and optimal concentration of aspirin for further experiments. Meanwhile, transwell assay was used to detect migration, and flow cytometry was used to measure apoptosis. Quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blotting were applied to analyze the expression levels of STOX1 and related genes.

RESULTS

Overexpression of STOX1 inhibited proliferation of JEG-3 cells through epidermal growth factor (EGF), vascular EGF (VEGF), and transforming growth factor beta 1 (TGF-β1) proteins, while suppressed migration through MMP2, MMP9, and E-cadherin proteins. In contrast, apoptosis of JEG-3 cells was elevated by STOX1 through Bcl-2, Bax, and Cox-2 proteins. Furthermore, we found that aspirin modulated the expression level of STOX1 and reversed proliferation and migration of STOX1-induced insufficient trophoblast cells.

CONCLUSION

The present study suggested that inhibition of the expression of STOX1 could promote the effects of aspirin in the treatment of preeclampsia.

The significance of the placental genome and methylome in fetal and maternal health

The placenta is a crucial organ for supporting a healthy pregnancy, and defective development or function of the placenta is implicated in a number of complications of pregnancy that affect both maternal and fetal health, including maternal preeclampsia, fetal growth restriction, and spontaneous preterm birth. In this review, we highlight the role of the placental genome in mediating fetal and maternal health by discussing the impact of a variety of genetic alterations, from large whole-chromosome aneuploidies to single-nucleotide variants, on placental development and function. We also discuss the placental methylome in relation to its potential applications for refining diagnosis, predicting pathology, and identifying genetic variants with potential functional significance. We conclude that understanding the influence of the placental genome on common placental-mediated pathologies is critical to improving perinatal health outcomes.

Personalized Therapy Against Preeclampsia by Replenishing Placental Protein 13 (PP13) Targeted to Patients With Impaired PP13 Molecule or Function

Hypertensive disorders affect about one third of all people aged 20 and above, and are treated with anti-hypertensive drugs. Preeclampsia (PE) is one form of such disorders that only develops during pregnancy. It affects ten million pregnant women globally and additionally causes fetal loss and major newborn disabilities. The syndrome's origin is multifactorial, and anti-hypertensive drugs are ineffective in treating it. Biomarkers are helpful for predict its development. Generic drugs, such as low dose aspirin, were proven effective in preventing preterm PE. However, it does not cure the majority of cases and many studies are underway for fighting PE with extended use of additional generic drugs, or through new drug development programs. This review focuses on placental protein 13 (PP13). This protein is only expressed in the placenta. Impaired PP13 DNA structure and/or its reduced mRNA expression leads to lower blood PP13 level that predict a higher risk of developing PE. Two polymorphic PP13 variants have been identified: (1) The promoter PP13 variant with an "A/A" genotype in the -98 position (versus "A/C" or "C/C"). Having the "A/A" genotype is coupled to lower PP13 expression, mainly during placental syncytiotrophoblast differentiation and, if associated with obesity and history of previous preeclampsia, it accurately predicts higher risk for developing the disorder. (2) A thymidine deletion at position 221 causes a frame shift in the open reading frame, and the formation of an early stop codon resulting in the formation of DelT221, a truncated variant of PP13. In pregnant rodents, both short- and long- term replenishment of PP13 causes reversible hypotension and vasodilation of uterine vessels. Long-term exposure is also accompanied by the development of larger placentas and newborns. Also, only w/t PP13 is capable of inducing leukocyte apoptosis, providing maternal immune tolerance to pregnancy. Based on published data, we propose a targeted PP13 therapy to fight PE, and consider the design and conduct of animal studies to explore this hypothesis. Accordingly, a new targeted therapy can be implemented in humans combining prediction and prevention.

Disturbed Placental Imprinting in Preeclampsia Leads to Altered Expression of DLX5, a Human-Specific Early Trophoblast Marker

Supplemental Digital Content is available in the text.

Background:

Preeclampsia is a complex and common human-specific pregnancy syndrome associated with placental pathology. The human specificity provides both intellectual and methodological challenges, lacking a robust model system. Given the role of imprinted genes in human placentation and the vulnerability of imprinted genes to loss of imprinting changes, there has been extensive speculation, but no robust evidence, that imprinted genes are involved in preeclampsia. Our study aims to investigate whether disturbed imprinting contributes to preeclampsia.

Methods:

We first aimed to confirm that preeclampsia is a disease of the placenta by generating and analyzing genome-wide molecular data on well-characterized patient material. We performed high-throughput transcriptome analyses of multiple placenta samples from healthy controls and patients with preeclampsia. Next, we identified differentially expressed genes in preeclamptic placentas and intersected them with the list of human imprinted genes. We used bioinformatics/statistical analyses to confirm association between imprinting and preeclampsia and to predict biological processes affected in preeclampsia. Validation included epigenetic and cellular assays. In terms of human specificity, we established an in vitro invasion-differentiation trophoblast model. Our comparative phylogenetic analysis involved single-cell transcriptome data of human, macaque, and mouse preimplantation embryogenesis.

Results:

We found disturbed placental imprinting in preeclampsia and revealed potential candidates, including GATA3 and DLX5, with poorly explored imprinted status and no prior association with preeclampsia. As a result of loss of imprinting, DLX5 was upregulated in 69% of preeclamptic placentas. Levels of DLX5 correlated with classic preeclampsia markers. DLX5 is expressed in human but not in murine trophoblast. The DLX5^high phenotype resulted in reduced proliferation, increased metabolism, and endoplasmic reticulum stress-response activation in trophoblasts in vitro. The transcriptional profile of such cells mimics the transcriptome of preeclamptic placentas. Pan-mammalian comparative analysis identified DLX5 as part of the human-specific regulatory network of trophoblast differentiation.

Conclusions:

Our analysis provides evidence of a true association among disturbed imprinting, gene expression, and preeclampsia. As a result of disturbed imprinting, the upregulated DLX5 affects trophoblast proliferation. Our in vitro model might fill a vital niche in preeclampsia research. Human-specific regulatory circuitry of DLX5 might help explain certain aspects of preeclampsia.

Targeting STOX1 in the therapy of preeclampsia

INTRODUCTION

Preeclampsia is a major pregnancy disease, explained partly by genetic predispositions. STOX1, a transcription factor discovered in 2005, was the first gene directly associated with genetic forms of the disease. Alterations of STOX1 expression as well as STOX1 variants have also been associated to Alzheimer's disease. These observations make of this gene a putative therapeutic target. Area covered: Two major isoforms (STOX1A and STOX1B) are encoded by the gene and are theoretically able to compete for the same binding site, while only the most complete (STOX1A) is supposed to be able to activate gene expression. This makes the ratio between STOX1A and STOX1B as well as their position inside the cell (nucleus or cytoplasm) crucial to understand how STOX1 functions. STOX1 appears to have multiple gene targets, especially in pathways connected to inflammation, oxidative stress, and cell cycle. Expert opinion: STOX1-directed therapies, could be directed either towards its targets (genes or pathways), or directly at STOX1. For this the addressing of STOX1 to various cell compartments could theoretically be modified; also it could be possible of altering the balance between the two isoforms, through selectively inhibiting one of them, possibly improving the outcomes in severe preeclampsia.

Nitroso-redox balance and mitochondrial homeostasis are regulated by STOX1, a pre-eclampsia-associated gene

AIMS

Storkhead box 1 (STOX1) is a winged-helix transcription factor that is implicated in the genetic forms of a high-prevalence human gestational disease, pre-eclampsia. STOX1 overexpression confers pre-eclampsia-like transcriptomic features to trophoblastic cell lines and pre-eclampsia symptoms to pregnant mice. The aim of this work was to evaluate the impact of STOX1 on free radical equilibrium and mitochondrial function, both in vitro and in vivo.

RESULTS

Transcriptome analysis of STOX1-transgenic versus nontransgenic placentas at 16.5 days of gestation revealed alterations of mitochondria-related pathways. Placentas overexpressing STOX1 displayed altered mitochondrial mass and were severely biased toward protein nitration, indicating nitroso-redox imbalance in vivo. Trophoblast cells overexpressing STOX1 displayed an increased mitochondrial activity at 20% O2 and in hypoxia, despite reduction of the mitochondrial mass in the former. STOX1 overexpression is, therefore, associated with hyperactive mitochondria, resulting in increased free radical production. Moreover, nitric oxide (NO) production pathways were activated, resulting in peroxynitrite formation. At low oxygen pressure, STOX1 overexpression switched the free radical balance from reactive oxygen species (ROS) to reactive nitrogen species (RNS) in the placenta as well as in a trophoblast cell line.

INNOVATION

In pre-eclamptic placentas, NO interacts with ROS and generates peroxynitrite and nitrated proteins as end products. This process will deprive the maternal organism of NO, a crucial vasodilator molecule.

CONCLUSION

Our data posit STOX1 as a genetic switch in the ROS/RNS balance and suggest an explanation for elevated blood pressure in pre-eclampsia.

Genetic aspects of preeclampsia and the HELLP syndrome

Both preeclampsia and the HELLP syndrome have their origin in the placenta. The aim of this study is to review genetic factors involved in development of preeclampsia and the HELLP syndrome using literature search in PubMed. A familial cohort links chromosomes 2q, 5q, and 13q to preeclampsia. The chromosome 12q is coupled with the HELLP syndrome. The STOX1 gene, the ERAP1 and 2 genes, the syncytin envelope gene, and the −670 Fas receptor polymorphisms are involved in the development of preeclampsia. The ACVR2A gene on chromosome 2q22 is also implicated. The toll-like receptor-4 (TLR-4) and factor V Leiden mutation participate both in development of preeclampsia and the HELLP syndrome. Carriers of the TT and the CC genotype of the MTHFR C677T polymorphism seem to have an increased risk of the HELLP syndrome. The placental levels of VEGF mRNA are reduced both in women with preeclampsia and in women with the HELLP syndrome. The BclI polymorphism is engaged in development of the HELLP syndrome but not in development of severe preeclampsia. The ACE I/D polymorphism affects uteroplacental and umbilical artery blood flows in women with preeclampsia. In women with preeclampsia and the HELLP syndrome several genes in the placenta are deregulated. Preeclampsia and the HELLP syndrome are multiplex genetic diseases.

(Epi)genetics of pregnancy-associated diseases

This review describes the current knowledge regarding genetics and epigenetics of pregnancy-associated diseases with placental origin. We discuss the effect on genetic linkage analyses when the fetal genotype determines the maternal phenotype. Secondly, the genes identified by genome-wide linkage studies to be associated with pre-eclampsia (ACVR2A, STOX1) and the HELLP-syndrome (LINC-HELLP) are discussed regarding their potential functions in the etiology of disease. Furthermore, susceptibility genes identified by candidate gene approaches (e.g., CORIN) are described. Next, we focus on the additional challenges that come when epigenetics also play a role in disease inheritance. We discuss the maternal transmission of the chromosome 10q22 pre-eclampsia linkage region containing the STOX1 gene and provide further evidence for the role of epigenetics in pre-eclampsia based on the cdkn1c mouse model of pre-eclampsia. Finally, we provide recommendations to unravel the genetics of pregnancy-associated diseases, specifically regarding clear definitions of patient groups and sufficient patient numbers, and the potential usefulness of (epi)genetic data in early non-invasive biomarker development.

Pathophysiology of hypertension in pre-eclampsia: a lesson in integrative physiology

Despite being one of the leading causes of maternal death and a major contributor of maternal and perinatal morbidity, the mechanisms responsible for the pathogenesis of pre-eclampsia have yet to be fully elucidated. However, it is evident that this is a complex disorder involving multiple organ systems, and by using integrative approaches, enormous progress has been made towards understanding the pathophysiology of pre-eclampsia. Growing evidence supports the concept that the placenta plays a central role in the pathogenesis of pre-eclampsia and that reduced uteroplacental perfusion, which develops as a result of abnormal cytotrophoblast invasion of spiral arterioles, triggers the cascade of events leading to the maternal disorder. Placental ischaemia leads to release of soluble placental factors, many of which are classified as anti-angiogenic or pro-inflammatory. Once these ischaemic placental factors reach the maternal circulation, they cause widespread activation and dysfunction of the maternal vascular endothelium that results in enhanced formation of endothelin-1 and superoxide, increased vascular sensitivity to angiotensin II and decreased formation of vasodilators such as nitric oxide. This review highlights these links between placental ischaemia, maternal endothelial activation and renal dysfunction in the pathogenesis of hypertension in pre-eclampsia.

Why preeclampsia still exists?

Preeclampsia (PE) is a deadly gestational disease affecting up to 10% of women and specific of the human species. Preeclampsia is clearly multifactorial, but the existence of a genetic basis for this disease is now clearly established by the existence of familial cases, epidemiological studies and known predisposing gene polymorphisms. PE is very common despite the fact that Darwinian pressure should have rapidly eliminated or strongly minimized the frequency of predisposing alleles. Consecutive pregnancies with the same partner decrease the risk and severity of PE. Here, we show that, due to this peculiar feature, preeclampsia predisposing-alleles can be differentially maintained according to the familial structure. Thus, we suggest that an optimal frequency of PE-predisposing alleles in human populations can be achieved as a result of a trade-off between benefits of exogamy, importance for maintaining genetic diversity and increase of the fitness owing to a stable paternal investment.

Preeclampsia-like symptoms induced in mice by fetoplacental expression of STOX1 are reversed by aspirin treatment

Preeclampsia (PE) is a common human-specific pregnancy disorder defined by hypertension and proteinuria during gestation and responsible for maternal and fetal morbimortality. STOX1, encoding a transcription factor, was the first gene associated with PE as identified by positional cloning approaches. Its overexpression in choriocarcinoma cells mimics the transcriptional consequences of PE in the human placenta. Here, we created transgenic mouse strains overexpressing human STOX1. Wild-type female mice crossed with transgenic male mice reproduce accurately the symptoms of severe PE: gestational hypertension, proteinuria, and elevated plasma levels of soluble fms-like tyrosine kinase 1 and soluble endoglin. Placental and kidney histology were altered. Symptoms were prevented or alleviated by aspirin treatment. STOX1-overexpressing mice constitute a unique model for studying PE, allow testing therapeutic approaches, and assessing the long-term effects of the preeclamptic syndrome.

Molecular genetics of preeclampsia and HELLP syndrome - a review

Preeclampsia is characterised by new onset hypertension and proteinuria and is a major obstetrical problem for both mother and foetus. Haemolysis elevated liver enzymes and low platelets (HELLP) syndrome is an obstetrical emergency and most cases occur in the presence of preeclampsia. Preeclampsia and HELLP are complicated syndromes with a wide variety in severity of clinical symptoms and gestational age at onset. The pathophysiology depends not only on periconceptional conditions and the foetal and placental genotype, but also on the capability of the maternal system to deal with pregnancy. Genetically, preeclampsia is a complex disorder and despite numerous efforts no clear mode of inheritance has been established. A minor fraction of HELLP cases is caused by foetal homozygous LCHAD deficiency, but for most cases the genetic background has not been elucidated yet. At least 178 genes have been described in relation to preeclampsia or HELLP syndrome. Confined placental mosaicism (CPM) is documented to cause early onset preeclampsia in some cases; the overall contribution of CPM to the occurrence of preeclampsia has not been adequately investigated yet. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.

The genetics of pre-eclampsia and other hypertensive disorders of pregnancy

Hypertension is the most frequent medical complication occurring during pregnancy. In this chapter, we aim to address the genetic contribution to these disorders, with specific focus on pre-eclampsia. The pathogenic mechanisms underlying pre-eclampsia remain to be elucidated; however, immune maladaptation, inadequate placental development and trophoblast invasion, placental ischaemia, oxidative stress and thrombosis are all thought to represent key factors in the development of disease. Furthermore, all of these components have genetic factors that may be involved in the pathogenic changes occurring. The familial nature of pre-eclampsia has been known for many years and, as such, extensive genetic research has been carried out in this area using strategies that include candidate gene studies and linkage analysis. Interactions between fetal and maternal genotypes, the effect of environmental factors, and epistasis will also be considered.

STOX1: Key player in trophoblast dysfunction underlying early onset preeclampsia with growth retardation

Currently, only two preeclampsia susceptibility genes (ACVR2A, STOX1) have been identified within confirmed regions with significant genome-wide linkage, although many genetic screens in multiple populations have been performed. In this paper, we focus on the STOX1 gene. The epigenetic status of this gene is discussed explaining the maternal transmission of the STOX1 susceptibility allele observed in preeclamptic families. The known upstream regulation and downstream effector genes of the transcription factor STOX1 are described. Finally, we propose a model in which we combine the cell type-specific and allele-specific effects of STOX1. This includes intrinsic effects (differential CpG island methylation) and extrinsic effects (regulation of effector genes).

STOX2 but not STOX1 is differentially expressed in decidua from pre-eclamptic women: data from the Second Nord-Trondelag Health Study

Variation in the Storkhead box-1 (STOX1) gene has previously been associated with pre-eclampsia. In this study, we assess candidate single nucleotide polymorphisms (SNPs) in STOX1 in an independent population cohort of pre-eclamptic (n = 1.139) and non-pre-eclamptic (n = 2.269) women (the HUNT2 study). We also compare gene expression levels of STOX1 and its paralogue, Storkhead box-2 (STOX2) in decidual tissue from pregnancies complicated by pre-eclampsia and/or fetal growth restriction (FGR) (n = 40) to expression levels in decidual tissue from uncomplicated pregnancies (n = 59). We cannot confirm association of the candidate SNPs to pre-eclampsia (P > 0.05). For STOX1, no differential gene expression was observed in any of the case groups, whereas STOX2 showed significantly lower expression in deciduas from pregnancies complicated by both pre-eclampsia and FGR as compared with controls (P = 0.01). We further report a strong correlation between transcriptional alterations reported previously in choriocarcinoma cells over expressing STOX1A and alterations observed in decidual tissue of pre-eclamptic women with FGR.

The importance of imprinting in the human placenta

As a field of study, genomic imprinting has grown rapidly in the last 20 years, with a growing figure of around 100 imprinted genes known in the mouse and approximately 50 in the human. The imprinted expression of genes may be transient and highly tissue-specific, and there are potentially hundreds of other, as yet undiscovered, imprinted transcripts. The placenta is notable amongst mammalian organs for its high and prolific expression of imprinted genes. This review discusses the development of the human placenta and focuses on the function of imprinting in this organ. Imprinting is potentially a mechanism to balance parental resource allocation and it plays an important role in growth. The placenta, as the interface between mother and fetus, is central to prenatal growth control. The expression of genes subject to parental allelic expression bias has, over the years, been shown to be essential for the normal development and physiology of the placenta. In this review we also discuss the significance of genes that lack conservation of imprinting between mice and humans, genes whose imprinted expression is often placental-specific. Finally, we illustrate the importance of imprinting in the postnatal human in terms of several human imprinting disorders, with consideration of the brain as a key organ for imprinted gene expression after birth.

The STOX1 genotype associated with pre-eclampsia leads to a reduction of trophoblast invasion by alpha-T-catenin upregulation

By using complementary in vitro and ex vivo approaches, we show that the risk allele (Y153H) of the pre-eclampsia susceptibility gene STOX1 negatively regulates trophoblast invasion by upregulation of the cell-cell adhesion protein alpha-T-catenin (CTNNA3). This is effectuated at the crucial epithelial-mesenchymal transition of proliferative into invasive extravillous trophoblast. This STOX1-CTNNA3 interaction is direct and includes Akt-mediated phosphorylated control of nucleo-cytoplasmic shuttling and ubiquitin-mediated degradation as shared with the FOX multigene family. This, to our knowledge, is the first time a genotype associated with pre-eclampsia has been shown to directly limit first trimester extravillous trophoblast invasion, the earliest hallmark of pre-eclampsia.

CDKN1C mutations in HELLP/preeclamptic mothers of Beckwith-Wiedemann Syndrome (BWS) patients

Preeclampsia is the development of new-onset hypertension with proteinuria after 20 weeks of gestation. HELLP syndrome (haemolysis, elevated liver enzymes, and low platelet count) is a severe form of preeclampsia with high rates of neonatal and maternal morbidity. In recent years, loss of function of cdkn1c (a tight-binding inhibitor of G1 cyclin/cyclin-dependent kinase complexes and a negative regulator of cell proliferation) has been observed in several mouse models of preeclampsia. In this paper, we report on three women with HELLP/preeclampsia who had children with Beckwith Wiedemann syndrome, a complex genetic disorder characterised, among other findings, by overgrowth, omphalocele and macroglossia. All three children displayed mutations in CDKN1C predicted to generate truncated proteins. Two of the mutations were maternally inherited while the third was de novo. This finding suggests a fetal contribution to the maternal disease. To the best of our knowledge this is the first report of CDKN1C mutations in children born to women with preeclampsia/HELLP syndrome, thus suggesting the involvement of an imprinted gene in the pathophysiology of preeclampsia.

STOX1 overexpression in choriocarcinoma cells mimics transcriptional alterations observed in preeclamptic placentas

BACKGROUND

Mutations in STOX1 were proposed to be causal for predisposing to preeclampsia, a hypertensive disorder originating from placental defects, affecting up to 10% of human pregnancies. However, after the first study published in 2005 three other groups have dismissed the polymorphism described in the first paper as a causal mutation.

METHODOLOGY AND PRINCIPAL FINDINGS

In the present study, we have produced a choriocarcinoma cell line overexpressing STOX1. This overexpression results in transcriptional modification of 12.5% of the genes, some of them being direct targets as shown by chromatin immunoprecipitation. STOX1 overexpression correlates strongly and specifically with transcriptomic alterations in preeclamptic placentas (r = 0.30, p = 9.10(-7)). Numerous known key modulators of preeclampsia (such as Endoglin, Syncytin, human chorionic gonadotrophin -hCG-, and Glial Cell Missing Homolog -GCM1-) were modified in these transformed choriocarcinoma cells.

CONCLUSIONS

Our results contribute to reconcile contradictory data concerning the involvement of STOX1 in preeclampsia. In addition, they strongly suggest that anomalies in STOX1 expression are associated with the onset of preeclampsia, thus indicating that this gene should be the target of future studies. Our cellular model could constitute an invaluable resource for studying specific aspects of this human disease.

Genes and the preeclampsia syndrome

Preeclampsia is specific to pregnancy and is still a leading cause of maternal and perinatal mortality and morbidity, affecting about 3% of women, but the underlying pathogenetic mechanisms still remain unclear. Immune maladaptation, placental ischemia and increased oxidative stress represent the main components discussed to be of etiologic importance, and they all may have genetic implications. Since the familial nature of preeclampsia is known for many years, extensive research on the genetic contribution to the pathogenesis of this severe pregnancy disorder has been performed. In this review, we will overview the linkage and candidate gene studies carried out so far as well as summarize important historical notes on the genetic hypotheses generated in preeclampsia research. Moreover, the influence of maternal and fetal genes and their interaction as well as the role of genomic imprinting in preeclampsia will be discussed.

Genetic and epigenetic factors contribute to the onset of preeclampsia

Preeclampsia (PE) is a major cause of perinatal materno-foetal morbidity and pregnancy-associated-mortality in industrialized countries. Clinically, PE associates maternal pregnancy-induced hypertension with proteinuria. PE is often considered as a two-stage disease. The first stage is a shallow cytotrophoblastic invasion which induces cycles of hypoxia-reoxygenation at the placental level. Subsequently an abnormal expression pattern occurs and is followed by the release of soluble factors and trophoblastic debris in the maternal blood flow. These stimuli trigger the second phase of the disease, the maternal syndrome. Although some molecular actors have been recently identified, mechanisms of the disease onset remains poorly understood. It seems that combinations of genetic, epigenetic and environmental factors are involved. Here, we suggest that epigenetic marks have to be considered to decipher the physiopathological process of PE. Since these marks must be established early and are traceable in the maternal blood flow, they could constitute a diagnosis tool.

STOX1 gene in pre-eclampsia and intrauterine growth restriction

The STOX1 gene, identified as a candidate gene for pre-eclampsia in Dutch women, is placentally expressed and subject to imprinting with preferential transmission of the maternal allele. In our study, STOX1-Y153H frequencies were similar in 157 women with pre-eclampsia (65%) and in 157 controls (64%) from the general Dutch population. In an isolated Dutch population, a distortion could not be demonstrated in the transmission of STOX1-Y153H variation from heterozygous mothers to offspring in 50 and 56 families with pregnancies complicated by pre-eclampsia or intrauterine growth restriction, respectively. Our findings do not confirm previous suggestions that STOX1 plays a major role in Dutch women with pre-eclampsia.