Microarray technology applied to the complex disorder of preeclampsia

Non-Coding RNAs in Preeclampsia-Molecular Mechanisms and Diagnostic Potential

Preeclampsia (PE) is a leading cause of maternal and neonatal morbidity and mortality worldwide. Defects in trophoblast invasion, differentiation of extravillous trophoblasts and spiral artery remodeling are key factors in PE development. Currently there are no predictive biomarkers clinically available for PE. Recent technological advancements empowered transcriptome exploration and led to the discovery of numerous non-coding RNA species of which microRNAs (miRNAs) and long non-coding RNAs (lncRNAs) are the most investigated. They are implicated in the regulation of numerous cellular functions, and as such are being extensively explored as potential biomarkers for various diseases. Altered expression of numerous lncRNAs and miRNAs in placenta has been related to pathophysiological processes that occur in preeclampsia. In the following text we offer summary of the latest knowledge of the molecular mechanism by which lnRNAs and miRNAs (focusing on the chromosome 19 miRNA cluster (C19MC)) contribute to pathophysiology of PE development and their potential utility as biomarkers of PE, with special focus on sample selection and techniques for the quantification of lncRNAs and miRNAs in maternal circulation.

Gene expression of four targets in situ of the first trimester maternal-fetoplacental interface

EPAS1, FSTL3, IGFBP1, and SEMA3C were localized to determine whether expression is decidual, trophoblastic, or both in the human first trimester maternal-fetoplacental interface. Identified on global genome-wide microarray analysis of chorionic villus sampling tissues in preclinical preeclampsia, these targets were predicted to interact by bioinformatics pathways analysis. In situ hybridization (ISH) with mRNA of each gene was conducted in 10 cases of archived first trimester termination tissues. Randomly selected areas of cells by tissue type yielded the relative proportion of cells expressing mRNA signal in decidual and fetoplacental sites. Data were analyzed using Shapiro-Wilk and Kruskal-Wallis tests (p ≤ .05). The average gestational age was 10.2 weeks. Expression signal for each gene differed by cell type (p < .001). FSTL3 expression was 17 times higher in cells of anchoring columns than areas of decidua without ISH signal. SEMA3C was three times higher in cells of anchoring columns than in decidua. EPAS1 was 1.31 times higher in cells of anchoring columns than in areas of decidua. IGFBP1 was 20 times higher in some decidua versus cells in anchoring columns or villous trophoblast. While all targets were expressed by both maternal and fetoplacental cells, our localizations identified which compartment had relatively higher expression of each gene.

Associating Symptom Phenotype and Genotype in Preeclampsia

Preeclampsia is a complex genetic disorder with an incompletely understood pathogenesis. Its phenotype may be better elucidated by integrating symptoms. This study aimed to identify symptoms by gestational age and associations with novel preeclampsia candidate genes. Women with a history of preeclampsia recruited from The Preeclampsia Registry completed clinical/demographic, symptom surveys and provided medical records. DNA extracted from saliva was processed with multiplexed assays for eight single-nucleotide polymorphisms (SNPs) selected to tag candidate genes and/or located in symptom susceptibility regions. Groups with versus without symptoms were compared using χ2. Associations between SNPs and symptoms were analyzed as genotype categories and presence/absence of the variant allele. Logistic regression modeling was conducted with exploratory p = .05. In 114 participants, 113 reported at least 1 of the 18 symptoms. Symptoms varied by trimester. Nine symptoms were associated with seven SNPs. Visual disturbances were associated with three SNPs and nausea/vomiting with two SNPs. Modeling adjustment for maternal age and parity resulted in 15 associations between 9 symptoms and 8 SNPs. Medical records demonstrated 100% concordance with self-reported diagnosis and 48% concordance with reported severity. Findings indicated novel symptom-genotype associations in preeclampsia. The small sample was self-selected, but results support future studies including medical records review. When validated, these results may lead to holistic phenotyping of women to characterize subsets of preeclampsia. This approach may optimize health in pregnancy and later life for mothers and offspring through prediction, prevention, and precision nursing care.

Developing Potential Candidates of Preclinical Preeclampsia

The potential for developing molecules of interest in preclinical preeclampsia from candidate genes that were discovered on gene expression microarray analysis has been challenged by limited access to additional first trimester trophoblast and decidual tissues. The question of whether these candidates encode secreted proteins that may be detected in maternal circulation early in pregnancy has been investigated using various proteomic methods. Pilot studies utilizing mass spectrometry based proteomic assays, along with enzyme linked immunosorbent assays (ELISAs), and Western immunoblotting in first trimester samples are reported. The novel targeted mass spectrometry methods led to robust multiple reaction monitoring assays. Despite detection of several candidates in early gestation, challenges persist. Future antibody-based studies may lead to a novel multiplex protein panel for screening or detection to prevent or mitigate preeclampsia.

FOXO1 expression in villous trophoblast of preeclampsia and fetal growth restriction placentas

Oxidative stress and increased apoptosis are implicated in the pathogenesis of many disorders of pregnancy, including preeclampsia (PE) and fetal growth restriction (FGR). Since the transcription factor FOXO1 (forkhead box protein O1) is implicated in the regulation of a variety of cellular processes, including resistance to oxidative stress, apoptosis and morphogenesis of the placenta, we examined whether FOXO1 expression is abnormal in placentas from patients with PE or FGR. Paracentral sections from grossly unremarkable areas of 9 or 10 placentas each from early third trimester patients (31.7±5.0 weeks) with mild PE, severe PE, FGR and a gestational age-matched comparison group (GA controls) were double immunostained for FOXO1 and E-cadherin, the latter distinguishing villous cytotrophoblast cells (CTB) from syncytiotrophoblast (STB). The numbers of FOXO1-positive and FOXO1 negative STB and CTB nuclei were determined on ten 20x objective fields of each placenta section by three observers who were blinded to the clinical outcome. The results were evaluated by a generalized linear mixed model. In mild PE, FOXO1-positive STB nuclei were significantly decreased in number and FOXO1-negative STB nuclei were increased as compared to GA controls. However, the number of FOXO1-positive and FOXO1-negative CTB nuclei were not significantly changes as compared to GA controls. In severe PE and FGR, the numbers of FOXO-positive and FOXO1-negative STB and CTB were not statistically different from GA controls. Since FOXO1 is critical for placental cellular morphogenesis, abnormal FOXO1 expression may contribute in part to the abnormal trophoblast differentiation in mild PE. The differences in FOXO1 expression in mild and severe PE are consistent with other studies suggesting that the two forms of PE are different disease processes.

Targeted gene analysis: increased B-cell lymphoma 6 in preeclamptic placentas

Preeclampsia is a leading cause for maternal and perinatal mortality and morbidity. Microarray-based transcriptional profiling has been widely used for identifying genes responsible for preeclampsia. These studies deliver multiple pictures of gene signatures, implying the complicated pathophysiology. In the present work, we designed our own gene array containing genes involved in various signaling transduction pathways and analyzed placental samples from patients with preeclampsia and controls. We verify that genes associated with angiogenesis and migration pathways are mostly altered in preeclamptic placentas. Interestingly, several genes including B-cell lymphoma 6 have been identified to be linked to preeclampsia. Increased expression of B-cell lymphoma 6 is correlated with enhanced FLT1 and LEPTIN, the hallmarks of preeclampsia. Moreover, the protein level of B-cell lymphoma 6 is elevated in preeclamptic placentas and is predominantly localized in the nucleus of villous cytotrophoblasts lying directly underneath the syncytial layer, suggestive of an involvement in the function of villous trophoblasts. Altered B-cell lymphoma 6, a key oncogene in B-cell lymphomagenesis, may be involved in the pathogenesis of preeclampsia, and further investigations are required to decipher the molecular mechanisms.

Genetics and preterm birth

Although the etiology of preterm birth is incompletely understood, phenotype classifications combined with recent technologies such as genome-wide association studies and next-generation sequencing could lead to discovering genotypes associated with preterm birth. Identifying genetic contributions will allow for genetic screening tests to predict or detect pregnancies with potential for preterm birth. In this article we discuss current knowledge regarding phenotype classifications, genotypes, and their associations with preterm birth.

The role of angiogenic, anti-angiogenic and vasoactive factors in pre-eclamptic African women: early- versus late-onset pre-eclampsia

Abstract

The pathogenesis and aetiology of pre-eclampsia (PE) is still unclear. We investigated the role of angiogenic, anti-angiogenic and vasoactive factors in black South African women with early- and late-onset PE. Serum soluble fms-like tyrosine kinase 1 (sFlt-1), soluble vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) levels were determined using the ELISA technique, and placental mRNA expression levels of sFlt-1, VEGF, PlGF and AT1 receptors were determined using real-time PCR.

Serum sFlt-1 levels were significantly elevated and PlGF significantly reduced in early-onset PE compared to the normotensive group. Placental VEGF mRNA expression levels were significantly reduced in the late-onset preeclamptic group compared with the normotensives. The placental mRNA expression of AT1 receptor in the late-onset pre-eclamptic group was relatively raised compared to the normotensives, suggesting hypersensitivity to pressor agents.

We believe that the excess of serum sFlt-1 and reduced VEGF and PlGF levels favour an anti-angiogenic state and endothelial dysfunction leading to PE, and that the aetiology and pathogenesis of early- and late-onset PE differ.

Variations in discovery-based preeclampsia candidate genes

Preeclampsia is a common and potentially lethal pregnancy disorder with lifelong increased risk of cardiovascular disease in survivors. Our prior global gene expression microarray analysis led to a novel set of 36 candidates in first trimester placentas of women who subsequently developed preeclampsia. In this report, we present preliminary studies demonstrating biomarkers of genotype and methylation variations in a subset of these candidate genes in maternal leukocyte and fetoplacental DNA of 28 case and 27 control dyads. We tested 84 single nucleotide polymorphisms (SNPs) using MassArray iPLEX and 50 CpG sites using EpiTYPER assays. Promising prediction modeling was identified with 25 SNPs selected using Fisher's exact tests (p ≤ 0.05) and 20 CpG sites selected on fold change. Genotype Distribution Analysis identified SNP variations that differed between nine paired cases versus paired controls. The findings validate the examined candidate genes and support feasibility of methods for further biomarker development. The integrative approach that was implemented begins to translate the 36 candidates toward clinical utility as a screening modality for preeclampsia.

Gene expression profiling of placentae from women with early- and late-onset pre-eclampsia: down-regulation of the angiogenesis-related genes ACVRL1 and EGFL7 in early-onset disease

The underlying mechanisms behind the obstetric condition pre-eclampsia (PE) are still unclear. Manifestation of PE is heterogeneous and it has therefore been proposed to be a syndrome with different causes rather than one disease with a specific aetiology. Recently, we showed differences in circulating angiogenic factors between two subgroups-early- and late-onset PE. To further elucidate the differences between the two, we investigated placental gene expression profiles. Whole genome microarray technology and bioinformatic analysis were used to evaluate gene expression profiles in placentae from early- (24-32 gestational weeks, n = 8) and late-onset (36-41 gestational weeks, n = 7) PE. The results were verified by using quantitative real-time (qRT)-PCR. We found significant differences in the expression of 196 genes in early- compared with late-onset PE, 45 of these genes showing a fold change above 2. Bioinformatic analysis revealed alterations in angiogenesis and regulation of cell motility. Two angiogenesis-associated transcripts (Egfl7 and Acvrl1) showed lower expression in early-onset PE versus late-onset PE (P = 0.037 and P = 0.003) and versus gestational age-matched controls (P = 0.007 and P = 0.011). We conclude that angiogenesis-associated genes are regulated in a different manner in the two subgroups, and that the gene expression profiles of early- and late-onset PE diverge, supporting the hypothesis of early- and late-onset PE being at least partly two separate entities.

Bridging global gene expression candidates in first trimester placentas with susceptibility loci from linkage studies of preeclampsia

Preeclampsia is as a leading cause of maternal and perinatal morbidity and mortality. Prevention, early identification, and individualized treatments may become feasible if reliable early biomarkers can be developed. Towards a systems biology framework, this review synthesizes prior linkage studies and genome scans of preeclampsia with candidates identified in a global gene expression microarray analysis of chorionic villus sampling (CVS) specimens from women who subsequently developed preeclampsia. Nearly 40% of these CVS candidate genes occurred in previously identified susceptibility loci for preeclampsia. Integration of genetic epidemiologic and functional gene expression data could help to elucidate preeclampsia as a complex disease resulting from multiple maternal and fetal/placental factors that each contributes a greater or lesser effect. These loci and related candidate genes are set to substantially improve insights into the first trimester pathogenesis of this pregnancy disorder.

Preeclampsia: pathophysiology and implications for care

Nurses are increasingly encountering pregnant/postpartum women with hypertensive disorders of pregnancy, of which preeclampsia is one of the most common. The Joint Commission published a Sentinel Event Alert in 2010 on prevention of maternal death. This report notes that one of the 5 leading causes of pregnancy-related mortality between 1991 and 1997 was "hypertensive disorder." Preeclampsia presents significant risk to the health of the mother and the fetus. Clearly, nurses must understand the pathophysiology, assessment, management, recurrence risk, and long-term implications of preeclampsia to participate fully in a management plan that promotes safe patient care.

A transcriptional profile of the decidua in preeclampsia

OBJECTIVE

We sought to obtain insight into possible mechanisms underlying preeclampsia using genomewide transcriptional profiling in decidua basalis.

STUDY DESIGN

Genomewide transcriptional profiling was performed on decidua basalis tissue from preeclamptic (n = 37) and normal (n = 58) pregnancies. Differentially expressed genes were identified and merged into canonical pathways and networks.

RESULTS

Of the 26,504 expressed transcripts detected, 455 were differentially expressed (P < .05; false discovery rate, P < .1). Both novel (ARL5B, SLITRK4) and previously reported preeclampsia-associated (PLA2G7, HMOX1) genes were identified. Pathway analysis revealed that tryptophan metabolism, endoplasmic reticulum stress, linoleic acid metabolism, notch signaling, fatty acid metabolism, arachidonic acid metabolism, and NRF2-mediated oxidative stress response were overrepresented canonical pathways.

CONCLUSION

In the present study single genes, canonical pathways, and gene-gene networks that are likely to play an important role in the pathogenesis of preeclampsia have been identified. Future functional studies are needed to accomplish a greater understanding of the mechanisms involved.

Gene expression in first trimester preeclampsia placenta

BACKGROUND

The goal of this study was to further validate eight candidate genes identified in a microarray analysis of first trimester placentas in preeclampsia.

MATERIAL AND METHOD

Surplus chorionic villus sampling (CVS) specimens of 4 women subsequently diagnosed with preeclampsia (PE) and 8 control women (C) without preeclampsia analyzed previously by microarray and 24 independent additional control samples (AS) were submitted for confirmatory studies by quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Downregulation was significant in FSTL3 in PE as compared to C and AS (p = .04). PAEP was downregulated, but the difference was only significant between C and AS (p = .002) rather than between PE and either of the control groups. Expression levels for CFH, EPAS1, IGFBP1, MMP12, and SEMA3C were not statistically different among groups, but trends were consistent with microarray results; there was no anti-correlation. S100A8 was not measurable in all samples, probably because different probes and primers were needed.

CONCLUSIONS

This study corroborates reduced FSTL3 expression in the first trimester of preeclampsia. Nonsignificant trends in the other genes may require follow-up in studies powered for medium or medium/large effect sizes. qRT-PCR verification of the prior microarray of CVS may support the placental origins of preeclampsia hypothesis. Replication is needed for the candidate genes as potential biomarkers of susceptibility, early detection, and/or individualized care of maternal-infant preeclampsia.

Gene expression profiling of placentas affected by pre-eclampsia

Several studies point to the placenta as the primary cause of pre-eclampsia. Our objective was to identify placental genes that may contribute to the development of pre-eclampsia. RNA was purified from tissue biopsies from eleven pre-eclamptic placentas and eighteen normal controls. Messenger RNA expression from pooled samples was analysed by microarrays. Verification of the expression of selected genes was performed using real-time PCR. A surprisingly low number of genes (21 out of 15,000) were identified as differentially expressed. Among these were genes not previously associated with pre-eclampsia as bradykinin B1 receptor and a 14-3-3 protein, but also genes that have already been connected with pre-eclampsia, for example, inhibin beta A subunit and leptin. A low number of genes were repeatedly identified as differentially expressed, because they may represent the endpoint of a cascade of events effectuated throughout gestation. They were associated with transcriptional regulation and vasoregulative pathways, along with a number of hypothetical proteins and gene sequences with unknown functions.

Altered global gene expression in first trimester placentas of women destined to develop preeclampsia

BACKGROUND

Preeclampsia is a pregnancy-specific disorder that remains a leading cause of maternal, fetal and neonatal morbidity and mortality, and is associated with risk for future cardiovascular disease. There are no reliable predictors, specific preventative measures or treatments other than delivery. A widely held view is that the antecedents of preeclampsia lie with impaired placentation in early pregnancy. Accordingly, we hypothesized dysregulation of global gene expression in first trimester placentas of women who later manifested preeclampsia.

METHODS

Surplus chorionic villus sampling (CVS) tissues were collected at 10-12 weeks gestation in 160 patients with singleton fetuses. Four patients developed preeclampsia, and their banked CVS specimens were matched to 8 control samples from patients with unaffected pregnancies. Affymetrix HG-U133 Plus 2.0 GeneChips were utilized for microarray analysis. Naïve Bayes prediction modeling and pathway analysis were conducted. qRT-PCR examined three of the dysregulated genes.

RESULTS

Thirty-six differentially expressed genes were identified in the preeclampsia placentas. qRT-PCR verified the microarray analysis. Thirty-one genes were down-regulated. Many were related to inflammation/immunoregulation and cell motility. Decidual gene dysregulation was prominent. No evidence was found for alterations in hypoxia and oxidative stress regulated genes.

CONCLUSIONS

To our knowledge, this is the first study to show dysregulation of gene expression in the early placentas of women approximately 6 months before developing preeclampsia, thereby reinforcing a placental origin of the disorder. We hypothesize that placentation in preeclampsia is compromised in the first trimester by maternal and fetal immune dysregulation, abnormal decidualization, or both, thereby impairing trophoblast invasion. Several of the genes provide potential targets for the development of clinical biomarkers in maternal blood during the first trimester. Supplementary materials are available for this article via the publisher's online edition.