Project description:Background: Preeclampsia, traditionally characterized by high blood pressure and proteinuria, is a common pregnancy complication, which affects 2-8% of all pregnancies. Although children born to women with preeclampsia have a higher risk of hypertension in later life, the mechanism of this increased risk is unknown. DNA methylation is an epigenetic modification that has been studied as a mediator of cellular memory of adverse exposures in utero. Since each cell type in the body has a unique DNA profile, cell subtype composition is a major confounding factor in studies of tissues with heterogeneous cell types. The best way to avoid this confounding effect is by using purified cell types. However, the use purified cell types in large cohort translational studies is difficult. The amnion, the inner layer of the fetal membranes of placenta, is derived from the epiblast and consists of two cell types, which are easy to isolate from the delivered placenta. In this study, we demonstrate the value of using amnion samples for DNA methylation studies, revealing distinctive patterns between fetuses exposed to preeclampsia or hypertension and fetuses from normal pregnancies. Results: We performed a genome-wide DNA methylation analysis, HELP-tagging, on 62 amnion samples from placentas of uncomplicated, normal pregnancies, and those with complications of preeclampsia or hypertension. Using a regression model approach, we found 123, 85 and 99 loci with high confidence hypertension-associated, proteinuria-associated and hypertension and proteinuria-associated DNA methylation changes, respectively. We also found that these differentially methylated regions overlap loci previously reported as differentially methylated regions in preeclampsia. Conclusions: Our findings support prior observations that preeclampsia is associated with changes of DNA methylation near genes that have previously been found to be dysregulated in preeclampsia. We propose that amnionic membranes represent a valuable surrogate fetal tissue on which to perform epigenome-wide association studies of adverse intrauterine conditions.

Project description:Hypertension in pregnancy is the leading cause of morbidity and mortality in pregnancy, affecting up to 10% of all gestations1. Hypertensive disorders of pregnancy include chronic hypertension, gestational hypertension, eclampsia and pre-eclampsia, all of which increase the risk of complications in both mothers and babies during gestation. Preeclampsia, in particular, is characterised by the new-onset of gestational hypertension in the presence of proteinuria or other organ damage. It affects 5-7% of pregnancies and causes approximately 76,000 maternal deaths and 500,000 foetal deaths worldwide each year2. The classification of preeclampsia has been evolving over the last decade. In 2013, American College of Obstetricians and Gynecologists (ACOG) and International Society for the Study of Hypertension in Pregnancy (ISSHP) in the absence of proteinuria included other symptoms/features including liver dysfunction, thrombocytopenia, cerebrovascular events or foetal growth restriction (FGR) in the diagnosis of preeclampsia 1,3,4. Despite the fact that preeclampsia is a multifactorial and heterogeneous disorder, it is now widely accepted that preeclampsia is stratified depending on the time of onset into: i) early-onset PE (EOPE) manifested before 34 weeks of gestation, and ii) late-onset PE (LOPE) manifested from 34 weeks of gestation. Although EOPE and LOPE share the same diagnostic criteria, these two phenotypes of preeclampsia lead to different outcomes. EOPE is commonly associated with FGR, abnormal uterine artery Doppler often leading to preterm birth and higher risk of post-pregnancy morbidities5,6. On the other hand, LOPE appears to be a less severe disorder, often with normal or slightly increased uterine resistance index and a low rate of FGR6,7. Distinct delineation between EOPE and LOPE is still not well understood, with most patients with preeclampsia presenting elements of both pathologies proposing a clinical spectrum for preeclampsia. The lack of untargeted discovery studies involving ‘omics’ analyses has impeded understanding of the molecular differences between these two phenotypes of preeclampsia. Notably, a study from 20058 utilised a proteomics approach using urine samples from a cohort of pregnant women with EOPE and healthy controls, however the differences between EOPE and LOPE were not elucidated. Another more recent bioinformatics study, identified overlapping pathogenic mechanisms between preeclampsia, hypertension and heart disease but could not stratify between EOPE and LOPE due to underreported of data related to individual phenotypes9. In this study, we conducted an unbiased, comprehensive proteomics investigation using plasma samples collected from patients with EOPE (n=17) and LOPE (n=11), compared with age- and BMI-matched normotensive controls (n=18). The use of plasma samples is able to better reflect the pathogenesis of EOPE and LOPE as systemic conditions centred by widespread endothelial dysfunction.

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Placental transcriptome analysis of hypertensive pregnancies identifies distinct gene expression profiles of preeclampsia superimposed on chronic hypertension

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