Naturally occurring variation in trophoblast invasion as a source of novel (epigenetic) biomarkers

DNA methylation landscape in pregnancy-induced hypertension: progress and challenges

Gestational hypertension (PIH), especially pre-eclampsia (PE), is a common complication of pregnancy. This condition poses significant risks to the health of both the mother and the fetus. Emerging evidence suggests that epigenetic modifications, particularly DNA methylation, may play a role in initiating the earliest pathophysiology of PIH. This article describes the relationship between DNA methylation and placental trophoblast function, genes associated with the placental microenvironment, the placental vascular system, and maternal blood and vascular function, abnormalities of umbilical cord blood and vascular function in the onset and progression of PIH, as well as changes in DNA methylation in the progeny of PIH, in terms of maternal, fetal, and offspring. We also explore the latest research on DNA methylation-based early detection, diagnosis and potential therapeutic strategies for PIH. This will enable the field of DNA methylation research to continue to enhance our understanding of the epigenetic regulation of PIH genes and identify potential therapeutic targets.

Anti-endothelial cell antibody rich sera from rheumatic heart disease patients induces proinflammatory phenotype and methylation alteration in endothelial cells

Rheumatic heart disease (RHD) is a major cause of cardiovascular morbidity and mortality in developing nations like India. RHD commonly affects the mitral valve which is lined by a single layer of endothelial cells (ECs). The role of ECs in mitral valve damage during RHD is not well elucidated. In here, anti-endothelial cell antibody from RHD patients has been used to stimulate the ECs (HUVECs and HMVECs). ECs proinflammatory phenotype with increased expression of TNFα, IL-6, IL-8, IFNγ, IL-1β, ICAM1, VCAM1, E-selectin, laminin B, and vimentin was documented in both ECs. The promoter hypomethylation of various key inflammatory cytokines (TNFα, IL-6, and IL-8), integrin (ICAM1) associated with leukocyte transendothelial migration, and extracellular matrix genes (vimentin, and laminin) were also observed. Further, the in-vitro data was in accordance with ex-vivo observations which correlated significantly with the etiological factors such as smoking, socioeconomic status, and housing. Thus, the study sheds light on the role of ECs in RHD which is a step forward in the elucidation of disease pathogenesis.

Imbalance between matrix metalloproteinases and their tissue inhibitors in preeclampsia and gestational trophoblastic diseases

The invasion cascade exhibited by placental trophoblasts and cancerous cells bears many similarities, and it is attributed to extracellular matrix degradation mediated by matrix metalloproteinases (MMPs). Although proper and controlled invasion by trophoblasts into the maternal uterus is an essential requirement for maintenance of normal pregnancy, any abnormality in this phenomenon results in the development of invasion-related disorders such as gestational trophoblastic diseases (GTDs) and preeclampsia. We studied the epigenetic basis of differential expression of two placental MMPs (MMP2 and MMP9) and tissue inhibitors of metalloproteinases (TIMP2 and TIMP1) during normal gestation and invasion-related disorders, i.e., preeclampsia and GTDs. Our study suggests the association of H3K9/27me3 with differential expression of these MMPs and their inhibitors, which regulate the placental invasion during normal pregnancy, whereas no role of CpG methylation was observed in the differential expression of MMPs/TIMPs. Further, development of GTDs was associated with abnormally higher expression of these MMPs and lower levels of their inhibitors, whereas the reverse trends were observed for MMPs and their TIMPs in case of preeclampsia, in association with abnormal changes in H3K9/27me3. These results suggest the involvement of higher levels of MMPs in an aggressive invasive behavior depicted by GTDs, whereas lower levels of these MMPs in shallow and poor invasive phenotype associated with preeclampsia. Thus, our study shows the significance of a proper balance regulated by histone trimethylation between differential expression of MMPs and their TIMPs for maintaining normal pregnancy and its deregulation as a contributing factor for pathogenesis of invasive disorders during pregnancy.

Variable DAXX gene methylation is a common feature of placental trophoblast differentiation, preeclampsia, and response to hypoxia

Placental functioning relies on the appropriate differentiation of progenitor villous cytotrophoblasts (CTBs) into extravillous cytotrophoblasts (EVCTs), including invasive EVCTs, and the multinucleated syncytiotrophoblast (ST) layer. This is accompanied by a general move away from a proliferative, immature phenotype. Genome-scale expression studies have provided valuable insight into genes that are associated with the shift to both an invasive EVCT and ST phenotype, whereas genome-scale DNA methylation analysis has shown that differentiation to ST involves widespread methylation shifts, which are counteracted by low oxygen. In the current study, we sought to identify DNA methylation variation that is associated with transition from CTB to ST in vitro and from a noninvasive to invasive EVCT phenotype after culture on Matrigel. Of the several hundred differentially methylated regions that were identified in each comparison, the majority showed a loss of methylation with differentiation. This included a large differentially methylated region (DMR) in the gene body of death domain-associated protein 6 (DAXX ), which lost methylation during both CTB syncytialization to ST and EVCT differentiation to invasive EVCT. Comparison to publicly available methylation array data identified the same DMR as among the most consistently differentially methylated genes in placental samples from preeclampsia pregnancies. Of interest, in vitro culture of CTB or ST in low oxygen increases methylation in the same region, which correlates with delayed differentiation. Analysis of combined epigenomics signatures confirmed DAXX DMR as a likely regulatory element, and direct gene expression analysis identified a positive association between methylation at this site and DAXX expression levels. The widespread dynamic nature of DAXX methylation in association with trophoblast differentiation and placenta-associated pathologies is consistent with an important role for this gene in proper placental development and function.-Novakovic, B., Evain-Brion, D., Murthi, P., Fournier, T., Saffery, R. Variable DAXX gene methylation is a common feature of placental trophoblast differentiation, preeclampsia, and response to hypoxia.

Amnion as a surrogate tissue reporter of the effects of maternal preeclampsia on the fetus

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, using purified cell types in large cohort translational studies is difficult. The amnion, the inner layer of the fetal membranes of the 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 proteinuria or hypertension and fetuses from normal pregnancies.

RESULTS

We performed a genome-wide DNA methylation analysis, HpaII tiny fragment Enrichment by Ligation-mediated PCR (HELP)-tagging, on 62 amnion samples from the placentas of uncomplicated, normal pregnancies and from 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. A gene ontology analysis showed DNA methylation changes to be selecting genes with different biological processes in exposure status. 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 amniotic membranes represent a valuable surrogate fetal tissue on which to perform epigenome-wide association studies of adverse intrauterine conditions.

Association of aberrant methylation at promoter regions of tumor suppressor genes with placental pathologies

Aim: The resemblance between invasive behavior of cancer cells and placental trophoblasts and the role of aberrant epigenetic regulation in cancer development is well known. Methods: We analyzed the role of promoter region CpG-methylation and H3K9/27me3 of tumor suppressor genes in normal and pathological pregnancies and utilized their CpG-methylation data to search for fetal DNA epigenetic marker in maternal blood. Results: CpG and H3K9/27-methylation associated decreased expression of RASSF1A and APC and increased expression of P16, RB1 and PRKCDBP was observed with advancing normal gestation. Gestational trophoblastic diseases and preeclampsia revealed gene-specific epigenetic deregulation of candidate tumor suppressor genes. Furthermore, APC and PRKCDBP showed the potential to act as fetal DNA epigenetic markers, similar to RASSF1A. Conclusion: Deregulation of methylation of tumor suppressor genes contributes to the development of preeclampsia and gestational trophoblastic diseases. APC and PRKCDBP may act as fetal DNA epigenetic markers for prenatal diagnosis.

Early Developmental and Evolutionary Origins of Gene Body DNA Methylation Patterns in Mammalian Placentas

Over the last 20-80 million years the mammalian placenta has taken on a variety of morphologies through both divergent and convergent evolution. Recently we have shown that the human placenta genome has a unique epigenetic pattern of large partially methylated domains (PMDs) and highly methylated domains (HMDs) with gene body DNA methylation positively correlating with level of gene expression. In order to determine the evolutionary conservation of DNA methylation patterns and transcriptional regulatory programs in the placenta, we performed a genome-wide methylome (MethylC-seq) analysis of human, rhesus macaque, squirrel monkey, mouse, dog, horse, and cow placentas as well as opossum extraembryonic membrane. We found that, similar to human placenta, mammalian placentas and opossum extraembryonic membrane have globally lower levels of methylation compared to somatic tissues. Higher relative gene body methylation was the conserved feature across all mammalian placentas, despite differences in PMD/HMDs and absolute methylation levels. Specifically, higher methylation over the bodies of genes involved in mitosis, vesicle-mediated transport, protein phosphorylation, and chromatin modification was observed compared with the rest of the genome. As in human placenta, higher methylation is associated with higher gene expression and is predictive of genic location across species. Analysis of DNA methylation in oocytes and preimplantation embryos shows a conserved pattern of gene body methylation similar to the placenta. Intriguingly, mouse and cow oocytes and mouse early embryos have PMD/HMDs but their placentas do not, suggesting that PMD/HMDs are a feature of early preimplantation methylation patterns that become lost during placental development in some species and following implantation of the embryo.

NIPT-based screening for Down syndrome and beyond: what do pregnant women think?

OBJECTIVE

The aim of the study is to study pregnant women's views on noninvasive prenatal testing (NIPT) for Down syndrome and the potential to test for a broader range of conditions.

METHODS

An online questionnaire available on the Dutch pregnancy fair website was completed by 381 pregnant women.

RESULTS

Of the women, 51% expressed interest in having NIPT, including 33% of women who had declined first-trimester screening. The majority (73%) thought that the uptake of screening would increase with NIPT. Most women agreed that testing for life-threatening (89%), severe physical (79%), or severe mental (76%) disorders should be offered. A minority (29%) felt that prenatal screening should also be offered for late-onset disorders. Most (41%) preferred to have a free choice from a list of disorders, 31% preferred a 'closed offer', and 26% preferred choosing between packages of disorders. Although most women (76%) thought that screening for a broad range of conditions would avoid much suffering, 39% feared that it would confront couples with choices, the implications of which would be difficult to grasp.

CONCLUSION

The results suggest that the uptake of screening will increase with NIPT. If NIPT will be offered for a broad range of conditions, it is crucial to find a way that facilitates rather than undermines well-informed decision-making.

How has the study of the human placenta aided our understanding of partially methylated genes?

While the human genome sequence is relatively uniform between the cells of an individual, the DNA methylation of the genome (methylome) has unique features in different cells, tissues and stages of development. Recent genome-wide sequencing of the methylome has revealed large partially methylated domains (PMDs) in the human placenta. Unlike CpG islands and Polycomb-regulated regions, which can also have low levels of methylation, placental PMDs cover approximately 37% of the human genome and are associated with inaccessible chromatin and the repression of tissue-specific genes. Here, we summarize the interesting biological questions that have arisen as a result of finding PMDs in the human placenta, including how PMDs form, what they do, how they evolved and how they might be relevant to human disease.

Placental pseudo-malignancy from a DNA methylation perspective: unanswered questions and future directions

The growing fetus is dependent on adequate placental function for delivery of essential nutrients and oxygen, and for waste removal. The placenta also plays an important protective role; shielding the developing baby from the maternal immune system and adverse environmental exposures. Fundamental to these processes is correct invasion of the decidua and remodeling of maternal vasculature, each of which show remarkable parallels to tumorogenesis, with the obvious exception that the former is usually a tightly controlled process. It is not surprising that these physiological similarities are mirrored in gene expression and epigenetic parallels, many not found in any other aspect of human development. In this perspective, we summarize known DNA methylation similarities between placenta and human tumors, and discuss the implications and knowledge gaps associated with these findings. We also speculate on the potential origin of common DNA methylation features in these two disparate aspects of human physiology.

Cavin-3 dictates the balance between ERK and Akt signaling

Cavin-3 is a tumor suppressor protein of unknown function. Using both in vivo and in vitro approaches, we show that cavin-3 dictates the balance between ERK and Akt signaling. Loss of cavin-3 increases Akt signaling at the expense of ERK, while gain of cavin-3 increases ERK signaling at the expense Akt. Cavin-3 facilitates signal transduction to ERK by anchoring caveolae to the membrane skeleton of the plasma membrane via myosin-1c. Caveolae are lipid raft specializations that contain an ERK activation module and loss of the cavin-3 linkage reduces the abundance of caveolae, thereby separating this ERK activation module from signaling receptors. Loss of cavin-3 promotes Akt signaling through suppression of EGR1 and PTEN. The in vitro consequences of the loss of cavin-3 include induction of Warburg metabolism (aerobic glycolysis), accelerated cell proliferation, and resistance to apoptosis. The in vivo consequences of cavin-3 knockout are increased lactate production and cachexia. DOI:http://dx.doi.org/10.7554/eLife.00905.001.