A strategy for identifying circulating placental RNA markers for fetal growth assessment

Establishment of the fetal-maternal interface: developmental events in human implantation and placentation

Early pregnancy is a complex and well-orchestrated differentiation process that involves all the cellular elements of the fetal-maternal interface. Aberrant trophoblast-decidual interactions can lead to miscarriage and disorders that occur later in pregnancy, including preeclampsia, intrauterine fetal growth restriction, and preterm labor. A great deal of research on the regulation of implantation and placentation has been performed in a wide range of species. However, there is significant species variation regarding trophoblast differentiation as well as decidual-specific gene expression and regulation. Most of the relevant information has been obtained from studies using mouse models. A comprehensive understanding of the physiology and pathology of human implantation and placentation has only recently been obtained because of emerging advanced technologies. With the derivation of human trophoblast stem cells, 3D-organoid cultures, and single-cell analyses of differentiated cells, cell type-specific transcript profiles and functions were generated, and each exhibited a unique signature. Additionally, through integrative transcriptomic information, researchers can uncover the cellular dysfunction of embryonic and placental cells in peri-implantation embryos and the early pathological placenta. In fact, the clinical utility of fetal-maternal cellular trafficking has been applied for the noninvasive prenatal diagnosis of aneuploidies and the prediction of pregnancy complications. Furthermore, recent studies have proposed a viable path toward the development of therapeutic strategies targeting placenta-enriched molecules for placental dysfunction and diseases.

Biosensors for Detection of Human Placental Pathologies: A Review of Emerging Technologies and Current Trends

Substantial growth in the biosensor research has enabled novel, sensitive and point-of-care diagnosis of human diseases in the last decade. This paper presents an overview of the research in the field of biosensors that can potentially predict and diagnosis of common placental pathologies. A survey of biomarkers in maternal circulation and their characterization methods is presented, including markers of oxidative stress, angiogenic factors, placental debris, and inflammatory biomarkers that are associated with various pathophysiological processes in the context of pregnancy complications. Novel biosensors enabled by microfluidics technology and nanomaterials is then reviewed. Representative designs of plasmonic and electrochemical biosensors for highly sensitive and multiplexed detection of biomarkers, as well as on-chip sample preparation and sensing for automatic biomarker detection are illustrated. New trends in organ-on-a-chip based placental disease models are highlighted to illustrate the capability of these in vitro disease models in better understanding the complex pathophysiological processes, including mass transfer across the placental barrier, oxidative stress, inflammation, and malaria infection. Biosensor technologies that can be potentially embedded in the placental models for real time, label-free monitoring of these processes and events are suggested. Merger of cell culture in microfluidics and biosensing can provide significant potential for new developments in advanced placental models, and tools for diagnosis, drug screening and efficacy testing.

Screening circulating proteins to identify biomarkers of fetal macrosomia

Objective

Fetal macrosomia is a major risk factor for shoulder dystocia, which can lead to birth asphyxia, maternal and neonatal traumatic injuries, and perinatal death. If macrosomia is diagnosed in the antenatal period, labour can be induced to decrease shoulder dystocia. But current clinical methods to diagnose fetal macrosomia antenatally perform with poor accuracy. Therefore, improved methods to accurately diagnose fetal macrosomia are required. Blood biomarkers that predict fetal macrosomia could be one such novel diagnostic strategy. We undertook a nested case–control study from a prospective collection of 1000 blood samples collected at 36 weeks’ gestation. We analysed plasma samples from 52 women who subsequently delivered a macrosomic (> 95th centile for gestational age) infant and 106 controls. Circulating concentrations of the proteins COBLL1, CSH1, HSD3B1, EGFL6, XAGE3, S100P, PAPPA-1, ERBB2 were assessed for their ability to predict macrosomic infants.

Results

We did not identify any significant changes in the plasma concentrations of COBLL1, CSH1, HSD3B1, EGFL6, XAGE3, S100P, PAPPA-1, ERBB2 from women who subsequently delivered macrosomic neonates relative to control samples. Although we have not identified any potential biomarkers of fetal macrosomia, we have ruled out these particular eight protein candidates.

Blood-based biomarkers in the maternal circulation associated with fetal growth restriction

Fetal growth restriction (FGR) is associated with threefold to fourfold increased risk of stillbirth. Identifying FGR, through its commonly used surrogate-the small-for-gestational-age (SGA, estimated fetal weight and/or abdominal circumference <10th centile) fetus-and instituting fetal surveillance and timely delivery decrease stillbirth risk. Methods available to clinicians for antenatal identification of SGA fetuses have surprisingly poor sensitivity. About 80% of cases remain undetected. Measuring the symphysis-fundal height detects only 20% of SGA fetuses, and even universal third trimester ultrasound detects, at best, 57% of those born SGA. There is an urgent need to find better ways to identify this at-risk cohort. This review summarises efforts to identify molecular biomarkers (proteins, metabolites, or ribonucleic acids) that could be used to better predict FGR. Most studies examining potential biomarkers to date have utilised case-control study designs without proceeding to validation in independent cohorts. To develop a robust test for FGR, large prospective studies are required with a priori validation plans and cohorts. Given that current clinical care detects 20% of SGA fetuses, even a screening test with ≥60% sensitivity at 90% specificity could be clinically useful, if developed. This may be an achievable aspiration. If discovered, such a test may decrease stillbirth.

Noninvasive Approaches to Prenatal Diagnosis: Historical Perspective and Future Directions

The field of prenatal screening and diagnosis has undergone enormous progress over the past four decades. Most of this period has been characterized by gradual improvements in the technical and public health aspects of prenatal screening for Down syndrome. Compared to the direct analysis of fetal cells from amniocentesis or chorionic villus sampling, noninvasive approaches using maternal blood or ultrasound have the great advantage of posing no risk of miscarriage to the pregnancy. Recent advances in molecular genetics and DNA sequencing have revolutionized both the accuracy and the range of noninvasive testing for genetic abnormalities using cell-free DNA in maternal plasma. Many of these advances have already been incorporated into clinical care, including diagnosis of fetal blood group and aneuploidy screening. The accelerated pace of these recent developments is creating not just technical and logistical challenges, but is also magnifying the ethical and public policy issues traditionally associated with this field.

Human Placental Growth Hormone Variant in Pathological Pregnancies

Growth hormone (GH), an endocrine hormone, primarily secreted from the anterior pituitary, stimulates growth, cell reproduction, and regeneration and is a major regulator of postnatal growth. Humans have two GH genes that encode two versions of GH proteins: a pituitary version (GH-N/GH1) and a placental GH-variant (GH-V/GH2), which are expressed in the syncytiotrophoblast and extravillous trophoblast cells of the placenta. During pregnancy, GH-V replaces GH-N in the maternal circulation at mid-late gestation as the major circulating form of GH. This remarkable change in spatial and temporal GH secretion patterns is proposed to play a role in mediating maternal adaptations to pregnancy. GH-V is associated with fetal growth, and its circulating concentrations have been investigated across a range of pregnancy complications. However, progress in this area has been hindered by a lack of readily accessible and reliable assays for measurement of GH-V. This review will discuss the potential roles of GH-V in normal and pathological pregnancies and will touch on the assays used to quantify this hormone.

Intrauterine growth retardation-associated syncytin b hypermethylation in maternal rat blood revealed by DNA methylation array analysis

BackgroundEmerging evidence suggests that DNA methylation in maternal blood is a promising target for intrauterine growth retardation (IUGR) screening, a common developmental toxicity. Here, we aimed to screen out IUGR-related DNA methylation status in maternal blood via high-throughput profiling.MethodsPregnant Wistar rats were subcutaneously administered nicotine (1 mg/kg) twice per day from gestational day (GD) 11 to GD20 to establish the IUGR model. MeDIP array assays and the following GO analysis were used to evaluate DNA methylation status in maternal blood. One placental development-associated gene was selected for further confirmation.ResultsGenes regulating the development of multiple organs and major body systems had changed DNA methylation frequencies in the maternal blood of IUGR rats. Placental development, which can affect the development of multiple fetal organs and induce IUGR, is a hypermethylated cluster consisting of four significantly changed genes, including syncytin b (Synb), Lrrc15, Met, and Tex19.1. With the most significant change, Synb hypermethylation in maternal blood was confirmed by bisulfite-sequencing PCR (BSP). Moreover, decreased Synb expression and histological changes were observed in IUGR placentae.ConclusionThe IUGR-associated DNA methylation profile in maternal blood, such as placenta-related Synb hypermethylation, provides evidence for further studies on possible IUGR biomarkers.

Integrative single-cell and cell-free plasma RNA transcriptomics elucidates placental cellular dynamics

The human placenta is a dynamic and heterogeneous organ critical in the establishment of the fetomaternal interface and the maintenance of gestational well-being. It is also the major source of cell-free fetal nucleic acids in the maternal circulation. Placental dysfunction contributes to significant complications, such as preeclampsia, a potentially lethal hypertensive disorder during pregnancy. Previous studies have identified significant changes in the expression profiles of preeclamptic placentas using whole-tissue analysis. Moreover, studies have shown increased levels of targeted RNA transcripts, overall and placental contributions in maternal cell-free nucleic acids during pregnancy progression and gestational complications, but it remains infeasible to noninvasively delineate placental cellular dynamics and dysfunction at the cellular level using maternal cell-free nucleic acid analysis. In this study, we addressed this issue by first dissecting the cellular heterogeneity of the human placenta and defined individual cell-type-specific gene signatures by analyzing more than 24,000 nonmarker selected cells from full-term and early preeclamptic placentas using large-scale microfluidic single-cell transcriptomic technology. Our dataset identified diverse cellular subtypes in the human placenta and enabled reconstruction of the trophoblast differentiation trajectory. Through integrative analysis with maternal plasma cell-free RNA, we resolved the longitudinal cellular dynamics of hematopoietic and placental cells in pregnancy progression. Furthermore, we were able to noninvasively uncover the cellular dysfunction of extravillous trophoblasts in early preeclamptic placentas. Our work showed the potential of integrating transcriptomic information derived from single cells into the interpretation of cell-free plasma RNA, enabling the noninvasive elucidation of cellular dynamics in complex pathological conditions.

Chorioamnionitis Occurring in Women With Preterm Rupture of the Fetal Membranes Is Associated With a Dynamic Increase in mRNAs Coding Cytokines in the Maternal Circulation

BACKGROUND

Preterm prelabor rupture of the fetal membranes (PPROM) is a significant contributor to the morbidity and mortality of preterm birth, particularly in the setting of chorioamnionitis. No sensitive or specific diagnostic or predictive test currently exists for the accurate diagnosis of chorioamnionitis. Our aim was to measure messenger RNA (mRNA) coding cytokines in the maternal blood and examine whether they were increased in association with chorioamnionitis at delivery.

METHODS/RESULTS

We performed a prospective cohort study of women recruited with PPROM at a mean gestational age of 28.9 weeks at risk of developing chorioamnionitis. Blood was sampled from participants, and the expression of mRNA coding for proinflammatory genes was measured in women with and without chorioamnionitis at the time of delivery as well as gestation-matched healthy controls. Expression was measured using quantitative polymerase chain reaction (PCR) and also digital PCR. Interleukin 1β (IL1B) mRNA expression in maternal blood was elevated in women with chorioamnionitis compared to gestation-matched controls. Importantly, among women admitted with PPROM, digital PCR confirmed a significant increase in IL1B expression in maternal blood in women with chorioamnionitis compared to women without chorioamnionitis. Polymerase chain reaction array revealed that CD14, nuclear factor of κ light polypeptide gene enhancer in B-cells 1 (NFKB1), and tumor necrosis factor receptor super family-interacting serine-threonine kinase 1 mRNA were significantly increased in women with chorioamnionitis compared to controls. Digital PCR confirmed that NFKB1 mRNA was significantly increased in patients with chorioamnionitis compared to controls and that CD14 levels increased over time in patients with PPROM having chorioamnionitis.

CONCLUSION

Measuring circulating proinflammatory mRNA in women with PPROM may distinguish those with chorioamnionitis from those without, in turn providing better targeted therapies and appropriate timing of delivery.

Prediction of Fetal Growth Restriction by Analyzing the Messenger RNAs of Angiogenic Factor in the Plasma of Pregnant Women

OBJECTIVE

To predict the occurrence of fetal growth restriction (FGR) by analyzing messenger RNA (mRNA) expression levels of vascular endothelial growth factor receptor 1 (fms-like tyrosine kinase 1 [Flt-1]) in maternal blood.

STUDY DESIGN

Eleven women with FGR were matched with 88 controls. Plasma samples were obtained during each trimester. The Flt-1 mRNA expression levels were compared between groups. Predicted probabilities were calculated, and sensitivity-specificity (receiver-operating characteristic [ROC]) curves were assessed based on regression models for each trimester measurement and possible combinations of measurements.

RESULTS

The mRNA levels of the FGR group during all trimesters were significantly higher than those of the control group. The ROC curve of combined first and second trimester data yielded a detection rate of 60% at a 10% false-positive rate, with an area under curve of 0.79.

CONCLUSION

The Flt-1 mRNA expression in maternal blood can be used as a marker to predict the development of FGR, long before a clinical diagnosis is made.

Maternal Plasma RNA Sequencing for Genome-Wide Transcriptomic Profiling and Identification of Pregnancy-Associated Transcripts

BACKGROUND

Analysis of circulating RNA in the plasma of pregnant women has the potential to serve as a powerful tool for noninvasive prenatal testing and research. However, detection of circulating RNA in the plasma in an unbiased and high-throughput manner has been technically challenging. Therefore, only a limited number of circulating RNA species in maternal plasma have been validated as pregnancy- and placenta-specific biomarkers.

METHODS

We explored the use of massively parallel sequencing for plasma transcriptome profiling in first-, second-, and third-trimester pregnant women. Genotyping was performed for amniotic fluid, placental tissues, and maternal blood cells, with exome-enriched sequencing.

RESULTS

In the early pregnancy group comprising 1 first- and 1 second-trimester pregnancy cases, the fetal contribution to the RNA pool in maternal plasma was 3.70%. The relative proportion of fetal contribution was increased to 11.28% in the late pregnancy group comprising 2 third-trimester pregnancy cases. The placental biallelic expression pattern of PAPPA (pregnancy-associated plasma protein A, pappalysin 1), a known pregnancy-specific gene, and the monoallelic expression pattern of H19 [H19, imprinted maternally expressed transcript (non-protein coding)], an imprinted maternally expressed gene, were also detected in the maternal plasma. Furthermore, by direct examination of the maternal plasma transcriptomic profiles before and after delivery, we identified a panel of pregnancy-associated genes.

CONCLUSIONS

Plasma RNA sequencing provides a holistic view of the maternal plasma transcriptomic repertoire. This technology is potentially valuable for using circulating plasma nucleic acids for prenatal testing and research.

The Role of RNAs and microRNAs in Non-Invasive Prenatal Diagnosis

In this paper, all possible clinical applications of circulating mRNA and miRNA for non-invasive prenatal diagnosis appearing in the medical literature so far are described. Data from the literature have also been reported and commented on along with some possible future applications.

Investigation of biological factors influencing the placental mRNA profile in maternal plasma

OBJECTIVE

Circulating placental-derived RNA is useful for noninvasive prenatal investigation. However, in addition to placental gene expression, there are limited investigations on other biological parameters that may affect the circulating placental RNA profile. In this study, we explored two of these potential parameters.

METHODS

We first demonstrated the existence of such biological parameters by comparing the relative levels of a panel of placental-derived transcripts between the placentas and maternal plasma by digital PCRs. We then compared the post-delivery clearance of the transcripts by serial plasma samples collected from pregnant women after delivery. We also studied the placental in vivo localization of the transcripts by in situ hybridization.

RESULTS

There was an imperfect correlation of the transcript levels between the placentas and maternal plasma, with placenta-specific 4 (PLAC4) mRNA showing the largest discrepancy. Although PLAC4 mRNA showed a similar clearance half-life with other transcripts, we observed a preferential localization of PLAC4 mRNA around the villous surface. We speculated that this phenomenon might play a role in favoring the release of PLAC4 mRNA molecules into maternal plasma.

CONCLUSION

We revealed that in addition to expression levels in the placenta, other biological factors might interplay to determine the maternal plasma profile of placental-derived RNAs.

Placental specific mRNA in the maternal circulation are globally dysregulated in pregnancies complicated by fetal growth restriction

CONTEXT

Fetal growth restriction (FGR) is a leading cause of perinatal mortality, yet no reliable screening test exists. Placental specific mRNA in the maternal circulation may reflect changes in the placental transcriptome in FGR and could be a novel biomarker for FGR.

OBJECTIVE

The aim of the study was to identify placental specific RNA detectable in the maternal circulation and examine whether they are differentially expressed in severe preterm FGR.

DESIGN

In silico screening was used to identify placental specific RNAs. Their expression in cases of severe FGR vs controls was examined in both maternal blood and placenta by microarray, RT-PCR, and in situ hybridization.

RESULTS

Via in silico analysis, we identified 137 genes very highly expressed in the placenta relative to other tissues. Using microarray, we found that they were detectable in the maternal blood and were globally dysregulated with preterm FGR; 75 genes (55%) had a ≥1.5-fold differential expression compared to controls. Eight genes (ERVWE-1, PSG1, PLAC4, TAC3, PLAC3, CRH, CSH1, and KISS1) were validated by RT-PCR to be significantly increased in both maternal blood and placenta in a larger cohort of severe FGR compared to controls. In situ hybridization confirmed PAPPA2 and ERVWE-1 localized to the syncytiotrophoblast.

CONCLUSION

There is global differential expression of placental specific mRNA in the maternal blood in pregnancies complicated by severe preterm FGR. Placental specific mRNA in maternal blood may represent a new class of biomarkers for preterm FGR.

Circulating mRNA for epidermal growth factor-like domain 7 (EGFL7) in maternal blood and early intrauterine growth restriction. A preliminary analysis

OBJECTIVE

To evaluate the alteration in epidermal growth factor-like domain 7 (EGFL7) mRNA expression in maternal blood from pregnancies affected by early-onset intrauterine growth restriction (IUGR) at 20-24 weeks.

METHOD

Case-control study encompassing six women with pregnancies affected by IUGR (cases) matched in a 1 : 7 ratio for gestational age and fetal gender with 42 controls. We quantified EGFL7 mRNA expression in normal and IUGR patients. Matched rank-sum analysis and multiples of median were used to evaluate differences of the marker of interest between cases and controls. Spearman regression analysis was used to correlate the estimated fetal weight at blood sampling with the EGFL7 mRNA values.

RESULTS

The mean observed rank in the IUGR group was significantly higher than that of controls (6.67 vs 4.19, p = 0.01). Pregnancies affected with IUGR exhibited 1.70-fold higher levels of maternal EGFL7 mRNA compared with matched controls (p = 0.014). EGFL7 mRNA values were inversely correlated with estimated fetal weight (Spearman's ρ = -0.429, p = 0.198).

CONCLUSION

Early IUGR at 20-24 weeks' gestation is associated with higher values of EGFL7 expression in maternal plasma.

Cell free expression of hif1α and p21 in maternal peripheral blood as a marker for preeclampsia and fetal growth restriction

Preeclampsia, a severe unpredictable complication of pregnancy, occurs in 6% of pregnancies, usually in the second or third trimester. The specific etiology of preeclampsia remains unclear, although the pathophysiological hallmark of this condition appears to be an inadequate blood supply to the placenta. As a result of the impaired placental blood flow, intrauterine growth restriction (IUGR) and consequential fetal oxidative stress may occur. Consistent with this view, pregnancies complicated by preeclampsia and IUGR are characterized by up-regulation of key transcriptional regulators of the hypoxic response including, hif1α and as well as p53 and its target genes. Recently, the presence of circulating cell-free fetal RNA has been documented in maternal plasma. We speculated that pregnancies complicated by preeclampsia and IUGR, will be associated with an abnormal expression of p53 and/or hif1α related genes in the maternal plasma. Maternal plasma from 113 singleton pregnancies (72 normal and 41 complicated pregnancies) and 19 twins (9 normal and 10 complicated pregnancies) were collected and cell free RNA was extracted. The expression of 18 genes was measured by one step real-time RT-PCR and was analyzed for prevalence of positive/negative expression levels. Results indicate that, among the genes examined, cell free plasma expressions of p21 and hif1α were more prevalent in pregnancies complicated by hypoxia and/or IUGR (p<0.001). To conclude, we present in this manuscript data to support the association between two possible surrogate markers of hypoxia and common complications of pregnancy. More work is needed in order to implement these findings in clinical practice.

Extracellular nucleic acids in maternal circulation as potential biomarkers for placental insufficiency

Since the placenta is being continuously remodeled during normal placental development, extracellular nucleic acids of both fetal and placental origin, packed into either trophoblast-derived apoptotic bodies or shedding syncytiotrophoblast microparticles, may be detected in maternal circulation during the course of normal gestation. Placental-insufficiency-related pregnancy complications have been shown to be associated with excessive placental trophoblast apoptosis and shedding of placenta debris. Recent advances in the field are reviewed with a focus on the diagnostic potential of particular molecular biomarkers and their eventual implementation in the currently used predictive and diagnostic algorithms for placental-insufficiency-related pregnancy complications.

Differential Expression of HrtA1 and ADAM12 in Placentas from Preeclamptic and Normotensive Pregnancies

BACKGROUND

High temperature requirement factor A 1 (HtrA1) and a disintegrin and metalloproteinase 12 (ADAM12), which play roles in placental implantation and placental growth, have been implicated in the pathogenesis of preeclampsia.

METHODS

We investigated relative mRNA expression of both genes in placental tissues from women with preeclampsia (N=18) (average gestational age 36 weeks) and an equal number of women with normotensive pregnancies (average gestational age 39 weeks). Real-time polymerase chain reaction was used to measure mRNA extracted from term placental biopsies. Differential gene expression was evaluated using Student's T-test and fold change analyses.

RESULTS

Statistically significant increases in placental HtRA1 (1.69-fold, p=0.030) and ADAM12 (1.48-fold, p=0.010) mRNA expression were observed among preeclamptic cases as compared with normotensive controls. HtrA1 expression was correlated with maternal age (p-value <0.01) among preeclampsia cases.

CONCLUSION

Increases in HtRA1 and ADAM12 placental gene expression in placentas from preeclamptic pregnancies are consistent with some earlier reports of altered serum protein concentrations in preeclamptic pregnancies. This adds to the literature suggesting that defects in placentation (e.g. involving trophoblast invasion) are of etiologic importance in preeclampsia.

The levels of hypoxia-regulated microRNAs in plasma of pregnant women with fetal growth restriction

MicroRNAs (miRNAs) are short non-coding RNAs that regulate gene expression at the post-transcriptional level. While mostly intracellular, a portion of cellular miRNAs is released to the circulation and their level in the plasma is altered in certain pathological conditions such as cancer, and also during pregnancy. We examined the circulating levels of a set of trophoblastic miRNAs, which we recently found to be regulated by hypoxia, in the plasma of pregnant women with fetal growth restriction (FGR). Pregnancy was associated with increased plasma levels of several placenta-specific miRNAs, compared to non-pregnant controls. Among pregnant women, the overall levels of miRNA species that we analyzed were increased by 1.84-fold (p < or = 0.01) in plasma of women with pregnancies complicated by FGR, but decreased in FGR placentas by 24% (p < or = 0.01) compared to values from uncomplicated pregnancies. Together, our results show that plasma concentration of miRNAs is regulated in pregnancy, and that FGR is associated with increased circulating miRNA levels, highlighting the need to explore plasma miRNAs as potential biomarkers for placental diseases.