Downregulation of notch signaling pathway in late preterm and term placentas from pregnancies complicated by preeclampsia

Measurement of Calprotectin and PTH in the Amniotic Fluid of Early Second Trimester Pregnancies and Their Impact on Fetuses with Growth Disorders: Are Their Levels Related to Oxidative Stress?

Background: During the early stages of human fetal development, the fetal skeleton system is chiefly made up of cartilage, which is gradually replaced by bone. Fetal bone development is mainly regulated by the parathyroid hormone parathormone (PTH) and PTH-related protein, with specific calprotectin playing a substantial role in cell adhesion and chemotaxis while exhibiting antimicrobial activity during the inflammatory osteogenesis process. The aim of our study was to measure the levels of PTH and calprotectin in early second trimester amniotic fluid and to carry out a comparison between the levels observed among normal full-term pregnancies (control group) and those of the groups of embryos exhibiting impaired or enhanced growth. Methods: For the present prospective study, we collected amniotic fluid samples from pregnancies that underwent amniocentesis at 15 to 22 weeks of gestational age during the period 2021-2023. Subsequently, we followed up on all pregnancies closely until delivery. Having recorded fetal birthweights, we then divided the neonates into three groups: small for gestational age (SGA), appropriate for gestational age (AGA), and large for gestational age (LGA). Results: In total, 64 pregnancies, including 14 SGA, 10 LGA, and 40 AGA fetuses, were included in our study. Both substances were detected in early second trimester amniotic fluid in both groups. Concentrations of calprotectin differed significantly among the three groups (p = 0.033). AGA fetuses had a lower mean value of 4.195 (2.415-6.425) IU/mL, whereas LGA fetuses had a higher mean value of 6.055 (4.887-13.950) IU/mL, while SGA fetuses had a mean value of 5.475 (3.400-9.177) IU/mL. Further analysis revealed that only LGA fetuses had significantly higher calprotectin concentrations compared to AGA fetuses (p = 0.018). PTH concentration was similar between the groups, with LGA fetuses having a mean value of 13.18 (9.51-15.52) IU/mL, while SGA fetuses had a mean value of 14.18 (9.02-16.00) IU/mL, and AGA fetuses had similar concentrations of 13.35 (9.05-15.81) IU/mL. The differences in PTH concentration among the three groups were not statistically significant (p = 0.513). Conclusions: Calprotectin values in the amniotic fluid in the early second trimester were higher in LGA fetuses compared to those in the SGA and AGA categories. LGA fetuses can possibly be in a state of low-grade chronic inflammation due to excessive fat deposition, causing oxidative stress in LGA fetuses and, eventually, the release of calprotectin. Moreover, PTH concentrations in the amniotic fluid of early second trimester pregnancies were not found to be statistically correlated with fetal growth abnormalities in either LGA or SGA fetuses. However, the early time of collection and the small number of patients in our study should be taken into account.

Integrated analysis of microRNA and mRNA expression profiles in Preeclampsia

BACKGROUND

Preeclampsia (PE), a pregnancy specific syndrome, is one kind of common gestational hypertension disease, which can cause maternal and perinatal mortality and morbidity. This study was conducted to identify key microRNAs (miRNAs), mRNAs and related signaling pathways in the pathogenesis of PE.

METHODS

Whole transcriptome sequencing and small RNA sequencing of the peripheral blood from 3 PE patients and 3 normal pregnant women were performed. Differential expressed (DE) miRNAs were identified using the DEseq2 package. Target genes of the selected upregulated and downregulated DE miRNAs were predicted. Based on the hypergeometric distribution of DE miRNA target genes, we analyzed GO enrichment and KEGG pathway enrichment using R.

RESULTS

Total 1291 and 1281 novel RNAs were obtained from the preeclampsia patients and healthy individuals. 70 miRNAs were screened out with significant levels with 51 significantly upregulated and 19 significantly downregulated. 44,306 genes were predicted as the targets of these miRNAs. Besides, KEGG pathway analysis revealed that the upregulated miRNAs were enriched in Glycosaminoglycan biosynthesis-chondroitin sulfate / dermatan sulfate, Base excision repair and the downregulated miRNAs were enriched in Tuberculosis, Phagosome.

CONCLUSION

We constructed regulatory networks of miRNAs and target genes, there were 2208 negative miRNA-mRNA interactions in total. The network and pathway information illustrate the potential functions of mRNAs and miRNAs in PE pathogenesis.

Cord blood DNA methylation signatures associated with preeclampsia are enriched for cardiovascular pathways: insights from the VDAART trial

BACKGROUND

Preeclampsia has been associated with maternal epigenetic changes, in particular DNA methylation changes in the placenta. It has been suggested that preeclampsia could also cause DNA methylation changes in the neonate. We examined DNA methylation in relation to gene expression in the cord blood of offspring born to mothers with preeclampsia.

METHODS

This study included 128 mother-child pairs who participated in the Vitamin D Antenatal Asthma Reduction Trial (VDAART), where assessment of preeclampsia served as secondary outcome. We performed an epigenome-wide association study of preeclampsia and cord blood DNA methylation (Illumina 450 K chip). We then examined gene expression of the same subjects for validation and replicated the gene signatures in independent DNA methylation datasets. Lastly, we applied functional enrichment and network analyses to identify biological pathways that could potentially be involved in preeclampsia.

FINDINGS

In the cord blood samples (n = 128), 263 CpGs were differentially methylated (FDR <0.10) in preeclampsia (n = 16), of which 217 were annotated. Top pathways in the functional enrichment analysis included apelin signaling pathway and other endothelial and cardiovascular pathways. Of the 217 genes, 13 showed differential expression (p's < 0.001) in preeclampsia and 11 had been previously related to preeclampsia (p's < 0.0001). These genes were linked to apelin, cGMP and Notch signaling pathways, all having a role in angiogenic process and cardiovascular function.

INTERPRETATION

Preeclampsia is related to differential cord blood DNA methylation signatures of cardiovascular pathways, including the apelin signaling pathway. The association of these cord blood DNA methylation signatures with offspring's long-term morbidities due to preeclampsia should be further investigated.

FUNDING

VDAART is funded by National Heart, Lung, and Blood Institute grants of R01HL091528 and UH3OD023268. HMK is supported by Jane and Aatos Erkko Foundation, Paulo Foundation, and the Pediatric Research Foundation. HM is supported by K01 award from NHLBI (1K01HL146977-01A1). PK is supported by K99HL159234 from NIH/NHLBI.

Hes-related family BHLH transcription factor with YRPW motif 1-activated proteasome 26S subunit, non-ATPase 14 regulates trophoblast function and endometrial angiogenesis

Proteasome 26S subunit, non-ATPase 14 (PSMD14) expression has been previously reported to be reduced in patients with pre-eclampsia (PE). The present study investigated the interaction network associated with the role of PSMD14 in PE. Reverse transcription-quantitative PCR (RT-qPCR) and western blotting were performed to determine the transfection efficacy following plasmid-based gene transfer of PSMD14 into HTR-8/SVneo cells. Cell proliferation was measured using an MTT assay and 5-ethynyl-2'-deoxyuridine staining. The expression of proliferation-related proteins, including Ki67 and PCNA, was determined using western blotting. Wound healing and Transwell assays were performed to measure cell invasion and migration, whilst the expression of migration-related proteins, including MMP2 and MMP9, was measured using western blotting. The angiogenesis of HUVECs following treatment with the HTR-8/SVneo cell culture supernatant was examined using tube formation assay. Following overexpression of Hes-related family BHLH transcription factor with YRPW motif 1 (HEY1) by transfection of pcDNA3.1 expression vector containing full-length human HEY1 or knockdown by transfection of shRNA plasmids targeting HEY1, the expression of HEY1 and PSMD14 was detected using RT-qPCR and western blotting. The potential interaction between HEY1 and the PSMD14 promoter was examined using dual-luciferase reporter and chromatin immunoprecipitation assays. PSMD14 overexpression was found to promote the proliferation, invasion, migration of HTR-8/SVneo cells and the angiogenesis of HUVECs following treatment with the HTR-8/SVneo cell culture supernatant, accompanied by enhanced expression of proliferation and migration-related proteins. Furthermore, the transcription factor HEY1 activated the expression of PSMD14. Knocking down HEY1 expression partially reversed the promoting effects of PSMD14 overexpression on the proliferation, invasion, migration, angiogenesis, proliferation and migration-related protein expression in trophoblasts. In conclusion, HEY1-activated PSMD14 promoted trophoblast proliferation, invasion and angiogenesis. Therefore, HEY1 and PSMD14 can be potential targets for PE treatment.

Common genetic variants with fetal effects on birth weight are enriched for proximity to genes implicated in rare developmental disorders

Birth weight is an important factor in newborn survival; both low and high birth weights are associated with adverse later-life health outcomes. Genome-wide association studies (GWAS) have identified 190 loci associated with maternal or fetal effects on birth weight. Knowledge of the underlying causal genes is crucial to understand how these loci influence birth weight and the links between infant and adult morbidity. Numerous monogenic developmental syndromes are associated with birth weights at the extreme ends of the distribution. Genes implicated in those syndromes may provide valuable information to prioritize candidate genes at the GWAS loci. We examined the proximity of genes implicated in developmental disorders (DDs) to birth weight GWAS loci using simulations to test whether they fall disproportionately close to the GWAS loci. We found birth weight GWAS single nucleotide polymorphisms (SNPs) fall closer to such genes than expected both when the DD gene is the nearest gene to the birth weight SNP and also when examining all genes within 258 kb of the SNP. This enrichment was driven by genes causing monogenic DDs with dominant modes of inheritance. We found examples of SNPs in the intron of one gene marking plausible effects via different nearby genes, highlighting the closest gene to the SNP not necessarily being the functionally relevant gene. This is the first application of this approach to birth weight, which has helped identify GWAS loci likely to have direct fetal effects on birth weight, which could not previously be classified as fetal or maternal owing to insufficient statistical power.

Implications for preeclampsia: hypoxia-induced Notch promotes trophoblast migration

In the first trimester of human pregnancy, low oxygen tension or hypoxia is essential for proper placentation and placenta function. Low oxygen levels and activation of signaling pathways have been implicated as critical mediators in the promotion of trophoblast differentiation, migration, and invasion with inappropriate changes in oxygen tension and aberrant Notch signaling both individually reported as causative to abnormal placentation. Despite crosstalk between hypoxia and Notch signaling in multiple cell types, the relationship between hypoxia and Notch in first trimester trophoblast function is not understood. To determine how a low oxygen environment impacts Notch signaling and cellular motility, we utilized the human first trimester trophoblast cell line, HTR-8/SVneo. Gene set enrichment and ontology analyses identified pathways involved in angiogenesis, Notch and cellular migration as upregulated in HTR-8/SVneo cells exposed to hypoxic conditions. DAPT, a γ-secretase inhibitor that inhibits Notch activation, was used to interrogate the crosstalk between Notch and hypoxia pathways in HTR-8/SVneo cells. We found that hypoxia requires Notch activation to mediate HTR-8/SVneo cell migration, but not invasion. To determine if our in vitro findings were associated with preeclampsia, we analyzed the second trimester chorionic villous sampling (CVS) samples and third trimester placentas. We found a significant decrease in expression of migration and invasion genes in CVS from preeclamptic pregnancies and significantly lower levels of JAG1 in placentas from pregnancies with early-onset preeclampsia with severe features. Our data support a role for Notch in mediating hypoxia-induced trophoblast migration, which may contribute to preeclampsia development.

Differential circular RNA expression profiles in umbilical cord blood exosomes from preeclampsia patients

Background

Exosomal circular RNAs (circRNAs) are emerging as important regulators of physiological development and disease pathogenesis. However, the roles of exosomal circRNAs from umbilical cord blood in preeclampsia (PE) occurrence remains poorly understood.

Methods

We used microarray technology to establish the differential circRNA expression profiles in umbilical cord blood exosomes from PE patients compared with normal controls. Bioinformatics analysis was conducted to further predict the potential effects of the differentially expressed circRNAs and their interactions with miRNAs.

Results

According to the microarray data, we identified 143 significantly up-regulated circRNAs and 161 significantly down-regulated circRNAs in umbilical cord blood exosomes of PE patients compared with controls. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathway analyses showed that circRNA parental genes involved in the regulation of metabolic process, trophoblast growth and invasion were significantly enriched, which play important roles in PE development. Moreover, pathway network was constructed to reveal the key pathways in PE, such as PI3K-Akt signaling pathway. Further circRNA/miRNA interactions analysis demonstrated that most exosomal circRNAs had miRNA binding sites, and some miRNAs were associated with PE.

Conclusions

Our results highlight the importance of exosomal circRNAs in the pathogenesis of PE and lay a foundation for extensive studies on the role of exosomal circRNAs in PE development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12884-021-03777-7.

Regulation of Uterine Spiral Artery Remodeling: a Review

Extravillous trophoblast remodeling of the uterine spiral arteries is essential for promoting blood flow to the placenta and fetal development, but little is known about the regulation of this process. A defect in spiral artery remodeling underpins adverse conditions of human pregnancy, notably early-onset preeclampsia and fetal growth restriction, which result in maternal and fetal morbidity and mortality. Many in vitro studies have been conducted to determine the ability of growth and other factors to stimulate trophoblast cells to migrate across a synthetic membrane. Clinical studies have investigated whether the maternal levels of various factors are altered during abnormal human pregnancy. Animal models have been established to assess the ability of various factors to recapitulate the pathophysiological symptoms of preeclampsia. This review analyzes the results of the in vitro, clinical, and animal studies and describes a nonhuman primate experimental paradigm of defective uterine artery remodeling to study the regulation of vessel remodeling.

Delta-Like 4-Notch signaling regulates trophoblast migration and invasion by targeting EphrinB2

The migration and invasion of trophoblasts during early pregnancy in known to play an important role in placental development, which ensures the oxygen and nutrients to the fetus. Accumulating evidences suggest that Delta-Like 4(DLL4)-Notch signaling may be involved in the process of trophoblast regulation. However, the potential role of DLL4-Notch signaling as well as its molecular mechanism in trophoblast controlling has not been fully studied. This study is designed to investigate the effects of DLL4-Notch signaling on trophoblast functions in human extravillous trophoblast cell line, HTR-8/SVneo. The possible molecular mechanism of DLL4-Notch signaling in trophoblast was also explored. We observed that activation of DLL4-Notch signaling enhanced cell migration and invasion ability while blockage of DLL4-Notch signaling impaired. Control of DLL4-Notch signaling did not affect cell viability. The expression of EphrinB2 was regulated by DLL4-Notch signaling. In addition, up-regulation of EphrinB2 resulted in the similar effects on trophoblast cell functions as DLL4-Notch signaling activation. Moreover, activation of DLL4-Notch signaling reversed the negative impact of EphrinB2 knock-down on trophoblasts migration and invasion. Our study suggested that DLL4-Notch signaling involved in the regulation of trophoblast migration and invasion, which may be induced by direct regulation of EphrinB2 expression.

RITA Is Expressed in Trophoblastic Cells and Is Involved in Differentiation Processes of the Placenta

Preeclampsia (PE) remains a leading cause of maternal and perinatal mortality and morbidity worldwide. Its pathogenesis has not been fully elucidated and no causal therapy is currently available. It is of clinical relevance to decipher novel molecular biomarkers. RITA (RBP-J (recombination signal binding protein J)-interacting and tubulin-associated protein) has been identified as a negative modulator of the Notch pathway and as a microtubule-associated protein important for cell migration and invasion. In the present work, we have systematically studied RITA’s expression in primary placental tissues from patients with early- and late-onset PE as well as in various trophoblastic cell lines. RITA is expressed in primary placental tissues throughout gestation, especially in proliferative villous cytotrophoblasts, in the terminally differentiated syncytiotrophoblast, and in migrating extravillous trophoblasts. RITA’s messenger RNA (mRNA) level is decreased in primary tissue samples from early-onset PE patients. The deficiency of RITA impairs the motility and invasion capacity of trophoblastic cell lines, and compromises the fusion ability of trophoblast-derived choriocarcinoma cells. These data suggest that RITA may play important roles in the development of the placenta and possibly in the pathogenesis of PE.

MicroRNAs in Uteroplacental Vascular Dysfunction

Pregnancy complications of preeclampsia and intrauterine growth restriction (IUGR) are major causes of maternal and perinatal/neonatal morbidity and mortality. Although their etiologies remain elusive, it is generally accepted that they are secondary to placental insufficiency conferred by both failure in spiral artery remodeling and uteroplacental vascular malfunction. MicroRNAs (miRNAs) are small no-coding RNA molecules that regulate gene expression at the post-transcriptional level. Increasing evidence suggests that miRNAs participate in virtually all biological processes and are involved in numerous human diseases. Differentially expressed miRNAs in the placenta are typical features of both preeclampsia and IUGR. Dysregulated miRNAs target genes of various signaling pathways in uteroplacental tissues, contributing to the development of both complications. In this review, we provide an overview of how aberrant miRNA expression in preeclampsia and IUGR impacts the expression of genes involved in trophoblast invasion and uteroplacental vascular adaptation.

MicroRNA-16 is involved in the pathogenesis of pre-eclampsia via regulation of Notch2

In recent years, the role of microRNAs (miRNAs) in pre-eclampsia (PE) has been demonstrated, while the relevant mechanisms of miR-16 in PE await to be unearthed. Thus, the aim of this study is to explore whether miR-16 exerts its function in PE, and we assumed that miR-16 may be implicated in the occurrence of PE by adjusting the biological functions of trophoblast cells via modulating Notch2. Placental tissues of pregnant women with normal pregnancy and PE were collected to detect the expression of miR-16, Notch2, and Notch3. The effects of miR-16 and Notch2 on the biological functions of BeWo and JEG-3 cells were further determined. Expression of miR-16 and Notch2 in trophoblast cells was detected by reverse transcription quantitative polymerase chain reaction and western blot assay. Downregulated Notch2 and upregulated miR-16 and Notch3 were found in placental tissues of PE. There was a negative correlation between Notch2 and miR-16 expression (r = -0.769), and a positive correlation between Notch3 and miR-16 expression (r = 0.676; p < .05). Overexpression of miR-16 inhibited proliferation, migration, and invasion, and facilitated the apoptosis of BeWo and JEG-3 cells, but overexpression of Notch2 reversed this trend. Overexpression of miR-16 inhibited Notch2 expression in BeWo and JEG-3 cells, and Notch2 was the target gene of miR-16. Our study highlights that overexpression of miR-16 is involved in PE by regulating the biological functions of trophoblast cells via inhibition of Notch2. This paper provides a new idea for further study of the pathogenesis of PE.

Role of proteases in dysfunctional placental vascular remodelling in preeclampsia

Preeclampsia is a syndrome characterised by vascular dysfunction, impaired angiogenesis, and hypertension during pregnancy. Even when the precise pathophysiology of preeclampsia remains elusive, impaired vascular remodelling and placental angiogenesis in the placental villi and defective trophoblast invasion of the uterus are proposed as crucial mechanisms in this syndrome. Reduced trophoblast invasion leads to reduced uteroplacental blood flow and oxygen availability and increased oxidative stress. These phenomena trigger the release of soluble factors into the maternal and foetoplacental circulation that are responsible of the clinical features of preeclampsia. New blood vessels generation as well as vascular remodelling are mechanisms that require expression and activity of different proteases, including matrix metalloproteases, a-disintegrin and metalloproteases, and a-disintegrin and metalloprotease with thrombospondin motifs. These proteases exert proteolysis of the extracellular matrix. Additionally, cathepsins, a family of proteolytic enzymes, are primarily located in lysosomes but are also released by cells to the extracellular space. This review focuses on the role that these proteases play in the regulation of the uterine trophoblast invasion and the placental vascular remodelling associated with preeclampsia.

Pregnancy exposure to atmospheric pollution and meteorological conditions and placental DNA methylation

BACKGROUND

Air pollution exposure represents a major health threat to the developing foetus. DNA methylation is one of the most well-known molecular determinants of the epigenetic status of cells. Blood DNA methylation has been proven sensitive to air pollutants, but the molecular impact of air pollution on new-borns has so far received little attention.

OBJECTIVES

We investigated whether nitrogen dioxide (NO₂), particulate matter (PM₁₀), temperature and humidity during pregnancy are associated with differences in placental DNA methylation levels.

METHODS

Whole-genome DNA-methylation was measured using the Illumina's Infinium HumanMethylation450 BeadChip in the placenta of 668 newborns from the EDEN cohort. We designed an original strategy using a priori biological information to focus on candidate genes with a specific expression pattern in placenta (active or silent) combined with an agnostic epigenome-wide association study (EWAS). We used robust linear regression to identify CpGs and differentially methylated regions (DMR) associated with each exposure during short- and long-term time-windows.

RESULTS

The candidate genes approach identified nine CpGs mapping to 9 genes associated with prenatal NO₂ and PM₁₀ exposure [false discovery rate (FDR) p < 0.05]. Among these, the methylation level of 2 CpGs located in ADORA2B remained significantly associated with NO₂ exposure during the 2nd trimester and whole pregnancy in the EWAS (FDR p < 0.05). EWAS further revealed associations between the environmental exposures under study and variations of DNA methylation of 4 other CpGs. We further identified 27 DMRs significantly (FDR p < 0.05) associated with air pollutants exposure and 13 DMRs with meteorological conditions.

CONCLUSIONS

The methylation of ADORA2B, a gene whose expression was previously associated with hypoxia and pre-eclampsia, was consistently found here sensitive to atmospheric pollutants. In addition, air pollutants were associated to DMRs pointing towards genes previously implicated in preeclampsia, hypertensive and metabolic disorders. These findings demonstrate that air pollutants exposure at levels commonly experienced in the European population are associated with placental gene methylation and provide some mechanistic insight into some of the reported effects of air pollutants on preeclampsia.

Elucidating the Pathogenesis of Pre-eclampsia Using In Vitro Models of Spiral Uterine Artery Remodelling

PURPOSE OF REVIEW

The aim of the study is to perform a critical assessment of in vitro models of pre-eclampsia using complementary human and cell line-based studies. Molecular mechanisms involved in spiral uterine artery (SUA) remodelling and trophoblast functionality will also be discussed.

RECENT FINDINGS

A number of proteins and microRNAs have been implicated as key in SUA remodelling, which could be explored as early biomarkers or therapeutic targets for prevention of pre-eclampsia. Various 2D and 3D in vitro models involving trophoblast cells, endothelial cells, immune cells and placental tissue were discussed to elucidate the pathogenesis of pre-eclampsia. Nevertheless, pre-eclampsia is a multifactorial disease, and the mechanisms involved in its pathogenesis are complex and still largely unknown. Further studies are required to provide better understanding of the key processes leading to inappropriate placental development which is the root cause of pre-eclampsia. This new knowledge could identify novel biomarkers and treatment strategies.

Notch2 and Notch3 suppress the proliferation and mediate invasion of trophoblast cell lines

Notch signaling pathways play important roles in cell fate and many diseases, including preeclampsia, the dysregulation of which may be the main cause of maternal mortality. This study aimed to investigate the roles of Notch2 and Notch3 in proliferation and invasion in trophoblast cell lines (BeWo and JAR). Small hairpin RNAs targeting Notch2/Notch3 and Notch2/Notch3-overexpression vectors were designed, constructed and transfected into BeWo and JAR cells. Quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting were then used to detect Notch2 and Notch3 mRNA and protein levels, and confirm the efficiency of silence and overexpression. Flow cytometry assays were conducted to evaluate the cell cycle of the two cell lines, and transwell assays were used to detect migration and invasion. Western blot analysis was also performed to show the alteration of the cell lines' physiological activities at protein level.When Notch2 was downregulated in BeWo cells, proliferation was dramatically promoted, while migration and invasion were significantly inhibited. When Notch2 was upregulated in JAR cells, proliferation was inhibited, but migration and invasion were promoted. After overexpression of Notch3 in BeWo cells, proliferation was downregulated, but migration and invasion were both upregulated. By contrast, the silencing of Notch3 expression in JAR cells significantly enhanced proliferation, but suppressed migration and invasion. These data indicated that Notch2 and Notch3 mediate the invasion and migration of BeWo and JAR cells, and may play a potential role in early onset severe preeclampsia.

Notch signalling in placental development and gestational diseases

Activation of Notch signalling upon cell-cell contact of neighbouring cells controls a plethora of cellular processes such as stem cell maintenance, cell lineage determination, cell proliferation, and survival. Accumulating evidence suggests that the pathway also critically regulates these events during placental development and differentiation. Herein, we summarize our present knowledge about Notch signalling in murine and human placentation and discuss its potential role in the pathophysiology of gestational disorders. Studies in mice suggest that Notch controls trophectoderm formation, decidualization, placental branching morphogenesis and endovascular trophoblast invasion. In humans, the particular signalling cascade promotes formation of the extravillous trophoblast lineage and regulates trophoblast proliferation, survival and differentiation. Expression patterns as well as functional analyses indicate distinct roles of Notch receptors in different trophoblast subtypes. Altered effects of Notch signalling have been detected in choriocarcinoma cells, consistent with its role in cancer development and progression. Moreover, deregulation of Notch signalling components were observed in pregnancy disorders such as preeclampsia and fetal growth restriction. In summary, Notch plays fundamental roles in different developmental processes of the placenta. Abnormal signalling through this pathway could contribute to the pathogenesis of gestational diseases with aberrant placentation and trophoblast function.

A Genome-Wide Association Study of a Biomarker of Nicotine Metabolism

Individuals with fast nicotine metabolism typically smoke more and thus have a greater risk for smoking-induced diseases. Further, the efficacy of smoking cessation pharmacotherapy is dependent on the rate of nicotine metabolism. Our objective was to use nicotine metabolite ratio (NMR), an established biomarker of nicotine metabolism rate, in a genome-wide association study (GWAS) to identify novel genetic variants influencing nicotine metabolism. A heritability estimate of 0.81 (95% CI 0.70-0.88) was obtained for NMR using monozygotic and dizygotic twins of the FinnTwin cohort. We performed a GWAS in cotinine-verified current smokers of three Finnish cohorts (FinnTwin, Young Finns Study, FINRISK2007), followed by a meta-analysis of 1518 subjects, and annotated the genome-wide significant SNPs with methylation quantitative loci (meQTL) analyses. We detected association on 19q13 with 719 SNPs exceeding genome-wide significance within a 4.2 Mb region. The strongest evidence for association emerged for CYP2A6 (min p = 5.77E-86, in intron 4), the main metabolic enzyme for nicotine. Other interesting genes with genome-wide significant signals included CYP2B6, CYP2A7, EGLN2, and NUMBL. Conditional analyses revealed three independent signals on 19q13, all located within or in the immediate vicinity of CYP2A6. A genetic risk score constructed using the independent signals showed association with smoking quantity (p = 0.0019) in two independent Finnish samples. Our meQTL results showed that methylation values of 16 CpG sites within the region are affected by genotypes of the genome-wide significant SNPs, and according to causal inference test, for some of the SNPs the effect on NMR is mediated through methylation. To our knowledge, this is the first GWAS on NMR. Our results enclose three independent novel signals on 19q13.2. The detected CYP2A6 variants explain a strikingly large fraction of variance (up to 31%) in NMR in these study samples. Further, we provide evidence for plausible epigenetic mechanisms influencing NMR.