Homeobox gene HLX1 expression is decreased in idiopathic human fetal growth restriction

Homeobox genes in the human placenta: Twists and turns on the path to find novel targets

Fetal growth restriction (FGR) is a clinically important human pregnancy disorder that is thought to originate early in pregnancy and while its aetiology is not well understood, the disorder is associated with placental insufficiency. Currently treatment for FGR is limited by increased surveillance using ultrasound monitoring and premature delivery, or corticosteroid medication in the third trimester to prolong pregnancy. There is a pressing need for novel strategies to detect and treat FGR at its early stage. Homeobox genes are well established as master regulators of early embryonic development and increasing evidence suggests they are also important in regulating early placental development. Most important is that specific homeobox genes are abnormally expressed in human FGR. This review focusses on identifying the molecular pathways controlled by homeobox genes in the normal and FGR-affected placenta. This information will begin to address the knowledge gap in the molecular aetiology of FGR and lay the foundation for identifying potential diagnostic and therapeutic targets.

Molecular regulators of defective placental and cardiovascular development in fetal growth restriction

Placental insufficiency is one of the major causes of fetal growth restriction (FGR), a significant pregnancy disorder in which the fetus fails to achieve its full growth potential in utero. As well as the acute consequences of being born too small, affected offspring are at increased risk of cardiovascular disease, diabetes and other chronic diseases in later life. The placenta and heart develop concurrently, therefore placental maldevelopment and function in FGR may have profound effect on the growth and differentiation of many organ systems, including the heart. Hence, understanding the key molecular players that are synergistically linked in the development of the placenta and heart is critical. This review highlights the key growth factors, angiogenic molecules and transcription factors that are common causes of defective placental and cardiovascular development.

The Potential Dual Role of H2.0-like Homeobox in the Tumorgenesis and Development of Colorectal Cancer and Its Prognostic Value

Background

H2.0-like homeobox (HLX) is highly expressed in several hematopoietic malignancies. However, the role of HLX in the carcinogenesis and progression of colorectal cancer (CRC) patients has rarely been reported.

Methods

In this study, the data were collected from The Cancer Genome Atlas and Gene Expression Omnibus databases. The diagnostic value of HLX was analyzed by the R package "pROC." The overall survival was estimated using the "survival" and "survminer" packages. A nomogram was established to predict 1-, 3-, and 5-year overall survival of CRC patients. The CIBERSORT software was employed to calculate the relative proportions of 22 immune cells.

Results

HLX expression was downregulated in CRC patients. Remarkably, HLX expression was increased with stage (stage I-stage III) of CRC, and the CRC patients with high HLX expression exhibited a poor prognosis. The promoter methylation level of HLX was prominently increased in CRC samples compared to paracancerous samples. We also found that the six miRNAs target HLX genes, leading to its downregulation, and HLX expression had a negative correlation with its downstream target gene BRI3BP in both CRC and normal samples. Finally, we found that the 12 immune infiltrating cells were observably different between high and low HLX expression groups. The HLX had a significant positive correlation with 8 immune checkpoints (PD-1 (PDCD1), CTLA4, PDL-1 (CD274), PDL-2 (PDCD1LG2), CD80, CD86, LAG3, and TIGIT) expressions.

Conclusion

HLX probably played a carcinostasis role in the early stages of CRC but exhibited a cancer-promoting effect in the advanced stages. Meanwhile, HLX could serve as a reliable prognostic indicator for CRC.

The Placental NLRP3 Inflammasome and Its Downstream Targets, Caspase-1 and Interleukin-6, Are Increased in Human Fetal Growth Restriction: Implications for Aberrant Inflammation-Induced Trophoblast Dysfunction

Fetal growth restriction (FGR) is commonly associated with placental insufficiency and inflammation. Nonetheless, the role played by inflammasomes in the pathogenesis of FGR is poorly understood. We hypothesised that placental inflammasomes are differentially expressed and contribute to the aberrant trophoblast function. Inflammasome gene expression profiles were characterised by real-time PCR on human placental tissues collected from third trimester FGR and gestation-matched control pregnancies (n = 25/group). The functional significance of a candidate inflammasome was then investigated using lipopolysaccharide (LPS)-induced models of inflammation in human trophoblast organoids, BeWo cells in vitro, and a murine model of FGR in vivo. Placental mRNA expression of NLRP3, caspases 1, 3, and 8, and interleukin 6 increased (>2-fold), while that of the anti-inflammatory cytokine, IL-10, decreased (<2-fold) in FGR compared with control pregnancies. LPS treatment increased NLRP3 and caspase-1 expression (>2-fold) in trophoblast organoids and BeWo cell cultures in vitro, and in the spongiotrophoblast and labyrinth in the murine model of FGR. However, the LPS-induced rise in NLRP3 was attenuated by its siRNA-induced down-regulation in BeWo cell cultures, which correlated with reduced activity of the apoptotic markers, caspase-3 and 8, compared to the control siRNA-treated cells. Our findings support the role of the NLRP3 inflammasome in the inflammation-induced aberrant trophoblast function, which may contribute to FGR.

Rs868058 in the Homeobox Gene HLX Contributes to Early-Onset Fetal Growth Restriction

Fetal growth restriction (FGR) is a condition that characterizes fetuses as too small for their gestational age, with an estimated fetal weight (EFW) below the 10th percentile and abnormal Doppler parameters and/or with EFW below the 3rd percentile. We designed our study to demonstrate the contribution of single nucleotide polymorphisms (SNPs) from DLX3 (rs11656951, rs2278163, and rs10459948), HLX (rs2184658, and 868058), ANGPT2 (−35 G > C), and ITGAV (rs3911238, and rs3768777) genes in maternal blood in FGR. A cohort of 380 women with singleton pregnancies consisted of 190 pregnancies with FGR and 190 healthy full-term controls. A comparison of the pregnancies with an early-onset FGR and healthy subjects showed that the AT heterozygotes in HLX rs868058 were significantly associated with an approximately two-fold increase in disease risk (p ≤ 0.050). The AT heterozygotes in rs868058 were significantly more frequent in the cases with early-onset FGR than in late-onset FGR in the overdominant model (OR 2.08 95% CI 1.11−3.89, p = 0.022), and after being adjusted by anemia, in the codominant model (OR 2.45 95% CI 1.23−4.90, p = 0.034). In conclusion, the heterozygous AT genotype in HLX rs868058 can be considered a significant risk factor for the development of early-onset FGR, regardless of adverse pregnancy outcomes in women.

Sex-Biased lncRNA Signature in Fetal Growth Restriction (FGR)

Impaired fetal growth is one of the most important causes of prematurity, stillbirth and infant mortality. The pathogenesis of idiopathic fetal growth restriction (FGR) is poorly understood but is thought to be multifactorial and comprise a range of genetic causes. This research aimed to investigate non-coding RNAs (lncRNAs) in the placentas of male and female fetuses affected by FGR. RNA-Seq data were analyzed to detect lncRNAs, their potential target genes and circular RNAs (circRNAs); a differential analysis was also performed. The multilevel bioinformatic analysis enabled the detection of 23,137 placental lncRNAs and 4263 of them were classified as novel. In FGR-affected female fetuses’ placentas (ff-FGR), among 19 transcriptionally active regions (TARs), five differentially expressed lncRNAs (DELs) and 12 differentially expressed protein-coding genes (DEGs) were identified. Within 232 differentially expressed TARs identified in male fetuses (mf-FGR), 33 encompassed novel and 176 known lncRNAs, and 52 DEGs were upregulated, while 180 revealed decreased expression. In ff-FGR ACTA2-AS1, lncRNA expression was significantly correlated with five DEGs, and in mf-FGR, 25 TARs were associated with DELs correlated with 157 unique DEGs. Backsplicing circRNA processes were detected in the range of H19 lncRNA, in both ff- and mf-FGR placentas. The performed global lncRNAs characteristics in terms of fetal sex showed dysregulation of DELs, DEGs and circRNAs that may affect fetus growth and pregnancy outcomes. In female placentas, DELs and DEGs were associated mainly with the vasculature, while in male placentas, disturbed expression predominantly affected immune processes.

Identification of methylation changes associated with positive and negative growth deviance in Gambian infants using a targeted methyl sequencing approach of genomic DNA

Low birthweight and reduced height gain during infancy (stunting) may arise at least in part from adverse early life environments that trigger epigenetic reprogramming that may favor survival. We examined differential DNA methylation patterns using targeted methyl sequencing of regions regulating gene activity in groups of rural Gambian infants: (a) low and high birthweight (DNA from cord blood (n = 16 and n = 20, respectively), from placental trophoblast tissue (n = 21 and n = 20, respectively), and DNA from peripheral blood collected from infants at 12 months of age (n = 23 and n = 17, respectively)), and, (b) the top 10% showing rapid postnatal length gain (high, n = 20) and the bottom 10% showing slow postnatal length gain (low, n = 20) based on z score change between birth and 12 months of age (LAZ) (DNA from peripheral blood collected from infants at 12 months of age). Using BiSeq analysis to identify significant methylation marks, for birthweight, four differentially methylated regions (DMRs) were identified in trophoblast DNA, compared to 68 DMRs in cord blood DNA, and 54 DMRs in 12‐month peripheral blood DNA. Twenty‐five DMRs were observed to be associated with high and low length for age (LAZ) at 12 months. With the exception of five loci (associated with two different genes), there was no overlap between these groups of methylation marks. Of the 194 CpG methylation marks contained within DMRs, 106 were located to defined gene regulatory elements (promoters, CTCF‐binding sites, transcription factor‐binding sites, and enhancers), 58 to gene bodies (introns or exons), and 30 to intergenic DNA. Distinct methylation patterns associated with birthweight between comparison groups were observed in DNA collected at birth (at the end of intrauterine growth window) compared to those established by 12 months (near the infancy/childhood growth transition). The longitudinal differences in methylation patterns may arise from methylation adjustments, changes in cellular composition of blood or both that continue during the critical postnatal growth period, and in response to early nutritional and infectious environmental exposures with impacts on growth and longer‐term health outcomes.

The role of insulin-like growth factor 2 receptor-mediated homeobox gene expression in human placental apoptosis, and its implications in idiopathic fetal growth restriction

Fetal growth restriction (FGR) is caused by poor placental development and function early in gestation. It is well known that placentas from women with FGR exhibit reduced cell growth, elevated levels of apoptosis and perturbed expression of the growth factors, cytokines and the homeobox gene family of transcription factors. Previous studies have reported that insulin-like growth factor-2 (IGF2) interacts with its receptor-2 (IGF2R) to regulate villous trophoblast survival and apoptosis. In this study, we hypothesized that human placental IGF2R-mediated homeobox gene expression is altered in FGR and contributes to abnormal trophoblast function. This study was designed to determine the association between IGF2R, homeobox gene expression and cell survival in pregnancies affected by FGR. Third trimester placentas were collected from FGR-affected pregnancies (n = 29) and gestation matched with control pregnancies (n = 30). Functional analyses were then performed in vitro using term placental explants (n = 4) and BeWo trophoblast cells. mRNA expression was determined by real-time PCR, while protein expression was examined by immunoblotting and immunohistochemistry. siRNA transfection was used to silence IGF2R expression in placental explants and the BeWo cell-line. cDNA arrays were used to screen for downstream targets of IGF2R, specifically homeobox gene transcription factors and apoptosis-related genes. Functional effects of silencing IGF2R were then verified by β-hCG ELISA, caspase activity assays and a real-time electrical cell-impedance assay for differentiation, apoptosis and cell growth potential, respectively. IGF2R expression was significantly decreased in placentas from pregnancies complicated by idiopathic FGR (P < 0.05 versus control). siRNA-mediated IGF2R knockdown in term placental explants and the trophoblast cell line BeWo resulted in altered expression of homeobox gene transcription factors, including increased expression of distal-less homeobox gene 5 (DLX5), and decreased expression of H2.0-Like Homeobox 1 (HLX) (P < 0.05 versus control). Knockdown of IGF2R transcription increased the expression and activity of caspase-6 and caspase-8 in placental explants, decreased BeWo proliferation and increased BeWo differentiation (all P < 0.05 compared to respective controls). This is the first study linking IGF2R placental expression with changes in the expression of homeobox genes that control cellular signalling pathways responsible for increased trophoblast cell apoptosis, which is a characteristic feature of FGR.

Disrupted placental serotonin synthetic pathway and increased placental serotonin: Potential implications in the pathogenesis of human fetal growth restriction

OBJECTIVES

Placental insufficiency contributes to altered maternal-fetal amino acid transfer, and thereby to poor fetal growth. An important placental function is the uptake of tryptophan and its metabolism to serotonin (5-HT) and kynurenine metabolites, which are essential for fetal development. We hypothesised that placental 5-HT content will be increased in pregnancies affected with fetal growth restriction (FGR).

METHODS

The components of the 5-HT synthetic pathway were determined in chorionic villus samples (CVS) from small-for gestation (SGA) and matched control collected at 10-12 weeks of human pregnancy; and in placentae from third trimester FGR and gestation-matched control pregnancies using the Fluidigm Biomarker array for mRNA expression, the activity of the enzyme TPH and 5-HT concentrations using an ELISA.

RESULTS

Gene expression for the rate limiting enzymes, TPH1 and TPH2; 5-HT transporter, SLC6A4; and 5-HT receptors HTR5A, HTR5B, HTR1D and HTR1E were detected in all CVS and third trimester placentae. No significant difference in mRNA was observed in SGA compared with control. Although there was no significant change in TPH1 mRNA, the mRNA of TPH2 and SLC6A4 was significantly decreased in FGR placentae (p < 0.05), while 5-HT receptor mRNA was significantly increased in FGR compared with control (p < 0.01). Placental TPH enzyme activity was significantly increased with a concomitant increase in the total placental 5-HT concentrations in FGR compared with control.

CONCLUSION

This study reports differential expression and activity of the key components of the 5-HT synthetic pathway associated with the pathogenesis of FGR. Further studies are required to elucidate the functional consequences of increased placental 5-HT in FGR pregnancies.

Formyl peptide receptor-2 is decreased in foetal growth restriction and contributes to placental dysfunction

STUDY QUESTION

What is the association between placental formyl peptide receptor 2 (FPR2) and trophoblast and endothelial functions in pregnancies affected by foetal growth restriction (FGR)?

SUMMARY ANSWER

Reduced FPR2 placental expression in idiopathic FGR results in significantly altered trophoblast differentiation and endothelial function in vitro.

WHAT IS KNOWN ALREADY

FGR is associated with placental insufficiency, where defective trophoblast and endothelial functions contribute to reduced feto-placental growth.

STUDY DESIGN, SIZE, DURATION

The expression of FPR2 in placental tissues from human pregnancies complicated with FGR was compared to that in gestation-matched uncomplicated control pregnancies (n = 25 from each group). Fpr2 expression was also determined in placental tissues obtained from a murine model of FGR (n = 4). The functional role of FPR2 in primary trophoblasts and endothelial cells in vitro was assessed in diverse assays in a time-dependent manner.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Placentae from third-trimester pregnancies complicated by idiopathic FGR (n = 25) and those from gestation-matched pregnancies with appropriately grown infants as controls (n = 25) were collected at gestation 27-40 weeks. Placental tissues were also collected from a spontaneous CBA/CaH × DBA/2 J murine model of FGR. Placental FPR2/Fpr2 mRNA expression was determined by real-time PCR, while protein expression was examined by immunoblotting and immunohistochemistry. siRNA transfection was used to silence FPR2 expression in primary trophoblasts and in human umbilical vein endothelial cells (HUVEC), and the quantitation of cytokines, chemokines and apoptosis was performed following a cDNA array analyses. Functional effects of trophoblast differentiation were measured using HCGB/β-hCG and syncytin-2 expression as well as markers of apoptosis, tumour protein 53 (TP53), caspase 8, B cell lymphoma 2 (BCL2) and BCL associated X (BAX). Endothelial function was assessed by proliferation, network formation and permeability assays.

MAIN RESULTS AND THE ROLE OF CHANCE

Placental FPR2/Fpr2 expression was significantly decreased in FGR placentae (n = 25, P < 0.05) as well as in murine FGR placentae compared to controls (n = 4, P < 0.05). FPR2 siRNA (siFPR2) in term trophoblasts significantly increased differentiation markers, HCGB and syncytin-2; cytokines, interleukin (IL)-6, CXCL8; and apoptotic markers, TP53, caspase 8 and BAX, but significantly reduced the expression of the chemokines CXCL12 and its receptors CXCR4 and CXCR7; CXCL16 and its receptor, CXCR6; and cytokine, IL-10, compared with control siRNA (siCONT). Treatment of HUVECs with siFPR2 significantly reduced proliferation and endothelial tube formation, but significantly increased permeability of HUVECs.

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

Reduced expression of placental FPR2/Fpr2 was observed in the third trimester at delivery after development of FGR, suggesting that FPR2 is associated with FGR pregnancies. However, there is a possibility that the decreased placental FPR2 observed in FGR may be a consequence rather than a cause of FGR, although our in vitro functional analyses using primary trophoblasts and endothelial cells suggest that FPR2 may have a direct or indirect regulatory role on trophoblast differentiation and endothelial function in FGR.

WIDER IMPLICATIONS OF THE FINDINGS

This is the first study linking placental FPR2 expression with changes in the trophoblast and endothelial functions that may explain the placental insufficiency observed in FGR.

STUDY FUNDING/COMPETING INTERESTS

P.M. and P.R.E. received funding from the Australian Institute of Musculoskeletal Science, Western Health, St. Albans, Victoria 3021, Australia. M.L. is supported by a Career Development Fellowship from the National Health and Medical Research Council (NHMRC; Grant no. 1047025). Monash Health is supported by the Victorian Government's Operational Infrastructure Support Programme. The authors declare that there is no conflict of interest in publishing this work.

Altered downstream target gene expression of the placental Vitamin D receptor in human idiopathic fetal growth restriction

Fetal growth restriction (FGR) affects up to 5% of pregnancies and is associated with significant perinatal complications. Maternal deficiency of vitamin D, a secosteroid hormone, is common in FGR-affected pregnancies. We recently demonstrated that decreased expression of the vitamin D receptor (VDR) in idiopathic FGR placentae could impair trophoblast growth. As strict regulation of cell-cycle genes in trophoblast cells is critical for optimal feto-placental growth, we hypothesised that pathologically decreased placental VDR contributes to aberrant regulation of cell-cycle genes. The study aims were to (i) identify the downstream cell-cycle regulatory genes of VDR in trophoblast cells, and (ii) determine if expression was changed in cases of FGR. Targeted cell-cycle gene cDNA arrays were used to screen for downstream targets of VDR in VDR siRNA-transfected BeWo and HTR-8/SVneo trophoblast-derived cell lines, and in third trimester placentae from FGR and gestation-matched control pregnancies (n = 25 each). The six candidate genes identified were CDKN2A, CDKN2D, HDAC4, HDAC6, TGFB2 and TGFB3. TGFB3 was prioritised for further validation, as its expression is largely unknown in FGR. Significantly reduced mRNA and protein expression of TGFB3 was verified in FGR placentae and the BeWo and HTR-8/SVneo trophoblast cell lines, using real-time PCR and immunoblotting respectively. In summary, decreased placental VDR expression alters the expression of regulatory cell-cycle genes in FGR placentae. Aberrant regulation of cell-cycle genes in the placental trophoblast cells may constitute a mechanistic pathway by which decreased placental VDR reduces feto-placental growth.

Expression of Homeobox Gene HLX and its Downstream Target Genes are Altered in Placentae From Discordant Twin Pregnancies

A discordant twin gestation, in which one fetus is significantly growth restricted, compared to the other normal twin, is a unique model that can be used to elucidate the mechanism(s) by which the intrauterine environment affects fetal growth. In many model systems, placental transcription factor genes regulate fetal growth. Transcription factors regulate growth through their activation or repression of downstream target genes that mediate important cell functions. The objective of this study was to determine the expression of the placental HLX homeobox gene transcription factor and its downstream target genes in dizygotic twins with growth discordance. In this cross-sectional study, HLX and its downstream target genes' retinoblastoma 1 (RB1) and cyclin kinase D (CDKN1C) expression levels were determined in placentae obtained from dichorionic diamniotic twin pregnancies (n = 23) where one of the twins was growth restricted. Fetal growth restriction (FGR) was defined as small for gestational age with abnormal umbilical artery Doppler indices when compared with the normal control co-twin. Homeobox gene HLX expression was significantly decreased at both the mRNA and protein levels in FGR twin placentae compared with the normal control co-twin placentae (p < .05). Downstream target genes CDKN1C and RB1 were also significantly decreased and increased, respectively, at both the mRNA and protein levels in FGR twin placentae compared with normal control co-twin placentae (p < .05). Together, these observations suggest an important association between HLX transcription factor expression and abnormal human placental development in discordant twin pregnancies.

Increased methylation and decreased expression of homeobox genes TLX1, HOXA10 and DLX5 in human placenta are associated with trophoblast differentiation

Homeobox genes regulate embryonic and placental development, and are widely expressed in the human placenta, but their regulatory control by DNA methylation is unclear. DNA methylation analysis was performed on human placentae from first, second and third trimesters to determine methylation patterns of homeobox gene promoters across gestation. Most homeobox genes were hypo-methylated throughout gestation, suggesting that DNA methylation is not the primary mechanism involved in regulating HOX genes expression in the placenta. Nevertheless, several genes showed variable methylation patterns across gestation, with a general trend towards an increase in methylation over gestation. Three genes (TLX1, HOXA10 and DLX5) showed inverse gains of methylation with decreasing mRNA expression throughout pregnancy, supporting a role for DNA methylation in their regulation. Proteins encoded by these genes were primarily localised to the syncytiotrophoblast layer, and showed decreased expression later in gestation. siRNA mediated downregulation of DLX5, TLX1 and HOXA10 in primary term villous cytotrophoblast resulted in decreased proliferation and increased expression of differentiation markers, including ERVW-1. Our data suggest that loss of DLX5, TLX1 and HOXA10 expression in late gestation is required for proper placental differentiation and function.

Maternal 25-hydroxyvitamin D is inversely correlated with foetal serotonin

OBJECTIVE

Maternal vitamin D deficiency during pregnancy has been linked to impaired neurocognitive development in childhood. The mechanism by which vitamin D affects childhood neurocognition is unclear but may be via interactions with serotonin, a neurotransmitter involved in foetal brain development. In this study, we aimed to explore associations between maternal and foetal vitamin D concentrations, and foetal serotonin concentrations at term.

STUDY DESIGN AND MEASUREMENTS

Serum 25-hydroxyvitamin D (25(OH)D, nmol/l) and serotonin (5-HT, nmol/l) concentrations were measured in maternal and umbilical cord blood from mother-infant pairs (n = 64). Association between maternal 25(OH)D, cord 25(OH)D and cord serotonin was explored using linear regression, before and after adjusting for maternal serotonin levels. We also assessed the effects of siRNA knockdown of the vitamin D receptor (VDR) and administration of 10 nm 1,25-dihydroxyvitamin D₃ on serotonin secretion in human umbilical vein endothelial cells (HUVECs) in vitro.

RESULTS

We observed an inverse relationship between both maternal and cord 25(OH)D concentrations with cord serotonin concentrations. The treatment of HUVECs with 1,25-dihydroxyvitamin D₃ in vitro decreased the release of serotonin (193·9 ±14·8 nmol/l vs 458·9 ± 317·5 nmol/l, control, P < 0·05). Conversely, inactivation of VDR increased serotonin release in cultured HUVECs.

CONCLUSIONS

These observations provide the first evidence of an inverse relationship between maternal 25(OH)D and foetal serotonin concentrations. We propose that maternal vitamin D deficiency increases foetal serotonin concentrations and thereby contributes to longer-term neurocognitive impairment in infants and children.

Homeobox gene TGIF-1 is increased in placental endothelial cells of human fetal growth restriction

Aberrant placental angiogenesis is associated with fetal growth restriction (FGR). In mice, targeted disruption of the homeobox gene, transforming growth β-induced factor (Tgif-1), which is also a transcription factor, causes defective placental vascularisation. Nevertheless, the role of TGIF-1 in human placental angiogenesis is unclear. We have previously reported increased TGIF-1 expression in human FGR placentae and demonstrated localisation of TGIF-1 protein in placental endothelial cells (ECs). However, its functional role remains to be investigated. In this study, we aimed to specifically compare TGIF-1 mRNA expression in placental ECs isolated from human FGR-affected pregnancies with gestation-matched control pregnancies in two independent cohorts from Australia and Canada and to identify the functional role of TGIF-1 in placental angiogenesis using the human umbilical vein endothelial cell-derived cell line, SGHEC-7, and primary human umbilical vein ECs. Real-time PCR revealed that TGIF-1 mRNA expression was significantly increased in ECs isolated from FGR-affected placentae compared with that of controls. The functional roles of TGIF-1 were determined in ECs after TGIF-1 siRNA transfection. TGIF-1 inactivation in ECs significantly reduced TGIF-1 at both the mRNA and protein levels, as well as the proliferative and invasive potential, but significantly increased the angiogenic potential. Using angiogenesis PCR screening arrays, we identified ITGAV, NRP-1, ANPGT-1 and ANPGT-2 as novel downstream targets of TGIF-1, after TGIF-1 inactivation in ECs. Collectively, these results show that TGIF-1 regulates EC function and the expression of angiogenic molecules; and when abnormally expressed, may contribute to the aberrant placental angiogenesis observed in FGR.

Intrauterine growth restriction - part 1

Intrauterine growth restriction (IUGR) is a major and silent cause of various morbidity and mortality for the fetal and neonatal population. It is defined as a rate of fetal growth that is less than normal for the growth potential of that specific infant. The terms IUGR and small for gestational age (SGA) are often used interchangeably, although there exists subtle differences between the two. IUGR/SGA is an end result of various etiologies that includes maternal, placental and fetal factors and recently added genetic factors too, also contribute to IUGR. In this review article we will cover the antenatal aspect of IUGR and management with proven preventive intervention.

An EG-VEGF-Dependent Decrease in Homeobox Gene NKX3.1 Contributes to Cytotrophoblast Dysfunction: A Possible Mechanism in Human Fetal Growth Restriction

Idiopathic fetal growth restriction (FGR) is frequently associated with placental insufficiency. Previous reports have provided evidence that endocrine gland-derived vascular endothelial growth factor (EG-VEGF), a placental secreted protein, is expressed during the first trimester of pregnancy, controls both trophoblast proliferation and invasion, and its increased expression is associated with human FGR. In this study, we hypothesize that EG-VEGF-dependent changes in placental homeobox gene expressions contribute to trophoblast dysfunction in idiopathic FGR. The changes in EG-VEGF-dependent homeobox gene expressions were determined using a homeobox gene cDNA array on placental explants of 8-12 wks gestation after stimulation with EG-VEGF in vitro for 24 h. The homeobox gene array identified a greater-than-five-fold increase in HOXA9, HOXC8, HOXC10, HOXD1, HOXD8, HOXD9 and HOXD11, while NKX 3.1 showed a greater-than-two-fold decrease in mRNA expression compared with untreated controls. Homeobox gene NKX3.1 was selected as a candidate because it is a downstream target of EG-VEGF and its expression and functional roles are largely unknown in control and idiopathic FGR-affected placentae. Real-time PCR and immunoblotting showed a significant decrease in NKX3.1 mRNA and protein levels, respectively, in placentae from FGR compared with control pregnancies. Gene inactivation in vitro using short-interference RNA specific for NKX3.1 demonstrated an increase in BeWo cell differentiation and a decrease in HTR-8/SVneo proliferation. We conclude that the decreased expression of homeobox gene NKX3.1 downstream of EG-VEGF may contribute to the trophoblast dysfunction associated with idiopathic FGR pregnancies.

Placental vitamin D receptor expression is decreased in human idiopathic fetal growth restriction

Fetal growth restriction (FGR) affects up to 5 % of pregnancies worldwide, and trophoblast function plays a significant role on the outcome. An epidemiological study has linked vitamin D deficiency to adverse perinatal outcomes, which include decreased birth weight. The placenta as an important source of vitamin D regulates its metabolism through the vitamin D receptor (VDR), but the mechanism by which VDR regulates trophoblast function is poorly understood. Our study aimed at determining placental VDR expression in FGR and gestation-matched control (GMC) pregnancies and identifying the actions of VDR in trophoblast differentiation and apoptosis. Placentae were collected from a well-defined cohort of idiopathic FGR and GMC pregnancies. VDR mRNA and protein expressions were determined by PCR, immunohistochemistry and immunoblotting, while functional consequences of VDR inactivation in vitro were determined on BeWo cells by determining changes in differentiation, attachment and apoptosis. Significant decreases in VDR mRNA expression (p = 0.0005) and protein expression (p = 0.0003) were observed in the FGR samples, while VDR inactivation, which showed markers for differentiation, cell attachment and apoptosis, was significantly increased. Thus, decreased placental VDR may contribute to uncontrolled premature differentiation and apoptosis of trophoblasts that are characteristics of idiopathic FGR pregnancies.

KEY MESSAGE

Fetal growth restriction (FGR) affects up to 5 % of all pregnancies worldwide. FGR is the second highest cause of perinatal mortality and morbidity. The placenta plays a pivotal role in vitamin D metabolism during pregnancy. Vitamin D deficiency is associated with adverse pregnancy outcomes. Placental vitamin D receptor expression is decreased in FGR.

Decreased STAT3 in human idiopathic fetal growth restriction contributes to trophoblast dysfunction

Abnormal trophoblast function is associated with fetal growth restriction (FGR). The JAK-STAT pathway is one of the principal signalling mechanisms by which cytokines and growth factors modulate cell proliferation, differentiation, cell migration and apoptosis. The expression of placental JAK-STAT genes in human idiopathic FGR is unknown. In this study, we propose the hypothesis that JAK-STAT pathway genes are differentially expressed in idiopathic FGR-affected pregnancies and contribute to abnormal feto-placental growth by modulating the expression of the amino acid transporter SNAT2, differentiation marker CGB/human chorionic gonadotrophin beta-subunit (β-hCG) and apoptosis markers caspases 3 and 8, and TP53. Expression profiling of FGR-affected placentae revealed that mRNA levels of STAT3, STAT2 and STAT5B decreased by 69, 52 and 50%, respectively, compared with gestational-age-matched controls. Further validation by real-time PCR and immunoblotting confirmed significantly lower STAT3 mRNA and STAT3 protein (total and phosphorylated) levels in FGR placentae. STAT3 protein was localised to the syncytiotrophoblast (ST) in both FGR and control placentae. ST differentiation was modelled by in vitro differentiation of primary villous trophoblast cells from first-trimester and term placentae, and by treating choriocarcinoma-derived BeWo cells with forskolin in cell culture. Differentiation in these models was associated with increased STAT3 mRNA and protein levels. In BeWo cells treated with siRNA targeting STAT3, the mRNA and protein levels of CGB/β-hCG, caspases 3 and 8, and TP53 were significantly increased, while that of SNAT2 was significantly decreased compared with the negative control siRNA. In conclusion, we report that decreased STAT3 expression in placentae may contribute to abnormal trophoblast function in idiopathic FGR-affected pregnancies.

Analysis of homeobox gene action may reveal novel angiogenic pathways in normal placental vasculature and in clinical pregnancy disorders associated with abnormal placental angiogenesis

Homeobox genes are essential for both the development of the blood and lymphatic vascular systems, as well as for their maintenance in the adult. Homeobox genes comprise an important family of transcription factors, which are characterized by a well conserved DNA binding motif; the homeodomain. The specificity of the homeodomain allows the transcription factor to bind to the promoter regions of batteries of target genes and thereby regulates their expression. Target genes identified for homeodomain proteins have been shown to control fundamental cell processes such as proliferation, differentiation, and apoptosis. We and others have reported that homeobox genes are expressed in the placental vasculature, but our knowledge of their downstream target genes is limited. This review highlights the importance of studying the cellular and molecular mechanisms by which homeobox genes and their downstream targets may regulate important vascular cellular processes such as proliferation, migration, and endothelial tube formation, which are essential for placental vasculogenesis and angiogenesis. A better understanding of the molecular targets of homeobox genes may lead to new therapies for aberrant angiogenesis associated with clinically important pregnancy pathologies, including fetal growth restriction and preeclampsia.

Review: placental homeobox genes and their role in regulating human fetal growth

The regulation of fetal growth is multifactorial and complex. Normal fetal growth is determined by the genetically predetermined growth potential and further modulated by maternal, fetal, placental, and environmental factors. The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by several growth factors, cytokines and transcription factors including homeobox genes. This review summarizes our current knowledge regarding homeobox genes in the human placenta and their differential expression and functions in human idiopathic fetal growth restriction (FGR). The review also describes the research strategies that were used for the identification of homeobox genes, their expression in FGR, functional role and target genes of homeobox genes in the trophoblasts and the hormonal regulators of homeobox gene expression in vitro. A better understanding of molecular pathways driven by placental homeobox genes and further elucidation of signaling pathways underlying the hormone-mediated homeobox gene developmental programs may offer novel strategies of targeted therapy for improving feto-placental growth in idiopathic FGR pregnancies.

Downstream targets of the homeobox gene DLX3 are differentially expressed in the placentae of pregnancies affected by human idiopathic fetal growth restriction

Human idiopathic fetal growth restriction (FGR) is associated with placental insufficiency. Previously, we reported that the expression of homeobox gene Distal-less 3 (DLX3) is increased in idiopathic FGR placentae and is a regulator of villous trophoblast differentiation. Here, we identify the downstream targets of DLX3 in trophoblast-derived cell lines. We modelled the high levels of DLX3 in FGR using an over-expression plasmid construct and complemented this using short-interference RNA (siRNA) for inactivation in cultured cells. Using a real-time PCR-based gene profiling, candidate target genes of DLX3 over-expression and inactivation were identified as regulators of trophoblast differentiation; GATA2 and PPARγ. The expression of GATA2 and PPARγ were further assessed in placental tissues and showed increased mRNA and protein levels in FGR-affected tissues compared with gestation-matched controls. We conclude that DLX3 orchestrates the expression of multiple regulators of trophoblast differentiation and that expression of these regulatory genes is abnormal in FGR.

Homeobox gene transforming growth factor β-induced factor-1 (TGIF-1) is a regulator of villous trophoblast differentiation and its expression is increased in human idiopathic fetal growth restriction

Abnormal trophoblast function is associated with human fetal growth restriction (FGR). Targeted disruption of homeobox gene transforming growth β-induced factor (TGIF-1) results in placental dysfunction in the mouse. The role of human TGIF-1 in placental cell function is unknown. The aims of this study were to determine the expression of TGIF-1 in human idiopathic FGR-affected placentae compared with gestation-matched controls (GMC), to elucidate the functional role of TGIF-1 in trophoblasts and to identify its downstream targets. Real-time PCR and immunoblotting revealed that TGIF-1 mRNA and protein expression was significantly increased in FGR-affected placentae compared with GMC (n = 25 in each group P < 0.05). Immunoreactive TGIF-1 was localized to the villous cytotrophoblasts, syncytiotrophoblast, microvascular endothelial cells and in scattered stromal cells in both FGR and GMC. TGIF-1 inactivation in BeWo cells using two independent siRNA resulted in significantly decreased mRNA and protein of trophoblast differentiation markers, human chorionic gonadotrophin (CGB/hCG), syncytin and 3β-hydroxysteroid dehydrogenase/3β-honest significant difference expression. Our data demonstrate that homeobox gene TGIF-1 is a potential up-stream regulator of trophoblast differentiation and the altered TGIF-1 expression may contribute to aberrant villous trophoblast differentiation in FGR.

Membrane-type matrix metalloproteinase 1 regulates trophoblast functions and is reduced in fetal growth restriction

Fetal growth restriction (FGR) results from placental insufficiency to adequately supply the fetus. This insufficiency involves impaired cytotrophoblast functions, including reduced migration and invasion, proliferation, and syncytium formation. Membrane-type matrix metalloproteinase 1 (MT1-MMP) is a key enzyme in these cellular processes. MT1-MMP exists in various forms: a 63-kDa proenzyme is synthesized as primary translation product, which is cleaved into a 57-kDa membrane-anchored active form. We hypothesized that reduced placental MT1-MMP in FGR impairs trophoblast functions. MT1-MMP mRNA and active enzyme was quantified in placentas from FGR and age-matched control pregnancies. MT1-MMP protein was localized in first-trimester and term placentas. Putative MT1-MMP functions in trophoblasts were determined using two blocking antibodies for measuring migration and proliferation, as well as fusion of primary trophoblasts and trophoblast-derived cells. MT1-MMP was expressed predominantly in the syncytiotrophoblast and the villous and extravillous cytotrophoblasts. In FGR placentas, levels of MT1-MMP mRNA and of active MT1-MMP protein were reduced (-34.2%, P < 0.05, and -21.5%, P < 0.01, respectively), compared with age-matched controls. MT1-MMP-blocking antibodies diminished migration, proliferation, and trophoblast fusion. We conclude that reduced placental MT1-MMP in FGR may contribute to the impaired trophoblast functions associated with this pathology.

Homeobox genes and down-stream transcription factor PPARγ in normal and pathological human placental development

The placenta provides critical transport functions between the maternal and fetal circulations during intrauterine development. Formation of this interface is controlled by nuclear transcription factors including homeobox genes. Here we summarize current knowledge regarding the expression and function of homeobox genes in the placenta. We also describe the identification of target transcription factors including PPARγ, biological pathways regulated by homeobox genes and their role in placental development. The role of the nuclear receptor PPARγ, ligands and target genes in human placental development is also discussed. A better understanding of these pathways will improve our knowledge of placental cell biology and has the potential to reveal new molecular targets for the early detection and diagnosis of pregnancy complications including human fetal growth restriction.

EG-VEGF controls placental growth and survival in normal and pathological pregnancies: case of fetal growth restriction (FGR)

Identifiable causes of fetal growth restriction (FGR) account for 30 % of cases, but the remainders are idiopathic and are frequently associated with placental dysfunction. We have shown that the angiogenic factor endocrine gland-derived VEGF (EG-VEGF) and its receptors, prokineticin receptor 1 (PROKR1) and 2, (1) are abundantly expressed in human placenta, (2) are up-regulated by hypoxia, (3) control trophoblast invasion, and that EG-VEGF circulating levels are the highest during the first trimester of pregnancy, the period of important placental growth. These findings suggest that EG-VEGF/PROKR1 and 2 might be involved in normal and FGR placental development. To test this hypothesis, we used placental explants, primary trophoblast cultures, and placental and serum samples collected from FGR and age-matched control women. Our results show that (1) EG-VEGF increases trophoblast proliferation ([(3)H]-thymidine incorporation and Ki67-staining) via the homeobox-gene, HLX (2) the proliferative effect involves PROKR1 but not PROKR2, (3) EG-VEGF does not affect syncytium formation (measurement of syncytin 1 and 2 and β hCG production) (4) EG-VEGF increases the vascularization of the placental villi and insures their survival, (5) EG-VEGF, PROKR1, and PROKR2 mRNA and protein levels are significantly elevated in FGR placentas, and (6) EG-VEGF circulating levels are significantly higher in FGR patients. Altogether, our results identify EG-VEGF as a new placental growth factor acting during the first trimester of pregnancy, established its mechanism of action, and provide evidence for its deregulation in FGR. We propose that EG-VEGF/PROKR1 and 2 increases occur in FGR as a compensatory mechanism to insure proper pregnancy progress.

Hepatocyte growth factor regulates HLX1 gene expression to modulate HTR-8/SVneo trophoblast cells

BACKGROUND

Paracrine signaling of the hepatocyte growth factor (HGF) cytokine plays an important role in survival and invasion ability of placental trophoblasts. However, the intracellular factors and biological pathways underlying these responses remain unclear.

METHODS

This study investigated whether HGF affected the expression of homeobox gene HLX1, which is principally expressed in reproductive tissues and in some immune cells, and evaluated the implications of such in the HGF-induced human trophoblast cell line HTR-8/SVneo.

RESULTS

HGF was found to up-regulate both HLX1 mRNA and protein levels. Transient transfection of small interfering RNA (siRNA) targeting HLX1 abrogated its induction by HGF. Functionally, HLX1 siRNA not only reduced the growth and invasion capacities of HTR-8/SVneo cells at the basal level, but also inhibited these responses induced by HGF treatment.

CONCLUSIONS

HLX1 is an essential downstream signaling component of HGF that leads to growth and invasiveness of trophoblast cells.

The role of homeobox genes in the development of placental insufficiency

Intrauterine growth restriction (IUGR) is an adverse pregnancy outcome associated with significant perinatal and pediatric morbidity and mortality, and an increased risk of chronic disease later in adult life. While a number of maternal, fetal and environmental factors are known causes of IUGR, the majority of IUGR cases are of unknown cause. These IUGR cases are frequently associated with placental insufficiency, possibly as a result of placental maldevelopment. Understanding the molecular mechanisms of abnormal placental development in IUGR associated with placental insufficiency is therefore of increasing importance. Here, we review our understanding of transcriptional control of normal placental development as well as human IUGR associated with placental insufficiency. We also assess the potential for understanding transcriptional control as a means for revealing new molecular targets for the detection, diagnosis and clinical management of IUGR associated with placental insufficiency.

Placental CLIC3 is increased in fetal growth restriction and pre-eclampsia affected human pregnancies

Chloride intracellular channel (CLIC) proteins constitute a subgroup of the glutathione-S-transferase (GSTs) superfamily. In humans, the CLIC family of proteins consists of six members, designated CLIC 1-6, which have a conserved C-terminal 240 residue module and one major transmembrane domain. CLIC proteins regulate fundamental cellular processes including regulation of chloride ion concentration, stabilization of cell membrane potential, trans-epithelial transport, regulation of cell volume and stimulation of apoptotic processes in response to cellular stress. Previously, we described the expression profile of a member of the CLIC family of proteins, CLIC3, in human placentae and fetal membranes. In the current study, we determined CLIC3 expression in placentae from pregnancies complicated with either fetal growth restriction (FGR, n=19), pre-eclampsia (PE, n=16) or both FGR and PE combined (n=12) compared to gestation-matched controls (n=13) using real-time PCR and a CLIC3 specific immunoassay. Significantly increased CLIC3 mRNA and protein were detected in placental extracts from pregnancies with FGR, PE and PE with FGR compared to controls. Our results suggest that increased expression of CLIC3 may play a role in abnormal placental function associated with the human pregnancy disorders FGR and PE.

Over-expression of Hlx homeobox gene in DC2.4 dendritic cell enhances its maturation and antigen presentation

Hlx as a Th1-specific transcription factor, it appears to drive maturation of Th1 and IFN-γ secretion in cooperation with T-bet. In this study, we established a stable Hlx-over-expressed dendritic cell line (DC2.4/Hlx), and investigated the possible effect of Hlx gene on maturation of dendritic cell-line (DC2.4). Results shown that over-expressed Hlx in DC2.4 up-regulated the transcription and expression of IFN-γ, increased the expression of maturation makers including CD40, CD80, CD86, MHC-I and MHC-II. Functional assay for DC2.4/Hlx showed that over-expressed Hlx increased the expression level of interleukin-12 in the supernatant and decreased DC endocytosis when cells were incubated in vitro. Furthermore, using a syngeneic T cell activation model, we found that DC2.4/Hlx could obviously present ovalbumin (OVA) antigen to T cell in OVA pre-immunized mice.

Placental syndecan expression is altered in human idiopathic fetal growth restriction

Pregnancy represents a hypercoagulable state characterized by increased thrombin generation. However, placentas from fetal growth restriction (FGR) pregnancies are characterized by increased fibrin deposition and thrombi in the vasculature, indicative of a further increase in thrombin activation and a disturbance in coagulation in this clinical setting. The cause of the coagulation disturbance observed in FGR pregnancies is currently unknown. Anticoagulant mechanisms are crucial in the regulation of thrombin activity, and current evidence suggests that syndecans are the principal placental anticoagulant proteoglycans. The aim of this study was to determine the localization, distribution, and expression of syndecans 1 to 4 in placentas complicated by idiopathic FGR compared with gestation-matched controls. Immunohistochemistry results revealed that all of the syndecans were localized to cells located closely to the maternal and fetal circulation. The mRNA and protein expression levels of both syndecan 1 and syndecan 2 were significantly decreased in FGR samples compared with controls. This is the first study to demonstrate the differential expression of syndecans 1 to 4 in idiopathic FGR placentas compared with controls. Reduced levels of syndecan expression may result in increased placental thrombosis in the uteroplacental circulation and may therefore contribute to the pathogenesis of FGR.

Regulation of epithelial-mesenchymal transition by homeobox gene DLX4 in JEG-3 trophoblast cells: a role in preeclampsia

The pathogenesis of preeclampsia is unclear but is thought to be related to shallow trophoblast invasion. An invasive phenotype is acquired by trophoblasts through the process of epithelial-mesenchymal transition (EMT). We proposed that EMT in trophoblasts is deregulated in preeclampsia. The homeobox gene DLX4 plays an important role in epithelial-mesenchymal interactions during embryonic and placental development. To elucidate the role of DLX4 in trophoblast EMT and preeclampsia, we investigated the expression of DLX4 in preeclampsia-affected placentas and the effect of DLX4 on EMT in trophoblast-derived JEG-3 cells. DLX4 expression was downregulated in preeclampsia-affected placentas and hypoxic JEG-3 cells. Knockdown of DLX4 by RNA interference (RNAi) inhibited the motility and invasion ability of JEG-3 cells, decreased the expression of E-cadherin, and upregulated the expression of the E-cadherin repressor Snail. Our findings suggest that decreased expression of DLX4 leads to the pathogenesis of preeclampsia by inhibiting EMT in trophoblasts and provides new insight into the pathophysiological mechanism of preeclampsia.

The role of placental homeobox genes in human fetal growth restriction

Fetal growth restriction (FGR) is an adverse pregnancy outcome associated with significant perinatal and paediatric morbidity and mortality, and an increased risk of chronic disease later in adult life. One of the key causes of adverse pregnancy outcome is fetal growth restriction (FGR). While a number of maternal, fetal, and environmental factors are known causes of FGR, the majority of FGR cases remain idiopathic. These idiopathic FGR pregnancies are frequently associated with placental insufficiency, possibly as a result of placental maldevelopment. Understanding the molecular mechanisms of abnormal placental development in idiopathic FGR is, therefore, of increasing importance. Here, we review our understanding of transcriptional control of normal placental development and abnormal placental development associated with human idiopathic FGR. We also assess the potential for understanding transcriptional control as a means for revealing new molecular targets for the detection, diagnosis, and clinical management of idiopathic FGR.

Reduced expression of netrin-1 is associated with fetal growth restriction

The objective of this study was to investigate the expression of netrin-1 in placenta from patients with fetal growth restriction (FGR) and its effect on the viability and apoptosis of human placental microvascular endothelial cells. Thirty-three patients with FGR (including eighteen severe cases) and twenty-four normal late pregnant women were investigated. The expression of netrin-1 in placental tissues was detected by employing immunohistochemistry, real-time PCR, and Western blotting. Human placental microvascular endothelial cells were isolated and, after treatment with netrin-1, examined for their viability and apoptosis by using MTT assay and flow cytometry. We demonstrated that the netrin-1 was present in placenta. Netrin-1 was significantly reduced in pregnant women with FGR as compared with the controls. Furthermore, netrin-1 enhanced the viability of human placental microvascular endothelial cells and inhibited their apoptosis. Netrin-1 may regulate the development of placental vessels and plays a key role in the pathogenesis of FGR.

Inter- and intra-individual variation in allele-specific DNA methylation and gene expression in children conceived using assisted reproductive technology

Epidemiological studies have reported a higher incidence of rare disorders involving imprinted genes among children conceived using assisted reproductive technology (ART), suggesting that ART procedures may be disruptive to imprinted gene methylation patterns. We examined intra- and inter-individual variation in DNA methylation at the differentially methylated regions (DMRs) of the IGF2/H19 and IGF2R loci in a population of children conceived in vitro or in vivo. We found substantial variation in allele-specific methylation at both loci in both groups. Aberrant methylation of the maternal IGF2/H19 DMR was more common in the in vitro group, and the overall variance was also significantly greater in the in vitro group. We estimated the number of trophoblast stem cells in each group based on approximation of the variance of the binomial distribution of IGF2/H19 methylation ratios, as well as the distribution of X chromosome inactivation scores in placenta. Both of these independent measures indicated that placentas of the in vitro group were derived from fewer stem cells than the in vivo conceived group. Both IGF2 and H19 mRNAs were significantly lower in placenta from the in vitro group. Although average birth weight was lower in the in vitro group, we found no correlation between birth weight and IGF2 or IGF2R transcript levels or the ratio of IGF2/IGF2R transcript levels. Our results show that in vitro conception is associated with aberrant methylation patterns at the IGF2/H19 locus. However, very little of the inter- or intra-individual variation in H19 or IGF2 mRNA levels can be explained by differences in maternal DMR DNA methylation, in contrast to the expectations of current transcriptional imprinting models. Extraembryonic tissues of embryos cultured in vitro appear to be derived from fewer trophoblast stem cells. It is possible that this developmental difference has an effect on placental and fetal growth.

We have screened a population of children conceived in vitro for epigenetic alterations at two loci that carry parent-of-origin specific methylation marks. We made the observation that epigenetic variability was greater in extraembryonic tissues than embryonic tissues in both groups, as has also been demonstrated in the mouse. The greater level of intra-individual variation in extraembryonic tissues of the in vitro group appears to result from these embryos having fewer trophoblast stem cells. We also made the unexpected observation that variability in parental origin-dependent epigenetic marking was poorly correlated with gene expression. In fact, there is such a high level of inter-individual variation in IGF2 transcript level that the presumed half-fold reduction in IGF2 mRNA accounted for by proper transcriptional imprinting versus complete loss of imprinting would account for less than 5% of the total population variance. Given this level of variability in the expression of an imprinted gene, the presumed operation of “parental conflict” as the selective force acting to maintain imprinted gene expression at the IGF2/H19 locus in the human should be revisited.

Downstream targets of homeobox gene HLX show altered expression in human idiopathic fetal growth restriction

Fetal growth restriction (FGR), a clinically significant pregnancy disorder, is poorly understood at the molecular level. This study investigates idiopathic FGR associated with placental insufficiency. Previously, we showed that the homeobox gene HLX is expressed in placental trophoblast cells and that HLX expression is significantly decreased in human idiopathic FGR. Here, we used the novel approach of identifying downstream targets of HLX in cell culture to detect potentially important genes involved in idiopathic FGR. Downstream targets were revealed by decreasing HLX expression in cultured trophoblast cells with HLX-specific small interfering RNAs to model human idiopathic FGR and comparing these levels with controls using a real-time PCR-based gene profiling system. Changes in candidate HLX target mRNA levels were verified in an independent trophoblast cell line, and candidate target gene expression was assessed in human idiopathic FGR-affected placentae (n = 25) compared with gestation-matched controls (n = 25). The downstream targets RB1 and MYC, cell cycle regulatory genes, showed significantly increased mRNA levels in FGR-affected tissues compared with gestation-matched controls, whereas CCNB1, ELK1, JUN, and CDKN1 showed significantly decreased mRNA levels (n = 25, P < 0.001, t-test). The changes for RB1 and CDKN1C were verified by Western blot analysis in FGR-affected placentae compared with gestation-matched controls (n = 6). We conclude that cell cycle regulatory genes RB1, MYC, CCNB1, ELK1, JUN, and CDKN1C, which control important trophoblast cell functions, are targets of HLX.

Sequence variants in the HLX gene at chromosome 1q41-1q42 in patients with diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a common birth defect for which few causative genes have been identified. Several candidate regions containing genes necessary for normal diaphragm development have been identified, including a 4-5 Mb deleted region at chromosome 1q41-1q42 from which the causative gene(s) has/have not been cloned. We selected the HLX gene from this interval as a candidate gene for CDH, as the Hlx homozygous null mouse has been reported to have diaphragmatic defects and the gene was described as being expressed in the murine diaphragm. We re-sequenced HLX in 119 CDH patients and identified four novel single nucleotide substitutions that predict amino acid changes: p.S12F, p.S18L, p.D173Y and p.A235V. These sequence alterations were all present in patients with isolated CDH, although patients with both isolated CHD and CDH with additional anomalies were studied. The single-nucleotide substitutions were absent in more than 186 control chromosomes. In-situ hybridization studies confirmed expression of Hlx in the developing murine diaphragm at the site of the junction of the diaphragm and the liver. Although functional studies to determine if these novel sequence variants altered the inductive activity of Hlx on the alpha-smooth muscle actin and SM22alpha promoters showed no significant differences between the variants and wild-type Hlx, sequence variants in HLX may still be relevant in the pathogenesis of CDH in combination with additional genetic and environmental factors.

GAPDH, 18S rRNA and YWHAZ are suitable endogenous reference genes for relative gene expression studies in placental tissues from human idiopathic fetal growth restriction

Comparative gene expression studies in the placenta may provide insights into molecular mechanisms of important genomic alterations in pregnancy disorders. Endogenous reference genes often referred to as housekeeping genes, are routinely used to normalise gene expression levels. For this reason, it is important that these genes be empirically evaluated for stability between placental samples including samples from complicated pregnancies. To address this issue, six candidate housekeeping genes including several commonly used ones (ACTB, GAPDH, 18S rRNA, TBP, SDHA and YWHAZ) were investigated for their expression stability in placentae obtained from pregnancies complicated by idiopathic FGR (n=25) and gestation-matched control pregnancies (n=25). Real-time PCR was performed using pre-validated gene expression assay kits. The geNorm program was used for gene stability measure (M) for the entire housekeeping genes in all control and FGR-affected placental samples. Results showed that GAPDH and 18S rRNA were most stable, with an average expression stability of M=0.441 and 0.443, respectively, followed by YWHAZ (M=0.472). SDHA, ACTB and TBP were the least stable housekeeping genes (M=0.495, 0.548 and 1.737, respectively). We recommend geometric averaging of two or more housekeeping genes to determine relative gene expression levels between FGR-affected and control placentae.

Homeodomain protein HLX is expressed primarily in cytotrophoblast cell types in the early pregnancy human placenta

Homeobox genes are a large family of transcription factors. Of these, the HLX homeobox gene (previously known as HLX1 and HB24) is important for normal placentation. We have previously shown that HLX mRNA expression is significantly reduced in fetal growth-restricted human placentae compared with control placentae. In this study, a rabbit polyclonal antibody to the homeodomain protein HLX was raised and characterised. Western analysis revealed a protein of 50 kDa. HLX protein was detected in cellular nuclei in the cytotrophoblast-derived cell lines HTR8/SVneo, SGHPL-4, JEG-3, JAR and BeWo. Dual labelling with cytokeratin 7 was used to determine the spatial distribution of HLX in the early placenta and fetal membranes, showing both a perinuclear and punctate nuclear distribution for HLX. In the early pregnancy placenta HLX was localised to villous cytotrophoblast, and extravillous cytotrophoblast nuclei in the proximal regions of the cytotrophoblast cell columns, but was not detected at significant levels in the syncytiotrophoblast. In first trimester placental bed biopsies, HLX expression was not localised to the nucleus but instead was found in the cytoplasm. We conclude that HLX is primarily expressed in cytotrophoblast cell types in the human placenta and propose that HLX is involved in cytotrophoblast proliferation and downregulation of cell differentiation.

Novel homeobox genes are differentially expressed in placental microvascular endothelial cells compared with macrovascular cells

Angiogenesis is fundamental to normal placental development and aberrant angiogenesis contributes substantially to placental pathologies. The complex process of angiogenesis is regulated by transcription factors leading to the formation of endothelial cells that line the microvasculature. Homeobox genes are important transcription factors that regulate vascular development in embryonic and adult tissues. We have recently shown that placental homeobox genes HLX, DLX3, DLX4, MSX2 and GAX are expressed in placental endothelial cells. Hence, the novel homeobox genes TLX1, TLX2, TGIF, HEX, PHOX1, MEIS2, HOXB7, and LIM6 were detected that have not been reported in endothelial cells previously. Importantly, these homeobox genes have not been previously reported in placental endothelial cells and, with the exception of HEX, PHOX1 and HOXB7, have not been described in any other endothelial cell type. Reverse transcriptase PCR was performed on cDNA from freshly isolated placental microvascular endothelial cells (PLEC), and the human placental microvascular endothelial cell line HPEC. cDNAs prepared from control term placentae, human microvascular endothelial cells (HMVEC) and human umbilical vein macrovascular endothelial cells (HUVEC) were used as controls. PCR analyses showed that all novel homeobox genes tested were expressed by all endothelial cells types. Furthermore, real-time PCR analyses revealed that homeobox genes TLX1, TLX2 and PHOX1 relative mRNA expression levels were significantly decreased in HUVEC compared with microvascular endothelial cells, while the relative mRNA expression levels of MEIS2 and TGIF were significantly increased in macrovascular cells compared with microvascular endothelial cells. Thus we have identified novel homeobox genes in microvascular endothelial cells and have shown that homeobox genes are differentially expressed between micro- and macrovascular endothelial cells.

In vitro differentiation of villous trophoblasts from pregnancies complicated by intrauterine growth restriction with and without pre-eclampsia

Highly purified (>99.99%) primary villous cytotrophoblasts from uncomplicated pregnancies and pregnancies complicated with intrauterine growth restriction (IUGR) alone, IUGR with pre-eclampsia (IUGR-PE) and PE alone were cultured for 5days and the extent of differentiation into syncytiotrophoblasts measured in terms of syncytialisation and secretion of chorionic gonadotropin (hCG) and placental lactogen (hPL). Three separate phenotypes were observed: (1) normal and IUGR-PE cells showed low syncytialisation and secretion of hCG and hPL, (2) IUGR cells showed the highest levels of syncytialisation and secretion and (3) PE cells showed high syncytialisation but low secretion. These results strongly suggest IUGR, IUGR-PE and PE to be distinct conditions in which villous cytotrophoblasts are either exposed to different environments or are genetically different.

Homeobox gene HLX1 is a regulator of colony stimulating factor-1 dependent trophoblast cell proliferation

The cytokine colony stimulating factor-1 (CSF-1) is a key regulator of the proliferation, differentiation and activation of mononuclear phagocytes. CSF-1 also plays an important role in reproduction. CSF-1 is produced in the placenta and activates signal transduction pathways that significantly increase the proliferation of placental trophoblast cells in culture. The target genes activated by CSF-1 mediated signal transduction in the nucleus are not well understood. Here, we use placental trophoblast cells to investigate potential downstream effector genes of CSF-1. HLX1 is a homeobox gene that controls proliferation in embryonic cell types and haematopoietic cell lineages. We have shown HLX1 is expressed in placental trophoblast cells but its functional role in the placenta is unknown. Following CSF-1 stimulation, HLX1 mRNA expression was significantly increased in SGHPL-4 and HTR-8/SVNeo cultured trophoblast cells (p<0.001, n=3). siRNA-mediated reduction of HLX1 mRNA levels with four independent oligonucleotides (siRNAs) resulted in significantly decreased cell proliferation in both cell lines (p<0.001, n=4). When HLX1 mRNA levels were reduced in the presence of CSF-1 stimulation, proliferation remained significantly decreased (p<0.001, n=4) in both the cell lines. We have shown for the first time that a homeobox gene, HLX1, is a downstream effector gene of CSF-1, that HLX1 regulates placental cell proliferation and that CSF-1 acts, at least in part, through HLX1 to control cell proliferation.

Homeobox genes are differentially expressed in macrovascular human umbilical vein endothelial cells and microvascular placental endothelial cells

Angiogenesis is fundamental to normal placental development. Aberrant angiogenesis within the placental terminal villi is a characteristic of significant placental pathologies and includes structural and vascular abnormalities as well as altered endothelial cell function, which substantially impacts on maternal-fetal exchange. Homeobox gene transcription factors regulate vascular development in embryonic and adult tissues, but their role in the placental microvasculature is not well known. In this study, we isolated and enriched human placental microvascular endothelial cells (PLEC) by a perfusion-based method and compared homeobox gene expression between PLEC and macrovascular human umbilical vein endothelial cells (HUVEC). Reverse transcriptase PCR detected mRNA expression of homeobox genes DLX3, DLX4, MSX2, GAX and HLX1 in both PLEC and HUVEC. DLX4 and HLX1 have not been previously detected in PLEC and with the exception of GAX, none of these homeobox genes have been previously identified in HUVEC. There was lower expression of HLX1 mRNA in HUVEC compared with PLEC. Using real-time PCR analysis PLEC HLX1 mRNA expression relative to housekeeping gene GAPDH was 0.9+/-0.06 fold of the calibrator (n=6) versus 0.2+/-0.06 (n=6) for HUVEC, p<0.001. These data provided evidence of heterogeneity in homeobox gene expression between microvascular PLEC and macrovascular HUVEC that most likely reflects significant differences in endothelial cell function in the two different cellular environments.