Expression of matrix metalloproteinase 12 is highly specific for non-proliferating invasive trophoblasts in the first trimester and temporally regulated by oxygen-dependent mechanisms including HIF-1A

Lnc-HZ06 down-regulates HIF1α protein levels in CoCl2-exposed hypoxic trophoblast cells and villous tissues of miscarriage patients

Hypoxia plays significant roles in various biological processes. In recent study, we have found that a novel lnc-HZ06 promotes the SUMOylation of HIF1α in hypoxic human trophoblast cells. Since environmental cobalt (Co) exposure causes trophoblast cell hypoxia, whether and how lnc-HZ06 might regulate the protein levels of HIF1α, an important biomarker of hypoxia, in CoCl2-exposed hypoxic trophoblast cells is still unexplored. In this study, we find that lnc-HZ06 is highly expressed in CoCl2-exposed trophoblast cells; and lnc-HZ06 further down-regulates HIF1α protein levels. In details, (1) lnc-HZ06 up-regulates METTL14 (methyltransferase-like 14) and increases m6A (N6-methyladenosine) RNA modification levels on VHL (a ubiquitin E3 ligase of HIF1α) mRNA, and thus enhances its mRNA stability and up-regulates VHL mRNA levels. (2) VHL interacts with the SUMOylated HIF1α and promotes the ubiquitination of HIF1α, and finally lnc-HZ06 promotes the ubiquitination degradation of HIF1α protein in CoCl2-exposed hypoxic trophoblast cells. Therefore, lnc-HZ06 promotes VHL-mediated HIF1α protein degradation and down-regulates HIF1α protein levels. The cellular mechanisms in hypoxic trophoblast cells were partially consistent to those in villous tissues of patients with unexplained miscarriage (UM), expect for no significantly different Co content in UM and healthy control (HC) villous tissues. Collectively, this study discovers novel regulatory roles of lnc-HZ06 and m6A modification and post-translational modification (SUMO/Ubiquitin) in HIF1α protein levels in hypoxic human trophoblast cells.

Matrix metalloproteinase-12 by M2 macrophages induced epithelial to mesenchymal transition in chronic rhinosinusitis with nasal polyps

Th2 inflammation and epithelial-mesenchymal transition (EMT) play crucial roles in the pathophysiology of chronic rhinosinusitis with nasal polyps (CRSwNP). This study aimed to investigate the hypothesis that MMP-12, produced by M2 macrophages, induces EMT in nasal epithelial cells, thereby contributing to airway inflammation and remodeling in CRSwNP. The expression levels of MMP-12 were measured by RT-PCR in CRS nasal mucosa and THP-1 cells. mRNA and protein levels of E-cadherin, vimentin, α-SMA, and fibronectin were determined using RT-PCR, western blotting, and immunofluorescence staining in primary nasal epithelial cells and air-liquid interface culture. The expression of MMP-12 was significantly increased in CRSwNP and M2-like THP-1 cells. In co-culture with primary nasal epithelial cells and M2-like THP-1 cells, E-cadherin expression was inhibited, and fibronectin, vimentin, and α-SMA expression were increased. MMP-12 decreased E-cadherin but induced fibronectin, vimentin, and α-SMA mRNA and protein expression in primary nasal epithelial cells and air-liquid interface culture. MMP408, an MMP-12 inhibitor, inhibited EMT-related factors. These findings suggest that MMP-12 expression in M2 macrophages induces EMT in nasal epithelial cells and may contribute to the pathogenesis of CRSwNP.

High-throughput mRNA-seq atlas of human placenta shows vast transcriptome remodeling from first to third trimester†

The placenta, composed of chorionic villi, changes dramatically across gestation. Understanding differences in ongoing pregnancies are essential to identify the role of chorionic villi at specific times in gestation and develop biomarkers and prognostic indicators of maternal-fetal health. The normative mRNA profile is established using next-generation sequencing of 124 first trimester and 43 third trimester human placentas from ongoing healthy pregnancies. Stably expressed genes (SEGs) not different between trimesters and with low variability are identified. Differential expression analysis of first versus third trimester adjusted for fetal sex is performed, followed by a subanalysis with 23 matched pregnancies to control for subject variability using the same genetic and environmental background. Placenta expresses 14,979 polyadenylated genes above sequencing noise (transcripts per million > 0.66), with 10.7% SEGs across gestation. Differentially expressed genes (DEGs) account for 86.7% of genes in the full cohort [false discovery rate (FDR) < 0.05]. Fold changes highly correlate between the full cohort and subanalysis (Pearson = 0.98). At stricter thresholds (FDR < 0.001, fold change > 1.5), there remains 50.1% DEGs (3353 upregulated in first and 4155 upregulated in third trimester). This is the largest mRNA atlas of healthy human placenta across gestation, controlling for genetic and environmental factors, demonstrating substantial changes from first to third trimester in chorionic villi. Specific differences and SEGs may be used to understand the specific role of the chorionic villi throughout gestation and develop first trimester biomarkers of placental health that transpire across gestation, which can be used for future development of biomarkers for maternal-fetal health.

Hypoxia causes trophoblast cell ferroptosis to induce miscarriage through lnc-HZ06/HIF1α-SUMO/NCOA4 axis

Defects of human trophoblast cells may induce miscarriage (abnormal early embryo loss), which is generally regulated by lncRNAs. Ferroptosis is a newly identified iron-dependent programmed cell death. Hypoxia is an important and unavoidable feature in mammalian cells. However, whether hypoxia might induce trophoblast cell ferroptosis and then induce miscarriage, as well as regulated by a lncRNA, was completely unknown. In this work, we discovered at the first time that hypoxia could result in ferroptosis of human trophoblast cells and then induce miscarriage. We also identified a novel lncRNA (lnc-HZ06) that simultaneously regulated hypoxia (indicated by HIF1α protein), ferroptosis, and miscarriage. In mechanism, HIF1α-SUMO, instead of HIF1α itself, primarily acted as a transcription factor to promote the transcription of NCOA4 (ferroptosis indicator) in hypoxic trophoblast cells. Lnc-HZ06 promoted the SUMOylation of HIF1α by suppressing SENP1-mediated deSUMOylation. HIF1α-SUMO also acted as a transcription factor to promote lnc-HZ06 transcription. Thus, both lnc-HZ06 and HIF1α-SUMO formed a positive auto-regulatory feedback loop. This loop was up-regulated in hypoxic trophoblast cells, in RM villous tissues, and in placental tissues of hypoxia-treated mice, which further induced ferroptosis and miscarriage by up-regulating HIF1α-SUMO-mediated NCOA4 transcription. Furthermore, knockdown of either murine lnc-hz06 or Ncoa4 could efficiently suppress ferroptosis and alleviate miscarriage in hypoxic mouse model. Taken together, this study provided new insights in understanding the regulatory roles of lnc-HZ06/HIF1α-SUMO/NCOA4 axis among hypoxia, ferroptosis, and miscarriage, and also offered an effective approach for treatment against miscarriage.

High-throughput mRNA-seq atlas of human placenta shows vast transcriptome remodeling from first to third trimester

Background

The placenta, composed of chorionic villi, changes dramatically across gestation. Understanding differences in ongoing pregnancies are essential to identify the role of chorionic villi at specific times in gestation and develop biomarkers and prognostic indicators of maternal- fetal health.

Methods

The normative mRNA profile is established using next-generation sequencing of 124 first trimester and 43 third trimester human placentas from ongoing healthy pregnancies. Stably expressed genes not different between trimesters and with low variability are identified. Differential expression analysis of first versus third trimester adjusted for fetal sex is performed, followed by a subanalysis with 23 matched pregnancies to control for subject variability using the same genetic and environmental background.

Results

Placenta expresses 14,979 mRNAs above sequencing noise (TPM>0.66), with 1,545 stably expressed genes across gestation. Differentially expressed genes account for 86.7% of genes in the full cohort (FDR<0.05). Fold changes highly correlate between the full cohort and subanalysis (Pearson = 0.98). At stricter thresholds (FDR<0.001, fold change>1.5), there are 6,941 differentially expressed protein coding genes (3,206 upregulated in first and 3,735 upregulated in third trimester).

Conclusion

This is the largest mRNA atlas of healthy human placenta across gestation, controlling for genetic and environmental factors, demonstrating substantial changes from first to third trimester in chorionic villi. Specific differences and stably expressed genes may be used to understand the specific role of the chorionic villi throughout gestation and develop first trimester biomarkers of placental health that transpire across gestation, which can be used for future development of biomarkers in maternal-fetal disease.

Are there foetal extracellular vesicles in maternal blood? Prospects for diagnostic biomarker discovery

Prenatal diagnosis of congenital disease improves clinical outcomes; however, as many as 50% of congenital heart disease cases are missed by current ultrasound screening methods. This indicates a need for improved screening technology. Extracellular vesicles (EVs) have attracted enormous interest in recent years for their potential in diagnostics. EVs mediate endocrine signalling in health and disease and are known to regulate aspects of embryonic development. Here, we critically evaluate recent evidence suggesting that EVs released from the foetus are able to cross the placenta and enter the maternal circulation. Furthermore, EVs from the mother appear to be transported in the reverse direction, whilst the placenta itself acts as a source of EVs. Experimental work utilising rodent models employing either transgenically encoded reporters or application of fluorescent tracking dyes provide convincing evidence of foetal-maternal crosstalk. This is supported by clinical data demonstrating expression of placental-origin EVs in maternal blood, as well as limited evidence for the presence of foetal-origin EVs. Together, this work raises the possibility that foetal EVs present in maternal blood could be used for the diagnosis of congenital disease. We discuss the challenges faced by researchers in translating these basic science findings into a clinical non-invasive prenatal test.

Nuclear Factor-Kappa B-induced miRNA-518a-5p represses trophoblast cell migration and invasion by the Nuclear Factor-Kappa B pathway

Preeclampsia is associated with the insufficient invasion of trophoblasts. NF-κB is a transcription factor in almost all mammalian cells and has been validated to be upregulated in the maternal circulation and placenta of women with preeclampsia. MiR-518a-5p is also overexpressed in pre-eclamptic placenta. The present study was designed to explore whether NF-κB can transcriptionally activate miR-518a-5p and investigate the influences of miR-518a-5p on the viability, apoptosis, migration, and invasion of HTR8/SVneo trophoblast. In situ hybridization and real time polymerase chain reaction were used to reveal miR-518a-5p expression in placenta tissues and HTR8/SVneo cells, respectively. Cell migration and invasion were detected using Transwell inserts. Our findings indicated that NF-κB p52, p50, and p65 can bind to miR-518a-5p gene promoter. MiR-518a-5p further influences the levels of p50 and p65 but not p52. HTR8/SVneo cell viability and apoptosis were not influenced by miR-518a-5p. However, miR-518a-5p represses the migratory/invasive capacities of HTR8/SVneo cell and decreased gelatinolytic activity of MMP2 and MMP9, which was reversed by an NF-κB inhibitor. To sum up, miR-518a-5p is induced by NF-κB and represses trophoblast cell migration and invasion by the NF-κB pathway.

An old friend with a new face: YB-1 and its role in healthy pregnancy and pregnancy-associated complications

By promoting tissue invasion, cell growth and angiogenesis, the Y-box binding protein (YB-1) became famous as multifunctional oncoprotein. However, this designation is telling only part of the story. There is one particular time in life when actual tumorigenic-like processes become undoubtedly welcome, namely pregnancy. It seems therefore reasonable that YB-1 plays also a crucial role in reproduction, and yet this biological aspect of the cold-shock protein has been overlooked for many years. To overcome this limitation, we would like to propose a new perspective on YB-1 and emphasize its pivotal functions in healthy pregnancy and pregnancy-related complications. Moreover, we will discuss findings obtained from cancer research in the light of reproductive events to elucidate the importance of YB-1 at the feto-maternal interface.

Modeling Trophoblast Cell-Guided Uterine Spiral Artery Transformation in the Rat

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-guided uterine spiral artery remodeling, which resembles human placentation. Uterine spiral arteries are extensively remodeled to deliver sufficient supply of maternal blood and nutrients to the developing fetus. Inadequacies in these key processes negatively impact fetal growth and development. Recent innovations in genome editing combined with effective phenotyping strategies have provided new insights into placental development. Application of these research approaches has highlighted both conserved and species-specific features of hemochorial placentation. The review provides foundational information on rat hemochorial placental development and function during physiological and pathological states, especially as related to the invasive trophoblast cell-guided transformation of uterine spiral arteries. Our goal is to showcase the utility of the rat as a model for in vivo mechanistic investigations targeting regulatory events within the uterine-placental interface.

Identification of Adrenomedullin-Induced S-Nitrosylated Proteins in JEG-3 Placental Cells

Extravillous cytotrophoblast (EVCT) is responsible for trophoblast invasion, which is important during placentation. Dysregulation of the process leads to pregnancy complications. S-nitrosylation of proteins is associated with cell invasion in many cell types. Adrenomedullin (ADM), a polypeptide expressed abundantly in the first-trimester placentas, induces EVCT invasion by upregulation of protein S-nitrosylation. This study aimed to identify the S-nitrosylated proteins induced by ADM in the JEG-3 placental cells. By using affinity chromatography followed by mass spectrometric analysis, tubulin, enolase, eukaryotic translation initiation factor 4A1, actin, annexin II (ANX II), and glyceraldehyde 3-phosphate dehydrogenaseprotein-1 were found to be S-nitrosylated by ADM. In vitro treatment with ADM or S-Nitrosoglutathione (GSNO) significantly increased the ANX II surface expression, but not its total expression in the JEG-3 cells. Translocation of ANX II to cell surface has been reported to act as a cell surface receptor to plasmin, plasminogen, and tissue plasminogen activator (tPA), thereby stimulating cell invasion and migration. However, in this study, ADM-induced surface expression of ANX II in the JEG-3 cells was not associated with changes in the secretory and membrane-bound tPA activities. Future studies are required to understand the roles of surface expression of S-nitrosylated ANX II on trophoblast functions. To conclude, this study provided evidences that ADM regulated the nitric oxide signaling pathway and modulated trophoblast invasion.

Paradigms for investigating invasive trophoblast cell development and contributions to uterine spiral artery remodeling

Uterine spiral arteries are extensively remodeled during placentation to ensure sufficient delivery of maternal blood to the developing fetus. Uterine spiral arterial remodeling is complex, as cells originating from both mother and developing conceptus interact at the maternal interface to regulate the extracellular matrix remodeling and vasculature restructuring necessary for successful placentation. Despite this complexity, one mechanism critical to spiral artery remodeling is trophoblast cell invasion into the maternal compartment. Invasive trophoblast cells include both interstitial and endovascular populations that exhibit spatiotemporal differences in uterine invasion, including proximity to uterine spiral arteries. Interstitial trophoblast cells invade the uterine parenchyma where they are interspersed among stromal cells. Endovascular trophoblast cells infiltrate uterine spiral arteries, replace endothelial cells, adopt a pseudo-endothelial cell phenotype, and engineer vessel remodeling. Impaired trophoblast cell invasion and, consequently, insufficient uterine spiral arterial remodeling can lead to the development of pregnancy disorders, such as preeclampsia, intrauterine growth restriction, and premature birth. This review provides insights into invasive trophoblast cells and their function during normal placentation as well as in settings of disease.

Preliminary RNA-microarray analysis of long non-coding RNA expression in abnormally invasive placenta

Long non-coding RNAs (lncRNAs) are reported to have important roles in placental development and function, but the role of lncRNAs in abnormally invasive placenta (AIP) remains elusive. In the present study, the differential expression profiles of lncRNAs were analyzed to identify novel targets for further study of AIP. A total of 10 lncRNAs were chosen for validation by reverse transcription-quantitative PCR. To further determine the functions of dysregulated lncRNAs and their corresponding mRNAs, functional enrichment analysis, coexpression analysis were performed. A total of 329 lncRNAs and 179 mRNAs were identified to be differently expressed between the invasive and control group. Gene ontology analysis revealed that the 10 most significantly enriched functions included upregulated mRNAs and the most significantly enriched term was related to the proteinaceous extracellular matrix (ECM). In the pathway analysis, the two most significantly enriched pathways were the TGF-β signaling pathway for upregulated mRNAs and the pentose phosphate pathway for downregulated mRNAs. Furthermore, for certain dysregulated lncRNAs, their associated mRNAs were also dysregulated. Of note, BMP and activin membrane-bound inhibitor and TGF-β-induced, as the target genes of the TGF-β pathway, were indicated to be closely related to the ECM and invasive placental cells. Their nearby lncRNAs G008916 and vault RNA2-1 were also significantly dysregulated. In conclusion, significant lncRNAs with the potential to serve as biomarkers for AIP were identified.

Adaptations of the human placenta to hypoxia: opportunities for interventions in fetal growth restriction

BACKGROUND

The placenta is the functional interface between the mother and the fetus during pregnancy, and a critical determinant of fetal growth and life-long health. In the first trimester, it develops under a low-oxygen environment, which is essential for the conceptus who has little defense against reactive oxygen species produced during oxidative metabolism. However, failure of invasive trophoblasts to sufficiently remodel uterine arteries toward dilated vessels by the end of the first trimester can lead to reduced/intermittent blood flow, persistent hypoxia and oxidative stress in the placenta with consequences for fetal growth. Fetal growth restriction (FGR) is observed in ∼10% of pregnancies and is frequently seen in association with other pregnancy complications, such as preeclampsia (PE). FGR is one of the main challenges for obstetricians and pediatricians, as smaller fetuses have greater perinatal risks of morbidity and mortality and postnatal risks of neurodevelopmental and cardio-metabolic disorders.

OBJECTIVE AND RATIONALE

The aim of this review was to examine the importance of placental responses to changing oxygen environments during abnormal pregnancy in terms of cellular, molecular and functional changes in order to highlight new therapeutic pathways, and to pinpoint approaches aimed at enhancing oxygen supply and/or mitigating oxidative stress in the placenta as a mean of optimizing fetal growth.

SEARCH METHODS

An extensive online search of peer-reviewed articles using PubMed was performed with combinations of search terms including pregnancy, placenta, trophoblast, oxygen, hypoxia, high altitude, FGR and PE (last updated in May 2020).

OUTCOMES

Trophoblast differentiation and placental establishment are governed by oxygen availability/hypoxia in early pregnancy. The placental response to late gestational hypoxia includes changes in syncytialization, mitochondrial functions, endoplasmic reticulum stress, hormone production, nutrient handling and angiogenic factor secretion. The nature of these changes depends on the extent of hypoxia, with some responses appearing adaptive and others appearing detrimental to the placental support of fetal growth. Emerging approaches that aim to increase placental oxygen supply and/or reduce the impacts of excessive oxidative stress are promising for their potential to prevent/treat FGR.

WIDER IMPLICATIONS

There are many risks and challenges of intervening during pregnancy that must be considered. The establishment of human trophoblast stem cell lines and organoids will allow further mechanistic studies of the effects of hypoxia and may lead to advanced screening of drugs for use in pregnancies complicated by placental insufficiency/hypoxia. Since no treatments are currently available, a better understanding of placental adaptations to hypoxia would help to develop therapies or repurpose drugs to optimize placental function and fetal growth, with life-long benefits to human health.

Perfluorobutane sulfonate exposure disrupted human placental cytotrophoblast cell proliferation and invasion involving in dysregulating preeclampsia related genes

We reported that maternal PFBS, an emerging pollutant, exposure is positively associated with preeclampsia which can result from aberrant trophoblasts invasion and subsequent placental ischemia. In this study, we investigated the effects of PFBS on trophoblasts proliferation/invasion and signaling pathways. We exposed a human trophoblast line, HTR8/SVneo, to PFBS. Cell viability, proliferation, and cell cycle were evaluated by the MTS assay, Ki-67 staining, and flow cytometry, respectively. We assessed cell migration and invasion with live-cell imaging-based migration assay and matrigel invasion assay, respectively. Signaling pathways were examined by Western blot, RNA-seq, and qPCR. PFBS exposure interrupted cell proliferation and invasion in a dose-dependent manner. PFBS (100 μM) did not cause cell death but instead significant cell proliferation without cell cycle disruption. PFBS (10 and 100 μM) decreased cell migration and invasion, while PFBS (0.1 μM) significantly increased cell invasion but not migration. Further, RNA-seq analysis identified dysregulated HIF-1α target genes that are relevant to cell proliferation/invasion and preeclampsia, while Western Blot data showed the activation of HIF-1α, but not Notch, ERK1/2, (PI3K)AKT, and P38 pathways. PBFS exposure altered trophoblast cell proliferation/invasion which might be mediated by preeclampsia-related genes, suggesting a possible association between prenatal PFBS exposure and adverse placentation.

Decidual Vasculopathy and Spiral Artery Remodeling Revisited III: Hypoxia and Re-oxygenation Sequence with Vascular Regeneration

Aim: Spiral artery remodeling at early pregnancy is characterized by two distinct mechanisms with two morphologic features, namely, trophoblastic-dependent vascular invasion with “plugging”, and trophoblastic-independent mural muscular hypertrophy/hyperplasia, both of which lead to the blocking or narrowing of the arterial lumen with the consequence of reduced maternal blood flow to the developing embryo. Methods: Review of historic literature in light of the new discovery of CD56 (NCAM) expression on endovascular trophoblasts at late gestation, in relation to placental lateral growth with vascular regeneration. Results: Reduced maternal blood flow to the embryo results in a hypoxic condition critical for trophectoderm differentiation and proliferation. Hypoxia is also important for the development of hemangioblasts of vasculogenesis, and hematopoiesis of the placental villi. Up to 13 weeks, both uteroplacental and fetoplacental circulations are established and hypoxic condition relieved for normal fetal/placenta development by ultrasonography. The persistence of trophoblastic plugging and/or mural muscular hypertrophy/hyperplasia leads to persistent reduced maternal blood flow to the placenta, resulting in persistent hypoxia and increased angiogenesis, with a constellation of pathologic features of maternal vascular malperfusion atlate gestation. Wilm’s tumor gene (WT1) expression appears to be central to steroid and peptide hormonal actions in early pregnancy, and vascular regeneration/restoration after pregnancy. Conclusions: Spiral artery remodeling at early pregnancy leads to hypoxia with vascular transformation, and the establishment of uteroplacental circulation results in relief of hypoxia. The hypoxia–re-oxygenation sequence may provide insights into the mechanism of normal fetal/placental development and associated pregnancy complications, such as preeclampsia.

The Role of NFκB in Healthy and Preeclamptic Placenta: Trophoblasts in the Spotlight

The NFκB protein family regulates numerous pathways within the cell-including inflammation, hypoxia, angiogenesis and oxidative stress-all of which are implicated in placental development. The placenta is a critical organ that develops during pregnancy that primarily functions to supply and transport the nutrients required for fetal growth and development. Abnormal placental development can be observed in numerous disorders during pregnancy, including fetal growth restriction, miscarriage, and preeclampsia (PE). NFκB is highly expressed in the placentas of women with PE, however its contributions to the syndrome are not fully understood. In this review we discuss the molecular actions and related pathways of NFκB in the placenta and highlight areas of research that need attention.

Matrix metalloproteinase-12 as an endogenous resolution promoting factor following myocardial infarction

Following myocardial infarction (MI), timely resolution of inflammation promotes wound healing and scar formation while limiting excessive tissue damage. Resolution promoting factors (RPFs) are agents that blunt leukocyte trafficking and inflammation, promote necrotic and apoptotic cell clearance, and stimulate scar formation. Previously identified RPFs include mediators derived from lipids (resolvins, lipoxins, protectins, and maresins), proteins (glucocorticoids, annexin A1, galectin 1, and melanocortins), or gases (CO, H₂S, and NO). Matrix metalloproteinase-12 (MMP-12; macrophage elastase) has shown promising RPF qualities in a variety of disease states. We review here the evidence that MMP-12 may serve as a novel RPF with potential therapeutic efficacy in the setting of MI.

Hypoxia‑induced expression of CXCR4 favors trophoblast cell migration and invasion via the activation of HIF‑1α

The placenta initially develops in a low‑oxygen environment up to week 8‑10 of gestation, and a low oxygen level is a critical factor in the regulation of trophoblast migration and invasion. CXC chemokine receptor 4 (CXCR4) is transcriptionally activated by hypoxia in cancer cells. However, whether CXCR4 is involved in hypoxia‑inducible factor (HIF)‑1α‑dependent trophoblastic migration and invasion in a physiologically hypoxic environment (3% O2) remains to be fully elucidated and requires further investigation. In the present study, the expression of CXCR4 in first‑trimester villi was investigated, as was the response of the trophoblast to hypoxia, and the role of CXCR4 and HIF‑1α in trophoblast migration and invasion. CXCR4 was significantly elevated in the first‑trimester villi compared with normal full‑term placentas. In vitro, the expression of CXCR4 at the mRNA and protein levels was increased in JEG3 cells exposed to 3% O2 in a time‑dependent manner, and the migratory and invasive abilities of the JEG3 cells were upregulated. In addition, CXCR4 knockdown by transfection with CXCR4‑specific small interfering (si)RNA decreased the migration and invasion of JEG3 cells exposed to 3% O2. Furthermore, synthetic siRNA specific for HIF‑1α significantly suppressed the expression of CXCR4 in JEG3 cells exposed to 3% O2, whereas pcDNA‑HIF‑1α significantly increased the expression of CXCR4. These results indicated that the hypoxia‑induced expression of CXCR4 promoted trophoblast cell migration and invasion via the activation of HIF‑1α, which is crucial during placentation.