Hypoxia and trophoblast differentiation: a key role for PPARγ

PPARγ Agonist Rosiglitazone and Antagonist GW9662: Antihypertensive Effects on Chronic Intermittent Hypoxia-Induced Hypertension in Rats

The increased incidence of hypertension associated with obstructive sleep apnea (OSA) presents significant physical, psychological, and economic challenges. Peroxisome proliferator-activated receptor gamma (PPARγ) plays a role in both OSA and hypertension, yet the therapeutic potential of PPARγ agonists and antagonists for OSA-related hypertension remains unexplored. Therefore, we constructed a chronic intermittent hypoxia (CIH)-induced hypertension rat model that mimics the pathogenesis of OSA-related hypertension in humans. The model involved administering PPARγ agonist rosiglitazone (RSG), PPARγ antagonist GW9662, or normal saline, followed by regular monitoring of blood pressure and thoracic aorta analysis using staining and electron microscopy. Intriguingly, our results indicated that both RSG and GW9662 appeared to potently counteract CIH-induced hypertension. In silico study suggested that GW9662's antihypertensive effect might mediated through angiotensin II receptor type 1 (AGTR1). Our findings provide insights into the mechanisms of OSA-related hypertension and propose novel therapeutic targets.

The Role of Sirtuin-1 (SIRT1) in the Physiology and Pathophysiology of the Human Placenta

Sirtuins, especially SIRT1, play a significant role in regulating inflammatory response, autophagy, and cell response to oxidative stress. Since their discovery, sirtuins have been regarded as anti-ageing and longevity-promoting enzymes. Sirtuin-regulated processes seem to participate in the most prevalent placental pathologies, such as pre-eclampsia. Furthermore, more and more research studies indicate that SIRT1 may prevent pre-eclampsia development or at least alleviate its manifestations. Having considered this, we reviewed recent studies on the role of sirtuins, especially SIRT1, in processes determining normal or abnormal development and functioning of the placenta.

Understanding PPARγ and Its Agonists on Trophoblast Differentiation and Invasion: Potential Therapeutic Targets for Gestational Diabetes Mellitus and Preeclampsia

The increasing incidence of pregnancy complications, particularly gestational diabetes mellitus (GDM) and preeclampsia (PE), is a cause for concern, as they can result in serious health consequences for both mothers and infants. The pathogenesis of these complications is still not fully understood, although it is known that the pathologic placenta plays a crucial role. Studies have shown that PPARγ, a transcription factor involved in glucose and lipid metabolism, may have a critical role in the etiology of these complications. While PPARγ agonists are FDA-approved drugs for Type 2 Diabetes Mellitus, their safety during pregnancy is not yet established. Nevertheless, there is growing evidence for the therapeutic potential of PPARγ in the treatment of PE using mouse models and in cell cultures. This review aims to summarize the current understanding of the mechanism of PPARγ in placental pathophysiology and to explore the possibility of using PPARγ ligands as a treatment option for pregnancy complications. Overall, this topic is of great significance for improving maternal and fetal health outcomes and warrants further investigation.

The Role of Peroxisome Proliferator-Activated Receptors in Preeclampsia

Preeclampsia is a common pregnancy-related hypertensive disorder. Often presenting as preexisting or new-onset hypertension complicated by proteinuria and/or end-organ dysfunction, preeclampsia significantly correlates with maternal and perinatal morbidity and mortality. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptor proteins that regulate gene expression. In order to investigate the role of PPARs in the pathophysiology of preeclampsia, we conducted a literature review using the MEDLINE and LIVIVO databases. The search terms "peroxisome proliferator-activated receptor", "PPAR", and "preeclampsia" were employed and we were able to identify 35 relevant studies published between 2002 and 2022. Different study groups reached contradictory conclusions in terms of PPAR expression in preeclamptic placentae. Interestingly, PPARγ agonists alone, or in combination with well-established pharmaceutical agents, were determined to represent novel, potent anti-preeclamptic treatment alternatives. In conclusion, PPARs seem to play a significant role in preeclampsia.

Regulators involved in trophoblast syncytialization in the placenta of intrauterine growth restriction

Placental dysfunction refers to the insufficiency of placental perfusion and chronic hypoxia during early pregnancy, which impairs placental function and causes inadequate supply of oxygen and nutrients to the fetus, affecting fetal development and health. Fetal intrauterine growth restriction, one of the most common outcomes of pregnancy-induced hypertensions, can be caused by placental dysfunction, resulting from deficient trophoblast syncytialization, inadequate trophoblast invasion and impaired vascular remodeling. During placental development, cytotrophoblasts fuse to form a multinucleated syncytia barrier, which supplies oxygen and nutrients to meet the metabolic demands for fetal growth. A reduction in the cell fusion index and the number of nuclei in the syncytiotrophoblast are found in the placentas of pregnancies complicated by IUGR, suggesting that the occurrence of IUGR may be related to inadequate trophoblast syncytialization. During the multiple processes of trophoblasts syncytialization, specific proteins and several signaling pathways are involved in coordinating these events and regulating placental function. In addition, epigenetic modifications, cell metabolism, senescence, and autophagy are also involved. Study findings have indicated several abnormally expressed syncytialization-related proteins and signaling pathways in the placentas of pregnancies complicated by IUGR, suggesting that these elements may play a crucial role in the occurrence of IUGR. In this review, we discuss the regulators of trophoblast syncytialization and their abnormal expression in the placentas of pregnancies complicated by IUGR.

NRF2 Serves a Critical Role in Regulation of Immune Checkpoint Proteins (ICPs) During Trophoblast Differentiation

Using cultured human trophoblast stem cells (hTSCs), mid-gestation human trophoblasts in primary culture, and gene-targeted mice, we tested the hypothesis that the multinucleated syncytiotrophoblast (SynT) serves a critical role in pregnancy maintenance through production of key immune modulators/checkpoint proteins (ICPs) under control of the O2-regulated transcription factor, NRF2/NFE2L2. These ICPs potentially act at the maternal-fetal interface to protect the hemiallogeneic fetus from rejection by the maternal immune system. Using cultured hTSCs, we observed that several ICPs involved in the induction and maintenance of immune tolerance were markedly upregulated during differentiation of cytotrophoblasts (CytTs) to SynT. These included HMOX1, kynurenine receptor, aryl hydrocarbon receptor, PD-L1, and GDF15. Intriguingly, NRF2, C/EBPβ, and PPARγ were markedly induced when CytTs fused to form SynT in a 20% O2 environment. Notably, when hTSCs were cultured in a hypoxic (2% O2) environment, SynT fusion and the differentiation-associated induction of NRF2, C/EBPβ, aromatase (CYP19A1; SynT differentiation marker), and ICPs were blocked. NRF2 knockdown also prevented induction of aromatase, C/EBPβ and the previously mentioned ICPs. Chromatin immunoprecipitation-quantitative PCR revealed that temporal induction of the ICPs in hTSCs and mid-gestation human trophoblasts cultured in 20% O2 was associated with increased binding of endogenous NRF2 to putative response elements within their promoters. Moreover, placentas of 12.5 days postcoitum mice with a global Nrf2 knockout manifested decreased mRNA expression of C/ebpβ, Pparγ, Hmox1, aryl hydrocarbon receptor, and Nqo1, another direct downstream target of Nrf2, compared with wild-type mice. Collectively, these compelling findings suggest that O2-regulated NRF2 serves as a key regulator of ICP expression during SynT differentiation.

Gal-2 Increases H3K4me3 and H3K9ac in Trophoblasts and Preeclampsia

Preeclampsia (PE) is a severe pregnancy disorder with a pathophysiology not yet completely understood and without curative therapy. The histone modifications H3K4me³ and H3K9ac, as well as galectin-2 (Gal-2), are known to be decreased in PE. To gain a better understanding of the development of PE, the influence of Gal-2 on histone modification in trophoblasts and in syncytialisation was investigated. Immunohistochemical stains of 13 PE and 13 control placentas were correlated, followed by cell culture experiments. An analysis of H3K4me³ and H3K9ac was conducted, as well as cell fusion staining with E-cadherin and β-catenin—both after incubation with Gal-2. The expression of H3K4me³ and H3K9ac correlated significantly with the expression of Gal-2. Furthermore, we detected an increase in H3K4me³ and H3K9ac after the addition of Gal-2 to BeWo/HVT cells. Moreover, there was increased fusion of HVT cells after incubation with Gal-2. Gal-2 is associated with the histone modifications H3K4me³ and H3K9ac in trophoblasts. Furthermore, syncytialisation increased after incubation with Gal-2. Therefore, we postulate that Gal-2 stimulates syncytialisation, possibly mediated by H3K4me³ and H3K9ac. Since Gal-2, as well as H3K4me³ and H3K9ac, are decreased in PE, the induction of Gal-2 might be a promising therapeutic target.

Esomeprazole inhibits hypoxia/endothelial dysfunction–induced autophagy in preeclampsia

Preeclampsia (PE) affects 3 to 5% of pregnant women worldwide and is associated with fetal and maternal morbidity and mortality. Although a complete understanding of PE remains elusive, it has been widely accepted that a dysfunction of the placenta plays a key role in the pathogenesis of PE. In this study, we investigated the role of excessive placental autophagy during PE pathogenesis and explored whether esomeprazole ameliorates PE by inhibiting the autophagy in the placenta. The PE cellular model was established by treating the cells’ L-NAME and hypoxia. The PE mice model was established by L-NAME administration and was confirmed by the increased systolic blood pressure (SBP) and urinary protein detected. The autophagy and key proteins were detected in human placental tissue, in cells, and in the mice model by Western blot and immunofluorescence staining. Results showed that excessive autophagy could be detected in human PE placental tissue, in the PE cellular model, and in the PE mice model. Hypoxia induces autophagy by activating AMPKα and inhibiting mTOR in vivo and in vitro. Esomeprazole inhibits L‐NAME-induced autophagy in mice by inhibiting AMPKα and activating mTOR. In conclusion, this study demonstrates that the excessive autophagy induced by the SIRT1/AMPKα-mTOR pathway plays a significant role in the pathogenesis of PE. However, esomeprazole treatment inhibits AMPKα but activates mTOR, resulting in the inhibition of autophagy in the placenta and, therefore, mitigates PE symptoms.

SIRT1: A Novel Protective Molecule in Pre-eclampsia

Pre-eclampsia is a severe pregnant complication, mainly characterized by insufficient trophoblast invasion, impaired uterine spiral artery remodeling, placental hypoxia and ischemia, and endothelial dysfunction. However, the potential mechanisms of pre-eclampsia remain unclear. SIRT1 is a NAD+-dependent deacetylase, involving in multiple biological processes, including energy metabolism, oxidative stress, inflammatory response, and cellular autophagy. Several studies showed that SIRT1 might play a vital role in the pathogenesis of pre-eclampsia. In this review, we aim to integrate the latest research on SIRT1 and pre-eclampsia to explore the comprehensive mechanisms of SIRT1 in pre-eclampsia. More specifically, SIRT1 might affect placental development and trophoblast invasion through autophagy and senescence in pre-eclampsia, and SIRT1 protects vascular endothelial cells from oxidative stress, inflammatory response, autophagy, and senescence. Furthermore, SIRT1 deficiency mice showed typical pre-eclampsia-like performances, which can be reversed via direct SIRT1 supplement or SIRT1 agonist treatment. Additionally, resveratrol, a SIRT1 agonist, attenuates vascular endothelial injury and placental dysfunction, and exerts protective effect on decreasing blood pressure. In this review, we provide new insights into the development of pre-eclampsia, which can establish a theoretical basis for prevention and treatment for pre-eclampsia. Besides, we also propose questions that still need to be further addressed in order to elucidate the comprehensive molecular mechanisms of pre-eclampsia in the future.

Regulation of Epigenetic Modifications in the Placenta during Preeclampsia: PPARγ Influences H3K4me3 and H3K9ac in Extravillous Trophoblast Cells

The aim of this study was to analyze the expression of peroxisome proliferator-activated receptor γ (PPARγ) and retinoid X receptor α (RxRα), a binding heterodimer playing a pivotal role in the successful trophoblast invasion, in the placental tissue of preeclamptic patients. Furthermore, we aimed to characterize a possible interaction between PPARγ and H3K4me3 (trimethylated lysine 4 of the histone H3), respectively H3K9ac (acetylated lysine 9 of the histone H3), to illuminate the role of histone modifications in a defective trophoblast invasion in preeclampsia (PE). Therefore, the expression of PPARγ and RxRα was analyzed in 26 PE and 25 control placentas by immunohistochemical peroxidase staining, as well as the co-expression with H3K4me3 and H3K9ac by double immunofluorescence staining. Further, the effect of a specific PPARγ-agonist (Ciglitazone) and PPARγ-antagonist (T0070907) on the histone modifications H3K9ac and H3K4me3 was analyzed in vitro. In PE placentas, we found a reduced expression of PPARγ and RxRα and a reduced co-expression with H3K4me3 and H3K9ac in the extravillous trophoblast (EVT). Furthermore, with the PPARγ-antagonist treated human villous trophoblast (HVT) cells and primary isolated EVT cells showed higher levels of the histone modification proteins whereas treatment with the PPARγ-agonist reduced respective histone modifications. Our results show that the stimulation of PPARγ-activity leads to a reduction of H3K4me3 and H3K9ac in trophoblast cells, but paradoxically decreases the nuclear PPARγ expression. As the importance of PPARγ, being involved in a successful trophoblast invasion has already been investigated, our results reveal a pathophysiologic connection between PPARγ and the epigenetic modulation via H3K4me3 and H3K9ac in PE.

Induction of the PPARγ (Peroxisome Proliferator-Activated Receptor γ)-GCM1 (Glial Cell Missing 1) Syncytialization Axis Reduces sFLT1 (Soluble fms-Like Tyrosine Kinase 1) in the Preeclamptic Placenta

[Figure: see text].

Role of the Peroxisome Proliferator Activated Receptors in Hypertension

Nuclear receptors represent a large family of ligand-activated transcription factors which sense the physiological environment and make long-term adaptations by mediating changes in gene expression. In this review, we will first discuss the fundamental mechanisms by which nuclear receptors mediate their transcriptional responses. We will focus on the PPAR (peroxisome proliferator-activated receptor) family of adopted orphan receptors paying special attention to PPARγ, the isoform with the most compelling evidence as an important regulator of arterial blood pressure. We will review genetic data showing that rare mutations in PPARγ cause severe hypertension and clinical trial data which show that PPARγ activators have beneficial effects on blood pressure. We will detail the tissue- and cell-specific molecular mechanisms by which PPARs in the brain, kidney, vasculature, and immune system modulate blood pressure and related phenotypes, such as endothelial function. Finally, we will discuss the role of placental PPARs in preeclampsia, a life threatening form of hypertension during pregnancy. We will close with a viewpoint on future research directions and implications for developing novel therapies.

Role of Peroxisome Proliferator-Activated Receptors (PPARs) in Trophoblast Functions

Peroxisome proliferator-activated receptors (PPARα, PPARβ/δ, and PPARγ) belong to the transcription factor family, and they are highly expressed in all types of trophoblast during pregnancy. The present review discusses currently published papers that are related to the regulation of PPARs via lipid metabolism, glucose metabolism, and amino acid metabolism to affect trophoblast physiological conditions, including differentiation, maturation, secretion, fusion, proliferation, migration, and invasion. Recent pieces of evidence have proven that the dysfunctions of PPARs in trophoblast lead to several related pregnancy diseases such as recurrent miscarriage, preeclampsia, intrauterine growth restriction, and gestational diabetes mellitus. Moreover, the underlying mechanisms of PPARs in the control of these processes have been discussed as well. Finally, this review's purposes are to provide more knowledge about the role of PPARs in normal and disturbed pregnancy with trophoblast, so as to find PPAR ligands as a potential therapeutic target in the treatment and prevention of adverse pregnancy outcomes.

PPARγ modulates refractive development and form deprivation myopia in Guinea pigs

Form deprivation myopia (FDM) is characterized by loss of choroidal thickness (ChT), reduced choroidal blood perfusion (ChBP), and consequently scleral hypoxia. In some tissues, changes in levels of peroxisome proliferator-activated receptor γ (PPARγ) expression modulate hypoxia-induced pathological responses. We determined if PPARγ modulates FDM through changes in ChT, ChBP, scleral hypoxia-inducible transcription factor (HIF-1α) that in turn regulate scleral collagen type 1 (COL1) expression levels in guinea pigs. Myopia was induced by occluding one eye, while the fellow eye served as control. They received daily peribulbar injections of either the PPARγ antagonist GW9662, or the GW1929 agonist, with or without ocular occlusion for 4 weeks. Ocular refraction and biometric parameters were estimated at baseline, 2 and 4 weeks post-treatment. ChT and ChBP were measured at the 2- and 4-week time points. Western blot analysis determined the expression levels of scleral HIF-1α and COL1. GW9662 induced a myopic shift in unoccluded eyes. Conversely, GW1929 inhibited FDM progression without affecting the refraction in unoccluded eyes. GW9662 reduced both ChT and ChBP in unoccluded eyes, while GW1929 inhibited their declines in occluded eyes. Scleral HIF-1α expression rose in GW9662-treated unoccluded eyes whereas GW1929 reduced HIF-1α upregulation in occluded eyes. GW9662 downregulated scleral COL1 expression in unoccluded eyes, while GW1929 reduced their decreases in occluded eyes. Therefore, PPARγ modulates collagen expression levels and FDM through an inverse relationship between changes in PPARγ and HIF-1α expression levels.

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.

Peroxisome proliferator-activated receptor gamma blunts endothelin-1-mediated contraction of the uterine artery in a murine model of high-altitude pregnancy

The environmental hypoxia of high altitude (HA) increases the incidence of intrauterine growth restriction (IUGR) approximately threefold. The peroxisome proliferator-activated receptor γ (PPAR-γ), a ligand-activated nuclear receptor that promotes vasorelaxation by increasing nitric oxide and downregulating endothelin-1 (ET-1) production, has been implicated in IUGR. Based on our prior work indicating that pharmacologic activation of the PPARγ pathway protects against hypoxia-associated IUGR, we used an experimental murine model to determine whether such effects may be attributed to vasodilatory effects in the uteroplacental circulation. Using wire myography, ex vivo vasoreactivity studies were conducted in uterine arteries (UtA) isolated from pregnant mice exposed to hypoxia or normoxia from gestational day 14.5 to 18.5. Exposure to troglitazone, a high-affinity PPARγ agonist-induced vasorelaxation in UtA preconstricted with phenylephrine, with HA-UtA showing increased sensitivity. Troglitazone blunted ET-1-induced contraction of UtA in hypoxic and normoxic dams equivalently. Immunohistological analysis revealed enhanced staining for ET-1 receptors in the placental labyrinthine zone in hypoxic compared to normoxic dams. Our results suggest that pharmacologic PPAR-γ activation, via its vasoactive properties, may protect the fetal growth under hypoxic conditions by improving uteroplacental perfusion and thereby justify further investigation into PPARγ as a therapeutic target for IUGR in pregnancies complicated by hypoxia.

Upregulated ARRDC3 limits trophoblast cell invasion and tube formation and is associated with preeclampsia

OBJECTIVE

Bioinformatics analysis indicated that the arrestin ARRDC3 was upregulated in placental tissue from patients with preeclampsia (PE). The study aimed to confirm the finding by examining placenta samples from women with and without early-onset PE and to investigate ARRDC3 roles in trophoblast function.

METHODS

ARRDC3 expression level and localization in placental tissue were determined by Western blot, real-time quantitative PCR and immunohistochemistry. An in vitro hypoxia and an in vitro ischemia (hypoxia/reoxygenation) cell models were used to determine the hypoxic and ischemic effects on ARRDC3 expression in extravillous trophoblast-derived HTR/8SVneo cells and trophoblast cell activity. The role of ARRDC3 in HTR8/SVneo cell proliferation, invasion and tube formation in vitro was investigated by testing the effects of ARRDC3 gene overexpression or siRNA-based gene silencing.

RESULTS

ARRDC3 expression was significantly elevated in placental tissue from women with early-onset PE compared to preterm birth pregnancies. ARRDC3 protein was localized in human placental trophoblasts. Hypoxia and ischemia both enhanced ARRDC3 protein expression in HTR8/SVneo cells. Hypoxia altered trophoblast cell activities. Overexpression of ARRDC3 in HTR8/SVneo cells suppressed cell invasion and tube formation. ARRDC3 gene silencing, by contrast, promoted invasion and tube formation under hypoxic conditions.

CONCLUSION

ARRDC3 was highly expressed in placental tissues of PE patients and directly affected biological activities of trophoblasts under hypoxic conditions. In regulation of ARRDC3- protein expression, ischemia (hypoxia/reoxygenation) are also important. These findings suggest that ARRDC3 may play a clinically significant role in the pathogenesis of PE.

Pharmacological activation of peroxisome proliferator-activated receptor γ (PPAR-γ) protects against hypoxia-associated fetal growth restriction

The hypoxia of high-altitude (HA) residence increases the risk of intrauterine growth restriction (IUGR) and preeclampsia 3-fold, augmenting perinatal morbidity and mortality and the risk for childhood and adult disease. Currently, no effective therapies exist to prevent these vascular disorders of pregnancy. The peroxisome proliferator-activated receptor γ (PPAR-γ) is an important regulator of uteroplacental vascular development and function and has been implicated in the pathogenesis of IUGR and preeclampsia. Here, we used a model of HA pregnancy in mice to determine whether hypoxia-induced fetal growth restriction reduces placental PPAR-γ protein expression and placental vascularization and, if so, to evaluate the effectiveness of the selective PPAR-γ agonist pioglitazone (PIO) for preventing hypoxia-induced IUGR. Hypoxia resulted in asymmetric IUGR, placental insufficiency, and reduced placental PPAR-γ expression; PIO prevented approximately half of the fetal growth restriction and attenuated placental insufficiency. PIO did not affect fetal growth under normoxia. Although PIO was beneficial for fetal growth, PIO treatment reduced placental vascular density of the labrynthine zone in normoxic and hypoxic (Hx) conditions, and mean vascular area was reduced in the Hx group. Our results suggest that pharmacological PPAR-γ activation is a potential strategy for preventing IUGR in pregnancies complicated by hypoxia, although further studies are needed to identify its likely metabolic or vascular mechanisms.-Lane, S. L., Dodson, R. B., Doyle, A. S., Park, H., Rathi, H., Matarrazo, C. J., Moore, L. G., Lorca, R. A., Wolfson, G. H., Julian, C. G. Pharmacological activation of peroxisome proliferator-activated receptor γ (PPAR-γ) protects against hypoxia-associated fetal growth restriction.

PPAR signaling pathway in the first trimester placenta from in vitro fertilization and embryo transfer

Placenta is a temporary critical organ related to fetal development and pregnancy outcomes. And epidemiologic data demonstrate an increased risk of placental abnormality after in vitro fertilization and embryo transfer (IVF-ET). This study aims to explore the molecular mechanism for PPAR signaling pathway in placenta subjected to IVF-ET in the first trimester. Four first trimester placenta samples from double chorionic twins to single reduction in IVF-ET only because of oviducts factors. The other four control placenta samples from double chorionic twin were derived from those unplanned spontaneously conceived pregnancy after the legal termination. Affymetrix HG-U133 Plus 2.0 Array was performed to evaluate the global gene expressions. We confirmed microarray results from 10 significant differential genes using RT-qPCR. And 10 deregulated gene products were stained in the first trimester placenta by immunohistochemistry. These differentially expressed genes in IVF-ET placentas were submitted to functional annotation of clustering tools of bioinformatics resources and gene ontology enrichment analysis. Schematic representation of placental PPAR signaling pathway was labelled by Kyoto Encyclopedia of Genes and Genomes (KEGG). Analysis results of early placental PPAR signaling pathway gene expression from 8 women demonstrated 34 genes with a significant change in expression between IVF-ET and control group, 25 up-regulated; 9 down-regulated. KEGG pathway analysis indicated that IVF-ET manipulation extensively over-activated PPAR signaling pathway. Immune tolerance, trophoblast invasion, syncytia formation, lipid and glucose metabolism, inflammatory response and other complex biological functions were disturbed. RT-qPCR results and proteins staining intensity were consisted with microarray. Placental gene expressions and functions in PPAR signaling pathway were affected by IVF-ET treatment in the first trimester, which may offer a potential mechanism for the pathogenesis of various adverse outcomes during the perinatal period.

Hypoxia-induced Downregulation of SRC-3 Suppresses Trophoblastic Invasion and Migration Through Inhibition of the AKT/mTOR Pathway: Implications for the Pathogenesis of Preeclampsia

Preeclampsia (PE) is characterized by poor placentation, consequent on aberrant extravillous trophoblast (EVT) cell function during placental development. The SRC family of proteins is important during pregnancy, especially SRC-3, which regulates placental morphogenesis and embryo survival. Although SRC-3 expression in mouse trophoblast giant cells has been documented, its role in the functional regulation of extravillous trophoblasts and the development of PE remains unknown. This study found that SRC-3 expression was significantly lower in placentas from PE pregnancies as compared to uncomplicated pregnancies. Additionally, both CoCl₂-mimicked hypoxia and suppression of endogenous SRC-3 expression by lentivirus short hairpin RNA attenuated the migration and invasion abilities of HTR-8/SVneo cells. Moreover, we demonstrated that SRC-3 physically interacts with AKT to regulate the migration and invasion of HTR-8 cells, via the AKT/mTOR pathway. We also found that the inhibition of HTR-8 cell migration and invasion by CoCl₂-mimicked hypoxia was through the SRC-3/AKT/mTOR axis. Our findings indicate that, in early gestation, accumulation of HIF-1α inhibits the expression of SRC-3, which impairs extravillous trophoblastic invasion and migration by directly interacting with AKT. This potentially leads to insufficient uterine spiral artery remodeling and placental hypoperfusion, and thus the development of PE.

Reduced Uteroplacental Perfusion Pressure (RUPP) causes altered trophoblast differentiation and pericyte reduction in the mouse placenta labyrinth

This study characterized the effect of the reduced utero-placental perfusion pressure (RUPP) model of placental insufficiency on placental morphology and trophoblast differentiation at mid-late gestation (E14.5). Altered trophoblast proliferation, reduced syncytiotrophoblast gene expression, increased numbers of sinusoidal trophoblast giant cells, decreased Vegfa and decreased pericyte presence in the labyrinth were observed in addition to changes in maternal blood spaces, the fetal capillary network and reduced fetal weight. Further, the junctional zone was characterized by reduced spongiotrophoblast and glycogen trophoblast with increased trophoblast giant cells. Increased Hif-1α and TGF-β-3 in vivo with supporting hypoxia studies in trophoblast stem (TS) cells in vitro, support hypoxia as a contributing factor to the RUPP placenta phenotype. Together, this study identifies altered cell populations within the placenta that may contribute to the phenotype, and thus support the use of RUPP in the mouse as a model of placenta insufficiency. As such, this model in the mouse provides a valuable tool for understanding the phenotypes resulting from genetic manipulation of isolated cell populations to further understand the etiology of placenta insufficiency and fetal growth restriction. Further this study identifies a novel relationship between placental insufficiency and pericyte depletion in the labyrinth layer.

Hypoxia and Placental Development

Hemochorial placentation is orchestrated through highly regulated temporal and spatial decisions governing the fate of trophoblast stem/progenitor cells. Trophoblast cell acquisition of specializations facilitating invasion and uterine spiral artery remodeling is a labile process, sensitive to the environment, and represents a process that is vulnerable to dysmorphogenesis in pathologic states. Hypoxia is a signal guiding placental development, and molecular mechanisms directing cellular adaptations to low oxygen tension are integral to trophoblast cell differentiation and placentation. Hypoxia can also be used as an experimental tool to investigate regulatory processes controlling hemochorial placentation. These developmental processes are conserved in mouse, rat, and human placentation. Consequently, elements of these developmental events can be modeled and hypotheses tested in trophoblast stem cells and in genetically manipulated rodents. Hypoxia is also a consequence of a failed placenta, yielding pathologies that can adversely affect maternal adjustments to pregnancy, fetal health, and susceptibility to adult disease. The capacity of the placenta for adaptation to environmental challenges highlights the importance of its plasticity in safeguarding a healthy pregnancy. Birth Defects Research 109:1309-1329, 2017.© 2017 Wiley Periodicals, Inc.

The role of Sirtuin1-PPARγ axis in placental development and function

Placental development is important for proper in utero growth and development of the fetus, as well as maternal well-being during pregnancy. Abnormal differentiation of placental epithelial cells, called trophoblast, is at the root of multiple pregnancy complications, including miscarriage, the maternal hypertensive disorder preeclampsia and intrauterine growth restriction. The ligand-activated nuclear receptor, PPARγ, and nutrient sensor, Sirtuin-1, both play a role in numerous pathways important to cell survival and differentiation, metabolism and inflammation. However, each has also been identified as a key player in trophoblast differentiation and placental development. This review details these studies, and also describes how various stressors, including hypoxia and inflammation, alter the expression or activity of PPARγ and Sirtuin-1, thereby contributing to placenta-based pregnancy complications.

Trophoblast lineage specification, differentiation and their regulation by oxygen tension

Development of the early embryo takes place under low oxygen tension. Under such conditions, the embryo implants and the trophectoderm, the outer layer of blastocyst, proliferate, forming the cytotrophoblastic shell, the early placenta. The cytotrophoblasts (CTBs) are the so-called epithelial 'stem cells' of the placenta, which, depending on the signals they receive, can differentiate into either extravillous trophoblast (EVT) or syncytiotrophoblast (STB). EVTs anchor the placenta to the uterine wall and remodel maternal spiral arterioles in order to provide ample blood supply to the growing fetus. STBs arise through CTB fusion, secrete hormones necessary for pregnancy maintenance and form a barrier across which nutrient and gas exchange can take place. The bulk of EVT differentiation occurs during the first trimester, before the onset of maternal arterial blood flow into the intervillous space of the placenta, and thus under low oxygen tension. These conditions affect numerous signaling pathways, including those acting through hypoxia-inducible factor, the nutrient sensor mTOR and the endoplasmic reticulum stress-induced unfolded protein response pathway. These pathways are known to be involved in placental development and disease, and specific components have even been identified as directly involved in lineage-specific trophoblast differentiation. Nevertheless, much controversy surrounds the role of hypoxia in trophoblast differentiation, particularly with EVT. This review summarizes previous studies on this topic, with the intent of integrating these results and synthesizing conclusions that resolve some of the controversy, but then also pointing to remaining areas, which require further investigation.

Peroxisome proliferator‑activated receptor γ mediates porcine placental angiogenesis through hypoxia inducible factor‑, vascular endothelial growth factor‑ and angiopoietin‑mediated signaling

Peroxisome proliferator-activated receptor (PPAR) γ has been reported to be implicated in placentation in mice. Previous studies have demonstrated that PPARγ is also expressed in porcine placenta, primarily localized in vascular endothelial cells (VECs). The present study aimed to investigate the roles of PPARγ during porcine placental angiogenesis and examine the molecular mechanisms involved in its actions. VECs were incubated with the PPARγ agonist rosiglitazone and the antagonist T0070907, and their angiogenic potential was evaluated using cellular impedance, wound healing and tube formation assays. Reverse transcription-quantitative polymerase chain reaction was used to assess the mRNA expression levels of angiogenic factors, including hypoxia-inducible factors (HIFs), vascular endothelial growth factor (VEGF) isoforms, VEGF receptors (VEGFRs) and angiopoietins (Angs). The results demonstrated that the adhesive, proliferative and migratory capabilities of VECs were potentiated by rosiglitazone and suppressed by T0070907. Notably, tube formation was invariably promoted during PPARγ activation and blockade. The mRNA expression levels of HIF1α, HIF2α, VEGFR2, VEGF188 and Ang-1 were revealed to be upregulated following treatment of VECs with rosiglitazone, whereas they were downregulated following treatment with T0070907. However, the mRNA expression levels of placental growth factor and VEGF120 were consistently downregulated following PPARγ activation and blockade, whereas VEGF164 mRNA levels remained unaltered. The results of the present study suggested that PPARγ may mediate porcine placental angiogenesis, by interfering with HIF-, VEGF- and angiopoietin-mediated signaling pathways.

Regulation of the placental BCRP transporter by PPAR gamma

Identifying regulators of placental breast cancer resistance protein (BCRP) expression is critical as downregulation of this transporter may increase exposure of the fetus to xenobiotics. Here, we sought to test whether the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) regulates BCRP expression in the placenta. To test this, human BeWo placental choriocarcinoma cells were cultured with the PPARγ agonist rosiglitazone or the PPARγ antagonist T0070907 for 24 h. Messenger RNA (mRNA) expression of syncytialization markers, GCM1 and hCGβ, as well as BCRP increased with PPARγ agonist treatment. Conversely, BCRP mRNA and protein expression decreased 30%-50% with PPARγ antagonist treatment. Rosiglitazone enhanced BCRP protein expression and transport activity, resulting in a 20% greater efflux of the substrate Hoechst 33342 compared with control cells. These results suggest that PPARγ can upregulate BCRP expression in the placenta, which may be important in understanding mechanisms that protect the fetus from xenobiotic exposure during development.

Differential expression of thioredoxin binding protein-2/Txnip in human placenta: Possible involvement of hypoxia in its suppression during early pregnancy

AIM

Thioredoxin binding protein-2 (TBP-2), which is identical to thioredoxin interacting protein (Txnip), controls cellular proliferation and differentiation. The aim of the present study was to compare TBP-2 protein and mRNA expression in human placenta during the three trimesters of pregnancy and to investigate the role of hypoxia in the change of these expressions in placental tissue. A secondary objective was to determine the gene expression of peroxisome proliferator-activated receptors (PPARs) in TBP-2 deficient placenta using TBP-2 gene disrupted mice (TBP-2^-/- ).

METHODS

Protein and mRNA expression of TBP-2 in human placenta from each trimester were analyzed by immunohistochemistry, Western blots, and by quantitative reverse-transcriptase-polymerase chain reaction. The effect of hypoxia on TBP-2 expression was tested using an explant culture of human placenta. In TBP-2^-/- mouse placenta, we detected PPAR mRNA expression.

RESULTS

TBP-2 was located in syncytiotrophoblasts and cytotrophoblasts, and also in the endothelium in human placenta. Its expression in the placenta was low in the first trimester, and increased in the second and third trimesters. Hypoxia decreased TBP-2 mRNA and protein expression in human placental explant culture. In TBP-2^-/- mice, placental mRNA levels of PPARα and γ were significantly suppressed compared with those in wild-type mice.

CONCLUSION

Hypoxia suppresses TBP-2 gene expression, which may ultimately alter placental development.

Increased risk for the development of preeclampsia in obese pregnancies: weighing in on the mechanisms

Preeclampsia (PE) is a pregnancy-specific disorder typically presenting as new-onset hypertension and proteinuria. While numerous epidemiological studies have demonstrated that obesity increases the risk of PE, the mechanisms have yet to be fully elucidated. Growing evidence from animal and human studies implicate placental ischemia in the etiology of this maternal syndrome. It is thought that placental ischemia is brought about by dysfunctional cytotrophoblast migration and invasion into the uterus and subsequent lack of spiral arteriole widening and placental perfusion. Placental ischemia/hypoxia stimulates the release of soluble placental factors into the maternal circulation where they cause endothelial dysfunction, particularly in the kidney, to elicit the clinical manifestations of PE. The most recognized of these factors are the anti-angiogenic sFlt-1 and pro-inflammatory TNF-α and AT1-AA, which promote endothelial dysfunction by reducing levels of the provasodilator nitric oxide and stimulating production of the potent vasoconstrictor endothelin-1 and reactive oxygen species. We hypothesize that obesity-related metabolic factors increase the risk for developing PE by impacting various stages in the pathogenesis of PE, namely, 1) cytotrophoblast migration and placental ischemia; 2) release of soluble placental factors into the maternal circulation; and 3) maternal endothelial and vascular dysfunction. This review will summarize the current experimental evidence supporting the concept that obesity and metabolic factors like lipids, insulin, glucose, and leptin affect placental function and increase the risk for developing hypertension in pregnancy by reducing placental perfusion; enhancing placental release of soluble factors; and by increasing the sensitivity of the maternal vasculature to placental ischemia-induced soluble factors.

Adaptive mechanisms controlling uterine spiral artery remodeling during the establishment of pregnancy

Implantation of the embryo into the uterus triggers the initiation of hemochorial placentation. The hemochorial placenta facilitates the acquisition of maternal resources required for embryo/fetal growth. Uterine spiral arteries form the nutrient supply line for the placenta and fetus. This vascular conduit undergoes gestation stage-specific remodeling directed by maternal natural killer cells and embryo-derived invasive trophoblast lineages. The placentation site, including remodeling of the uterine spiral arteries, is shaped by environmental challenges. In this review, we discuss the cellular participants controlling pregnancy-dependent uterine spiral artery remodeling and mechanisms responsible for their development and function.

BMP4 regulation of human trophoblast development

Since the derivation of human embryonic stem cells, and the subsequent generation of induced pluripotent stem cells, there has been much excitement about the ability to model and evaluate human organ development in vitro. The finding that these cells, when treated with BMP4, are able to generate the extraembryonic cell type, trophoblast, which is the predominant functional epithelium in the placenta, has not been widely accepted. This review evaluates this model, providing comparison to early known events during placentation in both human and mouse and addresses specific challenges. Keeping in mind the ultimate goal of understanding human placental development and pregnancy disorders, our aim here is two-fold: to distinguish gaps in our knowledge arising from mis- or over-interpretation of data, and to recognize the limitations of both mouse and human models, but to work within those limitations towards the ultimate goal.

Signaling pathways in mouse and human trophoblast differentiation: a comparative review

The mouse is often used as a model for understanding human placentation and offers multiple advantages, including the ability to manipulate gene expression in specific compartments and to derive trophoblast stem cells, which can be maintained or differentiated in vitro. Nevertheless, there are numerous differences between the mouse and human placentas, only the least of which are structural. This review aims to compare mouse and human placentation, with a focus on signaling pathways involved in trophoblast lineage-specific differentiation.

Hypoxic stress induces, but cannot sustain trophoblast stem cell differentiation to labyrinthine placenta due to mitochondrial insufficiency

Dysfunctional stem cell differentiation into placental lineages is associated with gestational diseases. Of the differentiated lineages available to trophoblast stem cells (TSC), elevated O2 and mitochondrial function are necessary to placental lineages at the maternal-placental surface and important in the etiology of preeclampsia. TSC lineage imbalance leads to embryonic failure during uterine implantation. Stress at implantation exacerbates stem cell depletion by decreasing proliferation and increasing differentiation. In an implantation site O2 is normally ~2%. In culture, exposure to 2% O2 and fibroblast growth factor 4 (FGF4) enabled the highest mouse TSC multipotency and proliferation. In contrast, hypoxic stress (0.5% O2) initiated the most TSC differentiation after 24h despite exposure to FGF4. However, hypoxic stress supported differentiation poorly after 4-7 days, despite FGF4 removal. At all tested O2 levels, FGF4 maintained Warburg metabolism; mitochondrial inactivity and aerobic glycolysis. However, hypoxic stress suppressed mitochondrial membrane potential and maintained low mitochondrial cytochrome c oxidase (oxidative phosphorylation/OxPhos), and high pyruvate kinase M2 (glycolysis) despite FGF4 removal. Inhibiting OxPhos inhibited optimum differentiation at 20% O2. Moreover, adding differentiation-inducing hyperosmolar stress failed to induce differentiation during hypoxia. Thus, differentiation depended on OxPhos at 20% O2; hypoxic and hyperosmolar stresses did not induce differentiation at 0.5% O2. Hypoxia-limited differentiation and mitochondrial inhibition and activation suggest that differentiation into two lineages of the labyrinthine placenta requires O2>0.5-2% and mitochondrial function. Stress-activated protein kinase increases an early lineage and suppresses later lineages in proportion to the deviation from optimal O2 for multipotency, thus it is the first enzyme reported to prioritize differentiation.