Status of VEGF in preeclampsia and its effect on endoplasmic reticulum stress in placental trophoblast cells

Phenylbutyric acid inhibits hypoxia-induced trophoblast apoptosis and autophagy in preeclampsia via the PERK/ATF-4/CHOP pathway

Preeclampsia (PE) is a common pregnancy complication with a high mortality rate. Abnormally activated endoplasmic reticulum stress (ERS) is believed to be responsible for the destruction of key placental cells-trophoblasts. Phenylbutyric acid (4-PBA), an ERS inhibitor, is involved in regulating the development of ERS-related diseases. At present, how 4-PBA affects trophoblasts and its mechanisms is still unclear. In this study, PE cell models were established by stimulating HTR-8/SVneo cells with hypoxia. To verify the underlying mechanisms of 4-PBA on PE, CCT020312, an activator of PERK, was also used. The results showed that 4-PBA restored hypoxia-induced trophoblast viability, inhibited HIF-1α protein expression, inflammation, and PERK/ATF-4/CHOP pathway. Hoechst 33342 staining and flow cytometry results confirmed that 4-PBA decreased hypoxia-induced apoptosis in trophoblasts. The results of the JC-1 analysis and apoptosis initiation enzyme activity assay also demonstrated that 4-PBA inhibited apoptosis related to the mitochondrial pathway. Furthermore, by detecting autophagy in trophoblasts, an increased number of autophagic vesicles, damaged mitochondria, enhanced dansylcadaverine fluorescence, enhanced levels of autophagy proteins Beclin-1, LC3II, and decreased p62 were seen in hypoxia-stimulated cells. These changes were reversed by 4-PBA. Furthermore, it was observed that CCT020312 reversed the effects of 4-PBA on the viability, apoptosis, and autophagosome number of hypoxia-induced trophoblasts. In summary, 4-PBA reduces autophagy and apoptosis via the PERK/ATF-4/CHOP pathway and mitochondrial pathway, thereby restoring the viability of hypoxic trophoblasts. These findings provide a solid evidence base for the use of 4-PBA in PE treatment and guide a new direction for improving the outcomes of patients with PE.

Protein Misfolding in Pregnancy: Current Insights, Potential Mechanisms, and Implications for the Pathogenesis of Preeclampsia

Protein misfolding disorders are a group of diseases characterized by supra-physiologic accumulation and aggregation of pathogenic proteoforms resulting from improper protein folding and/or insufficiency in clearance mechanisms. Although these processes have been historically linked to neurodegenerative disorders, such as Alzheimer's disease, evidence linking protein misfolding to other pathologies continues to emerge. Indeed, the deposition of toxic protein aggregates in the form of oligomers or large amyloid fibrils has been linked to type 2 diabetes, various types of cancer, and, in more recent years, to preeclampsia, a life-threatening pregnancy-specific disorder. While extensive physiological mechanisms are in place to maintain proteostasis, processes, such as aging, genetic factors, or environmental stress in the form of hypoxia, nutrient deprivation or xenobiotic exposures can induce failure in these systems. As such, pregnancy, a natural physical state that already places the maternal body under significant physiological stress, creates an environment with a lower threshold for aberrant aggregation. In this review, we set out to discuss current evidence of protein misfolding in pregnancy and potential mechanisms supporting a key role for this process in preeclampsia pathogenesis. Improving our understanding of this emerging pathophysiological process in preeclampsia can lead to vital discoveries that can be harnessed to create better diagnoses and treatment modalities for the disorder.

Hydrogen sulfide promotes migration of trophoblast cells by a Rho GTPase mediated actin cytoskeleton reorganization

INTRODUCTION

Preeclampsia (PE) arises due to defective spiral artery remodelling which may be due to deficient migration of trophoblast cells. Migration of human endothelial cells has been shown to be promoted via Hydrogen sulphide(H2S)/Rho GTPase Rac1 axis. This novel role of H2S and its downstream processes have not yet been studied in the development and function of the placental trophoblast cells.

METHODS

Placental tissues were obtained post-delivery from consented preeclamptic and normotensive mothers (n = 60). The protein expression levels of cystathionine-gamma-lyase (CSE) and cystathionine-beta-synthase (CBS) along with its downstream migratory molecules were compared in both the arms. The pro-migratory role of H2S was investigated in a first trimester placental cell line.

RESULTS

H2S promoted the migration of trophoblast cells in a Rho GTPase dependent manner mediated by actin cytoskeleton reorganization. The reduced levels of H2S producing enzymes in the PE placentae along with decreased levels of Rho GTPases (Rac1 and Rho A) corroborate the results of PAG and AOAA treatment in down regulating the Rho GTPases in the in vitro grown placental cultures. Reduction of the migratory potential of trophoblastic cells caused due to hypoxia/reoxygenation was rescued by upregulating the H2S expression with the use of NaHS as a H2S donor.

DISCUSSION

Exogenous H2S increases the migratory potential of the placental cells in culture conditions and also post hypoxia/reoxygenation injury. H2S as a gaso-transmitter holds a great potential as a therapeutic agent. Its long-term effects need to be investigated using model systems (rat/mouse) of PE following it up with clinical regulatory trials.

Effect of endoplasmic reticulum stress on human trophoblast cells: Survival triggering or catastrophe resulting in death

Endoplasmic reticulum (ER) stress has been reported to play a role in the pathogenesis of intrauterine growth retardation and preeclampsia, especially implantation failure. Although in vitro ER stress studies in human trophoblast cell line have been conducted in recent years, the influence of Thapsigargin on intracellular dynamics on calcium homeostasis has not been proven. Here, the effects of ER stress and impaired calcium homeostasis on apoptosis, autophagy, cytoskeleton, hypoxia, and adhesion molecules in 2D and spheroid cultures of human trophectoderm cells were investigated at gene expression and protein levels. Thapsigargin caused ER stress by increasing GRP78 gene expression and protein levels. Human trophectoderm cells displayed different characterization properties in 2D and spheroids. While it moves in the pathway of EIF2A and IRE1A mechanisms in 2D, it proceeds in the pathway of EIF2A and ATF6 mechanisms in spheroids and triggers different responses in survival and programmed cell death mechanisms such as apoptosis and autophagy. This led to changes in the cytoskeleton, cell adhesion molecules and cell-cell interactions by affecting the hypoxia mechanism.

Melatonin regulates proliferation, apoptosis and invasion of trophoblasts in preeclampsia by inhibiting endoplasmic reticulum stress

AIMS

Clinical evidence indicated the activation of endoplasmic reticulum stress (ERS) in pregnant women with preeclampsia (PE), and the regulatory role of melatonin (MT) in ERS. This study aims to explore the possible effect and mechanism of MT on ERS and on the infiltration of trophoblasts in PE.

METHODS

The serum expression levels of MT and GRP78 in pregnant women with PE were measured. The cell proliferation, invasion, migration and apoptosis of trophoblasts were also determined. The trophoblast cell infiltration in placenta tissues was detected in EVOS image system. The expressions of ERS related proteins were measured by RT-qPCR and western blot.

KEY RESULTS

The PE-serum treatment on HTR-8/SVneo cells led to activated ERS and suppressed cell biological functions. PE mouse models after MT treatment or 4-PBA treatment had reduced blood pressure, proteinuria, apoptosis and increased foetus and placenta weight, in addition to enhanced cell infiltration.

CONCLUSIONS

In vivo and in vitro evidence demonstrated MT can simultaneously suppress ERS and ASK1/JNK signal pathway in PE to promote the infiltration of trophoblasts.

Omega-3 and Vitamin E Supplementation Effect on Reactive Oxygen Species and Placental Vascular Endothelial Growth Factor: Pre-eclampsia Model

BACKGROUND: Pre-eclampsia (PE) has been associated with oxidative stress and inflammation. Omega-3 fatty acids and vitamin E have beneficial function to maintain cell membrane, prevent oxidative stress, and inhibit the production of proinflammatory cytokines. The purpose of the study was to determine the effect of omega-3 and vitamin E supplement to Reactive Oxygen Species (ROS) and placental Vascular Endothelial Growth Factor (VEGF) on PE rats model. AIM: This study aimed to investigate the effect of omega-3 and vitamin E supplementation on ROS and placental VEGF. METHODS: This research has been carried out at animal house and Biomedical Laboratory of the Medical Faculty Andalas University. The design of this research was experimental study with post-test only control group design. Thirty pregnant rats were divided into five groups. Group K-without treatment, group K+ was given L-NAME, group P1 was given L-NAME + omega-3, group P2 was given L-NAME + vitamin E, and group P3 was given L-NAME + omega-3 + vitamin E. The L-NAME dose was 50 mg/kg/day. At the 19th day of gestation, the pregnancy was terminated and the blood serum was used for examination of ROS and placental tissue was collected for examination of VEGF using ELISA kit. The data were analyzed by one-way ANOVA and post hoc test Bonferoni. RESULTS: The analysis results found that there were significant differences between omega-3 and vitamin E supplements on ROS levels and placental VEGF levels. Administration of omega-3 only or combination with vitamin E can effectively improve endothelial function by increasing the level of VEGF. CONCLUSION: Omega-3 (DHA 120 mg, EPA 180 mg) and vitamin E (α-tocopherol 300 iu) supplement decreased ROS and increased placental VEGF on pre-eclampsia rats model.

Serum From Preeclamptic Women Triggers Endoplasmic Reticulum Stress Pathway and Expression of Angiogenic Factors in Trophoblast Cells

Preeclampsia (PE) is a hypertensive disease of pregnancy-associated with placental cell death and endoplasmic reticulum (ER) stress. It is unknown whether systemic factors aggravate placental dysfunction. We investigated whether serum factors in pregnant women with PE activate ER stress and unfolded protein responses (UPRs) in placental explants and trophoblast cells lineage. We cultured placental explants from third-trimester term placentas from control non-preeclamptic (NPE) pregnant women with serum from women with PE or controls (NPE). In PE-treated explants, there was a significant increase in gene expression of GADD34, CHOP, and SDF2. At the protein level, GRP78, SDF2, p-eIF2α, and p-eIF2α/eIF2α ratio were also augmented in treated explants. Assays were also performed in HTR8/SV-neo trophoblast cell line to characterize the putative participation of trophoblast cells. In PE serum-treated protein levels of p-eIF2a and the ratio p-elF2 α/elF2α increased after 12 h of treatment, while the gene expression of GADD34, ATF4, and CHOP was greater than control. Increased expression of SDF2 was also detected after 24 h-cultured HTR8/SV-neo cells. PE serum increased sFLT1 gene expression and decreased PlGF gene expression in placental explants. Morphologically, PE serum increased the number of syncytial knots and reduced placental cell metabolism and viability. Analysis of the serum of pregnant women with PE through Raman spectroscopy showed changes in amino acids, carotenoids, lipids, and DNA/RNA, which may be associated with the induction of ER stress found in chorionic villi treated with this serum. In conclusion, this study provides evidence that the serum of pregnant women with PE may impact placental villi changing its morphology, viability, and secreted functional factors while triggers ER stress and an UPR. The differences between PE and control sera include molecules acting as inducing factors in these processes. In summary, the results obtained in our assays suggest that after the development of PE, the serum profile of pregnant women may be an additional factor that feeds a continuous imbalance of placental homeostasis. In addition, this study may expand the possibilities for understanding the pathogenesis of this disorder.

MicroRNAs targeting VEGF are related to vascular dysfunction in preeclampsia

In preeclampsia (PE), pre-existent maternal endothelial dysfunction leads to impaired placentation and vascular maladaptation. The vascular endothelial growth factor (VEGF) pathway is essential in the placentation process and VEGF expression is regulated through post-transcriptional modification by microRNAs (miRNAs). We investigated the expression of VEGF-related circulating miR-16, miR-29b, miR-126, miR-155 and miR-200c in PE vs healthy pregnancies (HPs), and their relation with vascular function, oxidative stress (OS) and systemic inflammation. In this case-control study, 24 women with early PE (<34 weeks) were compared with 30 women with HP. Circulating microRNA levels (RT-qPCR), OS and systemic inflammation were assessed in plasma samples (PE 29.5 vs HP 25.8 weeks) and related to extensive in vivo vascular function (flow-mediated dilatation (FMD), modified FMD (mFMD), carotid-femoral pulse wave velocity (CF-PWV), heart rate corrected augmentation index (AIx75) and reactive hyperemia index (RHI)). FMD, CF-PWV, AIx75 and RHI were all significantly impaired in PE (P<0.05). PE patients had reduced levels of miR-16 (5.53 ± 0.36 vs 5.84 ± 0.61) and increased levels of miR-200c (1.34 ± 0.57 vs 0.97 ± 0.68) (P<0.05). Independent of age and parity, miR-16 was related to impaired FMD (β 2.771, 95% C.I.: 0.023-5.519, P=0.048) and mFMD (β 3.401, 95% C.I.: 0.201-6.602, P=0.038). Likewise, miR-200c was independently associated with CF-PWV (β 0.513, 95% C.I.: 0.034-0.992, P=0.036). In conclusion, circulating levels of miR-16 were lower in PE, which correlated with impaired endothelial function. Circulating miR-200c was increased in PE and correlated with higher arterial stiffness. These findings suggest a post-transcriptional dysregulation of the VEGF pathway in PE and identify miR-16 and miR-200c as possible diagnostic biomarkers for PE.

Syncytiotrophoblast stress in early onset preeclampsia: The issues perpetuating the syndrome

Preeclampsia is a pregnancy-specific syndrome characterized by a sudden increase in blood pressure accompanied by proteinuria and/or maternal multi-system damage associated to poor fetal outcome. In early-onset preeclampsia, utero-placental perfusion is altered, causing constant and progressive damage to the syncytiotrophoblast, generating syncytiotrophoblast stress. The latter leads to the detachment and release of syncytiotrophoblast fragments, anti-angiogenic factors and pro-inflammatory molecules into maternal circulation, resulting in the emergence and persistence of the characteristic symptoms of this syndrome during pregnancy. Therefore, understanding the origin and consequences of syncytiotrophoblast stress in preeclampsia is vital to develop new therapeutic alternatives, focused on reducing the burden of this syndrome. In this review, we describe five central characteristics of syncytial stress that should be targeted or prevented in order to reduce preeclampsia symptoms: histological alterations, syncytiotrophoblast damage, antiangiogenic protein export, placental deportation, and altered syncytiotrophoblast turnover. Therapeutic management of these characteristics may improve maternal and fetal outcomes.

CREB-binding protein (CREBBP) and preeclampsia: a new promising target gene

Preeclampsia (PE) is a major complication of pregnancy and remains a leading cause of neonatal and maternal mortality worldwide. Several studies have revealed that the incidence of preeclampsia is high in mothers who carried a fetus with Rubinstein-Taybi Syndrome due to the mutation in CREBBP. We aimed to compare the expression level of the CERBBP gene between preeclamptic and healthy placenta in our study. The expression level of CREBBP gene was evaluated in a total of one hundred placental biopsies from PE patients and healthy pregnant women after delivery using quantitative real-time polymerase chain reaction (qRT-PCR). Moreover, the differential expression of CREBBP was assessed between the maternal and fetal sides of the placenta. Expression of the CREBBP gene was higher in preeclampsia patients compared with the controls (Fold change = 2.158; P = 0.018). Moreover, the gene expression was slightly higher in the fetal side of the placenta, although it was not significantly different (Fold change = 1.713, P = 0.254). Our findings show a role for CREBBP in the pathogenesis of PE. Due to the important role of CREBBP in angiogenesis and hypoxia, the gene may serve as a promising target in future studies.

Role of Vascular Endothelial Growth Factor (VEGF) in Human Embryo Implantation: Clinical Implications

Vascular endothelial growth factor (VEGF) is a well-known angiogenic factor that plays a critical role in various physiological and pathological processes. VEGF also contributes to the process of embryo implantation by enhancing embryo development, improving endometrial receptivity, and facilitating the interactions between the developing embryo and the endometrium. There is a correlation between the alteration of VEGF expression and reproductive failure, including recurrent implantation failure (RIF) and recurrent miscarriage (RM). In order to clarify the role of VEGF in embryo implantation, we reviewed recent literature concerning the expression and function of VEGF in the reproductive system around the time of embryo implantation and we provide a summary of the findings reported so far. We also explored the effects and the possible underlying mechanisms of action of VEGF in embryo implantation.

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.