O-GlcNAc Modification During Pregnancy: Focus on Placental Environment

Advances in post-translational modifications and recurrent spontaneous abortion

Recurrent spontaneous abortion (RSA) is defined as two or more pregnancy loss, which affects approximately 1-2 % of women's fertility. The etiology of RSA has not yet been fully revealed, which poses a great problem for clinical treatment. Post- translational modifications(PTMs) are chemical modifications that play a crucial role in the functional proteome. A considerable number of published studies have shown the relationship between post-translational modifications of various proteins and RSA. The study of PTMs contributes to elucidating the role of modified proteins in the pathogenesis of RSA, as well as the design of more effective diagnostic/prognostic tools and more targeted treatments. Most reviews in the field of RSA have only focused on RNA epigenomics research. The present review reports the latest research developments of PTMs related to RSA, such as glycosylation, phosphorylation, Methylation, Acetylation, Ubiquitination, etc.

Paternal DDT exposure induces sex-specific programming of fetal growth, placenta development and offspring's health phenotypes in a mouse model

Mounting evidence suggests that environmentally induced epigenetic inheritance occurs in mammals and that traits in the progeny can be shaped by parental environmental experiences. Epidemiological studies link parental exposure to environmental toxicants, such as the pesticide DDT, to health phenotypes in the progeny, including low birth and increased risk of chronic diseases later in life. Here, we show that the progeny of male mice exposed to DDT in the pre-conception period are born smaller and exhibit sexual dimorphism in metabolic function, with male, but not female, offspring developing severe glucose intolerance compared to controls. These phenotypes in DDT offspring were linked to reduced fetal growth and placenta size as well as placenta-specific reduction of glycogen levels and the nutrient sensor and epigenetic regulator OGT, with more pronounced phenotypes observed in male placentas. However, placenta-specific genetic reduction of OGT only partially replicates the metabolic phenotype observed in offspring of DDT-exposed males. Our findings reveal a role for paternal pre-conception environmental experiences in shaping placenta development and in fetal growth restriction. While many questions remain, our data raise the tantalizing possibility that placenta programming could be a mediator of environmentally induced intergenerational epigenetic inheritance of phenotypes and needs to be further evaluated.

A Metabolic Axis of Immune Intractability

Immune cells in the tumor niche robustly influence disease progression. Remarkably, in cancer, developmental pathways are reenacted. Many parallels between immune regulation of embryonic development and immune regulation of tumor progression can be drawn, with evidence clearly supporting an immune-suppressive microenvironment in both situations. In these ecosystems, metabolic and bioenergetic circuits guide and regulate immune cell differentiation, plasticity, and functional properties of suppressive and inflammatory immune subsets. As such, there is an emerging pattern of intersection across the dynamic process of ontogeny and the ever-evolving tumor neighborhood. In this article, we focus on the convergence of immune programming during ontogeny and in the tumor microenvironment. Exemplifying dysregulation of Hedgehog (Hh) activity, a key player during ontogeny, we highlight a critical convergence of these fields and the metabolic axis of the nutrient sensing hexosamine biosynthetic pathway (HBP) that integrates glucose, glutamine, amino acids, acetyl CoA, and uridine-5'-triphosphate (UTP), culminating in the synthesis of UDP-GlcNAc, a metabolite that functions as a metabolic and bioenergetic sensor. We discuss an emerging pattern of immune regulation, orchestrated by O-GlcNAcylation of key transcriptional regulators, spurring suppressive activity of dysfunctional immune cells in the tumor microenvironment.

Physiological and pathological evidence of O-GlcNAcylation regulation during pregnancy related process

O-GlcNAcylation is a dynamic and reversible post-translational modification (PTM) controlled by the enzymes O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). Changes in its expression lead to a breakdown in cellular homeostasis, which is linked to several pathological processes. Placentation and embryonic development are periods of high cell activity, and imbalances in cell signaling pathways can result in infertility, miscarriage, or pregnancy complications. O-GlcNAcylation is involved in cellular processes such as genome maintenance, epigenetic regulation, protein synthesis/degradation, metabolic pathways, signaling pathways, apoptosis, and stress response. Trophoblastic differentiation/invasion and placental vasculogenesis, as well as zygote viability and embryonic neuronal development, are all dependent on O-GlcNAcylation. This PTM is required for pluripotency, which is a required condition for embryonic development. Further, this pathway is a nutritional sensor and cell stress marker, which is primarily measured by the OGT enzyme and its product, protein O-GlcNAcylation. Yet, this post-translational modification is enrolled in metabolic and cardiovascular adaptations during pregnancy. Finally, evidence of how O-GlcNAc impacts pregnancy during pathological conditions such as hyperglycemia, gestational diabetes, hypertension, and stress disorders are reviewed. Considering this scenario, progress in understanding the role of O- GlcNAcylation in pregnancy is required.

Stress-Sensitive Regulators of Fetal Neurodevelopment in HIV and Preeclampsia: An Immunocytochemical Appraisal of Placental OGT and T4 Levels

Preeclampsia and HIV are a significant burden to maternal health globally, especially in low-middle income countries such as South Africa. In the KwaZulu-Natal province, SA antenatal HIV prevalence is 41.1%, while PE is 12%. PE and HIV infections are maternal stress and inflammation that impact placental function and fetal development. Therefore, this study investigated the impact of the comorbidity of PE and HIV on placental stress and neurodevelopment. Placentae were obtained from four cohorts of pregnant women: normotensive HIV negative, normotensive HIV positive, preeclamptic HIV negative, and preeclamptic HIV positive. The placental tissue sections were immunostained for OGT and T4. Our findings showed that the maternal weight, diastolic, and systolic blood pressures (BP) were higher in PE vs. the normotensive groups, irrespective of HIV status. In addition, significant changes were noticed in the placental weight, fetoplacental ratio, and placental efficiency coefficient. Our findings showed that the maternal weight, diastolic, and systolic blood pressures (BP) were statistically higher in the PE compared to the normotensive. No significant differences were observed between HIV positive and HIV negative groups. In addition, significant changes were noticed in the placental weight, fetoplacental ratio, and placental coefficient. Furthermore, considerable upregulation in the placental expression of OGT in both the conducting and exchange villi of PE and concomitant downregulation in HIV-positive patients compared with Normotensive and HIV-negative individuals, respectively. Our results provide inferential evidence on the dysregulation of OGT in the comorbidity of PE and HIV. This may mediate a compromised programmed outcome of an adverse maternal environment during pregnancy and consequently affect fetal development.

Disruption of O-GlcNAcylation Homeostasis Induced Ovarian Granulosa Cell Injury in Bovine

O-linked β-N-acetylglucosamine (O-GlcNAc) modification is a ubiquitous, reversible, and highly dynamic post-translational modification, which takes charge of almost all biological processes examined. However, little information is available regarding the molecular regulation of O-GlcNAcylation in granulosa cell function and glucose metabolism. This study focused on the impact of disrupted O-GlcNAc cycling on the proliferation and apoptosis of bovine granulosa cells, and further aimed to determine how this influenced glucose metabolism. Pharmacological inhibition of OGT with benzyl-2-acetamido-2-deoxy-α-D-galactopyranoside (BADGP) led to decreased cellular O-GlcNAc levels, as well as OGT and OGA protein expressions, whereas increasing O-GlcNAc levels with the OGA inhibitor, O-(2-acetamido-2-deoxy-D-gluco-pyranosylidene) (PUGNAc), resulted in elevated OGA protein expression and decreased OGT protein expression in granulosa cells. Dysregulated O-GlcNAc cycling reduced cell viability, downregulated the proliferation-related genes of CDC42 and PCNA transcripts, upregulated the pro-apoptotic genes of BAX and CASPASE-3 mRNA and the ratio of BAX/BCL-2, and increased the apoptotic rate. Glycolytic enzyme activities of hexokinase and pyruvate kinase, metabolite contents of pyruvate and lactate, mitochondrial membrane potential, ATP levels, and intermediate metabolic enzyme activities of succinate dehydrogenase and malate dehydrogenase involved in the tricarboxylic acid cycle, were significantly impaired in response to altered O-GlcNAc levels. Moreover, inhibition of OGT significantly increased the expression level of thioredoxin-interacting protein (TXNIP), but repression of OGA had no effect. Collectively, our results suggest that perturbation of O-GlcNAc cycling has a profound effect on granulosa cell function and glucose metabolism.

Protein O-GlcNAcylation as a nutrient sensor signaling placental dysfunction in hypertensive pregnancy

INTRODUCTION

During pregnancy, arterial hypertension may impair placental function, which is critical for a healthy baby's growth. Important proteins during placentation are known to be targets for O-linked β-N-acetylglucosamine modification (O-GlcNAcylation), and abnormal protein O-GlcNAcylation has been linked to pathological conditions such as hypertension. However, it is unclear how protein O-GlcNAcylation affects placental function and fetal growth throughout pregnancy during hypertension.

METHODS

To investigate this question, female Wistar and spontaneously hypertensive rats (SHR) were mated with male Wistar rats, and after pregnancy confirmation by vaginal smear, rats were divided into groups of 14, 17, and 20 days of pregnancy (DOPs). On the 14th, 17th, and 20th DOP, rats were euthanized, fetal parameters were measured, and placentas were collected for western blot, immunohistochemical, and morphological analyses.

RESULTS

SHR presented a higher blood pressure than the Wistar rats (p=0.001). Across all DOPs, SHR showed reduced fetal weight and an increase in small-for-gestational-age fetuses. While near-term placentas were heavier in SHR (p=0.006), placental efficiency decreased at 17 (p=0.01) and 20 DOPs (p<0.0001) in this group. Morphological analysis revealed reduced junctional zone area and labyrinth vasculature changes on SHR placentas in all DOPs. O-GlcNAc protein expression was lower in placentas from SHR compared with Wistar at 14, 17, and 20 DOPs. Decreased expression of O-GlcNAc transferase (p=0.01) and O-GlcNAcase (p=0.002) enzymes was found at 14 DOPs in SHR. Immunohistochemistry showed reduced placental O-GlcNAc content in both the junctional zone and labyrinth of the placentas from SHR. Periodic acid-Schiff analysis showed decreased glycogen cell content in the placentas from SHR at 14, 17, and 20 DOPs. Moreover, glucose transporter 1 expression was decreased in placentas from SHR in all DOPs.

CONCLUSIONS

These findings suggest that decreased protein O-GlcNAcylation caused by insufficient placental nutritional apport contributes to placental dysfunction during hypertensive pregnancy, impairing fetal growth.

Disruption of O-Linked N-Acetylglucosamine Signaling in Placenta Induces Insulin Sensitivity in Female Offspring

Placental dysfunction can lead to fetal growth restriction which is associated with perinatal morbidity and mortality. Fetal growth restriction increases the risk of obesity and diabetes later in life. Placental O-GlcNAc transferase (OGT) has been identified as a marker and a mediator of placental insufficiency in the setting of prenatal stress, however, its role in the fetal programming of metabolism and glucose homeostasis remains unknown. We aim to determine the long-term metabolic outcomes of offspring with a reduction in placental OGT. Mice with a partial reduction and a full knockout of placenta-specific OGT were generated utilizing the Cre-Lox system. Glucose homeostasis and metabolic parameters were assessed on a normal chow and a high-fat diet in both male and female adult offspring. A reduction in placental OGT did not demonstrate differences in the metabolic parameters or glucose homeostasis compared to the controls on a standard chow. The high-fat diet provided a metabolic challenge that revealed a decrease in body weight gain (p = 0.02) and an improved insulin tolerance (p = 0.03) for offspring with a partially reduced placental OGT but not when OGT was fully knocked out. Changes in body weight were not associated with changes in energy homeostasis. Offspring with a partial reduction in placental OGT demonstrated increased hepatic Akt phosphorylation in response to insulin treatment (p = 0.02). A partial reduction in placental OGT was protective from weight gain and insulin intolerance when faced with the metabolic challenge of a high-fat diet. This appears to be, in part, due to increased hepatic insulin signaling. The findings of this study contribute to the greater understanding of fetal metabolic programming and the effect of placental OGT on peripheral insulin sensitivity and provides a target for future investigation and clinical applications.

O-GlcNAcylation in Hyperglycemic Pregnancies: Impact on Placental Function

The dynamic cycling of N-acetylglucosamine, termed as O-GlcNAcylation, is a post-translational modification of proteins and is involved in the regulation of fundamental cellular processes. It is controlled by two essential enzymes, O-GlcNAc transferase and O-GlcNAcase. O-GlcNAcylation serves as a modulator in placental tissue; furthermore, increased levels of protein O-GlcNAcylation have been observed in women with hyperglycemia during pregnancy, which may affect the short-and long-term development of offspring. In this review, we focus on the impact of O-GlcNAcylation on placental functions in hyperglycemia-associated pregnancies. We discuss the following topics: effect of O-GlcNAcylation on placental development and its association with hyperglycemia; maternal-fetal nutrition transport, particularly glucose transport, via the mammalian target of rapamycin and AMP-activated protein kinase pathways; and the two-sided regulatory effect of O-GlcNAcylation on inflammation. As O-GlcNAcylation in the placental tissues of pregnant women with hyperglycemia influences near- and long-term development of offspring, research in this field has significant therapeutic relevance.

Protein O-GlcNAcylation Promotes Trophoblast Differentiation at Implantation

Embryo implantation begins with blastocyst trophectoderm (TE) attachment to the endometrial epithelium, followed by the breaching of this barrier by TE-derived trophoblast. Dynamic protein modification with O-linked β-N-acetylglucosamine (O-GlcNAcylation) is mediated by O-GlcNAc transferase and O-GlcNAcase (OGA), and couples cellular metabolism to stress adaptation. O-GlcNAcylation is essential for blastocyst formation, but whether there is a role for this system at implantation remains unexplored. Here, we used OGA inhibitor thiamet g (TMG) to induce raised levels of O-GlcNAcylation in mouse blastocysts and human trophoblast cells. In an in vitro embryo implantation model, TMG promoted mouse blastocyst breaching of the endometrial epithelium. TMG reduced expression of TE transcription factors Cdx2, Gata2 and Gata3, suggesting that O-GlcNAcylation stimulated TE differentiation to invasive trophoblast. TMG upregulated transcription factors OVOL1 and GCM1, and cell fusion gene ERVFRD1, in a cell line model of syncytiotrophoblast differentiation from human TE at implantation. Therefore O-GlcNAcylation is a conserved pathway capable of driving trophoblast differentiation. TE and trophoblast are sensitive to physical, chemical and nutritive stress, which can occur as a consequence of maternal pathophysiology or during assisted reproduction, and may lead to adverse neonatal outcomes and associated adult health risks. Further investigation of how O-GlcNAcylation regulates trophoblast populations arising at implantation is required to understand how peri-implantation stress affects reproductive outcomes.

Loss of O-GlcNAc transferase in neural stem cells impairs corticogenesis

The proper development of the cerebral cortex is essential for brain formation and functioning. O-GlcNAcylation, an important posttranslational modification, regulates the pathways critical for neuronal health and the survival of the cerebral cortex in neurodegenerative diseases. However, the role of O-GlcNAcylation in regulating cerebral cortical development at the embryonic and early postnatal (0-21 days) stages is still largely unknown. Here we report that the selective deletion of O-GlcNAc transferase (OGT) in neural stem cells (NSCs) in mice led to a series of severe brain developmental deficits, including dramatic shrinkage of cortical and hippocampal histoarchitecture, widespread neuronal apoptosis, decrease in cell proliferation, induction of endoplasmic reticulum (ER) stress, and inhibition of neuronal dendritic and axonal differentiation. The pathology of corticogenesis deficits caused by OGT deletion may largely rely on complicated biological processes, such as proliferation, apoptosis and differentiation. Our results suggest that dysfunctional O-GlcNAcylation in NSCs may be an important contributor to neurodevelopmental diseases.

O-GlcNAcylation on LATS2 disrupts the Hippo pathway by inhibiting its activity

The Hippo pathway plays a crucial role in maintaining tissue homeostasis. Generally, activated Hippo pathway effectors, YAP/TAZ, induce the transcription of their negative regulators, NF2 and LATS2, and this negative feedback loop maintains homeostasis of the Hippo pathway. However, YAP and TAZ are consistently hyperactivated in various cancer cells, enhancing tumor growth. Our study found that LATS2, a direct-inhibiting kinase of YAP/TAZ and a core component of the negative feedback loop in the Hippo pathway, is modified with O-GlcNAc. LATS2 O-GlcNAcylation inhibited its activity by interrupting the interaction with the MOB1 adaptor protein, thereby activating YAP and TAZ to promote cell proliferation. Thus, our study suggests that LATS2 O-GlcNAcylation is deeply involved in Hippo pathway dysregulation in cancer cells.

The Hippo pathway controls organ size and tissue homeostasis by regulating cell proliferation and apoptosis. The LATS-mediated negative feedback loop prevents excessive activation of the effectors YAP/TAZ, maintaining homeostasis of the Hippo pathway. YAP and TAZ are hyperactivated in various cancer cells which lead to tumor growth. Aberrantly increased O-GlcNAcylation has recently emerged as a cause of hyperactivation of YAP in cancer cells. However, the mechanism, which induces hyperactivation of TAZ and blocks LATS-mediated negative feedback, remains to be elucidated in cancer cells. This study found that in breast cancer cells, abnormally increased O-GlcNAcylation hyperactivates YAP/TAZ and inhibits LATS2, a direct negative regulator of YAP/TAZ. LATS2 is one of the newly identified O-GlcNAcylated components in the MST-LATS kinase cascade. Here, we found that O-GlcNAcylation at LATS2 Thr436 interrupted its interaction with the MOB1 adaptor protein, which connects MST to LATS2, leading to activation of YAP/TAZ by suppressing LATS2 kinase activity. LATS2 is a core component in the LATS-mediated negative feedback loop. Thus, this study suggests that LATS2 O-GlcNAcylation is deeply involved in tumor growth by playing a critical role in dysregulation of the Hippo pathway in cancer cells.

Environmental influences on placental programming and offspring outcomes following maternal immune activation

Adverse experiences during pregnancy induce placental programming, affecting the fetus and its developmental trajectory. However, the influence of 'positive' maternal experiences on the placenta and fetus remain unclear. In animal models of early life stress, environmental enrichment (EE) has ameliorated and even prevented associated impairments in brain and behavior. Here, using a maternal immune activation (MIA) model in rats, we test whether EE attenuates maternal, placental and/or fetal responses to an inflammatory challenge, thereby offering a mechanism by which fetal programming may be prevented. Moreover, we evaluate life-long EE exposure on offspring development and examine a constellation of genes and epigenetic writers that may protect against MIA challenges. In our model, maternal plasma corticosterone and interleukin-1β were elevated 3 h after MIA, validating the maternal inflammatory response. Evidence for developmental programming was demonstrated by a simultaneous decrease in the placental enzymes Hsd11b2 and Hsd11b2/Hsd11b1, suggesting disturbances in glucocorticoid metabolism. Reductions of Hsd11b2 in response to challenge is thought to result in excess glucocorticoid exposure to the fetus and altered glucocorticoid receptor expression, increasing susceptibility to behavioral impairments later in life. The placental, but not maternal, glucocorticoid implications of MIA were attenuated by EE. There were also sustained changes in epigenetic writers in both placenta and fetal brain as a consequence of environmental experience and sex. Following MIA, both male and female juvenile animals were impaired in social discrimination ability. Life-long EE mitigated these impairments, in addition to the sex specific MIA associated disruptions in central Fkbp5 and Oprm1. These data provide the first evidence that EE protects placental functioning during stressor exposure, underscoring the importance of addressing maternal health and well-being throughout pregnancy. Future work must evaluate critical periods of EE use to determine if postnatal EE experience is necessary, or if prenatal exposure alone is sufficient to confer protection.

Hyperglycemia-Induced Aberrant Cell Proliferation; A Metabolic Challenge Mediated by Protein O-GlcNAc Modification

Chronic hyperglycemia has been associated with an increased prevalence of pathological conditions including cardiovascular disease, cancer, or various disorders of the immune system. In some cases, these associations may be traced back to a common underlying cause, but more often, hyperglycemia and the disturbance in metabolic balance directly facilitate pathological changes in the regular cellular functions. One such cellular function crucial for every living organism is cell cycle regulation/mitotic activity. Although metabolic challenges have long been recognized to influence cell proliferation, the direct impact of diabetes on cell cycle regulatory elements is a relatively uncharted territory. Among other "nutrient sensing" mechanisms, protein O-linked β-N-acetylglucosamine (O-GlcNAc) modification emerged in recent years as a major contributor to the deleterious effects of hyperglycemia. An increasing amount of evidence suggest that O-GlcNAc may significantly influence the cell cycle and cellular proliferation. In our present review, we summarize the current data available on the direct impact of metabolic changes caused by hyperglycemia in pathological conditions associated with cell cycle disorders. We also review published experimental evidence supporting the hypothesis that O-GlcNAc modification may be one of the missing links between metabolic regulation and cellular proliferation.