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

Sex-specific effect of antenatal Zika virus infection on murine fetal growth, placental nutrient transporters, and nutrient sensor signaling pathways

Maternal Zika virus (ZIKV) infection during pregnancy has been associated with severe intrauterine growth restriction (IUGR), placental damage, metabolism disturbances, and newborn neurological abnormalities. Here, we investigated the impact of maternal ZIKV infection on placental nutrient transporters and nutrient-sensitive pathways. Immunocompetent (C57BL/6) mice were injected with Low (103 PFU-ZIKVPE243) or High (5 × 107 PFU-ZIKVPE243) ZIKV titers at gestational day (GD) 12.5, and tissue was collected at GD18.5 (term). Fetal-placental growth was impaired in male fetuses, which exhibited higher placental expression of the ZIKV infective marker, eukaryotic translation initiation factor 2 (eIF2α), but lower levels of phospho-eIF2α. There were no differences in fetal-placental growth in female fetuses, which exhibited no significant alterations in placental ZIKV infective markers. Furthermore, ZIKV promoted increased expression of glucose transporter type 1 (Slc2a1/Glut1) and decreased levels of glucose-6-phosphate in female placentae, with no differences in amino acid transport potential. In contrast, ZIKV did not impact glucose transporters in male placentae but downregulated sodium-coupled neutral amino acid 2 (Snat2) transporter expression. We also observed sex-dependent differences in the hexosamine biosynthesis pathway (HBP) and O-GlcNAcylation in ZIKV-infected pregnancies, showing that ZIKV can disturb placental nutrient sensing. Our findings highlight molecular alterations in the placenta caused by maternal ZIKV infection, shedding light on nutrient transport, sensing, and availability. Our results also suggest that female and male placentae employ distinct coping mechanisms in response to ZIKV-induced metabolic changes, providing insights into therapeutic approaches for congenital Zika syndrome.

Down-regulation of O-GlcNAcylation alleviates insulin signaling pathway impairment following arsenic exposure via suppressing the AMPK/mTOR-autophagy pathway

Impairment of the insulin signaling pathway is a key contributor to insulin resistance under arsenic exposure. Specifically, O-GlcNAcylation, an important post-translational modification, plays a crucial role in insulin resistance. Nevertheless, the concrete effect and mechanism of O-GlcNAcylation in arsenic-induced impairment of the insulin signaling pathway remain elusive. Herein, C57BL/6 mice were continuously fed arsenic-containing food, with a total arsenic concentration of 30 mg/kg. We observed that the IRS/Akt/GSK-3β insulin signaling pathway was impaired, and autophagy was activated in mouse livers and HepG2 cells exposed to arsenic. Additionally, O-GlcNAcylation expression in mouse livers and HepG2 cells was elevated, and the key O-GlcNAcylation homeostasis enzyme, O-GlcNAc transferase (OGT), was upregulated. In vitro, non-targeted metabolomic analysis showed that metabolic disorder was induced, and inhibition of O-GlcNAcylation restored the metabolic profile of HepG2 cells exposed to arsenic. In addition, we found that the compromised insulin signaling pathway was dependent on AMPK activation. Inhibition of AMPK mitigated autophagy activation and impairment of insulin signaling pathway under arsenic exposure. Furthermore, down-regulation of O-GlcNAcylation inhibited AMPK activation, thereby suppressing autophagy activation, and improving the impaired insulin signaling pathway. Collectively, our findings indicate that arsenic can impair the insulin signaling pathway by regulating O-GlcNAcylation homeostasis. Importantly, O-GlcNAcylation inhibition alleviated the impaired insulin signaling pathway by suppressing the AMPK/mTOR-autophagy pathway. This indicates that regulating O-GlcNAcylation may be a potential intervention for the impaired insulin signaling pathway induced by arsenic.

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.

Maternal-fetal cross-talk via the placenta: influence on offspring development and metabolism

Compelling epidemiological and animal experimental data demonstrate that cardiometabolic and neuropsychiatric diseases originate in a suboptimal intrauterine environment. Here, we review evidence suggesting that altered placental function may, at least in part, mediate the link between the maternal environment and changes in fetal growth and development. Emerging evidence indicates that the placenta controls the development and function of several fetal tissues through nutrient sensing, modulation of trophoblast nutrient transporters and by altering the number and cargo of released extracellular vesicles. In this Review, we discuss the development and functions of the maternal-placental-fetal interface (in humans and mice) and how cross-talk between these compartments may be a mechanism for in utero programming, focusing on mechanistic target of rapamycin (mTOR), adiponectin and O-GlcNac transferase (OGT) signaling. We also discuss how maternal diet and stress influences fetal development and metabolism and how fetal growth restriction can result in susceptibility to developing chronic disease later in life. Finally, we speculate how interventions targeting placental function may offer unprecedented opportunities to prevent cardiometabolic disease in future generations.

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.

The role of O-GlcNAcylation in development

O-GlcNAcylation is a dynamic post-translational modification performed by two opposing enzymes: O-GlcNAc transferase and O-GlcNAcase. O-GlcNAcylation is generally believed to act as a metabolic integrator in numerous signalling pathways. The stoichiometry of this modification is tightly controlled throughout all stages of development, with both hypo/hyper O-GlcNAcylation resulting in broad defects. In this Primer, we discuss the role of O-GlcNAcylation in developmental processes from stem cell maintenance and differentiation to cell and tissue morphogenesis.

Tet Enzyme-Mediated Response in Environmental Stress and Stress-Related Psychiatric Diseases

Mental disorders caused by stress have become a worldwide public health problem. These mental disorders are often the results of a combination of genes and environment, in which epigenetic modifications play a crucial role. At present, the genetic and epigenetic mechanisms of mental disorders such as posttraumatic stress disorder or depression caused by environmental stress are not entirely clear. Although many epigenetic modifications affect gene regulation, the most well-known modification in eukaryotic cells is the DNA methylation of CpG islands. Stress causes changes in DNA methylation in the brain to participate in the neuronal function or mood-modulating behaviors, and these epigenetic modifications can be passed on to offspring. Ten-eleven translocation (Tet) enzymes are the 5-methylcytosine (5mC) hydroxylases of DNA, which recognize 5mC on the DNA sequence and oxidize it to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Tet regulates gene expression at the transcriptional level through the demethylation of DNA. This review will elaborate on the molecular mechanism and the functions of Tet enzymes in environmental stress-related disorders and discuss future research directions.

O-GlcNAc transferase contributes to sex-specific placental deregulation in gestational diabetes

INTRODUCTION

Gestational diabetes (GDM) is traditionally thought to emerge from placental endocrine dysregulations, but recent evidence suggests that fetal sex can also impact GDM development. Understanding the molecular mechanisms through which sex modulates placenta physiology can help identify novel molecular targets for future clinical care. Thus, we investigated the nutrient-sensing O-GlcNAc pathway as a potential mediator of sex-specific placenta dysfunction in GDM.

METHODS

Expression levels of O-GlcNAc enzymes were measured in male and female (n = 9+/gender) human placentas based on the maternal diagnosis of GDM. We then simulated the observed differences in both BeWo cells and human syncytiotrophoblasts primary cells (SCT) from male and female origins (n = 6/gender). RNA sequencing and targeted qPCR were performed to characterize the subsequent changes in the placenta transcriptome related to gestational diabetes.

RESULTS

O-GlcNAc transferase (OGT) expression was significantly reduced only in male placenta collected from mothers with GDM compared to healthy controls. Similar downregulation of OGT in trophoblast-like BeWo male cells demonstrated significant gene expression deregulations that overlapped with known GDM-related genes. Notably, placental growth hormone (GH) production was significantly elevated, while compensatory factors against GH-related insulin resistance were diminished. Inflammatory and immunologic factors with toxic effects on pancreatic β cell mass were also increased, altogether leaning toward a decompensatory diabetic profile. Similar changes in hormone expression were confirmed in male human primary SCTs transfected with siOGT. However, down-regulating OGT in female primary SCTs did not impact hormone production.

CONCLUSION

Our study demonstrated the significant deregulation of placental OGT levels in mothers with GDM carrying a male fetus. When simulated in vitro, such deregulation impacted hormonal production in BeWo trophoblast cells and primary SCTs purified from male placentas. Interestingly, female placentas were only modestly impacted by OGT downregulation, suggesting that the sex-specific presentation observed in gestational diabetes could be related to O-GlcNAc-mediated regulation of placental hormone production.

The O-GlcNAc cycling in neurodevelopment and associated diseases

Proper neuronal development is essential to growth and adult brain function. Alterations at any step of this highly organized sequence of events, due to genetic mutations or environmental factors, triggers brain malformations, which are leading causes of diseases including epilepsy, intellectual disabilities, and many others. The role of glycosylation in neuronal development has been emphasized for many years, notably in studying human congenital disorders of glycosylation (CDGs). These diseases highlight that genetic defects in glycosylation pathways are almost always associated with severe neurological abnormalities, suggesting that glycosylation plays an essential role in early brain development. Congenital disorders of O-GlcNAcylation are no exception, and all mutations of the O-GlcNAc transferase (OGT) are associated with X-linked intellectual disabilities (XLID). In addition, mouse models and in vitro mechanistic studies have reinforced the essential role of O-GlcNAcylation in neuronal development and signaling. In this review, we give an overview of the role of O-GlcNAcylation in this critical physiological process and emphasize the consequences of its dysregulation.

Posttranslational modifications in diabetes: Mechanisms and functions

As one of the most widespread chronic diseases, diabetes and its accompanying complications affect approximately one tenth of individuals worldwide and represent a growing cause of morbidity and mortality. Accumulating evidence has proven that the process of diabetes is complex and interactive, involving various cellular responses and signaling cascades by posttranslational modifications (PTMs). Therefore, understanding the mechanisms and functions of PTMs in regulatory networks has fundamental importance for understanding the prediction, onset, diagnosis, progression, and treatment of diabetes. In this review, we offer a holistic summary and illustration of the crosstalk between PTMs and diabetes, including both types 1 and 2. Meanwhile, we discuss the potential use of PTMs in diabetes treatment and provide a prospective direction for deeply understanding the metabolic diseases.

O-GlcNAcylation: The Underestimated Emerging Regulators of Skeletal Muscle Physiology

O-GlcNAcylation is a highly dynamic, reversible and atypical glycosylation that regulates the activity, biological function, stability, sublocation and interaction of target proteins. O-GlcNAcylation receives and coordinates different signal inputs as an intracellular integrator similar to the nutrient sensor and stress receptor, which target multiple substrates with spatio-temporal analysis specifically to maintain cellular homeostasis and normal physiological functions. Our review gives a brief description of O-GlcNAcylation and its only two processing enzymes and HBP flux, which will help to better understand its physiological characteristics of sensing nutrition and environmental cues. This nutritional and stress-sensitive properties of O-GlcNAcylation allow it to participate in the precise regulation of skeletal muscle metabolism. This review discusses the mechanism of O-GlcNAcylation to alleviate metabolic disorders and the controversy about the insulin resistance of skeletal muscle. The level of global O-GlcNAcylation is precisely controlled and maintained in the “optimal zone”, and its abnormal changes is a potential factor in the pathogenesis of cancer, neurodegeneration, diabetes and diabetic complications. Although the essential role of O-GlcNAcylation in skeletal muscle physiology has been widely studied and recognized, it still is underestimated and overlooked. This review highlights the latest progress and potential mechanisms of O-GlcNAcylation in the regulation of skeletal muscle contraction and structural properties.

Placental Insulin Receptor Transiently Regulates Glucose Homeostasis in the Adult Mouse Offspring of Multiparous Dams

In pregnancies complicated by maternal obesity and gestational diabetes mellitus, there is strong evidence to suggest that the insulin signaling pathway in the placenta may be impaired. This may have potential effects on the programming of the metabolic health in the offspring; however, a direct link between the placental insulin signaling pathway and the offspring health remains unknown. Here, we aimed to understand whether specific placental loss of the insulin receptor (InsR) has a lasting effect on the offspring health in mice. Obesity and glucose homeostasis were assessed in the adult mouse offspring on a normal chow diet (NCD) followed by a high-fat diet (HFD) challenge. Compared to their littermate controls, InsR KO^placenta offspring were born with normal body weight and pancreatic β-cell mass. Adult InsR KO^placenta mice exhibited normal glucose homeostasis on an NCD. Interestingly, under a HFD challenge, adult male InsR KO^placenta offspring demonstrated lower body weight and a mildly improved glucose homeostasis associated with parity. Together, our data show that placenta-specific insulin receptor deletion does not adversely affect offspring glucose homeostasis during adulthood. Rather, there may potentially be a mild and transient protective effect in the mouse offspring of multiparous dams under the condition of a diet-induced obesogenic challenge.

The sex-specific difference in singleton birth weight after frozen embryo transfer compared with fresh embryo transfer: a secondary analysis of 3 randomized trials

OBJECTIVE

To assess whether the between-group difference in singleton birth weight following frozen vs. fresh embryo transfer varied with infant sex.

DESIGN

A post hoc exploratory secondary analysis of data from three multicenter randomized trials compared the live birth rates between freeze-only vs. fresh embryo transfer.

SETTING

Academic fertility centers.

PATIENT(S)

A total of 1,886 women who achieved singleton live birth after a frozen or fresh embryo transfer during these trials were included.

INTERVENTION(S)

Women underwent either a frozen or fresh embryo transfer.

MAIN OUTCOME MEASURE(S)

Mean birth weight, large for gestational age (LGA), and small for gestational age (SGA).

RESULT(S)

There was an interaction between the types of embryo transfer and infant sex on the birth weight and on the incidences of LGA and SGA. Among male infants, compared with singletons following fresh embryo transfer, singletons following frozen embryo transfer had higher mean birth weights (3,520.6 ± 526.1 vs. 3,345.1 ± 524.9 g), a higher risk of being LGA (25.2% vs. 15.7%), and a lower risk of being SGA (3.3% vs. 6.1%). However, among the female infants, no statistically significant difference was found in the mean birth weight (3,336.5 ± 514.8 vs. 3,299.5 ± 485.0 g) or the risks of being LGA (18.8% vs. 15.7%) or SGA (5.2% vs. 6.0%) between frozen and fresh embryo transfer.

CONCLUSION(S)

Male singletons born after frozen embryo transfer were more likely to have a higher birth weight than those born after fresh embryo transfer.