Maternal hyperglycemia alters glucose transport and utilization in mouse preimplantation embryos

Long-term culture induces Bax-dependent apoptosis in rat preimplantation embryos

Although rat preimplantation embryos are necessary for producing genetically modified rats, their in vitro culture remains a challenge. Rat zygotes can develop from the one-cell stage to the blastocyst stage in vitro; however, long-term culture reduces their developmental competence via an unknown mechanism. In this study, we examined how in vitro conditions affect rat preimplantation embryos, which may explain this reduced competence. Comprehensive gene expression analysis showed that genes related to apoptosis and energy metabolism were differentially expressed in rat embryos cultured long-term in vitro compared with those developed in vivo. Furthermore, we found that the expression of Bak1 and Bax, which are responsible for mitochondrial outer membrane permeabilization, were more upregulated in embryos cultured in vitro than those developed in vivo. Similarly, apoptosis-dependent DNA fragmentation was also exacerbated in in vitro culture conditions. Finally, gene disruption using CRISPR/Cas9 showed that Bax, but not Bak1, was responsible for these effects. These findings suggest that long-term in vitro culture induces Bax-dependent apoptosis through the mitochondrial pathway and may provide clues to improve the long-term culture of rat preimplantation embryos for genetic engineering research.

Embryonic diapause due to high glucose is related to changes in glycolysis and oxidative phosphorylation, as well as abnormalities in the TCA cycle and amino acid metabolism

Introduction

The adverse effects of high glucose on embryos can be traced to the preimplantation stage. This study aimed to observe the effect of high glucose on early-stage embryos.

Methods and results

Seven-week-old ICR female mice were superovulated and mated, and the zygotes were collected. The zygotes were randomly cultured in 5 different glucose concentrations (control, 20mM, 40mM, 60mM and 80mM glucose). The cleavage rate, blastocyst rate and total cell number of blastocyst were used to assess the embryo quality. 40 mM glucose was selected to model high glucose levels in this study. 40mM glucose arrested early embryonic development, and the blastocyst rate and total cell number of the blastocyst decreased significantly as glucose concentration was increased. The reduction in the total cell number of blastocysts in the high glucose group was attributed to decreased proliferation and increased cell apoptosis, which is associated with the diminished expression of GLUTs (GLUT1, GLUT2, GLUT3). Furthermore, the metabolic characterization of blastocyst culture was observed in the high-glucose environment.

Discussion

The balance of glycolysis and oxidative phosphorylation at the blastocyst stage was disrupted. And embryo development arrest due to high glucose is associated with changes in glycolysis and oxidative phosphorylation, as well as abnormalities in the TCA cycle and amino acid metabolism.

Mechanism of hyperproteinemia-induced damage to female reproduction in a genetic silkworm model

Hyperproteinemia is a metabolic disorder characterized by abnormally elevated plasma protein concentrations (PPC) in humans and animals. Here, a genetic silkworm model with high PPC was employed to investigate the effect of elevated PPC on female reproduction. Transcriptomic analysis revealed that high PPC induces downregulation of the ovarian development-related genes and disrupts ovarian sugar metabolism. Biochemical and endocrinal analyses revealed that high PPC increases trehalose and glucose levels in hemolymph and glycogen content in the fat body through activation of the gluconeogenic pathway and inhibition of the Insulin/Insulin-like growth factor signaling pathway-the serine/threonine kinase (IIS-AKT) pathway, thus disrupting characteristic metabolic homeostasis of sugar in the ovary. These resulted in ovarian developmental delay as well as reduced number and poor quality of eggs. Insulin supplementation effectively increased egg numbers by lowering blood sugar. These collective results provide new insights into the mechanisms by which high PPC negatively affects female reproduction and support the potential therapeutic effects of insulin.

Diagnostic workup of endocrine dysfunction in recurrent pregnancy loss: a cross-sectional study in Northeast China

Objective

To evaluate the prevalence of abnormal endocrine dysfunction for recurrent pregnancy loss (RPL) amongst patients with two versus three or more pregnancy losses.

Methods

This cross-sectional study retrospectively collected pre-pregnancy data of 537 women diagnosed with RPL in Shengjing Hospital of China Medical University from 2017 to 2022, including the baseline data of patients and the test results of endocrine factors. Several endocrine dysfunction included in this study were: thyroid dysfunction, obesity, hyperprolactinemia, polycystic ovary syndrome and blood glucose abnormality. Furthermore, vitamin D level were collected to study its relationship with endocrine dysfunction. Finally, we subdivided the patients according to the number of previous pregnancy loss and compared the prevalence of endocrine dysfunction between subgroups.

Results

Among 537 RPL patients, 278 (51.8%) patients had abnormal endocrine test results. The highest incidence of endocrine dysfunction was thyroid dysfunction (24.39%, 131/537), followed by hyperprolactinemia (17.34%, 85/490), obesity (10.8%, 58/537), polycystic ovary syndrome (10.50%, 56/533), and abnormal blood glucose (5.29%, 27/510). Only 2.47%(13/527) of patients have vitamin D level that reach the standard. After subdividing the population according to the number of pregnancy loss, we did not find that the incidence of endocrine dysfunction (P=0.813), thyroid dysfunction (P=0.905), hyperprolactinemia (P=0.265), polycystic ovary syndrome (P=0.638), blood glucose abnormality (P=0.616) and vitamin D deficiency (P=0.908) were different among patients with two versus three or more pregnancy losses. However, obesity (P=0.003) was found more frequently observed in patients with more times of pregnancy loss.

Conclusion

The prevalence of endocrine dysfunction in RPL population is high. There is no difference in the prevalence of endocrine dysfunction, except for obesity, among patients with two or more pregnancy losses, which may suggest investigations of endocrine dysfunction when patients have two pregnancy losses.

The effect of dietary habits on oocyte/sperm quality

The effects of diet and nutritional habits on reproductive cells can be categorized in a variety of ways. In this review, the literature is divided, based on the dietary consumption effects on oocytes and sperm. Topics on dietary patterns and the intrauterine effect of maternal nutrition are covered. In general fruits, vegetables, whole greens, fish, legumes, and also dietary sources containing unsaturated fats can improve reproductive germ cell quality. In epidemiological studies, the food intake frequency questionnaire is one of the most common methods to assess diet. Due to methodological heterogeneity in dietary assessment and inadequacy in the measurement of dietary intake in the questionnaires used, several unreliable results may be reported. Thus, the quality of evidence needs to be improved, since nutritional diets may not be so simply objective and they are inadequate to explain obvious underlining mechanisms. In addition, various compounds that may be ingested can affect molecular mechanisms, influenced by other external factors (drugs, pesticides, smoking, alcohol) and changes in human nutritional parameters. Artificial Intelligence has recently gained widespread interest and may have a role in accurate analysis of dietary patterns for optimal nutritional benefit. Therefore, future prospective randomized studies and objective measurements, consisting of molecular level analysis of the impact on cells and clear-cut methods are needed for accurate assessment of the effect of dietary habits on reproductive treatment.

Identification of the Inner Cell Mass and the Trophectoderm Responses after an In Vitro Exposure to Glucose and Insulin during the Preimplantation Period in the Rabbit Embryo

The prevalence of metabolic diseases is increasing, leading to more women entering pregnancy with alterations in the glucose-insulin axis. The aim of this work was to investigate the effect of a hyperglycemic and/or hyperinsulinemic environment on the development of the preimplantation embryo. In rabbit embryos developed in vitro in the presence of high insulin (HI), high glucose (HG), or both (HGI), we determined the transcriptomes of the inner cell mass (ICM) and the trophectoderm (TE). HI induced 10 differentially expressed genes (DEG) in ICM and 1 in TE. HG ICM exhibited 41 DEGs involved in oxidative phosphorylation (OXPHOS) and cell number regulation. In HG ICM, proliferation was decreased (p < 0.01) and apoptosis increased (p < 0.001). HG TE displayed 132 DEG linked to mTOR signaling and regulation of cell number. In HG TE, proliferation was increased (p < 0.001) and apoptosis decreased (p < 0.001). HGI ICM presented 39 DEG involved in OXPHOS and no differences in proliferation and apoptosis. HGI TE showed 16 DEG linked to OXPHOS and cell number regulation and exhibited increased proliferation (p < 0.001). Exposure to HG and HGI during preimplantation development results in common and specific ICM and TE responses that could compromise the development of the future individual and placenta.

Energy-Efficient, On-Demand Activation of Biosensor Arrays for Long-Term Continuous Health Monitoring

Wearable biosensors for continuous health monitoring, particularly those used for glucose detection, have a limited operational lifetime due to biodegradation and fouling. As a result, patients must change sensors frequently, increasing cost and patient discomfort. Arrays of multiple sensors, where the individual devices can be activated on demand, increase overall operational longevity, thereby reducing cost and improving patient outcomes. This work demonstrates the feasibility of this approach via decomposition of combustible nitrocellulose membranes that protect the individual sensors from exposure to bioanalytes using a current pulse. Metal contacts, connected by graphene-loaded PEDOT:PSS polymer on the surface of the membrane, deliver the required energy to decompose the membrane. Nitrocellulose membranes with a thickness of less than 1 µm consistently transfer on to polydimethylsiloxane (PDMS) wells. An electrical energy as low as 68 mJ has been shown to suffice for membrane decomposition.

High NOV/CCN3 expression during high-fat diet pregnancy in mice affects GLUT3 expression and the mTOR pathway

We investigated the expression levels of nephroblastoma overexpressed [NOV or CCN3 (cellular communication network factor 3)] in the serum and placenta of pregnant women and of pregnant mice fed a high-fat diet (HFD), and its effect on placental glucose transporter 3 (GLUT3) expression, to examine its role in gestational diabetes mellitus (GDM). NOV/CCN3 expression was increased in the mouse serum during pregnancy. At gestational day 18, NOV/CCN3 protein expression was increased in the serum and placenta of the HFD mice compared with that of mice fed a normal diet. Compared with non-GDM patients, the patients with GDM had significantly increased serum NOV/CCN3 protein expression and placental NOV/CCN3 mRNA expression. Therefore, we hypothesized that NOV/CCN3 signaling may be involved in the pathogenesis of GDM. We administered NOV/CCN3 recombinant protein via intraperitoneal injections to pregnant mice fed HFD or normal diet. NOV/CCN3 overexpression led to glucose intolerance. Combined with the HFD, NOV/CCN3 exacerbated glucose intolerance and caused insulin resistance. NOV/CCN3 upregulates GLUT3 expression and affects the mammalian target of rapamycin (mTOR) pathway in the GDM environment in vivo and in vitro. In summary, our results demonstrate, for the first time, the molecular mechanism of NOV/CCN3 signaling in maternal metabolism to regulate glucose balance during pregnancy. NOV/CCN3 may be a potential target for detecting and treating GDM.NEW & NOTEWORTHY NOV/CCN3 regulates glucose homeostasis in mice during pregnancy. NOV/CCN3 upregulates GLUT3 expression and affects the mTOR pathway in the GDM environment in vivo and in vitro.

Involvement of SIRT3-GSK3β deacetylation pathway in the effects of maternal diabetes on oocyte meiosis

OBJECTIVES

It has been widely reported that maternal diabetes impairs oocyte quality. However, the responsible mechanisms remain to be explored. In the present study, we focused on whether SIRT3-GSK3β pathway mediates the meiotic defects in oocytes from diabetic mice.

MATERIALS AND METHODS

GSK3β functions in mouse oocyte meiosis were first detected by targeted siRNA knockdown. Spindle assembly and chromosome alignment were visualized by immunostaining and analysed under the confocal microscope. PCR-based site mutation of specific GSK3β lysine residues was used to confirm which lysine residues function in oocyte meiosis. siRNA knockdown coupled with cRNA overexpression was performed to detect SIRT3-GSK3β pathway functions in oocyte meiosis. Immunofluorescence was performed to detect ROS levels. T1DM mouse models were induced by a single intraperitoneal injection of streptozotocin.

RESULTS

In the present study, we found that specific depletion of GSK3β disrupts maturational progression and meiotic apparatus in mouse oocytes. By constructing site-specific mutants, we further revealed that acetylation state of lysine (K) 15 on GSK3β is essential for spindle assembly and chromosome alignment during oocyte meiosis. Moreover, non-acetylation-mimetic mutant GSK3β-K15R is capable of partly preventing the spindle/chromosome anomalies in oocytes with SIRT3 knockdown. A significant reduction in SIRT3 protein was detected in oocytes from diabetic mice. Of note, forced expression of GSK3β-K15R ameliorates maternal diabetes-associated meiotic defects in mouse oocytes, with no evident effects on oxidative stress.

CONCLUSION

Our data identify GSK3β as a cytoskeletal regulator that is required for the assembly of meiotic apparatus, and discover a beneficial effect of SIRT3-dependent GSK3β deacetylation on oocyte quality from diabetic mice.

Pregnancy environment, and not preconception, leads to fetal growth restriction and congenital abnormalities associated with diabetes

Maternal diabetes can lead to pregnancy complications and impaired fetal development. The goal of this study was to use a mouse model of reciprocal embryo transfer to distinguish between the preconception and gestational effects of diabetes. To induce diabetes female mice were injected with a single high dose of streptozotocin and 3 weeks thereafter used as oocyte donors for in vitro fertilization (IVF) and as recipients for embryo transfer. Following IVF embryos were cultured to the blastocyst stage in vitro or transferred to diabetic and non-diabetic recipients. Diabetic and non-diabetic females did not differ in regard to the number of oocytes obtained after ovarian stimulation, oocytes ability to become fertilized, and embryo development in vitro. However, diabetic females displayed impaired responsiveness to superovulation. Reciprocal embryo transfer resulted in similar incidence of live fetuses and abortions, and no changes in placental size. However, fetuses carried by diabetic recipients were smaller compared to those carried by non-diabetic recipients, regardless hyperglycemia status of oocyte donors. Congenital abnormalities were observed only among the fetuses carried by diabetic recipients. The findings support that the diabetic status during pregnancy, and not the preconception effect of diabetes on oogenesis, leads to fetal growth restriction and congenital deformities.

Metabolic Profiling in Blastocoel Fluid and Blood Plasma of Diabetic Rabbits

Metabolic disorders of the mother adversely affect early embryo development, causing changes in maternal metabolism and consequent alterations in the embryo environment in the uterus. The goal of this study was to analyse the biochemical profiles of embryonic fluids and blood plasma of rabbits with and without insulin-dependent diabetes mellitus (DT1), to identify metabolic changes associated with maternal diabetes mellitus in early pregnancy. Insulin-dependent diabetes was induced by alloxan treatment in female rabbits 10 days before mating. On day 6 post-coitum, plasma and blastocoel fluid (BF) were analysed by ultrahigh performance liquid chromatography-tandem mass spectroscopy (UPLC-MS/MS) (Metabolon Inc. Durham, NC, USA). Metabolic datasets comprised a total of 284 and 597 compounds of known identity in BF and plasma, respectively. Diabetes mellitus had profound effects on maternal and embryonic metabolic profiles, with almost half of the metabolites changed. As predicted, we observed an increase in glucose and a decrease in 1,5-anhydroglucitol in diabetic plasma samples. In plasma, fructose, mannose, and sorbitol were elevated in the diabetic group, which may be a way of dealing with excess glucose. In BF, metabolites of the pentose metabolism were especially increased, indicating the need for ribose-based compounds relevant to DNA and RNA metabolism at this very early stage of embryo development. Other changes were more consistent between BF and plasma. Both displayed elevated acylcarnitines, body3-hydroxybutyrate, and multiple compounds within the branched chain amino acid metabolism pathway, suggesting that lipid beta-oxidation is occurring at elevated levels in the diabetic group. This study demonstrates that maternal and embryonic metabolism are closely related. Maternal diabetes mellitus profoundly alters the metabolic profile of the preimplantation embryo with changes in all subclasses of metabolites.

Effects of a Lactulose-Rich Diet on Fecal Microbiome and Metabolome in Pregnant Mice

Lactulose, a safe and beneficial molecule, can be used in food as a prebiotic and as an osmotic laxative during pregnancy. This work evaluated the effects of dietary lactulose on the gut microenvironment of pregnant mice using the fecal microbiota and metabolomic profiling. After 2 weeks of feeding, the Bifidobacterium and Bacteroides abundances in the mouse feces were significantly increased in the LAC-high (the diet supplemented with 15% lactulose) group. A total of 15 metabolites, including 1-monoolein, glucose-6-phosphate, and short-chain fatty acids, were increased significantly in the LAC-high group. The serum glucose and total cholesterol concentrations were significantly decreased, while the progesterone level was significantly increased in the lactulose-fed mice. In the LAC-high group, the colonic pH and intestinal permeability were decreased, while the immunoglobulins in the colonic epithelial cells and the small intestinal absorption capacity were significantly increased. These findings indicated that lactulose supplementation benefitted pregnancy performance in mice.

Poorly-Controlled Type 1 Diabetes Mellitus Impairs LH-LHCGR Signaling in the Ovaries and Decreases Female Fertility in Mice

PURPOSE

The aim of this study was to investigate how type I diabetes mellitus (T1D) affects the folliculogenesis and oocyte development, fertilization, and embryo development.

MATERIALS AND METHODS

A comparative animal study was conducted using two different mouse models of T1D, a genetic AKITA model and a streptozotocin-induced diabetes model. Ovarian function was assessed by gross observation, immunoblot, immunohistochemistry, oocyte counting, and ELISA for serum hormones (insulin, anti-Mullerian hormone, estradiol, testosterone, and progesterone). Maturation and developmental competence of metaphase II oocytes from control and T1D animals was evaluated by immunofluorescent and immunohistochemical detection of biomarkers and in vitro fertilization.

RESULTS

Animals from both T1D models showed increased blood glucose levels, while only streptozotocin (STZ)-injected mice showed reduced body weight. Folliculogenesis, oogenesis, and preimplantation embryogenesis were impaired in both T1D mouse models. Interestingly, exogenous streptozotocin injection to induce T1D led to marked decreases in ovary size, expression of luteinizing hormone/chorionic gonadotropin receptor in the ovaries, the number of corpora lutea per ovary, oocyte maturation, and serum progesterone levels. Both T1D models exhibited significantly reduced pre-implantation embryo quality compared with controls. There was no significant difference in embryo quality between STZ-injected and AKITA diabetic mice.

CONCLUSION

These results suggest that T1D affects folliculogenesis, oogenesis, and embryo development in mice. However, the physiological mechanisms underlying the observed reproductive effects of diabetes need to be further investigated.

High-fat diet affects pregestational adiposity and glucose tolerance perturbing gestational placental macronutrient transporters culminating in an obese offspring in wild-type and glucose transporter isoform 3 heterozygous null mice

We examined the effect of a high-fat diet (HFD) vs. control diet (CD) upon pregestational and gestational wild-type (wt) and glucose transporter (glut)3 heterozygous (glut3^+/-) female mice and observed an increase in pregestational body weights, white adiposity (wt > glut3^+/-), circulating cholesterol, and high-density lipoproteins, with glucose intolerance in both genotypes. The HFD-exposed offspring displayed reduced birth weight with catch up to CD-fed in wt vs. an increased birth weight persisting as such at weaning by day 21 in glut3^+/- mice. To decipher the mechanism behind this genotype-specific difference in the HFD offspring's phenotype, we first examined placental macronutrient transporters and noted HFD-induced increase in CD36 in wt with no change in other FATPs, sodium-coupled neutral amino acid transporters and system L amino acid transporter in both genotypes. In contrast, while placental Glut1 increased in both the genotypes, only Glut3 increased in the glut3^+/- genotype in response to HFD. Hence, we next assessed glut3^+/- embryonic (ES) cells under differing stressors of low glucose, hypoxia and inhibition of oxidative phosphorylation. Reduced Glut3-mediated glucose uptake in glut3^+/- vs. wt ES cells culminated in deficient growth. We conclude that maternal HFD affects the in utero growth potential of the offspring by altering placental CD36 and Glut1 concentrations. In contrast, a differential effect on placental Glut3 concentrations between glut3^+/- and wt genotypes is evident, with an increase occurring in the glut3^+/- genotype alone. Deficient Glut3 in ES cells interferes with glucose uptake, cell survival and growth being further exaggerated with low glucose, hypoxia and inhibition of oxidative phosphorylation.

Environmental Contaminants and Pancreatic Beta-Cells

Despite health policies as well as clinical and research efforts, diabetes prevalence is still rising around the world. A multitude of causes have been suggested for this increase, mostly related to familial background, the occidental diet which is rich in fat/carbohydrates, and sedentary life style. Type 2 diabetes involves malfunctions of the primary pancreatic beta-cells, usually attributed to local damage; however, it can be associated with other stressful environmental agents, such as chemical contaminants from food, plastic and air, among others. Indeed, exposure to these chemical agents during perinatal and adolescent life can increase the risk of developing cardiometabolic diseases later in life. This review explores data showing which environmental chemical agents may produce injury in beta-cells and further impair the insulinotropic process of type 2 diabetes. Additionally, it points the need to also consider unusual causes of metabolic diseases, such as environmental contaminants.

The status of diabetic embryopathy

Diabetic embryopathy is a theoretical enigma and a clinical challenge. Both type 1 and type 2 diabetic pregnancy carry a significant risk for fetal maldevelopment, and the precise reasons for the diabetes-induced teratogenicity are not clearly identified. The experimental work in this field has revealed a partial, however complex, answer to the teratological question, and we will review some of the latest suggestions.

Genetics of Type 2 Diabetes: It Matters From Which Parent We Inherit the Risk

Type 2 diabetes (T2D) results from a co-occurrence of genes and environmental factors. There are more than 120 genetic loci suggested to be associated with T2D, or with glucose and insulin levels in European and multi-ethnic populations. Risk of T2D is higher in the offspring if the mother rather than the father has T2D. Genetically, this can be associated with a unique parent-of-origin (PoO) transmission of risk alleles, and it relates to genetic programming during the intrauterine period, resulting in the inability to increase insulin secretion in response to increased demands imposed by insulin resistance later in life. Such PoO transmission is seen for variants in the KLF14, KCNQ1, GRB10, TCF7L2, THADA, and PEG3 genes. Here we describe T2D susceptibility genes associated with defects in insulin secretion, and thereby risk of overt T2D. This review emphasizes the need to consider distorted parental transmission of risk alleles by exploring the genetic risk of T2D.

Proanthocyanidins Prevent High Glucose-Induced Eye Malformation by Restoring Pax6 Expression in Chick Embryo

Gestational diabetes mellitus (GDM) is one of the leading causes of offspring malformations, in which eye malformation is an important disease. It has raised demand for therapy to improve fetal outcomes. In this study, we used chick embryo to establish a GDM model to study the protective effects of proanthocyanidins on eye development. Chick embryos were exposed to high glucose (0.2 mmol/egg) on embryo development day (EDD) 1. Proanthocyanidins (1 and 10 nmol/egg) were injected into the air sac on EDD 0. Results showed that both dosages of proanthocyanidins could prevent the eye malformation and rescue the high glucose-induced oxidative stress significantly, which the similar effects were showed in edaravone. However, proanthocyanidins could not decrease the glucose concentration of embryo eye. Moreover, the key genes regulating eye development, Pax6, was down-regulated by high glucose. Proanthocyanidins could restore the suppressed expression of Pax6. These results indicated proanthocyanidins might be a promising natural agent to prevent high glucose-induced eye malformation by restoring Pax6 expression.

Cell lineage allocation in equine blastocysts produced in vitro under varying glucose concentrations

Equine embryos developin vitroin the presence of high glucose concentrations, but little is known about their requirements for development. We evaluated the effect of glucose concentrations in medium on blastocyst development after ICSI. In experiment 1, there were no significant differences in rates of blastocyst formation among embryos cultured in our standard medium (DMEM/F-12), which contained >16 mM glucose, and those cultured in a minimal-glucose embryo culture medium (<1 mM; Global medium, GB), with either 0 added glucose for the first 5 days, then 20 mM (0-20) or 20 mM for the entire culture period (20-20). In experiment 2, there were no significant differences in the rates of blastocyst development (31–46%) for embryos cultured in four glucose treatments in GB (0-10, 0-20, 5-10, or 5-20). Blastocysts were evaluated by immunofluorescence for lineage-specific markers. All cells stained positively forPOU5F1. An inner cluster of cells was identified that included presumptive primitive endoderm cells (GATA6-positive) and presumptive epiblast (EPI) cells. The 5-20 treatment resulted in a significantly lower number of presumptive EPI-lineage cells than the 0-20 treatment did.GATA6-positive cells appeared to be allocated to the primitive endoderm independent of the formation of an inner cell mass, as was previously hypothesized for equine embryos. These data demonstrate that equine blastocyst development is not dependent on high glucose concentrations during early culture; rather, environmental glucose may affect cell allocation. They also present the first analysis of cell lineage allocation inin vitro-fertilized equine blastocysts. These findings expand our understanding of the factors that affect embryo development in the horse.

Dysregulated LIF-STAT3 pathway is responsible for impaired embryo implantation in a Streptozotocin-induced diabetic mouse model

The prevalence of diabetes is increasing worldwide with the trend of patients being young and creating a significant burden on health systems, including reproductive problems, but the effects of diabetes on embryo implantation are still poorly understood. Our study was to examine effects of diabetes on mouse embryo implantation, providing experimental basis for treating diabetes and its complications. Streptozotocin (STZ) was applied to induce type 1 diabetes from day 2 of pregnancy or pseudopregnancy in mice. Embryo transfer was used to analyze effects of uterine environment on embryo implantation. Our results revealed that the implantation rate is significantly reduced in diabetic mice compared to controls, and the change of uterine environment is the main reason leading to the decreased implantation rate. Compared to control, the levels of LIF and p-STAT3 are significantly decreased in diabetic mice on day 4 of pregnancy, and serum estrogen level is significantly higher. Estrogen stimulates LIF expression under physiological level, but the excessive estrogen inhibits LIF expression. LIF, progesterone or insulin supplement can rescue embryo implantation in diabetic mice. Our data indicated that the dysregulated LIF-STAT3 pathway caused by the high level of estrogen results in the impaired implantation in diabetic mice, which can be rescued by LIF, progesterone or insulin supplement.

The impact of mitochondrial function/dysfunction on IVF and new treatment possibilities for infertility

Mitochondria play vital roles in oocyte functions and they are critical indicators of oocyte quality which is important for fertilization and development into viable offspring. Quality-compromised oocytes are correlated with infertility, developmental disorders, reduced blastocyst cell number and embryo loss in which mitochondrial dysfunctions play a significant role. Increasingly, women affected by metabolic disorders such as diabetes or obesity and oocyte aging are seeking treatment in IVF clinics to overcome the effects of adverse metabolic conditions on mitochondrial functions and new treatments have become available to restore oocyte quality. The past decade has seen enormous advances in potential therapies to restore oocyte quality and includes dietary components and transfer of mitochondria from cells with mitochondrial integrity into mitochondria-impaired oocytes. New technologies have opened up new possibilities for therapeutic advances which will increase the success rates for IVF of oocytes from women with compromised oocyte quality.

Metabolic control of oocyte development: linking maternal nutrition and reproductive outcomes

Obesity, diabetes, and related metabolic disorders are major health issues worldwide. As the epidemic of metabolic disorders continues, the associated medical co-morbidities, including the detrimental impact on reproduction, increase as well. Emerging evidence suggests that the effects of maternal nutrition on reproductive outcomes are likely to be mediated, at least in part, by oocyte metabolism. Well-balanced and timed energy metabolism is critical for optimal development of oocytes. To date, much of our understanding of oocyte metabolism comes from the effects of extrinsic nutrients on oocyte maturation. In contrast, intrinsic regulation of oocyte development by metabolic enzymes, intracellular mediators, and transport systems is less characterized. Specifically, decreased acid transport proteins levels, increased glucose/lipid content and elevated reactive oxygen species in oocytes have been implicated in meiotic defects, organelle dysfunction and epigenetic alteration. Therefore, metabolic disturbances in oocytes may contribute to the diminished reproductive potential experienced by women with metabolic disorders. In-depth research is needed to further explore the underlying mechanisms. This review also discusses several approaches for metabolic analysis. Metabolomic profiling of oocytes, the surrounding granulosa cells, and follicular fluid will uncover the metabolic networks regulating oocyte development, potentially leading to the identification of oocyte quality markers and prevention of reproductive disease and poor outcomes in offspring.

Hypoxia-mediated carbohydrate metabolism and transport promote early-stage murine follicle growth and survival

Oxygen tension is critical for follicle growth and metabolism, especially for early-stage follicles, where vascularity is limited. Its role and underlying mechanism in the in vitro activation and maturation of immature to ovulatory follicles is largely unknown. In this study, early secondary (110 μm) murine follicles were isolated and encapsulated in alginate hydrogels to replicate the in vivo environment of the growing/maturing follicle. Encapsulated follicles were cultured for 8 days at either 2.5 or 20% O2. Survival (2.6-fold) and growth (1.2-fold) were significantly higher for follicles cultured at 2.5% compared with 20% O2. Using a mouse hypoxia-signaling pathway qRT-PCR array and GeneGo Metacore analysis, we found that direct target genes of the hypoxia-activated HIF1-complex were significantly upregulated in follicles cultured for 8 days at 2.5% compared with 20% O2, including the carbohydrate transport and metabolism genes Slc2a3, Vegfa, Slc2a1, Edn1, Pgk1, Ldha, and Hmox1. Other upregulated genes included carbohydrate transporters (Slc2a1, Slc2a3, and Slc16a3) and enzymes essential for glycolysis (Pgk1, Hmox1, Hk2, Gpi1, Pfkl, Pfkp, Aldoa, Gapdh, Pgam1, Eno1, Pkm2, and Ldha). For follicles cultured at 2.5% O2, a 7.2-fold upregulation of Vegfa correlated to an 18-fold increase in VEGFA levels, and a 3.2-fold upregulation of Ldha correlated to a 4.8-fold increase in lactate levels. Both VEGFA and lactate levels were significantly higher in follicles cultured at 2.5% compared with 20% O2. Therefore, enhanced hypoxia-mediated glycolysis is essential for growth and survival of early secondary follicles and provides vital insights into improving in vitro culture conditions.

Nanomaterial-mediated Biosensors for Monitoring Glucose

Real-time monitoring of physiological glucose transport is crucial for gaining new understanding of diabetes. Many techniques and equipment currently exist for measuring glucose, but these techniques are limited by complexity of the measurement, requirement of bulky equipment, and low temporal/spatial resolution. The development of various types of biosensors (eg, electrochemical, optical sensors) for laboratory and/or clinical applications will provide new insights into the cause(s) and possible treatments of diabetes. State-of-the-art biosensors are improved by incorporating catalytic nanomaterials such as carbon nanotubes, graphene, electrospun nanofibers, and quantum dots. These nanomaterials greatly enhance biosensor performance, namely sensitivity, response time, and limit of detection. A wide range of new biosensors that incorporate nanomaterials such as lab-on-chip and nanosensor devices are currently being developed for in vivo and in vitro glucose sensing. These real-time monitoring tools represent a powerful diagnostic and monitoring tool for measuring glucose in diabetes research and point of care diagnostics. However, concerns over the possible toxicity of some nanomaterials limit the application of these devices for in vivo sensing. This review provides a general overview of the state of the art in nanomaterial-mediated biosensors for in vivo and in vitro glucose sensing, and discusses some of the challenges associated with nanomaterial toxicity.

Diabetic uterus environment may play a key role in alterations of DNA methylation of several imprinted genes at mid-gestation in mice

BACKGROUND

Maternal diabetes mellitus not only has severe deleterious effects on fetal development, but also it affects transmission to the next generation. However, the underlying mechanisms for these effects are still not clear.

METHODS

We investigated the methylation patterns and expressions of the imprinted genes Peg3, Snrpn, and H19 in mid-gestational placental tissues and on the whole fetus utilizing the streptozotocin (STZ)-induced hyperglycemic mouse model for quantitative analysis of methylation by PCR and quantitative real-time PCR. The protein expression of Peg3 was evaluated by Western blot.

RESULTS

We found that the expression of H19 was significantly increased, while the expression of Peg3 was significantly decreased in dpc10.5 placentas of diabetic mice. We further found that the methylation level of Peg3 was increased and that of H19 was reduced in dpc10.5 placentas of diabetic mice. When pronuclear embryos of normal females were transferred to normal/diabetic (NN/ND) pseudopregnant females, the methylation and expression of Peg3 in placentas was also clearly altered in the ND group compared to the NN group. However, when the pronuclear embryos of diabetic female were transferred to normal pesudopregnant female mice (DN), the methylation and expression of Peg3 and H19 in dpc10.5 placentas was similar between the two groups.

CONCLUSIONS

We suggest that the effects of maternal diabetes on imprinted genes may primarily be caused by the adverse uterus environment.

Nanomaterial based self-referencing microbiosensors for cell and tissue physiology research

Physiological studies require sensitive tools to directly quantify transport kinetics in the cell/tissue spatial domain under physiological conditions. Although biosensors are capable of measuring concentration, their applications in physiological studies are limited due to the relatively low sensitivity, excessive drift/noise, and inability to quantify analyte transport. Nanomaterials significantly improve the electrochemical transduction of microelectrodes, and make the construction of highly sensitive microbiosensors possible. Furthermore, a novel biosensor modality, self-referencing (SR), enables direct measurement of real-time flux and drift/noise subtraction. SR microbiosensors based on nanomaterials have been used to measure the real-time analyte transport in several cell/tissue studies coupled with various stimulators/inhibitors. These studies include: glucose uptake in pancreatic β cells, cancer cells, muscle tissues, intestinal tissues and P. Aeruginosa biofilms; glutamate flux near neuronal cells; and endogenous indole-3-acetic acid flux near the surface of Zea mays roots. Results from the SR studies provide important insights into cancer, diabetes, nutrition, neurophysiology, environmental and plant physiology studies under dynamic physiological conditions, demonstrating that the SR microbiosensors are an extremely valuable tool for physiology research.

Hyperglycemia slows embryonic growth and suppresses cell cycle via cyclin D1 and p21

In pregnant women, the diabetic condition results in a three- to fivefold increased risk for fetal cardiac malformations as a result of elevated glucose concentrations and the resultant osmotic stress in the developing embryo and fetus. Heart development before septation in the chick embryo was studied under two hyperglycemic conditions. Pulsed hyperglycemia induced by daily administration of glucose during 3 days of development caused daily spikes in plasma glucose concentration. In a second model, sustained hyperglycemia was induced with a single injection of glucose into the yolk on day 0. The sustained model raised the average plasma glucose concentration from 70 mg/dL to 180 mg/dL and led to decreased gene expression of glucose transporter GLUT1. Both models of hyperglycemia reduced embryo size, increased mortality, and delayed development. Within the heart outflow tract, reduced proliferation of myocardial and endocardial cells resulted from the sustained hyperglycemia and hyperosmolarity. The cell cycle inhibitor p21 was significantly increased, whereas cyclin D1, a cell cycle promoter, decreased in sustained hyperglycemia compared with controls. The evidence suggests that hyperglycemia-induced developmental delays are associated with slowed cell cycle progression, leading to reduced cellular proliferation. The suppression of critical developmental steps may underlie the cardiac defects observed during late gestation under hyperglycemic conditions.

An intercellular pathway for glucose transport into mouse oocytes

Glucose is an essential nutrient for mammalian cells. Emerging evidence suggests that glucose within the oocyte regulates meiotic maturation. However, it remains controversial as to whether, and if so how, glucose enters oocytes within cumulus-oocyte complexes (COCs). We used a fluorescent glucose derivative (6-NBDG) to trace glucose transport within live mouse COCs and employed inhibitors of glucose transporters (GLUTs) and gap junction proteins to examine their distinct roles in glucose uptake by cumulus cells and the oocyte. We showed that fluorescent glucose enters both cumulus-enclosed and denuded oocytes. Treating COCs with GLUT inhibitors leads to simultaneous decreases in glucose uptake in cumulus cells and the surrounded oocyte but no effect on denuded oocytes. Pharmacological blockade of of gap junctions between the oocyte and cumulus cells significantly inhibited fluorescent glucose transport to oocytes. Moreover, we find that both in vivo hyperglycemic environment and in vitro high-glucose culture increase free glucose levels in oocytes via gap junctional channels. These findings reveal an intercellular pathway for glucose transport into oocytes: glucose is taken up by cumulus cells via the GLUT system and then transferred into the oocyte through gap junctions. This intercellular pathway may partly mediate the effects of high-glucose condition on oocyte quality.

Insulin-stimulated glucose uptake occurs in specialized cells within the cumulus oocyte complex

The oocyte exists within the mammalian follicle surrounded by somatic cumulus cells. These cumulus cells metabolize the majority of the glucose within the cumulus oocyte complex and provide energy substrates and intermediates such as pyruvate to the oocyte. The insulin receptor is present in cumulus cells and oocytes; however, it is unknown whether insulin-stimulated glucose uptake occurs in either cell type. Insulin-stimulated glucose uptake is thought to be unique to adipocytes, skeletal and cardiac muscle, and the blastocyst. Here, we show for the first time that many of the components required for insulin signaling are present in both cumulus cells and oocytes. We performed a set of experiments on mouse cumulus cells and oocytes and human cumulus cells using the nonmetabolizable glucose analog 2-deoxy-d-glucose to measure basal and insulin-stimulated glucose uptake. We show that insulin-stimulated glucose uptake occurs in both compact and expanded cumulus cells of mice, as well as in human cumulus cells. Oocytes, however, do not display insulin-stimulated glucose uptake. Insulin-stimulated glucose uptake in cumulus cells is mediated through phosphatidylinositol 3-kinase signaling as shown by inhibition of insulin-stimulated glucose uptake and Akt phosphorylation with the specific phosphatidylinositol 3-kinase inhibitor, LY294002. To test the effect of systemic in vivo insulin resistance on insulin sensitivity in the cumulus cell, cumulus cells from high fat-fed, insulin-resistant mice and women with polycystic ovary syndrome were examined. Both sets of cells displayed blunted insulin-stimulated glucose uptake. Our studies identify another tissue that, through a classical insulin-signaling pathway, demonstrates insulin-stimulated glucose uptake. Moreover, these findings suggest insulin resistance occurs in these cells under conditions of systemic insulin resistance.

Microbiosensors based on DNA modified single-walled carbon nanotube and Pt black nanocomposites

Glucose and ATP biosensors have important applications in diagnostics and research. Biosensors based on conventional materials suffer from low sensitivity and low spatial resolution. Our previous work has shown that combining single-walled carbon nanotubes (SWCNTs) with Pt nanoparticles can significantly enhance the performance of electrochemical biosensors. The immobilization of SWCNTs on biosensors remains challenging due to the aqueous insolubility originating from van der Waals forces. In this study, we used single-stranded DNA (ssDNA) to modify SWCNTs to increase solubility in water. This allowed us to explore new schemes of combining ssDNA-SWCNT and Pt black in aqueous media systems. The result is a nanocomposite with enhanced biosensor performance. The surface morphology, electroactive surface area, and electrocatalytic performance of different fabrication protocols were studied and compared. The ssDNA-SWCNT/Pt black nanocomposite constructed by a layered scheme proved most effective in terms of biosensor activity. The key feature of this protocol is the exploitation of ssDNA-SWCNTs as molecular templates for Pt black electrodeposition. The glucose and ATP microbiosensors fabricated on this platform exhibited high sensitivity (817.3 nA/mM and 45.6 nA/mM, respectively), wide linear range (up to 7 mM and 510 μM), low limit of detection (1 μM and 2 μM) and desirable selectivity. This work is significant to biosensor development because this is the first demonstration of ssDNA-SWCNT/Pt black nanocomposite as a platform for constructing both single-enzyme and multi-enzyme biosensors for physiological applications.

Glucose transporter-1 in the hypothalamic glial cells mediates glucose sensing to regulate glucose production in vivo

OBJECTIVE

Circulating glucose inhibits glucose production in normal rodents and humans, but this glucose effectiveness is disrupted in diabetes due partly to sustained hyperglycemia. We hypothesize that hyperglycemia in diabetes impairs hypothalamic glucose sensing to lower glucose production, and changes of glucose transporter-1 (GLUT1) in the hypothalamic glial cells are responsible for the deleterious effects of hyperglycemia in vivo.

RESEARCH DESIGN AND METHODS

We tested hypothalamic glucose effectiveness to increase hypothalamic glucose concentration and lower glucose production in rats induced with streptozotocin (STZ) uncontrolled diabetes, STZ and phlorizin, and whole-body and hypothalamic sustained hyperglycemia. We next assessed the content of glial GLUT1 in the hypothalamus, generated an adenovirus expressing GLUT1 driven by a glial fibrillary acidic protein (GFAP) promoter (Ad-GFAP-GLUT1), and injected Ad-GFAP-GLUT1 into the hypothalamus of rats induced with hyperglycemia. Pancreatic euglycemic clamp and tracer-dilution methodologies were used to assess changes in glucose kinetics in vivo.

RESULTS

Sustained hyperglycemia, as seen in the early onset of STZ-induced diabetes, disrupted hypothalamic glucose sensing to increase hypothalamic glucose concentration and lower glucose production in association with reduced GLUT1 levels in the hypothalamic glial cells of rats in vivo. Overexpression of hypothalamic glial GLUT1 in STZ-induced rats with reduced GLUT1 acutely normalized plasma glucose levels and in rats with selectively induced hypothalamic hyperglycemia restored hypothalamic glucose effectiveness.

CONCLUSIONS

Sustained hyperglycemia impairs hypothalamic glucose sensing to lower glucose production through changes in hypothalamic glial GLUT1, and these data highlight the critical role of hypothalamic glial GLUT1 in mediating glucose sensing to regulate glucose production.

The impact of obesity on egg quality

Obesity in women is a concern in many countries. This causes numerous health issues; however, this review focuses on the impact of obesity on women's reproduction, and in particular the oocyte. Data from infertility clinics and experimental animal models that address the effects of obesity are presented. Bidirectional communication and metabolic support from the surrounding cumulus cells are critical for oocyte development, and the impact of obesity on these cells is also addressed. Both oocyte maturation and metabolism are impaired due to obesity, negatively impacting further development. In addition to reproductive hormones, obesity induced elevations in insulin, glucose, or free fatty acids, and changes in adipokines appear to impact the developmental competence of the oocyte. The data indicate that any one of these hormones or metabolites can impair oocyte developmental competence in vivo, and the combination of all of these factors and their interactions are the subject of ongoing investigations.

Peptidoglycan induces necrosis and regulates cytokine production in murine trophoblast stem cells

PROBLEM

Intrauterine bacterial infection during pregnancy may lead to adverse outcome. The objective of this study was to assess whether peptidoglycan (PGN) derived from Gram-positive bacteria induces trophoblast stem (TS) cell death or alters TS cell cytokine production.

METHOD OF STUDY

Toll-like receptor (TLR) transcript expression was assessed by RT-PCR. Protein expression was determined by confocal microscopy or flow cytometry. 7-Aminoactinomycin D (7-AAD) staining was used to assess TS cell death. Morphological features of cell death were evaluated by transmission electron microscopy. The presence of cleaved caspase-3 and high mobility group box 1 (HMGB1) protein was examined by Western blot. Cytokine levels in cell supernatants were determined using a mouse cytokine 23-plex panel.

RESULTS

Toll-like receptor 2 and TLR4 protein was expressed from the 1-cell stage through the blastocyst stage of murine embryo development. Murine TS cells expressed TLR2 and TLR6 but not TLR1 or TLR4 RNA. Only TLR2 protein was detected at the plasma membrane of TS cells. PGN induced TS cell death by a caspase-3-independent mechanism. The cell death pathway induced by PGN was morphologically consistent with necrosis. Finally, PGN induced HMGB1 release and increased MIP-1β secretion while inhibiting the constitutive release of RANTES.

CONCLUSION

Peptidoglycan-induced TS cell necrosis and the subsequent release of HMGB1 and MIP-1β may regulate an infection-induced inflammatory response at the maternal-fetal interface and thus may play a role in the pathogenesis of infection-associated pregnancy complications.

A differential autophagic response to hyperglycemia in the developing murine embryo

Autophagy is critical to the process of development because mouse models have shown that lack of autophagy leads to developmental arrest during the pre-implantation stage of embryogenesis. The process of autophagy is regulated through signaling pathways, which respond to the cellular environment. Therefore, any alteration in the environment may lead to the dysregulation of the autophagic process potentially resulting in cell death. Using both in vitro and in vivo models to study autophagy in the pre-implantation murine embryo, we observed that the cells respond to environmental stressors (i.e. hyperglycemic environment) by increasing activation of autophagy in a differential pattern within the embryo. This upregulation is accompanied by an increase in apoptosis, which appears to plateau at high concentrations of glucose. The activation of the autophagic pathway was further confirmed by an increase in GAPDH activity in both in vivo and in vitro hyperglycemic models, which has been linked to autophagy through the activation of the Atg12 gene. Furthermore, this increase in autophagy in response to a hyperglycemic environment was observed as early as the oocyte stage. In conclusion, in this study, we provided evidence for a differential response of elevated activation of autophagy in embryos and oocytes exposed to a hyperglycemic environment.

Hypoxic-ischemic brain injury exacerbates neuronal apoptosis and precipitates spontaneous seizures in glucose transporter isoform 3 heterozygous null mice

We examined the effects of 45-min hypoxia (FiO(2) 0.08; Hx) vs. normoxia (FiO(2) 0.21; Nx) on the ipsilateral (Ipsi) and contralateral (Ctrl) sides of the brain in neuronal glucose transporter isoform 3 (Glut3) heterozygous null mice (glut3(+/-)) and their wild-type littermates (WT), undergoing unilateral carotid artery ligation. Glut3(+/-) mice, under Nx, demonstrated a compensatory increase in blood-brain barrier/glial Glut1 protein concentration and a concomitant increase in neuronal nitric oxide synthase (nNOS) enzyme activity and Bax protein, with a decrease in procaspase 3 protein (P < 0.05 each). After Hx, reoxygenation in FiO(2) of 0.21 led to no comparable adaptive up-regulation of the ipsilateral brain Glut3 or Glut1 protein at 4 hr and Glut1 at 24 hr in glut3(+/-) vs. WT. These brain Glut changes in glut3(+/-) but not WT mice were associated with an increase in proapoptotic Bax protein and caspase-3 enzyme activity (P < 0.01 each) and a decline in the antiapoptotic Bcl-2 and procaspase-3 proteins (P < 0.05 each). Glut3(+/-) mice after Hx demonstrated TUNEL-positive neurons with nuclear pyknosis in most ipsilateral (hypoxic-ischemia) brain regions. A subset (∼55%) of glut3(+/-) mice developed spontaneous seizures after hypoxic-ischemia, confirmed by electroencephalography, but the WT mice remained seizure-free. Pentylenetetrazole testing demonstrated an increased occurrence of longer lasting clinical seizures at a lower threshold in glut3(+/-) vs. WT mice, with no detectable differences in monamine neurotransmitters. We conclude that hypoxic-ischemic brain injury in glut3(+/-) mice exacerbates cellular apoptosis and necrosis and precipitates spontaneous seizures.

Dynamic glucoregulation and mammalian-like responses to metabolic and developmental disruption in zebrafish

Zebrafish embryos are emerging as models of glucose metabolism. However, patterns of endogenous glucose levels, and the role of the islet in glucoregulation, are unknown. We measured absolute glucose levels in zebrafish and mouse embryos, and demonstrate similar, dynamic glucose fluctuations in both species. Further, we show that chemical and genetic perturbations elicit mammalian-like glycemic responses in zebrafish embryos. We show that glucose is undetectable in early zebrafish and mouse embryos, but increases in parallel with pancreatic islet formation in both species. In zebrafish, increasing glucose is associated with activation of gluconeogenic phosphoenolpyruvate carboxykinase1 (pck1) transcription. Non-hepatic Pck1 protein is expressed in mouse embryos. We show using RNA in situ hybridization, that zebrafish pck1 mRNA is similarly expressed in multiple cell types prior to hepatogenesis. Further, we demonstrate that the Pck1 inhibitor 3-mercaptopicolinic acid suppresses normal glucose accumulation in early zebrafish embryos. This shows that pre- and extra-hepatic pck1 is functional, and provides glucose locally to rapidly developing tissues. To determine if the primary islet is glucoregulatory in early fish embryos, we injected pdx1-specific morpholinos into transgenic embryos expressing GFP in beta cells. Most morphant islets were hypomorphic, not a genetic, but embryos still exhibited persistent hyperglycemia. We conclude from these data that the early zebrafish islet is functional, and regulates endogenous glucose. In summary, we identify mechanisms of glucoregulation in zebrafish embryos that are conserved with embryonic and adult mammals. These observations justify use of this model in mechanistic studies of human metabolic disease.

Oscillatory glucose flux in INS 1 pancreatic β cells: a self-referencing microbiosensor study

Signaling and insulin secretion in β cells have been reported to demonstrate oscillatory modes, with abnormal oscillations associated with type 2 diabetes. We investigated cellular glucose influx in β cells with a self-referencing (SR) microbiosensor based on nanomaterials with enhanced performance. Dose-response analyses with glucose and metabolic inhibition studies were used to study oscillatory patterns and transporter kinetics. For the first time, we report a stable and regular oscillatory uptake of glucose (averaged period 2.9±0.6 min), which corresponds well with an oscillator model. This oscillatory behavior is part of the feedback control pathway involving oxygen, cytosolic Ca(2+)/ATP, and insulin secretion (periodicity approximately 3 min). Glucose stimulation experiments show that the net Michaelis-Menten constant (6.1±1.5 mM) is in between GLUT2 and GLUT9. Phloretin inhibition experiments show an EC(50) value of 28±1.6 μM phloretin for class I GLUT proteins and a concentration of 40±0.6 μM phloretin caused maximum inhibition with residual nonoscillating flux, suggesting that the transporters not inhibited by phloretin are likely responsible for the remaining nonoscillatory uptake, and that impaired uptake via GLUT2 may be the cause of the oscillation loss in type 2 diabetes. Transporter studies using the SR microbiosensor will contribute to diabetes research and therapy development by exploring the nature of oscillatory transport mechanisms.

Interferon gamma contributes to preimplantation embryonic development and to implantation site structure in NOD mice

BACKGROUND

Pre-eclampsia, a syndrome usually accompanied by incomplete spiral arterial modification, occurs at an increased frequency in diabetic women. Hyperglycemia in non-obese type 1 diabetic (NOD) mice impairs gestational spiral arterial remodeling despite high local levels of interferon gamma (Ifng), the triggering cytokine in mice. Pregnancies in NOD.Ifng(-/-) mice were assessed to investigate this issue.

METHODS

Fecundity was assessed using the breeding history, flushing of preimplantation embryos and histological and morphometric studies of implantation sites in normoglycemic (n-) and hyperglycemic (d-) females of NOD.Ifng(-/-) and NOD genotypes.

RESULTS

NOD.Ifng(-/-) but not NOD mice are mostly infertile. In NOD.Ifng(-/-), copulation often does not result in a post-implantation pregnancy. Defective fertilization and delayed preimplantation development limit n-NOD.Ifng(-/-) fertility, and both mechanisms are exacerbated by hyperglycemia. At mid-gestation, implantation sites in n-NOD.Ifng(-/-) and n-NOD mice are histologically similar. However, in d-NOD.Ifng(-/-), there is minimal development of spiral arteries, hypertrophy of the myometrial region containing uterine Natural Killer (uNK) cells and a deficit in cytoplasmic granule formation in the uNK cells.

CONCLUSIONS

Ifng contributes to the success of fertilization and to the rate of preimplantation mouse embryo development in normogylcemic and hyperglycemic pregnancies. A physiological role for this cytokine in human preimplantation development merits investigation.

A self referencing platinum nanoparticle decorated enzyme-based microbiosensor for real time measurement of physiological glucose transport

Glucose is the central molecule in many biochemical pathways, and numerous approaches have been developed for fabricating micro biosensors designed to measure glucose concentration in/near cells and/or tissues. An inherent problem for microsensors used in physiological studies is a low signal-to-noise ratio, which is further complicated by concentration drift due to the metabolic activity of cells. A microsensor technique designed to filter extraneous electrical noise and provide direct quantification of active membrane transport is known as self-referencing. Self-referencing involves oscillation of a single microsensor via computer-controlled stepper motors within a stable gradient formed near cells/tissues (i.e., within the concentration boundary layer). The non-invasive technique provides direct measurement of trans-membrane (or trans-tissue) analyte flux. A glucose micro biosensor was fabricated using deposition of nanomaterials (platinum black, multiwalled carbon nanotubes, Nafion) and glucose oxidase on a platinum/iridium microelectrode. The highly sensitive/selective biosensor was used in the self-referencing modality for cell/tissue physiological transport studies. Detailed analysis of signal drift/noise filtering via phase sensitive detection (including a post-measurement analytical technique) are provided. Using this highly sensitive technique, physiological glucose uptake is demonstrated in a wide range of metabolic and pharmacological studies. Use of this technique is demonstrated for cancer cell physiology, bioenergetics, diabetes, and microbial biofilm physiology. This robust and versatile biosensor technique will provide much insight into biological transport in biomedical, environmental, and agricultural research applications.

Murine trophoblast cells induce NK cell interferon-gamma production through KLRK1

Murine models suggest that natural killer (NK) cells are important for normal implantation site development, in part, through the production of interferon gamma (IFNG). As KLRK1 (NKG2D) is expressed on human and murine uterine NK (uNK) cells, we examined the role of KLRK1 in the interaction between murine trophoblasts and NK cells. Flow cytometric analysis revealed that both murine trophoblast stem (TS) cells and differentiated trophoblast giant cells expressed the KLRK1 ligand retinoic acid early transcript 1, or RAET1. Coculture of activated NK cells with either TS cells or giant cells led to the production of IFNG, as measured by ELISA. In addition, coculture with TS cells led to the downregulation of KLRK1. Both responses were inhibited by soluble KLRK1 ligand, but not by irrelevant protein. Further studies demonstrated the presence of KLRK1 ligand on uterine cells derived from either virgin or pregnant mice, although uterine RAET1 protein expression was upregulated in vitro by progesterone, but not estradiol. We suggest that the interaction of KLRK1 and RAET1 may be involved in IFNG production by uNK cells, and thus, this receptor-ligand pair may contribute to successful murine implantation site development.

Akt2 modulates glucose availability and downstream apoptotic pathways during development

Glucose is the primary energy substrate for eukaryotic cells and the predominant substrate for the brain. Studies suggest that glucose serves an additional role in the regulation of cellular functions, including viability. Zebrafish is a tractable system for defining the cellular and molecular mechanisms perturbed by impaired glucose transport and metabolism. Previously, we demonstrated a critical role for the facilitative glucose transporter, Glut1, in the regulation of embryonic brain development. In this study, we aim to identify mediators in this Glut1-sensitive process by investigating the role of the antiapoptotic kinase, Akt2. Results show that abrogating expression of akt2 causes a phenotype strikingly similar to that observed when glut1 expression is inhibited. akt2-deficient embryos exhibit increased neuronal apoptosis, impaired glucose uptake, and death by 72 h postfertilization. Similar to what was observed in the glut1 morphants, inhibiting the expression of the proapoptotic protein, bad, in the context of impaired akt2 expression results in the inhibition of apoptosis and rescue of the morphant embryos. Intriguingly, overexpression of glut1 in the akt2 morphants was also able to rescue these embryos. Quantitative reverse transcription-PCR analysis revealed decreased glut1 transcript expression in akt2 morphant embryos. Taken together, these data suggest that Akt2 modulates glucose availability by regulating Glut1 expression at the transcript level. These data support a role for akt2 in an integrative pathway directly linking glucose, Glut1 expression, and activation of apoptosis and demonstrate the dependence of akt2 on glucose availability for the maintenance of cellular viability, particularly in the central nervous system.

Maternal diabetes and oocyte quality

Maternal diabetes has been demonstrated to adversely affect preimplantation embryo development and pregnancy outcomes. Emerging evidence has implicated that these effects are associated with compromised oocyte competence. Several developmental defects during oocyte maturation in diabetic mice have been reported over past decades. Most recently, we further identified the structural, spatial and metabolic dysfunction of mitochondria in oocytes from diabetic mice, suggesting the impaired oocyte quality. These defects in the oocyte may be maternally transmitted to the embryo and then manifested later as developmental abnormalities in preimplantation embryo, congenital malformations, and even metabolic disease in the offspring. In this paper, we briefly review the effects of maternal diabetes on oocyte quality, with a particular emphasis on the mitochondrial dysfunction. The possible connection between dysfunctional oocyte mitochondria and reproductive failure of diabetic females, and the mechanism(s) by which maternal diabetes exerts its effects on the oocyte are also discussed.

Diabetes and apoptosis: neural crest cells and neural tube

Birth defects resulting from diabetic pregnancy are associated with apoptosis of a critical mass of progenitor cells early during the formation of the affected organ(s). Insufficient expression of genes that regulate viability of the progenitor cells is responsible for the apoptosis. In particular, maternal diabetes inhibits expression of a gene, Pax3, that encodes a transcription factor which is expressed in neural crest and neuroepithelial cells. As a result of insufficient Pax3, cardiac neural crest and neuroepithelial cells undergo apoptosis by a process dependent on the p53 tumor suppressor protein. This, then provides a cellular explanation for the cardiac outflow tract and neural tube and defects induced by diabetic pregnancy.

Glucose transporters in gametes and preimplantation embryos

The oocyte, sperm and preimplantation embryo have unique metabolic needs that must be met to ensure successful pregnancy. The family of facilitative glucose transporters (GLUTs) plays a major role in providing metabolic substrates to these tissues. The variety of GLUTs expressed in these tissues allows for flexibility to adapt to a changing environment. Alterations in glucose transport and metabolism at the earliest stages of development can impact fetal development. Research into the mechanisms of normal glucose transport into cells is critical for improving outcomes in the increasingly common diabetic maternal environment. Here, we review the current understanding in the distribution and role of glucose transporters in gametes and preimplantation embryos under normal and diabetic conditions.

Will the original glucose transporter isoform please stand up!

Monosaccharides enter cells by slow translipid bilayer diffusion by rapid, protein-mediated, cation-dependent cotransport and by rapid, protein-mediated equilibrative transport. This review addresses protein-mediated, equilibrative glucose transport catalyzed by GLUT1, the first equilibrative glucose transporter to be identified, purified, and cloned. GLUT1 is a polytopic, membrane-spanning protein that is one of 13 members of the human equilibrative glucose transport protein family. We review GLUT1 catalytic and ligand-binding properties and interpret these behaviors in the context of several putative mechanisms for protein-mediated transport. We conclude that no single model satisfactorily explains GLUT1 behavior. We then review GLUT1 topology, subunit architecture, and oligomeric structure and examine a new model for sugar transport that combines structural and kinetic analyses to satisfactorily reproduce GLUT1 behavior in human erythrocytes. We next review GLUT1 cell biology and the transcriptional and posttranscriptional regulation of GLUT1 expression in the context of development and in response to glucose perturbations and hypoxia in blood-tissue barriers. Emphasis is placed on transgenic GLUT1 overexpression and null mutant model systems, the latter serving as surrogates for the human GLUT1 deficiency syndrome. Finally, we review the role of GLUT1 in the absence or deficiency of a related isoform, GLUT3, toward establishing the physiological significance of coordination between these two isoforms.

Hyperglycemia reduces mitochondrial content and glucose transporter expression in mouse embryos developing in vitro

The objective of this research was to examine the effects of high concentrations of glucose on mouse embryos developing in vitro by studying embryo viability, mitochondrial content and expression of glucose transporters. Addition of 55 mM glucose to the culture medium of two-cell stage embryos significantly reduced the formation of morulae and blastocysts, resulting in fewer cells in the blastocyst stage embryos and increased levels of apoptosis. Quantitative reverse transcriptase (RT) PCR analysis revealed that the expression levels of the pro-apoptotic genes Bax and Casp3 at the blastocyst stage were increased significantly by the addition of either 25 or 55 mM glucose to the culture medium. However, addition of 25 or 55 mM glucose to the culture medium did not change the copy numbers of the apoptosis-related miRNAs mmu-mir-15a, mmu-mir-16 and mmu-mir-21. MitoTracker Green fluorescence revealed a decrease in the mitochondrial mass. The expression levels of the mitochondrial DNA-encoded genes Cox1 and Cox2 decreased sharply with the addition of 25 or 55 mM glucose to the culture medium. Both transcripts and protein synthesis of the glucose transporters Glut1 and Glut3 were reduced in blastocysts cultured in the presence of either 25 or 55 mM glucose. These results suggest that hyperglycemia reduces both mitochondrial content and expression levels of glucose transporters in mouse embryos developing in vitro and that this may result in apoptosis in these embryos.

Facilitative glucose transporter type 1 is differentially regulated by progesterone and estrogen in murine and human endometrial stromal cells

Embryo implantation is a highly synchronized event between an activated blastocyst and a receptive endometrium. The success of this process relies on the dynamic interplay of estrogen (E(2)) and progesterone (P(4)), however, the details of this interaction are not entirely clear. Recent data implicate E(2) and P(4) in the regulation of glucose utilization by affecting facilitative glucose transporter (GLUT) expression. In this study we examine GLUT1 expression in murine and human endometrial stromal cells (ESCs) using a primary culture system. We show that expression of GLUT1 is increased during ESC decidualization in vitro. P(4) up-regulates, whereas E(2) down-regulates, GLUT1 expression. In addition, P(4) increases and E(2) decreases glucose uptake in ESCs, suggesting that GLUT1 may be a major player in glucose utilization in these cells. Moreover, GLUT1 expression is increased in human ESCs when decidualized in vitro with P(4) and dibutyryl cAMP, suggesting a similar role for P(4) in human endometrium. In conclusion, an imbalance between P(4) and E(2) seen in patients with polycystic ovary syndrome, luteal phase defect, and recurrent pregnancy loss may have a critical impact on glucose utilization in the endometrial stroma, and, thus, may be responsible for endometrial dysfunction and failure of embryo implantation in these patient populations.

Metabolism of the viable mammalian embryo: quietness revisited

This review examines the 'Quiet Embryo Hypothesis' which proposes that viable preimplantation embryos operate at metabolite or nutrient turnover rates distributed within lower ranges than those of their less viable counterparts. The 'quieter' metabolism consistent with this hypothesis is considered in terms of (i) 'functional' quietness; the contrasting levels of intrinsic metabolic activity in different cell types as a consequence of their specialized functions, (ii) inter-individual embryo/cell differences in metabolism and (iii) loss of quietness in response to environmental stress. Data are reviewed which indicate that gametes and early embryos function in vivo at a lower temperature than core body temperature, which could encourage the expression of a quiet metabolism. We call for research to determine the optimum temperature for mammalian gamete/embryo culture. The review concludes by examining the key role of reactive oxygen species, which can induce molecular damage, trigger a cellular stress response and lead to a loss of quietness.