Advances in revealing the molecular targets downstream of oxidative stress-induced proapoptotic kinase signaling in diabetic embryopathy

Role and regulation of FOXO3a: new insights into breast cancer therapy

Breast cancer is the most common malignancy in the world, particularly affecting female cancer patients. Enhancing the therapeutic strategies for breast cancer necessitates identifying molecular drug targets that effectively eliminate tumor cells. One of these prominent targets is the forkhead and O3a class (FOXO3a), a member of the forkhead transcription factor subfamily. FOXO3a plays a pivotal role in various cellular processes, including apoptosis, proliferation, cell cycle regulation, and drug resistance. It acts as a tumor suppressor in multiple cancer types, although its specific role in cancer remains unclear. Moreover, FOXO3a shows promise as a potential marker for tumor diagnosis and prognosis in breast cancer patients. In addition, it is actively influenced by common anti-breast cancer drugs like paclitaxel, simvastatin, and gefitinib. In breast cancer, the regulation of FOXO3a involves intricate networks, encompassing post-translational modification post-translational regulation by non-coding RNA (ncRNA) and protein-protein interaction. The specific mechanism of FOXO3a in breast cancer urgently requires further investigation. This review aims to systematically elucidate the role of FOXO3a in breast cancer. Additionally, it reviews the interaction of FOXO3a and its upstream and downstream signaling pathway-related molecules to uncover potential therapeutic drugs and related regulatory factors for breast cancer treatment by regulating FOXO3a.

MicroRNA-322 overexpression reduces neural tube defects in diabetic pregnancies

BACKGROUND

Hyperglycemia from pregestational diabetes mellitus induces neural tube defects in the developing fetus. Folate supplementation is the only effective way to prevent neural tube defects; however, some cases of neural tube defects are resistant to folate. Excess folate has been linked to higher maternal cancer risk and infant allergy. Therefore, additional interventions are needed. Understanding the mechanisms underlying maternal diabetes mellitus-induced neural tube defects can identify potential targets for preventing such defects. Despite not yet being in clinical use, growing evidence suggests that microRNAs are important intermediates in embryonic development and can serve as both biomarkers and drug targets for disease intervention. Our previous studies showed that maternal diabetes mellitus in vivo activates the inositol-requiring transmembrane kinase/endoribonuclease 1α (IRE1α) in the developing embryo and that a high glucose condition in vitro reduces microRNA-322 (miR-322) levels. IRE1α is an RNA endonuclease; however, it is unknown whether IRE1α targets and degrades miR-322 specifically or whether miR-322 degradation leads to neural tube defects via apoptosis. We hypothesize that IRE1α can inhibit miR-322 in maternal diabetes mellitus-induced neural tube defects and that restoring miR-322 expression in developing neuroepithelium ameliorates neural tube defects.

OBJECTIVE

This study aimed to identify potential targets for preventing maternal diabetes mellitus-induced neural tube defects and to investigate the roles and relationship of a microRNA and an RNA endonuclease in mouse embryos exposed to maternal diabetes mellitus.

STUDY DESIGN

To determine whether miR-322 reduction is necessary for neural tube defect formation in pregnancies complicated by diabetes mellitus, male mice carrying a transgene expressing miR-322 were mated with nondiabetic or diabetic wide-type female mice to generate embryos with or without miR-322 overexpression. At embryonic day 8.5 when the neural tube is not yet closed, embryos were harvested for the assessment of 3 miR-322 transcripts (primary, precursor, and mature miR-322), tumor necrosis factor receptor-associated factor 3 (TRAF3), and neuroepithelium cell survival. Neural tube defect incidences were determined in embryonic day 10.5 embryos when the neural tube should be closed if there is no neural tube defect formation. To identify which miR-322 transcript is affected by maternal diabetes mellitus and high glucose conditions, 3 miR-322 transcripts were assessed in embryos from dams with or without diabetes mellitus and in C17.2 mouse neural stem cells treated with different concentrations of glucose and at different time points. To determine whether the endonuclease IRE1α targets miR-322, small interfering RNA knockdown of IRE1α or overexpression of inositol-requiring transmembrane kinase/endoribonuclease 1α by DNA plasmid transfection was used to determine the effect of IRE1α deficiency or overexpression on miR-322 expression. RNA immunoprecipitation was performed to reveal the direct targets of inositol-requiring transmembrane kinase/endoribonuclease 1α.

RESULTS

Maternal diabetes mellitus suppressed miR-322 expression in the developing neuroepithelium. Restoring miR-322 expression in the neuroepithelium blocked maternal diabetes mellitus-induced caspase-3 and caspase-8 cleavage and cell apoptosis, leading to a neural tube defect reduction. Reversal of maternal diabetes mellitus-inhibited miR-322 via transgenic overexpression prevented TRAF3 up-regulation in embryos exposed to maternal diabetes mellitus. Activated IRE1α acted as an endonuclease and degraded precursor miR-322, resulting in mature miR-322 reduction.

CONCLUSION

This study supports the crucial role of the IRE1α-microRNA-TRAF3 circuit in the induction of neuroepithelial cell apoptosis and neural tube defect formation in pregnancies complicated by diabetes mellitus and identifies IRE1α and miR-322 as potential targets for preventing maternal diabetes mellitus-induced neural tube defects.

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.

Calcium Supplementation on Glucose Tolerance, Oxidative Stress, and Reproductive Outcomes of Diabetic Rats and Their Offspring

Diabetes mellitus increases the risk of obstetric complications, morbidity, and infant mortality. Controlled nutritional therapy with micronutrients has been employed. However, the effect of calcium (Ca2+) supplementation on diabetic pregnancy is unclear. We aimed to evaluate whether diabetic rats supplemented with Ca2+ during pregnancy present better glucose tolerance, redox status, embryonic and fetal development, newborn weight, and the prooxidant and antioxidant balance of male and female pups. For this, newborn rats received the beta-cytotoxic drug streptozotocin for inducing diabetes on the day of birth. In adulthood, these rats were mated and treated with Ca2+ twice a day from day 0 to day 20 of pregnancy. On day 17, the pregnant rats were submitted to the oral glucose tolerance test (OGTT). At the end of pregnancy, they were anesthetized and killed to collect blood and pancreas samples. The uterine horns were exposed for an evaluation of maternal reproductive outcomes and embryofetal development, and the offspring's liver samples were collected for redox status measurement. Nondiabetic and diabetic rats supplemented with Ca2+ showed no influence on glucose tolerance, redox status, insulin synthesis, serum calcium levels, and embryofetal losses. The reduced rate of newborns classified as adequate for gestational age (AGA) and higher rates of LGA (large) and small (LGA) newborns and higher -SH and GSH-Px antioxidant activities in female pups were observed in diabetic dams, regardless of supplementation. Thus, maternal supplementation caused no improvement in glucose tolerance, oxidative stress biomarkers, embryofetal growth and development, and antioxidants in pups from diabetic mothers.

Neuroprotective Effect of a New Free Radical Scavenger HL-008 in an Ischemia-Reperfusion Injury Rat Model

Oxidative stress plays a critical role in cerebral ischemia-reperfusion injury. We have previously developed a powerful antioxidant, HL-008. This study aimed to investigate the neuroprotective function of HL-008. HL-008 efficacy in vitro and in vivo was evaluated using a PC-12 cell oxidative stress model induced by hydrogen peroxide and a rat model of middle cerebral artery occlusion, respectively. The MTT assay was used to analyze cell viability. 2,3,5-Triphenyltetrazolium chloride and Hematoxylin and Eosin staining, immunofluorescence, western blot, and proteomics were used to evaluate the infarction volume, brain tissue morphology, apoptosis, inflammation, and related pathways. Indicators related to oxidative levels were also detected. HL-008 significantly reduced the cerebral infarction volume induced by ischemia-reperfusion, improved the neurological score, alleviated oxidative stress and inflammation in the brain tissue, reduced glial cell activation, inhibited brain tissue apoptosis by influencing multiple signaling pathways, and had a neuroprotective effect. If HL-008 is successfully developed, it could significantly improve stroke patients' quality of life.

Potential role of FoxO3a in the regulation of trophoblast development and pregnancy complications

The forkhead box O3a protein (FoxO3a) has been reported to regulate tumour invasion and migration, but little is known about the molecular mechanism or its role in trophoblast invasion and migration into the uterus. In this study, we aim to explore its role in trophoblast development and placenta‐related pregnancy complications and the potential mechanism. Levels of FoxO3a and its phosphorylated form (p‐FoxO3a) in placental tissue from healthy pregnant women and pre‐eclampsia patients were first compared. Then, HTR‐8/SVneo cells were transfected with lentiviral vectors to deplete and overexpress FoxO3a. Western blot, immunohistochemistry, Cell Counting Kit‐8, wound‐healing assay, Matrigel invasion assay, cell apoptosis, cell cycle assay, RNA sequencing, qRT‐PCR and ChIP‐qPCR were performed on the cells to study the potential role of FoxO3a and the underlying mechanism. We found the expression of FoxO3a was decreased, whereas p‐FoxO3a was increased in pre‐eclampsia placentae. FoxO3a depletion significantly reduced transcription of the promoter region of intercellular cell adhesion molecule‐1 (ICAM1) gene in ChIP assays and led to reduced invasion and migration of trophoblast cells, arrested cell cycle in G1 phase and increased apoptosis under oxidative stress. Our results suggested that FoxO3a may play a role in the regulation of trophoblast invasion and migration during placental development, which may be because of its affinity to the ICAM1 promotor.

17β-Estradiol Promotes Apoptosis of HepG2 Cells Caused by Oxidative Stress by Increasing Foxo3a Phosphorylation

Liver cancer is associated with high mortality, particularly in patients infected with the hepatitis B virus. Treatment methods remain very limited. Here, we explored the effects of 17β-estradiol (E2) on apoptosis of various liver cell lines (LO2, HepG2, and HepG2.2.15 cells). Within a certain concentration range, 17β-estradiol induced oxidative stress and apoptosis of HepG2 cells, downregulated ERα-36 expression, and increased Akt and Foxo3a phosphorylation. p-Foxo3a became localized around the nucleus but did not enter the organelle. The levels of mRNAs encoding manganese superoxide dismutase (MnSOD) and catalase, to the promoters of which Foxo3a binds to trigger gene expression, were significantly reduced in HepG2 cells. 17β-estradiol had no obvious effects on LO2 or HepG2.2.15 cells. We speculate that 17β-estradiol may induce oxidative stress in HepG2 cells by increasing Foxo3a phosphorylation, thus promoting apoptosis. This may serve as a new treatment for hepatocellular carcinoma.

Dysglycemia in Pregnancy and Maternal/Fetal Outcomes

Maternal dysglycemia-including diabetes, impaired glucose tolerance, and impaired fasting glucose-affects one in six pregnancies worldwide and represents a significant health risk to the mother and the fetus. Maternal dysglycemia is an independent risk factor for perinatal mortality, major congenital anomalies, and miscarriages. Furthermore, it increases the longer-term risk of type 2 diabetes mellitus, metabolic syndrome, cardiovascular morbidity, malignancies, and ophthalmic, psychiatric, and renal diseases in the mother. The most commonly encountered form of maternal dysglycemia is gestational diabetes. Currently, international consensus does not exist for diagnostic criteria defining gestational diabetes at 24-28 weeks gestation, and potential diagnostic glucose thresholds earlier in gestation require further investigation. Likewise, recommendations regarding the timing and modality (e.g., lifestyle or pharmacological) of treatment vary greatly. Because a precise diagnosis determines the appropriate treatment and outcome of the pregnancy, it is imperative that a better definition of maternal dysglycemia and its treatment be achieved. This article will address some of the controversies related to diagnosing and managing maternal dysglycemia. In addition, the article will discuss the impact of maternal dysglycemia on complications experienced by the mother and infant, both at birth and in later life.

Deficiency of the oxidative stress-responsive kinase p70S6K1 restores autophagy and ameliorates neural tube defects in diabetic embryopathy

BACKGROUND

Autophagy is highly active in neuroepithelial cells of the developing neuroepithelium, and impairment of autophagy leads to neural tube defects. In this study, we have found that maternal diabetes suppresses autophagy that leads to neural tube defects and consequent cellular imbalance in the endoplasmic reticulum where critical events occur, leading to the induction of diabetic embryopathy. Because the mammalian target of rapamycin pathway suppresses autophagy, we hypothesized that 70 kDa ribosomal protein S6 kinase 1 (p70S6K1), a major downstream effector of mammalian target of rapamycin, mediates the inhibitory effect of maternal diabetes on autophagy in the developing neuroepithelium.

OBJECTIVE

We investigated whether p70S6K1 mediates the inhibitory effect of maternal diabetes on autophagy during neurulation. We also examined whether p70S6K1 deficiency restores autophagy and therefore relieves endoplasmic reticulum stress and inhibits maternal diabetes-induced apoptosis, which leads to reduction in neural tube defect incidence in diabetic embryopathy.

STUDY DESIGN

Female p70S6K1 heterogeneous knockout (p70S6K1+/-) mice were bred with male p70S6K1 heterogeneous knockout (p70S6K1+/-) mice to generate wild-type (WT), p70S6K1+/- and p70S6K1 knockout (p70S6K1-/-) embryos. Embryos at embryonic day 8.5 were harvested for the assessment of indices of autophagy, endoplasmic reticulum stress, and apoptosis. Neural tube defect incidence in embryos was determined at embryonic day 10.5. For in vitro studies, small interfering RNA knockdown of p70S6K1 in C17.2 mouse neural stem cells was used to determine the effect of p70S6K1 deficiency on autophagy impairment and endoplasmic reticulum stress under high glucose conditions.

RESULTS

Knockout of the Rps6kb1 gene, which encodes for p70S6K1, ameliorated maternal diabetes-induced NTDs and restored autophagosome formation in neuroepithelial cells suppressed by maternal diabetes. Maternal diabetes-suppressed conversion of LC3-I (microtubule-associated protein 1A/1B-light chain 3) to LC3-II, an index of autophagic activity, in neurulation stage embryos was abrogated in the absence of p70S6K1. p70S6K1 knockdown in neural stem cells also restored autophagosome formation and the conversion of LC3-I to LC3-II. The activation of the major unfolded protein response, indicated by phosphorylation of inositol-requiring enzyme 1 alpha, and protein kinase R-like endoplasmic reticulum kinase, and eukaryotic translation initiation factor 2α, and the increase of the endoplasmic reticulum stress marker, C/EBP homologous protein, were induced by maternal diabetes in vivo and high glucose in vitro. Unfolded protein response and endoplasmic reticulum stress induced by maternal diabetes or high glucose were reduced by Rps6kb1 deletion or p70S6K1 knockdown, respectively. Rps6kb1 knockout blocked maternal diabetes-induced caspase cleavage and neuroepithelial cell apoptosis. The superoxide dismutase mimetic Tempol abolished high glucose-induced p70S6K1 activation.

CONCLUSION

The study revealed the critical involvement of p70S6K1 in the pathogenesis of diabetic embryopathy.

FOXO3a accumulation and activation accelerate oxidative stress-induced podocyte injury

Podocyte injury is the primary cause of glomerular injury in diabetic nephropathy (DN). Advanced oxidation protein products (AOPPs), the triggers and markers of oxidative stress in DN, have been linked to podocyte damage. However, the underlying mechanism is not yet clear. Here, we investigated the potential role of FOXO3a, a key transcription factor in the response to stress, in mediating AOPPs-induced podocyte injury. We found that FOXO3a expression was increased in the glomeruli of kidney biopsies from patients with DN and it was positively correlated with proteinuria. The serum from patients with DN significantly increased FOXO3a and its downstream genes FasL and Bim, thereby inducing the high level of cleaved caspase3 and the loss of nephrin and podocin expressions in podocytes. Blockade of AOPPs signaling by a neutralizing antibody against the receptor of advanced glycation end products (αRAGE) abolished the effect of DN serum on podocytes, confirming the pathogenic role of AOPPs in DN serum. Downregulation of FOXO3a decreased AOPPs-induced podocyte apoptosis and restored the levels of podocyte markers nephrin and podocin, and upregulation of FOXO3a exacerbated these changes in podocytes after AOPPs treatment. Furthermore, FOXO3a specifically activated proapoptotic genes in podocytes only in the presence of AOPPs. Mechanistically, AOPPs increased the FOXO3a protein levels by inhibiting their autophagic degradation in a ROS/mTOR-dependent manner. Moreover AOPPs activated the accumulated FOXO3a by maintaining FOXO3a in the nucleus, and this process was dependent on ROS-mediated AKT signaling deactivation. These studies suggest that FOXO3a plays a critical role in mediating AOPPs-induced podocyte injury and reveal a new mechanistic linkage of oxidative stress, FOXO3a activation and podocyte injury in DN.

High Glucose Inhibits Neural Stem Cell Differentiation Through Oxidative Stress and Endoplasmic Reticulum Stress

Maternal diabetes induces neural tube defects by suppressing neurogenesis in the developing neuroepithelium. Our recent study further revealed that high glucose inhibited embryonic stem cell differentiation into neural lineage cells. However, the mechanism whereby high glucose suppresses neural differentiation is unclear. To investigate whether high glucose-induced oxidative stress and endoplasmic reticulum (ER) stress lead to the inhibition of neural differentiation, the effect of high glucose on neural stem cell (the C17.2 cell line) differentiation was examined. Neural stem cells were cultured in normal glucose (5 mM) or high glucose (25 mM) differentiation medium for 3, 5, and 7 days. High glucose suppressed neural stem cell differentiation by significantly decreasing the expression of the neuron marker Tuj1 and the glial cell marker GFAP and the numbers of Tuj1⁺ and GFAP⁺ cells. The antioxidant enzyme superoxide dismutase mimetic Tempol reversed high glucose-decreased Tuj1 and GFAP expression and restored the numbers of neurons and glial cells differentiated from neural stem cells. Hydrogen peroxide treatment imitated the inhibitory effect of high glucose on neural stem cell differentiation. Both high glucose and hydrogen peroxide triggered ER stress, whereas Tempol blocked high glucose-induced ER stress. The ER stress inhibitor, 4-phenylbutyrate, abolished the inhibition of high glucose or hydrogen peroxide on neural stem cell differentiation. Thus, oxidative stress and its resultant ER stress mediate the inhibitory effect of high glucose on neural stem cell differentiation.

Oxygen and lack of oxygen in fetal and placental development, feto-placental coupling, and congenital heart defects

Low oxygen concentration (hypoxia) is part of normal embryonic development, yet the situation is complex. Oxygen (O₂ ) is a janus gas with low levels signaling through hypoxia-inducible transcription factor (HIF) that are required for development of fetal and placental vasculature and fetal red blood cells. This results in coupling of fetus and mother around midgestation as a functional feto-placental unit (FPU) for O₂ transport, which is required for continued growth and development of the fetus. Defects in these processes may leave the developing fetus vulnerable to O₂ deprivation or other stressors during this critical midgestational transition when common septal and conotruncal heart defects (CHDs) are likely to arise. Recent human epidemiological and case-control studies support an association between placental dysfunction, manifest as early onset pre-eclampsia (PE) and increased serum bio-markers, and CHD. Animal studies support this association, in particular those using gene inactivation in the mouse. Sophisticated methods for gene inactivation, cell fate mapping, and a quantitative bio-reporter of O₂ concentration support the premise that hypoxic stress at critical stages of development leads to CHD. The secondary heart field contributing to the cardiac outlet is a key target, with activation of the un-folded protein response and abrogation of FGF signaling or precocious activation of a cardiomyocyte transcriptional program for differentiation, suggested as mechanisms. These studies provide a strong foundation for further study of feto-placental coupling and hypoxic stress in the genesis of human CHD.

Disturbed intracellular calcium homeostasis in neural tube defects in diabetic embryopathy

Pregnancies complicated by preexisting maternal diabetes mellitus are associated with a higher risk of birth defects in infants, known as diabetic embryopathy. The common defects seen in the central nervous system result from failure of neural tube closure. The formation of neural tube defects (NTDs) is associated with excessive programmed cell death (apoptosis) in the neuroepithelium under hyperglycemia-induced intracellular stress conditions. The early cellular response to hyperglycemia remains to be identified. We hypothesize that hyperglycemia may disturb intracellular calcium (Ca²⁺) homeostasis, which perturbs organelle function and apoptotic regulation, resulting in increased apoptosis and embryonic NTDs. In an animal model of diabetic embryopathy, we performed Ca²⁺ imaging and observed significant increases in intracellular Ca²⁺ ([Ca²⁺]_i) in the embryonic neural epithelium. Blocking T-type Ca²⁺ channels with mibefradil, but not L-type with verapamil, significantly blunted the increases in [Ca²⁺]_i, implicating an involvement of channel type-dependent Ca²⁺ influx in hyperglycemia-perturbed Ca²⁺ homeostasis. Treatment of diabetic pregnant mice with mibefradil during neurulation significantly reduced NTD rates in the embryos. This effect was associated with decreases in apoptosis, alleviation of endoplasmic reticulum stress, and increases of anti-apoptotic factors. Taken together, our data suggest an important role of Ca²⁺ influx in hyperglycemia-induced NTDs and of T-type Ca²⁺ channels as a potential target to prevent birth defects in diabetic pregnancies.

ASK1 induces retinal microvascular endothelial cell apoptosis through ER stress-associated pathway

Diabetic retinopathy (DR) is a major microvascular complication in patients with diabetes mellitus; it can cause a variety of eye problems in a high percentage of diabetic patients. The purpose of this study was to determine the role of apoptosis signal-regulating kinase 1 (ASK1) in the regulation of the endoplasmic reticulum (ER) stress-associated apoptosis pathway in microvascular endothelial cells. For in vivo studies, a streptozotocin (STZ)-induced diabetes model was used to assess apoptosis in retinal tissues. Apoptotic cell death was determined by TUNEL assay. For in vitro studies, a high glucose (HG)-induced retinal microvascular endothelial cell injury model was generated to evaluate apoptosis. Apoptotic rates were measured by flow cytometry and apoptosis-related proteins were detected by western blotting. We found that retinal microvascular endothelial cell apoptosis was increased in both animal and cell models. HG-induced apoptosis primarily occurred in an ER stress-dependent manner. HG-induced apoptosis was alleviated by inhibiting ASK1 with shRNA or a specific inhibitor, NQDI-1. TUNEL and western blot assays showed that ASK1 promoted the expression of ER stress-related proteins that are the master regulators of DR. Our study suggests that ASK1 functions as a promoter of DR through the ER stress-induced apoptosis pathway, and it may be a therapeutic target for DR.

Trehalose restores functional autophagy suppressed by high glucose

Autophagy is required for neurulation, and autophagy activators with minimal toxicity, such as the natural compound trehalose, a nonreducing disaccharide, possess high therapeutic value. To determine whether trehalose directly induces autophagy, FITC-labeled trehalose was used for tracing its presence in autophagosome complexes. Trehalose was as potent as rapamycin and starvation in inducing de novo autophagosome formation and increasing autophagosome flux in GFP-LC3 reporter cells and C17.2 neural stem cells. Trehalose effectively reversed high glucose-suppressed autophagy and reduced p62 protein expression. Trehalose abolished the disruption of autophagosome complexes under high glucose conditions in vitro and maternal diabetes in vivo. Autophagosomes induced by trehalose were functionally active, forming mitophagy and reticulophagy in removing damaged cellular organelles in neuroepithelial cells exposed to maternal diabetes. Thus, trehalose directly participated in functional autophagosome generation by incorporating itself into autophagosomes. These findings provide the mechanistic basis for the use of trehalose in preventing disruptive autophagy-associated pathogenesis.

The increased activity of a transcription factor inhibits autophagy in diabetic embryopathy

BACKGROUND

Maternal diabetes induces neural tube defects and stimulates the activity of the forkhead box O3 (Fox)O3a in the embryonic neuroepithelium. We previously demonstrated that deleting the FOXO3a gene ameliorates maternal diabetes-induced neural tube defects. Macroautophagy (hereafter referred to as "autophagy") is essential for neurulation. Rescuing autophagy suppressed by maternal diabetes in the developing neuroepithelium inhibits neural tube defect formation in diabetic pregnancy. This evidence suggests a possible link between FoxO3a and impaired autophagy in diabetic embryopathy.

OBJECTIVE

We aimed to determine whether maternal diabetes suppresses autophagy through FoxO3a, and if the transcriptional activity of FoxO3a is required for the induction of diabetic embryopathy.

STUDY DESIGN

We used a well-established type 1 diabetic embryopathy mouse model, in which diabetes was induced by streptozotocin, for our in vivo studies. To determine if FoxO3a mediates the inhibitory effect of maternal diabetes on autophagy in the developing neuroepithelium, we induced diabetic embryopathy in FOXO3a gene knockout mice and FoxO3a dominant negative transgenic mice. Embryos were harvested at embryonic day 8.5 to determine FoxO3a and autophagy activity and at embryonic day 10.5 for the presence of neural tube defects. We also examined the expression of autophagy-related genes. C17.2 neural stem cells were used for in vitro examination of the potential effects of FoxO3a on autophagy.

RESULTS

Deletion of the FOXO3a gene restored the autophagy markers, lipidation of microtubule-associated protein 1A/1B-light chain 3I to light chain 3II, in neurulation stage embryos. Maternal diabetes decreased light chain 3I-positive puncta number in the neuroepithelium, which was restored by deleting FoxO3a. Maternal diabetes also decreased the expression of positive regulators of autophagy (Unc-51 like autophagy activating kinase 1, Coiled-coil myosin-like BCL2-interacting protein, and autophagy-related gene 5) and the negative regulator of autophagy, p62. FOXO3a gene deletion abrogated the dysregulation of autophagy genes. In vitro data showed that the constitutively active form of FoxO3a mimicked high glucose in repressing autophagy. In cells cultured under high-glucose conditions, overexpression of the dominant negative FoxO3a mutant blocked autophagy impairment. Dominant negative FoxO3a overexpression in the developing neuroepithelium restored autophagy and significantly reduced maternal diabetes-induced apoptosis and neural tube defects.

CONCLUSION

Our study revealed that diabetes-induced FoxO3a activation inhibited autophagy in the embryonic neuroepithelium. We also observed that FoxO3a transcriptional activity mediated the teratogenic effect of maternal diabetes because dominant negative FoxO3a prevents maternal diabetes-induced autophagy impairment and neural tube defect formation. Our findings suggest that autophagy activators could be therapeutically effective in treating maternal diabetes-induced neural tube defects.

Offspring of mothers with hyperglycaemia in pregnancy: The short term and long-term impact. What is new?

The continuing rise in the global prevalence of diabetes and overweight or obesity has become a major burden for global health, as the pandemic is affecting both high and low-middle income countries (LMIC). At the same time, a similar pattern has been observed for all forms of hyperglycemia in pregnancy (HIP), diabetes during pregnancy and gestational diabetes. The offspring of mothers with HIP and/or overweight-obesity is receiving increasing attention as advances in early detection and treatment of HIP did not completely prevent macrosomia and its associated short-term perinatal disorders, whilst long term consequences are observed in the mother and in offspring as it reaches adulthood. This review discusses the current developments in the consequences of HIP in the offspring, with a particular focus on its long-term health at adulthood, and on intergenerational and transgenerational effects. HIP is emerging as one of the factors that can contribute, during the window of sensitivity to environmental cues constituted by the preconception, pregnancy, and early childhood, and as an amplifying factor linked to reproduction, to the current global epidemic of diabetes and non-communicable diseases (NCDs).

Modulation of nuclear factor-κB signaling and reduction of neural tube defects by quercetin-3-glucoside in embryos of diabetic mice

BACKGROUND

Diabetes mellitus in early pregnancy increases the risk of birth defects in infants. Maternal hyperglycemia stimulates the expression of nitric oxide synthase 2, which can be regulated by transcription factors of the nuclear factor-κB family. Increases in reactive nitrogen species generate intracellular stress conditions, including nitrosative, oxidative, and endoplasmic reticulum stresses, and trigger programmed cell death (or apoptosis) in the neural folds, resulting in neural tube defects in the embryo. Inhibiting nitric oxide synthase 2 can reduce neural tube defects; however, the underlying mechanisms require further delineation. Targeting nitric oxide synthase 2 and associated nitrosative stress using naturally occurring phytochemicals is a potential approach to preventing birth defects in diabetic pregnancies.

OBJECTIVE

This study aims to investigate the effect of quercetin-3-glucoside, a naturally occurring polyphenol flavonoid, in reducing maternal diabetes-induced neural tube defects in an animal model, and to delineate the molecular mechanisms underlying quercetin-3-glucoside action in regulating nitric oxide synthase 2 expression.

STUDY DESIGN

Female mice (C57BL/6) were induced to develop diabetes using streptozotocin before pregnancy. Diabetic pregnant mice were administered quercetin-3-glucoside (100 mg/kg) daily via gavage feeding, introduction of drug to the stomach directly via a feeding needle, during neurulation from embryonic day 6.5-9.5. After treatment at embryonic day 10.5, embryos were collected and examined for the presence of neural tube defects and apoptosis in the neural tube. Expression of nitric oxide synthase 2 and superoxide dismutase 1 (an antioxidative enzyme) was quantified using Western blot assay. Nitrosative, oxidative, and endoplasmic reticulum stress conditions were assessed using specific biomarkers. Expression and posttranslational modification of factors in the nuclear factor-κB system were investigated.

RESULTS

Treatment with quercetin-3-glucoside (suspended in water) significantly decreased neural tube defect rate and apoptosis in the embryos of diabetic mice, compared with those in the water-treated diabetic group (3.1% vs. 24.7%; P < .001). Quercetin-3-glucoside decreased the expression of nitric oxide synthase 2 and nitrosative stress (P < .05). It also increased the levels of superoxide dismutase 1 (P < .05), further increasing the antioxidative capacity of the cells. Quercetin-3-glucoside treatment also alleviated of endoplasmic reticulum stress in the embryos of diabetic mice (P < .05). Quercetin-3-glucoside reduced the levels of p65 (P < .05), a member of the nuclear factor-κB transcription factor family, but augmented the levels of the inhibitor of κBα (P < .05), which suppresses p65 nuclear translocation. In association with these changes, the levels of inhibitor of κB kinase-α and inhibitor of κBα phosphorylation were elevated (P < .05).

CONCLUSION

Quercetin-3-glucoside reduces the neural tube defects rate in the embryos of diabetic dams. Quercetin-3-glucoside suppresses nitric oxide synthase 2 and increases superoxide dismutase 1 expression, leading to alleviation of nitrosative, oxidative, and endoplasmic reticulum stress conditions. Quercetin-3-glucoside may regulate the expression of nitric oxide synthase 2 via modulating the nuclear factor-κB transcription regulation system. Quercetin-3-glucoside, a naturally occurring polyphenol that has high bioavailability and low toxicity, is a promising candidate agent to prevent birth defects in diabetic pregnancies.

Endoplasmic Reticulum Stress-Induced CHOP Inhibits PGC-1α and Causes Mitochondrial Dysfunction in Diabetic Embryopathy

Endoplasmic reticulum (ER) stress has been implicated in the development of maternal diabetes-induced neural tube defects (NTDs). ER stress-induced C/EBP homologous protein (CHOP) plays an important role in the pro-apoptotic execution pathways. However, the molecular mechanism underlying ER stress- and CHOP-induced neuroepithelium cell apoptosis in diabetic embryopathy is still unclear. Deletion of the Chop gene significantly reduced maternal diabetes-induced NTDs. CHOP deficiency abrogated maternal diabetes-induced mitochondrial dysfunction and neuroepithelium cell apoptosis. Further analysis demonstrated that CHOP repressed the expression of peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC-1α), an essential regulator for mitochondrial biogenesis and function. Both CHOP deficiency in vivo and knockdown in vitro restore high glucose-suppressed PGC-1α expression. In contrast, CHOP overexpression mimicked inhibition of PGC-1α by high glucose. In response to the ER stress inducer tunicamycin, PGC-1α expression was decreased, whereas the ER stress inhibitor 4-phenylbutyric acid blocked high glucose-suppressed PGC-1α expression. Moreover, maternal diabetes in vivo and high glucose in vitro promoted the interaction between CHOP and the PGC-1α transcriptional regulator CCAAT/enhancer binding protein-β (C/EBPβ), and reduced C/EBPβ binding to the PGC-1α promoter leading to markedly decrease in PGC-1α expression. Together, our findings support the hypothesis that maternal diabetes-induced ER stress increases CHOP expression which represses PGC-1α through suppressing the C/EBPβ transcriptional activity, subsequently induces mitochondrial dysfunction and ultimately results in NTDs.

Free Radical Damage in Ischemia-Reperfusion Injury: An Obstacle in Acute Ischemic Stroke after Revascularization Therapy

Acute ischemic stroke is a common cause of morbidity and mortality worldwide. Thrombolysis with recombinant tissue plasminogen activator and endovascular thrombectomy are the main revascularization therapies for acute ischemic stroke. However, ischemia-reperfusion injury after revascularization therapy can result in worsening outcomes. Among all possible pathological mechanisms of ischemia-reperfusion injury, free radical damage (mainly oxidative/nitrosative stress injury) has been found to play a key role in the process. Free radicals lead to protein dysfunction, DNA damage, and lipid peroxidation, resulting in cell death. Additionally, free radical damage has a strong connection with inducing hemorrhagic transformation and cerebral edema, which are the major complications of revascularization therapy, and mainly influencing neurological outcomes due to the disruption of the blood-brain barrier. In order to get a better clinical prognosis, more and more studies focus on the pharmaceutical and nonpharmaceutical neuroprotective therapies against free radical damage. This review discusses the pathological mechanisms of free radicals in ischemia-reperfusion injury and adjunctive neuroprotective therapies combined with revascularization therapy against free radical damage.

Oxidative stress-induced miR-27a targets the redox gene nuclear factor erythroid 2-related factor 2 in diabetic embryopathy

BACKGROUND

Maternal diabetes induces neural tube defects, and oxidative stress is a causal factor for maternal diabetes-induced neural tube defects. The redox gene nuclear factor erythroid 2-related factor 2 is the master regulator of the cellular antioxidant system.

OBJECTIVE

In this study, we aimed to determine whether maternal diabetes inhibits nuclear factor erythroid 2-related factor 2 expression and nuclear factor erythroid 2-related factor 2-controlled antioxidant genes through the redox-sensitive miR-27a.

STUDY DESIGN

We used a well-established type 1 diabetic embryopathy mouse model induced by streptozotocin for our in vivo studies. Embryos at embryonic day 8.5 were harvested for analysis of nuclear factor erythroid 2-related factor 2, nuclear factor erythroid 2-related factor 2-controlled antioxidant genes, and miR-27a expression. To determine if mitigating oxidative stress inhibits the increase of miR-27a and the decrease of nuclear factor erythroid 2-related factor 2 expression, we induced diabetic embryopathy in superoxide dismutase 2 (mitochondrial-associated antioxidant gene)-overexpressing mice. This model exhibits reduced mitochondria reactive oxygen species even in the presence of hyperglycemia. To investigate the causal relationship between miR-27a and nuclear factor erythroid 2-related factor 2 in vitro, we examined C17.2 neural stem cells under normal and high-glucose conditions.

RESULTS

We observed that the messenger RNA and protein levels of nuclear factor erythroid 2-related factor 2 were significantly decreased in embryos on embryonic day 8.5 from diabetic dams compared to those from nondiabetic dams. High-glucose also significantly decreased nuclear factor erythroid 2-related factor 2 expression in a dose- and time-dependent manner in cultured neural stem cells. Our data revealed that miR-27a was up-regulated in embryos on embryonic day 8.5 exposed to diabetes, and that high glucose increased miR-27a levels in a dose- and time-dependent manner in cultured neural stem cells. In addition, we found that a miR-27a inhibitor abrogated the inhibitory effect of high glucose on nuclear factor erythroid 2-related factor 2 expression, and a miR-27a mimic suppressed nuclear factor erythroid 2-related factor 2 expression in cultured neural stem cells. Furthermore, our data indicated that the nuclear factor erythroid 2-related factor 2-controlled antioxidant enzymes glutamate-cysteine ligase catalytic subunit, glutamate-cysteine ligase modifier subunit, and glutathione S-transferase A1 were down-regulated by maternal diabetes in embryos on embryonic day 8.5 and high glucose in cultured neural stem cells. Inhibiting miR-27a restored expression of glutamate-cysteine ligase catalytic subunit, glutamate-cysteine ligase modifier subunit, and glutathione S-transferase A1. Overexpressing superoxide dismutase 2 reversed the maternal diabetes-induced increase of miR-27a and suppression of nuclear factor erythroid 2-related factor 2 and nuclear factor erythroid 2-related factor 2-controlled antioxidant enzymes.

CONCLUSION

Our study demonstrates that maternal diabetes-induced oxidative stress increases miR-27a, which, in turn, suppresses nuclear factor erythroid 2-related factor 2 and its responsive antioxidant enzymes, resulting in diabetic embryopathy.

The current status and future of cardiac stem/progenitor cell therapy for congenital heart defects from diabetic pregnancy

Pregestational maternal diabetes induces congenital heart defects (CHDs). Cardiac dysfunction after palliative surgical procedures contributes to the high mortality of CHD patients. Autologous or allogeneic stem cell therapies are effective for improving cardiac function in animal models and clinical trials. c-kit+ cardiac progenitor cells (CPCs), the most recognized CPCs, have the following basic properties of stem cells: self-renewal, multicellular clone formation, and differentiation into multiple cardiac lineages. However, there is ongoing debate regarding whether c-kit+ CPCs can give rise to sufficient cardiomyocytes. A new hypothesis to address the beneficial effect of c-kit+ CPCs is that these cells stimulate endogenous cardiac cells through a paracrine function in producing a robust secretome and exosomes. The values of other cardiac CPCs, including Sca1+ CPCs and cardiosphere-derived cells, are beginning to be revealed. These cells may be better choices than c-kit+ CPCs for generating cardiomyocytes. Adult mesenchymal stem cells are considered immune-incompetent and effective for improving cardiac function. Autologous CPC therapy may be limited by the observation that maternal diabetes adversely affects the biological function of embryonic stem cells and CPCs. Future studies should focus on determining the mechanistic action of these cells, identifying new CPC markers, selecting highly effective CPCs, and engineering cell-free products.

Pregestational type 2 diabetes mellitus induces cardiac hypertrophy in the murine embryo through cardiac remodeling and fibrosis

BACKGROUND

Cardiac hypertrophy is highly prevalent in patients with type 2 diabetes mellitus. Experimental evidence has implied that pregnant women with type 2 diabetes mellitus and their children are at an increased risk of cardiovascular diseases. Our previous mouse model study revealed that maternal type 2 diabetes mellitus induces structural heart defects in their offspring.

OBJECTIVE

This study aims to determine whether maternal type 2 diabetes mellitus induces embryonic heart hypertrophy in a murine model of diabetic embryopathy.

STUDY DESIGN

The type 2 diabetes mellitus embryopathy model was established by feeding 4-week-old female C57BL/6J mice with a high-fat diet for 15 weeks. Cardiac hypertrophy in embryos at embryonic day 17.5 was characterized by measuring heart size and thickness of the right and left ventricle walls and the interventricular septum, as well as the expression of β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, desmin, and adrenomedullin. Cardiac remodeling was determined by collagen synthesis and fibronectin synthesis. Fibrosis was evaluated by Masson staining and determining the expression of connective tissue growth factor, osteopontin, and galectin-3 genes. Cell apoptosis also was measured in the developing heart.

RESULTS

The thicknesses of the left ventricle walls and the interventricular septum of embryonic hearts exposed to maternal diabetes were significantly thicker than those in the nondiabetic group. Maternal diabetes significantly increased β-myosin heavy chain, atrial natriuretic peptide, insulin-like growth factor-1, and desmin expression, but decreased expression of adrenomedullin. Moreover, collagen synthesis was significantly elevated, whereas fibronectin synthesis was suppressed, in embryonic hearts from diabetic dams, suggesting that cardiac remodeling is a contributing factor to cardiac hypertrophy. The cardiac fibrosis marker, galectin-3, was induced by maternal diabetes. Furthermore, maternal type 2 diabetes mellitus activated the proapoptotic c-Jun-N-terminal kinase 1/2 stress signaling and triggered cell apoptosis by increasing the number of terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end labeling-positive cells (10.4 ± 2.2% of the type 2 diabetes mellitus group vs 3.8 ± 0.7% of the nondiabetic group, P < .05).

CONCLUSION

Maternal type 2 diabetes mellitus induces cardiac hypertrophy in embryonic hearts. Adverse cardiac remodeling, including elevated collagen synthesis, suppressed fibronectin synthesis, profibrosis, and apoptosis, is implicated as the etiology of cardiac hypertrophy.

Protein kinase C-alpha suppresses autophagy and induces neural tube defects via miR-129-2 in diabetic pregnancy

Gene deletion-induced autophagy deficiency leads to neural tube defects (NTDs), similar to those in diabetic pregnancy. Here we report the key autophagy regulators modulated by diabetes in the murine developing neuroepithelium. Diabetes predominantly leads to exencephaly, induces neuroepithelial cell apoptosis and suppresses autophagy in the forebrain and midbrain of NTD embryos. Deleting the Prkca gene, which encodes PKCα, reverses diabetes-induced autophagy impairment, cellular organelle stress and apoptosis, leading to an NTD reduction. PKCα increases the expression of miR-129-2, which is a negative regulator of autophagy. miR-129-2 represses autophagy by directly targeting PGC-1α, a positive regulator for mitochondrial function, which is disturbed by maternal diabetes. PGC-1α supports neurulation by stimulating autophagy in neuroepithelial cells. These findings identify two negative autophagy regulators, PKCα and miR-129-2, which mediate the teratogenicity of hyperglycaemia leading to NTDs. We also reveal a function for PGC-1α in embryonic development through promoting autophagy and ameliorating hyperglycaemia-induced NTDs.

Diabetes-induced effects on cardiomyocytes in chick embryonic heart micromass and mouse embryonic D3 differentiated stem cells

Diabetes mellitus during pregnancy is a considerable medical challenge, since it is related to ‎augmented morbidity and mortality concerns for both the fetus ‎and the pregnant woman. Records show that the etiology of diabetic ‎embryopathy is complicated, as many teratological factors might be involved ‎in the mechanisms of diabetes mellitus-induced congenital malformation. ‎In this study, the potential cardiotoxic effect of hyperglycemia with hyperketonemia was investigated by using two in vitro models; primary chick embryonic cardiomyocytes and stem cell derived cardiomyocytes, where adverse effects were recorded in both systems. The cells were evaluated by changes in beating activity, cell activity, protein content, ROS production, DNA damage and differentiating stem cell migration. The diabetic formulae used produced an increase in DNA damage and a decline in cell migration in mouse embryonic stem cells. These results provide an additional insight into adverse effects during gestational diabetes mellitus and a recommendation for expectant mothers and maternity staff to monitor glycaemic levels months ahead of conception. This study also supports the recommendation of using antioxidants during pregnancy to prevent DNA damage by the production of ROS, which might result in heart defects as well as other developmental anomalies.

High glucose suppresses embryonic stem cell differentiation into cardiomyocytes : High glucose inhibits ES cell cardiogenesis

Background

Babies born to mothers with pregestational diabetes have a high risk for congenital heart defects (CHD). Embryonic stem cells (ESCs) are excellent in vitro models for studying the effect of high glucose on cardiac lineage specification because ESCs can be differentiated into cardiomyocytes. ESC maintenance and differentiation are currently performed under high glucose conditions, whose adverse effects have never been clarified.

Method

We investigated the effect of high glucose on cardiomyocyte differentiation from a well-characterized ESC line, E14, derived from mouse blastocysts. E14 cells maintained under high glucose (25 mM) failed to generate any beating cardiomyocytes using the hanging-drop embryonic body method. We created a glucose-responsive E14 cell line (GR-E14) through a graduated low glucose adaptation. The expression of stem cell markers was similar in the parent E14 cells and the GR-E14 cells.

Results

Glucose transporter 2 gene was increased in GR-E14 cells. When GR-E14 cells were differentiated into cardiomyocytes under low (5 mM) or high (25 mM) glucose conditions, high glucose significantly delayed the appearance and reduced the number of TNNT2 (Troponin T Type 2)-positive contracting cardiomyocytes. High glucose suppressed the expression of precardiac mesoderm markers, cardiac transcription factors, mature cardiomyocyte markers, and potassium channel proteins. High glucose impaired the functionality of ESC-derived cardiomyocytes by suppressing the frequencies of Ca²⁺ wave and contraction.

Conclusions

Our findings suggest that high glucose inhibits ESC cardiogenesis by suppressing key developmental genes essential for the cardiac program.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0446-5) contains supplementary material, which is available to authorized users.

microRNA expression profiling and functional annotation analysis of their targets modulated by oxidative stress during embryonic heart development in diabetic mice

Maternal pregestational diabetes mellitus (PGDM) induces congenital heart defects (CHDs). The molecular mechanism underlying PGDM-induced CHDs is unknown. microRNAs (miRNAs), small non-coding RNAs, repress gene expression at the posttranscriptional level and play important roles in heart development. We performed a global miRNA profiling study to assist in revealing potential miRNAs modulated by PGDM and possible developmental pathways regulated by miRNAs during heart development. A total of 149 mapped miRNAs in the developing heart were significantly altered by PGDM. Bioinformatics analysis showed that the majority of the 2111 potential miRNA target genes were associated with cardiac development-related pathways including STAT3 and IGF-1 and transcription factors (Cited2, Zeb2, Mef2c, Smad4 and Ets1). Overexpression of the antioxidant enzyme, superoxide dismutase 1, reversed PGDM-altered miRNAs, suggesting that oxidative stress is responsible for dysregulation of miRNAs. Thus, our study provides the foundation for further investigation of a miRNA-dependent mechanism underlying PGDM-induced CHDs.

The green tea polyphenol EGCG alleviates maternal diabetes-induced neural tube defects by inhibiting DNA hypermethylation

BACKGROUND

Maternal diabetes increases the risk of neural tube defects in offspring. Our previous study demonstrated that the green tea polyphenol, Epigallocatechin gallate, inhibits high glucose-induced neural tube defects in cultured embryos. However, the therapeutic effect of Epigallocatechin gallate on maternal diabetes-induced neural tube defects is still unclear.

OBJECTIVE

We aimed to examine whether Epigallocatechin gallate treatment can reduce maternal diabetes-induced DNA methylation and neural tube defects.

STUDY DESIGN

Nondiabetic and diabetic pregnant mice at embryonic day 5.5 were given drinking water with or without 1 or 10 μM Epigallocatechin gallate. At embryonic day 8.75, embryos were dissected from the visceral yolk sac for the measurement of the levels and activity of DNA methyltransferases, the levels of global DNA methylation, and methylation in the CpG islands of neural tube closure essential gene promoters. embryonic day 10.5 embryos were examined for neural tube defect incidence.

RESULTS

Epigallocatechin gallate treatment did not affect embryonic development because embryos from nondiabetic dams treated with Epigallocatechin gallate did not exhibit any neural tube defects. Treatment with 1 μM Epigallocatechin gallate did not reduce maternal diabetes-induced neural tube defects significantly. Embryos from diabetic dams treated with 10 μM Epigallocatechin gallate had a significantly lower neural tube defect incidence compared with that of embryos without Epigallocatechin gallate treatment. Epigallocatechin gallate reduced neural tube defect rates from 29.5% to 2%, an incidence that is comparable with that of embryos from nondiabetic dams. Ten micromoles of Epigallocatechin gallate treatment blocked maternal diabetes-increased DNA methyltransferases 3a and 3b expression and their activities, leading to the suppression of global DNA hypermethylation. Additionally, 10 μM Epigallocatechin gallate abrogated maternal diabetes-increased DNA methylation in the CpG islands of neural tube closure essential genes, including Grhl3, Pax3, and Tulp3.

CONCLUSION

Epigallocatechin gallate reduces maternal diabetes-induced neural tube defects formation and blocks the enhanced expression and activity of DNA methyltransferases, leading to the suppression of DNA hypermethylation and the restoration of neural tube closure essential gene expression. These observations suggest that Epigallocatechin gallate supplements could mitigate the teratogenic effects of hyperglycemia on the developing embryo and prevent diabetes-induced neural tube defects.

Type 2 diabetes mellitus induces congenital heart defects in murine embryos by increasing oxidative stress, endoplasmic reticulum stress, and apoptosis

BACKGROUND

Maternal type 1 and 2 diabetes mellitus are strongly associated with high rates of severe structural birth defects, including congenital heart defects. Studies in type 1 diabetic embryopathy animal models have demonstrated that cellular stress-induced apoptosis mediates the teratogenicity of maternal diabetes leading to congenital heart defect formation. However, the mechanisms underlying maternal type 2 diabetes mellitus-induced congenital heart defects remain largely unknown.

OBJECTIVE

We aim to determine whether oxidative stress, endoplasmic reticulum stress, and excessive apoptosis are the intracellular molecular mechanisms underlying maternal type 2 diabetes mellitus-induced congenital heart defects.

STUDY DESIGN

A mouse model of maternal type 2 diabetes mellitus was established by feeding female mice a high-fat diet (60% fat). After 15 weeks on the high-fat diet, the mice showed characteristics of maternal type 2 diabetes mellitus. Control dams were either fed a normal diet (10% fat) or the high-fat diet during pregnancy only. Female mice from the high-fat diet group and the 2 control groups were mated with male mice that were fed a normal diet. At E12.5, embryonic hearts were harvested to determine the levels of lipid peroxides and superoxide, endoplasmic reticulum stress markers, cleaved caspase 3 and 8, and apoptosis. E17.5 embryonic hearts were harvested for the detection of congenital heart defect formation using India ink vessel patterning and histological examination.

RESULTS

Maternal type 2 diabetes mellitus significantly induced ventricular septal defects and persistent truncus arteriosus in the developing heart, along with increasing oxidative stress markers, including superoxide and lipid peroxidation; endoplasmic reticulum stress markers, including protein levels of phosphorylated-protein kinase RNA-like endoplasmic reticulum kinase, phosphorylated-IRE1α, phosphorylated-eIF2α, C/EBP homologous protein, and binding immunoglobulin protein; endoplasmic reticulum chaperone gene expression; and XBP1 messenger RNA splicing, as well as increased cleaved caspase 3 and 8 in embryonic hearts. Furthermore, maternal type 2 diabetes mellitus triggered excessive apoptosis in ventricular myocardium, endocardial cushion, and outflow tract of the embryonic heart.

CONCLUSION

Similar to those observations in type 1 diabetic embryopathy, maternal type 2 diabetes mellitus causes heart defects in the developing embryo manifested with oxidative stress, endoplasmic reticulum stress, and excessive apoptosis in heart cells.

Superoxide dismutase 2 overexpression alleviates maternal diabetes-induced neural tube defects, restores mitochondrial function and suppresses cellular stress in diabetic embryopathy

Pregestational diabetes disrupts neurulation leading to neural tube defects (NTDs). Oxidative stress resulting from reactive oxygen species (ROS) plays a central role in the induction of NTD formation in diabetic pregnancies. We aimed to determine whether mitochondrial dysfunction increases ROS production leading to oxidative stress and diabetic embryopathy. Overexpression of the mitochondrion-specific antioxidant enzyme superoxide dismutase 2 (SOD2) in a transgenic (Tg) mouse model significantly reduced maternal diabetes-induced NTDs. SOD2 overexpression abrogated maternal diabetes-induced mitochondrial dysfunction by inhibiting mitochondrial translocation of the pro-apoptotic Bcl-2 family members, reducing the number of defective mitochondria in neuroepithelial cells, and decreasing mitochondrial membrane potential. Furthermore, SOD2 overexpression blocked maternal diabetes-increased ROS production by diminishing dihydroethidium staining signals in the developing neuroepithelium, and reducing the levels of nitrotyrosine-modified proteins and lipid hydroperoxide level in neurulation stage embryos. SOD2 overexpression also abolished maternal diabetes-induced endoplasmic reticulum stress. Finally, caspase-dependent neuroepithelial cell apoptosis enhanced by oxidative stress was significantly reduced by SOD2 overexpression. Thus, our findings support the hypothesis that mitochondrial dysfunction in the developing neuroepithelium enhances ROS production, which leads to oxidative stress and endoplasmic reticulum (ER) stress. SOD2 overexpression blocks maternal diabetes-induced oxidative stress and ER stress, and reduces the incidence of NTDs in embryos exposed to maternal diabetes.

High glucose-induced oxidative stress represses sirtuin deacetylase expression and increases histone acetylation leading to neural tube defects

Aberrant epigenetic modifications are implicated in maternal diabetes-induced neural tube defects (NTDs). Because cellular stress plays a causal role in diabetic embryopathy, we investigated the possible role of the stress-resistant sirtuin (SIRT) family histone deacetylases. Among the seven sirtuins (SIRT1-7), pre-gestational maternal diabetes in vivo or high glucose in vitro significantly reduced the expression of SIRT 2 and SIRT6 in the embryo or neural stem cells, respectively. The down-regulation of SIRT2 and SIRT6 was reversed by superoxide dismutase 1 (SOD1) over-expression in the in vivo mouse model of diabetic embryopathy and the SOD mimetic, tempol and cell permeable SOD, PEGSOD in neural stem cell cultures. 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), a superoxide generating agent, mimicked high glucose-suppressed SIRT2 and SIRT6 expression. The acetylation of histone 3 at lysine residues 56 (H3K56), H3K14, H3K9, and H3K27, putative substrates of SIRT2 and SIRT6, was increased by maternal diabetes in vivo or high glucose in vitro, and these increases were blocked by SOD1 over-expression or tempol treatment. SIRT2 or SIRT6 over-expression abrogated high glucose-suppressed SIRT2 or SIRT6 expression, and prevented the increase in acetylation of their histone substrates. The potent sirtuin activator (SRT1720) blocked high glucose-increased histone acetylation and NTD formation, whereas the combination of a pharmacological SIRT2 inhibitor and a pan SIRT inhibitor mimicked the effect of high glucose on increased histone acetylation and NTD induction. Thus, diabetes in vivo or high glucose in vitro suppresses SIRT2 and SIRT6 expression through oxidative stress, and sirtuin down-regulation-induced histone acetylation may be involved in diabetes-induced NTDs. The mechanism underlying pre-gestational diabetes-induced neural tube defects (NTDs) is still elusive. Our study unravels a new epigenetic mechanism in which maternal diabetes-induced oxidative stress represses sirtuin deacetylase 2 (SIRT2) and 6 (SIRT6) expression leading to histone acetylation and gene expression. SIRT down-regulation mediates the teratogenicity of diabetes leading to (NTD) formation. The study provides a mechanistic basis for the development of natural antioxidants and SIRT activators as therapeutics for diabetic embryopathy.

ROS and intracellular ion channels

Oxidative stress is a well-known driver of numerous pathological processes involving protein and lipid peroxidation and DNA damage. The resulting increase of pro-apoptotic pressure drives tissue damage in a host of conditions, including ischemic stroke and reperfusion injury, diabetes, death in acute pancreatitis and neurodegenerative diseases. Somewhat less frequently discussed, but arguably as important, is the signaling function of oxidative stress stemming from the ability of oxidative stress to modulate ion channel activity. The evidence for the modulation of the intracellular ion channels and transporters by oxidative stress is constantly emerging and such evidence suggests new regulatory and pathological circuits that can be explored towards new treatments for diseases in which oxidative stress is an issue. In this review we summarize the current knowledge on the effects of oxidative stress on the intracellular ion channels and transporters and their role in cell function.

New development of the yolk sac theory in diabetic embryopathy: molecular mechanism and link to structural birth defects

Maternal diabetes mellitus is a significant risk factor for structural birth defects, including congenital heart defects and neural tube defects. With the rising prevalence of type 2 diabetes mellitus and obesity in women of childbearing age, diabetes mellitus-induced birth defects have become an increasingly significant public health problem. Maternal diabetes mellitus in vivo and high glucose in vitro induce yolk sac injuries by damaging the morphologic condition of cells and altering the dynamics of organelles. The yolk sac vascular system is the first system to develop during embryogenesis; therefore, it is the most sensitive to hyperglycemia. The consequences of yolk sac injuries include impairment of nutrient transportation because of vasculopathy. Although the functional relationship between yolk sac vasculopathy and structural birth defects has not yet been established, a recent study reveals that the quality of yolk sac vasculature is related inversely to embryonic malformation rates. Studies in animal models have uncovered key molecular intermediates of diabetic yolk sac vasculopathy, which include hypoxia-inducible factor-1α, apoptosis signal-regulating kinase 1, and its inhibitor thioredoxin-1, c-Jun-N-terminal kinases, nitric oxide, and nitric oxide synthase. Yolk sac vasculopathy is also associated with abnormalities in arachidonic acid and myo-inositol. Dietary supplementation with fatty acids that restore lipid levels in the yolk sac lead to a reduction in diabetes mellitus-induced malformations. Although the role of the human yolk in embryogenesis is less extensive than in rodents, nevertheless, human embryonic vasculogenesis is affected negatively by maternal diabetes mellitus. Mechanistic studies have identified potential therapeutic targets for future intervention against yolk sac vasculopathy, birth defects, and other complications associated with diabetic pregnancies.

The Nrf2 Activator Vinylsulfone Reduces High Glucose-Induced Neural Tube Defects by Suppressing Cellular Stress and Apoptosis

The nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway is one of the primary pathways responsible for the cellular defense system against oxidative stress. Oxidative stress-induced apoptosis is a causal event in diabetic embryopathy. Thus, the Nrf2 pathway may play an important role in the induction of diabetic embryopathy. In the present study, we investigated the potentially protective effect of the Nrf2 activator, vinylsulfone, on high glucose-induced cellular stress, apoptosis, and neural tube defects (NTDs). Embryonic day 8.5 (E8.5) whole mouse embryos were cultured in normal (5 mmol/L) or high (16.7 mmol/L) glucose conditions, with or without vinylsulfone. At a concentration of 10 μmol/L, vinylsulfone had an inhibitory effect on high glucose-induced NTD formation, but it was not significant. At a concentration of 20 μmol/L, vinylsulfone significantly reduced high glucose-induced NTDs. In addition, 20 μmol/L vinylsulfone abrogated the high glucose-induced oxidative stress markers lipid hydroperoxide (LPO), 4-hydroxynonenal (4-HNE), and nitrotyrosine-modified proteins. The high glucose-induced endoplasmic reticulum (ER) stress biomarkers were also suppressed by 20 μmol/L vinylsulfone through the inhibition of phosphorylated protein kinase RNA-like ER kinase (PERK), inositol requiring protein 1α (IRE1a), eukaryotic initiation factor 2α (eIF2a), upregulated C/EBP-homologous protein (CHOP), binding immunoglobulin protein (BiP), and x-box binding protein 1 (XBP1) messenger RNA splicing. Furthermore, 20 μmol/L vinylsulfone abolished caspase 3 and caspase 8 cleavage, markers of apoptosis, in embryos cultured under high glucose conditions. The Nrf2 activator, vinylsulfone, is protective against high glucose-induced cellular stress, caspase activation, and subsequent NTD formation. Our data suggest that vinylsulfone supplementation is a potential therapy for diabetes-associated neurodevelopmental defects.

MiR-17 Downregulation by High Glucose Stabilizes Thioredoxin-Interacting Protein and Removes Thioredoxin Inhibition on ASK1 Leading to Apoptosis

Pregestational diabetes significantly increases the risk of neural tube defects (NTDs). Maternal diabetes activates an Apoptosis Signal-regulating Kinase 1 (ASK1)-initiated pathway, which triggers neural stem cell apoptosis of the developing neuroepithelium leading to NTD formation. How high glucose of diabetes activates ASK1 is still unclear. In this study, we investigated the mechanism underlying high glucose-induced ASK1 activation. High glucose suppressed miR-17 expression, which led to an increase in its target gene Txnip (Thioredoxin-interacting protein). High glucose-increased Txnip enhanced its binding to the ASK1 inhibitor, thioredoxin (Trx), and thereby sequestered Trx from the Trx-ASK1 complex. High glucose-induced ASK1 activation and consequent apoptosis were abrogated by either the miR-17 mimic or Txnip siRNA knockdown. In contrast, the miR-17 inhibitor or Txnip ectopic overexpression mimicked the stimulative effect of high glucose on ASK1 and apoptosis. Thus, our study demonstrated that miR-17 repression mediates the pro-apoptotic effect of high glucose, and revealed a new mechanism underlying ASK1 activation, in which decreased miR-17 removes Trx inhibition on ASK1 through Txnip.

Dominant negative FADD dissipates the proapoptotic signalosome of the unfolded protein response in diabetic embryopathy

Endoplasmic reticulum (ER) stress and caspase 8-dependent apoptosis are two interlinked causal events in maternal diabetes-induced neural tube defects (NTDs). The inositol-requiring enzyme 1α (IRE1α) signalosome mediates the proapoptotic effect of ER stress. Diabetes increases tumor necrosis factor receptor type 1R-associated death domain (TRADD) expression. Here, we revealed two new unfolded protein response (UPR) regulators, TRADD and Fas-associated protein with death domain (FADD). TRADD interacted with both the IRE1α-TRAF2-ASK1 complex and FADD. In vivo overexpression of a FADD dominant negative (FADD-DN) mutant lacking the death effector domain disrupted diabetes-induced IRE1α signalosome and suppressed ER stress and caspase 8-dependent apoptosis, leading to NTD prevention. FADD-DN abrogated ER stress markers and blocked the JNK1/2-ASK1 pathway. Diabetes-induced mitochondrial translocation of proapoptotic Bcl-2 members mitochondrial dysfunction and caspase cleavage were also alleviated by FADD-DN. In vitro TRADD overexpression triggered UPR and ER stress before manifestation of caspase 3 and caspase 8 cleavage and apoptosis. FADD-DN overexpression repressed high glucose- or TRADD overexpression-induced IRE1α phosphorylation, its downstream proapoptotic kinase activation and endonuclease activities, and apoptosis. FADD-DN also attenuated tunicamycin-induced UPR and ER stress. These findings suggest that TRADD participates in the IRE1α signalosome and induces UPR and ER stress and that the association between TRADD and FADD is essential for diabetes- or high glucose-induced UPR and ER stress.

Punicalagin exerts protective effect against high glucose-induced cellular stress and neural tube defects

Maternal diabetes-induced birth defects remain a significant health problem. Studying the effect of natural compounds with antioxidant properties and minimal toxicities on diabetic embryopathy may lead to the development of new and safe dietary supplements. Punicalagin is a primary polyphenol found in pomegranate juice, which possesses antioxidant, anti-inflammatory and anti-tumorigenic properties, suggesting a protective effect of punicalagin on diabetic embryopathy. Here, we examined whether punicalagin could reduce high glucose-induced neural tube defects (NTDs), and if this rescue occurs through blockage of cellular stress and caspase activation. Embryonic day 8.5 (E8.5) mouse embryos were cultured for 24 or 36 h with normal (5 mM) glucose or high glucose (16.7 mM), in presence or absence of 10 or 20 μM punicalagin. 10 μM punicalagin slightly reduced NTD formation under high glucose conditions; however, 20 μM punicalagin significantly inhibited high glucose-induced NTD formation. Punicalagin suppressed high glucose-induced lipid peroxidation marker 4-hydroxynonenal, nitrotyrosine-modified proteins, and lipid peroxides. Moreover, punicalagin abrogated endoplasmic reticulum stress by inhibiting phosphorylated protein kinase ribonucleic acid (RNA)-like ER kinase (p-PERK), phosphorylated inositol-requiring protein-1α (p-IRE1α), phosphorylated eukaryotic initiation factor 2α (p-eIF2α), C/EBP-homologous protein (CHOP), binding immunoglobulin protein (BiP) and x-box binding protein 1 (XBP1) mRNA splicing. Additionally, punicalagin suppressed high glucose-induced caspase 3 and caspase 8 cleavage. Punicalagin reduces high glucose-induced NTD formation by blocking cellular stress and caspase activation. These observations suggest punicalagin supplements could mitigate the teratogenic effects of hyperglycemia in the developing embryo, and possibly prevent diabetes-induced NTDs.

Maternal diabetes triggers DNA damage and DNA damage response in neurulation stage embryos through oxidative stress

DNA damage and DNA damage response (DDR) in neurulation stage embryos under maternal diabetes conditions are not well understood. The purpose of this study was to investigate whether maternal diabetes and high glucose in vitro induce DNA damage and DDR in the developing embryo through oxidative stress. In vivo experiments were conducted by mating superoxide dismutase 1 (SOD1) transgenic male mice with wild-type (WT) female mice with or without diabetes. Embryonic day 8.75 (E8.75) embryos were tested for the DNA damage markers, phosphorylated histone H2A.X (p-H2A.X) and DDR signaling intermediates, including phosphorylated checkpoint 1 (p-Chk1), phosphorylated checkpoint 2 (p-Chk2), and p53. Levels of the same DNA damage markers and DDR signaling intermediates were also determined in the mouse C17.2 neural stem cell line. Maternal diabetes and high glucose in vitro significantly increased the levels of p-H2A.X. Levels of p-Chk1, p-Chk2, and p53, were elevated under both maternal diabetic and high glucose conditions. SOD1 overexpression blocked maternal diabetes-induced DNA damage and DDR in vivo. Tempol, a SOD1 mimetic, diminished high glucose-induced DNA damage and DDR in vitro. In conclusion, maternal diabetes and high glucose in vitro induce DNA damage and activates DDR through oxidative stress, which may contribute to the pathogenesis of diabetes-associated embryopathy.

ASK1 mediates the teratogenicity of diabetes in the developing heart by inducing ER stress and inhibiting critical factors essential for cardiac development

Maternal diabetes in mice induces heart defects similar to those observed in human diabetic pregnancies. Diabetes enhances apoptosis and suppresses cell proliferation in the developing heart, yet the underlying mechanism remains elusive. Apoptosis signal-regulating kinase 1 (ASK1) activates the proapoptotic c-Jun NH2-terminal kinase 1/2 (JNK1/2) leading to apoptosis, suggesting a possible role of ASK1 in diabetes-induced heart defects. We aimed to investigate whether ASK1 is activated in the heart and whether deleting the Ask1 gene blocks diabetes-induced adverse events and heart defect formation. The ASK1-JNK1/2 pathway was activated by diabetes. Deleting Ask1 gene significantly reduced the rate of heart defects, including ventricular septal defects (VSDs) and persistent truncus arteriosus (PTA). Additionally, Ask1 deletion diminished diabetes-induced JNK1/2 phosphorylation and its downstream transcription factors and endoplasmic reticulum (ER) stress markers. Consistent with this, caspase activation and apoptosis were blunted. Ask1 deletion blocked the increase in cell cycle inhibitors (p21 and p27) and the decrease in cyclin D1 and D3 and reversed diabetes-repressed cell proliferation. Ask1 deletion also restored the expression of BMP4, NKX2.5, and GATA5, Smad1/5/8 phosphorylation, whose mutations or deletion result in reduced cell proliferation, VSD, and PTA formation. We conclude that ASK1 may mediate the teratogenicity of diabetes through activating the JNK1/2-ER stress pathway and inhibiting cell cycle progression, thereby impeding the cardiogenesis pathways essential for ventricular septation and outflow tract development.

Cellular Stress, Excessive Apoptosis, and the Effect of Metformin in a Mouse Model of Type 2 Diabetic Embryopathy

Increasing prevalence of type 2 diabetes in women of childbearing age has led to a higher incidence of diabetes-associated birth defects. We established a model of type 2 diabetic embryopathy by feeding 4-week-old female mice a high-fat diet (HFD) (60% fat). After 15 weeks on HFD, the mice showed characteristics of type 2 diabetes mellitus (DM) and were mated with lean male mice. During pregnancy, control dams fed a normal diet (10% fat) were maintained on either normal diet or HFD, serving as a control group with elevated circulating free fatty acids. DM dams produced offspring at a rate of 11.3% for neural tube defect (NTD) formation, whereas no embryos in the control groups developed NTDs. Elevated markers of oxidative stress, endoplasmic reticulum stress, caspase activation, and neuroepithelial cell apoptosis (causal events in type 1 diabetic embryopathy) were observed in embryos of DM dams. DM dams treated with 200 mg/kg metformin in drinking water ameliorated fasting hyperglycemia, glucose intolerance, and insulin resistance with consequent reduction of cellular stress, apoptosis, and NTDs in their embryos. We conclude that cellular stress and apoptosis occur and that metformin effectively reduces type 2 diabetic embryopathy in a useful rodent model.