Aberrant patterns of cellular communication in diabetes-induced embryopathy. I. Membrane signalling

Placental mitochondrial dysfunction with metabolic diseases: Therapeutic approaches

Both obesity and gestational diabetes mellitus (GDM) lead to poor maternal and fetal outcomes, including pregnancy complications, fetal growth issues, stillbirth, and developmental programming of adult-onset disease in the offspring. Increased placental oxidative/nitrative stress and reduced placental (trophoblast) mitochondrial respiration occur in association with the altered maternal metabolic milieu of obesity and GDM. The effect is particularly evident when the fetus is male, suggesting a sexually dimorphic influence on the placenta. In addition, obesity and GDM are associated with inflexibility in trophoblast, limiting the ability to switch between usage of glucose, fatty acids, and glutamine as substrates for oxidative phosphorylation, again in a sexually dimorphic manner. Here we review mechanisms underlying placental mitochondrial dysfunction: its relationship to maternal and fetal outcomes and the influence of fetal sex. Prevention of placental oxidative stress and mitochondrial dysfunction may improve pregnancy outcomes. We outline pathways to ameliorate deficient mitochondrial respiration, particularly the benefits and pitfalls of mitochondria-targeted antioxidants.

Pre-pregnancy Obesity as a Modifier of Gestational Diabetes and Birth Defects Associations: A Systematic Review

Objective Inconsistent findings of associations between gestational diabetes mellitus (GDM) and birth defects suggest unaccounted confounders may underlie the actual basis for such associations. We conducted a systematic review to assess observed associations between GDM and birth defects and the extent to which these could be explained by pre-pregnancy obesity. Methods Using a combination of search terms for GDM and birth defects, we searched PubMed, Scopus, CINAHL, and ClinicalTrials.gov for human-based studies published through September 2013. Studies were eligible for inclusion if they included information on maternal diabetes status, method of diagnosis of GDM, and assessment of birth defects. Twenty-four of 768 potential articles were included. We collected information on study design, location and period, method of determination of diabetes status, types of birth defects, and measures of association reported. Results There was no evidence for consistent association of GDM with birth defects, with the exception of a weak association between GDM and congenital heart defects. When stratified by maternal pre-pregnancy BMI, an association between GDM and congenital heart defects and between GDM and neural tube defects was evident only in women with both GDM and pre-pregnancy obesity. Conclusions for Practice Our findings suggest reported associations between GDM and birth defects may be due, in part, to undiagnosed metabolic disorders associated with obesity, such as pregestational diabetes mellitus, rather than GDM. These findings highlight the need for increased efforts for pre-pregnancy screening for undiagnosed diabetes and awareness of the importance of weight management among women of childbearing age with obesity.

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

Preexisting maternal diabetes is a high-risk factor of diabetic embryopathy, such as neural tube defects and congenital heart defects. Maternal diabetes significantly increases the production of reactive oxygen species, resulting in oxidative stress and diabetic embryopathy. Multiple cellular and metabolic factors contribute to these processes. Forkhead box O (FoxO)-3a has been demonstrated as a key transcription factor in the signaling transduction pathways responsible for maternal diabetes-induced birth defects. Apoptosis signal-regulating kinase 1 (ASK1) activated by oxidative stress stimulates nuclear translocation of FoxO3a, resulting in the overexpression of tumor necrosis factor receptor 1-associated death domain protein, which, in turn, leads to caspase-8 activation and apoptosis. Maternal diabetes-activated c-Jun N-terminal kinase (JNK)-1/2, downstream effectors of ASK1, can be blocked by superoxide dismutase-1 overexpression, suggesting that oxidative stress is responsible for JNK1/2 signaling activation. Deletion of JNK1/2 significantly suppressed the activity of FoxO3a. These observations indicate that maternal diabetes-induced oxidative stress stimulates the activation of ASK1, JNK1/2, FoxO3a, tumor necrosis factor receptor 1-associated death domain protein, caspase-8 cleavage, and finally, apoptosis and diabetic embryopathy.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

Effect of maternal diabetes on the embryo, fetus, and children: congenital anomalies, genetic and epigenetic changes and developmental outcomes

INTRODUCTION

Pregestational and gestational diabetes mellitus (PGDM; GDM) are significant health concerns because they are associated with an increased rate of malformations and maternal health complications.

METHODS

We reviewed the data that help us to understand the effects of diabetes in pregnancy.

RESULTS

Diabetic embryopathy can affect any developing organ system, but cardiovascular and neural tube defects are among the most frequent anomalies. Other complications include preeclampsia, preterm delivery, fetal growth abnormalities, and perinatal mortality. Neurodevelopmental studies on offspring of mothers with diabetes demonstrated increased rate of Gross and Fine motor abnormalities, of Attention Deficit Hyperactivity Disorder, learning difficulties, and possibly also Autism Spectrum Disorder. The mechanisms underlying the effects of maternal hyperglycemia on the developing fetus may involve increased oxidative stress, hypoxia, apoptosis, and epigenetic changes. Evidence for epigenetic changes are the following: not all progeny are affected and not to the same extent; maternal diet may influence pregnancy outcomes; and maternal diabetes alters embryonic transcriptional profiles and increases the variation between transcriptomic profiles as a result of altered gene regulation. Research in animal models has revealed that maternal hyperglycemia is a teratogen, and has helped uncover potential therapeutic targets which, when blocked, can mitigate or ameliorate the negative effects of diabetes on the developing fetus.

CONCLUSIONS

Tight metabolic control, surveillance, and labor management remain the cornerstone of care for pregnant women with diabetes, but advances in the field indicate that new treatments to protect the mother and baby are not far from becoming clinical realities.

New concepts in diabetic embryopathy

Diabetes mellitus is responsible for nearly 10% of fetal anomalies in diabetic pregnancies. Although aggressive perinatal care and glycemic control are available in developed countries, the birth defect rate in diabetic pregnancies remains higher than that in the general population. Major cellular activities (ie, proliferation and apoptosis) and intracellular metabolic conditions (ie, nitrosative, oxidative, and endoplasmic reticulum stress) have been shown to be associated with diabetic embryopathy using animal models. Translating advances made in animal studies into clinical applications in humans requires collaborative efforts across the basic research, preclinical, and clinical communities.

The essential role of protein kinase Cδ in diabetes-induced neural tube defects

BACKGROUND

Maternal diabetes causes neural tube defects (NTDs) in the embryos via activating protein kinase Cs (PKCs), which regulate programmed cell death (apoptosis). The aims of this study are to investigate the role of proapoptotic PKCδ in NTD formation and the underlying mechanisms.

METHODS

PKCδ heterozygous (pkcδ(+/-)) female mice were diabetic (DM) induced by intravenous injection of streptozotocin. Occurrence of NTDs was evaluated at embryonic day 11.5 and compared between wild type (WT) and PKCδ homozygous (pkcδ(-/-)) embryos. Changes in oxidative and endoplasmic reticulum (ER) stress-associated factors and stress-response c-Jun N-terminal kinases (JNKs) were assessed using Western blot assay.

RESULTS

Compared to DM/WT, the DM/PKCδ(-/-) embryos had significantly lower NTD rate and lower levels of oxidative and ER stress factors and JNK activation. These values were similar to those in the non-diabetic control group.

CONCLUSION

PKCδ plays a critical role in diabetes-induced NTDs, potentially through increasing oxidative and ER stress and JNK-associated stress-response pathways.

Epigallocatechin-3-gallate ameliorates hyperglycemia-induced embryonic vasculopathy and malformation by inhibition of Foxo3a activation

OBJECTIVE

Maternal hyperglycemia increases the risk of congenital malformations. Epigallocatechin-3-gallate (EGCG), a natural antioxidant purified from green tea, inhibits oxidative stress signaling. We propose that EGCG prevents hyperglycemia-induced malformation via inhibition of oxidative stress signaling. The objective of this study is to examine the effect of EGCG on hyperglycemia-induced adverse effects during embryonic development.

STUDY DESIGN

Day-9 rat conceptuses were cultured under euglycemic (150 mg/dL glucose) and hyperglycemic (300 mg/dL glucose) conditions in the presence or absence of 1 or 10 micromol/L of EGCG.

RESULTS

Both 1 and 10 micromol/L of EGCG significantly ameliorated hyperglycemia-induced embryonic vasculopathy and malformations. Hyperglycemia inactivated protein kinase B (Akt) by reducing phosphorylated Akt levels. EGCG reversed the inhibitory effect of hyperglycemia on Akt activation. EGCG also prevented hyperglycemia-reduced phosphorylated Forkhead transcription factor 3a levels.

CONCLUSION

EGCG prevented hyperglycemia-induced embryopathy through inhibition of Forkhead transcription factor 3a activation. This may have been mediated via the activation of Akt. These findings offer the potential for a possible pharmacological prophylaxis for hyperglycemia-induced embryonic malformations.

Obesity, diabetes, and links to congenital defects: a review of the evidence and recommendations for intervention

OBJECTIVE

To review evidence on the link between obesity and diabetes in pregnant women and the incidence of birth defects. In addition, the article offers recommendations for facilitating the broader scale implementation of evidence-based approaches to preventing obesity, particularly among pregnant women.

METHODS

A review of the evidence, primarily from epidemiologic studies, linking obesity and obesity-related metabolic disturbances in pregnant women to a range of birth defects. It also reviews potential mechanisms by which obesity and diabetes during pregnancy lead to damage in the developing embryo and highlights some evidence-based approaches to prevention. Finally it reviews policy options for positively impacting obesity and diabetes in this population.

RESULTS

Obesity and diabetes are a growing problem in the US population. This problem is particularly acute among women of childbearing age because the combination of obesity and diabetes is toxic to the developing fetus, which each contributing independently to embryopathy.

CONCLUSIONS

There is an urgent need for a national strategy for combating the growing and related problems of obesity and diabetes in the population. This strategy needs to encompass a spectrum of tax breaks, economic incentives, legislation, and educational approaches in order to be effective.

Blockade of c-Jun N-terminal kinase activation abrogates hyperglycemia-induced yolk sac vasculopathy in vitro

OBJECTIVE

Maternal hyperglycemia has an impact on both the function and morphology of the rodent visceral yolk sac; the objective of the present study was to determine whether hyperglycemia in vitro affects yolk sac vasculogenesis. Because maternal hyperglycemia triggers c-Jun N-terminal kinase (JNK) 1 and 2 activation in the yolk sac, we tested whether the inhibition of JNK activation would ameliorate hyperglycemia-induced yolk sac vasculopathy. In rodents, the yolk sac serves as the primitive placenta after implantation and before the formation of the chorioallantoic placenta. Furthermore, during this early stage, the nutrition from mother to embryo is considered to be facilitated by a tissue-to-tissue form of nutrition, referred to as histiotropic nutrition, and subsequently via yolk sac facilitation (hemotropic nutrition). In addition, during embryopathy, teratogen such as hyperglycemia is associated with concomitant injury to the yolk sac and embryo.

STUDY DESIGN

Rat embryos at embryonic day 9 were cultured under euglycemic (150 mg/dL glucose) and hyperglycemic (500 mg /dL glucose) conditions. JNK activation was inhibited using a JNK1/2-specific inhibitor SP60025 at concentrations of 40, 400, and 800 nM. After 48 hours, the development of yolk sac vasculatures was evaluated by assigning to arbitrative scores on the basis of yolk sac vasculature morphology. The correlation between yolk sac vasculature and embryonic malformation rates was assessed. Levels of phosphorylated JNK1/2 and Bcl-2-associated X protein (Bax) in the yolk sacs from conceptuses of the euglycemic and hyperglycemic groups were determined by Western blotting with densitometric quantification.

RESULTS

Under hyperglycemic conditions, yolk sac development was morphologically impaired. The yolk sac vasculature score of the hyperglycemic group was significantly lower than that of the euglycemic group. Yolk sac vasculature morphologic scores were inversely correlated with embryonic malformation rates. Levels of phosphorylated JNK1/2 and Bax in yolk sacs of the hyperglycemic group were significantly higher than those in yolk sacs of the euglycemic group. JNK1/2-specific inhibitor, SP600125, ameliorated the adverse effect of hyperglycemia on yolk sac vasculature development. Whereas the vasculature morphologic score of yolk sacs in the hyperglycemic group was 54% lower than that of euglycemic group, the vasculature morphologic score of yolk sacs in hyperglycemic plus 800 nM SP600125 group was as same as that in the euglycemic group. Thus, SP600125 at 800 nM completely reversed hyperglycemia-induced vasculopathy as well as embryopathy.

CONCLUSION

Hyperglycemia in vitro induces yolk sac vasculopathy. Embryonic malformation is inversely correlated with the yolk sac vasculature development, suggesting that hyperglycemia-induced yolk sac vasculopathy may be one of the causative factors in hyperglycemia-induced embryonic malformation. Blockade of JNK1/2 activation restores hyperglycemia-induced vasculopathy and reduces the malformation rates. These findings indicate that JNK1/2 activation mediates the deleterious effect of hyperglycemia on yolk sac vasculature and embryonic development.

Activation of oxidative stress signaling that is implicated in apoptosis with a mouse model of diabetic embryopathy

OBJECTIVE

A mouse model of diabetic embryopathy in C57BL/6J background was established to use the resources of genetically engineered mice in which a specific gene is deleted or overexpressed. To test whether our previous fundamental findings in the rat model of diabetic embryopathy are transferable to this mouse model of diabetic embryopathy, levels of phosphorylated-JNK1/2 (c-Jun N-terminal kinase 1 and 2) and apoptotic markers (cleaved caspase 3) were determined. To establish a link between oxidative stress signaling and diabetic embryopathy, levels of phosphorylated-p66Shc (which is a key signaling molecule that mediates oxidative stress-induced apoptosis) were evaluated.

STUDY DESIGN

Diabetes mellitus was induced in female C57BL/6J mice by an intravenous injection of streptozotocin (75 mg/kg). Glucose levels were controlled by the subcutaneous implantation of insulin pellets. The female mice were mated with normal male mice. At gestation day 5 or embryonic day 5 (E5), the insulin pellets were removed from a group of animals, which made them hyperglycemic (> 250 mg/dL glucose). The animals with retained insulin pellets served as controls. On embryonic day 11, mice were killed, and embryos were dissected from the uteri for examination. Embryos and yolk sacs from individual conceptus were collected. Levels of phosphorylated-JNK1/2, phosphorylated-p66Shc, and cleaved caspase 3 were determined in the embryos and yolk sacs.

RESULTS

Malformation rates in embryos from diabetic mice were 3-fold higher than those in embryos from nondiabetic or diabetic/euglycemic control groups. JNK1/2, especially p54 JNK isoform, which is predominantly expressed by jnk2 gene, was activated in malformed embryos and their respective yolk sacs from diabetic mice and was significantly higher than those in normally developed embryos and their respective yolk sacs from nondiabetic and diabetic mice. Correlating to JNK1/2 activation, phosphorylated-p66Shc was also significantly increased in malformed embryos and their respective yolk sacs from diabetic mice than in normally developed embryos and their respective yolk sacs from nondiabetic and diabetic mice. Cleaved caspase 3 was observed in malformed embryos from diabetic mice.

CONCLUSION

The present study shows that maternal hyperglycemia is able to induce embryonic dysmorphogenesis in C57BL/6J mice that is comparable with that seen in the rat model of diabetic embryopathy. Like the well-studied rat model of diabetic embryopathy, activation of JNK1/2 and p66Shc and the increase of apoptotic markers are manifested in this mouse model of diabetic embryopathy. These findings suggest that the activation of oxidative stress signaling in diabetic embryopathy leads to excessive embryonic cell apoptosis and ultimately embryonic dysmorphogenesis. To apply the powerful genetic approach to the research of diabetic embryopathy, a mouse is a better animal model than a rat because all gene knockout (deletion) and gene transgenic (gene overexpression) animals are made in the mouse. The mouse model of diabetic embryopathy that was established in the present study may serve as a suitable substitute for the rat model of diabetic embryopathy, thus enabling us and other investigators to use genetically engineered technologies in the study of diabetic embryopathy.

Involvement of c-Jun N-terminal kinases activation in diabetic embryopathy

The mechanisms for diabetic embryopathy are not well understood. JNK1/2 activation is increased in diabetic embryopathy, and antioxidants abolish JNK activation, and thus, ameliorate diabetic embryopathy. Phosphorylated SEK1 were significantly elevated in malformed embryos from diabetic mouse. In a dose-dependent manner, JNK inhibitor (SP600125) significantly reduced hyperglycemia-induced embryopathy. Malformation rates in embryos from the diabetic WT group were 15.6-fold higher than that in the non-diabetic WT control group. Jnk2 null mutant (JNKKO mice) was associated with a 71% reduction in the malformation rate of embryos under maternal diabetic conditions. Embryos cultured in 0.5mM sorbitol (JNK activator) had a malformation rate that was significantly higher than that of the control group. Pharmacological and genetic evidence from the present studies strongly support JNK activation being an indispensable mediator of diabetic embryopathy. JNK activation itself is sufficient to induce embryonic anomalies, and thus mimics the teratogenic effect of hyperglycemia.

Characterization of differential gene expression profiles in diabetic embryopathy using DNA microarray analysis

OBJECTIVE

The molecular mechanisms by which maternal diabetes impairs embryogenesis are not established. This study aimed to determine the developmental genes and molecular pathways that are involved in diabetic embryopathy, by comparing gene expression profiles in the yolk sacs between the embryos of diabetic and control rats by using DNA microarray analysis.

STUDY DESIGN

Diabetes was induced in female rats by injecting streptozotocin (65 mg/kg) intravenously. Glucose levels were controlled by subcutaneously implanting insulin pellets. The female rats were mated with normal male rats. At gestation day 4, the insulin pellets were removed from a group of animals, making them hyperglycemic. The animals with insulin pellets served as controls. At gestational day 12, embryos were explanted, and yolk sacs were collected. Total RNA, free of DNA contamination, was extracted from the yolk sacs. Complementary DNA probes were synthesized, labeled with Cy3 and Cy5 fluorescent dyes, and used to hybridize rat oligo-array containing 10,000 genes. Data were analyzed by using 1-sample t test on log2 ratios, with P < .05 representing a significant difference. The changes in expression levels of important genes were verified with the use of a real-time polymerase chain reaction (PCR).

RESULTS

Five microarray experiments produced consistent results. A total of 101 genes were found to be differentially expressed between the embryos of diabetic and control rats. Analyses that used PathwayAssist (Ariadne Genomics, Rockville, MD) revealed a number of potential signaling pathways and genes involved in insulin signaling and stress response (insulin 2, insulin-binding protein 1, GST pi1), cell growth (GAP43, CSF1R, HGF), calcium signaling (calbindin 3, CBP A6), and PKC signaling (PKCBP beta15, FABP5), in concert with prior biochemical and molecular findings.

CONCLUSION

These observations show significant alterations in expression of developmental and stress response genes in diabetic embryopathy, and demonstrate, for the first time, that the yolk sac cells express insulin during early development. In addition, these data also demonstrate that hyperglycemia induces altered gene expression, resulting in aberrant cell signaling, morphogenesis, and embryopathy.

Experimental mechanisms of diabetic embryopathy and strategies for developing therapeutic interventions

A high frequency of birth defects is seen in infants born to diabetic mothers. The mechanisms by which maternal hyperglycemia, the major teratogenic factor, induces embryonic malformations remain to be addressed. It has been shown that increases in programmed cell death are one of the factors causing embryonic malformations. Hyperglycemia-induced apoptosis is associated with oxidative stress, lipid peroxidation, and decreased antioxidant defense capacity in the embryos. Recent studies have revealed that mitogen-activated protein kinases as intracellular signaling factors are involved in hyperglycemia-induced embryopathy. Based on the findings, interventions to prevent embryonic malformations have been explored. Strategies include supplementation of molecules that are deficient in the embryos under hyperglycemic conditions and antioxidants to alleviate the adverse effects of oxidative stress. The ultimate goal is to develop multi-nutrient dietary supplements to eliminate embryonic abnormalities induced by maternal diabetes.

Dietary vitamin and lipid therapy rescues aberrant signaling and apoptosis and prevents hyperglycemia-induced diabetic embryopathy in rats

OBJECTIVE

Maternal diabetes causes developmental malformations in the embryo. Dietary supplementation with antioxidants can reduce the malformation rates in animal models. To investigate the molecular mechanisms underlying diabetes-induced embryonic abnormalities and dietary interventions, activity of mitogen-activated protein kinases and factors associated with apoptotic pathways were examined in the maternal diabetic rat model.

STUDY DESIGN

Diabetes was induced in pregnant rats using streptozotocin. In the yolk sacs of the embryos, activity of the extracellular signal-regulated kinases, Raf-1, and Akt was dramatically reduced in diabetic rats, whereas that of c-jun N-terminal kinases/stress-activated protein kinases was increased.

RESULTS

When the diabetic dams were fed with arachidonic acid, vitamin E, or a combination of arachidonic acid, vitamin E, and myoinositol, the changes in the expression of these kinases were reversed and correlated with the decreases in the rates of apoptosis and embryonic malformations.

CONCLUSION

These results suggest that mitogen-activated protein kinases are involved in diabetic embryopathy, and dietary supplementations can rescue the aberrant signaling pathways and reduce embryonic malformation rate.

Aberrant patterns of cellular communication in diabetes-induced embryopathy in rats: II, apoptotic pathways

OBJECTIVE

The objective was to test the hypothesis that hyperglycemia-induced injury of yolk sac cell membranes is associated with disruption of cellular apoptotic signaling pathways.

STUDY DESIGN

Pregnant rats were induced to become diabetic by injection of streptozotocin. Fourteen normal control and 24 diabetic rats were killed on day 12 of gestation. Yolk sac membranes in 3 conceptus groups (nondiabetic, diabetic with normal, or diabetic with malformed conceptus) were collected for study. DNA was extracted from yolk sac cells and assayed for fragmentation by using gel electrophoresis, which indicates apoptosis. Protein expression was evaluated by Western blot assays. Statistical analyses were performed with the Student t -test.

RESULTS

The level of phosphorylated Akt was significantly decreased, whereas that of the proapoptotic protein Bax was increased. These changes were correlated with the presence of DNA fragmentation in yolk sac cells of the diabetic malformed conceptuses.

CONCLUSION

Hyperglycemia-induced embryopathy involves apoptosis, during which the expression of proapoptotic protein Bax is upregulated and the activity of the cell-survival factor, Akt kinase, is decreased in yolk sac cells. These observations suggest that hyperglycemia of maternal diabetes triggers apoptotic signaling pathways and inhibits cell survival pathways, leading to embryonic malformations.