Diabetes teratogenicity in mice is accompanied with distorted expression of TGF-beta2 in the uterus

The role of glucose in physiological and pathological heart formation

Cells display distinct metabolic characteristics depending on its differentiation stage. The fuel type of the cells serves not only as a source of energy but also as a driver of differentiation. Glucose, the primary nutrient to the cells, is a critical regulator of rapidly growing embryos. This metabolic change is a consequence as well as a cause of changes in genetic program. Disturbance of fetal glucose metabolism such as in diabetic pregnancy is associated with congenital heart disease. In utero hyperglycemia impacts the left-right axis establishment, migration of cardiac neural crest cells, conotruncal formation and mesenchymal formation of the cardiac cushion during early embryogenesis and causes cardiac hypertrophy in late fetal stages. In this review, we focus on the role of glucose in cardiogenesis and the molecular mechanisms underlying heart diseases associated with hyperglycemia.

GESTATIONAL DIABETES MELLITUS AND THE DEVELOPMENT OF CLEFT LIP / PALATE IN NEWBORNS

Background

Several studies observed metabolic disorders in pregnancy as risk factors for birth defects, including orofacial clefts. Diabetes is associated with approx. 10% of the pregnancies, but in Romania, less than 5%. An obese and diabetic woman has 3 times more risk for an offspring with a craniofacial defect than healthy women suggesting that diabetes mellitus contributes to their pathogenesis with complex mechanisms.

Case report

We present the case of a newborn 4 days old, male with neonatal hypoglycemia, cleft lip and proportionate (symmetric) macrosomia. His mother is a 35 years old Caucasian woman with no important personal risk factors and no known history of diabetes mellitus. The glucose tolerance test performed to the mother at about 10 weeks during pregnancy led to the diagnosis of gestational diabetes.

Discussion

The gestational diabetes mellitus diagnosed since the 10^th week of pregnancy, the hyperglycemia status during pregnancy and the fetal overgrowth (macrosomia at birth) indicate the possible factors that lead to the Orofacial cleft (OFC).

Conclusion

With the increased prevalence of obesity, diabetes, and the evidence of association of these syndromes with OFCs, it is recommended that mothers planning to become pregnant to follow healthy habits, maintain healthy weight, and be screened for possible diabetes prior to conception and early in pregnancy.

Periconception onset diabetes is associated with embryopathy and fetal growth retardation, reproductive tract hyperglycosylation and impaired immune adaptation to pregnancy

Diabetes has been linked with impaired fertility but the underlying mechanisms are not well defined. Here we use a streptozotocin-induced diabetes mouse model to investigate the cellular and biochemical changes in conceptus and maternal tissues that accompany hyperglycaemia. We report that streptozotocin treatment before conception induces profound intra-cellular protein β-O-glycosylation (O-GlcNAc) in the oviduct and uterine epithelium, prominent in early pregnancy. Diabetic mice have impaired blastocyst development and reduced embryo implantation rates, and delayed mid-gestation growth and development. Peri-conception changes are accompanied by increased expression of pro-inflammatory cytokine Trail, and a trend towards increased Il1a, Tnf and Ifng in the uterus, and changes in local T-cell dynamics that skew the adaptive immune response to pregnancy, resulting in 60% fewer anti-inflammatory regulatory T-cells within the uterus-draining lymph nodes. Activation of the heat shock chaperones, a mechanism for stress deflection, was evident in the reproductive tract. Additionally, we show that the embryo exhibits elevated hyper-O-GlcNAcylation of both cytoplasmic and nuclear proteins, associated with activation of DNA damage (ɣH2AX) pathways. These results advance understanding of the impact of peri-conception diabetes, and provide a foundation for designing interventions to support healthy conception without propagation of disease legacy to offspring.

Modulation of diabetes-induced palate defects by maternal immune stimulation

Maternal diabetes can induce a number of developmental abnormalities in both laboratory animals and humans, including deformities of the face and palate. The incidence of birth defects in newborns of women with diabetes is approximately 3 to 5 times higher than among nondiabetics. In mice, nonspecific activation of the maternal immune system can reduce fetal abnormalities caused by various etiologies including hyperglycemia. This study was conducted to determine whether nonspecific maternal immune stimulation could reduce diabetes-induced palate defects and orofacial clefts. Female ICR mice were immune stimulated before induction of hyperglycemia with Freund's complete adjuvant (FCA), granulocyte-macrophage colony-stimulating factor (GM-CSF), or interferon-gamma (IFNgamma). Streptozocin was used to induce hyperglycemia (26-35 mmol blood glucose) in females before breeding. Fetuses from 12 to 18 litters per treatment group were collected on Day 17 of gestation. Palate width and length were measured, and the incidence of orofacial clefts was determined. Palate length and width were both decreased by maternal hyperglycemia. Maternal immune stimulation with GM-CSF or FCA limited the degree of palate shortening from the hyperglycemia. Each of the three immune stimulants attenuated significant narrowing of the palate. Rates of orofacial clefts were not significantly different between treatment groups. Palatogenesis is a complex process driven by cellular signals, which regulate cell growth and apoptosis. Dysregulation of cellular signals by maternal hyperglycemia can result in fetal malformations. Maternal immune stimulation may prevent dysregulation of these signaling pathways thus reducing fetal malformations and normalizing palate growth.

Insights into modeling streptozotocin-induced diabetes in ICR mice

Streptozotocin (STZ)-induced diabetes in ICR mice is often used to model diabetes mellitus and its complications, as well as other pathologies. In studies of diabetes progression and effects of newly developed treatments, experimental results may be difficult to interpret because blood glucose levels (BGLs) of untreated diabetic control animals tend to decline substantially during typical experimental time spans of 8-11 h. To address this problem, the authors examined several experimental conditions that might affect BGL stability, including STZ dose, initial mouse weight, fasting regimen and light:dark cycle. The authors found that diabetes severity was dependent on initial mouse weight and that weight loss after diabetes induction was less severe in heavier mice. Furthermore, a dose of 150 mg STZ per kg body weight was sufficient to induce stabilized acute diabetes without causing many complications. Finally, BGL could be stabilized in diabetic mice that were not treated with insulin by avoiding pre-fasting before an 8-h experiment and by allowing mice limited access to food during the experiment.

TNFalpha in the pathogenesis of diabetes-induced embryopathies: functions and targets

Hyperglycemia-induced increase in the production of reactive oxygen species (ROS) is proposed to be an initial step in the pathogenesis of diabetes-induced spontaneous abortions and structural inborn anomalies. However, the subsequent steps in this process are incompletely understood. One of the key molecules involved is tumor necrosis factor-alpha (TNFalpha): its expression is regulated by ROS and it regulates ROS production in turn. This cytokine has been the focus of many studies addressing the mechanisms of different forms of diabetes-induced embryopathies, such as early pregnancy loss, inborn anomalies, fetal growth retardation as well as some pathologies appearing during adult life. In this review, we analyze the results of these studies and discuss how TNFalpha may regulate the response of pre- and post-implantation stage embryos to diabetes-induced detrimental stimuli. The data presented in this review suggest that TNFalpha may play a dual role in the pathogenesis of diabetes-induced embryopathies. It may act both as a mediator of diabetes-induced embryotoxic stimuli leading to the death of peri-implantation stage embryos and, possibly, as a suppressor of diabetes-induced apoptosis in post-implantation stage embryos. It also appears that TNFalpha fulfills these functions via interaction with leukemia inhibitory factor (LIF) and the transcription factor NF-kappaB. These molecules are presently considered as attractive targets for the treatment of diabetes-induced complications. Therefore, further studies addressing their role in the mechanisms underlying diabetes-induced embryopathies are needed to evaluate the safety of such therapies for diabetic women of childbearing age.

Reduction in diabetes-induced craniofacial defects by maternal immune stimulation

BACKGROUND

Maternal diabetes can induce a number of developmental abnormalities in laboratory animals and humans, including facial deformities and defects in neural tube closure. The incidence of birth defects in newborns of diabetic women is approximately 3-5 times higher than among non-diabetics. In mice, non-specific activation of the maternal immune system can reduce fetal abnormalities caused by diverse etiologies, including diabetes induced neural tube defects. This study was conducted to determine whether non-specific maternal immune stimulation could reduce diabetes-induced craniofacial defects as well.

METHODS

Maternal immune function was stimulated before streptozocin (STZ) treatment by maternal footpad injection with Freund's complete adjuvant (FCA), maternal intraperitoneal (i.p.) injection with granulocyte-macrophage colony-stimulating factor (GM-CSF), or maternal i.p. injection with interferon-gamma (IFNgamma). Streptozocin (200 mg/kg i.p.) was used to induce hyperglycemia (26-35 mmol blood glucose) in female ICR mice before breeding. Fetuses from 12-18 litters per treatment group, were collected at Day 17 of gestation.

RESULTS

Craniofacial defects were observed in fetuses from all hyperglycemic groups. The incidence of defects was significantly decreased in fetuses from dams immune stimulated with IFNgamma or GM-CSF. The most common defects were reduced maxillary and mandibular lengths. Both were prevented by maternal stimulation with GM-CSF.

CONCLUSION

Maternal immune stimulation reduced the incidence of diabetic craniofacial embryopathy. The mechanisms for these protective effects are unknown but may involve maternal or fetal production of cytokines or growth factors that protect the fetus from the dysregulatory effects of hyperglycemia.

Developmental exposure of mice to TCDD elicits a similar uterine phenotype in adult animals as observed in women with endometriosis

Whether environmental toxicants impact an individual woman's risk for developing endometriosis remains uncertain. Although the growth of endometrial glands and stroma at extra-uterine sites is associated with retrograde menstruation, our studies suggest that reduced responsiveness to progesterone may increase the invasive capacity of endometrial tissue in women with endometriosis. Interestingly, our recent studies using isolated human endometrial cells in short-term culture suggest that experimental exposure to the environmental contaminant 2,3,7,8-tetracholorodibenzo-p-dioxin (TCDD) can alter the expression of progesterone receptor isotypes. Compared to adult exposure, toxicant exposure during development can exert a significantly greater biological impact, potentially affecting the incidence of endometriosis in adults. To address this possibility, we exposed mice to TCDD at critical developmental time points and subsequently examined uterine progesterone receptor expression and steroid responsive transforming growth factor-beta2 expression in adult animals. We find that the uterine phenotype of toxicant-exposed mice is markedly similarly to the endometrial phenotype of women with endometriosis.

Maternal Immunopotentiation Affects Caspase Activation and NF-kappaB DNA-binding Activity in Embryos Responding to an Embryopathic Stress

PROBLEM

Increased embryonic resistance to teratogenic stresses as a result of maternal immunopotentiation is associated with a decrease in the intensity of teratogen-induced apoptosis in target embryonic structures. These findings suggest that this effect of maternal immunopotentiation might be realized through modification of the expression of molecules regulating the teratogen-induced apoptotic process. To examine this possibility, we evaluated caspases 3, 8 and 9 activation as well as nuclear factor (NF)-kappaB DNA-binding activity in the embryos of immunopotentiated mice exposed to cyclophosphamide (CP).

METHODS OF STUDY

The rate of resorptions and the proportion of malformed fetuses in CP-treated mice were recorded on day 19 of pregnancy. Activity of caspases was tested in cytoplasmic extracts collected from the embryonic brain 24 hr after CP treatment using appropriate fluorometric kits, whereas NF-kappaB DNA-binding activity was evaluated in nuclear extracts using the electrophoretic mobility shift assay.

RESULTS

As in our previous studies, immunopotentiated CP-treated females exhibited a lower rate of resorptions or fetuses with open eyes than their non-immunopotentiated counterparts. In parallel, we observed that maternal immunopotentiation normalized the CP-induced activation of the tested caspases as well as the CP-induced suppression of NF-kappaB DNA-binding activity.

CONCLUSIONS

As caspases act as inducers of apoptosis, and NF-kappaB acts in CP-treated embryos as an apoptosis suppressor, the above results suggest that maternal immunopotentiation might affect embryonic sensitivity to embryopathic stresses via NF-kappaB- and caspases-associated pathways.

Diabetes teratogenicity is accompanied by alterations in macrophages and T cell subpopulations in the uterus and lymphoid organs

Insulin-dependent diabetes mellitus is a well-known teratogen, which might cause growth retardation, malformations and fetal death. We have previously shown, that potentiation of the maternal immune system (immunopotentiation) might protect the embryo from diabetes teratogenicity. Therefore, in the present study we further inquired whether diabetes teratogenicity might be associated with alterations in the level of immune effector cells in systemic and local lymphoid organs as well as in the uterus throughout pregnancy and whether the protection exerted by maternal immunopotentiation might be realized through its effect on those cells. Streptozotocin-induced diabetes in ICR mice was found to reduce pregnancy rate and fetal weight while increasing the resorption rate and the percentage of litters with malformed fetuses. These teratogenic effects were accompanied by a decreased percentage of cells expressing Mac-1, Thy-1.2, CD4 or CD8 in the spleen and inguinal as well as paraaortic lymph nodes, except for Mac-1 expression by splenocytes, which increased significantly in the beginning of pregnancy and decreased later. A different pattern was observed in the uterus, when the percentage of cells expressing these markers tended to increase in the beginning of pregnancy and decrease later. Intrauterine immunopotentiation with rat splenocytes was found to improve the reproductive performance of diabetic animals. This protective effect was accompanied by a general normalization of the level of the various cell surface markers, when in most cases their expression returned to that found in nonimmunopotentiated mice. Our results suggest that the protection exerted by maternal immunopotentiation on the embryo against diabetes teratogenicity might be mediated via its effect on the level of immune effector cells localized to uterus and lymphoid organs, which was found to be altered in diabetic mice.

Enhanced inflammatory response in neural tubes of embryos derived from diabetic mice exposed to a teratogen

Exposure of embryos to the teratogen cyclophosphamide (CP) and maternal diabetes is linked to pathogenesis of neural tube defects during development. Maternal diabetes aggravates the teratogen-induced inflammatory reaction leading to increased risk of neural tube defects in mouse embryos. The inflammatory reaction in the developing neural tube has been characterized by the presence of activated amoeboid microglia/brain macrophages and altered expression levels of cytokines. Although there were no obvious anomalies observed in the neural tubes of embryos from CP-treated non-diabetic mice, the frequency of neural tube defects was increased significantly in embryos of CP-treated diabetic mice. Moreover, there were more activated amoeboid microglia in the forebrain of CP-treated diabetic embryos compared to that in CP-treated non-diabetic mice. The expression of cytokines such as tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) in the fetal brain of normal and diabetic embryos was induced in the neural tubes after CP treatment. Furthermore, the mRNA expression levels of both genes were increased markedly in the neural tube of CP-treated diabetic embryos compared to that of CP-treated non-diabetic embryos as measured by quantitative real-time PCR. Immunohistochemically, more TNF-alpha- and TGF-beta1-positive cells, which included neurons and amoeboid microglia, were detected in CP-treated diabetic embryos than in CP-treated normal embryos. Maternal diabetes aggravates teratogen-induced inflammation, which is characterized in the developing neural tube by increased amoeboid microglia and enhanced expression of inflammatory cytokines. Although a definite link has yet to be elucidated, it is suggested that the increased rate of neural tube defects observed in CP-treated diabetic embryos may be due to upregulation of proinflammatory cytokines caused by maternal diabetes.

The role of pro- and anti-apoptotic molecular interactions in embryonic maldevelopment

PROBLEM

Pregnancy loss and the occurrence of inborn structural anomalies are often preceded by excessive apoptosis in targeted embryonic and extraembryonic tissues. Apoptogenic stimuli activate both death and survival, signaling cascades consisting of molecules acting as activators and effectors, or negative regulators of apoptosis. The interplay between these cascades determines whether the cell which is exposed to an apoptogenic stimulus dies or survives. This review summarizes the functioning of pro- and anti-apoptotic molecules in embryos responding to various teratogens. The effect of potentiation of the maternal immune system on these molecules is also discussed.

METHODS OF STUDY

The data on the functioning of various pro- and anti-apoptotic molecules in embryos exposed to various developmental toxicants, and embryos developing in a diabetic environment are reviewed. Techniques such as the TUNEL method, DNA fragmentation assay, electromobility shift assay (EMSA), fluorometric assay, immunohistochemistry, Western blot, In situ hybridization, have been used in our studies to detect apoptosis, and evaluate the functioning of molecules such as TNFalpha, caspases, NF-kappaB and IkappaB, p53, and bcl-2 in different embryonic and extraembryonic tissues.

RESULTS

Our and other data summarized in this review have demonstrated that the doses of developmental toxicants required to induce pregnancy loss and gross structural anomalies induce excessive apoptosis shortly after treatment. Depending on the intensity and type of targeted tissues, this apoptosis was accompanied by alterations in the activity of the molecules which act as activators and effectors (e.g. caspase 3, caspase 8, caspase 2, p53) or negative regulators (bcl-2, NF-kappaB) of apoptosis. Maternal immunopotentiation, which decreases the level of induced and spontaneous pregnancy loss and the incidence and severity of teratogen-induced structural anomalies has been shown to modulate the expression of these molecules both in embryonic tissues and at the feto-maternal interface.

CONCLUSIONS

The data presented in this review suggest that molecules such as TNFalpha, caspase 3, caspase 8, NF-kappaB, p53 and bcl-2, which are involved in the regulation of apoptosis, may also be involved in determining the sensitivity of the embryo to developmental toxicants. Maternal immunopotentiation may modulate the functioning of these molecules.