Congenital malformations, including neural tube defects (NTDs), are significantly increased in the offspring of diabetic mothers. We previously reported that in the embryos of a mouse model of diabetic pregnancy, NTDs are associated with reduced expression of the gene Pax-3, which encodes a transcription factor that regulates neural tube development, and that reduced expression of Pax-3 leads to neuroepithelial apoptosis. In this study, we used three approaches to test whether glucose alone could be responsible for these adverse effects of diabetes on embryonic development. First, primary culture of embryo tissue in medium containing 15 mmol/l glucose inhibited Pax-3 expression compared with culture in medium containing 5 mmol/l glucose. Second, inducing hyperglycemia in pregnant mice by subcutaneous glucose administration significantly inhibited Pax-3 expression (P < 0.05), as demonstrated by quantitative reverse transcription-polymerase chain reaction assay of Pax-3 mRNA, and also increased neural tube apoptosis (P < 0.05). NTDs were significantly increased in glucose-injected pregnancies when blood glucose levels were >250 mg/dl (P < 0.002) but not in moderately hyperglycemic pregnancies (150-250 mg/dl, P = 0.37). Third, phlorizin administration to pregnant diabetic mice reduced blood glucose levels and the rate of NTDs. As seen with glucose-injected pregnancies, the rate of NTDs in phlorizin-treated diabetic pregnancies was related to the severity of hyperglycemia, since NTDs were significantly increased in severely hyperglycemic (>250 mg/dl) diabetic pregnancies (P < 0.001) but not in moderately hyperglycemic pregnancies (150-250 mg/dl, P = 0.35). These two findings, that elevated glucose alone can cause the changes in Pax-3 expression observed during diabetic pregnancy and that the NTD rate rises with significant increases in blood glucose levels, suggest that congenital malformations associated with diabetic pregnancy are caused by disruption of regulatory gene expression in the embryo in response to elevated glucose.

Aims/hypothesis. Maternal diabetes increases oxidative stress in embryos. Maternal diabetes also inhibits expression of embryonic genes, most notably, Pax-3, which is required for neural tube closure. Here we tested the hypothesis that oxidative stress inhibits expression of Pax-3, thereby providing a molecular basis for neural tube defects induced by diabetic pregnancy. Methods. Maternal diabetes-induced oxidative stress was blocked with α-tocopherol (vitamin E), and oxidative stress was induced with the complex III electron transport inhibitor, antimycin A, using pregnant diabetic or non-diabetic mice, primary cultures of neurulating mouse embryo tissues, or differentiating P19 embryonal carcinoma cells. Pax-3 expression was assayed by quantitative RT-PCR, and neural tube defects were scored by visual inspection. Oxidation-induced DNA fragmentation in P19 cells was assayed by electrophoretic analysis.Results. Maternal diabetes inhibited Pax-3 expression and increased neural tube defects, and α-tocopherol blocked these effects. In addition, induction of oxidative stress with antimycin A inhibited Pax-3 expression and increased neural tube defects. In cultured embryo tissues, high glucose-inhibited Pax-3 expression, and this effect was blocked by α-tocopherol and GSHethyl ester, and Pax-3 expression was inhibited by culture with antimycin A. In differentiating P19 cells, antimycin A inhibited Pax-3 induction but did not induce DNA strand breaks. Conclusion/interpretation. Oxidative stress inhibits expression of Pax-3, a gene that is essential for neural tube closure. Impaired expression of essential developmental control genes could be the central mechanism by which neural tube defects occur during diabetic pregnancy, as well as other sources of oxidative stress. [Diabetologia (2003) 46:538-545]

Pax-3 is a transcription factor that is expressed in the neural tube, neural crest, and dermomyotome. We previously showed that apoptosis is associated with neural tube defects (NTDs) in Pax-3-deficient Splotch (Sp/Sp) embryos. Here we show that p53 deficiency, caused by germ-line mutation or by pifithrin-␣, an inhibitor of p53-dependent apoptosis, rescues not only apoptosis, but also NTDs, in Sp/Sp embryos. Pax-3 deficiency had no effect on p53 mRNA, but increased p53 protein levels. These results suggest that Pax-3 regulates neural tube closure by inhibiting p53-dependent apoptosis, rather than by inducing neural tube-specific gene expression.

Activation of the hexosamine pathway causes oxidative stress through depletion of GSH and consequent disruption of embryo gene expression. Activation of this pathway may contribute to diabetic teratogenesis.

Previously, we demonstrated that neural tube defects (NTDs) are significantly increased in a mouse model of diabetic pregnancy. In addition, expression of Pax-3, a gene encoding a transcription factor required for neural tube development, is significantly decreased. This suggests that diabetic embryopathy results from impaired expression of genes regulating essential morphogenetic processes. Here, we report that in one mouse strain, C57Bl/6J, embryos are resistant to the effects of maternal diabetes on NTDs and Pax-3 expression, in contrast to a susceptible strain, FVB, in which maternal diabetes significantly increases NTDs (P ‫؍‬ 0.02) and inhibits Pax-3 expression (P ‫؍‬ 0.01). Resistance to NTDs caused by diabetic pregnancy is a dominant trait, as demonstrated by heterozygous embryos of diabetic or nondiabetic mothers of either strain. There was no significant difference between strains in expression of genes that regulate free radical scavenging pathways, suggesting that susceptibility to oxidative stress does not account for the genetic differences. Understanding the genetic bases for differential susceptibility to altered gene expression and NTDs in diabetic mice may be important in delineating the mechanisms by which maternal hyperglycemia interferes with embryo gene expression. Moreover, if susceptibility to diabetic embryopathy is variable in humans as well as in mice, it may be possible to screen individuals at increased risk for this complication of diabetes. Diabetes 51: 2871-2874, 2002