Collaborative strategies for unraveling the complexity of birth defects

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Responses of the embryonic epigenome to maternal diabetes

Maternal diabetes and obesity are independent risk factors for neural tube defects, although it is unclear whether the effects are mediated by common pathogenic mechanisms. In this manuscript, we report a genome-wide survey of histone acetylation in neurulation stage embryos from mouse pregnancies with different metabolic conditions: maternal diabetes, and maternal consumption of a high fat content diet. We find that maternal diabetes, and independently, exposure to high-fat diet, are associated with increases and decreases of H3 and H4 histone acetylation in the embryo. Intriguingly, changes of H3K27 acetylation marks are significantly enriched near genes known to cause neural tube defects in mouse mutants. These data suggest that epigenetic changes in response to diet and metabolic condition may contribute to increased risk for neural tube defects in diabetic and obese pregnancies. Importantly, the responses to high-fat diet and maternal diabetes were distinct, suggesting that perturbed embryonic development under these conditions is mediated by different molecular pathways. This conclusion is supported by morphometric analyses that reveal a trend for maternal diabetes to delay embryonic development in the C57BL/6 strain, while high-fat diet appears to be associated with accelerated development. Taken together, our results link changes in histone acetylation to metabolic conditions during pregnancy, and implicate distinct epigenetic mechanisms in susceptibility to neural tube defects under conditions of maternal diabetes and obesity.

Resveratrol prevents impairment in activation of retinoic acid receptors and MAP kinases in the embryos of a rodent model of diabetic embryopathy

Diabetes induces impairments in gene expression during embryonic development that leads to premature and improper tissue specialization. Retinoic acid receptors (RARs and retinoid X receptor [RXRs]) and mitogen-activated protein kinases (MAPKs) play crucial roles during embryonic development, and their suppression or activation has been shown as a determinant of the fate of embryonic organogenesis. We studied the activation of RARs and MAPKs in embryonic day 12 (E12) in embryos of rats under normal, diabetic, and diabetic treated with resveratrol ([RSV]; 100 mg/kg body weight) conditions. We found downregulation of RARs and RXRs expressions as well as their DNA-binding activities in the embryos exhibiting developmental delays due to diabetes. Furthermore, the phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 was decreased and phosphorylation of c-Jun N-terminal kinase (JNK) 1/2 and p38 was increased. Interestingly, embryos of diabetic rats treated with RSV showed normalized patterns of RARs, RXRs, neuronal markers, and ERK, JNK and p38 phosphorylation.

Diabetic embryopathy: a role for the epigenome?

Embryonic development under adverse conditions, such as maternal diabetes or obesity during pregnancy, constitutes a major risk factor for birth defects, as well as for long-term health consequences and disease susceptibility in the offspring. While contributions from epigenetic changes have been invoked previously to explain the long-term changes in terms of developmental programming, we here review how maternal metabolism may directly affect the embryonic epigenome in relationship to teratogenic processes. We consider four epigenetic modalities--DNA methylation, non-coding RNA, transcription factors, and histone modifications--and their contribution to epigenetic memory, and discuss how epigenomic changes may mediate the altered control of embryonic gene expression brought about by maternal diabetes. In combination, the epigenomic modalities serve to define transcription-permissive domains of the genome, resulting in distinct epigenomic landscapes in different developmental cell types. We evaluate experimental approaches to characterize the epigenome in adverse pregnancy conditions, highlighting the role of next-generation sequencing on the technological side, while emphasizing the necessity to study defined cell populations in terms of biologic impact. Finally, we outline the challenges in moving from findings that correlate epigenomics to developmental phenotypes to scenarios that establish teratogenic causality.