Epigenetic processes in transmission of prenatally-induced phenotypes between generations

Babies born to mothers who have poor nutrition during pregnancy have an increased risk of heart attack, stroke, high blood pressure, type 2 diabetes mellitus and obesity when they become adults. There is emerging evidence that the consequences of such nutrition during pregnancy can be passed to grandchildren even when their daughters have adequate nutrition during pregnancy. These effects have been replicated in the offspring of rats fed a diet with reduced protein content during pregnancy. We have identified a mechanism by which poor nutrition during pregnancy can result in changes to how genes are controlled in the fetus and give which result in increased risk of disease in a future generation. This process of gene control is called epigenetics. In this project we will use the rat model to investigate the mechanism by which the diet of the mother changes the epigenetic control of genes in the next three generations of offspring. We already have evidence that this involves an enzyme called DNA methyltransferase-1 in the first generation and now we need to determine whether this enzyme is involved in subsequent generations. We have also shown adding folic acid to the mother's diet prevents changes in the epigenetic control of genes in the first generations. We will investigate whether folic acid can prevent changes in epigenetic control in successive generations.

Epidemiological studies and animal models show that poor nutrition before birth induces phenotypes associated with increased risk of non-communicable diseases, transmitted at least to the second generation. We have shown that induction of an altered metabolic phenotype in the offspring of rats fed a protein-restricted (PR) diet during pregnancy involves hypomethylation of specific gene promoters by a mechanism in which lower expression and binding activity of DNA methyltransferase (Dnmt)-1s has a central role. These effects were prevented by increasing the folic acid content of the PR diet. We are the first to show that induction of hypomethylation of the hepatic glucocorticoid receptor (GR) and PPARa in the F1 offspring by feeding a PR diet to F0 dams was transmitted to the F2 offspring through the female line even though F1 females received adequate nutrition. This study will investigate how changes in the epigenetic regulation of genes and altered metabolic phenotype are transmitted between generations. We will test the overall hypothesis that altered epigenetic regulation of Dnmt1s is transmitted between generations and that in each generation promoter methylation of specific genes is established by the activities of other Dnmts in oocytes and early embryos, but is lost during subsequent development due to lower Dnmt1s activity. We will use the well-established rat model of feeding a PR diet during pregnancy to investigate the epigenetic regulation of Dnmts by DNA methylation in oocytes and liver in three generations of offspring. Epigenotype and metabolic phenotype will be assessed in each generation by the methylation status and expression of hepatic GR and PPARa, expression of target genes and by markers of gluconeogenesis and fatty acid beta-oxidation. We will also determine whether increasing maternal folic acid intake during pregnancy interrupts transmission of altered epigenetic regulation and thus of adverse phenotypes between generations.