The effect of maternal nutrition on offspring gene regulation via epigenetic modulation

Maternal nutrition during pregnancy is an important intrauterine factor that results in persistent alteration of the offspring epigenome and associates with health outcome later in life. Both DNA methylation and histone modifications have been reported in a range of rat tissues including liver, kidney, skeletal muscle and adrenal gland following a restricted diet during gestation. These epigenetic events have also been shown to affect tumor suppressor loci in mammary gland cancer cells. However, it is not known how these tumor-suppressive genes are regulated by epigenetic changes in the mammary glands in vivo under maternal low-protein (LP) diet. One of my published projects examined the effect of maternal low-protein diet on the regulation of the p16 cell-cycle gene expression in the mammary gland of offspring rats. Timed-pregnant Sprague-Dawley rats were fed during gestation one of two isocaloric diets, control (18% casein) or low protein (LP, 9% casein). The expression of p16 mRNA in the mammary gland of the LP offspring was decreased by 75% vs. control. We also detected decreased p16 protein content in the mammary glands of pups gestated under the LP diet. Chromatin immunoprecipitation (ChIP) assay demonstrated that the altered p16 mRNA level and transcription rate in LP offspring resulted from histone modification changes, including the reduced acetylation of histone H4 and the dimethylation of histone H3 at lysine 4 residues within the p16 promoter region. I also found maternal protein restriction down-regulate p21 gene expression in the mammary gland of rat offspring. p21 is a key factor responsible for tumor suppressor p53-dependent cell cycle arrest and has been accepted as a prognostic marker of breast cancer. DNA methylation analysis using bisulfite sequencing did not detect a differing pattern at the p21 promoter between the offspring of control and LP groups. Reduced acetylation of histone H3 and dimethylation of H3K4 within the p21 promoter region was observed. These results supported the hypothesis that maternal protein restriction during pregnancy programs p16 and p21 expression through histone modification alterations in offspring mammary gland.;Maternal nutrition restriction can also lead to low birth weight, which is associated with increased risk of type II diabetes. In our recent study, we investigated the impact of a aternal low protein diet on the expression of the transcription factor CCAAT/enhancer-binding protein (C/EBPbeta) in offspring skeletal muscle. C/EBPbeta belongs to a family of transcription factors that regulates the expression of genes involved in energy homeostasis and muscle development. We observed sex-dependent differences in C/EBPbeta expression in offspring skeletal muscle subjected to a maternal protein-restricted diet. In female offspring skeletal muscle, both C/EBPbeta mRNA and protein levels were increased by maternal protein restriction. However, C/EBPbeta expression was not altered in other tissues or male offspring. Analysis of transcriptional and epigenetic regulation showed acetylated histone 3 and acetylated histone 4 at significantly increased levels at the C/EBPbeta promoter region in female LP pup's muscle. Correspondingly, downstream phosphoenolpyruvate carboxykinase (PEPCK) gene transcription was also up-regulated in female LP pups through the increased binding of C/EBPbeta at its promoter. On the other hand, GLUT4 is an insulin-regulated glucose transporter involved in insulin sensitivity and carbohydrate metabolism in muscle cells. We observed sex-dependent GLUT4 mRNA expression and increased GLUT4 protein content in female pup skeletal muscle with maternal low protein. The protein level of myocyte enhancer factor 2A (MEF2A), which has been known as an activator of GLUT4 transcription via the ability to carry out specific binding to the GLUT4 MEF2 binding sequence, increased in female LP pups. Modifications of chromatin structure, including acetylated histone 3, acetylated histone 4 and di-methylated histone 3 at lysine 4, were detected at a significantly increased level at the GLUT4 promoter region in female pup muscle following a maternal low protein diet. Glycogen content was also detected as up-regulated, accompanied by increased glycogen synthase in LP female offspring muscle. The induction of C/EBPbeta and GLUT4 expression in female offspring skeletal muscle by maternal protein restriction during pregnancy may indicate sex-dependent signaling response in energy metabolism to a low maternal protein diet.