Epigenetic effects of dietary supplementation and nutrition

• Main Author: Brant, Jason Orr
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2009
• Subjects: Genetics; Molecular biology; Nutrition
• ISBN: 9781124797786; 1124797785

DNA methylation is associated with long-term repression of transcription, and has generally been considered a fairly stable epigenetic mark. Changes in DNA methylation patterns were thought to normally only occur during embryonic and germ cell development, however recent reports have indicated nutritional insults, exposure to environmental toxins and aging can, in fact, alter DNA methylation patterns. Two experimental approaches were utilized in order to gain a better understanding of how nutritional insults result in altered DNA methylation. The first approach focused on the effects on DNA methylation due to exposure to a low protein diet in utero, on both a genome-wide scale and at specific loci. The results indicate that there were subtle changes in DNA methylation occurring at differentially methylated regions within the H19/Igf2 imprinted domain in animals exposed to a low protein diet during development. Additionally, it was demonstrated that the expression of H19 and Igf2 was also altered. These findings are important in that they indicate that exposure to nutritional insults in utero can induce epigenetic changes in offspring, however the genome-wide analysis indicates that that was no major changes occurring in DNA methylation in low protein compared to normal protein animals. The second approach involved examining the effects of folic acid supplementation and withdrawal in Chinese women of child bearing age on DNA methylation. Although the success in prevention of neural tube defects has been dramatic, and folic acid is generally considered to be safe, the long-term consequences of increased folate levels have yet to be extensively studied in long term clinical trials. Folate plays a major role in one carbon metabolism, and is involved in the methylation of DNA. In order to examine the effects of increased folate levels on DNA methylation, blood samples were analyzed from a population-based, randomized trial of folic acid supplementation and withdrawal. The results indicate that folic acid supplementation and withdrawal produced changes in DNA methylation in a locus-specific manner. Methylation-Specific PCR of the promoters of tumor suppressor genes (TSGs) indicate that there was an observable increase in DNA methylation after 6 months of folic acid supplementation in two out of ten subjects analyzed, which was no longer detectable after 3 months of withdrawal. No wide-spread hypermethylation of TSGs were detected. There were also dramatic changes in DNA methylation at the maternally imprinted SNRPN promoter, with a near complete loss of DNA methylation after 6 months of folic acid supplementation, and a complete loss after 3 months of folic acid withdrawal. Analysis of the L1 repetitive element determined that there was no major change in DNA methylation occurring at this element. Overall, this study has demonstrated that exposure to nutritional insults in utero can induce both changes in DNA methylation and in gene expression levels, and that dietary supplementation and withdrawal in an adult population can induce changes in DNA methylation. These results warrant further studies into the biological significance of these observed changes.