Role of DNA methylation in the dietary restriction mediated cellular memory.

An important facet of dietary restriction (DR) that has been largely overlooked is that DR can have early effects that create a cellular memory, which persists even when DR is discontinued. The goal of this study was to determine if DNA methylation played a role in the cellular memory of DR by examining the effect of short-term DR on gene expression and DNA methylation and determining if the changes in expression and DNA methylation persist when DR is discontinued and mice returned to ad libitum (AL) feeding. We show that DR can induce substantial changes in gene expression within 1 month of its implementation in various tissues, and more interestingly, ~19-50% of these changes in gene expression persist across the tissues even when DR is discontinued. We then determined whether DR induced changes in DNA methylation in the promoter of three candidate genes identified from our gene expression analysis (Pomc, Hsph1, and Nts1) that correlated with the changes in the expression of these genes. Decreased methylation at three specific CG sites in the promoter of the Nts1 gene encompassing the distal consensus AP-1 site was correlated with increased Nts1 expression. Both the promoter hypomethylation and increased Nts1 expression persisted even after DR was discontinued and mice fed AL, supporting our hypothesis that DNA methylation could play a role in the memory effect of DR. The changes in DNA methylation in the Nts1 gene are likely to occur in intestinal stem cells and could play a role in preserving the intestinal stem cell pool in DR mice.