DNA Methylation Profiles in a Polygenic Mouse Model of Diet-Induced Obesity

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DESCRIPTION (provided by applicant): Obesity is a major risk factor for the development of coronary heart disease (CHD) and non-insulin dependent diabetes mellitus (NIDDM). Although the results of twin studies and adoption studies provide strong support for a genetic influence on body weight, mutations causing obesity are rare in the population and major genes contributing to common obesity have not been identified. This has led to the suggestion that the variation in adiposity between individuals may be determined by multiple genetic loci with variations in any single gene producing only a moderate effect. In accordance with this formulation, obesity has been reported to be associated with differential gene expression, and the composite effect of these alterations may be at least partly responsible for the susceptibility to NIDDM and CHD. It is the long-term goal of this proposal to evaluate whether modifications in DNA methylation patterns that may result in either activation or silencing of genes can be detected when comparing obese and lean individuals. The first step in approaching this long-term goal is a proof-of-concept study using an animal model in an experimental setting. Provision of a high-fat diet to C57BL/6 mice results in increased body weight, hyperinsulinemia and insulin-resistance, and the accelerated appearance of aortic fatty streak lesions when compared to littermates fed normal mouse chow. The use of these mice will allow nutrient exposure to be varied while keeping genetic background constant. Based on previous reports that changes in DNA methylation may precede the development of atherosclerotic lesions in mice with a mutation in the apolipoprotein E gene causing elevated plasma cholesterol, the goal of this proposal is to test the hypotheses that (a) the pathogenesis of adult-onset obesity and atherosclerosis in wild- type mice fed an atherogenic diet may be correlated with functional differences in DNA methylation between treated and control animals and (b) that acquired variability in DNA methylation may be involved in normal aging and could contribute to the development of complex disease by pursuing the following specific aims: 1) to evaluate whether diet-induced obesity and atherosclerosis in C57BL/6 mice entails alterations in DNA methylation patterns in atherosclerotic lesions and other target organs by genome-wide microarray analysis. 2) to identify and clone methylated sequences, and validate that genes with altered methylation patterns detected by microarray analysis are regulated by methylation in vitro and in vivo. 3) to assess global and gene-specific DNA methylation in multiple tissues during aging in C57BL/6 mice. These experiments may reveal the role and sequence of DNA methylation changes in simultaneous disease processes in response to nutrition and other environmental influences, and may also yield a set of novel candidate genes that can later be tested in association studies in human cohorts. Consuming a high-fat diet is an environmental exposure that may alter DNA methylation and change gene expression. This will be studied first in mice to see whether this type of change could help to explain the increased risk for non-insulin dependent diabetes mellitus (NIDDM) and coronary heart disease (CHD) with obesity.