Nutr Res Pract.  2015 Aug;9(4):358-363. 10.4162/nrp.2015.9.4.358.

A lifelong exposure to a Western-style diet, but not aging, alters global DNA methylation in mouse colon

• Choi SW
• Tammen SA
• Liu Z
• Friso S

• KMID: 2313851
• DOI: http://doi.org/10.4162/nrp.2015.9.4.358

Abstract

BACKGROUND/OBJECTIVES
Previous studies have indicated that when compared to young mice, old mice have lower global DNA methylation and higher p16 promoter methylation in colonic mucosa, which is a common finding in colon cancer. It is also known that a Western-style diet (WSD) high in fat and calories, and low in calcium, vitamin D, fiber, methionine and choline (based on the AIN 76A diet) is tumorigenic in colons of mice. Because DNA methylation is modifiable by diet, we investigate whether a WSD disrupts DNA methylation patterns, creating a tumorigenic environment. SUBJECTVIES/METHODS: We investigated the effects of a WSD and aging on global and p16 promoter DNA methylation in the colon. Two month old male C57BL/6 mice were fed either a WSD or a control diet (AIN76A) for 6, 12 or 17 months. Global DNA methylation, p16 promoter methylation and p16 expression were determined by LC/MS, methyl-specific PCR and real time RT-PCR, respectively.
RESULTS
The WSD group demonstrated significantly decreased global DNA methylation compared with the control at 17 months (4.05 vs 4.31%, P = 0.019). While both diets did not change global DNA methylation over time, mice fed the WSD had lower global methylation relative to controls when comparing all animals (4.13 vs 4.30%, P = 0.0005). There was an increase in p16 promoter methylation from 6 to 17 months in both diet groups (P < 0.05) but no differences were observed between diet groups. Expression of p16 increased with age in both control and WSD groups.
CONCLUSIONS
In this model a WSD reduces global DNA methylation, whereas aging itself has no affect. Although the epigenetic effect of aging was not strong enough to alter global DNA methylation, changes in promoter-specific methylation and gene expression occurred with aging regardless of diet, demonstrating the complexity of epigenetic patterns.

Keyword

Western-style diet; aging; DNA methylation; colon; mouse

MeSH Terms

Aging*
Animals
Calcium
Choline
Colon*
Colonic Neoplasms
Diet*
DNA Methylation*
Epigenomics
Gene Expression
Humans
Male
Methionine
Methylation
Mice*
Mucous Membrane
Polymerase Chain Reaction
Vitamin D
Calcium
Choline
Methionine
Vitamin D

Figure

• 

  Fig. 1 Body weight changes during the dietary intervention.*P < 0.001, **P = 0.073, ***P = 0.053 (t-test) compared to control. WSD: western-style diet.

• 

  Fig. 2 Global DNA methylation changes in each diet group over the 17 months dietary intervention measured by LC/MS method. DNA methylation status was defined as the percentage of total cytosine (cytosine + 5-methylcytosine) that was in the 5-methylcytosine form.Values are mean ± SE. *denotes a P-value less than 0.05 (two-way ANOVA with Bonferroni's posthoc test).

• 

  Fig. 3 p16 promoter methylation changes during the dietary intervention measured by methyl specific PCR.Values are mean % methylation of CpG island ± SE. *Denotes a P-value less than 0.05 relative to the 6 month control group. †Denotes a P-value less than 0.05 relative to the 6 month WSD group. ‡P-trend < 0.0001 (regression analysis for both Control and WSD groups).

• 

  Fig. 4A Changes in p16 gene expression in all mice measured by RT-PCR.Values are mean expression (ΔCt) of p16 ± SE. Different letters (ex: a, b) denote a P-value less than 0.05.

• 

  Fig. 4B Changes in p16 gene expression in each diet group.Values are mean expression (ΔCt) of p16 ± SE. *Denotes a P-value less than 0.05 relative to the 6 month control group. †Denotes a P-value less than 0.05 relative to the 6 month WSD group. ‡P-trend for WSD = 0.003; §P-trend for Control = 0.07.

• 

  Fig. 5 Correlations between p16 promoter methylation and expression in each diet group.Control: P = 0.0156; R2 = 0.2216; Pearson Correlation = -0.508; WSD: P = 0.057; R2 = 0.1216; Pearson Correlation = -0.401

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