Aerobic exercise and DNA methylation in postmenopausal women: An ancillary analysis of the Alberta Physical Activity and Breast Cancer Prevention (ALPHA) Trial

<div><p>Physical activity is associated with a lower risk of breast, colon, and endometrial cancer. Epigenetic mechanisms such as changes in DNA methylation may help to explain these protective effects. We assessed the impact of a one year aerobic exercise intervention on DNA methylation biomarkers believed to play a role in carcinogenesis. The Alberta Physical Activity and Breast Cancer Prevention (ALPHA) Trial was a two-armed randomized controlled trial in 320 healthy, inactive, postmenopausal women with no history of cancer. In an ancillary analysis, frozen blood samples (n = 256) were reassessed for levels of DNA methylation within LINE-1 and Alu repeats as well as within the promoter regions of <i>APC</i>, <i>BRCA1</i>, <i>RASSF1</i>, and <i>hTERT</i> genes. Differences between the exercise and control arm at 12-months, after adjusting for baseline values, were estimated within an intent-to-treat and per-protocol analysis using linear regression. No significant differences in DNA methylation between the exercise and control arms were observed. In an exploratory analysis, we found that the prospective change in estimated VO₂max was negatively associated with <i>RASSF1</i> methylation in a dose-response manner (p-trend = 0.04). A year-long aerobic exercise intervention does not affect LINE-1, Alu, <i>APC</i>, <i>BRCA1</i>, <i>RASSF1</i>, or <i>hTERT</i> methylation in healthy, inactive, postmenopausal women. Changes in DNA methylation within these genomic regions may not mediate the association between physical activity and cancer in healthy postmenopausal women. Additional research is needed to validate our findings with <i>RASSF1</i> methylation.</p><p><b>Trial Registration:</b> ClinicalTrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT00522262" target="_blank">NCT00522262</a>.</p></div

CONSORT diagram of ALPHA trial ancillary study.

<p>This Consolidated Standards of Reporting Trials (CONSORT) diagram describes the inclusion and exclusion of participants included in the current trial.</p

Intent-to-treat analysis comparing changes in the DNA methylation outcomes between the exercise and control groups.

<p>Intent-to-treat analysis comparing changes in the DNA methylation outcomes between the exercise and control groups.</p

Per-protocol analysis comparing changes in the DNA methylation outcomes between the exercise and control groups.

<p>Per-protocol analysis comparing changes in the DNA methylation outcomes between the exercise and control groups.</p

Baseline characteristics of ALPHA trial participants included in intent-to-treat analysis.

<p>Baseline characteristics of ALPHA trial participants included in intent-to-treat analysis.</p

The association between the amount of exercise, weight loss, change in VO₂ max and DNA methylation during a year-long aerobic physical activity intervention.

<p>The association between the amount of exercise, weight loss, change in VO₂ max and DNA methylation during a year-long aerobic physical activity intervention.</p

Distribution of individuals by <i>RAD52</i> expression.

<p>Individuals were ordered by unsupervised clustering based on <i>RAD52</i> expression levels. Heatmap represents the scaled RPKM normalized values with higher expression levels represented in red and lower expression levels in blue. The individuals carrying a copy number gain (log₂(ratio) > 0.5) of <i>RAD52</i> are highlighted in green (light yellow otherwise). <i>RAD52</i> gain carriers seem to have the same high expression pattern and cluster together. Particularly in LUAD one of the 3 gain carriers has the highest <i>RAD52</i> expression level.</p

Demographic characteristics of the cases and controls included in the genetic susceptibility study of <i>RAD52</i>/rs10849605.

<p>OR, CI and p-values represent the risk of UADT in each substrata, adjusted for sex and study specific country of origin.</p><p>Demographic characteristics of the cases and controls included in the genetic susceptibility study of <i>RAD52</i>/rs10849605.</p

eQTL analysis.

<p>Boxplots showing the effect of the genotype for the SNP <i>RAD52</i> rs10849605 on <i>RAD52</i> tumor expression levels in HNSC, LUSC and LUAD. The risk allele (C) significantly increases <i>RAD52</i> expression levels (p = 9x10⁻⁴ and 8x10⁻⁴ respectively) in both squamous cancers but not in lung adenocarcinoma (p = 0.75). In contrast, there was no evidence for association between rs10849605 and expression levels of other genes in the 12p13.33 region (Table D in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0117639#pone.0117639.s001" target="_blank">S1 File</a>).</p

Association between <i>RAD52</i> SNP rs10849605 and UADT cancer risk.

<p>Squares represent ORs, size of the square represents the inverse of the variance of the log ORs, horizontal lines represent 95% CIs. The solid vertical line indicates OR = 1 and the dashed vertical line the overall OR under the log-additive model. p_het is the p-value for heterogeneity between the different subgroups. I2 is the % of observed variation across subgroups (negative I2 were set to 0).</p