Physically active individuals have a 20% - 30% reduced risk of developing colon cancer compared with sedentary individuals. Mechanisms to explain the relationship are not established, and little is known about the effects of exercise at the cellular level in humans. Observational data suggests that low levels of physical activity are associated with DNA hypermethylation of specific genes in blood, but there is a lack of research on either the direct effects of exercise on DNA methylation in target tissue (colon), or on the amount of exercise necessary to effect these changes. Aberrant DNA methylation of certain genes has been identified in the normal colon of people at risk for colon cancer and appears to reflect a ?field cancerization? process, whereby the normal colon is primed for carcinogenesis. Previous research assessed DNA methylation levels using established techniques that were unable to detect low levels. This application is in response to NCI PA-15-163 Exploratory/Developmental Clinical Research Grants in Obesity (R21) which invites grant applications that focus on biomarker effects of weight control methods such as physical activity. Using a novel method that we have developed (MethyLight droplet digital PCR, ddPCR), which accurately detects low levels of DNA methylation in normal colon tissue, we propose to investigate the effects of a 12-month exercise intervention on DNA methylation in 4 candidate genes linked to field cancerization in the colon (EVL, MGMT, p14, and ESR1). Sigmoid colon samples were collected at baseline in 202 initially sedentary men and women aged 40-75 years. Participants were randomized to moderate-to-vigorous intensity aerobic exercise (facility and home, goal 360 minutes/week) intervention (N=51 men, 49 women) or control (no change in exercise; N=51 men, 51 women). In the exercise group, mean exercise over 12 months was 370 min/wk in men (102% of goal) and 295 min/wk in women (82% of goal). 12 month sigmoid colon biopsies were obtained in 187 (93%) [N=48 men, N=43 women in the exercise group, and N=48 men and 48 women in the control group]. Primary analyses will test the intervention effect (intent-to-treat) on levels of DNA methylation of the 4 target genes. Secondary analyses will address effect modification by dose of exercise, weight change and fat mass change (measured by DXA). Exploratory analyses will address: 1) effect modification by sex, colorectal adenoma history, family history of colon cancer, intake of folate and B vitamins; and 2) correlations between baseline DNA methylation of the 4 candidate genes with colon crypt proliferation and apoptosis. The proposed research is highly novel, takes advantage of an existing resource, and will inform future trials testing effects of different types and doses of exercise on genome-wide DNA methylation.
This project will investigate the effects of physical activity on colon DNA methylation in genes related to colon cancer. Excessive DNA methylation is thought to be a risk factor for colon cancer, and no previous study has tested the effect of exercise on DNA methylation in the colon. We will investigate these effects in colon tissue samples from 202 initially sedentary men and women, who have completed an exercise trial.
