Smoking tobacco is widely known to leave its mark on the body: prematurely wrinkled skin, a “smoker’s cough,” and yellow teeth, among others. Now, a new collaborative study co-authored by University of Minnesota School of Public Health faculty shows that smoking also makes a long-term imprint on the body’s genome.
[Photo: Dr. Ellen Demarath]
The study was published in Circulation: Cardiovascular Genetics.
Study co-authors Associate Professor Weihua Guan and Professors James Pankow and Ellen Demerath focused on the epigenome, which is an aspect of human DNA expression that is regulated through the addition of chemical compounds to genes.
“This is the largest epigenome-wide study of smoking to date, and it shows how much and how long smoking might damage the epigenome in the general population,” said Dr. Demerath. “This is important because the idea that smoking does this by changing particular parts of the epigenome is new.”
Researchers examined a chemical change made by cells to genes called DNA methylation. The change involves the addition of one carbon and three hydrogen atoms, known as a methyl group, to a gene. Adding a methyl group turns the gene “off” and keeps it from producing proteins.
The researchers compared DNA methylation levels in blood samples of 16,000 people who currently smoked or had quit smoking to patterns in people who never smoked.
They found that smoking-related DNA methylation sites were associated with more than 7,000 genes, or one-third of known human genes. When people quit smoking, researchers found the majority of DNA methylation sites returned to levels seen in non-smokers within five years of quitting. However, some DNA methylation sites persisted even after 30 years of quitting.
Dr. Demerath said that the known signs of smoking in the body, called “biomarkers,” point to only recent smoking history and the discovery of the long-term methylation sites could serve as possible biomarkers of smoking exposure damage over time. The study also highlights particular gene pathways altered by smoking, which could be theoretically “reset” with pharmaceutical intervention to prevent or treat tobacco-related diseases.
Dr. Demerath suggests that future studies should examine body tissues other than blood, and include longitudinal, repeated snapshots of the epigenome from individuals before and after quitting smoking to see if the trends in DNA methylation continue.