Researchers have discovered that there are age and health-related differences in fragments of DNA located in the bloodstream, called cell-free DNA (cfDNA). These differences could ultimately be used to measure an individual’s biological age, which reveals whether a person’s body functions as older or younger than their chronological age.
The investigation was focused on cfDNA collected from blood samples of people in their 20s, 70s, and from healthy and unhealthy individuals that were over 100 years old. Across these four groups, the team detected differences in how the DNA was packaged.
A nucleosome is the basic unit of DNA packaging in which a segment of DNA is wrapped around a protein core. Nucleosome packing is one component of the epigenome, or chemical compounds that can change gene expression without affecting the DNA sequence.
The study revealed that nucleosomes were well-spaced in the DNA of 20-somethings, but had less structure in the older groups, especially among the unhealthy centenarians. In addition, the signal from nucleosome spacing for the healthy centenarians was more similar to the signal from the people in their 20s than people in their 70s.
Study lead author Nicola Neretti is an assistant professor of Molecular Biology, Cell Biology and Biochemistry at Brown University.
“Among other traits, healthy centenarians preserve the epigenomic profile of younger individuals,” said Professor Neretti. “As with anything in aging, many things work together, and it is not clear what the cause or the effect is. With our cfDNA test, we hope to gain understanding of these epigenetic changes and what they mean.”
Previous studies have established that cfDNA is produced by dying cells. As the cells die, the DNA is cut in between nucleosomes, explained Professor Neretti. Scientists first discovered cfDNA in the blood of cancer patients, and the fragments can be used to diagnose cancer.
“cfDNA is somewhat like a message in a bottle that captures what the cell looked like, epigenetically speaking, before it died,” said Professor Neretti. “A lot of cellular machinery is involved in maintaining nucleosome spacing, and these components can go downhill as you age. The nucleosomes don’t move apart or become more dense themselves. The nucleosome spacing is just the read-out of the changes of that machinery.”
Professor Neretti explained that a better understanding of the epigenetic changes involved in the aging process could lead to the development of treatments for age-related disorders, or may someday be used to determine whether a person’s body is aging well biologically.
The study is published in the journal Aging Cell.