Whether it’s the lines on our palms, the lumps on our heads or the pattern of our moles, for thousands of years, we humans have been looking to our bodies for predictions of the future. The advent of genetics has given us new tools with which to measure biological characteristics. Our ability to decode DNA has led to many insights into what a person’s future might hold, allowing us to identify genetic mutations that range from those that indicate a higher than average risk of having an early heart attack, to others that lower the risk of developing type 1 diabetes.
Now, researchers from the University of Glasgow and University of Exeter have shown that the length of telomeres, sections of DNA located at the ends of chromosomes, can be used to predict the lifespan of individual birds known as zebra finches.
Telomeres mark the ends of chromosomes and help to protect the genetic code that they contain, a bit like the plastic caps that protect the ends of shoelaces from fraying. Cells in most tissues within a plant or animal will repeatedly divide throughout that individual’s life, by a process known as mitosis. This involves a cell dividing to produce two new cells that are almost identical to the original. Every time this happens, DNA within the original cell is copied. By a quirk of this replication process, a short section of DNA is lost from the ends of telomeres, resulting in new cells with slightly shorter chromosomes than the original. The telomeres act as ‘sacrificial’ sections of DNA that protect the important regions in the middle of chromosomes that contain genes. When telomeres get very short, the cell can no longer divide or function properly.
Telomere shortening can be compensated for by an enzyme, telomerase, that adds new DNA to telomeres, thereby replacing sections that have been lost. However, telomerase production is reduced in animals such as humans and zebra finches once they develop beyond embryos, which means that telomere shortening occurs as individuals get older. The rate at which telomeres are shortened varies between individuals, as does the initial telomere length that they begin life with.
The idea that telomere shortening is linked to normal ageing is not a new one, although this current study, partly funded by the Wellcome Trust, is the first to measure telomere length in the same individuals from a young age. The researchers involved made initial telomere measurements from blood samples taken when the birds were 25 days old, and then at five other time-points throughout their natural lives (up to nine years).
Given that humans don’t live under controlled laboratory conditions and have life expectancies that are roughly ten times longer than zebra finches, why choose birds to study ageing?
“The zebra finch is a very good species for us to use,” Professor Pat Monaghan from the University of Glasgow, who led the research, told me. “It has the potential to live for a relatively long time, shows considerable variation in lifespan within a single captive population and is easy to keep and breed.” This makes it possible to study longevity over more than one generation, which would be far more difficult to do with humans.
“The basics of telomere biology are highly conserved across many animal groups, but there are variations,” says Monaghan. “Zebra finches, like humans, have little telomerase activity in adult body cells.”
Writing in the journal PNAS, Monaghan and her colleagues reported that they found a highly significant relationship between telomere length in early life and lifespan: individuals with longer telomeres at 25 days old lived significantly longer than those with shorter telomeres. By three years old, there was no significant relationship between telomere length and the birds’ subsequent lifespan.
“Our findings suggest that early-life telomere length is particularly important in influencing lifespan variation,” says Monaghan, explaining that telomere length in young individuals is likely influenced by a combination of inherited and environmental factors, such as exposure to stress.
Researchers will need to do more work to identify all of the factors involved and untangle their relative importance. The consequences of telomere shortening also need to be more fully understood. It’s not clear, for example, whether this shortening is actually contributing to the ageing process in some way, or is itself caused by changes in stem cells that occur as an individual ages.
With life’s clock ticking for us all, it will be interesting to see what is uncovered by future studies of ageing-related processes, such as telomere shortening. Perhaps it will include new treatments for degenerative diseases or even methods for influencing the ageing process itself? Such findings could ultimately provide the means not just to forecast the future, but to change it.
- Heidinger BJ, Blount JD, Boner W, Griffiths K, Metcalfe NB, & Monaghan P (2012). Telomere length in early life predicts lifespan. Proceedings of the National Academy of Sciences of the United States of America, 109 (5), 1743-8 PMID: 22232671