Genetic changes – known as somatic mutations – occur in all cells throughout the lifespan of an organism. While most of these mutations are harmless, some of them can impair normal cell functioning or even start a cell on the path to cancer. Since the 1950s, scientists have speculated that these mutations may also play a role in aging processes. However, due to technological limitations, they could not properly test this hypothesis.
Now, a research team led by the Wellcome Sanger Institute has analyzed the genomes of 16 mammal species – ranging from mice, rats, and rabbits to horses, tigers, and giraffes – in order to shed more light on the role of these genetic changes in ageing. They found that, despite huge variations in lifespan and size, different animal species tend to end their natural life with surprisingly similar numbers of somatic mutations. However, the results suggest that the longer the lifespan of a species, the slower the rate at which the mutations occur, thus lending support to the hypothesis that somatic mutations may play a crucial role in ageing.
“To find a similar pattern of genetic changes in animals as different from one another as a mouse and a tiger was surprising. But the most exciting aspect of the study has to be finding that lifespan is inversely proportional to the somatic mutation rate,” said study lead author Alex Cagan, a postdoctoral researcher on somatic evolution at the Wellcome Institute.
“This suggests that somatic mutations may play a role in ageing, although alternative explanations may be possible. Over the next few years, it will be fascinating to extend these studies into even more diverse species, such as insects or plants.”
“Animals often live much longer in zoos than they do in the wild, so our vets’ time is often spent dealing with conditions related to old age. The genetic changes identified in this study suggest that diseases of old age will be similar across a wide range of mammals, whether old age begins at seven months or 70 years, and will help us keep these animals happy and healthy in their later years,” added study co-author Simon Spiro, a wildlife veterinary pathologist at the Zoological Society of London.
Nevertheless, understanding the exact causes of ageing remains an unsolved question. Although somatic mutations appear to play a fundamental role in ageing, other processes such as protein aggregation and epigenetic changes are also likely to contribute to the molecular damage in our cells and tissues that is a well-known marker of old age. Further research is needed to compare the rates of all of these processes across species with different lifespans.
The study is published in the journal Nature.