- Written by James Gallagher
- Health and science reporter
According to a study, the lifespan of animals correlates with the rate at which their genetic code mutates.
Researchers have found that mammals – from tigers to humans – have roughly the same number of mutations by the time they die of old age.
But short-lived animals tend to exhaust their allotment faster, according to an analysis of 16 species.
According to the researchers, this discovery helps explain why we age and sheds light on one of cancer’s most complex mysteries.
Experts said the results obtained by researchers at the Wellcome Sanger Institute were “amazing” and “thought-provoking”.
Mutations are changes that creep into the instruction manual for building and working our bodies – our DNA.
These mutations have long been known to cause cancer, but whether they are important for aging has been debated for decades. Sanger researchers claim to have provided the “first empirical evidence” to suggest this.
They analyzed the incidence of mutations in species with a long life expectancy. They examined the DNA of a cat, black and white colobus, dog, ferret, giraffe, horse, human, lion, rat, naked rat, rabbit, rat, ring-tailed lemur and tiger.
The study, published in Nature, shows that mice undergo approximately 800 mutations per year during their short lifespan, which lasts just under four years.
The longer animals live, the fewer mutations they undergo each year.
Dogs have about 249 annual mutations, 160 lions and 99 giraffes, compared to an average of 47 for humans.
One of the researchers, Dr. Alex Kagan, described this pattern as “amazing” and that it was “really surprising and exciting” that all of the animals studied had approached “about 3,200” mutations in their lifetime.
If human DNA mutated at the same rate as mice, we would die with more than 50,000 genetic changes.
Dr Kagan told the BBC: “Despite their different ages, at the end of their lives mammals have the same number of mutations.”
“It’s the number, but what does it mean? It’s a mystery to us,” the researcher continues.
The cells of the body can reach a critical number of mutations and then die. There are also “few .” ideas [cellules] Misbehavior “begins to take over vital tissues, such as the heart, as we age, so that organs do not function properly.
However, it is unlikely that aging is the result of a single process within the body’s cells.
Telomere shortening and epigenetic changes are also thought to play a role. However, if there are mutations, one wonders if there are ways to slow down or even repair genetic damage.
The researchers want to know if this pattern holds for all life forms or just mammals. They plan to add fish to the analysis, including the Greenland shark, which can live for more than 400 years and is the world’s longest-living vertebrate.
The cancer paradox
In the field of oncology, there is a mystery known as the “Peto paradox”: why don’t large, long-lived animals have very high rates of cancer?
The more cells in your body and the longer you live, the more likely one of them will become cancerous. This must be bad news for elephants and whales.
Whales have trillions of cells [que nous]. “They shouldn’t be around because they will develop cancer before puberty,” says Dr. Kagan.
Large animals tend to live longer, so a slower mutation rate can help explain the discrepancy, but the researchers say it’s far from the only explanation.
Mice and naked giraffes live about the same age, with similar mutation rates, even though giraffes are thousands of times larger.
“You would expect the giraffe’s mutation rate to be lower than that, but it seems that body size doesn’t matter,” Dr. Kagan says.
Instead, the researchers say, other ways of suppressing cancer must have evolved, which could inspire new cancer treatments. For example, elephants have a higher number of copies of the DNA fragment that suppresses tumors.
The gap between 47 human mutations per year and 800 mouse mutations is large, says Dr. Alexander Gorelik and Dr. Camila Naxerova of Harvard Medical School.
“This difference is striking, given the broad general similarity between human and mouse genomes.
“These results are realistic.”
Dr Simon Spiro, a wildlife veterinary pathologist at the Zoological Society of London says: ‘Animals often live much longer in zoos than in the wild, so vets’ time is often spent managing conditions related to aging.
“The genetic changes identified in this study suggest that the pathology of aging will be similar across a wide range of mammals, whether aging begins at seven months or at 70.”
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