The surprising longevity lessons from the world’s oldest animal

You can be forgiven if you haven’t heard of the oceanic quahog, also known as the Icelandic quahog: it’s not the kind of animal that gets a lot of time on TV. It is a large bivalve mollusk that lives buried in the sand on both coasts of the Atlantic, from the southern heat of Florida and Cadiz in Spain to the colder waters of Quebec in Canada and Norway. If you’ve eaten clam chowder in the United States, you will almost certainly have eaten it. Its shell is finely aligned like the rings of a tree trunk, and like the rings of a tree, you can count these lines to know its age.

The oldest known specimen was called Hafrún by researchers, an Icelandic name meaning “mystery of the ocean.” Hafrún was born in 1499 and lived as his ancestors had for generations, quietly on a modest diet collected off the coast of Iceland. In this sense, there was nothing remarkable about his life, except that it went on and on – and on. In fact, this only ended in 2006, when it was dredged from the sea by a team from the University of Exeter, UK. Sclerochronologist Paul Butler was the researcher responsible for aging it. Sclerochronology involves analyzing bivalve shells to construct chronologies for their surrounding environments.

“Its age was initially published as just over 400 years old, but further reading of the growth lines and comparison with other shells showed it was actually 507 years old,” he tells me. It is likely that older ones still exist, especially in the cold waters around Iceland, where they appear to grow more slowly and live even longer. Is there an upper limit to their age? “It’s hard to believe that they live much longer,” says Butler, “even though we’ve already had the ages of a few individuals analyzed by a mathematician who said in principle that they could live forever.” Well, that’s mathematicians for you.

The key to the quahog’s longevity appears to lie in its mitochondria – the structures in our cells that use food to provide us with energy. By “we,” I mean us eukaryotes – all the complex organisms, from yew trees and mealworms to jellyfish and rabbits.

“Having robust mitochondria, like Arctica islandica, is essential for healthy aging in a wide variety of model species,” says Enrique Rodriguez, a mitochondria researcher at University College London.

Quahog mitochondria are literally tougher. They have a membrane more resistant to damage than that of other species. The membrane of a mitochondrion is filled with protein machinery that processes electrons and protons and generates ATP, the universal energy molecule used in cells. In clams, this machinery is larger and more grouped together, making it more robust. “Proteins are more complex and higher molecular weight structures,” Rodriguez explains. “They are more united.”

Thanks to this machinery, quahogs suffer less damage to their mitochondria. This is partly because they are more attentive to gathering together the billions of protons and electrons that pass through these membranes every second. When electrons leak, they produce reactive oxygen species (ROS), such as hydrogen peroxide, which cause damage. Rodriguez compares it to cars in a queue. In normal mitochondria, the red light at the head of the line causes cars to back up, their exhaust fumes spewing and harming the environment. In quahog mitochondria, however, the traffic light – in this case, a protein complex – is much more effective at moving traffic, and less exhaust escapes from cars.

But it’s not just the sturdy membrane that helps a quahog have a healthy lifespan. This is also because the quahogs mop up the escaping ROS. To use Rodriguez’s analogy, this would be like cleaning car exhaust.

Rodriguez compared the quahog’s antioxidant capacity with a range of related, shorter-lived species and found that it had three to 14 times the ability to mop up ROS. All of this supports what is known as the Mitochondrial Oxidative Stress Theory of Aging (MOSTA). This also appears to be responsible for the exceptional lifespan of the naked mole rat, which can live 40 years, more than six times longer than other rodents of the same size.

Pierre Blier, researcher in animal metabolism and aquaculture genetics at the University of Quebec, keeps quahogs in tanks in his laboratory to study the mechanism of their longevity. It confirms that ocean clams have a greater capacity to buffer oxidants. “Arctic islandica has mitochondria that are much more robust and capable of resisting ROS,” he says, supporting the MOSTA theory.

This begins to answer the question of how these animals live so long – but what about why? In other words, what was the selection pressure that led to the evolution of such robust mitochondria?

One clue comes from low oxygen levels in the clam’s environment. “Arctic “Naked mole rats can stay with the shell closed without using their gills to capture oxygen for about a week,” Rodriguez says. Their mitochondria had to evolve to survive for long periods of time with little or even no oxygen – known as anoxia – and then be robust enough to cope with a sudden influx of oxygen and buffer the resulting sudden increase in oxidative stress. the way their mitochondria are robust and designed to resist anoxia and reoxygenation stress and live a long lifespan. So it may be, he says, that selection for anoxia resulted in long lifespan, almost as a side effect.

The big question, of course, is whether we can strengthen our own mitochondria. In 2005, a team at the University of California, Irvine created transgenic mice that produced more of the antioxidant “cleaning” enzyme catalase in their mitochondria, which increased the mice’s lifespan by about five months – a significant amount when the normal lifespan is two years. Although it is now possible to genetically modify human mitochondria, we are far from understanding how to safely increase lifespan. So we need another method.

We know that exercise improves the performance of our mitochondria. We also know that Tibetan Sherpas, who live at high altitudes, have different mitochondria than lowland dwellers. A 2017 study looked at lowlanders and Sherpas who ascended to Everest Base Camp, about 5,300 meters above sea level. Sherpas were able to use oxygen better and had better protection against oxidative stress because their mitochondria were more robust – and this had a genetic basis.

Blier insists that A. islandica really has something to tell us about longevity. “My advice for living longer is to take care of your mitochondria: exercise, eat well and take cold showers… Cold showers seem to induce mitochondrial quality control mechanisms. »

Well, if it works for clams…