They feel no pain, don’t get cancer and look like baggy-skinned sausages with teeth: the naked mole rat is already famously weird. Now scientists have discovered what could be the subterranean rodents’ strangest trait yet: they can survive without oxygen by switching to a metabolic strategy normally used by plants.
By switching from a glucose-based metabolic system, which depends on oxygen, to one that uses fructose instead, mole rats can cope with nearly twenty minutes in air with 0% oxygen. Under the same conditions, a human would die within minutes.
“The naked mole rat has simply rearranged some basic building-blocks of metabolism to make it super-tolerant to low oxygen conditions,” said Thomas Park, professor of biological sciences at the University of Illinois at Chicago, who made the discovery after studying the species for 18 years.
The apparently unique metabolic strategy probably evolved along with the mole rats’ niche life-style, he said. The animals live in stuffy, hyper-crowded burrows, with chambers in which a hundred-odd colony mates sleep together in a heap of hairless bodies.
Scientists were aware that oxygen supplies in the mole rats’ tunnels drop to levels that would be unsurvivable for other land mammals, but until now had not tested the limits of their ability to cope with oxygen deprivation, or how this works biologically.
In the latest study, published in the journal Science, the team found that mole rats showed no ill effects after five hours breathing air with 5% oxygen – slightly lower that oxygen levels at the summit of Everest. Laboratory mice, by contrast, died within ten minutes.
In 0% oxygen, both the mice and mole rats quickly lost consciousness. But while the ordinary mice did not recover, the mole rats could survive in a state of suspended animation for more than 18 minutes.
Although humans, such as free divers, can train themselves not to breathe for more than ten minutes, they only manage to do this by effectively bolstering their oxygen levels beforehand.
“If you throw an ordinary person into 0%, it would be mere seconds or minutes,” said Jane Reznick, Park’s co-author, based at the Max Delbrück Center of Molecular Medicine in Berlin.
Grant McClelland, a biologist at McMaster University, Hamilton, who was not involved in the work, described the findings as extraordinary. “I wouldn’t have predicted this ability for any mammal,” he said.
As oxygen levels dropped, the animals stopped moving, their beady eyes shut and their pulse and breathing dramatically slowed. Most curiously, though, metabolic tests revealed a sudden spike in the levels of fructose in their blood.
“We were very surprised by this finding,” said Reznick.
The team discovered that instead of burning glucose to produce energy, the mole rats had switched to a fructose-based metabolic system, something only previously seen in plants.
In aerobic metabolism, which the body normally relies on, the mitochondria (the cell’s batteries) use broken-down glucose and oxygen to produce a molecule called ATP, which biologists call the cell’s energy currency. When oxygen is in short supply, the body switches to anaerobic metabolism, where glucose is converted to ATP without oxygen. However, this conversion is about twenty times less efficient, and only ever serves as an emergency stop-gap because the production of lactic acid has an inhibitory effect on the process, causing the metabolism to grind to a halt.
When mole rats switched to anaerobic metabolism, the scientists discovered, they started using fructose instead of glucose to make energy – and while this was still inefficient, energy production was steady.
“It’s a little amount of energy, but a steady amount, that can keep it going,” said Reznick.
Understanding how the animals switch to an alternative metabolic pathway could lead to treatments for patients suffering crises of oxygen deprivation, as in heart attacks and strokes, the scientists said. They are now investigating whether human cells might have a dormant ability to do the same thing.
Naked mole rats have fascinated scientists for decades. They can live more than 30 years, are cold-blooded, have a social hierarchy comparable to bees or ants, can run backwards and forward with equal ease, eat their own poo, can move their teeth individually like chopsticks and are one of the strangest looking creatures on the planet.
So how does the latest finding rank among their odd social and physical traits?
“Pretty highly,” says McClelland. “I’d say joint top with resistance to cancer.”