Study: Oxygen-Deprived Naked Mole-Rats Turn into ‘Plants’
Deprived of oxygen, African naked mole-rats ( Heterocephalus glaber ) can survive by metabolizing a type of sugar called fructose just as plants do, a new study says.
Prof. Gary Lewin holding a naked mole-rat ( Heterocephalus glaber ). Image credit: Roland Gockel, MDC.
The naked mole-rat is a nearly hairless and nearly sightless burrowing rodent found throughout most of Somalia, central Ethiopia, Djibouti, and much of northern and eastern Kenya.
The species lives in large colonies, which vary in number from 75 to 300 individuals, deep underground in hypoxic conditions.
The colonies are extended family groups, with overlapping generations. Reproduction is restricted to a single reproductive female (the queen), and at most three breeding males.
Adults are 3-4 inches (7-10 cm) long and weigh 30-35 grams. The queen and the breeding males are the largest individuals in the colony.
Naked mole-rats hold the record for the longest living rodent, living nearly 9 times longer than other species. They have been known to reach ages of 30 years. In captivity, they can live up to 28 years.
They feed on geophytic plants such as roots, bulbs, and tubers which are accessible underground. The foods they prefer are sporadically spread out so they travel great distances to get food.
“Naked mole-rats can dig tunnel systems spanning up to 12 miles (20 km) through the East African semi-desert. Before they finally reach the roots and storage tubers of desert plants, the diggers may come to a point of absolute exhaustion and have no oxygen left,” said lead co-author Professor Gary Lewin, a researcher at the Max Delbrück Center for Molecular Medicine in Berlin, Germany.
In humans, lab mice, and all other known mammals, when brain cells are starved of oxygen they run out of energy and begin to die.
But naked mole-rats have a backup: their brain cells start burning fructose, which produces energy anaerobically through a metabolic pathway that is only used by plants.
“This is just the latest remarkable discovery about the naked mole-rat — a cold-blooded mammal that lives decades longer than other rodents, rarely gets cancer, and doesn’t feel many types of pain,” said lead co-author Professor Thomas Park, of the University of Illinois at Chicago.
In the study, the researchers exposed naked mole-rats to low oxygen conditions in the lab and found that they released large amounts of fructose into the bloodstream. The fructose was transported into brain cells by molecular fructose pumps that in all other mammals are found only on cells of the intestine.
“Under experimental conditions, naked mole-rats tolerate hours of extreme hypoxia and survive 18 minutes of total oxygen deprivation (anoxia) without apparent injury,” the authors explained.
“During anoxia, the naked mole-rat switches to anaerobic metabolism fueled by fructose, which is actively accumulated and metabolized to lactate in the brain.”
“At oxygen levels low enough to kill a human within minutes, naked mole-rats can survive for at least 5 hours,” Prof. Park added.
“They go into a state of suspended animation, reducing their movement and dramatically slowing their pulse and breathing rate to conserve energy. And they begin using fructose until oxygen is available again.”
“The naked mole-rat is the only known mammal to use suspended animation to survive oxygen deprivation.”
The team also showed that naked mole-rats are protected from another deadly aspect of low oxygen — a buildup of fluid in the lungs called pulmonary edema that afflicts mountain climbers at high altitude.
Understanding how this strange social rodent switches to fructose as a fuel could lead to treatments for patients suffering crises of oxygen deprivation, as in heart attacks and strokes.
“I’m curious whether human cells could also be pushed to switch pathways,” Prof. Lewin said.
“”Patients who suffer an infarction or stroke experience irreparable damage after just a few minutes of oxygen deprivation. Since mice and naked mole-rats are 94% identical on the genetic level: theoretically, very few changes might be needed to adopt this unusual metabolism.”
The findings were published in the April 21 issue of the journal Science .