For its next giant leap forward, NASA plans to send astronauts to Mars by the 2030s. The 21-month trip presents unique challenges, particularly keeping people healthy during such a long space voyage. But what once seemed like an impossible solution is now gathering momentum: Hibernation.
In winter, many mammals enter a state of torpor, dropping their body temperature and slowing down their metabolism and brain activity to save energy. However, people can’t hibernate for a few reasons: Our bodies can’t store enough fat without harming ourselves, function at such low energy and brain activity levels, or survive a massive drop in body temperature. (Read about surprising hibernators in nature.)
Gerald Kerth, a zoologist at the University of Greifswald in Germany, studies hibernation in bats, which are smaller and easier to research than, say, brown bears.
In new laboratory experiments, Kerth and colleagues found major differences in how red blood cells in bats and humans behave when it’s cold: Namely, the bat cells change dramatically, allowing the animal’s body to optimize oxygen and survive cold weather.
The journey from Earth to Mars would take about 21 months.
Illustration by NASA/JPL-Caltech
“The dream of putting humans into a torpor state motivated us,” says Kerth, a co-author on the study, published recently in the journal Proceedings of the National Academy of Sciences .
“Now we have new and fascinating results, we want to understand more.”
Cellular superpowers In forests near the University of Greifswald lab, the scientists captured 35 wild noctule bats, which hibernate in large colonies. They collected the animals’ blood in the lab before releasing the noctule bats back to the forest. The team also took blood from Egyptian fruit bats living at the Friedrich Loeffler Institute, a nearby animal-disease research center. Lastly, they sourced blood from a human blood registry.
Altogether, the study authors amassed more than half a million red blood cells between the three species.
They compared human and bat cells with specialized computer software that analyzes cells as they’re stretched and squeezed by an external force.
“To my knowledge there’s never been such a detailed comparison between human and bat red blood cells,” says Kerth.
Noctule bats, widespread throughout Europe, Asia, and North Africa, hibernate during winter, allowing the mammals to survive temperatures as low as 19 degrees Fahrenheit.
The team observed how red blood cells of all three species reacted to three temperatures: 98.6 degrees Fahrenheit, roughly the core body temperature of humans and both bat species; 73 degrees Fahrenheit, or indoor room temperature; and 50 degrees Fahrenheit, the temperature at which wild noctule bats begin to hibernate.
As it got colder, both bat and human red blood cells became thicker and stiffer, but only bat red blood cells become significantly thicker relative to their stiffness. The colder it became, there was a greater ratio of thickness to stiffness in bat red blood cells. In contrast, the ratio of thickness to stiffness in human red blood cells stayed the same. (Read about bats’ disease-defying superpowers.)
The study authors hypothesize these tougher bat cells provide a big benefit: By staying in the lung capillaries and muscles for longer at low temperatures, the modified cells may boost oxygen uptake and distribution throughout the body.
Kerth adds that the Egyptian fruit bats may have retained their cell adaptation from an ancestor, even though they no longer use it to hibernate.
Challenges persist If scientists could change the human red blood cell membranes to mimic bats, it could bring us closer to human hibernation.
The new “study is one of many small pieces of the puzzle on the way to torpor in humans,” says Marcus Krüger, a molecular biologist researching space medicine at the Otto von Guericke University in Germany who wasn’t involved in the study.
“But many important questions remain unanswered, especially how to induce hibernation in humans. Is this something we could do through fat accumulation, food deprivation, pharmacological support?”
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