Morphing red blood cells help bats hibernate – and we could do it too

Bats modify their red blood cells to become thicker and more rigid when they hibernate – and if we can figure out how, people might one day be able to copy the process for medical treatments or long-distance space travel.

Animals hibernate to conserve energy during cold weather or when food becomes scarce, slowing their heart rate and dropping their body temperature to as low as 5°C (41°F) to enter a state known as torpor. This is only survivable if their blood continues to flow efficiently and supply oxygen to the body, but until now scientists haven’t fully understood how this happens.

We already know that red blood cells change shape to fit different pressures and blood vessel sizes, so Gerald Kerth at the University of Greifswald in Germany and his colleagues wondered if the cells of hibernating bats might morph to keep blood flowing in the cold.

To investigate, the team analysed hundreds of thousands of red blood cells from common noctule bats (Nyctalus noctula), which hibernate, and Egyptian fruit bats (Rousettus aegyptiacus), which don’t hibernate, along with ones from people.

The researchers found that, for all three species, red blood cells became less elastic and more viscous as temperatures dropped from 37°C to 23°C (99°F to 73°F). But when they cooled the cells even further to 10°C (50°F), the bat cells continued this metamorphosis, whereas the human cells did not.

Indeed, the bat cells – even those of non-hibernating bats, which probably maintained the evolutionary capacity – continued to become thick, stiff and functional even at very low temperatures. This change might be slowing down the cells as they pass through capillaries in the muscles and lungs, making them highly efficient at exchanging gases, like oxygen, throughout the body.

“It’s like how when you take your time at the supermarket instead of being rushed, you can really fill up your basket,” says Kerth. Exactly how this structural change happens is still unclear, but the team speculates that the mechanical properties of the bat red blood cell membranes play a key role.

The findings suggest that drugs could one day induce human red blood cell membranes to mimic the way the bat membranes react to the cold, says Kerth. Surgeons already use body cooling during certain procedures to slow down metabolism, which can help prevent organ damage in people experiencing heart attacks, organ transplants or major brain surgery. Being able to prolong that cooling time, or to drop the temperature even lower, could increase those benefits, says team member Carsten Scholz, also at the University of Greifswald.

In the more distant future, hibernation could also allow for efficient long-distance space travel requiring minimal food and other resources while preserving mental health during the journey. “There are benefits of putting humans at low temperature during interstellar flight,” says Kerth. “We’re not saying this is going to happen in the next three years. But it’s really a first step.”

The work shows that learning about how other mammals adapt to extreme environments can benefit humans, says Angelo D’Alessandro at the University of Colorado Anschutz. “Nature is full of yet-to-be-disclosed secrets that can teach us how to overcome present and future medical and technological challenges.”