Bears do it. So do groundhogs, squirrels, turtles and many other animals. Humans, however, can't hibernate — at least not right now.
But scientists exploring the genetic underpinnings of hibernation in animals think they may be able to unlock the same biological superpower in humans. That feat could transform medical care during both routine surgeries and dire medical emergencies when patients cannot immediately get access to lifesaving treatment. It could also make it possible for astronauts to snooze their way on long missions to Mars and other destinations in deep space.
The scientists think the ability to hibernate arose with the first ancestral mammal — a furry, tree-dwelling creature that lived 65 million years ago and eventually gave rise to most modern mammals, including humans. If they're right, the keys to hibernation may lie hidden in the human genome.
"It sounds like science fiction, but there is absolute biological truth to this, and we have used all sorts of comparative genomics and other tools to understand the universality," says Anne Yoder, a Duke University biologist who studies hibernation. "Pretty much everyone in the field agrees this is an ancestral mammalian capacity that most mammals have lost or just aren't using."
Hibernation is much more than extended sleep. It brings dramatic changes in metabolism, including a drop in body temperature and reductions in heart rate and breathing. Some warm-blooded animals spend weeks during which their body temperature falls from around 37 degrees Celsius to as low as 3 degrees Celsius, their hearts beat just a few times a minute and the body's energy consumption plummets.
Scientists are especially interested in the mechanisms that allow hibernating animals to return to full activity shortly after waking and avoid the health problems that affect humans after a few weeks in bed. These include bone loss, cardiovascular problems and muscle wasting.
"The applications we're looking at come out of our understanding of what these animals have to do to survive hibernation throughout the year," says Ashley Zhender, CEO of Fauna Bio, a San Francisco-based startup that is working to develop drugs for putting humans into hibernation.
Since at least 2002, emergency room doctors have been tapping in to the protective power of hibernation by using ice packs and cooling blankets to temporarily lower the body temperature of patients who are critically ill as a result of heart attack, brain injury, stroke or shock. Lowering body temperature by just a few degrees Celsius can protect the brain in particular by slowing metabolism, reducing swelling and delaying brain cell death that might normally occur due to lack of blood flow.
But the goal would be to replace this brute-force cooling technique — which can cause blood clotting problems and interfere with immune responses — with a process that works "naturally, safely, reversibly," says Hannah Carey, a professor of comparative biosciences at the University of Wisconsin-Madison School of Veterinary Medicine. Her lab is working with Fauna Bio on sharing hibernation data as part of a broader collaboration between the privately funded startup and the hibernation science community.
If such research succeeds, Fauna Bio hopes to replace the ice packs with a drug that can put people into hibernation by directly lowering their metabolism. A gentler cooling of the body would naturally follow as a result.
Decoding hibernation's past for the future
To create that hibernation wonder drug, researchers must first discover which groups of genes are activated during the hibernation process. That is why Fauna Bio is reaching out to many independent hibernation research groups in order to combine collections of biological tissue from different hibernator animals with new databases of sequenced genomes.
For example, Katie Grebek, cofounder and CSO of Fauna Bio, has developed a genome sequencing analysis of the 13-lined ground squirrel genome. Such ground squirrels are generally far easier to study than other hibernator animals such as endangered lemurs and potentially dangerous bears — although some stubborn hibernation researchers have been studying those animals too.
All those different animals don't necessarily have special genes unique to each species, says Will Israelsen, a postdoctoral fellow in biochemistry at the University of Texas Southwestern Medical Center in Dallas, Texas, who studies hibernation in jumping mice. Instead, hibernators probably have all the same hibernation-related genes but each species use them slightly differently. "If we can figure out how they regulate their biology, we'll be able to manipulate that in people for the benefit of medicine," Israelsen says.
Of course, medical benefits on Earth could also translate into medical benefits in space. SpaceWorks, an Atlanta-based aerospace engineering firm, is using NASA funding to explore how hibernation could protect astronauts from radiation damage, bone and muscle loss and other health issues during six-month space missions to Mars. The company is putting together a tech manual for how to put future astronauts into hibernation based on current ER medical procedures.
Even modern medicine's "targeted temperature management" approach that falls short of full hibernation could still protect astronauts and make future space missions both more affordable and feasible, says Doug Talk, an obstetrician and lead medical consultant for SpaceWorks Enterprises. Putting most of the crew into a low-metabolism state on shifts could eliminate much of the spacecraft mass normally reserved for storing food supplies or having a larger living space.
Such a spacecraft could even get away with less radiation shielding by having just enough to protect the crew's hibernation compartment. All those savings in spacecraft mass make a huge difference at a time when it still can cost about $10,000 per pound to launch anything into space. "It's a medical solution to an engineering problem," Talk says.
The true awakening of hibernation powers in humans still relies upon the ancestor mammal theory being proven correct. But if hibernating astronauts someday wake up to find themselves ready to enter Mars orbit, they can give thanks to a biological superpower that was millions of years in the making.
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