Squirrels Shed Light on Human Hibernation

Oct. 3, 2002 -- That haunting image from science fiction movies showing astronauts hibernating during long space voyages may not be as far-fetched as it seems.

We would be a bit closer if someone could figure out exactly how some other animal, say a ground squirrel, can put itself to sleep for the cold months of winter and then rouse itself in time for the first spring munchies.

No one is seriously working toward hibernating astronauts at the moment, because there's so much about it that we don't understand, but lots of scientists are taking a close look at ground squirrels, which may hold the key.

The 13-lined ground squirrel, the little critter seen around golf courses and lawns throughout Middle America, is on center stage in a number of laboratories because of its extraordinary ability to hibernate.

And because in some critical ways, it's a lot like us.

Super Squirrel

Where the research will lead is conjecture at this point, but it's quite possible that if we can figure out how the squirrel works its magic, we might be able to extend the shelf life of human organs during transplant procedures, and that alone would be a major breakthrough.

But that's not all.

"If we understood how these animals naturally undergo such extreme changes every year, like clockwork, we might be able to come up with therapies for humans and other animals that could help in trauma situations," says Hannah V. Carey, a professor of biosciences in the School of Veterinary Medicine at the University of Wisconsin, Madison. It might even help in controlling the bulging human waistline because "these animals are great examples of gaining weight, and losing weight, and gaining weight, and losing weight," she says.

All that interest is centered on a remarkable little critter that many consider a pest and often confuse with gophers. The 13-lined ground squirrel, so named because of 13 lines down it's back and sides, measures only about 6 inches long.

But each winter it survives for up to six months by lowering its heart and metabolic rates and reducing its body temperatures to just above freezing, which would be fatal to humans and nearly all other animals. Periodically, the squirrel rouses itself for reasons that are not clearly understood, and then returns to a state of torpor.

What the squirrel is doing, she says, is readjusting it's systems "to slow down the fire, slow down the metabolic burn, so it doesn't use as much energy."

It is one of the great physiological marvels of the natural world because the squirrel is able to protect and preserve its critical organs despite extreme biological insults over a period of several months.

Cool Organs

Carey believes the squirrel may hold the key to keeping vital human organs, like livers, viable for longer periods, thus greatly facilitating organ transplants. Currently, a human liver begins going downhill within a few hours after being extracted from a donor. What's amazing about the ground squirrel is it survives for months at body temperatures that are nearly identical to the near-freezing temperature at which human organs are kept during transplanting procedures.

Carey and a colleague, Jim Southard, a surgeon in the university's division of transplantation, have a room full of ground squirrels on the Wisconsin campus, and their research so far has had very promising results. The researchers harvested about 20 livers from hibernating squirrels to see how long the organs would remain viable while outside the animal.

Compared to that most ubiquitous of all lab animals, the rat, the squirrel is truly remarkable. A rat's liver is virtually useless after 24 hours to 48 hours, Carey says.

"But in the ground squirrel, we found no damage at 24 hours, no significant damage at 72 hours, and we went to 96 hours of cold storage and found no apparent damage," she says. "To remain viable for four days is just unheard of."

But how does it do it?

To help find an answer, the Wisconsin researchers have turned to a third collaborator, Sandy Martin of the University of Colorado's Health Sciences Center in Denver. Martin, a molecular biologist, is comparing the composition of livers extracted from squirrels while they were hibernating with livers taken during the summer.

Her goal is to find out what's different, or what changed, in the liver as the animal prepared for hibernation.Specifically, she's trying to identify the proteins in the liver's cells.

"It's the proteins that really are the machinery of how cells work," Carey says. Some proteins must be introduced or altered to prepare the organ for hibernation.

Understanding the Extreme

Other research suggests that those proteins are the work of genes that are remarkably similar to genes in nonhibernating mammals, including humans. Researchers at North Carolina State University in Raleigh have linked complex proteins called enzymes to two genes. One enzyme breaks up fatty acids and converts them into usable fats for fuel for the hibernating ground squirrels. The other enzyme helps conserve the squirrel's glucose.

That research team, led by Matthew T. Andrews, who is now at the University of Minnesota, is attempting to identify the enzymes that preserve the organs during the long slumber, and prepare the organs for the sudden jolt of coming out of hibernation and returning to normal functions and body temperatures.

"Physicians could use that knowledge to develop new strategies for prolonging the shelf life of human organs intended for transplants or for helping humans suffering from starvation, muscle atrophy, hypothermia and hypoxia," Andrews says.

Of course, shelf life is only part of the problem with organ transplants. The larger problem is a lack of donors. About 6,000 Americans die each year while waiting for a transplant, according to the National Institutes of Health.

But prolonging shelf life could help ensure that donated organs remain viable until they can be transplanted, and it may well be that the secrets to that process are contained in a furry little animal that burrows under ground and likes to dine on dandelion seeds and grasshoppers.

Andrews has suggested that if we can ever fully understand how the ground squirrel gets through life, we should be better equipped to adapt to extreme environmental changes, and possibly even go into hibernation during long journeys to other planets.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.