Grizzly bear genes change expression in hibernation

Research could lead to findings of new treatments for atrophy



Heiko Jansen, integrative neuroscience and physiology professor, discusses his knowledge and research on bear hibernation on Monday in the Veterinary and Biomedical Research Building.

CHERYL AARNIO, Evergreen reporter

WSU researchers have found that grizzly bear’s genes change more than genes in other animals during hibernation. These findings may lead to better treatments for diabetes and muscle atrophy in humans.

Heiko Jansen, professor in integrative physiology and neuroscience, said thousands of genes are expressed differently in bears both before and during hibernation than at other times of the year.

Joanna Kelley, associate professor of biological sciences, said researchers looked at the fat, muscle and liver tissues of grizzly bears.

Researchers were surprised that hibernation has thousands of genes that are changing, even within a single tissue, Jansen said. Most changes occurred in fat tissue.

Kelley said gene expression is like a light dimmer switch. The dimmer switch can be increased, so there is more light, similar to how gene expression can be increased.

Some of the changes occurring in the bears are in the insulin pathway, which is the pathway the body uses to take up glucose, Jansen said.

Bears create the same amount of insulin during hibernation as they do when they are active. However, there is a decrease in the amount of insulin receptor expression, Jansen said. The tissues are not taking in as much insulin during hibernation. Bears develop insulin resistance, similar to people who are diabetic.

“What bears can do every year is they can turn that insulin resistance off and become insulin sensitive again,” he said. “If we could learn what the secret to that switching is, we might be able to have novel treatments for human diabetes be developed.”

While thousands of genes in bears change expression, Jansen said that in other studies done with primates and rodents, gene expression during hibernation changed in a few hundred genes.

Kelley said this difference may be because bears need to do things differently than other animals because of body temperature differences. During hibernation, the body temperature of small hibernating animals is around 4 to 10 degrees Celsius while bears are around 32 degrees Celsius during hibernation.

She said this may mean that the findings from bears might be able to be more easily translated to humans because bear’s temperatures are closer to human’s temperatures.

Jansen said researchers also think that insulin resistance helps decrease the amount of energy that bears need to survive during hibernation.

The bear’s tissues are taking in less glucose, so there is less energy available, leading to a decrease in the bear’s metabolism, he said.

Jansen said that during hibernation, bears also do not lose bone mass even though they sleep for about 98 percent of the day. Bear’s muscles do not atrophy during hibernation unlike human muscle does during starvation.

If researchers can figure out what cell processes prevent muscle atrophy in bears, scientists could develop new treatments for human muscle atrophy, Kelley said.

To do this study, researchers took RNA from the tissues and sequenced the RNA fragments. Through that sequence, researchers could tell how much of a gene was expressed, Jansen said.

A segment of DNA can be turned into RNA, Kelley said. RNA is the intermediate step between DNA and proteins.

Researchers mapped the grizzly bear RNA to the relevant sequences of the brown bear genome, Kelley said.

They did this because a grizzly bear is a North American brown bear, Jansen said.

Researchers will look at the effects of certain genes in cell culture to determine more about insulin sensitivity, Jansen said.

“There’s so much going on, and we’re just scratching the surface. I think now the challenge is to actually test what we think the role of some of these things is,” he said.