Microbes help hibernating animals recycle nutrients and maintain muscle during the winter

To survive a long winter without food, hibernating animals (such as 13 ground squirrels) can slow down metabolism by as much as 99%, but important nutrients such as proteins to maintain muscle during hibernation. Is required. According to a new study at the University of Wisconsin-Madison, hibernating ground squirrels are assisted by microbes in the gut.

This discovery may be useful for long-term space voyages for people with muscle wasting disorders, and even astronauts.

“When an animal spends less time exercising, bones and muscles begin to atrophy and lose mass and function,” said Hannah Carrie, Professor Emeritus of the UW-Madison School of Veterinary Medicine and co-author of the new study. Announced today. (January 27) Journal Science. “If you don’t get dietary protein, resting people need another way to get what their muscles need.”

One of the key components of amino acids and proteins, the source of nitrogen, accumulates in the body of all animals (including humans) as urea, a component of urine. Researchers knew that urea that had migrated to the digestive tract of squirrels could be broken down by gut bacteria. Gut bacteria also need nitrogen for their proteins. However, researchers wanted to see if some of the urea nitrogen released by the microorganisms was also incorporated into the squirrel’s body.

They injected urea, made of traceable carbon and nitrogen isotopes, into the blood of squirrels in three stages: active summer days, early hibernation, and late winter. Some squirrels were treated with antibiotics to kill most of the microbes in the intestines. As expected, the isotope-containing nitrogen was released by some of the intestinal bacteria that decompose the infused urea.

“We tracked that nitrogen to the liver (of squirrels), primarily to the liver (used to make many proteins), and some to muscle,” said co-researcher Fariba Assadi. Porter, UW-Madison Honorary Biochemist says. Specializes in isotope tracking. She is also a scientist at the Integrated Biology and University Nuclear Magnetic Resonance Facility. “Seeing isotope-labeled nitrogen molecules move from the host to the microbial flora, converted by microorganisms into usable molecules and then returned to the host, essentially” recycled “in hibernating animals. We believe that there is. “

Researchers have observed two differences that support this microbial pathway. Squirrels, whose gut bacteria were largely depleted by antibiotics, had much less traceable nitrogen in the liver and muscles. And when researchers sequenced the genomes of microorganisms found in the intestines of squirrels, they found that as hibernation prolonged, the presence of genes involved in the production of an enzyme called urease increased.

“Urease is not made by animals. Only microorganisms that express urease can break down urea molecules and release their nitrogen,” Carrie, a researcher backed by the National Science Foundation. Says. “As long as the right microorganisms are present, it is a transaction between them and the host. Until the end of hibernation, each releases some of the nitrogen and overcomes them.”

Explaining the key to survival during hibernation can help people on a low nitrogen diet or those with disabilities that cause muscle atrophy. It may also allow humans to make long journeys to distant planets.

Putting space travelers into a hibernating state saves them a lot of food, water, and oxygen, produces less waste and carbon dioxide, and saves a lot of weight and fuel. Means to do.

“This process can theoretically reduce the rate of muscle loss in space, where exposure to microgravity always leads to muscle atrophy,” said the study’s co-author and now a professor of animal physiology at the university. Matthew Regan, a former postdoctoral fellow at UW-Madison, said. Of Montreal. “And this characteristic of hibernation beyond microbial-dependent processes in the intestine provides protection against other dangers of space flight such as ionizing radiation, so when translated into humans, hibernation-like conditions are simultaneously human. It has the potential to solve many of the challenges of space flight. “

Chris Burn Card

This study was funded by the National Science Foundation (IOS-1558044 and DGE-1747503), the National Institutes of Health (P41GM136463, P41GM103399, P41RR002301 and T32GM008349), and the Canadian Council for Natural Science and Engineering Research.