Thirteen-lined ground squirrels huddled for seasonal hibernation can slow their metabolic rates to as low as 1 percent of their waking activity. Credit: Photo courtesy Rob Streiffer
To get through a long winter season without food, hibernating animals– like the 13-lined ground squirrel– can slow their metabolism by as much as 99 percent, however they still require important nutrients like proteins to keep muscles while they hibernate. A brand-new research study from the University of Wisconsin– Madison reveals that hibernating ground squirrels get help from microbes in their guts.
The discovery could help individuals with muscle-wasting conditions and even astronauts on prolonged area trips.
” The longer any animal does not exercise, bones and muscles begin to atrophy and lose mass and function,” says Hannah Carey, an emeritus professor in the UW– Madison School of Veterinary Medicine and co-author of the brand-new study, released on January 27, 2022, in the journal Science. “Without any dietary protein being available in, hibernators need another way to get what their muscles require.”
One source of nitrogen, an essential foundation for amino acids and proteins, accumulates in the bodies of all animals (including humans) as urea, a component of urine. The researchers understood that urea that moved into the squirrels digestion system could be broken down by some gut microbes, which likewise require nitrogen for their own proteins. The researchers wanted to see if some of that urea nitrogen freed up by the microbes was also being included into the squirrels bodies.
They injected urea made with trackable isotopes of carbon and nitrogen into the blood of squirrels at 3 stages– throughout the active days of summer, early in winter season hibernation, and late in winter season. A few of the squirrels had actually likewise been treated with antibiotics to exterminate the majority of the microorganisms in their intestinal tracts. As predicted, isotope-containing nitrogen was launched by a few of the gut microorganisms that deteriorated the injected urea.
” We followed that nitrogen to (the) livers (of the squirrels), mainly– where it is utilized to make lots of proteins– and some to muscles,” says research study co-investigator Fariba Assadi-Porter, an UW– Madison emeritus biochemist who concentrates on tracking the isotopes. She is likewise a researcher in Integrative Biology and the universitys Nuclear Magnetic Resonance Facility. “We think were seeing the isotope-labeled nitrogen particles go from the host to the microbiome, then converted to functional particles by the microbes prior to coming back to the host once again, basically being recycled in the hibernating animal.”
The researchers observed two differences that support this microbial path. The squirrels whose gut microbes were mostly diminished by prescription antibiotics had far less of the trackable nitrogen in their liver and muscles. And when the scientists sequenced the genomes of microbes discovered in the squirrels guts, they found that as winter season hibernation dragged on there was an increase in the presence of genes connected to production of an enzyme called urease.
” Urease is not made by animals. Only microbes that reveal urease have the ability to divide the urea particle and release its nitrogen,” says Carey, whose work is supported by the National Science Foundation. “As long as the ideal microbes are present, its a transaction between them and the host– each get some of the nitrogen launched to tide them over till hibernation ends.”
Describing the keys to survival over the duration of hibernation could assist individuals on low-nitrogen diets or with conditions that trigger muscles to atrophy. It might likewise make it possible for people to make prolonged journeys to far-off worlds.
Putting area tourists into a hibernation-like state suggests they would not need to take as much food, water, and oxygen, and would produce less waste and co2, conserving large amounts of weight and fuel.
” This procedure could theoretically lower rates of muscle loss in area, where microgravity direct exposure invariably results in muscle atrophy,” states Matthew Regan, a research study co-author and previous UW– Madison postdoctoral scientist who is now a professor of animal physiology at the University of Montreal. “And since characteristics of hibernation beyond this gut microbe-dependent process provide defense against other dangers of space flight such as ionizing radiation, it is theoretically possible that, if translated to humans, hibernation-like states might fix various obstacles of human spaceflight all at once.”
Reference: “Nitrogen recycling through gut symbionts increases in ground squirrels over the hibernation season” by Matthew D. Regan, Edna Chiang, Yunxi Liu, Marco Tonelli, Kristen M. Verdoorn, Sadie R. Gugel, Garret Suen, Hannah V. Carey and Fariba M. Assadi-Porter, 27 January 2022, Science.DOI: 10.1126/ science.abh2950.
This research was funded by grants from the National Science Foundation (IOS-1558044 and DGE-1747503), the National Institutes of Health (P41GM136463, P41RR002301, p41gm103399 and t32gm008349) and the Natural Sciences and Engineering Research Council of Canada.
The researchers understood that urea that moved into the squirrels digestive tract might be broken down by some gut microbes, which also require nitrogen for their own proteins. The researchers wanted to see if some of that urea nitrogen freed up by the microbes was also being included into the squirrels bodies.
They injected urea made with trackable isotopes of carbon and nitrogen into the blood of squirrels at 3 phases– throughout the active days of summertime, early in winter hibernation, and late in winter season.” We followed that nitrogen to (the) livers (of the squirrels), mainly– where it is utilized to make lots of proteins– and some to muscles,” says research study co-investigator Fariba Assadi-Porter, an UW– Madison emeritus biochemist who specializes in tracking the isotopes. The squirrels whose gut microorganisms were mainly depleted by prescription antibiotics had far less of the trackable nitrogen in their liver and muscles.