The researchers observed two differences that support this microbial path. “We believe we’re seeing the isotope-labeled nitrogen molecules go from the host to the microbiome, then converted to usable molecules by the microbes before coming back to the host again, essentially being ‘recycled’ in the hibernating animal.”
She is also a scientist in Integrative Biology and the university’s Nuclear Magnetic Resonance Facility. “We followed that nitrogen to (the) livers (of the squirrels), primarily - where it is used to make many proteins - and some to muscles,” says study co-investigator Fariba Assadi-Porter, an UW–Madison emeritus biochemist who specializes in tracking the isotopes. As predicted, isotope-containing nitrogen was released by some of the gut microbes that degraded the injected urea. Some of the squirrels had also been treated with antibiotics to kill off the majority of the microbes in their intestines. They injected urea made with trackable isotopes of carbon and nitrogen into the blood of squirrels at three stages - during the active days of summer, early in winter hibernation and late in winter. But the researchers wanted to see if some of that urea nitrogen freed up by the microbes was also being incorporated into the squirrels’ bodies. The researchers knew that urea that moved into the squirrels’ digestive tract could be broken down by some gut microbes, which also need nitrogen for their own proteins. One source of nitrogen, a vital building block for amino acids and proteins, accumulates in the bodies of all animals (including humans) as urea, a component of urine. “Without any dietary protein coming in, hibernators need another way to get what their muscles need.” “The longer any animal doesn’t exercise, bones and muscles start 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 new study, published today (Jan. The discovery could help people with muscle-wasting disorders and even astronauts on extended space voyages.
A new study from the University of Wisconsin–Madison shows that hibernating ground squirrels get help from microbes in their guts. To get through a long winter without food, hibernating animals - like the 13-lined ground squirrel - can slow their metabolism by as much as 99 percent, but they still need important nutrients like proteins to maintain muscles while they hibernate. Thirteen-lined ground squirrels curled up for seasonal hibernation can slow their metabolic rates to as little as 1 percent of their waking activity.
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