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HIBERNATING ANIMALS NEED MICROBES

THROUGH WINTER TO SURVIVE

Microbes help hibernating

animals, recycle nutrients and
maintain muscle through winter.
Discovery may help people

with muscle wasting disorders
and astronauts for their space
voyages.
Thirteen-lined ground squirrels curled up for seasonal hibernation can slow their metabolic
rates to as little as 1 percent of their waking activity. Credit: Photo courtesy Rob Streiffer

To get through a long muscles need.” microbes that degraded researchers sequenced Putting space travelers
winter without food, hiber- the injected urea. the genomes of microbes into a hibernation-like
nating animals — like the One source of nitrogen, found in the squirrels’ guts, state means they wouldn’t
13-lined ground squirrel — a vital building block for “We followed that nitro- they found that as winter need to take as much food,
can slow their metabolism amino acids and proteins, gen to (the) livers (of the hibernation dragged on water, and oxygen, and
by as much as 99 percent, accumulates in the bodies squirrels), primarily — where there was an increase in would produce less waste
but they still need impor- of all animals (including it is used to make many the presence of genes and carbon dioxide, saving
tant nutrients like proteins humans) as urea, a compo- proteins — and some to related to production of an vast amounts of weight
to maintain muscles while nent of urine. The research- muscles,” says study co-in- enzyme called urease. and fuel.
they hibernate. A new ers knew that urea that vestigator Fariba Assa-
study from the University of moved into the squirrels’ di-Porter, an UW–Madison “Urease is not made by an-
Wisconsin–Madison shows digestive tract could be emeritus biochemist who imals. Only microbes that “This process could the-
that hibernating ground broken down by some gut specializes in tracking the express urease are able oretically reduce rates of
squirrels get help from microbes, which also need isotopes. She is also a sci- to split the urea molecule muscle loss in space, where
microbes in their guts. nitrogen for their own pro- entist in Integrative Biology and release its nitrogen,” microgravity exposure
teins. But the researchers and the university’s Nuclear says Carey, whose work is invariably leads to muscle
The discovery could help wanted to see if some of Magnetic Resonance supported by the National atrophy,” says Matthew
people with muscle-wast- that urea nitrogen freed up Facility. “We believe we’re Science Foundation. “As Regan, a study co-author
ing disorders and even by the microbes was also seeing the isotope-labeled long as the right microbes and former UW–Madison
astronauts on extended being incorporated into the nitrogen molecules go from postdoctoral researcher
space voyages. squirrels’ bodies. the host to the microbiome, are present, it’s a trans- who is now a professor of
then converted to usable action between them and animal physiology at the
“The longer any animal They injected urea made molecules by the microbes the host — each get some University of Montreal.
doesn’t exercise, bones with trackable isotopes of before coming back to of the nitrogen released to “And because characteris-
and muscles start to carbon and nitrogen into the host again, essential- tide them over until hiber- tics of hibernation beyond
atrophy and lose mass the blood of squirrels at ly being ‘recycled’ in the nation ends.” this gut microbe-depend-
and function,” says Han- three stages — during the hibernating animal.” ent process confer protec-
nah Carey, an emeritus active days of summer, Describing the keys to tion against other hazards
professor in the UW–Mad- early in winter hibernation, The researchers ob- survival over the duration
ison School of Veterinary and late in winter. Some of served two differences of hibernation could help of space flight such as
Medicine and co-author of the squirrels had also been that support this microbial people on low-nitrogen ionizing radiation, it is
the new study, published treated with antibiotics to path. The squirrels whose diets or with disorders that theoretically possible that,
on January 27, 2022, in the kill off the majority of the gut microbes were largely cause muscles to atrophy. if translated to humans, hi-
journal Science. “Without microbes in their intestines. depleted by antibiotics had It could also make it pos- bernation-like states could
any dietary protein coming As predicted, isotope-con- far less of the trackable sible for humans to make solve numerous challeng-
in, hibernators need an- taining nitrogen was re- nitrogen in their liver and lengthy trips to distant es of human spaceflight
other way to get what their leased by some of the gut muscles. And when the planets. simultaneously.”