These Arctic squirrels recycle muscle proteins to outlive winter

Arctic floor squirrels can survive harsh winters with below-freezing temps by holing up for some eight months with out consuming. These hibernators “stay on the most excessive fringe of existence, simply barely hovering over demise, and we don’t absolutely perceive how this works,” says Sarah Rice, a biochemist on the College of Alaska Fairbanks.

By snooping on what’s happening inside these squirrels, researchers now have a greater concept. Vitamins recycled from muscle breakdown assist the animals get by throughout hibernation, Rice and her colleagues report December 7 in Nature Metabolism. 

From autumn to spring, Arctic floor squirrels (Urocitellus parryii) hibernate in bouts of deep torpor. In a state akin to suspended animation, the squirrels breathe simply as soon as a minute, and their hearts beat 5 instances per minute. Each two or three weeks, the squirrels revive considerably for about 12 to 24 hours; their physique temperatures rise, and the animals shiver and sleep, however don’t eat, drink or defecate.

To watch the animals’ physique chemistry, “I labored in darkish, chilly chambers — completely quiet —surrounded by hibernating squirrels,” Rice says. Periodically, she rigorously withdrew blood from a tube inserted of their blood vessels.

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In the course of the squirrels’ torpor, Rice and her staff noticed a chemical sign displaying that skeletal muscle was slowly breaking down. That course of would launch compounds containing nitrogen, a component necessary for making the proteins present in muscle. However hibernators, together with these squirrels, are identified to hold on to muscle mass as they hibernate (SN: 2/17/11). So the scientists questioned whether or not the squirrels construct up new shops of protein throughout hibernation, and in that case, how.

Monitoring the move of nitrogen within the animals’ our bodies supplied clues. The researchers gave the critters a cocktail of chemical substances labeled with isotopes, types of components having completely different plenty. That exposed nitrogen going into amino acids, the constructing blocks of proteins, that fashioned within the animals’ muscle tissues and in addition within the lungs, kidneys and different areas of the physique throughout these transient durations between bouts of torpor.

By recycling vitamins from their muscle tissues, the squirrels maintain themselves and in addition keep away from a poisonous consequence of muscle breakdown, says staff member Kelly Drew, a neurochemist additionally on the College of Alaska Fairbanks. Throughout hibernation, nitrogen would in any other case find yourself in ammonia, which may construct as much as doubtlessly lethal ranges. As a substitute, the squirrels are capable of incorporate that nitrogen into new molecules, she says.

Different research have pointed to a task for the microbiome — the microbes residing on and inside animals — in recycling nitrogen whereas animals hibernate, says James Staples, an environmental physiologist at Western College in London, Canada, who was not a part of the work. Usually, the breakdown of proteins finally creates urea, a nitrogen-containing chemical that will get excreted. Microbes can scavenge that urea and launch its nitrogen again into the blood. However within the squirrels, the muscle is “being damaged down after which recycled straight again into these amino acids …  the intestine microbiome might not be as necessary as we thought it was once.”

Insights from hibernators may sometime assist people, says Sandy Martin, a biochemist on the College of Colorado College of Drugs in Aurora who was not concerned with the research. “Hibernators are so extraordinary” of their skills to face up to situations that people are extraordinarily delicate to, she says (SN:12/19/17). As an example, animals like these squirrels are much more immune to the hurt may result when organs don’t obtain needed blood move and oxygen. And harnessing hibernation-like approaches may show advantageous in circumstances the place a slower metabolism can be helpful, from routine surgical procedure to lengthy voyages in area, she says.

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