Do squirrels hibernate.1/15/2024 ![]() ![]() He did his experiments on squirrels with and without gut microbiomes at three times of the year: summer, when they were active and not hibernating early winter, when they were one month into fasting and hibernation and late winter, when they were four months into fasting and hibernation. “Essentially, seeing 13C and/or 15N in metabolites at these various steps indicated that they originated from urea, and thus, that the hibernator was using urea nitrogen salvage,” said Regan. That process, they found, led from the initial transport of urea from the blood into the gut, to the breakdown of urea into its component parts by gut microbes, to the flow of substances – called metabolites – containing urea nitrogen back into the animal, and finally to the eventual appearance of this urea nitrogen in tissue protein. These labels allowed them to track the urea-sourced carbon and nitrogen through the different steps of the urea nitrogen salvage process. To do that, in their lab they injected their test squirrels’ blood with “double-labeled” urea, meaning the urea’s carbon atom was 13C instead of the usual 12C, and its nitrogen atoms were 15N instead of the usual 14N. In his study, Regan designed a series of techniques and experiments to investigate the major steps in the urea salvage process and provide evidence for whether or not they occur in the 13-lined ground squirrel when it hibernates. “If,” Regan continued, “there is an overlap between the proteins in spaceflight and the ones from hibernation, then it suggests this process may have benefits to muscle health during spaceflight.” He is now continuing his work through a Canadian Space Agency research grant at UdeM, where he last year took up a position as assistant professor of animal physiology in the Department of Biological Sciences. “Because we know which muscle proteins are suppressed during spaceflight, we can compare these proteins with those that are enhanced by urea nitrogen salvage during hibernation,” said Regan, who carried out this research while a postdoc at the University of Wisconsin-Madison. ![]() If a way could be found to augment the astronauts’ muscle protein synthesis processes using urea nitrogen salvage, they could be able to achieve better muscle health during long voyages into deep space in spacecraft too small for the usual exercise equipment, the argument goes. How could this discovery be of use in space? Theoretically, Regan posits, by helping astronauts minimize their own muscle-loss problems caused by microgravity-induced suppression of protein synthesis and which they now try to reduce by intensively exercising. The theory posits that hibernators harness a metabolic trick of their gut microbes to recycle the nitrogen present in urea, a waste compound that is usually excreted as urine, and use it to build new tissue proteins. By studying a variety called the 13-lined ground squirrel that is common in North America, Matthew Regan has confirmed a theory known as “urea nitrogen salvage” dating back to the 1980s. Now, in research published in Science, an Université de Montréal biologist has figured out why, and his findings could have implications for, of all things, the future of space travel. How they avoid it, however, has been a mystery. ![]() ![]() Usually, this sort of prolonged fasting and inactivity would significantly reduce the mass and function of muscle, but hibernators don’t suffer this fate. When bears and ground squirrels hibernate in winter, they stop eating, lasting until spring simply on the fat reserves they’ve stored up in their bodies. ![]()
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