Gophers are cousins of squirrels, which live on the ground in burrows and not in trees. Also related to groundhogs and prairie dogs, but smaller, ground squirrels are used in animal physiology to study the mechanisms of hibernation.
These rodents, like bears, stop eating during the winter and survive until spring thanks to the fat reserves they store during the summer months.
This type of prolonged fasting and inactivity should significantly reduce muscle mass and function in these hibernating animals, but they do not suffer this fate. How they avoid it, however, remained a mystery., explains a press release published by UdeM.
This was before Matthew Regan’s work on the striped ground squirrel (Ictidomys tridecemlineatus) that populates the Prairie provinces and some US states.
His study, published in the journal ScienceHave (New window)Have (in English), confirms the theory of the recycling of urea nitrogen emitted in the 1980s and it could have repercussions on the lives of astronauts in space.
According to this theory, hibernators exploit a metabolic trick in their gut microbiota to recycle nitrogen present in urea, a waste product usually excreted as urine, and use it to make new tissue proteins., notes the press release.
Matthew Regan’s experiments were conducted on ground squirrels with and without gut microbiota at three times of the year:
- in summer, when they were active and not hibernating;
- at the beginning of winter, in hibernation for a month, when they were fasting;
- at the end of winter, when they had been fasting and hibernating for four months.
Essentially, the study results show that ground squirrels with an intact gut microbiota (composed of 100 trillion bacteria) scavenge nitrogen from urea during hibernation.
Importantly, squirrels with depleted gut microbiota showed no signs of urea nitrogen scavenging, […], confirming that this process depends entirely on the ability of gut bacteria to degrade urea, which squirrels themselves cannot do., says the researcher.
The work also found that the incorporation of urea nitrogen into squirrel tissue proteins is highest in late winter, suggesting that urea nitrogen recovery becomes more active as the hibernation season progresses.
In addition, the bacteria in the intestines themselves use urea nitrogen to make new proteins, which is useful to them, since they, like their host, are in hibernation conditions.
Thus, the squirrel and its bacteria both benefit from the scavenging of urea nitrogen, making this process a true symbiosis., continues the press release.
This reality means that squirrels come out of hibernation in the spring in good shape, ready for the breeding season.
” It is a period of intense physical activity for both males and females […]. Tissue function, particularly that of muscle tissue, is therefore very important for the success of the mating season. »
Theoretically, according to Matthew Regan, confirming the urea nitrogen recycling theory could help astronauts
to minimize their muscle loss caused by the suppression of protein synthesis induced by microgravity and which they are currently trying to counter with intensive exercise.
If a way is found to increase astronauts’ muscle protein synthesis processes using nitrogen scavenging from urea, their muscle condition could be maintained during long deep space journeys in spaceships too small for regular exercise equipment, explains the press release.
Since we know which muscle proteins disappear during spaceflight, we can compare these proteins with those that are boosted by urea nitrogen recovery during hibernation.
Although theoretically possible […] a lot of additional work is needed to transpose this mechanism […] to the human, adds Mr. Regan. The researcher is nevertheless encouraged by the results of another study dating from the early 1990s which showed that humans are able to recycle small amounts of urea nitrogen by this same process.
This suggests that the necessary mechanism is in place. You just have to optimize it, concludes the biologist, who is continuing his work thanks to a grant from the Canadian Space Agency.
In addition to implications for space travel and the health of astronauts, this discovery could have implications on Earth for hundreds of millions of people who suffer from wasted muscle mass due to undernourishment. or the aging process.