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Hibernating squirrels could open the doors to space for us

Staying in space for an extended period of time presents many challenges…and adorable rodents just might bring us the keys to some of them.

Hibernation is an unavoidable ritual for certain mammals; as winter approaches, they stock up on food and then go into hiding while waiting for the return of fine weather. Researchers have just discovered one of the keys to this instinctive behavior that has fascinated them for decades; a seemingly innocuous discovery, which could in fact have considerable repercussions on the side of… space exploration.

Because if you’ve ever watched even a single sci-fi series, you’ve probably seen humans doing something similar. Most commonly, this is a technology dubbed “cryo-sleep,” “hypersleep,” or one of many other variations. Like an animal in hibernation, a human in “hypersleep” can survive a very long time in a kind of artificial coma and resume a normal life afterwards.

For SF writers, it’s a fearsome script gadget which makes it possible to justify gigantic ellipses. But that does not prevent scientists who could not be more serious from thinking about still fictitious technology. And for good reason: the further humans venture into space, the longer the travel times will be, to the point of far exceeding human life expectancy. To prevent our civilization from finding itself in a dead end, we must therefore start developing these technologies now.

Spermophilus columbianus, a species of ground squirrel. © The Lilac Breasted Roller – WikiCommons

Hibernation, a fascinating mechanism

The concern is that the majority of the concepts in play are still pure fiction. To find a concrete starting point, American and Canadian researchers have focused on the natural mechanism that most resembles it, namely hibernation. Their favorite guinea pig: an adorable little ground squirrel called a ground squirrel (“who loves seeds” in Greek).

Like other hibernators, the ground squirrel enters a state of generalized torpor during the winter. His body temperature drops to levels that would be lethal to a human, and his metabolism shrinks to the bare minimum. The goal: to reduce its energy needs as much as possible to survive until spring.

It’s a technique that works extremely well, but we don’t know how. Because if a human tried to do the same, he would find himself faced with many health problems, such as marked muscular atrophy. But hibernators are able to preserve their muscle mass in order to wake up fresh as roaches after several months of inactivity.

Survival, a story of guts

How do they get there? Hannah V. Carey and Matthew Reagan, authors of the study, recall that this is a question on which researchers have broken their teeth for decades. But their team may be getting closer to the answer: They believe they might get a little help from the bacteria in their digestive system.

To reach this conclusion, they started from an already well-established observation: the digestive system of hibernators changes radically during the winter. “Dramatic changes in the structure and function of the gastrointestinal system occur at the onset of winter fasting”, they recall in their article. They therefore wondered if these changes were not a consequence, but rather the starting point of the hibernation process.

A really interesting start, but still far too vague. They needed a first link to attach the rest of the chain to, and unexpectedly, the researchers found it on the side of the cattle. The latter have indeed a formidable weapon to respond to the lack of protein: they use a process of recycling nitrogen, one of the fundamental bricks of many proteins.

One of the keys to the conquest of space could well be hidden at the level of the microbiota. © CDC – Unsplash

Recycle your own waste

This nitrogen, ruminants will seek it directly in urea – a compound present in urine, and which is one of the main waste products resulting from the degradation of proteins. Usually all of this material is lost during excretion. But in ruminants such as cows, there is a mechanism that allows nitrogen from urea to be recycled in the form of ammonia. This is then reused to form new proteins thanks to the bacteria present in their digestive system.

However, as specified above, the researchers suspect these same bacteria to have a link with the mechanisms of preservation of hibernators. So they wondered if this nitrogen recycling process could be one of the missing pieces of the puzzle.

To verify this, they injected a rather special solution into squirrels. This contained a slightly heavier isotope of nitrogen. The latter is used in the same way by the organism, but it is very slightly heavier; this allows it to track through the body. They were thus able to observe that this heavy nitrogen was used to make proteins before ending up in the form of urea… and that it was then recycled during hibernation, through the process described above.

A symbiosis that inspires researchers

This directly benefits the animal; it thus reconstitutes its stock of nitrogen and consequently of proteins, which allows it to get through the winter without sacrificing all of its muscle mass. But the researchers also highlighted a more unexpected point. The microbiota itself also reuses this nitrogen for its own survival, and can thus continue to provide this service to the organism that hosts it. It is therefore a real cooperation between the animal and its microbiota; we then speak of symbiosis.

The researchers conclude by explaining that this example of symbiosis has a certain clinical potential. It starts with public health; understanding how this recycling contributes to the preservation of muscles, and potentially the rest of the body, could provide therapeutic answers to the consequences of malnutrition or aging.

An interest in clinical medicine… and even in space

The team also considers that this work could benefit the aerospace industry of tomorrow. Indeed, it is common knowledge that the muscle mass of astronauts tends to melt in microgravity conditions. It is for this reason that they stick to a dense physical exercise program. But this is not enough; you only have to see the way astronauts stagger when they return to Earth to be convinced of this.

And it is for the moment only missions of a few months at most. To solve the problem within the framework of a journey of several years, it will therefore be necessary to develop complementary technologies. And a technology based on the microbiota of hibernators could well represent a lead of choice. Of course we are still very far away. But the team concludes their paper by citing work done in the 1990s, which shows that humans also recycle nitrogen through their microbiota – but in very small amounts. The machinery is in place”, they conclude. “All that remains is to optimize it..” If this work ends up leading to real measures against the effects of microgravity – or even laying the foundations for hypersleep technology, the aerospace industry will therefore owe a lot to these adorable rodents!

The text of the study is available here.

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