Hibernating for Deep Spaceflight with Ryan Sprenger

0:00Guys, am I right that we just did a whole show that answers the question, does a bear shit in space? yes we did and i'm just i'm just upset that i didn't come up with that right there just we got animals on earth that hibernate and if we're going to send people through space every sci-fi story is a hibernating crew and we finally found someone who's trying to solve that very problem yes yeah knowing that other mammals can do it and we're a mammal last i checked So we went there on StarTalk Special Edition coming up. Welcome to StarTalk, your place in the universe where science and pop culture collide.

0:47StarTalk begins right now. This is StarTalk Special Edition. And since it's Special Edition, you know my two co-hosts, Chuck Nice. Chuck, how you doing, man? Hey, Neil. I'm doing great, thanks. And not only, Chuck, we've got Gary O 'Reilly. All right, Gary, welcome back. Thank you. Always a pleasure. Today's topic is like, whoa, how come we didn't do this 10 years ago? We're going to talk about hibernation in space. Oh, don't sleep on this subject. Oh, came in early. I want me some hibernation stories here. So, Gary, set the scene here. What did you put together? We've all seen the sci-fi movies where the crew are in some kind of deep sleep.

1:31hurtling through deep space. But how is that going to be achieved? Turns out we actually may have to look to Mother Nature for our answer. Animals can hibernate for months at a time, from thin squirrels to big old bears. So if humans want to engage in interplanetary travel, they are most likely going to need to hibernate or enter a state of torpor. Can you get a non-hibernating animal, which is us humans, to hibernate. And for that, we are going to need an expert. Q, our guest, Ryan Sprenger, PhD, Senior Research Physiologist at Fauna Bio, a PhD in zoology with expertise in cardiopulmonary physiology.

2:18Also expertise in hibernation and extreme physiology, which I think is a vital component of his background and its effects on the cardiovascular system. FornaBio have been awarded a NASA grant through their NIAC program, which stands for NASA Innovative Advanced Concepts for a Study in Torpor in Animals for Space Health or STASH. Plus, the most important thing is Ryan is a startup fan, which makes him smart as well as cool. We love it. Ryan, welcome to StarTalk. Thank you so much for having me. I'm excited to be here. So what is torpor? That's a good question. What is torpor? So we define torpor in the field as a state of metabolic depression and body temperature depression.

3:08And so it's sort of this quiescent state where the body's been turned down. So depression in a biophysiological sense, not in a neurological sense. A little bit of a biophysiological sense in its root. but you also have a neurophysiological depression but not a depressive state as in an emotional that's all that's all i mean yes yes yeah yeah got it so so it's so a dialing down of the metabolism and the body temperature essentially the body pulling torpor so what's the difference between torpor and hibernation uh this is a this is a fun topic to to discuss at the hibernation conferences that we hold every four years but uh what the general field will say is hibernation is the season in which the animals will use torpor.

3:49And so torpor is the actual state in which the metabolism is low. Why do you have conferences only every four years? Are you hibernating in between? Yeah, yeah, precisely, precisely. Well, that's when good science gets done as well. Well, historically, it's taken longer to collect hibernation data because it's a seasonal event. Yeah, you only have a very limited window where you can study. Yeah. You can't go up to a bear in the summertime just like, hey man, you tired? Can you be tired? Mind you, you've got two hemispheres where winter is one time and in one and a different in another. So you might, I mean, it depends if you feel like picking up your bags and traveling.

4:32Yeah, well, actually, and that's why it was just this year we decided to shorten that as a community. We decided to shorten that conference because we're learning that hibernation is not just a cold season event. We're learning recently that warm animals will hibernate. Animals in warm climates will hibernate. They'll hibernate at warm temperatures. So we're learning that it's more widespread than we thought. Why do they do it? What is the purpose of hibernation for, like, if I'm a bear, right? We all think of hibernation. We automatically think of bears. So I use them as an example. Well, why not just be awake all year long and, you know, go get some food and or pack up on, you know, calories like some other animals do and then get through the lean time?

5:19What's the idea of, you know, dialing yourself down metabolically and taking a long nap? You mentioned it almost in your question. It costs a lot to do things is a really simple way of putting it. energetically energetically it costs a lot energetically to do i'm not thinking the bear has gotten these 20 in his wallet to get no no it's very costly to be a bear only you can prevent forest fires come on help a brother out

5:49yeah energetically it costs a lot and and so even if you wanted to pack on all that extra weight and try to make it through a period of what we like to term resource deprivation so this is a period where there's not as much water available, it's frozen or it's a drought. And there's not a lot of food available because of that reason. And so in these periods of resource deprivation, some mammals have decided over time to instead of increasing supply, they decrease demand. And that demand being your metabolism that they're turning down. Oh my, that scares me in a way just because I think about the climate and how it's changing.

6:26And when you talk about matters of deprivation, you know, or lack of resources, you know, we might find a time where maybe those bears won't hibernate because the water won't be frozen. And then we've encroached upon their land and they they're like, hey, you guys, you guys are supplying us with food. Like, cause you ever, you ever see the videos of them tearing open a car to get, to get to that picnic basket. You know, it's a little scary what you, when you describe hibernation that way for those reasons. Yeah, well, bears are very strong animals. That goes without saying. But yeah, climate change, actually, that's a big push in the field right now is to try to understand what climate change is going to do to hibernators, particularly the cold climate hibernators.

7:11Because again, we're seeing more and more warm climate hibernators. So we have an idea of what it might look like, but it is very different. So it's going to be a big change for a lot of these species. There has to be some positive benefit to hibernation. Otherwise, animals would have evolved not to do it. Most mammals don't do it. What are the benefits then to, I mean, apart from getting a good nap? Yeah, it would be the dream if you could. Yeah, the benefit as far as we can tell is these animals that use it are more resilient to periods in which there suddenly isn't availability of resources.

7:49Gotcha. And so a really great example of this actually is not in the Northern Hemisphere is where it's cold. It's the Southern Hemispheres in Australia where you have wildfire, big wildfires. And there's animals down there that after these periods of wildfire where there's now suddenly no food for a while, they'll go into torpor. And so these animals are more resilient now because they don't need that food and they can survive a little bit longer. They can just kind of stretch what resources they currently have in their body. Well, because cold-blooded animals barely eat anyway, right? I mean, we always show alligators as being voracious eaters, but I mean, we eat a lot because we have to maintain our body temperature apart from the air temperature surrounding us.

8:28If they are the air temperature, then their energy is for what? To run their brain. And if they want to just walk around a little bit. Exactly. So, yeah. And so you're exactly right. The cold-blooded animals, they don't eat a lot. They can go quite long periods. Alligators, I think, can go months to almost a year without eating. Yeah. Oh my God. And I've got a funny anecdote about that from my old advisor, but. There's nothing funny about a hungry alligator. I was about to say that. No, not at all. Not when you're around it, at least. Yeah. That's right. But yeah, they don't eat for long periods of time because they don't have to defend body temperature.

9:04So defending body temperature at a stable amount is very, it costs a lot of energy. So we're expending energy all the time just to keep our body temperature at 98.6 is what you're saying. Exactly. That's where all – so if you don't have that, I'll call it a problem. But if that's not necessary, then you're saving a lot of energy. You barely have to eat at all. You're running to stand still. You barely have to eat at all. Exactly. In fact, it's worse than that or better than that. You burn energy thermally just by maintaining your body temperature, but you also burn energy kinetically, right? by like moving against gravity or just moving at all.

9:43Okay. Consider how long it would take your body to burn the calories of a cupcake just by existing. You will easily burn the calories of a cupcake just by watching television. You can do that. Okay. Right. But then say, what do I have to do on a treadmill to burn the calories of a cupcake? It's like, I'm not doing that. Right. Yeah. That's damn near an hour running. Exactly. Exactly. Thermal energy is a huge consumer of energy relative to kinetic energy. But Ryan, get back to your answer there. If they're wildfires and they take out resources, you have to wait until the trees grow back and the bushes grow back.

10:27It seems to me that would require a much longer time than a typical hibernating bear for the resources to return if they have to recover from a wildfire yeah well i would describe it more of a strategy to stretch how long you can maintain in that area and so if you stay if you stay active anything else you've got days right if you stay torpid you've got months and they can stay in torpor i mean there's animals that again and these are in the northern hemispheres but there's animals that can stay torpid for nine months of the year oh and so it's it's quite a while and your your primary growth or your secondary growth, I should say, or your primary growth, sorry, your first shrubbery where you can start to get things to eat like insects and berries if they're coming up in those months.

11:11You could stretch yourself to get to those, I would say.

11:23Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son, Ernie, because we listen to StarTalk every night and support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

11:45Okay, so what does NASA want out of you here? And FaunaBio, is that a company you started? What is FaunaBio? Yeah, FaunaBio is not a company I started. It was started by three really intelligent ladies, Katie, Linda, and Ashley. I've never heard anyone say, my company was started by three stupid people. Okay, so. That's a good point. That's a good point. I just like to give them credit when it's due. They're really incredible, incredible human beings. The company is based on the premise that a lot, a lot of drug development could be benefited by looking at animals that have extreme physiology or rather looking at animals that are good at defending against diseases that humans are afflicted with naturally.

12:29And so one of the models that we use quite regularly is a hibernating species called a 13-line ground squirrel. And that species is fantastic against things like diabetes, ischemia reperfusion, for example. So this is after traumatic injury, loss of blood flow, loss of oxygen, you return that, you get tissue damage. Wait, you're saying the squirrel is resistant to diabetes? So at the beginning of the hibernation period, or before they start their hibernation season, they increase their body mass by over 100 % just adipose tissue. So let's say they weigh 100 grams, they'll go to 250 grams. They've added 150 grams of just fat.

13:06And they become completely insulin resistant during that period. And by the time the end of the hibernation season comes around, they reverse that insulin resistance and they're back to normal. Wow. It's a naturally reversible model of diabetes, essentially. That's insane. Yes. Yes. That's so, I mean, why isn't everybody studying? I mean, diabetes is a huge, huge problem in this country. Huge. So if we know we mammals are a branch of the tree of life, and so we have more in common with each other than either of us have with any other branch in the tree of life, why can't we just genetically steal these DNA secrets in these animals and then apply it to us for however we need.

13:51And is that what NASA is trying to get you to do for our future astronauts? Yes, yes. That is what fauna is trying to do using these extreme organisms. And hibernators aren't the only species that are extraordinary. There's a spiny mouse, for example, that has regenerative capabilities. So this is a mammal that can... Spiny mouse? Yes. Spiny mouse that has regenerative capabilities. What are the regenerative capabilities, you know, per se? Could we grow a tail or a leg, right? I don't know about a whole limb, but certainly tissue replacement. So neural tissue replacement, skin like normal tissue replacement, so skin.

14:23Is there not a chance for any mammal that hibernates for any length of time losing muscle density? This is another remarkable aspect of the hibernating species that have been studied to date. They don't. So, yeah, so this is incredible. And this is where NASA is interested. This is where we get into NASA, yeah. So if you break your arm, If you break your arm, your leg, you go into a cast for however many months that you have it on. You take it off. Your arms are different sizes. You've lost muscle mass. That's disuse atrophy is what it's called. I'm old enough to remember the old days where you were encouraged to not use the limb at all.

15:01There were no walking casts. There was no exercises you would do. And I had friends who broke limbs and they took off the cast. It was like the limbs of two different people on the same body. Yeah. Yeah. Yeah, and hibernators don't do that. It's incredible. Wow. Yeah. But you always see in the nature shows where the animal comes out of hibernation and then, sir, what's his name? I forget. And he's just like, and now the feverish search for food begins. Like, they immediately. How dare you forget Sir David Attenborough's name? That's his name, Sir David Attenborough. Yes, exactly. He's a Brit. We're allowed to forget a few.

15:43Yeah, yeah. Well, no, he's beloved everywhere. He's not even – like the whole world owns that guy. That's why I couldn't remember his name because everybody knows. So you're saying that the weight loss is not muscle density? Correct. So they put on fat, and then all they do is their body eats the fat. Yep. Ooh, because our body eats muscle. Muscle first. Yeah, our body eats muscle first. Ryan, why don't you fix us? Actually, we just, Fonda just signed a really awesome partnership with Eli Lilly trying to fix that. Yes, we're doing that. We're actively looking at that, actually. We're looking for new obesity targets to try to see how it is that we can change.

16:24We can say, have our metabolism say, yeah, we want to just consume adipose. We don't want to consume protein. We don't want to consume carbohydrates. You want to have your metabolism and eat it too. Exactly. Yeah, that's what we want to do. Ryan, in our research, we came across a nugget of information that is worrying and amazing in the same breath. How did we find out that hibernating animals have a level of protection from radiation? Yeah, this started in the early 50s. I think 51 was the first study that looked at irradiating hibernators. And so they basically gave them huge doses of gamma radiation.

17:05and what they learned was that these hibernating species survived the radiation far better than a rat, for example, and their protection against the radiation increased if they were in torpor, and so these species are uniquely protected against radiation. The study started in the early 50s. We still have not a great idea of why. It's not because the fat absorbs the gamma rays, is it no we think it has to do with reactive oxygen species please explain that what that is yeah reactive oxygen species are well i guess i'm not a chemist i couldn't tell you exactly what a reactive oxygen species is but it's a product of your metabolism and so these these reactive oxygen species they as as the term suggests they react with oxygen they cause all sorts of bad stuff to happen in your tissue damage tissue damage essentially and so when when radiation comes in and hits a hydrogen so like a proton comes in and gets a hydrogen or uh interacts with oxygen, it creates these reactive oxygen species that damage your body.

18:05And so if you've ever been to the store and everybody, the craze right now is antioxidants. If you've seen that in the store in your food, that's, that's, they're designed to counteract reactive oxygen species. I'm not anti anything, by the way. That's fair. And so that's where we think a lot of the protection is coming from is because these animals are really good at natural antioxidants. So they have them during the torpid state, But also with the reduction of metabolism, you get a reduction of the mitochondrial function, you get less oxygen in these tissues as well as less water. So there's less things for that radiation to interact with and create these reactive oxygen species.

18:40So less things, you mean there's less active biology to disrupt? Is that a way to say that? Yeah. And do the animals come out of hibernation after being radiated with gamma rays going like, bear, smash! What did that be? eat. No, no. The bear doesn't have to become Hulk. I do not want anyone to fire Gamma Rays at a bloody bear. Do not want that going green in Hulk. Don't, yeah. The chance is small, but it's big enough. So now, when squirrels go and they're not hibernating then, they just fill their lair with nuts and stay in for the winter and eat? Is that the deal? Or are they actually hibernating too?

19:22So the ones that everybody's seen in their life, the tree squirrels, big bushy tails, they don't hibernate. You're right. They're food-cashing animals. So instead of turning down demand, they store away supply, essentially, for the winter. So I can't sneak up on them during winter and get them. No, unfortunately not. There goes that theory. The squirrel is different from poking the bear. Yeah, that's very true. So there's no understanding biologically why a hibernating mammal would have more radiative resistance. It's not clear why that would be so evolutionarily. Is that right? That's a really great point.

20:00There really seems to be no reason evolutionarily why they would act, I shouldn't say actively, but why that trait might be selected for. So it's probably a passive consequence of some other thing that they've been defending against with the physiology of hibernation or torpor, I should say. So sort of accidentally becoming more protected against radiation is how I describe it. All right. So where does this go? You're trying to help NASA, at least for Mars missions, where it's nine months there and nine months back and two years on planet. Are there specific missions they're tasking you to think about?

20:36So right now we're in the conceptual phase of NIAC. There's three phases. Conceptual. Phase two is more you make the concept come to life and phase three is sort of flight mission. We're in the conceptual design. And NASA has turned its attention towards trying to figure out the hazards of space. Because with the Mars missions planned coming up, they don't have really a good answer for things like radiation, disuse atrophy, lengthy stay in space, essentially. And so they started to drive down different ways to mitigate this. And one of the ways that they've been really interested in is hibernation.

21:10And so our unit, what we're designing with NIAC right now, is actually just the ability for the first time in human history to study hibernation in space. because we don't even know if hibernation will work in space. Nobody's even thought to send a hibernating animal up and say, does it happen? Are there any primates that hibernate? Because I'm thinking theoretically if there are, then that might be possible for humans. They'd be even closer to us in the tree of life. Right, rather than trying to think about how we rework a bear or a squirrel or whatever it might be. Or a mouse. There is one primate, my son.

21:43That makes two primates then at least. Oh, there is. Okay. There are, so fat-tailed lemurs from Madagascar, they will use torpor quite well, actually. So there is a more related species to us that can use hibernation. Is this during ski season in Madagascar? I mean, when would they? Drought. Drought is the big one for Madagascar. Drought. Yeah. Drought. Yeah. So during the dry periods. So what chance is there that we share part of that code that will allow us as humans? We think actually a pretty good chance. So if you look evolutionarily, it seems that hibernation is a pretty basal condition.

22:24And what I mean by basal is that it's pretty far down in the tree of life. Deep in the tree of life. Yep. So you wouldn't have to gene splice it. You would just have to gene enable it. Unlock it. That's what we're thinking. Yeah, that's what we're thinking. Interesting. So now how do we know physiologically how they, because, you know, without water, we die very quickly. So what is happening physiologically? Are they storing water? Do their cells just retain it? I mean, what's going on? Do we know? Yeah, we have an idea. You got a photo machine in the back. Yeah. No one's ever been deep into a bear cave to deny that story.

23:06Yeah, that's true. Well, actually, I might know somebody who has been. Used to know someone who did. Yeah, used to. That's a good point. I mean, specifically with the Madagascar fat tail, because they're primates. And so, like I said, we die very quickly without water. So what's going on with them? Yeah, that unfortunately we don't know. They're incredibly endangered species. So more invasive studies on them are just, they just don't happen. So what we can do is whole animal physiology or survival physiology, but we can't really tell cellularly what's going on with the water and lemurs. Now we can infer from other hibernating species.

23:40and we know that they're really good at recycling the water that they do have. So there's a change in renal function essentially that allows them to recycle a little bit better. That means they don't eat, they don't pee the whole time? They don't eat, they don't drink, they don't pee, they don't poop. It's a complete shutdown in metabolism. Wow. And everything that comes from it. So what bodily system, what brain system is controlling all of this? Because it can't just be and that's it. Something's got to still be going on to control this. Yeah, there's tissues that are still active. So there are neural tissues that are still active.

24:14Generally speaking, the cortex is quite quiescent. So there's not a lot going on in the cortex. The neural tissue that we see going on is coming from either the brain, well, both the brainstem and the hypothalamus. So brainstems controlling all heart rate, respiratory rate, things like that, keeping your blood moving, even though it's moving more slowly and your lungs functioning. Obviously, with that, there's muscles that do stay active, like the diaphragm. Some of the upper respiratory muscles will stay active. The hypothalamus, I don't know if you've read about this tissue before. It's basically one of the main tissues controlling metabolism and body temperature.

24:49and so they are regulating really tightly where their metabolism is at and where their body temperature is at with the hypothalamus so that tissues are being active as well and that's actually in and of itself really interesting because you have tissues that are functioning in a mammal at four degrees celsius which is something that a human couldn't do right now we couldn't bring a human down to four degrees celsius and ask those tissues to continue to work you'd get complete neuronal failure. And so they've developed or evolved these ways to maintain tissue function despite it being really cold.

25:22Man, this sounds like sci-fi. It's so cool. Like, that's amazing. Yeah. So can we get quantitative here? So my basal metabolism, so just keeping my body temperature for 24 hours, I run through between 2 ,200 and 2 ,400 calories. Not for a man your size. Well, for me. Yeah. Nah. Yeah. Come on, man. What are you saying? You're too big to be living on those 2 ,000 calories. Get out of here. I didn't say 2 ,000. I said 2 ,400. 2 ,220. Around there. Okay. All right. If you say so. I mean, if that makes you comfortable.