Cell Biology of Aging, Mitochondria, Metabolism, Autophagy & Stress | Andrew Dillin | #155

About the guest: Andrew Dillin, PhD is Professor of Molecular & Cell Biology at UC-Berkeley and Howard Hughes Medical Institute investigator. His lab studies mechanisms of aging, mitochondrial biology, and related subjects.Episode summary: Nick and Dr. Dillin discuss: cell biology; mitochondria & the endoplasmic reticulum; aging & autophagy; mitochondrial biology in neurons; diet, exercise, and oxygen effects on mitochondrial health; and more.*This content is never meant to serve as medical advice.

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* Episode transcript below.

Full AI-generated transcript below. Beware of typos & mistranslations!

Andy Dillin 2:25

Thanks for having me. Nick.

Nick Jikomes 2:26

Can you give everyone just a brief overview of what you do? And what your lab studies?

Andy Dillin 2:32

Yeah. It's, it's a really interesting group of people that I work with. And we're we've sort of stumbled across a really interesting set of findings where we've uncovered that if you have different Seiler stress responses, if you engage them the right way, they can increase lifespan and healthspan and improve a lot of different things. And that was very exciting. But the really cool thing is you only have to engage them in the nervous system. And once they're engaged, they're the nervous system takes over and sort of coordinates this across the rest of the organism. And so for the last 20 years, we've been trying to figure out what that coordination is and what it looks like, and who's doing the coordinating. And, you know, evolutionarily, why would this evolved this way? You know, why doesn't every cell just set up its own stress response? And so on ability to do this? Why does it have a mass for cell types coordinate this?

Nick Jikomes 3:33

Yeah, so So you've studied so so the stress response, you know, in principle, you can imagine that each cell is almost like its own little island, it's going to age at its own rate, it's going to respond to whatever's happening right there to that cell. But on the other hand, you could also imagine that, you know, we are organisms with bodies, all of our cells have to be sort of aligned with a common interest in in survival and reproduction. So maybe there are mechanisms that allow full body communication across cells to coordinate stress responses and things like that. Before we get into some of the details there, I want to talk a little bit about some of the basic cell biology just to get people thinking about some of the the organelles and stuff that I think we'll talk about one very important organelle that many people have heard of, and maybe understand, you know, a slice of what these things do is the mitochondria. Can you just talk a little bit about mitochondria, what they are, and what they do, not only in terms of like, what what the average sort of biology student probably knows them for, but you know, the expanded list of important things they do?

Andy Dillin 4:40

Yeah, I think that's a great question. So first of all, I have to qualify that when I started my career. Number one, I never thought I'd work in mitochondria. And number two, I never thought I'd be labeled as a neuroscientist. But you know, it's, you just follow where the results send you and we discovered mitochondria in this pathway, and then it works in the nervous system. But to get your quote, you know, mitochondria, I mean, we all, you know, we hate saying this as mitochondrial biologists the powerhouse of the cell, that's what everyone recognizes them for, you know, the major energy producing organelle in your in your cell to produce to produce ATP, ATP, but also have a myriad of other functions. And when we think about that myriad of other functions, we need to actually go back and remember what mitochondria were. So you know, mitochondria were bacteria. And so billions of years ago, you know, one bacteria made another bacterium, and somehow the bacterium that got engulfed, figure it out to give up most of its genome to its hosts, and survive inside the host. And that happened, and it became a very symbiotic relationship. And that's how mitochondria evolved is out of that symbiotic event that happened. So,

Nick Jikomes 6:00

so one bacteria ate and other bacteria. And somehow, I imagine, we don't know exactly how this worked. But we know that the what became the mitochondria, that bacteria literally, like gave some of its genes to the host cell, and sort of that was like the deal. That's how alignment was achieved.

Andy Dillin 6:19

Yeah, the deal, you know, I think it had to be deals, plural, it had to happen over you know, over time giving up, you know, it didn't all at once give up 99% his genome, it probably did it, you know, over successive generations, but it's fascinating. You know, it's probably the most important biological event that happened on planet Earth, you know, is this ability of mitochondria to be in there, somebody, somebody else. And I was like, I would love to be able to go back in time and see how this event actually played out. Because it was probably tried many times, and it was unsuccessful, but you know, eventually became successful for for mitochondria. So in thinking about that, you know, he think about all the functions that a bacteria has, and you know, it has all of its other cellular functions. But also when it became a mitochondria, that was probably one of the first inner membranes inside of a cell. So of course, you know, you had the plasma membrane, but now you had an internal membrane structure. And so a lot of the cellular reactions that were happening inside of the free yoke you carry out before it got to mitochondria was happening in three dimensional space. But now you have a membrane to land on. Now, you can reduce those reactions down to two dimensions, because you can land on that surface and just control x and y coordinates. And so that probably like massively accelerated evolution, you know, us made reactions much more easier to attain. And so that allowed mitochondria to take on not just producing energy for the cell. But I mean, cholesterol synthesis happens there, iron biosynthesis happens. There's so many functions that mitochondria do. I mean, one of the major ones that we all know about is cell death, that organizes the death of a cell is that when things get really bad, the mitochondria recognize it first, and send out a signal to actually kill the cell. Is that actually an evolutionary thing from when it was a bacteria? Who knows? But there are all these things that mitochondria retained and gained as well when they became inside of the eukaryotes. And so I'm always just amazed, you know, we'll talk about some of the things that we've discovered that I'm still just sort of scratching my head saying, these mitochondria, you know, they were put inside of cells billions of years ago, they gave up most of their genome, but they retained 13 genes, couple T RNAs, yet they have so much control over the cell, but everyone's like, No, it's the nucleus, nucleus nucleus. But actually, the mitochondria are pretty darn important and actually drive a lot of cellular processes.

Nick Jikomes 9:00

And are they in every single cell of a multicellular animal like us? Yeah,

Andy Dillin 9:05

except for, you know, red blood cells that get rid of all the organelles? I see. But yeah, no, absolutely. And the this is also the most fascinating thing as well as that a mitochondria in your muscle cell looks very different than the mitochondria in your brain cell. So they've adapted, you know, they're adaptable to be whatever environment they're going to be in. They change the structure, they change their functions. You know, it's almost like these little aliens that are inside of us. And every single cell except for of course, the red blood cells.

Nick Jikomes 9:37

Yeah, I mean, and it is puzzling in one sense that you would see that much plasticity in something that has so few genes of its own, but I guess a lot of that is probably just coming from coordination back and forth with the nuclear genome.

Andy Dillin 9:49

Exactly. I mean, that is what everyone's begin to realize is that, you know, people always thought the mitochondria were their own entities, you know, functioning in the cytoplasm, but There's this massive communication that has these checkpoints going back and forth between the nucleus and the mitochondria. And definitely all of this stuff with the, you know, changing form and function and a cell type specific manner, is definitely coordinated by the nucleus, depending upon which energy status is required by the cell, what signaling events are happening, you know, what state the cells in what age the cell is, and, I mean, it's, I'm totally fascinated by mitochondria.

Nick Jikomes 10:29

Another I mean mitochondria, it just in the past few years, it seems they're becoming a hot topic, they're becoming way more famous than than they used to be, I think when when I was first a student, so we'll come back to mitochondria. Another organelle, that's really interesting, that I know far less about that I think is just talked about less is the endoplasmic reticulum, which we can just abbreviate to er, what is the ER, and what would be a very basic overview of what that part of a cell is doing?

Andy Dillin 11:02

Yeah, so in your cell, you're going to make new proteins. And the ones that are going to go outside of the cell, you know, to make the plasma proteins on the outside of the plasma membrane, or be secreted to talk to other cells all have to go through this structure, the endoplasmic reticulum. And that's sort of like the first processing center to know where to actually stick those proteins are they going to stay in some organelles inside the cell are they going to go actually outside. So the ER is like the, you know, the first processing center at the Amazon, you know, the big center where they sort out all the different orders, that's probably the way to think about the ER, it also has a really interesting evolutionary history, you know, it's mainly wrapped around the nucleus, it also extends out into the cytoplasm as well. And it's actually evolved to contact mitochondria and actually control mitochondrial functions. And so, you know, if you think about the nucleus, the ER, endoplasmic reticulum, and mitochondria, they're sort of working in concert, to create some form of homeostasis on energy production, protein production. And with that, which genes you're going to transcribe. So it's an interesting little trio that's working together.

Nick Jikomes 12:19

So so there's a lot of proteins that get made within a cell that actually gets shipped out to the plasma membrane of that cell, or just shipped out completely to go elsewhere to other cells or to get into the bloodstream or whatever. There is some processing that has to happen before they can do that the ER seems to be an important place for that. Can you give us a sense of like, what do we mean by processing there, what's happening to the proteins, what needs to happen to them before they can be shipped to the final destination?

Andy Dillin 12:46

Yeah, so I mean, the very first thing is they have to be imported into the Anaplasma curriculum. And they're they take on different folding states to determine if they're good enough that the soul made them good enough to send on to get further process and other organelles, such as the Golgi, to get decorated. So this is the beginning steps of, you know, we think of proteins is just the line of amino acids. But actually, what happens to the cells is that line of amino acids actually gets modified in many different ways. And in the secretory process, that getting proteins out of the cell, they get decorated with sugars, or like muscle groups. And there's a vast array of enzymes that do this, and the, I don't know enough about it. But there's enough, there's a whole set of enzymes that put on different decorations, that can signal different things to the outside of the cell, sorry about that, the signal different things the outside of the cell, and actually protect these proteins from the, you know, the bad things are on the outside of cell proteases, and things of that nature. So there's a whole bunch of modifications that actually occur.

Nick Jikomes 13:58

I see so so when our cells make proteins, you know, they're using DNA to ultimately make a sequence of amino acids. But that sequence of amino acids gets folded into a higher order structure that may or may not go perfectly. So there's quality control checkpoints built into this whole process to make sure the folding happens properly. Before these proteins, at least some of them get decorated with sugars and other things, then the reason they have all of these sugars and other things, sort of stapled or stitched to the outside of them has to do with things probably like their I would I would imagine that helps the cell know where to ship these things. It affects their longevity out in the environment, how stable they are, etc.

Andy Dillin 14:42

Yeah, absolutely. Absolutely. And then it also does structural things as well. So when they get to the outside of the cell, they actually serve structural properties. You know, there's massive sugar moieties that are added to proteins on the outside of the cell, either enormous Hyaluronic Acid is one of them. And it creates, you know, a several nanometer long fibers that actually decorate the outside of cell, which are thought, you know, to protect cells from invasion from pathogens, bacteria or viruses. So, I mean, the ear is a really important structure and, you know, over a third of the different proteins that are made actually go through the ER. So he said about a third, about a third. Yeah.

Nick Jikomes 15:25

And so what's the is the key difference there, whether they go through or not what you said before, related to whether or not they're going to be modified in order to be shipped outside the cell?

Andy Dillin 15:35

No, the first decision is made when the when the message is in the cytoplasm, and it is beginning to be translated. And if it has the right beginning amino acids, it partners with a molecule called SRP signal recognition particle, that drags it to the ER, and says, Oh, you have the right zip code, I'm going to put you into the now you're going to finish the rest of your translation, and actually be inserted into the ER.

Nick Jikomes 16:06

And so we talked about protein synthesis, the proteins can be modified with sugars. So there's, there's this is kind of one interesting part of cell biology, where are proteins and sugars are interacting? What about lipids themselves? So one thing I don't understand fully is, obviously, the cell membrane is made out of lipids, it's made out of fat molecules. Fats are, you know, they're components of other things as well. But where in the cell? are lipids being synthesized and packaged, and made and distributed? Like how does the cell you know, there must be a mechanism or mechanisms in place for it to construct its membrane and maintain its membrane? What is happening there?

Andy Dillin 16:50

I mean, that is also a major function of the ER is, you know, whether or not you're going to make a lipid droplet, that's going to stay in the state inside of the cell and be an energy source and a structural source for membranes, you know, for other cellular membranes, or if the lipid droplet actually stays inside of the ER, it becomes a Keiler micron that gets secreted out. And so, you know, you think about HDL and LDL is, you know, these lipid particles that we associate with hypercholesterolemia. You know, that's actually beginning in your EMR, making those kinds of microns.

Nick Jikomes 17:24

I see. So they're made in the cell, the ER is involved in the production of those things, and then they're secreted out. Exactly, exactly. Interesting. Okay, so well sort of keep keep some of those things in mind, I think we'll probably come back to the mitochondria in the ER in different ways. You've studied aging of the cell biology of aging. Before we sort of get into the discussion around aging, I want to ask you a vague question that I've asked many other researchers who study aging in all sorts of different ways. What exactly is aging? From your perspective as a cell biologist?

Andy Dillin 18:00

You know, that's a really interesting question. I actually just taught a class to our graduate students here yesterday about about aging. And I sort of view it, you know, I actually, we can all recognize what aging is, we all see it, we're all experts on it. You know, we're all we're all own internal experts on what aging is. But none of us really know what it is. And I've been studying it now for over 20 years. And I'm not sure I know what aging is, you know, I can recognize it, I can see it. And my best guess of what the process of aging actually is, is, you know, it's how well you built your system is that you know how well you put everything together until your time of reproduction, you know, you're sitting there maintaining your building, and then you're maintaining the structure. And once you're past reproduction, aging is really the rate at which that is probably falling apart. And, of course, you know, there's things that you can do to keep it from falling apart faster, you know, diet, exercise, sleeping, well, which we just talked about, I think are the three major things that we can do to help slow that decline. But I'm really under the feeling that it's really about how you build your system. And you know, as humans, we built our system pretty good. You know, we're in utero for nine months. And then it takes us a very long time to go through development, you know, after birth, to make a fully functional human. And so maybe that's why we live so much longer is that we've just built the system exceptionally well.

Nick Jikomes 19:42

And I would imagine so when we think about aging to you know, we already talked a little bit about how you know what the ER there's this. There are quality control mechanisms, right. So so cells are doing all sorts of things. There's a bajillion different mechanisms to do all of the things that are all of our cells are always doing But some of these mechanisms are specifically about making sure things are going right, making sure the proteins are made, right. And so I would imagine there are certain parts of cell biology, certain mechanisms that play an outsized role in things like aging, because if they break a bunch of other things that they regulate, then start braking. Right?

Andy Dillin 20:23

Yeah, I mean, it's, it's, you know, I love working on these quality control pathways. Because they're, they're ensuring the integrity of an entire system. So you know, we work on a quality control pathway for the mitochondria called the unfolded protein response. And its sole job, sole job is to monitor how well the mitochondria is functioning. And the mitochondria, you know, it's like 2000 different proteins, a bunch of membranes. And you have one system that is sitting there monitoring the integrity of all that. And so you're, you're boiling down to 1000 components to setting it as just one the stress response system. And it goes down with age, it actually goes down, right when reproduction stops. And so you know, figuring out ways to trick it to get back going again, you know, we've done this and several other people have done this, it actually is very beneficial. It's, you know, it's not the end all be all, but it makes the mitochondria function better, makes them last longer, makes them do the things they're supposed to do longer and better. But does it cause like, 100% increase in lifespan? No. But it definitely, you know, increases a little bit, and it actually delays things significantly. It's not, you know, there's probably other pathways that are required for other parts of the cell really just fixing one part, that's mitochondria.

Nick Jikomes 21:42

So there's, there's somehow some of these mechanisms are tied to reproductive viability?

Andy Dillin 21:49

Yes. That

Nick Jikomes 21:51

makes intuitive sense, right. Like, ultimately, the purpose of living things. I mean, in some sense, you could argue that the definition of a living thing is that it's, it's a, you know, a biological entity subject to, you know, Darwinian evolution. That's how a lot of people think about it anyway. And so obviously, the currency, there's going to be reproductive success. Obviously, there's lots of clear examples in nature where, you know, when you're done reproducing, the organisms done, lots of insects operate that way, you know, salmon operate that way. And then obviously, there's a window in which organisms such as ourselves, and many other things, you know, they are reproductively viable. And that window eventually closes one way or another. But in what sense is reproductive viability tied to aging? And so what I mean by that is, is it? So let's imagine two individuals in a population, they both reach reproductive maturity at the same time, then one of them engages in, you know, say several rounds of reproduction, and one of them does not. So they're both developmentally at the same stage at the same time, but one of them is engaging in reproductive acts, and one of them isn't all other things being equal, would that affect the rate of aging?

Andy Dillin 23:02

Oh, man, you're bringing it you're opening a huge can of worms. So there's this classic paper, Nature paper? Let me think about the date. Probably 99, I want to say 9899. And the title of it barren aristocrats live longer. And so they did a retro retroactive study looking at aristocratic women that gave birth versus didn't. And so they're trying to control that, when, where, and when was this just like the 1617 1800s. Okay. And so they're trying to control for environment as best they can by only looking at the aristocrats or they're living, you know, the best life possible at that time. And they look at the women there that gave birth versus the women that didn't, and the ones that didn't give birth outlive the ones that did. So it's a fascinating study, what it means and is it been revisited, you know, modern days? I don't know if it has or not, but it's a fascinating study that, you know, I think there is a lot of costs, especially to women for childbearing. It seems like there's a lot of energy, stress, you know, the other things are happening to the body that would, you know, obviously shorten our lifespan. So you could argue that that's why the barren aristocrats live longer.

Nick Jikomes 24:29

I see. And it's at least intuitive to imagine that in a sexually reproducing species, like humans, there could be very large sex differences here. Oh, absolutely. Yeah.

Andy Dillin 24:41

Yeah, I mean, the problem is, you know, men traditionally live shorter than women because of others. You know, testosterone is a pretty potent Anti Aging at certain levels. It makes us do stupid things.

Nick Jikomes 24:53

We say testosterone has an anti aging effect. No, I'm

Andy Dillin 24:56

saying that you know, as a joke, you know, it's as a you No as sad. Yeah, when you're 15 years old and all sudden you get flushed with a lot of testosterone. You know, if the first time you do some pretty crazy things that shorten your lifespan. Yeah.

Nick Jikomes 25:12

So anyways, going going back to sort of the cell biology of aging, I want to talk about this question that you've studied that I, you know, I've done a number of episodes on aging, but I've never talked about this piece, which is the coordination of aging across the cells in an individual body. So to what extent I'll just start out with a very basic question. So to what extent are each of the cells of my body independently aging? And to what extent are they being coordinated somehow?

Andy Dillin 25:40

Um, so I mean, they're definitely being coordinated. And you know, we're not the first ever I mean, insulin is probably the best coordinator there is to coordinate your glucose levels, inside of your cells and outside yourselves. So this has been known forever that, you know, there are central coordinators of these types of things. But to actually identify an aging pathway that itself coordinates across the entire organism. That's the one thing that we discovered. And that, you know, that stemmed out of this mitochondrial work where we were looking at, earlier on when I worked with Cynthia Kenyon Did you know she discovered and her and Gary Revkin that reduce insulin IGF one signaling makes animals the plot. So there's this pathway of modulating IGF signaling growth control, that's going to really factor into aging. And when I joined Cynthia's lab, I was very keen to know if that was the only pathway that could control aging. And so I went through and inactivated every single gene and this organisms body. And the vast majority of genes I uncovered were mitochondrial components, which I had never thought about mitochondria. Never thought I'd be working on it. But over and over again, our lab, Gary Ruskin's lab, many other labs uncovered the same genes, that when you inactivated, reduced mitochondrial function and made animals live long, and that was peculiar, but then the thing that was most peculiar, as you touched on this earlier, every single cell has mitochondria. And so and when we did our experiments, we were reducing mitochondrial function, every single cell, like okay,

Nick Jikomes 27:18

what exactly does that mean, reduce mitochondrial function. So

Andy Dillin 27:22

we were knocking down different nuclear encoded components of the mitochondria are the electron transport chain chain, chain, so we're reducing their function. So by and large, we're reducing mitochondrial function. And you could argue, well, which functions when we we know the electron transport chain functions, but many other functions were affected as well. And so, you know, this point about every mitochondria having every cell having mitochondria. When we did the experiments, we were knocking these down, and every single cell and seeing this great effect, this great increase in longevity. And I don't know why we did it. Well, I mean, it was sort of like a curiosity. In the beginning, as when I started my own lab were like, well, are all mitochondria equal, and contributing to the aging process? Because at the time, the reactive oxygen species theory of aging was very popular, and all mitochondria contribute to aging, and they're all giving their quanta to the aging process? And I said, Well, is that really true? And so what we did is we went and we knocked down mitochondrial function, and certain cell types, you know, not every single cell, but just a few cells at different times. And it was fascinating is that most cells, it didn't register in effect. If anything, it made the animals live shorter. There was one cell type, if we knocked it down on the nervous system, we recapitulated everything we did when we knocked it down, and all the cells I see.

Nick Jikomes 28:48

So if you knock down mitochondrial function across the board, every cell, you get this longevity effect, the animals live longer. If you do that, specifically in the nervous system, you get the same effect. Is that in all neurons? Is it in a different cell type is certain neurons? Now?

Andy Dillin 29:03

That's a great question. So when we first reported we did in all cell types, and we figured out that there's got to there, what these neurons are doing is that they're sensing mitochondrial stress, and they're sending out a signal to coordinate it with the rest of the organism. And we'll talk hopefully, we'll talk about why, why that happens. But we asked like why we started ask questions like which neurons are the responsible ones, and it really seems to be the serotonergic and the sensory neurons that are really playing a role in this. You can do other neurons, it doesn't matter. It's mainly those those sets of neurons that are doing this, and then further work and other groups did this in mice. And it's really in the you know, those neurons that control feeding the promisee AgRP in the hypothalamus, I see the same experiments, and they get this response turned on goes out in the periphery. So it's definitely conserved. Optimise we don't know about in humans in humans yet, but It is a serotonergic in the sensory neurons that are doing this. And they set up this beautiful system communicate with the rest of the organism that turn on the stress response. And what it does is it protects the animal from future stresses. So it's a, it's like an ectopic way of tricking the system is that you just touched the neurons, and then they relay the information of the rest of the organism and set up this really beneficial effect

Nick Jikomes 30:27

when these neurons are sensing mitochondrial stress elsewhere in the body under naturalistic conditions. How is that happening? How are they actually sensing the stress? What is the signal there? Yeah,

Andy Dillin 30:41

so that is a really so we've done it, we've done it with brute force genetic approaches, you know, mainly, what we do is because misfolded protein misfolding stress in the mitochondria. So John Hougen, rad discovered this in 2002, is that if you put misfolded proteins in the mitochondria, what happens is a signal gets sent to the nucleus to turn on the stress response pathway to come back and fix that challenge. And so we took advantage of John's discoveries. And, you know, we started making misfolding stress in the mitochondria. So you can do that many different ways. Put misfolded proteins in there, or there's big protein complexes, the electron transport chain, you can mess up the stoichiometry there and get that up and running, you know, get out to do it. You can mess with mitochondrial ribosomes. So you change the synthesis of proteins in there. And that causes stoichiometric imbalances. There's a lot of different ways that we can get this thing up and running, get this stress response turned on.

Nick Jikomes 31:48

And then that stress response, so that stress plants gets turned on, somehow that's detected centrally. So how do the neurons know that the stress runs has been turned on in some other cell?

Andy Dillin 32:02

So well, that we don't know yet. So all we know right now is that if we turn it on the neurons, the neurons can talk to everybody. If we turn on other cell types, those cell types don't talk to each other. And no one yet talks back to the neurons. So it seems to be a one way street. So far, I'm not ruling out that there's not these other forms of communication. We haven't uncovered them yet in our studies, and it's probably because we're limited in the way that we're looking at it. But right now, it seems like the stress has to be registered and the neurons, neurons and the glial cells, we can talk about that, but that's, but the neurons and glial cells register it and then they coordinated across the rest of the organism.

Nick Jikomes 32:46

And when so you said like, there's this involvement of the sensory neurons and the serotonergic neurons? Do we have any sense for why it's serotonergic? Neurons as opposed to some other type? Yeah,

Andy Dillin 33:00

so that's a really well, okay, so we can talk a lot about why this is originally first. I mean, a major question is, why is it originally in the nervous system? Now, Why can't every cell just determine for themselves? Why is there a master coordinator? And the nervous system seems logical, right? Because that's, that's what the nervous system is supposed to do is supposed to sense the environment and then create homeostasis internally, that's its major job. And so that makes sense. That's exactly what we're seeing. And why is it the sensory neurons and the serotonergic neurons? Well, serotonin is you know, it is a a communicator of stress. And so it makes sense, those types of neurons would actually be the Sentinels that get this response up and running. And if we knock out serotonin synthesis, we can't get this going at all. So serotonin is essential for getting this whole thing going. As long as there's also a hormone that's required as well, which is a it's called a wind lag. And, and it looks like it's also going to be conserved, at least its functions conserved in mice, and probably humans, it's gdF 15, or FGF. 21 is also a cytokine. That's what these things are called, is that when cells are stressed, especially in neurons, they will release these hormones to register with the rest of the body. So that you know, it's essential relocators like, Oh, my neurons are stressed out. Let's prepare the periphery for this impending stress that's going to happen. And so then that gets to the next question is, you know, the sensory neurons, what are they actually sensing? And so we do know that pathogens. So we're going back to remember, mitochondria are ancestral back bacteria. Yeah. Yeah. And if you give a pathogenic bacteria to an animal, it will it will turn on the stress response. Yeah. Because the mitochondria like oh my Yeah, there's somebody like me, in the environment that's trying to attack me, this pathogenic bacteria, let's protect ourselves. And so that was that's fascinating. But why sensory neurons. And so we've done this experiment where if we just have animals smell the pathogen, they're not being infected, they're not eating it, they're not touching it. They're just smelling it. They register that pathogen. And then they turn on this response to their neurons. And they communicate it to the periphery, just like all of our genetic experiments.

Nick Jikomes 35:36

So it's like a pre emptive. It's a pre emptive response.

Andy Dillin 35:38

It's a preempt so then if you take those animals that have smelt that pathogenic bacteria, and now expose them to a pathogen, have them infected, they're more resistant than the ones that didn't smell it.

Nick Jikomes 35:50

And what kind of animals are you talking about for these particular experiments?

Andy Dillin 35:53

So this is all in C. elegans, and nematode C. elegans so far that we're putting this in? So

Nick Jikomes 36:01

what's that? Little worms that can smell the bacteria? Yeah, little worms,

Andy Dillin 36:05

I can smell the bacteria. And it's only pathogenic. If they smell non pathogenic bacteria, it doesn't matter. It's only pathogenic.

Nick Jikomes 36:15

I see. So so. So these mechanisms can they're not merely reactive mechanisms, they're not, it's not like you need a stressor inside of you doing distress. They can preemptively respond based on the sensory detection of a stressor that could get into the body. Yeah, and and protect you preemptively protect the body? If that actually does happen.

Andy Dillin 36:37

Yeah, I mean, it's, you can tell I don't know if you and I've never met, but my voice right now is I'm just suffering from a little bit of cold. And I'm like, you know, this system that we have, where we let the pathogen into our body, then all sudden we're you react to it, do an innate immune response to it, and then do an adaptive response to it. I'm like that, why don't we have something that's more clever that detects it and the environment before it even infects us. And so that's where a lot of our research is going is that we're seeing that the stress response pathways are registered and sensory neurons first, and then they communicate to the rest of the body. And so what in the environment? Are they actually registering? And this first set of experiences, first set of papers that are coming out where they're registering pathogenic bacteria, I think is fascinating. Because when you want to know about a pathogen before it infects you, you're more resistant to it. So now we're trying to, you know, of course, see if this is conserved in vertebrates, and figure out what the smell is. I mean, I think the most fascinating ideas, if we can figure out what this smell that this pathogens putting off, can we actually just make a perfume and put that in the environment and make people more resistant to future pathogenic attacks.

Nick Jikomes 37:58

And when some of these stress response mechanisms turn on the protect the organism? What is that? Well, what's happening at the cellular level, what's happening that's doing the protecting? Yeah,

Andy Dillin 38:09

so. So we see that they turn on this mitochondrial stress response. But inside the cell, what happens is, we see the mitochondria divide. So they phys away from each other into small bundles. And I don't know exactly why that's a protective mechanism. Some people say that that's a way to allocate resources into smaller packets, you know, your defense mechanism is to divide and make yourself smaller, so that there's less opportunities to get, you know, destroy one giant mitochondria. If the pathogen is successful, it may just destroy one small piece of a mitochondria, not all of them, so it divides the mitochondria. The other fascinating thing that we're finding, so we're going to put another layer on top of this smelling pathogens. So if the animal is pregnant, it smells a pathogen, and then its progeny. So we take the pathogen away, the smell the pathogen away, and it only smells it, it's never infected. It's never In fact, it just smells it, let it smell it for a day or so. And then we let the animal reproduce and lay its and have its progeny. Those progeny have now turned on that stress response. And those progeny if you now expose them to the pathogen, are now resistant to the pathogen. So there's a wiring that's happening between the nervous system and the germline. That's preparing the future generation that hey, we came across a pathogen. It's more than likely that you're being born into a pathogenic environment. Let me set you up so that you can survive a little bit longer to make it to reproduction. Wow. That's pretty wild. Yeah. Is there any and so one final layer is that if you get rid of the germline, so Louisiana We'll just sterile they have no germline. If they smell the pathogen, they can't turn on the response on the periphery, in their own body in their own body. Because there has to be the impetus that, hey, I'm going to reproduce, let's protect the body. If there's no germline there, there's no point in actually setting it all up.

Nick Jikomes 40:17

Yeah, it I mean, it actually makes sense when it's time to think about it. Because, you know, from a Darwinian perspective, right, the whole purpose of mitigating stress and surviving at all, is to reproduce. And so it makes sense. There'd be something hooked up from the germline into these systems.

Andy Dillin 40:35

Yeah. Well, I'm glad to make sense to you. It was kind of a head scratcher. We're like, wow, this is really cool. And I mean, the editors loved it as well. It's like, oh, this is actually pretty fascinating with this happening.

Nick Jikomes 40:46

I mean, of course, you could imagine, right? There's obviously it would be possible to hook it up differently. It's not like you could write it's perfectly it's easy to imagine why, how you could have a stress response that's not literally hooked up to the presence of the germ line. But still, that's a that's an elegant way to really tie the end goal to these things.

Andy Dillin 41:11

Well, and also, if you're thinking about mitochondria, right, this is a mitochondrial stress response, you're detecting the pathogen, you're protecting the mitochondria in the progeny. And you have to have that germline in order to get the whole thing up and running. So there are the one cell type that cares the most about your mitochondria is your germline. So when you think so when you're when you're making your germ cells, you start out with 40,000 mitochondria. And then you eventually selected down to 40, to put into that germ cell into the O site. That's where most of all of your mitochondria come from. And as the 40 best, most pristine, you know, the best best mas Herati, Ferrari, whatever you want to use the best mitochondria, the rest gets selected out.

Nick Jikomes 41:56

I see. So there's some kind of selection mechanism there where the developing Oh site can determine the quality of the mitochondria. And then and then filter away the the bad ones.

Andy Dillin 42:06

Yep. Yeah. And that is, if it didn't, you know, your fidelity would go down dramatically. Over generations, if you weren't able to reset, you know, the germline is immortal. So it has to have the best of everything. And mitochondria is one of the major things that has to have. And if it didn't do that, you know, you may lose a minute per generation. And over successive generation, the lifespan of the organism has gone. It could do this. And so coordinating this with your sensory input from, you know, from the nervous system to now the germline I'm I mean, this is like the greatest time of my career. I mean, it's the things that the lab is discovering, and the way they're doing it, I'm just, it's just truly fascinating what they're doing. And every day, I'm like, Wait, that works that way. And it's like, oh, my gosh, wow. Really fascinating biology.

Nick Jikomes 42:58

So you mentioned mitochondrial fission. And again, I don't know a terrible amount about mitochondrial biology. But my understanding is that the the number and the size of mitochondria are important features within a cell, they tell you a lot about how old the cell is how well it's functioning at a high level, what is the size of the mitochondria? And the number of mitochondria per cell, generally tell us is that are those like good correlates of an animal's age of its ability to produce energy and so forth? Yeah,

Andy Dillin 43:30

I mean, the mitochondrial morphology is a metric. But it's not clear. How, I mean, the general theme is that if mitochondria break apart, the mitochondria aren't functioning as well. If they're fused together into a nice network, they're functioning better. But there's, you can break those correlations all the time. So it's really like, you know, the dynamics is really, there is a lot of dynamics that happens mitochondria, but it's not always accurate. And so it's, you know, we don't put a lot, you know, we're fascinated to see the dynamics happen, but I don't really understand entirely that it's always correlative to better mitochondria versus not better mitochondria. Now, the number of mitochondria that is a fascinating one is that, you know, some cells can have 1000 mitochondria, some cells can only have three mitochondria. And I mean, different cell types. I'm not saying the same cells, I want to clarify that, you know, within, you know, a certain cell type, that cell type will always have 1000, and the other cell type pillars will always have three. Now, that's a fascinating metric is like, how does the cell determine this? What is the counting mechanism? How is it known? And that is wide open space that's out there. But there is one idea out there that no matter what mitochondria are in excess, no matter what cell type it is, so with 1000 You're like, okay, yeah, of course it's an accessible The one that only has three, that actually the bioenergetics really is just that maybe only needed one. And so we have this excess of mitochondria. And that's, you know, 10 years ago, people were like we need more mitochondria. To have health, we have to increase mitochondria, we have to upregulate, this gene called PGC. One alpha that is required to make more mitochondria, we need to target that and make more mitochondria. We have a mitochondrial disease, let's just make more mitochondria. That's not actually turning out to be right, is that mitochondria are in excess. And the results that we have where we knocked down mitochondrial function, and actually get better health. Yeah, it goes against all of that. Because it's triggering the stress response, right? It's triggering this response to make the mitochondria. Yeah.

Nick Jikomes 45:46

And I Yeah, and naively, I would think, too, that more mitochondria, you know, on the one hand, you might think, Oh, more ATP, more resources. But on the other hand, more oxidative stress, more reactive oxygen species, more

Andy Dillin 45:57

oxidative stress, more, more volume taking up inside of the cell. I mean, there's lots of reasons. You know, it's kind of one of these things like when your car starts to break down, you go, you know, it's like, you go buy more cars, it's like, now you fix your car, you know, I'd rather have one really good functioning car than 10, sort of broken cars. And so making more mitochondria, as I think is not the way to go, it's actually making your mitochondria better.

Nick Jikomes 46:19

And how do we how do you guys measure that in cells? What Does better mean in terms of mitochondrial function?

Andy Dillin 46:27

I mean, we go down, we look exactly at mitochondrial function. So we look at how well they're producing ATP, how well they're utilizing oxygen. You know how well they're doing other enzymatic activities that are happening inside of the mitochondria is one of the one of the major drivers, you know, how well, you know, mitochondria have this amazing ability to pump protons across the membrane, they create this gradient to produce ATP. So just looking at that is one of the major things is, can they actually create a gradient?

Nick Jikomes 46:56

And in these sensory and serotonergic neurons, these sort of special neurons involved in this whole stress response? stuff? What are the mitochondria doing in those cells? are they behaving differently to those cells have weird mitochondria in some way? Oh, man, yeah,

Andy Dillin 47:17

this is I think I'm gonna, this is gonna be like the rest of my career. So we really want to know what those why those are, those mitochondria are more sensitive than mitochondria and dopaminergic neurons are mitochondria and other, you know, glutamatergic neurons, you know, what's the difference. And that's something that we're avidly that's like a major goal in our lab, is trying to figure this out. You know, there's one idea that the mitochondria are different. The other idea is that the stress response is dialed differently in those cells. And that those cells, you know, they're like the canary in the coal mine, like they, that stress response can be triggered, you know, just with very little change, and turn this response on. So there's two possibilities are happening there that we're actively trying to figure out. And I don't have an answer for I wish I had an answer, but I don't.

Nick Jikomes 48:13

Um, in terms of some stress response mechanisms that cells use to protect themselves. We talked about this unfolded protein response. There's also something that I know some some about, but not too much, which is the heat heat shock response. Can you talk a little bit about the heat shock response, and just the general ability of cells to respond to temperature differences from what's optimal?

Andy Dillin 48:40

Yeah, so the heat shock response is probably one of the most evolutionary ly ancient stress responses there are stemming way back from bacteria, sigma factor, sigma, 25, running, turning on the heat shock response conserved all the way up to humans. And, you know, it's sort of that that heat shock response, we talked about the mitochondrial stress response, the ER response, the heat shock response is sort of, is thought to monitor what's happening in the cytoplasm, you know, not in the other organelles, you know, all the other stuff. It's monitoring what's happening there. And it's a transcriptional response. That's when there is a stress to the cytoplasm. It turns on a bunch of repair enzymes and chaperones to come and refold that stress that's happening in the cytoplasm. Now, traditionally, it's called the heat shock response, because it's turned on by elevated heat, which, if you remember your second law of thermodynamics, that's going to actually drive free energy and actually cause proteins Miss fold. And so that's a major bases away, it's called the heat shock response. And, you know, the cha