Scientist Stories: Cynthia Kenyon, Genetics of Aging

It's a special honor to be here today and to receive this, this wonderful award. I want to thank Kathy for this amazing introduction. I think that's the nicest one I've ever had, ever. That's really, really nice. So yes, aging. So it wasn't that long ago, several decades, but still in all of history not that long ago, that people thought that, you know, it just happened. And the reason is, it's obvious, you just— it looks like you're just falling apart. Falling apart, so you can weigh, right? Entropy is taking over, so it fit with the idea that you're falling apart. And evolutionary biologists who think about this more deeply had actually arguments for why there couldn't be genes specifically dedicated to aging. And the reason is that they argue that aging happens after reproduction, and therefore if you change genes for— if there were genes for aging and you you change them, it would be too late to pass them on to your offspring, so there would be no way for them to be selected by evolutionary principles. So you could argue that that might or might not be true, but that was a very, very powerful paradigm in the field that kept people from really looking for, you know, a molecular basis for the rate of aging. Fortunately, however, I was from another field, developmental biology, And the field that I was from, we had just shown the whole field, my lab, but many other labs, that evolution had generated patterning mechanisms for development that were the same in all animals. The animals look different because the patterning mechanisms do different things, but it's the same basic blueprint, same genes. So that was really interesting, and that's number one. Number two, when you— so I was also influenced very much by these evolutionary theories, which is also good. And the other thing is, if you just look around and think, what you see is that different organisms, different kinds of animals, have very different lifespans. Compare us to the dog, for example. Very, very different lifespans. And why is that? Well, the reason there are different species is their genes are different, so the genes must also be having an influence on lifespan. And so if there are genes that have such a big influence on lifespan, and mutations occurring during evolution must have been responsible for these differences. Therefore, maybe there are still genes that affect lifespan in us, and if we change them, maybe we could change the way we age. So we studied our little worm, which— C. elegans— which is perfect, perfect for studying this kind of thing because it gets old and dies in just a few weeks. It's really, really nice. Yeah, you can do an experiment, then you can do another experiment, another, which is hard to do even in a mouse where it takes maybe 3 years. So there was at the time when I started really thinking about some of this yeast stuff at the time, there was a mutation that extended lifespan that had been studied by Tom Johnson for a long time. The problem was that it also reduced fertility, and there were other evolutionary theories about trade-offs between fertility and reproduction, so the possibility existed that maybe it lived long because it didn't reproduce. But, you know, armed with these thoughts about conservation of mechanisms like patterning mechanisms and this idea that different species have different genes for aging because how else do you change lifespans during evolution, I thought, you know, maybe there's some kind of a dial, some kind of universal control system for aging, like a thermostat. Maybe evolution just turned it up or down and then changed the rate of aging with, you know, different genes in different organisms to set the thermostat. So that's the kind of idea that I had. So we set out to look for long-lived mutants, and it was very hard to do this. I'll go into— I won't really go into this in great detail, but the field of aging was thought to be a complete and total waste of time. And backwater. Not by all people, but by the people that talk about it. Really seriously, by my social environment in science. A lot of the biologists, you know, at Berkeley, at UCSF, everywhere, thought, "Ugh, you're wasting your time because there can't be genes for it. It should just fall apart anyway." So, okay, so we looked at more longer views and Extremely amazingly, we found one right away, which is just great because it took a really long time to get anyone to work on it. This is a normal, beautiful C. elegans when it's young, moving around. And here's the great reason to study aging in worms. In just a couple weeks, that's what they look like. I mean, they look old. Even if you never saw a worm, you can tell that's an old one, which is kind of amazing too. And this is our mutant, same age. See? Yeah, wow. It's amazing. And they always look like this. So they don't just hang on. They actually age more slowly. So this is a change in one gene, one base pair out of 20,000, and you slow down the whole aging process and actually double the lifespan. So that changed everything, really. We did some experiments to show that fertility had nothing to do with it at all. So it said that there are genes that control aging. Evolutionary biologists notwithstanding, there were. And they also controlled healthspan. And later on, our lab and a lot of other labs showed that diseases of aging were also mitigated and delayed in these mice. Okay, so this— I like this slide just to, you know, the problem is when you tell someone, even if you tell someone you have a mutant that lives twice as long, they still think of someone that looks 90 but can run a marathon, you know? But that's not it. It's like this person who does not look 90 really is 90. That's what this is, and that's such a hard concept to get your brain around. You think about some people who are 100 really look a lot younger, but this is kind of a more extreme example of that. I mean, hypothetical example. A real example of more of a hypothetical— one time I showed this slide and people thought this was really true. This was— that was a big problem. So it was hypothetical. I fell asleep. Okay, but anyway, that's the concept that, you know, aging is— and this is worms, but remember, things that happen in worms happen similarly in other animals, at least all the things we knew about, like development and cell cycling and things like that. So who knew? So anyway, we and other— many other labs joined in the study of these genes, and we've learned a lot about them in the worm. Here's the lifespan. We learned right at the beginning that the So here you go. In fraction of animal's life, 100% in the beginning, all dead by the end of the month. Normal worms on the left. But look at this, the long-lived mutant is really just stunning. And then what we found, which is also interesting, is that if you just take away one other gene, change one other base pair that knocks out one other gene activity, you don't live long anymore. You look normal, you look nice and healthy, but you actually age a little bit faster. But otherwise, everything looks normal. But even though this mutation here is present in that animal, it can't perform anymore. So there are combinations of genes that are interacting with one another. So this is like a little circuit, and it really, really, really underscored the idea that there are— there's a regulatory problem for aging. Aging is regulated. Okay, the gene— this gene, the second one, is called DAF16. You can think about this. So let me just tell you one thing. So DAF2, the normal DAF2 gene, gene, since what we did when we made the change is we made it work less well. The normal gene— get ready— speeds up aging. It's like the Grim Reaper gene in the animal world. This is speaking of aging. The normal gene, the gene that's making you age faster, and if you knock that gene down, then you live longer. If you have this one, think of this as sweet 16, okay. So the normal function of this gene is to extend life. Just kidding. Keep you young. OK, so now what are these genes? Well, the DAP2 gene was cloned in the lab of Gary Ruvkin at Harvard, great scientist. He showed that it encodes hormone receptors. You know what hormones are, estrogen, testosterone. They're substances that circulate in your body, and they come in contact with the tissues, and they tell the tissues to do something different from what they were doing before. So this is a receptor for hormones, a hormone for aging. And what kind of receptor is it? Well, it's interesting because it's similar to the human receptors for insulin, which you know about in the context of diabetes, but also in the context of metabolism, that when you eat a meal, insulin is what allows you to take the sugar up into your cells and make fat out of it and so forth. I'm not really getting a good picture. I actually think it's better if I'm not. Right, and so then what about— so this is also, it's a regulatory gene. All of them are regulatory factors. And then, DAF16, we found, and also Gary's lab in parallel, found that this gene encodes a transcription factor. So that's a protein that gets on the DNA and switches genes on and off. Okay, so there are genes that regulate aging because there's never been more classical regulatory protein transcription factors and signaling protein signaling receptors. Okay, so that was a big paradigm shift. It doesn't just happen, it's regulated. All right, so how does it work? Well, with the DAF2 gene, we turn it down, not out. If you knock it out, remember it's the insulin receptor, worms die, mice die, people die. It's an essential gene, so turning it all the way down is not a good thing. Turning it down just a little bit very interestingly extends lifespan And part of the reason is because this sweet 16, DAF-16 protein goes into the nucleus and switches on about 600 or so, or on or off 600 or so new genes, as was shown by Colleen Murphy in my lab and several other labs. So then what happens? What do these genes do? These genes that DAF-16 is regulating can double the lifespan. What do they do? Turns out they do not just one thing, but lots of different things. Some genes they just switch on to one thing. Another set does something else. So what are they? Well, ah, I wanted to mention also here that DAF-16 is a transcription factor, a gene regulator, and it's not the only one that's activated in the DAF-2 mutant. There's one called heat shock factor that we found is needed for the long lifespan. Nrf2, SKIN1 was found by Keith Blackwell's lab to be required, and TGF was found by Gary's lab. And Malina Hansen's lab also to be required for the long lifespan. So this is a real big statewide physiological shift requiring lots of transcription factors, hundreds of thousands of genes changing to create this remarkable change in lifespan. Okay, so now how does it happen? Well, these cassettes that are activated do all sorts of things. Some activate autophagy, which is like a big recycling system for the worm, for animals in general. Some activate mitophagy, which is a recycling system for the little energy producers of cells, mitochondria. Some affect protein folding, helping damaged proteins to fold better than they normally would. Some actually fight nasty chemicals in the environment. That's called xenobiotic resistance. Some regulate metabolic changes, which actually turn out to be important —like how fat is transported in the worm—turn out to be important for lifespan. Some make them more protected against bacterial and other kinds of pathogens. So it's really interesting if you look at that. Each one of these is really interesting on its own. So you can ask the question, OK, to what extent can just activating autophagy all by itself extend lifespan? You can ask that kind of question for all these. And that's what our lab and many other labs are kind of doing for a long time now. But anyway, the main point is that the animal is really like rolling out the whole protective response, everything at once. The state of the bus, I'm going to say, shields up, you know. So it's like shoot down and ask questions later. They don't know what the problem is, maybe you can mention, but they're going to be— so they just become resistant to everything. Okay, so now it turns out you can activate the same life extension pathway in, or similar ones, overlapping ones, in many, many, many different ways, and I'm just going to list a few of them. You can do it by conditions in the environment. For example, several labs, Anne Bourret's lab and a lab in Japan, showed that caloric restriction, which is known to extend lifespan, certain kinds of caloric restriction, extend lifespan by activating RAF16 and going through this pathway. Our lab showed, interestingly, amazingly, that if you mess up the sensory neurons, neurons that allow the animals to smell or taste things in the environment, then the whole animal lives longer. It's the first indication that the nervous system controls lifespan. It's been shown to be true in other animals. Andy Dillon, who's here at Berkeley, showed that the same thing was true in mice, at least for some types of sensory neurons. Pretty amazing. You can actually— turns out, oxidative stressors are not good for you. If you give them enough of it, but if you give a very tiny little bit, for example, of a herbicide like paraquat, which is not good in high doses, but if you give just a little bit, you actually can extend the lifespan of the worm by 50%, which is amazing. Our lab found that, similar things were found by other labs, it's really interesting, but to do that you have to make the system. There are also things that you can do inside the animal, endogenous changes that you can make that can engage the system and extend lifespan. So we found that if you specifically take out the germ cells but leave the other reproductive tissues intact, that extends the lifespan of the worm, and it does so by activating daf-16. This isn't the same thing as just inhibiting fertility, it's a different thing. You have to have an empty gonad, and that will send out signals to the animal that will extend its lifespan. It doesn't whole interesting story that I don't have time to go into. The other thing is that there are little microRNAs. You've probably heard of microRNAs, a lot of you. They're very small RNAs that can bind to big RNAs, they're complementary to large RNAs that encode proteins, and they can regulate their expression. Well, they were first discovered in worms in the Horvitz lab, and they were discovered as developmental timers. They control phases of developed that happened at different times. So it turns out that the very same microRNAs, as shown by Frank Slack's lab at Yale, very same microRNAs can act in the adult, do act in the adult, to control the F16 activity, which regulates aging, which is pretty amazing. So as you can see, this is really a very central system that can be engaged in many ways. Node for, of all things, resilience and life extension. Okay, so now you also want to ask, um, where does it act? Is there like one cell that controls aging? So we asked that question. Now, once you knew that the DAF-2 gene was a hormone receptor, you know that there are hormones involved— insulin-like hormones, IGF-1-like hormones. And these hormones are going through the animal and get, you know, probably presumably touching lots of tissues, so that's a kind of systemic signal that can allow all the organs of the body to age in the same way, a coordinated aging system. But we found it's even deeper than that. My very first graduate student, before we knew anything, like even what Daphne did, he said, well, where does it act? Let me try to find out where it acts. And so you can do that with a technique called mosaic analysis in worms. As you heard, the development— not exactly, but the development of C. elegans is invariant. From animal to animal, and so you start with fertilized egg and you get this stereotyped set of cell divisions. And over here, this part of the lineage, the AB part, makes mostly the skin and the nervous system, and this part makes the inside. So what we did is we took DAF2 away either from this part or this part. So you'd think you'd get either old skin or old inside and young outside, or vice versa. But no, when we took DAF2 away from either one of these lineages, The whole animal, all the tissues were aging in the same rate as one. That's the first thing. And secondly, either one of these bosses, even though half the body of the animal was normal, was wild type, and the genotype would say age fast, they aged more slowly. So these are the mosaics here where this part had the long life allele, and this is the reciprocal one. They both live long. In both cases then, cells that would have been dying are kept alive because other cells in the animal have the DAF2 gene intact. So there must be downstream signals affecting aging as well. Here's another. So with DAF16, the sweet 16 transcription factor, you can do the same thing. You have a DAF2 mutant here, it was really long. Now you take away DAF16, transcription factor, now it's short like I showed you before. And now you put DAF16 back only in one tissue. And here is when you put it back only in the endoderm, the intestine of the animal. Um, then the whole animal slime. So again, the transcription factor— among the things the transcription factor is doing in these genes it's regulating is activating new hormones that leave the cell and go out and help other cells not to age so quickly. So it's really cool. It's a global, systemic, multifaceted, multi-properties resilience and life extension system for the worm. So we learned then from our lab and everywhere else studied that out the worm, which gave us really a deep truth about longevity. This is what I really want you to get. C. elegans has a hidden inside of itself. It has the potential to live twice as long as it normally would already, and we just, we didn't, you know, change the skin and do, you know, put Band-Aids all over all the tissues. We didn't do anything like that. We just changed one change, made one change in the regulatory system, allowed the animal to express the latent potential that I already have to live more long. So that's the first thing. Second, this pathway, the insulin and IGF-1 pathway, it's known already, as I said, to be involved in growth and the good life. You eat a meal, insulin comes on, takes your food up. IGF-1 promotes growth during development, for example. So these are hormones that are active under good conditions. Good conditions to promote, you know, the response to good conditions, metabolizing fast, maybe storing energy, etc. But what came out of this work that wasn't known before that's really key is that if you turn these things down just a little bit, all the way down you die, just a little bit down, then what happens is the animal interprets this, I think, as danger. There's something wrong, uh-oh, I'm in trouble, I might die, so it activates every single mechanism it can think of it can think of, teleologically speaking, to not die. And the very same mechanisms that keep it from dying because of an environmental condition also keep it from dying because of the stresses of aging. See? So the response to an environmental stress, like UV light or something like that, the cell has to protect itself better, so it's also going to be protected from things like free radical damage and, you know, other things that could drive aging. And the really cool thing is that this gives us an answer for all those evolutionary biologists who said that this can't possibly have genes that regulate aging. And the reason is that you can activate this protective system in animals before they reproduce. So if you— well, you can't. For example, you can calorically restrict young animals and and they will stop reproduction and they'll live a lot longer, and then when food comes along, now they'll reproduce. So you can see that changes in evolution that make the system work better and better can be passed on to the progeny, right? Because you know, you have two sets of worms, one doesn't have the protection, one does, you have less food, this set all dies, this set doesn't die, they want to reproduce. So you see, so the whole system can be built up and can be, you know, elaborated by evolution, and it can be enhanced and improved, and then it can— the whole thing can be passed on. But it's there now. It's there in the animal. It's sitting there in the genes, all hardwired into the genes. So changes in these genes, like to make gastric steam more active, for example, could in principle— that's the transcription pattern— could in principle extend the lifespan of an animal. So this pathway could be involved also for the evolution of long life. And I'll give you I'll give you some examples of that in a minute. So that's a whole paradigm shift that's really super cool, super cool. And it's not just a worm thing, it turns out. Big question, and this is a great answer, at least from my perspective, from everyone's perspective really. These same genes, you change them in worms, they just sit there like, 5 minutes, oh. You change them in, sorry, change them in flies, they live long. And she has been mice in the lung. So, um, so I'll just say this is a little bit of this pathway. This IGF-1 pathway is a very, very broad pathway in the animal. It starts in the brain, pituitary gland, liver in the response to growth hormone makes IGF-1. Target tissues can also make IGF-1. Now, so this is just a little diagram of all the hormones and some of the players here. And all these red arrows mean that in a mouse, if you change the gene that encodes that, the thing that the arrow is pointing to, like growth hormone, you can extend lifespan. So it's not just— you don't have to just change the IGF-1 receptor, which is DAF2. That would be something that would be sitting here, responding to— that would be DAF2. Or insulin. Insulin reduction can also extend lifespan. So, but it's It's a whole network. If you go inside the cell and you look inside at what happens in response to those hormones, it's a huge, huge complicated network. This is just even a part of it. But all the red boxes here correspond to— so this is— here's DAP2. Here's DAP16. Here's the pathway I didn't tell you about that connects these two. But then there's crosstalk over here with AMP kinase, TOR, or here as well. Anyway, so So basically everything with a red box, if you change it, you can extend lifespan in at least some animals, in many, many cases in mice. And the reason I mention mice is obviously they're mammals like we are, so that's, that's very cool. So what about evolution? Well, first of all, in domestic dogs, some of them were bred to be smaller. Now IGF-1 also controls growth, so if you turn down the gene, many animals are smaller. We showed for Amygdala, we have a a famous professor here at Berkeley, showed that when he was a postdoc in our lab, showed that when you turn— that you can get all the lifespan extension by turning DAF-2, which is an IGF-1 receptor, down only in the adult. So they develop normally, they're wild type, now you come in and turn it down, you get the whole life extension. So they might be smaller, they're not worm small, but flies would be smaller. But that's not because the gene, what it does in development, has anything to do with what it does in aging. They're uncoupled. Okay, so, um, so the small dogs live long, they can live really long, but great apes die in about 7 years, they get old and die, whereas humans can live to be 80 or more. It's really remarkable, it's a big life extension that's probably at least in part because they are IGF-1 mutants. I don't know if you've had that happen. This is a bat, a bat here, a little teeny weeny guy that lives 40 years, very active, every few seconds I think it catches an insect. And these guys have, if you look at the genes, the genes for the DAF2 gene of the animal and the growth hormone receptor gene of the animal are all messed up, they look like mutant genes, and if you read the sequence it would not encode a functional protein, and physiologically they look as though they they don't have these hormones. So that's presumably an example where changes in these genes drove the evolution of longevity. So in each species you can turn it up or down, but evolution can also change it. Most of that's mutations, you know, leading to a new species or changing a new species, and here's an example where that seems to have a really big effect on aging. There's also a whole bunch of those— there's no real smoking gun. We don't have people who live to be like 300 that have obvious deletions or changes just in one gene that we know about. I mean, there are no people like that, and so— but there are people who live to be 100 and who are pretty healthy, and there are lots of studies showing that those people are more likely to have gene changes in components of this network. So it probably does— which is good because people who live want to intervene and make interventions that can slow down aging in a healthy way, there's hope that we can intervene in this pathway in humans. I want to just mention a few other— oh, and I should mention before I go on to that, that for example, there's already a drug called rapamycin which inhibits TOR, which is one of those red boxes in that network that I said that's interconnected with all this. That drug is taken by people to affect graft rejections, to prevent rejections of organ transplants. And it causes some side effects, so don't rush out and take it. But in many other worms and yeast and flies and mice, it extends lifespan, again, in a pretty healthy way. So people are actually starting to do studies on dogs to see if that would extend the lifespan of dogs in a healthy way, very low doses. So I don't think you should take it because I would not recommend it because if you take something every day for lifespan, you want to be really sure that it's not going to hurt you, and there's never been a clinical trial for that in humans. But still, it's pretty cool because right now we have drugs that we can give to many animals that can extend their lifespan, and as you know, many of you are part of this effort, there are lots of— Calico, other companies, many companies are trying to make drugs that will slow down aging in humans. Every way. Just want to leave you by saying this isn't the only system that can affect lifespan. Judy's going to be talking about killing senescent cells. That affects inflammation, which is something that drives aging and reduces it, and they live longer. You can actually fiddle around with genes in the brain, in the brain that affect inflammation, that are regulators of inflammation but act in the brain, and either lengthen or shorten the lifespan of the mouse. Of a lab mouse, the lifespan of a mouse. You can— the microbiome, turns out, bacteria in your gut, can have a big effect on lifespan. You can give an old killifish, it's a little pretty little fish from Africa, and give an old one the microbiome from a young fish and it will live 50% longer. These are all really cool. Inhibiting respiration just slightly will extend lifespan. And telomerase, the thing that Liz Blackburn studies, the proteins that keep the ends of the chromosomes intact. There's a lab in Spain that has reported that if you overexpress this in old mice, the mice live longer. So I just want to say that's kind of like a— it's not about my work, but it's kind of a thank you to the whole field and also a, um, just a glimpse of all the many ways that you might think of intervening in human aging, more than we want to think about, to extend life. Okay, so I have a whole bunch of other things to tell you, why the germline is Pretty cool, but I can't. And then I study a way of, I don't know why I stretch so much, but I don't know. All right, come on, Sophia. Happens in frogs too. And there's also this little timeout an animal can have in a working cabinet. Really young when it actually ages, and that aging can be reversed. So in both cases, the germline and this little time-out period, what happens is you accumulate all these signs of aging, and then you can either fertilize the animal or give it food in this case, and you can erase signs of aging. So now that— it actually would have been nice if I didn't talk about it because it's about rejuvenation, not just aging. But I couldn't cancel. I just want to end by thanking the people who have been in my lab and UCSF, which made this all possible for me, which is really great. They allow people to do crazy things. And Calico, where I work now, which is like half research company and half drug company. And so you can basically search it, maybe you can work on drug policy. Thank you. And that's why I— Thank you, Cynthia.

That was wonderful, inspirational. A wise man once said time is relative. While we were sitting here, we were aging. Time was flying by. So I know you wanted to have a question and answer session, but I think we have to protect the rest of the program. So what we'll do—

it wasn't your —me and the people who came before you. I think we've gone too long.

We'll have the next session, and David Lindeman will introduce that, and then we'll sort of crunch the coffee break time down as we get there.