Era of Hope 2011 Plenary Sessions

Session Title: Afternoon Session – Breast Cancer Prevention and Risk

Title of Presentation: Aging Pathways and How They Relate to Breast Cancer

Malcolm C. Pike, PhD, Memorial Sloan-Kettering Cancer Center: The next speaker is Cynthia Kenyon, who is going to teach us how to live to 200 as far as I can understand. So I can't wait—.

Cynthia Kenyon, PhD, University of California, San Francisco: May I have the first slide, please? So the biggest risk factor for cancer is aging. It’s bigger than smoking; it’s bigger than anything else. So I’m going to be talking about aging and for many, many years you know—you notice it was on the list of non-modifiable factors. Anyway so we’re trying to get it off that list. So okay; so really for—for centuries, people have thought there is just nothing you can do about it; you just wear out like an old car, old shoe, and that’s it.

And however if you look around in nature you see something really interesting which is that—and we all know this if you have dogs or cats or you just must know it, the different kinds of animals age at really different rates. And this shows you the difference in life spans between mice and canaries and bats and it’s huge. So these animals have different life spans because they have different genes. That’s why they’re different from each other. So that makes you wonder whether there might be some genes, particular genes maybe, that have a big effect on life span.

So if that’s the case then if you knew what those genes were and you could study them and figure out how they exert their effect on aging and life span maybe you could eventually modulate their activities like with a pill to change the rate of aging perhaps. So we wanted to see if this could be the case, and this—we started studying aging in the early 1990s and we didn't study it in people. Instead we used this tiny little round worm, a microscopic little worm called C. elegans, and I’ll show you a movie of it in a minute.

But basically the idea was that if there are genes for aging then if you change some of these genes maybe you could slow down the rate of aging so the animal would live longer. And there already was known to be a—a C. elegans animal with a gene change that was reported to live somewhat longer. So we were optimistic.

So that’s what we started to do and amazingly we found the huge effect from one gene. We found that mutations that as gene changes that reduce the activity of a single gene called Daf-2 doubled the lifespan of the animal. And the Daf-2 gene encodes a hormone receptor that’s very similar to the hormone receptors that we have in our bodies for the hormones insulin and IGF-1. I should get some water; excuse me.

Okay; so this result was really, really interesting for many, many reasons. The first reason is that it showed that one single gene could have a huge effect, an enormous effect on the lifespan of the animal. If you look at this little curve here you see that in the end of 30 days all the normal worms shown in black are dead whereas the altered worms, the mutants are almost all alive and they aren't dead all of them until much later, so that’s pretty amazing.

The other thing, the next thing is that it says that aging is regulated by the genes and particularly it’s regulated by hormones, hormones that resemble insulin and IGF-1. Now these hormones were already known to influence in the case of insulin nutrient uptake into your tissues and in the case of IGF-1 growth. And what this result in our lab suggested was that maybe they had another function; they certainly did in the worm, the C. elegans, namely to control the rate of aging. And interestingly, it’s the opposite of what you might expect. The hormones actually speed up aging so they’re like the grim reaper in the worm, so when we make the cells less sensitive to the hormones by altering the—the receptor for the hormones so that it allows the cells to respond to the hormones and then the animal lives longer.

So I want to show you a movie because the thing that’s so cool about these worms is that they—it’s not that they just you know check into the nursing home and hang on; they actually age more slowly than normal. So here is—here is the little C. elegans, very cute; that’s a normal worm. And here’s the long-lived mutant when it’s young. So I just want to show you this because you might these are going to have some horrible life but they don’t seem to. They seem to be quite very perky, happy, healthy; they can have completely normal number of progeny.

Now these worms age really quickly and that’s why they’re great for—for studies in the lab. And you can see in just about 2 weeks, this is a—a worm that’s clearly in the worm nursing home. Its head is moving here, but that’s about it. And you’ll see some more. And then what you’re going to see in a minute is that the long-lived mutant at the same age looks much younger than normal. Here is a dead one and another really—poor little thing; it’s actually quite sad just to look at—so okay. Here we are; look that’s the altered worm at the exact same time, so they’re much younger and they are if you look at the tissues you can see that the individual tissues look much younger than normal.

And so I have a little story because usually when I talk about this I say well you know it would be like a 90 year-old person who looked 45, which is what it is. But people think it’s like a 90 year-old person who looks really good for 90 but it—it isn't. So I’m going to tell a little story. Just imagine that you are let’s say in your 30s; maybe you’re a guy. You’re—you’re single and you’re dating. So you go around and you meet someone that you really like, and you get to know her and you go out to a restaurant and then you ask her how old she is? And she says I’m 60. You see; I just told you the same thing but it didn't hit home until—. So it’s something—and the reason that you’re so struck by this is because you never could ever have imagined that this could ever happen in any animal but it—it did in these little worms.

So okay; I’ve never introduced this worm to a normal worm. I don’t know what it would be like. Okay; so we’ll move on here. Okay; so how does reducing the signaling of insulin and IGF-1 increase the lifespan of the worm? How does that happen? Well an important finding came from our lab. We discovered that a gene called Daf-16 is required for these mutants to live so long. Okay; so what is Daf-16? Daf-16 is a gene regulator protein or a transcription factor. And in Daf-2 mutants okay this protein, the gene encodes the protein that is the transcription factor. What it does is it regulates genes that influence lifespan. So here you see a cell from a tissue and here on the surface of the cell is the Daf-2 receptor. And you can see part of the receptor is outside, so it can bind to the hormones when they come by, and the other part is inside, okay where I can send signals into the cell. And this is showing you what happens in the long-lived animals. The receptor is actually still there and it’s still somewhat active. If you complete inactivate it, the worms die. It’s—these are essential hormones, but if it’s slightly inactivated then you get this long lifespan. And under those conditions the Daf-16, FOXO transcription factor is in the nucleus where the DNA is and it’s switching on or off a whole variety of genes.

And by the way, the worms—the name of this gene in the worm is Daf-16, and humans have similar ones and they’re called FOXO and so I’m going to be calling it either Daf-16 or FOXO and it means the same thing.

Okay; but what are the genes that are activated or changed by Daf-16 in order to allow the animal to live so long? Well there’s a whole bunch of them. Some are—encode antioxidant proteins that protect the worms from reactive oxygen species, some encode proteins called chaperones which help other proteins to fold correctly and to—they actually escort damage proteins to the garbage cans of the cells, so that the cells can recycle them. So these are very important proteins. Then there are metabolic genes; some of them, we don’t really know how—how they work. Some of them move fat around the bodies and when you turn those genes down actually the worms live long and they’re turned down in these—in these mutants because of Daf-16.

The animals are more resistant to pathogens than normal because they have a better innate immunity system and this gene regulator protein switches on genes that boost the immune system. And then there are a variety of others. So the thing that’s so cool about this is here you have one—one regulator protein, a gene regulator that actually acts on many different processes in the cell because it doesn’t just bind to one—here’s just binding to one gene, but it actually binds to about 500 and changes their activities. And so then we think that all these different types of processes occur coordinately at the same time all under the control of this one regulator. Okay; and that we think can extend lifespan.

Okay; now what about normal worms, the worms that age normally? Well here the Daf-2 receptor binds its hormone and that activates a highly conserved signaling pathway that ends up keeping the Daf-16 protein out of the nucleus away from the DNA. It—it phosphorylates the protein; that’s what these little dots are here and that prevents it from going in and activating these genes. So that’s why the normal worm doesn’t live long. But then you think well, what good is this for the worm? Well what if the worm has something that just keeps something else from happening that might be good for it?

And that’s a really good question and we think that this is probably the—the answer. So these hormones of like insulin and IGF-1 are hormones that are active under what are called replete conditions, so when food is present and there’s not a lot of crowding, the—the good life. And insulin under those conditions promotes the uptake of nutrients into the tissues; it allows the tissues to store nutrients, store fat, or glycogen or to use the nutrients for energy. And IGF-1 promotes growth. So these are hormones that are used under good conditions.

And as I told you already, if you have zero insulin or zero IGF-1 you die. Worms die, people die, so it’s—they’re essential. And I think that the thing that’s so interesting is what happens when you just have a little bit? So that would happen under perhaps harsh environmental conditions where the level of insulin is a little lower or maybe IGF-1 is a little lower. What we think happens is that those—those conditions which activate FOXO and protect the animal, those conditions are registered as kind of a danger signal so the animal then says okay FOXO become active, Daf-16 be active. It switches on all these protective responses and they do two things. They let the animal live longer and they also protect it from various stresses in the environment. These long-lived animals are resistant to all sorts of things—to high temperature, to pathogens, to UV light, to DNA damage, to many, many things.

So it’s really the animal’s defense system. It’s kind of like a—it’s like what the military tries to do right, to prevent any kind of—to protect you from all sorts of possible horrors.

So FOXO is—you can also compare them to a building—it to a building superintendent. So let’s suppose you have a building and you have FOXO as the superintendent and he’s a little lazy. So the building is deteriorating at some rate. And then he hears there’s going to be a hurricane. So he’s springs into action and gets on the telephone, which really that’s what FOXO does. He doesn’t actually do anything. FOXO binds to the DNA and turns on genes that actually do something. So he gets on the telephone and he calls the roofer and the—maybe the painter and the window boarding up guy and the floor repair guy. Anyway he fortifies the whole entire building, so when the hurricane comes it lasts much better than it otherwise would, and even after the hurricane is gone the building is in really good condition, so it can stay—it can live longer, okay. So that’s actually quite a nice analogy I think between what the system does—it senses danger and the real world.

So, what about other organisms? The amazing thing about all this—this all happened in little worms, C. elegans so you might think well, that’s great for these worms but really—. So anyway so here’s our little pathway for the worms. Here you have the Daf-2 and the hormones turning off, FOXO keeping it out of the nucleus so the animal normally doesn’t live long. And then if you knock this down you will leave this inhibition and FOXO can promote longevity. And this turns out the exact same thing happens in the fruit fly which is pretty different from a worm. You change and make the same gene changes and you get the same results. And in mice and like in humans there are separate receptors, one for IGF-1 and one for insulin. The—these guys have only one gene for that receptor, the response to both hormones but we have separate ones.

And anyway it turns out that you can get mice to live long by changing either the IGF-1 receptor activity just lowering it throughout the animal or by changing the insulin receptor but it depends in that case where you do it. If you take it away from the fat tissue the whole mouse lives long. If you take it away from the liver the mouse gets diabetes, so you have to—you have to do this you know a careful way.

But that’s not all. It turns out you can—you know there are other proteins that act—we say upstream of IGF-1 controlling IGF-1’s level in the animal, and you can change these genes or genes further upstream and get the mice to live longer, or you can go downstream here and change proteins that are—act inside the cell to help the cell respond properly to either insulin or IGF-1 and that will also increase lifespan.

Okay; and by the way, in every case that these animals have been tested they’re more resistant to tumors. And I’ll come back to that in a minute. FOXO is also more active in these mice. So what about humans? So there are hints now that we—we humans are susceptible to the effects that these—this pathway has on—on lifespan in animals that we may be susceptible to. There was a study done in the Ashkenazi Jewish population that found that centenarians, people who live to be 100 were more likely to carry mutations that reduce IGF-1 receptor activity. These are Daf-2 mutants; they’re more likely to be Daf-2 mutants than were those who died earlier.

And FOXO variants, so we all have FOXO genes but we don’t all have the exact same form of the gene, just like we all have eyes but some people have blue eyes and some people have brown eyes. It turns out there are specific forms of the FOXO 3-A gene, one of the FOXO genes, that have been associated with the ability to live to 90 or 100 in populations that have been studied all over the world. Each one of these stars here represents one of these populations that was studied and shown and—and then within the population those with certain forms live longer. So I think that really does suggest pretty strongly that we humans are susceptible to the effects of—of these—these genes on lifespan. So now the question is—first of all, the first question is really are we sure and we’re not absolutely sure; for example, we don’t know yet how these gene changes affect the activity of FOXO. Okay; so there’s some important questions that we don’t understand.

But we also don’t know if—if there is some effect if we can make it bigger, in other words, if we could tweak the system like maybe turn down the Daf-2 activity just a little bit more or make some other change to optimize the—the response pathway to get a longer lifespan.

And the long-lived mutants like I mentioned earlier are resistant to many age-related diseases. I listed cancer first here, but there’s protein aggregation diseases, cardiac disease, heart disease, so it’s really amazing—they’re resistant to all sorts of diseases and remember, they’re staying young longer and these are all age-related diseases suggesting maybe that there is a—you know maybe they’re staying young longer because they—sorry, they’re staying disease-resistant longer because they’re actually young. They’re not susceptible to the diseases until they’re older, okay. So that would make—that would make sense. But it—it is a really interesting question at the molecular level. What is it that ties an increase in lifespan to an increase in broad disease resistance?

And so one thing like I said, aging is cancer’s greatest risk factor so you might—you might ask what about these Daf-2 mutants or yeah in the worm or other animals? It turns out mutations that inhibit IGF-1 signaling which extend animal lifespan also reduce cancer and that’s true in the worms and the—and all sorts of those mouse mutants. And it’s also probably true in humans; P10 mutations which elevate IGF-1 signaling and down-regulate FOXO activity, they promote tumor growth. Okay; so P10 mutations are tumor mutations. And FOXO proteins conversely are tumor suppressors, okay so having more FOXO which extends lifespan like I just told you in animals also can counteract tumors. It can actually cause apoptosis or cell death in tumors.

So maybe lowering IGF-1 signaling in people will reduce tumor growth rates, and actually there are several clinical trials that are in progress now.

So we—we did little studies of—of tumors and worms and I’d like to just mention the results. The worms have a reproductive system shown here. It’s quite big; it’ll have 2,000 cells in it at the end. And normally it—the cells in the reproductive system stay there and they either proliferate as like germline stem cells or they develop into oocytes or so forth. But there are tumor mutants where the cells that would be oocytes actually turn into tumor cells and these are quite like ovarian tumors actually. The cells grow and grow and grow and then they just burst out of the gonad; they break it. They don’t really metastasis but they break it and they just fill up the animal and the animal is like a little rod and then it dies.

So we asked, what would happen if we took this tumor mutant—this is actually a mutation called the gold-one mutation that causes this tumor? So we asked what would happen if we crossed in the Daf-2 mutation? And we found that the—the Daf-2 mutation let them live. So here we are; here’s the normal life span in yellow. And the tumor mutation cuts that in half. And here we have the very long lifespan of the Daf-2 mutant in blue. And you see if we take the Daf-2 mutation and we put it in the gold-one mutant, the tumor mutant they don’t die. They—they have a normal lifespan. And if you look at the tumors they’re smaller; there’s more cell death and there is—and the rate of cell division in the tumor is smaller.

So that’s pretty cool. And FOXO—Daf-16 FOXO is actually promoting this tumor resistance in these animals. So we also checked other long-lived mutants or conditions that extend lifespan. You can get a lot of animals to live—to have longer lifespans if you feed them less. Caloric restriction extends lifespan. And you can also them to live longer actually if you reduce mitochondrial respiration, which is quite interesting. And we found that both of these conditions prevent those animals from dying of cancer or delay the—the death.

So basically in these studies we saw a really strong correlation between the rates of aging, which was slowed down and tumor growth which was also slowed down in the long-lived mutants. And if you think about it, it kind of makes sense because in nature it’s always the old individuals, the elderly ones that are most likely to get cancer. Dogs get cancer, most likely when they’re say you know 11 or 12. Mice get cancer after a year or so often. Humans are much more likely—you’re 100-times more likely to die of a tumor at age 65 than 35. So it’s—it’s very, very age-dependent, so it could be maybe some of the same gene changes in evolution, so probably we arose from animals that had very short lifespans. But—in evolution—so when the gene changes that extended lifespan in evolution may well have also at the same time delayed tumor growth or age-related diseases of all types because that way you know the longer you live, the more delayed the onset of all these age-related diseases would be.

So we went onto investigate this just a little more in worms. We looked for tumor genes among 734 genes that we knew were regulated by Daf-16, the FOXO transcription factor. And we found 29 genes that affected tumor growth, and sure enough, many of these 29 genes also affected the lifespan of normal tumor-free worms. So we saw among these genes many that affected both the ability of a normal worm to live long with no cancer and the ability of a tumor(ed) worm, worms with tumors to resist that—that—resist death from the tumor.

Okay; I’m just—I’m like really close to the end. And then 25—so one reason I wanted to show this is in case any of you are—I’m sure some of you are cancer researchers; 25% of these 29 genes turned out to be known cancer genes in humans. So maybe some of the other 75% of them are too. So if you’re looking for new genes to study you could look at this worm paper and maybe you would find something.

Here’s an example of one—I’m not going to go through it because of time. I won't go through this either because of time. Ah, so there are other ways—other mutations that can extend lifespan reducing TOR signaling. TOR is another nutrient sensor or increasing AMP kinase activity; that’s an energy sensor. Either one can extend lifespan in animals. And drugs that affect both of them seem to have anti-tumor properties, Rapamycin which inhibits TOR and Metformin which promotes the AMP kinase activity; both of those look like they antagonize tumor formation in people.

So basically from basic science we have just ordinary basic science—just being curious—why is it that—are there genes for aging? We may have come up with a whole new strategy for going after many diseases all at once by targeting aging. And in my own lab we started a new project now and now that we think humans are susceptible to look for small molecules that will delay human aging and age-related diseases by looking for molecules that cause human cells in culture—not worms, now—human cells, to acquire features that characterize the cells of long-lived mutants. And we’re really excited about this project. It’s a brand new way of approaching cancer I think, and since it’s new maybe we’ll find some—some—something like from left field that really works.

So these are the people that did the work and thank you very much for inviting me. And I’m sorry to go over time.