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Aging Genes: Genes and Cells that Determine the Lifespan of the Nematode C. elegans

Part 1: Genes that Control Aging

00:00:03.04 Hi, I'm Cynthia Kenyon and I'm going to be talking about genes that control aging.
00:00:08.24 So, you all know what aging is. There's an example of it in the slide.
00:00:15.18 And for many years, people thought that aging was just something that happened.
00:00:18.16 You just wear out like an old car. But I guess in the early 1990s or so, in the late 1980s,
00:00:24.27 I started to think more and more that aging was going to turn out
00:00:27.27 to be subject to active control by the genes.
00:00:30.22 And the reason I thought that is because everything else that people think just sort of happens
00:00:36.00 in a haphazard way in biology turns out to be regulated in a very elaborate way by the genes.
00:00:42.14 For example, if you look in nature what you see is that
00:00:45.12 different animals can have really different lifespans.
00:00:48.21 A mouse lives only two years, but a canary lives 15 years, and a bat can live 50 years.
00:00:54.11 So, these animals have extremely different lifespans in spite of the fact that
00:00:58.02 they're about the same size, and, even if they're living in the same place,
00:01:01.15 they have very different lifespans.
00:01:02.20 And the reason they have different lifespans is because they have different genes.
00:01:05.28 So that says right off the bat that there’s something
00:01:08.22 about these genes that's influencing their lifespan.
00:01:11.28 So the idea that I had was, look, if there are genes that actually control aging,
00:01:16.06 then if we change these genes we ought to be able to produce an animal that lives longer.
00:01:21.06 And then if we study the genes in more detail,
00:01:24.07 we'll be able to understand how aging is controlled.
00:01:28.00 So we didn't study this problem in people.
00:01:30.14 Instead, we studied it in my favorite little animal, C. elegans,
00:01:34.15 which is shown here for you that this is an old individual.
00:01:37.14 Now, what C. elegans is, is a very tiny little round worm that lives in the soil.
00:01:42.17 It’s about the size of a comma at the end of sentence. Very tiny.
00:01:46.20 And they're really good for studying things like aging
00:01:50.04 because they grow old and die in just about two weeks.
00:01:55.06 And we wondered, "Could C. elegans teach us anything about aging in humans?"
00:01:59.06 Because obviously, we like our worms, but we don't really only want to learn about the worms.
00:02:03.26 We really want to learn about people and higher animals, mammals.
00:02:07.15 So the question of course is: could studying aging in one of these little round worms
00:02:11.19 teach us any thing about humans? And I thought that the chances were pretty good that it could
00:02:16.27 because the idea that I had was that aging was actually going to be controlled by genes-
00:02:21.02 a set of genes that would be controlling aging in all animals. And the reason I thought that
00:02:26.13 is that many biological mechanisms that control other aspects of biology,
00:02:30.27 like how a muscle cell differentiates
00:02:33.02 or how an egg is fertilized, or how a cell divides happen in the very same way in all animals.
00:02:39.18 And, in fact, lots of genes that are important for people
00:02:42.27 were first discovered in these little C. elegans.
00:02:46.18 OK, now, we were very optimistic starting out that we would be able to find genes that extend lifespan.
00:02:52.07 And the reason was that there already was an animal that had an altered gene that lived longer.
00:02:57.20 And this was a mutant that had been identified by Michael Klass
00:03:01.07 and studied by Tom Johnson for a long time.
00:03:03.28 These worms lived about 30-50% longer than normal.
00:03:07.18 So we set out to look for long lived mutants and amazingly, we found that mutations
00:03:12.02 that damage one single gene in the worm, a gene whose name is DAF-2,
00:03:17.00 doubled the lifespan of the worm. So here you see a diagram of the lifespans of these worms.
00:03:24.20 So what we did is we took a whole population of worms
00:03:26.22 and we just let them age and asked how long they live.
00:03:30.00 So these here in black are normal worms here. And you can see that by day 30, the end of a month,
00:03:36.01 they’re all dead. So the fraction alive, what you see is over here, is now 0.
00:03:41.15 Whereas at the same time, our mutant worms, the worms that have only one gene change,
00:03:46.20 all the other genes are the same, are almost all still alive.
00:03:50.21 And it’s not until about twice as long, until 70 days, when they're all dead.
00:03:57.04 So, it’s incredible really. We just changed one gene, all the other genes are the same,
00:04:01.16 and the whole animal lives twice as long as normal.
00:04:05.18 And the really magical thing about these worms is that it’s not that they,
00:04:09.05 you know, get old and just hang on. They actually age more slowly than normal. So here
00:04:14.03 you see a normal C. elegans worm, quite beautiful, crawling along on its bacteria.
00:04:20.27 So this is a movie of these worms. What you're going to see first are the normal worms.
00:04:24.23 Here it is. A normal worm when it’s about the age of a college student.
00:04:27.28 It’s three days old, so it’s a young adult.
00:04:29.20 And you can see that they're very healthy. Now what you see here is the mutant worm,
00:04:33.24 the one that's going to live twice as long, when it’s also a young adult.
00:04:37.29 And what you see is that it’s very healthy. That's important.
00:04:41.10 It’s not sick when it’s young.
00:04:45.16 Now here, prepare yourself because this is a little bit sad, is the normal worm in just 2 weeks.
00:04:51.25 You see? Now the head here is moving. See the head? See it move?
00:04:58.00 There. But otherwise, it’s just lying there. It's in the nursing home basically, the old folks' home.
00:05:05.08 You're going to see some more worms in just a second. This worm is dead.
00:05:09.10 And again, this one, you see its head is moving but otherwise it's just lying there.
00:05:13.17 So these are what worms look like when they're old which is just when they're 2 weeks old.
00:05:17.07 And here is our long lived mutant. One gene change, that's all. And look at it! See? It looks healthy.
00:05:22.29 It’s moving around actively. They look much younger
00:05:25.23 than the worms... and this is like actually looking
00:05:28.23 at someone who's 90 and thinking that they're 45.
00:05:32.02 That's what it’s like. So it's like a miracle,
00:05:34.11 but it isn't a miracle. It’s science.
00:05:37.15 OK, so we want to know everything we possibly can about how changing one gene
00:05:42.20 can produce this miraculous appearance-a worm that doesn't get old on time.
00:05:49.03 The gene was cloned in the lab of Gary Ruvkun at Harvard.
00:05:52.16 And Gary's lab showed that the DAF-2 gene encodes a hormone receptor.
00:05:57.08 So here I've drawn for you a cell. This circle here's a cell.
00:06:00.11 And here we have the DAF-2 receptor, which is situated in the membrane of the cell
00:06:05.24 with one part out in the environment and the other part inside the cell.
00:06:09.17 And here are hormones that it's receiving here in green.
00:06:13.29 OK, so, what we have found was that the normal function of this hormone receptor
00:06:19.01 is to speed up aging. That's what this arrow means.
00:06:21.25 It means it promotes the aging process
00:06:23.24 because when we damage the gene with a mutation, the animals live long.
00:06:28.09 So the normal function is to speed up aging.
00:06:31.05 So, together our finding, along with the Ruvkun lab's findings, demonstrate that aging
00:06:36.23 is controlled and it's controlled by hormones.
00:06:39.28 Specifically, there are hormones in the worm that are speeding up the aging process.
00:06:45.01 They're making the worm get old faster.
00:06:49.03 Now, the really cool thing about this hormone receptor
00:06:51.14 is that it's similar to two hormone receptors in humans,
00:06:54.09 the receptors for insulin and IGF-1. These are two very well known hormones.
00:07:00.00 They're known to do the following. Insulin is known to promote
00:07:04.07 the uptake of nutrients into the tissues after a meal
00:07:06.23 and IGF-1, the IGF-1 receptor, is known to promote growth.
00:07:12.18 And so what our findings suggested in these little worms was that
00:07:16.02 maybe these hormones had another function that nobody knew about,
00:07:19.29 which is to speed up aging. Remember I told you that a lot of processes that happen
00:07:24.28 in these little worms happen the same way in higher animals.
00:07:28.07 OK, so the idea was that if these hormones are speeding up aging in worms
00:07:32.09 maybe they would be speeding up aging in other animals as well.
00:07:35.23 And that actually turns out to be the case as shown here in this slide.
00:07:41.15 First, over here we have the worm. This is the situation in C. elegans.
00:07:45.24 So we have the insulin and IGF-1 hormone activating (that's what this arrow means) the receptor.
00:07:51.25 And when the receptor's active it blocks longevity. That what this little cross bar is.
00:07:57.08 It means "blocks" longevity. So people who work on fruit flies, the Tater and Partridge labs
00:08:03.08 made the same kind of change in the gene that
00:08:06.00 encodes the fly hormone receptor for insulin and IGF-1.
00:08:09.21 And what they showed was that the flies lived longer.
00:08:12.27 That was true if you changed the insulin/IGF-1 receptor or
00:08:16.05 genes that act downstream of the pathway, down here.
00:08:20.09 And in mice, there are separate genes for the insulin receptor and the IGF-1 receptor.
00:08:25.16 There's one gene that encodes the insulin receptor and another one for the IGF-1 receptor.
00:08:29.10 And it turns out, amazingly enough, that if you change either one of these genes
00:08:33.14 mice can live longer. So first of all, the Halzenberger lab showed that if you
00:08:37.15 make a mutation in the IGF-1 receptor, in other words what you really do is…
00:08:41.26 A normal mouse has two copies of the gene, one from its mother and one from its father.
00:08:46.05 But if you make a mouse that has only one copy, so it's a heterozygous mouse,
00:08:50.14 it has half as much receptor. And what they found was that
00:08:54.02 these mice live long, about 20% longer than normal.
00:08:58.29 They're very healthy. They were completely fertile, and they had a normal metabolic rate.
00:09:04.27 The Kohn lab showed that if you remove the insulin receptor specifically from the fat tissue
00:09:10.05 the whole mouse lived longer and these mice were very lucky.
00:09:13.13 If you fed them a high fat diet, they didn't get fat.
00:09:15.23 OK, so it's really quite amazing because what this tells you
00:09:19.28 is that the insulin/IGF-1 hormone system is controlling
00:09:26.16 aging in all three of these very different kinds of animals
00:09:29.07 which suggests that it was actually controlling aging
00:09:31.18 during evolution in a common ancestor of these three animals.
00:09:36.00 And that common ancestor also gave rise to humans.
00:09:39.29 So, it suggests the possibility that maybe these genes also control aging in us.
00:09:45.11 So what about higher organisms? Do we know anything?
00:09:47.26 Well, very recently we learned something about dogs.
00:09:50.22 Now, dogs as you know come in different sizes.
00:09:53.02 Here's a Great Dane and here's a little Chihuahua here.
00:09:55.05 And it turns out that small dogs live a lot longer than large dogs.
00:10:01.04 So large dogs like a Great Dane live only 5-7 years,
00:10:06.01 whereas these little small guys can live up to twenty years. So it's very different.
00:10:10.13 And what was shown very recently was that
00:10:12.25 the reason that these small dogs are small is because they
00:10:16.12 have a mutation in the gene that encodes IGF-1,
00:10:19.27 which is the hormone that we've been talking about.
00:10:22.16 So that makes them small and as I say, small dogs are long lived, so it makes them long-lived as well.
00:10:28.01 So, this is really interesting for lots of reasons. First of all, these small dogs, they're real animals.
00:10:35.14 I mean the mutants are real animals, but they're laboratory animals.
00:10:38.09 But these small dogs are fully functional, happy, little, intelligent, little creatures.
00:10:42.13 So, that's one thing. You can have this low level of IGF-1 and they have much
00:10:48.00 lower levels of the IGF-1 hormone and be very healthy. But it also raises a question.
00:10:53.18 The question is: Would they have to be small to be long-lived?
00:10:59.14 So in other words, the IGF-1 gene is promoting two things, growth to be a big dog
00:11:05.20 number one and number two, long life. So can they be separated from one another?
00:11:11.01 Or would be you have to small to be long lived if you're a dog?
00:11:15.03 Well, I think the answer is you would not have to be small, and I'll tell you why I think that.
00:11:20.06 First of all, if you go back to this chart, the worms that we study
00:11:23.22 are not small. The fruit flies, if you make mutations
00:11:28.04 in this gene here, in the insulin/IGF-1 receptor
00:11:30.09 the flies are small and long lived, but if you just perturb the pathway slightly just a little bit
00:11:37.17 not too much, then you get flies that are still long lived,
00:11:41.02 but they're not small. They're big and long-lived.
00:11:43.26 Same with these mice. These mice here are not small.
00:11:47.08 They don't get fat, but they're not particularly small.
00:11:49.04 And these mice here, the IGF-1 receptor mice, the heterozygous mice
00:11:53.15 are almost completely the normal size. They're just a tiny bit smaller, almost completely normal.
00:11:57.29 And yet the mice live long. OK, so in all these animals it’s possible to uncouple the two of them.
00:12:04.19 And the second thing is if you think about it when would the hormone
00:12:08.03 be needed in the life of the animal
00:12:09.19 to make it large? Of course it would be needed during childhood, when it's developing into an adult.
00:12:16.09 When would the gene be needed for aging? Well, maybe not until it's an adult.
00:12:21.11 So, we did this experiment. We asked, "When is the
00:12:24.14 gene needed to control aging in our little worms?"
00:12:28.17 OK, this was done by Andrew Dillin when he was a post-doc in the lab.
00:12:31.15 So the question is: When does the DAF-2 receptor gene affect lifespan?
00:12:35.13 So what we did was to turn the activity of the gene down in different times in the animal's life.
00:12:45.02 And the way we did this was to subject the animals to something called RNAi.
00:12:49.26 Now if you don't know what it is, don't worry to much about it. Basically, all you have to know
00:12:53.09 is that it’s a way of inhibiting the function of any gene that you want. This is how it works.
00:13:01.12 If you feed a worm. Well, let me start over.
00:13:04.29 If you introduce double stranded RNA for a worm's gene or any gene into an animal
00:13:12.22 or into a cell, the double stranded RNA will initiate
00:13:16.27 a process that leads to the destruction of all of the mRNA
00:13:21.02 messengers in the cell (or lots of them anyway) for that particular gene.
00:13:25.27 And with worms, what's really cool is that you can have bacteria
00:13:28.25 express a worm gene in the form of double stranded RNA
00:13:32.10 and then you can feed the bacteria to the worms.
00:13:34.28 The bacteria go into the worms. They eat bacteria.
00:13:37.17 They go into the worms and then somehow the double stranded RNA
00:13:39.20 gets out of the bacteria and into the worm's cells and it catalyzes this break down
00:13:44.16 of messenger RNA inside the worm which essentially
00:13:47.22 does the same thing as making a mutation in the gene.
00:13:50.22 It knocks down the activity of the gene. So we did our timing experiments
00:13:55.15 in the following way, where we just took our worms and we grew them
00:13:58.25 on bacteria, normal bacteria until we wanted to turn the gene down
00:14:02.29 and then we took the worms off that bacteria
00:14:05.10 and put them on bacteria expressing double stranded RNAi
00:14:08.08 sorry, double stranded RNA for the gene and let them eat that bacteria.
00:14:13.27 So here's what we found. We found that if we turned the activity of that gene down throughout life,
00:14:18.21 that is if we put the worms on these RNAi bacteria
00:14:21.10 from the time of hatching, they had a long lifespan.
00:14:24.14 So now, here, the control are normal worms that have the DAF-2 gene completely active.
00:14:28.22 And here is what happens if you subject the animals to this RNAi from the time of hatching.
00:14:34.06 And sure enough...so they have the gene down when
00:14:36.28 they're growing up and when they're aging
00:14:39.11 and they live long. So what happens if we just turn it down only during adulthood?
00:14:44.12 Look, they live just as long. You see? So that tells us that the DAF-2 gene acts during adulthood
00:14:50.08 to affect lifespan because if you don't have it on when the animal's an adult,
00:14:55.21 if you turn it down when it's an adult,
00:14:57.09 if you don't have it on it doesn't...live correctly, it lives too long.
00:15:02.11 OK, and we did other experiments where we turned the gene down during development
00:15:06.15 and then we turned it back up when it was an adult,
00:15:09.15 and those experiments told us that DAF-2 acts
00:15:11.14 exclusively during adulthood to affect lifespan, OK?
00:15:16.05 So this gene is acting during development, you know, to do what ever it has to do.
00:15:22.15 For example, promote growth in these dogs.
00:15:24.25 But then, at least in worms it’s acting in the adult to control aging.
00:15:28.18 And there are hints that it's also acting in mice to control aging in the adult as well.
00:15:34.08 OK, so basically, it would be really interesting to take a tiny little dog like a Chihuahua
00:15:40.00 that's going to live, say, 15 or 20 years and give it IGF-1
00:15:43.25 when it’s a puppy and let it become a big dog and lower the IGF-1 levels
00:15:48.02 when it’s a adult and see if it lives long, and I bet it would based on these experiments.
00:15:55.11 OK, so this is all very good for our pets, but what about people?
00:15:59.13 Could this little worm, C. elegans actually lead us to the fountain of youth?
00:16:03.06 And I don't have the answer for you, but I can tell you that
00:16:05.05 there are some interesting unpublished data
00:16:07.20 floating around so keep your eyes open.
00:16:10.29 OK, so now, how do these hormones ultimately affect the rate of aging?
00:16:16.09 How does a hormone coursing around through the circulation affect the aging of an animal?
00:16:20.27 Wrinkles, grey hair, the nursing home, the whole shebang?
00:16:24.27 Well, our first clue came when we discovered that another gene,
00:16:28.28 a gene called DAF-16, is required for these daf-2 mutations to extend lifespan.
00:16:35.15 So, here in this graph you can see what happens if we take away the DAF-16 gene in a daf-2 mutant.
00:16:41.02 So in red here you see the long lifespan of the daf-2 mutant
00:16:44.03 and what you see in green here is the mutant that...it still has the daf-2 mutation
00:16:49.02 so it should live twice as long but we took away the daf-16 gene and now
00:16:53.01 you see it doesn't live long anymore.
00:16:55.08 So, DAF-16 is like a fountain of youth gene. It’s a gene whose normal function let's you live long.
00:17:01.09 In fact, we call it "sweet 16" for youthfulness.
00:17:08.03 OK, so what is DAF-16? Well, we cloned
00:17:10.07 the gene, and it was also cloned in the Ruvkun lab,
00:17:12.10 and it encodes a transcription factor. That is, it makes a protein that goes in
00:17:15.29 the nucleus and binds DNA and switches genes on and off.
00:17:20.03 So, if there ever were a regulatory protein, that's it.
00:17:22.25 In other words, there's no question that aging is subject to regulation
00:17:26.18 or to control because in order for these animals to live long,
00:17:30.05 they have to be expressing genes at different levels.
00:17:32.23 OK, so there's definitely a control system for aging.
00:17:37.03 OK, so what is it that the DAF-16 transcription factor
00:17:41.12 is controlling that lets the animals live long?
00:17:45.20 First of all, before I go into that let me just tell you a little bit more about the DAF-2 pathway.
00:17:52.04 So basically, I showed you before the DAF-2 receptor.
00:17:55.03 And what I'm showing you here in this slide is a summary
00:17:59.19 of information that was gathered from a lot of different laboratories,
00:18:03.10 primarily the laboratory of Gary Ruvkun but with important contributions from the Riddle lab,
00:18:07.15 the Thomas lab, our lab and Johnson's lab.
00:18:10.01 So what you see if that the way the hormones affect gene expression
00:18:18.10 is that they activate a highly conserved phosphorylation cascade or a kinase cascade
00:18:25.00 which ends up phosphorylating..these little yellow circles here are phosphate groups
00:18:30.10 attached to the DAF-16 transcription factor.
00:18:33.03 And when this happens the DAF-16 transcription factor
00:18:35.27 is not able to accumulate in the nucleus.
00:18:39.21 But, if you make mutations in DAF-2 or any of these downstream genes
00:18:43.09 here then the transcription factor no longer
00:18:45.23 gets phosphorylated, and it does accumulate in the nucleus
00:18:48.18 where it regulates genes that affect lifespan.
00:18:53.02 So, we needed to know: What are those genes? What are the genes that affect lifespan?
00:18:57.09 So nowadays there are really very good ways of asking
00:19:01.02 what genes in the animal are changed under a certain condition.
00:19:04.24 So worms have about 20,000 genes and you can actually profile all these 20,000 genes
00:19:11.24 using a technique called microarray analysis
00:19:14.13 to find out which genes are expressed at a higher level
00:19:17.21 or more active or which genes are less active in the long lived mutants.
00:19:21.05 So Colleen Murphy, a post-doc in the lab did that. She subjected these worms to
00:19:27.15 microarray analysis. What she found is that DAF-2
00:19:31.22 controls the expression of many different downstream genes.
00:19:35.07 OK, so here what this slide shows is the DAF-2 receptor
00:19:41.01 when it’s turned down by a mutation let's say.
00:19:44.05 The DAF-16 transcription factor becomes more active so that up arrow means more active
00:19:49.07 and as a consequence the expression of a lot of different genes changes.
00:19:53.05 Some go up, some go down.
00:19:56.02 OK, so that's interesting. Now, just because a gene
00:19:59.17 is more or less active doesn't mean it has anything to do with lifespan.
00:20:02.11 It could just be more or less active and not doing anything.
00:20:05.12 So we had to test that. So the way we tested this idea that these genes that were changing were
00:20:09.24 doing something to lifespan was again we used this RNAi technique.
00:20:13.25 So we took...we just made a list of all our genes
00:20:17.03 and at the top of the list we had the genes whose expression changed the most
00:20:20.14 in the long lived animal and at the bottom we had the ones that changed the least.
00:20:24.21 And we just started marching down the list, testing the activity of each individual gene with RNAi.
00:20:30.09 So we went to the refrigerator, opened it up,
00:20:32.05 got the bacteria out of it that were...or the freezer I guess,
00:20:35.11 got the bacteria out that expressed each one of these genes
00:20:40.12 whose expression changed in the long lived animal
00:20:42.13 and then we fed the long lived mutants those bacteria and we asked, "OK, if you knock down
00:20:48.12 like, this particular gene here, if you knock it down,
00:20:50.20 if it can't go up anymore, can that worm still live long?
00:20:54.05 And what about this one and what about this one?" And that's what we did.
00:20:57.06 And what we found was that lots of different genes affected lifespan.
00:21:01.04 So this shows you that inhibiting the activity of many of the genes that are turned up
00:21:06.03 in the long-lived daf-2 mutants shortens their lifespan.
00:21:09.15 OK, what you see here in black is the long lifespan
00:21:13.19 of the daf-2 mutant, and here as a control in this line
00:21:18.06 you see what happens if we subject these animals to RNAi for DAF-16, the transcription factor.
00:21:23.03 So, now we don't have the transcription factor so they can't live long.
00:21:26.08 But here what you see in color here are the lifespan curves of
00:21:30.03 lots of different populations of worms that have been subjected to RNAi
00:21:34.18 for any one of a number of those genes that were more active in the long lived mutant.
00:21:38.25 And you can see that now they don't live as long.
00:21:42.16 So, all of these genes here and more are needed for the long lifespan of the daf-2 mutant.
00:21:48.29 And there were some genes that were turned down in the long-lived mutants.
00:21:52.16 So we asked, "OK, are those genes preventing long lifespan?
00:21:57.18 If so, what would happen if you turned them down in the normal worm?"
00:22:00.15 So, we did that and what we found is that many genes that were turned down in the daf-2 mutants
00:22:05.10 also affect lifespan. And what we did here is we turned them down in normal animals.
00:22:10.21 So, here we have a control. It has a normal lifespan, OK? And each one of these lines here
00:22:16.23 corresponds to a set of normal worms with a good DAF-2 gene,
00:22:22.25 in which all we've done is to turn down
00:22:25.08 one of these many genes that are less active
00:22:28.19 in the long-lived mutant and you can see that they're living longer.
00:22:31.16 So, it’s really interesting. Both the genes that are turned up and the genes that are turned down
00:22:36.05 in the long-lived mutants make a difference.
00:22:39.16 OK, so what are these genes? Well, it turns out they do many different things.
00:22:43.14 Some encode antioxidant proteins. Some of these had already
00:22:47.22 been shown to be more active in the long lived mutants
00:22:49.27 by the lab of Gordon Lithgow and others, and we discovered some new ones.
00:22:54.29 But all together they include genes like superoxide dismutase,
00:22:58.18 metallothionine, glutathione S-transferases,
00:23:01.12 catalases, a whole variety of anti-oxidant proteins and
00:23:05.04 as I say inhibiting the function of these genes shortened the lifespan of the long lived mutant.
00:23:10.15 There were also genes that encode proteins called chaperones.
00:23:13.13 Now, what's a chaperone? A chaperone is a protein that just like the name suggests
00:23:17.21 takes care of other proteins. A chaperone protein will
00:23:20.21 bind to another protein physically and it will help it
00:23:24.06 assume the right shape, or if the protein is damaged it will actually escort
00:23:27.15 it to the cell's garbage can so the cell can get rid of it and make a new protein.
00:23:31.08 So, these genes encoding chaperones were more active in the long lived animals
00:23:36.02 and that made a difference because when we turn
00:23:38.04 the activity of these genes back down with RNAi,
00:23:41.00 the worms didn't live as long.
00:23:44.06 We also found a set of genes that are part of the worms innate immunity system,
00:23:48.24 genes whose protein products kill microorganisms.
00:23:52.25 These genes were much more active in the long-lived mutants.
00:23:56.06 And that's very interesting because we showed...
00:23:59.09 before that we had shown that if you feed worms
00:24:02.24 bacteria that can't divide, that can't proliferate, the worms live longer
00:24:08.14 suggesting that they're actually dying from infections and sure enough these long lived animals,
00:24:12.21 the daf-2 mutants, actually have more active anti-bacterial genes.
00:24:16.11 And actually the Ausubel and Ruvkun labs showed that
00:24:19.02 these long lived animals are resistant to pathogenic bacteria.
00:24:22.09 And then there were metabolic genes whose activities were changed.
00:24:26.19 So, for example, there are some genes that
00:24:28.08 whose normal function is to make proteins that transport
00:24:31.05 fat around the animal from place to place and these genes were less active in the long lived animals.
00:24:36.09 And when we made the genes less active in normal worms, they live longer.
00:24:40.05 And that's interesting because genes that transport fat or whose protein products transport fat
00:24:45.28 around the animal have been implicated in the ability of people to live to be a hundred.
00:24:52.03 People who live to be a hundred are called centenarians and it turns out that a lot of centenarians
00:24:56.28 seem to have mutations in genes whose function is to transport fat around the body.
00:25:02.00 And the mutations cause the genes to be less active just like these long-lived worms.
00:25:06.25 So there may be a link between this part of the worm pathway and centenarians.
00:25:12.00 And that was discovered by Nir Barzilai and other people.
00:25:16.12 OK, other labs, also, using different techniques identified
00:25:19.18 individual genes that are controlled by DAF-2 and DAF-16.
00:25:23.02 And again, they found that when they inhibited their activities
00:25:27.12 in many cases they affected the lifespan of the animal.
00:25:30.20 OK, so now let's look at the big picture here.
00:25:32.20 What we've seen is that these two genes, DAF-2 and DAF-16
00:25:37.20 together control a wide variety of subordinate genes, lots of them.
00:25:41.13 See, all these genes here, not just one but many.
00:25:45.29 OK? So, it's pretty neat. It’s actually kind of like a regulatory circuit or a little cassette
00:25:54.10 in which, you know, these control genes up here say,
00:25:59.10 you know, "Dance!" and all these genes down here say "OK, I will."
00:26:04.03 So it’s kind of like an orchestra where here we have the flutes
00:26:07.25 and the violins and the cellos and
00:26:09.21 the French horns and so forth. Each doing something different,
00:26:12.12 but all doing...everybody doing it at the same time.
00:26:15.24 And actually, I should point out...I didn't really emphasize this,
00:26:18.13 but it’s important, when you change any one of these genes
00:26:21.09 you get an affect on lifespan that is not as big as
00:26:25.05 the effect that you get when you change daf-16 or daf-2
00:26:28.05 suggesting that they act in a cumulative or additive way
00:26:31.00 to produce these huge effects on lifespan.
00:26:34.29 I just wanted to point out that DAF-16/FOXO, the transcription factor,
00:26:38.06 is actually a really important regulator of lifespan.
00:26:41.13 You can get C. elegans to live long as I said by changing the DAF-2 pathway,
00:26:47.06 the insulin/IGF-1 hormone pathway,
00:26:49.06 but you can also get them to live long by changing other genes.
00:26:51.25 You can get them to live long if you over-express the gene
00:26:55.24 encoding a protein called Heat Shock Factor
00:26:57.20 which is a stress response protein that protects worms from heat,
00:27:02.12 worms and other animals from heat.
00:27:04.05 Another stress response protein called Jun kinase
00:27:06.28 or a histone deacetylase protein called SIR-2.
00:27:10.23 Over-expressing any of these proteins in the worm extends lifespan.
00:27:15.10 And interestingly, in each case the lifespan extension requires DAF-16/FOXO.
00:27:20.25 OK, so while the drawing that I just showed you has,
00:27:23.11 you know, DAF-16 and DAF-2 up at the top
00:27:25.26 and then it branches down at the bottom,
00:27:28.15 maybe it’s more like a network where you have lots of inputs-
00:27:31.07 one from DAF-2, one from SIR-2, one from Jun kinases and so forth into DAF-16
00:27:36.16 which is like a node in a regulatory circuit in a way and then you have another bifurcation
00:27:42.17 where you regulate all the downstream genes. OK, so DAF-16 is a key regulator.
00:27:47.06 So, what does it all mean? Why should insulin and IGF-1,
00:27:52.12 which are essential hormones, why should inhibiting them extend lifespan?
00:27:58.01 Insulin and IGF-1 are very important, and they're very good for you.
00:28:01.23 If you don't have them you die. If you're a worm,
00:28:04.00 if you're a mouse, if you're a dog,
00:28:05.23 or a person, anybody--everybody dies.
00:28:09.18 So, they're very important because they promote growth and food storage.
00:28:14.19 So, again, why would inhibiting their activities extend lifespan?
00:28:19.24 Well, I think this is the way to think about it.
00:28:21.29 I think that what happens is that when you
00:28:23.26 lower the level of insulin or IGF-1 you actually shift the metabolism of the animal
00:28:28.26 from one that favors growth and storage of food,
00:28:33.18 and things like that, to one that favors maintenance.
00:28:37.10 So, low insulin/IGF-1 signaling or high heat shock factor or high Jun kinase or high SIR-2 activity
00:28:44.13 promotes cell maintenance and kind of resistance to stress.
00:28:48.23 And actually these long lived animals are very resistant to lots of environmental stresses.
00:28:53.06 This was shown by Tom Johnson's lab, first by Pam Larson's lab actually a long time ago
00:28:58.19 and more recently also to other stresses by Gordon Lithgow's lab.
00:29:01.22 But basically, they're resistant to heat,
00:29:04.00 to UV, to hydrogen peroxide, to paraquat, to all sorts of things.
00:29:09.26 And it may be that the same proteins
00:29:13.03 that make them resistant to these environmental insults
00:29:16.14 also allow them to be resistant to the toxic
00:29:18.23 products that build up say from reactive oxygen species
00:29:22.18 generated by the mitochondria during normal lifespan.
00:29:25.18 So there may be a connection between the resistance that an animal has to environmental stress
00:29:31.20 and its ability to live long.
00:29:34.07 And, like I said, some of those downstream genes that I told you about do both.
00:29:38.18 They make the animals resistance to environmental stress and to aging.
00:29:45.02 OK, so the way to think about it is that you can shift the physiology from one that favors growth
00:29:49.11 to one that favors stress resistance and maintenance. OK, and then there are lots of different
00:29:54.22 ways I think to accomplish this shift-by lowering insulin/IGF-1 levels, by activating SIR-2,
00:30:01.01 heat shock factor, lots of ways. OK. `
00:30:07.05 So what are the implications for this? Well, the implication again, as I said, is that
00:30:10.09 a longevity regulatory module exists. So, this is a regulatory module for lifespan.
00:30:15.14 This is a little set of gene interactions that's built into the cell
00:30:20.07 that allows the animal to live longer. We didn't have to introduce something from Mars to
00:30:25.13 get these animals to live longer. We just briefly perturbed genes that they already have.
00:30:31.08 And because they are connected to one another
00:30:32.28 in this way functionally we get the this big affect on lifespan.
00:30:36.26 So this actually brings up an interesting question,
00:30:39.01 which is how could this regulatory module evolve?
00:30:42.23 How could it have come around in evolution?
00:30:44.28 Well, it could be that there's an advantage for the worms to get old.
00:30:50.03 So they have, you know, genes that allow them to get old.
00:30:53.18 For example, maybe it prevents an older animal from
00:30:56.23 competing with its progeny which in the case of the worm has the exact same genes because
00:31:00.22 C. elegans is a hermaphrodite so it reproduces by self-fertilization. So that's one possibility.
00:31:07.00 But there's another possibility and in order for me to explain this other possibility
00:31:10.20 to you I have to tell you a little more about the lifespan, or, sorry...
00:31:13.18 I have to tell you a little more about the lifecycle of C. elegans.
00:31:16.24 And I'll do that here in this slide. Now, what you see up here is the egg.
00:31:21.13 This is...C. elegans hatches from an egg and then it grows up to be an adult.
00:31:26.23 And it goes through these four different stages
00:31:28.22 called L1, L2, L3 and L4 and then it becomes an adult.
00:31:31.26 Now, that's what it does if there's a lot of food.
00:31:34.20 But, if you take a C. elegans egg and you put it in an
00:31:39.00 environment where there's not a lot of food
00:31:41.28 and where the animals are all crowded together,
00:31:44.03 what happens is the animals don't grow up.
00:31:46.07 Instead of becoming normal L2d's here they actually, oh sorry, normal L2 animals here.
00:31:52.11 They become L2d animals here.
00:31:54.20 And then they enter a state called dauer. Now, what's a dauer?
00:31:59.17 Dauer is a German word that means "enduring."
00:32:02.15 And this is a kind of...it's like a hibernation kind of state except it’s not really hibernation,
00:32:08.07 it's also sort of like a bacterial spore.
00:32:10.14 Anyway, these animals can move around,
00:32:12.18 but they don't eat, and they don't grow,
00:32:15.03 and they don't reproduce. They're arrested. They're sort of suspended in time.
00:32:18.21 And if you then give them food again, they exit from this dauer stage
00:32:23.04 and then they grow up and become L4s.
00:32:26.23 OK, so I should also tell you the only time an animal can become a dauer is before puberty.
00:32:33.10 Puberty is when the reproductive system matures and that happens at this time.
00:32:36.29 So, if you take an adult animal and you restrict its food,
00:32:40.12 it doesn't become a dauer-only at this time right here.
00:32:44.03 OK, so what does this have to do with the evolution of aging?
00:32:47.13 Well, let me just tell you this, if you turned the DAF-2 gene off
00:32:51.08 instead of just down (we turned it down
00:32:53.08 when we got these animals that live long)
00:32:54.28 but if you turn it off what happens is the worms hatch...
00:32:58.24 well, if you turn it completely off it’s likely that they die,
00:33:01.17 but if you turn it down really far what happens is that they hatch from an egg here
00:33:07.16 and then they grow up to become dauers. They don't grow up, they become dauers.
00:33:16.01 OK. And then they just stay there. They never grow up.
00:33:19.03 So that means that you need the normal function of the DAF-2 gene to grow to be an adult.
00:33:25.18 Now remember I told you that we found out from doing timing experiments
00:33:29.06 that DAF-2 acts during the adult to affect aging.
00:33:32.17 Of course, it acts during development to affect the dauer
00:33:35.15 because it has to. It has to be on at this time in order for the animal not to become a dauer.
00:33:40.12 That is, to be able to grow up to become an adult you have to have the gene on at this time.
00:33:44.12 And then we show, like I told you, that you have to have it on again in the adult to age normally.
00:33:49.28 OK, what the DAF-2 gene is doing is two things:
00:33:53.07 during development, it's preventing the animal
00:33:56.25 from becoming a dauer,
00:33:57.28 and during the adult it's preventing the animal from living longer than it would otherwise live.
00:34:04.01 OK, so we know already that a lot of the same genes that are...whose expression is changed
00:34:12.14 in the long-lived adults that allows the worm to live long, that those same genes
00:34:16.10 have a different expression in the dauer.
00:34:18.05 They're turned either up or down, same as the adult in the dauer.
00:34:21.26 And dauers also are resistant to all sorts of stresses.
00:34:24.04 Like, if you take a dauer and you heat it up,
00:34:25.26 it doesn't die. If you put hydrogen peroxide or paraquat on it, it doesn't die.
00:34:30.03 If you shine UV on it, it doesn't die.
00:34:31.20 So they're very stress resistant just like the long-lived adults.
00:34:35.15 OK, so it's possible that this lifespan module that I've been telling you about
00:34:40.00 didn't evolve to control the lifespan of the adult.
00:34:44.05 Maybe instead it evolved along with other dauer specific functions
00:34:49.12 to allow the dauer to live for a long time. So think about this.
00:34:53.29 If...what this means...the fact that the animal can go into dauer is very beneficial for it.
00:34:57.09 Because it means that if food is limiting it doesn't have children that will all die.
00:35:02.29 It just stops and waits for conditions to improve and then it grows up and has children.
00:35:08.06 So, it’s obviously very advantageous for a worm to be able to become a dauer.
00:35:11.22 You can see that there's great survival benefit and that would be selected for during evolution.
00:35:16.18 But, once you have the regulatory system up and running,
00:35:19.18 so that it can extend lifespan of the dauer
00:35:22.23 (dauers can live a very long time)
00:35:23.28 well, there it is. It exists. So, it seems like it’s possible then
00:35:29.01 to elicit at least part of this program in the adult
00:35:33.13 so the animals can live long. Now, I should say, the long-lived adults-they're not dauers.
00:35:37.22 They're very active. They eat, unlike a dauer. They can be completely fertile, unlike a dauer.
00:35:42.27 So, they're not completely dauers. Just like little dogs aren't dauers, they're normal little animals.
00:35:48.10 OK. but I think that the same...like I said the same
00:35:52.25 regulatory module that can allow the animal
00:35:55.24 to become.. to live long
00:35:58.12 can also be used to protect it.
00:36:01.00 In fact, it would be interesting to study mammals when they're hibernating
00:36:04.26 to see if they have low levels of insulin/IGF-1 activity or high levels of DAF-16 activity.
00:36:10.06 That would be very interesting.
00:36:12.15 OK, so it could have evolved to permit survival
00:36:16.19 in response to environmental conditions of the dauer.
00:36:20.01 But, once it’s already up and running the same system
00:36:22.27 is there so it will automatically influence aging in the adult.
00:36:26.19 And this also leads me to suggest that changes in either the regulators,
00:36:30.14 like DAF-16 or DAF-2 or SIR-2 or heat shock factor, these other regulators
00:36:35.19 or in the downstream genes like the chaperones
00:36:37.27 and other genes may be responsible for increasing lifespan during evolution.
00:36:42.21 So, in other words maybe the bat lives a lot longer than the mouse because bats have
00:36:49.12 either lower, less active regulators or more active regulators or less or more active downstream genes.
00:36:57.20 OK, the next question I want to ask is a very interesting one having to do with hormones.
00:37:01.19 The question is: Could some kind of environmental signal affect the activity of this DAF-2 pathway?
00:37:08.05 Now, one thing about hormones is that...the cool thing about them
00:37:12.08 is that they don't have to be there all the time.
00:37:13.27 They can be...a hormone can be present under some circumstances but not others.
00:37:17.23 So, for example, the hormone testosterone is present in a developing XY human embryo.
00:37:25.17 And that's why the XY embryo develops into a male, but is not present in the XX embryo.
00:37:30.11 So that's an example of a hormone being present under some conditions but not others.
00:37:35.10 So, is it possible that there are some kind of
00:37:37.03 environmental conditions that affect the activity of
00:37:40.14 this DAF-2 pathway so that you could slow down aging?
00:37:44.23 I should just note that all the changes that we've made so far are changes where we actually
00:37:50.11 reach in and change the gene itself. We make a mutation in the gene.
00:37:54.23 But, what I'm trying to suggest here is that maybe
00:37:56.08 it would be possible to change the activity of the pathway
00:37:59.05 by changing something in the environment.
00:38:01.21 OK, so the first obvious idea is caloric restriction. So, this is a rat, a picture of a rat.
00:38:08.27 And if you...a normal rat lives about three years here.
00:38:12.23 But if you calorically restrict a rat, that is
00:38:14.24 if you give it less food than it wants to eat it will live a lot longer.
00:38:19.01 And not only that, it stays disease resistant,
00:38:21.03 they don't get cancer or a lot of other age related diseases.
00:38:23.25 It's kind of magical. It's really neat.
00:38:25.28 And...so you would think that the insulin/IGF-1 pathway would mediate the response
00:38:31.05 to caloric restriction because when you eat food your insulin levels rise.
00:38:39.07 And so, I just told you that if you keep the insulin level down, and IGF-1 levels down,
00:38:43.25 you live longer, at least in these animals.
00:38:46.29 So, it’s a nice model to think that if you...when you don't eat enough you lower the level of
00:38:54.03 these hormone pathways, the activity of these pathways and as a consequence you live longer.
00:38:59.21 It’s a very pleasing idea and it seems like it’s probably right.
00:39:03.02 It's not really clear actually yet whether it's true in the worm.
00:39:05.23 It may be and it may not be. There's some conflict there.
00:39:08.24 Or it may be in some conditions but not others.
00:39:10.14 But it is pretty clear that caloric restriction...that the response to caloric restriction
00:39:15.22 is mediated at least in part by the insulin/IGF-1 pathway in yeast. Yeast actually also have
00:39:21.20 a little insulin/IGF-1 pathway. They don't have the actual hormones,
00:39:24.28 but they have some of the genes that are downstream
00:39:27.17 of the receptor, one called AKT, here.
00:39:29.25 And if you change this gene, the yeast actually are small.
00:39:33.25 They're tiny little yeast and they live long.
00:39:36.19 And it turns out that that pathway, the group of Brian Kennedy and others showed
00:39:41.24 that pathway is required for the response to caloric restriction.
00:39:46.26 In fruit flies the Partridge lab showed that the same thing is probably true.
00:39:50.27 And in mice there's some really cool experiments recently from the Bartke lab.
00:39:55.16 Now, I didn't tell you this already, but the hormone IGF-1
00:39:59.06 is produced under the control of another hormone, growth hormone.
00:40:02.29 So growth hormone, which is made by the pituitary gland, stimulates the release of IGF-1.
00:40:09.06 And mice that lack the receptor for growth hormone are also long lived.
00:40:14.11 And what Andre Bartke showed was really interesting.
00:40:18.21 He showed that if you took these long lived mice
00:40:20.20 that don't have growth hormone receptor
00:40:23.08 and you calorically restrict them, they don't live any longer.
00:40:27.01 And it's pretty cool. You take a normal mouse
00:40:30.26 and a long lived growth hormone receptor mutant mouse.
00:40:36.29 One is already living long-the growth hormone receptor mutant mouse
00:40:39.27 and that mouse, its tissues are very sensitive to insulin already.
00:40:44.26 When you calorically restrict this mouse, the mutant mouse, it doesn't live any longer
00:40:49.10 and it doesn't become any more insulin sensitive.
00:40:51.19 But when you calorically restrict the normal mouse, it becomes just as insulin sensitive
00:40:56.20 as the mutant mouse, and it lives just as long as the mutant mouse.
00:41:00.25 OK, so it kind of turns into that mutant mouse in that physiologically sense.
00:41:04.14 Although, it's not a mutant, it's just a hungry mouse.
00:41:08.13 The cool thing is both lose weight.
00:41:11.00 In fact, these growth hormone receptor mice are
00:41:13.22 just a little bit on the chubby side to begin with.
00:41:16.00 But they lose weight. So, it looks as though these growth hormone receptor mutants
00:41:22.01 are actually reaping the benefits or caloric restriction without going hungry.
00:41:26.29 So, OK, now I get to the most important part of my talk
00:41:31.00 which is to acknowledge the people that did the work that I talked about.
00:41:33.18 Now, this list of names, these are people that did the work
00:41:36.18 in both part one and part two of my lecture series.
00:41:39.22 But the work I just talked about was done by...first it was started by Ramon Tabtiong.
00:41:45.09 Ramon was a rotation student who came to my lab
00:41:47.19 and discovered that daf-2 mutants were long lived.
00:41:50.21 And I was so happy, because it was extremely hard
00:41:53.24 to get anyone at the time to come and studying aging.
00:41:55.26 People generally thought that aging was something
00:41:57.28 that just happened and there was nothing to study.
00:42:00.12 So, I was very, very lucky that he came to the lab.
00:42:03.27 Colleen Murphy did the work on the lifespan regulatory module
00:42:09.06 that I talked about. She did the microarray analysis.
00:42:11.07 And she showed that some genes were turned up in the long lived mutants and others down.
00:42:14.24 And that that made a big difference.
00:42:16.28 Andy Dillin did the timing experiments I talked about
00:42:20.10 showing that the DAF-2 gene and DAF-16 also
00:42:23.05 act exclusively in the adult to affect aging.
00:42:25.24 And Kui Lin over here, Kui cloned the DAF-16 gene and showed
00:42:32.00 that the protein that is encoded by the DAF-16 gene
00:42:34.28 is a transcription factor that regulates gene expression.
00:42:38.24 OK, see you in part 2.

Part 2: Regulation of Aging by Signals from the Reproductive System

00:00:01.17 Welcome to part two of my lecture series. When we finished the first lecture
00:00:06.15 what we were talking about was whether there might be environmental factors
00:00:11.24 that could change the level of hormones present in the worm
00:00:15.14 that would then change the activity of the insulin/IGF-1 system
00:00:19.05 which would then lead to a longer lifespan.
00:00:22.10 And we discussed the possibility, or the likelihood
00:00:24.29 that the response to caloric restriction,
00:00:27.10 that is, eating less than you want to eat, is actually
00:00:31.05 mediated at least in part, in some animals through this insulin/IGF-1 pathway.
00:00:36.15 Now what I'm going to do is to tell you something
00:00:38.20 else that's really interesting that we discovered
00:00:40.19 which is that in C. elegans, sensory perception
00:00:45.13 regulates the insulin/IGF-1 pathway.
00:00:48.02 In other words, something that the worm
00:00:49.16 is either smelling or tasting is affecting its lifespan.
00:00:52.15 So, let me introduce you first to the sensory apparatus of the worm.
00:00:57.02 This is the beautiful face of C. elegans.
00:00:58.19 You can see its lips here. It has six lips. Here.
00:01:01.24 And what you see is...see right here? There's a little nostril.
00:01:04.10 There's another one right over here.
00:01:05.16 This is the nose of the worm and this is where the sensory neurons are.
00:01:10.07 So here you can see the sensory neurons.
00:01:11.22 Here are the endings. So here's the outside, here.
00:01:13.25 And this is the inside. The worm is now standing up.
00:01:17.12 So its head is up and its tail is down.
00:01:19.18 And you see these sensory neurons here. These are the endings.
00:01:22.08 So these little neurons allow the worms to smell
00:01:25.11 and taste things that are in the environment.
00:01:26.27 And worms move towards things they like, like sugar,
00:01:29.29 and away from things they don't like, like garlic.
00:01:32.02 But what we discovered in our lab was that mutations
00:01:37.03 that prevent the worm from smelling or tasting
00:01:39.20 as well as it normally would extend the lifespan of the animal.
00:01:43.02 So what you see here in this slide are lifespan curves
00:01:46.08 of nine different mutants. Each mutant is
00:01:50.15 defective in one gene that encodes a protein
00:01:54.28 that's required for sensory perception.
00:01:57.19 And what you can see is all the mutants are long-lived in red. You see them all?
00:02:00.20 They're long-lived. So one thing you should know is that
00:02:03.24 these worms are not calorically restricted.
00:02:05.25 They're eating as much food as they want.
00:02:08.05 They eat a lot of food, as much food as normal worms eat.
00:02:10.02 And if you calorically restrict a worm it has delayed reproduction,
00:02:13.28 but these worms don't have delayed reproduction.
00:02:17.00 So they're not calorically restricted, yet they're living longer.
00:02:20.05 So, we also found that we could change genes that...
00:02:24.04 all these lifespan curves that I'm showing you here
00:02:27.15 are from the lifespans of worms with defective genes
00:02:32.19 that are needed for the structures of these neurons.
00:02:35.00 But we also found that we could make mutations
00:02:37.18 or knock-down genes whose protein products are actually
00:02:41.16 specific chemosensory receptors, proteins that are situated
00:02:44.26 right here at the very tip of these neurons
00:02:46.29 with one face open to the outside world and the other end inside the neuron.
00:02:52.15 And knocking down those kinds of proteins also could increase lifespan.
00:02:59.07 OK, so this is our model. I'm not going to go into all the details about it.
00:03:03.26 The model is that there's in the environment
00:03:07.02 that worms are smelling or tasting that's affecting their lifespan.
00:03:10.08 And we think that at least part of the way this works
00:03:12.27 is by regulating the activity of the insulin/IGF-1 pathway.
00:03:16.25 Now, why do we think that? First of all, I told you earlier
00:03:20.07 that if you inhibit the activity of the DAF-2 hormone receptor
00:03:24.18 or this pathway in various different places, worms live long,
00:03:29.18 and that they have to have DAF-16, the transcription factor,
00:03:32.09 in order to live long.
00:03:33.24 And we found that DAF-16 was also required in order
00:03:37.11 for these sensory mutants to live long.
00:03:40.17 In fact, if you make a mutation that only affects
00:03:42.24 a protein right here, in the tip of the worms nose,
00:03:44.26 DAF-16 protein accumulates in all the nuclei
00:03:47.24 of all the cells in the animal. It's amazing.
00:03:49.29 Also, if we take a daf-2 mutant that already lives long,
00:03:53.17 and we make changes in these sensory genes, the worms don't live any longer.
00:04:00.25 OK, so this is our model. The model is that
00:04:03.11 the cell bodies of these sensory neurons,
00:04:06.09 which are shown here, contain the hormone.
00:04:08.08 And they do. We know...C. elegans has about 30 or 35 genes
00:04:12.02 that encode insulin and IGF-1 like proteins
00:04:14.24 and many of them are expressed in these neurons.
00:04:17.03 So, the idea is that there's something in the environment
00:04:19.09 that is regulating the activity or the release of these hormones.
00:04:24.02 So, for example, the idea is that when the worms
00:04:27.23 are in their normal environment
00:04:29.02 these hormones are being released rapidly
00:04:31.17 and so they bind to the receptor and speed up aging.
00:04:34.07 But when we make a mutation that knocks down the activity
00:04:37.13 of this pathway by screwing up these sensory neurons,
00:04:39.27 then there's less hormone so the activity of the receptor
00:04:43.20 is down so the worms live longer.
00:04:45.22 So that's our model.
00:04:48.07 So now we've been asking...it's clever I should say.
00:04:49.28 It's clever. I forgot to say this.
00:04:52.18 What the worms seem to be doing, possibly,
00:04:54.26 is responding in advance to a changing environment.
00:04:59.06 You can imagine, caloric restriction extends lifespan
00:05:01.25 but in order for that to happen you have to actually be hungry.
00:05:05.01 But if you just have to smell or taste the difference
00:05:06.29 you may be able to get a head start on a response to a poor environment.
00:05:12.08 OK, so the question is: Which neurons influence lifespan?
00:05:17.05 There's two possible models you can imagine.
00:05:19.09 One is that one neuron or one pair of neurons, one in each nostril
00:05:24.24 affects lifespan and that's it.
00:05:26.11 The other possibility is that all of those neurons in the nostrils are affecting lifespan.
00:05:31.19 Each one...there's 12 in each so each one would have
00:05:34.16 about one twelfth of the total amount of effect.
00:05:37.23 So we decided to see which was the case or if maybe there was
00:05:40.20 a third possibility by changing...
00:05:46.21 we decided to do this by killing individual neurons with a laser.
00:05:51.03 And so what we found was really interesting.
00:05:53.18 We found that killing one gustatory neuron or taste neuron
00:05:57.08 extends the lifespan of the animal. So let me show you how we did this.
00:06:00.22 This is a picture here of part...it's really the worm's throat here.
00:06:05.20 The nose is out here in this region.
00:06:09.00 And this is where the cell bodies are.
00:06:11.08 So we can take a laser and point it at one particular cell and kill that cell.
00:06:17.01 And we can do that in lots of animals and then see if the animals live longer.
00:06:21.07 And we found that if we kill this one particular cell,
00:06:23.14 they live long as you can see here in green.
00:06:28.21 And then what we found was the following.
00:06:30.03 That if we killed a different gustatory neuron
00:06:32.18 called J, which is located right there, called J,
00:06:37.01 as well as the first one (we killed both), they don't live any longer.
00:06:41.25 OK, isn't that interesting? So here we have one neuron that promotes longevity
00:06:46.26 and one neuron that inhibits longevity.
00:06:51.10 OK, so here's another way of just telling you what I already told you.
00:06:53.26 If we kill this one taste neuron, we have a long lifespan.
00:06:58.11 If we kill that same taste neuron plus J,
00:07:00.10 we live a normal life. We have a normal lifespan.
00:07:04.25 OK, now there are also neurons that mediate the response to smell.
00:07:08.00 So we can...to smells, they're olfactory neurons. So we can kill those neurons also.
00:07:12.15 So if you kill one of these smell neurons, in many cases, the worms live longer.
00:07:16.19 And actually, if you kill a taste neuron and a smell neuron,
00:07:20.06 both in the same animal, then they live even longer.
00:07:24.22 OK, so now what happens if we take an animal and we kill a smell neuron
00:07:28.15 plus J, plus this neuron?
00:07:32.27 Smell neuron plus J. Do we have a normal lifespan,
00:07:36.20 the way we did when we killed the taste neuron plus J?
00:07:40.01 Or do we have a long lifespan? The answer is we have a long lifespan.
00:07:43.25 OK, so killing J can affect the lifespan of an animal that lacks
00:07:50.09 the taste neuron but not an animal that lacks the smell neuron.
00:07:54.22 So, in other word, J is talking to this neuron but not this neuron.
00:08:01.11 You see? So they're having little, private conversations with each other.
00:08:04.05 So this is really interesting. We also find that if we kill
00:08:06.16 certain other neurons, nothing happens.
00:08:08.29 So it looks as though neither one of our two models is correct.
00:08:13.22 It's not just one neuron matters,
00:08:15.03 but it's also not the case that all the neurons have the same function.
00:08:18.23 It looks as though there's a lot of sensory discrimination
00:08:21.04 going on in the brain of this worm that's affecting its lifespan.
00:08:23.17 So, these and other findings I don't have time to
00:08:26.01 tell you about suggest that the lifespan of C. elegans is
00:08:29.04 influenced by its perception of both soluble compounds
00:08:33.14 that it tastes and volatile compounds that it smells in the environment.
00:08:38.00 So, of course, we always ask the question:
00:08:40.28 If smell and taste affects the lifespan of worms,
00:08:44.03 is this true in other organisms as well? And very recently it was shown that...
00:08:49.24 well, I'm going to get to humans in a minute.
00:08:51.22 Very recently it was shown that the fruit fly Drosophila
00:08:57.01 that its lifespan is also regulated by sensory perception.
00:09:00.27 In other words, if you change the ability of the fly to smell, it can live longer.
00:09:05.11 So what about humans? We don't know.
00:09:06.29 And it's kind of a scary thought that something that you smell or taste
00:09:09.09 could affect your lifespan. But, I'll just leave you with one thought,
00:09:12.12 which is that if you eat some food,
00:09:15.11 your insulin levels rise. But, if you also smell the food
00:09:19.28 that you're eating, they rise even more.
00:09:24.04 Alright, what about reproduction and aging?
00:09:26.16 It's a fascinating question of great interest to evolutionary biologists
00:09:30.03 and to everyone.
00:09:33.00 What is the link between longevity and reproduction?
00:09:36.13 I already sort of mentioned in lecture number one
00:09:38.08 that there's not a necessary decrease
00:09:42.29 in reproduction in order for daf-2 mutants to live long
00:09:46.27 And, in fact, there are a lot of long lived mutants now
00:09:49.02 that have even more progeny than normal.
00:09:52.16 So there doesn't have to be a direct trade off
00:09:55.04 between the length of life that you have
00:09:57.03 and the number of offspring that you can have, which is good.
00:09:59.29 However, I should tell you that if you lower the activity
00:10:02.17 of the daf-2 receptor a fair amount,
00:10:05.07 then you get a long-lived worm that does have fewer progeny.
00:10:09.22 OK, so the same gene, the daf-2 gene, controls reproduction and aging both.
00:10:15.16 But you can uncouple them from one another.
00:10:18.02 In other words, if you just lower the level of the gene a little bit,
00:10:20.13 you live long and you reproduce perfectly well. If you lower it a little bit more,
00:10:24.23 you still live long, but now you have problems reproducing.
00:10:30.08 So now we've talked actually about three things this gene does:
00:10:32.20 it controls reproduction; it controls growth, and it controls aging.
00:10:40.11 Now what I want to tell you is something really interesting
00:10:41.28 about the reproductive system and aging.
00:10:44.21 It turns out that the reproductive system
00:10:47.01 actually controls the aging of the worm.
00:10:50.24 So to tell you that first I have to introduce you to it.
00:10:53.00 So what you see here is the reproductive system of the worm
00:10:56.03 when it's just hatched from an egg.
00:10:58.13 It has four cells in it. These two blue cells here give rise to the germ line.
00:11:03.18 And these two green cells, here, give rise to the somatic reproductive tissues
00:11:09.16 like the uterus and the ovary and so forth.
00:11:12.19 Well, what we found several years ago was that removing the germ line,
00:11:16.13 again with a laser, extends lifespan.
00:11:18.28 So here in black you see a normal worm and in blue you see the lifespan
00:11:22.14 of a worm that doesn't have any germ cells
00:11:24.19 and they live a lot longer.
00:11:26.20 It's amazing, 60% longer. So you might think,
00:11:29.29 "Alright, are they living long because they're sterile?"
00:11:34.29 But, that's not the case and the reason we know that is because
00:11:38.07 if you take a laser and you kill all four cells,
00:11:40.24 they don't live long and now they have a normal lifespan.
00:11:43.17 So they're still sterile but they don't live long.
00:11:47.18 So what this means then is that both the germ cells
00:11:51.08 and the somatic cells are affecting lifespan.
00:11:54.18 So we have a new signaling pathway here:
00:11:56.25 from the reproductive system to the rest of the animal.
00:11:58.23 The germ cells somehow, these two blue cells,
00:12:01.29 are making something that is inhibiting longevity because
00:12:05.14 when we kill the germ cells the worms are living longer.
00:12:08.14 Whereas the green cells are making something that is promoting longevity
00:12:12.10 because when you kill those then you shorten the lifespan.
00:12:18.16 OK. So, we have sort of equal and opposite effects here.
00:12:22.10 So, the germs cells are kind of in charge. It's really interesting.
00:12:26.02 The germ cells are giving rise to the next generation.
00:12:29.08 They become the next generation,
00:12:30.19 but they're also controlling the aging of the body of the animal.
00:12:36.26 So they're in charge of everything.
00:12:37.24 So you might say, "Well, why is that?"
00:12:40.12 Is that so that an animal that lacks germ cells can live long,
00:12:43.21 which seems kind of odd?
00:12:44.24 But, so we thought, "Well, why might this have evolved,
00:12:47.07 a system like this?"
00:12:48.28 And our favorite idea is the following.
00:12:50.16 The idea is that maybe having the germ cells control
00:12:54.28 the aging of the body allows the animal to coordinate
00:12:58.21 the process of aging with reproduction.
00:13:03.05 OK. It's obviously important that an animal reproduce when it's in its prime.
00:13:06.26 So, let's just see what would happen, according to this model,
00:13:09.00 if something happened to the germ cells.
00:13:10.25 So, suppose the development of the germ cells were delayed somehow.
00:13:14.08 Well, then of course the animal would also reproduce later.
00:13:18.01 Its production of progeny would be delayed.
00:13:21.00 So you might worry. You might think, "Uh oh, I hope the
00:13:22.26 worm isn't going to be too old to have progeny."
00:13:25.12 But it wouldn't because you would also be slowing down the aging of the body.
00:13:31.26 So, that would keep the animal in its prime when it's ready to produce progeny.
00:13:35.27 So, you see how potentially this system could allow the animal to coordinate
00:13:40.06 two really important things it has to do; its rate of aging with its reproduction.
00:13:47.13 OK, so how does germ line removal extend lifespan?
00:13:50.10 Well, that same transcription factor DAF-16/FOXO
00:13:53.24 is required because in animals lacking that gene
00:13:57.02 if you kill the germ cells the worms don't live long.
00:13:59.16 They still have normal lifespan.
00:14:03.00 So DAF-16 is involved. And I'm not going
00:14:05.27 to go into all the details because I don't have time.
00:14:08.19 But what I'll just tell you is removing the germs cells activates
00:14:12.02 another kind of hormone pathway, a steroid hormone pathway.
00:14:15.11 And these hormone pathways activate DAF-16 which extends lifespan.
00:14:20.24 And this is work from two labs; from the Antebi lab
00:14:23.19 who's discovered a sterol hormone called dafachronic acid
00:14:28.29 that acts in this pathway and Etienne Baulieu's lab
00:14:32.18 in collaboration with our lab whose work implicates
00:14:35.21 a different steroid hormone, pregnenolone, in this pathway.
00:14:41.22 OK, so what happens now if we take a worm and we change the daf-2 gene
00:14:46.10 and the reproductive signaling system both in the same animal?
00:14:50.03 What we get is something quite amazing.
00:14:52.10 We get an animal that lives six times as long as normal.
00:14:55.02 So, normal worms in this experiment have a lifespan of 20 days on average.
00:14:59.12 These worms lived 126 days. And what's really spectacular
00:15:03.09 is that they stay young and healthy for a really long time.
00:15:06.28 So this is a movie of these worms when they were 144 days old.
00:15:10.21 And you can see that they're moving.
00:15:12.08 If you think back to the slide...the movie that I showed you
00:15:14.24 at the beginning of the first lecture series.
00:15:16.16 Remember that worms that were 13 days old, that were just lying there,
00:15:21.07 in the nursing home. These animals are ten times as old,
00:15:23.18 and they're still moving around.
00:15:25.09 So, it's absolutely remarkable that you could do this,
00:15:28.23 that you could make a few very small changes
00:15:30.22 and produce a six-fold extension of lifespan is just amazing.
00:15:35.11 And it really makes you...this would be like people that live to 500.
00:15:38.20 So it really makes you wonder just what's possible.
00:15:41.07 I'm not saying that people could live to 500. I don't know. We don't know.
00:15:46.01 But, in human terms that's what it would be like and they're on the golf course.
00:15:52.11 OK, what about mammals?
00:15:53.12 Could the reproductive system affect lifespan in mammals?
00:15:55.22 It does. The lab of Gary Anderson and Jim Carey have shown,
00:15:59.15 those two labs have shown
00:16:00.27 that if you take a mouse and you remove
00:16:04.02 its own reproductive organs, the female mouse,
00:16:06.23 and you let it get old and then you introduce
00:16:10.02 the reproductive tissues from a young mouse into an old mouse
00:16:14.23 the old recipient mouse lives longer.
00:16:18.24 So, in other words, putting young reproductive tissues into
00:16:21.25 an older mouse extends the lifespan of the older mouse.
00:16:24.27 It's amazing because somehow the reproductive system is sending signals
00:16:29.01 to the rest of the body telling it not to age as fast.
00:16:32.20 We don't know at all how this works or if it's
00:16:35.14 related to the system I've been telling you about.
00:16:37.08 But, it's pretty cool because it's the reproductive system.
00:16:42.15 OK, so now the last thing that I want to talk about in my lecture series here
00:16:47.06 is what links normal aging to age-related disease?
00:16:51.13 This is a really important question.
00:16:52.28 There are all sorts of diseases that you get at
00:16:56.07 a much higher frequency if you're old.
00:16:58.03 You're 100-times more likely to get a tumor at age,
00:17:01.09 say, 65 than you are at age 35, much more likely.
00:17:04.22 And the same with lots of other diseases like Alzheimer's disease,
00:17:07.00 cardiac malfunction, all sorts of things.
00:17:09.25 So, what is it? Why is it that an older individual is more susceptible.
00:17:15.00 Well, you can ask the question genetically.
00:17:18.11 You can say, "Here's a pathway, the DAF-16/DAF-2 pathway
00:17:21.14 that affects aging. So, does the same pathway affect age related disease?"
00:17:28.10 And the answer is yes. And it's quite remarkable just how pervasive this effect is.
00:17:33.19 So let's start here with worms.
00:17:34.26 You can cause worms to get Huntington's disease or Alzheimer's disease by
00:17:38.26 expressing the genes that cause those diseases
00:17:41.04 in the worm and it turns out that the long-lived daf-2 mutants
00:17:45.20 are resistant. They get the diseases but not until they're much older.
00:17:50.00 Worms, normal worms actually, develop a muscle condition
00:17:53.02 that's very similar to human sarcopenia
00:17:55.06 where the muscles start to deteriorate when they get old.
00:17:57.25 And the daf-2 mutants get that condition later.
00:18:02.28 In the case of flies they've done a very interesting experiment.
00:18:05.23 If you take an electrical shock and you
00:18:11.04 deliver it to the heart of a young fly at a certain strength, the fly is fine.
00:18:15.20 But if you give an old fly that same shock, its heart fails.
00:18:21.02 But if you take this long-lived insulin/IGF-1 receptor mutant fly
00:18:25.06 and you do the same thing to it,
00:18:27.12 you stress the heart, even when it's old,
00:18:29.10 even when it's on its deathbed, the heart's fine.
00:18:31.26 So, in this case the heart seems to be in better shape
00:18:34.03 than the rest of the animal.
00:18:38.09 So there's an affect on cardiac function.
00:18:39.26 In mice we know that cancer is delayed in these long-lived animals.
00:18:44.22 And there are unpublished reports now of a lot of
00:18:46.24 other diseases as well that are delayed.
00:18:50.11 OK, so it looks like these animals really are young in every sense of the word.
00:18:55.25 They look young and they're young in the sense that
00:18:57.29 they're not susceptible to age-related diseases.
00:19:00.11 OK, so I'm going to tell you a little bit now about one particular
00:19:03.15 age-related disease that we've been studying in our lab.
00:19:05.24 Oh, first before I do, I meant to tell you that this ushers in the possibility
00:19:10.15 of a brand new therapeutic strategy where we go after
00:19:15.01 lots of age-related diseases all at once by going after aging.
00:19:19.01 In other words, if we can slow down aging, then we can slow down
00:19:22.07 cancer, heart disease, protein aggregation diseases,
00:19:24.23 all the diseases of aging potentially.
00:19:26.15 So it's...we don't know if this would really work,
00:19:29.06 but it seems to be working for worms at least
00:19:33.09 and these other animals as well so the potential is huge.
00:19:37.17 And actually I founded a biotech company called
00:19:40.12 Elixir Pharmaceuticals that's trying to
00:19:43.27 develop compounds like that, to go after age related diseases
00:19:46.10 by going after aging itself, pathways that control aging.
00:19:51.23 OK, so now what I want to do is to tell you about
00:19:53.21 some work that we've been doing in our lab
00:19:55.03 on tumors that worms get. So, worms normally don't get tumors.
00:20:00.01 But you can cause them to get tumors with a mutation.
00:20:03.04 This is what...and these tumors affect the germ cells.
00:20:06.12 So, now what I want to do is introduce you to the
00:20:08.25 reproductive system of the normal adult worm.
00:20:10.29 I showed you before the reproductive system of the animal
00:20:13.12 at hatching when it only had four cells,
00:20:15.24 but now I'll show you what they look like when they're adults.
00:20:19.20 So what you can see is the reproductive system is huge,
00:20:22.09 here and it has these green cells, here, are the oocytes.
00:20:24.25 And these red cells here are the stem cells, the germ line stem cells that keep dividing in the adult
00:20:30.00 to replenish the germ cell population.
00:20:33.19 OK, so now mutations in a gene called GLD-1 which stands for germ line
00:20:38.08 defective number 1 cause germ line tumors.
00:20:42.07 And I'll show you what these look like.
00:20:43.10 What happens...so this is what the normal reproductive system looks like, again.
00:20:47.28 Here in green you see the oocytes.
00:20:49.15 But now look at this. In the mutant these oocytes
00:20:53.10 change their mind and they start to proliferate again.
00:20:56.22 They become very similar to these stem cells here.
00:20:58.29 And they divide and divide and divide and pretty soon
00:21:02.28 they fill up the whole gonad
00:21:03.28 and they burst out of the gonad and they fill
00:21:05.22 the whole entire animal up and then the animal dies.
00:21:08.11 So its lifespan is about half of what it would be normally.
00:21:12.22 OK, so we wanted to know: Do mutations
00:21:15.11 that extend lifespan delay the gld-1 tumor phenotype?
00:21:20.00 OK, do they delay the tumor?
00:21:23.26 OK, now there are lots of different longevity pathways in C. elegans.
00:21:27.29 And I'm just going to remind you of the ones I told you about
00:21:31.18 and tell you about a couple new ones.
00:21:32.29 First of all there's the insulin/IGF-1/FOXO signaling pathway
00:21:36.08 that I've been telling you about.
00:21:37.13 There's also caloric restriction, you can get worms...
00:21:40.10 you can calorically restrict worms by using a mutation
00:21:42.24 that prevents the animal from eating food very well.
00:21:45.05 That's an eat-2 mutant and those worms live longer.
00:21:49.04 You can also get worms to live long by perturbing
00:21:52.04 the mitochondria in various ways.
00:21:53.20 If you make mutations that inhibit respiration, worms live long.
00:21:57.24 And one of these mutations is one that's been studied
00:21:59.24 in the Hekimi lab called isp-1.
00:22:02.02 And another mutation that affects the production of ubiquinone
00:22:04.29 also studied in the Hekimi lab is called clk-1.
00:22:07.27 And these mutants also live long.
00:22:09.22 And this pathway seems to be different from either caloric
00:22:13.16 restriction or the insulin/IGF-1 pathway.
00:22:15.23 OK, so the question is: What happens to these tumors in these mutants?
00:22:23.15 All these pathways are conserved so it seems like
00:22:25.29 a reasonable question to ask because
00:22:28.00 what we learn in worms may have relevance for higher organisms.
00:22:32.19 And as I already told you, both caloric restriction and insulin/IGF-1 signaling
00:22:38.03 are known to extend lifespan and delay tumors in mice.
00:22:42.08 OK, so we wanted to see what we could learn from the worm.
00:22:44.28 So there were several possible outcomes. I should tell you right away that
00:22:50.10 there are mutations in mice that have been described that affect proteins like
00:22:54.29 p53 and other proteins that have a kind of bad effect on the animal.
00:22:59.15 They suppress the formation of tumors, but they speed up aging.
00:23:02.03 So there's a trade off there. You benefit by not having a tumor, but
00:23:06.10 you don't really benefit because you're dead anyway
00:23:07.24 because you die of premature aging.
00:23:10.19 So one possibility would be that any or all of these pathways
00:23:15.11 could actually cause the tumor...if the worms would live long
00:23:20.05 without the tumor, but they might speed up aging.
00:23:23.17 That's one possible outcome. The next possible outcome is that
00:23:26.14 there's no affect on the tumor.
00:23:27.16 In which case, the animals would still die from the tumor at a normal time.
00:23:30.12 And the third possibility is that these mutations would cause
00:23:34.28 the animals to get the tumors later in life.
00:23:38.00 So the animals would live longer.
00:23:40.20 And what we found is that all of the longevity mutations
00:23:43.12 extended the lifespans of the tumor mutants;
00:23:45.10 the caloric restriction mutations, the daf-2 mutations,
00:23:48.04 and also the mitochondrial mutations.
00:23:52.08 The daf-2 mutants were amazing.
00:23:53.22 They were completely immune to the lifespan shortening effects of the tumors.
00:23:57.03 This is normal worm here in gold.
00:23:58.20 That's its lifespan. They're all dead in this experiment by about 25 days.
00:24:05.14 And this is what happens if you just introduce the tumor
00:24:08.20 mutation into a normal worm.
00:24:10.08 You cut the lifespan in half.
00:24:12.09 And now out here you see the wonderful long daf-2 lifespan in red
00:24:16.10 and you see that it doesn't really shorten much at all,
00:24:18.26 if any. It's not statistically significantly different
00:24:22.03 if you introduce the gld-1 mutation.
00:24:26.14 In other words, in a daf-2 mutant the gld-1 mutation no longer kills the animal.
00:24:30.23 The tumor doesn't kill the animal. So, why not?
00:24:33.08 Here's what the animals look like. Let me just introduce you to this.
00:24:37.00 This is a little line drawing of the head of a worm.
00:24:39.07 Here's the pharynx, here. And this is the intestine here.
00:24:43.12 And what you see here in this drawing or this photograph are the nuclei
00:24:49.22 of cells that are stained with DAPI, which is a stain for DNA.
00:24:52.12 And now, look at this. This is the gld-1 tumor mutant.
00:24:56.04 And what you see is that the animal is just jam packed full of germ cells.
00:25:00.13 And that's why it dies very soon, very early.
00:25:04.06 But this is what the tumor looks like in the daf-2 mutant. It's much smaller.
00:25:09.16 There still...it doesn't look normal. You don't have the oocytes back,
00:25:13.00 but there are 50% fewer germ cells here.
00:25:16.24 And so it doesn't...it's no longer toxic or lethal to the animal.
00:25:20.12 OK, so how exactly do these longevity mutations inhibit the tumor?
00:25:25.10 What are they doing?
00:25:26.22 Well, first of all let's talk about what the gld-1 mutation does.
00:25:29.23 It does two things...it causes a tumor.
00:25:31.28 It does two things; it speeds up or it promotes cell division
00:25:37.16 and it prevents apoptosis. Apoptosis is programmed cell death.
00:25:42.00 So, in the gld-1 mutant...normally in a normal germ line some cells just die.
00:25:48.13 But in the gld-1 mutant they no longer die.
00:25:51.05 OK, so if you have fewer dead cells and you have more cell divisions,
00:25:55.04 you're going to get a tumor.
00:25:56.04 And that's what happens.
00:25:58.29 OK, so what do the daf-2 mutations do to delay the growth of the tumor?
00:26:04.13 Well, the first thing is they cause apoptosis to occur.
00:26:07.25 So here is the normal worm, called N2.
00:26:10.00 Here's the apoptosis that you see in the normal worm.
00:26:12.10 Here's the tumor mutant where it's gone.
00:26:14.12 And you see in the daf-2 mutant it comes back partly.
00:26:17.14 And here in this part you see these two little dots here
00:26:21.16 are little cells that are undergoing cell death.
00:26:24.15 They're stained with something that is specific for cells
00:26:28.22 that are undergoing apoptosis.
00:26:32.20 The daf-16 gene is required for this.
00:26:37.08 What about p53?
00:26:38.09 p53 is a famous tumor suppressor gene that's known
00:26:41.03 to play a role in apoptosis in mammals.
00:26:42.29 So is it required?
00:26:45.01 Yes, it is. Here what you see is a normal worm.
00:26:48.12 There's a certain amount of apoptosis.
00:26:52.04 Oh, I'm sorry, this is a worm treated with gld-1 RNAi so it has a tumor.
00:26:57.07 So the level is low. You have a little bit because the RNAi
00:27:00.01 is not quite as effective as the mutation.
00:27:01.24 It goes way up in a daf-2 mutant, and then it goes back down again if you take away p53.
00:27:08.17 Ok, now I have to tell you something interesting about this.
00:27:10.24 In C. elegans, p53 plays only a minor role
00:27:15.08 in germ cell death under normal conditions.
00:27:18.00 But, what we really see the effect of p53 is when you
00:27:23.03 take a worm and you shine...you expose it to gamma rays
00:27:28.03 or other agents that produce damage in DNA.
00:27:31.13 Then you get a lot of cell death, and that cell death
00:27:33.23 in the germ line requires p53.
00:27:36.29 OK, so I told you that cell death...sorry, I told you that
00:27:40.23 daf...sorry that p53 is required
00:27:43.12 for the increase in cell death that you get in a daf-2 mutant.
00:27:47.00 So we wondered, "Is it possible that a daf-2 mutant
00:27:49.16 is sort of similar to an animal that's been subjected to genic toxic stress.
00:27:53.22 So, in other words, are daf-2 mutations maybe inducing a response to stress?
00:27:58.14 And we think that's probably the case.
00:28:00.18 Part of the reason we think that is we found that DAF-16,
00:28:03.19 the transcription factor, is required for gamma rays
00:28:06.26 to trigger germ cell death in normal worms.
00:28:09.27 Both p53 and DAF-16 are needed for this extra cell death in the daf-2 mutant
00:28:14.23 and in a normal worm that you treat with gamma rays.
00:28:18.27 So, we also tested another, different kind of a tumor.
00:28:22.15 This tumor has a different name, it's called glp-1
00:28:25.06 and this is a tumor in which what happens is that the germ line stem cells
00:28:29.15 just keep dividing. The oocytes are still oocytes.
00:28:34.01 This is affecting a different population of cells.
00:28:36.01 In this case, what happens is that normally there's a receptor
00:28:39.29 on the surface of the stem cells that
00:28:41.13 receives a signal from the environment, from nearby cells, telling them to divide.
00:28:45.23 And what happens is that when the germ cells move away
00:28:49.28 from the source of the signal they stop dividing.
00:28:51.25 But in this mutant, the receptor for this signal
00:28:55.06 is just on all the time even if there's no signal.
00:28:57.29 So these cells just divide and divide and divide, and they make a tumor.
00:29:00.10 So what happens in this tumor?
00:29:03.06 We found that daf-2 mutants or mutations
00:29:05.25 also extend the lifespan of this tumor mutant,
00:29:07.24 but they don't trigger germ line cell death so they're doing it a different way,
00:29:11.14 specifically by cell proliferation. I'll get to that in a minute.
00:29:14.07 But, keep this in mind because I'll come back to this later.
00:29:17.10 So what about cell division? We found that daf-2 mutations reduce mitosis,
00:29:22.20 cell division, in both tumor mutants, in both gld-1 and glp-1.
00:29:26.29 So here you see dividing cells in the normal animal,
00:29:30.03 lots of dividing cells in the tumor mutant
00:29:32.14 and many fewer dividing cells in the...when you put
00:29:35.15 daf-2 mutations into the tumor mutant.
00:29:41.28 The cool thing is that daf-2 mutations don't just willy-nilly block cell division.
00:29:49.00 They only block cell division within the tumor.
00:29:51.11 Here's what happens. So here's the tumor, with lots of cell division.
00:29:54.26 And here's when you put a daf-2 mutation into the tumor,
00:29:58.10 into the animal containing the tumors.
00:30:00.14 Cell division goes down, but look what happens if you put a daf-2 mutation
00:30:03.19 into a normal worm.
00:30:06.00 We still get the same amount of germ cell proliferation, no effect.
00:30:11.00 So that's really neat. Somehow it knows which cells are the tumor cells.
00:30:14.00 I mean it doesn't really know consciously but you know,
00:30:16.25 teleologically, you could say that.
00:30:18.23 So I just want to stop for a second and pause here
00:30:21.04 and say that this...we see effects both on cell death and on cell proliferation.
00:30:25.25 And there's some similarities here between the worms
00:30:28.22 and vertebrates, and I'll point them out now.
00:30:30.25 One is, in humans it's known that mutations
00:30:35.19 that activate insulin and IGF-1 signaling cause cancer.
00:30:41.04 So we've shown the opposite in the worms.
00:30:43.02 We've shown that if you turn down insulin/IGF-1 signaling,
00:30:46.10 lower than it would be normally, you actually sort of cure cancer.
00:30:51.07 I mean you don't die from it anyway. I shouldn't say cancer either.
00:30:53.22 These are tumors. And I should make this clear.
00:30:55.13 These tumors they...a tumor is a group of cells that
00:31:01.06 is proliferating too much. It's over proliferating.
00:31:03.25 And that's what happens. That's why they're called tumors.
00:31:05.28 But the cells don't undergo the late stages of human cancer
00:31:09.18 like angiogenesis where they attract blood vessels
00:31:13.00 and they don't actually actively metastasize.
00:31:15.22 So they're a good model possibly for the early events of human tumors
00:31:19.10 but not the later ones. I should have made that point clear before.
00:31:22.02 But anyway, the cool thing is that what we've shown is that if you
00:31:25.08 inhibit this pathway you can actually do the opposite of what you would do
00:31:30.14 of what would be happening in a human that has a mutation that
00:31:33.19 increases the level of signal.
00:31:36.23 The second thing is, I told you before that
00:31:39.06 in the long-lived mice that have defects in this pathway
00:31:43.25 it's known that cancer levels are down and
00:31:46.14 what our findings suggest is that maybe DAF-16 and p53
00:31:50.09 are involved in this. Maybe that's the pathway.
00:31:52.07 Nothing is known about the pathway in the mice,
00:31:54.12 but maybe that's the pathway and maybe that's
00:31:56.10 affecting cell death as well as mitosis.
00:32:00.03 What about the other mutants?
00:32:01.05 Well, caloric restriction and mitochondrial mutations
00:32:04.07 also inhibit the tumor growth. Here's a picture, again,
00:32:08.11 a diagram of the head of the worm.
00:32:09.28 And here's the DAPI staining and this is the animal packed full of germ cells
00:32:14.11 and you can see that it's a lot better
00:32:15.24 if you, in this case, introduce a mutation that causes caloric restriction and
00:32:20.12 you get the same effect if you introduce
00:32:21.21 a mutation that affects the mitochondria.
00:32:24.18 They don't affect apoptosis (cell death),
00:32:28.14 but they do reduce the number of mitotic germ cells.
00:32:31.19 And amazingly none of them affect mitosis
00:32:35.01 in the normal germ line, none of them.
00:32:37.27 The daf-2 mutation I told you before and these
00:32:40.10 mitochondrial mutations and the eat-2 mutation,
00:32:42.21 none of them affect normal mitosis, just...they all
00:32:45.02 can tell the difference between normal mitosis and the tumor.
00:32:48.21 And so how do they do that? Why should this be?
00:32:52.04 Well, we have an idea and I think a clue comes from the stem cell tumor,
00:32:56.03 the glp-1 mutant that I told you about.
00:32:57.27 Now, in that tumor, daf-2 mutations inhibit cell divisions and those tumors,
00:33:04.05 the glp-1 tumors, are thought to consist of lots of normal germ line stem cells.
00:33:09.10 In other words, those tumors, if you recall, are different from...
00:33:13.15 are caused because the receptor for
00:33:18.00 a growth factor is...thinks it's on all the time.
00:33:22.07 It's mutant so it's constitutively active.
00:33:24.14 And that's why the cells are dividing.
00:33:26.08 But that receptor is normally active in those cells at a normal time.
00:33:29.20 So basically, I think what we've done in that mutant
00:33:32.03 is just to make many more copies of normal cells.
00:33:34.28 The cells aren't, probably, any different
00:33:37.00 from a normal cell, but they're just more of them.
00:33:38.21 And yet, when there's a lot of them,
00:33:41.03 you need DAF-2 for cell division and these other genes for cell division.
00:33:46.10 Whereas when there's just a few of them you don't.
00:33:48.29 So the model then is a tumor is a large metabolic load.
00:33:53.14 In other words, having all these cells
00:33:55.07 dividing and dividing may require a lot of energy, a lot of nutrients.
00:33:59.15 And perhaps these longevity pathways, which as I told you
00:34:02.25 shift the physiology of an animal from
00:34:04.26 one that favors growth to one that favors maintenance,
00:34:07.01 maybe they just can't support the tumor.
00:34:09.21 They can...it's not a problem for them to support
00:34:12.08 the small little group of germ line cells that are dividing normally.
00:34:18.05 But when you put a real big metabolic load on they just can't stand it.
00:34:22.00 And that's why I think the tumor cells are probably affected.
00:34:24.10 At least that's the model.
00:34:27.03 OK, so to summarize: daf-2 mutations do two things:
00:34:29.28 they induce a stress response that triggers apoptosis
00:34:33.02 in a p53 dependent fashion,
00:34:34.29 and they also reduce mitosis within the tumor,
00:34:38.20 and the other mutations specifically reduce mitosis.
00:34:41.24 This raises an interesting question of whether these clk-1 mutations
00:34:46.06 are going to turn out to affect tumors in mammals and stay tuned.
00:34:50.07 So, a few thoughts about this:
00:34:52.08 first of all, we see a really strong correlation in these worms between
00:34:56.21 the rates of normal aging and tumor growth
00:34:58.12 and a variety of different longevity mutants.
00:35:01.04 In nature it's generally the older individuals that are susceptible to cancer.
00:35:05.21 And it's not...the animals aren't...it's not the number of days they've been alive.
00:35:09.19 So, for example, people get high rates of cancer
00:35:12.20 after many decades, 60, 70 so forth, at high rates.
00:35:16.06 Whereas a dog gets cancer at the same high rate when it's 10 years old
00:35:20.14 and a mouse when it's just a year and a half.
00:35:22.16 But all these animal have in common the fact that they're elderly.
00:35:26.08 OK, so there's this correlation that you see in all animals
00:35:29.20 between being elderly and being susceptible to cancer.
00:35:32.07 And so it's really interesting that all these mutations
00:35:35.25 that increase lifespan also delay tumors,
00:35:38.00 and it suggests to me that maybe single gene mutations
00:35:41.07 in the genes that I've been telling you about or
00:35:43.02 the downstream genes they control link these two processes during evolution.
00:35:46.27 In other words, you have an animal with a short lifespan
00:35:48.26 and there's a mutation that
00:35:50.11 increases the lifespan. Maybe that same mutation
00:35:52.22 also makes it more tumor resistant.
00:35:54.25 So that if you keep doing this, you know,
00:35:57.02 through evolution pretty soon you get a human
00:35:58.14 that has a really long lifespan and stays really resistant to cancer for a long time.
00:36:04.05 OK, alright so I'm going to end now my lecture series.
00:36:07.09 And I just want to tell you about the people who did the experiments
00:36:09.25 I talked about in part two of my series.
00:36:12.26 I started off by talking about sensory perception.
00:36:15.16 Javier Apfeld is the one who discovered that sensory mutants
00:36:18.28 extend the lifespan of worms.
00:36:20.14 Joy Alcedo did the experiments of killing individual neurons and showing
00:36:23.24 that there's a really an elaborate sensory processing going on here
00:36:27.11 in the brain of the worm.
00:36:28.08 Honor Hsin showed that killing the germ cells extends lifespan.
00:36:33.18 And Kui, Natasha, Jen have worked on the reproductive system.
00:36:39.20 And also I mentioned that in collaboration with Florence Broue,
00:36:43.05 who was a graduate student in Etienne Baulieu's lab
00:36:45.11 and our lab...this collaboration resulted in the knowledge that steroid hormones
00:36:52.01 can influence the lifespan of C. elegans via this pathway.
00:36:57.22 And I also mentioned that Adam Antebi's lab working independently showed
00:37:00.27 that dafachronic acid, a sterol hormone, was part of this pathway.
00:37:04.20 Nuno Arantes-Oliveira produced these worms
00:37:07.23 that lived 6-times as long as normal, these amazing worms.
00:37:10.13 And Julie Pinkston did all the work on the tumors that I talked about.
00:37:14.17 OK, thank you very much.

Videos in this Talk
  • Part 1: Genes that Control Aging
    Part 1: Genes that Control Aging
    Audience:
    • General Public
    • Student
    • Researcher
    • Educators of H. School / Intro Undergrad
    • Educators of Adv. Undergrad / Grad
  • Part 2: Regulation of Aging by Signals from the Reproductive System
    Part 2: Regulation of Aging by Signals from the Reproductive System
    Audience:
    • Researcher
    • Educators of Adv. Undergrad / Grad
Speaker: Cynthia Kenyon
Total Duration: 1:20:02
Recorded: May 2007
Educator Resources for this Talk
All Talks in Development and Stem Cells

Talk Overview

Once it was thought that aging was just a random and haphazard process. Instead, the rate of aging turns out to be subject to regulation by transcription factors that respond to hormones and other signals. In the nematode C. elegans, in which many key discoveries about aging were first made, the aging process is subject to regulation by food intake, sensory perception, and signals from the reproductive system. Changing aging genes can lengthen lifespan by six fold, and can also delay age-related disease, such as the growth of tumors.

Speaker Bio

Cynthia Kenyon

Cynthia Kenyon

Cynthia Kenyon graduated valedictorian in chemistry and biochemistry from the University of Georgia in 1976. She received her PhD from MIT in 1981, where, in Graham Walker’s laboratory, she was the first to look for genes on the basis of their expression profiles, discovering that DNA damaging agents activate a battery of DNA repair genes… Continue Reading

Playlist: Model Organisms

Related Resources

Tatar, M, Bartke, A, Antebi A. The endocrine regulation of aging by insulin-like signals. Science 299. 1346. (2003)

Cynthia Kenyon, Jean Chang, Erin Gensch , Adam Rudner and Ramon Tabtiang. A C. elegans mutant that lives twice as long as wild type. Nature 366(6454), 461-464 (1993)

Kimura, KD, Tissenbaum, H, Liu and Ruvkun, G. daf-2, an insulin receptor-like gene that regulates longevity and diapause in Caenorhabditis elegans. Science 277, 942 (1977)

Honor Hsin and Cynthia Kenyon. Signals from the reproductive system regulate the lifespan of C. elegans. Nature 399(6734), 362-366 (1999)

Javier Apfeld and Cynthia Kenyon. Regulation of lifespan by sensory perception in Caenorhabditis elegans. Nature 420(6763), 804-809 (1999)

Kui Lin, Honor Hsin, Natasha Libina and Cynthia Kenyon. Regulation of the Caenorhabditis elegans longevity protein DAF-16 by insulin/IGF-1 and germline signaling. Nature Genetics 28(2), 139-145 (2001)

Andrew Dillin, Douglas K. Crawford and Cynthia Kenyon Timing Requirements for Insulin/IGF-1 Signaling in C. elegans. Science 298(5594), 830-34 (2002)

Coleen T. Murphy, Steven A. McCarroll, Cornelia I. Bargmann, Andrew Fraser, Ravi S. Kamath, Julie Ahringer, Hao Li and Cynthia Kenyon. Genes that Act Downstream of DAF-16 to Influence the Lifespan of Caenorhabditis elegans. Nature 424(6946), 277-283 (2003)

Nuno Arantes-Oliveira, Jen R. Berman and Cynthia Kenyon. Healthy animals with extreme longevity. Science 302(5645), 611 (2003)

Natasha Libina, Jen R. Berman and Cynthia Kenyon. Tissue-specific activities of C. elegans DAF-16 in the regulation of lifespan. Cell 115(4), 489-502 (2004)

Joy Alcedo and Cynthia Kenyon. Regulation of C. elegans Longevity by Specific Gustatory and Olfactory Neurons. Neuron 41(1), 45-55 (2004)

Julie M. Pinkston, Delia Garigan, Malene Hansen, and Cynthia Kenyon. Mutations that increase the life span of C. elegans inhibit tumor growth. Science 313(5789), 971-975 (2006)

Cynthia Kenyon. The plasticity of aging: insights from long-lived mutants. Cell 120(4), 449-460 (2005)

Reader Interactions

Comments

  1. Christopher Manley says

    Hello I am looking for a procedure and materials list for the lifespan altering experiment with C. eleagans. I will be trying recreating this experiment for a undergraduate research project any help will be greatly appretiated

    Reply

  2. Pedro Luiz Maciel Caetano says

    Your class is amazing. Once a teacher told me that a scientist is like a salesman, and you sold your idea very good! Congratulations

    Reply

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