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

Transcript of 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.

This material is based upon work supported by the National Science Foundation and the National Institute of General Medical Sciences under Grant No. 2122350 and 1 R25 GM139147. Any opinion, finding, conclusion, or recommendation expressed in these videos are solely those of the speakers and do not necessarily represent the views of the Science Communication Lab/iBiology, the National Science Foundation, the National Institutes of Health, or other Science Communication Lab funders.

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