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Skin Stem Cells: Their Biology and Promise for Medicine

Part 1: Skin Stem Cells: Their Biology and Promise for Regenerative Medicine

00:00:14.12 Hello.
00:00:15.12 My name is Elaine Fuchs.
00:00:17.02 I'm a professor at The Rockefeller University in New York City,
00:00:22.05 and I'm an investigator of the Howard Hughes Medical Institute.
00:00:26.16 And today I'd like to tell you about stem cells, about their biology and about
00:00:31.13 their promise for regenerative medicine.
00:00:36.18 So, let's go to the very beginnings of stem cell biology.
00:00:41.00 The word stem cell itself is a relatively recent word.
00:00:44.20 It was only in 1877 that Ernst Haeckel, a German scientist, coined the word stammzelle, or stem cell,
00:00:55.06 a fertilized egg that gives rise to all the cells in the body.
00:00:59.25 That was the initial definition of stem cells.
00:01:04.19 And then the word stem cell became popularized by EB Wilson, a famous cell biologist in the late 1800s,
00:01:11.25 who wrote about it in one of his books.
00:01:16.02 So then, it was about 30 years later when this person, Alexander Maximow, was a...
00:01:21.08 he was a Russian scientist.
00:01:23.26 He fled the Russian Revolution and joined the ranks of the University of Chicago.
00:01:28.28 He was a cytologist.
00:01:30.20 And just looking underneath the microscope at bone marrow cells, he saw some cells
00:01:36.19 that seemed undifferentiated.
00:01:38.24 And he predicted, at that time, that perhaps the bone marrow contained a cell that
00:01:46.01 can give rise to all the different hematopoietic cell lineages.
00:01:51.05 And that was the first notion that stem cells might not simply be restricted to
00:01:58.16 embryonic stem cells, the cells that can give rise to all the cells of our body, but actually that
00:02:02.26 different tissues might actually contain stem cells, adult tissue stem cells that had
00:02:09.22 a more restricted potential, being, in this case, able to give rise to the hematopoietic lineages.
00:02:16.18 But that was just a postulate.
00:02:20.02 And we now have to fast-forward some 60 years later, when these two individuals,
00:02:27.06 Ernest McCullough and James Till, back in 1961, did the remarkable experiment that demonstrated
00:02:33.20 the existence of adult tissue stem cells.
00:02:38.03 They took a laboratory animal, and they irradiated its bone marrow.
00:02:43.24 And then they took a healthy bone marrow, and one by one, put in the cells from
00:02:48.24 the healthy bone marrow until they found a single cell that could reconstitute the
00:02:55.13 entire hematopoietic cell lineages of the bone marrow.
00:02:59.04 And that was the first demonstration that tissue stem cells existed within adult...
00:03:08.06 the adult.
00:03:09.11 And that really opened the door for some really exciting biology to come.
00:03:15.02 So, let's fast-forward now, again, to... another 15 years or so, after the pioneering work
00:03:23.04 of Till and McCullough, and now it wasn't until the mid 1970s when this person,
00:03:30.24 Howard Green, who recently passed away... he was then at MIT, and he took a piece of
00:03:37.23 human skin, and was able to culture and passage cells from the piece of human skin,
00:03:45.22 and he could passage them endlessly under conditions where the cells could still make tissue.
00:03:52.25 This established the existence of the ability to culture adult tissue stem cells,
00:03:59.18 in this case stem cells coming from the skin.
00:04:02.13 So, let's take a look at some of the experiments that were done in those early days.
00:04:07.20 It was possible to effectively culture the embryo, in this case the adult skin stem cells,
00:04:17.00 and passage those cells.
00:04:18.03 And you see in the middle panel the chromosomes, the dark chromosomes within the cells.
00:04:24.15 These cells were rapidly dividing in culture.
00:04:28.06 And if you look at the bottom panel, what you see is actually reconstituted skin,
00:04:34.15 in this case reconstituted epidermis, that was generated entirely from these single stem cells
00:04:41.06 that were cultured.
00:04:42.17 In fact, we didn't call them stem cells at the time.
00:04:46.12 We called them keratinocytes, epidermal keratinocytes.
00:04:49.27 But effectively, these were tissue stem cells.
00:04:54.07 So, Howard Green very soon recognized the power of the technology that he had just developed
00:05:01.27 for the treatment, in this case, of burn patients.
00:05:05.01 He took skin from the unaffected area of a burn patient.
00:05:10.06 And then cultured those cells, grew sheets of epidermis, and then grafted those cells
00:05:16.27 onto the burned area of the patient.
00:05:21.00 Same patient, just taking good skin and expanding the cells in culture.
00:05:25.20 And the reason why that worked is that you could use growth factors and nutrients
00:05:30.09 that allowed the cells to grow fast, generate sheets of skin, in order to be able to be used
00:05:36.06 for burn therapy.
00:05:37.27 In those early days, Dr. Green was able to effectively cure or treat patients
00:05:47.24 that had burns up to 95% of the total surface of their skin.
00:05:53.04 Remarkable.
00:05:54.04 All generated from a few stem cells that were endlessly passaged in skin.
00:06:00.13 And we've learned a very important lesson from this.
00:06:03.08 Effectively, now, we have 35 years of success of the use of stem cells in a clinical setting.
00:06:10.09 And I think what one of the most remarkable aspects of that is that those patients
00:06:15.17 whose skin was almost entirely reconstituted from stem cell therapy, if you will,
00:06:23.16 never showed signs of abnormalities, never showed signs of genetic alterations in the skin,
00:06:31.01 or of cancer, that might give us an idea or a notion that culturing those cells long-term
00:06:38.11 might be deleterious for the cells in some way.
00:06:42.25 Remarkably, the skin of those patients still produced healthy epidermis.
00:06:50.13 This ability to culture stem cells in the... in the laboratory turned out to be the foundations
00:07:00.20 for embryonic stem cell research, which was going to come another five years after
00:07:07.00 Howard Green's pioneering work.
00:07:09.07 And there, the breakthrough was really the realization that stem cells cannot survive
00:07:15.22 on their own.
00:07:16.23 They require other cells for their sustenance.
00:07:20.24 And what Howard Green did in his breakthrough work to culture embryonic... to culture human
00:07:25.28 skin stem cells was basically the realization that epidermal stem cells rely upon
00:07:32.21 dermal cells in order for them to grow and be maintained.
00:07:36.06 So, he used what is called a fibroblast feeder layer, an irradiated layer of fibroblasts,
00:07:43.15 in order to be able to grow the human epidermal stem cells on top of it.
00:07:49.06 And that research then served as, also, the foundation for embryonic stem cell culture,
00:07:55.06 which also succeeded because of the addition of the fibroblast feeder layer.
00:08:01.14 So, what are stem cells, then?
00:08:04.13 Let's get down to the basics and the definition.
00:08:07.17 Basically, stem cells are cells that are able to make an animal, if we're talking about
00:08:15.07 embryonic stem cells.
00:08:17.02 The embryonic stem cells have all the power to reconstitute an entire animal.
00:08:24.11 Stem cells have the ability to make and replenish a tissue, if we're talking about adult stem cells.
00:08:30.28 So, adult stem cells replenish the tissue.
00:08:34.24 Embryonic stem cells have the capacity to make the animal.
00:08:40.07 And effectively, what we know about stem cells -- and particularly stem cells of adult tissues --
00:08:45.10 is that they have the ability to be able to generate not only self
00:08:49.25 -- so, that means that they can self-renew --
00:08:53.16 but they also have the ability to produce short-lived progenitors.
00:08:57.03 These are often rapidly proliferating progenitors that then go on to make the differentiated
00:09:02.16 cells of a tissue.
00:09:04.14 So, in this case, it would be the epidermis.
00:09:07.28 And it's often, then, the short-lived progenitor cells, or these transit-amplifying cells,
00:09:13.28 that have the ability to generate the bulk of the tissue.
00:09:17.21 The stem cells only divide relatively sparingly in most situations.
00:09:23.22 So, what are the differences, then, between embryonic and adult stem cells?
00:09:29.17 Embryonic stem cells are pluripotent, and they can generate all of the cells of the animal
00:09:35.12 except for the support cells or the placenta.
00:09:41.20 In the case of adult stem cells, these are usually multipotent, and can generate
00:09:47.08 several different tissues of our body.
00:09:49.00 Sometimes, they're unipotent, and can only generate a single tissue
00:09:54.09 or differentiated cell of our body.
00:09:56.25 So, in the first part of this series of lectures, I'd like to concentrate on embryonic stem cells,
00:10:05.15 on induced pluripotent stem cells, and on their applications to basic science,
00:10:11.11 medicine, and the pharmaceutical industry.
00:10:14.13 So, where do embryonic stem cells come from?
00:10:19.08 If we go to the early developing embryo, the blastocyst, that's just a few days old,
00:10:25.20 it consists of several hundred cells at the most.
00:10:29.28 And at this point, the blastocyst has a group of cells which are called inner cell mass cells.
00:10:40.06 And those are the cells that develop into the fetus, or the embryo.
00:10:50.07 The surrounding cells -- this single layer of cells that surround the inner cell mass --
00:10:55.20 are called the trophectoderm.
00:10:58.10 The trophectoderm is going to develop into the fetal support tissue for the embryo.
00:11:04.16 So, those cells do not give rise to any part of the embryo, but basically they're necessary
00:11:11.21 in the womb to be able to develop the fetus.
00:11:16.23 So, scientists learned that it's possible to take the inner cell mass cells, then,
00:11:23.05 and put those cells into a petri dish on a fibroblast feeder layer, or with the appropriate nutrients
00:11:32.08 that support the inner cell mass cells.
00:11:34.09 And now they can culture those cells.
00:11:38.15 That's the culture that are called cultures of embryonic stem cells.
00:11:44.17 That's where embryonic stem cells come from.
00:11:47.00 And thereafter, those embryonic stem cells can be passaged effectively endlessly,
00:11:54.06 just like, as I mentioned to you, epidermal stem cells were initially.
00:11:59.00 And these cells, now, though, have much more power than the cells of the skin.
00:12:05.06 So, why is this important?
00:12:07.26 Well, let's think about the future for regenerative medicine.
00:12:11.15 There are many different cell types for which we don't have very much information,
00:12:16.26 and for which there are many different types of human genetic diseases.
00:12:21.06 For nerve cells, we could generate, potentially, nerve cells, possibly for the treatment of
00:12:26.03 Parkinson's disease or Alzheimer's disease.
00:12:30.11 Scientists are excited about the ability to generate nerve cells for the treatment of
00:12:34.18 spinal cord injuries.
00:12:37.11 Scientists are excited about the ability to culture pancreatic islet cells for
00:12:44.04 the possible treatment of diabetes.
00:12:47.07 Muscle cells for muscular dystrophy, and sudden death heart syndrome.
00:12:51.17 Immune cells for immunodeficiency disorders.
00:12:56.04 Or, thinking about the treatment of cancers, it's possible to generate the stem cells
00:13:05.01 that derive or produce the cancers, and that's also possible in culture.
00:13:10.26 And scientists are very interested in utilizing these types of technologies in order to
00:13:17.08 be able to understand more about the biology.
00:13:20.02 So, it's not just the treatment of patients, but it's really understanding the biology
00:13:26.07 of how these cells develop and what gives them their properties, to be able to ultimately
00:13:33.10 come up with new cures and treatments for various different types of diseases.
00:13:38.27 And that involves not only the clinician and the scientists, but also
00:13:44.02 the pharmaceutical industry or the biotechnology industry.
00:13:46.26 So, let's take a look at a couple of examples of what embryonic stem cells can do.
00:13:54.07 In this case, human embryonic stem cells were treated with particular growth factors
00:14:00.04 that allowed these cells to differentiate into muscle cells.
00:14:06.00 And now, looking at the embryoid bodies -- and this is the work of Gordon Keller and his
00:14:12.00 colleagues at the University of Toronto -- you can see that the cells undergo this beating feature.
00:14:21.24 And you can see a few examples of that, of the cells basically in the culture dish, now,
00:14:27.23 undergoing the contractions that heart muscle cells do.
00:14:31.09 And interestingly, they undergo them in a synchronized fashion, in the way that
00:14:36.03 our heart cells do in our body.
00:14:39.01 So, in one of the very earliest experiments, done, now, a decade ago, scientists took embryonic stem cells
00:14:50.21 and differentiated them into neurons, and used them to treat paralysis of a rat,
00:14:57.21 in this case.
00:14:59.22 And here was the rat before the injection of embryonic stem cell... stem cells differentiated
00:15:07.28 into spinal cord neurons.
00:15:11.12 And here is the rat after the treatment.
00:15:15.13 Now, these were early studies.
00:15:17.17 Scientists have gotten much better at these sorts of treatments.
00:15:21.12 But again, these kinds of treatments are what ultimately will be necessary in order to
00:15:27.08 move the field forward, and in order to think about therapies for the future.
00:15:32.04 So, let's now go to 2017.
00:15:37.18 What are scientists doing now?
00:15:39.10 Well, now it's possible to differentiate the embryonic stem cells not only into a neuron
00:15:47.13 but into specific types of neurons.
00:15:49.26 There are hundreds of different types of neurons in the body.
00:15:53.08 In this case, they took human embryonic stem cell-derived cortical neurons and
00:16:01.00 grafted them into a mouse cortex.
00:16:03.22 So, the importance of this work I'll describe in a moment.
00:16:07.09 But these are the studies of Lorenz Studer, a scientist and one of my colleagues
00:16:12.19 across the street at Sloan Kettering Cancer Institute.
00:16:17.03 So in this case, the cells that you see in white, now, are human cortical neurons.
00:16:24.11 And the slice of tissue that you're looking at is a mouse brain.
00:16:29.11 Three months after the graft.
00:16:33.24 And even later after the graft.
00:16:37.02 Six months after the graft, there are still human cortical neurons that are existing
00:16:43.23 in the mouse brain.
00:16:44.26 And scientists are currently trying to understand, are they working in the right way?
00:16:50.03 Are they behaving as cortical neurons?
00:16:54.00 And this is important for the treatment of a whole number of different disorders.
00:17:03.20 And it allows scientists to learn more about the biology of Alzheimer's, of autism,
00:17:10.23 of schizophrenia, and many other disorders of the cortex of our brain.
00:17:16.28 So, what are the ethical issues involved?
00:17:21.19 Why is there so much controversy about embryonic stem cell research?
00:17:25.24 Well, on the one hand, it's important to know that human embryonic stem cells are cultured
00:17:33.24 from fertilized eggs.
00:17:36.06 And a religious argument would be against the culturing of fertilized eggs for anything
00:17:44.09 other than, basically, making a human being.
00:17:48.23 The counterpoint, however, is that human blastocysts and embryonic stem cells can be created with
00:17:56.24 only egg and sperm.
00:17:58.27 And they can be created in culture, with no womb required.
00:18:05.10 Additionally, the technology that I've just described to you involves the exact same steps
00:18:15.09 as an in vitro fertilization.
00:18:17.25 So, I think these types of technologies are technologies that have made great advances.
00:18:26.26 That said, there is the concern, the ethical concern, by some, that... that... that the
00:18:35.17 use of fertilized eggs for in vitro fertilization is one thing, but the use for research is
00:18:42.03 another.
00:18:43.21 So, embryonic... embryos from in vitro fertilization are indeed often now discarded or frozen or
00:18:53.22 unused.
00:18:55.17 And so, again, this issue is, well, the embryos could be implanted into a woman who
00:19:02.20 would like to have a child, and therefore it would be unethical to use those embryos for anything else.
00:19:09.04 On the other hand, the counterpoint to this argument is that it's still that many embryos
00:19:15.14 from in vitro fertilization are discarded, are unused.
00:19:20.01 And the other aspect is that they could be used for scientists to be able to learn
00:19:25.04 how to generate neurons, pancreatic islet cells, muscle cells, for treating human disorders and injuries.
00:19:33.04 So, what are the hurdles -- beyond the ethical concerns -- of what scientists would
00:19:39.21 need to do to be able to adapt this technology and take it one step further to the clinics?
00:19:45.13 Well, the first big step is that embryonic stem cells that are used to generate neurons
00:19:53.20 and then implanted into, for instance, an Alzheimer's patient would basically be rejected
00:20:02.00 from the body.
00:20:03.07 Because the immune system of your body recognizes foreign cells, and it eliminates them.
00:20:10.13 And so, what were the next steps that scientists came up with to generate stem cells that would
00:20:16.07 overcome the problem of immune rejection?
00:20:21.11 In this particular technology, this is the technology known as nuclear transfer,
00:20:27.00 in which case you take an unfertilized oocyte, now... in the previous version we were taking fertilized oocytes...
00:20:33.04 fertilized oocytes, or eggs.
00:20:36.09 Here, we're taking an unfertilized oocyte, removing and discarding the nucleus of an oocyte,
00:20:41.17 and then replacing it with a nucleus of an adult somatic cell, such as a skin cell.
00:20:49.01 This technology was actually technology that was performed all the way back in 1962
00:20:55.00 by John Gurdon, who recently won the Nobel Prize for these pioneering studies.
00:21:00.12 He used Xenopus eggs and basically modified the eggs in this way, using nuclear transfer,
00:21:07.09 in order to produce a hybrid cell, now -- a cell with the unfertilized oocyte from one cell
00:21:14.20 and the nucleus from another cell -- and used that in order to be able to develop
00:21:20.04 a normal tadpole.
00:21:23.14 In my laboratory, back about a decade ago, now, we used this type of technology
00:21:29.17 in order to take a skin stem cell, and basically used nuclear transfer in order to put that into
00:21:37.22 an unfertilized mouse oocyte.
00:21:39.26 And using that technology, we were able to clone, effectively, and create healthy mice.
00:21:47.27 So, that technology exists, and it's been successful.
00:21:52.27 And this is the gold standard of having a normal, healthy mouse that is produced
00:21:59.00 from one of these somatic cell nuclear transfer experiments.
00:22:02.23 The experiments, however, are fraught with some problems.
00:22:06.14 Not every mouse is normal.
00:22:08.28 And the efficiency is still leaving something to be desired.
00:22:13.25 But I think it's remarkable that that technology is actually successful.
00:22:18.03 So, how would one adapt this, then, to nuclear transfer to human research.
00:22:23.22 Obviously, we wouldn't want to use this for something like cloning at the level of human.
00:22:29.23 But there are more important types of approaches that could be used in this case.
00:22:34.19 We go to the first steps, only, in this case, an unfertilized human oocyte, remove and discard
00:22:40.24 its nucleus, and now replace it with the nucleus of an adult somatic cell, such as a skin cell.
00:22:47.18 And now, if we go to those hybrid cells, effectively, and culture them to the level of the blastocyst,
00:22:57.09 and then create inner cell mass cells, from which we can culture those cells, we can generate
00:23:03.10 embryonic stem cells.
00:23:05.03 Only now, the nucleus is basically the nucleus of the person who had the skin cells.
00:23:11.22 And in this case, that could be the patient.
00:23:15.16 And so, in this type of technology, now, the cell that is derived... such as a neuron,
00:23:23.12 derived from somatic cell nuclear transfer, would not be recognized as foreign,
00:23:29.09 and would be accepted by the person.
00:23:32.23 So, this gets us over the hurdle.
00:23:37.02 What happened at the biological level?
00:23:39.14 What about the biology?
00:23:40.22 Well, the biology that I've just described to you is the biology of something called
00:23:46.06 epigenetics.
00:23:49.04 We all know that all of the cells of our body have the same genes.
00:23:54.11 Every cell of our body has the same genes.
00:23:57.20 And yet during development, the genes are modified so that some genes are turned off in one cell,
00:24:03.22 turned on in another cell, and other genes are turned off in that cell,
00:24:08.17 turned on in another cell.
00:24:10.10 And that's what gives every cell of our body its own identity.
00:24:14.25 That's why our skin cell is a skin cell, a nerve cell is a neuron, epidermal stem cells,
00:24:21.18 muscle cells, liver cells, hair cells.
00:24:24.01 All of the cells of our body have their identity.
00:24:26.09 And they get it from the same DNA, but through epigenetics
00:24:31.19 -- turning on some genes and turning off others.
00:24:34.07 So, if you start with a skin cell that's turned off all sorts of genes that were expressed
00:24:40.07 in the embryonic stem cells, that modification of, this is my identity as skin cell,
00:24:47.01 has to be erased in order for the cell to do something else, like become an embryonic-like stem cell.
00:24:54.22 This phenomenon is called epigenetic reprogramming -- the ability to change the state of the
00:25:01.15 genes within a nucleus to... to be able to do something else, to turn on some genes and
00:25:08.13 to turn off others.
00:25:10.08 So, the experiment that I just described to you in somatic cell nuclear transfer basically
00:25:16.22 tells us that it's the cytoplasm of that unfertilized egg that must favor the unspecified state.
00:25:24.27 It's producing all sorts of different chromatin reprogramming factors that basically erase
00:25:31.19 the realization of that skin stem... of that skin... skin nuc... nucleus that it ever was
00:25:39.20 a skin cell.
00:25:41.27 There aren't any divisions that are required for the reprogramming event in somatic nuclear transfer,
00:25:47.15 so the experiment that I described to you is the reprogramming of the skin nucleus
00:25:55.14 just by the cytoplasmic factors from the unfertilized egg.
00:26:00.19 But... and this is, again, the religious ethical issue... is that reprogramming by
00:26:08.11 somatic nuclear transfer still involves an egg, in this case, an unfertilized, single embryonic cell.
00:26:15.22 So, how can we get around the problem of using human embryonic cells in order to be able
00:26:23.27 to create cells that exhibit an embryonic-like state that could be used for the kinds of
00:26:31.05 therapies that I've just mentioned?
00:26:33.16 So, let's go to the pioneering work of Shinya Yamanaka, who back in 2006, using mouse adult cells,
00:26:43.21 was able to reprogram those adult skin cells into becoming an embryonic-like cell
00:26:55.05 without the use of the oocyte cytoplasm, or without the use of the unfertilized egg.
00:27:01.18 So, the technology that Yamanaka did, and his coworkers, was to take an adult skin cell
00:27:11.06 and look at the differences between the adult skin cell and what kinds of
00:27:16.25 transcription factors the adult skin cell was making versus the embryonic stem cell and what kinds of
00:27:23.06 transcription factors the embryonic stem cell was making.
00:27:26.26 Effectively, what are the differences that give those two cells their identity?
00:27:32.18 And taking advantage of that, they then introduced a cohort of transcription factor genes
00:27:42.04 that expressed the embryonic stem cell-like transcription factor profile into the adult stem cell...
00:27:50.15 adult skin cell.
00:27:51.19 And then they began, one-by-one, taking out -- reducing the complexity of the transcription
00:27:58.24 factor profile -- until they found just four transcription factors that turned out to
00:28:04.24 be expressed by embryonic stem cells, not by adult skin cells, but could conform or reprogram
00:28:12.22 the skin cell to behave as if it was an embryonic stem cell.
00:28:19.00 In this case, they used retroviruses that harbored the genes encoding KLF4, Oct4, Sox2,
00:28:26.22 and cMyc.
00:28:28.26 And they put those into the adult skin cell.
00:28:32.10 And what they were able to do was to find cells within their culture that are called
00:28:40.02 induced pluripotent stem cells.
00:28:42.15 And these are cells that basically, for all practical purposes, are looking like
00:28:47.21 an embryonic stem cell, only now there's no oocyte -- fertilized or unfertilized -- that's required for
00:28:55.00 this technology.
00:28:57.07 So, what are the differences between genetic and epigenetic reprogramming?
00:29:04.22 Genetic reprogramming forces the switch by ectopically inducing active forms of KLF4,
00:29:11.27 OCT4, SOX2, and cMyc.
00:29:17.17 Epigenetic programming achieves the switch by changing the nuclear environment in a way
00:29:23.15 that causes its endogenous KLF4, OCT4, SOX2, and cMyc genes to be turned on.
00:29:31.26 Remember, all the cells of our body have the same genetic constitution.
00:29:36.13 Our skin cells have these genes.
00:29:40.09 It's just that our skin cells turn off these genes.
00:29:44.03 And so, by epigenetic programming, as I described to you in somatic cell nuclear transfer,
00:29:51.12 those genes are turned on again.
00:29:54.06 In this case, by genetic reprogramming, as I just described to you in the
00:29:59.00 pioneering studies of Shinya Yamanaka and his coworkers, those genes were actively...
00:30:05.21 an active form of those genes were provided to the skin cell.
00:30:09.22 So, during the conversion of a somatic to an induced pluripotent cell, the endogenous loci
00:30:17.19 for the SOX2, OCT4, KLF4, and cMyc genes are turned on after about 10 days of
00:30:27.01 sustained ectopic expression of these transcription factors.
00:30:30.07 And this was a remarkable breakthrough to realize this.
00:30:33.26 So, something about indu... introducing those four genes in an active state into
00:30:40.17 the adult skin cell resulted in the activation of those four genes within this skin cell zone chromatin
00:30:49.00 that were normally silent.
00:30:51.17 That was remarkable, and we now are understanding quite a bit about that process,
00:30:57.13 which I won't have time to tell you about in detail today.
00:31:00.23 Another remarkable change that occurred in the conversion of the skin cell to
00:31:06.03 a somatic iPS cell... to an induced pluripotent stem cell... was the silencing of the X chromosome.
00:31:13.26 Normally in our body, during development only one X chromosome ends up being active,
00:31:20.12 and the other X chromosome turns out to be silenced.
00:31:23.23 But at the early embryonic state, both X chromosomes are activated, and in the induction...
00:31:31.03 introduction to an iPS cell, basically this change effectively reverted.
00:31:38.08 Another amazing thing is that the ectopically-introduced genes encoding SOX2, OCT4, KLF4, and cMYC
00:31:50.14 turned out to be silenced after several days of sustained ectopic expression,
00:31:58.17 and after the endogenous SOX2, OCT4, KLF4, and cMYC genes were turned on.
00:32:06.05 So, only the transient ectopic expression of sustained activated transcription factors
00:32:15.07 that were expressed in embryonic stem cells turned out to be necessary in order to effectively
00:32:20.18 reset the undifferentiated clock of the adult skin cell.
00:32:25.20 Truly remarkable from a molecular biology understanding, and truly transformative
00:32:33.28 in terms of what induced pluripotent stem cells could do.
00:32:37.28 So, let's take a look at where we are in 2018 with regards to the current methods in
00:32:44.07 induced pluripotent stem cell, or iPS, reprogramming.
00:32:48.04 I've talked about genetic changes, the integration of the DNA of the active genes,
00:32:55.06 the active forms of the transcription factors, into the DNA of the skin cell.
00:32:59.28 That's a genetic reprogramming event.
00:33:03.17 And I've also talked to you about epigenetic targeting, no permanent gene changes.
00:33:09.11 And here, scientists have used chemicals, they've used small molecules,
00:33:14.28 they've used RNA in order to be able to epigenetically reprogram the adult skin cell without
00:33:21.18 the need to introduce foreign genes or ectopic expression of genes into these cells.
00:33:28.06 Remarkable advances, now, that just by putting a skin cell in a petri dish that...
00:33:34.20 using the right cocktail of chemicals, that it's possible now to convert that cell,
00:33:41.01 as if it was an embryonic-like cell.
00:33:44.00 So, if we now look at summarizing the progress on the somatic cell nuclear transfer
00:33:50.19 and induced pluripotent stem cell front, that it was back in 2007 when monkey embryonic stem cells
00:34:00.04 were cultured using skin nuclear transfer.
00:34:05.15 In 2013, human embryonic stem cells were cultured using adult skin nuclear transfer.
00:34:12.25 In 2007, I talked about the pioneering work of Shinya Yamanaka with regards to
00:34:19.26 producing human induced pluripotent stem cells by retroviral transfection of adult skin cells with
00:34:27.17 these four transcription factors.
00:34:29.07 I talked about... well, I actually didn't talk about, but I'll do so now... how we can
00:34:34.25 dispense with cMyc, oncogenic cMyc, because Myc is a potential oncogene.
00:34:42.03 It's an essential component of that cocktail that Shinya Yamanaka used in 2007.
00:34:47.24 But now, just a mere one to two years later, scientists figured out that
00:34:53.28 a different transcription factor, Nanog, which isn't oncogenic, basically could replace cMyc.
00:35:00.25 And so the early mice that scientists were creating using embryonic stem cell-like technology,
00:35:09.11 only with induced pluripotent stem cells... those early mice developed tumors.
00:35:14.25 Now, the mice... avoiding Myc as one of the four transcription factors, has basically
00:35:21.18 alleviated or eliminated that danger.
00:35:28.04 Between 2008 and 2013, scientists initially used adenoviral delivery instead of retroviral delivery.
00:35:37.12 Retroviruses integrate into the human stem cell... skin cell chromatin.
00:35:45.01 Adenoviruses don't.
00:35:46.11 They are transferred as episomes, and so eventually they're diluted out and lost.
00:35:52.18 Then scientists started to provide direct delivery of recombinant transcription factor proteins,
00:35:58.22 avoiding the genetic manipulation of the skin cell.
00:36:04.08 And then it was a few years later when scientists began to introduce modified stable RNA
00:36:10.19 for the pluripotency factors.
00:36:12.20 And then finally, scientists have been using small molecules and chemicals to
00:36:18.21 epigenetically switch on the embryonic-like gene expression program.
00:36:26.27 And then fast forward... what do we do with those induced pluripotent stem cells?
00:36:32.27 Now scientists have been making, initially, neurons, but now many different types of cells
00:36:39.09 of the body, basically by starting with these reprogrammed adult skin cells,
00:36:47.10 and effectively producing all the different types of cells in the body with induced pluripotent
00:36:53.01 stem cell technology.
00:36:54.01 So, I'll show you an example, this one again from my colleague Lorenz Studer at
00:37:01.06 the Sloan Kettering Cancer Institute.
00:37:04.06 And here I'm showing you iPS cell-derived peripheral sensory neurons, a whole dish of
00:37:12.10 peripheral sensory neurons, that are generated from these iPS cells.
00:37:17.14 Remarkably, now... it's now possible to be able to study these peripheral sensory neurons,
00:37:24.14 pain sensitive, to check out to see... use various different probes that might
00:37:29.08 allow them to see how pain might be received, and how it might be generated, how it might
00:37:38.05 be signaled back to, effectively, the brain.
00:37:43.11 So, are there clinical applications yet for iPS technology?
00:37:49.22 Well, the very first technology-driven therapy was for macular degeneration.
00:37:58.25 It was possible to take human iPS cells and differentiate them to make sheets of
00:38:04.17 these beautiful human retinal pigment epithelial cells.
00:38:08.24 And those are the cells that are degenerated in macular degeneration.
00:38:14.06 And so the very first clinical studies that were done with iPS cell technology were
00:38:19.26 those of Masayo Takahashi at the RIKEN Institute in Kobe, Japan.
00:38:26.02 Those studies were conducted back in September of 2014, the first-ever clinical trial
00:38:35.16 involving iPS cell technology.
00:38:38.02 Unfortunately, those studies were halted.
00:38:41.11 After the first two patients were treated, they started to show signs of improvement
00:38:47.06 in their vision.
00:38:48.06 But the problem was that when the scientists tested the DNA from the retinal pigment epithelial cells
00:38:55.13 what they found were several genetic abnormalities that might have been deleterious.
00:39:03.16 And so they stopped the studies and basically halted them.
00:39:07.08 So, it's illustrating that, despite the promise, there's still work to be done.
00:39:13.08 And scientists -- these scientists and others -- are now actively trying to figure out
00:39:19.02 how to be able to maintain and propagate these retinal pigment epithelial cells under conditions
00:39:25.14 where they don't acquire additional genetic alterations.
00:39:29.13 So, this work, then, is currently tabled until genetic stability can be further evaluated.
00:39:38.28 And ultimately, however, it should be a matter of time before such hurdles start to be overcome.
00:39:47.07 So, what about stem cell therapy for type I diabetes.
00:39:51.08 My colleague up at Harvard University, Doug Melton, has been working on this problem
00:39:57.17 for more than twenty years, since his son was first diagnosed with type I diabetes.
00:40:03.13 He changed the research that he was doing in order to focus on this problem,
00:40:08.14 and has made really remarkable advances in the course of these last twenty years.
00:40:13.09 So, what has he done?
00:40:15.18 He started with human embryonic stem cells.
00:40:18.08 But as researchers began to produce induced pluripotent stem cells, he's also used
00:40:24.12 induced pluripotent stem cells.
00:40:26.04 And now, remarkably, by understanding enough about pancreatic development, he could then
00:40:32.18 coax these cells through individual steps, one by one, to be able to produce
00:40:38.23 pancreatic beta cells, the cells that are degenerating in type I diabetes.
00:40:44.05 And remarkably, when introduced into a diabetic mouse, he was able to show that these
00:40:53.15 induced pluripotent stem cell-derived beta islet cells not only could survive, but basically also
00:41:03.02 had the ability to properly regulate glucose.
00:41:06.09 Remarkable breakthroughs.
00:41:07.22 But we're still left with some problems and challenges in diabetes, because as... as scientists
00:41:15.02 were working on developing more and more pancreatic beta islet cells in culture, other scientists
00:41:23.20 were beginning to realize that pancreatic type I diabetes is largely rooted as an autoimmune disease,
00:41:32.23 and that the autoimmune cells... that the immune cells of the patient are
00:41:37.03 basically attacking their own beta cells.
00:41:39.03 So, even if we generate buckets of beta islet cells, unless we overcome the problem of
00:41:46.15 the autoimmune attack, those cells will still be subject to the same types of attack
00:41:52.26 that the patient with type I diabetes has.
00:41:55.20 So, there are new hurdles to be overcome.
00:41:59.08 But I think these advances begin to illustrate for you just how many steps are involved
00:42:05.24 in the process, and just what advances scientists have made, and hopefully you'll begin to understand
00:42:11.11 just why advancing these types of technologies to the use of medicine turns out to have
00:42:19.08 so many steps involved, and are seemingly, for the public, so slow.
00:42:25.06 So, what can be done in the meantime as scientists are improving upon these various different techniques
00:42:30.07 and as safe induced pluripotent stem cell therapies are being developed?
00:42:36.05 Well, there's lots of work to be done.
00:42:39.06 Developing therapeutics for genetic degenerative diseases in vitro.
00:42:44.05 Parkinson's disease.
00:42:45.09 Huntington's disease.
00:42:47.02 Cardiomyopathies.
00:42:48.02 Sudden... sudden death syndrome.
00:42:50.23 Alzheimer's disease.
00:42:51.20 Diabetes.
00:42:52.12 Muscular dystrophy.
00:42:54.04 The ability to culture induced pluripotent stem cells and manipulate them genetically
00:42:59.04 to resemble these types of diseases all of a sudden gives scientists the first ability, now,
00:43:04.24 to really study these types of diseases in a petri dish in a way that for sure
00:43:11.15 is going to lead to new and improved therapies in the future.
00:43:15.26 So, once scientists can derive the right type of cell from induced pluripotent stem cells,
00:43:22.21 the cells, then, can be used in drug screens.
00:43:26.12 And effectively, in this case, Lorenz Studer, my colleague, has again been able to derive
00:43:34.17 cortical neurons, as I showed you.
00:43:36.20 Only now, instead of testing them for their activity in mouse brain, they can also
00:43:43.04 be used for activity screens for developing new drugs for the treatments of various different
00:43:49.02 degenerative disorders and genetic disorders.
00:43:52.15 So, these are advances for the future.
00:43:55.12 And... and I think a really exciting time for basic science and for translational science.

Part 2: Tapping the Potential of Adult Stem Cells

00:00:14.25 I'm Elaine Fuchs.
00:00:16.10 I'm a professor at The Rockefeller University in New York City.
00:00:21.04 I'm also an investigator of the Howard Hughes Medical Institute.
00:00:25.20 And today I'd like to tell you a little bit about tapping the potential of adult stem cells.
00:00:32.12 Every tissue of our body has to replenish dying cells, dead cells,
00:00:39.01 that through wear and tear are lost from our tissues.
00:00:43.18 50-70 billion cells die every day in our body, and they have to be replaced.
00:00:50.28 How does that happen?
00:00:52.09 Our body must repair its tissues, as well, when damaged.
00:00:56.26 How does that happen?
00:01:00.13 Every tissue of our body has reservoirs of stem cells for homeostasis and wound repair.
00:01:07.05 So, it's the stem cells that replace these 50-70 billion di... billion cells that die
00:01:13.13 every day in our body, and that also repair our wounds.
00:01:20.11 Some tissues turnover rapidly and have many stem cells.
00:01:24.24 Those are... such as hematopoietic stem cells, which regenerate the red blood cells and immune cells.
00:01:30.28 Or skin stem cells, which regenerate the epidermis and the hair follicles and our sweat glands.
00:01:37.02 Or intestinal stem cells, that rejuvenate the food adsorptive cells of our body.
00:01:44.00 Other tissues have very little regenerative capacity.
00:01:47.25 Our central and peripheral nervous system, for instance, pancreatic tissue, or cardiac tissue.
00:01:55.24 So, what are the characteristics of tissue stem cells that exist in adult tissues?
00:02:02.04 These cells have the capacity to divide, to produce more stem cells
00:02:06.21 -- that's a process known as self-renewal --
00:02:10.02 and they produce a differentiated tissue, such as the epidermis or the hair.
00:02:15.04 And they do so long-term.
00:02:19.09 These cells are relatively immature compared to their progeny, compared to the tissue cells.
00:02:27.19 They're typically multipotent; they're able to produce a subset of cell lineages.
00:02:33.14 Examples: hematopoietic stem cells can make the blood and immune cells;
00:02:38.13 skin stem cells can make the epidermis and hair.
00:02:43.23 It's only the fertilized egg that has unlimited potential, that can make all the cells of our body.
00:02:51.15 Tissue stem cells tend to be more restricted in what they can do.
00:02:55.28 And to understand why, we need to study the biology of adult tissue stem cells.
00:03:02.14 So, my laboratory studies the skin and skin stem cells.
00:03:06.25 And I've always thought that nature has clearly had a lot more fun and fancy in creating body surfaces
00:03:11.15 than she has in creating any of the ugly organs that most scientists work on.
00:03:18.13 My group works on the stem cells of the skin.
00:03:23.16 So, where do adult skin stem cells come from?
00:03:27.14 They began in early embryonic development, shortly after gastrulation, when the embryo
00:03:37.20 effectively turns inside-out and begins to develop into the animal.
00:03:44.10 The skin begins as a single layer of cells that are on the surface of the embryo.
00:03:51.03 Those are the cells that are going to give rise to the stratified epidermis that you see here.
00:03:58.15 They'll also generate the hair follicles.
00:04:01.04 They'll also generate the corneal surface of our eye, the sweat glands, and the mammary glands.
00:04:07.15 All of these cells come from this single layer of multipotent progenitor cells,
00:04:15.10 that are the origins of the stem cells of our adult skin.
00:04:20.07 So, skin stem cells provide the nearly endless supply of cells that replenish the epidermis
00:04:28.04 and the hairs of our body.
00:04:30.21 Can we isolate them?
00:04:32.02 Can we coax them to become hair as well as epidermis?
00:04:37.21 What value do they have in regenerative medicine?
00:04:42.12 Back when I was a graduate student, I was working on bacteria.
00:04:45.26 And I heard a lecture by Howard Green, who at the time was at MIT as a research scientist.
00:04:53.20 And Howard had developed a method where he could take a piece of human skin,
00:04:58.11 and put the cells into culture, and be able to propagate them endlessly, without losing their ability
00:05:04.20 to make skin.
00:05:06.08 I was just fascinated by his lecture.
00:05:09.18 And I knew then that I wanted to become a stem cell biologist.
00:05:18.09 So, here are examples, then, of the stem cells that are growing in culture.
00:05:24.20 And you can see by the dark chromosomes that these cells are actively dividing.
00:05:30.15 And they can be propagated, as I mentioned, endlessly.
00:05:34.20 Below, what you see is a three-dimensional, so-called organoid culture, or a tissue,
00:05:43.06 where we've reconstituted the epidermis starting from scratch using these cultured
00:05:48.05 human epidermal stem cells.
00:05:50.11 It looks pretty good compared to normal human skin epidermis.
00:05:57.04 So, Howard Green went on to develop this technology for the treatment of burn patients,
00:06:03.04 where he could take a small piece of the patient's good skin, propagate those cells in culture,
00:06:09.00 and make sheets -- hundreds of sheets of epidermal cells -- that then could be grafted
00:06:15.06 in the patient's bad skin.
00:06:16.27 So, the epidermal stem cells could be grown for months in a dish, and forever when grafted
00:06:23.16 onto a patient.
00:06:25.00 And this shows you an example of some of the grafted skin from one of these patients.
00:06:30.24 The patients that Howard Green treated successfully with these cultured human epidermal stem cells
00:06:37.05 from the patient covered up to 95% of the patient's burned skin,
00:06:43.16 with only 5% of the patient having unburned skin.
00:06:47.07 And from that stem cells could be cultured.
00:06:50.08 A remarkable advance.
00:06:53.17 After a year, the skin epidermis still looked like the normal skin epidermis would.
00:07:00.27 And it didn't show signs of cancer or deleterious effects that might give us an indication that
00:07:07.06 all of that culturing is a bad thing for these human epidermal stem cells.
00:07:13.04 Michele De Luca and Graziella Pellegrini, who were then studying in Howard Green's laboratory
00:07:22.06 and then started up their own labs in Italy, adapted the pioneering culturing procedures
00:07:28.23 that Howard Green had performed, in this case, to culture cornea or corneal epithelial cells
00:07:36.22 from a patient's stem cells of the cornea.
00:07:40.16 So, in this case, the patient had an industrial accident, where one of the eyes
00:07:46.12 -- the eye that you see here -- was blinded.
00:07:50.02 By taking stem cells from the healthy eye, culturing those cells, and producing a sheet
00:07:57.00 of corneal epithelial cells, it was possible, then, to graft it onto the blind eye.
00:08:02.25 And here is the result of the stem cell therapy: a restored corneal epithelium that effectively
00:08:11.00 restored the vision in this eye to this patient.
00:08:14.22 So, let's take a look at ten years later, after those experiments with the cornea were performed.
00:08:24.22 Just in the last month, there was a very successful report of whole body regenerative medicine
00:08:34.02 from disease-corrected epidermal stem cells.
00:08:38.01 And in this case, the patient, a seven-year-old boy, suffered from a genetic disorder known
00:08:45.15 as junctional epidermolysis bullosa.
00:08:49.05 This genetic disorder is due to recessive genetic mutations that can be either in the
00:08:55.18 laminin5, an extracellular matrix protein that's important for the epidermis
00:09:01.02 to adhere to the underlying dermis, or mutations in integrins alpha-6 or beta-4,
00:09:08.05 which are the integrins in the epidermal stem cells that are necessary to adhere the epidermis
00:09:14.16 to the underlying dermis.
00:09:16.15 And this particular patient had a disorder, or genetic lesion, in the laminin5 chain.
00:09:22.13 And as a consequence, the epidermis did not adhere, and effectively sluffed off
00:09:30.06 from the patient's body with the slightest of mechanical trauma.
00:09:34.10 The patient was near death at the point at which Michele De Luca, my colleague in Rome,
00:09:42.15 took on this task of working with German clinicians in order to be able to take a small sample
00:09:51.01 of the patient's cells, junctional epidermolysis bullosa-defective keratinocytes;
00:09:58.25 used gene therapy to be able to put back the normal laminin chain and to be able to excise
00:10:05.00 the genetic mutation of the patient; and effectively, at that point, then, generated healthy
00:10:12.20 human epidermal stem cells that could be maintained and propagated for generating sheets of epidermis
00:10:19.23 that were then grafted onto this patient.
00:10:23.11 So, this gene therapy of epidermal stem cells required only a very few number of stem cells
00:10:34.09 in order to be able to replenish, or repopulate, the entire epidermis of this patient
00:10:40.13 using whole-body regenerative medicine from disease-corrected epidermal stem cells.
00:10:45.18 And here is the boy today, basically able to go out and play in a way that he was
00:10:54.23 barely able to survive at the time of the therapy.
00:11:00.08 So, even a year ago, scientists did not think, or were concerned, that it might not be possible
00:11:10.15 to be able to produce normal, healthy epidermal stem cells from gene editing of the mutation
00:11:21.11 out of the stem cells.
00:11:24.02 And it also was doubtful that whole-body regenerative medicine would be possible to correct
00:11:31.04 the genetic basis of this disease, or to correct this genetic disease.
00:11:35.20 The patient's other cells still harbor that gene defect, but what the important aspect
00:11:42.26 of this is is that the patient -- the patient's skin epidermis -- is now corrected.
00:11:50.05 And this boy may be able to at least live a relatively normal life.
00:12:03.01 So, what are, then, the various different associated therapies that have followed
00:12:14.11 the culturing of epidermal stem cells that were first performed in 1975?
00:12:22.10 And now we have the correction of third-degree burns with epidermal stem cells, and the correction
00:12:29.24 of junctional epidermolysis bullosa with epidermal stem cells that have been gene edited.
00:12:36.04 In 1985, we had corneal epithelial stem cells to correct blindness from burns and from chemicals.
00:12:45.03 In 1992, Peterson and Bissell, scientists at Lawrence Berkeley Laboratory, and also
00:12:53.10 in Denmark, were able to produce milk-producing glands from human mammary epithelial stem cells
00:13:02.21 cultured in the laboratory.
00:13:05.01 And these have been enormously helpful, not only to study mammalian mammary biology,
00:13:11.11 but also to study breast cancer.
00:13:14.08 In 2013, Sato and Clevers made the impressive advance to be able to produce organoid cultures
00:13:25.11 from simple epithelia, from intestinal epithelial, lung epithelial, stomach, and liver stem cells.
00:13:32.09 These were, again, advances that took years for scientists to make with, again, the realization
00:13:39.20 that what's important is to understand enough about the biology of the stem cell to be able
00:13:45.18 to know about their environment and basically recreate the environment that that stem cell
00:13:51.22 normally has in its normal tissue, and recreate that in a culture dish.
00:13:56.27 It was determined early on, by Howard Green and others, for epidermal stem cells.
00:14:02.16 Many years later, it's now become possible to culture many different types of adult stem cells.
00:14:09.06 And so, here, by the use of the ability to culture, for instance, lung stem cells,
00:14:15.08 it was also possible in... again, in just the last year in the Netherlands, to be able to
00:14:21.02 treat a patient with cystic fibrosis by gene editing mini-lung organoid cultures grown
00:14:29.22 from the patient, and... and basically allow the patient to... to again be able to breathe properly,
00:14:41.05 and... and promise for the future.
00:14:47.17 So, where are we in 2018 with our knowledge about the biology of tissue stem cells?
00:14:56.13 Because it's the biology that is going to drive future advances in the clinics,
00:15:02.24 and also in the pharmaceutical and biotechnology industry.
00:15:06.11 So, what we know is that stem cells of adult tissues typically reside in niches, in defined
00:15:14.02 microenvironments.
00:15:15.07 That's true for the hair follicle, for the intestine, and for the hematopoietic system,
00:15:22.00 the three stem cells for which we know most about the stem cells and their niches.
00:15:30.23 When does a tissue stem cell decide, am I gonna make tissue, or am I going to be dormant,
00:15:38.22 or quiescent?
00:15:40.06 It's the interactions between the stem cell and its microenvironment, or the niche stem-cell interactions,
00:15:46.04 that make that decision.
00:15:48.27 When a stem cell is not making tissue and exists, for instance, in the skin, it basically
00:15:54.24 is receiving inhibitory signals from the microenvironment,
00:15:59.01 telling it to stay cool, be quiet, be dormant, and not make tissue.
00:16:05.21 But if a stem cell needs to make tissue, now there have to be interacting cues that are
00:16:12.26 positive-acting cues that are now going to override those inhibitory cues.
00:16:18.22 And at that point, those activated stem cells then go on to make short-lived progenitors,
00:16:24.11 which then go on to produce the bulk of the tissue.
00:16:27.13 And in the case of the skin, it would be, for instance, the epidermis or the hair follicle.
00:16:33.07 How many and how often stem cells are active depends upon the needs of the particular tissue.
00:16:40.22 So, we know a lot about the skin stem cells from my laboratory and other laboratories' research
00:16:47.01 over the last several decades now.
00:16:51.22 And we know that the tissue stem cells reside at the interface between the epidermis
00:16:57.09 and the dermis.
00:17:00.03 But they're defined in their task and also their program of gene expression
00:17:05.24 by their local niches.
00:17:06.25 So, the epidermal stem cells that reside in the innermost layer of the epidermis are in
00:17:12.14 a niche microenvironment that's very different from that of the hair follicle stem cells
00:17:17.23 that are located at the very base of the non-cycling portion of the hair follicle.
00:17:25.04 And that stem cell-niche interactions are what defines the stem cells in each of these
00:17:33.07 niches... niches, and tells the stem cells of the epidermis to make epidermis
00:17:38.24 -- produce our barrier -- whereas stem cells from the hair follicle to make hair.
00:17:45.23 So, my laboratory has studied the hair follicle for a number of years now.
00:17:51.13 It's really the perfect system to understand a basic biological problem.
00:17:56.07 And that is how stem cells transition between quiescence and tissue regeneration.
00:18:02.02 This is a problem that's faced by all the stem cells of our adult tissues.
00:18:06.26 And we've learned a lot about the various different interactions that are necessary.
00:18:11.23 We know that these red arrows are basically inter... inter-niche cells that are
00:18:17.15 sending out a signal called BMP that tells these stem cells, in purple, to be quiescent.
00:18:25.12 We know that at the base of the stem cell niche, there are signals -- new signals, activating signals --
00:18:30.14 called Wnts, which are produced by the hair follicle stem cells themselves,
00:18:36.25 and BMP inhibitors produced by the underlying green cell,
00:18:41.13 basically a pocket of specialized mesenchymal cells called dermal papilla cells.
00:18:45.27 And these are the pro-activating signals that are necessary to take the stem cells
00:18:51.24 out of their quiescent state and coax them to make hair.
00:18:55.18 So, when the threshold levels of activating signals overcome the inhibitory BMP signal,
00:19:02.26 then, the stem cells are basically activated.
00:19:06.25 They start to make those short-lived progeny.
00:19:09.16 And now the short-lived progeny may get a new signal, this one called sonic hedgehog.
00:19:15.02 Sonic hedgehog then acts in two ways, which we learned from conditional knockout
00:19:23.09 of both the receptor and the ligand.
00:19:26.02 What we learned is that sonic hedgehog first acts to stimulate the specialized mesenchymal cells,
00:19:32.17 the dermal papilla cells, to produce more BMP inhibitors and also pro-activating FGFs.
00:19:40.08 Then, several days later, sonic hedgehog acts on the quiescent stem cells, those purple cells,
00:19:48.23 to be able to restock the stem cells utilized in the course of tissue regeneration,
00:19:55.05 but also to produce the shaft that then grows downward, pushing the signaling center
00:20:02.21 away from the stem cell niche.
00:20:04.18 And now the stem cells return to quiescence, but the short-lived progeny produce hair
00:20:11.23 and the channel that the hair follicle sits in.
00:20:15.06 And so, in this way, we understand very well about how the hair cycle works because
00:20:23.28 once the hair cycle is begun and gets going, it's essentially the short-lived progenitors
00:20:30.26 that then do the bulk of making tissue, in this case, the hair in its channel.
00:20:35.19 So, the short-lived progenitors are short-lived.
00:20:38.10 Eventually, they lose their proliferative capacity, and undergo apoptosis and differentiation.
00:20:46.02 And now the system returns back to normal again, to reset the hair cycle.
00:20:52.15 So, what does it take to make a hair follicle?
00:20:56.24 I talked about the importance of the Wnt signal, but many years ago my laboratory activated
00:21:04.17 the Wnt signal... at the time we didn't even know it was a Wnt signal...
00:21:10.06 we activated its interacting partner known as beta-catenin.
00:21:15.04 And when we activated beta-catenin in the mouse skin, what we got is this super furry mouse,
00:21:20.11 relative to its brother next to it.
00:21:24.03 These mice ended up producing far more hair follicles than normal.
00:21:29.13 Initially, we were very excited by that.
00:21:32.19 But the downside of this is is that those mice develop tumors over time.
00:21:38.02 Obviously, not yet ready for primetime.
00:21:41.24 But it told us a very important thing, and that is that Wnt signaling is important in
00:21:47.06 dictating these unspecified progenitors to make a hair follicle, not to make epidermis.
00:21:54.14 So, when taken from their niche and cultured, the green stem cells that you see here,
00:22:01.05 of the hair follicle, turn out to acquire plasticity.
00:22:05.00 We can culture these stem cells much the same way that Howard Green cultured epidermal stem cells
00:22:11.03 many years ago.
00:22:13.01 And when we culture those cells, we can take a colony, or a clone, derived from one of
00:22:19.09 the single stem cells, and we can engraft it onto a mouse that doesn't have hair,
00:22:25.14 and those mice now can produce hair.
00:22:28.06 They also produce epidermis and sebaceous glands.
00:22:31.25 And that's something that they normally don't do.
00:22:35.01 Normally, they just make hair.
00:22:38.14 They will, however, make epidermis and sebaceous glands when the skin is wounded,
00:22:44.25 and when the epidermis and the sebaceous glands are missing.
00:22:47.16 So, the stem cells receive signals, in these case... in this case, wound signals,
00:22:54.04 that stimulate those stem cells to be able to make hair, but also to be able to make epidermis
00:22:59.21 and sebaceous glands, to replenish the tissues that were missing
00:23:04.13 as a consequence of the wound.
00:23:07.05 And when you take the stem cells out of context, out of the hair follicle niche,
00:23:11.23 and you put them into culture, now the stem cells kind of forget what they were supposed to do
00:23:18.13 when they're grafted back onto the skin.
00:23:20.20 And now they basically act like they're in a wound state, and effectively will also make
00:23:26.21 epidermis and sebaceous glands.
00:23:29.00 We call this phenomenon stem cell plasticity, and it's something that we see in
00:23:35.10 a variety of different stem cell... stem cells from tissues.
00:23:40.24 It's a phenomenon that basically allows a tissue to receive, essentially, a danger call
00:23:49.18 in a wound that tells the stem cells nearby to be able to repair and replenish the tissue
00:23:58.14 at all costs, and as fast as possible.
00:24:00.25 So, it's always the closest stem cells, then, to the wound that can repair it.
00:24:06.03 Unfortunately, these stem cells will not automatically make neurons or make other tissues
00:24:13.05 of our body without some manipulation.
00:24:15.27 But these stem cells will, however, naturally make not only hair follicles but also epidermis
00:24:24.16 and sebaceous glands.
00:24:26.26 So, we've studied these stem cells over the course of many years, now.
00:24:33.16 And we know that these stem cells are defined by their transcriptional profile, effectively,
00:24:41.16 the gene expression pattern that these stem cells make.
00:24:44.28 And we know a good deal about this.
00:24:46.20 We know that there are the transcription factors in purple, a variety of different transcription factors
00:24:52.19 that are made by these hair follicle stem cells and not by other stem cells,
00:24:59.03 at least as a cohort.
00:25:00.17 We know that there are some factors, like LGR5, which are made by a number of different stem cells:
00:25:05.27 intestinal epithelial stem cells, hair follicle stem cells, and many other
00:25:11.15 types of stem cells.
00:25:12.28 We know that integrins are a characteristic of many different types of stem cells,
00:25:18.22 and they're expressed at very high levels in the hair follicle stem cells.
00:25:23.11 And then for a quiescent stem cell, the niche signals basically produce a gene expression profile
00:25:31.09 by the stem cells that reflect reduced levels of Wnt signaling and reduced levels
00:25:37.04 of sonic hedgehog signaling.
00:25:39.00 Those are the pro-activating cues for the stem cells.
00:25:42.08 Whereas BMP signals and FGF18 signals, the inhibitory cues that tell those stem cells
00:25:48.19 to remain in quiescence, those signals are upregulated.
00:25:53.13 And then differentiation, whether it be differentiation for the epidermis or the sebaceous gland
00:25:58.27 or the hair follicle, all of those programs are suppressed by the stem cells.
00:26:04.13 So, their transcriptional program reflects the behavior of these stem cells.
00:26:11.10 We characterized the transcriptional program by taking the stem cells directly out of the tissue,
00:26:17.28 using fluorescence activated cell sorting to purify those cells,
00:26:21.26 and basically taking those RNAs and directly profiling them.
00:26:26.24 We also used a technology known as conditional knockout technology to be able to excise
00:26:34.19 the transcription factors from the skin of the animal.
00:26:39.06 When we excise TCF3 and TCF4 -- these are DNA binding proteins which can also bind beta-catenin,
00:26:46.15 which is a downstream Wnt effector -- we found that the loss of TCF3 and 4 basically no longer...
00:26:53.19 the stem cells can no longer maintain the quies... their... their activity.
00:26:59.20 We learned that the loss of Lhx2 is required for maintaining the stem cells.
00:27:05.11 And similarly, the loss of Sox9 is required for maintaining the stem cells.
00:27:11.06 Surprisingly, when we knocked out beta-catenin, what we found is no hair follicles made.
00:27:17.15 So, with no Wnt signaling there were no hair follicles made.
00:27:21.28 Interestingly, when we knocked out TCF3 and 4, even though it was necessary
00:27:27.20 to make a hair follicle, what we found to maintain the hair follicles stem cells... what we found
00:27:32.23 is a burst of hair growth.
00:27:35.02 So in this way, we learned that TCF3 and 4 antagonize what Wnt signaling can do,
00:27:41.10 and that keeps the stem cells in quiescence, because Wnt is typically a proliferation-associated factor.
00:27:49.04 Lhx2, in the absence, basically produces, where the stem cell niche was,
00:27:56.01 now a niche full of sebaceous gland.
00:27:58.05 So, Lhx2 is necessary to repress the differentiation program of the sebaceous gland while
00:28:06.12 the stem cells are stem cells in their native niche.
00:28:09.12 Sox9 represses the epidermal stem cell differentiation program.
00:28:14.26 And without Sox9, the hair follicle stem cell niche turns into an epidermal cyst.
00:28:19.28 So, we understand how these different factors are working and how these different transcription factors...
00:28:25.27 what they're necessary for.
00:28:28.13 So, let's put this all together now.
00:28:31.14 And I'll give you one example, and that is from BMP signaling, which I told you is important
00:28:37.12 to control stem cell quiescence.
00:28:40.23 So, we've learned, over the course of our studies, that the BMP interacting with
00:28:47.09 the BMP receptor on the stem cells is sufficient to activate the canonical transcription factor
00:28:55.18 called phospho-SMAD1, along with phospho... along with SMAD4, which then control, downstream,
00:29:02.03 a group of transcription factors that I've shown you here.
00:29:06.17 Together, these factors are necessary to control the quiescence of the stem cells.
00:29:13.11 So, we then looked at what happens in an aging mouse.
00:29:18.11 And what we found was that in the first hair cycle of the mouse, that happens relatively quickly.
00:29:26.08 Only a couple days separates the time at which one hair follicle has completed its cycle
00:29:32.11 and the next hair cycle begins.
00:29:34.05 But now, as the animals get older, there's longer and longer times between when our hairs grow
00:29:40.20 -- or when the animal's hair grows -- and when the hair, basically... when the stem cells
00:29:46.20 sit in quiescence.
00:29:48.05 They spend far longer sitting in quiescence than they do in the younger mice.
00:29:54.23 And when we traced this, what we found is that the dermis and the old fat,
00:30:01.26 or the old adipose tissue, of these older mice turned out to produce very high levels of BMP.
00:30:08.15 And that's what maintained these stem cells in their quiescent state.
00:30:12.15 We could treat the old mice with a drug called VIVIT which is an inhibitor of Nfatc1,
00:30:21.14 one of the transcription factors downstream of the BMP signal.
00:30:25.23 And we could regrow... reactivate those dormant hair follicle stem cells in order to make
00:30:32.05 a new round of hair growth.
00:30:34.07 And so, at this point in time in our studies, what we learned is that actually the stem cell numbers
00:30:39.16 still remain high in the older animal, but it's their activity that wanes with age.
00:30:46.10 So, hair grain is also a phenomenon that... that happens with age.
00:30:53.26 And in this study, what others, May...
00:30:57.11 Mayumi Ito and her coworkers, learned was that the melanocyte stem cells and
00:31:04.21 the hair follicle stem cells reside in the same niche, and they respond to similar signals.
00:31:09.24 And this was also the work of Emi Nishimura and her coworkers in Japan.
00:31:17.19 And so hair follicle and melanocytes stem cells are hanging out in the same niche.
00:31:22.18 They respond to the same signals.
00:31:25.02 And the importance of that is that the hair follicle stem cells and melanocytes stem cells
00:31:32.18 will get activated at the same time.
00:31:35.08 They'll differentiate so that the melanocyte cells will now begin producing pigment,
00:31:42.06 and the hair follicle cells will begin producing hair.
00:31:45.27 And at that time, the differentiated melanocytes can provide that pigment to the differentiating
00:31:53.00 hair cells.
00:31:54.04 And that's what gives our hair its color.
00:31:57.03 And so, when the stem cells of the hair follicle are unable to be able to produce hair,
00:32:04.09 so too, typically, the melanocytes stem cells end up being unable to be activated,
00:32:12.04 because they reside in the same niche.
00:32:14.05 So, one of my graduate students, Kenneth Lay, had the remarkable brilliant idea that perhaps
00:32:20.28 if he simply deleted these transcription factors that are important in controlling quiescence
00:32:29.01 downstream of the BMP pathway, that he might be able to accelerate the differences, then,
00:32:34.20 that exist between the younger mice and the older mice
00:32:38.06 with regards to the length of their hair cycle.
00:32:41.21 Could he reduce the length of time that stem cells spend in quiescence?
00:32:47.23 And the answer to that experiment was quite remarkable.
00:32:51.09 And in fact, now, the mice just kept on cranking out hair.
00:32:54.21 Their stem cells were almost constantly activated.
00:32:58.11 A new hair would grow, the process would go through its cycle, and then the cycle would
00:33:03.22 reinitiate again, over and over and over again.
00:33:07.13 So, this was pretty exciting for us.
00:33:12.20 And we began to wonder whether BMP inhibition could be the Fountain of Youth
00:33:17.26 for endless hair growth.
00:33:19.16 Well, unfortunately in science, things aren't always so simple.
00:33:24.14 And what happened was that the animals precociously became grey, sooner than did their counterparts.
00:33:32.14 And it turned out that when the transcription factor was mutated, and lacking,
00:33:39.05 while the hairs kept on being cranked out eventually the number of stem cells declined.
00:33:45.03 And that then led to a precocious graying and a precocious thinning of the hair.
00:33:52.07 So, we're not yet there.
00:33:54.06 But we have some predictions.
00:33:56.15 And the predictions might be that the key to the Fountain of Youth with regard to hair growth
00:34:00.17 is a well-balanced BMP.
00:34:03.01 Clearly, by cranking out and activating those stem cells continuously.... was deleterious
00:34:09.12 for the mouse's ability to produce hair endlessly.
00:34:14.21 But perhaps with a balance tempering those numbers of hair cycles, one might be able
00:34:21.14 to achieve the goal of being able to extend the ability of... time that individuals
00:34:27.27 could grow their hair.
00:34:29.17 So, BMP also plays an important role in development and development of the skin.
00:34:37.08 And here we were fascinated by the fact that the dermis instructs the fate of what
00:34:44.02 the epidermal bud would do.
00:34:46.06 So, in embryonic development, the skin begins as that single layer of epithelium and epidermal buds
00:34:54.09 begin to appear.
00:34:56.06 And those buds can become a mammary gland, they can become a hair bud, they can become
00:35:02.02 a sweat gland bud.
00:35:04.14 It's depending upon what the dermis is instructing them to do.
00:35:09.14 And so regionally, we end up getting these different appendages of the epithelium,
00:35:17.26 generated as a consequence of the different types of mesenchyme or the derm... dermis that we have.
00:35:23.10 It turns out that in most mammals there's a BMP signal called BMP5 which is
00:35:29.27 regionally spiking only in the paw skin of the animals.
00:35:33.00 And so what happens is that most of the body region of the animals has hair, and there's
00:35:37.20 very few sweat glands.
00:35:39.02 There's only sweat glands, or eccrine sweat glands, on their paws.
00:35:43.04 And eccrine sweat glands are what allows us, what allows our body, to thermoregulate.
00:35:48.20 It's what allows us to go out there and run a marathon as we sweat three liters of sweat
00:35:54.18 in so doing.
00:35:56.04 But most mammals can't do that, and they can't do it because they have fur instead of
00:36:02.17 sweat glands over their body surface.
00:36:05.13 And so we began to study this process.
00:36:09.07 And as we discovered, the BMP5 regionally spikes in the paw dermis.
00:36:15.22 It doesn't spike in the body dermis, and therefore the animals get hair exclusively.
00:36:21.11 But then when we looked at human embryonic development, what we discovered is that BMP5
00:36:28.22 seems to be deregulated in a different way in humans than it is even in higher primates.
00:36:35.15 And in this case, BMP5 spikes broadly and temporally in the body dermis, so that
00:36:41.14 the very first few waves of epidermal bud development are forming hair in humans,
00:36:50.08 but then that last wave, when BMP5 spikes over the body, basically we end up getting hair...
00:36:57.04 getting sweat glands over our body.
00:36:59.17 And that's what gives us those wonderful properties to be able to run marathons, and to be able
00:37:07.03 to sweat and survive in extreme climates relative to other... other animals.
00:37:15.02 So, what else can we do with these adult skin cells?
00:37:19.26 Well, in part one of my discussion, I already told you about the ability to change the behavior
00:37:29.05 of an adult skin cell, and turn it into an induced pluripotent stem cell, by the activity
00:37:37.28 of four transcription factors that are produced by, or expressed by, embryonic stem cells.
00:37:43.08 And that was a remarkable change and a remarkable advance because it allowed us, now,
00:37:48.24 to be able to culture neurons, pancreatic beta cells, heart cells, etc. in vitro, starting with
00:37:56.20 skin cells.
00:37:58.23 So, can we reprogram in smaller steps?
00:38:02.17 Well, our ability to be able to culture, for instance, hair follicle stem cells...
00:38:07.22 we now know that if we simply switch off LHX2, we can make sebocytes in culture.
00:38:13.25 If we switch off the transcription factor SOX9, we can make epidermis rather than hair.
00:38:21.10 And if we switch off the regulatory factors for NFATc1 or Foxc1, we can basically halt tissue...
00:38:28.02 we can... if we switch them on, we can halt tissue regeneration.
00:38:33.24 If we switch them off, we can favor hair follicle tissue regeneration and hair regeneration.
00:38:40.04 And finally, an interesting aspect is that if we simply give the hair follicle stem cell
00:38:47.04 a transcriptional regulatory factor called PAX, a particular type of the PAX transcription factor,
00:38:52.07 then we can instruct hair follicle stem cells to make corn...
00:38:56.18 to become corneal stem cells.
00:38:59.02 And when you think about cases where patients have both eyes that are blinded by some industrial burn,
00:39:05.05 then this type of potential reprogramming in smaller steps might offer the potential
00:39:12.02 for future therapy.
00:39:14.08 So, I'd like to switch, now, to a problem of, what do I mean by switching on genes and
00:39:21.14 switching off genes?
00:39:23.18 And two of my graduate students, Rene Adam and Hanseul Yang had the interest of being able
00:39:31.04 to examine the chromatin landscape, the gene expression landscape, of the... of the
00:39:40.03 hair follicle stem cells.
00:39:41.26 And what they learned from that is that there are about 350 genes that are expressed by
00:39:48.04 the hair follicle stem cells, that are regulated by very large enhancers
00:39:53.00 -- Rick Young has coined them "super enhancers" --
00:39:57.22 that bind all of the different transcription factors,
00:40:00.20 as we showed, that are expressed by the hair follicle stem cells.
00:40:04.28 So, Tcf3, Tcf4.
00:40:07.21 We talked about Sox9.
00:40:09.06 We talked about Lhx2 and Nfatc1.
00:40:12.20 And they all bind to relatively short stretches of DNA that are contained within these large
00:40:18.27 "super enhancers".
00:40:21.09 So, those short... short stretches of DNA seem to have the... not only the binding of
00:40:29.22 all these transcription factors, but they also have the sequence motifs to which
00:40:35.06 those transcription factors bind.
00:40:38.00 So, these genes turn out to be also the genes that are most important in maintaining
00:40:45.26 the hair follicle stem cells in their quiescent, undifferentiated state.
00:40:50.01 If we take a look at a handful of the 350 genes, then, that are these special genes
00:40:55.27 regulated by super enhancers, what we find is that they include the Sox9 gene, the Lhx2 gene,
00:41:03.13 the Nfatc1 gene, and DNA... the BMP downstream gene... transcription factor activators.
00:41:12.11 They also include the BMP inhibitor and the BMP receptor.
00:41:16.24 They include a Wnt inhibitor, Dkk3, and the Wnt receptor, or Frizzled.
00:41:22.17 They also include the integrin genes that I emphasized as being important for maintaining
00:41:28.22 hair follicle stem cells.
00:41:30.23 Effectively, this short list of super enhancer-regulated genes contains all of the critical information
00:41:38.14 that is necessary for these genes to be able to essentially be a hair follicle stem cell.
00:41:45.21 I also point out that many of the genes on this list have already been associated
00:41:51.00 with human genetic disorders of the hair and the skin.
00:41:56.15 So, what I've told you is that there's a master group of transcription factors for the skin
00:42:03.21 stem cells, but it also turns out that there's a master group of transcription factors
00:42:08.04 for every stem cell type.
00:42:10.11 And they're different for different stem cell types.
00:42:13.09 So, the first studies that were done were on embryonic stem cells.
00:42:18.15 And Rick Young and his coworkers showed that the super enhancers are regulated by
00:42:24.09 the transcription factors that are necessary to maintain embryonic stem cells.
00:42:30.13 What I've just showed you is that in an adult tissue stem cell, the hair follicle stem cell,
00:42:36.02 that there's a different cohort of transcription factors that are necessary to maintain
00:42:41.00 these stem cells in being hair follicle stem cells.
00:42:44.11 So, we're starting to dig deeper into understanding, what are the differences in embryonic versus
00:42:49.26 adult stem cells?
00:42:51.26 Another interesting aspect is that all of these transcription factors are only expressed
00:42:58.03 as a cohort in hair follicle stem cells.
00:43:01.04 So, you might see Tcf3, for instance, in brain stem cells.
00:43:05.17 You'll see Tcf4 in intestinal stem cells, Lhx2 in hematopoietic stem cells,
00:43:10.20 Sox9 in bone stem cells.
00:43:14.08 But the only place you see them all together at one place in time are
00:43:17.25 the hair follicle stem cells.
00:43:19.21 And it turns out that we can take advantage of that.
00:43:22.15 We can take one of these elements that contain the binding sites for all of these
00:43:29.10 different transcription factors, and we can use that to drive the expression of a fluorescent green protein
00:43:34.20 in mice.
00:43:36.22 And now, the fluorescent green protein is only expressed by the hair follicle stem cells
00:43:42.05 -- far more specificity than we've ever achieved simply by taking a chunk of chromatin or
00:43:49.24 a promoter region, an enhancer region, and using that to drive expression in mice.
00:43:56.09 So, this type of information is really important for researchers to be able to dig deeper into
00:44:02.23 the biology of stem cells, in this case the hair follicle stem cells.
00:44:08.05 We also are learning that stem cells change their gene expression program outside of their niche.
00:44:14.05 I already showed you that a stem cell outside of its niche, when grafted back onto the...
00:44:19.18 to an animal, can generate hair follicles, epidermis, and sebaceous glands.
00:44:24.25 But now, if we take a wound induced enhancer, if we characterize the chromatin state of
00:44:31.21 the stem cell while it's in the act of repairing a wound, and now identify those regulatory elements,
00:44:37.25 and use those to drive eGFP in a mice... in a mouse, now what we find is that
00:44:45.00 in the unwounded skin there's no activity.
00:44:48.14 And now we wound the skin, and the activity turns on.
00:44:52.00 So, these regulatory elements contain the information necessary to not only
00:44:58.27 maintain this stem cell, but in this case to tell the stem cell what to do, and to change
00:45:04.16 its program of gene expression if it's going to repair a wound versus if it's just going to replace
00:45:10.27 a cell that is dying in the tissue.
00:45:14.00 So, we're also looking at how skin inflammation elicits changes in gene expression in epidermal stem cells.
00:45:22.19 So, when stem cells receive an inflammatory assault, how do they respond?
00:45:29.05 And what we learned from our studies is that they respond, and they activate new genes.
00:45:36.11 And by taking the regulatory elements from those genes, we can use those to drive
00:45:42.01 the expression of, in this case, a reporter GFP gene.
00:45:45.13 So, here we've generated mice that express these particular reporter elements,
00:45:52.21 but they only do so when the skin has been subjected to inflammation.
00:45:57.24 So, in the naive skin, we see no expression of the eGFP protein.
00:46:05.03 In the presence of inflammation -- if we give the skin an inflammatory assault --
00:46:09.26 now we see the activation of these enhancer elements.
00:46:14.27 So we call these elements inflammation sensors.
00:46:18.03 And what we've found is that there are about 2,000 inflammation-sensing chromatin domains
00:46:23.17 that remain open in skin stem cells long after the inflammation has resolved.
00:46:30.20 These sensors rapidly, then, become activated again with... and activate their associated genes
00:46:37.20 when the skin sees inflammation again.
00:46:40.19 And that's a remarkable property, because, basically, this confers to the epidermal stem cells
00:46:47.03 a memory, an inflammatory memory, that it's seen the inflammation before.
00:46:52.28 And even though the gene expression program is normal in... after the information has resolved,
00:47:00.01 there are these hidden memory open chromatin domains that basically allow
00:47:05.24 the genes to be poised so that the genes can now be activated again, and activated quicker,
00:47:12.21 the next time inflammation occurs.
00:47:16.24 And why do we think that that's important or relevant?
00:47:20.17 Skin inflammation elicits marks on epidermal stem cell chromatin.
00:47:25.09 Remember that the epidermal stem cells are there for the long haul.
00:47:28.05 They see the inflammation; they remain in their active state, as stem cells,
00:47:34.16 long after the inflammation has resolved.
00:47:37.10 But they have that memory that they've seen the inflammation before.
00:47:41.24 That memory resides in the virtue of epigenetic marks.
00:47:47.26 And here are some examples.
00:47:49.08 There are columns, now, of the epigenetic marks that are shown, in this case... in control chromatin,
00:47:56.12 shown in gray, there's no epigenetic marks.
00:48:00.22 Now, there's inflammation, the skin experiences inflammation, and we see two epigenetic marks
00:48:08.16 appear: here in this gene on the right.
00:48:11.25 And now, 30 days later, what we find is those epigenetic marks are still there.
00:48:19.02 And even 6 months later, there's still traces of those epigenetic marks residing within
00:48:26.15 these... this chromatin.
00:48:29.16 So, the epidermal stem cells have a memory, harbored in chromatin, that they've seen
00:48:37.07 the inflammation before.
00:48:39.10 And what's the importance of that?
00:48:40.21 Well, let's think about psoriasis or atopic dermatitis or contact dermatitis infections.
00:48:47.24 The infections typically come and go.
00:48:53.26 And when they come back again, they typically come back to the same places.
00:48:58.26 We're now starting to understand why that is, because, effectively, the epidermal stem cells
00:49:04.14 have a memory.
00:49:06.05 They've seen the inflammation before so that, if they see it again, they respond faster
00:49:11.14 the next time.
00:49:12.20 So, what I've told you is that adult stem cells replenish dying cells of a tissue,
00:49:19.10 and that they repair wounds.
00:49:20.27 I've told you that they reside in niches whose crosstalk dictates their behavior.
00:49:26.15 I've told you that key stem cell genes are regulated by super enhancers that bind stem cell
00:49:32.13 transcription factors, as well as transcription factors that are induced by the niche microenvironment.
00:49:38.13 For infla... inflammation, for instance, it might be a phosphorylated,
00:49:43.11 active version of STAT3, along with the epidermal stem cell factors.
00:49:48.24 I've also told you that trained immunity, the memory of inflammation, is not a phenomenon
00:49:58.14 that's restricted to the immune system, but occurs in epidermal, and we think likely
00:50:03.26 other epithelial, stem cells that bear the brunt of inflammation.
00:50:09.05 Inflammatory bowel disease, for in... for instance, or certain types of lung inflammation.
00:50:14.12 Somehow the tissue remembers that it's seen the inflammation before.
00:50:18.11 So, for immune cells, trained immunity enhances the ability of the immune cells
00:50:26.04 to eliminate the infection if they see it again.
00:50:29.13 For epidermal stem cells, trained immunity enhances their ability to restore
00:50:34.22 the skin barrier when breached and to aid in recruiting the immune system.
00:50:39.22 And remember that the most important thing that the skin epithelium does is
00:50:45.13 basically to produce that barrier that keeps harmful microbes out, and essential bodily fluids in.
00:50:51.24 And whether we're wounding the skin, or whether we end up with a hyper...
00:50:56.02 hyperinflammatory response, the barrier is at risk.
00:51:01.04 And the epithelium, the epidermal stem cells, respond by trying to repair that barrier
00:51:06.16 as fast as they can.
00:51:08.06 Sometimes they're not very effective at doing it, and that then can lead to chronic wound-healing
00:51:13.28 or chronic inflammation.
00:51:15.25 And those are obviously areas that we'd like to be able to adapt our understanding for
00:51:21.26 to make progress in treating those diseases in the future.

Part 3: Cancer: Hijacking the Wound Repair Mechanisms Used by Stem Cells

00:00:14.02 My name is Elaine Fuchs.
00:00:15.24 I'm a professor at Rockefeller University in New York City, and I'm also an investigator
00:00:21.04 of the Howard Hughes Medical Institute.
00:00:23.23 All of the tissues of our body must be able to replenish dying cells and repair wounds.
00:00:30.25 We cannot get rid of those fundamental mechanisms; they're essential to life.
00:00:36.19 And yet it's those mechanisms that cancers hijack in order to take advantage of...
00:00:44.01 of, effectively, the ability of our stem cells to be mobilized and repair wounds,
00:00:49.22 this time doing it uncontrollably.
00:00:54.23 So, we study specifically squamous cell carcinomas.
00:00:59.08 These are the second most common cancer worldwide.
00:01:05.09 When we consider that squamous cell carcinomas are not only found in the skin,
00:01:10.04 but also head and neck, cervix, esophagus, cancers of the anal-genital tract, and some types of lung,
00:01:18.19 breast... and breast cancers, as well as skin cancers, now we're talking about
00:01:22.26 the sixth most deadly worldwide cancer.
00:01:27.09 And yet there's very few effective therapies for squamous cell carcinoma treatment.
00:01:34.12 So, what we've learned in the course of the field's studies on skin stem cells is that
00:01:43.18 squamous cell carcinomas of the skin can originate from skin stem cells.
00:01:49.22 They're there for the long haul, so they can acquire the mutations that ultimately
00:01:55.09 will lead to cancers and tumors.
00:02:00.06 So, some years ago, my laboratory isolated and characterized the tumor initiating cells,
00:02:08.19 the so-called cancer stem cells, if you will, that are giving rise to squamous cell carcinomas,
00:02:15.00 in this case using our favorite model system, the laboratory mouse.
00:02:20.23 The way in which we examined this was to generate a mouse that we could effectively
00:02:28.24 create by chemical carcinogenesis or by genetics skin cancers or squamous cell carcinomas.
00:02:36.24 And we isolated those squamous cell carcinomas, fractionated their cells using
00:02:42.18 fluorescence activated cell sorting, and then performed serial transplantation of each of the pools
00:02:49.02 that we isolated from the FACS machine, tested them one by one, individually,
00:02:55.02 to find out which one or ones had activity that would lead to the generation of
00:03:02.00 a new squamous cell carcinoma in a host recipient mouse.
00:03:06.26 We got this down to almost the near single-cell level, where we could take a single cell isolated
00:03:13.12 from a squamous cell carcinoma and introduce it into a host recipient mouse,
00:03:19.01 and get a squamous cell carcinoma.
00:03:21.19 That told us that we had a so-called cancer stem cell.
00:03:25.08 What does it look like?
00:03:26.20 So, we learned that the cancer stem cells produce a new set of transcription factors
00:03:33.05 that are different from the normal stem cells.
00:03:36.05 So, the cancer stem cells produce ETS2, ELK3, AP1, KLF5, and SOX2 and 9,
00:03:44.00 whereas the normal hair follicle stem cells produce Sox9, Tcf4, Tcf3, Nfatc1, Nfib, and Lhx2.
00:03:55.08 There's very little overlap in the transcriptional regulators between the hair follicle stem cells
00:03:59.21 and the cancer stem cells.
00:04:02.28 One of the interesting new sets of genes that are important in the squamous cell carcinoma
00:04:09.25 cancer stem cells are ETS and the ELK binding sites.
00:04:14.27 These are present in nearly all squamous cell carcinomas -- super-enhancers, those are the
00:04:19.21 regulatory elements that are controlling the activity of the stem cells -- and those factors
00:04:26.26 turn out to be phosphorylated and superactivated by a particular kinase, the MAP kinase
00:04:33.10 that is downstream from, in this case, oncogenic RAS or hyperactivated RAS,
00:04:39.08 which is frequent in squamous cell carcinomas.
00:04:42.25 So, the Ras/MAP kinase pathway, then, phosphorylates and activates ELK3 and ETS2.
00:04:50.14 And we don't yet exactly know how it works, whether it recruits histone acetylases,
00:04:56.19 or whether it increases the DNA binding affinity or the nucleosome binding affinity for the transcription factors,
00:05:03.27 but what we do know is that the phosphorylation and superactivation
00:05:09.13 of these transcription factors is critical with regards to altered,
00:05:14.27 malignant program of gene expression produced by these stem cells.
00:05:20.08 And we can also take advantage of cloning one of these regulatory elements that is
00:05:26.00 turned on in the squamous cell carcinoma stem cell.
00:05:29.15 And we can use that to express a GFP -- fluorescent green protein -- in mice.
00:05:35.28 And we just use a fluorescent red protein as a control.
00:05:41.10 But what we find is that the regulatory element, now, is specifically expressed in
00:05:50.22 the squamous cell carcinoma cells.
00:05:54.01 So, we know that the skin stem cells from squamous cell carcinoma originate from
00:06:00.05 the wild type skin stem cells.
00:06:02.07 But they don't look anything like the wild type skin stem cells.
00:06:07.25 They have a completely different program of gene expression.
00:06:11.09 They're expressing elevated levels of cyclins, which force these cells into a superproliferative state.
00:06:17.21 They express transforming growth factor alpha, a growth stimulator
00:06:22.22 for the squamous cell carcinoma cells.
00:06:25.22 They express certain cell survival genes that are long-term survival genes not normally
00:06:31.13 expressed by the hair follicle stem cells or by the epidermal stem cells.
00:06:35.22 They express genes which give... which are important for epithelial-to-mesenchymal transitions,
00:06:43.14 for invasion.
00:06:45.16 They express VEGF-A that recruits blood vessels to these stem cells, and so on and so forth.
00:06:54.25 These are, effectively, a list of genes that are implicated in many types of cancers.
00:07:01.26 And yet they're not properties of normal stem cells.
00:07:05.25 So, the cancer stem cells, as we're learning, reside at the tumor-stroma interface.
00:07:11.25 And that's very similar to what I described to you for the normal stem cells.
00:07:17.03 Epidermal stem cells and hair follicle stem cells reside at the epidermal-dermal interface.
00:07:23.15 And so too, now we're finding that squamous cell carcinoma stem cells reside at the interface
00:07:29.20 between the epithelium and the stroma.
00:07:31.24 But, now, the stroma is entirely different.
00:07:35.06 There are immune cells.
00:07:36.25 There are altered fibroblasts.
00:07:39.01 There are blood vessels.
00:07:41.10 There are a whole variety of different changes in the tumor microenvironment that
00:07:47.21 distinguish the stem cell microenvironment from its normal counterparts.
00:07:53.07 So, there's heterogeneity, also, that arises in the tumor microenvironment, and that turns out
00:08:00.03 to influence their behavior.
00:08:02.20 Wherever there is a blood vessel that comes up next to the tumor-stroma interface,
00:08:09.02 those stem cells, now, respond very differently, because the perivasculature contains a growth factor
00:08:15.22 called transforming growth factor beta, which is a member of the BMP superfamily
00:08:21.14 of signaling factors.
00:08:23.14 And now that signaling crosstalk between the perivasculature and the cancer stem cell
00:08:30.05 changes the properties of the cancer stem cells.
00:08:33.04 And it does so in a very important way.
00:08:35.26 First, the stem cells become slower cycling as a consequence of receiving this growth factor.
00:08:43.05 But more importantly, these stem cells become invasive.
00:08:48.26 And that is a very nasty thing.
00:08:51.02 So, in order to be able to study this, we engineered a mouse to mark the TGF-beta-sensing
00:08:57.12 stem cells of the tumor in red.
00:09:00.20 And we also engineered the mouse so that we could track the behavior of these TGF-beta-sensing stem cells
00:09:09.24 by activating them and their progeny -- following their progeny -- in green.
00:09:15.18 And so as you can see from the tumor, here, the green cells, the progeny, of the TGF-beta...
00:09:22.12 of the TGF-beta-sensing cells became invasive, and broke down the basement membrane of the tumor
00:09:30.26 and started to invade the stroma.
00:09:34.19 What's interesting is that this stroma is where the blood vessels are that
00:09:40.04 basically prompted this initiative effect.
00:09:42.13 And so we think that it's these cells that are then the ones that get into the bloodstream
00:09:48.07 and could be the roots of metastasis.
00:09:53.08 Another interesting and important aspect from these studies turned out that the TGF-beta-responding
00:09:59.16 stem cells have an increased resistance to chemotherapy.
00:10:03.13 So, the drug of choice for treating squamous cell carcinomas of the head neck is cisplatin.
00:10:10.17 And here we treated the tumor with cisplatin, and by day 3 you can see the blue cells,
00:10:16.27 which are the dead cells, are the majority of the tumor.
00:10:21.06 But the red cells that are here, the TGF-beta-responding cells, did not undergo apoptosis.
00:10:28.23 Are they doing something?
00:10:30.03 Perhaps they're just sitting there in the tumor.
00:10:32.09 So, in order to be able to determine this, we washed away the cisplatin, and we activated
00:10:39.07 the lineage-tracing marker so that these cells are now green, and all their progeny are green.
00:10:45.15 If these cells are responsible for regrowing the tumor, the tumor should be green.
00:10:52.00 And so we did that experiment.
00:10:55.06 And what we found is a green tumor.
00:10:57.16 And what this tells us is that by stem cells receiving this change in their microenvironment,
00:11:04.17 that prompts them to receive a TGF-beta signal, causes them to become slower cycling, invasive,
00:11:11.19 and resistant to chemotherapy.
00:11:14.21 So, what's the mechanism involved?
00:11:18.21 And here, there's probably multiple mechanisms.
00:11:21.06 We've looked at one of those.
00:11:23.16 And it involves a factor called NRF2.
00:11:26.17 This is a master regulator of a pathway called the glutathione pathway, and I'll get to that
00:11:32.19 in a moment.
00:11:34.05 NRF2 is normally kept at bay by virtue of its association with an inhibitory protein,
00:11:41.24 KEAP1.
00:11:43.03 And in response to TGF-beta, p21 is upregulated.
00:11:48.04 It competes for the binding of KEAP1 to NRF2.
00:11:53.15 And that then turns NRF2 into a stabilized activator of the glutathione regulatory pathway.
00:12:01.28 The glutathione metabolism genes then go up in the cancer stem cells.
00:12:07.01 And the ones that we identified that were up in the TGF-beta-responding stem cells
00:12:12.00 are those shown in red.
00:12:14.01 So, what's the glutathione pathway doing?
00:12:16.26 The glutathione pathway is what normal, healthy cells use to clear out nasty stuff like cisplatin,
00:12:25.13 in the course of chemotherapy, or reactive oxygen species, in the course of radiotherapy.
00:12:32.26 And so by upregulating the glutathione pathway... normally, it clears out all sorts of
00:12:39.13 nasty stuff from healthy stem cells.
00:12:41.18 But here it's clearing out all sorts of nasty stuff from the cancer stem cells, the cells
00:12:49.01 that we would like to get rid of.
00:12:51.01 So, is this relevant?
00:12:53.04 I've told you about studies in mice -- are they relevant to human?
00:12:56.20 So, here we looked at the glutathione expression program in squamous cell carcinomas of humans.
00:13:04.21 And what we learned is that the glutathione pathway is upregulated in a small cohort of
00:13:10.26 human patients with head and neck squamous cell carcinoma.
00:13:14.18 And when we looked at the prognosis of that small cohort, that cohort with
00:13:19.28 upregulated glutathione pathway genes turns out to be the cohort with the poorest prognosis,
00:13:27.15 suggesting that this is an important finding that could help us in terms of future treatments of cancer.
00:13:34.18 So, NRF2, the good and the bad.
00:13:39.05 NRF2 is what is normally contained in broccoli, in blueberries, and all the things that
00:13:46.15 we're told are really good for our health.
00:13:49.00 They are if we're healthy.
00:13:51.21 But for tumor patients or cancer patients, antioxidants may not necessarily be a good thing.
00:13:58.25 And it's something that is really going to bear the need for future studies, to be able
00:14:03.15 to explore deeper into this.
00:14:05.28 So, how do we go from taking the findings that we've made to, perhaps, the clinics
00:14:13.11 or to new therapies for the treatment of squamous cell carcinoma.
00:14:19.01 Well, to this end, we've engineered isogenic strains, or isogenic cells, that contain
00:14:27.08 the ability... a sensor that allows us to look at whether or not the cells are experiencing
00:14:32.12 TGF-beta or not.
00:14:34.22 We've also engineered the cells such that the... one type of squamous cell carcinoma cell
00:14:41.07 has the TGF-beta receptor on its surface, and we've excised the TGF-beta receptor
00:14:47.21 from the other cell, making it or rendering it unable to respond to TGF-beta.
00:14:53.02 So, here's an example.
00:14:55.11 The red reporter shows us nuclear red if TGF-beta signaling is on.
00:15:00.10 And you can see that if we co-culture the TGF-beta receptor positive and negative cells
00:15:06.00 in a dish, what we find is that when we add TGF-beta the cells that have the receptor
00:15:12.22 show nuclear red -- TGF-beta is on and signaling in those cells --
00:15:17.15 the green ones, TGF-beta is unable to signal.
00:15:20.25 So, now we can treat the cells with cisplatin.
00:15:24.04 And what we see on the left-hand panel is that if you don't add any TGF-beta and
00:15:31.01 you just add cisplatin, you kill all of the cells, as evidenced by the fact that they round up
00:15:37.01 and die.
00:15:38.06 On the right-hand side, if you treat the cells with TGF-beta, those cells able
00:15:43.10 to respond to TGF-beta are surviving the cisplatin, much the same as what I described to you for the tumor.
00:15:51.25 So, we can also see gamma-H2AX, a sign of DNA damage.
00:15:56.17 And again, DNA damage occurs in the cells that cannot respond to TGF-beta,
00:16:04.09 and the cells that can respond to TGF-beta are refractory.
00:16:07.04 So, what this tells us is that, basically, now we can start to think about therapeutics
00:16:13.19 that would be able to compromise the ability of these slow cycling cancer stem cells
00:16:19.26 that have high levels of glutathione to be able to kill those cells in the presence of, perhaps,
00:16:26.09 combinatorial drugs for... for these cells.
00:16:31.04 We also think that it might be possible, through combinatorial drugs and the use of TGF-beta inhibitors
00:16:39.08 in a very co... in a very specific way, to first kill off the bulk of the tumor cells
00:16:43.28 with cisplatin, for instance, and then mobilize those cancer stem cells
00:16:50.24 that are resistant with, perhaps, TGF-beta inhibitor drugs or antibodies, and then hit the tumor
00:16:57.28 again with cisplatin to wipe out the mobilized, activated cancer stem cells.
00:17:03.11 So, these are ideas that at the moment are just ideas, but we'd like to be able
00:17:08.25 to take these ideas to the practice, and ultimately to translational medicine.
00:17:14.11 But there are many mutations, genetic mutations, that exist within these human squamous cell carcinomas,
00:17:22.24 these solid tumors.
00:17:24.17 And ultimately, we'd like to know which ones are cancer-driving and which ones aren't.
00:17:30.15 So again, my laboratory has said whether we could harness the power of fly and worms,
00:17:37.20 and take advantage of fly and worm genetics, only apply it to the laboratory mouse.
00:17:43.03 Could... to be able to screen through and find out which of the genes that have been
00:17:48.13 mutated in cancer are actually causing the cancer.
00:17:52.17 And so here, two of my former lab members
00:17:57.22 -- Slobodan Beronja, who's running his own laboratory at the Fred Hutchinson Cancer Center,
00:18:02.16 and Geulah Livshits, who was a graduate student and is now postdoccing in a cancer laboratory --
00:18:10.00 came up with a method of carrying out rapid genetics in mice.
00:18:15.08 What they did was to take advantage of the fact that lentivirus only gets into the
00:18:21.09 very first cell layer that it sees, which, right after gastrulation, is the single layer
00:18:27.09 of surface ectodermal cells that are going to give rise to the epidermis, the hair follicles,
00:18:33.01 the mammary gland, the corneal covering of the eye, and the sweat glands.
00:18:38.15 And what they did was to, then, put the mother mouse under anesthesia at nine and a half days
00:18:45.15 of development, right after gastrulation, with her pups, and basically use ultrasound
00:18:51.19 to find the pups, and then use a microinjection needle to be able to inject high-titer lentivirus
00:18:59.07 just in the amniotic sac, the fluid that the embryo is bathing in.
00:19:03.14 So, in a non-invasive way, we expose the embryo to lentivirus.
00:19:10.09 We now seal up mom, let the pups develop.
00:19:13.09 In this case, we analyze the pups six days later.
00:19:16.11 And what we find is that the lentivirus is now integrated stably into the mouse genome.
00:19:22.27 And it only infected the cells of the epithelium, and did not get into the inner layers beneath it,
00:19:30.26 the dermis.
00:19:32.02 And what we find is that the red embryo, in this case carrying... the lentivirus carried
00:19:38.10 a red fluorescent protein, is now nicely infected over the entire mouse embryo epithelium.
00:19:46.20 And when you look at a cross-section of the tissue, you see that the epidermis and the hair follicles,
00:19:52.01 but no other cells of the skin, basically, were stably transduced with lentivirus.
00:19:59.13 So, what this allows us to do is put any gene we want, or down regulate any gene that we want,
00:20:05.14 or CRISPR/Cas edit any gene that we want, specifically in the skin epithelium
00:20:12.00 in a matter of days.
00:20:13.20 That used to take my laboratory years to accomplish.
00:20:18.03 Ten years later, we've basically been able to accelerate the pace at which we do research
00:20:25.00 in the laboratory.
00:20:26.22 We've now carried out rapid functional genetic screens... genes for... screening for,
00:20:34.17 what are the oncogenes in that group of different human mutations that are found in squamous cell carcinomas?
00:20:41.13 Who are the tumor suppressors?
00:20:44.11 What are the microRNAs that are drivers of squamous cell carcinoma?
00:20:51.18 And what genes are important in regulating the balance of growth and differentiation
00:20:56.18 in the skin epithelium?
00:20:58.23 These technologies and the advances that we've been able to make... carrying out even
00:21:03.27 whole genome-wide screens in mice, which were previously, just a few years ago, thought to be possible
00:21:10.14 only in worms or in fruit flies.
00:21:14.17 So, I hope I've been able to give you the insights, today, of why my laboratory studies the skin,
00:21:21.04 and why we continue to use it as an important model to be able to uncover
00:21:27.23 the basis of genetic disorders, and also the basis of cancers.
00:21:34.04 And for the goal, the broader objective, of basically making advances in the treatments
00:21:41.20 of human genetic diseases.
00:21:44.12 The work that we do is focused on mouse.
00:21:47.25 And there's always that need to be able to draw parallels between mouse and human.
00:21:52.18 But those kinds of approaches are now possible.
00:21:55.27 This is my laboratory.
00:21:57.17 It's an international laboratory of researchers from around the world who get together
00:22:03.20 with a common goal.
00:22:05.07 And that is to work together to be able to advance our knowledge of biology and, ultimately,
00:22:12.20 to make advances that can be useful in the clinics, and in the biotechnology and pharmaceutical industries.
00:22:20.19 Thank you.

Videos in this Talk
  • Part 1: Skin Stem Cells: Their Biology and Promise for Regenerative Medicine
    Part 1: Skin Stem Cells: Their Biology and Promise for Regenerative Medicine
    Audience:
    • Student
    • Researcher
    • Educators of H. School / Intro Undergrad
    • Educators of Adv. Undergrad / Grad
  • Part 2: Tapping the Potential of Adult Stem Cells
    Part 2: Tapping the Potential of Adult Stem Cells
    Audience:
    • Researcher
    • Educators of Adv. Undergrad / Grad
  • Part 3: Cancer: Hijacking the Wound Repair Mechanisms Used by Stem Cells
    Part 3: Cancer: Hijacking the Wound Repair Mechanisms Used by Stem Cells
    Audience:
    • Researcher
    • Educators of Adv. Undergrad / Grad
Speaker: Elaine Fuchs
Total Duration: 1:59:42
Recorded: December 2017
Educator Resources for this Talk
All Talks in Development and Stem Cells

Talk Overview

Dr. Fuchs begins her talk with a brief history of stem cells including the discovery in the 1970s that adult skin stem cells could be cultured in vitro indefinitely.  This early work provided the foundation for later advances in embryonic stem cell (ESC) culture. ESCs are special because they can generate all the different tissues of the body, thus providing great potential for use in regenerative medicine. The use of ESCs is controversial, however, so scientists have developed ways of generating pluripotent stem cells that do not use embryonic tissue.  Fuchs reviews methods such as nuclear transfer and the generation of induced pluripotent stem cells (iPSCs) by reprogramming adult somatic cells. Cells generated by these methods may be used for drug and therapy screening and they may provide treatments for human diseases such as macular degeneration, Parkinson’s and other degenerative diseases.

In her second talk, Fuchs focuses primarily on studies of adult skin stem cells.  Adult stem cells have the ability to make more stem cells and to generate the cells of a differentiated tissue. Skin stem cells can replenish the epidermis and make hair follicle cells. Skin grown in culture from just a few skin stem cells can be used to treat burn patients or replace damaged corneal epithelium.  Stem cells reside in specific niches or microenvironments and signals from the niche determine whether a stem cell is going to be quiescent or make tissue. Fuchs’ lab has studied hair follicle stem cells for many years and has identified the signals that activate hair follicle stem cells as well as the specific set of transcription factors that are upregulated in the activated stem cells. They have shown that many of the genes turned on during stem cell activation are regulated by super enhancers which sense the niche environment.

Squamous cell carcinomas (SCCs) are commonly occurring, dangerous cancers that may originate from skin stem cells. By developing methods to identify the stem cells that will lead to cancer, Fuchs’ lab has been able to study how these cells differ from normal skin stem cells. They found that the gene expression profile in normal versus cancer stem cells is very different and is likely the result of differences in the cancer stem cell niche. The tumor microenvironment may include immune cells and greater proximity to TGF-beta secreting blood vessels. Fuchs’ lab showed that cancer stem cells exposed to TGF-beta had increased expression of proteins in the glutathione metabolism pathway; the same pathway which is involved in the breakdown of chemotherapy drugs. Further studies in SCC patients, showed a strong correlation between increased mRNA levels for glutathione pathway proteins and decreased survival. These results suggest that drugs which block TGF-beta activity, in combination with other chemotherapeutics, may be an effective therapy for some SCC.

Speaker Bio

Elaine Fuchs

Elaine Fuchs

Elaine Fuchs is the Rebecca C. Lancefield Professor of Mammalian Cell Biology and Development at The Rockefeller University and an Investigator of the Howard Hughes Medical Institute. Her lab studies the role of skin stem cells in homeostasis and wound repair and how these processes go awry in cancer and inflammatory diseases.   Fuchs received… Continue Reading

Playlist: Stem Cells

Related Resources

Part 1
Li J, Greco V, Guasch G, Fuchs E, Mombaerts P.(2007) Mice cloned from skin cells. Proc Natl Acad Sci U S A.104(8):2738-43.

Takahashi K, Yamanaka S. (2006) Induction of pluripotent stem cells from mouse embryonic and adult fibroblast cultures by defined factors. Cell. 126(4):663-76.

Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K, Yamanaka S. (2007) Induction of pluripotent stem cells from adult human fibroblasts by defined factors. Cell. 131(5):861-72.

Okita K, Ichisaka T, Yamanaka S. (2007) Generation of germline-competent induced pluripotent stem cells. Nature. 448(7151):313-7.

Part 2
Green H, Kehinde O, Thomas J.(1979) Growth of cultured human epidermal cells into multiple epithelia suitable for grafting. Proc Natl Acad Sci U S A. 76(11):5665-8.

Hirsch T, Rothoeft T, Teig N, Bauer JW, Pellegrini G, De Rosa L, Scaglione D, Reichelt J, Klausegger A, Kneisz D, Romano O, Secone Seconetti A, Contin R, Enzo E, Jurman I, Carulli S, Jacobsen F, Luecke T, Lehnhardt M, Fischer M, Kueckelhaus M, Quaglino D, Morgante M, Bicciato S, Bondanza S, De Luca M. (2017) Regeneration of the entire human epidermis using transgenic stem cells.  Nature.551(7680):327-332.

Lay K, Kume T, Fuchs E. (2016)  FOXC1 maintains the hair follicle stem cell niche and governs stem cell quiescence to preserve long-term tissue-regenerating potential. Proc Natl Acad Sci USA. 113(11):E1506-15.

Adam RC, Yang H, Rockowitz S, Larsen SB, Nikolova M, Oristian DS, Polak L, Kadaja M, Asare A, Zheng D, Fuchs E. (2015) Pioneer factors govern super-enhancer dynamics in stem cell plasticity and lineage choice.  Nature. 521(7552):366-70.

Part 3
Schober M, Fuchs E.(2011)  Tumor-initiating stem cells of squamous cell carcinomas and their control by TGF-β and integrin/focal adhesion kinase (FAK) signaling. Proc Natl Acad Sci U S A. 108(26):10544-9.

Oshimori N, Oristian D, Fuchs E. (2015) TGF-β promotes heterogeneity and drug resistance in squamous cell carcinoma. Cell. 2015 Feb 26;160(5):963-976.

Reader Interactions

Comments

  1. Jane says

    I’m sorry but when you’re explaining the Wnt signaling, BPM, and Shh it was very confusing. Barely understood it.

    Reply

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