Placental Development • iBiology

Part 1: What is the Placenta?

00:00:07.08 Hi.
00:00:08.08 My name is Mana Parast, and I'm a perinatal pathologist and stem cell scientist
00:00:12.27 at the University of California, San Diego.
00:00:16.03 And today, I'm going to tell you about a very intriguing organ, an organ that none of us
00:00:22.08 would be able to survive the intrauterine period without.
00:00:26.06 And that organ is the placenta.
00:00:30.04 So, what is the placenta?
00:00:32.22 It is the connection between mom and baby.
00:00:36.13 It's also known as afterbirth, because it's delivered after the baby.
00:00:42.11 And those of us that study the placenta in cases of pregnancy complication also know it
00:00:48.22 as a diary of intrauterine life.
00:00:53.12 Now, placenta... and the placenta is literally forming a connection between mom and baby.
00:01:01.17 On one side, it's connected to the baby via the umbilical cord.
00:01:06.21 This is the connection through which the baby's blood flows into the placenta in order for it
00:01:15.21 to be loaded up with oxygen and nutrients, and then goes back to the baby.
00:01:21.24 On the flip side, it's attached to mom, and specifically, to the uterine lining called decidua.
00:01:31.13 Now, placentas come in all shapes and sizes.
00:01:36.15 This one has the umbilical cord attached to one side.
00:01:41.11 This one seems to have a little bit of extra tissue on the side.
00:01:47.01 This one looks a little pale, maybe a little bit lumpy on the fetal side.
00:01:54.18 And this one looks like it has an abnormal umbilical cord, and is a little bit green.
00:02:03.22 So, is there a significance to these different shapes and sizes and colors?
00:02:10.13 Well, let's examine them together.
00:02:15.14 So, with some of these placentas, what they help us with is to confirm clinical findings.
00:02:22.03 So, this placenta, with a little bit of extra tissue on the side... actually, what this is
00:02:29.05 is a blood clot that has been accumulating over the period of pregnancy, and led to
00:02:38.03 the premature delivery of this placenta at 27 weeks.
00:02:42.05 So, this finding actually confirms the clinical diagnosis of chronic abruption.
00:02:50.08 Sometimes, placentas can provide a hint at a diagnosis of an underlying disease in mom.
00:02:58.15 So, when this placenta came out, it was associated with a small-for-gestation baby.
00:03:07.06 On exam, we could see that the placenta shows areas of infarction or dead tissue.
00:03:15.20 And microscopically, this placenta was diagnosed with massive perivillous fibrin deposition.
00:03:23.16 This is a condition that's associated with maternal autoimmune disease.
00:03:27.23 And in fact, this mom went on to be diagnosed with lupus.
00:03:32.22 And this diagnosis came about because of this placental examination.
00:03:37.02 And it's important to... that she received this diagnosis, at this point in time,
00:03:42.25 because for her next pregnancy she will be able to be treated to prevent another instance of
00:03:49.02 intrauterine growth restriction.
00:03:51.22 At other times, placentas can provide a cause of stillbirth.
00:03:55.15 So, in this case, the placenta is shown to have a long hyper-twisted umbilical cord.
00:04:04.27 And a placental exam can give us some insight into recurrence of stillbirth
00:04:09.24 in subsequent pregnancies.
00:04:11.22 So, with the long umbilical cord, because the length of the cord is at least
00:04:17.28 partly determined by genetics, this woman is at a slightly increased risk of having stillbirth
00:04:25.09 due to a long cord in a subsequent pregnancy.
00:04:31.06 So, what I've shown you is that the placenta can really be the diary of intrauterine life.
00:04:37.13 But more recently, it's been called "the least understood human organ"
00:04:42.23 by the National Institute of Child Health and Human Development.
00:04:47.11 And this is in fact true as well.
00:04:49.21 We don't really understand how the placenta develops.
00:04:53.20 We don't have a good test to test its function during an ongoing pregnancy.
00:05:00.04 And even worse, we don't have any drugs to target the placenta when there is a pregnancy complication.
00:05:09.12 So, let me tell you about another devastating disease during pregnancy,
00:05:15.15 which is called preeclampsia.
00:05:18.04 Preeclampsia has also been called "the silent killer."
00:05:22.01 The symptoms of preeclampsia develop during the second half of pregnancy,
00:05:27.06 even though the disease is thought to originate early in pregnancy.
00:05:33.05 The symptoms include high blood pressure, and high protein in the urine -- or proteinuria --
00:05:41.09 which is a result of kidney dysfunction.
00:05:46.15 But the symptoms can vary.
00:05:48.01 They can range from just purely high blood pressure, or gestational hypertension,
00:05:55.06 all the way to eclampsia, where there's seizures, and to HELLP syndrome,
00:06:00.17 which includes liver failure and clotting disorders.
00:06:08.20 Preeclampsia happens in 5-8% percent of pregnancies worldwide.
00:06:13.19 Other than maternal complications, there is also neonatal complications,
00:06:18.11 the most common of which is intrauterine growth restriction.
00:06:23.05 There is no cure for preeclampsia except delivery.
00:06:26.26 And as a result, it's the leading cause of preterm deliveries.
00:06:34.08 A placenta from... a preeclamptic placenta shows a lot of pathology.
00:06:39.11 So, what you see here is a placenta with an infarct, or an area of dead tissue.
00:06:48.15 In addition, these placentas show evidence of maternal vascular disease, as is evident
00:06:55.11 on the clinical side by high blood pressure in mom.
00:06:59.06 But even around the infarction, or the dead tissue, the placenta, under the microscope,
00:07:07.24 appears very abnormal.
00:07:10.07 Basically, it shows evidence of abnormal placental development.
00:07:15.06 And we're not clear as to how this happens.
00:07:18.22 In order to better understand this disease, we have to understand placental development better.
00:07:26.07 Now, the placenta develops from the embryo, from... in particular, from the outer cells
00:07:36.09 of an embryo that are called trophoblast.
00:07:41.00 This outer layer of cells -- the trophoblast -- proliferate, expand, and differentiate
00:07:47.20 in order to give rise to the placenta at term.
00:07:54.24 The word trophoblast comes from the Greek word tropho, meaning "to feed."
00:08:00.13 And in fact, this is the primary function of these cells, in order to be able
00:08:07.18 to access maternal blood and then provide it to the growing placenta, and therefore the fetus.
00:08:15.08 The trophoblasts begin at a progenitor cell called a cytotrophoblast, or CTB.
00:08:23.20 And they have to differentiate into two different subtypes.
00:08:30.15 One is extravillous trophoblast, or EVT.
00:08:33.07 And the other is a multinucleated syncytiotrophoblast, or STB.
00:08:41.17 Now, EVT, extravillous trophoblasts develop early in pregnancy.
00:08:48.18 And they're perhaps the most crucial to pregnancy success.
00:08:51.18 So, before pregnancy, the maternal vessels look like this.
00:08:56.22 They are basically very small, and they can carry very little blood to a growing baby.
00:09:05.21 However, in... during the first trimester of pregnancy, the extravillous trophoblasts
00:09:13.24 actually invade and remodel maternal vessels, thereby allowing these vessels
00:09:20.01 to carry more blood to the growing feto placental unit.
00:09:25.24 The syncytiotrophoblasts develop in functional units units of the placenta
00:09:31.05 called the chorionic villi.
00:09:33.22 This is where the gas and nutrient exchange actually happens.
00:09:38.27 These units are comprised of fetal blood vessels in the middle and a layer of cytotrophoblasts,
00:09:48.26 and these progenitor cells then fuse to form the multinucleated syncytiotrophoblasts.
00:09:56.25 Syncytiotrophoblasts secrete the pregnancy hormone HCG.
00:10:01.22 And they are the cells that are responsible for gas and nutrient exchange.
00:10:08.11 If either one of these cell types doesn't differentiate properly, the result is
00:10:14.00 abnormal placental development.
00:10:15.19 So, if the extravillous trophoblasts, or EVT, don't differentiate well,
00:10:20.25 the placenta doesn't receive enough maternal blood.
00:10:25.15 If the syncytiotrophoblasts, on the other hand, don't differentiate properly,
00:10:30.22 that results in improper, insufficient gas and nutrient exchange.
00:10:36.15 Both of these can result in placental diseases, including preeclampsia and intrauterine growth restriction.
00:10:45.24 So, in summary, the placenta, as I've explained, is a diary of intrauterine life.
00:10:53.02 Placental examination cannot just confirm clinical findings, but it can also identify
00:10:59.26 underlying maternal disease.
00:11:01.19 It can provide a cause for unexplained stillbirths.
00:11:06.04 I've also explained that abnormalities in placental development can lead to
00:11:11.00 pregnancy complications, including preeclampsia and IUGR.
00:11:18.09 And I've also summarized the development of placental cells, or trophoblasts,
00:11:25.08 specifically from a cytotrophoblast progenitor state into either extravillous trophoblasts, or EVT,
00:11:32.17 which are invasive cells that help access maternal blood, or syncytiotrophoblasts, or STB,
00:11:40.05 which are multinucleated cells which help in gas and nutrient exchange.
00:11:45.16 I hope you stay tuned for the second part of the talk, where I'm going to discuss
00:11:49.23 how we can model and better understand human placental development.

Part 2: Modeling Placental Development

00:00:07.05 Hi.
00:00:08.06 My name is Mana Parast, and I'm a perinatal pathologist and stem cell biologist
00:00:13.09 at the University of California, San Diego.
00:00:16.04 So, in the first part of my talk, I talked about human placental development and
00:00:22.17 how the placenta develops from the layer of cells on the outer part of the embryo called trophoblasts.
00:00:30.15 These cells on the outside go on to proliferate and differentiate to form the placenta
00:00:37.23 that we see at term.
00:00:40.18 In this part of the talk, I'm going to tell you about how we can model human placental development
00:00:46.19 in order to understand pregnancy complications such as preeclampsia.
00:00:54.17 So, the mouse has been used very commonly as an animal model to study the development
00:01:00.22 of numerous organ systems.
00:01:03.24 However, compared to other organs, the placenta is an evolutionarily divergent organ.
00:01:11.23 So, what that means is that the mouse placenta has a very different placental structure and
00:01:18.09 different cell types, and in particular, is very different in terms of the early developmental pathways
00:01:25.13 that regulate its growth and development, compared to human.
00:01:31.20 In addition, placental diseases like preeclampsia are actually specific to higher primates.
00:01:38.04 Therefore, the mouse is a suboptimal model for studying human placental development.
00:01:48.27 So for this reason, a lot of scientists have turned to tissue culture, using cell lines
00:01:55.00 in the dish, in order to understand human placental development.
00:01:59.13 In particular, cell lines that are derived from placental tumors, called choriocarcinoma,
00:02:05.25 have been used.
00:02:07.05 However, these cells are genetically abnormal, and they do not recapitulate the function
00:02:13.03 of normal trophoblasts very well.
00:02:17.08 So, for this reason, we turned to cytotrophoblasts, primary cells that can be isolated from placentas
00:02:24.25 at delivery, as the gold standard.
00:02:28.10 However, these cells can only be differentiated into syncytiotrophoblasts,
00:02:34.16 and not into invasive extravillous trophoblasts.
00:02:39.08 More recently, human trophoblast stem cells have been derived that can be differentiated
00:02:45.06 into both syncytiotrophoblasts and extravillous trophoblasts.
00:02:50.06 However, these cells can only be derived from human embryos or early gestation human placentas.
00:02:58.06 And because of their origin, we cannot be sure whether there would have been
00:03:03.15 a pregnancy complication in these cases.
00:03:07.11 And hence, we don't know if we're studying normal or abnormal trophoblasts.
00:03:14.28 So, what if we could start from cells from a placenta at delivery, and take these cells
00:03:23.03 back in time into a time when they were like embryonic stem cells,
00:03:30.24 and differentiate them into cytotrophoblasts and syncytiotrophoblasts and extravillous trophoblasts?
00:03:41.20 And what if we could do this not just with cells from a normal placenta but also with abnor...
00:03:47.10 cells from an abnormal placenta, including a placenta from a patient with preeclampsia?
00:03:54.15 Then, we could potentially study the pathways of trophoblast differentiation that gave rise
00:04:01.19 to this particular diseased placenta.
00:04:05.06 Well, in fact, we can.
00:04:08.18 Using technology that has been recently developed, we can isolate cells from a placenta,
00:04:16.05 in particular from the umbilical cord -- these are mesenchymal stem cells --
00:04:21.11 that can be transduced with four specific genes:
00:04:28.02 KLF4, SOX2, OCT4, and MYC, known as KSOM for short, or reprogramming factors.
00:04:38.26 When these genes are expressed, are induced... introduced into these mesenchymal stem cells
00:04:45.27 for a short period of time, these cells can be turned into induced pluripotent stem cells,
00:04:52.06 or iPSCs.
00:04:53.26 iPSC, for all practical purposes, behave like embryonic stem cells.
00:05:01.20 And like embryonic stem cells, iPS cells can be differentiated into all different types
00:05:09.05 of embryonic tissues, including ectoderm tissues like brain and skin cells,
00:05:18.02 mesodermal tissues like bone or blood cells,
00:05:23.06 and endoderm tissues like lung and intestine.
00:05:29.00 Now, the question is, can iPSCs be differentiated also into placental cells, or trophoblasts?
00:05:37.04 And in fact, the answer is yes.
00:05:39.26 iPS cells, just like embryonic stem cells, have been shown by multiple groups,
00:05:46.12 using multiple different protocols, to be able to be differentiated into
00:05:50.22 both multinucleated syncytiotrophoblasts that can secrete HCG
00:05:56.16 and into invasive extravillous trophoblasts, which express HLA-G on their surface.
00:06:04.24 One of these particular protocols uses bone morphogenetic protein 4, or BMP4.
00:06:13.04 This particular protocol has been studied most extensively.
00:06:17.00 And about 10 years ago, our lab started using this protocol to study trophoblast differentiation.
00:06:25.15 But before we could study abnormal trophoblast differentiation, or diseased placentas,
00:06:33.25 using this protocol, we asked the question,
00:06:38.02 does this protocol recapitulate normal trophoblast differentiation?
00:06:43.00 That is, do the iPS cells differentiate first into cytotrophoblast progenitor cells,
00:06:51.10 before becoming terminally differentiated STB or EVT?
00:06:58.09 Cytotrophoblasts in the placenta express a specific nuclear protein called p63.
00:07:03.14 So, we started by asking the question, do... does BMP4 induce expression of p63 in iPS cells?
00:07:15.20 And we found that, in fact, it does.
00:07:19.08 So, after 4 or 5 days of BMP4 treatment, iPSCs lose their expression of OCT4 and gain expression
00:07:29.20 of trophoblast markers, including cytokeratin 7 and the cytotrophoblast marker p63.
00:07:38.04 Then, after a few more days of treatment with BMP4,
00:07:42.16 they start to express markers of iPSC trophoblasts, including HLA-G,
00:07:49.11 or markers of syncytiotrophoblasts, including HCG.
00:07:57.18 We then asked the question, is p63 required for trophoblast differentiation of iPSCs?
00:08:05.02 So, what we did was to down regulate expression of p63.
00:08:10.11 And what we found was that while p63 was not required for differentiation of iPSCs,
00:08:18.24 it was specifically required for their differentiation into trophoblasts, because we did not see...
00:08:24.28 in the absence of p63, we don't see induction of other trophoblast-associated markers,
00:08:32.07 such as HLA-G.
00:08:33.28 Since then, we have established a more refined...
00:08:39.26 what we call a two-step protocol for trophoblast differentiation of iPSCs.
00:08:46.01 This protocol still uses BMP4.
00:08:48.18 However, it separates the differentiation into two steps.
00:08:54.26 The first step is trophoblast lineage specification, by which iPSCs become cytotrophoblast progenitor cells.
00:09:05.12 And step II, where the cytotrophoblasts can in fact be replated and, in the presence of
00:09:11.21 feeder conditioned media and BMP4, differentiate further into STB and EVT.
00:09:21.09 This protocol offers the advantage of being able to pause... pause differentiation
00:09:30.25 at the cytotrophoblast stage and compare these iPSC-derived cytotrophoblasts
00:09:36.01 to primary cytotrophoblasts that are derived from a placenta.
00:09:41.18 And so, in order to see whether this protocol
00:09:47.02 can in fact recapitulate abnormal trophoblast differentiation, we started by studying hypoxia.
00:09:57.00 Because hypoxia is... has been very well studied with primary cytotrophoblasts,
00:10:02.24 and it's been shown to be able to inhibit differentiation into syncytiotrophoblasts.
00:10:09.22 It's been shown to inhibit HCG secretion.
00:10:14.18 And hypoxia, through a specific factor... transcription factor called hypoxia-inducible factor, or HIF,
00:10:22.07 has been shown to induce formation of extravillous trophoblasts, or EVT.
00:10:29.02 So, we asked, how do iPSC-derived cytotrophoblasts respond to hypoxia?
00:10:36.19 What we found is that, first of all, HCG secretion, as a marker of syncytiotrophoblasts,
00:10:44.14 is in fact inhibited under conditions of hypoxia, or low oxygen tension.
00:10:52.19 In addition, in the presence of an intact HIF complex, hypoxia was able to
00:10:59.13 increase the number of extravillous trophoblasts in culture, while in the presence...
00:11:05.17 in the absence of HIF complex,
00:11:11.04 hypoxia was not able to induce extravillous trophoblast differentiation.
00:11:18.27 We also studied another model in order to understand whether iPSC-derived cytotrophoblasts
00:11:27.03 can model abnormal trophoblast differentiation.
00:11:32.21 It is known that cytotrophoblasts that are isolated from trisomy 21 placentas
00:11:40.13 have a difficult time undergoing cell-cell fusion and becoming syncytiotrophoblasts.
00:11:44.12 It is also known that when these cells are treated with the growth factor activin
00:11:54.08 this can overcome this cell-cell fusion defect.
00:12:02.04 So, in collaboration with a group in Texas, we were able to obtain several trisomy 21 iPSC lines,
00:12:10.23 and we differentiated them into trophoblasts,
00:12:15.09 and found that during the second step of trophoblast differentiation the trisomy 21 iPS cells...
00:12:23.16 when compared to the disomy line that does not have any extra chromosomes,
00:12:29.20 the trisomy 21 iPSCs showed a reduced fusion index.
00:12:37.02 When we treated these cells with activin, we found that this defect in fusion
00:12:44.11 could in fact be rescued.
00:12:47.04 So, with these data in mind, we have moved on to model preeclampsia using iPSCs.
00:12:56.24 We have begun by banking a series of mesenchymal stem cells from umbilical cords of placentas
00:13:04.24 from preeclamptic patients.
00:13:07.13 And we have used the reprogramming factors to generate iPSCs from these lines.
00:13:13.10 And we are just now beginning to differentiate these cells into cytotrophoblasts,
00:13:18.23 and subsequently into STBs and EVTs to evaluate their phenotypes.
00:13:27.02 Based on previous publications, it is thought that preeclampsia is a... is a disease of
00:13:34.19 abnormal trophoblast differentiation.
00:13:36.15 And in particular, that EVT don't differentiate very well in this disease.
00:13:42.22 So, what we hope to find is that our iPSC model can also recapitulate this defect.
00:13:51.15 However, the iPSCs offer another advantage.
00:13:56.18 They provide a platform through which we can screen for small molecules and drugs for treatment
00:14:03.15 of preeclampsia.
00:14:06.14 In other words, we can look for small molecules or drugs that can enhance differentiation
00:14:12.01 of cytotrophoblasts into extravillous trophoblasts,
00:14:15.20 and potentially be able to prevent complications of this disease.
00:14:20.24 So, in summary, I've told you how the human placenta has been difficult to model,
00:14:28.25 and in particular that mice do not serve as a very good model
00:14:33.08 for studying human placental development.
00:14:36.17 I've shown you how induced pluripotent stem cells, or iPSCs, offer a novel method
00:14:43.02 for modeling trophoblast differentiation.
00:14:46.01 And I've shown you data that establishes proof of concept
00:14:50.15 that abnormalities of trophoblast differentiation can be modeled with iPSCs.
00:14:55.26 In particular, we have shown that both changes in the microenvironment, such as hypoxia,
00:15:02.15 and effects of abnormal chromosome number, such as trisomy 21, can...
00:15:09.23 can be recapitulated using iPSCs.
00:15:17.03 And we hope that, going forward, complex placental disorders,
00:15:21.01 such as preeclampsia and intrauterine growth restriction,
00:15:25.11 which arise based on a combination of both genetic aberration and the microenvironment,
00:15:30.22 can in fact be modeled using iPSCs.
00:15:36.15 And finally, I would like to end by thanking current and former members of my lab that are listed here;
00:15:45.20 collaborators, including Dr. Laurent and Dr. Ying Liu;
00:15:48.20 and our funding sources, without which we wouldn't be able to do this work.
00:15:53.00 Thank you.

Videos in this Talk

Part 1: What is the Placenta?
Audience:
- Student
- Researcher
- Educators of H. School / Intro Undergrad
- Educators of Adv. Undergrad / Grad
Part 2: Modeling Placental Development
Audience:
- Student
- Researcher
- Educators of H. School / Intro Undergrad
- Educators of Adv. Undergrad / Grad

Speaker: Mana Parast

Total Duration: 0:28:25

Recorded: September 2018

All Talks in Development and Stem Cells

Talk Overview

Dr. Mana Parast provides an introduction to placental development, the organ that every mammalian embryo needs for proper growth and development. The placenta derives from trophoblasts, embryonic cells located in the outermost layer of the embryo. Pre-eclampsia and other maternal factors can hinder placental development and therefore affect the development of the fetus. A better understanding on how defects associated with pregnancy disorders affect placental development could lead to novel therapeutics in the future.

In her second seminar, Parast explains the different models to study human placental development in-vitro. Scientists can derive induced pluripotent stem cells (iPSCs) from umbilical cord cells. Parast’s laboratory first differentiates the iPSCs into trophoblasts cells which can then generate the different cells found in the placenta. Her laboratory uses these placental cells to study developmental complications by comparing cells derived from normal pregnancies to cells derived from non-normal pregnancies (e.g. patients born from mothers with pre-eclampsia).

Speaker Bio

Mana Parast

Mana Parast

Dr. Mana Parast is a Professor in Residence at the University of California, San Diego. She earned her bachelor’s degree from the University of Rochester in 1994, and her medical (2002) and doctorate degree (2001) from the University of Virginia. She completed a residency in Anatomical Pathology at Emory University in 2005, and a fellowship… Continue Reading

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