Voiceover: This podcast is for informational and educational purposes only. It is not medical care or advice. Clinicians should rely on their own medical judgements when advising their patients. Patients in need of medical care should consult their personal care provider. Welcome to "That's Pediatrics", where we sit down with physicians, scientists, and experts to discuss the latest discoveries and innovations in pediatric healthcare.
Dr. Amanda Poholek: From UPMC Children's Hospital of Pittsburgh, this is, That's Pediatrics. I'm your co-host, Amanda Poholek, Assistant Professor of Pediatrics Immunology.
Dr. Arvind Srinath: And I'm your co-host, Arvind Srinath, Associate Professor in Pediatric Gastroenterology.
Dr. Poholek: Today our guest is Dr. Guang Li to talk to us about his research on growing a four-heart chamber in a dish. Dr. Li received his PhD training in the Chinese Academy of Sciences in Shanghai by studying the epigenetic regulation of plant organ development.
After that, he joined the Stanford Cardiovascular Institute as a post doc study heart development in mouse and human IPSC systems. And by combining single cell mRNA sequencing, single molecular and C-2 hybridization, machine learning, and advanced imaging techniques, he's systematically analyzed the temporal and spatial development of the heart at the single cell level.
In 2019, Dr. Li came to UPMC Children's Hospital to start his own lab where he continues to use high throughput technologies to answer questions about heart development as it's a critical embryonic developmental process. Thank you for being here. So tell us a little bit about your path to UPMC Children's Hospital and how you became interested in studying the development of the heart.
Dr. Guang Li: Oh, thank you so much Amanda. Thank you for having me. So it's my great honor to be here. So I actually started here three years ago. Before coming to Pittsburgh I was an instructor at Stanford University, as you have introduced. So I did a five years of postdoc training and one and a half year of instruction there.
So I was always, I will say, interested in developmental biology since I started to take the biology major in college. I started a planned development in my PhD, as you have mentioned as well. So I started an epigenetic regulation of the plant morphogenesis back then, but after graduation, I start to think about – to do something more related to medicine. So that's why I joined Stanford Cardiovascular Institute, Dr. Sean Wu's Lab, to study heart development. And after six plus years of training there. So I think I have entirely related to the heart development field.
Dr. Srinath: So from a clinician standpoint, here's a really basic question, but how do you study the developing heart?
Dr. Li: Yeah, we use two different models. We use mice and use human induced pluripotent stem cells as models. So for the mice we have different types of mice. Either have the genetic mutation that can cause the heart developmental defects or have those chance genes, those reporter genes that can lineage can enable a specific cell type and trace the lineage across the whole development of progression.
So we basically use the compilation of the two types of mice to understand the molecular and the cellular mechanisms during the heart development. And we also use another model, human induced pluripotent stem cells or called human iPSC.
So those cells can be generated from the human blood cells or human skin fibroblasts, for example. And those iPS cells or stem cells, they have the potential to need ified into 80 cell types in the heart. So then we can use those cells and to study the heart development in human.
Dr. Srinath: Are you studying these heart cells via biopsy or postmortem?
Dr. Li: We use the biopsy samples, but we usually just draw a blood, tube of blood from the patients that really all.
Dr. Srinath: Okay.
Dr. Li: But depends on the cells, right? Blood cells or skin fibroblasts.
Dr. Srinath,: Got it. Thank you.
Dr. Poholek: So obviously heart development is important in the context of a children's hospital. So can you tell us a little bit about, as you mentioned, the impact on human health. So how are children impacted by heart development when it goes awry and what percentage are of children are born with heart development issues?
Dr. Li: If the heart development does not go well, it can cause congenital heart defects. Congenital heart defects accounts for about one to 2% of all live births in the US and in the world. So the congenital heart defects can be mild or severe. For those mild congenital heart defects, for example, there're a hole in the sector they can heal by themselves maybe, I mean they may heal by themselves so there's no need for intervention. But for some severe types of congenital heart defects, they needed to be repaired by surgery or there are some severe defects, they just are too severe to be fixed by surgery or they can be fixed by surgery, but the heart will just function for a short time and then end up as heart failure.
So for those severe types of congenital heart defects, more research are required to understand the mechanisms in the heart development to help develop further or better treatments.
Dr. Poholek: So that really brings me to my next question, which is as a fellow researcher trying to find the way to do research in the lab that's going to impact human health, what are the big gaps in our knowledge of heart development and how is your lab working to close those gaps?
Dr. Li: Yeah, that's a great question. I have to say, I ask myself all the time. So I think as I said, we used two different models, mice and human iPS cells. So in mouse heart development after those, as I say, decades of research in this animal, in this model, we already know those big concepts.
We have accumulated enough knowledge in those big stage. So I think that the gap now we have is how to connect to those things and to understand how the cells at early stage have developed all the way to a functional organ. So that's one gap. I think another gap is we really do not know how much, we really do not know much about the heart development in human. Okay, most knowledge actually come from mice or other animals, such as Zebrafish. So this is another gap. So in my lab we basically to close the first gap, we are using those “omics” – Single-cell omics or Single-Cell transcriptomics, epigenomics – those approaches to understand the whole picture of the heart development across all the stages.
Basically to understand the biology in every single cell across all the stages. So that's our first try approach. And in humans, as I said, we are using human iPS cells to manage, differentiate, put pluripotent stem cell into different cardiac cells, 2D or three-dimensional differentiation system to understand the differentiation process in human.
Dr. Srinath: Can you go into little bit of detail with these “Omics” that you bring about in terms of how does that technology used and what does it entail?
Dr. Li: Yeah, so those “omics” actually have been advanced so much recently. We currently can go to the single cell label to understand the transcriptomics meaning the transcriptional genes expression.
Dr. Srinath: Got it.
Dr. Li: ...called MRA among a label in the cell across the whole gene, genomic genes in the single cell.
And we can also understand the epigenomics. It means the DNA modification or hista modification in the cell. And we can also understand the even proteomics, meaning the translated protein in this single cell at different stage. And now we have tools to map those Omic data back to their institute lo original spatial location. So this is called a spatial Omics.
So all those Omics to actually have combined can really give us idea how the cells actually can, how the cells actually function together to guide the cells at early stage all the way to the fully functional heart.
Dr. Srinath: Got it. Thank you for clarifying. And then looking forward, what clinical implications do you see moving forward from your work?
Dr. Li: Trying to understand the genes, how they express, how they function and that really relates to the congenital heart defects. For example, the genes we have identified that highly express certain cell types turns out to be associated or tightly associated with the congenital heart defects. So that can really give us insight how this disease have been caused in what kind of a cell type by what kind of genes at what kind of stage.
Dr. Srinath: Got it. Thank you for clarifying. Appreciate that.
Dr. Poholek: So once you have this, part of it is information gathering, you have these Omic tools that help you at the single cell level understand, Okay, let's see. Within the developing heart every cell, what genes are expressed, what proteins are expressed from those genes, and where are they as the cells differentiate?
Can you tell us, even if it's a bit speculative, how that information then translates into you being able to actually consider the idea of growing a heart in a dish and what implications that has. So we grow a heart and obviously this is a bit like the big goals to be able to grow the heart in the dish. But then once you've done it, what will that mean for our understanding of heart development and for potential therapeutic options for children and for patients?
Dr. Li: So that's a very important question. A very important goal of our research in mice is to translate into human. So I think of one important application is to use the knowledge to, if you can regrow a heart in a dish, that will be a very good demonstration. So currently, actually we have many used the gross factors. We have identified, so many labs have contributed, identified the gross factors that function in mouse heart development.
So we are using the knowledge in mice to manage, differentiate the iPS cells into hard cells. So we use a system called Organoid. So Organoid is a self-aggregate construct with in vivo-like features. So it is kind of like the in vivo heart. So we can differentiate or generate atrial or ventricular heart organoids. So as you may know, heart has four chambers two atrials and two ventricles. We think if just one chamber, that's not likely in vivo.
So we need a method to generate four chamber structures. So I think there are two different approaches to do that. One approach is to induce both atrial and ventricular organoids simultaneously or at once. That's very challenging because it turns out atrial and ventricular need different growth factors. And how can you actually spatially separate them in the dish.
Dr. Srinath: Got it.
Dr. Li: So the second approach is to generate atrial and ventricular organoid separately and then fuse them later. So that's the approach we took and we can generate atrial and ventricular and put them together and form at least the two chamber or four chamber organoids. But that's just the first step.
What we need to do is next is to add the other structures that's called the long-chamber structure such as valves, septums, conduction cells, all those have been well started in mice and we know those growth factors and we have protocols to generate them separately. And what we need to do is to add them together next either by fusion or figure out some way to need to spacey them or at once.
Dr. Poholek: So just to clarify, so at this point you can build half a heart in a dish with two of the four chambers and you can separately get a lot of the pieces of the heart. And so now the question is how do we make them all come together to be a single functioning unit?
Dr. Li: Yes.
Dr. Poholek: The heart. Yes.
Dr. Li: We can generate one atrial, one ventricular and we can put about one atrial one ventricular together but without a well. So we needed to induce the wells next.
Dr. Poholek: And these all and they'll beat even.
Dr. Li: They all beat.
Dr. Poholek: That's incredible.
Dr. Srinath: Wow.
Dr. Poholek: And this is from mouse cells?
Dr. Li: Human iPS cells.
Dr. Poholek: Human iPS cells. I see. Yeah, I guess I'm just curious, do they grow to the correct size even? Is there a way to,
Dr. Li: Oh...
Dr. Poholek: Cause the growth of an organ is also highly controlled, right?
Dr. Li: Yes. Yes.
Dr. Poholek: And so how do you make sure that the size of the organ, even if you've only got half of it is the correct size, et cetera?
Dr. Li: Yes. Exactly. The size actually can be controlled by some growth factors and you can add them to make them grow bigger or you can add the inhibitors to reduce the size. But if you need to generate the size match with the in vivo hearts, so then we need to figure out what's the right time point, time period and what's the right dosage of those growth factors.
Dr. Poholek: Wow, okay. And then I guess mean, can you share a little bit with us in your mind that big picture dream goal that we all have as scientists and what is it going to take to achieve that? And then once you have it, what will that mean for your field?
Dr. Li: You mean the, four chamber heart in a dish?
Dr. Poholek: Yeah.
Dr. Li: I think there is still a long way to go. I have to say because the heart looks simple but still actually quite complicated. They beat, that does not mean they're actually really fully functional.
So we need a real size of lumen. The main function of the heart is to pump blood to the whole body. So the lumen structure will be another critical. And then we need all the other types of cells such as fibroblasts, endothelial cells, or conduction cells.
This is still a long way to go, but once it succeeds, if we really have a fully functional, not fully partially functional, even four chamber heart, that will be huge because we can use that to model those all different types of congenital heart defects. How they actually have developed on the cellular level. And if we introduce a mutation that come from those patients, let's say associated with the patients, and then see what kind of defects they could lead.
And once we have those models and the next step is to use them to screen drugs, to identify the potential medicine, to treat those defects. So that will be, I will say, the two main applications we can have.
Dr. Srinath: So you're looking at prevention, which is fantastic. You're looking at prevention of these congenital heart defects as a long term goal. Is that falling an assumption that they're all due to a gene mutation or is there a subset which aren't due to a gene mutation in terms of congenital heart defects?
Dr. Li: Yeah, that's a good question. So I think that they are both right. Part of the congenital heart defects are caused by gene genetic mutations and some are not. Probably contributed by other factors such as glucose or alcohol, all those different factors. I think once we have this model, we can model both of those causes, right? Either genetic or non-genetic-
Dr. Srinath: Got it.
Dr. Li: Factors.
Dr. Srinath: Yeah. Thank you for clarifying. That's really interesting.
Dr. Li: Yeah, Thank you.
Dr. Poholek: I guess in the last few minutes, I kind of want to ask maybe what are the current challenges that your field faces or that you feel is a limitation of what you could really like to see achieved? And then maybe as a follow up, what do you hope to discover in the next five years?
Dr. Li: So I think that the limitation is really to connect those, as I mentioned. I think I really to connect those pieces. Another thing is to study the hard development in the human cells. Use the human iPSC or human organoid system.
I think what I want to achieve next is to further optimize the organoid system, to make the four chamber hearts actually as close as we can right to today in vivo like hearts. In vivo hearts. That will be one goal, but another goal is we still want needed to continue the study using the mouse models because our goal I think is to understand the biology in every single cell temporally and spatially across the whole development progression.
Dr. Srinath: Wow.
Dr. Poholek: Yeah, those are lofty goals, but I feel confident that you will achieve them.
Dr. Li: Oh, thank you so much.
Dr. Poholek: Thank you so much for sharing your research with us today and for taking the time out of your busy schedule to be here and talk to us about your science. We really appreciate it.
Dr. Li: Thank you so much.
Dr. Srinath: I echo Amanda, thank you so much. This was fascinating and I really appreciate you explaining what the amazing endeavors you're doing. Thank you.
Dr. Li: Thank you. I appreciate it.
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Guang Li, PhD
