May 19, 2022
This month on Episode 36 of Discover CircRes, host Cynthia St. Hilaire highlights original research articles featured in the April 29 and May 13 issues of Circulation Research. This episode also features a conversation with Dr Patricia Nguyen and Jessica D'Addabbo from Stanford University about their study, Human Coronary Plaque T-cells are Clonal and Cross-React to Virus and Self.
Article highlights:
Zanoli, et al. COVID-19 and Vascular Aging
Wang, et al. JP2NT Gene Therapy in a Mouse Heart Failure Mode
Harraz, et al. Piezo1 Is a Mechanosensor in CNS Capillaries
Zhao, et al. BAT sEVs in Exercise Cardioprotection
Cindy St. Hilaire: Hi, and welcome to Discover CircRes, the podcast of the American Heart Association's journal, Circulation Research. I'm your host, Dr Cyndy St. Hilaire, from the Vascular Medicine Institute at the University of Pittsburgh. And today, I'll be highlighting the articles from our April 29th and May 13th issues of Circulation Research. I also will speak with Dr Patricia Nguyen and Jessica D'Addabbo from Stanford University about their study, Human Coronary Plaque T-cells are Clonal and Cross-React to Virus and Self.
Cindy St. Hilaire: The first article I want to share is titled Vascular Dysfunction of COVID 19 Is Partially Reverted in the Long-Term. The first author is Agostino Gaudio and the corresponding author is Luca Zanoli. And they're from the University of Catania. Cardiovascular complications, such as endothelial dysfunction, arterial stiffness, thrombosis and heart disease are common in COVID 19. But how quickly such issues resolve, once the acute phase of the illness has passed, remains unclear. To find out, this group examined aortic and brachial pulse wave velocity, and other measures of arterial stiffness in 90 people who, several months earlier, had been hospitalized with COVID 19. These measurements were compared with data from 180 controls, matched for age, sex, ethnicity and body mass index, whose arterial stiffness had been assessed prior to the pandemic. 41 of the COVID patients were also examined 27 weeks later to assess any changes in arterial stiffness over time. Together, the data showed arterial stiffness was higher in COVID patients than in controls. And though it improved over time, it tended to remain higher than normal for almost a year after COVID.
Cindy St. Hilaire: This finding could suggest residual structural damage to the arterial walls or possibly, persistent low-grade inflammation in COVID patients. Either way, since arterial stiffness is a predictor of cardiovascular health, its potential longterm effects in COVID patients deserves further longitudinal studies.
Cindy St. Hilaire: The second article I want to share is titled Gene Therapy with the N-Terminus of Junctophilin-2 Improves Heart Failure in Mice. The first author is Jinxi Wang and the corresponding author is Long-Sheng Song from the University of Iowa. Junctophilin-2 is a protein with a split personality. Normally, it forms part of the heart's excitation contraction coupling machinery. But when the heart is stressed, JP2 literally splits in two, and sends its N-terminal domain, JP2NT, to the nucleus, where it suppresses transcription of genes involved in fibrosis, hypertrophy, inflammation and other heart failure related processes. However, if this stress is severe or sustained, the protective action of JP2NT is insufficient to halt the progressive failure. This group asked. "What if this N-terminal domain could be ramped up using gene therapy to aid a failing mouse heart?"
Cindy St. Hilaire: To answer this question, they injected adenoviral vectors encoding JP2NT into mice either before or soon after transaortic constriction, or TAC, tack, which is a method of experimentally inducing heart failure. They found, in both cases, that the injected animals fared better than the controls. Animals injected before TAC showed less severe cardiac remodeling than control mice, while those treated soon after TAC exhibited slower loss of heart function with reduced ventricle dilation and fibrosis. These data suggest that supplementing JP2NT, via gene therapy or other means, could be a promising strategy for treating heart failure. And this data provides a basis for future translational studies.
Cindy St. Hilaire: The third article I want to share is titled Piezo1 Is a Mechanosensor Channel in Central Nervous System Capillaries. The first and corresponding author is Osama Harraz from the University of Vermont. Neurovascular coupling is the process whereby transient activation of neurons leads to an upsurge in local blood flow to accommodate the increased metabolic needs of the cell. It's known that agents released from active neurons trigger changes in local capillaries that prompt vasodilation, but how these hemodynamic changes are sensed and controlled is not entirely clear. This group suspected that the mechanosensory protein Piezo1, a calcium channel that regulates dilation and constriction of other blood vessels, may be involved. But whether Piezo1 is even found in the microcirculation of the CNS was unknown. This group shows that Piezo1 is present in cortical capillaries of the brain and the retina of the mouse, and that it responds to changes in blood pressure and flow.
Cindy St. Hilaire: Ex vivo preparations of mouse retina showed that experimentally induced changes in hemodynamics caused calcium transients and related currents within capillary endothelial cells, and that these were dependent on the presence of Piezo1. While it is not entirely clear how Piezo1 influences cerebral blood flow, its pressure induced activation of CNS capillary endothelial cells suggest a critical role in neurovascular coupling.
Cindy St. Hilaire: The last article I want to share is titled Small Extracellular Vesicles from Brown Adipose Tissue Mediate Exercise Cardioprotection. The first authors are Hang Zhao and Xiyao Chen. And the corresponding authors are Fuyang Zhang and Ling Tao from the Fourth Military Medical University. Regular aerobic exercise is good for the heart and it increases the body's proportion of brown adipose tissue relative to white adipose tissue. This link has led to the idea that brown fat, possibly via its endocrinal activity, might somehow contribute to exercise related cardioprotection. Zhao and colleagues now show that, indeed, brown fat produces extracellular vesicles that are key to preserving heart health. While mice subjected to four weeks of aerobic exercise were better protected against subsequent heart injury than their sedentary counterparts, blocking the production of EVs prior to exercise significantly impaired this protection. Furthermore, injection of brown fat derived EVs into the hearts of mice lessened the impact of subsequent cardiac injury.
Cindy St. Hilaire: The team went on to identify micro RNAs within the vesicles responsible for this protection, showing that the micro RNAs suppressed an apoptosis pathway in cardiomyocytes. In identifying mechanisms and molecules involved in exercise related cardio protection, the work will inform the development of exercise mimicking treatments for people at risk of heart disease or who are intolerant to exercise.
Cindy St. Hilaire: Lastly, I want to bring up that the April 29th issue of Circulation Research also contains a short Review Series on pulmonary hypertension, with articles on: The Latest in Animal Models of Pulmonary Hypertension and Right Ventricular Failure, by Olivier Boucherat; Harnessing Big Data to Advance Treatment and Understanding of Pulmonary Hypertension, by Christopher Rhodes and colleagues; New Mutations and Pathogenesis of Pulmonary Hypertension: Progress and Puzzles in Disease Pathogenesis, by Christophe Guignabert and colleagues; Group 3 Pulmonary Hypertension From Bench to Bedside, by Corey Ventetuolo and colleagues; and Novel Approaches to Imaging the Pulmonary Vasculature and Right Heart, by Sudarshan Rajagopal and colleagues; and Understanding the Pathobiology of Pulmonary Hypertension Due to Left Heart Disease, by Jessica Huston and colleagues.
Cindy St. Hilaire: Today, Dr Patricia Nguyen and Jessica D'Addabbo, from Sanford University, are with me to discuss their study, Human Coronary Plaque T-cells are Clonal and Cross-React to Virus and Self. And this article is in our May 13th issue of Circulation Research. So, Trisha and Jessica, thank you so much for joining me today.
Jessica D'Addabbo: Thank you for having us.
Patricia Nguyen: Yes. Thank you for inviting us to your podcast. We're very excited to be here.
Cindy St. Hilaire: Yeah. And I know there's lots of authors involved in this study, so unfortunately we can't have everyone join us, but I appreciate you all taking the time.
Patricia Nguyen: This is like a humongous effort by many people in the group, including Roshni Roy Chowdhury, and Xianxi Huang, as well as Charles Chan and Mark Davis. So, we thank you.
Cindy St. Hilaire: So atherosclerosis, it stems from lipid deposition in the vascular wall. And that lipid deposition causes a whole bunch of things to happen that lead to a chronic inflammatory state. And there's many cells that can be inflammatory. And this study, your study, is really focusing on the role of T-cells in the atherosclerotic plaque. So, before we get into the nitty gritty details of your study, can you share with us, what is it that a T-cell does normally and what is it doing in a plaque? Or rather, let me rephrase that as, what did we know a T-cell was doing in a plaque before your study?
Patricia Nguyen: So, T-cells, as you know, are members of the adaptive immune system. They are the master regulators of the entire immune system, secreting cytokines and other proteins to attract immune cells to a diseased portion of the body, for example. T-cells have been characterized in plaque previously, mainly with immunohisto chemistry. And their characterization has also been recently performed using single cell technologies. Those studies have been restricted to mainly mirroring studies, studies in mice in their aortic walls, in addition to human carotid arteries. So, it is well known that T cells are found in plaque and a lot of attention has been given to the macrophage subset as the innate immune D. But let's not forget the T-cell because they're actually composed about... 50% in the plaque are T-cells.
Patricia Nguyen: And we were particularly interested in the T-cell population because we have a strong collaboration with Dr Mark Davis, who's actually the pioneer of T-cell biology and was the first to describe the T-cell receptor alpha beta receptor in his lab in the 1970s. So, he has developed many techniques to interrogate T-cell biology. And our collaboration with him has allowed us and enabled us to perform many of these single cell technologies. In addition, his colleague, Dr Chen, also was pivotal in helping us with the interrogation and understanding of the T-cells in plaque.
Cindy St. Hilaire: And I think one of the really neat strengths of your study is that you used human coronary artery plaques. So, could you walk us through? What was that like? I collect a lot of human tissue in my lab. I get a lot of aortic valves from the clinic. And it's a lot of logistics. And a lot of times, we're just fixing them, but you are not just fixing them. So, can you walk us through? What was that experimental process from the patient to the Petri dish? And also, could you tell us a little bit about your patient population that you sampled from?
Jessica D'Addabbo: So, these were coronary arteries that we got from patients receiving a heart transplant. So, they were getting a heart transplant for various reasons, and we would receive their old heart, and someone would help us dissect out the coronary arteries from these. And then, we would process each of these coronary arteries separately. And this happened at whatever hour the hearts came out of the patient.
Jessica D'Addabbo: So sometime, I was coming in at 3:00 AM with Dr Nguyen and we would be working on these hearts then, because we wanted the samples to be as fresh as possible. So, we would get the arteries. We would digest out the tissue. And then, we would have certain staining profiles that we wanted to look at so that we could put the cells on fax to be able to sort the cells, and then do all the downstream sequencing from there.
Cindy St. Hilaire: So, in terms of, I don't know, the time when you get that phone call that a heart's coming in to actually getting those single cells that you can either send a fax or send a sequencing, how long did that take, on a good day? Let's talk only about good days.
Jessica D'Addabbo: Yeah. A lot of factors went into that, sometimes depending on availability of things. But usually, we were ready with all of the materials in advance. So, I'd say it could be anywhere from six to 12 hours, it would take, to get everything sorted. Then, everything after that would happen. But that was just that critical period of making sure we got the cells fresh.
Patricia Nguyen: So we have to credit the CT surgeons at Stanford for setting up the program or the structure, infrastructure, that enables us to obtain this precious tissue. That is Jack Boyd and Joseph Woo of CT surgery. So, they have enabled human research on hearts by making these tissues available. Because as you know, a transplant... They can say the transplant's happening at 12:00 AM, but it actually doesn't happen until 4:00 AM. And I think it's very difficult for a lab to make that happen all the time. And I think having their support in this paper was critical. And this has allowed us, enabled us, to interrogate kind of the spectrum of disease, especially focusing on T-cells, which are... They make a portion of the plaque, but the plaque itself has not like a million cells that are immune. A lot of them are not immune. So, enabling us to get the tissue in a timely fashion where they're not out of the body for more than 30 minutes enables us to interrogate these small populations of cells.
Cindy St. Hilaire: That's actually the perfect segue to my next question, which is, how many cells in a plaque were you able to investigate with the single cell analysis? And what was the percentage again of the T-cells in those plaques or in... I guess you looked at different phases of plaque. So, what was that spectrum for the percentage of T-cells?
Patricia Nguyen: So, for 10X, for example, you need a minimum of 10,000 captured cells. You could do less, but the utility of the 10X is maximized with 10,000. So, many times before the ability to multiplex these tissues, we were doing like capturing 5,000 for example. And the number of cells follows kind of the disease progression, in the sense that as a disease is more severe, you have more immune cells, in general. And it kind of decreases as it becomes more fibrotic and scarred, like calcified. So, it was a bit challenging to get very early just lipid-only cells. And a lot of those, we captured like 3000 or something like that. And efficiency is like 80% perhaps. So, you kind of capture…
Cindy St. Hilaire: And also, how many excised hearts are going to have early athero? So, it's...
Patricia Nguyen: Well, there are... nonischemics will have...
Cindy St. Hilaire: Oh, okay. Okay.
Patricia Nguyen: So, the range was nonischemic to ischemic.
Cindy St. Hilaire: Oh great.
Patricia Nguyen: So, about a portion... I would say one third of the total heart transplants were ischemic. And a lot of them were non ischemic. But as you know, the nonischemic can mix with ischemia. And so, they could have mild to moderate disease in the other arteries, for example, but not severe like 70%/90% obstruction.
Cindy St. Hilaire: Wow. That's so great. That's amazing. Amazing sample size you have. So T-cell, it's kind of an umbrella term, right? There's many different types of T-cells. And when you start to get in the nitty gritty, they really do have distinct functions. So, what types of T-cells did you see and did you focus on in this study?
Jessica D'Addabbo: So, the two main types of T-cells are CD4 positive T-cells and CD8 positive T-cells. And we looked at both of these T-cells from patients. We usually sorted multiple plates from each. And then, with 10X, we captured both. But our major finding was actually that the CD8 positive t-cell population was more clonally expanded than the CD4 population, which led us to believe that these cells were more important in the coronary artery disease progression and in the study that we were doing because for a cell to be clonally expanded, it means it was previously exposed to an antigen. And so, if we're finding these T-cells that are clonally expanded in our plaques, then we're hypothesizing that they were likely exposed to some sort of antigen, and then expanded, and then settled into the plaque.
Cindy St. Hilaire: And when you're saying expansion, are you talking about them being exposed to the antigen in the plaque and expanding there? Or do you think they're being triggered in the periphery and then honing in as a more clonal population?
Patricia Nguyen: So, that's a great question. And unfortunately, I don't have the answer to that. So basically-
Jessica D'Addabbo: Next paper, next paper.
Patricia Nguyen: Exactly. So, we... Interesting to expand on Jessica's answer. Predominantly what was found, as you said, was memory T-cells, so memory T-cells expressing specific markers, so memory versus naive. And these were effector T-cells. And memory meaning they were previously expanded by antigen engagement, and just happened to be in the plaque for whatever reason. We do not know why T-cells specifically are attracted to the plaque, but they are obviously there. And they're in a memory state, if you will. And some of them did display activation markers, which suggested that they clonally expanded to an antigen. What that antigen is, is the topic of another paper. But certainly, it is important to understand that these patients that we recruit, because they were transplant patients, they're not actively infected, right? That is a exclusionary criteria for transplants, right?
Patricia Nguyen: So, that means these T-cells were there for unclear reasons. Why they're there is unclear. Whether they are your resident T-cells also is unclear, because the definition of resident T-cell still remains controversial. And you actually have to do lineage tracking studies to find out, "Okay, where... Did they come from the bone marrow? Did they come from the periphery? How did they get there?" Versus, "Okay. They were already there and they just expanded, for whatever reason, inside the plaque."
Cindy St. Hilaire: So, your title... It was a great title, with this provocative statement, "T-cells are clonal and cross react to virus and self." So, tell us a little bit more about this react to virus and self bit. What did your data show?
Jessica D'Addabbo: So, because of the way we sequenced the T-cell receptor, we were able to have paired alpha and beta chains. And because we knew the HLA type of the patients, we were able to put the sequences that we got out after we sequenced these through an algorithm called GLIPH, which allows us to look at the CDR3 region of the T cell receptor, which is the epitope binding region. And there are certain peptide. They're about anywhere from three to four amino acids long. These are mapped to certain binding specificities to known peptides. And so, basically, we were able to look at which epitopes were most common in our plaques. And we found that after comparing these to other epitopes, that these were actually more binding to virus.
Patricia Nguyen: So let me add to what Jessica stated, and kind of emphasize the value of the data set, if you will. So, this is, I believe, the first study that provides the complete TCR repertoire of coronary plaque, and actually any plaque that I know of, which is special because we know that there is specificity of TCR binding. It's more complicated than the antibody that binds directly from B cells to the antigen, because the T-cells bind processed antigen. So, the antigens are processed by antigen presenting cells like Dendritic cells and macrophages. And they have a specific HLA MHC class that they need to present to. And they need both arms, the antigen epitope and the MHC, to activate the T-cell. So unfortunately, it's not very direct to find the antigen that is actually activating the T-cell because we're only given a piece of it. Right?
Patricia Nguyen: But we have provided a comprehensive map of all the TCRs that we find in the plaque. And these TCRs have a sequence, an immuno acid sequence. And luckily, in the literature, there is a database of all TCR specificities. Okay. So, armed with our TCR repertoire, we can then match our TCR repertoire with an existing database of known TCR specificities. Surprisingly, the matching TCRs are specific to virus, like flu, EBV and CMB. And also, because this was done in the era of COVID, we thought it would be important to look at the coronavirus database. We did find that there were matches to the coronavirus database. Even though our finding is not specific to SARS, it does lend to some potential mechanistic link there as well.
So, because this is all computational, it is important to validate. So, the importance of validation requires us to put the TCR alpha beta chain into a Jurkat cell, which is a T-cell line that does not have alpha beta chains on it, and then expose it to what we think is the cognate antigen epitote, with the corresponding HLA MHC APC. Because you don't have all those pieces, it will not work. Yes. So importantly, we did find that what we predicted to have the specificity of a flu peptide had specificity to a flu peptide.
Patricia Nguyen: So then, the important question was, "Okay, these patients aren't infected, right? Why are these things here? Is there a potential cross reactivity with self peptides?"
Patricia Nguyen: So luckily, our collaborator, Dr Charles Chan, was able to connect us with another computational algorithm that he was familiar with, whereby we were able to take the peptide sequences from the flu and match them with peptide sequencing from proteins that are self and ubiquitous. And we demonstrated, again, these T-cells were activated in vitro. That is why we concluded that there's a potential cross reactivity between self and virus that can potentially lead to thrombosis associated with viral infections. Of course, this all needs to be proved in vivo.
Cindy St. Hilaire: Sure, sure.
Patricia Nguyen: It's that first step for other things.
Cindy St. Hilaire: The other big immune cell that we know is in atherosclerotic plaques and that's macrophages. And they can help to present antigens and things like that. And they also help to chew up the necrotic bits. And so, do you think that this T-cell component is an earlier, maybe disease driving, process or an adaptive process that goes awry as a secondary event?
Patricia Nguyen: So, I'm a fan of the T-cell. So... I'm with team T cell. I would like to think that it is playing an active role in pathology in this case and not a reactive role, in the sense of just being there. I think that the T-cell is actively communicating with other cells within the plaque, and promoting pro fibrotic and pro inflammatory reactions, depending on the T-cell. So, a subset of this paper was looking at kind of the interactions between the T-cell and other cells within the plaque, like macrophages and smooth muscle cells. And as we know, T-cells are activated and they produce cytokines. Those cytokines then communicate to other cells. And we found that, computationally, when you look at the transcriptome, there is a pro-inflammatory signature of the T-cell that resides in the more complex stage. And then, there's an anti-inflammatory signature that kind of resides in the transition between lipid and fibro atheroma, if you will.
Cindy St. Hilaire: So, do you know, or is it known, how dynamic these populations are? Obviously, the hearts that you got, the samples you got, didn't have active infections. But do you know perhaps even how long ago they happened, or even how soon after there might be an infection or an antigen presented that you could get this expansion? And could that be a real driver of rupture or thrombosis?
Patricia Nguyen: So, in theory, you would suppose that T-cells expanding and dividing and producing more and more cytokines would then lead to more macrophages coming, more of their production of proteinases that destroy the plaque. Right? So yes, in theory, yes. I think it's very difficult to kind of map the progression of T cell clonality in the current model that we have, because we're just collecting tissues. However, in the future, as organoids become more in science and kind of a primary tissue, where we can... For example, Mark Davis is making organoids with spleen, and also introducing skin to that.
Patricia Nguyen: And certainly, we could think of an organoid involving the vasculature with immune cells introduced. And so, I think, in the next phase, project 2.0, we can investigate what... like over time, if you could model atherosclerosis and the immune system contribution, T-cells as well as macrophages and other immune cells, you can then kind of map how it happens in humans. Because obviously, mice are different. We know that mice... Actually, the models of transgenic mice do not rupture. It's very hard to make them rupture. Right?
Cindy St. Hilaire: Well, if you stop feeding them high fat diet, the plaque goes away.
Patricia Nguyen: For sure, for sure. So I think.. I mean, Mark Davis is a huge proponent of human based research, like research on human tissue. And as a physician scientist, obviously I'm more inclined to do human based research. And Jessica's going to be a physician someday soon. And I'm sure she's more inclined to do human based research. And certainly, the mouse model and in vitro models are great because you can manipulate them. But ultimately, we are trying to cure human diseases.
Cindy St. Hilaire: Mice are not little humans. That's what we say in my lab. I similarly do a lot of human based stuff and it's amazing how great mice are for certain things, but still how much is not there when we need to really fully recapitulate a disease model.
So, my last question is kind of regarding this autoimmune angle of your findings. And that is, women tend to have more autoimmune diseases than men, but due to the fact that you are getting heart transplants, you've got a whole lot more men in your study than women. I think it was like 31 men to four women. But, I mean, what can you do? It's the nature of heart transplants. But I'm wondering, did you happen to notice...Maybe the sample size perhaps is too small, but were there any differences in the populations of these cells between women and men? And do you think there could be any differences regarding this more prevalence of autoimmune like reactions in women?
Patricia Nguyen: So, that's an interesting question, but you hit it on the nose when you said "Your sample is defined mainly by men." And in addition, the samples that were women tend to have less disease. And they tend to be nonischemic in etiology. So, I think that kind of restricts our analysis. And perhaps, I guess, future studies could model using female tissues, for example, instead of only male. But the limitation of all human studies is sample availability. And perhaps, human organoid research can be less limited by that. And certainly, mouse research has become more evenly distributed of male and female mice.
Cindy St. Hilaire: Yeah. Suffice it to say, human research is hard, but you managed to do an amazing and really important study. It was really elegant and well done. Congratulations on what is an epic amount of time. 12-hour experiments are no joke, and really beautiful data. So, thank you so much for joining me today, Dr Nguyen and Miss almost Dr D'Addabbo. Congrats and I'm really looking forward to seeing your future work.
Jessica D'Addabbo: Thank you so much.
Patricia Nguyen: Thanks so much.
Jessica D'Addabbo: Thank you for having us. This is wonderful.
Cindy St. Hilaire: That's it for the highlights from the April 29th and May 13th issues of Circulation Research. Thank you so much for listening. Please check out the Circ Res Facebook page and follow us on Twitter and Instagram with the handle @Circres and #Discover CircRes. Thank you to our guests: Dr Patricia Nguyen, and soon to be Doctor, Jessica D'Addabbo, from Stanford University.
This podcast was produced by Ishara Ratnayaka, edited by Melissa Stoner, and supported by the editorial team of Circulation Research. Copy text for the highlighted articles was provided by Ruth Williams. I'm your host, Dr Cindy St. Haler. And this is Discover CircRes, you're on the go source for the most exciting discoveries in basic cardiovascular research. This program is copyright of the American Heart Association 2022. The opinions expressed by the speakers of this podcast are their own and not necessarily those of the editors or of the American Heart Association. For more information, visit aha journals.org.