This month on Episode 40 of Discover CircRes, host Cynthia St. Hilaire highlights four original research articles featured in the September 2 and September 16 issues of the journal. This episode also features an interview with Dr Jun Yoshioka, and Dr Yoshinobu Nakayama, from the City University of New York, about their study, Interaction of ARRDC-4 with GLUT1 Mediates Metabolic Stress in the Ischemic Heart.
Article highlights:
Jin, et al. Gut Dysbiosis Promotes Preeclampsia
Mengozzi, et al. SIRT1 in Human Microvascular Dysfunction
Hu, et al. Racial Differences in Metabolomic Profiles and CHD
Garcia-Gonzales, et al. IRF7 Mediates Autoinflammation in Absence of ADAR1
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 Cindy St. Hilaire from the Vascular Medicine Institute at the University of Pittsburgh. And today I'm going to be highlighting some articles from September 2nd, and September 16th issues of CircRes. And I'm also going to have a conversation with Dr Jun Yoshioka, and Dr Yoshinobu Nakayama, from the City University of New York, about their study, Interaction of ARRDC-4 with GLUT1 Mediates Metabolic Stress in the Ischemic Heart. But, before I get to the interview, I'm going to highlight a few articles.
The first article is from our September 2nd issue, and it's titled, Gut Dysbiosis Promotes Preeclampsia by Regulating Macrophages, and Trophoblasts. The first author is Jiajia Jin, and the corresponding author is Qunye Zhang from the Chinese National Health Commission.
Preeclampsia is a late-stage pregnancy complication that can be fatal to the mother, and the baby. It's characterized by high blood pressure, and protein in the urine. The cause is unknown, but evidence suggests the involvement of inflammation, and impaired placental blood supply. Because gut dysbiosis can influence blood pressure, and inflammation has been observed in preeclamptic patients, Jin and colleagues examined this link more closely. They found that women with preeclampsia had altered gut microbiome. Specifically, a reduction in a species of bacteria that produced short-chain fatty acids, and lower short-chain fatty acid levels in their feces, in their serum, and in their placentas. And preeclamptic women had lower short-chain fatty acid levels in their feces, in their serum, and in their placentas compared with women without preeclampsia.
They found that fecal transfers from the preeclampsia women to rats with a form of the condition exacerbated the animals' preeclampsia symptoms, while fecal transfers from control humans alleviated the symptoms. Furthermore, giving rats an oral dose of short-chain fatty acids or short-chain fatty acid producing bacteria decreased the animals' blood pressure, reduced placental inflammation, and improved placental function. This work suggests that short-chain fatty acids, and gut microbiomes could be a diagnostic marker for preeclampsia. And microbial manipulations may even alleviate the condition.
The second article I want to share is also from our September 2nd issue, and it's titled, Targeting SIRT1 Rescues Age and Obesity-Induced Microvascular Dysfunction in Ex Vivo Human Vessels. And this study was led by Alessandro Mengozzi from University of Pisa.
With age, the endothelial lining of blood vessels can lose its ability to control vasodilation, causing the vessel to narrow and reduce blood flow. This decline in endothelial function has been associated with age related decrease in the levels of the enzyme, SIRT1. And artificially elevating SIRT1 in old mice improves animals' endothelial function. Obesity, which accelerates endothelial dysfunction, is also linked to low SIRT1 levels.
In light of these SIRT1 findings, Mengozzi, and colleagues examined whether increasing the enzyme's activity could improve the function of human blood vessels. The team collected subcutaneous microvessels from 27 young, and 28 old donors. And both age groups included obese, and non-obese individuals. SIRT1 levels in the tissue were, as expected, negatively correlated with age and obesity, and positively correlated with baseline endothelium dependent vasodilatory function. Importantly, incubating tissue samples from older, and obese individuals with a SIRT1 agonist, restored the vessel’s vasodilatory functions. This restoration involved a SIRT1 induced boost to mitochondrial function, suggesting that maintaining SIRT1 or its metabolic effect might be a strategy for preserving vascular health in aging, and in obesity.
The third article I want to share is from our September 16th issue. And this one is titled, Differences in Metabolomic Profiles Between Black And White Women and Risk of Coronary Heart Disease. The first author is Jie Hu, and the corresponding author is Kathryn Rexrode, and they're from Brigham and Women's Hospital, and Harvard University.
In the US, coronary heart disease, and coronary heart disease-related morbidity, and mortality is more prevalent among black women than white women. While racial differences in coronary heart disease risk factors, and socioeconomic status have been blamed, this group argues that these differences alone cannot fully explain the disparity. Metabolomic variation, independent of race, has been linked to coronary heart disease risk. Furthermore, because a person's metabolome is influenced by genetics, diet, lifestyle, environment and more, the authors say that it reflects accumulation of many cultural, and biological factors that may differ by race.
This group posited that if racial metabolomic differences are found to exist, then they might partially account for differences in coronary heart disease risk. This study utilized plasma samples from nearly 2000 black women, and more than 4500 white women from several different cohorts. The team identified a racial difference metabolomic pattern, or RDMP, consisting of 52 metabolites that were significantly different between black, and white women. This RDMP was strongly linked to coronary heart disease risk, independent of race, and known coronary heart disease risk factors. Thus, in addition to socioeconomic factors, such as access to healthcare, this study shows that racial metabolomic differences may underlie the coronary heart disease risk disparity.
The last article I want to share is also from our September 16th issue, and it is titled, ADAR1 Prevents Autoinflammatory Processes in The Heart Mediated by IRF7. The first author is Claudia Garcia-Gonzalez, and the corresponding author is Thomas Braun, and they are from Max Planck University.
It's essential for a cell to distinguish their own RNA from the RNA of an invading virus to avoid triggering immune responses inappropriately. To that end, each cell makes modifications, and edits its own RNA to mark it as self. One type of edit made to certain RNAs is the conversion of adenosines to inosines. And this is carried out by adenosine deaminase acting on RNA1 or ADAR1 protein. Complete loss of this enzyme causes strong innate immune auto reactivity, and is lethal to mice before birth. Interestingly, the effects of ADAR1 loss in specific tissues is thought to vary. And the effect in heart cells in particular has not been examined.
This study, which focused on the heart, discovered that mice lacking ADAR1 activity specifically in cardiomyocytes, exhibit autoinflammatory myocarditis that led to cardiomyopathy. However, the immune reaction was not as potent as in other cells lacking ADAR1. Cardiomyocytes did not exhibit the sort of upsurge in inflammatory cytokines, and apoptotic factors seen in other cells lacking ADAR1. And the animals themselves did not succumb to heart failure until 30 weeks of age. The author suggests that this milder reaction may ensure the heart resists apoptosis, and inflammatory damage because, unlike some other organs, it cannot readily replace cells.
Cindy St. Hilaire: Today I have with me, Dr Jun Yoshioka, and Dr Yoshinobu Nakayama, and they're from City University of New York. And today we're going to talk about their paper, Interaction of ARRDC4 With GLUT1 Mediates Metabolic Stress in The Ischemic Heart. And this is in our September 2nd issue of Circulation Research. So, thank you both so much for joining me today.
Jun Yoshioka: Thank you for having us. We are very excited to be here.
Cindy St. Hilaire: It's a great publication, and also had some really great pictures in it. So, I'm really excited to discuss it. So, this paper really kind of focuses on ischemia, and the remodeling in the heart that happens after an ischemic event. And for anyone who's not familiar, ischemia is a condition where blood flow, and thus oxygen, is restricted to a particular part of the body. And in the heart, this restriction often occurs after myocardial infarctions, also called heart attacks. And so, cardiomyocytes, they require a lot of energy for contraction, and kind of their basic functions. And in response to this lack of oxygen, cardiomyocytes switch their energy production substrate. And so, I'm wondering if before we start talking about your paper, you can just talk about the metabolic switch that happens in a cardiac myocyte in the healthy state versus in the ischemic state.
Jun Yoshioka: Sure. As you just said, that the heart never stops beating throughout the life. And it's one of the most energy demanding organs in the body. So, under normal conditions, cardiac ATP is mainly derived from fatty acid oxidation, and glucose metabolism contributes a little bit less in adult cardiomyocytes. However, under stress conditions such as ischemia, glucose uptake will become more critical when oxidative metabolism is interrupted by a lack of oxygen. That is because glycolysis is a primary anaerobic source of energy. We believe this metabolic adaptation is essential to preserve high energy phosphates and protect cardiomyocytes from lethal injuries. The concept of shifting the energy type of stress preference toward glucose, as you just said, has been actually long proposed as an effective therapy against MI. For example, GIK glucose insulin petition is classic.
Now, let me explain how glucose uptake is regulated. Glucose uptake is facilitated by multiple isophones of glucose transporters in cardiomyocytes. Mainly group one and group four, and the minor, with a minor contribution of more recently characterized STLT1. In this study, we were particularly interested in group one because group one is a basal glucose transporter.
Dr Ronglih Liao, and Dr Rong Tian's groups reported nearly two decades ago that the cardiac over-expression of group one prevents development of heart failure, and ischemic damage in mice. Since they are remarkable discoveries, the precise mechanism has not yet been investigated enough, at least to me. Especially how acute ischemic stress regulates group one function in cardiomyocytes. We felt that this mechanism is important because there is a potential to identify new strategies around group one, to reduce myocardiac ischemic damage. That is why we started this project hoping to review a new mechanism by which a protein family, called alpha-arrestins, controls cardiac metabolism under both normal, and diseased conditions.
Cindy St. Hilaire: That is a perfect segue for my next question, actually, which is, you were focusing on this arrestin-fold protein, arrestin domain-containing protein four or ARRDC4. So, what is this family of proteins? What are arrestin-fold proteins? And before your study, what was known about a ARCCD4, and its relationship to metabolism, and I guess specifically cardiomyocyte metabolism?
Jun Yoshioka: So, the arrestin mediated regulation of steroid signaling is actually common in cardiomyocytes. Especially beta, not the alpha, beta-arrestins have been well characterized as an adapter protein for beta-adrenergic receptors. Beta-arrestins combine to activate beta-adrenergic receptors on the plasma membrane, promote their endosomal recycling, and cause desensitization of beta-adrenergic signaling. Over the past decade, however, this family, the arrestin family, has been extended to include a new class of alpha-arrestins. But unlike beta-arrestins, the physiological functions of alpha-arrestins remain largely unclear based in mammalian cells. Humans, and mice have six members of alpha-arrestins including Txnip, thioredoxin interacting protein called Txnip, and five others named alpha domain-containing protein ARRDC1 2, 3, 4 and 5. Among them Txnip is the best studied alpha-arrestin. And Txnip is pretty much the only one shown to play a role in cardiac physiology.
Txnip was initially thought to connect alternative stress and metabolism. However, it is now known that the Txnip serves as an adapter protein for the endocytosis of group one, and group four to mediate acute suppression of glucose influx to cells. In fact, our group has previously shown that the Txnip knockout mice have an enhanced glucose uptake into the peripheral tissues, as well as into the heart. Now, in this study, our leading player is ARRDC4. The arrestin-domains of ARRDC4 have 42% amino acid sequence similarities to Txnip. This means that the structurally speaking ARRDC4 is a brother to Txnip. So, usually the functions of arrestins are expected to be related to their conserved arrestin-domains. So, we were wondering whether two brothers, Txnip, and ARRDC4, may share the same ability to inhibit the glucose transport. That was a starting point where we initiated this project.
Cindy St. Hilaire: That's great. And so, this link between ARRDC4, and the cardiac expression of gluten one and gluten four, I guess, mostly gluten one related to your paper, that really wasn't known. You went about this question kind of based on protein homology. Is that correct?
Jun Yoshioka: That is right.
Cindy St. Hilaire: And so, ARRDC4 can modulate glucose levels in the cell by binding, and if I understand it right, kind of helping that internalization process of glute one. Which makes sense. You know, when you have glucose come into the cell, you don't want too much. So, the kind of endogenous mechanism is to shut it off, and this ARRDC4 helps do that. But you also found that this adapter protein impacts cellular stress, and the cellular stress response. So, I was wondering if you could share a little bit more about that because I thought that was quite interesting. It's not just the metabolic impact of regulating glucose. There's also this cellular stress response.
Jun Yoshioka: Right? So, Txnip is known to induce oxidative stress. But about the ARRDC4, we found that ARRDC4 actually does not induce oxidative stress. Instead, we found that it reproducibly causes ER, stress rather than oxidative stress. So, let Yoshinobu talk about the ER stress part. Yoshinobu, can you talk about how you found the ER stress story?
Yoshinobu Nakayama: So, then let's talk about the, yeah, ER stress caused by ARRDC4. The ER stress caused by ARRDC4, year one was the biggest challenge in this study, because it's a little bit difficult to how we found a link of the glucose metabolism to the effect of the ARRDC4, only our stress. And at the other point of the project, we noticed that a ARRDC4 causes ER stress reproducibly, but we did not know how. So, both group one, and ARRDC4 are membrane proteins mainly localized near the plasma membrane. Then how does ARRDC4 regulate the biological process inside in the plasma radical? So, we then hypothesize that ARRDC4 induces intercellular glucose depravation by blocking cellular glucose uptake, and then interferes with protein glycosylation, thereby disturbing the ER apparatus. That makes sense because inhibition of group one trafficking by ARRDC4 was involved in the unfolded protein response in ischemic cardiomyocytes.
Cindy St. Hilaire: So how difficult was that to figure out? How long did that take you?
Yoshinobu Nakayama: How long? Yeah. Is this the question?
Cindy St. Hilaire: It's always a hard question.
Yoshinobu Nakayama: I think it's not several weeks. Maybe the monthly, months project. Yeah.
Cindy St. Hilaire: Okay. It's always fun when, you know, you're focusing on one angle, and then all of a sudden you realize, oh, there's this whole other thing going on. So, I thought it was a really elegant tie-in between the metabolism, but also just the cellular stress levels. It was really nice.
So, you created a full body knockout of ARRDC4 in the mouse, and you did all the proper kind of phenotyping. And at baseline everything's normal, except there's a little bit of changes in the blood glucose levels. But I also noticed when you looked at the expression of ARRDC4 in different tissues, it was very high in the lungs, and also in the intestines. And so, I know your study didn't focus on those tissues, but I was wondering if you could possibly speculate what ARRDC4 is doing in those tissues? Is it something similar? Do those cells under stress have any particular metabolic switching that's similar?
Jun Yoshioka: Well, actually we don't have any complete answer for that question, because like you said, we didn't focus on lung, and other tissues. But I could say that actually the brother of ARRDC4, Txnip, is also highly expressed in lung, and bronchus, and in those organs. So, it's interesting because, which means that, the molecule is very oxygen sensitive, I will say. Both brothers. But that's all we know for now. But that's a very great point. And then we are excited to, you know.
Cindy St. Hilaire. Yeah.
Jun Yoshioka: Move on to the other tissues.
Cindy St. Hilaire: I was thinking about it just because I've actually recently reviewed some papers on pulmonary hypertension. So, when I saw that expression, that was the first thing I thought of was, oh, they should put these mice in a sugen/hypoxia model, and see what happens.
Jun Yoshioka: Right?
Cindy St. Hilaire: So, there's an idea for you, Yoshinobu. A K-99 grant or something. And also, because it's a full body knockout, even when you're looking at the heart, obviously the cardiomyocytes are really the most metabolically active cell, but cardiac fibroblasts are also a major component of the heart tissue. And so, do you know, is the, I guess, effects or the protectiveness of the ARRDC4 knockout heart, is it mostly because of the role in the cardiomyocytes or is there a role for it also in the fibroblast?
Yoshinobu Nakayama: Yeah, that's a very great question. Yeah. So, although we use the systemic knockout mice in the study, we believe that the beneficial effect of ARRDC4 deficiency is cardiac, autonomous. But this is because cardioprotection was demonstrated in the isolated heart experiments. But, you know, root is still uniformly expressing all cell types within the heart.
To address this, we have tested the specific effects of ARRDC4 on cardiac fibroblasts, and inflammatory cells. ARRDC4 knockout hearts had a twofold increase in myocardial glucose uptake over wild-type hearts during insulin-free perfusion. However, an increase in glucose uptake in isolated cardiac fibroblast or inflammatory cells was relatively mild, with about 1.2 fold increase over wild-type cells.
Thus we conclude that cardiomyocytes are the measure contributed to the cardiac metabolic shift. And then the mechanism within cardiomyocytes should play the major role in cardioprotection.
Jun Yoshioka: I might, at one point, because, you know, the fibroblasts, they don't need to beat, right?
Cindy St. Hilaire: Right.
Jun Yoshioka: The inflammasome cells. They don't need to beat neither. So, they don't need that much energy. So, the cardiomyocytes energy metabolism is very important. So, that's why this mechanism is kind of more important in cardiomyocytes than other cell types.
Cindy St. Hilaire: Yeah. And I think, you know, your phenotyping of the mice at baseline show that there's really no effect in a cell that's not under stress. So, it's really, really nice finding. Yeah.
This article, I should say, is featured on the cover of the September 2nd Circulation Research issue. And it's got this really nice 3D modeling of the binding of ARRDC4 to glute one. And I was reading the paper, and the methods said, you use some AI for that. So, I'm sure other people have heard, too, AI in protein modeling is important. But AI in art, right? There's that new DALL-E 2 program. So how are you able to do this? How did that work?
Jun Yoshioka: So, our study used is called AlphaFold, which applies the artificial intelligence-based deep learning method. AlphaFold, nowadays, everybody really is interested in AlphaFold. AlphaFold uses structural, and genetic data to come up with a model of what the protein of interest should look like. So, that is also how we got the protein structure, ARRDC4. We think that the ability of AlphaFold to precisely predict the protein structure from amino acid sequence would be a huge benefit to life sciences, including of course, cardiovascular science research, because of high cost, and technical difficulties in experimental methods.
It's very useful if you can computationally predict the complex from individual structures of ARRDC4. And group one, which is actually structure of group one, is available in a protein data bank. But ARRDC4, it was not available. That's why we used AlphaFold.
And then we use the docking algorithm called Hdoc. So, based on these AI analysis, we could successfully identify specific residues in a C terminal arrestin domain as an international interface, that regulates group one function. So, we believe this AI method will pretty much accelerate efforts to understand the protein, protein interactions. And we believe that will enable more advanced drug discovery, for example, in very near future.
Cindy St. Hilaire: Yeah, it's really great. I started thinking about it in terms of some of the things I'm studying. So yeah, it was really nice.
Jun Yoshioka: Try next time.
Cindy St. Hilaire: Yeah, I will, I will. Actually, I went to the website, and was playing with it before I got on the call with you. So, how do you think your findings can be leveraged towards informing clinical decision making or even developing therapeutics?
Jun Yoshioka: So, let me talk about what needs to be done. There are more things we must do.
Cindy St. Hilaire: Always. Yeah.
Jun Yoshioka: One of the most clinically relevant questions is whether ARRDC4 inhibition actually can mitigate development of post MI heart failure, and reduce mortality in the chronic phase, not the acute phase. Because in this paper we just did the seven day post MI, which is kind of like acute to subacute phase. But you never know what's going to happen in the chronic phase, right? And that is actually not so simple to answer because there are so many issues that you should consider. For example, Dr E. Dale Abel's lab has reported previously that cardiomyacites, specific group one, knockout in mice does not really accelerate the transition from compensated hypotrophy to heart failure. Also, the same group has shown that the overexpression group one does not actually prevent LV dysfunction in the mouse model of pressure overload. So, it is possible that ARRDC knockout can be, do much, or even harmful to LV remodeling in a chronic phase because chronic phase, it's not, it's getting hypoxy conditions, right?
Cindy St. Hilaire: Yeah. So, it really might be something, I guess, personalized medicine is not the phrase I'm looking for. But I guess temporarily modulated, it would be something maybe we can figure out in an acute phase versus.
Jun Yoshioka: Chronic phase.
Cindy St. Hilaire: Yeah. Yeah.
Jun Yoshioka: This makes sense. Because, you know, high capacity of ATP synthesis, by oxidating metabolism, could be important for chronic heart failure. So, it's selecting substrates. Energy substrates is no longer, you know, that issue. So, I'm not sure I'm answering your question, but this is the point that we consider to move on to the next.
Cindy St. Hilaire: Well, that's great. And I think that was my next question, really. What is next? Are you really going to try to pinpoint where you could possibly target?
Jun Yoshioka: Right. So, the first point we have to figure out about chronic phase, and another point we are interested in, is what's going on at the level of mitochondria. Does ARRDC4 knockout hearts have a different activity of electron transport chain or glycolytic enzymes within mitochondria?
Cindy St. Hilaire: Or even mitochondrial fission infusion because it's, you know, it's a machinery.
Jun Yoshioka: Yeah. And how about the other essential pathways in glucose metabolism such as mTOR, AMPK and HEF1, and so on. So, all these must be determined to help understand the more precise role of ARRDC4 in cardiac metabolism, we believe.
Cindy St. Hilaire: It's a wonderful study, and now we have even more questions to ask using your great model. Congratulations again.
Yoshinobu Nakayama: Thank you so much.
Cindy St. Hilaire: Dr Yoshioka, and Dr Nakayama.
Jun Yoshioka: Thank you.
Cindy St. Hilaire: A wonderful paper, and congrats on getting the cover, and thank you so much for joining me today.
Jun Yoshioka: Thanks well so much for having us.
Yoshinobu Nakayama: Thank you.
Cindy St. Hilaire: That's it for the highlights from our September 2nd, and our September 16th issues of Circulation Research. Thank you so much for listening. Please check out our CircRes Facebook page, and follow us on Twitter, and Instagram with the handle @circres, and hashtag discovercircres. Thank you to our guests, Dr Jun Yoshioka, and Dr Yoshinobu Nakayama.
This podcast is produced by Ishara Ratnayaka, edited by Melissa Stonerm, and supported by the editorial team of Circulation Research. Some of the copy text for highlighted articles is provided by Ruth Williams. I'm your host, Dr Cindy St. Hilaire, and this is Discover CircRes, your 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 speakers in this podcast are their own, and not necessarily those of the editors or of the American Heart Association. For more information, please visit ahajournals.org.
