Discover CircRes – Détails, épisodes et analyse

This month on Episode 64 of Discover CircRes, host Cindy St. Hilaire highlights articles featured in the August 30th and September 13th issues of Circulation Research. This Episode also includes a discussion with Drs Stephanie Chung, Ahmed Gharib, and Khalid Abd-Elmoniem from NIDDK about their study, Endothelial Dysfunction in Youth-Onset Diabetes Type 2, A Clinical Translational Study.

Article highlights:

Zhao, et al. AMPK Phosphorylation of β-Arrestin-1 Blocking β-AR

Bashore, et al. Monocytes Profiling and Cardiovascular Disease

Chu, et al. Oxysterol-GPR183 Axis and Endothelial Senescence

Sigle, et al. Targeting Secreted Cyclophilin A in Failing Hearts

This month on Episode 63 of Discover CircRes, host Cindy St. Hilaire highlights articles featured in the August 2nd and August 16th issues of Circulation Research. This Episode also includes a discussion with Drs Chen Gao and Yibin Wang about their study, Glucagon Receptor Antagonist for Heart Failure with Preserved Ejection Fraction

Article highlights:

Douvdevany, et al. Imaging the Turnover of the Sarcomere

Quelquejay, et al. Wnk1 Deletion in Smooth Muscle Cells Induces Aortitis

Paulke, et al. The Role of Dysferlin in Cardiac Hypertrophy

Morais, et al. Predictors of Outcome in SPAN

This month on Episode 54 of Discover CircRes, host Cynthia St. Hilaire highlights three original research articles featured in the October 27th and November 10th issues of Circulation Research. This Episode also includes a discussion with Dr Sophie Susen and Dr Caterina Casari about their study, Shear Forces Induced Platelet Clearance Is a New Mechanism of Thrombocytopenia, published in the October 27th issue.

Article highlights:

Pass, et al. Single Nuclei Transcriptome of PAD Muscle

Liu, et al. Myocardial Recovery in DCM: CDCP1 and Fibrosis

Grego-Bessa, et al. Neuregulin-1 Regulates Chamber Morphogenesis

Agrawal, et al. A New Model of PH due to HFpEF

This month on Episode 53 of Discover CircRes, host Cynthia St. Hilaire highlights three original research articles featured in the September 29th and October 13th issues of Circulation Research. This Episode also includes a discussion with Dr Margaret Schwarz and Dr Dushani Ranasinghe about their study, Altered Smooth Muscle Cell Histone Acetylome by the SPHK2/S1P Axis Promotes Pulmonary Hypertension, published in the September 29 issue.

Article highlights:

Serio, et al. p300/CBP-Upregulated Glycolysis and Cardiac Aging

Sharifi, et al. ADAMTS-7 and TIMP-1 in Atherosclerosis

Zhang, et al. TMEM215 Represses Endothelial Apoptosis

Perike, et al. PPP1R12C Promotes Atrial Hypocontractility in AF

This month on Episode 52 of Discover CircRes, host Cynthia St. Hilaire highlights three original research articles featured in the September 1 and September 15th issues of Circulation Research. This Episode also includes a discussion with Dr Manuel Mayr about the study, Proteomic Atlas of Atherosclerosis, the Contribution of Proteoglycans to Sex Differences, Plaque Phenotypes and Outcomes, published in the September 15 issue.

Article highlights:

Sun, et al. CCND2 modRNA Remuscularization Hearts with AMI

Ho, et al. Lymphatic Genes Prevent Cardiac Valve Disease

Shanks, et al. Cardiac Vagal Activity Increases During Exercise

This month on Episode 51 of Discover CircRes, host Cynthia St. Hilaire highlights four original research articles featured in the August 4th and August 18th issues of Circulation Research. This Episode also includes a discussion with Dr Eric Small and Dr Xiaoyi Liu from the University of Rochester Medical Center about their article p53 Regulates the Extent of Fibroblast Proliferation and Fibrosis in Left Ventricular Pressure Overload, published in the July 21st issue of the journal.

Article highlights:

Régnier, et al. CTLA-4 Pathway Is Pivotal in Giant Cell Arteritis

Zarkada, et al. Chylomicrons Regulate Lacteal Permeability

Schuermans, et al. Age at Menopause, Telomere Length, and CAD

Bayer, et al. T-cell MyD88 Regulates Fibrosis in Heart Failure

This month on Episode 50 of Discover CircRes, host Cynthia St. Hilaire highlights four original research articles featured in the June 23, July 7, and July 21 issues of Circulation Research. This Episode also includes a discussion with BCVS Outstanding Early Career Investigator Award Qiongxin Wang from University of Washington St. Louis, Haobo Li from Massachusetts General Hospital, and Asma Boukhalfa from Tufts Medical Center.

Article highlights:

Tong, et al. The Role of DRP1 in Mitophagy

Abe, et al. ERK5-NRF2 Axis and Senescence-Associated Stemness

Dai, et al. Therapeutic Targeting of Endocytosis Defects in DCM

Weng, et al.  PDCD5 Suppresses Cardiac Fibrosis

This month on Episode 49 of Discover CircRes, host Cynthia St. Hilaire highlights two original research articles featured in the May 26th issue and provides an overview of the June 9th Compendium on Early Cardiovascular Disease of Circulation Research. This Episode also includes a discussion with Dr Tejasvi Dudiki and Dr Tatiana Byzova about their study, Mechanism of Tumor Platelet Communications in Cancer.

Article highlights:

Nichtová, et al. Mitochondria-SR Tethering and Cardiac Remodeling

Ferrucci, et al. Muscle Transcriptomic and Proteomic in PAD

Compendium on Early Cardiovascular Disease.

This month on Episode 48 of Discover CircRes, host Cynthia St. Hilaire highlights three original research articles featured in the April 28th issue of Circulation Research. This Episode also includes a discussion between Dr Mina Chung, Dr DeLisa Fairweather and Dr Milka Koupenova, who all contributed to manuscripts to the May 12th Compendium on Covid-19 and the Cardiovascular System.  

Article highlights:

Heijman, et al. Mechanisms of Enhanced SK-Channel Current in AF

Chen, et al. IL-37 Attenuates Platelet Activation

Enzan, et al. ZBP1 Protects Against Myocardial Inflammation

Compendium on Covid-19 and the Cardiovascular System.

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. Today, I'm going to be highlighting articles from our April 28th and May 12th issues of Circulation Research. I'm also going to have a chat with Dr Mina Chung, Dr DeLisa Fairweather and Dr Milka Koupenova, who all contributed to articles in the May 12th COVID Compendium. But before we have that interview, let's first talk about some highlights.

The first article I want to present is titled Enhanced Calcium-Dependent SK-Channel Gating and Membrane Trafficking in Human Atrial Fibrillation. This article is coming from the University of Essen by Heijman and Zhou, et al. Atrial fibrillation is one of the most common forms of heart arrhythmia in humans and is characterized by irregular, often rapid heartbeats that can cause palpitations, dizziness and extreme fatigue.

Atrial fibrillation can increase a person's risk of heart failure, and though treatments exist such as beta blockers, blood thinners and antiarrhythmia medications, they can have limited efficacy and side effects. A new family of drugs in development are those blocking small-conductance calcium-activated potassium channels called SK channels, which exhibit increased activity in animal models of AF and suppression of which attenuates the arrhythmia. In humans however, the relationship between SK channels and atrial fibrillation is less clear, at least in terms of SK channel mRNA levels. Because mRNA might not reflect actual channel activity, this group looked at just that and they found indeed that channel activity was increased in cardiomyocytes from atrial fibrillation patients compared to those from controls even though the mRNA and protein levels themselves were similar. The altered currents were instead due to changes in SK channel trafficking and membrane targeting.

By confirming that SK channels play a role in human atrial fibrillation, this work supports the pursuit of SK channel inhibitors as possible new atrial fibrillation treatments.

The next article I want to present is titled IL-37 Attenuates Platelet Activation and Thrombosis Through IL-1R8 Pathway. This article comes from Fudan University by Chen and Hong, et al. Thrombus formation followed by the rupture of a coronary plaque is a major pathophysiological step in the development of a myocardial infarction. Understanding the endogenous antithrombotic factors at play could provide insights and opportunities for developing treatments. With this in mind, Chen and Hong, et al. investigated the role of interleukin-1 receptor 8, or IL-1R8, which suppresses platelet aggregation in mice, and of IL-37, a newly discovered human interleukin that forms a complex with IL-1R8 and is found at increased levels in the blood of patients with myocardial infarction.

Indeed, the amount of IL-37 in myocardial infarction patients negatively correlates with platelet aggregation. They also show that treatment of human platelets in vitro with IL-37 suppresses the cell's aggregation and does so in a concentration-dependent manner. Moreover, injection of the protein into the veins of mice inhibits thrombus development and better preserves heart function even after myocardial infarction. Such effects were not seen in mice lacking IL-1R8. This suggests IL-37's antithrombotic action depends on its interaction with the receptor. Together, the results suggest IL-37 could be developed as a antithrombotic agent for use in MI patients or indeed perhaps other thrombotic conditions.

The last article I want to present before our interview is titled ZBP1 Protects Against Mitochondrial DNA-Induced Myocardial Inflammation in Failing Hearts. This article is coming from Kyushu University and is by Enzan, et al. Myocardial inflammation is a key factor in the pathological progression of heart failure and occurs when damaged mitochondria within the stricken cardiomyocyte release their DNA, triggering an innate inflammatory reaction. In a variety of cells, DNA sensors such as Z-DNA-binding protein 1 or ZBP1 are responsible for such mitochondrial DNA-induced inflammation. In theory then, it's conceivable that therapeutic suppression of ZBP1 might reduce myocardial inflammation in heart failure and preserve function. But as Enzan and colleagues have now discovered to their surprise, mice lacking ZBP1 exhibited worse, not better heart inflammation and more failure after induced myocardial infarction.

Indeed, the test animals' hearts had increased infiltration of immune cells, production of inflammatory cytokines and fibrosis together with decreased function compared with the hearts of mice with normal ZBP1 levels. Experiments in rodent cardiomyocytes further confirmed that loss of ZBP1 exacerbated mitochondrial DNA-induced inflammatory cytokine production while overexpression of ZBP1 had the opposite effect. While the reason behind ZBP1's opposing roles in different cells is not yet clear, the finding suggests that boosting ZBP1 activity in the heart might be a strategy for mitigating heart inflammation after infarction.

Cindy St. Hilaire:         The May 12th issue of Circulation Research is our COVID compendium, which consists of a series of 10 reviews on all angles of COVID-19 as it relates to cardiovascular health and disease. Today, three of the authors of the articles in this series are here with me. Dr Mina Chung is a professor of medicine at the Cleveland Clinic. She and Dr Tamanna Singh and their colleagues wrote the article, A Post Pandemic Enigma: The Cardiovascular Impact of Post-Acute Sequelae of SARS-CoV-2. Dr DeLisa Fairweather, professor of medicine, immunology and clinical and translational science at the Mayo Clinic, and she and her colleagues penned the article, COVID-19 Myocarditis and Pericarditis. Dr Milka Koupenova is an assistant professor of medicine at the UMass Chan School of Medical and she led the group writing the article, Platelets and SARS-CoV-2 During COVID-19: Immunity, Thrombosis, and Beyond. Thank you all for joining me today.

DeLisa Fairweather:    Thank you so much for having us.

Mina Chung:   Thank you.

Milka Koupenova:       Thank you for having us, Cindy.

Cindy St. Hilaire:         In addition to these three articles, we have another seven that are on all different aspects of COVID. Dr Messinger's group wrote the article, Interaction of COVID-19 With Common Cardiovascular Disorders. Emily Tsai covered cell-specific mechanisms in the heart of COVID-19 patients. Mark Chappell and colleagues wrote about the renin-angiotensin system and sex differences in COVID-19. Michael Bristow covered vaccination-associated myocarditis and myocardial injury. Jow Loacalzo and colleagues covered repurposing drugs for the treatment of COVID-19 and its cardiovascular manifestations. Dr Stephen Holby covered multimodality cardiac imaging in COVID, and Arun Sharma covered microfluidic organ chips in stem cell models in the fight against COVID-19.

Cindy St. Hilaire          As of today, worldwide, there have been over six hundred million individuals infected with the virus and more than six and a half million have died from COVID-19. In the US, we are about a sixth of all of those deaths.

Obviously now we're in 2023, the numbers of individuals getting infected and dying are much, much lower. As my husband read to me this morning, one doctor in Boston was quoted saying, "People are still getting wicked sick." In 75% of deaths, people have had underlying conditions and cardiovascular disease is found in about 60% of all those deaths. In the introduction to the compendium, you mentioned that the remarkable COVID-19 rapid response initiative released by the AHA, which again is the parent organization of Circ Research and this podcast, if I were to guess when that rapid response initiative started, I would've guessed well into the pandemic, but it was actually March 26th, 2020. I know in Pittsburgh, our labs have barely shut down. So how soon after we knew of SARS-CoV-2 and COVID, how soon after that did we know that there were cardiovascular complications?

Mina Chung:               I think we saw cardiovascular complications happening pretty early. We saw troponin increases very early. It was really amazing what AHA did in terms of this rapid response grant mechanism. You mentioned that the RFA was announced, first of all, putting it together by March 26th when we were just shutting down in March was pretty incredible to get even the RFA out. Then the grants were supposed to be submitted by April 6th and there were 750 grants that were put together and submitted. They were all reviewed within 10 days from 150 volunteer reviewers. The notices were distributed April 23rd, less than a month out.

Cindy St. Hilaire:         Amazing.

Mina Chung:               So this is an amazing, you're right, paradigm for grant requests and submissions and reviews.

DeLisa Fairweather:    For myocarditis, reports of that occurred almost immediately coming out of China, so it was incredibly rapid.

Cindy St. Hilaire:         Yeah, and that was a perfect lead up to my next question. Was myocarditis, I guess, the first link or the first clue that this was not just going to be a respiratory infection?

DeLisa Fairweather:    I think myocarditis appearing very early, especially it has a history both of being induced by viruses, but being strongly an autoimmune disease, the combination of both of those, I think, started to hint that something different was going to happen, although a lot of people probably didn't realize the significance of that right away.

Cindy St. Hilaire:         What other disease states, I guess I'm thinking viruses, but anything, what causes myocarditis and pericarditis normally and how unique is it that we are seeing this as a sequelae of COVID?

DeLisa Fairweather:    I think it's not surprising that we find it. Viruses around the world are the primary cause of myocarditis, although in South America, it's the parasite Trypanosoma cruzi. Really, many viruses that also we think target mitochondria, including SARS-CoV-2, have an important role in driving myocarditis. Also, we know that SARS-CoV-1 and MERS also reported myocarditis in those previous infections. We knew about it beforehand that they could cause myocarditis.

Cindy St. Hilaire:        Is it presenting differently in a COVID patient than say those South American patients with the... I forget the name of the organism you said, but does it come quickly or get worse quickly or is it all once you get it, it's the same progression?

DeLisa Fairweather:    Yeah. That's a good question. Basically, what we find is that no matter what the viral infection is, that myocarditis really appears for signs and symptoms and how we treat it identically and we see that with COVID-19. So that really isn't any different.

Cindy St. Hilaire:         Another huge observation that we noticed in COVID-19 patients, which was the increased risk of thrombic outcomes in the patients. Dr Koupenova, Milka, you are a world expert in platelets and viruses and so you and your team were leading the writing of that article. My guess is knowing what you know about platelets and viruses, this wasn't so surprising to you, but could you at least tell us the state of the field in terms of what we knew about viruses and platelets before COVID, before Feb 2020?

Milka Koupenova:       Before Feb 2020, we actually knew that influenza gets inside in platelets. It leads to not directly prothrombotic events, but it would lead to release of complement 3 from them. That complement 3 would actually increase the immunothrombosis by pushing neutrophils to release their DNA, forming aggregates. In cases when you have compromised endothelium and people with underlying conditions, you would expect certain thrombotic outcomes. That, we actually published 2019 and then 2020 hit. The difference between influenza and SARS-CoV-2, they're different viruses. They carry their genome in a different RNA strand. I remember thinking perhaps viruses are getting inside in platelets, but perhaps they do not. So we went through surprising discoveries that it seemed like it is another RNA virus. It also got into platelets. It was a bit hard to tweak things surrounding BSL-3 to tell you if the response was the same.

It is still not very clear how much SARS or rather what receptor, particularly when it gets inside would induce an immune response. There are some literature showing the MDA5, but not for sure, may be responsible. But what we found is that once it gets in platelets, it just induces this profound activation of programmed cell death pathways and release of extracellular vesicles and all these prothrombotic, procoagulant form of content that can induce damage around, because platelets are everywhere. So that how it started in 2019 and surprisingly progressed to 2021 or 2020 without the plan of really studying this virus.

Cindy St. Hilaire:         How similar and how different is what you observe in platelets infected, obviously in the lab, so I know it's not exactly the same, but how similar and how different is it between the flu? Do you know all the differences yet?

Milka Koupenova:       No offense here, they don't get infected.

Cindy St. Hilaire:         Okay.

Milka Koupenova:       Done the proper research. The virus does not impact platelets, but induces the response.

Cindy St. Hilaire:         Okay.

Milka Koupenova:       That goes back to sensing mechanism. Thank goodness platelets don't get infected because we would be in a particularly bad situation, but they remove the infectious virus from the plasma from what we can see with function.

Cindy St. Hilaire:         Got it. So they're helping the cleanup process and in that cleaning up is where the virus within them activates. That is a really complicated mechanism.

 Milka Koupenova:       Oh, they're sensing it in some form to alert the environment. It's hard to say how similar and how different they are unless you study them hint by hint next to each other. All I can tell is that particularly with SARS-C, you definitely see a lot more various kinds of extracellular vesicles coming out of them that you don't see the same way or rather through the same proportion with influenza. But what that means in how platelet activates the immune system with one versus the other, and that goes back to the prothrombotic mechanisms. That is exactly what needs to be studied and that was the call for this COVID compendium is to point out how much we have done as a team. As scientists who put heads together, as Mina said, superfast response, it's an amazing going back and looking at what happened to think of what we achieved.

There is so much more, so much more that we do not understand how one contributes to all of these profound responses in the organs themselves, such as myocarditis. We see it's important and that will be the problem that we're dealing from here on trying to figure it out and then long COVID, right?

Cindy St. Hilaire:         Yeah. Related to what you just said about the mechanism, this cleanup by the platelets or the act of cleaning up helps trigger their activation, is that partly why the antiplatelet and anticoagulant therapies failed in patients? Can you speculate on that? I know the jury's still out and there's a lot of work to be done, but is that part of why those therapies weren't beneficial?

Milka Koupenova:       The answer to that in my personally biased opinion is yes. Clearly, the antiplatelet therapies couldn't really control the classical activation of a platelet. So what I think we need to do from here on is to look at things that we don't understand that non-classically contribute to the thrombotic response downstream. If we manage to control the immune response in some way or the inflammation of the infection or how a platelet responds to a virus, then perhaps we can ameliorate a little bit of the downstream prothrombotic effect. So it's a lot more for us to trickle down and to understand in my personal opinion.

DeLisa Fairweather:    There is one thing that was really remarkable to me in hearing your experience, Milka, is that I had developed an autoimmune viral model of myocarditis in mice during my postdoc. So I've been studying that for the last 20 years. What is unique about that model is rather than using an adjuvant, we use a mild viral infection so it doesn't take very much virus at all going to the heart to induce it. I also, more recently, started studying extracellular vesicles really as a therapy, and in doing that, inadvertently found out that actually, the model that I'd created where we passage the virus through the heart to induce this autoimmune model, we were actually injecting extracellular vesicles into the mice and that's what was really driving the disease. This is really brought out. So from early days, I did my postdoc with Dr Noel Rose. If you've heard of him, he came up with the idea of autoimmune disease in the '50s. We had always, in that environment, really believed that viruses were triggering autoimmune disease and yet it took COVID before we could really prove that because no one could identify them.

Here we have an example and I think the incidence rates with COVID were so high for myocarditis because for the first time, we had distinguished symptoms of patients going to the doctor right at the beginning of their infection having an actual test to examine the virus, knowing whether it's present or not, whether PCR or antibody test, and then being able to see when myocarditis happened.

Cindy St. Hilaire:         Yeah. I think one thing we can all appreciate now is just some of the basic biology we've learned on the backend of this. Actually, those last comments really led well to the article that your team led, Dr Chung, about what we call long COVID, which I guess I didn't realize has an actual name, post-acute sequelae of SARS-CoV-2 or PASC is the now more formal name for long COVID. But what is it? We hinted at it that there's these bits about autoimmune and things like that. What counts as long COVID?

Mina Chung:   Yeah. Our article was led by Tamanna Singh. She did a fantastic job of putting this together. We've had, and others, theorized that the huge palette of symptoms that you can experience post-COVID, they can affect all these organ systems with brain fog, these atypical chest pains, postural orthostatic tachycardia, a lot of palpitations, atrial fibrillation, many weakness and fatigue. To us, really, you can get GI symptoms. We've been very interested in, is this an autoimmune phenomenon directed against nerves and all those things. It's also very interesting because many of the non-COVID syndromes that existed pre-COVID like POTS and chronic fatigue syndrome and a lot of other syndromes are associated with autoantibodies. So that is a very interesting area to explore. Is there a persistence of viral fragments. Is there autoimmunity? Is it also a component of persistence of the damage from the initial infection? So it's an area that still needs a lot of work and a lot of work is going into it, but this is like a post or inter pandemic of itself, so hopefully we'll get more insights into that.

Cindy St. Hilaire:         Yeah, it's really interesting. I have a friend who has very debilitating long COVID and one of her doctors had said, "If I didn't know any better, I would just describe this as a autoimmune type X." What do we know, I guess, about the current hypothesis of the pathogenesis of PASC? Are there any prevailing theories right now as to why it's occurring? Is the virus still active or is it these domino effects that are leading to multi-organ collapse of some sort?

Mina Chung:   Yeah. In some people, persistent viral particles can be identified for months, but whether or not that's what's triggering it, it's hard to know. We see more autoimmune disease that's been reported and various antibodies being reported. So those are clearly processes to be investigated. The microthrombosis is still up there in terms of potentially playing a role in long COVID.

Milka Koupenova:       Mina, you probably know better because you see patients, but to all I have been exposed to, long COVID does not really have a homogeneous symptom presentation and then a few theories as to what may be going on in these patients. Not everybody has a microthrombosis. Not everybody have a D-dimer elevated, but some people do. Some people have, as you pointed out, these spectacularly profound brain fog. People can't function. It's probably your friend, Cindy, right?

Cindy St. Hilaire:         Yeah.

Milka Koupenova:       So one of the theories that I have been, from a viral perspective, very interested in is that a lot of the symptoms in certain individuals such as fatigue, brain fog, sensitivity to light and skin can very well be explained by a flare-up of Epstein-Barr virus that may be what SARS-CoV-2 somehow is inducing. I don't know, DeLisa, what your experience with long COVID is as a scientist. I hope only. But I would like to hear your perspective too because it's so heterogeneous and it is amazing what happens.

DeLisa Fairweather:    I have a very interesting perspective from a number of different directions. One, as I mentioned before, my long history with Dr Rose and I've written many articles theorizing how viruses could cause autoimmune disease. This has grown and really, I think this has been extremely revealing during COVID for many of those theories. One thing that I write about in the review for this article is that mast cells, from all the research I've done with myocarditis in our model, mast cells are central to what is driving everything. We show they're the first innate immune cell acting as an antigen-presenting cell, completely driving the response in a susceptible pattern. One of the things that's very important in autoimmune disease is both sex and race. I'd say one of the big weaknesses we have in myocarditis pre-COVID and post-COVID has been ignoring what's going on with race.

In the United States, myocarditis is 90%, 95% white men that are under 50 years of age and most of the cases are under 40 or some of the ones really associated with sudden cardiac death are under 30. So it's very specific. I've been studying sex and race differences and we see those exact differences in our animal models. In animal models, whether you're susceptible or not depends on how many mast cells you have.

Well, I've proposed from the beginning, looking, I've written a lot of different sex difference reviews looking at viruses and autoimmune disease with different autoimmune diseases and hypothesizing and really seeing that mast cells do a lot of the things we're talking about. They have all of the receptors, the whole group of them that have been related to SARS-CoV-2 so they can be activated or stimulated by the virus itself. They act as a antigen-presenting cell. They're critical in the complement pathway as well as macrophages. We see the dominant immune phenotype really being macrophages. Mast cells just are usually not counted anywhere. And of course, these receptors, a lot of them have to do with enzymes and things that are all related to mast cells pathways. Then how they activate the immune response and lead it towards the pathway that leads to chronic autoimmune disease with increased autoantibodies in females, mast cells are very different by sex.

This has to do also when we talked in the Review about myocarditis and pericarditis. It's both those appearing. Although clinically, we have really boxed them as separate things, because there is some definite clinical pericarditis phenotypes that are different, myocarditis in animal models is always myopericarditis. It always then, in that outer pericardial areas where mast cells sit, they sit around the vascular area in most concentrated. So when they degranulate, we see inflammation coming in the vessel, but really concentrated with fibrosis there and along the pericardium. So that's very typical of what's going on. When we shift anything that shifts that, it changes whether you have more pericarditis or less pericarditis and the vascular inflammation by altering anything that affects the mast cells. I talk a little bit about in the review, I think there's only been a few recent things looking at it in COVID, but I think mast cells and certain susceptibility to autoimmune diseases that occur more often in women can really predispose.We need to pay more attention to mast cells and what they might indicate for all these pathways.

Milka Koupenova:       I think we should study the platelet mast cell access at this point.

DeLisa Fairweather:    Yes.

Milka Koupenova:       Because as you're talking about these sex differences, which is spectacular, these things to me are so mind-boggling how one, the infection itself would be more prevalent in men, but then long COVID is more prevalent in women. All of these things and why we understand so very little, what we found about a few years ago in the Framingham Heart Study in the platelets from those people is that all toll-like receptors are expressed at the higher level in women and they associate with different things between men and female. For instance, toll-like receptors in women will associate more with a prothrombotic response while in male with pro-inflammatory response. I think they grossly underestimate the amount of our sex differences from cell to cell.

DeLisa Fairweather:    It is, yeah.

Mina Chung:   One other thing that I learned about the sex differences from this compendium is Mark Chappell also notes, you mentioned TLR and TLR7 and ACE2 are X chromosome in an area that he says escapes X-linked inactivation. So it could very well be involved in further.

DeLisa Fairweather:

Further, yeah. And ACE2 is expressed more highly in male cells for what's been researched because of the sex difference in COVID, both the COVID infection

Cindy St. Hilaire:         So a variety of organ systems are impacted in patients with PASC, also referred to as long COVID, the lungs, the heart, the pancreas, the GI system, pretty much any system, the brain, nervous system. We've just been talking about the mast cell impact. I was really thinking in my head, well, the one thing that connects all of it is the vasculature. I'm a vascular biologist, so I have certain biases, I'm sure, but how much of the sequelae that we see is a function of vascular phenotypes?

Milka Koupenova:       I do think the vasculature is super important. It's clear that not all endothelial cells, for instance, will pick up the virus and respond to it. That's why you have this patchy breakage when you look at autopsies. Hence, platelets will respond according to what's local. That's why you find these micro thrombotic events at certain places. Why does it happen in each organ? How does the virus get to each organ to respond? Or is it just inflammation, but why is it in specific places? That's what we don't understand. That's where we need to go. Perhaps, as DeLisa points out, perhaps it's a lot more complicated than how we traditionally think of thrombosis. Actually, my personal bias, again 100% sure that it is a lot more complicated than the traditional mechanisms that we have understood, and that's where the immune system comes and autoimmunity perhaps stems from and they probably speak to each other, right? It's not just one thing.

DeLisa Fairweather:    Yeah. I think really, EVs are bringing lots of understanding. A lot of things we used to just think were maybe free-floating and the serum are inside EVs. I think that the immune response is perhaps even more specific than we ever thought and more regulated than we ever understood.  

When an EV comes through a cardiomyocyte, whether it's from the mitochondria or through a lysosome, is part of what goes into its outer membrane, something that tells the immune system that that came from the heart, so it knows to go. This will solve a lot of our questions with autoimmune disease if it's very specific like that. It doesn't just have to be the release of free-floating cardiac myosin. We know cardiac myosin is the driver of the autoimmune response in myocarditis, but they're probably  much more fine-tuned.

Cindy St. Hilaire:         Yeah. I just would love to end with hearing from each of you. You each have your own domain of specialty. If I gave you a massive pot of money, what would be the question you would want to tackle? What's the gap you would love to answer?

Milka Koupenova:       We still don't understand specifically what kind of vesicles are coming out, what are their contents in addition to those vesicles. We don't understand. When it comes to platelets, what comes from their granules? We see these breakages of the membrane. Those are non-granule proteins, and non-granule proteins, they serve as dangerous associated molecular pattern signals and can be profoundly inflammatory to the surrounding environment, can be procoagulant. What are those? How are they affecting the surrounding environment? Ultimately, why is there a microthrombi? Why is there not a profound thrombosis everywhere? Thank goodness there isn't, but why isn't? That's what I would do with my money.

DeLisa Fairweather:    I think I would do something very similar. All of our research in our animal model, on the one side, we are looking in this viral myocarditis animal model and finding the EVs that come from that are driving myocarditis. On the other hand, we're using EVs that come from healthy human plasma or fat, and we're seeing a profound downregulation of everything if you give it early and we're trying to see how late you can give it and still get an effect. So looking at those and really understanding the components in the context of COVID and COVID vaccines to understand those components, I really think that's the future of where we're going to find what's causing disease and also how we can find therapies. They may be able to reverse this.

Mina Chung:   Yeah, I'm interested very much in the autoimmunity and the autoantibodies that are    and how they may react with those microthrombi. Perhaps there's autoantibodies within a lot of that material. We're looking at using human and pluripotent stem cell-derived cell models to study the effects of those. That is what I would use our money for.

Cindy St. Hilaire:        Well, Dr Mina Chung, Dr DeLisa Fairweather, Dr Milka Koupenova, thank you all so much for joining me today and talking about not only the articles that you wrote and with your colleagues, but also other articles in this amazing compendium. I do think this is one of the first all-encompassing compendiums or group of articles that focus specifically on COVID and cardiovascular disease. So thank you all so much.

Mina Chung:   Thank you.

DeLisa Fairweather:    Thank you.

Milka Koupenova:       You're welcome.

Cindy St. Hilaire:         That's it for highlights from the April 28th and May 12th issues of Circulation Research. Thank you for listening. Please check out the CircRes Facebook page and follow us on Twitter and Instagram with the handle @circres and #DiscoverCircRes. Thank you to our guests, Dr Mina Chung, Dr DeLisa Fairweather and Dr Milka Koupenova. This podcast is produced by Ishara Ratnayaka, edited by Melissa Stoner and supported by the editorial team of Circulation Research. Some of the copy text for the 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 2023. 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, visit ahajournals.org.

This month on Episode 47 of Discover CircRes, host Cynthia St. Hilaire highlights three original research articles featured in the March 31 issue of Circulation Research. We’ll also provide an overview of the Compendium on Increased Risk of Cardiovascular Complications in Chronic Kidney Disease published in the April 14 issue. Finally, this episode features an interview with Dr Elizabeth Tarling and Dr Bethan Clifford from UCLA regarding their study, RNF130 Regulates LDLR Availability and Plasma LDL Cholesterol Levels.

Article highlights:

Shi, et al. LncRNAs Regulate SMC Phenotypic Transition

Chen, et al. Bilirubin Stabilizes Atherosclerotic Plaque

Subramaniam, et al. Mapping Non-Obvious cAMP Nanodomains by Proteomics

Compendium on Increased Risk of Cardiovascular Complications in Chronic Kidney Disease

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 share three articles selected from our March 31st issue of Circulation Research and give you a quick summary of our April 14th Compendium. I'm also excited to speak with Dr Elizabeth Tarling and Dr Bethan Clifford from UCLA regarding their study, RNF130 Regulates LDLR Availability and Plasma LDL Cholesterol Levels.

So first the highlights. The first article we're going to discuss is Discovery of Transacting Long Noncoding RNAs that Regulates Smooth Muscle Cell Phenotype. This article's coming from Stanford University and the laboratory of Dr Thomas Quertermous. Smooth muscle cells are the major cell type contributing to atherosclerotic plaques. And in plaque pathogenesis, the cells can undergo a phenotypic transition whereby a contractile smooth muscle cell can trans differentiate into other cell types found within the plaque, such as macrophage-like cells, osteoblast-like cells and fibroblast-like cells. These transitions are regulated by a network of genetic and epigenetic mechanisms, and these mechanisms govern the risk of disease.

The involvement of long non-coding RNAs, or Lnc RNAs as they're called, has been increasingly identified in cardiovascular disease. However, smooth muscle cell Lnc RNAs have not been comprehensively characterized and the regulatory role in the smooth muscle cell state transition is not thoroughly understood. To address this gap, Shi and colleagues created a discovery pipeline and applied it to deeply strand-specific RNA sequencing from human coronary artery smooth muscle cells that were stressed with different disease related stimuli. Subsequently, the functional relevancy of a few novel Lnc RNAs was verified in vitro.

From this pipeline, they identified over 4,500 known and over 13,000 unknown or previously unknown Lnc RNAs in human coronary artery smooth muscle cells. The genomic location of these long noncoding RNAs was enriched near coronary artery disease related transcription factor and genetic loci. They were also found to be gene regulators of smooth muscle cell identity. Two novel Lnc RNAs, ZEB-interacting suppressor or ZIPPOR and TNS1-antisense or TNS1-AS2, were identified by the screen, and this group discovered that the coronary artery disease gene, ZEB2, which is a transcription factor in the TGF beta signaling pathway, is a target for these Lnc RNAs. These data suggest a critical role for long noncoding RNAs in smooth muscle cell phenotypic transition and in human atherosclerotic disease.

Cindy St. Hilaire:              The second article I want to share is titled Destabilization of Atherosclerotic Plaque by Bilirubin Deficiency. This article is coming from the Heart Research Institute and the corresponding author is Roland Stocker. The rupture of atherosclerotic plaque contributes significantly to cardiovascular disease. Plasma concentrations of bilirubin, a byproduct of heme catabolism, is inversely associated with risk of cardiovascular disease, but the link between bilirubin and atherosclerosis is unknown.

Chen et el addressed this gap by crossing a bilirubin knockout mice to a atherosclerosis prone APOe knockout mouse. Chen et el addressed this gap by crossing the bilirubin knockout mouse to the atherosclerosis-prone APOE knockout mouse, and used the tandem stenosis model of plaque instability to address this question. Compared with their litter mate controls, bilirubin-APOE double knockouts showed signs of increased systemic oxidative stress, endothelial dysfunction, as well as hyperlipidemia. And they had higher atherosclerotic plaque burden.

Hemeatabolism was increased in unstable plaques compared with stable plaques in both of these groups as well as in human coronary arteries. In mice, the bilirubin deletion selectively destabilized unstable plaques and this was characterized by positive arterial remodeling and increased cap thinning, intra plaque hemorrhage, infiltration of neutrophils and MPO activity. Subsequent proteomics analysis confirmed bilirubin deletion enhanced extracellular matrix degradation, recruitment and activation of neutrophils and associated oxidative stress in the unstable plaque. Thus, bilirubin deficiency generates a pro atherogenic phenotype and selectively enhances neutrophil-mediated inflammation and destabilization of unstable plaques, thereby providing a link between bilirubin and cardiovascular disease risk.

Cindy St. Hilaire:              The third article I want to share is titled Integrated Proteomics Unveils Regulation of Cardiac Monocyte Hypertrophic Growth by a Nuclear Cyclic AMP Nano Domain under the Control of PDE3A. This study is coming from the University of Oxford in the lab of Manuela Zaccolo. Cyclic AMP is a critically important secondary messenger downstream from a myriad of signaling receptors on the cell surface. Signaling by cyclic AMP is organized in multiple distinct subcellular nano domains, regulated by cyclic AMP hydrolyzing phosphodiesterases or PDEs.

The cardiac beta adrenergic signaling has served as the prototypical system to elucidate this very complex cyclic AMP compartmentalization. Although studies in cardiac monocytes have provided an understanding of the location and the properties of a handful of these subcellular domains, an overview of the cellular landscape of the cyclic AMP nano domains is missing.

To understand the nanodynamics, Subramanian et al combined an integrated phospho proteomics approach that took advantage of the unique role that individual phosphodiesterases play in the control of local cyclic AMP. They combined this with network analysis to identify previously unrecognized cyclic AMP nano domains associated with beta adrenergic stimulation. They found that indeed this integrated phospho proteomics approach could successfully pinpoint the location of these signaling domains and it provided crucial cues to determine the function of previously unknown cyclic AMP nano domains.

The group characterized one such cellular compartment in detail and they showed that the phosphodiesterase PDE3A2 isoform operates in a nuclear nano domain that involves SMAD4 and HDAC1. Inhibition of PDE3 resulted in an increased HDAC1 phosphorylation, which led to an inhibition of its deacetylase activity, and thus derepression of gene transcription and cardiac monocyte hypertrophic growth. These findings reveal a very unique mechanism that explains the negative long-term consequences observed in patients with heart failure treated with PDE3 inhibitors.

Cindy St. Hilaire:              The April 14th issue is our compendium on Increased Risk of Cardiovascular Complications in Chronic Kidney Disease. Dr Heidi Noels from the University of Aachen is our guest editor of the 11 articles in this issue. Chronic kidney disease is defined by kidney damage or a reduced kidney filtration function. Chronic kidney disease is a highly prevalent condition affecting over 13% of the population worldwide and its progressive nature has devastating effects on patient health. At the end stage of kidney disease, patients depend on dialysis or kidney transplantation for survival. However, less than 1% of CKD patients will reach this end stage of chronic kidney disease. Instead, most of them with moderate to advanced chronic kidney disease will prematurely die and most often they die from cardiovascular disease. And this highlights the extreme cardiovascular burden patients with CKD have.

The titles of the articles in this compendium are the Cardio Kidney Patient Epidemiology, Clinical Characteristics, and Therapy by Nicholas Marx, the Innate Immunity System in Patients with Cardiovascular and Kidney Disease by Carmine Zoccali et al. NETs Induced Thrombosis Impacts on Cardiovascular and Chronic Kidney disease by Yvonne Doering et al. Accelerated Vascular Aging and Chronic Kidney Disease, The Potential for Novel Therapies by Peter Stenvinkel et al. Endothelial Cell Dysfunction and Increased Cardiovascular Risk in Patients with Chronic Kidney Disease by Heidi Noels et al. Cardiovascular Calcification Heterogeneity in Chronic Kidney Disease by Claudia Goettsch et al. Fibrosis in Pathobiology of Heart and Kidney From Deep RNA Sequencing to Novel Molecular Targets by Raphael Kramann et al. Cardiac Metabolism and Heart Failure and Implications for Uremic Cardiomyopathy by P. Christian Schulze et al. Hypertension as Cardiovascular Risk Factor in Chronic Kidney Disease by Michael Burnier et al. Role of the Microbiome in Gut, Heart, Kidney crosstalk by Griet Glorieux et al, and Use of Computation Ecosystems to Analyze the Kidney Heart Crosstalk by Joachim Jankowski et al.

These reviews were written by leading investigators in the field, and the editors of Circulation Research hope that this comprehensive undertaking stimulates further research into the path flow of physiological kidney-heart crosstalk, and on comorbidities and intra organ crosstalk in general.

Cindy St. Hilaire:              So for our interview portion of the episode I have with me Dr Elizabeth Tarling and Dr Bethan Clifford. And Dr Tarling is an associate professor in the Department of Medicine in cardiology at UCLA, and Dr Clifford is a postdoctoral fellow with the Tarling lab. And today we're going to be discussing their manuscript that's titled, RNF130 Regulates LDLR Availability and Plasma LDL Cholesterol Levels. So thank you both so much for joining me today.

Elizabeth Tarling:             Thank you for having us.

Bethan Clifford:               Yeah, thanks for having us. This is exciting.

Cindy St. Hilaire:              I guess first, Liz, how did you get into this line of research? I guess, before we get into that, I should disclose. Liz, we are friends and we've worked together in the ATVB Women's Leadership Committee. So full disclosure here, that being said, the editorial board votes on these articles, so it's not just me picking my friends. But it is great to have you here. So how did you enter this field, I guess, briefly?

Elizabeth Tarling:             Yeah, well briefly, I mean my training right from doing my PhD in the United Kingdom in the University of Nottingham has always been on lipid metabolism, lipoprotein biology with an interest in liver and cardiovascular disease. So broadly we've always been interested in this area and this line of research. And my postdoctoral research was on atherosclerosis and lipoprotein metabolism. And this project came about through a number of different unique avenues, but really because we were looking for regulators of LDL biology and plasma LDL cholesterol, that's sort of where the interest of the lab lies.

Cindy St. Hilaire:              Excellent. And Bethan, you came to UCLA from the UK. Was this a topic you were kind of dabbling in before or was it all new for you?

Bethan Clifford:               It was actually all completely new for me. So yeah, I did my PhD at the same university as Liz and when I started looking for postdocs, I was honestly pretty adamant that I wanted to stay clear away from lipids and lipid strategy. And then it wasn't until I started interviewing and meeting people and I spoke to Liz and she really sort of convinced me of the excitement and that the interest and all the possibilities of working with lipids and well now I won't go back, to be honest.

Cindy St. Hilaire:              And now here you are. Well-

Bethan Clifford:               Exactly.

Cindy St. Hilaire:              ... congrats on a wonderful study. So LDLR, so low density lipoprotein receptor, it's a major determinant of plasmid LDL cholesterol levels. And hopefully most of us know and appreciate that that is really a major contributor and a major risk for the development of atherosclerosis and coronary artery disease. And I think one thing people may not really appreciate, which your study kind of introduces and talks about nicely, is the role of the liver, right? And the role of receptor mediated endocytosis in regulating plasma cholesterol levels. And so before we kind of chat about the nitty-gritty of your study, could you just give us a brief summary of these key parts between plasma LDL, the LDL receptor and where it goes in your body?

Elizabeth Tarling:             Yeah. So the liver expresses 70% to 80% of the body's LDL receptor. So it's the major determinant of plasma lipoprotein plasma LDL cholesterol levels. And through groundbreaking work by Mike Brown and Joe Goldstein at the University of Texas, they really define this receptor mediated endocytosis by the liver and the LDL receptor by looking at patients with familial hypercholesterolemia. So those patients have mutations in the LDL receptor and they either express one functional copy or no functional copies of the LDL receptor and they have very, very large changes in plasma LDL cholesterol. And they have severe increases in cardiovascular disease risk and occurrence and diseases associated with elevated levels of cholesterol within the blood and within different tissues. And so that's sort of how the liver really controls plasma LDL cholesterol is through this receptor mediated endocytosis of the lipoprotein particle.

Cindy St. Hilaire:              There's several drugs now that can help regulate our cholesterol levels. So there's statins which block that rate limiting step of cholesterol biosynthesis, but there's this new generation of therapies, the PCSK9 inhibitors. And can you just give us a summary or a quick rundown of what are those key differences really? What is the key mechanism of action that these therapies are going after and is there room for more improvement?

Bethan Clifford:               Yeah, sure. So I mean I think you've touched on something that's really key about the LDR receptor is that it's regulated at so many different levels. So we have medications available that target the production of cholesterol and then as you mentioned this newer generation of things like PCSK9 inhibitors that sort of try and target LDL at the point of clearance from the plasma.

And in response to your question of is there room for more regulation, I would say that given the sort of continual rate of increased cholesterol in the general population and the huge risks associated with elevated cholesterol, there's always capacity for more to improve that and sort of generally improve the health of the population. And what we sort of found particularly exciting about RNF130 is that it's a distinct pathway from any of these regulatory mechanisms. So it doesn't regulate the level of transcription, it doesn't regulate PCSK9. Or in response to PCSK9, it's a completely independent pathway that could sort of improve or add to changes in cholesterol.

Cindy St. Hilaire:              So your study, it's focusing on the E3 ligase, RNF130. What is an E3 ligase, and why was this particular one of interest to you? How did you come across it?

Elizabeth Tarling:             is predTates Bethan joining the lab. This is, I think, again for the listeners and those people in training, I think it's really important to note this project has been going in the lab for a number of years and has really... Bethan was the one who came in and really took charge and helped us round it out. But it wasn't a quick find or a quick story. It had a lot of nuances to it. But we were interested in looking for new regulators of LDL cholesterol and actually through completely independent pathways we had found the RNF130 locus as being associated with LDL cholesterol in animals. And then it came out in a very specific genome-wide association study in the African American care study, the NHLBI care study. And so really what we started looking at, we didn't even know what it was.

Elizabeth Tarling:             So we asked ourselves, well what is this gene? What is this protein? And it's RNF, so that's ring finger containing protein 130 and ring stands for really interesting new gene. Somebody came up with the glorious name. But proteins that contain this ring domain are very characteristic and they are E3 ubiquitin ligases. And so they conjugate the addition of ubiquitin to a target protein and that signals for that protein to either be internalized and/or degraded through different decorative pathways within the cell. And so we didn't land on it because we were looking at E3 ligases, we really came at it from an LDL cholesterol perspective. And it was something that we hadn't worked on before and the study sort of blossomed from there.

Cindy St. Hilaire:              That's amazing and a beautiful, but also, I'm sure, heartbreaking story because these long projects are just... They're bears. So what does this RNF130 do to LDLR? What'd you guys find?

Bethan Clifford:               As Liz said, this is a long process, but one of the key factors of RNF130 is it's structurally characteristically looked like E3 ligase. So the first thing that Liz did and then I followed up with in the lab is to see is this E3 ligase ubiquitinating in vitro. And if it is going to ubiquitinate, what's it likely to regulate that might cause changes in plasma cholesterol that would explain these human genetic links that we saw published at the same time.

And so because the LDL cholesterol is predominantly regulated by the LDL receptor and the levels of it at the surface of the parasites in the liver, the first question we wanted to see is does RNF130 interact in any way with that pathway? And I'm giving you the brief view here of the LDL receptor. We obviously tested lots of different receptors. We tested lots of different endocytose receptors and lipid regulators, but the LDL receptor is the one that we saw could be ubiquitinated by RNF130 in vitro. And so then we wanted to sort of go on from there and establish, okay, if this E3 ubiquitin ligase, is it regulating LDL receptor? What does that mean in an animal context in terms of regulating LDL cholesterol?

Cindy St. Hilaire:              Yeah, and I guess we should also explain, ubiquitination, in terms of this receptor, and I guess related to Goldstein and Brown and receptor mediated endocytosis, like what does that actually mean for the liver cell and the cholesterol in the LDLR that is binding the receptor?

Bethan Clifford:               \So yes, ubiquitination is a really common regulatory mechanism actually across all sorts of different cells, all sorts of different receptors and proteins. And basically what it does is it signals for degradation of a protein. So a ubiquitin molecule is conjugated to its target such as in our case the LDL receptor and that ubiquitin tells the cell that this protein is ready for proteasomal degradation. And that's just one of the many things ubiquitination can do. It can also signal for a trafficking event, it can signal for a protein to protein interaction, but it's most commonly associated with the proteasomal degradation.

Cindy St. Hilaire:              So in terms of... I guess I'm thinking in terms of PCSK9, right? So those drugs are stemming from observations in humans, right? There were humans with gain and loss of function mutations, which caused either more or less of this LDLR receptor internalization. How is this RNF130 pathway different from the PCSK9 activities?

Elizabeth Tarling:             Yeah, so PCSK9 is a secreted protein, so it's made by hepatocyte and actually other cells in the body and it's secreted and it binds to the LDL particle, LDL receptor complex, and signals for its internalization and degradation in the proteasome. So this is not ubiquitination event, this is a completely different trafficking event. And so the RNF130, actually what Bethan showed, is it directly ubiquitinates the LDL receptor itself, signaling for an internalization event and then ultimately degradation of the LDR receptor through a decorative pathway, which we also define in the study.

So these are two unique mechanisms and actually some key studies that we did in the paper were to modulate RNF130 in animals that do not have PCSK9. And so in that system where in the absence of PCSK9 you have a lot of LDR receptor in the liver that's internalizing cholesterol. What happens when you overexpress RNF130? Do you still regulate at the LDL receptor? And you absolutely do. And so that again suggests that they're two distinct mechanisms and two distinct pathways.

Cindy St. Hilaire:              That was one thing I really loved about your paper is every kind of figure or section, the question that would pop up in my head, even ones that didn't pop in my head were beautifully answered with some of these really nice animal models, which is never an easy thing, right? And so one of the things that you brought up was difficulty in making one of the animal models. And so I'm wondering if you could share a little bit for that challenge. I think one thing that we always tend to hide is just science is hard and a lot of what we do doesn't work. And I really think especially for the trainees and really everyone out there, if we kind of share these things more, it's better. So what was one of the most challenging things in this study? And I guess I'm thinking about that floxed animal.

Elizabeth Tarling:             Yeah, so I'll speak a bit about that and then I'll let Bethan address because she was really the one on the ground doing a lot of the struggles. But again, we actually weren't going to include this information in the paper. And upon discussion and actually prompted by the reviewers of the paper and some of the questions that they asked us, we realized, you know what? It's actually really important to show this and show that this happens and that there are ways around it.

And so the first story is before Bethan even arrived in the lab, we had purchased embryonic stem cells that were knockout first condition already. And so this is a knockout strategy in which the exon of interest is flanked with lots of P sites so that you can create a flox animal, but also so you can create a whole body knockout just by the insertion of this knockout first cassette.

Elizabeth Tarling:             And so we got those mice actually in the first year of Bethan joining the lab. We finally got the chimeric mice and we were able to stop reading those mice. And at the same time we tried to generate our flox animals so that we could move on to do tissue-specific studies. And Bethan can talk about the pain associated with this. But over two years of breeding, we never got the right genotypes from the different crosses that you need to do to generate the flox animal.

And it was actually in discussions with Bethan where we decided we need to go back. We need to go back to those ESLs that we purchased five years ago and we need to figure out if all of the elements that the quality control step had told us were in place are actually present. And so Bethan went back and sequenced the whole locus and the cassette to figure out what pieces were present and we found that one of the essential locks P sites that's required for every single cross from the initial animal was absent and therefore we could actually never make the mouse we wanted to make.

And so that's sort of just a lesson for people going down that route and making these tools that we need in the lab to answer these questions is that despite paying extra money and getting all of the sort of QCs that you can get before you receive the ESLs, we should have gone back and done our own housekeeping and sort of a long journey told us when we went back that we didn't have what we thought we had at the beginning. And that was a real sticking point as Bethan can-

Cindy St. Hilaire:              Yeah. And so you know you're not alone. My very first postdoc that I did, I went with a mouse that they had also bought and were guaranteed that it was a knockout and it was not. And it is a painful lesson, but it is critical to... You get over it.

So Bethan, maybe you can also tell us a little bit about what are the other kind of next things you tried? You pivoted and you pivoted beautifully because all the models you used I thought were quite elegant in terms of exactly asking the question you wanted to ask in the right cells. So can you maybe explain some of the in vivo models you used for this study?

Bethan Clifford:               Sure, there are definitely a lot. So I mean I think Liz sort of encapsulated the trouble we have with the knockout really succinctly, but actually I want to just take this moment to sort of shout out to another postdoc in the Tarling lab, Kelsey Jarrett, who was really instrumental in the pivoting to a different model. So for the knockouts when we sort of established we didn't have exactly what we thought we did and then to compound that we also weren't getting the DeLiAn ratios breeding this whole body knockout.

We wanted to sort of look at a more transient knockout model. And that's where Kelsey really stepped in and sort of led the way and she generated AAV-CRISPR for us to target RNF130 specifically in the liver. And that had the added beauty of, one, not requiring breeding to get over this hurdle of the knockout being somewhat detrimental to breeding. But it also allowed us to ask the question of what RNF130 is doing specifically in the liver where the liver regulates LDL receptor and LDL cholesterol.

And so that was one of the key models that really, really helped get this paper over the finish line. But we did a whole barrage of experiments, as you've seen. We wanted to make sure... One of the key facets of the Tarling lab is whenever you do anything, no matter what you show Liz, it will always be, "Okay, you showed it to me one way, now show it to me a different way." Can you get the same result coming at it from different ways? And if you can't, why is that? What is the regulation behind that? And so that's really what the paper is doing is asking the same question in as many ways as we can accurately and appropriately probe what RNF130 does to the LDR receptor.

So we tried gain of function studies without adenovirus overexpression. We tried transient knockdown with antisense oligonucleotides, and then we did, as I said, the AAV-CRISPR knockdown with the help of Kelsey and our whole body knockout. And then we also repeated some of these studies such as the adenovirus and the ASO in specific genetic backgrounds. So in the absence of PCSK9, can we still regulate the LDL receptor? And then we also, just to really confirm this, in the absence of the LDL receptor, do we see a difference? And the answer is no, because this effect was really dependent on that LDL receptor being present. So there was a big combination.

Cindy St. Hilaire:              It was really nice, really a beautiful step-wise progression of how to solidly answer this question. But a lot of, I think, almost all you did was in mice. And so what is the genetic evidence for relevancy in humans? Can you discuss a little bit about those databases that you then went to to investigate, is this relevant in humans?

Bethan Clifford:               I think Liz might be better off answering that question.

Elizabeth Tarling:             And I think this sort of pivots on what Bethan was saying. So when we had struggles in the lab, it was a team environment and a collaboration between people in the lab that allowed us to make that leap and make those next experiments possible to then really answer that question. And to be able to include the antisense oligonucleotides required a collaboration with industry. We were very lucky to have a longstanding collaboration with Ionis, who provided the antisense oligonucleotides.

And for the human genetics side of things, that also was a collaboration with Marcus Seldin, who was a former postdoc with Jake Lusis and is now our PI at UC Irvine. And what he helped us do is dive into those summary level databases and ask from that initial study in the NHLBI care population, do we see associations of RNF130 expression in humans with LDL cholesterol with cardiovascular outcomes. And so one database which I would recommend everybody use, it's publicly available, is the StarNet database. And it's in the paper and the website is there. And that allowed us to search for RNF130.

Elizabeth Tarling:             And what it does is it asks how RNF130 expression in different tissues is associated with cardiometabolic outcomes and actual in CAD cases and controls, so people with and without heart disease. And we found that expression of RNF130 in the liver was extremely strongly correlated with the occurrence of cardiovascular disease in people with CAD. So in cases versus controls. And then we were also able to find many other polymorphisms in the RNF130 locus that were associated with LDL cholesterol in multiple different studies.

And I think the other message from this paper is this, unlike PCSK9 and unlike LDR receptor itself, which are single gene mutations that cause cardiovascular disease, there are many sub genome-wide significant loci that contribute to this multifactorial disease, which is extremely complex. And I think RNF130 falls within that bracket that those sort of just on the borderline of being genome-wide significant still play significant biological roles in regulating these processes. And they don't come up as a single gene hit for a disease, but combinatorialy they are associated with increased risk of disease and they have a molecular mechanism that's associated with the disease. And so that's what Marcus helped us do in terms of the human genetics is really understand that and get down to that level of data.

Cindy St. Hilaire:              Yeah. Yeah, it really makes you want to go back and look at those. Everyone always focuses on that really high peak and those analyses, but what are all those other ones above the noise, right? So it's really important.

Elizabeth Tarling:             I think it's really hard to do that. I think that's one where people... Again, it comes down to team science and the group of people that we brought together allowed us to ask that molecular question about how that signal was associated with the phenotype. I think by ourselves we wouldn't have been able to do it.

Cindy St. Hilaire:              Yeah. So your antisense oligonucleotide experiments, they were really nice. They showed, I think it was a four-week therapy, they showed that when you injected them expression of RNF130 went down by 90%. I think cholesterol in the animals was lowered by 50 points or so. Is this kind of a next viable option? And I guess related to that, cholesterol's extremely important for everything, right? Cell membrane integrity, our neurons, all sorts of things. Is it possible with something that is perhaps really as powerful as this to make cholesterol too low?

Elizabeth Tarling:             I think that what we know from PCSK9 gain and loss of function mutations is that you can drop your plasma cholesterol to very low levels and still be okay because there are people walking around with mutations that do that. I think RNF130 is a little different in that it's clearly regulatory in a homeostatic function in that it's ubiquitously expressed and it has this role in the liver to regulate LDL receptor availability, but there are no homozygous loss of function mutants people walking around, which tells us something else about how important it is in potentially other tissues and in other pathways. And we've only just begun to uncover what those roles might be.

So I think that as a therapy, it has great potential. We need to do a lot more studies to sort of move from rodent models into more preclinical models. But I do think that the human data tell us that it's really important in other places too. And so yeah, we need to think about how best it might work as a therapy. If it's combinatorial, if it's dosed. Those are the types of things that we need to think about.

Cindy St. Hilaire:              Yeah, it's really exciting. Do you know, are there other protein targets of RNF130? Is that related to my next question of what is next?

Elizabeth Tarling:             I mean, so I should point out, so Bethan unfortunately left the lab last year for a position at Amgen where she's working on obesity and metabolic disease. But before she left, she did two very, very cool experiments searching for new targets or additional targets of RNF130. Starting in the liver, but hopefully we'll move those into other tissues. And so she did gain of function RNF130 versus what loss of function we have of RNF130, and she did specific mass spec analysis of proteins that are ubiquitinated in those different conditions.

And by overlaying those data sets, we're hoping to carve out new additional targets of RNF130. And there are some, and they're in interesting pathways, which we have yet to completely test, but definitely there are additional pathways, at least when you overexpress and reduce expression. Now, whether they turn out to be, again, bonafide in vivo, actual targets that are biologically meaningful is sort of the next step.

Cindy St. Hilaire:              Yeah. Well, I'm sure with your very rigorous approach, you are going to find out and hopefully we'll see it here in the future. Dr Elizabeth Tarling and Dr Bethan Clifford, thank you so much for joining me today. I really enjoyed this paper. It's a beautiful study. I think it's a beautiful example, especially for trainees about kind of thoroughly and rigorously going through and trying to test your hypothesis. So thanks again.

Elizabeth Tarling:             Thank you.

Bethan Clifford:               Thank you very much.

Cindy St. Hilaire:              That's it for the highlights from the March 31st and April 14th issues of Circulation Research. Thank you for listening. Please check out the Circulation Research Facebook page and follow us on Twitter and Instagram with the handle @CircRes, and #DiscoverCircRes. Thank you to our guests, Dr Liz Tarling and Dr Bethan Clifford.

This podcast is produced by Ishara Ratnayaka, edited by Melissa Stoner, and supported by the editorial team of Circulation Research. I'm your host, Dr Cindy St. Hilaire, 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 speakers in this podcast are their own, and not necessarily those of the editors or of the American Heart Association. For more information, visit ahajournals.org.