November 2022 Discover Circ Res

This month on Episode 42 of Discover CircRes, host Cynthia St. Hilaire highlights four original research articles featured in the October 28 and November 11^th  issues of Circulation Research. This episode also features an interview with Dr Miguel Lopez-Ramirez and undergraduate student Bliss Nelson from University of California San Diego about their study, Neuroinflammation Plays a Critical Role in Cerebral Cavernous Malformations.

 

Article highlights:

 

Jia, et al. Prohibitin2 Maintains VSMC Contractile Phenotype

 

Rammah, et al. PPARg and Non-Canonical NOTCH Signaling in the OFT

 

Wang, et al. Histone Lactylation in Myocardial Infarction

 

Katsuki, et al. PCSK9 Promotes Vein Graft Lesion Development

 

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 articles from our October 28th and our November 11th issues of Circ Res. I'm also going to have a chat with Dr Miguel Lopez-Ramirez and undergraduate student Bliss Nelson, about their study, Neuroinflammation Plays a Critical Role in Cerebral Cavernous Malformations. But, before I get into the interviews, here are a few article highlights.

 

Cindy St. Hilaire:        The first article is from our October 28th issue, and the title is, PHB2 Maintains the Contractile Phenotype of Smooth Muscle Cells by Counteracting PKM Splicing. The corresponding author is Wei Kong, and the first authors are Yiting Jia and Chengfeng Mao, and they are all from Peking University. Insults to blood vessels, whether in the form of atherosclerosis, physical injury, or inflammation, can trigger vascular smooth muscle cells to transition from a contractile state to a proliferative and migratory one. Accompanying this conversion is a switch in the cells' metabolism from the mitochondria to glycolysis. But what controls this switch? To investigate, this group compared the transcriptomes of contractile and proliferative smooth muscle cells.

 

Among the differentially expressed genes, more than 1800 were reciprocally up and down regulated. Of those, six were associated with glucose metabolism, including one called Prohibitin-2, or PHB2, which the team showed localized to the artery wall. In cultured smooth muscle cells, suppression of PHB2 reduced expression of several contractile genes. While in rat arteries, injury caused a decrease in production of PHB2 itself, and of contractile markers.

 

Furthermore, expression of PHB2 in proliferative smooth muscle cells could revert these cells to a contractile phenotype. Further experiments revealed PHB2 controlled the splicing of the metabolic enzyme to up-regulate the phenotypic switch. Regardless of mechanism, the results suggest that boosting PHB2 might be a way to reduce adverse smooth muscle cell overgrowth and conditions such as atherosclerosis and restenosis.

 

Cindy St. Hilaire:        The second article I'm going to highlight is also from our October 28th issue, and the first authors are Mayassa Rammah and Magali Theveniau-Ruissy. And the corresponding authors are Francesca Rochais and Robert Kelly. And they are all from Marseille University. Abnormal development of the heart's outflow track, which ultimately forms the bases of the aorta and the pulmonary artery, accounts for more than 30% of all human congenital heart defects. To gain a better understanding of outflow tract development, and thus the origins of such defects, this group investigated the role of transcription factors thought to be involved in specifying the superior outflow tract, or SOFT, which gives rise to the subaortic myocardium, and the inferior outflow tract, which gives rise to the subpulmonary myocardium. Transcription factor S1 is over-expressed in superior outflow tract cells and the transcription factors, TBX1 and PPAR gamma, are expressed in inferior outflow tract cells.

 

And now this group has shown that TBX1 drives PPAR gamma expression in the inferior outflow tract, while Hess-1 surpasses PPAR gamma expression in the superior outflow tract. Indeed, in mouse embryos lacking TBX1, PPAR gamma expression was absent in the outflow tract. While in mouse embryos lacking Hess-1, PPAR gamma expression was increased and PPAR gamma positive cells were more widespread in the outflow tract.

 

The team also identified that signaling kinase DLK is an upstream activator of Hess-1 and a suppressor of PPAR gamma. In further detailing the molecular interplay regulating outflow tract patterning, the work will shed light on congenital heart disease etiologies, and inform potential interventions for future therapies.

 

Cindy St. Hilaire:        The third article I want to highlight is from our November 11th issue of Circulation Research, and the title is Histone Lactylation Boosts Reparative Gene Activation Post Myocardial Infarction. The first author is Jinjin Wang and the corresponding author is Maomao Zhang, and they're from Harbin Medical University. Lactylation of histones is a recently discovered epigenetic modification that regulates gene expression in a variety of biological processes. In inflammation, for example, a significant increase in histone lactylation is responsible for switching on reparative genes and macrophages when pro-inflammatory processes give way to pro-resolvin ones.

 

The role of histone lactylation in inflammation resolution has been shown in a variety of pathologies, but has not been examined in myocardial infarction. Wang and colleagues have now done just that. They isolated monocytes from the bone marrow and the circulation of mice at various time points after induced myocardial infarctions, and examined the cells' gene expression patterns. Within a day of myocardial infarction, monocytes from both bone marrow and the blood had begun upregulating genes involved in inflammation resolution. And, concordant with this, histone lactylation was dramatically increased in the cells, specifically at genes involved in repair processes.

 

The team went on to show that injection of sodium lactate into mice boosted monocyte histone lactylation and improved heart function after myocardial infarction, findings that suggest further studies of lactylation's pro-resolving benefits are warranted.

Cindy St. Hilaire:        The last article I want to highlight is titled, PCSK9 Promotes Macrophage Activation via LDL Receptor Independent Mechanisms. The first authors are Shunsuke Katsuki and Prabhash Kumar Jha, and the corresponding author is Masanori Aikawa, and they are from Brigham and Women's Hospital in Harvard. Statins are the go-to drug for lowering cholesterol in atherosclerosis patients. But the more recently approved PCSK9 inhibitors also lower cholesterol and can be used to augment or replace statins in patients where these drugs are insufficient.

 

PCSK9 is an enzyme that circulates in the blood and destroys the LDL receptor, thereby impeding the removal of bad cholesterol. The enzyme also appears to promote inflammation, thus potentially contributing to atherosclerosis in two ways. This group now confirms that PCSK9 does indeed promote pro-inflammatory macrophage activation and lesion development, and does so independent of its actions on the LDL receptor.

 

The team assessed PCSK9-induced lesions in animals with saphenous vein grafts, which are commonly used in bypass surgery but are prone to lesion regrowth. They found that LDL receptor lacking graft containing mice had greater graft macrophage accumulation and lesion development when PCSK9 activity was boosted than when it was not. The animal's macrophages also had higher levels of the pro-inflammatory factor expression. Together, this work shows that PCSK9 inhibitors provide a double punch against atherosclerosis and might be effective drugs for preventing the all too common failure of saphenous vein grafts.

 

Cindy St. Hilaire:        So, today with me I have Dr Miguel Lopez-Ramirez and undergraduate student Bliss Nelson from the University of California in San Diego, and we're going to talk about their study, Neuroinflammation Plays a Critical Role in Cerebral Cavernous Malformation Disease, and this article is in our November 11^th  issue of Circulation Research. Thank you both so much for joining me today. Before we talk about the science, want to just maybe tell me a little bit about yourselves?

 

Bliss Nelson:                My name is Bliss Nelson. I'm a member of Miguel Lopez-Ramirez's lab here at UC San Diego at the School of Medicine. I'm an undergraduate student here at UC San Diego. I'm actually a transfer student. I went to a community college here in California and I got involved in research after I transferred.

 

Cindy St. Hilaire:        What's your major?

 

Bliss Nelson:                I'm a cognitive science major.

 

Cindy St. Hilaire:        Excellent. You might be the first undergrad on the podcast, which is exciting.

 

Bliss Nelson:                Wow. What an honor. Thank so much.

 

Cindy St. Hilaire:        And Miguel, how about you?

 

Miguel Lopez-Ramirez: Yes, thank you. Well, first thank you very much for the opportunity to present our work through this media. It's very exciting for us. My name is Miguel Alejandro Lopez-Ramirez, and I'm an assistant professor in the Department of Medicine and Pharmacology here at UCSD.

Cindy St. Hilaire:        Wonderful. I loved your paper, because, well, first, I don't think I've talked about cerebral cavernous malformations. So what are CCMs, and why are they so bad?

 

Bliss Nelson:                Cerebral cavernous malformations, or CCMs for short, are common neurovascular lesions caused by a loss of function mutation in one of three genes. These genes are KRIT1, or CCM1, CCM2 and PDCD10, or CCM3, and generally regarded as an endothelial cell autonomous disease found in the central nervous system, so the brain and the spinal cord.

 

The relevance of CCMs is that it affects about one in every 200 children and adults,

and this causes a lifelong risk of chronic and acute hemorrhaging. CCMs can be

quiescent or dynamic lesions. If they are dynamic, they can enlarge, regress, or

behave progressively, producing repetitive hemorrhaging and exacerbations of the

disease.

 

Other side effects of the disease could be chronic bleedings, focal neurological deficits, headaches, epileptic seizures and, in some cases, death. There's no pharmacological treatment for CCMs. There's only one type of option some patients may have, which would be to have surgery to cut out the lesions. But of course this depends on where the lesion or lesions are in the central nervous system, if that's even an option. So sometimes there's no option these patients have, there's no treatment, which is what propels our lab to towards finding a pharmacological treatment or uncovering some of the mechanisms behind that.

 

Cindy St. Hilaire:        Do people who have CCM know that they have them or sometimes it not detected? And when it is detected, what are the symptoms?

 

Bliss Nelson:                Sometimes patients who have them may not show any symptoms either ever in their lifetime or until a certain point, so really the only way to find out if you were to have them is if you went to go get a brain scan, if you went to go see a doctor, or if you started having symptoms. But also, one of the issues with CCMs is that they're very hard to diagnose, and in the medical community there's a lack of knowledge for CCMs, so sometimes you may not get directed to the right specialist in time, or even ever, and be diagnosed.

 

Miguel Lopez-Ramirez: I will just add a little bit. It is fabulous, what you're doing. I think this is very, very good. But yes, that's why they're considered rare disease, because it's not obvious disease, so sometimes most of the patient, they go asymptomatic even when they have one lesions, but there's still no answers of why patients that are asymptomatics can become symptomatics. And there is a lot in neuro study, this study that we will start mentioning a little bit more in detail. We try to explain these transitions from silent or, quiescent, lesion, into a more active lesion that gives the disability to the patient.

 

Some of the symptoms, it can start even with headaches, or, in some cases, they have more neurological deficits that could be like weakness in the arms or loss of vision. In many cases also problems with the speech or balance. So it depends where the lesion is present, in the brain or in the spinal cord, the symptoms that the patient will experience. And some of the most, I will say, severe symptoms is the hemorrhagic stroke and the vascular thrombosis and seizure that the patients can present. Those would be the most significant symptoms that the patient will experience.

 

Cindy St. Hilaire:        What have been some limitations in the study of CCMs? What have been limitations in trying to figure out what's going on here?

 

Bliss Nelson:                The limitations to the disease is that, well, one, the propensity for lesions, or the disease, to come about, isn't known, so a lot of the labs that work on it, just going down to the basic building blocks of what's even happening in the disease is a major problem, because until that's well established, it's really hard to go over to the pharmacological side of treating the disease or helping patients with the disease, without knowing what's going on at the molecular level.

 

Cindy St. Hilaire:        You just mentioned molecular level. Maybe let's take a step back. What's actually going on at the cellular level in CCMs? What are the major cell types that are not happy, that shift and become unhappy cells? Which are the key players?

 

Bliss Nelson:                That's a great question and a great part of this paper. So when we're talking about the neuroinflammation in the disease, our paper, we're reporting the interactions between the endothelium, the astrocytes, leukocytes, microglia and neutrophils, and we've actually coined this term as the CaLM interaction.

 

Cindy St. Hilaire:        Great name, by the way.

 

Bliss Nelson:                Thank you. All props to Miguel. And if you look at our paper, in figure seven we actually have a great graphic that's showing this interaction in play, showing the different components happening and the different cell types involved in the CaLM interaction that's happening within or around the CCM lesions.

 

Cindy St. Hilaire:        What does a astrocyte normally do? I think our podcast listening base is definitely well versed in probably endothelial and smooth muscle cell and pericyte, but not many of us, not going to lie, including me, really know what a astrocyte does. So what does that cell do and why do we care about its interaction with the endothelium?

 

Miguel Lopez-Ramirez: Well, the astrocytes play a very important role. Actually, there are more astrocytes than any other cells in the central nervous system, so that can tell you how important they are. Obviously play a very important role maintaining the neurological synapses, maintaining also the hemostasis of the central nervous system by supporting not only the neurons during the neural communication, but also by supporting the blood vessels of the brain.

 

All this is telling us that also another important role is the inflammation, or the response to damage. So in this case, what also this study proposed, is that new signature for these reactive astrocytes during cerebral malformation disease. So understanding better how the vasculature with malformations can activate the astrocytes, and how the astrocytes can contribute back to these developing of malformations. It will teach us a lot of how new therapeutic targets can be implemented for the disease.

 

This is part of this work, and now we extend it to see how it can also contribute to the communication with immune cells as Bliss already mentioned.

 

Cindy St. Hilaire:        Is it a fair analogy to say that a astrocyte is more similar to a pericyte in the periphery? Is that accurate?

 

Miguel Lopez-Ramirez: No, actually there are pericytes in the central nervous system as well. They have

different roles. The pericyte is still a neuron cell that give the shape, plays a role in the contractility and maintains the integrity of the vessels, while the astrocyte is more like part of the immune system, but also part of the supporting of growth factors or maintaining if something leaks out of the vasculature to be able to capture that.

 

Cindy St. Hilaire:        You used a handful of really interesting mouse models to conduct this study. Can you tell us a little bit about, I guess, the base model for CCM and then some of the unique tools that you used to study the cells specifically?

 

Bliss Nelson:                Yeah, of course. I do a lot of the animal work in the lab. I'd love to tell you about the mouse model. So to this study we use the animal model with CCM3 mutation. We use this one because it is the most aggressive form of CCM and it really gives us a wide range of options to study the disease super intricately. We use tamoxifen-regulated Cre recombinase under the control of brain endothelial specific promoter, driving the silencing of the gene CCM3, which we call the PDCD10 betco animal, as you can see in our manuscript. To this, the animal without the Cre system, that does not develop any lesions, that we use as a control, we call the PDCD10 plox. And these animals are injected with the tamoxifen postnatally day one, and then for brain collection to investigate, wcollected at different stages. So we do P15, which we call the acute stage, P50, which we term the progressive stage, and then P80, which is the chronocytes stage. And after enough brain collections, we use them for histology, gene expression, RNA analysis, flow cytometry, and different imaging to help us further look into CCMs.

 

Cindy St. Hilaire:        How similar is a murine CCM to a human CCM? Is there really good overlap or are there some differences?

 

Miguel Lopez-Ramirez: Yes. So, actually, that's a very good question, and that's part of the work that we are doing. This model definitely has advantages in which the lesions of the vascular formations are in an adult and juvenile animals, which represent an advantage for the field in which now we will be able to test pharmacological therapies in a more meaningful, way where we can test different doses, different, again, approaches. But definitely, I mean, I think I cannot say that it's only one perfect model for to mimic the human disease. It's the complementary of multiple models that give us certain advantages in another, so the integration of this knowledge is what will help us to understand better the disease.

 

Cindy St. Hilaire:        That's great. I now want to hear a little bit about your findings, because they're really cool. So you took two approaches to study this, and the first was looking at the astrocytes and how they become these, what you're calling reactive astrocytes, and then you look specifically at the brain endothelium. So could you maybe just summarize those two big findings for us?

 

Miguel Lopez-Ramirez: Yeah, so, basically by doing these studies we use trangenic animal in this case that they give us the visibility to obtain the transcripts in the astrocytes. And basically this is very important because we don't need to isolate the cells, we don't need to manipulate anything, we just took all the ribosomes that were basically capturing the mRNAs and we profile those RNAs that are specifically expressed in the astrocytes.

 

By doing this, we actually went into looking at in depth the transcripts that were altered in the animals that developed the disease, in this case the cerebral cavernous malformation disease, and what we look at is multiple genes that were changing. Many of them were already described in our previous work, which were associated with hypoxia and angiogenesis. But what we found in this work is that now there were a lot of genes associated with inflammation and coagulation actually, which were not identified before.

 

What we notice is that now these astrocytes, during the initial phase of the vascular malformation, may play a more important role in angiogenesis or the degradation of the vessels. Later during the stage of the malformation, they play a more important role in the thrombosis, in the inflammation, and recruitment of leukocyte

 

That was a great advantage in this work by using this approach and looking in detail, these astrocytes. Also, we identified there were very important signature in these astrocytes that we refer as a reactive astrocytes with neuroinflammatory properties. In the same animals, basically, not in the same animal, but in the same basically the experimental approach, we isolated brain vasculature. And by doing the same, we actually identified not only the astrocyte but also the endothelium was quite a different pattern that we were not seeing before. And this pattern was also associated with inflammation, hypoxia and coagulation pathways.

 

That lead us to go into more detail of what was relevant in this vascular malformations. And one additional part that in the paper this is novel and very impactful, is that we identify inflammasome as a one important component, and particularly in those lesions that are multi-cavernous.

 

Now we have two different approaches. One, we see this temporality in which the lesions forms different patterns in which the initial phase maybe is more aneugenic, but as they become more progressive in chronocytes, inflammation and hypoxy pathways are more relevant for the recruitment of the inflammatory cells and also the precipitation of immunothrombosis.

 

But also what we notice is that inflammasome in endothelial and in the leukocytes may play an important role in the multi-cavernous formation, and that's something that we are looking in more detail, if therapeutics or also interventions in these pathways could ameliorate the transition of phases between single lesions into a more aggressive lesions.

 

Cindy St. Hilaire:        That's kind of one of the follow up questions I was thinking about too is, from looking at the data that you have, obviously to get a CCM, there's a physical issue in the vessel, right? It's not formed properly. Does that form influence the activation of the astrocyte, and then the astrocytes, I guess, secrete inflammatory factors, target more inflammation in the vessel? Or is there something coming from the CCM initially that's then activating the astrocyte? It's kind of a chicken and the egg question, but do you have a sense of secondary to the malformation, what is the initial trigger?

 

Miguel Lopez-Ramirez: The malformations in our model, and this is important in our model, definitely start by producing changes in the brain endothelial. And as you mention it, these endothelium start secreting molecules that actually directly affect the neighboring cells.

 

One of the first neighboring cells that at least we have identified to be affected is the astrocytes, but clearly could be also pericytes or other cells that are in the neurovascular unit or form part of the neurovascular unit. But what we have seen now is that this interaction gets extended into more robust interactions that what you were referring as the CaLM interactions.

 

Definitely I think during the vascular malformations maybe is the discommunication that we identify already few of those very strong iteration that is part of the follow up manuscript that we have. But also it could be the blood brain barrier breakdown and other changes in the endothelium could also trigger the activation of the astrocytes and brain cells.

 

Cindy St. Hilaire:        What does your data suggest about potential future therapies of CCM? I know you have a really intriguing statement or data that showed targeting NF-kappa B isn't likely going to be a good therapeutic strategy. So maybe tell us just a little bit about that, but also, what does that imply, perhaps, of what a therapeutic strategy could be?

 

Bliss Nelson:                Originally we did think that the inhibition of NF-kappa B would cause an improvement potentially downstream of the CCMs. And unexpectedly, to our surprise, the partial or total loss of the brain endothelial NF-kappa B activity in the chronic model of the mice, it didn't prevent or cause any improvement in the lesion genesis or neuroinflammation, but instead it resulted in a trend to increase the number of lesions and immunothrombosis, suggesting that the inhibition of it is actually worsening the disease and shouldn't be used as a target for therapeutical approaches.

 

Miguel Lopez-Ramirez: Yes, particularly that's also part of the work that we have ongoing in which NF-kappa B may also play a role in preventing the further increase of inflammation. So that is something that it can also be very important. And this is very particular for certain cell types. It's very little known what the NF-kappa B actually is doing in the brain endothelial during malformations or inflammation per se. So now it's telling us that this is something that we have to consider for the future.

 

Also, our future therapeutics of what we propose are two main therapeutic targets. One is the harmful hypoxia pathway, which involves activation, again, of the population pathway inflammation, but also the inflammasomes. So these two venues are part of our ongoing work in trying to see if we have a way to target with a more safe and basically efficient way this inflammation.

 

However, knowing the mechanisms of how these neuroinflammation take place is what is the key for understanding the disease. And maybe even that inflammatory and inflammatory compounds may not be the direct therapeutic approach, but by understanding these mechanisms, we may come with  new approaches that will help for safe and effective therapies.

 

Cindy St. Hilaire:        What was the most challenging part of this study? I'm going to guess it has something to do with the mice, but in terms of collecting the data or figure out what's going on, what was the most challenging?

 

Bliss Nelson:                To this, I'd like to say that I think our team is very strong. We work very well together, so I think even the most challenging part of completing this paper wasn't so challenging because we have a really strong support system among ourselves, with Miguel as a great mentor. And then there's also two postdocs in the lab who are also first authors that contributed a lot to it.

 

Cindy St. Hilaire:        Great. Well, I just want to commend both of you on an amazing, beautiful story. I loved a lot of the imaging in it, really well done, very technically challenging, I think, pulling out these specific sets of cells and investigating what's happening in them. Really well done study. And Bliss, as an undergraduate student, quite an impressive amount of work. And I congratulate both you and your team on such a wonderful story.

 

Bliss Nelson:                Thank you very much.

 

Miguel Lopez-Ramirez: Thank you for Bliss and also Elios and Edo and Katrine, who all contributed   

  enormously to the completion of this project.

 

Cindy St. Hilaire:        It always takes a team.

 

Miguel Lopez-Ramirez: Yes.

 

Cindy St. Hilaire:        Great. Well, thank you so much, and I can't wait to see what's next for this story.

 

Cindy St. Hilaire:        That's it for the highlights from October 28th and November 11th issues of Circulation Research. Thank you so much for listening. Please check out the Circ Res Facebook page and follow us on Twitter and Instagram with the handle @circres and #discovercircres. Thank you to our guests, Dr Miguel Lopez-Ramirez and Bliss Nelson. This podcast is produced by Ashara Retniyaka, edited by Melissa Stoner, and supported by the editorial team of Circulation Research. Some of the copy text for our highlighted articles is provided by Ruth Williams. 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, please visit ahagenerals.org.