Sep 8, 2020
This week’s episode includes author Charlotte Andersson and Associate Editor Naveed Sattar as they discuss familial clustering of aortic size, aneurysms, and dissections in the community.
Dr Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast, summary, and backstage pass to the journal and its editors. I'm Dr Carolyn Lam, Associate Editor from the National Heart Center and Duke national University of Singapore.
Dr Greg Hundley: And I'm Greg Hundley, director of the Pauley Heart Center at VCU health in Richmond, Virginia. Well, Carolyn, our feature this week has to do with aortic size, aneurysms, and predilection to dissection. But before we get to that, how about if we grab a cup of coffee and go through some of the other articles in the issue?
Dr Carolyn Lam: I got my coffee, Greg, and you know what? I'm going to start with quiz for you.
Dr Greg Hundley: All right.
Dr Carolyn Lam: True or false, in the setting of obesity and/or diabetes, cardiac substrate metabolism shifts towards increased fatty acid oxidation, while lipid accumulates in the heart? True or false? Of course, you're right. Oh, but there's a part two. Can you guess, by increasing fatty acid oxidation, will we induce or prevent obesity-induced lipotoxic cardiomyopathy?
Dr Greg Hundley: I'm going to say, because you asked it in the way you asked it, prevent.
Dr Carolyn Lam: Wow. All right. Well, the truth is we didn't really know before today's paper. The specific link between cardiac metabolism and lipotoxic cardiomyopathy was elusive and there was no specific therapy available for this condition. And these authors, Dr Rong Tian from University of Washington and colleagues, hypothesized that cardiac pathology-associated obesity would be attributable to the imbalance of fatty acid supply and oxidation. So using a diet-induced obesity model in the current study, they demonstrated that enhancing fatty acid oxidation through deletion of acetyl-CoA carboxylase 2, was sufficient to prevent obesity-induced cardiomyopathy.
So, increasing cardiac fatty acid oxidation alone does not cause cardiac dysfunction, but instead protects against cardiomyopathy in chronically obese mice. The cardiac-protective effect of increasing fatty acid oxidation and obese mice is through maintenance of Parkin-mediated mitophagy, and thus preventing mitochondrial dysfunction. These findings indicate that impaired mitophagy contributes to mitochondrial dysfunction in obese mice, and that targeting the Parkin-dependent pathway is a viable therapeutic intervention for obesity-induced cardiomyopathy.
Dr Greg Hundley: Very nice. Carolyn.
Dr Carolyn Lam: I'm going to be greedy and go on to my next paper. So Greg, do you think cardiac regeneration is possible?
Dr Greg Hundley: Well, Carolyn, I would have said, several years ago, no, but that trip that we took to China with Joe Hill and Hesham Sadek, our Associate Editor and our Chief Editor, convinced me otherwise. So I'm going to definitely answer yes on this one.
Dr Carolyn Lam: Oh, Greg, you're just too smart. And speaking of China, this next paper is from there, from co-corresponding authors, Dr Nie and Hu, from Fuwai Hospital National Center for Cardiovascular Disease and Chinese Academy of Medical Sciences and Peking Union Medical College. So, using seven genetic mouse lines, they identify that Oncostatin M is the top upregulated cytokine during neonatal heart regeneration. Oncostatin M is a pleiotropic secretory protein that belongs to the interleukin 6 family, and associates with the pathological process of dilated cardiomyopathy.
And these authors found that macrophages promote heart regeneration by secreting Oncostatin M, which promotes cardiomyocyte proliferation via a co-receptor, gp130. Employing RNA-seq and functional screening, they further found that Src-mediated gp130 triggered cardiomyocyte proliferation by activating the downstream signaling pathway involving Yap, with Y357 phosphorylation independent of the Hippo pathway. So the last thing that they did was show that gene therapy with adenovirus-associated virus and coding this activated gp130 improved heart regeneration and pumping function, thus serving as a potential therapeutic target. An amazing paper.
Dr Greg Hundley: Very nice, Carolyn. What a great summary and so much detail. Well, Carolyn, I'm going to turn our attention to catecholaminergic polymorphic ventricular tachycardia. And this article comes to us from Dr Jason Roberts, from the Western University. Carolyn, genetic variants in calsequestrin 2 can cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia, though isolated reports have identified arrhythmogenic phenotypes among heterozygotes. So in this study, a total of 112 individuals, including 36 catecholaminergic polymorphic ventricular tachycardia probands, 24 were homozygotes for compound heterozygotes, and 12 were pure heterozygotes, against 76 family members possessing at least one presumed pathogenic calsequestrin 2 variant. These were all identified.
Dr Carolyn Lam: Wow, a very precious cohort. So what did they find, Greg?
Dr Greg Hundley: This international multicenter study of calsequestrin 2 catecholaminergic polymorphic ventricular tachycardia really redefined its heritability and confirmed that pathogenic heterozygous calsequestrin 2 variants may manifest with a catecholaminergic polymorphic ventricular tachycardia phenotype, indicating a need to clinically screen these individuals. Among individuals heterozygous for a pathogenic calsequestrin 2 rare variant, medical therapy and exercise restriction are likely not necessary in the absence of the catecholaminergic polymorphic ventricular tachycardia phenotype. Though, you have to be certain over time, an intermittent clinical screening to ensure they remain phenotype-negative should be obtained.
Dr Carolyn Lam: Wow, Greg, clinically important study there. Well, I'm going to go back to the basic science world and talk about calcineurin. Now, calcineurin has long been implicated in the induction of pathological cardiac remodeling but has not been therapeutically targetable for the prevention of heart failure because of its pleiotropy and our lack of understanding of its specific protein-protein interactions and compartmentation within the cardiomyocyte.
Dr Greg Hundley: Okay. Carolyn, do you want me to give background on calcineurin?
Dr Carolyn Lam: No, Greg, you're off the hook. I'm going to give you some background on calcineurin. So, calcineurin is the calcium-calmodulin-dependent phosphatase that exists as a heterodimer, consisting of a catalytic subunit and a regulatory subunit. Now, of the three catalytic subunit isoforms, alpha, beta, gamma, it's the beta isoform that appears to be the most important for the development of cardiac hypertrophy. Binding of calcium to the calcineurin regulatory subunit enables binding of the calcium-calmodulin complex, thereby releasing auto-inhibition and freeing the enzyme to dephosphorylate downstream substrates. That's the background.
Now, in today's issue, we have this great paper from co-corresponding authors, Dr Kapiloff from Stanford University, and Dr Nikolaev from University Medical Center Hamburg. And, with their colleagues, they described the discovery of a calcineurin catalytic subunit beta binding protein Cdc42-interacting proteins 4, and I'm going to call that CIP4, which functions as a scaffold to sequester the pool of calcineurin near the sarcolemma of cardiomyocytes, where it regulates pro-hypertrophic signaling.
These findings have really important implications for understanding how cardiac calcineurin is selectively activated by stress signals, as opposed to the pleiotropic second messenger, calcium, that really floods the cardiomyocytes during each contractile cycle. Furthermore, the data provide proof of concept for an innovative therapeutic approach, whereby CIP4-anchoring activity is selectively inhibited to block the action of a small pathogenic pool of calcineurin as a means of treating heart failure. How about that? This is really discussed in an elegant editorial by doctors, Woulfe, Travers, and McKinsey.
Dr Greg Hundley: Very interesting, Carolyn. Sounds like another possibility for treating and managing heart failure. Well, let me share with you some of the other findings in our mailbag this week. First, I've got, from Professor Lang Li and Stephen Wiviott, they swap research correspondence regarding the prior publication entitled, Effect of Dapagliflozin on Atrial Fibrillation in Patients with Type 2 Diabetes Mellitus, Insights from the DECLARE-TIMI 58 Trial. And then Professor Laszlo Littmann has a nice ECG challenge for us related to a high-risk ECG that exposed some downstream worrisome vital signs.
Dr Carolyn Lam: In addition, there's a perspective piece by Dr Nambi discussing the fact that a zero-calcium score is desirable, but isn't enough to defer therapy, given that up to one-third of events will occur in this group. There's also an In Depth paper by Dr Borlaug, entitled, “Altered Hemodynamics and End Organ Damage in Heart Failure, The Impact on the Lung and Kidney,” and oh boy, this one is so beautifully illustrated. Just a must read for the understanding of the hemodynamics in the lung and kidney and heart failure. Next is a research letter by Dr Loeys on enrichment of rare variants in the Loeys-Dietz syndrome genes in spontaneous coronary artery dissection, and not in severe fibromuscular dysplasia. And finally, another research letter by Dr Arora on racial differences in serial NT-proBNP levels in heart failure management with insights from the GUIDE-IT Trial. What a rich issue, but let's move on to our future discussion, shall we?
Dr Greg Hundley: You bet, Carolyn.
Well, listeners, we're now getting to our feature discussion and it's very interesting this week where we're going to evaluate aortic aneurysms. And we have with us one of the lead authors of this paper, Dr Charlotte Andersson from Boston Medical Center, and our own Associate Editor, Naveed Sattar from Glasgow, Scotland. Charlotte, welcome to our feature discussion. Could you tell us a little bit about the background and the hypothesis that you put forward with this study?
Dr Charlotte Andersson: The background for this study was based on clinical work and what we observed in clinic. We had a few patients where we had been stricken by the fact that they came in with an acute aortic syndrome and they had a first-degree relative themself with the condition, but they did not look syndromic at all. And we started to wonder, what is the actual risk in the community, in people without obvious syndromic features of suffering from an aortic event itself. And although there are quite a few studies out there that have, to some degree, focused on the familial clustering of aortopathies, there is not a lot of information based on communities and whole entire populations. So we wanted to, frankly, estimate what is the incidence rates of aortic dissections and aortic aneurism in the community if you have a first-degree relative that has suffered from the disease themselves.
Dr Greg Hundley: How you organize your study and what was your population and what was your design?
Dr Charlotte Andersson: This study was actually based on two independent samples. First, we used the Framingham Heart study population that is very densely phenotypes over many years of spanning three generations of participants, where we looked at people who had at least one parent who had an aortic size in the upper quartile index to body-surface area and adjusted for age and sex. And we saw what's the risk of you, as a child, having an aortic size in the same upper quartile.
And second, we looked in the general Danish population, the Danish healthcare system is, as you probably know, governmental funded and we have very good registries of all hospitalizations, all outpatient visits, and so we were able to link more hard clinical events in people with and without a first-degree relative. What we did was we started time when people had an aortic dissection, we identified all the first-degree relatives in these people, and we matched them with up to 10 sex and age match controls from the general population without a first-degree relative with the disease.
Dr Greg Hundley: What did you find?
Dr Charlotte Andersson: We found that in the Framingham sample, if you had at least one parent who belongs into the upper quartile of aortic size, you had an odds ratio of two to three, adjusted for various clinical risk factors, such as hypertension and smoking yourself. And in Danish population, we found that if you had a first-degree relative with an aortopathy, the hazard rates for you developing the disease yourself was almost a tenfold-increase compared to age and sex match controls. And importantly, seemed like hazard ratios use were, more or less, unchanged when we start adjusting various known risk factors, such as bicuspid aortic valve, Marfan syndrome, and Ehlers-Danlos syndrome, normally those kinds of things. And we also found that the younger your proband were at the time of an acute event, the higher was your relative risk yourself. So among people who were below the age of 50 when they suffered an event, the hazard ratios were up to a 50-fold increase.
Dr Greg Hundley: Very nice. Naveed, what attracted you to this article as it was coming through the editorial process? And then second, how do we take the information that Charlotte's just conveyed and will be published here today, how do we take this in the context of what we already know about aortic aneurysms?
Dr Naveed Sattar: I think it's a beautiful study, so well done, Charlotte. I think it's a beautiful fusion. As Charlotte said, an in-depth cohort study, which has got very well-measured parameters of systematic points and a fantastic population-based data set from Denmark, which Sweden shares and Scotland shares and relatively small countries like us share. So small countries like Denmark punch above their weight in these kinds of studies, which is fantastic. But there's a rich seam of research that comes from these, and this is one of them. So I think that fusion of two data sets with different strengths and limitations combined giving off same signals is good.
I think, as Charlotte said, this is the first major population study to look at this question. So there's been people around the world who have got this sense that the aortic aneurism may well be familial, this provides, probably, some of the best data to suggest, yes, it definitely is.
Now the questions going forward is, okay, at what point do you screen everybody's got a family history with a proband, or do you screen those who've got a family history of younger probands? And I think what Charlotte and the team and other people around the world thar are going to look at this say,
"Okay, we now think, in addition to screening, for example, in the UK and the US we probably screen just men above 65, where most of the disease is, do we also then implement screening in younger people with family histories? And who do we screen, and when and how? And do we need to develop some kind of risk score?" And then when we do that screening, what do we do about it? Is going to be the questions and I'm sure Charlotte and her colleagues have thought about these things and it'd be interesting to see what her view is on those things. But I think it was a beautiful study in every sense.
Dr Greg Hundley: So Charlotte, he's really set you up nicely, what study do we need to perform next in this area? What are you and your group thinking about?
Dr Charlotte Andersson: Yeah, I think there are two implications of this study. First, clinical, as Naveed says. They already had a sense that aortic diseases were heritable, and I think these data definitely support that we should probably screen first-degree relatives. And I think, at some extent, this is what the guidelines already encourage us to do. So I'm not sure it would be feasible to randomize people or do a clinical trial where we screen some but not others. I'm not sure that would be ethical. I think the evidence is too strong for familial clustering and that we should probably screen these people.
But I think also, our estimates, they are so strong that I suspect that there are likely more genetic variants associated with non-syndromic aortopathies that we are not aware of just yet. So I think the next step would be to try to disentangle the genetics a little bit more. I have seen some preliminary analysis based on the UK Biobank, for instance, and I think there are more genetic variants to come up with also, more common genetic variants, at least, that we are not aware of just yet. So that would be the next step as I see it.
Dr Naveed Sattar: And that might particularity in younger probands.
Dr Charlotte Andersson: Right.
Dr Naveed Sattar: Those with the younger probands, because it looks like, as you said, the hazard ratio, the risks, are so high, it could also potentially be monogenic, but anyway.
Dr Charlotte Andersson: I agree.
Dr Greg Hundley: Well, Charlotte, Naveed, we really appreciate your time and taking this opportunity to discuss these really interesting findings and helping us understand that, truly, there may be a familial component to understanding this disease process, particularly in patients with aortic aneurysms that may go on to develop aortic dissections.
Well listeners, we hope you have a great week and on behalf of Carolyn and myself, catch you on The Run next week. This program is copyright, the American Heart Association, 2020.