Podcasts about traf2

This week, please join author Jonathan Sterne and Associate Editor Shinya Goto as they discuss the article "Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales." Dr. Carolyn Lam: Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the Journal and its editors. We're your co-hosts. I'm Dr. Carolyn Lam, associate editor from the National Heart Center and Duke National University of Singapore. Dr. Greg Hundley: And I'm Dr. Greg Hundley, associate editor, director of the Pauley Heart Center at VCU Health in Richmond, Virginia. Dr. Carolyn Lam: Oh, Greg, we've got a special treat for everyone today. We have a third co-host and he is none other than Peder Myhre from Norway! Really adding to the diversity of our podcast: me from Asia, you from the US, and Peder from Europe. Welcome, Peder. Dr. Peder Myhre: Thank you so much, Carolyn. It's truly an honor to be here and I'm looking forward to being part of this podcast today. Dr. Carolyn Lam: Awesome. Well, here we go. Looks like we have a feature paper, Greg? Dr. Greg Hundley: Absolutely, Carolyn. Peder, welcome. So, listeners, our feature today will involve COVID-19 and its association with arterial and venous thrombotic diseases. But before we get to that, we're going to all grab a cup of coffee from all over the world and get into some of the other articles in the issue. Peder, Carolyn, how about I go first? My first study involves a prospective cohort of 94,000 individuals from the UK Biobank, who had device-measured physical activity from 2013 to 2015 and were free from myocardial infarction and heart failure. Now, Peder and Carolyn, the study was performed because although objectively measured physical activity has been found associated with acute cardiovascular outcomes, it has not been found associated with heart failure and, of course, a syndrome that's been expanding worldwide. As such this study led by Carlos Celis-Morales from the University of Glasgow aimed to investigate the dose response relationship between device-measured physical activity and heart failure by intensity of the physical activity. Now physical activity was measured with a wrist-worn accelerometer and time spent on light, moderate, and vigorous intensity physical activity was extracted. Incidental heart failure was ascertained from linked hospital and death records. Dr. Peder Myhre: Wow, Greg. That sounds amazing. Tell us, what did they find? Dr. Greg Hundley: You bet, Peder! These investigators found that, compared with participants who undertook no moderate to vigorous intensity physical activity, those who performed 150 to 300 minutes per week of moderate intensity physical activity or 75 to 150 minutes per week of vigorous intensity physical activity were at lower risk of heart failure. Now, interestingly, the association between vigorous intensity physical activity and heart failure was a reverse J-shaped curve with a potentially lower risk reduction above 150 minutes per week. And so, the take-home message for this first paper is that device-measured physical activity, especially moderate intensity physical activity, was associated with a lower risk of heart failure. Probably current vigorous intensity physical activity recommendations should be encouraged, but not necessarily increased. In contrast, increasing moderate intensity physical activity may be beneficial, even among those meeting current recommendations. Dr. Peder Myhre: Wow, Greg. That was a great summary. And the second original research article today is about high density lipoproteins. As you know, raising HDL cholesterol levels to prevent cardiovascular disease remains a hot topic. HDL plays a key role in reverse cholesterol transport and may be cardioprotective and reduce infarct size in the setting of myocardial injury. Lecithin cholesterol acyl transferase, LCAT, is the rate limiting enzyme in the reverse cholesterol transport and a recombinant human LCAT called MEDI6012 has previously been shown to increase HDL cholesterol. So in this study from the corresponding author, Marc Bonaca from University of Colorado School of Medicine, the investigators in the real team is 63B multicenter placebo control trial investigated whether randomized patients to, MEDI6012 or placebo would reduce the infarct size as measured by cardiac MRI, 10 to 12 weeks after the STEMI. Dr. Greg Hundley: Very interesting, Peder. So, MRI assessments of LV mass after PCI. So, what did they find? Dr. Peder Myhre: So, Greg, the authors successfully enrolled 593 patients with a median age of 62 years and 78% males. And the median time from symptom onset to randomization was 146 minutes and only 13 minutes from hospitalization to randomization. And the index MI was anterior in 70% and 65% had TIMI Flow grade 0-1. And then to the main results at 12 weeks, the infarct size did not defer between the treatment group. So that was a 9.7% infarct size for MEDI6012 versus 10.5% for placebo with a P value of 0.79. And there was also no difference in noncalcified black volume. So the authors conclude that enhanced reverse cholesterol transport with recombinant human LCAT did not reduce infarct size or late regression of noncalcified coronary REPL at 12 weeks. Okay, Greg. So tell me about the 3rd paper you have today? Dr. Greg Hundley: Peder, what a great description on that previous paper, beautiful job there. So Peder, this next article pertains to cardio toxicity related to the administration of anthracycline-based chemotherapy. And an example would be Doxorubicin. And this occurs in patients often with certain types of cancer. As you know, Doxorubicin is still utilized for the treatment of leukemia, lymphoma, soft tissue sarcoma and in the setting of adjuvant breast cancer treatment. And so to this end, the authors, led by Lorrie Kirshenbaum from St. Boniface Hospital abstract research, wanted to assess cytokine mediated inflammation in myocellular injury, as a result of some of the inflammation that's induced by the administration of Doxorubicin. So as a little bit of background, cytokines, such as TNF alpha, have been implicated in cardiac dysfunction and toxicity associated with Doxorubicin. Now, while TNF alpha can elicit different cellular responses, including survival or death, the mechanisms underlying these divergent outcomes in the heart really somewhat remain cryptic. The E3 ubiquitin ligase, TRAF2, provides a critical signaling platform for K63 length poly ubiquitin nation of rip K1, crucial for NF-kB activation by TNF alpha and survival. Whether alterations in TNF alpha, TRAF2, NF-kB activation signaling underlie the cardiotoxic effects of Doxorubicin, remains poorly understood. So herein, these authors investigated TRAF2 signaling in the pathogenesis of Doxorubicin cardio toxicity. Dr. Peder Myhre: Oh wow, Greg. So we're talking mitochondrial dysfunction in Doxorubicin cardiomyopathy. So please tell me, what did they find and what were the clinical implications? Dr. Greg Hundley: Very nice. Peder, you remind me of Carolyn, asking me the clinical implications. Okay, so first, in mouse models and in vitro measures in rats, mouse and human pluripotent stem cell derived cardiomyocytes, these investigators monitored TNF alpha levels, LDH, cardiac ultra structure and function, mitochondrial biogenics, as you just suggested, and cardiac cell viability. They found that a novel signaling axis exists that functionally connects the cardiotoxic effects of Doxorubicin to proteasomal degradation of TRAF2. Disruption of the critical TRAF2 survival pathway by Doxorubicin, sensitizes cardiomyocytes to TNF alpha and BNIP3 mediated necrotic cell death. Perhaps, interventions that stabilize TRAF2, so here's the clinical implication, may prove beneficial in mitigating the cardiotoxic effects in cancer patients undergoing anthracycline-based chemotherapy. Dr. Carolyn Lam: So Greg, he may sound like me, but this is me going what an amazing summary and especially in something that is your specialty cardio-oncology, that's amazing. Thank you. Peder, I assume you've got one more paper? Dr. Peder Myhre: So Greg, now I'm going to sound like you and say that we are going to stay within the world of preclinical science. So genome-wide association studies have identified many genetic loci that are robustly associated with coronary artery disease. However, the underlying biological mechanisms are still unknown for most of these loci, hindering the progress to medical translation. And there is evidence to suggest that the genetic influence of coronary artery disease sociability may partly act through vascular smooth muscle cells. So corresponding author, Shu Ye from University of Leicester, performed genotyping, RNA sequencing and cell behavior assays on the large bank of vascular smooth muscle cells with an N of almost 1500. And through these extensive analysis, they saw to identify genes whose expression was influenced by coronary artery disease associated variants. Dr. Greg Hundley: Very nice, Peder. So, more about cardiac gene expression. So, what did they find? Dr. Peder Myhre: Approximately 60% of the known coronary artery disease associated variants show statistically significant effects in vascular smooth muscle cells and the study identified 84 candidate causal genes whose expression quantitative trait, loci signals in vascular smooth muscle cells, significantly co-localized with reported coronary artery disease association signals, of which 38 of them are potentially druggable, so, that was the clinical implications. The authors conclude that a large percentage of coronary artery disease loci can modulate genes, gene expression in vascular smooth muscle cells and influence these cell behavior. Several candidate causal genes identified are likely to be druggable and thus represent potential therapeutic targets. And Greg, accompanying this paper is a beautiful editorial by doctors O'Donnell and Bradner entitled "Bridging the Gap to Translating Genome-Wide Discoveries into Therapies to Prevent and Treat Atherosclerotic Cardiovascular Disease." Dr. Greg Hundley: Very nicely done Peder, very nicely done. Well, as usual, we have some other items, we call it in the mail bag because we receive these wonderful research letters and also research correspondence. So I'll go first. First, Dr. Al-Khatib has a research letter entitled, "Duration of Anticoagulation Interruption before Invasive Procedures and Outcomes in Patients with Atrial Fibrillation Insights from the Aristotle Trial." And also there's a nice ECG analysis by Dr. Tsai entitled, "A Peculiar Wide-Complex Tachycardia During Flecainide Treatment." Dr. Peder Myhre: Nice, Greg, and there's also an exchange on letters to the editors and the response from Professors Zhao and Ding, and again, a response from Professor Zhang regarding the prior letter by Jin et al. pertaining to the previously published article "Micro RNA, 210 Controls, Mitochondrial Metabolism and Protects Heart Function in Myocardial Infarction." Dr. Greg Hundley: Beautifully done, Peder. Oh, wow. Welcome to this team. We're so excited to have you. And now Carolyn, I think we're going to jump over to that feature discussion and learn a little bit more about COVID-19 and arterial and venous thrombotic disease. Dr. Carolyn Lam: You bet! Let's go, Greg and Peder. Now we all know that infection with COVID 19 induces a pro-thrombotic state, but the long term effects of COVID-19 on the incidence of vascular disease, both arterial and venous, remain unclear. That is until today's feature paper. We're so grateful to have corresponding author Dr. Jonathan Stern, from the University of Bristol, as well as our associate editor, Dr. Shinya Goto from Tokai University School of Medicine to join us and discuss this very important paper today. Jonathan, could you start us off on telling us why it's so important to look at this? Haven't we always known that infections, COVID or not, are associated with pro-thrombotic state? So what's so different about what you did and what you found this time? Dr. Jonathan Stern: So, yes, I think we already knew that serious infections, in particular infections leading to hospitalization, can result in thrombotic events, either arterial or venous. And it was also clear from January, February, March 2020, that COVID led to very serious infection and therefore was likely to lead to vascular events. The questions that we set out to address, beyond simply establishing that COVID does indeed do this, was to quantify by how much COVID multiplies the rate at which these thrombotic events occurred, to do that separately for different events, such as myocardial infarction, stroke, venous thromboembolism, pulmonary embolism. And then to importantly, because we analyzed a very large dataset, which we might want to talk about, to try to separate out the amount by which the rating events was multiplied over time and in important subgroups, for example, in hospital people who were hospitalized for their COVID, compared with people who weren't hospitalized for their COVID, by age and sex, and by other demographic characteristics. Dr. Carolyn Lam: I love that, you see, that really set out the novel information this added with, may I add, very important clinical implications, which we'll get to them. You've already teed me up to talk about this 48 million adults that you managed to look at. Oh my goodness! Tell us, how in the world did you do that? Dr. Jonathan Stern: Well, I think the first thing to say is that it's my absolute privilege to talk about this paper on behalf of a really incredible team that put the work together. And a lot of that work, or that work started with really unlocking the power of NHS data because of the COVID pandemic. So in the UK, we have a national health service, free at the point of delivery to everybody. The NHS assembled electronic health records, and there's been a long and proud history of research based on electronic health records in the UK. But for the first time, because of the pandemic, a combined data resource for the whole of England, so that's a population of about 58 million people, was established and that linked primary care data - data from family doctors, data on secondary care hospital admissions, data on COVID testing and subsequently, although it's not the subject of this paper, data on vaccination. So those data were all linked and put into one place within what's called a trusted research environment with very strict controls on what can be output from the environment in order to protect patient privacy. And that was really done during 2020. And then the analyses for this paper took place during 2021, and it was an enormous amount of work by a large and absolutely fantastic team of people across multiple UK universities and national health service institutions. Dr. Carolyn Lam: Wow. Bravo! We talk about big data, we talk about using it. I trained in the NHS system. Who knew that this could come out to reveal such important results? So thank you for that as a background, but now, tell us what you found please? Dr. Jonathan Stern: So we found that rates of these conditions, they were primarily acute lymph infarction and ischemic stroke, which we grouped together with other conditions as arterial thrombotic events, and then deep vein thrombosis and pulmonary embolism, which we grouped together with other conditions as venous events. And we found that rates were substantially multiplied immediately after a diagnosis of COVID by up to 748 times, that the amount by which rates were multiplied diminished with time since COVID, but importantly that even six months to a year after that first diagnosis of COVID, rates of venous events were still about double in people who'd had COVID, compared to people who had COVID. And we found, it seemed quite clear that the persistence of the elevated risk was longer for venous events than for arterial events. Dr. Carolyn Lam: Just really fascinating results and Shinya, could I ask, what are your thoughts on this? And as you were managing this paper, the implications? Dr. Shinya Goto: First of all, thank you very much, Jonathan, for choosing saturation for your great paper. I'm handling quite a lot of papers, but your paper was very attractive. As Carolyn mentioned, it's huge data! 48 million, it's surprising, and also you also pick up booster rate of arterial embolism event for years, and you have also shown adjusted rate is initially increased quite a lot and then decreased gradually. And even after two months, three months still, there is a persisted higher risk. And as you mentioned, for the venous thrombo embolism, it's persisted for more than year to year. It's surprising. COVID-19's a different disease. Perhaps COVID-19 infection cuts to the vascular endarterial cell, perhaps, your research raised a lot of research questions, like endarterial damage induced by COVID-19 in the past 6 months; I would say more than half a year to one year. So that mechanistical insight is very important. And you raise a lot of any clinical questions. Dr. Jonathan Stern: Well, thank you very much for your kind words and you are right, I think we are left with questions about maybe in three areas. Firstly, for how long is there an elevation in risk? I should probably say, for those who haven't read the paper, that these results relate to events that occurred in England and Wales during 2020. And so that is in an era before vaccination and when we were dealing with the original variant, and to some extent, the alpha variant. So we are still waiting to see what the implications were over longer periods, and we will be doing that, we will be extending follow up. In fact, we are at the moment extending those results. I think, secondly, we are left with questions about the mechanisms, which you articulated, and thirdly, there's the question about, well, what are the implications for clinical management of patients with COVID-19? And in particular, for patients who've had severe COVID-19, for example, severe enough to be hospitalized for it? Dr. Shinya Goto: Yeah, you have also showed a very important point that even known hospitalization for COVID-19, the risk of thrombosis becomes high. So it's very surprising. And even non-hospitalized patients have a higher risk of thrombosis. That is probably the huge difference between other virus infections and COVID-19. Dr. Jonathan Stern: Yes. The good news, if you weren't hospitalized for your COVID, is that the elevation in risk declines more rapidly for people with less severe COVID who weren't hospitalized than for people with more severe COVID who were hospitalized. But nonetheless, as you say, particularly in the first week, two weeks, three weeks after COVID, there is a clear elevation in the risk of both arterial and venous events, even if you were not hospitalized for your COVID. We should probably also bear in mind that these results for 2020, when there were severe constraints for some of the time on health service resources. So you probably had to be pretty sick to get hospitalized at that time. Dr. Carolyn Lam: That was a very important caveat that you just highlighted. So thank you for contextualizing those findings for us, Jonathan, but then I kind of wish all podcast guests were like you, and you already asked a question, I was going to ask you. Which is, okay, so what's the clinical implication? Should we all be taking some low dose NOAC or aspirin? Whether you're hospitalized or not? Or if you were in 2020? Because, jokes aside, I know that you found some very important risk factors? Or these events which had clinical implications? Could you expand on it? Dr. Jonathan Stern: So maybe I'd start by saying that we didn't find that these patterns varied dramatically either by sex or by age. And in fact, when we were planning the analyses, I was convinced that we would see dramatic differences in these hazard ratios by age. And, broadly speaking, the facts on a multiplicative scale, the amount by which your rate is multiplied, looked similar across age groups and by sex. On the other hand, we did see the amount by rates of arterial and venous events were multiplied, appeared greater in people of Asian ethnicity or Black ethnicity than in people of White ethnicity. A counterintuitive finding was that the amount by which your rate was multiplied is lower, if you've had a prior event than if you hadn't. Those are the sorts of extents to which we can say something about how your own characteristics predict the consequences once you've had COVID. In terms of management, obviously the pandemic has been tumultuous for medicine and for medical research and things have moved on greatly since the pre-vaccination era, 2020 and early 2021, to which these analyses relate. So the first thing to say is, don't get hospitalized with COVID, and the best way to not be hospitalized with COVID, is to be fully vaccinated for COVID. And that's a message that I think the whole of the medical profession has communicated loudly and clearly for a long time now. So the second thing is, well, okay, what about if, nonetheless, you got COVID, particularly severe COVID, and we discussed this in the team extensively, and I particularly want to mention the senior clinical author, Dr. Will Whiteley from the University of Edinburgh in this regard, and I think the main message here is that risk factor management, cardiovascular risk factor management is always important, but it's probably particularly important in people who've had severe COVID to review risk factor management and make sure that existing guidelines in terms of cholesterol lowering, blood pressure lowering and so on, are being adhered to. We don't... So the most important thing is adherence to existing cardiovascular risk management guidelines. I think we don't have evidence that specific additional interventions are indicated in people who've had COVID, and COVID now in the era of Omicron and widespread vaccination is not the same as COVID during 2020. Dr. Shinya Goto: Jonathan, you have raised a very important issue. I strongly recommend all audiences to read this paper. We have to know persistent or higher risk of myocardial infarction, ischemic stroke, may be controlled more regularly controlled. Don't fear the COVID-19 infection to visiting the healthcare professional. In my country, some of the population stopped coming to the healthcare professional because they fear so much about infection from the hospital or clinic. But it's very important to keep that regular control like static and blood pressure control. Maybe we don't have that data about aspiring or not, but strong message your paper gave is that risk factor control after COVID-19 is very important. Dr. Jonathan Stern: I completely agree. Dr. Carolyn Lam: And I would add to that, remember the days when people were stopping their ACE inhibitors and so on for those fear? So what a great message and thank you for giving us a little bit of a peek into the future of what you're planning next with more follow up, in a population that is vaccinated from a different strain perhaps. And I think this still encourages hopefully more trials and research into this whole area of how we should be managing these patients. Well, thank you so much both of you for discussing this very, very current relevant, important paper. Thank you for publishing it in circulation with us. And to the audience, thank you for joining us today. From Greg and I, you've been listening to Circulation on the Run, and don't forget to tune in again next week. Speaker 6: 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, please visit ahajournals.org.

Dr Carolyn Lam:     Welcome to Circulation on the Run, your weekly podcast summary and backstage pass to the journal and its editors. And Dr. Carolyn Lam, Associate Editor from the National Heart Center, and Duke National University at Singapore.                                 What is the effect of obesity and underweight status on perioperative outcomes of congenital heart operations?                                 Our feature paper this week sheds light from the Society of Thoracic Surgeons Database. More soon, right after these summaries.                                 The first original paper highlights the role of micro RNAs in metabolic remodeling and heart failure. As a reminder, micro RNAs are small, noncoding RNAs important in post transcriptional modification and influencing many cellular processes simultaneously.                                 First author, Dr. Heggermont, corresponding author, Dr. Heymans, and colleagues from Maastricht University in the Netherlands use mice subjected to pressure overload by means of endotension to infusion or transverse aortic constriction. They show that micro RNA 146A was up regulated in whole-heart tissues in these murine pressure overload models, as well in left ventricular biopsies of aortic stenosis patients. Over expression of micro RNA 146A in cardio cardiomyocytes provoked cardiac hypertrophy and left ventricular dysfunction in vivo, whereas genetic knockdown or pharmacological blockade of micro RNA 146A blunted the hypertrophic response and attenuated cardiac dysfunction in Vivo.                                 Mechanistically, micro RNA 146A reduced its target dihydrolipoyl succinyltransferase or DLST, a mitochondrial protein that functions as a TCA cycle transferase. DLST protein levels were reduced in pressure overload mice, while they were partially maintained in micro RNA 146A knockout mice. Furthermore, overexpression of DLST in wild type mice, protected against cardiac hypertrophy and dysfunction in Vivo. Thus, micro RNA 146A and its target DLST are important metabolic players in LV dysfunction. These results also opened the door to novel therapies to treat metabolic disturbances and improve energy efficiency of a failing heart.                                 Program cell death is critically involved in ischemic cardiac injury, pathologic cardiac remodeling, and heart failure progression. Our next paper sheds light on the regulatory mechanisms of necroptosis and its significance in the pathogenesis of heart failure. Using genetic mouse models, first authors Dr. Guo and Yin, corresponding author Dr. Liu, and colleagues from University of Washington in Seattle, identified a critical role for a tumor necrosis factor receptor associated factor 2 or TRAF2 in myocardial survival and homeostasis by suppressing necroptosis.                                 The authors delineated an important TRAF2 mediated NF-KB independent pro-survival pathway in the heart by suppressing necroptotic signaling. They identified novel molecular mechanisms whereby TRAF2 suppressed TNF receptor 1 mediated, receptor interacting protein 3 dependent necroptosis, which is critical for myocardial survival and homeostasis. Thus, this finding suggests that the necroptosis suppressing TRAF2 signaling pathway and its effectors may serve as novel therapeutic targets for pathologic cardiac remodeling and heart failure.                                 Our next paper tells us that cerebral hyperperfusion may be associated with accelerated cognitive decline and an increased risk of dementia in the general population. First author Dr. Walters, corresponding authors Dr. Ikram, and colleagues from Erasmus University Medical Center in Rotterdam, The Netherlands, measured cerebral blood flow by 2D phase contrast MRI in non-demented participants of the population based Rotterdam study. A 4,759 participants with a median age of 61 years, and a median follow up of 6.9 years, 123 participants developed dementia.                                 Lower cerebral perfusion was associated with higher risk of dementia and this risk was even higher with increasing severity of white matter hyperintensities on MRI. At cognitive reexamination after an average of 5.7 years, lower baseline perfusion was associated with accelerated decline in cognition, which was similar after excluding those with incident dementia, and again, most pronounced in individuals with higher volumes of white matter hyperintensities.                                 Thus, lower cerebral perfusion was associated with accelerated cognitive decline and increased risk of dementia in the general population. This association was modified by hypertension and cerebral small vessel disease, possibly reflecting impaired arteriola and capillary function. This paper calls for further long term study and evaluation of optimizing cerebral perfusion as a means to prevent cognitive deterioration, for example, in patients with heart failure or carotid artery stenosis.                                 Well, that wraps it up for our summaries. Now for our feature discussion. For today's feature discussion, we will be looking at data from the Society of Thoracic Surgeons Database. This time looking at the effect of body mass index on perioperative outcomes of congenital heart operations in children, adolescents, and young adults. To discuss this, we have none other than the first and corresponding author, Dr. Michael O'Byrne from Children's National Medical Center in Washington D.C., as well as Dr. Naveed Sattar, Associate Editor from University of Oxford. Welcome gentlemen. Dr Michael O'Byrne:       Good morning. Dr Naveed Sattar:            Good morning. Dr Carolyn Lam:                Michael, we know that extreme body mass indices, very high or very low, has been associated with increased risk of at first, perioperative outcomes in mainly older adults undergoing cardiac surgery. We also know about the obesity paradox in conditions like heart failure, so why was it important to look at this specific group of patients? Congenital heart patients and children, adolescents, and young adults? Dr Michael O'Byrne:       Yeah, I think that as a pediatric cardiologist, a lot of the data that we use to guide our management is extrapolated from adult studies. However, in this particular case, it wasn't clear necessarily that adult data would necessarily be applicable to children and adolescents and young adults. We are aware that there are epidemiologic trends that congenital heart disease population ages and there are also in increasing problems of obesity among children in the United States.                                 The convention wisdom among surgeons in the United States is that obesity would increase perioperative risk and the thought is that some combination of exposure to hypertension and diabetes and peripheral vascular disease might impede wound healing and that body habit as itself might be a risk for the technical approach in wound healing. Acknowledging that there's a lot of evidence both for extreme BMI being a risk in surgical patients and adults, but also the idea that obesity paradox might be important in children because the biological mechanisms might be different.                                 Children themselves are exposed, their sort of dose response or dose exposure is less, they're younger, and so haven't been obese for a prolonged period of time, so that the integrated effect of having diabetes, hypertension, and obesity might be less. At the same time, we also acknowledge that in children with heart disease, we have congenital cardiac disease, the same issues with cachexia and frailty are present. i.e. that children with very low body mass index might be assigned to their own medical frailty, or a part of a heart failure cachexia syndrome.                                 One of the challenges in dealing with children with congenital heart disease, however, as you know is that its rarer than cardiac disease of the aging and additionally, that the population is very heterogenous in terms of the actual defects that are present and the surgeries that are performed. It was relevant to look and see over a wide range of sort of technical complexity surgeries with a wide range of sort of intrinsic preoperative risk of perioperative outcome, whether or not BMI would be associated with an adverse outcome. Either operative mortality in this case, or a composite outcome of mortality, major adverse events, and wound infection. Dr Carolyn Lam:                Wow, that makes a lot of sense and congratulations. This is not just the first, it's huge and really comprehensive. Could you just tell us a little bit more about what you did and what you found? Dr Michael O'Byrne:       I think as this point, I'd have to acknowledge that the challenges that we described in terms of both a sample size and in terms of getting a representative sample, is a constant challenge in our field and we have to give credit to my co-authors Marshall and Jeff Jacobs for their work in developing the collaboration that allowed for the STS Congenital Heart Surgery Database to exist. Also, on top of shepherding the database, their research, along with the people at Duke Clinical Research Institute, they've developed a robust risk stratification model for mortality that we utilize as part of this study. Without that, this would be really be very challenging.                                 What we did is performed an observational cohort study using the STS Congenital Heart Surgery Database to look at the risk of perioperative mortality and composite outcome in patients undergoing surgery in the United States between 2010 and 2015. We looked at both the actual events, the sort of observed events, in terms of mortality and adverse events, and then created multivariate models to adjust for the known covariance.                                 We hypothesized that extreme BMI, either very high or very low, would be associated with increased risk of mortality and increased risk of that composite outcome. What we found that operative mortality and that perioperative adverse events occurred more frequently in obese and severely underweight subjects. However, because they have an unequal distribution of potentially important covariance, we used multivariate modeling to adjust for those covariance.                                 Our multivariate models for death, however, the severely underweight subjects had an odds ratio of 1.4 and obese subjects had an odds ratio of 1.3, but neither was specifically significant in that context. We sort of anticipated that with a possibility given the very low event rate. That's the reason we've used a composite outcome, a higher event rate.                                 For that composite outcome, in both different versions of the multivariate model that we used, the severely underweight subjects had an odds ratio of 1.5, underweight subjects had an odds ratio of 1.3, and obese subjects had an odds ratio of 1.2. An increased risk in all three of those populations of interest relative to normal weight or just overweight subjects. Dr Carolyn Lam:                We're always saying that at circulation we do want to publish papers that have direct and important clinical implications, so Naveed, could you share some thoughts on what this means clinically? Dr Naveed Sattar:            Yeah, I think they went through the review process and I think the paper was very well written. I think Michael and his colleagues clearly understood the strength and the limitations of the data so that you can only ever itself prove associations here and therefore, clinically when we push them on trying to make clinical inferences, I think clearly they recognize that once they find associations between obesity and adverse outcomes and underweight.                                 What they need to do next, now this is a paper that then leads you to think, "Well actually, I need to do some clinical trials to prove that module ..." You're preventing these outcomes or in very under knowledge where they're actually increasing the BMI but improving their nutrition, cannot also improve outcomes following surgery. Now those are tough things to do. Michael, what do you think from some of the clinical inference? My inferences were the associations were there, particularly for the normal [inaudible 00:12:35] outcomes, but actually to prove that, to make a difference, you probably might need to do some intervention trials or is that how you take it as well? Dr Michael O'Byrne:       I agree with you 100%. I think that as an epidemiologist, I think that what we see in an observational study like this is an association. The two next levels of research that are necessary at this point are to see whether or not in this population BMI is a modifiable factor in the short run before surgery, or even in the long run. And the second question to answer is whether those adjustments in BMI, if they are achievable, affect outcome with surgery. Absolutely.                                 It's a tremendous challenge, both logistically in organizing a study, and honestly, in terms of capturing a cohort that would be large enough, given that this is almost 100% of the surgeries that occurred over a six year period in the United States. Dr Naveed Sattar:            I looked at it and thought, "Well, the mortality association once you adjusted were not quite significant but are there any individuals you would not do surgery on based on their BMI based on these results? Dr Michael O'Byrne:       The motivation for the study is exactly to try to begin to shed light on that kind of question. I think that it might be what I would call a tiebreaker potentially, if you have a situation where a patient is near meeting criteria but isn't quite at a place where you need to do surgery at that point. It might dissuade you from proceeding immediately potentially pursuing a course that might adjust their BMI in the correct direction.                                 At the same time also, in a patient who's underweight particularly to evaluate whether their medical regimen has been optimized and if there are other residual lesions that can be addressed in a non-surgical or medical fashion. Dr Naveed Sattar:            I suppose the other trick with this type of research research is always trying to make sure that people understand these are the associations and not trying to attribute causality because it's always physical, isn't it? But I think you and your team did that very well and I'm sure we had a back and forth with review but I think your discussion section, your limitation section, is beautifully written and covers those kinds of caveats, which I think is important as well. Dr Michael O'Byrne:       I thank you for that. That's very complimentary and we certainly strived for that, but I think that you as an editor, and also in terms of the reviewers also, were very helpful in that sort of collaborative process to try to make sure that we're communicating it. It's not always clear in a project that takes months and years to finish when you're writing it necessarily, you may be constantly aware of trying to be clear in your communication but it's also helpful to have a reviewer from the outside carefully read the study. Dr Carolyn Lam:                That's wonderful and Michael, may I just join Naveed in congratulating you on beautiful paper? And maybe just one other little question, did you have any insights into the mechanisms of increased risk for composite events in the extremes of BMI? Dr Michael O'Byrne:       I think it's an important question. There's been a tremendous amount of research in adult cardiac disease about whether it is the BMI as a steady state or BMI changes immediately before and after surgery that are relevant in this case. From this kind of observational study, it's very hard and very challenging to try to make any sort of inferences about the causes. It would be an important part of any study moving forward to include ways to investigate that, and honestly, as an interventional cardiologist and epidemiologist, I probably would defer to Naveed, he might have more cogent and logical ideas about that than I do. Dr Naveed Sattar:            We've had lots of research from a whole variety of researchers. We all understand it's finally serious but recognize it's difficult, so one of the ways moving forward and I think Michael and his colleagues have this is if you have serial BMI data prior to surgery, that could try and inform on reverse causality because of the low BMI, but in terms of the mechanisms, remember these are associations, but I think mechanisms are well covered if you are obese and clearly you have risk factors for death, across the vasculature, across the cardiac functions, across the whole variety of things.                                 We know those mechanisms, question is, to what extent are they actually operating and causing increased risk in the surgical arena and that's a really tough ask. I think people can come up with a multitude of mechanisms. I think the key things, like this particular paper, is that there are potential mechanisms but these are associations ... Look, this is what we found, and clinically now we need to try and address this within the following types of interventions or at least provide some guidance to colleagues and clinicians.                                 Exactly as Michael says, if there is somebody who is approaching surgery whose quite obese, perhaps they should try and intervene to try and lessen their weight for a short period of time prior to [inaudible 00:17:07], you know what happens. It would be nice to do some big trials but I think doing trials in this area is going to be really tough, but with imagination, with good collaboration across centers, trials are not impossible. I think they can be done. Dr Michael O'Byrne:       Naveed, I think, actually articulated what I think is both the difficulty of doing that trial but also the importance of it. I think that looking at ... In these databases, we don't have a serial BMI and I think that's an important missing piece of information that we tried to address in our discussion and I think it's something that would be really valuable moving forward. And certainly testing interventions, whether they're medical, interventional, or surgical, to help these patients who are obese either lose or maintain an appropriate weight is the next step.                                 On the converse side, this research highlighted to me the prevalence of chachectic or underweight patients in our population and it's something that outside of the infant period, we don't necessarily think about tremendously and we don't think about it as a modifiable factor. I think that's another group of patients who also deserve some attention. Dr Carolyn Lam:                Listeners, you've been listening to Circulation on the Run. I'm sure you learned a lot as I did. Don't forget to tune in again next week.  

Paul DiCorleto explains how nonmuscle myosin limits proinflammatory signaling by tumor necrosis factor receptor 2.

Das Epstein-Barr Virus (EBV) ist mit einer Reihe von lebensbedrohlichen Krankheiten assoziiert. Dazu zählen unter anderem Nasopharynxkarzinome, Hodgkin-Lymphome und lymphoproliferative Erkrankungen nach Organtransplantationen. Dennoch gibt es bisher keinen wirksamen Therapieansatz, der sich spezifisch mit der Rolle von EBV in diesen malignen Erkrankungen auseinandersetzt. Das latente Membranprotein 1 (LMP1) ist das primäre Onkogen von EBV und essenziell für die Transformation von B-Zellen durch das Virus. Für eine effiziente Transformation von Zellen ist die Aktivierung verschiedener zellulärer Signalwege durch LMP1 notwendig. LMP1 besitzt jedoch keine enzymatische Aktivität und die Induktion der Signalwege ist somit abhängig von der Rekrutierung verschiedener zellulärer Adapterproteine. Die Ausbildung der notwendigen Signalkomplexe wird über zwei C-terminale Aktivierungs-Regionen (CTAR1 und CTAR2) vermittelt. Verschiedene Mitglieder der Tumornekrosefaktor (TNF)-Rezeptor-assoziierten Faktoren (TRAF)-Protein-Familie spielen bei der Induktion der Signalwege durch diese beiden CTAR-Domänen eine zentrale Rolle. Nach grundlegenden Protein-Protein-Interaktionsstudien zwischen LMP1 und rekombinanten TRAF-Proteinen wurde hier die Interaktion zwischen TRAF2 und LMP1 als Zielstruktur für Inhibitoren vorgestellt. TRAF2 ist essenziell für die Aktivierung des NF-κB-Signalweges durch die CTAR1-Domäne und somit für das Überleben EBV-transformierter Zellen. Die Bindung von TRAF2 an LMP1 wurde biochemisch näher charakterisiert und die gewonnen Erkenntnisse verwendet, um ein System zu etablieren, mit dem Inhibitoren gegen den Komplex aus LMP1 und TRAF2 identifiziert werden können. Dieses ELISA-basierte System erfüllt die Anforderungen, die allgemein an hochdurchsatzfähige Systeme gestellt werden. In einem Pilotscreen einer Bibliothek mit Naturstoffen wurden Substanzen identifiziert, die die Bindung von TRAF2 an LMP1 in vitro inhibierten. Die potenteste Substanz inhibierte die Interaktion von TRAF2 und LMP1 mit einem IC50 von 8 µM in diesen in vitro Studien. Weiterhin zeigte diese Substanz eine spezifische biologische Wirkung auf die Vitalität von EBV-transformierten B-Zellen. Zusätzlich konnte in den Protein-Protein-Interaktionsstudien zwischen den verschiedenen TRAF-Proteinen und LMP1 erstmals eine direkte Bindung von TRAF6 an LMP1 gezeigt werden. Entgegen der bisherigen Modellvorstellung, nach der TRAF6 indirekt über Adapterproteine an LMP1 gebunden wird, konnte hier gezeigt werden, dass TRAF6 direkt an die LMP1-Sequenz P379VQLSY innerhalb der CTAR2-Domäne bindet. Diese Sequenz ist essenziell für die Aktivierung verschiedener TRAF6-abhängiger Signalwege durch die CTAR2-Domäne. Auf der Oberfläche von TRAF6 wird die Bindung an LMP1 durch dieselbe Bindetasche vermittelt, über die auch die Interaktion mit zellulären Rezeptoren stattfindet. Diese direkte Interaktion zwischen LMP1 und TRAF6 ist wichtig für die Aktivierung des NF κB-Signalweges durch die CTAR2-Domäne. TRAF6-Mutanten, die nicht mehr in der Lage waren, mit LMP1 zu interagieren, waren ebenfalls nicht mehr dazu fähig, die Induktion von NF κB-Signalen durch die CTAR2-Domäne von LMP1 in embryonalen TRAF6-/- Mausfibroblasten wiederherzustellen. Ebenfalls konnte neben der direkten Bindung von TRAF6 an LMP1 hier eine weitere neue Protein-Protein-Interaktion für TRAF6 beschrieben werden. TRAF6 bindet direkt an das TNF-Rezeptor-assoziierte Todesdomänenprotein (TRADD). Die Interaktion zwischen TRAF6 und TRADD unterscheidet sich jedoch von der Bindung anderer TRAF-Proteine an TRADD. Die in vitro Studien zeigten, dass TRAF6 in der Lage ist, sowohl mit Teilen des N-Terminus, als auch mit Teilen des C-Terminus von TRADD zu interagieren. Diese bisher nicht beschriebene Art der direkten Interaktion von TRAF6 mit TRADD eröffnet neue Einblicke in den Aufbau des LMP1-Signalkomplexes.

In this work, we were able to take advantage of a deregulated wnt signaling pathway – a condition which is found in most gastrointestinal cancers, in particular in colorectal carcinomas. In order to restrict reporter gene expression to the desired cell type, we utilized the β-catenin dependent CTP4-promoter to restrict the expression of Firefly Luciferase and enhanced green fluorescent fusion protein (EGFPLuc) to cell lines with deregulated wnt signaling including SW480, LS174T, HepG2, Coga2 and Coga12. Stable cell lines containing this CTP4-driven EGFPLuc construct were established with the help of a lentiviral vector to monitor wnt activity by transgene expression. With these stably transduced cell lines, we performed a therapeutic target screen via siRNA-mediated knock-down of a number of potentially therapeutic targets within the wnt pathway – osteoprotegerin (OPG), Traf2 and Nck-interacting kinase (TNIK), SRY-related HMG-box (Sox2), protease-activated receptor 1 (PAR-1), β-catenin and transcription factor 4 (TCF4). The in vitro screening system was utilized as a prevalidation tool for therapeutically relevant targets. The degree of interference of our novel targets was determined and the search for a suitable siRNA target in colorectal cancer cells was narrowed down to β-catenin, PAR-1 and TNIK. As proof of principle the siRNA-mediated knock down of β-catenin was verified on mRNA and protein level in LS174T cells. After the initial read-out of various cell lines with different siRNAs has been established via the reduction of Luciferase expression levels, the biological effect of these targets were validated. For this purpose colony formation and cell motility/invasion assays were conducted for all relevant target cell lines. Furthermore in the in vitro experiments, the tumor-selectivtiy of the CTP4-promoter was employed in the delivery of the cytotoxic protein diphteria toxin A (DTA) in colorectal cancer target cells. Data evaluation of all in vitro assays pointed at reduced levels of proliferation, invasive behavior and aggressiveness, which yielded three candidates (PAR-1, TNIK and β-catenin) considered as viable for a treatment attempt in vivo. In the in vivo experiments, systemic delivery of siRNA against β-catenin, sticky siRNA targeting PAR-1 and plasmid DNA encoding for CTP4 controlled DTA were evaluated in a disseminated liver metastasis model of LS174T colorectal cancer. Specific knock-downs of β-catenin and PAR-1 were achieved which was confirmed via mRNA analysis. As for CTP4-DTA pDNA delivery the overall tumor load of the liver was reduced without any significant systemic toxicity, indicating specific DTA expression in tumor tissue. Also knock down of PAR1 using sticky siRNA significantly reduced tumor growth. All in all, the therapeutic effect of PAR-1 and β-catenin knock-down could be verified in various in vitro assays analyzing invasive behavior and anchorage independent growth and ultimately also in vivo. The tumor-specific expression of DTA pDNA could also be confirmed in vitro and was further investigated in an orthotopic liver dissemination model in NMRI nude mice.

TRADD spielt als Adaptermolekül eine zentrale Rolle in der Signaltransduktion von LMP1 und TNF-Rezeptor 1. Während es allerdings durch den TNFR1 neben der Aktivierung verschiedener Signalwege auch zur Induktion von Apoptose und Nekrose kommt, handelt es sich bei LMP1 um ein Protein mit transformierendem Potential. Bei den jeweiligen TRADD-Bindestellen von LMP1 und TNFR1 handelt es sich um zwei strukturell vollkommen unterschiedliche Domänen. Und auch auf der Seite von TRADD wird die Bindung über zwei verschiedene Domänen vermittelt. Im Rahmen dieser Doktorarbeit sollte die Frage beantwortet werden, ob die TRADD-Bindestelle intrinsisch die biologischen Effekte der Signaltransduktion bestimmt oder ob diese durch den Rezeptorkontext festgelegt werden. Zur Beantwortung dieser Frage wurde in einem Domain Swapping Experiment die TRADD-Bindestelle des konstitutiv aktiven LMP1-TNFR1 sowie des TNFR1 gegen die putative TRADD-Bindestelle von LMP1 ausgetauscht. Es konnte erstmals gezeigt werden, dass die Aminosäuren 370-386 die vollständige TRADD-Bindestelle von LMP1 umfassen. Weiter konnte gezeigt werden, dass diese Aminosäuren im LMP1-TNFR1- sowie im TNFR1-Kontext ausreichend sind, um den NF-κB und den JNK1 Signalweg zu aktivieren. Die Aktivierung des JNK1 Signalweges durch LMP1-TNFR1-CTAR2 verläuft unabhängig von TRAF2 und abhängig von TRAF6 und auch die Aktivierung des NF-κB Signalweges durch dieses Rezeptorkonstrukt verläuft TRAF6-abhängig. Damit konnte gezeigt werden, dass die LMP1-spezifischen Charakteristika der Signaltransduktion durch die TRADD-Bindestelle festgelegt und mit ihr zusammen übertragen werden. Obwohl die Aminosäuren 370-386 von LMP1 funktionell sind, sind sie auch im LMP1-TNFR1 sowie im TNFR1 Kontext nicht in der Lage Apoptose zu induzieren. Damit konnte im Rahmen dieser Doktorarbeit gezeigt werden, dass die Aminosäuren 370-386 von LMP1 intrinsisch und unabhängig vom Rezeptorkontext den nicht-apoptotischen Phänotyp der Signaltransduktion festlegen. Außerdem wurde im Rahmen dieser Doktorarbeit die Beteiligung von TRAF7 an der Signaltransduktion von LMP1 untersucht. Dazu wurde traf7 aus einer cDNA kloniert. Zusätzlich wurden verschiedene Deletionsmutanten sowie Fusionen mit dem fluoreszierenden Protein mRFP hergestellt. Es konnte eine Threonin-Phosphorylierung von TRAF7(1-383) nachgewiesen werden. Mittels Fluoreszenzmikroskopie konnte eine Lokalisierung von TRAF7 in vesikulären Strukturen beobachtet werden. Eine Mutante, der der RING- sowie der Zink-Finger fehlen, zeigte hingegen eine gleichmäßige zytosolische Verteilung. Außerdem konnte in dieser Doktorarbeit mit Hilfe von spezifischer siRNA gezeigt werden, dass TRAF7 an der Aktivierung des JNK1 Signalweges durch LMP1 beteiligt ist.

Mutationen im Parkin-Gen sind verantwortlich für eine autosomal rezessiv vererbbare Form der Parkinson-Erkrankung. Der Funktionsverlust von Parkin spielt eine zentrale Rolle bei der Pathogenese. Zu Beginn der vorliegenden Arbeit war lediglich bekannt, dass Parkin eine E3-Ubiquitin-Ligase-Aktivität besitzt und dass ein Funktionsverlust von Parkin offensichtlich zur Parkinson-Erkrankung führen kann. In der vorliegenden Doktorarbeit wurden zwei fundamentale Themenbereiche der Parkin-Forschung bearbeitet: 1. Die Analyse der Mechanismen der Inaktivierung von pathogenen Parkin-Mutanten. 2. Untersuchungen zur physiologischen Funktion von Parkin. Im ersten Teil dieser Arbeit konnten verschiedene Mechanismen der Parkin-Inaktivierung aufgeklärt werden, welche den Funktionsverlust von Parkin erklären. Pathogene C-terminale Deletionsmutationen führten zur Missfaltung und Aggregation von Parkin. Im Gegensatz zu Wildtyp-Parkin nahmen diese Mutanten spontan eine missgefaltete Konformation an und lagen in Form von zytosolischen Aggregaten vor. Pathogene Punktmutationen in der N-terminalen Ubiquitin-like (UBL)-Domäne verringerten die Stabilität von Parkin. Diese Mutanten wurden rasch über das Proteasom abgebaut. Im Rahmen dieser Untersuchungen konnte ferner gezeigt werden, dass in vivo zusätzlich zu Volllängen-Parkin eine kleinere Parkin-Spezies entsteht. Diese kleinere Parkin-Spezies ist gekennzeichnet durch das Fehlen der N-terminalen UBL-Domäne und wird aufgrund des Vorhandenseins eines internen Startcodons an Position 80 der humanen Parkin-Sequenz gebildet. Der zweite Teil der Arbeit konzentrierte sich auf die physiologische Funktion von Parkin. In Zellkultur-Modellen konnte festgestellt werden, dass Parkin nach Stressbehandlung hochreguliert wird und vor Stress-induziertem Zelltod schützt. Die Analyse von protektiven Signaltransduktionswegen konnte erstmalig zeigen, dass die Parkin-mediierte Aktivierung der NF-kappaB-Signaltransduktion essentiell ist für das neuroprotektive Potential von Parkin. Die vorliegende Arbeit lieferte Evidenz dafür, dass die E3-Ubiquitin-Ligase Parkin die NF-kappaB-Signalkaskade durch eine vermehrte regulierende Ubiquitylierung der zwei Signalmoleküle, IKK und TRAF2 aktiviert. Die in dieser Doktorarbeit dargestellten Ergebnisse ermöglichen Einblicke in die physiologische Funktion von Parkin sowie die Mechanismen, die zum Funktionsverlust von Parkin führen. Darüber hinaus können diese neuen Erkenntnisse einen Beitrag leisten zum besseren Verständnis pathogener Mechanismen der Parkinson-Erkrankung.

Das Adapterprotein TRADD spielt eine zentrale Rolle in der Signaltransduktion des zellulären TNF-Rezeptors 1 (TNF-R1) und des Latenten Membranproteins 1 (LMP1) vom Epstein-Barr-Virus. Im Gegensatz zur Situation am TNF-R1 bindet TRADD an LMP1 nicht über seine Todesdomäne, sondern über seinen N-terminalen Bereich. Betrachtet man die Zusammensetzung der TNF-R1 und LMP1 Signalkomplexe und der von diesen beiden Membranproteinen aktivierten Signalwege, sind ganz offensichtlich viele Gemeinsamkeiten zu erkennen. Dennoch ist die biologische Funktion dieser beiden Membranproteine zum Teil sehr unterschiedlich. Während der TNF-R1 maßgeblich an der Regulation inflammatorischer Prozesse beteiligt ist und in bestimmten Situationen die Zelle in den programmierten Zelltod (Apoptose) treiben kann, ist LMP1 essentiell an der Immortalisierung von B-Lymphozyten durch das Epstein-Barr-Virus beteiligt. LMP1 ist ein virales Onkogen, das die Expression mitogener Faktoren induziert und gleichzeitig Apoptose und Seneszenz inhibiert. Die Aufklärung der Signaltransduktion dieser beiden Membranproteine auf molekularer Ebene steht seit vielen Jahren im Zentrum intensiver Forschung. Das Ziel der vorliegenden Arbeit war es, die Rolle von TRADD in der Signaltransduktion von TNF-R1 und LMP1 zu klären. Da das einzig wirklich zuverlässige System zur Untersuchung der TRADD Proteinfunktionen ein TRADD „knockout“ Zellsystem ist, wurde im Rahmen dieser Doktorarbeit erstmals ein TRADD-defizientes Zellsystem mittels homologer Rekombination in humanen B-Lymphozyten (DG75) hergestellt. Im zweiten Teil dieser Arbeit wurde die Signaltransduktion von TNF-R1 und LMP1 in DG75 wildtyp und DG75 TRADD-defizienten Zellen untersucht. Dabei konnte erstmals gezeigt werden, dass TRADD für die Aktivierung des klassischen NF-κB Signalwegs sowohl durch die TNF-R1 Signaldomäne als auch durch LMP1 notwendig ist. Zusätzlich konnte durch die Entwicklung einer neuen, auf FACS-basierenden Methode zur Zelltodanalyse nach transienter Transfektion apoptotischer Gene, in DG75 TRADD-defizienten Zellen nachgewiesen werden, dass TRADD an der Induktion von Apoptose durch TNF-R1 essentiell beteiligt ist. Diese beiden Ergebnisse stützen das derzeitige Modell der TNF-R1 bzw. LMP1 Signaltransduktion. Dagegen konnte im Rahmen dieser Doktorarbeit festgestellt werden, dass TRADD weder für die Aktivierung des JNK1 Signalwegs durch die TNF-R1 Signaldomäne noch durch LMP1 benötigt wird. Im Fall von TNF-R1 stellt dieses Ergebnis das bis heute gültige Modell der TNF-R1 Signaltransduktion in Frage und zeigt, dass TRADD nicht das zentrale Adapterprotein zur Induktion aller wichtigen TNF-R1 Signalwege sein kann. Diese Ergebnisse konnten durch Experimente mit TRADD-siRNA in HeLa Zellen bestätigt werden. Abschließend konnte in dieser Arbeit erstmals gezeigt werden, dass TRAF2 unabhängig von TRADD mit dem TNF-R1 interagieren kann und von der TNF-R1 Signaldomäne in Abwesenheit von TRADD in „lipid rafts“ rekrutiert wird. Da TRAF2 für die TNF-R1-vermittelte JNK1 Aktivierung essentiell ist, könnte dies eine Erklärung für die TRADD-unabhängige Induktion des JNK1 Signalwegs durch TNF-R1 sein. Welches Molekül die Bindung von TRAF2 an TNF-R1 vermittelt, ist noch unklar und wird in Zukunft experimentell adressiert werden. Hierfür stellen die DG75 TRADD-defizienten Zellen ein wertvolles experimentelles System dar.

LMP1 ist das Hauptonkogen des humanen DNA-Tumorvirus EBV (Epstein-Barr Virus). LMP1 ist essentiell für die Immortalisierung von B-Zellen durch das Virus. Darüber hinaus transformiert LMP1 Nagerfibroblasten in Kultur. LMP1 agiert wie ein konstitutiv aktives Rezeptormolekül in der Plasmamembran und induziert intrazelluläre Signaltransduktion durch die Bindung von Signalmolekülen der TNF-Rezeptor Familie. Die bekannten LMP1 Signalwege können die biologischen Funktionen von LMP1 jedoch nur teilweise erklären. In meiner Arbeit sollten daher neue Komponenten der LMP1 Signaltransduktion identifiziert werden. Im ersten Teil der vorliegenden Arbeit konnte TRAF6 als essentielles und spezifisches Signalmolekül für die Induktion von p38 MAPK durch LMP1 auf einem MKK6-abhängigen Signalweg identifiziert werden. In TRAF6 defizienten Maus-Fibroblasten ist eine signifikante p38 MAPK-Aktivierung durch LMP1 von der ektopischen Expression von TRAF6 abhängig. Darüber hinaus ist TRAF6 ebenfalls in der Aktivierung von NF-κB, jedoch nicht von JNK1/AP-1 durch LMP1 involviert. Das PxQxT-Motiv in CTAR1 ist zusammen mit Tyrosin 384 in CTAR2 essentiell für die Aktivierung des LMP1p38 MAPK-Signalweges. Dominant- negatives TRADD, das direkt an CTAR2 bindet, inhibiert die Induktion von p38 MAPK durch LMP1. Zusammengefaßt zeigen diese Ergebnisse zum ersten Mal eine Rolle von TRAF6 als essentielles Signalmolekül in der Signalkaskade eines transformierenden Onkogens, das unterhalb von TRADD und TRAF2 agiert. Im zweiten Teil meiner Arbeit konnte JNK2 als eine weitere, durch LMP1 induzierte MAPK in B-Zellen identifiziert werden. Im Zuge dieser Arbeit wurden dominant-negative Mutanten von JNK1 und JNK2 hergestellt, deren Expression eine Aktivierung von AP-1 durch LMP1 inhibieren und damit eine Rolle von JNK1 und 2 in der Induktion von AP-1 beweisen. In einem konditionalen LMP1-System in B-Zellen induzierte NGF-R:LMP1 die Degradation des p53 Proteins. Dieser Effekt ist spezifisch für p53, erfolgt innerhalb weniger Minuten und ist dominant über der p53-stabilisierenden Wirkung von UV-Strahlung. Somit konnte erstmals ein EBV-spezifischer Mechanismus aufgedeckt werden, der zu einer Deaktivierung des Tumorsuppressors p53 beitragen könnte.