Identification of Cellular and Molecular Interactions between Stromal and Parenchymal Cells in Atrial Fibrillation
Led by Stéphane Hatem (Université Pierre et Marie Curie) and Stephan Rohr (Universität Bern). Assisted by Maastricht University and St George’s University of London.
Whereas a wealth of information exists on the role of abnormal parenchymal cell in cardiac arrhythmogenesis, less is known about the involvement of stromal cells in cardiac arrhythmias. Under normal conditions, the fibroblast (main stromal cell type of the heart) is responsible for producing and maintaining a regularly structured 3-dimensional network of collagen and elastin fibers that serves as a scaffold for the cardiomyocytes (the parenchymal cells). Apart from playing an essential role in the pump function of the heart, this scaffold is also essential to sustain the orderly 3- dimensional arrangement of cardiomyocytes which, once disturbed, strongly contributes to cardiac arrhythmias.
Reparatory processes initiated by age and a variety of insults to the heart (e.g pressure/volume overload and infarction), lead to structural remodelling of the heart that is typically associated with organ fibrosis and the appearance of activated fibroblasts (‘myofibroblasts’). Recent work in our labs has shown that myofibroblasts not only contributes to fibrosis by excessive production of collagen, but that it is capable of establishing direct electrical contact with cardiomyocytes that causes arrhythmogenic conditions like slow conduction and ectopic activity. Based on these observations, we believe that myofibroblasts can be a novel cellular target for antiarrhythmic therapy.
Within the EUTRAF project, we investigate the mechanisms governing the crosstalk between parenchymal and stromal cells in diseased hearts. We focus on the role of these processes in cardiac arrhythmogenesis in general and more specifically in Atrial Fibrillation. Our studies concentrate on delineating humoral and electrotonic interactions between both cell types. The effects of both types of crosstalk are investigated in respect to changes in cellular morphology, gap junctional coupling and alterations in the expression/ targeting of ion channels. Our study attempts to identify proteins involved in the formation of channel complexes and in the functional coupling between myofibroblasts and myocytes. Specifically, we examine the role played by scaffold and anchoring proteins in the functional coupling between both cell types. The experimental approach is based both on in-vitro (alteration of proteins expression) and appropriate in-vivo models as present in labs of other partners of this program. Experimental results will be used to establish computer models predicting the impact of intercellular crosstalk for arrhythmogenesis in healthy hearts. Moreover, upon pinpointing new arrhythmogenic mechanisms, appropriate strategies will be chosen to validate these findings in patients in collaboration with the clinicians of the EUTRAF network.
EUTRAF publications can be found on our Publication page
Identification and Validation of Novel Ion Channels and Transporters for Treatment of Persistent Atrial Fibrillation
Led by Dobromir Dobrev (University of Heidelberg) and Ursula Ravens (Technische Universität Dresden). Assisted by Medizinische Universität Graz, Philipps Universität Marburg, Sanofi Aventis Deutschland GmbH, University of Maastricht, Universitée Pierre et Marie Curie and Xention Ltd
Atrial fibrillation (AF) is a major public health problem and present therapies are inadequate. Novel mechanismdirected approaches have great promise for improving management of AF. It is well established that abnormal electrical properties of atrial cardiomyocytes are the main reason for impaired atrial impulse formation. Unlike strong evidence that altered atrial cardiomyocyte ion channels and transporters are major determinants of AF-related focal activity and refractoriness abbreviation, and persistence of AF, the molecular basis of these changes is incompletely understood. Here we aim at a coordinated effort to improve our understanding of the molecular basis of AF-related cardiomyocyte ion channel and transporters abnormalities, to identify key mechanisms of these changes as novel molecular biomarkers, and to translate this knowledge into novel mechanism-based therapeutic approaches.
Taking advantage of cutting-edge techniques and strategies in cell and molecular biology, calcium and sodium ions imaging, molecular electrophysiology, transgenic mouse lines and clinically-relevant large-animal models, our specific mission within EUTRAF is to:
- identify novel molecular “biomarkers” of abnormal ion channel function that promote transition of paroxysmal (short-term) to persistent AF,
- explore the molecular basis of cardiomyocyte ionic remodelling potentially fostering AF maintenance,
- establish molecular determinants of disturbed intracellular calcium homeostasis that support persistent AF,
- test and validate efficacy of novel pharmacological interventions targeting key cardiomyocyte ion channels and transporters that underlie persistent AF.
The identification of novel AF-specific molecular “biomarkers” of abnormal cardiomyocyte function will help to design atrial-selective drugs with pathologyspecific efficacy in persistent AF.
EUTRAF publications can be found on our Publication page. Assisted by Medizinische Universität Graz, Philipps Universität Marburg, Sanofi Aventis Deutschland GmbH, University of Maastricht, Universitée Pierre et Marie Curie and Xention Ltd myocytes Atrial myocyte with visualized potassium channel (IK,ACh) subunits (red) and nuclei (purple) Atrial fibrillation (AF) is a major public health problem and present therapies are inadequate. Novel mechanismdirected approaches have great promise for improving management of AF. It is well established that abnormal electrical properties of atrial cardiomyocytes are the main reason for impaired atrial impulse formation. Unlike strong evidence that altered atrial cardiomyocyte ion channels and transporters are major determinants of AF-related focal activity and refractoriness abbreviation, and persistence of AF, the molecular basis of these changes is incompletely understood. Here we aim at a coordinated effort to improve our understanding of the molecular basis of AF-related cardiomyocyte ion channel and transporters abnormalities, to identify key mechanisms of these changes as novel molecular biomarkers, and to translate this knowledge into novel mechanism-based therapeutic approaches. Human Myocyte Atrial myocyte with visualized potassium channel (IK,ACh) subunits (red) and nuclei (purple) Taking advantage of cutting-edge techniques and strategies in cell and molecular biology, calcium and sodium ions imaging, molecular electrophysiology, transgenic mouse lines and clinically-relevant large-animal models, our specific mission within EUTRAF is to: identify novel molecular “biomarkers” of abnormal ion channel function that promote transition of paroxysmal (short-term) to persistent AF, explore the molecular basis of cardiomyocyte ionic remodelling potentially fostering AF maintenance, establish molecular determinants of disturbed intracellular calcium homeostasis that support persistent AF, test and validate efficacy of novel pharmacological interventions targeting key cardiomyocyte ion channels and transporters that underlie persistent AF. The identification of novel AF-specific molecular “biomarkers” of abnormal cardiomyocyte function will help to design atrial-selective drugs with pathologyspecific efficacy in persistent AF. EUTRAF publications can be found on our Publication page.
Etiology-Specific Mechanisms in Atrial Fibrillation
Led by Andreas Götte (Otto von Guericke Universität Magdeburg) and Burkert Pieske (Medizinische Universität Graz). Assisted by Philipps Universität Marburg and Ernst Moritz Arndt Universität Greifswald
Concomitant diseases and conditions like arterial hypertension, heart failure, diabetes mellitus or ageing are present in about 90% of patients with atrial fibrillation (AF). The mechanisms how these factors contribute to generation and persistence of Atrial Fibrillation may differ substantially. We hypothesize that different underlying structural heart diseases cause distinct electrophysiological changes in the atria that require different therapeutic approaches to prevent Atrial Fibrillation.
Within EUTRAF, our main objective is to determine the specific impact of hypertension, diabetes mellitus, ageing, and gender on atrial function, electrophysiology, molecular biology, fibrosis, thrombogenesis and genomics. Qualitative and quantitative differences in atrial remodelling (ionic homeostasis and conduction disturbances) and the underlying mechanism (redox signalling in metabolic diseases, and interstitial matrix alterations) will be assessed and related to atrial vulnerability to arrhythmias.
Various models are used to investigate each etiology:
- Diabetes mellitus
In vitro cell/tissue culture is used for pharmacological interventions to identified disease-specific molecular pathways. Atrial Fibrillation is simulated in vitro by application of an electrical field on cardiomyocytes.
Human atrial myocardium (tissue slices, trabeculae, and isolated atrial myocytes) with different etiologies and at different stages of remodelling will be used to validate experimental findings. The characterisation of disease-specific atrial remodelling will help to identify etiology-specific therapeutic approaches and novel therapeutic drug targets for Atrial Fibrillation.
EUTRAF publications can be found on our Publication page.
Identification and Preclinical Testing of New ‘Upstream’ Therapeutic Targets for Sustained Atrial Fibrillation
Led by Barbara Casadei (University of Oxford). Assisted by University of Maastricht, Otto von Guericke Universität Magdeburg, Medizinische Universität Graz, Philipps Universität Marburg and Xention Ltd
Atrial fibrillation (AF) is known to induce progressive myocardial remodelling, which in turn promotes atrial fibrillation maintenance and increases vulnerability to relapse. Although these features have been extensively documented both in animal models and in humans, the mechanisms triggering electrical and structural remodelling in the fibrillating atrial myocardium have remained largely unexplored.
By using an integrated approach linking experimental findings to clinical investigations, we propose to investigate the role of myocardial calcium signalling and nitric oxide (NO)-redox imbalance in promoting and maintaining atrial fibrillation. We also explore the notion that an ‘upstream’ therapeutic approach, aimed at targeting signalling pathways involved in the development of the substrate that supports atrial fibrillation, may be have a major impact in the prevention and treatment of this common arrhythmia.
Within EUTRAF we address the following questions:
- Are changes in myocardial NO-redox imbalance important in promoting AF and AF-induce remodelling?
- What is the role of atrial energetic, mitochondrial dysfunction and excitationtranscription coupling in the AF-induced remodelling and the evolution towards sustained AF?
- Can the evolution towards sustained/permanent AF be arrested or reversed by targeting the substrate that supports AF?
These findings will provide novel insights on the regulation of some of the key proteins involved in AF-induced atrial remodelling and test the hypothesis that targeting signalling pathways involved in the development of the substrate that supports AF may have a major impact in the prevention and treatment of this arrhythmia.
EUTRAF publications can be found on our Publication page.
Translating Genetic Contributors to Atrial Fibrillation into Novel Therapeutic Targets
Led by Paulus Kirchhof and Frank U. Müller (Westfälische Wilhems – Universität Münster) Assisted by St George’s University of London, University of Maastricht, Université Pierre et Marie Curie, Technische Universität Dresden, Universität Bern, University of Oxford and Ruprecht Karls Universität Heidelberg
Atrial fibrillation (AF) is strongly associated with distinct genetic alterations (mutations). However, the impact of these mutations and the affected genes on the pathogenesis of AF is hitherto not understood. Moreover, other genes are differentially expressed (i.e. up- or downregulated) along with the development of progressive atrial dilatation and remodelling followed by persistent AF. The functional role of these genes in regard to the pathophysiology of AF is not clear. In this context, our aim is to identify genetically conferred mechanisms causing AF and its complications and of biomarkers in suitable genetically modified models.
Within EUTRAF, our aim is the identification of mechanisms underlying the pathogenesis of AF, in particular functionally relevant genes altered along the chronification of the arrhythmia. This may lead to the characterization of novel biochemical, molecular or functional biomarkers which may serve as novel diagnostic tools and/or as novel targets for future therapies of AF (see figure below).
We aim to identify novel AF-causing factors in models carrying genetic alterations in vivo, in the intact heart and at the cellular level. This includes novel techniques to characterize the entire sets of proteins (the “proteome”) or the respective nucleic acids (messenger RNAs; the “transcriptome”) as well as methods to understand functional alterations in detail down to the subcellular and molecular level. The relevance of molecular markers that precipitate AF will be tested in models and validated prospectively in tissue banks (biochemistry, molecular biology) and in clinical data bases (ECG, cardiac function, clinical parameters). Novel therapeutic interventions will be designed and tested to counter the AF-causing mechanisms identified.
EUTRAF publications can be found on our Publication page.
New Diagnostic Tools
Led by Ulrich Schotten (University of Maastricht). Assisted by St George’s University of London, Université Pierre et Marie Curie, CHU de Bordeaux, Westfälische Wilhems – Universität Münster, Otto von Guericke Universität Magdeburg and Osypka AG
Our Research consortium believes that the management of atrial fibrillation (AF) could be strongly improved by better diagnostic tools. Hence, the use of techniques enabling the characterization of electrophysiological changes in an individual patient would help to design a specific (“personalized”) therapeutic approach to treat this patient. In addition a better identification of patients at risk for onset or progression of AF would lead to a more effective preventive therapy.
Within EUTRAF, our team proposes to develop:
- a technique for rapid (real-time) and fully-automatic analysis of large amounts of fibrillation electrograms independent from the interpretation by an individual investigator. This technological development is necessary for the broad-scale use of activation mapping for quantification of the AF substrate complexity. So far, standardized analysis of large amounts of mapping data is limited by the need for manual editing of activation time points detected by semi-automatic algorithms. This difficulty is caused by the occurrence of complex fractionated atrial electrograms. To address this problem a probabilistic electrogram analysis in the spatio-temporal domain will be developed;
- new tools for ablation of sites which actively contribute to the generation of new wavefronts during AF. This will be achieved by constructing a catheter with a central RF electrode surrounded by several spines carrying 3 to 4 electrodes. Combined with an automatic electrogram analysis, such a catheter would allow ablation of sites at which the balance between generation and extinction of fibrillation waves is shifted towards generation of new waves;
- Development of non-invasive tools for the assessment of the complexity of conduction disturbances during AF. To quantify the complexity of the AF substrate in the right atrium, high density body surface ECG recordings from the chest of patients will be developed (including ECG Imaging and non-invasive imaging of atrial fibrosis and scar tissue).
Preclinical Testing to Characterise Atrial Substrate and Proof-of-concept Therapeutic Clinical Studies
Led by Michel Haissaguerre (CHU de Bordeaux). Assisted by University of Maastricht, Université Pierre et Marie Curie, Universität Bern, University of Oxford and Osypka AG
Atrial fibrillation (AF) is the most common arrhythmia in humans affecting about 1% of the entire population. Its incidence increases and 25 million of people are expected to suffer from AF by 2050. Many aspects of this atrial rhythm disorder remain unknown to scientists and doctors by many aspects. The mechanisms by which this arrhythmia initiate and perpetuate are largely ignored as the role of other conditions such as diabetes. Managing this arrhythmia is particularly frustrating, both for patients and doctors: anti-arrhythmic drugs available are frequently insufficient, interventional procedures are associated with better results but their success rate and safety still need to be improved. This therapeutic approach will be improved by a better understanding of the mechanisms leading to arrhythmia and those involved in these interventional procedures.
Within EUTRAF, our team proposes to bridge the knowledge from basic sciences to clinical applications to better understand the impact of various therapeutic approaches: Gene transfection elaborated in the different EUTRAF Research teams is used to better understand the impact of gene modification in various in vivo AF models. This strategy could help patients in the next 10 years, by avoiding heart surgery that frequently leads to post-operative complications; Computer modelling is also a useful tool to better understand arrhythmia mechanisms. This technology allows for unlimited simulation and could be used in the future to predict the impact of a given interventional procedure or anti-arrhythmic drug; our team also uses a body surface mapping system which is a kind of “super electrocardiogram”. This system helps to reconstruct the electrical activation of the heart from 256 chest electrodes. It is used to better understand the mechanisms of atrial fibrillation and the impact of anti-arrhythmic drugs. We anticipate that this approach will help screening patients and choosing the most appropriate (“personalised”) therapy; Ablation by catheters inserted in the heart through vessels is now possible. It mainly consists in isolating electrically pulmonary veins from the rest of the left atrium. This procedure is recognized and is part of the recommended therapies by international guidelines. However, the ablation catheter used at the present time has not evolved since 20 years and better results could be expected with more innovative tools. The EUTRAF consortium will design and validate new ablation catheters dedicated to pulmonary vein isolation.
Development of the IT Infrastructure for Knowledge Discovery
Led by Ali Oto, MITS (Media and Medical Information Technology Solutions). Assisted by all EUTRAF members
Data mining tools and machine learning algorithms integrate techniques from multivariate statistics, discrete mathematics, computer science, and engineering to discover hidden patterns, predict likely outcomes,and create actionable information from large scale datasets. The EUTRAF data mining system will learn from examples and will be able to classify the data, help with the automated discovery of previously unknown patterns and detect frequently occurring patterns over a period of time. Data will be continuously integrated within a data warehouse, on which existing data and EUTRAF data will be progressively analyzed using sophicsticated machine learning algorithms to build a risk model for the development and perpetuation of AF.
Within EUTRAF, our team proposes two main endeavours: to centralize data collection and collaboration; and to use machine learning techniques on the collected data to discover mechanistic relationships between biomarkers and the development and perpetuation of AF, to assess the predictive value of existing biomarkers, and to reveal new valuable biomarkers as well as new therapeutic targets. Our activities will culminate with the implementation of a web-based clinical decision support system (CDSS) which will be based on the rules extracted through machine learning on existing clinical datasets as well as experimental and clinical data gathered through the EUTRAF project.
Our strategy is:
- To create a data warehouse, and to implement thin-client interfaces for data entry, retrieval and sharing, as well as for collaboration on the data as well as on the results of knowledge discovery on the data;
- To implement the necessary security and privacy mechanisms per EU directives and EC recommendations for confidentiality of patient specific information;
- To integrate all relevant existing clinical datasets as well as relevant EUTRAF experimental and clinical research data into the data warehouse;
- To apply existing machine algorithms on large-scale data, develop and apply new machine learning algorithms on the data warehouse for rule extraction and knowledge discovery;
- To build an actionable risk model, and integrate all rules extracted through knowledge discovery into a thin-client clinical decision support system.
The CDSS will include a rule-based system learning the rules through data mining. This rule learning will be a progressive process ongoing throughout the course of the project. The rules and the risk model will be updated as more experimental and clinical data from the EUTRAF project becomes available. As a result, the rules extracted through data mining from the collected large data sets will be used as actionable knowledge to predict risks and complications related to AF. The CDSS is expected to be put into clinical use in institutions all across the Europe to help physicians evaluate with both the diagnosis as well as the ramifications of AF for a specific patient.