Ca2+ Cycling Impairment in Heart Failure Is Exacerbated by Fibrosis: Insights Gained From Mechanistic Simulations

[EN] Heart failure (HF) is characterized by altered Ca2+ cycling, resulting in cardiac contractile dysfunction. Failing myocytes undergo electrophysiological remodeling, which is known to be the main cause of abnormal Ca2+ homeostasis. However, structural remodeling, specifically proliferating fibroblasts coupled to myocytes in the failing heart, could also contribute to Ca2+ cycling impairment. The goal of the present study was to systematically analyze the mechanisms by which myocyte-fibroblast coupling could affect Ca2+ dynamics in normal conditions and in HF. Simulations of healthy and failing human myocytes were performed using established mathematical models, and cells were either isolated or coupled to fibroblasts. Univariate and multivariate sensitivity analyses were performed to quantify effects of ion transport pathways on biomarkers computed from intracellular [Ca2+] waveforms. Variability in ion channels and pumps was imposed and populations of models were analyzed to determine effects on Ca2+ dynamics. Our results suggest that both univariate and multivariate sensitivity analyses are valuable methodologies to shed light into the ionic mechanisms underlying Ca2+ impairment in HF, although differences between the two methodologies are observed at high parameter variability. These can result from either the fact that multivariate analyses take into account ion channels or non-linear effects of ion transport pathways on Ca2+ dynamics. Coupling either healthy or failing myocytes to fibroblasts decreased Ca2+ transients due to an indirect sink effect on action potential and thus on Ca2+ related currents. Simulations that investigated restoration of normal physiology in failing myocytes showed that Ca2+ cycling can be normalized by increasing SERCA and L-type Ca2+ current activity while decreasing Na+-Ca2+ exchange and SR Ca2+ leak. Changes required to normalize action potentials in failing myocytes depended on whether myocytes were coupled to fibroblasts. In conclusion, univariate and multivariate sensitivity analyses are helpful tools to understand how Ca2+ cycling is impaired in heart failure and how this can be exacerbated by coupling of myocytes to fibroblasts. The design of pharmacological actions to restore normal activity should take into account the degree of fibrosis in the failing heart.This work was partially supported by the National Science Foundation (MCB 1615677), the American Heart Association (15GRNT25490006), the "Plan Estatal de Investigacion Cientifica y Tecnica y de Innovacion 2013-2016 from the Ministerio de Economia, Industria y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) DPI2016-75799-R (AEI/FEDER, UE)", and the "Programa de Ayudas de Investigacion y Desarrollo (PAID-01-17)" from the Universitat Politecnica de Valencia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Mora-Fenoll, MT.; Ferrero De Loma-Osorio, JM.; Gómez García, JF.; Sobie, EA.; Trenor Gomis, BA. (2018). Ca2+ Cycling Impairment in Heart Failure Is Exacerbated by Fibrosis: Insights Gained From Mechanistic Simulations. Frontiers in Physiology. 9. https://doi.org/10.3389/fphys.2018.01194S9Aguilar, M., Qi, X. Y., Huang, H., Comtois, P., & Nattel, S. (2014). Fibroblast Electrical Remodeling in Heart Failure and Potential Effects on Atrial Fibrillation. Biophysical Journal, 107(10), 2444-2455. doi:10.1016/j.bpj.2014.10.014R. ALPERT, N., HASENFUSS, G., J. LEAVITT, B., P. ITTLEMAN, F., PIESKE, B., & A. MULIERI, L. (2000). A Mechanistic Analysis of Reduced Mechanical Performance in Human Heart Failure. Japanese Heart Journal, 41(2), 103-116. doi:10.1536/jhj.41.103Bers, D. M. (2000). Calcium Fluxes Involved in Control of Cardiac Myocyte Contraction. 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Extracellular matrix formation after transplantation of human embryonic stem cell-derived cardiomyocytes

Transplantation of human embryonic stem cell-derived cardiomyocytes (hESC-CM) for cardiac regeneration is hampered by the formation of fibrotic tissue around the grafts, preventing electrophysiological coupling. Investigating this process, we found that: (1) beating hESC-CM in vitro are embedded in collagens, laminin and fibronectin, which they bind via appropriate integrins; (2) after transplantation into the mouse heart, hESC-CM continue to secrete collagen IV, XVIII and fibronectin; (3) integrin expression on hESC-CM largely matches the matrix type they encounter or secrete in vivo; (4) co-transplantation of hESC-derived endothelial cells and/or cardiac progenitors with hESC-CM results in the formation of functional capillaries; and (5) transplanted hESC-CM survive and mature in vivo for at least 24 weeks. These results form the basis of future developments aiming to reduce the adverse fibrotic reaction that currently complicates cell-based therapies for cardiac disease, and to provide an additional clue towards successful engraftment of cardiomyocytes by co-transplanting endothelial cells

Characterization of Multiple Ion Channels in Cultured Human Cardiac Fibroblasts

Background: Although fibroblast-to-myocyte electrical coupling is experimentally suggested, electrophysiology of cardiac fibroblasts is not as well established as contractile cardiac myocytes. The present study was therefore designed to characterize ion channels in cultured human cardiac fibroblasts. Methods and Findings: A whole-cell patch voltage clamp technique and RT-PCR were employed to determine ion channels expression and their molecular identities. We found that multiple ion channels were heterogeneously expressed in human cardiac fibroblasts. These include a big conductance Ca2+-activated K+ current (BKCa) in most (88%) human cardiac fibroblasts, a delayed rectifier K+ current (IKDR) and a transient outward K+ current (Ito) in a small population (15 and 14%, respectively) of cells, an inwardly-rectifying K+ current (IKir) in 24% of cells, and a chloride current (ICl) in 7% of cells under isotonic conditions. In addition, two types of voltage-gated Na+ currents (INa) with distinct properties were present in most (61%) human cardiac fibroblasts. One was a slowly inactivated current with a persistent component, sensitive to tetrodotoxin (TTX) inhibition (INa.TTX, IC50 = 7.8 nM), the other was a rapidly inactivated current, relatively resistant to TTX (INa.TTXR, IC50 = 1.8 μM). RT-PCR revealed the molecular identities (mRNAs) of these ion channels in human cardiac fibroblasts, including KCa.1.1 (responsible for BKCa), Kv1.5, Kv1.6 (responsible for IKDR), Kv4.2, Kv4.3 (responsible for Ito), Kir2.1, Kir2.3 (for IKir), Clnc3 (for ICl), NaV1.2, NaV1.3, NaV1.6, NaV1.7 (for INa.TTX), and NaV1.5 (for INa.TTXR). Conclusions: These results provide the first information that multiple ion channels are present in cultured human cardiac fibroblasts, and suggest the potential contribution of these ion channels to fibroblast-myocytes electrical coupling. © 2009 Li et al.published_or_final_versio

Lessons Learned from Multi-scale Modeling of the Failing Heart

[EN] Heart failure constitutes a major public health problem worldwide. Affected patients experience a number of changes in the electrical function of the heart that predispose to potentially lethal cardiac arrhythmias. Due to the multitude of electrophysiological changes that may occur during heart failure, the scientific literature is complex and sometimes ambiguous, perhaps because these findings are highly dependent on the etiology, the stage of heart failure, and the experimental model used to study these changes. Nevertheless, a number of common features of failing hearts have been documented. Prolongation of the action potential (AP) involving ion channel remodeling and alterations in calcium handling have been established as the hallmark characteristics of myocytes isolated from failing hearts. Intercellular uncoupling and fibrosis are identified as major arrhythmogenic factors. Multi-scale computational simulations are a powerful tool that complements experimental and clinical research. The development of biophysically detailed computer models of single myocytes and cardiac tissues has contributed greatly to our understanding of processes underlying excitation and repolarization in the heart. The electrical, structural, and metabolic remodeling that arises in cardiac tissues during heart failure has been addressed from different computational perspectives to further understand the arrhythmogenic substrate. This review summarizes the contributions from computational modeling and simulation to predict the underlying mechanisms of heart failure phenotypes and their implications for arrhythmogenesis, ranging from the cellular level to whole-heart simulations. The main aspects of heart failure are presented in several related sections. An overview of the main electrophysiological and structural changes that have been observed experimentally in failing hearts is followed by the description and discussion of the simulation work in this field at the cellular level, and then in 2D and 3D cardiac structures. The implications for arrhythmogenesis in heart failure are also discussed including therapeutic measures, such as drug effects and cardiac resynchronization therapy. Finally, the future challenges in heart failure modeling and simulation will be discussed.This work was partially supported by (i) the "VI Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica" from the Ministerio de Economia y Competitividad of Spain and the European Commission (European Regional Development Funds ERDF-FEDER) (grant number TIN2012-37546-C03-01), and by (ii) Programa Prometeo de la Conselleria d'Educacio Formacio I Ocupacio, Generalitat Valenciana (grant number PROMETEO/2012/030).Gómez García, JF.; Cardona-Urrego, KE.; Trénor Gomis, BA. (2015). Lessons Learned from Multi-scale Modeling of the Failing Heart. Journal of Molecular and Cellular Cardiology. 89:146-159. https://doi.org/10.1016/j.yjmcc.2015.10.016S1461598

Electrophysiological and Structural Remodeling in Heart Failure Modulate Arrhythmogenesis. 1D Simulation Study

Background: Heart failure is a final common pathway or descriptor for various cardiac pathologies. It is associated with sudden cardiac death, which is frequently caused by ventricular arrhythmias. Electrophysiological remodeling, intercellular uncoupling, fibrosis and autonomic imbalance have been identified as major arrhythmogenic factors in heart failure etiology and progression. Objective: In this study we investigate in silico the role of electrophysiological and structural heart failure remodeling on the modulation of key elements of the arrhythmogenic substrate, i.e., electrophysiological gradients and abnormal impulse propagation. Methods: Two different mathematical models of the human ventricular action potential were used to formulate models of the failing ventricular myocyte. This provided the basis for simulations of the electrical activity within a transmural ventricular strand. Our main goal was to elucidate the roles of electrophysiological and structural remodeling in setting the stage for malignant life-threatening arrhythmias. Results: Simulation results illustrate how the presence of M cells and heterogeneous electrophysiological remodeling in the human failing ventricle modulate the dispersion of action potential duration and repolarization time. Specifically, selective heterogeneous remodeling of expression levels for the Na+ /Ca2+ exchanger and SERCA pump decrease these heterogeneities. In contrast, fibroblast proliferation and cellular uncoupling both strongly increase repolarization heterogeneities. Conduction velocity and the safety factor for conduction are also reduced by the progressive structural remodeling during heart failure. Conclusion: An extensive literature now establishes that in human ventricle, as heart failure progresses, gradients for repolarization are changed significantly by protein specific electrophysiological remodeling (either homogeneous or heterogeneous). Our simulations illustrate and provide new insights into this. Furthermore, enhanced fibrosis in failing hearts, as well as reduced intercellular coupling, combine to increase electrophysiological gradients and reduce electrical propagation. In combination these changes set the stage for arrhythmias.This work was partially supported by (i) the "VI Plan Nacional de Investigacion Cientifica, Desarrollo e Innovacion Tecnologica" from the Ministerio de Economia y Competitividad of Spain (grant number TIN2012-37546-C03-01) and the European Commission (European Regional Development Funds - ERDF - FEDER), (ii) the Direccion General de Politica Cientifica de la Generalitat Valenciana (grant number GV/2013/119), and (iii) Programa Prometeo (PROMETEO/2012/030) de la Conselleria d'Educacio Formacio I Ocupacio, Generalitat Valenciana. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Gómez García, JF.; Cardona, K.; Romero Pérez, L.; Ferrero De Loma-Osorio, JM.; Trénor Gomis, BA. (2014). Electrophysiological and Structural Remodeling in Heart Failure Modulate Arrhythmogenesis. 1D Simulation Study. PLoS ONE. 9(9). https://doi.org/10.1371/journal.pone.0106602S9

Spatial planning in the Baltic States, affected by depopulation

Three Northern European countries over the last century have had similar political experiences, in 1990–1991 they have re-established independence and developed an individual political and administrative system. From 2004, when all Baltic countries became members of the European Union, the land use and spatial planning systems were developed with many similarities, as well as differences. The topic of this study is a survey of the national land policies and spatial planning systems in Latvia, Lithuania and Estonia in the context of sustainable development, needs of society and depopulation. The aim of the article is to examine the problems, needs of society and tendencies in land usage, as well as systemic features of spatial planning in the Baltic countries. It is very important to analyse how countries realize the implementation of sustainable development strategies In land use planning and in the context of depopulation. It was found that the Baltic countries are facing similar problems in land use and spatial planning documents but there are also differences regarding planning procedures of documents, their hierarchy and types of planned measures. The study has shown that people in these countries want more natura environment and eco-industrial development. Also, it was approved as necessary to createan index (engineering method) of sustainability in spatial planning

Nuages auto-oscillants dans des pièges magnéto-optiques

In this Thesis, we study the fundamental aspects of self-oscillating atomic clouds in a large, balanced Magneto-Optical Trap (MOT). These instabilities bear analogies with astrophysical systems such as Cepheid variable stars, whose self-oscillations depend on radiation pressure and gravity, as well as technological systems such as confined plasmas, where self-oscillations may arise due to interactions between the plasma particles and the confining magnetic field. We begin with an experimental study of self-oscillating balanced MOT instabilities, investigating first the instability threshold behavior versus various MOT parameters, including magnetic field gradient, atom number and laser intensity. We proceed then investigating the spatio-temporal properties of the unstable regime and identify distinct instability regimes. Different analysis techniques are employed that allow us to learn about the oscillation modes of clouds of these regimes as well as the size distribution of the structures developing in clouds of these regimes. In a theoretical approach, we develop a kinetic 3D model for the MOT with many-atom effects included and successfully use it in numerical simulations of our instabilities. We find qualitative agreements with the instability thresholds from the experiments as well as predict experimentally obtained instability regimes. We investigate the impact of our model’s physical ingredients on the instabilities, to aid the understanding of the complex physics at work. Finally, we show a preliminary simulated result for a self-oscillating instability in the misaligned MOT, known to experimentally exist, in that way demonstrating that our developed numerical tool can be employed beyond the balanced MOT.Dans cette Thèse, nous étudions les aspects fondamentaux des nuages atomiques auto-oscillants dans un grand piège magnéto-optique (MOT, de l’anglais Magneto-Optical Trap) équilibré. Ces instabilités présentent des analogies avec des systèmes astrophysiques tels que les étoiles variables (Céphéides), dont les auto-oscillations dépendent de la pression de radiation et de la gravitation, ainsi que des systèmes technologiques tels que les plasmas confinés, où des auto-oscillations peuvent survenir en raison des interactions entre les particules de plasma et le champ magnétique de confinement. Nous commençons par une étude expérimentale des instabilités dans un MOT équilibré, en étudiant d'abord le comportement du seuil d'instabilité par rapport à divers paramètres du MOT, y compris le gradient de champ magnétique, le nombre d'atome et l'intensité laser. Nous procédons ensuite à l'étude des propriétés spatio-temporelles du régime instable et identifions des régimes d'instabilité distincts. Différentes techniques d'analyse sont employées qui permettent d’identifier les modes d'oscillation du nuage dans chacun de ces régimes. Nous étudions également le comportement des distributions des tailles des structures spatiales qui se développent dans le nuage. Dans une approche théorique, nous développons un modèle cinétique 3D pour le MOT en prenant en compte les interactions entre atomes et l'utilisons avec succès dans des simulations numériques de nos instabilités. Nous trouvons des accords qualitatifs avec les seuils d'instabilité issus des expériences et prédisons les régimes d'instabilité obtenus expérimentalement. Nous étudions l’impact des ingrédients physiques de notre modèle sur les instabilités, afin de faciliter la compréhension de la physique complexe à l’œuvre. Enfin, nous montrons un résultat numérique préliminaire pour une instabilité dans un MOT désaligné, observée expérimentalement, démontrant ainsi que notre outil numérique peut être utilisé au-delà du MOT équilibré

Self-oscillating clouds in magneto-optical traps

Dans cette Thèse, nous étudions les aspects fondamentaux des nuages atomiques auto-oscillants dans un grand piège magnéto-optique (MOT, de l’anglais Magneto-Optical Trap) équilibré. Ces instabilités présentent des analogies avec des systèmes astrophysiques tels que les étoiles variables (Céphéides), dont les auto-oscillations dépendent de la pression de radiation et de la gravitation, ainsi que des systèmes technologiques tels que les plasmas confinés, où des auto-oscillations peuvent survenir en raison des interactions entre les particules de plasma et le champ magnétique de confinement. Nous commençons par une étude expérimentale des instabilités dans un MOT équilibré, en étudiant d'abord le comportement du seuil d'instabilité par rapport à divers paramètres du MOT, y compris le gradient de champ magnétique, le nombre d'atome et l'intensité laser. Nous procédons ensuite à l'étude des propriétés spatio-temporelles du régime instable et identifions des régimes d'instabilité distincts. Différentes techniques d'analyse sont employées qui permettent d’identifier les modes d'oscillation du nuage dans chacun de ces régimes. Nous étudions également le comportement des distributions des tailles des structures spatiales qui se développent dans le nuage. Dans une approche théorique, nous développons un modèle cinétique 3D pour le MOT en prenant en compte les interactions entre atomes et l'utilisons avec succès dans des simulations numériques de nos instabilités. Nous trouvons des accords qualitatifs avec les seuils d'instabilité issus des expériences et prédisons les régimes d'instabilité obtenus expérimentalement. Nous étudions l’impact des ingrédients physiques de notre modèle sur les instabilités, afin de faciliter la compréhension de la physique complexe à l’œuvre. Enfin, nous montrons un résultat numérique préliminaire pour une instabilité dans un MOT désaligné, observée expérimentalement, démontrant ainsi que notre outil numérique peut être utilisé au-delà du MOT équilibré.In this Thesis, we study the fundamental aspects of self-oscillating atomic clouds in a large, balanced Magneto-Optical Trap (MOT). These instabilities bear analogies with astrophysical systems such as Cepheid variable stars, whose self-oscillations depend on radiation pressure and gravity, as well as technological systems such as confined plasmas, where self-oscillations may arise due to interactions between the plasma particles and the confining magnetic field. We begin with an experimental study of self-oscillating balanced MOT instabilities, investigating first the instability threshold behavior versus various MOT parameters, including magnetic field gradient, atom number and laser intensity. We proceed then investigating the spatio-temporal properties of the unstable regime and identify distinct instability regimes. Different analysis techniques are employed that allow us to learn about the oscillation modes of clouds of these regimes as well as the size distribution of the structures developing in clouds of these regimes. In a theoretical approach, we develop a kinetic 3D model for the MOT with many-atom effects included and successfully use it in numerical simulations of our instabilities. We find qualitative agreements with the instability thresholds from the experiments as well as predict experimentally obtained instability regimes. We investigate the impact of our model’s physical ingredients on the instabilities, to aid the understanding of the complex physics at work. Finally, we show a preliminary simulated result for a self-oscillating instability in the misaligned MOT, known to experimentally exist, in that way demonstrating that our developed numerical tool can be employed beyond the balanced MOT

Electrotonic modulation of cardiac impulse conduction by myofibroblasts

Structural remodeling of the myocardium associated with mechanical overload or cardiac infarction is accompanied by the appearance of myofibroblasts. These fibroblast-like cells express alpha-smooth muscle actin (alphaSMA) and have been shown to express connexins in tissues other than heart. The present study examined whether myofibroblasts of cardiac origin establish heterocellular gap junctional coupling with cardiomyocytes and whether ensuing electrotonic interactions affect impulse propagation. For this purpose, impulse conduction characteristics (conduction velocity [theta] and maximal upstroke velocity [dV/dtmax]) were assessed optically in cultured strands of cardiomyocytes, which were coated with fibroblasts of cardiac origin. Immunocytochemistry showed that cultured fibroblasts underwent a phenotype switch to alphaSMA-positive myofibroblasts that expressed connexin 43 and 45 both among themselves and at contact sites with cardiomyocytes. Myofibroblasts affected theta and dV/dtmax in a cell density-dependent manner; a gradual increase of myofibroblast-to-cardiomyocyte ratios up to 7:100 caused an increase of both theta and dV/dtmax, which was followed by a progressive decline at higher ratios. On full coverage of the strands with myofibroblasts (ratio >20:100), theta fell <200 mm/s. This biphasic dependence of theta and dV/dtmax on myofibroblast density is reminiscent of "supernormal conduction" and is explained by a myofibroblast density-dependent gradual depolarization of the cardiomyocyte strands from -78 mV to -50 mV as measured using microelectrode recordings. These findings suggest that myofibroblasts, apart from their role in structural remodeling, might contribute to arrhythmogenesis by direct electrotonic modulation of conduction and that prevention of their appearance might represent an antiarrhythmic therapeutic target