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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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