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Real-time visualization of titin dynamics reveals extensive reversible photobleaching in human induced pluripotent stem cell-derived cardiomyocytes.
Cadar AG, Feaster TK, Bersell KR, Wang L, Hong T, Balsamo JA, Zhang Z, Chun YW, Nam YJ, Gotthardt M, Knollmann BC, Roden DM, Lim CC, Hong CC
(2020) Am J Physiol Cell Physiol 318: C163-C173
MeSH Terms: Adult, Cell Differentiation, Cell Line, Connectin, Fluorescence Recovery After Photobleaching, Humans, Induced Pluripotent Stem Cells, Kinetics, Luminescent Proteins, Male, Microscopy, Fluorescence, Microscopy, Video, Myocytes, Cardiac, Recombinant Fusion Proteins, Reproducibility of Results, Sarcomeres
Show Abstract · Added March 24, 2020
Fluorescence recovery after photobleaching (FRAP) has been useful in delineating cardiac myofilament biology, and innovations in fluorophore chemistry have expanded the array of microscopic assays used. However, one assumption in FRAP is the irreversible photobleaching of fluorescent proteins after laser excitation. Here we demonstrate reversible photobleaching regarding the photoconvertible fluorescent protein mEos3.2. We used CRISPR/Cas9 genome editing in human induced pluripotent stem cells (hiPSCs) to knock-in mEos3.2 into the COOH terminus of titin to visualize sarcomeric titin incorporation and turnover. Upon cardiac induction, the titin-mEos3.2 fusion protein is expressed and integrated in the sarcomeres of hiPSC-derived cardiomyocytes (CMs). STORM imaging shows M-band clustered regions of bound titin-mEos3.2 with few soluble titin-mEos3.2 molecules. FRAP revealed a baseline titin-mEos3.2 fluorescence recovery of 68% and half-life of ~1.2 h, suggesting a rapid exchange of sarcomeric titin with soluble titin. However, paraformaldehyde-fixed and permeabilized titin-mEos3.2 hiPSC-CMs surprisingly revealed a 55% fluorescence recovery. Whole cell FRAP analysis in paraformaldehyde-fixed, cycloheximide-treated, and untreated titin-mEos3.2 hiPSC-CMs displayed no significant differences in fluorescence recovery. FRAP in fixed HEK 293T expressing cytosolic mEos3.2 demonstrates a 58% fluorescence recovery. These data suggest that titin-mEos3.2 is subject to reversible photobleaching following FRAP. Using a mouse titin-eGFP model, we demonstrate that no reversible photobleaching occurs. Our results reveal that reversible photobleaching accounts for the majority of titin recovery in the titin-mEos3.2 hiPSC-CM model and should warrant as a caution in the extrapolation of reliable FRAP data from specific fluorescent proteins in long-term cell imaging.
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16 MeSH Terms
Pharmacologic ATF6 activation confers global protection in widespread disease models by reprograming cellular proteostasis.
Blackwood EA, Azizi K, Thuerauf DJ, Paxman RJ, Plate L, Kelly JW, Wiseman RL, Glembotski CC
(2019) Nat Commun 10: 187
MeSH Terms: Activating Transcription Factor 6, Animals, Animals, Newborn, Cells, Cultured, Cerebral Infarction, Disease Models, Animal, Endoplasmic Reticulum, Female, Heart Ventricles, Humans, Kidney, Kidney Diseases, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Myocardial Infarction, Myocytes, Cardiac, Primary Cell Culture, Protective Agents, Proteostasis, Rats, Reperfusion Injury, Treatment Outcome, Unfolded Protein Response
Show Abstract · Added March 3, 2020
Pharmacologic activation of stress-responsive signaling pathways provides a promising approach for ameliorating imbalances in proteostasis associated with diverse diseases. However, this approach has not been employed in vivo. Here we show, using a mouse model of myocardial ischemia/reperfusion, that selective pharmacologic activation of the ATF6 arm of the unfolded protein response (UPR) during reperfusion, a typical clinical intervention point after myocardial infarction, transcriptionally reprograms proteostasis, ameliorates damage and preserves heart function. These effects were lost upon cardiac myocyte-specific Atf6 deletion in the heart, demonstrating the critical role played by ATF6 in mediating pharmacologically activated proteostasis-based protection of the heart. Pharmacological activation of ATF6 is also protective in renal and cerebral ischemia/reperfusion models, demonstrating its widespread utility. Thus, pharmacologic activation of ATF6 represents a proteostasis-based therapeutic strategy for ameliorating ischemia/reperfusion damage, underscoring its unique translational potential for treating a wide range of pathologies caused by imbalanced proteostasis.
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MeSH Terms
Muscle-specific stress fibers give rise to sarcomeres in cardiomyocytes.
Fenix AM, Neininger AC, Taneja N, Hyde K, Visetsouk MR, Garde RJ, Liu B, Nixon BR, Manalo AE, Becker JR, Crawley SW, Bader DM, Tyska MJ, Liu Q, Gutzman JH, Burnette DT
(2018) Elife 7:
MeSH Terms: Actin Cytoskeleton, Actins, Cell Line, Cell Line, Tumor, Formins, HeLa Cells, Humans, Microfilament Proteins, Microscopy, Confocal, Molecular Motor Proteins, Muscle Fibers, Skeletal, Myocytes, Cardiac, Myosin Heavy Chains, Nonmuscle Myosin Type IIB, RNA Interference, Sarcomeres, Stress Fibers
Show Abstract · Added March 27, 2019
The sarcomere is the contractile unit within cardiomyocytes driving heart muscle contraction. We sought to test the mechanisms regulating actin and myosin filament assembly during sarcomere formation. Therefore, we developed an assay using human cardiomyocytes to monitor sarcomere assembly. We report a population of muscle stress fibers, similar to actin arcs in non-muscle cells, which are essential sarcomere precursors. We show sarcomeric actin filaments arise directly from muscle stress fibers. This requires formins (e.g., FHOD3), non-muscle myosin IIA and non-muscle myosin IIB. Furthermore, we show short cardiac myosin II filaments grow to form ~1.5 μm long filaments that then 'stitch' together to form the stack of filaments at the core of the sarcomere (i.e., the A-band). A-band assembly is dependent on the proper organization of actin filaments and, as such, is also dependent on FHOD3 and myosin IIB. We use this experimental paradigm to present evidence for a unifying model of sarcomere assembly.
© 2018, Fenix et al.
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17 MeSH Terms
Bid maintains mitochondrial cristae structure and function and protects against cardiac disease in an integrative genomics study.
Salisbury-Ruf CT, Bertram CC, Vergeade A, Lark DS, Shi Q, Heberling ML, Fortune NL, Okoye GD, Jerome WG, Wells QS, Fessel J, Moslehi J, Chen H, Roberts LJ, Boutaud O, Gamazon ER, Zinkel SS
(2018) Elife 7:
MeSH Terms: Animals, Apoptosis, BH3 Interacting Domain Death Agonist Protein, Beclin-1, Cell Respiration, Fibrosis, Gene Expression Regulation, Genome-Wide Association Study, Genomics, Heart Diseases, Heart Ventricles, Humans, Mice, Inbred C57BL, Mitochondria, Mitochondrial Proton-Translocating ATPases, Mutation, Myeloid Progenitor Cells, Myocardial Infarction, Myocytes, Cardiac, Polymorphism, Single Nucleotide, Protein Multimerization, Protein Structure, Secondary, Protein Subunits, Reactive Oxygen Species, Reproducibility of Results, Up-Regulation
Show Abstract · Added December 11, 2018
Bcl-2 family proteins reorganize mitochondrial membranes during apoptosis, to form pores and rearrange cristae. In vitro and in vivo analysis integrated with human genetics reveals a novel homeostatic mitochondrial function for Bcl-2 family protein Bid. Loss of full-length Bid results in apoptosis-independent, irregular cristae with decreased respiration. mice display stress-induced myocardial dysfunction and damage. A gene-based approach applied to a biobank, validated in two independent GWAS studies, reveals that decreased genetically determined BID expression associates with myocardial infarction (MI) susceptibility. Patients in the bottom 5% of the expression distribution exhibit >4 fold increased MI risk. Carrier status with nonsynonymous variation in Bid's membrane binding domain, Bid, associates with MI predisposition. Furthermore, Bid but not Bid associates with Mcl-1, previously implicated in cristae stability; decreased MCL-1 expression associates with MI. Our results identify a role for Bid in homeostatic mitochondrial cristae reorganization, that we link to human cardiac disease.
© 2018, Salisbury-Ruf et al.
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26 MeSH Terms
Loss of CENP-F Results in Dilated Cardiomyopathy with Severe Disruption of Cardiac Myocyte Architecture.
Manalo A, Schroer AK, Fenix AM, Shancer Z, Coogan J, Brolsma T, Burnette DT, Merryman WD, Bader DM
(2018) Sci Rep 8: 7546
MeSH Terms: Animals, Cardiomyopathy, Dilated, Chromosomal Proteins, Non-Histone, Disease Models, Animal, Genetic Association Studies, Genetic Predisposition to Disease, Heart Failure, Humans, Intercellular Junctions, Loss of Function Mutation, Mice, Microfilament Proteins, Microtubules, Myocytes, Cardiac, Polymorphism, Single Nucleotide, Stroke Volume
Show Abstract · Added March 27, 2019
Centromere-binding protein F (CENP-F) is a very large and complex protein with many and varied binding partners including components of the microtubule network. Numerous CENP-F functions impacting diverse cellular behaviors have been identified. Importantly, emerging data have shown that CENP-F loss- or gain-of-function has critical effects on human development and disease. Still, it must be noted that data at the single cardiac myocyte level examining the impact of CENP-F loss-of-function on fundamental cellular behavior is missing. To address this gap in our knowledge, we analyzed basic cell structure and function in cardiac myocytes devoid of CENP-F. We found many diverse structural abnormalities including disruption of the microtubule network impacting critical characteristics of the cardiac myocyte. This is the first report linking microtubule network malfunction to cardiomyopathy. Importantly, we also present data demonstrating a direct link between a CENP-F single nucleotide polymorphism (snp) and human cardiac disease. In a proximate sense, these data examining CENP-F function explain the cellular basis underlying heart disease in this genetic model and, in a larger sense, they will hopefully provide a platform upon which the field can explore diverse cellular outcomes in wide-ranging areas of research on this critical protein.
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16 MeSH Terms
In Silico Pharmacoepidemiologic Evaluation of Drug-Induced Cardiovascular Complications Using Combined Classifiers.
Cai C, Fang J, Guo P, Wang Q, Hong H, Moslehi J, Cheng F
(2018) J Chem Inf Model 58: 943-956
MeSH Terms: Antineoplastic Agents, Cardiovascular System, Computational Biology, Computer Simulation, Drug Discovery, Drug-Related Side Effects and Adverse Reactions, Humans, Molecular Targeted Therapy, Myocytes, Cardiac, Pluripotent Stem Cells, Product Surveillance, Postmarketing, Safety
Show Abstract · Added October 1, 2018
Drug-induced cardiovascular complications are the most common adverse drug events and account for the withdrawal or severe restrictions on the use of multitudinous postmarketed drugs. In this study, we developed new in silico models for systematic identification of drug-induced cardiovascular complications in drug discovery and postmarketing surveillance. Specifically, we collected drug-induced cardiovascular complications covering the five most common types of cardiovascular outcomes (hypertension, heart block, arrhythmia, cardiac failure, and myocardial infarction) from four publicly available data resources: Comparative Toxicogenomics Database, SIDER, Offsides, and MetaADEDB. Using these databases, we developed a combined classifier framework through integration of five machine-learning algorithms: logistic regression, random forest, k-nearest neighbors, support vector machine, and neural network. The totality of models included 180 single classifiers with area under receiver operating characteristic curves (AUC) ranging from 0.647 to 0.809 on 5-fold cross-validations. To develop the combined classifiers, we then utilized a neural network algorithm to integrate the best four single classifiers for each cardiovascular outcome. The combined classifiers had higher performance with an AUC range from 0.784 to 0.842 compared to single classifiers. Furthermore, we validated our predicted cardiovascular complications for 63 anticancer agents using experimental data from clinical studies, human pluripotent stem cell-derived cardiomyocyte assays, and literature. The success rate of our combined classifiers reached 87%. In conclusion, this study presents powerful in silico tools for systematic risk assessment of drug-induced cardiovascular complications. This tool is relevant not only in early stages of drug discovery but also throughout the life of a drug including clinical trials and postmarketing surveillance.
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12 MeSH Terms
Inhibition of the -Subunit of Phosphoinositide 3-Kinase in Heart Increases Late Sodium Current and Is Arrhythmogenic.
Yang T, Meoli DF, Moslehi J, Roden DM
(2018) J Pharmacol Exp Ther 365: 460-466
MeSH Terms: Action Potentials, Animals, Arrhythmias, Cardiac, CHO Cells, Cricetulus, Dose-Response Relationship, Drug, Electrophysiological Phenomena, Enzyme Inhibitors, Female, Heart, Mice, Mice, Inbred C57BL, Myocytes, Cardiac, Phosphoinositide-3 Kinase Inhibitors, Sodium
Show Abstract · Added April 22, 2018
Although inhibition of phosphoinositide 3-kinase (PI3K) is an emerging strategy in cancer therapy, we and others have reported that this action can also contribute to drug-induced QT prolongation and arrhythmias by increasing cardiac late sodium current (I). Previous studies in mice implicate the PI3K- isoform in arrhythmia susceptibility. Here, we have determined the effects of new anticancer drugs targeting specific PI3K isoforms on I and action potentials (APs) in mouse cardiomyocytes and Chinese hamster ovary cells (CHO). Chronic exposure (10-100 nM; 5-48 hours) to PI3K--specific subunit inhibitors BYL710 (alpelisib) and A66 and a pan-PI3K inhibitor (BKM120) increased I in -transfected CHO cells and mouse cardiomyocytes. The specific inhibitors (10-100 nM for 5 hours) markedly prolonged APs and generated triggered activity in mouse cardiomyocytes (9/12) but not in controls (0/6), and BKM120 caused similar effects (3/6). The inclusion of water-soluble PIP3, a downstream effector of the PI3K signaling pathway, in the pipette solution reversed these arrhythmogenic effects. By contrast, inhibition of PI3K-, -, and - isoforms did not alter I or APs. We conclude that inhibition of cardiac PI3K- is arrhythmogenic by increasing I and this effect is not seen with inhibition of other PI3K isoforms. These results highlight a mechanism underlying potential cardiotoxicity of PI3K- inhibitors.
Copyright © 2018 by The American Society for Pharmacology and Experimental Therapeutics.
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15 MeSH Terms
Loss of the melanocortin-4 receptor in mice causes dilated cardiomyopathy.
Litt MJ, Okoye GD, Lark D, Cakir I, Moore C, Barber MC, Atkinson J, Fessel J, Moslehi J, Cone RD
(2017) Elife 6:
MeSH Terms: Adenosine Diphosphate, Animals, Cardiomyopathy, Dilated, Cell Respiration, Mice, Inbred C57BL, Mice, Knockout, Mitochondria, Myocardium, Myocytes, Cardiac, Reactive Oxygen Species, Receptor, Melanocortin, Type 4
Show Abstract · Added December 2, 2017
Haploinsufficiency of the melanocortin-4 receptor, the most common monogenetic obesity syndrome in humans, is associated with a reduction in autonomic tone, bradycardia, and incidence of obesity-associated hypertension. Thus, it has been assumed that melanocortin obesity syndrome may be protective with respect to obesity-associated cardiovascular disease. We show here that absence of the melanocortin-4 receptor (MC4R) in mice causes dilated cardiomyopathy, characterized by reduced contractility and increased left ventricular diameter. This cardiomyopathy is independent of obesity as weight matched diet induced obese mice do not display systolic dysfunction. cardiomyopathy is characterized by ultrastructural changes in mitochondrial morphology and cardiomyocyte disorganization. Remarkably, testing of myocardial tissue from mice exhibited increased ADP stimulated respiratory capacity. However, this increase in respiration correlates with increased reactive oxygen species production - a canonical mediator of tissue damage. Together this study identifies MC4R deletion as a novel and potentially clinically important cause of heart failure.
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11 MeSH Terms
Exposure to particulate matter induces cardiomyocytes apoptosis after myocardial infarction through NFκB activation.
Li X, Geng J, Chen Y, Chen F, Liu C, Xu Q, Zhao J, Hu J, Xie J, Xu B
(2017) Biochem Biophys Res Commun 488: 224-231
MeSH Terms: Animals, Apoptosis, Male, Mice, Myocardial Infarction, Myocytes, Cardiac, NF-kappa B, Particulate Matter
Show Abstract · Added September 11, 2017
Clinical evidence has indicated an increased myocardial infarction (MI) morbidity and mortality after exposure to air pollution (particulate matter<2.5 μm, PM2.5). However, the mechanisms by which PM2.5 aggravates MI remain unknown. Present study was to explore the adverse effect of PM2.5 on myocardium after MI and the potential mechanisms. Male mice with MI surgery were treated with PM2.5 by intranasal instillation. Neonatal mice ventricular myocytes (NMVMs) subjected to hypoxia were also incubated with PM2.5 to determine the role of PM2.5 in vitro. Exposure to PM2.5 significantly impaired the cardiac function and increased the infarct size in MI mice. TUNEL assay, flow cytometry and western blotting of Caspase 3, Bax and BCl-2 indicated that PM2.5 exposure could cause cellular apoptosis in vivo and in vitro. Besides, PM2.5 activated NFκB pathway and increased gene expression of IL-1β and IL-6 in NMVMs with hypoxia, which could be effectively reversed by SN-50-induced blockade of NFκB translocation to the nucleus. In summary, air pollution induces myocardium apoptosis and then impairs cardiac function and aggravates MI via NFκB activation.
Copyright © 2017 Elsevier Inc. All rights reserved.
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8 MeSH Terms
Azithromycin Causes a Novel Proarrhythmic Syndrome.
Yang Z, Prinsen JK, Bersell KR, Shen W, Yermalitskaya L, Sidorova T, Luis PB, Hall L, Zhang W, Du L, Milne G, Tucker P, George AL, Campbell CM, Pickett RA, Shaffer CM, Chopra N, Yang T, Knollmann BC, Roden DM, Murray KT
(2017) Circ Arrhythm Electrophysiol 10:
MeSH Terms: Action Potentials, Animals, Anti-Bacterial Agents, Arrhythmias, Cardiac, Azithromycin, CHO Cells, Calcium Channel Blockers, Calcium Channels, L-Type, Cricetulus, Dose-Response Relationship, Drug, Electrocardiography, Ambulatory, Female, HEK293 Cells, Heart Rate, Humans, KCNQ1 Potassium Channel, Mice, Inbred C57BL, Myocytes, Cardiac, NAV1.5 Voltage-Gated Sodium Channel, Potassium Channel Blockers, Potassium Channels, Inwardly Rectifying, Potassium Channels, Voltage-Gated, Rabbits, Sodium Channel Blockers, Telemetry, Time Factors, Transfection, Young Adult
Show Abstract · Added July 6, 2017
BACKGROUND - The widely used macrolide antibiotic azithromycin increases risk of cardiovascular and sudden cardiac death, although the underlying mechanisms are unclear. Case reports, including the one we document here, demonstrate that azithromycin can cause rapid, polymorphic ventricular tachycardia in the absence of QT prolongation, indicating a novel proarrhythmic syndrome. We investigated the electrophysiological effects of azithromycin in vivo and in vitro using mice, cardiomyocytes, and human ion channels heterologously expressed in human embryonic kidney (HEK 293) and Chinese hamster ovary (CHO) cells.
METHODS AND RESULTS - In conscious telemetered mice, acute intraperitoneal and oral administration of azithromycin caused effects consistent with multi-ion channel block, with significant sinus slowing and increased PR, QRS, QT, and QTc intervals, as seen with azithromycin overdose. Similarly, in HL-1 cardiomyocytes, the drug slowed sinus automaticity, reduced phase 0 upstroke slope, and prolonged action potential duration. Acute exposure to azithromycin reduced peak SCN5A currents in HEK cells (IC=110±3 μmol/L) and Na current in mouse ventricular myocytes. However, with chronic (24 hour) exposure, azithromycin caused a ≈2-fold increase in both peak and late SCN5A currents, with findings confirmed for I in cardiomyocytes. Mild block occurred for K currents representing I (CHO cells expressing hERG; IC=219±21 μmol/L) and I (CHO cells expressing KCNQ1+KCNE1; IC=184±12 μmol/L), whereas azithromycin suppressed L-type Ca currents (rabbit ventricular myocytes, IC=66.5±4 μmol/L) and I (HEK cells expressing Kir2.1, IC=44±3 μmol/L).
CONCLUSIONS - Chronic exposure to azithromycin increases cardiac Na current to promote intracellular Na loading, providing a potential mechanistic basis for the novel form of proarrhythmia seen with this macrolide antibiotic.
© 2017 American Heart Association, Inc.
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28 MeSH Terms