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Two-Pore-Domain Potassium (K 2P-) Channels: Cardiac Expression Patterns and Disease-Specific Remodelling Processes. Cells 2021; 10:cells10112914. [PMID: 34831137 PMCID: PMC8616229 DOI: 10.3390/cells10112914] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/18/2021] [Accepted: 10/22/2021] [Indexed: 12/23/2022] Open
Abstract
Two-pore-domain potassium (K2P-) channels conduct outward K+ currents that maintain the resting membrane potential and modulate action potential repolarization. Members of the K2P channel family are widely expressed among different human cell types and organs where they were shown to regulate important physiological processes. Their functional activity is controlled by a broad variety of different stimuli, like pH level, temperature, and mechanical stress but also by the presence of lipids or pharmacological agents. In patients suffering from cardiovascular diseases, alterations in K2P-channel expression and function have been observed, suggesting functional significance and a potential therapeutic role of these ion channels. For example, upregulation of atrial specific K2P3.1 (TASK-1) currents in atrial fibrillation (AF) patients was shown to contribute to atrial action potential duration shortening, a key feature of AF-associated atrial electrical remodelling. Therefore, targeting K2P3.1 (TASK-1) channels might constitute an intriguing strategy for AF treatment. Further, mechanoactive K2P2.1 (TREK-1) currents have been implicated in the development of cardiac hypertrophy, cardiac fibrosis and heart failure. Cardiovascular expression of other K2P channels has been described, functional evidence in cardiac tissue however remains sparse. In the present review, expression, function, and regulation of cardiovascular K2P channels are summarized and compared among different species. Remodelling patterns, observed in disease models are discussed and compared to findings from clinical patients to assess the therapeutic potential of K2P channels.
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2
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Feyen DAM, McKeithan WL, Bruyneel AAN, Spiering S, Hörmann L, Ulmer B, Zhang H, Briganti F, Schweizer M, Hegyi B, Liao Z, Pölönen RP, Ginsburg KS, Lam CK, Serrano R, Wahlquist C, Kreymerman A, Vu M, Amatya PL, Behrens CS, Ranjbarvaziri S, Maas RGC, Greenhaw M, Bernstein D, Wu JC, Bers DM, Eschenhagen T, Metallo CM, Mercola M. Metabolic Maturation Media Improve Physiological Function of Human iPSC-Derived Cardiomyocytes. Cell Rep 2021; 32:107925. [PMID: 32697997 PMCID: PMC7437654 DOI: 10.1016/j.celrep.2020.107925] [Citation(s) in RCA: 188] [Impact Index Per Article: 62.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2020] [Revised: 05/15/2020] [Accepted: 06/26/2020] [Indexed: 12/15/2022] Open
Abstract
Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) have enormous potential for the study of human cardiac disorders. However, their physiological immaturity severely limits their utility as a model system and their adoption for drug discovery. Here, we describe maturation media designed to provide oxidative substrates adapted to the metabolic needs of human iPSC (hiPSC)-CMs. Compared with conventionally cultured hiPSC-CMs, metabolically matured hiPSC-CMs contract with greater force and show an increased reliance on cardiac sodium (Na+) channels and sarcoplasmic reticulum calcium (Ca2+) cycling. The media enhance the function, long-term survival, and sarcomere structures in engineered heart tissues. Use of the maturation media made it possible to reliably model two genetic cardiac diseases: long QT syndrome type 3 due to a mutation in the cardiac Na+ channel SCN5A and dilated cardiomyopathy due to a mutation in the RNA splicing factor RBM20. The maturation media should increase the fidelity of hiPSC-CMs as disease models. Physiological immaturity of iPSC-derived cardiomyocytes limits their fidelity as disease models. Feyen et al. developed a low glucose, high oxidative substrate media that increase maturation of ventricular-like hiPSC-CMs in 2D and 3D cultures relative to standard protocols. Improved characteristics include a low resting Vm, rapid depolarization, and increased Ca2+ dependence and force generation.
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Affiliation(s)
- Dries A M Feyen
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA; Department of Cardiology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Wesley L McKeithan
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA; Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA, USA; Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Arne A N Bruyneel
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Sean Spiering
- Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA, USA; Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Larissa Hörmann
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Bärbel Ulmer
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Hui Zhang
- Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Francesca Briganti
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Michaela Schweizer
- Electron Microscopy Unit, Center for Molecular Neurobiology Hamburg, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Bence Hegyi
- Department of Pharmacology, University of California, Davis, Davis, CA, USA
| | - Zhandi Liao
- Department of Pharmacology, University of California, Davis, Davis, CA, USA
| | | | - Kenneth S Ginsburg
- Department of Pharmacology, University of California, Davis, Davis, CA, USA
| | - Chi Keung Lam
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Ricardo Serrano
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Christine Wahlquist
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA; Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA, USA; Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Alexander Kreymerman
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Michelle Vu
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Prashila L Amatya
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Charlotta S Behrens
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Sara Ranjbarvaziri
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Renee G C Maas
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA; Department of Cardiology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Matthew Greenhaw
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Daniel Bernstein
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Joseph C Wu
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA, USA
| | - Thomas Eschenhagen
- Institute of Experimental Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Christian M Metallo
- Department of Bioengineering, University of California, San Diego, San Diego, CA, USA
| | - Mark Mercola
- Cardiovascular Institute and Department of Medicine, Stanford University, Stanford, CA 94305, USA; Sanford-Burnham-Prebys Medical Discovery Institute, La Jolla, CA, USA; Department of Bioengineering, University of California, San Diego, San Diego, CA, USA.
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3
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Saadeh K, Fazmin IT. Mitochondrial Dysfunction Increases Arrhythmic Triggers and Substrates; Potential Anti-arrhythmic Pharmacological Targets. Front Cardiovasc Med 2021; 8:646932. [PMID: 33659284 PMCID: PMC7917191 DOI: 10.3389/fcvm.2021.646932] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2020] [Accepted: 01/26/2021] [Indexed: 12/31/2022] Open
Abstract
Incidence of cardiac arrhythmias increases significantly with age. In order to effectively stratify arrhythmic risk in the aging population it is crucial to elucidate the relevant underlying molecular mechanisms. The changes underlying age-related electrophysiological disruption appear to be closely associated with mitochondrial dysfunction. Thus, the present review examines the mechanisms by which age-related mitochondrial dysfunction promotes arrhythmic triggers and substrate. Namely, via alterations in plasmalemmal ionic currents (both sodium and potassium), gap junctions, cellular Ca2+ homeostasis, and cardiac fibrosis. Stratification of patients' mitochondrial function status permits application of appropriate anti-arrhythmic therapies. Here, we discuss novel potential anti-arrhythmic pharmacological interventions that specifically target upstream mitochondrial function and hence ameliorates the need for therapies targeting downstream changes which have constituted traditional antiarrhythmic therapy.
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Affiliation(s)
- Khalil Saadeh
- School of Clinical Medicine, University of Cambridge, Cambridge, United Kingdom.,Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom
| | - Ibrahim Talal Fazmin
- School of Clinical Medicine, University of Cambridge, Cambridge, United Kingdom.,Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.,Royal Papworth Hospital NHS Foundation Trust, Cambridge, United Kingdom
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Gowen BH, Reyes MV, Joseph LC, Morrow JP. Mechanisms of Chronic Metabolic Stress in Arrhythmias. Antioxidants (Basel) 2020; 9:antiox9101012. [PMID: 33086602 PMCID: PMC7603089 DOI: 10.3390/antiox9101012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Revised: 10/07/2020] [Accepted: 10/13/2020] [Indexed: 02/06/2023] Open
Abstract
Cardiac arrhythmias are responsible for many cardiovascular disease-related deaths worldwide. While arrhythmia pathogenesis is complex, there is increasing evidence for metabolic causes. Obesity, diabetes, and chronically consuming high-fat foods significantly increase the likelihood of developing arrhythmias. Although these correlations are well established, mechanistic explanations connecting a high-fat diet (HFD) to arrhythmogenesis are incomplete, although oxidative stress appears to be critical. This review investigates the metabolic changes that occur in obesity and after HFD. Potential therapies to prevent or treat arrhythmias are discussed, including antioxidants.
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Affiliation(s)
| | | | | | - John P. Morrow
- Correspondence: ; Tel.: +1-212-305-5553; Fax: +1-212-305-4648
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Ramadan NM, Malek HA, Rahman KAE, El-Kholy E, Shaalan D, Elkashef W. Liraglutide Effect on Ventricular Transient Outward K + Channel and Connexin-43 Protein Expression. Exp Clin Endocrinol Diabetes 2020; 129:899-907. [PMID: 32559789 DOI: 10.1055/a-1162-8196] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
BACKGROUND Human glucagon-like peptide-1 analogue, Liraglutide, has shown cardioprotective effects in animal and clinical studies of type 2 diabetes mellitus. This study was conducted to assess the effect of Liraglutide on diabetes-induced myocardial electrical remodeling. MATERIALS AND METHODS A rat model of type 2 diabetes mellitus was induced by high-fat diet and low dose Streptozotocin (35 mg/kg). Diabetic rats were randomized into 4 subgroups (n=6-7): diabetic-untreated, diabetics treated with Liraglutide, diabetics treated with Ramipril, and diabetics treated with Metformin in addition to a control group. Changes in serum glucose, insulin, lipid profile and revised quantitative insulin sensitivity check index (QUICKI index) were assessed. QT and QTc intervals were measured and the degree of cardiac interstitial and perivascular fibrosis was examined. The expression of myocardial Ito channel α subunits, gap junction protein; Kv 4.2/4.3 and connexin 43 (Cx43) respectively, were assessed by western blotting and immunohistochemistry. RESULTS Similar to Ramipril, both Liraglutide and Metformin effectively inhibited the diabetes-induced myocardial hypertrophy and fibrosis. However, Liraglutide treatment significantly improved Kv 4.2/4.3 and Cx43 expression/distribution and prevented diabetes-related QTc interval prolongation. CONCLUSIONS We have shown that pathological alterations in myocardial Cx43 expression and distribution, in addition to reduced Ito channel expression, may underlie the QTc interval prolongation in high-fat diet/STZ rat model of type 2 diabetes mellitus. The beneficial effects of Liraglutide, as those of Ramipril, on cardiac electrophysiology could be at least attributed to its direct ability to normalize expression and distribution of Cx43 and Ito channels in the diabetic rat heart.
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Affiliation(s)
- Nehal M Ramadan
- Department of Clinical Pharmacology, Mansoura University, Faculty of Medicine, Mansoura, Egypt
| | - Hala Abdel Malek
- Department of Clinical Pharmacology, Mansoura University, Faculty of Medicine, Mansoura, Egypt
| | - Karawan Abd-El Rahman
- Department of Clinical Pharmacology, Mansoura University, Faculty of Medicine, Mansoura, Egypt
| | - Elhamy El-Kholy
- Department of Clinical Pharmacology, Mansoura University, Faculty of Medicine, Mansoura, Egypt
| | - Dalia Shaalan
- Departments of Medical Biochemistry and Molecular Biology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
| | - Wagdi Elkashef
- Department of Pathology, Faculty of Medicine, Mansoura University, Mansoura, Egypt
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Li XY, Hou HT, Chen HX, Liu XC, Wang J, Yang Q, He GW. Preoperative plasma biomarkers associated with atrial fibrillation after coronary artery bypass surgery. J Thorac Cardiovasc Surg 2020; 162:851-863.e3. [PMID: 32197906 DOI: 10.1016/j.jtcvs.2020.01.079] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 01/15/2020] [Accepted: 01/29/2020] [Indexed: 12/14/2022]
Abstract
OBJECTIVES Postoperative atrial fibrillation (POAF) is a common complication in coronary artery bypass grafting (CABG) procedures. This prospective study aimed to investigate predisposition of proteins and metabolites correlated to POAF after CABG and related cellular pathways. METHODS Preoperative plasma samples from patients undergoing CABG procedures were prospectively collected. After CABG, the patients were grouped to POAF or sinus rhythm (N = 170; n = 90 in the discovery set and n = 80 in the validation set). The plasma samples were analyzed using proteomics, metabolomics, and bioinformatics to identify the differential proteins and differential metabolites. The correlation between differential proteins and POAF was also investigated by multivariable regression analysis and receiver operator characteristic analysis. RESULTS In the POAF(+) group, 29 differential proteins and 61 differential metabolites were identified compared with the POAF(-) group. The analysis of integrated omics revealed that preoperative alteration of peroxisome proliferators-activated receptor α and glutathione metabolism pathways increased the susceptibility of POAF after CABG. There was a correlation between plasma levels of apolipoprotein-C3, phospholipid transfer protein, glutathione peroxidase 3, cholesteryl ester transfer protein, and POAF. CONCLUSIONS The present study for first time at multi-omics levels explored the mechanism of POAF and validated the results in a new cohort of patients, suggesting preexisting differential proteins and differential metabolites in the plasma of patients prone to POAF after CABG. Dysregulation of peroxisome proliferators-activated receptor α and glutathione metabolism pathways related to metabolic remodeling and redox imbalance-associated electrical remodeling may play a key role in the pathogenesis of POAF. Lower plasma phospholipid transfer protein, apolipoprotein-C3, higher cholesteryl ester transfer protein and glutathione peroxidase 3 levels are linked with POAF. These proteins/metabolites may be developed as biomarkers to predict POAF.
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Affiliation(s)
- Xin-Ya Li
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Hai-Tao Hou
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Huan-Xin Chen
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Xiao-Cheng Liu
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Jun Wang
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Qin Yang
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China
| | - Guo-Wei He
- Center for Basic Medical Research and Department of Cardiovascular Surgery, TEDA International Cardiovascular Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Tianjin, China; Department of Cardiac Surgery, The First Affiliated Hospital, Zhejiang University, Hangzhou, China; School of Pharmacy, Wannan Medical College, Wuhu, Anhui, China; Department of Surgery, Oregon Health and Science University, Portland, Ore.
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7
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Borghetti G, Eisenberg CA, Signore S, Sorrentino A, Kaur K, Andrade-Vicenty A, Edwards JG, Nerkar M, Qanud K, Sun D, Goichberg P, Leri A, Anversa P, Eisenberg LM, Jacobson JT, Hintze TH, Rota M. Notch signaling modulates the electrical behavior of cardiomyocytes. Am J Physiol Heart Circ Physiol 2017; 314:H68-H81. [PMID: 28939651 DOI: 10.1152/ajpheart.00587.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Notch receptor signaling is active during cardiac development and silenced in myocytes after birth. Conversely, outward K+ Kv currents progressively appear in postnatal myocytes leading to shortening of the action potential (AP) and acquisition of the mature electrical phenotype. In the present study, we tested the possibility that Notch signaling modulates the electrical behavior of cardiomyocytes by interfering with Kv currents. For this purpose, the effects of Notch receptor activity on electrophysiological properties of myocytes were evaluated using transgenic mice with inducible expression of the Notch1 intracellular domain (NICD), the functional fragment of the activated Notch receptor, and in neonatal myocytes after inhibition of the Notch transduction pathway. By patch clamp, NICD-overexpressing cells presented prolonged AP duration and reduced upstroke amplitude, properties that were coupled with reduced rapidly activating Kv and fast Na+ currents, compared with cells obtained from wild-type mice. In cultured neonatal myocytes, inhibition of the proteolitic release of NICD with a γ-secretase antagonist increased transcript levels of the Kv channel-interacting proteins 2 (KChIP2) and enhanced the density of Kv currents. Collectively, these results indicate that Notch signaling represents an important regulator of the electrophysiological behavior of developing and adult myocytes by repressing, at least in part, repolarizing Kv currents. NEW & NOTEWORTHY We investigated the effects of Notch receptor signaling on the electrical properties of cardiomyocytes. Our results indicate that the Notch transduction pathway interferes with outward K+ Kv currents, critical determinants of the electrical repolarization of myocytes.
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Affiliation(s)
- Giulia Borghetti
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | - Carol A Eisenberg
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Sergio Signore
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | - Andrea Sorrentino
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | - Keerat Kaur
- Department of Physiology, New York Medical College, Valhalla, New York
| | | | - John G Edwards
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Mriganka Nerkar
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Khaled Qanud
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Dong Sun
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Polina Goichberg
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | - Annarosa Leri
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | - Piero Anversa
- Departments of Anesthesia and Medicine, and Division of Cardiovascular Medicine, Brigham and Women's Hospital, Harvard Medical School , Boston, Massachusetts
| | | | - Jason T Jacobson
- Department of Physiology, New York Medical College, Valhalla, New York.,Department of Cardiology, Westchester Medical Center, Valhalla, New York
| | - Thomas H Hintze
- Department of Physiology, New York Medical College, Valhalla, New York
| | - Marcello Rota
- Department of Physiology, New York Medical College, Valhalla, New York
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8
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Aromolaran AS, Boutjdir M. Cardiac Ion Channel Regulation in Obesity and the Metabolic Syndrome: Relevance to Long QT Syndrome and Atrial Fibrillation. Front Physiol 2017; 8:431. [PMID: 28680407 PMCID: PMC5479057 DOI: 10.3389/fphys.2017.00431] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 06/06/2017] [Indexed: 01/03/2023] Open
Abstract
Obesity and its associated metabolic dysregulation leading to metabolic syndrome is an epidemic that poses a significant public health problem. More than one-third of the world population is overweight or obese leading to enhanced risk of cardiovascular disease (CVD) incidence and mortality. Obesity predisposes to atrial fibrillation, ventricular, and supraventricular arrhythmias; conditions that are underlain by dysfunction in electrical activity of the heart. To date, current therapeutic options for cardiomyopathy of obesity are limited, suggesting that there is considerable room for development of therapeutic interventions with novel mechanisms of action that will help normalize rhythm in obese patients. Emerging candidates for modulation by obesity are cardiac ion channels and Ca handling proteins. However, the underlying molecular mechanisms of the impact of obesity on these channels/Ca handling proteins remain incompletely understood. Obesity is marked by accumulation of adipose tissue associated with a variety of adverse adaptations including dyslipidemia (or abnormal levels of serum free fatty acids), increased secretion of pro-inflammatory cytokines, fibrosis, hyperglycemia, and insulin resistance, that will cause electrical remodeling and thus predispose to arrhythmias. Further, adipose tissue is also associated with the accumulation of subcutaneous and visceral fat, which are marked by distinct signaling mechanisms. Thus, there may also be functional differences in the outcome of regional distribution of fat deposits on ion channel/Ca handling proteins expression. Evaluating alterations in their functional expression in obesity will lead to progress in the knowledge about the mechanisms responsible for obesity-related arrhythmias. These advances are likely to reveal new targets for pharmacological modulation. The objective of this article is to review cardiac ion channel/Ca handling proteins remodeling that predispose to arrhythmias. Understanding how obesity and related mechanisms lead to cardiac electrical remodeling is likely to have a significant medical and economic impact.
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Affiliation(s)
- Ademuyiwa S Aromolaran
- Cardiovascular Research Program, VA New York Harbor Healthcare SystemBrooklyn, NY, United States.,Departments of Medicine, Cell Biology and Pharmacology, State University of New York Downstate Medical CenterBrooklyn, NY, United States
| | - Mohamed Boutjdir
- Cardiovascular Research Program, VA New York Harbor Healthcare SystemBrooklyn, NY, United States.,Departments of Medicine, Cell Biology and Pharmacology, State University of New York Downstate Medical CenterBrooklyn, NY, United States.,Department of Medicine, New York University School of MedicineNew York, NY, United States
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9
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Pini A, Obara I, Battell E, Chazot PL, Rosa AC. Histamine in diabetes: Is it time to reconsider? Pharmacol Res 2016; 111:316-324. [DOI: 10.1016/j.phrs.2016.06.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 06/20/2016] [Accepted: 06/21/2016] [Indexed: 10/21/2022]
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10
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Yang KC, Nerbonne JM. Mechanisms contributing to myocardial potassium channel diversity, regulation and remodeling. Trends Cardiovasc Med 2015; 26:209-18. [PMID: 26391345 DOI: 10.1016/j.tcm.2015.07.002] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 07/11/2015] [Accepted: 07/12/2015] [Indexed: 01/19/2023]
Abstract
In the mammalian heart, multiple types of K(+) channels contribute to the control of cardiac electrical and mechanical functioning through the regulation of resting membrane potentials, action potential waveforms and refractoriness. There are similarly vast arrays of K(+) channel pore-forming and accessory subunits that contribute to the generation of functional myocardial K(+) channel diversity. Maladaptive remodeling of K(+) channels associated with cardiac and systemic diseases results in impaired repolarization and increased propensity for arrhythmias. Here, we review the diverse transcriptional, post-transcriptional, post-translational, and epigenetic mechanisms contributing to regulating the expression, distribution, and remodeling of cardiac K(+) channels under physiological and pathological conditions.
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Affiliation(s)
- Kai-Chien Yang
- Department of Pharmacology, National Taiwan University, Taipei, Taiwan; Division of Cardiology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
| | - Jeanne M Nerbonne
- Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO; Internal Medicine, Washington University School of Medicine, St. Louis, MO; Cardiovascular Division, Washington University School of Medicine, St. Louis, MO.
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11
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Murfitt L, Whiteley G, Iqbal MM, Kitmitto A. Targeting caveolin-3 for the treatment of diabetic cardiomyopathy. Pharmacol Ther 2015; 151:50-71. [PMID: 25779609 DOI: 10.1016/j.pharmthera.2015.03.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Accepted: 03/09/2015] [Indexed: 12/21/2022]
Abstract
Diabetes is a global health problem with more than 550 million people predicted to be diabetic by 2030. A major complication of diabetes is cardiovascular disease, which accounts for over two-thirds of mortality and morbidity in diabetic patients. This increased risk has led to the definition of a diabetic cardiomyopathy phenotype characterised by early left ventricular dysfunction with normal ejection fraction. Here we review the aetiology of diabetic cardiomyopathy and explore the involvement of the protein caveolin-3 (Cav3). Cav3 forms part of a complex mechanism regulating insulin signalling and glucose uptake, processes that are impaired in diabetes. Further, Cav3 is key for stabilisation and trafficking of cardiac ion channels to the plasma membrane and so contributes to the cardiac action potential shape and duration. In addition, Cav3 has direct and indirect interactions with proteins involved in excitation-contraction coupling and so has the potential to influence cardiac contractility. Significantly, both impaired contractility and rhythm disturbances are hallmarks of diabetic cardiomyopathy. We review here how changes to Cav3 expression levels and altered relationships with interacting partners may be contributory factors to several of the pathological features identified in diabetic cardiomyopathy. Finally, the review concludes by considering ways in which levels of Cav3 may be manipulated in order to develop novel therapeutic approaches for treating diabetic cardiomyopathy.
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Affiliation(s)
- Lucy Murfitt
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK
| | - Gareth Whiteley
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK
| | - Mohammad M Iqbal
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK
| | - Ashraf Kitmitto
- Institute of Cardiovascular Sciences, Faculty of Medical and Human Sciences, University of Manchester, M13 9NT, UK.
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12
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Yang KC, Kyle JW, Makielski JC, Dudley SC. Mechanisms of sudden cardiac death: oxidants and metabolism. Circ Res 2015; 116:1937-55. [PMID: 26044249 PMCID: PMC4458707 DOI: 10.1161/circresaha.116.304691] [Citation(s) in RCA: 87] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2014] [Accepted: 02/09/2015] [Indexed: 02/07/2023]
Abstract
Ventricular arrhythmia is the leading cause of sudden cardiac death (SCD). Deranged cardiac metabolism and abnormal redox state during cardiac diseases foment arrhythmogenic substrates through direct or indirect modulation of cardiac ion channel/transporter function. This review presents current evidence on the mechanisms linking metabolic derangement and excessive oxidative stress to ion channel/transporter dysfunction that predisposes to ventricular arrhythmias and SCD. Because conventional antiarrhythmic agents aiming at ion channels have proven challenging to use, targeting arrhythmogenic metabolic changes and redox imbalance may provide novel therapeutics to treat or prevent life-threatening arrhythmias and SCD.
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Affiliation(s)
- Kai-Chien Yang
- From the Department of Pharmacology (K.-C.Y.) and Division of Cardiology, Department of Internal Medicine (K.-C.Y.), National Taiwan University Hospital, Taipei, Taiwan; Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison (J.W.K., J.C.M.); and Lifespan Cardiovascular Institute, the Providence VA Medical Center, and Brown University, RI (S.C.D.)
| | - John W Kyle
- From the Department of Pharmacology (K.-C.Y.) and Division of Cardiology, Department of Internal Medicine (K.-C.Y.), National Taiwan University Hospital, Taipei, Taiwan; Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison (J.W.K., J.C.M.); and Lifespan Cardiovascular Institute, the Providence VA Medical Center, and Brown University, RI (S.C.D.)
| | - Jonathan C Makielski
- From the Department of Pharmacology (K.-C.Y.) and Division of Cardiology, Department of Internal Medicine (K.-C.Y.), National Taiwan University Hospital, Taipei, Taiwan; Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison (J.W.K., J.C.M.); and Lifespan Cardiovascular Institute, the Providence VA Medical Center, and Brown University, RI (S.C.D.).
| | - Samuel C Dudley
- From the Department of Pharmacology (K.-C.Y.) and Division of Cardiology, Department of Internal Medicine (K.-C.Y.), National Taiwan University Hospital, Taipei, Taiwan; Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison (J.W.K., J.C.M.); and Lifespan Cardiovascular Institute, the Providence VA Medical Center, and Brown University, RI (S.C.D.).
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Affiliation(s)
- J. P. Morrow
- Division of Cardiology; Department of Medicine; College of Physicians and Surgeons of Columbia University; New York NY USA
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Sato T, Kobayashi T, Kuno A, Miki T, Tanno M, Kouzu H, Itoh T, Ishikawa S, Kojima T, Miura T, Tohse N. Type 2 diabetes induces subendocardium-predominant reduction in transient outward K+ current with downregulation of Kv4.2 and KChIP2. Am J Physiol Heart Circ Physiol 2014; 306:H1054-65. [DOI: 10.1152/ajpheart.00414.2013] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In the present study, we examined if and how cardiac ion channels are modified by type 2 diabetes mellitus (T2DM). Subendocardial (Endo) myocytes and subepicardial (Epi) myocytes were isolated from left ventricles of Otsuka-Long-Evans-Tokushima Fatty rats (OLETF) rats, a rat model of T2DM, and Otsuka-Long-Evans-Tokushima (LETO) rats (nondiabetic control rats). Endo and Epi myocytes were used for whole cell patch-clamp recordings and for protein and mRNA analyses. Action potential durations in Endo and Epi myocytes were longer in OLETF rats than in LETO rats, and the difference was larger in Endo myocytes. Steady-state transient outward K+ current ( Ito) density was reduced in Endo but not Epi myocytes of OLETF rats compared with LETO rats, although the contribution of the fast component of Ito recovery from inactivation was smaller in both Endo and Epi myocytes of OLETF rats than in LETO rats. Kv4.2 protein was reduced only in Endo myocytes in OLETF rats, although voltage-gated K+ channel-interacting protein 2 (KChIP2) protein levels in both Endo and Epi myocytes were lower in OLETF rats than in LETO rats. Corresponding regional differences in mRNA levels of KChIP2 and Kv4.2 were observed between OLETF and LETO rats. mRNA levels of Iroquois homeobox 5 in Endo myocytes were 53% higher in OLETF rats than in LETO rats. Densities of inward rectifier K+ current and L-type Ca2+ current and mRNA levels of Kv4.3 and Kv1.4 were similar in OLETF and LETO rats. In conclusion, T2DM induces Endo-predominant prolongation of the action potential duration via a reduction of the fast component of Ito recovery from inactivation and reduced steady-state Ito, in which downregulation of Kv4.2 and KChIP2 may be involved. Increased Iroquois homeobox 5 expression may underlie Kv4.2 downregulation in T2DM.
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Affiliation(s)
- Tatsuya Sato
- Department of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo, Japan
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Takeshi Kobayashi
- Department of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Atsushi Kuno
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
- Department of Pharmacology, Sapporo Medical University School of Medicine, Sapporo, Japan; and
| | - Takayuki Miki
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Masaya Tanno
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Hidemichi Kouzu
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Takahito Itoh
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Satoko Ishikawa
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Takashi Kojima
- Department of Cell Science, Research Institute of Frontier Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Tetsuji Miura
- Department of Cardiovascular, Renal and Metabolic Medicine, Sapporo Medical University School of Medicine, Sapporo, Japan
| | - Noritsugu Tohse
- Department of Cellular Physiology and Signal Transduction, Sapporo Medical University School of Medicine, Sapporo, Japan
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15
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Morotti S, Edwards AG, McCulloch AD, Bers DM, Grandi E. A novel computational model of mouse myocyte electrophysiology to assess the synergy between Na+ loading and CaMKII. J Physiol 2014; 592:1181-97. [PMID: 24421356 DOI: 10.1113/jphysiol.2013.266676] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) hyperactivity in heart failure causes intracellular Na(+) ([Na(+)]i) loading (at least in part by enhancing the late Na(+) current). This [Na(+)]i gain promotes intracellular Ca(2+) ([Ca(2+)]i) overload by altering the equilibrium of the Na(+)-Ca(2+) exchanger to impair forward-mode (Ca(2+) extrusion), and favour reverse-mode (Ca(2+) influx) exchange. In turn, this Ca(2+) overload would be expected to further activate CaMKII and thereby form a pathological positive feedback loop of ever-increasing CaMKII activity, [Na(+)]i, and [Ca(2+)]i. We developed an ionic model of the mouse ventricular myocyte to interrogate this potentially arrhythmogenic positive feedback in both control conditions and when CaMKIIδC is overexpressed as in genetically engineered mice. In control conditions, simulation of increased [Na(+)]i causes the expected increases in [Ca(2+)]i, CaMKII activity, and target phosphorylation, which degenerate into unstable Ca(2+) handling and electrophysiology at high [Na(+)]i gain. Notably, clamping CaMKII activity to basal levels ameliorates but does not completely offset this outcome, suggesting that the increase in [Ca(2+)]i per se plays an important role. The effect of this CaMKII-Na(+)-Ca(2+)-CaMKII feedback is more striking in CaMKIIδC overexpression, where high [Na(+)]i causes delayed afterdepolarizations, which can be prevented by imposing low [Na(+)]i, or clamping CaMKII phosphorylation of L-type Ca(2+) channels, ryanodine receptors and phospholamban to basal levels. In this setting, Na(+) loading fuels a vicious loop whereby increased CaMKII activation perturbs Ca(2+) and membrane potential homeostasis. High [Na(+)]i is also required to produce instability when CaMKII is further activated by increased Ca(2+) loading due to β-adrenergic activation. Our results support recent experimental findings of a synergistic interaction between perturbed Na(+) fluxes and CaMKII, and suggest that pharmacological inhibition of intracellular Na(+) loading can contribute to normalizing Ca(2+) and membrane potential dynamics in heart failure.
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Affiliation(s)
- S Morotti
- Department of Pharmacology, University of California Davis, 451 Health Sciences Drive, GBSF rm 3502, Davis, CA 95616, USA.
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16
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Abstract
Since diabetic cardiomyopathy was first reported four decades ago, substantial information on its pathogenesis and clinical features has accumulated. In the heart, diabetes enhances fatty acid metabolism, suppresses glucose oxidation, and modifies intracellular signaling, leading to impairments in multiple steps of excitation–contraction coupling, inefficient energy production, and increased susceptibility to ischemia/reperfusion injury. Loss of normal microvessels and remodeling of the extracellular matrix are also involved in contractile dysfunction of diabetic hearts. Use of sensitive echocardiographic techniques (tissue Doppler imaging and strain rate imaging) and magnetic resonance spectroscopy enables detection of diabetic cardiomyopathy at an early stage, and a combination of the modalities allows differentiation of this type of cardiomyopathy from other organic heart diseases. Circumstantial evidence to date indicates that diabetic cardiomyopathy is a common but frequently unrecognized pathological process in asymptomatic diabetic patients. However, a strategy for prevention or treatment of diabetic cardiomyopathy to improve its prognosis has not yet been established. Here, we review both basic and clinical studies on diabetic cardiomyopathy and summarize problems remaining to be solved for improving management of this type of cardiomyopathy.
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Affiliation(s)
- Takayuki Miki
- Division of Cardiology, Second Department of Internal Medicine, School of Medicine, Sapporo Medical University, South-1 West-16, Chuo-ku, Sapporo, 060-8543, Japan
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Huang H, Amin V, Gurin M, Wan E, Thorp E, Homma S, Morrow JP. Diet-induced obesity causes long QT and reduces transcription of voltage-gated potassium channels. J Mol Cell Cardiol 2013; 59:151-8. [PMID: 23517696 DOI: 10.1016/j.yjmcc.2013.03.007] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2013] [Revised: 02/24/2013] [Accepted: 03/11/2013] [Indexed: 12/18/2022]
Abstract
In humans, obesity is associated with long QT, increased frequency of premature ventricular complexes, and sudden cardiac death. The mechanisms of the pro-arrhythmic electrophysiologic remodeling of obesity are poorly understood. We tested the hypothesis that there is decreased expression of voltage-gated potassium channels in the obese heart, leading to long QT. Using implanted telemeters, we found that diet-induced obese (DIO) wild-type mice have impaired cardiac repolarization, demonstrated by long QT, as well as more frequent ventricular ectopy, similar to obese humans. DIO mice have reduced protein and mRNA levels of the potassium channel Kv1.5 caused by a reduction of the transcription factor cyclic AMP response element binding protein (CREB) in DIO hearts. We found that CREB knock-down by siRNA reduces Kv1.5, CREB binds to the Kv1.5 promoter in the heart, and CREB increases transcription of mouse and human Kv1.5 promoters. The reduction in CREB protein during lipotoxicity can be rescued by inhibiting protein kinase D (PKD). Our results identify a mechanism for obesity-induced electrophysiologic remodeling in the heart, namely PKD-induced reduction of CREB, which in turn decreases expression of the potassium channel Kv1.5.
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Affiliation(s)
- Haiyan Huang
- Department of Medicine, Division of Cardiology, College of Physicians and Surgeons of Columbia University, New York, NY, USA
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18
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Olsen KB, Axelsen LN, Braunstein TH, Sørensen CM, Andersen CB, Ploug T, Holstein-Rathlou NH, Nielsen MS. Myocardial impulse propagation is impaired in right ventricular tissue of Zucker diabetic fatty (ZDF) rats. Cardiovasc Diabetol 2013; 12:19. [PMID: 23327647 PMCID: PMC3561236 DOI: 10.1186/1475-2840-12-19] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 01/14/2013] [Indexed: 01/31/2023] Open
Abstract
Background Diabetes increases the risk of cardiovascular complications including arrhythmias, but the underlying mechanisms remain to be established. Decreased conduction velocity (CV), which is an independent risk factor for re-entry arrhythmias, is present in models with streptozotocin (STZ) induced type 1 diabetes. Whether CV is also disturbed in models of type 2 diabetes is currently unknown. Methods We used Zucker Diabetic Fatty (ZDF) rats, as a model of type 2 diabetes, and their lean controls Zucker Diabetic Lean (ZDL) rats to investigate CV and its response to the anti-arrhythmic peptide analogue AAP10. Gap junction remodeling was examined by immunofluorescence and western blotting. Cardiac histomorphometry was examined by Masson`s Trichrome staining and intracellular lipid accumulation was analyzed by Bodipy staining. Results CV was significantly slower in ZDF rats (56±1.9 cm/s) compared to non-diabetic controls (ZDL, 66±1.6 cm/s), but AAP10 did not affect CV in either group. The total amount of Connexin43 (C×43) was identical between ZDF and ZDL rats, but the amount of lateralized C×43 was significantly increased in ZDF rats (42±12 %) compared to ZDL rats (30±8%), p<0.04. Judged by electrophoretic mobility, C×43 phosphorylation was unchanged between ZDF and ZDL rats. Also, no differences in cardiomyocyte size or histomorphometry including fibrosis were observed between groups, but the volume of intracellular lipid droplets was 4.2 times higher in ZDF compared to ZDL rats (p<0.01). Conclusion CV is reduced in type 2 diabetic ZDF rats. The CV disturbance may be partly explained by increased lateralization of C×43, but other factors are likely also involved. Our data indicates that lipotoxicity potentially may play a role in development of conduction disturbances and arrhythmias in type 2 diabetes.
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Affiliation(s)
- Kristine Boisen Olsen
- The Danish National Research Foundation Centre for Cardiac Arrhythmia and Department of Biomedical Sciences, Faculty of Health Sciences, University of Copenhagen, Blegdamsvej 3, Copenhagen DK-2200, Denmark
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Guzmán-Ruiz R, Gómez-Hurtado N, Gil-Ortega M, Somoza B, González MC, Aránguez I, Martín-Ramos M, González-Martín C, Delgado C, Fernández-Alfonso M, Ruiz-Gayo M. Remodeling of energy metabolism and absence of electrophysiological changes in the heart of obese hyperleptinemic mice. New insights into the pleiotropic role of leptin. Front Endocrinol (Lausanne) 2013; 4:175. [PMID: 24298268 PMCID: PMC3828673 DOI: 10.3389/fendo.2013.00175] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Accepted: 10/31/2013] [Indexed: 01/13/2023] Open
Abstract
Dietary treatment with high-fat diets (HFD) triggers diabetes and hyperleptinemia, concomitantly with a partial state of leptin resistance that affects hepatic and adipose tissue but not the heart. In this context, characterized by widespread steatosis, cardiac lipid content remains unchanged. As previously reported, HFD-evoked hyperleptinemia could be a pivotal element contributing to increase fatty-acid (FA) metabolism in the heart and to prevent cardiac steatosis. This metabolic adaptation might theoretically reduce energy efficiency in cardiomyocytes and lead to cardiac electrophysiological remodeling. Therefore the aim of the current study has been to investigate the impact of long-term HFD on cardiac metabolism and electrophysiological properties of the principal ionic currents responsible of the action potential duration in mouse cardiomyocytes. Male C57BL/6J mice were fed a control (10 kcal% from fat) or HFD (45 kcal% from fat) during 32 weeks. Quantification of enzymatic activities regulating mitochondrial uptake of pyruvate and FA showed an increase of both carnitine-palmitoyltransferase and citrate synthase activities together with a decrease of lactate dehydrogenase and pyruvate dehydrogenase activities. Increased expression of uncoupling protein-3, Mn-, and Cu/Zn-superoxide dismutases and catalase were also detected. Total glutathione/oxidized glutathione ratios were unaffected by HFD. These data suggest that HFD triggers adaptive mechanisms aimed at (i) facilitating FA catabolism, and (ii) preventing oxidative stress. All these changes did not affect the duration of action potentials in cardiomyocytes and only slightly modified electrocardiographic parameters.
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Affiliation(s)
- Rocío Guzmán-Ruiz
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
- Present address: Rocío Guzmán-Ruiz, Departamento de Biología Celular, Fisiología e Inmunología, Universidad de Córdoba, Spain
| | - Nieves Gómez-Hurtado
- Departamento de Farmacología. Facultad de Medicina, Universidad Complutense, Madrid, Spain
| | - Marta Gil-Ortega
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
| | - Beatriz Somoza
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
| | - M. Carmen González
- Departamento de Fisiología, Facultad de Medicina, Universidad Autónoma, Madrid, Spain
| | - Isabel Aránguez
- Departamento de Bioquímica, Facultad de Farmacia, Universidad Complutense, Madrid, Spain
| | - Miriam Martín-Ramos
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
| | - Carmen González-Martín
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
| | - Carmen Delgado
- Departamento de Farmacología. Facultad de Medicina, Universidad Complutense, Madrid, Spain
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Madrid, Spain
| | - Marisol Fernández-Alfonso
- Instituto Pluridisciplinar-Departamento de Farmacología, Facultad de Farmacia, Universidad Complutense, Madrid, Spain
| | - Mariano Ruiz-Gayo
- Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Madrid, Spain
- *Correspondence: Mariano Ruiz-Gayo, Departamento de Ciencias Farmacéuticas y de la Salud, Facultad de Farmacia, Universidad CEU-San Pablo, Campus de Montepríncipe – Boadilla del Monte, 28668 Madrid, Spain e-mail:
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20
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Yang KC, Tseng YT, Nerbonne JM. Exercise training and PI3Kα-induced electrical remodeling is independent of cellular hypertrophy and Akt signaling. J Mol Cell Cardiol 2012; 53:532-41. [PMID: 22824041 PMCID: PMC3432661 DOI: 10.1016/j.yjmcc.2012.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Revised: 06/30/2012] [Accepted: 07/02/2012] [Indexed: 12/25/2022]
Abstract
In contrast with pathological hypertrophy, exercise-induced physiological hypertrophy is not associated with electrical abnormalities or increased arrhythmia risk. Recent studies have shown that increased cardiac-specific expression of phosphoinositide-3-kinase-α (PI3Kα), the key mediator of physiological hypertrophy, results in transcriptional upregulation of ion channel subunits in parallel with the increase in myocyte size (cellular hypertrophy) and the maintenance of myocardial excitability. The experiments here were undertaken to test the hypothesis that Akt1, which underlies PI3Kα-induced cellular hypertrophy, mediates the effects of augmented PI3Kα signaling on the transcriptional regulation of cardiac ion channels. In contrast to wild-type animals, chronic exercise (swim) training of mice (Akt1(-/-)) lacking Akt1 did not result in ventricular myocyte hypertrophy. Ventricular K(+) current amplitudes and the expression of K(+) channel subunits, however, were increased markedly in Akt1(-/-) animals with exercise training. Expression of the transcripts encoding inward (Na(+) and Ca(2+)) channel subunits were also increased in Akt1(-/-) ventricles following swim training. Additional experiments in a transgenic mouse model of inducible cardiac-specific expression of constitutively active PI3Kα (icaPI3Kα) revealed that short-term activation of PI3Kα signaling in the myocardium also led to the transcriptional upregulation of ion channel subunits. Inhibition of cardiac Akt activation with triciribine in this (inducible caPI3Kα expression) model did not prevent the upregulation of myocardial ion channel subunits. These combined observations demonstrate that chronic exercise training and enhanced PI3Kα expression/activity result in transcriptional upregulation of myocardial ion channel subunits independent of cellular hypertrophy and Akt signaling.
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Affiliation(s)
- Kai-Chien Yang
- Department of Developmental Biology, Washington University Medical School, St. Louis, Missouri
| | - Yi-Tang Tseng
- Department of Pediatrics, Women and Infant’s Hospital of Rhode Island, The Warren Alpert Medical School of Brown University, Providence, Rhode Island
| | - Jeanne M. Nerbonne
- Department of Developmental Biology, Washington University Medical School, St. Louis, Missouri
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21
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Morrow JP, Katchman A, Son NH, Trent CM, Khan R, Shiomi T, Huang H, Amin V, Lader JM, Vasquez C, Morley GE, D'Armiento J, Homma S, Goldberg IJ, Marx SO. Mice with cardiac overexpression of peroxisome proliferator-activated receptor γ have impaired repolarization and spontaneous fatal ventricular arrhythmias. Circulation 2011; 124:2812-21. [PMID: 22124376 DOI: 10.1161/circulationaha.111.056309] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Diabetes mellitus and obesity, which confer an increased risk of sudden cardiac death, are associated with cardiomyocyte lipid accumulation and altered cardiac electric properties, manifested by prolongation of the QRS duration and QT interval. It is difficult to distinguish the contribution of cardiomyocyte lipid accumulation from the contribution of global metabolic defects to the increased incidence of sudden death and electric abnormalities. METHODS AND RESULTS In order to study the effects of metabolic abnormalities on arrhythmias without the complex systemic effects of diabetes mellitus and obesity, we studied transgenic mice with cardiac-specific overexpression of peroxisome proliferator-activated receptor γ 1 (PPARγ1) via the cardiac α-myosin heavy-chain promoter. The PPARγ transgenic mice develop abnormal accumulation of intracellular lipids and die as young adults before any significant reduction in systolic function. Using implantable ECG telemeters, we found that these mice have prolongation of the QRS and QT intervals and spontaneous ventricular arrhythmias, including polymorphic ventricular tachycardia and ventricular fibrillation. Isolated cardiomyocytes demonstrated prolonged action potential duration caused by reduced expression and function of the potassium channels responsible for repolarization. Short-term exposure to pioglitazone, a PPARγ agonist, had no effect on mortality or rhythm in WT mice but further exacerbated the arrhythmic phenotype and increased the mortality in the PPARγ transgenic mice. CONCLUSIONS Our findings support an important link between PPARγ activation, cardiomyocyte lipid accumulation, ion channel remodeling, and increased cardiac mortality.
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Affiliation(s)
- John P Morrow
- Columbia University, Division of Cardiology, PH 10-203, 622 W.168th St, New York, NY, USA.
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22
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Jeong EM, Liu M, Sturdy M, Gao G, Varghese ST, Sovari AA, Dudley SC. Metabolic stress, reactive oxygen species, and arrhythmia. J Mol Cell Cardiol 2011; 52:454-63. [PMID: 21978629 DOI: 10.1016/j.yjmcc.2011.09.018] [Citation(s) in RCA: 162] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2011] [Revised: 08/20/2011] [Accepted: 09/19/2011] [Indexed: 02/07/2023]
Abstract
Cardiac arrhythmias can cause sudden cardiac death (SCD) and add to the current heart failure (HF) health crisis. Nevertheless, the pathological processes underlying arrhythmias are unclear. Arrhythmic conditions are associated with systemic and cardiac oxidative stress caused by reactive oxygen species (ROS). In excitable cardiac cells, ROS regulate both cellular metabolism and ion homeostasis. Increasing evidence suggests that elevated cellular ROS can cause alterations of the cardiac sodium channel (Na(v)1.5), abnormal Ca(2+) handling, changes of mitochondrial function, and gap junction remodeling, leading to arrhythmogenesis. This review summarizes our knowledge of the mechanisms by which ROS may cause arrhythmias and discusses potential therapeutic strategies to prevent arrhythmias by targeting ROS and its consequences. This article is part of a Special Issue entitled "Local Signaling in Myocytes".
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Affiliation(s)
- Euy-Myoung Jeong
- Section of Cardiology, University of Illinois at Chicago, Chicago, IL 60612, USA.
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Cheng L, Yung A, Covarrubias M, Radice GL. Cortactin is required for N-cadherin regulation of Kv1.5 channel function. J Biol Chem 2011; 286:20478-89. [PMID: 21507952 DOI: 10.1074/jbc.m111.218560] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The intercalated disc serves as an organizing center for various cell surface components at the termini of the cardiomyocyte, thus ensuring proper mechanoelectrical coupling throughout the myocardium. The cell adhesion molecule, N-cadherin, is an essential component of the intercalated disc. Cardiac-specific deletion of N-cadherin leads to abnormal electrical conduction and sudden arrhythmic death in mice. The mechanisms linking the loss of N-cadherin in the heart and spontaneous malignant ventricular arrhythmias are poorly understood. To investigate whether ion channel remodeling contributes to arrhythmogenesis in N-cadherin conditional knock-out (N-cad CKO) mice, cardiac myocyte excitability and voltage-gated potassium channel (Kv), as well as inwardly rectifying K(+) channel remodeling, were investigated in N-cad CKO cardiomyocytes by whole cell patch clamp recordings. Action potential duration was prolonged in N-cad CKO ventricle myocytes compared with wild type. Relative to wild type, I(K,slow) density was significantly reduced consistent with decreased expression of Kv1.5 and Kv accessory protein, Kcne2, in the N-cad CKO myocytes. The decreased Kv1.5/Kcne2 expression correlated with disruption of the actin cytoskeleton and reduced cortactin at the sarcolemma. Biochemical experiments revealed that cortactin co-immunoprecipitates with Kv1.5. Finally, cortactin was required for N-cadherin-mediated enhancement of Kv1.5 channel activity in a heterologous expression system. Our results demonstrate a novel mechanistic link among the cell adhesion molecule, N-cadherin, the actin-binding scaffold protein, cortactin, and Kv channel remodeling in the heart. These data suggest that in addition to gap junction remodeling, aberrant Kv1.5 channel function contributes to the arrhythmogenic phenotype in N-cad CKO mice.
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Affiliation(s)
- Lan Cheng
- Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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24
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Matkovich SJ, Wang W, Tu Y, Eschenbacher WH, Dorn LE, Condorelli G, Diwan A, Nerbonne JM, Dorn GW. MicroRNA-133a protects against myocardial fibrosis and modulates electrical repolarization without affecting hypertrophy in pressure-overloaded adult hearts. Circ Res 2009; 106:166-75. [PMID: 19893015 DOI: 10.1161/circresaha.109.202176] [Citation(s) in RCA: 292] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
RATIONALE MicroRNA (miR)-133a regulates cardiac and skeletal muscle differentiation and plays an important role in cardiac development. Because miR-133a levels decrease during reactive cardiac hypertrophy, some have considered that restoring miR-133a levels could suppress hypertrophic remodeling. OBJECTIVE To prevent the "normal" downregulation of miR-133a induced by an acute hypertrophic stimulus in the adult heart. METHODS AND RESULTS miR-133a is downregulated in transverse aortic constriction (TAC) and isoproterenol-induced hypertrophy, but not in 2 genetic hypertrophy models. Using MYH6 promoter-directed expression of a miR-133a genomic precursor, increased cardiomyocyte miR-133a had no effect on postnatal cardiac development assessed by measures of structure, function, and mRNA profile. However, increased miR-133a levels increased QT intervals in surface electrocardiographic recordings and action potential durations in isolated ventricular myocytes, with a decrease in the fast component of the transient outward K+ current, I(to,f), at baseline. Transgenic expression of miR-133a prevented TAC-associated miR-133a downregulation and improved myocardial fibrosis and diastolic function without affecting the extent of hypertrophy. I(to,f) downregulation normally observed post-TAC was prevented in miR-133a transgenic mice, although action potential duration and QT intervals did not reflect this benefit. miR-133a transgenic hearts had no significant alterations of basal or post-TAC mRNA expression profiles, although decreased mRNA and protein levels were observed for the I(to,f) auxiliary KChIP2 subunit, which is not a predicted target. CONCLUSIONS These results reveal striking differences between in vitro and in vivo phenotypes of miR expression, and further suggest that mRNA signatures do not reliably predict either direct miR targets or major miR effects.
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Affiliation(s)
- Scot J Matkovich
- Center for Pharmacogenomics, Department of Medicine, Washington University School of Medicine, St Louis, MO 63110, USA
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25
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Affiliation(s)
- Andreas S Barth
- Division of Cardiology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Weber dos Santos R, Nygren A, Otaviano Campos F, Koch H, Giles WR. Experimental and theoretical ventricular electrograms and their relation to electrophysiological gradients in the adult rat heart. Am J Physiol Heart Circ Physiol 2009; 297:H1521-34. [DOI: 10.1152/ajpheart.01066.2008] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The electrical activity of adult mouse and rat hearts has been analyzed extensively, often as a prerequisite for genetic engineering studies or for the development of rodent models of human diseases. Some aspects of the initiation and conduction of the cardiac action potential in rodents closely resemble those in large mammals. However, rodents have a much higher heart rate and their ventricular action potential is triangular and very short. As a consequence, an interpretation of the electrocardiogram in the mouse and rat remains difficult and controversial. In this study, optical mapping techniques have been applied to an in vitro left ventricular adult rat preparation to obtain patterns of conduction and action potential duration measurements from the epicardial surface. This information has been combined with previously published mathematical models of the rat ventricular myocyte to develop a bidomain model for action potential propagation and electrogram formation in the rat left ventricle. Important insights into the basis for the repolarization waveform in the ventricular electrogram of the adult rat have been obtained. Notably, our model demonstrated that the biphasic shape of the rat ventricular repolarization wave can be explained in terms of the transmural and apex-to-base gradients in action potential duration that exist in the rat left ventricle.
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Affiliation(s)
| | - Anders Nygren
- Department of Physiology and Biophysics,
- Department of Electrical and Computer Engineering,
- Centre for Bioengineering Research and Education, and
| | - Fernando Otaviano Campos
- Department of Computer Science, Universidade Federal de Juiz de Fora, Juiz de Fora, Brazil
- Institute of Biophysics, Medical University of Graz, Graz, Austria; and
| | - Hans Koch
- Department of Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany
| | - Wayne R. Giles
- Department of Physiology and Biophysics,
- Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada
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Electrophysiological characteristics of heart ventricular papillary muscles in diabetic histidine decarboxylase knockout and wild-type mice. J Interv Card Electrophysiol 2009; 26:155-8. [DOI: 10.1007/s10840-009-9432-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Accepted: 07/15/2009] [Indexed: 11/25/2022]
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Li S, Nagothu KK, Desai V, Lee T, Branham W, Moland C, Megyesi JK, Crew MD, Portilla D. Transgenic expression of proximal tubule peroxisome proliferator-activated receptor-alpha in mice confers protection during acute kidney injury. Kidney Int 2009; 76:1049-62. [PMID: 19710628 DOI: 10.1038/ki.2009.330] [Citation(s) in RCA: 114] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Our previous studies suggest that peroxisome proliferator-activated receptor-alpha (PPARalpha) plays a critical role in regulating fatty acid beta-oxidation in kidney tissue and this directly correlated with preservation of kidney morphology and function during acute kidney injury. To further study this, we generated transgenic mice expressing PPARalpha in the proximal tubule under the control of the promoter of KAP2 (kidney androgen-regulated protein 2). Segment-specific upregulation of PPARalpha expression by testosterone treatment of female transgenic mice improved kidney function during cisplatin or ischemia-reperfusion-induced acute kidney injury. Ischemia-reperfusion injury or treatment with cisplatin in wild-type mice caused inhibition of fatty-acid oxidation, reduction of mitochondrial genes of oxidative phosphorylation, mitochondrial DNA, fatty-acid metabolism, and the tricarboxylic acid cycle. Similar injury in testosterone-treated transgenic mice resulted in amelioration of these effects. Similarly, there were increases in the levels of 4-hydroxy-2-hexenal-derived lipid peroxidation products in wild-type mice, which were also reduced in the transgenic mice. Similarly, necrosis of the S3 segment was reduced in the two injury models in transgenic mice compared to wild type. Our results suggest proximal tubule PPARalpha activity serves as a metabolic sensor. Its increased expression without the use of an exogenous PPARalpha ligand in the transgenic mice is sufficient to protect kidney function and morphology, and to prevent abnormalities in lipid metabolism associated with acute kidney injury.
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Affiliation(s)
- Shenyang Li
- Division of Nephrology, Departments of Internal Medicine and Immunology, University of Arkansas for Medical Sciences and Central Arkansas Veterans Healthcare System, Little Rock, Arkansas 72205, USA
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Niwa N, Nerbonne JM. Molecular determinants of cardiac transient outward potassium current (I(to)) expression and regulation. J Mol Cell Cardiol 2009; 48:12-25. [PMID: 19619557 DOI: 10.1016/j.yjmcc.2009.07.013] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2009] [Revised: 06/25/2009] [Accepted: 07/10/2009] [Indexed: 12/21/2022]
Abstract
Rapidly activating and inactivating cardiac transient outward K(+) currents, I(to), are expressed in most mammalian cardiomyocytes, and contribute importantly to the early phase of action potential repolarization and to plateau potentials. The rapidly recovering (I(t)(o,f)) and slowly recovering (I(t)(o,s)) components are differentially expressed in the myocardium, contributing to regional heterogeneities in action potential waveforms. Consistent with the marked differences in biophysical properties, distinct pore-forming (alpha) subunits underlie the two I(t)(o) components: Kv4.3/Kv4.2 subunits encode I(t)(o,f), whereas Kv1.4 encodes I(t)(o,s), channels. It has also become increasingly clear that cardiac I(t)(o) channels function as components of macromolecular protein complexes, comprising (four) Kvalpha subunits and a variety of accessory subunits and regulatory proteins that influence channel expression, biophysical properties and interactions with the actin cytoskeleton, and contribute to the generation of normal cardiac rhythms. Derangements in the expression or the regulation of I(t)(o) channels in inherited or acquired cardiac diseases would be expected to increase the risk of potentially life-threatening cardiac arrhythmias. Indeed, a recently identified Brugada syndrome mutation in KCNE3 (MiRP2) has been suggested to result in increased I(t)(o,f) densities. Continued focus in this area seems certain to provide new and fundamentally important insights into the molecular determinants of functional I(t)(o) channels and into the molecular mechanisms involved in the dynamic regulation of I(t)(o) channel functioning in the normal and diseased myocardium.
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Affiliation(s)
- Noriko Niwa
- Department of Developmental Biology, Washington University School of Medicine, 660 South Euclid Avenue, Box 8103, St. Louis, MO 63110-1093, USA
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Gross DR. Other Transgenic Animal Models Used in Cardiovascular Studies. ANIMAL MODELS IN CARDIOVASCULAR RESEARCH 2009. [PMCID: PMC7121723 DOI: 10.1007/978-0-387-95962-7_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Previous chapters have described a large number of transgenic animal models used to study specific cardiovascular syndromes. This chapter will fill in some gaps. Many of these transgenic animals were developed to study normal and/or abnormal physiological responses in other organ systems, or to study basic biochemical and molecular reactions or pathways. These models were then discovered to also have effects on the cardiovascular system, some of them unanticipated. A word of caution, particularly when highly inbred mouse strains are used to develop transgenic models - not all strains of a particular species are created equal. When cardiovascular parameters of age- and sex-matched A/J and C57BL/6J inbred mice were compared the C57BL/6J mice demonstrated eccentric physiologic ventricular hypertrophy, increased ventricular function, lower heart rates, and increased exercise endurance.1
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Thomsen MB, Sosunov EA, Anyukhovsky EP, Ozgen N, Boyden PA, Rosen MR. Deleting the accessory subunit KChIP2 results in loss of I(to,f) and increased I(K,slow) that maintains normal action potential configuration. Heart Rhythm 2008; 6:370-7. [PMID: 19251214 DOI: 10.1016/j.hrthm.2008.11.023] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/17/2008] [Accepted: 11/21/2008] [Indexed: 10/21/2022]
Abstract
BACKGROUND Four voltage-gated potassium currents, I(to,f) (K(V)4.2), I(to,s) (K(V)1.4), I(K,slow) (K(V)1.5+K(V)2.1), and I(SS) (TASK1), govern murine ventricular repolarization. Although the accessory subunit KChIP2 influences I(to,f) expression, in preliminary experiments we found that action potential duration (APD) is maintained in KChIP2 knockout mice. OBJECTIVE We tested the role of KChIP2 in regulating APD and studied the underlying ionic currents. METHODS We used microelectrode techniques, whole-cell patch clamp studies, and real-time polymerase chain reaction amplification to characterize ventricular repolarization and its determinants in wild-type and KChIP2(-/-) mice. RESULTS Despite comparable baseline action potentials, APD was more markedly prolonged by 4-aminopyridine (4-AP) in KChIP2(-/-) preparations. Peak K(+) current densities were similar in wild-type and KChIP2(-/-) cells (mean +/- SEM I(P): 28.3 +/- 2 (n = 27) vs. 29.2 +/- 2 pA/pF (n = 24), respectively; P > .05). Heteropodatoxin-2 (HpTx-2, 1 microM) had no effect on current amplitude in KChIP2(-/-) myocytes. The current fractions sensitive to 4-AP (50 microM and 1 mM) were larger in KChIP2(-/-) than wild-type (P < .05). Real-time polymerase chain reaction showed absence of KChIP2 and increased K(V)1.5 expression in KChIP2(-/-) ventricular myocardium. CONCLUSION KChIP2 deficiency eliminated HpTx-2-sensitive I(to,f), but had little impact on total APD, secondary to upregulation of 4-AP-sensitive I(K,slow) in association with increased K(V)1.5 expression. There is increased sensitivity to 4-AP-mediated APD prolongation in KChIP2(-/-). Thus, KChIP2 seems important for murine repolarization in circumstances of reduced repolarization reserve.
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Affiliation(s)
- Morten B Thomsen
- Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Copenhagen, Denmark
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