1
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Heinis FI, Thompson BR, Gulati R, Wheelwright M, Metzger JM. Myofilament-based physiological regulatory compensation preserves diastolic function in failing hearts with severe Ca2+ handling deficits. JCI Insight 2024; 9:e163334. [PMID: 38329806 PMCID: PMC11063947 DOI: 10.1172/jci.insight.163334] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Accepted: 02/02/2024] [Indexed: 02/10/2024] Open
Abstract
Severe dysfunction in cardiac muscle intracellular Ca2+ handling is a common pathway underlying heart failure. Here we used an inducible genetic model of severe Ca2+ cycling dysfunction by the targeted temporal gene ablation of the cardiac Ca2+ ATPase, SERCA2, in otherwise normal adult mice. In this model, in vivo heart performance was minimally affected initially, even though Serca2a protein was markedly reduced. The mechanism underlying the sustained in vivo heart performance in the weeks prior to complete heart pump failure and death is not clear and is important to understand. Studies were primarily focused on understanding how in vivo diastolic function could be relatively normal under conditions of marked Serca2a deficiency. Interestingly, data show increased cardiac troponin I (cTnI) serine 23/24 phosphorylation content in hearts upon Serca2a ablation in vivo. We report that hearts isolated from the Serca2-deficient mice retained near normal heart pump functional responses to β-adrenergic stimulation. Unexpectedly, using genetic complementation models, in concert with inducible Serca2 ablation, data show that Serca2a-deficient hearts that also lacked the central β-adrenergic signaling-dependent Serca2a negative regulator, phospholamban (PLN), had severe diastolic dysfunction that could still be corrected by β-adrenergic stimulation. Notably, integrating a serines 23/24-to-alanine PKA-refractory sarcomere incorporated cTnI molecular switch complex in mice deficient in Serca2 showed blunting of β-adrenergic stimulation-mediated enhanced diastolic heart performance. Taken together, these data provide evidence of a compensatory regulatory role of the myofilaments as a critical physiological bridging mechanism to aid in preserving heart diastolic performance in failing hearts with severe Ca2+ handling deficits.
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2
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Cao Y, Redd MA, Fang C, Mizikovsky D, Li X, Macdonald PS, King GF, Palpant NJ. New Drug Targets and Preclinical Modelling Recommendations for Treating Acute Myocardial Infarction. Heart Lung Circ 2023:S1443-9506(23)00139-7. [PMID: 37230806 DOI: 10.1016/j.hlc.2022.12.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Revised: 11/28/2022] [Accepted: 12/15/2022] [Indexed: 05/27/2023]
Abstract
Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide and the primary underlying risk factor for heart failure. Despite decades of research and clinical trials, there are no drugs currently available to prevent organ damage from acute ischaemic injuries of the heart. In order to address the increasing global burden of heart failure, drug, gene, and cell-based regeneration technologies are advancing into clinical testing. In this review we highlight the burden of disease associated with AMI and the therapeutic landscape based on market analyses. New studies revealing the role of acid-sensitive cardiac ion channels and other proton-gated ion channels in cardiac ischaemia are providing renewed interest in pre- and post-conditioning agents with novel mechanisms of action that may also have implications for gene- and cell-based therapeutics. Furthermore, we present guidelines that couple new cell technologies and data resources with traditional animal modelling pipelines to help de-risk drug candidates aimed at treating AMI. We propose that improved preclinical pipelines and increased investment in drug target identification for AMI is critical to stem the increasing global health burden of heart failure.
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Affiliation(s)
- Yuanzhao Cao
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Meredith A Redd
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Chen Fang
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Dalia Mizikovsky
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Xichun Li
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia
| | - Peter S Macdonald
- Cardiopulmonary Transplant Unit, St Vincent's Hospital, Sydney, NSW, Australia
| | - Glenn F King
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia; Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science, The University of Queensland, Brisbane, Qld, Australia
| | - Nathan J Palpant
- Institute for Molecular Bioscience, The University of Queensland, Brisbane, Qld, Australia.
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3
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Arif M, Nabavizadeh P, Song T, Desai D, Singh R, Bazrafshan S, Kumar M, Wang Y, Gilbert RJ, Dhandapany PS, Becker RC, Kranias EG, Sadayappan S. Genetic, clinical, molecular, and pathogenic aspects of the South Asian-specific polymorphic MYBPC3 Δ25bp variant. Biophys Rev 2020; 12:1065-1084. [PMID: 32656747 PMCID: PMC7429610 DOI: 10.1007/s12551-020-00725-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Accepted: 07/03/2020] [Indexed: 02/06/2023] Open
Abstract
Hypertrophic cardiomyopathy (HCM) is a cardiac genetic disease characterized by ventricular enlargement, diastolic dysfunction, and increased risk for sudden cardiac death. Sarcomeric genetic defects are the predominant known cause of HCM. In particular, mutations in the myosin-binding protein C gene (MYBPC3) are associated with ~ 40% of all HCM cases in which a genetic basis has been established. A decade ago, our group reported a 25-base pair deletion in intron 32 of MYBPC3 (MYBPC3Δ25bp) that is uniquely prevalent in South Asians and is associated with autosomal dominant cardiomyopathy. Although our studies suggest that this deletion results in left ventricular dysfunction, cardiomyopathies, and heart failure, the precise mechanism by which this variant predisposes to heart disease remains unclear. Increasingly appreciated, however, is the contribution of secondary risk factors, additional mutations, and lifestyle choices in augmenting or modifying the HCM phenotype in MYBPC3Δ25bp carriers. Therefore, the goal of this review article is to summarize the current research dedicated to understanding the molecular pathophysiology of HCM in South Asians with the MYBPC3Δ25bp variant. An emphasis is to review the latest techniques currently applied to explore the MYBPC3Δ25bp pathogenesis and to provide a foundation for developing new diagnostic strategies and advances in therapeutics.
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Affiliation(s)
- Mohammed Arif
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA.
| | - Pooneh Nabavizadeh
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Taejeong Song
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Darshini Desai
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Rohit Singh
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Sholeh Bazrafshan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Mohit Kumar
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Yigang Wang
- Department of Pathology and Laboratory Medicine, University of Cincinnati, College of Medicine, Cincinnati, OH, 45267, USA
| | - Richard J Gilbert
- Research Service, Providence VA Medical Center, Providence, RI, 02908, USA
| | - Perundurai S Dhandapany
- Centre for Cardiovascular Biology and Disease, Institute for Stem Cell Biology and Regenerative Medicine (inStem), Bangalore, India
- The Knight Cardiovascular Institute, Oregon Health and Science University, Portland, OR, USA
- Department of Medicine, Oregon Health and Science University, Portland, OR, USA
- Department of Molecular and Medical Genetics, Oregon Health and Science University, Portland, OR, USA
| | - Richard C Becker
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
| | - Evangelia G Kranias
- Department of Pharmacology and Systems Physiology, University of Cincinnati, College of Medicine, Cincinnati, OH, 45267, USA
| | - Sakthivel Sadayappan
- Division of Cardiovascular Health and Disease, Department of Internal Medicine, Heart, Lung and Vascular Institute, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, OH, 45267-0575, USA
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4
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Wheelwright M, Mikkila J, Bedada FB, Mandegar MA, Thompson BR, Metzger JM. Advancing physiological maturation in human induced pluripotent stem cell-derived cardiac muscle by gene editing an inducible adult troponin isoform switch. Stem Cells 2020; 38:1254-1266. [PMID: 32497296 DOI: 10.1002/stem.3235] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 05/11/2020] [Indexed: 01/11/2023]
Abstract
Advancing maturation of stem cell-derived cardiac muscle represents a major barrier to progress in cardiac regenerative medicine. Cardiac muscle maturation involves a myriad of gene, protein, and cell-based transitions, spanning across all aspects of cardiac muscle form and function. We focused here on a key developmentally controlled transition in the cardiac sarcomere, the functional unit of the heart. Using a gene-editing platform, human induced pluripotent stem cell (hiPSCs) were engineered with a drug-inducible expression cassette driving the adult cardiac troponin I (cTnI) regulatory isoform, a transition shown to be a rate-limiting step in advancing sarcomeric maturation of hiPSC cardiac muscle (hiPSC-CM) toward the adult state. Findings show that induction of the adult cTnI isoform resulted in the physiological acquisition of adult-like cardiac contractile function in hiPSC-CMs in vitro. Specifically, cTnI induction accelerated relaxation kinetics at baseline conditions, a result independent of alterations in the kinetics of the intracellular Ca2+ transient. In comparison, isogenic unedited hiPSC-CMs had no cTnI induction and no change in relaxation function. Temporal control of adult cTnI isoform induction did not alter other developmentally regulated sarcomere transitions, including myosin heavy chain isoform expression, nor did it affect expression of SERCA2a or phospholamban. Taken together, precision genetic targeting of sarcomere maturation via inducible TnI isoform switching enables physiologically relevant adult myocardium-like contractile adaptations that are essential for beat-to-beat modulation of adult human heart performance. These findings have relevance to hiPSC-CM structure-function and drug-discovery studies in vitro, as well as for potential future clinical applications of physiologically optimized hiPSC-CM in cardiac regeneration/repair.
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Affiliation(s)
- Matthew Wheelwright
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jennifer Mikkila
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Fikru B Bedada
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Mohammad A Mandegar
- Gladstone Institute of Cardiovascular Disease, San Francisco, California, USA
| | - Brian R Thompson
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Joseph M Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota, USA
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5
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Tajima K, Zheng F, Collange O, Barthel G, Thornton SN, Longrois D, Levy B, Audibert G, Malinovsky JM, Mertes PM. Time to Achieve Target Mean Arterial Pressure during Resuscitation from Experimental Anaphylactic Shock in an Animal Model. A Comparison of Adrenaline Alone or in Combination with Different Volume Expanders. Anaesth Intensive Care 2019; 41:765-73. [DOI: 10.1177/0310057x1304100612] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- K. Tajima
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Université de Lorraine, Vandœuvre-lès-Nancy, France
| | - F. Zheng
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Université de Lorraine, Vandœuvre-lès-Nancy, France
| | - O. Collange
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- éanimations Chirurgicales, SAMU, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
| | - G. Barthel
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Université de Lorraine, Vandœuvre-lès-Nancy, France
| | - S. N. Thornton
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Université de Lorraine, Vandœuvre-lès-Nancy, France
| | - D. Longrois
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Département d'Anesthésie-Réanimation Chirurgicale, Hôpital Bichat-Claude Bernard, Université Paris Diderot, Sorbonne Paris Cité, Paris, France
| | - B. Levy
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Service de Réanimation Médicale, Institut Lorrain du Coeur et des Vaisseaux, Vandoeuvre-lès-Nancy, France
| | - G. Audibert
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Département d'Anesthésie-Réanimation Chirurgicale, Centre Hospitalier Universitaire (CHU) Central, Nancy, France
| | - J. M. Malinovsky
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Département d'Anesthésie-Réanimation Chirurgicale, CHU de Reims, Reims, France
| | - P. M. Mertes
- Faculty of Medicine, Groupe choc, U1116 Inserm, University of Lorraine, Vandoeuvre-lès-Nancy, France
- Pôle Anesthésie, Réanimations Chirurgicales, SAMU, Hôpitaux Universitaires de Strasbourg, Strasbourg, France
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6
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Abstract
Understanding the causes and progression of heart disease presents a significant challenge to the biomedical community. The genetic flexibility of the mouse provides great potential to explore cardiac function at the molecular level. The mouse's small size does present some challenges in regards to performing detailed cardiac phenotyping. Miniaturization and other advancements in technology have made many methods of cardiac assessment possible in the mouse. Of these, the simultaneous collection of pressure and volume data provides a detailed picture of cardiac function that is not available through any other modality. Here a detailed procedure for the collection of pressure-volume loop data is described. Included is a discussion of the principles underlying the measurements and the potential sources of error. Anesthetic management and surgical approaches are discussed in great detail as they are both critical to obtaining high quality hemodynamic measurements. The principles of hemodynamic protocol development and relevant aspects of data analysis are also addressed.
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Affiliation(s)
- DeWayne Townsend
- Department of Integrative Biology and Physiology, University of Minnesota;
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7
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Pineda-Sanabria SE, Robertson IM, Sykes BD. Structure and Dynamics of the Acidosis-Resistant A162H Mutant of the Switch Region of Troponin I Bound to the Regulatory Domain of Troponin C. Biochemistry 2015; 54:3583-93. [DOI: 10.1021/acs.biochem.5b00178] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Sandra E. Pineda-Sanabria
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Ian M. Robertson
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - Brian D. Sykes
- Department of Biochemistry, ‡Department of Pediatrics, Faculty of Medicine & Dentistry, University of Alberta, Edmonton, AB T6G 2H7, Canada
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8
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Thompson BR, Metzger JM. Cell biology of sarcomeric protein engineering: disease modeling and therapeutic potential. Anat Rec (Hoboken) 2015; 297:1663-9. [PMID: 25125179 DOI: 10.1002/ar.22966] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Revised: 12/12/2013] [Accepted: 12/12/2013] [Indexed: 11/09/2022]
Abstract
The cardiac sarcomere is the functional unit for myocyte contraction. Ordered arrays of sarcomeric proteins, held in stoichiometric balance with each other, respond to calcium to coordinate contraction and relaxation of the heart. Altered sarcomeric structure-function underlies the primary basis of disease in multiple acquired and inherited heart disease states. Hypertrophic and restrictive cardiomyopathies are caused by inherited mutations in sarcomeric genes and result in altered contractility. Ischemia-mediated acidosis directly alters sarcomere function resulting in decreased contractility. In this review, we highlight the use of acute genetic engineering of adult cardiac myocytes through stoichiometric replacement of sarcomeric proteins in these disease states with particular focus on cardiac troponin I. Stoichiometric replacement of disease causing mutations has been instrumental in defining the molecular mechanisms of hypertrophic and restrictive cardiomyopathy in a cellular context. In addition, taking advantage of stoichiometric replacement through gene therapy is discussed, highlighting the ischemia-resistant histidine-button, A164H cTnI. Stoichiometric replacement of sarcomeric proteins offers a potential gene therapy avenue to replace mutant proteins, alter sarcomeric responses to pathophysiologic insults, or neutralize altered sarcomeric function in disease.
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Affiliation(s)
- Brian R Thompson
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
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9
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Thompson BR, Houang EM, Sham YY, Metzger JM. Molecular determinants of cardiac myocyte performance as conferred by isoform-specific TnI residues. Biophys J 2014; 106:2105-14. [PMID: 24853739 DOI: 10.1016/j.bpj.2014.04.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2014] [Revised: 03/14/2014] [Accepted: 04/04/2014] [Indexed: 11/27/2022] Open
Abstract
Troponin I (TnI) is the molecular switch of the sarcomere. Cardiac myocytes express two isoforms of TnI during development. The fetal heart expresses the slow skeletal TnI (ssTnI) isoform and shortly after birth ssTnI is completely and irreversibly replaced by the adult cardiac TnI (cTnI) isoform. These two isoforms have important functional differences; broadly, ssTnI is a positive inotrope, especially under acidic/hypoxic conditions, whereas cTnI facilitates faster relaxation performance. Evolutionary directed changes in cTnI sequence suggest cTnI evolved to favor relaxation performance in the mammalian heart. To investigate the mechanism, we focused on several notable TnI isoform and trans-species-specific residues located in TnI's helix 4 using structure/function and molecular dynamics analyses. Gene transduction of adult cardiac myocytes by cTnIs with specific helix 4 ssTnI substitutions, Q157R/A164H/E166V/H173N (QAEH), and A164H/H173N (AH), were investigated. cTnI QAEH is similar in these four residues to ssTnI and nonmammalian chordate cTnIs, whereas cTnI AH is similar to fish cTnI in these four residues. In comparison to mammalian cTnI, cTnI QAEH and cTnI AH showed increased contractility and slowed relaxation, which functionally mimicked ssTnI expressing myocytes. cTnI QAEH molecular dynamics simulations demonstrated altered intermolecular interactions between TnI helix 4 and cTnC helix A, specifically revealing a new, to our knowledge, electrostatic interaction between R171of cTnI and E15 of cTnC, which structurally phenocopied the ssTnI conformation. Free energy perturbation calculation of cTnC Ca(2+) binding for these conformations showed relative increased calcium binding for cTnI QAEH compared to cTnI. Taken together, to our knowledge, these new findings provide evidence that the evolutionary-directed coordinated acquisition of residues Q157, A164, E166, H173 facilitate enhanced relaxation performance in mammalian adult cardiac myocytes.
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Affiliation(s)
- Brian R Thompson
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota
| | - Evelyne M Houang
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota; Center for Drug Design, University of Minnesota Academic Health Center, Minneapolis, Minnesota
| | - Yuk Y Sham
- Center for Drug Design, University of Minnesota Academic Health Center, Minneapolis, Minnesota
| | - Joseph M Metzger
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, Minnesota.
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10
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pH-responsive titratable inotropic performance of histidine-modified cardiac troponin I. Biophys J 2012; 102:1570-9. [PMID: 22500757 DOI: 10.1016/j.bpj.2012.01.024] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2011] [Revised: 01/11/2012] [Accepted: 01/17/2012] [Indexed: 11/22/2022] Open
Abstract
Cardiac troponin I (cTnI) functions as the molecular switch of the thin filament. Studies have shown that a histidine button engineered into cTnI (cTnI A164H) specifically enhances inotropic function in the context of numerous pathophysiological challenges. To gain mechanistic insight into the basis of this finding, we analyzed histidine ionization states in vitro by studying the myofilament biophysics of amino acid substitutions that act as constitutive chemical mimetics of altered histidine ionization. We also assessed the role of histidine-modified cTnI in silico by means of molecular dynamics simulations. A functional in vitro analysis of myocytes at baseline (pH 7.4) indicated similar cellular contractile function and myofilament calcium sensitivity between myocytes expressing wild-type (WT) cTnI and cTnI A164H, whereas the A164R variant showed increased myofilament calcium sensitivity. Under acidic conditions, compared with WT myocytes, the myocytes expressing cTnI A164H maintained a contractile performance similar to that observed for the constitutively protonated cTnI A164R variant. Molecular dynamics simulations showed similar intermolecular atomic contacts between the WT and the deprotonated cTnI A164H variant. In contrast, simulations of protonated cTnI A164H showed various potential structural configurations, one of which included a salt bridge between His-164 of cTnI and Glu-19 of cTnC. This salt bridge was recapitulated in simulations of the cTnI A164R variant. These data suggest that differential histidine ionization may be necessary for cTnI A164H to act as a molecular sensor capable of modulating sarcomere performance in response to changes in the cytosolic milieu.
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11
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Palpant NJ, Bedada FB, Peacock B, Blazar BR, Metzger JM, Tolar J. Cardiac disease in mucopolysaccharidosis type I attributed to catecholaminergic and hemodynamic deficiencies. Am J Physiol Heart Circ Physiol 2010; 300:H356-65. [PMID: 21076027 DOI: 10.1152/ajpheart.00774.2010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac dysfunction is a common cause of death among pediatric patients with mutations in the lysosomal hydrolase α-l-iduronidase (IDUA) gene, which causes mucopolysaccharidosis type I (MPS-I). The purpose of this study was to analyze adrenergic regulation of cardiac hemodynamic function in MPS-I. An analysis of murine heart function was performed using conductance micromanometry to assess in vivo cardiac hemodynamics. Although MPS-I (IDUA(-/-)) mice were able to maintain normal cardiac output and ejection fraction at baseline, this cohort had significantly compromised systolic and diastolic function compared with IDUA(+/-) control mice. During dobutamine infusion MPS-I mice did not significantly increase cardiac output from baseline, indicative of blunted cardiac reserve. Autonomic tone, measured functionally by β-blockade, indicated that MPS-I mice required catecholaminergic stimulation to maintain baseline hemodynamics. Survival analysis showed mortality only among MPS-I mice. Linear regression analysis revealed that heightened end-systolic volume in the resting heart is significantly correlated with susceptibility to mortality in MPS-I hearts. This study reveals that cardiac remodeling in the pathology of MPS-I involves heightened adrenergic tone at the expense of cardiac reserve with cardiac decompensation predicted on the basis of increased baseline systolic volumes.
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Affiliation(s)
- Nathan J Palpant
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, University of Minnesota Academic Health Center, Minneapolis, Minnesota 55455, USA
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12
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Barnabei MS, Palpant NJ, Metzger JM. Influence of genetic background on ex vivo and in vivo cardiac function in several commonly used inbred mouse strains. Physiol Genomics 2010; 42A:103-13. [PMID: 20627938 DOI: 10.1152/physiolgenomics.00071.2010] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inbred mouse strains play a critical role in biomedical research. Genetic homogeneity within inbred strains and their general amenability to genetic manipulation have made them an ideal resource for dissecting the physiological function(s) of individual genes. However, the inbreeding that makes inbred mice so useful also results in genetic divergence between them. This genetic divergence is often unaccounted for but may be a confounding factor when comparing studies that have utilized distinct inbred strains. Here, we compared the cardiac function of C57BL/6J mice to seven other commonly used inbred mouse strains: FVB/NJ, DBA/2J, C3H/HeJ, BALB/cJ, 129X1/SvJ, C57BL/10SnJ, and 129S1/SvImJ. The assays used to compare cardiac function were the ex vivo isolated Langendorff heart preparation and in vivo real-time hemodynamic analysis using conductance micromanometry. We report significant strain-dependent differences in cardiac function between C57BL/6J and other commonly used inbred strains. C57BL/6J maintained better cardiac function than most inbred strains after ex vivo ischemia, particularly compared with 129S1/SvImJ, 129X1/SvJ, and C57BL/10SnJ strains. However, during in vivo acute hypoxia 129X1/SvJ and 129S1/SvImJ maintained relatively normal cardiac function, whereas C57BL/6J animals showed dramatic cardiac decompensation. Additionally, C3H/HeJ showed rapid and marked cardiac decompensation in response to esmolol infusion compared with effects of other strains. These findings demonstrate the complex effects of genetic divergence between inbred strains on cardiac function. These results may help inform analysis of gene ablation or transgenic studies and further demonstrate specific quantitative traits that could be useful in discovery of genetic modifiers relevant to cardiac health and disease.
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Affiliation(s)
- Matthew S Barnabei
- Department of Integrative Biology and Physiology, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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13
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Palpant NJ, Houang EM, Delport W, Hastings KEM, Onufriev AV, Sham YY, Metzger JM. Pathogenic peptide deviations support a model of adaptive evolution of chordate cardiac performance by troponin mutations. Physiol Genomics 2010; 42:287-99. [PMID: 20423961 DOI: 10.1152/physiolgenomics.00033.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In cardiac muscle, the troponin (cTn) complex is a key regulator of myofilament calcium sensitivity because it serves as a molecular switch required for translating myocyte calcium fluxes into sarcomeric contraction and relaxation. Studies of several species suggest that ectotherm chordates have myofilaments with heightened calcium responsiveness. However, genetic polymorphisms in cTn that cause increased myofilament sensitivity to activating calcium in mammals result in cardiac disease including arrhythmias, diastolic dysfunction, and increased susceptibility to sudden cardiac death. We hypothesized that specific residue modifications in the regulatory arm of troponin I (TnI) were critical in mediating the observed decrease in myofilament calcium sensitivity within the mammalian taxa. We performed large-scale phylogenetic analysis, atomic resolution molecular dynamics simulations and modeling, and computational alanine scanning. This study provides evidence that a His to Ala substitution within mammalian cardiac TnI (cTnI) reduced the thermodynamic potential at the interface between cTnI and cardiac TnC (cTnC) in the calcium-saturated state by disrupting a strong intermolecular electrostatic interaction. This key residue modification reduced myofilament calcium sensitivity by making cTnI molecularly untethered from cTnC. To meet the requirements for refined mammalian adult cardiac performance, we propose that compensatory evolutionary pressures favored mutations that enhanced the relaxation properties of cTn by decreasing its sensitivity to activating calcium.
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Affiliation(s)
- Nathan J Palpant
- Department of Integrative Biology and Physiology, University of Minnesota Academic Health Center, 321 Church Street SE, Minneapolis, MN 55455, USA
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