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Jones TLM, Woulfe KC. Considering impact of age and sex on cardiac cytoskeletal components. Am J Physiol Heart Circ Physiol 2024; 326:H470-H478. [PMID: 38133622 PMCID: PMC11219061 DOI: 10.1152/ajpheart.00619.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2023] [Revised: 12/08/2023] [Accepted: 12/21/2023] [Indexed: 12/23/2023]
Abstract
The cardiac cytoskeletal components are integral to cardiomyocyte function and are responsible for contraction, sustaining cell structure, and providing scaffolding to direct signaling. Cytoskeletal components have been implicated in cardiac pathology; however, less attention has been paid to age-related modifications of cardiac cytoskeletal components and how these contribute to dysfunction with increased age. Moreover, significant sex differences in cardiac aging have been identified, but we still lack a complete understanding to the mechanisms behind these differences. This review summarizes what is known about how key cardiomyocyte cytoskeletal components are modified because of age, as well as reported sex-specific differences. Thorough consideration of both age and sex as integral players in cytoskeletal function may reveal potential avenues for more personalized therapeutics.
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Affiliation(s)
- Timothy L M Jones
- Division of Cardiology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
| | - Kathleen C Woulfe
- Division of Cardiology, Department of Medicine, University of Colorado Anschutz Medical Campus, Aurora, Colorado, United States
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2
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Abstract
Striated cardiac and skeletal muscles play very different roles in the body, but they are similar at the molecular level. In particular, contraction, regardless of the type of muscle, is a precise and complex process involving the integral protein myofilaments and their associated regulatory components. The smallest functional unit of muscle contraction is the sarcomere. Within the sarcomere can be found a sophisticated ensemble of proteins associated with the thick filaments (myosin, myosin binding protein-C, titin, and obscurin) and thin myofilaments (actin, troponin, tropomyosin, nebulin, and nebulette). These parallel thick and thin filaments slide across one another, pulling the two ends of the sarcomere together to regulate contraction. More specifically, the regulation of both timing and force of contraction is accomplished through an intricate network of intra- and interfilament interactions belonging to each myofilament. This review introduces the sarcomere proteins involved in striated muscle contraction and places greater emphasis on the more recently identified and less well-characterized myofilaments: cardiac myosin binding protein-C, titin, nebulin, and obscurin. © 2017 American Physiological Society. Compr Physiol 7:675-692, 2017.
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Affiliation(s)
- Brian Leei Lin
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA
| | - Taejeong Song
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA.,Department of Internal Medicine, Heart, Lung and Vascular Institute, Division of Cardiovascular Health and Sciences, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
| | - Sakthivel Sadayappan
- Department of Cell and Molecular Physiology, Health Sciences Division, Loyola University Chicago, Maywood, Illinois, USA.,Department of Internal Medicine, Heart, Lung and Vascular Institute, Division of Cardiovascular Health and Sciences, University of Cincinnati College of Medicine, Cincinnati, Ohio, USA
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3
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TNNT1, TNNT2, and TNNT3: Isoform genes, regulation, and structure-function relationships. Gene 2016; 582:1-13. [PMID: 26774798 DOI: 10.1016/j.gene.2016.01.006] [Citation(s) in RCA: 135] [Impact Index Per Article: 16.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Revised: 12/31/2015] [Accepted: 01/05/2016] [Indexed: 12/18/2022]
Abstract
Troponin T (TnT) is a central player in the calcium regulation of actin thin filament function and is essential for the contraction of striated muscles. Three homologous genes have evolved in vertebrates to encode three muscle type-specific TnT isoforms: TNNT1 for slow skeletal muscle TnT, TNNT2 for cardiac muscle TnT, and TNNT3 for fast skeletal muscle TnT. Alternative splicing and posttranslational modifications confer additional structural and functional variations of TnT during development and muscle adaptation to various physiological and pathological conditions. This review focuses on the TnT isoform genes and their molecular evolution, alternative splicing, developmental regulation, structure-function relationships of TnT proteins, posttranslational modifications, and myopathic mutations and abnormal splicing. The goal is to provide a concise summary of the current knowledge and some perspectives for future research and translational applications.
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4
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Simon JN, Chowdhury SAK, Warren CM, Sadayappan S, Wieczorek DF, Solaro RJ, Wolska BM. Ceramide-mediated depression in cardiomyocyte contractility through PKC activation and modulation of myofilament protein phosphorylation. Basic Res Cardiol 2014; 109:445. [PMID: 25280528 DOI: 10.1007/s00395-014-0445-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2013] [Revised: 09/25/2014] [Accepted: 09/26/2014] [Indexed: 12/16/2022]
Abstract
Although ceramide accumulation in the heart is considered a major factor in promoting apoptosis and cardiac disorders, including heart failure, lipotoxicity and ischemia-reperfusion injury, little is known about ceramide's role in mediating changes in contractility. In the present study, we measured the functional consequences of acute exposure of isolated field-stimulated adult rat cardiomyocytes to C6-ceramide. Exogenous ceramide treatment depressed the peak amplitude and the maximal velocity of shortening without altering intracellular calcium levels or kinetics. The inactive ceramide analog C6-dihydroceramide had no effect on myocyte shortening or [Ca(2+)]i transients. Experiments testing a potential role for C6-ceramide-mediated effects on activation of protein kinase C (PKC) demonstrated evidence for signaling through the calcium-independent isoform, PKCε. We employed 2-dimensional electrophoresis and anti-phospho-peptide antibodies to test whether treatment of the cardiomyocytes with C6-ceramide altered myocyte shortening via PKC-dependent phosphorylation of myofilament proteins. Compared to controls, myocytes treated with ceramide exhibited increased phosphorylation of myosin binding protein-C (cMyBP-C), specifically at Ser273 and Ser302, and troponin I (cTnI) at sites apart from Ser23/24, which could be attenuated with PKC inhibition. We conclude that the altered myofilament response to calcium resulting from multiple sites of PKC-dependent phosphorylation contributes to contractile dysfunction that is associated with cardiac diseases in which elevations in ceramides are present.
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Affiliation(s)
- Jillian N Simon
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, IL, 60612, USA
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5
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Schlecht W, Zhou Z, Li KL, Rieck D, Ouyang Y, Dong WJ. FRET study of the structural and kinetic effects of PKC phosphomimetic cardiac troponin T mutants on thin filament regulation. Arch Biochem Biophys 2014; 550-551:1-11. [PMID: 24708997 DOI: 10.1016/j.abb.2014.03.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2014] [Revised: 03/27/2014] [Accepted: 03/28/2014] [Indexed: 01/31/2023]
Abstract
FRET was used to investigate the structural and kinetic effects that PKC phosphorylations exert on Ca(2+) and myosin subfragment-1 dependent conformational transitions of the cardiac thin filament. PKC phosphorylations of cTnT were mimicked by glutamate substitution. Ca(2+) and S1-induced distance changes between the central linker of cTnC and the switch region of cTnI (cTnI-Sr) were monitored in reconstituted thin filaments using steady state and time resolved FRET, while kinetics of structural transitions were determined using stopped flow. Thin filament Ca(2+) sensitivity was found to be significantly blunted by the presence of the cTnT(T204E) mutant, whereas pseudo-phosphorylation at additional sites increased the Ca(2+)-sensitivity. The rate of Ca(2+)-dissociation induced structural changes was decreased in the C-terminal end of cTnI-Sr in the presence of pseudo-phosphorylations while remaining unchanged at the N-terminal end of this region. Additionally, the distance between cTnI-Sr and cTnC was decreased significantly for the triple and quadruple phosphomimetic mutants cTnT(T195E/S199E/T204E) and cTnT(T195E/S199E/T204E/T285E), which correlated with the Ca(2+)-sensitivity increase seen in these same mutants. We conclude that significant changes in thin filament Ca(2+)-sensitivity, structure and kinetics are brought about through PKC phosphorylation of cTnT. These changes can either decrease or increase Ca(2+)-sensitivity and likely play an important role in cardiac regulation.
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Affiliation(s)
- William Schlecht
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Zhiqun Zhou
- The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA
| | - King-Lun Li
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Daniel Rieck
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA
| | - Yexin Ouyang
- The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA
| | - Wen-Ji Dong
- The Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164, USA; The Department of Integrated Neuroscience and Physiology, Washington State University, Pullman, WA 99164, USA.
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Posttranslational modifications of cardiac troponin T: An overview. J Mol Cell Cardiol 2013; 63:47-56. [DOI: 10.1016/j.yjmcc.2013.07.004] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Revised: 06/18/2013] [Accepted: 07/08/2013] [Indexed: 12/22/2022]
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Haizlip KM, Hiranandani N, Biesiadecki BJ, Janssen PML. Impact of hydroxyl radical-induced injury on calcium handling and myofilament sensitivity in isolated myocardium. J Appl Physiol (1985) 2012; 113:766-74. [PMID: 22773772 DOI: 10.1152/japplphysiol.01424.2011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hydroxyl radicals (OH) are involved in the pathogenesis of reperfusion injury and are observed in acute heart failure, stroke, and myocardial infarction. Two different subcellular defects are involved in the pathogenesis of OH injury, deranged calcium handling, and alterations of myofilament responsiveness, but their temporal impact on contractile function is not resolved. Initially, after brief OH exposure, there is a corresponding marked increase in diastolic calcium and diastolic force. We followed these parameters until a new steady-state level was reached at ~45 min post-OH exposure. At this new baseline, diastolic calcium had returned to near-normal, pre-OH levels, whereas diastolic force remained markedly elevated. An increased calcium sensitivity was observed at the new baseline after OH-induced injury compared with the pre-OH state. The acute injury that occurs after OH exposure is mainly due to calcium overload, while the later sustained myocardial dysfunction is mainly due to the altered/increased myofilament responsiveness.
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Affiliation(s)
- Kaylan M Haizlip
- Department of Physiology and Cell Biology, Ohio State University, Columbus, Ohio 43210-1218, USA
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8
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Protein kinase C depresses cardiac myocyte power output and attenuates myofilament responses induced by protein kinase A. J Muscle Res Cell Motil 2012; 33:439-48. [PMID: 22527640 DOI: 10.1007/s10974-012-9294-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2012] [Accepted: 04/09/2012] [Indexed: 01/13/2023]
Abstract
Following activation by G-protein-coupled receptor agonists, protein kinase C (PKC) modulates cardiac myocyte function by phosphorylation of intracellular targets including myofilament proteins cardiac troponin I (cTnI) and cardiac myosin binding protein C (cMyBP-C). Since PKC phosphorylation has been shown to decrease myofibril ATPase activity, we hypothesized that PKC phosphorylation of cTnI and cMyBP-C will lower myocyte power output and, in addition, attenuate the elevation in power in response to protein kinase A (PKA)-mediated phosphorylation. We compared isometric force and power generating capacity of rat skinned cardiac myocytes before and after treatment with the catalytic subunit of PKC. PKC increased phosphorylation levels of cMyBP-C and cTnI and decreased both maximal Ca(2+) activated force and Ca(2+) sensitivity of force. Moreover, during submaximal Ca(2+) activations PKC decreased power output by 62 %, which arose from both the fall in force and slower loaded shortening velocities since depressed power persisted even when force levels were matched before and after PKC. In addition, PKC blunted the phosphorylation of cTnI by PKA, reduced PKA-induced spontaneous oscillatory contractions, and diminished PKA-mediated elevations in myocyte power. To test whether altered thin filament function plays an essential role in these contractile changes we investigated the effects of chronic cTnI pseudo-phosphorylation on myofilament function using myocyte preparations from transgenic animals in which either only PKA phosphorylation sites (Ser-23/Ser-24) (PP) or both PKA and PKC phosphorylation sites (Ser-23/Ser-24/Ser-43/Ser-45/T-144) (All-P) were replaced with aspartic acid. Cardiac myocytes from All-P transgenic mice exhibited reductions in maximal force, Ca(2+) sensitivity of force, and power. Similarly diminished power generating capacity was observed in hearts from All-P mice as determined by in situ pressure-volume measurements. These results imply that PKC-mediated phosphorylation of cTnI plays a dominant role in depressing contractility, and, thus, increased PKC isozyme activity may contribute to maladaptive behavior exhibited during the progression to heart failure.
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9
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Kooij V, Stienen GJM, van der Velden J. The role of protein kinase C-mediated phosphorylation of sarcomeric proteins in the heart-detrimental or beneficial? Biophys Rev 2011; 3:107. [PMID: 28510060 DOI: 10.1007/s12551-011-0050-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Accepted: 06/08/2011] [Indexed: 10/18/2022] Open
Abstract
Protein kinase C (PKC) is a family of serine/threonine protein kinases, and alterations have been found in PKC isoform expression and localization in the failing heart. These alterations in PKC activation levels influence the PKC-mediated phosphorylation status of cellular target proteins involved in Ca2+-handling and sarcomeric contraction. The differences observed in the effects due to PKC-mediated phosphorylation may underlie part of the contractile dysfunction observed in the failing heart. It is therefore important to establish the beneficial and detrimental effects of this kinase in the healthy and failing heart. The function of PKC has been studied intensively; however, the complexity of the regulation of this kinase makes the interpretation of the different effects difficult. The main focus of this review is the (patho)physiological impact of phosphorylation of sarcomeric proteins, myosin light chain-2, troponin I and T, desmin, myosin binding protein-C, and titin by PKC.
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Affiliation(s)
- Viola Kooij
- Division of Cardiology, Johns Hopkins Bayview Proteomics Center, Johns Hopkins University, 5200 Eastern Avenue, MFL Bldg, Center Tower, Rm 601, Baltimore, MD, 21224, USA.
| | - Ger J M Stienen
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands
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Walker LA, Walker JS, Ambler SK, Buttrick PM. Stage-specific changes in myofilament protein phosphorylation following myocardial infarction in mice. J Mol Cell Cardiol 2009; 48:1180-6. [PMID: 19799909 DOI: 10.1016/j.yjmcc.2009.09.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2009] [Accepted: 09/18/2009] [Indexed: 11/18/2022]
Abstract
The response of cardiac muscle to an insult such as myocardial infarction includes changes in the expression of numerous signaling proteins and modulation of gene expression, as well as post-translational modifications of existing proteins. Most studies to date have defined these in end-stage cardiac muscle thus obviating consideration of the temporal progression that causes the heart to transition from a compensated to a decompensated phenotype. To explore these transitions, we examined contractile protein biochemistry in a mouse MI model at two early time points: 2 days and 2 weeks post-infarct and at two later time points: 2 and 4 months post-infarct. Phosphorylation of myofilament proteins was analyzed using phosphospecific staining of polyacrylamide gels, and whenever possible, phosphospecific antibodies. Phosphorylation of myosin binding protein c, the myosin regulatory light chain and troponin I were all decreased relative to sham operated animals at both early time points. However, by 2 months, total phosphorylation of all the major myofilament proteins normalized and at both 2 and 4 months, there was a significant increase in troponin I phosphorylation. One-dimensional IEF of troponin I coupled with phospho-specific antibody analysis demonstrated a redistribution of phosphorylation sites with a significant initial decline at the putative PKA sites, Serine 22,23, and a subsequent increase at the putative PKC site, serine 43,45. These data suggest that temporal changes in myofilament protein phosphorylation contribute both to the initial compensatory hyperdynamic response to myocardial infarction and subsequently to the gradual progression to myocardial failure.
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Affiliation(s)
- Lori A Walker
- University of Colorado Health Sciences Center, Department of Medicine/Cardiology, Aurora, CO 80045, USA.
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11
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Molnár A, Borbély A, Czuriga D, Ivetta SM, Szilágyi S, Hertelendi Z, Pásztor ET, Balogh Á, Galajda Z, Szerafin T, Jaquet K, Papp Z, Édes I, Tóth A. Protein Kinase C Contributes to the Maintenance of Contractile Force in Human Ventricular Cardiomyocytes. J Biol Chem 2009; 284:1031-9. [DOI: 10.1074/jbc.m807600200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
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12
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Gaze DC, Collinson PO. Multiple molecular forms of circulating cardiac troponin: analytical and clinical significance. Ann Clin Biochem 2008; 45:349-55. [DOI: 10.1258/acb.2007.007229] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Cardiac troponin T (cTnT) and I (cTnI) are highly specific and sensitive biomarkers of myocardial cell damage and are now accepted as the ‘gold standard’ diagnostic test for acute coronary syndrome and supersede the classical muscle enzyme biomarkers. While the understanding of the development and structure of the troponins has advanced, detailed biochemistry of the troponin molecules is complex and poorly understood. Many post-translational molecular forms of troponin are known to exist. The diversity of these circulating forms may have a clinical impact and the notion of a disease-specific troponin protein signature has been suggested. However, the effects of these multiple forms on commercial assay performance and their impact clinically are currently unknown and should be the focus of future research and assay design.
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Affiliation(s)
- David C Gaze
- Chemical Pathology, St George's Hospital, Blackshaw Road, Tooting, London SW17 0QT, UK
| | - Paul O Collinson
- Chemical Pathology, St George's Hospital, Blackshaw Road, Tooting, London SW17 0QT, UK
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Muroya S, Ohnishi-Kameyama M, Oe M, Nakajima I, Chikuni K. Postmortem changes in bovine troponin T isoforms on two-dimensional electrophoretic gel analyzed using mass spectrometry and western blotting: The limited fragmentation into basic polypeptides. Meat Sci 2007; 75:506-14. [DOI: 10.1016/j.meatsci.2006.08.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 08/23/2006] [Accepted: 08/23/2006] [Indexed: 10/24/2022]
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14
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Adamcová M, Stĕrba M, Simůnek T, Potácová A, Popelová O, Gersl V. Myocardial regulatory proteins and heart failure. Eur J Heart Fail 2006; 8:333-42. [PMID: 16309957 DOI: 10.1016/j.ejheart.2005.09.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/09/2004] [Revised: 07/01/2005] [Accepted: 09/22/2005] [Indexed: 10/25/2022] Open
Abstract
Cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are considered to be the most specific and sensitive biochemical markers of myocardial damage. Troponins have been studied in a wide range of clinical settings, including heart failure; however, there are few data on the role of regulatory proteins in the pathogenesis of heart failure, although a few interesting hypotheses have been proposed. A considerable body of evidence favours the view that alteration of the myocardial thin filament is the primary event leading to defective contractility of the failing myocardium, while the changes in Ca(2+) handling are a compensatory response. A better understanding of the role of regulatory proteins under different physiological and pathological conditions could lead to new therapeutic approaches in heart failure. Recently, calcium sensitisation has been proposed as a novel method by which cardiac performance may be enhanced via an increase in the affinity of troponin C for calcium but without affecting intracellular calcium concentration. To date, the only calcium sensitizer used in clinical practice is levosimendan.
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Affiliation(s)
- Michaela Adamcová
- Department of Physiology, Faculty of Medicine in Hradec Králové, Charles University in Prague, Simkova 870, 500 38 Hradec Králové, Czech Republic.
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15
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Jideama NM, Crawford BH, Hussain AKMA, Raynor RL. Dephosphorylation specificities of protein phosphatase for cardiac troponin I, troponin T, and sites within troponin T. Int J Biol Sci 2006; 2:1-9. [PMID: 16585947 PMCID: PMC1415850 DOI: 10.7150/ijbs.2.1] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2006] [Accepted: 03/01/2006] [Indexed: 11/25/2022] Open
Abstract
Protein dephosphorylation by protein phosphatase 1 (PP1), acting in concert with protein kinase C (PKC) and protein kinase A (PKA), is a pivotal regulatory mechanism of protein phosphorylation. Isolated rat cardiac myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 were used in determining dephosphorylation specificities, Ca2+-stimulated Mg2+ATPase activities, and Ca2+ sensitivities. In reconstituted troponin (Tn) complex, PP1 displayed distinct substrate specificity in dephosphorylation of TnT preferentially to TnI, in vitro. In situ phosphorylation of cardiomyocytes with calyculin A, a protein phosphatase inhibitor, resulted in an increase in the phosphorylation stiochiometry of TnT (0.3 to 0.5 (67%)), TnI (2.6 to 3.6 (38%)), and MLC2 (0.4 to 1.7 (325%)). These results further confirmed that though MLC2 is the preferred target substrate for protein phosphatase in the thick filament, the Tn complex (TnI and TnT) from thin filament and C-protein in the thick filament are also protein phosphatase substrates. Our in vitro dephosphorylation experiments revealed that while PP1 differentially dephosphorylated within TnT at multiple sites, TnI was uniformly dephosphorylated. Phosphopeptide maps from the in vitro experiments show that TnT phosphopeptides at spots 4A and 4B are much more resistant to PP1 dephosphorylation than other TnT phosphopeptides. Mg2+ATPase assays of myofibrils phosphorylated by PKC/PKA and dephosphorylated by PP1 delineated that while PKC and PKA phosphorylation decreased the Ca2+-stimulated Mg2+ATPase activities, dephosphorylation antagonistically restored it. PKC and PKA phosphorylation decreased Ca2+ sensitivity to 3.6 µM and 5.0 µM respectively. However, dephosphorylation restored the Mg2+ATPase activity of PKC (99%) and PKA (95%), along with the Ca2+ sensitivities (3.3 µM and 3.0 µM, respectively).
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Affiliation(s)
- Nathan M Jideama
- Department of Biological Sciences, Clark Atlanta University, Atlanta, GA 30314, USA.
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17
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Westfall MV, Lee AM, Robinson DA. Differential contribution of troponin I phosphorylation sites to the endothelin-modulated contractile response. J Biol Chem 2005; 280:41324-31. [PMID: 16236710 DOI: 10.1074/jbc.m506043200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac troponin I is a phosphorylation target for endothelin-activated protein kinase C. Earlier work in cardiac myocytes expressing nonphosphorylatable slow skeletal troponin I provided evidence that protein kinase C-mediated cardiac troponin I phosphorylation accelerates relaxation. However, replacement with the slow skeletal isoform also alters the myofilament pH response and the Ca2+ transient, which could influence endothelin-mediated relaxation. Here, differences in the Ca2+ transient could not explain the divergent relaxation response to endothelin in myocytes expressing cardiac versus slow skeletal troponin I nor could activation of Na+/H+ exchange. Three separate clusters within cardiac troponin I are phosphorylated by protein kinase C, and we set out to determine the contribution of the Thr144 and Ser23/Ser24 clusters to the endothelin-mediated contractile response. Myocyte replacement with a cardiac troponin I containing a Thr144 substituted with the Pro residue found in slow skeletal troponin I resulted in prolonged relaxation in response to acute endothelin compared with control myocytes. Ser23/Ser24 also is a target for protein kinase C phosphorylation of purified cardiac troponin I, and although this cluster was not acutely phosphorylated in intact myocytes, significant phosphorylation developed within 1 h after adding endothelin. Replacement of Ser23/Ser24 with Ala indicated that this cluster contributes significantly to relaxation during more prolonged endothelin stimulation. Overall, results with these mutants provide evidence that Thr144 plays an important role in the acute acceleration of relaxation, whereas Ser23/Ser24 contributes to relaxation during more prolonged activation of protein kinase C by endothelin.
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Affiliation(s)
- Margaret V Westfall
- Department of Surgery, University of Michigan, Ann Arbor, Michigan 48109, USA.
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Abstract
While the remodeling process in myocardial failure involves changes in ventricular structure and performance, it is now appreciated that it is also associated with changes in thin filament composition and function. As is discussed, changes at the level thick filament may affect thin filament activation in heart failure. Alterations in actin, troponin and tropomyosin isoform composition do not appear to be significant factors in human heart failure. In contrast, proteolytic degradation of troponin subunits are likely to be playing a functional role in some forms of cardiomyopathy (e.g. ischemic). Finally, phosphorylation of troponin I and troponin T by kinases (most notably protein kinase C) substantially affect thin filament function in failing human myocardium. These findings indicate that functional deficits in thin filament function in failing myocardium are largely reversible and create the potential for future targeted therapies in the treatment of this deadly disease.
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Affiliation(s)
- Peter VanBuren
- Department of Medicine, College of Medicine, University of Vermont, VT 05405, USA.
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19
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Giles TD, Sander GE. Diabetes mellitus and heart failure: basic mechanisms, clinical features, and therapeutic considerations. Cardiol Clin 2005; 22:553-68. [PMID: 15501623 DOI: 10.1016/j.ccl.2004.07.002] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Diabetic cardiomyopathy encompasses the spectrum from subclinical disease to the full-blown syndrome of congestive heart failure. The prevalence of type 2 diabetes mellitus is increasing at an alarming rate in the western world. and with it, the frequency of diabetes-related heart failure. There is at least early suggestion that target-driven, long-term, intensified intervention that is aimed at multiple risk factors in patients who have type 2 diabetes and microalbuminuria may reduce the risk of macrovascular (cardiovascular) and micro-vascular complications by approximately 50%. Thus, it is imperative that patients, particularly those who are at risk for the cardiovascular dysmetabolic syndrome, be screened aggressively for the presence of glucose intolerance and diabetes. When detected, all metabolic and cardio-vascular parameters should be evaluated and treated aggressively to reach currently recommended clinical targets. Such action will result in great benefit for patients by reducing morbidity and mortality and improving quality of life and will reduce the financial burden that is associated with this epidemic disease.
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Affiliation(s)
- Thomas D Giles
- Section of Cardiology, Louisiana State University Health Sciences Center, 1542 Tulane Avenue, New Orleans, LA 70112, USA.
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Metzger JM, Westfall MV. Covalent and noncovalent modification of thin filament action: the essential role of troponin in cardiac muscle regulation. Circ Res 2004; 94:146-58. [PMID: 14764650 DOI: 10.1161/01.res.0000110083.17024.60] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Troponin is essential for the regulation of cardiac contraction. Troponin is a sarcomeric molecular switch, directly regulating the contractile event in concert with intracellular calcium signals. Troponin isoform switching, missense mutations, proteolytic cleavage, and posttranslational modifications are known to directly affect sarcomeric regulation. This review focuses on physiologically relevant covalent and noncovalent modifications in troponin as part of a thematic series on cardiac thin filament function in health and disease.
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Affiliation(s)
- Joseph M Metzger
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Mich 48109, USA.
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Sumandea MP, Pyle WG, Kobayashi T, de Tombe PP, Solaro RJ. Identification of a functionally critical protein kinase C phosphorylation residue of cardiac troponin T. J Biol Chem 2003; 278:35135-44. [PMID: 12832403 DOI: 10.1074/jbc.m306325200] [Citation(s) in RCA: 155] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Cardiac Troponin T (cTnT) is one prominent substrate through which protein kinase C (PKC) exerts its effect on cardiomyocyte function. To determine the specific functional effects of the cTnT PKC-dependent phosphorylation sites (Thr197, Ser201, Thr206, and Thr287) we first mutated these residues to glutamate (E) or alanine (A). cTnT was selectively mutated to generate single, double, triple, and quadruple mutants. Bacterially expressed mutants were evaluated in detergent-treated mouse left ventricular papillary muscle fiber bundles where the endogenous troponin was replaced with a recombinant troponin complex containing either cTnT phosphorylated by PKC-alpha or a mutant cTnT. We simultaneously determined isometric tension development and actomyosin Mg-ATPase activity of the exchanged fiber bundles as a function of Ca2+ concentration. Our systematic analysis of the functional role of the multiple PKC phosphorylation sites on cTnT identified a localized region that controls maximum tension, ATPase activity, and Ca2+ sensitivity of the myofilaments. An important and novel finding of our study was that Thr206 is a functionally critical cTnT PKC phosphorylation residue. Its exclusive phosphorylation by PKC-alpha or replacement by Glu (mimicking phosphorylation) significantly decreased maximum tension, actomyosin Mg-ATPase activity, myofilament Ca2+ sensitivity, and cooperativity. On the other hand the charge modification of the other three residues together (T197/S201/T287-E) had no functional effect. Fibers bundles containing phosphorylated cTnT-wt (but not the T197/S201/T206/T287-E) exhibited a significant decrease of tension cost as compared with cTnT-wt.
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Affiliation(s)
- Marius P Sumandea
- Department of Physiology and Biophysics, Program in Cardiovascular Sciences, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA
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VanBuren P, Alix SL, Gorga JA, Begin KJ, LeWinter MM, Alpert NR. Cardiac troponin T isoforms demonstrate similar effects on mechanical performance in a regulated contractile system. Am J Physiol Heart Circ Physiol 2002; 282:H1665-71. [PMID: 11959629 DOI: 10.1152/ajpheart.00938.2001] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Alteration of troponin T (TnT) isoform expression has been reported in human and animal models of myocardial failure. The two adult beef cardiac TnT isoforms (TnT(3) and TnT(4)) were isolated for comparative functional analysis. Thin filaments were reconstituted containing pure populations of the isoforms. The in vitro motility assay was used to directly compare the effect of the two TnT isoforms on force and unloaded shortening as a function of free calcium. We found no significant differences between the two isoforms in terms of calcium sensitivity, cooperativity, or maximal activation (velocity and force) as assessed in a fully calcium-regulated system. Activation by myosin strong binding was similar for thin filaments containing either of the two TnT isoforms. Whereas maximally activated velocity and cooperativity was depressed at pH 6.5, no difference between thin filaments containing the two isoforms was detected. From the small magnitude of the TnT isoform shifts detected in myocardial failure and the lack of significant mechanical effect detected in the motility assay, variable TnT isoform expression is unlikely to be any functional significance in heart failure.
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Affiliation(s)
- Peter VanBuren
- Cardiology Unit, Department of Medicine, University of Vermont, Burlington, Vermont 05405, USA.
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Wu LL, Tang C, Liu MS. Altered phosphorylation and calcium sensitivity of cardiac myofibrillar proteins during sepsis. Am J Physiol Regul Integr Comp Physiol 2001; 281:R408-16. [PMID: 11448842 DOI: 10.1152/ajpregu.2001.281.2.r408] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Altered phosphorylation and Ca(2+) sensitivity of cardiac myofibrillar proteins during different phases of sepsis were investigated. Sepsis was induced by cecal ligation and puncture (CLP). The results show that phosphorylation of troponin I (TnI) was increased by 268% during the early phase (9 h after CLP) but decreased by 46% during the late phase (18 h after CLP) of sepsis. Phosphorylation of C protein was increased by 76% during the early phase but decreased by 41% during the late phase of sepsis. Phosphorylation of myosin light chain-2 (MLC-2) remained unaltered during the early phase but was decreased by 38% during the late phase of sepsis. Phosphorylation of TnT was unaffected during the progression of sepsis. The increases in the phosphorylation of TnI and C protein during early sepsis were associated with the decrease in the Ca(2+) sensitivity of myofilaments and the increases in myocardial changes in tension development (+dP/dt(max)) and cAMP level. The decreases in the phosphorylation of TnI and C protein during late sepsis coincided with the declines in the activities of myofibrillar ATPase, Ca(2+) sensitivity of myofilaments, myocardial +/-dP/dt(max), and cAMP content. The increases and the decreases in the phosphorylation of TnI and C protein, +/-dP/dt(max), and the tissue cAMP level were sensitive to isoproterenol stimulation and propranolol inhibition. These findings suggest that alterations in the phosphorylation of myofibrillar proteins, such as TnI, C protein, and MLC-2, and changes in the activities and the Ca(2+) sensitivity of myofibrillar ATPase may contribute to the altered cardiac function during the progression of sepsis. Furthermore, the sepsis-induced alterations in the phosphorylation and Ca(2+) sensitivity of cardiac myofibrillar proteins were mediated via a beta-adrenergic receptor pathway.
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Affiliation(s)
- L L Wu
- Department of Physiology and Pathophysiology, Peking University Health Sciences Center, Beijing 100083, China
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26
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Takeuchi Y, Kihara Y, Inagaki K, Yoneda T, Sasayama S. Endothelin-1 has a unique oxygen-saving effect by increasing contractile efficiency in the isolated rat heart. Circulation 2001; 103:1557-63. [PMID: 11257085 DOI: 10.1161/01.cir.103.11.1557] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND The effect of endothelin (ET)-1 on cardiac energetics is not fully understood. METHODS AND RESULTS In isolated, coronary-perfused rat hearts, we measured left ventricular contractility index (E(max)), pressure-volume area (PVA), and myocardial oxygen consumption (MVO(2)) before and after administration of ET-1 (1x10(-)(9) mol/L). ET-1 increased E(max) by 48+/-16% (P<0.01) and the total MVO(2) by 24+/-11% (P<0.01). The MVO(2)-PVA relations were linear both before and after ET-1 (r>0.99). ET-1 shifted MVO(2)-PVA upward, increasing the MVO(2) intercept by 24+/-13%. At the same time, ET-1 decreased the slope (S), with 1/S (contractile efficiency) being 46+/-5% before and 56+/-5% after ET-1 (P<0.01). ET-1-induced increases in E(max) and in contractile efficiency were abolished by an ET(A) receptor blocker (S-0139) but not by an ET(B) blocker (BQ-788). Although high [Ca(2+)] perfusion increased E(max) and the intercept to the same extent as ET-1, it did not change S. N(G)-Nitro-L-arginine (an inhibitor of nitric oxide synthase) increased the coronary perfusion pressure as much as ET-1, but S again remained unchanged. Dimethylamyloride (Na(+)/H(+) exchanger inhibitor) partially blocked the positive inotropic effect of ET-1 but not the ET-1-induced increase in the contractile efficiency. CONCLUSIONS Agonistic effects of ET-1 on the ET(A) receptor economized the chemomechanical conversion efficiency of the left ventricular unit myocardium by a mechanism independent of the Na(+)/H(+) exchanger. This unique oxygen-saving effect of ET-1 may play an adaptive role in the failing myocardium, in which local accumulation of ET-1 is present.
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Affiliation(s)
- Y Takeuchi
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
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27
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Abstract
Building a vertebrate heart is a complex task and involves several tissues, including the myocardium, endocardium, neural crest, and epicardium. Interactions between these tissues result in the changes in function and morphology (and also in the extracellular matrix, which serves as a substrate for morphological change) that are requisite for development of the heart. Some of the signaling pathways that mediate these changes have now been identified and several investigators are now filling in the missing pieces in these pathways in hopes of ultimately understanding the molecular mechanisms that govern healthy heart development. In addition, transcription factors that regulate various aspects of heart development have been identified. Transcription factors of the GATA and Nkx2 families are of particular importance for early specification of the heart field and for regulating expression of genes that encode proteins of the contractile apparatus. This chapter highlights some of the most significant discoveries made in the rapidly expanding field of heart development.
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Affiliation(s)
- M J Farrell
- Developmental Biology Program, Institute of Molecular Medicine and Genetics, Medical College of Georgia, Augusta 30912, USA
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Strasser RH, Simonis G, Schön SP, Braun MU, Ihl-Vahl R, Weinbrenner C, Marquetant R, Kübler W. Two distinct mechanisms mediate a differential regulation of protein kinase C isozymes in acute and prolonged myocardial ischemia. Circ Res 1999; 85:77-87. [PMID: 10400913 DOI: 10.1161/01.res.85.1.77] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
An activation of protein kinase C (PKC) in acute myocardial ischemia has been shown previously using its translocation to the plasma membrane as an indirect parameter. However, whether PKC remains activated or whether other mechanisms such as altered gene expression may mediate an isozyme-specific regulation in prolonged ischemia have not been investigated. In isolated perfused rat hearts, PKC activity and the expression of PKC cardiac isozymes were determined on the protein level using enzyme activities and Western blot analyses and on the mRNA level using reverse transcriptase-polymerase chain reaction after various periods of global ischemia (1 to 60 minutes). As early as 1 minute after the onset of ischemia, PKC activity is translocated from the cytosol to the particulate fraction without change in total cardiac enzyme activity. This translocation involves all major cardiac isozymes of PKC (ie, PKCalpha, PKCdelta, PKCepsilon, and PKCzeta). This rapid, nonselective activation of PKCs is only transient. In contrast, prolonged ischemia (>/=15 minutes) leads to an increased cardiac PKC activity (119+/-7 versus 190+/-8 pmol/min per mg protein) residing in the cytosol. This is associated with an augmented, subtype-selective isozyme expression of PKCdelta and PKCvarepsilon (163% and 199%, respectively). The specific mRNAs for PKCdelta (948+/-83 versus 1501+/-138 ag/ng total RNA, 30 minutes of ischemia) and PKCepsilon (1597+/-166 versus 2611+/-252 ag/ng total RNA) are selectively increased. PKCalpha and PKCzeta remain unaltered. In conclusion, two distinct activation and regulation processes of PKC are characterized in acute myocardial ischemia. The early, but transient, translocation involves all constitutively expressed cardiac isozymes of PKC, whereas in prolonged ischemia an increased total PKC activity is associated with an isozyme-selective induction of PKCepsilon and PKCdelta. Whether these fundamentally different activation processes interact remains to be elucidated.
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Affiliation(s)
- R H Strasser
- Department of Cardiology, Angiology, and Pulmology, University of Heidelberg, Medical Center, Heidelberg, Germany.
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29
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Abstract
Troponin T (TnT) is present in striated muscle of vertebrates and invertebrates as a group of homologous proteins with molecular weights usually in the 31-36 kDa range. It occupies a unique role in the regulatory protein system in that it interacts with TnC and TnI of the troponin complex and the proteins of the myofibrillar thin filament, tropomyosin and actin. In the myofibril the molecule is about 18 nm long and for much its length interacts with tropomyosin. The ability of TnT to form a complex with tropomyosin is responsible for locating the troponin complex with a periodicity of 38.5 nm along the thin filament of the myofibril. In addition to it structural role, TnT has the important function of transforming the TnI-TnC complex into a system, the inhibitory activity of which, on the tropomyosin-actomyosin MgATPase of the myofibril, becomes sensitive to calcium ions. Different genes control the expression of TnT in fast skeletal, slow skeletal and cardiac muscles. In all muscles, and particularly in fast skeletal, alternative splicing of mRNA produces a series of isoforms in a developmentally regulated manner. In consequence TnT exists in many more isoforms than any of the other thin filament proteins, the TnT superfamily. Despite the general homology of TnT isoforms, this alternative splicing leads to variable regions close to the N- and C-termini. As the isoforms have slightly different effects on the calcium sensitivity of the actomyosin MgATPase, modulation of the contractile response to calcium can occur during development and in different muscle types. TnT has recently aroused clinical interest in its potential for detecting myocardial damage and the association of mutations in the cardiac isoform with hypertrophic cardiomyopathy.
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Affiliation(s)
- S V Perry
- Department of Physiology, Medical School, University of Birmingham, UK
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Abstract
Protein phosphorylation acts a pivotal mechanism in regulating the contractile state of the heart by modulating particular levels of autonomic control on cardiac force/length relationships. Early studies of changes in cardiac protein phosphorylation focused on key components of the excitation-coupling process, namely phospholamban of the sarcoplasmic reticulum and myofibrillar troponin I. In more recent years the emphasis has shifted towards the identification of other phosphoproteins, and more importantly, the delineation of the mechanistic and signaling pathways regulating the various known phosphoproteins. In addition to cAMP- and Ca(2+)-calmodulin-dependent kinase processes, these have included regulation by protein kinase C and the ever-emerging family of growth factor-related kinases such as the tyrosine-, mitogen- and stress-activated protein kinases. Similarly, the role of protein dephosphorylation by protein phosphatases has been recognized as integral in modulating normal cardiac cellular function. Recent studies involving a variety of cardiovascular pathologies have demonstrated that changes in the phosphorylation states of key cardiac regulatory proteins may underlie cardiac dysfunction in disease states. The emphasis of this comprehensive review will be on discussing the role of cardiac phosphoproteins in regulating myocardial function and pathophysiology based not only on in vitro data, but more importantly, from ex vivo experiments with corroborative physiological and biochemical evidence.
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Affiliation(s)
- S T Rapundalo
- Department of Biochemistry, Parke-Davis Pharmaceutical Research, Division of Warner-Lambert, Ann Arbor, MI 48105, USA.
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Giles TD, Ouyang J, Kerut EK, Given MB, Allen GE, McIlwain EF, Greenberg SS. Changes in protein kinase C in early cardiomyopathy and in gracilis muscle in the BB/Wor diabetic rat. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:H295-307. [PMID: 9458880 DOI: 10.1152/ajpheart.1998.274.1.h295] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Hyperglycemia can upregulate protein kinase C (PKC), which may be an important mediator of the progression from normal heart and muscle function to diabetic myopathy in the myocardium and skeletal muscle in type 1 insulin-dependent diabetes mellitus (IDM). We evaluated this possibility during the early stage of IDM in BB/Wor diabetic (D) rats and age-matched BB/Wor diabetes-resistant (DR) rats. Interventricular septal thickness, E wave peak velocity of tricuspid inflow (both minimum and maximum), and left ventricular (LV) weight index were increased, and the rate of change in LV pressure (LV dP/dt) decreased in D rats subjected to M-mode and two-dimensional echocardiography and hemodynamic recording of heart rate, LV pressure (LVP), + LV dP/dt, -LV dP/dt, and LV end-diastolic pressure (LVEDP) in vivo and in vitro 41 days after the onset of hyperglycemia. Whole ventricle basal PKC activity was increased by 44.4 and 18.4% in the particulate and soluble fractions, respectively, from D rats compared with that from DR rats using r-32P phosphorylation of appropriate peptide substrates. When measured by Western blot gel densitometry, particulate PKC-alpha and PKC-delta content increased by 89 and 24%, respectively, but soluble PKC-beta and soluble and particulate PKC-epsilon were unchanged compared with that of DR rats. Similarly, gracilis muscle PKC activity and PKC-alpha and PKC-delta were elevated in the gracilis muscle, whereas that of the circulating neutrophil did not differ between the D and DR rats. Thus, in vivo, the early diabetic cardiomyopathy of the D rat is characterized by a restrictive LV with increased septal thickness and is associated with elevated PKC activity and increased amounts of myocardial particulate PKC-alpha and PKC-delta, which are also seen in the skeletal muscle. We conclude that increased PKC isozymes may play a pivotal role during IDM in the development of diabetic cardiomyopathy and skeletal muscle myopathy.
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Affiliation(s)
- T D Giles
- Department of Medicine, Louisiana State University Medical Center, New Orleans 70112, USA
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Malhotra A, Nakouzi A, Bowman J, Buttrick P. Expression and regulation of mutant forms of cardiac TnI in a reconstituted actomyosin system: role of kinase dependent phosphorylation. Mol Cell Biochem 1997; 170:99-107. [PMID: 9144323 DOI: 10.1023/a:1006865600519] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
When phosphorylated, the inhibitory subunit of troponin (TnI) causes a loss in calcium sensitivity and a decrease in actomyosin ATPase. To examine this process, we bacterially expressed wild type TnI and TnI mutants in which serine 22 and 23, a putative protein kinase A (PKA) site, and threonine 143, a putative protein kinase C (PKC) site, were replaced by alanine S22A/23A and TI43A. PKA dependent phosphorylation was approximately 90% reduced in the S22A/23A mutant and unaffected in T143A. PKC dependent phosphorylation was markedly reduced in T 143A relative both to a wild type construct and to S22A/23A, although some residual phosphorylation (likely at sites other than T143) was seen. The calcium sensitivity (i.e. inhibition of actomyosin ATPase in the presence of EGTA) and regulation of the reconstituted actomyosin system was preserved in the absence of phosphorylation using wild type TnI or either mutant. Calcium sensitivity was decreased by both PKA and PKC with the wild type TnI but was unaffected by PKA when the S22A/23A mutant was employed and by PKC when the T143A mutant was reconstituted. The calcium dependency of the ATPase curve was substantially right shifted when PKC phosphorylated wild type TnI was employed for regulation, and this was markedly attenuated when T143 A was reassociated (although a slight rightward shift and a reduction in maximal ATPase activity was still seen). These data confirm that phosphorylation of TnI by regulatory kinases plays a major role in the regulation of myofibrillar ATPase. The N-terminal serines (22 and 23) appear to be uniquely important for the PKA response whereas threonine 143 is involved in the PKC response although other residues may also have functional significance.
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Affiliation(s)
- A Malhotra
- Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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Sussman MA, Hamm-Alvarez SF, Vilalta PM, Welch S, Kedes L. Involvement of phosphorylation in doxorubicin-mediated myofibril degeneration. An immunofluorescence microscopy analysis. Circ Res 1997; 80:52-61. [PMID: 8978322 DOI: 10.1161/01.res.80.1.52] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Loss of myofilaments has been observed in both adaptive cardiac responses (i.e., hypertrophy) as well as in chemotheraputic use of antineoplastic drugs with cardiotoxic side effects (i.e., doxorubicin). An understanding of the degenerative process is a prerequisite for determining approaches to limit the cardiomyopathic changes associated with chronic heart disease or long-term chemotheraputic treatments. However, little is known about the specific events and molecular changes that initiate the degenerative process. To study this process, neonatal rat cardiomyocytes were treated with doxorubicin, which induced rapid and widespread thin-filament degeneration as observed by fluorescence confocal microscopy. Which demonstrated deterioration of sarcomeric thin-filament structure. Changes in the spontaneous beating of cardiomyocytes corresponding with myofibrillar degeneration were apparent using differential interference contrast video microscopy. After finding induction of kinase activity by doxorubicin in cultured cardiomyocytes, the protective effects of specific inhibitors of kinase activity were assessed for their ability to inhibit doxorubicin-induced myofibrillar break-down. Doxorubicin-induced changes appeared similar to the degeneration observed after treatment with a protein kinase activator (phorbol 12-myristate 13-acetate) or a serine-threonine protein phosphatase inhibitor (okadaic acid). Collectively, these results indicate that activation of protein kinase is an important event in the initiation of myofibrillar degeneration by doxorubicin. Further analyses of myofibrillar proteins with respect to biochemical modifications will be necessary to determine if phosphorylation events transmit signal(s) to initiate degeneration.
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Affiliation(s)
- M A Sussman
- Department of Biochemistry and Molecular Biology, University of Southern California School of Medicine, Los Angeles 90033, USA
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Jideama NM, Noland TA, Raynor RL, Blobe GC, Fabbro D, Kazanietz MG, Blumberg PM, Hannun YA, Kuo JF. Phosphorylation specificities of protein kinase C isozymes for bovine cardiac troponin I and troponin T and sites within these proteins and regulation of myofilament properties. J Biol Chem 1996; 271:23277-83. [PMID: 8798526 DOI: 10.1074/jbc.271.38.23277] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Protein kinase C (PKC) isozymes alpha, delta, epsilon, and zeta, shown to be expressed in adult rat cardiomyocytes, displayed distinct substrate specificities in phosphorylating troponin I and troponin T subunits in the bovine cardiac troponin complex. Thus, because they have different substrate affinities, PKC-alpha, -delta, and -epsilon phosphorylated troponin I more than troponin T, but PKC-zeta conversely phosphorylated the latter more than the former. Furthermore, PKC isozymes exhibited discrete specificities in phosphorylating distinct sites in these proteins as free subunits or in the troponin complex. Unlike other isozymes, PKC-delta was uniquely able to phosphorylate Ser-23/Ser-24 in troponin I, the bona fide phosphorylation sites for protein kinase A (PKA); and consequently, like PKA, it reduced Ca2+ sensitivity of Ca2+-stimulated MgATPase of reconstituted actomyosin S-1. In addition, PKC-delta, like PKC-alpha, readily phosphorylated Ser-43/Ser-45 (sites common for all PKC isozymes) and reduced maximal activity of MgATPase. In this respect, PKC-delta functioned as a hybrid of PKC-alpha and PKA. In contrast to PKC-alpha, -delta, and -epsilon, PKC-zeta exclusively phosphorylated two previously unknown sites in troponin T. Phosphorylation of troponin T by PKC-alpha resulted in decreases in both Ca2+ sensitivity and maximal activity, whereas phosphorylation by PKC-zeta resulted in a slight increase of the Ca2+ sensitivity without affecting the maximal activity of MgATPase. Most of the in vitro phosphorylation sites in troponin I and troponin T were confirmed in situ in adult rat cardiomyocytes. The present study has demonstrated for the first time distinct specificities of PKC isozymes for phosphorylation of two physiological substrates in the myocardium, with functional consequences.
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Affiliation(s)
- N M Jideama
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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Blobe GC, Stribling DS, Fabbro D, Stabel S, Hannun YA. Protein kinase C beta II specifically binds to and is activated by F-actin. J Biol Chem 1996; 271:15823-30. [PMID: 8663149 DOI: 10.1074/jbc.271.26.15823] [Citation(s) in RCA: 105] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The two most closely related isoenzymes of protein kinase C (PKC), PKC betaI and betaII, are distinct but highly homologous isoenzymes derived via alternative splicing of the same gene product. In this study, PKC betaII, but not PKC betaI, translocated to the actin cytoskeleton upon stimulation of cells with phorbol esters. In cells, antibodies to PKC betaII, but not to PKC betaI, co-immunoprecipitated actin. Using an actin-binding co-sedimentation assay, we show in vitro that PKC betaII, but not PKC betaI, binds to actin specifically. This binding was inhibited by peptides based on sequences unique to PKC betaII; thus defining an actin-binding site in PKC betaII that is not present in PKC betaI. The binding of PKC betaII to actin was not inhibited by kinase inhibitors of PKC (sphingosine and staurosporine), suggesting that prior activation and/or substrate phosphorylation are not required for the interaction of PKC betaII with actin. On the other hand, the interaction of PKC betaII with actin resulted in marked enhancement of autophosphorylation of PKC betaII and in an alteration in substrate specificity. These studies serve to define a novel functional domain in the carboxyl-terminal region of PKC beta, which is involved in directing isoenzyme-specific protein-protein interactions, and consequently, isoenzyme-specific functions in vivo.
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Affiliation(s)
- G C Blobe
- Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA
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36
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Lin D, Bobkova A, Homsher E, Tobacman LS. Altered cardiac troponin T in vitro function in the presence of a mutation implicated in familial hypertrophic cardiomyopathy. J Clin Invest 1996; 97:2842-8. [PMID: 8675696 PMCID: PMC507378 DOI: 10.1172/jci118740] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Familial hypertrophic cardiomyopathy (HCM) can be caused by dominant missense mutations in cardiac troponin T (TnT), alpha-tropomyosin, C-protein, or cardiac myosin heavy chain genes. The myosin mutations are known to impair function, but any functional consequences of the TnT mutations are unknown. This report describes the in vitro function of troponin containing an IIe91Asn mutation in rat cardiac TnT, corresponding to the HCM-causing Ile79Asn mutation in man. Mutant and wild-type TnT cDNAs were expressed in bacteria and the proteins purified and reconstituted with the other troponin subunits, the mutation had no effect on troponin's affinity for tropomyosin, troponin-induced binding of tropomyosin to actin, cooperative binding of myosin subfragment 1 to the thin filament, CA(2+)-sensitive regulation of thin filament-myosin subfragment 1 ATPase activity, or the CA2+ concentration dependence of this regulation. However, the mutation resulted in 50% faster thin filament movement over a surface coated with heavy meromyosin in in vitro motility assays. The increased sliding speed suggests an unexpected role for the amino terminal region of TnT in which this mutation occurs. The relationship between this faster motility and altered cardiac contraction in patients with HCM is discussed.
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Affiliation(s)
- D Lin
- Department of Internal Medicine, University of Iowa, Iowa City 52242, USA
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37
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Abstract
Understanding transmembrane signalling process is one of the major challenge of the decade. In most tissues, since Fisher and Krebs's discovery in the 1950's, protein phosphorylation has been widely recognized as a key event of this cellular function. Indeed, binding of hormones or neurotransmitters to specific membrane receptors leads to the generation of cytosoluble second messengers which in turn activate a specific protein kinase. Numerous protein kinases have been so far identified and roughly classified into two groups, namely serine/threonine and tyrosine kinases on the basis of the target acid although some more recently discovered kinases like MEK (or MAP kinase kinase) phosphorylate both serine and tyrosine residues. Protein kinase C is a serine/threonine kinase that was first described by Takai et al. [1] as a Ca- and phospholipid-dependent protein kinase. Later on, Kuo et al. [2] found that PKC was expressed in most tissues including the heart. The field of investigation became more complicated when it was found that the kinase is not a single molecular entity and that several isoforms exist. At present, 12 PKC isoforms and other PKC-related kinases [3] were identified in mammalian tissues. These are classified into three groups. (1) the Ca-activated alpha-, beta-, and gamma-PKCs which display a Ca-binding site (C2); (2) the Ca-insensitive delta-, epsilon-, theta-, eta-, and mu-PKCs. The kinases that belong to both of these groups display two cysteine-rich domains (C1) which bind phorbol esters (for recent review on PKC structure, see [4]). (3) The third group was named atypical PKCs and include zeta, lambda, and tau-PKCs that lack both the C2 and one cysteine-rich domain. Consequently, these isoforms are Ca-insensitive and cannot be activated by phorbol esters [5]. In the heart, evidence that multiple PKC isoforms exist was first provided by Kosaka et at. [6] who identified by chromatography at least two PKC-related isoenzymes. Numerous studies were thus devoted to the biochemical characterization of these isoenzymes (see [7] for review on cardiac PKCs) as well as to the identification of their substrates. This overview aims at updating the present knowledge on the expression, activation and functions of PKC isoforms in cardiac cells.
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Affiliation(s)
- M Pucéat
- Laboratoire de Physiopathologie Cardiovasculaire, INSERM U390, Montpellier, France
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38
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Abstract
Multiple closely related, yet distinct, isoforms exist for each of the cardiac contractile proteins. The isoform composition of the heart changes in response to developmental and physiologic cues. This paper reviews the molecular basis for cardiac contractile protein isoform diversity and the functional consequences of isoform shifts.
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Affiliation(s)
- R N Kitsis
- Department of Medicine (Cardiology), Albert Einstein College of Medicine, New York, USA
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39
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Noland TA, Guo X, Raynor RL, Jideama NM, Averyhart-Fullard V, Solaro RJ, Kuo JF. Cardiac troponin I mutants. Phosphorylation by protein kinases C and A and regulation of Ca(2+)-stimulated MgATPase of reconstituted actomyosin S-1. J Biol Chem 1995; 270:25445-54. [PMID: 7592712 DOI: 10.1074/jbc.270.43.25445] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The significance of site-specific phosphorylation of cardiac troponin I (TnI) by protein kinase C and protein kinase A in the regulation of Ca(2+)-stimulated MgATPase of reconstituted actomyosin S-1 was investigated. The TnI mutants used were T144A, S43A/S45A, and S43A/S45A/T144A (in which the identified protein kinase C phosphorylation sites, Thr-144 and Ser-43/ Ser-45, were, respectively, substituted by Ala) and S23A/S24A and N32 (in which the protein kinase A phosphorylation sites Ser-23/Ser-24 were either substituted by Ala or deleted). The mutations caused subtle changes in the kinetics of phosphorylation by protein kinase C, and all mutants were maximally phosphorylated to various extents (1.3-2.7 mol of phosphate/mol of protein). Protein kinase C could cross-phosphorylate protein kinase A sites but the reverse essentially could not occur. Compared to wild-type TnI and T144A, un-phosphorylated S43A/S45A, S43A/S45A/T144, S23A/ S24A, and N32 caused a decreased Ca2+ sensitivity of Ca(2+)-stimulated MgATPase of reconstituted actomyosin. S-1. Phosphorylation by protein kinase C of wild-type and all mutants except S43A/S45A and S43A/S45A/T144A caused marked reductions in both the maximal activity of Ca(2+)-stimulated MgATPase and apparent affinity of myosin S-1 for reconstitued (regulated) actin. It was further noted that protein kinase C acted in an additive manner with protein kinase A by phosphorylating Ser-23/Ser-24 to bring about a decreased Ca2+ sensitivity of the myofilament. It is suggested that Ser-43/Ser-45 and Ser-23/Ser-24 in cardiac TnI are important for normal Ca2+ sensitivity of the myofilament, and that phosphorylation of Ser-43/Ser-45 and Ser-23/Ser-24 is primarily involved in the protein kinase C regulation of the activity and Ca2+ sensitivity, respectively, of actomyosin S-1 MgATPase.
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Affiliation(s)
- T A Noland
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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40
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Jaquet K, Fukunaga K, Miyamoto E, Meyer HE. A site phosphorylated in bovine cardiac troponin T by cardiac CaM kinase II. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1248:193-5. [PMID: 7748902 DOI: 10.1016/0167-4838(95)00028-s] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Ca2+/Calmodulin-dependent protein kinase II isolated from heart phosphorylates bovine cardiac troponin T present in the holotroponin complex. Thr-190 has been determined as the main phosphorylation site.
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Affiliation(s)
- K Jaquet
- Ruhr-Universität Bochum, Institut für Physiologische Chemie, Abteilung für Biochemie Supramolekularer Systeme, Germany
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41
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Heyder S, Malhotra A, Rüegg JC. Myofibrillar Ca2+ sensitivity of cardiomyopathic hamster hearts. Pflugers Arch 1995; 429:539-45. [PMID: 7617444 DOI: 10.1007/bf00704159] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
We studied the Ca2+ responsiveness of skinned muscle fibre preparations from the right and left ventricles of normal (FIB) and genetically cardiomyopathic (Bio-To-2) Syrian hamsters. Thus, we compared the Ca2+/force relationships of preparations from myopathic hamsters to those of age-matched (11-16 months old) normal animals. The pCa (i.e. -log10 [Ca2+]) required for 50% force activation (Ca2+ sensitivity) was higher in the myopathic hamsters than in controls (pCa50 values of 5.3 +/- 0.03 and 5.17 +/- 0.04, respectively); this difference might be due to an alteration in regulatory proteins. Indeed, after extraction (with vanadate) and replacement of troponin I with bovine cardiac troponin the pCa50 values were similar (pCa 5.35) to those of bovine ventricular fibres. The Ca2+ sensitizer EMD 53998 (10 microM) increased Ca2+ sensitivity in preparations from normal and cardiomyopathic hamsters equally, by 0.4 pCa units. Incubation of fibre bundles with the catalytic subunit of cyclic-adenosine-monophosphate-dependent protein kinase decreased Ca2+ sensitivity, thereby "normalizing" the enhanced Ca2+ responsiveness of fibres from cardiomyopathic hamsters. It is not clear, however, whether the pathologically increased Ca2+ sensitivity of the hearts of aged myopathic hamsters reflects a maladaptation, or a compensatory mechanism of the failing heart.
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Affiliation(s)
- S Heyder
- II. Physiologisches Institut, University of Heidelberg, Germany
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42
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Equilibrium linkage analysis of cardiac thin filament assembly. Implications for the regulation of muscle contraction. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(18)43901-4] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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