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Qvit N, Lin AJ, Elezaby A, Ostberg NP, Campos JC, Ferreira JCB, Mochly-Rosen D. A Selective Inhibitor of Cardiac Troponin I Phosphorylation by Delta Protein Kinase C (δPKC) as a Treatment for Ischemia-Reperfusion Injury. Pharmaceuticals (Basel) 2022; 15:271. [PMID: 35337069 PMCID: PMC8950820 DOI: 10.3390/ph15030271] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 02/15/2022] [Accepted: 02/17/2022] [Indexed: 01/27/2023] Open
Abstract
Myocardial infarction is the leading cause of cardiovascular mortality, with myocardial injury occurring during ischemia and subsequent reperfusion (IR). We previously showed that the inhibition of protein kinase C delta (δPKC) with a pan-inhibitor (δV1-1) mitigates myocardial injury and improves mitochondrial function in animal models of IR, and in humans with acute myocardial infarction, when treated at the time of opening of the occluded blood vessel, at reperfusion. Cardiac troponin I (cTnI), a key sarcomeric protein in cardiomyocyte contraction, is phosphorylated by δPKC during reperfusion. Here, we describe a rationally-designed, selective, high-affinity, eight amino acid peptide that inhibits cTnI's interaction with, and phosphorylation by, δPKC (ψTnI), and prevents tissue injury in a Langendorff model of myocardial infarction, ex vivo. Unexpectedly, we also found that this treatment attenuates IR-induced mitochondrial dysfunction. These data suggest that δPKC phosphorylation of cTnI is critical in IR injury, and that a cTnI/δPKC interaction inhibitor should be considered as a therapeutic target to reduce cardiac injury after myocardial infarction.
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Affiliation(s)
- Nir Qvit
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
- The Azrieli Faculty of Medicine in the Galilee, Bar-Ilan University, Safed 1311502, Israel
| | - Amanda J. Lin
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
| | - Aly Elezaby
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
| | - Nicolai P. Ostberg
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
| | - Juliane C. Campos
- Department of Anatomy, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil;
| | - Julio C. B. Ferreira
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
- Department of Anatomy, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo 05508-000, Brazil;
| | - Daria Mochly-Rosen
- Center for Clinical Sciences Research, Department of Chemical & Systems Biology, Stanford University School of Medicine, 269 Campus Dr. Room 3145, Stanford, CA 94305, USA; (N.Q.); (A.J.L.); (A.E.); (N.P.O.); (J.C.B.F.)
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Wadthaisong M, Witayavanitkul N, Bupha‐Intr T, Wattanapermpool J, de Tombe PP. Chronic high-dose testosterone treatment: impact on rat cardiac contractile biology. Physiol Rep 2019; 7:e14192. [PMID: 31353833 PMCID: PMC6661270 DOI: 10.14814/phy2.14192] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2019] [Accepted: 07/09/2019] [Indexed: 01/28/2023] Open
Abstract
Androgen therapy provides cardiovascular benefits for hypogonadism. However, myocardial hypertrophy, fibrosis, and infarction have been reported in testosterone or androgenic anabolic steroid abuse. Therefore, better understanding of the factors leading to adverse results of androgen abuse is needed. The aim of the present study was to examine the impact of high dose of androgen treatment on cardiac biology, and whether exposure duration modulates this response. Male rats were treated with 10 mg/kg testosterone, three times a week, for either 4 or 12 weeks; vehicle injections served as controls. Four weeks of testosterone treatment induced an increase in ventricular wall thickness, indicative of concentric hypertrophy, as well as increased ejection fraction; in contrast, both parameters were blunted following 12 weeks of high-dose testosterone treatment. Cardiac myocyte contractile parameters were assessed in isolated electrically stimulated myocytes (sarcomere and intracellular calcium dynamics), and in chemically permeabilized isolated myocardium (myofilament force development and tension-cost). High-dose testosterone treatment for 4 weeks was associated with increased myocyte contractile parameters, while 12 weeks treatment induced significant depression of these parameters, mirroring the cardiac pump function results. In conclusion, chronic administration of high-dose testosterone initially induces increased cardiac function. However, this initial beneficial impact is followed by significant depression of cardiac pump function, myocyte contractility, and cardiac myofilament function. Our results indicate that chronic high-testosterone usage is of limited use and may, instead, induce significant cardiac dysfunction.
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Affiliation(s)
- Munthana Wadthaisong
- Department of Physiology, Faculty of ScienceMahidol UniversityBangkokThailand
- Department of Cell and Molecular PhysiologyLoyola University Chicago Health Sciences DivisionMaywoodIllinois
| | - Namthip Witayavanitkul
- Department of Physiology, Faculty of ScienceMahidol UniversityBangkokThailand
- Department of Cell and Molecular PhysiologyLoyola University Chicago Health Sciences DivisionMaywoodIllinois
| | - Tepmanas Bupha‐Intr
- Department of Physiology, Faculty of ScienceMahidol UniversityBangkokThailand
| | | | - Pieter P. de Tombe
- Department of Cell and Molecular PhysiologyLoyola University Chicago Health Sciences DivisionMaywoodIllinois
- Department of Physiology and BiophysicsUniversity of Illinois at ChicagoChicagoIllinois
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Marrocco V, Bogomolovas J, Ehler E, Dos Remedios CG, Yu J, Gao C, Lange S. PKC and PKN in heart disease. J Mol Cell Cardiol 2019; 128:212-226. [PMID: 30742812 PMCID: PMC6408329 DOI: 10.1016/j.yjmcc.2019.01.029] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 01/30/2019] [Accepted: 01/31/2019] [Indexed: 12/22/2022]
Abstract
The protein kinase C (PKC) and closely related protein kinase N (PKN) families of serine/threonine protein kinases play crucial cellular roles. Both kinases belong to the AGC subfamily of protein kinases that also include the cAMP dependent protein kinase (PKA), protein kinase B (PKB/AKT), protein kinase G (PKG) and the ribosomal protein S6 kinase (S6K). Involvement of PKC family members in heart disease has been well documented over the years, as their activity and levels are mis-regulated in several pathological heart conditions, such as ischemia, diabetic cardiomyopathy, as well as hypertrophic or dilated cardiomyopathy. This review focuses on the regulation of PKCs and PKNs in different pathological heart conditions and on the influences that PKC/PKN activation has on several physiological processes. In addition, we discuss mechanisms by which PKCs and the closely related PKNs are activated and turned-off in hearts, how they regulate cardiac specific downstream targets and pathways, and how their inhibition by small molecules is explored as new therapeutic target to treat cardiomyopathies and heart failure.
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Affiliation(s)
- Valeria Marrocco
- Division of Cardiology, School of Medicine, University of California-San Diego, La Jolla, USA
| | - Julius Bogomolovas
- Division of Cardiology, School of Medicine, University of California-San Diego, La Jolla, USA; Department of Cognitive and Clinical Neuroscience, Central Institute of Mental Health, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany
| | - Elisabeth Ehler
- Randall Centre for Cell and Molecular Biophysics, School of Basic and Medical Biosciences, School of Cardiovascular Medicine and Sciences, British Heart Foundation Research Excellence Centre, King's College London, New Hunt's House, Guy's Campus, London SE1 1UL, UK
| | | | - Jiayu Yu
- Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Department of Pathophysiology, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Chen Gao
- Division of Molecular Medicine, Department of Anesthesiology, David Geffen School of Medicine at UCLA, University of California-Los Angeles, Los Angeles, USA.
| | - Stephan Lange
- Division of Cardiology, School of Medicine, University of California-San Diego, La Jolla, USA; University of Gothenburg, Wallenberg Laboratory, Department of Molecular and Clinical Medicine, Institute of Medicine, Gothenburg, Sweden.
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Conserved salt-bridge competition triggered by phosphorylation regulates the protein interactome. Proc Natl Acad Sci U S A 2017; 114:13453-13458. [PMID: 29208709 DOI: 10.1073/pnas.1711543114] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Phosphorylation is a major regulator of protein interactions; however, the mechanisms by which regulation occurs are not well understood. Here we identify a salt-bridge competition or "theft" mechanism that enables a phospho-triggered swap of protein partners by Raf Kinase Inhibitory Protein (RKIP). RKIP transitions from inhibiting Raf-1 to inhibiting G-protein-coupled receptor kinase 2 upon phosphorylation, thereby bridging MAP kinase and G-Protein-Coupled Receptor signaling. NMR and crystallography indicate that a phosphoserine, but not a phosphomimetic, competes for a lysine from a preexisting salt bridge, initiating a partial unfolding event and promoting new protein interactions. Structural elements underlying the theft occurred early in evolution and are found in 10% of homo-oligomers and 30% of hetero-oligomers including Bax, Troponin C, and Early Endosome Antigen 1. In contrast to a direct recognition of phosphorylated residues by binding partners, the salt-bridge theft mechanism represents a facile strategy for promoting or disrupting protein interactions using solvent-accessible residues, and it can provide additional specificity at protein interfaces through local unfolding or conformational change.
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Cheng Y, Regnier M. Cardiac troponin structure-function and the influence of hypertrophic cardiomyopathy associated mutations on modulation of contractility. Arch Biochem Biophys 2016; 601:11-21. [PMID: 26851561 PMCID: PMC4899195 DOI: 10.1016/j.abb.2016.02.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Revised: 01/30/2016] [Accepted: 02/02/2016] [Indexed: 11/29/2022]
Abstract
Cardiac troponin (cTn) acts as a pivotal regulator of muscle contraction and relaxation and is composed of three distinct subunits (cTnC: a highly conserved Ca(2+) binding subunit, cTnI: an actomyosin ATPase inhibitory subunit, and cTnT: a tropomyosin binding subunit). In this mini-review, we briefly summarize the structure-function relationship of cTn and its subunits, its modulation by PKA-mediated phosphorylation of cTnI, and what is known about how these properties are altered by hypertrophic cardiomyopathy (HCM) associated mutations of cTnI. This includes recent work using computational modeling approaches to understand the atomic-based structural level basis of disease-associated mutations. We propose a viewpoint that it is alteration of cTnC-cTnI interaction (rather than the Ca(2+) binding properties of cTn) per se that disrupt the ability of PKA-mediated phosphorylation at cTnI Ser-23/24 to alter contraction and relaxation in at least some HCM-associated mutations. The combination of state of the art biophysical approaches can provide new insight on the structure-function mechanisms of contractile dysfunction resulting cTnI mutations and exciting new avenues for the diagnosis, prevention, and even treatment of heart diseases.
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Affiliation(s)
- Yuanhua Cheng
- University of Washington, Department of Bioengineering, Seattle, WA, USA
| | - Michael Regnier
- University of Washington, Department of Bioengineering, Seattle, WA, USA.
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Podobed P, Pyle WG, Ackloo S, Alibhai FJ, Tsimakouridze EV, Ratcliffe WF, Mackay A, Simpson J, Wright DC, Kirby GM, Young ME, Martino TA. The day/night proteome in the murine heart. Am J Physiol Regul Integr Comp Physiol 2014; 307:R121-37. [PMID: 24789993 DOI: 10.1152/ajpregu.00011.2014] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Circadian rhythms are essential to cardiovascular health and disease. Temporal coordination of cardiac structure and function has focused primarily at the physiological and gene expression levels, but these analyses are invariably incomplete, not the least because proteins underlie many biological processes. The purpose of this study was to reveal the diurnal cardiac proteome and important contributions to cardiac function. The 24-h day-night murine cardiac proteome was assessed by two-dimensional difference in gel electrophoresis (2D-DIGE) and liquid chromatography-mass spectrometry. Daily variation was considerable, as ∼7.8% (90/1,147) of spots exhibited statistical changes at paired times across the 24-h light- (L) dark (D) cycle. JTK_CYCLE was used to investigate underlying diurnal rhythms in corresponding mRNA. We next revealed that disruption of the L:D cycle altered protein profiles and diurnal variation in cardiac function in Langendorff-perfused hearts, relative to the L:D cycle. To investigate the role of the circadian clock mechanism, we used cardiomyocyte clock mutant (CCM) mice. CCM myofilaments exhibited a loss of time-of-day-dependent maximal calcium-dependent ATP consumption, and altered phosphorylation rhythms. Moreover, the cardiac proteome was significantly altered in CCM hearts, especially enzymes regulating vital metabolic pathways. Lastly, we used a model of pressure overload cardiac hypertrophy to demonstrate the temporal proteome during heart disease. Our studies demonstrate that time of day plays a direct role in cardiac protein abundance and indicate a novel mechanistic contribution of circadian biology to cardiovascular structure and function.
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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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Wijnker PJM, Sequeira V, Witjas-Paalberends ER, Foster DB, dos Remedios CG, Murphy AM, Stienen GJM, van der Velden J. Phosphorylation of protein kinase C sites Ser42/44 decreases Ca(2+)-sensitivity and blunts enhanced length-dependent activation in response to protein kinase A in human cardiomyocytes. Arch Biochem Biophys 2014; 554:11-21. [PMID: 24814372 PMCID: PMC4121669 DOI: 10.1016/j.abb.2014.04.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 04/29/2014] [Accepted: 04/29/2014] [Indexed: 10/25/2022]
Abstract
Protein kinase C (PKC)-mediated phosphorylation of troponin I (cTnI) at Ser42/44 is increased in heart failure. While studies in rodents demonstrated that PKC-mediated Ser42/44 phosphorylation decreases maximal force and ATPase activity, PKC incubation of human cardiomyocytes did not affect maximal force. We investigated whether Ser42/44 pseudo-phosphorylation affects force development and ATPase activity using troponin exchange in human myocardium. Additionally, we studied if pseudo-phosphorylated Ser42/44 modulates length-dependent activation of force, which is regulated by protein kinase A (PKA)-mediated cTnI-Ser23/24 phosphorylation. Isometric force was measured in membrane-permeabilized cardiomyocytes exchanged with human recombinant wild-type troponin or troponin mutated at Ser42/44 or Ser23/24 into aspartic acid (D) or alanine (A) to mimic phosphorylation and dephosphorylation, respectively. In troponin-exchanged donor cardiomyocytes experiments were repeated after PKA incubation. ATPase activity was measured in troponin-exchanged cardiac muscle strips. Compared to wild-type, 42D/44D decreased Ca(2+)-sensitivity without affecting maximal force in failing and donor cardiomyocytes. In donor myocardium, 42D/44D did not affect maximal ATPase activity or tension cost. Interestingly, 42D/44D blunted the length-dependent increase in Ca(2+)-sensitivity induced upon PKA-mediated phosphorylation. Since the drop in Ca(2+)-sensitivity at physiological Ca(2+)-concentrations is relatively large phosphorylation of Ser42/44 may result in a decrease of force and associated ATP utilization in the human heart.
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Affiliation(s)
- Paul J M Wijnker
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Experimental Pharmacology and Toxicology, Cardiovascular Research Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
| | - Vasco Sequeira
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
| | - E Rosalie Witjas-Paalberends
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands.
| | - D Brian Foster
- Department of Pediatrics/Division of Cardiology, Johns Hopkins University School of Medicine, Ross Bldg 1144/720 Rutland Avenue, Baltimore, MD 21205, USA.
| | | | - Anne M Murphy
- Department of Pediatrics/Division of Cardiology, Johns Hopkins University School of Medicine, Ross Bldg 1144/720 Rutland Avenue, Baltimore, MD 21205, USA.
| | - Ger J M Stienen
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands.
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU University Medical Center, Amsterdam, The Netherlands; ICIN-Netherlands Heart Institute, Utrecht, The Netherlands.
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Kooij V, Zhang P, Piersma SR, Sequeira V, Boontje NM, Wijnker PJM, Jiménez CR, Jaquet KE, dos Remedios C, Murphy AM, Van Eyk JE, van der Velden J, Stienen GJM. PKCα-specific phosphorylation of the troponin complex in human myocardium: a functional and proteomics analysis. PLoS One 2013; 8:e74847. [PMID: 24116014 PMCID: PMC3792062 DOI: 10.1371/journal.pone.0074847] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2013] [Accepted: 08/07/2013] [Indexed: 11/18/2022] Open
Abstract
Aims Protein kinase Cα (PKCα) is one of the predominant PKC isoforms that phosphorylate cardiac troponin. PKCα is implicated in heart failure and serves as a potential therapeutic target, however, the exact consequences for contractile function in human myocardium are unclear. This study aimed to investigate the effects of PKCα phosphorylation of cardiac troponin (cTn) on myofilament function in human failing cardiomyocytes and to resolve the potential targets involved. Methods and Results Endogenous cTn from permeabilized cardiomyocytes from patients with end-stage idiopathic dilated cardiomyopathy was exchanged (∼69%) with PKCα-treated recombinant human cTn (cTn (DD+PKCα)). This complex has Ser23/24 on cTnI mutated into aspartic acids (D) to rule out in vitro cross-phosphorylation of the PKA sites by PKCα. Isometric force was measured at various [Ca2+] after exchange. The maximal force (Fmax) in the cTn (DD+PKCα) group (17.1±1.9 kN/m2) was significantly reduced compared to the cTn (DD) group (26.1±1.9 kN/m2). Exchange of endogenous cTn with cTn (DD+PKCα) increased Ca2+-sensitivity of force (pCa50 = 5.59±0.02) compared to cTn (DD) (pCa50 = 5.51±0.02). In contrast, subsequent PKCα treatment of the cells exchanged with cTn (DD+PKCα) reduced pCa50 to 5.45±0.02. Two PKCα-phosphorylated residues were identified with mass spectrometry: Ser198 on cTnI and Ser179 on cTnT, although phosphorylation of Ser198 is very low. Using mass spectrometry based-multiple reaction monitoring, the extent of phosphorylation of the cTnI sites was quantified before and after treatment with PKCα and showed the highest phosphorylation increase on Thr143. Conclusion PKCα-mediated phosphorylation of the cTn complex decreases Fmax and increases myofilament Ca2+-sensitivity, while subsequent treatment with PKCα in situ decreased myofilament Ca2+-sensitivity. The known PKC sites as well as two sites which have not been previously linked to PKCα are phosphorylated in human cTn complex treated with PKCα with a high degree of specificity for Thr143.
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Affiliation(s)
- Viola Kooij
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
- Johns Hopkins Bayview Proteomics Center, Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
- * E-mail:
| | - Pingbo Zhang
- Johns Hopkins Bayview Proteomics Center, Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Sander R. Piersma
- OncoProteomics Laboratory, Department of Medical Oncology, VU Medical Center, Amsterdam, The Netherlands
| | - Vasco Sequeira
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
| | - Nicky M. Boontje
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
| | - Paul J. M. Wijnker
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
| | - Connie R. Jiménez
- OncoProteomics Laboratory, Department of Medical Oncology, VU Medical Center, Amsterdam, The Netherlands
| | - Kornelia E. Jaquet
- St Josef-Hospital/Bergmannsheil, Clinic of the Ruhr-University of Bochum, Bochum, Germany
| | - Cris dos Remedios
- Muscle Research Unit, Institute for Biomedical Research, The University of Sydney, Sydney, Australia
| | - Anne M. Murphy
- Institute of Molecular Cardiobiology, Department of Pediatrics, School of Medical, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Jennifer E. Van Eyk
- Johns Hopkins Bayview Proteomics Center, Department of Medicine, School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States of America
| | - Jolanda van der Velden
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
| | - Ger JM. Stienen
- Laboratory for Physiology, Institute for Cardiovascular Research, VU Medical Center, Amsterdam, The Netherlands
- Department of Physics and Astronomy, VU University, Amsterdam, The Netherlands
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Schulz EM, Wieczorek DF. Tropomyosin de-phosphorylation in the heart: What are the consequences? J Muscle Res Cell Motil 2013; 34:239-46. [DOI: 10.1007/s10974-013-9348-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2013] [Accepted: 05/24/2013] [Indexed: 11/30/2022]
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Lu QW, Wu XY, Morimoto S. Inherited cardiomyopathies caused by troponin mutations. JOURNAL OF GERIATRIC CARDIOLOGY : JGC 2013; 10:91-101. [PMID: 23610579 PMCID: PMC3627712 DOI: 10.3969/j.issn.1671-5411.2013.01.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 11/13/2012] [Accepted: 01/30/2013] [Indexed: 01/25/2023]
Abstract
Genetic investigations of cardiomyopathy in the recent two decades have revealed a large number of mutations in the genes encoding sarcomeric proteins as a cause of inherited hypertrophic cardiomyopathy (HCM), dilated cardiomyopathy (DCM), or restrictive cardiomyopathy (RCM). Most functional analyses of the effects of mutations on cardiac muscle contraction have revealed significant changes in the Ca(2+)-regulatory mechanism, in which cardiac troponin (cTn) plays important structural and functional roles as a key regulatory protein. Over a hundred mutations have been identified in all three subunits of cTn, i.e., cardiac troponins T, I, and C. Recent studies on cTn mutations have provided plenty of evidence that HCM- and RCM-linked mutations increase cardiac myofilament Ca(2+) sensitivity, while DCM-linked mutations decrease it. This review focuses on the functional consequences of mutations found in cTn in terms of cardiac myofilament Ca(2+) sensitivity, ATPase activity, force generation, and cardiac troponin I phosphorylation, to understand potential molecular and cellular pathogenic mechanisms of the three types of inherited cardiomyopathy.
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Affiliation(s)
- Qun-Wei Lu
- Key Laboratory of Molecular Biophysics of Ministry of Education, College of Life Science and Technology, Center for Human Genome Research, Huazhong University of Science and Technology, Wuhan 430074, China
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Myofilament incorporation and contractile function after gene transfer of cardiac troponin I Ser43/45Ala. Arch Biochem Biophys 2013; 535:49-55. [PMID: 23318976 DOI: 10.1016/j.abb.2012.12.021] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2012] [Revised: 12/21/2012] [Accepted: 12/23/2012] [Indexed: 11/23/2022]
Abstract
Phosphorylation of cardiac troponin I serines 43/45 (cTnISer43/45) by protein kinase C (PKC) is associated with cardiac dysfunction and yet there is disagreement about the role this cluster plays in modulating contractile performance. The present study evaluates the impact of phospho-null Ala substitutions at Ser43/45 (cTnISer43/45Ala) on contractile performance in intact myocytes. Viral-based gene transfer of cardiac troponin I (cTnI) or cTnISer43/45Ala resulted in time-dependent increases in expression, with 70-80% of endogenous cTnI replaced within 4days. Western analysis of intact and permeabilized myocytes along with immunohistochemistry showed each exogenous cTnI was incorporated into the sarcomere of myocytes. In contractile function studies, there were no differences in shortening and re-lengthening for cTnI and cTnISer43/45Ala-expressing myocytes 2days after gene transfer. However, more extensive replacement with cTnISer43/45Ala after 4days diminished peak shortening amplitude and accelerated re-lengthening measured as the time to 50% re-lengthening (TTR50%). A decrease in myofilament Ca(2+) sensitivity of tension also was observed in permeabilized myocytes expressing cTnISer43/45Ala and is consistent with accelerated re-lengthening observed in intact myocytes under basal conditions. Phosphorylation of cTnI Ser23/24 and the Ca(2+) transient were not changed in these myocytes. These results demonstrate extensive sarcomere expression of cTnISer43/45Ala directly modulates myofilament function under basal conditions. In further work, the accelerated re-lengthening observed in control or cTnI-expressing myocytes treated with the PKC agonist, endothelin-1 (ET, 10nM) was slowed in myocytes expressing cTnISer43/45Ala. This outcome may indicate Ser43/45 is targeted for phosphorylation by ET-activated PKC and/or influences transduction of this agonist-activated response.
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Kowlessur D, Tobacman LS. Significance of troponin dynamics for Ca2+-mediated regulation of contraction and inherited cardiomyopathy. J Biol Chem 2012; 287:42299-311. [PMID: 23066014 DOI: 10.1074/jbc.m112.423459] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ca(2+) dissociation from troponin causes cessation of muscle contraction by incompletely understood structural mechanisms. To investigate this process, regulatory site Ca(2+) binding in the NH(2)-lobe of subunit troponin C (TnC) was abolished by mutagenesis, and effects on cardiac troponin dynamics were mapped by hydrogen-deuterium exchange (HDX)-MS. The findings demonstrate the interrelationships among troponin's detailed dynamics, troponin's regulatory actions, and the pathogenesis of cardiomyopathy linked to troponin mutations. Ca(2+) slowed HDX up to 2 orders of magnitude within the NH(2)-lobe and the NH(2)-lobe-associated TnI switch helix, implying that Ca(2+) greatly stabilizes this troponin regulatory region. HDX of the TnI COOH terminus indicated that its known role in regulation involves a partially folded rather than unfolded structure in the absence of Ca(2+) and actin. Ca(2+)-triggered stabilization extended beyond the known direct regulatory regions: to the start of the nearby TnI helix 1 and to the COOH terminus of the TnT-TnI coiled-coil. Ca(2+) destabilized rather than stabilized specific TnI segments within the coiled-coil and destabilized a region not previously implicated in Ca(2+)-mediated regulation: the coiled-coil's NH(2)-terminal base plus the preceding TnI loop with which the base interacts. Cardiomyopathy-linked mutations clustered almost entirely within influentially dynamic regions of troponin, and many sites were Ca(2+)-sensitive. Overall, the findings demonstrate highly selective effects of regulatory site Ca(2+), including opposite changes in protein dynamics at opposite ends of the troponin core domain. Ca(2+) release triggers an intramolecular switching mechanism that propagates extensively within the extended troponin structure, suggests specific movements of the TnI inhibitory regions, and prominently involves troponin's dynamic features.
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Affiliation(s)
- Devanand Kowlessur
- Department of Medicine, University of Illinois, Chicago, Illinois 60612, USA
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14
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Jin W, Brown AT, Murphy AM. Cardiac myofilaments: from proteome to pathophysiology. Proteomics Clin Appl 2012; 2:800-10. [PMID: 21136880 DOI: 10.1002/prca.200780075] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
This review addresses the functional consequences of altered post-translational modifications of cardiac myofilament proteins in cardiac diseases such as heart failure and ischemia. The modifications of thick and thin filament proteins as well as titin are addressed. Understanding the functional consequences of altered protein modifications is an essential step in the development of targeted therapies for common cardiac diseases.
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Affiliation(s)
- Wenhai Jin
- Departments of Pediatrics, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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15
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Alderman SL, Klaiman JM, Deck CA, Gillis TE. Effect of cold acclimation on troponin I isoform expression in striated muscle of rainbow trout. Am J Physiol Regul Integr Comp Physiol 2012; 303:R168-76. [DOI: 10.1152/ajpregu.00127.2012] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In vertebrates each of the three striated muscle types (fast skeletal, slow skeletal, and cardiac) contain distinct isoforms of a number of different contractile proteins including troponin I (TnI). The functional characteristics of these proteins have a significant influence on muscle function and contractility. The purpose of this study was to characterize which TnI gene and protein isoforms are expressed in the different muscle types of rainbow trout ( Oncorhynchus mykiss) and to determine whether isoform expression changes in response to cold acclimation (4°C). Semiquantitative real-time PCR was used to characterize the expression of seven different TnI genes. The sequence of these genes, cloned from Atlantic salmon ( Salmo salar) and rainbow trout, were obtained from the National Center for Biotechnology Information databases. One-dimensional gel electrophoresis and tandem mass spectrometry were used to identify the TnI protein isoforms expressed in each muscle type. Interestingly, the results indicate that each muscle type expresses the gene transcripts of up to seven TnI isoforms. There are significant differences, however, in the expression pattern of these genes between muscle types. In addition, cold acclimation was found to increase the expression of specific gene transcripts in each muscle type. The proteomics analysis demonstrates that fast skeletal and cardiac muscle contain three TnI isoforms, whereas slow skeletal muscle contains four. No other vertebrate muscle to date has been found to express as many TnI protein isoforms. Overall this study underscores the complex molecular composition of teleost striated muscle and suggests there is an adaptive value to the unique TnI profiles of each muscle type.
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Affiliation(s)
- Sarah L. Alderman
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Jordan M. Klaiman
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Courtney A. Deck
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Todd E. Gillis
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
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16
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Hwang H, Robinson DA, Stevenson TK, Wu HC, Kampert SE, Pagani FD, Dyke DB, Martin JL, Sadayappan S, Day SM, Westfall MV. PKCβII modulation of myocyte contractile performance. J Mol Cell Cardiol 2012; 53:176-86. [PMID: 22587992 DOI: 10.1016/j.yjmcc.2012.05.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2011] [Revised: 05/03/2012] [Accepted: 05/04/2012] [Indexed: 12/26/2022]
Abstract
Significant up-regulation of the protein kinase Cβ(II) (PKCβ(II)) develops during heart failure and yet divergent functional outcomes are reported in animal models. The goal here is to investigate PKCβ(II) modulation of contractile function and gain insights into downstream targets in adult cardiac myocytes. Increased PKCβ(II) protein expression and phosphorylation developed after gene transfer into adult myocytes while expression remained undetectable in controls. The PKCβ(II) was distributed in a peri-nuclear pattern and this expression resulted in diminished rates and amplitude of shortening and re-lengthening compared to controls and myocytes expressing dominant negative PKCβ(II) (PKCβDN). Similar decreases were observed in the Ca(2+) transient and the Ca(2+) decay rate slowed in response to caffeine in PKCβ(II)-expressing myocytes. Parallel phosphorylation studies indicated PKCβ(II) targets phosphatase activity to reduce phospholamban (PLB) phosphorylation at residue Thr17 (pThr17-PLB). The PKCβ inhibitor, LY379196 (LY) restored pThr17-PLB to control levels. In contrast, myofilament protein phosphorylation was enhanced by PKCβ(II) expression, and individually, LY and the phosphatase inhibitor, calyculin A each failed to block this response. Further work showed PKCβ(II) increased Ca(2+)-activated, calmodulin-dependent kinase IIδ (CaMKIIδ) expression and enhanced both CaMKIIδ and protein kinase D (PKD) phosphorylation. Phosphorylation of both signaling targets also was resistant to acute inhibition by LY. These later results provide evidence PKCβ(II) modulates contractile function via intermediate downstream pathway(s) in cardiac myocytes.
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Affiliation(s)
- Hyosook Hwang
- Dept. of Surgery, Cardiac Surgery Section, University of Michigan, Ann Arbor, MI 48109, USA
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17
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Dong X, Sumandea CA, Chen YC, Garcia-Cazarin ML, Zhang J, Balke CW, Sumandea MP, Ge Y. Augmented phosphorylation of cardiac troponin I in hypertensive heart failure. J Biol Chem 2011; 287:848-57. [PMID: 22052912 DOI: 10.1074/jbc.m111.293258] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
An altered cardiac myofilament response to activating Ca(2+) is a hallmark of human heart failure. Phosphorylation of cardiac troponin I (cTnI) is critical in modulating contractility and Ca(2+) sensitivity of cardiac muscle. cTnI can be phosphorylated by protein kinase A (PKA) at Ser(22/23) and protein kinase C (PKC) at Ser(22/23), Ser(42/44), and Thr(143). Whereas the functional significance of Ser(22/23) phosphorylation is well understood, the role of other cTnI phosphorylation sites in the regulation of cardiac contractility remains a topic of intense debate, in part, due to the lack of evidence of in vivo phosphorylation. In this study, we utilized top-down high resolution mass spectrometry (MS) combined with immunoaffinity chromatography to determine quantitatively the cTnI phosphorylation changes in spontaneously hypertensive rat (SHR) model of hypertensive heart disease and failure. Our data indicate that cTnI is hyperphosphorylated in the failing SHR myocardium compared with age-matched normotensive Wistar-Kyoto rats. The top-down electron capture dissociation MS unambiguously localized augmented phosphorylation sites to Ser(22/23) and Ser(42/44) in SHR. Enhanced Ser(22/23) phosphorylation was verified by immunoblotting with phospho-specific antibodies. Immunoblot analysis also revealed up-regulation of PKC-α and -δ, decreased PKCε, but no changes in PKA or PKC-β levels in the SHR myocardium. This provides direct evidence of in vivo phosphorylation of cTnI-Ser(42/44) (PKC-specific) sites in an animal model of hypertensive heart failure, supporting the hypothesis that PKC phosphorylation of cTnI may be maladaptive and potentially associated with cardiac dysfunction.
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Affiliation(s)
- Xintong Dong
- Human Proteomics Program, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA
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18
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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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19
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Avner BS, Hinken AC, Yuan C, Solaro RJ. H2O2 alters rat cardiac sarcomere function and protein phosphorylation through redox signaling. Am J Physiol Heart Circ Physiol 2010; 299:H723-30. [PMID: 20562337 DOI: 10.1152/ajpheart.00050.2010] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ROS, such as H(2)O(2), are a component of pathological conditions in many organ systems and have been reported to be elevated in cardiac pathophysiology. The experiments presented here test the hypothesis that H(2)O(2) induces alterations in cardiac myofilament function by the posttranslational modification of sarcomeric proteins indirectly through PKC signaling. In vitro assessment of actomyosin Mg(2+)-ATPase activity of myofibrillar fractions showed blunted relative ATP consumption in the relaxed state (pCa 8.0) in response to treatment with 0.5 mM H(2)O(2) before myofilament isolation. The effect was attributable to downstream "redox signaling," inasmuch as the direct application of H(2)O(2) to isolated myofibrils did not alter Mg(2+)-ATPase activity. Ca(2+)-ATPase activity, which was used as a measure of myofibrillar myosin function, was unaffected by H(2)O(2). Functional experiments using rat cardiac trabeculae treated with 0.5 or 5 mM H(2)O(2) followed by detergent extraction of membranes demonstrated increased Ca(2+) sensitivity of force production, a faster rate of force redevelopment, and (for 5 mM) decreased maximum tension. Biochemical analysis of myocardial samples treated with 0.5 mM H(2)O(2) demonstrated increased phosphorylation of two sarcomeric proteins: cardiac troponin I and myosin-binding protein-C. These changes were eliminated by a general PKC inhibitor. However, H(2)O(2) and the general PKC activator PMA induced different phosphorylation patterns in cardiomyocytes in which PKC-delta was elevated by viral infection. These data provide evidence that PKC-dependent redox signaling affects the function of cardiac myofilaments and indicate modification of specific proteins through this signaling mechanism.
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Affiliation(s)
- Benjamin S Avner
- Department of Physiology and Biophysics and Center for Cardiovascular Research, College of Medicine, University of Illinois, Chicago, Illinois 60612-7342, USA
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20
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Kirk JA, MacGowan GA, Evans C, Smith SH, Warren CM, Mamidi R, Chandra M, Stewart AFR, Solaro RJ, Shroff SG. Left ventricular and myocardial function in mice expressing constitutively pseudophosphorylated cardiac troponin I. Circ Res 2009; 105:1232-9. [PMID: 19850940 DOI: 10.1161/circresaha.109.205427] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Protein kinase (PK)C-induced phosphorylation of cardiac troponin (cTn)I has been shown to regulate cardiac contraction. OBJECTIVE Characterize functional effects of increased PKC-induced cTnI phosphorylation and identify underlying mechanisms using a transgenic mouse model (cTnI(PKC-P)) expressing mutant cTnI (S43E, S45E, T144E). METHODS AND RESULTS Two-dimensional gel analysis showed 7.2+/-0.5% replacement of endogenous cTnI with the mutant form. Experiments included: mechanical measurements (perfused isolated hearts, isolated papillary muscles, and skinned fiber preparations), biochemical and molecular biological measurements, and a mathematical model-based analysis for integrative interpretation. Compared to wild-type mice, cTnI(PKC-P) mice exhibited negative inotropy in isolated hearts (14% decrease in peak developed pressure), papillary muscles (53% decrease in maximum developed force), and skinned fibers (14% decrease in maximally activated force, F(max)). Additionally, cTnI(PKC-P) mice exhibited slowed relaxation in both isolated hearts and intact papillary muscles. The cTnI(PKC-P) mice showed no differences in calcium sensitivity, cooperativity, steady-state force-MgATPase relationship, calcium transient (amplitude and relaxation), or baseline phosphorylation of other myofilamental proteins. The model-based analysis revealed that experimental observations in cTnI(PKC-P) mice could be reproduced by 2 simultaneous perturbations: a decrease in the rate of cross-bridge formation and an increase in calcium-independent persistence of the myofilament active state. CONCLUSIONS A modest increase in PKC-induced cTnI phosphorylation ( approximately 7%) can significantly alter cardiac muscle contraction: negative inotropy via decreased cross-bridge formation and negative lusitropy via persistence of myofilament active state. Based on our data and data from the literature we speculate that effects of PKC-mediated cTnI phosphorylation are site-specific (S43/S45 versus T144).
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Affiliation(s)
- Jonathan A Kirk
- Cardiovascular Systems Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219, USA
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21
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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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22
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Ayaz-Guner S, Zhang J, Li L, Walker JW, Ge Y. In vivo phosphorylation site mapping in mouse cardiac troponin I by high resolution top-down electron capture dissociation mass spectrometry: Ser22/23 are the only sites basally phosphorylated. Biochemistry 2009; 48:8161-70. [PMID: 19637843 DOI: 10.1021/bi900739f] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cardiac troponin I (cTnI) is the inhibitory subunit of cardiac troponin, a key myofilament regulatory protein complex located on the thin filaments of the contractile apparatus. cTnI is uniquely specific for the heart and is widely used in clinics as a serum biomarker for cardiac injury. Phosphorylation of cTnI plays a critical role in modulating cardiac function. cTnI is known to be regulated by protein kinase A and protein kinase C at five sites, Ser22/Ser23, Ser42/44, and Thr143, primarily based on results from in vitro phosphorylation assays by the specific kinase(s). However, a comprehensive characterization of phosphorylation of mouse cTnI occurring in vivo has been lacking. Herein, we have employed top-down mass spectrometry (MS) methodology with electron capture dissociation for precise mapping of in vivo phosphorylation sites of cTnI affinity purified from wild-type and transgenic mouse hearts. As demonstrated, top-down MS (analysis of intact proteins) is an extremely valuable technology for global characterization of labile phosphorylation occurring in vivo without a priori knowledge. Our top-down MS data unambiguously identified Ser22/23 as the only two sites basally phosphorylated in wild-type mouse cTnI with full sequence coverage, which was confirmed by the lack of phosphorylation in cTnI-Ala(2) transgenic mice where Ser22/23 in cTnI have been rendered nonphosphorylatable by mutation to alanine.
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Affiliation(s)
- Serife Ayaz-Guner
- Human Proteomics Program and Department of Physiology, School of Medicine and Public Health, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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23
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Shaw EE, Wood P, Kulpa J, Yang FH, Summerlee AJ, Pyle WG. Relaxin alters cardiac myofilament function through a PKC-dependent pathway. Am J Physiol Heart Circ Physiol 2009; 297:H29-36. [DOI: 10.1152/ajpheart.00482.2008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The pregnancy hormone relaxin (RLX) is a powerful cardiostimulatory peptide. Despite its well-characterized effects on the heart, the intracellular mechanisms responsible for RLX's positive inotropic effects are unknown. Cardiac myofilaments are the central contractile elements of the heart, and changes in the phosphorylation status of myofilament proteins are known to mediate changes in function. The first objective of this study was to determine whether RLX stimulates myofilament activation and alters the phosphorylation of one or more myofilament proteins. RLX works through a variety of intracellular signaling cascades in different tissue types. Protein kinases A (PKA) and C (PKC) are two common molecules implicated in RLX signaling and are known to affect myofilament function. Thus the second objective of this study was to determine whether RLX mediates its myocardial effects through PKA or PKC activation. Murine myocardium was treated with recombinant H2-RLX, and cardiac myofilaments were isolated. RLX increased cardiac myofilament force development at physiological levels of intracellular Ca2+ without altering myofilament ATP consumption. Myosin binding protein C, troponin T, and troponin I phosphorylation levels were increased with RLX treatment. Immunoblot analysis revealed an increase in myofilament-associated PKC-δ, decreases in PKC-α and -βII, but no effect on PKC-ε. Inhibition of PKC with chelerythrine chloride or PKC-δ with rottlerin prevented the RLX-dependent changes in myofilament function and protein phosphorylation. PKA antagonism with H-89 had no effect on the myofilament effects of RLX. This study is the first to show that RLX-dependent changes in myofilament-associated PKC alters myofilament activation in a manner consistent with its cardiostimulatory effects.
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24
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Christopher B, Pizarro GO, Nicholson B, Yuen S, Hoit BD, Ogut O. Reduced force production during low blood flow to the heart correlates with altered troponin I phosphorylation. J Muscle Res Cell Motil 2009; 30:111-23. [PMID: 19507043 DOI: 10.1007/s10974-009-9180-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2009] [Accepted: 04/09/2009] [Indexed: 01/08/2023]
Abstract
A rat model of low myocardial blood flow was established to test the hypothesis that post-translational changes to proteins of the thin and thick muscle filaments correlate with decreased cardiac contractility. Following 3 days of low blood flow by constriction of the left anterior descending artery, rat hearts demonstrated a reduction in fractional shortening at rest and a relative decline in fractional shortening when challenged with high dose versus low dose dobutamine, reflecting reduced energy reserves. Permeabilized fibers from low blood flow hearts demonstrated a decline in maximum force per cross-section and Ca2+ sensitivity as compared to their sham operated counterparts. An examination of sarcomeric proteins by twodimensional gel electrophoresis, mass spectrometry, and phospho-specific antibodies provided evidence for Ser23/24 and Ser43/45 phosphorylation of troponin I (TnI). Total TnI phosphorylation was not different between the groups, but Ser23/24 phosphorylation declined with low blood flow, implying an accompanying increase in phosphorylation at other sites of TnI. Affinity chromatography demonstrated that TnI from low blood flow myocardium had reduced relative affinity to Ca2+ bound troponin C compared to TnI from sham operated hearts, providing a mechanism for reduced Ca2+ sensitivity of force production in low blood flow fibers. These findings suggest that altered TnI function, due to changes in the distribution of phosphorylated sites, is an early contributor to reduced contractility of the heart.
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Affiliation(s)
- Bridgette Christopher
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH, 44106, USA
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25
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Adenosine triggers the nuclear translocation of protein kinase C epsilon in H9c2 cardiomyoblasts with the loss of phosphorylation at Ser729. J Cell Biochem 2009; 106:633-42. [DOI: 10.1002/jcb.22043] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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26
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Lai ZF, Chen YZ, Feng LP, Meng XM, Ding JF, Wang LY, Ye J, Li P, Cheng XS, Kitamoto Y, Monzen K, Komuro I, Sakaguchi N, Kim-Mitsuyama S. Overexpression of TNNI3K, a cardiac-specific MAP kinase, promotes P19CL6-derived cardiac myogenesis and prevents myocardial infarction-induced injury. Am J Physiol Heart Circ Physiol 2008; 295:H708-16. [PMID: 18552163 DOI: 10.1152/ajpheart.00252.2008] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
TNNI3K is a new cardiac-specific MAP kinase whose gene is localized to 1p31.1 and that belongs to a tyrosine kinase-like branch in the kinase tree of the human genome. In the present study we investigated the role of TNNI3K in the cardiac myogenesis process and in the repair of ischemic injury. Pluripotent P19CL6 cells with or without transfection by pcDNA6-TNNI3K plasmid were used to induce differentiation into beating cardiomyocytes. TNNI3K promoted the differentiation process, judging from the increasing beating mass and increased number of alpha-actinin-positive cells. TNNI3K improved cardiac function by enhancing beating frequency and increasing the contractile force and epinephrine response of spontaneous action potentials without an increase of the single-cell size. TNNI3K suppressed phosphorylation of cardiac troponin I, annexin-V(+) cells, Bax protein, and p38/JNK-mediated apoptosis. Intramyocardial administration of TNNI3K-overexpressing P19CL6 cells in mice with myocardial infarction improved cardiac performance and attenuated ventricular remodeling compared with injection of wild-type P19CL6 cells. In conclusion, our study clearly indicates that TNNI3K promotes cardiomyogenesis, enhances cardiac performance, and protects the myocardium from ischemic injury by suppressing p38/JNK-mediated apoptosis. Therefore, modulation of TNNI3K activity would be a useful therapeutic approach for ischemic cardiac disease.
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Affiliation(s)
- Zhong-Fang Lai
- Dept. of Pharmacology and Molecular Therapeutics, Graduate School of Medical Sciences, Kumamoto Univ., Kumamoto 860-8556, Japan.
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27
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Kobayashi T, Jin L, de Tombe PP. Cardiac thin filament regulation. Pflugers Arch 2008; 457:37-46. [PMID: 18421471 DOI: 10.1007/s00424-008-0511-8] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 03/19/2008] [Accepted: 03/25/2008] [Indexed: 12/17/2022]
Abstract
Myocardial contraction is initiated upon the release of calcium into the cytosol from the sarcoplasmic reticulum following membrane depolarization. The fundamental physiological role of the heart is to pump an amount blood that is determined by the prevailing requirements of the body. The physiological control systems employed to accomplish this task include regulation of heart rate, the amount of calcium release, and the response of the cardiac myofilaments to activator calcium ions. Thin filament activation and relaxation dynamics has emerged as a pivotal regulatory system tuning myofilament function to the beat-to-beat regulation of cardiac output. Maladaptation of thin filament dynamics, in addition to dysfunctional calcium cycling, is now recognized as an important cellular mechanism causing reduced cardiac pump function in a variety of cardiac diseases. Here, we review current knowledge regarding protein-protein interactions involved in the dynamics of thin filament activation and relaxation and the regulation of these processes by protein kinase-mediated phosphorylation.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology & Biophysics, University of Illinois at Chicago, Chicago, IL 60612, USA
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28
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Solaro RJ, Rosevear P, Kobayashi T. The unique functions of cardiac troponin I in the control of cardiac muscle contraction and relaxation. Biochem Biophys Res Commun 2007; 369:82-7. [PMID: 18162178 DOI: 10.1016/j.bbrc.2007.12.114] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2007] [Accepted: 12/11/2007] [Indexed: 01/02/2023]
Abstract
We review development of evidence and current perceptions of the multiple and significant functions of cardiac troponin I in regulation and modulation of cardiac function. Our emphasis is on the unique structure function relations of the cardiac isoform of troponin I, especially regions containing sites of phosphorylation. The data indicate that modifications of specific regions cardiac troponin I by phosphorylations either promote or reduce cardiac contractility. Thus, a homeostatic balance in these phosphorylations is an important aspect of control of cardiac function. A new concept is the idea that the homeostatic mechanisms may involve modifications of intra-molecular interactions in cardiac troponin I.
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics (M/C901) and Center for Cardiovascular Research, 835 South Wolcott Avenue, University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA
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29
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Mathur MC, Kobayashi T, Chalovich JM. Negative charges at protein kinase C sites of troponin I stabilize the inactive state of actin. Biophys J 2007; 94:542-9. [PMID: 17872964 PMCID: PMC2157249 DOI: 10.1529/biophysj.107.113944] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Alterations in the troponin complex can lead to increases or decreases in contractile activity. Most mutations of troponin that cause hypertrophic cardiomyopathy increase the activity of cardiac muscle fibers. In at least some cases these mutants stabilize the active state of regulated actin. In contrast, phosphorylation of troponin I at residues 43, 45, and 144 inhibits muscle contractility. To determine if alterations of troponin I that reduce activity do stabilize the inactive state of actin, we introduced negative charges at residues 43, 45, and 144 of troponin I to mimic a constitutively phosphorylated state. At saturating calcium, all mutants decreased ATPase rates relative to wild-type actin-tropomyosin-troponin. Reduced activation of ATPase activity was seen with a single mutation at S45E and was not further altered by mutating the other two sites. In the presence of low concentrations of NEM-S1, wild-type troponin was more active than the mutants. At high NEM-S1, the rates of wild-type and mutants approached the same limiting value. Changes in Ca(2+) affinity also support the idea that the equilibrium between states of actin-tropomyosin-troponin was shifted to the inactive state by mutations that mimic troponin I phosphorylation.
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Affiliation(s)
- Mohit C Mathur
- Department of Biochemistry and Molecular Biology, Brody School of Medicine at East Carolina University, Greenville, North Carolina, USA
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30
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Belin RJ, Sumandea MP, Allen EJ, Schoenfelt K, Wang H, Solaro RJ, de Tombe PP. Augmented Protein Kinase C-α–Induced Myofilament Protein Phosphorylation Contributes to Myofilament Dysfunction in Experimental Congestive Heart Failure. Circ Res 2007; 101:195-204. [PMID: 17556659 DOI: 10.1161/circresaha.107.148288] [Citation(s) in RCA: 128] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
It is becoming clear that upregulated protein kinase C (PKC) signaling plays a role in reduced ventricular myofilament contractility observed in congestive heart failure. However, data are scant regarding which PKC isozymes are involved. There is evidence that PKC-alpha may be of particular importance. Here, we examined PKC-alpha quantity, activity, and signaling to myofilaments in chronically remodeled myocytes obtained from rats in either early heart failure or end-stage congestive heart failure. Immunoblotting revealed that PKC-alpha expression and activation was unaltered in early heart failure but increased in end-stage congestive heart failure. Left ventricular myocytes were isolated by mechanical homogenization, Triton-skinned, and attached to micropipettes that projected from a force transducer and motor. Myofilament function was characterized by an active force-[Ca(2+)] relation to obtain Ca(2+)-saturated maximal force (F(max)) and myofilament Ca(2+) sensitivity (indexed by EC(50)) before and after incubation with PKC-alpha, protein phosphatase type 1 (PP1), or PP2a. PKC-alpha treatment induced a 30% decline in F(max) and 55% increase in the EC(50) in control cells but had no impact on myofilament function in failing cells. PP1-mediated dephosphorylation increased F(max) (15%) and decreased EC(50) ( approximately 20%) in failing myofilaments but had no effect in control cells. PP2a-dependent dephosphorylation had no effect on myofilament function in either group. Lastly, PP1 dephosphorylation restored myofilament function in control cells hyperphosphorylated with PKC-alpha. Collectively, our results suggest that in end-stage congestive heart failure, the myofilament proteins exist in a hyperphosphorylated state attributable, in part, to increased activity and signaling of PKC-alpha.
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Affiliation(s)
- Rashad J Belin
- Department of Physiology and Biophysics, Center for Cardiovascular Research, University of Illinois at Chicago, Chicago, IL 60612, USA
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31
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Chen-Izu Y, Ward CW, Stark W, Banyasz T, Sumandea MP, Balke CW, Izu LT, Wehrens XHT. Phosphorylation of RyR2 and shortening of RyR2 cluster spacing in spontaneously hypertensive rat with heart failure. Am J Physiol Heart Circ Physiol 2007; 293:H2409-17. [PMID: 17630346 DOI: 10.1152/ajpheart.00562.2007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
As a critical step toward understanding the role of abnormal intracellular Ca(2+) release via the ryanodine receptor (RyR(2)) during the development of hypertension-induced cardiac hypertrophy and heart failure, this study examines two questions: 1) At what stage, if ever, in the development of hypertrophy and heart failure is RyR(2) hyperphosphorylated at Ser(2808)? 2) Does the spatial distribution of RyR(2) clusters change in failing hearts? Using a newly developed semiquantitative immunohistochemistry method and Western blotting, we measured phosphorylation of RyR(2) at Ser(2808) in the spontaneously hypertensive rat (SHR) at four distinct disease stages. A major finding is that hyperphosphorylation of RyR(2) at Ser(2808) occurred only at late-stage heart failure in SHR, but not in age-matched controls. Furthermore, the spacing between RyR(2) clusters was shortened in failing hearts, as predicted by quantitative model simulation to increase spontaneous Ca(2+) wave generation and arrhythmias.
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Affiliation(s)
- Ye Chen-Izu
- Dept. of Internal Medicine, Univ. of Kentucky College of Medicine, 741 S. Limestone St., BBSRB, Rm. B255, Lexington, KY 40536-0509, USA.
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32
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Abstract
Transgenic and knockout mice can be used to study the genes and basic mechanisms involved in heart disease, and have therefore assumed a central role in modern cardiac research. MRI and MRS techniques have recently been developed for mice that enable the quantitative or semi-quantitative in vivo assessment of cardiac anatomy, function, perfusion, infarction, Ca(2+) influx, and metabolism. With these techniques, the normal mouse heart has been shown to be well suited as a model of human cardiac disease. The roles of individual genes in normal cardiac physiology have recently been studied by MR, including the role of neuronal nitric oxide synthase in beta-adrenergic stimulation, the roles of the inducible nitric oxide synthase and myoglobin in function, dilation, and energetics, and the role of cardiac troponin I in contractility. Furthermore, with a mouse model of myocardial infarction, the roles of the angiotensin II type 2 receptor, xanthine oxidase inhibitors, blood coagulation factor XIII, and inducible nitric oxide synthase in post-infarct function and remodeling have been further elucidated. Non-invasive in vivo MRI and MRS in mice provide a unique and powerful means for phenotyping genetically engineered mice and can improve our understanding of the roles of specific genes and proteins in cardiac physiology and pathophysiology.
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Affiliation(s)
- Frederick H Epstein
- Departments of Radiology and Biomedical Engineering, and the Cardiovascular Research Center, University of Virginia, Charlottesville, VA 22908, USA.
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33
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Bilchick KC, Duncan JG, Ravi R, Takimoto E, Champion HC, Gao WD, Stull LB, Kass DA, Murphy AM. Heart failure-associated alterations in troponin I phosphorylation impair ventricular relaxation-afterload and force-frequency responses and systolic function. Am J Physiol Heart Circ Physiol 2007; 292:H318-25. [PMID: 16936010 DOI: 10.1152/ajpheart.00283.2006] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent studies have found that selective stimulation of troponin (Tn)I protein kinase A (PKA) phosphorylation enhances heart rate-dependent inotropy and blunts relaxation delay coupled to increased afterload. However, in failing hearts, TnI phosphorylation by PKA declines while protein kinase C (PKC) activity is enhanced, potentially augmenting TnI PKC phosphorylation. Accordingly, we hypothesized that these site-specific changes deleteriously affect both rate-responsive cardiac function and afterload dependence of relaxation, both prominent phenotypic features of the failing heart. A transgenic (TG) mouse model was generated in which PKA-TnI sites were mutated to mimic partial dephosphorylation (Ser22 to Ala; Ser23 to Asp) and dominant PKC sites were mutated to mimic constitutive phosphorylation (Ser42 and Ser44 to Asp). The two highest-expressing lines were further characterized. TG mice had reduced fractional shortening of 34.7 ± 1.4% vs. 41.3 ± 2.0% ( P = 0.018) and slight chamber dilation on echocardiography. In vivo cardiac pressure-volume studies revealed near doubling of isovolumic relaxation prolongation with increasing afterload in TG animals ( P < 0.001), and this remained elevated despite isoproterenol infusion (PKA stimulation). Increasing heart rate from 400 to 700 beats/min elevated contractility 13% in TG hearts, nearly half the response observed in nontransgenic animals ( P = 0.005). This blunted frequency response was normalized by isoproterenol infusion. Abnormal TnI phosphorylation observed in cardiac failure may explain exacerbated relaxation delay in response to increased afterload and contribute to blunted chronotropic reserve.
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Affiliation(s)
- Kenneth C Bilchick
- Dept. of Pediatrics, Johns Hopkins Univ. School of Medicine, 720 Rutland Ave., Ross Bldg. 1144, Baltimore, MD 21205, USA
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34
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Hirano S, Kusakari Y, O-Uchi J, Morimoto S, Kawai M, Hongo K, Kurihara S. Intracellular mechanism of the negative inotropic effect induced by alpha1-adrenoceptor stimulation in mouse myocardium. J Physiol Sci 2006; 56:297-304. [PMID: 16884559 DOI: 10.2170/physiolsci.rp007306] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2006] [Accepted: 08/02/2006] [Indexed: 11/05/2022]
Abstract
Alpha(1)-adrenoceptor stimulation (alpha(1)ARS) shows a positive inotropic effect in most mammalian myocardium. In mouse myocardium, however, alpha(1)ARS showed the negative inotropic effect, of which intracellular mechanisms are not fully clarified. The purpose of this study is to investigate the intracellular mechanism of the negative inotropic effect by alpha(1)ARS in C57BL/6 mouse myocardium. We used isolated ventricular papillary muscles of C57BL/6 strain mouse which is widely used for genetic manipulation. We simultaneously measured isometric tension and intracellular Ca(2+) concentration ([Ca(2+)](i)) using the aequorin method. In twitch contraction, phenylephrine concentration-dependently (1-100 microM) decreased tension without significant changes in the Ca(2+) transient, and these effects were completely blocked by prazosin (3 microM) or calphostin C (a PKC inhibitor, 1 microM). Phorbol 12-myristate 13-acetate (PMA) (a PKC activator, 1 microM) decreased tension as observed in phenylephrine. After PMA application, the negative inotropic effect of phenylephrine disappeared. To estimate the Ca(2+) sensitivity, tetanic contraction was produced, and the relation between [Ca(2+)](i) and tension at a steady state was measured. Phenylephrine (10 microM) decreased the Ca(2+) sensitivity, and PMA showed a similar Ca(2+) desensitizing effect. These results suggest that the negative inotropic effect of phenylephrine in mouse myocardium can be explained by the decrease in the Ca(2+) sensitivity through the activation of PKC. The present result indicates that the effect of alpha(1)ARS differs among species and strains of experiment animals. Thus, we should be careful about using the results of mouse myocardium to understand the functions of the human heart.
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Affiliation(s)
- Shuta Hirano
- Department of Physiology II, The Jikei University School of Medicine, Minato-ku, Tokyo, 105-8461, Japan
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35
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Murphy AM. Heart failure, myocardial stunning, and troponin: a key regulator of the cardiac myofilament. ACTA ACUST UNITED AC 2006; 12:32-8; quiz 39-40. [PMID: 16470090 DOI: 10.1111/j.1527-5299.2006.04320.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
This review discusses post-translational modifications of myofilament regulatory proteins, particularly troponin, associated with heart failure and myocardial stunning--two common disease processes. Altered phosphorylation, partial proteolysis and, possibly, oxidative damage to myofilament proteins may result in abnormalities in both systolic and diastolic function. At a molecular level, these changes may lead to abnormalities in crossbridge cycling and tension development and result in inefficiencies in utilization of energy. Understanding these alterations may lead to new targeted therapies.
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Affiliation(s)
- Anne M Murphy
- Cardiology Division, Department of Pediatrics, Johns Hopkins University School of Medicine, Ross Building 1144, 720 Rutland Avenue, Baltimore, MD 21205, USA.
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36
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MacGowan GA. The myofilament force-calcium relationship as a target for positive inotropic therapy in congestive heart failure. Cardiovasc Drugs Ther 2006; 19:203-10. [PMID: 16142598 DOI: 10.1007/s10557-005-2465-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
To-date positive inotropic therapy in the treatment of congestive heart failure has resulted in adverse effects on long term survival. These agents increase calcium cycling through beta-adrenergic stimulation or phosphodiesterase inhibition. An alternative method of producing positive inotropy is to increase the myofilament sensitivity to calcium. This can occur at several levels within the myofilament, and has potential benefits with respect to avoiding increased calcium cycling and producing a more favourable energy efficient positive inotropy. A potential adverse effect of increasing calcium sensitivity is slowed relaxation and diastolic dysfunction. We have learnt a considerable amount about the function of specific sites within the myofilament by the use of genetically engineered mouse models, which have shown diverse effects of various myofilament sites on global left ventricular function. Levosimendan is a novel inotropic agent that has several mechanisms of action including calcium sensitization, and is undergoing clinical trials at present. This review article will provide a comprehensive molecular, biophysical and physiological insight into the concepts underlying the myofilament force-calcium relationship and its potential as a target for positive inotropic therapy in heart failure.
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Affiliation(s)
- Guy A MacGowan
- Dept of Cardiology, Freeman Hospital and University of Newcastle upon Tyne, Newcastle upon Tyne NE7 7DN, United Kingdom.
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37
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Montgomery DE, Rundell VLM, Goldspink PH, Urboniene D, Geenen DL, de Tombe PP, Buttrick PM. Protein kinase C epsilon induces systolic cardiac failure marked by exhausted inotropic reserve and intact Frank-Starling mechanism. Am J Physiol Heart Circ Physiol 2005; 289:H1881-8. [PMID: 15951344 DOI: 10.1152/ajpheart.00454.2005] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Myofilament dysfunction is a common point of convergence for many forms of heart failure. Recently, we showed that cardiac overexpression of PKC epsilon initially depresses myofilament activity and then leads to a progression of changes characteristic of human heart failure. Here, we examined the effects of PKC epsilon on contractile reserve, Starling mechanism, and myofilament activation in this model of end-stage dilated cardiomyopathy. Pressure-volume loop analysis and echocardiography showed that the PKC epsilon mice have markedly compromised systolic function and increased end-diastolic volumes. Dobutamine challenge resulted in a small increase in contractility in PKC epsilon mice but failed to enhance cardiac output. The PKC epsilon mice showed a normal length-dependent tension development in skinned cardiac muscle preparations, although Frank-Starling mechanism appeared to be compromised in the intact animal. Simultaneous measurement of tension and ATPase demonstrated that the maximum tension and ATPase were markedly lower in the PKC epsilon mice at any length or Ca2+ concentration. However, the tension cost was also lower indicating less energy expenditure. We conclude 1) that prolonged overexpression of PKC epsilon ultimately leads to a dilated cardiomyopathy marked by exhausted contractile reserve, 2) that PKC epsilon does not compromise the Frank-Starling mechanism at the myofilament level, and 3) that the Starling curve excursion is limited by the inotropic state of the heart. These results reflect the significance of the primary myofilament contractilopathy induced by phosphorylation and imply a role for PKC epsilon-mediated phosphorylation in myofilament physiology and the pathophysiology of decompensated cardiac failure.
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Affiliation(s)
- David E Montgomery
- Department of Medicine, Section of Cardiology, Univ. of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA
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38
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Abstract
Although well known as the location of the mechanism by which the cardiac sarcomere is activated by Ca2+ to generate force and shortening, the thin filament is now also recognized as a vital component determining the dynamics of contraction and relaxation. Molecular signaling in the thin filament involves steric, allosteric, and cooperative mechanisms that are modified by protein phosphorylation, sarcomere length and load, the chemical environment, and isoform composition. Approaches employing transgenesis and mutagenesis now permit investigation of these processes at the level of the systems biology of the heart. These studies reveal that the thin filaments are not merely slaves to the levels of Ca2+ determined by membrane channels, transporters and exchangers, but are actively involved in beat to beat control of cardiac function by neural and hormonal factors and by the Frank-Starling mechanism.
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Affiliation(s)
- Tomoyoshi Kobayashi
- Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
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39
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MacGowan GA, Rager J, Shroff SG, Mathier MA. In vivo alpha-adrenergic responses and troponin I phosphorylation: anesthesia interactions. J Appl Physiol (1985) 2004; 98:1163-70. [PMID: 15579573 DOI: 10.1152/japplphysiol.00959.2004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The mechanisms by which alpha-adrenergic stimulation of the heart in vivo can cause contractile dysfunction are not well understood. We hypothesized that alpha-adrenergic-mediated contractile dysfunction is mediated through protein kinase C phosphorylation of troponin I, which in in vitro experiments has been shown to reduce actomyosin Mg-ATPase activity. We studied pressure-volume loops in transgenic mice expressing mutant troponin I lacking protein kinase C phosphorylation sites and hypothesized altered responses to phenylephrine. As anesthesia agents can produce markedly different effects on contractility, we studied two agents: avertin and alpha-chloralose-urethane. With alpha-chloralose-urethane, at baseline, there were no contractile abnormalities in the troponin I mutants. Phenylephrine produced a 50% reduction in end-systolic elastance in wild-type controls, although a 9% increase in troponin I mutants (P <0.05). Avertin was associated with reduced contractility compared with alpha-chloralose-urethane. Avertin anesthesia, at baseline, produced a reduction in end-systolic elastance by 31% in the troponin I mutants compared with wild-type (P <0.05), and this resulted in further marked systolic and diastolic dysfunction with phenylephrine in the troponin I mutants. Dobutamine produced no significant difference in the contractile phenotype of the transgenic mice with either anesthetic regimen. In conclusion, these data (alpha-chloralose-urethane) demonstrate that alpha-adrenergic-mediated force reduction is mediated through troponin I protein kinase C phosphorylation. beta-Adrenergic responses are not mediated through this pathway. Altering the myofilament force-calcium relationship may result in in vivo increased sensitivity to negative inotropy. Thus choice of a negative inotropic anesthetic agent (avertin) with phenylephrine can lead to profound contractile dysfunction.
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Affiliation(s)
- Guy A MacGowan
- Freeman Hospital, Dept of Cardiology, Newcastle upon Tyne NE7 7DN, UK.
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40
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Goldspink PH, Montgomery DE, Walker LA, Urboniene D, McKinney RD, Geenen DL, Solaro RJ, Buttrick PM. Protein Kinase Cε Overexpression Alters Myofilament Properties and Composition During the Progression of Heart Failure. Circ Res 2004; 95:424-32. [PMID: 15242976 DOI: 10.1161/01.res.0000138299.85648.92] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
We report characterization of a transgenic mouse that overexpresses constitutively active protein kinase Cε in the heart and slowly develops a dilated cardiomyopathy with failure. The hemodynamic, mechanical, and biochemical properties of these hearts demonstrate a series of temporal events that mark the progression of the disease. In the 3-month transgenic (TG) animals, contractile properties and gene expression measurements are normal, but an increase in myofibrillar Ca
2+
sensitivity and thin filament protein phosphorylation is noted. At 6 months, there is a decrease in the myofibrillar Ca
2+
sensitivity, a significant increase in β-myosin heavy chain mRNA and protein, normal cardiac function, but a blunted response to an inotropic challenge. The transition at 9 months is especially interesting because age-related changes appear to contribute to the decline in function seen in the TG heart. At this point, there is a decline in baseline function and maximum tension produced by the myofibrils, which is coincident with the onset of atrial myosin light chain isoform re-expression in the ventricles. In the 12-month TG mice, there is clear hemodynamic and geometric evidence of failure. Alterations in the composition of the myofibrils persist but the phosphorylation of myosin light chain 2v is dramatically different at this age compared with all others. We interpret these data to implicate the disruption of the myofibrillar proteins and their interactions in the propagation of dilated cardiac disease.
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Affiliation(s)
- Paul H Goldspink
- Section of Cardiology, University of Illinois at Chicago, 840 S Wood St, M/C 715, Chicago, IL 60612, USA.
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41
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Sumandea MP, Burkart EM, Kobayashi T, De Tombe PP, Solaro RJ. Molecular and integrated biology of thin filament protein phosphorylation in heart muscle. Ann N Y Acad Sci 2004; 1015:39-52. [PMID: 15201148 DOI: 10.1196/annals.1302.004] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
An increasing body of evidence points to posttranslational modifications of the thin filament regulatory proteins, cardiac troponin T (cTnT) and cardiac troponin I (cTnI) by protein kinase C (PKC) phosphorylation as important in both long- and short-term regulation of cardiac function and potentially implicated in the transition between compensated hypertrophy and decompensation. The main sites for PKC-dependent phosphorylation on cTnI are Ser43, Ser45, and Thr144 and on cTnT are Thr197, Ser201, Thr206, and Thr287 (mouse sequence). We analyzed the function of each phosphorylation residue using a phosphorylation mimic approach introducing glutamates (E) at PKC phosphorylation sites and then measuring the isometric tension of fiber bundles exchanged with these mutants. We also directly phosphorylated cTnI and cTnT by PKC, incorporated the phosphorylated troponins in the myofilament lattice, and determined the isometric tension at varying Ca(2+) concentrations. We followed the experimental data with computational analysis prediction of helical content of cTnI and cTnT peptides that undergo phosphorylation. Here we summarize our recent data on the specific functional role of PKC phosphorylation sites of cTnI and cTnT.
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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, 60612, USA
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42
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Roman BB, Goldspink PH, Spaite E, Urboniene D, McKinney R, Geenen DL, Solaro RJ, Buttrick PM. Inhibition of PKC phosphorylation of cTnI improves cardiac performance in vivo. Am J Physiol Heart Circ Physiol 2004; 286:H2089-95. [PMID: 14726296 DOI: 10.1152/ajpheart.00582.2003] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Protein kinase C (PKC) modulates cardiomyocyte function by phosphorylation of intracellular targets including myofilament proteins. Data generated from studies on in vitro heart preparations indicate that PKC phosphorylation of troponin I (TnI), primarily via PKC-epsilon, may slow the rates of cardiac contraction and relaxation (+dP/dt and -dP/dt). To explore this issue in vivo, we employed transgenic mice [mutant TnI (mTnI) mice] in which the major PKC phosphorylation sites on cardiac TnI were mutated by alanine substitutions for Ser(43) and Ser(45) and studied in situ hemodynamics at baseline and increased inotropy. Hearts from mTnI mice exhibited increased contractility, as shown by a 30% greater +dP/dt and 18% greater -dP/dt than FVB hearts, and had a negligible response to isoproterenol compared with FVB mice, in which +dP/dt increased by 33% and -dP/dt increased by 26%. Treatment with phenylephrine and propranolol gave a similar result; FVB mouse hearts demonstrated a 20% increase in developed pressure, whereas mTnI mice showed no response. Back phosphorylation of TnI from mTnI hearts demonstrated that the mutation of the PKC sites was associated with an enhanced PKA-dependent phosphorylation independent of a change in basal cAMP levels. Our results demonstrate the important role that PKC-dependent phosphorylation of TnI has on the modulation of cardiac function under basal as well as augmented states and indicate interdependence of the phosphorylation sites of TnI in hearts beating in situ.
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Affiliation(s)
- Brian B Roman
- Section of Cardiology, University of Illinois, 840 S. Wood Street (M/C 715), Chicago, IL 60612, USA.
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43
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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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44
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Pyle WG, Chen Y, Hofmann PA. Cardioprotection through a PKC-dependent decrease in myofilament ATPase. Am J Physiol Heart Circ Physiol 2003; 285:H1220-8. [PMID: 12763745 DOI: 10.1152/ajpheart.00076.2003] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activation of myocardial kappa-opioid receptor-protein kinase C (PKC) pathways may improve postischemic contractile function through a myofilament reduction in ATP utilization. To test this, we first examined the effects of PKC inhibitors on kappa-opioid receptor-dependent cardioprotection. The kappa-opioid receptor agonist U50,488H (U50) increased postischemic left ventricular developed pressure and reduced postischemic end-diastolic pressure compared with controls. PKC inhibitors abolished the cardioprotective effects of U50. To determine whether kappa-opioid-PKC-dependent decreases in Ca2+-dependent actomyosin Mg2+-ATPase could account for cardioprotection, we subjected hearts to three separate actomyosin ATPase-lowering protocols. We observed that moderate decreases in myofibrillar ATPase were equally cardioprotective as kappa-opioid receptor stimulation. Immunoblot analysis and confocal microscopy revealed a kappa-opioid-induced increase in myofilament-associated PKC-epsilon, and myofibrillar Ca2+-independent PKC activity was increased after kappa-opioid stimulation. This PKC-myofilament association led to an increase in troponin I and C-protein phosphorylation. Thus we propose PKC-epsilon activation and translocation to the myofilaments causes a decrease in actomyosin ATPase, which contributes to the kappa-opioid receptor-dependent cardioprotective mechanism.
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Affiliation(s)
- W Glen Pyle
- Department of Physiology, University of Tennessee-Memphis, 894 Union Avenue, Memphis, TN 38163, USA
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Burkart EM, Sumandea MP, Kobayashi T, Nili M, Martin AF, Homsher E, Solaro RJ. Phosphorylation or glutamic acid substitution at protein kinase C sites on cardiac troponin I differentially depress myofilament tension and shortening velocity. J Biol Chem 2003; 278:11265-72. [PMID: 12551921 DOI: 10.1074/jbc.m210712200] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
There is evidence that multi-site phosphorylation of cardiac troponin I (cTnI) by protein kinase C is important in both long- and short-term regulation of cardiac function. To determine the specific functional effects of these phosphorylation sites (Ser-43, Ser-45, and Thr-144), we measured tension and sliding speed of thin filaments in reconstituted preparations in which endogenous cTnI was replaced with cTnI phosphorylated by protein kinase C-epsilon or mutated to cTnI-S43E/S45E/T144E, cTnI-S43E/S45E, or cTnI-T144E. We used detergent-skinned mouse cardiac fiber bundles to measure changes in Ca(2+)-dependence of force. Compared with controls, fibers reconstituted with phosphorylated cTnI, cTnI-S43E/S45E/T144E, or cTnI-S43E/S45E were desensitized to Ca(2+), and maximum tension was as much as 27% lower, whereas fibers reconstituted with cTnI-T144E showed no change. In the in vitro motility assay actin filaments regulated by troponin complexes containing phosphorylated cTnI or cTnI-S43E/S45E/T144E showed both a decrease in Ca(2+) sensitivity and maximum sliding speed compared with controls, whereas filaments regulated by cTnI-S43E/S45E showed only decreased maximum sliding speed and filaments regulated by cTnI-T144E demonstrated only desensitization to Ca(2+). Our results demonstrate novel site specificity of effects of PKC phosphorylation on cTnI function and emphasize the complexity of modulation of the actin-myosin interaction by specific changes in the thin filament.
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Affiliation(s)
- Eileen M Burkart
- University of Illinois at Chicago, Department of Physiology and Biophysics, Program in Cardiovascular Sciences, College of Medicine, Chicago, Illinois 60612, USA
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Solaro RJ. The Special Structure and Function of Troponin I in Regulation of Cardiac Contraction and Relaxation. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 538:389-401; discussion 401-2. [PMID: 15098685 DOI: 10.1007/978-1-4419-9029-7_36] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
In this chapter I review evidence for a pivotal role of the sarcomeric thin filament protein, troponin I, in cardiac muscle activation and its modulation by covalent modifications, sarcomere length, and intracellular pH. This evidence demonstrates that the cardiac variant of troponin I (cTnI), which is the only isoform expressed in the adult myocardium, has unique structure and function that are specialized for extrinsic and intrinsic control of cardiac contraction and relaxation.
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Affiliation(s)
- R John Solaro
- Department of Physiology and Biophysics (M/C 901), University of Illinois at Chicago, College of Medicine, Chicago, IL 60612, USA
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Jweied EE, McKinney RD, Walker LA, Brodsky I, Geha AS, Massad MG, Buttrick PM, de Tombe PP. Oncology nurse practitioner provides continuity of care. Am J Physiol Heart Circ Physiol 1992; 289:H2478-83. [PMID: 16085678 DOI: 10.1152/ajpheart.00638.2005] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Diabetes mellitus is associated with a distinct cardiomyopathy. Whether cardiac myofilament function is altered in human diabetes mellitus is unknown. Myocardial biopsies were obtained from seven diabetic patients and five control, nondiabetic patients undergoing coronary artery bypass surgery. Myofilament function was assessed by determination of the developed force-Ca2+ concentration relation in skinned cardiac cells from flash-frozen human biopsies. Separate control experiments revealed that flash freezing of biopsy specimens did not affect myofilament function. All patients in the diabetes mellitus cohort were classified as Type 2 diabetes mellitus patients, and most showed signs of diastolic dysfunction. Diabetes mellitus was associated with depressed myofilament function, that is, decreased Ca2+ sensitivity (29%, P < 0.05 vs. control) and a trend toward reduction of maximum Ca2+-saturated force (29%, P = 0.08 vs. control). The slope of the force-Ca2+ concentration relation (Hill coefficient) was not affected by diabetes, however. We conclude that human diabetes mellitus is associated with decreased cardiac myofilament function. Depressed cardiac myofilament Ca2+ responsiveness may underlie the decreased ventricular function characteristic of human diabetic cardiomyopathy.
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Affiliation(s)
- Eias E Jweied
- Dept. of Physiology and Biophysics, (M/C 901 College of Medicine, Univ. of Illinois at Chicago, 835 S. Wolcott Ave., Chicago, IL 60612, USA
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