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Khokhlova A, Myachina T, Butova X, Kochurova A, Polyakova E, Galagudza M, Solovyova O, Kopylova G, Shchepkin D. The Acute Effects of Leptin on the Contractility of Isolated Rat Atrial and Ventricular Cardiomyocytes. Int J Mol Sci 2022; 23:ijms23158356. [PMID: 35955485 PMCID: PMC9369024 DOI: 10.3390/ijms23158356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2022] [Revised: 07/22/2022] [Accepted: 07/27/2022] [Indexed: 02/01/2023] Open
Abstract
Leptin is a pleiotropic peptide playing an important role in the regulation of cardiac functions. It is not clear whether leptin directly modulates the mechanical function of atrial cardiomyocytes. We compared the acute effects of leptin on the characteristics of mechanically non-loaded sarcomere shortening and cytosolic Ca2+ concentration ([Ca2+]i) transients in single rat atrial and ventricular cardiomyocytes. We also studied the functional properties of myosin obtained from cardiomyocytes using an in vitro motility assay and assessed the sarcomeric protein phosphorylation. Single cardiomyocytes were exposed to 5, 20, and 60 nM leptin for 60 min. In ventricular cardiomyocytes, 60 nM leptin depressed sarcomere shortening amplitude and decreased the rates of shortening and relaxation. These effects were accompanied by a decrease in the phosphorylation of cMyBP-C, an increase in Tpm phosphorylation, and a slowdown of the sliding velocity of thin filaments over myosin in the in vitro motility assay. In contrast, in atrial cardiomyocytes, the phosphorylation of cMyBP-C and TnI increased, and the characteristics of sarcomere shortening did not change. Leptin had no effect on the characteristics of [Ca2+]i transients in ventricular cardiomyocytes, while 5 nM leptin prolonged [Ca2+]i transients in atrial cardiomyocytes. Thus, leptin-induced changes in contractility of ventricular cardiomyocytes may be attributed to the direct effects of leptin on cross-bridge kinetics and sarcomeric protein properties rather than changes in [Ca2+]i. We also suggest that the observed differences between atrial and ventricular cardiomyocytes may be associated with the peculiarities of the expression of leptin receptors, as well as signaling pathways in the atrial and ventricular myocardium.
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Affiliation(s)
- Anastasia Khokhlova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
- Correspondence:
| | - Tatiana Myachina
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
| | - Xenia Butova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
| | - Anastasia Kochurova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
| | - Ekaterina Polyakova
- Almazov National Medical Research Centre, Institute of Experimental Medicine, Akkuratova Str. 2, 197341 Saint-Petersburg, Russia; (E.P.); (M.G.)
| | - Michael Galagudza
- Almazov National Medical Research Centre, Institute of Experimental Medicine, Akkuratova Str. 2, 197341 Saint-Petersburg, Russia; (E.P.); (M.G.)
| | - Olga Solovyova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
| | - Galina Kopylova
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
| | - Daniil Shchepkin
- Institute of Immunology and Physiology, Russian Academy of Sciences, Pervomajskaya Str. 106, 620049 Yekaterinburg, Russia; (T.M.); (X.B.); (A.K.); (O.S.); (G.K.); (D.S.)
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2
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Kirsh AJ, Juracic ES, Petrick HL, Monaco CMF, Barbeau PA, Tupling AR, Holloway GP. Dietary nitrate does not alter cardiac function, calcium handling proteins, or SERCA activity in the left ventricle of healthy rats. Appl Physiol Nutr Metab 2020; 45:1049-1053. [PMID: 32379978 DOI: 10.1139/apnm-2020-0078] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Dietary nitrate has been shown to increase cytosolic calcium concentrations within the heart, which would necessitate greater calcium sequestration for relaxation. In the present study we demonstrate that while nitrate supplementation reduced blood pressure, calcium-handling protein content, sarco(endo)plasmic reticulum Ca-ATPase 2a (SERCA) enzymatic properties, and left ventricular function were not altered. In addition, nitrite did not alter in vitro SERCA activity. Combined, these data suggest that in healthy rats, dietary nitrate does not increase left ventricle SERCA-related calcium-handling properties. Novelty Dietary nitrate decreases blood pressure but does not alter left ventricular calcium-handling protein content or SERCA activity in healthy rats.
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Affiliation(s)
- Aleah J Kirsh
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
| | - Emma S Juracic
- Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada
| | - Heather L Petrick
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
| | - Cynthia M F Monaco
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
| | - Pierre-Andre Barbeau
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
| | - A Russell Tupling
- Department of Kinesiology, University of Waterloo, Waterloo, ON, Canada
| | - Graham P Holloway
- Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada
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3
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Dong J, Gao C, Liu J, Cao Y, Tian L. TSH inhibits SERCA2a and the PKA/PLN pathway in rat cardiomyocytes. Oncotarget 2018; 7:39207-39215. [PMID: 27206677 PMCID: PMC5129926 DOI: 10.18632/oncotarget.9393] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 04/16/2016] [Indexed: 11/25/2022] Open
Abstract
Elevated thyroid-stimulating hormone (TSH) levels often accompany impaired LV diastolic function and subtle systolic dysfunction in subclinical hypothyroidism (sHT). These cardiac dysfunctions are characterized by increases in mean aortic acceleration and pre-ejection/ejection time ratios. To explore the mechanism underlying these pathologies, we investigated the effects of TSH on sarcoplasmic reticulum calcium ATPase (SERCA2a) activity and expression in neonatal rat cardiomyocytes. TSH inhibited SERCA2a activity and expression by binding to TSH receptors in cardiomyocyte membranes and inhibiting the protein kinase A/phoshpolamban (PKA/PLN) signaling pathway. These results suggest that increases in serum TSH levels contribute to the development of cardiac diastolic and systolic dysfunction.
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Affiliation(s)
- Jiajia Dong
- Department of Endocrinology, Gansu Provincial Hospital, Lanzhou, Gansu, China
| | - Cuixia Gao
- Department of Ultrasonic Diagnosis, Gansu Provincial Hospital, Lanzhou, Gansu, China
| | - Jing Liu
- Department of Endocrinology, Gansu Provincial Hospital, Lanzhou, Gansu, China
| | - Yunshan Cao
- Department of Cardiology, Gansu Provincial Hospital, Lanzhou, Gansu, China
| | - Limin Tian
- Department of Endocrinology, Gansu Provincial Hospital, Lanzhou, Gansu, China
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4
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Kraev A. Insertional Mutagenesis Confounds the Mechanism of the Morbid Phenotype of a PLN R9C Transgenic Mouse Line. J Card Fail 2018; 24:115-125. [PMID: 29325795 DOI: 10.1016/j.cardfail.2017.12.009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Revised: 12/18/2017] [Accepted: 12/21/2017] [Indexed: 12/29/2022]
Abstract
BACKGROUND A mouse line with heterozygous transgenic expression of phospholamban carrying a substitution of cysteine for arginine 9 (TgPLNR9C) under the control of α-myosin heavy chain (αMHC) promoter features dilated cardiomyopathy, heart failure, and premature death. METHODS AND RESULTS Determination of transgene chromosomal localization by conventional methods shows that in this line the transgenic array of 13 PLNR9C expression cassettes, arranged in a head-to-tail tandem orientation, have integrated into the bidirectional promoter of the αMHC (Myh6) gene and the gene for the regulatory noncoding RNA Myheart (Mhrt), both of which are known to be involved in cardiac development and pathology. Expression of the noncoding RNA Mhrt in TgPLNR9C mice exhibits profound deregulation, despite the presence of the second, intact allele. CONCLUSIONS The TgPLNR9C mouse strain is, in the best case, a functionally ambiguous phenocopy of the human PLNR9C heterozygote, because a similar constellation of genetically programmed events can not occur in a patient. Publications featuring "cardiac-specific overexpression" are focused on the phenotype and typically forgo the definition of the transgene integration site or transgene temporal expression profile, so caution should be exercised in attributing clinical relevance to pathologic phenomena observed in αMHC-driven transgenes.
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Affiliation(s)
- Alexander Kraev
- University of Toronto, 27 King's College Circle, Toronto, Ontario M5S 1A1, Canada.
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5
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Blatter LA. The intricacies of atrial calcium cycling during excitation-contraction coupling. J Gen Physiol 2017; 149:857-865. [PMID: 28798277 PMCID: PMC5583713 DOI: 10.1085/jgp.201711809] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2017] [Accepted: 07/12/2017] [Indexed: 12/20/2022] Open
Abstract
Blatter discusses the initiation and spread of Ca release, Ca store depletion, and release termination in atrial myocytes.
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Affiliation(s)
- Lothar A Blatter
- Department of Physiology and Biophysics, Rush University Medical Center, Chicago, IL
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Maxwell JT, Blatter LA. A novel mechanism of tandem activation of ryanodine receptors by cytosolic and SR luminal Ca 2+ during excitation-contraction coupling in atrial myocytes. J Physiol 2017; 595:3835-3845. [PMID: 28028837 DOI: 10.1113/jp273611] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 12/01/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS In atrial myocytes excitation-contraction coupling is strikingly different from ventricle because atrial myocytes lack a transverse tubule membrane system: Ca2+ release starts in the cell periphery and propagates towards the cell centre by Ca2+ -induced Ca2+ release from the sarcoplasmic reticulum (SR) Ca2+ store. The cytosolic Ca2+ sensitivity of the ryanodine receptor (RyRs) Ca2+ release channel is low and it is unclear how Ca2+ release can be activated in the interior of atrial cells. Simultaneous confocal imaging of cytosolic and intra-SR calcium revealed a transient elevation of store Ca2+ that we termed 'Ca2+ sensitization signal'. We propose a novel paradigm of atrial ECC that is based on tandem activation of the RyRs by cytosolic and luminal Ca2+ through a 'fire-diffuse-uptake-fire' (or FDUF) mechanism: Ca2+ uptake by SR Ca2+ pumps at the propagation front elevates Ca2+ inside the SR locally, leading to luminal RyR sensitization and lowering of the cytosolic Ca2+ activation threshold. ABSTRACT In atrial myocytes Ca2+ release during excitation-contraction coupling (ECC) is strikingly different from ventricular myocytes. In many species atrial myocytes lack a transverse tubule system, dividing the sarcoplasmic reticulum (SR) Ca2+ store into the peripheral subsarcolemmnal junctional (j-SR) and the much more abundant central non-junctional (nj-SR) SR. Action potential (AP)-induced Ca2+ entry activates Ca2+ -induced Ca2+ release (CICR) from j-SR ryanodine receptor (RyR) Ca2+ release channels. Peripheral elevation of [Ca2+ ]i initiates CICR from nj-SR and sustains propagation of CICR to the cell centre. Simultaneous confocal measurements of cytosolic ([Ca2+ ]i ; with the fluorescent Ca2+ indicator rhod-2) and intra-SR ([Ca2+ ]SR ; fluo-5N) Ca2+ in rabbit atrial myocytes revealed that Ca2+ release from j-SR resulted in a cytosolic Ca2+ transient of higher amplitude compared to release from nj-SR; however, the degree of depletion of j-SR [Ca2+ ]SR was smaller than nj-SR [Ca2+ ]SR . Similarly, Ca2+ signals from individual release sites of the j-SR showed a larger cytosolic amplitude (Ca2+ sparks) but smaller depletion (Ca2+ blinks) than release from nj-SR. During AP-induced Ca2+ release the rise of [Ca2+ ]i detected at individual release sites of the nj-SR preceded the depletion of [Ca2+ ]SR , and during this latency period a transient elevation of [Ca2+ ]SR occurred. We propose that Ca2+ release from nj-SR is activated by cytosolic and luminal Ca2+ (tandem RyR activation) via a novel 'fire-diffuse-uptake-fire' (FDUF) mechanism. This novel paradigm of atrial ECC predicts that Ca2+ uptake by sarco-endoplasmic reticulum Ca2+ -ATPase (SERCA) at the propagation front elevates local [Ca2+ ]SR , leading to luminal RyR sensitization and lowering of the activation threshold for cytosolic CICR.
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Affiliation(s)
- Joshua T Maxwell
- Department of Molecular Biophysics and Physiology, Rush University Medical Centre, Chicago, IL, 60612, USA
| | - Lothar A Blatter
- Department of Molecular Biophysics and Physiology, Rush University Medical Centre, Chicago, IL, 60612, USA
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7
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Desmond PF, Muriel J, Markwardt ML, Rizzo MA, Bloch RJ. Identification of Small Ankyrin 1 as a Novel Sarco(endo)plasmic Reticulum Ca2+-ATPase 1 (SERCA1) Regulatory Protein in Skeletal Muscle. J Biol Chem 2015; 290:27854-67. [PMID: 26405035 DOI: 10.1074/jbc.m115.676585] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Indexed: 01/06/2023] Open
Abstract
Small ankyrin 1 (sAnk1) is a 17-kDa transmembrane (TM) protein that binds to the cytoskeletal protein, obscurin, and stabilizes the network sarcoplasmic reticulum in skeletal muscle. We report that sAnk1 shares homology in its TM amino acid sequence with sarcolipin, a small protein inhibitor of the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA). Here we investigate whether sAnk1 and SERCA1 interact. Our results indicate that sAnk1 interacts specifically with SERCA1 in sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle, and in COS7 cells transfected to express these proteins. This interaction was demonstrated by co-immunoprecipitation and an anisotropy-based FRET method. Binding was reduced ~2-fold by the replacement of all of the TM amino acids of sAnk1 with leucines by mutagenesis. This suggests that, like sarcolipin, sAnk1 interacts with SERCA1 at least in part via its TM domain. Binding of the cytoplasmic domain of sAnk1 to SERCA1 was also detected in vitro. ATPase activity assays show that co-expression of sAnk1 with SERCA1 leads to a reduction of the apparent Ca(2+) affinity of SERCA1 but that the effect of sAnk1 is less than that of sarcolipin. The sAnk1 TM mutant has no effect on SERCA1 activity. Our results suggest that sAnk1 interacts with SERCA1 through its TM and cytoplasmic domains to regulate SERCA1 activity and modulate sequestration of Ca(2+) in the sarcoplasmic reticulum lumen. The identification of sAnk1 as a novel regulator of SERCA1 has significant implications for muscle physiology and the development of therapeutic approaches to treat heart failure and muscular dystrophies linked to Ca(2+) misregulation.
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Affiliation(s)
- Patrick F Desmond
- From the Department of Physiology and Program in Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland 21230
| | | | | | | | - Robert J Bloch
- From the Department of Physiology and Program in Biochemistry and Molecular Biology, University of Maryland, Baltimore, Maryland 21230
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8
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Ye LF, Zheng YR, Wang LH. Effects of Shenmai injection and its bioactive components following ischemia/reperfusion in cardiomyocytes. Exp Ther Med 2015; 10:1348-1354. [PMID: 26622490 PMCID: PMC4578100 DOI: 10.3892/etm.2015.2662] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2014] [Accepted: 06/24/2015] [Indexed: 12/20/2022] Open
Abstract
The aim of the present study was to determine whether the myocardial protective function of Shenmai injection (SM) during ischemia/reperfusion (I/R) is attributable to its regulation of intracellular calcium (Ca2+) and phospholamban (PLB) levels. Cultured neonatal Sprague Dawley rat cardiomyocytes were used to compare the effects of normoxia, total saponins of Panax ginseng (TSPG), ginsenoside Rg1 (Rg1) and SM treatments in rat myocardial cells following I/R. For each of these treatment groups, the mRNA and protein levels of PLB and the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) were evaluated, in addition to the cytoplasmic Ca2+ concentration [Ca2+]i and the rate of apoptosis. The results indicated that I/R markedly decreased phosphorylated PLB and SERCA expression and that SM was able to mitigate this effect, while TPSG and Rg1 were not. Furthermore, SM appeared to prevent aberrant apoptosis and restore the depleted [Ca2+]i resulting from I/R. The protective efficacy of SM against heart disease following I/R may, therefore, be due in part to its effect on intracellular Ca2+ homeostasis. SM may exert its protective effects by relieving PLB inhibition, and the pharmacodynamic actions of SM appear to be significantly more effective than those of its bioreactive components, TPSG and Rgl.
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Affiliation(s)
- Li-Fang Ye
- Department of Cardiology, First Affiliated Hospital, Medical College of Zhejiang University, Hangzhou, Zhejiang 310003, P.R. China
| | - Ya-Ru Zheng
- Department of Cardiology, First Affiliated Hospital, Medical College of Zhejiang University, Hangzhou, Zhejiang 310003, P.R. China
| | - Li-Hong Wang
- Department of Cardiology, People's Hospital of Zhejiang Province, Hangzhou, Zhejiang 310014, P.R. China
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9
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Stammers AN, Susser SE, Hamm NC, Hlynsky MW, Kimber DE, Kehler DS, Duhamel TA. The regulation of sarco(endo)plasmic reticulum calcium-ATPases (SERCA). Can J Physiol Pharmacol 2015; 93:843-54. [PMID: 25730320 DOI: 10.1139/cjpp-2014-0463] [Citation(s) in RCA: 99] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The sarco(endo)plasmic reticulum calcium ATPase (SERCA) is responsible for transporting calcium (Ca(2+)) from the cytosol into the lumen of the sarcoplasmic reticulum (SR) following muscular contraction. The Ca(2+) sequestering activity of SERCA facilitates muscular relaxation in both cardiac and skeletal muscle. There are more than 10 distinct isoforms of SERCA expressed in different tissues. SERCA2a is the primary isoform expressed in cardiac tissue, whereas SERCA1a is the predominant isoform expressed in fast-twitch skeletal muscle. The Ca(2+) sequestering activity of SERCA is regulated at the level of protein content and is further modified by the endogenous proteins phospholamban (PLN) and sarcolipin (SLN). Additionally, several novel mechanisms, including post-translational modifications and microRNAs (miRNAs) are emerging as integral regulators of Ca(2+) transport activity. These regulatory mechanisms are clinically relevant, as dysregulated SERCA function has been implicated in the pathology of several disease states, including heart failure. Currently, several clinical trials are underway that utilize novel therapeutic approaches to restore SERCA2a activity in humans. The purpose of this review is to examine the regulatory mechanisms of the SERCA pump, with a particular emphasis on the influence of exercise in preventing the pathological conditions associated with impaired SERCA function.
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Affiliation(s)
- Andrew N Stammers
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre
| | - Shanel E Susser
- b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre.,c Department of Physiology, Faculty of Health Sciences, University of Manitoba
| | - Naomi C Hamm
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre
| | - Michael W Hlynsky
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre
| | - Dustin E Kimber
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre
| | - D Scott Kehler
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre
| | - Todd A Duhamel
- a Health, Leisure & Human Performance Research Institute, Faculty of Kinesiology & Recreation Management, University of Manitoba.,b Institute of Cardiovascular Sciences, St. Boniface Hospital Research Centre.,c Department of Physiology, Faculty of Health Sciences, University of Manitoba
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10
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Cerra MC, Imbrogno S. Phospholamban and cardiac function: a comparative perspective in vertebrates. Acta Physiol (Oxf) 2012; 205:9-25. [PMID: 22463608 DOI: 10.1111/j.1748-1716.2012.02389.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Phospholamban (PLN) is a small phosphoprotein closely associated with the cardiac sarcoplasmic reticulum (SR). Dephosphorylated PLN tonically inhibits the SR Ca-ATPase (SERCA2a), while phosphorylation at Ser16 by PKA and Thr17 by Ca(2+) /calmodulin-dependent protein kinase (CaMKII) relieves the inhibition, and this increases SR Ca(2+) uptake. For this reason, PLN is one of the major determinants of cardiac contractility and relaxation. In this review, we attempted to highlight the functional significance of PLN in vertebrate cardiac physiology. We will refer to the huge literature on mammals in order to describe the molecular characteristics of this protein, its interaction with SERCA2a and its role in the regulation of the mechanic and the electric performance of the heart under basal conditions, in the presence of chemical and physical stresses, such as β-adrenergic stimulation, response to stretch, force-frequency relationship and intracellular acidosis. Our aim is to provide the basis to discuss the role of PLN also on the cardiac function of nonmammalian vertebrates, because so far this aspect has been almost neglected. Accordingly, when possible, the literature on PLN will be analysed taking into account the nonuniform cardiac structural and functional characteristics encountered in ectothermic vertebrates, such as the peculiar and variable organization of the SR, the large spectrum of response to stresses and the disaptive absence of crucial proteins (i.e. haemoglobinless and myoglobinless species).
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Affiliation(s)
| | - S. Imbrogno
- Department of Cell Biology; University of Calabria; Arcavacata di Rende (CS); Italy
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11
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Korajoki H, Vornanen M. Expression of SERCA and phospholamban in rainbow trout (Oncorhynchus mykiss) heart: comparison of atrial and ventricular tissue and effects of thermal acclimation. J Exp Biol 2012; 215:1162-9. [DOI: 10.1242/jeb.065102] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
In the heart of rainbow trout (Oncorhynchus mykiss), the rate of contraction and Ca2+ uptake into the sarcoplasmic reticulum (SR) are faster in atrial than ventricular muscle, and contraction force relies more on SR Ca2+ stores after acclimation to cold. This study tested the hypothesis that differences in contractile properties and Ca2+ regulation between atrial and ventricular muscle, and between warm-(WA) and cold-acclimated (CA) trout hearts, are associated with differences in expression of sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA) and/or phospholamban (PLN), an inhibitor of the cardiac SERCA. Quantitative PCR (SERCA only) and antibodies raised against SERCA and PLN were used to determine abundances of SERCA2 transcripts and SERCA and PLN proteins, respectively, in atrium and ventricle of trout acclimated to cold (+4°C, CA) and warm (+18°C, WA) temperatures. Expression of SERCA2 transcripts was 1.6 and 2.1 times higher in atrium than ventricle of WA and CA trout, respectively (P<0.05). At the protein level, differences in SERCA expression between atrium and ventricle were 6.1- and 23-fold for WA and CA trout, respectively (P<0.001). Acclimation to cold increased SERCA2 transcripts 2.6- and 2.0-fold in atrial and ventricular muscle, respectively (P<0.05). At the protein level, cold-induced elevation of SERCA (4.6-fold) was noted only in atrial (P<0.05) but not in ventricular tissue (P>0.05). The expression pattern of PLN was similar to that of the SERCA protein, but chamber-specific and temperature-induced differences were much smaller than in the case of SERCA. In the ventricle, PLN/SERCA ratio was 2.1 and 7.0 times higher than in the atrium for WA and CA fish, respectively. These findings are consistent with the hypothesis that low PLN/SERCA ratio in atrial tissue enables faster SR Ca2+ reuptake and thus contributes to faster kinetics of contraction in comparison with ventricular muscle. Similarly, cold-induced decrease in PLN/SERCA ratio may be associated with faster contraction kinetics of the CA trout heart, in particular in the atrial muscle.
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Affiliation(s)
- Hanna Korajoki
- University of Eastern Finland, Department of Biology, PO Box 111, 80101 Joensuu, Finland
| | - Matti Vornanen
- University of Eastern Finland, Department of Biology, PO Box 111, 80101 Joensuu, Finland
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12
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Cerra MC, Imbrogno S. Phospholamban and cardiac function: a comparative perspective in vertebrates. Acta Physiol (Oxf) 2012. [DOI: 10.1111/j.1748-1716.2011.02389.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - S. Imbrogno
- Department of Cell Biology; University of Calabria; Arcavacata di Rende (CS); Italy
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13
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Tupling AR, Bombardier E, Gupta SC, Hussain D, Vigna C, Bloemberg D, Quadrilatero J, Trivieri MG, Babu GJ, Backx PH, Periasamy M, MacLennan DH, Gramolini AO. Enhanced Ca2+ transport and muscle relaxation in skeletal muscle from sarcolipin-null mice. Am J Physiol Cell Physiol 2011; 301:C841-9. [PMID: 21697544 DOI: 10.1152/ajpcell.00409.2010] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sarcolipin (SLN) inhibits sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) pumps. To evaluate the physiological significance of SLN in skeletal muscle, we compared muscle contractility and SERCA activity between Sln-null and wild-type mice. SLN protein expression in wild-type mice was abundant in soleus and red gastrocnemius (RG), low in extensor digitorum longus (EDL), and absent from white gastrocnemius (WG). SERCA activity rates were increased in soleus and RG, but not in EDL or WG, from Sln-null muscles, compared with wild type. No differences were seen between wild-type and Sln-null EDL muscles in force-frequency curves or maximum rates of force development (+dF/dt). Maximum relaxation rates (-dF/dt) of EDL were higher in Sln-null than wild type across a range of submaximal stimulation frequencies, but not during a twitch or peak tetanic contraction. For soleus, no differences were seen between wild type and Sln-null in peak tetanic force or +dF/dt; however, force-frequency curves showed that peak force during a twitch and 10-Hz contraction was lower in Sln-null. Changes in the soleus force-frequency curve corresponded with faster rates of force relaxation at nearly all stimulation frequencies in Sln-null compared with wild type. Repeated tetanic stimulation of soleus caused increased (-dF/dt) in wild type, but not in Sln-null. No compensatory responses were detected in analysis of other Ca(2+) regulatory proteins using Western blotting and immunohistochemistry or myosin heavy chain expression using immunofluorescence. These results show that 1) SLN regulates Ca(2+)-ATPase activity thereby regulating contractile kinetics in at least some skeletal muscles, 2) the functional significance of SLN is graded to the endogenous SLN expression level, and 3) SLN inhibitory effects on SERCA function are relieved in response to repeated contractions thus enhancing relaxation rates.
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14
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Wang Y, Ji Y, Xing Y, Li X, Gao X. Astragalosides rescue both cardiac function and sarcoplasmic reticulum Ca²⁺ transport in rats with chronic heart failure. Phytother Res 2011; 26:231-8. [PMID: 21656599 DOI: 10.1002/ptr.3492] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2010] [Revised: 03/07/2011] [Accepted: 03/08/2011] [Indexed: 11/10/2022]
Abstract
The study investigated the beneficial effects of astragalosides (AS) on cardiac performance in rats with chronic heart failure. Chronic heart failure was produced by left anterior descending coronary artery ligation, and the therapeutic efficacy of astragalosides at 10, 20 and 40 mg/kg was evaluated. Five weeks after the operation, cardiac function was deficient and sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) activity was significantly reduced. Moreover, SERCA mRNA decreased, while expression of the SERCA down-regulator phospholamban (PLB) was significantly increased. Phosphorylated phospholamban (P-PLB), the form that does not inhibit SERCA, was also reduced by chronic heart failure. Treatment with AS improved left ventricle function and cardiac structure, reversed the depression of SERCA activity, and increased P-PLB. These results suggest that the cardioprotective effect of AS may be due to the increase in P-PLB protein, which disinhibits SERCA activity. Rescue of sarcoplasmic reticulum Ca²⁺ cycling by astragalosides could normalize excitation-contraction coupling and improve overall cardiac function.
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Affiliation(s)
- Yi Wang
- TCM Research Center, Tianjin University of Traditional Chinese Medicine, Tianjin 300193, China
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15
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The Isolated Work-Performing and Ejecting Mouse Heart Preparation Comparison and Quantification of Cardiac Performance in Transgenic and Wild-Type Mice. ACTA ACUST UNITED AC 2011. [DOI: 10.1007/978-1-4615-1653-8_9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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16
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Hiranandani N, Billman GE, Janssen PML. Effects of hydroxyl radical induced-injury in atrial versus ventricular myocardium of dog and rabbit. Front Physiol 2010; 1:25. [PMID: 21423367 PMCID: PMC3059949 DOI: 10.3389/fphys.2010.00025] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2010] [Accepted: 07/22/2010] [Indexed: 11/13/2022] Open
Abstract
Despite the widespread use of ventricular tissue in the investigation involving hydroxyl radical Aim: (OH*) injury, one of the most potent mediators in ischemia-reperfusion injury, little is known about the impact on atrial myocardium. In this study we thus compared the OH*-induced injury response between atrial and right ventricular muscles from both rabbits and dogs under identical experimental conditions. Methods: Small, contracting ventricular and atrial rabbit and dog trabeculae were directly exposed to OH*, and contractile properties were examined and quantified. Results: A brief OH* exposure led to transient rigor like contracture with marked elevation of diastolic tension and depression of developed force. Although the injury response showed similarities between atrial and ventricular myocardium, there were significant differences as well. In rabbit atrial muscles, the development of the contracture and its peak was much faster as compared to ventricular muscles. Also, at the peak of contracture, both rabbit and dog atrial muscles show a lesser degree of contractile dysfunction. Conclusion:These results indicate that both atrial and ventricular muscles develop a rigor-like contracture after acute OH*-induced injury, and atrial muscles showed a lesser degree of contractile dysfunction. Comparison of dog versus rabbit tissue shows that the response was similar in magnitude, but slower to develop in dog tissue.
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Affiliation(s)
- Nitisha Hiranandani
- Department of Physiology and Cell Biology, College of Medicine, The Ohio State University Columbus, OH, USA
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17
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Threonine-5 at the N-terminus can modulate sarcolipin function in cardiac myocytes. J Mol Cell Cardiol 2009; 47:723-9. [PMID: 19631655 DOI: 10.1016/j.yjmcc.2009.07.014] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2009] [Revised: 07/10/2009] [Accepted: 07/15/2009] [Indexed: 11/20/2022]
Abstract
Sarcolipin (SLN) has emerged as an important regulator of the atrial sarcoplasmic reticulum (SR) Ca2+ transport. The inhibitory effect of SLN on cardiac SR Ca2+ ATPase (SERCA) pump can be relieved by beta-adrenergic stimulation, which indicates that SLN is a reversible inhibitor. However, the mechanism of this reversible regulation of SERCA pump by SLN is yet to be determined. In the current study using adult rat ventricular myocytes we provide evidence that the threonine 5 (T5) residue at the N-terminus of SLN which is conserved among various species, critically regulates the SLN function. Point mutation of T5-->alanine exerts an inhibitory effect on myocyte contractility and calcium transients similar to that of wild-type SLN, whereas mutation of T5-->glutamic acid which mimics the phosphorylation abolished the inhibitory function of SLN. Our results showed that T5 can be phosphorylated in vitro by calcium-calmodulin dependent protein kinase II (CaMKII). Blocking the CaMKII activity in WT-SLN overexpressing myocytes using autocamtide inhibitory peptide completely abolished the beta-adrenergic response. Taken together, our data suggest that T5 is the key amino acid which modulates SLN function via phosphorylation/dephosphorylation mechanisms through CaMKII pathway.
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18
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Bhupathy P, Babu GJ, Periasamy M. Sarcolipin and phospholamban as regulators of cardiac sarcoplasmic reticulum Ca2+ ATPase. J Mol Cell Cardiol 2007; 42:903-11. [PMID: 17442337 PMCID: PMC2743185 DOI: 10.1016/j.yjmcc.2007.03.738] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2006] [Revised: 02/15/2007] [Accepted: 03/02/2007] [Indexed: 01/26/2023]
Abstract
The cardiac sarcoplasmic reticulum calcium ATPase (SERCA2a) plays a critical role in maintaining the intracellular calcium homeostasis during cardiac contraction and relaxation. It has been well documented over the years that altered expression and activity of SERCA2a can lead to systolic and diastolic dysfunction. The activity of SERCA2a is regulated by two structurally similar proteins, phospholamban (PLB) and sarcolipin (SLN). Although, the relevance of PLB has been extensively studied over the years, the role SLN in cardiac physiology is an emerging field of study. This review focuses on the advances in the understanding of the regulation of SERCA2a by SLN and PLB. In particular, it highlights the similarities and differences between the two proteins and their roles in cardiac patho-physiology.
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Affiliation(s)
| | | | - Muthu Periasamy
- Corresponding Author: Address- 304 Hamilton Hall, 1645 Neil Avenue, Columbus OH, 43210, USA, Phone # 614-292-2310, Fax # 614-292-4888,
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19
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Vangheluwe P, Sipido KR, Raeymaekers L, Wuytack F. New perspectives on the role of SERCA2's Ca2+ affinity in cardiac function. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2006; 1763:1216-28. [PMID: 17005265 DOI: 10.1016/j.bbamcr.2006.08.025] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Accepted: 08/10/2006] [Indexed: 11/21/2022]
Abstract
Cardiomyocyte relaxation and contraction are tightly controlled by the activity of the cardiac sarco(endo)plasmic reticulum (SR) Ca2+ transport ATPase (SERCA2a). The SR Ca2+ -uptake activity not only determines the speed of Ca(2+) removal during relaxation, but also the SR Ca2+ content and therefore the amount of Ca2+ released for cardiomyocyte contraction. The Ca2+ affinity is the major determinant of the pump's activity in the physiological Ca2+ concentration range. In the heart, the affinity of the pump for Ca2+ needs to be controlled between narrow borders, since an imbalanced affinity may evoke hypertrophic cardiomyopathy. Several small proteins (phospholamban, sarcolipin) adjust the Ca2+ affinity of the pump to the physiological needs of the cardiomyocyte. It is generally accepted that a chronically reduced Ca2+ affinity of the pump contributes to depressed SR Ca2+ handling in heart failure. Moreover, a persistently lower Ca2+ affinity is sufficient to impair cardiomyocyte SR Ca2+ handling and contractility inducing dilated cardiomyopathy in mice and humans. Conversely, the expression of SERCA2a, a pump with a lower Ca2+ affinity than the housekeeping isoform SERCA2b, is crucial to maintain normal cardiac function and growth. Novel findings demonstrated that a chronically increased Ca2+ affinity also may trigger cardiac hypertrophy in mice and humans. In addition, recent studies suggest that some models of heart failure are marked by a higher affinity of the pump for Ca2+, and hence by improved cardiomyocyte relaxation and contraction. Depressed cardiomyocyte SR Ca2+ uptake activity may therefore not be a universal hallmark of heart failure.
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Affiliation(s)
- P Vangheluwe
- Laboratory of Physiology, University of Leuven, Herestraat 49, bus 802, B-3000 Leuven, Belgium.
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20
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Vangheluwe P, Schuermans M, Zádor E, Waelkens E, Raeymaekers L, Wuytack F. Sarcolipin and phospholamban mRNA and protein expression in cardiac and skeletal muscle of different species. Biochem J 2005; 389:151-9. [PMID: 15801907 PMCID: PMC1184547 DOI: 10.1042/bj20050068] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The widely held view that SLN (sarcolipin) would be the natural inhibitor of SERCA1 (sarcoplasmic/endoplasmic-reticulum Ca2+-ATPase 1), and PLB (phospholamban) its counterpart for SERCA2 inhibition is oversimplified and partially wrong. The expression of SLN and PLB mRNA and protein relative to SERCA1 or SERCA2 was assessed in ventricle, atrium, soleus and EDL (extensor digitorum longus) of mouse, rat, rabbit and pig. SLN protein levels were quantified by means of Western blotting using what appears to be the first successfully generated antibody directed against SLN. Our data confirm the co-expression of PLB and SERCA2a in cardiac muscle and the very low levels (in pig and rabbit) or the absence (in rat and mouse) of PLB protein in the slow skeletal muscle. In larger animals, the SLN mRNA and protein expression in the soleus and EDL correlates with SERCA1a expression, but, in rodents, SLN mRNA and protein show the highest abundance in the atria, which are devoid of SERCA1. In the rodent atria, SLN could therefore potentially interact with PLB and SERCA2a. No SLN was found in the ventricles of the different species studied, and there was no compensatory SLN up-regulation for the loss of PLB in PLB(-/-) mouse. In addition, we found that SLN expression was down-regulated at the mRNA and protein level in the atria of hypertrophic hearts of SERCA2(b/b) mice. These data suggest that superinhibition of SERCA by PLB-SLN complexes could occur in the atria of the smaller rodents, but not in those of larger animals.
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Affiliation(s)
- Peter Vangheluwe
- *Laboratory of Physiology, O/N Gasthuisberg, K.U. Leuven, Herestraat 49, B-3000 Leuven, Belgium
| | - Marleen Schuermans
- *Laboratory of Physiology, O/N Gasthuisberg, K.U. Leuven, Herestraat 49, B-3000 Leuven, Belgium
| | - Ernö Zádor
- †Institute of Biochemistry, Faculty of Medicine, University of Szeged, Dom ter 9, P.O. Box 427, H-6701 Szeged, Hungary
| | - Etienne Waelkens
- ‡Laboratory of Biochemistry, O/N Gasthuisberg, K.U. Leuven, Herestraat 49, B-3000 Leuven, Belgium
| | - Luc Raeymaekers
- *Laboratory of Physiology, O/N Gasthuisberg, K.U. Leuven, Herestraat 49, B-3000 Leuven, Belgium
| | - Frank Wuytack
- *Laboratory of Physiology, O/N Gasthuisberg, K.U. Leuven, Herestraat 49, B-3000 Leuven, Belgium
- To whom correspondence should be addressed (email )
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21
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Tavi P, Pikkarainen S, Ronkainen J, Niemelä P, Ilves M, Weckström M, Vuolteenaho O, Bruton J, Westerblad H, Ruskoaho H. Pacing-induced calcineurin activation controls cardiac Ca2+ signalling and gene expression. J Physiol 2004; 554:309-20. [PMID: 14565991 PMCID: PMC1664772 DOI: 10.1113/jphysiol.2003.053579] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Accepted: 10/16/2003] [Indexed: 12/19/2022] Open
Abstract
Calcineurin, a Ca(2+)-calmodulin-dependent protein phosphatase (PP2B) is one of the links between Ca(2+) signals and regulation of gene transcription in cardiac muscle. We studied the Ca(2+) signal specificity of calcineurin activation experimentally and with modelling. In the rat atrial preparation, an increase in pacing frequency increased nuclear activity of the calcineurin-sensitive transcription factor, nuclear factor of activated T-cells (NFAT), 2-fold in a cyclosporin A (CsA)-sensitive manner. In line with this, modelling results predicted that the frequency of cardiac Ca(2+) transients encodes the stimulus for calcineurin activation. We further observed experimentally that calcineurin inhibition by CsA modulated Ca(2+) release in a Ca(2+)-dependent manner. CsA had no effect on [Ca(2+)](i) at a pacing frequency of 1 Hz but it significantly suppressed the amplitude of Ca(2+) transients, systolic [Ca(2+)](i) and time averaged [Ca(2+)](i) at 6 Hz. Calcineurin had a differential role in the expression of immediate-early genes B-type natriuretic peptide (BNP) and c-fos. CsA inhibited the pacing-induced BNP gene expression, whereas pacing alone had no effect on the expression of c-fos. However, in the presence of CsA, c-fos mRNA levels were significantly augmented by increased pacing frequency. These results show that frequency-dependent calcineurin activation has a specific role in [Ca(2+)](i) regulation and gene expression, constantly recruited by varying cardiac Ca(2+) signals.
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Affiliation(s)
- Pasi Tavi
- Department of Physiology, Biocentre Oulu, University of Oulu, Finland.
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22
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Abstract
This review focuses on recent studies investigating the genetic regulatory mechanisms leading to formation of morphologically, functionally, and molecularly distinct cardiac chambers. The regulation of four representative chamber-specific genes that have been studied in detail is reviewed. These genes include the atrial-specific genes, myosin light chain-2a (MLC2a), slow myosin heavy chain-3 (slow MyHC3), and atrial natriuretic factor (ANF) and the ventricular specific gene, myosin light chain-2v (MLC2v). Comparison of these promoters reveals some generalizations about the regulatory mechanisms involved in chamber-specific gene expression but, equally, indicates the large gaps in the knowledge concerning this intriguing genetic program.
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Affiliation(s)
- Eric M Small
- Department of Cell Biology and Anatomy, University of Arizona Health Sciences Center, 1501 N. Campbell Avenue, Tucson, AZ 85724-5044, USA
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23
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Tsubakihara M, Williams NK, Keogh A, dos Remedios CG. Comparison of gene expression between left atria and left ventricles from non-diseased humans. Proteomics 2003; 4:261-70. [PMID: 14730688 DOI: 10.1002/pmic.200300539] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
We examine the reliability and accuracy of gene array technology in analyzing differences in gene expression between human non-diseased left atrium and left ventricle. We have used cDNA gene arrays and validated those data by carefully designed quantitative real-time polymerase chain reaction (PCR). We have identified pitfalls using cDNA gene array technology based on comparisons with other gene array studies and with changes reported for the levels of expression of the genes corresponding to these cDNAs. The high error rate reported here underscores the cautionary comments reported by others in this field.
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Affiliation(s)
- Masako Tsubakihara
- Institute for Biomedical Research, University of Sydney, Sydney, Australia.
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24
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Minamisawa S, Wang Y, Chen J, Ishikawa Y, Chien KR, Matsuoka R. Atrial chamber-specific expression of sarcolipin is regulated during development and hypertrophic remodeling. J Biol Chem 2003; 278:9570-5. [PMID: 12645548 DOI: 10.1074/jbc.m213132200] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Intracellular Ca2+ regulation is critical in the normal cardiac function and development of pathologic hearts. Phospholamban, an endogenous inhibitor of sarcoplasmic reticulum Ca2+ ATPase in the sarcoplasmic reticulum, plays an important role in Ca2+ cycling in heart. Recently, sarcolipin has been identified as having a similar function as phospholamban in skeletal muscle. Because phospholamban is differentially expressed in atrial and ventricular myocardia and its expression is often altered in diseased hearts, we investigated the cardiac chamber specificity of sarcolipin expression and its regulation during development and hypertrophic remodeling. Northern blot analysis revealed that the expression of mouse sarcolipin mRNA was most abundant in the atria and was undetectable in the ventricles, indicating an atrial chamber-specific expression pattern. Atrial chamber-specific expression of sarcolipin mRNA was increased during development. These findings were confirmed by in situ hybridization studies. In addition, sarcolipin expression was down-regulated in the atria of hypertrophic heart when induced by ventricular specific overexpression of the activated H-ras gene. In humans, sarcolipin mRNA was also expressed in the atria but not detected in the ventricles, although sarcolipin expression was most abundant in skeletal muscle. Taken together, sarcolipin is likely to be an atrial chamber-specific regulator of Ca2+ cycling in heart.
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Affiliation(s)
- Susumu Minamisawa
- Department of Pediatric Cardiology, Institute of Advanced Biomedical Engineering and Science, Graduate School of Medicine, Tokyo Women's Medical University, Tokyo 162-8666, Japan.
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25
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Zhao XS, Gallardo TD, Lin L, Schageman JJ, Shohet RV. Transcriptional mapping and genomic analysis of the cardiac atria and ventricles. Physiol Genomics 2002; 12:53-60. [PMID: 12502795 DOI: 10.1152/physiolgenomics.00086.2002] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The atria and ventricles of the heart have distinct development, structure, and physiology. However, only a few of the genes that underlie the differences between these tissues are known. We used a murine cardiac cDNA microarray to identify genes differentially expressed in the atria and ventricles. The reliability of these findings is supported by highly concordant repetition of hybridization, recognition of previously known atrial and ventricular isoforms of contractile proteins, and confirmation of results by quantitative PCR and in situ hybridization. We examined the most differentially regulated genes for evolutionarily conserved noncoding sequences and found that atrial-expressed genes have more predicted myocyte enhancer factor-2 (MEF2) binding sites than ventricle-predominant genes. We confirmed that messages for MEF2 family members are more abundant in the atria, as are their protein products. Moreover, the activity of a transgenic reporter construct for MEF2 activity is preferentially upregulated in the atria in response to hypertrophic stimuli. This study provides a greater understanding of the molecular differences between atria and ventricles and establishes the framework for an anatomically detailed evaluation of cardiac transcriptional regulation.
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Affiliation(s)
- Xiao-Song Zhao
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas 75390-8573, USA
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26
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Jane-wit D, Yu M, Edling AE, Kataoka S, Johnson JM, Stull LB, Moravec CS, Tuohy VK. A novel class II-binding motif selects peptides that mediate organ-specific autoimmune disease in SWXJ, SJL/J, and SWR/J mice. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2002; 169:6507-14. [PMID: 12444161 DOI: 10.4049/jimmunol.169.11.6507] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Idiopathic dilated cardiomyopathy (DCM) is responsible for approximately 25% of all cases of congestive heart failure. We have recently shown that immunization of autoimmune-susceptible SWXJ mice with whole cardiac myosin leads to T cell-mediated experimental autoimmune myocarditis (EAMC) and DCM. We have now identified two disease-inducing peptides from cardiac alpha-myosin heavy chain (CAMHC). Our approach involved the use of a novel MHC class II-binding motif contained in several peptides known to be immunogenic in SWXJ (H-2(q,s)) mice or in the parental SJL/J (H-2(s)) or SWR/J (H-2(q)) mouse strains. Two of four CAMHC peptides containing the -KXXS- peptide motif were found to be immunogenic. Immunization of SWXJ or parental SJL/J and SWR/J mice with CAMHC peptides palpha406-425 or palpha1631-1650 resulted in EAMC and DCM, characterized by inflammation, fibrosis, and decompensated right-sided ventricular dilatation. Despite mediating high incidences of severe disease, both peptides were found to be cryptic determinants, thereby providing further evidence for the importance and perhaps predominance of self crypticity in autoimmunity. Both peptides showed dual parental I-A(q) and I-A(s) restriction and mediated passive transfer of disease with activated CD4(+) T cells. An intact motif was necessary for antigenicity because loss of activity occurred in peptides containing nonconservative substitutions at the motif's terminal lysine and serine residues. Our studies provide a new model for EAMC and DCM in strains of mice widely used in autoimmune studies. Moreover, the -KXXS- motif may be particularly useful in implicating previously overlooked proteins as autoimmune targets and in facilitating the development of new organ-specific autoimmune mouse models for human diseases.
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Affiliation(s)
- Daniel Jane-wit
- Department of Immunology, Lerner Research Institute, Cleveland Clinic Foundation, OH 44195, USA
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27
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Shenoy R, Klein I, Ojamaa K. Differential regulation of SR calcium transporters by thyroid hormone in rat atria and ventricles. Am J Physiol Heart Circ Physiol 2001; 281:H1690-6. [PMID: 11557559 DOI: 10.1152/ajpheart.2001.281.4.h1690] [Citation(s) in RCA: 42] [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
Thyroid hormone exerts positive inotropic effects on the heart mediated in part by its regulation of calcium transporter proteins, including sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA2), phospholamban (PLB), and Na(+)/Ca(2+) exchanger (NCX). To further understand the potential cardiac chamber-specific effects of thyroid hormone action, we compared the triiodo-L-thyronine (T(3)) responsiveness of calcium transporter proteins in atrial versus ventricular tissues. Rats were rendered hypothyroid by ingestion of propylthiouracil, and a subgroup of animals was treated with T(3) for 7 days (7 microg/day by constant infusion). Atrial and left ventricular (LV) tissue homogenates were analyzed for expression of SERCA2, PLB, and NCX proteins by Western blot analysis. SERCA2 protein significantly decreased by 50% in hypothyroid LV and was normalized by T(3) treatment. In contrast, SERCA2 protein in atria was unaltered in the hypothyroid state. PLB protein expression significantly increased by 1.6- and 5-fold in the hypothyroid LV and atria, respectively, and returned to euthyroid levels with T(3) treatment. Expression of NCX protein showed a greater response to T(3) treatment in atria tissue than in ventricular tissue. Sarcoplasmic reticulum calcium cycling is determined in part by the ratio of SERCA2 to PLB. This ratio was sixfold higher in the atria compared with LV, suggesting that PLB may play a minor role in the regulation of SERCA2 function in normal atria. We conclude that calcium transporter proteins are responsive to thyroid hormone in a chamber-specific manner, with atria showing a greater change in protein content in response to T(3). The differential effect on atria may account for the occurrence of atrial rather than ventricular arrhythmias in response to even mild degrees of thyrotoxicosis.
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Affiliation(s)
- R Shenoy
- Division of Endocrinology, Department of Medicine, North Shore-Long Island Jewish Health System and New York University School of Medicine, New York, New York 11030, USA
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28
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Kaasik A, Paju K, Minajeva A, Ohisalo J. Decreased expression of phospholamban is not associated with lower beta-adrenergic activation in rat atria. Mol Cell Biochem 2001; 223:109-15. [PMID: 11681711 DOI: 10.1023/a:1017945810355] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The aim of the study was to find out whether low phospholamban level in atria as compared with ventricles is associated with differences in sarcoplasmic reticular Ca2+-uptake and contractile performance. Relationship between phospholamban and beta-adrenergic stimulation in rat left atria and papillary muscles were examined by means of contractile measurements, sarcoplasmic reticular oxalate-supported Ca2+-uptake, and Western blotting of phosphorylated phospholamban. Phosphoprotein determination after beta-adrenergic stimulation demonstrated that the levels of Ser16 and Thr17 phosphorylated phospholamban in atria remained at about one-third of that in ventricles. However, comparison of sarcoplasmic reticular Ca2+-uptake in control and isoproterenol perfused preparations demonstrated that the effect of beta-adrenergic stimulation on sarcoplasmic reticular Ca2+-uptake was stronger in atrial preparations. Moreover, atria responded to isoproterenol with much larger increases in developed tension, contractility and relaxation rates than papillary muscles. Thus, despite lower level of phospholamban, the beta-adrenergic activation of sarcoplasmic reticular Ca2+-uptake and contractile indices are higher in atria.
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Affiliation(s)
- A Kaasik
- Department of Pharmacology, University of Tartu, Estonia
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29
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Brittsan AG, Carr AN, Schmidt AG, Kranias EG. Maximal inhibition of SERCA2 Ca(2+) affinity by phospholamban in transgenic hearts overexpressing a non-phosphorylatable form of phospholamban. J Biol Chem 2000; 275:12129-35. [PMID: 10766848 DOI: 10.1074/jbc.275.16.12129] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholamban is a phosphoprotein in the cardiac sarcoplasmic reticulum (SR) which regulates the apparent Ca(2+) affinity of the SR Ca(2+)-ATPase (SERCA2). To determine the levels of phospholamban which are associated with maximal inhibition of SERCA2, several lines of transgenic mice were generated which expressed increasing levels of a non-phosphorylatable form of phospholamban (S16A,T17A) specifically in the heart. This mutant form of phospholamban was chosen to prevent phosphorylation as a compensatory mechanism in vivo. Quantitative immunoblotting revealed increased phospholamban protein levels of 1.8-, 2.6-, 3.7-, and 4.7-fold in transgenic hearts compared with wild types. There were no changes in the expression levels of SERCA2, calsequestrin, calreticulin, and ryanodine receptor. Assessment of SR Ca(2+) uptake in hearts of transgenic mice indicated increases in the inhibition of the affinity of SERCA2 for Ca(2+) with increased phospholamban expression. Maximal inhibition was obtained at phospholamban expression levels of 2.6-fold or higher. Transgenic hearts with functional saturation in phospholamban:SERCA2 (>/=2.6:1) exhibited increases in beta-myosin heavy chain expression, associated with cardiac hypertrophy. These findings demonstrate that overexpression of a non-phosphorylatable form of phospholamban in transgenic mouse hearts resulted in saturation of the functional phospholamban:SERCA2 ratio at 2.6:1 and suggest that approximately 40% of the SR Ca(2+) pumps are functionally regulated by phospholamban in vivo.
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Affiliation(s)
- A G Brittsan
- Department of Pharmacology and Cell Biophysics, University of Cincinnati, Cincinnati, Ohio 45267, USA
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Zhai J, Schmidt AG, Hoit BD, Kimura Y, MacLennan DH, Kranias EG. Cardiac-specific overexpression of a superinhibitory pentameric phospholamban mutant enhances inhibition of cardiac function in vivo. J Biol Chem 2000; 275:10538-44. [PMID: 10744747 DOI: 10.1074/jbc.275.14.10538] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Phospholamban is a regulator of the Ca(2+) affinity of the cardiac sarcoplasmic reticulum Ca(2+) ATPase (SERCA2a) and of cardiac contractility. In vitro expression studies have shown that several mutant phospholamban monomers are superinhibitory, suggesting that monomeric phospholamban is the active species. However, a phospholamban Asn(27) --> Ala (N27A) mutant, which maintained a normal pentamer to monomer ratio, was shown to act as a superinhibitor of SERCA2a Ca(2+) affinity. To determine whether the pentameric N27A mutant is superinhibitory in vivo, transgenic mice with cardiac-specific overexpression of mutant phospholamban were generated. Quantitative immunoblotting revealed a 61 +/- 6% increase in total phospholamban in mutant hearts, with 90% of the overexpressed protein being pentameric. The EC(50) value for Ca(2+) dependence of Ca(2+) uptake was 0.69 +/- 0.07 microM in mutant hearts, compared with 0.29 +/- 0.02 microM in wild-type hearts or 0. 43 +/- 0.03 microM in hearts overexpressing wild-type PLB by 2-fold. Myocytes from phospholamban N27A mutant hearts also exhibited more depressed contractile parameters than wild-type phospholamban overexpressing cells. The shortening fraction was 52%, rates of shortening and relengthening were 46% and 38% respectively, and time for 80% decay of the Ca(2+) signal was 146%, compared with wild-types (100%). Langendorff-perfused mutant hearts also demonstrated depressed contractile parameters. Furthermore, in vivo echocardiography showed a depression in the ratio of early to late diastolic transmitral velocity and a 79% prolongation of the isovolumic relaxation time. Isoproterenol stimulation did not fully relieve the depressed contractile parameters at the cellular, organ, and intact animal levels. Thus, pentameric phospholamban N27A mutant can act as a superinhibitor of the affinity of SERCA2a for Ca(2+) and of cardiac contractility in vivo.
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Affiliation(s)
- J Zhai
- Department of Pharmacology and Cell Biophysics, University of Cincinnati, Cincinnati, Ohio 45267-0575, USA
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31
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Arai M. Function and regulation of sarcoplasmic reticulum Ca2+-ATPase: advances during the past decade and prospects for the coming decade. JAPANESE HEART JOURNAL 2000; 41:1-13. [PMID: 10807524 DOI: 10.1536/jhj.41.1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
In cardiac muscle, the contraction-relaxation cycle is tightly controlled by the regulated release and uptake of intracellular Ca2+ between sarcoplasmic reticulum and cytoplasm. A major protein controlling Ca2+ cycling is Ca2+-ATPase (SERCA2a) located in the sarcoplasmic reticulum membrane. The function of SERCA2a protein is regulated by the phosphorylatable protein, phospholamban. Phosphorylation of phospholamban releases its inhibitory effect on SERCA2a through direct molecular interaction. Recently, mice whose SERCA2a function is increased (overexpression of the gene) or lost (knock out) were developed. These mice demonstrated that SERCA2a pump levels are a major determinant of cardiac muscle contractility and relaxation. These studies open the prospect that the overexpression of SERCA2a can correct cardiac dysfunction seen in heart failure. Advances in knowledge concerning the function and gene regulation of SERCA2a are discussed in this review.
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Affiliation(s)
- M Arai
- Second Department of Internal Medicine, Gunma University School of Medicine, Maebashi, Japan
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Sarsero D, Molenaar P, Kaumann AJ, Freestone NS. Putative beta 4-adrenoceptors in rat ventricle mediate increases in contractile force and cell Ca2+: comparison with atrial receptors and relationship to (-)-[3H]-CGP 12177 binding. Br J Pharmacol 1999; 128:1445-60. [PMID: 10602323 PMCID: PMC1571781 DOI: 10.1038/sj.bjp.0702936] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
1. We identified putative beta4-adrenoceptors by radioligand binding, measured increases in ventricular contractile force by (-)-CGP 12177 and (+/-)-cyanopindolol and demonstrated increased Ca2+ transients by (-)-CGP 12177 in rat cardiomyocytes. 2. (-)-[3H]-CGP 12177 labelled 13 - 22 fmol mg-1 protein ventricular beta1, beta2-adrenoceptors (pKD approximately 9.0) and 50 - 90 fmol mg-1 protein putative beta4-adrenoceptors (pKD approximately 7.3). The affinity values (pKi) for (beta1,beta2-) and putative beta4-adrenoceptors, estimated from binding inhibition, were (-)-propranolol 8.4, 5.7; (-)-bupranolol 9.7, 5.8; (+/-)-cyanopindolol 10.0,7.4. 3. In left ventricular papillary muscle, in the presence of 30 microM 3-isobutyl-1-methylxanthine, (-)-CGP 12177 and (+/-)-cyanopindolol caused positive inotropic effects, (pEC50, (-)-CGP 12177, 7.6; (+/-)-cyanopindolol, 7.0) which were antagonized by (-)-bupranolol (pKB 6.7 - 7.0) and (-)-CGP 20712A (pKB 6.3 - 6.6). The cardiostimulant effects of (-)-CGP 12177 in papillary muscle, left and right atrium were antagonized by (+/-)-cyanopindolol (pKP 7.0 - 7.4). 4. (-)-CGP 12177 (1 microM) in the presence of 200 nM (-)-propranolol increased Ca2+ transient amplitude by 56% in atrial myocytes, but only caused a marginal increase in ventricular myocytes. In the presence of 1 microM 3-isobutyl-1-methylxanthine and 200 nM (-)-propranolol, 1 microM (-)-CGP 12177 caused a 73% increase in Ca2+ transient amplitude in ventricular myocytes. (-)-CGP 12177 elicited arrhythmic transients in some atrial and ventricular myocytes. 5. Probably by preventing cyclic AMP hydrolysis, 3-isobutyl-1-methylxanthine facilitates the inotropic function of ventricular putative beta4-adrenoceptors, suggesting coupling to Gs protein-adenylyl cyclase. The receptor-mediated increases in contractile force are related to increases of Ca2+ in atrial and ventricular myocytes. The agreement of binding affinities of agonists with cardiostimulant potencies is consistent with mediation through putative beta4-adrenoceptors labelled with (-)-[3H]-CGP 12177.
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Affiliation(s)
- Doreen Sarsero
- Department of Pharmacology, University of Melbourne, Parkville, 3052, Victoria, Australia
| | - Peter Molenaar
- Department of Pharmacology, University of Melbourne, Parkville, 3052, Victoria, Australia
- Cardiovascular Research Unit, Department of Medicine, University of Queensland, Prince Charles Hospital, Chermside, 4032, Queensland, Australia
- Author for correspondence:
| | - Alberto J Kaumann
- Laboratory of Molecular Signalling, The Babraham Institute, Cambridge, CB2 4AT, U.K
- Physiological Laboratory, University of Cambridge, Cambridge, CB2 3EG, U.K
| | - Nicholas S Freestone
- Laboratory of Molecular Signalling, The Babraham Institute, Cambridge, CB2 4AT, U.K
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Weil J, Eschenhagen T, Fleige G, Mittmann C, Orthey E, Scholz H. Localization of preproenkephalin mRNA in rat heart: selective gene expression in left ventricular myocardium. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:H378-84. [PMID: 9683423 DOI: 10.1152/ajpheart.1998.275.2.h378] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
The enkephalins are derived from a common precursor protein known as preproenkephalin (ppENK). Enkephalins appear to be one of the endogenous ligands for the opiate receptors. In the rat the ventricular myocardium contains more ppENK mRNA than any other tissue. To gain further insight into the role of cardiac enkephalins, the regional and developmental distribution of ppENK mRNA was studied by Northern blotting and in situ hybridization. In the early postnatal period, ppENK mRNA is low in atrial and ventricular myocardium. With maturation, ppENK expression increases threefold in left and right ventricular tissue, but not in the atria or cardiac conductive system. Interestingly, ppENK mRNA levels are four times higher in the left than in the right chamber. Thus, to our knowledge, ppENK is the only gene exhibiting marked differences in expression between the adult right and left ventricle. Given the left-side preference of ppENK expression, the possibility is raised that the left ventricle is an endocrine organ that supplies the body with enkephalins.
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Affiliation(s)
- J Weil
- Abteilung Allgemeine Pharmakologie, Universitäts-Krankenhaus Eppendorf, D-20246 Hamburg, Germany
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Haghighi K, Kadambi VJ, Koss KL, Luo W, Harrer JM, Ponniah S, Zhou Z, Kranias EG. In vitro and in vivo promoter analyses of the mouse phospholamban gene. Gene 1997; 203:199-207. [PMID: 9426251 DOI: 10.1016/s0378-1119(97)00514-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
To determine the mechanisms responsible for regulation of the phospholamban (PLB) gene expression, a critical regulatory phosphoprotein in cardiac muscle, the mouse PLB gene was isolated and promoter analysis was performed in vitro and in vivo. The PLB gene consists of two exons separated by a single large intron. Deletion analysis revealed that a 7-kb 5' flanking fragment (including exon 1, the entire intron and part of exon 2) was necessary for maximal transcriptional activity in H9c2 and L6 cell lines. Interestingly, deletion of a 2.4-kb intronic region, which contained repetitive elements, caused a dramatic increase in CAT activity in both these cell lines. In vivo analysis indicated that the PLB fusion gene containing 7 kb of the 5'-flanking region was capable of cardiac specific gene expression in transgenic mice. Furthermore, these mice exhibited 3-fold higher levels of CAT activity in the ventricles compared with the atria, mimicking endogenous PLB mRNA expression. Our findings suggest that: (a) PLB gene expression may be regulated by the interplay of cis-acting regulatory elements located within the 5' flanking and intronic regions; and (b) the 7-kb upstream region is capable of directing cardiac-specific and compartment-specific expression in vivo.
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Affiliation(s)
- K Haghighi
- Department of Pharmacology and Cell Biophysics, University of Cincinnati, College of Medicine, OH 45267-0575, USA
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35
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Minajeva A, Kaasik A, Paju K, Seppet E, Lompré AM, Veksler V, Ventura-Clapier R. Sarcoplasmic reticulum function in determining atrioventricular contractile differences in rat heart. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:H2498-507. [PMID: 9374790 DOI: 10.1152/ajpheart.1997.273.5.h2498] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The relationships between the contractile characteristics and the sarcoplasmic reticulum (SR) function of rat atrial and ventricular trabeculae were compared. The isometric developed tension (DT) and the rates of contraction (+ dT/dt) and relaxation (-dT/dt) normalized to cross-sectional area were 3.7, 2.2, and 1.8 times lower, respectively, in intact atrial strips compared with ventricular strips, whereas + dT/dt and -dT/dt (normalized to DT) were 2.3 and 2.8 times higher, respectively, in atria. Atria exhibited a maximal potentiation of DT after shorter rest periods than ventricles and a lower reversal for prolonged rest periods. Caffeine-induced tension transients in saponin-permeabilized fibers suggested that the Ca2+ concentration released in atrial myofibrils reached a lower maximum and decayed more slowly than in ventricular preparations. However, the tension-time integrals indicated an equivalent capacity of sequestrable Ca2+ in SR from both tissues. In atrial, as in ventricular myocardium, the SR Ca2+ uptake was more efficiently supported by ATP produced by the SR-bound MM form of creatine kinase (CK; MM-CK) than by externally added ATP, suggesting a tight functional coupling between the SR Ca2+ adenosinetriphosphatase (ATPase) and MM-CK. The maximal rate of oxalate-supported Ca2+ uptake was two times higher in atrial than in ventricular tissue homogenates. The SR Ca(2+)-ATPase 2a mRNA content normalized to 18S RNA was 38% higher in atria than in ventricles, whereas the amount of mRNA encoding the alpha-myosin heavy chain, calsequestrin, and the ryanodine receptor was similar in both tissues. Thus a lower amount of readily releasable Ca2+ together with a faster uptake rate may partly account for the shorter time course and lower tension development in intact atrial myocardium compared with ventricular myocardium.
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Affiliation(s)
- A Minajeva
- Department of Pathological Physiology, Medical Faculty, University of Tartu, Estonia
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Slack JP, Grupp IL, Luo W, Kranias EG. Phospholamban ablation enhances relaxation in the murine soleus. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:C1-6. [PMID: 9252436 DOI: 10.1152/ajpcell.1997.273.1.c1] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Phospholamban (PLB) is expressed in slow-twitch skeletal, cardiac, and smooth muscles. Several studies have indicated that it is an important regulator of basal contractility and the stimulatory responses to isoproterenol in the mammalian heart. To determine whether PLB is also a key modulator of slow-twitch skeletal muscle contractility, we examined isometric twitch contractions of isolated, intact soleus muscles from wild-type (WT) and PLB-deficient mice in parallel. Soleus muscles from PLB-deficient mice exhibited a significant (25%) decrease in the time to half relaxation, with no change in contraction time compared with WT soleus muscles. The observed enhancement of relaxation in the PLB-deficient soleus was not associated with alterations in the protein levels of either the sarcoplasmic reticular Ca(2+)-adenosinetriphosphatase or the ryanodine receptor. Examination of the effects of isoproterenol on the twitch kinetics of these muscles revealed 1) no effect on the contraction times of either WT or PLB-deficient muscles and 2) a significant decrease in the half relaxation time of the WT soleus, whereas this parameter remained unchanged in the PLB-deficient muscle. Furthermore, with maximal isoproterenol stimulation, the half relaxation time of the WT soleus was similar to that of the nonstimulated PLB-deficient soleus. These results suggest that PLB is a key determinant of relaxation in slow-twitch skeletal muscle under basal conditions and during isoproterenol stimulation.
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Affiliation(s)
- J P Slack
- Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0575, USA
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Koss KL, Grupp IL, Kranias EG. The relative phospholamban and SERCA2 ratio: a critical determinant of myocardial contractility. Basic Res Cardiol 1997; 92 Suppl 1:17-24. [PMID: 9202840 DOI: 10.1007/bf00794064] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Phospholamban is a regulatory phosphoprotein which modulates the active transport of Ca2+ by the cardiac sarcoplasmic reticular Ca(2+)-ATPase enzyme (SERCA2) into the lumen of the sarcoplasmic reticulum. Phospholamban, which is a reversible inhibitor of SERCA2, represses the enzyme's activity, and this inhibition is relieved upon phosphorylation of phospholamban in response to beta-adrenergic stimulation. In this way, phospholamban is an important regulator of SERCA2-mediated myocardial relaxation during diastole. This report centers on the hypothesis that the relative levels of phospholamban: SERCA2 in cardiac muscle plays an important role in the muscle's overall contractility status. This hypothesis was tested by comparing the contractile parameters of: a) murine atrial and ventricular muscles, which differentially express phospholamban, and b) murine wild-type and phospholamban knock-out hearts. These comparisons revealed that atrial muscles, which have a 4.2-fold lower phospholamban: SERCA2 ratio than ventricular muscles, exhibited rates of force development and relaxation of tension, which were three-fold faster that these parameters for ventricular muscles. Similar comparisons were made via analyses of left-ventricular pressure development recorded for isolated, work-performing hearts from wild-type and phospholamban knock-out mice. In these studies, hearts from phospholamban knock-out mice, which were devoid of phospholamban, exhibited enhanced parameters of left-ventricular contractility in comparison to wild-type hearts. These results suggest that the relative phospholamban: SERCA2 ratio is critical in the regulation of myocardial contractility and alterations in this ratio may contribute to the functional deterioration observed during heart failure.
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Affiliation(s)
- K L Koss
- Dept. of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267-0575, USA
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Ohkusa T, Noma T, Ueyama T, Hisamatsu Y, Yano M, Esato K, Nakazawa A, Matsuzaki M. Differences in sarcoplasmic reticulum gene expression in myocardium from patients undergoing cardiac surgery. Quantification of steady-state levels of messenger RNA using the reverse transcription-polymerase chain reaction. Heart Vessels 1997; 12:1-9. [PMID: 9288554 DOI: 10.1007/bf01747496] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Little is known about any alterations in sarcoplasmic reticulum (SR) gene expression associated with cardiac diseases of varying degrees of severity. We assessed, using the reverse transcription-polymerase chain reaction (RT-PCR) technique, SR Ca2+ transport protein gene expression in small tissue samples from failing hearts in patients undergoing cardiac surgery. Total RNA was extracted from 30- to 50-mg samples from the hearts of 13 patients with coronary artery disease, congenital heart disease, or valvular heart disease. We used RT-PCR to synthesize and amplify cDNA encoding cardiac SR Ca(2+)-ATPase, ryanodine receptor (RYR), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The amount of each mRNA in the sample was expressed relative to the amount of GAPDH mRNA. The expression level of each mRNA was correlated with the cardiac functional index. The mRNA levels for Ca(2+)-ATPase and RYR varied between heart samples, but showed a positive correlation with left ventricular ejection fraction. Ca(2+)-ATPase mRNA levels showed in inverse relationship with plasma brain natriuretic peptide. In addition, we isolated partial cDNA encoding a human cardiac RYR. The cDNA consisted of 487 nucleotides, and the nucleotide and deduced amino acid sequences showed 93% and 99% homology, respectively, to those of rabbit cardiac RYR. These results suggest that decreased levels of mRNA for SR Ca2+ transport protein could be related to abnormal cardiac function, regardless of the etiology of the heart disease. RT-PCR provides a rapid and economical way of quantifying the expression of multiple genes in small specimens and may, therefore, aid understanding of the pathophysiology and treatment of heart disease.
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Affiliation(s)
- T Ohkusa
- Second Department of Internal Medicine, Yamaguchi University School of Medicine, Japan
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Abstract
The Ca2+ concentration within the myocyte is an important determinant of myocardial contractility. Substantial changes in the cellular processes responsible for transport of Ca2+ ions across the sarcolemmal and sarcoplasmic reticulum membranes occur during maturation of the heart. In this article, the mechanisms underlying these changes and their impact on myocardial performance are discussed in detail.
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Affiliation(s)
- L Mahony
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas 75235-9063, USA
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Remppis A, Greten T, Schäfer BW, Hunziker P, Erne P, Katus HA, Heizmann CW. Altered expression of the Ca(2+)-binding protein S100A1 in human cardiomyopathy. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1313:253-7. [PMID: 8898862 DOI: 10.1016/0167-4889(96)00097-3] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The Ca(2+)-binding protein S100A1 displays a tissue-specific expression pattern with highest levels in myocardium and has been shown to interact with SR-proteins regulating the Ca(2+)-induced Ca(2+)-release. We, therefore, hypothesized that changes in S100A1 gene expression might correlate with the pathognomonic finding of altered SR Ca(2+)-transients in human end stage heart failure. To test this hypothesis, we established a specific and sensitive method to analyse S100A1 expression in cardiac tissues by employing hydrophobic interaction-chromatography and reversed-phase high performance liquid chromatography (RP-HPLC) coupled with Electron-Ionisation-Mass-Spectrometry (ESI-MS). Porcine myocardium showed a differential expression of S100A1 with relative protein concentrations of 62 +/- 8% in the right ventricle (RV), 57 +/- 9% in the right atrium (RA), and 25 +/- 15% in the left atrium (LA) as compared to the left ventricle (LV) (100 +/- 10%; P < 0.001). Northern blot analyses confirmed a likewise distribution of porcine S100A1 mRNA implying a regulation on the transcriptional level. Analyses of left ventricular specimen of patients with end stage heart failure (CHF, n = 6; CHD, n = 6) revealed significantly reduced S100A1 protein levels, while integration of S100A1 peaks after RP-HPLC yielded two groups of patients with < 76% (69 +/- 7%, n = 6) and < 35% (23 +/- 12%, n = 6) respectively as compared to controls (100 +/- 8%, n = 3). These data demonstrate for the first time that S100A1 is differentially expressed in myocardium and that in human cardiomyopathy a reduced expression of S100A1 may contribute to a compromised contractility.
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Affiliation(s)
- A Remppis
- Abteilung für Klinische Chemie, Kinderspital, Universität Zürich, Switzerland
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41
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Kaumann AJ, Sanders L, Lynham JA, Bartel S, Kuschel M, Karczewski P, Krause EG. Beta 2-adrenoceptor activation by zinterol causes protein phosphorylation, contractile effects and relaxant effects through a cAMP pathway in human atrium. Mol Cell Biochem 1996; 163-164:113-23. [PMID: 8974046 DOI: 10.1007/bf00408647] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Evidence from ventricular preparations of cat, sheep, rat and dog suggests that both beta 1-adrenoceptors (beta 1AR) and beta 2-adrenoceptors (beta 2AR) mediate positive inotropic effects but that only beta 1AR do it through activation of a cAMP pathway. On the other hand, our evidence has shown that both beta 1AR and beta 2AR hasten relaxation of isolated human myocardium consistent with a common cAMP pathway. We have now investigated in the isolated human right atrial appendage, a tissue whose beta-AR comprise around 2/3 of beta 1AR and 1/3 of beta 2AR, whether or not beta 2AR-mediated effects occur via activation of a cAMP pathway. We carried out experiments on atria obtained from patients without advanced heart failure undergoing open heart surgery. To activate beta 2AR, we used the beta 2AR-selective ligand zinterol. Experiments were carried out on paced atrial strips (1 Hz) and tissue homogenates and membrane particles. Zinterol caused positive inotropic and lusitropic (i.e. reduction of t1/2 of relaxation) effects with EC50 values of 3 and 2 nM, respectively. The zinterol-evoked effects were unaffected by the beta 1AR-selective antagonist CGP 20712A (300 nM) but blocked surmountably by the beta 2AR-selective antagonist ICI 118551 (50 nM) which reduced both EC50 values to 1 microM. Zinterol stimulated adenylyl cyclase activity with an EC50 of 30 nM and intrinsic activity of 0.75 with respect to (-)-isoprenaline (600 microM); the effects were resistant to blockade by CGP 20712A (300 nM) but antagonised surmountably by ICI 118551 (50 nM). Zinterol bound to membrane beta AR labelled with (-)-[125I] cyanopindolol with higher affinity for beta 2AR than for beta 1AR; the binding to beta 2AR but not to beta 1AR was reduced by GTP gamma S (10 microM). In the presence of CGP 20712A (300 nM) (-)-isoprenaline (400 microM) (to activate both beta 1AR and beta 2AR maximally) and zinterol (10 microM) increased contractile force 3.4-fold and 2.5-fold respectively and reduced relaxation t1/2 by 32% and 18% respectively. These effects of (-)-isoprenaline and zinterol were associated (5 min incubation) with phosphorylation (pmol P/mg supernatant protein) of troponin I and C-protein to values of 8.4 +/- 2.0 vs 12.4 +/- 2.3 and 10.1 +/- 2.5 vs 8.6 +/- 1.6 respectively. (-)-Isoprenaline and zinterol also caused phosphorylation of phospholamban (1.8 +/- 0.3 vs 0.4 +/- 0.1 pmol P/mg respectively) specifically at serine residues. We conclude that in human atrial myocardium activation of both beta 1AR and beta 2AR leads to cAMP-dependent phosphorylation of proteins involved in augmenting both contractility and relaxation.
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Affiliation(s)
- A J Kaumann
- Human Pharmacology Laboratory, Babraham Institute, Cambridge, UK
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42
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Kadambi VJ, Ponniah S, Harrer JM, Hoit BD, Dorn GW, Walsh RA, Kranias EG. Cardiac-specific overexpression of phospholamban alters calcium kinetics and resultant cardiomyocyte mechanics in transgenic mice. J Clin Invest 1996; 97:533-9. [PMID: 8567978 PMCID: PMC507048 DOI: 10.1172/jci118446] [Citation(s) in RCA: 227] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Phospholamban is the regulator of the cardiac sarcoplasmic reticulum (SR) Ca(2+)-ATPase activity and an important modulator of basal contractility in the heart. To determine whether all the SR Ca(2+)-ATPase enzymes are subject to regulation by phospholamban in vivo, transgenic mice were generated which overexpressed phospholamban in the heart, driven by the cardiac-specific alpha-myosin heavy chain promoter. Quantitative immunoblotting revealed a twofold increase in the phospholamban protein levels in transgenic hearts compared to wild type littermate hearts. The transgenic mice showed no phenotypic alterations and no changes in heart/body weight, heart/lung weight, and cardiomyocyte size. Isolated unloaded cardiac myocytes from transgenic mice exhibited diminished shortening fraction (63%) and decreased rates of shortening (64%) and relengthening (55%) compared to wild type (100%) cardiomyocytes. The decreases in contractile parameters of transgenic cardiomyocytes reflected decreases in the amplitude (83%) of the Ca2+ signal and prolongation (131%) in the time for decay of the Ca2+ signal, which was associated with a decrease in the apparent affinity of the SR Ca(2+)-ATPase for Ca2+ (56%), compared to wild type (100%) cardiomyocytes. In vivo analysis of left ventricular systolic function using M mode and pulsed-wave Doppler echocardiography revealed decreases in fractional shortening (79%) and the normalized mean velocity of circumferential shortening (67%) in transgenic mice compared to wild type (100%) mice. The differences in contractile parameters and Ca2+ kinetics in transgenic cardiomyocytes and the depressed left ventricular systolic function in transgenic mice were abolished upon isoproterenol stimulation. These findings indicate that a fraction of the Ca(2+)-ATPases in native SR is not under regulation by phospholamban. Expression of additional phospholamban molecules results in: (a) inhibition of SR Ca2+ transport; (b) decreases in systolic Ca2+ levels and contractile parameters in ventricular myocytes; and (c) depression of basal left ventricular systolic function in vivo.
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Affiliation(s)
- V J Kadambi
- Department of Pharmacology, University of Cincinnati, College of Medicine, Ohio 45267, USA
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