1
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Velmurugan S, Liu T, Chen KC, Despa F, O'Rourke B, Despa S. Distinct Effects of Mitochondrial Na +/Ca 2+ Exchanger Inhibition and Ca 2+ Uniporter Activation on Ca 2+ Sparks and Arrhythmogenesis in Diabetic Rats. J Am Heart Assoc 2023; 12:e029997. [PMID: 37421267 PMCID: PMC10382117 DOI: 10.1161/jaha.123.029997] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2023] [Accepted: 05/26/2023] [Indexed: 07/10/2023]
Abstract
Background Mitochondrial dysfunction contributes to the cardiac remodeling triggered by type 2 diabetes (T2D). Mitochondrial Ca2+ concentration ([Ca2+]m) modulates the oxidative state and cytosolic Ca2+ regulation. Thus, we investigated how T2D affects mitochondrial Ca2+ fluxes, the downstream consequences on myocyte function, and the effects of normalizing mitochondrial Ca2+ transport. Methods and Results We compared myocytes/hearts from transgenic rats with late-onset T2D (rats that develop late-onset T2D due to heterozygous expression of human amylin in the pancreatic β-cells [HIP] model) and their nondiabetic wild-type (WT) littermates. [Ca2+]m was significantly lower in myocytes from diabetic HIP rats compared with WT cells. Ca2+ extrusion through the mitochondrial Na+/Ca2+ exchanger (mitoNCX) was elevated in HIP versus WT myocytes, particularly at moderate and high [Ca2+]m, while mitochondrial Ca2+ uptake was diminished. Mitochondrial Na+ concentration was comparable in WT and HIP rat myocytes and remained remarkably stable while manipulating mitoNCX activity. Lower [Ca2+]m was associated with oxidative stress, increased sarcoplasmic reticulum Ca2+ leak in the form of Ca2+ sparks, and mitochondrial dysfunction in T2D hearts. MitoNCX inhibition with CGP-37157 reduced oxidative stress, Ca2+ spark frequency, and stress-induced arrhythmias in HIP rat hearts while having no significant effect in WT rats. In contrast, activation of the mitochondrial Ca2+ uniporter with SB-202190 enhanced spontaneous sarcoplasmic reticulum Ca2+ release and had no significant effect on arrhythmias in both WT and HIP rat hearts. Conclusions [Ca2+]m is reduced in myocytes from rats with T2D due to a combination of exacerbated mitochondrial Ca2+ extrusion through mitoNCX and impaired mitochondrial Ca2+ uptake. Partial mitoNCX inhibition limits sarcoplasmic reticulum Ca2+ leak and arrhythmias in T2D hearts, whereas mitochondrial Ca2+ uniporter activation does not.
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Affiliation(s)
- Sathya Velmurugan
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKYUSA
| | - Ting Liu
- Division of Cardiology, Department of MedicineThe Johns Hopkins UniversityBaltimoreMDUSA
| | - Kuey C. Chen
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKYUSA
| | - Florin Despa
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKYUSA
| | - Brian O'Rourke
- Division of Cardiology, Department of MedicineThe Johns Hopkins UniversityBaltimoreMDUSA
| | - Sanda Despa
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKYUSA
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2
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Gopal Viswanathan V, Verma N, D. Winford E, Kotiya D, E. Radulescu L, Leibold N, C. Chen K, Despa S, A. Hill D, Muehlbauer M, R. Bain J, Despa F. Abstract 128:
In Vivo
Downregulation Of Pancreatic Amylin In Diabetic Mice Improves Recognition Memory. Stroke 2023. [DOI: 10.1161/str.54.suppl_1.128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Hypersecretion of amylin, a β-cell hormone that regulates satiation, is common in individuals with prediabetes and is associated with pancreatic amyloid deposition and type-2 diabetes. Evidence has emerged that increased circulating levels of amyloid-forming human amylin may potentially impair brain function. Because mouse amylin is non-amyloidogenic, we generated transgenic mice with
conditional
pancreatic expression of amyloid-forming human amylin to study how
in vivo
knockdown of human amylin expression influences brain function during the development of type-2 diabetes. Males and females were fed a high-fat diet starting at 3 months of age to induce amylin hypersecretion and glucose dysregulation. Males developed hyperglycemia at 5 months of age, whereas females showed glucose dysregulation 3-4 months later. At 5 months of age, human amylin-expressing male mice were randomly assigned to either amylin downregulation group (by peritoneal tamoxifen injection) or control group (maintained amylin expression) (n = 10/group). Two months later, we assessed brain function with the novel object recognition test and performed comparative non-targeted metabolomics and global RNA-seq analyses of hippocampal tissue. Mice with downregulated human amylin show enhanced recognition memory index (p < 0.001) and lower blood glucose levels (p < 0.001) compared to those that continued to express human amylin. This was associated with increased hippocampal levels of glycolysis metabolites, including lactic acid (p < 0.01), glucose-6-phosphate (p = 0.06), and fructose (p = 0.07). Hippocampal gene-expression patterns between the two mouse groups revealed extensive compensatory changes in gene expression related to glucose metabolism. In conclusion, amylin downregulation in diabetic mice improves systemic glucose homeostasis and memory. Molecular processes associated with improved memory involve increased hippocampal glycolytic fluxes and compensatory gene expression.
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3
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Verma N, Velmurugan GV, Winford E, Coburn H, Kotiya D, Leibold N, Radulescu L, Despa S, Chen KC, Van Eldik LJ, Nelson PT, Wilcock DM, Jicha GA, Stowe AM, Goldstein LB, Powel DK, Walton JH, Navedo MF, Nystoriak MA, Murray AJ, Biessels GJ, Troakes C, Zetterberg H, Hardy J, Lashley T, Despa F. Aβ efflux impairment and inflammation linked to cerebrovascular accumulation of amyloid-forming amylin secreted from pancreas. Commun Biol 2023; 6:2. [PMID: 36596993 PMCID: PMC9810597 DOI: 10.1038/s42003-022-04398-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 12/21/2022] [Indexed: 01/04/2023] Open
Abstract
Impairment of vascular pathways of cerebral β-amyloid (Aβ) elimination contributes to Alzheimer disease (AD). Vascular damage is commonly associated with diabetes. Here we show in human tissues and AD-model rats that bloodborne islet amyloid polypeptide (amylin) secreted from the pancreas perturbs cerebral Aβ clearance. Blood amylin concentrations are higher in AD than in cognitively unaffected persons. Amyloid-forming amylin accumulates in circulating monocytes and co-deposits with Aβ within the brain microvasculature, possibly involving inflammation. In rats, pancreatic expression of amyloid-forming human amylin indeed induces cerebrovascular inflammation and amylin-Aβ co-deposits. LRP1-mediated Aβ transport across the blood-brain barrier and Aβ clearance through interstitial fluid drainage along vascular walls are impaired, as indicated by Aβ deposition in perivascular spaces. At the molecular level, cerebrovascular amylin deposits alter immune and hypoxia-related brain gene expression. These converging data from humans and laboratory animals suggest that altering bloodborne amylin could potentially reduce cerebrovascular amylin deposits and Aβ pathology.
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Affiliation(s)
- Nirmal Verma
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA
| | | | - Edric Winford
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- Department of Neuroscience, University of Kentucky, Lexington, KY, USA
| | - Han Coburn
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
| | - Deepak Kotiya
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA
| | - Noah Leibold
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA
| | - Laura Radulescu
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA
| | - Kuey C Chen
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA
- UKHC Genomics Laboratory, University of Kentucky, Lexington, KY, USA
| | - Linda J Van Eldik
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY, USA
| | - Peter T Nelson
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY, USA
| | - Donna M Wilcock
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY, USA
- Department of Physiology, University of Kentucky, Lexington, KY, USA
| | - Gregory A Jicha
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, KY, USA
- Department of Neurology, University of Kentucky, Lexington, KY, USA
| | - Ann M Stowe
- Department of Neurology, University of Kentucky, Lexington, KY, USA
| | | | - David K Powel
- Magnetic Resonance Imaging and Spectroscopy Center, University of Kentucky, Lexington, KY, USA
| | | | - Manuel F Navedo
- Department of Pharmacology, University of California, Davis, CA, USA
| | | | - Andrew J Murray
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, CB2 3EG, UK
| | - Geert Jan Biessels
- Department of Neurology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Claire Troakes
- Basic and Clinical Neuroscience Department, King's College London, London, UK
| | - Henrik Zetterberg
- Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Mölndal, Sweden
- Clinical Neurochemistry Laboratory, Sahlgrenska University Hospital, Mölndal, Sweden
- Department of Neurodegenerative Disease, UCL Queen Square Institute of Neurology, Queen Square, London, WC1N 3BG, UK
- UK Dementia Research Institute at UCL and Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, London, UK
| | - John Hardy
- Department of Neurodegenerative Disease, UCL Queen Square Institute of Neurology, Queen Square, London, WC1N 3BG, UK
- UK Dementia Research Institute at UCL and Department of Neurodegenerative Disease, UCL Institute of Neurology, University College London, London, UK
- Reta Lila Weston Institute, UCL Queen Square Institute of Neurology, 1 Wakefield Street, London, WC1N 1PJ, UK
- UCL Movement Disorders Centre, University College London, London, UK
- Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong SAR, China
| | - Tammaryn Lashley
- Department of Neurodegenerative Disease, UCL Queen Square Institute of Neurology, Queen Square, London, WC1N 3BG, UK
- Queen Square Brain Bank for Neurological Disorders, Department of Clinical and Movement Neuroscience, UCL Queen Square Institute of Neurology, London, UK
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, USA.
- The Research Center for Healthy Metabolism, University of Kentucky, Lexington, KY, USA.
- Department of Neuroscience, University of Kentucky, Lexington, KY, USA.
- Department of Neurology, University of Kentucky, Lexington, KY, USA.
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4
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Swietach P, Despa S. Channelling protons out of the heart. J Physiol 2022; 600:2551-2552. [PMID: 35490392 PMCID: PMC9322403 DOI: 10.1113/jp283250] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Accepted: 04/28/2022] [Indexed: 11/24/2022] Open
Affiliation(s)
- Pawel Swietach
- Department of Physiology Anatomy & Genetics Parks Road Oxford OX1 3PT UK
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences University of Kentucky 900 S Limestone, CTW 465 Lexington KY 40536 USA
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5
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Velmurugan S, Mair H, Yin G, Despa F, Despa S. Inhibition of sodium glucose cotransporter 1 reduces arrhythmogenesis in diabetic rats. Biophys J 2022. [DOI: 10.1016/j.bpj.2021.11.1237] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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6
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Verma N, Srodulski S, Velmurugan S, Hoskins A, Pandey VK, Despa F, Despa S. Gestational diabetes triggers postpartum cardiac hypertrophy via activation of calcineurin/NFAT signaling. Sci Rep 2021; 11:20926. [PMID: 34686739 PMCID: PMC8536766 DOI: 10.1038/s41598-021-00422-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Accepted: 10/12/2021] [Indexed: 01/11/2023] Open
Abstract
Population-based studies identified an association between a prior pregnancy complicated by gestational diabetes mellitus (GDM) and cardiac hypertrophy and dysfunction later in life. It is however unclear whether GDM initiates this phenotype and what are the underlying mechanisms. We addressed these questions by using female rats that express human amylin (HIP rats) as a GDM model and their wild-type (WT) littermates as the normal pregnancy model. Pregnant and two months postpartum HIP females had increased left-ventricular mass and wall thickness compared to non-pregnant HIP females, which indicates the presence of concentric hypertrophy. These parameters were unchanged in WT females during both pregnancy and postpartum periods. Hypertrophic Ca2+-dependent calcineurin/NFAT signaling was stimulated two months after giving birth in HIP females but not in the WT. In contrast, the CaMKII/HDAC hypertrophy pathway was active immediately after giving birth and returned to the baseline by two months postpartum in both WT and HIP females. Myocytes from two months postpartum HIP females exhibited slower Ca2+ transient relaxation and higher diastolic Ca2+ levels, which may explain calcineurin activation. No such effects occurred in the WT. These results suggest that a GDM-complicated pregnancy accelerates the development of pathological cardiac remodeling likely through activation of calcineurin/NFAT signaling.
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Affiliation(s)
- Nirmal Verma
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Sarah Srodulski
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Sathya Velmurugan
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Amanda Hoskins
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Vivek K Pandey
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, CTW 465, Lexington, KY, 40536, USA.
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7
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Ly H, Verma N, Sharma S, Kotiya D, Despa S, Abner EL, Nelson PT, Jicha GA, Wilcock DM, Goldstein LB, Guerreiro R, Brás J, Hanson AJ, Craft S, Murray AJ, Biessels GJ, Troakes C, Zetterberg H, Hardy J, Lashley T, AESG, Despa F. The association of circulating amylin with β-amyloid in familial Alzheimer's disease. Alzheimers Dement (N Y) 2021; 7:e12130. [PMID: 33521236 PMCID: PMC7816817 DOI: 10.1002/trc2.12130] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 11/13/2020] [Accepted: 11/25/2020] [Indexed: 01/11/2023]
Abstract
INTRODUCTION This study assessed the hypothesis that circulating human amylin (amyloid-forming) cross-seeds with amyloid beta (Aβ) in early Alzheimer's disease (AD). METHODS Evidence of amylin-AD pathology interaction was tested in brains of 31 familial AD mutation carriers and 20 cognitively unaffected individuals, in cerebrospinal fluid (CSF) (98 diseased and 117 control samples) and in genetic databases. For functional testing, we genetically manipulated amylin secretion in APP/PS1 and non-APP/PS1 rats. RESULTS Amylin-Aβ cross-seeding was identified in AD brains. High CSF amylin levels were associated with decreased CSF Aβ42 concentrations. AD risk and amylin gene are not correlated. Suppressed amylin secretion protected APP/PS1 rats against AD-associated effects. In contrast, hypersecretion or intravenous injection of human amylin in APP/PS1 rats exacerbated AD-like pathology through disruption of CSF-brain Aβ exchange and amylin-Aβ cross-seeding. DISCUSSION These findings strengthened the hypothesis of circulating amylin-AD interaction and suggest that modulation of blood amylin levels may alter Aβ-related pathology/symptoms.
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Affiliation(s)
- Han Ly
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA,The Research Center for Healthy MetabolismUniversity of KentuckyLexingtonKentuckyUSA
| | - Nirmal Verma
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA,The Research Center for Healthy MetabolismUniversity of KentuckyLexingtonKentuckyUSA
| | - Savita Sharma
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA
| | - Deepak Kotiya
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA,The Research Center for Healthy MetabolismUniversity of KentuckyLexingtonKentuckyUSA
| | - Sanda Despa
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA,The Research Center for Healthy MetabolismUniversity of KentuckyLexingtonKentuckyUSA
| | - Erin L. Abner
- Department of EpidemiologyCollege of Public HealthUniversity of KentuckyLexingtonKentuckyUSA,Sanders‐Brown Center on AgingUniversity of KentuckyLexingtonKentuckyUSA
| | - Peter T. Nelson
- Sanders‐Brown Center on AgingUniversity of KentuckyLexingtonKentuckyUSA
| | - Gregory A. Jicha
- Sanders‐Brown Center on AgingUniversity of KentuckyLexingtonKentuckyUSA,Department of NeurologyUniversity of KentuckyLexingtonKentuckyUSA
| | - Donna M. Wilcock
- Sanders‐Brown Center on AgingUniversity of KentuckyLexingtonKentuckyUSA,Department of PhysiologyUniversity of KentuckyLexingtonKentuckyUSA
| | | | - Rita Guerreiro
- Center for Neurodegenerative ScienceVan Andel Research InstituteGrand RapidsMichiganUSA
| | - José Brás
- Center for Neurodegenerative ScienceVan Andel Research InstituteGrand RapidsMichiganUSA
| | - Angela J. Hanson
- Memory & Brain Wellness CenterUniversity of WashingtonSeattleWashingtonUSA
| | - Suzanne Craft
- Department of Gerontology and Geriatric MedicineWake Forest School of MedicineWinston‐SalemNorth CarolinaUSA
| | - Andrew J. Murray
- Department of PhysiologyDevelopment and NeuroscienceUniversity of CambridgeCambridgeUK
| | - Geert Jan Biessels
- Department of NeurologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Claire Troakes
- Basic and Clinical Neuroscience DepartmentKing's College LondonLondonUK
| | - Henrik Zetterberg
- Department of Psychiatry and NeurochemistryInstitute of Neuroscience and PhysiologyThe Sahlgrenska Academy at the University of GothenburgMölndalSweden,Clinical Neurochemistry LaboratorySahlgrenska University HospitalMölndalSweden,Department of Neurodegenerative DiseaseUCL Queen Square Institute of NeurologyQueen Square, LondonUK,UK Dementia Research Institute at UCL and Department of Neurodegenerative DiseaseUCL Institute of NeurologyUniversity College LondonLondonUK
| | - John Hardy
- Department of Neurodegenerative DiseaseUCL Queen Square Institute of NeurologyQueen Square, LondonUK,UK Dementia Research Institute at UCL and Department of Neurodegenerative DiseaseUCL Institute of NeurologyUniversity College LondonLondonUK,Reta Lila Weston InstituteUCL Queen Square Institute of NeurologyLondonUK,UCL Movement Disorders CentreUniversity College LondonLondonUK,Institute for Advanced StudyThe Hong Kong University of Science and TechnologyHong Kong SARChina
| | - Tammaryn Lashley
- Department of Neurodegenerative DiseaseUCL Queen Square Institute of NeurologyQueen Square, LondonUK,Queen Square Brain Bank for Neurological DisordersDepartment of Clinical and Movement NeuroscienceUCL Queen Square Institute of NeurologyLondonUK
| | - AESG
- Alzheimer's disease Exome Sequencing Group: Guerreiro R, Brás J, Sassi C, Gibbs JR, Hernandez D, Lupton MK, Brown K, Morgan K, Powell J, Singleton A, Hardy J.
| | - Florin Despa
- Department of Pharmacology and Nutritional SciencesUniversity of KentuckyLexingtonKentuckyUSA,The Research Center for Healthy MetabolismUniversity of KentuckyLexingtonKentuckyUSA,Department of NeurologyUniversity of KentuckyLexingtonKentuckyUSA
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8
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Verma N, Liu M, Ly H, Loria A, Campbell KS, Bush H, Kern PA, Jose PA, Taegtmeyer H, Bers DM, Despa S, Goldstein LB, Murray AJ, Despa F. Diabetic microcirculatory disturbances and pathologic erythropoiesis are provoked by deposition of amyloid-forming amylin in red blood cells and capillaries. Kidney Int 2020; 97:143-155. [PMID: 31739987 PMCID: PMC6943180 DOI: 10.1016/j.kint.2019.07.028] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2019] [Revised: 07/23/2019] [Accepted: 07/25/2019] [Indexed: 01/11/2023]
Abstract
In the setting of type-2 diabetes, there are declines of structural stability and functionality of blood capillaries and red blood cells (RBCs), increasing the risk for microcirculatory disturbances. Correcting hyperglycemia is not entirely effective at reestablishing normal cellular metabolism and function. Therefore, identification of pathological changes occurring before the development of overt hyperglycemia may lead to novel therapeutic targets for reducing the risk of microvascular dysfunction. Here we determine whether RBC-capillary interactions are altered by prediabetic hypersecretion of amylin, an amyloid forming hormone co-synthesized with insulin, and is reversed by endothelial cell-secreted epoxyeicosatrienoic acids. In patients, we found amylin deposition in RBCs in association with type-2 diabetes, heart failure, cancer and stroke. Amylin-coated RBCs have altered shape and reduced functional (non-glycated) hemoglobin. Amylin-coated RBCs administered intravenously in control rats upregulated erythropoietin and renal arginase expression and activity. We also found that diabetic rats expressing amyloid-forming human amylin in the pancreas (the HIP rat model) have increased tissue levels of hypoxia-inducible transcription factors, compared to diabetic rats that express non-amyloid forming rat amylin (the UCD rat model). Upregulation of erythropoietin correlated with lower hematocrit in the HIP model indicating pathologic erythropoiesis. In the HIP model, pharmacological upregulation of endogenous epoxyeicosatrienoic acids protected the renal microvasculature against amylin deposition and also reduced renal accumulation of HIFs. Thus, prediabetes induces dysregulation of amylin homeostasis and promotes amylin deposition in RBCs and the microvasculature altering RBC-capillary interaction leading to activation of hypoxia signaling pathways and pathologic erythropoiesis. Hence, dysregulation of amylin homeostasis could be a therapeutic target for ameliorating diabetic vascular complications.
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Affiliation(s)
- Nirmal Verma
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Miao Liu
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Han Ly
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Analia Loria
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Kenneth S Campbell
- Department of Physiology, University of Kentucky, Lexington, Kentucky, USA
| | - Heather Bush
- Department of Biostatistics, College of Public Health, University of Kentucky, Lexington, Kentucky, USA
| | - Philip A Kern
- Division of Endocrinology, Department of Medicine, University of Kentucky, Lexington, Kentucky, USA
| | - Pedro A Jose
- Department of Medicine, Division of Renal Diseases and Hypertension, The George Washington University School of Medicine and Health Sciences, Washington, DC, USA
| | - Heinrich Taegtmeyer
- Department of Internal Medicine, McGovern Medical School at University of Texas Health, Houston, Texas, USA
| | - Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, California, USA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA
| | - Larry B Goldstein
- Department of Neurology, University of Kentucky, Lexington, Kentucky, USA
| | - Andrew J Murray
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, UK
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky, USA; Department of Neurology, University of Kentucky, Lexington, Kentucky, USA.
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9
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Abstract
Intracellular Na
+
concentration ([Na
+
]
i
) regulates Ca
2+
cycling, oxidative state and electrical stability of the heart. [Na
+
]
i
is linked to glucose uptake through the Na
+
-glucose cotransporter (SGLT). The SGLT1 isoform is present in the heart and its overexpression causes hypertrophy and left-ventricular dysfunction. Here, we hypothesized that cardiac SGLT activity is increased in type-2 diabetes (T2D), which causes myocyte Na
+
overload and results in oxidative stress and exacerbated sarcoplasmic reticulum (SR) Ca
2+
leak. To test this hypothesis, we analyzed myocardial tissue from humans with/without T2D and compared rats with late-onset T2D that display diabetic cardiomyopathy similar to that seen in humans (HIP rats) with their non-diabetic littermates (WT). SGLT1 expression was increased in hearts from T2D patients compared to non-diabetic individuals and in hearts from HIP
vs
. WT rats. SGLT inhibition significantly decreased the uptake of both glucose and Na
+
in myocytes from HIP rats but not in WT, which indicates that SGLT function is increased in T2D hearts. While SGLT1 upregulation may partially compensate for the reduced insulin-dependent glucose uptake, the ensuing raise in Na
+
influx resulted in elevated [Na
+
]
i
in HIP myocytes (by 3 mM compared to WT). Higher [Na
+
]
i
causes oxidative stress by activating the
mitochondrial
Na
+
/Ca
2+
exchanger (mitoNCX), which lowers mitochondrial [Ca
2+
] and thus slows down regeneration of the antioxidant NADPH. In agreement with a role for elevated [Na
+
]
i
in causing oxidative stress in T2D hearts, H
2
O
2
production was increased in HIP myocytes
vs
. WT and mitoNCX inhibition, which uncouples mitochondria from [Na
+
]
i
, significantly reduced H
2
O
2
production in HIP hearts. Oxidative stress enhances the SR Ca
2+
leak directly through oxidation of ryanodine receptors (RyRs) and indirectly via CaMKII activation and consequent RyR phosphorylation. SR Ca
2+
leak was augmented in myocytes from HIP
vs
. WT rats and mitoNCX inhibition significantly reduced the leak in HIP myocytes, but not in the WT. Thus, our data indicate that SGLT activity is enhanced in myocytes from T2D rats, which increases Na
+
influx and causes Na
+
overload. Elevated [Na
+
]
i
contributes to oxidative stress and abnormal SR Ca
2+
leak in diabetic hearts.
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10
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Popescu I, Yin G, Velmurugan S, Erickson JR, Despa F, Despa S. Lower sarcoplasmic reticulum Ca 2+ threshold for triggering afterdepolarizations in diabetic rat hearts. Heart Rhythm 2019; 16:765-772. [PMID: 30414461 PMCID: PMC6491240 DOI: 10.1016/j.hrthm.2018.11.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Indexed: 01/11/2023]
Abstract
BACKGROUND Type 2 diabetes (T2D) increases arrhythmia risk through incompletely elucidated mechanisms. Ventricular arrhythmias could be initiated by delayed afterdepolarizations (DADs) resulting from elevated spontaneous sarcoplasmic reticulum (SR) Ca2+ release (SR Ca2+ leak). OBJECTIVE The purpose of this study was to test the role of DADs and SR Ca2+ leak in triggering arrhythmias in T2D hearts. METHODS We compared rats with late-onset T2D that display pancreatic and cardiac phenotypes similar to those in humans with T2D (HIP rats) and their nondiabetic littermates (wild type [WT]). RESULTS HIP rats showed higher propensity for premature ventricular complexes and ventricular tachyarrhythmias, whereas HIP myocytes displayed more frequent DADs and had lower SR Ca2+ content than WT. However, the threshold SR Ca2+ at which depolarizing transient inward currents (Itis) are generated was also significantly decreased in HIP myocytes and was below the actual SR Ca2+ load, which explains the increased DAD incidence despite reduced Ca2+ in SR. In agreement with these findings, Ca2+ spark frequency was augmented in myocytes from HIP vs WT rats, which suggests activation of ryanodine receptors (RyRs) in HIP hearts. Indeed, RyR phosphorylation (by CaMKII and protein kinase A) and oxidation are enhanced in HIP hearts, whereas there is no RyR O-GlcNAcylation in either HIP or control hearts. CaMKII inhibition dissipated the difference in Ca2+ spark frequency between HIP and WT myocytes. CONCLUSION The threshold SR Ca2+ for generating depolarizing Itis is lower in T2D because of RyR activation after hyperphosphorylation and oxidation, which favors the occurrence of DADs despite low SR Ca2+ loads.
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Affiliation(s)
- Iuliana Popescu
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky
| | - Guo Yin
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky
| | - Sathya Velmurugan
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky
| | - Jeffrey R Erickson
- Department of Physiology and HeartOtago, University of Otago, Dunedin, New Zealand
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, Kentucky.
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11
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Abstract
By controlling the function of various sarcolemmal and mitochondrial ion transporters, intracellular Na+ concentration ([Na+]i) regulates Ca2+ cycling, electrical activity, the matching of energy supply and demand, and oxidative stress in cardiac myocytes. Thus, maintenance of myocyte Na+ homeostasis is vital for preserving the electrical and contractile activity of the heart. [Na+]i is set by the balance between the passive Na+ entry through numerous pathways and the pumping of Na+ out of the cell by the Na+/K+-ATPase. This equilibrium is perturbed in heart failure, resulting in higher [Na+]i. More recent studies have revealed that [Na+]i is also increased in myocytes from diabetic hearts. Elevated [Na+]i causes oxidative stress and augments the sarcoplasmic reticulum Ca2+ leak, thus amplifying the risk for arrhythmias and promoting heart dysfunction. This mini-review compares and contrasts the alterations in Na+ extrusion and/or Na+ uptake that underlie the [Na+]i increase in heart failure and diabetes, with a particular emphasis on the emerging role of Na+ - glucose cotransporters in the diabetic heart.
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Affiliation(s)
- Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY, United States
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12
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Stewart BD, Scott CE, McCoy TP, Yin G, Despa F, Despa S, Kekenes-Huskey PM. Computational modeling of amylin-induced calcium dysregulation in rat ventricular cardiomyocytes. Cell Calcium 2017; 71:65-74. [PMID: 29604965 DOI: 10.1016/j.ceca.2017.11.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Revised: 11/30/2017] [Accepted: 11/30/2017] [Indexed: 01/08/2023]
Abstract
Hyperamylinemia is a condition that accompanies obesity and precedes type II diabetes, and it is characterized by above-normal blood levels of amylin, the pancreas-derived peptide. Human amylin oligomerizes easily and can deposit in the pancreas [1], brain [2], and heart [3], where they have been associated with calcium dysregulation. In the heart, accumulating evidence suggests that human amylin oligomers form moderately cation-selective [4,5] channels that embed in the cell sarcolemma (SL). The oligomers increase membrane conductance in a concentration-dependent manner [5], which is correlated with elevated cytosolic Ca2+. These findings motivate our core hypothesis that non-selective inward Ca2+ conduction afforded by human amylin oligomers increase cytosolic and sarcoplasmic reticulum (SR) Ca2+ load, which thereby magnifies intracellular Ca2+ transients. Questions remain however regarding the mechanism of amylin-induced Ca2+ dysregulation, including whether enhanced SL Ca2+ influx is sufficient to elevate cytosolic Ca2+ load [6], and if so, how might amplified Ca2+ transients perturb Ca2+-dependent cardiac pathways. To investigate these questions, we modified a computational model of cardiomyocytes Ca2+ signaling to reflect experimentally-measured changes in SL membrane permeation and decreased sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) function stemming from acute and transgenic human amylin peptide exposure. With this model, we confirmed the hypothesis that increasing SL permeation alone was sufficient to enhance Ca2+ transient amplitudes. Our model indicated that amplified cytosolic transients are driven by increased Ca2+ loading of the SR and that greater fractional release may contribute to the Ca2+-dependent activation of calmodulin, which could prime the activation of myocyte remodeling pathways. Importantly, elevated Ca2+ in the SR and dyadic space collectively drive greater fractional SR Ca2+ release for human amylin expressing rats (HIP) and acute amylin-exposed rats (+Amylin) mice, which contributes to the inotropic rise in cytosolic Ca2+ transients. These findings suggest that increased membrane permeation induced by oligomeratization of amylin peptide in cell sarcolemma contributes to Ca2+ dysregulation in pre-diabetes.
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Affiliation(s)
- Bradley D Stewart
- Department of Chemistry, University of Kentucky, 505 Rose St. Chemistry-Physics Building, Lexington, KY 40506, USA
| | - Caitlin E Scott
- Department of Chemistry, University of Kentucky, 505 Rose St. Chemistry-Physics Building, Lexington, KY 40506, USA
| | - Thomas P McCoy
- Department of Family & Community Nursing, University of North Carolina - Greensboro, 1008 Administration Dr. McIver Building, Greensboro, NC 27412, USA
| | - Guo Yin
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, UK Medical Center, MN 150, Lexington, KY 40536, USA
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, UK Medical Center, MN 150, Lexington, KY 40536, USA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, UK Medical Center, MN 150, Lexington, KY 40536, USA.
| | - Peter M Kekenes-Huskey
- Department of Chemistry, University of Kentucky, 505 Rose St. Chemistry-Physics Building, Lexington, KY 40506, USA.
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13
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Liao Z, Ginsburg KS, Bartos DC, Jiang Y, Despa S, Bers DM. High Diastolic Sodium Influx in Heart Failure has Drug-Sensitivities Like Late Sodium Current, but Produces Inward Current at Diastolic Potentials. Biophys J 2017. [DOI: 10.1016/j.bpj.2016.11.1802] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
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14
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Van Steenbergen A, Balteau M, Ginion A, Ferté L, Battault S, Ravenstein CDMD, Balligand JL, Daskalopoulos EP, Gilon P, Despa F, Despa S, Vanoverschelde JL, Horman S, Koepsell H, Berry G, Hue L, Bertrand L, Beauloye C. Sodium-myoinositol cotransporter-1, SMIT1, mediates the production of reactive oxygen species induced by hyperglycemia in the heart. Sci Rep 2017; 7:41166. [PMID: 28128227 PMCID: PMC5269587 DOI: 10.1038/srep41166] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 12/16/2016] [Indexed: 01/04/2023] Open
Abstract
Hyperglycemia (HG) stimulates the production of reactive oxygen species in the heart through activation of NADPH oxidase 2 (NOX2). This production is independent of glucose metabolism but requires sodium/glucose cotransporters (SGLT). Seven SGLT isoforms (SGLT1 to 6 and sodium-myoinositol cotransporter-1, SMIT1) are known, although their expression and function in the heart remain elusive. We investigated these 7 isoforms and found that only SGLT1 and SMIT1 were expressed in mouse, rat and human hearts. In cardiomyocytes, galactose (transported through SGLT1) did not activate NOX2. Accordingly, SGLT1 deficiency did not prevent HG-induced NOX2 activation, ruling it out in the cellular response to HG. In contrast, myo-inositol (transported through SMIT1) reproduced the toxic effects of HG. SMIT1 overexpression exacerbated glucotoxicity and sensitized cardiomyocytes to HG, whereas its deletion prevented HG-induced NOX2 activation. In conclusion, our results show that heart SMIT1 senses HG and triggers NOX2 activation. This could participate in the redox signaling in hyperglycemic heart and contribute to the pathophysiology of diabetic cardiomyopathy.
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Affiliation(s)
- Anne Van Steenbergen
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Magali Balteau
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Audrey Ginion
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Laura Ferté
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Sylvain Battault
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | | | - Jean-Luc Balligand
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pole of Pharmacology and Therapeutics, Brussels, Belgium.,Cliniques Universitaires Saint-Luc, Department of Medicine, Brussels, Belgium
| | - Evangelos-Panagiotis Daskalopoulos
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Patrick Gilon
- Université Catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle d'Endocrinologie, Diabète et Nutrition, Brussels, Belgium
| | - Florin Despa
- University of Kentucky, Department of Pharmacology and Nutritional Sciences, Lexington, KY, USA
| | - Sanda Despa
- University of Kentucky, Department of Pharmacology and Nutritional Sciences, Lexington, KY, USA
| | - Jean-Louis Vanoverschelde
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium.,Cliniques Universitaires Saint Luc, Division of Cardiology, Brussels, Belgium
| | - Sandrine Horman
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Hermann Koepsell
- University of Würzburg, Department of Molecular Plant Physiology and Biophysics, Julius von Sachs Institute, Würzburg, Germany
| | - Gerard Berry
- Harvard Medical School, Children's Hospital Boston, Division of Genetics and Genomics, Department of Pediatrics, Boston, MA, USA
| | - Louis Hue
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium.,Université catholique de Louvain, de Duve Institute, Brussels, Belgium
| | - Luc Bertrand
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium
| | - Christophe Beauloye
- Université catholique de Louvain, Institut de Recherche Expérimentale et Clinique, Pôle de Recherche Cardiovasculaire, Brussels, Belgium.,Cliniques Universitaires Saint Luc, Division of Cardiology, Brussels, Belgium
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15
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Liu M, Verma N, Peng X, Srodulski S, Morris A, Chow M, Hersh LB, Chen J, Zhu H, Netea MG, Margulies KB, Despa S, Despa F. Hyperamylinemia Increases IL-1β Synthesis in the Heart via Peroxidative Sarcolemmal Injury. Diabetes 2016; 65:2772-83. [PMID: 27335231 PMCID: PMC5001184 DOI: 10.2337/db16-0044] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2016] [Accepted: 06/09/2016] [Indexed: 12/29/2022]
Abstract
Hypersecretion of amylin is common in individuals with prediabetes, causes amylin deposition and proteotoxicity in pancreatic islets, and contributes to the development of type 2 diabetes. Recent studies also identified amylin deposits in failing hearts from patients with obesity or type 2 diabetes and demonstrated that hyperamylinemia accelerates the development of heart dysfunction in rats expressing human amylin in pancreatic β-cells (HIP rats). To further determine the impact of hyperamylinemia on cardiac myocytes, we investigated human myocardium, compared diabetic HIP rats with diabetic rats expressing endogenous (nonamyloidogenic) rat amylin, studied normal mice injected with aggregated human amylin, and developed in vitro cell models. We found that amylin deposition negatively affects cardiac myocytes by inducing sarcolemmal injury, generating reactive aldehydes, forming amylin-based adducts with reactive aldehydes, and increasing synthesis of the proinflammatory cytokine interleukin-1β (IL-1β) independently of hyperglycemia. These results are consistent with the pathological role of amylin deposition in the pancreas, uncover a novel contributing mechanism to cardiac myocyte injury in type 2 diabetes, and suggest a potentially treatable link of type 2 diabetes with diabetic heart disease. Although further studies are necessary, these data also suggest that IL-1β might function as a sensor of myocyte amylin uptake and a potential mediator of myocyte injury.
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Affiliation(s)
- Miao Liu
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
| | - Nirmal Verma
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
| | - Xiaoli Peng
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
| | - Sarah Srodulski
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
| | - Andrew Morris
- Division of Cardiovascular Medicine, Gill Heart Institute, University of Kentucky, Lexington, KY
| | - Martin Chow
- Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY
| | - Louis B Hersh
- Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY
| | - Jing Chen
- Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY
| | - Haining Zhu
- Department of Molecular and Cellular Biochemistry, College of Medicine, University of Kentucky, Lexington, KY
| | - Mihai G Netea
- Department of Internal Medicine, Radboud University Nijmegen Medical Center, Nijmegen, the Netherlands
| | - Kenneth B Margulies
- Cardiovascular Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, College of Medicine, University of Kentucky, Lexington, KY
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16
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Affiliation(s)
- Sanda Despa
- From the Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); IHU LIRYC, Fondation Université Bordeaux, Bordeaux, France (E.V.); and Institut de Mathématiques de Bordeaux, University of Bordeaux, Talence, France (E.V.).
| | - Edward Vigmond
- From the Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); IHU LIRYC, Fondation Université Bordeaux, Bordeaux, France (E.V.); and Institut de Mathématiques de Bordeaux, University of Bordeaux, Talence, France (E.V.).
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17
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Popescu I, Galice S, Mohler PJ, Despa S. Elevated local [Ca2+] and CaMKII promote spontaneous Ca2+ release in ankyrin-B-deficient hearts. Cardiovasc Res 2016; 111:287-94. [PMID: 27131508 DOI: 10.1093/cvr/cvw093] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 04/27/2016] [Indexed: 11/13/2022] Open
Abstract
AIMS Loss-of-function mutations in the cytoskeletal protein ankyrin-B (AnkB) cause ventricular tachyarrhythmias in humans. Previously, we found that a larger fraction of the sarcoplasmic reticulum (SR) Ca(2+) leak occurs through Ca(2+) sparks in AnkB-deficient (AnkB(+/-)) mice, which may contribute to arrhythmogenicity via Ca(2+) waves. Here, we investigated the mechanisms responsible for increased Ca(2+) spark frequency in AnkB(+/-) hearts. METHODS AND RESULTS Using immunoblots and phospho-specific antibodies, we found that phosphorylation of ryanodine receptors (RyRs) by CaMKII is enhanced in AnkB(+/-) hearts. In contrast, the PKA-mediated RyR phosphorylation was comparable in AnkB(+/-) and wild-type (WT) mice. CaMKII inhibition greatly reduced Ca(2+) spark frequency in myocytes from AnkB(+/-) mice but had little effect in the WT. Global activities of the major phosphatases PP1 and PP2A were similar in AnkB(+/-) and WT hearts, while CaMKII autophosphorylation, a marker of CaMKII activation, was increased in AnkB(+/-) hearts. Thus, CaMKII-dependent RyR hyperphosphorylation in AnkB(+/-) hearts is caused by augmented CaMKII activity. Intriguingly, CaMKII activation is limited to the sarcolemma-SR junctions since non-junctional CaMKII targets (phospholamban, HDAC4) are not hyperphosphorylated in AnkB(+/-) myocytes. This local CaMKII activation may be the consequence of elevated [Ca(2+)] in the junctional cleft caused by reduced Na(+)/Ca(2+) exchange activity. Indeed, using the RyR-targeted Ca(2+) sensor GCaMP2.2-FBKP12.6, we found that local junctional [Ca(2+)] is significantly elevated in AnkB(+/-) myocytes. CONCLUSIONS The increased incidence of pro-arrhythmogenic Ca(2+) sparks and waves in AnkB(+/-) hearts is due to enhanced CaMKII-mediated RyR phosphorylation, which is caused by higher junctional [Ca(2+)] and consequent local CaMKII activation.
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Affiliation(s)
- Iuliana Popescu
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, Lexington, KY 40536, USA
| | - Samuel Galice
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
| | - Peter J Mohler
- The Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA Department of Physiology and Cell Biology, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA Department of Internal Medicine, The Ohio State University Wexner Medical Center, Columbus, OH 43210, USA
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, 900 S Limestone, Lexington, KY 40536, USA
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18
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Clancy CE, Chen-Izu Y, Bers DM, Belardinelli L, Boyden PA, Csernoch L, Despa S, Fermini B, Hool LC, Izu L, Kass RS, Lederer WJ, Louch WE, Maack C, Matiazzi A, Qu Z, Rajamani S, Rippinger CM, Sejersted OM, O'Rourke B, Weiss JN, Varró A, Zaza A. Deranged sodium to sudden death. J Physiol 2015; 593:1331-45. [PMID: 25772289 DOI: 10.1113/jphysiol.2014.281204] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Accepted: 10/14/2014] [Indexed: 12/19/2022] Open
Abstract
In February 2014, a group of scientists convened as part of the University of California Davis Cardiovascular Symposium to bring together experimental and mathematical modelling perspectives and discuss points of consensus and controversy on the topic of sodium in the heart. This paper summarizes the topics of presentation and discussion from the symposium, with a focus on the role of aberrant sodium channels and abnormal sodium homeostasis in cardiac arrhythmias and pharmacotherapy from the subcellular scale to the whole heart. Two following papers focus on Na(+) channel structure, function and regulation, and Na(+)/Ca(2+) exchange and Na(+)/K(+) ATPase. The UC Davis Cardiovascular Symposium is a biannual event that aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The focus on Na(+) in the 2014 symposium stemmed from the multitude of recent studies that point to the importance of maintaining Na(+) homeostasis in the heart, as disruption of homeostatic processes are increasingly identified in cardiac disease states. Understanding how disruption in cardiac Na(+)-based processes leads to derangement in multiple cardiac components at the level of the cell and to then connect these perturbations to emergent behaviour in the heart to cause disease is a critical area of research. The ubiquity of disruption of Na(+) channels and Na(+) homeostasis in cardiac disorders of excitability and mechanics emphasizes the importance of a fundamental understanding of the associated mechanisms and disease processes to ultimately reveal new targets for human therapy.
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Affiliation(s)
- Colleen E Clancy
- Department of Pharmacology, University of California, Davis, Genome Building Rm 3503, Davis, CA, 95616-8636, USA
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19
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Lambert R, Srodulski S, Peng X, Margulies KB, Despa F, Despa S. Intracellular Na+ Concentration ([Na+]i) Is Elevated in Diabetic Hearts Due to Enhanced Na+-Glucose Cotransport. J Am Heart Assoc 2015; 4:e002183. [PMID: 26316524 PMCID: PMC4599504 DOI: 10.1161/jaha.115.002183] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Background Intracellular Na+ concentration ([Na+]i) regulates Ca2+ cycling, contractility, metabolism, and electrical stability of the heart. [Na+]i is elevated in heart failure, leading to arrhythmias and oxidative stress. We hypothesized that myocyte [Na+]i is also increased in type 2 diabetes (T2D) due to enhanced activity of the Na+–glucose cotransporter. Methods and Results To test this hypothesis, we used myocardial tissue from humans with T2D and a rat model of late-onset T2D (HIP rat). Western blot analysis showed increased Na+–glucose cotransporter expression in failing hearts from T2D patients compared with nondiabetic persons (by 73±13%) and in HIP rat hearts versus wild-type (WT) littermates (by 61±8%). [Na+]i was elevated in HIP rat myocytes both at rest (14.7±0.9 versus 11.4±0.7 mmol/L in WT) and during electrical stimulation (17.3±0.8 versus 15.0±0.7 mmol/L); however, the Na+/K+-pump function was similar in HIP and WT cells, suggesting that higher [Na+]i is due to enhanced Na+ entry in diabetic hearts. Indeed, Na+ influx was significantly larger in myocytes from HIP versus WT rats (1.77±0.11 versus 1.29±0.06 mmol/L per minute). Na+–glucose cotransporter inhibition with phlorizin or glucose-free solution greatly reduced Na+ influx in HIP myocytes (to 1.20±0.16 mmol/L per minute), whereas it had no effect in WT cells. Phlorizin also significantly decreased glucose uptake in HIP myocytes (by 33±9%) but not in WT, indicating an increased reliance on the Na+–glucose cotransporter for glucose uptake in T2D hearts. Conclusions Myocyte Na+–glucose cotransport is enhanced in T2D, which increases Na+ influx and causes Na+ overload. Higher [Na+]i may contribute to arrhythmogenesis and oxidative stress in diabetic hearts.
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Affiliation(s)
- Rebekah Lambert
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (R.L., S.S., X.P., F.D., S.D.)
| | - Sarah Srodulski
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (R.L., S.S., X.P., F.D., S.D.)
| | - Xiaoli Peng
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (R.L., S.S., X.P., F.D., S.D.)
| | - Kenneth B Margulies
- Cardiovascular Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA (K.B.M.)
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (R.L., S.S., X.P., F.D., S.D.)
| | - Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (R.L., S.S., X.P., F.D., S.D.)
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20
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Verma N, Mina M, Liu M, Nystoriak M, Srodulski S, Peng XL, Brelsfoard J, Bachstetter A, Pascual C, Xie X, Saatman K, Van Eldik L, Navedo M, Despa S, Despa F. Abstract W P252: Amylin Vasculopathy, a Novel Mechanism of Cerebrovascular Injury and Neurologic Deficits in Diabetes. Stroke 2015. [DOI: 10.1161/str.46.suppl_1.wp252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Human amylin is an amyloidogenic hormone that forms toxic oligomers that kill the insulin-producing β-cells in the pancreas of patients with type-2 diabetes. We recently showed that the pancreatic amylin pathology is also linked with cerebrovascular dementia and diabetic heart disease by increased circulating levels of toxic oligomerized amylin. Here, we tested the hypothesis that the cerebrovascular accumulation of oligomerized amylin injures the brain, leading to neurologic deficits independently of hyperglycemia.
A diabetic rat model overexpressing amyloidogenic human amylin in the pancreas (the HIP rat) and appropriate controls were used to investigate mechanistically cerebrovascular effects of amylin accumulation. As controls, we employed wild-type (WT) littermates and age- and glucose-matched diabetic rats expressing only non-amyloidogenic WT amylin, which does not accumulate in pancreas or other organs. Compared to controls, HIP rats showed reduced exploratory drive, vestibulomotor performance and recognition memory. Cortical arteries isolated from HIP rats displayed a ~40% higher myogenic tone (P<0.05), which correlates with an increased mean arterial blood pressure by ~20% (P<0.05). We also found elevated lipid peroxidation (by 18±3%; P<0.05) and activated Ca
2+
-mediated hypertrophy signaling in cortical smooth muscle cells from HIP rats compared to control rats. Serial staining with the ED1 antibody and amylin antibody indicates possible activated microglia/macrophages which are clustering in blood vessel areas positive for amylin infiltration. Multiple inflammatory markers are expressed in HIP rat brains compared to control rats, confirming that amylin deposition induces an inflammatory response.
Overall, our data suggest that cerebrovascular amylin deposition is associated with neurologic deficits via mechanisms of vascular dysfunction, oxidative stress and neuroinflammation.
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Affiliation(s)
| | | | - Miao Liu
- Pharmacology, Univ of Kentucky, Lexington, KY
| | | | | | | | | | | | | | - Xinmin Xie
- Pharmacology, Afasci Rsch Laboratory, Redwood, CA
| | | | | | | | - Sanda Despa
- Pharmacology, Univ of Kentucky, Lexington, KY
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Despa S, Sharma S, Harris TR, Dong H, Li N, Chiamvimonvat N, Taegtmeyer H, Margulies KB, Hammock BD, Despa F. Cardioprotection by controlling hyperamylinemia in a "humanized" diabetic rat model. J Am Heart Assoc 2014; 3:jah3658. [PMID: 25146704 PMCID: PMC4310392 DOI: 10.1161/jaha.114.001015] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
BACKGROUND Chronic hypersecretion of the pancreatic hormone amylin is common in humans with obesity or prediabetic insulin resistance and induces amylin aggregation and proteotoxicity in the pancreas. We recently showed that hyperamylinemia also affects the cardiovascular system. Here, we investigated whether amylin aggregates interact directly with cardiac myocytes and whether controlling hyperamylinemia protects the heart. METHODS AND RESULTS By Western blot, we found abundant amylin aggregates in lysates of cardiac myocytes from obese patients, but not in controls. Aggregated amylin was elevated in failing hearts, suggesting a role in myocyte injury. Using rats overexpressing human amylin in the pancreas (HIP rats) and control myocytes incubated with human amylin, we show that amylin aggregation at the sarcolemma induces oxidative stress and Ca(2+) dysregulation. In time, HIP rats developed cardiac hypertrophy and left-ventricular dilation. We then tested whether metabolites with antiaggregation properties, such as eicosanoid acids, limit myocardial amylin deposition. Rats were treated with an inhibitor of soluble epoxide hydrolase, the enzyme that degrades endogenous eicosanoids. Treatment doubled the blood concentration of eicosanoids, which drastically reduced incorporation of aggregated amylin in cardiac myocytes and blood cells, without affecting pancreatic amylin secretion. Animals in the treated group showed reduced cardiac hypertrophy and left-ventricular dilation. The cardioprotective mechanisms included the mitigation of amylin-induced cardiac oxidative stress and Ca(2+) dysregulation. CONCLUSIONS The results suggest blood amylin as a novel therapeutic target in diabetic heart disease and elevating blood levels of antiaggregation metabolites as a pharmacological strategy to reduce amylin aggregation and amylin-mediated cardiotoxicity.
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Affiliation(s)
- Sanda Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (S.D., S.S., F.D.) Saha Cardiovascular Research Center, University of Kentucky, Lexington, KY (S.D., F.D.)
| | - Savita Sharma
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (S.D., S.S., F.D.)
| | - Todd R Harris
- Department of Entomology, University of California, Davis, CA (T.R.H., H.D., B.D.H.)
| | - Hua Dong
- Department of Entomology, University of California, Davis, CA (T.R.H., H.D., B.D.H.)
| | - Ning Li
- Department of Internal Medicine, University of California, Davis, CA (N.L., N.C.)
| | - Nipavan Chiamvimonvat
- Department of Internal Medicine, University of California, Davis, CA (N.L., N.C.) Department of Veterans Affairs, Northern California Health Care System, Mather, CA (N.C.)
| | - Heinrich Taegtmeyer
- Department of Internal Medicine, The University of Texas School of Medicine at Houston, Houston, TX (H.T.)
| | - Kenneth B Margulies
- Cardiovascular Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA (K.B.M.)
| | - Bruce D Hammock
- Department of Entomology, University of California, Davis, CA (T.R.H., H.D., B.D.H.)
| | - Florin Despa
- Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington, KY (S.D., S.S., F.D.) Saha Cardiovascular Research Center, University of Kentucky, Lexington, KY (S.D., F.D.)
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Abstract
RATIONALE Intracellular Ca(2+) concentration ([Ca(2+)]i) is regulated and signals differently in various subcellular microdomains, which greatly enhances its second messenger versatility. In the heart, sarcoplasmic reticulum Ca(2+) release and signaling are controlled by local [Ca(2+)]i in the junctional cleft ([Ca(2+)]Cleft), the small space between sarcolemma and junctional sarcoplasmic reticulum. However, methods to measure [Ca(2+)]Cleft directly are needed. OBJECTIVE To construct novel sensors that allow direct measurement of [Ca(2+)]Cleft. METHODS AND RESULTS We constructed cleft-targeted [Ca(2+)] sensors by fusing Ca(2+)-sensor GCaMP2.2 and a new lower Ca(2+)-affinity variant GCaMP2.2Low to FKBP12.6, which binds with high affinity and selectivity to ryanodine receptors. The fluorescence pattern, affinity for ryanodine receptors, and competition by untagged FKBP12.6 demonstrated that FKBP12.6-tagged sensors are positioned to measure local [Ca(2+)]Cleft in adult rat myocytes. Using GCaMP2.2Low-FKBP12.6, we showed that [Ca(2+)]Cleft reaches higher levels with faster kinetics than global [Ca(2+)]i during excitation-contraction coupling. Diastolic sarcoplasmic reticulum Ca(2+) leak or sarcolemmal Ca(2+) entry may raise local [Ca(2+)]Cleft above bulk cytosolic [Ca(2+)]i ([Ca(2+)]Bulk), an effect that may contribute to triggered arrhythmias and even transcriptional regulation. We measured this diastolic standing [Ca(2+)]Cleft-[Ca(2+)]Bulk gradient with GCaMP2.2-FKBP12.6 versus GCaMP2.2, using [Ca(2+)] measured without gradients as a reference point. This diastolic difference ([Ca(2+)]Cleft=194 nmol/L versus [Ca(2+)]Bulk=100 nmol/L) is dictated mainly by the sarcoplasmic reticulum Ca(2+) leak rather than sarcolemmal Ca(2+) flux. CONCLUSIONS We have developed junctional cleft-targeted sensors to measure [Ca(2+)]Cleft versus [Ca(2+)]Bulk and demonstrated dynamic differences during electric excitation and a standing diastolic [Ca(2+)]i gradient, which could influence local Ca(2+)-dependent signaling within the junctional cleft.
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Affiliation(s)
- Sanda Despa
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.).
| | - Bo Shui
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.)
| | - Julie Bossuyt
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.)
| | - Di Lang
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.)
| | - Michael I Kotlikoff
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.)
| | - Donald M Bers
- From the Department of Pharmacology, University of California, Davis (S.D., J.B., D.L., D.M.B.); Department of Pharmacology and Nutritional Sciences, University of Kentucky, Lexington (S.D.); and Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY (B.S., M.I.K.).
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Galice S, Despa S. Ankyrin-B Reduction Enhances Calcium Sparks via CamkII. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.1849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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24
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Correll RN, Eder P, Burr AR, Despa S, Davis J, Bers DM, Molkentin JD. Overexpression of the Na+/K+ ATPase α2 but not α1 isoform attenuates pathological cardiac hypertrophy and remodeling. Circ Res 2013; 114:249-256. [PMID: 24218169 DOI: 10.1161/circresaha.114.302293] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE The Na+ / K+ ATPase (NKA) directly regulates intracellular Na+ levels, which in turn indirectly regulates Ca2+ levels by proximally controlling flux through the Na+ / Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse-mode Ca2+ entry through NCX1, as well as less efficient Ca2+ clearance. OBJECTIVE To determine whether maintaining lower intracellular Na+ levels by NKA overexpression in the heart would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 to protect the heart. METHODS AND RESULTS Cardiac-specific transgenic mice overexpressing either NKA-α1 or NKA-α2 were generated and subjected to pressure overload hypertrophic stimulation. We found that although increased expression of NKA-α1 had no protective effect, overexpression of NKA-α2 significantly decreased cardiac hypertrophy after pressure overload in mice at 2, 10, and 16 weeks of stimulation. Remarkably, total NKA protein expression and activity were not altered in either of these 2 transgenic models because increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. NKA-α2 overexpression but not NKA-α1 led to significantly faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. Mechanistically, overexpressed NKA-α2 showed greater affinity for Na+ compared with NKA-α1, leading to more efficient clearance of this ion. Furthermore, overexpression of NKA-α2 but not NKA-α1 was coupled to a decrease in phospholemman expression and phosphorylation, which would favor greater NKA activity, NCX1 activity, and Ca2+ removal. CONCLUSIONS Our results suggest that the protective effect produced by increased expression of NKA-α2 on the heart after pressure overload is due to more efficient Ca2+ clearance because this isoform of NKA preferentially enhances NCX1 activity compared with NKA-α1.
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Affiliation(s)
- Robert N Correll
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Petra Eder
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.,Comprehensive Heart Failure Center, University of Würzburg, Würzburg, Germany
| | - Adam R Burr
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Sanda Despa
- Department of Pharmacology, UC Davis, Davis, California, USA
| | - Jennifer Davis
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
| | - Donald M Bers
- Department of Pharmacology, UC Davis, Davis, California, USA
| | - Jeffery D Molkentin
- Department of Pediatrics, University of Cincinnati, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.,Howard Hughes Medical Institute, Cincinnati, Ohio, USA
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Correll RN, Eder P, Burr AR, Despa S, Davis J, Bers DM, Molkentin JD. Abstract 197: Overexpression of the Na+/K+ ATPase a2 But Not a1 Isoform Attenuates Pathological Cardiac Hypertrophy and Remodeling. Circ Res 2013. [DOI: 10.1161/res.113.suppl_1.a197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The Na+/K+ ATPase (NKA) directly regulates intracellular Na+ levels, which indirectly regulate Ca2+ levels by controlling flux through the Na+/Ca2+ exchanger (NCX1). Elevated Na+ levels have been reported during heart failure, which permits some degree of reverse mode Ca2+ entry through NCX1 and less efficient Ca2+ clearance. To determine if lower intracellular Na+ levels would enhance forward-mode Ca2+ clearance and prevent reverse-mode Ca2+ entry through NCX1 as a protective measure, we generated cardiac-specific transgenic mice overexpressing either the NKA-α1 or α2 isoform and subjected them to pressure overload hypertrophic stimulation. We found that while increased expression of the NKA-α1 isoform had no protective effect, overexpression of NKA-α2 significantly decreased cardiac hypertrophy after pressure overload at 2, 10 and 16 weeks of stimulation. Remarkably, total NKA protein expression was not altered in either of these 2 transgenic models, as increased expression of one isoform led to a concomitant decrease in the other endogenous isoform. While total NKA ATPase activity and intracellular Na+ levels were unchanged in either overexpression model, and both showed reduced Ca2+ transient amplitudes and sarcoplasmic reticulum Ca2+ load, only NKA-α2 overexpression led to faster removal of bulk Ca2+ from the cytosol in a manner requiring NCX1 activity. This increased NCX1 activity, though correlated with improved outcome after pressure overload, did not affect signaling through Ca2+-sensitive signaling pathways such as calcineurin/nuclear factor of activated T-cells, Ca2+/calmodulin-dependent kinase II, or protein kinase Cα. Overexpression of NKA-α2 did, however, result in reduced expression of phospholemman (PLM), an inhibitor of NKA activity (when dephosphorylated) and NCX1 activity (when phosphorylated). Our results suggest that the protective effect produced by increased expression of NKA-α2 after pressure overload is likely due to: 1) Na+ regulation in a unique signaling microdomain distinct from NKA-α1, and 2) downregulation of PLM expression that removes a negative regulator of NCX1 activity, both leading to preservation of forward-mode NCX1 activity during disease, in association with optimized cardiac function.
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Affiliation(s)
| | - Petra Eder
- Cincinnati Children’s Hosp, Cincinnati, OH
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26
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Avkiran M, Despa S, Shattock MJ. The salt of the earth: focus on Na⁺ regulation in the cardiac myocyte. J Mol Cell Cardiol 2013; 61:1. [PMID: 23770060 DOI: 10.1016/j.yjmcc.2013.06.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 05/13/2013] [Indexed: 11/24/2022]
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Abstract
In the heart, intracellular Na(+) concentration ([Na(+)]i) is a key modulator of Ca(2+) cycling, contractility and cardiac myocyte metabolism. Several Na(+) transporters are electrogenic, thus they both contribute to shaping the cardiac action potential and at the same time are affected by it. [Na(+)]i is controlled by the balance between Na(+) influx through various pathways, including the Na(+)/Ca(2+) exchanger and Na(+) channels, and Na(+) extrusion via the Na(+)/K(+)-ATPase. [Na(+)]i is elevated in HF due to a combination of increased entry through Na(+) channels and/or Na(+)/H(+) exchanger and reduced activity of the Na(+)/K(+)-ATPase. Here we review the major Na(+) transport pathways in cardiac myocytes and how they participate in regulating [Na(+)]i in normal and failing hearts. This article is part of a Special Issue entitled "Na(+) Regulation in Cardiac Myocytes."
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Affiliation(s)
- Sanda Despa
- Department of Pharmacology, University of California, Davis, CA, USA.
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28
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Sato D, Despa S, Bers DM. Can the sodium-calcium exchanger initiate or suppress calcium sparks in cardiac myocytes? Biophys J 2012; 102:L31-3. [PMID: 22768959 DOI: 10.1016/j.bpj.2012.03.051] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 02/02/2012] [Accepted: 03/22/2012] [Indexed: 11/28/2022] Open
Abstract
Positive feedback of Calcium (Ca)-induced Ca release is the mechanism of Ca spark formation in cardiac myocytes. To initiate this process, a certain amount of Ca in the cleft space is necessary. When the membrane potential becomes higher during excitation-contraction coupling, Ca can enter through both Ca current (I(CaL)) and sodium-calcium exchanger (NCX) and may activate ryanodine receptors to initiate a Ca spark. On the other hand, at the resting membrane potential (V(m) ~-80 mV), NCX removes Ca from the cell (forward mode). If Ca released from the sarcoplasmic reticulum is quickly removed via forward mode NCX before Ca-induced Ca release starts, the Ca release becomes nonspark Ca leak. This would also be influenced by the cleft/noncleft distribution of NCX, which is unknown. Using a physiologically detailed mathematical model of subcellular Ca cycling, we analyze how NCX strength and distribution alter Ca spark formation. During excitation-contraction coupling, most Ca sparks are induced by I(CaL) with very few due to NCX current. At the resting membrane potential if most NCX is localized to the cleft, spontaneous Ca sparks are significantly reduced.
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Guglielmino K, Jackson K, Harris TR, Vu V, Dong H, Dutrow G, Evans JE, Graham J, Cummings BP, Havel PJ, Chiamvimonvat N, Despa S, Hammock BD, Despa F. Pharmacological inhibition of soluble epoxide hydrolase provides cardioprotection in hyperglycemic rats. Am J Physiol Heart Circ Physiol 2012; 303:H853-62. [PMID: 22865388 DOI: 10.1152/ajpheart.00154.2012] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Glycemic regulation improves myocardial function in diabetic patients, but finding optimal therapeutic strategies remains challenging. Recent data have shown that pharmacological inhibition of soluble epoxide hydrolase (sEH), an enzyme that decreases the endogenous levels of protective epoxyeicosatrienoic acids (EETs), improves glucose homeostasis in insulin-resistant mice. Here, we tested whether the administration of sEH inhibitors preserves cardiac myocyte structure and function in hyperglycemic rats. University of California-Davis-type 2 diabetes mellitus (UCD-T2DM) rats with nonfasting blood glucose levels in the range of 150-200 mg/dl were treated with the sEH inhibitor 1-(1-acetypiperidin-4-yl)-3-adamantanylurea (APAU) for 6 wk. Administration of APAU attenuated the progressive increase of blood glucose concentration and preserved mitochondrial structure and myofibril morphology in cardiac myocytes, as revealed by electron microscopy imaging. Fluorescence microscopy with Ca(2+) indicators also showed a 40% improvement of cardiac Ca(2+) transients in treated rats. Sarcoplasmic reticulum Ca(2+) content was decreased in both treated and untreated rats compared with control rats. However, treatment limited this reduction by 30%, suggesting that APAU may protect the intracellular Ca(2+) effector system. Using Western blot analysis on cardiac myocyte lysates, we found less downregulation of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA), the main route of Ca(2+) reuptake in the sarcoplasmic reticulum, and lower expression of hypertrophic markers in treated versus untreated UCD-T2DM rats. In conclusion, APAU enhances the therapeutic effects of EETs, resulting in slower progression of hyperglycemia, efficient protection of myocyte structure, and reduced Ca(2+) dysregulation and SERCA remodeling in hyperglycemic rats. The results suggest that sEH/EETs may be an effective therapeutic target for cardioprotection in insulin resistance and diabetes.
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Despa S, Lingrel JB, Bers DM. Na(+)/K)+)-ATPase α2-isoform preferentially modulates Ca2(+) transients and sarcoplasmic reticulum Ca2(+) release in cardiac myocytes. Cardiovasc Res 2012; 95:480-6. [PMID: 22739122 DOI: 10.1093/cvr/cvs213] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
AIMS Na(+)/K(+)-ATPase (NKA) is essential in regulating [Na(+)](i), and thus cardiac myocyte Ca(2+) and contractility via Na(+)/Ca(2+) exchange. Different NKA-α subunit isoforms are present in the heart and may differ functionally, depending on specific membrane localization. In smooth muscle and astrocytes, NKA-α2 is located at the junctions with the endo(sarco)plasmic reticulum, where they could regulate local [Na(+)], and indirectly junctional cleft [Ca(2+)]. Whether this model holds for cardiac myocytes is unclear. METHODS AND RESULTS The ouabain-resistant NKA-α1 cannot be selectively blocked to assess its effect. To overcome this, we used mice in which NKA-α1 is ouabain sensitive and NKA-α2 is ouabain resistant (SWAP mice). We measured the effect of ouabain at low concentration on [Na(+)](i), Ca(2+) transients, and the fractional sarcoplasmic reticulum (SR) Ca(2+) release in cardiac myocytes from wild-type (WT; NKA-α2 inhibition) and SWAP mice (selective NKA-α1 block). At baseline, Na(+) and Ca(2+) regulations are similar in WT and SWAP mice. For equal levels of total NKA inhibition (~25%), ouabain significantly increased Ca(2+) transients (from ΔF/F(0)= 1.5 ± 0.1 to 1.8 ± 0.1), and fractional SR Ca(2+) release (from 24 ± 3 to 29 ± 3%) in WT (NKA-α2 block) but not in SWAP myocytes (NKA-α1 block). This occurred despite a similar and modest increase in [Na(+)](i) (~2 mM) in both groups. The effect in WT mice was mediated specifically by NKA-α2 inhibition because at a similar concentration ouabain had no effect in transgenic mice where both NKA-α1 and NKA-α2 are ouabain resistant. CONCLUSION NKA-α2 has a more prominent role (vs. NKA-α1) in modulating cardiac myocyte SR Ca(2+) release.
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Affiliation(s)
- Sanda Despa
- Department of Pharmacology, University of California at Davis, Genome Building Rm 3513, Davis, CA 95616-8636, USA
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Despa S, Margulies KB, Chen L, Knowlton AA, Havel PJ, Taegtmeyer H, Bers DM, Despa F. Hyperamylinemia contributes to cardiac dysfunction in obesity and diabetes: a study in humans and rats. Circ Res 2012; 110:598-608. [PMID: 22275486 DOI: 10.1161/circresaha.111.258285] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Hyperamylinemia is common in patients with obesity and insulin resistance, coincides with hyperinsulinemia, and results in amyloid deposition. Amylin amyloids are generally considered a pancreatic disorder in type 2 diabetes. However, elevated circulating levels of amylin may also lead to amylin accumulation and proteotoxicity in peripheral organs, including the heart. OBJECTIVE To test whether amylin accumulates in the heart of obese and type 2 diabetic patients and to uncover the effects of amylin accumulation on cardiac morphology and function. METHODS AND RESULTS We compared amylin deposition in failing and nonfailing hearts from lean, obese, and type 2 diabetic humans using immunohistochemistry and Western blots. We found significant accumulation of large amylin oligomers, fibrils, and plaques in failing hearts from obese and diabetic patients but not in normal hearts and failing hearts from lean, nondiabetic humans. Small amylin oligomers were even elevated in nonfailing hearts from overweight/obese patients, suggesting an early state of accumulation. Using a rat model of hyperamylinemia transgenic for human amylin, we observed that amylin oligomers attach to the sarcolemma, leading to myocyte Ca(2+) dysregulation, pathological myocyte remodeling, and diastolic dysfunction, starting from prediabetes. In contrast, prediabetic rats expressing the same level of wild-type rat amylin, a nonamyloidogenic isoform, exhibited normal heart structure and function. CONCLUSIONS Hyperamylinemia promotes amylin deposition in the heart, causing alterations of cardiac myocyte structure and function. We propose that detection and disruption of cardiac amylin buildup may be both a predictor of heart dysfunction and a novel therapeutic strategy in diabetic cardiomyopathy.
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Affiliation(s)
- Sanda Despa
- Department of Pharmacology, University of California-Davis, 451 Health Sciences Drive, Davis, CA 95616, USA.
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Jackson K, Despa S, Despa F. Circulating Amylin Amyloid Oligomers Accumulate in the Heart and Induce Cardiomyocyte Dysfunction in a Rat Model of Type-2 Diabetes. Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.1856] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Sato D, Despa S, Bers DM. Can the Sodium-Calcium Exchanger Initiate or Supress Calcium Sparks in Cardiac Myocytes? Biophys J 2012. [DOI: 10.1016/j.bpj.2011.11.567] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Khafaga M, Bossuyt J, Li JC, Lee LL, Elliott JH, Despa S, Bers DM. Na Pump E960 Site is Critical for the Interaction with Phospholemman. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.2726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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Despa S, Koch B, Margulies KB, Bers D, Despa F. Intrinsically Disordered Islet Amyloid Polypeptide Is a Pathogenic Link Between Type-2 diabetes and Heart Disease. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.1467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Bossuyt J, Li JC, Khafaga M, Lee LL, Mamikonian L, Despa S, Bers DM. Identification of Phospholemman Residues Critical to Phospholemman Oligomerization and Na Pump Association. Biophys J 2011. [DOI: 10.1016/j.bpj.2010.12.2735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
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Han F, Bossuyt J, Martin JL, Despa S, Bers DM. Role of phospholemman phosphorylation sites in mediating kinase-dependent regulation of the Na+-K+-ATPase. Am J Physiol Cell Physiol 2010; 299:C1363-9. [PMID: 20861470 DOI: 10.1152/ajpcell.00027.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phospholemman (PLM) is a major target for phosphorylation mediated by both PKA (at Ser68) and PKC (at both Ser63 and Ser68) in the heart. In intact cardiac myocytes, PLM associates with and inhibits Na(+)-K(+)-ATPase (NKA), mainly by reducing its affinity for internal Na(+). The inhibition is relieved upon PLM phosphorylation by PKA or PKC. The aim here was to distinguish the role of the Ser63 and Ser68 PLM phosphorylation sites in mediating kinase-induced modulation of NKA function. We expressed wild-type (WT) PLM and S63A, S68A, and AA (Ser63 and Ser68 to alanine double mutant) PLM mutants in HeLa cells that stably express rat NKA-α(1) and we measured the effect of PKA and PKC activation on NKA-mediated intracellular Na(+) concentration decline. PLM expression (WT or mutant) significantly decreased the apparent NKA affinity for internal Na(+) and had no significant effect on the maximum pump rate (V(max)). PKA activation with forskolin (20 μM) restored NKA Na(+) affinity in cells expressing WT but not AA PLM and did not affect V(max) in either case. Similarly, PKC activation with 300 nM phorbol 12,13-dibutyrate increased NKA Na(+) affinity in cells expressing WT, S63A, and S68A PLM and had no effect in cells expressing AA PLM. Neither forskolin nor phorbol 12,13-dibutyrate affected NKA function in the absence of PLM. We conclude that PLM phosphorylation at either Ser63 or Ser68 is both necessary and sufficient for completely relieving the PLM-induced NKA inhibition.
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Affiliation(s)
- Fei Han
- Department of Pathology, Northwestern University, Feinberg School of Medicine, Chicago, Illinois, USA
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Camors E, Mohler PJ, Bers DM, Despa S. Increased Ca Sparks and Waves Frequency and Unchanged [Na]i in Hearts from Ankyrin-B Heterozygous Mice. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.3913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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Despa S, Andronic F, Thai P, Walton JH, Margulies KB, Bers DM, Despa F. Iapp Preamyloid Oligomers Accumulate in the Heart and Contribute to Cardiac Dysfunction in Type-2 Diabetes. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.1386] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
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Despa S, Wu Y, Lingrel JB, Stefani E, Bers D. Na/K-ATpase α2-Subunit Preferentially Modulates Ca Transients and SR Ca Release in Cardiac Myocytes. Biophys J 2010. [DOI: 10.1016/j.bpj.2009.12.1075] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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Abstract
Intracellular Na(+) concentration ([Na(+)](i)) is very important in modulating the contractile and electrical activity of the heart. Upon electrical excitation of the myocardium, voltage-dependent Na(+) channels open, triggering the upstroke of the action potential (AP). During the AP, Ca(2+) enters the myocytes via L-type Ca(2+) channels. This triggers Ca(2+) release from the sarcoplasmic reticulum (SR) and thus activates contraction. Relaxation occurs when cytosolic Ca(2+) declines, mainly due to re-uptake into the SR via SR Ca(2+)-ATPase and extrusion from the cell via the Na(+)/Ca(2+) exchanger (NCX). NCX extrudes one Ca(2+) ion in exchange for three Na(+) ions and its activity is critically regulated by [Na(+)](i). Thus, via NCX, [Na(+)](i) is centrally involved in the regulation of intracellular [Ca(2+)] and contractility. Na(+) brought in by Na(+) channels, NCX and other Na(+) entry pathways is extruded by the Na(+)/K(+) pump (NKA) to keep [Na(+)](i) low. NKA is regulated by phospholemman, a small sarcolemmal protein that associates with NKA. Unphosphorylated phospholemman inhibits NKA by decreasing the pump affinity for internal Na(+) and this inhibition is relieved upon phosphorylation. Here we discuss the main characteristics of the Na(+) transport pathways in cardiac myocytes and their physiological and pathophysiological relevance.
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Affiliation(s)
- Donald M Bers
- Department of Pharmacology, University of California, Davis, Davis, CA 95616-8636, USA.
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Bossuyt J, Despa S, Han F, Hou Z, Robia SL, Lingrel JB, Bers DM. Isoform specificity of the Na/K-ATPase association and regulation by phospholemman. J Biol Chem 2009; 284:26749-57. [PMID: 19638348 DOI: 10.1074/jbc.m109.047357] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM) phosphorylation mediates enhanced Na/K-ATPase (NKA) function during adrenergic stimulation of the heart. Multiple NKA isoforms exist, and their function/regulation may differ. We combined fluorescence resonance energy transfer (FRET) and functional measurements to investigate isoform specificity of the NKA-PLM interaction. FRET was measured as the increase in the donor fluorescence (CFP-NKA-alpha1 or CFP-NKA-alpha2) during progressive acceptor (PLM-YFP) photobleach in HEK-293 cells. Both pairs exhibited robust FRET (maximum of 23.6 +/- 3.4% for NKA-alpha1 and 27.5 +/- 2.5% for NKA-alpha2). Donor fluorescence depended linearly on acceptor fluorescence, indicating a 1:1 PLM:NKA stoichiometry for both isoforms. PLM phosphorylation induced by cAMP-dependent protein kinase and protein kinase C activation drastically reduced the FRET with both NKA isoforms. However, submaximal cAMP-dependent protein kinase activation had less effect on PLM-NKA-alpha2 versus PLM-NKA-alpha1. Surprisingly, ouabain virtually abolished NKA-PLM FRET but only partially reduced co-immunoprecipitation. PLM-CFP also showed FRET to PLM-YFP, but the relationship during progressive photobleach was highly nonlinear, indicating oligomers involving >or=3 monomers. Using cardiac myocytes from wild-type mice and mice where NKA-alpha1 is ouabain-sensitive and NKA-alpha2 is ouabain-resistant, we assessed the effects of PLM phosphorylation on NKA-alpha1 and NKA-alpha2 function. Isoproterenol enhanced internal Na(+) affinity of both isoforms (K((1/2)) decreased from 18.1 +/- 2.0 to 11.5 +/- 1.9 mm for NKA-alpha1 and from 16.4 +/- 2.5 to 10.4 +/- 1.5 mm for NKA-alpha2) without altering maximum transport rate (V(max)). Protein kinase C activation also decreased K((1/2)) for both NKA-alpha1 and NKA-alpha2 (to 9.4 +/- 1.0 and 9.1 +/- 1.1 mm, respectively) but increased V(max) only for NKA-alpha2 (1.9 +/- 0.4 versus 1.2 +/- 0.5 mm/min). In conclusion, PLM associates with and modulates both NKA-alpha1 and NKA-alpha2 in a comparable but not identical manner.
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Affiliation(s)
- Julie Bossuyt
- Department of Pharmacology, University of California, Davis, California 95616, USA
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Han F, Tucker AL, Lingrel JB, Despa S, Bers DM. Extracellular potassium dependence of the Na+-K+-ATPase in cardiac myocytes: isoform specificity and effect of phospholemman. Am J Physiol Cell Physiol 2009; 297:C699-705. [PMID: 19570895 DOI: 10.1152/ajpcell.00063.2009] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac Na(+)-K(+)-ATPase (NKA) regulates intracellular Na(+), which in turn affects intracellular Ca(2+) and contractility via the Na(+)/Ca(2+) exchanger. Extracellular K(+) concentration ([K(+)]) is a central regulator of NKA activity. Phospholemman (PLM) has recently been recognized as a critical regulator of NKA in the heart. PLM reduces the intracellular Na(+) affinity of NKA, an effect relieved by PLM phosphorylation. Here we tested whether the NKA alpha(1)- vs. alpha(2)- isoforms have different external K(+) sensitivity and whether PLM and PKA activation affects the NKA affinity for K(+) in mouse cardiac myocytes. We measured the external [K(+)] dependence of the pump current generated by the ouabain-resistant NKA isoform in myocytes from wild-type (WT) mice (i.e., current due to NKA-alpha(1)) and mice in which the NKA isoforms have swapped ouabain affinities (alpha(1) is ouabain sensitive and alpha(2) is ouabain resistant) to assess current due to NKA-alpha(2). We found that NKA-alpha(1) has a higher affinity for external K(+) than NKA-alpha(2) [half-maximal pump activation (K(0.5)) = 1.5 +/- 0.1 vs. 2.9 +/- 0.3 mM]. The apparent external K(+) affinity of NKA was significantly lower in myocytes from WT vs. PLM-knockout mice (K(0.5) = 2.0 +/- 0.2 vs. 1.05 +/- 0.08 mM). However, PKA activation by isoproterenol (1 microM) did not alter the K(0.5) of NKA for external K(+) in WT myocytes. We conclude that 1) NKA-alpha(1) has higher affinity for K(+) than NKA-alpha(2) in cardiac myocytes, 2) PLM decreases the apparent external K(+) affinity of NKA, and 3) phosphorylation of PLM at the cytosolic domain does not alter apparent extracellular K(+) affinity of NKA.
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Affiliation(s)
- Fei Han
- Department of Pathology, Northwestern University, Feinberg School of Chicago, Chicago, Illinois, USA
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Despa S, Tucker AL, Bers DM. Phospholemman-mediated activation of Na/K-ATPase limits [Na]i and inotropic state during beta-adrenergic stimulation in mouse ventricular myocytes. Circulation 2008; 117:1849-55. [PMID: 18362230 DOI: 10.1161/circulationaha.107.754051] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Cardiac Na/K-ATPase (NKA) regulates intracellular Na ([Na](i)), which in turn affects intracellular Ca and thus contractility via Na/Ca exchange. Recent evidence shows that phosphorylation of the NKA-associated small transmembrane protein phospholemman (PLM) mediates beta-adrenergic-induced NKA stimulation. METHODS AND RESULTS Here, we tested whether PLM phosphorylation during beta-adrenergic activation limits the rise in [Na](i), Ca transient amplitude, and triggered arrhythmias in mouse ventricular myocytes. In myocytes from wild-type (WT) mice, [Na](i) increased on field stimulation at 2 Hz from 11.1+/-1.8 mmol/L to a plateau of 15.2+/-1.5 mmol/L. Isoproterenol induced a decrease in [Na](i) to 12.0+/-1.2 mmol/L. In PLM knockout (PLM-KO) mice in which beta-adrenergic stimulation does not activate NKA, [Na](i) also increased at 2 Hz (from 10.4+/-1.2 to 17.0+/-1.5 mmol/L) but was unaltered by isoproterenol. The PLM-mediated decrease in [Na](i) in WT mice could limit the isoproterenol-induced inotropic state. Indeed, the isoproterenol-induced increase in the amplitude of Ca transients was significantly smaller in the WT mice (5.2+/-0.4- versus 7.1+/-0.5-fold in PLM-KO mice). This also was the case for the sarcoplasmic reticulum Ca content, which increased by 1.27+/-0.09-fold in WT mice versus 1.53+/-0.09-fold in PLM-KO mice. The higher sarcoplasmic reticulum Ca content in PLM-KO versus WT mice was associated with an increased propensity for spontaneous Ca transients and contractions in PLM-KO mice. CONCLUSIONS These data suggest that PLM phosphorylation and NKA stimulation are an integral part of the sympathetic fight-or-flight response, tempering the rise in [Na](i) and cellular Ca loading and perhaps limiting Ca overload-induced arrhythmias.
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Affiliation(s)
- Sanda Despa
- Department of Physiology, Loyola University Chicago, Maywood, Ill, USA
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Abstract
The Na+/K+-ATPase (NKA) is the main route for Na+ extrusion from cardiac myocytes. Different NKA α-subunit isoforms are present in the heart. NKA-α1 is predominant, although there is a variable amount of NKA-α2 in adult ventricular myocytes of most species. It has been proposed that NKA-α2 is localized mainly in T-tubules (TT), where it could regulate local Na+/Ca2+ exchange and thus cardiac myocyte Ca2+. However, there is controversy as to where NKA-α1 vs. NKA-α2 are localized in ventricular myocytes. Here, we assess the TT vs. external sarcolemma (ESL) distribution functionally using formamide-induced detubulation of rat ventricular myocytes, NKA current (IPump) measurements and the different ouabain sensitivity of NKA-α1 (low) and NKA-α2 (high) in rat heart. Ouabain-dependent IPump inhibition in control myocytes indicates a high-affinity NKA isoform (NKA-α2, K1/2 = 0.38 ± 0.16 μM) that accounts for 29.5 ± 1.3% of IPump and a low-affinity isoform (NKA-α1, K1/2 = 141 ± 17 μM) that accounts for 70.5% of IPump. Detubulation decreased cell capacitance from 164 ± 6 to 120 ± 8 pF and reduced IPump density from 1.24 ± 0.05 to 1.02 ± 0.05 pA/pF, indicating that the functional density of NKA is significantly higher in TT vs. ESL. In detubulated myocytes, NKA-α2 accounted for only 18.2 ± 1.1% of IPump. Thus, ∼63% of IPump generated by NKA-α2 is from the TT (although TT are only 27% of the total sarcolemma), and the NKA-α2/NKA-α1 ratio in TT is significantly higher than in the ESL. The functional density of NKA-α2 is ∼4.5 times higher in the T-tubules vs. ESL, whereas NKA-α1 is almost uniformly distributed between the TT and ESL.
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Affiliation(s)
- Sanda Despa
- Dept. of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Ave., Maywood, IL 60153, USA
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Abstract
Ca(2+) in cardiac myocytes regulates contractility and relaxation, and Ca(2+) and Na (+)regulation are linked via Na(+)/Ca(2+) exchange (NCX). Heart failure (HF) is accompanied by contractile dysfunction and arrhythmias, both of which may be due to altered cellular Ca(2+) handling. Smaller Ca(2+) transient and sarcoplasmic reticulum (SR) Ca(2+) content cause systolic dysfunction in HF. The reduced SR Ca(2+) content is due to: (a) reduced SR Ca(2+)-ATPase function (which also contributes to diastolic dysfunction), (b) increased expression and function of NCX (which competes with SR Ca(2+)-ATPase during relaxation, but preserves diastolic function), and (c) enhanced diastolic SR Ca(2+) leak. Relative contributions of these may vary with HF etiology and stage. Triggered arrhythmias (e.g., delayed afterdepolarizations [DADs]) are prominent in HF. DADs are due to spontaneous SR Ca(2+) release and consequent activation of transient inward NCX current, which in HF allows DADs to more readily trigger arrhythmogenic action potentials. Thus NCX and Na(+) are critical in systolic and diastolic function and arrhythmias. [Na(+)](i) is elevated in HF, which may limit SR unloading and provide some Ca(2+) influx during the HF action potential, thus limiting the depression of systolic function. High [Na(+)](i) in HF is due to enhanced Na(+) influx. Cellular Na(+)/K(+)-ATPase (NKA) function appears unaltered, despite reduced NKA expression. This dichotomy led us to test NKA regulation by phospholemman (PLM). We find that PLM regulates NKA in a manner analogous to phospholamban regulation of SR Ca(2+)-ATPase (i.e., inhibition that is relieved by PLM phosphorylation). We measured intermolecular FRET between PLM and NKA, which is reduced upon PLM phosphorylation. The lower expression level of more phosphorylated PLM in HF may explain the above dichotomy. Thus, altered Ca(2+) and Na(+) handling contributes to altered contractile function and arrhythmogenesis in HF.
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Affiliation(s)
- Donald M Bers
- Department of Physiology, Stritch School of Medicine, Loyola University Chicago, 2160 South First Avenue, Maywood, IL 60153-5500, USA.
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Berry RG, Despa S, Fuller W, Bers DM, Shattock MJ. Differential distribution and regulation of mouse cardiac Na+/K+-ATPase alpha1 and alpha2 subunits in T-tubule and surface sarcolemmal membranes. Cardiovasc Res 2006; 73:92-100. [PMID: 17157829 DOI: 10.1016/j.cardiores.2006.11.006] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Revised: 10/16/2006] [Accepted: 11/07/2006] [Indexed: 10/23/2022] Open
Abstract
OBJECTIVES Two Na+/K+-ATPase (NKA) alpha-subunit isoforms, alpha1 and alpha2, are expressed in the adult mouse heart. The subcellular distribution of these isoforms in T-tubule and surface sarcolemmal (SSL) membranes and their regulation by cAMP-dependent protein kinase (PKA) is unclear. METHODS We used formamide-induced detubulation of mouse ventricular myocytes to investigate differential functional distribution and regulation by PKA of alpha1 and alpha2 in T-tubule versus SSL membranes by measuring NKA current (I(pump)) and NKA-mediated Na+ efflux (-d[Na](i)/dt). RESULTS I(pump) is composed of 88% alpha(1)-mediated I(pump) (Ialpha1) and 12% alpha2-mediated I(pump) (Ialpha2). alpha1 and alpha2 subunits demonstrate distinct ouabain affinities (105+/-6 and 0.3+/-0.1 micromol/L respectively) but similar affinity for intracellular Na+ (K(1/2)Na+ of 16.6+/-0.8 and 16.7+/-2.6 mmol/L respectively). Detubulation reduced (i) I(pump) density (1.42+/-0.1 to 1.20+/-0.04 pA/pF), (ii) cell capacitance (181+/-12 to 127+/-17 pF), and (iii) Ialpha2 contribution (12 to 6%). Total I(pump) density was approximately 60% higher in T-tubule (1.94 pA/pF, derived) vs. SSL membranes. Although T-tubule membranes represent only 30% of total surface area, they generate approximately 70% of Ialpha2 and approximately 37% of Ialpha1. Ialpha1 density was substantially higher than Ialpha2 in SSL (Ialpha1:Ialpha2 = 16:1) but this was markedly reduced in T-tubules (4:1). In addition to differential localisation, isoprenaline (ISO, 1 micromol/L) significantly increased alpha1-mediated NKA Na+ affinity (from 16.6+/-0.8 to 13.3+/-1.4 mmol/L) and caused a small increase in maximal NKA Na+ efflux rate. ISO had no effect on alpha2-mediated NKA activity. CONCLUSION These data suggest that NKA alpha1 and alpha2 subunits are differentially localised and regulated by PKA in T-tubule and SSL membranes and may have distinct regulatory roles in cardiac excitation-contraction coupling.
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Affiliation(s)
- Roger G Berry
- Cardiac Physiology, King's College London, The Rayne Institute, St Thomas' Hospital, London SE1 7EH, UK
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Abstract
Because phospholemman (PLM) regulates the Na(+)/K(+) pump (NKA) and is a major cardiac phosphorylation target for both protein kinase A (at Ser68) and protein kinase C (PKC) (at both Ser63 and Ser68), we evaluated whether PLM mediates the PKC-dependent regulation of NKA function and protein kinase A/PKC crosstalk in ventricular myocytes. PKC was activated by PDBu (300 nmol/L), and we measured NKA-mediated [Na(+)](i) decline (fluorescence measurements) and current (I(pump)) (voltage clamp). In wild-type mouse myocytes, PDBu increased PLM phosphorylation at Ser63 and Ser68, I(pump) (both at 10 and 100 mmol/L Na(+) in the pipette solution) and maximal NKA-mediated Na(+) extrusion rate (V(max)) from 7.9+/-1.1 to 12.7+/-1.9 mmol.L(-1) per minute without altering NKA affinity for internal Na(+) (K(0.5)). In PLM knockout mice, PDBu had no effect on either V(max) or K(0.5). After pretreatment with isoproterenol (ISO) (1 mumol/L), PDBu still increased the NKA V(max) and PLM phosphorylation at Ser63 and Ser68. Conversely, after pretreatment with PDBu, ISO further increased the Na(+) affinity of NKA and phosphorylation at Ser68, as it did alone without PDBu. The final NKA activity was independent of the application sequence. The NKA activity in PLM knockout myocytes, after normalizing the protein level, was similar to that after PDBu and ISO treatment. We conclude that (1) PLM mediates the PKC-dependent activation of NKA function in cardiac myocytes, (2) PDBu and ISO effects are additive in the mouse (affecting mainly V(max) and K(0.5), respectively), and (3) PDBu and ISO combine to activate NKA in wild-type to the level found in the PLM knockout mouse.
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Affiliation(s)
- Fei Han
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 S First Ave, Maywood, IL 60153, USA
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Bossuyt J, Despa S, Martin JL, Bers DM. Phospholemman phosphorylation alters its fluorescence resonance energy transfer with the Na/K-ATPase pump. J Biol Chem 2006; 281:32765-73. [PMID: 16943195 DOI: 10.1074/jbc.m606254200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phospholemman (PLM) or FXYD1 is a major cardiac myocyte phosphorylation target upon adrenergic stimulation. Prior immunoprecipitation and functional studies suggest that phospholemman associates with the Na/K-pump (NKA) and mediates adrenergic Na/K-pump regulation. Here, we tested whether the NKA-PLM interaction is close enough to allow fluorescence resonance energy transfer (FRET) between cyan and yellow fluorescent (CFP/YFP) fusion proteins of Na/K pump and phospholemman and whether phospholemman phosphorylation alters such FRET. Co-expressed NKA-CFP and PLM-YFP in HEK293 cells co-localized in the plasma membrane and exhibited robust FRET. Selective acceptor photobleach increased donor fluorescence (F(CFP)) by 21.5 +/- 4.1% (n = 13), an effect nearly abolished when co-expressing excess phospholemman lacking YFP. Activation of protein kinase C or A progressively and reversibly decreased FRET assessed by either the fluorescence ratio (F(YFP)/F(CFP)) or the enhancement of donor fluorescence after acceptor bleach. After protein kinase C activation, forskolin did not further reduce FRET, but after forskolin pretreatment, protein kinase C could still reduce FRET. This agreed with phospholemman phosphorylation measurements: by protein kinase C at both Ser-63 and Ser-68, but by protein kinase A only at Ser-68. Expression of PLM-YFP and PLM-CFP resulted in even stronger FRET than for NKA-PLM (F(CFP) increased by 37 +/- 1% upon YFP photobleach), and this FRET was enhanced by phospholemman phosphorylation, consistent with phospholemman multimerization. Co-expressed PLM-CFP and Na/Ca exchange-YFP were highly membrane co-localized, but FRET was undetectable. We conclude that phospholemman and Na/K-pump are in very close proximity (FRET occurs) and that phospholemman phosphorylation alters the interaction of Na/K-pump and phospholemman.
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Affiliation(s)
- Julie Bossuyt
- Department of Physiology, Loyola University Chicago, 2160 S. First Avenue, Maywood, IL 60153, USA
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Berry RG, Fuller W, Despa S, Bers DM, Shattock MJ. Differential distribution of mouse cardiac Na/K ATPase α1 and α2-subunit function in T-tubule and surface sarcolemmal membranes. J Mol Cell Cardiol 2006. [DOI: 10.1016/j.yjmcc.2006.03.226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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