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Trum M, Wagner S, Maier LS, Mustroph J. CaMKII and GLUT1 in heart failure and the role of gliflozins. Biochim Biophys Acta Mol Basis Dis 2020; 1866:165729. [PMID: 32068116 DOI: 10.1016/j.bbadis.2020.165729] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2019] [Revised: 02/11/2020] [Accepted: 02/12/2020] [Indexed: 12/14/2022]
Abstract
Empagliflozin, a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, has been shown to reduce mortality and hospitalization for heart failure in diabetic patients in the EMPA-REG-OUTCOME trial (Zinman et al., 2015). Surprisingly, dapagliflozin, another SGLT2 inhibitor, exerted comparable effects on clinical endpoints even in the absence of diabetes mellitus (DAPA-HF trial) (McMurray et al., 2019). There is a myriad of suggested underlying mechanisms ranging from improved glycemic control and hemodynamic effects to altered myocardial metabolism, inflammation, neurohumoral activation and intracellular ion homeostasis. Here, we review the effects of gliflozins on cardiac electro-mechanical coupling with an emphasis on novel CaMKII-mediated pathways and on cardiac glucose and ketone metabolism in the failing heart. We focus on empagliflozin as it is the gliflozin with the most abundant experimental evidence for direct effects on the heart. Where useful, we aim to compare empagliflozin to other gliflozins. To facilitate understanding of empagliflozin-induced alterations, we first give a short summary of the pathophysiological role of CaMKII in heart failure, as well as cardiac changes of glucose and ketone body metabolism in the failing heart.
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Affiliation(s)
- M Trum
- Department of Internal Medicine II, University Hospital Regensburg, Regensburg, Germany
| | - S Wagner
- Department of Internal Medicine II, University Hospital Regensburg, Regensburg, Germany
| | - L S Maier
- Department of Internal Medicine II, University Hospital Regensburg, Regensburg, Germany
| | - J Mustroph
- Department of Internal Medicine II, University Hospital Regensburg, Regensburg, Germany.
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Changes of Blood-Brain Barrier and Brain Parenchymal Protein Expression Levels of Mice under Different Insulin-Resistance Conditions Induced by High-Fat Diet. Pharm Res 2019; 36:141. [PMID: 31367840 DOI: 10.1007/s11095-019-2674-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Accepted: 07/20/2019] [Indexed: 12/13/2022]
Abstract
PURPOSE The purpose of the present study was to investigate changes of blood-brain barrier (BBB) and brain parenchymal protein expression due to type II diabetes mellitus (T2DM) induced by a high-fat diet (HFD) by using SWATH-based quantitative proteomics. METHODS Mice were fed a HFD for 2 or 10 weeks, and then SWATH-based quantitative proteomic analysis, western blot analysis, immunohistochemistry and functional transport studies were performed. RESULTS In brain capillaries, expression levels of BBB transporters (Glut1, P-glycoprotein) and tight-junction proteins (claudin-5, occludin) were significantly reduced in HFD mice at 2 weeks, but recovered to the levels in the normal diet (ND) group at 10 weeks. P-glycoprotein function at the BBB was reduced at 2 weeks. In the cerebral cortex and hippocampus, neurofilament, which is important for neuronal function, was decreased in HFD mice at 2 weeks, but recovered at 10 weeks. CONCLUSION Our results suggest that changes in the status of insulin resistance influence expression of BBB transporters, which in turn may alter the expression of cognitive function-related proteins.
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Gutiérrez Aguilar GF, Alquisiras-Burgos I, Espinoza-Rojo M, Aguilera P. Glial Excitatory Amino Acid Transporters and Glucose Incorporation. ADVANCES IN NEUROBIOLOGY 2017; 16:269-282. [PMID: 28828615 DOI: 10.1007/978-3-319-55769-4_13] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Excitatory amino acid transporters (EAATs) expressed in astrocytes remove the glutamate released by neurons in and around the synaptic cleft. In this manner, astrocytes preserve the signaling functions mediated by glutamate on synapses and prevent excitotoxicity. Additionally, EAAT activation stimulates glucose utilization in astrocytes, linking neuronal activity with astrocyte metabolism. In this chapter, we briefly review the characteristics of the EAATs and the glucose transporters (GLUTs) expressed in the brain. Thereafter, we focus on the effect of EAATs activation and its association with glucose utilization in astrocytes, specifically addressing the role played by Na+ and Ca2+ ions. Next, we analyze evidence that proposes mechanisms by which the activity of GLUTs could be modulated after EAAT activation (e.g., kinases altering GLUTs traffic to cell membrane). Finally, we analyzed the current knowledge on EAAT function during energy deficiency as a possible inducer of GLUT expression to prevent neuronal damage.
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Affiliation(s)
- Germán Fernando Gutiérrez Aguilar
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", Insurgentes Sur #3877, Col. La Fama, Tlalpan, Ciudad de México, 14269, México
| | - Ivan Alquisiras-Burgos
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", Insurgentes Sur #3877, Col. La Fama, Tlalpan, Ciudad de México, 14269, México
| | - Mónica Espinoza-Rojo
- Laboratorio de Biología Molecular y Genómica, Universidad Autónoma de Guerrero, Chilpancingo, Guerrero, 39087, México
| | - Penélope Aguilera
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", Insurgentes Sur #3877, Col. La Fama, Tlalpan, Ciudad de México, 14269, México.
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Role of plasma membrane caveolae/lipid rafts in VEGF-induced redox signaling in human leukemia cells. BIOMED RESEARCH INTERNATIONAL 2014; 2014:857504. [PMID: 24738074 PMCID: PMC3967716 DOI: 10.1155/2014/857504] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Accepted: 01/21/2014] [Indexed: 12/02/2022]
Abstract
Caveolae/lipid rafts are membrane-rich cholesterol domains endowed with several functions in signal transduction and caveolin-1 (Cav-1) has been reported to be implicated in regulating multiple cancer-associated processes, ranging from tumor growth to multidrug resistance and angiogenesis. Vascular endothelial growth factor receptor-2 (VEGFR-2) and Cav-1 are frequently colocalized, suggesting an important role played by this interaction on cancer cell survival and proliferation. Thus, our attention was directed to a leukemia cell line (B1647) that constitutively produces VEGF and expresses the tyrosine-kinase receptor VEGFR-2. We investigated the presence of VEGFR-2 in caveolae/lipid rafts, focusing on the correlation between reactive oxygen species (ROS) production and glucose transport modulation induced by VEGF, peculiar features of tumor proliferation. In order to better understand the involvement of VEGF/VEGFR-2 in the redox signal transduction, we evaluated the effect of different compounds able to inhibit VEGF interaction with its receptor by different mechanisms, corroborating the obtained results by immunoprecipitation and fluorescence techniques. Results here reported showed that, in B1647 leukemia cells, VEGFR-2 is present in caveolae through association with Cav-1, demonstrating that caveolae/lipid rafts act as platforms for negative modulation of VEGF redox signal transduction cascades leading to glucose uptake and cell proliferation, suggesting therefore novel potential targets.
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Vieceli Dalla Sega F, Zambonin L, Fiorentini D, Rizzo B, Caliceti C, Landi L, Hrelia S, Prata C. Specific aquaporins facilitate Nox-produced hydrogen peroxide transport through plasma membrane in leukaemia cells. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:806-14. [PMID: 24440277 DOI: 10.1016/j.bbamcr.2014.01.011] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2013] [Revised: 12/09/2013] [Accepted: 01/10/2014] [Indexed: 12/30/2022]
Abstract
In the last decade, the generation and the role of reactive oxygen species (ROS), particularly hydrogen peroxide, in cell signalling transduction pathways have been intensively studied, and it is now clear that an increase of ROS level affects cellular growth and proliferation pathways related to cancer development. Hydrogen peroxide (H2O2) has been long thought to permeate biological membranes by simple diffusion since recent evidence challenged this notion disclosing the role of aquaporin water channels (AQP) in mediating H2O2 transport across plasma membranes. We previously demonstrated that NAD(P)H oxidase (Nox)-generated ROS sustain glucose uptake and cellular proliferation in leukaemia cells. The aim of this study was to assess whether specific AQP isoforms can channel Nox-produced H2O2 across the plasma membrane of leukaemia cells affecting downstream pathways linked to cell proliferation. In this work, we demonstrate that AQP inhibition caused a decrease in intracellular ROS accumulation in leukaemia cells both when H2O2 was produced by Nox enzymes and when it was exogenously added. Furthermore, AQP8 overexpression or silencing resulted to modulate VEGF capacity of triggering an H2O2 intracellular level increase or decrease, respectively. Finally, we report that AQP8 is capable of increasing H2O2-induced phosphorylation of both PI3K and p38 MAPK and that AQP8 expression affected positively cell proliferation. Taken together, the results here reported indicate that AQP8 is able to modulate H2O2 transport through the plasma membrane affecting redox signalling linked to leukaemia cell proliferation.
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Affiliation(s)
| | - Laura Zambonin
- Department of Pharmacy and Biotechnology, University of Bologna, Italy
| | - Diana Fiorentini
- Department of Pharmacy and Biotechnology, University of Bologna, Italy
| | - Benedetta Rizzo
- Department for Life Quality Studies, University of Bologna, Italy
| | - Cristiana Caliceti
- Department of Cardiology and Laboratory for Technologies of Advanced Therapies (LTTA Center), University Hospital of Ferrara and Maria Cecilia Hospital, GVM Care&Research, E.S: Health Science Foundation, Cotignola, Italy
| | | | - Silvana Hrelia
- Department for Life Quality Studies, University of Bologna, Italy
| | - Cecilia Prata
- Department of Pharmacy and Biotechnology, University of Bologna, Italy
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Characterization and Modulation of Glucose Uptake in a Human Blood–Brain Barrier Model. J Membr Biol 2013; 246:669-77. [DOI: 10.1007/s00232-013-9583-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2013] [Accepted: 08/04/2013] [Indexed: 10/26/2022]
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Quercetin and epigallocatechin gallate inhibit glucose uptake and metabolism by breast cancer cells by an estrogen receptor-independent mechanism. Exp Cell Res 2013; 319:1784-1795. [DOI: 10.1016/j.yexcr.2013.05.001] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 04/02/2013] [Accepted: 05/02/2013] [Indexed: 12/16/2022]
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Chen SJ, Zhang W, Tong Q, Conrad K, Hirschler-Laszkiewicz I, Bayerl M, Kim JK, Cheung JY, Miller BA. Role of TRPM2 in cell proliferation and susceptibility to oxidative stress. Am J Physiol Cell Physiol 2013; 304:C548-60. [PMID: 23302782 DOI: 10.1152/ajpcell.00069.2012] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The transient receptor potential (TRP) channel TRPM2 is an ion channel that modulates cell survival. We report here that full-length (TRPM2-L) and short (TRPM2-S) isoform expression was significantly increased in human neuroblastoma compared with adrenal gland. To differentiate the roles of TRPM2-L and TRPM2-S in cell proliferation and survival, we established neuroblastoma SH-SY5Y cell lines stably expressing either TRPM2 isoform or empty vector. Cells expressing TRPM2-S showed significantly enhanced proliferation, downregulation of phosphatase and tensin homolog (PTEN), and increased protein kinase B (Akt) phosphorylation and cell surface glucose transporter 1 (Glut1) compared with cells expressing TRPM2-L or empty vector. ERK phosphorylation was increased, and forkhead box O 3a (FOXO3a) levels were decreased. Inhibitor studies demonstrated that enhanced proliferation was dependent on phosphatidylinositol 3-kinase/Akt, ERK, and NADPH oxidase activation. On the other hand, TRPM2-S-expressing cells were significantly more susceptible to cell death induced by low H2O2 concentrations (50-100 μM), whereas TRPM2-L-expressing cells were protected. This was associated with a significant increase in FOXO3a, MnSOD (SOD2), and membrane Glut1 in TRPM2-L-expressing cells compared with TRPM2-S expressing cells. We conclude that TRPM2 channels occupy a key role in cell proliferation and survival following oxidative stress in neuroblastoma. Our results suggest that overexpression of TRPM2-S results in increased proliferation through phosphatidylinositol 3-kinase/Akt and ERK pathways, while overexpression of TRPM2-L confers protection against oxidative stress-induced cell death through FOXO3a and SOD. TRPM2 channels may represent a novel future therapeutic target in diseases involving oxidative stress.
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Affiliation(s)
- Shu-jen Chen
- Department of Pediatrics, Pennsylvania State University College of Medicine, Milton S. Hershey Medical Center, PO Box 850, Hershey, PA 17033, USA
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Caliceti C, Zambonin L, Prata C, Vieceli Dalla Sega F, Hakim G, Hrelia S, Fiorentini D. Effect of plasma membrane cholesterol depletion on glucose transport regulation in leukemia cells. PLoS One 2012; 7:e41246. [PMID: 22859971 PMCID: PMC3408441 DOI: 10.1371/journal.pone.0041246] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2012] [Accepted: 06/22/2012] [Indexed: 11/19/2022] Open
Abstract
GLUT1 is the predominant glucose transporter in leukemia cells, and the modulation of glucose transport activity by cytokines, oncogenes or metabolic stresses is essential for their survival and proliferation. However, the molecular mechanisms allowing to control GLUT1 trafficking and degradation are still under debate. In this study we investigated whether plasma membrane cholesterol depletion plays a role in glucose transport activity in M07e cells, a human megakaryocytic leukemia line. To this purpose, the effect of cholesterol depletion by methyl-β-cyclodextrin (MBCD) on both GLUT1 activity and trafficking was compared to that of the cytokine Stem Cell Factor (SCF). Results show that, like SCF, MBCD led to an increased glucose transport rate and caused a subcellular redistribution of GLUT1, recruiting intracellular transporter molecules to the plasma membrane. Due to the role of caveolae/lipid rafts in GLUT1 stimulation in response to many stimuli, we have also investigated the GLUT1 distribution along the fractions obtained after non ionic detergent treatment and density gradient centrifugation, which was only slightly changed upon MBCD treatment. The data suggest that MBCD exerts its action via a cholesterol-dependent mechanism that ultimately results in augmented GLUT1 translocation. Moreover, cholesterol depletion triggers GLUT1 translocation without the involvement of c-kit signalling pathway, in fact MBCD effect does not involve Akt and PLCγ phosphorylation. These data, together with the observation that the combined MBCD/SCF cell treatment caused an additive effect on glucose uptake, suggest that the action of SCF and MBCD may proceed through two distinct mechanisms, the former following a signalling pathway, and the latter possibly involving a novel cholesterol dependent mechanism.
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Affiliation(s)
- Cristiana Caliceti
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Laura Zambonin
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Cecilia Prata
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | | | - Gabriele Hakim
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Silvana Hrelia
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
| | - Diana Fiorentini
- Biochemistry Department “G. Moruzzi”, Alma Mater Studiorum-University of Bologna, Bologna, Italy
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Maraldi T, Prata C, Vieceli Dalla Sega F, Caliceti C, Zambonin L, Fiorentini D, Hakim G. NAD(P)H oxidase isoform Nox2 plays a prosurvival role in human leukaemia cells. Free Radic Res 2010; 43:1111-21. [PMID: 19707918 DOI: 10.1080/10715760903186132] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The mechanism involved in the prosurvival effect of interleukin-3 on the human acute myeloid leukaemia cell line M07e is investigated. A decrease in intracellular reactive oxygen species (ROS) content, glucose transport activity and cell survival was observed in the presence of inhibitors of plasma membrane ROS sources, such as diphenylene iodonium and apocynin, and by small interference RNA for Nox2. Moreover, IL-3 incubation stimulated the synthesis of Nox2 cytosolic sub-unit p47phox and glucose transporter Glut1. Thus, the inhibition of ROS generation by Nox inhibitors stimulated apoptosis showing that ROS production, induced by IL-3 via Nox2, protects leukaemic cells from cell death. Also incubation with receptor tyrosine kinase inhibitors, such as anti-leukaemic drugs blocking the stem cell factor receptor (c-kit), showed similar effects, hinting that IL-3 transmodulates c-kit phosphorylation. These mechanisms may play an important role in acute myeloid leukaemia treatment, representing a novel therapeutic target.
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Affiliation(s)
- Tullia Maraldi
- Department of Anatomy and Histology, University of Modena and Reggio Emilia, Modena, Italy
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Prata C, Maraldi T, Fiorentini D, Zambonin L, Hakim G, Landi L. Nox-generated ROS modulate glucose uptake in a leukaemic cell line. Free Radic Res 2009; 42:405-14. [DOI: 10.1080/10715760802047344] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Maraldi T, Prata C, Fiorentini D, Zambonin L, Landi L, Hakim G. Signal processes and ROS production in glucose transport regulation by thrombopoietin and granulocyte macrophage-colony stimulation factor in a human leukaemic cell line. Free Radic Res 2009; 41:1348-57. [DOI: 10.1080/10715760701730347] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Slaby O, Lebiedz D. Oscillatory NAD(P)H waves and calcium oscillations in neutrophils? A modeling study of feasibility. Biophys J 2009; 96:417-28. [PMID: 19167293 DOI: 10.1016/j.bpj.2008.09.044] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2008] [Accepted: 09/29/2008] [Indexed: 11/17/2022] Open
Abstract
The group of Howard Petty has claimed exotic metabolic wave phenomena together with mutually phase-coupled NAD(P)H- and calcium-oscillations in human neutrophils. At least parts of these phenomena are highly doubtful due to extensive failure of reproducibility by several other groups and hints that unreliable data from the Petty lab are involved in publications concerning circular calcium waves. The aim of our theoretical spatiotemporal modeling approach is to propose a possible and plausible biochemical mechanism which would, in principle, be able to explain metabolic oscillations and wave phenomena in neutrophils. Our modeling suggests the possibility of a calcium-controlled glucose influx as a driving force of metabolic oscillations and a potential role of polarized cell geometry and differential enzyme distribution for various NAD(P)H wave phenomena. The modeling results are supposed to stimulate further controversial discussions of such phenomena and potential mechanisms and experimental efforts to finally clarify the existence and biochemical basis of any kind of temporal and spatiotemporal patterns of calcium signals and metabolic dynamics in human neutrophils. Independent of Petty's observations, they present a general feasibility study of such phenomena in cells.
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Maraldi T, Prata C, Fiorentini D, Zambonin L, Landi L, Hakim G. Induction of apoptosis in a human leukemic cell line via reactive oxygen species modulation by antioxidants. Free Radic Biol Med 2009; 46:244-52. [PMID: 19013234 DOI: 10.1016/j.freeradbiomed.2008.10.027] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/17/2008] [Revised: 09/12/2008] [Accepted: 10/03/2008] [Indexed: 10/21/2022]
Abstract
In the human acute myeloid leukemia cell line M07e, the growth factor interleukin-3 (IL-3) induces ROS formation, positively affecting Glut1-mediated glucose uptake and cell survival. The effect of IL-3 and exogenous hydrogen peroxide on cell viability seems to be mediated through inhibition of the cell death commitment, as shown by apoptotic markers such as caspase activities, apoptotic nuclei, and changes in the amount of proteins belonging to the Bcl-2 family. The pivotal role of ROS is confirmed using various antioxidants, such as EUK-134, ebselen, TEMPO, and hydroxylamine probe. In fact, these antioxidants, acting through different mechanisms, decrease glucose transport activity and cell proliferation activated by IL-3 or by low concentrations of hydrogen peroxide. Moreover, antioxidants foster programmed cell death commitment, as shown by the cited apoptotic parameters. EUK-134, a combined superoxide dismutase/catalase mimetic, opposes the effects of IL-3 and H(2)O(2), decreasing phosphorylation levels of signaling enzymes such as Akt, Src tyrosine kinase, and ERK. Results show that ROS production induced by IL-3 can protect leukemic cells from apoptosis, the effect being counteracted by antioxidants. This mechanism may play an important role in supporting acute myeloid leukemia treatment, thus representing a novel therapeutic strategy.
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Affiliation(s)
- Tullia Maraldi
- Department of Biochemistry G. Moruzzi, University of Bologna, Via Irnerio 48, 40126, Bologna, Italy
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Porras OH, Ruminot I, Loaiza A, Barros LF. Na(+)-Ca(2+) cosignaling in the stimulation of the glucose transporter GLUT1 in cultured astrocytes. Glia 2008; 56:59-68. [PMID: 17924581 DOI: 10.1002/glia.20589] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Glutamate triggers an acute stimulation of the glucose transporter GLUT1 in cultured astrocytes, a phenomenon thought to facilitate energy delivery to active areas in the brain. Here we have explored the cell signaling mechanisms involved in this response. Half-stimulation of GLUT1 occurred at low micromolar glutamate, thus within the physiological range estimated in brain interstitium. The effect was mimicked by D-aspartate and inhibited by L-threo-beta-benzyloxyaspartate or Na(+) replacement with NMDG(+), showing the participation of the Na(+)-glutamate co-transporter. AMPA and the mGLURI agonist DHPG had no effect. The stimulation of GLUT1 was fully inhibited by ouabain, but independent activation of the Na(+)/K(+) ATPase pump with gramicidin did not affect glucose transport. Simultaneous with the Na(+) rise, glutamate and D-aspartate triggered a Ca(2+)signal, whose inhibition with BAPTA prevented the stimulation of GLUT1. However, an isolated Ca(2+) signal, triggered with endothelin 1, ATP or DHPG, did not affect glucose transport. The stimulation of GLUT1 could finally be mimicked by simultaneous induction of Na(+) and Ca(2+) signals. The requirement for both cations in the stimulation of the astrocytic glucose transporter, may help to explain how glucose metabolism in the brain is strongly activated by glutamate, but not by GABA or by inter-astrocytic signaling.
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Affiliation(s)
- Omar H Porras
- Centro de Estudios Científicos (CECS), Av. Arturo Prat 514, Casilla 1469, Valdivia, Chile
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Leybaert L, De Bock M, Van Moorhem M, Decrock E, De Vuyst E. Neurobarrier coupling in the brain: Adjusting glucose entry with demand. J Neurosci Res 2007; 85:3213-20. [PMID: 17265466 DOI: 10.1002/jnr.21189] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Glucose transport over the blood-brain barrier (BBB) is a nonrate-limiting step and has therefore received little attention as a possible adjustment point within the transport reaction cascade from blood glucose to brain cell glycolysis. Considerations of the normal working point of facilitated BBB glucose shuttling via the GLUT-1 protein indicate that the transport is working at about one-third of T(max) under basal conditions. Substitution of T(max) estimates indicates that the transport is then just enough to keep up with glucose consumption, maintaining the steady state. After brain activation, glucose transport has to be stimulated, and this can be accomplished by increasing the driving force or changing the T(max) and/or K(t) parameters of BBB transport. The first possibility involves a decrease of brain interstitial glucose with subsequent flow stimulation according to the law of mass action (LMA), whereas the second possibility involves signaling from activated neurons to the BBB, a regulation loop that we propose to be called "neurobarrier coupling" (NBC). Theoretical analysis of the LMA effect and comparison with data on glucose dynamics during brain activation suggest that this factor alone only covers about half of the stimulation necessary to bring glucose delivery into line with the elevated glucose consumption during activation. Adjusting glucose entry with demand thus probably involves both LMA and NBC effects, depending on the degree of brain activation. Further work is needed to demonstrate NBC effects following physiological brain activation in vivo and to identify the signals that lead to NBC in in vitro experiments.
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Affiliation(s)
- Luc Leybaert
- Department of Physiology and Pathophysiology, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium.
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