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Vyssokikh MY, Vigovskiy MA, Philippov VV, Boroday YR, Marey MV, Grigorieva OA, Vepkhvadze TF, Kurochkina NS, Manukhova LA, Efimenko AY, Popov DV, Skulachev VP. Age-Dependent Changes in the Production of Mitochondrial Reactive Oxygen Species in Human Skeletal Muscle. BIOCHEMISTRY. BIOKHIMIIA 2024; 89:299-312. [PMID: 38622097 DOI: 10.1134/s0006297924020093] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2023] [Revised: 01/30/2024] [Accepted: 02/01/2024] [Indexed: 04/17/2024]
Abstract
A decrease in muscle mass and its functionality (strength, endurance, and insulin sensitivity) is one of the integral signs of aging. One of the triggers of aging is an increase in the production of mitochondrial reactive oxygen species. Our study was the first to examine age-dependent changes in the production of mitochondrial reactive oxygen species related to a decrease in the proportion of mitochondria-associated hexokinase-2 in human skeletal muscle. For this purpose, a biopsy was taken from m. vastus lateralis in 10 young healthy volunteers and 70 patients (26-85 years old) with long-term primary arthrosis of the knee/hip joint. It turned out that aging (comparing different groups of patients), in contrast to inactivity/chronic inflammation (comparing young healthy people and young patients), causes a pronounced increase in peroxide production by isolated mitochondria. This correlated with the age-dependent distribution of hexokinase-2 between mitochondrial and cytosolic fractions, a decrease in the rate of coupled respiration of isolated mitochondria and respiration when stimulated with glucose (a hexokinase substrate). It is discussed that these changes may be caused by an age-dependent decrease in the content of cardiolipin, a potential regulator of the mitochondrial microcompartment containing hexokinase. The results obtained contribute to a deeper understanding of age-related pathogenetic processes in skeletal muscles and open prospects for the search for pharmacological/physiological approaches to the correction of these pathologies.
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Affiliation(s)
- Mikhail Yu Vyssokikh
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992, Russia.
- National Medical Research Center for Obstetrics, Gynecology and Perinatology Named after Academician V. I. Kulakov, Moscow, 117997, Russia
- Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, 123007, Russia
| | - Maksim A Vigovskiy
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, 119192, Russia
| | - Vladislav V Philippov
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, 119192, Russia
| | - Yakov R Boroday
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, 119192, Russia
| | - Mariya V Marey
- National Medical Research Center for Obstetrics, Gynecology and Perinatology Named after Academician V. I. Kulakov, Moscow, 117997, Russia
| | - Olga A Grigorieva
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, 119192, Russia
| | - Tatiana F Vepkhvadze
- Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, 123007, Russia
| | - Nadezhda S Kurochkina
- Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, 123007, Russia
| | - Ludmila A Manukhova
- National Medical Research Center for Obstetrics, Gynecology and Perinatology Named after Academician V. I. Kulakov, Moscow, 117997, Russia
| | - Anastasiya Yu Efimenko
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, 119192, Russia
| | - Daniil V Popov
- Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, 123007, Russia
| | - Vladimir P Skulachev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119992, Russia
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2
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Guard SE, Chapnick DA, Poss ZC, Ebmeier CC, Jacobsen J, Nemkov T, Ball KA, Webb KJ, Simpson HL, Coleman S, Bunker E, Ramirez A, Reisz JA, Sievers R, Stowell MHB, D'Alessandro A, Liu X, Old WM. Multiomic Analysis Reveals Disruption of Cholesterol Homeostasis by Cannabidiol in Human Cell Lines. Mol Cell Proteomics 2022; 21:100262. [PMID: 35753663 PMCID: PMC9525918 DOI: 10.1016/j.mcpro.2022.100262] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 06/12/2022] [Accepted: 06/21/2022] [Indexed: 01/18/2023] Open
Abstract
The nonpsychoactive cannabinoid, cannabidiol (CBD), is Food and Dug Administration approved for treatment of two drug-resistant epileptic disorders and is seeing increased use among the general public, yet the mechanisms that underlie its therapeutic effects and side-effect profiles remain unclear. Here, we report a systems-level analysis of CBD action in human cell lines using temporal multiomic profiling. FRET-based biosensor screening revealed that CBD elicits a sharp rise in cytosolic calcium, and activation of AMP-activated protein kinase in human keratinocyte and neuroblastoma cell lines. CBD treatment leads to alterations in the abundance of metabolites, mRNA transcripts, and proteins associated with activation of cholesterol biosynthesis, transport, and storage. We found that CBD rapidly incorporates into cellular membranes, alters cholesterol accessibility, and disrupts cholesterol-dependent membrane properties. Sustained treatment with high concentrations of CBD induces apoptosis in a dose-dependent manner. CBD-induced apoptosis is rescued by inhibition of cholesterol synthesis and potentiated by compounds that disrupt cholesterol trafficking and storage. Our data point to a pharmacological interaction of CBD with cholesterol homeostasis pathways, with potential implications in its therapeutic use.
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Affiliation(s)
- Steven E Guard
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Douglas A Chapnick
- Department of Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
| | - Zachary C Poss
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Christopher C Ebmeier
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Jeremy Jacobsen
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Travis Nemkov
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver, Aurora, Colorado, USA
| | - Kerri A Ball
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Kristofor J Webb
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Helen L Simpson
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Stephen Coleman
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Eric Bunker
- Department of Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
| | - Adrian Ramirez
- Department of Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
| | - Julie A Reisz
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver, Aurora, Colorado, USA
| | - Robert Sievers
- Department of Chemistry and Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA
| | - Michael H B Stowell
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA
| | - Angelo D'Alessandro
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver, Aurora, Colorado, USA
| | - Xuedong Liu
- Department of Biochemistry, University of Colorado Boulder, Boulder, Colorado, USA
| | - William M Old
- Department of Molecular, Cellular & Developmental Biology, University of Colorado Boulder, Boulder, Colorado, USA.
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3
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Coupling of GABA Metabolism to Mitochondrial Glucose Phosphorylation. Neurochem Res 2021; 47:470-480. [PMID: 34623563 DOI: 10.1007/s11064-021-03463-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 09/15/2021] [Accepted: 10/04/2021] [Indexed: 10/20/2022]
Abstract
Glucose and oxygen (O2) are vital to the brain. Glucose metabolism and mitochondria play a pivotal role in this process, culminating in the increase of reactive O2 species. Hexokinase (HK) is a key enzyme on glucose metabolism and is coupled to the brain mitochondrial redox modulation by recycling ADP for oxidative phosphorylation (OXPHOS). GABA shunt is an alternative pathway to GABA metabolism that increases succinate levels, a Krebs cycle intermediate. Although glucose and GABA metabolisms are intrinsically connected, their interplay coordinating mitochondrial function is poorly understood. Here, we hypothesize that the HK and the GABA shunt interact to control mitochondrial metabolism differently in the cortex and the hypothalamus. The GABA shunt stimulated mitochondrial O2 consumption and H2O2 production higher in hypothalamic synaptosomes (HSy) than cortical synaptosomes (CSy). The GABA shunt increased the HK coupled to OXPHOS activity in both population of synaptosomes, but the rate of activation was higher in HSy than CSy. Significantly, malonate and vigabatrin blocked the effects of the GABA shunt in the HK activity coupled to OXPHOS. It indicates that the glucose phosphorylation is linked to GABA and Krebs cycle reactions. Together, these data shed light on the HK and SDH role on the metabolism of each region fed by GABA turnover, which depends on the neurons' metabolic route.
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Sullivan CR, Koene RH, Hasselfeld K, O'Donovan S, Ramsey A, McCullumsmith RE. Neuron-specific deficits of bioenergetic processes in the dorsolateral prefrontal cortex in schizophrenia. Mol Psychiatry 2019; 24:1319-1328. [PMID: 29497148 PMCID: PMC6119539 DOI: 10.1038/s41380-018-0035-3] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 12/07/2017] [Accepted: 01/15/2018] [Indexed: 12/20/2022]
Abstract
Schizophrenia is a devastating illness that affects over 2 million people in the United States and costs society billions of dollars annually. New insights into the pathophysiology of schizophrenia are needed to provide the conceptual framework to facilitate development of new treatment strategies. We examined bioenergetic pathways in the dorsolateral prefrontal cortex (DLPFC) of subjects with schizophrenia and control subjects using western blot analysis, quantitative real-time polymerase chain reaction, and enzyme/substrate assays. Laser-capture microdissection-quantitative polymerase chain reaction was used to examine these pathways at the cellular level. We found decreases in hexokinase (HXK) and phosphofructokinase (PFK) activity in the DLPFC, as well as decreased PFK1 mRNA expression. In pyramidal neurons, we found an increase in monocarboxylate transporter 1 mRNA expression, and decreases in HXK1, PFK1, glucose transporter 1 (GLUT1), and GLUT3 mRNA expression. These results suggest abnormal bioenergetic function, as well as a neuron-specific defect in glucose utilization, in the DLPFC in schizophrenia.
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Affiliation(s)
- Courtney R. Sullivan
- Corresponding author: , Phone number: 513-558-4855, Mail address: 231 Albert Sabin Way, Care 5830, Cincinnati, Ohio, 45267-2827
| | - Rachael H. Koene
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH
| | - Kathryn Hasselfeld
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH
| | - Sinead O'Donovan
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH
| | - Amy Ramsey
- Department of Pharmacology and Toxicology, University of Toronto, ON, Canada
| | - Robert E. McCullumsmith
- Department of Psychiatry and Behavioral Neuroscience, University of Cincinnati, Cincinnati, OH
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Puthumana JS, Regenold WT. Glucose-6-phosphate dehydrogenase activity in bipolar disorder and schizophrenia: Relationship to mitochondrial impairment. J Psychiatr Res 2019; 112:99-103. [PMID: 30875545 DOI: 10.1016/j.jpsychires.2019.03.004] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 02/15/2019] [Accepted: 03/04/2019] [Indexed: 12/15/2022]
Abstract
Glucose-6-phosphate dehydrogenase (G6PD) is the first and rate-limiting enzyme of the pentose phosphate pathway that is essential to maintaining cellular redox balance. G6PD is especially plentiful in brain, and its deficiency has been linked to mood and psychotic disorders. We measured G6PD activity spectrophotometrically in four groups of 15 parietal somatosensory association cortex [Brodmann area (BA) 7] tissue samples (N = 60) from individuals with bipolar disorder (BPD); nonpsychotic unipolar major depression (UPD); schizophrenia (SCZ), and controls without psychiatric illness (CON). We report for the first time brain G6PD activity levels in these disorders. G6PD activity did not differ by brain group. In BPD and SCZ brains, however, it correlated significantly and inversely with percent of hexokinase 1 (HK1) in the tissue homogenate mitochondrial fraction as determined previously in another set of tissue samples obtained from the same brains and brain region. The correlation in SCZ brains lost statistical significance after controlling for brain pH. This finding indicates a positive relationship in BPD brains between G6PD activity and HK1 mitochondrial detachment, an indicator of mitochondrial impairment associated with increased mitochondrial generation of reactive oxygen species. We speculate that this relationship could be evidence that G6PD activity is proportionate to and may be a compensatory response to oxidative stress in the BA7 region of BPD brains. Future research should focus on clarifying the relationships among G6PD activity, markers of oxidative stress, brain pH, and evidence of mitochondrial impairment, particularly HK1 mitochondrial detachment, in brains of individuals with G6PD deficiency, BPD and SCZ.
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Affiliation(s)
- Joseph S Puthumana
- University of Maryland School of Medicine, 655 W Baltimore Street, Baltimore, MD, 21201, USA.
| | - William T Regenold
- University of Maryland School of Medicine, Department of Psychiatry, 22 S. Greene St, Baltimore, MD, 21201, USA.
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VDAC electronics: 5. Mechanism and computational model of hexokinase-dependent generation of the outer membrane potential in brain mitochondria. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2599-2607. [PMID: 30291922 DOI: 10.1016/j.bbamem.2018.10.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Revised: 09/07/2018] [Accepted: 10/02/2018] [Indexed: 01/01/2023]
Abstract
Glycolysis plays a key role in brain energy metabolism. The initial and rate-limiting step of brain glycolysis is catalyzed mainly by hexokinase I (HKI), the majority of which is bound to the mitochondrial outer membrane (MOM), mostly through the mitochondrial inter-membrane contact sites formed by the voltage-dependent anion channel (VDAC, outer membrane) and the adenine nucleotide translocator (ANT, inner membrane). Earlier, we proposed a mechanism for the generation of the mitochondrial outer membrane potential (OMP) as a result of partial application of the inner membrane potential (IMP) to MOM through the electrogenic ANT-VDAC-HK inter-membrane contact sites. According to this previous mechanism, the Gibbs free energy of the hexokinase reaction might modulate the generated OMP (Lemeshko, Biophys. J., 2002). In the present work, a new computational model was developed to perform thermodynamic estimations of the proposed mechanism of IMP-HKI-mediated generation of OMP. The calculated OMP was high enough to electrically regulate MOM permeability for negatively charged metabolites through free, unbound VDACs in MOM. On the other hand, the positive-inside polarity of OMP generated by the IMP-HKI-mediated mechanism is expected to protect mitochondria against elevated concentrations of cytosolic Ca2+. This computational analysis suggests that metabolically-dependent generation of OMP in the brain mitochondria, controlled by many factors that modulate VDAC1-HKI interaction, VDAC's voltage-gating properties and permeability, might represent one of the physiological mechanisms of regulation of the brain energy metabolism and of neuronal death resistance, and might also be involved in various neurodegenerative disorders, such as Alzheimer's disease.
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7
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Ziamajidi N, Jamshidi S, Ehsani-Zonouz A. In-silico and in-vitro investigation on the phenylalanine metabolites' interactions with hexokinase of Rat's brain mitochondria. J Bioenerg Biomembr 2017; 49:139-147. [PMID: 28275929 DOI: 10.1007/s10863-017-9698-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Accepted: 02/22/2017] [Indexed: 10/20/2022]
Abstract
Hexokinase (HK) is the first enzyme of glycolysis pathway. In brain, most dominant form of HK, HK-I, binds reversibly to the outer mitochondria membrane. Those metabolites that affect binding or releasing of the enzyme from the mitochondria have regulatory effect on glucose consumption of the cell. In this study destructive effect of phenylalanine and its metabolites in relation to glucose metabolism in brain have been studied. The results show that phenylpyruvic acid decreases the activity of enzyme in the presence and absence of glucose-6-phosphate (G6P) and increases the release of the enzyme from mitochondria, whereas phenylalanine and phenyllactic acid have no such effects. Obtained Interactions and elicited binding energies of docking and MD simulations also showed more affinity for phenylpyruvic acid compared with the other potent inhibitors for hexokinase after the natural product of G6P. It is possible that phenylpyruvic acid is the cause of the reduction of glucose consumption by decreasing hexokinase activity and the higher inhibitory function. Therefore, production of ATP declines in brain cells.
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Affiliation(s)
- Nasrin Ziamajidi
- Department of Clinical Biochemistry, School of Medicine, Hamadan University of Medical Sciences, Hamadan, Iran.
| | - Shirin Jamshidi
- School of Medicine, Shahid Beheshti University of Medical Sciences and Health services, Tehran, Iran
| | - Abdolvahab Ehsani-Zonouz
- Department of Biochemistry, School of Medicine, Iran University of Medical Sciences, Tehran, Iran
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8
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Scaini G, Rezin GT, Carvalho AF, Streck EL, Berk M, Quevedo J. Mitochondrial dysfunction in bipolar disorder: Evidence, pathophysiology and translational implications. Neurosci Biobehav Rev 2016; 68:694-713. [PMID: 27377693 DOI: 10.1016/j.neubiorev.2016.06.040] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2015] [Revised: 06/26/2016] [Accepted: 06/30/2016] [Indexed: 01/05/2023]
Abstract
Bipolar disorder (BD) is a chronic psychiatric illness characterized by severe and biphasic changes in mood. Several pathophysiological mechanisms have been hypothesized to underpin the neurobiology of BD, including the presence of mitochondrial dysfunction. A confluence of evidence points to an underlying dysfunction of mitochondria, including decreases in mitochondrial respiration, high-energy phosphates and pH; changes in mitochondrial morphology; increases in mitochondrial DNA polymorphisms; and downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration. Mitochondria play a pivotal role in neuronal cell survival or death as regulators of both energy metabolism and cell survival and death pathways. Thus, in this review, we discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BD. The final part of this review discusses mitochondria as a potential target of therapeutic interventions in BD.
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Affiliation(s)
- Giselli Scaini
- Translational Psychiatry Program, Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, TX, USA; Laboratory of Bioenergetics, Graduate Program in Health Sciences, Health Sciences Unit, Universidade do Extremo Sul Catarinense, Criciúma, SC, Brazil
| | - Gislaine T Rezin
- Laboratory of Clinical and Experimental Pathophysiology, Graduate Program in Health Sciences, Universidade do Sul de Santa Catarina, Tubarão, SC, Brazil
| | - Andre F Carvalho
- Translational Psychiatry Research Group and Department of Clinical Medicine, Faculty of Medicine, Federal University of Ceara, Fortaleza, CE, Brazil
| | - Emilio L Streck
- Laboratory of Bioenergetics, Graduate Program in Health Sciences, Health Sciences Unit, Universidade do Extremo Sul Catarinense, Criciúma, SC, Brazil
| | - Michael Berk
- Deakin University, IMPACT Strategic Research Centre, School of Medicine, Faculty of Health, Geelong, Victoria, Australia; Orygen, The National Centre of Excellence in Youth Mental Health and The Centre for Youth Mental Health, The Department of Psychiatry and The Florey Institute for Neuroscience and Mental Health, The University of Melbourne, Parkville, Australia
| | - João Quevedo
- Translational Psychiatry Program, Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, TX, USA; Center of Excellence on Mood Disorders, Department of Psychiatry and Behavioral Sciences, McGovern Medical School, The University of Texas Health Science Center at Houston (UTHealth), Houston, TX, USA; Neuroscience Graduate Program, The University of Texas Graduate School of Biomedical Sciences at Houston, Houston, TX, USA; Laboratory of Neurosciences, Graduate Program in Health Sciences, Health Sciences Unit, University of Southern Santa Catarina (UNESC), Criciúma, SC, Brazil.
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Agnihotri S, Zadeh G. Metabolic reprogramming in glioblastoma: the influence of cancer metabolism on epigenetics and unanswered questions. Neuro Oncol 2015; 18:160-72. [PMID: 26180081 DOI: 10.1093/neuonc/nov125] [Citation(s) in RCA: 179] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2014] [Accepted: 06/15/2015] [Indexed: 12/21/2022] Open
Abstract
A defining hallmark of glioblastoma is altered tumor metabolism. The metabolic shift towards aerobic glycolysis with reprogramming of mitochondrial oxidative phosphorylation, regardless of oxygen availability, is a phenomenon known as the Warburg effect. In addition to the Warburg effect, glioblastoma tumor cells also utilize the tricarboxylic acid cycle/oxidative phosphorylation in a different capacity than normal tissue. Altered metabolic enzymes and their metabolites are oncogenic and not simply a product of tumor proliferation. Here we highlight the advantages of why tumor cells, including glioblastoma cells, require metabolic reprogramming and how tumor metabolism can converge on tumor epigenetics and unanswered questions in the field.
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Affiliation(s)
- Sameer Agnihotri
- MacFeeters-Hamilton Brain Tumor Centre, Toronto, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada (S.A., G.Z.); Department of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Canada (G.Z)
| | - Gelareh Zadeh
- MacFeeters-Hamilton Brain Tumor Centre, Toronto, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada (S.A., G.Z.); Department of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto, Canada (G.Z)
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siRNA Screening Identifies the Host Hexokinase 2 (HK2) Gene as an Important Hypoxia-Inducible Transcription Factor 1 (HIF-1) Target Gene in Toxoplasma gondii-Infected Cells. mBio 2015; 6:e00462. [PMID: 26106078 PMCID: PMC4479703 DOI: 10.1128/mbio.00462-15] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Although it is established that oxygen availability regulates cellular metabolism and growth, little is known regarding how intracellular pathogens use host factors to grow at physiological oxygen levels. Therefore, large-scale human small interfering RNA screening was performed to identify host genes important for growth of the intracellular protozoan parasite Toxoplasma gondii at tissue oxygen tensions. Among the genes identified by this screen, we focused on the hexokinase 2 (HK2) gene because its expression is regulated by hypoxia-inducible transcription factor 1 (HIF-1), which is important for Toxoplasma growth. Toxoplasma increases host HK2 transcript and protein levels in a HIF-1-dependent manner. In addition, parasite growth at 3% oxygen is restored in HIF-1-deficient cells transfected with HK2 expression plasmids. Both HIF-1 activation and HK2 expression were accompanied by increases in host glycolytic flux, suggesting that enhanced HK2 expression in parasite-infected cells is functionally significant. Parasite dependence on host HK2 and HIF-1 expression is not restricted to transformed cell lines, as both are required for parasite growth in nontransformed C2C12 myoblasts and HK2 is upregulated in vivo following infection. While HK2 is normally associated with the cytoplasmic face of the outer mitochondrial membrane at physiological O2 levels, HK2 relocalizes to the host cytoplasm following infection, a process that is required for parasite growth at 3% oxygen. Taken together, our findings show that HIF-1-dependent expression and relocalization of HK2 represent a novel mechanism by which Toxoplasma establishes its replicative niche at tissue oxygen tensions. Little is known regarding how the host cell contributes to the survival of the intracellular parasite Toxoplasma gondii at oxygen levels that mimic those found in tissues. Our previous work showed that Toxoplasma activates the expression of an oxygen-regulated transcription factor that is required for growth. Here, we report that Toxoplasma regulates the abundance and activity of a key host metabolic enzyme, hexokinase 2, by activating HIF-1 and by promoting dissociation of hexokinase 2 from the mitochondrial membrane. Collectively, our data reveal HIF-1/hexokinase 2 as a novel target for an intracellular pathogen that acts by reprograming the host cell’s metabolism to create an environment conducive for parasite replication at physiological oxygen levels.
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11
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Regenold WT, Pratt M, Nekkalapu S, Shapiro PS, Kristian T, Fiskum G. Mitochondrial detachment of hexokinase 1 in mood and psychotic disorders: implications for brain energy metabolism and neurotrophic signaling. J Psychiatr Res 2012; 46:95-104. [PMID: 22018957 DOI: 10.1016/j.jpsychires.2011.09.018] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/21/2011] [Revised: 09/12/2011] [Accepted: 09/29/2011] [Indexed: 01/08/2023]
Abstract
The pathophysiology of mood and psychotic disorders, including unipolar depression (UPD), bipolar disorder (BPD) and schizophrenia (SCHZ), is largely unknown. Numerous studies, from molecular to neuroimaging, indicate that some individuals with these disorders have impaired brain energy metabolism evidenced by abnormal glucose metabolism and mitochondrial dysfunction. However, underlying mechanisms are unclear. A critical feature of brain energy metabolism is attachment to the outer mitochondrial membrane (OMM) of hexokinase 1 (HK1), an initial and rate-limiting enzyme of glycolysis. HK1 attachment to the OMM greatly enhances HK1 enzyme activity and couples cytosolic glycolysis to mitochondrial oxidative phosphorylation, through which the cell produces most of its adenosine triphosphate (ATP). HK1 mitochondrial attachment is also important to the survival of neurons and other cells through prevention of apoptosis and oxidative damage. Here we show, for the first time, a decrease in HK1 attachment to the OMM in postmortem parietal cortex brain tissue of individuals with UPD, BPD and SCHZ compared to tissue from controls without psychiatric illness. Furthermore, we show that HK1 mitochondrial detachment is associated with increased activity of the polyol pathway, an alternative, anaerobic pathway of glucose metabolism. These findings were observed in samples from both medicated and medication-free individuals. We propose that HK1 mitochondrial detachment could be linked to these disorders through impaired energy metabolism, increased vulnerability to oxidative stress, and impaired brain growth and development.
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Affiliation(s)
- W T Regenold
- Department of Psychiatry, University of Maryland School of Medicine, Baltimore, MD 21201, USA.
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12
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Kruszynska YT, Ciaraldi TP, Henry RR. Regulation of Glucose Metabolism in Skeletal Muscle. Compr Physiol 2011. [DOI: 10.1002/cphy.cp070218] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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13
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Perevoshchikova IV, Zorov SD, Kotova EA, Zorov DB, Antonenko YN. Hexokinase inhibits flux of fluorescently labeled ATP through mitochondrial outer membrane porin. FEBS Lett 2010; 584:2397-402. [DOI: 10.1016/j.febslet.2010.04.033] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2010] [Revised: 04/13/2010] [Accepted: 04/13/2010] [Indexed: 12/23/2022]
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14
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Marklund N, Sihver S, Hovda DA, Långström B, Watanabe Y, Ronquist G, Bergström M, Hillered L. Increased Cerebral Uptake of [18F]Fluoro-Deoxyglucose but not [1-14C]Glucose Early following Traumatic Brain Injury in Rats. J Neurotrauma 2009; 26:1281-93. [DOI: 10.1089/neu.2008.0827] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- Niklas Marklund
- Department of Neuroscience, Unit of Neurosurgery, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
| | - Sven Sihver
- Department of Neuroscience, Unit of Pharmacology, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
| | - David A. Hovda
- UCLA Brain Injury Research Center, Departments of Neurosurgery and Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, University of California–Los Angeles, Los Angeles, California
| | - Bengt Långström
- Department of Biochemistry and Organic Chemistry, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
| | - Yasuyoshi Watanabe
- Department of Neuroscience, Osaka Bioscience Institute, Osaka, Japan
- Department of Physiology, Osaka City University, Osaka, Japan
| | - Gunnar Ronquist
- Department of Medical Sciences, Biochemical Structure And Function, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
| | - Mats Bergström
- Department of Biochemistry and Organic Chemistry, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
| | - Lars Hillered
- Department of Neuroscience, Unit of Neurosurgery, Uppsala University CSO, Imanet, and Uppsala Applied Science Laboratory, Uppsala, Sweden
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15
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Marklund N, Sihver S, Hovda D, Långström B, Watanabe Y, Ronquist G, Bergström M, Hillered L. INCREASED CEREBRAL UPTAKE OF [18F]FLUORO-DEOXYGLUCOSE BUT NOT [1-14C]GLUCOSE EARLY FOLLOWING TRAUMATIC BRAIN INJURY IN RATS. J Neurotrauma 2009. [DOI: 10.1089/neu.2008-0827] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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16
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Arboleda G, Morales LC, Benítez B, Arboleda H. Regulation of ceramide-induced neuronal death: cell metabolism meets neurodegeneration. ACTA ACUST UNITED AC 2008; 59:333-46. [PMID: 18996148 DOI: 10.1016/j.brainresrev.2008.10.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 10/09/2008] [Accepted: 10/13/2008] [Indexed: 12/14/2022]
Abstract
The present review explores the role of ceramides in neuronal apoptosis, as well as the recent discovery of the signaling pathways involved in this process placing particular emphasis on the correlation between cellular metabolism and neuronal death. Endogenous levels of ceramides are increased following various pro-apoptotic stimuli which have been identified as potential causes of chronic and acute neurodegenerative diseases. Ceramides induce changes in multiple enzymes and cell signaling components. The early inhibition of the neuronal survival pathway regulated by phosphatidil-inositol-3-kinase/protein kinase B or AKT mediated by ceramide may be a relevant early event in the decision of neuronal survival/death. It may perturb several molecular and metabolic functions. In particular it might decrease glycolysis through rapid modulation of hexokinase activity. This would in turn generate limited amounts of mitochondrial substrates leading to mitochondrial dysfunction and neuronal apoptosis. Subtle and early metabolic alterations caused by inhibition of the PI3K/AKT pathway mediated by ceramide may potentially work with genes associated with neurodegenerative diseases such as Parkinson's and Alzheimer's disease. Together they may be determinant steps in downstream events leading to neuronal apoptosis. Therefore, reinforcement of the PI3K/AKT pathway could constitute an important neuroprotective strategy.
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Affiliation(s)
- Gonzalo Arboleda
- Grupo de Neurociencias, Departamento de Patología, Facultad de Medicina, Universidad Nacional de Colombia, Bogotá, Colombia.
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17
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Glucose phosphorylation and mitochondrial binding are required for the protective effects of hexokinases I and II. Mol Cell Biol 2007; 28:1007-17. [PMID: 18039843 DOI: 10.1128/mcb.00224-07] [Citation(s) in RCA: 189] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Alterations in glucose metabolism have been demonstrated for diverse disorders ranging from heart disease to cancer. The first step in glucose metabolism is carried out by the hexokinase (HK) family of enzymes. HKI and II can bind to mitochondria through their N-terminal hydrophobic regions, and their overexpression in tissue culture protects against cell death. In order to determine the relative contributions of mitochondrial binding and glucose-phosphorylating activities of HKs to their overall protective effects, we expressed full-length HKI and HKII, their truncated proteins lacking the mitochondrial binding domains, and catalytically inactive proteins in tissue culture. The overexpression of full-length proteins resulted in protection against cell death, decreased levels of reactive oxygen species, and possibly inhibited mitochondrial permeability transition in response to H(2)O(2). However, the truncated and mutant proteins exerted only partial effects. Similar results were obtained with primary neonatal rat cardiomyocytes. The HK proteins also resulted in an increase in the phosphorylation of voltage-dependent anion channel (VDAC) through a protein kinase Cepsilon (PKCepsilon)-dependent pathway. These results suggest that both glucose phosphorylation and mitochondrial binding contribute to the protective effects of HKI and HKII, possibly through VDAC phosphorylation by PKCepsilon.
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18
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Arboleda G, Huang TJ, Waters C, Verkhratsky A, Fernyhough P, Gibson RM. Insulin-like growth factor-1-dependent maintenance of neuronal metabolism through the phosphatidylinositol 3-kinase-Akt pathway is inhibited by C2-ceramide in CAD cells. Eur J Neurosci 2007; 25:3030-8. [PMID: 17561816 DOI: 10.1111/j.1460-9568.2007.05557.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Ceramide is a lipid second-messenger generated in response to stimuli associated with neurodegeneration that induces apoptosis, a mechanism underlying neuronal death in Parkinson's disease. We tested the hypothesis that insulin-like growth factor-1 (IGF-1) could mediate a metabolic response in CAD cells, a dopaminergic cell line of mesencephalic origin that differentiate into a neuronal-like phenotype upon serum removal, extend processes resembling neurites, synthesize abundant dopamine and noradrenaline and express the catecholaminergic biosynthetic enzymes tyrosine hydroxylase and dopamine beta-hydroxylase, and that this process was phosphatidylinositol 3-kinase (PI 3-K)-Akt-dependent and could be inhibited by C(2)-ceramide. The metabolic response was evaluated as real-time changes in extracellular acidification rate (ECAR) using microphysiometry. The IGF-1-induced ECAR response was associated with increased glycolysis, determined by increased NAD(P)H reduction, elevated hexokinase activity and Akt phosphorylation. C(2)-ceramide inhibited all these changes in a dose-dependent manner, and was specific, as it was not induced by the inactive C(2)-ceramide analogue C(2)-dihydroceramide. Inhibition of the upstream kinase, PI 3-K, also inhibited Akt phosphorylation and the metabolic response to IGF-1, similar to C(2)-ceramide. Decreased mitochondrial membrane potential occurred after loss of Akt phosphorylation. These results show that IGF-1 can rapidly modulate neuronal metabolism through PI 3-K-Akt and that early metabolic inhibition induced by C(2)-ceramide involves blockade of the PI 3-K-Akt pathway, and may compromise the first step of glycolysis. This may represent a new early event in the C(2)-ceramide-induced cell death pathway that could coordinate subsequent changes in mitochondria and commitment of neurons to apoptosis.
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Affiliation(s)
- Gonzalo Arboleda
- Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester, UK.
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19
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Yamamoto T, Yamada A, Watanabe M, Yoshimura Y, Yamazaki N, Yoshimura Y, Yamauchi T, Kataoka M, Nagata T, Terada H, Shinohara Y. VDAC1, having a shorter N-terminus than VDAC2 but showing the same migration in an SDS-polyacrylamide gel, is the predominant form expressed in mitochondria of various tissues. J Proteome Res 2007; 5:3336-44. [PMID: 17137335 DOI: 10.1021/pr060291w] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The voltage-dependent anion channel (VDAC) is a pore-forming protein expressed in the outer membrane of eukaryotic mitochondria. Three isoforms of it, i.e., VDAC1, VDAC2, and VDAC3, are known to be expressed in mammals; however, the question as to which is the main isoform in mitochondria is still unanswered. To address this question, we first prepared standard VDACs by using a bacterial expression system and raised various antibodies against them by using synthetic peptides as immunogens. Of the three bacterially expressed VDAC isoforms, VDAC3 showed faster migration in SDS-polyacrylamide gels than VDAC1 and VDAC2, although VDAC2 is longer than VDAC1 and VDAC3, due to a 12-amino acid extension of its N-terminal region. Even with careful structural characterization of the expressed VDACs by LC-MS/MS analysis, serious structural modifications of VDACs causing changes in their migration in SDS-polyacrylamide gels were not detected. Next, immunoreactivities of the raised antibodies toward these bacterially expressed VDAC isoforms were evaluated. Trials to prepare specific antibodies against the three individual VDAC isoforms were not successful except in the case of VDAC1. However, using a synthetic peptide corresponding to the highly conserved region among the three VDACs, we were successful in preparing an antibody showing essentially equal immunoreactivities toward all three VDACs. When mitochondrial outer membrane proteins of various rat tissues were subjected to 2-dimensional electrophoresis followed by immunoblotting with this antibody, six immunoreactive protein spots were detected. These spots were characterized by LC-MS/MS analysis, and the signal intensities among the spots were compared. As a result, the signal intensity of the spot representing VDAC1 was the highest, and thus, VDAC1 was concluded to be the most abundantly expressed of the three VDAC isoforms in mammalian mitochondria.
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Affiliation(s)
- Takenori Yamamoto
- Institute for Genome Research, University of Tokushima, Kuramotocho-3, Tokushima 770-8503, Japan
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20
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Tabernero A, Medina JM, Giaume C. Glucose metabolism and proliferation in glia: role of astrocytic gap junctions. J Neurochem 2006; 99:1049-61. [PMID: 16899068 DOI: 10.1111/j.1471-4159.2006.04088.x] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Astrocytes play a well-established role in brain metabolism, being a key element in the capture of energetic compounds from the circulation and in their delivery to active neurons. Their metabolic status is affected in many pathological situations, such as gliomas, which are the most common brain tumors. This proliferative dysfunction is associated with changes in gap junctional communication, a property strongly developed in normal astrocytes studied both in vitro and in vivo. Here, we summarize and discuss the findings that have lead to the identification of a link between gap junctions, glucose uptake, and proliferation. Indeed, the inhibition of gap junctional communication is associated with an increase in glucose uptake due to a rapid change in the localization of both GLUT-1 and type I hexokinase. This effect persists due to the up-regulation of GLUT-1 and type I hexokinase and to the induction of GLUT-3 and type II hexokinase. In addition, cyclins D1 and D3 have been found to act as sensors of the inhibition of gap junctions and have been proposed to play the role of mediators in the mitogenic effect observed. Conversely, in C6 glioma cells, characterized by a low level of intercellular communication, an increase in gap junctional communication reduces glucose uptake by releasing type I and type II hexokinases from the mitochondria and decreases the exacerbated rate of proliferation due to the up-regulation of the Cdk inhibitors p21 and p27. Identification of the molecular actors involved in these pathways should allow the determination of potential therapeutic targets that could lead to the testing of alternative strategies to prevent, or at least slow down, the proliferation of glioma cells.
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Affiliation(s)
- Arantxa Tabernero
- Departamento de Bioquímica y Biología Molecular, Edificio Departamental, Universidad de Salamanca, Salamanca, Spain.
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21
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Robey RB, Hay N. Mitochondrial hexokinases, novel mediators of the antiapoptotic effects of growth factors and Akt. Oncogene 2006; 25:4683-96. [PMID: 16892082 DOI: 10.1038/sj.onc.1209595] [Citation(s) in RCA: 388] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Cell survival has been closely linked to both trophic growth factor signaling and cellular metabolism. Such couplings have obvious physiologic and pathophysiologic implications, but their underlying molecular bases remain incompletely defined. As a common mediator of both the metabolic and anti-apoptotic effects of growth factors, the serine/threonine kinase Akt - also known as protein kinase B or PKB - is capable of regulating and coordinating these inter-related processes. The glucose dependence of the antiapoptotic effects of growth factors and Akt plus a strong correlation between Akt-regulated mitochondrial hexokinase association and apoptotic susceptibility suggest a major role for hexokinases in these effects. Mitochondrial hexokinases catalyse the first obligatory step of glucose metabolism and directly couple extramitochondrial glycolysis to intramitochondrial oxidative phosphorylation, and are thus well suited to play this role. The ability of Akt to regulate energy metabolism appears to have evolutionarily preceded the capacity to control cell survival. This suggests that Akt-dependent metabolic regulatory functions may have given rise to glucose-dependent antiapoptotic effects that evolved as an adaptive sensing system involving hexokinases and serve to ensure mitochondrial homeostasis, thereby coupling metabolism to cell survival. We hypothesize that the enlistment of Akt and hexokinase in the control of mammalian cell apoptosis evolved as a response to the recruitment of mitochondria to the apoptotic cascade. The central importance of mitochondrial hexokinases in cell survival also suggests that they may represent viable therapeutic targets in cancer.
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Affiliation(s)
- R B Robey
- Research and Development Service, White River Junction VA Medical Center, White River Junction, VT 05009-0001, USA
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22
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Affiliation(s)
- J E Wilson
- Department of Biochemistry, Michigan State University, East Lansing 48824
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23
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Nogueira FN, Santos MFD, Nicolau J. Influence of streptozotocin-induced diabetes on hexokinase activity of rat salivary glands. J Physiol Biochem 2005; 61:421-7. [PMID: 16440596 DOI: 10.1007/bf03168448] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
The influence of diabetes on the enzyme hexokinase (HK) was examined in the salivary glands of rats. Diabetes was induced by an intraperitoneal injection of streptozotocin (60 mg/Kg body weight) in overnight fasted rats (180-200 g). The animals were killed 48 hours and 30 days after the induction of diabetes and the submandibular and parotid salivary glands extracted for use. Hyperglycemia was evaluated by determining the blood sugar. The area occupied by each intralobular component, acini, ducts, total parenchyma and stroma was measured, and no differences were observed compared with control. In the soluble fraction of the submandibular gland, no difference in the specific activity of HK was observed, between the diabetic and control animals, however, the activity per gland and per g of tissue showed lower values than control. The specific activity of the bound form was reduced in the diabetic gland. The results obtained for the parotid gland were different from the submandibular. The specific activity of both the soluble and bound forms were increased in the diabetic animals. The DEAE-cellulose column chromatography of the soluble and bound forms of the enzyme from both glands showed a first peak appearing during the washing of the column and two other peaks were eluted by the gradient. Thus, three isoenzymes in the submandibular and parotid salivary glands for the control and diabetic rats have been found.
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Affiliation(s)
- F N Nogueira
- Oral Biology Research Center, Faculty of Dentistry, University of São Paulo, Brazil
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24
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Sánchez-Alvarez R, Tabernero A, Medina JM. The increase in gap junctional communication decreases the rate of glucose uptake in C6 glioma cells by releasing hexokinase from mitochondria. Brain Res 2005; 1039:189-98. [PMID: 15781061 DOI: 10.1016/j.brainres.2005.01.079] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2004] [Revised: 01/21/2005] [Accepted: 01/21/2005] [Indexed: 10/25/2022]
Abstract
We have previously shown that the enhancement of glucose uptake caused by the inhibition of gap junctional communication is a consequence of the increase in astrocyte proliferation. Since C6 glioma cells are highly proliferative and are poorly coupled through gap junctions, we used these cells to investigate the effect of increasing gap junctional communication on the rate of glucose uptake. Previous work by us had shown that tolbutamide increases gap junctional communication in C6 glioma cells, as does dbcAMP, a classical activator of gap junctional communication. In this work, our results show that both tolbutamide and dbcAMP reduce the rate of glucose uptake in C6 glioma cells and that their effects are additive. The main glucose transporters expressed in C6 glioma cells are GLUT-1 and GLUT-3. Neither the expression nor the cellular localization of either GLUT-1 or GLUT-3 were modified by increasing gap junctional communication. The estimation of glucose uptake with 2-deoxyglucose includes not only glucose transport but also glucose phosphorylation, which in C6 glioma cells is mainly catalyzed by type I and type II hexokinase. Our results reveal that the increase in gap junctional communication caused by tolbutamide and dbcAMP is associated with a decrease in the activity of hexokinase. In agreement with this, tolbutamide and dbcAMP caused a rapid change in the localization of both type I and type II hexokinase, which were detached from the mitochondria to the cytosol.
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Affiliation(s)
- Rosa Sánchez-Alvarez
- Departamento de Bioquímica y Biología Molecular, INCYL, Universidad de Salamanca, Edificio Departamental, Pza Doctores de la Reina s/n. 37007 Salamanca, Spain
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25
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Huang TJ, Verkhratsky A, Fernyhough P. Insulin enhances mitochondrial inner membrane potential and increases ATP levels through phosphoinositide 3-kinase in adult sensory neurons. Mol Cell Neurosci 2005; 28:42-54. [PMID: 15607940 DOI: 10.1016/j.mcn.2004.08.009] [Citation(s) in RCA: 103] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2004] [Revised: 07/08/2004] [Accepted: 08/18/2004] [Indexed: 11/21/2022] Open
Abstract
We tested the hypothesis that neurotrophic factors control neuronal metabolism by directly regulating mitochondrial function in the absence of effects on survival. Real-time whole cell fluorescence video microscopy was utilized to analyze mitochondrial inner membrane potential (Delta Psi(m)), which drives ATP synthesis, in cultured adult sensory neurons. These adult neurons do not require neurotrophic factors for survival. Insulin and other neurotrophic factors increased Delta Psi(m) 2-fold compared with control over a 6- to 24-h period (P < 0.05). Insulin modulated Delta Psi(m) by activation of the phosphoinositide 3-kinase (PI 3-K) pathway. Insulin also induced rapid and long-term (30 h) PI 3-K-dependent phosphorylation of Akt and cAMP response element binding protein (CREB). Additionally, insulin elevated the redox state of the mitochondrial NAD(P)H pool, increased hexokinase activity (first committed step of glycolysis), and raised ATP levels. This study demonstrates that insulin utilizes the PI 3-K/Akt pathway to augment ATP synthesis that we propose contributes to the energy requirement for neurotrophic factor-driven axon regeneration.
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Affiliation(s)
- Tze-Jen Huang
- School of Biological Sciences, University of Manchester, Manchester M13 9PT, UK
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26
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Cesar MDC, Wilson JE. All three isoforms of the voltage-dependent anion channel (VDAC1, VDAC2, and VDAC3) are present in mitochondria from bovine, rabbit, and rat brain. Arch Biochem Biophys 2004; 422:191-6. [PMID: 14759607 DOI: 10.1016/j.abb.2003.12.030] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2003] [Revised: 12/22/2003] [Indexed: 11/30/2022]
Abstract
All three isoforms of the voltage-dependent anion channel (VDAC) were detected by immunoblot analysis of mitochondria isolated from rat, rabbit, and bovine brain. All three isoforms were associated with mitochondria after fractionation of rat brain extracts on sucrose density gradients. No VDAC isoforms were detected in non-mitochondrial fractions. Relative levels of the mRNAs coding the VDAC isoforms in rat, rabbit, and bovine brain were determined by RT-PCR. In all three species, the mRNA for VDAC2 was predominant. Relative to the mRNA for VDAC3, mRNAs for both VDAC1 and VDAC2 were more highly expressed in bovine brain than in rat brain. These results are consistent with the possibility that differences in relative expression of VDAC isoforms may be a factor in determining the species-dependent ratio of Type A:Type B hexokinase binding sites on brain mitochondria.
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27
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Majewski N, Nogueira V, Robey RB, Hay N. Akt inhibits apoptosis downstream of BID cleavage via a glucose-dependent mechanism involving mitochondrial hexokinases. Mol Cell Biol 2004; 24:730-40. [PMID: 14701745 PMCID: PMC343797 DOI: 10.1128/mcb.24.2.730-740.2004] [Citation(s) in RCA: 235] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2003] [Revised: 08/18/2003] [Accepted: 10/27/2003] [Indexed: 11/20/2022] Open
Abstract
The serine/threonine kinase Akt/protein kinase B inhibits apoptosis induced by a variety of stimuli, including overexpression or activation of proapoptotic Bcl-2 family members. The precise mechanisms by which Akt prevents apoptosis are not completely understood, but Akt may function to maintain mitochondrial integrity, thereby preventing cytochrome c release following an apoptotic insult. This effect may be mediated, in part, via promotion of physical and functional interactions between mitochondria and hexokinases. Here we show that growth factor deprivation induced proteolytic cleavage of the proapoptotic Bcl-2 family member BID to yield its active truncated form, tBID. Activated Akt inhibited mitochondrial cytochrome c release and apoptosis following BID cleavage. Akt also antagonized tBID-mediated BAX activation and mitochondrial BAK oligomerization, two downstream events thought to be critical for tBID-induced apoptosis. Glucose deprivation, which impaired the ability of Akt to maintain mitochondrion-hexokinase association, prevented Akt from inhibiting BID-mediated apoptosis. Interestingly, tBID independently elicited dissociation of hexokinases from mitochondria, an effect that was antagonized by activated Akt. Ectopic expression of the amino-terminal half of hexokinase II, which is catalytically active and contains the mitochondrion-binding domain, consistently antagonized tBID-induced apoptosis. These results suggest that Akt inhibits BID-mediated apoptosis downstream of BID cleavage via promotion of mitochondrial hexokinase association and antagonism of tBID-mediated BAX and BAK activation at the mitochondria.
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Affiliation(s)
- Nathan Majewski
- Department of Biochemistry and Molecular Genetics (M/C 669), College of Medicine, University of Illinois at Chicago, 900 S. Ashland Avenue, Chicago, IL 60607, USA
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28
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Wilson JE. Isozymes of mammalian hexokinase: structure, subcellular localization and metabolic function. J Exp Biol 2003; 206:2049-57. [PMID: 12756287 DOI: 10.1242/jeb.00241] [Citation(s) in RCA: 761] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The first step in metabolism of glucose (Glc) is usually phosphorylation, catalyzed by hexokinase. However, the Glc-6-P produced can then enter one or more of several alternative pathways. Selective expression of isozymic forms of hexokinase, differing in catalytic and regulatory properties as well as subcellular localization, is likely to be an important factor in determining the pattern of Glc metabolism in mammalian tissues/cells. Despite their overall structural similarity, the Type I, Type II and Type III isozymes differ in important respects. All three isozymes are inhibited by the product, Glc-6-P, but with the Type I isozyme, this inhibition is antagonized by P(I), whereas with the Type II and Type III isozymes, P(i) actually causes additional inhibition. Reciprocal changes in intracellular levels of Glc-6-P and P(i) are closely associated with cellular energy status, and it is proposed that the response of the Type I isozyme to these effectors adapts it for catabolic function, introducing Glc into glycolytic metabolism for energy production. In contrast, the Type II, and probably the Type III, isozymes are suggested to serve primarily anabolic functions, e.g. to provide Glc-6-P for glycogen synthesis or metabolism via the pentose phosphate pathway for lipid synthesis. Type I hexokinase binds to mitochondria through interaction with porin, the protein that forms channels through which metabolites traverse the outer mitochondrial membrane. Several experimental approaches have led to the conclusion that the Type I isozyme, bound to actively phosphorylating mitochondria, selectively uses intramitochondrial ATP as substrate. Such interactions are thought to facilitate coordination of the introduction of Glc into glycolysis, via the hexokinase reaction, with the terminal oxidative stages of Glc metabolism occurring in the mitochondria, thus ensuring an overall rate of Glc metabolism commensurate with cellular energy demands and avoiding excessive production of lactate. The Type II isozyme also binds to mitochondria. Whether such coupling occurs with mitochondrially bound Type II hexokinase in normal tissues, and how it might be related to the proposed anabolic role of this isozyme, remain to be determined. The Type III isozyme lacks the hydrophobic N-terminal sequence known to be critical for binding of the Type I and Type II isozymes to mitochondria. Immunolocalization studies have indicated that, in many cell types, the Type III has a perinuclear localization, the possible metabolic consequences of which remain unclear.
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Affiliation(s)
- John E Wilson
- Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
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29
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Affiliation(s)
- Leif Hertz
- Hong Kong DNA Chips, Ltd., Kowloon, Hong Kong, China
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30
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Robey RB, Ma J, Santos AVP, Noboa OA, Coy PE, Bryson JM. Regulation of mesangial cell hexokinase activity and expression by heparin-binding epidermal growth factor-like growth factor: epidermal growth factors and phorbol esters increase glucose metabolism via a common mechanism involving classic mitogen-activated protein kinase pathway activation and induction of hexokinase II expression. J Biol Chem 2002; 277:14370-8. [PMID: 11782486 DOI: 10.1074/jbc.m111722200] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Heparin-binding epidermal growth factor -like growth factor (HB-EGF) expression and hexokinase (HK) activity are increased in various pathologic renal conditions. Although the mitogenic properties of HB-EGF have been well characterized, its effects on glucose (Glc) metabolism have not. We therefore examined the possibility that HB-EGF might regulate HK activity and expression in glomerular mesangial cells, which constitute the principal renal cell type affected by a variety of pathologic conditions. Protein kinase C (PKC)-dependent classic mitogen-activated protein kinase (MAPK) pathway activation has been associated with increased HK activity in this cell type, so we also examined dependence upon these signaling intermediates. HB-EGF (> or =10 nm) increased total HK activity over 50% within 12-24 h, an effect mimicked by other EGF receptor agonists, but not by IGF-1 or elevated Glc. EGF receptor and classic MAPK pathway antagonists prevented this increase, as did general inhibitors of gene transcription and protein synthesis. Both HB-EGF and phorbol esters activated the classic MAPK pathway, albeit via PKC-independent and PKC-dependent mechanisms, respectively. Both stimuli were associated with increased HK activity, selectively increased HKII isoform expression, and increased Glc metabolism via both the glycolytic-tricarboxylic acid cycle route and the pentose phosphate pathway. HB-EGF thus constitutes a novel regulator of mesangial cell HK activity and Glc metabolism. HKII is the principal regulated isoform in these cells, as it is in insulin-sensitive peripheral tissues, such as muscle. However, the uniform requirement for classic MAPK pathway activation distinguishes HKII regulation in mesangial cells from that observed in muscle. These findings suggest a novel mechanism whereby growth factors may couple metabolism to glomerular injury.
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Affiliation(s)
- R Brooks Robey
- Department of Medicine, University of Illinois at Chicago College of Medicine, Chicago, Illinois 60612, USA.
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Bryson JM, Coy PE, Gottlob K, Hay N, Robey RB. Increased hexokinase activity, of either ectopic or endogenous origin, protects renal epithelial cells against acute oxidant-induced cell death. J Biol Chem 2002; 277:11392-400. [PMID: 11751868 DOI: 10.1074/jbc.m110927200] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glucose (Glc) metabolism protects cells against oxidant injury. By virtue of their central position in both Glc uptake and utilization, hexokinases (HKs) are ideally suited to contribute to these effects. Compatible with this hypothesis, endogenous HK activity correlates inversely with injury susceptibility in individual renal cell types. We recently reported that ectopic HK expression mimics the anti-apoptotic effects of growth factors in cultured fibroblasts, but anti-apoptotic roles for HKs have not been examined in other cell types or in a cellular injury model. We therefore evaluated HK overexpression for the ability to mitigate acute oxidant-induced cell death in an established epithelial cell culture injury model. In parallel, we examined salutary heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) treatment for the ability to 1) increase endogenous HK activity and 2) mimic the protective effects of ectopic HK expression. Both HK overexpression and HB-EGF increased Glc-phosphorylating capacity and metabolism, and these changes were associated with markedly reduced susceptibility to acute oxidant-induced apoptosis. The uniform Glc dependence of these effects suggests an important adaptive role for Glc metabolism, and for HK activity in particular, in the promotion of epithelial cell survival. These findings also support the contention that HKs contribute to the protective effects of growth factors.
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Affiliation(s)
- Jane M Bryson
- Department of Medicine, College of Medicine, University of Illinois, Chicago 60612, USA
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32
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de Cerqueira Cesar M, Wilson JE. Functional characteristics of hexokinase bound to the type a and type B sites of bovine brain mitochondria. Arch Biochem Biophys 2002; 397:106-12. [PMID: 11747316 DOI: 10.1006/abbi.2001.2639] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Hexokinase is released from Type A sites of brain mitochondria in the presence of glucose 6-phosphate (Glc-6-P); enzyme bound to Type B sites remains bound. Hexokinase of freshly isolated bovine brain mitochondria (Type A:Type B, approximately 40:60) selectively uses intramitochondrial ATP as substrate and is relatively insensitive to the competitive (vs ATP) inhibitor and Glc-6-P analog, 1,5-anhydroglucitol 6-phosphate (1,5-AnG-6-P). After removal of hexokinase bound at Type A sites, the remaining enzyme, bound at Type B sites, does not show selectivity for intramitochondrial ATP and has increased sensitivity to 1,5-AnG-6-P. Thus, the properties of the enzyme bound at Type B sites are modified by removal of hexokinase bound at Type A sites. It is suggested that mechanisms for regulation of mitochondrial hexokinase activity, and thereby cerebral glycolytic metabolism, may depend on the ratio of Type A:Type B sites, which varies in different species.
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Abstract
Two isoforms of hexokinase (type I and type II) are expressed in skeletal muscle; however, the intracellular distribution of these hexokinase isoforms in human skeletal muscle is unclear. The current study was undertaken to assess this issue because binding of hexokinase to subcellular structures is considered to be an important mechanism in the regulation of glucose phosphorylation. Vastus lateralis muscle was obtained from healthy lean individuals. Muscle homogenate was separated at 45,000g into particulate and cytosolic fractions. The activity and subcellular distribution of hexokinase isozymes in human skeletal muscle was determined using ion-exchange chromatography and a highly sensitive high-performance liquid chromatography-based hexokinase assay. This criterion method was used to validate a modified thermal inactivation method for distinguishing type I and type II isoforms. Mean hexokinase activity was 3.88 +/- 0.65 U/g wet wt or 0.64 +/- 0.11 U/mU creatine kinase (CrK) in the particulate fraction and 0.45 +/- 0.22 U/g wet wt or 0.07 +/- 0.03 U/mU CrK in the cytosolic fraction. Hexokinase I and II accounted for 70-75 and 25-30% of total hexokinase activity, respectively. Nearly all (95%) of hexokinase I activity (0.52 +/- 0.09 U/mU CrK) was found in the particulate fraction, consistent with the known high affinity of hexokinase I for mitochondria. Hexokinase II activity was also largely bound to the particulate fraction (72%), but 28% was found within the cytosolic fraction. Thus, within the particulate fraction, the relative contributions of hexokinase I and hexokinase II were 81 and 19%, whereas within the cytosolic fraction, the relative contributions for hexokinase I and hexokinase II were 37 and 63%.
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Affiliation(s)
- V B Ritov
- Department of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
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Gottlob K, Majewski N, Kennedy S, Kandel E, Robey RB, Hay N. Inhibition of early apoptotic events by Akt/PKB is dependent on the first committed step of glycolysis and mitochondrial hexokinase. Genes Dev 2001; 15:1406-18. [PMID: 11390360 PMCID: PMC312709 DOI: 10.1101/gad.889901] [Citation(s) in RCA: 711] [Impact Index Per Article: 30.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The serine/threonine kinase Akt/PKB is a major downstream effector of growth factor-mediated cell survival. Activated Akt, like Bcl-2 and Bcl-xL, prevents closure of a PT pore component, the voltage-dependent anion channel (VDAC); intracellular acidification; mitochondrial hyperpolarization; and the decline in oxidative phosphorylation that precedes cytochrome c release. However, unlike Bcl-2 and Bcl-xL, the ability of activated Akt to preserve mitochondrial integrity, and thereby inhibit apoptosis, requires glucose availability and is coupled to its metabolism. Hexokinases are known to bind to VDAC and directly couple intramitochondrial ATP synthesis to glucose metabolism. We provide evidence that such coupling serves as a downstream effector function for Akt. First, Akt increases mitochondria-associated hexokinase activity. Second, the antiapoptotic activity of Akt requires only the first committed step of glucose metabolism catalyzed by hexokinase. Finally, ectopic hexokinase expression mimics the ability of Akt to inhibit cytochrome c release and apoptosis. We therefore propose that Akt increases coupling of glucose metabolism to oxidative phosphorylation and regulates PT pore opening via the promotion of hexokinase-VDAC interaction at the outer mitochondrial membrane.
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Affiliation(s)
- K Gottlob
- Department of Molecular Genetics, University of Illinois at Chicago, Chicago, Illinois 60607, USA
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35
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Hashimoto M, Wilson JE. Membrane potential-dependent conformational changes in mitochondrially bound hexokinase of brain. Arch Biochem Biophys 2000; 384:163-73. [PMID: 11147827 DOI: 10.1006/abbi.2000.2085] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Previously characterized monoclonal antibodies (Mabs) were used in a study of Type I hexokinase from rat brain. Based on the relative reactivity of these Mabs with soluble and mitochondrially bound forms, binding to mitochondria was shown to affect specific epitopic regions in both N- and C-terminal halves of the enzyme and to modulate conformational changes induced by binding of the ligands, Glc or ATP. Reactivities with Mabs recognizing epitopes in two defined regions of the N-terminal half and one defined region of the C-terminal half of the mitochondrially bound enzyme were selectively affected by mitochondrial membrane potential, or by addition of oligomycin, carboxyatractyloside, or bongkrekic acid. The Glc-6-P analog, 1 ,5-anhydroglucitol-6-P, was much more effective as a competitive inhibitor against extramitochondrial ATP than against intramitochondrial ATP generated by oxidative phosphorylation. These results provide further insight into the role of hexokinase-mitochondrial interactions in regulation of cerebral glucose metabolism.
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Affiliation(s)
- M Hashimoto
- Department of Biochemistry, Michigan State University, East Lansing 48824-1319, USA
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36
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Golestani A, Nemat-Gorgani M. Hexokinase 'binding sites' of normal and tumoral human brain mitochondria. Mol Cell Biochem 2000; 215:115-21. [PMID: 11204446 DOI: 10.1023/a:1026562920315] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Interaction of type I hexokinase (HK-I) with the mitochondria obtained from the biopsy specimens of normal and tumoral human brain tissues was studied in the present investigation. This effort was undertaken with the aim of exploring possible differences in the mode of association of the enzyme with the outer mitochondrial membrane in the described sources. Results indicate that the two 'sites' for binding of HK-I suggested in the literature, based on extensive studies carried out on rat brain mitochondria, are similarly present in the human brain mitochondria. Differences in the microenvironments of HK binding, as reflected by the presented data, are suggested to be of importance in regulation of the catalytic potential of the bound enzyme. The real metabolic significance of this association in relation to cancer and its practical importance would need further investigation.
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Affiliation(s)
- A Golestani
- Institute of Biochemisty and Biophysics, University of Tehran, Iran
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37
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Sui D, Wilson JE. Interaction of insulin-like growth factor binding protein-4, Miz-1, leptin, lipocalin-type prostaglandin D synthase, and granulin precursor with the N-terminal half of type III hexokinase. Arch Biochem Biophys 2000; 382:262-74. [PMID: 11068878 DOI: 10.1006/abbi.2000.2019] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin-like growth factor binding protein-4, Miz-1, leptin, prostaglandin D synthase, and granulin precursor were identified as proteins interacting with the N-terminal half of mammalian Type III hexokinase (HKIII) in the yeast two-hybrid method. These interactions were confirmed by in vitro binding studies. All five of these proteins, and their mRNAs, were present in PC12 cells, as shown by immunoblotting and RT-PCR, respectively. All were coimmunoprecipitated from PC12 extracts with an antibody against HKIII, but not with anti-Type I hexokinase. Moreover, all of these proteins were coimmunoprecipitated using antileptin as precipitating antibody, indicating the existence of a macromolecular complex including these five proteins and HKIII. Transfection of M+R 42 cells with HKIII-green fluorescent protein (GFP) reporter constructs gave a diffuse intracellular fluorescence. Cotransfection with leptin or Miz-1 resulted in distinctly different localization of the HKIII-GFP fusion protein, at intracellular sites coincident with localization of leptin-GFP or Miz-1-GFP reporter constructs.
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Affiliation(s)
- D Sui
- Department of Biochemistry, Michigan State University, East Lansing 48824, USA
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38
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Sarin S, Gill KD. Dichlorvos induced alterations in glucose homeostasis: possible implications on the state of neuronal function in rats. Mol Cell Biochem 1999; 199:87-92. [PMID: 10544956 DOI: 10.1023/a:1006930511459] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The present study was carried out to assess the effect of chronic dichlorvos exposure on various aspects of glucose homeostasis in different regions of rat brain. Dichlorvos administration caused a significant depletion in the brain glycogen content accompanied with an increase in the activity of glycogen phosphorylase. The activities of key glycolytic enzymes, hexokinase, phosphofructokinase and lactate dehydrogenase were decreased significantly following dichlorvos exposure. The decreased glycolytic flux was further reflected in terms of decreased regional glucose utilization, determined by measuring 14C-glucose influx. The altered neuronal glucose homeostasis had a significant impact on the neurobehavioural patterns of dichlorvos treated animals which was reflected in terms of severe deterioration in their memory and learning functions.
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Affiliation(s)
- S Sarin
- Department of Biochemistry, Postgraduate Institute of Medical Education and Research, Chandigarh, India
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39
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Mannella CA. Conformational changes in the mitochondrial channel protein, VDAC, and their functional implications. J Struct Biol 1998; 121:207-18. [PMID: 9615439 DOI: 10.1006/jsbi.1997.3954] [Citation(s) in RCA: 116] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The voltage-dependent, anion-selective channel (VDAC) is generally considered the main pathway for metabolite diffusion across the mitochondrial outer membrane. It also interacts with several mitochondrial and cytosolic proteins, including kinases and cytochrome c. Sequence analysis and circular dichroism suggest that the channel is a bacterial porin-like beta-barrel. However, unlike bacterial porins, VDAC does not form tight trimeric complexes and is easily gated (reversibly closed) by membrane potential and low pH. Circular dichroism indicates that the protein undergoes a major conformational change at pH < 5, involving decreased beta-sheet and increased alpha-helical content. Electron microscopy of two-dimensional crystals of fungal VDAC provides direct information about the size and shape of its lumen and suggests that the N-terminal domain forms a mobile alpha-helix. It is proposed that the N-terminal domain normally resides in a groove in the lumen wall and that gating stimuli favor its displacement, destabilizing the putative beta-barrel. Partial closure would result from subsequent larger-scale structural rearrangements in the protein, possibly corresponding to the conformational change observed at pH < 5.
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Affiliation(s)
- C A Mannella
- Wadsworth Center, New York State Department of Health, Albany 12201-0509, USA
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40
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Aflalo C, Azoulay H. Binding of rat brain hexokinase to recombinant yeast mitochondria: effect of environmental factors and the source of porin. J Bioenerg Biomembr 1998; 30:245-55. [PMID: 9733091 DOI: 10.1023/a:1020544803475] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Heterologous binding of rat brain hexokinase to wild type, porinless, and recombinant yeast mitochondria expressing human porin was assessed, partially characterized, and compared to that in the homologous system (rat liver mitochondria). With porin-containing yeast mitochondria it is shown that (i) a significant, saturable association occurs; (ii) its extent and apparent affinity, correlated with the origin of porin, are enhanced in the presence of dextran; (iii) the binding requires Mg ions and apparently follows a complex cooperative mechanism. This heterologous association does not seem to differ fundamentally from that in the homologous system and represents a good basis for molecular studies in yeast. With porinless yeast mitochondria, binding occurs at much lower affinity, but to many more sites per mitochondrion. The results indicating a major but not exclusive role for porin in the binding are discussed in terms of (i) the mode and mechanism of binding, and (ii) the suitability of the rat hexokinase-yeast mitochondria couple for the study of heterogeneous catalysis in reconstituted cellular model systems.
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Affiliation(s)
- C Aflalo
- Department of Life Sciences, The Ben Gurion University of the Negev, Beer Sheva, Israel
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41
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Cesar MDC, Wilson JE. Further studies on the coupling of mitochondrially bound hexokinase to intramitochondrially compartmented ATP, generated by oxidative phosphorylation. Arch Biochem Biophys 1998; 350:109-17. [PMID: 9466827 DOI: 10.1006/abbi.1997.0497] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Hexokinase, bound to nonphosphorylating rat brain mitochondria, exhibits Michaelis-Menten kinetic behavior, with an apparent K(m) for ATP of 0.44 +/- 0.08 mM. After initiation of oxidative phosphorylation, a steady-state rate of Glc phosphorylation is maintained despite the fact that extramitochondrial [ATP] continues to increase but remains well below saturating levels (i.e., < 0.4 mM). This independence from extramitochondrial [ATP] is taken to indicate that hexokinase is not utilizing extramitochondrial ATP as substrate, but rather draws substrate ATP from an intramitochondrial compartment supplied by oxidative phosphorylation. The steady-state rate of Glc phosphorylation by hexokinase bound to phosphorylating mitochondria is not altered by increase in total rate of ATP production resulting from addition of hexokinase-depleted mitochondria to the system. In contrast, the steady-state rate of Glc phosphorylation by yeast hexokinase, which does not bind to mitochondria, is directly related to the total rate of ATP production in the system. These results are also consistent with the view that, during oxidative phosphorylation, mitochondrially bound hexokinase is selectively using intramitochondrially compartmented ATP; such substrate selectivity would be expected to require physical association of hexokinase with the mitochondria and be dependent solely on the oxidative phosphorylation activity of the hexokinase-bearing organelles. The K(m) for Glc is only modestly affected by the binding of hexokinase to mitochondria and not further altered upon induction of active oxidative phosphorylation, suggesting that neither binding nor oxidative phosphorylation greatly affects the conformation of the Glc binding site. The reliance on intramitochondrial ATP is suggested to result from oxidative phosphorylation-dependent changes in the interaction between the mitochondrial surface and the regions of the hexokinase molecule involved in binding ATP.
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Affiliation(s)
- M de C Cesar
- Department of Biochemistry, Michigan State University, East Lansing 48824-1319, USA
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42
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Abstract
The concentration of ATP generated by yeast mitochondria and consumed by yeast hexokinase was monitored using native firefly luciferase in solution, or recombinant luciferase localized at the surface of mitochondria. In the absence of hexokinase, both probes perform similarly in detecting exogenous or mitochondrially-generated ATP. The steady-state concentrations of ATP can be reduced in a dose-dependent manner by hexokinase. With hexokinase added in large excess, the localized probe reports substantial ATP concentrations while none is detectable by soluble luciferase. Thus, ATP accumulates near the membrane where it appears, relatively to solution, and vice versa for ADP. The extent of nucleotide gradients is shown to be correlated with the specific activity of oxidative phosphorylation and with the viscosity of the medium, but independent of the concentration of the organelles. A simple model involving diffusional restrictions is presented to describe this behavior. The metabolic and evolutionary implications of cellular catalysis limitation by physical processes are discussed.
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Affiliation(s)
- C Aflalo
- Department of Life Sciences, The Ben Gurion University of the Negev, Beer Sheva, Israel
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43
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Sui D, Wilson JE. Structural determinants for the intracellular localization of the isozymes of mammalian hexokinase: intracellular localization of fusion constructs incorporating structural elements from the hexokinase isozymes and the green fluorescent protein. Arch Biochem Biophys 1997; 345:111-25. [PMID: 9281318 DOI: 10.1006/abbi.1997.0241] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Fusion constructs incorporating structural elements from mammalian isozymes of hexokinase, Types I-IV, in frame with sequence encoding the green fluorescent protein (GFP) have been made and expressed in hexokinase-deficient M + R 42 cells. Fusion proteins incorporating catalytically active regions from the Type II isozyme, or the entire Type IV sequence, were expressed in catalytically active form. The intracellular localization of the fusion proteins was determined using confocal microscopy. Fusion proteins including the N-terminal halves of the Type I or Type II isozymes were targeted to mitochondria, while the N-terminal half of the Type III isozyme did not confer mitochondrial targeting. The mitochondrial targeting signal was represented by the hydrophobic sequence at the extreme N-termini ("binding domain") of the Type I and Type II isozymes. Inclusion of the binding domain from the Type I isozyme was sufficient to confer mitochondrial binding on GFP itself as well as on constructs including the N-terminal half of Type III hexokinase. However, the Type I hexokinase binding domain was not sufficient to cause mitochondrial targeting of a construct containing the Type IV sequence. These results suggest that, although the binding domain is critical for mitochondrial targeting, other interactions involving an adjacent structure might also play a role. Fusion proteins including the N-terminal half of Type I hexokinase became dissociated from mitochondria under conditions favorable for accumulation of intracellular Glc-6-P. The 2-deoxy analog was much less effective than Glc in causing mitochondrial dissociation of the fusion construct, in accord with previous studies showing 2-deoxy-Glc-6-P to be much less effective than Glc-6-P at promoting release of Type I hexokinase from mitochondria. Dissociation, induced by formation of Glc-6-P or 2-deoxy-Glc-6-P, did not occur with the fusion protein including only the binding domain of Type I hexokinase. This is consistent with previous studies indicating that Glc-6-P-dependent dissociation results from binding of this ligand to a site in the N-terminal half of the enzyme, but which is not likely to be present in the small segment represented by the binding domain. These studies demonstrate the usefulness of this approach in defining structural elements involved in targeting hexokinase isozymes to specific subcellular locations and modulation of that intracellular location by perturbations of metabolic status.
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Affiliation(s)
- D Sui
- Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824-1319, USA
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44
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Wilson JE. Homologous and heterologous interactions between hexokinase and mitochondrial porin: evolutionary implications. J Bioenerg Biomembr 1997; 29:97-102. [PMID: 9067807 DOI: 10.1023/a:1022472124746] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Binding of the Type I isozyme of mammalian hexokinase to mitochondria is mediated by the porin present in the outer mitochondrial membrane. Type I hexokinase from rat brain is avidly bound by rat liver mitochondria while, under the same conditions, there is no significant binding to mitochondria from S. cerevisiae. Previously published work demonstrates the lack of significant interaction of yeast hexokinase with mitochondria from either liver or yeast. Thus, structural features required for the interaction of porin and hexokinase must have emerged during evolution of the mammalian forms of these proteins. If these structural features serve no functional role other than facilitating this interaction of hexokinase with mitochondria, it seems likely that they evolved in synchrony since operation of selective pressures on the hexokinase-mitochondrial interaction would require the simultaneous presence of hexokinase and porin capable of at least minimal interaction, and be responsive to changes in either partner that affected this interaction. Recent studies have indicated that a second type of binding site, which may or may not involve porin, is present on mammalian mitochondria. There are also reports of hexokinase binding to mitochondria in plant tissues, but the nature of the binding site remains undefined.
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Affiliation(s)
- J E Wilson
- Department of Biochemistry, Michigan State University, East Lansing 48824-1319, USA
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45
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Lynch RM, Carrington W, Fogarty KE, Fay FS. Metabolic modulation of hexokinase association with mitochondria in living smooth muscle cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 270:C488-99. [PMID: 8779911 DOI: 10.1152/ajpcell.1996.270.2.c488] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Hexokinase isoform I binds to mitochondria of many cell types. It has been hypothesized that this association is regulated by changes in the concentrations of specific cellular metabolites. To study the distribution of hexokinase in living cells, fluorophore-labeled functional hexokinase I was prepared. After microinjection into A7r5 smooth muscle cells, hexokinase localized to distinct structures identified as mitochondria. The endogenous hexokinase demonstrated a similar distribution with the use of immunocytochemistry. 2-Deoxyglucose elicited an increase in glucose 6-phosphate (G-6-P) and a decrease in ATP levels and diminished hexokinase binding to mitochondria in single cells. 3-O-methylglucose elicited slowly developing decreases in all three parameters. In contrast, cyanide elicited a rapid decrease in both ATP and hexokinase binding. Analyses of changes in metabolite levels and hexokinase binding indicate a positive correlation between binding and cell energy state as monitored by ATP. On the other hand, only in the presence of 2-deoxyglucose was the predicted inverse correlation between binding and G-6-P observed. Unlike the relatively large changes in distribution observed with the fluorescent-injected hexokinase, cyanide caused only a small decrease in the localization of endogenous hexokinase with mitochondria. These findings suggest that changes in the concentrations of specific metabolites can alter the binding of hexokinase I to specific sites on mitochondria. Moreover, the apparent difference in sensitivity of injected and endogenous hexokinase to changes in metabolites may reflect the presence of at least two classes of binding mechanisms for hexokinase, with differential sensitivity to metabolites.
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Affiliation(s)
- R M Lynch
- Department of Physiology, University of Arizona, Tucson 85724, USA
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46
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Affiliation(s)
- J Henriksson
- Department of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden
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47
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Devi BG, Henderson GI, Frosto TA, Schenker S. Effect of acute ethanol exposure on cultured fetal rat hepatocytes: relation to mitochondrial function. Alcohol Clin Exp Res 1994; 18:1436-42. [PMID: 7695041 DOI: 10.1111/j.1530-0277.1994.tb01447.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Studies from our laboratory have shown that short-term ethanol exposure inhibits epidermal growth factor-dependent replication of cultured fetal rat hepatocytes, along with a drop in ATP level, and that these effects could be caused, at least in part, by ethanol-induced oxidative stress. In these prior studies, mitochondrial morphology was abnormal and membrane lipid peroxidation products were increased, along with reduced transmembrane potential and enhanced permeability to sucrose. To define the effects of ethanol on mitochondrial function further, the present study examines the impact of ethanol exposure on mitochondrial electron transport chain components. A 24-hr exposure of cultured fetal rat hepatocytes to ethanol (2.5 mg/ml) reduced mitochondrial complex I activity by 16% (p < 0.05), complex IV by 28% (p < 0.05), and succinate dehydrogenase by 23% (p < 0.05). This reduction was paralleled by lower ADP translocase activity (24%, p < 0.05) and diminished mitochondrial glutathione (GSH) (20%, p < 0.05). Pretreatment with 0.1 mM S-adenosyl methionine, before ethanol exposure, normalized mitochondrial GSH along with activities of complex I, complex IV, and succinate dehydrogenase. A 3-hr exposure of isolated mitochondria (which do not metabolize ethanol) to ethanol (2.5 mg/ml), inhibited the activities of complex I (19%, p < 0.05), complex IV (24%, p < 0.05), and of ATP synthesis (20%, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- B G Devi
- Department of Medicine, University of Texas Health Science Center at San Antonio 78284-7878
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48
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Affiliation(s)
- M Erecińska
- Department of Pharmacology, University of Pennsylvania, Philadelphia
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49
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Whallon JH, Preller A, Wilson JE. Reflection confocal imaging of type I and type III isozymes of hexokinase in PC12 cells. SCANNING 1994; 16:111-117. [PMID: 7516249 DOI: 10.1002/sca.4950160208] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Reflection confocal microscopy was used to determine the intracellular distribution of Type I and III isozymes of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) in PC12 cells; detection was by staining with diaminobenzidine as a substrate for horseradish peroxidase-conjugated antimouse immunoglobulins bound to isozyme-specific monoclonal antibodies. With both isozymes, detection of the staining pattern was significantly enhanced by reflection confocal imaging compared with viewing with transmitted brightfield optics. For Type I, prominent staining of cytoplasmic organelles having a distribution consistent with that of mitochondria was noted. For Type III, intense staining at the nuclear periphery was observed. A distinct punctate pattern along the nuclear surface implied a nonuniform distribution of the Type III hexokinase and may represent preferential association with nuclear pore structures. A study of technical factors involved in optimizing the reflection image was conducted. We demonstrate that both the choice of objective and the thickness of the mounting medium are critical to successful imaging, and we describe a simple test for assessing the suitability of objectives in any system.
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Affiliation(s)
- J H Whallon
- Laser Scanning Microscope Laboratory, Michigan State University, East Lansing 48824-1325
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50
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Colombini M. Chapter 4 Anion Channels in the Mitochondrial Outer Membrane. CURRENT TOPICS IN MEMBRANES 1994. [DOI: 10.1016/s0070-2161(08)60819-9] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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