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Lopez-Fabuel I, Garcia-Macia M, Buondelmonte C, Burmistrova O, Bonora N, Alonso-Batan P, Morant-Ferrando B, Vicente-Gutierrez C, Jimenez-Blasco D, Quintana-Cabrera R, Fernandez E, Llop J, Ramos-Cabrer P, Sharaireh A, Guevara-Ferrer M, Fitzpatrick L, Thompton CD, McKay TR, Storch S, Medina DL, Mole SE, Fedichev PO, Almeida A, Bolaños JP. Aberrant upregulation of the glycolytic enzyme PFKFB3 in CLN7 neuronal ceroid lipofuscinosis. Nat Commun 2022; 13:536. [PMID: 35087090 PMCID: PMC8795187 DOI: 10.1038/s41467-022-28191-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2020] [Accepted: 01/12/2022] [Indexed: 02/06/2023] Open
Abstract
CLN7 neuronal ceroid lipofuscinosis is an inherited lysosomal storage neurodegenerative disease highly prevalent in children. CLN7/MFSD8 gene encodes a lysosomal membrane glycoprotein, but the biochemical processes affected by CLN7-loss of function are unexplored thus preventing development of potential treatments. Here, we found, in the Cln7∆ex2 mouse model of CLN7 disease, that failure in autophagy causes accumulation of structurally and bioenergetically impaired neuronal mitochondria. In vivo genetic approach reveals elevated mitochondrial reactive oxygen species (mROS) in Cln7∆ex2 neurons that mediates glycolytic enzyme PFKFB3 activation and contributes to CLN7 pathogenesis. Mechanistically, mROS sustains a signaling cascade leading to protein stabilization of PFKFB3, normally unstable in healthy neurons. Administration of the highly selective PFKFB3 inhibitor AZ67 in Cln7∆ex2 mouse brain in vivo and in CLN7 patients-derived cells rectifies key disease hallmarks. Thus, aberrant upregulation of the glycolytic enzyme PFKFB3 in neurons may contribute to CLN7 pathogenesis and targeting PFKFB3 could alleviate this and other lysosomal storage diseases.
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Affiliation(s)
- Irene Lopez-Fabuel
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain.
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain.
| | - Marina Garcia-Macia
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain
| | - Costantina Buondelmonte
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | | | - Nicolo Bonora
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - Paula Alonso-Batan
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - Brenda Morant-Ferrando
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - Carlos Vicente-Gutierrez
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain
| | - Daniel Jimenez-Blasco
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain
| | - Ruben Quintana-Cabrera
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain
| | - Emilio Fernandez
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain
| | - Jordi Llop
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Donostia-San Sebastián, Spain
| | - Pedro Ramos-Cabrer
- CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), Donostia-San Sebastián, Spain
- Ikerbasque, Basque Foundation for Science, Bilbao, Spain
| | - Aseel Sharaireh
- Centre for Bioscience, Manchester Metropolitan University, Manchester, M1 5GD, UK
| | - Marta Guevara-Ferrer
- Centre for Bioscience, Manchester Metropolitan University, Manchester, M1 5GD, UK
| | - Lorna Fitzpatrick
- Centre for Bioscience, Manchester Metropolitan University, Manchester, M1 5GD, UK
| | | | - Tristan R McKay
- Centre for Bioscience, Manchester Metropolitan University, Manchester, M1 5GD, UK
| | - Stephan Storch
- University Children's Research@Kinder-UKE, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Diego L Medina
- Telethon Institute of Genetics and Medicine (TIGEM), High Content Screening Facility, Via Campi Flegrei 34, 80078, Pozzuoli, Italy
- Medical Genetics Unit, Department of Medical and Translational Science, Federico II University, 80138, Naples, Italy
| | - Sara E Mole
- MRC Laboratory for Molecular Biology and GOS Institute of Child Health, University College London, London, UK
| | | | - Angeles Almeida
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain
| | - Juan P Bolaños
- Institute of Functional Biology and Genomics (IBFG), Universidad de Salamanca, CSIC, Salamanca, Spain.
- Institute of Biomedical Research of Salamanca (IBSAL), Hospital Universitario de Salamanca, Salamanca, Spain.
- Centro de Investigación Biomédica en Red de Fragilidad y Envejecimiento Saludable (CIBERFES), Madrid, Spain.
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2
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Zaninello M, Palikaras K, Naon D, Iwata K, Herkenne S, Quintana-Cabrera R, Semenzato M, Grespi F, Ross-Cisneros FN, Carelli V, Sadun AA, Tavernarakis N, Scorrano L. Inhibition of autophagy curtails visual loss in a model of autosomal dominant optic atrophy. Nat Commun 2020; 11:4029. [PMID: 32788597 PMCID: PMC7423926 DOI: 10.1038/s41467-020-17821-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2020] [Accepted: 07/21/2020] [Indexed: 01/06/2023] Open
Abstract
In autosomal dominant optic atrophy (ADOA), caused by mutations in the mitochondrial cristae biogenesis and fusion protein optic atrophy 1 (Opa1), retinal ganglion cell (RGC) dysfunction and visual loss occur by unknown mechanisms. Here, we show a role for autophagy in ADOA pathogenesis. In RGCs expressing mutated Opa1, active 5’ AMP-activated protein kinase (AMPK) and its autophagy effector ULK1 accumulate at axonal hillocks. This AMPK activation triggers localized hillock autophagosome accumulation and mitophagy, ultimately resulting in reduced axonal mitochondrial content that is restored by genetic inhibition of AMPK and autophagy. In C. elegans, deletion of AMPK or of key autophagy and mitophagy genes normalizes the axonal mitochondrial content that is reduced upon mitochondrial dysfunction. In conditional, RGC specific Opa1-deficient mice, depletion of the essential autophagy gene Atg7 normalizes the excess autophagy and corrects the visual defects caused by Opa1 ablation. Thus, our data identify AMPK and autophagy as targetable components of ADOA pathogenesis. Autosomal dominant optic atrophy is caused by mutations in the mitochondrial fusion protein OPA1. Here, the authors show that AMPK-induced autophagy depletes mitochondria in axons of retinal ganglion cells and that autophagic inhibition reverses vision loss in a mouse model.
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Affiliation(s)
- Marta Zaninello
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy.,IRCCS Fondazione Santa Lucia, Via Ardeatina 306, Rome, Italy
| | - Konstantinos Palikaras
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece.,Department of Basic Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece
| | - Deborah Naon
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy
| | - Keiko Iwata
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy
| | - Stephanie Herkenne
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,IRCCS Fondazione Santa Lucia, Via Ardeatina 306, Rome, Italy
| | - Ruben Quintana-Cabrera
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy
| | - Martina Semenzato
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy.,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy
| | - Francesca Grespi
- Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy
| | | | - Valerio Carelli
- IRCCS Institute of Neurological Sciences of Bologna, Bellaria Hospital, Bologna, Italy.,Unit of Neurology, Department of Biomedical and Neuromotor Sciences (DIBINEM), University of Bologna, Bologna, Italy
| | - Alfredo A Sadun
- Doheny Eye Institute, Los Angeles, CA, USA.,Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA
| | - Nektarios Tavernarakis
- Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, Heraklion, Crete, Greece.,Department of Basic Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece
| | - Luca Scorrano
- Veneto Institute of Molecular Medicine, Via Orus 2, Padova, Italy. .,Department of Biology, University of Padova, Via U. Bassi 58B, Padova, Italy.
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3
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Abstract
Assembly factors are necessary for the formation of mitochondrial supercomplexes (SCs) and in making cellular respiration more efficient. In a recent study, Balsa et al. (Mol. Cell, 2019) report that nutrient-induced endoplasmic reticulum (ER) stress engages PERK-eIF2α-mediated transcription of the SCs assembly factor SCAF1, events that coordinate ER stress and SCs formation to improve bioenergetics.
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Affiliation(s)
- Ruben Quintana-Cabrera
- Institute of Functional Biology and Genomics, University of Salamanca, 37007 Salamanca, Spain; Institute of Biomedical Research of Salamanca, University Hospital of Salamanca, University of Salamanca, CSIC, 37007 Salamanca, Spain; Department of Biochemistry and Molecular Biology, University of Salamanca, 37007 Salamanca, Spain; CIBERFES, Institute of Health Carlos III, 28029 Madrid, Spain
| | - Maria Eugenia Soriano
- Department of Biology, University of Padova, Via U. Bassi 58/B, Padova 35121, Italy.
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4
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Cseh AM, Fabian Z, Quintana-Cabrera R, Szabo A, Eros K, Soriano ME, Gallyas F, Scorrano L, Sumegi B. PARP Inhibitor PJ34 Protects Mitochondria and Induces DNA-Damage Mediated Apoptosis in Combination With Cisplatin or Temozolomide in B16F10 Melanoma Cells. Front Physiol 2019; 10:538. [PMID: 31133874 PMCID: PMC6514236 DOI: 10.3389/fphys.2019.00538] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2019] [Accepted: 04/15/2019] [Indexed: 12/24/2022] Open
Abstract
PARP-1 inhibition has recently been employed in both mono- and combination therapies in various malignancies including melanoma with both promising and contradicting results reported. Although deeper understanding of the underlying molecular mechanisms may help improving clinical modalities, the complex cellular effects of PARP inhibitors make disentangling of the mechanisms involved in combination therapies difficult. Here, we used two cytostatic agents used in melanoma therapies in combination with PARP inhibition to have an insight into cellular events using the B16F10 melanoma model. We found that, when used in combination with cisplatin or temozolomide, pharmacologic blockade of PARP-1 by PJ34 augmented the DNA-damaging and cytotoxic effects of both alkylating compounds. Interestingly, however, this synergism unfolds relatively slowly and is preceded by molecular events that are traditionally believed to support cell survival including the stabilization of mitochondrial membrane potential and morphology. Our data indicate that the PARP inhibitor PJ34 has, apparently, opposing effects on the mitochondrial structure and cell survival. While, initially, it stimulates mitochondrial fusion and hyperpolarization, hallmarks of mitochondrial protection, it enhances the cytotoxic effects of alkylating agents at later stages. These findings may contribute to the optimization of PARP inhibitor-based antineoplastic modalities.
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Affiliation(s)
- Anna Maria Cseh
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, Pécs, Hungary.,Department of Biology, University of Padova, Padua, Italy
| | - Zsolt Fabian
- Department of Medical Chemistry, Molecular Biology and Pathobiochemistry, Faculty of Medicine, Semmelweis University, Budapest, Hungary
| | - Ruben Quintana-Cabrera
- Institute of Functional Biology and Genomics, University of Salamanca, Consejo Superior de Investigaciones Científicas, Salamanca, Spain.,Institute of Biomedical Research of Salamanca, University Hospital of Salamanca, University of Salamanca, Consejo Superior de Investigaciones Científicas, Salamanca, Spain.,CIBERFES, Instituto de Salud Carlos III, Madrid, Spain
| | - Aliz Szabo
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, Pécs, Hungary.,Nuclear-Mitochondrial Interactions Research Group, Hungarian Academy of Sciences, Budapest, Hungary
| | - Krisztian Eros
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, Pécs, Hungary.,Nuclear-Mitochondrial Interactions Research Group, Hungarian Academy of Sciences, Budapest, Hungary.,Szentagothai Research Centre, University of Pécs, Pécs, Hungary
| | - Maria Eugenia Soriano
- Department of Biology, University of Padova, Padua, Italy.,Venetian Institute of Molecular Medicine, Padua, Italy
| | - Ferenc Gallyas
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, Pécs, Hungary.,Nuclear-Mitochondrial Interactions Research Group, Hungarian Academy of Sciences, Budapest, Hungary.,Szentagothai Research Centre, University of Pécs, Pécs, Hungary
| | - Luca Scorrano
- Department of Biology, University of Padova, Padua, Italy.,Venetian Institute of Molecular Medicine, Padua, Italy
| | - Balazs Sumegi
- Department of Biochemistry and Medical Chemistry, Medical School, University of Pécs, Pécs, Hungary.,Nuclear-Mitochondrial Interactions Research Group, Hungarian Academy of Sciences, Budapest, Hungary.,Szentagothai Research Centre, University of Pécs, Pécs, Hungary
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5
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Quintana-Cabrera R, Mehrotra A, Rigoni G, Soriano ME. Who and how in the regulation of mitochondrial cristae shape and function. Biochem Biophys Res Commun 2017; 500:94-101. [PMID: 28438601 DOI: 10.1016/j.bbrc.2017.04.088] [Citation(s) in RCA: 63] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Accepted: 04/17/2017] [Indexed: 12/19/2022]
Abstract
Mitochondrial adaptation to different physiological conditions highly relies on the regulation of mitochondrial ultrastructure, particularly at the level of cristae compartment. Cristae represent the membrane hub where most of the respiratory complexes embed to account for OXPHOS and energy production in the form of adenosine triphosphate (ATP). Changes in cristae number and shape define the respiratory capacity as well as cell viability. The identification of key regulators of cristae morphology and the understanding of their contribution to the mitochondrial ultrastructure and function have become an strategic goal to understand mitochondrial disorders and to exploit as therapeutic targets. This review summarizes the known regulators of cristae ultrastructure and discusses their contribution and implications for mitochondrial dysfunction.
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Affiliation(s)
- R Quintana-Cabrera
- Department of Biology, University of Padova, Padova, 35121, Italy; Venetian Institute of Molecular Medicine, Padova 35129, Italy
| | - A Mehrotra
- Department of Biology, University of Padova, Padova, 35121, Italy
| | - G Rigoni
- Department of Biology, University of Padova, Padova, 35121, Italy
| | - M E Soriano
- Department of Biology, University of Padova, Padova, 35121, Italy.
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6
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Cogliati S, Frezza C, Soriano ME, Varanita T, Quintana-Cabrera R, Corrado M, Cipolat S, Costa V, Casarin A, Gomes LC, Perales-Clemente E, Salviati L, Fernandez-Silva P, Enriquez JA, Scorrano L. Mitochondrial cristae shape determines respiratory chain supercomplexes assembly and respiratory efficiency. Cell 2013; 155:160-71. [PMID: 24055366 PMCID: PMC3790458 DOI: 10.1016/j.cell.2013.08.032] [Citation(s) in RCA: 845] [Impact Index Per Article: 76.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 07/25/2013] [Accepted: 08/19/2013] [Indexed: 11/20/2022]
Abstract
Respiratory chain complexes assemble into functional quaternary structures called supercomplexes (RCS) within the folds of the inner mitochondrial membrane, or cristae. Here, we investigate the relationship between respiratory function and mitochondrial ultrastructure and provide evidence that cristae shape determines the assembly and stability of RCS and hence mitochondrial respiratory efficiency. Genetic and apoptotic manipulations of cristae structure affect assembly and activity of RCS in vitro and in vivo, independently of changes to mitochondrial protein synthesis or apoptotic outer mitochondrial membrane permeabilization. We demonstrate that, accordingly, the efficiency of mitochondria-dependent cell growth depends on cristae shape. Thus, RCS assembly emerges as a link between membrane morphology and function. Dissociation of cristae remodeling from OMM permeabilization Cristae shape determines assembly of respiratory chain supercomplexes Efficiency of mitochondrial respiration and cellular growth depends on cristae shape
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Affiliation(s)
- Sara Cogliati
- Dulbecco-Telethon Institute, Venetian Institute of Molecular Medicine, Via Orus 2, 35129 Padova, Italy; Department of Biology, University of Padova, Via U. Bassi 58B, 35121 Padova, Italy
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7
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Abstract
Hydrogen peroxide (H2O2) is an important regulator of cell redox status and signaling pathways. However, if produced in excess, it can trigger oxidative damage, which can be counteracted by the antioxidant systems. Amongst these, the glutathione (GSH) precursor, γ-glutamylcysteine (γGC), has recently been shown to detoxify H2O2 in a glutathione peroxidase-1 (GPx1)-dependent fashion. To analyze how both γGC and GSH reduce H2O2, we have taken advantage of a colorimetric assay that allows simple and reliable quantification of H2O2 in the micromolar range. Whereas most assays rely on coupled enzymatic reactions, this method determines the formation of a ferric thiocyanate derivative after direct Fe(2+) oxidation by H2O2. Here, we detail the procedure and considerations to determine H2O2 reduction by both γGC and GSH, either from cell samples or in vitro reactions with purified enzymes from GSH metabolism.
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Affiliation(s)
- Ruben Quintana-Cabrera
- Institute of Functional Biology and Genomics (IBFG), Department of Biochemistry and Molecular Biology, University of Salamanca-CSIC, Salamanca, Spain
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8
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Skytt DM, Klawonn AM, Stridh MH, Pajęcka K, Patruss Y, Quintana-Cabrera R, Bolaños JP, Schousboe A, Waagepetersen HS. siRNA knock down of glutamate dehydrogenase in astrocytes affects glutamate metabolism leading to extensive accumulation of the neuroactive amino acids glutamate and aspartate. Neurochem Int 2012; 61:490-7. [PMID: 22542772 DOI: 10.1016/j.neuint.2012.04.014] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2012] [Revised: 04/02/2012] [Accepted: 04/11/2012] [Indexed: 11/27/2022]
Abstract
Glutamate is the most abundant excitatory neurotransmitter in the brain and astrocytes are key players in sustaining glutamate homeostasis. Astrocytes take up the predominant part of glutamate after neurotransmission and metabolism of glutamate is necessary for a continuous efficient removal of glutamate from the synaptic area. Glutamate may either be amidated by glutamine synthetase or oxidatively metabolized in the mitochondria, the latter being at least to some extent initiated by oxidative deamination by glutamate dehydrogenase (GDH). To explore the particular importance of GDH for astrocyte metabolism we have knocked down GDH in cultured cortical astrocytes employing small interfering RNA (siRNA) achieving a reduction of the enzyme activity by approximately 44%. The astrocytes were incubated for 2h in medium containing either 1.0mM [(15)NH(4)(+)] or 100 μM [(15)N]glutamate. For those exposed to [(15)N]glutamate an additional 100 μM was added after 1h. Metabolic mapping was performed from isotope incorporation measured by mass spectrometry into relevant amino acids of cell extracts and media. The contents of the amino acids were measured by HPLC. The (15)N incorporation from [(15)NH(4)(+)] into glutamate, aspartate and alanine was decreased in astrocytes exhibiting reduced GDH activity. However, the reduced GDH activity had no effect on the cellular contents of these amino acids. This supports existing in vivo and in vitro studies that GDH is predominantly working in the direction of oxidative deamination and not reductive amination. In contrast, when exposing the astrocytes to [(15)N]glutamate, the reduced GDH activity led to an increased (15)N incorporation into glutamate, aspartate and alanine and a large increase in the content of glutamate and aspartate. Surprisingly, this accumulation of glutamate and net-synthesis of aspartate were not reflected in any alterations in either the glutamine content or labeling, but a slight increase in mono labeling of glutamine in the medium. We suggest that this extensive net-synthesis of aspartate due to lack of GDH activity is occurring via the concerted action of AAT and the part of TCA cycle operating from α-ketoglutarate to oxaloacetate, i.e. the truncated TCA cycle.
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Affiliation(s)
- Dorte M Skytt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
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