1
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Kjær C, Palasca O, Barzaghi G, Bak LK, Durhuus RKJ, Jakobsen E, Pedersen L, Bartels ED, Woldbye DPD, Pinborg LH, Jensen LJ. Differential Expression of the β3 Subunit of Voltage-Gated Ca 2+ Channel in Mesial Temporal Lobe Epilepsy. Mol Neurobiol 2023; 60:5755-5769. [PMID: 37341859 PMCID: PMC10471638 DOI: 10.1007/s12035-023-03426-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 06/05/2023] [Indexed: 06/22/2023]
Abstract
The purpose of this study was to identify and validate new putative lead drug targets in drug-resistant mesial temporal lobe epilepsy (mTLE) starting from differentially expressed genes (DEGs) previously identified in mTLE in humans by transcriptome analysis. We identified consensus DEGs among two independent mTLE transcriptome datasets and assigned them status as "lead target" if they (1) were involved in neuronal excitability, (2) were new in mTLE, and (3) were druggable. For this, we created a consensus DEG network in STRING and annotated it with information from the DISEASES database and the Target Central Resource Database (TCRD). Next, we attempted to validate lead targets using qPCR, immunohistochemistry, and Western blot on hippocampal and temporal lobe neocortical tissue from mTLE patients and non-epilepsy controls, respectively. Here we created a robust, unbiased list of 113 consensus DEGs starting from two lists of 3040 and 5523 mTLE significant DEGs, respectively, and identified five lead targets. Next, we showed that CACNB3, a voltage-gated Ca2+ channel subunit, was significantly regulated in mTLE at both mRNA and protein level. Considering the key role of Ca2+ currents in regulating neuronal excitability, this suggested a role for CACNB3 in seizure generation. This is the first time changes in CACNB3 expression have been associated with drug-resistant epilepsy in humans, and since efficient therapeutic strategies for the treatment of drug-resistant mTLE are lacking, our finding might represent a step toward designing such new treatment strategies.
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Affiliation(s)
- Christina Kjær
- Biomedical Laboratory Science, Department of Technology, Faculty of Health and Technology, University College Copenhagen, Sigurdsgade 26, 1St, 2200 Copenhagen, Denmark
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Oana Palasca
- Disease Systems Biology Program, Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen, Denmark
| | - Guido Barzaghi
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
- European Molecular Biology Laboratory (EMBL), Genome Biology Unit, Heidelberg, Germany
- Faculty of Biosciences, Collaboration for Joint PhD Degree Between EMBL and Heidelberg University, Heidelberg, Germany
| | - Lasse K. Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
- Dept. of Clinical Biochemistry, 2600 RigshospitaletCopenhagen, Denmark
| | - Rúna K. J. Durhuus
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
- Specific Pharma A/S, Borgmester Christiansens Gade 40, 2450 Copenhagen, SV Denmark
| | - Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
- Takeda Pharma A/S, Delta Park 45, 2665 Vallensbaek Strand, Denmark
| | - Louise Pedersen
- Biomedical Laboratory Science, Department of Technology, Faculty of Health and Technology, University College Copenhagen, Sigurdsgade 26, 1St, 2200 Copenhagen, Denmark
- Dept. of Clinical Biochemistry, 2600 RigshospitaletCopenhagen, Denmark
| | - Emil D. Bartels
- Dept. of Clinical Biochemistry, 2600 RigshospitaletCopenhagen, Denmark
- Department of Clinical Medicine, University of Copenhagen, Copenhagen, Denmark
| | - David P. D. Woldbye
- Department of Neuroscience, University of Copenhagen, 2200 Copenhagen, Denmark
| | - Lars H. Pinborg
- Epilepsy Clinic & Neurobiology Research Unit, Copenhagen University Hospital, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Lars Juhl Jensen
- Disease Systems Biology Program, Faculty of Health and Medical Sciences, Novo Nordisk Foundation Center for Protein Research, University of Copenhagen, Copenhagen, Denmark
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Jakobsen E, Andersen JV, Christensen SK, Siamka O, Larsen MR, Waagepetersen HS, Aldana BI, Bak LK. Pharmacological inhibition of mitochondrial soluble adenylyl cyclase in astrocytes causes activation of AMP-activated protein kinase and induces breakdown of glycogen. Glia 2021; 69:2828-2844. [PMID: 34378239 DOI: 10.1002/glia.24072] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Revised: 06/28/2021] [Accepted: 07/30/2021] [Indexed: 12/17/2022]
Abstract
Mobilization of astrocyte glycogen is key for processes such as synaptic plasticity and memory formation but the link between neuronal activity and glycogen breakdown is not fully known. Activation of cytosolic soluble adenylyl cyclase (sAC) in astrocytes has been suggested to link neuronal depolarization and glycogen breakdown partly based on experiments employing pharmacological inhibition of sAC. However, several studies have revealed that sAC located within mitochondria is a central regulator of respiration and oxidative phosphorylation. Thus, pharmacological sAC inhibition is likely to affect both cytosolic and mitochondrial sAC and if bioenergetic readouts are studied, the observed effects are likely to stem from inhibition of mitochondrial rather than cytosolic sAC. Here, we report that a pharmacologically induced inhibition of sAC activity lowers mitochondrial respiration, induces phosphorylation of the metabolic master switch AMP-activated protein kinase (AMPK), and decreases glycogen stores in cultured primary murine astrocytes. From these data and our discussion of the literature, mitochondrial sAC emerges as a key regulator of astrocyte bioenergetics. Lastly, we discuss the challenges of investigating the functional and metabolic roles of cytosolic versus mitochondrial sAC in astrocytes employing the currently available pharmacological tool compounds.
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Affiliation(s)
- Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Jens V Andersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Sofie K Christensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Olga Siamka
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Martin R Larsen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Blanca I Aldana
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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3
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Jensen PSH, Johansen M, Bak LK, Jensen LJ, Kjær C. Yield and Integrity of RNA from Brain Samples are Largely Unaffected by Pre-analytical Procedures. Neurochem Res 2020; 46:447-454. [PMID: 33249516 DOI: 10.1007/s11064-020-03183-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2020] [Revised: 11/13/2020] [Accepted: 11/17/2020] [Indexed: 11/28/2022]
Abstract
Gene expression studies are reported to be influenced by pre-analytical factors that can compromise RNA yield and integrity, which in turn may confound the experimental findings. Here we investigate the impact of four pre-analytical factors on brain-derived RNA: time-before-collection, tissue specimen size, tissue collection method, and RNA isolation method. We report no significant differences in RNA yield or integrity between 20 mg and 60 mg tissue samples collected in either liquid nitrogen or the RNAlater stabilizing solution. Isolation of RNA employing the TRIzol reagent resulted in a higher yield compared to isolation via the QIAcube kit while the latter resulted in RNA of slightly better integrity. Keeping brain tissue samples at room temperature for up to 160 min prior to collection and isolation of RNA resulted in no significant difference in yield or integrity. Our findings have significant practical and financial consequences for clinical genomic departments and other laboratory settings performing large-scale routine RNA expression analysis of brain samples.
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Affiliation(s)
- Pernille Søs Hovgaard Jensen
- Department of Technology, Faculty of Health and Technology, University College Copenhagen, 2200, Copenhagen, Denmark
| | - Maja Johansen
- Department of Technology, Faculty of Health and Technology, University College Copenhagen, 2200, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lars Juhl Jensen
- Disease Systems Biology Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Christina Kjær
- Department of Technology, Faculty of Health and Technology, University College Copenhagen, 2200, Copenhagen, Denmark. .,Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark.
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4
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Krarup S, Mertz C, Jakobsen E, Lindholm SEH, Pinborg LH, Bak LK. Distinct effects on cAMP signaling of carbamazepine and its structural derivatives do not correlate with their clinical efficacy in epilepsy. Eur J Pharmacol 2020; 886:173413. [PMID: 32758572 DOI: 10.1016/j.ejphar.2020.173413] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Revised: 07/07/2020] [Accepted: 07/23/2020] [Indexed: 01/06/2023]
Abstract
The antiepileptic sodium channel blocker, carbamazepine, has long been known to be able to attenuate cAMP signals. This could be of clinical importance since cAMP signaling has been shown to be involved in epileptogenesis and seizures. However, no information on the ability to affect cAMP signaling is available for the marketed structural derivatives, oxcarbazepine and eslicarbazepine acetate or their dominating metabolite, licarbazepine. Thus, we employed a HEK293 cell line stably expressing a cAMP biosensor to assess the effect of these two drugs on cAMP accumulation. We find that oxcarbazepine does not affect cAMP accumulation whereas eslicarbazepine acetate, surprisingly, is able to enhance cAMP accumulation. Since the transcription of ADCY8 (adenylyl cyclase isoform 8; AC8) has been found to be elevated in epileptic tissue from patients, we subsequently expressed AC8 in the HEK293 cells. In the AC8-expressing cells, oxcarbazepine was now able to attenuate whereas eslicarbazepine maintained its ability to increase cAMP accumulation. However, at all concentrations tested, licarbazepine demonstrated no effect on cAMP accumulation. Thus, we conclude that the effects exerted by carbamazepine and its derivatives on cAMP accumulation do not correlate with their clinical efficacy in epilepsy. However, this does not disqualify cAMP signaling per se as a potential disease-modifying drug target for epilepsy since more potent and selective inhibitors may be of therapeutic value.
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Affiliation(s)
- Sara Krarup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Christoffer Mertz
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Sandy E H Lindholm
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lars H Pinborg
- Epilepsy Clinic and Neurobiology Research Unit, Copenhagen University Hospital, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark.
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5
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Andersen JV, Jakobsen E, Westi EW, Lie MEK, Voss CM, Aldana BI, Schousboe A, Wellendorph P, Bak LK, Pinborg LH, Waagepetersen HS. Extensive astrocyte metabolism of γ-aminobutyric acid (GABA) sustains glutamine synthesis in the mammalian cerebral cortex. Glia 2020; 68:2601-2612. [PMID: 32584476 DOI: 10.1002/glia.23872] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2020] [Revised: 05/26/2020] [Accepted: 05/28/2020] [Indexed: 12/15/2022]
Abstract
Synaptic transmission is closely linked to brain energy and neurotransmitter metabolism. However, the extent of brain metabolism of the inhibitory neurotransmitter γ-aminobutyric acid (GABA), and the relative metabolic contributions of neurons and astrocytes, are yet unknown. The present study was designed to investigate the functional significance of brain GABA metabolism using isolated mouse cerebral cortical slices and slices of neurosurgically resected neocortical human tissue of the temporal lobe. By using dynamic isotope labeling, with [15 N]GABA and [U-13 C]GABA as metabolic substrates, we show that both mouse and human brain slices exhibit a large capacity for GABA metabolism. Both the nitrogen and the carbon backbone of GABA strongly support glutamine synthesis, particularly in the human cerebral cortex, indicative of active astrocytic GABA metabolism. This was further substantiated by pharmacological inhibition of the primary astrocytic GABA transporter subtype 3 (GAT3), by (S)-SNAP-5114 or 1-benzyl-5-chloro-2,3-dihydro-1H-indole-2,3-dione (compound 34), leading to significant reductions in oxidative GABA carbon metabolism. Interestingly, this was not the case when tiagabine was used to specifically inhibit GAT1, which is predominantly found on neurons. Finally, we show that acute GABA exposure does not directly stimulate glycolytic activity nor oxidative metabolism in cultured astrocytes, but can be used as an additional substrate to enhance uncoupled respiration. These results clearly show that GABA is actively metabolized in astrocytes, particularly for the synthesis of glutamine, and challenge the current view that synaptic GABA homeostasis is maintained primarily by presynaptic recycling.
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Affiliation(s)
- Jens V Andersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Emil W Westi
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Maria E K Lie
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Caroline M Voss
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Blanca I Aldana
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Petrine Wellendorph
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lars H Pinborg
- Epilepsy Clinic and Neurobiology Research Unit, Copenhagen University Hospital, University of Copenhagen, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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6
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Lønsmann I, Bak LK. Potential role of adenylyl cyclase 8 signaling complexes in regulating insulin secretion from pancreatic beta cells. Cell Signal 2020; 72:109635. [PMID: 32283257 DOI: 10.1016/j.cellsig.2020.109635] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 04/09/2020] [Accepted: 04/09/2020] [Indexed: 12/25/2022]
Abstract
Glucose-stimulated insulin secretion from pancreatic β cells is mediated by Ca2+ influx and amplified by stimulation of GLP-1-receptors through cAMP-based signaling pathways. Interestingly, it has been found that glucose-induced Ca2+ signals can induce concurrent adenylyl cyclase isoform 8 (AC8)-mediated cAMP signals and, conversely, that GLP-1-receptor-mediated cAMP signals are able to induce Ca2+ signals. In this review, we explore the signaling complexes revolving around AC8 in modulating insulin release, from the initial discovery of the importance of this AC isoform to recent investigations of its interacting molecular partners. We suggest that investigating the structural assembly of the proteins associated with AC8 in β cells might reveal how this particular protein complex could be targeted to modify insulin secretion. Specifically, we suggest that disrupting the protein-protein interaction between A-kinase anchoring protein 79 (AKAP79) and AC8 could lead to disinhibition of AC8 activity and increased insulin secretion. Potentially, AC8 protein interactions could become a future target in type 2 diabetic patients with dysfunction of insulin secretion.
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Affiliation(s)
- Ida Lønsmann
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Denmark.
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7
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Kjær C, Barzaghi G, Bak LK, Goetze JP, Yde CW, Woldbye D, Pinborg LH, Jensen LJ. Transcriptome analysis in patients with temporal lobe epilepsy. Brain 2019; 142:e55. [DOI: 10.1093/brain/awz265] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Christina Kjær
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
- Department of Technology, Faculty of Health and Technology, University College Copenhagen, 2200, Copenhagen, Denmark
| | - Guido Barzaghi
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Jens P Goetze
- Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark
| | | | - David Woldbye
- Department of Neuroscience, University of Copenhagen, Copenhagen, Denmark
| | - Lars H Pinborg
- Epilepsy Clinic and Neurobiology Research Unit, Copenhagen University Hospital, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lars Juhl Jensen
- Disease Systems Biology Program, Novo Nordisk Foundation Center for Protein Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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8
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Mertz C, Krarup S, Jensen CD, Lindholm SEH, Kjær C, Pinborg LH, Bak LK. Aspects of cAMP Signaling in Epileptogenesis and Seizures and Its Potential as Drug Target. Neurochem Res 2019; 45:1247-1255. [PMID: 31414342 DOI: 10.1007/s11064-019-02853-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/30/2019] [Accepted: 08/03/2019] [Indexed: 12/19/2022]
Abstract
Epilepsy is one of the most common chronic neurological conditions. Today, close to 30 different medications to prevent epileptic seizures are in use; yet, far from all patients become seizure free upon medical treatment. Thus, there is a need for new pharmacological approaches including novel drug targets for the management of epilepsy. Despite the fact that a role for cAMP signaling in epileptogenesis and seizures was first suggested some four decades ago, none of the current medications target the cAMP signaling system. The reasons for this are probably many including limited knowledge of the underlying biology and pathology as well as difficulties in designing selective drugs for the different components of the cAMP signaling system. This review explores selected aspects of cAMP signaling in the context of epileptogenesis and seizures including cAMP response element binding (CREB)-mediated transcriptional regulation. We discuss the therapeutic potential of targeting cAMP signaling in epilepsy and point to an increased knowledge of the A-kinase anchoring protein-based signaling hubs as being of seminal importance for future drug discovery within the field. Further, in terms of targeting CREB, we argue that targeting upstream cAMP signals might be more fruitful than targeting CREB itself. Finally, we point to astrocytes as cellular targets in epilepsy since cAMP signals may regulate astrocytic K+ clearance affecting neuronal excitability.
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Affiliation(s)
- Christoffer Mertz
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Sara Krarup
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Cecilie D Jensen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Sandy E H Lindholm
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Christina Kjær
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark.,Department of Technology, Faculty of Health and Technology, University College Copenhagen, 2200, Copenhagen, Denmark
| | - Lars H Pinborg
- Epilepsy Clinic & Neurobiology Research Unit, Copenhagen University Hospital, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark.
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9
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Bogetofte H, Jensen P, Ryding M, Schmidt SI, Okarmus J, Ritter L, Worm CS, Hohnholt MC, Azevedo C, Roybon L, Bak LK, Waagepetersen H, Ryan BJ, Wade-Martins R, Larsen MR, Meyer M. PARK2 Mutation Causes Metabolic Disturbances and Impaired Survival of Human iPSC-Derived Neurons. Front Cell Neurosci 2019; 13:297. [PMID: 31333417 PMCID: PMC6624735 DOI: 10.3389/fncel.2019.00297] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [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: 01/14/2019] [Accepted: 06/18/2019] [Indexed: 12/22/2022] Open
Abstract
The protein parkin, encoded by the PARK2 gene, is vital for mitochondrial homeostasis, and although it has been implicated in Parkinson’s disease (PD), the disease mechanisms remain unclear. We have applied mass spectrometry-based proteomics to investigate the effects of parkin dysfunction on the mitochondrial proteome in human isogenic induced pluripotent stem cell-derived neurons with and without PARK2 knockout (KO). The proteomic analysis quantified nearly 60% of all mitochondrial proteins, 119 of which were dysregulated in neurons with PARK2 KO. The protein changes indicated disturbances in oxidative stress defense, mitochondrial respiration and morphology, cell cycle control, and cell viability. Structural and functional analyses revealed an increase in mitochondrial area and the presence of elongated mitochondria as well as impaired glycolysis and lactate-supported respiration, leading to an impaired cell survival in PARK2 KO neurons. This adds valuable insight into the effect of parkin dysfunction in human neurons and provides knowledge of disease-related pathways that can potentially be targeted for therapeutic intervention.
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Affiliation(s)
- Helle Bogetofte
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.,Oxford Parkinson's Disease Centre, Medical Sciences Division, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Pia Jensen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Matias Ryding
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Sissel I Schmidt
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Justyna Okarmus
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Louise Ritter
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Christina S Worm
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark
| | - Michaela C Hohnholt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Carla Azevedo
- Department of Experimental Medical Science, Wallenberg Neuroscience Center, Lund University, Lund, Sweden
| | - Laurent Roybon
- Department of Experimental Medical Science, Wallenberg Neuroscience Center, Lund University, Lund, Sweden
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Brent J Ryan
- Oxford Parkinson's Disease Centre, Medical Sciences Division, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Richard Wade-Martins
- Oxford Parkinson's Disease Centre, Medical Sciences Division, Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Martin R Larsen
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark
| | - Morten Meyer
- Department of Neurobiology Research, Institute of Molecular Medicine, University of Southern Denmark, Odense, Denmark.,Brain Research - Inter-Disciplinary Guided Excellence, University of Southern Denmark, Odense, Denmark
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10
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Jakobsen E, Lange SC, Bak LK. Soluble adenylyl cyclase-mediated cAMP signaling and the putative role of PKA and EPAC in cerebral mitochondrial function. J Neurosci Res 2019; 97:1018-1038. [PMID: 31172581 DOI: 10.1002/jnr.24477] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Revised: 05/16/2019] [Accepted: 05/16/2019] [Indexed: 12/20/2022]
Abstract
Mitochondria produce the bulk of the ATP in most cells, including brain cells. Regulating this complex machinery to match the energetic needs of the cell is a complicated process that we have yet to understand in its entirety. In this context, 3',5'-cyclic AMP (cAMP) has been suggested to play a seminal role in signaling-metabolism coupling and regulation of mitochondrial ATP production. In cells, cAMP signals may affect mitochondria from the cytosolic side but more recently, a cAMP signal produced within the matrix of mitochondria by soluble adenylyl cyclase (sAC) has been suggested to regulate respiration and thus ATP production. However, little is known about these processes in brain mitochondria, and the effectors of the cAMP signal generated within the matrix are not completely clear since both protein kinase A (PKA) and exchange protein activated by cAMP 1 (EPAC1) have been suggested to be involved. Here, we review the current knowledge and relate it to brain mitochondria. Further, based on measurements of respiration, membrane potential, and ATP production in isolated mouse brain cortical mitochondria we show that inhibitors of sAC, PKA, or EPAC affect mitochondrial function in distinct ways. In conclusion, we suggest that brain mitochondria do regulate their function via sAC-mediated cAMP signals and that both PKA and EPAC could be involved downstream of sAC. Finally, due to the role of faulty mitochondrial function in a range of neurological diseases, we expect that the function of sAC-cAMP-PKA/EPAC signaling in brain mitochondria will likely attract further attention.
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Affiliation(s)
- Emil Jakobsen
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Sofie C Lange
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen, Copenhagen, Denmark
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11
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Reuschlein AK, Jakobsen E, Mertz C, Bak LK. Aspects of astrocytic cAMP signaling with an emphasis on the putative power of compartmentalized signals in health and disease. Glia 2019; 67:1625-1636. [PMID: 31033018 DOI: 10.1002/glia.23622] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 03/29/2019] [Accepted: 03/29/2019] [Indexed: 12/17/2022]
Abstract
This review discusses aspects of known and putative compartmentalized 3',5'-cyclic adenosine monophosphate (cAMP) signaling in astrocytes, a cell type that has turned out to be a key player in brain physiology and pathology. cAMP has attracted less attention than Ca2+ in recent years, but could turn out to rival Ca2+ in its potential to drive cellular functions and responses to intra- and extracellular cues. Further, Ca2+ and cAMP are known to engage in extensive crosstalk and cAMP signals often take place within subcellular compartments revolving around multi-protein signaling complexes; however, we know surprisingly little about this in astrocytes. Here, we review aspects of astrocytic cAMP signaling, provide arguments for an increased interest in this subject, suggest possible future research directions within the field, and discuss putative drug targets.
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Affiliation(s)
- Ann-Kathrin Reuschlein
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Christoffer Mertz
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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12
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DiNuzzo M, Walls AB, Öz G, Seaquist ER, Waagepetersen HS, Bak LK, Nedergaard M, Schousboe A. State-Dependent Changes in Brain Glycogen Metabolism. Adv Neurobiol 2019; 23:269-309. [PMID: 31667812 DOI: 10.1007/978-3-030-27480-1_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
A fundamental understanding of glycogen structure, concentration, polydispersity and turnover is critical to qualify the role of glycogen in the brain. These molecular and metabolic features are under the control of neuronal activity through the interdependent action of neuromodulatory tone, ionic homeostasis and availability of metabolic substrates, all variables that concur to define the state of the system. In this chapter, we briefly describe how glycogen responds to selected behavioral, nutritional, environmental, hormonal, developmental and pathological conditions. We argue that interpreting glycogen metabolism through the lens of brain state is an effective approach to establish the relevance of energetics in connecting molecular and cellular neurophysiology to behavior.
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Affiliation(s)
- Mauro DiNuzzo
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Gülin Öz
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, MN, USA
| | | | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Maiken Nedergaard
- Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.,Center for Translational Neuromedicine, University of Rochester Medical School, Rochester, NY, USA
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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13
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Jakobsen E, Lange SC, Andersen JV, Desler C, Kihl HF, Hohnholt MC, Stridh MH, Rasmussen LJ, Waagepetersen HS, Bak LK. The inhibitors of soluble adenylate cyclase 2-OHE, KH7, and bithionol compromise mitochondrial ATP production by distinct mechanisms. Biochem Pharmacol 2018; 155:92-101. [PMID: 29940175 DOI: 10.1016/j.bcp.2018.06.023] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 06/18/2018] [Indexed: 12/25/2022]
Abstract
Soluble adenylate cyclase (sAC) is a non-plasma membrane-bound isoform of the adenylate cyclases signaling via the canonical second messenger, 3',5'-cyclic AMP (cAMP). sAC is involved in key physiological processes such as insulin release, sperm motility, and energy metabolism. Thus, sAC has attracted interest as a putative drug target and attempts have been made to develop selective inhibitors. Since sAC has a binding constant for its substrate, ATP, in the millimolar range, reductions in mitochondrial ATP production may be part of the mechanism-of-action of sAC inhibitors and the potential of these compounds to study the physiological outcomes of inhibition of sAC might be severely hampered by this. Here, we evaluate the effects of two commonly employed inhibitors, 2-OHE and KH7, on mitochondrial ATP production and energy metabolism. For comparison, we included a recently identified inhibitor of sAC, bithionol. Employing mitochondria isolated from mouse brain, we show that all three compounds are able to curb ATP production albeit via distinct mechanisms. Bithionol and KH7 mainly inhibit ATP production by working as a classical uncoupler whereas 2-OHE mainly works by decreasing mitochondrial respiration. These findings were corroborated by investigating energy metabolism in acute brain slices from mice. Since all three sAC inhibitors are shown to curb mitochondrial ATP production and affect energy metabolism, caution should be exercised when employed to study the physiological roles of sAC or for validating sAC as a drug target.
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Affiliation(s)
- Emil Jakobsen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Sofie C Lange
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Jens V Andersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Claus Desler
- Center for Healthy Aging, Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Henriette F Kihl
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Michaela C Hohnholt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Malin H Stridh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Lene J Rasmussen
- Center for Healthy Aging, Department of Cellular and Molecular Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark.
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14
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Abstract
The brain contains a fairly low amount of glycogen, mostly located in astrocytes, a fact that has prompted the suggestion that glycogen does not have a significant physiological role in the brain. However, glycogen metabolism in astrocytes is essential for several key physiological processes and is adversely affected in disease. For instance, diminished ability to break down glycogen impinges on learning, and epilepsy, Alzheimer's disease, and type 2 diabetes are all associated with abnormal astrocyte glycogen metabolism. Glycogen metabolism supports astrocytic K+ and neurotransmitter glutamate uptake and subsequent glutamine synthesis-three fundamental steps in excitatory signaling at most brain synapses. Thus, there is abundant evidence for a key role of glycogen in brain function. Here, we summarize the physiological brain functions that depend on glycogen, discuss glycogen metabolism in disease, and investigate how glycogen breakdown is regulated at the cellular and molecular levels.
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark.
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark.
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
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15
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
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16
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Bak LK, Walls AB. CrossTalk opposing view: lack of evidence supporting an astrocyte-to-neuron lactate shuttle coupling neuronal activity to glucose utilisation in the brain. J Physiol 2018; 596:351-353. [PMID: 29292507 DOI: 10.1113/jp274945] [Citation(s) in RCA: 61] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Anne B Walls
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
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17
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Abstract
Astrocytes are crucial cells in the brain that are intimately coupled with neuronal metabolism. A new paper from San Martín et al. provides evidence that physiological levels of the gaseous signal molecule NO can rapidly and reversibly increase astrocyte metabolism of glucose and production of lactate. A proposed neurological coupling-from the potential source of NO, endothelial cells, to the potential beneficiary from the lactate, neurons-prompts new questions regarding the controversial role of lactate in the brain.
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Affiliation(s)
- Lasse K Bak
- From the Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
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18
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Aldana BI, Zhang Y, Lihme MF, Bak LK, Nielsen JE, Holst B, Hyttel P, Freude KK, Waagepetersen HS. Characterization of energy and neurotransmitter metabolism in cortical glutamatergic neurons derived from human induced pluripotent stem cells: A novel approach to study metabolism in human neurons. Neurochem Int 2017; 106:48-61. [DOI: 10.1016/j.neuint.2017.02.010] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2016] [Revised: 01/19/2017] [Accepted: 02/20/2017] [Indexed: 02/01/2023]
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19
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Zhang Y, Schmid B, Nikolaisen NK, Rasmussen MA, Aldana BI, Agger M, Calloe K, Stummann TC, Larsen HM, Nielsen TT, Huang J, Xu F, Liu X, Bolund L, Meyer M, Bak LK, Waagepetersen HS, Luo Y, Nielsen JE, Holst B, Clausen C, Hyttel P, Freude KK. Patient iPSC-Derived Neurons for Disease Modeling of Frontotemporal Dementia with Mutation in CHMP2B. Stem Cell Reports 2017; 8:648-658. [PMID: 28216144 PMCID: PMC5355623 DOI: 10.1016/j.stemcr.2017.01.012] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [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: 08/27/2016] [Revised: 01/16/2017] [Accepted: 01/17/2017] [Indexed: 12/23/2022] Open
Abstract
The truncated mutant form of the charged multivesicular body protein 2B (CHMP2B) is causative for frontotemporal dementia linked to chromosome 3 (FTD3). CHMP2B is a constituent of the endosomal sorting complex required for transport (ESCRT) and, when mutated, disrupts endosome-to-lysosome trafficking and substrate degradation. To understand the underlying molecular pathology, FTD3 patient induced pluripotent stem cells (iPSCs) were differentiated into forebrain-type cortical neurons. FTD3 neurons exhibited abnormal endosomes, as previously shown in patients. Moreover, mitochondria of FTD3 neurons displayed defective cristae formation, accompanied by deficiencies in mitochondrial respiration and increased levels of reactive oxygen. In addition, we provide evidence for perturbed iron homeostasis, presenting an in vitro patient-specific model to study the effects of iron accumulation in neurodegenerative diseases. All phenotypes observed in FTD3 neurons were rescued in CRISPR/Cas9-edited isogenic controls. These findings illustrate the relevance of our patient-specific in vitro models and open up possibilities for drug target development. FTD3 neurons show abnormalities in endosomes and mitochondria Parkinson's and Alzheimer's disease core genes are altered in FTD3 neurons Iron homeostasis is perturbed in FTD3 neurons Impairments in FTD3 neurons are rescued in CRISPR/Cas9-edited isogenic controls
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Affiliation(s)
- Yu Zhang
- Stem Cells and Embryology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark.
| | | | - Nanett K Nikolaisen
- Stem Cells and Embryology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark
| | | | - Blanca I Aldana
- Neurometabolism Research Unit, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Mikkel Agger
- Stem Cell and Developmental Neurobiology Group, Department of Neurobiology Research, University of Southern Denmark, 5000 Odense C, Denmark
| | - Kirstine Calloe
- The Physiology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark
| | | | - Hjalte M Larsen
- Stem Cells and Embryology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark
| | - Troels T Nielsen
- Neurogenetics Clinic & Research Lab, Danish Dementia Research Centre, Department of Neurology, Rigshospitalet, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Jinrong Huang
- BGI-Shenzhen, 518083 Shenzhen, China; China National GeneBank-Shenzhen, BGI-Shenzhen, 518083 Shenzhen, China
| | - Fengping Xu
- BGI-Shenzhen, 518083 Shenzhen, China; China National GeneBank-Shenzhen, BGI-Shenzhen, 518083 Shenzhen, China
| | - Xin Liu
- BGI-Shenzhen, 518083 Shenzhen, China; China National GeneBank-Shenzhen, BGI-Shenzhen, 518083 Shenzhen, China
| | - Lars Bolund
- Danish Regenerative Engineering Alliance for Medicine (DREAM), Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark
| | - Morten Meyer
- Stem Cell and Developmental Neurobiology Group, Department of Neurobiology Research, University of Southern Denmark, 5000 Odense C, Denmark
| | - Lasse K Bak
- Neurometabolism Research Unit, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Helle S Waagepetersen
- Neurometabolism Research Unit, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Yonglun Luo
- Danish Regenerative Engineering Alliance for Medicine (DREAM), Department of Biomedicine, Aarhus University, 8000 Aarhus C, Denmark
| | - Jørgen E Nielsen
- Neurogenetics Clinic & Research Lab, Danish Dementia Research Centre, Department of Neurology, Rigshospitalet, University of Copenhagen, 2100 Copenhagen, Denmark
| | | | | | | | - Poul Hyttel
- Stem Cells and Embryology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark
| | - Kristine K Freude
- Stem Cells and Embryology Group, Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark.
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20
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Bak LK, Schousboe A. Misconceptions regarding basic thermodynamics and enzyme kinetics have led to erroneous conclusions regarding the metabolic importance of lactate dehydrogenase isoenzyme expression. J Neurosci Res 2017; 95:2098-2102. [DOI: 10.1002/jnr.23994] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Revised: 11/07/2016] [Accepted: 11/09/2016] [Indexed: 01/30/2023]
Affiliation(s)
- Lasse K. Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
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21
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Nissen JD, Lykke K, Bryk J, Stridh MH, Zaganas I, Skytt DM, Schousboe A, Bak LK, Enard W, Pääbo S, Waagepetersen HS. Expression of the human isoform of glutamate dehydrogenase, hGDH2, augments TCA cycle capacity and oxidative metabolism of glutamate during glucose deprivation in astrocytes. Glia 2016; 65:474-488. [PMID: 28032919 DOI: 10.1002/glia.23105] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 11/23/2016] [Accepted: 11/30/2016] [Indexed: 01/06/2023]
Abstract
A key enzyme in brain glutamate homeostasis is glutamate dehydrogenase (GDH) which links carbohydrate and amino acid metabolism mediating glutamate degradation to CO2 and expanding tricarboxylic acid (TCA) cycle capacity with intermediates, i.e. anaplerosis. Humans express two GDH isoforms, GDH1 and 2, whereas most other mammals express only GDH1. hGDH1 is widely expressed in human brain while hGDH2 is confined to astrocytes. The two isoforms display different enzymatic properties and the nature of these supports that hGDH2 expression in astrocytes potentially increases glutamate oxidation and supports the TCA cycle during energy-demanding processes such as high intensity glutamatergic signaling. However, little is known about how expression of hGDH2 affects the handling of glutamate and TCA cycle metabolism in astrocytes. Therefore, we cultured astrocytes from cerebral cortical tissue of hGDH2-expressing transgenic mice. We measured glutamate uptake and metabolism using [3 H]glutamate, while the effect on metabolic pathways of glutamate and glucose was evaluated by use of 13 C and 14 C substrates and analysis by mass spectrometry and determination of radioactively labeled metabolites including CO2 , respectively. We conclude that hGDH2 expression increases capacity for uptake and oxidative metabolism of glutamate, particularly during increased workload and aglycemia. Additionally, hGDH2 expression increased utilization of branched-chain amino acids (BCAA) during aglycemia and caused a general decrease in oxidative glucose metabolism. We speculate, that expression of hGDH2 allows astrocytes to spare glucose and utilize BCAAs during substrate shortages. These findings support the proposed role of hGDH2 in astrocytes as an important fail-safe during situations of intense glutamatergic activity. GLIA 2017;65:474-488.
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Affiliation(s)
- Jakob D Nissen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Kasper Lykke
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Jaroslaw Bryk
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany
| | - Malin H Stridh
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Ioannis Zaganas
- Neurology Laboratory, School of Health Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete, Greece
| | - Dorte M Skytt
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
| | - Wolfgang Enard
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany
| | - Svante Pääbo
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, 02109, Germany
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Science, University of Copenhagen, Copenhagen, 2100, Denmark
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22
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Hohnholt MC, Andersen VH, Bak LK, Waagepetersen HS. Glucose, Lactate and Glutamine but not Glutamate Support Depolarization-Induced Increased Respiration in Isolated Nerve Terminals. Neurochem Res 2016; 42:191-201. [DOI: 10.1007/s11064-016-2036-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2016] [Revised: 08/12/2016] [Accepted: 08/16/2016] [Indexed: 12/28/2022]
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23
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Jayakumar AR, Bak LK, Rama Rao KV, Waagepetersen HS, Schousboe A, Norenberg MD. Neuronal Cell Death Induced by Mechanical Percussion Trauma in Cultured Neurons is not Preceded by Alterations in Glucose, Lactate and Glutamine Metabolism. Neurochem Res 2016; 41:307-15. [PMID: 26729365 DOI: 10.1007/s11064-015-1801-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2015] [Revised: 12/07/2015] [Accepted: 12/09/2015] [Indexed: 11/24/2022]
Abstract
Traumatic brain injury (TBI) is a devastating neurological disorder that usually presents in acute and chronic forms. Brain edema and associated increased intracranial pressure in the early phase following TBI are major consequences of acute trauma. On the other hand, neuronal injury, leading to neurobehavioral and cognitive impairments, that usually develop months to years after single or repetitive episodes of head trauma, are major consequences of chronic TBI. The molecular mechanisms responsible for TBI-induced injury, however, are unclear. Recent studies have suggested that early mitochondrial dysfunction and subsequent energy failure play a role in the pathogenesis of TBI. We therefore examined whether oxidative metabolism of (13)C-labeled glucose, lactate or glutamine is altered early following in vitro mechanical percussion-induced trauma (5 atm) to neurons (4-24 h), and whether such events contribute to the development of neuronal injury. Cell viability was assayed using the release of the cytoplasmic enzyme lactate dehydrogenase (LDH), together with fluorescence-based cell staining (calcein and ethidium homodimer-1 for live and dead cells, respectively). Trauma had no effect on the LDH release in neurons from 1 to 18 h. However, a significant increase in LDH release was detected at 24 h after trauma. Similar findings were identified when traumatized neurons were stained with fluorescent markers. Additionally (13)C-labeling of glutamate showed a small, but statistically significant decrease at 14 h after trauma. However, trauma had no effect on the cycling ratio of the TCA cycle at any time-period examined. These findings indicate that trauma does not cause a disturbance in oxidative metabolism of any of the substrates used for neurons. Accordingly, such metabolic disturbance does not appear to contribute to the neuronal death in the early stages following trauma.
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Affiliation(s)
- A R Jayakumar
- Laboratory of Neuropathology, Veterans Affairs Medical Center, Miami, FL, USA
| | - L K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - K V Rama Rao
- Laboratory of Neuropathology, Veterans Affairs Medical Center, Miami, FL, USA
| | - H S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - A Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - M D Norenberg
- Laboratory of Neuropathology, Veterans Affairs Medical Center, Miami, FL, USA. .,Department of Pathology (D-33), University of Miami School of Medicine, P.O. Box 016960, Miami, FL, 33101, USA. .,Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, FL, USA.
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24
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Lange SC, Winkler U, Andresen L, Byhrø M, Waagepetersen HS, Hirrlinger J, Bak LK. Dynamic Changes in Cytosolic ATP Levels in Cultured Glutamatergic Neurons During NMDA-Induced Synaptic Activity Supported by Glucose or Lactate. Neurochem Res 2015; 40:2517-26. [PMID: 26184116 DOI: 10.1007/s11064-015-1651-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Revised: 06/17/2015] [Accepted: 06/23/2015] [Indexed: 11/30/2022]
Abstract
We have previously shown that synaptic transmission fails in cultured neurons in the presence of lactate as the sole substrate. Thus, to test the hypothesis that the failure of synaptic transmission is a consequence of insufficient energy supply, ATP levels were monitored employing the ATP biosensor Ateam1.03YEMK. While inducing synaptic activity by subjecting cultured neurons to two 30 s pulses of NMDA (30 µM) with a 4 min interval, changes in relative ATP levels were measured in the presence of lactate (1 mM), glucose (2.5 mM) or the combination of the two. ATP levels reversibly declined following NMDA-induced neurotransmission activity, as indicated by a reversible 10-20 % decrease in the response of the biosensor. The responses were absent when the NMDA receptor antagonist memantine was present. In the presence of lactate alone, the ATP response dropped significantly more than in the presence of glucose following the 2nd pulse of NMDA (approx. 10 vs. 20 %). Further, cytosolic Ca(2+) homeostasis during NMDA-induced synaptic transmission is partially inhibited by verapamil indicating that voltage-gated Ca(2+) channels are activated. Lastly, we showed that cytosolic Ca(2+) homeostasis is supported equally well by both glucose and lactate, and that a pulse of NMDA causes accumulation of Ca(2+) in the mitochondrial matrix. In summary, we have shown that ATP homeostasis during neurotransmission activity in cultured neurons is supported by both glucose and lactate. However, ATP homeostasis seems to be negatively affected by the presence of lactate alone, suggesting that glucose is needed to support neuronal energy metabolism during activation.
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Affiliation(s)
- Sofie C Lange
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Ulrike Winkler
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, University of Leipzig, Liebigstr. 27, 04103, Leipzig, Germany
| | - Lars Andresen
- Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, 15 Grønnegårdsvej, 1870, Frederiksberg, Denmark
| | - Mathilde Byhrø
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark
| | - Johannes Hirrlinger
- Faculty of Medicine, Carl-Ludwig-Institute for Physiology, University of Leipzig, Liebigstr. 27, 04103, Leipzig, Germany.,Department of Neurogenetics, Max-Planck-Institute for Experimental Medicine, Hermann-Rein-Str. 3, 37075, Göttingen, Germany
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100, Copenhagen, Denmark.
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Schousboe A, Waagepetersen HS, Leke R, Bak LK. Effects of hyperammonemia on brain energy metabolism: controversial findings in vivo and in vitro. Metab Brain Dis 2014; 29:913-7. [PMID: 24577633 DOI: 10.1007/s11011-014-9513-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 02/14/2014] [Indexed: 12/21/2022]
Abstract
The literature related to the effects of elevated plasma ammonia levels on brain energy metabolism is abundant, but heterogeneous in terms of the conclusions. Thus, some studies claim that ammonia has a direct, inhibitory effect on energy metabolism whereas others find no such correlation. In this review, we discuss both recent and older literature related to this controversial topic. We find that it has been consistently reported that hepatic encephalopathy and concomitant hyperammonemia lead to reduced cerebral oxygen consumption. However, this may not be directly linked to an effect of ammonia but related to the fact that hepatic encephalopathy is always associated with reduced brain activity, a condition clearly characterized by a decreased CMRO2. Whether this may be related to changes in GABAergic function remains to be elucidated.
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Affiliation(s)
- Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen Ø, Denmark
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26
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Iversen P, Mouridsen K, Hansen MB, Jensen SB, Sørensen M, Bak LK, Waagepetersen HS, Schousboe A, Ott P, Vilstrup H, Keiding S, Gjedde A. Oxidative metabolism of astrocytes is not reduced in hepatic encephalopathy: a PET study with [(11)C]acetate in humans. Front Neurosci 2014; 8:353. [PMID: 25404890 PMCID: PMC4217371 DOI: 10.3389/fnins.2014.00353] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2014] [Accepted: 10/14/2014] [Indexed: 12/31/2022] Open
Abstract
In patients with impaired liver function and hepatic encephalopathy (HE), consistent elevations of blood ammonia concentration suggest a crucial role in the pathogenesis of HE. Ammonia and acetate are metabolized in brain both primarily in astrocytes. Here, we used dynamic [(11)C]acetate PET of the brain to measure the contribution of astrocytes to the previously observed reduction of brain oxidative metabolism in patients with liver cirrhosis and HE, compared to patients with cirrhosis without HE, and to healthy subjects. We used a new kinetic model to estimate uptake from blood to astrocytes and astrocyte metabolism of [(11)C]acetate. No significant differences of the rate constant of oxidation of [(11)C]acetate (k 3) were found among the three groups of subjects. The net metabolic clearance of [(11)C]acetate from blood was lower in the group of patients with cirrhosis and HE than in the group of healthy subjects (P < 0.05), which we interpret to be an effect of reduced cerebral blood flow rather than a reflection of low [(11)C]acetate metabolism. We conclude that the characteristic decline of whole-brain oxidative metabolism in patients with cirrhosis with HE is not due to malfunction of oxidative metabolism in astrocytes. Thus, the observed decline of brain oxidative metabolism implicates changes of neurons and their energy turnover in patients with HE.
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Affiliation(s)
- Peter Iversen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital Aarhus, Denmark
| | - Kim Mouridsen
- Center of Functionally Integrative Neuroscience, Aarhus University Aarhus, Denmark
| | - Mikkel B Hansen
- Center of Functionally Integrative Neuroscience, Aarhus University Aarhus, Denmark
| | - Svend B Jensen
- Department of Nuclear Medicine, Aalborg University Hospital Aalborg, Denmark ; Department of Chemistry and Biochemistry, Aalborg University Aalborg, Denmark
| | - Michael Sørensen
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital Aarhus, Denmark ; Department of Hepatology and Gastroenterology, Aarhus University Hospital Aarhus, Denmark
| | - Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Helle S Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Peter Ott
- Department of Hepatology and Gastroenterology, Aarhus University Hospital Aarhus, Denmark
| | - Hendrik Vilstrup
- Department of Hepatology and Gastroenterology, Aarhus University Hospital Aarhus, Denmark
| | - Susanne Keiding
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital Aarhus, Denmark ; Department of Hepatology and Gastroenterology, Aarhus University Hospital Aarhus, Denmark ; Brain Research and Integrative Neuroscience Laboratory, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
| | - Albert Gjedde
- Department of Nuclear Medicine and PET Centre, Aarhus University Hospital Aarhus, Denmark ; Center of Functionally Integrative Neuroscience, Aarhus University Aarhus, Denmark ; Brain Research and Integrative Neuroscience Laboratory, Department of Neuroscience and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen Copenhagen, Denmark
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Müller MS, Pedersen SE, Walls AB, Waagepetersen HS, Bak LK. Isoform-selective regulation of glycogen phosphorylase by energy deprivation and phosphorylation in astrocytes. Glia 2014; 63:154-62. [PMID: 25130497 DOI: 10.1002/glia.22741] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Accepted: 07/29/2014] [Indexed: 11/07/2022]
Abstract
Glycogen phosphorylase (GP) is activated to degrade glycogen in response to different stimuli, to support both the astrocyte's own metabolic demand and the metabolic needs of neurons. The regulatory mechanism allowing such a glycogenolytic response to distinct triggers remains incompletely understood. In the present study, we used siRNA-mediated differential knockdown of the two isoforms of GP expressed in astrocytes, muscle isoform (GPMM), and brain isoform (GPBB), to analyze isoform-specific regulatory characteristics in a cellular setting. Subsequently, we tested the response of each isoform to phosphorylation, triggered by incubation with norepinephrine (NE), and to AMP, increased by glucose deprivation in cells in which expression of one GP isoform had been silenced. Successful knockdown was demonstrated on the protein level by Western blot, and on a functional level by determination of glycogen content showing an increase in glycogen levels following knockdown of either GPMM or GPBB. NE triggered glycogenolysis within 15 min in control cells and after GPBB knockdown. However, astrocytes in which expression of GPMM had been silenced showed a delay in response to NE, with glycogen levels significantly reduced only after 60 min. In contrast, allosteric activation of GP by AMP, induced by glucose deprivation, seemed to mainly affect GPBB, as only knockdown of GPBB, but not of GPMM, delayed the glycogenolytic response to glucose deprivation. Our results indicate that the two GP isoforms expressed in astrocytes respond to different physiological triggers, therefore conferring distinct metabolic functions of brain glycogen.
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Affiliation(s)
- Margit S Müller
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, 2100, Denmark
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Müller MS, Fox R, Schousboe A, Waagepetersen HS, Bak LK. Astrocyte glycogenolysis is triggered by store-operated calcium entry and provides metabolic energy for cellular calcium homeostasis. Glia 2014; 62:526-34. [PMID: 24464850 DOI: 10.1002/glia.22623] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 12/11/2013] [Accepted: 12/16/2013] [Indexed: 01/14/2023]
Abstract
Astrocytic glycogen, the only storage form of glucose in the brain, has been shown to play a fundamental role in supporting learning and memory, an effect achieved by providing metabolic support for neurons. We have examined the interplay between glycogenolysis and the bioenergetics of astrocytic Ca(2+) homeostasis, by analyzing interdependency of glycogen and store-operated Ca(2+) entry (SOCE), a mechanism in cellular signaling that maintains high endoplasmatic reticulum (ER) Ca(2+) concentration and thus provides the basis for store-dependent Ca(2+) signaling. We stimulated SOCE in primary cultures of murine cerebellar and cortical astrocytes, and determined glycogen content to investigate the effects of SOCE on glycogen metabolism. By blocking glycogenolysis, we tested energetic dependency of SOCE-related Ca(2+) dynamics on glycogenolytic ATP. Our results show that SOCE triggers astrocytic glycogenolysis. Upon inhibition of adenylate cyclase with 2',5'-dideoxyadenosine, glycogen content was no longer significantly different from that in unstimulated control cells, indicating that SOCE triggers astrocytic glycogenolysis in a cAMP-dependent manner. When glycogenolysis was inhibited in cortical astrocytes by 1,4-dideoxy-1,4-imino-D-arabinitol, the amount of Ca(2+) loaded into ER via sarco/endoplasmic reticulum Ca(2)-ATPase (SERCA) was reduced, which suggests that SERCA pumps preferentially metabolize glycogenolytic ATP. Our study demonstrates SOCE as a novel pathway in stimulating astrocytic glycogenolysis. We also provide first evidence for a new functional role of brain glycogen, in providing local ATP to SERCA, thus establishing the bioenergetic basis for astrocytic Ca(2+) signaling. This mechanism could offer a novel explanation for the impact of glycogen on learning and memory.
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Affiliation(s)
- Margit S Müller
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
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Abstract
Metabolism of glutamate, the main excitatory neurotransmitter and precursor of GABA, is exceedingly complex and highly compartmentalized in brain. Maintenance of these neurotransmitter pools is strictly dependent on the de novo synthesis of glutamine in astrocytes which requires both the anaplerotic enzyme pyruvate carboxylase and glutamine synthetase. Glutamate is formed directly from glutamine by deamidation via phosphate activated glutaminase a reaction that also yields ammonia. Glutamate plays key roles linking carbohydrate and amino acid metabolism via the tricarboxylic acid (TCA) cycle, as well as in nitrogen trafficking and ammonia homeostasis in brain. The anatomical specialization of astrocytic endfeet enables these cells to rapidly and efficiently remove neurotransmitters from the synaptic cleft to maintain homeostasis, and to provide glutamine to replenish neurotransmitter pools in both glutamatergic and GABAergic neurons. Since the glutamate-glutamine cycle is an open cycle that actively interfaces with other pathways, the de novo synthesis of glutamine in astrocytes helps to maintain the operation of this cycle. The fine-tuned biochemical specialization of astrocytes allows these cells to respond to subtle changes in neurotransmission by dynamically adjusting their anaplerotic and glycolytic activities, and adjusting the amount of glutamate oxidized for energy relative to direct formation of glutamine, to meet the demands for maintaining neurotransmission. This chapter summarizes the evidence that astrocytes are essential and dynamic partners in both glutamatergic and GABAergic neurotransmission in brain.
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Affiliation(s)
- Arne Schousboe
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen, 2100, Copenhagen, Denmark
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Walls AB, Bak LK, Sonnewald U, Schousboe A, Waagepetersen HS. Metabolic Mapping of Astrocytes and Neurons in Culture Using Stable Isotopes and Gas Chromatography-Mass Spectrometry (GC-MS). Brain Energy Metabolism 2014. [DOI: 10.1007/978-1-4939-1059-5_4] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Dam G, Keiding S, Munk OL, Ott P, Vilstrup H, Bak LK, Waagepetersen HS, Schousboe A, S⊘rensen M. Reply: To PMID 22886493. Hepatology 2013; 58:833-4. [PMID: 23280960 DOI: 10.1002/hep.26149] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 11/01/2012] [Indexed: 12/07/2022]
Affiliation(s)
- Gitte Dam
- Department of Nuclear Medicine & PET Center; Aarhus University Hospital; Aarhus Denmark
| | - Susanne Keiding
- Department of Nuclear Medicine & PET Center; Aarhus University Hospital; Aarhus Denmark
- Department of Hepato-Gastroenterology; Aarhus University Hospital; Aarhus Denmark
| | - Ole L. Munk
- Department of Nuclear Medicine & PET Center; Aarhus University Hospital; Aarhus Denmark
| | - Peter Ott
- Department of Hepato-Gastroenterology; Aarhus University Hospital; Aarhus Denmark
| | - Hendrik Vilstrup
- Department of Hepato-Gastroenterology; Aarhus University Hospital; Aarhus Denmark
| | - Lasse K. Bak
- Department of Drug Design and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Helle S. Waagepetersen
- Department of Drug Design and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Arne Schousboe
- Department of Drug Design and Pharmacology; Faculty of Health and Medical Sciences; University of Copenhagen; Copenhagen Denmark
| | - Michael S⊘rensen
- Department of Nuclear Medicine & PET Center; Aarhus University Hospital; Aarhus Denmark
- Department of Hepato-Gastroenterology; Aarhus University Hospital; Aarhus Denmark
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Dadsetan S, Kukolj E, Bak LK, Sørensen M, Ott P, Vilstrup H, Schousboe A, Keiding S, Waagepetersen HS. Brain alanine formation as an ammonia-scavenging pathway during hyperammonemia: effects of glutamine synthetase inhibition in rats and astrocyte-neuron co-cultures. J Cereb Blood Flow Metab 2013; 33:1235-41. [PMID: 23673435 PMCID: PMC3734774 DOI: 10.1038/jcbfm.2013.73] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/18/2013] [Revised: 04/11/2013] [Accepted: 04/13/2013] [Indexed: 01/29/2023]
Abstract
Hyperammonemia is a major etiological toxic factor in the development of hepatic encephalopathy. Brain ammonia detoxification occurs primarily in astrocytes by glutamine synthetase (GS), and it has been proposed that elevated glutamine levels during hyperammonemia lead to astrocyte swelling and cerebral edema. However, ammonia may also be detoxified by the concerted action of glutamate dehydrogenase (GDH) and alanine aminotransferase (ALAT) leading to trapping of ammonia in alanine, which in vivo likely leaves the brain. Our aim was to investigate whether the GS inhibitor methionine sulfoximine (MSO) enhances incorporation of (15)NH4(+) in alanine during acute hyperammonemia. We observed a fourfold increased amount of (15)NH4 incorporation in brain alanine in rats treated with MSO. Furthermore, co-cultures of neurons and astrocytes exposed to (15)NH4Cl in the absence or presence of MSO demonstrated a dose-dependent incorporation of (15)NH4 into alanine together with increased (15)N incorporation in glutamate. These findings provide evidence that ammonia is detoxified by the concerted action of GDH and ALAT both in vivo and in vitro, a mechanism that is accelerated in the presence of MSO thereby reducing the glutamine level in brain. Thus, GS could be a potential drug target in the treatment of hyperammonemia in patients with hepatic encephalopathy.
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Affiliation(s)
- Sherry Dadsetan
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Bak LK, Waagepetersen HS, Sørensen M, Ott P, Vilstrup H, Keiding S, Schousboe A. Role of branched chain amino acids in cerebral ammonia homeostasis related to hepatic encephalopathy. Metab Brain Dis 2013; 28:209-15. [PMID: 23371316 DOI: 10.1007/s11011-013-9381-7] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/13/2012] [Accepted: 01/17/2013] [Indexed: 12/30/2022]
Abstract
Hepatic encephalopathy (HE) is associated with increased ammonia levels in plasma and brain. Different treatment strategies have been developed to ameliorate the detrimental effects of the ammonia load. One such strategy is based on the finding of a low level of the branched chain amino acids (BCAAs) in plasma of patients suffering from HE and the assumption that in particular isoleucine could be beneficial to brain energy metabolism as it is metabolized to the tricarboxylic acid cycle intermediate and precursor succinyl-CoA and acetyl-CoA, respectively. This would enable de novo synthesis of glutamine via α-ketoglutarate and glutamate and at the same time stimulate oxidative metabolism. The present mini-review summarizes the metabolic basis for this hypothesis delineating studies in the brain in vivo as well as in cultured neural cells aimed at elucidating the metabolism of the BCAAs focusing on isoleucine. The conclusion is that isoleucine appears at least partially to act in this fashion albeit its metabolism is quantitatively relatively modest. In addition, a short section on the role of the BCAAs in synaptic ammonia homeostasis is included along with some thoughts on the role of the BCAAs in other pathologies such as cancer.
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark.
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Pajęcka K, Nielsen CW, Hauge A, Zaganas I, Bak LK, Schousboe A, Plaitakis A, Waagepetersen HS. Glutamate dehydrogenase isoforms with N-terminal (His)6- or FLAG-tag retain their kinetic properties and cellular localization. Neurochem Res 2013; 39:487-99. [PMID: 23619558 DOI: 10.1007/s11064-013-1042-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 04/08/2013] [Accepted: 04/09/2013] [Indexed: 10/26/2022]
Abstract
Glutamate dehydrogenase (GDH) is a crucial enzyme on the crossroads of amino acid and energy metabolism and it is operating in all domains of life. According to current knowledge GDH is present only in one functional isoform in most animals, including mice. In addition to this housekeeping enzyme (hGDH1 in humans), humans and apes have acquired a second isoform (hGDH2) with a distinct tissue expression profile. In the current study we have cloned both mouse and human GDH constructs containing FLAG and (His)6 small genetically-encoded tags, respectively. The hGDH1 and hGDH2 constructs containing N-terminal (His)6 tags were successfully expressed in Sf9 cells and the recombinant proteins were isolated to ≥95 % purity in a two-step procedure involving ammonium sulfate precipitation and Ni(2+)-based immobilized metal ion affinity chromatography. To explore whether the presence of the FLAG and (His)6 tags affects the cellular localization and functionality of the GDH isoforms, we studied the subcellular distribution of the expressed enzymes as well as their regulation by adenosine diphosphate monopotassium salt (ADP) and guanosine-5'-triphosphate sodium salt (GTP). Through immunoblot analysis of the mitochondrial and cytosolic fraction of the HEK cells expressing the recombinant proteins we found that neither FLAG nor (His)6 tag disturbs the mitochondrial localization of GDH. The addition of the small tags to the N-terminus of the mature mitochondrial mouse GDH1 or human hGDH1 and hGDH2 did not change the ADP activation or GTP inhibition pattern of the proteins as compared to their untagged counterparts. However, the addition of FLAG tag to the C-terminus of the mouse GDH left the recombinant protein fivefold less sensitive to ADP activation. This finding highlights the necessity of the functional characterization of recombinant proteins containing even the smallest available tags.
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Affiliation(s)
- Kamilla Pajęcka
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
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Dam G, Keiding S, Munk OL, Ott P, Vilstrup H, Bak LK, Waagepetersen HS, Schousboe A, Sørensen M. Hepatic encephalopathy is associated with decreased cerebral oxygen metabolism and blood flow, not increased ammonia uptake. Hepatology 2013; 57:258-65. [PMID: 22886493 DOI: 10.1002/hep.25995] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Revised: 12/15/2011] [Accepted: 07/11/2012] [Indexed: 12/19/2022]
Abstract
UNLABELLED Studies have shown decreased cerebral oxygen metabolism (CMRO(2)) and blood flow (CBF) in patients with cirrhosis with hepatic encephalopathy (HE). It remains unclear, however, whether these disturbances are associated with HE or with cirrhosis itself and how they may relate to arterial blood ammonia concentration and cerebral metabolic rate of blood ammonia (CMRA). We addressed these questions in a paired study design by investigating patients with cirrhosis during and after recovery from an acute episode of HE type C. CMRO(2), CBF, and CMRA were measured by dynamic positron emission tomography (PET)/computed tomography (CT). Ten patients with cirrhosis were studied during an acute episode of HE; nine were reexamined after recovery. Nine patients with cirrhosis with no history of HE served as controls. Mean CMRO(2) increased from 0.73 μmol oxygen/mL brain tissue/min during HE to 0.91 μmol oxygen/mL brain tissue/min after recovery (paired t test; P < 0.05). Mean CBF increased from 0.28 mL blood/mL brain tissue/min during HE to 0.38 mL blood/mL brain tissue/min after recovery (P < 0.05). After recovery from HE, CMRO(2) and CBF were not significantly different from values in the control patients. Arterial blood ammonia concentration decreased 20% after recovery (P < 0.05) and CMRA was unchanged (P > 0.30); both values were higher than in the control patients (both P < 0.05). CONCLUSION The low values of CMRO(2) and CBF observed during HE increased after recovery from HE and were thus associated with HE rather than the liver disease as such. The changes in CMRO(2) and CBF could not be linked to blood ammonia concentration or CMRA.
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Affiliation(s)
- Gitte Dam
- PET Centre & Department of Nuclear Medicine, Aarhus University Hospital, Aarhus, Denmark.
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Schousboe A, Bak LK, Waagepetersen HS. Astrocytic Control of Biosynthesis and Turnover of the Neurotransmitters Glutamate and GABA. Front Endocrinol (Lausanne) 2013; 4:102. [PMID: 23966981 PMCID: PMC3744088 DOI: 10.3389/fendo.2013.00102] [Citation(s) in RCA: 193] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2013] [Accepted: 07/31/2013] [Indexed: 01/20/2023] Open
Abstract
Glutamate and GABA are the quantitatively major neurotransmitters in the brain mediating excitatory and inhibitory signaling, respectively. These amino acids are metabolically interrelated and at the same time they are tightly coupled to the intermediary metabolism including energy homeostasis. Astrocytes play a pivotal role in the maintenance of the neurotransmitter pools of glutamate and GABA since only these cells express pyruvate carboxylase, the enzyme required for de novo synthesis of the two amino acids. Such de novo synthesis is obligatory to compensate for catabolism of glutamate and GABA related to oxidative metabolism when the amino acids are used as energy substrates. This, in turn, is influenced by the extent to which the cycling of the amino acids between neurons and astrocytes may occur. This cycling is brought about by the glutamate/GABA - glutamine cycle the operation of which involves the enzymes glutamine synthetase (GS) and phosphate-activated glutaminase together with the plasma membrane transporters for glutamate, GABA, and glutamine. The distribution of these proteins between neurons and astrocytes determines the efficacy of the cycle and it is of particular importance that GS is exclusively expressed in astrocytes. It should be kept in mind that the operation of the cycle is associated with movement of ammonia nitrogen between the two cell types and different mechanisms which can mediate this have been proposed. This review is intended to delineate the above mentioned processes and to discuss quantitatively their relative importance in the homeostatic mechanisms responsible for the maintenance of optimal conditions for the respective neurotransmission processes to operate.
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Affiliation(s)
- Arne Schousboe
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
- *Correspondence: Arne Schousboe, Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, 2100 Copenhagen, Denmark e-mail:
| | - Lasse K. Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
| | - Helle S. Waagepetersen
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark
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Lange SC, Bak LK, Waagepetersen HS, Schousboe A, Norenberg MD. Primary cultures of astrocytes: their value in understanding astrocytes in health and disease. Neurochem Res 2012; 37:2569-88. [PMID: 22926576 DOI: 10.1007/s11064-012-0868-0] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2012] [Revised: 08/01/2012] [Accepted: 08/01/2012] [Indexed: 12/26/2022]
Abstract
During the past few decades of astrocyte research it has become increasingly clear that astrocytes have taken a central position in all central nervous system activities. Much of our new understanding of astrocytes has been derived from studies conducted with primary cultures of astrocytes. Such cultures have been an invaluable tool for studying roles of astrocytes in physiological and pathological states. Many central astrocytic functions in metabolism, amino acid neurotransmission and calcium signaling were discovered using this tissue culture preparation and most of these observations were subsequently found in vivo. Nevertheless, primary cultures of astrocytes are an in vitro model that does not fully mimic the complex events occurring in vivo. Here we present an overview of the numerous contributions generated by the use of primary astrocyte cultures to uncover the diverse functions of astrocytes. Many of these discoveries would not have been possible to achieve without the use of astrocyte cultures. Additionally, we address and discuss the concerns that have been raised regarding the use of primary cultures of astrocytes as an experimental model system.
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Affiliation(s)
- Sofie C Lange
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100 Copenhagen, Denmark
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Bak LK, Johansen ML, Schousboe A, Waagepetersen HS. Valine but not leucine or isoleucine supports neurotransmitter glutamate synthesis during synaptic activity in cultured cerebellar neurons. J Neurosci Res 2012; 90:1768-75. [PMID: 22589238 DOI: 10.1002/jnr.23072] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/25/2011] [Revised: 03/19/2012] [Accepted: 03/22/2012] [Indexed: 11/06/2022]
Abstract
Synthesis of neuronal glutamate from α-ketoglutarate for neurotransmission necessitates an amino group nitrogen donor; however, it is not clear which amino acid(s) serves this role. Thus, the ability of the three branched-chain amino acids (BCAAs), leucine, isoleucine, and valine, to act as amino group nitrogen donors for synthesis of vesicular neurotransmitter glutamate was investigated in cultured mouse cerebellar (primarily glutamatergic) neurons. The cultures were superfused in the presence of (15) N-labeled BCAAs, and synaptic activity was induced by pulses of N-methyl-D-aspartate (300 μM), which results in release of vesicular glutamate. At the end of the superfusion experiment, the vesicular pool of glutamate was released by treatment with α-latrotoxin (3 nM, 5 min). This experimental paradigm allows a separate analysis of the cytoplasmic and vesicular pools of glutamate. Amount and extent of (15) N labeling of intracellular amino acids plus vesicular glutamate were analyzed employing HPLC and LC-MS analysis. Only when [(15) N]valine served as precursor did the labeling of both cytoplasmic and vesicular glutamate increase after synaptic activity. In addition, only [(15) N]valine was able to maintain the amount of vesicular glutamate during synaptic activity. This indicates that, among the BCAAs, only valine supports the increased need for synthesis of vesicular glutamate.
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Affiliation(s)
- Lasse K Bak
- Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
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39
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Leke R, de Oliveira DL, Mussulini BHM, Pereira MS, Kazlauckas V, Mazzini G, Hartmann CR, Silveira TR, Simonsen M, Bak LK, Waagepetersen HS, Keiding S, Schousboe A, Portela LV. Impairment of the organization of locomotor and exploratory behaviors in bile duct-ligated rats. PLoS One 2012; 7:e36322. [PMID: 22586467 PMCID: PMC3346757 DOI: 10.1371/journal.pone.0036322] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 03/30/2012] [Indexed: 12/16/2022] Open
Abstract
Hepatic encephalopathy (HE) arises from acute or chronic liver diseases and leads to several problems, including motor impairment. Animal models of chronic liver disease have extensively investigated the mechanisms of this disease. Impairment of locomotor activity has been described in different rat models. However, these studies are controversial and the majority has primarily analyzed activity parameters. Therefore, the aim of the present study was to evaluate locomotor and exploratory behavior in bile duct-ligated (BDL) rats to explore the spatial and temporal structure of behavior. Adult female Wistar rats underwent common bile duct ligation (BDL rats) or the manipulation of common bile duct without ligation (control rats). Six weeks after surgery, control and BDL rats underwent open-field, plus-maze and foot-fault behavioral tasks. The BDL rats developed chronic liver failure and exhibited a decrease in total distance traveled, increased total immobility time, smaller number of rearings, longer periods in the home base area and decreased percentage of time in the center zone of the arena, when compared to the control rats. Moreover, the performance of the BDL rats was not different from the control rats for the elevated plus-maze and foot-fault tasks. Therefore, the BDL rats demonstrated disturbed spontaneous locomotor and exploratory activities as a consequence of altered spatio-temporal organization of behavior.
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Affiliation(s)
- Renata Leke
- Department of Biochemistry, ICBS, Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sol, Brazil.
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Kreft M, Bak LK, Waagepetersen HS, Schousboe A. Aspects of astrocyte energy metabolism, amino acid neurotransmitter homoeostasis and metabolic compartmentation. ASN Neuro 2012; 4:e00086. [PMID: 22435484 PMCID: PMC3338196 DOI: 10.1042/an20120007] [Citation(s) in RCA: 63] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2012] [Revised: 03/06/2012] [Accepted: 03/21/2012] [Indexed: 02/08/2023] Open
Abstract
Astrocytes are key players in brain function; they are intimately involved in neuronal signalling processes and their metabolism is tightly coupled to that of neurons. In the present review, we will be concerned with a discussion of aspects of astrocyte metabolism, including energy-generating pathways and amino acid homoeostasis. A discussion of the impact that uptake of neurotransmitter glutamate may have on these pathways is included along with a section on metabolic compartmentation.
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Key Words
- amino acid
- astrocyte
- compartmentation
- energy
- metabolism
- α-kg, α-ketoglutarate
- aat, aspartate aminotransferase
- cfp, cyan fluorescence protein
- dab, diaminobenzidine
- fret, fluorescence resonance energy transfer
- [glc]i, intracellular glucose concentration
- gaba, γ-aminobutyric acid
- gaba-t, gaba aminotransferase
- gdh, glutamate dehydrogenase
- glut, glucose transporter
- gp, glycogen phosphorylase
- gs, glutamine synthetase
- gsk3, gs kinase 3
- pag, phosphate-activated glutaminase
- pi3k, phosphoinositide 3-kinase
- pkc, protein kinase c
- tca, tricarboxylic acid
- yfp, yellow fluorescence protein
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Affiliation(s)
- Marko Kreft
- *LNMCP, Institute of Pathophysiology, Faculty of Medicine and CPAE, Department of Biology, Biotechnical Faculty, University of Ljubljana and Celica Biomedical Center, Slovenia
| | - Lasse K Bak
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Helle S Waagepetersen
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
| | - Arne Schousboe
- †Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, 2100, Copenhagen, Denmark
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Obel LF, Müller MS, Walls AB, Sickmann HM, Bak LK, Waagepetersen HS, Schousboe A. Brain glycogen-new perspectives on its metabolic function and regulation at the subcellular level. Front Neuroenergetics 2012; 4:3. [PMID: 22403540 PMCID: PMC3291878 DOI: 10.3389/fnene.2012.00003] [Citation(s) in RCA: 137] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/10/2011] [Accepted: 02/13/2012] [Indexed: 11/14/2022]
Abstract
Glycogen is a complex glucose polymer found in a variety of tissues, including brain, where it is localized primarily in astrocytes. The small quantity found in brain compared to e.g., liver has led to the understanding that brain glycogen is merely used during hypoglycemia or ischemia. In this review evidence is brought forward highlighting what has been an emerging understanding in brain energy metabolism: that glycogen is more than just a convenient way to store energy for use in emergencies—it is a highly dynamic molecule with versatile implications in brain function, i.e., synaptic activity and memory formation. In line with the great spatiotemporal complexity of the brain and thereof derived focus on the basis for ensuring the availability of the right amount of energy at the right time and place, we here encourage a closer look into the molecular and subcellular mechanisms underlying glycogen metabolism. Based on (1) the compartmentation of the interconnected second messenger pathways controlling glycogen metabolism (calcium and cAMP), (2) alterations in the subcellular location of glycogen-associated enzymes and proteins induced by the metabolic status and (3) a sequential component in the intermolecular mechanisms of glycogen metabolism, we suggest that glycogen metabolism in astrocytes is compartmentalized at the subcellular level. As a consequence, the meaning and importance of conventional terms used to describe glycogen metabolism (e.g., turnover) is challenged. Overall, this review represents an overview of contemporary knowledge about brain glycogen and its metabolism and function. However, it also has a sharp focus on what we do not know, which is perhaps even more important for the future quest of uncovering the roles of glycogen in brain physiology and pathology.
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Affiliation(s)
- Linea F Obel
- Faculty of Health and Medical Sciences, Department of Drug Design and Pharmacology, University of Copenhagen Copenhagen, Denmark
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Obel LF, Andersen KMH, Bak LK, Schousboe A, Waagepetersen HS. Effects of adrenergic agents on intracellular Ca2+ homeostasis and metabolism of glucose in astrocytes with an emphasis on pyruvate carboxylation, oxidative decarboxylation and recycling: implications for glutamate neurotransmission and excitotoxicity. Neurotox Res 2011; 21:405-17. [PMID: 22194159 DOI: 10.1007/s12640-011-9296-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2011] [Revised: 11/17/2011] [Accepted: 11/29/2011] [Indexed: 12/26/2022]
Abstract
Glucose and glycogen are essential sources of energy for maintaining glutamate homeostasis as well as glutamatergic neurotransmission. The metabolism of glycogen, the location of which is confined to astrocytes, is affected by norepinephrine (NE), and hence, adrenergic signaling in the astrocyte might affect glutamate homeostasis with implications for excitatory neurotransmission and possibly excitotoxic neurodegeneration. In order to study this putative correlation, cultured astrocytes were incubated with 2.5 mM [U-(13)C]glucose in the presence and absence of NE as a time course for 1 h. Employing mass spectrometry, labeling in intracellular metabolites was determined. Moreover, the involvement of Ca(2+) in the noradrenergic response was studied. In unstimulated astrocytes, the labeling pattern of glutamate, aspartate, malate and citrate confirmed important roles for pyruvate carboxylation and oxidative decarboxylation in astrocytic glucose metabolism. Importantly, pyruvate carboxylation was best visualized at 10 min of incubation. The abundance and pattern of labeling in lactate and alanine indicated not only an extensive activity of malic enzyme (initial step for pyruvate recycling) but also a high degree of compartmentalization of the pyruvate pool. Stimulating with 1 μM NE had no effect on labeling patterns and glycogen metabolism, whereas 100 μM NE increased glutamate labeling and decreased labeling in alanine, the latter supposedly due to dilution from degradation of non-labeled glycogen. It is suggested that further experiments uncovering the correlation between adrenergic and glutamatergic pathways should be performed in order to gain further insight into the role of astrocytes in brain function and dysfunction, the latter including excitotoxicity.
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Affiliation(s)
- Linea F Obel
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, 2 Universitetsparken, 2100 Copenhagen, Denmark
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Schousboe A, Sickmann HM, Bak LK, Schousboe I, Jajo FS, Faek SAA, Waagepetersen HS. Neuron-glia interactions in glutamatergic neurotransmission: roles of oxidative and glycolytic adenosine triphosphate as energy source. J Neurosci Res 2011; 89:1926-34. [PMID: 21919035 DOI: 10.1002/jnr.22746] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2010] [Revised: 06/16/2011] [Accepted: 06/20/2011] [Indexed: 02/01/2023]
Abstract
Glutamatergic neurotransmission accounts for a considerable part of energy consumption related to signaling in the brain. Chemical energy is provided by adenosine triphosphate (ATP) formed in glycolysis and tricarboxylic acid (TCA) cycle combined with oxidative phosphorylation. It is not clear whether ATP generated in these pathways is equivalent in relation to fueling of the energy-requiring processes, i.e., vesicle filling, transport, and enzymatic processing in the glutamatergic tripartite synapse (the astrocyte and pre- and postsynapse). The role of astrocytic glycogenolysis in maintaining theses processes also has not been fully elucidated. Cultured astrocytes and neurons were utilized to monitor these processes related to glutamatergic neurotransmission. Inhibitors of glycolysis and TCA cycle in combination with pathway-selective substrates were used to study glutamate uptake and release monitored with D-aspartate. Western blotting of glyceraldehyde-3-P dehydrogenase (GAPDH) and phosphoglycerate kinase (PGK) was performed to determine whether these enzymes are associated with the cell membrane. We show that ATP formed in glycolysis is superior to that generated by oxidative phosphorylation in providing energy for glutamate uptake both in astrocytes and in neurons. The neuronal vesicular glutamate release was less dependent on glycolytic ATP. Dependence of glutamate uptake on glycolytic ATP may be at least partially explained by a close association in the membrane of GAPDH and PGK and the glutamate transporters. It may be suggested that these enzymes form a complex with the transporters and the Na(+) /K(+) -ATPase, the latter providing the sodium gradient required for the transport process.
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Affiliation(s)
- A Schousboe
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark
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Leke R, Bak LK, Iversen P, Sørensen M, Keiding S, Vilstrup H, Ott P, Portela LV, Schousboe A, Waagepetersen HS. Synthesis of neurotransmitter GABA via the neuronal tricarboxylic acid cycle is elevated in rats with liver cirrhosis consistent with a high GABAergic tone in chronic hepatic encephalopathy. J Neurochem 2011; 117:824-32. [PMID: 21395584 DOI: 10.1111/j.1471-4159.2011.07244.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Hepatic encephalopathy (HE) is a neuropsychiatric complication to liver disease. It is known that ammonia plays a role in the pathogenesis of HE and disturbances in the GABAergic system have been related to HE. Synthesis of GABA occurs by decarboxylation of glutamate formed by deamidation of astrocyte-derived glutamine. It is known that a fraction of glutamate is decarboxylated directly to GABA (referred to as the direct pathway) and that a fraction undergoes transamination with formation of alpha-ketoglutarate. The latter fraction is cycled through the neuronal tricarboxylic acid cycle, an energy-generating pathway, prior to being employed for GABA synthesis (the indirect pathway). We have previously shown that ammonia induces an elevation of the neuronal tricarboxylic acid cycle activity. Thus, the aims of the present study were to determine if increased levels of ammonia increase GABA synthesis via the indirect pathway in a rat model of HE induced by bile-duct ligation and in co-cultures of neurons and astrocytes exposed to ammonia. Employing (13) C-labeled precursors and subsequent analysis by mass spectrometry, we demonstrated that more GABA was synthesized via the indirect pathway in bile duct-ligated rats and in co-cultures subjected to elevated ammonia levels. Since the indirect pathway is associated with synthesis of vesicular GABA, this might explain the increased GABAergic tone in HE.
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Affiliation(s)
- Renata Leke
- PET Centre, Department of Medicine V, Aarhus University Hospital, Aarhus, Denmark
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Leke R, Bak LK, Anker M, Melø TM, Sørensen M, Keiding S, Vilstrup H, Ott P, Portela LV, Sonnewald U, Schousboe A, Waagepetersen HS. Detoxification of ammonia in mouse cortical GABAergic cell cultures increases neuronal oxidative metabolism and reveals an emerging role for release of glucose-derived alanine. Neurotox Res 2010; 19:496-510. [PMID: 20480276 DOI: 10.1007/s12640-010-9198-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2009] [Revised: 03/22/2010] [Accepted: 05/03/2010] [Indexed: 12/24/2022]
Abstract
Cerebral hyperammonemia is believed to play a pivotal role in the development of hepatic encephalopathy (HE), a debilitating condition arising due to acute or chronic liver disease. In the brain, ammonia is thought to be detoxified via the activity of glutamine synthetase, an astrocytic enzyme. Moreover, it has been suggested that cerebral tricarboxylic acid (TCA) cycle metabolism is inhibited and glycolysis enhanced during hyperammonemia. The aim of this study was to characterize the ammonia-detoxifying mechanisms as well as the effects of ammonia on energy-generating metabolic pathways in a mouse neuronal-astrocytic co-culture model of the GABAergic system. We found that 5 mM ammonium chloride affected energy metabolism by increasing the neuronal TCA cycle activity and switching the astrocytic TCA cycle toward synthesis of substrate for glutamine synthesis. Furthermore, ammonia exposure enhanced the synthesis and release of alanine. Collectively, our results demonstrate that (1) formation of glutamine is seminal for detoxification of ammonia; (2) neuronal oxidative metabolism is increased in the presence of ammonia; and (3) synthesis and release of alanine is likely to be important for ammonia detoxification as a supplement to formation of glutamine.
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Affiliation(s)
- Renata Leke
- Department of Biochemistry, ICBS, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil
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Schousboe A, Sickmann HM, Walls AB, Bak LK, Waagepetersen HS. Functional importance of the astrocytic glycogen-shunt and glycolysis for maintenance of an intact intra/extracellular glutamate gradient. Neurotox Res 2010; 18:94-9. [PMID: 20306167 DOI: 10.1007/s12640-010-9171-5] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 01/10/2010] [Accepted: 03/05/2010] [Indexed: 11/24/2022]
Abstract
It has been proposed that a considerable fraction of glucose metabolism proceeds via the glycogen-shunt consisting of conversion of glucose units to glycogen residues and subsequent production of glucose-1-phosphate to be metabolized in glycolysis after conversion to glucose-6-phosphate. The importance of this as well as the significance of ATP formed in glycolysis versus that formed by the concerted action of the tricarboxylic acid (TCA) cycle processes and oxidative phosphorylation for maintenance of glutamate transport capacity in astrocytes is discussed. It is argued that glycolytically derived energy in the form of ATP may be of particular functional importance in this context.
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Affiliation(s)
- Arne Schousboe
- Faculty of Pharmaceutical Sciences, Department of Pharmacology and Pharmacotherapy, University of Copenhagen, Universitetsparken 2, 2100, Copenhagen, Denmark.
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Leke R, Bak LK, Schousboe A, Waagepetersen HS. Erratum to: Demonstration of Neuron-Glia Transfer of Precursors for Gaba Biosynthesis in a Co-Culture System of Dissociated Mouse Cerebral Cortex. Neurochem Res 2009. [DOI: 10.1007/s11064-009-0062-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Bak LK, Walls AB, Schousboe A, Ring A, Sonnewald U, Waagepetersen HS. Neuronal glucose but not lactate utilization is positively correlated with NMDA-induced neurotransmission and fluctuations in cytosolic Ca2+ levels. J Neurochem 2009; 109 Suppl 1:87-93. [PMID: 19393013 DOI: 10.1111/j.1471-4159.2009.05943.x] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although the brain utilizes glucose for energy production, individual brain cells may to some extent utilize substrates derived from glucose. Thus, it has been suggested that neurons consume extracellular lactate during synaptic activity. However, the precise role of lactate for fueling neuronal activity is still poorly understood. Recently, we demonstrated that glucose metabolism is up-regulated in cultured glutamatergic neurons during neurotransmission whereas that of lactate is not. Here, we show that utilization of glucose but not lactate correlates with NMDA-induced neurotransmitter glutamate release in cultured cerebellar neurons from mice. Pulses of NMDA at 30, 100, and 300 microM, leading to a progressive increase in both cytosolic [Ca2+] and release of glutamate, increased uptake and metabolism of glucose but not that of lactate as evidenced by mass spectrometric measurement of 13C incorporation into intracellular glutamate. In this manuscript, a cascade of events for the preferential neuronal utilization of glucose during neurotransmission is suggested and discussed in relation to our current understanding of neuronal energy metabolism.
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Affiliation(s)
- Lasse K Bak
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark.
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Bak LK, Iversen P, Sørensen M, Keiding S, Vilstrup H, Ott P, Waagepetersen HS, Schousboe A. Metabolic fate of isoleucine in a rat model of hepatic encephalopathy and in cultured neural cells exposed to ammonia. Metab Brain Dis 2009; 24:135-45. [PMID: 19067142 DOI: 10.1007/s11011-008-9123-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/02/2008] [Accepted: 10/28/2008] [Indexed: 01/11/2023]
Abstract
Hepatic encephalopathy is a severe neuropathological condition arising secondary to liver failure. The pathogenesis is not well understood; however, hyperammonemia is considered to be one causative factor. Hyperammonemia has been suggested to inhibit tricarboxylic acid (TCA) cycle activity, thus affecting energy metabolism. Furthermore, it has been suggested that catabolism of the branched-chain amino acid isoleucine may help curb the effect of hyperammonemia by by-passing the TCA cycle block as well as providing the carbon skeleton for glutamate and glutamine synthesis thus fixating ammonia. Here we present novel results describing [U-(13)C]isoleucine metabolism in muscle and brain analyzed by mass spectrometry in bile duct ligated rats, a model of chronic hepatic encephalopathy, and discuss them in relation to previously published results from neural cell cultures. The metabolism of [U-(13)C]isoleucine in muscle tissue was about five times higher than that in the brain which, in turn, was lower than in corresponding cell cultures. However, synthesis of glutamate and glutamine was supported by catabolism of isoleucine. In rat brain, differential labeling patterns in glutamate and glutamine suggest that isoleucine may primarily be metabolized in the astrocytic compartment which is in accordance with previous findings in neural cell cultures. Lastly, in rat brain the labeling patterns of glutamate, aspartate and GABA do not suggest any significant inhibition by ammonia of TCA cycle activity which corresponds well to findings in neural cell cultures. Branched-chain amino acids including isoleucine are used for treating hepatic encephalopathy and the present findings shed light on the possible mechanism involved. The low turn-over of isoleucine in rat brain suggests that this amino acid does not serve the role of providing metabolites pertinent to TCA cycle function and hence energy formation as well as the necessary carbon skeleton for subsequent ammonia fixation in hyperammonemia. The higher metabolism of isoleucine in muscle could, however, contribute to ammonia fixation and thus likely be of value in the treatment of hepatic encephalopathy.
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Affiliation(s)
- Lasse K Bak
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
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Bak LK, Johansen ML, Schousboe A, Waagepetersen HS. Among the branched-chain amino acids, only valine metabolism is up-regulated in astrocytes during glutamate exposure. J Neurosci Res 2008; 85:3465-70. [PMID: 17497675 DOI: 10.1002/jnr.21347] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Glutamate homeostasis during glutamatergic neurotransmission is predominantly maintained via functioning of the glutamate-glutamine cycle. However, the glutamate-glutamine cycle explains only the fate of the carbon atoms but not that of the accompanying transfer of nitrogen from neurons to astrocytes. In this respect, a putative branched-chain amino acid (BCAA) shuttle has been suggested for transfer of amino nitrogen. Metabolism of BCAAs was investigated in cultured cerebellar astrocytes in a superfusion paradigm employing (15)N-labeled leucine, isoleucine, or valine. Some cultures were exposed to pulses of glutamate (50 microM; 10 sec every 2 min; 75 min in total) to mimic conditions during glutamatergic synaptic activity. (15)N labeling of glutamate, aspartate, glutamine, alanine, and the three BCAAs was determined by using mass spectrometry. Incorporation of (15)N into intracellular glutamate from [(15)N]leucine, [(15)N]isoleucine, or [(15)N]valine amounted to about 40-50% and differed only slightly among the individual BCAAs. Interestingly, label (%) in glutamate from [(15)N]valine was not decreased upon exposure to exogenous glutamate, which was in contrast to a marked decrease in labeling (%) from [(15)N]leucine or [(15)N]isoleucine. This suggests an up-regulation of transamination involving only valine during repetitive exposure to glutamate. It is suggested that valine in particular might have an important function as an amino acid translocated between neuronal and astrocytic compartments, a function that might be up-regulated during synaptic activity.
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Affiliation(s)
- Lasse K Bak
- Department of Pharmacology and Pharmacotherapy, Faculty of Pharmaceutical Sciences, University of Copenhagen, Copenhagen, Denmark
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