Conditional Knockout of GLT-1 in Neurons Leads to Alterations in Aspartate Homeostasis and Synaptic Mitochondrial Metabolism in Striatum and Hippocampus

McNair, Laura F.; Andersen, Jens V.; Nissen, Jakob D.; Sun, Yan; Fischer, Kathryn D.; Hodgson, Nathaniel; Du, Muzi; Aoki, Chiye; Waagepetersen, Helle S.; Rosenberg, Paul A.; Aldana, Blanca I.

doi:10.1007/s11064-020-03000-7

Cited by 20 publications

(26 citation statements)

References 64 publications

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“…By exposing slices to [U-13 C]glutamate and then using mass spectrometry, we were able to measure the 13 C label in intracellular glutamate as well as TCA cycle intermediates and derived amino acids (Figure 8A). We found a significant decrease in the 13 C-labeling of intracellular glutamate [t = 4.212, p = 0.000524, n = 10 WT animals, n = 10 KO animals], consistent with the synapsin 1-Cre driven deletion of GLT-1 in neurons and previous studies of the impact of knockout of GLT-1 in neurons on uptake radiolabeled glutamate into synaptosomes (Petr et al, 2015;Rimmele and Rosenberg, 2016;Zhou et al, 2019;McNair et al, 2020). These studies establish that even though neuronal GLT-1 is a small fraction of total brain GLT-1, it is capable of actual transport of glutamate across the plasma membrane of axon terminals, and, in fact, mediates a disproportionately large fraction of uptake of glutamate into synaptosomes when assayed using radiolabeled substrate.…”

Section: Impaired Glutamate Metabolism In Hippocampal Slices Of Neuronal Glt-1 Kosupporting

confidence: 87%

“…We have previously reported that synGLT-1 KO mice at 8-10 weeks of age had increased density of mitochondria in synaptic terminals in the cortex and hippocampus, and increased cristae packing density in these two regions as well as in the striatum, possibly an adaptive response to decreased access to glutamate as a substrate for synaptic mitochondrial metabolism (McNair et al, 2019(McNair et al, , 2020. Since the electrophysiological phenotype we observed occurred in slices from 20 weeks old mice, we wanted to determine whether similar ultrastructural changes were present in this older cohort of mice (Figure 7).…”

Section: Mk801 In the Recovery Acsf Restores Fepsp Generationmentioning

confidence: 99%

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Neuronal Loss of the Glutamate Transporter GLT-1 Promotes Excitotoxic Injury in the Hippocampus

Rimmele

Andersen

et al. 2021

Front. Cell. Neurosci.

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GLT-1, the major glutamate transporter in the mammalian central nervous system, is expressed in presynaptic terminals that use glutamate as a neurotransmitter, in addition to astrocytes. It is widely assumed that glutamate homeostasis is regulated primarily by glutamate transporters expressed in astrocytes, leaving the function of GLT-1 in neurons relatively unexplored. We generated conditional GLT-1 knockout (KO) mouse lines to understand the cell-specific functions of GLT-1. We found that stimulus-evoked field extracellular postsynaptic potentials (fEPSPs) recorded in the CA1 region of the hippocampus were normal in the astrocytic GLT-1 KO but were reduced and often absent in the neuronal GLT-1 KO at 40 weeks. The failure of fEPSP generation in the neuronal GLT-1 KO was also observed in slices from 20 weeks old mice but not consistently from 10 weeks old mice. Using an extracellular FRET-based glutamate sensor, we found no difference in stimulus-evoked glutamate accumulation in the neuronal GLT-1 KO, suggesting a postsynaptic cause of the transmission failure. We hypothesized that excitotoxicity underlies the failure of functional recovery of slices from the neuronal GLT-1 KO. Consistent with this hypothesis, the non-competitive NMDA receptor antagonist MK801, when present in the ACSF during the recovery period following cutting of slices, promoted full restoration of fEPSP generation. The inclusion of an enzymatic glutamate scavenging system in the ACSF conferred partial protection. Excitotoxicity might be due to excess release or accumulation of excitatory amino acids, or to metabolic perturbation resulting in increased vulnerability to NMDA receptor activation. Previous studies have demonstrated a defect in the utilization of glutamate by synaptic mitochondria and aspartate production in the synGLT-1 KO in vivo, and we found evidence for similar metabolic perturbations in the slice preparation. In addition, mitochondrial cristae density was higher in synaptic mitochondria in the CA1 region in 20–25 weeks old synGLT-1 KO mice in the CA1 region, suggesting compensation for loss of axon terminal GLT-1 by increased mitochondrial efficiency. These data suggest that GLT-1 expressed in presynaptic terminals serves an important role in the regulation of vulnerability to excitotoxicity, and this regulation may be related to the metabolic role of GLT-1 expressed in glutamatergic axon terminals.

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Section: Impaired Glutamate Metabolism In Hippocampal Slices Of Neuronal Glt-1 Kosupporting

confidence: 87%

Section: Mk801 In the Recovery Acsf Restores Fepsp Generationmentioning

confidence: 99%

Neuronal Loss of the Glutamate Transporter GLT-1 Promotes Excitotoxic Injury in the Hippocampus

Rimmele

Andersen

et al. 2021

Front. Cell. Neurosci.

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“…In neurons, EAAT2 co-localizes with the α 1 and α 3 isoforms of the Na + /K + -ATPase, but this colocalization is looser than that with the α 2 isoform in astrocytes, suggesting a less efficient interaction between EAAT2 and the Na + /K + -ATPase in neurons (Melone et al, 2019). Neuronal EAAT2 appears to be required to provide glutamate to synaptic mitochondria, and is therefore linked to energy metabolism (Petr et al, 2015;Fischer et al, 2018;McNair et al, 2019McNair et al, , 2020Sharma et al, 2019). By contrast, astrocytic EAAT2 is crucial to ensure survival, resistance to epilepsy, and prevent cognitive decline.…”

Section: The Surface Mobility and Cellular Distribution Of Eaat2mentioning

confidence: 99%

“…Loss of astrocytic EAAT2 leads to early deficits, whereas loss of neuronal EAAT2 leads to late-onset deficits in long-term memory and spatial reference learning (Sharma et al, 2019). These findings are important because they identify neuronal and astrocytic EAAT2 as contributing to different aspects of cognitive function and, potentially, as different therapeutic targets in cognitive decline (Petr et al, 2015;Fischer et al, 2018;McNair et al, 2019McNair et al, , 2020Sharma et al, 2019).…”

Section: The Surface Mobility and Cellular Distribution Of Eaat2mentioning

confidence: 99%

Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression

Ryan

Ingram

Scimemi

2021

Front. Cell. Neurosci.

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Neurotransmitter transporters limit spillover between synapses and maintain the extracellular neurotransmitter concentration at low yet physiologically meaningful levels. They also exert a key role in providing precursors for neurotransmitter biosynthesis. In many cases, neurons and astrocytes contain a large intracellular pool of transporters that can be redistributed and stabilized in the plasma membrane following activation of different signaling pathways. This means that the uptake capacity of the brain neuropil for different neurotransmitters can be dynamically regulated over the course of minutes, as an indirect consequence of changes in neuronal activity, blood flow, cell-to-cell interactions, etc. Here we discuss recent advances in the mechanisms that control the cell membrane trafficking and biophysical properties of transporters for the excitatory, inhibitory and modulatory neurotransmitters glutamate, GABA, and dopamine.

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“…In 1992, the three major glutamate transporters of the forebrain were cloned, including EAAC1 ( Kanai and Hediger, 1992 ), GLAST ( Storck et al, 1992 ), and GLT-1 ( Pines et al, 1992 ), which represent approximately 1% of total protein in the forebrain ( Lehre and Danbolt, 1998 ). Although GLT-1 for over a decade after its discovery was assumed to be expressed exclusively in astrocytes ( Rimmele and Rosenberg, 2016 ), it was ultimately shown to be the primary glutamate transporter expressed in axon terminals ( Chen et al, 2004 ; Petr et al, 2015 ) where it serves an important metabolic function in providing glutamate as a substrate for synaptic mitochondria ( McNair et al, 2020 ). Recent work has strongly implicated GLT-1 in the pathogenesis of Alzheimer’s disease ( Sharma et al, 2019 ; Zott et al, 2019 ) emphasizing the importance of understanding the fine regulation of the concentrations of glutamate and other glutamate agonists in and around synapses.…”

Section: Topa Quinone a Catechol-derived Excitotoxinmentioning

confidence: 99%

The Redox Biology of Excitotoxic Processes: The NMDA Receptor, TOPA Quinone, and the Oxidative Liberation of Intracellular Zinc

Aizenman

Loring

Reynolds³

et al. 2020

Front. Neurosci.

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This special issue of Frontiers in Neuroscience-Neurodegeneration celebrates the 50th anniversary of John Olney's seminal work introducing the concept of excitotoxicity as a mechanism for neuronal cell death. Since that time, fundamental research on the pathophysiological activation of glutamate receptors has played a central role in our understanding of excitotoxic cellular signaling pathways, leading to the discovery of many potential therapeutic targets in the treatment of acute or chronic/progressive neurodegenerative disorders. Importantly, excitotoxic signaling processes have been found repeatedly to be closely intertwined with oxidative cellular cascades. With this in mind, this review looks back at long-standing collaborative efforts by the authors linking cellular redox status and glutamate neurotoxicity, focusing first on the discovery of the redox modulatory site of the N-methyl-D-aspartate (NMDA) receptor, followed by the study of the oxidative conversion of 3,4-dihydroxyphenylalanine (DOPA) to the non-NMDA receptor agonist and neurotoxin 2,4,5-trihydroxyphenylalanine (TOPA) quinone. Finally, we summarize our work linking oxidative injury to the liberation of zinc from intracellular metal binding proteins, leading to the uncovering of a signaling mechanism connecting excitotoxicity with zinc-activated cell death-signaling cascades.

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Conditional Knockout of GLT-1 in Neurons Leads to Alterations in Aspartate Homeostasis and Synaptic Mitochondrial Metabolism in Striatum and Hippocampus

Cited by 20 publications

References 64 publications

Neuronal Loss of the Glutamate Transporter GLT-1 Promotes Excitotoxic Injury in the Hippocampus

Neuronal Loss of the Glutamate Transporter GLT-1 Promotes Excitotoxic Injury in the Hippocampus

Regulation of Glutamate, GABA and Dopamine Transporter Uptake, Surface Mobility and Expression

The Redox Biology of Excitotoxic Processes: The NMDA Receptor, TOPA Quinone, and the Oxidative Liberation of Intracellular Zinc

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