Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system. An extracellular accumulation of glutamate causes excessive activation of glutamate receptors and cell death through excitotoxic mechanisms. Unlike other classical neurotransmitters, that are recycled directly into the presynaptic nerve terminal, most glutamate is cleared by two astroglial glutamate transporters, called GLAST and GLT-1 (or EAAT1 and EAAT2). These transporters maintain very low synaptic concentrations of glutamate, estimated at ~25 nM, in an environment that contains millimolar concentrations of glutamate. These transporters are enriched on the fine processes of astrocytes that sheath synapses. We recently developed physical evidence (co-immunoprecipitation, mass spectrometry, reverse immunoprecipitations) and anatomic evidence (co-localization in individual astrocytes in organotypic slice cultures) that these transporters exst in a complex with the Na+/K+ ATPase, most of the enzymes in glycolysis, and mitochondria. This complex is observed in fine processes of astroglia. In the first aim, we will identify specifi domains of GLT-1 and GLAST that support the interactions/co- compartmentalization. We wish to identify potential scaffolding proteins that may form a linkage between the transporters and mitochondria. As has been observed with mitochondria at synapses or at nodes of Ranvier, we propose that neural activity recruits mitochondria to regions where transporters are enriched. In the second aim, we will study the effects of neuronal activity on this co-compartmentalization and define the mechanisms involved. Finally, we will test the hypothesis that formation of these complexes is required for glutamate-dependent changes in glycolysis and a shift in glutamate metabolism (from conversion to glutamine to glutamate oxidation). Compartmentalization of the astroglial glutamate transporters with these proteins and mitochondria provides an opportunity to spatially match energy production and buffering capacity. It also has implications for disposition of the glutamate. Therefore, our proposed research will impact our understanding of fundamental aspects of glutamate handling and metabolism. They will also define a novel molecular mechanism that matches astroglial energetic demands to changes in neuronal activity.

Public Health Relevance

For approximately two decades, it has been clear that failure to clear glutamate contributes to the brain damage observed in stroke, neurodevelopmental disorders, and neurodegenerative diseases. This failure to clear glutamate occurs, at least in part, because of impaired energy mobilization. Our long-term goal is to understand how extracellular glutamate is controlled so that it will be possible to intervene and prevent the debilitating effects of these disorders.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project (R01)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-MDCN-T (93))
Program Officer
Stewart, Randall R
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Children's Hospital of Philadelphia
United States
Zip Code
Sengupta, Shaon; Yang, Guang; O'Donnell, John C et al. (2016) The circadian gene Rev-erbα improves cellular bioenergetics and provides preconditioning for protection against oxidative stress. Free Radic Biol Med 93:177-89
Robinson, Michael B; Jackson, Joshua G (2016) Astroglial glutamate transporters coordinate excitatory signaling and brain energetics. Neurochem Int 98:56-71
O'Donnell, John C; Jackson, Joshua G; Robinson, Michael B (2016) Transient Oxygen/Glucose Deprivation Causes a Delayed Loss of Mitochondria and Increases Spontaneous Calcium Signaling in Astrocytic Processes. J Neurosci 36:7109-27
Jackson, Joshua G; Robinson, Michael B (2015) Reciprocal Regulation of Mitochondrial Dynamics and Calcium Signaling in Astrocyte Processes. J Neurosci 35:15199-213
Raju, Karthik; Doulias, Paschalis-Thomas; Evans, Perry et al. (2015) Regulation of brain glutamate metabolism by nitric oxide and S-nitrosylation. Sci Signal 8:ra68
Jackson, Joshua G; O'Donnell, John C; Krizman, Elizabeth et al. (2015) Displacing hexokinase from mitochondrial voltage-dependent anion channel impairs GLT-1-mediated glutamate uptake but does not disrupt interactions between GLT-1 and mitochondrial proteins. J Neurosci Res 93:999-1008
Jackson, Joshua G; O'Donnell, John C; Takano, Hajime et al. (2014) Neuronal activity and glutamate uptake decrease mitochondrial mobility in astrocytes and position mitochondria near glutamate transporters. J Neurosci 34:1613-24
Whitelaw, Brendan S; Robinson, Michael B (2013) Inhibitors of glutamate dehydrogenase block sodium-dependent glutamate uptake in rat brain membranes. Front Endocrinol (Lausanne) 4:123
Bauer, Deborah E; Jackson, Joshua G; Genda, Elizabeth N et al. (2012) The glutamate transporter, GLAST, participates in a macromolecular complex that supports glutamate metabolism. Neurochem Int 61:566-74
Genda, Elizabeth N; Jackson, Joshua G; Sheldon, Amanda L et al. (2011) Co-compartmentalization of the astroglial glutamate transporter, GLT-1, with glycolytic enzymes and mitochondria. J Neurosci 31:18275-88