Fast neuronal inhibition in the adult brain is critically dependent on the ability of neurons to synthesize the inhibitory neurotransmitter ?-aminobutyric acid (GABA) that mediates its actions via ionotropic GABAA and metabotropic GABAB receptors. Deficits in GABAergic inhibition are central to epilepsy and a plethora of other neuropsychiatric disorders. The major metabolic precursor for GABA synthesis by neurons is glutamine, which in turn is supplied by astrocytes. The ability of astrocytes to export glutamine i dependent upon the activity of the astrocyte-specific enzyme glutamine synthetase (GS). The significance of GS for brain function has been revealed by the use of specific inhibitors and gene deletion. These manipulations lead to seizures and death that result from decreased synaptic inhibition. Consistent with this, deficits in GS expression are found in the brains of epileptics and animal models of epilepsy. To date, however, there have been no systematic experiments to evaluate how the activity of GS is regulated to meet the demands of neurons for glutamine, and if deficits in these processes contribute to epileptogenesis. These issues will be addressed here. Preliminary results suggest that GS expression is subject to powerful regulation by astrocytic GABABRs. 2+ GABABRs are heterodimeric G-protein coupled receptors which couple to Gi/o, to modulate Ca transients, and inhibit the activity of adenylate cyclase. Preliminary studies have revealed that astrocytic GABABRs act to stabilize GS by reducing its ubiquitination and subsequent degradation. To understand the significance of this finding, we have created a mouse in which the expression of astrocytic GABABRs can be specifically ablated. These mice have decreased steady state expression levels of GS, spontaneous seizures, and premature death. Based on these observations we hypothesize that: Astrocytic GABABRs prevent the ubiquitin-dependent degradation of GS and thereby ensure the continued availability of glutamine for neuronal GABA synthesis. This proposal will center on three aims that are detailed below:
Aim 1. To test the hypothesis that astrocytic GABABRs regulate the stability of GS.
Aim 2. To test the hypothesis that ablating the expression of astrocytic GABABRs results in GS degradation, spontaneous seizures and death.
Aim 3. To test the hypothesis that reducing astrocytic GABABR expression compromises synaptic inhibition and neuronal viability. Together these experiments will provide unique insights into the role that astrocytic GABABRs play in regulating GS expression, fast synaptic inhibition and epileptogenesis. Collectively these studies may lead to the development of novel therapies to increase the activity of GS to alleviate the burdens of epilepsy

Public Health Relevance

Our studies are intended to provide insights into the role that gamma aminobutyric acid type B receptors play in regulating a specific enzyme found only in astrocytes. These insights have the potential to lead to the development of novel therapies to modulate the activity of this enzyme and ultimately to alleviate the burdens of epilepsy.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS081986-01
Application #
8458789
Study Section
Clinical Neuroplasticity and Neurotransmitters Study Section (CNNT)
Program Officer
Whittemore, Vicky R
Project Start
2012-09-30
Project End
2017-06-30
Budget Start
2012-09-30
Budget End
2013-06-30
Support Year
1
Fiscal Year
2012
Total Cost
$360,938
Indirect Cost
$142,188
Name
Tufts University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
039318308
City
Boston
State
MA
Country
United States
Zip Code
02111
Rifkin, Robert A; Moss, Stephen J; Slesinger, Paul A (2017) G Protein-Gated Potassium Channels: A Link to Drug Addiction. Trends Pharmacol Sci 38:378-392
Mukherjee, Jayanta; Cardarelli, Ross A; Cantaut-Belarif, Yasmine et al. (2017) Estradiol modulates the efficacy of synaptic inhibition by decreasing the dwell time of GABAA receptors at inhibitory synapses. Proc Natl Acad Sci U S A 114:11763-11768
Trattnig, Sarah M; Gasiorek, Agnes; Deeb, Tarek Z et al. (2016) Copper and protons directly activate the zinc-activated channel. Biochem Pharmacol 103:109-17
Munoz, Michaelanne B; Padgett, Claire L; Rifkin, Robert et al. (2016) A Role for the GIRK3 Subunit in Methamphetamine-Induced Attenuation of GABAB Receptor-Activated GIRK Currents in VTA Dopamine Neurons. J Neurosci 36:3106-14
Nakamura, Yasuko; Morrow, Danielle H; Modgil, Amit et al. (2016) Proteomic Characterization of Inhibitory Synapses Using a Novel pHluorin-tagged ?-Aminobutyric Acid Receptor, Type A (GABAA), ?2 Subunit Knock-in Mouse. J Biol Chem 291:12394-407
Vien, Thuy N; Moss, Stephen J; Davies, Paul A (2016) Regulating the Efficacy of Inhibition Through Trafficking of ?-Aminobutyric Acid Type A Receptors. Anesth Analg 123:1220-1227
Kelley, Matthew R; Deeb, Tarek Z; Brandon, Nicholas J et al. (2016) Compromising KCC2 transporter activity enhances the development of continuous seizure activity. Neuropharmacology 108:103-10
Walker, Kendall R; Modgil, Amit; Albrecht, David et al. (2016) Genetic Deletion of the Clathrin Adaptor GGA3 Reduces Anxiety and Alters GABAergic Transmission. PLoS One 11:e0155799
Mircsof, Dennis; Langouët, Maéva; Rio, Marlène et al. (2015) Mutations in NONO lead to syndromic intellectual disability and inhibitory synaptic defects. Nat Neurosci 18:1731-6
Sivakumaran, Sudhir; Cardarelli, Ross A; Maguire, Jamie et al. (2015) Selective inhibition of KCC2 leads to hyperexcitability and epileptiform discharges in hippocampal slices and in vivo. J Neurosci 35:8291-6

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