Tonic inhibition determines the excitability of neurons and the activity of neuronal circuits through the persistent activity of specialized populations of high affinity extrasynaptic ?-aminobutyric acid A receptors (GABAARs), that are the principle targets of neurosteroids. Neurosteroids are widely accepted as endogenous regulators of GABAergic inhibition. Fluctuations in the levels of neurosteroids are accepted to play a critical role in epilepsy, and are also relevant to autism, anxiety, depression, premenstrual syndrome and schizophrenia. However, to date, there is a fundamental gap in understanding how fluctuations in the levels of neurosteroids change extrasynaptic GABAAR subunit expression levels, which are a significant factor in the changes in GABAergic inhibition that occur in a plethora of neuropsychiatric disorders. Our long-term goal is to fully understand the mechanism by which neurosteroids influence the expression levels of extrasynaptic GABAARs. In this proposal we will address the role that neurosteroids play in protein kinase C (PKC)-dependent phosphorylation of ?4 subunit-containing GABAARs. We will determine how this influences the cell surface accumulation of the GABAAR subtypes that mediate tonic inhibition. Our central hypothesis is that neurosteroids modulate the phosphorylation of GABAARs assembled from ?4?3 and ? subunits, which mediate the majority of tonic inhibition in the dentate gyrus and thalamus. Neurosteroids specifically potentiate PKC-dependent phosphorylation of serine 443 (S443) in the ?4 subunit. This increased phosphorylation leads to enhanced insertion of receptors composed of ?4?3 and ? subunits into the plasma membrane that originate within the secretory pathway. These enhancements of receptor cell surface stability are responsible for sustained increases in the efficacy of tonic inhibition. Guided by strong preliminary data, this hypothesis will be tested by pursuing three specific aims: (1) Determining the role of PKC-dependent phosphorylation in modulating the specific cell surface accumulation of GABAARs that mediate tonic inhibition (2) Visualizing neurosteroid- mediated changes in cell surface stability and membrane trafficking of GABAARs and (3) Ascertaining the effects of neurosteroid-dependent phosphorylation on the activity of GABAARs and the efficacy of tonic inhibition. In summary this proposal will demonstrate a new and unexpected mechanism by which neurosteroids exert persistent and sustained changes in the efficacy of tonic inhibition. Understanding neurosteroid-mediated changes in phosphorylation and cell surface expression of GABAARs has the potential to translate into better understanding of neuropsychiatric disorders. Moreover such information is likely to lead to the development of more efficacious treatments for anxiety, depression, premenstrual syndrome, schizophrenia and substance abuse.

Public Health Relevance

Fluctuations in the levels of neurosteroids change the expression of GABAA receptor subtypes that mediate tonic inhibition. The proposed research describes a novel mechanism by which neurosteroids regulate tonic inhibition and will act as a first step in the development of new and better interventions for people with neuropsychiatric disorders that include anxiety, epilepsy, depression, premenstrual syndrome and schizophrenia.

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
1R01MH097446-01A1
Application #
8438898
Study Section
Molecular Neuropharmacology and Signaling Study Section (MNPS)
Program Officer
Desmond, Nancy L
Project Start
2012-12-01
Project End
2017-11-30
Budget Start
2012-12-01
Budget End
2013-11-30
Support Year
1
Fiscal Year
2013
Total Cost
$439,699
Indirect Cost
$159,427
Name
Tufts University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
039318308
City
Boston
State
MA
Country
United States
Zip Code
02111
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
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
Nakamura, Yasuko; Morrow, Danielle H; Modgil, Amit et al. (2016) Proteomic Characterization of Inhibitory Synapses Using a Novel pHluorin-tagged γ-Aminobutyric Acid Receptor, Type A (GABAA), α2 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 γ-Aminobutyric Acid Type A Receptors. Anesth Analg 123:1220-1227
Vien, Thuy N; Modgil, Amit; Abramian, Armen M et al. (2015) Compromising the phosphodependent regulation of the GABAAR β3 subunit reproduces the core phenotypes of autism spectrum disorders. Proc Natl Acad Sci U S A 112:14805-10
Silayeva, Liliya; Deeb, Tarek Z; Hines, Rochelle M et al. (2015) KCC2 activity is critical in limiting the onset and severity of status epilepticus. Proc Natl Acad Sci U S A 112:3523-8
Nakamura, Yasuko; Darnieder, Laura M; Deeb, Tarek Z et al. (2015) Regulation of GABAARs by phosphorylation. Adv Pharmacol 72:97-146
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
Terunuma, Miho; Haydon, Philip G; Pangalos, Menelas N et al. (2015) Purinergic receptor activation facilitates astrocytic GABAB receptor calcium signalling. Neuropharmacology 88:74-81

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