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
Hines, Rochelle M; Maric, Hans Michael; Hines, Dustin J et al. (2018) Developmental seizures and mortality result from reducing GABAA receptor ?2-subunit interaction with collybistin. Nat Commun 9:3130
Moore, Yvonne E; Deeb, Tarek Z; Chadchankar, Heramb et al. (2018) Potentiating KCC2 activity is sufficient to limit the onset and severity of seizures. Proc Natl Acad Sci U S A 115:10166-10171
Newman, Emily L; Terunuma, Miho; Wang, Tiffany L et al. (2018) A Role for Prefrontal Cortical NMDA Receptors in Murine Alcohol-Heightened Aggression. Neuropsychopharmacology 43:1224-1234
Wobst, Heike J; Wesolowski, Steven S; Chadchankar, Jayashree et al. (2017) Cytoplasmic Relocalization of TAR DNA-Binding Protein 43 Is Not Sufficient to Reproduce Cellular Pathologies Associated with ALSIn vitro. Front Mol Neurosci 10:46
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
Modgil, Amit; Parakala, Manasa L; Ackley, Michael A et al. (2017) Endogenous and synthetic neuroactive steroids evoke sustained increases in the efficacy of GABAergic inhibition via a protein kinase C-dependent mechanism. Neuropharmacology 113:314-322
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
Kang, Ji-Yong; Chadchankar, Jayashree; Vien, Thuy N et al. (2017) Deficits in the activity of presynaptic ?-aminobutyric acid type B receptors contribute to altered neuronal excitability in fragile X syndrome. J Biol Chem 292:6621-6632
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

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