Regulator of G Protein Signaling Protein Suppression of G o Protein-Mediated 2A Adrenergic Receptor Inhibition of Mouse Hippocampal CA3 Epileptiform Activity

Department of Pharmacology, Physiology and Therapeutics, School of Medicine and Health Sciences, University of North Dakota, Grand Forks, ND 58202-9037, USA.
Molecular pharmacology (Impact Factor: 4.13). 02/2009; 75(5):1222-30. DOI: 10.1124/mol.108.054296
Source: PubMed


Activation of G protein-coupled alpha(2) adrenergic receptors (ARs) inhibits epileptiform activity in the hippocampal CA3 region. The specific mechanism underlying this action is unclear. This study investigated which subtype(s) of alpha(2)ARs and G proteins (Galpha(o) or Galpha(i)) are involved in this response using recordings of mouse hippocampal CA3 epileptiform bursts. Application of epinephrine (EPI) or norepinephrine (NE) reduced the frequency of bursts in a concentration-dependent manner: (-)EPI > (-)NE > (+)NE. To identify the alpha(2)AR subtype involved, equilibrium dissociation constants (pK(b)) were determined for the selective alphaAR antagonists atipamezole (8.79), rauwolscine (7.75), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride (WB-4101; 6.87), and prazosin (5.71). Calculated pK(b) values correlated best with affinities determined previously for the mouse alpha(2A)AR subtype (r = 0.98, slope = 1.07). Furthermore, the inhibitory effects of EPI were lost in hippocampal slices from alpha(2A)AR-but not alpha(2C)AR-knockout mice. Pretreatment with pertussis toxin also reduced the EPI-mediated inhibition of epileptiform bursts. Finally, using knock-in mice with point mutations that disrupt regulator of G protein signaling (RGS) binding to Galpha subunits to enhance signaling by that G protein, the EPI-mediated inhibition of bursts was significantly more potent in slices from RGS-insensitive Galpha(o)(G184S) heterozygous (Galpha(o)+/GS) mice compared with either Galpha(i2)(G184S) heterozygous (Galpha(i2)+/GS) or control mice (EC(50) = 2.5 versus 19 and 23 nM, respectively). Together, these findings indicate that the inhibitory effect of EPI on hippocampal CA3 epileptiform activity uses an alpha(2A)AR/Galpha(o) protein-mediated pathway under strong inhibitory control by RGS proteins. This suggests a possible role for RGS inhibitors or selective alpha(2A)AR agonists as a novel antiepileptic drug therapy.

Download full-text


Available from: Brianna Goldenstein
  • Source
    • "If enhanced Ga o -mediated presynaptic inhibition occurred in inhibitory (GABAergic) neurons, as has been proposed for the epileptogenic Nav1.1 LOF mutants (Yu et al. 2006), one could see hyper-excitability due to suppressed inhibitory tone. This is consistent with our prior observation of reduced in vitro excitability in hippocampal slices from mice carrying our mutation (Goldenstein et al. 2009). In that model, the ability of epinephrine to suppress hippocampal epileptiform discharges was enhanced in the Ga o "
    [Show abstract] [Hide abstract]
    ABSTRACT: G protein-coupled receptors strongly modulate neuronal excitability but there has been little evidence for G protein mechanisms in genetic epilepsies. Recently, four patients with epileptic encephalopathy (EIEE17) were found to have mutations in GNAO1, the most abundant G protein in brain, but the mechanism of this effect is not known. The GNAO1 gene product, Gαo, negatively regulates neurotransmitter release. Here, we report a dominant murine model of Gnao1-related seizures and sudden death. We introduced a genomic gain-of-function knock-in mutation (Gnao1+/G184S) that prevents Go turnoff by Regulators of G protein signaling proteins. This results in rare seizures, strain-dependent death between 15 and 40 weeks of age, and a markedly increased frequency of interictal epileptiform discharges. Mutants on a C57BL/6J background also have faster sensitization to pentylenetetrazol (PTZ) kindling. Both premature lethality and PTZ kindling effects are suppressed in the 129SvJ mouse strain. We have mapped a 129S-derived modifier locus on Chromosome 17 (within the region 41–70 MB) as a Modifer of G protein Seizures (Mogs1). Our mouse model suggests a novel gain-of-function mechanism for the newly defined subset of epileptic encephalopathy (EIEE17). Furthermore, it reveals a new epilepsy susceptibility modifier Mogs1 with implications for the complex genetics of human epilepsy as well as sudden death in epilepsy. Electronic supplementary material The online version of this article (doi:10.1007/s00335-014-9509-z) contains supplementary material, which is available to authorized users.
    Full-text · Article · Apr 2014 · Mammalian Genome
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Recent evidence suggests that G protein-coupled receptors, especially those linked to G(alpha)(i), contribute to the mechanisms of anesthetic action. Regulator of G protein signaling (RGS) proteins bind to activated G(alpha)(i) and inhibit signal transduction. Genomic knock-in mice with an RGS-insensitive G(alpha)(i2) G184S (G(alpha)(i2) GS) allele exhibit enhanced G(alpha)(i2) signaling and provide a novel approach for investigating the role of G(alpha)(i2) signaling and RGS proteins in general anesthesia. We anesthetized homozygous G(alpha)(i2) GS/GS and wild-type (WT) mice with isoflurane and quantified time (in seconds) to loss and resumption of righting response. During recovery from isoflurane anesthesia, breathing was quantified in a plethysmography chamber for both lines of mice. G(alpha)(i2) GS/GS mice required significantly less time for loss of righting and significantly more time for resumption of righting than WT mice. During recovery from isoflurane anesthesia, G(alpha)(i2) GS/GS mice exhibited significantly greater respiratory depression. Poincaré analyses show that GS/GS mice have diminished respiratory variability compared with WT mice. Modulation of G(alpha)(i2) signaling by RGS proteins alters loss and resumption of wakefulness and state-dependent changes in breathing.
    Full-text · Article · Nov 2009 · Anesthesia and analgesia
  • [Show abstract] [Hide abstract]
    ABSTRACT: Signaling via G-protein-coupled receptors (GPCRs) is central for the function of biological systems. Many clinically used drugs target GPCRs directly or target molecules involved in GPCR signaling. As an alternative to targeting receptors directly, one could modulate signaling cascades downstream of receptor activation. In recent years, there has been substantial interest in a family of proteins called regulators of G protein signaling (RGS) proteins. They modulate GPCR signaling by accelerating GTP hydrolysis on active Galpha subunits, thereby reducing the amplitude and duration of signaling. Modulating RGS activity would be a useful strategy to control GPCR signaling. An RGS inhibitor would be expected to enhance GPCR signaling and could do so in a tissue- or pathway-specific manner. Apart from the central GAP (GTPase accelerating protein) activity, many RGS proteins also have other functions like regulating protein-protein interactions, subcellular localization of signaling molecules, and protein translation. It is clear that these proteins serve important functions in a number of physiological and pathophysiological processes, and they are emerging as potential drug targets. This chapter gives an overview of what is currently known about biological functions of RGS proteins based on in vivo and in vitro data. We also summarize the current status in targeting RGS proteins in drug discovery.
    No preview · Article · Dec 2010 · Progress in molecular biology and translational science
Show more