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Mahadevan V, Dargaei Z, Ivakine EA, Hartmann AM, Ng D, Chevrier J, Ormond J, Nothwang HG, McInnes RR, Woodin MA. Neto2-null mice have impaired GABAergic inhibition and are susceptible to seizures. Front Cell Neurosci 2015; 9:368. [PMID: 26441539 PMCID: PMC4585209 DOI: 10.3389/fncel.2015.00368] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 09/04/2015] [Indexed: 11/27/2022] Open
Abstract
Neto2 is a transmembrane protein that interacts with the neuron-specific K+-Cl− cotransporter (KCC2) in the central nervous system (CNS). Efficient KCC2 transport is essential for setting the neuronal Cl− gradient, which is required for fast GABAergic inhibition. Neto2 is required to maintain the normal abundance of KCC2 in neurons, and increases KCC2 function by binding to the active oligomeric form of this cotransporter. In the present study, we characterized GABAergic inhibition and KCC2-mediated neuronal chloride homeostasis in pyramidal neurons from adult hippocampal slices. Using gramicidin perforated patch clamp recordings we found that the reversal potential for GABA (EGABA) was significantly depolarized. We also observed that surface levels of KCC2 and phosphorylation of KCC2 serine 940 (Ser940) were reduced in Neto2−/− neurons compared to wild-type controls. To examine GABAergic inhibition we recorded spontaneous inhibitory postsynaptic currents (sIPSCs) and found that Neto2−/− neurons had significant reductions in both their amplitude and frequency. Based on the critical role of Neto2 in regulating GABAergic inhibition we rationalized that Neto2-null mice would be prone to seizure activity. We found that Neto2-null mice demonstrated a decrease in the latency to pentylenetetrazole (PTZ)-induced seizures and an increase in seizure severity.
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Affiliation(s)
- Vivek Mahadevan
- Department of Cell and Systems Biology, University of Toronto Toronto, ON, Canada
| | - Zahra Dargaei
- Department of Cell and Systems Biology, University of Toronto Toronto, ON, Canada
| | - Evgueni A Ivakine
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children Research Institute Toronto, ON, Canada
| | - Anna-Maria Hartmann
- Department of Systematic and Evolutionary Biology, Institute for Biology and Environmental Sciences, Carl von Ossietzky University Oldenburg Oldenburg, Germany
| | - David Ng
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children Research Institute Toronto, ON, Canada ; Departments of Neuroscience, Biochemistry and Molecular Biophysics, Columbia University New York City, NY, USA
| | - Jonah Chevrier
- Department of Cell and Systems Biology, University of Toronto Toronto, ON, Canada
| | - Jake Ormond
- Department of Cell and Systems Biology, University of Toronto Toronto, ON, Canada ; RIKEN Brain Sciences Institute Tokyo, Japan
| | - Hans Gerd Nothwang
- Neurogenetics Group, Center of Excellence Hearing4All, School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg Oldenburg, Germany
| | - Roderick R McInnes
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children Research Institute Toronto, ON, Canada ; Departments of Human Genetics and Biochemistry, McGill University and Lady Davis Institute, Jewish General Hospital Montreal, QC, Canada
| | - Melanie A Woodin
- Department of Cell and Systems Biology, University of Toronto Toronto, ON, Canada
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102
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Titz S, Sammler EM, Hormuzdi SG. Could tuning of the inhibitory tone involve graded changes in neuronal chloride transport? Neuropharmacology 2015; 95:321-31. [PMID: 25843644 DOI: 10.1016/j.neuropharm.2015.03.026] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 03/17/2015] [Accepted: 03/24/2015] [Indexed: 11/15/2022]
Abstract
Hyperpolarizing synaptic inhibition through GABAA and glycine receptors depends on the presence of the neuronal cation-chloride-cotransporter protein, KCC2. Several transcriptional and post-transcriptional mechanisms have been shown to regulate KCC2 and thereby influence the polarity and efficacy of inhibitory synaptic transmission. It is unclear however whether regulation of KCC2 enables the transporter to attain different levels of activity thus allowing a neuron to modulate the strength of inhibitory synaptic transmission to its changing requirements. We therefore investigated whether phosphorylation can allow KCC2 to achieve distinct levels of [Cl(-)]i in neurons. We generated a variety of KCC2 alanine dephosphorylation mimics and used NH4(+)-induced pHi shifts in cultured hippocampal neurons to quantify the rate of KCC2 transport activity exhibited by these mutants. To explore the relationship between KCC2 transport and GABAA receptor-mediated current amplitudes we performed gramicidine perforated-patch recordings. The correlation between EGABA and NH4(+)-induced pHi shifts enabled an estimate of the range of chloride extrusion possible by kinase/phosphatase regulation of KCC2. Our results demonstrate that KCC2 transport can vary considerably in magnitude depending on the combination of alanine mutations present on the protein. Transport can be enhanced to sufficiently high levels that hyperpolarizing GABAA responses may be obtained even in neurons with an extremely negative resting membrane potential and at high extracellular K(+) concentrations. Our findings highlight the significant potential for regulating the inhibitory tone by KCC2-mediated chloride extrusion and suggest that cellular signaling pathways may act combinatorially to alter KCC2 phosphorylation/dephosphorylation and thereby tune the strength of synaptic inhibition.
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Affiliation(s)
- Stefan Titz
- Institute for Physiology und Pathophysiology, University of Heidelberg, Im Neuenheimer Feld 326, 69120 Heidelberg, Germany.
| | - Esther M Sammler
- Division of Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK
| | - Sheriar G Hormuzdi
- Division of Neuroscience, Ninewells Hospital and Medical School, University of Dundee, Dundee DD1 9SY, UK.
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