γ-Aminobutyric A Receptor (GABAAR) Regulates Aquaporin 4 Expression in the Subependymal Zone: RELEVANCE TO NEURAL PRECURSORS AND WATER EXCHANGE

Yuting Li,Udo Schmidt-Edelkraut,Fabian Poetz,Ilaria Oliva,Claudia Mandl,Gabriele Hölzl-Wenig,Kai Schönig,Dusan Bartsch,Francesca Ciccolini

doi:10.1074/jbc.m114.618686

Abstract

Activation of γ-aminobutyric A receptors (GABA(A)Rs) in the subependymal zone (SEZ) induces hyperpolarization and osmotic swelling in precursors, thereby promoting surface expression of the epidermal growth factor receptor (EGFR) and cell cycle entry. However, the mechanisms underlying the GABAergic modulation of cell swelling are unclear. Here, we show that GABA(A)Rs colocalize with the water channel aquaporin (AQP) 4 in prominin-1 immunopositive (P(+)) precursors in the postnatal SEZ, which include neural stem cells. GABA(A)R signaling promotes AQP4 expression by decreasing serine phosphorylation associated with the water channel. The modulation of AQP4 expression by GABA(A)R signaling is key to its effect on cell swelling and EGFR expression. In addition, GABA(A)R function also affects the ability of neural precursors to swell in response to an osmotic challenge in vitro and in vivo. Thus, the regulation of AQP4 by GABA(A)Rs is involved in controlling activation of neural stem cells and water exchange dynamics in the SEZ.

Highlights

GABAARs regulate osmotic tension in promininϩ neural stem cells and ependymal cells
We used flow cytometry to measure expression levels of epidermal growth factor receptor (EGFR) and prominin-1 and purify the following cell populations from the subependymal zone (SEZ) of neonatal mice: Pϩ/Elow cells consisting of ependymal cells and quiescent neural stem cells (NSCs); Pϩ/Ehigh cells being highly enriched in activated NSCs; PϪ/Ehigh cells enriched in transit-amplifying precursors (TAPs) and pre-neuroblasts; and PϪ/Elow cells representing mostly neuroblasts [7, 9, 17]
As we had previously found that neural precursors display benzodiazepine-sensitive GABAARs, we investigated by qRTPCR the expression of GABAAR ␣ subunits 1, 2, 3, and 5, which confer high affinity binding of benzodiazepines, and of gabra 4 and GABAAR␦ subunits, which are not associated with benzodiazepine sensitivity

Summary

Introduction

Results: GABAAR activation increases surface expression of AQP4, thereby affecting water exchange between the subependyma and the lateral ventricle. Activation of ␥-aminobutyric A receptors (GABAARs) in the subependymal zone (SEZ) induces hyperpolarization and osmotic swelling in precursors, thereby promoting surface expression of the epidermal growth factor receptor (EGFR) and cell cycle entry. We show that GABAARs colocalize with the water channel aquaporin (AQP) 4 in prominin-1 immunopositive (P؉) precursors in the postnatal SEZ, which include neural stem cells. The modulation of AQP4 expression by GABAAR signaling is key to its effect on cell swelling and EGFR expression. GABAAR function affects the ability of neural precursors to swell in response to an osmotic challenge in vitro and in vivo. The regulation of AQP4 by GABAARs is involved in controlling activation of neural stem cells and water exchange dynamics in the SEZ

Methods

Results

Conclusion