Autocrine/Paracrine Activation of the GABA_AReceptor Inhibits the Proliferation of Neurogenic Polysialylated Neural Cell Adhesion Molecule-Positive (PSA-NCAM⁺) Precursor Cells from Postnatal Striatum

Abstract

GABA and its type A receptor (GABA A R) are present in the immature CNS and may function as growth-regulatory signals during the development of embryonic neural precursor cells. In the present study, on the basis of their isopycnic properties in a buoyant density gradient, we developed an isolation procedure that allowed us to purify proliferative neural precursor cells from early postnatal rat striatum, which expressed the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). These postnatal striatal PSA-NCAM ϩ cells were shown to proliferate in the presence of epidermal growth factor (EGF) and formed spheres that preferentially generated neurons in vitro. We demonstrated that PSA-NCAM ϩ neuronal precursors from postnatal striatum expressed GABA A R subunits in vitro and in situ. GABA elicited chloride currents in PSA-NCAM ϩ cells by activation of functional GABA A R that displayed a typical pharmacological profile. GABA A R activation in PSA-NCAM ϩ cells triggered a complex intracellular signaling combining a tonic inhibition of the mitogen-activated protein kinase cascade and an increase of intracellular calcium concentration by opening of voltagegated calcium channels. We observed that the activation of GABA A R in PSA-NCAM ϩ neuronal precursors from postnatal striatum inhibited cell cycle progression both in neurospheres and in organotypic slices. Furthermore, postnatal PSA-NCAM ϩ striatal cells synthesized and released GABA, thus creating an autocrine/paracrine mechanism that controls their proliferation. We showed that EGF modulated this autocrine/paracrine loop by decreasing GABA production in PSA-NCAM ϩ cells. This demonstration of GABA synthesis and GABA A R function in striatal PSA-NCAM ϩ cells may shed new light on the understanding of key extrinsic cues that regulate the developmental potential of postnatal neuronal precursors in the CNS.

GABAA Receptor Signaling Induces Osmotic Swelling and Cell Cycle Activation of Neonatal Prominin+ Precursors

“…Neuroblasts in the SEZ are sensitive to benzodiazepines [7,8]. As we had found that PS þ /EGFR high and PS þ /EGFR low cells express a similar range of GABA A R subunits (Supporting Information Fig.…”

“…GABA signaling exerts a complex regulation also in the adult subependymal zone (SEZ) where neuroblasts and glial fibrillary acidic protein (GFAP)-expressing cells, which include stem cells as well as astrocytes, regulate ambient GABA levels, by mediating its nonsynaptic release and uptake, respectively [5]. In turn, GABA A R activation downregulates neuroblast proliferation and migration [6][7][8]. Activation of GABA A R also inhibits the proliferation of GFAP-expressing cells in the adult niche [5].…”

Cell cycle restriction by histone H2AX limits proliferation of adult neural stem cells

“…GABA can be released via phasic release through Ca 2+ -dependent vesicular exocytosis from neurons and by tonic release, independent of action potentials and vesicles, by permeation through the Bestrophin 1 anion channel in neurons and glia (39). Neuroblasts within the germinal zone release GABA tonically, which acts on GFAP + progenitors in the SVZ, negatively affecting proliferation (10,40,41). Bestrophin 1 gates GABA already at very low (i.e., resting) intracellular Ca 2+ concentrations (100 nM) but increases release with increasing Ca 2+ concentrations (39).…”

Nonsynaptic GABA signaling in postnatal subventricular zone controls proliferation of GFAP-expressing progenitors

“…GABA plays an important signaling role in developmental processes, such as embryonic cell proliferation and migration 12-17 as well as regulating the migratory speed and production of neuroblasts in postnatal SVZ 11,18 . To support GABAergic signaling from neuroblasts to GFAP-expressing cells, the expression of GABA receptors in GFAP-expressing cells has yet to be demonstrated.…”