Allosteric potentiation of GABAA receptor promotes survival and maturation of oligodendroglial cells in vitro via Ca2+/CaMK/AKT signaling pathway.

Oligodendrocytes (OLs) and their precursor cells (OPCs) express specific receptors to GABA; however, the direct functional consequences of their activation remain not fully determined. It has been shown that expression of functional γ-aminobutyric acid (GABA) type A receptors (GABAARs) in OPCs and OLs is controlled by their contact with neurons. This suggests a role for GABAergic signaling in OPC-neuron dialogue establishment and their differentiation toward mature OLs. Here, OPCs (NG2+) isolated from rat (postnatal day 11) optic nerve, maintained in vitro, were used to directly study the functional role of the GABA signal. The oligodendroglial GABAAR activity was specifically enhanced using N-butyl-β-carboline-3-carboxylate (β-CCB), a potent positive allosteric modulator (PAM). β-CCB effects were compared with those of ganaxolone (Gx), a synthetic allopregnanolone analog and unspecific PAM of GABAARs. It was found that medium supplemented with one or both PAMs increased cell survival. This effect was eliminated in the presence of GABAAR antagonists, such as gabazine or bicuculline, and it was dependent on intracellular Ca2+ increase, which activated the AKT pathway through Ca2+-calmodulin-dependent kinases (CaMKs) acting upstream. In addition, a morphometric analysis showed that both PAMs promoted an increase in cellular complexity commonly associated with cell maturation, increasing the average cell area, number, and length of branches per cell, as well as the branch point number. These direct actions on NG2+ cells would explain, at least in part, the positive effects that GABAergic signaling stimulation has on the myelination process in several experimental models, both in vitro and in vivo.NEW & NOTEWORTHY Oligodendrocyte precursor cells express GABAARs and release GABA into the extracellular milieu; however, direct consequences of receptor activation remain unclear. In this work, we demonstrate that positive allosteric modulation of the GABAAR increases cell survival in vitro and promotes morphological changes associated with maturation. Both effects are generated by an increase in intracellular Ca2+ and activation of Ca2+-CaM-dependent kinases signaling pathway, which subsequently promote AKT phosphorylation, triggering antiapoptotic signals.