PKCε and allopregnanolone: functional cross-talk at the GABAA receptor level

Abstract

Changes in GABAergic inhibition occur during physiological processes, during response to drugs and in various pathologies. These changes can be achieved through direct allosteric modifications at the γ-amino butyric acid (GABA) type A (GABAA) receptor protein level, or by altering the synthesis, trafficking and stability of the receptor. Neurosteroids (NSs) and protein kinase C (PKC) are potent modulators of GABAA receptors and their effects are presumably intermingled, even though evidence for this hypothesis is only partially explored. However, several PKC isoforms are able to phosphorylate the GABAA receptor, producing different functional effects. We focused on the ε isoform, that has been correlated to the sensitivity of the GABAA receptor to allosteric modulators and whose expression may be regulated in peripheral sensory neurons by NSs. The cross-talk between PKC-ε and NSs, leading to changes in GABAA receptor functionality, is considered and discussed in this perspective.

Keywords: GABAA receptor; PKCepsilon; neurosteroids; phosphorylation site; receptor traffiking.

Figure 1

(A) Electrophysiological traces showing the effect of Allo on GABA-evoked currents recorded from cortical neurons in culture (7DIV). The upper trace shows a recording from a control cell (red) and the lower trace is from a cell intracellularly perfused with the peptide εV1–2, a PKC-ε inhibitor. (B) Dose response curves of Allo effect in control and in the presence of the peptide eV1–2. Each point is the mean+/−SE of 8–15 cells. PKC-ε blockade did not change the potency of Allo but affected its efficacy. (C) Assessment of PKC-ε gene expression changes (as fold changes) in primary culture of dorsal root ganglia (DRG) neuron after 24 h exposure to 10⁻⁶ M Allo (white column), or to the culture conditioned medium obtained from Schwann cell cultures treated with 10⁻⁶ M Allo (gray column). The relative quantification of mRNA was obtained by quantitative real time PCR. Data were normalized to the housekeeping genes α-tubulin and β2-microglobulin and expressed as difference (^ΔΔCt) vs. controls, then averaged for each experimental group. The black column represents the controls (DRG neurons treated with vehicle, ethanol). Experiments were repeated at least three times (*p < 0.05 Anova Test).

Figure 2

Schematic plot of the possible cross-talks among PKC-ε, Allopregnanolone and GABA_A receptors.