Neurosteroid allopregnanolone regulates EAAC1‐mediated glutamate uptake and triggers actin changes in Schwann cells

Abstract

Recent evidence shows that neurotransmitters (e.g., GABA, Ach, adenosine, glutamate) are active on Schwann cells, which form myelin sheaths in the peripheral nervous system under different pathophysiologic conditions. Glutamate, the most important excitatory neurotransmitter, has been recently involved in peripheral neuropathies, thus prevention of its toxic effect is desirable to preserve the integrity of peripheral nervous system and Schwann cells physiology. Removal of glutamate from the extracellular space is accomplished by the high affinity glutamate transporters, so we address our studies to analyze their functional presence in Schwann cells. We first demonstrate that Schwann cells express the EAAC1 transporter in the plasma membrane and in intracellular vesicular compartments of the endocytic recycling pathways. Uptake experiments confirm its presence and functional activity in Schwann cells. Secondly, we demonstrate that the EAAC1 activity can be modulated by exposure to the neurosteroid allopregnanolone 10 nM (a progesterone metabolite proved to support Schwann cells). Transporter up-regulation by allopregnanolone is rapid, does not involve protein neo-synthesis and is prevented by actin depolymerization. Allopregnanolone modulation involves GABA-A receptor and PKC activation, promotes the exocytosis of the EAAC1 transporter from intracellular stores to the Schwann cell membrane, in actin-rich cell tips, and modifies the morphology of cell processes. Finally, we provide evidence that glutamate transporters control the allopregnanolone-mediated effects on cell proliferation. Our findings are the first to demonstrate the presence of a functional glutamate uptake system, which can be dynamically modulated by allopregnanolone in Schwann cells. Glutamate transporters may represent a potential therapeutic target to control Schwann cell physiology.