Modulation of EAAC1-mediated Glutamate Uptake and Actin organization In Schwann Cells

We recently observed that Schwann cells, the myelin-forming cells in the peripheral nervous system, express the high-affinity glutamate transporter EAAC1/EAAT3 in the plasma membrane and in intracellular vesicular compartments in vitro and in vivo [1]. The transporter was functional and its activity was increased by exposure to the neurosteroid allopregnanolone (ALLO, 10 nM). The ALLO effects required GABA-A receptors and PKC activation. Transport up-regulation was rapid, did not involve protein neo-synthesis and was prevented by actin depolymerisation, thus suggesting a rearrangement of the actin cytoskeleton in the phenomenon. To verify this hypothesis, Schwann cells were transfected with a GFP-EAAC1 construct [2] and the transporter’s surface density was measured by Total Internal Reflection Microscopy (TIRFM), which allows the selective excitation of labeled proteins located in or immediately below the plasma membrane (100 nm above the glass coverslip). ALLO incubation for 30 min determined a dynamic rearrangement of the cortical actin cytoskeleton: actin accumulated at the leading edge of cells and in filopodia, whose number and length was significantly increased by the treatment. A parallel redistribution of EAAC1 from intracellular structures to actin-positive Schwann cell tips was measured. Both these effects were prevented by treatment with cytocalasinD, further supporting a role of actin rearrangement in the ALLO effect. Finally, we provide evidence that glutamate transporters control the ALLO-mediated effects on Schwann cell proliferation. In conclusion, we propose a cellular mechanism in which ALLO induces a dynamic remodeling of the actin cytoskeleton, leading to increased surface density of the glutamate transporter EAAC1 in Schwann cells; this process represents the principal glutamate clearance system in Schwann cells. Understanding the molecular mechanisms through which ALLO controls Schwann cell differentiation and proliferation may be of interest to develop new therapeutic approaches for treating peripheral neuropathies and promoting regenerative processes. Reference List [1] Perego et al, 2009. Acta Physiologica 197 (672): 93. [2] D’Amico et al, 2010. Traffic. 11(11):1455-1470