Blood glutamate EAAT(2)-cell grabbing therapy in cerebral ischemia

BACKGROUND: Excitatory amino acid transporter 2 (EAAT(2)) plays a pivotal role in glutamate clearance in the adult brain, thereby preventing excitotoxic effects. Considering the high efficacy of EAAT(2) for glutamate uptake, we hypothesized that the expression of this transporter in mesenchymal stem cells (MSCs) for systemic administration could yield a cell-based glutamate-grabbing therapy, combining the intrinsic properties of these cells with excitotoxic protection. METHODS: To address this hypothesis, EAAT(2)-encoding cDNA was introduced into MSCs and human embryonic kidney 293 cells (HEK cells) as the control cell line. EAAT(2) expression and functionality were evaluated by in vitro assays. Blood glutamate-grabbing activity was tested in healthy and ischemic rat models treated with 3 × 10(6) and 9 × 10(6) cells/animal. FINDINGS: The expression of EAAT(2) in both cell types conferred the expected glutamate-grabbing activity in in vitro and in vivo studies. The functional improvement observed in ischemic rats treated with EAAT(2)–HEK at low dose, confirmed that this effect was indeed mediated by the glutamate-grabbing activity associated with EAAT(2) functionality. Unexpectedly, both cell doses of non-transfected MSCs induced higher protection than transfected EAAT(2)–MSCs by another mechanism independent of the glutamate-grabbing capacity. INTERPRETATION: Although the transfection procedure most likely interferes with some of the intrinsic protective mechanisms of mesenchymal cells, the results show that the induced expression of EAAT(2) in cells represents a novel alternative to mitigate the excitotoxic effects of glutamate and paves the way to combine this strategy with current cell therapies for cerebral ischemia.