Glial restricted precursors protect against chronic glutamate neurotoxicity of motor neurons in vitro

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Abstract
We have examined the expression of glutamate transporters in primary and immortalized glial precursors (GRIPs). We subsequently transduced these cells with the GLT1 glutamate transporter and examined the ability of these cells to protect motor neurons in an organotypic spinal cord culture. We show that glial restricted precursors and GRIP-derived astrocytes predominantly express glutamate transporters GLAST and GLT1. Oligodendrocyte differentiation of GRIPs results in downregulation of all glutamate transporter subtypes. Having identified these precursor cells as potential vectors for delivering glutamate transporters to regions of interest, we engineered a line of GRIPS that overexpress the glutamate transporter GLT1. These cells (G3 cells) have a nearly fourfold increase in glutamate transporter expression and at least a twofold increase in the Vmax for glutamate transport. To assess whether G3 seeding can protect motor neurons from chronic glutamate neurotoxicity, G3s were seeded onto rat organotypic spinal cord cultures. These cultures have previously been used extensively to understand pathways involved in chronic glutamate neurotoxicity of motor neurons. After G3 seeding, cells integrated into the culture slice and resulted in levels of glutamate transport sufficient to enhance total glutamate uptake. To test whether neuroprotection was related to glutamate transporter overexpression, we isolated GRIPS from the GLT1 null mouse to serve as controls. The seeding of G3s resulted in a reduction of motor neuron cell death. Hence, we believe that these cells may potentially play a role in cell-based neuroprotection from glutamate excitotoxicity.