Glutamate is the major neurotransmitter of the brain, whose extracellular levels 
are tightly controlled by glutamate transporters. Five glutamate transporters in 
the human brain (EAAT1-5) are present on both astroglia and neurons. We 
characterize the profile of three different human astroglial progenitors in 
vitro: human glial restricted precursors (HGRP), human astrocyte precursors 
(HAPC), and early-differentiated astrocytes. EAAT 1, EAAT3, and EAAT4 are all 
expressed in GRPs with a subsequent upregulation of EAAT1 following 
differentiation of GRPs into GRP-derived astrocytes in the presence of bone 
morphogenic protein (BMP-4). This corresponds to a significant increase in the 
glutamate transport capacity of these cells. EAAT2, the transporter responsible 
for the bulk of glutamate transport in the adult brain, is not expressed as a 
full-length protein, nor does it appear to have functional significance (as 
determined by the EAAT2 inhibitor dihydrokainate) in these precursors. A splice 
variant of EAAT2, termed EAAT2b, does appear to be present in low levels, 
however. EAAT3 and EAAT4 expression is reduced as glial maturation progresses 
both in astrocyte precursors and early-differentiated astrocytes and is 
consistent with their role in adult tissues as primarily neuronal glutamate 
transporters. These human glial precursors offer several advantages as tools for 
understanding glial biology because they can be passaged extensively in the 
presence of mitogens, afford the potential to study the temporal changes in 
glutamate transporter expression in a tightly controlled fashion, and are 
cultured in the absence of neuronal coculture, allowing for the independent 
study of astroglial biology.