Reduced expression of glutamate transporter EAAT2 and impaired glutamate transport in human primary astrocytes exposed to HIV-1 or gp120

Abstract

L-Glutamate is the major excitatory neurotransmitter in the brain. Astrocytes maintain low levels of synaptic glutamate by high-affinity uptake and defects in this function may lead to neuronal cell death by excitotoxicity. We tested the effects of HIV-1 and its envelope glycoprotein gp120 upon glutamate uptake and expression of glutamate transporters EAAT1 and EAAT2 in fetal human astrocytes in vitro. Astrocytes isolated from fetal tissues between 16 and 19 weeks of gestation expressed EAAT1 and EAAT2 RNA and proteins as detected by Northern blot analysis and immunoblotting, respectively, and the cells were capable of specific glutamate uptake. Exposure of astrocytes to HIV-1 or gp120 significantly impaired glutamate uptake by the cells, with maximum inhibition within 6 h, followed by gradual decline during 3 days of observation. HIV-1-infected cells showed a 59% reduction in V(max) for glutamate transport, indicating a reduction in the number of active transporter sites on the cell surface. Impaired glutamate transport after HIV-1 infection or gp120 exposure correlated with a 40-70% decline in steady-state levels of EAAT2 RNA and protein. EAAT1 RNA and protein levels were less affected. Treatment of astrocytes with tumor necrosis factor-alpha (TNF-alpha) decreased the expression of both EAAT1 and EAAT2, but neither HIV-1 nor gp120 were found to induce TNF-alpha production by astrocytes. These findings demonstrate that HIV-1 and gp120 induce transcriptional downmodulation of the EAAT2 transporter gene in human astrocytes and coordinately attenuate glutamate transport by the cells. Reduction of the ability of HIV-1-infected astrocytes to take up glutamate may contribute to the development of neurological disease.

EAAT2 regulation and splicing: relevance to psychiatric and neurological disorders

“…Human primary astrocytes exposed to HIV-1, or its envelope glycoprotein gp120, exhibit a decrease in glutamate uptake that is accompanied by reduced EAAT2 RNA and protein expression. 122 Another group found that EAAT2 expression is increased during replication of the virus in macrophages, while glutamate uptake is decreased. 123 The reduced ability of astrocytes infected with the virus to take up glutamate may contribute to the neurological deficits that are linked to the disease.…”

Synergistic increases in intracellular Ca2+, and the release of MCP‐1, RANTES, and IL‐6 by astrocytes treated with opiates and HIV‐1 Tat

“…Deficits in excitatory amino acid transporter-2 (EAAT2) glutamate transporter expression by human astrocytes have also been noted in response to gp120 or HIV exposure (Wang et al, 2003). Astroglial impairment may contribute to the dysfunction or death of naïve bystanders including neighboring neurons and uninfected glia (Lipton, 1994;Bagasra et al, 1996;Lipton, 1998;Nath and Geiger, 1998;Kolson et al, 1998;Haughey et al, 1999;Kaul et al, 2001).…”

Astrocyte CD38: Links to Neuroinflammation in HAND

“…Under normal physiological conditions, astrocytes selectively regulate extracellular levels of glutamate to maintain homeostasis in the neuronal microenvironment mainly through glutamate transporters (Rothstein et al, 1996). Previous work on primary human astrocytes has shown downregulation of excitatory amino acid transporter 2 (EAAT2) upon activation of astrocytes with HIV-1 gp120, leading to reduction in glutamate uptake (Wang et al, 2003). Glutamate transporter activity and inhibition of glutamate uptake can also be mediated by MAPKs and NF-B in astrocytes (Abe and Saito, 2001;Jayakumar et al, 2006).…”