Human immunodeficiency virus type 1 clade B and C gp120 differentially induce neurotoxin arachidonic acid in human astrocytes: implications for neuroAIDS

Abstract

HIV-1 clades (subtypes) differentially contribute to the neuropathogenesis of HIV-associated dementia (HAD) in neuroAIDS. HIV-1 envelop protein, gp120, plays a major role in neuronal function. It is not well understood how these HIV-1 clades exert these neuropathogenic differences. The N-methyl-D: -aspartate (NMDA) receptor-reduced glutamine synthesis could lead to secretion of neurotoxins such as arachidonic acid (AA) which plays a significant role in the neuropathogenic mechanisms in neuroAIDS. We hypothesize that clade B and C gp120 proteins exert differential effects on human primary astrocytes by production of the neurotoxin arachidonic acid. Our results indicate that clade B gp120 significantly downregulated NMDA receptor gene and protein expression, and level of glutamine while increasing expression of prostaglandin E2 (PGE(2)) and thromboxane A2 receptor (TBXA(2) R) compared to HIV-1 clade C gp120 protein. Thus, our studies for the first time demonstrate that HIV-1 clade B-gp120 protein appears to induce higher levels of expression of the neuropathogenic molecule cyclooxygenase-2 (COX-2)-mediated arachidonic acid by-products, PGE(2), and TBXA(2) R compared to HIV-1 clade C gp120 protein. These studies suggest that HIV-1 clade B and C gp120 proteins may play a differential role in the neuropathogenesis of HAD in neuroAIDS.

Fig. 1

Effect of HIV-1 clade B and C gp120 protein on NMDA receptor gene expression by dose-response (a) and kinetics (b) in human astrocytes. Astrocytes (1 × 10⁶ cells/ml) were separately treated with HIV-1 clade B (Bal) and C (CN54) gp120 at 5–100 ng/ml for 24 h and 25 ng/ml for 12, 24, and 48 h. RNA was extracted and reverse transcribed followed by quantitative real-time PCR for NMDA receptor and housekeeping gene β-actin-specific primers. Data are expressed as mean±SD of TAI values of three independent experiments

Fig. 2

Effect of HIV-1 clade B and C gp120 protein on NMDA Receptor gene expression in human astrocytes. Astrocytes (1×10⁶ cells/ml) were separately treated with HIV-1 clade B (Bal, MN, and JRCSF) and C (CN54) gp120 at 25 ng/ml for 24 h, and the NMDA receptor expression was quantified by quantitative real-time PCR. Data are expressed as mean±SD of TAI values of three independent experiments

Fig. 3

Effect of HIV-1 clade B and C gp120 protein on PGE₂ (a) and TBXA2 R (b) gene expression in human astrocytes. Astrocytes (1 × 10⁶ cells/ml) were separately treated with HIV-1 clade B (Bal) and C gp120 (CN54) at 25 ng/ml for 24 h, and the PGE₂ and TBXA2 R expression were quantified by quantitative real-time PCR. Data are expressed as mean±SD of TAI values of three independent experiments

Fig. 4

Effect of HIV-1 clade B and C gp120 protein on glutamine and glutamate levels. Astrocytes (1 × 10⁶ cells/ml) were separately treated with HIV-1 clade B (Bal) and C (CN54) gp120 at 25 ng/ml for 24 h, and the cell lysates were examined for glutamine (a) and glutamate level (b). Data are expressed as mean±SD of three independent experiments

Fig. 5

Effect of HIV-1 clade B and C gp120 protein on NMDA Receptor (NR2A) and glutamine synthetase (GS) protein expression. Astrocytes (1×10⁶ cells/ml) were separately treated with HIV-1 clade B and C gp120 at 25 ng/ml for 24 h and analyzed by Western blot. a The dose-response effect of NR2A protein in gp120 clade B (Bal) and clade C (CN54). b A representative experiment: lane 1 control, lane 2 gp120 Bal, lane 3 MN, lane 4 JRCSF, lane 5 CN54 on NR2A protein and densitometric evaluation (c). d A representative experiment: lane 1 control, lane 2 gp120 Bal, lane 3 CN54 on glutamate synthetase protein and densitometric evaluation (e). Data are representative of three independent experiments

Fig. 6

Effect of HIV-1 clade B- and C-gp120 protein on COX-2 (PGE₂) (a), densitometry evaluation (b), TBXA2 (c), and densitometry evaluation (d). Astrocytes (1×10⁶ cells/ml) were separately treated with HIV-1 clade B (Bal) and C (CN54) gp120 at 25 ng/ml for 24 h and analyzed by Western blot. Data are representative of three independent experiments