Abstract
BackgroundNeurocognitive impairments remain prevalent in HIV-1 infected individuals despite current antiretroviral therapies. It is increasingly becoming evident that astrocytes play a critical role in HIV-1 neuropathogenesis through the production of proinflammatory cytokines/chemokines. HIV-1 viral protein R (Vpr) plays an important role in neuronal dysfunction; however, its role in neuroinflammation is not well characterized. The major objective of this study was to determine the effect of Vpr in induction of proinflammatory chemokine CCL5 in astrocytes and to define the underlying mechanism(s).MethodsSVGA astrocytes were either mock transfected or were transfected with a plasmid encoding HIV-1 Vpr, and the cells were harvested at different time intervals. The mRNA level of CCL5 expression was quantified using real-time RT-PCR, and cell culture supernatants were assayed for CCL5 protein concentration. Immunocytochemistry was performed on HIV-1 Vpr transfected astrocytes to check CCL5 expression. Various signaling mechanisms such as p38 MAPK, PI3K/Akt, NF-κB and AP-1 were explored using specific chemical inhibitors and siRNAs.ResultsHIV-1 Vpr transfected astrocytes exhibited time-dependent induction of CCL5 as compared to mock-transfected astrocytes at both the mRNA and protein level. Immunostained images of astrocytes transfected with HIV-1 Vpr also showed much higher accumulation of CCL5 in comparison to untransfected and mock-transfected astrocytes. Pre-treatment with NF-κB (SC514) and PI3K/Akt (LY294002) inhibitor partially abrogated CCL5 mRNA and protein expression levels as opposed to untreated controls after HIV-1 Vpr transfection. Specific siRNAs against p50 and p65 subunits of NF-κB, p38δ MAPK, Akt-2 and Akt-3, and AP-1 transcription factor substantially inhibited the production of CCL5 in HIV-1 Vpr transfected astrocytes.ConclusionThese results demonstrate the ability of HIV-1 Vpr to induce CCL5 in astrocytes in a time-dependent manner. Furthermore, this effect was observed to be mediated by transcription factors NF-κB and AP-1 and involved the p38-MAPK and PI3K/Akt pathway.
Highlights
HIV-1 enters the central nervous system (CNS) very early in the course of the disease and causes productive infection in the perivascular macrophages and microglia of the brain [1,2,3]
Time-dependent induction of CCL5 by HIV-1 viral protein R (Vpr) in SVGA astrocytes The expression levels of CCL5 are known to be increased in the CSF of individuals suffering from HAND
We transfected SVGA astrocytes with a plasmid encoding HIV-1 Vpr using Lipofectamine 2000 reagent to ascertain whether viral protein R has any role in increased CCL5 expression
Summary
HIV-1 enters the central nervous system (CNS) very early in the course of the disease and causes productive infection in the perivascular macrophages and microglia of the brain [1,2,3]. The milder form of neurocognitive impairment, minor cognitive motor disorder (MCMD), remains prevalent in the HAART era, affecting an estimated 40% − 50% of HIV-infected individuals, while the more severe forms of dementia have been substantially reduced [4]. Astrocytes are the most abundant cell type in the brain and play a primary role in the maintenance of homeostasis in the brain. The HIV-infected cells in the CNS release viral particles such as gp120 and Tat in the brain microenvironment. These viral particles have been demonstrated to elicit inflammatory responses from the glial cells and have been implicated in neuronal apoptosis [16,17]. The major objective of this study was to determine the effect of Vpr in induction of proinflammatory chemokine CCL5 in astrocytes and to define the underlying mechanism(s)
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