Neuronal apoptosis by HIV-1 Vpr: contribution of proinflammatory molecular networks from infected target cells

Abstract

BackgroundHuman immunodeficiency virus type 1 (HIV-1) induces neuronal dysfunction through host cellular factors and viral proteins including viral protein R (Vpr) released from infected macrophages/microglia. Vpr is important for infection of terminally differentiated cells such as macrophages. The objective of this study was to assess the effect of Vpr in the context of infectious virus particles on neuronal death through proinflammatory cytokines released from macrophages.MethodsMonocyte-derived macrophages (MDM) were infected with either HIV-1 wild type (HIV-1wt), Vpr deleted mutant (HIV-1∆Vpr) or mock. Cell lysates and culture supernatants from MDMs were analyzed for the expression and release of proinflammatory cytokines by quantitative reverse transcription-PCR and enzyme-linked immunosorbent assay respectively. Mitogen-activated protein kinases (MAPK) were analyzed in activated MDMs by western blots. Further, the effect of Vpr on neuronal apoptosis was examined using primary neurons exposed to culture supernatants from HIV-1wt, HIV-1∆Vpr or mock-infected MDMs by Annexin-V staining, MTT and Caspase - Glo® 3/7 assays. The role of interleukin (IL)-1β, IL-8 and tumor necrosis factor (TNF)-α on neuronal apoptosis was also evaluated in the presence or absence of neutralizing antibodies against these cytokines.ResultsHIV-1∆Vpr-infected MDMs exhibited reduced infection over time and specifically a significant downregulation of IL-1β, IL-8 and TNF-α at the transcriptional and/or protein levels compared to HIV-1wt-infected cultures. This downregulation was due to impaired activation of p38 and stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK) in HIV-1∆Vpr-infected MDMs. The association of SAPK/JNK and p38 to IL-1β and IL-8 production was confirmed by blocking MAPKs that prevented the elevation of IL-1β and IL-8 in HIV-1wt more than in HIV-1∆Vpr-infected cultures. Supernatants from HIV-1∆Vpr-infected MDMs containing lower concentrations of IL-1β, IL-8 and TNF-α as well as viral proteins showed a reduced neurotoxicity compared to HIV-1wt-infected MDM supernatants. Reduction of neuronal death in the presence of anti-IL-1β and anti-IL-8 antibodies only in HIV-1wt-infected culture implies that the effect of Vpr on neuronal death is in part mediated through released proinflammatory factors.ConclusionCollectively, these results demonstrate the ability of HIV-1∆Vpr to restrict neuronal apoptosis through dysregulation of multiple proinflammatory cytokines in the infected target cells either directly or indirectly by suppressing viral replication.

Vpr Enhances Tumor Necrosis Factor Production by HIV-1-Infected T Cells

“…Here, we infected CD4 ϩ T cells with wildtype or vpr-deleted viruses and observed that Vpr stimulates the secretion of TNF in productively infected cells. Our results confirm and extend earlier studies showing that CD4 ϩ T lymphocytes, dendritic cells, and macrophages infected by HIV produce higher levels of TNF in the presence of Vpr (79,81,82). Using inhibitors of reverse transcription and integration, as well as ⌬vpr viruses complemented in trans with HA-Vpr, we found that de novo synthesis of Vpr was required for this effect.…”

“…Vpr has been reported to inhibit the secretion of type I interferon (IFN) (33,62,72,73) and of other proinflammatory cytokines such as tumor necrosis factor (TNF), MIP-1␣, MIP-1␤, and RANTES (74,75). In contrast, other studies suggested that Vpr stimulates type I IFN production in astrocytes (76) and induces interferon-stimulated genes (ISGs) in macrophages and monocytes (77,78) and the proinflammatory cytokines interleukin-1␤ (IL-1␤), IL-8, and TNF in various cells (70,71,(79)(80)(81)(82). These opposing results may reflect cell type differences or the use of different methods to express Vpr (infection, overexpression of Vpr, and treatment with Vpr recombinant protein).…”

An Overview of Human Immunodeficiency Virus Type 1-Associated Common Neurological Complications: Does Aging Pose a Challenge?

“…Vpr alone induces the production of pro-inflammatory cytokines, such as IL-6, IL-8, MCP-1, and CCL5, from astrocytes and macrophages [169, 181, 182]. Induction of cytokines involves the activation of p38 MAPK, JNK MAPK, TLR4/MyD88, and NF-0κB signaling pathways [169, 183]. Infusion of Vpr-transfected astrocytes into the hippocampus impairs spatial and recognition memory in rats and induces morphological changes in neurons with reduced expression of synaptophysin [184].…”

The Effects of Neurotrophins and the Neuropeptides VIP and PACAP on HIV-1 Infection: Histories with Opposite Ends

“…Although HIV-1 does not replicate in neurons, its productive infection in other cell types leads to the release of neurotoxic viral proteins, such as Tat, Nef, Vpr and gp120 [30,31,32,33]. These viral proteins induce neuronal apoptosis and affect axonal projections to their targets, impairing neuronal plasticity and function [34,35,36,37,38,39,40,41]. Moreover, the chronic immune activation due to HIV-1 proteins and other antigens (as discussed below) results in a persistent proinflammatory condition in the CNS with concomitant homing of anti-HIV-1-specific CD8+ T lymphocytes to this site, which may accentuate the cell death [42].…”

“…The HIV-1 proteins Tat, Nef, gp120 and Vpr can cause neuronal loss, either due to proapoptotic stimuli or by impairing axonal projections and neuronal plasticity/function, especially in sympathetic neurons [34,35,36,37,38,39,40,41]. NT signaling through Trk receptors has been associated with anti-apoptotic activity and with enhancement of synaptic connections, and many works, using different cellular models and treatment strategies, have shown that NGF and BDNF are able to recover neuronal plasticity impaired by HIV-1 proteins and to rescue neuronal cells from HIV-1-induced apoptosis [119,120,121,122].…”