Design of a non-glycosylated outer domain-derived HIV-1 gp120 immunogen that binds to CD4 and induces neutralizing antibodies

The outer domain (OD) of the HIV-1 envelope glycoprotein gp120 is an important target for vaccine design as it contains a number of conserved epitopes, including a large fraction of the CD4 binding site. Attempts to design OD-based immunogens in the past have met with little success. We report the design and characterization of an Escherichia coli-expressed OD-based immunogen (OD(EC)), based on the sequence of the HxBc2 strain. The OD(EC)-designed immunogen lacks the variable loops V1V2 and V3 and incorporates 11 designed mutations at the interface of the inner and the outer domains of gp120. Biophysical studies showed that OD(EC) is folded and protease-resistant, whereas OD(EC) lacking the designed mutations is highly aggregation-prone. In contrast to previously characterized OD constructs, OD(EC) bound CD4 and the broadly neutralizing antibody b12 but not the non-neutralizing antibodies b6 and F105. Upon immunization in rabbits, OD(EC) was highly immunogenic, and the sera showed measurable neutralization for four subtype B and one subtype C virus including two b12-resistant viruses. In contrast, sera from rabbits immunized with gp120 did not neutralize any of the viruses. OD(EC) is the first example of a gp120 fragment-based immunogen that yields significant neutralizing antibodies.

Moderate ethanol preconditioning of rat brain cultures engenders neuroprotection against dementia-inducing neuroinflammatory proteins: possible signaling mechanisms

There is no question that chronic alcohol (ethanol) abuse, a leading worldwide problem, causes neuronal dysfunction and brain damage. However, various epidemiologic studies in recent years have indicated that in comparisons with abstainers or never-drinkers, light/moderate alcohol consumers have lower risks of age-dependent cognitive decline and/or dementia, including Alzheimer's disease (AD). Such reduced risks have been variously attributed to favorable circulatory and/or cerebrovascular effects of moderate ethanol intake, but they could also involve ethanol "preconditioning" phenomena in brain glia and neurons. Here we summarize our experimental studies showing that moderate ethanol preconditioning (MEP; 20-30 mM ethanol) of rat brain cultures prevents neurodegeneration due to beta-amyloid, an important protein implicated in AD, and to other neuroinflammatory proteins such as gp120, the human immunodeficiency virus 1 envelope protein linked to AIDS dementia. The MEP neuroprotection is associated with suppression of neurotoxic protein-evoked initial increases in [Ca(+2)](i) and proinflammatory mediators--e.g., superoxide anion, arachidonic acid, and glutamate. Applying a sensor --> transducer --> effector model to MEP, we find that onset of neuroprotection correlates temporally with elevations in "effector" heat shock proteins (HSP70, HSP27, and phospho-HSP27). The effector status of HSPs is supported by the fact that inhibiting HSP elevations due to MEP largely restores gp120-induced superoxide potentiation and subsequent neurotoxicity. As upstream mediators, synaptic N-methyl-d-aspartate receptors may be initial prosurvival sensors of ethanol, and protein kinase C epsilon and focal adhesion kinase are likely transducers during MEP that are essential for protective HSP elevations. Regarding human consumption, we speculate that moderate ethanol intake might counter incipient cognitive deterioration during advanced aging or AD by exerting preconditioning-like suppression of ongoing neuroinflammation related to amyloidogenic protein accumulation.

HIV entry inhibitors: progress in development and application

This review discusses recent progress in the development of anti-HIV agents, with emphasis on small molecule HIV-1 entry inhibitors. The entry inhibitors primarily target HIV-1 envelope glycoproteins or the cellular receptors, CD4 and chemokine receptors. Two of the entry inhibitors, enfuvirtide and maraviroc, have been approved by the US FDA for AIDS therapy. The drug resistance associated with some of the entry inhibitors will also be discussed.

c-FLIPL regulates PKC via AP-2 to inhibit Bax-mediated apoptosis induced by HIV-1 gp120 in Jurkat cells

c-FLIPL, an inhibitor of caspase 8, is known to inhibit the Fas/caspase 8 apoptotic pathway; however, its involvement of Bax/mitochondrial apoptosis is not well understood. Using human cells, Jurkat cell line, induced with HIV-1 gp120, we studied the effects of c-FLIPL on Bax/mitochondrial apoptosis. We found that the induction of apoptosis by HIV-1 envelope protein, gp120, involved the activation of both Bax-dependent and death receptor-mediated pathways, and HIV-1 infection deceased c-FLIPL expression. Interestingly, c-FLIPL expression downregulated protein kinase C (PKC) expression at the transcript level involving activated protein-2 (AP-2). c-FLIPL expression reduced AP-2 protein levels required to promote PKC protein expression and PKC-associated inactive form of Bax, and inhibited Bax activation, suggesting that c-FLIPL inhibits Bax activation via modulating PKC expression at the transcriptional level involving AP-2 during gp120 treatment. Collectively, these findings further corroborate the concept that gp120 plays an important role, via involvement of molecules such as c-FLIPL, in apoptotic cell death due to HIV-1 infection.

Inducible nitric oxide synthase is involved in the oxidation stress induced by HIV-1 gp120 in human retina pigment epithelial cells

BACKGROUND

The human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120 has been implicated in the development of AIDS-associated retinopathy. The present study tested the hypothesis that gp120 may induce oxidative stress including up regulation of inducible nitric oxide synthase (iNOS) and production of malondialdehyde (MDA) and nitric oxide (NO) to mediate retinopathy in retinal pigment epithelial (RPE) cells.

METHODS

Human RPE cell line D407 was cultured and treated with gp120. HIV-1 gp120 protein induced lipid peroxidation product MDA. NO production and iNOS expression were examined in vitro by spectrophomtometry, real-time PCR, Western blotting, and confocal microscope.

RESULTS

Addition of gp120 was able to induce RPE cells to produce NO and MDA in time- and dose-dependent manners (P < 0.05). Similarly, gp120 was also capable of up-regulating iNOS mRNA and protein in D407 cells in time- and dose-dependent manners.

CONCLUSIONS

Gp120 induces oxidative stress in D407 cell by stimulating MDA and NO production, which is mediated by up-regulating iNOS expression. Gp120 may mediate oxidation stress in AIDS-associated retinopathy.

Activation of the extrinsic caspase pathway in cultured cortical neurons requires p53-mediated down-regulation of the X-linked inhibitor of apoptosis protein to induce apoptosis

Cultured cortical neurons exposed to the Human Immunodeficiency Virus gp120 coat protein undergo apoptosis involving activation of both caspase-8 and caspase-9. Additionally, gp120-mediated neuronal apoptosis requires the pro-apoptotic transcription factor p53. As caspase-8-induced apoptosis does not typically require p53, we examined the possibility of a novel role for p53 in caspase-8 activation initiated by gp120. We observed that gp120 treatment of cultured cortical neurons induced caspase-8 activity and Bid cleavage independently of p53, but induction of caspase-3 enzymatic activity required p53 expression. These findings suggested the possibility that p53 down-regulates a caspase-3 inhibitor. We observed high-level expression of the caspase-3/9 inhibitor X-linked inhibitor of apoptosis protein (XIAP) in cultured cortical neurons. Adenoviral expression of p53 or induction of endogenous p53 by camptothecin treatment reduced XIAP protein in neurons. Infection with a p53 expressing adenovirus increased expression of the mRNA for Omi/HtrA2, a protease that cleaves and inactivates XIAP. These findings suggest that p53 regulates neuronal apoptosis, in part, by suppressing the anti-apoptotic protein XIAP via transcriptional activation of Omi/HtrA2.

Differential regulation of Mn-superoxide dismutase in neurons and astroglia by HIV-1 gp120: Implications for HIV-associated dementia

HIV-associated dementia, like several other neurodegenerative diseases, is characterized by selective degeneration of neurons amidst survival of glial cells like astroglia. The molecular basis of such selective susceptibility within the same milieu remains largely unknown. Neurons are rarely infected by the virus. However, they are vulnerable to viral products, like HIV-1 coat protein gp120. Interestingly, gp120 induced oxidative stress in neurons, but not in astroglia. This led us to postulate that astroglia were armed with a more efficient antioxidant system than neurons. Here, we report that the constitutive level of MnSOD (SOD2), the major cellular antioxidant enzyme, is significantly higher in astroglia than in neurons. Furthermore, gp120 treatment enhanced MnSOD levels in astroglia but decreased the same in neurons. This increase in astroglial MnSOD was dependent on NF-kappaB, the crucial transcription factor required for sod2 gene transcription. Blocking NF-kappaB with p65-antisense, p65-si-RNA, or a specific inhibitor, NBD peptide, led to reduced MnSOD levels and enhanced vulnerability of astroglia to gp120. Additionally, neurons were found to have a lower constitutive level of NF-kappaB p65 than astrocytes. Overexpression of p65 increased the level of MnSOD in neurons. This, in turn, elicited greater neuronal resistance to gp120. Taken together, our study suggests that astroglia manifest a higher threshold for gp120-induced lethality than neurons due to greater MnSOD availability, which is demonstrated due to greater level of NF-kappaB p65.

Recombinant Mycobacterium bovis bacillus Calmette-Guerin elicits human immunodeficiency virus type 1 envelope-specific T lymphocytes at mucosal sites

A successful vaccine vector for human immunodeficiency virus type 1 (HIV-1) should induce anti-HIV-1 T-cell immune responses at mucosal sites. We have constructed recombinant Mycobacterium bovis bacillus Calmette-Guérin (rBCG) expressing an HIV-1 group M consensus envelope (Env) either as a surface, intracellular, or secreted protein as an immunogen. rBCG containing HIV-1 env plasmids engineered for secretion induced optimal Env-specific T-cell gamma interferon enzyme-linked immunospot responses in murine spleen, female reproductive tract, and lungs. While rBCG-induced T-cell responses to HIV-1 envelope in spleen were lower than those induced by adenovirus prime/recombinant vaccinia virus (rAd-rVV) boost, rBCG induced comparable responses to rAd-rVV immunization in the female reproductive tract and lungs. T-cell responses induced by rBCG were primarily CD4(+), although rBCG alone did not induce anti-HIV-1 antibody. However, rBCG could prime for a protein boost by HIV-1 envelope protein. Thus, rBCG can serve as a vector for induction of anti-HIV-1 consensus Env cellular responses at mucosal sites.

Gatekeeper role of 14-3-3tau protein in HIV-1 gp120-mediated apoptosis of human endothelial cells by inactivation of Bad

OBJECTIVE

HIV-1-associated dementia (HAD) is a major neurological complication often observed in the advanced stages of AIDS. We have reported that 14-3-3 proteins in cerebrospinal fluid, reflecting neuronal cell destruction, is a real-time marker of HAD progression. This study was designed to examine the role of 14-3-3 proteins in HAD.

DESIGN

An in-vitro human umbilical vein endothelial cells (HUVEC) model of gp120 protein-induced apoptosis to study the protective role of 14-3-3 in HIV-1 gp120/CXCR4-mediated cell death.

METHODS

The alpha-chemokine receptor-mediated cell death by HIV-1 envelope protein, gp120, the critical event that causes neuron loss and endothelial cell injury, was evaluated in HUVEC undergoing gp120-induced apoptosis through the CXCR4 receptor. We studied the effects of siRNA for each 14-3-3 isoform on the death of HUVEC treated with CXCR4-preferring gp120 (IIIB).

RESULTS

Gp120 increased the expression of 14-3-3tau in HUVEC. The binding of Gp120 to CXCR4 induced apoptosis of HUVEC through decreased binding of 14-3-3tau to the pro-apoptotic molecule, Bad. Treatment of the cells with dsRNA against 14-3-3tau enhanced the gp120-mediated dephosphorylation of Bad and its association with Bcl-XL in mitochondria, accelerating the gp120-induced apoptosis, whereas suppression of Bad by RNAi rescued the cells from apoptosis triggered by gp120.

CONCLUSIONS

The specific up-regulation of 14-3-3tau in HUVEC negatively regulated gp120/CXCR4-mediated cell death by protecting Bad dephosphorylation.

HIV-1 gp120 as well as alcohol affect blood-brain barrier permeability and stress fiber formation: involvement of reactive oxygen species

BACKGROUND

HIV-1 infection commonly leads to serious HIV-1-associated neurological disorders, such as HIV-1-associated encephalopathy and dementia. In addition, alcohol is commonly used and/or abused among AIDS patients, but it is unclear whether alcohol affects the disease progression and if it affects it, how this occurs. We hypothesized that alcohol could affect the blood-brain barrier (BBB) integrity and thus could affect the onset and/or progression of HIV-associated neurological disorders.

METHODS

Human brain microvascular endothelial cells (HBMEC) in a BBB model system were pretreated with alcohol (17 and 68 mM) and subsequently coexposed with HIV-1 gp120. Expression of chemokine receptors CCR3, CCR5, and CXCR4 was assessed by enzyme-linked immunosorbent assay and real-time polymerase chain reaction. Changes in the permeability of the HBMEC monolayer were assessed using paracellular markers [(3)H]inulin or propidium iodide. Actin rearrangements in HBMEC were visualized by fluorescence microscopy and viability assessed using Live/Dead stain.

RESULTS

Both gp120 and alcohol increased the permeability of the BBB model by up to 141%, without affecting HBMEC viability. Cotreatment with alcohol and gp120 did not result in a significant synergistic effect. Gp120 permeability involved chemokine receptor CCR5. Alcohol did not affect chemokine receptor expression on brain endothelial cells. Both gp120 and alcohol reorganized the cytoskeleton and induced stress fiber formation. Inhibition of reactive oxygen species (ROS) formation through NADPH blocked the effects of both gp120 and alcohol on permeability and stress fiber formation.

CONCLUSION

These results indicate that both HIV-1 gp120 and alcohol induce stress fibers, causing increased permeability of the human BBB endothelium. Alcohol (68 mM)-mediated permeability increase was linked to ROS formation. The alcohol-mediated physiological changes in the HBMEC monolayers may increase diffusion of plasma components and viral penetration across the BBB. This suggests that alcohol, especially at levels attained in heavy drinkers, can potentially contribute in a negative fashion to HIV-1 neuropathogenesis.

Neonatal intrahippocampal gp120 injection: an examination early in development

The presence of human immunodeficiency virus type 1 (HIV-1) in the brain is believed to be responsible for mediating the pathogenesis of neurological abnormalities through the viral toxins gp120 and Tat. Numerous studies indicate neurotoxic effects of the HIV-1-protein Tat, with demonstrated neurobehavioral and cognitive alterations. However, less clear is the neurotoxic effect of gp120 on neurobehavior. This study was designed to characterize the potential deficits in sensory-motor and preattentive functions, following intrahippocampal administration of gp120. Using a randomized-block design, male and female pups of eight Sprague-Dawley litters were injected bilaterally with either vehicle (VEH) (1 microl volume) or one of the three gp120 doses (1.29, 12.9, or 129 ng/microl) at postnatal day (P)1. Sensory-motor functions were assessed at P3, as measured by the righting reflex and at P8, as measured by negative geotaxis. At P24 animals were tested on preattentive processes, as indexed by sensorimotor gating. Sensorimotor gating was measured by prepulse inhibition (PPI) of the auditory startle response (ASR) (ISIs of 0, 8, 40, 80, 120, and 4000 ms, six trial blocks, Latin-square design). Results indicated gp120-induced neurotoxicity on the righting reflex but not negative geotaxis. For sensorimotor gating, the PPI test demonstrated a reduced inhibition response on peak ASR latency as the dose of gp120 increased. No effect was noted for response inhibition on peak ASR amplitude. These data suggest that intrahippocampal injection of gp120 (0, 1.29, 12.9, or 129 ng/microl) had transient neurotoxic effects on sensory-motor function and limited effects on preattentive processes early in development.

N-methyl-D-aspartate autoreceptors respond to low and high agonist concentrations by facilitating, respectively, exocytosis and carrier-mediated release of glutamate in rat hippocampus

Presynaptic NMDA autoreceptors regulating glutamate release have rarely been investigated. High-micromolar N-methyl-D-aspartate (NMDA) was reported to elicit glutamate release from hippocampal synaptosomes in a Ca(2+)-independent manner by reversal of excitatory amino acid transporters. The aim of this work was to characterize excitatory amino acid release evoked by low-micromolar NMDA from glutamatergic axon terminals. Purified rat hippocampal synaptosomes were prelabelled with [(3)H]D-aspartate ([(3)H]D-ASP) and exposed in superfusion to varying concentrations of NMDA in the presence of 1 microM glycine. The release of [(3)H]D-ASP and also that of endogenous glutamate provoked by 10 microM NMDA were external Ca(2+) dependent and sensitive to the NMDA channel blocker MK-801 but insensitive to the glutamate transporter inhibitor DL-TBOA, which, on the contrary, prevented the Ca(2+)-independent release evoked by 100 microM NMDA. The NMDA (10 microM) response was blocked by 1 nM Zn(2+) and 1 microM ifenprodil, compatible with the involvement of a NR1/NR2A/NR2B assembly, although the presence of two separate receptor populations, i.e., NR1/NR2A and NR1/NR2B, cannot be excluded. This response was strongly antagonized by submicromolar (0.01-1 microM) concentrations of kynurenic acid and was mimicked by quinolinic acid (1-100 microM) plus 1 microM glycine. Finally, the HIV-1 protein gp120 potently mimicked the NMDA co-agonists glycine and D-serine, being significantly effective at 30 pM. In conclusion, glutamatergic nerve terminals possess NMDA autoreceptors mediating different types of release when activated by different agonist concentrations: low-micromolar glutamate would potentiate glutamate exocytosis, whereas higher glutamate concentrations would also provoke carrier-mediated release.

HIV-1 gp120/V3-derived epitopes promote activation-induced cell death to superantigen-stimulated CD4+/CD45RO+ T cells

The third hypervirable (V3) domain of the HIV-1 envelope glycoprotein gp120 has been implicated in HIV pathogenesis via co-receptor usage of chemokine receptors CCR5 and CXCR4. As the protagonist cell populations in the asymptomatic phase of HIV-1 infection are infected macrophages and effector/memory (CD45RO+) CD4+ T cells that express CCR5, we established an in vitro model using human primary monocyte-derived macrophages and lymphocytes to investigate the role of V3 in affecting antigen presentation. We used staphylococcal enterotoxin A (SEA) as a superantigen at a low concentration of 1ng/ml, to activate naïve CD4+ T cells. Exposure of cells to SEA and lipoV3-liposomes increased the percentage of CD4+/CD45RO+/CCR5+ T cell population as compared to cells treated with SEA and plain liposomes. A consequent decrease of the percentage of CD4+/CD45RO+/CXCR4+ subset was observed. The V3-mediated activation was competitively inhibited by soluble V3-derived peptides with higher cationic charge. V3 enhanced also apoptosis as demonstrated by flow cytometry and intracellular calcium ion assays. These results reinforce the postulation that V3 alters the antigen presentation function itself, independent of specific antigens, thus leading to an enhanced activation-induced cell death (AICD) of responding T cells.

Intracerebroventricular infusions of gp120 inhibit weight gain and induce atrophy in the hippocampus and neostriatum without affecting cognition

The HIV envelope protein, gp120, has been proposed to be a key agent in the development of AIDS dementia complex (ADC). To elucidate CNS effects that gp120 alone may be inducing in ADC, the present study investigated changes in weight, motor activity, cognitive function and corresponding neuropathology in rats given daily bilateral infusions of gp120 intracerebroventricularly for 7 days. gp120 inhibited weight gain, but had no measurable effects on motor activity or water maze cognitive performance. Nonetheless, gp120 infusions did induce both hippocampal and neostriatal atrophy. Thus, gp120 alone can cause ADC-related neuropathologic and weight changes, but gp120 alone was not sufficient to induce impairments in spatial learning and memory.

Human immunodeficiency virus gp120-induced apoptosis of human neuroblastoma cells in the absence of CXCR4 internalization

The chemokine receptor CXCR4 functions as human immunodeficiency virus (HIV)-1 coreceptor and is involved in acquired immunodeficiency virus (AIDS) neuropathogenesis. CXCR4 is expressed by most cell types in the brain, including microglia, astrocytes, and neurons. Studies have shown that the HIV envelope protein gp120 binds to neuronal CXCR4 and activates signal transduction pathways leading to apoptosis. However, the natural CXCR4 ligand (CXCL12) has been referred to induce both neuronal survival and death. Here the authors used flow cytometry to determine whether gp120 and CXCL12 differ in their ability to induce CXCR4 internalization in the human neuroblastoma cells SH-SY5Y, which constitutively express CXCR4. As expected, increasing concentration of CXCL12 reduced surface expression of CXCR4 in a time-and concentration-dependent manner. Conversely, gp120IIIB (monomeric or oligomeric, in presence or absence of soluble CD4) did not change CXCR4 membrane levels. Similar results were obtained in a murine lymphocyte cell line (300-19) stably expressing human CXCR4. Nevertheless, gp120IIIB was still able to activate intracellular signaling and proapoptotic pathways, via CXCR4. These results show that gp120IIIB toxicity and signaling do not require CXCR4 internalization in SH-SY5Y cells, and suggest that the viral protein may alter normal CXCR4 trafficking thus, interfering with activation of prosurvival pathways.

Human immunodeficiency virus type 1 envelope glycoprotein gp120 induces tumor necrosis factor-alpha in astrocytes

gp120 induction of the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) was studied in cultures of purified astrocytes. Incubation of pure mouse cortical astrocytes with gp120 IIIB induced the expression of TNF-alpha mRNA, assessed by in situ hybridization. Anti- TNF-alpha immunocytochemical staining of gp120 IIIB stimulated astrocytes indicated the presence of TNF-alpha. gp120 IIIB treatment also stimulated secretion of bioactive TNF-alpha from astrocytes, which was prevented by inhibitors of transcription and translation. Hippocampal and cerebellar astrocytes displayed similar behaviors. Further, gp120 displayed cytotoxicity for astrocytes that depended on macromolecular synthesis. The data are the first to show gp120 IIIB induction of de novo TNF-alpha production by pure astrocytes. Because TNF-alpha exerts a wide array of effects in the brain of infected individuals and has HIV-1 inducing activity as well, induction of this cytokine by gp120 IIIB in astrocytes may contribute importantly to the pathogenesis of AIDS dementia complex. Since TNF-alpha can stimulate astrocyte reactivity and proliferation by an autocrine mechanism, the extent of the gp120 effect could conceivably increase with HIV-1 disease progression in a self-amplifying loop, involving other cell types, thus favoring both virus persistence and a chronic disease state.

Increased immunogenicity of human immunodeficiency virus gp120 engineered to express Galalpha1-3Galbeta1-4GlcNAc-R epitopes

The glycan shield comprised of multiple carbohydrate chains on the human immunodeficiency virus (HIV) envelope glycoprotein gp120 helps the virus to evade neutralizing antibodies. The present study describes a novel method for increasing immunogenicity of gp120 vaccine by enzymatic replacement of sialic acid on these carbohydrate chains with Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal) epitopes. These epitopes are ligands for the natural anti-Gal antibody constituting approximately 1% of immunoglobulin G in humans. We hypothesize that vaccination with gp120 expressing alpha-gal epitopes (gp120(alphagal)) results in in vivo formation of immune complexes with anti-Gal, which targets vaccines for effective uptake by antigen-presenting cells (APC), due to interaction between the Fc portion of the antibody and Fcgamma receptors on APC. This in turn results in effective transport of the vaccine to lymph nodes and effective processing and presentation of gp120 immunogenic peptides by APC for eliciting a strong anti-gp120 immune response. This hypothesis was tested in alpha-1,3-galactosyltransferase knockout mice, which produce anti-Gal. Mice immunized with gp120(alphagal) produced anti-gp120 antibodies in titers that were >100-fold higher than those measured in mice immunized with comparable amounts of gp120 and effectively neutralized HIV. T-cell response, measured by ELISPOT, was much higher in mice immunized with gp120(alphagal) than in mice immunized with gp120. It is suggested that gp120(alphagal) can serve as a platform for anti-Gal-mediated targeting of additional vaccinating HIV proteins fused to gp120(alphagal), thereby creating effective prophylactic vaccines.

Antioxidant enzyme gene delivery to protect from HIV-1 gp120-induced neuronal apoptosis

Human immunodeficiency virus-1 (HIV-1) infection in the central nervous system (CNS) may lead to neuronal loss and progressively deteriorating CNS function: HIV-1 gene products, especially gp120, induce free radical-mediated apoptosis. Reactive oxygen species (ROS), are among the potential mediators of these effects. Neurons readily form ROS after gp120 exposure, and so might be protected from ROS-mediated injury by antioxidant enzymes such as Cu/Zn-superoxide dismutase (SOD1) and/or glutathione peroxidase (GPx1). Both enzymes detoxify oxygen free radicals. As they are highly efficient gene delivery vehicles for neurons, recombinant SV40-derived vectors were used for these studies. Cultured mature neurons derived from NT2 cells and primary fetal neurons were transduced with rSV40 vectors carrying human SOD1 and/or GPx1 cDNAs, then exposed to gp120. Apoptosis was measured by terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay. Transduction efficiency of both neuron populations was >95%, as assayed by immunostaining. Transgene expression was also ascertained by Western blotting and direct assays of enzyme activity. Gp120 induced apoptosis in a high percentage of unprotected NT2-N. Transduction with SV(SOD1) and SV(GPx1) before gp120 challenge reduced neuronal apoptosis by >90%. Even greater protection was seen in cells treated with both vectors in sequence. Given singly or in combination, they protect neuronal cells from HIV-1-gp120 induced apoptosis. We tested whether rSV40 s can deliver antioxidant enzymes to the CNS in vivo: intracerebral injection of SV(SOD1) or SV(GPx1) into the caudate putamen of rat brain yielded excellent transgene expression in neurons. In vivo transduction using SV(SOD1) also protected neurons from subsequent gp120-induced apoptosis after injection of both into the caudate putamen of rat brain. Thus, SOD1 and GPx1 can be delivered by SV40 vectors in vitro or in vivo. This approach may merit consideration for therapies in HIV-1-induced encephalopathy.

HIV-1 viral envelope glycoprotein gp120 triggers an inflammatory response in cultured rat astrocytes and regulates the functional expression of P-glycoprotein

In this work, we examined the ability of gp120, a human immunodeficiency virus-1 (HIV-1) viral envelope glycoprotein, to trigger the innate immune response in astrocytes, an HIV-1 brain cellular target, and we investigated the functional expression of the ATP-binding cassette membrane transporter P-glycoprotein (P-gp) in primary cultures of rat astrocytes treated with gp120 or cytokines [tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6]. Standard 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium and d-mannitol uptake assays confirmed that HIV-1(96ZM651) gp120 treatment did not alter cell viability or membrane permeability. Semiquantitative reverse-transcriptase polymerase chain reaction analysis and enzyme-linked immunosorbent assay demonstrated increased TNF-alpha, IL-1beta, and IL-6 mRNA and protein expression in cultures treated with HIV-1(96ZM651) gp120, suggesting in vitro activation of immune responses. Cytokine secretion was detected when CXCR4 but not CCR5 was inhibited with a specific antibody, implying that cytokine secretion is primarily mediated via CCR5 in astrocytes triggered with HIV-1(96ZM651) gp120. P-gp protein expression was increased in astrocyte cultures exposed to TNF-alpha (2.9-fold) or IL-1beta (1.6-fold) but was decreased profoundly in the presence of IL-6 (8.9-fold), suggesting that IL-6 is primarily involved in modulating P-gp expression. In parallel, after HIV-1(96ZM651) gp120 treatment, immunoblotting analysis showed a significant decrease in P-gp expression (4.7-fold). Furthermore, the accumulation of two P-gp substrates, digoxin and saquinavir (an HIV-1 protease inhibitor), was enhanced (1.5- to 1.8-fold) in HIV-1(96ZM651) gp120-treated astrocyte monolayers but was not altered by P-gp inhibitors [e.g., valspodar (PSC833) and elacridar (GF120918)], suggesting a loss of transport activity. Taken together, these data imply that HIV-1(96ZM651) gp120 or cytokine treatment modulate P-gp functional expression in astrocytes, which may lead to complex drug-transporter interactions during HIV-1 encephalitis-associated immune responses.

Induction of glial fibrillary acidic protein expression in astrocytes by nitric oxide

Increased expression of glial fibrillary acidic protein (GFAP) represents astroglial activation and gliosis during neurodegeneration. However, the molecular mechanism behind increased expression of GFAP in astrocytes is poorly understood. The present study was undertaken to explore the role of nitric oxide (NO) in the expression of GFAP. Bacterial lipopolysachharides (LPSs) induced the production of NO and the expression of GFAP in mouse primary astrocytes. Either a scavenger of NO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO)] or an inhibitor of inducible nitric oxide synthase [l-N6-(I-iminoethyl)-lysine hydrochloride] blocked this induction of GFAP expression. Similarly, other inducers of NO production such as interferon-gamma, interleukin-1beta, human immunodeficiency virus type 1 gp120, fibrillar amyloid beta peptides, and double-stranded RNA (polyinosinic-polycytidilic acid) also induced the expression of GFAP through NO. The role of NO in the expression of GFAP was supported further by increased expression of GFAP by S-nitroso glutathione (GSNO), an NO donor. Interestingly, inhibition of nuclear factor kappaB (NF-kappaB) suppressed LPS- but not GSNO-induced expression of GFAP, suggesting that NO does not require NF-kappaB to induce GFAP and that NF-kappaB functions upstream of NO production. However, inhibition of LPS- and GSNO-induced expression of GFAP either by NS-2028 [a specific inhibitor of guanylate cyclase (GC)] or by KT5823 [a specific inhibitor of cGMP-activated protein kinase (PKG)], and induction of GFAP expression by either 8-Br cGMP (a cell-permeable cGMP analog) or MY-5445 (a specific inhibitor of cGMP phosphodiesterase) suggests that NO induces GFAP via GC-cGMP-PKG. This study illustrates a novel biological role of NO in regulating the expression of GFAP in astrocytes through the GC-cGMP-PKG pathway that may participate in the pathogenesis of neurodegenerative disorders.

Human immunodeficiency virus type 1 gp120 inhibits long-term potentiation via chemokine receptor CXCR4 in rat hippocampal slices

Human immunodeficiency virus type 1 (HIV-1) infection in its human host often results in progressive dementia and encephalopathy in adults and children, respectively. The mechanisms underlying virus-induced neurocognitive dysfunction are not fully understood. However, several studies strongly suggest that secretory viral and immune products from infected brain macrophages and microglia affect the onset and tempo of disease. One critical neurotoxin among these secretory products is the HIV-1 envelope glycoprotein gp120. To better understand how HIV-1 gp120 may affect cognitive function, we studied its effects on long-term potentiation (LTP) in the CA1 region of rat hippocampus, the brain region best linked to learning and memory. Although no effects were observed on basal synaptic transmission, HIV-1 gp120 inhibited LTP in a concentration-dependent manner in the presence of gamma-aminobutyric acid type A (GABAA) receptor antagonist. Heat-inactivated gp120 failed to block LTP. The HIV-1 gp120-mediated LTP inhibition was blocked by T140, a chemokine receptor CXCR4 antagonist, demonstrating gp120 inhibition of LTP via CXCR4. HIV-1 gp120 V3 loop peptides mimicked the inhibitory effects of HIV-1 gp120 protein on LTP. Monoclonal antibodies against the V3 loop epitope KRIHI eliminated the HIV-1 gp120 effects on LTP. These results further underscore the importance of HIV-1 gp120 in the pathogenesis of HIV-1-associated cognitive impairments seen during progressive viral infection.

Mechanisms of apoptosis induction by the HIV-1 envelope

The envelope glycoprotein complex (Env) of human immunodeficiency virus-1 (HIV-1) can induce apoptosis by a cornucopia of distinct mechanisms. A soluble Env derivative, gp120, can kill cells through signals that are transmitted by chemokine receptors such as CXCR4. Cell surface-bound Env (gp120/gp41), as present on the plasma membrane of HIV-1-infected cells, can kill uninfected bystander cells expressing CD4 and CXCR4 (or similar chemokine receptors, depending on the Env variant) by at least three different mechanisms. First, a transient interaction involving the exchange of lipids between the two interacting cells ('the kiss of death') may lead to the selective death of single CD4-expressing target cells. Second, fusion of the interacting cells may lead to the formation of syncytia which then succumb to apoptosis in a complex pathway involving the activation of several kinases (cyclin-dependent kinase-1, Cdk1; checkpoint kinase-2, Chk2; mammalian target of rapamycin, mTOR; p38 mitogen-activated protein kinase, p38 MAPK; inhibitor of NF-kappaB kinase, IKK), as well as the activation of several transcription factors (NF-kappaB, p53), finally resulting in the activation of the mitochondrial pathway of apoptosis. Third, if the Env-expressing cell is at an early stage of imminent apoptosis, its fusion with a CD4-expressing target cell can precipitate the death of both cells, through a process that may be considered as contagious apoptosis and which does not involve Cdk1, mTOR, p38 nor p53, yet does involve mitochondria. Activation of some of the above- mentioned lethal signal transducers have been detected in patients' tissues, suggesting that HIV-1 may indeed trigger apoptosis through molecules whose implication in Env-induced killing has initially been discovered in vitro.

Cell death in HIV dementia

Many patients infected with human immunodeficiency virus type-1 (HIV-1) suffer cognitive impairment ranging from mild to severe (HIV dementia), which may result from neuronal death in the basal ganglia, cerebral cortex and hippocampus. HIV-1 does not kill neurons by infecting them. Instead, viral proteins released from infected glial cells, macrophages and/or stem cells may directly kill neurons or may increase their vulnerability to other cell death stimuli. By binding to and/or indirectly activating cell surface receptors such as CXCR4 and the N-methyl-D-aspartate receptor, the HIV-1 proteins gp120 and Tat may trigger neuronal apoptosis and excitotoxicity as a result of oxidative stress, perturbed cellular calcium homeostasis and mitochondrial alterations. Membrane lipid metabolism and inflammation may also play important roles in determining whether neurons live or die in HIV-1-infected patients. Drugs and diets that target oxidative stress, excitotoxicity, inflammation and lipid metabolism are in development for the treatment of HIV-1 patients.

Apoptosis in SIV infection

Pathogenic human immunodeficiency virus (HIV)/Simian immunodeficiency virus (SIV) infection is associated with increased T-cell apoptosis. In marked contrast to HIV infection in humans and SIV infection in macaques, the SIV infection of natural host species is typically nonpathogenic despite high levels of viral replication. In these nonpathogenic primate models, no observation of T-cell apoptosis was observed, suggesting that either SIV is less capable of directly inducing apoptosis in natural hosts (likely as a result of coevolution/coadaptation with the host) or, alternatively, that the indirect T-cell apoptosis plays the key role in determining the HIV-associated T-cell depletion and progression to acquired immune deficiency syndrome (AIDS). Understanding the molecular and cellular mechanisms responsible for the disease-free equilibrium in natural hosts for SIV infection, including those determining the absence of high levels of T-cell apoptosis, is likely to provide important clues regarding the mechanisms of AIDS pathogenesis in humans.

HIV-1 infection and AIDS: consequences for the central nervous system

Infection with the human immunodeficiency virus-1 (HIV-1) can induce severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia. After infiltrating peripheral immune competent cells, in particular macrophages, HIV-1 provokes a neuropathological response involving all cell types in the brain. HIV-1 also incites activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways and disrupt neuronal and glial function. This review will discuss recently uncovered pathologic neuroimmune and degenerative mechanisms contributing to neuronal damage induced by HIV-1 and potential approaches for development of future therapeutic intervention.