gp120, a human immunodeficiency virus-1 coat protein, augments excitotoxic hippocampal injury in perinatal rats

HIV-1 Glycoprotein 120 Enhancement of N-Methyl-D-Aspartate NMDA Receptor-Mediated Excitatory Postsynaptic Currents: Implications for HIV-1-Associated Neural Injury

It is widely accepted that human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein 120 (gp120) plays an important role in HIV-1-induced neural injury and pathogenesis of HIV-1-associated dementia (HAND). Multiple pathways have been proposed for gp120-induced neurotoxicity, amongst is the activation of N-Methyl-D-Aspartate receptors (NMDARs). It has been shown that gp120 causes neuronal injury or death and gp120 transgenic mice exhibit neurological similarity to that of HAND, all of which can be blocked or attenuated by NMDAR antagonists. Several lines of evidence indicate the subtype and location of activated NMDARs are key determinants of the nature of NMDAR physiology. To examine the subtype and the location of NMDARs affected by gp120, we studied gp120 on subtype NMDAR-mediated EPSCs in the CA1 region of rat hippocampal slices through "blind" whole-cell patch recordings. Our results showed bath application of gp120 increased both NR2A- and NR2B-mediated EPSCs possibly via a presynaptic mechanism, with much stronger effect on NR2B-mediated EPSCs. In contrast, gp120 failed on enhancing AMPA receptor-mediated EPSCs. Ca²⁺ imaging studies revealed that gp120 potentiated glutamate-induced increase of intracellular Ca²⁺ concentration in rat hippocampal neuronal cultures which were blocked by a NMDAR antagonist, but not by an AMPA receptor antagonist, indicating gp120 induces Ca²⁺ influx through NMDARs. Further investigations demonstrated that gp120 increased the EPSCs mediated by extrasynaptic NR2BRs. Taken together, these results demonstrate that gp120 interacts with both NR2A and NR2B subtypes of NMDARs with a predominant action on the extrasynaptic NR2B, implicating a role NR2B may play in HIV-1-associated neuropathology.

Loss of cerebellar neurons in the progression of lentiviral disease: effects of CNS-permeant antiretroviral therapy

BACKGROUND

The majority of investigations on HIV-associated neurocognitive disorders (HAND) neglect the cerebellum in spite of emerging evidence for its role in higher cognitive functions and dysfunctions in common neurodegenerative diseases.

METHODS

We systematically investigated the molecular and cellular responses of the cerebellum as contributors to lentiviral infection-induced neurodegeneration, in the simian immunodeficiency virus (SIV)-infected rhesus macaque model for HIV infection and HAND. Four cohorts of animals were studied: non-infected controls, SIV-infected asymptomatic animals, and SIV-infected AIDS-diseased animals with and without brain-permeant antiretroviral treatment. The antiretroviral utilized was 6-chloro-2',3'-dideoxyguanosine (6-Cl-ddG), a CNS-permeable nucleoside reverse transcriptase inhibitor. Quantitation of granule cells and Purkinje cells, of an established biomarker of SIV infection (gp41), of microglial/monocyte/macrophage markers (IBA-1, CD68, CD163), and of the astroglial marker (GFAP) were used to reveal cell-specific cerebellar responses to lentiviral infection and antiretroviral therapy (ART). The macromolecular integrity of the blood brain barrier was tested by albumin immunohistochemistry.

RESULTS

Productive CNS infection was observed in the symptomatic stage of disease, and correlated with extensive microglial/macrophage and astrocyte activation, and widespread macromolecular blood brain barrier defects. Signs of productive infection, and inflammation, were reversed upon treatment with 6-Cl-ddG, except for a residual low-grade activation of microglial cells and astrocytes. There was an extensive loss of granule cells in the SIV-infected asymptomatic cohort, which was further increased in the symptomatic stage of the disease and persisted after 6-Cl-ddG (administered after the onset of symptoms of AIDS). In the symptomatic stage, Purkinje cell density was reduced. Purkinje cell loss was likewise unaffected by 6-Cl-ddG treatment at this time.

CONCLUSIONS

Our findings suggest that neurodegenerative mechanisms are triggered by SIV infection early in the disease process, i. e., preceding large-scale cerebellar productive infection and marked neuroinflammation. These affect primarily granule cells early in disease, with later involvement of Purkinje cells, indicating differential vulnerability of the two neuronal populations. The results presented here indicate a role for the cerebellum in neuro-AIDS. They also support the conclusion that, in order to attenuate the development of motor and cognitive dysfunctions in HIV-positive individuals, CNS-permeant antiretroviral therapy combined with anti-inflammatory and neuroprotective treatment is indicated even before overt signs of CNS inflammation occur.

Curcumin improves synaptic plasticity impairment induced by HIV-1gp120 V3 loop

Curcumin has been shown to significantly improve spatial memory impairment induced by HIV-1 gp120 V3 in rats, but the electrophysiological mechanism remains unknown. Using extracellular microelectrode recording techniques, this study confirmed that the gp120 V3 loop could suppress long-term potentiation in the rat hippocampal CA1 region and synaptic plasticity, and that curcumin could antagonize these inhibitory effects. Using a Fura-2/AM calcium ion probe, we found that curcumin resisted the effects of the gp120 V3 loop on hippocampal synaptosomes and decreased Ca²⁺ concentration in synaptosomes. This effect of curcumin was identical to nimodipine, suggesting that curcumin improved the inhibitory effects of gp120 on synaptic plasticity, ameliorated damage caused to the central nervous system, and might be a potential neuroprotective drug.

HIV Associated Neurocognitive Disorders

Human immunodeficiency virus type 1 is associated with the development of neurocognitive disorders in many infected individuals, including a broad spectrum of motor impairments and cognitive deficits. Despite extensive research, the pathogenesis of HIV-associated neurocognitive disorders (HAND) is still not clear. This review provides a comprehensive view of HAND, including HIV neuroinvasion, HAND diagnosis and different level of disturbances, influence of highly-active antiretroviral therapy to HIV-associated dementia (HAD), possible pathogenesis of HAD, etc. Together, this review will give a thorough and clear understanding of HAND, especially HAD, which will be vital for future research, diagnosis and treatment.

Wingless-type mammary tumor virus integration site family, member 5A (Wnt5a) regulates human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein 120 (gp120)-induced expression of pro-inflammatory cytokines via the Ca2+/calmodulin-dependent protein kinase II (CaMKII) and c-Jun N-terminal kinase (JNK) signaling pathways

BACKGROUND

HIV-1 infection causes chronic neuroinflammation in the central nervous system (CNS).

RESULTS

The spinal cytokine up-regulation induced by HIV-1 gp120 protein depends on Wnt5a/CaMKII and/or Wnt5a/JNK pathways.

CONCLUSION

gp120 stimulates cytokine expression in the spinal cord dorsal horn by activating Wnt5a signaling.

SIGNIFICANCE

The finding reveals Wnt signaling-mediated novel mechanisms by which HIV-1 may cause neuroinflammation. Chronic expression of pro-inflammatory cytokines critically contributes to the pathogenesis of HIV-associated neurological disorders (HANDs), but the host mechanism that regulates the HIV-induced cytokine expression in the CNS remains elusive. Here, we present evidence for a crucial role of Wnt5a signaling in the expression of pro-inflammatory cytokines in the spinal cord induced by a major HIV-envelope protein, gp120. Wnt5a is mainly expressed in spinal neurons, and rapidly up-regulated by intrathecal injection (i.t.) of gp120. We show that inhibition of Wnt5a by specific antagonists blocks gp120-induced up-regulation of IL-1β, IL-6, and TNF-α in the spinal cord. Conversely, injection (i.t.) of purified recombinant Wnt5a stimulates the expression of these cytokines. To elucidate the role of the Wnt5a-regulated signaling pathways in gp120-induced cytokine expression, we have focused on CaMKII and JNKs, the well characterized down-stream targets of Wnt5a signaling. We find that Wnt5a is required for gp120 to activate CaMKII and JNK signaling. Furthermore, we demonstrate that the Wnt5a/CaMKII pathway is critical for the gp120-induced expression of IL-1β, whereas the Wnt5a/JNK pathway is for TNF-α expression. Meanwhile, the expression of IL-6 is co-regulated by both pathways. These results collectively suggest that Wnt5a signaling cascades play a crucial role in the regulation of gp120-induced expression of pro-inflammatory cytokines in the CNS.

Morphine efficacy is altered in conditional HIV-1 Tat transgenic mice

Opiate abuse reportedly can exaggerate complications of human immunodeficiency virus type-1 (HIV-1) infection in the central nervous system (CNS), while opiate drugs are often indicated in the treatment of HIV-1-related neuropathic pain. Despite this quandary, few studies have assessed the relationship between the duration or extent of HIV-1 infection and the intrinsic neurobehavioral responsiveness to opioids. To address this problem, doxycycline (DOX)-inducible HIV-Tat(1-86) transgenic mice were used as a model for HIV-1-associated neurocognitive disorders, which permitted the regulation of Tat exposure and duration. The effects of continuous Tat induction on the activity of morphine were examined at weekly intervals using standard behavioral assays for nociception and motor function. In the spinal cord, Tat mRNA levels did not increase until the second and third weeks following induction, which corresponded to a significant loss of morphine antinociception as assessed in the tail-flick test. Alternatively, in the striatum, sustained increases in Tat mRNA expression during the second week of induction coincided with significant decreases in rotarod performance and interactions with morphine. Importantly, the behavioral effects of morphine differed depending on the timing and location of Tat expression, with increases in Tat transcript levels in the spinal cord and striatum corresponding to significant alterations in morphine-dependent nociception and rotarod performance, respectively. Assuming Tat levels contribute to the clinical manifestations of HIV-1, the results suggest that regional differences in viral load and opioid phenotype might influence the nature and degree that opiate responsiveness is altered in HIV-1-infected individuals.

HIV-1 gp120-induced axonal injury detected by accumulation of β-amyloid precursor protein in adult rat corpus callosum

HIV-1 brain infection induces neurodegeneration. While most studies focus on HIV-1-mediated neuronal injury, relatively few have investigated HIV-1-associated white matter damage. Corpus callosum (CC) is one of frequently involved white matter structures in HIV-1-associated white matter damage. Utilizing a model of ex vivo treatment of brain slice containing CC with HIV-1 glycoprotein 120 (gp120), we examined axonal injury by analyzing β-amyloid precursor protein (β-APP) accumulation in the axon. Incubation of CC slice with gp120 produced a significant higher density of β-APP in the CC tissue compared with non-gp120-treated controls, suggesting the presence of axonal damage in the CC. The gp120-induced CC axonal damage was blocked by a chemokine CXCR4 receptor antagonist T140 but not by an NMDA receptor blocker MK801 as demonstrated by Western blot analysis of β-APP, indicating that gp120 evokes the CC axonal injury through CXCR4 receptor. Immunocytochemical studies revealed a surprisingly high density of CXCR4-positive immunoreactivity in the CC. The CXCR4-positive labeling was distributed along the nerve fibers. Moreover, double labeling of anti-CXCR4 with either anti-neuronal nuclei or anti-myelin/oligodendrocyte-specific protein antibody revealed co-localization of CXCR4 and myelin/oligodendrocytes in some fiber-like structures, inferring that some neurons and oligodendrocytes in the CC express CXCR4. Taken together, these results indicate that gp120 induced axonal damage via CXCR4 in the CC.

The endocannabinoid system in gp120-mediated insults and HIV-associated dementia

Endocannabinoids (eCBs) include a group of lipid mediators that act as endogenous agonists at cannabinoid (CB(1), CB(2)) and vanilloid (TRPV1) receptors. In the last two decades a number of eCBs-metabolizing enzymes have been discovered that, together with eCBs and congeners, target receptors and proteins responsible for their transport and intracellular trafficking form the so-called "endocannabinoid system" (ECS). Within the central nervous system ECS elements participate in neuroprotection against neuroinflammatory/neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and multiple sclerosis. More recently, a role for eCBs has been documented also in human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120-mediated insults, and in HIV-associated dementia (HAD). The modulation of ECS in the latter disease conditions is the subject of this review, that will also address the molecular mechanisms underlying the neuroprotective effects of eCBs. In particular, the interactions between neurons and glia during neuroinflammation, and the alterations of ECS in these cells upon gp120 insults and HAD will be discussed, along with the potential therapeutic exploitation of ECS-oriented drugs for the treatment of HAD and related disorders.

Enhanced PD-1 expression by T cells in cerebrospinal fluid does not reflect functional exhaustion during chronic human immunodeficiency virus type 1 infection

During chronic viral infections, T cells are exhausted due to constant antigen exposure and are associated with enhanced programmed death 1 (PD-1) expression. Deficiencies in the PD-1/programmed death-ligand 1 (PD-L1) pathway are associated with autoimmune diseases, including those of the central nervous system (CNS). To understand the role of PD-1 expression in regulating T-cell immunity in the CNS during chronic infection, we characterized PD-1 expression in cerebrospinal fluid (CSF) and blood of individuals with chronic human immunodeficiency virus type 1 (HIV-1) infection. PD-1 expression was higher on HIV-specific CD8(+) T cells than on total CD8(+) T cells in both CSF and blood. PD-1 expression on CSF T cells correlated positively with CSF HIV-1 RNA and inversely with blood CD4(+) T-cell counts, suggesting that HIV-1 infection drives higher PD-1 expression on CSF T cells. However, in every HIV-positive individual, PD-1 expression was higher on T cells in CSF than on those in blood, despite HIV-1 RNA levels being lower. Among healthy HIV-negative controls, PD-1 expression was higher in CSF than in blood. Furthermore, frequencies of the senescence marker CD57 were lower on CSF T cells than on blood T cells, consistent with our prior observation of enhanced ex vivo functional capacity of CSF T cells. The higher PD-1 expression level on CSF T cells therefore does not reflect cellular exhaustion but may be a mechanism to downregulate immune-mediated tissue damage in the CNS. As inhibition of the PD-1/PD-L1 pathway is pursued as a therapeutic option for viral infections, potential effects of such a blockade on development of autoimmune responses in the CNS should be considered.

Enhancement of human immunodeficiency virus (HIV)-specific CD8+ T cells in cerebrospinal fluid compared to those in blood among antiretroviral therapy-naive HIV-positive subjects

During untreated human immunodeficiency virus type 1 (HIV-1) infection, virus-specific CD8(+) T cells partially control HIV replication in peripheral lymphoid tissues, but host mechanisms of HIV control in the central nervous system (CNS) are incompletely understood. We characterized HIV-specific CD8(+) T cells in cerebrospinal fluid (CSF) and peripheral blood among seven HIV-positive antiretroviral therapy-naïve subjects. All had grossly normal brain magnetic resonance imaging and spectroscopy and normal neuropsychometric testing. Frequencies of epitope-specific CD8(+) T cells by direct tetramer staining were on average 2.4-fold higher in CSF than in blood (P = 0.0004), while HIV RNA concentrations were lower. Cells from CSF were readily expanded ex vivo and responded to a broader range of HIV-specific human leukocyte antigen class I restricted optimal peptides than did expanded cells from blood. HIV-specific CD8(+) T cells, in contrast to total CD8(+) T cells, in CSF and blood were at comparable maturation states, as assessed by CD45RO and CCR7 staining. The strong relationship between higher T-cell frequencies and lower levels of viral antigen in CSF could be the result of increased migration to and/or preferential expansion of HIV-specific T cells within the CNS. This suggests an important role for HIV-specific CD8(+) T cells in control of intrathecal viral replication.

Neonatal intrahippocampal injection of the HIV-1 proteins gp120 and Tat: differential effects on behavior and the relationship to stereological hippocampal measures

HIV-1 proteins, such as Tat and gp120, are believed to play a crucial role in the central nervous system (CNS) pathology of acquired immune deficiency syndrome (AIDS). The present study sought to determine the potential role of Tat and/or gp120 on behavioral development and the relationship to the long-term effects of the HIV-1 proteins on the rat hippocampus. Male pups of 13 Sprague-Dawley litters were bilaterally injected on postnatal day (P)1. Every litter contributed an animal to each of four treatment condition: VEH (0.5 microl sterile buffer), gp120 (100 ng), Tat (25 microg) or combined gp120+Tat (100 ng+25 microg). Body weight was not affected by either protein treatment. Tat revealed a transient effect on many of the behavioral assessments early in development as well as on preattentive processes and spatial memory in adulthood. Gp120 had more selective effects on negative geotaxis (P8-P10) and on locomotor activity (P94-P96). Combined gp120+Tat effects were noted for eye opening with potential interactive effects of gp120 and Tat on negative geotaxis. Anatomical assessment at approximately 7 1/2 months of age was conducted by using design-based stereology to quantify the total cell number in five hippocampal subregions [granule layer (GL), hilus of the dentate gyrus (DGH), cornu ammonis fields (CA)2/3, CA1, and subiculum (SUB)] [Fitting, S., Booze, R.M., Hasselrot, U., Mactutus, C.F., 2007a. Differential long-term neurotoxicity of HIV-1 proteins in the rat hippocampal formation: a design-based stereological study. Hippocampus 18(2), 135-147]. A relationship between early reflex development and estimated cell number in the adult hippocampus was indicated by simple regression analyses. In addition, estimated number of neurons and astrocytes in the DGH explained 81% of the variance of the distribution of searching behavior in the probe test. Collectively, these data indicate that the DGH may participate in the spatial memory alterations observed in adulthood consequent to neonatal exposure to HIV-1 proteins.

NeuroAIDS: characteristics and diagnosis of the neurological complications of AIDS

The neurological complications of AIDS (NeuroAIDS) include neurocognitive impairment and HIV-associated dementia (HAD; also known as AIDS dementia and HIV encephalopathy). HAD is the most significant and devastating central nervous system (CNS) complications associated with HIV infection. Despite recent advances in our knowledge of the clinical features, pathogenesis, and neurobiological aspects of HAD, it remains a formidable scientific and therapeutic challenge. An understanding of the mechanisms of HIV neuroinvasion, CNS proliferation, and HAD pathogenesis provide a basis for the interpretation of the diagnostic features of HAD and its milder form, HIV-associated minor cognitive/motor disorder (MCMD). Current diagnostic strategies are associated with significant limitations, but it is hoped that the use of biomarkers may assist researchers and clinicians in predicting the onset of the disease process and in evaluating the effects of new therapies.

Differential long-term neurotoxicity of HIV-1 proteins in the rat hippocampal formation: a design-based stereological study

The human immunodeficiency virus type 1 (HIV-1) proteins, gp120 and Tat, are believed to play a role in mediating central nervous system (CNS) pathology in HIV-1 infected patients. Using design-based stereology, we examined the role of neonatal intrahippocampal injections of gp120 and Tat on the adult hippocampus ( approximately 7(1/2) month). Postnatal day (P)1-treated Sprague-Dawley rats were bilaterally injected with vehicle (VEH, 0.5 microl sterile buffer), gp120 (100 ng), Tat (25 microg) or combined gp120 + Tat (100 ng + 25 microg). Using Nissl-stained tissue sections, we quantified total neurons in five subregions of the rat hippocampus [granual layer (GL), hilus of the dentate gyrus (DGH), cornu ammonis fields (CA)2/3, CA1, and subiculum (SUB)], and total glial cells (astrocytes and oligodendrocytes) in two subregions (DGH and SUB). Estimates of cell area and cell volume were taken in the DGH. There was a significant reduction of neuron number in the CA2/3 subfield by Tat and gp120, and a significant reduction in the DGH by Tat only. For glial cells, numbers of astrocytes in the DGH and SUB were increased by the Tat protein, whereas no effects were noted for gp120. Finally, for oligodendrocytes Tat increased cell number in the DGH but not in any other region; gp120 had no detectable effect in any brain region. Estimates of cell area and cell volume of the three different cell types revealed no significant differences between treatments. Collectively, these results suggest differential effects of gp120 and Tat on the estimated total number of neurons, as well as on the number of glial cells.

Neurobiology of HIV

The importance of HIV cognitive impairment, including HIV associated dementia (HAD) and minor cognitive/motor disorder, has continued in the era of highly active antiretroviral therapy (HAART). Despite the relative efficacy of HAART in controlling HIV disease, there is no treatment which specifically targets the cause of HAD nor promotes neuronal protection from the effects of the virus. Much work has been done to elucidate the complex signalling pathways, effects of virus and viral proteins, and dysregulation of endogenous targets which lead to HIV associated neurotoxicity, but the concise mechanism remains elusive. It is widely accepted that the majority of viral replication in the brain occurs in monocyte derived macrophages (MDM) and microglia, and immune activation of these cells, along with astrocytic cells, may be the most important cause of neurotoxicity in the central nervous system (CNS). Additional complications arise when co-factors such as drug use, age related neuropathology, and other viruses are present. Further exploration of the molecular mechanisms leading to HIV neurotoxicity and neurodegeneration may reveal targets for prophylactic neuroprotective or other CNS-specific drugs. Given the variable success of the current HAART drugs against virus in the CNS, such therapies would greatly benefit the HIV infected population as they live longer and more productive lives.

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.

Neonatal intrahippocampal glycoprotein 120 injection: the role of dopaminergic alterations in prepulse inhibition in adult rats

Following neonatal hippocampal administration on postnatal day 1, the dose-response effects of the human immunodeficiency virus 1 protein glycoprotein 120 (gp120) were studied in vivo on prepulse inhibition (PPI) in adulthood. Furthermore, the role of dopaminergic alterations was examined as a within-subject factor. Using a randomized-block design, male and female pups of eight Sprague-Dawley litters were injected bilaterally with either vehicle (1 microl volume) or gp120 (1.29, 12.9, or 129 ng/microl). At 9 months of age, rats were injected s.c. with saline (SAL) (0.1 ml/kg) and tested on preattentive processes, as indexed by sensorimotor gating. Sensorimotor gating was measured by PPI of the auditory startle response (ASR) [interstimulus intervals (ISIs) of 0, 8, 40, 80, 120, and 4000 ms, six trial blocks, Latin square design]. One month later, the animals were treated with a D(1)/D(2) agonist, apomorphine (APO) (0.1 mg/kg) and again tested for PPI. A significant attenuation of the baseline ASR by APO was noted. No significant effects were noted on control ASR trials (ISIs, 0 and 4000 ms). For the SAL condition, response inhibition was significantly reduced as a function of gp120 dose, and the inflection of the inhibition curve was significantly altered for the high-gp120 dose-treated animals. A gp120 treatment x APO drug interaction was evident on amplitude, but not latency, of the response inhibition, with an enhanced inhibition in the APO condition, collapsed across ISIs (08-120 ms) as the neonatal-injected gp120 dose increased. Use of APO to probe integrity of the dopaminergic system suggests long-lasting alterations in neuronal responses consequent to neonatal gp120 exposure.

HIV-1 associated dementia: symptoms and causes

Despite the use of highly active antiretroviral therapy (HAART), neuronal cell death remains a problem that is frequently found in the brains of HIV-1-infected patients. HAART has successfully prevented many of the former end-stage complications of AIDS, however, with increased survival times, the prevalence of minor HIV-1 associated cognitive impairment appears to be rising among AIDS patients. Further, HIV-1 associated dementia (HAD) is still prevalent in treated patients as well as attenuated forms of HAD and CNS opportunistic disorders. HIV-associated cognitive impairment correlates with the increased presence in the CNS of activated, though not necessarily HIV-1-infected, microglia and CNS macrophages. This suggests that indirect mechanisms of neuronal injury and loss/death occur in HIV/AIDS as a basis for dementia since neurons are not themselves productively infected by HIV-1. In this review, we discussed the symptoms and causes leading to HAD. Outcome from this review will provide new information regarding mechanisms of neuronal loss in AIDS patients.

Neonatal hippocampal Tat injections: developmental effects on prepulse inhibition (PPI) of the auditory startle response

The current estimate of children (<15 years) living with HIV and AIDS is 2.2 million. The major source of infection occurs through vertical transmission of the virus from mother to child during delivery [UNAIDS/WHO, 2005. AIDS Epidemic Update. UNAIDS, Geneva]. Recent studies have shown that timing of HIV-1 infection might be related to the onset and rate of progression of CNS disease. The effects of HIV on the brain are thought to be mediated indirectly through the viral toxins Tat and gp120. This study characterized developmental effects on PPI following intrahippocampal administration of Tat. On postnatal day (P)1, one male and one female pup from each of eight Sprague-Dawley litters were bilaterally injected with 50 microg Tat or saline (1 microl volume). Animals were tested for PPI of the auditory startle response (ASR) (ISIs of 0, 8, 40, 80, 120, and 4000 ms, six trial blocks, Latin-square design) on days 30, 60 and 90. Tat altered PPI and the pattern of alterations was different for males and females. For males, a leftward shift was evident in the ISI for maximal inhibition of the response on day 30 and on day 60 (chi(2)(1)=4.7, p< or =.03, and chi(2)(1)=5.3, p< or =.02, respectively), but not on day 90. For females, Tat altered peak ASR latency across PPI trials (8-120 ms) at all days of testing (30, 60, and 90 days of age), as indexed by orthogonal component analyses, indicating less modulation of PPI by ISI. Data collected from a second group that were tested only once at 90 days of age, suggested that the observed adverse Tat effects for males and females early in development were maintained with age. Thus, the diminishing TAT effect on PPI at day 90 in a longitudinal study design was attributed to repeated testing, rather than 'recovery of function'. Collectively, the data suggested that hippocampal Tat injections in neonatal rats produced alterations in the pre-attentive process of sensorimotor gating, as indexed by PPI.

The neuropathogenesis of AIDS

HIV-associated dementia (HAD) is an important complication of the central nervous system in patients who are infected with HIV-1. Although the incidence of HAD has markedly decreased since it has become possible to effectively control viral replication in the blood by administering highly active antiretroviral therapy, a less severe form of HAD, comprising a milder cognitive and motor disorder, is now potentially a serious problem. Brain macrophages and microglia are the key cell types that are infected by HIV-1 in the central nervous system, and they are likely to mediate the neurodegeneration seen in patients with HAD; however, the precise pathogenesis of this neurodegeneration is still unclear. Here, we discuss the studies that are being carried out to determine the respective contributions of infection, and monocyte and macrophage activation, to disease progression.

Human immunodeficiency virus type 1 genetic diversity in the nervous system: Evolutionary epiphenomenon or disease determinant?

Over the past decade there has been a revolution in the understanding and care of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS)-associated disease. Much of this progress stems from a broader recognition of the importance of differences in viral types, including receptor preference(s), replication properties, and reservoirs, as contributing factors to immunosuppresion and disease progression. In contrast, there is limited conceptualizatin of viral diversity and turnover in the brain and circulation in relation to neurocognitive impairments. Herein, the authors review current concepts regarding viral molecular diversity and phenotypes together with features of HIV-1 neuroinvasion, neurotropism, neurovirulence and neurosusceptiblity. Viral genetic and antigenic diversity is reduced within the brain compared to blood or other systemic organs within individuals. Conversely, viral molecular heterogeneity is greater in patients with HIV-associated dementia compared to nondemented patients, depending on the viral gene examined. Individual viral proteins exert multiple neuropathogenic effects, although the neurological consequences of different viral polymorphisms remain uncertain. Nonetheless, host genetic polymorphisms clearly influence neurological disease outcomes and likely dictate both acquired and innate immune responses, which in turn shape viral evolution within the host. Emerging issues include widespread antiretroviral therapy resistance and increasing awareness of viral superinfections together with viral recombination, all of which are likely to impact on both HIV genetic variation and neuropathogenesis. With the persisting prevalence of HIV-induced neurocognitive disabilities, despite marked improvements in managing immunosuppression, it remains imperative to fully define and understand the mechanisms by which viral dynamics and diversity contribute to neurological disease, permitting the development of new therapeutic strategies.

gp120 neurotoxicity fails to induce heat shock defenses, while the over expression of hsp70 protects against gp120

gp120, the coat glycoprotein of HIV, can damage CNS neurons. This appears to mostly involve an indirect pathway in which gp120 infects microglia, triggering the release of cytokines and glutamatergic excitotoxins which then damage neurons. A well-characterized response of cells to insults is to mobilize the heat stress response, a defense that has a number of protective consequences. We tested the capacity of gp120, at a dose well-documented to be neurotoxic, to activate the heat shock response in cultures from cortex and hippocampus, two brain regions sensitive to the neurotoxic effects of gp120. We found that gp120 failed to induce expression of hsp70, hsp25 or hsp90 in cortical or hippocampal cultures, under conditions where induction can be demonstrated in response to other insults. The failure of gp120 to induce a heat shock response is significant because we subsequently demonstrated that such an induction would have been beneficial. Specifically, over expression of hsp70 with a herpes viral amplicon vector protected cultured hippocampal neurons from gp120 neurotoxicity.

Effects of glucocorticoids in the gp120-induced inhibition of glutamate uptake in hippocampal cultures

Studies examining the development of AIDS Related Dementia have concentrated on neurotoxic properties of the HIV viral coat protein, gp120. We have previously shown that this neurotoxicity can be exacerbated by glucocorticoids (GCs), the stress hormones secreted by the adrenal. Moreover, GCs also worsen several of the mechanisms mediating gp120 neurotoxicity, such as increased calcium flux, ROS generation, and energy depletion. Gp120 interferes with the reuptake of glutamate in glia cultures, another possible mechanism by which it can be neurotoxic. This paper examines the role of GCs in exacerbating this phenomenon. It was found that while GCs do not exacerbate the decrease in reuptake of glutamate in glia cultures, they do enhance the decrease in mixed neuronal cultures and this latter effect appears to be energy-dependent.

Expression of excitatory amino acid transporter-1 in brain macrophages and microglia of HIV-infected patients. A neuroprotective role for activated microglia?

Recent experimental studies showed that activated macrophages/microglia (AMM) express excitatory amino acid transporters (EAATs), suggesting that, in addition to their neurotoxic properties, they also have a neuroprotective role by clearing extracellular glutamate and producing antioxidant glutathione. To test this hypothesis in human, the brain of 12 HIV-positive patients and 3 controls were immunostained for EAAT-1. EAAT-1 was expressed by AMM in all HIV-infected cases but not in HIV-negative controls. Expression varied according to the disease stage. In 5 cases with active HIV-encephalitis (HIVE), AMM strongly expressed EAAT-1 in the white matter and basal ganglia, analogous to HLA-DR and CD68 expression. There was weaker expression in the cortex and perineuronal microglial cells were not involved. In a case with "burnt out" HIVE following highly active antiretroviral therapy (HAART), EAAT-1 expression was mild, identical to that of HLA-DR and CD68 in the white matter and cortex and involved perineuronal microglial cells. In 3 AIDS patients without HIVE and in 3 pre-AIDS cases, EAAT-1 expression in the white matter was weaker than HLA-DR and CD68 expression; there was stronger correlation in the gray matter where perineuronal microglial cells were stained predominantly. Our findings in humans tend to confirm that AMM, particularly perineuronal microglial cells, play a neuroprotective role in the early stages of HIV infection and, possibly, following treatment. This is in keeping with the early microglial activation seen in pre-AIDS cases, and the late occurrence of neuronal loss. It may also explain the reversible cognitive disorders following treatment in some cases.

Expression of excitatory amino acid transporter-2 (EAAT-2) and glutamine synthetase (GS) in brain macrophages and microglia of SIVmac251-infected macaques

Na+-dependent transporters for glutamate (excitatory amino acid transporters, EAATs) clear extracellular glutamate in the brain and prevent excitotoxic neuronal damage. Glutamine synthetase (GS) provides metabolic support for neurones by producing the neurotrophic amino acid glutamine. EAAT and GS expression has recently been demonstrated in macrophages and microglial cells in vitro, and in two models of acute inflammation in vivo. This observation might modify our current understanding of brain inflammation, which considers activated microglia and brain macrophages as the main neurotoxic cells through their production of a variety of neurotoxins, including glutamate. EAAT and GS expression by these cells would entail neuroprotective and neurotrophic properties, counterbalancing the deleterious consequences of microglial activation. Macaque infection by the simian immunodeficiency virus (SIV) is considered the most relevant model for human acquired immunodeficiency syndrome (AIDS), including chronic inflammation of the brain at the early asymptomatic stage of the infection, followed by an AIDS-like disease where neuronal death occurs. We studied the expression of EAAT-2 and GS in the brains of three SIVmac251-infected and two noninfected cynomolgus macaques. We found that both microglia and brain macrophages expressed EAAT-2 and GS in infected primates, suggesting that these cells might, like astrocytes, clear extracellular glutamate and provide glutamine to neurones. Microglia and macrophages could thus have neuroprotective and neurotrophic properties in addition to their production of neurotoxins. This finding might explain the contrast between early intense microglial activation and the late occurrence of neuronal apoptotic cell death, which is mainly observed at the terminal stage of the disease.

Calcium dysregulation and neuronal apoptosis by the HIV-1 proteins Tat and gp120

Patients with AIDS often develop cognitive and motor dysfunction that results from damage to synapses and death of neurons in brain regions such as the hippocampus and basal ganglia. This brain syndrome, called AIDS dementia or HIV encephalitis, is believed to result from the infection of one or more populations of mitotic brain cells with HIV-1, which then release viral proteins that are toxic to neurons. Two neurotoxic HIV-1 proteins have been identified, the viral coat protein gp120 and the transcription regulator Tat. Each of these proteins can induce apoptosis of cultured neurons and can render neurons vulnerable to excitotoxicity and oxidative stress. Gp120 and Tat also cause neuronal dysfunction and death in rodents in vivo. Both gp120 and Tat disrupt neuronal calcium homeostasis by perturbing calcium-regulating systems in the plasma membrane and endoplasmic reticulum. Accordingly, drugs that stabilize cellular calcium homeostasis can protect neurons against the toxic effects of gp120 and Tat. By altering voltage-dependent calcium channels, glutamate receptor channels, and membrane transporters, the HIV-1 proteins promote calcium overload, oxyradical production, and mitochondrial dysfunction. A better understanding of how gp120 and Tat disrupt neuronal calcium homeostasis may lead to the development of novel treatments for AIDS patients.

Effect of GP120 on glutathione peroxidase activity in cortical cultures and the interaction with steroid hormones

GP120 (the protein component of the HIV viral coat) is neurotoxic and may contribute to the cell loss associated with AIDS-related dementia. Previously, it has been shown in rat cortical mixed cultures that gp120 increased the accumulation of hydrogen peroxide and superoxide, two reactive oxygen species (ROS). We now demonstrate that gp120 increased activity of the key antioxidant glutathione peroxidase (GSPx), presumably as a defensive mechanism against the increased ROS load. Both estrogen and glucocorticoids (GCs), the adrenal steroid released during stress, blunted this gp120 effect on GSPx activity. The similar effects of estrogen and of GCs are superficially surprising, given prior demonstrations that GCs exacerbated and estrogens protected against gp120 neurotoxicity. We find that these similar effects of estrogen and GCs on GSPx regulation arose, in fact, from very different routes, which are commensurate with these prior reports. Specifically, estrogen has demonstrated antioxidant properties that may prevent the ROS increase (therefore acting as a neuroprotective agent) and rendered unnecessary the compensatory GSPx increased activity. To verify this we have added H2O2 to estrogen + gp120-treated cells, and GSPx activity was increased. However, with addition of H2O2 to GCs + gp120-treated cells there was no increase in activity. GCs appeared to decrease enzyme production and or activity and therefore under insult conditions ROS levels rose in the cell resulting in increased neurotoxicity. Overexpression of GSPx enzyme via herpes vector system reversed the GCs-induced loss of enzyme and eliminated the GCs exacerbation of gp120 neurotoxicity.

Neuroimmune and neurovirological aspects of human immunodeficiency virus infection

Like most lentiviruses, HIV-1 causes both immune suppression and neurological disease. Neurological disease may occur at any stage of HIV infection but is most apparent with severe immune suppression. Cognitive impairment, reflected strikingly by HIV-associated dementia, has attracted intense interest since the outset of the HIV epidemic, and understanding of its pathogenesis has been spurred on by the emergence of several hypotheses outlining potential pathogenic mechanisms. The release of inflammatory molecules by HIV-infected microglia and macrophages and the concurrent neuronal damage play central roles in the conceptualization of HIV neuropathogenesis. Many inflammatory molecules appear to contribute to the pathogenic cascade and their individual roles remain undefined. At the same time, the abundance of virus in the brain and the type or strain of virus found in the brain may also be important codeterminants of neurological disease, as shown for other neurotropic viruses. Coreceptor use by HIV found in the brain appears to closely mirror what has been reported in systemic macrophages. The impact of HAART on viral genotype and phenotype found in the brain, and its relationship to clinical disease, remain uncertain. Several interesting animal models have been developed, using other lentiviruses, transgenic animals, and HIV-infected SCID mice, that may prove useful in future pathogenesis and therapeutic studies. Despite the progress in the understanding of HIV neuropathogenesis, many questions remain unanswered.

Exploitation of the HIV-1 coat glycoprotein, gp120, in neurodegenerative studies in vivo

Neuronal loss has often been described at post-mortem in the brain neocortex of patients suffering from AIDS. Neuroinvasive strains of HIV infect macrophages, microglial cells and multinucleated giant cells, but not neurones. Processing of the virus by cells of the myelomonocytic lineage yields viral products that, in conjunction with potentially neurotoxic molecules generated by the host, might initiate a complex network of events which lead neurones to death. In particular, the HIV-1 coat glycoprotein, gp120, has been proposed as a likely aetiologic agent of the described neuronal loss because it causes death of neurones in culture. More recently, it has been shown that brain neocortical cell death is caused in rat by intracerebroventricular injection of a recombinant gp120 coat protein, and that this occurs via apoptosis. The latter observation broadens our knowledge in the pathophysiology of the reported neuronal cell loss and opens a new lane of experimental research for the development of novel therapeutic strategies to limit damage to the brain of patients suffering from HIV-associated dementia.

Preclinical psychopharmacology of AIDS-associated dementia: lessons to be learned from the cognitive psychopharmacology of other dementias

Following a brief discussion of the epidemiology, underlying neuropathological mechanisms, neuropsychological symptoms and present treatment strategies of AIDS-associated dementia (AAD), parallels are drawn between the longer standing research on drugs for the treatment of other cognitive disorders, particularly senile dementia, and ongoing efforts to develop psychopharmacological approaches for the treatment of the cognitive impairments in AAD. Important aspects of hypotheses designed to guide such a research are indicated with the help of a speculative, paradigmatic hypothesis concerning the role of cortical cholinergic inputs in AAD. Furthermore, aspects of validity of animal models, and cognition as a crucial intervening variable in the effects of potential treatments, are evaluated.

Monocyte chemoattractant protein-1 is a mediator of acute excitotoxic injury in neonatal rat brain

Monocyte chemoattractant protein-1 is a chemokine with potent monocyte activating and chemotactic effects. Monocyte chemoattractant protein-1 gene and protein expression is rapidly up-regulated in response to a variety of acute and chronic central nervous system disorders. The activation and recruitment of microglia and monocytes into areas of inflammation may play a critical role in the pathogenesis of acute brain injury. Monocyte chemoattractant protein-1 could be a pathophysiologically important mediator of the microglial and monocyte responses in the brain. Using a well-characterized model of acute excitotoxic brain injury in neonatal rats, experiments were designed to evaluate whether monocyte chemoattractant protein-1 plays a role in the progression of tissue damage. Direct co-administration of recombinant monocyte chemoattractant protein-1 with the excitotoxin N-methyl-D-aspartate exacerbated injury, both in the striatum and in the hippocampus, by 55% and 167%, respectively. Complementary experiments to determine the effect of functional inhibition of monocyte chemoattractant protein-1, using an anti-monocyte chemoattractant protein-1-neutralizing antibody, revealed that co-administration of the antibody with N-methyl-D-aspartate attenuated tissue injury in the striatum and hippocampus by 57% and 39%, respectively.Together, these data suggest that monocyte chemoattractant protein-1 is a mediator of acute excitotoxic brain injury in neonatal rats and that inflammatory mechanisms contribute significantly to the pathogenesis of acute neonatal brain injury. Whether chemokines are pathophysiologically relevant mediators of neuronal injury in human neonates remains to be determined.

Neuronal glycolytic pathway impairment induced by HIV envelope glycoprotein gp120

Neurological impairment is a common feature of Acquired Immunodeficiency Syndrome (AIDS); functional alterations have been reported both in central and peripheral nervous system and the Human Immunodeficiency Virus (HIV) envelope glycoprotein gp120 has been proposed as a neurotoxin acting through a calcium-dependent mechanism. On the other hand it has been reported that gp120 treatment also induce about a 20% decrease in the cerebral glucose utilization and in the cellular ATP levels. The reported observations were performed on experimental system where also non-neuronal cells where present; in order to evaluate whether a direct interaction between HIV proteins and neuronal cells takes place, we used a neuroblastoma cultures where only neuronal cells are present. We analysed the effects of gp120 on the N18TG2 neuroblastoma clone. Treatments were performed both on growing and confluent cultures. Short time treatment with gp120 of confluent cultures causes a 25% reduction in the level of neuron-specific enolase, resulting in a similar decrease of oxygen consumption. Long time exposure of growing cells also causes a reduction in cell survival. Furthermore, using a membrane-specific fluorescent probe we observed that gp120 produces an increase of membrane trafficking. These observations suggest a direct interaction between the viral envelope protein and neuronal cells, which results in an alteration of glycolytic metabolism. This alteration may be related to the neurologic impairments observed in AIDS patients.

The effects of steroid hormones in HIV-related neurotoxicity: a mini review

This review examines the interaction of steroid hormones, glucocorticoids and estrogen, and gp120, a possible causal agent of acquired immune deficiency syndrome-related dementia complex. The first part of the review examines the data and mechanisms by which gp120 may cause neurotoxicity and by which these steroid hormones effect cell death in general. The second part of the review summarizes recent experiments that show how these steroid hormones can modulate the toxic effects of gp120 and glucocorticoids exacerbating toxicity, and estrogen decreasing it. We then examine the limited in vivo and clinical data relating acquired immune deficiency syndrome-related dementia complex and steroid hormones and speculate on the possible clinical significance of these findings with respect to acquired immune deficiency syndrome-related dementia complex.

gp120 induces cell death in human neuroblastoma cells through the CXCR4 and CCR5 chemokine receptors

To infect target cells, the human immunodeficiency virus (HIV) type I (HIV-1) must engage not only the well-known CD4 molecule, but it also requires one of several recently described coreceptors. In particular, the CXCR4 (LESTR/fusin) receptor allows fusion and entry of T-tropic strains of HIV, whereas CCR5 is the major coreceptor used by primary HIV-1 strains that infect macrophages and CD4(+) T-helper cells (M-tropic viruses). In addition, the alpha chemokine SDF1alpha and the beta chemokines MIP1alpha, MIP1beta, and RANTES, natural ligands of CXCR4 and CCR5, respectively, are potent soluble inhibitors of HIV infection by blocking the binding between the viral envelope glycoprotein gp120 and the coreceptors. Approximately two-thirds of individuals with acquired immunodeficiency syndrome (AIDS) show neurologic complications, which are referred to a syndrome called AIDS dementia complex or HIV-1-associated cognitive/motor complex. The HIV-1 coat glycoprotein gp120 has been proposed as the major etiologic agent for neuronal damage, mediating both direct and indirect effects on the CNS. Furthermore, recent findings showing the presence of chemokine receptors on the surface of different cell types resident in the CNS raise the possibility that the association of gp120 with these receptors may contribute to the pathogenesis of neurological dysfunction. Here, we address the possible role of alpha and beta chemokines in inhibiting gp120-mediated neurotoxicity using the human neuroblastoma CHP100 cell line as an experimental model. We have previously shown that, in CHP100 cells, picomolar concentrations of gp120 produce a significant increase in cell death, which seems to proceed through a Ca(2+) - and NMDA receptor-dependent cascade. In this study, we gained insight into the mechanism(s) of neurotoxicity elicited by the viral glycoprotein. We found that CHP100 cells constitutively express both CXCR4 and CCR5 receptors and that stimulation with phorbol 12-myristate 13-acetate down-regulates their expression, thus preventing gp120-induced cell death. Furthermore, all the natural ligands of these receptors exerted protective effects against gp120-mediated neuronal damage, although with different efficiencies. These findings, together with our previous reports, suggest that the neuronal injury observed in HIV-1 infection could be due to direct (or indirect) interactions between the viral protein gp120 and chemokine and/or NMDA receptors.

Glucocorticoids exacerbate the deleterious effects of gp120 in hippocampal and cortical explants

Glucocorticoids (GCs), the adrenal steroids secreted during stress, can compromise the ability of hippocampal neurons to survive numerous necrotic insults. We have previously observed that GCs worsen the deleterious effects of gp120, the glycoprotein of the acquired immune deficiency syndrome virus, which can indirectly damage neurons and which is thought to play a role in the neuropathological features of human immunodeficiency virus infection. Specifically, GCs augment gp120-induced calcium mobilization, ATP depletion, decline in mitochondrial potential, and neurotoxicity in fetal monolayer cultures from a number of brain regions. In the present report, we demonstrate a similar gp120/GC synergy in adult hippocampal and cortical explants. We generated explants from rats that were either adrenalectomized, adrenally intact, or intact and treated with corticosterone to produce levels seen in response to major stressors. Metabolic rates in explants were then indirectly assessed with silicon microphysiometry, and cytosolic calcium concentrations were assessed with fura-2 fluorescent microscopy. We observed that basal levels of GCs tonically augment the disruptive effects of gp120 on metabolism in the CA1 cell field of the hippocampus and in the cortex. Moreover, raising GC concentrations into the stress range exacerbated the ability of gp120 to mobilize cytosolic calcium in a number of hippocampal cell fields. Finally, we observed that the synthetic GC prednisone had similarly exacerbating effects on gp120. Thus, GCs can worsen the deleterious effects of gp120 in a system that is more physiologically relevant than the fetal monolayer culture and in a region-specific manner.

Tumor necrosis factor-a attenuates N-methyl-D-aspartate-mediated neurotoxicity in neonatal rat hippocampus

Tumor necrosis factor-a TNFa. has been implicated in the pathophysiology of acute neonatal brain injury. We hypothesized that acute brain injury would induce TNFa expression and that exogenous TNFa would influence the severity of N-methyl-D-aspartate-induced tissue damage. We performed two complementary groups of experiments to evaluate the potential role s. of TNFa in a neonatal rodent model of excitotoxic injury, elicited by intracerebral injection of N-methyl-D-aspartate. We used immunohistochemistry and ELISA to evaluate N-methyl-D-aspartate-induced changes in TNFa expression, and we co-injected TNFa with N-methyl-D-aspartate, to evaluate the effect of this cytokine on the severity of tissue injury. Both intra-hippocampal and intra-striatal injection of N-methyl-D-aspartate 5 nmol. stimulated TNFa expression. Increased TNFa expression was detected 3-12 h after lesioning; TNFa was localized both in glial cells in the corpus callosum, and in cells with the morphology of interneurons in the ipsilateral hippocampus, striatum, cortex and thalamus. Intra-hippocampal or intra-striatal administration of TNFa 50 ng. alone did not elicit neuropathologic damage. In the hippocampus, when co-injected with N-methyl-D-aspartate 5 or 10 nmol., TNFa 50 ng. attenuated excitotoxic injury by 35%-57%, compared to controls co-injected with heat-treated TNFa. In contrast, in the striatum, co-injection of TNFa with N-methyl-D-aspartate had no effect on the severity of the ensuing damage. The data indicate that TNFa is rapidly produced in glial cells and neurons after an excitotoxic insult in the neonatal rat brain, and that administration of exogenous TNFa results in region-specific attenuation of excitotoxic damage. We speculate that endogenous TNFa may modulate the tissue response to excitotoxic injury in the developing brain.

Tat, a human immunodeficiency virus-1-derived protein, augments excitotoxic hippocampal injury in neonatal rats

To test the hypothesis that the human immunodeficiency virus-1-derived Tat protein may cause neuronal damage in the CNS, we evaluated the neurotoxicity of recombinant human immunodeficiency virus-1-derived Tat in vivo in seven-day-old rats. The intrinsic neurotoxicity of Tat (250 ng-1 microg) and the effects of direct intra-hippocampal co-infusion of Tat with N-methyl-D-aspartate were assessed. Extent of injury in the lesioned hippocampus was evaluated five days later, based on histopathology and morphometric measurements of hippocampal volume. To confirm that any observed neurotoxic effects were attributable to Tat bioactivity, all experiments included controls that received equal amounts of heat-treated (boiled) Tat. Intra-hippocampal injection of Tat, alone, elicited minimal focal tissue damage immediately adjacent to the injection track, and no hippocampal atrophy. Co-injection of Tat (500 ng) with N-methyl-D-aspartate (5 nmol, threshold excitotoxic dose) doubled the severity of hippocampal injury, quantified by comparison of bilateral hippocampal volumes, in comparison with animals that received heat-treated Tat or saline co-injections; in animals that received injections of N-methyl-D-aspartate (5 nmol) in combination with saline, heat-treated Tat, or Tat [mean(+/-S.E.M.) % volume loss values in the lesioned hippocampus were: 11(+/-3), 11(+/-3), and 26(+/-3), respectively (P<0.002, ANOVA)]. Co-injection of 100 ng Tat with 5 nmol N-methyl-D-aspartate exacerbated the severity of excitotoxic injury to a similar extent, whereas co-injection of 20 ng Tat had no effect on N-methyl-D-aspartate-mediated injury. Treatment with the N-methyl-D-aspartate antagonist 3-((RS)-2-carboxypiperazin4-yl)-propyl-1-phosphonic acid (20 mg/kg) markedly attenuated hippocampal injury resulting from co-injection of 100 ng Tat with N-methyl-D-aspartate [mean(+/-S.E.M.) % volume loss in lesioned hippocampus: 0.1(+/-2) in 3-((RS)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid-treated vs 19(+/-3) in controls, P<0.001, ANOVA]. Co-injection of Tat had no effect on N-methyl-D-aspartate-mediated striatal damage or on alpha-amino-3-hydroxy-5-methylisoxazole-4-pro hippocampal damage. These data support the hypothesis that locally released Tat could exert neurotoxic effects, mediated by N-methyl-D-aspartate receptor activation, in vivo in the immature brain.

Neuronal death induced by brain-derived human immunodeficiency virus type 1 envelope genes differs between demented and nondemented AIDS patients

Human immunodeficiency virus type 1 (HIV-1) infection of the brain results in viral replication primarily in macrophages and microglia. Despite frequent detection of viral genome and proteins in the brains of AIDS patients with and without HIV dementia, only 20% of AIDS patients become demented. To investigate the role of viral envelope gene variation in the occurrence of dementia, we examined regions of variability in the viral envelope gene isolated from brains of AIDS patients. Brain-derived HIV-1 V1-V2 envelope sequences from seven demented and six nondemented AIDS patients displayed significant sequence differences between clinical groups, and by phylogenetic analysis, sequences from the demented group showed clustering. Infectious recombinant viruses containing brain-derived V3 sequences from both clinical groups were macrophagetropic, and viruses containing brain-derived V1, V2, and V3 sequences from both clinical groups spread efficiently in macrophages. In an indirect in vitro neurotoxicity assay using supernatant fluid from HIV-1-infected macrophages, recombinant viruses from demented patients induced greater neuronal death than viruses from nondemented patients. Thus, the HIV-1 envelope diversity observed in these patient groups appeared to influence the release of neurotoxic molecules from macrophages and might account in part for the variability in occurrence of dementia in AIDS patients.

Excitotoxic brain injury stimulates expression of the chemokine receptor CCR5 in neonatal rats

Chemokines interact with specific G-protein-coupled receptors to activate and direct recruitment of immune cells. Some chemokines are up-regulated in pathological conditions of the central nervous system, and recently several chemokine receptors, including CCR5, were identified in the brain. However, little is known about the regulation of expression of chemokine receptors in the brain. Direct intracerebral injection of N-methyl-D-aspartate (NMDA), an excitatory amino acid agonist, elicits reproducible focal excitotoxic brain injury; in neonatal rats, intrahippocampal NMDA injection stimulates expression of pro-inflammatory cytokines and elicits a robust microglia/monocyte response. We hypothesized that NMDA-induced neurotoxicity would also stimulate expression of CCR5 in the neonatal rat brain. We evaluated the impact of intrahippocampal injections of NMDA on CCR5 expression in postnatal day 7 rats. Reverse transcription polymerase chain reaction revealed an increase in hippocampal CCR5 mRNA expression 24 hours after lesioning, and in situ hybridization analysis demonstrated that CCR5 mRNA was expressed in the lesioned hippocampus and adjacent regions. Western blot analysis demonstrated increased CCR5 protein in hippocampal tissue extracts 32 hours after lesioning. Complementary immunocytochemistry studies identified both infiltrating microglia/monocytes and injured neurons as the principal CCR5-immunoreactive cells. These results provide the first evidence that acute excitotoxic injury regulates CCR5 expression in the developing rat brain.

The human immunodeficiency virus-1 envelope protein gp120 binds through its V3 sequence to the glycine site of N-methyl-D-aspartate receptors mediating noradrenaline release in the hippocampus

Recent results show that the HIV-1 protein gp120 can enhance N-methyl-D-aspartate receptor-mediated release of noradrenaline from CNS nerve endings. We now investigate the mechanism of this action, including the structural determinants of the gp120 effect and the nature of its binding sites. The N-methyl-D-aspartate-evoked release of [3H]noradrenaline from rat hippocampal synaptosomes was potentiated similarly by gp120 and gp160; gp41 was ineffective. The regions of gp120 involved appear to be outside the CD4-binding domain of the protein, because gp120 retained its activity after pretreatment with N-carbomethoxycarbonyl-D-prolyl-D-phenylalanine, a compound known to inhibit binding of gp120 to CD4 receptors. Moreover, sequences of gp120 critical for binding to CD4 did not mimic the effect of gp120. Preincubation of synaptosomes with anti-galactocerebroside antibodies did not affect gp120 activity. The protein effect was retained by peptides mimicking its V3 sequence, including the cyclic V3 "universal peptide" and the linear V3 sequence BRU-C-34-A, but not RP-135 (a central portion of BRU-C-34-A). The block of the N-methyl-D-aspartate-induced [3H]noradrenaline release by 7-chlorokynurenate, an antagonist at the N-methyl-D-aspartate receptor glycine site, was competitively reversed by glycine, by V3 and by BRU-C-34-A. When added with N-methyl-D-aspartate, V3 was three to four orders of magnitude more potent than glycine (EC50 values: about 20 pM and 150 nM, respectively) in enhancing [3H]noradrenaline release. Gp120 did not release glycine or serine from synaptosomes, thus excluding indirect actions through these agents. To conclude, gp120 may act following recognition by its V3 sequence of a high-affinity site possibly coincident with the glycine site of N-methyl-D-aspartate receptors present on hippocampal terminals of noradrenergic neurons. Considering the importance of N-methyl-D-aspartate receptor activation and of noradrenaline in cognitive processes, the effects of gp120 and V3 described here may be relevant to the pathology of AIDS dementia.

The HIV envelope protein gp120 in the nervous system: interactions with nitric oxide, interleukin-1beta and nerve growth factor signalling, with pathological implications in vivo and in vitro

The neuronal loss often described at post-mortem in the brain neocortex of patients suffering from AIDS has been proposed to be responsible for the development of the AIDS dementia complex. Neuroinvasive strains of the HIV virus infect macrophages, microglial cells, and multinucleated giant cells, but not neurones. Processing of the virus by cells of the myelomonocytic lineage yields viral products known to initiate a complex network of events that may lead to the death of neurones and to the development of AIDS-associated neurological syndrome. The HIV-1 coat protein gp120, in particular, has been proposed as a likely etiologic agent of the described neuronal loss because it causes the death of neurones in culture. More recently, it has been shown that brain cortical cell death caused in rats by intracerebroventricular injection of gp120 occurs via apoptosis. This observation broadens our knowledge of the pathophysiology of the reported neuronal cell loss and opens a new avenue of experimental research for the development of novel therapeutic strategies for the treatment of patients suffering from AIDS-associated neurological syndrome.

Axonal sprouting in hippocampus of cats infected with feline immunodeficiency virus (FIV)

Neurologic dysfunction and neuropathology are common findings in patients infected with HIV and in cats infected with feline immunodeficiency virus (FIV). The pathogenesis of lentivirus-associated alterations in the central nervous system (CNS) is multifactorial. Because seizures, alterations in memory, and behavioral changes are clinical manifestations in adults and children infected with HIV, we explored the possibility that changes in neuronal structure may occur in the hippocampus. To do this, we examined the dentate gyrus of FIV-infected cats, an animal model of HIV infection. Neuropathologic findings included gliosis within the hilus of the dentate gyrus and granule cell axonal sprouting. Using the Timm's method, which labels axons of dentate gyrus granule cells, abnormally high amounts of staining were observed in the inner one third of the molecular layer in 45% of FIV-infected cats (n = 11) and in none of the controls (n = 19). Prominent axonal sprouting was seen in three FIV-infected cats that were infected as kittens, suggesting that younger cats may be more susceptible. Axon reorganization of the dentate granule cells has been hypothesized to underlie complex partial seizure activity in human temporal lobe epilepsy. These results suggest that FIV infection causes granule cell axon reorganization in the hippocampus of cats. A similar neuropathogenetic mechanism may contribute to neurologic dysfunction in HIV-infected patients.