HIV envelope protein-induced neuronal damage and retardation of behavioral development in rat neonates

α-Synuclein triggers cofilin pathology and dendritic spine impairment via a PrPC-CCR5 dependent pathway

Cognitive dysfunction and dementia are critical symptoms of Lewy Body dementias (LBD). Specifically, alpha-synuclein (αSyn) accumulation in the hippocampus leading to synaptic dysfunction is linked to cognitive deficits in LBD. Here, we investigated the pathological impact of αSyn on hippocampal neurons. We report that either αSyn overexpression or αSyn pre-formed fibrils (PFFs) treatment triggers the formation of cofilin-actin rods, synapse disruptors, in cultured hippocampal neurons and in the hippocampus of synucleinopathy mouse models and of LBD patients. In vivo, cofilin pathology is present concomitantly with synaptic impairment and cognitive dysfunction. Rods generation prompted by αSyn involves the co-action of the cellular prion protein (PrPC) and the chemokine receptor 5 (CCR5). Importantly, we show that CCR5 inhibition, with a clinically relevant peptide antagonist, reverts dendritic spine impairment promoted by αSyn. Collectively, we detail the cellular and molecular mechanism through which αSyn disrupts hippocampal synaptic structure and we identify CCR5 as a novel therapeutic target to prevent synaptic impairment and cognitive dysfunction in LBD.

Chemokine Receptor Antagonists Prevent and Reverse Cofilin-Actin Rod Pathology and Protect Synapses in Cultured Rodent and Human iPSC-Derived Neurons

Synapse loss is the principal cause of cognitive decline in Alzheimer's disease (AD) and related disorders (ADRD). Synapse development depends on the intricate dynamics of the neuronal cytoskeleton. Cofilin, the major protein regulating actin dynamics, can be sequestered into cofilactin rods, intra-neurite bundles of cofilin-saturated actin filaments that can disrupt vesicular trafficking and cause synaptic loss. Rods are a brain pathology in human AD and mouse models of AD and ADRD. Eliminating rods is the focus of this paper. One pathway for rod formation is triggered in ~20% of rodent hippocampal neurons by disease-related factors (e.g., soluble oligomers of Amyloid-β (Aβ)) and requires cellular prion protein (PrPC), active NADPH oxidase (NOX), and cytokine/chemokine receptors (CCRs). FDA-approved antagonists of CXCR4 and CCR5 inhibit Aβ-induced rods in both rodent and human neurons with effective concentrations for 50% rod reduction (EC50) of 1-10 nM. Remarkably, two D-amino acid receptor-active peptides (RAP-103 and RAP-310) inhibit Aβ-induced rods with an EC50 of ~1 pM in mouse neurons and ~0.1 pM in human neurons. These peptides are analogs of D-Ala-Peptide T-Amide (DAPTA) and share a pentapeptide sequence (TTNYT) antagonistic to several CCR-dependent responses. RAP-103 does not inhibit neuritogenesis or outgrowth even at 1 µM, >106-fold above its EC50. N-terminal methylation, or D-Thr to D-Ser substitution, decreases the rod-inhibiting potency of RAP-103 by 103-fold, suggesting high target specificity. Neither RAP peptide inhibits neuronal rod formation induced by excitotoxic glutamate, but both inhibit rods induced in human neurons by several PrPC/NOX pathway activators (Aβ, HIV-gp120 protein, and IL-6). Significantly, RAP-103 completely protects against Aβ-induced loss of mature and developing synapses and, at 0.1 nM, reverses rods in both rodent and human neurons (T½ ~ 3 h) even in the continuous presence of Aβ. Thus, this orally available, brain-permeable peptide should be highly effective in reducing rod pathology in multifactorial neurological diseases with mixed proteinopathies acting through PrPC/NOX.

Hippocampal Neuronal Loss in Infant Macaques Orally Infected with Virulent Simian Immunodeficiency Virus (SIV)

The neurological impact of Human Immunodeficiency Virus (HIV) on children includes loss of brain growth, motor abnormalities and cognitive dysfunction. Despite early antiretroviral treatment (ART) intervention to suppress viral load, neurological consequences of perinatal HIV-1 infection persist. Utilizing the pediatric simian immunodeficiency virus (SIV) infection model, we tested the hypothesis that early-life SIV infection depletes neuronal population in the hippocampus. A total of 22 ART-naïve infant rhesus macaques (Macaca mulatta) from previous studies were retrospectively analyzed. Infant macaques were either intravenously (IV) inoculated with highly virulent SIVmac251 at ~1 week of age and monitored for 6-10 weeks, or orally challenged with SIVmac251 from week 9 of age onwards with a monitoring period of 10-23 weeks post-infection (19-34 weeks of age), and SIV-uninfected controls were euthanized at 16-17 weeks of age. We have previously reported that the IV SIVmac251-infected neonatal macaques (Group 1) displayed a 42% neuronal reduction throughout the hippocampal cornu ammonis (CA) fields. The orally-infected infant macaques displayed a 75% neuronal reduction in the CA1 region compared to controls and 54% fewer neurons than IV SIV infants. The CA2 region showed a similar pattern, with a 67% reduction between orally-infected SIV subjects and controls and a 40% difference between IV-and orally-infected SIV groups. In the CA3 region, there were no significant differences between these groups, however both SIV-infected groups had significantly fewer pyramidal neurons than control subjects. There was no correlation between plasma viral load and neuronal populations in any of the CA fields. The loss of hippocampal neurons may contribute to the rapid neurocognitive decline associated with pediatric HIV infection. While each subfield showed vulnerability to SIV infection, the CA1 and CA2 subregions demonstrated a potentially enhanced vulnerability to pediatric SIV infection. These data underscore the need for early diagnosis and treatment, including therapeutics targeting the central nervous system (CNS).

Of mice and monkeys: can animal models be utilized to study neurological consequences of pediatric HIV-1 infection?

Pediatric human immunodeficiency virus (HIV-1) infection remains a global health crisis. Children are much more susceptible to HIV-1 neurological impairments than adults, which can be exacerbated by coinfections. Neurological characteristics of pediatric HIV-1 infection suggest dysfunction in the frontal cortex as well as the hippocampus; limited MRI data indicate global cerebral atrophy, and pathological data suggest accelerated neuronal apoptosis in the cortex. An obstacle to pediatric HIV-1 research is a human representative model system. Host-species specificity of HIV-1 limits the ability to model neurological consequences of pediatric HIV-1 infection in animals. Several models have been proposed including neonatal intracranial injections of HIV-1 viral proteins in rats and perinatal simian immunodeficiency virus (SIV) infection of infant macaques. Nonhuman primate models recapitulate the complexity of pediatric HIV-1 neuropathogenesis while rodent models are able to elucidate the role specific viral proteins exert on neurodevelopment. Nonhuman primate models show similar behavioral and neuropathological characteristics to pediatric HIV-1 infection and offer a stage to investigate early viral mechanisms, latency reservoirs, and therapeutic interventions. Here we review the relative strengths and limitations of pediatric HIV-1 model systems.

Sera from children with autism induce autistic features which can be rescued with a CNTF small peptide mimetic in rats

Autism is a neurodevelopmental disorder characterized clinically by impairments in social interaction and verbal and non-verbal communication skills as well as restricted interests and repetitive behavior. It has been hypothesized that altered brain environment including an imbalance in neurotrophic support during early development contributes to the pathophysiology of autism. Here we report that sera from children with autism which exhibited abnormal levels of various neurotrophic factors induced cell death and oxidative stress in mouse primary cultured cortical neurons. The effects of sera from autistic children were rescued by pre-treatment with a ciliary neurotrophic factor (CNTF) small peptide mimetic, Peptide 6 (P6), which was previously shown to exert its neuroprotective effect by modulating CNTF/JAK/STAT pathway and LIF signaling and by enhancing brain derived neurotrophic factor (BDNF) expression. Similar neurotoxic effects and neuroinflammation were observed in young Wistar rats injected intracerebroventricularly with autism sera within hours after birth. The autism sera injected rats demonstrated developmental delay and deficits in social communication, interaction, and novelty. Both the neurobiological changes and the behavioral autistic phenotype were ameliorated by P6 treatment. These findings implicate the involvement of neurotrophic imbalance during early brain development in the pathophysiology of autism and a proof of principle of P6 as a potential therapeutic strategy for autism.

Targeting the glutamatergic system for the treatment of HIV-associated neurocognitive disorders

The accumulation of excess glutamate in the extracellular space as a consequence of CNS trauma, neurodegenerative diseases, infection, or deregulation of glutamate clearance results in neuronal damage by excessive excitatory neurotransmission. Glutamate excitotoxicity is thought to be one of several mechanisms by which HIV exerts neurotoxicity that culminates in HIV-associated neurocognitive disorders (HAND). Excess glutamate is released upon HIV infection of macrophage/microglial cells and has been associated with neurotoxicity mediated by gp120, transactivator of transcription (Tat) and other HIV proteins. Several strategies have been used over the years to try to prevent glutamate excitotoxicity. Since the main toxic effects of excess glutamate are thought to be due to excitotoxicity from over activation of glutamate receptors, antagonists of these receptors have been popular therapeutic targets. Early work to ameliorate the effects of excess extracellular glutamate focused on NMDA receptor antagonism, but unfortunately, potent blockade of this receptor has been fraught with side effects. One alternative to direct receptor blockade has been the inhibition of enzymes responsible for the production of glutamate such as glutaminase and glutamate carboxypeptidase II. Another approach has been to regulate the transporters responsible for modulation of extracellular glutamate such as excitatory amino acid transporters and the glutamate-cystine antiporter. There is preliminary experimental evidence that these approaches have potential therapeutic utility for the treatment of HAND. These efforts however, are at an early stage where the next steps are dependent on the identification of drug-like inhibitors as well as the development of predictive neuroAIDS animal models.

CXCL12 signaling in the development of the nervous system

Chemokines are small, secreted proteins that have been shown to be important regulators of leukocyte trafficking and inflammation. All the known effects of chemokines are transduced by action at a family of G protein coupled receptors. Two of these receptors, CCR5 and CXCR4, are also known to be the major cellular receptors for HIV-1. Consideration of the evolution of the chemokine family has demonstrated that the chemokine Stromal cell Derived Factor-1 or SDF1 (CXCL12) and its receptor CXCR4 are the most ancient members of the family and existed in animals prior to the development of a sophisticated immune system. Thus, it appears that the original function of chemokine signaling was in the regulation of stem cell trafficking and development. CXCR4 signaling is important in the development of many tissues including the nervous system. Here we discuss the manner in which CXCR4 signaling can regulate the development of different structures in the central and peripheral nervous systems and the different strategies employed to achieve these effects.

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.

In vivo microdialysis in awake, freely moving rats demonstrates HIV-1 Tat-induced alterations in dopamine transmission

Individuals infected with human immunodeficiency virus (HIV) may develop neuropsychological impairment, and a modest percentage may progress to HIV-associated dementia (HAD). Research using human and nonhuman, in vitro and in vivo models, demonstrates that subcortical dopamine (DA) systems may be particularly vulnerable to HIV-induced neurodegeneration. The goal of the current investigation is to provide an understanding of the extent to which the HIV-1 protein Tat induces alterations in striatal DA transmission using in vivo brain microdialysis in awake, freely moving rats. The current study was designed to investigate Tat-induced neuronal dysfunction between 24-h and 48-h post-Tat administration, and demonstrates a reduction in evoked DA for the Tat-treated group relative to vehicle-treated group at 24 and 48 h. The Tat-induced reduction of DA overflow by 24 h suggests dysfunction of nerve terminals, and a compromised DA system in Tat-treated animals. Furthermore, the current study provides direct support for HIV-associated decline of DA function at a systemic level, helping to characterize the functional outcome of the relatively large amount of research on the molecular and behavioral levels of HIV-induced neurotoxicity. This initial study may provide additional characteristics of Tat-induced neuronal dysfunction to inform research on therapeutic intervention, and it provides a springboard for future in vivo research currently needed in the field.

Alteration of blood-brain barrier function by methamphetamine and cocaine

The integrity of the blood-brain barrier (BBB) plays an important role in maintaining a safe neural microenvironment in the brain. Loss of BBB integrity has been recognized as a major cause of profound brain alterations. Psychoactive drugs such as methamphetamine (METH) or cocaine are well-known drugs of abuse that can alter the permeability of the BBB via various mechanisms. In addition, the neurotoxicity of METH is well documented, and alterations in BBB function can contribute to this toxicity. A great deal of effort has been devoted to understanding the cellular and molecular mechanisms of the action of these drugs in the central nervous system. However, only a few investigations have focused on the effects of METH and cocaine on BBB function. The aim of this short review is to summarize our present knowledge of this subject.

Growth and puberty in children with HIV infection

Children with perinatal HIV infection may present with clinical features of endocrine dysfunction such as growth failure and pubertal delay. Pediatric care providers and pediatric endocrinologists should implement appropriate preventive, screening, and therapeutic strategies to maximize survival and quality of life in these children. Growth and pubertal delay can be exacerbated by a variety of treatable infectious, endocrine, nutritional, and immunological disorders. Timely diagnosis and appropriate treatment of these conditions may lead to improvement or even normalization of growth and puberty. HIV-infected children with advanced disease should undergo periodic growth evaluation, including GH levels, IGF-I, IGF binding protein 3 and androgens, in order to identify subclinical endocrine dysfunction. However, little is known about the association between HIV infection and endocrine dysfunction in children. Highly active antiretroviral therapy may also be associated with endocrine dysfunction with consequences on growth and puberty. Growth retardation and pubertal delay are always seen in children with advanced HIV infection and are often related to the proinflammatory milieu found in advanced AIDS. Growth and pubertal impairment are markers of advanced disease and require proper evaluation. A dysregulation of the hypothalamic-pituitary axis, toxic or allergic drug reactions may play a role in growth and pubertal delay of HIV-infected children. These dysfunctions require careful monitoring, in order to assess metabolic alterations that may be important in regulation of growth among HIV infected children. Better understanding of the mechanisms leading to impairment of growth and puberty in children with perinatal HIV-1 infection might lead to appropriate treatment when required.

Neurotoxic profiles of HIV, psychostimulant drugs of abuse, and their concerted effect on the brain: current status of dopamine system vulnerability in NeuroAIDS

There are roughly 30-40 million HIV-infected individuals in the world as of December 2007, and drug abuse directly contributes to one-third of all HIV infections in the United States. Antiretroviral therapy has increased the lifespan of HIV-seropositives, but CNS function often remains diminished, effectively decreasing quality of life. A modest proportion may develop HIV-associated dementia, the severity and progression of which is increased with drug abuse. HIV and drugs of abuse in the CNS target subcortical brain structures and DA systems in particular. This toxicity is mediated by a number of neurotoxic mechanisms, including but not limited to, aberrant immune response and oxidative stress. Therefore, novel therapeutic strategies must be developed that can address a wide variety of disparate neurotoxic mechanisms and apoptotic cascades. This paper reviews the research pertaining to the where, what, and how of HIV and cocaine/methamphetamine toxicity in the CNS. Specifically, where these toxins most affect the brain, what aspects of the virus are neurotoxic, and how these toxins mediate neurotoxicity.

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.

Interactions of HIV and methamphetamine: cellular and molecular mechanisms of toxicity potentiation

Methamphetamine (METH) is a highly addictive psychostimulant drug, whose abuse has reached epidemic proportions worldwide. METH use is disproportionally represented among populations at high risks for developing HIV infection or who are already infected with the virus. Psychostimulant abuse has been reported to exacerbate the cognitive deficits and neurodegenerative abnormalities observed in HIV-positive patients. Thus, the purpose of the present paper is to review the clinical and basic observations that METH potentiates the adverse effects of HIV infection. An additional purpose is to provide a synthesis of the cellular and molecular mechanisms that might be responsible for the increased toxicity observed in co-morbid patients. The reviewed data indicate that METH and HIV proteins, including gp120, gp41, Tat, Vpr and Nef, converge on various caspase-dependent death pathways to cause neuronal apoptosis. The role of reactive microgliosis in METH- and in HIV-induced toxicity is also discussed.

Blockage of VIP during mouse embryogenesis modifies adult behavior and results in permanent changes in brain chemistry

Vasoactive intestinal peptide (VIP) regulates growth and development during the early postimplantation period of mouse embryogenesis. Blockage of VIP with a VIP antagonist during this period results in growth restriction, microcephaly, and developmental delays. Similar treatment of neonatal rodents also causes developmental delays and impaired diurnal rhythms, and the adult brains of these animals exhibit neuronal dystrophy and increased VIP binding. These data suggest that blockage of VIP during the development of the nervous system can result in permanent changes to the brain. In the current study, pregnant mice were treated with a VIP antagonist during embryonic days 8 through 10. The adult male offspring were examined in tests of novelty, paired activity, and social recognition. Brain tissue was examined for several measures of chemistry and gene expression of VIP and related compounds. Glial cells from the cortex of treated newborn mice were plated with neurons and examined for VIP binding and their ability to enhance neuronal survival. Treated adult male mice exhibited increased anxiety-like behavior and deficits in social behavior. Brain tissue exhibited regionally specific changes in VIP chemistry and a trend toward increased gene expression of VIP and related compounds that reached statistical significance in the VIP receptor, VPAC-1, in the female cortex. When compared to control astrocytes, astrocytes from treated cerebral cortex produced further increases in neuronal survival with excess synaptic connections and reduced VIP binding. In conclusion, impaired VIP activity during mouse embryogenesis resulted in permanent changes to both adult brain chemistry/cell biology and behavior with aspects of autism-like social deficits.

Neonatal mice of the Down syndrome model, Ts65Dn, exhibit upregulated VIP measures and reduced responsiveness of cortical astrocytes to VIP stimulation

The Ts65Dn segmental mouse model of Down syndrome (DS) possesses a triplication of the section of chromosome 16 that is most homologous to the human chromosome 21 that is trisomic in DS. This model exhibits many of the characteristics of DS including small size, developmental delays, and a decline of cholinergic systems and cognitive function with age. Recent studies have shown that vasoactive intestinal peptide (VIP) systems are upregulated in aged Ts65Dn mice and that VIP dysregulation during embryogenesis is followed by the hypotonia and developmental delays as seen in both DS and in Ts65Dn mice. Additionally, astrocytes from aged Ts65Dn brains do not respond to VIP stimulation to release survival-promoting substances. To determine if VIP dysregulation is age-related in Ts65Dn mice, the current study examined VIP and VIP receptors (VPAC-1 and VPAC-2) in postnatal day 8 Ts65Dn mice. VIP and VPAC-1 expression was significantly increased in the brains of trisomic mice compared with wild-type mice. VIP-binding sites were also significantly increased in several brain areas of young Ts65Dn mice, especially in the cortex, caudate/putamen, and hippocampus. Further, in vitro treatment of normal neurons with conditioned medium from VIP-stimulated Ts65Dn astrocytes from neonatal mice did not enhance neuronal survival. This study indicates that VIP anomalies are present in neonatal Ts65Dn mice, a defect occurs in the signal transduction mechanism of the VPAC-1 VIP receptor, cortical astrocytes from neonatal brains are dysfunctional, and further, that VIP dysregulation may play a significant role in DS.

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.

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.

Cerebrospinal and peripheral human immunodeficiency virus type 1 load in a multisite, randomized, double-blind, placebo-controlled trial of D-Ala1-peptide T-amide for HIV-1-associated cognitive-motor impairment

D-Ala1-peptide T-amide (DAPTA) has shown neuroprotection in vitro against gp120-induced loss of dendritic arborization and is promulgated as a CCR5 antagonist. A multisite, randomized, double-blind clinical trial of DAPTA versus placebo prior to combination antiretroviral therapy conducted with human immunodeficiency virus (HIV)-1 seropositive participants having cognitive impairment showed no overall cognitive effect, though subgroups with greater impairment and CD4 cell counts of 201 to 500 cells/mm3 at baseline showed significant improvement. The objective of this study was to examine whether intranasal administration of DAPTA at a dose of 2 mg three times per day (tid) was associated with a reduction of cerebrospinal fluid (CSF) and peripheral (plasma and serum) viral load among a subgroup of participants completing 6 months of treatment. Baseline and 6-month CSF (n = 92) and peripheral (plasma n = 33; serum n = 24) viral load were measured by the Roche Ultrasensitive assay, version 1.5, with reflexive use of the AMPLICOR assay and preservation of the blind. A DAPTA treatment indicator variable was tested using generalized linear models on change in viral load. Peripheral load (combined plasma and serum) was significantly reduced in the DAPTA-treated group. No group differences in CSF viral load were found. This retrospective study on a limited subgroup of the original trial sample indicated that DAPTA treatment may reduce peripheral viral load without concomitant CSF effects. Future studies should be undertaken to confirm the existence of this result and the CSF-periphery dissociation observed with respect to HIV-1-associated cognitive-motor impairment.

HIV-1 gp120 enhances giant depolarizing potentials via chemokine receptor CXCR4 in neonatal rat hippocampus

In the immature hippocampus, the giant depolarizing potentials (GDPs) are recurrent network-driven synaptic events generated by gamma-aminobutyric acid (GABA), which in neonatal life is depolarizing and excitatory. The GDPs enable a high degree of synchrony in immature neurons and participate in activity-dependent growth and synapse formation. To understand how human immunodeficiency virus type one (HIV-1) infection in the immature brain impairs brain growth and development, we studied the effects of HIV-1 envelope glycoprotein, gp120, a viral toxin shed in abundance by infected cells, on spontaneous occurring GDPs recorded in the CA3 pyramidal cells in neonatal (P2-P6) Sprague-Dawley rat hippocampal slices using whole-cell patch technique. Bath application of gp120 produced a sustained enhancement of GDP frequency in a concentration-dependent manner without affecting passive membrane properties, suggesting that the site of action is most likely on neural network, other than on the recorded neurons. The gp120-induced enhancement of GDPs was blocked by T140, a highly specific antagonist for the chemokine receptor, CXCR4, indicating the involvement of CXCR4 in the gp120-induced increase of GDPs. Bath application of stromal cell-derived factor-1alpha (SDF-1alpha), the only CXCR4 ligand, mimicked the effects of gp120 on GDPs, supporting the engagement of CXCR4 receptors in the gp120-induced increase of GDP occurrence. Further studies revealed the involvement of protein kinase A/C in the gp120-induced enhancement of GDPs. These results demonstrate that gp120 enhances GDPs in the neonatal rat hippocampus. This enhancement may cause an excessive increase in intracellular calcium and resultant neuronal injury, leading to retardation of the brain and behavioural development as seen in paediatric AIDS patients.

Reduction in phosphorylated heavy neurofilament in the cerebellum in HIV disease

In the absence of significant neuronal infection HIV induces neuronal damage and death. The pathogenesis of this process is not clear and can only be assessed in the HIV infected brain by examining surviving neuronal populations. Cerebellar Purkinje cells are a model population. We have already demonstrated glutamate receptor alterations in these neurons in AIDS, and in the current study we have investigated the phosphorylation status of heavy neurofilament (NF-H), which is under the control of various intracellular kinases. While the number of Purkinje cells expressing non-phosphorylated NF-H was unchanged, the number of Purkinje cells expressing phosphorylated NF-H was decreased by 36% in the HIV group. This may be a marker of neuronal damage, and possibly indicate alteration in the activity of various intracellular signalling kinase pathways in the HIV infected brain.

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.

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.

Mouse behavioural analysis in systems biology

Molecular techniques allowing in vivo modulation of gene expression have provided unique opportunities and challenges for behavioural studies aimed at understanding the function of particular genes or biological systems under physiological or pathological conditions. Although various animal models are available, the laboratory mouse (Mus musculus) has unique features and is therefore a preferred animal model. The mouse shares a remarkable genetic resemblance and aspects of behaviour with humans. In this review, first we describe common mouse models for behavioural analyses. As both genetic and environmental factors influence behavioural performance and need to be carefully evaluated in behavioural experiments, considerations for designing and interpretations of these experiments are subsequently discussed. Finally, common behavioural tests used to assess brain function are reviewed, and it is illustrated how behavioural tests are used to increase our understanding of the role of histaminergic neurotransmission in brain function.

Borna disease virus replication in organotypic hippocampal slice cultures from rats results in selective damage of dentate granule cells

In the hippocampus of Borna disease virus (BDV)-infected newborn rats, dentate granule cells undergo progressive cell death. BDV is noncytolytic, and the pathogenesis of this neurodevelopmental damage in the absence of immunopathology remains unclear. A suitable model system to study early events of the pathology is lacking. We show here that organotypic hippocampal slice cultures from newborn rat pups are a suitable ex vivo model to examine BDV neuropathogenesis. After challenging hippocampal slice cultures with BDV, we observed a progressive loss of calbindin-positive granule cells 21 to 28 days postinfection. This loss was accompanied by reduced numbers of mossy fiber boutons when compared to mock-infected cultures. Similarly, the density of dentate granule cell axons, the mossy fiber axons, appeared to be substantially reduced. In contrast, hilar mossy cells and pyramidal neurons survived, although BDV was detectable in these cells. Despite infection of dentate granule cells 2 weeks postinfection, the axonal projections of these cells and the synaptic connectivity patterns were comparable to those in mock-infected cultures, suggesting that BDV-induced damage of granule cells is a post-maturation event that starts after mossy fiber synapses are formed. In summary, we find that BDV infection of rat organotypic hippocampal slice cultures results in selective neuronal damage similar to that observed with infected newborn rats and is therefore a suitable model to study BDV-induced pathology in the hippocampus.

In Vitro Methods in the Study of Viral and Prion Permeability Across the Blood–Brain Barrier

(1) Infectious agents capable of entering the central nervous system (CNS) produce some of the most dreaded diseases known to man. The infectious agent within the CNS is often protected by the blood-brain barrier (BBB), shielded from endogenous and exogenous anti-infectious agents. (2) The use of in vitro methods offers many advantages to the study of how infectious agents interact with the BBB. Two such agents which negotiate the BBB early in the course of disease before damage to the BBB are the autoimmune deficiency syndrome virus, or human immunodeficiency virus 1, and scrapie prion. Our laboratories have used in vitro methods to study these agents. (3) Here, we review some of the results form our laboratories and those of others.

Molecular makeup of HIV-1 envelope protein

A broad range of structural, functional, and immunological similarities between HIV-1 gp120 and human proteins, especially those participating in immune responses, highlight gp120 as a pleiotropic protein that can in different ways affect many important functions of the human immune system. Here we described some of these properties of HIV-1 gp120 that represent the main obstacle in the development of effective and safe AIDS vaccine.

Protective peptides that are orally active and mechanistically nonchiral

Previous reports identified two peptides that mimic the action of neuroprotective proteins derived from astrocytes. These peptides, NAPVSIPQ and SALLRSIPA, prevent neuronal cell death produced by electrical blockade, N-methyl-d-aspartate, and beta-amyloid peptide (25-35). In the present study, all d-amino acid peptides of NAPVSIPQ and SALLRSIPA were synthesized and compared respectively to the corresponding all l-amino acid peptides. In rat cerebral cortical test cultures cotreated with 1 microM tetrodotoxin, the d-amino acid peptides produced similar potency and efficacy for neuroprotection as that observed for their respective l-amino acid peptides. Since all these peptides tested individually exhibited attenuation of efficacy at concentrations of >10 pM, combinations of these peptides were tested for possible synergies. Equimolar d-NAPVSIPQ and d-SALLRSIPA combination treatment produced potent neuroprotection (EC(50), 0.03 fM) that did not attenuate with increasing concentrations. Similarly, the combination of l-NAPVSIPQ and d-SALLRSIPA also had high potency (EC(50), 0.07 fM) without attenuation of efficacy. Combined administration of peptides was tested in a model of fetal alcohol syndrome and in a model of learning impairment: apolipoprotein E knockout mice. Intraperitoneal administration of d-NAPVSIPQ plus d-SALLRSIPA to pregnant mice (embryonic day 8) attenuated fetal demise after treatment with an acute high dose of alcohol. Furthermore, oral administration of d-NAPVSIPQ plus d-SALLRSIPA significantly increased fetal survival after maternal alcohol treatment. Apolipoprotein E knockout mice injected with d-NAPVSIPQ plus d-SALLRSIPA showed improved performance in the Morris water maze. These studies suggest therapeutic potential for the combined administration of neuroprotective peptides that can act through a mechanism independent of chiral recognition.

Hippocampal synaptic dysfunction in a murine model of human immunodeficiency virus type 1 encephalitis

Alterations in hippocampal physiology affect cognition in human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). The mechanism for how this occurs is not well understood. To address this, we investigated how changes in synaptic transmission and plasticity are affected by viral infection and macrophage activation using a severe combined immunodeficiency mouse model of human HIV-1 encephalitis (HIVE). HIVE was induced in mice by stereotactic injection of HIV-1-infected human monocyte-derived macrophages (MDM) into the striatum. Animals were sacrificed after 3, 7 and 15 days. Hippocampal slices were prepared from HIV-1, MDM- and sham-injected animals. Electrically evoked field excitatory postsynaptic potentials were recorded in the CA1 region of the hippocampus. Neuronal physiology was assessed by input-output and by long-term potentiation (LTP) assays. We observed that a higher stimulation intensity (mA) was required to induce a 1-mV response in the HIVE mice (0.32+/-0.06) compared with shams (0.17+/-0.01) at day 7. The stimulation intensities at day 15 were 0.44+/-0.07 and 0.23+/-0.05 in the HIVE and shams, respectively. An impairment of synaptic function was detected through measuring synaptic responses induced by stimuli with different intensities. Paired-pulse facilitation (PPF) showed deficits in HIVE mice at days 3, 7, and 15. At day 3, PPF ratios were 1.13+/-0.02 and 1.24+/-0.04 in HIVE and sham. The induction and maintenance of LTP was also impaired in HIVE mice. The average magnitude of LTP was 131.23+/-15.26% of basal in HIVE as compared with sham animals of 232.63+/-24.18%. MDM-injected mice showed an intermediate response. Taken together, the results show a range of neuronal synaptic transmission and plasticity changes in HIVE mice that may reflect the mechanisms of cognitive dysfunction in human HAD.

Intracerebral HIV-1 glycoprotein 120 produces sickness behavior and pituitary-adrenal activation in rats: role of prostaglandins

HIV infection is associated with profound neurobehavioral and neuroendocrine impairments. Previous studies demonstrated that HIV causes neuropathological alterations indirectly, via shedding of glycoprotein 120 (gp120) within the brain. To extend these findings, we examined the neurobehavioral and neuroendocrine effects of central administration of gp120, as well as the role of brain prostaglandins in mediating these effects. Intracerebroventricular (i.c.v.) injection of gp120 in rats produced a marked sickness behavior syndrome, consisting of reduced exploratory behavior, suppressed consumption of food and saccharin solution, and reduced body weight. Gp120 also induced a significant febrile response and increased serum levels of ACTH and corticosterone. Following i.c.v. gp120 administration, the ex vivo production of PGE2 by the hypothalamus, frontal cortex, and hippocampus was significantly elevated, and indomethacin, a prostaglandin synthesis inhibitor, attenuated this elevation. Pre-treatment with indomethacin reduced the fever and adrenocortical activation induced by gp120 administration, but not its behavioral effects. These findings indicate that gp120 may be responsible for some of the behavioral and endocrine abnormalities seen in HIV-infected patients. Prostaglandins are important mediators of the physiological, but not the behavioral effects of brain gp120.

HIV-1 gp120 proteins and gp160 peptides are toxic to brain endothelial cells and neurons: possible pathway for HIV entry into the brain and HIV-associated dementia

Breakdown of the blood-brain barrier is commonly seen in patients with human immunodeficiency virus (HIV)-associated dementia, despite the lack of productive HIV-infection of the brain endothelium. Through this damaged blood-brain barrier, HIV and HIV-infected monocytes/macrophages infiltrate the brain and further infect microglia and brain macrophages. Neuronal cell death and dysfunction are the underlying cause of HIV-associated dementia, but no productive HIV-infection of neurons has been documented. It is likely that secreted viral products play a major role in blood-brain barrier damage and neuronal cell death. The aim of the present study was to examine the effect of HIV-1 gp160 peptides and gp120 proteins on brain microvascular endothelial cells and neurons from both human and rats. Four of the 7 gp160 peptides tested evoked significant neurotoxicity. Two different full-length recombinant HIV gp120 proteins (HIV-1CM235 gp120 and HIV-1MN gp120) also induced neuronal and brain endothelial cell death, and concentrations as little as 1 ng/ml evoked pronounced morphological changes in these cells and marked cytotoxicity. This study suggests that HIV proteins and peptides that are shed in vivo may be directly involved in blood-brain barrier damage and neuronal cell death in HIV-associated dementia.

Mechanisms of HIV type 1-induced cognitive impairment: evidence for hippocampal cholinergic involvement with overstimulation of the VIPergic system by the viral coat protein core

HIV-1 is associated with a neuroAIDS syndrome that includes cognitive impairment. Several components of HIV-1 are capable of affecting cognition, but which of these is the major mediator is unknown. We injected into the lateral cerebral ventricle of mice HIV-1 pseudoviruses expressing the full viral genome with or without the viral coat glycoproteins, gp120/gp41. Only virus possessing gp120/gp41 induced defects in memory as assessed in an active avoidance T-maze footshock paradigm. By itself, gp120 also induced impairments that were reversed by hippocampal cholinergic stimulation. Paradoxically, low doses of gp120 could improve memory. Such low-dose, paradoxic improvement is a characteristic of substances that impair memory by overstimulating pathways that normally sustain memory. Consistent with this, a low, but not a high, dose of gp120 reversed memory impairment induced by overstimulation of the VIPergic system, a memory-sustaining pathway. Further characterization showed that two strains of gp120 (SF and MN) were equally effective at improving memory and that, unlike other actions of gp120, glycation was not required. We conclude that (1) the predominant cognitive-impairing component of HIV-1 is its viral coat glycoproteins, (2) gp120 impairs memory by overstimulating pathways that normally sustain memory, (3) the cognitive effect of gp120 is mediated by its protein core, and (4) gp120 likely impairs memory by affecting the cholinergic/VIPergic system.

Chemokine release is associated with the protective action of PACAP-38 against HIV envelope protein neurotoxicity

The envelope protein (gp120) of the human immunodeficiency virus produces neuronal cell death in cultures that can be prevented by co-treatment with pituitary adenylate activating peptide-38 (PACAP-38) or chemokines. To investigate the hypothesis that a functional relationship exists between these two protectants, the release of chemokines was measured in rat astrocyte cultures after PACAP-38 treatment. Chemokine analyses were performed by immunoaffinity capillary electrophoresis. Bell-shaped dose-responses for PACAP-mediated release of chemokines into the culture medium were observed with EC(50)'s of 3 x 10(15) M (RANTES: regulated upon activation normal T cell expressed and secreted), 3 x 10(-11) M (MIP-1 beta) and 10(-7)M (MIP-1 alpha). In addition, PACAP-mediated depletion of chemokines from cultured astrocytes exhibited inverted bell-shaped curves, with similar EC(50)'s to those observed for chemokine measurements of the medium. Comparative studies with structurally related peptides (vasoactive intestinal peptide [VIP] and secretin) revealed that PACAP was the most potent secretagogue for RANTES on astrocyte cultures. Gp120-mediated neuronal cell death was prevented by co-treatment with PACAP-38, although the efficacy of protection varied significantly among the gp120 isolates. A bi-model dose-response was observed with EC(50)'s of 3 x 10(-15) and 3 x 10(-11) M. Co-treatment with neutralizing antiserum to RANTES attenuated PACAP-mediated protection from toxicity associated with gp120. In contrast to previous studies with VIP and gp120 toxicity, co-treatment with anti-MIP-1 alpha did not affect PACAP-induced protection. These studies support the hypothesis that PACAP produces neuroprotection from gp120 toxicity, in part, through the release of RANTES and this mechanism is distinct from that observed with VIP.

Decreased expression of MAP-2 and GAD in the brain of cats infected with feline immunodeficiency virus

HIV-1 infection is often complicated by the dysfunction of central nervous system (CNS). Degenerative neuronal changes as well as neuronal loss have been documented in individuals with acquired immunodeficiency syndrome. Feline immunodeficiency virus (FIV) causes similar CNS manifestation and FIV infected cats provide an animal model for human immunodeficiency virus infection in humans. In this study, we examined the brain of FIV-infected cats and controls with immunohistochemical techniques using antibodies to microtubule-associated protein 2 (MAP-2) and glutamic acid decarboxylase (GAD). We found a significant decrease in expression of MAP-2 and GAD in neurons of infected animals compared to controls. In contrast, the expression of neurofilaments and glial fibrillary acidic protein was rather increased. The changes observed in the brain were similar to those seen in humans undergoing the normal aging process as well as those suffering from neurological diseases like Alzheimer's disease and other dementing disorders. These changes in the feline brain give insight into the deleterious effects of FIV on the CNS.

Peptide T inhibits HIV-1 infection mediated by the chemokine receptor-5 (CCR5)

Peptide T, which is derived from the V2 region of HIV-1, inhibits replication of R5 and dual-tropic (R5/X4) HIV-1 strains in monocyte-derived macrophages (MDMs), microglia, and primary CD4(+)T cells. Little to no inhibition by peptide T was observed with lab adapted X4 viruses such as IIIB, MN, or NL4-3 propagated in CD4(+) T cells or in the MAGI entry assay. The more clinically relevant R5/X4 early passage patient isolates were inhibited via either the X4 or R5 chemokine receptors, although inhibition was greater with R5 compared to X4 receptors. Virus inhibition ranged from 60 to 99%, depending on the assay, receptor target, viral isolate and amount of added virus. Peak inhibitory effects were detected at concentrations from 10(-12) to 10(-9) M. Peptide T acted to block viral entry as it inhibited in the MAGI cell assay and blocked infection in the luciferase reporter assay using HIV virions pseudotyped with ADA envelope. These results using early passage virus grown in primary cells, together with two different entry reporter assays, show that peptide T selectively inhibits HIV replication using chemokine receptor CCR5 compared to CXC4, explaining past inconsistencies of in vitro antiviral effects.

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.

Microglia in HIV-associated neurological diseases

Human immunodeficiency virus type-1 (HIV-1) is a neurotropic virus linked to a variety of progressive neurologic disorders. This review describes our current understanding of how HIV-1 enters the nervous system and interacts with neuronal and non-neuronal cells to initiate and sustain neurologic dysfunction. The overwhelming majority of cells infected with HIV-1 in the nervous system are microglia/macrophages. Microglial/macrophage infection leads to immune dysregulation as well as production and release of cytotoxic molecules. Interaction of these infected cells with astrocytes may accelerate neurotoxic mechanisms. A hypothetical scenario for how HIV-1 infection leads to neurologic disease is presented.

Neuropathology of NFHgp160 transgenic mice expressing HIV-1 env protein in neurons

The physiopathology of HIV-1 dementia remains largely hypothetical. Although several sets of evidence point towards an indirect multicellular inflammatory pathway, gp120, one of the HIV-1 env products, was shown to be very cytotoxic for neurons in vitro. To explore a direct pathway in the physiopathology of dementia in AIDS, we developed transgenic mouse models carrying the HIV-1 env proteins gp 120 and gp 41 (gp 160) under the control of the human light neurofilament and murine heavy neurofilament promoters. To date, this is the first mouse model in which the HIV-1 env protein can be detected in neurons by immunohistochemistry. The expression is found in several brainstem and spinal cord gray structures and in the cerebellum in one of the mouse lines bearing the NFHgp160 transgene. The morphological findings at 3 months are subtle and are dominated by a watery, dendritic degeneration and a reactive gliosis. At 12 months, the evidence of neuronal degeneration and loss is present along with various degenerative phenomena involving synapses, dendrites and axons, including axonal swellings. Cytoskeletal abnormalities were found by immunohistochemistry. Chronic inflammation was also observed in the leptomeninges of the spinal cord and brainstem and in the cerebellar white matter. These models thus offer an exciting sequence of morphological findings initiated by the neuronal expression of the HIV-1 env proteins and offer a different tool to explore the neuronal dysfunction in AIDS.

Direct role of plasma membrane-expressed gp120/41 in toxicity to human astrocytes induced by HIV-1-infected macrophages

OBJECTIVE

To compare astrocyte toxicity induced by plasma membrane-expressed gp120/41 and soluble gp120.

DESIGN

Analysis of morphological alterations and lactate dehydrogenase (LDH) release from astrocytes in culture with monocytes infected with HIV-1, microglia expressing Env of a macrophage-tropic HIV-1 isolate or soluble Env.

METHODS

Primary human embryonic astrocytes were cultured with: monocytes infected with two M-tropic HIV-1 isolates (HIV-1(9533), HIV-1(BX08)); human microglia infected with the defective Semliki Forest virus (SFV) vector coding for the env gene of HIV-1(BX08) isolate (SFVenvBX08); and soluble gp140 purified from baby hamster kidney cells transfected with the env gene of HIV-1(BX08) lacking the intracytoplasmic region of gp41 (SFVdelta envBX08). Gp120 mRNA levels were assessed by quantitative reverse transcriptase-polymerase chain reaction and the protein was detected by immunofluorescence in infected monocytes or microglia.

RESULTS

Contact of HIV-infected monocytes induced morphological changes in astrocytes and a 137% increase in LDH release at day 2 of co-culture compared with controls (uninfected monocytes). Gp120/41(BX08)-expressing microglia induced a 170% increase in LDH release (relative to SFVLacZ-infected microglia). Pretreatment of co-cultures with an anti-gp120 monoclonal antibody (mAb; NEA-9305) directed against the V3 loop inhibited LDH release. Soluble purified gp140 from BX08 isolate induced only a weak LDH release (104%). Finally, cytotoxicity was not blocked by treatment of the co-culture with Bordetella pertussis toxin, an inhibitor of Gi alpha protein-dependent receptors.

CONCLUSION

HIV envelope glycoprotein expressed at the plasma membrane induced astrocyte damage more efficiently than its soluble counterpart. The V3 loop was involved in toxicity induction through a pathway independent of the Gi alpha protein-coupled receptor.

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.

HIV-1 coat glycoprotein gp120 induces apoptosis in rat brain neocortex by deranging the arachidonate cascade in favor of prostanoids

Human immunodeficiency virus type-1 coat glycoprotein gp 120 causes delayed programmed cell death (apoptosis) in rat brain neocortex. Here, we investigated the possible role of the arachidonate cascade and membrane peroxidation in this process. It is shown that gp 120 causes a rapid increase in the activity and expression of the arachidonate-metabolizing enzyme prostaglandin H synthase, paralleled by increased prostaglandin E(2) levels. The selective inhibitor of prostaglandin H synthase indomethacin inhibited enzyme activity, reduced prostaglandin E(2) content, and partially protected neocortex against gp 120-induced apoptosis. Conversely, the activity and expression of the arachidonate-metabolizing enzyme 5-lipoxygenase decreased upon gp 120 treatment, as well as the level of its product, leukotriene B(4). Treatment with gp 120 also reduced membrane lipid peroxidation, and this may be implicated in the execution of programmed cell death. These results suggest that early derangement of the arachidonate cascade in favor of prostanoids may be instrumental in the execution of delayed apoptosis in the brain neocortex of rats.

Evidence of blood-brain barrier alteration and activation in HIV-1 gp120 transgenic mice

OBJECTIVE

To verify whether HIV envelope protein gp120 changes the blood-brain barrier in vivo, as a fundamental mechanism of early central nervous system damage by HIV-1.

DESIGN

Analysis of the functional integrity and immune activation of the blood-brain barrier in brains of HIV-1 gp120 transgenic mice secreting circulating gp120 at levels similar to those detected in AIDS patients.

METHODS

Number of vessels/mm2 section area with perivascular albumin and percentage of vessels expressing adhesion molecules (ICAM-1 and VCAM-1) were determined by immunohistochemistry in frozen brains from autopsied transgenic and non-transgenic mice. The percentage of vessels showing substance P immunoreactivity was also calculated, as this neuropeptide is known to mediate the increase in permeability of the rat brain endothelium in vitro caused by HIV-1 gp120.

RESULTS

The number of vessels with albumin extravasation was significantly higher in transgenic than non-transgenic mice brains (P = 0.0003). A greater percentage of ICAM-1- and VCAM-1-positive brain vessels in transgenic than non-transgenic mice was shown (P = 0.0017 and P = 0.0008 respectively). Significant immunoreactivity for substance P was detected in brain vessels in transgenic mice and a significant correlation was found between the percentage of substance P-positive and ICAM-1-positive brain vessels (P < 0.0001) in transgenic mice.

CONCLUSIONS

These findings demonstrate that HIV-1 gp120 is capable of changing and activating in vivo the vascular component of the blood-brain barrier.

VIP and D-ala-peptide T-amide release chemokines which prevent HIV-1 GP120-induced neuronal death

Vasoactive intestinal peptide (VIP) and DAPTA (D-ala(1)-peptide T-amide, a gp120-derived octapeptide homologous to VIP) prevent neuronal cell death produced by five variants of HIV-1 (human immunodeficiency virus) envelope protein (gp120). VIP or DAPTA treatment of astrocyte cultures resulted in the release of macrophage inflammatory protein-1alpha (MIP-1alpha) and RANTES, beta chemokines known to block gp120 interactions with microglial chemokine receptors. In rat cerebral cortical cultures, gp120-induced neuronal killing was partially or completely prevented by chemokines that stimulate the CXCR4, CCR3 or CCR5 chemokine receptors. Chemokines exhibited marked differences in potency and efficacy in preventing toxicity associated with five gp120 variants (LAV/BRU, CM243, RF, SF2, and MN). RANTES had the broadest and most potent inhibition (IC(50)<3 pM for RF isolate). An octapeptide derived from RANTES also exhibited neuroprotection from gp120 (RF isolate) toxicity (IC(50)=0.3 microM). Treatment with chemokines alone had no detectable effect on neuronal cell number. However, antiserum to MIP-1alpha produced neuronal cell death that was prevented by co-treatment with MIP-1alpha, suggesting that this endogenous chemokine exerts a tonic regulation important to neuronal survival. The neuroprotective action of VIP on gp120 was attenuated by co-treatment with anti-MIP-1alpha. These studies suggest that the neuroprotective action of VIP is linked in part to its release of MIP-1alpha. Furthermore, neuroprotection produced by chemokines is dependent on both the type of chemokine and the variant structure of gp120 and may be relevant to drug strategies for the treatment of AIDS dementia.

Feline immunodeficiency virus envelope protein (FIVgp120) causes electrophysiological alterations in rats

Close to 20% of the patients infected with the AIDS virus develops neurological deficit; eventhough HIV does not invade neurons. Consistently with the neurological deficit, HIV(+) subjects show abnormalities in brainstem auditory and visual evoked potentials (BSAEP and VEP) and in sleep patterns. The HIV-derived glycoprotein 120 has been postulated as a neurotoxic; therefore, it may be playing a crucial role in the generation of BSAEP and VEP, as well as in sleep disturbances. To study the role of the virus-derived proteins on the development of these electrophysiological signals' alterations, we have used the feline immunodeficiency virus (FIV)-derived gp120 and evaluated the changes in these electrophysiological signals. We employed 15 adult male Sprague-Dawley rats (250-350 g), chronically implanted for evoked potential and sleep recordings. Results showed that the i.c.v. administration of FIVgp120 (5 ng/10 microliter) produces changes in the latency of both cortical auditory evoked potentials (CAEPs) and VEPs and a decrease in both REM sleep and SWS. These data support the notion that FIVgp120 is neurotoxic to the central nervous system of cats and rats and that this protein suffices to cause electrophysiological alterations. In addition, it suggests that a similar effect may be occurring in humans as a result of HIVgp120's neurotoxic effects.

Effects of wheatgerm agglutinin and aging on the regional brain uptake of HIV-1GP120

HIV-1 is associated with infection and altered functions of the CNS, especially in the elderly. Most studies indicate that HIV-1 is not evenly distributed throughout the CNS but is concentrated in deep brain nuclei. This study examined whether regional or age-related differences in the permeability of the blood-brain barrier to gp120, the viral coat of HIV-1, exist. The initial concentration of gp120 in 10 brain regions correlated with vascular content in young and old mice. Susceptibility to wheatgerm agglutinin (WGA)-induced uptake of gp120, which relates to endothelial cell internalization, varied regionally, with no induction of uptake into the striatum or hypothalamus but with large increases in the cerebellum, cortex, and midbrain. Transport across the BBB, as measured by the unidirectional influx rate (Ki), also varied regionally with the hypothalamus, hippocampus, and pons-medulla showing the highest values for Ki and the striatum the lowest. These regional variations in the permeability of the BBB to gp120 could contribute to the inhomogeneous distribution of HIV-1 within the CNS whereas the failure to see differences with aging suggests other causes underlie the susceptibility of the elderly to the CNS manifestations of AIDS.

Involvement of interleukin-1beta in the mechanism of human immunodeficiency virus type 1 (HIV-1) recombinant protein gp120-induced apoptosis in the neocortex of rat

The effect of subchronic intracerebroventricular injection of the human immunodeficiency virus type 1 (HIV-1) recombinant protein gp120 (100 ng, given daily for up to seven consecutive days) on interleukin-1beta expression was studied by immunohistochemistry in the brain of adult rats. In comparison to control, bovine serum albumin (300 ng, given intracerebroventricularly for up to seven days) -treated animals (n=6), interleukin-1beta immunoreactivity increased in the brain cortex and hippocampus of rats (n=6) receiving a single injection of the viral protein 24 h before analysis with more substantial increases being observed in these regions of the brain (n=6) after seven days treatment. Double-labelling immunofluorescence experiments support a neuronal and, possibly, a microglial cell origin for gp120-enhanced interleukin-1beta expression. Transmission electron microscopy analysis of brain tissue sections revealed that combination treatments (given intracerebroventricularly daily for seven days) with gp120 (100 ng) and interleukin-1 receptor antagonist (80 ng) or with the interleukin converting enzyme inhibitor II (100 pmol), but not with leupeptin (100 pmol), prevented apoptotic death of rat (n=6/group) brain cortical cells typically elicited by the viral protein. These data demonstrate that gp120 enhances interleukin-1beta expression in the brain and this may be involved in the mechanism underlying apoptosis induced by gp120 in the brain cortex of rat. Further support to this hypothesis comes from the evidence that intracerebroventricular injection of murine recombinant interleukin-1beta (200 U, given daily for seven consecutive days) produces DNA fragmentation in the brain cortex of rat (n=6). Interestingly, the latter treatment enhanced nerve growth factor level in the hippocampus but not in the cerebral cortex and this coincides with a similar effect recently reported in identical brain areas of rats treated likewise with gp120. In conclusion, the present data demonstrate that treatment with gp120 enhances interleukin-1beta expression and this participates in the mechanism of apoptotic cell death in the brain cortex of rat. By contrast, in the hippocampus, gp120-enhanced interleukin-1beta expression elevates nerve growth factor that may prevent or delay apoptosis in this plastic region of the rat brain.