Impaired spatial cognition and synaptic potentiation in a murine model of human immunodeficiency virus type 1 encephalitis

HIV-induced neuroinflammation inhibits oligodendrocyte maturation via glutamate-dependent activation of the PERK arm of the integrated stress response

Despite combined antiretroviral therapy (cART), HIV-associated neurocognitive disorder (HAND) affects 30-50% of HIV-positive patients. Importantly, persistent white matter pathologies, specifically corpus callosum thinning and disruption of white matter microstructures observed in patients with HAND despite viral control through cART, raise the possibility that HIV infection in the setting of suboptimal cART may perturb oligodendrocyte (OL) maturation, function and/or survival, influencing HAND persistence in the cART era. To examine the effect of HIV infection on OL maturation, we used supernatants of primary human monocyte-derived macrophages infected with HIV (HIV/MDMs) to treat primary cultures of rat oligodendrocyte precursor cells (OPCs) during their differentiation to mature OLs. Using immunostaining for lineage-specific markers, we found that HIV/MDMs significantly inhibited OPC maturation. Based on our previous studies, we examined the potential role of several signaling pathways, including ionotropic glutamate receptors and the integrated stress response (ISR), and found that AMPA receptors (AMPAR)/kainic acid (KA) receptors (KARs) mediated the HIV/MDMs-induced defect in OL maturation. We also found that the treatment of OPC cultures with glutamate or AMPAR/KAR agonists phenocopied this effect. Blocking ISR activation, specifically the PERK arm of the ISR, protected OPCs from HIV/MDMs-mediated inhibition of OL maturation. Further, while glutamate, AMPA, and KA activated the ISR, inhibition of AMPAR/KAR activation prevented ISR induction in OPCs and rescued OL maturation. Collectively, these data identify glutamate signaling via ISR activation as a potential therapeutic pathway to ameliorate white matter pathologies in HAND and highlight the need for further investigation of their contribution to cognitive impairment.

Japanese Encephalitis Virus Infection Results in Transient Dysfunction of Memory Learning and Cholinesterase Inhibition

Cholinergic system has an important role in memory and learning. Abnormal cognitive and behavioral changes have been reported in Japanese encephalitis (JE), but their basis has not been comprehensively evaluated. In this study, we report memory and learning and its association with acetylcholinesterase (AChE) activity, JE virus titer, and with histopathological observations in a rat model of JE. Wistar rats were intracerebrally inoculated on 12th day with 3 × 10⁶ pfu/ml of JE virus. Memory and learning were assessed by the active and passive avoidance tests on 10, 33, and 48 days post inoculation (dpi). After 10, 33, and 48 dpi AChE activity, Japanese encephalitis virus (JEV) titer and histopathological changes were studied in the frontal cortex, thalamus, midbrain, cerebellum, and hippocampus. There was significant impairment in memory and learning on 10 dpi which started improving from 33 dpi to 48 dpi by active avoidance test. Passive avoidance test showed decrease in transfer latency time of retention trial compared to acquisition on first, second, and third retention day trial compared to controls. AChE inhibition was more marked in the hippocampus, frontal cortex, and cerebellum on 10 dpi. However, AChE activity started improving from 33 dpi to 48 dpi. AChE activity in the thalamus and midbrain correlated with active avoidance test on 10 dpi and 33 dpi. Histopathological studies also revealed improvement on 33 and 48 compared to 10 dpi. The present study demonstrates transient memory and learning impairment which was associated with reduction in AChE, JEV titer, and damage in different brain regions of JEV infected rats.

Impact of Increased Astrocyte Expression of IL-6, CCL2 or CXCL10 in Transgenic Mice on Hippocampal Synaptic Function

An important aspect of CNS disease and injury is the elevated expression of neuroimmune factors. These factors are thought to contribute to processes ranging from recovery and repair to pathology. The complexity of the CNS and the multitude of neuroimmune factors that are expressed in the CNS during disease and injury is a challenge to an understanding of the consequences of the elevated expression relative to CNS function. One approach to address this issue is the use of transgenic mice that express elevated levels of a specific neuroimmune factor in the CNS by a cell type that normally produces it. This approach can provide basic information about the actions of specific neuroimmune factors and can contribute to an understanding of more complex conditions when multiple neuroimmune factors are expressed. This review summarizes studies using transgenic mice that express elevated levels of IL-6, CCL2 or CXCL10 through increased astrocyte expression. The studies focus on the effects of these neuroimmune factors on synaptic function at the Schaffer collateral to CA1 pyramidal neuron synapse of the hippocampus, a brain region that plays a key role in cognitive function.

Neuroinflammation and Behavior in HIV-1 Transgenic Rats Exposed to Chronic Adolescent Stress

Highly active antiretroviral therapy (HAART) has improved prognosis for people living with HIV (PLWH) and dramatically reduced the incidence of AIDS. However, even when viral load is controlled, PLWH develop psychiatric and neurological disorders more frequently than those living without HIV. Adolescents with HIV are particularly susceptible to the development of psychiatric illnesses and neurocognitive impairments. While both psychiatric and neurocognitive disorders have been found to be exacerbated by stress, the extent to which chronic stress and HIV-1 viral proteins interact to impact behavior and relevant neuroinflammatory processes is unknown. Determination of the individual contributions of stress and HIV to neuropsychiatric disorders is heavily confounded in humans. In order to isolate the influence of HIV-1 proteins and chronic stress on behavior and neuroinflammation, we employed the HIV-1 transgenic (Tg) rat model, which expresses HIV-1 proteins with a gag and pol deletion, allowing for viral protein expression without viral replication. This Tg line has been characterized as a model of HAART-controlled HIV-1 infection due to the lack of viral replication but continued presence of HIV-1 proteins. We exposed male and female adolescent HIV-1 Tg rats to a mixed-modality chronic stress paradigm consisting of isolation, social defeat and restraint, and assessed behavior, cerebral vascularization, and neuroinflammatory endpoints. Stress, sex, and presence of the HIV-1 transgene impacted weight gain in adolescent rats. Female HIV-1 Tg rats showed decreases in central tendency during the light cycle in the open field regardless of stress exposure. Both male and female HIV-1 Tg rats exhibited decreased investigative behavior in the novel object recognition task, but no memory impairments. Adolescent stress had no effect on the tested behaviors. Microglia in female HIV-1 Tg rats exhibited a hyper-ramified structure, and gene expression of complement factor B was increased in the hippocampus. In addition, adolescent stress exposure increased microglial branching and junctions in female wild-type rats without causing any additional increase in HIV-1 rats. These data suggest that the presence of HIV-1 proteins during development leads to alterations in behavioral and neuroinflammatory endpoints that are not further impacted by concurrent chronic adolescent stress.

Associations between brain microstructures, metabolites, and cognitive deficits during chronic HIV-1 infection of humanized mice

Background

Host-species specificity of the human immunodeficiency virus (HIV) limits pathobiologic, diagnostic and therapeutic research investigations to humans and non-human primates. The emergence of humanized mice as a model for viral infection of the nervous system has overcome such restrictions enabling research for HIV-associated end organ disease including behavioral, cognitive and neuropathologic deficits reflective of neuroAIDS. Chronic HIV-1 infection of NOD/scid-IL-2Rg_c^null mice transplanted with human CD34⁺ hematopoietic stem cells (CD34-NSG) leads to persistent viremia, profound CD4⁺ T lymphocyte loss and infection of human monocyte-macrophages in the meninges and perivascular spaces. Murine cells are not infected with virus.

Methods

Changes in mouse behavior were measured, starting at 8 weeks after viral infection. These were recorded coordinate with magnetic resonance spectroscopy metabolites including N-acetylaspartate (NAA), creatine and choline. Diffusion tensor magnetic resonance imaging (DTI) was recorded against multispectral immunohistochemical staining for neuronal markers that included microtubule associated protein-2 (MAP2), neurofilament (NF) and synaptophysin (SYN); for astrocyte glial fibrillary acidic protein (GFAP); and for microglial ionized calcium binding adaptor molecule 1 (Iba-1). Oligodendrocyte numbers and integrity were measured for myelin associated glycoprotein (MAG) and myelin oligodendrocyte glycoprotein (MOG) antigens.

Results

Behavioral abnormalities were readily observed in HIV-1 infected mice. Longitudinal open field activity tests demonstrated lack of habituation indicating potential for memory loss and persistent anxiety in HIV-1 infected mice compared to uninfected controls. End-point NAA and creatine in the cerebral cortex increased with decreased MAG. NAA and glutamate decreased with decreased SYN and MAG. Robust inflammation reflected GFAP and Iba-1 staining intensities. DTI metrics were coordinate with deregulation of NF, Iba-1, MOG and MAG levels in the whisker barrel and MAP2, NF, MAG, MOG and SYN in the corpus callosum.

Conclusions

The findings are consistent with some of the clinical, biochemical and pathobiologic features of human HIV-1 nervous system infections. This model will prove useful towards investigating the mechanisms of HIV-1 induced neuropathology and in developing novel biomarkers and therapeutic strategies for disease.

Electronic supplementary material

The online version of this article (doi:10.1186/1750-1326-9-58) contains supplementary material, which is available to authorized users.

Combination of methamphetamine and HIV-1 gp120 causes distinct long-term alterations of behavior, gene expression, and injury in the central nervous system

Methamphetamine (METH) abuse is frequent in individuals infected with human immunodeficiency virus type-1 (HIV-1) and is suspected to aggravate HIV-associated neurocognitive disorders (HAND). METH is a psychostimulant that compromises several neurotransmitter systems and HIV proteins trigger neuronal injury but the combined effects of viral infection and METH abuse are incompletely understood. In this study we treated transgenic mice expressing the HIV envelope protein gp120 in the brain (HIV-1 gp120tg) at 3-4 months of age with an escalating-dose, multiple-binge METH regimen. The long-term effects were analyzed after 6-7 months of drug abstinence employing behavioral tests and analysis of neuropathology, electrophysiology and gene expression. Behavioral testing showed that both HIV-1 gp120tg and WT animals treated with METH displayed impaired learning and memory. Neuropathological analysis revealed that METH similar to HIV-1 gp120 caused a significant loss of neuronal dendrites and pre-synaptic terminals in hippocampus and cerebral cortex of WT animals. Electrophysiological studies in hippocampal slices showed that METH exposed HIV-1 gp120tg animals displayed reduced post-tetanic potentiation, whereas both gp120 expression and METH lead to reduced long-term potentiation. A quantitative reverse transcription-polymerase chain reaction array showed that gp120 expression, METH and their combination each caused a significant dysregulation of specific components of GABAergic and glutamatergic neurotransmission systems, providing a possible mechanism for synaptic dysfunction and behavioral impairment. In conclusion, both HIV-1 gp120 and METH caused lasting behavioral impairment in association with neuropathology and altered gene expression. However, combined METH exposure and HIV-1 gp120 expression resulted in the most pronounced, long lasting pre- and post-synaptic alterations coinciding with impaired learning and memory.

Glutamate metabolism and HIV-associated neurocognitive disorders

HIV-1 infection can lead to neurocognitive impairment collectively known as HIV-associated neurocognitive disorders (HAND). Although combined antiretroviral treatment (cART) has significantly ameliorated HIV's morbidity and mortality, persistent neuroinflammation and neurocognitive dysfunction continue. This review focuses on the current clinical and molecular evidence of the viral and host factors that influence glutamate-mediated neurotoxicity and neuropathogenesis as an important underlying mechanism during the course of HAND development. In addition, discusses potential pharmacological strategies targeting the glutamatergic system that may help prevent and improve neurological outcomes in HIV-1-infected subjects.

Conditional Tat protein expression in the GT-tg bigenic mouse brain induces gray matter density reductions

Tat (Trans-activator of transcription) is implicated in the neuropathogenesis of HIV-1 infection and known to contribute to neuronal damage and learning and memory impairments. However, direct neuroanatomical demonstration of Tat pathobiology is limited. GT-tg bigenic mice with a doxycycline (Dox)-inducible and brain-selective tat gene were used to test the hypothesis that conditional induction of Tat activity in brain can induce gray matter density abnormalities. Ultra high spatial resolution ex vivo magnetic resonance imaging (MRI) combined with a voxel based morphometry (VBM) analysis revealed gray matter density reductions in the sublenticular extended amygdala, the amygdala, the amygdala-hippocampal area, piriform and peri-/entorhinal cortices, and hypothalamus, in Tat-expressing GT-tg mice compared to Dox-treated C57Bl/6J mice. These neuroanatomical abnormalities are consistent with regions expected to be abnormal based on behavioral deficits exhibited by Tat-expressing mice (Carey et al., 2012). These experiments provide the first neuroimaging evidence that conditional Tat protein expression in the GT-tg bigenic mouse model alters brain structure. The findings warrant future studies to further characterize effects of conditional Tat expression on brain structure. Such studies may improve our understanding of the neurological underpinnings of neuroAIDS and the neurodegeneration associated with HIV-1 infection, potentially leading to new treatments.

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.

Translational spatial task and its relationship to HIV-associated neurocognitive disorders and apolipoprotein E in HIV-seropositive women

HIV-associated neurocognitive disorders (HAND) continue to be a neurological complication of HIV infection in the era of combined antiretroviral therapy. Hippocampal neurodegeneration and dysfunction occurs as a result of HIV infection, but few studies to date have assesses spatial learning and memory function in patients with HAND. We used the Memory Island (MI) test to study the effects of HIV infection, apolipoprotein E (ApoE) allele status, and cerebral spinal fluid (CSF) ApoE protein levels on spatial learning and memory in our cohort of Hispanic women. The MI test is a virtual reality-based computer program that tests spatial learning and memory and was designed to resemble the Morris Water Maze test of hippocampal function widely used in rodent studies. In the current study, HIV-seropositive women (n = 20) and controls (n = 16) were evaluated with neuropsychological (NP) tests, the MI test, ApoE, and CSF ApoE assays. On the MI, the HIV-seropositive group showed significant reduced learning and delayed memory performance compared with HIV-seronegative controls. When stratified by cognitive performance on NP tests, the HIV-seropositive, cognitively impaired group performed worse than HIV-seronegative controls in ability to learn and in the delayed memory trial. Interestingly, differences were observed in the results obtained by the NP tests and the MI test for ε4 carriers and noncarriers: NP tests showed effects of the ε4 allele in HIV-seronegative women but not HIV-seropositive ones, whereas the converse was true for the MI test. Our findings suggest that the MI test is sensitive in detecting spatial deficits in HIV-seropositive women and that these deficits may arise relatively early in the course of HAND.

Towards therapeutic applications of arthropod venom k(+)-channel blockers in CNS neurologic diseases involving memory acquisition and storage

Potassium channels are the most heterogeneous and widely distributed group of ion channels and play important functions in all cells, in both normal and pathological mechanisms, including learning and memory processes. Being fundamental for many diverse physiological processes, K⁺-channels are recognized as potential therapeutic targets in the treatment of several Central Nervous System (CNS) diseases, such as multiple sclerosis, Parkinson's and Alzheimer's diseases, schizophrenia, HIV-1-associated dementia, and epilepsy. Blockers of these channels are therefore potential candidates for the symptomatic treatment of these neuropathies, through their neurological effects. Venomous animals have evolved a wide set of toxins for prey capture and defense. These compounds, mainly peptides, act on various pharmacological targets, making them an innumerable source of ligands for answering experimental paradigms, as well as for therapeutic application. This paper provides an overview of CNS K⁺-channels involved in memory acquisition and storage and aims at evaluating the use of highly selective K⁺-channel blockers derived from arthropod venoms as potential therapeutic agents for CNS diseases involving learning and memory mechanisms.

Rodent models for HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) reflect the spectrum of neural impairments seen during chronic viral infection. Current research efforts focus on improving antiretroviral and adjunctive therapies, defining disease onset and progression, facilitating drug delivery, and halting neurodegeneration and viral resistance. Because HIV is species-specific, generating disease in small-animal models has proved challenging. After two decades of research, rodent HAND models now include those containing a human immune system. Antiviral responses, neuroinflammation and immunocyte blood-brain barrier (BBB) trafficking follow HIV infection in these rodent models. We review these and other rodent models of HAND and discuss their unmet potential in reflecting human pathobiology and in facilitating disease monitoring and therapeutic discoveries.

Expression of HIV-Tat protein is associated with learning and memory deficits in the mouse

HIV-Tat protein has been implicated in the pathogenesis of HIV-1 neurological complications (i.e., neuroAIDS), but direct demonstrations of the effects of Tat on behavior are limited. GT-tg mice with a doxycycline (Dox)-inducible and brain-selective tat gene coding for Tat protein were used to test the hypothesis that the activity of Tat in brain is sufficient to impair learning and memory processes. Western blot analysis of GT-tg mouse brains demonstrated an increase in Tat antibody labeling that seemed to be dependent on the dose and duration of Dox pretreatment. Dox-treated GT-tg mice tested in the Barnes maze demonstrated longer latencies to find an escape hole and displayed deficits in probe trial performance versus uninduced GT-tg littermates, suggesting Tat-induced impairments of spatial learning and memory. Reversal learning was also impaired in Tat-induced mice. Tat-induced mice additionally demonstrated long-lasting (up to one month) deficiencies in novel object recognition learning and memory performance. Furthermore, novel object recognition impairment was dependent on the dose and duration of Dox exposure, suggesting that Tat exposure progressively mediated deficits. These experiments provide evidence that Tat protein expression is sufficient to mediate cognitive abnormalities seen in HIV-infected individuals. Moreover, the genetically engineered GT-tg mouse may be useful for improving our understanding of the neurological underpinnings of neuroAIDS-related behaviors.

HIV and SIV induce alterations in CNS CaMKII expression and activation: a potential mechanism for cognitive impairment

The molecular mechanisms underlying learning and memory impairment in patients with HIV-associated neurological disease have remained unclear. Calcium/calmodulin-dependent kinase II (CaMKII) has key roles in synaptic potentiation and memory storage in neurons and also may have immunomodulatory functions. To determine whether HIV and simian immunodeficiency virus (SIV) induce alterations in CaMKII expression and/or activation (autophosphorylation) in the brain, we measured CaMKII alterations by quantitative immunoblotting in both an in vitro HIV/neuronal culture model and in vivo in an SIV-infected macaque model of HIV-associated neurological damage. Using primary rat hippocampal neuronal cultures treated with culture supernatants harvested from HIV-1-infected human monocyte-derived macrophages (HIV/MDM), we found that CaMKII activation declined after exposure of neurons to HIV/MDM. Consistent with our in vitro measurements, a significant decrease in CaMKII activation was present in both the hippocampus and frontal cortex of SIV-infected macaques compared with uninfected animals. In SIV-infected animals, total CaMKII expression in the hippocampus correlated well with levels of synaptophysin. Furthermore, CaMKII expression in both the hippocampus and frontal cortex was inversely correlated with viral load in the brain. These findings suggest that alterations in CaMKII may compromise synaptic function in the early phases of chronic neurodegenerative processes induced by HIV.

Age matters

The age of an experimental animal can be a critical variable, yet age matters are often overlooked within neuroscience. Many studies make use of young animals, without considering possible differences between immature and mature subjects. This is especially problematic when attempting to model traits or diseases that do not emerge until adulthood. In this commentary we discuss the reasons for this apparent bias in age of experimental animals, and illustrate the problem with a systematic review of published articles on long-term potentiation. Additionally, we review the developmental stages of a rat and discuss the difficulty of using the weight of an animal as a predictor of its age. Finally, we provide original data from our laboratory and review published data to emphasize that development is an ongoing process that does not end with puberty. Developmental changes can be quantitative in nature, involving gradual changes, rapid switches, or inverted U-shaped curves. Changes can also be qualitative. Thus, phenomena that appear to be unitary may be governed by different mechanisms at different ages. We conclude that selection of the age of the animals may be critically important in the design and interpretation of neurobiological studies.

Age-dependent spatial memory loss can be partially restored by immune activation

Aging is often associated with a decline in hippocampus-dependent spatial memory. Here, we show that functional cell-mediated immunity is required for the maintenance of hippocampus-dependent spatial memory. Sudden imposition of immune compromise in young mice caused spatial memory impairment, whereas immune reconstitution reversed memory deficit in immune-deficient mice. Analysis of hippocampal gene expression suggested that immune-dependent spatial memory performance was associated with the expression of insulin-like growth factor (Igf1) and of genes encoding proteins related to presynaptic activity (Syt10, Cplx2). We further showed that memory loss in aged mice could be attributed to age-related attenuation of the immune response and could be reversed by immune system activation. Homeostatic-driven proliferation of lymphocytes, which expands the existing T cell repertoire, restored spatial memory deficits in aged mice. Thus, our results identify a novel function of the immune system in the maintenance of spatial memory and suggest an original approach for arresting or reversing age-associated memory loss.

HIV-1-infected and/or immune-activated macrophages regulate astrocyte CXCL8 production through IL-1beta and TNF-alpha: involvement of mitogen-activated protein kinases and protein kinase R

Monocyte infiltration is an important pathogenic event in human immunodeficiency virus type one (HIV-1) associated dementia (HAD). CXCL8 (Interleukin 8, IL-8), a CXC chemokine that elicits chemotaxis of neutrophils, has recently been found to recruit monocytes or synergistically enhance CCL2-mediated monocyte migration. In this report, we demonstrate CXCL8 levels in the cerebrospinal fluid of HAD patients are higher than HIV-1 seropositive patients without neurological impairment. The underlying mechanisms regulating CXCL8 production during disease are not completely understood. We investigated the role of HIV-1-infected and immune-competent macrophages, the principal target cell and mediator of neuronal injury in HAD, in regulating astrocyte CXCL8 production. Immune-activated and HIV-1-infected human monocyte-derived-macrophages (MDM) conditioned media (MCM) induced production of CXCL8 by human astrocytes. This CXCL8 production was dependent on MDM IL-1beta and TNF-alpha production following viral and immune activation. CXCL8 production was reduced by inhibitors for mitogen-activated protein kinases (MAPKs), including p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinases (ERK1/2). Moreover, prolonged IL-1beta or TNF-alpha treatment activated double-stranded RNA-activated protein kinase (PKR). Inhibition of PKR prevented elevated CXCL8 production in astrocytes. We conclude that IL-1beta and TNF-alpha, produced from HIV-1-infected and immune-competent macrophages, are critical in astrocyte CXCL8 production. Multiple protein kinases, including p38, JNK, ERK1/2, and PKR, participate in the inflammatory response of astrocytes. These observations will help to identify effective therapeutic strategies to reduce high-levels of CXCL8-mediated CNS inflammation during HAD.

Voltage-gated potassium channels in human immunodeficiency virus type-1 (HIV-1)-associated neurocognitive disorders

Human immunodeficiency virus type-1 (HIV-1)-associated dementia (HAD), a severe form of HIV-associated neurocognitive disorders (HAND), describes the cognitive impairments and behavioral disturbances which afflict many HIV-infected individuals. Although the precise mechanism leading to HAD is incompletely understood, it is commonly accepted its progression involves a critical mass of infected and activated mononuclear phagocytes (brain perivascular macrophages and microglia) releasing immune and viral products in the brain. These cellular and viral products induce neuronal dysfunction and injury via various signaling pathways. Emerging evidence indicates voltage-gated potassium (K(v)) channels, key regulators of cell excitability and animal behavior (learning and memory), are involved in the pathogenesis of HAD/HAND. Here we survey the literature and find that HAD-related alterations in cellular and viral products can increase neuronal K(v) channel activity, leading to neuronal dysfunction and cognitive deficits. Thus, neuronal K(v) channels may be a new target in the effort to develop therapies for HAD and perhaps other inflammatory neurodegenerative disorders.

Modulation of innate immunity by copolymer-1 leads to neuroprotection in murine HIV-1 encephalitis

Virus-infected and immune-competent mononuclear phagocytes (MP; perivascular macrophages and microglia) drive the neuropathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. Modulation of the MP phenotype from neurodestructive to neuroprotective underlies adjunctive therapeutic strategies for human disease. We reasoned that, as Copolymer-1 (Cop-1) can induce neuroprotective activities in a number of neuroinflammatory and neurodegenerative disorders, it could directly modulate HIV-1-infected MP neurotoxic activities. We now demonstrate that, in laboratory assays, Cop-1-stimulated virus-infected human monocyte-derived macrophages (MDM) protect against neuronal injury. Severe combined immune-deficient (SCID) mice were stereotactically injected with HIV-1-infected human MDM, into the basal ganglia, to induce HIV-1 encephalitis (HIVE). Cop-1 was administered subcutaneously for 7 days. In HIVE mice, Cop-1 treatment led to anti-inflammatory and neuroprotective responses. Reduced micro- and astrogliosis, and conserved NeuN/MAP-2 levels were observed in virus-affected brain regions in Cop-1-treated mice. These were linked to interleukin-10 and brain-derived neurotrophic factor expression and downregulation of inducible nitric oxide synthase. The data, taken together, demonstrate that Cop-1 can modulate innate immunity and, as such, improve disease outcomes in an animal model of HIVE.

Lipopolysaccharide-induced cerebral inflammatory damage and the therapeutic effect of platelet activating factor receptor antagonist

OBJECTIVE

To investigate lipopolysaccharide (LPS) induced acute cerebral inflammatory damage and the therapeutic effect of ginkgolide B (BN52021).

METHODS

Thirty Sprague-Dawley rats were randomly divided into 3 groups (n = 10 for each group): Control group, Model group and Treatment group (treated with BN52021). LPS were injected into the fourth ventricle of rat to make a neuroinflammatory murine model. Morris water maze was used to detect the learning and memory ability of rats; changes of synapse number and subcellular ultrastructures were observed under a transmission electron microscope; OX-42 positive microglia in the brain was detected by immunohistochemical method.

RESULTS

The average escape latency in the Treatment group were significantly shortened than that in the Model group; and the percentage of swimming distance traveled in platform quadrant accounting for total distance increased markedly. The rough endoplasmic reticulum and polyribosomes in the Treatment group were more than that in the Model group, but the number of synapses seemed to have no obvious change. The number of OX-42 positive microglia in the Treatment group decreased markedly than that in the Model group, and the grey density of OX-42-positive cells increased significantly.

CONCLUSION

LPS can induce inflammatory damages to the brain, but the damage could be antagonized by BN52021. Platelet activating factor receptor antagonist may offer an effective therapy for neurodegeneration diseases.

Phosphorylation of claudin-5 and occludin by rho kinase in brain endothelial cells

Critical to the proper maintenance of blood-brain-barrier (BBB) integrity are the endothelial tight junctions (TJs). Posttranslational modifications of essential endothelial TJ proteins, occludin and claudin-5, contribute and possibly disrupt BBB integrity. Our previous work has shown that Rho kinase (RhoK) activation mediates occludin and claudin-5 phosphorylation resulting in diminished barrier tightness and enhanced monocyte migration across BBB in the setting of human immunodeficiency virus-1 encephalitis (HIVE). To determine whether RhoK can directly phosphorylate TJ proteins, we examined phosphorylation of cytoplasmic domains of recombinant claudin-5 and occludin by RhoK. We found that RhoK predominately phosphorylated two sites on occludin (T382 and S507) and one site on claudin-5 (T207). Specific anti-phosphopeptide antibodies were developed for these sites, allowing the detection of phosphorylated occludin at T382 and S507, and claudin-5 at T207 from full-length recombinant occludin and claudin-5 transiently expressed in COS-7 cells and mouse brain microvascular endothelial cells. Finally, these phosphospecific antibodies demonstrated enhanced staining of brain endothelial cells in the mouse model for HIVE and human HIVE brains featuring mononuclear cell infiltration across disrupted BBB. Our results demonstrated the direct phosphorylation of occludin and claudin-5 by RhoK at specific sites, which was increased in encephalitic brain tissue. These antibodies could be useful reagents for monitoring BBB dysfunction in vivo.

Pathogenesis of Human Immunodeficiency Virus Type-1 (HIV-1)-Associated Dementia: Role of Voltage-Gated Potassium Channels

HIV-1-associated dementia (HAD) describes the cognitive impairments and behavioral disturbances which afflict many HIV-infected individuals. Although the incidence of HAD has decreased significantly in the era of HAART, it remains a significant complication of HIV-1 infection as patients with acquired immune deficient syndrome (AIDS) live longer, antiretroviral drugs remain unable to effectively cross the blood-brain barrier (BBB), and HIV-1 resistance grows due to viral strain mutation. Although the precise mechanism leading to HAD is incompletely understood, it is commonly accepted its progression involves a critical mass of infected and activated mononuclear phagocytes (MP; brain perivascular macrophages and microglia) releasing immune and viral products in brain. These cellular and viral products induce neuronal dysfunction and injury via various signaling pathways. Emerging evidence indicates that voltage-gated potassium (K(v)) channels, key regulators of cell excitability and animal behavior (learning and memory), are involved in the pathogenesis of HAD/HAND. Here we survey the literature and find HAD related alterations in cellular and viral products can alter MP and neuronal K(v) channel activity, leading to MP and neuronal dysfunction and cognitive deficits. Thus, MP and neuronal K(v) channels may be a new target in the effort to develop therapies for HAD and perhaps other inflammatory neurodegenerative disorders.

Protecting the synapse: evidence for a rational strategy to treat HIV-1 associated neurologic disease

Loss of synaptic integrity and function appears to underlie neurologic deficits in patients with HIV-1-associated dementia (HAD) and other chronic neurodegenerative diseases. Because synaptic injury often long precedes neuronal death and surviving neurons possess a remarkable capacity for synaptic repair and functional recovery, we hypothesize that therapeutic intervention to protect synapses has great potential to improve neurologic function in HAD and other diseases. We discuss findings from both HAD and Alzheimer's disease to demonstrate that the disruption of synaptic structure and function that can occur during excitotoxic injury and neuroinflammation represents a likely substrate for neurologic deficits. Based on available evidence, we provide a rationale for future studies aimed at identifying molecular targets for synaptic protection in neurodegenerative disease. Whereas patients with HAD beginning antiretroviral therapy have shown reversal of neurologic symptoms that is unique for patients with chronic neurodegenerative conditions, we propose that the potential for such reversal is not unique.

Cognitive dysfunction in HIV encephalitic SCID mice correlates with levels of Interferon-alpha in the brain

BACKGROUND

Interferon alpha (IFNalpha) is an antiviral cytokine produced in response to viral infection. IFNalpha also acts as a neuromodulatory molecule in the central nervous system (CNS). Elevated IFNalpha in the CNS causes cognitive deficits.

OBJECTIVE

To determine if elevated levels of IFNalpha in an HIV encephalitis mouse model correlate with cognitive deficits.

METHODS

C57BL/6J SCID mice were inoculated intracerebrally (i.c.) with HIV infected or uninfected (control) macrophages and cognitively tested in a water escape radial arm maze. After behavioral testing was completed, immunohistochemistry and ELISA were used to examine brain pathology and IFNalpha expression.

RESULTS

Mice injected i.c. with HIV infected macrophages exhibited significantly more working memory errors, particularly in trials with the highest memory load. Immunohistochemistry indicated increased mouse IFNalpha staining prevalent on neurons and glial cells in the brains of mice with HIV infected macrophages compared to mice with uninfected control macrophages. In addition, IFNalpha levels in the brain correlated directly with working memory errors for mice with HIV infected macrophages.

CONCLUSIONS

These data suggest that the cognitive deficit noted for the C57BL/6J SCID mice with HIV infected macrophages is mediated by the infection induced increase in IFNalpha.

Spatial learning and memory in HIV-1 transgenic rats

HIV-1 infection of the central nervous system impairs neural, cognitive, and behavioral functioning in patients despite antiretroviral therapy. However, studying mechanisms underlying HIV-1-related neurological and cognitive dysfunction has been limited without an adequate animal model. A novel, noninfectious HIV-1 transgenic (HIV-1Tg) rat model was recently created that expresses an HIV-1 provirus with a deletion of functional gag and pol genes. This HIV-1Tg rat reportedly develops clinical manifestations of human HIV disease and thus appears to mimic the persistent infection that results from the presence of HIV viral proteins in the host. We evaluated the HIV-1Tg rat model using the Morris water maze, a popular paradigm for testing learning and memory deficits in rodents. Because of congenital cataracts in HIV-1Tg rats, however, the traditional use of visual navigational cues in this paradigm were precluded. We first designed a modified Morris water maze and demonstrated that neurologically intact rats can effectively learn the water maze in the absence of visual cues and in the presence of non-visual navigation cues. We then tested HIV-1Tg rats in this modified Morris water maze. These HIV-1Tg rats showed a deficit in learning how to swim to the location of the hidden platform but did not show a deficit in their memory of the general location of the hidden platform. These results suggest that the noninfectious HIV-1Tg rat can be a valid model for the behavioral studies of HIV-related neurological dysfunction.

Battle of animal models

This is a brief summary of the animal models session held during the 12th Annual Meeting of the Society on NeuroImmune Pharmacology, Santa Fe, NM, USA. This session provided important information for participants on availability and utility of animal models for the studies of HIV-1 central nervous system infection and drug abuse. It highlighted animal model relevance to human disease/condition, its utility for the studies of pathogenesis, potential importance for the development of therapeutics, and demonstrated limitations/pitfalls.

Novel delivery system enhances efficacy of antiretroviral therapy in animal model for HIV-1 encephalitis

Most potent antiretroviral drugs (e.g., HIV-1 protease inhibitors) poorly penetrate the blood-brain barrier. Brain distribution can be limited by the efflux transporter, P-glycoprotein (P-gp). The ability of a novel drug delivery system (block co-polymer P85) that inhibits P-gp, to increase the efficacy of antiretroviral drugs in brain was examined using a severe combined immunodeficiency (SCID) mouse model of HIV-1 encephalitis (HIVE). Severe combined immunodeficiency mice inoculated with HIV-1 infected human monocyte-derived macrophages (MDM) into the basal ganglia were treated with P85, antiretroviral therapy (ART) (zidovudine, lamivudine and nelfinavir (NEL)), or P85 and ART. Mice were killed on days 7 and 14, and brains were evaluated for levels of viral infection. Antiviral effects of NEL, P85, or their combination were evaluated in vitro using HIV-1 infected MDM and showed antiretroviral effects of P85 alone. In SCID mice injected with virus-infected MDM, the combination of ART-P85 and ART alone showed a significant decrease of HIV-1 p24 expressing MDM (25% and 33% of controls, respectively) at day 7 while P85 alone group was not different from control. At day 14, all treatment groups showed a significant decrease in percentage of HIV-1 infected MDM as compared with control. P85 alone and combined ART-P85 groups showed the most significant reduction in percentage of HIV-1 p24 expressing MDM (8% to 22% of control) that were superior to the ART alone group (38% of control). Our findings indicate major antiretroviral effects of P85 and enhanced in vivo efficacy of antiretroviral drugs when combined with P85 in a SCID mouse model of HIVE.

Highly active antiretroviral therapy of cognitive dysfunction and neuronal abnormalities in SCID mice with HIV encephalitis

Our objective was to determine if highly active antiretroviral therapy (HAART), previously shown to ameliorate several pathological features of HIV encephalitis (HIVE) in a SCID mouse model, would also reduce additional established pathological features of HIV: cognitive dysfunction, TNF-alpha, production, and reduced MAP-2 expression. SCID mice with HIVE and control mice inoculated with uninfected monocytes were administered HAART or saline. The HIV pathological features evaluated included astrogliosis, viral load, neuronal apoptosis, MAP-2 expression, mouse TNF-alpha mRNA production and learning acquisition and retention. HAART reduced the HIV-induced viral load, and the astro- and microgliosis as previously observed; this effect was extended to HIV-induced increases in TNF-alpha mRNA production. In contrast, although HIV produced the cognitive deficits previously observed and also decreased MAP-2 expression in the area surrounding the injected HIV-infected human monocytes, HAART did not attenuate these effects. Interestingly, there was no neuronal apoptosis evident at the time point reflecting the above pathology. The results of this study combined with previous reports indicate that HAART reduces TNF-alpha mRNA, viral load and astrogliosis; however, HAART does not improve HIV-induced cognitive dysfunction or MAP-2 decreases. These results suggest that viral load, astrogliosis, TNF- alpha and apoptosis are not prominent in the pathogenesis of early functional deficits related to decreased MAP-2 expression or cognitive dysfunction in HIVE in SCID mice.

The phospholipid mediator platelet-activating factor mediates striatal synaptic facilitation

The phospholipid mediator platelet-activating factor (PAF), an endogenous modulator of glutamatergic neurotransmission, can also be secreted by brain mononuclear phagocytes during HIV-1 infection. Platelet-activating factor can induce neuronal apoptosis by NMDA receptor-dependent and independent mechanisms. We now demonstrate that acute administration of sublethal doses of PAF to striatal slices augments synaptic facilitation in striatal neurons following high-frequency stimulation, which can be blocked by PAF receptor antagonists, suggesting that striatal synaptic facilitation can be augmented by PAF receptor agonism. We also demonstrate that repeated sublethal doses of PAF during tetanic stimulation can greatly increase the magnitude of postsynaptic potentials and action potentials, but a lethal dose of PAF destroys the capacity of corticostriatal synapses to achieve this augmented synaptic facilitation. Thus, the relative concentration and temporal pattern of PAF expression at glutamatergic synapses may govern whether it acts in a physiologic or pathophysiologic manner during striatal neurotransmission.

(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.

Disrupted spatial memory is a consequence of picornavirus infection

Picornaviruses are a socioeconomically important family of viruses that includes the rhinoviruses and enteroviruses. Many of these viruses, including the "common cold" Coxsackie virus A21, maintain neurovirulent potential and may induce hippocampal injury. The behavioral implications of this injury have not been adequately explored. Using C57BL/6J mice infected with Theiler's murine encephalomyelitis virus, we examined the formation of spatial memories using the Morris water maze test. Virus-infected mice had greater search error compared to sham-infected animals during the location of a hidden platform and were unable to discriminate the location of the training quadrant during the final probe trial. Furthermore, sham-infected mice were place responders whereas virus-infected mice were cue responders, indicating a lack of spatial memory formation in infected animals. Importantly, the degree of memory impairment was correlated to the extent of hippocampal injury. This suggests that picornavirus infection of the human CNS may also result in at least some degree of neurologic deficit. An important implication of such subclinical virus-induced neurologic deficit is that the injury may accumulate over the lifetime of the individual, eventually leading to the manifestation of clinical cognitive or memory deficits.

Macrophage-induced inflammation affects hippocampal plasticity and neuronal development in a murine model of HIV-1 encephalitis

Cognitive, behavioral, and motor impairments, during progressive human immunodeficiency virus type 1 (HIV-1) infection, are linked to activation of brain mononuclear phagocytes (MP; perivascular macrophages and microglia). Activated MPs effect a giant cell encephalitis and neuroinflammatory responses that are mirrored in severe combined immunodeficient (SCID) mice injected with human monocyte-derived macrophages (MDM). Whether activated human MDMs positioned in the basal ganglia affect hippocampal neuronal plasticity, the brain subregion involved in learning and memory, is unknown. Thus, immunohistochemical techniques were used for detection of newborn neurons (polysialylated neuronal cell adhesion molecule [PSA-NCAM]) and cell proliferation (Ki-67) to assay MDM effects on neuronal development in mouse models of HIV-1 encephalitis. Immunodeficient (C.B.-17/SCID and nonobese diabetic/SCID, NOD/SCID) and immune competent (C.B.-17) mice were injected with uninfected or HIV-1-infected MDM. Sham-operated or unmanipulated mice served as controls. Neuronal plasticity was evaluated in the hippocampal dentate gyrus (DG) at days 7 and 28. By day 7, increased numbers of Ki-67+ cells, PSA-NCAM+ cells and dendrites in DG were observed in sham-operated animals. In contrast, significant reductions in neuronal precursors and altered neuronal morphology paralleled increased microglial activation in both HIV-1-infected and uninfected MDM-injected animals. DG cellular composition was restored at day 28. We posit that activated MDM induce inflammation and diminish DG neuronal plasticity. These data provide novel explanations for the cognitive impairments manifested during advanced HIV-1 infection.

The signaling and apoptotic effects of TNF-related apoptosis-inducing ligand in HIV-1 associated dementia

HIV-1 Associated Dementia (HAD) develops during progressive HIV-1 infection and is characterized by cognitive impairments, behavioral disorders and potential progressive motor abnormality. Abnormal inflammation within the central nervous system (CNS), activation of macrophage/microglia and involvement of proinflammatory cytokines have been suggested as primary factors in the pathogenesis of HAD. Impairment of neuronal function and neuronal cell death are believed to be the end pathophysiological result of HAD. TNF-related apoptosis-inducing ligand (TRAIL), a member of the TNF family of cytokines, was suggested to participate in apoptotic cell death during HAD. As a death ligand, TRAIL was originally thought to target only tumor cells. TRAIL is not typically present in CNS; however, emerging data show that TRAIL can be induced by immune stimuli on macrophage and microglia, major disease effector cells during HAD. Upregulated TRAIL may then cause neuronal apoptosis through direct interaction with TRAIL receptors on neurons or through macrophage death-mediated release of neurotoxins. In this review, we summarize the pivotal role of TRAIL in HAD and TRAIL-initiated intracellular death cascades that culminate in neuronal apoptosis as observed in HAD.

Rodent model systems for studies of HIV-1 associated dementia

Understanding of HIV-1 neuropathogenesis and development of rationale therapeutic approaches requires relevant animal models. The putative mechanisms of neuroinflammatory and neurotoxic events triggered by HIV-1 brain infection are reflected by a number of rodent models. These include transgenic animals (either expressing viral proteins or pro-inflammatory factors), infection with murine retroviruses, and severe combined immunodeficient (SCID) mice reconstituted with human lymphocytes and injected intracerebrally with HIV-1-infected human monocyte-derived macrophages. The potential importance and limitations of the models in reflecting human disease are discussed with emphasis on their utility for development of therapies to combat HIV-1-associated neurologic impairment.

The AIDS dementia complex: clinical and basic neuroscience with implications for novel molecular therapies

The AIDS dementia complex (ADC, also referred to as HIV-associated cognitive impairment) is a common disorder among HIV-infected patients associated with both inflammatory and neurodegenerative processes. This review describes recent advances in the clinical and basic neurosciences of HIV infection and discusses the multivariable nature of what has become a chronic disorder in the context of highly active antiretroviral therapies (HAART). Since its initial description twenty years ago, advances in cell and molecular biology along with those in neuroimaging have furthered our understanding of the underlying pathogenic mechanisms. The clinical and neuropsychological profile of ADC is generally consistent with a "frontal-subcortical" pattern of injury. Neuropathogenesis is largely driven by indirect mechanisms mediated by infected, or more commonly, immune activated macrophages, which secrete viral and host-derived factors. Magnetic resonance spectroscopy (MRS) provides a robust in vivo method to measure the inflammatory and neurotoxic events triggered by these factors and their associated signals. Although the use of combined or highly active antiretroviral therapies (HAART) has significantly improved survival rates, cerebral injury and cognitive impairment remain common events. Factors such as aging and chronic infection will likely impact the course of this disease, its pathogenesis, and treatment. The combined observations presented in this review suggest a number of critical areas for future inquiry.

Coregistration of quantitative proton magnetic resonance spectroscopic imaging with neuropathological and neurophysiological analyses defines the extent of neuronal impairments in murine human immunodeficiency virus type-1 encephalitis

Relatively few immune-activated and virus-infected mononuclear phagocytes (MP; perivascular macrophages and microglia) may affect widespread neuronal dysfunction during human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). Indeed, histopathological evidence of neuronal dropout often belies the extent of cognitive impairment. To define relationships between neuronal function and histopathology, proton magnetic resonance spectroscopic imaging (1H MRSI) and hippocampal long-term potentiation (LTP) were compared with neuronal and glial immunohistology in a murine model of HIV-1 encephalitis (HIVE). HIV-1(ADA)-infected human monocyte-derived macrophages (MDM) were stereotactically injected into the subcortex of severe combined immunodeficient (SCID) mice. Sham-operated and unmanipulated mice served as controls. Seven days after cell injection, brain histological analyses revealed a focal giant cell encephalitis, with reactive astrocytes, microgliosis, and neuronal dropout. Strikingly, significant reductions in N-acetyl aspartate concentration ([NAA]) and LTP levels in HIVE mice were in both injected and contralateral hemispheres and in brain subregions, including the hippocampus, where neuropathology was limited or absent. The data support the importance of 1H MRSI as a tool for assessing neuronal function for HAD. The data also demonstrate that a highly focal encephalitis can produce global deficits for neuronal function and metabolism.

Inhibition of indoleamine 2,3-dioxygenase (IDO) enhances elimination of virus-infected macrophages in an animal model of HIV-1 encephalitis

Indoleamine 2,3-dioxygenase (IDO) is the rate-limiting enzyme in the kynurenine pathway of tryptophan metabolism. IDO activity is linked with immunosuppression by its ability to inhibit lymphocyte proliferation, and with neurotoxicity through the generation of quinolinic acid and other toxins. IDO is induced in macrophages by HIV-1 infection, and it is up regulated in macrophages in human brain tissue with HIV-1 encephalitis (HIVE). Using a model of HIVE, we investigated whether IDO inhibitor 1-methyl-d-tryptophan (1-MT) could affect the generation of cytotoxic T lymphocytes (CTLs) and clearance of virus-infected macrophages from the brain. Severe combined immunodeficient mice were reconstituted with human peripheral blood lymphocytes, and encephalitis was induced by intracranial injection of autologous HIV-1-infected monocyte-derived macrophages (MDMs). Animals treated with 1-MT demonstrated increased numbers of human CD3+, CD8+, CD8+/interferon-gamma+ T cells, and HIV-1(gag/pol)-specific CTLs in peripheral blood compared with controls. At week 2 after MDM injection in the basal ganglia, mice treated with 1-MT showed a 2-fold increase in CD8+ T lymphocytes in the areas of the brain containing HIV-1-infected MDMs compared with untreated controls. By week 3, 1-MT-treated mice showed 89% reduction in HIV-infected MDMs in brain as compared with controls. Thus, manipulation of immunosuppressive IDO activity in HIVE may enhance the generation of HIV-1-specific CTLs, leading to elimination of HIV-1-infected macrophages in brain.

The HIV-1 coat protein gp120 regulates CXCR4-mediated signaling in neural progenitor cells

We demonstrate that hCD4-primed gp120IIIB interacts with CXCR4 receptors expressed by postnatal mouse neural progenitor cells and elicits robust Ca(2+) signals. The chemokine SDF-1 acted as a chemoattractant and a mitogenic stimulus for these neural progenitor cells. Although hCD4/gp120 was not able to produce chemoattraction or increase proliferation, it completely blocked the ability of SDF-1 to produce these effects. Thus, gp120 can act both as an agonist and de facto antagonist of CXCR4-mediated signaling in neural progenitor cells. It is possible that the ability of hCD4/gp120 to block SDF-1 signaling in neural progenitors may contribute to the neuropathological effects of HIV-1.

Proinflammatory synergism of ethanol and HIV-1 Tat protein in brain tissue

Human immunodeficiency virus type 1 (HIV-1) Tat protein is a potent transactivator of viral replication. It is actively released from HIV-infected cells and has been shown to induce cell injury effects. Alcohol abuse is a risk factor of HIV infection and we hypothesize that alcohol and Tat may interact in an additive or synergistic fashion to influence molecular processes which can contribute to their toxic effects. To study this possibility, we investigated the effects of two intraperitoneal injections of ethanol (EtOH, 3 g/kg each, 16 h apart) and a single intracerebral injection of Tat (25 microg/microl into the right hippocampus, injected 12 h after the first EtOH injection) on generation of cellular oxidative stress, DNA binding activity of redox-responsive transcription factors, and induction of inflammatory genes in the hippocampus and corpus striatum of mouse brain. As compared to control animals, treatment with EtOH plus Tat resulted in increased production of reactive oxygen species in both brain regions. In addition, DNA binding activities of nuclear factor-kappaB (NF-kappaB) and CREB in both brain regions and SP-1 in the hippocampus were more pronounced in mice injected with Tat plus EtOH as compared to the effects of Tat or EtOH alone. Among studied inflammatory genes, induction of IL-1beta and MCP-1 was potentiated in animals injected with EtOH plus Tat. These results indicate that Tat and EtOH can cross-amplify their cellular effects, leading to alterations of redox-regulated inflammatory pathways in the brain. Such potentiation of proinflammatory stimulation may further contribute to CNS pathology in HIV-infected patients who are alcohol abusers.

Is repetitive opportunistic infection in AIDS patients the effective mechanism for neurodegeneration in terms of endlessly amplifying cytokine/chemokine effect?

With strict reference to how AIDS dementia somehow evolves from HIV infection through stages of initial monocyte-macrophage stimulation via a series of transendothelial and infiltrative events, it is perhaps significant to consider systemic body involvement by the HIV-associated processes to culminate in a concerted series of effects involving cascades and amplifications of action of cytokines and chemokines. Indeed, in terms that would implicate neurons only secondarily in AIDS dementia, one might perhaps consider HIV-1-dementia as an effective result of ongoing inflammation in the brain dependent not only on macrophage-microglial activation and replication, but also on glial participation in an overall process particularly conducive to increasing the brain HIV-1 load. In effect, perhaps, HIV encephalitis would constitute a system of mutually self-enhancing series of events ranging from macrophage-monocyte activation and replication on the one hand, and also HIV-1-induced cellular effects on the other that would result in progressively amplifying neuronal injury induced by cytokines and chemokines in AIDS patients suffering from repetitive opportunistic infections.

Mononuclear phagocyte immunity and the neuropathogenesis of HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1)-associated dementia is a neuroinflammatory brain disorder that is fueled by viral infection and immune activation of brain mononuclear phagocytes (MP; macrophages and microglia). MP serve as a reservoir for persistent viral infection, a vehicle for viral dissemination throughout the brain, and a major source of neurotoxic products that when produced in abundance, affect neuronal function. Such neurotoxic substances secreted by MP lead to clinical neurological impairment (cognitive, behavior, and motor abnormalities), which occurs usually years after the initial viral infection. How HIV-1 evades the immune function characteristic for MP as a first line of defense, including phagocytosis and intracellular killing, is not well understood despite more than two decades of study. In this report, we review the complex role(s) played by MP in the neuropathogenesis of HIV-1 infection. The clinical manifestations, pathology and pathogenesis, and treatment options are discussed in relationship to innate and adaptive immunity. Particular emphasis is given to the diversity of MP functions and how it may affect the disease process and manifestations. New insights into disease mechanisms are provided by advances in enhanced magnetic resonance imaging and proteomics to identify cell movement and genetic profiles of disease. New therapeutic strategies are discussed based on current knowledge of HIV-1-associated dementia pathogenesis.

Human immunodeficiency virus type 1 protein gp120 causes neuronal cell death in the rat brain by activating caspases

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system is associated with microglia activation and neuronal apoptosis, alterations that are also caused by the HIV-1 envelope glycoprotein 120 (gp120) alone. This study was undertaken to examine the onset of gp120 neurotoxicity, the type of cell death and which cells of the adult rat brain are more sensitive to the toxic action of gp120. Gp120 or vehicle were injected chronically (daily for 3 or 7 days) into the lateral ventricle. Magnetic resonance imaging revealed hypertensive areas in the cortical and hippocampal gray matter in gp120-treated rats 7-10 days after the first injection, suggesting vasogenic edema. This phenomenon was accompanied by an enlargement of the lateral and third ventricles. Immunohistochemical analyses were then carried out to examine the toxic effect of gp120 at a cellular level. Several markers of apoptosis, including activated caspase-3 were observed at both 3 and 7 days throughout brains of gp120-treated rats, especially in the cerebral cortex. In this area, most of the apoptotic cells exhibited a pyramidal shape and were Nissl positive, indicative of neurons. Few non-neuronal cells exhibited signs of apoptosis. The results of the present study support the notion that gp120 is neurotoxic in vivo and provide evidence that gp120 activates a caspase-dependent apoptotic pathway.

Human microglial cell isolation from adult autopsy brain: brain pH, regional variation, and infection with human immunodeficiency virus type 1

Microglia are the main source of productive infection by human immunodeficiency virus type 1 (HIV-1) in the central nervous system (CNS). Infection of microglia is difficult to study because nonhuman microglia are not infected by HIV-1, adult human microglia from surgically removed brain tissues are scarce, and fetal human microglial cells differ from adult cells in potentially important ways. Adult autopsies are a potential source of brain tissue for HIV-1 research, but the technique of isolating and infecting cells postmortem is not completely standardized. The authors determined optimal conditions for isolating and infecting adult microglial cells using 18 adult autopsy brain specimens from HIV-1-infected and noninfected decedents. The yield of mixed glial cells overall was on average 0.5 x 10(6) cells per gram of wet tissue. There was no correlation between the number of microglia isolated and the postmortem interval (PMI), HIV seropositivity, age, or gender. Brain pH accounted for about 41% of yield variability; a pH of less than 6.0 generally was not compatible with adequate cell recovery. The highest microglial cell yields were derived from anterior brain sectors (frontal lobe and temporal lobe) versus occipital lobe and cerebellum. A PMI of up to 25.5 h produced excellent cell yields in frontal lobe samples with high brain pH. HIV-1 infection of frontal lobe microglia was 100% successful using both CXCR4- and CCR5-tropic strains of HIV-1. With proper selection of cases and brain region, autopsy brain specimens are a dependable source of viable microglial cells to study CNS HIV-1 infection.

Methamphetamine potentiates HIV-1 Tat protein-mediated activation of redox-sensitive pathways in discrete regions of the brain

Tat is a major regulatory protein encoded by human immunodeficiency viral genome, which has been implicated in the pathogenesis of HIV infection, including neurologic complications associated with this disease. In addition, drug abuse has been identified as a major risk factor of HIV infection. We hypothesize that abusive drugs, such as methamphetamine (METH), can directly influence specific molecular processes that can further contribute to toxic effects of Tat. To elucidate the molecular signaling pathways of Tat- and/or METH-induced toxicity, we investigated the effects of a single injection of Tat (25 microg/microl into the right hippocampus) and/or METH (10 mg/kg, intraperitoneally) on the generation of cellular oxidative stress, DNA-binding activity of specific redox-responsive transcription factors, and expression of inflammatory genes. Administration of Tat or METH resulted in stimulation of cellular oxidative stress and activation of redox-regulated transcription factors in the cortical, striatal, and hippocampal regions of the mouse brain. In addition, DNA-binding activities of NF-kappaB, AP-1, and CREB in the frontal cortex and hippocampus were more pronounced in mice injected with Tat plus METH compared to the effects of Tat or METH alone. Intercellular adhesion molecule-1 gene expression also was upregulated in a synergistic manner in cortical, striatal, and hippocampal regions in mice which received injections of Tat combined with METH compared to the effects of these agents alone. Moreover, synergistic effects of Tat plus METH on the tumor necrosis factor-alpha and interleukin-1beta mRNA levels were observed in the striatal region. These results indicate that Tat and METH can cross-amplify their cellular effects, leading to alterations of redox-regulated inflammatory pathways in the brain. Such synergistic proinflammatory stimulation may have significant implications in HIV-infected patients who abuse drugs.

Microglia in human immunodeficiency virus-associated neurodegeneration

Infection with the human immunodeficiency virus (HIV) is associated with a syndrome of cognitive and motor abnormalities that may develop in the absence of opportunistic infections. Neurons are not productively infected by HIV. Thus, one hypothesis to explain the pathophysiology of HIV-associated dementia (HAD) suggests that signals released from other infected cell types in the CNS secondarily lead to neuronal injury. Microglia are the predominant resident CNS cell type productively infected by HIV-1. Neurologic dysfunction in HAD appears to be a consequence of microglial infection and activation. Several neurotoxic immunomodulatory factors are released from infected and activated microglia, leading to altered neuronal function, synaptic and dendritic degeneration, and eventual neuronal apoptosis. This review summarizes findings from clinical/pathological studies, animal models, and in vitro models of HAD. Most of these studies support the hypothesis that altered microglial physiology is the nidus for a cascade of events leading to neuronal dysfunction and death. Several molecular mediators of neuronal injury in HAD that emanate from microglia have been identified, and strategies for altering the impact of these neurotoxins are discussed.

HIV-1-associated dementia: a metabolic encephalopathy perpetrated by virus-infected and immune-competent mononuclear phagocytes

Infection of the nervous system by HIV-1 commonly causes a broad range of cognitive, behavioral, and motor abnormalities called, in its most severe form, HIV-1-associated dementia (HAD). HAD is a metabolic encephalopathy caused by productive viral infection of brain mononuclear phagocytes (MPs) (perivascular and parenchymal brain macrophages and microglia) and sustained by paracrine-amplified, inflammatory, neurotoxic responses. MP neurotoxins are, in large measure, homeostatic secretory products that can have a negative effect on neuronal cell function when produced in abundance. Proinflammatory cytokines, chemokines, platelet-activating factor, arachidonic acid and its metabolites, nitric oxide, quinolinic acid, progeny virions, and viral structural and regulatory proteins are all included as part of these cellular and viral toxic elements. In addition, neuronal damage can occur directly by engaging specific receptors or through inducing widespread inflammatory activities in brain tissue that ultimately induce neuronal demise. The mechanisms for immune-and viral-mediated neural injury in HAD are made more striking by the effects of abused drugs on cognitive function. Ultimately, linkages between neuronal function and disordered MP immunity will provide insights into how HIV-1 infection of the brain leads to compromised mental function as well as providing clues into the pathogenesis of other neurodegenerative disorders.