Pathogenesis of human immunodeficiency virus-induced neurological disease

Diffusion imaging in brain infections

Diffusion-weighted magnetic resonance imaging (DWI) provides image contrasts that are different from conventional magnetic resonance techniques. DWI is particularly sensitive for detecting acute ischemic stroke, but it also has many other clinical applications, including the evaluation of central nervous system (CNS) infections. This article addresses the role of DWI in the differential diagnosis of CNS infections, and discusses the most common DWI findings for each type of infection.

Cerebral signal intensity abnormalities on T2-weighted MR images in HIV patients with highly active antiretroviral therapy: relationship with clinical parameters and interval changes

RATIONALE AND OBJECTIVES

The aim of this study was to assess the relationship between immune state and cerebral signal intensity abnormalities (SIAs) on T2-weighted magnetic resonance images in subjects with human immunodeficiency virus type 1 infection and highly active antiretroviral therapy.

MATERIALS AND METHODS

Thirty-two subjects underwent a total of 109 magnetic resonance studies. The presence of human immunodeficiency virus-associated neurocognitive disorder, categorized CD4(+) T lymphocyte count, and plasma viral load were assessed for relationship with the severity and interval change of SIAs for different anatomic locations of the brain.

RESULTS

Subjects with multifocal patterns of SIAs had CD4(+) cell counts < 200 cells/μL in 66.0%, whereas subjects with diffuse patterns of SIAs had CD4(+) cell counts < 200 cells/μL in only 31.4% (P < .001). Subjects without SIAs in the basal ganglia had CD4(+) cell counts < 200 cells/μL in 37.0%, whereas subjects with minor and moderate SIAs in the basal ganglia had CD4(+) cell counts < 200 cells/μL in 78.3% and 80.0%, respectively (P < .005). The percentage of subjects with CD4(+) cell counts < 200 cells/μL was 85.7% when there were progressive periventricular SIA changes and 45.5% when periventricular SIA changes were stable in follow-up (P < .05).

CONCLUSIONS

The presence and progression of cerebral SIAs on T2-weighted magnetic resonance images reflecting cerebral infection with human immunodeficiency virus are significantly related to impaired immune state as measured by CD4(+) cell count.

HIV-1 Tat-mediated induction of platelet-derived growth factor in astrocytes: role of early growth response gene 1

HIV-associated neurologic disorders (HAND) are estimated to affect almost 60% of HIV-infected individuals. HIV encephalitis, the pathologic correlate of the most severe form of HAND, is often characterized by glial activation, cytokine-chemokine dysregulation, and neuronal damage and loss. However, the severity of HIV encephalitis correlates better with glial activation rather than viral load. Using the macaque model, it has been demonstrated that SIV encephalitis correlates with increased expression of the mitogen platelet-derived growth factor (PDGF) B chain in the brain. The goal of this study was to explore the role of PDGF-B chain in HIV-associated activation and proliferation of astrocytes. Specifically, the data demonstrate that exposure of rat and human astrocytes to the HIV-1 protein Tat resulted in the induction of PDGF at both the mRNA and protein levels. Furthermore, PDGF-BB induction was regulated by activation of ERK1/2 and JNK signaling pathways and the downstream transcription factor early growth response 1. Chromatin immunoprecipitation assays demonstrated binding of Egr-1 to the PDGF-B promoter. Exposure of astrocytes to PDGF-BB in turn led to increased proliferation and the release of proinflammatory cytokines MCP-1 and IL-1β. Because astrogliosis is linked to disease severity, understanding its regulation by PDGF-BB could aid in the development of therapeutic intervention strategies for HAND.

Impact of short-term combined antiretroviral therapy on brain virus burden in simian immunodeficiency virus-infected and CD8+ lymphocyte-depleted rhesus macaques

Antiretroviral drugs suppress virus burden in the cerebrospinal fluid of HIV-infected individuals; however, the direct effect of antiretrovirals on virus replication in brain parenchyma is poorly understood. We investigated the effect of short-term combined antiretroviral therapy (CART) on brain virus burden in rhesus monkeys using the CD8-depletion model of accelerated simian immunodeficiency virus (SIV) encephalitis. Four monkeys received CART (consisting of the nonpenetrating agents PMPA and RCV) for four weeks, beginning 28 days after SIV inoculation. Lower virus burdens were measured by real-time RT-PCR in four of four regions of brain from monkeys that received CART as compared with four SIV-infected, untreated controls; however, the difference was only significant for the frontal cortex (P < 0.05). In contrast, significantly lower virus burdens were measured in plasma and four of five lymphoid compartments from animals that received CART. Surprisingly, despite normalization of neuronal function in treated animals, the numbers of activated macrophages/microglia and the magnitude of TNF-alpha mRNA expression in brain were similar between treated animals and controls. These results suggest that short-term therapy with antiretrovirals that fail to penetrate the blood-cerebrospinal fluid barrier can reduce brain virus burden provided systemic virus burden is suppressed; however, longer treatment may be required to completely resolve encephalitic lesions and microglial activation, which may reflect the longer half-life of the principal target cells of HIV/SIV in the brain (macrophages) versus lymphoid tissues (T lymphocytes).

Cooperative induction of CXCL10 involves NADPH oxidase: Implications for HIV dementia

With the increasing prevalence of HIV-associated neurocognititve disorders (HAND), understanding the mechanisms by which HIV-1 induces neuro-inflammation and subsequent neuronal damage is important. The hallmark features of HIV-encephalitis, the pathological correlate of HIV-associated Dementia (HAD), are gliosis, oxidative stress, chemokine dysregulation, and neuronal damage/death. Since neurons are not infected by HIV-1, the current thinking is that these cells are damaged indirectly by pro-inflammatory chemokines released by activated glial cells. CXCL10 is a neurotoxic chemokine that is upregulated in astroglia activated by HIV-1 Tat, IFN-gamma, and TNF-alpha. In this study we have demonstrated that HIV-1 Tat increases CXCL10 expression in IFN-gamma and TNF-alpha stimulated human astrocytes via NADPH oxidase. We have shown that the treatment of astrocytes with a mixture of Tat and cytokines leads to a respiratory burst that is abrogated by apocynin, an NADPH oxidase inhibitor. Pretreatment of Tat, IFN-gamma, and TNF-alpha stimulated astrocytes with apocynin also resulted in concomitant inhibition of CXCL10 expression. Additionally, apocynin was also able to reduce Tat and cytokine-mediated activation of the corresponding signaling molecules Erk1/2, Jnk, and Akt with a decrease in activation and nuclear translocation of NF-kappaB, important regulators of CXCL10 induction. Understanding the mechanisms involved in reducing both oxidative stress and the release of pro-inflammatory agents could lead to the development of therapeutics aimed at decreasing neuro-inflammation in patients suffering from HAD.

The neuropathogenesis of feline immunodeficiency virus infection: barriers to overcome

Feline immunodeficiency virus (FIV), like human immunodeficiency virus (HIV)-1, is a neurotropic lentivirus, and both natural and experimental infections are associated with neuropathology. FIV enters the brain early following experimental infection, most likely via the blood-brain and blood-cerebrospinal fluid barriers. The exact mechanism of entry, and the factors that influence this entry, are not fully understood. As FIV is a recognised model of HIV-1 infection, understanding such mechanisms is important, particularly as HIV enters the brain early in infection. Furthermore, the development of strategies to combat this central nervous system (CNS) infection requires an understanding of the interactions between the virus and the CNS. In this review the results of both in vitro and in vivo FIV studies are assessed in an attempt to elucidate the mechanisms of viral entry into the brain.

HIV-associated neurocognitive disorder: pathogenesis and therapeutic opportunities

Human immunodeficiency virus type 1 (HIV) infection presently affects more that 40 million people worldwide, and is associated with central nervous system (CNS) disruption in at least 30% of infected individuals. The use of highly active antiretroviral therapy has lessened the incidence, but not the prevalence of mild impairment of higher cognitive and cortical functions (HIV-associated neurocognitive disorders) as well as substantially reduced a more severe form dementia (HIV-associated dementia). Furthermore, improving neurological outcomes will require novel, adjunctive therapies that are targeted towards mechanisms of HIV-induced neurodegeneration. Identifying such molecular and pharmacological targets requires an understanding of the events preceding irreversible neuronal damage in the CNS, such as actions of neurotoxins (HIV proteins and cellular factors), disruption of ion channel properties, synaptic damage, and loss of adult neurogenesis. By considering the specific mechanisms and consequences of HIV neuropathogenesis, unified approaches for neuroprotection will likely emerge using a tailored, combined, and non-invasive approach.

Differences in NMDA receptor expression during human development determine the response of neurons to HIV-tat-mediated neurotoxicity

HIV infection of the CNS can result in neurologic dysfunction in a significant number of infected individuals. NeuroAIDS is characterized by neuronal injury and loss, yet there is no evidence of HIV infection in neurons. Thus, neuronal damage and dropout are likely due to indirect effects of HIV infection of other CNS cells, through elaboration of inflammatory factors and neurotoxic viral proteins, including the viral transactivating protein tat. We and others demonstrated that tat induces apoptosis in differentiated mature human neurons. We now demonstrate that the high level of tat toxicity observed in human neurons involves specific developmental stages that correlate with N-methyl-D-aspartate receptor (NMDAR) expression, and that tat toxicity is also dependent upon the species being analyzed. Our results indicate that tat treatment of primary cultures of differentiated human neurons with significant amounts of NMDAR expression induces extensive apoptosis. In contrast, tat treatment induces only low levels of apoptosis in primary cultures of immature human neurons with low or minimal expression of NMDAR. In addition, tat treatment has minimal effect on rat hippocampal neurons in culture, despite their high expression of NMDAR. We propose that this difference may be due to low expression of the NR2A subunit. These findings are important for an understanding of the many differences among tissue culture systems and species used to study HIV-tat-mediated toxicity.

Evidence for predilection of macrophage infiltration patterns in the deeper midline and mesial temporal structures of the brain uniquely in patients with HIV-associated dementia

Background

HIV-1 penetrates the central nervous system, which is vital for HIV-associated dementia (HAD). But the role of cellular infiltration and activation together with HIV in the development of HAD is poorly understood.

Methods

To study activation and infiltration patterns of macrophages, CD8+ T cells in relation to HIV in diverse CNS areas of patients with and without dementia. 46 brain regions from two rapidly progressing severely demented patients and 53 regions from 4 HIV+ non-dementia patients were analyzed. Macrophage and CD8+ T cell infiltration of the CNS in relation to HIV was assessed using immuno-histochemical analysis with anti-HIV (P24), anti-CD8 and anti-CD68, anti-S-100A8 and granzyme B antibodies (cellular activation). Statistical analysis was performed with SPSS 12.0 with Student's t test and ANOVA.

Results

Overall, the patterns of infiltration of macrophages and CD8+ T cells were indiscernible between patients with and without dementia, but the co-localization of macrophages and CD8+ T cells along with HIV P24 antigen in the deeper midline and mesial temporal structures of the brain segregated the two groups. This predilection of infected macrophages and CD8+ T cells to the middle part of the brain was unique to both HAD patients, along with unique nature of provirus gag gene sequences derived from macrophages in the midline and mesial temporal structures.

Conclusion

Strong predilection of infected macrophages and CD8+ T cells was typical of the deeper midline and mesial temporal structures uniquely in HAD patients, which has some influence on neurocognitive impairment during HIV infection.

PDGF-mediated protection of SH-SY5Y cells against Tat toxin involves regulation of extracellular glutamate and intracellular calcium

The human immunodeficiency virus (HIV-1) protein Tat has been implicated in mediating neuronal apoptosis, one of the hallmark features of HIV-associated dementia (HAD). Mitigation of the toxic effects of Tat could thus be a potential mechanism for reducing HIV toxicity in the brain. In this study we demonstrated that Tat-induced neurotoxicity was abolished by NMDA antagonist-MK801, suggesting the role of glutamate in this process. Furthermore, we also found that pretreatment of SH-SY5Y cells with PDGF exerted protection against Tat toxicity by decreasing extracellular glutamate levels. We also demonstrated that extracellular calcium chelator EGTA was able to abolish PDGF-mediated neuroprotection, thereby underscoring the role of calcium signaling in PDGF-mediated neuroprotection. We also showed that Erk signaling pathway was critical for PDGF-mediated protection of cells. Additionally, blocking calcium entry with EGTA resulted in suppression of PDGF-induced Erk activation. These findings thus underscore the role of PDGF-mediated calcium signaling and Erk phosphorylation in the protection of cells against HIV Tat toxicity.

Proinflammatory cytokines and HIV-1 synergistically enhance CXCL10 expression in human astrocytes

HIV encephalitis (HIVE), the pathologic correlate of HIV-associated dementia (HAD) is characterized by astrogliosis, cytokine/chemokine dysregulation, and neuronal degeneration. Increasing evidence suggests that inflammation is actively involved in the pathogenesis of HAD. In fact, the severity of HAD/HIVE correlates more closely with the presence of activated glial cells than with the presence and amount of HIV-infected cells in the brain. Astrocytes, the most numerous cell type within the brain, provide an important reservoir for the generation of inflammatory mediators, including interferon-gamma inducible peptide-10 (CXCL10), a neurotoxin and a chemoattractant, implicated in the pathophysiology of HAD. Additionally, the proinflammatory cytokines, IFN-gamma and TNF-alpha, are also markedly increased in CNS tissues during HIV-1 infection. In this study, we hypothesized that the interplay of host cytokines and HIV-1 could lead to enhanced expression of the toxic chemokine, CXCL10. Our findings demonstrate a synergistic induction of CXCL10 mRNA and protein in human astrocytes exposed to HIV-1 and the proinflammatory cytokines. Signaling molecules, including JAK, STATs, MAPK (via activation of Erk1/2, AKT, and p38), and NF-kappaB were identified as instrumental in the synergistic induction of CXCL10. Understanding the mechanisms involved in HIV-1 and cytokine-mediated up-regulation of CXCL10 could aid in the development of therapeutic modalities for HAD.

HIV-1 Tat co-operates with IFN-gamma and TNF-alpha to increase CXCL10 in human astrocytes

HIV-associated neurological disorders (HAND) are estimated to affect 60% of the HIV infected population. HIV-encephalitis (HIVE), the pathological correlate of the most severe form of HAND is often characterized by glial activation, cytokine/chemokine dysregulation, and neuronal damage and loss. However, the severity of HIVE correlates better with glial activation rather than viral load. One of the characteristic features of HIVE is the increased amount of the neurotoxic chemokine, CXCL10. This chemokine can be released from astroglia activated with the pro-inflammatory cytokines IFN-γ and TNF-α, in conjunction with HIV-1 Tat, all of which are elevated in HIVE. In an effort to understand the pathogenesis of HAND, this study was aimed at exploring the regulation of CXCL10 by cellular and viral factors during astrocyte activation. Specifically, the data herein demonstrate that the combined actions of HIV-1 Tat and the pro-inflammatory cytokines, IFN-γ and TNF-α, result in the induction of CXCL10 at both the RNA and protein level. Furthermore, CXCL10 induction was found to be regulated transcriptionally by the activation of the p38, Jnk, and Akt signaling pathways and their downstream transcription factors, NF-κB and STAT-1α. Since CXCL10 levels are linked to disease severity, understanding its regulation could aid in the development of therapeutic intervention strategies for HAND.

Lymphocyte migration through the blood-brain barrier (BBB) in feline immunodeficiency virus infection is significantly influenced by the pre-existence of virus and tumour necrosis factor (TNF)-alpha within the central nervous system (CNS): studies using an in vitro feline BBB model

AIMS

In human immunodeficiency virus infection, macrophage-tropic and lymphotropic viruses exist in the host. Central nervous system (CNS) infection is an early and ongoing event, important to understand when developing strategies to treat infection. Some knowledge exists on macrophage-tropic virus interactions with the blood-brain barrier (BBB), and the aim of this study was to investigate lymphotropic lentivirus interactions with the BBB.

METHODS

Interactions of the lymphotropic feline immunodeficiency virus (FIV) with an in vitro model of the feline BBB were evaluated in scenarios to mimic in vivo infections.

RESULTS

Cell-free FIV crossed the BBB in very low quantities, and in the presence of tumour necrosis factor (TNF)-alpha, BBB integrity was unaffected. However, cell-associated FIV readily crossed the BBB, but BBB integrity was not significantly altered. Transmigration of uninfected and infected lymphocytes increased in response to TNF-alpha, accompanied by a moderate disruption of barrier integrity and an upregulation of vascular cell adhesion molecule-1 rather than intercellular adhesion molecule-1. Significant enhancement of migration and disruption of BBB tight junctions occurred when infected cells and TNF-alpha were added to the brain side of the BBB and this enhancement was not mediated through additional TNF-alpha production.

CONCLUSIONS

Small quantities of virus in the brain together with TNF-alpha have the potential to stimulate greater cell and viral entry into the CNS and this is likely to involve important factors other than further TNF-alpha production. Lymphotropic lentivirus entry to the CNS is governed by many factors similar to macrophage-tropic strains.

White matter abnormalities revealed by diffusion tensor imaging in non-demented and demented HIV+ patients

HIV associated dementia (HAD) is the most advanced stage of central nervous system disease caused by HIV infection. Previous studies have demonstrated that patients with HAD exhibit greater cerebral and basal ganglia atrophy than non-demented HIV+ (HND) patients. However, the extent to which white matter is affected in HAD patients compared to HND patients remains elusive. This study is designed to address the potential white matter abnormalities through the utilization of diffusion tensor imaging (DTI) in both HND and HAD patients. DTI and T1-weighted images were acquired from 18 healthy controls, 21 HND and 8 HAD patients. T1 image-based registration was performed to 1) parcellate the whole brain white matter into major white matter regions, including frontal, parietal, temporal and occipital white matter, corpus callosum and internal capsule for statistical comparisons of the mean DTI values, and 2) warp all DTI parametric images towards the common template space for voxel-based analysis. The statistical comparisons were performed with four DTI parameters including fractional anisotropy (FA), mean (MD), axial (AD), and radial (RD) diffusivities. With Whitney U tests on the mean DTI values, both HND and HAD demonstrated significant differences from the healthy control in multiple white matter regions. In addition, HAD patients exhibited significantly elevated MD and RD in the parietal white matter when compared to HND patients. In the voxel-based analysis, widespread abnormal regions were identified for both HND and HAD patients, although a much larger abnormal volume was observed in HAD patients for all four DTI parameters. Furthermore, both region of interest (ROI) based and voxel-based analyses revealed that RD was affected to a much greater extent than AD by HIV infection, which may suggest that demyelination is the prominent disease progression in white matter.

Retrograde and anterograde transport of HIV protein gp120 in the nervous system

Neurodegeneration and gliosis are prominent pathological features of subjects with human immunodeficiency virus (HIV) dementia complex (HAD). In these patients, neurodegeneration occurs in uninfected neurons. In addition, these patients develop sensory neuropathy despite the antiretroviral therapy. The HIV protein gp120, which mimics some of the pathological alterations seen in HAD, is retrogradely transported in rodent neurons. However, it is still unclear whether gp120 can also be transported anterogradely and whether axonal transport can occur in the peripheral nervous system (PNS). To determine whether gp120 is transported retrogradely and/or anterogradely, we injected gp120IIIB together with the retrograde tracer fluoro-ruby (FR) or the anterograde tracer 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyamine perchlorate (DiI) into the rat superior colliculi. We discovered that gp120 is retrogradely transported with FR along a direct pathway from the superior colliculus to the retina and anterogradely transported with DiI to several areas of the occipital cortex. To determine whether gp120 is also axonally transported in the peripheral nerves, gp120 and FR were injected into the sciatic nerve. No gp120 immunoreactivity was found in the sciatic nerve or dorsal root ganglia, suggesting that gp120 axonal transport does not occur in the PNS. Gp120 axonal transport may play a role in neuronal injury. Therefore, we examined apoptosis at various time points after gp120 injection. Activated caspase-3 was evident within neurons transporting gp120. These results indicate that axonal transport of gp120 might exacerbate the pathogenesis of HIV-1.

Amount of HIV DNA in peripheral blood mononuclear cells is proportional to the severity of HIV-1-associated neurocognitive disorders

Human immunodeficiency virus (HIV) DNA in peripheral blood mononuclear cells was previously associated with neuropsychological function. By including individuals encompassing the full range of HIV-1-associated neurocognitive disorders, this study reports results from subjects with normal cognition, minor cognitive motor disorder, and HIV-1-associated dementia. Individuals with normal cognition had relatively low HIV DNA levels compared to those with minor cognitive motor disorder and HIV-1-associated dementia. Neuropsychological deficits were significantly associated with entry HIV DNA in all domains. These findings demonstrate for the first time that the severity of HIV-1-associated neurocognitive disorders is proportional to the amount of circulating HIV DNA.

RNA from Borna disease virus in patients with schizophrenia, schizoaffective patients, and in their biological relatives

Numerous interactions of the immune system with the central nervous system have been described recently. Mood and psychotic disorders, such as severe depression and schizophrenia, are both heterogeneous disorders regarding clinical symptomatology, the acuity of symptoms, the clinical course, the treatment response, and probably also the etiology. Detection of p24 RNA from Borna disease virus (BDV) by the reverse transcriptase polymerase chain reaction in patients with schizophrenia, schizoaffective disorder, and in their biological relatives was evaluated. The subjects were 27 schizophrenic and schizoaffective patients, 27 healthy controls, 20 relatives without psychiatric disease, and 24 relatives with mood disorder, who attended the Psychiatric Ambulatory of Londrina State University, Paraná, Brazil. The subjects were interviewed by structured diagnostic criteria categorized according to the Diagnostic and Statistical Manual of Mental Disorders-IV, axis I, (SCID-IV). The mean duration of illness in schizophrenic and schizoaffective patients was 15.341+/-1.494 years and the median age at onset was 22.4+/-7.371 years. There were no significant differences in gender (P=0.297), age (P=0.99), albumin (P=0.26), and body mass index (kg/m(2)) (p=0.28), among patients, controls, and relatives. Patients and biological relatives had significantly higher positive p24 RNA BDV detection than controls (P=0.04); however, the clinical significance of BDV remains to be clarified.

Roles of MCP-1 in development of HIV-dementia

The encephalopathy caused by HIV, known clinically as HIV-associated dementia (HAD) and pathologically as HIV encephalitis (HIVE), results from intense infiltration of mononuclear cells, productive replication of the virus in monocyte-derived macrophages/microglia, abortive replication in astrocytes and activation of macrophages/microglia and astrocytes leading to neuronal degeneration in the brains of infected persons. Recent findings have suggested that development of HAD is based more on the activation process than on direct evidence of virus replication in the brain. Since HAD is based on the encephalitic process, major studies have been directed to the mechanisms regulating the inflammatory process. Monocyte chemoattractant protein 1, MCP-1, is a chemokine that is implicated in this process and also in the development of activation in the brain. In this review, we have attempted to identify mechanisms that induce expression of MCP-1 in the brain and the role that it plays in recruitment of mononuclear cells from blood to brain and in the activation processes of inflammatory and neural cells that lead to development of degenerative changes in the neuronal population.

CD40-CD40 ligand interactions in human microglia induce CXCL8 (interleukin-8) secretion by a mechanism dependent on activation of ERK1/2 and nuclear translocation of nuclear factor-kappaB (NFkappaB) and activator protein-1 (AP-1)

CXCL8 is a CXC chemokine that recruits leukocytes to sites of inflammation. Expression of CXCL8 in the CNS has been demonstrated in neuroinflammatory diseases, including human immunodeficiency virus (HIV-1) encephalitis, but the mechanism of secretion of this chemokine is not fully understood. CD40 is a 50-kDa protein on the surface of microglia, and we have previously shown that it is increased in expression in HIV-1-infected brain tissue as well as by interferon-gamma (IFNgamma) in tissue culture. We examined the expression and regulation of CXCL8 in cultured human fetal microglia after ligation of CD40 with soluble trimeric CD40 ligand (sCD40L) as well as the expression of CXCL8 on microglia in HIV encephalitic brain tissue sections. Treatment of cultured microglia with IFNgamma + sCD40L resulted in significant induction of CXCL8. This expression was mediated by activation of the ERK1/2 MAPK pathway, as demonstrated by ELISA and Western blot using a specific inhibitor (U0126). Gel shift analyses demonstrated that NFkappaB and AP-1, but not C/EBPbeta, mediate microglial CXCL8 production. We also found increased colocalization of CXCL8 with CD68/CD40-positive cells in HIV encephalitic brain tissue compared with HIV-infected nonencephalitic and normal tissue. Thus, CD40-CD40L interactions facilitate chemokine expression, leading to the influx of inflammatory cells into the CNS. These events can lead to the pathology that is associated with neuroinflammatory diseases.

Cerebrospinal fluid viral load and intrathecal immune activation in individuals infected with different HIV-1 genetic subtypes

Background

HIV-1 exhibits a high degree of genetic diversity and is presently divided into 3 distinct HIV-1 genetic groups designated major (M), non-M/non-O (N) and outlier (O). Group M, which currently comprises 9 subtypes (A-D, F-H, J and K), at least 34 circulating recombinant forms (CRFs) and several unique recombinant forms (URFs) is responsible for most of the HIV-1 epidemic. Most of the current knowledge of HIV-1 central nervous system (CNS) infection is based on subtype B. However, subtypes other than subtype B account for the majority of global HIV-1 infections. Therefore, we investigated whether subtypes have any influence on cerebrospinal fluid (CSF) markers of HIV-1 CNS infection.

Methodology/Principal Findings

CSF HIV-1 RNA, CSF neopterin and CSF white blood cell (WBC) count were measured in patients infected with different HIV-1 subtypes. Using multivariate regression analysis, no differences in the CSF WBC count, neopterin and viral load were found between various HIV-1 subtypes.

Conclusions

We did not find any subtype-dependent differences in the markers evaluated in this study.

Factors influencing cerebrospinal fluid and plasma HIV-1 RNA detection rate in patients with and without opportunistic neurological disease during the HAART era

Background

In the central nervous system, HIV replication can occur relatively independent of systemic infection, and intrathecal replication of HIV-1 has been observed in patients with HIV-related and opportunistic neurological diseases. The clinical usefulness of HIV-1 RNA detection in the cerebrospinal fluid (CSF) of patients with opportunistic neurological diseases, or the effect of opportunistic diseases on CSF HIV levels in patients under HAART has not been well defined. We quantified CSF and plasma viral load in HIV-infected patients with and without different active opportunistic neurological diseases, determined the characteristics that led to a higher detection rate of HIV RNA in CSF, and compared these two compartments.

Methods

A prospective study was conducted on 90 HIV-infected patients submitted to lumbar puncture as part of a work-up for suspected neurological disease. Seventy-one patients had active neurological diseases while the remaining 19 did not.

Results

HIV-1 RNA was quantified in 90 CSF and 70 plasma samples. The HIV-1 RNA detection rate in CSF was higher in patients with neurological diseases, in those with a CD4 count lower than 200 cells/mm³, and in those not receiving antiretroviral therapy, as well as in patients with detectable plasma HIV-1 RNA. Median viral load was lower in CSF than in plasma in the total population, in patients without neurological diseases, and in patients with toxoplasmic encephalitis, while no significant difference between the two compartments was observed for patients with cryptococcal meningitis and HIV-associated dementia. CSF viral load was lower in patients with cryptococcal meningitis and neurotoxoplasmosis under HAART than in those not receiving HAART.

Conclusion

Detection of HIV-1 RNA in CSF was more frequent in patients with neurological disease, a CD4 count lower than 200 cells/mm³ and detectable plasma HIV-1. Median HIV-1 RNA levels were generally lower in CSF than in plasma but some patients showed higher CSF levels, and no difference between these two compartments was observed in patients with cryptococcal meningitis and HIV-associated dementia, suggesting the presence of intrathecal viral replication in these patients. HAART played a role in the control of CSF HIV levels even in patients with cryptococcal meningitis and neurotoxoplasmosis in whom viral replication is potentially higher.

Pathogenetic mechanisms of severe acute respiratory syndrome

Severe acute respiratory syndrome (SARS) is an acute respiratory disease with significant morbidity and mortality. While its clinical manifestations have been extensively studied, its pathogenesis is not yet fully understood. A limited number of autopsy studies have revealed that the lungs and the immune system are the organs that sustain the most severe damage. Other organs affected include the kidneys, brain, digestive tract, heart, liver, thyroid gland and urogenital tract. The primary target cells are pneumocytes and enterocytes, both cell types abundantly expressing angiotensin-converting enzyme 2 which is the main SARS-CoV receptor. Other cell types infected include the epithelial cells of renal tubules, cerebral neurons, and immune cells. The pathology of this disease results from both direct and indirect injury. Direct injury is caused by infection of the target cells by the virus. Indirect injury mainly results from immune responses, circulatory dysfunction, and hypoxia. In this review, we summarize the major pathological findings at the gross, cellular and molecular levels and discuss the various possible mechanisms that may contribute to the pathogenesis of SARS. The implications of the proposed pathogenesis for prevention, diagnosis and therapy of the disease are discussed.

Investigation of adenovirus occurrence in pediatric tumor entities

Adenoviruses (AdVs) contain genes coding for proteins with transforming potential, and certain AdV serotypes have been shown to induce tumors in rodents. However, data on the possible oncogenicity of AdVs in humans are scarce. We have therefore employed a real-time quantitative PCR (RQ-PCR) assay permitting highly sensitive detection of all 51 currently known human AdV serotypes to screen more than 500 tumor specimens derived from 17 different childhood cancer entities including leukemias, lymphomas, and solid tumors. Most tumor entities analyzed showed no evidence for the presence of AdV sequences, but AdV DNA was detected by RQ-PCR in different brain tumors including 25/30 glioblastomas, 22/30 oligodendrogliomas, and 20/30 ependymomas. Nonmalignant counterparts of AdV-positive brain tumors, including specimens of ependymal cells, plexus choroideus, and periventricular white matter, were screened for control purposes and revealed the presence of AdV DNA in most specimens tested. Identification of the AdV types present in positive malignant and nonmalignant brain tissue specimens revealed predominantly representatives of species B and D and, less commonly, C. To exclude contamination as a possible cause of false-positive results, specimens with AdV sequences detectable by PCR were subsequently analyzed by in situ hybridization, which confirmed the PCR findings in all instances. The central nervous system appears to represent a common site of AdV infection with virus persistence, thus providing the first evidence for the possible contribution of AdVs to the multistep process of tumor pathogenesis in brain tissue.

Evidence for BAG3 modulation of HIV-1 gene transcription

A family of co-chaperone proteins that share the Bcl-2-associated athanogene (BAG) domain are involved in a number of cellular processes, including proliferation and apoptosis. Among these proteins, BAG3 has received increased attention due to its high levels in several disease models and ability to associate with Hsp70 and a number of other molecular partners. BAG3 expression is stimulated during cell response to stressful conditions, such as exposure to high temperature, heavy metals, and certain drugs. Here, we demonstrate that BAG3 expression is elevated upon HIV-1 infection of human lymphocytes and fetal microglial cells. Furthermore, BAG3 protein was detectable in the cytoplasm of reactive astrocytes in HIV-1-associated encephalopathy biopsies, suggesting that induction of BAG3 is part of the host cell response to viral infection. To assess the impact of BAG3 upregulation on HIV-1 gene expression, we performed transcription assays and demonstrated that BAG3 can suppress transcription of the HIV-1 long terminal repeat (LTR) in microglial cells. This activity was mapped to the kappaB motif of the HIV-1 LTR. Results from in vitro and in vivo binding assays revealed that BAG3 suppresses interaction of the p65 subunit of NF-kappaB with the kappaB DNA motif of the LTR. Results from binding and transcriptional assay identified the C-terminus of BAG3 as a potential domain involved in the observed inhibitory effect of BAG3 on p65 activity. These observations reveal a previously unrecognized cell response, that is, an increase in BAG3, elicited by HIV-1 infection, and may provide a new avenue for the suppression of HIV-1 gene expression.

Current Update on HIV-associated Vascular Disease and Endothelial Dysfunction

Highly active antiretroviral therapy (HAART) has greatly reduced the risk of early death from opportunistic infections and extended the lifespan of people infected with the human immunodeficiency virus (HIV). Thus, many complications and organic damage in the HIV-infected population emerge. Cardiovascular disease as coronary artery disease has become a matter of particular concern. Its incidence is greatly increased in the HIV-infected population over that of people of the same age in the absence of general cardiovascular risk factors. Despite several clinical and laboratory studies in the association between HIV infection and cardiovascular disease, the pathogenic mechanisms of this significant clinical problem are largely unknown and are now under active investigation. Endothelial dysfunction is possibly the most plausible link between HIV infection and atherosclerosis. Increased expression of adhesion molecules such as intercellular adhesion molecule (ICAM)-1 and endothelial adhesion molecule (E-selectin) and inflammatory cytokines such as tumor necrosis factor (TNF)-alpha and interleukin (IL-6 has been reported in HIV-positive patients. The effect of HAART on endothelial function in HIV-positive patients is also demonstrated. In this review, we focus on the recent research update of HIV-associated vascular disease and vascular injury. We analyze and discuss the recent clinical and laboratory investigations on the effect of HIV, viral protein, and HAART therapy on endothelial injury and vascular disease; identify the areas of controversy and clinical relevance; and suggest some directions for future research.

HIV-1 gp120 compromises blood-brain barrier integrity and enhances monocyte migration across blood-brain barrier: implication for viral neuropathogenesis

Human immunodeficiency virus-1 (HIV-1) encephalitis is characterized by brain infiltration of virus-infected monocytes and macrophages. Cellular products and viral proteins secreted by infected cells likely play an important role in blood-brain barrier (BBB) impairment and the development of HIV-1-associated dementia (HAD). We previously demonstrated that HIV-1 envelope glycoprotein gp120 induces toxicity and alters expression of tight junction proteins in human brain microvascular endothelial cells (HBMECs). Here, we delineate the mechanisms of gp120-induced BBB dysfunction. Human brain microvascular endothelial cells expressed HIV-1 co-receptors (CCR5 and CXCR4). Exposure of HBMECs to gp120 derived from macrophage (CCR5) or lymphocyte (CXCR4)-tropic viruses decreased BBB tightness, increased permeability, and enhanced monocyte migration across in vitro BBB models. Blood-brain barrier integrity was restored after gp120 removal. CCR5 antibodies and inhibitors of myosin light chain kinase or protein kinase C (PKC) blocked gp120-enhanced monocyte migration and permeability of BBB in vitro. Exposure of HBMECs to gp120 induced release of intracellular calcium ([Ca(2+)](i)) that was prevented by CCR5 antibody and partially blocked by CXCR4 antagonist. Human immunodeficiency virus-1 gp120 activated three PKC isoforms in HBMECs [PKC-alpha/betaII, PKC(pan)-betaII and PKC-zeta/lambda]. Furthermore, specific PKC inhibitors (acting at the ATP-binding and calcium release site) blocked gp120-induced PKC activation and prevented increase in BBB permeability, supporting the biologic significance of these results. Thus, gp120 can cause dysfunction of BBB via PKC pathways and receptor mediated [Ca(2+)](i) release leading to cytoskeletal alterations and increased monocyte migration.

HIV proviral DNA associated with decreased neuropsychological function

The authors previously found a strong association between elevated HIV proviral DNA (HIV DNA) and a diagnosis of HIV-1-associated dementia (HAD) vs. normal cognition. It is unclear whether HIV DNA globally affects the diagnosis of HAD or whether the effect is limited to individual neuropsychological deficits. This exploratory study examined baseline HIV DNA and its association with individual neuropsychological deficits. HIV DNA was significantly associated with baseline neuropsychological deficits independent of age, ethnicity, IQ, and plasma HIV-1 RNA levels. However, HIV DNA did not predict future changes in neuropsychological deficits. The data suggest that HIV DNA and neuropsychological deficits may co-vary over time.

Iopamidol-Induced Meningoencephalopathy in an Hiv-Seropositive Patient

Central nervous system infectious and metabolic abnormalities are common in HIV-positive patients. Drug therapy, opportunistic infections, the clinical course of HIV disease itself, and very rarely iodinated radiographic contrast agents can all be linked to these abnormalities. The following case describes an HIV-seropositive patient who developed encephalopathy after undergoing a cervical myelogram that utilized iopamidol dye (Isovue-M 300 mg/mL).

Cerebrospinal Fluid Viral Loads Reach Less than 2 Copies/ML in HIV-1-Infected Patients with Effective Antiretroviral Therapy

Background

A low-grade persisting viraemia despite long-term treatment with highly active antiretroviral therapy (HAART) has previously been demonstrated in HIV-1-infected patients. Whether ongoing viral replication also could be detected in cerebrospinal fluid (CSF) in those circumstances has not been studied before.

Methods

Paired CSF and blood samples from 13 neurologically asymptomatic HIV-1-infected patients on stable HAART were analysed regarding HIV-1 RNA, by using a PCR assay with a detection limit of 2 copies/ml.

Results

All 13 patients had HIV-1 RNA <2 copies/ml in CSF, compared with 8/13 in plasma.

Conclusion

We could not demonstrate any persistent viral replication in the CSF of neurologically asymptomatic HIV-1-infected patients on effective HAART, rendering it unlikely that CSF acts as a viral reservoir in this category of patients.

Axonal transport of human immunodeficiency virus type 1 envelope protein glycoprotein 120 is found in association with neuronal apoptosis

Patients infected by human immunodeficiency virus type 1 (HIV-1) develop acquired immune deficiency syndrome-associated dementia complex (ADC), a disorder characterized by a broad spectrum of motor impairments and cognitive deficits. The number of cells in the brain that are productively infected by HIV-1 is relatively small and consists predominantly of macrophages and microglia, yet HIV-1 causes widespread neuronal loss. A better understanding of the pathogenic mechanisms mediating HIV-1 neurotoxicity is crucial for developing effective neuroprotective therapies against ADC. The HIV-1 envelope glycoprotein 120 (gp120), which is shed from the virus, is one of the agents causing neuronal cell death. However, the cellular mechanisms underlying its neurotoxic effect remain unclear. We report that gp120 injected into the rat striatum or hippocampus is sequestered by neurons and subsequently retrogradely transported to distal neurons that project to these brain areas. Cleaved caspase-3 and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling, hallmarks of apoptosis, were seen in neurons internalizing and transporting gp120. The retrograde transport of gp120 and apoptosis were mediated by the chemokine receptor CXCR4 because AMD3100, a selective CXCR4 inhibitor, blocked both events. Furthermore, colchicine or nocodazole, two inhibitors of intracellular trafficking, abolished gp120-mediated apoptosis in distal areas. These results indicate that axonal transport of gp120 might play a role in HIV-1-mediated widespread neuronal cell death.

Multidrug Resistance-Associated Proteins: Expression and Function in the Central Nervous System

Drug delivery to the brain is highly restricted, since compounds must cross a series of structural and metabolic barriers to reach their final destination, often a cellular compartment such as neurons, microglia, or astrocytes. The primary barriers to the central nervous system are the blood-brain and blood-cerebrospinal fluid barriers. Through structural modifications, including the presence of tight junctions that greatly limit paracellular transport, the cells that make up these barriers restrict diffusion of many pharmaceutically active compounds. In addition, the cells that comprise the blood-brain and blood-cerebrospinal fluid barriers express multiple ATP-dependent, membrane-bound, efflux transporters, such as members of the multidrug resistance-associated protein (MRP) family, which contribute to lowered drug accumulation. A relatively new concept in brain drug distribution just beginning to be explored is the possibility that cellular components of the brain parenchyma could act as a "second" barrier to brain permeation of pharmacological agents via expression of many of the same transporters. Indeed, efflux transporters expressed in brain parenchyma may facilitate the overall export of xenobiotics from the central nervous system, essentially handing them off to the barrier tissues. We propose that these primary and secondary barriers work in tandem to limit overall accumulation and distribution of xenobiotics in the central nervous system. The present review summarizes recent knowledge in this area and emphasizes the clinical significance of MRP transporter expression in a variety of neurological disorders.

HIV tat and neurotoxicity

HIV tat is the transactivator of HIV-1, supporting efficient viral replication by stabilizing the transcription of viral genes. Tat can be released from HIV-infected cells and alter several functions in uninfected cells. In the brain, tat induces neuronal dysfunction/toxicity, even though neurons cannot be directly infected with HIV, resulting in CNS pathology, such as the dementia and encephalitis associated with NeuroAIDS. This review discusses the most recent data addressing tat-induced neurotoxicity and integrates these new findings in the context of NeuroAIDS.

CCL2/monocyte chemoattractant protein-1 mediates enhanced transmigration of human immunodeficiency virus (HIV)-infected leukocytes across the blood-brain barrier: a potential mechanism of HIV-CNS invasion and NeuroAIDS

Encephalitis and dementia associated with acquired immunodeficiency syndrome (AIDS) are characterized by leukocyte infiltration into the CNS, microglia activation, aberrant chemokine expression, blood-brain barrier (BBB) disruption, and eventual loss of neurons. Little is known about whether human immunodeficiency virus 1 (HIV-1) infection of leukocytes affects their ability to transmigrate in response to chemokines and to alter BBB integrity. We now demonstrate that HIV infection of human leukocytes results in their increased transmigration across our tissue culture model of the human BBB in response to the chemokine CCL2, as well as in disruption of the BBB, as evidenced by enhanced permeability, reduction of tight junction proteins, and expression of matrix metalloproteinases (MMP)-2 and MMP-9. HIV-infected cells added to our model did not transmigrate in the absence of CCL2, nor did this condition alter BBB integrity. The chemokines CXCL10/interferon-gamma-inducible protein of 10 kDa, CCL3/macrophage inflammatory protein-1alpha, or CCL5/RANTES (regulated on activation normal T-cell expressed and secreted) did not enhance HIV-infected leukocyte transmigration or BBB permeability. The increased capacity of HIV-infected leukocytes to transmigrate in response to CCL2 correlated with their increased expression of CCR2, the chemokine receptor for CCL2. These data suggest that CCL2, but not other chemokines, plays a key role in infiltration of HIV-infected leukocytes into the CNS and the subsequent pathology characteristic of NeuroAIDS.

RACK1 has the nerve to act: structure meets function in the nervous system

The receptor for activated protein kinase C 1 (RACK1) is an intracellular adaptor protein. Accumulating evidence attributes to this member of the tryptophan-aspartate (WD) repeat family the role of regulating several major nervous system pathways. Structurally, RACK1 is a seven-bladed-beta-propeller, interacting with diverse proteins having distinct structural folds. When bound to the IP3 receptor, RACK1 regulates intracellular Ca2+ levels, potentially contributing to processes such as learning, memory and synaptic plasticity. By binding to the NMDA receptor, it dictates neuronal excitation and sensitivity to ethanol. When bound to the stress-induced acetylcholinesterase variant AChE-R, RACK1 is implicated in stress responses and behavior, compatible with reports of RACK1 modulations in brain ageing and in various neurodegenerative diseases. This review sheds new light on both the virtues and the variety of neuronal RACK1 interactions and their physiological consequences.

Nevirapine uptake into the central nervous system of the Guinea pig: an in situ brain perfusion study

The presence of human immunodeficiency virus (HIV) in the central nervous system (CNS) is associated with the development of HIV-1-associated dementia (HAD), a major cause of HIV-related mortality. To eradicate HIV in the CNS, anti-HIV drugs need to reach the brain and cerebrospinal fluid (CSF) in therapeutic concentrations. This involves passage through the blood-brain and blood-CSF barriers. Using a well established guinea pig in situ brain perfusion model, this study investigated whether nevirapine [6H-dipyrido(3,2-b:2',3'-e)(1,4)diazepin-6-one,11-cyclopropyl-5,11-dihydro-4-methyl], a non-nucleoside reverse transcriptase inhibitor (NNRTI), could effectively accumulate in the CNS. [(3)H]Nevirapine was coperfused with [(14)C]mannitol (a vascular/paracellular permeability marker) through the carotid arteries for up to 30 min, and accumulation in the brain, CSF, and choroid plexus was measured. [(3)H]Nevirapine uptake into the cerebrum was greater than uptake of [(14)C]mannitol, indicating significant passage across the blood-brain barrier and accumulation into the brain (this was further confirmed with capillary depletion and high-performance liquid chromatography analyses). Likewise, [(3)H]nevirapine showed a great ability to cross the blood-CSF barrier and accumulate in the CSF, compared with [(14)C]mannitol. The CNS accumulation of [(3)H]nevirapine was unaffected by 100 muM nevirapine, suggesting that passage across the blood-brain barrier can occur by diffusion. Furthermore, coperfusion with 100 muM efavirenz [2H-3,1-benzoxazin-2-one, 6-chloro-4-(cyclopropylethynyl)-1,4-dihydro-4-(trifluoromethyl)-, (4S)-; another NNRTI] did not significantly alter CNS accumulation of [(3)H]nevirapine, indicating that the efficacy of nevirapine in the CNS would not be altered by the addition of this drug to a combination therapy. Together, these data indicate that this anti-HIV drug should be beneficial in the eradication of HIV within the CNS and the subsequent treatment of HAD.

HIV-1 RNA levels in cerebrospinal fluid and plasma and their correlation with opportunistic neurological diseases in a Brazilian AIDS reference hospital

BACKGROUND: Plasma HIV RNA levels reflect systemic viral replication but in CNS it may occur relatively independent of systemic infection, yet clinical application of CSF HIV-1 RNA levels is less clear. OBJECTIVE: to compare CSF and plasma HIV-1 RNA levels of patients with different opportunistic neurological diseases to those without neurological disease, as well as to correlate these levels with the outcome of the disease and use of HAART. METHOD: 97 patients who had lumbar puncture for routine work up of suspected neurological diseases, were divided in 2 groups: without neurological disease (23) and with neurological disease (74). NASBA was used for plasma and CSF HIV RNA. RESULTS: Median CSF viral load was higher in toxoplasmic encephalitis, cryptococcal meningitis, HIV dementia and neurological diseases without a defined etiology when compared to patients without neurological disease. There was no difference between plasma viral load in patients with and without neurological diseases. Median viral load was higher in plasma and CSF among patients who died when compared to those successfully treated. CSF and plasma viral load were lower in patients with opportunistic diseases on HAART than without HAART. CONCLUSION: CSF viral load was higher in patients with any neurological disease, but this difference was not present in plasma viral load, suggesting that neurological disease influences more the CSF than plasma compartments. Notwithstanding different neurological diseases were not possible to be diferentiated by the levels of CSF HIV-1.

Immunological aetiology of major psychiatric disorders: evidence and therapeutic implications

Historically, immunological research in psychiatry was based on empirical findings and early epidemiological studies indicating a possible relationship between psychiatric symptoms and acute infectious diseases. However, aetiopathological explanations for psychiatric disorders are no longer closely related to acute infection. Nevertheless, immune hypotheses have been discussed in schizophrenia, affective disorders and infantile autism in the last decades. Although the variability between the results of the epidemiological studies conducted to date is strikingly high, there is still some evidence that the immune system might play a role in the aetiopathogenesis of these three psychiatric diseases, at least in subgroups of patients. In anxiety disorders immunological research is still very much in its infancy, and the few and inconsistent data of immune changes in these patients are believed to reflect the influence of short- or long-term stress exposure. Nevertheless, there are also some hints raising the possibility that autoimmune mechanisms could interrupt neurotransmission, which would be of significance in certain patients with anxiety and panic disorders. Drug and alcohol (ethanol) dependence are not believed to be primarily influenced by an immunological aetiology. On the other hand, immune reactions due to different drugs of abuse and alcohol may directly or indirectly influence the course of concomitant somatic diseases. In different organic brain disorders the underlying somatic disease is defined as a primary immune or autoimmune disorder, for instance HIV infection or systemic lupus erythematosus (SLE). For other neurodegenerative disorders, such as Alzheimer's disease, immunoaetiopathological mechanisms are supported by experimental and clinical studies. Treatment strategies based on immune mechanisms have been investigated in patients with schizophrenia and affective disorders. Furthermore, some antipsychotics and most antidepressants are known to have direct or indirect effects on the immune system. Different immunotherapies have been used in autism, including transfer factor, pentoxifylline, intravenous immunoglobulins and corticosteroids. Immunosuppressive and/or immunomodulating agents are well established methods for treating the neuropsychiatric sequelae of immune or autoimmune disorders, for example AIDS and SLE. Therapeutic approaches in Alzheimer's disease also apply immunological methods such as strategies of active/passive immunisation and NSAIDs. Considering the comprehensive interactive network between mind and body, future research should focus on approaches linking targets of the different involved systems.

Human endogenous retrovirus expression profiles in samples from brains of patients with schizophrenia and bipolar disorders

The detection and identification of retroviral transcripts in brain samples, cerebrospinal fluid, and plasma of individuals with recent-onset schizophrenia and schizoaffective disorders suggest that activation or upregulation of distinct human endogenous retroviruses (HERVs) may play a role in the etiopathogenesis of neuropsychiatric diseases. To test this hypothesis, we performed a comprehensive microarray-based analysis of HERV transcriptional activity in human brains. We investigated 50 representative members of 20 HERV families in a total of 215 brain samples derived from individuals with schizophrenia or bipolar disorders and matched controls. A characteristic brain-specific retroviral activity profile was found that consists of members of the class I families HERV-E, HERV-F, and ERV9 and members of HERV-K taxa. In addition to these constitutively expressed HERVs, a number of differentially active HERV elements were identified in all brain samples independent of the disease pattern that may reflect differences in the genetic background of the tested individuals. Only a subgroup of the HML-2 family (HERV-K10) was significantly overrepresented in both bipolar-disorder- and schizophrenia-associated samples compared to healthy brains, suggesting a potential association with disease. Real-time PCR analysis of HERV env transcripts with coding capacity potentially involved in neuroinflammatory conditions revealed that env expression of HERV-W, HERV-FRD, and HML-2 remains unaffected regardless of the clinical picture. Our data suggest that HERV transcription in brains is weakly correlated with schizophrenia and related diseases but may be influenced by the individual genetic background, brain-infiltrating immune cells, or medical treatment.

Cells of the central nervous system as targets and reservoirs of the human immunodeficiency virus

The availability of highly active antiretroviral therapies (HAART) has not eliminated HIV-1 infection of the central nervous system (CNS) or the occurrence of HIV-associated neurological problems. Thus, the neurobiology of HIV-1 is still an important issue. Here, we review key features of HIV-1-cell interactions in the CNS and their contributions to persistence and pathogenicity of HIV-1 in the CNS. HIV-1 invades the brain very soon after systemic infection. Various mechanisms have been proposed for HIV-1 entry into the CNS. The most favored hypothesis is the migration of infected cells across the blood-brain barrier ("Trojan horse" hypothesis). Virus production in the CNS is not apparent before the onset of AIDS, indicating that HIV-1 replication in the CNS is successfully controlled in pre-AIDS. Brain macrophages and microglia cells are the chief producers of HIV-1 in brains of individuals with AIDS. HIV-1 enters these cells by the CD4 receptor and mainly the CCR5 coreceptor. Various in vivo and cell culture studies indicate that cells of neuroectodermal origin, particularly astrocytes, may also be infected by HIV-1. These cells restrict virus production and serve as reservoirs for HIV-1. A limited number of studies suggest restricted infection of oligodendrocytes and neurons, although infection of these cells is still controversial. Entry of HIV-1 into neuroectodermal cells is independent of the CD4 receptor, and a number of different cell-surface molecules have been implicated as alternate receptors of HIV-1. HIV-1-associated injury of the CNS is believed to be caused by numerous soluble factors released by glial cells as a consequence of HIV-1 infection. These include both viral and cellular factors. Some of these factors can directly induce neuronal injury and death by interacting with receptors on neuronal membranes (neurotoxic factors). Others can activate uninfected cells to produce inflammatory and neurotoxic factors and/or promote infiltration of monocytes and T-lymphocytes, thus amplifying the deleterious effects of HIV-1 infection. CNS responses to HIV-1 infection also include mechanisms that enhance neuronal survival and strengthen crucial neuronal support functions. Future challenges will be to develop strategies to prevent HIV-1 spread in the brain, bolster intrinsic defense mechanisms of the brain and to elucidate the impact of long-term persistence of HIV-1 on CNS functions in individuals without AIDS.

Compartmentalized human immunodeficiency virus type 1 present in cerebrospinal fluid is produced by short-lived cells

Human immunodeficiency virus type 1 (HIV-1) invades the central nervous system (CNS) during primary infection and persists in this compartment by unknown mechanisms over the course of infection. In this study, we examined viral population dynamics in four asymptomatic subjects commencing antiretroviral therapy to characterize cellular sources of HIV-1 in the CNS. The inability to monitor viruses directly in the brain poses a major challenge in studying HIV-1 dynamics in the CNS. Studies of HIV-1 in cerebrospinal fluid (CSF) provide a useful surrogate for the sampling of virus in the CNS, but they are complicated by the fact that infected cells in local CNS tissues and in the periphery contribute to the population pool of HIV-1 in CSF. We utilized heteroduplex tracking assays to differentiate CSF HIV-1 variants that were shared with peripheral blood plasma from those that were compartmentalized in CSF and therefore presumably derived from local CNS tissues. We then tracked the relative decline of individual viral variants during the initial days of antiretroviral therapy. We found that HIV-1 variants compartmentalized in CSF declined rapidly during therapy, with maximum half-lives of approximately 1 to 3 days. These kinetics emulate the decline in HIV-1 produced from short-lived CD4+ T cells in the periphery, suggesting that a similarly short-lived, HIV-infected cell population exists within the CNS. We propose that short-lived CD4+ T cells trafficking between the CNS and the periphery play an important role in amplifying and maintaining HIV-1 populations in the CNS during the asymptomatic phase of infection.

HIV-1 gp120 proteins alter tight junction protein expression and brain endothelial cell permeability: implications for the pathogenesis of HIV-associated dementia

Breakdown of the blood-brain barrier (BBB) is commonly seen in patients with HIV-associated dementia (HAD) despite the lack of productive infection of the brain endothelium. It is likely that secreted viral products play a major role in BBB damage and the development of HAD. The objective of this study is to determine the effects of gp120 proteins on brain endothelial cell permeability and junctional protein expression. Our results showed that treatment of cultured human brain endothelial cells with gp120 for 24 hours results in increased permeability of the endothelial monolayer. Also, gp120 proteins caused disruption and downregulation of the tight junction proteins ZO-1, ZO-2, and occludin in these cells. Other junctional proteins such as claudin-1 and claudin-5 were unaffected by gp120 treatment. These data demonstrate that HIV gp120 proteins alter both the functional and molecular properties of the BBB, which could increase trafficking of HIV, infected cells, and toxic humoral factors into the central nervous system and contribute to the pathogenesis of HAD.

Neuroimaging in human immunodeficiency virus infection

Human immunodeficiency virus (HIV) is associated with central nervous system (CNS) changes that may affect cerebral blood flow (CBF), metabolism, structure, and diffusion. Each of the available neuroimaging techniques offers unique insight into the neural mechanisms underlying HIV, as well as a potential means of monitoring disease progression and treatment response. The purpose of the article is to provide a review of experimental studies evaluating changes related to HIV with imaging techniques, including single-photon emission computed tomography (SPECT), positron emission tomography (PET), volumetric magnetic resonance imaging (MRI), functional MRI (fMRI), magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), and perfusion MRI (pMRI).

Circulating proviral HIV DNA and HIV-associated dementia

OBJECTIVE

Individuals continue to develop HIV-1-associated dementia (HAD) despite treatment with highly active antiretroviral therapy (HAART). Monocytes/macrophages (M/MPhi) can harbor proviral DNA that is not eradicated by HAART. To determine if HAD is associated with the level of HIV-1 infection within circulating leukocytes, we quantified HIV-1 DNA copy number in peripheral blood mononuclear cells (PBMC), and in PBMC subsets.

DESIGN

Cross-sectional analysis within the Hawaii Aging with HIV Cohort comparing participants with HAD to those with normal cognition (NC).

METHODS

Real-time PCR assays assessing HIV DNA copy number/1 x 10 cells were performed on PBMC and subsets.

RESULTS

Individuals with HAD (n = 27) had a median (interquartile range) of 9.11 (37.20) HIV DNA per 1 x 10 PBMC compared to 0.49 (0.89) HIV DNA per 1 x 10 PBMC in individuals with NC (n = 22). Using a univariate analysis in the subset of individuals with undetectable viral load (HAD, n = 11; NC, n = 13), the odds of HAD attributable to HIV DNA copy number was 2.76 (1.28-5.94), P < 0.01. Preliminary analysis of a small subset of patients (n = 5) suggested that the primary source of HIV DNA may be the activated M/MPhi (CD14/CD16) subset.

CONCLUSIONS

These findings suggest a potentially important association between circulating provirus and HAD.

Patterns of gene dysregulation in the frontal cortex of patients with HIV encephalitis

The neurodegenerative process in HIV encephalitis (HIVE) is associated with extensive damage to the dendritic and synaptic structure that often leads to cognitive impairment. Several mechanisms might be at play, including release of neurotoxins, oxidative stress and decreased activity of neurotrophic factors. Furthermore, HIV-mediated dysregulation of genes involved in neuronal maintenance might play an important role. For this purpose, cRNA was prepared from the brains of 17 AIDS patients for analysis with the Affymetrix Human U95Av2 GeneChip and analyzed with the GeneSpring Expression Analysis Software. Out of 12,625 genes analyzed, 74 were downregulated and 59 were upregulated compared to controls. Initial alternative analysis of RNA was performed by ribonuclease protection assay (RPA). In cases with HIVE, downregulated genes included neuronal molecules involved in synaptic plasticity and transmission (ion channels, synaptogyrin, synapsin II), cell cycle (p35, p39, CDC-L2, CDC42, PAK1) and signaling molecules (PI3K, Ras-Raf-MEK1), transcription factors and cytoskeletal components (MAP-1B, MAP-2, tubulin, adducin-2). Upregulated genes included those involved in neuroimmune (IgG, MHC, beta2microglobulin) and anti-viral responses (interferon-inducible molecules), transcription (STAT1, OLIG2, Pax-6) and signaling modulation (MEK3, EphB1) of the cytoskeleton (myosin, aduccin-3, radixin, dystrobrevin). Taken together, this study suggests that HIV proteins released from infected macrophages might not only induce a neuroinflammatory response, but also may promote neurodegeneration by interfering with neuronal transcription of genes involved in regulating signaling and cytoskeletal molecules important in maintaining synapto-dendritic functioning and integrity.

Drug abuse and neuropathogenesis of HIV infection: role of DC-SIGN and IDO

Dendritic cells are the critical mediators of various immune responses and are the first line of defense against any infection including HIV. They play a major role in harboring HIV and the subsequent infection of T cells and passage of virus through the blood-brain barrier (BBB). The recently discovered DC-specific, CD4-independent HIV attachment receptor, DC-SIGN, and T-cell suppressing factor, indolamine 2,3-dioxygenase (IDO), are known to play a critical role in the immuno-neuropathogenesis of HIV infection. Since brain microvascular cells (BMVEC) express dendritic cell (DC)-specific C type ICAM-3 grabbing nonintegrin (DC-SIGN), it is possible that DC-SIGN may play a critical role in human immunodeficiency virus-type 1 (HIV-1) infection and migration of infected DC across BBB. Matrix metalloproteinases (MMPs) are proteolytic enzymes known to be responsible for maintenance, turnover and integrity of extracellular matrix. Our results show that cocaine upregulates IDO and DC-SIGN expression by DC. Further, cocaine upregulates DC-SIGN and MMPs in BMVEC supporting the hypothesis that cocaine causes membrane permeability facilitating endothelial transmigration of infected DC in to the CNS. Targeting DC-SIGN and IDO with specific monoclonal antibodies, inexpensive synthetic antagonists, antisense oligonucleotides and siRNA may lead to develop novel treatment strategies particularly in high-risk populations such as cocaine users.

An update on the neuropathology of HIV in the HAART era

This review compares the neuropathology of highly active antiretroviral therapy (HAART)-treated HIV+ individuals with the reported central nervous system (CNS) findings from the pre-HAART era. HAART has had considerable success in combating HIV-related immune collapse and has prevented many of the former end-stage complications of AIDS. However, with increased survival times the prevalence of minor HIV-associated cognitive impairment appears to be rising among treated patients and this may be a particular risk for older individuals. HIV encephalitis (HIVE) is still prevalent in treated patients although attenuated forms of HIVE and CNS opportunistic disorders are also observed. Some subjects show very significant CNS lymphocytic infiltrates in the context of HAART-induced immune reconstitution. HIV-associated cognitive impairment correlates best with the increased presence of activated, though not necessarily infected, microglia and CNS macrophages. This suggests that indirect mechanisms of neuronal injury and loss occur in HIV/AIDS as a basis for dementia since neurones are not themselves productively infected. Research to elucidate the mechanisms of neuronal injury in HIV/AIDS may contribute to the understanding of CNS function not only in HAART-treated subjects but also in other neurodegenerative disorders.

Microarray analysis of activated mixed glial (microglia) and monocyte-derived macrophage gene expression

Since macrophage activation can now be studied at a global level using modern microarray and proteomic analyses, discovery of novel macrophage activation genes is inevitable and important for understanding HIV-associated dementia (HAD). We isolated two different types of primary human macrophages: microglia and monocyte-derived macrophages (MDM) from brain tissue and whole blood, respectively. The microarray analysis of differentially regulated macrophage activation genes reported here supports our previous assertions that the mixed glia (MIX) cultured in starvation conditions (DMEM alone) are a non-activated, or "quiescent", tissue culture model for studying macrophage activation in the brain. Transcript levels from these quiescent cultures provided a background level of gene expression and allowed for the identification of upregulated macrophage activation genes in the MIX brain cultures upon treatment with an array of soluble activation factors: serum components, cytokines, and growth factors. We found that 914 genes in the MIX cultures and 734 genes in the MDM cultures had a greater than twofold increase in expression. We discovered 180 genes with expression that was increased more than twofold in both culture types. Microarray-specific statistical analyses were performed to complement fold change analysis: significance analysis of microarrays (SAM) and Partek Pro. In the MIX cultures, we detected over a 100-fold increase in IL-1beta and TIMP1 transcription; Caspase 9, S100A8 and 9, MMP12, IL-8, monocyte chemotactic protein 1 (MCP1), MRC-1, and IL-6 were also upregulated. Activation of starved MDM cultures resulted in fewer upregulated genes compared to MIX cultures. Genes upregulated in both MIX and MDM included CCL2 (MCP1), CCL7, CXCL5, TNFSF14, kinases, and phosphatases. These microarray data may provide leads for identifying previously unknown neurotoxins, disease biomarkers, and pathways responsible for the neuronal apoptosis observed in HAD and for the eventual identification of therapeutic targets and treatments.