Dopamine deficits and regulation of the cAMP second messenger system in brains of simian immunodeficiency virus-infected rhesus monkeys

Alpha-synuclein and RNA viruses: Exploring the neuronal nexus

Alpha-synuclein (α-syn), known for its pivotal role in Parkinson's disease, has recently emerged as a significant player in neurotropic RNA virus infections. Upregulation of α-syn in various viral infections has been found to impact neuroprotective functions by regulating neurotransmitter synthesis, vesicle trafficking, and synaptic vesicle recycling. This review focuses on the multifaceted role of α-syn in controlling viral replication by modulating chemoattractant properties towards microglial cells, virus-induced ER stress signaling, anti-oxidative proteins expression. Furthermore, the text underlines the α-syn-mediated regulation of interferon-stimulated genes. The review may help suggest potential therapeutic avenues for mitigating the impact of RNA viruses on the central nervous system by exploiting α-syn neuroprotective biology.

Advancing the preclinical study of comorbid neuroHIV and substance use disorders: Current perspectives and future directions

Human immunodeficiency virus (HIV) remains a persistent public health concern throughout the world. Substance use disorders (SUDs) are a common comorbidity that can worsen treatment outcomes for people living with HIV. The relationship between HIV infection and SUD outcomes is likely bidirectional, making clear interrogation of neurobehavioral outcomes challenging in clinical populations. Importantly, the mechanisms through which HIV and addictive drugs disrupt homeostatic immune and CNS function appear to be highly overlapping and synergistic within HIV-susceptible reward and motivation circuitry in the central nervous system. Decades of animal research have revealed invaluable insights into mechanisms underlying the pathophysiology SUDs and HIV, although translational studies examining comorbid SUDs and HIV are very limited due to the technical challenges of modeling HIV infection preclinically. In this review, we discuss preclinical animal models of HIV and highlight key pathophysiological characteristics of each model, with a particular emphasis on rodent models of HIV. We then review the implementation of these models in preclinical SUD research and identify key gaps in knowledge in the field. Finally, we discuss how cutting-edge behavioral neuroscience tools, which have revealed key insights into the neurobehavioral mechanisms of SUDs, can be applied to preclinical animal models of HIV to reveal potential, novel treatment avenues for comorbid HIV and SUDs. Here, we argue that future preclinical SUD research would benefit from incorporating comorbidities such as HIV into animal models and would facilitate the discovery of more refined, subpopulation-specific mechanisms and effective SUD prevention and treatment targets.

Synaptic dysfunction is associated with alterations in the initiation of goal-directed behaviors: Implications for HIV-1-associated apathy

Individuals living with human immunodeficiency virus type 1 (HIV-1) exhibit an increased prevalence of neuropsychiatric comorbities (e.g., apathy) relative to their seronegative counterparts. Given the profound functional consequences associated with apathy, characterizing the multidimensional neuropsychiatric syndrome, and associated neural mechanisms, following chronic HIV-1 viral protein exposure remains a critical need. HIV-1-associated apathy was examined by quantifying goal-directed behaviors, indexed using voluntary wheel running, during the diurnal and nocturnal cycle. Apathetic behaviors in the HIV-1 transgenic (Tg) rat were characterized by a profound decrease in the number of running bouts during both the diurnal and nocturnal cycle, supporting a prominent deficit in the self-initiation of spontaneous behaviors. Additionally, HIV-1 Tg animals exhibited a decreased reinforcing efficacy of voluntary wheel running during the nocturnal cycle. Following the completion of voluntary wheel running, synaptic dysfunction in medium spiny neurons (MSNs) of the nucleus accumbens core (NAcc) was examined as a potential neural mechanism underlying HIV-1-associated apathy. HIV-1 Tg animals displayed prominent synaptic dysfunction in MSNs of the NAcc, characterized by enhanced dendritic branching complexity and a population shift towards an immature dendritic spine phenotype relative to control animals. Synaptic dysfunction, which accounted for 42.0% to 68.5% of the variance in the number of running bouts, was strongly associated with the self-initiation of spontaneous behaviors. Establishment of the relationship between synaptic dysfunction and apathy affords a key target for the development of novel therapeutics and cure strategies for affective alterations associated with HIV-1.

HIV-Associated Apathy/Depression and Neurocognitive Impairments Reflect Persistent Dopamine Deficits

Individuals living with human immunodeficiency virus type 1 (HIV-1) are often plagued by debilitating neurocognitive impairments and affective alterations;the pathophysiology underlying these deficits likely includes dopaminergic system dysfunction. The present review utilized four interrelated aims to critically examine the evidence for dopaminergic alterations following HIV-1 viral protein exposure. First, basal dopamine (DA) values are dependent upon both brain region andexperimental approach (i.e., high-performance liquid chromatography, microdialysis or fast-scan cyclic voltammetry). Second, neurochemical measurements overwhelmingly support decreased DA concentrations following chronic HIV-1 viral protein exposure. Neurocognitive impairments, including alterations in pre-attentive processes and attention, as well as apathetic behaviors, provide an additional line of evidence for dopaminergic deficits in HIV-1. Third, to date, there is no compelling evidence that combination antiretroviral therapy (cART), the primary treatment regimen for HIV-1 seropositive individuals, has any direct pharmacological action on the dopaminergic system. Fourth, the infection of microglia by HIV-1 viral proteins may mechanistically underlie the dopamine deficit observed following chronic HIV-1 viral protein exposure. An inclusive and critical evaluation of the literature, therefore, supports the fundamental conclusion that long-term HIV-1 viral protein exposure leads to a decreased dopaminergic state, which continues to persist despite the advent of cART. Thus, effective treatment of HIV-1-associated apathy/depression and neurocognitive impairments must focus on strategies for rectifying decreases in dopamine function.

HIV Neuropathogenesis in the Presence of a Disrupted Dopamine System

Antiretroviral therapy (ART) has transformed HIV into a chronic condition, lengthening and improving the lives of individuals living with this virus. Despite successful suppression of HIV replication, people living with HIV (PLWH) are susceptible to a growing number of comorbidities, including neuroHIV that results from infection of the central nervous system (CNS). Alterations in the dopaminergic system have long been associated with HIV infection of the CNS. Studies indicate that changes in dopamine concentrations not only alter neurotransmission, but also significantly impact the function of immune cells, contributing to neuroinflammation and neuronal dysfunction. Monocytes/macrophages, which are a major target for HIV in the CNS, are responsive to dopamine. Therefore, defining more precisely the mechanisms by which dopamine acts on these cells, and the changes in cellular function elicited by this neurotransmitter are necessary to develop therapeutic strategies to treat neuroHIV. This is especially important for vulnerable populations of PLWH with chemically altered dopamine concentrations, such as individuals with substance use disorder (SUD), or aging individuals using dopamine-altering medications. The specific neuropathologic and neurocognitive consequences of increased CNS dopamine remain unclear. This is due to the complex nature of HIV neuropathogenesis, and logistical and technical challenges that contribute to inconsistencies among cohort studies, animal models and in vitro studies, as well as lack of demographic data and access to human CNS samples and cells. This review summarizes current understanding of the impact of dopamine on HIV neuropathogenesis, and proposes new experimental approaches to examine the role of dopamine in CNS HIV infection. Graphical abstract HIV Neuropathogenesis in the Presence of a Disrupted Dopamine System. Both substance abuse disorders and the use of dopaminergic medications for age-related diseases are associated with changes in CNS dopamine concentrations and dopaminergic neurotransmission. These changes can lead to aberrant immune function, particularly in myeloid cells, which contributes to the neuroinflammation, neuropathology and dysfunctional neurotransmission observed in dopamine-rich regions in HIV+ individuals. These changes, which are seen despite the use antiretroviral therapy (ART), in turn lead to further dysregulation of the dopamine system. Thus, in individuals with elevated dopamine, the bi-directional interaction between aberrant dopaminergic neurotransmission and HIV infection creates a feedback loop contributing to HIV associated neurocognitive dysfunction and neuroHIV. However, the distinct contributions and interactions made by HIV infection, inflammatory mediators, ART, drugs of abuse, and age-related therapeutics are poorly understood. Defining more precisely the mechanisms by which these factors influence the development of neurological disease is critical to addressing the continued presence of neuroHIV in vulnerable populations, such as HIV-infected older adults or drug abusers. Due to the complexity of this system, understanding these effects will require a combination of novel experimental modalities in the context of ART. These will include more rigorous epidemiological studies, relevant animal models, and in vitro cellular and molecular mechanistic analysis.

HIV, Tat and dopamine transmission

Human Immunodeficiency Virus (HIV) is a progressive infection that targets the immune system, affecting more than 37 million people around the world. While combinatorial antiretroviral therapy (cART) has lowered mortality rates and improved quality of life in infected individuals, the prevalence of HIV associated neurocognitive disorders is increasing and HIV associated cognitive decline remains prevalent. Recent research has suggested that HIV accessory proteins may be involved in this decline, and several studies have indicated that the HIV protein transactivator of transcription (Tat) can disrupt normal neuronal and glial function. Specifically, data indicate that Tat may directly impact dopaminergic neurotransmission, by modulating the function of the dopamine transporter and specifically damaging dopamine-rich regions of the CNS. HIV infection of the CNS has long been associated with dopaminergic dysfunction, but the mechanisms remain undefined. The specific effect(s) of Tat on dopaminergic neurotransmission may be, at least partially, a mechanism by which HIV infection directly or indirectly induces dopaminergic dysfunction. Therefore, precisely defining the specific effects of Tat on the dopaminergic system will help to elucidate the mechanisms by which HIV infection of the CNS induces neuropsychiatric, neurocognitive and neurological disorders that involve dopaminergic neurotransmission. Further, this will provide a discussion of the experiments needed to further these investigations, and may help to identify or develop new therapeutic approaches for the prevention or treatment of these disorders in HIV-infected individuals.

The dopamine-related polymorphisms BDNF, COMT, DRD2, DRD3, and DRD4 are not linked with changes in CSF dopamine levels and frequency of HIV infection

We showed previously that higher levels in CSF dopamine in HIV patients are associated with the presence of the dopamine transporter (DAT) 10/10-repeat allele which was also detected more frequently in HIV-infected individuals compared to uninfected subjects. In the current study, we investigated further whether other genetic dopamine (DA)-related polymorphisms may be related with changes in CSF DA levels and frequency of HIV infection in HIV-infected subjects. Specifically, we studied genetic polymorphisms of brain-derived neurotrophic factor, catechol-O-methyltransferase, and dopamine receptors DRD2, DRD3, and DRD4 genetic polymorphisms in uninfected and HIV-infected people in two different ethnical groups, a German cohort (Caucasian, 72 individuals with HIV infection and 22 individuals without HIV infection) and a South African cohort (Xhosan, 54 individuals with HIV infection and 19 individuals without HIV infection). We correlated the polymorphisms with CSF DA levels, HIV dementia score, CD4⁺ T cell counts, and HIV viral load. None of the investigated DA-related polymorphisms was associated with altered CSF DA levels, CD4⁺ T cell count, viral load, and HIV dementia score. The respective allele frequencies were equally distributed between HIV-infected patients and controls. Our findings do not show any influence of the studied genetic polymorphisms on CSF DA levels and HIV infection. This is in contrast to what we found previously for the DAT 3'UTR VNTR and highlights the specific role of the DAT VNTR in HIV infection and disease.

The cross-talk of HIV-1 Tat and methamphetamine in HIV-associated neurocognitive disorders

Antiretroviral therapy has dramatically improved the lives of human immunodeficiency virus 1 (HIV-1) infected individuals. Nonetheless, HIV-associated neurocognitive disorders (HAND), which range from undetectable neurocognitive impairments to severe dementia, still affect approximately 50% of the infected population, hampering their quality of life. The persistence of HAND is promoted by several factors, including longer life expectancies, the residual levels of virus in the central nervous system (CNS) and the continued presence of HIV-1 regulatory proteins such as the transactivator of transcription (Tat) in the brain. Tat is a secreted viral protein that crosses the blood–brain barrier into the CNS, where it has the ability to directly act on neurons and non-neuronal cells alike. These actions result in the release of soluble factors involved in inflammation, oxidative stress and excitotoxicity, ultimately resulting in neuronal damage. The percentage of methamphetamine (MA) abusers is high among the HIV-1-positive population compared to the general population. On the other hand, MA abuse is correlated with increased viral replication, enhanced Tat-mediated neurotoxicity and neurocognitive impairments. Although several strategies have been investigated to reduce HAND and MA use, no clinically approved treatment is currently available. Here, we review the latest findings of the effects of Tat and MA in HAND and discuss a few promising potential therapeutic developments.

Estrous cycle and HIV-1 Tat protein influence cocaine-conditioned place preference and induced locomotion of female mice

The HIV-1 trans-activator of transcription (Tat) protein, interacts with psychostimulants to potentiate cocaine-reward in rodents. Sex steroids may protect against Tat-induced deficits. Female GT-tg transgenic mice conditionally-expressed Tat protein targeted to brain via a doxycycline-dependent, GFAP-linked promoter. Mice were tested for cocaine-conditioned place preference (CPP) and cocaine-induced locomotion when in the proestrous (high-hormone) or diestrous (low-hormone) phases of their estrous cycle. Cocaine-CPP was potentiated by Tat induction via 50, 100, or 125 (but not 25) mg/kg doxycycline daily treatment for 7 days. Diestrous mice exposed to Tat protein demonstrated significantly greater cocaine-CPP than did proestrous mice. Tat induction interacted with estrous cycle to decrease acute cocaine-induced locomotion among Tat-induced diestrous mice, but not their uninduced or proestrous counterparts, and attenuated cocaine-sensitization. In a cocaine-challenge, previously cocaine-sensitized mice demonstrated greater cocaine-locomotion over cocaine-naive counterparts and Tat-induction attenuated locomotion. Altogether, data demonstrate Tat and circulating sex steroid influences over cocaine-reward and psychostimulation.

Neuropathological sequelae of Human Immunodeficiency Virus and apathy: A review of neuropsychological and neuroimaging studies

Apathy remains a common neuropsychiatric disturbance in the Human Immunodeficiency Virus (HIV-1) despite advances in anti-retroviral treatment (ART). The goal of the current review is to recapitulate findings relating apathy to the deleterious biobehavioral effects of HIV-1 in the post-ART era. Available literatures demonstrate that the emergence of apathy with other neurocognitive and neuropsychiatric symptoms may be attributed to neurotoxic effects of viral proliferation, e.g., aggregative effect of Tat and gp120 on apoptosis, transport and other enzymatic reactions amongst dopaminergic neurons and neuroglia. An assortment of neuroimaging modalities converge on the severity of apathy symptoms associated with the propensity of the virus to replicate within frontal-striatal brain circuits that facilitate emotional processing. Burgeoning research into functional brain connectivity also supports the effects of microvascular and neuro-inflammatory injury linked to aging with HIV-1 on the presentation of neuropsychiatric symptoms. Summarizing these findings, we review domains of HIV-associated neurocognitive and neuropsychiatric impairment linked to apathy in HIV. Taken together, these lines of research suggest that loss of affective, cognitive and behavioral inertia is commensurate with the neuropathology of HIV-1.

Early microstructural white matter changes in patients with HIV: a diffusion tensor imaging study

BACKGROUND

Previous studies have reported white matter (WM) brain alterations in asymptomatic patients with human immunodeficiency virus (HIV).

METHODS

We compared diffusion tensor imaging (DTI) derived WM fractional anisotropy (FA) between HIV-patients with and without mild macroscopic brain lesions determined using standard magnetic resonance imaging (MRI). We furthermore investigated whether WM alterations co-occurred with neurocognitive deficits and depression. We performed structural MRI and DTI for 19 patients and 19 age-matched healthy controls. Regionally-specific WM integrity was investigated using voxel-based statistics of whole-brain FA maps and region-of-interest analysis. Each patient underwent laboratory and neuropsychological tests.

RESULTS

Structural MRI revealed no lesions in twelve (HIV-MRN) and unspecific mild macrostructural lesions in seven patients (HIV-MRL). Both analyses revealed widespread FA-alterations in all patients. Patients with HIV-MRL had FA-alterations primarily adjacent to the observed lesions and, whilst reduced in extent, patients with HIV-MRN also exhibited FA-alterations in similar regions. Patients with evidence of depression showed FA-increase in the ventral tegmental area, pallidum and nucleus accumbens in both hemispheres, and patients with evidence of HIV-associated neurocognitive disorder showed widespread FA-reduction.

CONCLUSION

These results show that patients with HIV-MRN have evidence of FA-alterations in similar regions that are lesioned in HIV-MRL patients, suggesting common neuropathological processes. Furthermore, they suggest a biological rather than a reactive origin of depression in HIV-patients.

Drugs of abuse, dopamine, and HIV-associated neurocognitive disorders/HIV-associated dementia

Although the incidence of HIV-associated dementia (HAD) has declined, HIV-associated neurocognitive disorders (HAND) remain a significant health problem despite use of highly active antiretroviral therapy. In addition, the incidence and/or severity of HAND/HAD are increased with concomitant use of drugs of abuse, such as cocaine, marijuana, and methamphetamine. Furthermore, exposure to most drugs of abuse increases brain levels of dopamine, which has been implicated in the pathogenesis of HIV. This review evaluates the potential role of dopamine in the potentiation of HAND/HAD by drugs of abuse. In the brain, multiplication of HIV in infected macrophages/microglia could result in the release of HIV proteins such as gp120 and Tat, which can bind to and impair dopamine transporter (DAT) functions, leading to elevated levels of dopamine in the dopaminergic synapses in the early asymptomatic stage of HIV infection. Exposure of HIV-infected patients to drugs of abuse, especially cocaine and methamphetamine, can further increase synaptic levels of dopamine via binding to and subsequently impairing the function of DAT. This accumulated synaptic dopamine can diffuse out and activate adjacent microglia through binding to dopamine receptors. The activation of microglia may result in increased HIV replication as well as increased production of inflammatory mediators such as tumor necrosis factor (TNF)-alpha and chemokines. Increased HIV replication can lead to increased brain viral load and increased shedding of HIV proteins, gp120 and Tat. These proteins, as well as TNF-alpha, can induce cell death of adjacent dopaminergic neurons via apoptosis. Autoxidation and metabolism of accumulated synaptic dopamine can lead to generation of reactive oxygen species (hydrogen peroxide), quinones, and semiquinones, which can also induce apoptosis of neurons. Increased cell death of dopaminergic neurons can eventually lead to dopamine deficit that may exacerbate the severity and/or accelerate the progression of HAND/HAD.

Increased dopaminergic neurotransmission in therapy-naïve asymptomatic HIV patients is not associated with adaptive changes at the dopaminergic synapses

Central dopaminergic (DA) systems are affected during human immunodeficiency virus (HIV) infection. So far, it is believed that they degenerate with progression of HIV disease because deterioration of DA systems is evident in advanced stages of infection. In this manuscript we found that (a) DA levels are increased and DA turnover is decreased in CSF of therapy-naïve HIV patients in asymptomatic infection, (b) DA increase does not modulate the availability of DA transporters and D2-receptors, (c) DA correlates inversely with CD4+ numbers in blood. These findings show activation of central DA systems without development of adaptive responses at DA synapses in asymptomatic HIV infection. It is probable that DA deterioration in advanced stages of HIV infection may derive from increased DA availability in early infection, resulting in DA neurotoxicity. Our findings provide a clue to the synergism between DA medication or drugs of abuse and HIV infection to exacerbate and accelerate HIV neuropsychiatric disease, a central issue in the neurobiology of HIV.

Imaging serotonergic transmission with [11C]DASB-PET in depressed and non-depressed patients infected with HIV

INTRODUCTION

Site-selective imaging can provide significant insight into the mechanism of HIV-associated neurological disease. The goal of this study was to evaluate the involvement of serotonergic transmission in HIV-associated depression using [(11)C]DASB, a serotonin transporter (5-HTT)-specific radiopharmaceutical for positron emission tomography (PET).

METHODS

Nine depressed HIV+ subjects (HIV-D), 9 non-depressed HIV+ subjects (HIV-ND) and 7 healthy controls (HC) underwent an MRI scan and a [(11)C]DASB-PET scan. The outcome measure was 5-HTT binding potential normalized to non-displaceable tissue radioligand (BP(ND)).

RESULTS

HIV-ND subjects had lower mean regional 5-HTT BP(ND) estimates across regions compared to HC, while HIV-D subjects demonstrated higher mean regional binding values than HIV-ND subjects in most regions. Prior to correction for the false discovery rate, HIV-ND had significantly lower BP(ND) values compared to HC subjects in two regions (insula and anterior cingulate) and all HIV+ patients had significantly lower binding than HC in all regions except for the midbrain, thalamus and pons. After correction for the false discovery rate, only the insula showed significantly lower binding in HIV+ subjects compared to HC (P<0.0045). Despite a significant difference in the duration of illness between the HIV-D and HIV-ND groups, there was no definite correlation between the duration of illness and BP(ND).

CONCLUSION

Lower [(11)C]DASB binding in HIV+ patients compared to HC may reflect serotonergic neuronal loss as a component of generalized HIV-associated neurodegeneration. Higher mean regional BP(ND) values in HIV-D compared to HIV-ND subjects could reflect increased density of 5-HTT, leading to increased clearance of serotonin from the synapse, which could account, in part, for symptoms of depression. The lack of correlation between duration of illness and binding argues against these findings being the result of differential neurodegeneration only. Our findings suggest a possible role for dysregulated serotonergic transmission in HIV-associated depression.

Further characterization of the spatial learning deficit in the human immunodeficiency virus-1 transgenic rat

Human immunodeficiency virus (HIV)-associated dementia (HAD) encompasses a spectrum of cognitive and motor deficits resulting from the progression of central nervous system abnormalities caused by the HIV-1 virus. With the advent of highly active antiretroviral therapy (HAART), these deficits have become milder, but more prevalent as the population of HIV-positive individuals ages. Mild impairment in cognition has also been identified in asymptomatic HIV-1 patients. The noninfectious HIV-1 transgenic (Tg) rat recently developed to study the pathogenesis of acquired immunodeficiency syndrome (AIDS) may also be useful for the study of the early and chronic effects of HIV-1 on learning and cognition. In a previous study, we demonstrated that HIV-1Tg rats show a deficit in learning how to swim to a hidden platform in a modified water maze task compared to normal and transgenic controls. In the present study, we replicate this result and demonstrate that HIV-1Tg rats also show a significant deficit in reversal learning and new strategy learning. These results indicate that the HIV-1Tg rat is a promising model in which to study the neuropathogenic mechanisms that can cause cognitive deficits in patients with HAD as well as asymptomatic HIV-positive individuals.

Memantine upregulates BDNF and prevents dopamine deficits in SIV-infected macaques: a novel pharmacological action of memantine

N-methyl-D-aspartate (NMDA) receptor activation is involved in the pathogenetic cascades of neurodegenerative disorders including human immunodeficiency virus (HIV) dementia. Memantine, an uncompetitive NMDA receptor antagonist, which has been recently approved for the treatment of Alzheimer's disease, is being discussed as a potential adjunctive therapeutic substance for HIV dementia. We used simian immunodeficiency virus-infected rhesus macaques to assess the effects of memantine on brain dysfunction and brain pathology within 3-5 months after initial infection during early asymptomatic stage of disease. We had shown previously that within this time frame, marked changes were evident in the dopaminergic systems. Memantine was administered two weeks post infection, at peak viremia, in order to prevent early NMDA receptor activation due to immune mediators. We found that memantine prevented onset of dopamine deficits in the brains of SIV-infected macaques, without affecting early brain pathology or peripheral course of infection. Memantine specifically upregulated mRNA and protein expression of the neurotrophic factor brain-derived neurotrophic factor (BDNF), suggesting that the protective effect of memantine on dopamine function may be mechanistically remote from NMDA receptor antagonism. This novel pharmacological action of memantine may also be relevant for other neurodegenerative disorders and supports the involvement of neurotrophic factors in adult brain neuroprotection.

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

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

Neurobiology of HIV, psychiatric and substance abuse comorbidity research: workshop report

Viral infections can cause persistent and progressive changes in emotional and cognitive functions. The viral-induced imbalances in neuronal network functioning may precipitate or accentuate psychiatric conditions in vulnerable individuals, in part, as a function of the host response to proinflammatory cytokines resulting from infection or brain injury. Research indicates that the mediators of psychiatric illnesses and HIV-neuropathogenesis utilize similar brain structures, neurocircuitry and receptor systems. The genetic, cellular and molecular mechanisms contributing to HIV neuropathogenesis and its late stage clinical correlate, HIV-associated-dementia (HAD), are active areas of neuroAIDS research. The study of HIV in the context of psychiatric comorbidities and comorbid pathogenesis is in a fledgling stage despite epidemiological studies suggesting that >60% of HIV infected individuals will suffer from at least one major psychiatric disorder during the course of infection. Depression is the primary comorbid disorder but anxiety and substance abuse disorders are also considerable in certain HIV(+) populations. Certain substances of abuse and the biological mediators of psychiatric illnesses reportedly interact in the brain and presumptively worsen HIV-related neuropathogenesis and survival measures. A panel of experts discussed approaches for studying the neuroscience of HIV and psychiatric comorbidity at a basic, mechanistic level since they co-exist in high proportion in the human population. Recommended approaches ranged from improving human consent forms and maximizing the value of repository resources to novel research designs and identifying human and animal endophenotypes.

Biostatistical analysis of gene microarrays reveals diverse expression clusters between macaque subspecies in brain SIV infection

In this study we investigated differences in the gene expression profiling of the brains of rhesus macaques that were uninfected or infected with SIV in the asymptomatic stage or AIDS. The main aim was to use biostatistical methods to classify brain gene expression following SIV infection, without consideration of the biological significance of the individual genes. We also used data from animals treated with different pharmacological substances such as dopaminergic drugs, N-methyl-D-aspartate (NMDA) antagonists or antioxidants during the early stage of infection as these animals exhibited an accelerated or attenuated neuropsychiatric disease progression. We found macaque subspecies to be a more important factor for disease classification based on gene expression profiling than clinical symptoms or neuropathological findings. It is noteworthy that SIV-infected pharmacologically-treated. Chinese animals clustered near uninfected animals independent on the outcome of the treatment, whereas untreated SIV infected animals were clustered in a separate subtree. It is clear from this study that NeuroAIDS is a diverse disease entity and that SIV brain genes can be differentially regulated, depending on the disease type as well as changed dependent on the monkey subspecies.

Impaired performance on the object retrieval-detour test of executive function in the SIV/macaque model of AIDS

NeuroAIDS, the neurological, motor, and cognitive impairments that occur in acquired immunodeficiency syndrome (AIDS) patients, is characterized by compromised function in frontal cortical and subcortical brain regions including impairments in motor control, reaction time, and executive functions. Executive function is a cognitive domain involving the regulation of behavior, including inhibitory control. The present study evaluated the effects of simian immunodeficiency virus (SIV) infection on the object retrieval detour (ORD) task to assess inhibitory control. The ORD task measures the ability to inhibit the prepotent response of reaching directly toward a food reinforcer placed in a transparent box. The box has one open side, and the animal must inhibit the initial reaching response and look to see which side is open. Subjects were 12 experimentally naive pigtailed macaques; six monkeys were infected with SIV. Baseline performance was compared to performance under "terminal" conditions (the week prior to the scheduled euthanasia) to determine if progression of SIV disease led to decreased ORD performance. SIV-infected monkeys acquired ORD performance at the same levels as uninfected control monkeys, and had similar latencies and error rates. However, in the terminal week there was a significant difference between the groups in the number of barrier reach errors (touching the side of the transparent box). Three individual SIV-infected monkeys were impaired on ORD performance both in terms of errors and speed of performance. Given the sensitivity of ORD performance to dopaminergic dysfunction, these results further implicate dopaminergic dysfunction as a mechanism of cognitive and motor impairments in NeuroAIDS.

Involvement of cytokines in human immunodeficiency virus-1 protein Tat and methamphetamine interactions in the striatum

Human immunodeficiency virus-1 (HIV-1) infection of the brain causes elevation in pro-inflammatory cytokines and inflammatory changes in the striatum. HIV-1-infected individuals who also abuse drugs including the psychostimulant methamphetamine (MA) develop more severe encephalitis and neuronal damage compared to HIV-1-infected patients who do not abuse drugs. In previous studies, we demonstrated that the HIV-1 protein Tat and MA interacted to cause enhanced loss of dopamine in the rat striatum via the destruction of dopaminergic terminals. Since both Tat and MA activate glia and induce cytokine production, we investigated the role of cytokines in the synergistic neurotoxicity induced by Tat and MA using cytokine arrays. Significant increases in monocyte chemotactic protein (MCP-1), interleukin-1 alpha (IL-1alpha) and tissue inhibitor of metalloproteinase-1 (TIMP-1) levels were noted 4 h following Tat + MA treatment compared to saline, Tat or MA. MCP-1 and TIMP-1 levels remained elevated 16 h after Tat + MA compared to saline or MA but were not different from the Tat-treated group at this time point. Weak, but significant elevations in cytokine-induced neutrophil chemoattractant-3 (CINC-3), ciliary neurotrophic factor (CNTF) and macrophage inflammatory protein-3 alpha (MIP-3alpha) were also noted with Tat + MA. The interaction of Tat and MA was prevented in mice genetically deficient in MCP-1 with a consequent attenuation of Tat + MA neurotoxicity. Our findings suggest that HIV-1 infection with concurrent drug abuse might profoundly increase chemokine levels in the striatum resulting in enhanced damage to the dopaminergic system.

Molecular mechanisms of HIV-1 associated neurodegeneration

Since identification of the human immunodeficiency virus-1 (HIV-1), numerous studies suggest a link between neurological impairments, in particular dementia, with acquired immunodeficiency syndrome (AIDS) with alarming occurrence worldwide. Approximately, 60% of HIV-infected people show some form of neurological impairment, and neuropathological changes are found in 90% of autopsied cases. Approximately 30% of untreated HIV-infected persons may develop dementia. The mechanisms behind these pathological changes are still not understood. Mounting data obtained by in vivo and in vitro experiments suggest that neuronal apoptosis is a major feature of HIV associated dementia (HAD), which can occur in the absence of direct infection of neurons. The major pathway of neuronal apoptosis occurs indirectly through release of neurotoxins by activated cells in the central nervous system (CNS) involving the induction of excitotoxicity and oxidative stress. In addition a direct mechanism induced by viral proteins in the pathogenesis of HAD may also play a role. This review focuses on the molecular mechanisms of HIV-associated dementia and possible therapeutic strategies.

Early impairment in dopaminergic neurotransmission in brains of SIV-infected rhesus monkeys due to microglia activation

Movement disorders are a common neurological complication of immunodeficiency virus infection and are thought to result from dopaminergic dysfunction in the basal ganglia. We measured levels of dopamine, and its metabolites homovanillic acid and 3,4-dihydroxyphenylacetic acid, in the putamen of healthy and simian immunodeficiency virus (SIV)-infected rhesus monkeys from infection until the development of AIDS. Changes in expression levels of cAMP response element binding protein (CREB), a transcription factor involved in the signalling pathway of dopamine, were also examined. Furthermore, we isolated microglia from the same animals and investigated their activation status in order to explore whether neurochemical findings are associated with immune activation. Plasma and CSF viral RNA load, T-cell analysis and basal ganglia histopathology provided information about disease progression in the animals. Putamen dopamine content was significantly reduced within 3 months of SIV infection, due to decreased dopamine synthesis initially, followed by loss of tyrosine hydroxylase-positive cells in substantia nigra, and accompanied by a decrease in total CREB expression. Pharmacological manipulation of dopaminergic tone with L-DOPA and selegiline showed that the reduction in CREB expression was due to reduced levels of dopamine. These neurochemical changes were significantly correlated with microglia activation in the absence of gross histopathological lesions. Our data demonstrate that putamen dopaminergic function is impaired during SIV infection and indicate that microglia may trigger endogenous mechanisms involved in the dysfunction of dopaminergic systems.

Yeast genome-wide screen reveals dissimilar sets of host genes affecting replication of RNA viruses

Viruses are devastating pathogens of humans, animals, and plants. To further our understanding of how viruses use the resources of infected cells, we systematically tested the yeast single-gene-knockout library for the effect of each host gene on the replication of tomato bushy stunt virus (TBSV), a positive-strand RNA virus of plants. The genome-wide screen identified 96 host genes whose absence either reduced or increased the accumulation of the TBSV replicon. The identified genes are involved in the metabolism of nucleic acids, lipids, proteins, and other compounds and in protein targeting/transport. Comparison with published genome-wide screens reveals that the replication of TBSV and brome mosaic virus (BMV), which belongs to a different supergroup among plus-strand RNA viruses, is affected by vastly different yeast genes. Moreover, a set of yeast genes involved in vacuolar targeting of proteins and vesicle-mediated transport both affected replication of the TBSV replicon and enhanced the cytotoxicity of the Parkinson's disease-related alpha-synuclein when this protein was expressed in yeast. In addition, a set of host genes involved in ubiquitin-dependent protein catabolism affected both TBSV replication and the cytotoxicity of a mutant huntingtin protein, a candidate agent in Huntington's disease. This finding suggests that virus infection and disease-causing proteins might use or alter similar host pathways and may suggest connections between chronic diseases and prior virus infection.