Mechanisms of HIV-tat-induced phosphorylation of N-methyl-D-aspartate receptor subunit 2A in human primary neurons: implications for neuroAIDS pathogenesis

SIV infection induces alterations in gene expression and loss of interneurons in Rhesus Macaque frontal cortex during early systemic infection

Understanding the neurobiological mechanisms underlying HIV-associated neurocognitive decline in people living with HIV is frequently complicated by an inability to analyze changes across the course of the infection and frequent presence of comorbid psychiatric and substance use disorders. Preclinical non-human primate simian immunodeficiency virus (SIV) models help address these shortcomings. However, SIV studies frequently target protracted endpoints, limiting our understanding of the neuromolecular alterations during the early post-infection window. To begin to address this knowledge gap, we utilized single nuclei transcriptomics to examine frontal cortex samples of rhesus macaques 10- and 20-days post-SIV infection, compared to non-infected controls. We identify and validated a decrease in inhibitory neurons during the early post infection window, representing a potential substrate of longer-term injury and neurocognitive impairment in people living with HIV. Differential expression identified alterations in cellular subtype gene expression that persisted over the 20-day time course and short-lived differences only detected at 10-days post-SIV infection. In silico predicted regulatory mechanisms and dysregulated neural signaling pathways are presented. Analysis of cell-cell interaction networks identify altered signal pathways in the frontal cortex that may represent regional alterations in cell-cell communications. In total, these results identify cell type-specific molecular mechanisms putatively capable of underlying long-term neurocognitive alterations in persons living with HIV.

The Impact of HIV on Early Brain Aging-A Pathophysiological (Re)View

Background/Objectives: This review aims to provide a comprehensive understanding of how HIV alters normal aging trajectories in the brain, presenting the HIV-related molecular mechanisms and pathophysiological pathways involved in brain aging. The review explores the roles of inflammation, oxidative stress, and viral persistence in the brain, highlighting how these factors contribute to neuronal damage and cognitive impairment and accelerate normal brain aging. Additionally, it also addresses the impact of antiretroviral therapy on brain aging and the biological markers associated with its occurrence. Methods: We extensively searched PubMed for English-language articles published from 2000 to 2024. The following keywords were used in the search: "HIV", "brain", "brain aging", "neuroinflammation", "HAART", and "HAND". This strategy yielded 250 articles for inclusion in our review. Results: A combination of blood-brain barrier dysfunction, with the direct effects of HIV on the central nervous system, chronic neuroinflammation, telomere shortening, neurogenesis impairments, and neurotoxicity associated with antiretroviral treatment (ART), alters and amplifies the mechanisms of normal brain aging. Conclusions: Current evidence suggests that HIV infection accelerates neurodegenerative processes of normal brain aging, leading to cognitive decline and structural brain changes at an earlier age than typically observed in the general population.

Levetiracetam Prevents Neurophysiological Changes and Preserves Cognitive Function in the Human Immunodeficiency Virus (HIV)-1 Transactivator of Transcription Transgenic Mouse Model of HIV-Associated Neurocognitive Disorder

Human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND) affects nearly half of the 39 million people living with HIV. HAND symptoms range from subclinical cognitive impairment to dementia; the mechanisms that underlie HAND remain unclear and there is no treatment. The HIV protein transactivator of transcription (TAT) is thought to contribute to HAND because it persists in the central nervous system and elicits neurotoxicity in animal models. Network hyperexcitability is associated with accelerated cognitive decline in neurodegenerative disorders. Here we show that the antiepileptic drug levetiracetam (LEV) attenuated aberrant excitatory synaptic transmission, protected synaptic plasticity, reduced seizure susceptibility, and preserved cognition in inducible TAT (iTAT) transgenic male mice. iTAT mice had an increased frequency of spontaneous excitatory postsynaptic currents in hippocampal slice recordings and impaired long-term potentiation, a form of synaptic plasticity that underlies learning and memory. Two-week administration of LEV by osmotic minipump prevented both impairments. Kainic acid administered to iTAT mice induced a higher maximum behavioral seizure score, longer seizure duration, and shorter latency to first seizure, consistent with a lower seizure threshold. LEV treatment prevented these in vivo signs of hyperexcitability. Lastly, in the Barnes maze, iTAT mice required more time to reach the goal, committed more errors, and received lower cognitive scores relative to iTAT mice treated with LEV. Thus, TAT expression drives functional deficits, suggesting a causative role in HAND. As LEV not only prevented aberrant synaptic activity in iTAT mice but also prevented cognitive dysfunction, it may provide a promising pharmacological approach to the treatment of HAND. SIGNIFICANCE STATEMENT: Approximately half of people living with human immunodeficiency virus (HIV) also suffer from HIV-associated neurocognitive disorder (HAND), for which there is no treatment. The HIV protein transactivator of transcription (TAT) causes toxicity that is thought to contribute to HAND. Here, the antiepileptic drug levetiracetam (LEV) prevented synaptic and cognitive impairments in a TAT-expressing mouse. LEV is widely used to treat seizures and is well-tolerated in humans, including those with HIV. This study supports further investigation of LEV-mediated neuroprotection in HAND.

Something to talk about; crosstalk disruption at the neurovascular unit during HIV infection of the CNS

Although treatable with antiretroviral therapy, HIV infection persists in people living with HIV (PLWH). It is well known that the HIV virus finds refuge in places for which antiretroviral medications do not reach therapeutic levels, mainly the CNS. It is clear that as PLWH age, the likelihood of developing HIV-associated neurological deficits increases. At the biochemical level neurological dysfunction is the manifestation of altered cellular function and ineffective intercellular communication. In this review, we examine how intercellular signaling in the brain is disrupted in the context of HIV. Specifically, the concept of how the blood-brain barrier can be a convergence point for crosstalk, is explored. Crosstalk between the cells of the neurovascular unit (NVU) (endothelium, pericytes, astrocytes, microglia and neurons) is critical for maintaining proper brain function. In fact, the NVU allows for rapid matching of neuronal metabolic needs, regulation of blood-brain barrier (BBB) dynamics for nutrient transport and changes to the level of immunosurveillance. This review invites the reader to conceptually consider the BBB as a router or convergence point for NVU crosstalk, to facilitate a better understanding of the intricate signaling events that underpin the function of the NVU during HIV associated neuropathology.

Anti-N-methyl-D-aspartate Receptor Encephalitis in People Living with HIV: Case Report and Literature Review

With the increase in the number of cases of autoimmune encephalitis (AE), the cerebrospinal fluid (CSF) of people living with HIV (PLWH) showing abnormal behavior, cognitive impairment or abnormal movements should be actively screened for the antibody panel of AE. Early recognition and treatment can prevent severe seizures or coma and markedly improve the prognosis of patients. The first-line immunotherapy for AE includes intravenous methylprednisolone and immunoglobulin. However, whether long-time immunosuppressive maintenance therapy is needed is debated. For PLWH, immunosuppressive therapy and even steroids could be more challenging. Here, we review and summarize the clinical characteristics often reported cases and report one case from our center to improve the diagnosis and treatment of anti-N-methyl-D-aspartate receptor encephalitis in PLWH.

Identification, Quantification, and Characterization of HIV-1 Reservoirs in the Human Brain

The major barrier to cure HIV infection is the early generation and extended survival of HIV reservoirs in the circulation and tissues. Currently, the techniques used to detect and quantify HIV reservoirs are mostly based on blood-based assays; however, it has become evident that viral reservoirs remain in tissues. Our study describes a novel multi-component imaging method (HIV DNA, mRNA, and viral proteins in the same assay) to identify, quantify, and characterize viral reservoirs in tissues and blood products obtained from HIV-infected individuals even when systemic replication is undetectable. In the human brains of HIV-infected individuals under ART, we identified that microglia/macrophages and a small population of astrocytes are the main cells with integrated HIV DNA. Only half of the cells with integrated HIV DNA expressed viral mRNA, and one-third expressed viral proteins. Surprisingly, we identified residual HIV-p24, gp120, nef, vpr, and tat protein expression and accumulation in uninfected cells around HIV-infected cells suggesting local synthesis, secretion, and bystander uptake. In conclusion, our data show that ART reduces the size of the brain's HIV reservoirs; however, local/chronic viral protein secretion still occurs, indicating that the brain is still a major anatomical target to cure HIV infection.

Astrocytes are HIV reservoirs in the brain: A cell type with poor HIV infectivity and replication but efficient cell-to-cell viral transfer

The major barrier to eradicating Human immunodeficiency virus-1 (HIV) infection is the generation of tissue-associated quiescent long-lasting viral reservoirs refractory to therapy. Upon interruption of anti-retroviral therapy (ART), HIV replication can be reactivated. Within the brain, microglia/macrophages and a small population of astrocytes are infected with HIV. However, the role of astrocytes as a potential viral reservoir is becoming more recognized because of the improved detection and quantification of HIV viral reservoirs. In this report, we examined the infectivity of human primary astrocytes in vivo and in vitro, and their capacity to maintain HIV infection, become latently infected, be reactivated, and transfer new HIV virions into neighboring cells. Analysis of human brain tissue sections obtained from HIV-infected individuals under effective and prolonged ART indicates that a small population of astrocytes has integrated HIV-DNA. In vitro experiments using HIV-infected human primary astrocyte cultures confirmed a low percentage of astrocytes had integrated HIV-DNA, with poor to undetectable replication. Even in the absence of ART, long-term culture results in latency that could be transiently reactivated with histone deacetylase inhibitor, tumor necrosis factor-alpha (TNF-α), or methamphetamine. Reactivation resulted in poor viral production but efficient cell-to-cell viral transfer into cells that support high viral replication. Together, our data provide a new understanding of astrocytes' role as viral reservoirs within the central nervous system (CNS).

Mechanisms of neuronal dysfunction in HIV-associated neurocognitive disorders

HIV-associated neurocognitive disorder (HAND) is characterized by cognitive and behavioral deficits in people living with HIV. HAND is still common in patients that take antiretroviral therapies, although they tend to present with less severe symptoms. The continued prevalence of HAND in treated patients is a major therapeutic challenge, as even minor cognitive impairment decreases patient’s quality of life. Therefore, modern HAND research aims to broaden our understanding of the mechanisms that drive cognitive impairment in people with HIV and identify promising molecular pathways and targets that could be exploited therapeutically. Recent studies suggest that HAND in treated patients is at least partially induced by subtle synaptodendritic damage and disruption of neuronal networks in brain areas that mediate learning, memory, and executive functions. Although the causes of subtle neuronal dysfunction are varied, reversing synaptodendritic damage in animal models restores cognitive function and thus highlights a promising therapeutic approach. In this review, we examine evidence of synaptodendritic damage and disrupted neuronal connectivity in HAND from clinical neuroimaging and neuropathology studies and discuss studies in HAND models that define structural and functional impairment of neurotransmission. Then, we report molecular pathways, mechanisms, and comorbidities involved in this neuronal dysfunction, discuss new approaches to reverse neuronal damage, and highlight current gaps in knowledge. Continued research on the manifestation and mechanisms of synaptic injury and network dysfunction in HAND patients and experimental models will be critical if we are to develop safe and effective therapies that reverse subtle neuropathology and cognitive impairment.

The Glutamate System as a Crucial Regulator of CNS Toxicity and Survival of HIV Reservoirs

Glutamate (Glu) is the most abundant excitatory neurotransmitter in the central nervous system (CNS). HIV-1 and viral proteins compromise glutamate synaptic transmission, resulting in poor cell-to-cell signaling and bystander toxicity. In this study, we identified that myeloid HIV-1-brain reservoirs survive in Glu and glutamine (Gln) as a major source of energy. Thus, we found a link between synaptic compromise, metabolomics of viral reservoirs, and viral persistence. In the current manuscript we will discuss all these interactions and the potential to achieve eradication and cure using this unique metabolic profile.

Possible N-methyl-D-aspartate receptor antibody-mediated encephalitis in the setting of HIV cerebrospinal fluid escape

Discordant elevations of cerebrospinal fluid (CSF) human immunodeficiency virus (HIV) ribonucleic acid (RNA) in chronically treated patients known as 'CSF escape' may present as acute encephalitis. Infectious encephalitis caused by herpes simplex virus (HSV) and other neurotropic viruses have been identified as potential triggers of anti-N-methyl-D-aspartate receptor (NMDAR) encephalitis. Autoantibody-mediated encephalitis has been infrequently reported in HIV infected patients and may mimic HIV encephalitis. We report two adults infected with HIV presenting with encephalopathy and seizures. Case 1 had a monophasic encephalopathy with detection of NMDAR antibodies in the context of HIV CSF escape. There was a clinical response to immunotherapy and anti-retroviral therapy adjustment. Case 2 initially presented in non-convulsive status epilepticus associated with HIV CSF escape. He responded to treatment with anti-epileptic drugs and anti-retroviral therapy alteration, but had two further neurological relapses. NMDAR antibodies were detected during the relapses and a clinical response was observed following treatment with immunotherapy. Clinicians should consider autoimmune encephalitis in HIV infected patients presenting with encephalopathy and seizures, particularly in cases with concomitant HIV CSF escape.

Anti-NMDA-receptor Encephalitis in an Adolescent With HIV Infection and Review of the Literature

Anti-N-Methyl-D-Aspartate-receptor encephalitis is the most common antibody-mediated autoimmune encephalopathy. A HIV-infected African boy presented with subacute psychosis as manifestation of anti-N-Methyl-D-Aspartate-receptor encephalitis. Intravenous immunoglobulin and corticosteroids induced complete remission. Although this is the first pediatric case described, 5 adult cases have been reported. The role of HIV in the etiology of this autoimmune condition requires further exploration.

Viral infections of the central nervous system in Africa

Viral infections are a major cause of human central nervous system infection, and may be associated with significant mortality, and long-term sequelae. In Africa, the lack of effective therapies, limited diagnostic and human resource facilities are especially in dire need. Most viruses that affect the central nervous system are opportunistic or accidental pathogens. Some of these viruses were initially considered harmless, however they have now evolved to penetrate the nervous system efficiently and exploit neuronal cell biology thus resulting in severe illness. A number of potentially lethal neurotropic viruses have been discovered in Africa and over the course of time shown their ability to spread wider afield involving other continents leaving a devastating impact in their trail. In this review we discuss key viruses involved in central nervous system disease and of major public health concern with respect to Africa. These arise from the families of Flaviviridae, Filoviridae, Retroviridae, Bunyaviridae, Rhabdoviridae and Herpesviridae. In terms of the number of cases affected by these viruses, HIV (Retroviridae) tops the list for morbidity, mortality and long term disability, while the Rift Valley Fever virus (Bunyaviridae) is at the bottom of the list. The most deadly are the Ebola and Marburg viruses (Filoviridae). This review describes their epidemiology and key neurological manifestations as regards the central nervous system such as meningoencephalitis and Guillain-Barré syndrome. The potential pathogenic mechanisms adopted by these viruses are debated and research perspectives suggested.

Mechanisms of neuropathogenesis in HIV and HCV: similarities, differences, and unknowns

HIV and hepatitis C virus (HCV) have both been associated with cognitive impairment. Combination antiretroviral therapy (cART) has dramatically changed the nature of cognitive impairment in HIV-infected persons, while the role of direct-acting antivirals (DAA) in neurocognition of HCV-infected individuals remains unclear. Also, whether HIV and HCV interact to promote neurocognitive decline or whether they each contribute an individual effect continues to be an open question. In this work, we review the virally mediated mechanisms of HIV- and HCV-mediated neuropathogenesis, with an emphasis on the role of dual infection, and discuss observed changes with HIV viral suppression and HCV functional cure on neurocognitive impairments.

Scaling Synapses in the Presence of HIV

A defining feature of HIV-associated neurocognitive disorder (HAND) is the loss of excitatory synaptic connections. Synaptic changes that occur during exposure to HIV appear to result, in part, from a homeostatic scaling response. Here we discuss the mechanisms of these changes from the perspective that they might be part of a coping mechanism that reduces synapses to prevent excitotoxicity. In transgenic animals expressing the HIV proteins Tat or gp120, the loss of synaptic markers precedes changes in neuronal number. In vitro studies have shown that HIV-induced synapse loss and cell death are mediated by distinct mechanisms. Both in vitro and animal studies suggest that HIV-induced synaptic scaling engages new mechanisms that suppress network connectivity and that these processes might be amenable to therapeutic intervention. Indeed, pharmacological reversal of synapse loss induced by HIV Tat restores cognitive function. In summary, studies indicate that there are temporal, mechanistic and pharmacological features of HIV-induced synapse loss that are consistent with homeostatic plasticity. The increasingly well delineated signaling mechanisms that regulate synaptic scaling may reveal pharmacological targets suitable for normalizing synaptic function in chronic neuroinflammatory states such as HAND.

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.

Mechanisms of HIV Neuropathogenesis: Role of Cellular Communication Systems

BACKGROUND

One of the major complications of Human Immunodeficiency Virus (HIV) infection is the development of HIV-Associated Neurocognitive Disorders (HANDs) in approximately 50-60% of HIV infected individuals. Despite undetectable viral loads in the periphery owing to anti-retroviral therapy, neuroinflammation and neurocognitive impairment are still prevalent in HIV infected individuals. Several studies indicate that the central nervous system (CNS) abnormalities observed in HIV infected individuals are not a direct effect of viral replication in the CNS, rather these neurological abnormalities are associated with amplification of HIV specific signals by unknown mechanisms. We propose that some of these mechanisms of damage amplification are mediated by gap junction channels, pannexin and connexin hemichannels, tunneling nanotubes and microvesicles/exosomes.

OBJECTIVE

Our laboratory and others have demonstrated that HIV infection targets cell to cell communication by altering all these communication systems resulting in enhanced bystander apoptosis of uninfected cells, inflammation and viral infection. Here we discuss the role of these communication systems in HIV neuropathogenesis.

CONCLUSION

In the current manuscript, we have described the mechanisms by which HIV "hijacks" these host cellular communication systems, leading to exacerbation of HIV neuropathogenesis, and to simultaneously promote the survival of HIV infected cells, resulting in the establishment of viral reservoirs.

Macrophages and Phospholipases at the Intersection between Inflammation and the Pathogenesis of HIV-1 Infection

Persistent low grade immune activation and chronic inflammation are nowadays considered main driving forces of the progressive immunologic failure in effective antiretroviral therapy treated HIV-1 infected individuals. Among the factors contributing to this phenomenon, microbial translocation has emerged as a key driver of persistent immune activation. Indeed, the rapid depletion of gastrointestinal CD4⁺ T lymphocytes occurring during the early phases of infection leads to a deterioration of the gut epithelium followed by the translocation of microbial products into the systemic circulation and the subsequent activation of innate immunity. In this context, monocytes/macrophages are increasingly recognized as an important source of inflammation, linked to HIV-1 disease progression and to non-AIDS complications, such as cardiovascular disease and neurocognitive decline, which are currently main challenges in treated patients. Lipid signaling plays a central role in modulating monocyte/macrophage activation, immune functions and inflammatory responses. Phospholipase-mediated phospholipid hydrolysis leads to the production of lipid mediators or second messengers that affect signal transduction, thus regulating a variety of physiologic and pathophysiologic processes. In this review, we discuss the contribution of phospholipases to monocyte/macrophage activation in the context of HIV-1 infection, focusing on their involvement in virus-associated chronic inflammation and co-morbidities.

HIV-1 Tat causes cognitive deficits and selective loss of parvalbumin, somatostatin, and neuronal nitric oxide synthase expressing hippocampal CA1 interneuron subpopulations

Memory deficits are characteristic of HIV-associated neurocognitive disorders (HAND) and co-occur with hippocampal pathology. The HIV-1 transactivator of transcription (Tat), a regulatory protein, plays a significant role in these events, but the cellular mechanisms involved are poorly understood. Within the hippocampus, diverse populations of interneurons form complex networks; even subtle disruptions can drastically alter synaptic output, resulting in behavioral dysfunction. We hypothesized that HIV-1 Tat would impair cognitive behavior and injure specific hippocampal interneuron subtypes. Male transgenic mice that inducibly expressed HIV-1 Tat (or non-expressing controls) were assessed for cognitive behavior or had hippocampal CA1 subregions evaluated via interneuron subpopulation markers. Tat exposure decreased spatial memory in a Barnes maze and mnemonic performance in a novel object recognition test. Tat reduced the percentage of neurons expressing neuronal nitric oxide synthase (nNOS) without neuropeptide Y immunoreactivity in the stratum pyramidale and the stratum radiatum, parvalbumin in the stratum pyramidale, and somatostatin in the stratum oriens, which are consistent with reductions in interneuron-specific interneuron type 3 (IS3), bistratified, and oriens-lacunosum-moleculare interneurons, respectively. The findings reveal that an interconnected ensemble of CA1 nNOS-expressing interneurons, the IS3 cells, as well as subpopulations of parvalbumin- and somatostatin-expressing interneurons are preferentially vulnerable to HIV-1 Tat. Importantly, the susceptible interneurons form a microcircuit thought to be involved in feedback inhibition of CA1 pyramidal cells and gating of CA1 pyramidal cell inputs. The identification of vulnerable CA1 hippocampal interneurons may provide novel insight into the basic mechanisms underlying key functional and neurobehavioral deficits associated with HAND.

NMDARs Adapt to Neurotoxic HIV Protein Tat Downstream of a GluN2A-Ubiquitin Ligase Signaling Pathway

HIV-associated neurocognitive disorder (HAND) affects approximately half of HIV-infected patients. Infected non-neuronal cells release neurotoxic factors such as the viral protein transactivator of transcription (Tat) that potentiate NMDAR function. NMDARs regulate synaptic changes observed after exposure to HIV proteins, which may underlie cognitive impairment in HAND patients. Here, we used patch-clamp recording to measure NMDAR-mediated currents in rat hippocampal cultures after exposure to Tat. Tat (4-16 h) potentiated NMDA-evoked whole-cell current and increased the NMDAR:AMPAR ratio of evoked EPSCs. Potentiated currents adapted back to baseline amplitudes after 24 h of exposure to Tat. Pharmacological inhibition of GluN2A-containing NMDARs prevented adaptation, but inhibition of GluN2B-containing NMDARs did not. Pharmacological and genetic approaches determined that potentiated NMDARs activated the kinase Akt, which then activated the E3 ubiquitin ligase Mdm2. Inhibition of protein synthesis prevented adaptation, suggesting that Mdm2 altered gene expression, possibly through its well known target p53. Expression of GFP-tagged GluN1 subunits resulted in fluorescent puncta that colocalized with synaptic markers. Tat (24 h) caused an Mdm2-dependent loss of NMDAR puncta on a timescale similar to adaption of NMDAR function. Activation of the Mdm2 pathway degrades PSD-95, a scaffolding protein that clusters NMDARs at the synapse and enhances their function. Adaptation to the continued presence of excitotoxins that potentiate NMDARs such as HIV Tat may protect from excessive NMDAR activation while also contributing to the synaptic loss that correlates with cognitive decline in HAND.

SIGNIFICANCE STATEMENT

Synaptodendritic damage correlates with cognitive decline in HIV-associated neurocognitive disorder (HAND). In a cell culture model, we show that the HIV protein transactivator of transcription (Tat) initially potentiates NMDARs that then adapt to the presence of the toxin. Adaptation of NMDAR function was mediated by a GluN2A/Akt/Mdm2 pathway not previously linked to neuroinflammatory disorders such as HAND. Activation of this pathway caused a loss of synaptic NMDAR clusters. Decreased NMDAR function may result from a homeostatic response gone awry and underlie impaired synaptic function in HAND.

Anti-NMDAR antibodies in new-onset psychosis. Positive results in an HIV-infected patient

The role of neuronal surface autoantibodies (NSAs) in non-encephalitic psychosis is of recent and controversial interest. Most of the studies relating NSAs with psychosis are retrospective and only focused on the N-methyl-d-aspartate glutamate receptor (NMDAR). Our goal was to evaluate the prevalence of IgG antibodies against the NMDAR NR1 subunit (NMDAR-Abs) along with five additional NSAs in 61 first psychotic episode patients and 47 matched controls. We found two patients positive for NMDAR-Abs (3.3%). One of them was eventually considered to have been misdiagnosed and reclassified as encephalitis. The other met the criteria for bipolar I disorder, presented no neurological symptoms and had a comorbid HIV infection of vertical transmission. This is the first reported case of an HIV-infected patient with psychosis associated with NSAs. This study shows that patients presenting with clinically incomplete forms of anti-NMDAR encephalitis, with predominant or isolated psychiatric symptoms, can remain undetected if no ancillary tests are performed. To improve patient diagnosis and treatment of individuals with a first psychotic episode, more detailed neurological examinations might be needed. Further studies are required to better clarify the role of NSAs in the neuropsychiatric effects of HIV infection.

Methamphetamine compromises gap junctional communication in astrocytes and neurons

Methamphetamine (meth) is a central nervous system (CNS) stimulant that results in psychological and physical dependency. The long-term effects of meth within the CNS include neuronal plasticity changes, blood-brain barrier compromise, inflammation, electrical dysfunction, neuronal/glial toxicity, and an increased risk to infectious diseases including HIV. Most of the reported meth effects in the CNS are related to dysregulation of chemical synapses by altering the release and uptake of neurotransmitters, especially dopamine, norepinephrine, and epinephrine. However, little is known about the effects of meth on connexin (Cx) containing channels, such as gap junctions (GJ) and hemichannels (HC). We examined the effects of meth on Cx expression, function, and its role in NeuroAIDS. We found that meth altered Cx expression and localization, decreased GJ communication between neurons and astrocytes, and induced the opening of Cx43/Cx36 HC. Furthermore, we found that these changes in GJ and HC induced by meth treatment were mediated by activation of dopamine receptors, suggesting that dysregulation of dopamine signaling induced by meth is essential for GJ and HC compromise. Meth-induced changes in GJ and HC contributed to amplified CNS toxicity by dysregulating glutamate metabolism and increasing the susceptibility of neurons and astrocytes to bystander apoptosis induced by HIV. Together, our results indicate that connexin containing channels, GJ and HC, are essential in the pathogenesis of meth and increase the sensitivity of the CNS to HIV CNS disease. Methamphetamine (meth) is an extremely addictive central nervous system stimulant. Meth reduced gap junctional (GJ) communication by inducing internalization of connexin-43 (Cx43) in astrocytes and reducing expression of Cx36 in neurons by a mechanism involving activation of dopamine receptors (see cartoon). Meth-induced changes in Cx containing channels increased extracellular levels of glutamate and resulted in higher sensitivity of neurons and astrocytes to apoptosis in response to HIV infection.

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.

Mass spectrometric phosphoproteome analysis of HIV-infected brain reveals novel phosphorylation sites and differential phosphorylation patterns

PURPOSE

To map the phosphoproteome and identify changes in the phosphorylation patterns in the HIV-infected and uninfected brain.

EXPERIMENTAL DESIGN

Parietal cortex from individuals with and without HIV infection were lysed and trypsinized. The peptides were labeled with iTRAQ reagents, combined, phospho-enriched by titanium dioxide chromatography, and analyzed by LC-MS/MS with high resolution.

RESULTS

Our phosphoproteomic workflow resulted in the identification of 112 phosphorylated proteins and 17 novel phosphorylation sites in all the samples that were analyzed. The phosphopeptide sequences were searched for kinase substrate motifs, which revealed potential kinases involved in important signaling pathways. The site-specific phosphopeptide quantification showed that peptides from neurofilament medium polypeptide, myelin basic protein, and 2'-3'-cyclic nucleotide-3' phosphodiesterase have relatively higher phosphorylation levels during HIV infection.

CONCLUSIONS AND CLINICAL RELEVANCE

This study has enriched the global phosphoproteome knowledge of the human brain by detecting novel phosphorylation sites on neuronal proteins and identifying differentially phosphorylated brain proteins during HIV infection. Kinases that lead to unusual phosphorylations could be therapeutic targets for the treatment of HIV-associated neurocognitive disorders.

Curcumin ameliorates hippocampal neuron damage induced by human immunodeficiency virus-1

Our previous studies have shown that infection with the gp120 V3 loop can cause human immunodeficiency virus-1 associated neurocognitive disorders. Curcumin has been shown to improve these effects to some degree, but the precise mechanisms remain unknown. The present study analyzed the neuroprotective effect and mechanism of curcumin in relation to hippocampal neurons. Results showed that 1 nmol/L gp120 V3 loop suppressed the growth of synapses. After administration of 1 μmol/L curcumin, synaptic growth improved. Curcumin is neuroprotective against gp120 V3 loop-induced neuronal damage by inhibiting the activation of L-type calcium currents, relieving intracellular Ca(2+) overload, promoting Bcl-2 expression, and inhibiting Bax activation. The effect of curcumin was identical to nimodipine, suggesting that curcumin has the same neuroprotective effects against gp120 V3 loop-induced neuronal damage.

Development of imaging techniques to study the pathogenesis of biosafety level 2/3 infectious agents

Despite significant advances in microbiology and molecular biology over the last decades, several infectious diseases remain global concerns, resulting in the death of millions of people worldwide each year. According to the Center for Disease Control (CDC) in 2012, there were 34 million people infected with HIV, 8.7 million new cases of tuberculosis, 500 million cases of hepatitis, and 50-100 million people infected with dengue. Several of these pathogens, despite high incidence, do not have reliable clinical detection methods. New or improved protocols have been generated to enhance detection and quantitation of several pathogens using high-end microscopy (light, confocal, and STORM microscopy) and imaging software. In the current manuscript, we discuss these approaches and the theories behind these methodologies. Thus, advances in imaging techniques will open new possibilities to discover therapeutic interventions to reduce or eliminate the devastating consequences of infectious diseases.

HIV-1 protein Tat produces biphasic changes in NMDA-evoked increases in intracellular Ca2+ concentration via activation of Src kinase and nitric oxide signaling pathways

HIV-associated neurocognitive disorders afflict about half of HIV-infected patients. HIV-infected cells shed viral proteins, such as the transactivator of transcription (Tat), which can cause neurotoxicity by over activation of NMDA receptors. Here, we show that Tat causes a time-dependent, biphasic change in NMDA-evoked increases in intracellular Ca(2+) concentration ([Ca(2+)]i). NMDA-evoked responses were potentiated following 2-h exposure to Tat (50 ng/mL). Tat-induced potentiation of NMDA-evoked increases in [Ca(2+)]i peaked by 8 h and then adapted by gradually reversing to baseline by 24 h and eventually dropping below control by 48 h. Tat-induced potentiation of NMDA-evoked responses was blocked by inhibition of lipoprotein receptor-related protein (LRP) or Src tyrosine kinase. Potentiation was unaffected by inhibition of nitric oxide synthase (NOS). However, NOS activity was required for adaptation. Adaptation was also prevented by inhibition of soluble guanylate cyclase (sGC) and cyclic guanosine monophosphate-dependent protein kinase G (PKG). Together, these findings indicate that Tat potentiates NMDA-evoked increases in [Ca(2+)]i via LRP-dependent activation of Src and that this potentiation adapts via activation of the NOS/sGC/PKG pathway. Adaptation may protect neurons from excessive Ca(2+) influx and could reveal targets for the treatment of HIV-associated neurocognitive disorders. HIV-associated neurocognitive disorders (HAND) afflict about half of HIV-infected patients. HIV-infected cells shed viral proteins, such as the transactivator of transcription (Tat), which can cause neurotoxicity by over activation of NMDA receptors (NMDARs). We show that HIV-1 Tat evoked biphasic changes in NMDA-evoked [Ca(2+) ]i responses. Initially, Tat potentiated NMDA-evoked responses following LRP-mediated activation of Src kinase. Subsequently, Tat-induced NMDAR potentiation adapted by activation of a NOS/sGC/PKG pathway that attenuated NMDA-evoked increases in [Ca(2+)]i . Adaptation may be a novel neuroprotective mechanism to prevent excessive Ca(2+) influx. Solid and dashed arrows represent direct and potentially indirect connections, respectively.

HIV-1 Tat-mediated apoptosis in human blood-retinal barrier-associated cells

HIV-1-associated ocular complications, such as microvasculopathies, can lead to the loss of vision in HIV-1-infected patients. Even in patients under highly active antiretroviral therapy, ocular lesions are unavoidable. Ocular complications have been demonstrated to be closely related to the breakdown of the blood-retinal-barrier (BRB); however, the underlying mechanism is not clear. The data from this study indicated that the HIV-1 Tat protein induced the apoptosis of human retinal microvascular endothelial cells (HRMECs) and retinal pigmen epithelium (RPE) cells, which compose the inner BRB and the outer BRB, respectively. In addition, this study found that the activation of N-methyl-D-aspartate receptors (NMDARs) was involved in the apoptosis of RPE cells, but it caused no changes in HRMECs. Furthermore, both cell types exhibited enhanced expression of Bak, Bax and Cytochrome c. The inhibition of Tat activity protected against the apoptosis induced by NMDAR activation and prevented the dysregulation of Bak, Bax and Cytochrome c, revealing an important role for the mitochondrial pathway in HIV-1 Tat-induced apoptosis. Together, these findings suggest a possible mechanism and may identify a potential therapeutic strategy for HIV-1-associated ocular complications.

Roles and functions of HIV-1 Tat protein in the CNS: an overview

Nearly 50% of HIV-infected individuals suffer from some form of HIV-associated neurocognitive disorders (HAND). HIV-1 Tat (a key HIV transactivator of transcription) protein is one of the first HIV proteins to be expressed after infection occurs and is absolutely required for the initiation of the HIV genome transcription. In addition to its canonical functions, various studies have shown the deleterious role of HIV-1 Tat in the development and progression of HAND. Within the CNS, only specific cell types can support productive viral replication (astrocytes and microglia), however Tat protein can be released form infected cells to affects HIV non-permissive cells such as neurons. Therefore, in this review, we will summarize the functions of HIV-1 Tat proteins in neural cells and its ability to promote HAND.

Clade C HIV-1 isolates circulating in Southern Africa exhibit a greater frequency of dicysteine motif-containing Tat variants than those in Southeast Asia and cause increased neurovirulence

BACKGROUND

HIV-1 Clade C (Subtype C; HIV-1C) is responsible for greater than 50% of infections worldwide. Unlike clade B HIV-1 (Subtype B; HIV-1B), which is known to cause HIV associated dementia (HAD) in approximately 15% to 30% of the infected individuals, HIV-1C has been linked with lower prevalence of HAD (0 to 6%) in India and Ethiopia. However, recent studies report a higher prevalence of HAD in South Africa, Zambia and Botswana, where HIV-1C infections predominate. Therefore, we examined whether Southern African HIV-1C is genetically distinct and investigated its neurovirulence. HIV-1 Tat protein is a viral determinant of neurocognitive dysfunction. Therefore, we focused our study on the variations seen in tat gene and its contribution to HIV associated neuropathogenesis.

RESULTS

A phylogenetic analysis of tat sequences of Southern African (South Africa and Zambia) HIV isolates with those from the geographically distant Southeast Asian (India and Bangladesh) isolates revealed that Southern African tat sequences are distinct from Southeast Asian isolates. The proportion of HIV - 1C variants with an intact dicysteine motif in Tat protein (C30C31) was significantly higher in the Southern African countries compared to Southeast Asia and broadly paralleled the high incidence of HAD in these countries. Neuropathogenic potential of a Southern African HIV-1C isolate (from Zambia; HIV-1C 1084i), a HIV-1C isolate (HIV-1 IndieC1) from Southeast Asia and a HIV-1B isolate (HIV-1 ADA) from the US were tested using in vitro assays to measure neurovirulence and a SCID mouse HIV encephalitis model to measure cognitive deficits. In vitro assays revealed that the Southern African isolate, HIV-1C 1084i exhibited increased monocyte chemotaxis and greater neurotoxicity compared to Southeast Asian HIV-1C. In neurocognitive tests, SCID mice injected with MDM infected with Southern African HIV-1C 1084i showed greater cognitive dysfunction similar to HIV-1B but much higher than those exposed to Southeast Asian HIV - 1C.

CONCLUSIONS

We report here, for the first time, that HIV-1C from Southern African countries is genetically distinct from Southeast Asian HIV-1C and that it exhibits a high frequency of variants with dicysteine motif in a key neurotoxic HIV protein, Tat. Our results indicate that Tat dicysteine motif determines neurovirulence. If confirmed in population studies, it may be possible to predict neurocognitive outcomes of individuals infected with HIV-1C by genotyping Tat.

Drug induced increases in CNS dopamine alter monocyte, macrophage and T cell functions: implications for HAND

Central nervous system (CNS) complications resulting from HIV infection remain a major public health problem as individuals live longer due to the success of combined antiretroviral therapy (cART). As many as 70 % of HIV infected people have HIV associated neurocognitive disorders (HAND). Many HIV infected individuals abuse drugs, such as cocaine, heroin or methamphetamine, that may be important cofactors in the development of HIV CNS disease. Despite different mechanisms of action, all drugs of abuse increase extracellular dopamine in the CNS. The effects of dopamine on HIV neuropathogenesis are not well understood, and drug induced increases in CNS dopamine may be a common mechanism by which different types of drugs of abuse impact the development of HAND. Monocytes and macrophages are central to HIV infection of the CNS and to HAND. While T cells have not been shown to be a major factor in HIV-associated neuropathogenesis, studies indicate that T cells may play a larger role in the development of HAND in HIV infected drug abusers. Drug induced increases in CNS dopamine may dysregulate functions of, or increase HIV infection in, monocytes, macrophages and T cells in the brain. Thus, characterizing the effects of dopamine on these cells is important for understanding the mechanisms that mediate the development of HAND in drug abusers.

The study of candidate genes related to the neurodevelopmental hypothesis of anorexia nervosa: classical association study versus decision tree

In this research, we conducted a study of genes connected with the neurodevelopmental hypothesis of anorexia nervosa, using classical statistical and data-mining methods to establish a relationship with disease risk and algorithms to identify the best genetic predictors of anorexia nervosa.

Soy isoflavones genistein and daidzein exert anti-apoptotic actions via a selective ER-mediated mechanism in neurons following HIV-1 Tat(1-86) exposure

Background

HIV-1 viral protein Tat partially mediates the neural dysfunction and neuronal cell death associated with HIV-1 induced neurodegeneration and neurocognitive disorders. Soy isoflavones provide protection against various neurotoxic insults to maintain neuronal function and thus help preserve neurocognitive capacity.

Methodology/Principal Findings

We demonstrate in primary cortical cell cultures that 17β-estradiol or isoflavones (genistein or daidzein) attenuate Tat_1–86-induced expression of apoptotic proteins and subsequent cell death. Exposure of cultured neurons to the estrogen receptor antagonist ICI 182,780 abolished the anti-apoptotic actions of isoflavones. Use of ERα or ERβ specific antagonists determined the involvement of both ER isoforms in genistein and daidzein inhibition of caspase activity; ERβ selectively mediated downregulation of mitochondrial pro-apoptotic protein Bax. The findings suggest soy isoflavones effectively diminished HIV-1 Tat-induced apoptotic signaling.

Conclusions/Significance

Collectively, our results suggest that soy isoflavones represent an adjunctive therapeutic option with combination anti-retroviral therapy (cART) to preserve neuronal functioning and sustain neurocognitive abilities of HIV-1 infected persons.

HIV-1 Tat protein inhibits neurosecretion by binding to phosphatidylinositol (4,5) bisphosphate

HIV-1 Tat enables viral transcription and is also actively released by infected cells. Extracellular Tat can enter uninfected cells and affect some cellular functions. Here, we examine the effects of Tat protein on the secretory activity of neuroendocrine cells. When added to the culture medium of chromaffin and PC12 cells, Tat was actively internalized and strongly impaired exocytosis as measured by carbon fiber amperometry and growth hormone (GH) release assay. Expression of Tat mutants that do not bind to phosphatidylinositol-(4,5)-bisphophate (PI(4,5)P2) did not affect secretion, and overexpression of phosphatidylinositol 4 phosphate 5-kinase (PIP5K), the major PI(4,5)P2 synthesizing enzyme, significantly rescued the Tat-induced inhibition of neurosecretion. This suggests that the inhibition of exocytosis may be the consequence of PI(4,5)P2 sequestration. Accordingly expression of Tat in PC12 cells interfered with the secretagogue-dependent recruitment of annexin A2 to the plasma membrane, a PI(4,5)P2-binding protein that promotes the formation of lipid microdomains that are required for exocytosis. In addition Tat significantly prevented the reorganization of the actin cytoskeleton necessary for the movement of secretory vesicles towards plasma membrane fusion sites. Thus, the capacity of extracellular Tat to enter neuroendocrine cells and sequester plasma membrane PI(4,5)P2 perturbs several PI(4,5)P2-dependent players of the exocytotic machinery, thereby affecting neurosecretion. We propose that Tat-induced inhibition of exocytosis is involved in the neuronal disorders associated with HIV-1 infection.

Cocaine and HIV-1 interplay: molecular mechanisms of action and addiction

Human immunodeficiency virus (HIV) infection is now being driven by drug-abusing populations. Epidemiological studies on drug abusers with AIDS link abuse of cocaine, even more than other drugs, to increased incidence of HIV seroprevalence and progression to AIDS. Both cell culture and animal studies demonstrate that cocaine can both potentiate HIV replication and can potentiate HIV proteins to cause enhanced glial cell activation, neurotoxicity, and breakdown of the blood-brain barrier. Based on the ability of both HIV proteins and cocaine to modulate NMDA receptor on neurons, NMDA receptors have been suggested as a common link underlying the crosstalk between drug addiction and HIV infection. While the role of dopamine system as a major target of cocaine cannot be overlooked, recent studies on the role of sigma receptors in mediating the effects of cocaine in both cell and organ systems warrants a deeper understanding of their functional role in the field. In this review, recent findings on the interplay of HIV infection and cocaine abuse and their possible implications in mode of action and/or addiction will be discussed.

Direct effects of HIV-1 Tat on excitability and survival of primary dorsal root ganglion neurons: possible contribution to HIV-1-associated pain

The vast majority of people living with human immunodeficiency virus type 1 (HIV-1) have pain syndrome, which has a significant impact on their quality of life. The underlying causes of HIV-1-associated pain are not likely attributable to direct viral infection of the nervous system due to the lack of evidence of neuronal infection by HIV-1. However, HIV-1 proteins are possibly involved as they have been implicated in neuronal damage and death. The current study assesses the direct effects of HIV-1 Tat, one of potent neurotoxic viral proteins released from HIV-1-infected cells, on the excitability and survival of rat primary dorsal root ganglion (DRG) neurons. We demonstrated that HIV-1 Tat triggered rapid and sustained enhancement of the excitability of small-diameter rat primary DRG neurons, which was accompanied by marked reductions in the rheobase and resting membrane potential (RMP), and an increase in the resistance at threshold (R(Th)). Such Tat-induced DRG hyperexcitability may be a consequence of the inhibition of cyclin-dependent kinase 5 (Cdk5) activity. Tat rapidly inhibited Cdk5 kinase activity and mRNA production, and roscovitine, a well-known Cdk5 inhibitor, induced a very similar pattern of DRG hyperexcitability. Indeed, pre-application of Tat prevented roscovitine from having additional effects on the RMP and action potentials (APs) of DRGs. However, Tat-mediated actions on the rheobase and R(Th) were accelerated by roscovitine. These results suggest that Tat-mediated changes in DRG excitability are partly facilitated by Cdk5 inhibition. In addition, Cdk5 is most abundant in DRG neurons and participates in the regulation of pain signaling. We also demonstrated that HIV-1 Tat markedly induced apoptosis of primary DRG neurons after exposure for longer than 48 h. Together, this work indicates that HIV-1 proteins are capable of producing pain signaling through direct actions on excitability and survival of sensory neurons.

Programmed neuronal cell death induced by HIV-1 tat and methamphetamine

Apoptosis and autophagy are the two major types of programmed cell death (PCD) in neurons. Homeostatic autophagy often precedes apoptosis, and when apoptosis is blocked, the failure to keep homeostasis will lead to necrosis instead. It has been reported that human immunodeficiency virus (HIV) infected methamphetamine (Meth) abusers represent greater neuropathological abnormalities than Meth abusers or HIV-positive non-Meth users. Recent publications suggest that Tat and Meth when administered together result in greater neuronal damage than when administered separately. However, the cellular events of the combined Tat-Meth effect have not yet been fully characterized. Therefore, we investigated the effects of Tat and/or Meth on apoptosis and autophagy to elucidate whether PCD was involved in Tat and/or Meth-induced neuronal damage. Annexin-V-FITC/PI staining assay was used to detect cellular apoptosis using a neuroblastoma cell line SH-SY5Y. Cellular ultrastructural changes were observed under transmission electron microscopy (TEM). Flow-cytometric data showed apoptosis following Meth treatment, and more extensive apoptosis with Tat + Meth treatment. The most important finding was that the autophagosome and/or multilamellar bodies (MLBs) were most pronounced with Tat + Meth treatment, were less so with Meth treatment, and infrequent with Tat treatment. This suggests the involvement of autophagy and apoptosis in Tat with Meth-elicited cell damage. However, the relation between apoptosis and autophagy remains unknown in this experiment. Further research is needed to analyze the relation among related molecules. A thorough understanding of this multifaceted relationship will be critical for the assessment of therapeutic modalities for patients with HIV with drug abuse.

PrPC, the cellular isoform of the human prion protein, is a novel biomarker of HIV-associated neurocognitive impairment and mediates neuroinflammation

Of the 33 million people infected with the human immunodeficiency virus (HIV) worldwide, 40-60% of individuals will eventually develop neurocognitive sequelae that can be attributed to the presence of HIV-1 in the central nervous system (CNS) and its associated neuroinflammation despite antiretroviral therapy. PrP(C) (protease resistant protein, cellular isoform) is the nonpathological cellular isoform of the human prion protein that participates in many physiological processes that are disrupted during HIV-1 infection. However, its role in HIV-1 CNS disease is unknown. We demonstrate that PrP(C) is significantly increased in both the CNS of HIV-1-infected individuals with neurocognitive impairment and in SIV-infected macaques with encephalitis. PrP(C) is released into the cerebrospinal fluid, and its levels correlate with CNS compromise, suggesting it is a biomarker of HIV-associated neurocognitive impairment. We show that the chemokine (c-c Motif) Ligand-2 (CCL2) increases PrP(C) release from CNS cells, while HIV-1 infection alters PrP(C) release from peripheral blood mononuclear cells. Soluble PrP(C) mediates neuroinflammation by inducing astrocyte production of both CCL2 and interleukin 6. This report presents the first evidence that PrP(C) dysregulation occurs in cognitively impaired HIV-1-infected individuals and that PrP(C) participates in the pathogenesis of HIV-1-associated CNS disease.