Brain-derived neurotrophic factor as a prototype neuroprotective factor against HIV-1-associated neuronal degeneration

Differential Associations Between BDNF and Memory Across Older Black and White Adults With HIV Disease

BACKGROUND

Brain-derived neurotrophic factor (BDNF) shows consistent associations with memory across many clinical populations, including dementia. Less is understood about the association between BDNF and memory functioning in people living with HIV (PWH).

METHODS

A sample of 173 adults aged 50+ (n = 100 HIV+ and n = 73 HIV seronegative) completed a comprehensive neurobehavioral assessment and blood draw. Linear regressions predicting memory domains (learning, delayed recall, and recognition) were conducted including race (White vs. Black/African American), HIV status, BDNF, and their interactions.

RESULTS

For learning and delayed recall, significant (P < 0.05) main effects for race and interactions for BDNF x race and HIV status x race were found, whereas for recognition, only a BDNF x race interaction emerged. In adjusted models, BDNF x race interactions remained for learning and delayed recall. To determine effect size, correlations were conducted between BDNF and memory domains stratified by HIV serostatus and race, and small-medium associations between BDNF and learning and delayed recall (rho = 0.29, P < 0.01; rho = 0.22, P = 0.045), but no recognition (rho = 0.12, P = 0.29) were found among Black/African American PWH. BDNF was not significantly associated with memory domains in White PWH or either HIV- sample. Follow-up analyses showed BDNF-memory specificity, such that race X BDNF interactions did not emerge for other cognitive domains.

CONCLUSIONS

While limited by cross-sectional design among a small sample, particularly of White individuals, results indicate that BDNF may serve as a promising biomarker reflecting memory functioning in PWH, particularly Black/African Americans. Further work is needed to replicate findings and determine mechanisms for racial differences in BDNF associations with memory.

7,8-Dihydroxyflavone improves neuropathological changes in the brain of Tg26 mice, a model for HIV-associated neurocognitive disorder

The combined antiretroviral therapy era has significantly increased the lifespan of people with HIV (PWH), turning a fatal disease to a chronic one. However, this lower but persistent level of HIV infection increases the susceptibility of HIV-associated neurocognitive disorder (HAND). Therefore, research is currently seeking improved treatment for this complication of HIV. In PWH, low levels of brain derived neurotrophic factor (BDNF) has been associated with worse neurocognitive impairment. Hence, BDNF administration has been gaining relevance as a possible adjunct therapy for HAND. However, systemic administration of BDNF is impractical because of poor pharmacological profile. Therefore, we investigated the neuroprotective effects of BDNF-mimicking 7,8 dihydroxyflavone (DHF), a bioactive high-affinity TrkB agonist, in the memory-involved hippocampus and brain cortex of Tg26 mice, a murine model for HAND. In these brain regions, we observed astrogliosis, increased expression of chemokine HIV-1 coreceptors CXCR4 and CCR5, neuroinflammation, and mitochondrial damage. Hippocampi and cortices of DHF treated mice exhibited a reversal of these pathological changes, suggesting the therapeutic potential of DHF in HAND. Moreover, our data indicates that DHF increases the phosphorylation of TrkB, providing new insights about the role of the TrkB-Akt-NFkB signaling pathway in mediating these pathological hallmarks. These findings guide future research as DHF shows promise as a TrkB agonist treatment for HAND patients in adjunction to the current antiviral therapies.

Small molecule modulation of the p75 neurotrophin receptor suppresses age- and genotype-associated neurodegeneration in HIV gp120 transgenic mice

The persistence of HIV in the central nervous system leads to cognitive deficits in up to 50% of people living with HIV even with systemic suppression by antiretroviral treatment. The interaction of chronic inflammation with age-associated degeneration places these individuals at increased risk of accelerated aging and other neurodegenerative diseases and no treatments are available that effectively halt these processes. The adverse effects of aging and inflammation may be mediated, in part, by an increase in the expression of the p75 neurotrophin receptor (p75^NTR) which shifts the balance of neurotrophin signaling toward less protective pathways. To determine if modulation of p75^NTR could modify the disease process, we treated HIV gp120 transgenic mice with a small molecule ligand designed to engage p75^NTR and downregulate degenerative signaling. Daily treatment with 50 mg/kg LM11A-31 for 4 months suppressed age- and genotype-dependent activation of microglia, increased microtubule associated protein-2 (MAP-2), reduced dendritic varicosities and slowed the loss of parvalbumin immunoreactive neurons in the hippocampus. An age related accumulation of microtubule associated protein Tau was identified in the hippocampus in extracellular clusters that co-expressed p75^NTR suggesting a link between Tau and p75^NTR. Although the significance of the relationship between p75^NTR and Tau is unclear, a decrease in Tau-1 immunoreactivity as gp120 mice entered old age (>16 months) suggests that the Tau may transition to more pathological modifications; a process blocked by LM11A-31. Overall, the effects of LM11A-31 are consistent with strong neuroprotective and anti-inflammatory actions that have significant therapeutic potential.

HIV-1 gp120 Upregulates Brain-Derived Neurotrophic Factor (BDNF) Expression in BV2 Cells via the Wnt/β-Catenin Signaling Pathway

HIV-1 gp120 plays a critical role in the pathogenesis of HIV-associated pain, but the underlying molecular mechanisms are incompletely understood. This study aims to determine the effect and possible mechanism of HIV-1 gp120 on BDNF expression in BV2 cells (a murine-derived microglial cell line). We observed that gp120 (10 ng/ml) activated BV2 cells in cultures and upregulated proBDNF/mBDNF. Furthermore, gp120-treated BV2 also accumulated Wnt3a and β-catenin, suggesting the activation of the Wnt/β-catenin pathway. We demonstrated that activation of the pathway by Wnt3a upregulated BDNF expression. In contrast, inhibition of the Wnt/β-catenin pathway by either DKK1 or IWR-1 attenuated BDNF upregulation induced by gp120 or Wnt3a. These findings collectively suggest that gp120 stimulates BDNF expression in BV2 cells via the Wnt/β-catenin signaling pathway.

HIV-1 gp120 envelope glycoprotein determinants for cytokine burst in human monocytes

The first step of HIV infection involves the interaction of the gp120 envelope glycoprotein to its receptor CD4, mainly expressed on CD4⁺ T cells. Besides its role on HIV-1 entry, the gp120 has been shown to be involved in the production of IL-1, IL-6, CCL20 and other innate response cytokines by bystander, uninfected CD4⁺ T cells and monocytes. However, the gp120 determinants involved in these functions are not completely understood. Whether signalling leading to cytokine production is due to CD4 or other receptors is still unclear. Enhanced chemokine receptor binding and subsequent clustering receptors may lead to cytokine production. By using a comprehensive panel of gp120 mutants, here we show that CD4 binding is mandatory for cytokine outburst in monocytes. Our data suggest that targeting monocytes in HIV-infected patients might decrease systemic inflammation and the potential tissue injury associated with the production of inflammatory cytokines. Understanding how gp120 mediates a cytokine burst in monocytes might help develop new approaches to improve the chronic inflammation that persists in these patients despite effective suppression of viremia by antiretroviral therapy.

Incretin hormones regulate microglia oxidative stress, survival and expression of trophic factors

The incretin hormones glucagon-like peptide (GLP)-1 and glucose-dependent insulinotropic polypeptide (GIP) are primarily known for their metabolic function in the periphery. GLP-1 and GIP are secreted by intestinal endocrine cells in response to ingested nutrients. Both GLP-1 and GIP stimulate the production and release of insulin from pancreatic β cells as well as exhibit several growth-regulating effects on peripheral tissues. GLP-1 and GIP are also present in the brain, where they provide modulatory and anti-apoptotic signals to neurons. However, very limited information is available regarding the effects of these hormones on glia, the immune and supporting cells of the brain. Therefore, we set out to resolve whether primary human microglia and astrocytes, two subtypes of glial cells, express the GLP-1 receptor (GLP-1R) and GIP receptor (GIPR), which are necessary to detect and respond to GLP-1 and GIP, respectively. We further tested whether these hormones, similar to their effects on neuronal cells, have growth-regulating, antioxidant and anti-apoptotic effects on microglia. We show for the first time expression of the GLP-1R and the GIPR by primary human microglia and astrocytes. We demonstrate that GLP-1 and GIP reduce apoptotic death of murine BV-2 microglia through the binding and activation of the GLP-1R and GIPR, respectively, with subsequent activation of the protein kinase A (PKA) pathway. Moreover, we reveal that incretins upregulate BV-2 microglia expression of brain derived neurotrophic factor (BDNF), glial cell-line derived neurotrophic factor (GDNF) and nerve growth factor (NGF) in a phosphoinositide 3-kinase (PI3K)- and PKA-dependent manner. We also show that incretins reduce oxidative stress in BV-2 microglia by inhibiting the accumulation of intracellular reactive oxygen species (ROS) and release of nitric oxide (NO), as well as by increasing the expression of the antioxidant glutathione peroxidase 1 (GPx1) and superoxide dismutase 1 (SOD1). We confirm these results by demonstrating that GLP-1 and GIP also inhibit apoptosis of primary murine microglia, and upregulate expression of BDNF by primary murine microglia. These results indicate that GLP-1 and GIP affect several critical homeostatic functions of microglia, and could therefore be tested as a novel therapeutic treatment option for brain disorders that are characterized by increased oxidative stress and microglial degeneration.

In Vitro Modulation of TrkB Receptor Signaling upon Sequential Delivery of Curcumin-DHA Loaded Carriers Towards Promoting Neuronal Survival

PURPOSE

To in vitro investigate the capacity of carrier-free and lipid-nanoparticle (NP)-encapsulated phytochemical compounds to prevent neuronal damage through neurotrophin potentiating activities. Delivery of molecules promoting the neurotrophin receptor signaling in the central nervous system (CNS) present ongoing interest for combination therapy development.

METHODS

Super-resolution Stimulated Emission Depletion (STED) microscopy imaging and flow cytometry analysis were employed to study the expression of the neurotrophin TrkB receptor in a neuronal cell model, which is highly responsive to binding of brain-derived neurotrophic factor (BDNF). Dual drug-loaded nanoparticle formulations, prepared by self-assembly of lyotropic lipids and PEGylated amphiphile derivatives, were delivered to differentiated human neuroblastoma SH-SY5Y cells subjected to degenerative conditions.

RESULTS

The expression of BDNF in the intra and extracellular domains was quantified by ELISA and flow cytometry after sequential treatment of the degenerating SH-SY5Y cells by neurotherapeutic formulations. Flow cytometry was also used to assess the phosphorylation of the transcription factor cAMP response element-binding protein (CREB) in the intracellular domain as a result of the treatment by nanoformulations.

CONCLUSION

Over time, dual drug formulations (curcumin and docosahexaenoic acid (DHA)) promoted the neuronal survival and repair processes through enhanced BDNF secretion and increased phosphorylation of CREB as compared to untreated degenerating cells.

HIV-1 proteins, Tat and gp120, target the developing dopamine system

In 2014, 3.2 million children (< 15 years of age) were estimated to be living with HIV and AIDS worldwide, with the 240,000 newly infected children in the past year, i.e., another child infected approximately every two minutes [1]. The primary mode of HIV infection is through mother-to-child transmission (MTCT), occurring either in utero, intrapartum, or during breastfeeding. The effects of HIV-1 on the central nervous system (CNS) are putatively accepted to be mediated, in part, via viral proteins, such as Tat and gp120. The current review focuses on the targets of HIV-1 proteins during the development of the dopamine (DA) system, which appears to be specifically susceptible in HIV-1-infected children. Collectively, the data suggest that the DA system is a clinically relevant target in chronic HIV-1 infection, is one of the major targets in pediatric HIV-1 CNS infection, and may be specifically susceptible during development. The present review discusses the development of the DA system, follows the possible targets of the HIV-1 proteins during the development of the DA system, and suggests potential therapeutic approaches. By coupling our growing understanding of the development of the CNS with the pronounced age-related differences in disease progression, new light may be shed on the neurological and neurocognitive deficits that follow HIV-1 infection.

Brain derived neurotrophic factor and cognitive status: the delicate balance among people living with HIV, with and without alcohol abuse

INTRODUCTION

The advent of combination antiretroviral therapy(cART) has lead to a significant reduction in morbidity and mortality among people living with HIV(PLWH). However, HIV-associated neurocognitive disorders (HAND) still remain a significant problem. One possible mechanism for the persistence of these disorders is through the effect of HIV on brain-derived neurotrophic factor (BDNF). BDNF is influenced by various factors including hazardous alcohol use (HAU), which is prevalent among PLWH. This study attempts to elucidate the relationships between HAU, BDNF and HAND.

METHODS

Cross-sectional analyses were conducted on a sample of 199 hazardous alcohol users and 198 non-HAU living with HIV. Members of each group were matched according to sociodemographic characteristics and CD4 count. Research procedures included validated questionnaires, neuropsychological assessments and a blood sample to obtain BDNF and immune measurements.

RESULTS

Hazardous alcohol users showed either significantly lower or significantly higher BDNF levels compared to the Non-hazardous (OR=1,4; 95% CI: 1-2.1, p = 0.003). Therefore, for additional analyses, subjects were categorized based on BDNF values in: Group 1 < 4000, Group 2: 4001-7,999 (reference group), and Group 3 for those >8,000 pg/mL. Groups 1 and 3 performed significantly worse than those in Group 2 in the domains of processing speed, auditory-verbal and visuospatial learning and memory. Multivariate analyses confirmed that HAU and BDNF are significant contributors of HAND.

CONCLUSION

Our findings offer novel insights into the relationships between BDNF, and alcohol use among PLWH. Our results also lend support to expanding clinical movement to use BDNF as an intervention target for PLWH, in those with evidence of deficiencies, and highlight the importance of including HAUat the inception of clinical trials.

5-HT7 receptor activation promotes an increase in TrkB receptor expression and phosphorylation

The serotonin (5-HT) type 7 receptor is expressed throughout the CNS including the cortex and hippocampus. We have previously demonstrated that the application of 5-HT7 receptor agonists to primary hippocampal neurons and SH-SY5Y cells increases platelet-derived growth factor (PDGF) receptor expression and promotes neuroprotection against N-methyl-D-aspartate-(NMDA)-induced toxicity. The tropomyosin-related kinase B (TrkB) receptor is one of the receptors for brain-derived neurotrophic factor (BDNF) and is associated with neurodevelopmental and neuroprotective effects. Application of LP 12 to primary cerebral cortical cultures, SH-SY5Y cells, as well as the retinal ganglion cell line, RGC-5, increased both the expression of full length TrkB as well as its basal phosphorylation state at tyrosine 816. The increase in TrkB expression and phosphorylation was observed as early as 30 min after 5-HT7 receptor activation. In addition to full-length TrkB, kinase domain-deficient forms may be expressed and act as dominant-negative proteins toward the full length receptor. We have identified distinct patterns of TrkB isoform expression across our cell lines and cortical cultures. Although TrkB receptor expression is regulated by cyclic AMP and Gαs-coupled GPCRs in several systems, we demonstrate that, depending on the model system, pathways downstream of both Gαs and Gα12 are involved in the regulation of TrkB expression by 5-HT7 receptors. Given the number of psychiatric and degenerative diseases associated with TrkB/BDNF deficiency and the current interest in developing 5-HT7 receptor ligands as pharmaceuticals, identifying signaling relationships between these two receptors will aid in our understanding of the potential therapeutic effects of 5-HT7 receptor ligands.

Genetic, transcriptomic, and epigenetic studies of HIV-associated neurocognitive disorder

The Human Genome Project, coupled with rapidly evolving high-throughput technologies, has opened the possibility of identifying heretofore unknown biological processes underlying human disease. Because of the opaque nature of HIV-associated neurocognitive disorder (HAND) neuropathogenesis, the utility of such methods has gained notice among NeuroAIDS researchers. Furthermore, the merging of genetics with other research areas has also allowed for application of relatively nascent fields, such as neuroimaging genomics, and pharmacogenetics, to the context of HAND. In this review, we detail the development of genetic, transcriptomic, and epigenetic studies of HAND, beginning with early candidate gene association studies and culminating in current "omics" approaches that incorporate methods from systems biology to interpret data from multiple levels of biological functioning. Challenges with this line of investigation are discussed, including the difficulty of defining a valid phenotype for HAND. We propose that leveraging known associations between biology and pathology across multiple levels will lead to a more reliable and valid phenotype. We also discuss the difficulties of interpreting the massive and multitiered mountains of data produced by current high-throughput omics assays and explore the utility of systems biology approaches in this regard.

The longitudinal and interactive effects of HIV status, stimulant use, and host genotype upon neurocognitive functioning

Both human immunodeficiency virus (HIV)-1 infection and illicit stimulant use can adversely impact neurocognitive functioning, and these effects can be additive. However, significant variability exists such that as-of-yet unidentified exogenous and endogenous factors affect one's risk for neurocognitive impairment. Literature on both HIV and stimulant use indicates that host genetic variants in immunologic and dopamine-related genes are one such factor. In this study, the individual and interactive effects of HIV status, stimulant use, and genotype upon neurocognitive functioning were examined longitudinally over a 10-year period. Nine hundred fifty-two Caucasian HIV+ and HIV- cases from the Multicenter AIDS Cohort Study were included. All cases had at least two comprehensive neurocognitive evaluations between 1985 and 1995. Pre-highly active antiretroviral therapy (HAART) data were examined in order to avoid the confounding effect of variable drug regimens. Linear mixed models were used, with neurocognitive domain scores as the outcome variables. No four-way interactions were found, indicating that HIV and stimulant use do not interact over time to affect neurocognitive functioning as a function of genotype. Multiple three-way interactions were found that involved genotype and HIV status. All immunologically related genes found to interact with HIV status affected neurocognitive functioning in the expected direction; however, only C-C chemokine ligand 2 (CCL2) and CCL3 affected HIV+ individuals specifically. Dopamine-related genetic variants generally affected HIV-negative individuals only. Neurocognitive functioning among HIV+ individuals who also used stimulants was not significantly different from those who did not use stimulants. The findings support the role of immunologically related genetic differences in CCL2 and CCL3 in neurocognitive functioning among HIV+ individuals; however, their impact is minor. Being consistent with findings from another cohort, dopamine (DA)-related genetic differences do not appear to impact the longitudinal neurocognitive functioning of HIV+ individuals.

Monocytes-derived macrophages mediated stable expression of human brain-derived neurotrophic factor, a novel therapeutic strategy for neuroAIDS

HIV-1 associated dementia remains a significant public health burden. Clinical and experimental research has shown that reduced levels of brain-derived neurotrophic factor (BDNF) may be a risk factor for neurological complications associated with HIV-1 infection. We are actively testing genetically modified macrophages for their possible use as the cell-based gene delivery vehicle for the central nervous system (CNS). It can be an advantage to use the natural homing/migratory properties of monocyte-derived macrophages to deliver potentially neuroprotective BDNF into the CNS, as a non-invasive manner. Lentiviral-mediated gene transfer of human (h)BDNF plasmid was constructed and characterized. Defective lentiviral stocks were generated by transient transfection of 293T cells with lentiviral transfer plasmid together with packaging and envelope plasmids. High titer lentiviral vector stocks were harvested and used to transduce human neuronal cell lines, primary cultures of human peripheral mononocyte-derived macrophages (hMDM) and murine myeloid monocyte-derived macrophages (mMDM). These transduced cells were tested for hBDNF expression, stability, and neuroprotective activity. The GenomeLab GeXP Genetic Analysis System was used to evaluate transduced cells for any adverse effects by assessing gene profiles of 24 reference genes. High titer vectors were prepared for efficient transduction of neuronal cell lines, hMDM, and mMDM. Stable secretion of high levels of hBDNF was detected in supernatants of transduced cells using western blot and ELISA. The conditioned media containing hBDNF were shown to be protective to neuronal and monocytic cell lines from TNF-α and HIV-1 Tat mediated cytotoxicity. Lentiviral vector-mediated gene transduction of hMDM and mMDM resulted in high-level, stable expression of the neuroprotective factorBDNF in vitro. These findings form the basis for future research on the potential use of BDNF as a novel therapy for neuroAIDS.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Suppression of immunodeficiency virus-associated neural damage by the p75 neurotrophin receptor ligand, LM11A-31, in an in vitro feline model

Feline immunodeficiency virus (FIV) infection like human immunodeficiency virus (HIV), produces systemic and central nervous system disease in its natural host, the domestic cat, that parallels the pathogenesis seen in HIV-infected humans. The ability to culture feline nervous system tissue affords the unique opportunity to directly examine interactions of infectious virus with CNS cells for the development of models and treatments that can then be translated to a natural infectious model. To explore the therapeutic potential of a new p75 neurotrophin receptor ligand, LM11A-31, we evaluated neuronal survival, neuronal damage and calcium homeostasis in cultured feline neurons following inoculation with FIV. FIV resulted in the gradual appearance of dendritic beading, pruning of processes and shrinkage of neuronal perikarya in the neurons. Astrocytes developed a more activated appearance and there was an enhanced accumulation of microglia, particularly at longer times post-inoculation. Addition of 10 nM LM11A-31, to the cultures greatly reduced or eliminated the neuronal pathology as well as the FIV effects on astrocytes and microglia. LM11A-31 also, prevented the development of delayed calcium deregulation in feline neurons exposed to conditioned medium from FIV treated macrophages. The suppression of calcium accumulation prevented the development of foci of calcium accumulation and beading in the dendrites. FIV replication was unaffected by LM11A-31. The strong neuroprotection afforded by LM11A-31 in an infectious in vitro model indicates that LM11A-31 may have excellent potential for the treatment of HIV-associated neurodegeneration.

Functional polymorphisms in dopamine-related genes: effect on neurocognitive functioning in HIV+ adults

Dopaminergic dysfunction is a putative mechanism underlying HIV-associated neurocognitive disorders. Dopamine transporter (DAT), brain-derived neurotrophic factor (BDNF), and catechol-O-methyltransferase (COMT) have been specifically implicated. We report analyses examining the main effects of functional polymorphisms within dopamine-modulating genes, as well as their interactive effects with disease severity, upon neurocognitive functioning in HIV+ adults.

METHOD

A total of 184 HIV+ adults were included in the analysis. Three polymorphisms were examined within dopamine-modulating genes: COMT val158met, BDNF val66met, and the DAT 3' variable number tandem repeat. Separate hierarchical regression analyses for five neurocognitive domains (working memory, processing speed, learning, memory, motor) were conducted. Predictor variables were age, ethnicity, gender, education, CD4+ T-cell count, current depression, genotype, and an interaction term capturing genotype and disease severity (CD4).

RESULTS

None of the polymorphisms or HIV disease variables significantly improved the hierarchical regression models. Younger age, higher education, and Caucasian ethnicity were almost invariably associated with better functioning across all five cognitive domains. A trend was noted for current depression as a predictor of motor and learning ability.

CONCLUSION

This study did not find evidence to support direct or interactive effects of dopamine-related genes and HIV disease severity on neurocognitive functioning.

Protein changes in CSF of HIV-infected patients: evidence for loss of neuroprotection

To begin to unravel the complexity of HIV-associated changes in the brain, broader, multifaceted analyses of cerebrospinal fluid (CSF) are needed that examine a wide range of proteins reflecting different functions. To provide the first broad profiles of protein changes in the CSF of HIV-infected patients, we used antibody arrays to measure 120 cytokines, chemokines, growth factors, and other proteins. CSF from HIV-infected patients with a range of cognitive deficits was compared to CSF from uninfected, cognitively normal patients to begin to identify protein changes associated with HIV infection and neurological disease progression. Uninfected patients showed relatively consistent patterns of protein expression. Highly expressed proteins in CSF included monocyte chemotactic protein-1, tissue inhibitors of metalloproteases, granulocyte colony-stimulating factor, adiponectin, soluble tumor necrosis factor receptor-1, urokinase-type plasminogen activator receptor, and insulin-like growth factor binding protein-2. Inflammatory and anti-inflammatory cytokines were expressed at low levels. HIV-infected patients showed increases in inflammatory proteins (interferon-gamma, tumor necrosis factor-alpha), anti-inflammatory proteins (IL-13), and chemokines but these correlated poorly with neurological status. The strongest correlation with increasing severity of neurological disease was a decline in growth factors, particularly, brain-derived neurotrophic factor and NT-3. These studies illustrate that HIV infection is associated with parallel changes in both inflammatory and neuroprotective proteins in the CSF. The inverse relationship between growth factors and neurological disease severity suggests that a loss of growth factor neuroprotection may contribute to the development of neural damage and may provide useful markers of disease progression.

The nerve growth factor reduces APOBEC3G synthesis and enhances HIV-1 transcription and replication in human primary macrophages

Macrophages infected with HIV-1 sustain viral replication for long periods of time, functioning as viral reservoirs. Therefore, recognition of factors that maintain macrophage survival and influence HIV-1 replication is critical to understanding the mechanisms that regulate the HIV-1-replicative cycle. Because HIV-1-infected macrophages release the nerve growth factor (NGF), and NGF neutralization reduces viral production, we further analyzed how this molecule affects HIV-1 replication. In the present study, we show that NGF stimulates HIV-1 replication in primary macrophages by signaling through its high-affinity receptor Tropomyosin-related Kinase A (TrKA), and with the involvement of reticular calcium, protein kinase C, extracellular signal-regulated kinase, p38 kinase, and nuclear factor-κB. NGF-induced enhancement of HIV-1 replication occurred during the late events of the HIV-1-replicative cycle, with a concomitant increase in viral transcription and production. In addition, NGF reduced the synthesis of the cellular HIV-1 restriction factor APOBEC3G and also overrode its interferon-γ-induced up-regulation, allowing the production of a well-fitted virus. Because NGF-TrKA signaling is a crucial event for macrophage survival, it is possible that NGF-induced HIV-1 replication plays a role in the maintenance of HIV-1 reservoirs. Our study may contribute to the understanding of the immunopathogenesis of HIV-1 infection and provide insights about approaches aimed at limiting viral replication in HIV-1 reservoirs.

HIV neurotoxicity: potential therapeutic interventions

Individuals suffering from human immunodeficiency virus type 1 (HIV-1) infection suffer from a wide range of neurological deficits. The most pronounced are the motor and cognitive deficits observed in many patients in the latter stages of HIV infection. Gross postmortem inspection shows cortical atrophy and widespread neuronal loss. One of the more debilitating of the HIV-related syndromes is AIDS-related dementia, or HAD. Complete understanding of HIV neurotoxicity has been elusive. Both direct and indirect toxic mechanisms have been implicated in the neurotoxicity of the HIV proteins, Tat and gp120. The glutamatergic system, nitric oxide, calcium, oxidative stress, apoptosis, and microglia have all been implicated in the pathogenesis of HIV-related neuronal degeneration. The aim of this review is to summarize the most recent work and provide an overview to the current theories of HIV-related neurotoxicity and potential avenues of therapeutic interventions to prevent the neuronal loss and motor/cognitive deficits previously described.

The endocannabinoid system in gp120-mediated insults and HIV-associated dementia

Endocannabinoids (eCBs) include a group of lipid mediators that act as endogenous agonists at cannabinoid (CB(1), CB(2)) and vanilloid (TRPV1) receptors. In the last two decades a number of eCBs-metabolizing enzymes have been discovered that, together with eCBs and congeners, target receptors and proteins responsible for their transport and intracellular trafficking form the so-called "endocannabinoid system" (ECS). Within the central nervous system ECS elements participate in neuroprotection against neuroinflammatory/neurodegenerative diseases like Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and multiple sclerosis. More recently, a role for eCBs has been documented also in human immunodeficiency virus-1 (HIV-1) envelope glycoprotein gp120-mediated insults, and in HIV-associated dementia (HAD). The modulation of ECS in the latter disease conditions is the subject of this review, that will also address the molecular mechanisms underlying the neuroprotective effects of eCBs. In particular, the interactions between neurons and glia during neuroinflammation, and the alterations of ECS in these cells upon gp120 insults and HAD will be discussed, along with the potential therapeutic exploitation of ECS-oriented drugs for the treatment of HAD and related disorders.

Curcumin improves spatial memory impairment induced by human immunodeficiency virus type 1 glycoprotein 120 V3 loop peptide in rats

AIMS

Human immunodeficiency virus-1 (HIV-1)-associated dementia (HAD) is a significant consequence of HIV infection. Although highly active antiretroviral therapy (HAART) has dramatically decreased HIV-1 load in acquired immune deficiency syndrome (AIDS) patients, HAART does not completely protect against the development of HAD, therefore novel strategies for the prevention and treatment are urgently needed. In this study, we chose curcumin which has a neuroprotective role and tested the effect against neuron damage induced by HIV-1gp120 V3 loop peptide.

MAIN METHODS

Rats were given 150 ng gp120 V3 peptide by intracerebroventricular (ICV) infusion for 3 days to establish the cognitive dysfunction model. After recovery from the surgery, the rats in treatment groups were given curcumin by intragastric infusion for 2 weeks. Subsequently, we used the Morris water maze test, long-term potentiation (LTP) recording, biochemical measurement of oxidative damage, Nissl staining, and BDNF immunostaining to evaluate the neuropathological changes and the effect of curcumin on rats.

KEY FINDINGS

Our results documented that the gp120 V3 peptide induced impairment of spatial learning and memory, inhibited LTP in the CA1 region of the hippocampus, and mediated oxidative stress and neuronal injury. These impairments were ameliorated by intragastric infusion of curcumin.

SIGNIFICANCE

These results suggested that dietary supplementation of curcumin may be a potential therapeutic strategy for the treatment and/or prevention of HAD.

The role of host genetics in the susceptibility for HIV-associated neurocognitive disorders

Despite progress in the treatment of the Human Immunodeficiency virus (HIV), there continues to be a high prevalence of infected individuals who develop neurocognitive deficits and disorders. Our understanding of the potential cause of HIV-associated neurocognitive disorders (HAND) continues to develop on many fronts. Among them is the study of host genetics. Here, we review the most current information regarding the association between host genetics and risk for HIV infection, AIDS, and HAND. We focus on the role of dopamine dysfunction in the etiology of HAND, and propose a number of genetic polymorphisms within genes related to dopaminergic functioning and other neurobiological factors that may confer vulnerability or protection against HAND.

M- and T-tropic HIVs promote apoptosis in rat neurons

Neuronal loss, reactive astrocytes, and other abnormalities are seen in the brain of individuals with acquired immune deficiency syndrome-associated Dementia Complex (ADC). Human immunodeficiency virus-1 (HIV-1) is believed to be the main agent causing ADC. However, little is known about the molecular and cellular mechanisms of HIV-1 neurotoxicity considering that HIV-1 does not infect post-mitotic neurons and that viral load does not necessarily correlate with ADC. Various viral proteins, such as the envelope protein gp120 and the transcription activator Tat, have been shown to induce neuronal apoptosis through direct and indirect mechanisms both in vitro and in vivo. Progeny HIV-1 virions can also cause neuronal death. However, it has not been fully established yet whether HIV-1 promotes neuronal apoptosis by a direct mechanism. To explore the neurotoxic effect of HIV-1, we exposed rat cerebellar granule cells and cortical neurons in culture to two different strains of HIV-1, IIIB and BaL, T- and M-tropic strains that utilize CXCR4 and CCR5 coreceptors, respectively, to infect cells. We observed that both viruses elicit a time-dependent apoptotic cell death in these cultures without inducing a productive infection as determined by the absence of the core protein of HIV-1, p24, in cell lysates. Instead, neurons were gp120 positive, suggesting that the envelope protein is shed by the virus and then subsequently internalized by neurons. The CXCR4 receptor antagonist AMD3100 or the CCR5 receptor inhibitor D-Ala-peptide T-amide blocked HIV IIIB and HIV Bal neurotoxicity, respectively. In contrast, the N-methyl-D-aspartate receptor blocker MK801 failed to protect neurons from HIV-mediated apoptosis, suggesting that HIV-1 neurotoxicity can be initiated by the viral protein gp120 binding to neuronal chemokine receptors.

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

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

Brain-derived neurotrophic factor prevents human immunodeficiency virus type 1 protein gp120 neurotoxicity in the rat nigrostriatal system

Human immunodeficiency virus type 1 (HIV-1) causes neuronal degeneration and, at a late stage, creates HIV-associated dementia (HAD) and other neurological abnormalities. Therefore, the need for neuroprotective agents is great. However, therapeutic agents that reduce HIV neurotoxicity are difficult to characterize and develop because rodents are not infected by HIV. This study was undertaken to develop an animal model of HIV neurotoxicity by using the HIV-1 envelope glycoprotein 120 (gp120). Vehicle or gp120 was injected acutely in the striatum of adult rats. gp120 produced loss of nigrostriatal neurons, as shown both by histochemical analysis of brain sections for apoptosis and biochemical determination of dopamine. The neurotrophin brain-derived neurotrophic factor (BDNF) delivered by a recombinant adeno-associated viral vector prevented gp120 toxicity. This study's results support the notion that gp120 produces a widespread neurotoxicity similar to that observed in HIV-positive individuals and that BDNF may be a suitable neuroprotective agent for HAD.

Oxidative stress and protein oxidation in the brain of water drinking and alcohol drinking rats administered the HIV envelope protein, gp120

Possible roles of oxidative stress and protein oxidation on alcohol-induced augmentation of cerebral neuropathy in gp120 administered alcohol preferring rats drinking either pure water (W rats) or a free-choice ethanol and water (E rats) for 90 days. This study showed that peripherally administered gp120 accumulated into the brain, liver, and RBCs samples from water drinking - gp120 administered rats (Wg rats) and ethanol drinking - gp120 administered rats (Eg rats), although gp120 levels in samples from Eg rats were significantly greater than the levels in samples from Wg rats. The brain samples from ethanol drinking-saline administered (EC) and Wg rats exhibited comparable levels of free radicals that were significantly lower than the levels in Eg rats. Peroxiredoxin-I (PrxI) activity in the brain samples exhibited the following pattern: Wg >> >> WC >> EC > Eg. Total protein-carbonyl and carbonylated hippocampal cholinergic neurostimulating peptide precursor protein levels, but not N-acetylaspartate or N-acetyl aspartylglutamate or total protein-thiol levels, paralleled the free radical levels in the brain of all four groups. This suggests PrxI inhibition may be more sensitive indicator of oxidative stress than measuring free radicals or metabolites. As PrxI oxidation in WC, Wg, and EC rats was reversible, while PrxI oxidation in Eg rats was not, we suggest that alcohol drinking and gp120 together hyperoxidized and inactivated PrxI that suppressed free radical neutralization in the brain of Eg rats. In conclusion, chronic alcohol drinking, by carbonylating and hyperoxidizing free radical neutralization proteins, augmented the gp120-induced oxidative stress that may be associated with an increase in severity of the brain neuropathy.

Brain-derived neurotrophic factor prevents the nigrostriatal degeneration induced by human immunodeficiency virus-1 glycoprotein 120 in vivo

Glycoprotein 120 (gp120) from the T-tropic strain of the human immunodeficiency virus type 1 has been shown to cause neuronal apoptosis through activation of the chemokine receptor CXCR4. Therefore, reducing CXCR4 expression may prevent gp120-mediated apoptosis. Brain-derived neurotrophic factor (BDNF) is known to reduce both gp120 neurotoxicity and CXCR4 expression in vitro. The scope of this work is to establish whether BDNF is neuroprotective against gp120 in vivo and, if so, whether this effect correlates with its ability to down-regulate CXCR4. Serotype 2 adeno-associated viral vector encoding for BDNF (rAAV-BDNF) or control vector was microinjected into the striata of adult rats. Two weeks later gp120 was injected into the same striatum, and apoptosis determined. Pretreatment with rAAV-BDNF prior to gp120 microinjection prevented caspase-3 activation as well as in situ terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling in the striatum and substantia nigra. In addition, rAAV-BDNF reversed the loss of tyrosine hydroxylase immunoreactivity induced by gp120 in both areas. CXCR4 expression was then determined by immunohistochemistry and RT-PCR, and found to be decreased in striata of rAAV-BDNF-treated rats. Conversely, BDNF heterozygous mice exhibited an increase in CXCR4 mRNA levels compared to wild-type littermates. Our data suggest that down-regulation of CXCR4 expression may contribute to the neuroprotective activity of BDNF against gp120 toxicity in the basal ganglia.

Neurotoxins and neurotoxicity mechanisms. an overview

Neurotoxins represent unique chemical tools, providing a means to 1) gain insight into cellular mechanisms of apopotosis and necrosis, 2) achieve a morphological template for studies otherwise unattainable, 3) specifically produce a singular phenotype of denervation, and 4) provide the starting point to delve into processes and mechanisms of nerve regeneration and sprouting. There are many other notable uses of neurotoxins in neuroscience research, and ever more being discovered each year. The objective of this review paper is to highlight the broad areas of neuroscience in which neurotoxins and neurotoxicity mechanism come into play. This shifts the focus away from neurotoxins per se, and onto the major problems under study today. Neurotoxins broadly defined are used to explore neurodegenerative disorders, psychiatric disorders and substance use disorders. Neurotoxic mechanisms relating to protein aggregates are indigenous to Alzheimer disease, Parkinson's disease. NeuroAIDS is a disorder in which microglia and macrophages have enormous import. The gap between the immune system and nervous system has been bridged, as neuroinflammation is now considered to be part of the neurodegenerative process. Related mechanisms now arise in the process of neurogenesis. Accordingly, the entire spectrum of neuroscience is within the purview of neurotoxins and neurotoxicity mechanisms. Highlights on discoveries in the areas noted, and on selective neurotoxins, are included, mainly from the past 2 to 3 years.

Neuroimmunity and the blood-brain barrier: molecular regulation of leukocyte transmigration and viral entry into the nervous system with a focus on neuroAIDS

HIV infection of the central nervous system (CNS) can result in neurologic dysfunction with devastating consequences in a significant number of individuals with AIDS. Two main CNS complications in individuals with HIV are encephalitis and dementia, which are characterized by leukocyte infiltration into the CNS, microglia activation, aberrant chemokine expression, blood-brain barrier (BBB) disruption, and eventual damage and/or loss of neurons. One of the major mediators of NeuroAIDS is the transmigration of HIV-infected leukocytes across the BBB into the CNS. This review summarizes new key findings that support a critical role of the BBB in regulating leukocyte transmigration. In addition, we discuss studies on communication among cells of the immune system, BBB, and the CNS parenchyma, and suggest how these interactions contribute to the pathogenesis of NeuroAIDS. We also describe some of the animal models that have been used to study and characterize important mechanisms that have been proposed to be involved in HIV-induced CNS dysfunction. Finally, we review the pharmacologic interventions that address neuroinflammation, and the effect of substance abuse on HIV-1 related neuroimmunity.