Neuronal survival and resistance to HIV-1 Tat toxicity in the primary culture of rat fetal neurons

Suppression of HIV and cocaine-induced neurotoxicity and inflammation by cell penetrable itaconate esters

HIV-associated neurological disorder (HAND) is a serious complication of HIV infection, marked by neurotoxicity induced by viral proteins like Tat. Substance abuse exacerbates neurocognitive impairment in people living with HIV. There is an urgent need for effective therapeutic strategies to combat HAND comorbid with Cocaine Use Disorder (CUD). Our analysis of the HIV and cocaine-induced transcriptomes in primary cortical cultures revealed a significant overexpression of the macrophage-specific gene, aconitate decarboxylase 1 (Acod1), caused by the combined insults of HIV and cocaine. ACOD1 protein converts the tricarboxylic acid intermediate cis-aconitate into itaconate during the activation of inflammation. The itaconate produced facilitates cytokine production and subsequently activates anti-inflammatory transcription factors, shielding macrophages from infection-induced cell death. While the role of itaconate' in limiting inflammation has been studied in peripheral macrophages, its immunometabolic function remains unexplored in HIV and cocaine-exposed microglia. We assessed in this model system the potential of 4-octyl-itaconate (4OI), a cell-penetrable esterified form of itaconate known for its potent anti-inflammatory properties and potential therapeutic applications. We administered 4OI to primary cortical cultures exposed to Tat and cocaine. 4OI treatment increased the number of microglial cells in both untreated and Tat±Cocaine-treated cultures and also reversed the morphological altercations induced by Tat and cocaine. In the presence of 4OI, microglial cells also appeared more ramified, resembling the quiescent microglia. Consistent with these results, 4OI treatment inhibited the secretion of the proinflammatory cytokines IL-1α, IL-1β, IL-6, and MIP1-α induced by Tat and cocaine. Transcriptome profiling further determined that Nrf2 target genes such as NAD(P)H quinone oxidoreductase 1 (Nqo1), Glutathione S-transferase Pi (Gstp1), and glutamate cysteine ligase catalytic (Gclc), were most significantly activated in Tat-4OI treated cultures, relative to Tat alone. Further, genes associated with cytoskeleton dynamics in inflammatory microglia were downregulated by 4OI treatment. Together, the results strongly suggest 4-octyl-itaconate holds promise as a potential candidate for therapeutic development aimed at addressing HAND coupled with CUD comorbidities.

Inhibition of the Dead Box RNA Helicase 3 Prevents HIV-1 Tat and Cocaine-Induced Neurotoxicity by Targeting Microglia Activation

HIV-1 Associated Neurocognitive Disorder (HAND) is a common and clinically detrimental complication of HIV infection. Viral proteins, including Tat, released from infected cells, cause neuronal toxicity. Substance abuse in HIV-infected patients greatly influences the severity of neuronal damage. To repurpose small molecule inhibitors for anti-HAND therapy, we employed MOLIERE, an AI-based literature mining system that we developed. All human genes were analyzed and prioritized by MOLIERE to find previously unknown targets connected to HAND. From the identified high priority genes, we narrowed the list to those with known small molecule ligands developed for other applications and lacking systemic toxicity in animal models. To validate the AI-based process, the selective small molecule inhibitor of DDX3 helicase activity, RK-33, was chosen and tested for neuroprotective activity. The compound, previously developed for cancer treatment, was tested for the prevention of combined neurotoxicity of HIV Tat and cocaine. Rodent cortical cultures were treated with 6 or 60 ng/ml of HIV Tat and 10 or 25 μM of cocaine, which caused substantial toxicity. RK-33 at doses as low as 1 μM greatly reduced the neurotoxicity of Tat and cocaine. Transcriptome analysis showed that most Tat-activated transcripts are microglia-specific genes and that RK-33 blocks their activation. Treatment with RK-33 inhibits the Tat and cocaine-dependent increase in the number and size of microglia and the proinflammatory cytokines IL-6, TNF-α, MCP-1/CCL2, MIP-2, IL-1α and IL-1β. These findings reveal that inhibition of DDX3 may have the potential to treat not only HAND but other neurodegenerative diseases. Graphical Abstract RK-33, selective inhibitor of Dead Box RNA helicase 3 (DDX3) protects neurons from combined Tat and cocaine neurotoxicity by inhibition of microglia activation and production of proinflammatory cytokines.

HIV-1 Tat: Role in Bystander Toxicity

HIV Tat protein is a critical protein that plays multiple roles in HIV pathogenesis. While its role as the transactivator of HIV transcription is well-established, other non-viral replication-associated functions have been described in several HIV-comorbidities even in the current antiretroviral therapy (ART) era. HIV Tat protein is produced and released into the extracellular space from cells with active HIV replication or from latently HIV-infected cells into neighboring uninfected cells even in the absence of active HIV replication and viral production due to effective ART. Neighboring uninfected and HIV-infected cells can take up the released Tat resulting in the upregulation of inflammatory genes and activation of pathways that leads to cytotoxicity observed in several comorbidities such as HIV associated neurocognitive disorder (HAND), HIV associated cardiovascular impairment, and accelerated aging. Thus, understanding how Tat modulates host and viral response is important in designing novel therapeutic approaches to target the chronic inflammatory effects of soluble viral proteins in HIV infection.

HIV Infection Induces Extracellular Cathepsin B Uptake and Damage to Neurons

HIV-associated neurocognitive disorders prevail in 20-50 percent of infected individuals. Macrophages transmigrate through the blood brain barrier during HIV-1 infection, triggering neuronal dysfunction. HIV-infected macrophages secrete cathepsin B (CATB), and serum amyloid p component (SAPC), inducing neuronal apoptosis by an unknown mechanism. We hypothesized that HIV infection facilitates CATB/SAPC secretion from macrophages followed by neuronal internalization, promoting dysfunction. SK-N-SH neuronal cells were exposed to active recombinant histidine-tagged cathepsin B (His-CATB). His-CATB entry was tracked by intracellular flow cytometry, and neuronal dysfunction was verified by western blot. Macrophage-derived extracellular vesicles (EVs) were tested for the presence of CATB and SAPC. Neurons internalized His-CATB, an effect that was partially decreased by pre-treatment with anti-CATB antibody. Pre-treatment with CATB and SAPC antibodies decreased cleavage of caspase-3 and restored synaptophysin in neurons. Neurons exposed to macrophage-conditioned media differentially internalized His-CATB, dependent on the HIV replication levels. Finally, CATB and SAPC were secreted in EVs. We report for the first time that CATB is secreted from macrophages both free and in EVs, and is internalized by neurons. Moreover, HIV-replication levels modulate the amount of CATB neuronal uptake, and neuronal dysfunction can be decreased with CATB antibodies. In conclusion, the CATB/SAPC complex represents a novel target against HIV-associated neurocognitive disorders.

Human Immunodeficiency Virus Type 1 gp120 and Tat Induce Mitochondrial Fragmentation and Incomplete Mitophagy in Human Neurons

HIV enters the central nervous system (CNS) during the early stages of infection and can cause neurological dysfunction, including neurodegeneration and neurocognitive impairment. The specific autophagy responsible for removal of damaged mitochondria (mitophagy) and mitochondrial dynamics constitute neuronal mitochondrial quality control mechanisms and are impaired in neurodegenerative disorders and numerous other diseases. The release of HIV proteins gp120 and Tat from infected cells is thought to play an important role in HIV-associated neurocognitive disorders (HAND), but the mechanism(s) leading to impairment are poorly understood. Here, we report that exposure of human primary neurons (HPNs) to HIV gp120 and Tat accelerates the balance of mitochondrial dynamics toward fission (fragmented mitochondria) and induces perinuclear aggregation of mitochondria and mitochondrial translocation of dynamin-related protein 1 (DRP1), leading to neuronal mitochondrial fragmentation. HIV gp120 and Tat increased the expression of microtubule-associated protein 1 light chain 3 beta (LC3B) protein and induced selective recruitment of Parkin/SQSTM1 to the damaged mitochondria. Using either a dual fluorescence reporter system expressing monomeric red fluorescent protein and enhanced green fluorescent protein targeted to mitochondria (mito-mRFP-EGFP) or a tandem light chain 3 (LC3) vector (mCherry-EGFP-LC3), both HIV proteins were found to inhibit mitophagic flux in human primary neurons. HIV gp120 and Tat induced mitochondrial damage and altered mitochondrial dynamics by decreasing mitochondrial membrane potential (ΔΨm). These findings indicate that HIV gp120 and Tat initiate the activation and recruitment of mitophagy markers to damaged mitochondria in neurons but impair the delivery of mitochondria to the lysosomal compartment. Altered mitochondrial dynamics associated with HIV infection and incomplete neuronal mitophagy may play a significant role in the development of HAND and accelerated aging associated with HIV infection.IMPORTANCE Despite viral suppression by antiretrovirals, HIV proteins continue to be detected in infected cells and neurologic complications remain common in infected people. Although HIV is unable to infect neurons, viral proteins, including gp120 and Tat, can enter neurons and can cause neuronal degeneration and neurocognitive impairment. Neuronal health is dependent on the functional integrity of mitochondria, and damaged mitochondria are subjected to mitochondrial control mechanisms. Multiple lines of evidence suggest that specific elimination of damaged mitochondria through mitophagy and mitochondrial dynamics play an important role in CNS diseases. Here, we show that in human primary neurons, gp120 and Tat favor the balance of mitochondrial dynamics toward enhanced fragmentation through the activation of mitochondrial translocation of DRP1 to the damaged mitochondria. However, mitophagy fails to go to completion, leading to neuronal damage. These findings support a role for altered mitophagy in HIV-associated neurological disorders and provide novel targets for potential intervention.

Network analysis of hippocampal neurons by microelectrode array in the presence of HIV-1 Tat and cocaine

HIV-associated neurocognitive disorders affecting greater than 30% of patients are caused by HIV-1 infection of the CNS, and in part, include neurotoxic effects of the viral transactivator of transcription, Tat protein. In addition to increasing the risk for becoming HIV infected, cocaine abuse enhances the neuropathogenic impacts of HIV-1. To investigate the outcome of Tat and cocaine interference in the hippocampal neuronal network, cross-rank-corrlation was employed to develop a systematic framework to assess hippocampal neurons behavior cultured on multielectrode arrays. Tat and cocaine differentially disturbed neuronal spiking rates, amplitude, synchronous activity, and oscillations within the hippocampal neuronal network via potentiation of inhibitory neurotransmission. The Tat-mediated impairment of neuronal spiking was reversible by removal of Tat, which restored neuronal activity. The presence of astrocytes co-cultured with neuronal networks diminished the effects of Tat and cocaine on neuron function suggesting a role for astrocytes in stabilizing neuronal behavior and increasing neuronal spontaneous activities such as bursting amplitude, frequency, and wave propagation rate. Taken together, our studies indicate that the HIV protein Tat and cocaine impair hippocampal neuronal network functioning and that the presence of astrocytes alleviates network dysfunction pointing to a newly discovered pathway through which ionic homeostasis is maintained by neuron-glial crosstalk in the CNS.

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.

Human Immunodeficiency Virus Promotes Mitochondrial Toxicity

Combined antiretroviral therapies (cART) have had remarkable success in reducing morbidity and mortality among patients infected with human immunodeficiency virus (HIV). However, mild forms of HIV-associated neurocognitive disorders (HAND), characterized by loss of synapses, remain. cART may maintain an undetectable HIV RNA load but does not eliminate the expression of viral proteins such as trans-activator of transcription (Tat) and the envelope glycoprotein gp120 in the brain. These two viral proteins are known to promote synaptic simplifications by several mechanisms, including alteration of mitochondrial function and dynamics. In this review, we aim to outline the many targets and pathways used by viral proteins to alter mitochondria dynamics, which contribute to HIV-induced neurotoxicity. A better understanding of these pathways is crucial for the development of adjunct therapies for HAND.

HIV-1 Tat and cocaine mediated synaptopathy in cortical and midbrain neurons is prevented by the isoflavone Equol

Illicit drugs, such as cocaine, are known to increase the likelihood and severity of HIV-1 associated neurocognitive disorders (HAND). In the current studies synaptic integrity was assessed following exposure to low concentrations of the HIV-1 viral protein Tat 1-86B, with or without cocaine, by quantifying filamentous actin (F-actin) rich structures (i.e., puncta and dendritic spines) on neuronal dendrites in vitro. In addition, the synapse-protective effects of either R-Equol (RE) or S-Equol (SE; derivatives of the soy isoflavone, daidzein) were determined. Individually, neither low concentrations of HIV-1 Tat (10 nM) nor low concentrations of cocaine (1.6 μM) had any significant effect on F-actin puncta number; however, the same low concentrations of HIV-1 Tat + cocaine in combination significantly reduced dendritic synapses. This synaptic reduction was prevented by pre-treatment with either RE or SE, in an estrogen receptor beta dependent manner. In sum, targeted therapeutic intervention with SE may prevent HIV-1 + drug abuse synaptopathy, and thereby potentially influence the development of HAND.

Anti-tat Hutat2:Fc mediated protection against tat-induced neurotoxicity and HIV-1 replication in human monocyte-derived macrophages

BACKGROUND

HIV-1 Tat is essential for HIV replication and is also a well-known neurotoxic factor causing HIV-associated neurocognitive disorder (HAND). Currently, combined antiretroviral therapy targeting HIV reverse transcriptase or protease cannot prevent the production of early viral proteins, especially Tat, once HIV infection has been established. HIV-infected macrophages and glial cells in the brain still release Tat into the extracellular space where it can exert direct and indirect neurotoxicity. Therefore, stable production of anti-Tat antibodies in the brain would neutralize HIV-1 Tat and thus provide an effective approach to protect neurons.

METHODS

We constructed a humanized anti-Tat Hutat2:Fc fusion protein with the goal of antagonizing HIV-1 Tat and delivered the gene into cell lines and primary human monocyte-derived macrophages (hMDM) by an HIV-based lentiviral vector. The function of the anti-Tat Hutat2:Fc fusion protein and the potential side effects of lentiviral vector-mediated gene transfer were evaluated in vitro.

RESULTS

Our study demonstrated that HIV-1-based lentiviral vector-mediated gene transduction resulted in a high-level, stable expression of anti-HIV-1 Tat Hutat2:Fc in human neuronal and monocytic cell lines, as well as in primary hMDM. Hutat2:Fc was detectable in both cells and supernatants and continued to accumulate to high levels within the supernatant. Hutat2:Fc protected mouse cortical neurons against HIV-1 Tat86-induced neurotoxicity. In addition, both secreted Hutat2:Fc and transduced hMDM led to reducing HIV-1BaL viral replication in human macrophages. Moreover, lentiviral vector-based gene introduction did not result in any significant changes in cytomorphology and cell viability. Although the expression of IL8, STAT1, and IDO1 genes was up-regulated in transduced hMDM, such alternation in gene expression did not affect the neuroprotective effect of Hutat2:Fc.

CONCLUSIONS

Our study demonstrated that lentivirus-mediated gene transfer could efficiently deliver the Hutat2:Fc gene into primary hMDM and does not lead to any significant changes in hMDM immune-activation. The neuroprotective and HIV-1 suppressive effects produced by Hutat2:Fc were comparable to that of a full-length anti-Tat antibody. This study provides the foundation and insights for future research on the potential use of Hutat2:Fc as a novel gene therapy approach for HAND through utilizing monocytes/macrophages, which naturally cross the blood-brain barrier, for gene delivery.

Synaptodendritic recovery following HIV Tat exposure: neurorestoration by phytoestrogens

HIV-1 infects the brain and, despite antiretroviral therapy, many infected individuals suffer from HIV-1-associated neurocognitive disorders (HAND). HAND is associated with dendritic simplification and synaptic loss. Prevention of synaptodendritic damage may ameliorate or forestall neurocognitive decline in latent HIV-1 infections. The HIV-1 transactivating protein (Tat) is produced during viral latency in the brain and may cause synaptodendritic damage. This study examined the integrity of the dendritic network after exposure to HIV-1 Tat by labeling filamentous actin (F-actin)-rich structures (puncta) in primary neuronal cultures. After 24 h of treatment, HIV-1 Tat was associated with the dendritic arbor and produced a significant reduction of F-actin-labeled dendritic puncta as well as loss of dendrites. Pre-treatment with either of two plant-derived phytoestrogen compounds (daidzein and liquiritigenin), significantly reduced synaptodendritic damage following HIV-1 Tat treatment. In addition, 6 days after HIV-1 Tat treatment, treatment with either daidzein, or liquiritigenin enhanced recovery, via the estrogen receptor, from HIV-1 Tat-induced synaptodendritic damage. These results suggest that either liquiritigenin or daidzein may not only attenuate acute synaptodendritic injury in HIV-1 but may also promote recovery from synaptodendritic damage. The HIV-1 transactivating protein (Tat) is produced during viral latency in the brain. Treatment with either daidzein or liquiritigenin restored the loss of synaptic connectivity produced by HIV-1 Tat. This neurorestoration was mediated by estrogen receptors (ER). These results suggest that plant-derived phytoestrogens may promote recovery from HIV-1-induced synaptodendritic damage.

HIV-1 Tat protein variants: critical role for the cysteine region in synaptodendritic injury

HIV-1 enters the central nervous system early in infection; although HIV-1 does not directly infect neurons, HIV-1 may cause a variety of neurological disorders. Neuronal loss has been found in HIV-1, but synaptodendritic injury is more closely associated with the neurocognitive disorders of HIV-1. The HIV-1 transactivator of transcription (Tat) protein causes direct and indirect damage to neurons. The cysteine rich domain (residues 22-37) of Tat is important for producing neuronal death; however, little is known about the effects of the Tat protein functional domains on the dendritic network. The ability of HIV-1 Tat 1-101 Clades B and C, Tat 1-86 and Tat 1-72 proteins, as well as novel peptides (truncated 47-57, 1-72δ31-61, and 1-86 with a mutation at Cys22) to produce early synaptodendritic injury (24h), relative to later cell death (48h), was examined using cell culture. Treatment of primary hippocampal neurons with Tat proteins 1-72, 1-86 and 1-101B produced a significant early reduction in F-actin labeled puncta, implicating that these peptides play a role in synaptodendritic injury. Variants with a mutation, deletion, or lack of a cysteine rich region (1-86[Cys22], 1-101C, 1-72δ31-61, or 47-57) did not cause a significant reduction in F-actin rich puncta. Tat 1-72, 1-86, and 1-101B proteins did not significantly differ from one another, indicating that the second exon (73-86 or 73-101) does not play a significant role in the reduction of F-actin puncta. Conversely, peptides with a mutation, deletion, or lack of the cysteine rich domain (22-37) failed to produce a loss of F-actin puncta, indicating that the cysteine rich domain plays a key role in synaptodendritic injury. Collectively, these results suggest that for Tat proteins, 1) synaptodendritic injury occurs early, relative to cell death, and 2) the cysteine rich domain of the first exon is key for synaptic loss. Preventing such early synaptic loss may attenuate HIV-1 associated neurocognitive disorders.

Human immunodeficiency virus-1 protein Tat induces excitotoxic loss of presynaptic terminals in hippocampal cultures

Human immunodeficiency virus (HIV) infection of the CNS produces dendritic damage that correlates with cognitive decline in patients with HIV-associated neurocognitive disorders (HAND). HIV-induced neurotoxicity results in part from viral proteins shed from infected cells, including the HIV transactivator of transcription (Tat). We previously showed that Tat binds to the low density lipoprotein receptor-related protein (LRP), resulting in overactivation of NMDA receptors, activation of the ubiquitin-proteasome pathway, and subsequent loss of postsynaptic densities. Here, we show that Tat also induces a loss of presynaptic terminals. The number of presynaptic terminals was quantified using confocal imaging of synaptophysin fused to green fluorescent protein (Syn-GFP). Tat-induced loss of presynaptic terminals was secondary to excitatory postsynaptic mechanisms because treatment with an LRP antagonist or an NMDA receptor antagonist inhibited this loss. Treatment with nutlin-3, an E3 ligase inhibitor, prevented Tat-induced loss of presynaptic terminals. These data suggest that Tat-induced loss of presynaptic terminals is a consequence of excitotoxic postsynaptic activity. We previously found that ifenprodil, an NR2B subunit-selective NMDA receptor antagonist, induced recovery of postsynaptic densities. Here we show that Tat-induced loss of presynaptic terminals was reversed by ifenprodil treatment. Thus, Tat-induced loss of presynaptic terminals is reversible, and this recovery can be initiated by inhibiting a subset of postsynaptic NMDA receptors. Understanding the dynamics of synaptic changes in response to HIV infection of the CNS may lead to the design of improved pharmacotherapies for HAND patients.

15-deoxy-Δ¹²,¹⁴ -prostaglandin J₂ inhibits human immunodeficiency virus-1 tat-induced monocyte chemoattractant protein-1/CCL2 production by blocking the extracellular signal-regulated kinase-1/2 signaling pathway independently of peroxisome proliferator-activated receptor-γ and heme oxygenase-1 in rat hippocampal slices

Human immunodeficiency virus (HIV)-induced inflammation, and its consequences within the central nervous system (CNS), must be countered by multiple pharmacologic agents, and 15-deoxy-Δ(12,14) -prostaglandin J(2) (15d-PGJ2) may hold promise in the treatment of pathologies associated with this inflammatory response. 15d-PGJ2 can repress the inflammatory response by means of peroxisome proliferator-activated receptor-γ (PPARγ)-dependent and -independent mechanisms. However, its precise role and antiinflammatory mechanism in the hippocampus remain poorly understood. In the present study, rat hippocampal slices were stimulated with full-length HIV-1 Tat protein to investigate the role of 15d-PGJ2 8in the hippocampal inflammatory response. Pretreatment of slices with 15d-PGJ2 markedly reduced Tat-induced monocyte chemoattractant protein-1 (MCP-1/CCL2) production. Interestingly, the PPARγ antagonist GW9662 did not inhibit action of 15d-PGJ2, confirming the latter's PPARγ-independent mechanism of mediating antiinflammatory effects. Despite 15d-PGJ2's increasing the expression of heme oxygenase-1 (HO-1), its action was not abrogated by the HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX), nor was it recapitulated by HO-1 inducers such as cobalt protoporphyrin (CoPP). Moreover, short interfering RNA (siRNA)-directed knockdown of HO-1 did not abolish the antiinflammatory action of 15d-PGJ2 against Tat-induced MCP-1 production in human microglia-like THP-1 cells. Conversely, 15d-PGJ2 suppressed Tat-induced ERK1/2 activation, decreasing MCP-1 production upon Tat stimulation. The NADPH oxidase inhibitors DPI and apocynin also abrogated Tat-stimulated ERK1/2 activation, reducing MCP-1 production. Collectively, these data demonstrate that the antiinflammatory effects of 15d-PGJ2 on the hippocampus are exerted through inhibition of Tat-mediated ERK1/2 activation, coupled with that of a redox-sensitive pathway, independent of PPARγ and HO-1.

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.

D1/NMDA receptors and concurrent methamphetamine+ HIV-1 Tat neurotoxicity

The interactive effects of HIV-1 infection and methamphetamine (METH) abuse in producing cognitive dysfunction represent a serious medical problem; however, the neural mechanisms underlying this interactive neurotoxicity remain elusive. In this study, we report that a combination of low, sub-toxic doses of METH + HIV-1 Tat 1-86 B, but not METH + HIV-1 gp120, directly induces death of rodent midbrain neurons in vitro. The effects of D1- and NMDA-receptor specific antagonists (SCH23390 and MK-801, respectively) on the neurotoxicity of different doses of METH or HIV-1 Tat alone and on the METH + HIV-1Tat interaction in midbrain neuronal cultures suggest that the induction of the cell death cascade by METH and Tat requires both dopaminergic (D1) and N-methyl D-aspartate (NMDA) receptor-mediated signaling. This interactive METH+Tat neurotoxicity does not occur in cultures of hippocampal neurons, which are predominately glutamatergic, express very low levels of dopamine receptors, and have no functional dopamine transporter (DAT). Thus, the presence of a subpopulation of neurons capable of dopamine release/uptake is essential for METH+Tat induction of the cell death cascade. Overall, our results support the hypothesis that METH and HIV-1 Tat disrupt the normal conjunction of signaling between D1 and NMDA receptors, resulting in neural dysfunction and death.

Oxygen matters: tissue culture oxygen levels affect mitochondrial function and structure as well as responses to HIV viroproteins

Mitochondrial dysfunction is implicated in a majority of neurodegenerative disorders and much study of neurodegenerative disease is done on cultured neurons. In traditional tissue culture, the oxygen level that cells experience is dramatically higher (21%) than in vivo conditions (1-11%). These differences can alter experimental results, especially, pertaining to mitochondria and oxidative metabolism. Our results show that primary neurons cultured at physiological oxygen levels found in the brain showed higher polarization, lower rates of ROS production, larger mitochondrial networks, greater cytoplasmic fractions of mitochondria and larger mitochondrial perimeters than those cultured at higher oxygen levels. Although neurons cultured in either physiological oxygen or atmospheric oxygen exhibit significant increases in mitochondrial reactive oxygen species (ROS) production when treated with the human immunodeficiency virus (HIV) virotoxin trans-activator of transcription, mitochondria of neurons cultured at physiological oxygen underwent depolarization with dramatically increased cell death, whereas those cultured at atmospheric oxygen became hyperpolarized with no increase in cell death. Studies with a second HIV virotoxin, negative regulation factor (Nef), revealed that Nef treatment also increased mitochondrial ROS production for both the oxygen conditions, but resulted in mitochondrial depolarization and increased death only in neurons cultured in physiological oxygen. These results indicate a role for oxidative metabolism in a mechanism of neurotoxicity during HIV infection and demonstrate the importance of choosing the correct, physiological, culture oxygen in mitochondrial studies performed in neurons.

Morphine potentiates neurodegenerative effects of HIV-1 Tat through actions at μ-opioid receptor-expressing glia

Individuals infected with human immunodeficiency virus-1 who abuse opiates can have a higher incidence of virus-associated neuropathology. Human immunodeficiency virus does not infect neurons, but viral proteins such as transactivator of transcription and glycoprotein 120, originating from infected glia, are neurotoxic. Moreover, functional changes in glial cells that enhance inflammation and reduce trophic support are increasingly implicated in human immunodeficiency virus neuropathology. In previous studies, co-exposure with morphine enhanced transactivator of transcription neurotoxicity towards cultured striatal neurons. Since those cultures contained µ-opioid receptor-expressing astroglia and microglia, and since glia are the principal site of infection in the central nervous system, we hypothesized that morphine synergy might be glially mediated. A 60 hour, repeated measures paradigm and multiple co-culture models were used to investigate the cellular basis for opiate-enhanced human immunodeficiency virus neurotoxicity. Morphine co-exposure significantly enhanced transactivator of transcription-induced neuron death when glia were present. Synergistic effects of morphine on transactivator of transcription neurotoxicity were greatest with neuron-glia contact, but also occurred to a lesser extent with glial conditioned medium. Importantly, synergy was lost if glia, but not neurons, lacked µ-opioid receptors, indicating that opiate interactions with human immunodeficiency virus converge at the level of µ-opioid receptor-expressing glia. Morphine enhanced transactivator of transcription-induced inflammatory effectors released by glia, elevating reactive oxygen species, increasing 3-nitrotyrosine production by microglia, and reducing the ability of glia to buffer glutamate. But neuron survival was reduced even more with glial contact than with exposure to conditioned medium, suggesting that noxious elements associated with cell contact augment the toxicity due to soluble factors. Similar morphine-transactivator of transcription synergy was also observed in studies with the clade C sequence of HIV-1 transactivator of transcription, which did not cause neuron death unless morphine was present. Several paradoxical observations related to opiate effects were noted when µ-opioid receptors were specifically ablated from either glia or neurons. This suggests that µ-opioid receptor loss in isolated cell types can fundamentally distort cell-to-cell signalling, revealing opponent processes that may exist in individual cell types. Our findings show the critical role of glia in orchestrating neurotoxic interactions of morphine and transactivator of transcription, and support the emerging concept that combined exposure to opiates and human immunodeficiency virus drives enhanced pathology within the central nervous system.

Potent enhancement of GFP uptake into HT-29 cells and rat skin permeation by coincubation with tat peptide

The delivery enhancements of green fluorescent protein (GFP), a model reporter protein into/transepithelial colon adenocarcinoma (HT-29) cells and excised rat skin by coincubation, by simple mixing or as fusion protein with HIV1-trans-activating transcriptional (Tat), a cell-penetrating peptide, have been described. By simple mixing, Tat/GFP mixture could increase the cellular uptake of GFP into HT-29 cells by 4.25-fold and 1.79-fold of GFP and Tat-GFP fusion protein, respectively. The incubation time showed no effect on the cellular uptake of Tat/GFP and Tat-GFP. In transepithelial study, Tat-GFP demonstrated the highest ability to penetrate through the HT-29 cells of about 1.3-fold and 1.2-fold of GFP and Tat/GFP, respectively. Only Tat/GFP gave lower cytotoxicity than Tat or GFP alone. In transdermal delivery study, Tat/GFP showed better transdermal delivery profile with higher cumulative amount than Tat-GFP in stratum corneum (SC), viable epidermis and dermis, and the receiver compartment of the diffusion cell with the highest fluxes of 7.42 and 35.6; 8.87-fold and 5.57-fold of GFP and Tat-GFP in SC and receiver compartment, respectively. This study demonstrated an efficient enhancement of GFP uptake into cells and through excised rat skin by simple mixing with Tat peptide, which can be further applied for the development of protein drug delivery systems.

Extracellular HIV-1 Tat upregulates TNF-α dependent MCP-1/CCL2 production via activation of ERK1/2 pathway in rat hippocampal slice cultures: inhibition by resveratrol, a polyphenolic phytostilbene

Human immunodeficiency virus-1 (HIV-1) associated dementia (HAD) has been attributed to an encephalitis resulting from intense infiltration of monocytes. Evidence suggests that the viral protein Tat, which is released actively from HIV-1 infected cells, can contribute significantly to this process. Therefore, the principal objective of this study was to evaluate the potential molecular basis for the role of extracellular HIV-1 Tat in the induction of monocyte chemotactic protein-1 (MCP-1/CCL2) in the hippocampus, which is primarily linked to cognitive function and most commonly damaged in HAD. We also attempted to identify the mechanism by which resveratrol (trans-3,5,4'-trihydroxystilbene) modulates MCP-1 release in hippocampal tissues exposed to Tat. An ex vivo study using rat hippocampal slices demonstrated a time- and dose-dependent increase in MCP-1 production from Tat-treated hippocampal tissues. This increase was accompanied by the activation of the MEK/ERK pathway and TNF-α production. Tat-induced MCP-1 release was abrogated by inhibitors of tyrosine kinases (TK), herbimycin A or genistein, a finding that supports the MAPK signaling mechanism. The inhibition of the ERK1/2 pathway with SL327 induced a near-complete abolition of the observed Tat-induced effects. Furthermore, anti-TNF-α antibodies suppressed Tat-induced MCP-1 release. Resveratrol, to a level similar to that of SL327, downregulated Tat-induced proinflammatory responses via the inactivation of ERK1/2. These results indicate that the activation of the ERK1/2 pathway and TK are critical factors in the production of TNF-α and MCP-1 in the Tat-exposed hippocampus. Additionally, the inhibition of Tat-induced production of MCP-1 and TNF-α via the inactivation of the ERK1/2 pathway may represent the anti-inflammatory mechanism of resveratrol in the hippocampus.

ER-β mediates 17β-estradiol attenuation of HIV-1 Tat-induced apoptotic signaling

The protective actions of estrogen have been well evaluated in various models of neurodegeneration. These neuroprotective mechanisms may include a direct neuronal antiapoptotic effect as estrogen modulates actions of key regulators of the mitochondrial/intrinsic apoptotic cascade. We tested the ability of estrogen to protect against apoptotic signaling in cortical cell cultures exposed to Tat 1-86 (50 nM), and additionally, whether the beneficial actions of estrogen involved an estrogen receptor sensitive mechanism. We demonstrated that estrogen pretreatment significantly delayed Tat-induced cell death in primary cortical cultures. Pretreatment with 17β-estradiol (10 nM) attenuated the increased expression of antiapoptotic protein Bcl-2, proapoptotic protein Bax and activation of caspases linked to mitochondrial apoptotic pathway following Tat exposure. In addition, select components of apoptotic pathway signaling appear more sensitive to estrogen receptor (ER) activation, as the addition of ER antagonist ICI 182780 reversed estrogen downregulation of Bax and caspase 3, while estrogen effects on Tat-induced Bcl-2 and caspase 9 expression were maintained. Moreover, the addition of preferential ERα and ERβ antagonists (MPP dihydrochloride and PHTPP) indicated that estrogen effects on caspase 3 may be mediated by both receptor subtypes, whereas, was more involved in estrogen effects on Bax. Our data suggest that estrogen intervenes against HIV-1 Tat-induced cortical neuronal dysfunction via intersecting mitochondrial apoptotic pathway signaling in an ER-sensitive manner.

E2F1 localizes predominantly to neuronal cytoplasm and fails to induce expression of its transcriptional targets in human immunodeficiency virus-induced neuronal damage

As human immunodeficiency virus (HIV) does not induce neuronal damage by direct infection, the mechanisms of neuronal damage or loss in HIV-associated dementia (HAD) remain unclear. We have shown previously that immunoreactivity of transcription factor, E2F1, increases in neurons, localizing predominantly to the cytoplasm, in HIV-associated pathologies. Here we confirm that E2F1 localization is predominantly cytoplasmic in primary postmitotic neurons in vitro and cortical neurons in vivo. To determine whether E2F1 contributes to neuronal death in HAD via transactivation of target promoters, we assessed the mRNA and protein levels of several classical E2F1 transcriptional targets implicated in cell cycle progression and apoptosis in an in vitro model of HIV-induced neurotoxicity and in cortical autopsy tissue from patients infected with HIV. By Q-PCR, we show that mRNA levels of E2F1 transcriptional targets implicated in cell cycle progression (E2F1, Cyclin A, proliferating cell nuclear antigen (PCNA), and dyhydrofolate reductase (DHFR)) and apoptosis (caspases 3, 8, 9 and p19(ARF)) remain unchanged in an in vitro model of HIV-induced neurotoxicity. Further, we show that protein levels of p19(ARF), Cyclin A, and PCNA are not altered in vitro or in the cortex of patients with HAD. We propose that the predominantly cytoplasmic localization of E2F1 in neurons may account for the lack of E2F1 target transactivation in neurons responding to HIV-induced neurotoxicity.

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

HIV infection of the central nervous system results in neurological dysfunction in a large number of individuals. NeuroAIDS is characterized by neuronal injury and loss, yet there is no evidence of HIV-infected neurons. Neuronal damage and dropout must therefore be due to indirect effects of HIV infection of other central nervous system cells through elaboration of inflammatory factors and neurotoxic viral proteins, including the viral transactivator, tat. We previously demonstrated that HIV-tat-induced apoptosis in human primary neurons is dependent on N-methyl-D-aspartate receptor (NMDAR) activity. NMDAR activity is regulated by various mechanisms including NMDAR phosphorylation, which may lead to neuronal dysfunction and apoptosis in pathological conditions. We now demonstrate that tat treatment of human neurons results in tyrosine (Y) phosphorylation of the NMDAR subunit 2A (NR2A) in a src kinase-dependent manner. In vitro kinase assays and in vivo data indicated that NR2A Y1184, Y1325, and Y1425 are phosphorylated. Tat treatment of neuronal cultures enhanced phosphorylation of NR2A Y1325, indicating that this site is tat sensitive. Human brain tissue sections from HIV-infected individuals with encephalitis showed an increased phosphorylation of NR2A Y1325 in neurons as compared with uninfected and HIV-infected individuals without encephalitis. These findings suggest new avenues of treatment for HIV-associated cognitive impairment.

HIV-1 protein-mediated amyloidogenesis in rat hippocampal cell cultures

Since the beginning of the highly active antiretroviral therapy (HAART) era, epidemiological evidence indicates an increasing incidence of Alzheimer's (AD)-like brain pathology in aging HIV patients. Emerging evidence warns of potential convergent mechanisms underlying HIV- and Abeta-mediated neurodegeneration. We found that HIV-1 Tat B and gp120 promote the secretion of Abeta 1-42 in primary rat fetal hippocampal cell cultures. Our results demonstrate that the variant of Tat expressed by the neurotropic subtype of HIV-1 virus (HIV-1 clade B) specifically induces both the release of amyloidogenic Abeta 1-42 and the accumulation of cell-bound amyloid aggregates. The results of the research rationalize testing of the ability of beta-amyloid aggregation inhibitors to attenuate HIV protein-mediated cognitive deficits in animal models of NeuroAIDS. The long-term goal of the study is to evaluate the potential benefits of anti-amyloidogenic therapies for management of cognitive dysfunction in aging HIV-1 patients.

Attenuated neurotoxicity of the transactivation-defective HIV-1 Tat protein in hippocampal cell cultures

This study reports that the cysteine 22-->glycine 22 substitution in the HIV-1 Tat 1-86 B significantly attenuates its neurotoxicity. Consistent with previous studies, direct interactions of rat hippocampal cells with Tat 1-86 B were shown to cause dose-dependent and time-dependent neurotoxicity associated with activation of caspases from the mitochondrial apoptotic pathway. Despite the similar binding/uptake properties, Cys22 Tat 1-86 B failed to induce significant neurotoxicity and activation of caspases 9 and 3/7 in hippocampal primary cultures. Results of the study underscore the important role of cysteine-rich domain in mechanism of Tat-mediated neurotoxicity.