HIV-1 coreceptors CCR5 and CXCR4 both mediate neuronal cell death but CCR5 paradoxically can also contribute to protection

CCR5 deficiency accelerates lipopolysaccharide-induced astrogliosis, amyloid-beta deposit and impaired memory function

Chemokine receptors are implicated in inflammation and immune responses. Neuro-inflammation is associated with activation of astrocyte and amyloid-beta (Aβ) generations that lead to pathogenesis of Alzheimer disease (AD). Previous our study showed that deficiency of CC chemokine receptor 5 (CCR5) results in activation of astrocytes and Aβ deposit, and thus memory dysfunction through increase of CC chemokine receptor 2 (CCR2) expression. CCR5 knockout mice were used as an animal model with memory dysfunction. For the purpose LPS was injected i.p. daily (0.25 mg/kg/day). The memory dysfunctions were much higher in LPS-injected CCR5 knockout mice compared to CCR5 wild type mice as well as non-injected CCR5 knockout mice. Associated with severe memory dysfuction in LPS injected CCR5 knockout mice, LPS injection significant increase expression of inflammatory proteins, astrocyte activation, expressions of β-secretase as well as Aβ deposition in the brain of CCR5 knockout mice as compared with that of CCR5 wild type mice. In CCR5 knockout mice, CCR2 expressions were high and co-localized with GFAP which was significantly elevated by LPS. Expression of monocyte chemoattractant protein-1 (MCP-1) which ligands of CCR2 also increased by LPS injection, and increment of MCP-1 expression is much higher in CCR5 knockout mice. BV-2 cells treated with CCR5 antagonist, D-ala-peptide T-amide (DAPTA) and cultured astrocytes isolated from CCR5 knockout mice treated with LPS (1 μg/ml) and CCR2 antagonist, decreased the NF-ĸB activation and Aβ level. These findings suggest that the deficiency of CCR5 enhances response of LPS, which accelerates to neuro-inflammation and memory impairment.

In vitro modeling of HIV proviral activity in microglia

Microglia, the resident macrophages of the brain, play a key role in the pathogenesis of HIV-associated neurocognitive disorders (HAND) due to their productive infection by HIV. This results in the release of neurotoxic viral proteins and pro-inflammatory compounds which negatively affect the functionality of surrounding neurons. Because models of HIV infection within the brain are limited, we aimed to create a novel microglia cell line with an integrated HIV provirus capable of recreating several hallmarks of HIV infection. We utilized clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 gene editing technology and integrated a modified HIV provirus into CHME-5 immortalized microglia to create HIV-NanoLuc CHME-5. In the modified provirus, the Gag-Pol region is replaced with the coding region for NanoLuciferase (NanoLuc), which allows for the rapid assay of HIV long terminal repeat activity using a luminescent substrate, while still containing the necessary genetic material to produce established neurotoxic viral proteins (e.g. tat, nef, gp120). We confirmed that HIV-NanoLuc CHME-5 microglia express NanoLuc, along with the HIV viral protein Nef. We subsequently exposed these cells to a battery of experiments to modulate the activity of the provirus. Proviral activity was enhanced by treating the cells with pro-inflammatory factors lipopolysaccharide (LPS) and tumor necrosis factor alpha and by overexpressing the viral regulatory protein Tat. Conversely, genetic modification of the toll-like receptor-4 gene by CRISPR/Cas9 reduced LPS-mediated proviral activation, and pharmacological application of NF-κB inhibitor sulfasalazine similarly diminished proviral activity. Overall, these data suggest that HIV-NanoLuc CHME-5 may be a useful tool in the study of HIV-mediated neuropathology and proviral regulation.

Transgenic mice expressing HIV-1 envelope protein gp120 in the brain as an animal model in neuroAIDS research

HIV-1 infection causes injury to the central nervous system (CNS) and is often associated with neurocognitive disorders. One model for brain damage seen in AIDS patients is the transgenic (tg) mouse expressing a soluble envelope protein gp120 of HIV-1 LAV in the brain in astrocytes under the control of the promoter of glial fibrillary acidic protein. These GFAP-gp120tg mice manifest several key neuropathological features observed in AIDS brains, such as decreased synaptic and dendritic density, increased numbers of activated microglia, and pronounced astrocytosis. Several recent studies show that brains of GFAP-gp120tg mice and neurocognitively impaired HIV patients share also a significant number of differentially regulated genes, activation of innate immunity and other cellular signaling pathways, disturbed neurogenesis, and learning deficits. These findings support the continued relevance of the GFAP-gp120tg mouse as a useful model to investigate neurodegenerative mechanisms and develop therapeutic strategies to mitigate the consequences associated with HIV infection of the CNS, neuroAIDS, and HAND.

IFNβ Protects Neurons from Damage in a Murine Model of HIV-1 Associated Brain Injury

Infection with human immunodeficiency virus-1 (HIV-1) causes brain injury. Type I interferons (IFNα/β) are critical mediators of any anti-viral immune response and IFNβ has been implicated in the temporary control of lentiviral infection in the brain. Here we show that transgenic mice expressing HIV-1 envelope glycoprotein 120 in their central nervous system (HIVgp120tg) mount a transient IFNβ response and provide evidence that IFNβ confers neuronal protection against HIVgp120 toxicity. In cerebrocortical cell cultures, neuroprotection by IFNβ against gp120 toxicity is dependent on IFNα receptor 1 (IFNAR1) and the β-chemokine CCL4, as IFNAR1 deficiency and neutralizing antibodies against CCL4, respectively, abolish the neuroprotective effects. We find in vivo that IFNβ mRNA is significantly increased in HIVgp120tg brains at 1.5, but not 3 or 6 months of age. However, a four-week intranasal IFNβ treatment of HIVgp120tg mice starting at 3.5 months of age increases expression of CCL4 and concomitantly protects neuronal dendrites and pre-synaptic terminals in cortex and hippocampus from gp120-induced damage. Moreover, in vivo and in vitro data suggests astrocytes are a major source of IFNβ-induced CCL4. Altogether, our results suggest exogenous IFNβ as a neuroprotective factor that has potential to ameliorate in vivo HIVgp120-induced brain injury.

Endocytic Trafficking of HIV gp120 is Mediated by Dynamin and Plays a Role in gp120 Neurotoxicity

Neurons that endocytose the human immunodeficiency virus-1 (HIV) protein gp120 exhibit neurite retraction and activation of caspase-3, suggesting that the endocytic process may be crucial for gp120-mediated neuronal injury. The goal of this study is to demonstrate that internalization and accumulation of gp120 play a role in its neurotoxic effects. In mammalian cells, endocytosis is primarily a dynamin-dependent process. To establish whether gp120 is endocytosed in a dynamin-dependent manner, we used fibroblasts in which deletion of dynamins was induced by tamoxifen. We observed a robust reduction of intracellular gp120 immunoreactivity in tamoxifen-treated cells. To examine whether endocytosis of gp120 is crucial for its neurotoxic effect, we blocked gp120 internalization into primary rat cortical neurons by dynasore, an inhibitor of the dynamin GTP-ase activity. We found that dynasore blocks both gp120 internalization and neurotoxicity. We then utilized gp120-loaded mesoporous silica nanoparticles to deliver gp120 intracellularly. We established that once internalized, gp120 is neurotoxic regardless of chemokine receptor activation. Our data suggest that dynamin-dependent endocytosis of gp120 is critical for its neurotoxicity.

Productive infection of human neural progenitor cells by R5 tropic HIV-1: opiate co-exposure heightens infectivity and functional vulnerability

OBJECTIVE

HIV type-1 (HIV-1) causes a spectrum of central nervous system (CNS) complications; many are worsened by opiate co-exposure. Human neural progenitor cells (hNPCs) give rise to all CNS neurons and macroglia. We tested the hypothesis that hNPC maturation and fate are altered by HIV and opiates, contributing to HIV-1-related neuropathology. Reports of hNPC infection remain controversial. We rigorously examined this question, testing whether hNPCs propogated infection, and whether HIV affected hNPCs absent their infection.

DESIGN AND METHODS

Primary hNPCs were characterized over multiple passages. Following R5 HIV-1BaL exposure, p24, Nef, and tat assays monitored infection; a serial dilution approach tested infection transfer to naive hNPCs. Bromodeoxyuridine uptake, population doubling time, and immunostaining assessed proliferation and differentiation. Morphine co-exposure assessed opiate interactions. Supernatant from HIV-1BaL-infected PBMCs (HIVsup), HIV-1BaL, and ultraviolet light-inactivated HIVsup were compared to test effects of inflammatory milieu versus virus or infection per se.

RESULTS

The hNPCs (CD4/CD8/Iba/CXC3CL1/CD11b) were infectable and could transfer infection to naive hNPCs. Infection was partly blocked by maraviroc, implicating CCR5. HIVsup reduced hNPC proliferation and caused premature differentiation into neurons/astroglia. Effects on proliferation were due to soluble factors/viral proteins, not infection per se. Morphine co-exposure exacerbated certain functional consequences of HIVsup, and sustained the infection of hNPCs.

CONCLUSION

hNPCs can be infected and propagate virus in vitro. hNPCs or their progeny may represent an underappreciated viral reservoir. Factors from infected cells alter hNPC proliferation and neural cell maturation, which likely compromises CNS structure and function. Morphine-HIV interactions may worsen dysfunction and sustain infection.

Neuronal Stress and Injury Caused by HIV-1, cART and Drug Abuse: Converging Contributions to HAND

Multiple mechanisms appear to contribute to neuronal stress and injury underlying HIV-associated neurocognitive disorders (HAND), which occur despite the successful introduction of combination antiretroviral therapy (cART). Evidence is accumulating that components of cART can itself be neurotoxic upon long-term exposure. In addition, abuse of psychostimulants, such as methamphetamine (METH), seems to compromise antiretroviral therapy and aggravate HAND. However, the combined effect of virus and recreational and therapeutic drugs on the brain is still incompletely understood. However, several lines of evidence suggest a shared critical role of oxidative stress, compromised neuronal energy homeostasis and autophagy in promotion and prevention of neuronal dysfunction associated with HIV-1 infection, cART and psychostimulant use. In this review, we present a synopsis of recent work related to neuronal stress and injury induced by HIV infection, antiretrovirals (ARVs) and the highly addictive psychostimulant METH.

HIV Glycoprotein Gp120 Impairs Fast Axonal Transport by Activating Tak1 Signaling Pathways

Sensory neuropathies are the most common neurological complication of HIV. Of these, distal sensory polyneuropathy (DSP) is directly caused by HIV infection and characterized by length-dependent axonal degeneration of dorsal root ganglion (DRG) neurons. Mechanisms for axonal degeneration in DSP remain unclear, but recent experiments revealed that the HIV glycoprotein gp120 is internalized and localized within axons of DRG neurons. Based on these findings, we investigated whether intra-axonal gp120 might impair fast axonal transport (FAT), a cellular process critical for appropriate maintenance of the axonal compartment. Significantly, we found that gp120 severely impaired both anterograde and retrograde FAT. Providing a mechanistic basis for these effects, pharmacological experiments revealed an involvement of various phosphotransferases in this toxic effect, including members of mitogen-activated protein kinase pathways (Tak-1, p38, and c-Jun N-terminal Kinase (JNK)), inhibitor of kappa-B-kinase 2 (IKK2), and PP1. Biochemical experiments and axonal outgrowth assays in cell lines and primary cultures extended these findings. Impairments in neurite outgrowth in DRG neurons by gp120 were rescued using a Tak-1 inhibitor, implicating a Tak-1 mitogen-activated protein kinase pathway in gp120 neurotoxicity. Taken together, these observations indicate that kinase-based impairments in FAT represent a novel mechanism underlying gp120 neurotoxicity consistent with the dying-back degeneration seen in DSP. Targeting gp120-based impairments in FAT with specific kinase inhibitors might provide a novel therapeutic strategy to prevent axonal degeneration in DSP.

CXCL12-induced neurotoxicity critically depends on NMDA receptor-gated and L-type Ca2+ channels upstream of p38 MAPK

Background

The chemokine receptor CXCR4 (CD184) and its natural ligand CXCL12 contribute to many physiological processes, including decisions about cell death and survival in the central nervous system. In addition, CXCR4 is a co-receptor for human immunodeficiency virus (HIV)-1 and mediates the neurotoxicity of the viral envelope protein gp120. However, we previously observed that CXCL12 also causes toxicity in cerebrocortical neurons but the cellular mechanism remained incompletely defined.

Methods

Primary neuronal-glial cerebrocortical cell cultures from rat were exposed to a neurotoxicity-inducing CXCL12 concentration for different times and the activity of the stress-associated mitogen-activated protein kinase p38 (p38 MAPK) was assessed using an in vitro kinase assay. Neurotoxicity of CXCL12 and cellular localization of p38 MAPK was analyzed by immunofluorescence microscopy. Pharmacological inhibition of NMDA-type glutamate receptor-gated ion channels (NMDAR) of l-type Ca²⁺ channels was employed during 12- and 24-h exposure to neurotoxic amounts of CXCL12 to study the effects on active p38 MAPK and neuronal survival by Western blotting and microscopy, respectively. Neurotoxicity of CXCL12 was also assessed during pharmacological inhibition of p38 MAPK.

Results

Here, we show that a neurotoxic amount of CXCL12 triggers a significant increase of endogenous p38 MAPK activity in cerebrocortical cells. Immunofluorescence and Western blotting experiments with mixed neuronal-glial and neuron-depleted glial cerebrocortical cells revealed that the majority of active/phosphorylated p38 MAPK was located in neurons. Blockade of NMDAR-gated ion channels or l-type Ca²⁺ channels both abrogated an increase of active p38 MAPK and toxicity of CXCL12 in cerebrocortical neurons. Inhibition of l-type Ca²⁺ channels with nimodipine kept the active kinase at levels not significantly different from baseline while blocking NMDAR with MK-801 strongly reduced phosphorylated p38 MAPK below baseline. Finally, we confirmed that directly blocking p38 MAPK also abrogated neurotoxicity of CXCL12.

Conclusions

Our findings link CXCL12-induced neuronal death to the regulation of NMDAR-gated ion channels and l-type Ca²⁺ channels upstream of p38 MAPK activation.

CXCR4 and NMDA Receptors Are Functionally Coupled in Rat Hippocampal Noradrenergic and Glutamatergic Nerve Endings

Previous studies had shown that the HIV-1 capsidic glycoprotein gp120 (strain IIIB) modulates presynaptic release-regulating NMDA receptors on noradrenergic and glutamatergic terminals. This study aims to assess whether the chemokine CXC4 receptors (CXCR4s) has a role in the gp120-mediated effects. The effect of CXCL12, the endogenous ligand at CXCR4, on the NMDA-mediated releasing activity was therefore investigated. Rat hippocampal synaptosomes were preloaded with [³H]noradrenaline ([³H]NA) or [³H]D-aspartate ([³H]D-Asp) and acutely exposed to CXCL12, to NMDA or to both agonists. CXCL12, inactive on its own, facilitated the NMDA-evoked tritium release. The NMDA antagonist MK-801 abolished the NMDA/CXCL12-evoked tritium release of both radiolabelled tracers, while the CXCR4 antagonist AMD 3100 halved it, suggesting that rat hippocampal nerve endings possess presynaptic release-regulating CXCR4 receptors colocalized with NMDA receptors. Accordingly, Western blot analysis confirmed the presence of CXCR4 proteins in synaptosomal plasmamembranes. In both synaptosomal preparations, CXCL12-induced facilitation of NMDA-mediated release was dependent upon PLC-mediated src-induced events leading to mobilization of Ca²⁺ from intraterminal IP₃-sensitive stores Finally, the gp120-induced facilitation of NMDA-mediated release of [³H]NA and [³H]D-Asp was prevented by AMD 3100. We propose that CXCR4s are functionally coupled to NMDA receptors in rat hippocampal noradrenergic and glutamatergic terminals and account for the gp120-induced modulation of the NMDA-mediated central effects. The NMDA/CXCR4 cross-talk could have a role in the neuropsychiatric symptoms often observed in HIV-1 positive patients.

Identification of a binding site of the human immunodeficiency virus envelope protein gp120 to neuronal-specific tubulin

Human immunodeficiency virus-1 (HIV) promotes synaptic simplification and neuronal apoptosis, and causes neurological impairments termed HIV-associated neurological disorders. HIV-associated neurotoxicity may be brought about by acute and chronic mechanisms that still remain to be fully characterized. The HIV envelope glycoprotein gp120 causes neuronal degeneration similar to that observed in HIV-associated neurocognitive disorders subjects. This study was undertaken to discover novel mechanisms of gp120 neurotoxicity that could explain how the envelope protein promotes neurite pruning. Gp120 has been shown to associate with various intracellular organelles as well as microtubules in neurons. We then analyzed lysates of neurons exposed to gp120 with liquid chromatography mass spectrometry for potential protein interactors. We found that one of the proteins interacting with gp120 is tubulin β-3 (TUBB3), a major component of neuronal microtubules. We then tested the hypothesis that gp120 binds to neuronal microtubules. Using surface plasmon resonance, we confirmed that gp120 binds with high affinity to neuronal-specific TUBB3. We have also identified the binding site of gp120 to TUBB3. We then designed a small peptide (Helix-A) that displaced gp120 from binding to TUBB3. To determine whether this peptide could prevent gp120-mediated neurotoxicity, we cross-linked Helix-A to mesoporous silica nanoparticles (Helix-A nano) to enhance the intracellular delivery of the peptide. We then tested the neuroprotective property of Helix-A nano against three strains of gp120 in rat cortical neurons. Helix-A nano prevented gp120-mediated neurite simplification as well as neuronal loss. These data propose that gp120 binding to TUBB3 could be another mechanism of gp120 neurotoxicity. We propose a novel direct mechanism of human immunodeficiency virus neurotoxicity. Our data show that the viral protein gp120 binds to neuronal specific tubulin β-3 and blocks microtubule transport. Displacing gp120 from binding to tubulin by a small peptide prevents gp120-mediated neuronal loss. Our study reveals a novel target for developing adjunct therapies against viral infection that promotes neurocognitive disorders.

HIV-1 gp120Bal down-Regulates Phosphorylated NMDA Receptor Subunit 1 in Cortical Neurons via Activation of Glutamate and Chemokine Receptors

HIV-1 envelope glycoprotein gp120 (gp120) is a major virulence protein implicated in the pathogenesis of HIV-associated neurocognitive disorders (HAND). Although gp120 has been suggested to cause synaptic and neuronal injuries by disrupting NMDA receptor (NMDAR) function, the underlying mechanism is unclear. Here, we show that gp120Bal down-regulates the phosphorylation of the NMDAR subunit1 NR1 (at Ser896 and Ser897), which is essential for NMDAR function. This effect of gp120Bal is blocked by specific antagonists of both NMDA and AMPA receptors, indicating a critical role of synaptic activation. Furthermore, AMD3100 and maraviroc, antagonists of CCR5 and CXCR4 chemokine receptors, respectively, inhibit the effect of gp120Bal on NR1, suggesting that CXCR4 and CCR5 activation are involved. These findings may provide mechanistic insights into the synaptopathogenesis caused by HIV-1 infection.

Beneficial properties of maraviroc on neuropathic pain development and opioid effectiveness in rats

Targeting chemokine signaling pathways is crucial in neuropathy development. In this study, we investigated the influence of chronic administration of maraviroc (CCR5 antagonist) on nociception and opioid effectiveness during neuropathy, which develops as a result of chronic constriction injury (CCI) of the sciatic nerve. To investigate the mechanism of action of maraviroc, we measured the expression of glial cell markers, CCR5 and certain CCR5 ligands (CCL3, CCL4, CCL5, CCL7, CCL11), in the spinal cord and dorsal root ganglia (DRG) of vehicle- and maraviroc-treated, CCI-exposed rats. Our results demonstrate that chronic intrathecal administration of maraviroc diminished neuropathic pain symptoms on day 7 post-CCI. Western blot analysis showed that maraviroc diminished protein level of Iba-1 and GFAP and reversed the up-regulated CCR5 expression observed in spinal cord and DRG after CCI. Additionally, using qRT-PCR, we demonstrated that CCR5 and some of its pronociceptive ligands (CCL3, CCL4, CCL5) increased in the spinal cord after nerve injury, and maraviroc effectively diminished those changes. However, CCL11 spinal expression was undetectable, even after injury. In vitro primary culture studies showed that CCL3, CCL4, CCL5 and CCL7 (but not CCL11) were of microglial and astroglial origin and were up-regulated after LPS stimulation. Our results indicate that maraviroc not only attenuated the development of neuropathic pain symptoms due to significant modulation of neuroimmune interactions but also intensified the analgesic properties of morphine and buprenorphine. In sum, our results suggest the pharmacological modulation of CCR5 by maraviroc as a novel therapeutic approach for co-treatment of patients receiving opioid therapy for neuropathy.

Expression of CHRFAM7A and CHRNA7 in neuronal cells and postmortem brain of HIV-infected patients: considerations for HIV-associated neurocognitive disorder

Despite the recent advances in antiretroviral therapy, human immunodeficiency virus type 1 (HIV-1) remains a global health threat. HIV-1 affects the central nervous system by releasing viral proteins that trigger neuronal death and neuroinflammation, and promotes alterations known as HIV-associated neurocognitive disorders (HAND). This disorder is not fully understood, and no specific treatments are available. Recently, we demonstrated that the HIV-1 envelope protein gp120IIIB induces a functional upregulation of the α7-nicotinic acetylcholine receptor (α7) in neuronal cells. Furthermore, this upregulation promotes cell death that can be abrogated with receptor antagonists, suggesting that α7 may play an important role in the development of HAND. The partial duplication of the gene coding for the α7, known as CHRFAM7A, negatively regulates α7 expression but its role in HIV infection has not been studied. Hence, we studied both CHRNA7 and CHRFAM7A regulation patterns in various gp120IIIB in vitro conditions. In addition, we measured CHRNA7 and CHRFAM7A expression levels in postmortem brain samples from patients suffering from different stages of HAND. Our results demonstrate the induction of CHRNA7 expression accompanied by a significant downregulation of CHRFAM7A in neuronal cells when exposed to pathophysiological concentrations of gp120IIIB. Our results suggest a dysregulation of CHRFAM7A and CHRNA7 expressions in the basal ganglia from postmortem brain samples of HIV+ subjects and expand the current knowledge about the consequences of HIV infection in the brain.

MTHFSD and DDX58 are novel RNA-binding proteins abnormally regulated in amyotrophic lateral sclerosis

Tar DNA-binding protein 43 (TDP-43) is an RNA-binding protein normally localized to the nucleus of cells, where it elicits functions related to RNA metabolism such as transcriptional regulation and alternative splicing. In amyotrophic lateral sclerosis, TDP-43 is mislocalized from the nucleus to the cytoplasm of diseased motor neurons, forming ubiquitinated inclusions. Although mutations in the gene encoding TDP-43, TARDBP, are found in amyotrophic lateral sclerosis, these are rare. However, TDP-43 pathology is common to over 95% of amyotrophic lateral sclerosis cases, suggesting that abnormalities of TDP-43 play an active role in disease pathogenesis. It is our hypothesis that a loss of TDP-43 from the nucleus of affected motor neurons in amyotrophic lateral sclerosis will lead to changes in RNA processing and expression. Identifying these changes could uncover molecular pathways that underpin motor neuron degeneration. Here we have used translating ribosome affinity purification coupled with microarray analysis to identify the mRNAs being actively translated in motor neurons of mutant TDP-43(A315T) mice compared to age-matched non-transgenic littermates. No significant changes were found at 5 months (presymptomatic) of age, but at 10 months (symptomatic) the translational profile revealed significant changes in genes involved in RNA metabolic process, immune response and cell cycle regulation. Of 28 differentially expressed genes, seven had a ≥ 2-fold change; four were validated by immunofluorescence labelling of motor neurons in TDP-43(A315T) mice, and two of these were confirmed by immunohistochemistry in amyotrophic lateral sclerosis cases. Both of these identified genes, DDX58 and MTHFSD, are RNA-binding proteins, and we show that TDP-43 binds to their respective mRNAs and we identify MTHFSD as a novel component of stress granules. This discovery-based approach has for the first time revealed translational changes in motor neurons of a TDP-43 mouse model, identifying DDX58 and MTHFSD as two TDP-43 targets that are misregulated in amyotrophic lateral sclerosis.

Antiretrovirals, Methamphetamine, and HIV-1 Envelope Protein gp120 Compromise Neuronal Energy Homeostasis in Association with Various Degrees of Synaptic and Neuritic Damage

HIV-1 infection frequently causes HIV-associated neurocognitive disorders (HAND) despite combination antiretroviral therapy (cART). Evidence is accumulating that components of cART can themselves be neurotoxic upon long-term exposure. In addition, abuse of psychostimulants, such as methamphetamine, seems to aggravate HAND and compromise antiretroviral therapy. However, the combined effect of virus and recreational and therapeutic drugs on the brain is poorly understood. Therefore, we exposed mixed neuronal-glial cerebrocortical cells to antiretrovirals (ARVs) (zidovudine [AZT], nevirapine [NVP], saquinavir [SQV], and 118-D-24) of four different pharmacological categories and to methamphetamine and, in some experiments, the HIV-1 gp120 protein for 24 h and 7 days. Subsequently, we assessed neuronal injury by fluorescence microscopy, using specific markers for neuronal dendrites and presynaptic terminals. We also analyzed the disturbance of neuronal ATP levels and assessed the involvement of autophagy by using immunofluorescence and Western blotting. ARVs caused alterations of neurites and presynaptic terminals primarily during the 7-day incubation and depending on the specific compounds and their combinations with and without methamphetamine. Similarly, the loss of neuronal ATP was context specific for each of the drugs or combinations thereof, with and without methamphetamine or viral gp120. Loss of ATP was associated with activation of AMP-activated protein kinase (AMPK) and autophagy, which, however, failed to restore normal levels of neuronal ATP. In contrast, boosting autophagy with rapamycin prevented the long-term drop of ATP during exposure to cART in combination with methamphetamine or gp120. Our findings indicate that the overall positive effect of cART on HIV infection is accompanied by detectable neurotoxicity, which in turn may be aggravated by methamphetamine.

Novel p75 neurotrophin receptor ligand stabilizes neuronal calcium, preserves mitochondrial movement and protects against HIV associated neuropathogenesis

Human immunodeficiency virus (HIV) rapidly penetrates into the brain and establishes a persistent infection of macrophages/microglia. Activation of these cells by HIV results in the secretion of soluble factors that destabilize neuronal calcium homeostasis, encourage oxidative stress and result in neural damage. This damage is thought to underlie the cognitive-motor dysfunction that develops in many HIV-infected patients. Studies have suggested that neurotrophins may protect neurons from the toxic effects of HIV-associated proteins. To better understand the pathogenic mechanisms and the neuroprotective potential of neurotrophin ligands, we evaluated neuronal damage, calcium homeostasis and mitochondrial functions after exposure of cultured rat neurons directly to HIV gp120 or to conditioned medium from human monocyte-derived macrophages treated with gp120. We then assessed the ability of a new non-peptide p75 neurotrophin receptor ligand, LM11A-31, to stabilize calcium homeostasis and prevent the development of pathology. Each toxic challenge resulted in a delayed accumulation of intracellular calcium coupled to a decrease in the rate of calcium clearance from the cell. The delayed calcium accumulation correlated with the development of focal dendritic swellings (beading), cytoskeletal damage and impaired movement of mitochondria. Addition of LM11A-31 to the cultures at nanomolar concentrations eliminated cell death, significantly reduced the pathology, suppressed the delayed accumulation of calcium and restored mitochondrial movements. The potent neuroprotection and the stabilization of calcium homeostasis indicate that LM11A-31 may have excellent potential for the treatment of HIV-associated neurodegeneration.

Chronic morphine and HIV-1 Tat promote differential central nervous system trafficking of CD3+ and Ly6C+ immune cells in a murine Streptococcus pneumoniae infection model

Background

Persistent systemic infection results in excessive trafficking of peripheral immune cells into the central nervous system (CNS), thereby contributing to sustained neuroinflammation that leads to neurocognitive deficits. In this study, we explored the role of opportunistic systemic infection with Streptococcus pneumoniae in the recruitment of peripheral leukocytes into the CNS and its contribution to HIV-1-associated neurocognitive disorders in opioid-dependent individuals.

Methods

Wild-type B6CBAF1 (wt), μ-opioid receptor knockout (MORKO), FVB/N luciferase transgenic, and Toll-like receptor 2 and 4 knockout (TLR2KO and TLR4KO) mice were subcutaneously implanted with morphine/placebo pellet followed by HIV-1 Transactivator of transcription (Tat) protein injection intravenously and S. pneumoniae administration intraperitoneally. On postoperative day 5, brains perfused with phosphate-buffered saline were harvested and subjected to immunohistochemistry (for bacterial trafficking and chemokine ligand generation), flow cytometry (for phenotypic characterization of CNS trafficked immune cells), Western blot, and real-time PCR (for ligand expression).

Results

Our results show differential leukocyte trafficking of T lymphocytes (CD3+) and inflammatory monocytes (Ly6C+) into the CNS of mice treated with morphine, HIV-1 Tat, and/or S. pneumoniae. In addition, we demonstrate a Trojan horse mechanism for bacterial dissemination across the blood-brain barrier into the CNS by monocytes. Activation of TLRs on microglia induced a chemokine gradient that facilitated receptor-dependent trafficking of peripheral immune cells into the CNS. HIV-1 Tat induced trafficking of Ly6C+ and CD3+ cells into the CNS; infection with S. pneumoniae facilitated infiltration of only T lymphocytes into the CNS. We also observed differential chemokine secretion in the CNS, with CCL5 being the predominant chemokine following HIV-1 Tat treatment, which was potentiated further with morphine. S. pneumoniae alone led to preferential induction of CXCL12. Furthermore, we attributed a regulatory role for TLRs in the chemokine-mediated trafficking of leukocytes into the CNS. Chronic morphine and HIV-1 Tat, in the context of systemic S. pneumoniae co-infection, differentially modulated induction of TLR2/4, which consequently facilitated trafficking of TLR2 → CD3 + CCR5+ and TLR4 → Ly6C+(CCR5+/CXCR4+) immune cells into the CNS.

Conclusion

Our murine study suggests that secondary infection in opioid-dependent individuals infected with HIV-1 augments peripheral leukocyte trafficking as a consequence of sustained chemokine gradients in the CNS.

Pharmacological induction of CCL5 in vivo prevents gp120-mediated neuronal injury

The human immunodeficiency virus (HIV) envelope protein gp120 promotes neuronal injury which is believed to cause HIV-associated neurocognitive disorders. Therefore, blocking the neurotoxic effect of gp120 may lead to alternative strategies to reduce the neurotoxic effect of HIV. In vitro, the neurotoxic effect of M-tropic gp120BaL is reduced by the chemokine CCL5, the natural ligand of CCR5 receptors. To determine whether CCL5 reduces the toxic effect of gp120BaL in vivo, animals were intrastriatally injected with lentiviral vectors overexpressing CCL5 prior to an intrastriatal injection of gp120BaL (400 ng). Neuronal injury was determined by silver staining, cleaved caspase-3 and TUNEL. Overexpression of CCL5 decreased gp120-mediated neuronal injury. CCL5 expression can be up-regulated by chronic morphine. Therefore, we examined whether morphine reduces the neurotoxic effect of gp120BaL. Rats stereotaxically injected with gp120BaL into the striatum received saline or chronic morphine for five days (10 mg/kg escalating to 30 mg/kg twice a day). Morphine-treated rats showed a decrease in all markers used to determine neuronal degeneration compared to saline-treated rats. The neuroprotective effect of morphine was significantly attenuated by expressing CCL5 shRNA. Our results suggest that compounds that increase the endogenous production of CCL5 may be used to reduce the pathogenesis of HIV-associated neurocognitive disorders.

CCR5 knockout prevents neuronal injury and behavioral impairment induced in a transgenic mouse model by a CXCR4-using HIV-1 glycoprotein 120

The innate immune system has been implicated in several neurodegenerative diseases, including HIV-1-associated dementia. In this study, we show that genetic ablation of CCR5 prevents microglial activation and neuronal damage in a transgenic model of HIV-associated brain injury induced by a CXCR4-using viral envelope gp120. The CCR5 knockout (KO) also rescues spatial learning and memory in gp120-transgenic mice. However, the CCR5KO does not abrogate astrocytosis, indicating it can occur independently from neuronal injury and behavioral impairment. To characterize further the neuroprotective effect of CCR5 deficiency we performed a genome-wide gene expression analysis of brains from HIVgp120tg mice expressing or lacking CCR5 and nontransgenic controls. A comparison with a human brain microarray study reveals that brains of HIVgp120tg mice and HIV patients with neurocognitive impairment share numerous differentially regulated genes. Furthermore, brains of CCR5 wild-type and CCR5KO gp120tg mice express markers of an innate immune response. One of the most significantly upregulated factors is the acute phase protein lipocalin-2 (LCN2). Using cerebrocortical cell cultures, we find that LCN2 is neurotoxic in a CCR5-dependent fashion, whereas inhibition of CCR5 alone is not sufficient to abrogate neurotoxicity of a CXCR4-using gp120. However, the combination of pharmacologic CCR5 blockade and LCN2 protects neurons from toxicity of a CXCR4-using gp120, thus recapitulating the finding in CCR5-deficient gp120tg mouse brain. Our study provides evidence for an indirect pathologic role of CCR5 and a novel protective effect of LCN2 in combination with inhibition of CCR5 in HIV-associated brain injury.

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.

PACAP27 is protective against tat-induced neurotoxicity

Human immunodeficiency virus type-1 (HIV) infection of the central nervous system promotes neuronal injury and apoptosis that culminate in HIV-associated neurocognitive disorders (HAND). Viral proteins, such as transactivator of transcription (Tat), have emerged as leading candidates to explain HIV-mediated neurotoxicity, though the mechanism remains unclear. To determine the effects of Tat, rat cortical neurons were exposed to nanomolar concentrations of Tat for various time points. Within a few hours, Tat induced the production of reactive oxygen species (ROS), and other indices of mitochondrial destabilization. In addition, we observed a significant induction of DNA double-strand breaks (DSBs) by Tat. We next investigated the neuroprotective activity of the pituitary adenylate cyclase-activating polypeptide 27 (PACAP27) against these cardinal features of Tat-induced neurodegeneration. PACAP27 (100 nM) inhibited all Tat-mediated toxic effects including DNA DSBs. Importantly, PACAP27 prevented the induction of neuronal loss induced by Tat. The neuroprotective effect of PACAP27 is correlated with its ability to release the anti-apoptotic chemokine CCL5. Our data support a mechanism of Tat neurotoxicity in which Tat induces mitochondrial destabilization, thus increasing the release of ROS, which causes DNA DSBs leading to cell death. PACAP27, through CCL5, mitigates the effects of Tat-induced neuronal dysfunction, suggesting that PACAP27 could be a new strategy for an adjunct therapy against HIV-associated neurocognitive disorders.

CCR5 inhibition prevents cardiac dysfunction in the SIV/macaque model of HIV

Background

Diastolic dysfunction is a highly prevalent cardiac abnormality in asymptomatic as well as ART‐treated human immunodeficiency virus (HIV) patients. Although the mechanisms underlying depressed cardiac function remain obscure, diastolic dysfunction in SIV‐infected rhesus macaques is highly correlated with myocardial viral load. As cardiomyocytes are not productively infected, damage may be an indirect process attributable to a combination of pro‐inflammatory mediators and viral proteins.

Methods and Results

Given the diverse roles of CCR5 in mediating recruitment of leukocytes to inflammatory sites and serving as a receptor for HIV entry into cells, we investigated the role of CCR5 in the SIV/macaque model of diastolic dysfunction. We found that in SIV‐infected macaques, CCR5 inhibition dramatically impacted myocardial viral load measured by qRT‐PCR and prevented diastolic dysfunction measured by echocardiography. Complementary in vitro experiments using fluorescence microscopy showed that CCR5 ligands impaired contractile function of isolated cardiomyocytes, thus identifying CCR5 signaling as a novel mediator of impaired cardiac mechanical function.

Conclusions

Together, these findings incriminate SIV/HIV gp120‐CCR5 as well as chemokine‐CCR5 interactions in HIV‐associated cardiac dysfunction. These findings also have important implications for the treatment of HIV‐infected individuals: in addition to antiviral properties and reduced chemokine‐mediated recruitment and activation of inflammatory cells, CCR5 inhibition may provide a cardioprotective benefit by preventing cardiomyocyte CCR5 signaling.

Neuroimmune mechanisms of alcohol and drug addiction

Alcohol and other drugs of abuse have significant impacts on the neuroimmune system. Studies have demonstrated that drugs of abuse interact with the neuroimmune system and alter neuroimmune gene expression and signaling, which in turn contribute to various aspects of addiction. As the key component of the CNS immune system, neuroimmune factors mediate neuroinflammation and modulate a wide range of brain function including neuronal activity, endocrine function, and CNS development. These neuromodulatory properties of immune factors, together with their essential role in neuroinflammation, provide a new framework to understand neuroimmune mechanisms mediating brain functional and behavioral changes contributing to addiction. This chapter highlights recent advances in understanding neuroimmune changes associated with exposure to alcohol and other drugs of abuse, including opiates, marijuana, methamphetamine, and cocaine. It provides a brief overview on what we know about neuroimmune signaling and its role in drug action and addiction.

Animal models for depression associated with HIV-1 infection

Antiretroviral therapy has greatly extended the lifespan of people living with human immunodeficiency virus (PLHIV). As a result, the long-term effects of HIV infection, in particular those originating in the central nervous system (CNS), such as HIV associated depression, have gained importance. Animal models for HIV infection have proved very useful for understanding the disease and developing treatment strategies. However, HIV associated depression remains poorly understood and so far there is neither a fully satisfactory animal model, nor a pathophysiologically guided treatment for this condition. Here we review the neuroimmunological, neuroendocrine, neurotoxic and neurodegenerative basis for HIV depression and discuss strategies for employing HIV animal models, in particular humanized mice which are susceptible to HIV infection, for the study of HIV depression.

CCL5 and cytokine expression in the rat brain: differential modulation by chronic morphine and morphine withdrawal

Opioids have been shown to influence the immune system and to promote the expression of pro-inflammatory cytokines in the central nervous system. However, recent data have shown that activation of opioid receptors increases the expression and release of the neuroprotective chemokine CCL5 from astrocytes in vitro. To further define the interaction between CCL5 and inflammation in response to opioids, we have examined the effect of chronic morphine and morphine withdrawal on the in vivo expression of CCL5 as well as of pro-inflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Rats undergoing a chronic morphine paradigm (10 mg/kg increasing to 30 mg/kg, twice a day for 5 days) showed a twofold increase of CCL5 protein and mRNA within the cortex and striatum. No changes were observed in the levels of IL-1β and TNF-α. Naltrexone blocked the effect of morphine. A chronic morphine paradigm with no escalating doses (10 mg/kg, twice a day) did not alter CCL5 levels compared to saline-treated animals. On the contrary, rats undergoing spontaneous morphine withdrawal exhibited lower levels of CCL5 within the cortex as well as increased levels of pro-inflammatory cytokines and Iba-1 positive cells than saline-treated rats. Overall, these data suggest that morphine withdrawal may promote cytokines and other inflammatory responses that have the potential of exacerbating neuronal damage.

Impaired neurogenesis and neurite outgrowth in an HIV-gp120 transgenic model is reversed by exercise via BDNF production and Cdk5 regulation

Human immunodeficiency virus (HIV) infection-associated neurocognitive disorders is accompanied with brain atrophy. In these patients, impairment of adult neurogenesis and neurite outgrowth in the hippocampus may contribute to cognitive dysfunction. Although running exercises can enhance neurogenesis and normalize neurite outgrowth, the underlying molecular mechanisms are not well understood. The HIV envelope protein, gp120, has been shown to impair neurogenesis. Using a gp120 transgenic mouse model, we demonstrate that exercise stimulated neural progenitor cell (NPC) proliferation in the hippocampal dentate gyrus and increased the survival rate and generation of newborn cells. However, sustained exercise activity was necessary as the effects were reversed by detraining. Exercise also normalized dendritic outgrowth of neurons. Furthermore, it increased the expression of hippocampal brain-derived neurotrophic factor (BDNF) and normalized hyperactivation of cyclin-dependent kinase 5 (Cdk5). Hyperactivated Cdk5 or gp120 treatment led to aberrant neurite outgrowth and BDNF treatment normalized the neurite outgrowth in NPC cultures. These results suggest that sustained exercise has trophic activity on the neuronal lineage which is mediated by Cdk5 modulation of the BDNF pathway.

Chemokine co-receptor CCR5/CXCR4-dependent modulation of Kv2.1 channel confers acute neuroprotection to HIV-1 glycoprotein gp120 exposure

Infection with human immunodeficiency virus-1 (HIV-1) within the brain has long been known to be associated with neurodegeneration and neurocognitive disorder (referred as HAND), a condition characterized in its early stages by declining cognitive function and behavioral disturbances. Mechanistically, the HIV-1 coat glycoprotein 120 (gp120) has been suggested to be a critical factor inducing apoptotic cell death in neurons via the activation of p38 mitogen-activated protein kinase (MAPK), upon chronic exposure to the virus. Here we show that acute exposure of neurons to HIV-1 gp120 elicits a homeostatic response, which provides protection against non-apoptotic cell death, involving the major somatodendritic voltage-gated K⁺ (Kv) channel Kv2.1 as the key mediator. The Kv2.1 channel has recently been shown to provide homeostatic control of neuronal excitability under conditions of seizures, ischemia and neuromodulation/neuroinflammation. Following acute exposure to gp120, cultured rat hippocampal neurons show rapid dephosphorylation of the Kv2.1 protein, which ultimately leads to changes in specific sub-cellular localization and voltage-dependent channel activation properties of Kv2.1. Such modifications in Kv2.1 are dependent on the activation of the chemokine co-receptors CCR5 and CXCR4, and subsequent activation of the protein phosphatase calcineurin. This leads to the overall suppression of neuronal excitability and provides neurons with a homeostatic protective mechanism. Specific blockade of calcineurin and Kv2.1 channel activity led to significant enhancement of non-apoptotic neuronal death upon acute gp120 treatment. These observations shed new light on the intrinsic homeostatic mechanisms of neuronal resilience during the acute stages of neuro-HIV infections.

Redox pioneer: Professor Stuart A. Lipton

[Figure: see text] Stuart A. Lipton, M.D., Ph.D. is recognized here as a Redox Pioneer because of his publication of four articles that have been cited more than 1000 times, and 96 reports which have been cited more than 100 times. In the redox field, Dr. Lipton is best known for his work on the regulation by S-nitrosylation of the NMDA-subtype of neuronal glutamate receptor, which provided early evidence for in situ regulation of protein activity by S-nitrosylation and a prototypic model of allosteric control by this post-translational modification. Over the past several years, Lipton's group has pioneered the discovery of aberrant protein nitrosylation that may contribute to a number of neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis (Lou Gehrig's disease). In particular, the phenotypic effects of rare genetic mutations may be understood to be enhanced or mimicked by nitrosative (and oxidative) modifications of cysteines and thereby help explain common sporadic forms of disease. Thus, Lipton has contributed in a major way to the understanding that nitrosative stress may result from modifications of specific proteins and may operate in conjunction with genetic mutation to create disease phenotype. Lipton (collaborating with Jonathan S. Stamler) has also employed the concept of targeted S-nitrosylation to produce novel neuroprotective drugs that act at allosteric sites in the NMDA receptor. Lipton has won a number of awards, including the Ernst Jung Prize in Medicine, and is an elected fellow of the AAAS. Antioxid. Redox Signal. 19, 757-764.

Distinct modifications in Kv2.1 channel via chemokine receptor CXCR4 regulate neuronal survival-death dynamics

The chemokine stromal cell-derived factor-1α (SDF-1α) has multiple effects on neuronal activity, survival, and death under conditions that generate a proinflammatory microenvironment within the brain, via signaling through C-X-C-type chemokine receptor 4 (CXCR4), although the underlying cellular/molecular mechanisms are unclear. Using rat hippocampal neurons, we investigated distinct modifications in the voltage-gated K⁺ (Kv) channel Kv2.1 in response to short- and long-term SDF-1α/CXCR4-mediated signaling as an underlying mechanism for CXCR4-dependent regulation of neuronal survival and death. Acute exposure of neurons to SDF-1α led to dynamic dephosphorylation and altered localization of Kv2.1 channel, resulting in enhanced voltage-dependent activation of Kv2.1-based delayed-rectifier Kv currents (I(DR)). These changes were dependent on CXCR4- and/or NMDA receptor-mediated activation of calcineurin and provide neuroprotection. However, prolonged SDF-1α treatment leads to CXCR4-mediated activation of p38 mitogen-activated protein kinase, resulting in phosphorylation of Kv2.1 at S800 and enhanced surface trafficking of the channel protein, resulting in increased I(DR)/Kv2.1 current density. This, in combination with sustained dephosphorylation-induced enhancement of the voltage-dependent activation of I(DR)/Kv2.1, predisposed neurons to excessive K⁺ efflux, a vital step for the neuronal apoptotic program. Such apoptotic death was dependent on CXCR4 and Kv2.1 function and was absent in cells expressing the Kv2.1-S800A mutant channel. Furthermore, similar modifications in Kv2.1 and CXCR4/Kv2.1-dependent apoptosis were observed following treatment of neurons with the human immunodeficiency virus-1 (HIV-1) glycoprotein gp120. Therefore, distinct modifications in Kv2.1 in response to short- and long-term CXCR4-mediated signaling could provide a basis for neuroprotection or apoptosis in neuropathologies, such as neuroinflammation, stroke, brain tumors, and HIV-associated neurodegeneration.

When human immunodeficiency virus meets chemokines and microglia: neuroprotection or neurodegeneration?

Chemokines are chemotactic cytokines that were originally discovered as promoters of leukocyte proliferation and mobility. In recent years, however, evidence has demonstrated constitutive expression of chemokines and chemokine receptors in a variety of cells in the central and peripheral nervous system and has proposed a role for chemokines in neurodegenerative diseases characterized by inflammation and microglia proliferation. In addition, chemokine receptors, and in particular CXCR4 and CCR5, mediate human immunodeficiency virus type 1 (HIV) infection of immunocompetent cells as well as microglia. Subsequently, HIV, through a variety of mechanisms, promotes synapto-dendritic alterations and neuronal loss that ultimately lead to motor and cognitive impairments. These events are accompanied by microglia activation. Nevertheless, a microglia-mediated mechanism of neuronal degeneration alone cannot fully explain some of the pathological features of HIV infected brain such as synaptic simplification. In this article, we present evidence that some of the microglia responses to HIV are beneficial and neuroprotective. These include the ability of microglia to release anti-inflammatory cytokines, to remove dying cells and to promote axonal sprouting.

Platelet-derived growth factor (PDGF)-BB-mediated induction of monocyte chemoattractant protein 1 in human astrocytes: implications for HIV-associated neuroinflammation

Chemokine (C-C motif) ligand 2, also known as monocyte chemoattractant protein 1 (MCP-1) is an important factor for the pathogenesis of HIV-associated neurocognitive disorders (HAND). The mechanisms of MCP-1-mediated neuropathogenesis, in part, revolve around its neuroinflammatory role and the recruitment of monocytes into the central nervous system (CNS) via the disrupted blood-brain barrier (BBB). We have previously demonstrated that HIV-1/HIV-1 Tat upregulate platelet-derived growth factor (PDGF)-BB, a known cerebrovascular permeant; subsequently, the present study was aimed at exploring the regulation of MCP-1 by PDGF-BB in astrocytes with implications in HAND. Specifically, the data herein demonstrate that exposure of human astrocytes to HIV-1 LAI elevated PDGF-B and MCP-1 levels. Furthermore, treating astrocytes with the human recombinant PDGF-BB protein significantly increased the production and release of MCP-1 at both the RNA and protein levels. MCP-1 induction was regulated by activation of extracellular-signal-regulated kinase (ERK)1/2, c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein (MAP) kinases and phosphatidylinositol 3-kinase (PI3K)/Akt pathways and the downstream transcription factor, nuclear factor κB (NFκB). Chromatin immunoprecipitation (ChIP) assays demonstrated increased binding of NFκB to the human MCP-1 promoter following PDGF-BB exposure. Conditioned media from PDGF-BB-treated astrocytes increased monocyte transmigration through human brain microvascular endothelial cells (HBMECs), an effect that was blocked by STI-571, a tyrosine kinase inhibitor (PDGF receptor (PDGF-R) blocker). PDGF-BB-mediated release of MCP-1 was critical for increased permeability in an in vitro BBB model as evidenced by blocking antibody assays. Since MCP-1 is linked to disease severity, understanding its modulation by PDGF-BB could aid in understanding the proinflammatory responses in HAND. These results suggest that astrocyte activation by PDGF-BB exaggerates monocyte recruitment into the brain via MCP-1 and underscores the critical role astrocytes play in HAND.

Opiate drug use and the pathophysiology of neuroAIDS

Opiate abuse and HIV-1 have been described as interrelated epidemics, and even in the advent of combined anti-retroviral therapy, the additional abuse of opiates appears to result in greater neurologic and cognitive deficits. The central nervous system (CNS) is particularly vulnerable to interactive opiate-HIV-1 effects, in part because of the unique responses of microglia and astroglia. Although neurons are principally responsible for behavior and cognition, HIV-1 infection and replication in the brain is largely limited to microglia, while astroglia and perhaps glial progenitors can be latently infected. Thus, neuronal dysfunction and injury result from cellular and viral toxins originating from HIV-1 infected/exposed glia. Importantly, subsets of glial cells including oligodendrocytes, as well as neurons, express µ-opioid receptors and therefore can be direct targets for heroin and morphine (the major metabolite of heroin in the CNS), which preferentially activate µ-opioid receptors. This review highlights findings that neuroAIDS is a glially driven disease, and that opiate abuse may act at multiple glial-cell types to further compromise neuron function and survival. The ongoing, reactive cross-talk between opiate drug and HIV-1 co-exposed microglia and astroglia appears to exacerbate critical proinflammatory and excitotoxic events leading to neuron dysfunction, injury, and potentially death. Opiates enhance synaptodendritic damage and a loss of synaptic connectivity, which is viewed as the substrate of cognitive deficits. We especially emphasize that opioid signaling and interactions with HIV-1 are contextual, differing among cell types, and even within subsets of the same cell type. For example, astroglia even within a single brain region are heterogeneous in their expression of µ-, δ-, and κ-opioid receptors, as well as CXCR4 and CCR5, and Toll-like receptors. Thus, defining the distinct targets engaged by opiates in each cell type, and among brain regions, is critical to an understanding of how opiate abuse exacerbates neuroAIDS.

Isobaric tagging-based quantification by mass spectrometry of differentially regulated proteins in synaptosomes of HIV/gp120 transgenic mice: implications for HIV-associated neurodegeneration

HIV/gp120 transgenic mice manifest neuropathological features similar to HIV-associated neurocognitive disorders (HAND) in humans, including astrogliosis, microglia activation, and decreased neuronal synapses. Here, proteomic screening of synaptosomes from HIV/gp120 transgenic mice was conducted to determine potential neuronal markers and drug targets associated with HAND. Synaptosomes from 13 month-old wild-type (wt) and HIV/gp120 transgenic mouse cortex were subjected to tandem mass tag (TMT) labeling and subsequent analysis using an LTQ-Orbitrap mass spectrometer in pulsed-Q dissociation (PQD) mode for tandem mass spectrometry (MS/MS). A total of 1301 proteins were identified in both wt and HIV/gp120 transgenic mice. Three of the most differentially-regulated proteins were validated by immunoblotting. To elucidate putative pathways associated with the proteomic profile, 107 proteins manifesting a ≥1.5 fold change in expression were analyzed using a bioinformatics pathway analysis tool. This analysis revealed direct or indirect involvement of the phosphotidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, a well-known neuronal survival pathway. Immunoblots confirmed a lower phospho (p)Akt/Akt ratio in synaptosomes from HIV/gp120 transgenic animals compared to wt, suggesting that this neuroprotective pathway was inactivated in the HIV/gp120 transgenic brain. Based on this information, we then compared immunoblots of pAkt/Akt in the forebrains of these mice as well as in human postmortem brain. We observed a significant decrease in the pAkt/Akt ratio in synaptosomes and forebrain of HIV/gp120 transgenic compared to wt mice, and a similar decrease in human forebrain from HAND patients compared to neurologically unimpaired HIV+ and HIV- controls. Moreover, mechanistic insight into an additional pathway for decreased Akt activity in HIV/gp120 mouse brains and human HAND brains was shown to occur via S-nitrosylation of Akt protein, a posttranslational modification known to inhibit Akt activity and contribute to neuronal cell injury and death. Thus, MS proteomic profiling in the HIV/gp120 transgenic mouse predicted dysregulation of the PI3K/Akt pathway observed in human brains with HAND, providing evidence that this mouse is a useful disease model and that the Akt pathway may provide multiple drug targets for the treatment of HIV-related dementias.

Genetic knockouts suggest a critical role for HIV co-receptors in models of HIV gp120-induced brain injury

Infection with HIV-1 frequently affects the brain and causes NeuroAIDS prior to the development of overt AIDS. The HIV-1 envelope protein gp120 interacts with host CD4 and chemokine co-receptors to initiate infection of macrophages and lymphocytes. In addition, the virus or fragments of it, such as gp120, cause macrophages to produce neurotoxins and trigger neuronal injury and apoptosis. Moreover, the two major HIV co-receptors, the chemokine receptors CCR5 and CXCR4, serve numerous physiological functions and are widely expressed beyond immune cells, including cells in the brain. Therefore, HIV co-receptors are poised to play a direct and indirect part in the development of NeuroAIDS. Although rodents are not permissive to infection with wild type HIV-1, viral co-receptors - more than CD4 - are highly conserved between species, suggesting the animals can be suitable models for mechanistic studies addressing effects of receptor-ligand interaction other than infection. Of note, transgenic mice expressing HIV gp120 in the brain share several pathological hallmarks with NeuroAIDS brains. Against this background, we will discuss recently completed or initiated, ongoing studies that utilize HIV co-receptor knockout and viral gp120-transgenic mice as models for in vitro and in vivo experimentation in order to address the potential roles of HIV gp120 and its co-receptors in the development of NeuroAIDS.

Morphine and gp120 toxic interactions in striatal neurons are dependent on HIV-1 strain

A rigorously controlled, cell culture paradigm was used to assess the role of HIV-1 gp120 ± morphine in mediating opioid-HIV interactive toxicity in striatal neurons. Computerized time-lapse microscopy tracked the fate of individual neurons co-cultured with mixed-glia from mouse striata during opioid and gp120 exposure. Subpopulations of neurons and astroglia displayed μ-opioid receptor, CXCR4, and CCR5 immunoreactivity. While gp120 alone was or tended to be neurotoxic irrespective of whether X4-tropic gp120(IIIB), R5-tropic gp120(ADA), or dual-tropic gp120(MN) was administered, interactive toxicity with morphine differed depending on HIV-1 strain. For example, morphine only transiently exacerbated gp120(IIIB)-induced neuronal death; however, in combination with gp120(MN), morphine caused sustained increases in the rate of neuronal death compared to gp120(MN) alone that were prevented by naloxone. Alternatively, gp120(ADA) significantly increased the rate of neuron death, but gp120(ADA) toxicity was unaffected by morphine. The transient neurotoxic interactions between morphine and gp120(IIIB) were abrogated in the absence of glia suggesting that glia contribute significantly to the interactive pathology with chronic opiate abuse and neuroAIDS. To assess how mixed-glia might contribute to the neurotoxicity, the effects of morphine and/or gp120 on the production of reactive oxygen species (ROS) and on glutamate buffering were examined. All gp120 variants, and to a lesser extent morphine, increased ROS and/or decreased glutamate buffering, but together failed to show any interaction with morphine. Our findings indicate that HIV-1 strain-specific differences in gp120 are critical determinants in shaping both the timing and pattern of neurotoxic interactions with opioid drugs.

Up-regulation of the neuronal nicotinic receptor α7 by HIV glycoprotein 120: potential implications for HIV-associated neurocognitive disorder

Approximately 30-50% of the >30 million HIV-infected subjects develop neurological complications ranging from mild symptoms to dementia. HIV does not infect neurons, and the molecular mechanisms behind HIV-associated neurocognitive decline are not understood. There are several hypotheses to explain the development of dementia in HIV(+) individuals, including neuroinflammation mediated by infected microglia and neuronal toxicity by HIV proteins. A key protein associated with the neurological complications of HIV, gp120, forms part of the viral envelope and can be found in the CSF of infected individuals. HIV-1-gp120 interacts with several receptors including CD4, CCR5, CXCR4, and nicotinic acetylcholine receptors (nAChRs). However, the role of nAChRs in HIV-associated neurocognitive disorder has not been investigated. We studied the effects of gp120(IIIB) on the expression and function of the nicotinic receptor α7 (α7-nAChR). Our results show that gp120, through activation of the CXCR4 chemokine receptor, induces a functional up-regulation of α7-nAChRs. Because α7-nAChRs have a high permeability to Ca(2+), we performed TUNEL staining to investigate the effects of receptor up-regulation on cell viability. Our data revealed an increase in cell death, which was blocked by the selective antagonist α-bungarotoxin. The in vitro data are supported by RT-PCR and Western blot analysis, confirming a remarkable up-regulation of the α7-nAChR in gp120-transgenic mice brains. Specifically, α7-nAChR up-regulation is observed in mouse striatum, a region severely affected in HIV(+) patients. In summary, CXCR4 activation induces up-regulation of α7-nAChR, causing cell death, suggesting that α7-nAChR is a previously unrecognized contributor to the neurotoxicity associated with HIV infection.

HIV-1 infection and neurocognitive impairment in the current era

Brain HIV-1-infection may result in a syndrome of profound cognitive, behavioral and motor impairment known as AIDS dementia complex (ADC) in adults and HIV-related encephalopathy in children. Although the introduction of highly active antiretroviral therapy (HAART) has prolonged and improved the lives of infected individuals, it is clear that HAART does not provide complete protection against neurological damage in HIV/AIDS. HIV-1 associated dementia is a complex phenomenon, which could be the result of several mechanisms caused by those players using different intracellular signaling pathways. Understanding the causes of neurodegeneration during HIV-1 infection and the factors which certain individuals develop disease can provide researches on new therapeutic targets to positively affect disease outcomes. Controlling CNS viral replication with HAART is an essential primary approach, but it should be complemented with adjunctive CNS-directed therapeutics. Understanding the nature of HIV-1 infection within the CNS as well as inflammatory responses will ultimately lead to the elimination of HIV-associated neurocognitive disorders.

HIV envelope-mediated, CCR5/α4β7-dependent killing of CD4-negative γδ T cells which are lost during progression to AIDS

HIV infects and replicates in CD4+ T cells but effects on host immunity and disease also involve depletion, hyper-activation, and modification of CD4-negative cell populations. In particular, the depletion of CD4-negative γδ T cells is common to all HIV+ individuals. We found that soluble or cell-associated envelope glycoproteins from CCR5-tropic strains of HIV could bind, activates the p38-caspase pathway, and induce the death of γδ cells. Envelope binding requires integrin α4β7 and chemokine receptor CCR5 which are at high levels and form a complex on the γδ T cell membrane. This receptor complex facilitated V3 loop binding to CCR5 in the absence of CD4-induced conformational changes. Cell death was increased by antigen stimulation after exposure to envelope glycoprotein. Direct signaling by envelope glycoprotein killed CD4-negative γδ T cells and reproduced a defect observed in all patients with HIV disease.

HIV-1 envelope protein gp120 up regulates CCL5 production in astrocytes which can be circumvented by inhibitors of NF-κB pathway

HIV associated neurological disorders (HAND) is a common neurological complication in patients infected with HIV. The proinflammatory cytokines and chemokines produced by astrocytes play a pivotal role in neuroinflammatory processes in the brain and viral envelope gp120 has been implicated in this process. In view of increased levels of CCL5 observed in the CSF of HIV-1 infected patients, we studied the effects of gp120 on CCL5 expression in astrocytes and the possible mechanisms responsible for those effects. Transfection of the SVGA astrocyte cell line with a plasmid encoding gp120 resulted in a time-dependent increase in expression levels of CCL5 in terms of mRNA and protein by 24.6 ± 2.67- and 35.2 ± 6.1-fold, respectively. The fluorescent images showed localization of CCL5 in the processes of the astrocytes. The gp120-specific siRNA abrogated the gp120-mediated increase in CCL5 expression. We also explored a possible mechanism for the effects of gp120 on CCL5 expression. Using a specific inhibitor for the NF-κB pathway, we demonstrated that levels of gp120 induction of CCL5 expression can be abrogated by 44.6 ± 4.2% at the level of mRNA and 51.8 ± 5.0% at the protein level. This was further confirmed by knocking down NF-κB through the use of siRNA.

Cocaine hijacks σ1 receptor to initiate induction of activated leukocyte cell adhesion molecule: implication for increased monocyte adhesion and migration in the CNS

Human immunodeficiency virus (HIV)-associated increase in monocyte adhesion and trafficking is exacerbated by cocaine abuse. The underlying mechanisms involve cocaine-mediated upregulation of adhesion molecules with subsequent disruption of the blood-brain barrier (BBB). Recently, a novel activated leukocyte cell adhesion molecule (ALCAM) has been implicated in leukocyte transmigration across the endothelium. We now show that upregulation of ALCAM in the brain endothelium seen in HIV(+)/cocaine drug abusers paralleled increased CD68 immunostaining compared with HIV(+)/no cocaine or uninfected controls, suggesting the important role of ALCAM in promoting leukocyte infiltration across the BBB. Furthermore, ALCAM expression was increased in cocaine-treated mice with concomitant increase in monocyte adhesion and transmigration in vivo, which was ameliorated by pretreating with the neutralizing antibody to ALCAM, lending additional support to the role of ALCAM. This new concept was further confirmed by in vitro experiments. Cocaine-mediated induction of ALCAM in human brain microvascular endothelial cells through the translocation of σ receptor to the plasma membrane, followed by phosphorylation of PDGF-β (platelet-derived growth factor-β) receptor. Downstream activation of mitogen-activated protein kinases, Akt, and NF-κB (nuclear factor-κB) pathways resulted in induced expression of ALCAM. Functional implication of upregulated ALCAM was confirmed using cell adhesion and transmigration assays. Neutralizing antibody to ALCAM ameliorated this effect. Together, these findings implicate cocaine-mediated induction of ALCAM as a mediator of increased monocyte adhesion/transmigration into the CNS.

Signaling through the P38 and ERK pathways: a common link between HIV replication and the immune response

One of the defining characteristics of HIV is its ability to manipulate the human immune response to promote its own replication. Since the beginning of the epidemic, there has been controversy whether a robust immune response to the virus is beneficial or detrimental for the host. Therefore, the effects of HIV on signaling pathways and cytokine production need to be characterized in order to distinguish between protective immune responses and inappropriate immune activation. Cytokine and biomarker expression during HIV infection results from the combined effects of intracellular signaling pathways orchestrated by kinases like P38 and ERK. The P38 and ERK Mitogen-Activated Protein Kinase (MAPK) pathways govern the regulation of cytokines (IL-2, IL-10, and TNF-α) as well biomarkers (PD-1, Fas/FasL, among others) that are skewed in chronic HIV infection. HIV utilizes the P38 and ERK pathways to produce new virions and to deplete CD4+ T cells from the host's immune system. Understanding the interplay between HIV and the cytokines induced by activation of the P38 and ERK pathways may provide insights into HIV immunopathogenesis and the development of a protective vaccine.

Methamphetamine and HIV-1 gp120 effects on lipopolysaccharide stimulated matrix metalloproteinase-9 production by human monocyte-derived macrophages

Monocytes/macrophages are a primary source of human immunodeficiency virus (HIV-1) in the central nervous system (CNS). Macrophages infected with HIV-1 produce a plethora of factors, including matrix metalloproteinase-9 (MMP-9) that may contribute to the development of HIV-1-associated neurocognitive disorders (HAND). MMP-9 plays a pivotal role in the turnover of the extracellular matrix (ECM) and functions to remodel cellular architecture. We have investigated the role of methamphetamine and HIV-1 gp120 in the regulation of lipopolysaccaride (LPS) induced-MMP-9 production in monocyte-derived macrophages (MDM). Here, we show that LPS-induced MMP-9 gene expression and protein secretion are potentiated by incubation with methamphetamine alone and gp120 alone. Further, concomitant incubation with gp120 and methamphetamine potentiated LPS-induced MMP-9 expression and biological activity in MDM. Collectively methamphetamine and gp120 effects on MMPs may modulate remodeling of the extracellular environment enhancing migration of monocytes/macrophages to the CNS.

Toll-like receptor expression and activation in astroglia: differential regulation by HIV-1 Tat, gp120, and morphine

In this study, we aimed to determine whether morphine alone or in combination with HIV-1 Tat or gp120 affects the expression of Toll-like receptors (TLRs) by astrocytes and to assess whether TLRs expressed by astrocytes function in the release of inflammatory mediators in vitro. TLR profiling by immunofluorescence microscopy, flow cytometry, in-cell westerns, and RT-PCR showed that subpopulations of astrocytes possessed TLR 2, TLR3, TLR4, and TLR9 antigenicity. Exposure to HIV-1 Tat, gp120, and/or morphine significantly altered the proportion of TLR-immunopositive and/or TLR expression by astroglia in a TLR-specific manner. Subsets of astroglia displayed significant increases in TLR2 with reciprocal decreases in TLR9 expression in response to Tat or gp120 ± morphine treatment. TLR9 expression was also significantly decreased by morphine alone. Exposing astrocytes to the TLR agonists LTA (TLR2), poly I:C (TLR3), LPS (TLR4) and unmethylated CpG ODN (TLR9) resulted in increased secretion of MCP-1/CCL2 and elevations in reactive oxygen species. TLR3 and TLR4 stimulation increased the secretion of TNF-α, IL-6, and RANTES/CCL5, while activation of TLR2 caused a significant increase in nitric oxide levels. The results suggest that HIV-1 proteins and/or opioid abuse disrupt the innate immune response of the central nervous system (CNS) which may lead to increased pathogenicity.

CXCR4 and CCR5 ligands cooperate in monocyte and lymphocyte migration and in inhibition of dual-tropic (R5/X4) HIV-1 infection

One of the most important functions of chemokines and their receptors is the regulation of directional migration of leukocytes within tissues. In specific tissue compartments, cells are exposed to multiple chemokines presented in complex dimensional and temporal patterns. Therefore, a leukocyte requires the mechanisms to integrate the various directional signals it receives from different chemoattractants. In this study, we report that CCL3, CCL5, and CCL8, three potent mononuclear cell chemoattractants, are able to synergize with the homeostatic chemokine CXCL12 in the migration of CD14(+) monocytes, CD3(+) T-lymphocytes, or PHA-activated lymphoblasts. In addition, CCL5 augmented the CXCR4 ligand-driven ERK phosphorylation in mononuclear cells. Furthermore, the synergistic effect between CCL5 and CXCL12 in monocyte chemotaxis is inhibited in the presence of specific CCR1 antibody and AMD3100, but not by maraviroc. In HIV-1 infection assays, a combination of CXCL12 and CCL5 cooperated to inhibit the replication of the dual-tropic (R5/X4) HIV-1 HE strain. Finally, although the dual-tropic HIV-1 strain was barely suppressed by AMD3100 or maraviroc alone, HIV-1 infection was completely blocked by the combination of these two receptor antagonists. Our data demonstrate the cooperation between CCL5 and CXCL12, which has implications in migration of monocytes/lymphocytes during inflammation and in HIV-1 infection.

Mitogen-activated protein kinase p38 in HIV infection and associated brain injury

Infection with human immunodeficiency virus-1 (HIV-1) often leads to HIV-associated neurocognitive disorders (HAND) prior to the progression to acquired immunodeficiency syndrome (AIDS). At the cellular level, mitogen-activated protein kinases (MAPK) provide a family of signal transducers that regulate many processes in response to extracellular stimuli and environmental stress, such as viral infection. Recently, evidence has accumulated suggesting that p38 MAPK plays crucial roles in various pathological processes associated with HIV infection, ranging from macrophage activation to neurotoxicity and impairment of neurogenesis to lymphocyte apoptosis. Thus, p38 MAPK, which has generally been linked to stress-related signal transduction, may be an important mediator in the development of AIDS and HAND.