Human immunodeficiency virus type 1 gp120 inhibits long-term potentiation via chemokine receptor CXCR4 in rat hippocampal slices

Methamphetamine augments HIV-1 gp120 inhibition of synaptic transmission and plasticity in rat hippocampal slices: Implications for methamphetamine exacerbation of HIV-associated neurocognitive disorders

Methamphetamine (Meth) abuse and human immunodeficiency virus type 1 (HIV-1) infection are two major public health problems worldwide. Being frequently comorbid with HIV-1 infection, Meth abuse exacerbates neurocognitive impairment in HIV-1-infected individuals even in the era of combined antiretroviral therapy. While a large body of research have studied the individual effects of Meth and HIV-1 envelope glycoprotein 120 (gp120) in the brain, far less has focused on their synergistic influence. Moreover, it is well-documented that the hippocampus is the primary site of spatial learning and long-term memory formation. Dysregulation of activity-dependent synaptic transmission and plasticity in the hippocampus is believed to impair neurocognitive function. To uncover the underlying mechanisms for increased incidence and severity of HIV-1-associated neurocognitive disorders (HAND) in HIV-1-infected patients with Meth abuse, we investigated acute individual and combined effects of Meth (20 μM) and gp120 (200 pM) on synaptic transmission and plasticity in the CA1 region of young adult male rat hippocampus, a brain region known to be vulnerable to HIV-1 infection. Our results showed that acute localized application of Meth and gp120 each alone onto the CA1 region reduced short-term dynamics of input-output responses and frequency facilitation, and attenuated long-term potentiation (LTP) induced by either high frequency stimulation or theta burst stimulation. A synergistic augmentation on activity-dependent synaptic plasticity was observed when Meth and gp120 were applied in combination. Paired-pulse facilitation results exhibited an altered facilitation ratio, suggesting a presynaptic site of action. Further studies revealed an involvement of microglia NLRP3 inflammasome activation in Meth augmentation of gp120-mediated attenuation of LTP. Taken together, our results demonstrated Meth augmented gp120 attenuation of LTP in the hippocampus. Since LTP is the accepted experimental analog of learning at the synaptic level, such augmentation may underlie Meth exacerbation of HAND observed clinically.

Reduced intrinsic excitability of CA1 pyramidal neurons in human immunodeficiency virus (HIV) transgenic rats

The hippocampus is involved in key neuronal circuits that underlie cognition, memory, and anxiety, and it is increasingly recognized as a vulnerable structure that contributes to the pathogenesis of HIV-associated neurocognitive disorder (HAND). However, the mechanisms responsible for hippocampal dysfunction in neuroHIV remain unknown. The present study used HIV transgenic (Tg) rats and patch-clamp electrophysiological techniques to study the effects of the chronic low-level expression of HIV proteins on hippocampal CA1 pyramidal neurons. The dorsal and ventral areas of the hippocampus are involved in different neurocircuits and thus were evaluated separately. We found a significant decrease in the intrinsic excitability of CA1 neurons in the dorsal hippocampus in HIV Tg rats by comparing neuronal spiking induced by current step injections and by dynamic clamp to simulate neuronal spiking activity. The decrease in excitability in the dorsal hippocampus was accompanied by a higher rate of excitatory postsynaptic currents (EPSCs), whereas CA1 pyramidal neurons in the ventral hippocampus in HIV Tg rats had higher EPSC amplitudes. We also observed a reduction of hyperpolarization-activated nonspecific cationic current (Ih) in both the dorsal and ventral hippocampus. Neurotoxic HIV proteins have been shown to increase neuronal excitation. The lower excitability of CA1 pyramidal neurons that was observed herein may represent maladaptive homeostatic plasticity that seeks to stabilize baseline neuronal firing activity but may disrupt neural network function and contribute to HIV-associated neuropsychological disorders, such as HAND and depression.

Reversal of Cognitive Impairment in gp120 Transgenic Mice by the Removal of the p75 Neurotrophin Receptor

Activation of the p75 neurotrophin receptor (p75NTR), by the proneurotrophin brain-derived neurotrophic factor (proBDNF), triggers loss of synapses and promotes neuronal death. These pathological features are also caused by the human immunodeficiency virus-1 (HIV) envelope protein gp120, which increases the levels of proBDNF. To establish whether p75NTR plays a role in gp120-mediated neurite pruning, we exposed primary cultures of cortical neurons from p75NTR^–/– mice to gp120. We found that the lack of p75NTR expression significantly reduced gp120-mediated neuronal cell death. To determine whether knocking down p75NTR is neuroprotective in vivo, we intercrossed gp120 transgenic (tg) mice with p75NTR heterozygous mice to obtain gp120tg mice lacking one or two p75NTR alleles. The removal of p75NTR alleles inhibited gp120-mediated decrease of excitatory synapses in the hippocampus, as measured by the levels of PSD95 and subunits of the N-methyl-D-Aspartate receptor in synaptosomes. Moreover, the deletion of only one copy of the p75NTR gene was sufficient to restore the cognitive impairment observed in gp120tg mice. Our data suggest that activation of p75NTR is one of the mechanisms crucial for the neurotoxic effect of gp120. These data indicate that p75NTR antagonists could provide an adjunct therapy against synaptic simplification caused by HIV.

HIV-associated neurodegeneration: exploitation of the neuronal cytoskeleton

Human immunodeficiency virus-1 (HIV) infection of the central nervous system damages synapses and promotes axonal injury, ultimately resulting in HIV-associated neurocognitive disorders (HAND). The mechanisms through which HIV causes damage to neurons are still under investigation. The cytoskeleton and associated proteins are fundamental for axonal and dendritic integrity. In this article, we review evidence that HIV proteins, such as the envelope protein gp120 and transactivator of transcription (Tat), impair the structure and function of the neuronal cytoskeleton. Investigation into the effects of viral proteins on the neuronal cytoskeleton may provide a better understanding of HIV neurotoxicity and suggest new avenues for additional therapies.

Changes in Chemokines and Chemokine Receptors Expression in a Mouse Model of Alzheimer's Disease

The amyloid precursor protein plus presenilin-1 (APP/PS1) mice are a frequently-used model for Alzheimer's disease studies (AD). However, the data relevant to which proteins are involved in inflammatory mechanism are not sufficiently well-studied using the AD mouse model. Using behavioral studies, quantitative RT-PCR and Western-blot techniques, significant findings were determined by the expression of proteins involved in inflammation comparing APP/PS1 and Wild type mice. Increased GFAP expression could be associated with the elevation in number of reactive astrocytes. IL-3 is involved in inflammation and ABDF1 intervenes normally in the transport across cell membranes and both were found up-regulated in APP/PS1 mice compared to Wild type mice. Furthermore, CCR5 expression was decreased and both CCL3 and CCL4 chemokines were highly expressed indicating a possible gliosis and probably an increase in chemotaxis from lymphocytes and T cell generation. We also noted for the first time, a CCR8 increase expression with diminution of its CCL1 chemokine, both normally involved in protection from bacterial infection and demyelination. Control of inflammatory proteins will be the next step in understanding the progression of AD and also in determining the mechanisms that can develop in this disease.

N-(Pivaloyloxy)alkoxy-carbonyl Prodrugs of the Glutamine Antagonist 6-Diazo-5-oxo-l-norleucine (DON) as a Potential Treatment for HIV Associated Neurocognitive Disorders

Aberrant excitatory neurotransmission associated with overproduction of glutamate has been implicated in the development of HIV-associated neurocognitive disorders (HAND). The glutamine antagonist 6-diazo-5-oxo-l-norleucine (DON, 14) attenuates glutamate synthesis in HIV-infected microglia/macrophages, offering therapeutic potential for HAND. We show that 14 prevents manifestation of spatial memory deficits in chimeric EcoHIV-infected mice, a model of HAND. 14 is not clinically available, however, because its development was hampered by peripheral toxicities. We describe the synthesis of several substituted N-(pivaloyloxy)alkoxy-carbonyl prodrugs of 14 designed to circulate inert in plasma and be taken up and biotransformed to 14 in the brain. The lead prodrug, isopropyl 6-diazo-5-oxo-2-(((phenyl(pivaloyloxy)methoxy)carbonyl)amino)hexanoate (13d), was stable in swine and human plasma but liberated 14 in swine brain homogenate. When dosed systemically in swine, 13d provided a 15-fold enhanced CSF-to-plasma ratio and a 9-fold enhanced brain-to-plasma ratio relative to 14, opening a possible clinical path for the treatment of HAND.

HIV-1 Glycoprotein 120 Enhancement of N-Methyl-D-Aspartate NMDA Receptor-Mediated Excitatory Postsynaptic Currents: Implications for HIV-1-Associated Neural Injury

It is widely accepted that human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein 120 (gp120) plays an important role in HIV-1-induced neural injury and pathogenesis of HIV-1-associated dementia (HAND). Multiple pathways have been proposed for gp120-induced neurotoxicity, amongst is the activation of N-Methyl-D-Aspartate receptors (NMDARs). It has been shown that gp120 causes neuronal injury or death and gp120 transgenic mice exhibit neurological similarity to that of HAND, all of which can be blocked or attenuated by NMDAR antagonists. Several lines of evidence indicate the subtype and location of activated NMDARs are key determinants of the nature of NMDAR physiology. To examine the subtype and the location of NMDARs affected by gp120, we studied gp120 on subtype NMDAR-mediated EPSCs in the CA1 region of rat hippocampal slices through "blind" whole-cell patch recordings. Our results showed bath application of gp120 increased both NR2A- and NR2B-mediated EPSCs possibly via a presynaptic mechanism, with much stronger effect on NR2B-mediated EPSCs. In contrast, gp120 failed on enhancing AMPA receptor-mediated EPSCs. Ca²⁺ imaging studies revealed that gp120 potentiated glutamate-induced increase of intracellular Ca²⁺ concentration in rat hippocampal neuronal cultures which were blocked by a NMDAR antagonist, but not by an AMPA receptor antagonist, indicating gp120 induces Ca²⁺ influx through NMDARs. Further investigations demonstrated that gp120 increased the EPSCs mediated by extrasynaptic NR2BRs. Taken together, these results demonstrate that gp120 interacts with both NR2A and NR2B subtypes of NMDARs with a predominant action on the extrasynaptic NR2B, implicating a role NR2B may play in HIV-1-associated neuropathology.

CCR5 is a suppressor for cortical plasticity and hippocampal learning and memory

Although the role of CCR5 in immunity and in HIV infection has been studied widely, its role in neuronal plasticity, learning and memory is not understood. Here, we report that decreasing the function of CCR5 increases MAPK/CREB signaling, long-term potentiation (LTP), and hippocampus-dependent memory in mice, while neuronal CCR5 overexpression caused memory deficits. Decreasing CCR5 function in mouse barrel cortex also resulted in enhanced spike timing dependent plasticity and consequently, dramatically accelerated experience-dependent plasticity. These results suggest that CCR5 is a powerful suppressor for plasticity and memory, and CCR5 over-activation by viral proteins may contribute to HIV-associated cognitive deficits. Consistent with this hypothesis, the HIV V3 peptide caused LTP, signaling and memory deficits that were prevented by Ccr5 knockout or knockdown. Overall, our results demonstrate that CCR5 plays an important role in neuroplasticity, learning and memory, and indicate that CCR5 has a role in the cognitive deficits caused by HIV.

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.

Association of Hippocampal Magnetic Resonance Imaging With Learning and Memory Deficits in HIV-1-Seropositive Patients

OBJECTIVE

To investigate the relationship between cognitive impairment and hippocampal morphological and functional changes in HIV-seropositive patients.

METHODS

Thirty HIV+ patients who complain of memory decrease and 15 healthy volunteers were recruited. Performances of learning and memory were assessed using Hopkins Verbal Learning Test-Revised (HVLT-R) and Brief Visuospatial Memory Test-Revised (BVMT-R). Bilateral hippocampal volume, apparent diffusion coefficient (ADC) value, fractional anisotropy value, and magnetic resonance spectroscopy variables of bilateral hippocampus and parahippocampal gyrus were detected by 3.0 T magnetic resonance scanner.

RESULTS

We found significant differences in all cognitive outcomes but one between HIV+ and HIV- patients. There was a difference in the ADC value of left parahippocampal gyrus between mild-impairment group and severe-impairment group (P = 0.018). We found differences in the choline (Cho), Cho/creatinine (Cr), and N-acetylaspartate/Cr of left hippocampus (P = 0.002, P = 0.008, P = 0.002) and the Cho/Cr of right parahippocampal gyrus (P = 0.023) between HIV+ and HIV- patients and in the myoinositol of left hippocampus (P = 0.003) and the glutamate and glutamine of right hippocampus (P < 0.001) between mild-impairment group and severe-impairment group. We found significant positive correlations between N-acetylaspartate/Cr of left hippocampus and outcomes of HVLT-R and BVMT-R. There were significant negative correlations between ADC values of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R and between Cho and Cho/Cr of hippocampus and parahippocampal gyrus and outcomes of HVLT-R and BVMT-R.

CONCLUSIONS

The performance of verbal learning and visual memory was significantly decreased in HIV-1-seropositive patients. The cognitive impairment of HIV infection was associated with conductive function and metabolic changes of hippocampus and parahippocampal gyrus in this study.

Heme oxygenase-1 dysregulation in the brain: implications for HIV-associated neurocognitive disorders

Heme oxygenase-1 (HO-1) is a highly inducible and ubiquitous cellular enzyme that subserves cytoprotective responses to toxic insults, including inflammation and oxidative stress. In neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease and multiple sclerosis, HO-1 expression is increased, presumably reflecting an endogenous neuroprotective response against ongoing cellular injury. In contrast, we have found that in human immunodeficiency virus (HIV) infection of the brain, which is also associated with inflammation, oxidative stress and neurodegeneration, HO-1 expression is decreased, likely reflecting a unique role for HO-1 deficiency in neurodegeneration pathways activated by HIV infection. We have also shown that HO-1 expression is significantly suppressed by HIV replication in cultured macrophages which represent the primary cellular reservoir for HIV in the brain. HO-1 deficiency is associated with release of neurotoxic levels of glutamate from both HIV-infected and immune-activated macrophages; this glutamate-mediated neurotoxicity is suppressed by pharmacological induction of HO-1 expression in the macrophages. Thus, HO-1 induction could be a therapeutic strategy for neuroprotection against HIV infection and other neuroinflammatory brain diseases. Here, we review various stimuli and signaling pathways regulating HO-1 expression in macrophages, which could promote neuronal survival through HO-1-modulation of endogenous antioxidant and immune modulatory pathways, thus limiting the oxidative stress that can promote HIV disease progression in the CNS. The use of pharmacological inducers of endogenous HO-1 expression as potential adjunctive neuroprotective therapeutics in HIV infection is also discussed.

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.

Lack of CCR5 modifies glial phenotypes and population of the nigral dopaminergic neurons, but not MPTP-induced dopaminergic neurodegeneration

Constitutive expression of C-C chemokine receptor (CCR) 5 has been detected in astrocytes, microglia and neurons, but its physiological roles in the central nervous system are obscure. The bidirectional interactions between neuron and glial cells through CCR5 and its ligands were thought to be crucial for maintaining normal neuronal activities. No study has described function of CCR5 in the dopaminergic neurodegeneration in Parkinson's disease. In order to examine effects of CCR5 on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic neurodegeneration, we employed CCR5 wild type (WT) and knockout (KO) mice. Immunostainings for tyrosine hydroxylase (TH) exhibited that CCR5 KO mice had lower number of TH-positive neurons even in the absence of MPTP. Difference in MPTP (15mg/kg×4 times, 2hr interval)-mediated loss of TH-positive neurons was subtle between CCR5 WT and KO mice, but there was larger dopamine depletion, behavioral impairments and microglial activation in CCR5 deficient mice. Intriguingly, CCR5 KO brains contained higher immunoreactivity for monoamine oxidase (MAO) B which was mainly localized within astrocytes. In agreement with upregulation of MAO B, concentration of MPP+ was higher in the substantia nigra and striatum of CCR5 KO mice after MPTP injection. We found remarkable activation of p38 MAPK in CCR5 deficient mice, which positively regulates MAO B expression. These results indicate that CCR5 deficiency modifies the nigrostriatal dopaminergic neuronal system and bidirectional interaction between neurons and glial cells via CCR5 might be important for dopaminergic neuronal survival.

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.

The CC chemokine receptor 5 regulates olfactory and social recognition in mice

Chemokines are chemotactic cytokines that regulate cell migration and are thought to play an important role in a broad range of inflammatory diseases. The availability of chemokine receptor blockers makes them an important therapeutic target. In vitro, chemokines are shown to modulate neurotransmission. However, it is not very clear if chemokines play a role in behavior and cognition. Here we evaluated the role of CC chemokine receptor 5 (CCR5) in various behavioral tasks in mice using Wt (Ccr5⁺/⁺) and Ccr5-null (Ccr5⁻/⁻)mice. Ccr5⁻/⁻ mice showed enhanced social recognition. Administration of CC chemokine ligand 3 (CCL3), one of the CCR5-ligands, impaired social recognition. Since the social recognition task is dependent on the sense of olfaction, we tested olfactory recognition for social and non-social scents in these mice. Ccr5⁻/⁻ mice had enhanced olfactory recognition for both these scents indicating that enhanced performance in social recognition task could be due to enhanced olfactory recognition in these mice. Spatial memory and aversive memory were comparable in Wt and Ccr5⁻/⁻ mice. Collectively, these results suggest that chemokines/chemokine receptors might play an important role in olfactory recognition tasks in mice and to our knowledge represents the first direct demonstration of an in vivo role of CCR5 in modulating social behavior in mice. These studies are important as CCR5 blockers are undergoing clinical trials and can potentially modulate behavior.

Interleukin-1β causes long-term potentiation deficiency in a mouse model of septic encephalopathy

Sepsis induces multiple organ dysfunction syndrome including septic encephalopathy (SE), which results in cognitive impairment. However, an effective treatment for SE remains unknown. We determined the role of interleukin-1β (IL-1β) in long-term potentiation (LTP) deficiency after SE. At first, endotoxin level in the blood was increased at 24 h after cecum ligation and puncture (CLP) (i.e. SE model). Second, the expression of IL-1β and its receptor in the hippocampus was determined by immunohistochemistry and immunoblotting. The number of Iba1-positive cells and their expression of IL-1β were enhanced by CLP with disruption of the blood brain barrier. Also, Iba1, IL-1β, and occludin protein expressions were consistent with immunohistochemical results. Third, we used an electrophysiological technique and observed the LTP deficiency, a hallmark of learning and memory, in the slices of hippocampus after CLP. Since type 1 interleukin-1 receptors (IL-1R1s) on neuronal cells were increased in the hippocampus, we utilized IL-1R1 antagonist. Pre-incubation with IL-1R1 antagonist for 30 min before recording of field excitatory post-synaptic potentials (fEPSPs) in the hippocampus canceled LTP deficiency after CLP. These results suggest the novel importance of IL-1β in synaptic plasticity deficiency associated with sepsis-induced brain inflammation. In a mouse model of SE, IL-1R1 inhibition is important in protecting synaptic function of the hippocampus after induction of SE.

HIV-1 gp120-induced axonal injury detected by accumulation of β-amyloid precursor protein in adult rat corpus callosum

HIV-1 brain infection induces neurodegeneration. While most studies focus on HIV-1-mediated neuronal injury, relatively few have investigated HIV-1-associated white matter damage. Corpus callosum (CC) is one of frequently involved white matter structures in HIV-1-associated white matter damage. Utilizing a model of ex vivo treatment of brain slice containing CC with HIV-1 glycoprotein 120 (gp120), we examined axonal injury by analyzing β-amyloid precursor protein (β-APP) accumulation in the axon. Incubation of CC slice with gp120 produced a significant higher density of β-APP in the CC tissue compared with non-gp120-treated controls, suggesting the presence of axonal damage in the CC. The gp120-induced CC axonal damage was blocked by a chemokine CXCR4 receptor antagonist T140 but not by an NMDA receptor blocker MK801 as demonstrated by Western blot analysis of β-APP, indicating that gp120 evokes the CC axonal injury through CXCR4 receptor. Immunocytochemical studies revealed a surprisingly high density of CXCR4-positive immunoreactivity in the CC. The CXCR4-positive labeling was distributed along the nerve fibers. Moreover, double labeling of anti-CXCR4 with either anti-neuronal nuclei or anti-myelin/oligodendrocyte-specific protein antibody revealed co-localization of CXCR4 and myelin/oligodendrocytes in some fiber-like structures, inferring that some neurons and oligodendrocytes in the CC express CXCR4. Taken together, these results indicate that gp120 induced axonal damage via CXCR4 in the CC.

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.

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

AIMS

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

MAIN METHODS

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

KEY FINDINGS

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

SIGNIFICANCE

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

Multiple roles of chemokine CXCL12 in the central nervous system: a migration from immunology to neurobiology

Chemotactic cytokines (chemokines) have been traditionally defined as small (10-14kDa) secreted leukocyte chemoattractants. However, chemokines and their cognate receptors are constitutively expressed in the central nervous system (CNS) where immune activities are under stringent control. Why and how the CNS uses the chemokine system to carry out its complex physiological functions has intrigued neurobiologists. Here, we focus on chemokine CXCL12 and its receptor CXCR4 that have been widely characterized in peripheral tissues and delineate their main functions in the CNS. Extensive evidence supports CXCL12 as a key regulator for early development of the CNS. CXCR4 signaling is required for the migration of neuronal precursors, axon guidance/pathfinding and maintenance of neural progenitor cells (NPCs). In the mature CNS, CXCL12 modulates neurotransmission, neurotoxicity and neuroglial interactions. Thus, chemokines represent an inherent system that helps establish and maintain CNS homeostasis. In addition, growing evidence implicates altered expression of CXCL12 and CXCR4 in the pathogenesis of CNS disorders such as HIV-associated encephalopathy, brain tumor, stroke and multiple sclerosis (MS), making them the plausible targets for future pharmacological intervention.

Neuronal chemokines: versatile messengers in central nervous system cell interaction

Whereas chemokines are well known for their ability to induce cell migration, only recently it became evident that chemokines also control a variety of other cell functions and are versatile messengers in the interaction between a diversity of cell types. In the central nervous system (CNS), chemokines are generally found under both physiological and pathological conditions. Whereas many reports describe chemokine expression in astrocytes and microglia and their role in the migration of leukocytes into the CNS, only few studies describe chemokine expression in neurons. Nevertheless, the expression of neuronal chemokines and the corresponding chemokine receptors in CNS cells under physiological and pathological conditions indicates that neuronal chemokines contribute to CNS cell interaction. In this study, we review recent studies describing neuronal chemokine expression and discuss potential roles of neuronal chemokines in neuron-astrocyte, neuron-microglia, and neuron-neuron interaction.

Egr3, a synaptic activity regulated transcription factor that is essential for learning and memory

Learning and memory depend upon poorly defined synaptic and intracellular modifications that occur in activated neurons. Mitogen activated protein kinase-extracellular regulated kinase (MAPK-ERK) signaling and de novo protein synthesis are essential aspects of enduring memory formation, but the precise effector molecules of MAPK-ERK signaling in neurons are not well defined. Early growth response (Egr) transcriptional regulators are examples of MAPK-ERK regulated genes and Egr1 (zif268) has been widely recognized as essential for some aspects of learning and memory. Here we show that Egr3, a transcriptional regulator closely related to Egr1, is essential for normal hippocampal long-term potentiation (LTP) and for hippocampal and amygdala dependent learning and memory. In the absence of Egr3, the defects in learning and memory appear to be independent of Egr1 since Egr1 protein levels are not altered in amygdala, hippocampus or cortex. Moreover, unlike Egr1-deficient mice which have impairments in late phase hippocampal LTP and consolidation of some forms of long-term hippocampus- and amygdala-dependent memory, Egr3-deficient mice have profound defects in early- and late-phase hippocampal LTP, as well as short-term and long-term hippocampus- and amygdala-dependent learning and memory. Thus, Egr3 has an essential role in learning and memory processing that appears to be partly distinct from the role of Egr1.