Glucocorticoids exacerbate the deleterious effects of gp120 in hippocampal and cortical explants

HIV Neuroinfection and Alzheimer's Disease: Similarities and Potential Links?

Environmental factors such as chemicals, stress and pathogens are now widely believed to play important roles in the onset of some brain diseases, as they are associated with neuronal impairment and acute or chronic inflammation. Alzheimer’s disease (AD) is characterized by progressive synaptic dysfunction and neurodegeneration that ultimately lead to dementia. Neuroinflammation also plays a prominent role in AD and possible links to viruses have been proposed. In particular, the human immunodeficiency virus (HIV) can pass the blood-brain barrier and cause neuronal dysfunction leading to cognitive dysfunctions called HIV-associated neurocognitive disorders (HAND). Similarities between HAND and HIV exist as numerous factors involved in AD such as members of the amyloid and Tau pathways, as well as stress-related pathways or blood brain barrier (BBB) regulators, seem to be modulated by HIV brain infection, leading to the accumulation of amyloid plaques or neurofibrillary tangles (NFT) in some patients. Here, we summarize findings regarding how HIV and some of its proteins such as Tat and gp120 modulate signaling and cellular pathways also impaired in AD, suggesting similarities and convergences of these two pathologies.

Perceived and post-traumatic stress are associated with decreased learning, memory, and fluency in HIV-infected women

OBJECTIVE

Psychological risk factors (PRFs) are associated with impaired learning and memory in HIV-infected (HIV+) women. We determined the dynamic nature of the effects of PRFs and HIV serostatus on learning and memory over time.

DESIGN

Multi-center, prospective cohort study METHODS:: Every two years between 2009 and 2013 (3 times), 646 HIV+ and 300 demographically-similar HIV-uninfected (HIV-) women from the Women's Interagency HIV Study completed neuropsychological (NP) testing and questionnaires measuring PRFs (perceived stress, post-traumatic stress disorder (PTSD) symptoms, depressive symptoms). Using mixed-effects regressions, we examined separate and interactive associations between HIV-serostatus and PRFs on performance over time.

RESULTS

HIV+ and HIV- women had similar rates of PRFs. Fluency was the only domain where performance over time depended on the combined influence of HIV-serostatus and stress or PTSD (p's < 0.05); not depression. In HIV, higher stress and PTSD were associated with a greater cognitive decline in performance (p's < 0.05) versus lower stress and PTSD. Irrespective of time, performance on learning and memory depended on the combined influence of HIV-serostatus and stress or PTSD (p's ≤ 0.05). In the context of HIV, stress and PTSD were negatively associated with performance. Effects were pronounced on learning among HIV+ women without effective treatment or viral suppression. Regardless of time or HIV-serostatus, all PRFs were associated with lower speed, global NP, and executive function.

CONCLUSIONS

More than depression, perceived stress and PTSD symptoms are treatment targets to potentially improve fluency, learning, and memory in women living with HIV particularly when HIV treatment is not optimal.

Expression of gp120 in mice evokes anxiety behavior: Co-occurrence with increased dendritic spines and brain-derived neurotrophic factor in the amygdala

Human immunodeficiency virus type 1 (HIV) infection of the brain produces cognitive and motor disorders. In addition, HIV positive individuals exhibit behavioral alterations, such as apathy, and a decrease in spontaneity or emotional responses, typically seen in anxiety disorders. Anxiety can lead to psychological stress, which has been shown to influence HIV disease progression. These considerations underscore the importance of determining if anxiety in HIV is purely psychosocial, or if by contrast, there are the molecular cascades associated directly with HIV infection that may mediate anxiety. The present study had two goals: (1) to determine if chronic exposure to viral proteins would induce anxiety-like behavior in an animal model and (2) to determine if this exposure results in anatomical abnormalities that could explain increased anxiety. We have used gp120 transgenic mice, which display behavior and molecular deficiencies similar to HIV positive subjects with cognitive and motor impairments. In comparison to wild type mice, 6 months old gp120 transgenic mice demonstrated an anxiety like behavior measured by open field, light/dark transition task, and prepulse inhibition tests. Moreover, gp120 transgenic mice have an increased number of spines in the amygdala, as well as higher levels of brain-derived neurotrophic factor and tissue plasminogen activator when compared to age-matched wild type. Our data support the hypothesis that HIV, through gp120, may cause structural changes in the amygdala that lead to maladaptive responses to anxiety.

Prefrontal cortical volume loss is associated with stress-related deficits in verbal learning and memory in HIV-infected women

Deficits in verbal learning and memory are a prominent feature of neurocognitive function in HIV-infected women, and are associated with high levels of perceived stress. To understand the neurobiological factors contributing to this stress-related memory impairment, we examined the association between stress, verbal memory, and brain volumes in HIV-infected women. Participants included 38 HIV-infected women (Mean age=43.9years) from the Chicago Consortium of the Women's Interagency HIV Study (WIHS). Participants underwent structural magnetic resonance imaging (MRI) and completed standardized measures of verbal learning and memory and stress (Perceived Stress Scale-10; PSS-10). Brain volumes were evaluated in a priori regions of interest, including the medial temporal lobe (MTL) and prefrontal cortex (PFC). Compared to HIV-infected women with lower stress (PSS-10 scores in lower two tertiles), HIV-infected women with higher stress (scores in the top tertile), performed worse on measures of verbal learning and memory and showed smaller volumes bilaterally in the parahippocampal gyrus, superior frontal gyrus, middle frontal gyrus, and inferior frontal gyrus (p's<0.05). Reduced volumes in the inferior frontal gyrus, middle frontal gyrus, and superior frontal gyrus (all right hemisphere) were negatively associated with verbal learning and memory performance. Prefrontal cortical atrophy is associated with stress-related deficits in verbal learning and memory in HIV-infected women. The time course of these volume losses in relation to memory deficits has yet to be elucidated, but the magnitude of the volumetric differences between women with higher versus lower stress suggests a prolonged vulnerability due to chronic stress and/or early life trauma.

Inflammation in schizophrenia: A question of balance

In the past decade, there has been renewed interest in immune/inflammatory changes and their associated oxidative/nitrosative consequences as key pathophysiological mechanisms in schizophrenia and related disorders. Both brain cell components (microglia, astrocytes, and neurons) and peripheral immune cells have been implicated in inflammation and the resulting oxidative/nitrosative stress (O&NS) in schizophrenia. Furthermore, down-regulation of endogenous antioxidant and anti-inflammatory mechanisms has been identified in biological samples from patients, although the degree and progression of the inflammatory process and the nature of its self-regulatory mechanisms vary from early onset to full-blown disease. This review focuses on the interactions between inflammation and O&NS, their damaging consequences for brain cells in schizophrenia, the possible origins of inflammation and increased O&NS in the disorder, and current pharmacological strategies to deal with these processes (mainly treatments with anti-inflammatory or antioxidant drugs as add-ons to antipsychotics).

The association of perceived stress and verbal memory is greater in HIV-infected versus HIV-uninfected women

In contrast to findings from cohorts comprised primarily of HIV-infected men, verbal memory deficits are the largest cognitive deficit found in HIV-infected women from the Women's Interagency HIV Study (WIHS), and this deficit is not explained by depressive symptoms or substance abuse. HIV-infected women may be at greater risk for verbal memory deficits due to a higher prevalence of cognitive risk factors such as high psychosocial stress and lower socioeconomic status. Here, we investigate the association between perceived stress using the Perceived Stress Scale (PSS-10) and verbal memory performance using the Hopkins Verbal Learning Test (HVLT) in 1009 HIV-infected and 496 at-risk HIV-uninfected WIHS participants. Participants completed a comprehensive neuropsychological test battery which yielded seven cognitive domain scores, including a primary outcome of verbal memory. HIV infection was not associated with a higher prevalence of high perceived stress (i.e., PSS-10 score in the top tertile) but was associated with worse performance on verbal learning (p < 0.01) and memory (p < 0.001), as well as attention (p = 0.02). Regardless of HIV status, high stress was associated with poorer performance in those cognitive domains (p's < 0.05) as well as processing speed (p = 0.01) and executive function (p < 0.01). A significant HIV by stress interaction was found only for the verbal memory domain (p = 0.02); among HIV-infected women only, high stress was associated with lower performance (p's < 0.001). That association was driven by the delayed verbal memory measure in particular. These findings suggest that high levels of perceived stress contribute to the deficits in verbal memory observed in WIHS women.

Mechanisms of HIV-1 Tat neurotoxicity via CDK5 translocation and hyper-activation: role in HIV-associated neurocognitive disorders

The advent of more effective antiretroviral therapies has reduced the frequency of HIV dementia, however the prevalence of milder HIV associated neurocognitive disorders [HAND] is actually rising. Neurodegenerative mechanisms in HAND might include toxicity by secreted HIV-1 proteins such as Tat, gp120 and Nef that could activate neuro-inflammatory pathways, block autophagy, promote excitotoxicity, oxidative stress, mitochondrial dysfunction and dysregulation of signaling pathways. Recent studies have shown that Tat could interfere with several signal transduction mechanisms involved in cytoskeletal regulation, cell survival and cell cycle re-entry. Among them, Tat has been shown to hyper-activate cyclin-dependent kinase [CDK] 5, a member of the Ser/Thr CDKs involved in cell migration, angiogenesis, neurogenesis and synaptic plasticity. CDK5 is activated by binding to its regulatory subunit, p35 or p39. For this manuscript we review evidence showing that Tat, via calcium dysregulation, promotes calpain-1 cleavage of p35 to p25, which in turn hyper-activates CDK5 resulting in abnormal phosphorylation of downstream targets such as Tau, collapsin response mediator protein-2 [CRMP2], doublecortin [DCX] and MEF2. We also present new data showing that Tat interferes with the trafficking of CDK5 between the nucleus and cytoplasm. This results in prolonged presence of CDK5 in the cytoplasm leading to accumulation of aberrantly phosphorylated cytoplasmic targets [e.g.: Tau, CRMP2, DCX] that impair neuronal function and eventually lead to cell death. Novel therapeutic approaches with compounds that block Tat mediated hyper-activation of CDK5 might be of value in the management of HAND.

Neurocognitive function in bipolar disorder: a comparison between bipolar I and II disorder and matched controls

BACKGROUND

Cognitive deficits have been documented in patients with bipolar disorder. Further, it has been suggested that the degree and type of cognitive impairment differ between bipolar I and bipolar II disorder, but data is conflicting and remains inconclusive. This study aimed to clarify the suggested differences in cognitive impairment between patients with bipolar I and II disorder in a relatively large, clinically stable sample while controlling for potential confounders.

METHODS

67 patients with bipolar I disorder, 43 with bipolar II disorder, and 86 randomly selected population-based healthy controls were compared. A number of neuropsychological tests were administered, assessing verbal and visual memory and executive functions. Patients were in a stable phase during testing.

RESULTS

Patients with bipolar type I and type II were cognitively impaired compared to healthy controls, but there were no statistically significant differences between the two subtypes. The strongest predictor of cognitive impairment within the patient group was current antipsychotic treatment.

CONCLUSIONS

The present study suggests that the type and degree of cognitive dysfunction is similar in bipolar I and II patients. Notably, treatment with antipsychotics - but not a history of psychosis - was associated with more severe cognitive impairment. Given that patients with bipolar I disorder are more likely to be on antipsychotic drugs, this might explain why some previous studies have found that patients with type I bipolar disorder are more cognitively impaired than those with type II.

HIV neurotoxicity: potential therapeutic interventions

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

The impact of environmental risk factors on HIV-associated cognitive decline in children

Both the human immunodeficiency virus (HIV) and environmental stress have been independently associated with decreased cognitive functioning in children. Given that they are also known to have a strong relationship with each other, the present study sought to test the hypothesis that children in conditions of high environmental risk would be at greater risk for the cognitive complications related to immunosuppression. A retrospective review was conducted to examine the records of 141 children treated at a large pediatric AIDS clinic from 1993 to 2000. CD4+ lymphocyte levels were recorded from laboratory results and IQ scores were recorded from routine psychological evaluations. Key indicators of environmental risk were collected and combined into one measure of overall environmental risk. Pearson product moment correlations were conducted to examine the relationship between environmental risk, age-adjusted CD4 and IQ. Results indicated a significant correlation between CD4 and IQ, with higher levels of immunocompetence predicting higher IQ scores. When subjects were dichotomized based on their environmental risk score, there was no relationship between CD4 count and IQ in the low environmental risk group. In contrast, CD4 was positively associated with IQ in the high environmental risk group. It is proposed that this may be due to gp120 levels in immunocompromised children being particularly toxic to the hippocampus and cortex under conditions of high stress but not so under conditions of low stress.

HIV-1 viral genes and mitochondrial apoptosis

The mitochondrion is an organelle that regulates various cellular functions including the production of energy and programmed cell death. Aberrant mitochondrial function is often concomitant with various cytopathies and medical disorders. The mitochondrial membrane plays a key role in the induction of cellular apoptosis, and its destabilization, as triggered by both intracellular and extracellular stimuli, results in the release of proapoptotic factors into the cytosol. Not surprisingly, proteins from the human immunodeficiency virus type 1 (HIV) have been implicated in exploiting this organelle to promote the targeted depletion of key immune cells, which assists in viral evasion of the immune system and contributes to the characteristic global immunodeficiency observed during progression of disease. Here we review the mechanisms by which HIV affects the mitochondrion, and suggest that various viral-associated genes may directly regulate apoptotic cell death.

Effects of peroxisome proliferator-activated receptor gamma agonists on brain glucose and glutamate transporters after stress in rats

Repeated stress causes an energy-compromised status in the brain, with a decrease in glucose utilization by the brain cells, which might account for excitotoxicity processes seen in this condition. In fact, brain glucose metabolism mechanisms are impaired in some neurodegenerative disorders, including stress-related neuropsychopathologies. More recently, it has been demonstrated that some synthetic peroxisome proliferator-activated receptor gamma (PPARgamma) agonists increase glucose utilization in rat cortical slices and astrocytes, as well as inhibit brain oxidative damage after repeated stress, which add support for considering these drugs as potential neuroprotective agents. To assess if stress causes glucose utilization impairment in the brain and to study the mechanisms by which this effect is achieved, young-adult male Wistar rats (control and immobilized for 6 h during 7 or 14 consecutive days, S7, S14) were i.p. injected with the natural ligand 15-deoxy-Delta-12,14-prostaglandin J2 (PGJ2, 120 microg/kg) or the high-affinity ligand rosiglitazone (RG, 3 mg/kg) at the onset of stress. Repeated immobilization during 1 or 2 weeks produces a decrease in brain cortical synaptosomal glucose uptake, and this effect was prevented by treatment with both natural and synthetic PPARgamma ligands by restoring protein expression of the neuronal glucose transporter, GLUT-3 in membrane fractions. On the other hand, treatment with PPARgamma ligands prevents stress-induced ATP loss in rat brain. Finally, repeated immobilization stress also produces a decrease in brain cortical synaptosomal glutamate uptake, and this effect was prevented by treatment with PPARgamma ligands by restoring synaptosomal protein expression of the glial glutamate transporter, EAAT2. In summary, our results demonstrate that 15d-PGJ2 and the thiazolidinedione rosiglitazone increase neuronal glucose metabolism, restore brain ATP levels and prevent the impairment in glutamate uptake mechanisms induced by exposure to stress, suggesting that this class of drugs may be therapeutically useful in conditions in which brain glucose levels or availability are limited after exposure to stress.

A 24 h corticosterone exposure exacerbates excitotoxic insult in rat hippocampal slice cultures independently of glucocorticoid receptor activation or protein synthesis

Elevations in circulating concentrations of glucocorticoids (GC) may increase the expression and/or sensitivity of ionotropic transmitter receptors in brain. For example, recent evidence suggests that acute and chronic GC exposure may alter the number and/or function of N-methyl-D-aspartate (NMDA)-type glutamate receptors, effects that may sensitize the brain to excitotoxic insults. The present studies examined the ability of short-term (24 h) corticosterone (CORT) exposure to potentiate NMDA-induced cytotoxicity in rat hippocampal slice cultures. Additional studies evaluated the role of mineralocorticoid (MR) and glucocorticoid receptor (GR) function, as well as de novo protein synthesis, in potentiation of toxicity by corticosterone exposure. Hippocampal slice cultures were exposed to NMDA (20 microM) for 24 h with cytotoxicity assessed by fluorescent detection of propidium iodide uptake. Exposure to NMDA caused significant propidium iodide uptake in each hippocampal region, while 24 h CORT (0.001-1 microM) exposure alone did not significantly increase propidium iodide uptake. Co-exposure of cultures to CORT and NMDA synergistically increased propidium iodide uptake in each hippocampal region, effects that were prevented by co-exposure to a non-toxic concentration of MK-801 (20 microM). In contrast, 24 h exposure with the MR antagonist spironolactone (1-10 microM), the GR antagonist RU-486 (1-10 microM), or the protein synthesis inhibitor cycloheximide (1 microM) failed to reduce the significant increase in propidium iodide uptake. These data suggest that relatively brief elevations in CORT levels may sensitize the hippocampus to injury independently of GC receptor activity and protein synthesis.

Choline exposure reduces potentiation of N-methyl-D-aspartate toxicity by corticosterone in the developing hippocampus

Exposure to high levels of glucocorticoids (GCs) may adversely affect neuronal viability, particularly in the developing hippocampus, via increased function or sensitivity of N-methyl-D-aspartate (NMDA)-type glutamate receptors. Conversely, choline supplementation in the developing brain may reduce the severity of subsequent insult. The present studies aimed to examine the extent to which short-term exposure to high concentrations of corticosterone would produce neuronal injury mediated by NMDA receptor activity. These studies also assessed the ability of choline to prevent this form of injury via interactions with nicotinic acetylcholine receptors (nAChRs) expressing the alpha7 subunit. Organotypic hippocampal slice cultures derived from neonatal rat were pre-treated for 72 h with corticosterone (100 nM) alone or with choline (0.1-10 mM), prior to a brief (1 h) NMDA exposure (5 microM). NMDA exposure produced significant cellular damage, reflected as increased fluorescence of the non-vital marker propidium iodide, in the CA1 region. While exposure to corticosterone alone did not produce damage, pre-treatment of cultures with corticosterone markedly exacerbated NMDA-induced toxicity. Pre-treatment with choline (> or =1 mM) alone or in combination with corticosterone markedly reduced subsequent NMDA toxicity, effects blocked by co-exposure to methyllycaconitine (100 nM), an antagonist active at nAChRs expressing the alpha7 subunit. These data suggest that even short-term exposure to high concentrations of GCs may adversely affect neuronal viability and that choline supplementation protects the brain from NMDA receptor-mediated damage, including that associated with hypercortisolemia.

N-butyryl glucosamine increases matrix gene expression by chondrocytes

Proteoglycan synthesis is dependent on N-acetyl glucosamine (GlcNAc) produced by the hexosamine biosynthetic pathway or obtained exogenously. Although used therapeutically to relieve symptoms of osteoarthritis, the actions of glucosamine and its analogs on cartilage are poorly understood. The purpose of this study was to determine the effects on chondrocytes of N-acylated-glucosamine analogs bearing alkyl chains of different lengths. Chondrocytes isolated from neonatal rat femoral condyles were cultured in the presence of glucosamine analogs. GlcNAc, N-proprionyl glucosamine (GlcNPro), or N-butyryl glucosamine (GlcNBu) did not alter cell number, lactate dehydrogenase release, or metabolic acid production, consistent with lack of cytotoxicity. Treatment of chondrocyte cultures with GlcNBu for 6 days significantly increased levels of type II collagen and aggrecan mRNA as determined by Northern blot analysis. In contrast, GlcNAc and GlcNPro had no significant effect. A significant increase in type II collagen mRNA was induced by GlcNBu within 3 days. GlcNBu did not alter stability of type II collagen mRNA, suggesting it acts on gene transcription. We have previously shown that tumor necrosis factor-alpha (TNFalpha) decreases levels of type II collagen mRNA. However, chondrocytes pretreated with GlcNBu maintained type II collagen mRNA at control levels in the presence of TNFalpha. These results establish that the N-butyrylated analog of glucosamine but not GlcNAc promotes matrix gene expression by chondrocytes. Thus, GlcNBu has the potential for use as a chondro-protective agent in osteoarthritis.

Postpartum maternal corticosterone decreases maternal and neonatal antibody levels and increases the susceptibility of newborn mice to herpes simplex virus-associated mortality

The effects of corticosterone on the transmammary transfer of herpes simplex virus (HSV)-specific antibody and the ability of the neonate to survive HSV-2 infection were assessed. Increased postpartum maternal corticosterone reduced the levels of total and HSV-specific IgG in the serum and milk of mothers. Neonates nursed by these mothers received increased levels of corticosterone and decreased levels of total and HSV-specific IgG. Accordingly, these neonates were more susceptible to HSV-2-associated mortality; however, survival was restored through passive immunization with HSV-specific antibody. These studies demonstrate that postpartum elevations in corticosterone compromise a mother's ability to provide protective antibody to their offspring.

(−)-nicotine ameliorates corticosterone's potentiation of N-methyl-d-aspartate receptor-mediated cornu ammonis 1 toxicity

Hypercortisolemia, long-term exposure of the brain to high concentrations of stress hormones (i.e. cortisol), may occur in patients suffering from depression, alcoholism, and other disorders. This has been suggested to produce neuropathological effects, in part, via increased function or sensitivity of N-methyl-d-aspartate (NMDA)-type glutamate receptors. Given that cigarette smoking is highly prevalent in some of these patient groups and nicotine has been shown to reduce toxic consequences of NMDA receptor function, it may be suggested that nicotine intake may attenuate the neurotoxic effects of hypercortisolemia. To investigate this possibility, organotypic hippocampal slice cultures derived from rat were pre-treated with corticosterone (0.001-1 microM) alone or in combination with selective glucocorticoid receptor antagonists for 72-h prior to a brief (1-h) NMDA exposure (5 microM). Pre-treatment with corticosterone (0.001-1 microM) alone did not cause hippocampal damage, while NMDA exposure produced significant cellular damage in the cornu ammonis (CA)1 subregion. No significant damage was observed in the dentate gyrus or CA3 regions following NMDA exposure. Pre-treatment of cultures with corticosterone (0.1-1 microM) markedly exacerbated NMDA-induced CA1 and dentate gyrus region damage. This effect in the CA1 region was prevented by co-administration of the glucocorticoid receptor antagonist RU486 (>or=1 microM), but not spironolactone (1-10 microM), a mineralocorticoid receptor antagonist. In a second series of studies, both acute and pre-exposure of cultures to (-)-nicotine (1-10 microM) significantly reduced NMDA toxicity in the CA1 region. Co-administration of cultures to (-)-nicotine (1-10 microM) with 100 nM corticosterone prevented corticosterone's exacerbation of subsequent CA1 insult. This protective effect of (-)-nicotine was not altered by co-exposure of cultures to 10 microM dihydro-beta-erythroidine but was blocked by co-exposure to 100 nM methyllycaconitine, suggesting the involvement of nicotinic acetylcholine receptors possessing the alpha7* subunit. The present studies suggest a role for hypercortisolemia in sensitizing the hippocampal NMDA receptor system to pathological activation and indicate that prolonged nicotine exposure attenuates this sensitization. Thus, it is possible that one consequence of heavy smoking in those suffering from hypercortisolemia may be a reduction of neuronal injury and sparing of cellular function.

Alcohol and withdrawal: from animal research to clinical issues

The withdrawal syndrome in alcohol-dependent patients appears to be a major stressful event whose intensity increases with repetition of detoxifications according to a kindling process. Disturbances in the balance between excitatory and inhibitory neural processes are reflected in a perturbed physical state while disturbances in the balance between positive and negative reinforcements are reflected in a perturbed mood state. Our purpose is to link the different behavioral outcomes occurring during withdrawal with specific biological brain mechanisms from the animal to the human being. Better understanding of the various biological mechanisms underlying withdrawal from alcohol will be the key to design and to apply appropriate pharmaceutical management, together with appropriate therapy aimed at inducing protracted abstinence.

Mitochondrial control of cell death induced by HIV-1-encoded proteins

In most examples of physiological or pathological cell death, mitochondrial membrane permeabilization (MMP) constitutes an early critical event of the lethal process. Signs of MMP that precede nuclear apoptosis include the translocation of cytochrome c and apoptosis-inducing factor (AIF) from mitochondria to an extra-mitochondrial localization, as well as the dissipation of the mitochondrial transmembrane potential. MMP also occurs in HIV-1-induced apoptosis. Different HIV-1 encoded proteins (Env, Vpr, Tat, PR) can directly or indirectly trigger MMP, thereby causing cell death. The gp120/gp41 Env complex constitutes an example for an indirect MMP inducer. Env expressed on the plasma membrane of HIV-1 infected (or Env-transfected) cells mediates cell fusion with CD4/CXCR4-expressing uninfected cells. After a cell type-dependent latency period, syncytia then undergo MMP and apoptosis. Vpr exemplifies a direct MMP inducer. Vpr binds to the adenine nucleotide translocator (ANT), a mitochondrial inner membrane protein which also interacts with apoptosis-regulatory proteins from the Bcl-2/Bax family. Binding of Vpr to ANT favors formation of a non-specific pore leading to MMP. The structural motifs of the Vpr protein involved in MMP are conserved among most pathogenic HIV-1 isolates and determine the cytotoxic effect of Vpr. These data suggest the possibility that viruses employ multiple strategies to regulate host cell apoptosis by targeting mitochondria.

Neuronal glycolytic pathway impairment induced by HIV envelope glycoprotein gp120

Neurological impairment is a common feature of Acquired Immunodeficiency Syndrome (AIDS); functional alterations have been reported both in central and peripheral nervous system and the Human Immunodeficiency Virus (HIV) envelope glycoprotein gp120 has been proposed as a neurotoxin acting through a calcium-dependent mechanism. On the other hand it has been reported that gp120 treatment also induce about a 20% decrease in the cerebral glucose utilization and in the cellular ATP levels. The reported observations were performed on experimental system where also non-neuronal cells where present; in order to evaluate whether a direct interaction between HIV proteins and neuronal cells takes place, we used a neuroblastoma cultures where only neuronal cells are present. We analysed the effects of gp120 on the N18TG2 neuroblastoma clone. Treatments were performed both on growing and confluent cultures. Short time treatment with gp120 of confluent cultures causes a 25% reduction in the level of neuron-specific enolase, resulting in a similar decrease of oxygen consumption. Long time exposure of growing cells also causes a reduction in cell survival. Furthermore, using a membrane-specific fluorescent probe we observed that gp120 produces an increase of membrane trafficking. These observations suggest a direct interaction between the viral envelope protein and neuronal cells, which results in an alteration of glycolytic metabolism. This alteration may be related to the neurologic impairments observed in AIDS patients.

The effects of steroid hormones in HIV-related neurotoxicity: a mini review

This review examines the interaction of steroid hormones, glucocorticoids and estrogen, and gp120, a possible causal agent of acquired immune deficiency syndrome-related dementia complex. The first part of the review examines the data and mechanisms by which gp120 may cause neurotoxicity and by which these steroid hormones effect cell death in general. The second part of the review summarizes recent experiments that show how these steroid hormones can modulate the toxic effects of gp120 and glucocorticoids exacerbating toxicity, and estrogen decreasing it. We then examine the limited in vivo and clinical data relating acquired immune deficiency syndrome-related dementia complex and steroid hormones and speculate on the possible clinical significance of these findings with respect to acquired immune deficiency syndrome-related dementia complex.