Interactions between HIV-infected monocyte-derived macrophages and human brain microvascular endothelial cells result in increased expression of CC chemokines

Circulating cytokines and vascular dementia: A bi-directional Mendelian randomization study

Inflammatory responses are associated with the development of vascular dementia (VaD). Circulating cytokines modulate the inflammatory response and are important for the immune system. To further elucidate the role of the immune system in VaD, we used Mendelian randomization (MR) to comprehensively and bi-directionally assess the role of circulating cytokines in VaD. Using state-of-the-art genome-wide association studies, we primarily assessed whether different genetic levels of 41 circulating cytokines affect the risk of developing VaD and, in turn, whether the genetic risk of VaD affects these circulating cytokines. We used inverse variance weighting (IVW) and several other MR methods to assess the bidirectional causality between circulating cytokines and VaD, and performed sensitivity analyses. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was inversely associated with VaD risk [odds ratio (OR): 0.74, 95 % confidence interval (CI): 0.60-0.92, P = 0.007, 0.007]. VaD was associated with seven circulating cytokines: macrophage inflammatory protein 1b (MIP-1 beta) [OR: 1.05, 95 % CI: 1.01-1.08, P = 0.009], Interleukin-12p70 (IL-12) [OR: 1.04, 95 % CI: 1.00-1.08, P = 0.047], Interleukin-17 (IL-17) [OR: 1.04, 95 % CI: 1.00-1.07, P = 0.038], Interleukin-7 (IL-7) [OR: 1.07, 95 % CI: 1.02-1.12, P = 0.009], Interferon gamma (IFN-γ) [OR: 1.03, 95 % CI: 1.00-1.07, P = 0.046], Granulocyte-colony stimulating factor (GCSF) [OR: 1.06, 95 % CI: 1.02-1.09, P = 0.001], Fibroblast growth factor (FGF) [P = 0.001], and Fibroblast growth factor (FGF) [P = 0.001]. Fibroblast growth factor basic (FGF-Basic) [OR: 1.04, 95 % CI: 1.01-1.08, P = 0.02] were positively correlated. Circulating cytokines are associated with VaD, and further studies are needed to determine whether they are effective targets for intervention to prevent or treat VaD.

A candidate gene study of intermediate histopathological phenotypes in HIV-associated neurocognitive disorders

HIV-associated neurocognitive disorders (HAND) describe a spectrum of neuropsychological impairment caused by HIV-1 infection. While the sequence of cellular and physiological events that lead to HAND remains obscure, it likely involves chronic neuroinflammation. Host genetic markers that increase the risk for HAND have been reported, but replication of such studies is lacking, possibly due to inconsistent application of a behavioral phenotype across studies. In the current study, we used histopathologic phenotypes in order to validate putative risk alleles for HAND. The National NeuroAIDS Tissue Consortium, a longitudinal study of the neurologic manifestations of HIV. Data and specimens were obtained from 175 HIV-infected adults. After determining several potential covariates of neurocognitive functioning, we quantified levels of six histopathological markers in the frontal lobe in association with neurocognitive functioning: SYP, MAP 2, HLA-DR, Iba1, GFAP, and β-amyloid. We then determined alleles of 15 candidate genes for their associations with neurocognitive functioning and histopathological markers. Finally, we identified the most plausible causal pathway based on our data using a multi-stage linear regression-based mediation analysis approach. None of the genetic markers were associated with neurocognitive functioning. Of the histopathological markers, only MAP 2 and SYP were associated with neurocognitive functioning; however, MAP 2 and SYP did not vary as a function of genotype. Mediation analysis suggests a causal pathway in which presynaptic degeneration (SYP) leads to somatodendritic degeneration (MAP 2) and ultimately neurocognitive impairment. This study did not support the role of host genotype in the histopathology underlying HAND. The findings lend further support for synaptodendritic degeneration as the proximal underlying neuropathological substrate of HAND.

Endothelins in inflammatory neurological diseases

Endothelins were discovered more than thirty years ago as potent vasoactive compounds. Beyond their well-documented cardiovascular properties, however, the contributions of the endothelin pathway have been demonstrated in several neuroinflammatory processes and the peptides have been reported as clinically relevant biomarkers in neurodegenerative diseases. Several studies report that endothelin-1 significantly contributes to the progression of neuroinflammatory processes, particularly during infections in the central nervous system (CNS), and is associated with a loss of endothelial integrity at the blood brain barrier level. Because of the paucity of clinical trials with endothelin-1 antagonists in several infectious and non-infectious neuroinflammatory diseases, it remains an open question whether the 21 amino acid peptide is a mediator/modulator rather than a biomarker of the progression of neurodegeneration. This review focuses on the potential roles of endothelins in the pathology of neuroinflammatory processes, including infectious diseases of viral, bacterial or parasitic origin in which the synthesis of endothelins or its pharmacology have been investigated from the cell to the bedside in several cases, as well as in non-infectious inflammatory processes such as neurodegenerative disorders like Alzheimers Disease or central nervous system vasculitis.

Personalized Risk Index for Neurocognitive Decline Among People With Well-Controlled HIV Infection

BACKGROUND

Little is known about the predictors of neurocognitive decline in HIV+ individuals with good virological control. Identification of modifiable risk factors would allow targeted interventions to reduce the risk of decline in higher risk individuals. The objective of this study was to develop a risk index to predict neurocognitive decline over 3 years in aviremic HIV+ individuals.

METHODS

As part of the CNS HIV Anti-Retroviral Therapy Effects Research (CHARTER) study, HIV+ adults completed clinical evaluation and neuropsychological tests every 6 months. Group-based trajectory analysis was used to detect patterns of neurocognitive change; individuals who deteriorated ≥ 0.5 SD on at least one neuropsychological test were considered decliners. Multiple logistic regression was used to identify baseline sociodemographic, clinical, biological, and lifestyle factors associated with decline in the subgroup that was consistently aviremic during the first 3 years. A risk index was developed using the beta-coefficients from the final regression model.

RESULTS

Neurocognitive decline occurred in 23 of 191 (12%) participants followed longitudinally. The baseline factors that predicted decline were glomerular filtration rate ≤50 mL/min, known duration of HIV infection ≥15 years, education ≤12 years, and cerebrospinal fluid protein >45 mg/dL.

CONCLUSIONS

Using this analytic approach, neurocognitive decline was uncommon in this sample of aviremic HIV+ individuals. The 3-year risk of decline ranged from 2% in those with no risk factors to 95% in those with all 4. The strongest predictor was glomerular filtration rate, also a predictor of cardiovascular disease. This raises the possibility that controlling vascular risk factors could reduce the risk of neurocognitive decline.

Common gene-network signature of different neurological disorders and their potential implications to neuroAIDS

The neurological complications of AIDS (neuroAIDS) during the infection of human immunodeficiency virus (HIV) are symptomized by non-specific, multifaceted neurological conditions and therefore, defining a specific diagnosis/treatment mechanism(s) for this neuro-complexity at the molecular level remains elusive. Using an in silico based integrated gene network analysis we discovered that HIV infection shares convergent gene networks with each of twelve neurological disorders selected in this study. Importantly, a common gene network was identified among HIV infection, Alzheimer's disease, Parkinson's disease, multiple sclerosis, and age macular degeneration. An mRNA microarray analysis in HIV-infected monocytes showed significant changes in the expression of several genes of this in silico derived common pathway which suggests the possible physiological relevance of this gene-circuit in driving neuroAIDS condition. Further, this unique gene network was compared with another in silico derived novel, convergent gene network which is shared by seven major neurological disorders (Alzheimer's disease, Parkinson's disease, Multiple Sclerosis, Age Macular Degeneration, Amyotrophic Lateral Sclerosis, Vascular Dementia, and Restless Leg Syndrome). These networks differed in their gene circuits; however, in large, they involved innate immunity signaling pathways, which suggests commonalities in the immunological basis of different neuropathogenesis. The common gene circuits reported here can provide a prospective platform to understand how gene-circuits belonging to other neuro-disorders may be convoluted during real-time neuroAIDS condition and it may elucidate the underlying-and so far unknown-genetic overlap between HIV infection and neuroAIDS risk. Also, it may lead to a new paradigm in understanding disease progression, identifying biomarkers, and developing therapies.

Multilevel analysis of neuropathogenesis of neurocognitive impairment in HIV

The neuropathogenesis of HIV-associated neurocognitive disorders (HAND) remains puzzling. We interrogated several levels of data (host genetic, histopathology, brain viral load, and neurocognitive) to identify histopathological changes most relevant to HAND. The design of the study is a clinicopathological study employing genetic association analyses. Data and brain tissue from 80 HIV-infected adults were used. Markers in monocyte chemoattractant protein-1 (MCP-1), interleukin 1-alpha (IL1-α), macrophage inflammatory protein 1-alpha (MIP1-α), DRD3, DRD2, and apolipoprotein E (ApoE) were genotyped. Microtubule associated protein 2 (MAP2), synaptophysin (SYP), human leukocyte antigen-DR (HLA-DR), glial fibrillary acidic protein (GFAP), amyloid beta (A-Beta), and ionized calcium-binding adaptor molecule-1 (Iba-1) immunoreactivity were quantified in the frontal cortex, putamen, and hippocampus. A composite score for each marker (mean of the three brain regions) was used. Neurocognitive functioning and other clinical variables were determined within 1 year of death. Brain HIV RNA viral load was available for a subset of cases. MAP2 and SYP proved most relevant to neurocognitive functioning. Immunoreactivity of these markers, as well as A-Beta and Iba-1, was correlated with brain HIV RNA viral load. Several genetic markers in combination with other factors predicted histopathology: HIV blood viral load, MIP1-α genotype, and DRD3 genotype predicted Iba-1 immunoreactivity; the duration of infection and IL1-α genotype predicted GFAP immunoreactivity; ApoE genotype and age at death predicted A-Beta immunoreactivity. These data indicate that HIV replication in the brain is the primary driving force leading to neuroinflammation and dysfunctional protein clearance, as reflected by A-Beta and Iba-1. Downstream to these changes are synaptodendritic degeneration, which is the immediate histopathological substrate of the neurocognitive impairment characteristic of HAND. These intermediate histopathological phenotypes are influenced by host genetic polymorphisms in genes encoding cytokines/chemokines, neuronal protein clearance pathways, and dopaminergic factors.

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.

Towards nanomedicines for neuroAIDS

Although highly active antiretroviral therapy (HAART) has resulted in remarkable decline in the morbidity and mortality in AIDS patients, controlling HIV infections still remain a global health priority. HIV access to the CNS serves as the natural viral preserve because most antiretroviral (ARV) drugs possess inadequate or zero delivery across the brain barriers. Thus, development of target-specific, effective, safe, and controllable drug-delivery approach is an important health priority for global elimination of AIDS progression. Emergence of nanotechnology in medicine has shown exciting prospect for development of novel drug delivery systems to administer the desired therapeutic levels of ARV drugs in the CNS. Neuron-resuscitating and/or antidependence agents may also be delivered in the brain through nanocarriers to countercheck the rate of neuronal degradation during HIV infection. Several nanovehicles such as liposomes, dendrimers, polymeric nanoparticles, micelles, and solid lipid nanoparticles have been intensively explored. Recently, magnetic nanoparticles and monocytes/macrophages have also been used as carrier to improve the delivery of nanoformulated ARV drugs across the blood-brain barrier. Nevertheless, more rigorous research homework has to be elucidated to sort out the shortcomings that affect the target specificity, delivery, release, and/or bioavailability of desired amount of drugs for treatment of neuroAIDS.

Current status of chemokines in the adult CNS

Chemokines - chemotactic cytokines - are small secreted proteins that attract and activate immune and non-immune cells in vitro and in vivo. It has been suggested that chemokines and their receptors play a role in the central nervous system (CNS), in addition to their well established role in the immune system. We focus here on three chemokines-CXCL12 (C-X-C motif ligand 12), CCL2 (C-C motif ligand 2), and CX3CL1 (C-X-3C motif ligand 1) - and their principal receptors - CXCR4 (C-X-C motif receptor 4), CCR2 (C-C motif receptor 2) and CX3CR1 (C-X-3C motif receptor 1), respectively. We first introduce the classification of chemokines and their G-protein coupled receptors and the main signaling pathways triggered by receptor activation. We then discuss the cellular distribution of CXCL12/CXCR4, CCL2/CCR2 and CX3CL1/CX3CR1 in adult brain and the neurotransmission and neuromodulation effects controlled by these chemokines in the adult CNS. Changes in the expression of CXCL12, CCL2 and CX3CL1 and their respective receptors are also increasingly being implicated in the pathogenesis of CNS disorders, such as Alzheimer's disease, Parkinson's disease, HIV-associated encephalopathy, stroke and multiple sclerosis, and are therefore plausible targets for future pharmacological intervention. The final section thus discusses the role of these chemokines in these pathophysiological states. In conclusion, the role of these chemokines in cellular communication may make it possible: (i) to identify new pathways of neuron-neuron, glia-glia or neuron-glia communications relevant to both normal brain function and neuroinflammatory and neurodegenerative diseases; (ii) to develop new therapeutic approaches for currently untreatable brain diseases.

Astrocytes contacting HIV-1-infected macrophages increase the release of CCL2 in response to the HIV-1-dependent enhancement of membrane-associated TNFα in macrophages

The presence of human immunodeficiency virus (HIV)-infected macrophages in the parenchyma of central nervous system is an hallmark of acquired immunodeficiency syndrome-related neuroinflammation. Once penetrated the blood-brain barrier (BBB), macrophages closely interact with astrocytes, beginning with those lying beneath the BBB endothelium. By investigating the consequences of the cell-cell interaction between HIV-infected macrophages and astrocytes, we observed that the HIV-1 expression in macrophagic cells correlated with increased chemotactic activity in supernatants of astroglial cells. Gene array analysis revealed an impressive increase in the transcription of the gene for the CCL2/MCP-1 chemokine in astroglial cells isolated from HIV-1-infected co-cultures compared with cells from uninfected co-cultures. This phenomenon coupled with the increase in CCL2 release and depended on the cell-cell contact. In addition, it was a consequence of the HIV-1-induced enhancement of membrane-associated tumor necrosis factor-α in macrophagic cells, and correlated with increased levels of nuclear factor kappaB activation in astroglial cells. These observations could mirror a mechanism of recruitment of leukocytes through the BBB, likely contributing to the increase in both viral load and inflammation in central nervous system of HIV-infected patients.

CNS inflammation and macrophage/microglial biology associated with HIV-1 infection

Human immunodeficiency virus type 1 (HIV-1) infection of the central nervous system (CNS) can result in neurological dysfunction with devastating consequences in a significant proportion of individuals with acquired immune deficiency syndrome. HIV-1 does not infect neurons directly but induces damage indirectly through the accumulation of activated macrophage/microglia (M/M) cells, some of which are infected, that release neurotoxic mediators including both cellular activation products and viral proteins. One mechanism for the accumulation of activated M/M involves the development in infected individuals of an activated peripheral blood monocyte population that traffics through the blood-brain barrier, a process that also serves to carry virus into CNS and establish local infection. A second mechanism involves the release by infected and activated M/M in the CNS of chemotactic mediators that recruit additional monocytes from the periphery. These activated M/M, some of which are infected, release a number of cytokines and small molecule mediators as well as viral proteins that act on bystander cells and in turn activate them, thus amplifying the cascade. These viral proteins and cellular products have neurotoxic properties as well, both directly and through induction of astrocyte dysfunction, which ultimately lead to neuronal injury and death. In patients effectively treated with antiretroviral therapy, frank dementia is now uncommon and has been replaced by milder forms of neurocognitive impairment, with less frequent and more focal neuropathology. This review summarizes key findings that support the critical role and mechanisms of monocyte/macrophage activation and inflammation as a major component for HIV-1 encephalitis or HIV-1 associated dementia.

Neurotoxic profiles of HIV, psychostimulant drugs of abuse, and their concerted effect on the brain: current status of dopamine system vulnerability in NeuroAIDS

There are roughly 30-40 million HIV-infected individuals in the world as of December 2007, and drug abuse directly contributes to one-third of all HIV infections in the United States. Antiretroviral therapy has increased the lifespan of HIV-seropositives, but CNS function often remains diminished, effectively decreasing quality of life. A modest proportion may develop HIV-associated dementia, the severity and progression of which is increased with drug abuse. HIV and drugs of abuse in the CNS target subcortical brain structures and DA systems in particular. This toxicity is mediated by a number of neurotoxic mechanisms, including but not limited to, aberrant immune response and oxidative stress. Therefore, novel therapeutic strategies must be developed that can address a wide variety of disparate neurotoxic mechanisms and apoptotic cascades. This paper reviews the research pertaining to the where, what, and how of HIV and cocaine/methamphetamine toxicity in the CNS. Specifically, where these toxins most affect the brain, what aspects of the virus are neurotoxic, and how these toxins mediate neurotoxicity.

Tight junction regulation by morphine and HIV-1 tat modulates blood-brain barrier permeability

Human immunodeficiency virus (HIV)-1 patients who abuse opiates are at a greater risk of developing neurological complications of AIDS. Alterations in blood-brain barrier (BBB) integrity are associated with cytoskeletal disorganization and disruption of tight junction (TJ) integrity. We hypothesize that opiates in combination with HIV-1 viral proteins can modulate TJ expression in primary brain microvascular endothelial cells (BMVEC), thereby compromising BBB integrity and exacerbating HIV-1 neuropathogenesis. We investigated the effect of morphine and/or tat on the expression of TJ proteins ZO-1, JAM-2, Occludin and P-glycoprotein and the functional effects of TJ modulation in BMVEC. Morphine and/or tat, via the activation of pro-inflammatory cytokines, intracellular Ca(2+) release, and activation of myosin light chain kinase, modulated TJ expression resulting in decreased transendothelial electric resistance and enhanced transendothelial migration across the BBB. These studies may lead to the development of novel anti-HIV-1 therapeutics that target specific TJ proteins, thus preventing TJ disruption in opiate using HIV-1 patients.

Roles of MCP-1 in development of HIV-dementia

The encephalopathy caused by HIV, known clinically as HIV-associated dementia (HAD) and pathologically as HIV encephalitis (HIVE), results from intense infiltration of mononuclear cells, productive replication of the virus in monocyte-derived macrophages/microglia, abortive replication in astrocytes and activation of macrophages/microglia and astrocytes leading to neuronal degeneration in the brains of infected persons. Recent findings have suggested that development of HAD is based more on the activation process than on direct evidence of virus replication in the brain. Since HAD is based on the encephalitic process, major studies have been directed to the mechanisms regulating the inflammatory process. Monocyte chemoattractant protein 1, MCP-1, is a chemokine that is implicated in this process and also in the development of activation in the brain. In this review, we have attempted to identify mechanisms that induce expression of MCP-1 in the brain and the role that it plays in recruitment of mononuclear cells from blood to brain and in the activation processes of inflammatory and neural cells that lead to development of degenerative changes in the neuronal population.

HIV-1 activates proinflammatory and interferon-inducible genes in human brain microvascular endothelial cells: putative mechanisms of blood-brain barrier dysfunction

The mechanisms underlying blood-brain barrier (BBB) dysfunction seen in human immunodeficiency virus 1 (HIV-1) infection are poorly understood; however, they are believed to be caused by interactions of human brain microvascular endothelial cells (HBMEC) with virus-infected macrophages. Using a transwell system and Affymetrix arrays, we investigated HIV-1-induced genomic changes in HBMEC after coculture with HIV-1-infected or -uninfected monocyte-derived macrophages (MDM). Differentially expressed genes were determined by linear modeling and then were grouped by hierarchical clustering. Compared to HBMEC cocultured with noninfected MDM, 184 probe sets corresponding to 84 genes were differentially expressed in HBMEC cocultured with HIV-infected MDM. Genes activated in HIV-1 MDM-exposed HBMEC included proinflammatory cytokines and chemokines, tumor necrosis factor-alpha-induced proteins, interferon (IFN)-inducible genes, intercellular adhesion molecule-1, transcription factors of the nuclear factor-kappaB family, and signal transducer and activator of transcription 1. Analysis of molecular networks and canonical pathways associated with differentially expressed genes suggest that HIV-1 causes BBB impairment by mechanisms involving inflammation, cytokine, and IFN signaling in HBMEC.

Impaired placental neovascularization in mice with pregnancy-associated hypertension

Preeclampsia is a serious disorder that may result in severe morbidity and mortality for mother and fetus, and it is thought that the placental dysfunction is important in the pathogenesis of preeclampsia. As the model of preeclampsia, we previously generated a transgenic mouse model that developed pregnancy-associated hypertension (PAH) by mating females expressing human angiotensinogen with males expressing human renin. In PAH mice, maternal blood pressure started to rise from days 12 to 13 of gestation (E12-13) to term (E19-20), which is accompanied by the fetal intrauterine growth retardation and systemic maternal disorders including proteinuria and convulsion. To understand the pathology of the complications in PAH mice that overlap with those in human preeclampsia, we analyzed the PAH placenta sequentially from the onset of hypertension to the term of delivery. In PAH placenta, histological analysis revealed that the microvessel densities of fetal vasculature at term were significantly lower than those of normal placenta, and the majority of terminal vessels of PAH placenta were lacking for pericytes and basement membrane. The interaction between fetal vasculature and maternal blood canal at labyrinth of PAH placenta was morphologically distorted, and the expression patterns of key molecules in neovascularization of PAH placenta were distinct from those of normal placenta during pregnancy. In addition, maternal plasma level of soluble form of vascular endothelial growth factor receptor-1 (sVEGFR-1) was significantly increased in PAH at E19. Furthermore, in uteroplacental site, in situ proteolytic activity of PAH mice was suppressed from E16 to term compared to that of normal pregnancy, and the expression of matrix metalloproteinase-2 mRNA was strikingly downregulated at E16 in PAH mice. Collective data suggest that the impairments of fetoplacental neovascularization and uteroplacental remodeling contribute to the development of complications in PAH.

Methamphetamine alters blood brain barrier permeability via the modulation of tight junction expression: Implication for HIV-1 neuropathogenesis in the context of drug abuse

The pathogenesis of human immunodeficiency virus (HIV) associated encephalopathy is attributed to infiltration of the central nervous system (CNS) by HIV-1 infected mononuclear cells that transmigrate across the blood brain barrier (BBB). The endothelial tight junctions (TJ) of the blood brain barrier (BBB) play a critical role in controlling cellular traffic into the CNS. Neuropathogenesis of HIV-1 is exacerbated by drugs of abuse such as methamphetamine (Meth) which are capable of dysregulating BBB function. HIV-1 viral proteins like gp120 are both neurotoxic and cytotoxic and have been implicated in the development of HIV-1 dementia (HAD). We hypothesize that gp120 in synergy with Meth can alter BBB permeability via the modulation of tight junction expression. We investigated the effect of Meth and/or gp120 on the basal expression of TJ proteins ZO-1, JAM-2, Occludin, Claudin-3 and Claudin-5, using in vitro cultures of the primary brain microvascular endothelial cells (BMVEC). Further, the functional effects of TJ modulation were assessed using an in vitro BBB model, that allowed measurement of BBB permeability using TEER measurements and transendothelial migration of immunocompetent cells. Our results show that both Meth and gp120 individually and in combination, modulated TJ expression, and these effects involved Rho-A activation. Further, both Meth and gp120 alone and in combination significantly decreased transendothelial resistance across the in vitro BBB and the enhanced transendothelial migration of immunocompetent cells across the BBB. An understanding of the mechanisms of BBB breakdown that lead to neurotoxicity is crucial to the development of therapeutic modalities for Meth abusing HAD patients.

Crosstalk between components of the blood brain barrier and cells of the CNS in microglial activation in AIDS

During the progression of AIDS, a majority of patients develop cognitive disorders such as HIV encephalitis (HIVE) and AIDS dementia complex (ADC), which correlate closely with macrophage infiltration into the brain and microglial activation. Microglial activation occurs in response to infection, inflammation and neurological disorders including HIVE, Alzheimer's disease, Parkinson's disease and multiple sclerosis. Microglia can be activated by immunoreactive cells independent of, but enhanced by HIV infection, from at least two routes. Activation may occur from signals originating from activated monocytes and lymphocytes in the blood stream, which initiate a cascade of stimuli that ultimately reach microglia in the brain or from activated macrophages/microglia/astrocytes within the brain. Effects of microglial activation stemming from both systemic and CNS HIV infection act together to commence signaling feedback, leading to HIVE and increased neurodegeneration. Most recent data indicate that in AIDS patients, microglial activation in the brain with subsequent release of excitotoxins, cytokines and chemokines leads to neurodegeneration and cognitive impairment. Since the presence of HIV in the brain results from migration of infected monocytes and lymphocytes across the vascular boundary, the development of novel therapies aimed at protecting the integrity of the blood brain barrier (BBB) upon systemic HIV infection is critical for controlling CNS infection.

CD163 Identifies a Unique Population of Ramified Microglia in HIV Encephalitis (HIVE)

The idea that CNS ramified microglia are quiescent has been challenged by studies that show that microglia without the classic signs of activation can be phagocytic and appear with shorter, thicker ramifications. These semi-activated cells may constitute a form of microglia that has not been previously recognized in neuropathological conditions and may contribute to the pathology and dysfunction in these disorders. This study investigated the expression of CD 163, a cell surface marker whose normal expression is restricted to monocytes/macrophages, in cases of HIV or SIV encephalitis (HIVE/SIVE), Alzheimer disease, and variant Creutzfeldt-Jakob disease. In HIVE/SIVE, in addition to reacting with CNS macrophages, CD163 antibody staining was shown to highlight ramified microglia. Such reactivity was especially notable in grey matter ramified microglia and was greater than that of another typically used marker, HLA-DR. CD163 expression was only observed in infected/affected tissue, in contrast to that shown with another microglia marker, GLUT5, which has recently been shown to identify all microglia regardless of disease state. Although activated microglia were present in the other disorders, as evidenced by strong HLA-DR expression, there was very little CD163 immunoreactivity. The activation state identified by CD163 has not been previously recognized and may have a positive or negative impact on neuronal damage shown in HIV-associated dementia.

Infiltration of the brain by pathogens causes Alzheimer's disease

Despite very numerous studies on Alzheimer's disease (AD), especially on amyloid plaques and neurofibrillary tangles, little information has been obtained thus on the causes of the disease. Evidence is described here that implicates firstly herpes simplex virus type 1 (HSV1) as a strong risk factor when it is present in brain of carriers of the type 4 allele of the gene for apolipoprotein E (APOE-4). Indirect support comes from studies indicating the role of APOE in several diverse diseases of known pathogen cause. A second putative risk factor is the bacterium, Chlamydia pneumoniae. This pathogen has been identified and localized in AD brain. Current studies aimed at "proof of principle" address the entry of the organism into the CNS, the neuroinflammatory response to the organism, and the role that the organism plays in triggering AD pathology. An infection-based animal model demonstrates that following intranasal inoculation of BALB/c mice with C. pneumoniae, amyloid plaques/deposits consistent with those observed in the AD brain develop, thus implicating this infection in the etiology of AD.

Potential role of MCP-1 in endothelial cell tight junction 'opening': signaling via Rho and Rho kinase

The expression of the monocyte chemoattractant protein-1 (MCP-1) receptor CCR2 by brain endothelial cells suggests that MCP-1 may have other functions than purely driving leukocyte migration into brain parenchyma during inflammation. This study examines one of these potential novel roles of MCP-1 regulation of endothelial permeability using primary cultures of mouse brain endothelial cells. MCP-1 induces reorganization of actin cytoskeleton (stress fiber formation) and redistribution of tight junction proteins, ZO-1, ZO-2 occludin and claudin-5, from the Triton X-100-soluble to the Triton X-100-insoluble fractions. These morphological changes are associated with a decrease in transendothelial electrical membrane resistance and an increase in [14C]inulin permeability. MCP-1 did not induce these events in brain endothelial cells prepared from mice genotype CCR2-/-. The Rho kinase inhibitor Y27632 and inhibition of Rho (C3 exoenzyme, and dominant negative mutant of Rho, RhoT19N) prevented MCP-1-induced stress fiber assembly, reorganization of tight junction proteins and alterations in endothelial permeability. In all, this suggests that a small GTPase Rho and Rho kinase have a pivotal role in MCP-1-induced junction disarrangement. These data are the first to strongly suggest that MCP-1, via CCR2 present on brain endothelial cells, contributes to increased brain endothelial permeability.

CD14+ cell dysfunction in patients with chronic active hepatitis B

AIM: To study the functional states of CD14⁺ cells in peripheral blood mononuclear cell (PBMCs) by analyzing the expression of early active antigen, production of pro-inflammatory cytokines and phagocytosis with flow cytometry (FCM).

METHODS: PBMCs were isolated from 11 patients with chronic active hepatitis B and 10 healthy blood donors, and 4-color flow cytometry and gate setting techniques were applied. The percentage of CD14⁺ cells and level of CD14 antigen were tested by FCM, after gate setting with CD14, side scatter (SSC) and activation-linked surface antigen (CD69) expression rate, percentage of TNF-α producing cells, level of intro-cellular TNF-α, the percentage of phagocytes and the ability of phagocytosis were investigated.

RESULTS: The SSC mean value of CD14⁺ cell of HBV patients was higher than that of health control (P < 0.01); There were no difference between two testing groups on the percentage of CD14⁺ cells and level of CD14 antigen, however the level of CD14 antigen was positively associated with the percentage of CD14⁺ cells. CD14/69 double expression rate was significantly higher than that of control group (P < 0.01); No difference was observed on CD14/TNF-α double stain cells between testing groups; In comparison with control group, the level of cellular TNF-α in HBV group was higher (P < 0.05). In control group, the percentage of TNF-α producing cells were correlated with SSC value and number of phagocytes that expressed CD14/69. There was no difference in phagocytes that expressed CD14/69 in two groups. As compared with the control group, there was more phagocytostic CD14⁺ cells in HBV group (P < 0.01), but the mean phagocytosis amount was significantly lower in this group (P < 0.05), and the number of phagocyte was negatively correlated with the level of CD14 antigen; while the SSC value and number of TNF-αproducing cells were negatively correlated with level of CD14 antigen.

CONCLUSION: CD14⁺ cells in PBMCs from chronic active hepatitis B patients are over activated in a dysfunction stage.

Growth hormone prevents human immunodeficiency virus-induced neuronal p53 expression

Growth hormone (GH) is neuroprotective, presumably through its actions on GH receptor-mediated pathways. Here, we examined the effects of GH using in vitro and in vivo assays of human immunodeficiency virus (HIV)-induced neuronal injury. Neuronal cultures were in assays of neurotoxicity induced by supernatants from HIV-1 tat-transfected monocytoid cells (Tat supernatant). GH treatment reduced neuronal death compared with untreated cultures (p < 0.001), which was blocked by a GH receptor antagonist, B2036. Tat supernatant-induced p53 expression in neurons was also reduced by GH treatment. Expression of both p53 and GH receptor were increased in brain tissue from HIV-infected persons compared with controls (p < 0.05). Mice receiving intrastriatal implants of Tat supernatant and treated with GH showed less neurobehavioral abnormalities together with reduced neuroinflammation and neuronal injury compared with untreated animals (p < 0.01). Three acquired immunodeficiency syndrome-defined patients with neurocognitive impairment were serially evaluated during daily GH treatment showing a sustained improvement in neuropsychological performance (p < 0.01). GH prevents neuronal death through its actions on neurons involving a p53-mediated pathway and also improved in vivo neurological function, indicating that GH may have a role in the treatment of HIV-induced neurodegeneration.

Up-regulation of proteinase-activated receptor 1 expression in astrocytes during HIV encephalitis

Proteinase-activated receptor 1 (PAR-1) is a G protein-coupled receptor that is activated by thrombin and is implicated in the pathogenesis of inflammation. Although PAR-1 is expressed on immunocompetent cells within the brain such as astrocytes, little is known about its role in the pathogenesis of inflammatory brain diseases. Herein, we investigated PAR-1 regulation of brain inflammation by stimulating human astrocytic cells with thrombin or the selective PAR-1-activating peptide. Activated cells expressed significantly increased levels of IL-1 beta, inducible NO synthase, and PAR-1 mRNA. Moreover, supernatants of these same cells were neurotoxic, which was inhibited by an N-methyl-D-aspartate receptor antagonist. Striatal implantation of the PAR-1-activating peptide significantly induced brain inflammation and neurobehavioral deficits in mice compared with mice implanted with the control peptide or saline. Since HIV-related neurological disease is predicated on brain inflammation and neuronal injury, the expression of PAR-1 in HIV encephalitis (HIVE) was investigated. Immunohistochemical analysis revealed that PAR-1 and (pro)-thrombin protein expression was low in control brains, but intense immunoreactivity was observed on astrocytes in HIVE brains. Similarly, PAR-1 and thrombin mRNA levels were significantly increased in HIVE brains compared with control and multiple sclerosis brains. These data indicated that activation and up-regulation of PAR-1 probably contribute to brain inflammation and neuronal damage during HIV-1 infection, thus providing new therapeutic targets for the treatment of HIV-related neurodegeneration.

Central nervous system damage, monocytes and macrophages, and neurological disorders in AIDS

This review focuses on the role of the extended macrophage/monocyte family in the central nervous system during HIV or SIV infection. The accumulated data, buttressed by recent experimental results, suggest that these cells play a central, pathogenic role in retroviral-associated CNS disease. While the immune system is able to combat the underlying retroviral infection, the accumulation and widespread activation of macrophages, microglia, and perivascular cells in the CNS are held in check. However, with the collapse of the immune system and the disappearance of the CD4(+) T cell population, productive infection reemerges, especially in CNS macrophages. These cells, as well as noninfected macrophages, are stimulated to high levels of activation. When members of this cell group become highly activated, they elaborate a wide spectrum of deleterious substances into the neural parenchyma. In the final phases of HIV or SIV infection, this chronic, widespread, and dramatic level of macrophage/monocyte/microglial activation constitutes a self-sustaining state of macrophage dysregulation, which results in pathological alterations and the emergence of various neurological problems.

Morphine Regulates Gene Expression of α- and β-Chemokines and Their Receptors on Astroglial Cells Via the Opioid μ Receptor

The brain is a target organ for recreational drugs and HIV-1. Epidemiological data demonstrate that opioid abuse is a risk factor for HIV-1 infection and progression to AIDS. Chemokines and their receptors have been implicated in the neuropathogenesis of HIV-1 infections. However, little is known about the effects of opioids on the expression of chemokines and their receptors (the latter also are HIV-1 coreceptors) by cells of the CNS. Herein we describe the effects of morphine on gene expression of the alpha- and beta-chemokines and their receptors by the astrocytoma cell line U87 and by primary normal human astrocyte (NHA) cultures. U87 cells treated with morphine showed significant down-regulation of IL-8 gene expression, whereas expression of the IL-8 receptor CXCR2 was reciprocally up-regulated as detected by RT-PCR. Treatment of NHAs with morphine suppressed IL-8 and macrophage-inflammatory protein-1beta gene expression, whereas expression of their receptor genes, CCR3 and CCR5, was simultaneously enhanced. These morphine-induced effects on U87 and NHA cells were reversed by the opioid mu receptor antagonist beta-funaltrexamine. Morphine also enhanced the constitutive expression of the opioid mu receptor on astroglial cells. Our results support the hypothesis that opioids play a significant role in the susceptibility of the CNS to HIV-1 infection and subsequent encephalopathy by inhibiting local production of HIV-1-protective chemokines (IL-8 and macrophage-inflammatory protein-1beta) and enhancing expression of HIV-1 entry coreceptor genes (CCR3, CCR5, and CXCR2) within the CNS. These effects of opioids appear to be mediated through the opioid mu receptor that we demonstrated on astroglial cells.

HIV-1 Tat neurotoxicity is prevented by matrix metalloproteinase inhibitors

The release of potentially neurotoxic molecules by HIV-infected brain macrophages is accompanied by neuronal injury and death that results in the development of HIV-associated dementia (HAD). Among the potential neurotoxins implicated in the development of HAD is the HIV-1 transactivating protein, Tat. To investigate the mechanism by which Tat causes neurotoxicity, brain-derived Tat sequences from nondemented (Tat-ND) and demented (Tat-HAD) AIDS patients, which differed primarily in the augmenting region of Tat, were expressed in U937 monoblastoid cells and primary human macrophages. Cells expressing Tat-HAD protein exhibited elevated matrix metalloproteinase (MMP)-2 and -7 release and activation, but cells expressing Tat-ND did not exhibit enhanced MMP expression. Conditioned media from Tat-HAD-transfected cells caused significantly greater neuronal death (15.4 +/- 4.3%) than did Tat-ND (4.4 +/- 2.1%) or nontransfected (2.1 +/- 0.8%) cell-derived conditioned media. The neurotoxicity induced by Tat-HAD was inhibited by anti-MMP-2 or -7 antibodies (p < 0.005) but not by antibodies against MMP-9 or Tat. Similarly, scid/nod mice receiving striatal implants of Tat-HAD-transfected cells exhibited greater neurobehavioral abnormalities and neuronal loss (p < 0.005) than did animals receiving Tat-ND or nontransfected cells, which were reduced by treatment with the MMP inhibitor prinomastat (p < 0.005). These findings indicate that Tat causes neuronal death through an indirect mechanism that is Tat sequence dependent and involves the induction of MMPs.