Astrocyte expression of aging-associated markers positively correlates with neurodegeneration in the frontal lobe of the rhesus macaque brain

Introduction

As the population over the age of 65 increases, rates of neurodegenerative disorders and dementias will rise - necessitating further research into the cellular and molecular mechanisms that contribute to brain aging. With the critical importance of astrocytes to neuronal health and functioning, we hypothesized that alterations in astrocyte expression of aging-associated markers p16INK4a (p16) and sirtuin 1 (SIRT1) with age would correlate with increased rates of neurodegeneration, as measured by FluoroJade C (FJC) staining.

Methods

To test this hypothesis, 19 rhesus macaques at the Tulane National Primate Research Center were selected based on the following criteria: archival FFPE CNS tissue available to use, no noted neuropathology, and an age range of 5-30 years. Tissues were cut at 5 μm and stained for GFAP, p16, SIRT1, and FJC, followed by whole-slide imaging and HALO® image analysis for percentage of marker-positive cells and relative intensity of each stain.

Results

We found the percentage of p16+ cells increases with age in total cells and astrocytes of the frontal (p = 0.0021, p = 0.0012 respectively) and temporal (p = 0.0226, p = 0.0203 respectively) lobes, as well as the relative intensity of p16 staining (frontal lobe: p = 0.0060; temporal lobe: p = 0.0269). For SIRT1, we found no correlation with age except for an increase in the relative intensity of SIRT1 in the temporal lobe (p = 0.0033). There was an increase in neurodegeneration, as measured by the percentage of FJC+ cells in the frontal lobe with age (p = 0.0057), as well as in the relative intensity of FJC staining in the frontal (p = 0.0030) and parietal (p = 0.0481) lobes. Importantly, increased p16 and SIRT1 expression in astrocytes correlated with increasing neurodegeneration in the frontal lobe (p = 0.0009, p = 0.0095 respectively).

Discussion

Together, these data suggest that age-associated alterations in astrocytes contribute to neurodegeneration and provide a target for mechanistic studies in the future.

Advances in HIV therapeutics and cure strategies: findings obtained through non-human primate studies

Human immunodeficiency virus (HIV), the main contributor of the ongoing AIDS epidemic, remains one of the most challenging and complex viruses to target and eradicate due to frequent genome mutation and immune evasion. Despite the development of potent antiretroviral therapies, HIV remains an incurable infection as the virus persists in latent reservoirs throughout the body. To innovate a safe and effective cure strategy for HIV in humans, animal models are needed to better understand viral proliferation, disease progression, and therapeutic response. Nonhuman primates infected with simian immunodeficiency virus (SIV) provide an ideal model to study HIV infection and pathogenesis as they are closely related to humans genetically and express phenotypically similar immune systems. Examining the clinical outcomes of novel treatment strategies within nonhuman primates facilitates our understanding of HIV latency and advances the development of a true cure to HIV.

Imaging of surface microdomains on individual extracellular vesicles in 3-D

Extracellular vesicles (EVs) are secreted from all cell types and are intimately involved in tissue homeostasis. They are being explored as vaccine and gene therapy platforms, as well as potential biomarkers. As their size is below the diffraction limit of light microscopy, direct visualizations have been daunting and single-particle studies under physiological conditions have been hampered. Here, direct stochastic optical reconstruction microscopy (dSTORM) was employed to visualize EVs in three-dimensions and to localize molecule clusters such as the tetraspanins CD81 and CD9 on the surface of individual EVs. These studies demonstrate the existence of membrane microdomains on EVs. These were confirmed by Cryo-EM. Individual particle visualization provided insights into the heterogeneity, structure, and complexity of EVs not previously appreciated.

Extracellular Vesicles as a Means of Viral Immune Evasion, CNS Invasion, and Glia-Induced Neurodegeneration

Extracellular vesicles (EVs) are small, membrane-bound vesicles released by cells as a means of intercellular communication. EVs transfer proteins, nucleic acids, and other biologically relevant molecules from one cell to another. In the context of viral infections, EVs can also contain viruses, viral proteins, and viral nucleic acids. While there is some evidence that the inclusion of viral components within EVs may be part of the host defense, much of the research in this field supports a pro-viral role for EVs. Packaging of viruses within EVs has repeatedly been shown to protect viruses from antibody neutralization while also allowing for their integration into cells otherwise impervious to the virus. EVs also bidirectionally cross the blood-brain barrier (BBB), providing a potential route for peripheral viruses to enter the brain while exiting EVs may serve as valuable biomarkers of neurological disease burden. Within the brain, EVs can alter glial activity, increase neuroinflammation, and induce neurotoxicity. The purpose of this mini-review is to summarize research related to viral manipulation of EV-mediated intercellular communication and how such manipulation may lead to infection of the central nervous system, chronic neuroinflammation, and neurodegeneration.

Transcriptional signatures of Zika virus infection in astrocytes

Astrocytes are an early and important target of Zika virus (ZIKV) infection in the developing brain, but the impacts of infection on astrocyte function remain controversial. Given that nonhuman primate (NHP) models of ZIKV infection replicate aspects of neurologic disease seen in human infections, we cultured primary astrocytes from the brain tissue of infant rhesus macaques and then infected the cells with Asian or African lineage ZIKV to identify transcriptional patterns associated with infection in these cells. The African lineage virus appeared to have greater infectivity and promote stronger antiviral signaling, but infection by either strain ultimately produced typical virus response patterns. Both viruses induced hypoxic stress, but the Asian lineage strain additionally had an effect on metabolic and lipid biosynthesis pathways. Together, these findings describe an NHP astrocyte model that may be used to assess transcriptional signatures following ZIKV infection.

CRISPR based editing of SIV proviral DNA in ART treated non-human primates

Elimination of HIV DNA from infected individuals remains a challenge in medicine. Here, we demonstrate that intravenous inoculation of SIV-infected macaques, a well-accepted non-human primate model of HIV infection, with adeno-associated virus 9 (AAV9)-CRISPR/Cas9 gene editing construct designed for eliminating proviral SIV DNA, leads to broad distribution of editing molecules and precise cleavage and removal of fragments of the integrated proviral DNA from the genome of infected blood cells and tissues known to be viral reservoirs including lymph nodes, spleen, bone marrow, and brain among others. Accordingly, AAV9-CRISPR treatment results in a reduction in the percent of proviral DNA in blood and tissues. These proof-of-concept observations offer a promising step toward the elimination of HIV reservoirs in the clinic.

Culture Model for Non-human Primate Choroid Plexus

While there are murine and rat choroid plexus epithelial cell cultures, a translationally relevant model for choroid plexus activation and function is still lacking. The rhesus macaque is the gold standard for modeling viral infection and activation of CNS, including HIV-associated neurocognitive disorders. We have developed a rhesus macaque choroid plexus epithelial cell culture model which we believe to be suitable for studies of inflammation associated with viral infection of the CNS. Epithelial morphology and function were assessed using vimentin, phalloidin, the tight junction protein zonula-occludens-1 (ZO-1), and focal adhesion kinase (FAK). Choroid plexus epithelial cell type was confirmed using immunofluorescence with two proteins highly expressed in the choroid plexus: transthyretin and α-klotho. Finally, barrier properties of the model were monitored using pro- and anti-inflammatory mediators (TNF-α, the TLR2 agonist PamCys3K, and dexamethasone). When pro-inflammatory TNF-α was added to the xCelligence wells, there was a decrease in barrier function, which decreased in a step-wise fashion with each additional administration. This barrier function was repaired upon addition of the steroid dexamethasone. The TLR2 agonist PAM3CysK increased barrier functions in TNF-α treated wells. We have presented a model of the blood-CSF barrier that will allow study into pro- and anti-inflammatory conditions in the brain, while simultaneously measuring real time changes to epithelial cells.

A Method to Investigate Astrocyte and Microglial Morphological Changes in the Aging Brain of the Rhesus Macaque

With a rapidly aging population, studies of neuroinflammation and degeneration associated with eugeric aging are becoming critical. Using the unique archive at the Tulane National Primate Research Center as a resource, we have developed tools to quantify morphological changes in astrocytes and microglia across the life span of monkeys. This method can be used for morphometric studies of multiple parameters simultaneously in an unbiased manner.

Adverse event following live attenuated chikungunya vaccine in a cynomolgus macaque with pre-existing chronic hydrocephalus

A cynomolgus macaque (Macaca fascicularis) with a pre-existing, undiagnosed, subclinical but severe cerebral hydrocephalus was enrolled in a study of long-term immunogenicity of the IRES/CHIK vaccine. The animal began showing signs of neurological dysfunction post-vaccination, which progressed and ultimately resulted in euthanasia. The underlying brain abnormality was revealed at necropsy and was subsequently investigated with gross and microscopic examination. This becomes the first reported case of an adverse event following administration of a live attenuated vaccine and suggests the possibility of an increased susceptibility risk of unwanted adverse outcome associated with vaccination in populations with pre-existing conditions such as hydrocephalus.

Self-injurious behaviours in rhesus macaques: Potential glial mechanisms

BACKGROUND

Self-injurious behaviour (SIB) can be classified as intentional, direct injuring of body tissue usually without suicidal intent. In its non-suicidal form it is commonly seen as a clinical sign of borderline personality disorder, autism, PTSD, depression, and anxiety affecting a wide range of ages and conditions. In rhesus macaques SIB is most commonly manifested through hair plucking, self-biting, self-hitting, and head banging. SIB in the form of self-biting is observed in approximately 5-15% of individually housed monkeys. Recently, glial cells are becoming recognised as key players in regulating behaviours.

METHOD

The goal of this study was to determine the role of glial activation, including astrocytes, in macaques that had displayed SIB. To this end, we performed immunohistochemistry and next generation sequence of brain tissues from rhesus macaques with SIB.

RESULTS

Our studies showed increased vimentin, but not nestin, expression on astrocytes of macaques displaying SIB. Initial RNA Seq analyses indicate activation of pathways involved in tissue remodelling, neuroinflammation and cAMP signalling.

CONCLUSIONS

Glia are most probably activated in primates with self-injury, and are therefore potential novel targets for therapeutics.

Current and Future Therapeutic Strategies for Lentiviral Eradication from Macrophage Reservoirs

Macrophages, one of the most abundant populations of leukocytes in the body, function as the first line of defense against pathogen invaders. Human Immunodeficiency virus 1 (HIV-1) remains to date one of the most extensively studied viral infections. Naturally occurring lentiviruses in domestic and primate species serve as valuable models to investigate lentiviral pathogenesis and novel therapeutics. Better understanding of the role macrophages play in HIV pathogenesis will aid in the advancement towards a cure. Even with current efficacy of first- and second-line Antiretroviral Therapy (ART) guidelines and future efficacy of Long Acting Slow Effective Release-ART (LASER-ART); ART alone does not lead to a cure. The major challenge of HIV eradication is viral latency. Latency Reversal Agents (LRAs) show promise as a possible means to eradicate HIV-1 from the body. It has become evident that complete eradication will need to include combinations of various effective therapeutic strategies such as LASER-ART, LRAs, and gene editing. Review of the current literature indicates the most promising HIV eradication strategy appears to be LASER-ART in conjunction with viral and receptor gene modifications via the CRISPR/Cas9 system. Graphical abstract A multimodal approach to HIV treatment including gene editing, LASER-ART, and latency reversal agents may provide a means to achieve HIV eradication.

Chronic Viral Neuroinflammation: Speculation on Underlying Mechanisms

Viral infection in the brain can be acute or chronic, with the responses often producing foci of increasingly cytotoxic inflammation. This can lead to effects beyond the central nervous system (CNS). To stimulate discussion, this commentary addresses four questions: What drives the development of human immunodeficiency virus (HIV)-associated neurocognitive disorders, does the phenotype of macrophages in the CNS spur development of HIV encephalitis (HIVE), does continual activation of astrocytes drive the development of HIV-associated neurocognitive disorders/subclinical disease, and neuroinflammation: friend or foe? A unifying theory that connects each question is the issue of continued activation of glial cells, even in the apparent absence of simian immunodeficiency virus/HIV in the CNS. As the CNS innate immune system is distinct from the rest of the body, it is likely there could be a number of activation profiles not observed elsewhere.

Nef Secretion into Extracellular Vesicles or Exosomes Is Conserved across Human and Simian Immunodeficiency Viruses

Extracellular vesicles (EVs) or exosomes have been implicated in the pathophysiology of infections and cancer. The negative regulatory factor (Nef) encoded by simian immunodeficiency virus (SIV) and human immunodeficiency virus (HIV) plays a critical role in the progression to AIDS and impairs endosomal trafficking. Whether HIV-1 Nef can be loaded into EVs has been the subject of controversy, and nothing is known about the connection between SIV Nef and EVs. We find that both SIV and HIV-1 Nef proteins are present in affinity-purified EVs derived from cultured cells, as well as in EVs from SIV-infected macaques. Nef-positive EVs were functional, i.e., capable of membrane fusion and depositing their content into recipient cells. The EVs were able to transfer Nef into recipient cells. This suggests that Nef readily enters the exosome biogenesis pathway, whereas HIV virions are assembled at the plasma membrane. It suggests a novel mechanism by which lentiviruses can influence uninfected and uninfectable, i.e., CD4-negative, cells.IMPORTANCE Extracellular vesicles (EVs) transfer biologically active materials from one cell to another, either within the adjacent microenvironment or further removed. EVs also package viral RNAs, microRNAs, and proteins, which contributes to the pathophysiology of infection. In this report, we show that both human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) incorporate the virus-encoded Nef protein into EVs, including EVs circulating in the blood of SIV-infected macaques and that this presents a novel mechanism of Nef transfer to naive and even otherwise non-infectable cells. Nef is dispensable for viral replication but essential for AIDS progression in vivo Demonstrating that Nef incorporation into EVs is conserved across species implicates EVs as novel mediators of the pathophysiology of HIV. It could help explain the biological effects that HIV has on CD4-negative cells and EVs could become biomarkers of disease progression.

Glial cell morphological and density changes through the lifespan of rhesus macaques

How aging impacts the central nervous system (CNS) is an area of intense interest. Glial morphology is known to affect neuronal and immune function as well as metabolic and homeostatic balance. Activation of glia, both astrocytes and microglia, occurs at several stages during development and aging. The present study analyzed changes in glial morphology and density through the entire lifespan of rhesus macaques, which are physiologically and anatomically similar to humans. We observed apparent increases in gray matter astrocytic process length and process complexity as rhesus macaques matured from juveniles through adulthood. These changes were not attributed to cell enlargement because they were not accompanied by proportional changes in soma or process volume. There was a decrease in white matter microglial process length as rhesus macaques aged. Aging was shown to have a significant effect on gray matter microglial density, with a significant increase in aged macaques compared with adults. Overall, we observed significant changes in glial morphology as macaques age indicative of astrocytic activation with subsequent increase in microglial density in aged macaques.

The flavivirus dengue induces hypertrophy of white matter astrocytes

Flaviviruses, including Zika and dengue (DENV), pose a serious global threat to human health. Of the 50+ million humans infected with DENV annually, approximately 1-3 % progress to severe disease manifestations, dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Several factors are suspected to mediate the course of infection and pathogenesis of DENV infection. DHF and DSS are associated with vascular leakage and neurological sequelae. Our hypothesis was that altered astrocyte activation and morphology would alter the dynamics of the extracellular space and hence, neuronal and vascular function. We investigated the mechanisms of neuropathogenesis DENV infection in rhesus macaques. There were decreased numbers of GFAP immunopositive astrocytes per unit area, although those that remained had increased arbor length and complexity. This was combined with structural hypertrophy of white matter astrocytes in the absence of increased vascular leakage. Combined, these studies show how even low-grade infection with DENV induces measurable changes within the parenchyma of infected individuals.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

Naltrexone treatment reverses astrocyte atrophy and immune dysfunction in self-harming macaques

The role of glia in the development and treatment of behavioral abnormalities is understudied. Recent reports have observed glial activation in several disorders, including depression, autism spectrum disorders and self-injurious behaviors (SIB). In the current study, we examined SIB in the physiologically and anatomically relevant nonhuman primate (NHP) model. At the Tulane National Primate Research Center (TNPRC), approximately 5% of singly housed macaques develop symptoms of SIB. We have previously demonstrated that naltrexone hydrochloride can be effective in reducing SIB. We have also demonstrated that the astrocytes of animals with SIB are distinctly atrophic and display heightened innate immune activation compared with control animals. We have added a third group of animals (five macaques identified with SIB and treated with oral naltrexone at a dose of 3.2mg/kg) to the previous cohort (six macaques with a history of SIB but not treated, and nine animals with no history of SIB) for this study. Gray and white matter astrocytes from frontal cortical tissue were examined following necropsy. Innate immune activation of astrocytes, which was increased in SIB animals, was markedly decreased in animals receiving naltrexone, as was atrophy of both grey and white matter astrocytes. This was concomitant with improved behavioral correlates. Preventing astrocyte activation in select areas of the brain to reduce injurious behavior is an innovative concept with implications for mental health studies. Differences in multiple areas of primate brain would help determine how self-injurious behavior develops. These studies suggest a stronger role for astrocytes in the cellular events associated with self-injurious behaviors.

New advances on glial activation in health and disease

In addition to being the support cells of the central nervous system (CNS), astrocytes are now recognized as active players in the regulation of synaptic function, neural repair, and CNS immunity. Astrocytes are among the most structurally complex cells in the brain, and activation of these cells has been shown in a wide spectrum of CNS injuries and diseases. Over the past decade, research has begun to elucidate the role of astrocyte activation and changes in astrocyte morphology in the progression of neural pathologies, which has led to glial-specific interventions for drug development. Future therapies for CNS infection, injury, and neurodegenerative disease are now aimed at targeting astrocyte responses to such insults including astrocyte activation, astrogliosis and other morphological changes, and innate and adaptive immune responses.

A novel real-time CTL assay to measure designer T-cell function against HIV Env(+) cells

BACKGROUND

To increase the immunosurveillance in HIV infection, we used retroviral vectors expressing CD4-chimeric antigen receptors (CARs) to genetically modify autologous T cells and redirect CTL toward HIV. The CD4 extracellular domain targets envelope and the intracellular signaling domains activate T cells. The maC46 fusion inhibitor binds HIV and blocks viral replication.

METHODS

We stimulated rhesus PBMCs with antibodies to CD3/CD28 and cotransduced T cells with CD4-CAR and maC46 vectors. CD4-CAR-transduced T cells were added to Env(+) 293T cells at E:T of 1:1. Killing of target cells was measured as reduced impedance.

RESULTS

We observed gene expression in 60-70% of rhesus CD3(+) CD8(+) T cells with the individual vectors and in 35% of the cells with both vectors. CD4-CAR-transduced populations specifically killed Env(+) cells.

CONCLUSIONS

In these studies, we showed that designer T cells were redirected to kill Env(+) cells. Control of viremia without HAART would revolutionize treatment for HIV patients.

Form follows function: astrocyte morphology and immune dysfunction in SIV neuroAIDS

Cortical function is disrupted in neuroinflammatory disorders, including HIV-associated neurocognitive disorders (HAND). Astrocyte dysfunction includes retraction of foot processes from the blood-brain barrier and decreased removal of neurotransmitters from synaptic clefts. Mechanisms of astrocyte activation, including innate immune function and the fine neuroanatomy of astrocytes, however, remain to be investigated. We quantified the number of glial fibrillary acidic protein (GFAP)-labeled astrocytes per square millimeter and the proportion of astrocytes immunopositive for Toll-like receptor 2 (TLR2) to examine innate immune activation in astrocytes. We also performed detailed morphometric analyses of gray and white matter astrocytes in the frontal and parietal lobes of rhesus macaques infected with simian immunodeficiency virus (SIV), both with and without encephalitis, an established model of AIDS neuropathogenesis. Protoplasmic astrocytes (gray matter) and fibrous astrocytes (deep white matter) were imaged, and morphometric features were analyzed using Neurolucida. Gray matter and white matter astrocytes showed no change in cell body size in animals infected with SIV regardless of encephalitic status. In SIV-infected macaques, both gray and white matter astrocytes had shorter, less ramified processes, resulting in decreased cell arbor compared with controls. SIV-infected macaques with encephalitis showed decreases in arbor length in white matter astrocytes and reduced complexity in gray matter astrocytes compared to controls. These results provide the first evidence that innate immune activation of astrocytes is linked to altered cortical astrocyte morphology in SIV/HIV infection. Here, we demonstrate that astrocyte remodeling is correlated with infection. Perturbed neuron-glia signaling may be a driving factor in the development of HAND.

Innate immune activation in the pathogenesis of a murine model of globoid cell leukodystrophy

Globoid cell leukodystrophy is a lysosomal storage disease characterized by the loss of galactocerebrosidase. Galactocerebrosidase loss leads to the accumulation of psychosine and subsequent oligodendrocyte cell death, demyelination, macrophage recruitment, and astroglial activation and proliferation. To date, no studies have elucidated the mechanism of glial cell activation and cytokine and chemokine up-regulation and release. We explored a novel explanation for the development of the pathological changes in the early stages of globoid cell leukodystrophy associated with toll-like receptor (TLR) 2 up-regulation in the hindbrain and cerebellum as a response to dying oligodendrocytes. TLR2 up-regulation on microglia/macrophages coincided with morphological changes consistent with activation at 2 and 3 weeks of age. TLR2 up-regulation on activated microglia/macrophages resulted in astrocyte activation and marked up-regulation of cytokines/chemokines. Because oligodendrocyte cell death is an important feature of globoid cell leukodystrophy, we tested the ability of TLR2 reporter cells to respond to oligodendrocyte cell death. These reporter cells responded in vitro to medium conditioned by psychosine-treated oligodendrocytes, indicating the likelihood that oligodendrocytes release a TLR2 ligand during apoptosis. TLRs are a member of the innate immune system and initiate immune and inflammatory events; therefore, the identification of TLR2 as a potential driver in the activation of central nervous system glial activity in globoid cell leukodystrophy may provide important insight into its pathogenesis.

Microglia activation by SIV-infected macrophages: alterations in morphology and cytokine secretion

HIV infection in the brain and the resultant encephalitis affect approximately one third of individuals infected with HIV, regardless of treatment with antiretroviral drugs. Microglia are the resident phagocytic cell type in the brain, serving as a "first responder" to neuroinvasion by pathogens. The early events of the microglial response to productively infected monocyte/macrophages entering the brain can best be investigated using in vitro techniques. We hypothesized that activation of microglia would be specific to the presence of simian immunodeficiency virus (SIV)-infected macrophages as opposed to responses to macrophages in general. Purified microglia were grown and stimulated with control or SIV-infected macrophages. After 6 h, aliquots of the supernatant were analyzed for 23 cytokines using Millipore nonhuman primate-specific kit. In parallel experiments, morphologic changes and cytokine expression by individual microglia were examined by immunofluorescence. Surprisingly, the presence of macrophages was more important to the microglial response rather than whether the macrophages were infected with SIV. None of the cytokines examined were unique to co-incubation with SIV-infected macrophages compared with control macrophages, or their supernatants. Media from SIV-infected macrophages, however, did induce secretion of higher levels of IL-6 and IL-8 than the other treatments. As resident macrophages in the brain, microglia would be expected to have a strong response to infiltrate innate immune cells such as monocyte/macrophages. This response is triggered by incubation with macrophages, irrespective of whether or not they are infected with SIV, indicating a rapid, generalized immune response when infiltrating macrophages entering the brain.

An inverted blood-brain barrier model that permits interactions between glia and inflammatory stimuli

The blood-brain barrier (BBB) is increasingly being recognized as a site of special scientific importance. Numerous models of the BBB have been constructed over the past years with increasingly mechanistic studies of fundamental questions of cell biology and neuroimmunology. However, there has been a limiting factor of not being able to perform real-time studies of BBB function utilizing 3D models. Equally, real-time models have been limited mainly to 2D models comprised solely of endothelial cells (ECs). To measure changes in the electrical resistance across a BBB model, when adding inflammatory or stem cells which will interact with co-cultured glial cells has, to date, been beyond the capabilities of models. We have cultured an inverted BBB model with ECs on electrodes which are on the lower surface of xCELLigence Cell Invasion Migration plates. Glial cells were cultured in the basal well with foot processes extending through the filters to make contact with the ECs. SIV-infected macrophages decreased electrical resistance of the EC monolayer when added to the "parenchymal" face of the model. We present a novel inverted blood-brain barrier model that allow real time analyses of endothelial cell adhesion during modeled neuroinflammation.

The stress-response factor SigH modulates the interaction between Mycobacterium tuberculosis and host phagocytes

The Mycobacterium tuberculosis stress response factor SigH plays a crucial role in modulating the pathogen's response to heat, oxidative-stress, envelope damage and hypoxia. We hypothesized that the lack of this key stress response factor would alter the interaction between the pathogen and its host cells. We compared the interaction of Mtb, Mtb:Δ-sigH and a strain where the mutation had been genetically complemented (Mtb: Δ-sigH:CO) with primary rhesus macaque bone marrow derived macrophages (Rh-BMDMs). The expression of numerous inducible and homeostatic (CCL) β-chemokines and several apoptotic markers was induced to higher levels in the cells infected with Mtb:Δ-sigH, relative to Mtb or the complemented strain. The differential expression of these genes manifested into functional differences in chemotaxis and apoptosis in cells infected with these two strains. The mutant strain also exhibited reduced late-stage survival in Rh-BMDMs. We hypothesize that the product of one or more SigH-dependent genes may modulate the innate interaction of Mtb with host cells, effectively reducing the chemokine-mediated recruitment of immune effector cells, apoptosis of infected monocytes and enhancing the long-term survival and replication of the pathogen in this milieu The significantly higher induction of Prostaglandin Synthetase 2 (PTGS2 or COX2) in Rh-BMDMs infected with Mtb relative to Mtb: Δ-sigH may explain reduced apoptosis in Mtb-infected cells, as PTGS2 is known to inhibit p53-dependent apoptosis.The SigH-regulon modulates the innate interaction of Mtb with host phagocytes, perhaps as part of a strategy to limit its clearance and prolong its survival. The SigH regulon appears to be required to modulate innate immune responses directed against Mtb.

Association of FAK activation with lentivirus-induced disruption of blood-brain barrier tight junction-associated ZO-1 protein organization

Expression of tight junction proteins between brain microvascular endothelial cells (BMECs) of the blood-brain barrier (BBB) is lost during development of human immunodeficiency virus (HIV) encephalitis (HIVE). Although many studies have focused on the strains of virus that induce neurological sequelae or on the macrophages/microglia that are associated with development of encephalitis, the molecular signaling pathways within the BMECs involved have yet to be resolved. We have previously shown that there is activation and disruption of an in vitro BBB model using lentivirus-infected CEMx174 cells. We and others have shown similar disruption in vivo. Therefore, it was of interest to determine if the presence of infected cells could disrupt intact cerebral microvessels immediately ex vivo, and if so, which signaling pathways were involved. The present data demonstrate that disruption of tight junctions between BMECs is mediated through activation of focal adhesion kinase (FAK) by phosphorylation at TYR-397. Inhibition of FAK activation is sufficient to prevent tight junction disruption. Thus, it may be possible to inhibit the development of HIVE by using inhibitors of FAK.

Acquired immunodeficiency syndrome and the blood-brain barrier

The blood-brain barrier (BBB) plays a critical role in normal physiology of the central nervous system by regulating what reaches the brain from the periphery. The BBB also plays a major role in neurologic disease including neuropathologic sequelae associated with infection by human immunodeficiency virus (HIV) in humans and the closely related simian immunodeficiency virus (SIV) in macaques. In this review, we provide an overview of the function, structure, and components of the BBB, followed by a more detailed discussion of the subcellular structures and regulation of the tight junction. We then discuss the ways in which HIV/SIV affects the BBB, largely through infection of monocytes/macrophages, and how infected macrophages crossing the BBB ultimately results in breakdown of the barrier.

Activation of the blood-brain barrier by SIV (simian immunodeficiency virus) requires cell-associated virus and is not restricted to endothelial cell activation

The primary cell infected during acute HIV neuropathogenesis is the monocyte-derived macrophage. We have demonstrated that there is activation of the BBB (blood-brain barrier) during acute viral infection and at terminal AIDS. However, it has never been determined if there is a requirement for the virus to be carried through the BBB or how these Trojan horses would be induced to cross the BBB. We added SIVmac251-infected (SIV is simian immunodeficiency virus) mononuclear cells (and their supernatants) to the luminal or abluminal compartment of our BBB model. There was activation of both sides of the BBB model, only if viral-infected cells were added to the luminal compartment, as opposed to the addition of cell-free supernatants. This suggests that cell-associated virus is essential for the activation of the BBB. This, in turn, would be expected to lead to further infiltration of cells capable of viral infection. VCAM-1 (vascular cell adhesion molecule 1) staining revealed, for the first time, that there is an absolute requirement for virally infected cells, and not just the presence of virus for the activation of the BBB.

Characterization of an in vitro rhesus macaque blood-brain barrier

The blood-brain barrier (BBB) has been modeled in vitro in a number of species, including rat, cow and human. Coculture of multiple cell types is required for the correct expression of tight junction proteins by microvascular brain endothelial cells (MBEC). Markers of inflammation, especially MHC-II, and cell adhesion molecules, such as VCAM-1, are not expressed on the luminal surface of the barrier under resting conditions. The rhesus macaque model has been used to study early events of HIV-neuropathogenesis in vivo, but a suitable in vitro model has not been available for detailed mechanistic studies. Here we describe an in vitro rhesus macaque blood-brain barrier that utilizes autologous MBEC and astrocytes. We believe that this model is highly relevant for examining immunological events at the blood-brain barrier and demonstrate its potential usefulness for examining early events in AIDS neuropathogenesis.

Enhanced expression of proinflammatory cytokines in the central nervous system is associated with neuroinvasion by simian immunodeficiency virus and the development of encephalitis

Inflammatory cytokines are believed to play an important role in the pathogenesis of human immunodeficiency virus type 1-associated encephalitis. To examine this in the simian immunodeficiency virus (SIV)-infected macaque model of neuroAIDS, inflammatory cytokine gene expression was evaluated in the brains of macaques infected with pathogenic SIV(mac251) by reverse transcriptase PCR. Interleukin-1 beta was readily detected in the brains of all animals evaluated, regardless of infection status or duration of infection. Tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) transcripts were undetectable in the brains of uninfected control animals but were upregulated at 7 and 14 days postinoculation. At the terminal stage of infection, TNF-alpha and IFN-gamma transcripts were coexpressed in the brains of four of five animals with SIV encephalitis (SIVE). Within an encephalitic brain, TNF-alpha and IFN-gamma transcripts were detected in six of seven regions with histologic evidence of SIVE, suggesting a direct relationship between neuropathology and altered cytokine gene expression. With combined fluorescent in situ hybridization and immunofluorescence, TNF-alpha-expressing cells were frequently identified as CD68-positive macrophages within perivascular lesions. These observations provide evidence that cytokines produced by activated inflammatory macrophages are an important element in the pathogenesis of SIVE.

Rhesus macaque brain microvessel endothelial cells behave in a manner phenotypically distinct from umbilical vein endothelial cells

Activation of endothelium is a critical step in leukocyte recruitment to the CNS and in development of neurological diseases, such as HIV-associated dementia. Due to limited availability of early disease course data, it is important to develop in vitro models of the blood-brain barrier (BBB) that can be used to address these early events. No such model of the BBB has been established for the macaque. Here, we characterize rhesus microvascular brain endothelial cells (MBEC), comparing them with rhesus umbilical vein endothelial cells (RUVEC), and discuss their suitability for future use in developing in vitro models of simian immunodeficiency virus (SIV) neuropathogenesis. We conclude that MBEC are distinct from RUVEC with respect to growth characteristics, culture requirements, morphology and expression of surface molecules important for leukocyte adhesion and immune activation.

Macaques with rapid disease progression and simian immunodeficiency virus encephalitis have a unique cytokine profile in peripheral lymphoid tissues

The influence of host cytokine response on viral load, disease progression, and neurologic lesions was investigated in the simian immunodeficiency virus (SIV)-infected macaque model of AIDS. Cytokine gene expression (interleukin-1beta [IL-1beta], IL-2, IL-6, IL-10, gamma interferon [IFN-gamma], and tumor necrosis factor alpha [TNF-alpha]) and viral loads were evaluated by semiquantitative reverse transcription-PCR in lymph nodes of 5 control animals and 28 animals infected with SIVmac251 at the terminal stages of AIDS. Infected animals showed higher expression of IFN-gamma, IL-6, and IL-10 mRNAs compared with controls. Levels of all cytokines were comparable between animals with rapid (survival, <200 days) or slow/normal (survival, >200 days) disease progression. However, among rapid progressors, the eight animals with SIV encephalitis had a unique cytokine profile (increased IL-2, IL-6, and IFN-gamma) that was associated with higher viral loads. These observations provide evidence that host cytokine responses may influence SIV neuropathogenesis independent of disease progression.

Thymosin beta 4 sulfoxide is an anti-inflammatory agent generated by monocytes in the presence of glucocorticoids

The possibility that glucocorticoids upregulate the expression of anti-inflammatory mediators is an exciting prospect for therapy in inflammatory diseases, because these molecules could give the therapeutic benefits of steroids without toxic side effects. Supernatants from monocytes and macrophages cultured in the presence of glucocorticoids increase the dispersion of neutrophils from a cell pellet in the capillary tube migration assay. This supernatant factor, unlike other neutrophil agonists, promotes dispersive locomotion of neutrophils at uniform concentration, lowers their adhesion to endothelial cells, inhibits their chemotactic response to fMLP and induces distinctive morphological changes. Here we show that thymosin beta4 sulfoxide is generated by monocytes in the presence of glucocorticoids and acts as a signal to inhibit an inflammatory response. In vitro, thymosin beta4 sulfoxide inhibited neutrophil chemotaxis, and in vivo, the oxidized peptide, but not the native form, was a potent inhibitor of carrageenin-induced edema in the mouse paw. Thymosin beta4 is unique, because oxidation attenuates its intracellular G-actin sequestering activity, but greatly enhances its extracellular signaling properties. This description of methionine oxidation conferring extracellular function on a cytosolic protein may have far-reaching implications for future strategies of anti-inflammatory therapy.

AY-31,906, a novel high ceiling diuretic: characterization of its relative potassium-sparing actions in rats and dogs

AY-31,906, exo-2-amino-4-[(bicyclo[2.2.1]hept-2-yl)amino-N-[[1- methylethyl)amino]carbonyl]-5-pyrimidinesulfonamide, exhibited potent diuretic and natriuretic activity in rats and dogs. After p.o. administration, AY-31,906 was 1.5- and 12.3-times more potent as a natriuretic than furosemide in rats and dogs, respectively, whereas it was 0.5- and 6.1-times as potent after i.v. administration. The maximum natriuretic effect of AY-31,906 in both species was similar to that observed with furosemide. At equiactive natriuretic p.o. doses in both species, AY-31,906 produced a greater increase in the urinary ratio of Na/K than furosemide, indicating a relative potassium-sparing effect. AY-31,906 produced significant increases in the fractional excretion of sodium and chloride in dogs at a dose that produced no statistically significant changes in the fractional excretion of potassium, glomerular filtration rate or renal plasma flow. After p.o. administration, the onset of activity of AY-31,906 occurred within the 1st hr in both rats and dogs and preliminary data demonstrated that the activity lasted for approximately 2 hr in rats and 4 hr in dogs. Clearance studies in conscious dogs suggest that AY-31,906 inhibited electrolyte reabsorption in the ascending limb of the loop of Henle and, unlike furosemide, AY-31,906 had no activity at the proximal tubule. These results indicate that AY-31,906 is a potent, high ceiling diuretic with relative potassium-sparing properties. The compound is well absorbed after p.o. administration with diuretic activity occurring in the 1st hr.

Rapid onset of vascular wall protein synthesis with increase in lability of blood pressure in rabbits

1. Structural and functional changes resulting from baroreceptor denervation were studied in rabbits 4 days after surgery. 2. After section of the aortic and carotid sinus nerves, arterial pressure was characteristically labile although the mean pressures were not significantly different from those of control animals. 3. The responsiveness of isolated ear arteries and cephalic veins from deafferented animals to noradrenaline and electrical stimulation of their sympathetic innervation was similar in both groups. 4. Neuronal uptake of noradrenaline into arterial tissue was similar in both groups, although uptake into the cephalic veins of deafferented animals was less than in the control group. 5. [3H]Thymidine uptake, an index of DNA synthesis, was similar in both groups, radioautography revealing no difference in smooth muscle cell labelling. 6. Uptake of [3H]proline, an indicator of protein synthesis, by aorta, ear, brachial, basilar and renal arteries from deafferented animals was greater than in control animals. 7. Baroreceptor denervation altered protein metabolism in the arterial wall.

Relaxation of smooth muscle following contraction elicited by sympathetic nerve stimulation in vivo

1. A method for studying in vivo the process of neuroeffector transmission in the nictitating membrane and nasal blood vessels of the cat is described. 2. Administration of desmethylimipramine or cocaine caused increases in both the amplitude and duration of the nasal and membrane responses which may be explained by inhibition of neuronal uptake of noradrenaline. 3. Phenoxybenzamine depressed the responses to nerve stimulation, but had little effect on the relationship between response amplitude and rate of recovery. 4. The relationship between response amplitude and rate of recovery is discussed and related to the sigmoid shape of a log concentration-response curve.