Copolymer-1 induces adaptive immune anti-inflammatory glial and neuroprotective responses in a murine model of HIV-1 encephalitis

Neurogenesis after Spinal Cord Injury: State of the Art

Neurogenesis in the adult state is the process of new neuron formation. This relatively infrequent phenomenon comprises four stages: cell proliferation, cell migration, differentiation, and the integration of these cells into an existing circuit. Recent reports suggest that neurogenesis can be found in different regions of the Central Nervous System (CNS), including the spinal cord (SC). This process can be observed in physiological settings; however, it is more evident in pathological conditions. After spinal cord injury (SCI), the activation of microglial cells and certain cytokines have shown to exert different modulatory effects depending on the presence of inflammation and on the specific region of the injury site. In these conditions, microglial cells and cytokines are considered to play an important role in the regulation of neurogenesis after SCI. The purpose of this article is to present an overview on neural progenitor cells and neurogenic and non-neurogenic zones as well as the cellular and molecular regulation of neurogenesis. Additionally, we will briefly describe the recent advances in the knowledge of neurogenesis after SCI.

Type I Interferons in NeuroHIV

Infection with Human Immunodeficiency Virus (HIV)-1 continues to cause HIV-associated neurocognitive disorders despite combined antiretroviral therapy. Interferons (IFNs) are important for any antiviral immune response, but the lasting production of IFNα causes exhaustive activation leading eventually to progression to AIDS. Expression of IFNα in the HIV-exposed central nervous system has been linked to cognitive impairment and inflammatory neuropathology. In contrast, IFNβ exerts anti-inflammatory effects, appears to control, at least temporarily, lentiviral infection in the brain and provides neuroprotection. The dichotomy of type I IFN effects on HIV-1 infection and the associated brain injury will be discussed in this review, because the underlying mechanisms require further investigation to allow harnessing these innate immune factors for therapeutic purposes.

Brain Invasion by CD4(+) T Cells Infected with a Transmitted/Founder HIV-1BJZS7 During Acute Stage in Humanized Mice

Human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND) is one of the common causes of cognitive dysfunction and morbidity among infected patients. However, to date, it remains unknown if a transmitted/founder (T/F) HIV-1 leads to neurological disorders during acute phase of infection. Since it is impossible to answer this question in humans, we studied NOD.Cg-Prkdc scid Il2rgtm1Wjl/SzJ mice (NSG) reconstituted with human PBMC (NSG-HuPBL), followed by the peritoneal challenge with the chronic HIV-1JR-FL and the T/F HIV-1BJZS7, respectively. By measuring viral load, P24 antigenemia and P24(+) cells in peripheral blood and various tissue compartments, we found that systemic infections were rapidly established in NSG-HuPBL mice by both HIV-1 strains. Although comparable peripheral viral loads were detected during acute infection, the T/F virus appeared to cause less CD4(+) T cell loss and less numbers of infected cells in different organs and tissue compartments. Both viruses, however, invaded brains with P24(+)/CD3(+) T cells detected primarily in meninges, cerebral cortex and perivascular areas. Critically, brain infections with HIV-1JR-FL but not with HIV-1BJZS7 resulted in damaged neurons together with activated microgliosis and astrocytosis as determined by significantly increased numbers of Iba1(+) microglial cells and GFAP(+) astrocytes, respectively. The increased Iba1(+) microglia was correlated positively with levels of P24 antigenemia and negatively with numbers of NeuN(+) neurons in brains of infected animals. Our findings, therefore, indicate the establishment of two useful NSG-HuPBL models, which may facilitate future investigation of mechanisms underlying HIV-1-induced microgliosis and astrocytosis.

HIV-1, methamphetamine and astrocytes at neuroinflammatory Crossroads

As a popular psychostimulant, methamphetamine (METH) use leads to long-lasting, strong euphoric effects. While METH abuse is common in the general population, between 10 and 15% of human immunodeficiency virus-1 (HIV-1) patients report having abused METH. METH exacerbates the severity and onset of HIV-1-associated neurocognitive disorders (HAND) through direct and indirect mechanisms. Repetitive METH use impedes adherence to antiretroviral drug regimens, increasing the likelihood of HIV-1 disease progression toward AIDS. METH exposure also directly affects both innate and adaptive immunity, altering lymphocyte numbers and activity, cytokine signaling, phagocytic function and infiltration through the blood brain barrier. Further, METH triggers the dopamine reward pathway and leads to impaired neuronal activity and direct toxicity. Concurrently, METH and HIV-1 alter the neuroimmune balance and induce neuroinflammation, which modulates a wide range of brain functions including neuronal signaling and activity, glial activation, viral infection, oxidative stress, and excitotoxicity. Pathologically, reactive gliosis is a hallmark of both HIV-1- and METH-associated neuroinflammation. Significant commonality exists in the neurotoxic mechanisms for both METH and HAND; however, the pathways dysregulated in astroglia during METH exposure are less clear. Thus, this review highlights alterations in astrocyte intracellular signaling pathways, gene expression and function during METH and HIV-1 comorbidity, with special emphasis on HAND-associated neuroinflammation. Importantly, this review carefully evaluates interventions targeting astrocytes in HAND and METH as potential novel therapeutic approaches. This comprehensive overview indicates, without a doubt, that during HIV-1 infection and METH abuse, a complex dialog between all neural cells is orchestrated through astrocyte regulated neuroinflammation.

Differential Effects of Pharmacologic and Genetic Modulation of NMDA Receptor Activity on HIV/gp120-Induced Neuronal Damage in an In Vivo Mouse Model

HIV-associated neurocognitive disorder (HAND) consists of motor and cognitive dysfunction in a relatively large percentage of patients with AIDS. Prior work has suggested that at least part of the neuronal and synaptic damage observed in HAND may occur due to excessive stimulation of NMDA-type glutamate receptors (NMDARs). Here, we compared pharmacological and genetic manipulation of NMDAR activity using an improved derivative of the NMDAR antagonist memantine, termed NitroMemantine, and the modulatory NMDAR subunit GluN3A in the HIV/gp120 transgenic (tg) mouse model of HAND. Interestingly, we found that while both NitroMemantine and GluN3A have been shown to inhibit NMDAR activity, NitroMemantine protected synapses in gp120-tg mice, but overexpression of GluN3A augmented the damage. Given recent findings in the field, one explanation for this apparently paradoxical result is the location of the NMDARs primarily affected, with NitroMemantine inhibiting predominantly extrasynaptic pathologically activated NMDARs, but GluN3A disrupting normal NMDAR-mediated neuroprotective activity via inhibition of synaptic NMDARs.

The impact of HIV-1 on neurogenesis: implications for HAND

HIV-1 infection, in addition to its destructive effects on the immune system, plays a role in the development of neurocognitive deficits. Indeed up to 50% of long-term HIV infected patients suffer from HIV-associated neurocognitive disorders (HAND). These deficits have been well characterized and defined clinically according to a number of cognitive parameters. HAND is often accompanied by atrophy of the brain including inhibition of neurogenesis, especially in the hippocampus. Many mechanisms have been proposed as contributing factors to HAND including induction of oxidative stress in the central nervous system (CNS), chronic microglial-mediated neuroinflammation, amyloid-beta (Aβ) deposition, hyperphosphorylated tau protein, and toxic effects of combination antiretroviral therapy (cART). In these review we focus solely on recent experimental evidence suggesting that disturbance by HIV-1 results in impairment of neurogenesis as one contributing factor to HAND. Impaired neurogenesis has been linked to cognitive deficits and other neurodegenerative disorders. This article will highlight recently identified pathological mechanisms which potentially contribute to the development of impaired neurogenesis by HIV-1 or HIV-1-associated proteins from both animal and human studies.

Nano-NRTIs demonstrate low neurotoxicity and high antiviral activity against HIV infection in the brain

Antiviral therapy using nucleoside reverse transcriptase inhibitors (NRTIs) is neurotoxic and has low efficiency in eradication of HIV-1 harbored in central nervous system (CNS). Previously, we reported that active 5'-triphosphates of NRTIs encapsulated in cationic nanogels (nano-NRTIs) suppress HIV-1 activity more efficiently than NRTIs and exhibit reduced mitochondrial toxicity [Vinogradov SV, Poluektova LY, Makarov E, Gerson T, Senanayake MT. Nano-NRTIs: efficient inhibitors of HIV type-1 in macrophages with a reduced mitochondrial toxicity. Antivir Chem Chemother. 2010; 21:1-14. Makarov E, Gerson T, Senanayake T, Poluektova LY, Vinogradov. Efficient suppression of Human Immunodeficiency Virus in Macrophages by Nano-NRTIs. Antiviral Res. 2010; 86(1):A38-9]. Here, we demonstrated low neurotoxicity and excellent antiviral activity of nano-NRTIs decorated with the peptide (AP) binding brain-specific apolipoprotein E receptor. Nano-NRTIs induced lower levels of apoptosis and formation of reactive oxygen species, a major cause of neuron death, than free NRTIs. Optimization of size, surface decoration with AP significantly increased brain accumulation of nano-NRTIs. The efficient CNS delivery of nano-NRTIs resulted in up to 10-fold suppression of retroviral activity and reduced virus-associated inflammation in humanized mouse model of HIV-1 infection in the brain. Our data provide proof of the advanced efficacy of nano-NRTIs as safer alternative of current antiviral drugs.

FROM THE CLINICAL EDITOR

This team of investigators demonstrated low neurotoxicity and excellent anti-HIV activity of nano-nucleoside reverse transcriptase inhibitors decorated with the peptide (AP) binding brain-specific apolipoprotein E receptor, providing proof of enhanced efficacy and a safer alternative compared with current antiviral drugs.

Chronic mild stress eliminates the neuroprotective effect of Copaxone after CNS injury

Copolymer (Cop)-1, also known as glatiramer acetate, is an active compound of Copaxone, a drug widely used by patients with multiple sclerosis (MS). Copaxone functions in MS through two mechanisms of action, namely immunomodulation and neuroprotection. Because the immune system is suppressed or altered in depressed individuals, and since depression is often associated with neurological conditions, we were interested in examining whether the neuroprotective effect of Copaxone persists under conditions of stress-induced depressive behavior. We exposed mice to unpredictable chronic mild stress for 4 weeks and then treated them with three doses of Copaxone at 3-day intervals, with the last dose given immediately before the mice underwent a crush injury to the optic nerve. Whereas nonstressed mice exhibited a strong neuroprotective response after Copaxone treatment, this effect was completely absent in mice that underwent chronic mild stress. Interestingly, when Copaxone was combined with Prozac, the neuroprotective effect of Copaxone was regained, suggesting that chronic mild stress interferes with the neuroprotective effect of Copaxone. These results may shed a light on mechanism of action of Copaxone and lead to new combined therapies for neurodegenerative and neuroinflammatory disorders.

Glatiramer Acetate administration does not reduce damage after cerebral ischemia in mice

Inflammation plays a key role in ischemic stroke pathophysiology: microglial/macrophage cells and type-1 helper cells (Th1) seem deleterious, while type-2 helper cells (Th2) and regulatory T cells (Treg) seem protective. CD4 Th0 differentiation is modulated by microglial cytokine secretion. Glatiramer Acetate (GA) is an immunomodulatory drug that has been approved for the treatment of human multiple sclerosis by means of a number of mechanisms: reduced microglial activation and pro-inflammatory cytokine production, Th0 differentiation shifting from Th2 to Th2 and Treg with anti-inflammatory cytokine production and increased neurogenesis. We induced permanent (pMCAo) or transient middle cerebral artery occlusion (tMCAo) and GA (2 mg) or vehicle was injected subcutaneously immediately after cerebral ischemia. Mice were sacrificed at D3 to measure neurological deficit, infarct volume, microglial cell density and qPCR of TNFα and IL-1β (pro-inflammatory microglial cytokines), IFNγ (Th2 cytokine), IL-4 (Th2 cytokine), TGFβ and IL-10 (Treg cytokines), and at D7 to evaluate neurological deficit, infarct volume and neurogenesis assessment. We showed that in GA-treated pMCAo mice, infarct volume, microglial cell density and cytokine secretion were not significantly modified at D3, while neurogenesis was enhanced at D7 without significant infarct volume reduction. In GA-treated tMCAo mice, microglial pro-inflammatory cytokines IL-1β and TNFα were significantly decreased without modification of microglial/macrophage cell density, cytokine secretion, neurological deficit or infarct volume at D3, or modification of neurological deficit, neurogenesis or infarct volume at D7. In conclusion, Glatiramer Acetate administered after cerebral ischemia does not reduce infarct volume or improve neurological deficit in mice despite a significant increase in neurogenesis in pMCAo and a microglial pro-inflammatory cytokine reduction in tMCAo.

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

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

Adequate Time Window and Environmental Factors Supporting Retinal Graft Cell Survival in rd Mice

Postnatal photoreceptor cells can be integrated into the wild-type adult retina in mice, and retinal transplantation is now one therapeutic option for retinal degenerative diseases when photoreceptor degeneration is the primary cause of the disease. The aim of this study was to specify the optimal time window during the course of retinal degeneration and to modulate the host and/or graft environment for a successful transplantation. We first studied the background features of the mice with phosphodiesterase 6b (PDE6b) gene mutation (rd; C3H/Hej) and found that the infiltration of microglia and glial fibrillary acidic protein (GFAP) expression once increased at the peak of rod death (∼2-3 weeks of age) but then reduced for a following period until gliosis began to take place with enhanced GFAP expression (∼8 weeks of age). The postnatal retinal cells (p4-p7) were successfully transplanted during this period with neurite extension into the host retina. In later transplantations (6 or 8 weeks of age), graft cells survived better in the presence of chondroitinase ABC (ChABC), which digests chondroitin sulfate proteoglycan (CSPG), an essential component of gliosis. In contrast, in earlier transplantations (4 weeks of age), graft cells survived better in the presence of valproic acid (VPA), a neural differentiating reagent, or glatiramer acetate, an immune modulator. These suggest that, immediately after the outer nuclear layer (ONL) degeneration, an inflammatory reaction may be easily induced but the host neurons may be more able to accept donor cells in the presence of neural differentiating factor. These results will help optimize transplantation conditions when we consider clinical application.

Rodent models for HIV-associated neurocognitive disorders

Human immunodeficiency virus (HIV)-associated neurocognitive disorders (HAND) reflect the spectrum of neural impairments seen during chronic viral infection. Current research efforts focus on improving antiretroviral and adjunctive therapies, defining disease onset and progression, facilitating drug delivery, and halting neurodegeneration and viral resistance. Because HIV is species-specific, generating disease in small-animal models has proved challenging. After two decades of research, rodent HAND models now include those containing a human immune system. Antiviral responses, neuroinflammation and immunocyte blood-brain barrier (BBB) trafficking follow HIV infection in these rodent models. We review these and other rodent models of HAND and discuss their unmet potential in reflecting human pathobiology and in facilitating disease monitoring and therapeutic discoveries.

High glucose stimulates TNFα and MCP-1 expression in rat microglia via ROS and NF-κB pathways

AIM

To investigate whether high glucose stimulates the expression of inflammatory cytokines and the possible mechanisms involved.

METHODS

ELISA and real-time PCR were used to determine the expression of the inflammatory factors, and a chemiluminescence assay was used to measure the production of reactive oxygen species (ROS).

RESULTS

Compared to low glucose (10 mmol/L), treatment with high glucose (35 mmol/L) increased the secretion of tumor necrosis factor (TNF)α and monocyte chemotactic protein-1 (MCP-1), but not interleukin (IL)-1β and IL-6, in a time-dependent manner in primary cultured rat microglia. The mRNA expression of TNFα and MCP-1 also increased in response to high glucose. This upregulation was specific to high glucose because it was not observed in the osmotic control. High-glucose treatment stimulated the formation of ROS. Furthermore, treatment with the ROS scavenger NAC significantly reduced the high glucose-induced TNFα and MCP-1 secretion. In addition, the nuclear factor kappa B (NF-κB) inhibitors MG132 and PDTC completely blocked the high glucose-induced TNFα and MCP-1 secretion.

CONCLUSION

We found that high glucose induces TNFα and MCP-1 secretion as well as mRNA expression in rat microglia in vitro, and this effect is mediated by the ROS and NF-κB pathways.

Links between progressive HIV-1 infection of humanized mice and viral neuropathogenesis

Few rodent models of human immunodeficiency virus type one (HIV-1) infection can reflect the course of viral infection in humans. To this end, we investigated the relationships between progressive HIV-1 infection, immune compromise, and neuroinflammatory responses in NOD/scid-IL-2Rγ(c)(null) mice reconstituted with human hematopoietic CD34(+) stem cells. Human blood-borne macrophages repopulated the meninges and perivascular spaces of chimeric animals. Viral infection in lymphoid tissue led to the accelerated entry of human cells into the brain, marked neuroinflammation, and HIV-1 replication in human mononuclear phagocytes. A meningitis and less commonly an encephalitis followed cM-T807 antibody-mediated CD8(+) cell depletion. We conclude that HIV-1-infected NOD/scid-IL-2Rγ(c)(null) humanized mice can, at least in part, recapitulate lentiviral neuropathobiology. This model of neuroAIDS reflects the virological, immunological, and early disease-associated neuropathological components of human disease.

Glatiramer acetate attenuates pro-inflammatory T cell responses but does not directly protect neurons from inflammatory cell death

Glatiramer acetate (GA) is a synthetic, random, basic copolymer capable of modulating adaptive T cell responses. In animal models of various inflammatory and degenerative central nervous system disorders, GA-induced T cells cross the blood-brain barrier, secrete high levels of anti-inflammatory cytokines and neurotrophins, and thus both reduce neuronal damage and promote neurogenesis. Recently, it has been suggested that GA itself may permeate the (impaired) blood-brain-barrier and directly protect neurons under conditions of inflammation-mediated neurodegeneration. To test this hypothesis, we examined the direct effects of GA on neuronal functionality and T cell-mediated neuronal apoptosis in culture, acute brain slices, and focal experimental autoimmune encephalomyelitis. GA caused a depolarization of the resting membrane potential and led to an immediate impairment of action potential generation in neurons. Moreover, GA-incubated neurons underwent dose-dependent apoptosis. Apoptosis of ovalbumin peptide-loaded major histocompatibility complex class I-expressing neurons induced by ovalbumin-specific effector T cells could be reduced by pre-incubation of T cells, but not neurons with GA. Similar results could be found using acute brain slices. In focal experimental autoimmune encephalomyelitis, lesion size and neuronal apoptosis could be limited by pretreating rats with GA, whereas intracerebral GA application into the inflammatory lesion had no effect on neuronal survival. Our data suggest that GA attenuates adaptive pro-inflammatory T cell responses, but does not exert direct neuroprotective effects.

Erythropoietin plus insulin-like growth factor-I protects against neuronal damage in a murine model of human immunodeficiency virus-associated neurocognitive disorders

OBJECTIVE

Prolonged human immunodeficiency virus-1 (HIV-1) infection leads to neurological debilitation, including motor dysfunction and frank dementia. Although pharmacological control of HIV infection is now possible, HIV-associated neurocognitive disorders (HAND) remain intractable. Here, we report that chronic treatment with erythropoietin (EPO) and insulin-like growth factor-I (IGF-I) protects against HIV/gp120-mediated neuronal damage in culture and in vivo.

METHODS

Initially, we tested the neuroprotective effects of various concentrations of EPO, IGF-I, or EPO+IGF-I from gp120-induced damage in vitro. To assess the chronic effects of EPO+IGF-I administration in vivo, we treated HIV/gp120-transgenic or wild-type mice transnasally once a week for 4 months and subsequently conducted immunohistochemical analyses.

RESULTS

Low concentrations of EPO+IGF-I provided neuroprotection from gp120 in vitro in a synergistic fashion. In vivo, EPO+IGF-I treatment prevented gp120-mediated neuronal loss, but did not alter microgliosis or astrocytosis. Strikingly, in the brains of both humans with HAND and gp120-transgenic mice, we found evidence for hyperphosphorylated tau protein (paired helical filament-I tau), which has been associated with neuronal damage and loss. In the mouse brain following transnasal treatment with EPO+IGF-I, in addition to neuroprotection we observed increased phosphorylation/activation of Akt (protein kinase B) and increased phosphorylation/inhibition of glycogen synthase kinase (GSK)-3beta, dramatically decreasing downstream hyperphosphorylation of tau. These results indicate that the peptides affected their cognate signaling pathways within the brain parenchyma.

INTERPRETATION

Our findings suggest that chronic combination therapy with EPO+IGF-I provides neuroprotection in a mouse model of HAND, in part, through cooperative activation of phosphatidylinositol 3-kinase/Akt/GSK-3beta signaling. This combination peptide therapy should therefore be tested in humans with HAND.

Brain ingress of regulatory T cells in a murine model of HIV-1 encephalitis

CD4+CD25+ regulatory T cells (Treg) transform the HIV-1 infected macrophage from a neurotoxic to a neuroprotective phenotype. This was demonstrated previously in a murine model of HIV-1 encephalitis induced by intracranial injection of HIV-1/vesicular stomatitis virus-infected bone marrow macrophages. In this report, relationships between Treg ingress of end organ tissues, notably the brain, and neuroprotection were investigated. Treg from EGFP-transgenic donor mice were expanded, labeled with indium-111, and adoptively transferred. Treg distribution was assayed by single photon emission computed tomography and immunohistochemistry. Treg readily migrated across the blood brain barrier and were retained within virus-induced neuroinflammatory sites. In non-inflamed peripheral tissues (liver and spleen) Treg were depleted. These observations demonstrate that Treg migrate to sites of inflammation where they modulate immune responses.

Immunoregulation of a CB2 receptor agonist in a murine model of neuroAIDS

Chronic HIV-1 infection commonly affects behavioral, cognitive, and motor functions in the infected human host and is commonly referred to as HIV-1-associated neurocognitive disorders (HAND). This occurs, in measure, as a consequence of ingress of leukocytes into brain perivascular regions. Such cells facilitate viral infection and disease by eliciting blood-brain barrier and neuronal network dysfunctions. Previous works demonstrated that the endocannabinoid system modulates neuroimmunity and as such neuronal and glial functions. Herein, we investigated CB2R receptor expression in murine HIV-1 encephalitis (HIVE) and the abilities of a highly selective CB2R agonist, Gp1a, to modulate disease. HIV-1-infected human monocyte-derived macrophages were injected into the caudate and putamen of immunodeficient mice reconstituted with human peripheral blood lymphocytes (hu-PBL/HIVE). Brains of hu-PBL/HIVE mice showed microglial activation and increased expression of CB2R, but not CB1R or GPR55. Gp1a substantively reduced infiltration of human cells into the mouse brain and reduced HLA DQ activation. Gp1a down modulated CCR5 expression on human cells in the spleen with an increase in Fas ligand expression. Our results support the notion that CB2 receptor agonists may be a viable therapeutic candidate for HAND.

A coat of many colors: neuroimmune crosstalk in human immunodeficiency virus infection

The use of antiretroviral therapy has reduced mortality and increased the quality of life of HIV-1-infected people, particularly in more developed countries where access to treatment is more widespread. However, morbidities continue, which include HIV-1-associated neurocognitive disorders (HAND). Subtle cognitive abnormalities and low-level viral replication underlie disease. The balance between robust antiviral adaptive immunity, neuronal homeostatic mechanisms, and neuroprotective factors on one hand and toxicities afforded by dysregulated immune activities on the other govern disease. New insights into the pathobiological processes for neuroimmune-linked disease and ways to modulate such activities for therapeutic gain are discussed. Better understanding of the complexities of immune regulation during HAND can improve diagnosis and disease outcomes but is also relevant for the pathogenesis of a broad range of neurodegenerative disorders.

Neuromodulatory activities of CD4+CD25+ regulatory T cells in a murine model of HIV-1-associated neurodegeneration

HIV-1-associated neurocognitive impairments are intrinsically linked to microglial immune activation, persistent viral infection, and inflammation. In the era of antiretroviral therapy, more subtle cognitive impairments occur without adaptive immune compromise. We posit that adaptive immunity is neuroprotective, serving in both the elimination of infected cells through CD8(+) cytotoxic T cell activities and the regulation of neuroinflammatory responses of activated microglia. For the latter, little is known. Thus, we studied the neuromodulatory effects of CD4(+) regulatory T cells (Treg; CD4(+)CD25(+)) or effector T cells in HIV-1-associated neurodegeneration. A newly developed HIV-1 encephalitis mouse model was used wherein murine bone marrow-derived macrophages are infected with a full-length HIV-1(YU2)/vesicular stomatitis viral pseudotype and injected into basal ganglia of syngeneic immunocompetent mice. Adoptive transfer of CD3-activated Treg attenuated astrogliosis and microglia inflammation with concomitant neuroprotection. Moreover, Treg-mediated anti-inflammatory activities and neuroprotection were associated with up-regulation of brain-derived neurotrophic factor and glial cell-derived neurotrophic factor expression and down-regulation of proinflammatory cytokines, oxidative stress, and viral replication. Effector T cells showed contrary effects. These results, taken together, demonstrate the importance of Treg in disease control and raise the possibility of their utility for therapeutic strategies.

Spatial learning impairment, enhanced CDK5/p35 activity, and downregulation of NMDA receptor expression in transgenic mice expressing tau-tubulin kinase 1

Tau-tubulin kinase-1 (TTBK1) is involved in phosphorylation of tau protein at specific Serine/Threonine residues found in paired helical filaments, suggesting its role in tauopathy pathogenesis. We found that TTBK1 levels were upregulated in brains of human Alzheimer' disease (AD) patients compared with age-matched non-AD controls. To understand the effects of TTBK1 activation in vivo, we developed transgenic mice harboring human full-length TTBK1 genomic DNA (TTBK1-Tg). Transgenic TTBK1 is highly expressed in subiculum and cortical pyramidal layers, and induces phosphorylated neurofilament aggregation. TTBK1-Tg mice show significant age-dependent memory impairment as determined by radial arm water maze test, which is associated with enhancement of tau and neurofilament phosphorylation, increased levels of p25 and p35, both activators of cyclin-dependent protein kinase 5 (CDK5), enhanced calpain I activity, and reduced levels of hippocampal NMDA receptor types 2B (NR2B) and D. Enhanced CDK5/p35 complex formation is strongly correlated with dissociation of F-actin from p35, suggesting the inhibitory mechanism of CDK5/p35 complex formation by F-actin. Expression of recombinant TTBK1 in primary mouse cortical neurons significantly downregulated NR2B in a CDK5- and calpain-dependent manner. These data suggest that TTBK1 in AD brain may be one of the underlying mechanisms inducing CDK5 and calpain activation, NR2B downregulation, and subsequent memory dysfunction.

Glatiramer acetate reduces the risk for experimental cerebral malaria: a pilot study

Background

Cerebral malaria (CM) is associated with high mortality and morbidity caused by a high rate of transient or persistent neurological sequelae. Studies on immunomodulatory and neuroprotective drugs as ancillary treatment in murine CM indicate promising potential. The current study was conducted to evaluate the efficacy of glatiramer acetate (GA), an immunomodulatory drug approved for the treatment of relapsing remitting multiple sclerosis, in preventing the death of C57Bl/6J mice infected with Plasmodium berghei ANKA.

Methods and Results

GA treatment led to a statistically significant lower risk for developing CM (57.7% versus 84.6%) in treated animals. The drug had no effect on the course of parasitaemia. The mechanism of action seems to be an immunomodulatory effect since lower IFN-gamma levels were observed in treated animals in the early course of the disease (day 4 post-infection) which also led to a lower number of brain sequestered leukocytes in treated animals. No direct neuro-protective effect such as an inhibition of apoptosis or reduction of micro-bleedings in the brain was found.

Conclusion

These findings support the important role of the host immune response in the pathophysiology of murine CM and might lead to the development of new adjunctive treatment strategies.

IFN-gamma and IL-4 differentially shape metabolic responses and neuroprotective phenotype of astrocytes

Astrocytes can either exacerbate or ameliorate secondary degeneration at sites of injury in the CNS but the contextual basis for eliciting these opposing phenotypes is poorly understood. In this study, we demonstrate that the two major cytokines produced by Th1 and Th2 cells, interferon-gamma (IFN-gamma), and interleukin-4 (IL-4), respectively, contribute differentially to shaping a neuroprotective response in astrocytes. While IFN-gamma protects the ability of oxidatively stressed murine astrocytes to clear extracellular glutamate in culture, IL-4 has no effect at any concentration that was tested (10-100 ng/mL). The enhanced release of neuroprotective thiols and lactate by astrocytes in response to T cell stimulation is mimicked by both IL-4 and IFN-gamma. When co-administered, IL-4 abrogated the protective effect of low IFN-gamma on the glutamate clearance function of oxidatively stressed astrocytes in a dose-dependent manner. Astrocyte-conditioned media obtained from cells cultured in the presence of IL-4 (10 or 100 ng/mL) or IFN-gamma (10 ng/mL) decreased by approximately 2-fold, neuronal apoptosis induced by oxidative stress in vitro. However, unlike IL-4, IFN-gamma at high concentrations (100 ng/mL) was not neuroprotective. Our studies with IFN-gamma and IL-4 suggest that a balanced Th1 and Th2 cytokine response might be needed for protecting two key astrocytic functions, glutamate clearance and thiol secretion and might be pertinent to neuroprotective approaches that are aimed at inhibition of an initial pro-inflammatory response to injury or its sustained boosting.

Protective autoimmunity in the nervous system

The immune system can play both detrimental and beneficial roles in the nervous system. Multiple arms of the immune system, including T cells, B cells, NK cells, mast cells, macrophages, dendritic cells, microglia, antibodies, complement and cytokines participate in limiting damage to the nervous system during toxic, ischemic, hemorrhagic, infective, degenerative, metabolic and immune-mediated insults and also assist in the process of repair after injury has occurred. Immune cells have been shown to produce neurotrophic growth factors and interact with neurons and glial cells to preserve them from injury and stimulate growth and repair. The immune system also appears to participate in proliferation of neural progenitor stem cells and their migration to sites of injury. Neural stem cells can also modify the immune response in the central and peripheral nervous system to enhance neuroprotective effects. Evidence for protective and reparative functions of the immune system has been found in diverse neurologic diseases including traumatic injury, ischemic and hemorrhagic stroke, multiple sclerosis, infection, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis). Existing therapies including glatiramer acetate, interferon-beta and immunoglobulin have been shown to augment the protective and regenerative aspects of the immune system in humans, and other experimental interventions such as vaccination, minocycline, antibodies and neural stem cells, have shown promise in animal models of disease. The beneficent aspects of the immune response in the nervous system are beginning to be appreciated and their potential as pharmacologic targets in neurologic disease is being explored.

Adaptive immune neuroprotection in G93A-SOD1 amyotrophic lateral sclerosis mice

Background

Innate neuroimmune dysfunction is a pathobiological feature of amyotrophic lateral sclerosis (ALS). However, links, if any, between disease and adaptive immunity are poorly understood. Thus, the role of T cell immunity in disease was investigated in human G93A superoxide dismutase 1 (SOD1) transgenic (Tg) mice and subsequently in ALS patients.

Methods and Findings

Quantitative and qualitative immune deficits in lymphoid cell and T cell function were seen in G93A-SOD1 Tg mice. Spleens of Tg animals showed reductions in size, weight, lymphocyte numbers, and morphological deficits at terminal stages of disease compared to their wild-type (Wt) littermates. Spleen sizes and weights of pre-symptomatic Tg mice were unchanged, but deficits were readily seen in T cell proliferation coincident with increased annexin-V associated apoptosis and necrosis of lymphocytes. These lymphoid deficits paralleled failure of Copolymer-1 (COP-1) immunization to affect longevity. In addition, among CD4⁺ T cells in ALS patients, levels of CD45RA⁺ (naïve) T cells were diminished, while CD45RO⁺ (memory) T cells were increased compared to age-matched caregivers. In attempts to correct mutant SOD1 associated immune deficits, we reconstituted SOD1 Tg mice with unfractionated naïve lymphocytes or anti-CD3 activated CD4⁺CD25⁺ T regulatory cells (Treg) or CD4⁺CD25⁻ T effector cells (Teff) from Wt donor mice. While naive lymphocytes failed to enhance survival, both polyclonal-activated Treg and Teff subsets delayed loss of motor function and extended survival; however, only Treg delayed neurological symptom onset, whereas Teff increased latency between disease onset and entry into late stage.

Conclusions

A profound and progressive immunodeficiency is operative in G93A-SOD1 mice and is linked to T cell dysfunction and the failure to elicit COP-1 neuroprotective immune responses. In preliminary studies T cell deficits were also observed in human ALS. These findings, taken together, suggest caution in ascribing vaccination outcomes when these animal models of human ALS are used for study. Nonetheless, the abilities to improve neurological function and life expectancy in G93A-SOD1 Tg mice by reconstitution with activated T cells do provide opportunities for therapeutic intervention.

Proteomic modeling for HIV-1 infected microglia-astrocyte crosstalk

Background

HIV-1-infected and immune competent brain mononuclear phagocytes (MP; macrophages and microglia) secrete cellular and viral toxins that affect neuronal damage during advanced disease. In contrast, astrocytes can affect disease by modulating the nervous system's microenvironment. Interestingly, little is known how astrocytes communicate with MP to influence disease.

Methods and Findings

MP-astrocyte crosstalk was investigated by a proteomic platform analysis using vesicular stomatitis virus pseudotyped HIV infected murine microglia. The microglial-astrocyte dialogue was significant and affected microglial cytoskeleton by modulation of cell death and migratory pathways. These were mediated, in part, through F-actin polymerization and filament formation. Astrocyte secretions attenuated HIV-1 infected microglia neurotoxicity and viral growth linked to the regulation of reactive oxygen species.

Conclusions

These observations provide unique insights into glial crosstalk during disease by supporting astrocyte-mediated regulation of microglial function and its influence on the onset and progression of neuroAIDS. The results open new insights into previously undisclosed pathogenic mechanisms and open the potential for biomarker discovery and therapeutics that may influence the course of HIV-1-mediated neurodegeneration.

Amino acid copolymer-specific IL-10-secreting regulatory T cells that ameliorate autoimmune diseases in mice

IL-10-secreting regulatory T cell lines specific to glatiramer acetate [poly(Y,E,A,K)n] or poly(Y,F,A,K)n have been established from the enlarged spleen and lymph nodes that result from copolymer treatment of SJL mice in which experimental autoimmune encephalomyelitis was induced by PLP139-151. These CD4+CD25+T cell lines secrete high levels of IL-10 and IL-13 but only small amounts of IL-4 and virtually no TGF-beta, IL-17, IL-6, IFN-gamma, or TNF-alpha. Their phenotypes are particularly characterized by the absence of Foxp3 and the presence of two TNFR family members, CD30 and GITR. The lines proliferated specifically to the immunizing copolymers but were autoantigen-nonspecific, in that the same T cell line could suppress autoimmunity induced by three different autoantigens in SJL mice, i.e., PLP139-151(EAE), MBP85-99 (EAE), and bovine peripheral nerve myelin (experimental autoimmune neuritis), indicating they function by bystander suppression.

Modulation of innate immunity by copolymer-1 leads to neuroprotection in murine HIV-1 encephalitis

Virus-infected and immune-competent mononuclear phagocytes (MP; perivascular macrophages and microglia) drive the neuropathogenesis of human immunodeficiency virus type 1 (HIV-1) infection. Modulation of the MP phenotype from neurodestructive to neuroprotective underlies adjunctive therapeutic strategies for human disease. We reasoned that, as Copolymer-1 (Cop-1) can induce neuroprotective activities in a number of neuroinflammatory and neurodegenerative disorders, it could directly modulate HIV-1-infected MP neurotoxic activities. We now demonstrate that, in laboratory assays, Cop-1-stimulated virus-infected human monocyte-derived macrophages (MDM) protect against neuronal injury. Severe combined immune-deficient (SCID) mice were stereotactically injected with HIV-1-infected human MDM, into the basal ganglia, to induce HIV-1 encephalitis (HIVE). Cop-1 was administered subcutaneously for 7 days. In HIVE mice, Cop-1 treatment led to anti-inflammatory and neuroprotective responses. Reduced micro- and astrogliosis, and conserved NeuN/MAP-2 levels were observed in virus-affected brain regions in Cop-1-treated mice. These were linked to interleukin-10 and brain-derived neurotrophic factor expression and downregulation of inducible nitric oxide synthase. The data, taken together, demonstrate that Cop-1 can modulate innate immunity and, as such, improve disease outcomes in an animal model of HIVE.

T cell independent mechanism for copolymer-1-induced neuroprotection

Despite active investigation of copolymer-1 (Cop-1) for nearly 40 years the mechanisms underlying its neuroprotective properties remain contentious. Nonetheless, current dogma for Cop-1 neuroprotective activities in autoimmune and neurodegenerative diseases include bystander suppression of autoimmune T cells and attenuation of microglial responses. In this report, we demonstrate that Cop-1 interacts directly with primary human neurons and decreases neuronal cell death induced by staurosporine or oxidative stress. This neuroprotection is mediated through protein kinase Calpha and brain-derived neurotrophic factor. Dendritic cells (DC) uptake Cop-1, deliver it to the injury site, and release it in an active form. Interactions between Cop-1 and DC enhance DC blood brain barrier migration. In a rat model with optic nerve crush injury, Cop-1-primed DC induce T cell independent neuroprotection. These findings may facilitate the development of neuroprotective approaches using DC-mediated Cop-1 delivery to diseased nervous tissue.