Chemokines in the CNS: plurifunctional mediators in diverse states

Neuronal apoptosis is mediated by CXCL10 overexpression in simian human immunodeficiency virus encephalitis

Inflammatory mediators play a crucial role in the pathophysiology of several neurodegenerative diseases including acquired immune deficiency syndrome dementia complex. In the present study we identified a link between CXCL10 overexpression in the brain and human immunodeficiency virus dementia and demonstrated the presence of the chemokine CXCL10 and its receptor, CXCR3, in the neurons in the brains of macaques with simian human immunodeficiency virus encephalitis. Using human fetal brain cultures, we showed that treatment of these cells with either SHIV89.6P or viral gp120 resulted in induction of CXCL10 in neurons. Cultured neurons treated with the chemokine developed increased membrane permeability followed by apoptosis via activation of caspase-3. We confirmed the relevance of these findings in sections of human and macaque brains with encephalopathy demonstrating that neurons expressing CXCL10 also expressed caspase-3.

Induction of glial L-CCR mRNA expression in spinal cord and brain in experimental autoimmune encephalomyelitis

Chemokines and chemokine receptors are important regulators of leukocyte trafficking and immune response. It is well established that chemokines and their receptors are also expressed in the central nervous system (CNS), where their expression has been associated with various neuroinflammatory diseases, such as multiple sclerosis (MS). One of the most important chemokines involved in MS pathology is CCL2 (previously known as MCP-1). CCL2, released by glial cells, activates the chemokine receptor CCR2, causing the infiltration of blood monocytes in tissues affected by MS. There is evidence, however, that CCL2 also has local effects on CNS cells, including induction or modulation of cytokine release and synthesis of matrix metalloproteinases, that might contribute to CNS pathology. These effects are most likely independent of CCR2, since CCR2 expression in glial cells is rarely observed. We have recently provided evidence for the presence of an alternative CCL2 receptor in glial cells called L-CCR and have investigated the expression of L-CCR mRNA in a murine EAE model. It is shown that L-CCR mRNA is expressed in infiltrating macrophages during EAE, but not in infiltrating T cells. Prominent expression of L-CCR mRNA was detected in astrocytes and microglia already at early time points throughout the brain and spinal cord supporting the hypothesis that L-CCR expression in glial cells is related to CNS inflammation.

Hippocampal gene expression profiles in passive avoidance conditioning

Many experiments in the past have demonstrated the requirement of de novo gene expression during the long-term retention of learning and memory. Although previous studies implicated individual genes or genetic pathways in learning and memory, the collective behaviours of the genes is mostly unknown. We have used genome-scale screening by microarray analysis to examine the hippocampal expression of more than 1200 genes relevant to neurobiology during instrumental conditioning. Training rats on a step-through passive avoidance task led to unique patterns of gene expression when compared to naïve animals or those exposed to the conditioned or the unconditioned stimulus alone. The newly identified genes afford a quantitative view of the changes which accompany conditioning at the genomic level and enable deeper insights into the molecular basis underlying learning and memory.

Effector stage CC chemokine receptor-1 selective antagonism reduces multiple sclerosis-like rat disease

We have studied the role of the chemokine receptor CCR1 during the effector stage of myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in DA rats. In situ hybridization histochemistry revealed local production of the CCR1 ligands CCL3 (MIP-1 alpha) and CCL5 (RANTES), as well as large numbers of CCR1 and CCR5 expressing cells within inflammatory brain lesions. A low-molecular weight CCR1 selective antagonist potently abrogated both clinical and histopathological disease signs during a 5-day treatment period, without signs of peripheral immune compromise. Thus, we demonstrate therapeutic targeting of CCR1-dependent leukocyte recruitment to the central nervous system in a multiple sclerosis (MS)-like rat model.

Adenosine A3 receptor-induced CCL2 synthesis in cultured mouse astrocytes

During neuropathological conditions, high concentrations of adenosine are released, stimulating adenosine receptors in neurons and glial cells. It has recently been shown that stimulation of adenosine receptors in glial cells induces the release of neuroprotective substances such as NGF, S-100beta, and interleukin-6 (IL-6). It has therefore been suggested that glial adenosine receptors are involved in neuroprotection. Since recently neuroprotective effects of the chemokine CCL2 (formerly known as MCP-1) have been reported, we investigated the possible effect of adenosine receptor stimulation on glial CCL2 synthesis. Here we show that stimulation of cultured murine astrocytes with the selective adenosine A3 receptor agonist 2-chloro-N6-(3-iodobenzyl)-N-methyl-5'-carbamoyladenosine (CL-IB-MECA) induced the release of CCL2. Specific ligands for adenosine A1 or A2 receptors did not affect CCL2 release. Furthermore, CL-IB-MECA-induced CCL2 synthesis was inhibited by adenosine A3 receptor antagonists. These results show that stimulation of adenosine A3 receptors in astrocytes induced the release of CCL2, thus supporting the assumption that adenosine receptors in glial cells regulate the synthesis of neuroprotective substances.

Selective inactivation of CCR5 and decreased infectivity of R5 HIV-1 strains mediated by opioid-induced heterologous desensitization

The opiates are well-established immunomodulatory factors, and recent evidence suggests that mu- and delta-opioid receptor ligands alter chemokine-driven chemotactic responses through the process of heterologous desensitization. In the present report, we sought to examine the capacity of mu- and delta-opioids to modulate the function of chemokine receptors CCR5 and CXCR4, the two major human immunodeficiency virus (HIV) coreceptors. We found that the chemotactic responses to the CCR1/5 ligand CCL5/regulated on activation, normal T expressed and secreted, but not the CXCR4 ligand stromal cell-derived factor-1alpha/CXCL12 were inhibited following opioid pretreatment. Studies were performed with primary monocytes and Chinese hamster ovary cells transfected with CCR5 and the micro-opioid receptor to determine whether cross-desensitization of CCR5 was a result of receptor internalization. Using radiolabeled-binding analysis, flow cytometry, and confocal microscopy, we found that the heterologous desensitization of CCR5 was not associated with a significant degree of receptor internalization. Despite this, we found that the cross-desensitization of CCR5 by opioids was associated with a decrease in susceptibility to R5 but not X4 strains of HIV-1. Our findings are consistent with the notion that impairment of the normal signaling activity of CCR5 inhibits HIV-1 coreceptor function. These results have significant implications for our understanding of the effect of opioids on the regulation of leukocyte trafficking in inflammatory disease states and the process of coreceptor-dependent HIV-1 infection. The interference with HIV-1 uptake by heterologous desensitization of CCR5 suggests that HIV-1 interaction with this receptor is not passive but involves a signal transduction process.

Widely expressed transcripts for chemokine receptor CXCR1 in identified glutamatergic, ?-aminobutyric acidergic, and cholinergic neurons and astrocytes of the rat brain: A single-cell reverse transcription-multiplex polymerase chain reaction study

Increasing evidence suggests that the chemokine interleukin (IL)-8/CXCL8 plays important roles in CNS development, neuronal survival, modulation of excitability, and neuroimmune response. Recently, we have shown that CXCL8 can acutely modulate ion channel activity in septal neurons expressing receptors CXCR1 and/or CXCR2. This was a surprising finding, insofar as CXCR1 expression had not been described for the mammalian brain. Here we investigated whether CXCR1 transcripts are present in other brain regions, whether they are expressed at the single-cell level in molecularly identified neurons and astrocytes, and how they are regulated during early postnatal development. In addition, possible cellular colocalization of CXCR1 and CXCR2 transcripts was examined. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) revealed that CXCR1 mRNAs were expressed in the septum, striatum, hippocampus, cerebellum, and cortex (temporoparietal and entorhinal) at different levels and appeared to be regulated independently from CXCR2 during development. By using RT multiplex PCR on acutely dissociated cells from these brain regions, we show that CXCR1 transcripts were expressed in 83% of 84 sampled neurons displaying cholinergic (choline acetyltransferase mRNAs), gamma-aminobutyric acidergic (glutamic acid decarboxylases 65 and 67 mRNAs), or glutamatergic (vesicular glutamate transporters 1 and 2 mRNAs) phenotypes. CXCR1 and CXCR2 transcripts were colocalized in 45% of neurons sampled and also were present in some glial fibrillary acidic protein mRNA-expressing astrocytes. This is the first study to demonstrate the widespread expression of CXCR1 transcripts in the brain and suggests that CXCR1 may have hitherto unsuspected roles in neuromodulation and inflammation.

Neurologic consequences of HIV infection in the era of HAART

In this brief review, we present a summary of the clinical presentation of HIV-associated dementia (HAD), HAD in the highly active antiretroviral therapy (HAART) era, the immunopathogenesis of HAD, and the possible role of a recently described novel macrophage-derived protein in HAD. Different aspects of the clinical presentation of HAD will be reviewed as well as the results of recent autopsy studies demonstrating that although HAART dramatically decreased the incidence of opportunistic infections and malignancies in the central nervous system, it has reduced but not eliminated HIV encephalopathy. This suggests a direct cytopathic effect of HIV on neuronal tissue. Consequently, the immunopathogenesis of HAD and the role of neurotoxins produced by brain macrophages and microglial cells will be reviewed including the possible role of a recently cloned macrophage-derived proapoptotic factor, soluble HIV apoptotic protein (SHIVA) identified in our laboratory. HAART therapy reduces the incidence of opportunistic infections, the direct pathogenic effect of HIV, especially on neuronal tissue, may become of increasing importance.

HIV-induced metalloproteinase processing of the chemokine stromal cell derived factor-1 causes neurodegeneration

The mechanisms of neurodegeneration that result in human immunodeficiency virus (HIV) type 1 dementia have not yet been identified. Here, we report that HIV-infected macrophages secrete the zymogen matrix metalloproteinase-2 (MMP-2), which is activated by exposure to MT1-MMP on neurons. Stromal cell-derived factor 1 alpha (SDF-1), a chemokine overexpressed by astrocytes during HIV infection, was converted to a highly neurotoxic protein after precise proteolytic processing by active MMP-2, which removed the N-terminal tetrapeptide. Implantation of cleaved SDF-1(5-67) into the basal ganglia of mice resulted in neuronal death and inflammation with ensuing neurobehavioral deficits that were abrogated by neutralizing antibodies to SDF-1 and an MMP inhibitor drug. Hence, this study identifies a new in vivo neurotoxic pathway in which cleavage of a chemokine by an induced metalloproteinase results in neuronal apoptosis that leads to neurodegeneration.

Tumor necrosis factor-alpha at the crossroads of neuronal life and death during HIV-associated dementia

Human immunodeficiency type-1 (HIV-1) infection is known to cause disorders of the CNS, including HIV-associated dementia (HAD). It is suspected that tumor necrosis factor-alpha (TNF-alpha) released by infected microglia and macrophages play a role in neuronal injury seen in HAD patients. Accordingly, studies suggest that the level of TNF-alpha mRNA increases with increasing severity of dementia in patients, and that inhibitors of TNF-alpha release reduces neuronal injury in murine model of HAD. However, the exact role of TNF-alpha in relation to neuronal dysfunction is a matter of ongoing debate. One school of thought hails TNF-alpha as the inducer and mediator of neurodegeneration and their evidence suggest that TNF-alpha kill neurons directly by recruiting caspases or may kill indirectly by various means. In sharp contrast to this, another concept theory envisages a role for TNF-alpha in negotiating neuroprotection during HAD. The current compilation examines these contradictory concepts, and evaluates their efficacy in the light of TNF-alpha signaling. It also attempts to elaborate the current consensus outlook of TNF-alpha's role during HAD.

Chemokines and matrix metalloproteinase-9 in leukocyte recruitment to the central nervous system

Chemokines and matrix metalloproteinases (MMPs) play key roles in leukocyte migration across the blood-brain barrier (BBB) in infectious and inflammatory diseases, including multiple sclerosis (MS). In MS some chemokine receptors are expressed by an increased percentage of T cells in blood, the CSF concentration of chemokine ligands for these receptors is increased, and there is accumulation of T cells expressing relevant chemokine receptors in CSF and in the CNS parenchyma. Chemokine receptor expression patterns appear to reflect disease activity and disease stage in MS. MMPs are constitutively expressed or induced by proinflammatory cytokines and chemokines in leukocytes and CNS-resident cells. Several MMPs are expressed in MS plaques, and the CSF concentration of MMP-9 is increased in MS. The CSF concentration of MMP-9 may reflect disease activity in MS, and the CSF concentration of MMP-9 is higher in patients carrying the MS-associated HLA type DRB1 1501. We review how chemokines and MMP-9 may be involved in the pathogenesis of MS by controlling leukocyte migration between different functional compartments. Measuring expression of these molecules may find use as surrogate markers of disease activity in MS, and interfering with their function holds promise as a novel therapeutic strategy in MS.

Tumor necrosis factor is required for RANTES-induced astrocyte monocyte chemoattractant protein-1 production

Astrocytes respond to stimulation with the chemokine RANTES (regulated on activation, normal T cell expressed) by production of a series of cytokines and chemokines, including tumor necrosis factor-alpha (TNF-alpha) and monocyte chemoattractant protein-1 (MCP-1). In the present study we demonstrate that RANTES induces TNF, which in turn stimulates subsequent production of MCP-1. TNF-R1 (p55) serves as the principal receptor responsible for MCP-1 synthesis. The results define an astrocyte proinflammatory cascade that amplifies synthesis of proinflammatory mediators. The implications of these findings to inflammatory diseases of the central nervous system are discussed.

Aberrated levels of cerebrospinal fluid chemokines in Guillain-Barré syndrome and chronic inflammatory demyelinating polyradiculoneuropathy

Infiltration of spinal nerve roots and peripheral nerves by macrophages and T cells are rather consistent immunopathologic findings in patients with Guillain-Barré syndrome (GBS) and chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). Chemokines play a central role in recruitment of leukocytes to inflamed tissue. Chemokines have been implicated in the pathogenesis of the experimental autoimmune neuritis (EAN), which represents an animal model of GBS, but the role of chemokines in GBS and CIDP is not clear. Since chemokines may be released into CSF from inflamed spinal nerve roots, we studied the concentrations of the chemokines MCP-1, MIP-1beta, MIP-3beta, IP-10, SDF-1alpha, RANTES, and SLC in the CSF by sandwich ELISA in patients over the course of GBS and CIDP, before and after immunomodulatory treatment. Controls consisted of patients with noninflammatory neurological disorders. Patients examined in the acute phase of GBS prior to treatment with intravenous high dose immunoglobulins (IvIg) had elevated CSF levels of MCP-1 (a chemoattractant for blood monocytes and dendritic cells) and IP-10 (a chemoattractant for T cells). Patients with CIDP examined prior to immunomodulatory treatment had elevated CSF levels of MIP-3beta (a chemoattractant for mature dendritic cells, naïve and recently activated T cells) and IP-10. Levels of MIP-3beta tended to decreased during follow-up in those CIDP patients responding favorably to immunomodulatory treatment. CSF levels of MCP-1 and IP-10 correlated with the CSF:plasma albumin ratio in both GBS and CIDP patients. In CIDP patients, CSF levels of MIP-3beta also correlated with the CSF:plasma albumin ratio. These data implicate MCP-1 and IP-10 in the pathogenesis of GBS, and IP-10 and MIP-3beta in the pathogenesis of CIDP.

Frequency modulation of synchronized Ca2+ spikes in cultured hippocampal networks through G-protein-coupled receptors

Synchronized spontaneous Ca2+ spikes in networked neurons represent periodic burst firing of action potentials, which are believed to play a major role in the development and plasticity of neuronal circuitry. How these network activities are shaped and modulated by extrinsic factors during development, however, remains to be studied. Here we report that synchronized Ca2+ spikes among cultured hippocampal neurons can be modulated by two small factors that act on G-protein-coupled receptors (GPCRs): the neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) and the chemokine SDF-1 (stromal cell-derived factor-1). PACAP effectively increases the frequency of the synchronized Ca2+ spikes when applied acutely; the PACAP potentiation of Ca2+ spikes requires the activation of the PACAP-specific PAC1 GPCRs and is mediated by the activation of cAMP signaling pathway. SDF-1, on the other hand, significantly reduces the frequency of these Ca2+ spikes through the activation of its specific GPCR CXCR4; the inhibitory action of SDF-1 is mediated by the inhibition of cAMP pathway through the Gi component of GPCRs. Taken together, these results demonstrate that synchronized neuronal network activity can be effectively modulated by physiologically and developmentally relevant small factors that act on GPCRs to target the cAMP pathway. Such modulation of neuronal activity through GPCRs may represent a significant mechanism that underlies the neuronal plasticity during neural development and functioning.

The chemokine receptor CXCR4 regulates cell-cycle proteins in neurons

Neurons express a variety of chemokine receptors that regulate neuronal signaling and survival, including CXCR4 and CCR5, the two major human immunodeficiency virus (HIV) coreceptors. However, the role of chemokine receptors in HIV neuropathology and neuroinflammatory disorders is still unclear. This study aims to determine whether chemokine receptors regulate the activity of cell-cycle proteins in neurons and evaluate the possibility that alterations of these proteins are involved in HIV neuropathogenesis. The authors studied the effect of the chemokine stromal cell-derived factor (SDF)-1alpha, the natural CXCR4 ligand, and an X4-using variant of gp120 on the activity of cell-cycle proteins involved in neuronal apoptosis and differentiation, such as Rb and E2F-1. Changes in expression, localization, and phosphorylation/activation of Rb and E2F-1 induced by SDF-1alpha (20 nM) gp120(IIIB) (200 pM) were analyzed in primary cultures of rat neurons and in a human cell line expressing recombinant CXCR4. The data indicate that changes in the nuclear and cytosolic levels of Rb--which result in the functional loss of this protein--are associated with apoptosis in hippocampal or cerebellar granule neurons and in cell lines. SDF-1alpha, which is able to rescue these neurons from apoptosis, induces a time-dependent increase of total Rb expression while decreasing the nuclear content of phosphorylated (Ser780/Ser795) Rb and the transcriptional activity of E2F-1. The HIV envelope protein gp120(IIIB) exerts opposite effects at the nuclear level. These data indicate that CXCR4 affects cell-cycle proteins in neurons and raise the possibility that chemokines may contribute to neuronal survival by repressing the activity of E2F-dependent apoptotic genes and maintaining neurons in a highly differentiated and quiescent state. This state may be altered during neuroinflammatory conditions and/or by HIV-derived proteins.

Overexpression of monocyte chemoattractant protein 1 in the brain exacerbates ischemic brain injury and is associated with recruitment of inflammatory cells

Brain cells produce cytokines and chemokines during the inflammatory process after stroke both in animal models and in patients. Monocyte chemoattractant protein 1 (MCP-1), one of the proinflammatory chemokines, can attract monocytes to the tissue where MCP-1 is overexpressed. However, the role of MCP-1 elevation in stroke has not been explored in detail. The authors hypothesized that elevated MCP-1 levels would lead to increased influx of monocytes and increased brain infarction size in stroke induced by middle cerebral artery occlusion with partial reperfusion. There were no differences in blood pressure, blood flow, or vascular architecture between wild-type mice and transgenic MBP-JE mice. Twenty-four to 48 hours after middle cerebral artery occlusion, brain infarction volumes after ischemia were significantly larger in MBP-JE mice than in wild-type controls and were accompanied by increased local transmigration and perivascular accumulation of macrophages and neutrophils. These results indicate that MCP-1 can contribute to inflammatory injury in stroke.

CC chemokines mediate leukocyte trafficking into the central nervous system during murine neurocysticercosis: role of gamma delta T cells in amplification of the host immune response

According to a previous report, the degree of the host immune response highly correlates with severity of the disease in the murine model for neurocysticercosis. In wild-type mice, Mesocestoides corti infection induced a rapid and extensive accumulation of gamma delta T cells and macrophages in the brain. NK cells, dendritic cells, alpha beta T cells, and B cells were also recruited to the brain but at lower levels. In contrast, gamma delta T-cell-deficient mice exhibited decreased cellular infiltration and reduced central nervous system (CNS) pathology. To understand the mechanisms of leukocyte recruitment into the CNS, chemokine expression was analyzed in infected brains in the present study. MCP-1 (CCL2), MIP-1 alpha (CCL3), and MIP-1 beta (CCL4) were up-regulated within 2 days after M. corti infection. Protein expression of RANTES (CCL5), eotaxin (CCL11), and MIP-2 was detected later, at 1 week postinfection. Correlating with the decreased cellular infiltration, delta chain T-cell receptor-deficient (TCR delta(-/-)) mice exhibited substantially reduced levels of most of the chemokines analyzed (with the exception of eotaxin). The results suggest that gamma delta T cells play an important role in the CNS immune response by producing chemokines such as MCP-1 and MIP-1 alpha, enhancing leukocyte trafficking into the brain during murine neurocysticercosis.

Role of the alpha-chemokine stromal cell-derived factor (SDF-1) in the developing and mature central nervous system

alpha-chemokines, which control the activation and directed migration of leukocytes, participate in the inflammatory processes in host defense response. One of the alpha-chemokines, CXCL12 or stromal cell-derived factor 1 (SDF-1), not only regulates cell growth and migration of hematopoietic stem cells but may also play a central role in brain development as we discuss here. SDF-1 indeed activates the CXCR4 receptor expressed in a variety of neural cells, and this signaling results in diverse biological effects. It enhances migration and proliferation of cerebellar granule cells, chemoattracts microglia, and stimulates cytokine production and glutamate release by astrocytes. Moreover, it elicits postsynaptic currents in Purkinje cells, triggers migration of cortical neuron progenitors, and produces pain by directly exciting nociceptive neurons. By modulating cell signaling and survival during neuroinflammation, SDF-1 may also play a role in the pathogenesis of brain tumors, experimental allergic encephalitis, and the nervous system dysfunction associated with acquired immunodeficiency syndrome.

Microsurgical intraluminal middle cerebral artery occlusion model in rodents

OBJECTIVES

Focal brain ischemia induced in rodents by occlusion of the middle cerebral artery (MCA) is a widely used paradigm of human brain infarct. The objective of this study is to compare the effectiveness and reproducibility of MCA filament occlusion model in rats and mice.

MATERIALS AND METHODS

A total of 140 rodents (69 rats and 71 mice) were operated. Ninety-five animals were subjected to MCA occlusion; the surgical procedure consisted of introducing an uncoated surgical nylon monofilament into the cervical common carotid artery (CCA) and advancing it intracranially to permanently block blood flow into the right MCA. Forty-five sham-occluded rodents underwent CCA ligation. Surgical success, autopsy confirmed success and mortality rate were evaluated. Effective MCA occlusion was confirmed by the evidence of motor neurological deficit, by histopathology, immunohistochemistry (IHC) and reverse transcriptase-polymerase chain reaction (RT-PCR). IHC was performed in a randomly selected number of animals to detect the protein product of monocyte chemoattractant protein-1. The brain tissue in mice was examined by RT-PCR for the expression of macrophage inflammatory protein-1 alpha mRNA.

RESULTS

Surgical success rate was 89% in the rats, significantly lower than that in the mice (100%, P < 0.05). Autopsy confirmed success rate in the rats, 60%, was also significantly different from that in the mice (92.5%, P < 0.001). The operative mortality rate was 4.3% in the rats and 15% in the mice.

CONCLUSION

The present study demonstrates that the microsurgical filament occlusion of the MCA can be more successfully performed in mice. The lower rate of success in rats seems to be as a result of the architecture of the carotid canal in this animal. No previous reports, using a considerable number of animals, have compared the feasibility of intraluminal model in the rat with that in the mouse.

Electrophysiological analysis of neuronal chemokine receptors

Several studies have shown that neurons in the central and peripheral nervous systems express a variety of chemokine receptors (CKRs). Activation of these receptors can influence neuronal signaling by regulating synaptic transmission and neuronal excitability. This article presents electrophysiological methods that are currently used to study the normal and pathophysiological role for CKRs in the nervous system. Conventional electrophysiological methods such as patch-clamp recording of isolated neurons, brain slices, and heterologous expression systems are described. In addition, single-cell reverse transcription-polymerase chain reaction is discussed as a technique that can be used in conjunction with patch-clamp recording to further investigate the molecular basis of neuronal CKR activation.

T cells infiltrate the brain in murine and human transmissible spongiform encephalopathies

CD4 and CD8 T lymphocytes infiltrate the parenchyma of mouse brains several weeks after intracerebral, intraperitoneal, or oral inoculation with the Chandler strain of mouse scrapie, a pattern not seen with inoculation of prion protein knockout (PrP(-/-)) mice. Associated with this cellular infiltration are expression of MHC class I and II molecules and elevation in levels of the T-cell chemokines, especially macrophage inflammatory protein 1beta, IFN-gamma-inducible protein 10, and RANTES. T cells were also found in the central nervous system (CNS) in five of six patients with Creutzfeldt-Jakob disease. T cells harvested from brains and spleens of scrapie-infected mice were analyzed using a newly identified mouse PrP (mPrP) peptide bearing the canonical binding motifs to major histocompatibility complex (MHC) class I H-2(b) or H-2(d) molecules, appropriate MHC class I tetramers made to include these peptides, and CD4 and CD8 T cells stimulated with 15-mer overlapping peptides covering the whole mPrP. Minimal to modest K(b) tetramer binding of mPrP amino acids (aa) 2 to 9, aa 152 to 160, and aa 232 to 241 was observed, but such tetramer-binding lymphocytes as well as CD4 and CD8 lymphocytes incubated with the full repertoire of mPrP peptides failed to synthesize intracellular gamma interferon (IFN-gamma) or tumor necrosis factor alpha (TNF-alpha) cytokines and were unable to lyse PrP(-/-) embryo fibroblasts or macrophages coated with (51)Cr-labeled mPrP peptide. These results suggest that the expression of PrP(sc) in the CNS is associated with release of chemokines and, as shown previously, cytokines that attract and retain PrP-activated T cells and, quite likely, bystander activated T cells that have migrated from the periphery into the CNS. However, these CD4 and CD8 T cells are defective in such an effector function(s) as IFN-gamma and TNF-alpha expression or release or lytic activity.

LPS-induced expression of a novel chemokine receptor (L-CCR) in mouse glial cells in vitro and in vivo

There is increasing evidence that chemokines, specialized regulators of the peripheral immune system, are also involved in the physiology and pathology of the CNS. It is known that glial cells (astrocytes and microglia) express various chemokine receptors like CCR1, -3, -5, and CXCR4. We have investigated the possible expression of the known CC chemokine receptors (CCR1-8 and D6) in murine glial cells. In addition, we examined possible glial expression of the orphan CC chemokine receptor L-CCR that has been identified previously in murine macrophages. We report here expression of L-CCR mRNA in murine astrocytes and microglia. Furthermore, L-CCR mRNA expression was strongly induced after application of bacterial lipopolysaccharide (LPS), both in vitro and in vivo. Functional studies and binding experiments using biotinylated monocyte chemoattractant protein (MCP)-1 (CCL2) indicate that CCL2 could be a candidate chemokine ligand for glial L-CCR. Based on the data presented, it is suggested that L-CCR is a functional glial chemokine receptor that is important in neuroimmunology.

Quinolinic acid upregulates chemokine production and chemokine receptor expression in astrocytes

Within the brain, quinolinic acid (QUIN) is an important neurotoxin, especially in AIDS dementia complex (ADC). Its production by monocytic lineage cells is increased in the context of inflammation. However, it is not known whether QUIN promotes inflammation. Astrocytes are important in immunoregulation within the brain and so we chose to examine the effects of QUIN on the astrocyte. Using purified primary human fetal astrocyte cultures, we determined chemokine production using ELISA assays and RT-PCR and chemokine receptor expression using immunocytochemistry and RT-PCR with QUIN in comparison to TNFalpha, IL-1beta, and IFNgamma. We found that QUIN induces astrocytes to produce large quantities of MCP-1 (CCL2) and lesser amounts of RANTES (CCL5) and IL-8 (CXCL8). QUIN also increases SDF-1alpha (CXCL12), HuMIG (CXCL9), and fractalkine (CX(3)CL1) mRNA expression. Moreover, QUIN leads to upregulation of the chemokine receptor expression of CXCR4, CCR5, and CCR3 in human fetal astrocytes. Most of these effects were comparable to those induced by TNFalpha, IL-1beta, and IFNgamma. The present work represents the first evidence that QUIN induces chemokine and chemokine receptor expression in astrocytes and is at least as potent as classical mediators such as inflammatory cytokines. These results suggest that QUIN may be critical in the amplification of brain inflammation, particularly in ADC.

The role of MCP-1 (CCL2) and CCR2 in multiple sclerosis and experimental autoimmune encephalomyelitis (EAE)

Multiple sclerosis (MS) is the commonest inflammatory demyelinating disease of the human central nervous system (CNS). In MS, CNS inflammation is associated with demyelination and axonal degeneration, which leads to clinical presentation. Expression and cellular localization of CCL2/MCP-1 and CCR2 in MS have been described in the three compartments: brain, cerebrospinal fluid (CSF) and blood. Evidence from descriptive, transgenic, knockout and neutralizing studies of experimental autoimmune encephalomyelitis (EAE) points towards a nonredundant role of CCL2 and CCR2 in the recruitment of inflammatory infiltrate into the CNS. Hence, CCL2 and CCR2 may be targets for specific and effective treatment in MS.

Induction of apoptosis by HIV-1-infected monocytic cells

We have previously described a soluble 6000-Da peptide produced by an HIV-1-infected human macrophage cell line, clone 43(HIV), which induces apoptosis in T and B cells. We have identified this factor as the novel cDNA clone FL14676485 that encodes for the human hypothetical protein, FLJ21908. The FL14676485 cDNA clone was isolated from a 43(HIV) lambda ZAP Escherichia coli expression library and screened with a panel of rabbit and mouse anti-apoptotic Abs. We transfected the FL14676485 clone into Bosc cells and non-HIV-1-infected 43 cells. Western blot analysis of lysates from the FL14676485-transfected 43 cells and Bosc cells using anti-proapoptotic factor Abs revealed a protein with a molecular mass of 66 kDa corresponding to the size of the full-length gene product of the FL14676485 clone, while Western blot of the supernatant demonstrated a doublet of 46-kDa and 6000-Da peptide that corresponds to our previously described proapoptotic factor. Primary HIV-1(BaL)-infected monocytes also produce the FLJ21908 protein. Supernatants from these transfected cells induced apoptosis in PBMC, CD4(+), and CD8(+) T and B cells similar to the activity of our previously described proapoptotic factor. PCR analysis of 43 cells and 43(HIV) cells revealed a base pair fragment of 420 bp corresponding to the FL14676485 gene product in 43(HIV) cells, but not in 43 cells. The FLJ21908 protein induces apoptosis through activation of caspase-9 and caspase-3. We have further demonstrated that the FLJ21908 protein has apoptotic activity in the SH-SY5Y neuronal cell line and can be detected in brain and lymph tissue from HIV-1-infected patients who have AIDS dementia. The FLJ21908 protein may contribute to the apoptosis and dementia observed in AIDS patients.

Signalling pathways involved in the chemotactic activity of CXCL12 in cultured rat cerebellar neurons and CHP100 neuroepithelioma cells

We compared the signal transduction pathways activated by stromal cell-derived factor-1 (CXCL12) chemokine in two different cell systems: primary cultures of rat cerebellar granule neurons (CGN) and human neuroepithelioma CHP100 cells. Both cell types express functional CXC chemokine receptor 4 (CXCR4), which is coupled both to extracellular signal-regulated kinase (ERK) and Akt phosphorylation pathways. The activation of ERK shows different dependency on the phosphatidylinositol 3-kinase (PI3-K) pathway and different sensitivity to pertussis toxin (PTX) treatment, indicative of coupling to different G proteins in the two cell systems considered. We demonstrate that the inhibition of either the ERK kinase or the PI3-K pathways blocks the CXCL12 induced-chemotaxis in CHP100 cells; while only PI3-K activity is stringently necessary for CGN migration.

CC chemokine receptor 8 in the central nervous system is associated with phagocytic macrophages

CC chemokine receptor 8 (CCR8) has been detected in vitro on type 2 helper and regulatory lymphocytes, which might exert beneficial functions in multiple sclerosis (MS) and on macrophages and microglia, possibly promoting tissue injury in MS lesions. To discriminate the relevant expression pattern in vivo, we defined the cell types that expressed CCR8 in MS lesions and determined the relationship of CCR8 expression and demyelinating activity. CCR8 was not expressed on T cells but was associated with phagocytic macrophages and activated microglia in MS lesions and directly correlated with demyelinating activity. To identify factors associated with CCR8 expression, the study was extended to other central nervous system (CNS) pathologies. CCR8 was consistently expressed on phagocytic macrophages and activated microglia in stroke and progressive multifocal leukoencephalopathy, but not expressed on microglia in pathologies that lacked phagocytic macrophages such as senile change of the Alzheimer's type. CCR8 was up-regulated by macrophage differentiation and activating stimuli in vitro. In summary CNS CCR8 expression was associated with phagocytic macrophages and activated microglial cells in human CNS diseases, suggesting that CCR8 may be a feasible target for therapeutic intervention in MS. CCR8 expression may also indicate a selective program of mononuclear phagocyte gene expression.

Expression of AMPA-type glutamate receptors in HEK cells and cerebellar granule neurons impairs CXCL2-mediated chemotaxis

We find that cerebellar granule neurons (CGN) obtained from newborn rats (p3) migrate in response to both CXC chemokine ligand-2 (CXCL2) and -12 (CXCL12), while CGN from p7 rats are unresponsive to CXCL2. The expression of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA)-type glutamate receptor 1 (GluR1) greatly impairs the chemotaxis induced by CXCL2 in CXCR2-expressing HEK cells. By immunoprecipitation, we show that CXCR2 is associated with AMPA receptors (AMPARs) in p7 CGN, and with GluR1 co-expressed in HEK cells. Taken together, these results suggest that the association between CXCR2 and AMPARs results in the inhibition of CXCL2-dependent chemotaxis, and may represent a molecular mechanism underlying the modulation of nerve cell migration.

Quinolinic acid up-regulates chemokine production and chemokine receptor expression in astrocytes

Within the brain, quinolinic acid (QUIN) is an important neurotoxin, especially in AIDS dementia complex (ADC). Its production by monocytic lineage cells is increased in the context of inflammation. However, it is not known whether QUIN promotes inflammation. Astrocytes are important in immuno-regulation within the brain and so we chose to examine the effects of QUIN on the astrocyte. Using purified cultures of primary human foetal astrocyte, we determined chemokine production using ELISA assays and RT-PCR, and chemokine receptor expression using immunocytochemistry and RT-PCR with QUIN in comparison to TNF-alpha/IFN-gamma. We found that QUIN induces astrocytes to produce large quantities of MCP-1 (CCL2), and lesser amounts of RANTES (CCL5), IL-8 (CXCL8). QUIN also increases SDF-1alpha (CXCL12), HuMIG (CXCL9) and fractalkine (CX3CL1) mRNA expression. Moreover, QUIN leads to up-regulation of the chemokine receptor expression of CXCR4, CCR5, and CCR3 in human foetal astrocytes. Most of these effects were comparable to those induced by TNF-alpha/IFN-gamma. The present work represents the first evidence that QUIN induces chemokine and chemokine receptor expression in astrocytes and is at least as potent as classical mediators such as inflammatory cytokines. These results suggest that QUIN may be critical in the amplification of brain inflammation particularly in ADC.

CXCR4 is a major chemokine receptor on glioma cells and mediates their survival

Chemokines were described originally in the context of providing migrational cues for leukocytes. They are now known to have broader activities, including those that favor tumor growth. We addressed whether and which chemokines may be important promoters of the growth of the incurable brain neoplasm, malignant gliomas. Analyses of 16 human glioma lines for the expression of chemokine receptors belonging to the CXCR and CCR series revealed low to negligible levels of all receptors, with the exception of CXCR4 that was expressed by 13 of 16 lines. All six resected human glioma specimens showed similarly high CXCR4 expression. The CXCR4 on glioma lines is a signaling receptor in that its agonist, stromal cell-derived factor-1 (SDF-1; CXCL12), produced rapid phosphorylation of mitogen-activated protein kinases. Furthermore, SDF-1 induced the phosphorylation of Akt (protein kinase B), a kinase associated with survival, and prevented the apoptosis of glioma cells when serum was withdrawn from the culture medium. SDF-1 also mediated glioma chemotaxis, in accordance with this better known role of chemokines. We conclude that glioma cells express a predominant chemokine receptor, CXCR4, and that this functions to regulate survival in part through activating pathways such as Akt.

Chemokine regulation of macrophage recruitment into the olfactory epithelium following target ablation: involvement of macrophage inflammatory protein-1alpha and monocyte chemoattractant protein-1

Target ablation by olfactory bulbectomy synchronizes the degenerative cell death of olfactory receptor neurons (ORNs), infiltration of macrophages, and proliferation of progenitor cells, leading to neurogenesis, ORN replacement, and regeneration of the sensory epithelium. Although macrophages participate in the degenerative and regenerative events, little is known of the molecular and cellular mechanisms associated with their recruitment during the earliest period following target ablation. Macrophage inflammatory protein-1alpha (MIP-1alpha) and monocyte chemoattractant protein-1 (MCP-1), which are members of the CC or beta-chemokine subfamily, are chemoattractants for monocytes/macrophages. Shortly after target ablation, the protein and mRNA levels for MIP-1alpha and MCP-1 were up-regulated, showing peak expression levels from 16 hr to 3 days post-OBX; this coincided with the pattern of infiltration of activated F4/80(+) macrophages. The mRNAs for MIP-1alpha and MCP-1, as well as their cognate receptors CCR1 and CCR2, respectively, were localized in resident and infiltrating macrophages in numbers commensurate with those of F4/80-immunopositive macrophages in adjacent tissue sections. The mRNA(+) macrophages were localized within olfactory epithelial compartments that corresponded with their proposed functions associated with phagocytosis, proliferation, and infiltration. Our data support the hypothesis that MIP-1alpha and MCP-1 are chemoattractant chemokines associated with the recruitment of macrophages into the olfactory epithelium shortly after target ablation.

Slit proteins, potential endogenous modulators of inflammation

Recent studies suggest that molecules important for guiding neuronal migration and axon path-finding also play a role in modulating leukocyte chemotaxis. Neuronal migration and leukocyte chemotaxis may share some common regulatory mechanisms. Intracellular signal transduction mechanisms guiding neuronal migration and leukocyte chemotaxis are beginning to be elucidated. Studying molecular mechanisms modulating cell migration may provide new insights into understanding of endogenous inhibitors of inflammation.

Local neuroinflammation and the progression of Alzheimer's disease

Postmortem immunohistochemical studies have revealed a state of chronic inflammation limited to lesioned areas of brain in Alzheimer's disease. Some key actors in this inflammation are activated microglia (brain macrophages), proteins of the classical complement cascade, the pentraxins, cytokines, and chemokines. The inflammation does not involve the adaptive immune system or peripheral organs, but is rather due to the phylogenetically much older innate immune system, which appears to operate in most tissues of the body. Chronic inflammation can damage host tissue and the brain may be particularly vulnerable because of the postmitotic nature of neurons. Many of the inflammatory mediators have been shown to be locally produced and selectively elevated in affected regions of Alzheimer's brain. Moreover, studies of tissue in such degenerative processes as atherosclerosis and infarcted heart suggest a similar local innate immune reaction may be important in such conditions. Much epidemiological and limited clinical evidence suggests that nonsteroidal anti-inflammatory drugs may impede the onset and slow the progression of Alzheimer's disease. But these drugs strike at the periphery of the inflammatory reaction. Much better results might be obtained if drugs were found that could inhibit the activation of microglia or the complement system in brain, and combinations of drugs aimed at different inflammatory targets might be much more effective than single agents.

Neuronal migration and molecular conservation with leukocyte chemotaxis

Cell migration is essential in species ranging from bacteria to humans (for recent reviews, see Lauffenburger and Horwitz 1996; Mitchison and Cramer 1996; Montell 1999). In the amoebae Dictyostelium discoideum, cell migration is involved in chemotaxis toward food sources and in aggregation (for review, see Devreotes and Zigmond 1988; Parent and Devreotes 1999; Chung et al. 2001). In higher vertebrates, cell migration plays crucial roles in multiple physiological and pathological processes. During embryonic and neonatal development, cell migration is crucial in morphogenetic processes such as gastrulation, cardiogenesis, and the formation of the nervous system (for review, see Hatten and Mason 1990; Rakic 1990; Hatten and Heintz 1998; Bentivoglio and Mazzarello 1999). In adult animals, cell migration is required for leukocyte trafficking and inflammatory responses (for review, see McCutcheon 1946; Harris 1954; Devreotes and Zigmond 1988). In tumoriogenesis, tumor-induced angiogenesis and tumor metastasis both involve cell migration. Although it is well known that cell migration is necessary for all these processes, our understanding of mechanisms controlling cell migration is still limited. Here we briefly review the significance of neuronal migration and focus on recent studies on the directional guidance of neuronal migration, discussing the possibility that guidance mechanisms for neurons are conserved with those for other somatic cells.

The chemokine system in neuroinflammation: an update

Chemokines and their receptors govern physiologic and pathologic leukocyte trafficking. The function of the chemokine system may be of particular interest for hematogenous leukocyte infiltration of the central nervous system (CNS) because of the distinct character of CNS inflammation and the exquisite specificity with which the chemokine system regulates cellular migration events. This review summarizes recent information about the expression and function of elements of the chemokine system in CNS inflammatory processes. Animal models of CNS demyelinating disease and the corresponding human disorder, multiple sclerosis are both considered.

CXC chemokine receptors in the central nervous system: Role in cerebellar neuromodulation and development

Chemokines and their receptors are constitutively present in the central nervous system (CNS), expressed in neurons and glial cells. Much evidence suggests that, beyond their involvement in neuroinflammation, these proteins play a role in neurodevelopment and neurophysiological signaling. The goal of this review is to summarize recent information concerning expression, signaling, and function of CXC chemokine receptor in the CNS, with the main focus on the developmental and neuromodulatory actions of chemokines in the cerebellum.

TGF-beta1 upregulates CX3CR1 expression and inhibits fractalkine-stimulated signaling in rat microglia

Following peripheral nerve transection, CX3CR1 and TGF-beta1 are increased in a time-dependent manner within the injured facial motor nucleus. To explore the relationship between TGF-beta1 and CX3CR1 in the CNS, the effects of TGF-beta1 on CX3CR1 mRNA, protein and fractalkine-dependent stimulation of signal transduction cascades in primary cultures of rat microglia were examined. TGF-beta1 increased steady state levels of CX3CR1 mRNA, 125I-fractalkine binding sites and blunted fractalkine-stimulated ERK1/2 phosphorylation. The half-life of CX3CR1 mRNA was unaltered by TGF-beta1 and two potential Smad binding elements (SBEs) were identified in the rat CX3CR1 promoter. TGF-beta1 may shift fractalkine-dependent signaling away from activation of ERK1/2 towards other pathways and/or may provide a mechanism for microglia to more strongly adhere to neurons.

Interferon-gamma differentially modulates the release of cytokines and chemokines in lipopolysaccharide- and pneumococcal cell wall-stimulated mouse microglia and macrophages

During bacterial infections of the CNS, activated microglia could support leucocyte recruitment to the brain through the synthesis of cyto- and chemokines. In turn, invading leucocytes may feedback on microglial cells to influence their chemokine release pattern. Here, we analyzed the capacity of interferon-gamma (IFNgamma) to serve as such a leucocyte-to-microglia signal. Production of cyto- and chemokines was stimulated in mouse microglia cultures by treatments with lipopolysaccharide (LPS) from Gram-negative Escherichia coli or cell walls from Gram-positive Streptococcus pneumoniae (PCW). IFNgamma presence during the stimulation (0.1-100 ng/mL) modulated the patterns of LPS- and PCW-induced cyto- and chemokine release in a dose-dependent, potent and complex manner. While amounts of TNFalpha and IL-6 remained nearly unchanged, IFNgamma enhanced the production of IL-12, MCP-1 and RANTES, but attenuated that of KC, MIP-1alpha and MIP-2. Release modulation was obtained with IFNgamma preincubation (treatment of cells before LPS or PCW administration), coincubation and even delayed addition to an ongoing LPS or PCW stimulation. Together the changes observed for the microglial chemokine release under IFNgamma would shift the chemoattractive profile from favouring neutrophils to a preferential attraction of monocytes and T lymphocyte populations--as actually seen during the course of bacterial meningitis. The findings support the view of activated microglia as a major intrinsic source for an instant production of a variety of chemokines and suggest that leucocyte-derived IFNgamma could potentially regulate the microglial chemokine release pattern.

Differential sensitivities of pyrogenic chemokine fevers to cyclooxygenase isozymes antibodies

It has been proposed that prostaglandin (PG)E(2) production via a process catalyzed by the inducible isoform of cyclooxygenase (COX)-2 and activation of specific PGE(2) receptor subtypes within the preoptic/anterior hypothalamus (AH/POA) is the last step and unique pathway in the induction of a fever. However, many data support the existence of a PG-independent pathway. That is, other more rapid mechanisms, which involve the constitutive COX-1 isozyme, may be more critical for a PG-dependent fever. Thus, we examined the role of both COX isoforms in the AH/POA in fevers induced by macrophage inflammatory protein (MIP)-1beta, a PG-independent pyrogen, and RANTES (regulated on activation, normal T-cells expressed and secreted), a PG-dependent pyrogen. In freely moving rats, two independent polyclonal antibodies were used which neutralize COX-1 and COX-2. The microinjection of either MIP-1beta or RANTES into the pyrogen-sensitive region of the AH/POA induced an intense fever of rapid onset. Peripheral pretreatment with an antipyretic dose of dexamethasone which prevents COX-2 expression, or the microinjections into the AH/POA of either anti-COX-1 or anti-COX-2, blocked the febrile response induced by RANTES but not that induced by MIP-1beta. These results provide strong evidence for the existence of rapid mechanisms in the AH/POA which involve both COX isozymes during the fever induced by RANTES, and further support the existence of an alternative PG-independent pathway in the febrile response.

Calcium signaling in microglial cells

Receptor-mediated Ca(2+) signals are a common signal transduction mechanism in all living cells, including microglia. Recent years have brought major advances in our understanding of microglial Ca(2+) signaling. More than 20 receptor/ligand interactions leading to Ca(2+) signals in microglia have been described so far, and it seems that this is just the beginning. The literature has grown rapidly during the past few years, especially in regard to chemokine and ATP/UTP receptor signaling. This article presents a brief overview of the basics of Ca(2+) signaling, reviews the current literature on microglial Ca(2+) signaling, and discusses the current challenges and possible future directions of this emerging field.