Mouse astrocytes respond to the chemokines MCP-1 and KC, but reverse transcriptase-polymerase chain reaction does not detect mRNA for the KC or new MCP-1 receptor

Particulate Air pollution mediated effects on insulin resistance in mice are independent of CCR2

Background

Chronic exposure to fine ambient particulate matter (PM_2.5) induces insulin resistance. CC-chemokine receptor 2 (CCR2) appears to be essential in diet-induced insulin resistance implicating an important role for systemic cellular inflammation in the process. We have previously suggested that CCR2 is important in PM_2.5 exposure-mediated inflammation leading to insulin resistance under high fat diet situation. The present study assessed the importance of CCR2 in PM_2.5 exposure-induced insulin resistance in the context of normal diet.

Methods and Results

C57BL/6 and CCR2^-/- mice were subjected to exposure to concentrated ambient PM_2.5 or filtered air for 6 months. In C57BL/6 mice, concentrated ambient PM_2.5 exposure induced whole-body insulin resistance, macrophage infiltration into the adipose tissue, and upregulation of phosphoenolpyruvate carboxykinase (PEPCK) in the liver. While CCR2 deficiency reduced adipose macrophage content in the PM_2.5-exposed animals, it did not improve systemic insulin resistance. This lack of improvement in insulin resistance was paralleled by increased hepatic expression of genes in PEPCK and inflammation.

Conclusion

CCR2 deletion failed to attenuate PM_2.5 exposure-induced insulin resistance in mice fed on normal diet. The present study indicates that PM_2.5 may dysregulate glucose metabolism directly without exerting proinflammatory effects.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-017-0187-3) contains supplementary material, which is available to authorized users.

Absence of CCL2 and CCL3 Ameliorates Central Nervous System Grey Matter But Not White Matter Demyelination in the Presence of an Intact Blood-Brain Barrier

A broad spectrum of diseases is characterized by myelin abnormalities, oligodendrocyte pathology, and concomitant glia activation, among multiple sclerosis (MS). Our knowledge regarding the factors triggering gliosis and demyelination is scanty. Chemokines are pivotal for microglia and astrocyte activation and orchestrate critical steps during the formation of central nervous system (CNS) demyelinating lesions. Redundant functions of chemokines complicate, however, the study of their functional relevance. We used the cuprizone model to study redundant functions of two chemokines, CCL2/MCP1 and CCL3/MIP1α, which are critically involved in the pathological process of cuprizone-induced demyelination. First, we generated a mutant mouse strain lacking functional genes of both chemokines and demonstrated that double-mutant animals are viable, fertile, and do not present with gross abnormalities. Astrocytes and peritoneal macrophages, cultured form tissues of these animals did neither express CCL2 nor CCL3. Exposure to cuprizone resulted in increased CCL2 and CCL3 brain levels in wild-type but not mutant animals. Cuprizone-induced demyelination, oligodendrocyte loss, and astrogliosis were significantly ameliorated in the cortex but not corpus callosum of chemokine-deficient animals. In summary, we provide a novel powerful model to study the redundant function of two important chemokines. Our study reveals that chemokine function in the CNS redounds to region-specific pathophysiological events.

Absence of CC chemokine receptors 2a and 2b from human adipose lineage cells

Previous results have suggested the existence of receptors for monocyte chemoattractant protein-1 (MCP-1), CC chemokine receptors 2 (CCR2), in human adipocytes and their involvement in mediating effects of MCP-1 on adipocyte functions. However, the presence of CCR2 present on non-adipose-lineage cells of adipose tissue has not been excluded. We have used human Simpson-Golabi-Behmel-Syndrome (SGBS) preadipocytes and in-vitro-differentiated mature adipocytes to investigate the expression of CCR2 in human (pre)adipocytes. We found that the cells are devoid of CCR2 receptor protein and mRNA expression and fail to respond to treatment with all known CCR2 chemokine agonists. CCR2 is also absent from (pre)adipocytes prepared in vitro from human multipotent adipose-derived stem cells, bone-marrow-derived mesenchymal stem cells, or from primary (pre)adipocytes. Conditions mimicking proinflammatory changes in adipose tissue did not induce CCR2 receptor expression. We conclude that CCR2 is absent from human adipose lineage cells. Functional effects previously described for MCP-1 in human adipose tissue may be mediated indirectly through paracrine effects on non-adipose-lineage cells or by a (pre)adipocyte receptor for MCP-1 distinct from CCR2.

Overexpressing the CCL2 chemokine in an epithelial ovarian cancer cell line results in latency of in vivo tumourigenicity

The frequent loss of heterozygosity of chromosome (Chr) 17 in epithelial ovarian cancer (EOC), particularly high-grade ovarian serous carcinomas (HGOSCs), has been attributed to the disruption of known tumour suppressor genes, such as TP53 (17p13), as well as other genes on this chromosome that alone or in combination have a role in EOC. In a transcriptome analysis of Chr17 genes, we observed significant underexpression of the chemokine CCL2 (17q12) in a small set of HGOSC samples relative to normal ovarian surface epithelial cells and a significant upregulation of CCL2 in the TP53-mutated OV-90 EOC cell line rendered non-tumourigenic as a consequence of genetic manipulation. Here, we report that overexpressing CCL2 in OV-90 resulted in latency of tumour formation at intraperitoneal (i.p.) but not subcutaneous sites in a mouse xenograft model. Overexpressing CCL2 affected cell morphology and exerted modest, but not significant effects on cell viability, colony formation and cell migration. We report significant underexpression of CCL2 by transcriptome analysis (P=0.015) and by immunohistochemistry in 77% of HGOSC samples (n=65). Absent or a very low level of protein expression by immunohistochemistry was also observed in 71% of additional HGOSC samples (n=122). However, CCL2 protein expression did not significantly correlate with overall or disease-free survival. The epithelial cells of normal fallopian tubes, a purported origin of HGOSC, exhibited expression of CCL2 protein by immunohistochemistry. Our results affirm that CCL2 underexpression is a significant feature of HGOSC samples, and that CCL2 overexpression in an EOC cell line model affects tumourigenic potential in the i.p. setting.

KSRP: a checkpoint for inflammatory cytokine production in astrocytes

Chronic inflammation in the central nervous system (CNS) is a central feature of many neurodegenerative and autoimmune diseases. As an immunologically competent cell, the astrocyte plays an important role in CNS inflammation. It is capable of expressing a number of cytokines such as tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) that promote inflammation directly and through the recruitment of immune cells. Checkpoints are therefore in place to keep tight control over cytokine production. Adenylate/uridylate-rich elements (ARE) in the 3' untranslated region of cytokine mRNAs serve as a major checkpoint by regulating mRNA stability and translational efficiency. Here, we examined the impact of KH-type splicing regulatory protein (KSRP), an RNA binding protein which destabilizes mRNAs via the ARE, on cytokine expression and paracrine phenotypes of primary astrocytes. We identified a network of inflammatory mediators, including TNF-α and IL-1β, whose expression increased 2 to 4-fold at the RNA level in astrocytes isolated from KSRP(-/-) mice compared to littermate controls. Upon activation, KSRP(-/-) astrocytes produced TNF-α and IL-1β at levels that exceeded control cells by 15-fold or more. Conditioned media from KSRP(-/-) astrocytes induced chemotaxis and neuronal cell death in vitro. Surprisingly, we observed a prolongation of half-life in only a subset of mRNA targets and only after selective astrocyte activation. Luciferase reporter studies indicated that KSRP regulates cytokine gene expression at both transcriptional and post-transcriptional levels. Our results outline a critical role for KSRP in regulating pro-inflammatory mediators and have implications for a wide range of CNS inflammatory and autoimmune diseases.

CCL2 binding is CCR2 independent in primary adult human astrocytes

Chemokines are low relative molecular mass proteins, which have chemoattractant actions on many cell types. The chemokine, CCL2, has been shown to play a major role in the recruitment of monocytes in central nervous system (CNS) lesions in multiple sclerosis (MS). Since resident astrocytes constitute a major source of chemokine synthesis including CCL2, we were interested to assess the regulation of CCL2 by astrocytes. We showed that CCL2 bound to the cell surface of astrocytes and binding was not modulated by inflammatory conditions. However, CCR2 protein was not detected nor was activation of the classical CCR2 downstream signaling pathways. Recent studies have shown that non-signaling decoy chemokine receptors bind and modulate the expression of chemokines at site of inflammation. Here, we show that the D6 chemokine decoy receptor is constitutively expressed by primary human adult astrocytes at both mRNA and protein level. In addition, CCL3, which binds to D6, but not CCL19, which does not bind to D6, displaced CCL2 binding to astrocytes; indicating that CCL2 may bind to this cell type via the D6 receptor. Our results suggest that CCL2 binding to primary adult human astrocytes is CCR2-independent and is likely to be mediated via the D6 decoy chemokine receptor. Therefore we propose that astrocytes are implicated in both the establishment of chemokine gradients for the migration of leukocytes into and within the CNS and in the regulation of CCL2 levels at inflammatory sites in the CNS.

Monocyte/macrophage chemokine receptor CCR2 mediates diabetic renal injury

Monocyte/macrophage recruitment correlates strongly with the progression of renal impairment in diabetic nephropathy (DN). C-C chemokine receptor (CCR)2 regulates monocyte/macrophage migration into injured tissues. However, the direct role of CCR2-mediated monocyte/macrophage recruitment in diabetic kidney disease remains unclear. We report that pharmacological blockade or genetic deficiency of CCR2 confers kidney protection in Ins2(Akita) and streptozotocin (STZ)-induced diabetic kidney disease. Blocking CCR2 using the selective CCR2 antagonist RS504393 for 12 wk in Ins2(Akita) mice significantly attenuated albuminuria, the increase in blood urea nitrogen and plasma creatinine, histological changes, and glomerular macrophage recruitment compared with vehicle. Furthermore, mice lacking CCR2 (CCR2(-/-)) mimicked CCR2 blockade by reducing albuminuria and displaying less fibronectin mRNA expression and inflammatory cytokine production compared with CCR2(+/+) mice, despite comparable blood glucose levels. Bone marrow-derived monocytes from CCR2(+/+) or CCR2(-/-) mice adoptively transferred into CCR2(-/-) mice reversed the renal tissue-protective effect in diabetic CCR2(-/-) mice as evaluated by increased urinary albumin excretion and kidney macrophage recruitment, indicating that CCR2 is not required for monocyte migration from the circulation into diabetic kidneys. These findings provide evidence that CCR2 is necessary for monocyte/macrophage-induced diabetic renal injury and suggest that blocking CCR2 could be a novel therapeutic approach in the treatment of DN.

MCP-1 upregulates amylin expression in murine pancreatic β cells through ERK/JNK-AP1 and NF-κB related signaling pathways independent of CCR2

Background

Amylin is the most abundant component of islet amyloid implicated in the development of type 2 diabetes. Plasma amylin levels are elevated in individuals with obesity and insulin resistance. Monocyte chemoattractant protein-1 (MCP-1, CCL2) is involved in insulin resistance of obesity and type 2 diabetes. We investigated the effect of MCP-1 on amylin expression and the underlying mechanisms with murine pancreatic β-cell line MIN6 and pancreatic islets.

Methodology/Principal Findings

We found that MCP-1 induced amylin expression at transcriptional level and increased proamylin and intermediate forms of amylin at protein level in MIN6 cells and islets. However, MCP-1 had no effect on the expressions of proinsulin 1 and 2, as well as prohormone convertase (PC) 1/3 and PC2, suggesting that MCP-1 specifically induces amylin expression in β-cells. Mechanistic studies showed that although there is no detectable CCR2 mRNA in MIN6 cells and islets, pretreatment of MIN6 cells with pertussis toxin inhibited MCP-1 induced amylin expression, suggesting that alternative Gi-coupled receptor(s) mediates the inductive effect of MCP-1. MCP-1 rapidly induced ERK1/2 and JNK phosphorylation. Inhibitors for MEK1/2 (PD98059), JNK (SP600125) or AP1 (curcumin) significantly inhibited MCP-1-induced amylin mRNA expression. MCP-1 failed to induce amylin expression in pancreatic islets isolated from Fos knockout mice. EMSA showed that JNK and ERK1/2 were involved in MCP-1-induced AP1 activation. These results suggest that MCP-1 induces murine amylin expression through AP1 activation mediated by ERK1/2 or JNK. Further studies showed that treatment of MIN6 cells with NF-κB inhibitor or overexpression of IκBα dominant-negative construct in MIN6 cells significantly inhibited MCP-1-induced amylin expression, suggesting that NF-κB related signaling also participates in MCP-1-induced murine amylin expression.

Conclusions/Significance

MCP-1 induces amylin expression through ERK1/2/JNK-AP1 and NF-κB related signaling pathways independent of CCR2. Amylin upregulation by MCP-1 may contribute to elevation of plasma amylin in obesity and insulin resistance.

NOV/CCN3 upregulates CCL2 and CXCL1 expression in astrocytes through beta1 and beta5 integrins

Increasing evidence suggests that CCN matricellular proteins play important roles in inflammation. One of the major cell types that handle inflammation in the brain is the astrocyte, which, upon activation, dramatically increases its production of cytokines and chemokines. Here, we report that NOV/CCN3, added to primary cultured rat brain astrocytes, markedly increased the expression of CCL2 and CXCL1 chemokines, as indicated by ELISA and RT-qPCR assays. This effect was selective, as the production of thirteen other cytokines and chemokines was not affected by NOV. NOV expression by astrocytes was demonstrated by immunocytochemistry and Western blot analysis, and astrocyte transfection with NOV small interfering RNA (siRNA) markedly decreased CXCL1 and CCL2 production, indicating that endogenous NOV played a major role in the control of astrocytic chemokine synthesis. NOV was shown to mediate several of its actions through integrins. Here, we observed that siRNAs against integrins beta1 and beta5 decreased basal and abrogated NOV-stimulated astrocyte expression of CCL2 and CXCL1, respectively. Using a panel of kinase inhibitors, we demonstrated that NOV action on CCL2 and CXCL1 production involved a Rho/ROCK/JNK/NF-kappaB and a Rho/qROCK/p38/NF-kappaB pathway, respectively. Thus, distinct integrins and signaling mechanisms are involved in NOV-induced production of CCL2 and CXCL1 in astrocytes. Finally, astrocytic expression of NOV was detected in rat brain tissue sections, and NOV intracerebral injection increased CCL2 and CXCL1 brain levels in vivo. Altogether, our data shed light on the signaling pathways operated by NOV and strongly suggest that NOV mediates astrocyte activation and, therefore, might play a role in neuroinflammation.

CCL2 modulates cytokine production in cultured mouse astrocytes

Background

The chemokine CCL2 (also known as monocyte chemoattractant protein-1, or MCP-1) is upregulated in patients and rodent models of traumatic brain injury (TBI), contributing to post-traumatic neuroinflammation and degeneration by directing the infiltration of blood-derived macrophages into the injured brain. Our laboratory has previously reported that Ccl2-/- mice show reduced macrophage accumulation and tissue damage, corresponding to improved motor recovery, following experimental TBI. Surprisingly, Ccl2-deficient mice also exhibited delayed but exacerbated secretion of key proinflammatory cytokines in the injured cortex. Thus we sought to further characterise CCL2's potential ability to modulate immunoactivation of astrocytes in vitro.

Methods

Primary astrocytes were isolated from neonatal wild-type and Ccl2-deficient mice. Established astrocyte cultures were stimulated with various concentrations of lipopolysaccharide (LPS) and interleukin (IL)-1β for up to 24 hours. Separate experiments involved pre-incubation with mouse recombinant (r)CCL2 prior to IL-1β stimulation in wild-type cells. Following stimulation, cytokine secretion was measured in culture supernatant by immunoassays, whilst cytokine gene expression was quantified by real-time reverse transcriptase polymerase chain reaction.

Results

LPS (0.1-100 μg/ml; 8 h) induced the significantly greater secretion of five key cytokines and chemokines in Ccl2-/- astrocytes compared to wild-type cells. Consistently, IL-6 mRNA levels were 2-fold higher in Ccl2-deficient cells. IL-1β (10 and 50 ng/ml; 2-24 h) also resulted in exacerbated IL-6 production from Ccl2-/- cultures. Despite this, treatment of wild-type cultures with rCCL2 alone (50-500 ng/ml) did not induce cytokine/chemokine production by astrocytes. However, pre-incubation of wild-type astrocytes with rCCL2 (250 ng/ml, 12 h) prior to stimulation with IL-1β (10 ng/ml, 8 h) significantly reduced IL-6 protein and gene expression.

Conclusions

Our data indicate that astrocytes are likely responsible for the exacerbated cytokine response seen in vivo post-injury in the absence of CCL2. Furthermore, evidence that CCL2 inhibits cytokine production by astrocytes following IL-1β stimulation, suggests a novel, immunomodulatory role for this chemokine in acute neuroinflammation. Further investigation is required to determine the physiological relevance of this phenomenon, which may have implications for therapeutics targeting CCL2-mediated leukocyte infiltration following TBI.

CCL3 correlates with the number of mood disturbances and personality changes in patients with Alzheimer's disease

Although Alzheimer's disease (AD) is a primary degenerative disorder, a microglial-mediated inflammatory response, provoked by amyloid beta (Abeta), contributes to the neurodegeneration and subsequently to the cell loss. Since such an inflammatory contribution to neurodegeneration may influence disease progression, a basic question arises concerning the mechanisms of possible clinical signs dependent on inflammatory reactions. In the present study we investigated the levels of CCL3 in the peripheral blood of AD patients and correlated findings with the results of clinical tests such as the Mini-Mental State Examination (MMSE) and the Global Deterioration Scale (GDS), as well as with disturbances of behaviour, mood and personality, thereby extending the spectrum of clinical symptoms to ones not assessed by the MMSE or the GDS. CCL3 levels were lower in patients with AD but correlated positively with such noncognitive symptoms as mood disturbances and personality changes.We found that CCL3 did not correlate with the severity of dementia as assessed by the MMSE or with the degree of disease deterioration as assessed by the GDS. The results from our study on CCL3 levels in AD may, in part, explain the mechanisms of some concomitant, noncognitive clinical features of the disease.

Chemokine CCL2 and its receptor CCR2 are increased in the hippocampus following pilocarpine-induced status epilepticus

Background

Neuroinflammation occurs after seizures and is implicated in epileptogenesis. CCR2 is a chemokine receptor for CCL2 and their interaction mediates monocyte infiltration in the neuroinflammatory cascade triggered in different brain pathologies. In this work CCR2 and CCL2 expression were examined following status epilepticus (SE) induced by pilocarpine injection.

Methods

SE was induced by pilocarpine injection. Control rats were injected with saline instead of pilocarpine. Five days after SE, CCR2 staining in neurons and glial cells was examined using imunohistochemical analyses. The number of CCR2 positive cells was determined using stereology probes in the hippocampus. CCL2 expression in the hippocampus was examined by molecular assay.

Results

Increased CCR2 was observed in the hippocampus after SE. Seizures also resulted in alterations to the cell types expressing CCR2. Increased numbers of neurons that expressed CCR2 was observed following SE. Microglial cells were more closely apposed to the CCR2-labeled cells in SE rats. In addition, rats that experienced SE exhibited CCR2-labeling in populations of hypertrophied astrocytes, especially in CA1 and dentate gyrus. These CCR2+ astroctytes were not observed in control rats. Examination of CCL2 expression showed that it was elevated in the hippocampus following SE.

Conclusion

The data show that CCR2 and CCL2 are up-regulated in the hippocampus after pilocarpine-induced SE. Seizures also result in changes to CCR2 receptor expression in neurons and astrocytes. These changes might be involved in detrimental neuroplasticity and neuroinflammatory changes that occur following seizures.

Binding and uptake of A beta1-42 by primary human astrocytes in vitro

Clearance of the amyloid-beta peptide (A beta) as a remedy for Alzheimer's disease (AD) is a major target in on-going clinical trials. In vitro studies confirmed that A beta is taken up by rodent astrocytes, but knowledge on human astrocyte-mediated A beta clearance is sparse. Therefore, by means of flow cytometry and confocal laser scanning microscopy (CLSM), we evaluated the binding and internalization of A beta1-42 by primary human fetal astrocytes and adult astrocytes, isolated from nondemented subjects (n = 8) and AD subjects (n = 6). Furthermore, we analyzed whether alpha1-antichymotrypsin (ACT), which is found in amyloid plaques and can influence A beta fibrillogenesis, affects the A beta uptake by human astrocytes. Upon over night exposure of astrocytes to FAM-labeled A beta1-42 (10 microM) preparations, (80.7 +/- 17.7)% fetal and (52.9 +/- 20.9)% adult A beta-positive astrocytes (P = 0.018) were observed. No significant difference was found in A beta1-42 uptake between AD and non-AD astrocytes, and no influence of ApoE genotype on A beta1-42 uptake was observed in any group. There was no difference in the percentage of A beta-positive cells upon exposure to A beta1-42 (10 microM) combined with ACT (1,000:1, 100:1, and 10:1 molar ratio), versus A beta1-42 alone. CLSM revealed binding of A beta1-42 to the cellular surfaces and cellular internalization of smaller A beta1-42 fragments. Under these conditions, there was no increase in cellular release of the proinflammatory chemokine monocyte-chemoattractant protein 1, as compared with nontreated control astrocytes. Thus, primary human astrocytes derived from different sources can bind and internalize A beta1-42, and fetal astrocytes were more efficient in A beta1-42 uptake than adult astrocytes.

Astrocyte- and endothelial-targeted CCL2 conditional knockout mice: critical tools for studying the pathogenesis of neuroinflammation

While the expression of the C-C chemokine ligand 2 (CCL2) in the central nervous system (CNS) is associated with numerous neuroinflammatory conditions, the critical cellular sources of this chemokine, which is responsible for disease processes-as well as associated pathogenic mechanisms, remain unresolved. As the potential for anti-CCL2 therapeutics in treating neuroinflammatory disease is likely to be contingent upon effective drug delivery to the source(s) and/or target(s) of CCL2 action in the CNS, tools to highlight the course of CCL2 action during neuroinflammation are imperative. In response to this need, we used the Cre/loxP and FLP-FRT recombination system to develop the first two, cell-conditional CCL2 knockout mice-separately targeting CCL2 gene elimination to astrocytes and endothelial cells, both of which have been considered to play crucial though undefined roles in neuroinflammatory disease. Specifically, mice containing a floxed CCL2 allele were intercrossed with GFAP-Cre or Tie2-Cre transgenic mice to generate mice with CCL2-deficient astrocytes (astrocyte KO) or endothelial cells (endothelial KO), respectively. Polymerase chain reaction, reverse transcription polymerase chain reaction/quantitative reverse transcriptase polymerase chain reaction, and enzyme-linked immunosorbent assay of CCL2 gene, RNA, and protein, respectively, from cultured astrocytes and brain microvascular endothelial cells (BMEC) established the efficiency and specificity of the CCL2 gene deletions and a CCL2 null phenotype in these CNS cells. Effective cell-conditional knockout of CCL2 was also confirmed in an in vivo setting, wherein astrocytes and BMEC were retrieved by immune-guided laser capture microdissection from their in situ positions in the brains of mice experiencing acute, lipopolysaccharide-mediated endotoxemia to induce CCL2 gene expression. In vivo analysis further revealed apparent cross-talk between BMEC and astrocytes regarding the regulation of astrocyte CCL2 expression. Use of astrocyte KO and endothelial KO mice should prove critical in elaborating the pathogenic mechanisms of and optimizing the treatments for neuroinflammatory disease.

GABAergic activities enhance macrophage inflammatory protein-1alpha release from microglia (brain macrophages) in postnatal mouse brain

Microglial cells (brain macrophages) invade the brain during embryonic and early postnatal development, migrate preferentially along fibre tracts to their final position and transform from an amoeboid to a ramified morphology. Signals by which the invading microglia communicate with other brain cells are largely unknown. Here, we studied amoeboid microglia in postnatal corpus callosum obtained from 6- to 8-day-old mice. These cells accumulated on the surface of acute brain slices. Whole-cell patch-clamp recordings revealed that the specific GABA(A) receptor agonist muscimol triggered a transient increase in conductance typical for inward rectifying potassium channels in microglia. This current increase was not mediated by microglial GABA(A) receptors since microglial cells removed from the slice surface no longer reacted and cultured microglia only responded when a brain slice was placed in their close vicinity. Muscimol triggered a transient increase in extracellular potassium concentration ([K(+)](o)) in brain slices and an experimental elevation of [K(+)](o) mimicked the muscimol response in microglial cells. Moreover, in adult brain slices, muscimol led only to a minute increase in [K(+)](o) and microglial cells failed to respond to muscimol. In turn, an increase in [K(+)](o) stimulated the release of chemokine macrophage inflammatory protein-1alpha (MIP1-alpha) from brain slices and from cultures of microglia but not astrocytes. Our observations indicate that invading microglia in early postnatal development sense GABAergic activities indirectly via sensing changes in [K(+)](o) which results in an increase in MIP1-alpha release.

Monocyte chemoattractant protein-1 secreted by adipose tissue induces direct lipid accumulation in hepatocytes

For many years, adipose tissue has been mainly considered as an inert reservoir for storing triglycerides. Since the discovery that adipocytes may secrete a variety of bioactive molecules (hormones, chemokines, and cytokines), an endocrine and paracrine role for white adipose tissue (WAT) in the regulation of energy balance and other physiological processes has been established, particularly with regard to brain and muscle. In contrast, little is known about the interactions of WAT with liver. Hence, we examined the effect of the secretory products of WAT on hepatocytes. Conditioned medium of human WAT explants induced significant steatosis in hepatocyte cell lines. Factor(s) responsible for the conditioned medium-induced steatosis were screened by a battery of blocking antibodies against different cytokines/chemokines shown to be secreted by WAT. In contrast to interleukin-8 and interleukin-6, the monocyte chemoattractant protein-1 was capable of inducing steatosis in hepatocytes in a time-dependent manner at concentrations similar to those found in conditioned medium. Incubation of conditioned medium with antimonocyte chemoattractant protein-1 antibodies prevented triglyceride accumulation. Investigation of the mechanism leading to the triglyceride accumulation showed that both a diminution of apolipoprotein B secretion and an increase in phosphoenolpyruvate carboxykinase messenger RNA may be involved.

CONCLUSION

The monocyte chemoattractant protein-1 secreted by adipose tissue may induce steatosis not only recruiting macrophages but also acting directly on hepatocytes.

The effect of CXCL1 on human fetal oligodendrocyte progenitor cells

Chemokine CXCL1 is abundantly present in proliferative zones during brain development and in regions of remyelination, suggesting that it influences development of oligodendrocyte progenitors (OPC) in these regions. We studied in vitro the effects and possible mechanisms by which CXCL1 acts on human fetal OPC. In organotypic slice cultures of human fetal cortical ventricular/subventricular (VZ/SVZ) zones, blocking of CXCL1 signaling reduced significantly the proliferation of OPC. Moreover, exogenously added CXCL1 induced increase of OPC proliferation. Treatments of purified OPC cultures and cell depletion experiments demonstrated that this effect of CXCL1 was mainly indirect, mediated through astrocytes. We identified that CXCL1 acted through the extracellular signal regulated kinase (ERK1/2) pathway, activated primarily in astrocytes. In vitro, astrocytes stimulated with CXCL1 released several cytokines, but only the release of interleukin-6 (IL-6) was completely blocked by inhibition of ERK1/2 pathway. When released IL-6 was neutralized in slices, a decrease in OPC proliferation was demonstrated, while addition of IL-6 was able to return OPC proliferation in astrocyte-depleted slices to the control level. These results suggest that in the human fetal brain CXCL1 promotes proliferation of early OPC, acting in part through an ERK1/2-dependent pathway and release of IL-6 from astrocytes.

Neuronal chemokines: versatile messengers in central nervous system cell interaction

Whereas chemokines are well known for their ability to induce cell migration, only recently it became evident that chemokines also control a variety of other cell functions and are versatile messengers in the interaction between a diversity of cell types. In the central nervous system (CNS), chemokines are generally found under both physiological and pathological conditions. Whereas many reports describe chemokine expression in astrocytes and microglia and their role in the migration of leukocytes into the CNS, only few studies describe chemokine expression in neurons. Nevertheless, the expression of neuronal chemokines and the corresponding chemokine receptors in CNS cells under physiological and pathological conditions indicates that neuronal chemokines contribute to CNS cell interaction. In this study, we review recent studies describing neuronal chemokine expression and discuss potential roles of neuronal chemokines in neuron-astrocyte, neuron-microglia, and neuron-neuron interaction.

Calcium-sensing receptor stimulates secretion of an interferon-γ-induced monokine (CXCL10) and monocyte chemoattractant protein-3 in immortalized GnRH neurons

Biology of GnRH neurons is critically dependent on extracellular Ca(2+) (Ca(2+) (o)). We evaluated differences in gene expression patterns with low and high Ca(2+) (o) in an immortalized GnRH neuron line, GT1-7 cells. Mouse global oligonucleotide microarray was used to evaluate transcriptional differences among the genes regulated by elevated Ca(2+) (o). Our result identified two interferon-gamma (IFNgamma)-inducible chemokines, CXCL9 and CXCL10, and a beta chemokine, monocyte chemoattractant protein-3 (MCP-3/CCL7), being up-regulated in GT1-7 cells treated with high Ca(2+) (o) (3.0 mM) compared with low Ca(2+) (o) (0.5 mM). Up-regulation of these mRNAs by elevated Ca(2+) (o) was confirmed by quantitative PCR. Elevated Ca(2+) (o) stimulated secretion of CXCL10 and MCP-3 but not CXCL9 in GT1-7 cells, and this effect was mediated by an extracellular calcium-sensing receptor (CaR) as the dominant negative CaR attenuated secretion of CXCL10 and MCP-3. CXCL10 and MCP-3 were localized in mouse GnRH neurons in the preoptic hypothalamus. Suppression of K(+) channels (BK channels) with 25 nM charybdotoxin inhibited high-Ca(2+) (o)-stimulated CXCL10 release. Accordingly, CaR activation by a specific CaR agonist, NPS-467, resulted in the activation of a Ca(2+)-activated K(+) channel in these cells. CaR-mediated MCP-3 secretion involves the PI3 kinase pathway in GT1-7 cells. MCP-3 stimulated chemotaxis of astrocytes treated with transforming growth factor-beta (TGFbeta). With TGFbeta-treated astrocytes, we next observed that conditioned medium from GT1-7 cells treated with high Ca(2+) promoted chemotaxis of astrocytes, and this effect was attenuated by a neutralizing antibody to MCP-3. These results implicate CaR as an important regulator of GnRH neuron function in vivo by stimulating secretion of heretofore unsuspected cytokines, i.e., CXCL10 and MCP-3.

Brain cytokine synthesis induced by an intraparenchymal injection of LPS is reduced in MCP-1-deficient mice prior to leucocyte recruitment

We have previously shown that ischaemic lesions are smaller in monocyte chemoattractant protein-1-deficient (MCP-1(-/-)) mice than in wild-type (wt) controls. In addition to its role as a monocyte chemoattractant, monocyte chemoattractant protein-1 (MCP-1) has been proposed to contribute to lesion progression after focal ischaemia by driving local cytokine synthesis by resident glia. To investigate this hypothesis we injected lipopolysaccharide (LPS) into the brain parenchyma of MCP-1(-/-) mice and compared the resulting inflammatory response and production of proinflammatory cytokines to those in wt mice. Microglial and astrocyte morphological activation was the same in the two strains, but MCP-1(-/-) mice showed significantly lower levels of proinflammatory cytokine synthesis; interleukin-1beta (IL-1beta) and tumour necrosis factor-alpha (TNF-alpha) levels were up to 50% lower than in wt controls after 6 h. This reduced synthesis of proinflammatory cytokines occurred well before leucocyte recruitment to the central nervous system (CNS) is observed in this model of acute inflammation and thus cannot be attributed to lower numbers of recruited monocytes at the site of injury. We propose that MCP-1 contributes to acute CNS inflammation by pleiotropic mechanisms. In addition to being a potent chemoattractant for monocytes, we provide evidence here that MCP-1 can modify the responsiveness of CNS glia to acute inflammatory stimuli prior to leucocyte recruitment, thereby acting as a priming stimulus for cytokine synthesis in cells such as microglia.

Chemokines and glial cells: a complex network in the central nervous system

Chemokines are small secreted proteins that are essential for the recruitment and activation of specific leukocyte subsets at sites of inflammation and for the development and homeostasis of lymphoid and nonlymphoid tissues. During the past decade, chemokines and their receptors have also emerged as key signaling molecules in neuroinflammatory processes and in the development and functioning of the central nervous system. Neurons and glial cells, including astrocytes, oligodendrocytes, and microglia, have been identified as cellular sources and/or targets of chemokines produced in the central nervous system in physiological and pathological conditions. In this article, we provide an update of chemokines and chemokine receptors expressed by glial cells focusing on their biological functions and implications in neurological diseases.

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.

MCP-1-dependent signaling in CCR2(-/-) aortic smooth muscle cells

Monocyte chemoattractant protein-1 (MCP-1, CCL2) is a mediator of inflammation that has been implicated in the pathogenesis of a wide variety of human diseases. CCR2, a heterotrimeric G-coupled receptor, is the only known receptor that functions at physiologic concentrations of MCP-1. Despite the importance of CCR2 in mediating MCP-1 responses, several recent studies have suggested that there may be another functional MCP-1 receptor. Using arterial smooth muscle cells (SMC) from CCR2(-/-) mice, we demonstrate that MCP-1 induces tissue-factor activity at physiologic concentrations. The induction of tissue factor by MCP-1 is blocked by pertussis toxin and 1,2-bis(O-aminophenyl-ethane-ethan)-N,N,N',N'-tetraacetic acid-acetoxymethyl ester, suggesting that signal transduction through the alternative receptor is G(alphai)-coupled and dependent on mobilization of intracellular Ca(2+). MCP-1 induces a time- and concentration-dependent phosphorylation of the mitogen-activated protein kinases p42/44. The induction of tissue factor activity by MCP-1 is blocked by PD98059, an inhibitor of p42/44 activation, but not by SB203580, a selective p38 inhibitor. These data establish that SMC possess an alternative MCP-1 receptor that signals at concentrations of MCP-1 that are similar to those that activate CCR2. This alternative receptor may be important in mediating some of the effects of MCP-1 in atherosclerotic arteries and in other inflammatory processes.

Caveolin-1 knockdown by small interfering RNA suppresses responses to the chemokine monocyte chemoattractant protein-1 by human astrocytes

Astrocytes regulate the integrity of the blood-brain barrier and influence inflammatory processes in the central nervous system. The pro-inflammatory chemokine monocyte chemoattractant protein-1 (MCP-1), which is both released by and stimulates astrocytes, is thought to play a crucial role in both these activities. Because astrocytes have been shown to possess caveolae, vesicular structures that participate in intracellular transport and signal transduction events, we reasoned that expression of the major structural protein of these organelles, caveolin-1, might feature critically in the cellular responses to MCP-1. To test this hypothesis, caveolin-1 level was "knocked down" in human astrocyte cultures by using a small interfering RNA approach. This method resulted in efficient (>90% loss) and specific knockdown of caveolin-1 expression while sparring glial fibrillary acidic protein as well as several other proteins involved in endocytosis. Astrocytes suffering caveolin-1 loss showed diminished ability to down-modulate and internalize the MCP-1 receptor (CCR2) in response to exposure to this chemokine and also demonstrated significantly reduced capacity to undergo chemotaxis and calcium flux when MCP-1-stimulated. The results highlight a potentially prominent role for caveolae and/or caveolin-1 in mediating astrocyte responses to MCP-1, a feature that might significantly dictate the progression of inflammatory events at the blood-brain barrier.

MCP-1 deficiency is associated with reduced intimal hyperplasia after arterial injury

Monocyte chemoattractant protein (MCP)-1 is abundant in smooth muscle cells (SMC) and macrophages of atherosclerotic plaques and in the injured arterial wall. MCP-1 and its receptor, CCR2, are important mediators of macrophage accumulation and atherosclerotic plaque progression. We have recently reported that CCR2(-/-) mice have a approximately 60% decrease in intimal hyperplasia and medial DNA synthesis in response to femoral arterial injury. We have now examined the response to femoral arterial injury in MCP-1(-/-) mice. MCP-1 deficiency was associated with a approximately 30% reduction in intimal hyperplasia at 4 weeks and was not associated with diminished medial DNA synthesis. Despite inducing tissue factor in SMC culture, MCP-1 deficiency was not associated with a decrease in neointimal tissue factor after injury. These data suggest that MCP-1 and CCR2 deficiencies have distinct effects on arterial injury. The effects of MCP-1 on intimal hyperplasia may be mediated largely through SMC migration.

Expression of L-CCR in HEK 293 cells reveals functional responses to CCL2, CCL5, CCL7, and CCL8

It has become clear in the past years that chemokines and chemokine receptors are pivotal regulators of cellular communication and trafficking. In addition to the approximately 20 chemokine receptors that have been cloned and described, various orphan receptors with a chemokine receptor-like structure are known. We have investigated the orphan mouse chemokine receptor (L-CCR) in HEK 293 cells, a receptor that was originally described in a mouse macrophage cell line. Cells expressing this receptor show pertussis toxin-sensitive chemotaxis and small intracellular calcium transients in response to the chemokines CCL2, CCL7, CCL8, and CCL5. Biotinylated CCL2 binds to L-CCR-expressing cells, and transfection experiments with an L-CCR-green fluorescent protein fusion protein showed L-CCR expression in the membranes of recombinant HEK 293 cells. Although radioligand binding was not detected, it is suggested that L-CCR is a functional chemokine receptor.

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.

Adult mouse astrocytes degrade amyloid-beta in vitro and in situ

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterized by excessive deposition of amyloid-beta (Abeta) peptides in the brain. One of the earliest neuropathological changes in AD is the accumulation of astrocytes at sites of Abeta deposition, but the cause or significance of this cellular response is unclear. Here we show that cultured adult mouse astrocytes migrate in response to monocyte chemoattractant protein-1 (MCP-1), a chemokine present in AD lesions, and cease migration upon interaction with immobilized Abeta(1-42). We also show that astrocytes bind and degrade Abeta(1-42). Astrocytes plated on Abeta-laden brain sections from a mouse model of AD associate with the Abeta deposits and reduce overall Abeta levels in these sections. Our results suggest a novel mechanism for the accumulation of astrocytes around Abeta deposits, indicate a direct role for astrocytes in degradation of Abeta and implicate deficits in astroglial clearance of Abeta in the pathogenesis of AD. Treatments that increase removal of Abeta by astrocytes may therefore be a critical mechanism to reduce the neurodegeneration associated with AD.

Expression of chemokines and their receptors in human and simian astrocytes: evidence for a central role of TNF alpha and IFN gamma in CXCR4 and CCR5 modulation

Chemokines are key mediators of the selective migration of leukocytes that occurs in neurodegenerative diseases and related inflammatory processes. Astrocytes, the most abundant cell type in the CNS, have an active role in brain inflammation. To ascertain the role of astrocytes during neuropathological processes, we have investigated in two models of primary cells (human fetal and simian adult astrocytes) the repertoire of chemokines and their receptors expressed in response to inflammatory stimuli. We demonstrated that, in the absence of any stimulation, human fetal and simian adult astrocytes express mRNA for receptors APJ, BOB/GPR15, Bonzo/CXCR6, CCR2, CCR3, CCR5, CCR8, ChemR23, CXCR3/GPR9, CXCR4, GPR1, and V28/CX3CR1. Moreover, TNFalpha and IL-1beta significantly increase BOB/GPR15, CCR2, and V28/CX3CR1 mRNA levels in both models. Furthermore, TNFalpha and IFNgamma act synergistically to induce expression of the major coreceptors for HIV infection, CXCR4 and CCR5, at both the mRNA and protein levels in human and simian astrocytes, whereas CCR3 expression was not affected by cytokine treatment. Finally, TNFalpha/IFNgamma was the most significant cytokine combination in leading to a pronounced upregulation in a comparable, time-dependent manner of the production of chemokines IP-10/CXCL10, RANTES/CCL5, MIG/CXCL9, MCP-1/CCL2, and IL-8/CXCL8. In summary, these data suggest that astrocytes serve as an important source of chemokines under the dependence of a complex cytokine regulation, and TNFalpha and IFNgamma are important modulators of chemokines and chemokine receptor expression in human as well as simian astrocytes. Finally, with the conditions we used, there was no difference between species or age of tissue.

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.

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.

Pertussis toxin-induced reversible encephalopathy dependent on monocyte chemoattractant protein-1 overexpression in mice

In this report we describe pertussis toxin-induced reversible encephalopathy dependent on monocyte chemoattractant protein-1 (MCP-1) overexpression (PREMO), a novel animal model that exhibits features of human encephalopathic complications of inflammatory disorders such as viral meningoencephalitis and Lyme neuroborreliosis as well as the mild toxic encephalopathy that commonly precedes relapses of multiple sclerosis (MS). Overexpression of the mouse MCP-1 gene product (classically termed JE) in astrocytes, the major physiological CNS cellular source of MCP-1, failed to induce neurological impairment. Unexpectedly, transgenic (tg) mice overexpressing MCP-1 at a high level (MCP-1(hi)) manifested transient, severe encephalopathy with high mortality after injections of pertussis toxin (PTx) plus complete Freund's adjuvant (CFA). Surviving mice showed markedly improved function and did not relapse during a prolonged period of observation. Tg mice that expressed lower levels of MCP-1 were affected minimally after CFA/PTx injections, and tg expression of other chemokines failed to elicit this disorder. The disorder was significantly milder in mice lacking T-cells, which therefore play a deleterious role in this encephalopathic process. Disruption of CC chemokine receptor 2 (CCR2) abolished both CNS inflammation and encephalopathy, identifying CCR2 as a relevant receptor for this disorder. Proinflammatory and type 1 cytokines including TNF-alpha, IL-1beta, IFN-gamma, IL-2, RANTES, and IP-10 were elevated in CNS tissues from mice with PREMO. These studies characterize a novel model of reversible inflammatory encephalopathy that is dependent on both genetic and environmental factors.

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.

Functional expression of CCR2 by human fetal astrocytes

Astrocytes from different sources bind the chemokine monocyte chemoattractant factor (MCP-1), yet functional expression in these cells of CCR2, the major receptor for this ligand, has been a matter of controversy. Here we show that cultured human fetal astrocytes express CCR2 at the mRNA and protein levels, and display chemotaxis and calcium flux in response to MCP-1. Surface CCR2 protein expression and MCP-1 binding activity were observed to undergo near parallel downmodulation and recovery following MCP-1 exposure, supporting the argument that CCR2, and not another receptor, mediates MCP-1 ligation in these cells. Downmodulation was further determined to occur via receptor internalization, and to apparently proceed via both clathrin-coated vesicles and caveolae, the latter being a novel mode for the endocytosis of chemokine receptors. Insofar as MCP-1 is thought to mediate inflammatory and developmental processes within the central nervous system (CNS), such astrocyte responses to this chemokine are likely to significantly impact physiological and pathophysiological events at the blood-brain barrier and within the CNS parenchyma.

RANTES stimulates inflammatory cascades and receptor modulation in murine astrocytes

Cultured mouse astrocytes respond to the CC chemokine RANTES by production of chemokine and cytokine transcripts. Stimulation of astrocytes with 1 nM RANTES or 3-10 nM of the structurally related chemokines (eotaxin, macrophage inflammatory protein-1alpha and -beta [MIP-1alpha, MIP-1beta]) induced transcripts for KC, monocyte chemoattractant protein-1 (MCP-1), tumor necrosis factor-alpha (TNF-alpha), MIP-1alpha, MIP-2, and RANTES in a chemokine and cell-specific fashion. Synthesis of chemokine (KC and MCP-1) and cytokine (TNF-alpha) proteins was also demonstrated. RANTES-mediated chemokine synthesis was specifically inhibited by pertussis toxin, indicating that G-protein-coupled chemokine receptors participated in astrocyte signaling. Astrocytes expressed CCR1 and CCR5 (the redundant RANTES receptors). Astrocytes derived from mice with targeted mutations of either CCR1 or CCR5 respond after RANTES stimulation, suggesting multiple chemokine receptors may separately mediate RANTES responsiveness in astrocytes. Preliminary data suggest activation of the MAP kinase pathway is also critical for RANTES-mediated signaling in astrocytes. Treatment with RANTES specifically modulated astrocyte receptors upregulating intercellular adhesion molecule 1 (ICAM-1) and downregulating CX3CR1 expression. Thus, after chemokine treatment, astrocytes release proinflammatory mediators and reprogram their surface molecules. The combined effects of RANTES may serve to amplify inflammatory responses within the central nervous system.

Differential roles of CC chemokine ligand 2/monocyte chemotactic protein-1 and CCR2 in the development of T1 immunity

CCR2 and its major ligand, chemokine ligand 2 (CCL2)/monocyte chemotactic protein-1, have been found to influence T1/T2 immune response polarization. Our objective was to directly compare the roles of CCR2 and CCL2 in T1/T2 immune response polarization using a model of pulmonary Cryptococcus neoformans infection. Either deletion of CCR2 or treatment of wild-type mice with CCL2 neutralizing Ab produced significant and comparable reductions in macrophage and T cell recruitment into the lungs following infection. Both CCL2 neutralization and CCR2 deficiency resulted in significantly diminished IFN-gamma production, and increased IL-4 and IL-5 production by lung leukocytes (T1 to T2 switch), but only CCR2 deficiency promoted pulmonary eotaxin production and eosinophilia. In the lung-associated lymph nodes (LALN), CCL2-neutralized mice developed Ag-specific IFN-gamma-producing cells, while CCR2 knockout mice did not. LALN from CCR2 knockout mice also had fewer MHCII(+)CD11c(+) and MHCII(+)CD11b(+) cells, and produced significantly less IL-12p70 and TNF-alpha when stimulated with heat-killed yeast than LALN from wild-type or CCL2-neutralized mice, consistent with a defect in APC trafficking in CCR2 knockout mice. Neutralization of CCL2 in CCR2 knockout mice did not alter immune response development, demonstrating that the high levels of CCL2 in these mice did not play a role in T2 polarization. Therefore, CCR2 (but not CCL2) is required for afferent T1 development in the lymph nodes. In the absence of CCL2, T1 cells polarize in the LALN, but do not traffic from the lymph nodes to the lungs, resulting in a pulmonary T2 response.

Monocyte chemoattractant protein-1 deficiency is protective in a murine stroke model

Inflammatory processes have been implicated in the pathogenesis of brain damage after stroke. In rodent stroke models, focal ischemia induces several proinflammatory chemokines, including monocyte chemoattractant protein-1 (MCP-1). The individual contribution to ischemic tissue damage, however, is largely unknown. To address this question, the authors subjected MCP-1-deficient mice (MCP-1-/-) to permanent middle cerebral artery occlusion (MCAO). Measurement of basal blood pressure, cerebral blood flow, and blood volume revealed no differences between wild-type (wt) and MCP-1-/- mice. MCAO led to similar cerebral perfusion deficits in wt and MCP-1-/- mice, excluding differences in the MCA supply territory and collaterals. However, compared with wt mice, the mean infarct volume was 29% smaller in MCP-1-/- mice 24 hours after MCAO (P = 0.022). Immunostaining showed a reduction of phagocytic macrophage accumulation within infarcts and the infarct border in MCP-1-/- mice 2 weeks after MCAO. At the same time point, the authors found an attenuation of astrocytic hypertrophy in the infarct border and thalamus in MCP-1-/- mice. However, these effects on macrophages and astrocytes in MCP-1-/- mice occurred too late to suggest a protective role in acute infarct growth. Of note: at 6 hours after MCAO, MCP-1-/- mice produced significantly less interleukin-1beta in ischemic tissue; this might be related to tissue protection. The results of this study indicate that inhibition of MCP-1 signaling could be a new acute treatment approach to limit infarct size after stroke.

Expression of beta-chemokines and chemokine receptors in human fetal astrocyte and microglial co-cultures: potential role of chemokines in the developing CNS

Chemokines play specific roles in directing the recruitment of leukocyte subsets into inflammatory foci within the central nervous system (CNS). The involvement of these cytokines as mediators of inflammation is widely accepted. Recently, it has become evident that cells of the CNS (astrocytes, microglia, and neurons) not only synthesize, but also respond functionally or chemotactically to chemokines. We previously reported developmental events associated with colonization of the human fetal CNS by mononuclear phagocytes (microglial precursors), which essentially takes place within the first two trimesters of life. As part of the array of signals driving colonization, we noted specific anatomical distribution of chemokines and chemokine receptors expressed during this period. In order to further characterize expression of these molecules, we have isolated and cultured material from human fetal CNS. We demonstrate that unstimulated subconfluent human fetal glial cultures express high levels of CCR2 and CXCR4 receptors in cytoplasmic vesicles. Type I astrocytes, and associated ameboid microglia in particular, express high levels of surface and cytoplasmic CXCR4. Of the chemokines tested (MIP-1alpha, MIP-1beta, MCP-1, MCP-3, RANTES, SDF-1, IL-8, IP-10), only MIP-1alpha, detected specifically on microglia, was expressed both constitutively and consistently. Low variable levels of MCP-1, MIP-1alpha, and RANTES were also noted in unstimulated glial cultures. Recombinant human chemokines rhMCP-1 and rhMIP-1alpha also displayed proliferative effects on glial cultures at [10 ng/ml], but displayed variable effects on CCR2 levels on these cells. rhMCP-1 specifically upregulated CCR2 expression on cultured glia at [50 ng/ml]. It is gradually becoming evident that chemokines are important in embryonic development. The observation that human fetal glial cells and their progenitors express specific receptors for chemokines and can be stimulated to produce MCP-1, as well as proliferate in response to chemokines, supports a role for these cytokines as regulatory factors during development.

Lack of CCR2 results in increased mortality and impaired leukocyte activation and trafficking following infection of the central nervous system with a neurotropic coronavirus

In the present study, we evaluated the role of CCR2 in a model of viral-induced neurologic disease. An orchestrated expression of chemokines, including the CCR2 ligands monocyte chemoattractant protein-1/CCL2 and monocyte chemoattractant protein-3/CCL7, occurs within the CNS following infection with mouse hepatitis virus (MHV). Infection of mice lacking CCR2 (CCR2(-/-)) with MHV resulted in increased mortality and enhanced viral recovery from the brain that correlated with reduced (p < or = 0.04) T cell and macrophage/microglial (determined by F4/80 Ag expression, p < or = 0.004) infiltration into the CNS. Moreover, MHV-infected CCR2(-/-) mice displayed a significant decrease in Th1-associated factors IFN-gamma (p < or = 0.001) and RANTES/CCL5 (p < or = 0.002) within the CNS as compared with CCR2(+/+) mice. Further, peripheral CD4(+) and CD8(+) T cells from immunized CCR2(-/-) mice displayed a marked reduction in IFN-gamma production in response to viral Ag and did not migrate into the CNS of MHV-infected recombination-activating gene (RAG)1(-/-) mice following adoptive transfer. In addition, macrophage/microglial infiltration into the CNS of RAG1(-/-) mice receiving CCR2(-/-) splenocytes was reduced (p < or = 0.05), which correlated with a reduction in the severity of demyelination (p < or = 0.001) as compared with RAG1(-/-) mice receiving splenocytes from CCR2(+/+) mice. Collectively, these results indicate an important role for CCR2 in host defense and disease by regulating leukocyte activation and trafficking.

Chemokines and their receptors in the central nervous system

Chemokines are a family of proteins associated with the trafficking of leukocytes in physiological immune surveillance and inflammatory cell recruitment in host defence. They are classified into four classes based on the positions of key cystiene residues: C, CC, CXC, and CX3C. Chemokines act through both specific and shared receptors that all belong to the superfamily of G-protein-coupled receptors. Besides their well-established role in the immune system, several recent reports have demonstrated that these proteins also play a role in the central nervous system (CNS). In the CNS, chemokines are constitutively expressed by microglial cells, astrocytes, and neurons, and their expression can be increased after induction with inflammatory mediators. Constitutive expression of chemokines and chemokine receptors has been observed in both developing and adult brains, and the role played by these proteins in the normal brain is the object of intense study by many research groups. Chemokines are involved in brain development and in the maintenance of normal brain homeostasis; these proteins play a role in the migration, differentiation, and proliferation of glial and neuronal cells. The chemokine stromal cell-derived factor 1 and its receptor, CXCR4, are essential for life during development, and this ligand-receptor pair has been shown to have a fundamental role in neuron migration during cerebellar formation. Chemokine and chemokine receptor expression can be increased by inflammatory mediators, and this has in turn been associated with several acute and chronic inflammatory conditions. In the CNS, chemokines play an essential role in neuroinflammation as mediators of leukocyte infiltration. Their overexpression has been implicated in different neurological disorders, such as multiple sclerosis, trauma, stroke, Alzheimer's disease, tumor progression, and acquired immunodeficiency syndrome-associated dementia. An emerging area of interest for chemokine action is represented by the communication between the neuroendocrine and the immune system. Chemokines have hormone-like actions, specifically regulating the key host physiopathological responses of fever and appetite. It is now evident that chemokines and their receptors represent a plurifunctional family of proteins whose actions on the CNS are not restricted to neuroinflammation. These molecules constitute crucial regulators of cellular communication in physiological and developmental processes.

Astrocytes express functional chemokine receptors

Multiple lines of evidence are presented characterizing the functional expression of chemokine receptors CXCR4, CCR1, CCR5, and CX3CR1 on astrocytes. Most of these receptors are expressed at low levels and may only be detectable on a subset of cells during disease or following cytokine induction. The expression of CXCR2, CCR2, CCR3, CCR10, CCR11, and several orphan receptors associated with HIV-1 infection has also been proposed. The appearance of several chemokine receptors implies a wider role for chemokines in the regulation of central nervous system functions. Available evidence indicates that selected chemokines induce further chemokine synthesis in astrocytes providing a mechanism to amplify inflammatory responses in the central nervous system.

Characterization of binding sites for chemokines MCP-1 and MIP-1alpha on human brain microvessels

The presence of binding sites for the beta chemokines monocyte chemoattractant protein-1 (MCP-1) and macrophage inflammatory protein-1alpha (MIP-1alpha) has recently been identified on human brain microvessels. We extend these findings in this report to reveal that such sites exemplify characteristics of the recognized major receptors for MCP-1 and MIP-1alpha: CCR2, and CCR1 and CCR5, respectively. Specifically, labeled MCP-1 binding to isolated brain microvessels was inhibited by unlabeled MCP-1 and MCP-3, the latter another CCR2 ligand, but not by MIP-1alpha. Inhibition of labeled MIP-1alpha binding was achieved with unlabeled MIP-1alpha and RANTES, the latter a beta chemokine that binds to both CCR1 and CCR5, but not by MCP-1. Labeled MIP-1alpha binding was also antagonized by unlabeled MCP-3, which is also recognized by CCR1, and MIP-1beta, which is a ligand for CCR5. Labeled MCP-1 and MIP-1alpha were further observed to be internalized within the endothelial cells of brain microvessels, following their binding to the microvascular surface at 37 degrees C. Additionally, exposure of microvessels to unlabeled MCP-1 or MIP-1alpha was accompanied by the initial loss and subsequent recovery of surface binding sites for these chemokines, which occurred on a time scale consistent with ligand-induced endocytosis and recycling. These collective features bear striking similarity to those that characterize interactions of MCP-1 and MIP-1alpha with their receptors on leukocytes and underscore the concept of cognate chemokine receptors on brain microvascular endothelium.

Macrophage inflammatory protein-2 and KC induce chemokine production by mouse astrocytes

Astrocytes are specialized cells of the CNS that are implicated in the pathogenesis of multiple sclerosis and experimental allergic encephalomyelitis. In acute and relapsing-remitting experimental allergic encephalomyelitis, the neutrophil chemoattractant CXC chemokines macrophage-inflammatory protein (MIP)-2 and KC are associated with reactive astrocytes in the parenchyma. In vitro treatment of primary astrocyte cultures with nanomolar concentrations of MIP-2 or KC markedly up-regulated expression of the monocyte/T cell chemoattractants monocyte chemoattractant protein-1, inflammatory protein-10, and RANTES by a mechanism that includes stabilization of mRNA. Production of TNF-alpha and IL-6 transcripts were also noted, as was autocrine induction of MIP-2 and KC message. In addition, low levels of MIP-1alpha and MIP-1beta were induced following treatment with MIP-2 or KC. These effects are specific to astrocytes as MIP-2 treatment of microglial cells failed to elicit chemokine production. The astrocyte chemokine receptor for MIP-2 has 2.5 nM affinity for ligand. Astrocytes from CXCR2-deficient mice still respond to KC and MIP-2, indicating the presence of an alternative or novel high affinity receptor for these ligands. We propose that this KC/MIP-2 chemokine cascade may contribute to the persistence of mononuclear cell infiltration in demyelinating autoimmune diseases.

Large and sustained induction of chemokines during impaired wound healing in the genetically diabetic mouse: prolonged persistence of neutrophils and macrophages during the late phase of repair

Chemokines are seen as the stimuli that largely control leukocyte migration. To assess whether the severely impaired process of cutaneous repair observed in genetically diabetic db/db mice is associated with a dysregulated infiltration of immune cells, we determined the expressional kinetics for the murine growth-regulated oncogene/melanoma growth stimulatory activity homolog macrophage inflammatory protein-2, and the macrophage chemoattractant protein-1, respectively. Wound repair in db/db mice was characterized by a sustained inflammatory response and a prolonged expression of macrophage inflammatory protein-2 and macrophage chemoattractant protein-1. Immuno-histochemistry revealed that keratinocytes at the wound margins expressed macrophage chemoattractant protein-1, whereas macrophage inflammatory protein-2 immunopositive signals were observed only in keratinocytes of hair follicles located adjacent to the wound site. Inactivation studies using neutralizing antibodies against macrophage chemoattractant protein-1 or macrophage inflammatory protein-2 indicated that sustained expression of these chemokines participated in a prolonged presence of neutrophils and macrophages at the wound site during diabetic repair. Furthermore, our data provide evidence that late infiltration (day 13 after injury) of neutrophils and macrophages into wounds in db/db mice was associated with a simultaneous downregulation of mRNA for receptors specific for macrophage inflammatory protein-2 and macrophage chemoattractant protein-1 in these animals.

CCR2 expression determines T1 versus T2 polarization during pulmonary Cryptococcus neoformans infection

Pulmonary clearance of the encapsulated yeast Cryptococcus neoformans requires the development of T1-type immunity. The objective of this study was to determine the role of CCR2 in leukocyte recruitment and development of T1-type cell-mediated immunity during pulmonary C. neoformans infection. Intratracheal inoculation of C. neoformans into CCR2 knockout (CCR2-/-) mice produced a prolonged pulmonary infection (5000-fold CFU at 6 wk compared with CCR2+/+ mice) and significant dissemination to the spleen and brain (160- and 800-fold greater). In addition, CCR2 deficiency resulted in significantly reduced recruitment of macrophages (weeks 1-3) and CD8+ T cells (weeks 1-2) into the lungs. The immune response in CCR2-/- mice was characterized by chronic pulmonary eosinophilia, crystal deposition in the lungs, pulmonary leukocyte production of IL-4 and IL-5 but not IFN-gamma, lack of anticryptococcal delayed-type hypersensitivity, and high levels of serum IgE. These results demonstrate that expression of CCR2 is required for the development of a T1-type response to C. neoformans infection and lack of CCR2 results in a switch to a T2-type response. Thus, CCR2 plays a critical role in promoting the development of T1- over T2-type immune responses in the lung following cryptococcus infection.

Chemokines and chemokine receptors in the pathogenesis of multiple sclerosis

In recent years we have seen growing evidence for the role of chemokines in the pathogenesis of several infectious and non-infectious inflammatory CNS disease states, including Multiple Sclerosis (MS) and its animal model, experimental allergic encephalomyelitis (EAE). An increase in proinflammatory chemokines has been associated with demyelinating lesions and clinical neurological dysfunction in patients with MS; these chemokines could be potential targets for MS therapy. Besides a clearly defined role in mediating leukocyte migration, these and other chemokines may act as immunoregulatory molecules in the driving to Th1/Th2 responses, switch of cytokine profiles, and the induction of tolerance. Since chemokine receptors have now been identified on macrophages, microglia, astrocytes, and endothelial cells as well as neurons in the CNS, chemokine/receptor interactions may mediate functional responses in a variety of CNS cell types during the course of inflammatory disease states. Therefore, clarification of the roles of chemokines and their receptors in the pathogenesis of EAE and MS will be useful in establishing immunotherapeutic strategies for these neurological autoimmune disorders.