TNF-alpha down-regulates CXCR4 expression in primary murine astrocytes

Aberrant regulation of CXCR4 in cancer via deviant microRNA-targeted interactions

CXCR4 is involved in many facets of cancer, including being a major player in establishing metastasis. This is in part due to the deregulation of CXCR4, which can be attributed to many genetic and epigenetic mechanisms, including aberrant microRNA-CXCR4 interaction. MicroRNAs (miRNAs) are a type of small non-coding RNA that primarily targets the 3' UTR of mRNA transcripts, which in turn suppresses mRNA and subsequent protein expression. In this review, we reported and characterized the many aberrant miRNA-CXCR4 interactions that occur throughout human cancers. In particular, we reported known target sequences located on the 3' UTR of CXCR4 transcripts that tumour suppressor miRNAs bind and therefore regulate expression by. From these aberrant interactions, we also documented affected downstream genes/pathways and whether a particular tumour suppressor miRNA was reported as a prognostic marker in its respected cancer type. In addition, a limited number of cancer-causing miRNAs coined 'oncomirs' were reported and described in relation to CXCR4 regulation. Moreover, the mechanisms underlying both tumour suppressor and oncomir deregulations concerning CXCR4 expression were also explored. Furthermore, the miR-146a-CXCR4 axis was delineated in oncoviral infected endothelial cells in the context of virus-causing cancers. Lastly, miRNA-driven therapies and CXCR4 antagonist drugs were discussed as potential future treatment options in reported cancers pertaining to deregulated miRNA-CXCR4 interactions.

Leishmania donovani and HIV co-infection in vitro: Identification and characterization of main molecular players

The incidence of Leishmania/HIV co-infection is growing and few studies detail the cellular processes and macromolecules participating in co-infection. Thus, the goal of this study was to partially describe the Leishmania/HIV co-infection events by measuring molecular and functional parameters associated with both pathogens in vitro. MT-4 cells (human T-lymphocytes), primary monocytes, and peripheral blood mononuclear cells were exposed to HIV and/or Leishmania donovani. The cytopathic effects generated by the pathogens were observed through microscopy. Viral replication was assessed by monitoring p24 protein levels and parasitic proliferation/infectivity was determined using Giemsa staining. Changes in molecular markers were evaluated by ELISA and fluorescence assays. Our results showed that our system reassembles the main parameters previously described for Leishmania/HIV co-infection in patients in terms of potentiation of parasitic and viral replication/infectivity, amplification of syncytia induction, and alterations of cell viability. In addition, an amplification in NF-κB activation, changes in CXCR4/CCR5 surface expression, and a Th1→Th2 variation in cytokine/chemokine secretion were demonstrated. Altogether, this study could contribute to gain a deep understanding of the molecular events associated with Leishmania/HIV co-infection.

Progress toward rationally designed small-molecule peptide and peptidomimetic CXCR4 antagonists

Over the last 5 years, X-ray structures of CXCR4 in complex with three different ligands (the small-molecule antagonist IT1t, the polypeptide antagonist CVX15 and the viral chemokine antagonist vMIP-II) have been released. In addition to the inherent scientific value of these specific X-ray structures, they provide a reliable structural foundation for studies of the molecular interactions between CXCR4 and its key peptide ligands (CXCL12 and HIV-1 gp120), and serve as valuable templates for further development of small-molecule CXCR4 antagonists with therapeutic potential. We here review recent computational studies of the molecular interactions between CXCR4 and its peptide ligands – based on the X-ray structures of CXCR4 – and the current status of small-molecule peptide and peptidomimetic CXCR4 antagonists.

Chemokine receptor Cxcr4 contributes to kidney fibrosis via multiple effectors

Kidney fibrosis is the final common pathway for virtually every type of chronic kidney disease and is a consequence of a prolonged healing response that follows tissue inflammation. Chronic kidney inflammation ultimately leads to progressive tissue injury and scarring/fibrosis. Several pathways have been implicated in the progression of kidney fibrosis. In the present study, we demonstrate that G protein-coupled chemokine (C-X-C motif) receptor (CXCR)4 was significantly upregulated after renal injury and that sustained activation of Cxcr4 expression augmented the fibrotic response. We demonstrate that after unilateral ureteral obstruction (UUO), both gene and protein expression of Cxcr4 were highly upregulated in tubular cells of the nephron. The increased Cxcr4 expression in tubules correlated with their increased dedifferentiated state, leading to increased mRNA expression of platelet-derived growth factor (PDGF)-α, transforming growth factor (TGF)-β1, and concurrent loss of bone morphogenetic protein 7 (Bmp7). Ablation of tubular Cxcr4 attenuated UUO-mediated fibrotic responses, which correlated with a significant reduction in PDGF-α and TGF-β1 levels and preservation of Bmp7 expression after UUO. Furthermore, Cxcr4(+) immune cells infiltrated the obstructed kidney and further upregulate their Cxcr4 expression. Genetic ablation of Cxcr4 from macrophages was protective against UUO-induced fibrosis. There was also reduced total kidney TGF-β1, which correlated with reduced Smad activation and α-smooth muscle actin levels. We conclude that chronic high Cxcr4 expression in multiple effector cell types can contribute to the pathogenesis of renal fibrosis by altering their biological profile. This study uncovered a novel cross-talk between Cxcr4-TGF-β1 and Bmp7 pathways and may provide novel targets for interrupting the progression of fibrosis.

Novel role for NFAT3 in ERK-mediated regulation of CXCR4

The G-protein coupled chemokine (C-X-C motif) receptor CXCR4 is linked to cancer, HIV, and WHIM (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis) syndrome. While CXCR4 is reported to be overexpressed in multiple human cancer types and many hematological cancer cell lines, we have observed poor in vitro cell surface expression of CXCR4 in many solid tumor cell lines. We explore further the possible factors and pathways involved in regulating CXCR4 expression. Here, we showed that MEK-ERK signaling pathway and NFAT3 transcriptional factor plays a novel role in regulating CXCR4 expression. When cultured as 3D spheroids, HeyA8 ovarian tumor cells showed a dramatic increase in surface CXCR4 protein levels as well as mRNA transcripts. Furthermore, HeyA8 3D spheroids showed a decrease in phospho-ERK levels when compared to adherent cells. The treatment of adherent HeyA8 cells with an inhibitor of the MEK-ERK pathway, U0126, resulted in a significant increase in surface CXCR4 expression. Additional investigation using the PCR array assay comparing adherent to 3D spheroid showed a wide range of transcription factors being up-regulated, most notably a > 20 fold increase in NFAT3 transcription factor mRNA. Finally, chromatin immunoprecipitation (ChIP) analysis showed that direct binding of NFAT3 on the CXCR4 promoter corresponds to increased CXCR4 expression in HeyA8 ovarian cell line. Taken together, our results suggest that high phospho-ERK levels and NFAT3 expression plays a novel role in regulating CXCR4 expression.

Involvement of TNF-α in differential gene expression pattern of CXCR4 on human marrow-derived mesenchymal stem cells

Cell therapy and tissue repair are used in a variety of diseases including tissue and organ transplantation, autoimmune diseases and cancers. Now mesenchymal stem cells (MSCs) are an attractive and promising source for cell-based therapy according to their individual characteristics. Soluble factors which are able to induce MSCs migration have a vital role in cell engraftment and tissue regeneration. Tumor necrosis factor α (TNF-α) is a major cytokine present in damaged tissues. We have investigated the pattern of gene expression of chemokine receptor CXCR4 in nine groups of human bone marrow-derived MSCs stimulated with TNF-α in different dose and time manner. Comparison of TNF-α treated with untreated MSCs revealed the highest expression level of CXCR4 after treatment with 1, and 10 ng/ml of TNF-α in 24 h, and the production of CXCR4 mRNA was regulated up to 216 and 512 fold, respectively. Our results demonstrated the differential gene expression pattern of chemokine receptor CXCR4 in human marrow-derived MSCs stimulated with inflammatory cytokine TNF-α. These findings suggest that in vitro control of both dose and time factors may be important in stem cell migration capacity, and perhaps in future-stem cell transplantation therapies.

Inhibition of astroglial NF-κB enhances oligodendrogenesis following spinal cord injury

BACKGROUND

Astrocytes are taking the center stage in neurotrauma and neurological diseases as they appear to play a dominant role in the inflammatory processes associated with these conditions. Previously, we reported that inhibiting NF-κB activation in astrocytes, using a transgenic mouse model (GFAP-IκBα-dn mice), results in improved functional recovery, increased white matter preservation and axonal sparing following spinal cord injury (SCI). In the present study, we sought to determine whether this improvement, due to inhibiting NF-κB activation in astrocytes, could be the result of enhanced oligodendrogenesis in our transgenic mice.

METHODS

To assess oligodendrogenesis in GFAP-IκBα-dn compared to wild-type (WT) littermate mice following SCI, we used bromodeoxyuridine labeling along with cell-specific immuno-histochemistry, confocal microscopy and quantitative cell counts. To further gain insight into the underlying molecular mechanisms leading to increased white matter, we performed a microarray analysis in naïve and 3 days, 3 and 6 weeks following SCI in GFAP-IκBα-dn and WT littermate mice.

RESULTS

Inhibition of astroglial NF-κB in GFAP-IκBα-dn mice resulted in enhanced oligodendrogenesis 6 weeks following SCI and was associated with increased levels of myelin proteolipid protein compared to spinal cord injured WT mice. The microarray data showed a large number of differentially expressed genes involved in inflammatory and immune response between WT and transgenic mice. We did not find any difference in the number of microglia/leukocytes infiltrating the spinal cord but did find differences in their level of expression of toll-like receptor 4. We also found increased expression of the chemokine receptor CXCR4 on oligodendrocyte progenitor cells and mature oligodendrocytes in the transgenic mice. Finally TNF receptor 2 levels were significantly higher in the transgenic mice compared to WT following injury.

CONCLUSIONS

These studies suggest that one of the beneficial roles of blocking NF-κB in astrocytes is to promote oligodendrogenesis through alteration of the inflammatory environment.

HIV-1, methamphetamine and astrocyte glutamate regulation: combined excitotoxic implications for neuro-AIDS

Glutamate, the most abundant excitatory transmitter in the brain can lead to neurotoxicity when not properly regulated. Excitotoxicity is a direct result of abnormal regulation of glutamate concentrations in the synapse, and is a common neurotoxic mediator associated with neurodegenerative disorders. It is well accepted that methamphetamine (METH), a potent central nervous stimulant with high abuse potential, and human immunodeficiency virus (HIV)-1 are implicated in the progression of neurocognitive malfunction. Both have been shown to induce common neurodegenerative effects such as astrogliosis, compromised blood brain barrier integrity, and excitotoxicity in the brain. Reduced glutamate uptake from neuronal synapses likely leads to the accumulation of glutamate in the extracellular spaces. Astrocytes express the glutamate transporters responsible for majority of the glutamate uptake from the synapse, as well as for vesicular glutamate release. However, the cellular and molecular mechanisms of astrocyte-mediated excitotoxicity in the context of METH and HIV-1 are undefined. Topics reviewed include dysregulation of the glutamate transporters, specifically excitatory amino acid transporter-2, metabotropic glutamate receptor(s) expression and the release of glutamate by vesicular exocytosis. We also discuss glutamate concentration dysregulation through astrocytic expression of enzymes for glutamate synthesis and metabolism. Lastly, we discuss recent evidence of various astrocyte and neuron crosstalk mechanisms implicated in glutamate regulation. Astrocytes play an essential role in the neuropathologies associated with METH/HIV-1-induced excitotoxicity. We hope to shed light on common cellular and molecular pathways astrocytes share in glutamate regulation during drug abuse and HIV-1 infection.

SDF-1/CXCL12: its role in spinal cord injury

The chemokine stromal cell-derived factor 1 (SDF-1/CXCL12), is not only the most ancient, but also one of the most potent chemotactic factors. Orchestrating the migration of cells as well as promoting axon outgrowth in the presence of myelin inhibitors, SDF-1 is fundamental to central nervous system development, homeostasis and traumatic injury. SDF-1 attracts endogenous stem/precursor cells and immune cells to the injury site and, upon local infusion, enhances axonal sprouting following spinal cord injury. Together these features make SDF-1 a very exciting molecule for spinal cord repair.

Angiogenic effects of stromal cell-derived factor-1 (SDF-1/CXCL12) variants in vitro and the in vivo expressions of CXCL12 variants and CXCR4 in human critical leg ischemia

PURPOSE

Critical leg ischemia (CLI) is associated with a high morbidity and mortality. Therapeutic angiogenesis is still being investigated as a possible alternative treatment option for CLI. CXCL12, a chemokine, is known to have two spliced variants, CXCL12alpha and CXCL12beta, but the significance remains unknown. The study investigated the angiogenic effects of CXCL12, protein expressions of CXCL12, and the receptor CXCR4 in human CLI.

METHODS

In vitro, human microvascular endothelial cells (HMEC-1) were used. Cell proliferation was assessed using methylene blue assay and cell count method. Apoptosis was determined by counting the pyknotic nuclei after 4'-6-diamidino-2-phenylindole staining and confirmed by caspase-3 assay. We employed matrigel as capillary tube formation assay. The activity of signaling pathways was measured using Western blotting. In vivo, gastrocnemius biopsies were obtained from the lower limbs of patients with CLI and controls (n = 12 each). Immunohistochemistry, double immunofluorescence labeling, and Western blotting were then performed.

RESULTS

CXCL12 attenuated HMEC-1 apoptosis (P < .01), stimulated cell proliferation (P < .05) and capillary tube formation (P < .01). Compared with CXCL12alpha, CXCL12beta has a greater effect on apoptosis and cell proliferation (P < .01). Treatment with both variants resulted in time-dependent activation of PI3K/Akt and p44/42 but not p38 MAP kinase. In CLI, CXCL12alpha was expressed by skeletal muscle fibers with minimal expression of CXCL12beta. CXCR4 was extensively expressed and colocalized to microvessels. A significant 2.6-fold increase in CXCL12alpha and CXCR4 expressions (P < .01) were noted in CLI but not for CXCL12beta (P > .05).

CONCLUSIONS

The study showed that CXCL12beta had more potent angiogenic properties but was not elevated in human CLI biopsies. This provided an interesting finding on the role of CXCL12 variants in pathophysiologic angiogenic response in CLI.

The CXCR4 antagonist AMD3100 suppresses hypoxia-mediated growth hormone production in GH3 rat pituitary adenoma cells

Pituitary adenomas produce the chemokine stromal cell-derived factor (SDF-1α/CXCL12) and its receptor, CXCR4. A recent study indicated that CXCL12 and CXCR4 are concomitantly up-regulated in hypoxia. The objective of this study was to analyze the molecular mechanism of hypoxia-mediated CXCR4 up-regulation and assess the effect of pharmacological inhibition of CXCR4 by the receptor blocker, AMD3100, on pituitary function. CXCR4 expression in pituitary adenoma tissues was determined by a tissue microarray analysis of 62 pituitary adenoma samples. CXCR4 expression was significantly elevated and positively correlated with Knosp grade in pituitary adenomas (P < 0.005), and was higher in macroadenoma and growth hormone (GH)-producing adenomas. Pre-operative serum GH levels were significantly correlated with CXCR4 levels in the microarray (P < 0.0001). The relative expression of genes/gene categories that were modulated by up-regulated CXCL12/CXCR4 signaling was determined by a comparative transcriptome analysis of wild-type and CXCR4-knockdown cells in normoxia and hypoxia using the rat GH-producing and prolactin-producing pituitary adenoma cell line, GH3. Real-time reverse transcriptase-polymerase chain reaction analysis (RT-PCR) showed that CXCR4 mRNA expression in GH3 cells was increased by hypoxia (1% oxygen), and a cDNA microarray analysis revealed that inhibin β-C expression was diminished. siRNA-mediated CXCR4 knockdown blocked the hypoxia-induced decrease in inhibin β-C mRNA expression, as did inhibition of CXCR4 activity with AMD3100. An ELISA study demonstrated that GH secretion by wild-type GH3 cells was moderately enhanced by hypoxia and further potentiated by exposure to recombinant SDF-1α/CXCL12 protein. Conversely, hypoxia-induced GH secretion was reduced in CXCR4-silenced cells and in cells treated with the CXCR4 antagonist, AMD3100, notwithstanding the presence of SDF-1α/CXCL12 protein. These latter observations reflect the failure of hypoxia to suppress expression of inhibin β-C in cells deficient in CXCR4 or in which CXCR4 signaling was blocked. Together, these results indicate that the SDF-1α/CXCL12-CXCR4 signaling pathway interfaces with the classical endocrine pathway to up-regulate GH production via suppression of inhibin β-C. Because it blocks CXCR4 and prevents hypoxia-induced down-regulation of inhibin β-C expression, AMD3100 has promise as a molecular-targeting agent in the treatment of GH-producing adenomas.

Transforming growth factor-beta1 upregulates the expression of CXC chemokine receptor 4 (CXCR4) in human breast cancer MCF-7 cells

AIM

To investigate whether rhTGF-beta1 or a recombinant vector encoding a fusion protein comprising an extracellular domain of TGF-beta receptor II and an IgG Fc fragment) affects the regulation of CXC chemokine receptor 4 (CXCR4) expression in MCF-7 human breast cancer cells.

METHODS

MCF-7 breast cancer cells were treated with rhTGF-beta1 or transfected with a recombinant vector, pIRES2-EGFP-TbetaRII-Fc. Expression of CXCR4 in these cells was then analyzed at the mRNA and protein levels by quantitative RT-PCR and flow cytometry assay, respectively. A transwell assay was used to measure the chemotactic response of these cells to SDF-1alpha.

RESULTS

CXCR4 mRNA and protein expression were upregulated in TGF-beta1-treated MCF-7 cells. These cells also demonstrated an enhanced chemotactic response to SDF-1alpha. In MCF-7 cells transiently transfected with pIRES2-EGFP-TbetaRII-Fc, a fusion protein named TbetaRII-Fc (approximately 41 kDa) was produced and secreted. In these transfected cells, there was a reduction in CXCR4 expression and in the SDF-1alpha-mediated chemotactic response.

CONCLUSION

TGF-beta1 upregulated CXCR4 expression in MCF-7 cells, which subsequently enhanced the SDF-1alpha-induced chemotactic response. The results suggest a link between TGF-beta1 and CXCR4 expression in MCF-7 human breast cancer cells, which may be one of the mechanisms of TGF-beta1-mediated enhancement of metastatic potential in breast cancer cells.

Multiple roles of chemokine CXCL12 in the central nervous system: a migration from immunology to neurobiology

Chemotactic cytokines (chemokines) have been traditionally defined as small (10-14kDa) secreted leukocyte chemoattractants. However, chemokines and their cognate receptors are constitutively expressed in the central nervous system (CNS) where immune activities are under stringent control. Why and how the CNS uses the chemokine system to carry out its complex physiological functions has intrigued neurobiologists. Here, we focus on chemokine CXCL12 and its receptor CXCR4 that have been widely characterized in peripheral tissues and delineate their main functions in the CNS. Extensive evidence supports CXCL12 as a key regulator for early development of the CNS. CXCR4 signaling is required for the migration of neuronal precursors, axon guidance/pathfinding and maintenance of neural progenitor cells (NPCs). In the mature CNS, CXCL12 modulates neurotransmission, neurotoxicity and neuroglial interactions. Thus, chemokines represent an inherent system that helps establish and maintain CNS homeostasis. In addition, growing evidence implicates altered expression of CXCL12 and CXCR4 in the pathogenesis of CNS disorders such as HIV-associated encephalopathy, brain tumor, stroke and multiple sclerosis (MS), making them the plausible targets for future pharmacological intervention.

HIV-1 envelope glycoprotein 120 induces cyclooxygenase-2 expression in astrocytoma cells through a nuclear factor-kappaB-dependent mechanism

Human immunodeficiency virus-1 gp120 alters astroglial function, which compromises the function of the nearby of neuronal cells contributing to the cognitive impairment in human immunodeficiency virus-1 infection. Cyclooxygenase (COX)-2 has been involved in this process, although the intracellular pathways and second messengers involved are yet unknown. We have investigated the role of gp120-induced COX-2 in the astrocytoma human cell line U-87, and the different pathways involved in this activation. COX-2 mRNA and protein expression were detected in gp120-stimulated cells. Moreover, gp120 induces COX-2 promoter transcription. The effect of gp120 was abrogated by a neutralizing antibody against the chemokine receptor CXCR4 neutralizing antibody. Analysis of the promoter show that deletion or mutation of a proximal nuclear factor (NF)-kappaB site completely abrogated gp120-dependent transcription. NF-kappaB but neither Activating protein-1 nor nuclear factor of activated T-cells-dependent transcription was induced by gp120, as shown by reporter and electrophoretic mobility shift assays. In addition, transfection assays with the NF-kappaB inhibitor, IkappaBalpha, prevented gp120-mediated COX-2 induction. In contrast, there was no inhibition of COX-2 promoter transcription by expressing a dominant negative c-Jun, or nuclear factor of activated T-cells constructs. The antioxidant pyrrolidine dithiocarbamate inhibited COX-2 protein expression and COX-2 transcriptional activity induced by gp120. Thus, our results indicate that gp120 induced COX-2 transcription through NF-kappaB activation in astrocytoma cells.

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.

Regulation of CXCR4 signaling

The chemokine receptor CXCR4 belongs to the large superfamily of G protein-coupled receptors, and is directly involved in a number of biological processes including organogenesis, hematopoiesis, and immune response. Recent evidence has highlighted the role of CXCR4 in a variety of diseases including HIV, cancer, and WHIM syndrome. Importantly, the involvement of CXCR4 in cancer metastasis and WHIM syndrome appears to be due to dysregulation of the receptor leading to enhanced signaling. Herein we review what is currently known regarding the regulation of CXCR4 and how dysregulation contributes to disease progression.

Modulation of neuronal CXCR4 by the micro-opioid agonist DAMGO

The chemokine receptor CXCR4 regulates neuronal survival and differentiation and is involved in a number of pathologies, including cancer and human immunodeficiency virus (HIV). Recent data suggest that chemokines act in concert with neurotransmitters and neuropeptides, such as opioids. This study aimed to determine whether mu-opioid agonists alter the effect of CXCL12 (the specific CXCR4 ligand) on central neurons. Neuronal expression of CXCR4 and micro-opioid receptors (MORs) was analyzed by Western blot, immunostaining, and flow cytometry. Single-cell studies showed that all CXCR4-positive neurons coexpress MORs. Treatment of neuronal cultures with the selective MOR agonist DAMGO or the endogenous peptide endomorphin-1 inhibited intracellular signaling pathways (ERK1/2 and Akt) activated by CXCL12. Furthermore, DAMGO abolished the neuroprotective effect of CXCL12 in N-methyl-d-aspartate (NMDA) neurotoxicity studies. The effects of DAMGO and endomorphin-1 were inhibited by a general or a micro-specific opioid receptor antagonist, and not caused by changes in neuronal CXCR4 levels. DAMGO did not affect CXCL12-induced internalization of CXCR4. The authors propose that interactions between MOR and CXCR4 signaling can modulate the action of CXCL12 on neuronal survival-which may have important implications to neuroAIDS as well as other neuroinflammatory disorders.

Suprachiasmatic astrocytes as an interface for immune-circadian signalling

The hypothalamic suprachiasmatic nuclei (SCN), the site of a mammalian circadian clock, exhibit a dense immunoreactivity for glial fibrillary acidic protein (GFAP), a specific marker for astrocytes. Although there is evidence of a circadian variation in GFAP-IR in the hamster SCN and of the participation of glial cells in input and output mechanisms of the clock, the role of these cells within the circadian system is not clearly understood. The fact that astroglia can express and respond to cytokines suggests that they could work as mediators of immune signals to the circadian system. In the present study, we have found a daily variation of GFAP-IR in the mouse SCN, peaking during the light phase. In addition, we have identified GFAP and nuclear factor-kappaB (NF-kappaB) in glial cells within the SCN and in primary cultures of the mouse SCN. Moreover, SCN glia cultures were transfected with an NF-kappaB/luc construct whose transcriptional activity was increased with lipopolysaccharide 2 mug/ml, tumor necrosis factor-alpha 20 ng/ml, or interleukin-1alpha 100 ng/ml, after 12 hr of stimulation. These results suggest that the glial cells of the SCN can mediate input signals to the mouse circadian system coming from the immune system via NF-kappaB signaling.

Up-regulation of CXCR4 Expression in PC-3 Cells by Stromal-Derived Factor-1α (CXCL12) Increases Endothelial Adhesion and Transendothelial Migration: Role of MEK/ERK Signaling Pathway–Dependent NF-κB Activation

The chemokine stromal-derived factor-1alpha (SDF-1alpha/CXCL-12) and its receptor, CXCR4, play a crucial role in adhesion and transendothelium migration (TEM) of prostate cancer cells. We tested the hypothesis that enhanced expression of CXCR4 in prostate cancer cells is dependent upon SDF-1alpha-mediated activation of nuclear factor-kappaB (NF-kappaB). SDF-1alpha increased the CXCR4 mRNA and protein expression in PC-3 cells but not in LNCaP cells. Similarly, SDF-1alpha enhanced the NF-kappaB-dependent transcriptional activity in PC-3 cells but not in LNCaP cells. SDF-1alpha increased PC-3 cell adhesion to the human umbilical vein endothelial cell monolayer and enhanced TEM, which was abrogated with anti-CXCR4 monoclonal antibody (mAb). Suppression of NF-kappaB activity in PC-3 cells by a mutant IkappaBalpha super-repressor adenoviral vector decreased the CXCR4 mRNA expression and inhibited adhesion and TEM. Transient overexpression of p65 subunit of NF-kappaB in PC-3 cells up-regulated CXCR4 receptor expression and increased the adhesion and TEM of these cells in response to SDF-1alpha gradient. Treatment of PC-3 cells with SDF-1alpha leads to nuclear translocation of NF-kappaB protein within 15 to 30 minutes, which correlated with IkappaBalpha phosphorylation. A p42/44 mitogen-activated protein kinase [MAPK, extracellular signal regulated kinase-1/2 (ERK-1/2)] biphasic activation pattern was observed in these cells at 15 minutes and 3 hours after SDF-1alpha treatment. Phosphorylation of IkappaB kinase alpha was observed within 30 minutes, which was blocked by PD98059 [MAPK kinase (MEK) inhibitor]. PD98059 cotreatment significantly inhibited SDF-1alpha-induced NF-kappaB reporter activity and CXCR4 receptor expression as shown by flow cytometry. These data suggest that SDF-1alpha-induced expression of CXCR4 in PC-3 cells is dependent on MEK/ERK signaling cascade and NF-kappaB activation.

Tumor necrosis factor alpha leads to increased cell surface expression of CXCR4 in SK-N-MC cells

Both host and viral factors play an important role in the pathogenesis of human immunodeficiency virus (HIV)-associated bran injury. In this study, the authors examined the interactions between tumor necrosis factor (TNF)-alpha, CXCR4, the alpha chemokine receptor, and three HIV isolates, including the T-tropic viruses, HIV-1(MN) and HIV-1(IIIB), and the dual tropic virus, HIV-1(89.6). The authors show by flow cytometry that treatment of differentiated SK-N-MC cells with TNF-alpha induces a significant increase in the cell surface expression of CXCR4 in a time- and dose-dependent manner. The effect is partly regulated at the level of transcription. To assess the biological significance of this finding, we show that TNF-alpha potentiates the ability of the above mentioned HIV isolates to induce neuronal apoptosis and that the effect is significantly reduced by pretreating cells with monoclonal antibodies to either CXCR4 and TNF-alpha. Together these results suggest that TNF-alpha may render neuronal cells vulnerable to the apoptotic effects of HIV by increasing the cell surface expression of CXCR4 and thus identify another mechanism by which TNF-alpha contributes to the pathogenesis of HIV-associated brain injury.

Human immunodeficiency virus type 1 envelope glycoprotein 120 induces cyclooxygenase-2 expression in neuroblastoma cells through a nuclear factor-kappaB and activating protein-1 mediated mechanism

Induction of cyclooxygenase-2 (COX-2) in the brain of people infected with human immunodeficiency virus type 1 (HIV-1) has been proposed as a cause of cognitive impairment in AIDS dementia. Here, we have analyzed the molecular mechanism by which its induction takes place in neuroblastoma cells. The HIV-1 envelope protein gp120 was able to induce COX-2 mRNA and protein in several human neuroblastoma cell lines, which express CXCR4 and CCR5 but not CD4. Moreover, gp120 induces COX-2 promoter transcription. Sequential deletions of the promoter show that deletion of a distal nuclear factor-kappaB (NF-kappaB) site abrogated gp120-dependent transcription. More importantly, overexpression of NF-kappaB inhibitory subunit, IkappaBalpha, completely abrogated gp120-induced COX-2 activity. However, transfection of p65/relA NF-kappaB was not enough to induce COX-2 transcription, suggesting that NF-kappaB was necessary but not sufficient to control COX-2 transcription induced by gp120. In addition to NF-kappaB, activating protein-1 (AP-1) but not nuclear factor of activated T cells (NFAT)-dependent transcription was induced by gp120. Transfection of a dominant negative mutant c-Jun protein, TAM-67, efficiently blocked the induction of COX-2 promoter by gp120, confirming AP-1 requirement. Moreover, gp120 rapidly activates the c-Jun amino-terminal kinase (JNK) and p38 mitogen-activated protein kinase phosphorylation. The importance of NF-kappaB and AP-1 in COX-2 promoter and protein induction was corroborated by using pharmacological NF-kappaB, p38 and JNK inhibitors.

Expression of CXCR4 and Its Down-Regulation by IFN-γ in Head and Neck Squamous Cell Carcinoma

PURPOSE

The functional expression of CXCR4, which plays roles in cell migration and proliferation in response to its unique ligand stromal cell-derived factor-1 (SDF-1), has been reported in variety of carcinomas. However, CXCR4 expression and its functional role in head and neck squamous cell carcinomas (HNSCC) remain unclear. In this study, we investigated CXCR4 expression and analyzed its functions in HNSCC cell lines. We also attempted to regulate CXCR4 expression using cytokines, such as interleukin-1beta, tumor necrosis factor-alpha, and IFN-gamma. Finally, we investigated correlation between CXCR4 expression and clinical features in patients with HNSCC.

EXPERIMENTAL DESIGN

Six HNSCC cell lines were used in this study. Reverse transcription-PCR and flow cytometry analysis were shown for CXCR4 expressions with or without stimulations of cytokines. SDF-1-mediated cell migration was assayed in Matrigel-coated chemotaxis chamber. The SDF-1-mediated cell proliferation was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The SDF-1-mediated signaling pathways were analyzed by Western blot analysis. Biopsy specimens from 56 patients with HNSCC were used for immunohistologic analysis.

RESULTS

The significant CXCR4 expression was found in HSQ-89, IMC-3, and Nakamura cells. The SDF-1-mediated cell migration and proliferation were observed in CXCR4-positive cells. SDF-1 also promoted rapid phosphorylation of extracellular signal-regulated kinase 1/2 and Akt signaling pathways in CXCR4-positive cells. The SDF-1-mediated cell migration and proliferation of CXCR4-positive cells were inhibited by neutralization of CXCR4. Among three cytokines tested, IFN-gamma significantly reduced CXCR4 expression and SDF-1-induced cell migration and proliferation of CXCR4-positive cells. Immunohistologic analysis revealed that patients with advanced neck status and patients who developed distant metastases showed significantly higher CXCR4 expression, and the cause-specific survival of patients with CXCR4-expression was significantly shorter. Furthermore, multivariate analysis confirmed that CXCR4 positive was the independent factor for cause-specific death.

CONCLUSION

Our results may provide an insight into future therapeutic agent that inhibits tumor metastasis and progression via down-regulating CXCR4 expression in patients with HNSCC.

HIV-infection of the central nervous system: the tightrope walk of innate immunity

Infection of the central nervous system (CNS) by HIV is a frequent and sometimes very early event in the course of HIV pathogenesis. Possible consequences are diverse symptoms of neurological dysfunction, but also the establishment of a lifelong latent viral reservoir in the brain. Whereas in the periphery innate and adaptive immunity are equal partners, the blood-brain barrier (BBB) with its restricted access of peripheral immune effectors shifts this balance in favour of the local innate immunity. Four main elements of cerebral innate immunity are discussed in the present article, including two cell types with immunological functions and two soluble immune systems: (1) the stimulation of microglial cells as the predominant brain-resident immune cell and the main local reservoir for the virus; (2) the reaction of astrocytes in response to viral infection; (3) the activation of the local complement system as important soluble immune cascade; and (4) the role of chemokines and cytokines which help to conduct and cross-link the interplay between the different immune elements. These components of the cerebral innate immunity do not act separately from each other but form a functional immunity network. A dual role of these components with both harmful and protective effects further enhances the complexity of the mutual interactions.

CC and CXC chemokine receptors mediate migration, proliferation, and matrix metalloproteinase production by fibroblast-like synoviocytes from rheumatoid arthritis patients

OBJECTIVE

To explore the potential involvement of the chemokine system in synoviocyte-mediated tissue destruction in rheumatoid arthritis (RA), we studied the expression profile of chemokine receptors and their function in the migration, proliferation, and matrix metalloproteinase (MMP) production of cultured fibroblast-like synoviocytes (FLS) from RA patients.

METHODS

The presence of CC and CXC chemokine receptors on cultured FLS was studied at the messenger RNA (mRNA) level by reverse transcriptase-polymerase chain reaction and at the cell surface expression level by flow cytometry. Variations in cytosolic calcium influx induced by chemokine stimulation were assessed by flow cytometry on Fura Red-preloaded FLS. Two-compartment transwell chambers were used for FLS chemotaxis assays. Cell growth was measured by a fluorescence-based proliferation assay. Gelatinase and collagenase activities were determined by a fibril degradation assay and zymography.

RESULTS

FLS constitutively expressed the receptors CCR2, CCR5, CXCR3, and CXCR4, both at the cell surface and mRNA levels, but failed to express CCR3 and CCR6. Significant intracytosolic calcium influx was observed on FLS challenged with monocyte chemotactic protein 1 (MCP-1), stromal cell-derived factor 1alpha (SDF-1alpha), and interferon-inducible protein 10 (IP-10). Stimulation with MCP-1, SDF-1alpha, IP-10, and monokine induced by interferon-gamma enhanced the migration and proliferation of FLS. These chemokines, in addition to RANTES, increased in a dose- and time-dependent manner the gelatinase and collagenase activities in cell-free supernatants of cultured FLS. Interestingly, the chemokine-mediated up-regulation of MMP activities was significantly abrogated by the presence of anti-interleukin-1beta, but not anti-tumor necrosis factor alpha, blocking antibodies.

CONCLUSION

These data suggest that through modulation of the migration, proliferation, and MMP production by FLS, the chemokine system may play a more direct role in the destructive phase of RA than is currently suspected, and thus emphasize the relevance of chemokines and their receptors as potential therapeutic targets in this disease.

Mobilization of CD34/CXCR4+, CD34/CD117+, c-met+ stem cells, and mononuclear cells expressing early cardiac, muscle, and endothelial markers into peripheral blood in patients with acute myocardial infarction

BACKGROUND

Adult stem cells can contribute to myocardial regeneration after ischemic injury. Bone marrow and skeletal muscles contain a population of CXCR4+ cells expressing genes specific for muscle progenitor cells that can be mobilized into the peripheral blood. The aims of the study were (1) to confirm the presence of early tissue-committed cells expressing cardiac, muscle, and endothelial markers in populations of mononuclear cells in peripheral blood and (2) to assess the dynamics and magnitude of the mobilization of CD34+, CD117+, CXCR4+, c-met+, CD34/CD117+, and CD34/CXCR4+ stem cells into peripheral blood in relation to inflammatory and hematopoietic cytokines in patients with ST-segment-elevation acute myocardial infarction (STEMI).

METHODS AND RESULTS

Fifty-six patients with STEMI (<12 hours), 39 with stable angina, and 20 healthy control subjects were enrolled. Real-time reverse transcription-polymerase chain reaction (RT-PCR) was used for detection of tissue-specific markers. The number of the cells was assessed by use of a flow cytometer on admission, after 24 hours, and after 7 days. RT-PCR revealed increased expression of mRNA (up to 3.5-fold increase) for specific cardiac (GATA4, MEF2C, Nkx2.5/Csx), muscle (Myf5, Myogenin, MyoD), and endothelial (VE-cadherin, von Willebrand factor) markers in peripheral blood mononuclear cells. The number of CD34/CXCR4+ and CD34/CD117+ and c-met+ stem cells in peripheral blood was significantly higher in STEMI patients than in stable angina and healthy subjects, peaking on admission, without further significant increase after 24 hours and 7 days.

CONCLUSIONS

The study demonstrates in the setting of STEMI a marked mobilization of mononuclear cells expressing specific cardiac, muscle, and endothelial markers as well as CD34/CXCR4+ and CD34/CD117+ and c-met+ stem cells and shows that stromal cell-derived factor-1 is an important factor influencing the mobilization.

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.

Cyclic AMP and tumor necrosis factor-alpha regulate CXCR4 gene expression in Schwann cells

Rat peripheral nerve Schwann cells have been shown to express the alpha-chemokine receptor CXCR4 as well as the corresponding ligand stromal cell-derived factor-1 (SDF-1). We have investigated gene regulatory mechanisms acting on the expression of CXCR4 in cultured rat Schwann cells and found that receptor expression at transcript- and protein levels is directly dependent on intracellular cyclic AMP. Such increased levels of CXCR4 expression were found to be efficiently reversed by the action of tumor necrosis factor-alpha (TNFalpha). We also provide evidence that the POU box transcription factor Oct-6/SCIP is involved in the control of CXCR4 transcription. Finally, we could demonstrate that CXCR4 activation by SDF-1alpha increases the number of dying Schwann cells, indicating that this receptor/ligand interaction is modulating cell survival. Our data, therefore, suggest that in the Schwann cell lineage signal transduction cascades controlled by the activation of TNF- and CXCR4 receptors are functionally coupled.

A small-molecule antagonist of CXCR4 inhibits intracranial growth of primary brain tumors

The vast majority of brain tumors in adults exhibit glial characteristics. Brain tumors in children are diverse: Many have neuronal characteristics, whereas others have glial features. Here we show that activation of the Gi protein-coupled receptor CXCR4 is critical for the growth of both malignant neuronal and glial tumors. Systemic administration of CXCR4 antagonist AMD 3100 inhibits growth of intracranial glioblastoma and medulloblastoma xenografts by increasing apoptosis and decreasing the proliferation of tumor cells. This reflects the ability of AMD 3100 to reduce the activation of extracellular signal-regulated kinases 1 and 2 and Akt, all of which are pathways downstream of CXCR4 that promote survival, proliferation, and migration. These studies (i) demonstrate that CXCR4 is critical to the progression of diverse brain malignances and (ii) provide a scientific rationale for clinical evaluation of AMD 3100 in treating both adults and children with malignant brain tumors.

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.

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.

A potential role for CXCR3 chemokines in the response to ocular HSV infection

Corneal infection with herpes simplex virus (HSV) leads to the recruitment of immune cells to the eye itself, the trigeminal ganglion and the brainstem. In addition, some resident cells in these target tissues are infected by HSV, activated during the inflammatory response or both. Chemokine signaling is an important component of the regulatory circuit governing the host immune response to virus infection. This review discusses chemokine responses in relation to HSV infection of the cornea emphasizing the role of CXCR3 chemokine signaling by the IFN-gamma inducible ligands MIG, IP10 and I-TAC and includes discussion of their potential role in immunopathology in the nervous system.

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.

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.

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.

Up-Regulation of FPR2, a Chemotactic Receptor for Amyloid β 1–42 (Aβ42), in Murine Microglial Cells by TNFα

Human FPRL1 and its mouse homologue FPR2 are functional receptors for several exogenous and host-derived chemotactic peptides, including amyloid beta(42) (A beta(42)), a critical pathogenic factor in Alzheimer's disease. We investigated the effect of TNF alpha on the expression and function of FPR2 in mouse microglial cells, a crucial inflammatory cell type in the CNS. Primary murine microglia and a cell line N9 in resting state expressed low levels of FPR2 gene and lacked the response to chemotactic agonists for this receptor. Incubation with TNF alpha, however, increased microglial expression of FPR2 gene, in association with potent chemotactic responses to FPR2-specific agonists including A beta(42). The effect of TNF alpha was dependent on the p55 TNF alpha receptor and activation of MAP kinase p38. TNF alpha concomitantly down-regulated microglial response to the chemokine SDF-1 alpha. Thus, by selectively up-regulating FPR2 in microglia, TNF alpha has the capacity to amplify host response in inflammatory diseases in the CNS.

Stromal cell-derived factor-1alpha in unstable angina: potential antiinflammatory and matrix-stabilizing effects

BACKGROUND

Chemokines play a pathogenic role in atherogenesis and plaque destabilization by activating and directing leukocytes into the atherosclerotic plaque. However, stromal cell-derived factor (SDF)-1 was recently found to have antiinflammatory effects, and we hypothesized that this chemokine could play a beneficial role in coronary artery disease.

METHODS AND RESULTS

Plasma levels of SDF-1alpha were significantly decreased in patients with stable (n=30) and unstable angina (n=30) compared with healthy control subjects (n=20), particularly in those with unstable disease. By flow cytometry and RNase protection assay, we found decreased surface expression but increased gene expression of the SDF-1alpha receptor CXCR-4 in peripheral blood mononuclear cells (PBMC) from patients with stable angina and patients with unstable angina. In vitro, SDF-1alpha (500 ng/mL) reduced both unstimulated and endotoxin/mitogen-stimulated mRNA and protein levels of monocyte chemoattractant protein-1, interleukin-8, matrix metalloproteinase-9, and tissue factor while increasing tissue inhibitor of metalloproteinases-1 in PBMC from patients with unstable angina. The SDF-1alpha-mediated suppression of monocyte chemoattractant protein-1 and interleukin-8 appears to involve cAMP/protein kinase A type I-dependent pathways. Finally, although SDF-1alpha suppressed the spontaneous release of these inflammatory mediators in unstable angina, enhancing effects were seen in unstimulated PBMC from healthy control subjects, possibly reflecting that PBMC in unstable angina are preactivated in vivo.

CONCLUSIONS

In contrast to several other chemokines, our findings suggest that SDF-1alpha, at least in high concentrations, may mediate antiinflammatory and matrix-stabilizing effects in unstable angina. These effects may promote plaque stabilization, and therapeutic intervention that enhances SDF-1alpha activity could potentially be beneficial in acute coronary syndromes.

Chemokine expression in myocardial ischemia: MIP-2 dependent MCP-1 expression protects cardiomyocytes from cell death

Chemokines are small molecular weight proteins that play important roles in inflammation. Originally described as chemotactic cytokines, chemokines stimulate the influx of leukocytes into specific tissue compartments. These molecules also modulate gene expression in both infiltrating and resident cells to mediate a vast array of cellular functions, and their importance in disease processes has been well documented. This study examined the expression of chemokines during myocardial ischemia and established a pathway by which two, MIP-2 and JE/MCP-1, modulate cardiac myocyte viability during this process. To focus on the direct effects of chemokines on these cells, a mouse model of ischemia without reperfusion was used. The expression of chemokines and chemokine receptors was induced in the left ventricular free wall as early as 1 h post-ischemia, with the most significant increases in MIP-2 (CXCL2) and JE/MCP-1 (CCL2). Expression of their respective receptors, CXCR2 and CCR2, was also induced. Similar changes in gene expression occurred at the mRNA and protein levels in isolated neonatal mouse cardiac myocytes stimulated by hypoxia. Antibody to MIP-2 inhibited hypoxia-induced JE/MCP-1 expression, demonstrating that MIP-2 is critical for this event. Moreover, in vivo intramyocardial injection of either an adenovirus expressing MIP-2 or the recombinant protein itself was sufficient to upregulate JE/MCP-1 production even in the absence of ischemia. Thus, MIP-2 regulates JE/MCP-1 expression both in cell culture and in vivo. Furthermore, JE/MCP-1 markedly decreased hypoxia-induced cell death in cultured cardiac myocytes. Thus, JE/MCP-1 appears to mediate an unanticipated survival pathway in target cardiac myocytes themselves. These findings indicate an important role for MIP-2 and JE/MCP-1 in regulating the response of cardiac myocytes to myocardial ischemia.

Glial cells as targets for cytotoxic immune mediators

Oligodendrocytes and Schwann cells are the glia principally responsible for the synthesis and maintenance of myelin. Damage may occur to these cells in a number of conditions, but perhaps the most studied are the idiopathic inflammatory demyelinating diseases, multiple sclerosis in the CNS, and Guillain-Barré syndrome and its variants in the peripheral nervous system (PNS). This article explores the effects on these cells of cytotoxic immunological and inflammatory mediators: similarities are revealed, of which perhaps the most important is the sensitivity of both Schwann cells and oligodendrocytes to many such agents. This area of research is, however, characterised and complicated by numerous and often very substantial inter-observer discrepancies. Marked variability in cell culture techniques, and in assays of cell damage and death, provide artifactual explanations for some of this variability; true inter-species differences also contribute. Not the least important conclusion centres on the limited capacity of in vitro studies to reveal disease mechanisms: cell culture findings merely illustrate possibilities which must then be tested ex vivo using human tissue samples affected by the relevant disease.

TNF-alpha mediates SDF-1 alpha-induced NF-kappa B activation and cytotoxic effects in primary astrocytes

Stromal-derived cell factor-1 alpha (SDF-1 alpha; CXCL12) and its receptor, CXCR4, are constitutively expressed on neuroepithelial cells and are believed to be involved in both development and pathological processes, such as AIDS-associated neurologic disorders. Here, we demonstrate that SDF-1 alpha activates NF-kappa B, stimulates production of chemokines and cytokines, and induces cell death in primary astrocytes, effects that depend on ongoing secretion of TNF-alpha. SDF-1 alpha upregulated TNF-alpha mRNA and protein secretion, as well as TNF receptor 2 expression. TNF-alpha treatment mimicked SDF-1 alpha induction of NF-kappa B, IL-1 alpha/beta, and RANTES, as well as cell death; neutralizing antibodies against TNF-alpha opposed these responses. We also found that SDF-1 alpha activated Erk1 and Erk2 (Erk1/2) MAPK in a biphasic fashion. Early Erk1/2 activation was stimulated directly by SDF-1 alpha and late activation was mediated by TNF-alpha. PD98059 suppression of early Erk1/2 activation correlated with reduction of SDF-1 alpha-induced TNF-alpha expression. Late Erk1/2 activation was involved in TNF-alpha-stimulated NF-kappa B activation and cytokine induction. SDF-1 alpha was induced in reactive CXCR4-positive astrocytes near axotomized spinal cord motor neurons, consistent with autocrine SDF-1/CXCR4 signaling in these cells. We propose that these novel effects of SDF-1 alpha are relevant to the pathogenic and developmental roles of SDF-1 alpha in the CNS.