Expression of stromal cell-derived factor-1 and CXCR4 chemokine receptor mRNAs in cultured rat glial and neuronal cells

Bradykinin B1 Receptor Affects Tumor-Associated Macrophage Activity and Glioblastoma Progression

Bradykinin is a small active peptide and is considered an inflammatory mediator in several pathological conditions. Bradykinin exerts its effects by coupling to its receptors, including bradykinin B1 (B1R) and bradykinin B2. B1R has been implicated in the development of various cancers. Our previous study reported that B1R promoted glioblastoma (GBM) development by supporting the migration and invasion of GBM cells. However, the mechanisms underlying the effects of B1R on tumor-associated macrophages (TAMs) and GBM progression remain unknown. Accordingly, to explore the regulatory effects of B1R overexpression (OE) in GBM on tumor-associated immune cells and tumor progression, we constructed a B1R wild-type plasmid and developed a B1R OE model. The results reveal that B1R OE in GBM promoted the expression of ICAM-1 and VCAM-1-cell adhesion molecules-in GBM. Moreover, B1R OE enhanced GBM cell migration ability and monocyte attachment. B1R also regulated the production of the protumorigenic cytokines and chemokines IL-6, IL-8, CXCL11, and CCL5 in GBM, which contributed to tumor progression. We additionally noted that B1R OE in GBM increased the expression of CD68 in TAMs. Furthermore, B1R OE reduced the level of reactive oxygen species in GBM cells by upregulating heme oxygenase-1, an endogenous antioxidant protein, thereby protecting GBM cells from oxidative stress. Notably, B1R OE upregulated the expression of programmed death-ligand 1 in both GBM cells and macrophages, thus providing resistance against T-cell response. B1R OE in GBM also promoted tumor growth and reduced survival rates in an intracranial xenograft mouse model. These results indicate that B1R expression in GBM promotes TAM activity and modulates GBM progression. Therefore, B1R could be an effective target for therapeutic methods in GBM.

Identification of blood-derived candidate gene markers and a new 7-gene diagnostic model for multiple sclerosis

Background

Multiple sclerosis (MS) is a central nervous system disease with a high disability rate. Modern molecular biology techniques have identified a number of key genes and diagnostic markers to MS, but the etiology and pathogenesis of MS remain unknown.

Results

In this study, the integration of three peripheral blood mononuclear cell (PBMC) microarray datasets and one peripheral blood T cells microarray dataset allowed comprehensive network and pathway analyses of the biological functions of MS-related genes. Differential expression analysis identified 78 significantly aberrantly expressed genes in MS, and further functional enrichment analysis showed that these genes were associated with innate immune response-activating signal transduction (p = 0.0017), neutrophil mediated immunity (p = 0.002), positive regulation of innate immune response (p = 0.004), IL-17 signaling pathway (p < 0.035) and other immune-related signaling pathways. In addition, a network of MS-specific protein–protein interactions (PPI) was constructed based on differential genes. Subsequent analysis of network topology properties identified the up-regulated CXCR4, ITGAM, ACTB, RHOA, RPS27A, UBA52, and RPL8 genes as the hub genes of the network, and they were also potential biomarkers of MS through Rap1 signaling pathway or leukocyte transendothelial migration. RT-qPCR results demonstrated that CXCR4 was obviously up-regulated, while ACTB, RHOA, and ITGAM were down-regulated in MS patient PBMC in comparison with normal samples. Finally, support vector machine was employed to establish a diagnostic model of MS with a high prediction performance in internal and external datasets (mean AUC = 0.97) and in different chip platform datasets (AUC = (0.93).

Conclusion

This study provides new understanding for the etiology/pathogenesis of MS, facilitating an early identification and prediction of MS.

The Role of Cytokines and Chemokines in Shaping the Immune Microenvironment of Glioblastoma: Implications for Immunotherapy

Glioblastoma is the most common form of primary brain tumour in adults. For more than a decade, conventional treatment has produced a relatively modest improvement in the overall survival of glioblastoma patients. The immunosuppressive mechanisms employed by neoplastic and non-neoplastic cells within the tumour can limit treatment efficacy, and this can include the secretion of immunosuppressive cytokines and chemokines. These factors can play a significant role in immune modulation, thus disabling anti-tumour responses and contributing to tumour progression. Here, we review the complex interplay between populations of immune and tumour cells together with defined contributions by key cytokines and chemokines to these intercellular interactions. Understanding how these tumour-derived factors facilitate the crosstalk between cells may identify molecular candidates for potential immunotherapeutic targeting, which may enable better tumour control and improved patient survival.

Protective Effect of CXCR4 Antagonist CX807 in a Rat Model of Hemorrhagic Stroke

Intracerebral hemorrhage (ICH) is a major cause of stroke, with high mortality and morbidity. There is no effective pharmacological therapy for ICH. Previous studies have indicated that CXCR4 antagonists reduced microglia activation, attenuated infiltration of T cells, and improved functional recovery in ischemic stroke animals. The interaction of CXCR4 antagonists and ICH has not been characterized. The purpose of this study is to examine the neuroprotective action of a novel CXCR4 antagonist CX807 against ICH. In primary cortical neuronal and BV2 microglia co-culture, CX807 reduced glutamate-mediated neuronal loss and microglia activation. Adult rats were locally administered with collagenase VII to induce ICH. CX807 was given systemically after the ICH. Early post-treatment with CX807 improved locomotor activity in ICH rats. Brain tissues were collected for qRTPCR and histological staining. ICH upregulated the expression of CXCR4, CD8, TNFα, IL6, and TLR4. The immunoreactivity of IBA1 and CD8, as well as TUNEL labeling, were enhanced in the perilesioned area. CX807 significantly mitigated these responses. In conclusion, our data suggest that CX807 is neuroprotective and anti-inflammatory against ICH. CX807 may have clinical implications for the treatment of hemorrhagic stroke.

Inhibiting the Migration of M1 Microglia at Hyperacute Period Could Improve Outcome of tMCAO Rats

AIM

To study whether inhibiting microglia migration to the ischemic boundary zone (IBZ) at the early phase could improve neurological outcomes after stroke.

METHODS

The transient middle cerebral artery occlusion (tMCAO) was induced in adult male Sprague-Dawley rats. AMD3100, a highly selective CXC-chemokine receptor 4 (CXCR4) antagonist, was used to inhibit microglia migration. Microglia was evaluated by immunofluorescence in vivo, and their migration was tested by transwell assay in vitro. Expressions of cytokines were detected by real-time PCR. Infarct volume was determined by triphenyltetrazolium chloride (TTC) staining. Functional recovery of tMCAO rats was evaluated by behavior tests.

RESULTS

M1 microglia in the IBZ was rapidly increased within 3 days after tMCAO, accompanied with enhanced expression of CXCR4. Chemokine CXC motif chemokine ligand 12 (CXCL12) was also increased in the IBZ. And AMD3100 could obviously decline M1 microglia migration induced by CXCL12 and secretion of related inflammatory cytokines in the IBZ after stroke. This was accompanied by significant attenuated infarct volume and improved neurological outcomes.

CONCLUSION

This study confirms the protective efficacy of inhibiting microglia migration at the hyperacute phase as a therapeutic strategy for ischemic stroke in tMCAO model of rats, and its therapeutic time window could last for 24 h after cerebral ischemia reperfusion.

CXCL12 impairs the acquisition and extinction of auditory fear conditioning in rats via crosstalk with GABAergic system

OBJECTIVE

Chemokines, such as CXCL12, are signaling molecules playing an important role in immune regulations. Chemokine upsurge has also been associated with neuroinflammatory conditions characterized with cognitive impairments. Recently, some in-vitro data suggests that CXCL12 is a potential neuromodulator and interacts with GABAergic system, but, so far, whether these effects translate into alterations in neural and behavioral functions has not been investigated.

METHODS

In the present study, we used auditory fear conditioning as a model to define the contribution of CXCL12/CXCR4 on fear-related cognitive disorders. We microinjected different dosages of CXCL12 into the bilateral amygdala of rats to investigate their behavioral effects on the acquisition and extinction of conditioned fear memory. Moreover, we pretreated the rats with the selective CXCR4 receptor antagonist (AMD3100), GABAA antagonist (bicuculline) and GABAB antagonist (CGP55845) to examine whether the CXCL12 induced changes could be reversed.

RESULTS

We found that intra-amygdala infusion of CXCL12 impaired the acquisition and extinction of conditioned fear response. Pretreatment with AMD3100, rescued the CXCL12 induced impairments, indicating that CXCL12 produced the effects by activating CXCR4 receptors. Furthermore, both bicuculline and CGP55845 prevented CXCL12 from impairing the rat's ability of conditioned learning, indicating a crosstalk between CXCL12/CXCR4 and GABAergic system.

CONCLUSION

Our data suggest that the chemokine CXCL12 is able to regulate neurotransmitter mechanisms involved in associative learning functions, and the effect of GABAergic agents on CXCL12/CXCR4 may be new therapeutic potentials for neuroinflammatory diseases.

Simultaneous Activation of Induced Heterodimerization between CXCR4 Chemokine Receptor and Cannabinoid Receptor 2 (CB2) Reveals a Mechanism for Regulation of Tumor Progression

The G-protein-coupled chemokine receptor CXCR4 generates signals that lead to cell migration, cell proliferation, and other survival mechanisms that result in the metastatic spread of primary tumor cells to distal organs. Numerous studies have demonstrated that CXCR4 can form homodimers or can heterodimerize with other G-protein-coupled receptors to form receptor complexes that can amplify or decrease the signaling capacity of each individual receptor. Using biophysical and biochemical approaches, we found that CXCR4 can form an induced heterodimer with cannabinoid receptor 2 (CB2) in human breast and prostate cancer cells. Simultaneous, agonist-dependent activation of CXCR4 and CB2 resulted in reduced CXCR4-mediated expression of phosphorylated ERK1/2 and ultimately reduced cancer cell functions such as calcium mobilization and cellular chemotaxis. Given that treatment with cannabinoids has been shown to reduce invasiveness of cancer cells as well as CXCR4-mediated migration of immune cells, it is plausible that CXCR4 signaling can be silenced through a physical heterodimeric association with CB2, thereby inhibiting subsequent functions of CXCR4. Taken together, the data illustrate a mechanism by which the cannabinoid system can negatively modulate CXCR4 receptor function and perhaps tumor progression.

Stromal Cell-Derived Factor-1α Plays a Crucial Role Based on Neuroprotective Role in Neonatal Brain Injury in Rats

Owing to progress in perinatal medicine, the survival of preterm newborns has markedly increased. However, the incidence of cerebral palsy has risen in association with increased preterm birth. Cerebral palsy is largely caused by cerebral hypoxic ischemia (HI), for which there are no effective medical treatments. We evaluated the effects of stromal cell-derived factor-1α (SDF-1α) on neonatal brain damage in rats. Left common carotid (LCC) arteries of seven-day-old Wistar rat pups were ligated, and animals were exposed to hypoxic gas to cause cerebral HI. Behavioral tests revealed that the memory and spatial perception abilities were disturbed in HI animals, and that SDF-1α treatment improved these cognitive functions. Motor coordination was also impaired after HI but was unimproved by SDF-1α treatment. SDF-1α reduced intracranial inflammation and induced cerebral remyelination, as indicated by the immunohistochemistry results. These data suggest that SDF-1α specifically influences spatial perception abilities in neonatal HI encephalopathy.

Transplanted iNSCs migrate through SDF-1/CXCR4 signaling to promote neural recovery in a rat model of spinal cord injury

The ability of transplanted induced neural stem cells (iNSCs) to promote functional recovery after spinal cord injury and the mechanism by which iNSCs migrate to injured areas are poorly understood. Stromal cell-derived factor-1 (SDF-1) is a cytokine, whereas CXCR4 is its cognate receptor. The aim of this study was to determine whether SDF-1 regulates the migration of iNSCs and to explore the potential mechanism by which iNSCs promotes functional recovery. In-vitro experiments demonstrated that SDF-1 induces a concentration-dependent migration of iNSCs. Pretreatment with the CXCR4-specific antagonist AMD3100 significantly prevented the migration of iNSCs. We found that the expression of SDF-1 increased significantly in spinal cord lesions and was mainly associated with neurons and astrocytes. We also demonstrated that transplanted green fluorescent protein-labeled iNSCs were localized to regions where SDF-1 was highly expressed. In addition, iNSC-treated animals showed significantly improved functional recovery as assessed by BBB at 7 days after injection compared with controls. iNSCs also increased cell proliferation, enhanced vascularity, and reduced apoptosis. These results suggest that upregulated SDF-1 plays an important role in the migration of iNSCs to the injured region and that iNSCs are beneficial for functional recovery after spinal cord injury.

Neurobiology of microglial action in CNS injuries: receptor-mediated signaling mechanisms and functional roles

Microglia are the first line of immune defense against central nervous system (CNS) injuries and disorders. These highly plastic cells play dualistic roles in neuronal injury and recovery and are known for their ability to assume diverse phenotypes. A broad range of surface receptors are expressed on microglia and mediate microglial 'On' or 'Off' responses to signals from other host cells as well as invading microorganisms. The integrated actions of these receptors result in tightly regulated biological functions, including cell mobility, phagocytosis, the induction of acquired immunity, and trophic factor/inflammatory mediator release. Over the last few years, significant advances have been made toward deciphering the signaling mechanisms related to these receptors and their specific cellular functions. In this review, we describe the current state of knowledge of the surface receptors involved in microglial activation, with an emphasis on their engagement of distinct functional programs and their roles in CNS injuries. It will become evident from this review that microglial homeostasis is carefully maintained by multiple counterbalanced strategies, including, but not limited to, 'On' and 'Off' receptor signaling. Specific regulation of theses microglial receptors may be a promising therapeutic strategy against CNS injuries.

CXCL12 in astrocytes contributes to bone cancer pain through CXCR4-mediated neuronal sensitization and glial activation in rat spinal cord

Background

Previous studies have demonstrated that chemokine CXCL12 and its receptor CXCR4 are critical for pain sensitization, but the mechanisms involved are not clear. In this study, we investigated the specific cellular mechanisms of CXCL12/CXCR4 chemokine signaling in the development and maintenance of bone cancer pain after tumor cell implantation (TCI).

Methods

TCI in the tibial cavity of rats was used to establish a bone cancer pain model. Mechanical allodynia and thermal hyperalgesia were determined by measuring the paw withdrawal threshold and latency, respectively. The protein expression and cellular localization of CXCL12 and CXCR4 were detected by western blot and immunofluorescence staining. The sensitization of neurons, activation of astrocytes and microglia were examined by observing the immunofluorescence intensity of c-Fos, GFAP and IBA1.

Results

Our results demonstrated that CXCL12 was upregulated in a time-related manner, both in the dorsal root ganglia and spinal cord after TCI. Spinal CXCL12 was predominately expressed in astrocytes, and an intrathecal injection of astrocyte metabolic inhibitor fluorocitrate or selective JNK inhibitor SP600125 abolished TCI-induced CXCL12 production. A single intrathecal injection of a CXCL12 neutralizing antibody (10 μg/10 μl) at day 10 after TCI transiently reversed bone cancer pain in a dose-dependent manner. Whereas repetitive intrathecal administration of a CXCL12 neutralizing antibody (10 μg/10 μl, once a day from day 3 to 5 after TCI) significantly delayed the onset of TCI-induced pain behaviors for nearly five days. Spinal CXCR4 was also upregulated after TCI and colocalized with neurons, astrocytes and microglia. Blocking CXCR4 suppressed TCI-induced activation of neurons, astrocytes and microglia in the spinal cord at day 14. Repeated intrathecal administration of AMD3100 (5 μg/10 μl, once a day for three days) significantly delayed and suppressed the initiation and persistence of bone cancer pain in the early phase (at day 5, 6 and 7 after TCI) and in the late phase (at day 12, 13 and 14 after TCI) of bone cancer, respectively.

Conclusions

Taken together, these results demonstrate that CXCL12/CXCR4 signaling contributed to the development and maintenance of bone cancer pain via sensitizing neurons and activating astrocytes and microglia. Additionally, this chemokine signaling may be a potential target for treating bone cancer pain.

CXCR4 and CXCR7 form a functional receptor unit for SDF-1/CXCL12 in primary rodent microglia

AIMS

Microglial cells have been originally identified as a target for the CXC chemokine, SDF-1, by their expression of CXCR4. More recently, it has been recognized that SDF-1 additionally binds to CXCR7, which depending on the cell type acts as either a nonclassical, a classical or a scavenger chemokine receptor. Here, we asked whether primary microglial cells additionally express CXCR7 and if so how this chemokine receptor functions in this cell type.

METHODS

CXCR4 and CXCR7 expression was analysed in cultured rat microglia and in the brain of animals with permanent occlusion of the middle cerebral artery (MCAO) by either Western blotting, RT-PCR, flow cytometry and/or immunocytochemistry. The function of CXCR4 and CXCR7 was assessed in the presence of selective antagonists.

RESULTS

Cultured primary rat microglia expressed CXCR4 and CXCR7 to similar levels. Treatment with SDF-1 resulted in the activation of Erk1/2 and Akt signalling. Erk1/2 and Akt signalling were required for subsequent SDF-1-dependent promotion of microglial proliferation. In contrast, Erk1/2 signalling was sufficient for SDF-1-induced migration of microglial cells. Both SDF-1-dependent signalling and the resulting effects on microglial proliferation and migration were abrogated following pharmacological inactivation of either CXCR4 or CXCR7. Moreover, treatment of cultured microglia with lipopolysaccharide resulted in the co-ordinated up-regulation of CXCR4 and CXCR7 expression. Likewise, reactive microglia accumulating in the area adjacent to the lesion core in MCAO rats expressed both CXCR4 and CXCR7.

CONCLUSIONS

CXCR4 and CXCR7 form a functional receptor unit in microglial cells, which is up-regulated during activation of microglia both in vitro and in vivo.

The role of CXCR4 in highly malignant human gliomas biology: current knowledge and future directions

Given the extensive histomorphological heterogeneity of high-grade gliomas, in terms of extent of invasiveness, angiogenesis, and necrosis and the poor prognosis for patients despite the advancements made in therapeutic management. The identification of genes associated with these phenotypes will permit a better definition of glioma heterogeneity, which may ultimately lead to better treatment strategies. CXCR4, a cell surface chemokine receptor, is implicated in the growth, invasion, angiogenesis and metastasis in a wide range of malignant tumors, including gliomas. It is overexpressed in glioma cells according to tumor grade and in glioma tumor initiating cells. There have been various reports suggesting that CXCR4 is required for tumor proliferation, invasion, angiogenesis, and modulation of the immune response. It may also serve as a prognostic factor in characterizing subsets of glioblastoma multiforme, as patients with CXCR4-positive gliomas seem to have poorer prognosis after surgery. Aim of this review was to analyze the current literature on biological effects of CXCR4 activity and its role in glioma pathogenesis. A better understanding of CXCR4 pathway in glioma will lead to further investigation of CXCR4 as a novel putative therapeutic target.

CXCL12 chemokine and its receptors as major players in the interactions between immune and nervous systems

The chemokine CXCL12/stromal cell-derived factor 1 alpha has first been described in the immune system where it functions include chemotaxis for lymphocytes and macrophages, migration of hematopoietic cells from fetal liver to bone marrow and the formation of large blood vessels. Among other chemokines, CXCL12 has recently attracted much attention in the brain as it has been shown that it can be produced not only by glial cells but also by neurons. In addition, its receptors CXCR4 and CXCR7, which are belonging to the G protein-coupled receptors family, are abundantly expressed in diverse brain area, CXCR4 being a major co-receptor for human immunodeficiency virus 1 entry. This chemokine system has been shown to play important roles in brain plasticity processes occurring during development but also in the physiology of the brain in normal and pathological conditions. For example, in neurons, CXCR4 stimulation has been shown regulate the synaptic release of glutamate and γ-aminobutyric acid (GABA). It can also act post-synaptically by activating a G protein activated inward rectifier K⁺ (GIRK), a voltage-gated K channel Kv2.1 associated to neuronal survival, and by increasing high voltage activated Ca²⁺ currents. In addition, it has been recently evidenced that there are several cross-talks between the CXCL12/CXCR4–7 system and other neurotransmitter systems in the brain (such as GABA, glutamate, opioids, and cannabinoids). Overall, this chemokine system could be one of the key players of the neuro-immune interface that participates in shaping the brain in response to changes in the environment.

Functions of the chemokine receptor CXCR4 in the central nervous system and its regulation by μ-opioid receptors

Activation of the G protein-coupled receptor CXCR4 by its chemokine ligand CXCL12 regulates a number of physiopathological functions in the central nervous system, during development as well as later in life. In addition to the more classical roles of the CXCL12/CXCR4 axis in the recruitment of immune cells or migration and proliferation of neural precursor cells, recent studies suggest that CXCR4 signaling also modulates synaptic function and neuronal survival in the mature brain, through direct and indirect effects on neurons and glia. These effects, which include regulation of glutamate receptors and uptake, and of dendritic spine density, can significantly alter the ability of neurons to face excitotoxic insults. Therefore, they are particularly relevant to neurodegenerative diseases featuring alterations of glutamate neurotransmission, such as HIV-associated neurocognitive disorders. Importantly, CXCR4 signaling can be dysregulated by HIV viral proteins, host HIV-induced factors, and opioids. Potential mechanisms of opioid regulation of CXCR4 include heterologous desensitization, transcriptional regulation and changes in receptor expression levels, opioid-chemokine receptor dimer or heteromer formation, and the newly described modulation by the protein ferritin heavy chain-all leading to inhibition of CXCR4 signaling. After reviewing major effects of chemokines and opioids in the CNS, this chapter discusses chemokine-opioid interactions in neuronal and immune cells, focusing on their potential contribution to HIV-associated neurocognitive disorders.

Evidence for high translational potential of mesenchymal stromal cell therapy to improve recovery from ischemic stroke

Although ischemic stroke is a major cause of morbidity and mortality, current therapies benefit only a small proportion of patients. Transplantation of mesenchymal stromal cells (MSC, also known as mesenchymal stem cells or multipotent stromal cells) has attracted attention as a regenerative therapy for numerous diseases, including stroke. Mesenchymal stromal cells may aid in reducing the long-term impact of stroke via multiple mechanisms that include induction of angiogenesis, promotion of neurogenesis, prevention of apoptosis, and immunomodulation. In this review, we discuss the clinical rationale of MSC for stroke therapy in the context of their emerging utility in other diseases, and their recent clinical approval for treatment of graft-versus-host disease. An analysis of preclinical studies examining the effects of MSC therapy after ischemic stroke indicates near-universal agreement that MSC have significant favorable effect on stroke recovery, across a range of doses and treatment time windows. These results are interpreted in the context of completed and ongoing human clinical trials, which provide support for MSC as a safe and potentially efficacious therapy for stroke recovery in humans. Finally, we consider principles of brain repair and manufacturing considerations that will be useful for effective translation of MSC from the bench to the bedside for stroke recovery.

Tetramethylpyrazine (TMP) protects cerebral neurocytes and inhibits glioma by down regulating chemokine receptor CXCR4 expression

The survival in patients with malignant gliomas still remains limited and novel treatment strategies are urgently needed. Tetramethylpyrazine (TMP) extracted from the Chinese herb Chuanxiong, has been suggested to have a therapeutic potential towards glioma primarily through its neural protection activity. However, the exact mechanisms correlating TMP's antitumor function and neural protection have not been yet elucidated. Thus, this study aimed to investigate TMP's molecular target in tumor inhibition and neural protection. The primary cultured cerebral neurocytes were treated with 100 μM TMP for 14 days in vitro. We found TMP can effectively promote neurons survival, compared to controls. TMP effectively inhibits H2O2-induced rise of [Ca(2+)]i and glutamate releasing in cerebral neurocytes, compared to controls. In addition, we verify previous results that TMP significantly decreases the migration and proliferation of C6 glioma cells. Using glioma-neuronal co-culturing system, we further confirm TMP bioactivity in inhibition of glioma cells and protection of cerebral neurocytes. More importantly, our study demonstrates that the expression of chemokine receptor, CXCR4, which plays a key role in tumor development and various neurodegenerative diseases, is significantly decreased in both cerebral neurocytes and C6 glioma cells with TMP treatment, cultured alone or co-cultured. Compared with CXCR4 antagonist, AMD3100, TMP is more effective on glioma inhibition and neural protection. Glutamate concentration in medium of co-culturing system was lower after treatment with 100 μM TMP. Therefore, our findings suggest that TMP-mediated suppression of C6 gliomas and neural protection involves inhibition of CXCR4 expression. Thus, this study provides new insights into TMP's therapeutic potential in the treatment of malignant gliomas.

Current status of chemokines in the adult CNS

Chemokines - chemotactic cytokines - are small secreted proteins that attract and activate immune and non-immune cells in vitro and in vivo. It has been suggested that chemokines and their receptors play a role in the central nervous system (CNS), in addition to their well established role in the immune system. We focus here on three chemokines-CXCL12 (C-X-C motif ligand 12), CCL2 (C-C motif ligand 2), and CX3CL1 (C-X-3C motif ligand 1) - and their principal receptors - CXCR4 (C-X-C motif receptor 4), CCR2 (C-C motif receptor 2) and CX3CR1 (C-X-3C motif receptor 1), respectively. We first introduce the classification of chemokines and their G-protein coupled receptors and the main signaling pathways triggered by receptor activation. We then discuss the cellular distribution of CXCL12/CXCR4, CCL2/CCR2 and CX3CL1/CX3CR1 in adult brain and the neurotransmission and neuromodulation effects controlled by these chemokines in the adult CNS. Changes in the expression of CXCL12, CCL2 and CX3CL1 and their respective receptors are also increasingly being implicated in the pathogenesis of CNS disorders, such as Alzheimer's disease, Parkinson's disease, HIV-associated encephalopathy, stroke and multiple sclerosis, and are therefore plausible targets for future pharmacological intervention. The final section thus discusses the role of these chemokines in these pathophysiological states. In conclusion, the role of these chemokines in cellular communication may make it possible: (i) to identify new pathways of neuron-neuron, glia-glia or neuron-glia communications relevant to both normal brain function and neuroinflammatory and neurodegenerative diseases; (ii) to develop new therapeutic approaches for currently untreatable brain diseases.

Chemotaxis of T-cells after infection of human choroid plexus papilloma cells with Echovirus 30 in an in vitro model of the blood-cerebrospinal fluid barrier

Enterovirus is the most common pathogen causing viral meningitis especially in children. Besides the blood-brain barrier (BBB) the choroid plexus, which forms the blood-cerebrospinal-fluid (CSF) barrier (BCSFB), was shown to be involved in the pathogenesis of enteroviral meningitis. In a human in vitro model of the BCSFB consisting of human choroid plexus papilloma cells (HIBCPP), the permissiveness of plexus epithelial cells for Echovirus 30 (EV30) was analyzed by immunoblotting and quantitative real-time PCR (Q-PCR). HIBCPP could be directly infected by EV30 from the apical as well as from the physiological relevant basolateral side. During an infection period of 5h no alterations of barrier function and cell viability could be observed. Analysis of the cytokine/chemokine-profile following enteroviral infection with a cytometric bead array (CBA) and Q-PCR revealed an enhanced secretion of PanGRO (CXCL1, CXCL2 and CXCL3), IL8 and CCL5. Q-PCR showed a significant upregulation of CXCL1, CXCL2 and CXCL3 in a time dependant manner. However, there was only a minor effect of HIBCPP-infection with EV30 on transepithelial T lymphocyte migration with or without the chemoattractant CXCL12. Moreover, CXCL3 did not significantly enhance T cell migrations. Therefore additional factors must be involved for the in vivo reported enhanced T cell migration into the CNS in the context of enteroviral meningitis. As HIBCPP are permissive for infection with EV30, they constitute a valuable human in vitro model to study viral infection at the BCSFB.

Potentials of endogenous neural stem cells in cortical repair

In the last few decades great thrust has been put in the area of regenerative neurobiology research to combat brain injuries and neurodegenerative diseases. The recent discovery of neurogenic niches in the adult brain has led researchers to study how to mobilize these cells to orchestrate an endogenous repair mechanism. The brain can minimize injury-induced damage by means of an immediate glial response and by initiating repair mechanisms that involve the generation and mobilization of new neurons to the site of injury where they can integrate into the existing circuit. This review highlights the current status of research in this field. Here, we discuss the changes that take place in the neurogenic milieu following injury. We will focus, in particular, on the cellular and molecular controls that lead to increased proliferation in the Sub ventricular Zone (SVZ) as well as neurogenesis. We will also concentrate on how these cellular and molecular mechanisms influence the migration of new cells to the affected area and their differentiation into neuronal/glial lineage that initiate the repair mechanism. Next, we will discuss some of the different factors that limit/retard the repair process and highlight future lines of research that can help to overcome these limitations. A clear understanding of the underlying molecular mechanisms and physiological changes following brain damage and the subsequent endogenous repair should help us develop better strategies to repair damaged brains.

Overexpression of CXCR4 in mesenchymal stem cells promotes migration, neuroprotection and angiogenesis in a rat model of stroke

BACKGROUND

Stromal cell-derived factor-1 (SDF-1) and its cognate receptor, chemokine (C-X-C motif) receptor 4 (CXCR4), are involved in the migration of stem cells.

AIM

To test the hypothesis that mesenchymal stem cells (MSCs) with genetically modified CXCR4 can promote their own recruitment around the ischemic core.

METHODS

Lentiviral vectors were used to overexpress the CXCR4-eGFP fusion protein (CXCR4/eGFP) or eGFP only (eGFP) or to introduce siRNA targeting endogenous CXCR4 (siRNA/eGFP) in rat mesenchymal stem cells (rMSCs). Rats were injected with either the transduced rMSCs or PBS as a control via the femoral vein following a left middle cerebral artery occlusion (MCAO).

RESULTS

One week after MCAO, immunofluorescence staining revealed a significant increase in the number of eGFP-positive cells surrounding the infarct areas in the CXCR4-rMSC-treated group compared to the rMSC-treated control group. Conversely, there was a significant reduction in the number of eGFP-positive cells in the siRNA-rMSC-treated group. Moreover, there was an increase in the capillary vascular volume of the peri-infarct area, a reduction in the volume of the cerebral infarction and improved neurological function in the CXCR4-rMSC-treated group compared to those in the rMSC-, siRNA-rMSC- or PBS-treated groups.

CONCLUSION

CXCR4 overexpression in the rMSCs promoted their mobilization and enhanced neuroprotection in a rat cerebral ischemia model. This strategy may be a useful therapeutic approach for treating ischemic stroke.

Predifferentiated brain-derived adult human progenitor cells migrate toward ischemia after transplantation to the adult rat brain

BACKGROUND

The adult human brain contains neural stem/progenitor cells (AHNPCs) that can survive transplantation into the adult rat brain, migrate toward a lesion, and display limited neuronal differentiation in vivo.

OBJECTIVE

To investigate the effect of manipulating AHNPCs before grafting by predifferentiation, ie, initiating neuronal differentiation before transplantation, and to determine whether this cell priming would affect their ability to migrate in vivo.

METHODS

AHNPCs were prepared from temporal lobe resections for epilepsy. Seven days after global brain ischemia, predifferentiated AHNPCs (exposed to basic fibroblast growth factor, heparin, and laminin) were transplanted to the left hippocampus. Four and 10 weeks after transplantation, brain sections were analyzed by immunohistochemistry.

RESULTS

Transplanted primed cells expressed committed neuronal markers at a much earlier stage compared with nonprimed AHNPCs and were found colabeled with human markers within the damaged CA1 region 4 weeks after grafting. Furthermore, predifferentiated AHNPCs migrated preferentially into an ischemic lesion, similar to their undifferentiated counterparts. The chemoattractant effect from the expression of stromal cell-derived factor-1α (SDF-1α) in ischemic CA1 on AHNPCs expressing CXC chemokine receptor 4 (CXCR4) may explain this preference in migration in vivo.

CONCLUSION

The plasticity of neural progenitors derived from the adult human brain may be greater than previously assumed in that manipulation before grafting may influence the phenotypes seen in vivo. The SDF-1α-CXCR4 axis is involved in the targeted migration toward an ischemic lesion in the adult rat brain, similar to previous reports on endogenous progenitors in rats and grafted fetal human neural progenitors.

The chemokine SDF-1/CXCL12 contributes to the 'homing' of umbilical cord blood cells to a hypoxic-ischemic lesion in the rat brain

Previous studies have shown that transplanted human umbilical cord blood (hUCB)-derived mononuclear cells exert therapeutic effects in various animal models of CNS impairments, including those of perinatal hypoxic-ischemic brain injury. However, the mechanisms of how transplanted cells exert their beneficial effects on the damaged tissue are still unclear. As detection of hUCB cells at the lesion site coincides with the therapeutic effects observed in our model, we investigated the role of the chemokine stromal derived factor (SDF)-1 (CXCL12) as a possible candidate for chemotaxis-mediated 'homing' of transplanted hUCB cells to a hypoxic-ischemic lesion in the perinatal rat brain. Following the hypoxic-ischemic insult expression of SDF-1 significantly increased in lesioned brain hemispheres and was mainly associated with astrocytes. Transplanted hUCB cells expressing the SDF-1 receptor CXCR4 migrated to the lesion site within one day. Inhibition of SDF-1 by application of neutralizing antibodies in vivo resulted in a significantly reduced number of hUCB cells at the lesioned area. The increase in glial SDF-1 expression shortly after induction of the lesion and hUCB cells expressing the corresponding receptor makes SDF-1 a potential chemotactic factor for hUCB cell migration. The reduction of hUCB cells present at the lesion site upon functional inhibition of SDF-1 strengthens the view that the SDF-1/CXCR4 axis is of major importance for cell 'homing'.

Localization of CXCR4 in the forebrain of the adult rat

Chemokines are small secreted proteins that act as chemoattractants, and their role as neuromodulators in the brain has recently been appreciated. CXCL12 is one of the few chemokines found in neurons and expressed constitutively in the central nervous system. Previous data from our laboratory demonstrate the ability of CXCL12 to modulate the behavioral effects of cocaine, and this modulation is dependent on the central site of administration of CXCL12. The present study used single-staining immunohistochemical and dual-staining immunofluorescent methods to determine the localization of the CXCL12 receptor, CXCR4, in the caudate putamen and nucleus accumbens of the adult rat brain. Results demonstrated that individual neurons in both the caudate putamen and lateral shell of the nucleus accumbens express both CXCR4 and D1 dopamine receptors. Immunofluorescent studies showed that CXCR4 was co-expressed with ChAT, a marker for cholinergic neurons, and with GAD C38, a marker for GABAergic neurons, in the caudate putamen and lateral shell of the accumbens. No evidence of CXCR4 was found in the medial shell or core regions of the nucleus accumbens. These data demonstrate that CXCR4 is expressed by subpopulations of cholinergic and GABAergic neurons in the striatum and suggest that CXCR4 is well-positioned to modulate striatal function.

Melanin-concentrating hormone producing neurons: Activities and modulations

Regulation of energy homeostasis in animals involves adaptation of energy intake to its loss, through a perfect regulation of feeding behavior and energy storage/expenditure. Factors from the periphery modulate brain activity in order to adjust food intake as needed. Particularly, "first order" neurons from arcuate nucleus are able to detect modifications in homeostatic parameters and to transmit information to "second order" neurons, partly located in the lateral hypothalamic area. These "second order" neurons have widespread projections throughout the brain and their proper activation leads them to a coordinated response associated to an adapted behavior. Among these neurons, melanin-concentrating hormone (MCH) expressing neurons play an integrative role of the various factors arising from periphery, first order neurons and extra-hypothalamic arousal systems neurons and modulate regulation of feeding, drinking and seeking behaviors. As regulation of MCH release is correlated to regulation of MCH neuronal activity, we focused this review on the electrophysiological properties of MCH neurons from the lateral hypothalamic area. We first reviewed the knowledge on the endogenous electrical properties of MCH neurons identified according to various criteria which are described. Then, we dealt with the modulations of the electrical activity of MCH neurons by different factors such as glucose, glutamate and GABA, peptides and hormones regulating feeding and transmitters of extra-hypothalamic arousal systems. Finally, we described the current knowledge on the modulation of MCH neuronal activity by cytokines and chemokines. Because of such regulation, MCH neurons are some of the best candidate to account for infection-induced anorexia, but also obesity.

Developmental expression profile of the CXCL12gamma isoform: insights into its tissue-specific role

The CXCL12gamma chemokine arises by alternative splicing from Cxcl12, an highly conserved gene that plays pivotal, non-redundant roles during development. The interaction of the highly cationic carboxy-terminal (C-ter) domain of CXCL12gamma with glycosaminoglycans (GAG) critically determines the biological properties of this chemokine. Indeed, CXCL12gamma isoform displays sustained in vivo recruitment of leukocytes and endothelial progenitor cells as compared to other CXCL12 isoforms. Despite the important, specific roles of CXCL12gamma in vivo, the current knowledge about its distribution in embryo and adult tissues is scarce. In this study, we have characterized by both RT-PCR and immunohistochemistry the expression profile and tissue distribution of CXCL12gamma, which showed a distinct mRNA expression pattern during organogenesis that correlates with the specific expression of the CXCL12 gamma protein in several tissues and cell types during development. Our results support the biological relevance of CXCL12 gamma in vivo, and shed light on the specific roles that this novel isoform could play in muscle development and vascularization as well as on the regulation of essential homeostatic functions during the embryonic development.

CXCR3 activation by lentivirus infection suppresses neuronal autophagy: neuroprotective effects of antiretroviral therapy

Previous studies have implicated CXCL12 in the neuropathogenesis of HIV infection. Proteolysis of CXCL12 generates a neurotoxic molecule, CXCL12(5-67), which engages and activates CXCR3, in addition to exhibiting increased expression in the brains of patients with HIV-associated dementia (HAD). Herein, we investigated CXCR3-mediated neuronal injury, particularly, its contribution to autophagy suppression and the concomitant effects of antiretroviral therapy using human brain samples and models of HIV neuropathogenesis. Neurons in the brains of HAD patients and feline immunodeficiency virus (FIV)-infected animals, as well as cultured human neurons, expressed CXCR3, which was modulated in a ligand-specific manner. Exposure of human neurons to CXCL12(5-67) caused a reduction in the autophagy-associated molecule LC3 (P<0.05) and neuronal survival (P<0.05), which recapitulated findings in FIV- and HIV-infected brains (P<0.05). Oral didanosine (ddI) treatment of FIV-infected animals reduced neurobehavioral abnormalities in conjunction with diminished plasma viral load (P<0.05). F4/80 transcript abundance and CXCL12(5-67) immunoreactivity were reduced with restored neuronal LC3 expression in the brains of FIV-infected animals after ddI treatment (P<0.05). ddI treatment also prevented microglial activation and depletion of synaptic proteins in the cortex of FIV-infected animals (P<0.05). These findings indicate that the beneficial effects of ddI might be a consequence of a reduced systemic viral burden and concurrent leukocyte activation, leading to diminished neuroinflammation with preservation of neuronal autophagy by regulating CXCR3 activation.

Modulation of cocaine-induced activity by intracerebral administration of CXCL12

The role of chemokines in immune function is clearly established. Recent evidence suggests that these molecules also play an important role in the central nervous system as modulators of neuronal activity. The chemokine CXCL12 has been identified in several regions of the adult rat brain including the substantia nigra, ventral tegmental area and caudate putamen. CXCR4, a receptor activated by CXCL12, is expressed by dopaminergic neurons in the substantia nigra. The present study tested the effects of intracranial injections of CXCL12 on cocaine-induced locomotion and stereotypic activity in adult male Sprague-Dawley rats. Results demonstrate that intracerebral ventricular administration of CXCL12 (25 ng/4 microl) 15 min prior to cocaine (20 mg/kg intraperitoneal (i.p.)) produced a significant potentiation of both ambulatory and stereotypic activity as compared to cocaine alone. The effects of CXCL12 were blocked by administration of the selective CXCR4 antagonist, AMD 3100. Administration of CXCL12 into specific brain regions was performed to further understand the site of action of CXCL12. Bilateral administration of CXCL12 (25 ng/0.5 microl) into the ventral tegmental area 15 min prior to cocaine (20 mg/kg i.p.) significantly potentiated cocaine-induced ambulatory activity, whereas microinjections of CXCL12 into the caudate putamen selectively increased stereotypy. Conversely, administration of CXCL12 into the lateral shell of the nucleus accumbens resulted in an inhibition of cocaine-stimulated ambulatory activity. No alterations in ambulatory or stereotypic activity were observed following CXCL12 administration into the core of the nucleus accumbens. These results demonstrate that CXCL12 can modulate the behavioral effects produced by cocaine in a brain region-specific manner.

SDF-1alpha up-regulates interleukin-6 through CXCR4, PI3K/Akt, ERK, and NF-kappaB-dependent pathway in microglia

Stromal cell-derived factor-1 (SDF-1), also known as CXCL12, and its receptor CXC chemokine receptor 4 (CXCR4) express in various kinds of cells in central nervous system. The SDF-1/CXCR4 signaling pathway is regulated by diverse biological effects. SDF-1 is up-regulated in the ischemic penumbra following stroke and has been known to be associated with the homing of bone marrow cells to injury. However, the effect of SDF-1alpha/CXCR4 on cytokine production in microglia is mostly unknown. Here, we demonstrated that SDF-1alpha enhanced IL-6 production in both primary cultured microglia and BV-2 microglia. We further investigated the signaling pathway involved in IL-6 production stimulated by SDF-1alpha in microglia. SDF-1alpha increased IL-6 production in both protein and mRNA levels. These effects were attenuated by ERK, phosphatidylinositol 3-kinase (PI3K), NF-kappaB inhibitors, and IkappaB protease inhibitor. Stimulation of microglia with SDF-1alpha also increased Akt and ERK1/2 phosphorylation. In addition, SDF-1alpha treatment also increased IkappaB kinase alpha/beta (IKK alpha/beta) phosphorylation, IkappaBalpha phosphorylation, IkappaBalpha degradation, p65 phosphorylation at Ser(276), translocation of p65 and p50 from cytosol to nucleus and kappaB-luciferase activity. Moreover, SDF-1alpha-mediated increase of kappaB-luciferase activity was inhibited by pre-transfection of DN-p85, DN-Akt or DN-ERK2. Increase of IKK alpha/beta phosphorylation and binding of p65 and p50 to the NF-kappaB element were both antagonized by PI3K and ERK inhibitors. Our results demonstrate a mechanism linking SDF-1alpha and IL-6, and provide additional support for the notion that SDF-1alpha plays a regulatory role in microglia activation.

Imaging correlates of leukocyte accumulation and CXCR4/CXCL12 in multiple sclerosis

OBJECTIVE

To compare leukocyte accumulation and expression of the chemokine receptor/ligand pair CXCR4/CXCL12 in magnetic resonance imaging-defined regions of interest (ROIs) in brains from patients with chronic multiple sclerosis. We studied the following ROIs: normal-appearing white matter (NAWM); regions abnormal only on T2-weighted images (T2 only); and regions abnormal on T2- and T1-weighted images with an abnormal magnetization transfer ratio (T2/T1/MTR).

DESIGN

Case-control study.

SETTING

Cleveland Clinic.

PATIENTS

Brain tissue was acquired from 5 patients with secondary progressive multiple sclerosis (MS) and 5 nonneurological controls.

INTERVENTION

Magnetic resonance imaging pathological correlations were performed on the 5 cases. Based on imaging characteristics, 30 ROIs were excised.

MAIN OUTCOME MEASURE

Using immunohistochemical analysis, we evaluated myelin status, leukocyte accumulation, and CXCR4/CXCL12 expression in the MS ROIs and white matter regions from the 5 nonneurological controls.

RESULTS

Eight of 10 T2/T1/MTR regions were chronic active or chronic inactive demyelinated lesions, whereas only 2 of 10 T2-only regions were demyelinated and characterized as active or chronic active lesions. Equivalent numbers of CD68+ leukocytes (the predominant cell type) were present in myelinated T2-only regions as compared with NAWM. Parenchymal T cells were significantly increased in T2/T1/MTR ROIs as compared with T2-only regions and NAWM. Expression of CXCR4 and phospho-CXCR4 were found on reactive microglia and macrophages in T2-only and T2/T1/MTR lesions. CXCL12 immunoreactivity was detected in astrocytes, astrocytic processes, and vascular elements in inflamed MS lesions.

CONCLUSIONS

Inflammatory leukocyte accumulation was not increased in myelinated MS ROIs with abnormal T2 signal as compared with NAWM. Robust expression of CXCR4/CXCL12 on inflammatory elements in MS lesions highlights a role of this chemokine/receptor pair in central nervous system inflammation.

Serofendic acid promotes stellation induced by cAMP and cGMP analogs in cultured cortical astrocytes

We investigated the effect of serofendic acid, a neuroprotective substance derived from fetal calf serum, on the morphological changes in cultured cortical astrocytes. Cultured astrocytes developed a stellate morphology with several processes following exposure to dibutylyl cAMP (dbcAMP), a membrane-permeable cAMP analog; 8-Br-cGMP, a membrane-permeable cGMP analog; or phorbol-12-myristate-13-acetate (PMA), a protein kinase C activator. Serofendic acid significantly accelerated the stellation induced by dbcAMP- and 8-Br-cGMP. In contrast, the PMA-induced stellation was not affected by serofendic acid. Next, we attempted to elucidate the mechanism underlying the dbcAMP-induced stellation and explore the site of action of serofendic acid. Both the stellation induced by dbcAMP and the promotional effect of serofendic acid were partially inhibited by KT5720, a specific protein kinase A (PKA) inhibitor. Furthermore, serofendic acid failed to facilitate the stellation induced by Y-27632, an inhibitor of Rho-associated kinase (ROCK). These results indicate that serofendic acid promotes dbcAMP- and 8-Br-cGMP-induced stellation and the promotional effect on dbcAMP-induced stellation is mediated at least partly by the regulation of PKA activity and not by controlling ROCK activity.

Chemokine receptor CXCR4 as a therapeutic target for neuroectodermal tumors

Chemokines (chemotactic cytokines) are a family of proteins associated with the trafficking and activation of leukocytes and other cell types in immune surveillance and inflammatory response. Besides their roles in the immune system, they play pleiotropic roles in tumor initiation, promotion, and progression. Chemokines can be classified into four subfamilies of chemokines, CXC, CC, C, or CX3C, based on their number and spacing of conserved cysteine residues near the N-terminus. This CXC subfamily can be further subclassified into two groups, depending on the presence or absence of a tripeptide motif glutamic acid-leucine-arginine (ELR) in the N-terminal domain. ELR(-)CXCL12, which binds to CXCR4 has been frequently implicated in various cancers. Over the past several years, studies have increasingly shown that the CXCR4/CXCL12 axis plays critical roles in tumor progression, such as invasion, angiogenesis, survival, homing to metastatic sites. This review focuses on involvement of CXCR4/CXCL12 interaction in neuroectodermal cancers and their therapeutic potentials. As an attractive therapeutic target of CXCR4/CXCL12 axis for cancer chemotherapy, development history and application of CXCR4 antagonists are described.

Role of the CXCR4/CXCL12 signaling axis in breast cancer metastasis to the brain

Breast cancer is the most common malignancy and second leading cause of cancer death in women. Ninety percent of mortality in breast cancer is often associated with metastatic progression or relapse in patients. Critical stages in the development of aggressive breast cancer include the growth of primary tumors and their ability to spread to foreign organs and form metastases, as well as the establishment of an independent blood supply within the new tumors. Hence, it is imperative to characterize the key molecules that regulate the metastasis of human breast cancer cells. The expression of CXCR4/CXCL12 in breast tumors has been correlated with a poor prognosis, increased metastasis, resistance to conventional therapeutic agents and a poor outcome in the pathogenesis of breast cancer. However, effective anti-CXCR4 therapy remains a challenge. Here, we will review the putative involvement of the CXCR4/CXCL12 signaling axis in breast cancer metastasis to the brain. Characterization of signaling events important for breast cancer cell growth and their metastasis to the brain should provide insights into breast cancer therapies and improved, successful treatments for breast cancer.

How cytokines can influence the brain: a role for chemokines?

Following inflammation or infection, cytokines are released in the blood. Besides their effect on the immune system, cytokines can also act in the brain to modulate our behaviors, inducing for example anorexia when produced in large amount. This review focuses on our current knowledge on how cytokines can influence the brain and the behaviors through several possible pathways: modulating peripheral neurons which project to the brain through the vagus nerve, modulating the levels of hormones such as leptin which can act to the brain through the humoral pathway and possibly acting directly in the brain, through the local production of cytokines and chemokines such as SDF-1alpha/CXCL12.

Chemokines and neuromodulation

Chemokines are not only mediators of the immune system and expressed in inflammatory situations. They are also constitutively expressed in the brain in both glial cells and neurons. Several recent evidence suggest that they can have a neurotransmitter/neuromodulatory role on brain functions similar to several neuropeptides reported so far. The aim of this short review is to illustrate that point using two chemokine systems, SDF-1/CXCL12 and its receptor CXCR4 and MCP-1/CCL2 and its receptor CCR2.

Bi-directional heterologous desensitization between the major HIV-1 co-receptor CXCR4 and the kappa-opioid receptor

We previously characterized multiple interactions between chemokine and opioid G protein-coupled receptors (GPCR), and we found both mu and delta-opioid receptors cross-desensitize CCR1, CCR2, CCR5, but not CXCR4. Here we report that the kappa-opioid receptor (KOR) is able to cross-desensitize CXCR4, and this phenomenon is bi-directional. Chemotactic responses by KOR activation are diminished with prior activation of CXCR4. Additionally, calcium mobilization assays show these cross-desensitization processes occur within seconds of receptor activation, and target receptor internalization is not responsible for desensitization between these receptors. These results have implications for several essential processes including neuronal and lymphocyte development, inflammatory responses, and pain/sensitivity.

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.

The chemokine stromal cell-derived factor-1/CXCL12 activates the nigrostriatal dopamine system

We recently demonstrated that dopaminergic (DA) neurons of the rat substantia nigra constitutively expressed CXCR4, receptor for the chemokine stromal cell-derived factor-1 (SDF-1)/CXCL12 (SDF-1). To check the physiological relevance of such anatomical observation, in vitro and in vivo approaches were used. Patch clamp recording of DA neurons in rat substantia nigra slices revealed that SDF-1 (10 nmol/L) induced: (i) a depolarization and increased action potential frequency; and (ii) switched the firing pattern of depolarized DA neurons from a tonic to a burst firing mode. This suggests that SDF-1 could increase DA release from neurons. Consistent with this hypothesis, unilateral intranigral injection of SDF-1 (50 ng) in freely moving rat decreased DA content and increased extracellular concentrations of DA and metabolites in the ipsilateral dorsal striatum, as shown using microdialysis. Furthermore, intranigral SDF-1 injection induced a contralateral circling behavior. These effects of SDF-1 were mediated via CXCR4 as they were abrogated by administration of a selective CXCR4 antagonist. Altogether, these data demonstrate that SDF-1, via CXCR4, activates nigrostriatal DA transmission. They show that the central functions of chemokines are not restricted, as originally thought, to neuroinflammation, but extend to neuromodulatory actions on well-defined neuronal circuits in non-pathological conditions.

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.

CXCR4 and SDF1 expression in human meningiomas: a proliferative role in tumoral meningothelial cells in vitro

Chemokines participate in cellular processes associated with tumor proliferation, migration, and angiogenesis. We previously demonstrated that stromal cell-derived factor 1 (SDF1) exerts a mitogenic activity in glioblastomas through the activation of its receptor CXCR4. Here we studied the expression of this chemokine in human meningiomas and its possible role in cell proliferation. Reverse transcriptase-PCR analysis for CXCR4 and SDF1 was performed on 55 human meningiomas (47 WHO grade I, 5 WHO II, and 3 WHO III). Immunolabeling for CXCR4 and SDF1 was performed on paraffin-embedded sections of these tumors. [(3)H]Thymidine uptake and Western blot analyses were performed on primary meningeal cell cultures of tumors to evaluate the proliferative activity of human SDF1alpha (hSDF1alpha) in vitro and the involvement of extracellular signal-regulated kinase 1/2 (ERK1/2) activation in this process. CXCR4 mRNA was expressed by 78% of the tumor specimens and SDF1 mRNA by 53%. CXCR4 and SDF1 were often detected in the same tumor tissues and colocalized with epithelial membrane antigen immunostaining. In 9 of 12 primary cultures from meningiomas, hSDF1alpha induced significant cell proliferation that was strongly reduced by the mitogen-activated protein kinase kinase inhibitor PD98059, involving ERK1/2 activation in the proliferative signal of hSDF1alpha. In fact, CXCR4 stimulation led to ERK1/2 phosphorylation/activation. In addition, the hSDF1alpha-induced cell proliferation was significantly correlated with the MIB1 staining index in the corresponding surgical specimen. In conclusion, we found that human meningiomas express CXCR4 and SDF1 and that hSDF1alpha induces proliferation in primary meningioma cell cultures through the activation of ERK1/2.

Selective migration and engraftment of bone marrow mesenchymal stem cells in rat lumbar dorsal root ganglia after sciatic nerve constriction

Bone marrow mesenchymal stem cells (MSCs) preferentially migrate to the injured hemisphere when administered intravenously to rats with traumatic or ischemic brain injuries. In this study, we have investigated the localization of MSCs injected into the lumbar-4 dorsal root ganglion (L4-DRG) of rats with a sciatic nerve single ligature nerve constriction (SLNC). MSCs were isolated by their adherence to plastic, cultured until confluence and labelled with Hoechst. Animals with a unilateral injection of MSCs were subjected to an ipsilateral, bilateral or contralateral SLNC. After 9 days, they were perfused and the lumbar DRGs were dissected out, cut in a cryostat and observed with a fluorescence microscope. Large numbers of Hoechst-positive cells were observed in the injected L4-DRG, distributed around primary afferent neurons, resembling the anatomical localization of glial cells. In animals with an ipsilateral SLNC, some cells were detected in the ipsilateral L3, L5 or L6-DRGs but not in the contralateral ganglia. In animals with a bilateral lesion, MSCs migrated to both the ipsilateral and contralateral DRGs whereas in animals with a contralateral ligature, MSCs migrated to the contralateral DRGs. These results suggest that MSCs preferentially engraft in DRGs hosting primary sensory neurons affected by a lesion of their peripheral branches. Further studies should be carried out in order to elucidate the molecular mechanisms involved in this migration and homing, in order to evaluate the possible use of MSCs as a new therapeutic strategy for the treatment of peripheral nerve neuropathies.

A role for CXCL12 (SDF-1alpha) in the pathogenesis of multiple sclerosis: regulation of CXCL12 expression in astrocytes by soluble myelin basic protein

The pathogenic mechanisms that contribute to multiple sclerosis (MS) include leukocyte chemotaxis into the central nervous system (CNS) and the production of inflammatory mediators, resulting in oligodendrocyte damage, demyelination, and neuronal injury. Thus, factors that regulate leukocyte entry may contribute to early events in MS, as well as to later stages of lesion pathogenesis. CXCL12 (SDF-1alpha), a chemokine essential in CNS development and a chemoattractant for resting and activated T cells, as well as monocytes, is constitutively expressed at low levels in the CNS and has been implicated in T cell and monocyte baseline trafficking. To determine whether CXCL12 is increased in MS, immunohistochemical analyses of lesions of chronic active and chronic silent MS were performed. CXCL12 protein was detected on endothelial cells (EC) in blood vessels within normal human brain sections and on a small number of astrocytes within the brain parenchyma. In active MS lesions, CXCL12 levels were high on astrocytes throughout lesion areas and on some monocytes/macrophages within vessels and perivascular cuffs, with lesser staining on EC. In silent MS lesions, CXCL12 staining was less than that observed in active MS lesions, and also was detected on EC and astrocytes, particularly hypertrophic astrocytes near the lesion edge. Experiments in vitro demonstrated that IL-1beta and myelin basic protein (MBP) induced CXCL12 in astrocytes by signaling pathways involving ERK and PI3-K. Human umbilical vein EC did not produce CXCL12 after treatment with MBP or IL-1beta. However, these EC cultures expressed CXCR4, the receptor for CXCL12, suggesting that this chemokine may activate EC to produce other mediators involved in MS. In agreement, EC treatment with CXCL12 was found to upregulate CCL2 (MCP-1) and CXCL8 (IL-8) by PI3-K and p38-dependent mechanisms. Our findings suggest that increased CXCL12 may initiate and augment the inflammatory response during MS.

Expression of CXC chemokine receptors 1-5 and their ligands in human glioma tissues: role of CXCR4 and SDF1 in glioma cell proliferation and migration

Chemokines have been involved in cellular processes associated to malignant transformation such as proliferation, migration and angiogenesis. The expression of five CXC chemokine receptors and their main ligands was analysed by RT-PCR in 31 human astrocytic neoplasms. The mRNAs for all the receptors analysed were identified in a high percentage of tumours, while their ligands showed lower expression. CXCR4 and SDF1 were the most frequently mRNA identified (29/31 and 13/31 of the gliomas studied, respectively). Thus, we further analysed the cell localization of CXCR4 and SDF1 in immunohistochemistry experiments. We show a marked co-localization of CXCR4 and SDF1 in tumour cells, mainly evident in psudolpalisade and microcystic degeneration areas and in the vascular endothelium. In addition, hSDF1alpha induced a significant increase of DNA synthesis in primary human glioblastoma cell cultures and chemotaxis in a glioblastoma cell line. These results provide evidence of the expression of multiple CXC chemokines and their receptors in brain tumours and that in particular CXCR4 and SDF1 sustain proliferation and migration of glioma cells to promote malignant progression.