Embryonic expression of the mRNA for the rat homologue of the fusin/CXCR-4 HIV-1 co-receptor

The chemokine receptor CXCR4 regulates satellite cell activation, early expansion, and self-renewal, in response to skeletal muscle injury

Acute skeletal muscle injury is followed by satellite cell activation, proliferation, and differentiation to replace damaged fibers with newly regenerated muscle fibers, processes that involve satellite cell interactions with various niche signals. Here we show that satellite cell specific deletion of the chemokine receptor CXCR4, followed by suppression of recombination escapers, leads to defects in regeneration and satellite cell pool repopulation in both the transplantation and in situ injury contexts. Mechanistically, we show that endothelial cells and FAPs express the gene for the ligand, SDF1α, and that CXCR4 is principally required for proper activation and for transit through the first cell division, and to a lesser extent the later cell divisions. In the absence of CXCR4, gene expression in quiescent satellite cells is not severely disrupted, but in activated satellite cells a subset of genes normally induced by activation fail to upregulate normally. These data demonstrate that CXCR4 signaling is essential to normal early activation, proliferation, and self-renewal of satellite cells.

Targeting CXCL12/CXCR4 Signaling with AMD3100 Might Selectively Suppress CXCR4+ T-Cell Chemotaxis Leading to the Alleviation of Chronic Prostatitis

Background

Chronic nonbacterial prostatitis (CNP) has a high incidence, low cure rate, and unclear pathogenesis. Here, we aimed to systematically identify effective diagnostic and therapeutic targets for CNP.

Methods

Prostate tissues were obtained from established mouse models and negative controls and were used for mRNA array sequencing and immunohistochemistry (IHC) staining. Predominant pathways were identified based on pathway enrichment analysis and pharmaceutical experiments. We also investigated the functional role of CXCL12 on CP, a critical factor belonging to the predominant chemotaxis pathway, and employed IHC staining to explore the influence of the CXCL12/CXCR4 axis on the activation of the NF-κB, AKT, and STAT3 signaling pathways. Serum samples derived from both CNP cases and healthy controls were used to determine the secretion level of CXCL12.

Results

By employing mRNA array sequencing and immunohistochemistry, we found that CXCR4, CXCL12, CD44, and OFLM4 were highly expressed in the infiltrated inflammatory T cells of the prostate tissues generated from CNP mice, while they were rarely expressed on the epithelial cells. Based on the pathway enrichment results, we applied pathway inhibitors to suppress the activity of these classic pathways. We found that targeting the CXCL12/CXCR4 axis with its specific antagonist AMD3100 remarkably alleviated inflammatory infiltration of the prostate in CNP models. Similar results were obtained when we replaced AMD3100 with adenovirus-associated virus (AAV)-shCxcl12. To clarify the potential mechanisms of how the CXCL12/CXCR4 axis influences the pathogenesis of CNP, we tested the classical downstream pathways. The results suggested that p-Akt, p-STAT3, and p-NF-κB were more highly expressed on the inflammatory cells of the prostate derived from the CNP model and were partly suppressed after applying AMD3100 or delivering AAV-shCxcl12, indicating that the CXCL12/CXCR4 axis potentially functioned through AKT/NF-κB and STAT3 signaling to influence the pathogenesis of CNP.

Conclusion

Our study provides potential diagnostic biomarkers and therapeutic targets for CNP.

Nile tilapia CXCR4, the receptor of chemokine CXCL12, is involved in host defense against bacterial infection and chemotactic activity

CXC chemokine receptor 4 (CXCR4), a member of seven-transmembrane (7-TM) G-protein-coupled receptor superfamily, is the receptor of the CXC chemokine ligand 12 (CXCL12), and plays important roles in host defense and inflammation. In the current study, we cloned and identified a homolog of CXCR4 from Nile tilapia (Oreochromis niloticus), designated as OnCXCR4. The open reading frame of OnCXCR4 is 1149 bp encoding a peptide of 382 amino acids, and the predicted molecular weight is 42.65 kDa OnCXCR4 shares common features of CXCR4 family, including a 7-TM domain and a characteristic CXC motif (containing CYC). Expression analysis showed that OnCXCR4 constitutively expresses in various tested tissues of Nile tilapia, with the highest level in the anterior kidney. When stimulated with Streptococcus agalactiae, Aeromonas hydrophila, Poly(I:C), or LPS in vivo and in vitro, the expression of OnCXCR4 was significantly regulated. AMD3100, a CXCR4 antagonist, could not only inhibit the chemotactic activity of the recombinant OnCXCL12 protein on the leukocytes from anterior kidney, but also reduce the expression of OnCXCR4 significantly. Taken together, these results of our study above indicate that OnCXCR4 may play important roles in host defense against bacterial infectionin in Nile tilapia, and being a receptor of OnCXCL12 to exert functions.

A review of pharmacological and pharmacokinetic properties of stachydrine

Stachydrine is extracted from the leaves of Leonurus japonicus Houtt (or Motherwort, "Yi Mu Cao" in Traditional Chinese Medicine) and is the major bioactive ingredient. So far, stachydrine has demonstrated various bioactivities for the treatment of fibrosis, cardiovascular diseases, cancers, uterine diseases, brain injuries, and inflammation. The pharmacological and pharmacokinetic properties of stachydrine up to 2019 have been comprehensively searched and summarized. This review provides an updated summary of recent studies on the pharmacological activities of stachydrine. Many studies have demonstrated that stachydrine has strong anti-fibrotic properties (on various types of fibrosis) by inhibiting ECM deposition and decreasing inflammatory and oxidative stress through multiple molecular mechanisms (including TGF-β, ERS-mediated apoptosis, MMPs/TIMPs, NF-κB, and JAK/STAT). The cardioprotective and vasoprotective activities of stachydrine are related to its inhibition of β-MHC, excessive autophagy, SIRT1, eNOS uncoupling and TF, promotion of SERCA, and angiogenesis. In addition to its anticancer action, regulation of the uterus, neuroprotective effects, etc. the pharmacokinetic properties of stachydrine are also discussed.

Prospective non-invasive evaluation of CXCR4 expression for the diagnosis of MALT lymphoma using [68Ga]Ga-Pentixafor-PET/MRI

MALT lymphomas express the chemokine receptor CXCR4 on a regular basis, and [68Ga]Ga-Pentixafor-PET has been shown to quantify CXCR4 expression non-invasively. We, therefore, aimed to evaluate [68Ga]Ga-Pentixafor-PET/MRI for the non-invasive assessment of MALT lymphomas.

Methods: We included 36 MALT lymphoma patients, who had not undergone previous systemic or radiation therapy, in our prospective, IRB-approved, proof-of-concept study. Involved anatomic regions were the orbit (n=14), stomach (n=10), lungs (n=5), and other sites (soft-tissues n=3; adrenal gland, tonsils, parotid gland, and urinary bladder n=1, respectively). MRI sequences included an axial 2-point Dixon T1 VIBE SPAIR 3D sequence for PET attenuation correction; a coronal T2 HASTE sequence; and an axial echo-planar imaging SPAIR-based diffusion-weighted sequence (DWI) obtained during free-breathing (b-values, 50 and 800), with corresponding ADC (apparent diffusion coefficient) maps.

Results: In 33/36 patients, there were MALT lymphomas with an increased uptake of [68Ga]Ga-Pentixafor; all current lymphoma manifestations showed an increased uptake and, accordingly, were positive on the PET/MRI. The remaining three patients had undergone surgery for their orbital MALT lymphomas prior to PET/MRI. Mean SUVmax was 8.6 ± 4.7, mean SUVmean was 4.7 ± 1.8, and mean SUVpeak was 8.0 ± 4.2. The mean SUVmax of the liver was 1.8, and the mean tumor-to-liver ratio was 2.9 ± 2.0. There were no significant differences in SUVmax (P=0.22), SUVmean (P=0.53), SUVpeak (P=0.29), or SUVt/l (P=0.92) between the four anatomic regions (orbit, stomach, lungs, other). The mean tumor volume was 146 ± 499.

Conclusions: Our results thus indicate that [68Ga]Ga-Pentixafor-PET is feasible for the assessment of MALT lymphomas, with a good tumor-to-background ratio in terms of radiotracer uptake.

Modulation of Neuroinflammation in the Central Nervous System: Role of Chemokines and Sphingolipids

Neuroinflammation is a process involved in the pathogenesis of different disorders, both autoimmune, such as neuropsychiatric systemic lupus erythematosus, and degenerative, such as Alzheimer's and Parkinson's disease. In the central nervous system, the local milieu is tightly regulated by different mediators, among which are chemoattractant cytokines, also known as chemokines. These small molecules are able to modulate trafficking of immune cells in the course of nervous system development or in response to tissue damage, and different patterns of chemokine molecule and receptor expression have been described in several neuroinflammatory disorders. In recent years, a number of studies have highlighted a pivotal role of sphingolipids in regulating neuroinflammation. Sphingolipids have different functions, among which are the control of leukocyte egress from lymphonodes into inflamed tissues, the expression of various mediators of inflammation and a direct effect on the cells of the central nervous system as regulators of neuroinflammation. In the future, a better knowledge of these two groups of mediators could provide insight into the pathogenesis of neuroinflammatory disorders and could help develop novel diagnostic tools and therapeutic strategies.

Dynamic Cholesterol-Conditioned Dimerization of the G Protein Coupled Chemokine Receptor Type 4

G protein coupled receptors (GPCRs) allow for the transmission of signals across biological membranes. For a number of GPCRs, this signaling was shown to be coupled to prior dimerization of the receptor. The chemokine receptor type 4 (CXCR4) was reported before to form dimers and their functionality was shown to depend on membrane cholesterol. Here, we address the dimerization pattern of CXCR4 in pure phospholipid bilayers and in cholesterol-rich membranes. Using ensembles of molecular dynamics simulations, we show that CXCR4 dimerizes promiscuously in phospholipid membranes. Addition of cholesterol dramatically affects the dimerization pattern: cholesterol binding largely abolishes the preferred dimer motif observed for pure phospholipid bilayers formed mainly by transmembrane helices 1 and 7 (TM1/TM5-7) at the dimer interface. In turn, the symmetric TM3,4/TM3,4 interface is enabled first by intercalating cholesterol molecules. These data provide a molecular basis for the modulation of GPCR activity by its lipid environment.

Electroacupuncture modulates stromal cell-derived factor-1α expression and mobilization of bone marrow endothelial progenitor cells in focal cerebral ischemia/reperfusion model rats

Stromal cell-derived factor-1α(SDF-1α) plays a crucial role in regulating the mobilization, migration and homing of endothelial progenitor cells(EPCs). Electroacupuncture(EA), a modern version of Traditional Chinese Medicine, can improve neurological recovery and angiogenesis in cerebral ischemic area. This study aimed to investigate the effects of electroacupuncture(EA) on the mobilization and migration of bone marrow EPCs and neurological functional recovery in rats model after focal cerebral ischemia/reperfusion and the potentially involved mechanisms. Sprague-Dawley rats received filament occlusion of the right middle cerebral artery for 2h followed by reperfusion for 12h, 1d, 2d, 3d, 7d respectively. Rats were randomly divided into sham group, model group and EA group. After 2h of the reperfusion, EA was given at the "Baihui" (GV 20)/Siguan ("Hegu" (LI 4)/"Taichong" (LR 3)) acupoints in the EA group. Modified neurological severity score (mNSS) was used to assess the neurological functional recovery. EPCs number and SDF-1α level in bone marrow(BM) and peripheral blood(PB) were detected by using fluorescence-activated cell sorting (FACS) analysis and quantitative real time polymerase chain reaction (qRT-PCR) respectively. An mNSS test showed that EA treatment significantly improved the neurological functional outcome. EPCs number in PB and BM were obviously increased in the EA group. After cerebral ischemia, the SDF-1α level was decreased in BM while it was increased in PB, which implied a gradient of SDF-1α among BM and PB after ischemia. It suggested that the forming of SDF-1α concentration gradient can induce the mobilization and homing of EPCs. Eletroacupuncture as a treatment can accelerate and increase the forming of SDF-1α concentration gradient to further induce the mobilization of EPCs and angiogenesis in ischemic brain and improve the neurological function recovery.

Genes related to antiviral activity, cell migration, and lysis are differentially expressed in CD4(+) T cells in human t cell leukemia virus type 1-associated myelopathy/tropical spastic paraparesis patients

Human T cell leukemia virus type 1 (HTLV-1) preferentially infects CD4(+) T cells and these cells play a central role in HTLV-1 infection. In this study, we investigated the global gene expression profile of circulating CD4(+) T cells from the distinct clinical status of HTLV-1-infected individuals in regard to TAX expression levels. CD4(+) T cells were isolated from asymptomatic HTLV-1 carrier (HAC) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients in order to identify genes involved in HAM/TSP development using a microarray technique. Hierarchical clustering analysis showed that healthy control (CT) and HTLV-1-infected samples clustered separately. We also observed that the HAC and HAM/TSP groups clustered separately regardless of TAX expression. The gene expression profile of CD4(+) T cells was compared among the CT, HAC, and HAM/TSP groups. The paxillin (Pxn), chemokine (C-X-C motif ) receptor 4 (Cxcr4), interleukin 27 (IL27), and granzyme A (Gzma) genes were differentially expressed between the HAC and HAM/TSP groups, regardless of TAX expression. The perforin 1 (Prf1) and forkhead box P3 (Foxp3) genes were increased in the HAM/TSP group and presented a positive correlation to the expression of TAX and the proviral load (PVL). The frequency of CD4(+)FOXP3(+) regulatory T cells (Treg) was higher in HTLV-1-infected individuals. Foxp3 gene expression was positively correlated with cell lysis-related genes (Gzma, Gzmb, and Prf1). These findings suggest that CD4(+) T cell activity is distinct between the HAC and HAM/TSP groups.

Characterization and expression of the CXCR1 and CXCR4 in miiuy croaker and evolutionary analysis shows the strong positive selection pressures imposed in mammal CXCR1

The innate immune system can recognize non-self, danger signals, and pathogen associated molecular patterns and provides a first line of antimicrobial host defense. Therefore, it plays an instructive role and is pretty important in vertebrates. In innate immune responses, CXCRs act as the main receptors of CXC chemokines and play a vital role in host defense and inflammation. In present study, we cloned two cDNA molecules of CXCR1 and CXCR4 in Miichthys miiuy (miiuy croaker). In these two genes, we found the most highly conserved DRY motif in the second intracellular loop adjacent to the third transmembrane domain. The expressions of CXCR1 and CXCR4 showed that they were ubiquitously expressed in ten normal tissues. After infection with Vibrio anguillarum and Vibrio harveyi, the expressions of CXCRs in the immune tissues were significantly regulated in most of tissues except that of CXCR1 in the kidney after V. harveyi injection. Evolutionary analysis showed that only the ancestral lineages of CXCR4 in amphibians underwent positive selection, indicating that the ancestors of amphibians boarded the land and had to further evolve to adapt to terrestrial environments. Multiple ML methods were implemented to detect the robust positively selected candidates for sites. In total, we detected 12 and 3 positively selected sites in the subsets of current mammal and fish CXCR1 genes, and only one site under positive selection was found in mammalian CXCR4 subsets. These positively selected sites were mainly located in the extracellular domains of CXCRs. The sliding window analysis and evolution test tended to favor positive selection acting on the N-terminal domain of CXCR1, which was the critical region for ligand/receptor signaling for neutrophils and receptor-ligand interaction, indicating that the N-terminal of CXCR1 in mammals underwent more positive selection than that of fish.

CXCR4 signaling regulates radial glial morphology and cell fate during embryonic spinal cord development

Embryonic meninges secrete the chemokine SDF-1/CXCL12 as a chemotactic guide for migrating neural stem cells, but SDF-1 is not known to directly regulate the functions of radial glia. Recently, the developing meninges have been shown to regulate radial glial function, yet the mechanisms and signals responsible for this phenomenon remain unclear. Moreover, as a nonmigratory cell type, radial glia do not conform to traditional models associated with chemokine signaling in the central nervous system. Using fluorescent transgenes, in vivo genetic manipulations and pharmacological techniques, we demonstrate that SDF-1 derived from the meninges exerts a CXCR4-dependent effect on radial glia. Deletion of CXCR4 expression by radial glia influences their morphology, mitosis, and progression through both oligodendroglial and astroglial lineages. Additionally, disruption of CXCR4 signaling in radial glia has a transient effect on the migration of oligodendrocyte progenitors. These data indicate that a specific chemokine signal derived from the meninges has multiple regulatory effects on radial glia.

Chemokine CXCL12 and its receptors in the developing central nervous system: emerging themes and future perspectives

Homeostatic chemokine CXCL12 (also known as SDF-1) and its receptor CXCR4 are indispensable for the normal development of the nervous system. This chemokine system plays a plethora of functions in numerous neural developmental processes, from which the underlying molecular and cellular mechanisms are beginning to be unravelled. Recent identification of CXCR7 as a second receptor for CXCL12 provides opportunities to gain deeper insights into how CXCL12 operates in the nervous system. Here, we review the diverse roles of CXCL12 in the developing central nervous system, summarize the recent progress in uncovering CXCR7 functions, and discuss the emerging common themes from these works and future perspectives.

Migration and fate of therapeutic stem cells in different brain disease models

Stem cells have a number of properties, which make them excellent candidates for the treatment of various neurologic disorders, the most important of which being their ability to migrate to and differentiate predictably at sites of pathology in the brain. The disease-directed migration and well-characterized differentiation patterns of stem cells may eventually provide a powerful tool for the treatment of both localized and diffuse disease processes within the human brain. A thorough understanding of the molecular mechanisms governing their migratory properties and their choice between different differentiation programs is essential if these cells are to be used therapeutically in humans. This review focuses on summarizing the migration and differentiation of therapeutic neural and mesenchymal stem cells in different disease models in the brain and also discusses the promise of these cells to eventually treat various forms of neurologic disease.

The blood-brain barrier, chemokines and multiple sclerosis

The infiltration of leukocytes into the central nervous system (CNS) is an essential step in the neuropathogenesis of multiple sclerosis (MS). Leukocyte extravasation from the bloodstream is a multistep process that depends on several factors including fluid dynamics within the vasculature and molecular interactions between circulating leukocytes and the vascular endothelium. An important step in this cascade is the presence of chemokines on the vascular endothelial cell surface. Chemokines displayed along the endothelial lumen bind chemokine receptors on circulating leukocytes, initiating intracellular signaling that culminates in integrin activation, leukocyte arrest, and extravasation. The presence of chemokines at the endothelial lumen can help guide the movement of leukocytes through peripheral tissues during normal immune surveillance, host defense or inflammation. The expression and display of homeostatic or inflammatory chemokines therefore critically determine which leukocyte subsets extravasate and enter the peripheral tissues. Within the CNS, however, infiltrating leukocytes that cross the endothelium face additional boundaries to parenchymal entry, including the abluminal presence of localizing cues that prevent egress from perivascular spaces. This review focuses on the differential display of chemokines along endothelial surfaces and how they impact leukocyte extravasation into parenchymal tissues, especially within the CNS. In particular, the display of chemokines by endothelial cells of the blood brain barrier may be altered during CNS autoimmune disease, promoting leukocyte entry into this immunologically distinct site. Recent advances in microscopic techniques, including two-photon and intravital imaging have provided new insights into the mechanisms of chemokine-mediated capture of leukocytes within the CNS.

Spatio-temporal changes of SDF1 and its CXCR4 receptor in the dorsal root ganglia following unilateral sciatic nerve injury as a model of neuropathic pain

There is a growing evidence that chemokines and their receptors play a role in inducing and maintaining neuropathic pain. In the present study, unilateral chronic constriction injury (CCI) of rat sciatic nerve under aseptic conditions was used to investigate changes for stromal derived factor-1 (SDF1) and its CXCR4 receptor in lumbal (L4-L5) and cervical (C7-C8) dorsal root ganglia (DRG) from both sides of naïve, CCI-operated and sham-operated rats. All CCI-operated rats displayed mechanical allodynia and thermal hyperalgesia in hind paws ipsilateral to CCI, but forepaws exhibited only temporal changes of sensitivity not correlated with alterations in SDF1 and CXCR4 proteins. Naïve DRG displayed immunofluorescence for SDF1 (SDF1-IF) in the satellite glial cells (SGC) and CXCR4-IF in the neuronal bodies with highest intensity in small- and medium-sized neurons. Immunofluorescence staining and Western blot analysis confirmed that unilateral CCI induced bilateral alterations of SDF1 and CXCR4 proteins in both L4-L5 and C7-C8 DRG. Only lumbal DRG were invaded by ED-1+ macrophages exhibiting SDF1-IF while elevation of CXCR4-IF was found in DRG neurons and SGC but not in ED-1+ macrophages. No attenuation of mechanical allodynia, but reversed thermal hyperalgesia, in ipsi- and contralateral hind paws was found in CCI-operated rats after i.p. administration of CXCR4 antagonist (AMD3100). These results indicate that SDF1/CXCR4 changes are not limited to DRG associated with injured nerve but that they also spread to DRG non-associated with such nerve. Functional involvement of these alterations in DRG non-associated with injured nerve in neuropathic pain remains to be elucidated.

CXCL12 increases human neural progenitor cell proliferation through Akt-1/FOXO3a signaling pathway

CXCL12, a ligand for the chemokine receptor CXCR4, is well known in mediating neural progenitor cell (NPC) migration during neural development. However, the effects of CXCL12 on human NPC proliferation and its associated signaling pathways remain unclear. The transcription factor, FOXO3a, a downstream target of Akt-1, is critical for cell cycle control and may also play an important role in regulating NPC proliferation. In this study, we found that CXCL12 promotes human NPC proliferation as determined by the proliferation marker Ki67 and BrdU incorporation. This CXCL12-mediated NPC proliferation was associated with an increase in Akt-1 and FOXO3a phosphorylation in a time- and dose-dependent manner. The CXCR4 antagonist (T140) or inhibitors for G proteins (Pertussis toxin) and phosphoinositide 3-kinase (PI3K) (LY294002) abolished CXCL12-mediated NPC proliferation and phosphorylation of Akt-1 and FOXO3a. The roles of Akt-1 and FOXO3a in CXCL12-mediated NPC proliferation were further investigated by using adenoviral over-expression in NPCs. Over-expression of dominant-negative Akt-1 or wild-type FOXO3a in NPC abrogated CXCL12-mediated proliferation. These data suggest that CXCL12-mediated NPC proliferation is reliant upon the phosphorylation of Akt-1 and FOXO3a and gives insight to an essential role of CXCL12 in neurogenesis. Understanding this mechanism may facilitate the development of novel therapeutic targets for NPC proliferation during neurogenesis.

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.

Therapeutic targeting of microenvironmental interactions in leukemia: mechanisms and approaches

In hematological malignancies, there are dynamic interactions between leukemic cells and cells of the bone marrow microenvironment. Specific niches within the bone marrow microenvironment provide a sanctuary for subpopulations of leukemic cells to evade chemotherapy-induced death and allow acquisition of a drug-resistant phenotype. This review focuses on molecular and cellular biology of the normal hematopoietic stem cell and the leukemia stem cell niche, and of the molecular pathways critical for microenvironment/leukemia interactions. The key emerging therapeutic targets include chemokine receptors (CXCR4), adhesion molecules (VLA4 and CD44), and hypoxia-related proteins HIF-1alpha and VEGF. Finally, the genetic and epigenetic abnormalities of leukemia-associated stroma will be discussed. This complex interplay provides a rationale for appropriately tailored molecular therapies targeting not only leukemic cells but also their microenvironment to ensure improved outcomes in leukemia.

CXCR4, inhibitors and mechanisms of action

In this review, the author discusses recent advances in anti-HIV inhibitors, targeting CXCR4, including natural and modified chemokines, peptides and organic compounds, their mechanisms of action, and the molecular process of virus invasion of immune cells. Peptides with strong anti-HIV activity exhibit several common features, such as electrostatic charges, cyclization, beta-turns and dimerization induced by a sulphide bond. Organic compounds, such as cyclams, display a unique metal-mediated mechanism in the binding process to its target CXCR4. Understanding of their mechanisms of action may be useful for the design of more effective drugs. Consecutive interactions of viral glycoprotein gp120 with CD4 and the co-receptor, CXCR4 or another co-receptor CCR5 on the cell surface leads to virus invasion into host cells. The molecular details of the binding between HIV glycoproteins and the co-receptors also provide a basis for anti-HIV therapy.

CXCR4/SDF-1 system modulates development of GnRH-1 neurons and the olfactory system

Stromal cell-derived factor 1 (SDF-1) and its receptor CXCR4 influence neuronal migration and have been identified in nasal regions. Gonadotropin releasing hormone-1 (GnRH-1) neurons migrate from nasal regions into the developing forebrain, where postnatally they control reproduction. This study examined the role of SDF-1/CXCR4 in development of the GnRH-1/olfactory systems. Migrating GnRH-1 neurons were CXCR4 immunopositive as were the fibers along which they migrate. SDF-1 transcripts were detected in olfactory epithelium and vomeronasal organ, while SDF-1 immunoreactivity highlighted the GnRH-1 migratory pathway. CXCR4-deficient mice showed a decrease in GnRH-1 cells at the nasal forebrain junction and in brain, but the overall migratory pathway remained intact, no ectopic GnRH-1 cells were detected and olfactory axons reached the olfactory bulb. To further characterize the influence of SDF-1/CXCR4 in the GnRH-1 system, nasal explants were used. CXCR4 expression in vitro was similar to that in vivo. SDF-1 was detected in a dorsal midline cell cluster as well as in migrating GnRH-1 cells. Treatment of explants with bicyclam AMD3100, a CXCR4 antagonist, attenuated GnRH-1 neuronal migration and sensory axon outgrowth. Moreover, the number of GnRH-1 neurons in the explant periphery was reduced. The effects were blocked by coincubation with SDF-1. Removal of midline SDF-1 cells did not alter directional outgrowth of olfactory axons. These results indicate that SDF-1/CXCR4 signaling in not necessary for olfactory axon guidance but rather influences sensory axon extension and GnRH-1 neuronal migration, and maintains GnRH-1 neuronal expression as the cells move away from nasal pit regions.

Role of mesenchymal stem cells in regenerative medicine: application to bone and cartilage repair

BACKGROUND

Mesenchymal stem cells (MSC) are multipotent cells with the ability to differentiate into mesenchyme-derived cells including osteoblasts and chondrocytes.

OBJECTIVE

To provide an overview and expert opinion on the in vivo ability of MSC to home into tissues, their regenerative properties and potential applications for cell-based therapies to treat bone and cartilage disorders.

METHODS

Data sources including the PubMed database, abstract booklets and conference proceedings were searched for publications pertinent to MSC and their properties with emphasis on the in vivo studies and clinical use in cartilage and bone regeneration and repair. The search included the most current information possible.

CONCLUSION

MSC can migrate to injured tissues and some of their reparative properties are mediated by paracrine mechanisms including their immunomodulatory actions. MSC possess a critical potential in regenerative medicine for the treatment of skeletal diseases, such as osteoarthritis or fracture healing failure, where treatments are partially effective or palliative.

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.

Modulation of network-driven, GABA-mediated giant depolarizing potentials by SDF-1alpha in the developing hippocampus

Chemokine stromal cell-derived factor-1 (SDF-1, or CXCL12) plays an important role in brain development and functioning. Whole-cell patch clamp recordings were conducted on CA3 neurons in hippocampal slices prepared from neonatal rats between postnatal days 2 and 6 to study the modulatory effects of SDF-1alpha on network-driven, gamma-aminobutyric-acid-mediated giant depolarizing potentials (GDPs), a hallmark of the developing hippocampus. We found that SDF-1alpha, the only natural ligand for chemokine CXC motif receptor 4 (CXCR4), decreased GDP firing without significant effects on neuronal passive membrane properties in neonatal hippocampal neurons. The SDF-1alpha-mediated decrease in GDP firing was blocked by T140, a CXCR4 receptor antagonist, suggesting that SDF-1alpha modulates GDP firing via CXCR4. We also showed that endogenous SDF-1 exerts a tonic inhibitory action on GDPs in the developing hippocampus. As SDF-1/CXCR4 are highly expressed in the developing brain and GDPs are involved in activity-dependent synapse formation and functioning, the inhibitory action of SDF-1alpha on GDPs may reflect a potential mechanism for chemokine regulation of neural development in early neonatal life.

Chemokines: a new class of neuromodulator?

Chemokines are not only found in the immune system or expressed in inflammatory conditions: they are constitutively present in the brain in both glial cells and neurons. Recently, the possibility has been raised that they might act as neurotransmitters or neuromodulators. Although the evidence is incomplete, emerging data show that chemokines have several of the characteristics that define neurotransmitters. Moreover, their physiological actions resemble those of neuromodulators in the sense that chemokines usually have few effects by themselves in basal conditions, but modify the induced release of neurotransmitters or neuropeptides. These findings, together with the pharmacological development of agonists and antagonists that are selective for chemokine receptors and can cross the blood-brain barrier, open a new era of research in neuroscience.

HIV-1 infection and AIDS: consequences for the central nervous system

Infection with the human immunodeficiency virus-1 (HIV-1) can induce severe and debilitating neurological problems that include behavioral abnormalities, motor dysfunction and frank dementia. After infiltrating peripheral immune competent cells, in particular macrophages, HIV-1 provokes a neuropathological response involving all cell types in the brain. HIV-1 also incites activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes and glutamate receptor-mediated excitotoxicity, all of which can trigger numerous downstream signaling pathways and disrupt neuronal and glial function. This review will discuss recently uncovered pathologic neuroimmune and degenerative mechanisms contributing to neuronal damage induced by HIV-1 and potential approaches for development of future therapeutic intervention.

A role for CXCR4 signaling in survival and migration of neural and oligodendrocyte precursors

Oligodendrocyte development is controlled by a number of survival and migratory factors. The present study shows that signaling of CXCR4 receptor by the chemokine CXCL12 regulates survival and migration of neural precursors (NP) as well as oligodendrocyte progenitors (OP). CXCR4 is expressed by E14 striatal NP and OP generated by neurospheres. In CXCR4-defective mice, the number of NP in neurosphere outgrowth was twofold less than in wild-type (WT) mice; NP radial cell migration was also decreased. In contrast, the addition of CXCL12 to WT NP increased radial migration from the sphere in a dose-dependent manner with a maximal response at 200 nM. When oligodendrocytes differentiated in neurosphere outgrowth, CXCR4 was downregulated. OP isolated from newborn brain coexpressed CXCR4 with platelet-derived growth factor receptor-alpha (PDGFR alpha) or chondroitin sulfate proteoglycan; receptor expression also decreased during differentiation in vitro. Neonatal OP showed a peak migratory response to 20 nM of CXCL12 in chemotactic chambers, a migration inhibited by a CXCR4 antagonist and anti-CXCL12 antibody. In the embryonic spinal cord, the number of OP-expressing PDGFR alpha was reduced more than twofold in CXCR4-defective mice compared with WT and the ratio of ventral to dorsal OP was significantly increased. This indicates a defect in OP survival and their dorsal migration from the ventral cord region, probably because CXCR4(-/-) OP are unable to respond to CXCL12 made by vascular endothelia and the pia mater. We propose that CXCR4 signaling regulate survival and outward chemotactic migration of OP during embryonic and postnatal CNS development.

The chemokine stromal cell-derived factor-1 regulates the migration of sensory neuron progenitors

Chemokines and their receptors are essential for the development and organization of the hematopoietic/lymphopoietic system and have now been shown to be expressed by different types of cells in the nervous system. In mouse embryos, we observed expression of the chemokine (CXC motif) receptor 4 (CXCR4) by neural crest cells migrating from the dorsal neural tube and in the dorsal root ganglia (DRGs). Stromal cell-derived factor-1 (SDF-1), the unique agonist for CXCR4, was expressed along the path taken by crest cells to the DRGs, suggesting that SDF-1/CXCR4 signaling is needed for their migration. CXCR4 null mice exhibited small and malformed DRGs. Delayed migration to the DRGs was suggested by ectopic cells expressing tyrosine receptor kinase A (TrkA) and TrkC, neurotrophin receptors required by DRG sensory neuron development. In vitro, the CXCR4 chemokine receptor was upregulated by migratory progenitor cells just as they exited mouse neural tube explants, and SDF-1 acted as a chemoattractant for these cells. Most CXCR4-expressing progenitors differentiated to form sensory neurons with the properties of polymodal nociceptors. Furthermore, DRGs contained a population of progenitor cells that expressed CXCR4 receptors in vitro and differentiated into neurons with a similar phenotype. Our findings indicate an important role for SDF-1/CXCR4 signaling in directing the migration of sensory neuron progenitors to the DRG and potentially in other aspects of development once the DRGs have coalesced.

High-level expression of functional chemokine receptor CXCR4 on human neural precursor cells

Neural precursor cells (NPCs) are self-renewing, multipotent progenitors that give rise to neurons, astrocytes and oligodendrocytes in the central nervous system (CNS). Fetal NPCs have attracted attention for their potential use in studying normal CNS development. Several studies of rodent neural progenitors have suggested that chemokines and their receptors are involved in directing NPC migration during CNS development. In this study, we established a consistent system to culture human NPCs and examined the expression of chemokine receptors on these cells. NPCs were found to express the markers nestin and CD133 and to differentiate into neurons, astrocytes and oligodendrocytes at the clonal level. Flow cytometry and RNase protection assay (RPA) indicated that NPCs express high levels of CXCR4 and low levels of several other chemokine receptors. When examined using a chemotaxis assay, NPCs were able to respond to CXCL12/SDF-1alpha, a ligand of CXCR4. Treatment with anti-CXCR4 antibody or HIV-1 gp120 abolished the migratory response of NPCs towards CXCL12/SDF-1alpha. These findings suggest that CXCR4 may play a significant role in directing NPC migration during CNS development.

Chemokine receptors are expressed widely by embryonic and adult neural progenitor cells

We investigated the expression and functions of chemokine receptors in neural progenitor cells isolated from embryonic and adult mice. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis demonstrated mRNA expression for most known chemokine receptors in neural progenitor cells grown as neurospheres from embryonic (E17) and adult (4-week-old) mice. The expression of CXCR4 receptors was demonstrated further in E17 neurospheres using immunohistochemistry, in situ hybridization, Northern blot analysis and fura-2-based Ca(2+) imaging. Most neurospheres grown from E17 mice responded to stromal cell-derived factor-1 (SDF-1/CXCL12) in Ca(2+) imaging studies. In addition, immunohistochemical studies demonstrated that these neurospheres consisted of dividing cells that uniformly colocalized nestin and CXCR4 receptors. Differentiation of E17 neurospheres yielded astrocytes and neurons exhibiting several different phenotypes, including expression of calbindin, calretinin, gamma-aminobutyric acid (GABA), and glutamate, and many also coexpressed CXCR4 receptors. In addition, neurospheres grown from the subventricular zone (SVZ) of 4-week-old mice exhibited large increases in Ca(2+) in response to CXCL12 and several other chemokines. In comparison, neurospheres prepared from olfactory bulb of adult mice exhibited only small Ca(2+) responses to CXCL12, whereas neurospheres prepared from hippocampus were insensitive to CXCL12, although they did respond to other chemokines. Investigations designed to investigate whether CXCL12 can act as a chemoattractant demonstrated that cells dissociated from E17 or adult SVZ neurospheres migrated toward an CXCL12 gradient and this was blocked by the CXCR4 antagonist AMD3100. These results illustrate widespread chemokine sensitivity of embryonic and adult neural progenitor cells and support the view that chemokines may be of general importance in control of progenitor cell migration in embryonic and adult brain.

Stromal cell-derived factor 1-mediated CXCR4 signaling in rat and human cortical neural progenitor cells

Stromal cell-derived factor 1 (SDF-1) and the chemokine receptor CXCR4 are highly expressed in the nervous system. Knockout studies have suggested that both SDF-1 and CXCR4 play essential roles in cerebellar, hippocampal, and neocortical neural cell migration during embryogenesis. To extend these observations, CXCR4 signaling events in rat and human neural progenitor cells (NPCs) were examined. Our results show that CXCR4 is expressed in abundance on rat and human NPCs. Moreover, SDF-1alpha induced increased NPCs levels of inositol 1,4,5-triphosphate, extracellular signal-regulated kinases 1/2, Akt, c-Jun N-terminal kinase, and intracellular calcium whereas it diminished cyclic adenosine monophosphate. Finally, SDF-1alpha can induce human NPC chemotaxis in vitro, suggesting that CXCR4 plays a functional role in NPC migration. Both T140, a CXCR4 antagonist, and pertussis toxin (PTX), an inactivator of G protein-coupled receptors, abrogated these events. Ultimately, this study suggested that SDF-1alpha can influence NPC function through CXCR4 and that CXCR4 is functional on NPC.

Expression of the chemokine receptor Cxcr4 mRNA during mouse brain development

The expression of Cxcr4 mRNA that encodes the receptor for the chemokine Sdf1 was studied during mouse brain development using in situ hybridization, from E9.5 to maturity at P21. At embryonic stages, expression is prominent in ventricular zones of stem cell proliferation. This abates during the postnatal period in parallel to the depopulation of ventricular zones. In addition, the Cxcr4 gene is expressed in some differentiating neuronal populations at E12.5, E14.5 and E17.5, such as scattered cells in the reticular formation, cranial nerve nuclei, peripheral ganglia, cerebellar external granule cells, zona incerta, ventral lateral geniculate thalamic nuclei, olfactory glomerular layer, hippocampal primordium and telencephalic preplate. High levels of expression are detected in preplate derivatives in all sectors of the marginal zone (MZ) of the telencephalic vesicles, including Cajal-Retzius (CR) cells, other MZ cells and subplate neurons. Cxcr4 expression is progressively downregulated postnatally, but remains significantly associated in the adult with Bergman glia in the cerebellum, the subgranular layer of the dentate gyrus, and the olfactory glomerular layer. In contrast, expression of Sdf1 mRNA is confined to the meninges and, in embryos, to the telencephalic intermediate zone. This expression pattern suggests that Sdf1 and its receptor Cxcr4 may exert trophic influences on precursor cell proliferation and some neuronal targets that remain to be identified and studied further.

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.

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

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

Expression of the chemokine receptor CXCR4 and its ligand stromal cell-derived factor 1 in human brain tumors and their involvement in glial proliferation in vitro

Chemokines are a family of proteins that chemoattract and activate cells by interacting with specific receptors on the surface of their targets. They are grouped into four classes based on the position of key cysteine residues: C, CC, CXC, and CX3C. Stromal cell-derived factor 1 (SDF1), the ligand of the CXCR4 receptor, is a CXC chemokine involved in chemotaxis and brain development that also acts as coreceptor for HIV-1 infection. It has been proposed that CXCR4 is overexpressed and required for proliferation in human brain tumor cells. We previously demonstrated that CXCR4 and SDF1 are expressed in culture of cortical type I rat astrocytes, cortical neurons, and cerebellar granule cells. In this study, we analyzed the expression of CXCR4 and SDF1 in four human brain tumor tissues, showing that CXCR4 is expressed in all tumors analyzed, whereas SDF1 is expressed only in two tumor tissues. We also investigated the possible functions of CXCR4 expressed in rat type I cortical astrocytes, demonstrating that SDF1alpha stimulates the proliferation of these cells in vitro. Moreover, we studied by western blot the intracellular pathway involved in cell proliferation, demonstrating that SDF1alpha induces the ERK1/2 phosphorylation that is reduced by the PD98059 compound, an MEK inhibitor.

Interleukin-6 and cAMP induce stromal cell-derived factor-1 chemotaxis in astroglia by up-regulating CXCR4 cell surface expression. Implications for brain inflammation

The chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 control the migration of neurons and microglial cells in the central nervous system. Although functional CXCR4 is also expressed by astroglia, recent studies have failed to observe a chemotactic response of these cells to SDF-1. Here, we demonstrate that SDF-1-dependent chemotaxis can be induced by treating cultured cortical astroglia with either dibutyryl cyclic AMP (dbcAMP; 10(-4) m) or interleukin-6 (IL-6; 10 ng/ml). Flow cytometric analysis revealed that both the dbcAMP- and IL-6-induced onset of SDF-1-dependent chemotaxis of astroglia are due to the increased cell surface expression of CXCR4. In addition, dbcAMP and IL-6 also increased CXCR4 transcript levels, further suggesting that both treatments primarily affect CXCR4 surface expression in astroglia by stimulation of gene expression. Moreover, unlike the case with IL-6 and dbcAMP, which allowed for an optimal chemotactic response to SDF-1 only after 48 h, a similar chemotactic response, associated with an increase in CXCR4 cell surface expression, already occurred after 24 h when astroglial cultures were maintained with medium conditioned by IL-6- or dbcAMP-pretreated astrocytes, indicating that the stimulatory effects of IL-6 and cAMP on CXCR4 cell surface expression involve a secondary mechanism. The findings that elevated extracellular levels of IL-6 or factors positively coupled to cAMP result in increased CXCR4 cell surface expression levels and subsequent SDF-1-dependent chemotaxis in central nervous system astrocytes point to a crucial role of this chemokine during reactive gliosis and human immunodeficiency virus-mediated dementia.

Characterization of chemokines and their receptors in the central nervous system: physiopathological implications

Chemokines represent key factors in the outburst of the immune response, by activating and directing the leukocyte traffic, both in lymphopoiesis and in immune surveillance. Neurobiologists took little interest in chemokines for many years, until their link to acquired immune deficiency syndrome-associated dementia became established, and thus their importance in this field has been neglected. Nevertheless, the body of data on their expression and role in the CNS has grown in the past few years, along with a new vision of brain as an immunologically competent and active organ. A large number of chemokines and chemokine receptors are expressed in neurons, astrocytes, microglia and oligodendrocytes, either constitutively or induced by inflammatory mediators. They are involved in many neuropathological processes in which an inflammatory state persists, as well as in brain tumor progression and metastasis. Moreover, there is evidence for a crucial role of CNS chemokines under physiological conditions, similar to well known functions in the immune system, such as proliferation and developmental patterning, but also peculiar to the CNS, such as regulation of neural transmission, plasticity and survival.

Role of the chemokine SDF-1 as the meningeal attractant for embryonic cerebellar neurons

Migration of neuronal precursor cells from the external germinal layer (EGL) to the internal granular layer (IGL) is a crucial process in the development of the mammalian cerebellar cortex. These cells make up the only precursor population known to migrate away from the surface of the brain. We studied the role of the chemokine stromal-derived factor 1 (SDF-1) in the cerebellar tissue of rats and knockout mice and found (i) that it functions as an attractive guidance cue for neuronal migration and (ii) that its secretion from non-neuronal meningeal tissue is important for controlling the migration of embryonic EGL cells.

Abnormal development of the hippocampal dentate gyrus in mice lacking the CXCR4 chemokine receptor

We investigated the role of the CXCR4 chemokine receptor in development of the mouse hippocampus. CXCR4 mRNA is expressed at sites of neuronal and progenitor cell migration in the hippocampus at late embryonic and early postnatal ages. mRNA for stromal cell-derived factor 1 (SDF-1), the only known ligand for the CXCR4 receptor, is expressed close to these migration sites, in the meninges investing the hippocampal primordium and the primordium itself. In mice engineered to lack the CXCR4 receptor, the morphology of the hippocampal dentate gyrus (DG) is dramatically altered. Gene expression markers for DG granule neurons and bromodeoxyuridine labeling of dividing cells revealed an underlying defect in the stream of postmitotic cells and secondary dentate progenitor cells that migrate toward and form the DG. In the absence of CXCR4, the number of dividing cells in the migratory stream and in the DG itself is reduced, and neurons appear to differentiate prematurely before reaching their target. Our findings indicate a role for the SDF-1/CXCR4 chemokine signaling system in DG morphogenesis. Finally, the DG is unusual as a site of adult neurogenesis. We find that both CXCR4 and SDF-1 are expressed in the adult DG, suggesting an ongoing role in DG morphogenesis.

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

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

Chemokines and their receptors in the central nervous system

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

Stromal cell-derived factor-1alpha induces astrocyte proliferation through the activation of extracellular signal-regulated kinases 1/2 pathway

Stromal cell-derived factor-1 (SDF-1), the ligand of the CXCR4 receptor, is a chemokine involved in chemotaxis and brain development that also acts as co-receptor for HIV-1 infection. We previously demonstrated that CXCR4 and SDF-1alpha are expressed in cultured type-I cortical rat astrocytes, cortical neurones and cerebellar granule cells. Here, we investigated the possible functions of CXCR4 expressed in rat type-I cortical astrocytes and demonstrated that SDF-1alpha stimulated the proliferation of these cells in vitro. The proliferative activity induced by SDF-1alpha in astrocytes was reduced by PD98059, indicating the involvement of extracellular signal-regulated kinases (ERK1/2) in the astrocyte proliferation induced by CXCR4 stimulation. This observation was further confirmed showing that SDF-1alpha treatment selectively activated ERK1/2, but not p38 or stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). Moreover, both astrocyte proliferation and ERK1/2 phosphorylation, induced by SDF-1alpha, were inhibited by pertussis toxin (PTX) and wortmannin treatment indicating the involvement of a PTX sensitive G-protein and of phosphatidyl inositol-3 kinase in the signalling of SDF-1alpha. In addition, Pyk2 activation represent an upstream components for the CXCR4 signalling to ERK1/2 in astrocytes. To our knowledge, this is the first report demonstrating a proliferative effect for SDF-1alpha in primary cultures of rat type-I astrocytes, and showing that the activation of ERK1/2 is responsible for this effect. These data suggest that CXCR4/SDF-1 should play an important role in physiological and pathological glial proliferation, such as brain development, reactive gliosis and brain tumour formation.

Developmental pattern of expression of the alpha chemokine stromal cell-derived factor 1 in the rat central nervous system

Stromal cell-derived factor 1 (SDF-1) is an alpha-chemokine that stimulates migration of haematopoietic progenitor cells and development of the immune system. SDF-1 is also abundantly and selectively expressed in the developing and mature CNS, as we show here. At embryonic day 15, SDF-1 transcripts were detected in the germinal periventricular zone and in the deep layer of the forming cerebral cortex. At birth, granule cells in the cerebellum and glial cells of the olfactory bulb outer layer showed an SDF-1 in situ hybridization signal that decreased progressively within the next 2 weeks. In other regions such as cortex, thalamus and hippocampus, SDF-1 transcripts detected at birth progressively increased in abundance during the postnatal period. SDF-1 protein was identified by immunoblot and/or immunocytochemistry in most brain regions where these transcripts were detected. SDF-1 was selectively localized in some thalamic nuclei and neurons of the fifth cortical layer as well as in pontine and brainstem nuclei which relay the nociceptive response. The presence of SDF-1 transcripts in cerebellar granule cells was correlated with their migration from the external to the inner granular layers with disappearance of the signal when migration was completed. In contrast, SDF1 mRNA signal increased during formation of the hippocampal dentate gyrus and stayed high in this region throughout life. The selective and regulated expression of SDF-1 in these regions suggests a role in precursor migration, neurogenesis and, possibly, synaptogenesis. Thus this alpha chemokine may be as essential to nervous system function as it is to the immune system.

Expression pattern of CXCR3, CXCR4, and CCR3 chemokine receptors in the developing human brain

Chemokine receptors are essential components of the immune and central nervous systems, but little is known about their distribution during development. We evaluated the distribution of 3 chemokine receptors: CXCR3, CXCR4, and CCR3 in the human developing brain. Of these, CXCR3 was the only receptor expressed in fetal brain at 26 wk of gestation and its expression was restricted to glial cells, endothelial cells, and the choroid plexus. Neuronal staining was only seen at term in the Purkinje cells of the cerebellum. CCR3 appeared only at term in both neurons and glial cells. The expression pattern of these 2 receptors in the late gestation and term resembled that of adults. CXCR4 could not be detected in the fetal brain on neurons nor on glial cells. By examining pediatric cases, we determined that CXCR4 expression commences sometimes between 3.5 and 4.5 yr. Two of the chemokine receptors examined, CCR3 and CXCR4, can be used as co-receptor together with CD4 for HIV entry, but neither was expressed during the second trimester of pregnancy. Our findings suggest that it is unlikely that CCR3 or CXCR4 play a major role in HIV-1 transmission in the fetal brain before 37 wk of gestation.

Characterization and visualization of [125I] stromal cell-derived factor-1alpha binding to CXCR4 receptors in rat brain and human neuroblastoma cells

Stromal cell-Derived Factor-1 (SDF-1alpha), binds to the seven-transmembrane G protein-coupled CXCR4 receptor and modulates cell migration, differentiation, and proliferation. CXCR4 has been reported to be expressed in various tissues including brain. Moreover, CXCR4 has recently been shown to be one of the coreceptors for HIV-1 infection which could be implicated in HIV encephalitis. In the present study, the binding properties and autoradiographic distribution of [125I]SDF-1alpha binding to CXCR4 were characterized in the adult rat brain. SDF-1alpha binding and CXCR4 coupling system were also studied in human neuroblastoma cell line SK-N-SH. The binding of [125I]SDF-1alpha on rat brain sections was specific, time-dependent and reversible. The highest densities of CXCR4 were detected in the choroid plexus of the lateral and the dorsal third ventricle. Lower densities of [125I]SDF-1alpha binding sites were observed in various brain regions including cerebral cortex, anterior olfactory nuclei, hippocampal formation, thalamic nuclei, blood vessels and pituitary gland. In the choroid plexus, the IC(50) and K(d) of [125I]SDF-1alpha binding were respectively 0.6 nM and 0. 36 nM. Similar IC(50) values were obtained in other brain structures. A CXCR4 antagonist, bicyclam, competed with SDF-1alpha binding (30% inhibition at 10(-6) M). In SK-N-SH cells, [125I]SDF-1alpha bound to CXCR4 with a K(d) of 5.0 nM and a maximal binding capacity of 460 fmol/mg of protein. SDF-1alpha induced a rapid and transient intracellular calcium increase in SK-N-SH cells. These findings suggest that CXCR4 is highly expressed in some brain structures and have a regulatory role in the nervous system. The significance of this expression in the brain parenchyma and more specifically in the choroid plexus remains to be clarified in the normal as well as in the infected brain.

Characterization of a Xenopus laevis CXC chemokine receptor 4: implications for hematopoietic cell development in the vertebrate embryo

Previous reports have shown that the Gi-protein-coupled CXC chemokine receptor 4 is activated by stromal cell-derived factor 1 (SDF-1). The receptor is present in many cell types and regulates a variety of cellular functions, including chemotaxis, adhesion, hematopoiesis, and organogenesis. To examine the role of CXCR4 as a regulator of organogenesis in the vertebrate embryo, we have isolated a cDNA encoding the Xenopus laevis homologue of CXCR4 (xCXCR4). The encoded polypeptide was functionally reconstituted with recombinant Gi2 in baculovirus-infected insect cells. Although xCXCR4 shares only 42% of its extracellular residues with mammalian CXCR4, it is indistinguishable from human CXCR4 in terms of its activation by human SDF-1alpha and SDF-1beta. The fact that only 19 of these residues are specifically present in the extracellular portions of CXCR4 suggests that these residues may be involved in recognizing SDF-1 and/or mediating CXCR4 activation by SDF-1. Xenopus CXCR4 mRNA expression was up-regulated during early neurula stages and remained high during early organogenesis. Whole mount in situ hybridization analysis showed abundant expression of xCXCR4 mRNA in the nervous system, including forebrain, hindbrain, and sensory organs, and in neural crest cells. xCXCR4 mRNA was also detected in the dorsal lateral plate, the first site of definitive hematopoiesis in the amphibian embryo corresponding to aorta-gonad-mesonephros or para-aortic splanchnopleura in mammals. This observation suggests that SDF-1 and CXCR4 are involved in regulating the migratory behavior of hematopoietic stem cells colonizing the larval or fetal liver. The hematopoietic defects observed in mice lacking SDF-1 or CXCR4 may, at least in part, be explained by a disturbance of this migration.

Differential signalling of the chemokine receptor CXCR4 by stromal cell-derived factor 1 and the HIV glycoprotein in rat neurons and astrocytes

CXCR4 is the Gi protein-linked seven-transmembrane receptor for the alpha chemokine stromal cell-derived factor 1 (SDF-1), a chemoattractant for lymphocytes. This receptor is highly conserved between human and rodent. CXCR4 is also a coreceptor for entry of human immunodeficiency virus (HIV) in T cells and is expressed in the CNS. To investigate how these CXCR4 ligands influence CNS development and/or function, we have examined the expression and signalling of this chemokine receptor in rat neurons and astrocytes in vitro. CXCR4 transcripts and protein are synthesized by both cell types and in E15 brain neuronal progenitors. In these progenitors, SDF-1, but not gp120 (the HIV glycoprotein), induced activation of extracellular signal regulated kinases (ERKs) 1/2 and a dose-dependent chemotactic response. This chemotaxis was inhibited by Pertussis toxin, which uncouples Gi proteins and the bicyclam AMD3100, a highly selective CXCR4 antagonist, as well as by an inhibitor of the MAP kinase pathway. In differentiated neurons, both SDF-1 and the glycoprotein of HIV, gp120, triggered activation of ERKs with similar kinetics. These effects were significantly inhibited by Pertussis toxin and the CXCR4 antagonist. Rat astrocytes also responded to SDF-1 signalling by phosphorylation of ERKs but, in contrast to cortical neurons, no kinase activation was induced by gp120. Thus neurons and astrocytes can respond differently to signalling by SDF-1 and/or gp120. As SDF-1 triggers directed migration of neuronal progenitors, this alpha chemokine may play a role in cortex development. In differentiated neurons, both natural and viral ligands of CXCR4 activate ERKs and may therefore influence neuronal function.