The peculiarities of the SDF-1/CXCL12 system: in some cells, CXCR4 and CXCR7 sing solos, in others, they sing duets

Astragaloside IV restores Th17/Treg balance via inhibiting CXCR4 to improve chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) has a high fatality rate and poses a great threat to human health. Astragaloside IV (AS-IV) is proven to attenuate cigarette smoke (CS)-induced pulmonary inflammation, based on which this research focuses on the mechanism of AS-IV in COPD.

METHODS

To evaluate the effects of AS-IV, CD4+ T cells received different concentrations of AS-IV. CD4+ T cell viability, T helper 17 (Th17)/regulatory T (Treg) markers and CXCR4 expressions in CD4+ T cells or spleen/lung tissues were detected by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide assay, quantitative real-time polymerase chain reaction and Western blot. The proportions of Treg and Th17 cells were assessed by flow cytometry. Enzyme-linked immune sorbent assay was employed to determine cytokine contents in serum and lung tissues.

RESULTS

AS-IV with concentration exceeding 40 µM inhibited CD4+ T cell viability. In vitro, AS-IV suppressed the expressions of CXCR4, retinoid-related orphan receptor γt (RORγt), and interleukin (IL)-17A as well as Th17 cells but promoted the expressions of forkhead box p3 (Foxp3) and IL-10 as well as Treg cells, while CXCR4 overexpression reversed the effects of AS-IV. In vivo, AS-IV alleviated COPD, and CS-induced Th17/Treg imbalance in mice and reduced CS-induced down-regulation of IL-10 in serum and lung tissues and Foxp3 and up-regulation of IL-1β, tumor necrosis factor alpha (TNF-α), IL-6, and IL-17A in serum and lung tissues and RORγt. AS-IV mitigated CS-induced CXCR4 up-regulation. Above effects of AS-IV on mice were offset by CXCR4 overexpression.

CONCLUSIONS

AS-IV restores Th17/Treg balance via impeding CXCR4 to ameliorate COPD.

Umbilical cord mesenchymal stem cells overexpressing CXCR7 facilitate treatment of ARDS-associated pulmonary fibrosis via inhibition of Notch/Jag1 mediated by the Wnt/β-catenin pathway

The therapeutic efficacy of umbilical cord mesenchymal stem cells (UCMSCs) in acute respiratory distress syndrome (ARDS) is mainly limited by the efficiency of homing of UCMSCs toward tissue damage. C-X-C chemokine receptor type 7 (CXCR7), which is involved in the mobilization of UCMSCs, is only expressed on the surface of a small proportion of UCMSCs. This study examined whether overexpression of CXCR7 in UCMSCs (UCMSCsOE-CXCR7) could improve their homing efficiency, and therefore, improve their effectiveness in fibrosis repair at the site of lung injury caused by ARDS. A lentiviral vector expressing CXCR7 was built and then transfect into UCMSCs. The impacts of CXCR7 expression of the proliferationand homing of UCMSCs were examined in a lipopolysaccharide-induced ARDS mouse model. The potential role and underlying mechanism of CXCR7 were examined by performing scratch assays, transwell assays, and immunoassays. The therapeutic dose and treatment time of UCMSCsOE-CXCR7 were directly proportional to their therapeutic effect on lung injury. In addition, overexpression of CXCR7 increased SDF-1-induced proliferation and migration of lung epithelial cells (Base-2b cells), and upregulation of CXCR7 inhibited α-SMA expression, suggesting that CXCR7 may have a role in alleviating pulmonary fibrosis caused by ARDS. Overexpression of CXCR7 in UCMSCs may improve their therapeutic effect of acute lung injury mouse, The mechanism of fibrosis repair by CXCR7 is inhibition of Jag1 via suppression of the Wnt/β-catenin pathway under the chemotaxis of SDF-1.

Gene Structure Analysis of Chemokines and Their Receptors in Allotetraploid Frog, Xenopus laevis

Chemokines, relatively small secreted proteins, are involved in cell migration and function in various biological events, including immunity, morphogenesis, and disease. Due to their nature, chemokines tend to be a target of hijacking of immunity by virus and therefore show an exceptionally high mutation rate. Xenopus laevis is considered an excellent model to investigate the effect of whole-genome duplication for gene family evolution. Because its allotetraploidization occurred around 17–18 million years ago, ancestral subgenomes L and S were well conserved. Based on the gene model of human and diploid frog Xenopus tropicalis, we identified 52 chemokine genes and 26 chemokine receptors in X. laevis. The retention rate of the gene in the X. laevis L and S subgenomes was 96% (45/47) and 68% (32/47), respectively. We conducted molecular phylogenetic analysis and found clear orthologies in all receptor genes but not in the ligand genes, suggesting rapid divergences of the ligand. dN/dS calculation demonstrated that dN/dS ratio greater than one was observed in the four ligand genes, cxcl8b.1.S, cxcl18.S, ccl21.S, and xcl1.L, but nothing in receptor genes. These results revealed that the whole-genome duplication promotes diversification of chemokine ligands in X. laevis while conserving the genes necessary for homeostasis, suggesting that selective pressure also supports a rapid divergence of the chemokines in amphibians.

Cellular crosstalk of glomerular endothelial cells and podocytes in diabetic kidney disease

Diabetic kidney disease (DKD) is a serious microvascular complication of diabetes and is the leading cause of end-stage renal disease (ESRD). Persistent proteinuria is an important feature of DKD, which is caused by the destruction of the glomerular filtration barrier (GFB). Glomerular endothelial cells (GECs) and podocytes are important components of the GFB, and their damage can be observed in the early stages of DKD. Recently, studies have found that crosstalk between cells directly affects DKD progression, which has prospective research significance. However, the pathways involved are complex and largely unexplored. Here, we review the literature on cellular crosstalk of GECs and podocytes in the context of DKD, and highlight specific gaps in the field to propose future research directions. Elucidating the intricates of such complex processes will help to further understand the pathogenesis of DKD and develop better prevention and treatment options.

C‑X‑C receptor 7 agonist acts as a C‑X‑C motif chemokine ligand 12 inhibitor to ameliorate osteoclastogenesis and bone resorption

The C-X-C receptor (CXCR) 7 agonist, VUF11207, is a chemical compound that binds specifically to CXCR7, and negatively regulates C-X-C motif chemokine ligand 12 (CXCL12) and CXCR4-induced cellular events. Lipopolysaccharide (LPS) can induce inflammatory cytokines and pathological bone loss. LPS also induces expression of CXCL12, enhancing sensitivity to receptor activator of NF-κB ligand (RANKL) and tumor necrosis factor-α (TNF-α) in vivo. RANKL and TNF-α induce the differentiation of osteoclasts into osteoclast precursors and bone resorption. The current study was performed to examine the effects of a CXCR7 agonist on osteoclastogenesis and bone resorption induced by LPS in vivo. In addition, the mechanisms underlying these in vivo effects were investigated by in vitro experiments. Eight-week-old male C57BL/6J mice were subcutaneously injected over the calvariae with LPS alone or LPS and CXCR7 agonist. After sacrifice, the number of osteoclasts and the bone resorption area were measured. In vitro experiments were performed to investigate the effects of CXCL12 and CXCR7 agonist on osteoclastogenesis induced by RANKL and TNF-α. Mice injected with LPS and CXCR7 agonist showed significantly reduced osteoclastogenesis and bone resorption compared with mice injected with LPS alone. Moreover, the CXCR7 agonist inhibited CXCL12 enhancement of RANKL- and TNF-α-induced osteoclastogenesis in vitro. Thus, CXCR7 agonist inhibited LPS-induced osteoclast-associated cytokines, such as RANKL and TNF-α, as well as RANKL- and TNF-α-induced osteoclastogenesis in vitro by modulating CXCL12-mediated enhancement of osteoclastogenesis. In conclusion, CXCR7 agonist reduced CXCL12-mediated osteoclastogenesis and bone resorption.

Atypical Roles of the Chemokine Receptor ACKR3/CXCR7 in Platelet Pathophysiology

The manifold actions of the pro-inflammatory and regenerative chemokine CXCL12/SDF-1α are executed through the canonical GProteinCoupledReceptor CXCR4, and the non-canonical ACKR3/CXCR7. Platelets express CXCR4, ACKR3/CXCR7, and are a vital source of CXCL12/SDF-1α themselves. In recent years, a regulatory impact of the CXCL12-CXCR4-CXCR7 axis on platelet biogenesis, i.e., megakaryopoiesis, thrombotic and thrombo-inflammatory actions have been revealed through experimental and clinical studies. Platelet surface expression of ACKR3/CXCR7 is significantly enhanced following myocardial infarction (MI) in acute coronary syndrome (ACS) patients, and is also associated with improved functional recovery and prognosis. The therapeutic implications of ACKR3/CXCR7 in myocardial regeneration and improved recovery following an ischemic episode, are well documented. Cardiomyocytes, cardiac-fibroblasts, endothelial lining of the blood vessels perfusing the heart, besides infiltrating platelets and monocytes, all express ACKR3/CXCR7. This review recapitulates ligand induced differential trafficking of platelet CXCR4-ACKR3/CXCR7 affecting their surface availability, and in regulating thrombo-inflammatory platelet functions and survival through CXCR4 or ACKR3/CXCR7. It emphasizes the pro-thrombotic influence of CXCL12/SDF-1α exerted through CXCR4, as opposed to the anti-thrombotic impact of ACKR3/CXCR7. Offering an innovative translational perspective, this review also discusses the advantages and challenges of utilizing ACKR3/CXCR7 as a potential anti-thrombotic strategy in platelet-associated cardiovascular disorders, particularly in coronary artery disease (CAD) patients post-MI.

Emerging Roles of the Atypical Chemokine Receptor 3 (ACKR3) in Cardiovascular Diseases

Chemokines, and their receptors play a crucial role in the pathophysiology of cardiovascular diseases (CVD). Chemokines classically mediate their effects by binding to G-protein-coupled receptors. The discovery that chemokines can also bind to atypical chemokine receptors (ACKRs) and initiate alternative signaling pathways has changed the paradigm regarding chemokine-related functions. Among these ACKRs, several studies have highlighted the exclusive role of ACKR3, previously known as C-X-C chemokine receptor type 7 (CXCR7), in CVD. Indeed, ACKR3 exert atheroprotective, cardioprotective and anti-thrombotic effects through a wide range of cells including endothelial cells, platelets, inflammatory cells, fibroblasts, vascular smooth muscle cells and cardiomyocytes. ACKR3 functions as a scavenger receptor notably for the pleiotropic chemokine CXCL12, but also as a activator of different pathways such as β-arrestin-mediated signaling or modulator of CXCR4 signaling through the formation of ACKR3-CXCR4 heterodimers. Hence, a better understanding of the precise roles of ACKR3 may pave the way towards the development of novel and improved therapeutic strategies for CVD. Here, we summarize the structural determinant characteristic of ACKR3, the molecules targeting this receptor and signaling pathways modulated by ACKR3. Finally, we present and discuss recent findings regarding the role of ACKR3 in CVD.

CXCL12 in Pancreatic Cancer: Its Function and Potential as a Therapeutic Drug Target

Simple Summary

Pancreatic cancer is a challenging disease to treat effectively. Fibroblasts associated with pancreatic cancer contribute to disease progression by secreting factors that enhance tumor cell survival and help tumor cells avoid detection by the immune system. This overview focuses on a chemokine, CXCL12, produced by cancer-associated fibroblasts and how CXCL12 signaling enhances pancreatic cancer progression by contributing to various hallmarks of cancer including, but not limited to, tumor growth and evasion of immune response. These pro-oncogenic functions of CXCL12 make it an attractive target in pancreatic cancer. We discuss the different approaches in development to therapeutically target CXCL12 and finally propose a novel approach, the use of the farnesyl transferase inhibitor tipifarnib to inhibit CXCL12 expression in pancreatic fibroblasts.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a disease with limited therapeutic options and dismal long-term survival. The unique tumor environment of PDAC, consisting of desmoplastic stroma, immune suppressive cells, and activated fibroblasts, contributes to its resistance to therapy. Activated fibroblasts (cancer-associated fibroblasts and pancreatic stellate cells) secrete chemokines and growth factors that support PDAC growth, spread, chemoresistance, and immune evasion. In this review, we focus on one such chemokine, CXCL12, secreted by the cancer-associated fibroblasts and discuss its contribution to several of the classical hallmarks of PDAC and other tumors. We review the various therapeutic approaches in development to target CXCL12 signaling in PDAC. Finally, we propose an unconventional use of tipifarnib, a farnesyl transferase inhibitor, to inhibit CXCL12 production in PDAC.

An overview of mesenchymal stem cells and their potential therapeutic benefits in cancer therapy

There has been increased interest in using stem cells for regenerative medicine and cancer therapy in the past decade. Mesenchymal stem cells (MSCs) are among the most studied stem cells due to their unique characteristics, such as self-renewal and developmental potency to differentiate into numerous cell types. MSC use has fewer ethical challenges compared with other types of stem cells. Although a number of studies have reported the beneficial effects of MSC-based therapies in treating various diseases, their contribution to cancer therapy remains controversial. The behaviour of MSCs is determined by the interaction between intrinsic transcriptional genes and extrinsic environmental factors. Numerous studies continue to emerge, as there is no denying the potential of MSCs to treat a wide variety of human afflictions. Therefore, the present review article provided an overview of MSCs and their differences compared with embryonic stem cells, and described the molecular mechanisms involved in maintaining their stemness. In addition, the article examined the therapeutic application of stem cells in the field of cancer. The present article also discussed the current divergent roles of MSCs in cancer therapy and the future potential in this field.

EGR1 as a potential marker of prognosis in extranodal NK/T-cell lymphoma

Extranodal natural killer T-cell lymphoma (ENKTL) is an aggressive malignancy with a dismal prognosis. In the present study, gene expression profiling was performed to provide more information on ENKTL molecular signature and offer a rationale for further investigation of prognostic markers in ENKTL. NanoString nCounter Analysis encompassing 133 target genes was used to compare gene expression levels of 43 ENKTL tumor samples. The majority of the patients were under 60 years of age (79.1%); 32 (74.4%) patients had nasal type ENKTL and 23 patients (53.5%) had intermediate/high risk ENKTL based on the prognostic index for natural killer cell lymphoma (PINK). The median follow-up was 15.9 months and the median overall survival (OS) was 16.1 months (95% CI 13.0-69.8). EGR1 upregulation was consistently identified in the localized stage with a low risk of prognostic index based on the PINK. Among the six significantly relevant genes for EGR1 expression, high expression levels of genes, including CD59, GAS1, CXCR7, and RAMP3, were associated with a good survival prognosis. The in vitro test showed EGR1 modulated the transcriptional activity of the target genes including CD59, GAS1, CXCR7, and RAMP3. Downregulation of EGR1 and its target genes significantly inhibited apoptosis and decreased chemosensitivity and attenuated radiation-induced apoptosis. The findings showed EGR1 may be a candidate for prognostic markers in ENKTL. Considerable additional characterization may be necessary to fully understand EGR1.

Identification of CXCL11 as part of chemokine network controlling skeletal muscle development

The chemokine, CXCL12, and its receptors, CXCR4 and CXCR7, play pivotal roles during development and maintenance of limb muscles. CXCR7 additionally binds CXCL11, which uses CXCR3 as its prime receptor. Based on this cross-talk, we investigate whether CXCL11 would likewise affect development and/or function of skeletal muscles. Western blotting and immunolabelling demonstrated the developmentally restricted expression of CXCL11 in rat limb muscles, which was contrasted by the continuous expression of its receptors in proliferating and differentiating C2C12 cells as well as in late embryonic to adult rat limb muscle fibres. Consistent with a prime role in muscle formation, functional studies identified CXCL11 as a potent chemoattractant for undifferentiated C2C12 cells and further showed that CXCL11 does neither affect myoblast proliferation and differentiation nor metabolic/catabolic pathways in formed myotubes. The use of selective receptor antagonists unravelled complementary effects of CXCL11 and CXCL12 on C2C12 cell migration, which either require CXCR3/CXCR7 or CXCR4, respectively. Our findings provide new insights into the chemokine network controlling skeletal muscle development and function and, thus, might provide a base for future therapies of muscular diseases.

Immune Adaptation of Colorectal Cancer Stem Cells and Their Interaction With the Tumor Microenvironment

Metastasis is the primary cause of death in colorectal cancer (CRC) patients. Emerging evidence has shown that CRC stem cells (CRCSCs) play a significant role in metastatic dissemination and tumor recurrence. However, strategies for targeting CRCSCs are limited because CRCSCs are resistant to therapeutic interventions and because the tumor microenvironment (TME) provides a supportive niche. Moreover, growing evidence highlights the critical role of CRCSCs in immune adaptation and modulation of the TME. CRCSCs escape immune surveillance by avoiding recognition by the innate immune system and shaping the TME through exosomes, cytokines, and chemokines to generate an immunosuppressive niche that facilitates cancer progression. In this review, we summarize studies investigating the immunomodulatory properties of CRCSCs and their underlying mechanisms in order to improve the efficacy of treatment strategies against advanced CRC.

Role of the stromal cell derived factor-1 in the biological functions of endothelial progenitor cells and its underlying mechanisms

Stromal cell derived factor-1 (SDF-1) is a chemokine that plays a critical role in the homing of stem and progenitor cells, including endothelial progenitor cells (EPCs). However, little research has been undertaken to evaluate the roles of SDF-1 in the biological functions of EPCs and related signaling pathways. The present study aimed to investigate the biological functions of EPCs in response to SDF-1, as well as the underlying mechanisms. The effects of SDF-1 treatment on EPC proliferation, migration and tube formation were assessed by performing MTS, Transwell and in vitro tube formation assays, respectively. The phosphorylation status of Akt and ERK was evaluated by western blotting. The present results indicated that SDF-1 treatment enhanced EPC proliferation, migration and tube formation compared with the control group. Furthermore, SDF-1-induced EPC proliferation was significantly reduced following treatment with a C-X-C Motif Chemokine Receptor 4 antagonist (AMD3100), a PI3K inhibitor (LY294002) and the mitogen-activated protein kinase kinase inhibitor (MEK; PD98059). SDF-1-induced migration and angiogenesis were significantly suppressed by the PI3K inhibitor, but not the MEK inhibitor. Moreover, SDF-1 significantly increased the protein expression levels of phosphorylated (p)-Akt and p-ERK; however, SDF-1-induced effects on protein expression were suppressed by AMD3100, LY294002 and PD98059. Thus, SDF-1-induced EPC proliferation was mediated by activation of the Akt and ERK signaling pathways, whereas SDF-1-mediated EPC migration and tube formation only involved activation of the Akt signaling pathway.

Overexpression of CXCR7 accelerates tumor growth and metastasis of lung cancer cells

Background

Under physiological conditions, CXCL12 modulates cell proliferation, survival, angiogenesis, and migration mainly through CXCR4. Interestingly, the newly discovered receptor CXCR7 for CXCL12 is highly expressed in many tumor cells as well as tumor-associated blood vessels, although the level of CXCR7 in normal cells is low. Recently, many studies have suggested that CXCR7 promotes cell growth and metastasis in more than 20 human malignancies, among which lung cancer is the leading cause of cancer-associated deaths worldwide. Thus, the mechanism of CXCR7 in the progression of lung cancer is urgently needed.

Methods

First, we explored CXCR4 and CXCR7 expression in human lung cancer specimens and cell lines by immunohistochemistry, western blot and flow cytometry. Then, we chose the human lung adenocarcinoma cell line A549 that stably overexpressed CXCR7 through the way of lentivirus-mediated transduction. Next, “wound healing” assay and transwell assay were applied to compare the cell migration and invasion ability, and stripe assay was used to evaluate the cell polarization. Last, our team established a mouse xenograft model of human lung cancer and monitored tumor proliferation and metastasis by firefly luciferase bioluminescence imaging in SCID/Beige mice.

Results

In clinical lung cancer samples, CXCR7 expression was almost not detected in normal tissue but upregulated in lung tumor tissue, whereas, CXCR4 was highly expressed in both normal and tumor tissues. Furthermore, overexpression of CXCR7 enhanced A549 cell migration and polarization in vitro. Besides, mouse xenograft model of human lung cancer showed that CXCR7 promoted primary lung tumor’s growth and metastasis to the second organ, such as liver or bone marrow in SCID/Beige mice in vivo.

Conclusions

This study describes the multiple functions of CXCR7 in lung cancer. Thus, these results suggest that CXCR7 may be a malignancy marker and may provide a novel target for anticancer therapy.

Mechanisms by Which the MBD2/miR-301a-5p/CXCL12/CXCR4 Pathway Regulates Acute Exacerbations of Chronic Obstructive Pulmonary Disease

Background

Chronic obstructive pulmonary disease (COPD) is characterized by irreversible expiratory airflow obstruction, and its chronic course is worsened by recurrent acute exacerbations. Our previous microarray assay identified microRNA (miR)-301a-5p as being associated with progression of acute exacerbation of COPD (AE-COPD); however, the mechanism underlying COPD pathogenesis remains unknown.

Methods

Samples of serum and peripheral blood mononuclear cells (PBMCs) were isolated from healthy control subjects and patients with stable COPD (R-COPD) or with an acute exacerbation of COPD (AE-COPD). Human HULEC-5a and human bronchial epithelial (HBE) cells were transfected with methyl-CpG-binding domain protein 2 (MBD2), sh-MBD2, miR-301a-5p mimics or an inhibitor, and then stimulated with cigarette smoke extract (CSE). Conditioned medium co-culture assays were performed by adding the supernatant of medium derived from HULEC-5a cells transfected with miR-301a-5p mimics or inhibitor into wells containing si-c-x-c motif chemokine receptor 4 (CXCR4)-transfected-lung fibroblasts or human leukemic THP-1 cell line macrophages. Transwell assays were performed to analyze cell migration.

Results

Our analysis of clinical samples showed that decreased miR-301a-5p levels in patients with AE-COPD were positively correlated with levels of MBD2 expression, but negatively correlated with levels of chemokine ligand C-X-C motif chemokine ligand 12 (CXCL12) expression. MBD2 overexpression significantly promoted miR-301a-5p production, but suppressed CXCL12 production in HULEC-5a and HBE cells. CXCL12 was confirmed to be a direct target of miR-301a-5p. CXCR4 knockdown significantly enhanced the suppressive effect of miR-301a-5p mimics and attenuated the promotional effects of the miR-301a-5p inhibitor on the migration of circulating fibroblasts and macrophages, as well as the expression levels of phospho-mitogen-activated protein kinase (p-MEK) and phospho-protein kinase B (p-AKT).

Conclusion

In summary, the MBD2/miR-301a-5p/CXCL12/CXCR4 pathway was shown to affect the migration of lung fibroblasts and monocyte-derived macrophages, which may play an important role during COPD exacerbations.

Chemokine receptor CXCR7 non-cell-autonomously controls pontine neuronal migration and nucleus formation

Long distance tangential migration transports neurons from their birth places to distant destinations to be incorporated into neuronal circuits. How neuronal migration is guided during these long journeys is still not fully understood. We address this issue by studying the migration of pontine nucleus (PN) neurons in the mouse hindbrain. PN neurons migrate from the lower rhombic lip first anteriorly and then turn ventrally near the trigeminal ganglion root towards the anterior ventral hindbrain. Previously we showed that in mouse depleted of chemokine receptor CXCR4 or its ligand CXCL12, PN neurons make their anterior-to-ventral turn at posteriorized positions. However, the mechanism that spatiotemporally controls the anterior-to-ventral turning is still unclear. Furthermore, the role of CXCR7, the atypical receptor of CXCL12, in pontine migration has yet to be examined. Here, we find that the PN is elongated in Cxcr7 knockout due to a broadened anterior-to-ventral turning positions. Cxcr7 is not expressed in migrating PN neurons en route to their destinations, but is strongly expressed in the pial meninges. Neuroepithelium-specific knockout of Cxcr7 does not recapitulate the PN phenotype in Cxcr7 knockout, suggesting that CXCR7 acts non-cell-autonomously possibly from the pial meninges. We show further that CXCR7 regulates pontine migration by modulating CXCL12 protein levels.

Exosomes from SIRT1-Overexpressing ADSCs Restore Cardiac Function by Improving Angiogenic Function of EPCs

Acute myocardial infarction (AMI) is one of the leading causes of mortality in cardiovascular diseases. The aim of this study was to investigate whether exosomes from Sirtuin 1 (SIRT1)-overexpressing adipose-derived stem cells (ADSCs) had a protective effect on AMI. The expression of C-X-C chemokine receptor type 7 (CXCR7) was significantly downregulated in peripheral blood endothelial progenitor cells (EPCs) from AMI patients (AMI-EPCs) compared with that in healthy donors, which coincided with impaired tube formation. The exosomes from SIRT1 overexpression in ADSCs (ADSCs-SIRT1-Exos) increased the expression of C-X-C motif chemokine 12 (CXCL12) and nuclear factor E2 related factor 2 (Nrf2) in AMI-EPCs, which promoted migration and tube formation of AMI-EPCs, and overexpression of CXCR7 helped AMI-EPCs to restore the function of cell migration and tube formation. Moreover, CXCR7 was downregulated in the myocardium of AMI mice, and knockout of CXCR7 exacerbated AMI-induced impairment of cardiovascular function. Injection of ADSCs-SIRT1-Exos increased the survival and promoted the recovery of myocardial function with reduced infarct size and post-AMI left ventricular remodeling, induced vasculogenesis, and decreased AMI-induced myocardial inflammation. These findings showed that ADSCs-SIRT1-Exos may recruit EPCs to the repair area and that this recruitment may be mediated by Nrf2/CXCL12/CXCR7 signaling.

Beneficial Effect of IL-4 and SDF-1 on Myogenic Potential of Mouse and Human Adipose Tissue-Derived Stromal Cells

Under physiological conditions skeletal muscle regeneration depends on the satellite cells. After injury these cells become activated, proliferate, and differentiate into myofibers reconstructing damaged tissue. Under pathological conditions satellite cells are not sufficient to support regeneration. For this reason, other cells are sought to be used in cell therapies, and different factors are tested as a tool to improve the regenerative potential of such cells. Many studies are conducted using animal cells, omitting the necessity to learn about human cells and compare them to animal ones. Here, we analyze and compare the impact of IL-4 and SDF-1, factors chosen by us on the basis of their ability to support myogenic differentiation and cell migration, at mouse and human adipose tissue-derived stromal cells (ADSCs). Importantly, we documented that mouse and human ADSCs differ in certain reactions to IL-4 and SDF-1. In general, the selected factors impacted transcriptome of ADSCs and improved migration and fusion ability of cells in vitro. In vivo, after transplantation into injured muscles, mouse ADSCs more eagerly participated in new myofiber formation than the human ones. However, regardless of the origin, ADSCs alleviated immune response and supported muscle reconstruction, and cytokine treatment enhanced these effects. Thus, we documented that the presence of ADSCs improves skeletal muscle regeneration and this influence could be increased by cell pretreatment with IL-4 and SDF-1.

IL-4 and SDF-1 Increase Adipose Tissue-Derived Stromal Cell Ability to Improve Rat Skeletal Muscle Regeneration

Skeletal muscle regeneration depends on the satellite cells, which, in response to injury, activate, proliferate, and reconstruct damaged tissue. However, under certain conditions, such as large injuries or myopathies, these cells might not sufficiently support repair. Thus, other cell populations, among them adipose tissue-derived stromal cells (ADSCs), are tested as a tool to improve regeneration. Importantly, the pro-regenerative action of such cells could be improved by various factors. In the current study, we tested whether IL-4 and SDF-1 could improve the ability of ADSCs to support the regeneration of rat skeletal muscles. We compared their effect at properly regenerating fast-twitch EDL and poorly regenerating slow-twitch soleus. To this end, ADSCs subjected to IL-4 and SDF-1 were analyzed in vitro and also in vivo after their transplantation into injured muscles. We tested their proliferation rate, migration, expression of stem cell markers and myogenic factors, their ability to fuse with myoblasts, as well as their impact on the mass, structure and function of regenerating muscles. As a result, we showed that cytokine-pretreated ADSCs had a beneficial effect in the regeneration process. Their presence resulted in improved muscle structure and function, as well as decreased fibrosis development and a modulated immune response.

CXCL11 promotes tumor progression by the biased use of the chemokine receptors CXCR3 and CXCR7

The chemokine, CXCL11, is highly expressed in different solid tumors and controls tumor growth, metastasis, and lymphocyte infiltration. Although of potential clinical interest, it is presently unknown whether these tumor-promoting activities involve the CXCL11 receptors, CXCR3 and/or CXCR7. This issue is further intrigued by the fact that CXCR3 exists in the two functionally divergent splice variants, CXCR3A and CXCR3B, which exert pro- and anti-tumorigenic influences, respectively. To unravel the role of the various CXCL11 receptors in tumor progression, we have now defined their role in CXCL11-induced chemotaxis of the tumor cell lines, A549, C33-A, DLD-1, MDA-MB-231, and PC-3. CXCL11-induced cell migration was either sensitive to the CXCR3 antagonist, ÀMG487 (DLD-1), the CXCR7 antagonist, CCX771 (C33-A, PC-3), or both (A549, MDA-231). Moreover, in C33-A and PC-3 cells, but not in the other tumor cells, pharmacological activation and inhibition of CXCR3B prevented and potentiated CXCL11-induced cell migration, respectively. Both immunocytochemistry and Western blot analysis finally revealed that the observed cell type specific organization of the CXCL11 system is not the result of differences in expression levels or subcellular location of CXCL11 receptors. Our findings imply that the therapeutic use of CXCR3 antagonists in cancer patients requires exact knowledge of the organization of the CXCR3 system in the respective tumor.

CD44v6 engages in colorectal cancer progression

CD44 is a transmembrane glycoprotein. When the CD44 gene is expressed, its pre-messenger RNA (mRNA) can be alternatively spliced into mature mRNAs that encode several CD44 isoforms. The mRNA assembles with ten standard exons, and the sixth variant exon encodes CD44v6, which engages in a variety of biological processes, including cell growth, apoptosis, migration, and angiogenesis. Mechanistically, CD44v6 interacts with hyaluronic acid (HA) or osteopontin, or it acts as a coreceptor for various cytokines, such as epidermal growth factor, vascular endothelial growth factor, hepatocyte growth factor, and C-X-C motif chemokine 12. In this context, the receptor tyrosine kinase or G protein-coupled receptor-associated signaling pathways, including mitogen-activated protein kinase/extracellular-signal-regulated kinase and phosphoinositide-3-kinase/Akt, are activated. Using these actions, homeostasis or regeneration can be facilitated among normal tissues. However, overexpression of the mature mRNA encoding CD44v6 can induce cancer progression. For example, CD44v6 assists colorectal cancer stem cells in colonization, invasion, and metastasis. Overexpression of CD44v6 predicts poor prognosis in patients with colorectal cancer, as patients with a large number of CD44v6-positive cells in their tumors are generally diagnosed at late stages. Thus, the clinical significance of CD44v6 in colorectal cancer deserves consideration. Preclinical results have indicated satisfactory efficacies of anti-CD44 therapy among several cancers, including prostate cancer, pancreatic cancer, and gastric cancer. Moreover, clinical trials aiming to evaluate the pharmacokinetics, pharmacodynamics, efficacy, and toxicity of a commercialized anti-CD44 monoclonal antibody developed by Roche (RO5429083) have been conducted among patients with CD44-expressing malignant tumors, and a clinical trial focusing on the dose escalation of this antibody is ongoing. Thus, we are hopeful that anti-CD44 therapy will be applied in the treatment of colorectal cancer in the future.

CXCR7 expression in diffuse large B-cell lymphoma identifies a subgroup of CXCR4+ patients with good prognosis

The CXCR4/CXCL12 axis has been extensively associated with different types of cancer correlating with higher aggressiveness and metastasis. In diffuse large B-cell lymphoma (DLBCL), the expression of the chemokine receptor CXCR4 is involved in the dissemination of malignant B cells and is a marker of poor prognosis. CXCR7 is a chemokine receptor that binds to the same ligand as CXCR4 and regulates de CXCR4-CXCL12 axis. These findings together with the report of CXCR7 prognostic value in several tumor types, led us to evaluate the expression of CXCR7 in diffuse large B-cell lymphoma biopsies. Here, we describe that CXCR7 receptor is an independent prognostic factor that associates with good clinical outcome. Moreover, the expression of CXCR7 associates with increased survival in CXCR4+ but not in CXCR4- DLBCL patients. Thus, the combined immunohistochemical evaluation of both CXCR7 and CXCR4 expression in DLBCL biopsies may improve their prognostic value as single markers. Finally, we show that CXCR7 overexpression in vitro is able to diminish DLBCL cell survival and increase their sensitivity to antitumor drugs. Hence, further studies on the CXCR7 receptor may establish its role in DLBCL and the molecular mechanisms that modulate CXCR4 activity.

Mesenchymal stem cells over-expressing cxcl12 enhance the radioresistance of the small intestine

The chemokine C-X-C motif chemokine 12 (CXCL12) greatly impacts various biological processes in mammals, including cell survival, growth and migration. Mesenchymal stem cells (MSCs) are promising tools for carrying foreign genes to treat radiation-induced injuries in the intestinal epithelium. In this study, human adipose-derived MSCs were constructed to over-express the mouse cxcl12 gene to treat such injuries. In vitro, because of the high levels of mouse CXCL12 in conditioned medium produced by mouse cxcl12 gene-modified cells, phosphorylation of Akt at Ser473 and Erk1/2 at Thr202/Thr204 was increased within crypt cells of irradiated organoids compared with unmodified controls. Moreover, intracellular stabilization of β-catenin was achieved after treatment of mouse cxcl12 gene-modified cells with conditioned medium. As a result, survival of crypt cells was maintained and their proliferation was promoted. When delivering mouse cxcl12 gene-modified cells into irradiated BALB/c nude mice, mice were rescued despite the clearance of cells from the host within 1 week. Irradiated mice that received mouse cxcl12 gene-modified MSCs exhibited reduced serum levels of interleukin-1α (IL-1α) and IL-6 as well as elevated levels of CXCL12. Additionally, epithelial recovery from radiation stress was accelerated compared with the irradiated-alone controls. Moreover, mouse cxcl12 gene-modified MSCs were superior to unmodified cells at strengthening host repair responses to radiation stress as well as presenting increased serum CXCL12 levels and decreased serum IL-1α levels. Furthermore, the number of crypt cells that were positive for phosphorylated Akt at Ser473 and phosphorylated Erk1/2 at Thr202/Thr204 increased following treatment with mouse cxcl12 gene-modified MSCs. Thus, cxcl12 gene-modified MSCs confer radioresistance to the intestinal epithelium.

The 5T4 oncofetal glycoprotein does not act as a general organizer of the CXCL12 system in cancer cells

The chemokine, CXCL12, promotes cancer growth and metastasis through interaction with either CXCR4 and/or CXCR7. This tumor-specific organization of the CXCL12 system obscures current therapeutic approaches, aiming at the selective inactivation of CXCL12 receptors. Since it has been previously suggested that the cellular use of CXCR4 or CXCR7 is dictated by the 5T4 oncofetal glycoprotein, we have now tested whether 5T4 would represent a general and reliable marker for the organization of the CXCL12 system in cancer cells. The CXCR4 antagonist, AMD3100, as well as the CXCR7 antagonist, CCX771, demonstrated that the cancer cell lines A549, C33A, DLD-1, MDA-231, and PC-3 use either CXCR7 and/or CXCR4 for mediating CXCL12-induced chemotaxis and cell proliferation. The use of CXCL12 receptors as well as their subcellular localization remained unchanged in most cell lines following siRNA-mediated depletion of 5T4. In distinct cell lines, inhibition of 5T4 expression, however, modulated tumor cell migration and proliferation per se. Collectively our analyses fail to demonstrate general organizational influences of 5T4 of the CXCL12 system in different cancer cell lines, and, hence, dismiss its future use as a diagnostic marker.

Chemokine receptor 7 overexpression promotes mesenchymal stem cell migration and proliferation via secreting Chemokine ligand 12

Great interest has been shown in mesenchymal stem cell (MSC) therapy in a wide variety of clinical domains. However, the therapeutic efficiency depends on the proliferation and migration of MSCs. Chemokine receptors are involved in regulating the proliferation and migration to the specific organs of MSCs in different microenvironments. CXC receptor seven (CXCR7), a newly discovered Chemokine ligand 12 (CXCL12) receptor, has organ specificity for tumour migration. We hypothesized that CXCR7 expression affects proliferation and migration of MSCs. In present study, we constructed long-term and stable mMSCs lines overexpressing and suppressing CXCR7 modifications with lentiviral vectors. The transduction efficiencies, mRNA and protein expression of CXCR7 were significantly regulated. CXCR7 gene overexpression promoted mMSCs proliferation and migration, whereas suppressing CXCR7 had the opposite effect. Additional CXCL12 improved the vertical migration of mMSCs. The overexpression of CXCR7 increased the MSC-secreted CXCL12, VCAM-1, CD44 and MMP2 levels, which contributed to the improvement of mMSC proliferation and migration. Therefore, overexpressing CXCR7 improved the proliferation and migration of mMSCs, which may be attributable to the CXCL12 secreted by MSCs, leading to a positive feedback loop for CXCL12/CXCR7 axis. Our results may provide a potential method for improving the treatment effectiveness of mMSCs by overexpressing CXCR7.

The chemokines CXCL12 and CXCL14 differentially regulate connective tissue markers during limb development

Connective tissues (CT) support and connect organs together. Understanding the formation of CT is important, as CT deregulation leads to fibrosis. The identification of CT specific markers has contributed to a better understanding of CT function during development. In developing limbs, Osr1 transcription factor is involved in the differentiation of irregular CT while the transcription factor Scx labels tendon. In this study, we show that the CXCL12 and CXCL14 chemokines display distinct expression pattern in limb CT during chick development. CXCL12 positively regulates the expression of OSR1 and COL3A1, a collagen subtype of irregular CT, while CXCL14 activates the expression of the tendon marker SCX. We provide evidence that the CXCL12 effect on irregular CT involves CXCR4 receptor and vessels. In addition, the expression of CXCL12, CXCL14 and OSR genes is suppressed by the anti-fibrotic BMP signal. Finally, mechanical forces, known to be involved in adult fibrosis, control the expression of chemokines, CT-associated transcription factors and collagens during limb development. Such unexpected roles of CXCL12 and CXCL14 chemokines during CT differentiation can contribute to a better understanding of the fibrosis mechanisms in adult pathological conditions.

The Role of SDF-1/CXCR4/CXCR7 in Neuronal Regeneration after Cerebral Ischemia

Stromal cell-derived factor-1 is a chemoattractant produced by bone marrow stromal cell lines. It is recognized as a critical factor in the immune and central nervous systems (CNSs) as well as exerting a role in cancer. SDF-1 activates two G protein-coupled receptors, CXCR4 and CXCR7; these are expressed in both developing and mature CNSs and participate in multiple physiological and pathological events, e.g., inflammatory response, neurogenesis, angiogenesis, hematopoiesis, cancer metastasis, and HIV infection. After an ischemic stroke, SDF-1 levels robustly increase in the penumbra regions and participate in adult neural functional repair. Here we will review recent findings about SDF-1 and its receptor, analyse their functions in neurogeneration after brain ischemic injury: i.e., how the system promotes the proliferation, differentiation and migration of neural precursor cells and mediates axonal elongation and branching.

CXCL12 and CXCR7 are relevant targets to reverse cell adhesion-mediated drug resistance in multiple myeloma

Cell adhesion-mediated drug resistance (CAM-DR) by the bone marrow (BM) is fundamental to multiple myeloma (MM) propagation and survival. Targeting BM protection to increase the efficacy of current anti-myeloma treatment has not been extensively pursued. To extend the understanding of CAM-DR, we hypothesized that the cytotoxic effects of novel anti-myeloma agents may be abrogated by the presence of BM stroma cells (BMSCs) and restored by addition of the CXCL12 antagonist NOX-A12 or the CXCR4 inhibitor plerixafor. Following this hypothesis, we evaluated different anti-myeloma agents alone, with BMSCs and when combined with plerixafor or NOX-A12. We verified CXCR4, CD49d (also termed ITGA4) and CD44 as essential mediators of BM adhesion on MM cells. Additionally, we show that CXCR7, the second receptor of stromal-derived-factor-1 (CXCL12), is highly expressed in active MM. Co-culture proved that co-treatment with plerixafor or NOX-A12, the latter inhibiting CXCR4 and CXCR7, functionally interfered with MM chemotaxis to the BM. This led to the resensitization of MM cells to the anti-myeloma agents vorinostat and pomalidomide and both proteasome inhibitors bortezomib and carfilzomib. Within a multicentre phase I/II study, NOX-A12 was tested in combination with bortezomib-dexamethasone, underlining the feasibility of NOX-A12 as an active add-on agent to antagonize myeloma CAM-DR.

Emerging roles of the CXCL12/CXCR4 axis in pancreatic cancer progression and therapy

Chemokine networks regulate a variety of cellular, physiological, and immune processes. These normal functions can become appropriated by cancer cells to facilitate a more hospitable niche for aberrant cells by enhancing growth, proliferation, and metastasis. This is especially true in pancreatic cancer, where chemokine signaling is a vital component in the development of the supportive tumor microenvironment and the signaling between the cancer cells and surrounding stromal cells. Although expression patterns vary among cancer types, the chemokine receptor CXCR4 has been implicated in nearly every major malignancy and plays a prominent role in pancreatic cancer development and progression. This receptor, in conjunction with its primary chemokine ligand CXCL12, promotes pancreatic cancer development, invasion, and metastasis through the management of the tumor microenvironment via complex crosstalk with other pathways. Thus, CXCR4 likely contributes to the poor prognoses observed in patients afflicted with this malignancy. Recent exploration of combination therapies with CXCR4 antagonists have demonstrated improved outcomes, and abolishing the contribution of this pathway may prove crucial to effectively treat pancreatic cancer at both the primary tumor and metastases.

Elevating CXCR7 Improves Angiogenic Function of EPCs via Akt/GSK-3β/Fyn-Mediated Nrf2 Activation in Diabetic Limb Ischemia

RATIONALE

Endothelial progenitor cells (EPCs) respond to stromal cell-derived factor 1 (SDF-1) through chemokine receptors CXCR7 and CXCR4. Whether SDF-1 receptors involves in diabetes mellitus-induced EPCs dysfunction remains unknown.

OBJECTIVE

To determine the role of SDF-1 receptors in diabetic EPCs dysfunction.

METHODS AND RESULTS

CXCR7 expression, but not CXCR4 was reduced in EPCs from db/db mice, which coincided with impaired tube formation. Knockdown of CXCR7 impaired tube formation of EPCs from normal mice, whereas upregulation of CXCR7 rescued angiogenic function of EPCs from db/db mice. In normal EPCs treated with oxidized low-density lipoprotein or high glucose also reduced CXCR7 expression, impaired tube formation, and increased oxidative stress and apoptosis. The damaging effects of oxidized low-density lipoprotein or high glucose were markedly reduced by SDF-1 pretreatment in EPCs transduced with CXCR7 lentivirus but not in EPCs transduced with control lentivirus. Most importantly, EPCs transduced with CXCR7 lentivirus were superior to EPCs transduced with control lentivirus for therapy of ischemic limbs in db/db mice. Mechanistic studies demonstrated that oxidized low-density lipoprotein or high glucose inhibited protein kinase B and glycogen synthase kinase-3β phosphorylation, nuclear export of Fyn and nuclear localization of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), blunting Nrf2 downstream target genes heme oxygenase-1, NAD(P)H dehydrogenase (quinone 1) and catalase, and inducing an increase in EPC oxidative stress. This destructive cascade was blocked by SDF-1 treatment in EPCs transduced with CXCR7 lentivirus. Furthermore, inhibition of phosphatidylinositol 3-kinase/protein kinase B prevented SDF-1/CXCR7-mediated Nrf2 activation and blocked angiogenic repair. Moreover, Nrf2 knockdown almost completely abolished the protective effects of SDF-1/CXCR7 on EPC function in vitro and in vivo.

CONCLUSIONS

Elevated expression of CXCR7 enhances EPC resistance to diabetes mellitus-induced oxidative damage and improves therapeutic efficacy of EPCs in treating diabetic limb ischemia. The benefits of CXCR7 are mediated predominantly by a protein kinase B/glycogen synthase kinase-3β/Fyn pathway via increased activity of Nrf2.

CXCL12/CXCR4/CXCR7 Chemokine Axis in the Central Nervous System: Therapeutic Targets for Remyelination in Demyelinating Diseases

The chemokine CXCL12 plays a vital role in regulating the development of the central nervous system (CNS) by binding to its receptors CXCR4 and CXCR7. Recent studies reported that the CXCL12/CXCR4/CXCR7 axis regulates both embryonic and adult oligodendrocyte precursor cells (OPCs) in their proliferation, migration, and differentiation. The changes in the expression and distribution of CXCL12 and its receptors are tightly associated with the pathological process of demyelination in multiple sclerosis (MS), suggesting that modulating the CXCL12/CXCR4/CXCR7 axis may benefit myelin repair by enhancing OPC recruitment and differentiation. This review aims to integrate the current findings of the CXCL12/CXCR4/CXCR7 signaling pathway in the CNS and to highlight its role in oligodendrocyte development and demyelinating diseases. Furthermore, this review provides potential therapeutic strategies for myelin repair by analyzing the relevance between the pathological changes and the regulatory roles of CXCL12/CXCR4/CXCR7 during MS.

CXCL12 retargeting of an adenovirus vector to cancer cells using a bispecific adapter

Ad vectors are promising delivery vehicles for cancer therapeutic interventions. However, their application is limited by promiscuous tissue tropism and hepatotoxicity. This limitation can be avoided by altering the native tropism of Ads so that they can be redirected to the target cells through alternate cellular receptors. The CXCR4 chemokine receptor belongs to a large superfamily of G-protein-coupled receptors and is known to be upregulated in a wide variety of cancers, including breast cancer and melanoma. These receptors have been associated with cancer cell survival, progression, and metastasis. In the current study, an Ad to cancer cells overexpressing CXCR4 by using a bispecific adapter, sCAR-CXCL12, was retargeted. The sCAR-CXCL12 adapter contained the soluble ectodomain form of the native Ad5 receptor (sCAR), which was fused to a mature human chemokine ligand, CXCL12, through a short peptide linker. A dramatic increase in the infectivity of cancer cells using a targeted Ad vector compared with an untargeted vector was observed. Furthermore, sCAR-CXCL12 attenuated Ad infection of liver ex vivo and in vivo and enhanced Ad vector infection of xenograft tumors implanted in immunodeficient SCID-bg mice. Thus, the sCAR-CXCL12 adapter could be used to retarget Ad vectors to chemokine receptor-positive tumors.

Interaction of chemokine receptor CXCR4 in monomeric and dimeric state with its endogenous ligand CXCL12: coarse-grained simulations identify differences

Despite the recent resolutions of the crystal structure of the chemokine receptor CXCR4 in complex with small antagonists or viral chemokine, a description at the molecular level of the interactions between the full-length CXCR4 and its endogenous ligand, the chemokine CXCL12, in relationship with the receptor recognition and activation, is not yet completely elucidated. Moreover, since CXCR4 is able to form dimers, the question of whether the CXCR4-CXCL12 complex has a 1:1 or 2:1 preferential stoichiometry is still an open question. We present here results of coarse-grained protein-protein docking and molecular dynamics simulations of CXCL12 in association with CXCR4 in monomeric and dimeric states. Our proposed models for the 1:1 and 2:1 CXCR4-CXCL12 quaternary structures are consistent with recognition and activation motifs of both partners provided by the available site-directed mutagenesis data. Notably, we observed that in the 2:1 complex, the chemokine N-terminus makes more steady contacts with the receptor residues critical for binding and activation than in the 1:1 structure, suggesting that the 2:1 stoichiometry would favor the receptor signaling activity with respect to the 1:1 association.

Requirement of CXCL12-CXCR7 signaling for CD20(-) CD138(-) double-negative population in lymphoplasmacytic lymphoma

Cancer cells with tumorigenic potential are limited to a small subpopulation known as cancer-initiating cells (CICs). Recently we investigated a candidate of CICs of lymphoplasmacytic lymphoma (LPL), which is positive for both B-cell marker CD20 and plasma-cell marker CD138. We reported that the subpopulation of CD20(-) CD138(-) phenotype, in which both markers were negative was a candidate of CICs in LPL using LPL cell line, MWCL-1. CICs are known to be plastic under stressed condition, in which non-CICs are changed to CICs. In the present study, we investigated the plasticity of CICs of LPL, and found that hypoxia induced the conversion of CD20(+) CD138(-) to CD20(-) CD138(-) phenotype. We then searched for markers preferentially expressed in CD20(-) CD138(-) subpopulation, and the chemokine receptor CXCR7 was isolated. When cultured with CXCL12, a ligand of CXCR7, the number of CD20(-) CD138(-) cells increased in a time- and dose-dependent manner. In addition, hypoxia enhanced the expression level of CXCL12 in MWCL-1. In clinical samples of LPL, a few tumor cells expressed CXCR7, in which CD20 expression was not detected. These results indicated that hypoxia and CXCL12-CXCR7 axis appeared to be advantageous microenvironments to CD20(-) CD138(-) cells.

Cxcr4 is transiently expressed in both epithelial and mesenchymal compartments of nascent hair follicles but is not required for follicle formation

Hair follicle (HF) morphogenesis relies on the coordinated exchange of signals between mesenchymal and epithelial compartments of embryonic skin. Chemokine receptor Cxcr4 expression was recently identified in dermal condensates (DCs) of nascent HFs, but its role in promoting HF morphogenesis remains unknown. Our analyses confirmed Cxcr4 expression in condensate cells, and additionally revealed transient Cxcr4 expression in incipient epithelial hair placodes. Placodal Cxcr4 appeared prior to detection in DCs, representing a switch of expression between epithelial and mesenchymal compartments. To explore the functional role of this receptor in both compartments for early HF formation, we conditionally ablated Cxcr4 with condensate-targeting Tbx18(cre) knock-in and epidermis-targeting Krt14-cre transgenic mice. Conditional knockouts for both crosses were viable throughout embryogenesis and into adulthood. Morphological and biochemical marker analyses revealed comparable numbers of HFs forming in knockout embryos compared to wild-type littermate controls in both cases, suggesting that neither dermal nor epithelial Cxcr4 expression is required for early HF morphogenesis. We conclude that Cxcr4 expression and chemokine signaling through this receptor in embryonic mouse skin is dispensable for HF formation.

Diversity and Inter-Connections in the CXCR4 Chemokine Receptor/Ligand Family: Molecular Perspectives

CXCR4 and its ligand CXCL12 mediate the homing of progenitor cells in the bone marrow and their recruitment to sites of injury, as well as affect processes such as cell arrest, survival, and angiogenesis. CXCL12 was long thought to be the sole CXCR4 ligand, but more recently the atypical chemokine macrophage migration inhibitory factor (MIF) was identified as an alternative, non-cognate ligand for CXCR4 and shown to mediate chemotaxis and arrest of CXCR4-expressing T-cells. This has complicated the understanding of CXCR4-mediated signaling and associated biological processes. Compared to CXCL12/CXCR4-induced signaling, only few details are known on MIF/CXCR4-mediated signaling and it remains unclear to which extent MIF and CXCL12 reciprocally influence CXCR4 binding and signaling. Furthermore, the atypical chemokine receptor 3 (ACKR3) (previously CXCR7) has added to the complexity of CXCR4 signaling due to its ability to bind CXCL12 and MIF, and to evoke CXCL12- and MIF-triggered signaling independently of CXCR4. Also, extracellular ubiquitin (eUb) and the viral protein gp120 (HIV) have been reported as CXCR4 ligands, whereas viral chemokine vMIP-II (Herpesvirus) and human β3-defensin (HBD-3) have been identified as CXCR4 antagonists. This review will provide insight into the diversity and inter-connections in the CXCR4 receptor/ligand family. We will discuss signaling pathways initiated by binding of CXCL12 vs. MIF to CXCR4, elaborate on how ACKR3 affects CXCR4 signaling, and summarize biological functions of CXCR4 signaling mediated by CXCL12 or MIF. Also, we will discuss eUb and gp120 as alternative ligands for CXCR4, and describe vMIP-II and HBD-3 as antagonists for CXCR4. Detailed insight into biological effects of CXCR4 signaling und underlying mechanisms, including diversity of CXCR4 ligands and inter-connections with other (chemokine) receptors, is clinically important, as the CXCR4 antagonist AMD3100 has been approved as stem cell mobilizer in specific disease settings.

Dual targeting of the chemokine receptors CXCR4 and ACKR3 with novel engineered chemokines

The chemokine CXCL12 and its G protein-coupled receptors CXCR4 and ACKR3 are implicated in cancer and inflammatory and autoimmune disorders and are targets of numerous antagonist discovery efforts. Here, we describe a series of novel, high affinity CXCL12-based modulators of CXCR4 and ACKR3 generated by selection of N-terminal CXCL12 phage libraries on live cells expressing the receptors. Twelve of 13 characterized CXCL12 variants are full CXCR4 antagonists, and four have Kd values <5 nm. The new variants also showed high affinity for ACKR3. The variant with the highest affinity for CXCR4, LGGG-CXCL12, showed efficacy in a murine model for multiple sclerosis, demonstrating translational potential. Molecular modeling was used to elucidate the structural basis of binding and antagonism of selected variants and to guide future designs. Together, this work represents an important step toward the development of therapeutics targeting CXCR4 and ACKR3.

CXCR7 expression disrupts endothelial cell homeostasis and causes ligand-dependent invasion

The homeostatic function of endothelial cells (EC) is critical for a number of physiological processes including vascular integrity, immunity, and wound healing. Indeed, vascular abnormalities resulting from EC dysfunction contribute to the development and spread of malignancies. The alternative SDF-1/CXCL12 receptor CXCR7 is frequently and specifically highly expressed in tumor-associated vessels. In this study, we investigate whether CXCR7 contributes to vascular dysfunction by specifically examining the effect of CXCR7 expression on EC barrier function and motility. We demonstrate that CXCR7 expression in EC results in redistribution of CD31/PECAM-1 and loss of contact inhibition. Moreover, CXCR7+ EC are deficient in barrier formation. We show that CXCR7-mediated motility has no influence on angiogenesis but contributes to another motile process, the invasion of CXCR7+ EC into ligand-rich niches. These results identify CXCR7 as a novel manipulator of EC barrier function via alteration of PECAM-1 homophilic junctions. As such, aberrant expression of CXCR7 in the vasculature has the potential to disrupt vascular homeostasis and could contribute to vascular dysfunction in cancer systems.

CXCR4 Antagonist AMD3100 Suppresses the Long-Term Abnormal Structural Changes of Newborn Neurons in the Intraventricular Kainic Acid Model of Epilepsy

Abnormal hippocampal neurogenesis is a prominent feature of temporal lobe epilepsy (TLE) models, which is thought to contribute to abnormal brain activity. Stromal cell-derived factor-1 (SDF-1) and its specific receptor CXCR4 play important roles in adult neurogenesis. We investigated whether treatment with the CXCR4 antagonist AMD3100 suppressed aberrant hippocampal neurogenesis, as well as the long-term consequences in the intracerebroventricular kainic acid (ICVKA) model of epilepsy. Adult male rats were randomly assigned as control rats, rats subjected to status epilepticus (SE), and post-SE rats treated with AMD3100. Animals in each group were divided into two subgroups (acute stage and chronic stage). We used immunofluorescence staining of BrdU and DCX to analyze the hippocampal neurogenesis on post-SE days 10 or 74. Nissl staining and Timm staining were used to evaluate hippocampal damage and mossy fiber sprouting, respectively. On post-SE day 72, the frequency and mean duration of spontaneous seizures were measured by electroencephalography (EEG). Cognitive function was evaluated by Morris water maze testing on post-SE day 68. The ICVKA model of TLE resulted in aberrant neurogenesis such as altered proliferation, abnormal dendrite development of newborn neurons, as well as spontaneous seizures and spatial learning impairments. More importantly, AMD3100 treatment reversed the aberrant neurogenesis seen after TLE, which was accompanied by decreased long-term seizure activity, though improvement in spatial learning was not seen. AMD3100 could suppress long-term seizure activity and alter adult neurogenesis in the ICVKA model of TLE, which provided morphological evidences that AMD3100 might be beneficial for treating chronic epilepsy.

The chemokine receptor CXCR7 interacts with EGFR to promote breast cancer cell proliferation

Background

Recent advances have revealed a significant contribution of chemokines and their receptors in tumor growth, survival after chemotherapy, and organ-specific metastasis. The CXC chemokine receptor-7 (CXCR7) is the latest chemokine receptor implicated in cancer. Although over expressed in breast cancer cell lines and tumor tissues, its mechanism of action in breast cancer (BrCa) growth and metastasis is unclear. Studies in other cancers have implicated CXCR7 in cell proliferation, anti-apoptotic activity and cell-cell adhesion. The present study was initiated to examine the pattern of CXCR7 expression and its role in regulation of growth signaling in breast cancer.

Methods

The contribution of CXCR7 in BrCa cell proliferation was investigated in representative cell lines using real time quantitative PCR (q-PCR), proliferation assays, immunohistochemistry and immunoblotting. Phenotypic changes were examined after CXCR7 specific cDNA and siRNA transfection and expression levels were monitored by q-PCR. Further, the association of CXCR7 with epidermal growth factor receptor (EGFR) and modulation of its activity were investigated by western blotting, immunofluorescence, and in-situ proximity ligation assays in human BrCa cells and tissues.

Results

CXCR7 was expressed in both, estrogen receptor (ER) positive and negative BrCa cell lines. CXCR7 was also expressed unevenly in normal breast tissues and to a much higher extent in ER + cancer tissues. Depletion of CXCR7 in MCF7 BrCa cells by RNA interference decreased proliferation and caused cell cycle arrest. Further, proximity ligation assay (PLA) revealed colocalization of CXCR7 with EGFR in cancer tissues and cancer cell lines. CXCR7 depletion reduced levels of phospho-EGFR at Tyrosine1110 after EGF-stimulation and also reduced phosphorylation of ERK1/2, indicating a potentially direct impact on mitogenic signaling in MCF7 cells. Using siRNA to knockdown β-arrestin2 in cells with EGFR over expression we were able to nearly deplete the CXCR7-EGFR colocalization events, suggesting that β-arrestin2 acts as a scaffold to enhance CXCR7 dependent activation of EGFR after EGF stimulation.

Conclusions

These results demonstrate coupling of CXCR7 with EGFR to regulate proliferation of BrCa cells and suggest an important ligand-independent role of CXCR7 in BrCa growth. Thus, the CXCR7-EGFR axis is a promising target for breast cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-198) contains supplementary material, which is available to authorized users.

Review article: chemokines as orchestrators of autoimmune hepatitis and potential therapeutic targets

BACKGROUND

Chemokines contribute to the pathogenesis of autoimmune hepatitis by directing the migration and positioning of inflammatory and immune cells within the liver.

AIM

Describe the liver-infiltrating effector cell populations in autoimmune hepatitis, indicate the chemokines that influence their migration, describe the role of chemokines in hepatic fibrosis and identify chemokine-directed treatment opportunities.

METHODS

Studies cited in Pub Med from 1972 to 2014 for autoimmune hepatitis, chemokines in liver disease, pathogenesis of autoimmune hepatitis and chemokine therapy were selected.

RESULTS

T helper type 17 lymphocytes expressing CXCR3 and CCR6 are attracted to the liver by the secretion of CXCL9, CXCL10 and CXCL11. These cells recruit pro-inflammatory T helper type 1 lymphocytes expressing CXCR3 and CCR5 by secreting CXCL10. Resident natural killer T cells expressing CXCR6 migrate in response to the local secretion of CXCL16, and they modulate the inflammatory response. T helper type 2 lymphocytes expressing CCR4 are attracted by CCL17 and CCL22, and they dampen the expansion of pro-inflammatory cells. Regulatory T cells expressing CXCR3 are attracted by the secretion of CXCL9, and they help dampen the pro-inflammatory responses. CCL2, CCL3, CCL5, CXCL4, CXCL10 and CXCL16 promote fibrosis by activating or attracting hepatic stellate cells, and CX3CL1 may prevent fibrosis by affecting the apoptosis of monocytes.

CONCLUSIONS

Chemokines are requisites for mobilising, directing and positioning the effector cells in immune-mediated liver disease. They are feasible therapeutic targets in autoimmune hepatitis, and the evaluation of monoclonal antibodies that neutralise the pro-inflammatory ligands or designer peptides that block receptor activity are investigational opportunities.

Defining an optimal stromal derived factor-1 presentation for effective recruitment of mesenchymal stem cells in 3D

In "situ" tissue engineering is a promising approach in regenerative medicine, envisaging to potentiate the physiological tissue repair processes by recruiting the host's own cellular progenitors at the lesion site by means of bioactive materials. Despite numerous works focused the attention in characterizing novel chemoattractant molecules, only few studied the optimal way to present signal in the microenvironment, in order to recruit cells more effectively. In this work, we have analyzed the effects of gradients of stromal derived factor-1 (SDF-1) on the migratory behavior of human mesenchymal stem cells (MSCs). We have characterized the expression of the chemokine-associated receptor, CXCR4, using cytofluorimetric and real-time PCR analyses. Gradients of SDF-1 were created in 3D collagen gels in a chemotaxis chamber. Migration parameters were evaluated using different chemoattractant concentrations. Our results show that cell motion is strongly affected by the spatio-temporal features of SDF-1 gradients. In particular, we demonstrated that the presence of SDF-1 not only influences cell motility but alters the cell state in terms of SDF-1 receptor expression and productions, thus modifying the way cells perceive the signal itself. Our observations highlight the importance of a correct stimulation of MSCs by means of SDF-1 in order to implement on effective cell recruitment. Our results could be useful for the creation of a "cell instructive material" that is capable to communicate with the cells and control and direct tissue regeneration. Biotechnol. Bioeng. 2014;111: 2303-2316. © 2014 Wiley Periodicals, Inc.