The pleiotropic effects of the SDF-1-CXCR4 axis in organogenesis, regeneration and tumorigenesis

Hematopoietic stem cell development, niches, and signaling pathways

Hematopoietic stem cells (HSCs) play a key role in hematopoietic system that functions mainly in homeostasis and immune response. HSCs transplantation has been applied for the treatment of several diseases. However, HSCs persist in the small quantity within the body, mostly in the quiescent state. Understanding the basic knowledge of HSCs is useful for stem cell biology research and therapeutic medicine development. Thus, this paper emphasizes on HSC origin, source, development, the niche, and signaling pathways which support HSC maintenance and balance between self-renewal and proliferation which will be useful for the advancement of HSC expansion and transplantation in the future.

The mesenchymal tumor microenvironment: a drug-resistant niche

Drug and radiation resistance represent a challenge for most anticancer therapies. Diverse experimental approaches have provided evidence that the tumor-associated microenvironment constitutes both a protective shell that impedes drug or radiation access and a permissive or promotive microenvironment that encourages a nurturing cancer (i.e., cancer stem cell) niche where tumor cells overcome treatment- and cancer-induced stresses. Better understanding of the effects of the tumor microenvironment on cancer cells before, during and immediately after chemo- or radiotherapy is imperative to design new therapies aimed at targeting this tumor-protective niche. This review summarizes some of the known mesenchymal stromal effects that account for drug resistance, the main signal transduction pathways associated with this resistance and the therapeutic efforts directed to increase the success of current therapies. Special emphasis is given to environment-mediated drug resistance in general and to cell adhesion-mediated drug resistance in particular.

α-cell role in β-cell generation and regeneration

This review considers the role of α-cells in β-cell generation and regeneration. We present recent evidence obtained from lineage-tracing studies showing that α-cells can serve as progenitors of β-cells and present a hypothetical model how injured β-cells might activate α-cells in adult islets to promote β-cell regeneration. β-cells appear to arise by way of their trans-differentiation from undifferentiated α progenitor cells, pro-α-cells, both during embryonic development of the islets and in the adult pancreas in response to β-cell injuries. Plasticity of α-cells is endowed by the expression of the gene encoding proglucagon, a prohormone that can give rise to glucagon and glucagon-like peptides (GLPs). The production of glucagon from proglucagon is characteristic of fully-differentiated α-cells whereas GLP-1 is a product of undifferentiated α-cells. GLP-1, a cell growth and survival factor, is proposed to promote the expansion of neurogenin3-expressing, undifferentiated pro-α-cells during development. β-cells arise from pro-α-cells by a change in the relative amounts of the transcription factors Arx and Pax4, master regulators of the α- and β-cell lineages, respectively. A paracrine/autocrine model is proposed whereby injuries of β-cells in adult islets induce the production and release of factors, such as stromal cell-derived factor-1, that cause the de-differentiation of adjacent α-cells into pro-α-cells. Pro-α-cells produce GLP-1 and its receptor that renders them competent to trans-differentiate into β-cells. The trans-differentiation of pro-α-cells into β-cells provides a potentially exploitable mechanism for the regeneration of β-cells in individuals with type 1 diabetes.

Stromal cell-derived factor-1/CXC receptor 4 and β1 integrin interaction regulates urokinase-type plasminogen activator expression in human colorectal cancer cells

The stromal cell-derived factor-1 (SDF-1)/CXC receptor 4 (CXCR4) axis has been shown to play a role in colorectal cancer progression. In addition, the protease urokinase-type plasminogen activator (uPA) is an important factor in tumor cell invasion and metastasis. However, the mechanism by which SDF-1 mediates uPA expression in human colorectal cancer cells remains unknown. We investigated the molecular mechanism governing the interaction between SDF-1 stimulation and uPA expression in three human colon cancer cell lines (DLD-1, SW48, and COLO 205). We found that SDF-1 stimulation led to an increase in the expression and secretion of uPA in these cells. Experiments involving specific inhibitors and small interfering RNA demonstrated that the activation of p38 mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/Akt pathways are critical for SDF-1-induced uPA expression. Analysis of transcription factor binding using ELISA and chromatin immunoprecipitation assays revealed that SDF-1 increased Sp1- and AP-1-DNA-binding activities in DLD-1 cells. Inhibition of Sp1 and AP-1 activation blocked the SDF-1-induced expression and activity of the uPA promoter. The effect of SDF-1 on DLD-1 signaling and uPA expression was mediated by the CXCR4/β1 integrin axis. In summary, our findings elucidate the mechanisms of SDF-1/CXCR4 downstream signaling and provide insights into the function of SDF-1 in colon cancer cells.

Chemokine CXCL12 activates dual CXCR4 and CXCR7-mediated signaling pathways in pancreatic cancer cells

BACKGROUND

Previously assumed to be a select ligand for chemokine receptor CXCR4, chemokine CXCL12 is now known to activate both CXCR4 and CXCR7. However, very little is known about the co-expression of these receptors in cancer cells.

METHODS

We used immunohistochemistry to determine the extent of co-expression in pancreatic cancer tissue samples and immunoblotting to verify expression in pancreatic cancer cell lines. In cell culture studies, siRNA was used to knock down expression of CXCR4, CXCR7, K-Ras and β-arrestin -2 prior to stimulating the cells with CXCL12. Activation of the mitogen-activated protein kinase pathway (MAPK) was assessed using both a Raf-pull down assay and western blotting. The involvement of the receptors in CXCL12-mediated increases in cell proliferation was examined via an ATP-based proliferation assay.

RESULTS

First, we discovered frequent CXCR4/CXCR7 co-expression in human pancreatic cancer tissues and cell lines. Next, we observed consistent increases in ERK1/2 phosphorylation after exposure to CXCL12 or CXCL11, a CXCR7 agonist, in pancreatic cancer cell lines co-expressing CXCR4/CXCR7. To better characterize the receptor-mediated pathway(s), we knocked down CXCR4 or CXCR7, exposed the cells to CXCL12 and examined subsequent effects on ERK1/2. We observed that CXCR7 mediates the CXCL12-driven increase in ERK1/2 phosphorylation. Knockdown of CXCR4 expression however, decreased levels of K-Ras activity. Conversely, KRAS knockdown greatly reduced CXCL12-mediated increases in ERK1/2 phosphorylation. We then evaluated the role of β-arrestin-2, a protein directly recruited by chemokine receptors. We observed that β-arrestin-2 knockdown also inhibited increases in ERK1/2 phosphorylation mediated by both CXCR4 and CXCR7. Finally, we investigated the mechanism for CXCL12-enhanced cell proliferation and found that either receptor can modulate cell proliferation.

CONCLUSIONS

In summary, our data demonstrate that CXCR4 and CXCR7 are frequently co-expressed in human pancreatic cancer tissues and cell lines. We show that β-arrestin-2 and K-Ras dependent pathways coordinate the transduction of CXCL12 signals. Our results suggest that the development of therapies based on inhibiting CXCL12 signaling to halt the growth of pancreatic cancer should be focused at the ligand level in order to account for the contributions of both receptors to this signaling pathway.

SDF-1 activates papillary label-retaining cells during kidney repair from injury

The adult kidney contains a population of low-cycling cells that resides in the papilla. These cells retain for long periods S-phase markers given as a short pulse early in life; i.e., they are label-retaining cells (LRC). In previous studies in adult rat and mice, we found that shortly after acute kidney injury many of the quiescent papillary LRC started proliferating (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009; Oliver JA, Maarouf O, Cheema FH, Martens TP, Al-Awqati Q. J Clin Invest 114: 795-804, 2004) and, with cell-tracking experiments, we found upward migration of some papillary cells including LRC (Oliver JA, Klinakis A, Cheema FH, Friedlander J, Sampogna RV, Martens TP, Liu C, Efstratiadis A, Al-Awqati Q. J Am Soc Nephrol 20: 2315-2327, 2009). To identify molecular cues involved in the activation (i.e., proliferation and/or migration) of the papillary LRC that follows injury, we isolated these cells from the H2B-GFP mice and found that they migrated and proliferated in response to the cytokine stromal cell-derived factor-1 (SDF-1). Moreover, in a papillary organ culture assay, the cell growth out of the upper papilla was dependent on the interaction of SDF-1 with its receptor Cxcr4. Interestingly, location of these two proteins in the kidney revealed a complementary location, with SDF-1 being preferentially expressed in the medulla and Cxcr4 more abundant in the papilla. Blockade of Cxcr4 in vivo prevented mobilization of papillary LRC after transient kidney ischemic injury and worsened its functional consequences. The data indicate that the SDF-1/Cxcr4 axis is a critical regulator of papillary LRC activation following transient kidney injury and during organ repair.

Down-regulation of CXCL12 by DNA hypermethylation and its involvement in gastric cancer metastatic progression

BACKGROUND

Chemokine receptors are now known to play an important role in cancer growth and metastasis. However, there is little information regarding chemokine expression in gastric cancer. In this study, we examined CXCL12 expression in gastric cancer and also evaluated whether the down-regulation of CXCL12 is due to aberrant methylation of the gene.

METHODS

CXCL12 expression was examined using real-time reverse-transcription polymerase chain reaction (RT-PCR), immunofluorescence, flow cytometry, and immunohistochemistry, and the methylation status of the gene was evaluated by methylation-specific PCR (MSP) in normal gastric and gastric cancer cell lines and 35 primary gastric carcinomas and corresponding nonmalignant gastric tissues.

RESULTS

The down-regulation of CXCL12 was observed in gastric cancer cell lines and primary gastric carcinomas, while decreased expression of CXCL12 protein was significantly associated with lymph node metastasis and histological grade. And this down-regulation was found to be in accordance with aberrant methylation of the gene. Hypermethylation of the gene was observed in 65.7% (23 of 35) of the primary gastric carcinomas, while it was found in only 11.4% (4/35) of the corresponding nonmalignant tissues. Furthermore, CXCL12 expression was restored in gastric cancer cell lines after treatment with the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dC), and demethylation of the highly metastatic cells SGC-7901 induced invasion suppression of the cells. For two CXCL12 receptors, CXCR4 and CXCR7, the mRNA levels remained almost unchanged with the 5-Aza-dC treatment.

CONCLUSIONS

Collectively, our results suggest that the aberrant methylation of CXCL12 frequently occurs in the down-regulation of CXCL12 in gastric cancers and that it may play a role in the metastasis of gastric cancer.

The IKKα-dependent NF-κB p52/RelB noncanonical pathway is essential to sustain a CXCL12 autocrine loop in cells migrating in response to HMGB1

HMGB1 is a chromatin architectural protein that is released by dead or damaged cells at sites of tissue injury. Extracellular HMGB1 functions as a proinflammatory cytokine and chemoattractant for immune effector and progenitor cells. Previously, we have shown that the inhibitor of NF-κB kinase (IKK)β- and IKKα-dependent NF-κB signaling pathways are simultaneously required for cell migration to HMGB1. The IKKβ-dependent canonical pathway is needed to maintain expression of receptor for advanced glycation end products, the ubiquitously expressed receptor for HMGB1, but the target of the IKKα non-canonical pathway was not known. In this study, we show that the IKKα-dependent p52/RelB noncanonical pathway is critical to sustain CXCL12/SDF1 production in order for cells to migrate toward HMGB1. Using both mouse bone marrow-derived macrophages and mouse embryo fibroblasts (MEFs), it was observed that neutralization of CXCL12 by a CXCL12 mAb completely eliminated chemotaxis to HMGB1. In addition, the HMGB1 migration defect of IKKα KO and p52 KO cells could be rescued by adding recombinant CXCL12 to cells. Moreover, p52 KO MEFs stably transduced with a GFP retroviral vector that enforces physiologic expression of CXCL12 also showed near normal migration toward HMGB1. Finally, both AMD3100, a specific antagonist of CXCL12's G protein-coupled receptor CXCR4, and an anti-CXCR4 Ab blocked HMGB1 chemotactic responses. These results indicate that HMGB1-CXCL12 interplay drives cell migration toward HMGB1 by engaging receptors of both chemoattractants. This novel requirement for a second receptor-ligand pair enhances our understanding of the molecular mechanisms regulating HMGB1-dependent cell recruitment to sites of tissue injury.

Stromal-Cell-Derived Factor-1 (SDF-1)/CXCL12 as Potential Target of Therapeutic Angiogenesis in Critical Leg Ischaemia

In the Western world, peripheral vascular disease (PVD) has a high prevalence with high morbidity and mortality. In a large percentage of these patients, lower limb amputation is still required. Studies of ischaemic skeletal muscle disclosed evidence of endogenous angiogenesis and adaptive skeletal muscle metabolic changes in response to hypoxia. Chemokines are potent chemoattractant cytokines that regulate leukocyte trafficking in homeostatic and inflammatory processes. More than 50 different chemokines and 20 different chemokine receptors have been cloned. The chemokine stromal-cell-derived factor-1 (SDF-1 aka CXCL12) is a constitutively expressed and inducible chemokine that regulates multiple physiological processes, including embryonic development and organ homeostasis. The biologic effects of SDF-1 are mediated by chemokine receptor CXCR4, a 352 amino acid rhodopsin-like transmembrane-specific G protein-coupled receptor (GPCR). There is evidence that the administration of SDF-1 increases blood flow and perfusion via recruitment of endothelial progenitor cells (EPCs). This review will focus on the role of the SDF-1/CXCR4 system in the pathophysiology of PVD and discuss their potential as therapeutic targets for PVD.

Differential adhesive properties of sequestered asexual and sexual stages of Plasmodium falciparum on human endothelial cells are tissue independent

The protozoan parasite Plasmodium falciparum, responsible for the most severe form of malaria, is able to sequester from peripheral circulation during infection. The asexual stage parasites sequester by binding to endothelial cell receptors in the microvasculature of various organs. P. falciparum gametocytes, the developmental stages responsible for parasite transmission from humans to Anopheles mosquitoes, also spend the almost ten days necessary for their maturation sequestered away from the peripheral circulation before they are released in blood mainstream. In contrast to those of asexual parasites, the mechanisms and cellular interactions responsible for immature gametocyte sequestration are largely unexplored, and controversial evidence has been produced so far on this matter. Here we present a systematic comparison of cell binding properties of asexual stages and immature and mature gametocytes from the reference P. falciparum clone 3D7 and from a patient parasite isolate on a panel of human endothelial cells from different tissues. This analysis includes assays on human bone marrow derived endothelial cell lines (HBMEC), as this tissue has been proposed as a major site of gametocyte maturation. Our results clearly demonstrate that cell adhesion of asexual stage parasites is consistently more efficient than that, virtually undetectable of immature gametocytes, irrespectively of the endothelial cell lines used and of parasite genotypes. Importantly, immature gametocytes of both lines tested here do not show a higher binding efficiency compared to asexual stages on bone marrow derived endothelial cells, unlike previously reported in the only study on this issue. This indicates that gametocyte-host interactions in this tissue are unlikely to be mediated by the same adhesion processes to specific endothelial receptors as seen with asexual forms.

Identification of anti-malarial compounds as novel antagonists to chemokine receptor CXCR4 in pancreatic cancer cells

Despite recent advances in targeted therapies, patients with pancreatic adenocarcinoma continue to have poor survival highlighting the urgency to identify novel therapeutic targets. Our previous investigations have implicated chemokine receptor CXCR4 and its selective ligand CXCL12 in the pathogenesis and progression of pancreatic intraepithelial neoplasia and invasive pancreatic cancer; hence, CXCR4 is a promising target for suppression of pancreatic cancer growth. Here, we combined in silico structural modeling of CXCR4 to screen for candidate anti-CXCR4 compounds with in vitro cell line assays and identified NSC56612 from the National Cancer Institute's (NCI) Open Chemical Repository Collection as an inhibitor of activated CXCR4. Next, we identified that NSC56612 is structurally similar to the established anti-malarial drugs chloroquine and hydroxychloroquine. We evaluated these compounds in pancreatic cancer cells in vitro and observed specific antagonism of CXCR4-mediated signaling and cell proliferation. Recent in vivo therapeutic applications of chloroquine in pancreatic cancer mouse models have demonstrated decreased tumor growth and improved survival. Our results thus provide a molecular target and basis for further evaluation of chloroquine and hydroxychloroquine in pancreatic cancer. Historically safe in humans, chloroquine and hydroxychloroquine appear to be promising agents to safely and effectively target CXCR4 in patients with pancreatic cancer.

Mesenchymal niches of bone marrow in cancer

Over the last decade, genetic and cell biology studies have indicated that tumour growth is not only determined by malignant cancer cells themselves, but also by the tumour microenvironment. Cells present in the tumour microenvironment include fibroblasts, vascular, smooth muscle, adipocytes, immune cells and mesenchymal stem cells (MSC). The nature of the relationship between MSC and tumour cells appears dual and whether MSC are pro- or anti-tumorigenic is a subject of controversial reports. This review is focused on the role of MSC and bone marrow (BM) niches in cancer.

Cationic liposome-mediated CXCR4 gene delivery into hematopoietic stem/progenitor cells: implications for clinical transplantation and gene therapy

The chemokine stromal cell-derived factor (SDF)-1α/CXCL12 and its receptor CXC chemokine receptor 4 (CXCR4) play a crucial role in the homing/engraftment and retention of hematopoietic stem/progenitor cells (HSPCs) in the bone marrow. It has been shown using the viral gene transfer technique that CXCR4 overexpression on human CD34(+) HSPC significantly improves their engraftment in murine models. However, clinical trials with gene therapy have revealed safety concerns related to the immunogenicity of the viral carriers, due to the random integration of viral genes into the host genome. Therefore, a method for CXCR4 gene delivery into HSPC that is safe, nonviral, and highly efficient is needed to improve clinical transplantation and gene therapies. In this work, we investigated the nonviral CXCR4 gene delivery into HSPC using the cationic liposome agent IBAfect. We used CD34(+) cells from cord blood and the models of immature hematopoietic cells expressing CD34 antigen, namely, leukemic cell lines KG-1a and KG-1. Transfection efficiency was determined by flow cytometric analysis 12, 24, 48, and 72 h after transfection, and the viability of cells analyzed by trypan blue exclusion and MTS assays. The functional response of CXCR4-transfected HSPC toward an SDF-1α gradient was determined by chemotaxis assay. We found that ~25% transfection is achieved for KG-1a and KG-1 cells and 20% for HSPC, and that the viability of CXCR4-transfected HSPC is not significantly altered. More importantly, overexpression of CXCR4 using IBAfect significantly increased the chemotaxis of KG-1 cells and HSPC toward SDF-1α. However, we tested 2 other commercially available cationic liposomes (Lipofectamine 2000 and 1,2-dioleoyl-3-trimethylammonium-propane [DOTAP]) in parallel, and we found that they failed to deliver the CXCR4 gene into cells under the same conditions. These results suggest that IBAfect-mediated in vitro gene delivery to overexpress CXCR4 on HSPC is a safe and efficient technique with great potential for improving the efficacy of HSPC transplantation and gene therapy protocols.

Molecular pathogenesis of pancreatic cancer and clinical perspectives

Pancreatic cancer remains stubbornly resistant to many key cytotoxic chemotherapeutic agents and novel targeted therapies. The molecular heterogeneity of this cancer may account for therapy failures to date, although our growing arsenal of novel targeted agents could translate into patient survival. The main objectives of this review are to elucidate histological subtypes of pancreatic neoplasms that exhibit the characteristic of a gradual process of differentiation from benign entities to malignant ones. In addition, important genes, molecular abnormalities, and significant pathways of pancreatic cancer are analyzed and a potential clinical interpretation is presented (p16/cdkn2a, k-ras mutations, smad-4/tgf-/stat3, stk-11, braf, brca-2, neurotensin, mucs proteins, palb2, mitochondrial mutations, DNA mismatch repair genes, methylation, microrna expression, epithelial-to-mesenchymal transition, egfr mutations, the pi3k-akt-mtor pathway, the vegf pathway, heat shock proteins, cxcr4, the cox pathway, the src pathway, the hedgehog pathway, pancreatic stellate cells, a progression model, and molecular events in uncommon pancreatic tumors). Finally, future therapeutic directions are elucidated.

Stromal cell derived factor-1α enhances bone formation based on in situ recruitment: a histologic and histometric study in rabbit calvaria

Histological methods were used to assess whether in situ recruitment using stromal cell derived factor-1α (SDF-1α) enhances bone formation. Four defects were created in the calvarias of 16 rabbits and filled with: (1) a blood clot only (group C); (2) autogenous bone particles (AB, 0.2 ml) (group AB); (3) AB (0.1 ml) + bone marrow derived stromal stem cells (group ABC); or (4) AB (0.1 ml) + SDF-1α (group ABS). Bone formation was significantly greater in groups AB and ABC compared with group ABS after 2 weeks (P < 0.05). Bone formation was similar between groups AB, ABC, and ABS after 4 weeks (P > 0.05). SDF-1α is a promising candidate for in situ recruitment in bone regeneration.

Testosterone in newly diagnosed, antipsychotic-naive men with nonaffective psychosis: a test of the accelerated aging hypothesis

OBJECTIVE

Schizophrenia has been associated with age-related abnormalities, including abnormal glucose tolerance, increased pulse pressure, increased inflammation, abnormal stem cell signaling, and shorter telomere length. These metabolic abnormalities and other findings suggest that schizophrenia and related disorders might be associated with accelerated aging. Testosterone activity has a progressive decline with increasing age.

METHODS

We tested the hypothesis that circulating biologically active testosterone is lower in newly diagnosed, antipsychotic-naive male patients with nonaffective psychosis than in matched control subjects.

RESULTS

Patients (n = 33) were matched to control subjects (n = 33) for age, sex, body mass index, socioeconomic status of the family of origin, and smoking. The free androgen index, a measure of biologically active testosterone, was significantly lower in the psychosis group (mean [standard deviation] = 57.7% [26.1]) than in control subjects (71.6% [27.0], p = .04), with an effect size of 0.53. Multivariate analysis also supported the findings. In the psychosis group, free androgen index had a significant negative correlation with the conceptual disorganization item (r = -0.35, p = .049) but not with reality distortion (r = -0.21, p = .24), negative symptoms (r = 0.004, p = .98), or depression (r = -0.014, p = .94).

CONCLUSIONS

Lower testosterone level is consistent with accelerated aging in nonaffective psychosis, but further testing of this hypothesis is needed.

Role of SDF-1 as a regulatory chemokine in renal regeneration after acute kidney injury

Both the homing of hematopoietic stem cells (HSCs) to the bone marrow and their engraftment in recipients of bone marrow transplants are primarily mediated by the chemokine stromal-derived factor-1 (SDF-1) or CXCL12, which activates CXCR4, its cognate receptor on HSCs. We showed that the recruitment and temporary attachment of CXCR4-expressing cells, such as HSCs and a fraction of mesenchymal stem cells (MSCs), to the kidney, following ischemia/reperfusion acute kidney injury, are similarly mediated by robustly upregulated SDF-1 in the kidney, indicating that such organ injury appears to lead to the transient expression of a facultative stem cell niche. This SDF-1 response of the injured kidney facilitates both the mobilization from the bone marrow and homing of precursor cells, and other CXCR4-expressing cells such as administered MSCs, to the kidney, where they aid in its protection and repair. Similar responses have been observed subsequent to the injury of other solid organs such as the heart, liver, and brain.

Nef from SIV(mac239) decreases proliferation and migration of adenoid-cystic carcinoma cells and inhibits angiogenesis

The HIV/SIV accessory protein Nef is known to down-modulate cell surface receptors that are required for virus entry such as CD4, CCR5 and CXCR4 to block lethal viral superinfection of the infected cell. The chemokine receptor CXCR4 also plays an important role in promoting cell proliferation, metastasis and tumor angiogenesis. Therefore it was of interest to evaluate if Nef can down-regulate CXCR4 in tumor cells since this could affect these critical prognostic parameters. The CXCR4-expressing cell line ACC3 that was derived from a salivary gland adenoid cystic carcinoma (ACC) of the head and neck was transfected with Nef from SIV(mac239) and cell surface expression of the receptor was monitored by FACS analysis. Real time proliferation of cells was measured with the xCELLigence system (Roche, Mannheim, Germany). Cell migration was detected by an in vitro scratch assay. Similarly, COS-7 cells were co-transfected with CXCR4 and Nef and were treated as described for ACC3. In vitro tube formation was deployed to assess the effect of Nef on angiogenesis. siRNA was used for CXCR4 knockdown. Cell surface down-modulation of endogenous CXCR4 could be observed in ACC3 cells after Nef-transfection as well as in COS-7 cells after co-transfection of CXCR4 and Nef. Proliferation as well as migration of Nef-transfected ACC3 tumor cells appeared significantly reduced. In vitro tube formation was significantly lowered after Nef-transfection or CXCR4 knockdown with siRNA. SIV-Nef could serve as an interesting tool to study the biologic behavior of CXCR4-expressing tumors such as ACC. Deploying SIV-Nef thereby could help in the discovery of new therapeutic approaches for the treatment of ACC and other CXCR4-expressing tumors.

Circulating osteogenic cells: implications for injury, repair, and regeneration

The aim of this review is to provide a critical reading of recent literature pertaining to the presence of circulating, fluid-phase osteoblastic cells and their possible contribution to bone formation. We have termed this group of cells collectively as circulating osteogenic precursor (COP) cells. We present evidence for their existence, methods used for their isolation and identification, possible physiological and pathophysiological roles, cellular origins, and possible mechanisms for their migration to target tissues.

Stromal cell-derived factor-1 (SDF-1)/chemokine (C-X-C motif) receptor 4 (CXCR4) axis activation induces intra-islet glucagon-like peptide-1 (GLP-1) production and enhances beta cell survival

AIMS/HYPOTHESIS

The endogenous production of stromal cell-derived factor-1 (SDF-1) in beta cells in transgenic mice attenuates the development of diabetes in response to streptozotocin. Here we propose that beta cell injury induces SDF-1 production, and the SDF-1/chemokine (C-X-C motif) receptor 4 (CXCR4) interaction auto-activates Sdf1 expression, resulting in the autocrine production of SDF-1 by beta cells and the paracrine activation of glucagon-like peptide-1 (GLP-1) production by alpha cells.

METHODS

SDF-1 production in adult mouse and human islets and rat INS-1 cells was measured in models of beta cell injury. The paracrine actions of SDF-1 on GLP-1 production in alpha cells were explored. The potential synergism between the growth-promoting actions of GLP-1 and the pro-survival actions of SDF-1 on the preservation of cell mass was evaluated by cell viability assays.

RESULTS

In adult islets and INS-1 cells, Sdf1 expression was re-induced in response to injury. The interaction of SDF-1 with its receptor on alphaTC1 cells activated protein kinase Akt, stimulated cell proliferation and induced the expression of prohormone convertase 1/3 and the consequent production of GLP-1 in alpha cells. The combination of GLP-1 and SDF-1 additively enhanced both the growth and longevity of INS-1 beta cells.

CONCLUSIONS/INTERPRETATION

The results of these studies suggest that in response to beta cell injury and the ensuing induction of SDF-1, the biological function of alpha cells switches from the production of glucagon to the provision of the local growth factor GLP-1 which, in combination with SDF-1, promotes the growth, survival and viability of the beta cells.

PPARgamma2 Regulates a Molecular Signature of Marrow Mesenchymal Stem Cells

Bone formation and hematopoiesis are anatomically juxtaposed and share common regulatory mechanisms. Bone marrow mesenchymal stromal/stem cells (MSC) contain a compartment that provides progeny with bone forming osteoblasts and fat laden adipocytes as well as fibroblasts, chondrocytes, and muscle cells. In addition, marrow MSC provide an environment for support of hematopoiesis, including the development of bone resorbing osteoclasts. The PPARgamma2 nuclear receptor is an adipocyte-specific transcription factor that controls marrow MSC lineage allocation toward adipocytes and osteoblasts. Increased expression of PPARgamma2 with aging correlates with changes in the MSC status in respect to both their intrinsic differentiation potential and production of signaling molecules that contribute to the formation of a specific marrow micro-environment. Here, we investigated the effect of PPARgamma2 on MSC molecular signature in respect to the expression of gene markers associated exclusively with stem cell phenotype, as well as genes involved in the formation of a stem cell supporting marrow environment. We found that PPARgamma2 is a powerful modulator of stem cell-related gene expression. In general, PPARgamma2 affects the expression of genes specific for the maintenance of stem cell phenotype, including LIF, LIF receptor, Kit ligand, SDF-1, Rex-1/Zfp42, and Oct-4. Moreover, the antidiabetic PPARgamma agonist TZD rosiglitazone specifically affects the expression of "stemness" genes, including ABCG2, Egfr, and CD44. Our data indicate that aging and anti-diabetic TZD therapy may affect mesenchymal stem cell phenotype through modulation of PPARgamma2 activity. These observations may have important therapeutic consequences and indicate a need for more detailed studies of PPARgamma2 role in stem cell biology.

MicroRNA-146a and AMD3100, two ways to control CXCR4 expression in acute myeloid leukemias

CXCR4 is a negative prognostic marker in acute myeloid leukemias (AMLs). Therefore, it is necessary to develop novel ways to inhibit CXCR4 expression in leukemia. AMD3100 is an inhibitor of CXCR4 currently used to mobilize cancer cells. CXCR4 is a target of microRNA (miR)-146a that may represent a new tool to inhibit CXCR4 expression. We then investigated CXCR4 regulation by miR-146a in primary AMLs and found an inverse correlation between miR-146a and CXCR4 protein expression levels in all AML subtypes. As the lowest miR-146a expression levels were observed in M5 AML, we analyzed the control of CXCR4 expression by miR-146a in normal and leukemic monocytic cells and showed that the regulatory miR-146a/CXCR4 pathway operates during monocytopoiesis, but is deregulated in AMLs. AMD3100 treatment and miR-146a overexpression were used to inhibit CXCR4 in leukemic cells. AMD3100 treatment induces the decrease of CXCR4 protein expression, associated with miR-146a increase, and increases sensitivity of leukemic blast cells to cytotoxic drugs, this effect being further enhanced by miR-146a overexpression. Altogether our data indicate that miR-146a and AMD3100, acting through different mechanism, downmodulate CXCR4 protein levels, impair leukemic cell proliferation and then may be used in combination with anti-leukemia drugs, for development of new therapeutic strategies.

Palmitoylated SDF1α shows increased resistance against proteolytic degradation in liver homogenates

The chemokine stromal cell-derived factor-1α (SDF1α) is strongly involved in organogenesis, as well as inflammation and tissue repair, and acts by attracting different kinds of stem and progenitor cells. Therefore, it constitutes an interesting compound for drug development in regenerative medicine. However, it is prone to inactivation by proteolytic cleavage in human serum. Accordingly, it has to be stabilized against enzymatic degradation for any therapeutic application. We synthesized a palmitoylated SDF1α analogue by native chemical ligation. Both the N-terminal thioester and the C-terminal palmitoylated fragment were prepared by solid-phase peptide synthesis. The activity of the refolded and pure compound was determined by an inositol phosphate turnover assay and revealed no loss in receptor activation. Additionally, resistance to proteolytic degradation was investigated in porcine liver homogenates and showed a near sevenfold increased half time. This study is a proof of principle approach for the lipidation of SDF1α and provides a basis for further engineering of the chemokine in order to increase its therapeutic value.

The expression of CXCL12 and CXCR4 in gastric cancer and their correlation to lymph node metastasis

The purpose of this study was to investigate the expression of CXCL12 and its receptor CXCR4 in gastric cancer and to determine their relationship with lymph node metastasis. Fifty patients with pathologically confirmed gastric cancer were analyzed from September 2004 to December 2004. The expression levels of CXCL12 and CXCR4 were examined by immunohistochemical staining in the primary gastric tumor tissues, adjacent normal mucosa tissues, and metastatic lymph nodes and were analyzed along with clinicopathological risk factors, to determine their correlation with the prognosis. Positive staining for CXCL12 and CXCR4 was identified in 90.0 and 80.0% of the primary gastric tumor tissues, respectively, with significantly higher expression intensities observed in the primary gastric tumor tissues than in the adjacent normal mucosa tissues (P < 0.01 and P = 0.01, respectively). Positive staining for CXCL12 and CXCR4 was identified in 94.4 and 91.7% of metastatic lymph nodes, respectively, with significantly higher expression intensities in the metastatic lymph nodes than in the adjacent normal mucosa tissues (P < 0.01 and P = 0.01, respectively). Expression of CXCL12 in the primary gastric tumor tissues was not significantly associated with the clinicopathological characteristics of the tumor or the disease prognosis. However, the intensity of CXCR4 staining in primary tumor tissues was positively related with lymph node metastasis, TNM staging, and disease prognosis (P = 0.04, 0.03, 0.03, respectively). CXCL12 and CXCR4 are related to formation of gastric tumors and lymph node metastasis. Furthermore, the expression of CXCR4 could be used as a biomarker to predict malignant features of gastric cancer.

The role of CXCR7 on the adhesion, proliferation and angiogenesis of endothelial progenitor cells

Previous studies confirmed that stromal cell-derived factor 1 (SDF-1) was a principal regulator of retention, migration and mobilization of haematopoietic stem cells and endothelial progenitor cells (EPCs) during steady-state homeostasis and injury. CXC chemokine receptor 4 (CXCR4) has been considered as the unique receptor of SDF-1 and as the only mediator of SDF-1-induced biological effects for many years. However, recent studies found that SDF-1 could bind to not only CXCR4 but also CXC chemokine receptor 7 (CXCR7). The evidence that SDF-1 binds to the CXCR7 raises a concern how to distinguish the potential contribution of the SDF-1/CXCR7 pathway from SDF-1/CXCR4 pathway in all the processes that were previously attributed to SDF-1/CXCR4. In this study, the role of CXCR7 in EPCs was investigated in vitro. RT-PCR, Western blot and flow cytometry assay demonstrate that both CXCR4 and CXCR7 were expressed highly in EPCs. The adhesion of EPCs induced by SDF-1 was inhibited by blocking either CXCR4 or CXCR7 with their antibodies or antagonists. SDF-1 regulated the migration of EPCs via CXCR4 but not CXCR7. However, the transendothelial migration of EPCs was inhibited by either blocking of CXCR4 or CXCR7. Both CXCR7 and CXCR4 are essential for the tube formation of EPCs induced by SDF-1. These results suggested that both CXCR7 and CXCR4 are important for EPCs in response to SDF-1, indicating that CXCR7 may be another potential target molecule for angiogenesis-dependent diseases.

17β-Estradiol enhances the recruitment of bone marrow-derived endothelial progenitor cells into infarcted myocardium by inducing CXCR4 expression

BACKGROUND

17β-Estradiol (E2) has been thought to produce cardioprotective effects by mediating bone marrow-derived endothelial progenitor cells (EPC) for cardiac repair in the setting of acute myocardial infarction (AMI). However, the underlying mechanism of action of E2 on EPC remains unclear. CXCR4 is a critical modulator in homing of EPC. Accordingly, we hypothesized that E2 exerts beneficial effects through enhancing EPC homing to infarcted myocardium via mediating CXCR4 pathway.

METHODS AND RESULTS

Migratory capacity and CXCR4 expression of EPC from ovariectomized BALB/C mice were detected after being incubated with various E2 concentrations for various incubation times. For in vivo studies, EPC were labeled with superparamagnetic ion oxide (SPIO) for tracing, and ovariectomized mice were grouped (n=11) after inducing AMI to receive saline without cells or with 3 × 10(6) non-preconditioned EPC, 100 nmol/L E2 preconditioned EPC, CXCR4 inhibitor AMD3100 (5 μg/mL) preconditioned EPC, or EPC pretreated with E2 plus AMD3100. The number of homing EPC in infarcted myocardium and left ventricular (LV) function, dimensions and fibrosis were measured. In vitro data showed that E2 increased migratory activity and functional CXCR4 expression of EPC. However, these effects were completely blocked by AMD3100. In vivo data in E2 group displayed a greater number of homing EPC, decreased fibrosis of LV, and significant improvement in cardiac function. Nevertheless, effects of E2 preconditioning were abrogated by AMD3100.

CONCLUSIONS

We conclude that E2 enhances the recruitment of EPC into infarcted myocardium by up-regulating functional CXCR4 expression, resulting in improving recovery after myocardial infarction.

Bradykinin promotes the chemotactic invasion of primary brain tumors

Primary brain tumors, gliomas, diffusely invade the brain by active cell migration either intraparenchymal, along white matter tracts or along blood vessels. The close relationship of glioma with the vasculature assures a continuous supply of oxygen and nutrients essential for cell growth, and exposes cells to a variety growth factors, chemokines, cytokines, and kinins. Signals that attract glioma cells to blood vessels are poorly understood. It has been shown that vascular endothelial cells can initiate the bradykinin (BK) signaling cascade and two bradykinin receptors, B1 and B2, have been identified and cloned. In this study we show that glioma cells isolated from patient biopsies express bradykinin 2 receptors (B2R) whose activation causes intracellular Ca(2+) oscillations. Through time-lapse video-microscopy experiments we show that BK significantly enhances glioma cell migration/invasion. We further show that BK acts as a chemoattractant guiding glioma cells toward blood vessels in acute rat brain slices. The number of cells associated with blood vessels is decreased when B2R are either pharmacologically inhibited or B2R eliminated through short-hairpin RNA knockdown. These data strongly suggest that bradykinin, acting via B2R, acts as an important signal directing the invasion of glioma cells toward blood vessels. A clinically approved B2R antagonist is available that could be used as anti-invasive drug in glioma patients in the future.

SCORE Study report #11: incidences of neovascular events in eyes with retinal vein occlusion

PURPOSE

To investigate in The Standard Care versus COrticosteroid for REtinal Vein Occlusion (SCORE) Study: (1) incidences of neovascular events and retinal capillary nonperfusion (abbreviated as "nonperfusion"), and their relationship with treatment groups; (2) neovascular incidences by nonperfusion status; and (3) pertinent baseline factors for their potential risk for neovascular events.

DESIGN

Two multicenter, randomized clinical trials, 1 evaluating participants with central retinal vein occlusion (CRVO) and the other evaluating participants with branch retinal vein occlusion (BRVO).

PARTICIPANTS

At 36 months, data were available for 81 participants with CRVO and 128 with BRVO.

INTERVENTION

Standard care (observation or grid photocoagulation) versus 1 or 4 mg intravitreal triamcinolone.

MAIN OUTCOME MEASURES

Neovascularization of the iris (NVI), neovascular glaucoma (NVG), disc or retinal neovascularization (NVD/NVE), preretinal or vitreous hemorrhage (PRH/VH), and nonperfusion.

RESULTS

The cumulative 36-month incidences for CRVO and BRVO eyes, respectively, were 8.5% and 2.4% for NVI or NVG; 8.8% and 7.6% for NVD/NVE or PRH/VH. There were no differences in incidences of neovascular events or risk of nonperfusion when comparing the 3 treatment groups within diseases. For CRVO at 36 months, 16.6% of eyes with ≥5.5 disc areas of nonperfusion versus 4.0% of eyes with <5.5 disc areas of nonperfusion developed NVG (P = 0.0003); for BRVO at 36 months, 14.6% versus 2.4% developed NVD/NVE (P<0.0001). Similar results were noted for most other neovascular events. Nonperfusion was the only significant baseline factor for neovascularization in BRVO, with the risk of a neovascular event increasing with greater disc areas of nonperfusion, and the highest risk noted at ≥5.5 disc areas.

CONCLUSIONS

In the SCORE Study, triamcinolone treatment was not associated with lower incidences of neovascular events or nonperfusion status compared with observation or grid photocoagulation. Cumulative 36-month incidences for most neovascular events were significantly higher for nonperfused than perfused eyes. Greater baseline disc areas of nonperfusion increased the risk of neovascularization in BRVO but not CRVO eyes, possibly owing to obscuration of retinal capillary details caused by dense hemorrhage at baseline for CRVO eyes. Increased risk of neovascularization was noted below the historical threshold of 10 disc areas of nonperfusion for retinal vein occlusion.

Effects of AMD3100 subconjunctival injection on alkali burn induced corneal neovascularization in mice

AIM

To investigate the therapeutic effects of local and systemic administration of AMD3100 for alkali burn induced corneal neovascularization (CNV) in mice.

METHODS

CNV was induced in vivo by alkaline burn of cornea in C57BL/6 mice. AMD3100 was administrated topically by subconjunctival injection or systemically by intraperitoneal injection for 7 days; balanced salt solution was administrated topically or systemically as a control respectively. Inflammatory index was evaluated by slit-lamp biomicroscopy and inflammatory cells infiltrated to cornea tissue were detected by histologic analysis at multiple time points. CNV was compared between the local and systemic treated mice 2 weeks after alkali burn, as quantified by CD34 immunostaining. Fluorescence-Activated Cell Sorter Analysis was used to investigate the mobilizing effects of EPC in mice after subconjunctival injected or intraperitoneal injected AMD3100. Immunohistochemistry was used to detect the expression of endothelial progenitor cells (EPC) marker proteins VEGFR2 and CD34.

RESULTS

Three days after alkali burn, infiltration of inflammatory cells was found in corneal tissue. At the first 7 days of local injection group, the number of inflammatory cells was significantly lower than that in systemic injection group. CNV could be seen at the 7(th) day, and at the 14(th) day reached the peak, then started to decrease. The number of CNV in the subconjunctival injection group was 7.57±1.26 per 0.034mm(2), compared to a number of 14.87±2.21 per 0.034mm(2) in the control group (P<0.05). On the contrary, the number of CNV in the intraperitoneal injection group was a little higher than that in the control group, 16.34±1.53 per 0.034mm(2)vs 13.26±1.87 per 0.034mm(2). The research also showed that intraperitoneally, but not subconjunctivally injected AMD3100 could mobilize EPC. On the other hand, subconjunctival, but not intraperitoneally injected AMD3100 could reduce the expression of EPC marker proteins.

CONCLUSION

In mice locally administrated AMD3100 can reduce the number of alkali burn induced CNV. The number of inflammatory cells and inflammatory responses in corneal tissue.

The influence of intraoperative pleural perfusion with matrine-cisplatin or cisplatin on stromal cell-derived factor-1 in non-small cell lung cancer patients with subclinical pleural metastasis

The early diagnosis and treatment of non-small cell lung cancer (NSCLC) in patients with subclinical pleural metastasis is currently a challenge. In an effort to establish a method for the diagnosis and treatment of these patients, we conducted a single-blind study during which intraoperative pleural lavage cytology (PLC) was performed in 164 patients with NSCLC without obvious pleural effusion. Stromal cell-derived factor-1 (SDF-1) serum concentrations were analyzed using enzyme-linked immunoassay on day 1 prior to tumor resection and on day 7 postoperatively. Western blot analysis was used for the detection of CXCR4 protein expression in resected tumors. Intraoperative pleural perfusion chemotherapy, with either cisplatin or cisplatin plus matrine, was given to patients with positive PLC. A group of 30 patients with NSCLC that did not undergo intraoperative PLC were used as a control group. Of the 164 study patients, 41 (25%) patients had positive PLC. Serum SDF-1 concentrations were higher in PLC-positive patients compared with patients negative for PLC and control patients. Serum SDF-1 concentrations were also lower at postoperative day 7 in patients treated with cisplatin plus matrine compared with control patients and those perfused with cisplatin alone. A lower incidence of chemotherapy-related adverse events was observed in patients treated with cisplatin plus matrine versus those treated with cisplatin alone during the first postoperative month. Patients with positive PLC showed a higher CXCR4 protein expression than patients with negative PLC. Based on the results of this study, PLC combined with serum SDF-1 concentration measurements may be considered as an effective index to determine the risk of subclinical pleural metastasis in patients with lung cancer. In addition, cisplatin plus matrine was confirmed as an initial approach for pleural perfusion and was superior to cisplatin alone.

Regulation of CXCL12 expression by canonical Wnt signaling in bone marrow stromal cells

CXCL12 (stromal cell-derived factor-1, SDF-1), produced by stromal and endothelial cells including cells of the bone marrow, binds to its receptor CXCR4 and this axis regulates hematopoietic cell trafficking. Recently, osteoclast precursor cells were found to express CXCR4 and a potential role for the CXCL12-CXCR4 axis during osteoclast precursor cell recruitment/retention and development was proposed as a regulator of bone resorption. We examined the role of canonical Wnt signaling in regulating the expression of CXCL12 in bone marrow stromal cells. In mouse stromal ST2 cells, CXCL12 mRNA was expressed, while its expression was reduced in Wnt3a over-expressing ST2 (Wnt3a-ST2) cells or by treatment with lithium chloride (LiCl). Wnt3a decreased CXCL12 levels in culture supernatants from mouse bone marrow stromal cells. The culture supernatant from Wnt3a-ST2 cells also reduced migratory activity of bone marrow-derived cells in a Transwell migration assay. Silencing of glycogen synthase kinase-3β decreased CXCL12 expression, suggesting that the canonical Wnt signaling pathway regulates CXCL12 expression. In a transfection assay, LiCl down-regulated the activity of a reporter gene, a 1.8kb fragment of the 5'-flanking region of the CXCL12 gene. These results show that canonical Wnt signaling regulates CXCL12 gene expression at the transcriptional level, and this is the first study linking chemokine expression to canonical Wnt signaling.

Stromal-derived factor-1/CXCR4 signaling: indispensable role in homing and engraftment of hematopoietic stem cells in bone marrow

Homing and engraftment of hematopoietic stem/progenitor cells (HSPCs) in bone marrow is the major determining factor in success of hematopoietic stem cell transplantation. This is a complex, multistep process orchestrated by the coordinated interplay between adhesion molecules, cytokines, growth factors, and regulatory cofactors, many of which remain to be defined. Recent studies have highlighted the pivotal role of unique stromal-derived factor-1 (SDF-1)/CXCR4 signaling in the regulation of HSPC homing and subsequent engraftment. In addition, studies suggest that SDF-1/CXCR4 signaling acts as an essential survival-promoting factor of transplanted HSPCs as well as maintenance of quiescent HSCs in bone marrow niche. These pleiotropic effects exerted by SDF-1/CXCR4 axis make this unique signaling initiator very promising, not only for optimal hematopoietic reconstitution but also for the development of innovative approaches to achieve restoration, regeneration, or repair of other damaged tissues potentially amendable to reversal by stem cell transplantation. This goal can only be achieved when the role of SDF-1/CXCR4 axis in hematopoietic transplantation is clearly defined. Hence, this review presents current knowledge of the mechanisms through which SDF-1/CXCR4 signaling promotes restoration of hematopoiesis by regulating the homing and engraftment of HSPCs.

We have got you 'covered': how the meninges control brain development

The meninges have traditionally been viewed as specialized membranes surrounding and protecting the adult brain from injury. However, there is increasing evidence that the fetal meninges play important roles during brain development. Through the release of diffusible factors, the meninges influence the proliferative and migratory behaviors of neural progenitors and neurons in the forebrain and hindbrain. Meningeal cells also secrete and organize the pial basement membrane (BM), a critical anchor point for the radially oriented fibers of neuroepithelial stem cells. With its emerging role in brain development, the potential that defects in meningeal development may underlie certain congenital brain abnormalities in humans should be considered. In this review, we will discuss what is known about assembly of the fetal meninges and review the role of meningeal-derived proteins in mouse and human brain development.

[Dysfunctions of the CXCL12 (SDF-1)/CXCR4 signaling axis in the WHIM syndrome and the idiopathic CD4(+) T-cell lymphocytopenia]

Chemokines are small cytokine-like secreted proteins that govern migration of leukocytes to their specific niches in lymphoid organs and to inflammatory sites. They mediate their functions by binding to and activating chemokine receptors, which belong to the heptahelical G protein-coupled receptor family. The CXC chemokine Stromal cell Derived Factor-1 (SDF-1/CXCL12) is the sole natural ligand for the broadly expressed CXCR4 receptor and acts as a chemoattractant for many leukocyte subsets. The CXCL12/CXCR4 axis exerts critical activities in homeostatic processes such as organogenesis, hematopoiesis and leukocyte trafficking. Dysregulations of CXCR4 signaling and/or expression are associated with several infectious, inflammatory, autoimmune and malignant conditions. In light of recent data, we review here CXCR4 dysfunctions unveiled in two rare human immunodeficiency disorders, one characterized by a gain of CXCR4 function, the WHIM syndrome, and the other by a loss of CXCR4 function, the idiopathic CD4(+) T-cell lymphocytopenia.

Migratory strategies of normal and malignant stem cells

The regulated migration of stem cells is critical for organogenesis during development and for tissue -homeostasis and repair during adulthood. Human bone marrow (BM) represents an accessible reservoir containing regenerative cell types from hematopoietic, endothelial, and mesenchymal-stromal lineages that together coordinate hematopoiesis and promote the repair of damaged vasculature and tissues throughout the body. Thus, a detailed understanding of lineage-specific stem cell mobilization, homing, and subsequent engraftment in areas of injury or disease is of critical importance to the rational development of novel cell-mediated regenerative therapies. Stem cell trafficking via the circulation from site of origin to peripheral tissues requires fundamental molecular pathways governing (1) niche-specific deadhesion of progenitor cells; (2) chemoattraction to guide progenitor cell homing; and (3) interstitial navigation and adhesion/retention of recruited progenitor cells. This overview chapter summarizes the diversity of migratory strategies employed by hematopoietic, endothelial, and mesenchymal-stromal progenitor cells during repair and regeneration after tissue damage. Further elucidation of stem cell homing and migration pathways will allow greater application of stem cells for targeted cell therapy and/or drug delivery for tissue repair. Strikingly similar migratory mechanisms appear to govern the in vivo migration of recently characterized cancer stem cells (CSC) in leukemias and solid tumors, indicating that conserved principles of stem cell migration and niche specificity will provide new information to target CSC in anticancer therapy.

Overlapping and distinct role of CXCR7-SDF-1/ITAC and CXCR4-SDF-1 axes in regulating metastatic behavior of human rhabdomyosarcomas

We have demonstrated that the α-chemokine stromal-derived factor (SDF)-1-CXCR4 axis plays an important role in rhabdomyosarcoma (RMS) metastasis. With the recent description of CXCR7, a new receptor for SDF-1 that also binds the interferon-inducible T-cell α chemoattractant (ITAC) chemokine, we became interested in the role of the CXCR7-SDF-1/ITAC axis in RMS progression. To address this issue, we evaluated 6 highly metastatic alveolar (A)RMS and 3 less metastatic embryonal (E)RMS cell lines and found that all these cell lines express CXCR7. Although CXCR4 was expressed at a much higher level by highly metastatic ARMS lines, CXCR7 was present at a high level on ERMS lines. We also noticed that CXCR7 expression on RMS cells was downregulated in hypoxic conditions. More importantly, the CXCR7 receptor on RMS cell lines was functional after stimulation with ITAC and SDF-1 as evidenced by mitogen-activated protein kinase (MAPK)p42/44 and AKT phosphorylation as well as CXCR7 internalization, chemotaxis, cell motility and adhesion assays. Similarly to CXCR4, signaling from activated CXCR7 was not associated with increased RMS proliferation or cell survival. Moreover, CXCR7(+) RMS cells responded to SDF-1 and I-TAC in the presence of CXCR4 antagonists (T140, AMD3100). Furthermore, while intravenous injection of RMS cells with overexpressed CXCR7 resulted in increased seeding efficiency of tumor cells to bone marrow, CXCR7 downregulation showed the opposite effect. In conclusion, the CXCR7-SDF-1/ITAC axis is involved in the progression of RMS; targeting of the CXCR4-SDF-1 axis alone without simultaneous blockage of CXCR7 will be an inefficient strategy for inhibiting SDF-1-mediated prometastatic responses of RMS cells.

Gene expression profiles following intracoronary injection of mesenchymal stromal cells using a porcine model of chronic myocardial infarction

BACKGROUND AIMS

We evaluated the therapeutic potential of injection of in vitro differentiated bone marrow mesenchymal stromal cells (MSC) using a swine model.

METHODS AND RESULTS

Myocardial infarction was induced by coronary occlusion. Three groups (n = 5 each) were analyzed: one group received an injection of 17.8 ± 9.3 × 10(6) 5-azacytidine-treated allogeneic MSC 1 month after infarction; a placebo group received an injection of medium; and controls were kept untreated. After 4 weeks, heart samples were taken from three infarcted areas, interventricular septa, ventricles and atria. Gene expression profiles of genes related to contractility (Serca2a), fibrosis (Col1a1), cardiomyogenesis (Mef2c, Gata4 and Nkx2.5) and mobilization of stem cells (Sdf1, Cxcr4 and c-kit) were compared by quantitative real-time PCR (qRT-PCR). Gene expression profiles varied in different heart areas. Thus Serca2a expression was reduced in infarcted groups in all heart regions except for the left ventricles, where Col1a1 was overexpressed. The expression of genes related to cardiomyogenesis decreased in the infarcted zones and left atria compared with healthy hearts. Interestingly, increased expression of Cxcr4 was detected in infarcted regions of MSC-treated pigs compared with the placebo group.

CONCLUSIONS

Infarction induced changes in expression of genes involved in various biologic processes. Genes involved in cardiomyogenesis were downregulated in the left atrium. The intracoronary injection of MSC resulted in localized changes in the expression of Cxcr4.

CXCR4 nanobodies (VHH-based single variable domains) potently inhibit chemotaxis and HIV-1 replication and mobilize stem cells

The important family of G protein-coupled receptors has so far not been targeted very successfully with conventional monoclonal antibodies. Here we report the isolation and characterization of functional VHH-based immunoglobulin single variable domains (or nanobodies) against the chemokine receptor CXCR4. Two highly selective monovalent nanobodies, 238D2 and 238D4, were obtained using a time-efficient whole cell immunization, phage display, and counterselection method. The highly selective VHH-based immunoglobulin single variable domains competitively inhibited the CXCR4-mediated signaling and antagonized the chemoattractant effect of the CXCR4 ligand CXCL12. Epitope mapping showed that the two nanobodies bind to distinct but partially overlapping sites in the extracellular loops. Short peptide linkage of 238D2 with 238D4 resulted in significantly increased affinity for CXCR4 and picomolar activity in antichemotactic assays. Interestingly, the monovalent nanobodies behaved as neutral antagonists, whereas the biparatopic nanobodies acted as inverse agonists at the constitutively active CXCR4-N3.35A. The CXCR4 nanobodies displayed strong antiretroviral activity against T cell-tropic and dual-tropic HIV-1 strains. Moreover, the biparatopic nanobody effectively mobilized CD34-positive stem cells in cynomolgus monkeys. Thus, the nanobody platform may be highly effective at generating extremely potent and selective G protein-coupled receptor modulators.

SDF-1-enhanced cardiogenesis requires CXCR4 induction in pluripotent stem cells

Transformation of pluripotent stem cells into cardiac tissue is the hallmark of cardiogenesis, yet pro-cardiogenic signals remain partially understood. Preceding cardiogenic induction, a surge in CXCR4 chemokine receptor expression in the early stages of stem cell lineage specification coincides with the acquisition of pre-cardiac profiles. Accordingly, CXCR4 selection, in conjunction with mesoderm-specific VEGF type II receptor FLK-1 co-expression, segregates cardiogenic populations. To assess the functionality of the CXCR4 biomarker, targeted activation and disruption were here exploited in the context of embryonic stem cell-derived cardiogenesis. Implicated as a cardiogenic hub through unbiased bioinformatics analysis, induction of the CXCR4/SDF-1 receptor-ligand axis triggered enhanced beating activity in stem cell progeny. Gene expression knockdown of CXCR4 disrupted spontaneous embryoid body differentiation and blunted the expression of cardiogenic markers MEF2C, Nkx2.5, MLC2a, MLC2v, and cardiac-MHC. Exogenous SDF-1 treatment failed to rescue cardiogenic-deficient phenotype, demonstrating a requirement for CXCR4 expression in mediating SDF-1 effects. Thus, a pro-cardiogenic signaling role for the CXCR4/SDF1 axis is herein revealed within pluripotent stem cell progenitors, exposing a functional target to promote lineage-specific differentiation.

Combinational polymorphisms of seven CXCL12-related genes are protective against breast cancer in Taiwan

Many single nucleotide polymorphisms (SNPs) have been found to be associated with breast cancer, but their SNP interactions are seldom addressed. In this study, we focused on the joint effect for SNP combinations of seven CXCL12-related genes involved in major cancer-related pathways. SNP genotyping was determined by PCR-restriction fragment length polymorphism (RFLP) in this study (case = 220, control = 334). Different numbers of combinational SNPs with genotypes called the SNP barcodes from different chromosomes were used to evaluate their joint effect on breast cancer risk. Except for vascular endothelial growth factor (VEGF) rs3025039-CT, none of these SNPs were found to individually contribute to breast cancer risk. However, for two combined SNPs, the proportion of subjects with breast cancer was significantly low in the SNP barcode with CC-GG genotypes in rs2228014-1801157 (CXCR4-CXCL12) compared to those with non-CC-GG genotypes. Similarly, the SNP barcode of rs12812942-rs2228014-rs3025039 (CD4-CXCR4-VEGF) and rs12812942-rs3136685-rs2228014-rs1801157 (CD4- CCR7-CXCR4-CXCL12) with specific genotype patterns (AT-CC-CC and AT-AG-CC-GG) among three and four combinational SNPs were significantly low in breast cancer occurrence. More SNP combinations larger than five SNPs were also addressed, and these showed similar effects. After controlling for age, and comparing their corresponding non-SNP barcodes, the estimated odds ratios for breast cancer ranged between 0.20 and 0.71 for specific SNP barcodes with two to seven SNPs. In conclusion, we have associated the potential combined CXCL12-related SNPs with genotypes that were protective against breast cancer, and that may contribute to identification of a low-risk population for the development of breast cancer.

New advances on critical implications of tumor- and metastasis-initiating cells in cancer progression, treatment resistance and disease recurrence

Accumulating lines of experimental evidence have revealed that the malignant transformation of multipotent tissue-resident adult stem/progenitor cells into cancer stem/progenitor cells endowed with a high self-renewal capacity and aberrant multilineage differentiation potential may be at origin of the most types of human aggressive and recurrent cancers. Based on new cancer stem/progenitor cell concepts of carcinogenesis, it is suggested that a small subpopulation of highly tumorigenic and migrating cancer stem/progenitor cells, also designated as cancer- and metastasis-initiating cells, can provide critical roles for primary tumor growth, metastases at distant tissues and organs, treatment resistance and disease relapse. Particularly, cancer initiation and progression to locally invasive and metastatic stages is often associated with a persistent activation of distinct developmental signaling pathways in these immature cells during epithelial-mesenchymal transition program. The signaling cascades that are often deregulated in cancer stem/progenitor cells include hedgehog, epidermal growth factor receptor (EGFR), Wnt/beta-catenin, NOTCH, polycomb gene product BMI-1 and/or stromal cell-derived factor-1 (SDF-1)/CXC chemokine receptor 4 (CXCR4). Importantly, the results from recent investigations have also indicated that different cancer subtypes may harbor distinct subsets and/or number of cancer-initiating cells during cancer progression as well as before or after therapy initiation and disease recurrence. Therefore, the identification of the molecular transforming events that frequently occur in cancer- and metastasis-initiating cells versus their differentiated progenies is of immense interest to develop new targeting approach for improving current therapies against aggressive, metastatic, recurrent and lethal cancers.

Chemokines at the crossroads of tumor-fibroblast interactions that promote malignancy

Cells of the tumor microenvironment play active roles in determining the malignancy phenotype. The host cells and the cancer cells cross-talk via a large variety of soluble factors, whose effects on both partners determine the final outcome of the tumorigenic process. In this review, we focus on the interactions between cancer cells and fibroblasts that are found in their proximity in the growing and progressing tumor and describe the roles of chemokines in mediating such cross-talks. Cancer-associated fibroblasts (CAFs, also termed tumor-associated fibroblasts) were found recently to acquire properties that promote tumor development and metastasis formation, as is also the case for specific members of the chemokine family. In this review, we suggest that there is a bidirectional cross-talk between tumor cells and CAFs, which leads via chemokine activities to increased malignancy. This cross-talk is manifested by the fact that cancer cells release factors that enhance the ability of the fibroblasts to secrete a variety of tumor-promoting chemokines, which then act back on the malignant cells to promote their proliferative, migratory, and invasive properties. The CAF-released chemokines also affect the tumor microenvironment, leading to increased angiogenesis and possibly to an elevated presence of cancer-supporting macrophages in tumors. Here, we describe these bidirectional interactions and the chemokines that are involved in these processes: mainly the CXCL12-CXCR4 pair but also other chemokines, including CCL2, CCL5, CCL7, CXCL8, and CXCL14. The overall findings suggest that chemokines stand at the crossroads of tumor-CAF interactions that lead to increased malignancy in many cancer diseases.

Wnt signaling in pancreatic islets

The Wnt signaling pathway is critically important not only for stem cell amplification, differentiation, and migration, but also is important for organogenesis and the development of the body plan. Beta-catenin/TCF7L2-dependent Wnt signaling (the canonical pathway) is involved in pancreas development, islet function, and insulin production and secretion. The glucoincretin hormone glucagon-like peptide-1 and the chemokine stromal cell-derived factor-1 modulate canonical Wnt signaling in beta-cells which is obligatory for their mitogenic and cytoprotective actions. Genome-wide association studies have uncovered 19 gene loci that confer susceptibility for the development of type 2 diabetes. At least 14 of these diabetes risk alleles encode proteins that are implicated in islet growth and functioning. Seven of them are either components of, or known target genes for, Wnt signaling. The transcription factor TCF7L2 is particularly strongly associated with risk for diabetes and appears to be fundamentally important in both canonical Wnt signaling and beta-cell functioning. Experimental loss of TCF7L2 function in islets and polymorphisms in TCF7L2 alleles in humans impair glucose-stimulated insulin secretion, suggesting that perturbations in the Wnt signaling pathway may contribute substantially to the susceptibility for, and pathogenesis of, type 2 diabetes. This review focuses on considerations of the hormonal regulation of Wnt signaling in islets and implications for mutations in components of the Wnt signaling pathway as a source for risk-associated alleles for type 2 diabetes.

Strategies to enhance umbilical cord blood stem cell engraftment in adult patients

Umbilical cord blood (UCB) has been used successfully as a source of hematopoietic stem cells (HSCs) for allogeneic transplantation in children and adults in the treatment of hematologic diseases. However, compared with marrow or mobilized peripheral blood stem cell grafts from adult donors, significant delays in the rates and kinetics of neutrophil and platelet engraftment are noted after UCB transplant. These differences relate in part to the reduced numbers of HSCs in UCB grafts. To improve the rates and kinetics of engraftment of UCB HSC, several strategies have been proposed, including ex vivo expansion of UCB HSCs, addition of third-party mesenchymal cells, intrabone delivery of HSCs, modulation of CD26 expression, and infusion of two UCB grafts. This article will focus on ex vivo expansion of UCB HSCs and strategies to enhance UCB homing as potential solutions to overcome the problem of low stem cell numbers in a UCB graft.