CCL2 Regulates Angiogenesis via Activation of Ets-1 Transcription Factor

Diabetes impairs the angiogenic potential of adipose-derived stem cells by selectively depleting cellular subpopulations

Introduction

Pathophysiologic changes associated with diabetes impair new blood vessel formation and wound healing. Mesenchymal stem cells derived from adipose tissue (ASCs) have been used clinically to promote healing, although it remains unclear whether diabetes impairs their functional and therapeutic capacity.

Methods

In this study, we examined the impact of diabetes on the murine ASC niche as well as on the potential of isolated cells to promote neovascularization in vitro and in vivo. A novel single-cell analytical approach was used to interrogate ASC heterogeneity and subpopulation dynamics in this pathologic setting.

Results

Our results demonstrate that diabetes alters the ASC niche in situ and that diabetic ASCs are compromised in their ability to establish a vascular network both in vitro and in vivo. Moreover, these diabetic cells were ineffective in promoting soft tissue neovascularization and wound healing. Single-cell transcriptional analysis identified a subpopulation of cells which was diminished in both type 1 and type 2 models of diabetes. These cells were characterized by the high expression of genes known to be important for new blood vessel growth.

Conclusions

Perturbations in specific cellular subpopulations, visible only on a single-cell level, represent a previously unreported mechanism for the dysfunction of diabetic ASCs. These data suggest that the utility of autologous ASCs for cell-based therapies in patients with diabetes may be limited and that interventions to improve cell function before application are warranted.

Depletion of the aryl hydrocarbon receptor in MDA-MB-231 human breast cancer cells altered the expression of genes in key regulatory pathways of cancer

The aryl hydrocarbon receptor (AhR), a transcription factor that is best known for its role in mediating the toxic responses elicited by poly aromatic hydrocarbons as well as many other environmental factors; is also involved in breast cancer progression. We previously reported that stable knockdown of AhR decreased the tumorigenic properties of the highly metastatic MDA-MB-231 breast cancer cell line; whereas ectopic overexpression of AhR was sufficient to transform immortalized human mammary epithelial cells to exhibit malignant phenotypes. In the present study we investigated the genes that are differentially regulated by AhR and are controlling cellular processes linked to breast cancer. We used Affymetrix Human GeneChip 1.0-ST whole transcriptome arrays to analyze alterations of gene expression resulting from stable AhR knockdown in the MDA-MB-231 breast cancer cell line. The expression of 144 genes was significantly altered with a ≥2.0-fold change and a multiple test corrected p-value ≤0.05, as a result of AhR knockdown. We demonstrate that AhR knockdown alters the expression of several genes known to be linked to cancer. These genes include those involved in tryptophan metabolism (KYNU), cell growth (MUC1 and IL8), cell survival (BIRC3 and BCL3), cell migration and invasion (S100A4 and ABI3), multi-drug resistance (ABCC3) and angiogenesis (VEGFA and CCL2). The identification of the genes and pathways affected by AhR depletion provides new insight into possible molecular events that could explain the reported phenotypic changes. In conclusion AhR knockdown alters the expression of genes known to enhance or inhibit cancer progression; tipping the balance towards a state that counteracts tumor progression.

CXC and CC chemokines as angiogenic modulators in nonhaematological tumors

Chemokines are a superfamily of structurally homologous heparin-binding proteins that includes potent inducers and inhibitors of angiogenesis. The imbalance between angiogenic and angiostatic chemokine activities can lead to abnormalities, such as chronic inflammation, dysplastic transformation, and even tumor development and spreading. In this review, we summarize the current literature regarding the role of chemokines as modulators of tumor angiogenesis and their potential role as therapeutic targets in patients with nonhaematological tumors.

Clinical-Grade Human Neural Stem Cells Promote Reparative Neovascularization in Mouse Models of Hindlimb Ischemia

Objective—

CTX0E03 (CTX) is a clinical-grade human neural stem cell (hNSC) line that promotes angiogenesis and neurogenesis in a preclinical model of stroke and is now under clinical development for stroke disability. We evaluated the therapeutic activity of intramuscular CTX hNSC implantation in murine models of hindlimb ischemia for potential translation to clinical studies in critical limb ischemia.

Approach and Results—

Immunodeficient (CD-1 Fox nu/nu ) mice acutely treated with hNSCs had overall significantly increased rates and magnitude of recovery of surface blood flow (laser Doppler), limb muscle perfusion (fluorescent microspheres, P <0.001), and capillary and small arteriole densities in the ischemic limb (fluorescence immunohistochemistry, both P <0.001) when compared with the vehicle-treated group. Hemodynamic and anatomic improvements were dose related and optimal at a minimum dose of 3×10 5 cells. Dose-dependent improvements in blood flow and increased vessel densities by hNSC administration early after ischemia were confirmed in immunocompetent CD-1 and streptozotocin-induced diabetic mice, together with marked reductions in the incidence of necrotic toes ( P <0.05). Delayed administration of hNSCs, 7 days after occlusion, produced restorative effects when comparable with acute treatment of 35 days after hindlimb ischemia. Histological studies in hindlimb ischemia immunocompetent mice for the first 7 days after treatment revealed short-term hNSC survival, transient elevation of early host muscle inflammatory, and angiogenic responses and acceleration of myogenesis.

Conclusions—

hNSC therapy represents a promising treatment option for critical limb ischemia.

Tumor-conditioned Gr-1(+)CD11b(+) myeloid cells induce angiogenesis through the synergistic action of CCL2 and CXCL16 in vitro

Gr-1(+)CD11b(+) cells can suppress innate and adaptive immunity, and the functional immunosuppressive characteristics of these cells can be modulated by the tumor microenvironment. Since Gr-1(+)CD11(+) cells are also involved in tumor-associated angiogenesis, we hypothesized that the angiogenic nature of Gr-1(+)CD11b(+) cells could be regulated by the tumor milieu. To address this hypothesis, we imitated a tumor microenvironment by exposing Gr-1(+)CD11b(+) cells isolated from spleen of 4T1 mammary carcinoma-bearing mice to tumor-conditioned medium. Supernatants from tumor-conditioned Gr-1(+)CD11b(+) cells significantly induced capillary-like tube formation and migration of human umbilical vein endothelial cells (HUVECs) compared to naive Gr-1(+)CD11b(+) cells. Incubation of Gr-1(+)CD11b(+) cells with tumor-conditioned medium induced production of pro-angiogenic chemokines CCL2 and CXCL16. Pretreatment with an anti-CCL2 antibody, but not an anti-CXCL16 antibody, suppressed the angiogenic effects of tumor-conditioned Gr-1(+)CD11b(+) cells on HUVECs. Simultaneous neutralization of CCL2 and CXCL16 significantly inhibited tube formation and migration of HUVECs compared to the sole neutralization against CCL2. Supernatants from tumor-conditioned Gr-1(+)CD11b(+) cells induced phosphorylation of ERK1/2 in HUVECs, and inhibition of the ERK pathway blocked angiogenic effects. ERK pathway activity was partially abrogated by neutralization of CCL2 and more suppressed by simultaneous neutralization of CCL2 and CXCL16. These results collectively indicate that CCL2 and CXCL16 chemokines produced by tumor-conditioned Gr-1(+)CD11b(+) myeloid cells synergistically induce angiogenesis in vitro by stimulating the ERK1/2 signaling pathway. Thus, regulation of Gr-1(+)CD11b(+) cells in the tumor microenvironment may contribute to angiogenesis through the secretion of pro-angiogenic chemokines.

SDF-1/CXCR4 axis promotes directional migration of colorectal cancer cells through upregulation of integrin αvβ6

Colorectal cancer (CRC) displays a predilection for metastasis to liver. Although stromal cell-derived factor-1 (SDF-1)/CXCR4 plays an important role in the liver metastasis, the molecular mechanism still remains obscure. We previously reported that integrin αvβ6 was implicated in the progression of CRC. However, no data are currently available on the cross talk between CXCR4 and αvβ6. In the present study, we first demonstrated the cross talk between CXCR4 and αvβ6 and their role in liver metastasis of CRC. We analyzed 159 human CRC samples and found that expression of CXCR4 and αvβ6 was significantly associated with liver metastasis, and interestingly expression of αvβ6 significantly correlated with expression of CXCR4. Both CXCR4 and αvβ6 were highly expressed in metastatic CRC cell lines HT-29 and WiDr, whereas both of them were exiguous in non-metastatic cell line Caco-2. Furthermore, inhibition of αvβ6 significantly decreased SDF-1α-induced cell migration in vitro. SDF-1/CXCR4 could upregulate αvβ6 expression through phosphorylation of ERK and activation of Ets-1 transcription factor. In conclusion, we demonstrate that SDF-1/CXCR4 induces directional migration and liver metastasis of CRC cells by upregulating αvβ6 through ERK/Ets-1 pathway. These data support combined inhibition of CXCR4 and αvβ6 to prevent development of liver metastasis of CRC.

FGFR4 promotes stroma-induced epithelial-to-mesenchymal transition in colorectal cancer

Tumor cells evolve by interacting with the local microenvironment; however, the tumor-stroma interactions that govern tumor metastasis are poorly understood. In this study, proteomic analyses reveal that coculture with tumor-associated fibroblasts (TAF) induces significant overexpression of FGFR4, but not other FGFRs, in colorectal cancer cell lines. Mechanistic study shows that FGFR4 plays crucial roles in TAF-induced epithelial-to-mesenchymal transition (EMT) in colorectal cancer cell lines. Accumulated FGFR4 in cell membrane phosphorylates β-catenin, leading to translocation of β-catenin into the nucleus. Further, TAF-derived CCL2 and its downstream transcription factor, Ets-1, are prerequisites for TAF-induced FGFR4 upregulation. Furthermore, FGFR4-associated pathways are shown to be preferentially activated in colorectal tumor samples, and direct tumor metastasis in a mouse metastasis model. Our study shows a pivotal role of FGFR4 in tumor-stroma interactions during colorectal cancer metastasis, and suggests novel therapeutic opportunities for the treatment of colorectal cancer.

A computational model predicting disruption of blood vessel development

Vascular development is a complex process regulated by dynamic biological networks that vary in topology and state across different tissues and developmental stages. Signals regulating de novo blood vessel formation (vasculogenesis) and remodeling (angiogenesis) come from a variety of biological pathways linked to endothelial cell (EC) behavior, extracellular matrix (ECM) remodeling and the local generation of chemokines and growth factors. Simulating these interactions at a systems level requires sufficient biological detail about the relevant molecular pathways and associated cellular behaviors, and tractable computational models that offset mathematical and biological complexity. Here, we describe a novel multicellular agent-based model of vasculogenesis using the CompuCell3D (http://www.compucell3d.org/) modeling environment supplemented with semi-automatic knowledgebase creation. The model incorporates vascular endothelial growth factor signals, pro- and anti-angiogenic inflammatory chemokine signals, and the plasminogen activating system of enzymes and proteases linked to ECM interactions, to simulate nascent EC organization, growth and remodeling. The model was shown to recapitulate stereotypical capillary plexus formation and structural emergence of non-coded cellular behaviors, such as a heterologous bridging phenomenon linking endothelial tip cells together during formation of polygonal endothelial cords. Molecular targets in the computational model were mapped to signatures of vascular disruption derived from in vitro chemical profiling using the EPA's ToxCast high-throughput screening (HTS) dataset. Simulating the HTS data with the cell-agent based model of vascular development predicted adverse effects of a reference anti-angiogenic thalidomide analog, 5HPP-33, on in vitro angiogenesis with respect to both concentration-response and morphological consequences. These findings support the utility of cell agent-based models for simulating a morphogenetic series of events and for the first time demonstrate the applicability of these models for predictive toxicology.

Monocyte chemoattractant protein-1/CCL2 produced by stromal cells promotes lung metastasis of 4T1 murine breast cancer cells

MCP-1/CCL2 plays an important role in the initiation and progression of cancer. Since tumor cells produce MCP-1, they are considered to be the main source of this chemokine. Here, we examined whether MCP-1 produced by non-tumor cells affects the growth and lung metastasis of 4T1 breast cancer cells by transplanting them into the mammary pad of WT or MCP-1^−/− mice. Primary tumors at the injected site grew similarly in both mice; however, lung metastases were markedly reduced in MCP-1^−/− mice, with significantly longer mouse survival. High levels of MCP-1 mRNA were detected in tumors growing in WT, but not MCP-1^−/− mice. Serum MCP-1 levels were increased in tumor-bearing WT, but not MCP-1^−/− mice. Transplantation of MCP-1^−/− bone marrow cells into WT mice did not alter the incidence of lung metastasis, whereas transplantation of WT bone marrow cells into MCP-1^−/− mice increased lung metastasis. The primary tumors of MCP-1^−/− mice consistently developed necrosis earlier than those of WT mice and showed decreased infiltration by macrophages and reduced angiogenesis. Interestingly, 4T1 cells that metastasized to the lung constitutively expressed elevated levels of MCP-1, and intravenous injection of 4T1 cells producing a high level of MCP-1 resulted in increased tumor foci in the lung of WT and MCP-1^−/− mice. Thus, stromal cell-derived MCP-1 in the primary tumors promotes lung metastasis of 4T1 cells, but tumor cell-derived MCP-1 can also contribute once tumor cells enter the circulation. A greater understanding of the source and role of this chemokine may lead to novel strategies for cancer treatment.

Effects of interleukin-1β and tumor necrosis factor-α on macrophage inflammatory protein-3α production in synovial fibroblast-like cells from human temporomandibular joints

Background

Interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are key mediators of the intracapsular pathological conditions of the temporomandibular joint (TMJ). Therefore, the gene expression profiles in synovial fibroblast-like cells (SFCs) from patients with internal derangement of the TMJ were examined after they were stimulated with IL-1β or TNF-α to determine which genes were altered.

Methods

Ribonucleic acid was isolated from SFCs after IL-1β or TNF-α treatment. Gene expression profiling was performed using oligonucleotide microarray analysis. On the basis of the results of this assay, we investigated the kinetics of macrophage inflammatory protein-3α (MIP-3α) gene expression using PCR, and protein production in TMJ SFCs stimulated by IL-1β or TNF-α using an ELISA. Inhibition experiments were performed with MAPK and NFκB inhibitors. SFCs were stimulated with IL-1β or TNF-α after treatment with inhibitors. The MIP-3α levels were measured using an ELISA.

Results

Macrophage inflammatory protein-3α was the gene most upregulated by IL-1β- or TNF-α stimulation. The mRNA and protein levels of MIP-3α increased in response to IL-1β in a time-dependent manner. In contrast, during TNF-α stimulation, the MIP-3α mRNA levels peaked at 4 h, and the protein levels peaked at 8 h. In addition, the IL-1β- and TNF-α-stimulated MIP-3α production was potently reduced by the MAPK and NFκB signaling pathway inhibitors.

Conclusion

Interleukin-1β and TNF-α increased the MIP-3α production in SFCs via the MAPK and NFκB pathways. These results suggest that the production of MIP-3α from stimulation with IL-1β or TNF-α is one factor associated with the inflammatory progression of the internal derangement of the TMJ.

Gadd45a suppresses tumor angiogenesis via inhibition of the mTOR/STAT3 protein pathway

Gadd45a, a p53-regulated and DNA damage-inducible gene, is implicated in protection against tumor malignancy, although the underlying mechanism remains to be defined further. Here we demonstrate that Gadd45a plays an important role in suppression of tumor angiogenesis. Gadd45a deletion significantly increases microvessel density in tumors and stimulates an angiogenic response in a chicken embryo chorioallantoic membrane assay. Disruption of endogenous Gadd45a promotes tube formation and migration of endothelial cells. We further show that Gadd45a deletion increases phosphorylation of STAT3 at Ser-727 and, in turn, elevates the STAT3 transcriptional activity. This process substantially induces both expression and secretion of VEGFa, a STAT3 responsive gene, and promotes tumor angiogenesis. Interestingly, Gadd45a is able to physically associate with mammalian target of rapamycin (mTOR), a kinase that mediates Ser-727 phosphorylation of STAT3. The interaction of Gadd45a with mTOR suppresses STAT3 phosphorylation at Ser-727 and leads to down-regulated expression of VEGFa. Further analysis reveals that Gadd45a overexpression attenuates the association between mTOR and STAT3, whereas Gadd45a disruption strengthens this interaction, indicating that Gadd45a suppression of STAT3 phosphorylation is mainly through the dissociation of mTOR with STAT3. Taken together, these findings provide the first evidence that Gadd45a inhibits tumor angiogenesis via blocking of the mTOR/STAT3 pathway.

Hypoxic preconditioning induces stroke tolerance in mice via a cascading HIF, sphingosine kinase, and CCL2 signaling pathway

The induction of ischemic tolerance by preconditioning provides a platform to elucidate endogenous mechanisms of stroke protection. In these studies, we characterize the relationship between hypoxia-inducible factor (HIF), sphingosine kinase 2 (SphK2), and chemokine (C-C motif) ligand 2 (CCL2) in models of hypoxic or pharmacological preconditioning-induced ischemic tolerance. A genetics-based approach using SphK2- and CCL2-null mice showed both SphK2 and CCL2 to be necessary for the induction of ischemic tolerance following preconditioning with hypoxia, the hypoxia-mimetic cobalt chloride, or the sphingosine-1-phosphate (S1P) agonist FTY720. A pharmacological approach confirmed the necessity of HIF signaling for all three preconditioning stimuli, and showed that the SphK/S1P pathway transduces tolerance via the S1P(1) receptor. In addition, our data suggest significant cross-talk between HIF and SphK2-produced S1P signaling, which together act to up-regulate CCL2 expression. Overall, HIF, SphK, S1P, and CCL2 participate in a signaling cascade to induce the gene expression responsible for the stroke-tolerant phenotype established by hypoxic and FTY720 preconditioning. The identification of these common molecular mediators involved in signaling the genomic response to multiple preconditioning stimuli provides several targets for therapeutic manipulation.

Multi-walled carbon nanotube directed gene and protein expression in cultured human aortic endothelial cells is influenced by suspension medium

The use and production of multi-walled carbon nanotubes (MWCNTs) have significantly increased over the last decade due to their versatility in numerous applications. Their unique physical and chemical properties make them desirable for various biomedical applications, but the same properties also raise concerns about their safety to human health, particularly at the cellular level. The vascular endothelium could be exposed to nanomaterials either by direct intravenous administration in nanomedicine or by translocation following inhalational exposure in an occupational setting. We hypothesized that direct exposure to MWCNTs will increase the expression of inflammatory markers in human aortic endothelial cells (HAEC). We also investigated the effect of the route of exposure on activation by changing the suspension medium of the MWCNTs. HAEC were treated in vitro with MWCNTs (1 or 10 μg/cm(2)) suspended in either cell culture medium [(M)-MWCNTs] or 10% clinical grade pulmonary surfactant [(S)-MWCNTs]. The zeta potential of the (S)-MWCNTs was significantly more negative than the (M)-MWCNTs suggesting a more stable suspension. Treatment of HAEC with (S)-MWCNTs; as compared to (M)-MWCNTs resulted in a significantly higher up-regulation of mRNA transcripts for cell adhesion molecules VCAM1, SELE, ICAM1 and the chemokine CCL2. Time dependent changes in VCAM1 and CCL2 protein levels were confirmed by immunofluorescence, flow cytometry and ELISA. A label free quantitative mass spectrometry proteomic analysis was utilized to compare protein expression patterns between the two suspensions of MWCNTs. We identified significant expression changes in >200 unique proteins in MWCNT treated HAEC. However, the two suspensions of MWCNTs resulted in different protein expression patterns with the eIF2 pathway as the only common pathway identified between the two suspensions. These data suggest that direct exposure to MWCNTs induces acute inflammatory and protein expression changes in HAEC, which is influenced by the type of media used for suspension of MWCNTs and their resulting zeta potential.

The role of CXC chemokines and their receptors in the progression and treatment of tumors

Chemokines are a class of functional chemotactic peptides that contribute to a number of tumor-related processes. They are functionally defined as soluble factors that are able to control the directional migration of leukocytes, in particular, during infection and inflammation. It appears, however, that the biological effects mediated by chemokines are far more complex, and virtually all cells, including many tumor cell types, can express chemokines and chemokine receptors. A growing body of evidence indicates that they also contribute to a number of tumor-related processes, such as tumor cell growth, angiogenesis/angiostasis, local invasion, and mediate organ-specific metastases of cancer. The CXC chemokine class is a subfamily of a large family of chemokines. During the occurrence and development of tumor cells, this chemokine class is often accompanied by a series of molecular and biological changes. The CXC chemokine subfamily is closely related to the body's immune response to tumors and biological behaviors of tumors. In this paper, CXC chemokines and their role in the progression and treatment of tumors will be reviewed.

CCL2 upregulation triggers hypoxic preconditioning-induced protection from stroke

Background

A brief exposure to systemic hypoxia (i.e., hypoxic preconditioning; HPC) prior to transient middle cerebral artery occlusion (tMCAo) reduces infarct volume, blood-brain barrier disruption, and leukocyte migration. CCL2 (MCP-1), typically regarded as a leukocyte-derived pro-inflammatory chemokine, can also be directly upregulated by hypoxia-induced transcription. We hypothesized that such a hypoxia-induced upregulation of CCL2 is required for HPC-induced ischemic tolerance.

Methods

Adult male SW/ND4, CCL2-null, and wild-type mice were used in these studies. Cortical CCL2/CCR2 message, protein, and cell-type specific immunoreactivity were determined following HPC (4 h, 8% O₂) or room air control (21% O₂) from 6 h through 2 weeks following HPC. Circulating leukocyte subsets were determined by multi-parameter flow cytometry in naïve mice and 12 h after HPC. CCL2-null and wild-type mice were exposed to HPC 2 days prior to tMCAo, with immunoneutralization of CCL2 during HPC achieved by a monoclonal CCL2 antibody.

Results

Cortical CCL2 mRNA and protein expression peaked at 12 h after HPC (both p < 0.01), predominantly in cortical neurons, and returned to baseline by 2 days. A delayed cerebral endothelial CCL2 message expression (p < 0.05) occurred 2 days after HPC. The levels of circulating monocytes (p < 0.0001), T lymphocytes (p < 0.0001), and granulocytes were decreased 12 h after HPC, and those of B lymphocytes were increased (p < 0.0001), but the magnitude of these respective changes did not differ between wild-type and CCL2-null mice. HPC did decrease the number of circulating CCR2⁺ monocytes (p < 0.0001) in a CCL2-dependent manner, but immunohistochemical analyses at this 12 h timepoint indicated that this leukocyte subpopulation did not move into the CNS. While HPC reduced infarct volumes by 27% (p < 0.01) in wild-type mice, CCL2-null mice subjected to tMCAo were not protected by HPC. Moreover, administration of a CCL2 immunoneutralizing antibody prior to HPC completely blocked (p < 0.0001 vs. HPC-treated mice) the development of ischemic tolerance.

Conclusions

The early expression of CCL2 in neurons, the delayed expression of CCL2 in cerebral endothelial cells, and CCL2-mediated actions on circulating CCR2⁺ monocytes, appear to be required to establish ischemic tolerance to focal stroke in response to HPC, and thus represent a novel role for this chemokine in endogenous neurovascular protection.

Dissecting the autocrine and paracrine roles of the CCR2-CCL2 axis in tumor survival and angiogenesis

The CCL2 CCR2 axis is likely to contributes to the development and progression of cancer diseases by two major mechanisms; autocrine effect of CCL2 as a survival/growth factor for CCR2+ cancer cells and, the attraction of CCR2+ CX₃CR1+tumor associated macrophages that in the absence of CCR2 hardly migrate. Thus far no in vivo system has been set up to differentiate the selective contribution of each of these features to cancer development. Here we employed a chimera animal model in which all non-malignant cells are CCR2-/-, but all cancer cells are CCR2+, combined with an adoptive transfer system of bone marrow (BM) CX₃CR1+ cells from CCR2+ mice harboring a targeted replacement of the CX₃CR1gene by an enhanced green fluorescent protein (EGFP) reporter gene (cx₃cr1(gfp)), together with the CD45.1 congene. Using this system we dissected the selective contribution of CX₃CR1+CCR2+ cells, which comprise only about 7% of CD11b+ BM cells, to tumor development and angiogenesis. Showing that aside for their direct pro-angiogenic effect they are essential for the recruitment of other CD11b+ cells to the tumor site. We further show that the administration of CCR2-Ig, that selectively and specifically neutralize CCL2, to mice in which CCR2 is expressed only on tumor cells, further suppressed tumor development, implicating for the key role of this chemokine supporting tumor survival in an autocrine manner. This further emphasizes the important role of CCL2 as a target for therapy of cancer diseases.

Chemokines as markers of local inflammation and angiogenesis in patients with chronic subdural hematoma: a prospective study

OBJECTIVE

The goal of this study was to investigate the chemokines CCL2, CXCL8, CXCL9 and CXCL10 as markers of the inflammatory responses in chronic subdural hematoma (CSDH).

METHODS

Samples of peripheral venous blood and CSDH fluid (obtained during surgery) in 76 adult patients were prospectively analyzed. Chemokine values were assessed by a Multiplex antibody bead kit.

RESULTS

We found significantly higher levels of chemokines CCL2, CXCL8, CXCL9 and CXCL10 in hematoma fluid compared with serum.

CONCLUSIONS

Chemokines are elevated in the hematoma cavity of patients with CSDH. It is likely that these signaling modulators play an important role in promoting local inflammation. Furthermore, biological activity of CCL2 and CXCL8 may promote neovascularization within the outer CSDH membrane, and a compensatory angiostatic activity of CXCL9 and CXCL10 may contribute to repairing this disorder. This phenomenon was restricted to the hematoma site, and the systemic chemokine levels might not reflect local immune responses.

The Tumor-Promoting Flow of Cells Into, Within and Out of the Tumor Site: Regulation by the Inflammatory Axis of TNFα and Chemokines

Tumors are dynamic organs, in which active processes of cell motility affect disease course by regulating the composition of cells at the tumor site. While sub-populations of tumor-promoting leukocytes are recruited inward and endothelial cell migration stands in the basis of vascular branching throughout the tumor, cancer cells make their way out of the primary site towards specific metastatic sites. This review describes the independent and cross-regulatory roles of inflammatory chemokines and of the inflammatory cytokine tumor necrosis factor α (TNFα) in determining cell motility processes that eventually have profound effects on tumor growth and metastasis. First, the effects of inflammatory chemokines such as CCL2 (MCP-1), CCL5 (RANTES) and CXCL8 (IL-8) are described, regulating the inward flow of leukocyte sub-populations with pro-tumoral activities, such as tumor-associated macrophages (TAM), myeloid-derived suppressor cells (MDSC), tumor-associated neutrophils (TAN), Th17 cells and Tregs. Then, the ability of inflammatory chemokines to induce endothelial cell migration, sprouting and tube formation is discussed, with its implications on tumor angiogenesis. This part is followed by an in depth description of the manners by which TNFα potentiates the above activities of the inflammatory chemokines, alongside with its ability to directly induce migratory processes in the tumor cells thus promoting metastasis. Note worthy is the ability of TNFα to induce in the tumor cells the important process of epithelial-to-mesenchymal transition (EMT). Emphasis is given to the ability of TNFα to establish an inflammatory network with the chemokines, and in parallel to form a cell re-modeling network together with transforming growth factor β (TGFβ). The review concludes by discussing the implications of such networks on disease course, and on the future design of therapeutic measures in cancer.

Tissue Factor Regulates Microvessel Formation and Stabilization by Induction of Chemokine (C-C motif) Ligand 2 Expression

Objective—

Tissue factor (TF) triggers arterial thrombosis. TF is also able to initiate cellular signaling mechanisms leading to angiogenesis. Because high cardiovascular risk atherosclerotic plaques show significant angiogenesis, our objective was to investigate whether TF is able to trigger and stabilize atherosclerotic plaque neovessel formation.

Methods and Results—

In this study, we showed, by real-time confocal microscopy in 3-dimensional basement membrane cocultures, that TF in human microvascular endothelial cells (HMEC-1) and in human vascular smooth muscle cells (HVSMCs) plays an important role in the formation of capillary-like networks. TF silencing in endothelial cells and smooth muscle cells inhibits the formation of tube-like structures with stable phenotype. Using an in vivo model, we observed that TF inhibition in either HMEC-1 or HVSMCs reduced their shared ability to form new capillaries. The phenotypic changes induced by TF silencing were linked to reduced chemokine (C-C motif) ligand 2 (CCL2) expression in endothelial cells. Wound healing and chemotactic assays demonstrated that TF-induced release of CCL2 stimulated HVSMC migration to HMEC-1.

Conclusion—

Endogenous TF regulates CCL2 production in endothelial cells. Secreted CCL2 mediates the angiogenic effect of TF by recruiting smooth muscle cells toward endothelial cells and facilitates the maturation of newly formed microvessels.

The role of chemokines and their receptors in angiogenesis

Chemokines are a vertebrate-specific group of small molecules that regulate cell migration and behaviour in diverse contexts. So far, around 50 chemokines have been identified in humans, which bind to 18 different chemokine receptors. These are members of the seven-transmembrane receptor family. Initially, chemokines were identified as modulators of the immune response. Subsequently, they were also shown to regulate cell migration during embryonic development. Here, we discuss the influence of chemokines and their receptors on angiogenesis, or the formation of new blood vessels. We highlight recent advances in our understanding of how chemokine signalling might directly influence endothelial cell migration. We furthermore examine the contributions of chemokine signalling in immune cells during this process. Finally, we explore possible implications for disease settings, such as chronic inflammation and tumour progression.

A theoretical molecular network for dyslexia: integrating available genetic findings

Developmental dyslexia is a common specific childhood learning disorder with a strong heritable component. Previous studies using different genetic approaches have identified several genetic loci and candidate genes for dyslexia. In this article, we have integrated the current knowledge on 14 dyslexia candidate genes suggested by cytogenetic findings, linkage and association studies. We found that 10 of the 14 dyslexia candidate genes (ROBO1, KIAA0319, KIAA0319L, S100B, DOCK4, FMR1, DIP2A, GTF2I, DYX1C1 and DCDC2) fit into a theoretical molecular network involved in neuronal migration and neurite outgrowth. Based on this, we also propose three novel dyslexia candidate genes (SLIT2, HMGB1 and VAPA) from known linkage regions, and we discuss the possible involvement of genes emerging from the two reported genome-wide association studies for reading impairment-related phenotypes in the identified network.

Suppression of uPA and uPAR blocks radiation-induced MCP-1 mediated recruitment of endothelial cells in meningioma

Chemokines play a vital role in recruiting various cell types in the process of tissue repair. Radiation, a major therapeutic modality in cancer treatment, has been described to induce inflammatory response that might lead to the expression of several chemokines. In the present study, we investigated the mechanism of monocyte chemoattractant protein-1 (MCP-1) induction by radiation in meningioma cell lines and the paracrine effect on human microvascular endothelial cells (HMEC). After radiation, meningioma cell lines (IOMM Lee and SF-3061) showed an increased expression of MCP-1. In addition, irradiated meningioma cancer cell conditioned medium (CM) showed an increased ability to attract HMEC and to stimulate MCP-1-induced protein (MCPIP), VEGF and angiogenin expression in HMEC. This chemotactic activity and angiogenic stimulator effect on HMEC were almost abrogated by depleting MCP-1 from the irradiated cancer cell CM. Further, inhibition of either ERK activation/expression or NF-κB nuclear translocation hindered radiation-induced MCP-1 expression in both meningioma cell lines. Further, supplementing cancer cells with exogenous ATF-uPA (with and without radiation) activated ERK phosphorylation, nuclear translocation of the NF-κB p65 sub-unit (Rel-A), and MCP-1 expression. Downregulation of uPA and uPAR, simultaneously by transfecting the cancer cells with bi-cistronic siRNA-expressing plasmid (pU) inhibited radiation-induced ERK activation, nuclear translocation of Rel-A, NF-κB DNA binding activity, and MCP-1 expression. In addition, pU-transfected cancer cells (with or without radiation) reduced radiation-induced MCP-1 and blocked the recruitment of other cell types during the inflammatory process induced by radiation both in in vitro and in vivo conditions.

Chemokines in angiogenesis

Chemokines are a family of small heparin-binding proteins, mostly known for their role in inflammation and immune surveillance, which have emerged as important regulators of angiogenesis. Chemokines influence angiogenesis either through recruitment of pro-angiogenic immune cells and endothelial progenitors to the neo-vascular niche or via direct regulation of endothelial function downstream of activation of G-protein coupled chemokine receptors. The dual function of chemokines in regulating immune response and angiogenesis confers a central role in modulating the tissue microenvironment. Therefore, chemokines may constitute attractive targets for therapeutic intervention in several pathological disorders. This review will summarize the current understanding of the role of chemokines in angiogenesis, and give an overview of angiostatic and angiogenic chemokines and their crosstalk with other angiogenic factors.

TLR4 inhibits mesenchymal stem cell (MSC) STAT3 activation and thereby exerts deleterious effects on MSC-mediated cardioprotection

Background

Bone marrow-derived mesenchymal stem cells (MSC) improve myocardial recovery after ischemia/reperfusion (I/R) injury. These effects are mediated in part by the paracrine secretion of angiogenic and tissue growth-promoting factors. Toll-like receptor 4 (TLR4) is expressed by MSC and induces apoptosis and inhibits proliferation in neuronal progenitors as well as many other cell types. It is unknown whether knock-out (KO) of TLR4 will change the paracrine properties of MSC and in turn improve MSC-associated myocardial protection.

Methodology/Principal Findings

This study explored the effect of MSC TLR4 on the secretion of angiogenic factors and chemokines in vitro by using ELISA and cytokine array assays and investigated the role of TLR4 on MSC-mediated myocardial recovery after I/R injury in an isolated rat heart model. We observed that MSC isolated from TLR4 KO mice exhibited a greater degree of cardioprotection in a rat model of myocardial I/R injury. This enhanced protection was associated with increased angiogenic factor production, proliferation and differentiation. TLR4-dificiency was also associated with decreased phosphorylation of PI-3K and AKT, but increased activation of STAT3. siRNA targeting of STAT3 resulted in attenuation of the enhanced cardioprotection of TLR4-deficient MSC.

Conclusions/Significance

This study indicates that TLR4 exerts deleterious effects on MSC-derived cardioprotection following I/R by a STAT3 inhibitory mechanism.

Chemokines as mediators of tumor angiogenesis and neovascularization

Chemokines are a superfamily of structurally homologous heparin-binding proteins that influence tumor growth and metastasis. Several members of the CXC and CC chemokine families are potent inducers of neovascularization, whereas a subset of the CXC chemokines are potent inhibitors. In this paper, we review the current literature regarding the role of chemokines as mediators of tumor angiogenesis and neovascularization.

The role of ets factors in tumor angiogenesis

Angiogenesis is a critical component of tumor growth. A number of growth factors, including VEGF, FGF, and HGF, have been implicated as angiogenic growth factors that promote tumor angiogenesis in different types of cancer. Ets-1 is the prototypic member of the Ets transcription factor family. Ets-1 is known to be a downstream mediator of angiogenic growth factors. Expression of Ets-1 in a variety of different tumors is associated with increased angiogenesis. A role for other selected members of the Ets transcription factor family has also been shown to be important for the development of tumor angiogenesis. Because Ets factors also express a number of other important genes involved in cell growth, they contribute not only to tumor growth, but to disease progression. Targeting Ets factors in mouse tumor models through the use of dominant-negative Ets proteins or membrane permeable peptides directed at competitively inhibiting the DNA binding domain has now demonstrated the therapeutic potential of inhibiting selected Ets transcription factors to limit tumor growth and disease progression.

CCL2 is induced by chemotherapy and protects prostate cancer cells from docetaxel-induced cytotoxicity

BACKGROUND

Metastatic prostate cancer is either inherently resistant to chemotherapy or rapidly acquires this phenotype after chemotherapy exposure. In this study, we identified a docetaxel-induced resistance mechanism centered on CCL2.

METHODS

We compared the gene expression profiles in individual human prostate cancer specimens before and after exposure to chemotherapy collected from previously untreated patients who participated in a clinical trial of preoperative chemotherapy. Subsequently, we used the gain- and loss-of-function approach in vitro to identify a potential mechanism underlying chemotherapy resistance.

RESULTS

Among the molecular signatures associated with treatment, several genes that regulate the inflammatory response and chemokine activity were upregulated including a significant increase in transcripts encoding the CC chemokine CCL2. Docetaxel increased CCL2 expression in prostate cancer cell lines in vitro. CCL2-specific siRNA inhibited LNCaP and LAPC4 cell proliferation and enhanced the growth inhibitory effect of low-dose docetaxel. In contrast, overexpression of CCL2 or recombinant CCL2 protein stimulated prostate cancer cell proliferation and rescued cells from docetaxel-induced cytotoxicity. This protective effect of CCL2 was associated with activation of the ERK/MAP kinase and PI3K/AKT, inhibition of docetaxel-induced Bcl2 phosphorylation at serine 70, phosphorylation of Bad, and activation of caspase-3. The addition of a PI3K/AKT inhibitor Ly294002 reversed the CCL2 protection and was additive to docetaxel-induced toxicity.

CONCLUSION

These results support a mechanism of chemotherapy resistance mediated by cellular stress responses involving the induction of CCL2 expression and suggest that inhibiting CCL2 activity could enhance therapeutic responses to taxane-based therapy.

Induction of angiogenic chemokine CCL2 by human herpesvirus 8 chemokine receptor

Human herpesvirus 8 (HHV-8) is associated with Kaposi's sarcoma (KS), an endothelial cell lesion believed to be initiated and driven primarily by cytokine dysregulation. Among the viral proteins suspected as contributing to viral pathogenesis is the lytically expressed viral G protein-coupled receptor (vGPCR), which can induce various cellular cytokines. CC ligand-2 (CCL2/MCP-1) is a vGPCR-regulated angiogenic chemokine found at elevated levels in KS lesions and induced by HHV-8 infection of endothelial cells. Here we show that vGPCR induces CCL2 in endothelial cells via activation of C/EBPbeta and that vGPCR and C/EBPbeta are critical components of CCL2 induction by HHV-8 infection of endothelial cultures. To our knowledge, this is the first report of vGPCR-mediated cytokine induction, and its characterization, in the context of virus infection. Our results identify a mechanism by which vGPCR can contribute, in a host cell shutoff-independent manner, to viral pathogenesis.

Chorioamnionitis stimulates angiogenesis in saccular stage fetal lungs via CC chemokines

The fetal lung vasculature forms in tandem with developing airways. Whereas saccular airway morphogenesis is arrested in bronchopulmonary dysplasia (BPD), the potential vascular phenotype in BPD at this stage of development is less well-understood. As inflammation increases the risk of BPD and induces arrest of saccular airway morphogenesis, we tested the effects of Escherichia coli LPS on fetal mouse lung vascular development. Injecting LPS into the amniotic fluid of Tie2-lacZ endothelial reporter mice at embryonic day 15 stimulated angiogenesis in the saccular stage fetal lung mesenchyme. LPS also increased the number of endothelial cells in saccular stage fetal mouse lung explants. Inflammation appeared to directly promote vascular development, as LPS stimulated pulmonary microvascular endothelial cell angiogenesis, cell migration, and proliferation in vitro. Whereas LPS did not increase expression of VEGF, angiopoietin-1 (Ang-1), Tie2, fetal liver kinase-1 (Flk-1), fms-like tyrosine kinase-1 (Flt-1), PDGFA, PDGFB, heparin-binding EGF-like growth factor (HB-EGF), or connective tissue growth factor (CTGF), LPS did stimulate the production of the angiogenic CC chemokines macrophage inflammatory protein-1α (MIP-1α) and monocyte chemoattractant protein-1 (MCP-1). Both MIP-1α and MCP-1 increased angiogenesis in fetal mouse lung explants. In addition, inhibitory antibodies against MIP-1α and MCP-1 blocked the effects of LPS on fetal lung vascular development, suggesting these chemokines are downstream mediators of LPS-induced angiogenesis. We speculate that an inflammation-mediated surge in angiogenesis could lead to formation of aberrant alveolar capillaries in the lungs of patients developing BPD.

Roles of Ets-1 and p70S6 kinase in chondrogenic and gliogenic specification of mouse mesencephalic neural crest cells

Fibroblast growth factors (FGFs) have been shown to promote the chondrogenic and gliogenic specification of mouse mesencephalic neural crest cells through Notch signaling [Nakanishi, K., Chan, S.Y., Ito, K., 2007. Notch signaling is required for the chondrogenic specification of mouse mesencephalic neural crest cells. Mech. Dev. 124, 190-203; Ijuin, K., Nakanishi, K., Ito, K., 2008. Different downstream pathways for Notch signaling are required for gliogenic and chondrogenic specification of mouse mesencephalic neural crest cells. Mech. Dev. 125, 462-474]. In the present study, we analyzed FGF signaling pathways in chondrogenic and gliogenic specification. The promotion of chondrogenesis by FGF-2 was significantly suppressed by U0126, an inhibitor of the extracellular signal-regulated protein kinase (Erk) pathway, and by Erk-1 siRNA. Chondrogenesis was also prevented by the dominant negative Ets-1 expression vector. In contrast, Ets-1 was irrelevant to gliogenesis. The promotion of gliogenesis by FGF-2 was not only inhibited by U0126 but also by LY294002 and rapamycin, inhibitors of the Akt pathway, and by Akt-1 siRNA. Furthermore, gliogenesis was dramatically prevented by blocking the expression of p70S6 kinase (p70S6k), which is activated by both the Erk and Akt pathways, with p70S6k siRNA. These results suggest that Ets-1 activated by the Erk pathway promotes chondrogenic specification and p70S6k activated by both the Erk and Akt pathways plays an important role in gliogenic specification.

Angiogenesis in rheumatoid arthritis

Angiogenesis is the formation of new capillaries from pre-existing vessels. A number of soluble and cell-bound factors may stimulate neovascularization. The perpetuation of angiogenesis involving numerous soluble and cell surface-bound mediators has been associated with rheumatoid arthritis (RA). These angiogenic mediators, among others, include growth factors, primarily vascular endothelial growth factor (VEGF) and hypoxia-inducible factors (HIFs), as well as pro-inflammatory cytokines, various chemokines, matrix components, cell adhesion molecules, proteases and others. Among the several potential angiogenesis inhibitors, targeting of VEGF, HIF-1, angiogenic chemokines, tumor necrosis factor-alpha and the alpha(V)beta(3) integrin may attenuate the action of angiogenic mediators and thus synovial angiogenesis. In addition, some naturally produced or synthetic compounds including angiostatin, endostatin, paclitaxel, fumagillin analogues, 2-methoxyestradiol and thalidomide may be included in the management of RA.

Regulation of angiogenesis by ETS transcription factors

Transcription factors of the ETS family are important regulators of endothelial gene expression. Here, we review the evidence that ETS factors regulate angiogenesis and briefly discuss the target genes and pathways involved. Finally, we discuss novel evidence that shows how these transcription factors act in a combinatorial fashion with others, through composite sites that may be crucial in determining endothelial specificity in gene transcription.

ATP stimulates chemokine production via a store-operated calcium entry pathway in C6 glioma cells

Background

Glioma present as one of the most challenging cancers to treat, however, understanding of tumor cell biology is not well understood. Extracellular adenosine triphosphate (ATP) could serve as a critical signaling molecule regulating tumor development. This study has examined pharmacological modulation of calcium (Ca²⁺) entry through store-operated channels (SOC) on cellular expression and production of immune-cell mobilizing chemokines in ATP-stimulated C6 glioma cells.

Methods

Calcium spectrofluorometry was carried out to measure mobilization of intracellular Ca²⁺ [Ca²⁺]i following ATP stimulation of rat C6 glioma cells. Pretreatment with two inhibitors of SOC, SKF96365 or gadolinium, was used to examine for effects on [Ca²⁺]i. RT-PCR was performed to determine effects of purinergic stimulation on C6 cell expression of metabotropic P2Y receptors (P2YR) and the chemokines, monocyte chemoattractant protein-1 (MCP-1) and interleukin-8 (IL-8). ELISA was carried out to measure production of MCP-1 and IL-8 with ATP stimulation of glioma cells.

Results

Application of ATP (at 100 μM) to C6 glioma induced an increase in [Ca²⁺]i with the response exhibiting two components of decay. In the presence of the SOC inhibitors, SKF96365 or gadolinium, or with Ca²⁺-free solution, ATP responses lacked a slow phase suggesting the secondary component was due to SOC-mediated influx of Ca²⁺. RT-PCR confirmed expression of purinergic P2Y-subtype receptors in C6 cells which would serve as a precursor to activation of SOC. In addition, ATP-stimulated C6 cells showed enhanced expression of the chemokines, MCP-1 and IL-8, with SKF96365 or gadolinium effective in reducing chemokine expression. Gadolinium treatment of ATP-stimulated C6 cells was also found to inhibit the production of MCP-1 and IL-8.

Conclusion

These results suggest ATP-induced Ca²⁺ entry, mediated by activation of SOC in C6 glioma, as a mechanism leading to increased cellular expression and release of chemokines. Elevated levels of MCP-1 and IL-8 are predicted to enhance the mobility of tumor cells and promote recruitment of microglia into developing tumors thereby supporting tumor growth.

Role of MCP-1 in cardiovascular disease: molecular mechanisms and clinical implications

Many of the major diseases, including cardiovascular disease, are widely recognized as inflammatory diseases. MCP-1 (monocyte chemotactic protein-1) plays a critical role in the development of cardiovascular diseases. MCP-1, by its chemotactic activity, causes diapedesis of monocytes from the lumen to the subendothelial space where they become foam cells, initiating fatty streak formation that leads to atherosclerotic plaque formation. Inflammatory macrophages probably play a role in plaque rupture and the resulting ischaemic episode as well as restenosis after angioplasty. There is strong evidence that MCP-1 plays a major role in myocarditis, ischaemia/reperfusion injury in the heart and in transplant rejection. MCP-1 also plays a role in cardiac repair and manifests protective effects under certain conditions. Such protective effects may be due to the induction of protective ER (endoplasmic reticulum) stress chaperones by MCP-1. Under sustained ER stress caused by chronic exposure to MCP-1, the protection would break down resulting in the development of heart failure. MCP-1 is also involved in ischaemic angiogenesis. The recent advances in our understanding of the molecular mechanisms that might be involved in the roles that MCP-1 plays in cardiovascular disease are reviewed. The gene expression changes induced by the signalling events triggered by MCP-1 binding to its receptor include the induction of a novel zinc-finger protein called MCPIP (MCP-1-induced protein), which plays critical roles in the development of the pathophysiology caused by MCP-1 production. The role of the MCP-1/CCR2 (CC chemokine receptor 2) system in diabetes, which is a major risk factor for cardiovascular diseases, is also reviewed briefly. MCP-1/CCR2- and/or MCPIP-targeted therapeutic approaches to intervene in inflammatory diseases, including cardiovascular diseases, may be feasible.

Angiogenesis and its targeting in rheumatoid arthritis

Angiogenesis, the development of new capillaries, is involved in leukocyte ingress into the synovium during the development and progression of rheumatoid arthritis. Several soluble and cell surface-bound mediators including growth factors, cytokines, chemokines, proteolytic matrix-degrading enzymes, cell adhesion molecules and others may promote synovial neovascularization. On the other hand, endogenous angiostatic factors, such as angiostatin, endostatin, interleukin-4 (IL-4), IL-13, interferons and some angiostatic chemokines are also produced within the rheumatoid synovium, however, their effects are insufficient to control synovial angiogenesis and inflammation. Several specific and non-specific strategies have been developed to block the action of angiogenic mediators. The first line of angiostatic agents include vascular endothelial growth factor (VEGF), angiopoietin, alpha(V)beta(3) integrin antagonist, as well as non-specific angiogenesis inhibitors including traditional disease-modifying agents (DMARDs), anti-tumor necrosis factor biologics, angiostatin, endostatin, fumagillin analogues or thalidomide. Potentially any angiostatic compound could be introduced to studies using animal models of arthritis or even to human rheumatoid arthritis trials.

A destructive cascade mediated by CCL2 facilitates prostate cancer growth in bone

Monocyte chemoattractant protein 1 (CCL2) is a recently identified prominent regulator of prostate cancer growth and metastasis. The purpose of this study was to investigate the mechanistic role of CCL2 in prostate cancer growth in bone. The present study found that CCL2 was up-regulated in osteoblasts (3-fold by PC-3 and 2-fold by VCaP conditioned medium) and endothelial cells (2-fold by PC-3 and VCaP conditioned medium). Parathyroid hormone-related protein (PTHrP) treatment of osteoblastic cells up-regulated CCL2 and was blocked by a PTHrP antagonist, suggesting that prostate cancer-derived PTHrP plays an important role in elevation of osteoblast-derived CCL2. CCL2 indirectly increased blood vessel formation in endothelial cells through vascular endothelial growth factor-A, which was up-regulated 2-fold with administration of CCL2 in prostate cancer cells. In vivo, anti-CCL2 treatment suppressed tumor growth in bone. The decreased tumor burden was associated with decreased bone resorption (serum TRAP5b levels were decreased by 50-60% in anti-CCL2-treated animals from VCaP or PC-3 cell osseous lesions) and microvessel density was decreased by 70% in anti-CCL2-treated animals with bone lesions from VCaP cells. These data suggest that a destructive cascade is driven by tumor cell-derived, PTHrP-mediated induction of CCL2, which facilitates tumor growth via enhanced osteoclastic and endothelial cell activity in bone marrow. Taken together, CCL2 mediates the interaction between tumor-derived factors and host-derived chemokines acting in cooperation to promote skeletal metastasis.

Chemokines as mediators of neovascularization

Chemokines are a superfamily of homologous heparin-binding proteins, first described for their role in recruiting leukocytes to sites of inflammation. Chemokines have since been recognized as key factors mediating both physiological and pathological neovascularization in such diverse clinical settings as malignancy, wound repair, chronic fibroproliferative disorders, myocardial ischemia, and atherosclerosis. Members of the CXC chemokine family, structurally defined as containing the ELR amino acid motif, are potent inducers of angiogenesis, whereas another subset of the CXC chemokines inhibits angiogenesis. In addition, CCL2, a CC chemokine ligand, has been implicated in arteriogenesis. In this article, we review the current literature on the role of chemokines as mediators of neovascularization.

MCP-1 deficiency delays regression of pathologic retinal neovascularization in a model of ischemic retinopathy

PURPOSE

The present study investigates whether retinal neovascularization (NV) and apoptosis are altered in MCP-1-deficient ((-/-)) mice in the OIR model.

METHODS

Postnatal day (P) 7 MCP-1(-/-) and C57BL/6 (B6) mice were exposed to 75% oxygen for 5 days and then recovered in room air. Immunostaining was performed to localize macrophages/microglia within retinal whole mounts and cross-sections. Retinopathy was qualitatively assessed in FITC-dextran-perfused retinas, and preretinal NV was quantified on P17, P21, and P24. TUNEL analysis was used to compare apoptosis between B6 and MCP-1(-/-) mice.

RESULTS

MCP-1(-/-) and B6 mice revealed normal vascular development in room air controls and similar vaso-obliteration in oxygen-exposed mice on P12. MCP-1(-/-) mice exhibited significantly reduced vascular tuft-associated F4/80(+) cells compared with B6 mice. FITC-dextran-perfused retinas exhibited prominent neovascular tufts on P17, and quantification of preretinal nuclei revealed no significant differences between MCP-1(-/-) and B6 mice. In contrast, on P21 and P24, MCP-1(-/-) mice exhibited significant increases in preretinal neovascular nuclei compared with B6 controls. These increases in NV in the MCP-1(-/-) mice were associated with a significant reduction in vascular tuft apoptosis.

CONCLUSIONS

The results demonstrate that the absence of MCP-1 does not alter normal retinal vascular development. Furthermore, MCP-1(-/-) mice exhibit a similar neovascular response on P17. However, the reduction in tuft-associated macrophages/microglia in the MCP-1(-/-) mice correlates with reduced vascular tuft apoptosis and delayed regression of retinal NV. These findings suggest that macrophages/microglia may contribute to tuft regression through their proapoptotic properties.

Mechanisms of Disease: angiogenesis in inflammatory diseases

Angiogenesis, the development of new vessels, is an important process in health and disease. The perpetuation of neovascularization in inflammatory diseases, such as rheumatoid arthritis, spondyloarthropathies and some systemic autoimmune diseases, might facilitate the ingress of inflammatory cells into the synovium and, therefore, stimulate pannus formation. Disorders associated with perpetuated neovascularization are considered to be angiogenic inflammatory diseases. Several angiogenic mediators, including growth factors, cytokines, matrix metalloproteinases, matrix macromolecules, cell adhesion receptors, chemokines and chemokine receptors, have been implicated in the process of capillary formation. There is a regulatory network in inflamed tissues that is involved in the upregulation or downregulation of angiogenesis. Endogenous angiostatic factors downregulate neovascularization and might act as angiostatic agents. Furthermore, angiogenesis might be targeted by several specific approaches that could be therapeutically used to control inflammatory diseases.

Interferon-gamma-dependent mechanisms of mycobacteria-induced pulmonary immunopathology: the role of angiostasis and CXCR3-targeted chemokines for granuloma necrosis

The mechanisms leading to granuloma caseation, a hallmark of tuberculosis (TB) in humans, are poorly understood. Lung histopathology of C57BL/6 (WT) mice 16 weeks after aerosol infection with Mycobacterium avium strain TMC724 is uniquely characterized by centrally necrotizing granulomas, strongly resembling human TB lesions. However, IFN-gamma-deficient (GKO) and IFN-gamma-receptor-deficient (GRKO) mice did not develop granuloma necrosis following M. avium infection. Comparison of differentially expressed genes in infected WT and GKO lungs by DNA microarray and RNase protection assays revealed that the angiostatic chemokines CXCL9-11 were significantly reduced in GKO mice. In contrast, angiogenic mediators such as angiopoietin and vascular endothelial growth factor, and angiogenic chemokines such as CXCL2, CCL3, and CCL4, remained unchanged or were expressed at higher levels than in infected WT mice, suggesting impaired neovascularization of the granuloma as a possible mechanism for caseation in WT mice. Granuloma vascularization was significantly decreased in central, but not peripheral, areas of granulomas of infected WT compared to GKO mice. In contrast to GRKO mice, WT mice showed signs of severe hypoxia in cells immediately surrounding the necrotic core of granulomas as measured immunohistochemically with a reagent detecting pimonidazole adducts. To test the hypothesis that CXCR3, the common receptor for the angiostatic chemokines CXCL9-11, is involved in granuloma caseation, histomorphology was assessed in M. avium-infected mice deficient for CXCR3 (CXCR3-KO). 16 weeks after infection, these mice developed caseating granulomas similar to WT mice. We conclude that IFN-gamma causes a dysbalance between angiostatic and angiogenic mediators and a concomitant reduction in granuloma vascularization, but that CXCR3-targeted chemokines are not sufficient to induce granuloma necrosis in a mouse model of mycobacteria-induced immunopathology.

Coordinated Expression of Ets-1, pERK1/2, and VEGF in Retina of Streptozotocin-Induced Diabetic Rats

PURPOSE

To investigate the role played by E26 transformation-specific-1 (Ets-1), a transcription factor, and extracellular signal-regulated kinase 1/2 (ERK1/2) in the expression of vascular endothelial growth factor (VEGF), and the interaction of Ets-1 and ERK1/2 in the retina of diabetic rats.

METHODS

Diabetes was induced in rats by an intraperitoneal injection of streptozotocin (STZ). To follow the time course in the expression of Ets-1, phosphorylated ERK1/2 (pERK1/2), and VEGF, rats were killed at 1, 2, 4, and 8 weeks after the injection of STZ, and total proteins were extracted from the isolated retinas. An adenovirus vector encoding dominant-negative Ets-1 and an inhibitor of PD98059 was injected intravitreally to investigate the effects of Ets-1 blockade and ERK1/2 inhibition on the expression of VEGF. Four weeks after the first intravitreal injection, total proteins and total RNA were extracted from the retinas for Western blot and Northern blot analyses.

RESULTS

The expression of Ets-1, pERK1/2, and VEGF in the retina increased in a time-dependent manner after STZ injection. The phosphorylation of ERK1/2 and protein level of VEGF were significantly reduced following intravitreal Ets-1. Inhibition of ERK1/2 phosphorylation resulted in a significant reduction in the expression of Ets-1 and the level of VEGF protein.

CONCLUSIONS

These results indicate that in the retina of STZ-induced diabetic rats: (1) the alterations of Ets-1, pERK1/2, and VEGF are approximately synchronized; (2) the phosphorylation of ERK1/2 is regulated by the expression of Ets-1; (3) the production of Ets-1 protein is dependent on the ERK1/2 pathway, and (4) the protein level of VEGF is regulated by both Ets-1 expression and ERK1/2 phosphorylation. We propose that VEGF, Ets-1, and ERK1 act synergistically in the development of diabetic retinopathy.

Vascular permeability in ocular disease and the role of tight junctions

Vascular permeability is closely linked with angiogenesis in a number of pathologies. In the retina, the normally well-developed blood-retinal barrier is altered in a host of eye diseases preceding or commensurate with angiogenesis. This review examines the literature regarding the tight junction complex that establishes the blood-retinal barrier focusing on the transmembrane proteins occludin and the claudin family and the membrane associated protein zonula occludens. The changes observed in these proteins associated with vascular and epithelial permeability is discussed. Finally, novel literature addressing the link between the tight junction complex and angiogenesis is considered.