Stromal cell-derived factor-1alpha induces tube-like structure formation of endothelial cells through phosphoinositide 3-kinase

TraSig: inferring cell-cell interactions from pseudotime ordering of scRNA-Seq data

A major advantage of single cell RNA-sequencing (scRNA-Seq) data is the ability to reconstruct continuous ordering and trajectories for cells. Here we present TraSig, a computational method for improving the inference of cell-cell interactions in scRNA-Seq studies that utilizes the dynamic information to identify significant ligand-receptor pairs with similar trajectories, which in turn are used to score interacting cell clusters. We applied TraSig to several scRNA-Seq datasets and obtained unique predictions that improve upon those identified by prior methods. Functional experiments validate the ability of TraSig to identify novel signaling interactions that impact vascular development in liver organoids.Software https://github.com/doraadong/TraSig .

SDF1/CXCR4 axis facilitates the angiogenesis via activating the PI3K/AKT pathway in degenerated discs

Symptomatic degenerative disc disease (DDD) is considered the leading cause of chronic lower back pain (LBP). As one of the main features of intervertebral disc degeneration (IDD), vascular ingrowth plays a crucial role in the progression of LBP. Stromal cell‑derived factor 1 (SDF1) and its receptor C‑X‑C receptor 4 (CXCR4) were reported to be overexpressed in the degenerated intervertebral discs, suggesting that they may be involved in the pathogenesis of IDD. Moreover, SDF1 has been identified to induce neovascularization in rheumatoid arthritis disease. However, the roles of the SDF1/CXCR4 axis in the neovascularization of IDD remain unclear. Therefore, the objective of the present study was to elucidate whether the SDF1/CXCR4 axis takes part in neovascularization in degenerated intervertebral discs and its underlying mechanisms. Adenovirus infection was used to upregulate SDF1 expression in primary nucleus pulposus cells (NPCs). The effects of SDF1 on the proliferation and angiogenesis of vascular endothelial cells (VECs) were assessed by Cell Counting Kit‑8 and tube formation assays after VECs were treated with the supernatants derived from SDF1 overexpressed or not treated NPCs. Transwell chambers using the supernatants from NPCs as chemokines were applied to assess VEC migration and invasion. AMD3100, MK‑2206 and SF1670 were used to antagonize CXCR4, AKT serine/threonine kinase 1 (AKT) and phosphatase and tensin homolog (PTEN) in VECs. The results revealed that SDF1 overexpression significantly increased the ratio of phosphorylated AKT to AKT and decreased PTEN expression in NPCs, as well as enhanced the proliferation, migration, invasion and angiogenesis abilities of VECs. However, these effects induced by SDF1 overexpression in NPCs were all reversed when VECs were pretreated with AMD3100 or MK‑2206, whereas enhanced by SF1670 treatment. Collectively, the present study indicated that enhancement of the SDF1/CXCR4 axis in NPCs can significantly accelerate angiogenesis by regulating the PTEN/phosphatidylinositol‑3‑kinase/AKT pathway.

Muscle-derived SDF-1α/CXCL12 modulates endothelial cell proliferation but not exercise training-induced angiogenesis

Chemokines are critical mediators of angiogenesis in several physiological and pathological conditions; however, a potential role for muscle-derived chemokines in exercise-stimulated angiogenesis in skeletal muscle remains poorly understood. Here, we postulated that the chemokine stromal cell-derived factor-1 (SDF-1α/C-X-C motif chemokine ligand 12: CXCL12), shown to promote neovascularization in several organs, contributes to angiogenesis in skeletal muscle. We found that CXCL12 is abundantly expressed in capillary-rich oxidative soleus and exercise-trained plantaris muscles. CXCL12 mRNA and protein were also abundantly expressed in muscle-specific peroxisome proliferator-activated receptor γ coactivator 1α transgenic mice, which have a high proportion of oxidative muscle fibers and capillaries when compared with wild-type littermates. We then generated CXCL12 muscle-specific knockout mice but observed normal baseline capillary density and normal angiogenesis in these mice when they were exercise trained. To get further insight into a potential CXCL12 role in a myofiber-endothelial cell crosstalk, we first mechanically stretched C2C12 myotubes, a model known to induce stretch-related chemokine release, and observed increased CXCL12 mRNA and protein. Human umbilical vein endothelial cells (HUVECs) exposed to conditioned medium from cyclically stretched C2C12 myotubes displayed increased proliferation, which was dependent on CXCL12-mediated signaling through the CXCR4 receptor. However, HUVEC migration and tube formation were unaltered under these conditions. Collectively, our findings indicate that increased muscle contractile activity enhances CXCL12 production and release from muscle, potentially contributing to endothelial cell proliferation. However, redundant signals from other angiogenic factors are likely sufficient to sustain normal endothelial cell migration and tube formation activity, thereby preserving baseline capillary density and exercise training-mediated angiogenesis in muscles lacking CXCL12.

SDF1/CXCR7 Signaling Axis Participates in Angiogenesis in Degenerated Discs via the PI3K/AKT Pathway

Degenerative disc disease (DDD) is the main cause of low back pain, and the ingrowth of new blood vessels is one of its pathological features. The stromal cell-derived factor 1 (SDF1)/CXCR7 signaling axis plays a role in these physiological and pathological activities. The aims of this study were to explore whether this signaling axis participates in the angiogenesis of degenerated intervertebral discs (IVDs) and to define its underlying mechanism. In this study, we cocultured human nucleus pulposus cells (NPCs) and vascular endothelial cells (VECs) and regulated the expression of SDF1/CXCR7 to investigate the effect of VEC angiogenesis by NPCs. The results revealed that angiogenesis was enhanced with increased SDF1 and that angiogenesis was weakened with the inhibition of CXCR7. We found that PI3K/AKT was involved in the downstream pathway in the coculture. VEC angiogenesis induction by NPCs was enhanced with an increase in pAKT or a decrease in PTEN. We conclude that the SDF1/CXCR7 signaling axis plays a role in the angiogenesis of degenerated IVD through the PI3K/AKT pathway.

Chemokines and Chemokine Receptors: Orchestrating Tumor Metastasization

Metastasis still represents the primary cause of cancer morbidity and mortality worldwide. Chemokine signalling contributes to the overall process of cancer growth and metastasis, and their expression in both primary tumors and metastatic lesions correlate with prognosis. Chemokines promote tumor metastasization by directly supporting cancer cell survival and invasion, angiogenesis, and by indirectly shaping the pre-metastatic niches and antitumor immunity. Here, we will focus on the relevant chemokine/chemokine receptor axes that have been described to drive the metastatic process. We elaborate on their role in the regulation of tumor angiogenesis and immune cell recruitment at both the primary tumor lesions and the pre-metastatic foci. Furthermore, we also discuss the advantages and limits of current pharmacological strategies developed to target chemokine networks for cancer therapy.

CXCL12 enhances angiogenesis through CXCR7 activation in human umbilical vein endothelial cells

Angiogenesis is the process by which new vessels form from existing vascular networks. Human umbilical vein endothelial cells (HUVECs) may contribute to the study of vascular repair and angiogenesis. The chemokine CXCL12 regulates multiple cell functions, including angiogenesis, mainly through its receptor CXCR4. In contrast to CXCL12/CXCR4, few studies have described roles for CXCR7 in vascular biology, and the downstream mechanism of CXCR7 in angiogenesis remains unclear. The results of the present study showed that CXCL12 dose-dependently enhanced angiogenesis in chorioallantoic membranes (CAMs) and HUVECs. The specific activation of CXCR7 with TC14012 (a CXCR7 agonist) resulted in the significant induction of tube formation in HUVECs and in vivo. Further evidence suggested that CXCL12 induced directional polarization and migration in the HUVECs, which is necessary for tube formation. Moreover, CXCR7 translocalization was observed during the polarization of HUVECs in stripe assays. Finally, treatment with TC14012 also significantly increased PI3K/Akt phosphorylation, and tube formation was blocked by treating HUVECs with an Akt inhibitor. Overall, this study indicated that CXCL12-stimulated CXCR7 acts as a functional receptor to activate Akt for angiogenesis in HUVECs and that CXCR7 may be a potential target molecule for endothelial regeneration and repair after vascular injury.

MiR 20a,-20b and -200c are involved in hydrogen sulfide stimulation of VEGF production in human placental trophoblasts

Hydrogen sulfide (H2S) has been implicated to angiogenesis in various tissues. We sought to investigate the role of hydrogen sulfide (H2S) in regulating production of vascular endothelial growth factor (VEGF) proteins, the key factors of angiogenesis and vasculogenesis, in placenta.

METHODS

Placental tissues were obtained from pregnant women with preeclampsia and healthy pregnant women who underwent elective cesarean section. Explants and trophoblasts were isolated from healthy placentas and treated with H2S donor and precursor. Western blotting was used to determine the levels of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The levels of VEGF mRNA, miR miR-200c,-20a and -20b were determined by quantitative real time PCR.

RESULTS

NaHS and l-cysteine increased VEGF but not placenta growth factor (PlGF) production in cultured explants and trophoblasts. Transfection of CBS and CSE siRNA reversed the stimulatory effect of l-cysteine on VEGF production in placental cells. H2S prolonged the half-life of VEGF mRNA and decreased the expression of miR-200c,-20a and -20b in placental cells. MiR-200c mimic and inhibitor affected VEGF mRNA and protein level, whereas miR-20a or -20b mimic and inhibitor affect VEGF protein release but not mRNA expression. The expression level of miR-200c,-20a and -20b as well as the level of CBS, CSE and VEGF were downregulated in preeclamptic placentas.

CONCLUSION

H2S produced via CSE and CBS plays a critical role in VEGF production in human placenta. Reduced expression of CSE and CBS may contribute to the abnormal production of angiogenic factors in preeclamptic placenta.

The Combination of Vascular Endothelial Growth Factor and Stromal Cell-Derived Factor Induces Superior Angiogenic Sprouting by Outgrowth Endothelial Cells

Endothelial progenitor cells are being broadly explored for the treatment of ischemic cardiovascular diseases, but their response to molecules commonly used to promote the growth of new blood vessels has not been fully characterized. In this study, angiogenic sprout formation in a 3-dimensional, in vitro model by one type of endothelial progenitor, outgrowth endothelial cells (OECs), was characterized in response to exposure to stromal cell-derived factor (SDF) and vascular endothelial growth factor (VEGF) and then compared to mature endothelial cells. Exposure to SDF alone did not increase angiogenic sprouting in comparison to control media, while a combination of VEGF and SDF demonstrated greater potency than VEGF alone for all cell types. Together, VEGF and SDF reduced the sprout initiation time and maintained sprouting levels over time. In direct competition with mature endothelial cells, OECs preferentially localized to the tip cell position, suggesting an enhanced sprouting potential. Overall, these results reveal the impact of the combination of VEGF and SDF on endothelial cell sprouting, and support the enhanced potential of OECs, as opposed to mature endothelial cells, for treating ischemic diseases.

Human cardiosphere-derived cells from advanced heart failure patients exhibit augmented functional potency in myocardial repair

OBJECTIVES

This study sought to compare the regenerative potency of cells derived from healthy and diseased human hearts.

BACKGROUND

Results from pre-clinical studies and the CADUCEUS (CArdiosphere-Derived aUtologous stem CElls to reverse ventricUlar dySfunction) trial support the notion that cardiosphere-derived cells (CDCs) from normal and recently infarcted hearts are capable of regenerating healthy heart tissue after myocardial infarction (MI). It is unknown whether CDCs derived from advanced heart failure (HF) patients retain the same regenerative potency.

METHODS

In a mouse model of acute MI, we compared the regenerative potential and functional benefits of CDCs derived from 3 groups: 1) non-failing (NF) donor: healthy donor hearts post-transplantation; 2) MI: patients who had an MI 9 to 35 days before biopsy; and 3) HF: advanced cardiomyopathy tissue explanted at cardiac transplantation.

RESULTS

Cell growth and phenotype were identical in all 3 groups. Injection of HF CDCs led to the greatest therapeutic benefit in mice, with the highest left ventricular ejection fraction, thickest infarct wall, most viable tissue, and least scar 3 weeks after treatment. In vitro assays revealed that HF CDCs secreted higher levels of stromal cell-derived factor (SDF)-1, which may contribute to the cells' augmented resistance to oxidative stress, enhanced angiogenesis, and improved myocyte survival. Histological analysis indicated that HF CDCs engrafted better, recruited more endogenous stem cells, and induced greater angiogenesis and cardiomyocyte cell-cycle re-entry. CDC-secreted SDF-1 levels correlated with decreases in scar mass over time in CADUCEUS patients treated with autologous CDCs.

CONCLUSIONS

CDCs from advanced HF patients exhibit augmented potency in ameliorating ventricular dysfunction post-MI, possibly through SDF-1–mediated mechanisms.

Chemokine receptor CXCR7 is a functional receptor for CXCL12 in brain endothelial cells

The chemokine CXCL12 regulates multiple cell functions through its receptor, CXCR4. However, recent studies have shown that CXCL12 also binds a second receptor, CXCR7, to potentiate signal transduction and cell activity. In contrast to CXCL12/CXCR4, few studies have focused on the role of CXCR7 in vascular biology and its role in human brain microvascular endothelial cells (HBMECs) remains unclear. In this report, we used complementary methods, including immunocytofluorescence, Western blot, and flow cytometry analyses, to demonstrate that CXCR7 was expressed on HBMECs. We then employed short hairpin RNA (shRNA) technology to knockdown CXCR7 in HBMECs. Knockdown of CXCR7 in HBMECs resulted in significantly reduced HBMEC proliferation, tube formation, and migration, as well as adhesion to matrigel and tumor cells. Blocking CXCR7 with a specific antibody or small molecule antagonist similarly disrupted HBMEC binding to matrigel or tumor cells. We found that tumor necrosis factor (TNF)-α induced CXCR7 in a time and dose-response manner and that this increase preceded an increase in vascular cell adhesion molecule-1 (VCAM-1). Knockdown of CXCR7 resulted in suppression of VCAM-1, suggesting that the reduced binding of CXCR7-knockdown HBMECs may result from suppression of VCAM-1. Collectively, CXCR7 acted as a functional receptor for CXCL12 in brain endothelial cells. Targeting CXCR7 in tumor vasculature may provide novel opportunities for improving brain tumor therapy.

SDF-1/CXCR4 signaling preserves microvascular integrity and renal function in chronic kidney disease

The progressive decline of renal function in chronic kidney disease (CKD) is characterized by both disruption of the microvascular architecture and the accumulation of fibrotic matrix. One angiogenic pathway recently identified as playing an essential role in renal vascular development is the stromal cell-derived factor-1α (SDF-1)/CXCR4 pathway. Because similar developmental processes may be recapitulated in the disease setting, we hypothesized that the SDF-1/CXCR4 system would regulate microvascular health in CKD. Expression of CXCR4 was observed to be increased in the kidneys of subtotally nephrectomized (SNx) rats and in biopsies from patients with secondary focal segmental glomerulosclerosis (FSGS), a rodent model and human correlate both characterized by aberration of the renal microvessels. A reno-protective role for local SDF-1/CXCR4 signaling was indicated by i) CXCR4-dependent glomerular eNOS activation following acute SDF-1 administration; and ii) acceleration of renal function decline, capillary loss and fibrosis in SNx rats treated with chronic CXCR4 blockade. In contrast to the upregulation of CXCR4, SDF-1 transcript levels were decreased in SNx rat kidneys as well as in renal fibroblasts exposed to the pro-fibrotic cytokine transforming growth factor β (TGF-β), the latter effect being attenuated by histone deacetylase inhibition. Increased renal SDF-1 expression was, however, observed following the treatment of SNx rats with the ACE inhibitor, perindopril. Collectively, these observations indicate that local SDF-1/CXCR4 signaling functions to preserve microvascular integrity and prevent renal fibrosis. Augmentation of this pathway, either purposefully or serendipitously with either novel or existing therapies, may attenuate renal decline in CKD.

Expression and functional heterogeneity of chemokine receptors CXCR4 and CXCR7 in primary patient-derived glioblastoma cells

Glioblastoma (GBM) is the most common primary brain tumor in adults. The poor prognosis and minimally successful treatments of these tumors indicates a need to identify new therapeutic targets. Therapy resistance of GBMs is attributed to heterogeneity of the glioblastoma due to genetic alterations and functional subpopulations. Chemokine receptors CXCR4 and CXCR7 play important roles in progression of various cancers although the specific functions of the CXCL12-CXCR4-CXCR7 axis in GBM are less characterized. In this study we examined the expression and function of CXCR4 and CXCR7 in four primary patient-derived GBM cell lines of the proliferative subclass, investigating their roles in in vitro growth, migration, sphere and tube formation. CXCR4 and CXCR7 cell surface expression was heterogeneous both between and within each cell line examined, which was not reflected by RT-PCR analysis. Variable percentages of CXCR4+CXCR7- (CXCR4 single positive), CXCR4-CXCR7+ (CXCR7 single positive), CXCR4+CXCR7+ (double positive), and CXCR4-CXCR7- (double negative) subpopulations were evident across the lines examined. A subpopulation of slow cell cycling cells was enriched in CXCR4 and CXCR7. CXCR4+, CXCR7+, and CXCR4+/CXCR7+ subpopulations were able to initiate intracranial tumors in vivo. CXCL12 stimulated in vitro cell growth, migration, sphere formation and tube formation in some lines and, depending on the response, the effects were mediated by either CXCR4 or CXCR7. Collectively, our results indicate a high level of heterogeneity in both the surface expression and functions of CXCR4 and CXCR7 in primary human GBM cells of the proliferative subclass. Should targeting of CXCR4 and CXCR7 provide clinical benefits to GBM patients, a personalized treatment approach should be considered given the differential expression and functions of these receptors in GBM.

Platelets: key players in vascular inflammation

Review on platelet function in inflammation and atherosclerosis.

Platelets play a crucial role in the physiology of the primary hemostasis and in the pathophysiological activity of arterial thrombosis, provide rapid protection against bleeding, and catalyze the formation of stable blood clots via the coagulation cascade. Over the past years, it has become clear that platelets are important, not only in hemostasis and thrombosis but also in inflammation and in distinct aspects of atherosclerosis. Nowadays, platelets are known to have a large variety of functions. Platelets are able to interact with a large variety of cell types, such as leukocytes, endothelial cells, and SMCs, and these interactions have been implicated in the pathophysiology of vascular inflammation. In addition, platelets carry a highly inflammatory payload and are able to transport, synthesize, and deposit cytokines, chemokines, and lipid mediators, thereby initiating and propagating atherosclerotic disease. In this review, the current state of the art of the proinflammatory functions in the context of atherosclerotic cardiovascular disease will be outlined.

Non-thermal dielectric barrier discharge plasma induces angiogenesis through reactive oxygen species

Vascularization plays a key role in processes such as wound healing and tissue engineering. Non-thermal plasma, which primarily produces reactive oxygen species (ROS), has recently emerged as an efficient tool in medical applications including blood coagulation, sterilization and malignant cell apoptosis. Liquids and porcine aortic endothelial cells were treated with a non-thermal dielectric barrier discharge plasma in vitro. Plasma treatment of phosphate-buffered saline (PBS) and serum-free medium increased ROS concentration in a dose-dependent manner, with a higher concentration observed in serum-free medium compared with PBS. Species concentration inside cells peaked 1 h after treatment, followed by a decrease 3 h post treatment. Endothelial cells treated with a plasma dose of 4.2 J cm(-2) had 1.7 times more cells than untreated samples 5 days after plasma treatment. The 4.2 J cm(-2) plasma dose increased two-dimensional migration distance by 40 per cent compared with untreated control, while the number of cells that migrated through a three-dimensional collagen gel increased by 15 per cent. Tube formation was also enhanced by plasma treatment, with tube lengths in plasma-treated samples measuring 2.6 times longer than control samples. A fibroblast growth factor-2 (FGF-2) neutralizing antibody and ROS scavengers abrogated these angiogenic effects. These data indicate that plasma enhanced proliferation, migration and tube formation is due to FGF-2 release induced by plasma-produced ROS. Non-thermal plasma may be used as a potential tool for applying ROS in precise doses to enhance vascularization.

Differences in donor CXCR4 expression levels are correlated with functional capacity and therapeutic outcome of angiogenic treatment with endothelial colony forming cells

CXCR4 expression is important for cell migration and recruitment, suggesting that the expression levels of CXCR4 may be correlated with functional activity of implanted cells for therapeutic neovascularization. Here, we examined differences between umbilical cord blood (CB) donors in the CXCR4 levels of endothelial colony forming cells (ECFCs), which are a subtype of endothelial progenitor cells (EPCs). We investigated the relationships between CXCR4 expression level and SDF-1alpha-induced vascular properties in vitro, and their in vivo contributions to neovascularization. We found that ECFCs isolated from different donors showed differences in CXCR4 expression that were linearly correlated with SDF-1alpha-induced migratory capacity. ECFCs with high CXCR4 expression showed enhanced ERK and Akt activation in response to SDF-1alpha. In addition, SDF-1alpha-induced migration and ERK1/2, Akt, and eNOS activation were reduced by AMD3100, a CXCR4-specific peptide antagonist, or by siRNA-CXCR4. Administration of high-CXCR4-expressing ECFCs resulted in a significant increase in therapeutic potential for blood flow recovery, tissue healing and capillary density compared to low-CXCR4-expressing ECFCs in hindlimb ischemia. Taken together, the functional differences among ECFCs derived from different donors depended on the level of CXCR4 expression, suggesting that CXCR4 expression levels in ECFCs could be a predictive marker for success of ECFC-based angiogenic therapy.

Role of HIF-1alpha in proton-mediated CXCR4 down-regulation in endothelial cells

AIMS

Acidification is associated with a variety of pathological and physiological conditions. In the present study, we aimed at investigating whether acidic pH may regulate endothelial cell (EC) functions via the chemokine receptor CXCR4, a key modulator of EC biological activities.

METHODS AND RESULTS

Exposure of ECs to acidic pH reversibly inhibited mRNA and protein CXCR4 expression, CXCL12/stromal cell-derived factor (SDF)-1-driven EC chemotaxis in vitro, and CXCR4 expression and activation in vivo in a mouse model. Further, CXCR4 signalling impaired acidosis-induced rescue from apoptosis in ECs. The inhibition of CXCR4 expression occurred transcriptionally and was hypoxia-inducible factor (HIF)-1alpha-dependent as demonstrated by both HIF-1alpha and HIF-1alpha dominant negative overexpression, by HIF-1alpha silencing, and by targeted mutation of the -29 to -25 hypoxia response element (HRE) in the -357/-59 CXCR4 promoter fragment. Moreover, chromatin immunoprecipitation (ChIP) analysis showed endogenous HIF-1alpha binding to the CXCR4 promoter that was enhanced by acidification.

CONCLUSION

The results of the present study identify CXCR4 as a key player in the EC response to acidic pH and show, for the first time, that HRE may function not only as an effector of hypoxia, but also as an acidosis response element, and raise the possibility that this may constitute a more general mechanism of transcriptional regulation at acidic pH.

Microfluidic endothelium for studying the intravascular adhesion of metastatic breast cancer cells

Background

The ability to properly model intravascular steps in metastasis is essential in identifying key physical, cellular, and molecular determinants that can be targeted therapeutically to prevent metastatic disease. Research on the vascular microenvironment has been hindered by challenges in studying this compartment in metastasis under conditions that reproduce in vivo physiology while allowing facile experimental manipulation.

Methodology/Principal Findings

We present a microfluidic vasculature system to model interactions between circulating breast cancer cells with microvascular endothelium at potential sites of metastasis. The microfluidic vasculature produces spatially-restricted stimulation from the basal side of the endothelium that models both organ-specific localization and polarization of chemokines and many other signaling molecules under variable flow conditions. We used this microfluidic system to produce site-specific stimulation of microvascular endothelium with CXCL12, a chemokine strongly implicated in metastasis.

Conclusions/Significance

When added from the basal side, CXCL12 acts through receptor CXCR4 on endothelium to promote adhesion of circulating breast cancer cells, independent of CXCL12 receptors CXCR4 or CXCR7 on tumor cells. These studies suggest that targeting CXCL12-CXCR4 signaling in endothelium may limit metastases in breast and other cancers and highlight the unique capabilities of our microfluidic device to advance studies of the intravascular microenvironment in metastasis.

Insulin enhances proliferation and viability of human umbilical vein endothelial cells

This investigation is a follow-up to our previous in vivo studies revealing that rapid stretch increases tissue insulin in murine skin flaps, coincident with the up-regulation of key angiogenic effectors and enhanced vascularization. In the present study, we used human umbilical vein endothelial cells (HUVECs) as an in vitro model system to determine the role of insulin in the chemical signals regulating the processes of proliferation and viability (survival). MTT-based colorimetric methods demonstrated that insulin enhances proliferation and survival of HUVECs. Western blot analysis revealed that protein kinase B (pAkt [Thr(308)]) and vascular endothelial growth factor (VEGF) were the insulin-responsive intermediates in proliferating endothelial cells (ECs). In insulin-enhanced survival, both pAkt (Thr(308)) and pAkt (Ser(473)) were activated in HUVECs. However, no change in VEGF expression accompanied pAkt activation. The beneficial effects of insulin were abrogated by insulin receptor (IR)/insulin-like growth factor receptor (IGFR) or phosphoinositide-3 kinase (PI3-K) blockade, suggesting that insulin-induced EC proliferation and viability are mediated through pIR/pIGFR and PI3-K effectors. These data provide new insights into the beneficial effects of insulin on vascularization and tissue viability, providing a mechanistic link to the enhancement of healing in acutely stretched skin.

The roles of chemokine CXCL12 in embryonic and brain tumor angiogenesis

The formation of blood vessels in embryos and tumors are different processes but under the control of common molecular mechanisms. Chemokine CXCL12 involved in both embryonic and tumor angiogenesis. In this review, we summarize recent advances in understanding the roles of CXCL12 in brain tumor angiogenesis/vasculogenesis. CXCL12 and its cognate receptors are abnormally induced in brain tumors, in particular in tumor cells and endothelium. Pathologically enhanced CXCL12 signaling may promote the formation of new vessels through recruiting circulating endothelial progenitor cells or directly enhancing the migration/growth of endothelial cells. Therefore, CXCL12 signaling represents an important mechanism that regulates brain tumor angiogenesis/vasculogenesis and may provide potential targets for anti-angiogenic therapy in malignant gliomas.

Acute stretch promotes endothelial cell proliferation in wounded healing mouse skin

We have developed a novel in vivo model utilizing acute stretch to investigate endothelial cell proliferation as a marker of vascular growth in healing mouse skin. This study is a follow-up to ones revealing immediate stretch improves blood flow, decreases total tissue necrosis, and induces tissue insulin transcription. Dorsal distally based flaps of skin were stretched for 3 min using linear (skin hook) plus hemispherical load cycling (inflated subcutaneous silicone catheter). Unstretched, wounded skin along the back and sternum served as postoperative controls. Laser Doppler flowmetry demonstrated a threefold increase in flap perfusion at postoperative day 7. A stretch-induced sixfold increase in endothelial cell mitogenesis accompanied enhancements in blood flow and extracorporal wound healing over the sternum. Western blots revealed up-regulation/activation of insulin and mitogenic signaling intermediates in stretched skin. Activated insulin and insulin growth factor receptors (pIR/pIGFR), protein kinase B (Akt, pAkt), vascular endothelial growth factor (VEGF) and vascular endothelial growth factor receptor 2 (flk-1) were among the identified stretch-responsive intermediates. These results indicate the benefits of acute stretch are mediated through enhanced vascularity as evidenced by endothelial cell mitogenesis and up-regulation/activation of insulin and key angiogenic effectors in dorsal distally based skin flaps.

A novel bone morphogenetic protein signaling in heterotypic cell interactions in prostate cancer

We examined the effect of the extracellular bone morphogenetic protein (BMP) 2 and 7, which are up-regulated in the prostate adenocarcinomas of the conditional Pten deletion mouse model, on primary cultures of cancer-associated fibroblasts (CAF) derived from these tumors. In the CAF, we show that BMP2 or BMP7, but not transforming growth factor beta-1, can strikingly stimulate secretion of stromal cell-derived factor-1 (SDF-1), also known as CXCL12. The CAF cells express type I and type II BMP receptors as well as the receptor for SDF-1, CXCR4. SDF-1 activation is associated with BMP-induced Smad phosphorylation, and the stimulatory effect is blocked by BMP antagonist, noggin. The findings that BMP treatment can increase SDF-1 pre-mRNA levels in a time-dependent manner and actinomycin D treatment can abolish stimulatory effect of BMP suggest a transcriptional modulation of SDF-1 by BMP signaling. Using a human microvascular endothelial cell line, we show that SDF-1 present in the conditioned medium from the stimulated CAF can significantly induce tube formation, an effect relating to angiogenic function. Furthermore, we found that BMP2 can also protect the CAF from serum starvation-induced apoptosis independent of SDF-1, implying that BMP may induce other factors to sustain the survival of these cells. In short, this report establishes a novel BMP-SDF-1 axis in the prostate tumor along with a new prosurvival effect of BMP that when considered together with our previously described oncogenic properties of BMP indicate a circuitry for heterotypic cell interactions potentially critical in prostate cancer.

E7080, a novel inhibitor that targets multiple kinases, has potent antitumor activities against stem cell factor producing human small cell lung cancer H146, based on angiogenesis inhibition

E7080 is an orally active inhibitor of multiple receptor tyrosine kinases including VEGF, FGF and SCF receptors. In this study, we show the inhibitory activity of E7080 against SCF-induced angiogenesis in vitro and tumor growth of SCF-producing human small cell lung carcinoma H146 cells in vivo. E7080 inhibits SCF-driven tube formation of HUVEC, which express SCF receptor, KIT at the IC(50) value of 5.2 nM and it was almost identical for VEGF-driven one (IC(50) = 5.1 nM). To assess the role of SCF/KIT signaling in tumor angiogenesis, we evaluated the effect of imatinib, a selective KIT kinase inhibitor, on tumor growth of H146 cells in nude mice. Imatinib did not show the potent antitumor activity in vitro (IC(50) = 2,200 nM), because H146 cells did not express KIT. However, oral administration of imatinib at 160 mg/kg clearly slowed tumor growth of H146 cells in nude mice, accompanied by decreased microvessel density. Oral administration of E7080 inhibited tumor growth of H146 cells at doses of 30 and 100 mg/kg in a dose-dependent manner and caused tumor regression at 100 mg/kg. While anti-VEGF antibody also slowed tumor growth, it did not cause tumor regression. These results indicate that KIT signaling has a role in tumor angiogenesis of SCF-producing H146 cells, and E7080 causes regression of H146 tumors as a result of antiangiogenic activity mediated by inhibition of both KIT and VEGF receptor signaling. E7080 may provide therapeutic benefits in the treatment of SCF-producing tumors.

Chemokines in tumor angiogenesis and metastasis

Chemokines are a large group of low molecular weight cytokines that are known to selectively attract and activate different cell types. Although the primary function of chemokines is well recognized as leukocyte attractants, recent evidences indicate that they also play a role in number of tumor-related processes, such as growth, angiogenesis and metastasis. Chemokines activate cells through cell surface seven trans-membranes, G-protein-coupled receptors (GPCR). The role played by chemokines and their receptors in tumor pathophysiology is complex as some chemokines favor tumor growth and metastasis, while others may enhance anti-tumor immunity. These diverse functions of chemokines establish them as key mediators between the tumor cells and their microenvironment and play critical role in tumor progression and metastasis. In this review, we present some of the recent advances in chemokine research with special emphasis on its role in tumor angiogenesis and metastasis.

Downregulation of Fes inhibits VEGF-A-induced chemotaxis and capillary-like morphogenesis by cultured endothelial cells

The aim of this study was to determine whether the downregulation of endogenous Fes by siRNA in cultured endothelial cells affects vascular endothelial growth factor-A (VEGF-A)-induced chemotaxis and capillary-like morphogenesis, which are considered as angiogenic cellular responses in vitro. VEGF-A-treatment induced autophosphorylation of Fes in cultured endothelial cells.LY294002, a phosphoinositide 3-kinase inhibitor, significantly inhibited VEGF-A-induced chemotaxis and capillary-like morphogenesis.Downregulation of Fes attenuated these VEGF-A-induced cellular responses but LY294002 did not produce further inhibition of these responses. Downregulation of Fes neither affected VEGF-A-induced autophosphorylation of VEGF receptor 2 nor mitogen-activated protein kinase activation, but markedly decreased Akt activation.Taken together, our novel results indicate the involvement of Fes in VEGF-A-induced cellular responses by cultured endothelial cells.

PRDM6 is enriched in vascular precursors during development and inhibits endothelial cell proliferation, survival, and differentiation

The mechanisms that regulate the differentiation program of multipotential stem cells remain poorly understood. In order to define the cues that delineate endothelial commitment from precursors, we screened for candidate regulatory genes in differentiating mouse embryoid bodies. We found that the PR/SET domain protein, PRDM6, is enriched in flk1(+) hematovascular precursor cells using a microarray-based approach. As determined by 5' RACE, full-length PRDM6 protein contains a PR domain and four Krüppel-like zinc fingers. In situ hybridization in mouse embryos demonstrates staining of the primitive streak, allantois, heart, outflow tract, paraaortic splanchnopleura (P-Sp)/aorto-gonadal-mesonephric (AGM) region and yolk sac, all sites known to be enriched in vascular precursor cells. PRDM6 is also detected in embryonic and adult-derived endothelial cell lines. PRDM6 is co-localized with histone H4 and methylates H4-K20 (but not H3) in vitro and in vivo, which is consistent with the known participation of PR domains in histone methyltransferase activity. Overexpression of PRDM6 in mouse embryonic endothelial cells induces apoptosis by activating caspase-3 and inducing G1 arrest. PRDM6 inhibits cell proliferation as determined by BrdU incorporation in endothelial cells, but not in rat aortic smooth muscle cells. Overexpression of PRDM6 also results in reduced tube formation in cultured endothelial cells grown in Matrigel. Taken together, our data indicate that PRDM6 is expressed by vascular precursors, has differential effects in endothelial cells and smooth muscle cells, and may play a role in vascular precursor differentiation and survival by modulating local chromatin-remodeling activity within hematovascular subpopulations during development.

Akt is a key modulator of endothelial progenitor cell trafficking in ischemic muscle

Trafficking of transplanted endothelial progenitor cells (EPCs) to ischemic tissue is enhanced by stromal-derived factor 1 (SDF-1) and vascular endothelial growth factor (VEGF). However, it has not been studied how these cytokines modulate the local milieu to entrap EPCs. This study was performed to elucidate a molecular pathway of trafficking EPCs through Akt and to test its application as an adjuvant modality to increase EPC homing. In a mouse hind limb ischemia model, systemically administered 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine-labeled mouse EPCs showed three stages of homing to ischemic limb: adhesion to endothelial cells (ECs), incorporation to capillary, and transendothelial migration into extravascular space. As an underlying mechanism to control adhesion of EPCs to ECs, we found that Akt was activated in ECs of ischemic muscle by ischemia-induced VEGF and SDF-1. In vitro and in vivo experiments using adenoviral vector for constitutively active or dominant-negative Akt genes showed that activated Akt enhanced intercellular adhesion molecule 1 (ICAM-1) expression on ECs. Akt activation in ECs also enhanced EPC incorporation to ECs and transendothelial migration in vitro experiments. Activated Akt was sufficient for induction of EPC homing even in normal hind limb, where VEGF or SDF-1 was not increased. Finally, local Akt gene transfer to ischemic limb significantly enhanced homing of systemically administered EPCs, new vessel formation, blood flow recovery, and tissue healing. Akt plays a key role in EPC homing to ischemic limb by controlling ICAM-1 and transendothelial migration. Modulation of Akt in the target tissue may be an adjunctive measure to enhance homing of systemically administered stem cells, suggesting a possibility of cell-and-gene hybrid therapy. Disclosure of potential conflicts of interest is found at the end of this article.

The multifaceted roles of chemokines in malignancy

Tumor development and progression are multifactorial processes, regulated by a large variety of intrinsic and microenvironmental factors. A key role in cancer is played by members of the chemokine superfamily. Chemokines and their receptors are expressed by tumor cells and by host cells, in primary tumors and in specific metastatic loci. The effects of chemokines on tumorigenesis are diverse: While some members of the superfamily significantly support this process, others inhibit fundamental events required for tumor establishment and metastasis. The current review describes the multifaceted roles of chemokines in malignancy, addressing four major aspects of their activities: (1) inducing leukocyte infiltration to tumors and regulating immune functions, with emphasis on tumor-associated macrophages (and the chemokines CCL2, CCL5), T cells (and the chemokines CXCL9, CXCL10) and dendritic cells (and the chemokines CCL19, CCL20, CCL21); (2) directing the homing of tumor cells to specific metastatic sites (the CXCL12-CXCR4 axis); (3) regulating angiogenic processes (mainly the ELR(+)-CXC and non-ELR-CXC chemokines); (4) acting directly on the tumor cells to control their malignancy-related functions. Together, these different chemokine functions establish a net of interactions between the tumor cells and their microenvironment, and partly dictate the fate of the malignancy cascade.

Protective effects of transcription factor HESR1 on retinal vasculature

HESR1 is a basic helix-loop-helix transcription factors regulated by the Notch signaling pathway in vertebrate and Drosophila embryos, and is related to the HES/Hairy/E (sp1) family. HESR1 is a downstream target of Notch in endothelial cells and could be an effector of Notch signaling in these cells. HESR1 is necessary for the induction of a tubular network and for continued maintenance of mature and quiescent blood vessels. To examine the role of HESR1 in retinal neovascularization, we transfected retinal vascular endothelial cells (HRCECs) with the HESR1 gene and studied its effects on the expression of angiogenic factors, on the proliferation and migration of endothelial cells, and on the formation of tube-like structures (TLSs). Overexpression of HESR1 downregulated VEGFR-2 expression, upregulated occludin expression, inhibited the migration and proliferation of HRCECs, and inhibited the formation of TLSs. Thus, HESR1 plays a key role in the finely tuned network of molecules involved in the regulation of retinal vascular homeostasis. HESR1 seems to inhibit the vessel-promoting effects of VEGF, shift endothelial cells from a proliferative state to a quiescent state, and restore normal vessel structures. Expression of the HESR1 gene in retinal vascular endothelial cells may protect retinal blood vessels and may be useful in the treatment of diseases involving damage to the retinal vasculature, including diabetic retinopathy, age-related macular degeneration, and retinal vein occlusion.

Stromal cell-derived factor 1 (CXCL12) binds to endothelial cells and signals through a receptor different from CXCR4

Stromal cell-derived factor 1 (CXCL12) is an angiogenic chemokine that is believed to act solely via its cognate receptor CXCR4. Evidence is now provided for the existence of a different CXCL12 binding and signaling receptor on endothelial cells. Bovine aortic endothelial cells (BAECs) strongly expressed CXCR4 and exhibited high binding capacity for fluorescently labeled CXCL12. However, CXCL12 binding was not correlated with the CXCR4 expression level and was virtually unaffected by the specific CXCR4 antagonists AMD3100 or T22. Similar observations were made in endothelial cells of mouse and human origin. Also, AMD3100 failed to block CXCL12 internalization and CXCL12-induced intracellular signal transduction via extracellular signal-regulated kinases 1/2 in BAECs. In contrast, CXCL12 binding and signaling were almost completely inhibited by the CXCR4 antagonist in T-lymphoid SupT1 cells. Together, our data point to the existence of an additional receptor through which CXCL12 exerts its biological effects in endothelial cells.

EphB2 and EphB4 receptors forward signaling promotes SDF-1-induced endothelial cell chemotaxis and branching remodeling

The complex molecular mechanisms that drive endothelial cell movement and the formation of new vessels are poorly understood and require further investigation. Eph receptor tyrosine kinases and their membrane-anchored ephrin ligands regulate cell movements mostly by cell-cell contact, whereas the G-protein-coupled receptor CXCR4 and its unique SDF-1 chemokine ligand regulate cell movement mostly through soluble gradients. By using biochemical and functional approaches, we investigated how ephrinB and SDF-1 orchestrate endothelial cell movement and morphogenesis into capillary-like structures. We describe how endogenous EphB2 and EphB4 signaling are required for the formation of extracellular matrix-dependent capillary-like structures in primary human endothelial cells. We further demonstrate that EphB2 and EphB4 activation enhance SDF-1-induced signaling and chemotaxis that are also required for extracellular matrix-dependent endothelial cell clustering. These results support a model in which SDF-1 gradients first promote endothelial cell clustering and then EphB2 and EphB4 critically contribute to subsequent cell movement and alignment into cord-like structures. This study reveals a requirement for endogenous Eph signaling in endothelial cell morphogenic processes, uncovers a novel link between EphB forward signaling and SDF-1-induced signaling, and demonstrates a mechanism for cooperative regulation of endothelial cell movement.

Fibroblast growth factor-2 induces the activation of Src through Fes, which regulates focal adhesion disassembly

Cell migration is regulated by focal adhesion (FA) turnover. Fibroblast growth factor-2 (FGF-2) induces FA disassembly in the murine brain capillary endothelial cell line IBE, leading to FGF-2-directed chemotaxis. We previously showed that activation of Src and Fes by FGF-2 was involved in chemotaxis of IBE cells. In this study, we examined the interplay between Src and Fes. FGF-2 treatment decreased the number of FA in IBE cells, but not in cells expressing dominant-negative Fes (denoted KE5-15 cells). FGF-2 induced the activation of Src and subsequent binding to and phosphorylation of Cas in IBE cells, but not in KE5-15 cells. Focal adhesion kinase (FAK) activation and tyrosine phosphorylation by Src were also delayed in KE5-15 cells compared to parental cells. FGF-2 induced activation of Src within FA in IBE cells, but not in KE5-15 cells. Downregulation of Fes or FAK using small interfering RNA diminished Src activation by FGF-2 within FA. These findings suggest that activation of Fes by FGF-2 enhances FAK-dependent activation of Src within FA, promoting FGF-2-induced disassembly of focal adhesions.

Inhibition of cyclooxygenase-2 disrupts tumor vascular mural cell recruitment and survival signaling

Much evidence supports an important role for the inducible enzyme cyclooxygenase-2 (COX-2) in tumor angiogenesis. Previous studies have focused on the role of COX-2 in stimulating endothelial proliferation, with blockade of this enzyme impairing endothelial homeostasis. However, recent data suggest that COX-2 also regulates molecules implicated in endothelial trafficking with pericytes/vascular mural cells (VMC), an interaction crucial to vessel stability. We investigated the role of COX-2 in vascular assembly by testing the effect of the specific COX-2 inhibitor SC-236 in an orthotopic xenograft model of human Wilms' tumor. Tumor growth was significantly suppressed by SC-236 (78% at day 28, 55% at day 35). Perfusion studies and immunostaining showed a marked decrease in vasculature, particularly in small vessels. Specifically, SC-236 inhibited participation of VMC in xenograft vessels. SC-236-treated tumors developed segmentally dilated, architecturally erratic tumor vessels with decreased nascent pericytes and scant mature VMC. Although vascular endothelial growth factor expression was unchanged, expression of the chemokine receptor CXCR4 was decreased in tumor vessels, consistent with defective homing of vascular progenitor cells. Vascular expression of phosphorylated platelet-derived growth factor receptor-beta was also diminished, indicating impaired VMC-endothelial trafficking. Consistent with the key role of this interaction in vessel homeostasis, vascular cells in SC-236-treated tumors displayed markedly diminished phosphorylated Akt, indicating disrupted survival signaling. These results show that SC-236 causes defective vascular assembly by attenuating incorporation of VMC into tumor vessels, impairing endothelial survival, and raise the possibility that blockade of COX-2 may provide therapeutic synergies with antiangiogenic molecules that more selectively target endothelial cells.

Neovasculogenic Therapy to Augment Perfusion and Preserve Viability in Ischemic Cardiomyopathy

BACKGROUND

Ischemic cardiomyopathy is a global health concern with limited therapy. We recently described endogenous revascularization utilizing granulocyte-macrophage colony stimulating factor (GMCSF) to induce endothelial progenitor cell (EPC) production and intramyocardial stromal cell-derived factor-1alpha (SDF) as a specific EPC chemokine. The EPC-mediated neovascularization and enhancement of myocardial function was observed. In this study we examined the regional biologic mechanisms underlying this therapy.

METHODS

Lewis rats underwent left anterior descending coronary artery (LAD) ligation and developed ischemic cardiomyopathy over 6 weeks. Three weeks after ligation, the animals received either subcutaneous GMCSF and intramyocardial SDF injections or saline injections as control. Six weeks after LAD ligation circulating EPC density was studied by flow cytometry. Quadruple immunofluorescent vessel staining for mature, proliferating vasculature was performed. Confocal angiography was utilized to identify fluorescein lectin-lined vessels to assess perfusion. Ischemia reversal was studied by measuring myocardial adenosine triphosphate (ATP) levels. Myocardial viability was assayed by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling detection of apoptosis and quantitation of myofilament density.

RESULTS

The GMCSF/SDF therapy enhanced circulating leukocyte (13.1 +/- 4.5 x 10(6) vs 3.1 +/- 0.5 x 10(6)/cc, p = 0.001, n = 6) and EPC (14.2 +/- 6.6 vs 2.2 +/- 2.1/cc, p = 0.001, n = 6) concentrations. Tetraimmunofluorescent labeling demonstrated enhanced stable vasculature with this therapy (39.2 +/- 8.1 vs 25.4 +/- 5.1%, p = 0.006, n = 7). Enhanced perfusion was shown by confocal microangiography of borderzone lectin-labeled vessels (28.2 +/- 5.4 vs 11.5 +/- 3.0 vessels/high power field [hpf], p = 0.00001, n = 10). Ischemia reversal was demonstrated by enhanced cellular ATP levels in the GMCSF/SDF borderzone myocardium (102.5 +/- 31.0 vs 26.9 +/- 4.1 nmol/g, p = 0.008, n = 5). Borderzone cardiomyocyte viability was noted by decreased apoptosis (3.2 +/- 1.4% vs 5.4 +/- 1.0%, p = 0.004, n = 10) and enhanced cardiomyocyte density (40.0 +/- 5.6 vs 27.0 +/- 6 myofilaments/hpf, p = 0.01, n=10).

CONCLUSIONS

Endogenous revascularization for ischemic cardiomyopathy utilizing GMCSF EPC upregulation and SDF EPC chemokinesis upregulates circulating EPCs, enhances vascular stability, and augments myocardial function by enhancing perfusion, reversing cellular ischemia, and increasing cardiomyocyte viability.

Pigment epithelium-derived factor inhibits fibroblast-growth-factor-2-induced capillary morphogenesis of endothelial cells through Fyn

Pigment epithelium-derived factor (PEDF) exerts anti-angiogenic actions. However, the signal-transduction pathways regulated by PEDF remain to be elucidated. We show here that PEDF inhibited fibroblast growth factor 2 (FGF-2) induced capillary morphogenesis of a murine brain capillary endothelial cell line (IBE cells) and of human umbilical-vein endothelial cells (HUVECs) cultured on growth-factor-reduced Matrigel. We previously showed that FGF-2-mediated capillary morphogenesis was blocked by the Src-kinase inhibitor PP2 and that expression of dominant negative Fyn in IBE cells inhibited capillary morphogenesis. We examined the effect of PEDF on kinase activity of Fyn and found that PEDF downregulated FGF-2-promoted Fyn activity by tyrosine phosphorylation at the C-terminus in a Fes-dependent manner. In a stable IBE cell line expressing kinase-inactive Fes (KE5-15 Fes cells), PEDF failed to inhibit FGF-2-induced capillary morphogenesis or Fyn activity. PEDF induced the colocalization of Fyn and Fes in IBE cells expressing wild-type Fes, but not in KE5-15 Fes cells. In addition, wild-type Fes increased the tyrosine phosphorylation of Fyn in vitro, suggesting that Fes might directly phosphorylate Fyn. Expression of constitutively active Fyn (Y531F) in IBE cells exhibited capillary morphogenesis in the absence of FGF-2 and was resistant for PEDF treatment. Our results suggest that PEDF downregulates Fyn through Fes, resulting in inhibition of FGF-2-induced capillary morphogenesis of endothelial cells.

Laminar shear stress inhibits CXCR4 expression on endothelial cells: functional consequences for atherogenesis

Laminar shear stress (LSS) represents a major athero-protective stimulus. However, the mechanisms for this effect are poorly characterized. As chemokine receptors modulate endothelial cell functions, we hypothesized that at least some LSS effects on endothelial cells (ECs) may be due to LSS-dependent changes in chemokine receptor expression and function. Exposure of Human umbilical vein endothelial cells (HUVECs) to 15 dynes/cm2/sec(-1) LSS strongly inhibited CXC chemokine receptor 4 (CXCR4) expression at the transcriptional level and impaired stromal-derived factor (SDF)-1/CXCL12-driven chemotaxis. On the contrary, low shear stress (SS; 4 dynes/cm2/sec(-1)) only marginally affected CXCR4 expression when compared with static control cells. Differently from CXCR4, the expression of SDF-1 mRNA was not affected by LSS treatment. CXCR4 overexpression induced a dose-dependent endothelial cell apoptosis that was enhanced by SDF-1 treatment and was caspase-dependent. CXCR4 overexpression inhibited the LSS-mediated antiapoptotic effect on ECs and was associated to impairment of LSS-induced ERK1/2 phosphorylation. These findings suggest that LSS-induced CXCR4 down-regulation may contribute to endothelial cell survival. Interestingly, the expression of the proatherogenic chemokines MCP-1 and IL-8 was induced by SDF-1 treatment and by CXCR4 overexpression in HUVECs. Further, the known LSS-induced inhibition of MCP-1 expression was impaired in CXCR4 overexpressing ECs. Finally, CXCR4 was abundantly expressed by human atherosclerotic plaque endothelium that is exposed to low/absent shear stress, while it was poorly expressed by minimally diseased carotid artery endothelium. In conclusion, LSS-dependent CXCR4 down-regulation may contribute to atheroprotection by favoring the integrity of the endothelial barrier and by inhibiting MCP-1 and IL-8 expression.

Rac and Rho play opposing roles in the regulation of hypoxia/reoxygenation-induced permeability changes in pulmonary artery endothelial cells

Hypoxia/reoxygenation-induced changes in endothelial permeability are accompanied by endothelial actin cytoskeletal and adherens junction remodeling, but the mechanisms involved are uncertain. We therefore measured the activities of the Rho GTPases Rac1, RhoA, and Cdc42 during hypoxia/reoxygenation and correlated them with changes in endothelial permeability, remodeling of the actin cytoskeleton and adherens junctions, and production of ROS. Dominant negative forms of Rho GTPases were introduced into cells by adenoviral gene transfer and transfection, and inhibitors of NADPH oxidase, PI3 kinase, and Rho kinase were used to characterize the signaling pathways involved. In some experiments constitutively activated forms of RhoA and Rac1 were also used. We show for the first time that hypoxia/reoxygenation-induced changes in endothelial permeability result from coordinated actions of the Rho GTPases Rac1 and RhoA. Rac1 and RhoA rapidly respond to changes in oxygen tension, and their activity depends on NADPH oxidase- and PI3 kinase-dependent production of ROS. Rac1 acts upstream of RhoA, and its transient inhibition by acute hypoxia leads to activation of RhoA followed by stress fiber formation, dispersion of adherens junctions, and increased endothelial permeability. Reoxygenation strongly activates Rac1 and restores cortical localization of F-actin and VE-cadherin. This effect is a result of Rac1-mediated inhibition of RhoA and can be prevented by activators of RhoA, L63RhoA, and lysophosphatidic acid. Cdc42 activation follows the RhoA pattern of activation but has no effect on actin remodeling, junctional integrity, or endothelial permeability. Our results show that Rho GTPases act as mediators coupling cellular redox state to endothelial function.

The CXCL12-CXCR4 chemotactic pathway as a target of adjuvant breast cancer therapies

Dose-dense adjuvant breast cancer chemotherapy is a new treatment strategy that aims to improve tumour control by using more frequent cytotoxic dosing together with continuous granulocyte colony-stimulating factor (G-CSF) to minimize neutropaenia. In addition to stimulating neutrophil proliferation, G-CSF mobilizes neutrophils from the bone marrow through proteolytic disruption of the chemokine receptor CXCR4 and its chemotactic ligand CXCL12. As breast cancers also express CXCR4 and oestrogen induces CXCL12, the success of dose-dense treatment could partly reflect inhibition of CXCR4-dependent micrometastatic homing and/or paracrine survival, and suggests a benefit of adjuvant oestrogen suppression for patients with oestrogen-receptor-negative, CXCR4-positive disease.

Role of high expression levels of CXCR4 in tumor growth, vascularization, and metastasis

Hormone refractory metastatic prostate cancer remains an incurable disease. We found that high expression levels of the chemokine receptor CXCR4 correlated with the presence of metastatic disease in prostate cancer patients. Positive staining for CXCL12, the ligand for CXCR4, was mainly present in the tumor-associated blood vessels and basal cell hyperplasia. Subcutaneous xenografts of PC3 and 22Rv1 prostate tumors that overexpressed CXCR4 in NOD/SCID mice were two- to threefold larger in volume and weight vs. controls. Moreover, blood vessel density, functionality, invasiveness of tumors into the surrounding tissues, and metastasis to the lymph node and lung were significantly increased in these tumors. Neutralizing the interactions of CXCL12/CXCR4 in vivo with CXCR4 specific antibodies inhibited the CXCR4-dependent tumor growth and vascularization. In vitro, CXCL12 induced the proliferation and VEGF secretion but not migration of PC3 and 22Rv1 cells overexpressing CXCR4. Similar effects of CXCR4 overexpression on tumor growth in vivo were also noted in two breast cancer lines, suggesting that the observed effect of CXCR4 is not unique to prostate tumor cells. Thus high levels of the chemokine receptor CXCR4 induce a more aggressive phenotype in prostate cancer cells and identify CXCR4 as a potential therapeutic target in advanced cases of metastatic prostate cancer.

Vascular defects in gain-of-function fps/fes transgenic mice correlate with PDGF- and VEGF-induced activation of mutant Fps/Fes kinase in endothelial cells

BACKGROUND

Fps/Fes is a cytoplasmic tyrosine kinase that is abundantly expressed in the myeloid, endothelial, epithelial, neuronal and platelet lineages. Genetic manipulation in mice has uncovered potential roles for this kinase in hematopoiesis, innate immunity, inflammation and angiogenesis.

OBJECTIVE

We have utilized a genetic approach to explore the role of Fps/Fes in angiogenesis.

METHODS

A hypervascular line of mice generated by expression of a 'gain-of-function' human fps/fes transgene (fps(MF)) encoding a myristoylated variant of Fps (MFps) was used in these studies. The hypervascular phenotype of this line was extensively characterized by intravital microscopy and biochemical approaches.

RESULTS

fps(MF) mice exhibited 1.6-1.7-fold increases in vascularity which was attributable to increases in the number of secondary vessels. Vessels were larger, exhibited varicosities and disorganized patterning, and were found to have defects in histamine-induced permeability. Biochemical characterization of endothelial cell (EC) lines derived from fps(MF) mice revealed that MFps was hypersensitive to activation by vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF).

CONCLUSIONS

MFps mediates enhanced sensitization to VEGF and PDGF signaling in ECs. We propose that this hypersensitization contributes to excessive angiogenic signaling and that this underlies the observed hypervascular phenotype of fps(MF) mice. These phenotypes recapitulate important aspects of the vascular defects observed in both VEGF and angiopoietin-1 transgenic mice. The fps/fes proto-oncogene product therefore represents a novel player in the regulation of angiogenesis, and the fps(MF) line of mice constitutes a unique new murine model for the study of this process.

Stem cell factor/c-kit signaling promotes the survival, migration, and capillary tube formation of human umbilical vein endothelial cells

c-kit receptor tyrosine kinase is a marker of progenitor cells, which differentiate into blood and/or vascular endothelial cells, and has an important role in the amplification/mobilization of progenitor cells. c-kit is expressed in mature endothelial cells, but its role there is unclear. Stem cell factor, a c-kit ligand, dose-dependently promoted survival, migration, and capillary tube formation of human umbilical vein endothelial cells. These effects mimicked those of vascular endothelial growth factor, except that stem cell factor did not sufficiently support proliferation of these cells. After exposing cells to this factor, Akt, Erk1/2, and c-kit were immediately (</=5 min) and dose-dependently tyrosinephosphorylated. STI-571, a c-kit inhibitor, dose-dependently attenuated these phosphorylations and inhibited stem cell factor-promoted survival and capillary tube formation over the same dose range. Wortmannin and LY294002, inhibitors of phosphoinositide 3-kinase, and PD98059, an inhibitor of MEK, abrogated survival and capillary tube formation, indicating that Akt and Erk1/2 should promote survival and capillary tube formation of these endothelial cells at a locus downstream to stem cell factor/c-kit signaling. Akt was more strongly phosphorylated, whereas Erk1/2 and p38 were more weakly phosphorylated with stem cell factor than with vascular endothelial growth factor. Phospholipase Cgamma was phosphorylated only with the latter, indicating that stem cell factor/c-kit signaling is somewhat different.

Activated Fps/Fes partially rescues the in vivo developmental potential of Flk1-deficient vascular progenitor cells

Relatively little is known about the modulators of the vascular endothelial growth factor A (VEGF-A)/Flk1 signaling cascade. To functionally characterize this pathway, VEGF-A stimulation of endothelial cells was performed. VEGF-A–mediated Flk1 activation resulted in increased translocation of the endogenous Fps/Fes cytoplasmic tyrosine kinase to the plasma membrane and increased tyrosine phosphorylation, suggesting a role for Fps/Fes in VEGF-A/Flk1 signaling events. Addition of a myristoylation consensus sequence to Fps/Fes resulted in VEGF-A–independent membrane localization of Fps/Fes in endothelial cells. Expression of the activated Fps/Fes protein in Flk1-deficient embryonic stem (ES) cells rescued their contribution to the developing vascular endothelium in vivo by using ES cell–derived chimeras. Activated Fps/Fes contributed to this rescue event by restoring the migratory potential to Flk1 null progenitors, which is required for movement of hemangioblasts from the primitive streak region into the yolk sac proper. Activated Fps/Fes in the presence of Flk1 increased the number of hemangioblast colonies in vitro and increased the number of mesodermal progenitors in vivo. These results suggest that Fps/Fes may act synergistically with Flk1 to modulate hemangioblast differentiation into the endothelium. We have also demonstrated that activated Fps/Fes causes hemangioma formation in vivo, independently of Flk1, as a result of increasing vascular progenitor density.

PI3K inhibitors block skeletogenesis but not patterning in sea urchin embryos

Skeletogenesis in the sea urchin embryo is a simple model of biomineralization, pattern formation, and cell-cell communication during embryonic development. The calcium carbonate skeletal spicules are secreted by primary mesenchyme cells (PMCs), but the skeletal pattern is dictated by the embryonic ectoderm. Although the process of skeletogenesis is well characterized, there is little molecular understanding of the basis of patterning within this system. In this study, we examined the contribution of phosphatidylinositide 3-kinase (PI3K)-mediated signaling to the skeletogenic process in sea urchin embryos by using the well-established PI3K inhibitors LY294002 and wortmannin. Our results show that PI3K inhibitors specifically and reversibly block skeletogenesis, and that this blockade occurs within the PMCs rather than in the ectoderm, because the inhibitors block spiculogenesis in cultured micromeres. Our results are consistent with a model in which PI3K signaling is required, not for pattern sensing or interpretation but rather for the biomineralization process itself in the sea urchin embryo.

The role of c-Fes in vascular endothelial growth factor-A-mediated signaling by endothelial cells

c-Fes plays pivotal roles in angiogenic cellular responses of endothelial cells. Here we examined the role of c-Fes in vascular endothelial growth factor-A (VEGF-A)-mediated signaling pathways in endothelial cells. We introduced either wild-type or kinase-inactive c-Fes in porcine aortic endothelial (PAE) cell lines, which endogenously express VEGF receptor (VEGFR)-1, and PAE cells ectopically expressing VEGFR-2 (denoted KDR/PAE cells) and generated stable cell lines. VEGF-A induced autophosphorylation of c-Fes only in KDR/PAE cells, suggesting that VEGFR-2 was required for its activation. Expression of kinase-inactive c-Fes failed to demonstrate dominant negative effect on VEGF-A-induced chemotaxis and capillary morphogenesis. Phosphoinositide 3-kinase (PI3-kinase) was activated in KDR/PAE cells and c-Fes contributed to this process in a kinase activity-dependent manner. However, VEGFR-2, insulin receptor substrate-1, and c-Src were also involved in VEGF-A-induced activation of PI3-kinase, resulting in the compensation in cells expressing kinase-inactive c-Fes. Interestingly, overexpression of wild-type c-Fes in PAE cells induced VEGF-A-independent capillary morphogenesis. Considered collectively, VEGF-A activated PI3-kinase partly through c-Fes and increase in c-Fes kinase activity enhanced capillary morphogenesis by yet unknown signaling pathways.