Defining conditions for covalent immobilization of angiogenic growth factors onto scaffolds for tissue engineering

Rapid vascularization of engineered tissues in vitro and in vivo remains one of the key limitations in tissue engineering. We propose that angiogenic growth factors covalently immobilized on scaffolds for tissue engineering can be used to accomplish this goal. The main objectives of this work were: (a) to derive desirable experimental conditions for the covalent immobilization of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1) on porous collagen scaffolds; and (b) to determine whether primary endothelial cells respond to these scaffolds with covalently immobilized angiogenic factors. VEGF and Ang1 were covalently immobilized onto porous collagen scaffolds, using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) chemistry. To improve covalent immobilization conditions: (a) different reaction buffers [phosphate-buffered saline (PBS), distilled water, or 2-(N-morpholino)ethanesulphonic acid (MES)] were used; and (b) step immobilization was compared to bulk immobilization. In step immobilization, growth factors are applied after EDC activation of the scaffold, while in bulk immobilization, reagents are simultaneously applied to the scaffold. PBS as the reaction buffer resulted in higher amounts of VEGF and Ang1 immobilized (ELISA), higher cell proliferation rates (XTT) and increased lactate metabolism compared to water and MES as the reaction buffers. Step immobilization in PBS buffer was also more effective than bulk immobilization. Immobilized growth factors resulted in higher cell proliferation and lactate metabolism compared to soluble growth factors used at comparable concentrations. Tube formation by CD31-positive cells was also observed in collagen scaffolds with immobilized VEGF or Ang1 using H5V and primary rat aortic endothelial cells but not on control scaffolds.

The association of the angiopoietin/Tie-2 system with the development of metastasis and leukocyte migration in neuroendocrine tumors

The aim of this study was to explore the possible involvement of the angiopoietin (Ang)-1, -2/Tie-2 system in the development, growth, and metastases evolution of gastroenteropancreatic-neuroendocrine tumors (GEP-NETs). We prospectively examined the serum levels of Tie-2, Ang-1, and Ang-2 by ELISA in 42 patients with proven GEP-NETs and 27 controls. We also determined the expression of the Ang/Tie-2 system in freshly isolated peripheral blood monocytes and in tumor cells from malignant primary tumors and/or liver metastases samples from GEP-NET patients by flow cytometry and/or RT-PCR. Furthermore, the function of the Ang/Tie-2 system in monocytes from controls and patients was assessed by a chemotaxis assay. GEP-NET patients showed enhanced serum levels of soluble form of Tie-2 (sTie-2), Ang-1, and Ang-2 (P<0.05 in all cases), compared to controls. sTie-2 and Ang-2 levels were significantly higher in GEP-NETs with metastases compared to those with no metastases. In addition, a significant correlation was detected between Ang-2 levels and chromogranin A or sTie-2 concentrations or 5-hydroxy-indole acetic acid excretion (r=0.71, r=0.60, and r=0.81 respectively, P<0.01 in all cases). Furthermore, we observed an enhanced expression of Ang-1, Ang-2, and Tie-2 in freshly isolated tumor cells from GEP-NET both by immunohistochemistry and by RT-PCR. Interestingly, an enhanced expression and function of Tie-2 was detected in monocytes from GEP-NET patients. Our data suggest that the Ang/Tie-2 system is involved in the growth and development of metastases of GEP-NETs, and that favors the recruitment of Tie-2(+) monocytes to the tumor site, where they can promote inflammation and angiogenesis.

A peroxynitrite decomposition catalyst prevents 60% O2-mediated rat chronic neonatal lung injury

Exposure of newborn rats to 60% O2 for 14days results in a chronic neonatal lung injury characterized by parenchymal thickening, impaired alveolarization, evidence of pulmonary hypertension, and pulmonary vascular pruning. The contribution of peroxynitrite to this injury was assessed by treating pups with a peroxynitrite decomposition catalyst, 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron(III) chloride (FeTPPS), at 30microg/g/day. Body and lung weights and postfixation lung volumes were all slightly, but significantly, reduced by exposure to 60% O2 and this was attenuated by a concurrent FeTPPS intervention. The FeTPPS intervention had no impact on increased neutrophil or macrophage influx into the lung, but attenuated 60% O2-induced reductions in the lung contents of vascular endothelial-derived growth factor, its receptor-2, and angiopoietin and increases in 8-isoprostane and preproendothelin-1. The 60% O2-induced parenchymal thickening and impairment of alveologenesis, as well as vascular pruning and peripheral vessel medial wall thickening, were attenuated by FeTPPS, despite a persistent inflammatory cell influx. Pups exposed to 60% O2 and treated with FeTPPS had enhanced alveolar formation relative to control pups. We conclude that peroxynitrite plays a critical role in the development of chronic neonatal lung injury.

Angiopoietin-1 induces migration of monocytes in a tie-2 and integrin-independent manner

Angiopoietin-1 (Ang-1) is an angiogenic growth factor that activates Tie-2 and integrins to promote vessel wall remodeling. The recent finding of the potential proatherogenic effects of Ang-1 prompted us to investigate whether Ang-1 promotes monocyte chemotaxis, endothelial binding, and transendothelial migration, key events in the progression of atherosclerosis. Here, we show that Ang-1 induces chemotaxis of monocytes in a manner that is independent of Tie-2 and integrin binding but dependent on phosphoinositide 3-kinase and heparin. In addition, Ang-1 promoted phosphoinositide 3-kinase-dependent binding of monocytes to endothelial monolayers and stimulated transendothelial migration. Fluorescence-activated cell sorting analysis showed that exogenous Ang-1 adheres directly to monocytes as well as to human umbilical endothelial cells, but neither Tie-2 mRNA nor protein were expressed by primary monocytes. Although Ang-1 binding to human umbilical endothelial cells was partially Tie-2 and integrin dependent, Ang-1 binding to monocytes was independent of these factors. Finally, preincubation of monocytes with soluble heparin abrogated Ang-1 binding to monocytes and migration, and partially prevented Ang-1 binding to human umbilical endothelial cells. In summary, Ang-1 induces chemotaxis of monocytes by a mechanism that is dependent on phosphoinositide 3-kinase and heparin but independent of Tie-2 and integrins. The ability of Ang-1 to recruit monocytes suggests it may play a role in inflammatory angiogenesis and may promote atherosclerosis.

Amniotic fluid angiopoietin-1, angiopoietin-2, and soluble receptor tunica interna endothelial cell kinase-2 levels and regulation in normal pregnancy and intraamniotic inflammation-induced preterm birth

BACKGROUND

Angiopoietin-1 (Ang-1) and Ang-2 act selectively on endothelial cells by engaging the Tunica interna endothelial cell kinase-2 (Tie2) receptor. A soluble form of Tie2 (sTie2) blocks angiopoietin bioactivity.

OBJECTIVE

The aim of the study was to characterize changes and expression patterns of Ang-1, Ang-2, and sTie2 in amniotic fluid (AF) and placenta during human pregnancy and intraamniotic inflammation (IAI)-induced preterm birth.

DESIGN AND SETTING

We conducted a cross-sectional study at a tertiary university hospital.

PATIENTS

AF levels of Ang-1, Ang-2, and sTie2 were evaluated in 176 women during second trimester (n = 40), third trimester (n = 37), and preterm labor (positive IAI, n = 50; negative IAI, n = 49). Placenta and cord blood of select women were analyzed.

MAIN OUTCOME MEASURES

Ang-1, Ang-2, sTie2, and IL-6 were evaluated by ELISA. Real-time PCR measured Ang-1, Ang-2, and Tie2 placental mRNA levels. Placenta was immunostained for Ang-1 and Ang-2. Placental explant cultures were stimulated with lipopolysaccharide, Pam3Cys, and modulators of protein synthesis/secretion (cycloheximide, monensin, and brefeldin A).

RESULTS

In normal pregnancy, the levels and ratios of AF Ang-1, Ang-2, and sTie2 varied with gestational age (GA) (P < 0.001). PCR revealed corresponding changes in placental Ang-1 and Ang-2, but not Tie2, mRNA. IAI raised AF Ang-1, Ang-2, and sTie2 above the expected level for GA without affecting their placental mRNA. Ang-2 immunoreactivity appeared enhanced in areas of villous edema. AF Ang-2/Ang-1 ratio was an important determinant of cord blood IL-6 (P < 0.001). Ex-vivo, sTie2 release was increased by Golgi disrupting but not bacterial mimic agents.

CONCLUSIONS

Ang-1, Ang-2, and sTie2 are physiological constituents of AF that are GA and IAI regulated. Ang-2/Ang-1 ratio may play a role in modulating the fetal inflammatory response to IAI. Placental sTie2 shedding likely involves a Golgi-mediated mechanism.

Delayed neovascularization in inflammation-induced corneal neovascularization in interleukin-10-deficient mice

PURPOSE

To investigate the potential modulatory role of interleukin-10 (IL-10) in the suture model for corneal neovascularization.

METHODS

Neovascularized areas were measured on corneal flat-mounts in IL-10(-/-) and wild-type C57BL6 mice. The inflammatory cellular response was characterized with immunohistochemistry. Gene expression was measured by real-time polymerase chain reaction.

RESULTS

IL-10(-/-) mice showed a delayed neovascular response compared to wild-type animals at day 6 after suture, when approximately half of the cornea was neovascularized. No apparent differences in inflammatory responses or in messenger RNA (mRNA) expression for proangiogenic factors were detected in IL-10(-/-) versus wild-type mice.

CONCLUSION

IL-10 appears to have a proangiogenic effect in the suture model for corneal neovascularization that cannot be explained by either IL-10's anti-inflammatory effect or apparent cross-talk with the angiogenic factors vascular endothelial growth factor (VEGF)-A, metalloproteinase (MMP)-2 and MMP-9, angiopoietin (Ang)-1 and Ang-2.

COMP-Ang1, a chimeric form of Angiopoietin 1, enhances BMP2-induced osteoblast differentiation and bone formation

INTRODUCTION

Angiogenesis is closely associated with bone formation, especially endochondral ossification. Angiopoietin 1 (Ang1) is a specific growth factor functioning to generate a stable and matured vasculature through the Tie2 receptor/PI3K/AKT pathway. Recently cartilage oligomeric matrix protein (COMP)-Ang1, an Ang1 variant which is more potent than native Ang1 in phosphorylating Tie2 receptor and AKT, was developed. This study was designed to examine the effects of angiogenic COMP-Ang1 on BMP2-induced osteoblast differentiation and bone formation.

METHODS

Expression of endogenous Ang-1 and its binding receptor Tie 2 mRNA was examined in osteoblast-like cells and primary mouse calvarial cells by RT-PCR analysis, and was also monitored during osteoblast differentiation induced by BMP-2 and/or ascorbic acid and beta-glycerophosphate. Effects of COMP-Ang-1 on osteoblast differentiation and mineralization were evaluated by alkaline phosphatase (ALP) activity and osteocalcin (OC) production, and Alizarin red stain. For a molecular mechanism, Western blot and OG2 and 6xOSE promoter assays were done. For in vivo evaluation, adenoviral (Ad) vectors containing COMP-Ang-1 or BMP-2 gene were administered into thigh muscle of mice, and after 2 weeks bone formation was analyzed by micro-computed tomography and histology. Angiogenic event of COMP-Ang1 was confirmed by immunofluorescence analysis with anti-CD31 antibody.

RESULTS

Expression of Tie2 receptor was significantly increased in the course of osteoblast differentiation. Treatment or overexpression of COMP-Ang1 enhanced BMP2-induced ALP activity, OC production, and mineral deposition in a dose-dependent manner. In addition, COMP-Ang1 synergistically increased OG2 and 6xOSE promoter activities of BMP2, and sustained p38, Smad and AKT phosphorylation of BMP2. Notably, in vivo intramuscular injection of COMP-Ang1 dose-dependently enhanced BMP2-induced ectopic bone formation with increases in CD31 reactivity.

CONCLUSIONS

These results suggest that COMP-Ang1 synergistically enhanced osteoblast differentiation and bone formation through potentiating BMP2 signaling pathways and angiogenesis. Combination of BMP2 and COMP-Ang1 should be clinically useful for therapeutic application to fracture and destructive bone diseases.

Angiopoietin-1 inhibits mouse glomerular endothelial cell senescence via Tie2 receptor-modulated ERK1/2 signaling

BACKGROUND

The vasculature plays a key role in the progression of renal damage in aging, with reduction in glomerular and peritubular capillary density and decreased endothelial proliferative response. In this study, we examined the role of angiopoietin-1 (Ang1) in H(2)O(2)-induced senescence in mouse glomerular endothelial cells (MGECs) and the signaling pathway involved.

METHODS

MGECs were subjected to H(2)O(2)-induced senescence, which was evaluated by senescence-associated beta-galactosidase (SA-beta-Gal) staining, cell cycle analysis and expression of p16. Endothelial cell function was assessed by nitric oxide, von Willebrand factor secretion and capillary-like structure formation. Signal transduction was examined by Western blot with or without a specific inhibitor.

RESULTS

Ang1 significantly inhibited H(2)O(2)-induced senescence in MGECs, attenuated SA-beta-Gal activity, resumed growth, and downregulated p16(INK4a) levels. Moreover, Ang1 regulated the secretion and capillary-like structure formation of endothelial cells with aging. However, these changes were markedly blocked by treatment with Ang2, sTie2-Fc and PD98059. Ang1 treatment markedly increased elevated Tie2 and ERK1/2 phosphorylation levels which were reduced by Ang2 and sTie2-Fc. PD98059 substantially reduced senescence while not altering Ang1-stimulated phosphor-Tie2 stimulation.

CONCLUSION

The present studies suggest that Ang1 inhibits H(2)O(2)-induced senescence in MGECs via the Ang1-Tie2-ERK1/2 signaling pathway.

[The diagnostic value of microsatellite LOH analysis and the prognostic relevance of angiogenic gene expression in urinary bladder cancer]

Bladder cancer is the second most common malignancy affecting the urinary system. Currently, histology is the only tool that determines therapy and patients' prognosis. As the treatment of non-invasive (Ta/T1) and muscle invasive (T2-T4) bladder tumors are completely different, correct staging is important, although it is often hampered by disturbing factors. Molecular methods offer new prospects for early disease detection, confirmation of unclear histological findings and prognostication. Applying molecular biological methods, the present study is searching for answers to current diagnostic and prognostic problems in bladder carcinoma. We analyzed tumor, blood and/or urine samples of 334 bladder cancer patients and 117 control individuals. Genetic alterations were analyzed in urine samples of patients and controls, both by PCR-based microsatellite loss of heterozigosity (LOH) analysis using 12 fluorescently labeled primers and by DNA hybridization based UroVysion FISH technique using 4 probes, to assess the diagnostic values of these methods. Whole genome microsatellite analysis (with 400 markers) was performed in tumor and blood specimens of bladder cancer patients to find chromosomal regions, the loss of which may be associated with tumor stage. Furthermore, we assessed the prognostic value of Tie2, VEGF, Angiopoietin-1 and -2. We concluded that DNA analysis of voided urine samples by microsatellite analysis and FISH are sensitive and non-invasive methods to detect bladder cancer. Furthermore, we established a panel of microsatellite markers that could differentiate between non-invasive and invasive bladder cancer. However, further analyses in a larger cohort of patients are needed to assess their specificity and sensitivity. Finally, we identified high Ang-2 and low Tie2 gene expression as significant and independent risk factors of tumor recurrence and cancer related survival.

Expression and release of angiopoietin-1 from human neutrophils: intracellular mechanisms

We recently demonstrated that Tie2 receptor activation on human neutrophils by both angiopoietins (Ang1 and Ang2) promoted platelet-activating factor synthesis, beta(2)-integrin activation, and cell migration. Herein, we wanted to assess if human neutrophils express angiopoietins and further delineate their mechanisms of release. Employing Reverse transcriptase-polymerase chain reaction, Real time quantitative transcriptase-polymerase chain reaction, FACScan analysis and ELISA approaches, we observed that neutrophils express Ang1 but not Ang2. For each condition, vascular endothelial growth factor (VEGF) detection was performed as positive control. Using nitrogen cavitation, we observed that Ang1 is localized in the cytosolic fraction whereas VEGF is found in beta-granules. Treatment of neutrophils with phorbol myristate acetate (PMA), N-Formyl-Met-Leu-Phe (fMLP) and tumor necrosis factor-alpha (TNF-alpha) induced VEGF release. Maximal effect was observed with PMA (80 nM) stimulation inducing a complete release of VEGF content (565 +/- 100 pg/ml; 6 x 10(6) neutrophils), corresponding to a 18.9-fold increase as compared to phosphate buffer saline (PBS) treated neutrophils. By contrast, only a treatment with PMA (80 nM) induced Ang1 release. PMA treatment induced also a complete release of Ang1 (661 +/- 148 pg/ml; 6 x 10(6) neutrophils), corresponding to 2.8-fold increase as compared to PBS-treated neutrophils. In both cases, PMA-mediated release of VEGF and Ang1 was nearly maximal by 15 min. Finally, we observed that the induction of Ang1 release was calcium-independent whereas VEGF release was not. These data demonstrate the capacity of human neutrophils to synthesize Ang1, which is stored and released differently as compared to VEGF. These data suggest a different cascade of events regarding the distribution of selected growth factors during inflammation and angiogenesis.

[Assessment of the selected, late phase of angiogenesis factors' concentration in colorectal cancer patients]

Angiogenesis is a process of new blood vessels creating based on existing already vascularisation. This composed and multistage mechanism, which is responsible for growth of the tissues and organs, plays a crucial role in neoplasia. The exact role of particular cells, cytokines and extracellular matrix in cancerogenesis is still discussing. An identification of it is the key to searching the antiangiogenic substances breaking simultaneously neoplastic proliferation. THE AIM OF THE STUDY was to compare the angiopoietin-1(Ang-1), angiopoietin-2 (Ang-2) and Tie-2 receptor (rec. Tie-2) concentrations in the serum of colorectal cancer patients with concentrations of these factors in the serum of healthy people. Moreover the aim of the study was to assess the correlation between the concentrations of these factors and stage of clinical neoplasm progression.

MATERIAL AND METHODS

The study included 35 patients hospitalized in the Department of General Surgery due to confirmed by histopatological examination colorectal cancer, between 2006 to 2007. The group of examined patients consisted of 9 women and 26 men with ages between 39 to 81 (average 67.20+/-8.85). The control group consisted of 11 healthy people. The examinations relied on the 10 ml of blood sampling from all the patients, in fasting state, one day before the operation. 10 ml of blood, in the healthy group was also sampled in fasting state. Afterwards all blood samples, 30 minutes after collecting, were centrifuged with velocity 6000 rotation per minute. The gaining serum was freezed in temperature -80 degrees C. The concentrations of Ang-1, Ang-2 and rec.Tie-2 were measured with ELISA method.

RESULTS

Among examined patients with colorectal cancer, the statistically significant, higher concentration of Ang-2 in comparison with control group was revealed (6239.7+/-3482.3 pg/ml vs. 2954.9+/-9624.2 pg/ml). The concentration of Ang-2 among the patients from III and IV group according to the clinical and pathomorfological progression classification was statistically significant, higher than in I and II group of the patients (III: 8668,8+/-4938.57 pg/ml; IV: 9002.1+/-5380.92 pg/ml vs. I: 4672.3+/-1808.7 pg/ml; II: 5284.8+/-3204.2 pg/ml). The concentration of Ang-1 and rec. Tie-2 in blood of all the patients with colorectal cancer didn't statistically differ from the control group (Ang-1: 42339.9+/-20197.2 pg/ml vs. 48976.4+/-2284.5 pg/ml; rec.Tie-2; 14.4+/-5.1 vs. 16.8+/-6.2 ng/ml).

CONCLUSIONS

The concentration of Ang-2 in the colorectal patients was statistically higher than in the control group. The increase concentration of Ang-2 correlated with the stage of colorectal cancer's clinical progression. The higher concentration of Ang-2 may eventually become a helpful marker in diagnostic and assessment of colorectal cancer's clinical progression stage.

Skeletal muscle sings a choral stem cell lullaby

Constraint of stem cell number in skeletal muscle is investigated by Abou-Khalil et al. (2009), in this issue of Cell Stem Cell. Their results attribute it both to autocrine positive feedback and to paracrine signals from the surrounding cellular community.

Autocrine and paracrine angiopoietin 1/Tie-2 signaling promotes muscle satellite cell self-renewal

Mechanisms governing muscle satellite cell withdrawal from cell cycle to enter into quiescence remain poorly understood. We studied the role of angiopoietin 1 (Ang1) and its receptor Tie-2 in the regulation of myogenic precursor cell (mpc) fate. In human and mouse, Tie-2 was preferentially expressed by quiescent satellite cells in vivo and reserve cells (RCs) in vitro. Ang1/Tie-2 signaling, through ERK1/2 pathway, decreased mpc proliferation and differentiation, increased the number of cells in G0, increased expression of RC-associated markers (p130, Pax7, Myf-5, M-cadherin), and downregulated expression of differentiation-associated markers. Silencing Tie-2 had opposite effects. Cells located in the satellite cell neighborhood (smooth muscle cells, fibroblasts) upregulated RC-associated markers by secreting Ang1 in vitro. In vivo, Tie-2 blockade and Ang1 overexpression increased the number of cycling and quiescent satellite cells, respectively. We propose that Ang1/Tie-2 signaling regulates mpc self-renewal by controlling the return to quiescence of a subset of satellite cells.

The mechanism of increased vascular permeability in renal ischemic reperfusion injury: potential role of angiopoietin-1 and hyaluronan

BACKGROUND

One striking feature observed during renal ischemia reperfusion injury (IRI) is the increase in interstitial fluid and infiltration, which reflects an increase in vascular permeability. Angiopoietin-1 (Ang-1) prevents vascular leakage and inflammation. Hyaluronic acid (HA) has a high capacity to bind and retain water and is pro-inflammatory factor.

MATERIAL AND METHOD

The authors evaluated the expression of Ang-1 and HA during renal IRI bilaterally for 30 minutes. Renal tissue was sent for pathologic study, proteins expression, and mRNA in renal IRI at 24 and 48 hr.

RESULTS

At 24 hr post-injury, histopathology studies revealed severe tubular epithelial cell (TEC) necrosis, peritubular capillary (PTC) congestion, mild interstitial infiltration, and edema. Histopathology at 48 hr post-injury showed a progressive increased degree of PTC congestion, interstitial infiltration and edema. In normal kidney, Ang-1 was abundant in glomerulus and PTC patterns, while HA is absent in the cortex but present in the medulla. At 24 and 48 h rpost-IRI, kidney cortex and medulla showed a reduced Ang-1 staining but with an increase in HA staining. Western blot analysis showed that levels of Ang-1 expression decreased to 44% of normal levels at 24 hr post-IRI and further declined to 31% at 48 hr post-IRI. Using real time RT-PCR, Ang-1 expression declined to 15% of normal levels at 24 hr post-IRI and sustained at 48 hr post-IRI.

CONCLUSION

These results suggest that lowered Ang-1 expression levels and increased HA may contribute to an increased permeability and inflammation of microcirculation in renal IRI.

Temporal changes of angiopoietins and Tie2 expression in rat lungs after monocrotaline-induced pulmonary hypertension

Angiogenic factors such as vascular endothelial growth factor (VEGF) are implicated in pulmonary hypertension (PH). However, the pathway of angiogenic factor-mediated pathologic angiogenesis in PH remains unclear. In this study, we evaluated the temporal expression of angiopoietin (Ang) 1, Ang2, and their receptor (Tie2) as well as VEGF, endothelial nitric oxide synthase (eNOS), inducible NOS (iNOS), and heme oxygenase 1 (HO1) in the monocrotaline-induced PH model. Histologic evaluation showed pathologic vascular remodeling in the arteries of lung sections 1 wk after monocrotaline treatment. Protein levels of Ang1, Ang2, eNOS, iNOS, HO1, and VEGF were increased 1 wk after monocrotaline treatment but Tie2 protein levels were decreased 2 wk afterward. These results suggest that Ang2 mediates vascular remodeling in PH by decreasing Tie2 expression. Therefore, the Ang-Tie2 system may play a role in the pathophysiology of PH.

Regulation of Tie2 Expression by Angiopoietin—Potential Feedback System

To study a potential feedback system in the angiopoietin (Ang)-Tie2 system, the authors examined effects of Ang1 and Ang2 on Tie2 expression on human umbilical vein endothelial cells (HUVECs) with or without stimulation by a potent inflammatory cytokine, tumor necrosis factor-alpha (TNF-alpha). Ang1, but not Ang2, down-regulated Tie2 expression on HUVECs without TNF-alpha stimulation. Both Ang1 and Ang2 attenuated TNF-alpha-induced Tie2 up-regulation. Regulation of Tie2 expression by Ang1 or Ang2 was not dependent on phosphatidylinositol 3-kinase. The Ang-Tie2 system appears to have an autoregulatory feedback system that may be regulating the overall activity of the Tie2 system in both physiological and pathological conditions.

A Single Local Injection of Recombinant VEGF Receptor 2 But Not of Tie2 Inhibits Retinal Neovascularization in the Mouse

PURPOSE

The purpose of this study was to develop pharmacological therapeutic alternatives for ischemia-induced proliferative retinopathy.

METHODS

C57BL/6J mice were placed in 76% oxygen on postnatal day 7 (P7) for 5 days. On P12 recombinant, chimeric vascular endothelial growth factor (sVEGF-R2) or sTie2 was injected intravitreally in one eye. The fellow eye received a control injection. On P17, retinal wholemounts were prepared after perfusion with fluorescein-dextran to quantify the retinopathy.

RESULTS

A single intravitreal injection of sVEGF-R2 reduced pathologic vascular changes significantly (p = 0.02). No significant effect was observed after intravitreal application of sTie2 (p = 0.07), although Ang-2 was upregulated in control animals without treatment as neovascularization developed and Ang-1 was constantly transcribed (ratio PCR).

CONCLUSIONS

sVEGF-R2 interferes with VEGF signaling via VEGF-R2 receptor. Thus, local application of soluble receptors for angiogenic factors is a possible therapy for proliferative retinopathy. Receptors with a wide range of ligands might prove more useful for local application than those binding few or antagonistic ligands.

Maturation of blood vessels by haematopoietic stem cells and progenitor cells: involvement of apelin/APJ and angiopoietin/Tie2 interactions in vessel caliber size regulation

Apelin is a recently-isolated bioactive peptide from bovine gastric extract. The gene encodes a protein of 77 amino acids, which can generate two active polypeptides, long (42-77) and short (65-77). Both peptides ligate and activate APJ, a G protein-coupled receptor expressed in the cardiovascular and central nervous systems. Although an essential role for the apelin/APJ system in blood vessel formation has been reported in Xenopus, its precise function in mammals is unclear. Blood vessel tube formation is accomplished by two main mechanisms: 1) single cell hollowing, in which a lumen forms within the cytoplasm of a single endothelial cell (EC), and 2) cord hollowing in which a luminal cavity is created de novo between ECs in a thin cylindrical cord. Molecular control of either single cell or cord hollowing has not been precisely determined. Angiopoietin-1 (Ang1) has been reported to induce enlargement of blood vessels. Apelin is produced from ECs upon activation of Tie2, a cognate receptor of Ang1, expressed on ECs. It has been suggested that apelin induces cord hollowing by promoting proliferation and aggregation/assembly of ECs. During angiogenesis, haematopoietic stem cells (HSCs) and progenitor cells (HPCs) are frequently observed in the perivascular region. They produce Ang1 and induce migration of ECs, resulting in a fine vascular network. Moreover, HSCs/HPCs can induce apelin production from ECs. Therefore, this review article posits that HSCs/HPCs regulate caliber size of blood vessels via apelin/APJ and Angiopoietin/Tie2 interactions.

[Significance of a reversal expression of the angiopoietin-1 and 2 in oral squamous cell carcinoma]

OBJECTIVE

To investigate the significance of Angiopoietin-1 (Ang-1), Angiopoietin-2 (Ang-2) expression in angiogenesis, vessel maturation, progress and prognosis of oral squamous cell carcinoma (OSCC).

METHODS

The expression of Ang-1, Ang-2, vascular endothelial growth factor (VEGF), CD34 and alpha-smooth muscle actin (alpha-SMA) were studied in 62 human OSCCs, 30 adjacent noncancerous oral tissues and 10 normal oral mucosa by conventional immunohistochemistry. Microvessel density (MVD) and vessel maturation index (VMI) were also assessed with double-labeling immunohistochemistry staining against CD34, a marker of pan-endothelial cells, and that against alpha-SMA, a marker of mural cells (pericytes/smooth muscle cells). The images were analyzed with BioMias system.

RESULTS

Ang-1/Ang-2 protein expression ratio were significantly lower in OSCC than that in adjacent noncancerous oral tissues and normal oral mucosa (t were -5.42 and -6.234, all P<0.01). There were significantly different Ang-1/Ang-2 protein expression ratio in different tumor' lymph node metastasis status and MVD groups and VMI groups, respectively (t were 3.421, -3.221, 3.824, all P<0.01). The patients with low Ang-1/Ang-2 protein expression ratio and high VEGF protein expression were found to have a significantly higher MVD when compared to others (t were 2.055, 2.345, 2.985, all P<0.05). Ang-1/Ang-2 protein expression ratio had a tendency to be a prognostic factor (chi2=3.383, P=0.066).

CONCLUSIONS

The reversion of Ang-1 and Ang-2 expression may plays an important role in the development and progression of OSCC. It is closely associated with the angiogenesis, vessel maturation and prognosis of OSCC.

Estrogen stimulates the human endometrium to express a factor(s) that promotes vascular smooth muscle cell migration as an early step in microvessel remodeling

Vascular smooth muscle cell (VSMC) migration is a pivotal early step in blood vessel remodeling; however, very little is known about the regulation of this process in the human endometrium during the menstrual cycle. In this study, explants of human endometrium were incubated with estradiol and/or progesterone and the conditioned medium (CM) applied to cultures of VSMC to test the hypothesis that estrogen and progesterone stimulate endometrial cells to secrete a factor(s) that promotes VSMC migration. Endometrial explants were composed of highly organized glands and stroma. VSMC migration (cells migrated in 21 h/mm(2) fibronectin-coated semipermeable membrane) in the presence of CM from human endometrial explants obtained in the proliferative phase of the menstrual cycle and incubated for 24 h with estradiol was approximately threefold greater (P < 0.001) than with medium alone and greater (P < 0.05) than with CM from explants treated with estradiol plus progesterone or progesterone. It is concluded, therefore, that estrogen stimulates endometrial secretion of a factor(s) that promotes VSMC migration as an early step in vessel remodeling within the endometrium.

[Angiogenesis in different clinical phases of chronic myeloid leukemia]

Angiogensis plays the crucial role in growth and dissemination of neoplastic diseases, both for solid tumors and hematopoietic malignancies. Development of the abundant neoplastic vasculature results from an imbalance between pro- and antiangiogenic regulatory mechanisms. The investigation was focused on expression of the main regulatory angiogeneic factors in different phases of chronic myeloid leukemia (CML) and on influence of leukemic cells on the human umbilical vein endothelial cells proliferation. The groups of 29 patients with CML and of 14 healthy controls were enrolled to the study. The expression of vascular endothelial growth factor (VEGF), basic fibroblast growth factor, interleukin-8, angiopoetin-1, platelet factor-4, extracellular matrix metalloproteinases (MMP) -2 and -9 as well as tissue inhibitors of metalloproteinases was determined in peripheral blood and bone marrow mononuclear cells with the use of quantitative real-time PCR method and additionally the concentration of VEGF with the flow cytofluorometry. We evaluated the phosphorylation of endothelial mitogen activated protein kinase in human umbilical vein endothelial cells after incubation in CML cells conditioned media, applying Western blot technique. We determined an influence of the leukemic cells on the endothelial cells proliferation with the colorimetric metabolic MTT test. We showed, that in peripheral blood and bone marrow mononuclear cells in CML patients most of the studied factors were increased at the time of CML diagnosis and became lower in remission. In newly diagnosed CML patients an expression of VEGF, MMP-2 and MMP-9 was particularly elevated. In remission, the levels of VEGF and metalloproteinases, specifically MMP-9, were decreased. If failed to achieve remission, the patients presented the elevated expression of most of the investigated angiogenic factors. In the acceleration or blast crisis phase angiopoetin, VEGF and MMP-2 levels were particularly high. We noticed the markedly enhanced human umbilical vein endothelium proliferation after an incubation in CML cells conditioned media, both in the test of mitogen activated protein kinase phosphorylation in endothelial cells and in the metabolic test for the proliferation intensity of endothelium. The differences of an angiogeneic potential found between clinical phases of CML, and the ability of leukemic cells to stimulate endothelial proliferation, point at the significance of neovascularisation in CML pathogenesis. Further studies are necessary to delineate the possibility of the use of angiogenic inhibitors in the treatment of this malignancy.

Beta-adrenergic receptor regulation of growth factor protein levels in human choroidal endothelial cells

Remodeling of the choroidal vasculature is a prominent factor in age-related macular degeneration. While many of the growth factors involved in this vascular remodeling are known, their regulation remains much less so. The hypothesis of the present study was that stimulation of human choroidal endothelial cells with the beta-adrenergic receptor agonist isoproterenol would lead to an increase in pigment epithelial derived factor (PEDF) and angiopoietin 1 (Ang1), markers of a stable vasculature. Protein levels of PEDF and Ang1 were significantly increased following stimulation with isoproterenol. However, isoproterenol also significantly increased protein levels of vascular endothelial cell growth factor, which is active during vasculature remodeling. These data suggest that beta-adrenergic receptor agonists are likely upstream of a number of growth factors implicated in ocular disease and have multiple effects on choroidal endothelial cells. Modulation of this signaling in the choroid may offer a new avenue for therapeutics.

Platelet granule secretion continuously prevents intratumor hemorrhage

Cancer is associated with a prothrombogenic state capable of platelet activation. Platelets, on the other hand, can support angiogenesis, a process involved in the progression of tumor growth and metastasis. However, it is unclear whether platelet/tumor interactions substantially contribute to tumor physiology. We investigated whether platelets stabilize tumor vessels and studied the underlying mechanisms. We induced severe acute thrombocytopenia in mice bearing s.c. Lewis lung carcinoma or B16F10 melanoma. Intravital microscopy revealed that platelet depletion led to a rapid destabilization of tumor vessels with intratumor hemorrhage starting as soon as 30 min after induction of thrombocytopenia. Using an inhibitor of glycoprotein Ibalpha (GPIbalpha) and genetically engineered mice with platelet adhesion defects, we investigated the role of platelet adhesion receptors in stabilizing tumor vessels. We found that a single defect in either GPIbalpha, von Willebrand factor, P-selectin, or platelet integrin activation did not lead to intratumor hemorrhage. We then compared the ability of transfused resting and degranulated platelets to prevent intratumor hemorrhage. Whereas resting platelets prevented thrombocytopenia-induced tumor bleeding, circulating degranulated platelets did not. This suggests that the prevention of intratumor hemorrhage by platelets relies on the secretion of the content of platelet granules. Supporting this hypothesis, we further found that thrombocytopenia dramatically impairs the balance between propermeability and antipermeability factors in tumor-bearing animals, in particular depleting blood of angiopoietin-1 and serotonin. Our results show a crucial contribution of platelets to tumor homeostasis through continuous prevention of severe intratumor hemorrhage and consequent cell death. The study also suggests platelet function as a reasonable target for specific destabilization of tumor vessels.

[Expression of angiopoietin-1,2 and its relationship with angiogenesis in laryngeal squamous cell carcinoma]

OBJECTIVE

To investigate the expression of Angiopoietin-1,2 in laryngeal squamous cell carcinoma (LSCC) and the relationship between Angiopoietin-1,2 expression and clinicopathologic parameters and microvessel density (MVD) marked by CD105, and also evaluate the significance of co-expression of Ang-2 and vascular endothelial cell growth factor (VEGF) in tumor angiogenesis.

METHOD

The expression of Ang-1,2 and VEGF in samples of tumor, para cancer and normal mucosa were detected by immunohistochemical method.

RESULT

The expression of Angiopoietin-1,2 were identified in LSCC, para cancer tissue and normal mucosa. The VEGF expression was only existed in LSCC. The expression of Ang-1,2 were significantly higher in LSCC than in para cancer tissue (P < 0.05) and normal mucosa (P < 0.01). In the clinicopathologic parameters, only the expression of Ang-2 was closely correlated with clinical stages and MVD (all P < 0.05). There was no significant correlation between the expression of Ang-1,2 and tumor differentiation degree (all P > 0.05). When the expression of Ang-2 and VEGF were both positive, the mean value of MVD was higher than others (P < 0.05).

CONCLUSION

These results suggest that overexpression of Ang-1,2 may play a very important role in the development of LSCC and are closely correlated with angiogenesis. Ang-2 promote angiogenesis when interacting with VEGF.