Notoginsenoside R1 activates the Ang2/Tie2 pathway to promote angiogenesis.

BACKGROUND: Therapeutic angiogenesis is a novel strategy for the treatment of ischemic diseases that involves promotion of angiogenesis in ischemic tissues via the use of proangiogenic agents. However, effective proangiogenic drugs that activate the Ang2/Tie2 signaling pathway remain scarce. PURPOSE: We aimed to investigate the proangiogenic activity of notoginsenoside R1 (NR1) isolated from total saponins of Panax notoginseng with regard to activation of the Ang2/Tie2 signaling pathway. METHODS: We examined the proangiogenic effects of NR1 by assessing the effects of NR1 on the proliferation, migration, invasion and tube formation of human umbilical vein endothelial cells (HUVECs). The aortic ring assay and vascular endothelial growth factor receptor inhibitor (VRI)-induced vascular regression in the zebrafish model were used to confirm the proangiogenic effects of NR1 ex vivo and in vivo. Furthermore, the molecular mechanism was investigated by Western blot analysis. RESULTS: We found that NR1 promoted the proliferation, mobility and tube formation of HUVECs in vitro. NR1 also increased the number of sprouting vessels in rat aortic rings and rescued VRI-induced vascular regression in zebrafish. NR1-induced angiogenesis was dependent on Tie2 receptor activation mediated by increased autocrine Ang2 in HUVECs, and inhibition of the Ang2/Tie2 pathway abrogated the proangiogenic effects of NR1. CONCLUSIONS: Our results suggest that NR1 promotes angiogenesis by activating the Ang2/Tie2 signaling pathway. Thus, NR1-induced activation of the Ang2/Tie2 pathway is an effective proangiogenic approach. NR1 may be useful agent for the treatment of ischemic diseases.

Angiopoietin-1 protects 3T3-L1 preadipocytes from saturated fatty acid-induced cell death.

Cross talk between endothelial cells and adipocytes is vital to adipocyte functions, but little is known about the mechanisms or factors controlling the process. Angiogenesis is a critical component linking the endothelium to healthy adipogenesis, yet it is not known if or how it is involved in adipocyte physiology. Therefore, the purpose of this study was to determine the effect of angiopoietin-1 (Ang-1) and -2 (Ang-2) as well as their receptor, Tie-2, on adipocyte physiology. 3T3-L1 pre- and mature adipocytes were found to express Ang-1, Ang-2, and Tie-2, which decrease upon polyunsaturated fatty acid treatment. Furthermore, 3T3-L1 cells treated with recombinant Ang-1 or Ang-2 increased expression of the antiapoptotic gene Bcl-x and decreased expression of the proapoptotic gene Casp-8. Next, preadipocytes were treated with saturated fatty acids (SFAs) to induce cell stress. SFA-mediated splicing of X-box-binding protein-1 was reduced by co-treatment with Ang-1, and cell viability was improved in the presence of SFAs + Ang-1. Taken together, these results indicate that Ang-1 may protect preadipocytes from SFA-induced apoptosis and endoplasmic reticulum stress.

Cathepsin D plays a role in endothelial-pericyte interactions during alteration of the blood-retinal barrier in diabetic retinopathy.

Inflammation plays an important role in the pathogenesis of diabetic retinopathy. We have previously demonstrated the effect of cathepsin D (CD) on the mechanical disruption of retinal endothelial cell junctions and increased vasopermeability, as well as increased levels of CD in retinas of diabetic mice. Here, we have also examined the effect of CD on endothelial-pericyte interactions, as well as the effect of dipeptidyl peptidase-4 (DPP4) inhibitor on CD in endothelial-pericyte interactions in vitro and in vivo. Cocultured cells that were treated with pro-CD demonstrated a significant decrease in the expression of platelet-derived growth factor receptor-ß, a tyrosine kinase receptor that is required for pericyte cell survival; N-cadherin, the key adherens junction protein between endothelium and pericytes; and increases in the vessel destabilizing agent, angiopoietin-2. The effect was reversed in cells that were treated with DPP4 inhibitor along with pro-CD. With pro-CD treatment, there was a significant increase in the phosphorylation of the downstream signaling protein, PKC-α, and Ca2+/calmodulin-dependent protein kinase II in endothelial cells and pericytes, which disrupts adherens junction structure and function, and this was significantly reduced with DPP4 inhibitor treatment. Increased CD levels, vasopermeability, and alteration in junctional-related proteins were observed in the retinas of diabetic rats, which were significantly changed with DPP4 inhibitor treatment. Thus, DPP4 inhibitors may be used as potential adjuvant therapeutic agents to treat increased vascular leakage observed in patients with diabetic macular edema.-Monickaraj, F., McGuire, P., Das, A. Cathepsin D plays a role in endothelial-pericyte interactions during alteration of the blood-retinal barrier in diabetic retinopathy.

Arid1a regulates response to anti-angiogenic therapy in advanced hepatocellular carcinoma.

BACKGROUND & AIMS: AT-rich interaction domain 1a (Arid1a), a component of the chromatin remodeling complex, has emerged as a tumor suppressor gene. It is frequently mutated in hepatocellular carcinoma (HCC). However, it remains unknown how Arid1a suppresses HCC development and whether Arid1a deficiency could be exploited for therapy, we aimed to explore these questions. METHODS: The expression of Arid1a in human and mouse HCCs was determined by immunohistochemical (IHC) staining. Gene expression was determined by quantitative PCR, ELISA or western blotting. Arid1a knockdown HCC cell lines were established by lentiviral-based shRNA. Tumor angiogenesis was quantified based on vessel density. The regulation of angiopoietin (Ang2) expression by Arid1a was identified by chromatin immunoprecipitation (ChIP) assay. The tumor promoting function of Arid1a loss was studied with a xenograft model in nude mice and diethylnitrosamine (DEN)-induced HCC in Arid1a conditional knockout mice. The therapeutic values of Ang2 antibody and sorafenib treatment were evaluated both in vitro and in vivo. RESULTS: We demonstrate that Arid1a deficiency, occurring in advanced human HCCs, is associated with increased vessel density. Mechanistically, loss of Arid1a causes aberrant histone H3K27ac deposition at the angiopoietin-2 (Ang2) enhancer and promoter, which eventually leads to ectopic expression of Ang2 and promotes HCC development. Ang2 blockade in Arid1a-deficient HCCs significantly reduces vessel density and tumor progression. Importantly, sorafenib treatment, which suppresses H3K27 acetylation and Ang2 expression, profoundly halts the progression of Arid1a-deficient HCCs. CONCLUSIONS: Arid1a-deficiency activates Ang2-dependent angiogenesis and promotes HCC progression. Loss of Arid1a in HCCs confers sensitivity to Ang2 blockade and sorafenib treatment. LAY SUMMARY: AT-rich interaction domain 1a (Arid1a), is a tumor suppressor gene. Arid1a-deficiency promotes Ang2-dependent angiogenesis leading to hepatocellular carcinoma progression. Arid1a-deficiency also sensitizes tumors to Ang2 blockade by sorafenib treatment.

Complementary actions of melatonin on angiogenic factors, the angiopoietin/Tie2 axis and VEGF, in co­cultures of human endothelial and breast cancer cells.

Melatonin exerts oncostatic activity in breast cancer through antiangiogenic actions. There, the aim of the present study was to ascertain whether melatonin modulates, in a coordinated action, angiopoietin-1 (ANG-1), ANG-2, their cognate Tie2 receptor and VEGF in co-cultures of human endothelial cells (HUVECs) and breast cancer (MCF-7) cells. To accomplish this we used co-cultures of human breast cancer cells (MCF-7) or non-malignant human mammary epithelial cells (MCF­10A) with endothelial cells (HUVECs). The presence of breast cancer cells increased HUVEC proliferation and 1 mM melatonin prevented this effect. ANG-1, ANG-2 and VEGF levels in co-culture media and mRNA expression were upregulated and Tie2 mRNA expression was downregulated in the HUVECs and MCF-7. Melatonin (1 mM) downregulated ANG-1, ANG-2 and VEGF levels in the co-culture media and mRNA expression in both types of cells and upregulated Tie2 mRNA expression in HUVECs. ANG-1, ANG-2, Tie2 and VEGF mRNA expression were not modified during HUVEC/MCF-10A co-culture. Estradiol (10 nM) increased ANG-1, ANG-2 and VEGF mRNA expression in HUVECs and melatonin (1 mM) counteracted this effect. We conclude that melatonin simultaneously coordinates downregulation of angiopoietins with a reduction in VEGF, which could be an effective therapeutic strategy for blocking tumor angiogenesis.

Angiopoietin 2 in placentation and tumor biology: The yin and yang of vascular biology.

There are several parallels between placental and tumor biology. Both require rapid acquisition of a blood supply to supply oxygen and nutrients, the placenta through neoangiogenesis and tumors by co-opting the existing vasculature. In addition, successful pregnancy also requires remodeling of the maternal uterine spiral arteries. Angiopoietins (Angs) are a family of angiogenic growth factors, the best studied being Ang-1 and Ang-2, which signal through the membrane tyrosine kinase receptor Tie2, and in simple terms have opposite effects with Ang-1 acting to stabilize newly formed blood vessels and Ang-2 having a destabilizing effect. The roles of Ang-1, and in particular Ang-2 in placental and tumor biology are discussed in this review.

MLC901 Favors Angiogenesis and Associated Recovery after Ischemic Stroke in Mice.

BACKGROUND: There is increasing evidence that angiogenesis, through new blood vessel formation, results in improved collateral circulation and may impact the long-term recovery of patients. In this study, we first investigated the preventive action of a 5-week pretreatment of MLC901, an herbal extract preparation derived from Chinese medicine, against the deleterious effects of ischemic stroke and its effects on angiogenesis in a model of focal ischemia in mice. METHODS: The stroke model was induced by 60 min of middle cerebral artery occlusion followed by reperfusion. MLC901 was administered in the drinking water of animals (6 g/l) for 5 weeks before ischemia and then during reperfusion. RESULTS: MLC901 treatment increased the survival rate, reduced the cerebral infarct area and attenuated the blood brain barrier leakage as well as the neurologic dysfunction following ischemia and reperfusion. We provide evidence that MLC901 enhances endothelial cell proliferation and angiogenesis by increasing the number of neocortical vessels in the infarcted area. MLC901 regulates the expression of hypoxic inducible factor 1α and its downstream targets such as vascular endothelial growth factor and angiopoietins 1 and 2. This work also shows that erythropoietin is an important player in the enhancement of angiogenesis by MLC901. CONCLUSIONS: These results demonstrate therapeutic properties of MLC901, in addition to those previously described, in stimulating revascularization, neuroprotection and repair of the neurovascular unit after ischemic stroke.

Electroacupuncture improves recovery after hemorrhagic brain injury by inducing the expression of angiopoietin-1 and -2 in rats.

BACKGROUND: Angiopoietin (Ang) is one of the major effectors of angiogenesis, playing a critical role in neurovascular remodeling after stroke. Acupuncture has been widely used for treating stroke in China for a long time. Recently, we have demonstrated that electroacupuncture (EA) can accelerate intracerebral hemorrhage (ICH)-induced angiogenesis in rats. In the present study, we investigated the effect of EA on the expression of Ang-1 and Ang-2 in the brain after ICH. METHODS: ICH was induced by stereotactic injection of collagenase type VII into the right globus pallidus. Adult male Sprague-Dawley rats were randomized into the following four groups: sham-operation (SHAM), stroke-no electroacupuncture (SNE), stroke-EA at the Zusanli acupoint (SEZ), and stroke-EA at a nonacupoint (SEN). EA was applied to the bilateral Zusanli (ST36) acupoint in the SEZ group and a nonacupoint in the SEN group. The expression of Ang-1 and Ang-2 was evaluated by immunohistochemistry and quantitative real-time reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Some Ang-1 and Ang-2 immunoreactive microvessels with a dilated outline were detected in the perihematomal tissues after ICH, and the vessels extended into the clot from the surrounding area since day 7. The expression of Ang-1 increased notably as long as 2 weeks after ICH, while Ang-2 immunoreactivity declined at about 7 days following a striking upregulation at 3 days. EA at the Zusanli (ST36) acupoint upregulated the expression of Ang-1 and Ang-2 at both the protein and mRNA levels. However, EA at a nonacupoint had little effect on the expression of Ang-1 and Ang-2. CONCLUSIONS: Our data suggest that EA at the Zusanli (ST36) acupoint exerts neuroprotective effects on hemorrhagic stroke by upregulation of Ang-1 and Ang-2.

Treatment with EGCG in NSCLC leads to decreasing interstitial fluid pressure and hypoxia to improve chemotherapy efficacy through rebalance of Ang-1 and Ang-2.

AIM: Microvasculature and microenvironment play important roles in proliferation, invasion, metastasis and prognosis in non-small cell lung cancer (NSCLC), which might be altered by many anti-angiogenic drugs. Epigallocatechin-3-gallate (EGCG), a natural anti-angiogenesis agent refined from green tea, was defined to have multiple effects on angiogenesis factors, such as endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and angiopoietins (ANGs). Hypothesizing that EGCG might regulate microvasculature and microenvironment in NSCLC, the effects of EGCG on microvessel density (MVD), expression of Ang-1 and Ang-2, interstitial fluid pressure (IFP), tumor hypoxia, and chemotherapy sensitivity were examined. METHODS AND RESULTS: EGCG treatment of A549 cells in mice bearing xenografts in vivo led to a significant decrease of MVD detected by CD31, and of Ang-2 expression detected by quantum dots double-label immunofluorescence assessment, while Ang-1 decreased with no significance. Decreased IFP was measured by the Wink-in-needle method, while hypoxia was assessed by polarographic electrode and pimonidazole (PIMO) immunohistochemistry. Assuming that these changes would increase response to chemotherapy, tumor growth studies were p[erformed in nude mice with xenografts, which were then treated with EGCG and the chemotherapeutic agent cisplatin. EGCG therapy combined with cisplatin led to synergistic inhibition of tumor growth, compared with administration of each treatment separately (P < 0.001). According to linear regression analysis, IFP was positively correlated with PIMO staining (R(2) = 0.618, P = 0.002), Ang-2 was correlated with MVD (R(2) = 0.423, P = 0.022), IFP (R(2) = 0.663, P = 0.01) and PIMO staining (R(2) = 0.694, P = 0.01). CONCLUSION: IFP and delivery of oxygen might be improved by rebalance of Ang-1/Ang-2 under the treatment of EGCG in NSCLC, which also acts as a sensitizer of chemotherapy. These studies established a new mechanism for using EGCG as an adjuvant chemotherapy agent through modifying microvasculature and microenvironment.

Selective V(1a) agonism attenuates vascular dysfunction and fluid accumulation in ovine severe sepsis.

Vasopressin analogs are used as a supplement to norepinephrine in septic shock. The isolated effects of vasopressin agonists on sepsis-induced vascular dysfunction, however, remain controversial. Because V(2)-receptor stimulation induces vasodilation and procoagulant effects, a higher V(1a)- versus V(2)-receptor selectivity might be advantageous. We therefore hypothesized that a sole, titrated infusion of the selective V(1a)-agonist Phe(2)-Orn(8)-Vasotocin (POV) is more effective than the mixed V(1a)-/V(2)-agonist AVP for the treatment of vascular and cardiopulmonary dysfunction in methicillin resistant staphylococcus aureus pneumonia-induced, ovine sepsis. After the onset of hemodynamic instability, awake, chronically instrumented, mechanically ventilated, and fluid resuscitated sheep were randomly assigned to receive continuous infusions of either POV, AVP, or saline solution (control; each n = 6). AVP and POV were titrated to maintain mean arterial pressure above baseline - 10 mmHg. When compared with that of control animals, AVP and POV reduced neutrophil migration (myeloperoxidase activity, alveolar neutrophils) and plasma levels of nitric oxide, resulting in higher mean arterial pressures and a reduced vascular leakage (net fluid balance, chest and abdominal fluid, pulmonary bloodless wet-to-dry-weight ratio, alveolar and septal edema). Notably, POV stabilized hemodynamics at lower doses than AVP. In addition, POV, but not AVP, reduced myocardial and pulmonary tissue concentrations of 3-nitrotyrosine, VEGF, and angiopoietin-2, thereby leading to an abolishment of cumulative fluid accumulation (POV, 9 ± 15 ml/kg vs. AVP, 110 ± 13 ml/kg vs. control, 213 ± 16 ml/kg; P < 0.001 each) and an attenuated cardiopulmonary dysfunction (left ventricular stroke work index, PaO(2)-to-FiO(2) ratio) versus control animals. Highly selective V(1a)-agonism appears to be superior to unselective vasopressin analogs for the treatment of sepsis-induced vascular dysfunction.

Propranolol inhibition of ß-adrenergic receptor does not suppress pathologic neovascularization in oxygen-induced retinopathy.

PURPOSE: Retinopathy of prematurity (ROP) is a leading cause of blindness in children and is, in its most severe form, characterized by uncontrolled growth of vision-threatening pathologic vessels. Propranolol, a nonselective ß-adrenergic receptor blocker, was reported to protect against pathologic retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR). Based on this single animal study using nonstandard evaluation of retinopathy, clinical trials are currently ongoing to evaluate propranolol treatment in stage 2 ROP patients who tend to experience spontaneous disease regression and are at low risk of blindness. Because these ROP patients are vulnerable premature infants who are still in a fragile state of incomplete development, the efficacy of propranolol treatment in retinopathy needs to be evaluated thoroughly in preclinical animal models of retinopathy and potential benefits weighed against potential adverse effects. METHODS: Retinopathy was induced by exposing neonatal mice to 75% oxygen from postnatal day (P) 7 to P12. Three routes of propranolol treatment were assessed from P12 to P16: oral gavage, intraperitoneal injection, or subcutaneous injection, with doses varying between 2 and 60 mg/kg/day. At P17, retinal flatmounts were stained with isolectin and quantified with a standard protocol to measure vasoobliteration and pathologic neovascularization. Retinal gene expression was analyzed with qRT-PCR using RNA isolated from retinas of control and propranolol-treated pups. RESULTS: None of the treatment approaches at any dose of propranolol (up to 60 mg/kg/day) were effective in preventing the development of retinopathy in a mouse model of OIR, evaluated using standard techniques. Propranolol treatment also did not change retinal expression of angiogenic factors including vascular endothelial growth factor. CONCLUSIONS: Propranolol treatment via three routes and up to 30 times the standard human dose failed to suppress retinopathy development in mice. These data bring into question whether propranolol through inhibition of ß-adrenergic receptors is an appropriate therapeutic approach for treating ROP.

Angiogenesis of the frozen-thawed human fetal ovarian tissue at the early stage after xenotransplantation and the positive effect of Salviae miltiorrhizae.

Cryopreserving ovarian tissue followed by transplantation has been suggested to preserve fertility for young cancer survivors. However, ischemia in the early stage after transplantation causes massive follicle loss. The aim was to investigate the histological and ultrastructural characteristics of the frozen-thawed human fetal ovarian tissue after xenotransplantation and the effects of Salviae miltiorrhizae (SM) on the angiogenesis. The human fetal ovarian tissues were frozen-thawed, xenografted into the immunodeficient nu/nu mice, and then collected 2, 7, and 28 days after transplantation. SM was administered. Compared with that of the frozen-thawed ovarian tissue, the total follicle number of the grafts was greatly reduced. Nearly half of the primordial follicles were damaged at different levels on day 2. Moreover, edema was prevalent in the stroma during the first week after the graft, especially on day 2. The microvessel density of the grafts was increased on day 2, reached a peak on day 7, and then declined on day 28. Both healthy primordial follicle proportion and the total healthy primordial follicles pool in the SM group were significantly higher than those of the control group (P = 0.003 and P = 0.001). We found a statistically significant difference of microvessel density between the two groups on day 2 (P < 0.001). In the frozen-thawed fetal ovarian grafts, angiogenesis has been begun on day 2, and the first week is the critical time for the grafts to regain their function, in which SM can facilitate graft vascularization and improve the preservation of primordial follicles.

Noninvasive up-regulation of angiopoietin-2 and fibroblast growth factor-2 in bone marrow by pulsed electromagnetic field therapy.

BACKGROUND: Pulsed electromagnetic field (PEMF) therapy has been widely used in clinical practice for bone fracture healing. However, the mechanism of its action remains to be elucidated. Our object was to investigate the mechanism by which PEMF accelerates bone fracture healing. METHODS: We used 20 mice in this study. Ten mice received PEMF for 10 h/day for 1 week via the coils of a PEMF stimulation device (PEMF group), while the remaining 10 mice did not (control group). The femurs were harvested immediately after euthanasia to examine the proteins included in the bone marrow. The proteins examined by Western blotting were growth factors with angiogenetic activities, including tunica interna endothelial cell kinase-2, angiopoietin-1, angiopoietin-2, fibroblast growth factor-2, and vascular endothelial growth factor. The expression levels of angiogenesis-related proteins extracted from the bone marrow of each mouse were compared. RESULTS: The expression levels of angiopoietin-2 and fibroblast growth factor-2 were significantly higher in the PEMF group than in the control group. This difference suggests that PEMF may induce an angiogenesis-prone environment in the bone marrow. Such angiogenesis acceleration represents one possible mechanism for the acceleration of bone fracture healing by PEMF. There were no significant differences between the two groups for the expression levels of tunica interna endothelial cell kinase-2, angiopoietin-1, and vascular endothelial growth factor. The lack of increase in tunica interna endothelial cell kinase-2 expression may indicate that PEMF does not unnecessarily increase blood vessels in normal bone marrow. The lack of an increase in the expression level of vascular endothelial growth factor suggests that PEMF does not have invasive effects including the induction of hypoxic conditions and inflammation on the bone marrow. CONCLUSION: The angiogenesis-promoting function of PEMF may contribute to its mechanism to noninvasively accelerate bone fracture healing.

[The effect of danshen on the angiogenesis of the frozen-thawed human fetal ovarian tissue after transplantation].

AIM: (1) To investigate the mRNA expression of the key angiogenic growth factors in the grafts after transplantation. (2) To investigate the potential impact of danshen (Chinese traditional medicine) administration on grafts angiogenesis. METHODS: The frozen-thawed ovarian tissue from aborted fetus were xenografted into the renal capsule of the nude mice, recovered 48 h, 7 d and 28 d after respectively. Either danshen or saline (as the control) was administered after transplantation. RESULTS: The mRNA levels of VEGF showed a temporary raise in 48 h after transplantation, then decreased in one week, and no significant difference was fund between the control group and danshen group. Ang-2 was increased in 48 h after transplantation, when Danshen group was significantly higher than the control group (P < 0.05). The microvessel density significantly increased in all the tissues after transplantation. The control group peaked on day 7 after transplantation, while danshen group peaked in 48 h and kept correspondingly steady after that. CONCLUSION: Early angiogenesis began within 48 h after transplantation of the thawed human fetal ovarian tissue, and its microvessel density peaked within the first week after transplantation. Our results also suggested that the use of danshen injection in conjunction with transplantation could facilitate revascularization of the grafts.

Interaction of estrogen and tumor necrosis factor alpha in endothelial cell migration and early stage of angiogenesis.

The role of estrogen replacement therapy in postmenopausal women remains controversial. The authors hypothesized that contradictory results with estrogen therapy may be explained by estrogen's potent proangiogenic property, which could be protective in women without atherosclerotic disease but in the presence of chronic inflammation, could lead to destabilization of atherosclerotic plaques. The authors thus examined the interaction between 17beta-estradiol (E2) and the inflammatory cytokine tumor necrosis factor alpha (TNFalpha) in an early stage of angiogenesis. Human umbilical endothelial cells were grown to confluence. Migration was assessed with a wound assay and proliferation was assessed with 5-bromo-2'-deoxyuridine (BrDU). Cells were treated with medium alone, TNFalpha at 0.3, 1, or 20 ng/ml, E2 at 20 nM, or the combination of E2 and TNFalpha. The authors used real-time polymerase chain reaction (PCR) to measure changes in expression of the angiogenesis genes angiopoeitin-2 (Ang-2), vacular endothelial growth factor (VEGF)-A and -C, and interleukin (IL)-8. A large dose of TNFalpha (20 ng/ml) inhibited healing at 24 to 48 h and the addition of E2 preserved some healing. E2 by itself doubled migration, with only a minimal effect on proliferation. A low dose of TNFalpha (0.3 ng/ml) had no effect on migration, 1.0 ng/ml moderately increased it, but the addition of E2 to both doses of TNFalpha increased migration. There was no change in migration when cells were pretreated with E2 and given TNFalpha after wounding, whereas pretreatment with TNFalpha followed by E2 significantly increased wound healing. The nitric oxide synthase (NOS) inhibitor N-nitro-l-arginine-methyl ester (l-NAME) completely blocked the E2 effect on migration. TNFalpha (0.3 and 1.0 ng/ml) increased expression of VEGF-C (2.8 +/- 0.1- and 2.5 +/- 0.2-fold, respectively) and IL-8 (32.8 +/- 1.2- and 42.7 +/- 3.6-fold, respectively) mRNA, but E2 had no significant effect on these molecules. E2 increases the angiogenic activity of TNFalpha. This could potentially worsen the stability of complex atherosclerotic plaques and increase cardiovascular events.

Angiopoietin/Tie2 signaling, tumor angiogenesis and inflammatory diseases.

Mounting evidence demonstrates that the formation of new blood vessels, termed angiogenesis, plays critical roles in human disease development and progression. Based on these findings, there has been a tremendous effort to investigate the molecular mechanisms that drive blood vessel growth in adult tissues. Compared to physiological angiogenesis, inflammation is often accompanied with pathological angiogenesis and often is the underlying causes of many diseases such as cancer, arthritis, atherosclerosis, and others. Inflammation induces angiogenesis and reciprocally, angiogenesis facilitate inflammation. A study of the interaction between angiogenesis and inflammation will enhance our understanding of the mechanisms of diseases. It may generate novel approaches for therapy. Tie2 was recently identified as a receptor tyrosine kinase expressed principally on vascular endothelium, making it an attractive molecular target for angiogenic therapy. This review discusses the regulation of Tie2 and its angiopoietin ligand family in inflammation-associated angiogenesis focusing on cancer, arthritis, and atherosclerosis. The complexity of angiogenesis and context-dependent regulation of angiopoietin/Tie2 signaling in angiogenesis requires further studies.