Tie2 mRNA Research Articles

Loss of PECAM-1 Function Impairs Alveolarization

The final stage of lung development in humans and rodents occurs principally after birth and involves the partitioning of the large primary saccules into smaller air spaces by the inward protrusion of septae derived from the walls of the saccules. Several observations in animal models implicate angiogenesis as critical to this process of alveolarization, but all anti-angiogenic treatments examined to date have resulted in endothelial cell (EC) death. We therefore targeted the function of platelet endothelial cell adhesion molecule, (PECAM-1), an EC surface molecule that promotes EC migration and has been implicated in in vivo angiogenesis. Administration of an anti-PECAM-1 antibody that inhibits EC migration, but not proliferation or survival in vitro, disrupted normal alveolar septation in neonatal rat pups without reducing EC content. Three-dimensional reconstruction of lungs showed that pups treated with a blocking PECAM-1 antibody had remodeling of more proximal branches resulting in large tubular airways. Subsequent studies in PECAM-1-null mice confirmed that the absence of PECAM-1 impaired murine alveolarization, without affecting EC content, proliferation, or survival. Further, cell migration was reduced in lung endothelial cells isolated from these mice. These data suggest that the loss of PECAM-1 function compromises postnatal lung development and provide evidence that inhibition of EC function, in contrast to a loss of viable EC, inhibits alveolarization.

Suppressive Effect of 2,3,7,8-Tetrachlorodibenzo-p-dioxin on Vascular Remodeling That Takes Place in the Normal Labyrinth Zone of Rat Placenta during Late Gestation

The maintenance of the placental vasculature is essential for sustaining normal fetal growth. On the basis of our previous observation that fetal death was accompanied by placental hypoxia upon exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (R. Ishimura et al., 2002a, Toxicol. Appl. Pharmacol. 185, 197-206), we here investigated the effects of TCDD on the placenta, focusing on the development of the labyrinth zone. Holtzman rats were administered a single oral dose of 1.6 mug of TCDD/kg body weight or an equivalent volume of vehicle (control) on gestation day (GD) 15, and placental tissues were analyzed on GD20. Immunohistochemical staining showed that the exposure to TCDD decreased the size of maternal blood sinusoids and caused the constriction of fetal capillaries in the placenta. In contrast, we found that vascular remodeling occurred in the labyrinth zone of normal rat placenta; that is, the vascular development in the normal labyrinth zone during the late gestation (from GD16 to GD20) showed dilated maternal blood sinusoids and fetal capillaries accompanied by a decrease in thickness and the apoptosis of trophoblasts. The present results demonstrate that this remodeling is suppressed by TCDD, which is further supported by the decreased expression level of Tie2 mRNA, the gene which is associated with vascular remodeling, and also by the decrease in the number of apoptotic trophoblasts in TCDD-exposed rats. The present study provided a new finding on the development of the vasculature in the labyrinth zone during the late gestation under normal conditions and showed the inhibition of vascular remodeling in TCDD-exposed rats.

Adrenocorticotropin Preferentially Up-Regulates Angiopoietin 2 in the Human Fetal Adrenal Gland: Implications for Coordinated Adrenal Organ Growth and Angiogenesis

ACTH is the key tropic hormone for the human fetal adrenal (HFA). Because vascular development must be coordinated with organ growth, ACTH may regulate local angiogenic factors, thereby influencing HFA angiogenesis. We previously demonstrated that ACTH up-regulates vascular endothelial growth factor in HFA cortical cells. A newer angiogenic factor family, the angiopoietins (Angs), also plays critical roles. Ang1 stabilizes, whereas Ang2 destabilizes vessels, increasing responsiveness to angiogenic stimuli. The objective of this study was to investigate expression and ACTH regulation of Angs and their receptor Tie2 in the HFA. Studies were conducted involving RNA, frozen sections, and primary cell cultures from HFAs (14-24 wk) and human adult adrenal RNA. Angs and Tie2 mRNA levels were determined by real-time quantitative RT-PCR, Ang2 and Tie2 were localized by immunostaining, and ACTH regulation of Angs was investigated by real-time quantitative RT-PCR, Western blot, and ELISA. Mean HFA Ang2 to Ang1 mRNA ratio was 6.3-fold higher than adult adrenals (P < 0.001). Ang2 was localized predominantly in the HFA periphery, whereas Tie2 demonstrated endothelial localization. In isolated HFA cortical cells, ACTH up-regulated Ang mRNA levels in a time- and dose-dependent manner, with the balance favoring Ang2. Ang2 protein levels were elevated in ACTH-stimulated HFA cortical cells and conditioned medium. 8-Bromoadenosine cAMP and forskolin mimicked ACTH effects on the Angs. Higher HFA Ang2 to Ang1 ratios may reflect greater vascular remodeling than in the adult. Angs, particularly Ang2, in concert with vascular endothelial growth factor, may mediate ACTH tropic action, ensuring coordination of HFA growth, steroidogenesis, and angiogenesis.

Expression of Angiopoietin 1, 2 and Their Common Receptor Tie2 in Human Gastric Carcinoma: Implication for Angiogenesis

Angiogenesis, formation of new microvessels providing oxygen and nutrient supply, is essential for tumor growth. It is dependent on the production of angiogenic growth factors by tumor cells. Angiopoietin 1 (Ang-1) and 2 (Ang-2) and their common receptor, Tie2, are thought to be critical regulators of tumor angiogenesis. We examined expression of Ang-1, Ang-2, and their common receptor Tie2 mRNAs and proteins in gastric cancers using in situ hybridization and immunohistochemistry. We also investigated the relationship between their expression and differentiation of cancer cells, lymph node metastasis, tumor size, depth of cancer cell invasion, TNM staging and microvessel density (MVD). The expression of Ang-1, Ang-2, and Tie2 mRNA in cancer cells significantly correlated with the MVD (p<0.001, <0.001 and =0.019, respectively). Ang-1 and Tie2 positivity correlated with advanced gastric cancers (p<0.05) and larger cancers had higher positive rates of Ang-1, Ang-2, and Tie2 mRNA expression (p<0.001, =0.010 and =0.039, respectively). Significant positive correlations were also found between mRNA expression of Tie2 and those of Ang-1 and Ang-2 (p<0.01 and <0.001, respectively). These findings indicate that the expression of Ang-1 and Ang-2 is important for tumor angiogenesis, and suggest a possible role of autocrine/paracrine function of angiopoietin/Tie2 system in gastric cancer progression.

The expression of angiopoietin-1, angiopoietin-2, Tie-2 and vascular endothelial growth factor mRNA in normal ovary, benign ovarian cyst, and epithelial ovarian cancer

Objective : Vascular endothelial growth factor (VEGF) increases angiogenesis. It is known that one of angiogenetic factors, angiopoietin-1 (Ang-1) stabilizes maturity of normal vessels and angiopoietin-2 (Ang-2) antagonizes the action of angiopoietin-1 by binding Tie-2 that is their receptor. Recently those factors are known to be involved in carcinogenesis. The aim was to investigate the mRNA expression of those factors in epithelial ovarian cancer including normal ovary and ovarian cyst and to evaluate their role in ovarian carcinogenesis. Methods : The tissue samples of 16 ovarian cyst, and 29 epithelial ovarian cancer patients who were diagnosed at Ewha Woman's University MokDong Hospital from 1997 to 2003, and 18 normal ovary subjects who had hysterectomy and salpingoophorectomy due to uterine myoma and confirmed as normal controls, were obtained. The mRNA expressions of Angiopoietin-1, Angiopoietin-2, Tie-2 and Vascular endothelial growth factor were measured by Quantitative Competitive polymerase chain reaction (PCR). Their expressions were analyzed with ANOVA test and Spearman correlation test. Results : The expressions of Ang-1 mRNA were higher in normal ovary than those of ovarian cyst and ovarian cancer (p

Expression of angiopoietins, Tie2 and vascular endothelial growth factor in angiogenesis and progression of hepatocellular carcinoma

To investigate the significance of angiopoietins, Tie2 and vascular endothelial growth factor (VEGF) expression in the angiogenesis and progress of hepatocellular carcinoma (HCC). Fresh surgically resected specimens of HCC and noncancerous liver (NCL) tissue from 38 patients with HCC were obtained, and expression of angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), Tie2, and VEGF messenger RNA (mRNA) was examined by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). Expression pattern of each gene in HCC and NCL tissue specimens was compared and the potential role and interaction in angiogenesis of HCC were analyzed. Genes' expression level and its relationship with tumor's clinicopathological parameters were also investigated. Immunohistochemical staining of CD34 was performed to determine the microvessel density (MVD) and Ang-2/Ang-1 ratio was calculated. Relationships between Ang-2/Ang-1 ratio, VEGF and MVD and clinicopathological features were also tested so as to evaluate their significance in the progression of HCC. Ang-2 and VEGF mRNAs in HCC were significantly higher than those in NCL tissue (P < 0.05), whereas the Ang-1 and Tie2 mRNAs showed no statistical significance (P > 0.05), though slightly lower level of Ang-1 mRNA in HCC was observed. Ang-2/Ang-1 ratio and VEGF were both positively correlated to MVD. The Ang-2/ Ang-1 ratio, Ang-2 and VEGF were all associated with tumor's clinicopathological parameters (P < 0.05) except for histological grades (P > 0.05). Ang-1 and Tie2 levels in different clinicopathological groups were not significantly different (P > 0.05). Dominant Ang-2 expression against Ang-1 through Tie2 receptor in the presence of VEGF plays a critical role in initiating early neovascularization and transformation of noncancerous liver to hepatocellular carcinoma. Its consequently constant operation in formed HCC induces further angiogenesis and progression of HCC.

Superior Cervical Ganglionectomy Induces Changes in Growth Factor Expression in the Rat Retina

To determine whether sympathetic nerves regulate expression of known angiogenic growth factors. Surgical sympathectomy (SNX) was used to remove sympathetic innervation to the eye. Real-time PCR was used to measure steady state mRNA expression of VEGF, VEGFR-2, angiopoietin-1, and Tie2. Western blot analysis was performed to assess protein expression. Blood-retinal barrier (BRB) permeability surface area product (PS) was measured using enhanced MRI on a separate group of control and SNX rats. mRNA of both VEGF and VEGFR-2 decreased significantly at 6 weeks after SNX. VEGF protein expression also decreased significantly. VEGFR-2 protein was unchanged. Both angiopoietin-1 and Tie2 mRNA expression increased significantly after SNX. Immunoblot analysis showed that angiopoietin-1 protein expression coincided with its mRNA expression. Tie2 protein expression was unaffected. Sympathetic denervation did not significantly increase BRB PS. Surgical SNX results in a reduction in VEGF gene and protein expression, while increasing protein expression of Ang-1. These findings suggest that sympathetic nerves regulate the expression of angiogenic growth factors in rat retina.

Placental Expression of Angiopoietin-1, Angiopoietin-2 and Tie-2 during Placental Development in an Ovine Model of Placental Insufficiency-Fetal Growth Restriction

Fetal growth restriction (FGR) is associated with increased perinatal morbidity and mortality, and often results from functional placental insufficiency. Placentation requires extensive vasculogenesis and subsequent angiogenesis, in both maternal and fetal tissues. Angiopoietin-1 (Ang-1) and Angiopoietin-2 (Ang-2) are angiogenic growth factors expressed in the placenta, and compete for binding to a common receptor, Tunica interna endothelial cell kinase-2 (Tie-2). Our objective was to examine Ang-1, Ang-2 and Tie-2 expression in ovine placental tissue obtained from normal and FGR pregnancies throughout gestation. Fetal cotyledon and maternal caruncle tissue concentrations of Ang-1, Ang-2 and Tie-2 mRNA were assessed by real-time reverse transcriptase-polymerase chain reaction and protein concentrations were assessed by Western immunoblot analysis, at 55, 90 and 135 d gestational age (dGA). Concentrations of Ang-1, Ang-2 and Tie-2 mRNA in FGR fetal cotyledons were increased at 55 dGA, and Tie-2 mRNA concentrations were decreased in FGR fetal cotyledons and maternal caruncles at 135 dGA. Immunoblot analysis demonstrated increased concentrations of Ang-2 in the fetal cotyledon at 55 dGA, and lower concentrations at 135 dGA. In contrast, concentrations of Tie-2 were increased at 90 dGA, but tended to decrease at 135 dGA in FGR maternal caruncles. The changes observed during early- to mid-gestation may result in increased branching angiogenesis, but may also set the stage for increased nonbranching angiogenesis during late gestation, altered placental architecture and placental insufficiency that result in FGR.

Circulating Tie2-Expressing Cells Are Increased in Multiple Myeloma Patients, Correlate with Serum Pleiotrophin Levels and May Develop from This Myeloma Angiogenic and Growth Factor.

Tie2, an endothelial cell-specific receptor kinase, plays an important role in tumor angiogenesis. This protein is essential to the development of embryonic vasculature as well as vascular growth and maintenance in adult tissues. Because of the increasing importance that angiogenesis has been shown to play in multiple myeloma (MM), we determined the number of Tie2-expressing cells in the peripheral blood (PB) of MM patients and its relationship to the serum levels and gene expression of a recently identified angiogenic factor, pleiotrophin (PTN). We have recently demonstrated that PTN is expressed and secreted by MM tumor cells, and serum levels of this protein are highly elevated in MM patients. We quantified the number of Tie2-positive cells in MM patients (n=15) and age-matched control subjects (n=10) using an immunohistochemical technique. Tie2-expressing cells were significantly elevated in the PB mononuclear cells (MCs) from MM patients compared to the normal controls (p<0.05). We also analyzed gene expression for Tie2 in these same samples using RT-PCR. The results showed that Tie2 mRNA was strongly expressed in the PBMCs from MM patients whereas control samples showed no or low expression of this gene. Serum levels of PTN were tested with ELISA, and PTN mRNA concentrations were quantified by RT-PCR in PBMCs from these same patients and control subjects. The results showed that serum levels of PTN correlated with the number of Tie2-expressing PBMCs in MM patients (R2=0.5778). PTN mRNA levels also correlated with Tie2 gene expression in PBMC samples. We further examined whether monocyte colony stimulating factor (mCSF), PTN and vascular endothelial growth factor (VEGF) may be capable of inducing Tie2 expression in highly purified human monocytes that lack Tie2 expression. Normal PB monocytes were purified using density centrifugation followed by anti-CD14 micro-bead affinity column selection. Although none of these three proteins alone or the combinations of either VEGF and mCSF or VEGF and PTN induced Tie2 gene expression in the monocytes following one week of incubation, the combination of PTN (100 nM) and mCSF (20 nM) led to expression of Tie2 in these cells. We quantified the proportion of cells expressing Tie2 in these samples with RT-PCR using serial dilutional analysis with B or T cells that lack Tie2 expression, and showed that approximately 0.1–1.0% of the monocytes expressed this gene following incubation with PTN and mCSF. Moreover, the addition of VEGF (20 ng/ml) to PTN and mCSF increased the proportion of cells expressing Tie2 (to >10%). Anti-PTN antibody blocked the induction of Tie2 gene expression in these monocytes by this cytokine combination. These results show that Tie2-expressing cells are elevated in the peripheral blood of MM patients, and correlate with PTN serum and PTN mRNA expression. PTN in combination with VEGF and mCSF induces Tie2 gene expression in a large proportion of circulating human monocytes. These results suggest that MM patients show increased numbers of vasculogenic progenitors in their circulation that may result from the presence of elevated levels of circulating angiogenic factors including PTN and VEGF.

Internal Translation Initiation Mediated by the Angiogenic Factor Tie2

Tie2 is an endothelium-specific receptor tyrosine kinase required for normal blood vessel maturation. We report that Tie2 mRNA translation is maintained under hypoxic conditions. To identify the mechanism responsible for this, we undertook structure/function analysis of the Tie2 5'-untranslated region (UTR). Transcription start site mapping indicates the existence of a several mRNA isoforms containing unusually long 5'-UTRs (>350 nucleotides) with five upstream open reading frames. We find internal ribosome binding activity that allows the Tie2 mRNA to initiate in a cap-independent fashion. Our data provide a framework for understanding how Tie2 mRNA is translated despite a cumbersome structured 5'-UTR and how its production is secured under unfavorable environmental conditions.

The expression of angiopoietin-tie system members in CL during oestrous cycle and induced luteolysis in cow

Local mechanisms of angiogenesis and angiolysis in the corpus luteum (CL) directly relate to the luteal function. Recently, several studies have shown that members of the angiopoietin-tie system regulate remodelling of microvasculature in the ovary. The aim of this study was to determine the mRNA profiles of the angiopoietins ANPT-1 and ANPT-2 and the receptors Tie1 and Tie2 during different stages of bovine corpora lutea (CL) function. The CL were classified into 4 stages of oestrous cycle: early: Day 2–5, mid: Day 8–12, late: Day 15–17 and regressing: Day >18. For the experimental luteolysis cows during mid luteal stage (Days 8–12) were injected with PGF2α analogue (Cloprostenol) and CL were collected by transvaginal ovariectomy before and at 2, 4, 12, 24, 48 and 64h after PGF2α injection. The expression of ANPT-1, ANPT-2, Tie1 and Tie2 mRNA in the bovine CL during the oestrous cycle and PGF2α induced luteolysis (real-time changes before and after injection) was investigated by RT-PCR. The levels of ANPT-1 mRNA in early and regressing CL were lower (p<0.05) than those in mid and late CL, whereas ANPT-2 mRNA expression did not change during the oestrous cycle. Consequently, the ANPT-2/ANPT-1 ratio (an index of instability of blood vessels) was high in the early and regressing CL. The Tie1 mRNA expression did not change, while Tie2 mRNA expression decreased as the CL aged. During PGF2α induced luteolysis, ANPT-2 mRNA expression was acutely and temporally increased at 2h after PGF2α injection. The expression of ANPT-1 mRNA was decreased from 4h after PGF2α injection and remained at low levels, which results in gradual increase in the ANPT-2/ANPT-1 ratio. It is likely that the decrease of ANPT-1 is a basic mechanism of vascular remodelling in CL. Tie1 mRNA decreased at 64h while Tie2 mRNA declined at 48h after PGF2α. These data indicate that the ANPT-Tie system is involved in the local mechanisms regulating angiogenesis and angiolysis in the developing and regressing CL in cow.

Expression of VEGF and angiopoietins in subfoveal membranes from patients with age-related macular degeneration

Vascular endothelial growth factor (VEGF) and angiopoietins are key regulators of angiogenesis. The purpose of this study was to measure mRNA levels of these factors and of their receptors in surgically excised subfoveal membranes from patients with age-related macular degeneration (AMD) and to evaluate their relevance as prognostic markers of postsurgical recurrence of choroidal neovascularization (CNV). Prospective observational case series. setting: Institutional. study population: In a prospective series of 24 patients (aged 51 to 91 years) with classic CNV of AMD diagnosed less than 6 months previously, 24 subfoveal membranes (one eye per patient) were surgically removed and collected. Thirteen patients underwent treatment for recurrence of CNV within 6 months of surgery. main outcome measures: Four 8-mu sections were prepared from each membrane for immunohistochemical determination of vascular density (CD31 immunostaining). The remaining tissue was used for preparation of total RNA. The levels of VEGF-A, VEGF-R1, VEGF-R2, neuropilin-1, angiopoietin-1, angiopoietin-2, Tie-2, and hypoxanthine phosphoribosyltransferase mRNAs were determined by real-time reverse-transcriptase polymerase chain reaction. Vascular endothelial growth factor, angiopoietin-1, and angiopoietin-2 appeared to be expressed to variable levels in most samples, whereas Tie-2, VEGF-R1, and VEGF-R2 were undetectable. Low levels of VEGF expression correlated with postsurgical recurrence of CNV (P = .07). Angiopoietin-1 and angiopoietin-2 levels did not predict recurrence (P > .1). The results indicate that at the time of surgical excision, subfoveal membranes express angiopoietin-1, VEGF, and, to a lesser degree, angiopoietin-2. Because CNV appears to recur less often in membranes expressing high levels of VEGF, we hypothesize that VEGF acts as a stabilizer of neovessels at this stage of the disease.

Changes of mRNA expression of vascular endothelial growth factor, angiopoietins and their receptors during the periovulatory period in eCG/hCG-treated immature female rats

Angiogenic factors can induce the perifollicular capillary network in the theca interna that shows marked changes in and around the preovulatory luteinizing hormone (LH) surge. To get more information on their functional crosstalk, the aim of the present study was to investigate the manner of mRNA expression of vascular endothelial growth factors (VEGFs) 120, 164, angiopoietin (Ang)-1, Ang-2 and their specific receptors during the periovulatory phase. We used an established equine and human chorionic gonadotropins (eCG/hCG)-derived experimental model capable of stimulating naturally occurring follicular maturation, ovulation and corpus luteum (CL) formation. On day 28 postpartum, immature female rats were administrated s.c. with 10 IU of eCG to promote follicular development, followed 48 hr later by i.p. administration of 20 IU of hCG. Ovaries were dissected at 0, 6, 12, 18 and 24 hr after hCG treatment, and were obtained on day 30 in the untreated control. After induction of follicular growth by the eCG treatment, each mRNA expression of VEGF 120, VEGF 164, Neuropilin-1 and Flt-1 significantly increased. The peaks in mRNA expressions of VEGF120 and VEGF164 were both found at 18 hr after hCG treatment. Flk-1 mRNA expression maintained up to 6 hr after hCG treatment, and then decreased at 12, 18 and 24 hr after hCG treatment. Ang-2 mRNA expression increased in the ovaries at 6 and 12 hr after hCG treatment. Tie-2 mRNA expression decreased at 24 hr after the treatment of gonadotropins. Our findings suggest that ovarian vascular formation during the periovulatory period including preovulatory follicles, ovulation and CL formation may develop via crosstalk of the VEGF-Flt-1 and Ang-Tie2 systems.

Expression and function of the angiopoietin receptor Tie-2 in human eosinophils

Increased vascularity of bronchial mucosa is closely related to the expression of angiogenic factors, which contribute to the pathogenesis of diseases such as asthma bronchiale. Here we examine the effects of the angiogenic growth factors angiopoietin 1 and angiopoietin 2 on eosinophil function in vitro and possible involvement of the angiopoietin receptor Tie-2. Eosinophil migration was studied by micropore filter assays. Signaling mechanisms required for angiopoietin-dependent migration were tested by using signaling enzyme blockers. Tie-2 mRNA and receptor expression on the cell surface of eosinophils was demonstrated in RT-PCR and by fluorescence-activated cell sorting analysis. Angiopoietin 1 significantly stimulated eosinophil chemotaxis via activation of phosphodiesterase, phosphatidylinositol 3'-kinase, and tyrosine kinases. The effect on eosinophil migration of angiopoietin 1 was reversed by an antibody against the Tie-2 receptor and by angiopoietin 2. Incubation of eosinophils with angiopoietin 1 abolished the chemotactic effects of vascular endothelial growth factor on human eosinophils via the Tie-2 receptor. Finally, Tie-2 expression by human eosinophils was demonstrated on the transcriptional and protein level. Data suggest that angiopoietin 1 stimulates directed migration and possibly inhibits vascular endothelial growth factor-induced eosinophil chemotaxis via its Tie-2 receptor, which is expressed by eosinophils. Thus, angiopoietin 1 may play an important role in the modulation of eosinophilic inflammation.

Endothelial PAS domain protein 1 gene promotes angiogenesis through the transactivation of both vascular endothelial growth factor and its receptor, Flt-1.

Endothelial PAS domain protein 1 (EPAS1) is a basic-helix-loop-helix/PAS domain transcription factor that is expressed preferentially in vascular endothelial cells. EPAS1 shares high homology with hypoxia-inducible factor-1alpha (HIF-1alpha) and is reported to transactivate vascular endothelial growth factor (VEGF), fetal liver kinase-1 (Flk-1), and Tie2 promoters. In this study, we analyzed the role of EPAS1 in the process of angiogenesis. Using microarray technology, we looked for target genes regulated by EPAS1 in vascular endothelial cells. A total of 130 genes were upregulated by EPAS1, including fms-like tyrosine kinase-1 (Flt-1). Reporter analysis using human Flt-1 promoter and gel mobility shift assays showed that the heterodimer of EPAS1 and aryl hydrocarbon receptor nuclear translocator binds directly to HIF-1-binding site upstream of Flt-1 promoter and transactivates it. Small interfering RNA targeted to EPAS1 but not HIF-1alpha attenuated desferrioxamine-induced Flt-1 mRNA expression, thus EPAS1 is thought to play an essential role in hypoxic induction of Flt-1 gene. Furthermore, using mouse wound healing models, we demonstrated that adenovirus-mediated delivery of EPAS1 gene significantly induced the expression of VEGF, Flt-1, Flk-1, and Tie2 mRNA at the wound site and promoted mature angiogenesis. The proportion of the number of mural cells in newly formed vessels was significantly higher in EPAS1-treated wound area than VEGF-treated area. In conclusion, EPAS1 promotes Flt-1 gene expression and induces mRNA expression of VEGF, Flk-1, and Tie2, leading to enhancement of mature angiogenesis in vivo. Thus, EPAS1 may contribute to the construction of mature vessels by modulating the coordinated expressions of VEGF, Flt-1, Flk-1, and Tie2.

IFC (Aims and Scope)

Sinusoidal endothelial cells and hepatocytes increase in number after partial resection and necrosis of the liver, and contribute to both reconstruction and capillarization of the sinusoids through interaction with stellate cells. The mechanism underlying such interaction was evaluated regarding angiopoietins and tie receptors essential for blood vessel formation. Hepatic mRNA expressions of angiopoietin-1, angiopoietin-2 and tie-2 were increased at 168 h after 70% liver resection with sinusoidal reconstruction in rats, and also at 48 h with sinusoidal capillarization in the liver of rats given carbon tetrachloride (CCl4). Tie-2 mRNA expression was detected in sinusoidal endothelial cells and stellate cells isolated from normal rats, and in activated stellate cells from CCl4-intoxicated rats. The mRNA expressions of angiopoietin-1 and angiopoietin-2 were detectable in Kupffer cells, sinusoidal endothelial cells and stellate cells in normal rats, but increased in activated stellate cells and macrophages after CCl4-intoxication. Both angiopoietins and tie-2 were immunohistochemically stained along the sinusoids of 70% hepatectomized rats and in necrotic areas of CCl4-intoxicated rats. Angiopoietin-1 and angiopoietin-2 may be involved in both reconstruction and capillarization of the sinusoids in rat liver after partial resection and necrosis through interaction between stellate cells and sinusoidal and vascular endothelial cells via tie-2 receptor.

Angiopoietin/tie receptors system may play a role during reconstruction and capillarization of the hepatic sinusoids after partial hepatectomy and liver necrosis in rats.

Sinusoidal endothelial cells and hepatocytes increase in number after partial resection and necrosis of the liver, and contribute to both reconstruction and capillarization of the sinusoids through interaction with stellate cells. The mechanism underlying such interaction was evaluated regarding angiopoietins and tie receptors essential for blood vessel formation. Hepatic mRNA expressions of angiopoietin-1, angiopoietin-2 and tie-2 were increased at 168h after 70% liver resection with sinusoidal reconstruction in rats, and also at 48h with sinusoidal capillarization in the liver of rats given carbon tetrachloride (CCl(4)). Tie-2 mRNA expression was detected in sinusoidal endothelial cells and stellate cells isolated from normal rats, and in activated stellate cells from CCl(4)-intoxicated rats. The mRNA expressions of angiopoietin-1 and angiopoietin-2 were detectable in Kupffer cells, sinusoidal endothelial cells and stellate cells in normal rats, but increased in activated stellate cells and macrophages after CCl(4)-intoxication. Both angiopoietins and tie-2 were immunohistochemically stained along the sinusoids of 70% hepatectomized rats and in necrotic areas of CCl(4)-intoxicated rats. Angiopoietin-1 and angiopoietin-2 may be involved in both reconstruction and capillarization of the sinusoids in rat liver after partial resection and necrosis through interaction between stellate cells and sinusoidal and vascular endothelial cells via tie-2 receptor.

Enhanced expression of angiopoietin-2 and the Tie2 receptor but not angiopoietin-1 or the Tie1 receptor in a rat model of myocardial infarction.

Modulation of Tie2 receptor activity by angiopoietin ligands is crucial for angiogenesis, blood vessel maturation, and vascular endothelium integrity. The role of the angiopoietin (Ang) and Tie system in myocardial infarction is not well understood. To investigate the participation of the Ang/Tie in myocardial infarction, adult Sprague-Dawley rats with ligation of the left anterior descending coronary artery to induce myocardial infarction were studied. Ang1, Ang2, Tie1, and Tie2 were measured immediately after ligation of the coronary artery, and at 6 h, 1 and 3 days, and 1, 2, 3 and 4 weeks after ligation by Northern blotting, Western blotting, and immunohistochemical staining. Ang2 mRNA significantly increased from 2 weeks (2.1-fold) to 4 weeks (2.9-fold) after the infarction in the left ventricular free wall. Tie2 mRNA increased significantly from 1 week (2.1-fold) to 4 weeks (3.8-fold) after the infarction. Ang2 protein also significantly increased from 3 days (1.9-fold) to 4 weeks (3-fold) after the infarction in the left ventricular free wall. Tie2 protein increased 2.4-fold at 3 weeks and 2.8-fold at 4 weeks after the infarction. Neither Ang1 nor Tie1 mRNA or protein showed any significant change at any time point after the infarction. The ratio of Ang2/Ang1 mRNA and protein in the study group was higher than that in the control group. Ang2 and Tie2 expression in nonischemic myocardium showed no significant change. Immunohistochemical study also showed increased immunoreactivity of Ang2 and Tie2 at the infarct border. In conclusion, Ang2 and Tie2 expressions significantly increased both spatial and temporal patterns after myocardial infarction in the rat ventricular myocardium, while Ang1 and Tie1 receptor expression did not.

Enhanced Expression of Angiopoietin-2 and the Tie2 Receptor but Not Angiopoietin-1 or the Tie1 Receptor in a Rat Model of Myocardial Infarction

Modulation of Tie2 receptor activity by angiopoietin ligands is crucial for angiogenesis, blood vessel maturation, and vascular endothelium integrity. The role of the angiopoietin (Ang) and Tie system in myocardial infarction is not well understood. To investigate the participation of the Ang/Tie in myocardial infarction, adult Sprague-Dawley rats with ligation of the left anterior descending coronary artery to induce myocardial infarction were studied. Ang1, Ang2, Tie1, and Tie2 were measured immediately after ligation of the coronary artery, and at 6 h, 1 and 3 days, and 1, 2, 3 and 4 weeks after ligation by Northern blotting, Western blotting, and immunohistochemical staining. Ang2 mRNA significantly increased from 2 weeks (2.1-fold) to 4 weeks (2.9-fold) after the infarction in the left ventricular free wall. Tie2 mRNA increased significantly from 1 week (2.1-fold) to 4 weeks (3.8-fold) after the infarction. Ang2 protein also significantly increased from 3 days (1.9-fold) to 4 weeks (3-fold) after the infarction in the left ventricular free wall. Tie2 protein increased 2.4-fold at 3 weeks and 2.8-fold at 4 weeks after the infarction. Neither Ang1 nor Tie1 mRNA or protein showed any significant change at any time point after the infarction. The ratio of Ang2/Ang1 mRNA and protein in the study group was higher than that in the control group. Ang2 and Tie2 expression in nonischemic myocardium showed no significant change. Immunohistochemical study also showed increased immunoreactivity of Ang2 and Tie2 at the infarct border. In conclusion, Ang2 and Tie2 expressions significantly increased both spatial and temporal patterns after myocardial infarction in the rat ventricular myocardium, while Ang1 and Tie1 receptor expression did not.

Expression and Clinical Significance of Angiopoietin-2 and its Receptor Tie-2 in Invasive Breast Cancer

Purpose: Breast carcinomas are highly malignant tumor that the angiogenesis factor, vascular endothelial growth factor and its receptors are overexpressed. To elucidate the role of Angiopoietin-2 (ANG2) and ANG2 receptor Tie-2 in invasive ductal carcinoma, we examined the expression of ANG2, and Tie-2 at the mRNA and protein levels in human breast cancer cell lines and samples. Methods: Total RNA from 22 breast cancer patient biopsies were extracted. ANG2 and Tie-2 mRNA expression was measured by means of reverse transcription-PCR assay. Results: RT-PCR indicated that the ANG2 and Tie-2 mRNA levels in carcinoma samples were significantly higher than those of the adjacent non-neoplastic breast tissues. For ANG2 and Tie-2, 41 of 71 invasive ductal carcinomass (58%) showed high expressions in Immunohistochemistry. Immunohistochemical analysis demonstrated that ANG2 and Tie-2 were expressed by both tumor cells and endothelial elements. Expression in tumor cells were confirmed by studying a panel of human breast carcinoma cell lines cultured by RT-PCR. Our study showed that the ANG2 positivity was correlated with axillary lymph node metastasis among the clinicopathological parameter and confirmed that high expressions of ANG2 correlated highly with the axillary lymph node metastases, histological grade, positive PR status, and age, and Tie-2 expression correlated significantly with the p53 status. Moreover, ANG2 and Tie-2 co-expression correlated significantly with the axillary lymph node metastases, compared with ANG2(-)/Tie-2 (-) and ANG2 (+)/Tie-2 (-) or ANG2 (-)/Tie-2 (+) cases. Conclusion: These findings suggested that ANG2 and Tie-2 might be involved in the progression of invasive ductal carcinomas through autocrine and paracrine signaling and that it may be clinically useful in selecting patients who could benefit from adjuvant treatment by further study. (Journal of Korean Breast Cancer Society 2004;7:84-91) ꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏꠏ