VEGF is required for growth and survival in neonatal mice.
We employed two independent approaches to inactivate the angiogenic protein VEGF in newborn mice: inducible, Cre-loxP- mediated gene targeting, or administration of mFlt(1-3)-IgG, a soluble VEGF receptor chimeric protein. Partial inhibition of VEGF achieved by inducible gene targeting resulted in increased mortality, stunted body growth and impaired organ development, most notably of the liver. Administration of mFlt(1-3)-IgG, which achieves a higher degree of VEGF inhibition, resulted in nearly complete growth arrest and lethality. Ultrastructural analysis documented alterations in endothelial and other cell types. Histological and biochemical changes consistent with liver and renal failure were observed. Endothelial cells isolated from the liver of mFlt(1-3)-IgG-treated neonates demonstrated an increased apoptotic index, indicating that VEGF is required not only for proliferation but also for survival of endothelial cells. However, such treatment resulted in less significant alterations as the animal matured, and the dependence on VEGF was eventually lost some time after the fourth postnatal week. Administration of mFlt(1-3)-IgG to juvenile mice failed to induce apoptosis in liver endothelial cells. Thus, VEGF is essential for growth and survival in early postnatal life. However, in the fully developed animal, VEGF is likely to be involved primarily in active angiogenesis processes such as corpus luteum development. (+info)
Socs1 binds to multiple signalling proteins and suppresses steel factor-dependent proliferation.
We have identified Socs1 as a downstream component of the Kit receptor tyrosine kinase signalling pathway. We show that the expression of Socs1 mRNA is rapidly increased in primary bone marrow-derived mast cells following exposure to Steel factor, and Socs1 inducibly binds to the Kit receptor tyrosine kinase via its Src homology 2 (SH2) domain. Previous studies have shown that Socs1 suppresses cytokine-mediated differentiation in M1 cells inhibiting Janus family kinases. In contrast, constitutive expression of Socs1 suppresses the mitogenic potential of Kit while maintaining Steel factor-dependent cell survival signals. Unlike Janus kinases, Socs1 does not inhibit the catalytic activity of the Kit tyrosine kinase. In order to define the mechanism by which Socs1-mediated suppression of Kit-dependent mitogenesis occurs, we demonstrate that Socs1 binds to the signalling proteins Grb-2 and the Rho-family guanine nucleotide exchange factors Vav. We show that Grb2 binds Socs1 via its SH3 domains to putative diproline determinants located in the N-terminus of Socs1, and Socs1 binds to the N-terminal regulatory region of Vav. These data suggest that Socs1 is an inducible switch which modulates proliferative signals in favour of cell survival signals and functions as an adaptor protein in receptor tyrosine kinase signalling pathways. (+info)
Differential regulation of vascular endothelial growth factor and its receptor fms-like-tyrosine kinase is mediated by nitric oxide in rat renal mesangial cells.
Under conditions associated with local and systemic inflammation, mesangial cells and invading immune cells are likely to be responsible for the release of large amounts of nitric oxide (NO) in the glomerulus. To further define the mechanisms of NO action in the glomerulus, we attempted to identify genes which are regulated by NO in rat glomerular mesangial cells. We identified vascular endothelial growth factor (VEGF) and its receptor fms-like tyrosine kinase (FLT-1) to be under the regulatory control of exogenously applied NO in these cells. Using S-nitroso-glutathione (GSNO) as an NO-donating agent, VEGF expression was strongly induced, whereas expression of its FLT-1 receptor simultaneously decreased. Expressional regulation of VEGF and FLT-1 mRNA was transient and occurred rapidly within 1-3 h after GSNO treatment. Expression of a second VEGF-specific receptor, fetal liver kinase-1 (FLK-1/KDR), could not be detected. The inflammatory cytokine interleukin-1beta mediated a moderate increase in VEGF expression after 24 h and had no influence on FLT-1 expression. In contrast, platelet-derived growth factor-BB and basic fibroblast growth factor had no effect on VEGF expression, but strongly induced FLT-1 mRNA levels. Obviously, there is a differential regulation of VEGF and its receptor FLT-1 by NO, cytokines and growth factors in rat mesangial cells. (+info)
Early induction of angiogenetic signals in gliomas of GFAP-v-src transgenic mice.
Angiogenesis is a prerequisite for solid tumor growth. Glioblastoma multiforme, the most common malignant brain tumor, is characterized by extensive vascular proliferation. We previously showed that transgenic mice expressing a GFAP-v-src fusion gene in astrocytes develop low-grade astrocytomas that progressively evolve into hypervascularized glioblastomas. Here, we examined whether tumor progression triggers angiogenetic signals. We found abundant transcription of vascular endothelial growth factor (VEGF) in neoplastic astrocytes at surprisingly early stages of tumorigenesis. VEGF and v-src expression patterns were not identical, suggesting that VEGF activation was not only dependent on v-src. Late-stage gliomas showed perinecrotic VEGF up-regulation similarly to human glioblastoma. Expression patterns of the endothelial angiogenic receptors flt-1, flk-1, tie-1, and tie-2 were similar to those described in human gliomas, but flt-1 was expressed also in neoplastic astrocytes, suggesting an autocrine role in tumor growth. In crossbreeding experiments, hemizygous ablation of the tumor suppressor genes Rb and p53 had no significant effect on the expression of VEGF, flt-1, flk-1, tie-1, and tie-2. Therefore, expression of angiogenic signals is an early event during progression of GFAP-v-src tumors and precedes hypervascularization. Given the close similarities in the progression pattern between GFAP-v-src and human gliomas, the present results suggest that these mice may provide a useful tool for antiangiogenic therapy research. (+info)
Exposure to hyperoxia decreases the expression of vascular endothelial growth factor and its receptors in adult rat lungs.
Exposure to high levels of inspired oxygen leads to respiratory failure and death in many animal models. Endothelial cell death is an early finding, before the onset of respiratory failure. Vascular endothelial growth factor (VEGF) is highly expressed in the lungs of adult animals. In the present study, adult Sprague-Dawley rats were exposed to >95% FiO2 for 24 or 48 hours. Northern blot analysis revealed a marked reduction in VEGF mRNA abundance by 24 hours, which decreased to less than 50% of control by 48 hours. In situ hybridization revealed that VEGF was highly expressed in distal airway epithelial cells in controls but disappeared in the oxygen-exposed animals. Immunohistochemistry and Western blot analyses demonstrated that VEGF protein was decreased at 48 hours. TUNEL staining demonstrated the presence of apoptotic cells coincident with the decline in VEGF. Abundance of VEGF receptor mRNAs (Flt-1 and KDR/Flk) decreased in the late time points of the study (48 hours), possibly secondary to the loss of endothelial cells. We speculate that VEGF functions as a survival factor in the normal adult rat lung, and its loss during hyperoxia contributes to the pathophysiology of oxygen-induced lung damage. (+info)
Signal transduction and biological function of placenta growth factor in primary human trophoblast.
Placenta growth factor (PlGF), a member of the vascular endothelial growth factor family of angiogenic factors, is prominently expressed by trophoblast. In addition to its role as a paracrine angiogenic factor within the placenta and endometrium, presence of its receptor, Flt-1, on trophoblast suggests that PlGF also may have an autocrine role(s) in regulating trophoblast function. To elucidate its role in trophoblast, we examined the signal transduction and functional responses of primary human trophoblast to PlGF. Exogenous PlGF induced specific activation of the stress-activated protein kinase (SAPK) pathways, c-Jun-N terminal kinase (JNK) and p38 kinase, in primary term trophoblast with little to no induction of the extracellular signal regulated kinase (ERK-1 and -2) pathways. In contrast, PlGF induced significant ERK-1 and -2 activity in human umbilical vein endothelial cells but did not induce JNK or p38 activity. PlGF-induced activation of the SAPK signaling pathways protected trophoblast from growth factor withdrawal-induced apoptosis, but it did not protect trophoblast from apoptosis induced by the pro-inflammatory cytokines, interferon gamma and tumor necrosis factor alpha. These results provide the first direct evidence of a biochemical and functional role for PlGF/Flt-1 in normal trophoblast and suggest that aberrant PlGF expression during pregnancy may impact upon trophoblast function as well as vascularity within the placental bed. (+info)
Hypoxia induces permeability in brain microvessel endothelial cells via VEGF and NO.
In this study, an in vitro model of the blood-brain barrier, consisting of porcine brain-derived microvascular endothelial cells (BMEC), was used to evaluate the mechanism of hypoxia-induced hyperpermeability. We show that hypoxia-induced permeability in BMEC was completely abolished by a neutralizing antibody to vascular endothelial growth factor (VEGF). In contrast, under normoxic conditions, addition of VEGF up to 100 ng/ml did not alter monolayer barrier function. Treatment with either hypoxia or VEGF under normoxic conditions induced a twofold increase in VEGF binding sites and VEGF receptor 1 (Flt-1) mRNA expression in BMEC. Hypoxia-induced permeability also was prevented by the nitric oxide (NO) synthase inhibitor NG-monomethyl-L-arginine, suggesting that NO is involved in hypoxia-induced permeability changes, which was confirmed by measurements of the cGMP level. During normoxia, treatment with VEGF (5 ng/ml) increased permeability as well as cGMP content in the presence of several antioxidants. These results suggest that hypoxia-induced permeability in vitro is mediated by the VEGF/VEGF receptor system in an autocrine manner and is essentially dependent on reducing conditions stabilizing the second messenger NO as the mediator of changes in barrier function of BMEC. (+info)
Expression of mRNA for vascular endothelial growth factor transmembraneous receptors Flt1 and KDR, and the soluble receptor sflt in cycling human endometrium.
The aim of this study was to quantify and localize the mRNA expression of the vascular endothelial growth factor (VEGF) receptors Flt1, KDR and sflt, in human endometrium throughout the menstrual cycle. Since neoangiogenesis is crucial during embryonic implantation, we postulate that endometrial receptivity to VEGF may be altered during the luteal phase in order to support implantation. Human endometrium was collected and specified as early proliferative (n = 3), mid-proliferative (n = 4), late proliferative (n = 3), early secretory (n = 2), mid-secretory (n = 4), and late secretory (n = 4). Competitive reverse transcription-polymerase chain reaction (RT-PCR) was performed to evaluate the mRNA values throughout the menstrual cycle. Additionally, four samples were separated into epithelial and stromal-enriched cell fractions and competitive RT-PCR was carried out to specify the distribution of the mRNA expression. While mRNA for the transmembraneous receptors Flt1 and KDR was shown to be present at almost constant values throughout the menstrual cycle, the soluble receptor, sflt, had a three-fold higher level of transcription during mid-proliferative and late proliferative when compared with early proliferative and the entire secretory phase. The expression of Flt1, KDR and sflt mRNA was detected in both isolated endometrial epithelial and stromal cell fractions. In conclusion, the down-regulation of sflt, which functions as a soluble antagonist, during the luteal phase may act to sensitize the maternal endothelial receptors to angiogenetic stimuli secreted by the implanting embryo. (+info)