Effect of hypoxia and endothelial loss on vascular smooth muscle cell responsiveness to VEGF-A: role of flt-1/VEGF-receptor-1 (original) (raw)
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British Journal of Pharmacology, 2005
We have previously shown that hypoxia makes vascular smooth muscle cells (VSMCs) responsive to placental growth factor (PlGF) through the induction of functional fms-like tyrosine kinase (Flt-1) receptors. The aim of this study was to investigate the molecular mechanisms involved in the PlGF effects on proliferation and contraction of VSMCs previously exposed to hypoxia (3% O 2). 2 In cultured rat VSMCs exposed to hypoxia, PlGF increased the phosphorylation of protein kinase B (Akt), p38 and STAT3; activation of STAT3 was higher than that of other kinases. In agreement with this finding, the proliferation of hypoxia-treated VSMCs in response to PlGF was significantly impaired by the p38 and the phosphatidylinositol 3-kinase inhibitors SB202190 and LY294002, respectively, and was almost completely prevented by AG490, a janus tyrosine kinase (JAK)/signal transducer and activator of transcription (STAT) inhibitor. 3 Since hypoxia was able to reverse the vasorelaxant effect of PlGF into a vasoconstrictor response, the mechanism of this latter effect was also investigated. Significant Flt-1 activity was measured in isolated preparations from rat aorta exposed to hypoxia. Inhibitors of mitogen-activated protein kinase kinase, Akt and STAT3 induced a modest inhibition of the vasoconstrictor response to PlGF, while the p38 inhibitor SB202190 markedly impaired the PlGF-induced contractile response. These effects were selectively mediated by Flt-1 without any involvement of foetal liver kinase-1 receptors. 4 These data are the first evidence that different intracellular pathways activated by Flt-1 receptor in VSMCs are involved in diverse biological effects of PlGF: while mitogen activated protein kinase kinase/extracellular signal regulated kinase 1/2 and JAK/STAT play a role in VSMC proliferation, p38 is involved in VSMC contraction. These findings may highlight the role of PlGF in vascular pathology.
Human Reproduction, 2008
BACKGROUND: Pre-eclampsia is a pregnancy disorder characterized by a maternal endothelial cell dysfunction associated with low levels of circulating placental growth factor (PlGF) and increased levels of total vascular endothelial growth factor (VEGF), soluble VEGF receptor-1 (sVEGFR-1), and soluble endoglin, a transforming growth factor b1 and 3 coreceptor. Here, we tested the hypothesis that these altered levels of angiogenic cytokines and of the anti-angiogenic soluble forms of cytokine receptors could be the consequence of hypoxia. METHODS: Normal human umbilical vein endothelial cells, immortalized first trimester extravillous trophoblast cells (HTR8/SVneo) and first trimester placental villi explants (8 -14 weeks) were used for culture under normoxia (20% O 2 ) or hypoxia (1% O 2 ). Culture media were collected for the measurement of cytokines by enzyme-linked immunosorbent assay. Total RNA was extracted for RT-PCR analysis. RESULTS: Under hypoxia, villous trophoblast expressed higher levels of VEGF, VEGFR-1, sVEGFR-1 and VEGFR-2 mRNAs (P < 0.001), and secreted more VEGF and sVEGFR-1 proteins (P < 0.05). In contrast, PlGF mRNA and protein were decreased in 1% O 2 (P < 0.001), whereas endoglin (Eng) was not modulated. Additionally, sVEGFR-1 directly abolished VEGF/PlGF-induced angiogenesis in the rat aortic ring assay. CONCLUSIONS: Our results support the hypotheses that, in pre-eclampsia, (i) overproduction of VEGF family factors by pre-eclamptic placenta is a consequence of induced hypoxia; (ii) overproduction of sVEGFR-1 by hypoxic villous trophoblast accounts for maternal free VEGF depletion; (iii) low circulating level of free PlGF is not only related to sVEGFR-1 overproduction, but also to hypoxiainduced mRNA down-regulation; (iv) Eng is not modulated by hypoxia.
Differential regulation of VEGF by TGF- and hypoxia in rat proximal tubular cells
AJP: Renal Physiology, 2004
VEGF expression by proximal tubular epithelial cells may play a critical role in maintaining peritubular capillary endothelium in renal disease. Two major processes involved in renal injury include hypoxia (from vasoconstriction or vascular injury) and transforming growth factor (TGF)-β-dependent fibrosis, both of which are known to stimulate VEGF. Because the TGF-β/Smad pathway is activated in hypoxia, we tested the hypothesis that the induction of VEGF in hypoxia could be partially dependent on TGF-β. Rat proximal tubular (NRK52E) cells treated with TGF-β under normoxic conditions secreted VEGF at 24 h, and this was significantly reduced by blocking Smad activation by overexpressing the inhibitory Smad7 or by blocking p38 and ERK1/2 MAP kinase activation or protein kinase C activation with specific inhibitors. With acute hypoxia, rat proximal tubular cells also express VEGF mRNA and protein as well as TGF-β. However, the induction of VEGF occurs before synthesis of TGF-β and is no...
Febs Letters, 1995
Vascular endothelial growth factor (VEGF) mRNA expression was analysed in rabbit vascular smooth muscle cells following exposure to hypoxia and platelet-derived growth factor-BB (PDGF-BB). Hypoxia potently upregulated VEGF mRNA steady-state levels in a time-and concentration-dependent manner reaching a maximum level (~30-fold increase) after 12-24 h at 0% 02. In contrast, PDGF-BB caused a modest increase in VEGF expression. However, the combination of PDGF-BB and a threshold hypoxic stimulus (2.5% O2 for 4 h) had a marked synergistic effect. Synergy between hypoxia and PDGF-BB was selective for VEGF expression as hypoxia had no effect on the PDGF-induced upregulation of the proto-oncogene c-myc. These results raise the possibility that hypoxia and PDGF-BB may act in concert to induce VEGF expression in the arterial wall during the development of atherosclerosis.
Differential activation of vascular genes by hypoxia in primary endothelial cells
Experimental Cell Research, 2004
Changes in the local environment, such as reduced oxygen tension (hypoxia), elicit transcriptional activation of a variety of genes in mammalian cells. Here we have analyzed the effect of hypoxia in different vascular endothelial cells (ECs) with emphasis on hypoxiaregulated transcription factors and genes of importance for blood vessel dynamics. While hypoxia induced the transcription factor hypoxiainducible factor-1a (HIF-1a) in all endothelial cells tested, the closely related HIF-2a protein was markedly induced in microvascular/ capillary endothelial cells, but only weakly or not at all in artery and vein endothelial cells. Furthermore, microvascular/capillary endothelial cells responded to hypoxia with increased number of transcripts encoding vascular endothelial growth factor-A (VEGF-A), VEGF receptor-2, the angiopoietin receptor Tie2, platelet-derived growth factor-B (PDGF-B), and inducible nitric oxide synthase (iNOS). In vein endothelial cells, hypoxia instead increased transcripts encoding lymphatic vascular components VEGF-C,-D, and VEGF receptor-3. Finally, reduced VEGF receptor levels and phosphorylation indicated establishment of a functional autocrine VEGF-A loop in hypoxic endothelial cells. Our results show that endothelial cells, derived from different vascular beds, mount different transcriptional responses to changes in oxygen tension.
Molecular and cellular biochemistry, 2000
Tissue hypoxia has been identified as being a particularly important stimulus for triggering angiogenesis. Here we report early effects of hypoxia/reoxygenation (H/R) on the protein expression profiles and localization patterns of the VEGF and Angiopoietin-Tie systems in adult rat myocardium. Western blot as well as immunohistochemical analyses were performed on hearts obtained from rats exposed to various durations of in vivo systemic hypoxemic hypoxia followed by 24 h reoxygenation. The relative time course of protein expression in response to increasing durations of hypoxia, as indicated from our experiments, seems to suggest the involvement of the VEGF system and the Ang-Tie system in early angiogenesis. An apparent relationship between the expression profiles of Flk-1 and Ang-2 was observed. The most significant and interesting relationship which came to light was the surprisingly coincident yet opposite temporal trends between Ang-1 and Ang-2 protein levels. In the 1 h hypoxia...
Molecular and Cellular Biology, 1995
Expression of vascular endothelial growth factor (VEGF), an endothelial cell-specific mitogen and a potent angiogenic factor, is upregulated in response to a hypoxic or hypoglycemic stress. Here we show that the increase in steady-state levels of VEGF mRNA is partly due to transcriptional activation but mostly due to increase in mRNA stability. Both oxygen and glucose deficiencies result in extension of the VEGF mRNA half-life in a protein synthesis-dependent manner. Viewing VEGF as a stress-induced gene, we compared its mode of regulation with that of other stress-induced genes. Results showed that under nonstressed conditions, VEGF shares with the glucose transporter GLUT-1 a relatively short half-life (0.64 and 0.52 h, respectively), which is extended fourfold and more than eightfold, respectively, when cells are deprived of either oxygen or glucose. In contrast, the mRNAs of another hypoxia-inducible and hypoglycemia-inducible gene, grp78, as well as that of HSP70, were not stabilized by these metabolic insults. To show that VEGF and GLUT-1 are coinduced in differentially stressed microenvironments, multicell spheroids representing a clonal population of glioma cells in which each cell layer is differentially stressed were analyzed by in situ hybridization. Cellular microenvironments conducive to induction of VEGF and GLUT-1 were completely coincidental. These findings show that two different consequences of tissue ischemia, namely, hypoxia and glucose deprivation, induce VEGF and GLUT-1 expression by similar mechanisms. These proteins function, in turn, to satisfy the tissue needs through expanding its vasculature and improving its glucose utilization, respectively.
Induction of Hypoxia-inducible Factor 1 Gene Expression by Vascular Endothelial Growth Factor
Journal of Biological Chemistry, 2008
Transcriptional regulation of vascular endothelial growth factor (VEGF) is critically dependent on hypoxia-inducible factor 1 (HIF-1). However, not only hypoxia, but selected growth factors can induce HIF-1. High levels of both VEGF and HIF-1 coexist in certain conditions, e.g. tumors. Nonetheless, the possibility that the stimulatory relationship between HIF-1 and VEGF may be bi-directional has not been addressed up to date. The present study in endothelial cells analyzed whether HIF-1 is regulated by a product of its own transcriptionally activated genes, namely, VEGF. As a main finding, VEGF-A 165 induced the increase of HIF-1␣ mRNA and HIF-1␣ protein and nuclear translocation. Autologous endothelial cell VEGF mRNA and protein were also increased upon exposure to exogenous VEGF. The signaling implication of reactive oxygen species was examined by comparison with H 2 O 2 and hypoxanthine/xanthine oxidase and by the superoxide dismutase mimetic, MnTMPyP, the Rac1-NAD(P)H oxidase complex inhibitor, apocynin, transfection of a dominant negative Rac1 mutant, and transfection of a p67phox antisense oligonucleotide. Superoxide anion, largely dependent on Rac1-NAD(P)H oxidase complex activity, was the critical signaling element. The transductional functionality of the pathway was confirmed by means of a reporter gene flanked by a transcription site-related VEGF sequence and by quantitative PCR. In summary, the present results reveal a previously undescribed action of VEGF on the expression of its own transcription factor, HIF-1, and on VEGF itself. This effect is principally mediated by superoxide anion, therefore identifying a new, potentially relevant role of reactive oxygen species in VEGF signaling.
Induction of Hypoxia-inducible Factor 1α Gene Expression by Vascular Endothelial Growth Factor
Journal of Biological Chemistry, 2008
Transcriptional regulation of vascular endothelial growth factor (VEGF) is critically dependent on hypoxia-inducible factor 1 (HIF-1). However, not only hypoxia, but selected growth factors can induce HIF-1. High levels of both VEGF and HIF-1 coexist in certain conditions, e.g. tumors. Nonetheless, the possibility that the stimulatory relationship between HIF-1 and VEGF may be bi-directional has not been addressed up to date. The present study in endothelial cells analyzed whether HIF-1 is regulated by a product of its own transcriptionally activated genes, namely, VEGF. As a main finding, VEGF-A 165 induced the increase of HIF-1␣ mRNA and HIF-1␣ protein and nuclear translocation. Autologous endothelial cell VEGF mRNA and protein were also increased upon exposure to exogenous VEGF. The signaling implication of reactive oxygen species was examined by comparison with H 2 O 2 and hypoxanthine/xanthine oxidase and by the superoxide dismutase mimetic, MnTMPyP, the Rac1-NAD(P)H oxidase complex inhibitor, apocynin, transfection of a dominant negative Rac1 mutant, and transfection of a p67phox antisense oligonucleotide. Superoxide anion, largely dependent on Rac1-NAD(P)H oxidase complex activity, was the critical signaling element. The transductional functionality of the pathway was confirmed by means of a reporter gene flanked by a transcription site-related VEGF sequence and by quantitative PCR. In summary, the present results reveal a previously undescribed action of VEGF on the expression of its own transcription factor, HIF-1, and on VEGF itself. This effect is principally mediated by superoxide anion, therefore identifying a new, potentially relevant role of reactive oxygen species in VEGF signaling.