Determination of hypoxic region by hypoxia marker in developing mouse embryos in vivo: a possible signal for vessel development.

Hypoxia is a well-known signal for angiogenesis, but the recent proposal that hypoxia exists in developing embryonic tissues and that it induces vascular development remains to be proven. In the present study, we demonstrate the presence of hypoxia in normal developing embryos by means of a hypoxia marker, pimonidazole, and its associated antibody. Our data clearly show that hypoxia marker immunoreactivity was highly detected in developing neural tubes, heart, and intersomitic mesenchyme at an early stage of organogenesis, suggesting that hypoxia may exist in the early stages of embryo development. We also found that hypoxia inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) were spatiotemporally co-localized with possible hypoxic regions in embryos. Investigation of platelet endothelial cell adhesion molecule (PECAM) expression provides evidence that endothelial cells proliferate and form the vessels in the hypoxic region in developing organs. Furthermore, we found that hypoxia induced both HIF-1alpha and VEGF in F9 embryonic stem and differentiated cells. Thus, we suggest that hypoxia may exist widely in developing embryonic tissues and that it may act as a signal for embryonic blood vessel formation in vivo.     

Expression of HIF-1alpha, VEGF and VEGF receptors in the carotid body of chronically hypoxic rat

We examined the protein expression and localization of HIF-1alpha, VEGF, VEGF receptors in the carotid body (CB) of rats breathing 10% inspired oxygen for up to 4 weeks. The immunoreactivity (IR) of HIF-1alpha was distributed numerously in the nuclei of glomus (type-I) and other cells since hypoxia for 1 day, but was faint and scattered in the normoxic CBs. Cytoplasmic staining of the VEGF was intense in glomus cells of the hypoxic but not the normoxic group. The IR levels of HIF-1alpha and VEGF reached plateau at 4 weeks, and the IRs of VEGFR-1 and VEGFR-2 were strongly positive in the hypoxic group. Yet, the expression of VEGFR-1-IR was mild, whereas the VEGFR-2-IR was intense in normoxic CBs, suggesting an upregulation of VEGFR-1 but not VEGFR-2 in hypoxia. Hence, HIF-1 may activate the expression of VEGF and VEGFR-1 in the CB and the expression of VEGF in the chemoreceptors may play a paracrine role in the vascular remodeling during chronic hypoxia.     

Hypoxia-inducible factor 1 and VEGF upregulate CXCR4 in glioblastoma: implications for angiogenesis and glioma cell invasion

Hypoxia and hypoxia-inducible factor-1 (HIF-1) play a critical role in glioblastoma multiforme (GBMs). CXCR4 is involved in angiogenesis and is upregulated by HIF-1alpha. CXCR4 is a chemokine receptor for stromal cell-derived factor-1 (SDF-1)alpha, also known as CXCL12. We hypothesized that CXCR4 would be upregulated by hypoxia in GBMs. First, we investigated the expression of HIF-1alpha and CXCR4 in GBMs. CXCR4 was consistently found colocalized with HIF-1alpha expression in pseudopalisading glioma cells around areas of necrosis. In addition, angiogenic tumor vessels were strongly positive for CXCR4. Next, we tested the in vitro effect of hypoxia and vascular endothelial growth factor (VEGF) on the expression of CXCR4 in glioma cell lines and in human brain microvascular endothelial cells (HBMECs). Exposure to hypoxia induced significant expression of CXCR4 and HIF-1alpha in glioma cells, whereas treatment with exogenous VEGF increased CXCR4 expression in HBMECs. We also transfected U87MG glioma cells with an HIF-1alpha construct and observed that CXCR4 was upregulated in these cells even in normoxic conditions. We then used a lentivirus-mediated shRNA expression vector directed against HIF-1alpha. When exposed to hypoxia, infected cells failed to show HIF-1alpha and CXCR4 upregulation. We performed migration assays under normoxic and hypoxic conditions in the presence or absence of AMD3100, a CXCR4 inhibitor. There was a significant increase in the migration of U87MG and LN308 glioma cells in hypoxic conditions, which was inhibited in the presence of AMD3100. These studies demonstrate the critical role played by hypoxia and CXCR4 in glioma cell migration. Based on these studies, we suggest that hypoxia regulates CXCR4 in GBMs at two levels. First, through HIF-1alpha in the pseudopalisading tumor cells themselves and, secondly, by the VEGF-stimulated angiogenic response in HBMECs. We believe this knowledge may lead to a potentially important two-pronged therapy against GBM progression using chemotherapy targeting CXCR4.     

Angiogenesis in gliomas: biology and molecular pathophysiology

Glioblastoma multiforme (GBM) is characterized by exuberant angiogenesis, a key event in tumor growth and progression. The pathologic mechanisms driving this change and the biological behavior of gliomas remain unclear. One mechanism may involve cooption of native blood vessels by glioma cells inducing expression of angiopoietin-2 by endothelial cells. Subsequently, vascular apoptosis and involution leads to necrosis and hypoxia. This in turn induces angiogenesis that is associated with expression of hypoxia-inducible factor (HIF)-1alpha and vascular endothelial growth factor (VEGF) in perinecrotic pseudopalisading glioma cells. Here we review the molecular and cellular mechanisms implicated in HIF-1-dependent and HIF-1-independent glioma-associated angiogenesis. In GBMs, both tumor hypoxia and genetic alterations commonly occur and act together to induce the expression of HIF-1. The angiogenic response of the tumor to HIF-1 is mediated by HIF-1-regulated target genes leading to the upregulation of several proangiogenic factors such as VEGF and other adaptive response molecules. Understanding the roles of these regulatory processes in tumor neovascularization, tumor growth and progression, and resistance to therapy will ultimately lead to the development of improved antiangiogenic therapies for GBMs.     

Expression of hypoxia-inducible factors in human endometrium and suppression of matrix metalloproteinases under hypoxic conditions do not support a major role for hypoxia in regulating tissue breakdown at menstruation

BACKGROUND: Classical studies in monkeys suggested that menstruation results from vasoconstriction, hypoxia and necrosis. The heterodimeric hypoxia-inducible factor (HIF) complex is critical in oxygen homeostasis via increased stability of HIF-1alpha/2alpha monomers, and these act as markers of hypoxia. We hypothesized that focal hypoxia in perimenstrual endometrium results in locally increased matrix metalloproteinases (MMP), leading to tissue destruction. METHODS: HIF-1alpha, HIF-2alpha and HIF-1beta were immunolocalized in cycling endometrium. Endometrial stromal cells were cultured under hypoxic and normoxic conditions and MMP measured by zymography and Western blots. RESULTS: HIF-1alpha and HIF-2alpha were detected in only some endometrial samples, and not confined to the perimenstrual tissue. Where present, they were primarily cytoplasmic, not nuclear. HIF-1beta was localized in epithelium, leukocytes and some decidual cells. Cultured endometrial stromal cells responded to hypoxia with increased cellular HIF-1alpha and secreted vascular endothelial growth factor. ProMMP-1 and proMMP-3 production was reduced in response to hypoxia regardless of the steroidal milieu (no added steroids, estrogen or estrogen plus progesterone). Active MMP-2 and membrane type 1 MMP but not proMMP-2 or proMMP-9 production were also inhibited by hypoxia. CONCLUSIONS: These results do not support a role for hypoxia in the focally increased production and activation of MMP observed prior to and during menstruation.     

Basic FGF augments hypoxia induced HIF-1-alpha expression and VEGF release in T47D breast cancer cells

AIM: Both hypoxia inducible factor 1 (HIF-1) and basic fibroblast growth factor (bFGF) play important roles in tumour angiogenesis. This study was designed to clarify the cooperative effect of these two mediators in induction of vascular endothelial cell growth factor (VEGF) release from breast cancer and probe possible mechanisms involved. METHODS: Release of VEGF from a breast cancer cell line (T47D) was quantitated by enzyme linked immunosorbent assay (ELISA). Expression of HIF-1 and ERK was assayed using Western blotting. Transient transfection and dual luciferase reporter assay were used to study HIF-1 transactivity. RESULTS: The data showed that hypoxia induced the expression of HIF-1alpha protein, the transactivity of HIF-1 and the release of VEGF. bFGF further augmented these hypoxic inductions. The PI3K pathway was required for these processes as demonstrated by application of PI3Kinase inhibitor (LY294002) or mutant construct transfections. In contrast, the MEK1 inhibitor PD98059 showed no effect on either activation of HIF-1 or VEGF release, which is in agreement with our finding that ERK1/2 was not activated by hypoxia. Under hypoxic conditions, bFGF activated the MEK1/ERK pathway. PD98059 blocked the activation of ERK1/2 and suppressed bFGF-induced HIF-1 transactivity, yet the protein expression of HIF-1alpha or VEGF release was not affected by PD98059. CONCLUSION: bFGF augments hypoxia induced VEGF release mainly through the PI3K pathway and partly depending on HIF-1 activity. Elucidation of this mechanism may provide a new target for anti-angiogenesis in cancer therapy.     

Correlation between VEGF and HIF-1alpha expression in human oral squamous cell carcinoma

Understanding the development and progression of oral cancer is critical in the quest for successful therapeutic intervention. The hypoxic microenvironment present in human oral tumor in vivo may actively influence tumor growth and neovascularization. This study correlates expression of both VEGF and HIF-1alpha in normal keratinocytes and oral cancer cell lines and determine whether hypoxia played a role in VEGF and HIF-1alpha regulation. Three human oral cancer cell lines and three normal keratinocytes were exposed to both normoxia and hypoxia culture conditions. Northern and Western blot analysis were used to assess VEGF and HIF-1alpha expression in the different culture conditions. ELISA assays were performed to measure VEGF production in the different cell lines tested. Hypoxia upregulated VEGF and HIF-1alpha expression on both normal and oral cancer cell lines, with a statistically significant difference between normal and oral cancer cell lines. Pattern of hypoxia-induced VEGF mRNA level tightly followed the HIF-1alpha mRNA expression in the cell lines tested. These results suggest that hypoxia regulates both VEGF and HIF-1alpha expression in head and neck carcinoma cell lines, thus establishing a biochemical pathway between tumor hypoxia and neoangiogenesis in these aggressive neoplasms.     

缺氧诱导因子-1α在结直肠腺癌中的表达及意义

目的　观察低氧培养条件下人结肠腺癌SW4 80细胞及人结直肠腺癌组织中缺氧诱导因子 1α(HIF 1α)mRNA、蛋白表达 ,探讨HIF 1α在结直肠腺癌中的表达及在肿瘤血管形成中的作用。方法　免疫组织化学链霉素抗生物素蛋白 过氧化物酶法 (SP法 )检测SW4 80细胞及结直肠腺瘤、腺癌组织中HIF 1α、血管内皮生长因子 (VEGF)蛋白表达 ;采用CD34标记血管内皮细胞计数微血管密度 (MVD)。用蛋白印迹法检测SW4 80细胞HIF 1α蛋白表达 ;原位杂交检测HIF 1αmRNA。结果　RT PCR结果显示 :低氧组SW4 80细胞HIF 1αmRNA表达显著升高 ,为常氧组的 2 33倍。低氧 genistein组HIF 1αmRNA表达为常氧组的 5 0 7%。原位杂交结果表明 :HIF 1αmRNA表达低氧组 (0 16 2 8± 0 0 0 85 )显著高于常氧组 (0 12 0 1± 0 0 0 38)和低氧 genistein组 (0 115 4± 0 0 0 5 6 ,P <0 0 5 )。免疫细胞化学染色显示 ,低氧组细胞HIF 1α、VEGF蛋白表达水平显著高于常氧组 (P <0 0 1,P <0 0 5 )和低氧 genistein组 (P <0 0 1,P <0 0 5 )。蛋白印迹结果显示 :低氧组HIF 1α蛋白表达显著高于常氧组 ,为常氧组 3 5 4倍。低氧 genistein组HIF 1α蛋白约为常氧组的 5 8 9%。结直肠腺瘤和腺癌HIF 1αmRNA阳性表达率分别为 38 9% (7/