Showing papers on "Angiogenesis published in 2001"
TL;DR: It is shown that bone marrow from adult humans contains endothelial precursors with phenotypic and functional characteristics of embryonic hemangioblasts, and that these can be used to directly induce new blood vessel formation in the infarct-bed and proliferation of preexisting vasculature after experimental myocardial infarction.
Abstract: Left ventricular remodeling is a major cause of progressive heart failure and death after myocardial infarction. Although neoangiogenesis within the infarcted tissue is an integral component of the remodeling process, the capillary network is unable to support the greater demands of the hypertrophied myocardium, resulting in progressive loss of viable tissue, infarct extension and fibrous replacement. Here we show that bone marrow from adult humans contains endothelial precursors with phenotypic and functional characteristics of embryonic hemangioblasts, and that these can be used to directly induce new blood vessel formation in the infarct-bed (vasculogenesis) and proliferation of preexisting vasculature (angiogenesis) after experimental myocardial infarction. The neoangiogenesis resulted in decreased apoptosis of hypertrophied myocytes in the peri-infarct region, long-term salvage and survival of viable myocardium, reduction in collagen deposition and sustained improvement in cardiac function. The use of cytokine-mobilized autologous human bone-marrow-derived angioblasts for revascularization of infarcted myocardium (alone or in conjunction with currently used therapies) has the potential to significantly reduce morbidity and mortality associated with left ventricular remodeling.
2,688 citations
TL;DR: It is reported that embryonic angiogenesis in mice was not affected by deficiency of PlGF, andTransplantation of wild-type bone marrow rescued the impairedAngiogenesis and collateral growth in Pgf−/− mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow–derived cells.
Abstract: Vascular endothelial growth factor (VEGF) stimulates angiogenesis by activating VEGF receptor-2 (VEGFR-2). The role of its homolog, placental growth factor (PlGF), remains unknown. Both VEGF and PlGF bind to VEGF receptor-1 (VEGFR-1), but it is unknown whether VEGFR-1, which exists as a soluble or a membrane-bound type, is an inert decoy or a signaling receptor for PlGF during angiogenesis. Here, we report that embryonic angiogenesis in mice was not affected by deficiency of PlGF (Pgf-/-). VEGF-B, another ligand of VEGFR-1, did not rescue development in Pgf-/- mice. However, loss of PlGF impaired angiogenesis, plasma extravasation and collateral growth during ischemia, inflammation, wound healing and cancer. Transplantation of wild-type bone marrow rescued the impaired angiogenesis and collateral growth in Pgf-/- mice, indicating that PlGF might have contributed to vessel growth in the adult by mobilizing bone-marrow-derived cells. The synergism between PlGF and VEGF was specific, as PlGF deficiency impaired the response to VEGF, but not to bFGF or histamine. VEGFR-1 was activated by PlGF, given that anti-VEGFR-1 antibodies and a Src-kinase inhibitor blocked the endothelial response to PlGF or VEGF/PlGF. By upregulating PlGF and the signaling subtype of VEGFR-1, endothelial cells amplify their responsiveness to VEGF during the 'angiogenic switch' in many pathological disorders.
1,664 citations
TL;DR: The compelling evidence that NF-κB is dysregulated in many forms of cancer and that its inhibition is a logical therapy for certain cancers and for adjuvant approaches to cancer therapy is described.
Abstract: The abilities of NF-κB to promote cell proliferation, suppress apoptosis, promote cell migration, and suppress differentiation apparently have been co-opted by cellular and viral oncoproteins to promote oncogenesis (Figure (Figure2).2). Direct evidence, using both in vitro and in vivo models, indicates that NF-κB is required for oncogenesis, probably at multiple levels. NF-κB likely plays an important role in the early events of oncogenesis, possibly functioning primarily in protecting against transformation-associated apoptosis. In most late-stage tumor cells, classic NF-κB (the p50-p65 heterodimer) is clearly not the only survival factor, because its inhibition does not induce apoptosis in many of these tumor cells. This observation suggests that other events have occurred to upregulate NF-κB–independent cell survival pathways. However, clearly some cancer cells depend on NF-κB for their survival. NF-κB also can contribute to cell progression by transcriptionally upregulating cyclin D1 with corresponding hyperphosphorylation of the tumor suppressor protein Rb. The induction of NF-κB–controlled proliferation may correlate with loss of differentiation in certain settings (47), which may promote oncogenesis. NF-κB is known to regulate certain genes associated with metastasis, such as matrix metalloproteinase 9, tissue plasminogen activator, and ICAM-1. Thus, a more relevant role for NF-κB in later-stage oncogenesis may be to promote metastasis and angiogenesis. Although many tumor cells display some level of constitutive nuclear NF-κB, higher levels of NF-κB and the transcriptional potential of NF-κB can be further enhanced in response to certain types of chemotherapy. Consistent with this, inhibition of NF-κB in parallel with certain (but apparently not all) chemotherapy treatments strongly enhances the apoptotic potential of the chemotherapy. This observation indicates that NF-κB plays an important role in inducible chemoresistance and establishes NF-κB inhibition as a new adjuvant approach in chemotherapy.
1,478 citations
TL;DR: It is demonstrated that HER2 signaling induced by overexpression in mouse 3T3 cells or heregulin stimulation of human MCF-7 breast cancer cells results in increased HIF-1α protein and VEGF mRNA expression that is dependent upon activity of PI3K, AKT, and the downstream kinase FRAP.
Abstract: Angiogenesis is essential for tumorigenesis as well as metastasis (11, 16, 64), and vascular density is an important prognostic factor in breast cancer (19, 27, 58, 59). Vascular endothelial growth factor (VEGF) plays a major role in tumor angiogenesis (10), and its expression in breast cancer is inversely correlated with patient survival (29, 30). VEGF expression can be induced by exposure of tumor cells to hypoxia or growth factors and, in both cases, this expression is due in part to increased VEGF gene transcription that is mediated by hypoxia-inducible factor 1 (HIF-1) (6, 9, 12, 22, 44, 63, 65).
HIF-1 is a heterodimer composed of HIF-1α and HIF-1β subunits (56, 57). Whereas HIF-1β is constitutively expressed, the expression and activity of the HIF-1α subunit are induced by exposure of cells to hypoxia or growth factors (reviewed in reference 49). HIF-1 activates the transcription of genes whose products are required for critical aspects of tumor progression including angiogenesis (plasminogen activator inhibitor 1 and VEGF), iron homeostasis (transferrin and transferrin receptor), and metabolic adaptation (glucose transporters and glycolytic enzymes), as well as several factors that affect tumor cell survival or proliferation (endothelin 1, inducible nitric oxide synthase, and insulin-like growth factor 2).
HIF-1α is overexpressed in primary and metastatic human tumors (1, 4, 5, 53, 62, 66). In breast cancer, HIF-1α overexpression can be detected in ductal carcinoma in situ but not in benign ductal hyperplasia (5), i.e., in early-stage cancer prior to invasion but concomitant with increased angiogenesis (15). HIF-1 activity is increased both by intratumoral hypoxia and by genetic alterations, including loss-of-function mutations in the tumor suppressor genes encoding p53, PTEN, and VHL (von Hippel-Lindau protein) as well as gain-of-function mutations in oncogenes that activate the phosphatidylinositol 3-kinase (PI3K), SRC, and mitogen-activated protein (MAP) kinase signal-transduction pathways (24, 34, 40, 41, 47, 48, 65, 66, 68). Loss or gain of HIF-1 activity is negatively and positively correlated, respectively, with tumor growth and angiogenesis in xenograft assays (6, 24, 28, 33, 40, 44, 45).
Among the genetic alterations identified in human breast cancer, one of the most important is the increased activity of the HER2 receptor tyrosine kinase encoded by the ERBB2 gene on chromosome 17q21, which occurs in approximately one-third of breast tumors and is associated with increased tumor grade, chemotherapy resistance, and decreased rates of patient survival (36, 43, 50, 51). Overexpression of HER2 transforms human mammary epithelial and mouse 3T3 cells and imparts resistance against the chemotherapeutic agents tamoxifen and Taxol (32, 39, 61). Treatment of breast cancer cells with a neutralizing antibody against HER2 results in a dose-dependent inhibition of VEGF expression (38). A humanized monoclonal antibody to HER2 inhibits breast cancer growth and has been approved for treatment of HER2-overexpressing tumors (35). Unlike other members of the epidermal growth factor receptor (EGFR) family, HER2 has tyrosine kinase activity in the absence of any known ligand. HER2 heterodimerizes with the EGFR family members HER3 and HER4, which bind the ligand heregulin (55). In breast cancer cells, heregulin activates AKT (also known as protein kinase B) via the PI3K pathway (31). HER2 overexpression is also associated with increased AKT activity (67). Recently, HER2 overexpression or heregulin stimulation has been shown to induce VEGF mRNA and protein expression in cancer cell lines (3, 60).
Because HIF-1 has been shown to lie downstream of EGFR and PI3K-AKT signaling and upstream of VEGF expression in tumor cells (9, 65, 68), we have analyzed HIF-1 activity in HER2-overexpressing 3T3 cells and heregulin-stimulated MCF-7 cells. Our results indicate that HIF-1 contributes to the induction of VEGF expression in these cells. Because hypoxia (52) and mutations in the tumor suppressor genes VHL (7, 54) and p53 (40) induce HIF-1 activity by inhibiting the ubiquitination and proteasomal degradation of HIF-1α (20, 26, 46), it was assumed that receptor tyrosine kinase signaling induced HIF-1α expression by the same mechanism. However, our results demonstrate that HER2 signaling induces HIF-1α protein synthesis rather than inhibiting its degradation, thus representing a novel mechanism for the regulation of HIF-1 and VEGF expression.
1,269 citations
TL;DR: This is the first clinical demonstration showing that lineage-committed EPCs and MNCCD34+, their putative precursors, are mobilized during an acute ischemic event in humans.
Abstract: Background—Endothelial progenitor cells (EPCs) circulate in adult peripheral blood (PB) and contribute to neovascularization. However, little is known regarding whether EPCs and their putative precursor, CD34-positive mononuclear cells (MNCCD34+), are mobilized into PB in acute ischemic events in humans. Methods and Results—Flow cytometry revealed that circulating MNCCD34+ counts significantly increased in patients with acute myocardial infarction (n=16), peaking on day 7 after onset, whereas they were unchanged in control subjects (n=8) who had no evidence of cardiac ischemia. During culture, PB-MNCs formed multiple cell clusters, and EPC-like attaching cells with endothelial cell lineage markers (CD31, vascular endothelial cadherin, and kinase insert domain receptor) sprouted from clusters. In patients with acute myocardial infarction, more cell clusters and EPCs developed from cultured PB-MNCs obtained on day 7 than those on day 1. Plasma levels of vascular endothelial growth factor significantly incre...
1,189 citations
TL;DR: A novel mechanism of action of statin treatment in patients with stable CAD is defined: the augmentation of circulating EPCs with enhanced functional activity.
Abstract: Background—Therapeutic neovascularization may constitute an important strategy to salvage tissue from critical ischemia. Circulating bone marrow–derived endothelial progenitor cells (EPCs) were shown to augment the neovascularization of ischemic tissue. In addition to lipid-lowering activity, hydroxymethyl glutaryl coenzyme A reductase inhibitors (statins) reportedly promote the neovascularization of ischemic tissue in normocholesterolemic animals. Methods and Results—Fifteen patients with angiographically documented stable coronary artery disease (CAD) were prospectively treated with 40 mg of atorvastatin per day for 4 weeks. Before and weekly after the initiation of statin therapy, EPCs were isolated from peripheral blood and counted. In addition, the number of hematopoietic precursor cells positive for CD34, CD133, and CD34/kinase insert domain receptor was analyzed. Statin treatment of patients with stable CAD was associated with an ≈1.5-fold increase in the number of circulating EPCs by 1 week after ...
1,064 citations
TL;DR: Evidence accumulating over the last decade has established the fundamental role of vascular endothelial growth factor (VEGF) as a key regulator of normal and abnormal angiogenesis, and numerous clinical trials are presently testing the hypothesis that inhibition of VEGF may have therapeutic value.
Abstract: Evidence accumulating over the last decade has established the fundamental role of vascular endothelial growth factor (VEGF) as a key regulator of normal and abnormal angiogenesis. The biological effects of VEGF are mediated by two tyrosine kinase receptors, Flt-1 (VEGFR-1) and KDR (VEGFR-2). The signaling and biological properties of these two receptors are strikingly different. VEGF is essential for early development of the vasculature to the extent that inactivation of even a single allele of the VEGF gene results in embryonic lethality. VEGF is also required for female reproductive functions and endochondral bone formation. Substantial evidence also implicates VEGF as an angiogenic mediator in tumors and intraocular neovascular syndromes, and numerous clinical trials are presently testing the hypothesis that inhibition of VEGF may have therapeutic value.
1,060 citations
TL;DR: Although PC deficiency appears to have direct effects on EC number before E 13.5, the subsequent increased VEGF-A levels may further abrogate microvessel architecture, promote vascular permeability, and contribute to formation of the edematous phenotype observed in late gestation PDGF-B and PDGFR-beta knock out embryos.
Abstract: The association of pericytes (PCs) to newly formed blood vessels has been suggested to regulate endothelial cell (EC) proliferation, survival, migration, differentiation, and vascular branching. Here, we addressed these issues using PDGF-B– and PDGF receptor-β (PDGFR-β)–deficient mice as in vivo models of brain angiogenesis in the absence of PCs. Quantitative morphological analysis showed that these mutants have normal microvessel density, length, and number of branch points. However, absence of PCs correlates with endothelial hyperplasia, increased capillary diameter, abnormal EC shape and ultrastructure, changed cellular distribution of certain junctional proteins, and morphological signs of increased transendothelial permeability. Brain endothelial hyperplasia was observed already at embryonic day (E) 11.5 and persisted throughout development. From E 13.5, vascular endothelial growth factor-A (VEGF-A) and other genes responsive to metabolic stress became upregulated, suggesting that the abnormal microvessel architecture has systemic metabolic consequences. VEGF-A upregulation correlated temporally with the occurrence of vascular abnormalities in the placenta and dilation of the heart. Thus, although PC deficiency appears to have direct effects on EC number before E 13.5, the subsequent increased VEGF-A levels may further abrogate microvessel architecture, promote vascular permeability, and contribute to formation of the edematous phenotype observed in late gestation PDGF-B and PDGFR-β knock out embryos.
1,030 citations
TL;DR: The results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.
Abstract: Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons.
1,029 citations
TL;DR: The basic molecular mechanisms governing how endothelial cells, periendothelial cells and matrix molecules interact with each other and with numerous growth factors and receptors, to form blood vessels have been presented and are being extended to further understand pathological angiogenesis associated with disorders.
Abstract: The basic molecular mechanisms governing how endothelial cells, periendothelial cells and matrix molecules interact with each other and with numerous growth factors and receptors, to form blood vessels have been presented. The many insights gained from this basic knowledge are being extended to further understand pathological angiogenesis associated with disorders such as arterial stenosis, myocardial ischemia, atherosclerosis, allograft transplant stenosis. wound healing and tissue repair. As a result, novel angiogenic and anti-angiogenic molecules are rapid-ly entering the clinic, with the promise of relief from a host of medical disorders.
1,002 citations
TL;DR: Vascular endothelial growth factor (VEGF) is a secreted mitogen highly specific for cultured endothelial cells and plays a central role in both angiogenesis and vasculogenesis, most notably the neovascularisation of growing tumours.
Abstract: Vascular endothelial growth factor (VEGF) is a secreted mitogen highly specific for cultured endothelial cells. In vivo VEGF induces microvascular permeability and plays a central role in both angiogenesis and vasculogenesis. VEGF is a promising target for therapeutic intervention in certain pathological conditions that are angiogenesis dependent, most notably the neovascularisation of growing tumours. Through alternative mRNA splicing, a single gene gives rise to several distinct isoforms of VEGF, which differ in their expression patterns as well as their biochemical and biological properties. Two VEGF receptor tyrosine kinases (VEGFRs) have been identified, VEGFR-1 (Flt-1) and VEGFR-2 (KDR/Flk-1). VEGFR-2 seems to mediate almost all observed endothelial cell responses to VEGF, whereas roles for VEGFR-1 are more elusive. VEGFR-1 might act predominantly as a ligand-binding molecule, sequestering VEGF from VEGFR-2 signalling. Several isoform-specific VEGF receptors exist that modulate VEGF activity. Neuropilin-1 acts as a co-receptor for VEGF(165), enhancing its binding to VEGFR-2 and its bioactivity. Heparan sulphate proteoglycans (HSPGs), as well as binding certain VEGF isoforms, interact with both VEGFR-1 and VEGFR-2. HSPGs have a wide variety of functions, such as the ability to partially restore lost function to damaged VEGF(165) and thereby prolonging its biological activity.
TL;DR: BMI may constitute a novel safety strategy for achieving optimal therapeutic angiogenesis by the natural ability of the BM cells to secrete potent angiogenic ligands and cytokines as well as to be incorporated into foci of neovascularization.
Abstract: Background Bone marrow implantation (BMI) was shown to enhance angiogenesis in a rat ischemic heart model. This preclinical study using a swine model was designed to test the safety and therapeutic...
TL;DR: The current knowledge of FGF- and VEGF-induced signal transduction that leads to specific biological responses will be summarized and the manner in which this knowledge is being exploited to regulate angiogenesis will be discussed.
TL;DR: It is suggested that eNOS plays a predominant role in VEGF-induced angiogenesis and vascular permeability in vivo, and selective modulation of eN OS activity is a promising strategy for altering angiogenic and vascular porousness in vivo.
Abstract: Nitric oxide (NO) plays a critical role in vascular endothelial growth factor (VEGF)-induced angiogenesis and vascular hyperpermeability. However, the relative contribution of different NO synthase (NOS) isoforms to these processes is not known. Here, we evaluated the relative contributions of endothelial and inducible NOS (eNOS and iNOS, respectively) to angiogenesis and permeability of VEGF-induced angiogenic vessels. The contribution of eNOS was assessed by using an eNOS-deficient mouse, and iNOS contribution was assessed by using a selective inhibitor [l-N(6)-(1-iminoethyl) lysine, l-NIL] and an iNOS-deficient mouse. Angiogenesis was induced by VEGF in type I collagen gels placed in the mouse cranial window. Angiogenesis, vessel diameter, blood flow rate, and vascular permeability were proportional to NO levels measured with microelectrodes: Wild-type (WT) > or = WT with l-NIL or iNOS(-/-) > eNOS(-/-) > or = eNOS(-/-) with l-NIL. The role of NOS in VEGF-induced acute vascular permeability increase in quiescent vessels also was determined by using eNOS- and iNOS-deficient mice. VEGF superfusion significantly increased permeability in both WT and iNOS(-/-) mice but not in eNOS(-/-) mice. These findings suggest that eNOS plays a predominant role in VEGF-induced angiogenesis and vascular permeability. Thus, selective modulation of eNOS activity is a promising strategy for altering angiogenesis and vascular permeability in vivo.
TL;DR: It is demonstrated that VEGF‐C‐induced lymphangiogenesis mediates tumour cell dissemination and the formation of lymph node metastases.
Abstract: Metastasis is a frequent and lethal complication of cancer. Vascular endothelial growth factor-C (VEGF-C) is a recently described lymphangiogenic factor. Increased expression of VEGF-C in primary tumours correlates with dissemination of tumour cells to regional lymph nodes. However, a direct role for VEGF-C in tumour lymphangiogenesis and subsequent metastasis has yet to be demonstrated. Here we report the establishment of transgenic mice in which VEGF-C expression, driven by the rat insulin promoter (Rip), is targeted to beta-cells of the endocrine pancreas. In contrast to wild-type mice, which lack peri-insular lymphatics, RipVEGF-C transgenics develop an extensive network of lymphatics around the islets of Langerhans. These mice were crossed with Rip1Tag2 mice, which develop pancreatic beta-cell tumours that are neither lymphangiogenic nor metastatic. Double-transgenic mice formed tumours surrounded by well developed lymphatics, which frequently contained tumour cell masses of beta-cell origin. These mice frequently developed pancreatic lymph node metastases. Our findings demonstrate that VEGF-C-induced lymphangiogenesis mediates tumour cell dissemination and the formation of lymph node metastases.
TL;DR: This review will focus preferentially on the role of chemokines duringskin wound healing and intends to provide an update on the multiplefunctions of individual chemokine functions during the phases of woundrepair.
Abstract: Healing of wounds is one of the most complex biological events after birth as a result of the interplay of different tissue structures and a large number of resident and infiltrating cell types. The latter are mainly constituted by leukocyte subsets (neutrophils, macrophages, mast cells, and lymphocytes), which sequentially infiltrate the wound site and serve as immunological effector cells but also as sources of inflammatory and growth-promoting cytokines. Recent data demonstrate that recruitment of leukocyte subtypes is tightly regulated by chemokines. Moreover, the presence of chemokine receptors on resident cells (e.g., keratinocytes, endothelial cells) indicates that chemokines also contribute to the regulation of epithelialization, tissue remodeling, and angiogenesis. Thus, chemokines are in an exclusive position to integrate inflammatory events and reparative processes and are important modulators of human-skin wound healing. This review will focus preferentially on the role of chemokines during skin wound healing and intends to provide an update on the multiple functions of individual chemokines during the phases of wound repair.
TL;DR: It is concluded that vasculogenic endothelial cells and nascent vessels are critical for the earliest stages of organogenesis, prior to blood vessel function.
Abstract: The embryonic role of endothelial cells and nascent vessels in promoting organogenesis, prior to vascular function, is unclear. We find that early endothelial cells in mouse embryos surround newly specified hepatic endoderm and delimit the mesenchymal domain into which the liver bud grows. In flk-1 mutant embryos, which lack endothelial cells, hepatic specification occurs, but liver morphogenesis fails prior to mesenchyme invasion. We developed an embryo tissue explant system that permits liver bud vasculogenesis and show that in the absence of endothelial cells, or when the latter are inhibited, there is a selective defect in hepatic outgrowth. We conclude that vasculogenic endothelial cells and nascent vessels are critical for the earliest stages of organogenesis, prior to blood vessel function.
TL;DR: Platelet-released sphingosine 1-phosphate, linked to Rac- and Rho-dependent cytoskeletal rearrangement, may act late in angiogenesis to stabilize newly formed vessels, which often display abnormally increased vascular permeability.
Abstract: Substances released by platelets during blood clotting are essential participants in events that link hemostasis and angiogenesis and ensure adequate wound healing and tissue injury repair. We assessed the participation of sphingosine 1-phosphate (Sph-1-P), a biologically active phosphorylated lipid growth factor released from activated platelets, in the regulation of endothelial monolayer barrier integrity, which is key to both angiogenesis and vascular homeostasis. Sph-1-P produced rapid, sustained, and dose-dependent increases in transmonolayer electrical resistance (TER) across both human and bovine pulmonary artery and lung microvascular endothelial cells. This substance also reversed barrier dysfunction elicited by the edemagenic agent thrombin. Sph-1-P-mediated barrier enhancement was dependent upon G(ialpha)-receptor coupling to specific members of the endothelial differentiation gene (Edg) family of receptors (Edg-1 and Edg-3), Rho kinase and tyrosine kinase-dependent activation, and actin filament rearrangement. Sph-1-P-enhanced TER occurred in conjunction with Rac GTPase- and p21-associated kinase-dependent endothelial cortical actin assembly with recruitment of the actin filament regulatory protein, cofilin. Platelet-released Sph-1-P, linked to Rac- and Rho-dependent cytoskeletal rearrangement, may act late in angiogenesis to stabilize newly formed vessels, which often display abnormally increased vascular permeability.
TL;DR: It is proposed that vascular trauma may induce release of chemokines, such as VEGF, that promotes rapid mobilization of CEPs to the peripheral circulation and strategies to improve the mobilization and incorporation of Ceps may contribute to the acceleration of vascularization of the injured vascular tissue.
Abstract: Bone marrow (BM)-derived circulating endothelial precursor cells (CEPs) are thought to play a role in postnatal angiogenesis Emerging evidence suggests that angiogenic stress of vascular trauma may induce mobilization of CEPs to the peripheral circulation In this regard, we studied the kinetics of CEP mobilization in two groups of patients who experienced acute vascular insult secondary to burns or coronary artery bypass grafting (CABG) In both burn and CABG patients, there was a consistent, rapid increase in the number of CEPs, determined by their surface expression pattern of vascular endothelial growth factor receptor 2 (VEGFR2), vascular endothelial cadherin (VE-cadherin), and AC133 Within the first 6 to 12 hours after injury, the percentage of CEPs in the peripheral blood of burn or CABG patients increased almost 50-fold, returning to basal levels within 48 to 72 hours Mobilized cells also formed late-outgrowth endothelial colonies (CFU-ECs) in culture, indicating that a small, but significant, number of circulating endothelial cells were BM-derived CEPs In parallel to the mobilization of CEPs, there was also a rapid elevation of VEGF plasma levels Maximum VEGF levels were detected within 6 to 12 hours of vascular trauma and decreased to baseline levels after 48 to 72 hours Acute elevation of VEGF in the mice plasma resulted in a similar kinetics of mobilization of VEGFR2(+) cells On the basis of these results, we propose that vascular trauma may induce release of chemokines, such as VEGF, that promotes rapid mobilization of CEPs to the peripheral circulation Strategies to improve the mobilization and incorporation of CEPs may contribute to the acceleration of vascularization of the injured vascular tissue
TL;DR: In mouse models of lung cancer and atherosclerosis, it was found that nicotine enhanced lesion growth in association with an increase in lesion vascularity, and these effects were mediated through nicotinic acetylcholine receptors at nicotine concentrations that are pathophysiologically relevant.
Abstract: We provide anatomic and functional evidence that nicotine induces angiogenesis. We also show that nicotine accelerates the growth of tumor and atheroma in association with increased neovascularization. Nicotine increased endothelial-cell growth and tube formation in vitro, and accelerated fibrovascular growth in vivo. In a mouse model of hind-limb ischemia, nicotine increased capillary and collateral growth, and enhanced tissue perfusion. In mouse models of lung cancer and atherosclerosis, we found that nicotine enhanced lesion growth in association with an increase in lesion vascularity. These effects of nicotine were mediated through nicotinic acetylcholine receptors at nicotine concentrations that are pathophysiologically relevant. The endothelial production of nitric oxide, prostacyclin and vascular endothelial growth factor might have a role in these effects.
TL;DR: It is demonstrated here that VEGFR‐2 blockade with SU5416 in combination with chronic hypobaric hypoxia causes severe pulmonary hypertension associated with precapillary arterial occlusion by proliferating endothelial cells.
Abstract: Our understanding of the pathobiology of severe pulmonary hypertension, usually a fatal disease, has been hampered by the lack of information of its natural history. We have demonstrated that, in human severe pulmonary hypertension, the precapillary pulmonary arteries show occlusion by proliferated endothelial cells. Vascular endothelial growth factor (VEGF) and its receptor 2 (VEGFR-2) are involved in proper maintenance, differentiation, and function of endothelial cells. We demonstrate here that VEGFR-2 blockade with SU5416 in combination with chronic hypobaric hypoxia causes severe pulmonary hypertension associated with precapillary arterial occlusion by proliferating endothelial cells. Prior to and concomitant with the development of severe pulmonary hypertension, lungs of chronically hypoxic SU5416-treated rats show significant pulmonary endothelial cell death, as demonstrated by activated caspase 3 immunostaining and TUNEL. The broad caspase inhibitor Z-Asp-CH2-DCB prevents the development of intravascular pulmonary endothelial cell growth and severe pulmonary hypertension caused by the combination of SU5416 and chronic hypoxia.
TL;DR: As basic knowledge about the control of angiogenesis and its role in tumor growth and metastasis increases, it may be possible in the future to develop specific anti-angiogenic agents that offer a potential therapy for cancer and angiogenic diseases.
TL;DR: A review examines the role of the matrix metalloproteinase (MMP) and plasminogen activator (PA)-plasmin systems during angiogenesis, finding a role for gelatinases, membrane-type 1 MMP, and PA inhibitor 1 has been clearly defined in a number of model systems.
Abstract: Extracellular proteolysis is an absolute requirement for new blood vessel formation (angiogenesis). This review examines the role of the matrix metalloproteinase (MMP) and plasminogen activator (PA)-plasmin systems during angiogenesis. Specifically, a role for gelatinases (MMP-2, MMP-9), membrane-type 1 MMP (MMP-14), the urokinase-type PA receptor, and PA inhibitor 1 has been clearly defined in a number of model systems. The MMP and PA-plasmin systems have also been implicated in experimental vascular tumor formation, and their role during this process will be examined. Antiproteolysis, particularly in the context of angiogenesis, has become a key target in therapeutic strategies aimed at inhibiting tumor growth and other diseases associated with neovascularization.
TL;DR: This work shows the first evidence that the developmental growth plate in mammals is hypoxic, and that this hypoxia occurs in its interior rather than at its periphery, and finds that VEGF expression in the growth plate is regulated through both HIF-1alpha-dependent and -independent mechanisms.
Abstract: Breakdown or absence of vascular oxygen delivery is a hallmark of many common human diseases, including cancer, myocardial infarction, and stroke. The chief mediator of hypoxic response in mammalian tissues is the transcription factor hypoxia-inducible factor 1 (HIF-1), and its oxygen-sensitive component HIF-1alpha. A key question surrounding HIF-1alpha and the hypoxic response is the role of this transcription factor in cells removed from a functional vascular bed; in this regard there is evidence indicating that it can act as either a survival factor or induce growth arrest and apoptosis. To study more closely how HIF-1alpha functions in hypoxia in vivo, we used tissue-specific targeting to delete HIF-1alpha in an avascular tissue: the cartilaginous growth plate of developing bone. We show here the first evidence that the developmental growth plate in mammals is hypoxic, and that this hypoxia occurs in its interior rather than at its periphery. As a result of this developmental hypoxia, cells that lack HIF-1alpha in the interior of the growth plate die. This is coupled to decreased expression of the CDK inhibitor p57, and increased levels of BrdU incorporation in HIF-1alpha null growth plates, indicating defects in HIF-1alpha-regulated growth arrest occurs in these animals. Furthermore, we find that VEGF expression in the growth plate is regulated through both HIF-1alpha-dependent and -independent mechanisms. In particular, we provide evidence that VEGF expression is up-regulated in a HIF-1alpha-independent manner in chondrocytes surrounding areas of cell death, and this in turn induces ectopic angiogenesis. Altogether, our findings have important implications for the role of hypoxic response and HIF-1alpha in development, and in cell survival in tissues challenged by interruption of vascular flow; they also illustrate the complexities of HIF-1alpha response in vivo, and they provide new insights into mechanisms of growth plate development.
TL;DR: It is indicated that hypoxia enhances HDAC function and that HDAC is closely involved in angiogenesis through suppression of Hypoxia-responsive tumor suppressor genes.
Abstract: Low oxygen tension influences tumor progression by enhancing angiogenesis; and histone deacetylases (HDAC) are implicated in alteration of chromatin assembly and tumorigenesis. Here we show induction of HDAC under hypoxia and elucidate a role for HDAC in the regulation of hypoxia-induced angiogenesis. Overexpressed wild-type HDAC1 downregulated expression of p53 and von Hippel–Lindau tumor suppressor genes and stimulated angiogenesis of human endothelial cells. A specific HDAC inhibitor, trichostatin A (TSA), upregulated p53 and von Hippel–Lindau expression and downregulated hypoxia-inducible factor-1α and vascular endothelial growth factor. TSA also blocked angiogenesis in vitro and in vivo. TSA specifically inhibited hypoxia-induced angiogenesis in the Lewis lung carcinoma model. These results indicate that hypoxia enhances HDAC function and that HDAC is closely involved in angiogenesis through suppression of hypoxia-responsive tumor suppressor genes.
TL;DR: Vascular endothelial growth factor (VEGF) significantly increased macrophage levels in bone marrow and peripheral blood and increased plaque area 5-, 14- and 4-fold compared with controls at weeks 1, 2 and 3, respectively.
Abstract: Vascular endothelial growth factor (VEGF) can promote angiogenesis but may also exert certain effects to alter the rate of atherosclerotic plaque development. To evaluate this potential impact on plaque progression, we treated cholesterol-fed mice doubly deficient in apolipoprotein E/apolipoprotein B100 with low doses of VEGF (2 microg/kg) or albumin. VEGF significantly increased macrophage levels in bone marrow and peripheral blood and increased plaque area 5-, 14- and 4-fold compared with controls at weeks 1, 2 and 3, respectively. Plaque macrophage and endothelial cell content also increased disproportionately over controls. In order to confirm that the VEGF-mediated plaque progression was not species-specific, the experiment was repeated in cholesterol-fed rabbits at the three-week timepoint, which showed comparable increases in plaque progression.
TL;DR: In this paper, VEGF and angiopoietin-1 (Ang-1) levels were elevated by injecting recombinant protein or adenoviral vectors expressing soluble VEGFs165, matrix-bound VEGf189, or Ang-1 into mice, which was associated with an induction of hematopoiesis and increased marrow cellularity.
Abstract: Tyrosine kinase receptors for angiogenic factors vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1) are expressed not only by endothelial cells but also by subsets of hematopoietic stem cells (HSCs). To further define their role in the regulation of postnatal hematopoiesis and vasculogenesis, VEGF and Ang-1 plasma levels were elevated by injecting recombinant protein or adenoviral vectors expressing soluble VEGF165, matrix-bound VEGF189, or Ang-1 into mice. VEGF165, but not VEGF189, induced a rapid mobilization of HSCs and VEGF receptor (VEGFR)2+ circulating endothelial precursor cells (CEPs). In contrast, Ang-1 induced delayed mobilization of CEPs and HSCs. Combined sustained elevation of Ang-1 and VEGF165 was associated with an induction of hematopoiesis and increased marrow cellularity followed by proliferation of capillaries and expansion of sinusoidal space. Concomitant to this vascular remodeling, there was a transient depletion of hematopoietic activity in the marrow, which was compensated by an increase in mobilization and recruitment of HSCs and CEPs to the spleen resulting in splenomegaly. Neutralizing monoclonal antibody to VEGFR2 completely inhibited VEGF165, but not Ang-1–induced mobilization and splenomegaly. These data suggest that temporal and regional activation of VEGF/VEGFR2 and Ang-1/Tie-2 signaling pathways are critical for mobilization and recruitment of HSCs and CEPs and may play a role in the physiology of postnatal angiogenesis and hematopoiesis.
TL;DR: An inhibitory PAS (Per/Arnt/Sim) domain protein, IPAS, which is a basic helix-loop-helix (bHLH)/PAS protein structurally related to HIFs, is described, which demonstrates dominant negative regulation of HIF-mediated control of gene expression.
Abstract: Alteration of gene expression is a crucial component of adaptive responses to hypoxia. These responses are mediated by hypoxia-inducible transcription factors (HIFs)1,2. Here we describe an inhibitory PAS (Per/Arnt/Sim) domain protein, IPAS, which is a basic helix-loop-helix (bHLH)/PAS protein structurally related to HIFs. IPAS contains no endogenous transactivation function but demonstrates dominant negative regulation of HIF-mediated control of gene expression. Ectopic expression of IPAS in hepatoma cells selectively impairs induction of genes involved in adaptation to a hypoxic environment, notably the vascular endothelial growth factor (VEGF) gene, and results in retarded tumour growth and tumour vascular density in vivo. In mice, IPAS was predominantly expressed in Purkinje cells of the cerebellum and in corneal epithelium of the eye. Expression of IPAS in the cornea correlates with low levels of expression of the VEGF gene under hypoxic conditions. Application of an IPAS antisense oligonucleotide to the mouse cornea induced angiogenesis under normal oxygen conditions, and demonstrated hypoxia-dependent induction of VEGF gene expression in hypoxic corneal cells. These results indicate a previously unknown mechanism for negative regulation of angiogenesis and maintenance of an avascular phenotype.
TL;DR: Recent findings suggest important roles for the vasodilators nitric oxide and prostacyclin, in linking post-receptor signaling networks to downstream biological effects and in mediating some in vivo endothelial functions of VEGF.
Abstract: The central role of vascular endothelial growth factor (VEGF) in angiogenesis in health and disease makes it attractive both as a therapeutic target for anti-angiogenic drugs and as a pro-angiogenic cytokine for the treatment of ischaemic heart disease. While VEGF binds to two receptor protein tyrosine kinases, VEGFR1 (Flt-1) and VEGFR2 (KDR), most biological functions of VEGF are mediated via VEGFR2, and the role of VEGFR1 is currently unknown. Neuropilin-1, a non-tyrosine kinase transmembrane molecule, may function as a co-receptor for VEGFR2. Considerable progress has recently been made towards delineating the signal transduction pathways distal to activation of VEGFR2. Activation of the mitogen-activated protein kinase, protein kinase C and Akt pathways are all strongly implicated in mediating diverse cellular biological functions of VEGF, including cell survival, proliferation, the generation of nitric oxide and prostacyclin and angiogenesis. Upregulation of metalloproteinases, activation of focal adhesion kinase and interactions between VEGF receptors and integrins are strongly implicated in VEGF-induced endothelial cell migration. Recent findings suggest important roles for the vasodilators nitric oxide and prostacyclin, in linking post-receptor signaling networks to downstream biological effects and in mediating some in vivo endothelial functions of VEGF.
TL;DR: It is shown that RECK regulates two other MMPs, MMP-2 and MT1-MMP, known to be involved in cancer progression, that mice lacking a functional RECK gene die around E10.5 and vascular sprouting is dramatically suppressed in tumors derived from RECK-expressing fibrosarcoma cells grown in nude mice.