Vascular endothelial growth factor (VEGF) - part 2: in endocrinology and oncology

Endocrine glands are well vascularised and the structure of their vessels facilitates the exchange of various substances, including hormones. These glands are a frequent experimental model in research on VEGF and angiogenesis. VEGF participates in the pathogenesis of diabetes. Diabetic nephropathy is in essence a microvascular disease that develops as a result of a confluence of haemodynamic and metabolic perturbations. Diabetic retinopathy is the commonest microvascular complication of diabetes mellitus and is the leading cause of blindness. In diabetic retinopathy, ischaemic states, and hence tissue hypoxia and angiogenesis, take place. The participation of angiogenesis and VEGF in the pathogenesis of neoplastic disease has been described in many papers. VEGF protein and mRNA have been found in cancers of the thyroid, bronchus, lungs, oesophagus, stomach, colon, liver, breast, ovary, uterus, kidney, and urinary bladder, and in malignant tumours of the brain and bone. There have been many reports of the connections between the degree of VEGF expression and tumour aggression and prognosis in patients. Richly vascularised are GEP NET. In neuroendocrine tumours, strong expression of VEGF, Flt-1 and KDR in relation to the unchanged surrounding tissues has been demonstrated. Depending on the disease entity or the degree of its severity, attempts to apply angiogenic and antiangiogenic therapy have being made. Antiangiogenic therapy (usually regarded as a form of cancer therapy) is based on: 1. inhibitory effects of proangiogenic ligands and their receptors; 2. stimulation or delivery of angiogenesis inhibitors; and 3. direct destruction of neoplastic tumour vasculature.     

miR-152/LIN28B axis modulates high-glucose-induced angiogenesis in human retinal endothelial cells via VEGF signaling

Diabetic retinopathy (DR) is a serious complication of diabetes contributing to blindness in patients. Inhibiting retinal neovascularization is a potent strategy for diabetic retinopathy treatment. Reportedly, the stable expression of lin-28 homolog B (LIN28B), a member of the highly conserved RNA-binding protein LIN28 family, could promote vascular endothelial growth factor (VEGF) expression; herein, we investigated the role and mechanism of LIN28B in diabetic retinopathy progression from the perspective of microRNA (miRNA) regulation. We identified miR-152 as a miRNA that may target the LIN28B 3′-untranslated region and can be significantly downregulated under high-glucose (HG) condition. The expression of miR-152 was remarkably suppressed, whereas the expression of LIN28B was significantly increased under HG condition within both human retinal endothelial cells (hRECs) and retinal microvascular endothelial cell line (hRMECs). miR-152 overexpression significantly suppressed, while LIN28B overexpression promoted the angiogenesis and the protein levels of proangiogenesis factors in both hRECs and hRMECs. More importantly, LIN28B overexpression could remarkably attenuate the effect of miR-152 overexpression. In summary, miR-152 overexpression could inhibit HG-induced angiogenesis in both hRECs and hRMECs via targeting LIN28B and suppressing VEGF signaling. Further, in vivo experiments are needed for the application of miR-152/LIN28B axis in the treatment for diabetic retinopathy.     

Modulation of IL-1β and VEGF expression in rat diabetic retinopathy after PACAP administration

Diabetic retinopathy (DR) is a microvascular complication of diabetes. Hyperglycemic/hypoxic microenvironment concurs to aberrant angiogenesis characterizing the pathology and activates many downstream target genes including inflammatory cytokines and vasoactive peptides, such as interleukin-1β (IL-1β) and vascular endothelial growth factor (VEGF).It has been largely demonstrated that pituitary adenylate cyclase-activating peptide (PACAP) plays a protective effect in DR. In the present study, we investigated the role of PACAP to protect retinal tissue through IL-1β and VEGF expression. Diabetes was induced in rats by streptozotocin (STZ) injection, and one week later a single intravitreal injection of 100 μM PACAP was administrated. Analyses of IL-1β and VEGF levels were performed three weeks after diabetes induction.The results demonstrated that a single intraocular administration of PACAP significantly reduced the expression of IL-1β in diabetic animals. Moreover, it affects VEGF and its receptors (VEGFRs) levels and interferes with their retinal layers distribution as showed by confocal microscopy analysis. In particular, PACAP treatment downregulates VEGF and VEGFRs that are increasingly expressed in STZ-treated animals as compared to controls. These results indicate that PACAP plays an important role to attenuate the early phase of DR.     

高压氧在治疗糖尿病视网膜病变中的应用进展

糖尿病视网膜病变是糖尿病最常见、最主要的微血管并发症之一,其高发病率、高致盲率特征严重威胁着人类的健康和生存质量。长期的高糖状态导致视网膜缺血缺氧是糖尿病视网膜病变的主要发病原因。控制高血糖和改善组织缺氧无疑是防治糖尿病微血管病变的有效方法之一。而高压氧治疗是许多急慢性疾病的首选或辅助治疗方法。已有大量证据表明,高压氧治疗对视网膜静脉阻塞及黄斑囊样水肿、缺血性视神经病变、中心性浆液性脉络膜视网膜病变等眼病安全有效。本文就高压氧在糖尿病视网膜病变中的应用进行综述和讨论。     

Role of matrix metalloproteinase-2 and -9 in the development of diabetic retinopathy

Diabetic retinopathy represents the most common causes of vision loss in patients affected by diabetes mellitus. The cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. One of the earliest changes in the development of retinopathy is the accelerated apoptosis of retinal microvascular cells and the formation of acellular capillaries by unknown mechanism. Results of a recent research suggest an important role of matrix metalloproteinases (MMPs) in the development of diabetic retinopathy. MMPs are a large family of proteinases that remodel extracellular matrix components, and under pathological condition, its induction is considered as a negative regulator of cell survival; and in diabetes, latent MMPs are activated in the retina and its capillary cells, and activation of MMP-2 and -9 induces apoptosis of retinal capillary cells. This review will focus on the MMP-2 and MMP-9 in the diabetic retina with special reference to oxidative stress, mitochondria dysfunction, inflammation and angiogenesis, as well as summarizing the current information linking these proteins to pathogenesis of diabetic retinopathy.     

Angiotensin and diabetic retinopathy

Diabetic retinopathy develops in patients with both type 1 and type 2 diabetes and is the major cause of vision loss and blindness in the working population. In diabetes, damage to the retina occurs in the vasculature, neurons and glia resulting in pathological angiogenesis, vascular leakage and a loss in retinal function. The renin-angiotensin system is a causative factor in diabetic microvascular complications inducing a variety of tissue responses including vasoconstriction, inflammation, oxidative stress, cell hypertrophy and proliferation, angiogenesis and fibrosis. All components of the renin-angiotensin system including the angiotensin type 1 and angiotensin type 2 receptors have been identified in the retina of humans and rodents. There is evidence from both clinical and experimental models of diabetic retinopathy and hypoxic-induced retinal angiogenesis that the renin-angiotensin system is up-regulated. In these situations, retinal dysfunction has been linked to angiotensin-mediated induction of growth factors including vascular endothelial growth factor, platelet-derived growth factor and connective tissue growth factor. Evidence to date indicates that blockade of the renin-angiotensin system can confer retinoprotection in experimental models of diabetic retinopathy and ischemic retinopathy. This review examines the role of the renin-angiotensin system in diabetic retinopathy and the potential of its blockade as a treatment strategy for this vision-threatening disease.     

Ganglioside GM3 inhibits VEGF/VEGFR-2-mediated angiogenesis: direct interaction of GM3 with VEGFR-2

Angiogenesis is associated with growth, invasion, and metastasis of human solid tumors. Aberrant activation of endothelial cells and induction of microvascular permeability by a vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2) signaling pathway is observed in pathological angiogenesis including tumor, wound healing, arthritis, psoriasis, diabetic retinopathy, and others. Here, we show that GM3 regulated the activity of various downstream signaling pathways and biological events through the inhibition of VEGF-stimulated VEGFR-2 activation in vascular endothelial cells in vitro. Furthermore, GM3 strongly blocked VEGF-induced neovascularization in vivo, in models including the chick chorioallantoic membrane and Matrigel plug assay. Interestingly, GM3 suppressed VEGF-induced VEGFR-2 activation by blocking its dimerization and also blocked the binding of VEGF to VEGFR-2 through a GM3-specific interaction with the extracellular domain of VEGFR-2, but not with VEGF. Primary tumor growth in mice was inhibited by subcutaneous injection of GM3. Immunohistochemical analyses showed GM3 inhibition of angiogenesis and tumor cell proliferation. GM3 also resulted in the suppression of VEGF-stimulated microvessel permeability in mouse skin capillaries. These results suggest that GM3 inhibits VEGFR-2-mediated changes in vascular endothelial cell function and angiogenesis, and might be of value in anti-angiogenic therapy.     

miRNA-dependent cross-talk between VEGF and Ang-2 in hypoxia-induced microvascular dysfunction

Ocular neovascularization is a vision-threatening complication of ischemic retinopathy that develops in various ocular disorders, such as retinopathy of prematurity (ROP) and diabetic retinopathy. Both Ang-2 and VEGF are implicated in this pathogenesis. However, their inter-regulation still remains elusive. Competitive endogenous RNAs (ceRNAs) are messenger RNA (mRNA) molecules that affect each other expression through the competition for the shared miRNA. Herein, we assessed whether the expression of Ang-2 and VEGF is interdependent through the sequestration of common miRNAs. Bioinformatics prediction and 3′-UTR luciferase assay revealed that Ang-2 and VEGF is commonly targeted by miR-351. Silencing either Ang-2 or VEGF increases the availabilities of shared miR-351, therefore reduces the activity of Luc-Ang-2 3′-UTR. The interdependence of VEGF and Ang-2 is miRNA- and 3′-UTR dependent, as silencing Dicer abolishes the interdependence. We also found that miR-351 dependency of VEGF-Ang-2 crosstalk occurs in retinal endothelial cells and rat retinas. miR-351 over-expression significantly reduces the level of VEGF and Ang-2 expression in vivo and in vitro. Overall, miRNA-dependent crosstalk between Ang-2 and VEGF plays a role in hypoxia-induced microvascular response. miRNA-based therapy can affect the expression of Ang-2 and VEGF, which represents a therapeutic potential for the treatment of vascular disease.     

The anti-angiogenesis role of FBXW7 in diabetic retinopathy by facilitating the ubiquitination degradation of c-Myc to orchestrate the HDAC2

Diabetic retinopathy (DR) is the most prevalently occurring microvascular complication in diabetic patients that triggers severe visual impairments. The anti-angiogenesis role of FBXW7 has been identified in breast cancer. Therefore, this study intends to decipher the mechanism of FBXW7 in angiogenesis of DR. DR model was induced on mice using high-glucose (HG) and high-fat diet, and retinal microvascular endothelial cells (RMECs) isolated from normal mice were induced with HG, followed by evaluation of FBXW7, Ki67, HIF-1α and VEGF expression by immunofluorescence, immunohistochemistry or Western blot analysis. After gain- and loss-of-function assays in normal and DR mice, angiogenesis was assessed by CD31 fluorescence staining and Western blot analysis. After ectopic expression and silencing experiments in HG-induced RMECs, RMEC proliferation, migration and angiogenesis were, respectively, determined by EdU, Transwell and in vitro angiogenesis assays. The impact of FBXW7 on the ubiquitination of c-Myc was studied by cycloheximide chase assay and proteasome inhibition, and the binding of c-Myc to HDAC2 promoter by dual-luciferase reporter gene experiment. DR mice and HG-induced RMECs possessed down-regulated FBXW7 and up-regulated Ki67, HIF-1α and VEGF. Silencing FBXW7 enhanced angiogenesis in normal mouse retinal tissue, but overexpressing FBXW7 or silencing c-Myc diminished angiogenesis in DR mouse retinal tissue. Overexpressing FBXW7 or silencing c-Myc depressed proliferation, migration and angiogenesis in HG-induced RMECs. FBXW7 induced c-Myc ubiquitination degradation, and c-Myc augmented HDAC2 expression by binding to HDAC2 promoter. Conclusively, our data provided a novel sight of anti-angiogenesis role of FBXW7 in DR by modulating the c-Myc/HDAC2 axis.     

The Decrease of Mineralcorticoid Receptor Drives Angiogenic Pathways in Colorectal Cancer

Angiogenesis plays a crucial role in tumor growth and progression. Low expression of mineralocorticoid receptor (MR) in several malignant tumors correlates with disease recurrence and overall survival. Previous studies have shown that MR expression is decreased in colorectal cancer (CRC). Here we hypothesize that decreased MR expression can contribute to angiogenesis and poor patient survival in colorectal malignancies. In a cohort of CRC patients, we analyzed tumor MR expression, its correlation with tumor microvascular density and its impact on survival. Subsequently, we interrogated the role of MR in angiogenesis in an in vitro model, based on the colon cancer cell line HCT116, ingenierized to re-express a physiologically controlled MR. In CRC, decreased MR expression was associated with increased microvascular density and poor patient survival. In pchMR transfected HCT116, aldosterone or natural serum steroids largely inhibited mRNA expression levels of both VEGFA and its receptor 2/KDR. In CRC, MR activation may significantly decrease angiogenesis by directly inhibiting dysregulated VEGFA and hypoxia-induced VEGFA mRNA expression. In addition, MR activation attenuates the expression of the VEGF receptor 2/KDR, possibly dampening the activation of a VEGFA/KDR dependent signaling pathway important for the survival of tumor cells under hypoxic conditions.     

Identification of the RNA polymerase II subunit hsRPB7 as a novel target of the von Hippel-Lindau protein

Inactivation of the von Hippel-Lindau (VHL) tumor suppressor gene is linked to the hereditary VHL disease and sporadic clear cell renal cell carcinomas (CCRCC). VHL-associated tumors are highly vascularized, a characteristic associated with overproduction of vascular endothelial growth factor (VEGF). The VHL protein (pVHL) is a component of the ubiquitin ligase E3 complex, targeting substrate proteins for ubiquitylation and subsequent proteasomic degradation. Here, we report that the pVHL can directly bind to the human RNA polymerase II seventh subunit (hsRPB7) through its beta-domain, and naturally occurring beta-domain mutations can decrease the binding of pVHL to hsRPB7. Introducing wild-type pVHL into human kidney tumor cell lines carrying endogenous mutant non-functional pVHL facilitates ubiquitylation and proteasomal degradation of hsRPB7, and decreases its nuclear accumulation. pVHL can also suppress hsRPB7-induced VEGF promoter transactivation, mRNA expression and VEGF protein secretion. Together, our results suggest that hsRPB7 is a downstream target of the VHL ubiquitylating complex and pVHL may regulate angiogenesis by targeting hsRPB7 for degradation via the ubiquitylation pathway and preventing VEGF expression.     

Polycomb Repressive Complex 2 Regulates MiR-200b in Retinal Endothelial Cells: Potential Relevance in Diabetic Retinopathy

Glucose-induced augmented vascular endothelial growth factor (VEGF) production is a key event in diabetic retinopathy. We have previously demonstrated that downregulation of miR-200b increases VEGF, mediating structural and functional changes in the retina in diabetes. However, mechanisms regulating miR-200b in diabetes are not known. Histone methyltransferase complex, Polycomb Repressive Complex 2 (PRC2), has been shown to repress miRNAs in neoplastic process. We hypothesized that, in diabetes, PRC2 represses miR-200b through its histone H3 lysine-27 trimethylation mark. We show that human retinal microvascular endothelial cells exposed to high levels of glucose regulate miR-200b repression through histone methylation and that inhibition of PRC2 increases miR-200b while reducing VEGF. Furthermore, retinal tissue from animal models of diabetes showed increased expression of major PRC2 components, demonstrating in vivo relevance. This research established a repressive relationship between PRC2 and miR-200b, providing evidence of a novel mechanism of miRNA regulation through histone methylation.     

高压氧治疗糖尿病视网膜病变的研究进展

糖尿病视网膜病变是糖尿病最常见、最主要的微血管并发症之一,具有高发病率,高致盲率的特点,严重影响了人类的生存质量。控制高血糖和改善组织缺氧无疑是防治糖尿病微血管病变的有效方法。如果对糖尿病视网膜病变及时进行治疗,能延缓其发展并能提高病人的生活质量。近年来,随着对糖尿病发病机制的深入研究,很多方法用于防治糖尿病视网膜病人都取得了一定的疗效。而高压氧治疗是许多急慢性疾病的首选治疗方法。已有基础和临床研究证实,高压氧治疗对糖尿病视网膜病变安全有效。因此,作为一种新疗法,高压氧疗法可能会为糖尿病视网膜病变的治疗带来更广泛的应用前景。     

The genesis of peritumoral vasogenic brain edema and tumor cysts: a hypothetical role for tumor-derived vascular permeability factor.

Cerebral edema and fluid-filled cysts are common accompaniments of brain tumors. They contribute to the mass effect imposed by the primary tumor and are often responsible for a patient''s signs and symptoms. Cerebral edema significantly increases the morbidity associated with tumor biopsy, excision, radiation therapy, and chemotherapy. Both edema and cyst formation are thought to result from a deficiency in the blood-brain barrier, with consequent extravasation of water, electrolytes, and plasma proteins from altered tumor microvessels. The resultant expansion of the cerebral interstitial space contributes to the elevated intracranial pressure observed with brain tumors. Departure from the typical blood-brain barrier microvascular architecture may only partially explain the occurrence of edema and tumor cyst formation. Biochemical mediators have also been implicated in vascular extravasation. Vascular permeability factor or vascular endothelial growth factor (VPF/VEGF) is a protein that has recently been isolated from a variety of tumors including human brain tumors. VPFb is an extraordinarily potent inducer of both microvascular extravasation (edemagenesis) and the formation of new blood vessels (angiogenesis). Its role in tumor growth and progression would therefore appear pivotal. Herein, the author presents an updated account of the investigation of VPF. Historical and clinical perspectives of the study and treatment of tumor associated edema are provided. The efficacy of high-dose dexamethasone in the treatment of neoplastic brain edema is discussed. A hypothetical role for VPF in edemagenesis is presented and discussed. It is hoped that an expanded understanding of the mechanisms responsible for the genesis of edema will ultimately facilitate therapeutic intervention.     

Quantitation of angiogenesis and its correlation with vascular endothelial growth factor expression in astrocytic tumors

OBJECTIVE: To quantitate tumor angiogenesis by establishing intratumoral microvessel density (IMD), to study vascular endothelial growth factor (VEGF) expression in different grades of astrocytomas and to correlate VEGF expression with tumor angiogenesis. STUDY DESIGN: Forty cases of astrocytic neoplasms (10 of each grade) were assessed for tumor angiogenesis and VEGF expression. The panendothelial marker CD31 was used to highlight microvessels. Tumor angiogenesis was quantitated as IMD count per square millimeter in areas of high vascularity, or "hot spots," using an image analyzer. VEGF expression was studied in sections of the tumors. IMD counts per square millimeter and VEGF expression were correlated with histologic grade. The angiogenic potential of tumors as reflected by IMD counts per square millimeter was correlated with the intensity of VEGF expression. RESULTS: Vascular proliferation in high grade gliomas was significantly higher as compared to that in low grade gliomas. IMD count per square millimeter revealed a positive correlation with histologic grade in high grade gliomas. Pilocytic astrocytoma and low grade astrocytoma as a group had comparable IMD counts per square millimeter. VEGF expression paralleled IMD counts in rare high grade gliomas only. CONCLUSION: Malignant progression in astrocytoma is heralded and accompanied by increased angiogenesis. VEGF is an important angiogenic factor in high grade gliomas since its expression parallels the increased IMD counts in these tumors. In contrast, in low grade gliomas, angiogenic factors other than VEGF may contribute to vascular proliferation. The results emphasize the role of antiangiogenic therapy as an optimal tool in therapeutic strategies as they become available.     

Role of YKL-40 in the angiogenesis, radioresistance, and progression of glioblastoma

Glioblastoma is one of the most fatal cancers, characterized by a strong vascularized phenotype. YKL-40, a secreted glycoprotein, is overexpressed in patients with glioblastomas and has potential as a novel tumor biomarker. The molecular mechanisms of YKL-40 in glioblastoma development, however, are poorly understood. Here, we aimed to elucidate the role YKL-40 plays in the regulation of VEGF expression, tumor angiogenesis, and radioresistance. YKL-40 up-regulated VEGF expression in glioblastoma cell line U87, and both YKL-40 and VEGF synergistically promote endothelial cell angiogenesis. Interestingly, long term inhibition of VEGF up-regulated YKL-40. YKL-40 induced coordination of membrane receptor syndecan-1 and integrin αvβ5, and triggered a signaling cascade through FAK(397) to ERK-1 and ERK-2, leading to elevated VEGF and enhanced angiogenesis. In addition, γ-irradiation of U87 cells increased YKL-40 expression that protects cell death through AKT activation and also enhances endothelial cell angiogenesis. Blockade of YKL-40 activity or expression decreased tumor growth, angiogenesis, and metastasis in xenografted animals. Immunohistochemical analysis of human glioblastomas revealed a correlation between YKL-40, VEGF, and patient survival. These findings have shed light on the mechanisms by which YKL-40 promotes tumor angiogenesis and malignancy, and thus provide a therapeutic target for tumor treatment.     

糖尿病视网膜病变的基因治疗

糖尿病视网膜病变（diabetic retinopathy,DR）是糖尿病的主要并发症之一,大量的研究表明DR早期表现为视网膜神经细胞退化性改变,晚期出现新生血管及增殖膜,目前尚没有有效的治疗方法,严重危害患者视力。基因治疗为探索DR的治疗方法提供了新的手段,本文就目前DR的基因治疗研究现状和进展作一综述。