Expression of placenta growth factor is regulated by both VEGF and hyperglycaemia via VEGFR-2

Sexually dimorphic differences in angiogenesis markers predict brain aging trajectories

Aberrant angiogenesis could contribute to cognitive impairment, representing a therapeutic target for preventing dementia. However, most angiogenesis studies focus on model organisms. To test the relevance of angiogenesis to human cognitive aging, we evaluated associations of circulating blood markers of angiogenesis with brain aging trajectories in two deeply phenotyped human cohorts (n=435, age 74 + 9) with longitudinal cognitive assessments, biospecimens, structural brain imaging, and clinical data. Machine learning and traditional statistics revealed sex dimorphic associations of plasma angiogenic growth factors with brain aging outcomes. Specifically, angiogenesis is associated with higher executive function and less brain atrophy in younger women (not men), a directionality of association that reverses around age 75. Higher levels of basic fibroblast growth factor, known for pleiotropic effects on multiple cell types, predicted favorable cognitive trajectories. This work demonstrates the relevance of angiogenesis to brain aging with important therapeutic implications for vascular cognitive impairment and dementia.

Retinopathy of prematurity: A review of pathophysiology and signaling pathways

Retinopathy of prematurity (ROP) is a vasoproliferative disorder of the retina and a leading cause of visual impairment and childhood blindness worldwide. The disease is characterized by an early stage of retinal microvascular degeneration, followed by neovascularization that can lead to subsequent retinal detachment and permanent visual loss. Several factors play a key role during the different pathological stages of the disease. Oxidative and nitrosative stress and inflammatory processes are important contributors to the early stage of ROP. Nitric oxide synthase and arginase play important roles in ischemia/reperfusion-induced neurovascular degeneration. Destructive neovascularization is driven by mediators of the hypoxia-inducible factor pathway, such as vascular endothelial growth factor and metabolic factors (succinate). The extracellular matrix is involved in hypoxia-induced retinal neovascularization. Vasorepulsive molecules (semaphorin 3A) intervene preventing the revascularization of the avascular zone. This review focuses on current concepts about signaling pathways and their mediators, involved in the pathogenesis of ROP, highlighting new potentially preventive and therapeutic modalities. A better understanding of the intricate molecular mechanisms underlying the pathogenesis of ROP should allow the development of more effective and targeted therapeutic agents to reduce aberrant vasoproliferation and facilitate physiological retinal vascular development.

Endothelium dysfunction in hind limb arteries of male Zucker Diabetic-Sprague Dawley rats

Endothelium dysfunction produces peripheral vascular disease comorbidities in type 2 diabetes, including hypertension, and critical limb ischemia. In this study we aimed to test endothelial dysfunction, the vasodilator effects of a proteinase-activated receptor 2 (PAR2) agonist (2fLIGRLO), and thromboxane A₂ synthase inhibitor (ozagrel) on PAR2 vasodilation in hind limb arteries ex vivo, using Zucker Diabetic-Sprague Dawley (ZDSD) rats, a model of type 2 diabetes. Male Sprague Dawley rats (SD) and ZDSD were fed a high-fat content 'Western diet' from 16 to 20 weeks of age (wks) then fed a standard laboratory diet. We identified diabetic ZDSD rats by two consecutive blood glucose measurements > 12.5 mM, based on weekly monitoring. We used acetylcholine, 2fLIGRLO, and nitroprusside with wire-myograph methods to compare relaxations of femoral, and saphenous arteries from diabetic ZDSD (21-23 wks) to age-matched normoglycemic SD. All arteries showed evidence of endothelium dysfunction using acetylcholine (reduced maximum relaxations, reduced sensitivity), and higher sensitivities to 2fLIGRLO, and nitroprusside in ZDSD vs SD. Ozagrel treatment of ZDSD distal segments, and end-branches of saphenous arteries decreased their sensitivities to 2fLIGRLO. We tested aortas for altered expression of endothelium-specific gene targets using PCR array and qPCR. PAR2, and placental growth factor gene transcripts were 1.5, and 4-times higher in ZDSD than SD aortas. Hind limb arteries of ZDSD exhibit endothelium dysfunction having less GPCR agonist induced vasodilation by endothelial NO-release. Different expression of several endothelial genes in ZDSD vs SD aortas, including PAR2, suggests altered inflammatory, and angiogenesis signaling pathways in the endothelium of ZDSD.

Hyperglycaemia up-regulates placental growth factor (PlGF) expression and secretion in endothelial cells via suppression of PI3 kinase-Akt signalling and activation of FOXO1

Placenta growth factor (PlGF) is a pro-inflammatory angiogenic mediator that promotes many pathologies including diabetic complications and atherosclerosis. Widespread endothelial dysfunction precedes the onset of these conditions. As very little is known of the mechanism(s) controlling PlGF expression in pathology we investigated the role of hyperglycaemia in the regulation of PlGF production in endothelial cells. Hyperglycaemia stimulated PlGF secretion in cultured primary endothelial cells, which was suppressed by IGF-1-mediated PI3K/Akt activation. Inhibition of PI3K activity resulted in significant PlGF mRNA up-regulation and protein secretion. Similarly, loss or inhibition of Akt activity significantly increased basal PlGF expression and prevented any further PlGF secretion in hyperglycaemia. Conversely, constitutive Akt activation blocked PlGF secretion irrespective of upstream PI3K activity demonstrating that Akt is a central regulator of PlGF expression. Knock-down of the Forkhead box O-1 (FOXO1) transcription factor, which is negatively regulated by Akt, suppressed both basal and hyperglycaemia-induced PlGF secretion, whilst FOXO1 gain-of-function up-regulated PlGF in vitro and in vivo. FOXO1 association to a FOXO binding sequence identified in the PlGF promoter also increased in hyperglycaemia. This study identifies the PI3K/Akt/FOXO1 signalling axis as a key regulator of PlGF expression and unifying pathway by which PlGF may contribute to common disorders characterised by endothelial dysfunction, providing a target for therapy.

Agents that Modulate Peritoneal Membrane Structure and Function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

Histopathological study with immunohistochemical expression of vascular endothelial growth factor in placentas of hyperglycemic and diabetic women

AIMS AND OBJECTIVES

Spectrum of hyperglycemia in pregnancy includes gestational diabetes mellitus (GDM), mild hyperglycemia, and overt diabetes. Many authors have worked on morphological changes of the placenta in diabetes, but few studies have correlated histopathological changes with vascular endothelial growth factor (VEGF) immunoexpression. The aim of this study was to detect different histopathological changes in various groups of diabetic placentas and to correlate with VEGF immunoexpression.

MATERIALS AND METHODS

Pregnant women were screened for diabetes. They were subsequently divided into normoglycemic (12 cases), GDM (33 cases), mild hyperglycemic (13 cases), and overt diabetes (18 cases). Placentas collected were subjected to histopathological examination. VEGF expressions were studied by immunohistochemistry.

RESULTS

Overt diabetic placenta displayed villous immaturity (44.4%), villous edema (38.9%), chorangiosis (61.1%), fibrinoid substance deposition (38.9%), and Hofbauer cell hyperplasia in 44.4% cases. GDM placentas displayed villous immaturity (45.5%), villous edema (45.5%), chorangiosis (42.4%), and fibrinoid substance deposition in 75.6% cases. Mild hyperglycemic placentas displayed villous immaturity (38.5%), chorangiosis (61.5%), and fibrinoid substance deposition in 61.5% cases. VEGF immunoexpression in GDM placentas was absent in all placental components except syncytiotrophoblast. VEGF expression in overt diabetic placentas was increased in syncytiotrophoblast and capillary endothelium compared to normoglycemic placentas. Mild hyperglycemic placentas expressed similar VEGF expression in all components when compared to normoglycemic controls. However, it displayed weak expression in vessel endothelium.

CONCLUSION

Histopathological changes in diabetic placentas might be a consequence of altered or abnormal VEGF expression in diabetic placentas. Pathogenesis and VEGF expression in GDM placentas are significantly different from overt diabetic placentas.

Genetic interaction between placental growth factor and vascular endothelial growth factor A in psoriasis

Background

Expression of vascular endothelial growth factor A (VEGFA) is increased in chronic inflammatory skin diseases, including psoriasis, and loci for two VEGFA single nucleotide polymorphisms are associated with early‐onset psoriasis (presenting before the age of 40 years). Studies have suggested that expression of placenta growth factor (PGF) is also upregulated in cutaneous inflammation and that VEGFA‐mediated angiogenesis may be dependent on the simultaneous presence of PGF within the skin.

Aim

To elucidate the biological importance of PGF in psoriasis.

Methods

We investigated whether two commonly occurring PGF polymorphisms were associated with early‐onset psoriasis and the genetic interaction between VEGFA and PGF in psoriasis.

Results

We observed a significant (P = 0.04) association between rs2268614 TT and rs2268615 AA genotypes of PGF and early‐onset psoriasis. In addition, genetic complement, comprising the PGF rs2268615 AA genotype and the VEGFA −460 (rs833061) T allele, was significantly associated with the development of early‐onset psoriasis (P < 0.03). We identified that the VEGFA genotype influences PGF expression (P = 0.001) and that mean plasma levels of PGF are lower in patients with severe psoriasis compared with those with mild–moderate disease (P = 0.04).

Conclusion

Our observed genetic interaction between PGF and VEGFA appears relevant to psoriasis, a disease with an angiogenic basis, and may influence development of an antiangiogenic approach to treatment.

Distinct downstream signaling and the roles of VEGF and PlGF in high glucose-mediated injuries of human retinal endothelial cells in culture

Vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) plays a crucial role in breakdown of the blood-retinal barrier due to hyperpermeability in diabetic retinopathy (DR). However, the distinct signaling driven by VEGF and PlGF in the pathogenesis of DR remains unclear. In this study, we investigated VEGF- and PlGF- related signaling pathways and their roles in cultured human microvascular retinal endothelial cells (hRECs) under high glucose conditions (HG; 25 mM). Apoptotic cell death was evaluated, and FITC conjugated bovine serum albumin across monolayer hRECs served as an index of permeability. Western blots were used to assess the protein levels of VEGF and PlGF, as well as the phosphorylation of p38MAPK, STAT1 and Erk1/2. Knockdown of VEGF and PlGF was performed by using siRNA. Following HG treatment, increases of VEGF and PlGF as well as PKC activity were detected in hRECs. Increased phosphorylations of p38MAPK^{Thr180/Thr182}, STAT1^Ser727, and Erk1/2^{Tyr202/Tyr185} as well as VEGFR1^Tyr1213 and VEGFR2^Tyr1175 were also detected in HG-treated hRECs. Inhibition of PKC activity by Go 6976 prevented HG-induced increases of phosphor-Erk1/2 and nitric oxide synthase (NOS1) expressions as well as hyperpermeability, whereas inhibition of p38MAPK pathway by SB203580 selectively suppressed activation of STAT1 and decreased apoptotic cell death under HG conditions. Moreover, VEGF knockdown predominantly inhibited activation of VEGFR2, and phosphorylation of p38MAPK and STAT1, as well as apoptotic cell death in HG-treated hRECs. Nevertheless, PlGF knockdown mainly suppressed phosphorylation of VEGFR1, PKC, and Erk1/2, as well as NOS1 expressions and hyperpermeability. Taken together, we provide evidence demonstrating that HG-induced elevation of PlGF is responsible for hyperpermeability mainly through increasing activation of PKC-Erk1/2-NOS axis via VEGFR1, while HG-induced elevation of VEGF is associated with induction of apoptotic cell death mainly through increasing activation of p38MAPK/STAT1 signaling via VEGFR2.

Plasma Placental Growth Factor Concentrations Are Elevated Well in Advance of Type 2 Diabetes Mellitus Onset: Prospective Data From the WHS

Background

Pathologic angiogenesis is a hallmark of type 2 diabetes mellitus (T2DM) microvascular complications and may modulate adipogenesis and precede the onset of clinical diabetes mellitus; however, longitudinal data are unavailable. Placental growth factor is a potent proangiogenic factor that stimulates the formation of mature and durable vessels but is understudied in human diseases.

Methods and Results

We conducted a prospective case‐cohort study of baseline placental growth factor and incident T2DM within the WHS (Women's Health Study). A random sample of incident T2DM cases (n=491) occurring over a 15‐year follow‐up period was selected and compared with a reference subcohort (n=561). Case subjects were matched to the reference risk set on 5‐year age groups and race. All subjects in this analysis were required to have a hemoglobin A_1c <6.5% at WHS enrollment. Median baseline levels of placental growth factor were higher in case subjects compare to the reference subcohort (18.0 pg/mL versus 17.2 pg/mL) but were only weakly correlated with glycemic measures and not associated with obesity. The risk of diabetes mellitus increased across placental growth factor quartile in the base model (hazard ratios, 1.00, 1.14, 1.46, and 2.14; P‐trend<0.001) and in multivariable‐adjusted models accounting for clinical T2DM risk factors (hazard ratios, 1.00, 1.17, 1.45, and 2.61; P‐trend<0.001). These findings were not substantially altered by further adjustment for high‐sensitivity C‐reactive protein, hemoglobin A_1c, or fasting insulin and remained robust in sensitivity analyses excluding those diagnosed within 2 years of enrollment and those with baseline hemoglobin A_1c ≥6.0%.

Conclusions

Elevated placental growth factor levels are associated with future T2DM independent of traditional risk factors, measures of glycemia, insulin resistance, and high‐sensitivity C‐reactive protein. These prospective data suggest that pathologic angiogenesis may occur well before the clinical onset of T2DM and thus may have relevance to vascular complications of this disease.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00000479.

The role of placental growth factor (PlGF) and its receptor system in retinal vascular diseases

Placental growth factor (PlGF) is a member of the vascular endothelial growth factor (VEGF) family. Upon binding to VEGF- and neuropilin-receptor sub-types, PlGF modulates a range of neural, glial and vascular cell responses that are distinct from VEGF-A. As PlGF expression is selectively associated with pathological angiogenesis and inflammation, its blockade does not affect the healthy vasculature. PlGF actions have been extensively described in tumor biology but more recently there has been accumulating preclinical evidence that indicates that this growth factor could have an important role in retinal diseases. High levels of PlGF have been found in aqueous humor, vitreous and/or retina of patients exhibiting retinopathies, especially those with diabetic retinopathy (DR) and neovascular age-related macular degeneration (nvAMD). Expression of this growth factor seems to correlate closely with many of the key pathogenic features of early and late retinopathy in preclinical models. For example, studies using genetic modification and/or pharmacological treatment to block PlGF in the laser-induced choroidal neovascularization (CNV) model, oxygen-induced retinopathy model, as well as various murine diabetic models, have shown that PlGF deletion or inhibition can reduce neovascularization, retinal leakage, inflammation and gliosis, without affecting vascular development or inducing neuronal degeneration. Moreover, an inhibitory effect of PlGF blockade on retinal scarring in the mouse CNV model has also been recently demonstrated and was found to be unique for PlGF inhibition, as compared to various VEGF inhibition strategies. Together, these preclinical results suggest that anti-PlGF therapy might have advantages over anti-VEGF treatment, and that it may have clinical applications as a standalone treatment or in combination with anti-VEGF. Additional clinical studies are clearly needed to further elucidate the role of PlGF and its potential as a therapeutic target in ocular diseases.

Identification of proteins associated with clinical and pathological features of proliferative diabetic retinopathy in vitreous and fibrovascular membranes

Purpose

To identify the protein profiles in vitreous associated with retinal fibrosis, angiogenesis, and neurite formation in epiretinal fibrovascular membranes (FVMs) in patients with proliferative diabetic retinopathy (PDR).

Methods

Vitreous samples of 5 non-diabetic control patients with vitreous debris and 7 patients with PDR membranes were screened for 507 preselected proteins using the semi-quantitative RayBio® L-series 507 antibody array. From this array, 60 proteins were selected for a custom quantitative antibody array (Raybiotech, Human Quantibody® array), analyzing 7 control patients, 8 PDR patients with FVMs, and 5 PDR patients without FVMs. Additionally, mRNA levels of proteins of interest were measured in 10 PDR membranes and 11 idiopathic membranes and in retinal tissues and cells to identify possible sources of protein production.

Results

Of the 507 proteins screened, 21 were found to be significantly elevated in PDR patients, including neurogenic and angiogenic factors such as neuregulin 1 (NRG1), nerve growth factor receptor (NGFR), placental growth factor (PlGF) and platelet derived growth factor (PDGF). Angiopoietin-2 (Ang2) concentrations were strongly correlated to the degree of fibrosis and the presence of FVMs in patients with PDR. Protein correlation analysis showed PDGF to be extensively co-regulated with other proteins, including thrombospondin-1 and Ang2. mRNA levels of glial-derived and brain/derived neurotrophic factor (GDNF and BDNF) were elevated in PDR membranes. These results were validated in a second study of 52 vitreous samples of 32 PDR patients and 20 control patients.

Conclusions

This exploratory study reveals protein networks that potentially contribute to neurite outgrowth, angiogenesis and fibrosis in the formation of fibrovascular membranes in PDR. We identified a possible role of Ang2 in fibrosis and the formation of FVMs, and of the neurotrophic factors NRG1, PDGF and GDNF in neurite growth that occurs in all FVMs in PDR.

Influences of placental growth factor on mouse retinal vascular development

BACKGROUND

Placental growth factor (PGF) is important for wound-healing and vascular collaterogenesis. PGF deficiency is associated with preeclampsia, a hypertensive disease of human pregnancy. Offspring born to preeclamptic mothers display cognitive impairments and brain vascular and neurostructural deviations. Low PGF production during development may contribute to alterations in offspring cerebrovascular beds. Retina is a readily accessible part of the central nervous system with a well-described pattern of vascular development in mice. Impacts of PGF deficiency were addressed during mouse retinal vascularization.

RESULTS

Retinal vessels were compared between Pgf^-/- and congenic C57BL/6 (B6) mice. PGF deficiency altered neonatal retinal vascularization patterns. Some anatomic alterations persisted into adulthood, particularly in males. Greater arterial wall collagen IV expression was found in adult Pgf^-/- females. Pregnancy (studied in adult females at gestational days 11.5 or 18.5) induced subtle changes upon the mother's retinal vasculature but these pregnancy-induced changes did not differ between genotypes. Significant sex-related differences occurred between adult male and female B6 although sexually dimorphic retinal vascular differences were absent in B6 neonates.

CONCLUSIONS

Overall, PGF has a role in retinal vascular angiogenesis and vessel organization during development but does not affect retinal vessel adaptations in adult females during pregnancy. Developmental Dynamics 246:700-712, 2017. © 2017 Wiley Periodicals, Inc.

Occludin downregulation in high glucose is regulated by SSTR2 via the VEGF/NRP1/Akt signaling pathway in RF/6A cells

Occludin is a tight junction protein that forms the permeability barrier, which is typically disturbed in ischemic associated diseases. The aim of the present study was to determine whether somatostatin receptor 2 (SSTR₂) in RF/6A cells is involved in the modulation of the downregulation of occludin induced by high glucose, and to evaluate the implicated molecules. RF/6A cells were maintained in Dulbecco's modified Eagle medium and treated with 0 or 30 mM D-glucose. SSTR₂ agonist octreotide (OCT), OCT with SSTR₂ antagonist cycle-somatostatin (c-SOM) and neuropilin 1 (NRP1) inhibitor ATWLPPR, respectively, were administered to RF/6A cells under high glucose conditions. Cell apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick-end labeling. Western blot analysis was used to detect the protein expression level of SSTR₂, occludin, vascular endothelial growth factor (VEGF), protein kinase B (Akt), phosphorylated Akt (p-Akt), extracellular signal-related kinases (ERK) and p-ERK proteins. The amount of VEGF released was determined by ELISA. Notably, the level of occludin reduced significantly under high glucose conditions. The results indicated that the administration of OCT prevented the reduction of occludin induced by high glucose, and co-administration with c-SOM reversed the effect of OCT. Increased VEGF secretion and expression of VEGF, p-Akt and p-ERK in RF/6A cells induced by high glucose were inhibited by OCT. ATWLPPR also prevented the downregulation of occludin, but did not inhibit p-Akt and p-ERK levels under high glucose conditions. The current study concluded that the activation of SSTR₂ prevents high glucose-induced occludin downregulation in RF/6A cells, and VEGF, NRP1, p-Akt and p-ERK were implicated in this process. The pharmacological effects of SSTR₂ targeting to endothelium may be used to assess the role of resistance of permeability and anti-inflammation.

Vitreous levels of placental growth factor correlate with activity of proliferative diabetic retinopathy and are not influenced by bevacizumab treatment

PurposePlacental growth factor (PlGF) is a member of the VEGF family that plays an important role in experimental models of diabetic retinopathy and retinal neovascularization. We aimed to investigate whether vitreous levels of PlGF correlated with proliferative diabetic retinopathy (PDR) status, VEGF levels, and bevacizumab treatment. We also analysed PDR membranes to confirm the presence of the PlGF receptor, FLT1, in endothelial cells.MethodsThis was a case-control study: undiluted vitreous fluid samples were obtained from 28 active PDR patients without preoperative bevacizumab treatment, 21 active PDR patients with preoperative bevacizumab treatment, 18 inactive PDR patients, and 21 control patients. PlGF and VEGF levels in samples were determined by enzyme-linked immunosorbent assay. Immunohistochemistry for FLT1 was performed on human PDR membranes.ResultsCompared to control, vitreous PlGF levels were higher in both active PDR without bevacizumab (P<0.0001) and with bevacizumab (P<0.0001). There was no significant difference in PlGF between active PDR patients without and with bevacizumab (P=0.56). Compared to active PDR, PlGF levels were significantly reduced in inactive PDR (P=0.004). PlGF levels were highly correlated with VEGF levels in active PDR. VEGFR1 was expressed in endothelial cells in human PDR membranes.ConclusionThe strong correlation of PlGF levels with PDR disease status and expression of FLT1 in human PDR membranes suggest that PlGF has a pathogenic role in proliferative diabetic retinopathy. Therapeutic targeting of PlGF with agents like aflibercept may be beneficial.

Response to anti-VEGF-A treatment of retinal pigment epithelial cells in vitro

PURPOSE

The neovascular or wet form of age-related macular degeneration is characterized by the growth of abnormal blood vessels in the retina stimulated by vascular endothelial growth factors (VEGF). In the last decade, several anti-VEGF drugs have been developed for treating neovascular diseases of the eyes. This study was conducted to compare the effects of 2 anti-VEGF-A drugs, ranibizumab and aflibercept, on the expression and secretion of VEGF family members in retinal pigment epithelial cells (RPE) in vitro.

METHODS

ARPE-19 cells were exposed for 24 hours to ranibizumab or aflibercept at clinical dose concentration. Cell viability and expression and secretion of VEGF-A, VEGF-B, VEGF-C, and placental growth factor (PlGF) were evaluated respectively by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

RESULTS

Ranibizumab and aflibercept did not affect ARPE-19 cell viability after 24 hours of treatment. Ranibizumab increased expression of VEGF-A and PlGF. On the contrary, expression and secretion of VEGF-C was decreased by ranibizumab. PlGF secretion was not affected by ranibizumab. Aflibercept strongly increased VEGF-A and PlGF expression but reduced their detection on the culture media, and decreased expression and secretion of VEGF-C. No effect on expression and secretion of VEGF-B was observed after exposure to these drugs.

CONCLUSIONS

Ranibizumab and aflibercept exert similar effects on VEGF expression and secretion, leading to establishing an antiangiogenic environment. Increased VEGF-A expression observed in RPE cells treated with these drugs suggests a compensatory response of the cells to the lack of VEGF-A.

Placental expression of the angiogenic placental growth factor is stimulated by both aldosterone and simulated starvation

Aldosterone is an important factor supporting placental growth and fetal development. Recently, expression of placental growth factor (PlGF) has been observed in response to aldosterone exposure in different models of atherosclerosis. Thus, we hypothesized that aldosterone up-regulates growth-adaptive angiogenesis in pregnancy, via increased placental PlGF expression. We followed normotensive pregnant women (n = 24) throughout pregnancy and confirmed these results in a second independent first trimester cohort (n = 36). Urinary tetrahydroaldosterone was measured by gas chromatography-mass spectrometry and corrected for creatinine. Circulating PlGF concentrations were determined by ELISA. Additionally, cultured cell lines, adrenocortical H295R and choriocarcinoma BeWo cells, as well as primary human third trimester trophoblasts were tested in vitro. PlGF serum concentrations positively correlated with urinary tetrahydroaldosterone corrected for creatinine in these two independent cohorts. This observation was not due to PlGF, which did not induce aldosterone production in cultured H295R cells. On the other hand, PlGF expression was specifically enhanced by aldosterone in the presence of forskolin (p < 0.01) in trophoblasts. A pronounced stimulation of PlGF expression was observed with reduced glucose concentrations simulating starvation (p < 0.001). In conclusion, aldosterone stimulates placental PlGF production, enhancing its availability during human pregnancy, a response amplified by reduced glucose supply. Given the crucial role of PlGF in maintaining a healthy pregnancy, these data support a key role of aldosterone for a healthy pregnancy outcome.

Nornicotine and Nicotine Induced Neovascularization via Increased VEGF/PEDF Ratio

PURPOSE

The purpose of the current study was to evaluate the influences of nornicotine and nicotine (NT) in cigarette smoke on the expression of vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) in retinal pigment epithelium cells and human umbilical vein endothelial cells (HUVECs). Furthermore, the angiogenic behaviors of endothelial cells under nornicotine and NT treatment were assessed by using in vitro methods.

METHODS

ARPE-19 cells and HUVECs were treated with different concentrations of either nornicotine or NT for different periods of time. The cell proliferative effect was investigated by using the method of MTT analysis. HUVEC migration and tube formation were assessed by using the scratch assay and Matrigel models. The expressions of VEGF and PEDF gene and protein in both types of cells were examined by real-time RT-PCR and Western blot.

RESULTS

There was no proliferation of ARPE-19 cells following treatment with various concentrations of nornicotine or NT. In contrast, nornicotine or NT significantly stimulated HUVEC proliferation, migration and tube formation. Nornicotine and NT upregulated the expression of VEGF but suppressed the expression of PEDF at both mRNA and protein levels in a dose- and time-dependent manner in ARPE-19 cells and HUVECs.

CONCLUSIONS

Our results demonstrate that nornicotine and NT promoted endothelial cellular proliferation, migration and tube formation of HUVECs in vitro. These effects might be partly due to simultaneous modulation of VEGF/PEDF signaling in ARPE-19 cells and HUVECs.

The pathophysiology of retinopathy of prematurity: an update of previous and recent knowledge

Retinopathy of prematurity (ROP) is a disease that can cause blindness in very low birthweight infants. The incidence of ROP is closely correlated with the weight and the gestational age at birth. Despite current therapies, ROP continues to be a highly debilitating disease. Our advancing knowledge of the pathogenesis of ROP has encouraged investigations into new antivasculogenic therapies. The purpose of this article is to review the findings on the pathophysiological mechanisms that contribute to the transition between the first and second phases of ROP and to investigate new potential therapies. Oxygen has been well characterized for the key role that it plays in retinal neoangiogenesis. Low or high levels of pO2 regulate the normal or abnormal production of hypoxia-inducible factor 1 and vascular endothelial growth factors (VEGF), which are the predominant regulators of retinal angiogenesis. Although low oxygen saturation appears to reduce the risk of severe ROP when carefully controlled within the first few weeks of life, the optimal level of saturation still remains uncertain. IGF-1 and Epo are fundamentally required during both phases of ROP, as alterations in their protein levels can modulate disease progression. Therefore, rhIGF-1 and rhEpo were tested for their abilities to prevent the loss of vasculature during the first phase of ROP, whereas anti-VEGF drugs were tested during the second phase. At present, previous hypotheses concerning ROP should be amended with new pathogenetic theories. Studies on the role of genetic components, nitric oxide, adenosine, apelin and β-adrenergic receptor have revealed new possibilities for the treatment of ROP. The genetic hypothesis that single-nucleotide polymorphisms within the β-ARs play an active role in the pathogenesis of ROP suggests the concept of disease prevention using β-blockers. In conclusion, all factors that can mediate the progression from the avascular to the proliferative phase might have significant implications for the further understanding and treatment of ROP.

Ranibizumab efficiently blocks migration but not proliferation induced by growth factor combinations including VEGF in retinal endothelial cells

Background

Proliferation and migration of retinal endothelial cells (REC) are associated with the development of proliferative diabetic retinopathy. REC proliferation is stimulated by isoforms of vascular endothelial growth factor-A (i.e., VEGF₁₂₁ and VEGF₁₆₅), basic fibroblast growth factor (bFGF), and insulin-like growth factor (IGF-1) of which VEGF₁₆₅ also enhances migration of REC. Effects induced by VEGF-A can be blocked with ranibizumab, a VEGF-binding Fab fragment used in therapy of diabetic macular edema. In this study, we investigated potential angiogenic effects of placental growth factors (PlGF-1, PlGF-2) as other members of the VEGF family and whether the primary action of VEGF₁₆₅ is modulated in the presence of bFGF, IGF-1 and PlGF-1/-2. We also studied how effects of growth factor combinations can be attenuated with ranibizumab.

Methods

Effects of single growth factors or their combinations on proliferation and migration of immortalized bovine retinal endothelial cells (iBREC) were studied with or without ranibizumab or the inhibitor of VEGF receptors KRN951.

Results

Proliferation of iBREC was significantly stimulated by 1–100 ng/ml PlGF-1 or PlGF-2, but additive effects were not observed with various combinations of the tested growth factors. Ranibizumab neutralized VEGF’s effect on proliferation but was not effective when the other growth factors were used in combination with VEGF. bFGF and IGF-1 but not PlGF-1 or PlGF-2 stimulated iBREC migration as single agents, and they further enhanced VEGF-induced migration. The effects of such growth factor combinations including VEGF on migration were efficiently blocked by targeting only VEGF with ranibizumab. Migration induced by VEGF plus bFGF and IGF-1 was also almost completely inhibited by KRN951 interfering with VEGF receptor signalling.

Conclusions

Migration but not proliferation of iBREC induced by combinations of bFGF, IGF-1, PlGF-1 or PlGF-2 together with VEGF is efficiently suppressed by ranibizumab. VEGF-mediated signalling through VEGFR2 seems to control REC migration dominantly in the presence of other growth factors.

Targeting the IRE1α/XBP1 and ATF6 arms of the unfolded protein response enhances VEGF blockade to prevent retinal and choroidal neovascularization

Although anti-vascular endothelial growth factor (VEGF) treatments reduce pathological neovascularization in the eye and in tumors, the regression is often not sustainable or is incomplete. We investigated whether vascular endothelial cells circumvent anti-VEGF therapies by activating the unfolded protein response (UPR) to override the classic extracellular VEGF pathway. Exposure of endothelial cells to VEGF, high glucose, or H2O2 up-regulated the X-box binding protein-1/inositol-requiring protein-1 (IRE1) α and activating transcription factor 6 (ATF6) arms of the UPR compared with untreated cells. This was associated with increased expression in α-basic crystallin (CRYAB), which has previously bound VEGF. siRNA knockdown or pharmacological blockade of IRE1α, ATF6, or CRYAB increased intracellular VEGF degradation and decreased full-length intracellular VEGF. Inhibition of IRE1α, ATF6, or CRYAB resulted in an approximately 40% reduction of in vitro angiogenesis, which was further reduced in combination with a neutralizing antibody against extracellular VEGF. Blockade of IRE1α or ATF6 in the oxygen-induced retinopathy or choroidal neovascularization mouse models caused an approximately 35% reduction in angiogenesis. However, combination therapy of VEGF neutralizing antibody with UPR inhibitors or siRNAs reduced retinal/choroidal neovascularization by a further 25% to 40%, and this inhibition was significantly greater than either treatment alone. In conclusion, activation of the UPR sustains angiogenesis by preventing degradation of intracellular VEGF. The IRE1α/ATF6 arms of the UPR offer a potential therapeutic target in the treatment of pathological angiogenesis.

Neuropilin-2 and vascular endothelial growth factor receptor-3 are up-regulated in human vascular malformations

Despite multiple previous studies in the field of vascular anomalies, the mechanism(s) leading to their development, progression and maintenance has remained unclear. In this study, we have characterized the expression levels of vascular endothelial growth factors and their receptors in 33 human vascular anomalies. Analysis with quantitative real-time PCR and gene-specific assays showed higher expression of neuropilin-2 (NRP2) and VEGF-receptor-3 (VEGFR-3) mRNAs in vascular malformations (VascM) as compared to infantile hemangiomas (Hem). In addition, the expression levels of PlGF and VEGF-C mRNA were significantly higher in venous VascM when compared to the other VascM and Hem. Higher expression of NRP2 and VEGFR-3 were confirmed by immunohistochemistry. To further study the importance of NRP2 and VEGFR-3, endothelial cell (EC) cultures were established from vascular anomalies. It was found that NRP2 and VEGFR-3 mRNA levels were significantly higher in some of the VascM ECs as compared to human umbilical vein ECs which were used as control cells in the study. Furthermore, adenoviral delivery of soluble decoy NRP2 prevented the proliferation of ECs isolated from most of the vascular anomalies. Our findings suggest that NRP2 functions as a factor maintaining the pathological vascular network in these anomalies. Thus, NRP2 could become a potential therapeutic target for the diagnosis and treatment of vascular anomalies.

Effects of lactation and pregnancy on gene expression of endometrium of Holstein cows at day 17 of the estrous cycle or pregnancy

Objectives were to determine effects of lactation and pregnancy on endometrial gene expression on d 17 of the estrous cycle and pregnancy. Heifers (n = 33) were assigned randomly after parturition to lactating (L, n = 17) or nonlactating (NL, n = 16) groups. Cows were subjected to an ovulation synchronization program for a timed artificial insemination (TAI); 10 cows in L and 12 in NL were inseminated. Slaughter occurred 17 d after the day equivalent to TAI, and intercaruncular endometrial tissues were collected. Gene expression was determined by DNA microarray analysis for pregnant (L, n = 8; NL, n = 6) and noninseminated cyclic (L, n = 7; NL, n = 4) cows. Differentially expressed genes were selected with a P-value <0.01 and absolute expression >40. In addition, a fold effect >1.5 was used as a criterion for genes affected by pregnancy. In total, 210 genes were differentially regulated by lactation (136 downregulated and 74 upregulated), and 702 genes were differentially regulated by pregnancy (407 downregulated and 295 upregulated). The interaction effect of pregnancy and lactation affected 61 genes. Genes up- and downregulated in pregnant cows were associated with several gene ontology terms, such as defense response and interferon regulatory factor, cell adhesion, and extracellular matrix. The gene ontology analyses of up- and downregulated genes of lactating cows revealed terms related to immunoglobulin-like fold, immune response, COMM domain, and non-membrane-bounded organelle. Several genes upregulated by lactation, such as IGHG1, IGLL1, IGK, and TRD, were related to immune function, particularly for B cells and γδ T cells. Developmental genes related to limb and neural development and glucose homeostasis (e.g., DKK1, RELN, PDK4) were downregulated by lactation, whereas an interaction was also detected for RELN. The stated genes associated with immune function and developmental genes expressed in the endometrium affected by lactational state are possible candidate genes for interventions to improve fertility of lactating dairy cows.

Effects of intravitreal injection of KH902, a vascular endothelial growth factor receptor decoy, on the retinas of streptozotocin-induced diabetic rats

AIMS

KH902 is a fusion protein that can bind vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) through its binding ligand taken from the domains of VEGF receptor 1 and VEGF receptor 2 (VEGFR2). This study was to investigate the effects of intravitreal injection of KH902 on the retinas of streptozotocin-induced diabetic rats.

METHODS

Two weeks after induction of diabetes, the left eyes of diabetic rats in each group received an intravitreal injection of phosphate-buffered saline (PBS), Avastin or KH902 solution, respectively. Four weeks after intravitreal injection, retinal electrophysiological function and the integrity of inner blood retinal barrier (iBRB) were measured by electroretinogram and Evans blue perfusion. The protein levels of VEGF signal pathway were assayed by western blot. The expression and distribution of claudin-5 and occludin were analysed by double immunofluorescent staining under confocal microscope. The expression of VEGFR2 and PlGF was measured by immunohistochemistry.

RESULTS

Four weeks after intravitreal injection, KH902-treated rats had better retinal electrophysiological function, less retinal vessel leakage and lower levels of VEGFR2, PI3K, AKT, p-AKT, p-ERK and p-SRC than PBS or Avastin-treated rats. The distribution of claudin-5 and occludin in the retinal vessels of diabetic rats treated by KH902 was smoother and more uniform than those of diabetic rats treated by PBS or Avastin. The expression of PlGF and VEGFR2 in KH902-treated rats was decreased compared with those in PBS or Avastin-treated rats.

CONCLUSIONS

KH902 could improve retinal electrophysiological function and inhibit the breakdown of iBRB by inhibiting the expression of VEGFR2, PlGF and PI3K, and the activation of SRC, AKT and ERK.

γ-Secretase and presenilin mediate cleavage and phosphorylation of vascular endothelial growth factor receptor-1

We have reported previously that pigment epithelium-derived factor (PEDF) can, via γ-secretase-mediated events, inhibit VEGF-induced angiogenesis in microvascular endothelial cells by both (a) cleavage and intracellular translocation of a C-terminal fragment of VEGF receptor-1 (VEGFR1) and (b) inhibition of VEGF-induced phosphorylation of VEGFR1. Using site-direct mutagenesis and transfection of wild type and mutated receptors into endothelial cells, we showed that transmembrane cleavage of VEGFR1 occurs at valine 767 and that a switch from valine to alanine at this position prevented cleavage and formation of a VEGFR1 intracellular fragment. Using siRNA to selectively knock down protein-tyrosine phosphatases (PTPs) in endothelial cells, we demonstrated that vascular endothelial PTP is responsible for dephosphorylation of activated VEGFR1. PEDF up-regulation of full-length presenilin 1 (Fl.PS1) facilitated the association of vascular endothelial PTP and VEGFR1. Knockdown of Fl.PS1 prevented dephosphorylation of VEGFR1, whereas up-regulation of Fl.PS1 stimulated VEGFR1 dephosphorylation. Fl.PS1 associated with VEGFR1 within 15 min after PEDF treatment. In conclusion, we determined the PEDF-mediated events responsible for VEGFR1 signaling and identified full-length presenilin as a critical adaptor molecule in the dephosphorylation of VEGFR1. This greater understanding of the regulation of VEGFR1 signaling will help identify novel anti-VEGF therapeutic strategies.

Vascular endothelial growth factor (VEGF) and VEGF-receptor expression in placenta of hyperglycemic pregnant women

Hyperglycemia occurs in a variety of conditions such as overt diabetes, gestational diabetes and mild hyperglycemia, all of which are generally defined based on the oral glucose tolerance test and glucose profiles. Whereas diabetes has received considerable attention in recent decades, few studies have examined the mechanisms of mild hyperglycemia and its associated disturbances. Mild gestational hyperglycemia is associated with macrosomia and a high risk of perinatal mortality. Morphologically, the placenta of these women is characterized by an increase in the number of terminal villi and capillaries, presumably as part of a compensatory mechanism to maintain homeostasis at the maternal-fetal interface. In this study, we analised the expression of VEGF and its receptors VEGFR-1 (Flt-1) and VEGFR-2 (KDR) in placentas from mildly hyperglycemic women. This expression was compared with that of normoglycemic women and women with gestational and overt diabetes. Immunohistochemistry revealed strong staining for VEGF and VEGFR-2 in vascular and trophoblastic cells of mildly hyperglycemic women, whereas the staining for VEGFR-1 was discrete and limited to the trophoblast. The pattern of VEGF and VEGF-receptor reactivity in placentas from women with overt diabetes was similar to that of normoglycemic women. In women with gestational diabetes, strong staining for VEGFR-1 was observed in vascular and trophoblastic cells whereas VEGF and VEGFR-2 were detected only in the trophoblast. The expression of these proteins was confirmed by western blotting, which revealed the presence of an additional band of 75 kDa. In the decidual compartment, only extravillous trophoblast reacted with all antibodies. Morphological analysis revealed collagen deposition around large arteries in all groups with altered glycemia. These findings indicate a placental response to altered glycemia that could have important consequences for the fetus. The change in the placental VEGF/VEGFR expression ratio in mild hyperglycemia may favor angiogenesis in placental tissue and could explain the hypercapillarization of villi seen in this gestational disturbance.

Maternal plasma soluble fms-like tyrosine kinase-1 and placental growth factor levels as biochemical markers of gestational hypertension for Malaysian mothers

AIMS

To establish baseline levels of maternal plasma soluble fms-like tyrosine kinase-1 (sFlt-1) and placental growth factor (PlGF) among normotensive Malaysian mothers and to compare the marker levels between normotensives and mothers with gestational hypertension (GH).

METHODS

Plasma sFlt-1 and PlGF were measured by enzyme-linked immunosorbent assay in an unmatched, case-control study. The results were subjected to normality testing and analyzed by Mann-Whitney U-tests.

RESULTS

Among normotensive mothers, both sFlt-1and PlGF showed a general increase in levels from the 24th to 32nd weeks of pregnancy. PlGF levels in normotensive mothers with gestational diabetes mellitus were reduced compared to those without the disease, while levels of sFlt-1 were elevated. Mothers with GH had reduced levels of PlGF with increased levels of sFlt-1 when compared to normotensive mothers. Among the normotensive mothers followed up until delivery, the inversed pattern of reduced PlGF and increased sFlt-1 marker levels was found in 40% of those who developed GH later in pregnancy.

CONCLUSIONS

Plasma levels of sFlt-1and PlGF in normotensive mothers may be influenced by gestational diabetes mellitus and GH. GH mothers show an inversed pattern of marker levels compared to normotensive mothers.

The balance of autocrine VEGF-A and VEGF-C determines podocyte survival

Podocytes are an important component of the glomerular filtration barrier and are the major source of vascular endothelial growth factor (VEGF) in the glomerulus. The role of VEGF for the phenotype of the glomerular endothelium has been intensely studied; however, the direct effects of autocrine VEGF on the podocyte are largely unknown. In this study we characterized the expression of VEGF isoforms and VEGF receptors in cultured human podocytes and examined direct effects on cell signaling and apoptosis after stimulation with exogenous VEGF or ablation of autocrine VEGF. We identified VEGF-A and VEGF-C as the dominant isoforms in human podocytes and showed that autocrine levels of both are important for the intracellular activation of antiapoptotic phosphoinositol 3-kinase/AKT and suppression of the proapoptotic p38MAPK via VEGFR-2. We demonstrated that ablation of VEGF-A or VEGF-C as well as treatment with bevacizumab or a VEGFR-2/-3 tyrosine kinase inhibitor led to reduced podocyte survival. In contrast, ablation of VEGF-B had no effect on podocyte survival. Treatment with exogenous VEGF-C reversed the effect of VEGF-A neutralization, and exogenous VEGF-A abrogated the effect of VEGF-C ablation in human podocytes. Our results underline the importance of autocrine VEGF for podocyte survival and indicate the delicate balance of VEGF-A and VEGF-C to influence progression of glomerular diseases.

Effect of impaired glucose tolerance during pregnancy on the expression of VEGF receptors in human placenta

The aim of the present study was to determine the expression of vascular endothelial growth factor (VEGF) receptors VEGFR-1, VEGFR-2 and VEGFR-3 in placentas from pregnancies complicated by altered glycaemia. Placentas from women with physiological pregnancies (Group 1), pregnancies complicated by minor degree of glucose intolerance (MDGI, Group 2) and by gestational diabetes mellitus (GDM) treated with insulin (Group 3) were collected. Immunohistochemistry, RT-PCR and western blot were employed to evaluate receptor expression. In the three study groups, VEGFR-1 immunoreactivity was detected in all the placental components. VEGFR-2 immunoreactivity was observed in the vessels of all the placentas from Groups 1 and 2, but only in some placentas of Group 3. VEGFR-3 reactivity was observed in all the components of Group 1; in Groups 2 and 3 reactivity was observed in some portions of the trophoblast or the whole trophoblast, and in the stroma. VEGFR-1 and VEGFR-2 mRNA levels in Groups 2 and 3 were significantly higher compared with Group 1, whereas those of VEGFR-3 were significantly lower. Receptor protein levels were significantly lower in Groups 2 and 3 compared with Group 1. These findings demonstrated dysregulation of expression of the three placental receptors, both in GDM and in MDGI.

Lower uterine artery blood flow and higher endothelin relative to nitric oxide metabolite levels are associated with reductions in birth weight at high altitude

Reduced uteroplacental blood flow is hypothesized to play a key role in altitude-associated fetal growth restriction. It is unknown whether reduced blood flow is a cause or consequence of reduced fetal size. We asked whether determinants of uteroplacental blood flow were altered prior to reduced fetal growth and whether vasoactive and/or angiogenic factors were involved. Women residing at low (LA; 1,600 m, n = 18) or high altitude (HA; 3,100 m, n = 25) were studied during pregnancy (20, 30, and 36 wk) and 4 mo postpartum (PP) using Doppler ultrasound. In each study, endothelin (ET-1), nitric oxide metabolites (NO(x)), soluble fms-like tyrosine kinase (sFlt-1) and placental growth factor (PlGF) levels were quantified. At HA, birth weights were lower (P < 0.01) and small-for-gestational age was more common (P < 0.05) compared with LA. HA was associated with lower uterine artery (UA) diameter (P < 0.01) and blood flow (P < 0.05). Altitude did not affect ET-1, sFlt-1 or PlGF; however, ET-1/NO(x) was greater and NO(x) lower during pregnancy and PP at HA vs. LA. ET-1/NO(x) was negatively associated with birth weight (20 wk, P < 0.01; 36 wk, P = 0.05) at LA and HA combined. At HA, UA blood flow (30 wk) was positively associated with birth weight (dagger). UA blood flow and ET-1/NO(x) levels accounted for 45% (20 wk) and 32% (30 wk) of birth weight variation at LA and HA combined, primarily attributed to effects at HA. We concluded that elevated ET-1/NO(x) and altered determinants of uteroplacental blood flow occur prior to altitude-associated reductions in fetal growth, and therefore, they are likely a cause rather than a consequence of smaller fetal size.

Placenta growth factor not vascular endothelial growth factor A or C can predict the early recurrence after radical resection of hepatocellular carcinoma

The purpose of this study was to evaluate the relationship between the expression of PlGF in tumor tissue and clinical outcomes in HCC patients. Tumor PlGF and vascular endothelial growth factor (VEGF)-A and VEGF-C mRNA were analyzed. Results demonstrated that patients with PlGF expression levels higher than median tended to have early recurrence compared to patients with PlGF expression lower than median (P=.031). In patients with AJCC stage II-III disease, this difference was even more significant (P=.002). In contrast, VEGF-A and VEGF-C could not predict early recurrence-free survival. Since PlGF expression correlated with early recurrence of HCC, PlGF may be an important prognostic indicator in HCC.

Vascular endothelial growth factor C promotes survival of retinal vascular endothelial cells via vascular endothelial growth factor receptor-2

AIM

To determine vascular endothelial growth factor C (VEGF-C) expression in retinal endothelial cells, its antiapoptotic potential and its putative role in diabetic retinopathy.

METHOD

Cultured retinal endothelial cells and pericytes were exposed to tumour necrosis factor (TNF)alpha and VEGF-C expression determined by reverse transcriptase-polymerase chain reaction. Secreted VEGF-C protein levels in conditioned media from endothelial cells were examined by western blotting analysis. The ability of VEGF-C to prevent apoptosis induced by TNFalpha or hyperglycaemia in endothelial cells was assessed by flow cytometry. The expression of VEGF-C in diabetic retinopathy was studied by immunohistochemistry of retinal tissue.

RESULT

VEGF-C was expressed by both vascular endothelial cells and pericytes. TNFalpha up regulated both VEGF-C and vascular endothelial growth factor receptor-2 (VEGFR)-2 expression in endothelial cells in a dose-dependent manner, but had no effect on VEGFR-3. Flow cytometry results showed that VEGF-C prevented endothelial cell apoptosis induced by TNFalpha and hyperglycaemia and that the antiapoptotic effect was mainly via VEGFR-2. In pericytes, the expression of VEGF-C mRNA remained stable on exogenous TNFalpha treatment. VEGF-C immunostaining was increased in retinal vessels in specimens with diabetes compared with retinal specimens from controls without diabetes.

CONCLUSION

In retinal endothelial cells, TNFalpha stimulates the expression of VEGF-C, which in turn protects endothelial cells from apoptosis induced by TNFalpha or hyperglycaemia via VEGFR-2 and thus helps sustain retinal neovascularisation.

Ocular angiogenesis: the role of growth factors

Ocular angiogenesis, the formation of new vessels from the existing vascular tree, is a major cause of severe vision loss. It can affect different structures in the eye, including the retina, choroid and cornea. During the last decade our knowledge in the mechanisms underlying ocular angiogenesis has increased dramatically. We have witnessed the identification of key molecules. Many are classified as growth factors due to their biological properties, regulating angiogenesis. This knowledge has propelled the development of a new group of therapeutic tools, the antiangiogenic agents. This review gives an update on the role of growth factors in ocular angiogenesis from both a basic and a clinical perspective.

Vascular endothelial growth factor is an important determinant of sepsis morbidity and mortality

Sepsis, the systemic inflammatory response to infection, is a leading cause of morbidity and mortality. The mechanisms of sepsis pathophysiology remain obscure but are likely to involve a complex interplay between mediators of the inflammatory and coagulation pathways. An improved understanding of these mechanisms should provide an important foundation for developing novel therapies. In this study, we show that sepsis is associated with a time-dependent increase in circulating levels of vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) in animal and human models of sepsis. Adenovirus-mediated overexpression of soluble Flt-1 (sFlt-1) in a mouse model of endotoxemia attenuated the rise in VEGF and PlGF levels and blocked the effect of endotoxemia on cardiac function, vascular permeability, and mortality. Similarly, in a cecal ligation puncture (CLP) model, adenovirus–sFlt-1 protected against cardiac dysfunction and mortality. When administered in a therapeutic regimen beginning 1 h after the onset of endotoxemia or CLP, sFlt peptide resulted in marked improvement in cardiac physiology and survival. Systemic administration of antibodies against the transmembrane receptor Flk-1 but not Flt-1 protected against sepsis mortality. Adenovirus-mediated overexpression of VEGF but not PlGF exacerbated the lipopolysaccharide-mediated toxic effects. Together, these data support a pathophysiological role for VEGF in mediating the sepsis phenotype.

VEGF-A regulates the expression of VEGF-C in human retinal pigment epithelial cells

AIM

To determine the expression and regulation of vascular endothelial growth factor C (VEGF-C), and its receptor VEGFR-3, in human retinal pigment epithelial (RPE) cells and to consider their angiogenic role in choroidal neovascularisation (CNV).

METHOD

The expression of VEGF-C and VEGFR-3 in cultured human RPE was confirmed by immunostaining, PCR, western blotting, and ELISA. Cultured RPE cells were exposed to VEGF-A and glucose and VEGF-C and VEGFR-3 changes in gene expression determined by RT-PCR. Secreted VEGF-C protein in conditioned media from RPE was examined by western blotting and ELISA analysis. The ability of VEGF-C to elicit tube formation in choroidal endothelial cells was assayed by an in vitro Matrigel model.

RESULT

VEGF-A and glucose upregulated VEGF-C mRNA expression and increased the secretion of VEGF-C protein into the culture medium. VEGF-A, but not glucose alone, stimulated VEGFR-3 mRNA expression. VEGF-C acted synergistically with VEGF-A to promote in vitro tube formation by choroidal endothelial cells.

CONCLUSION

VEGF-A has a critical role in the orchestration of VEGF-C expression in RPE cells and the synergistic action of VEGF-C with VEGF-A may play an important part in the aetiology of CNV.

Upregulation of placental growth factor by vascular endothelial growth factor via a post-transcriptional mechanism

Vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) are key angiogenic stimulators during normal development and wound healing, as well as in a variety of pathological conditions. Recent studies have demonstrated a synergistic effect of VEGF and PlGF in pathological angiogenesis and suggest a role for PlGF in amplifying VEGF action in endothelial cells. We show here in the mouse model of oxygen-induced retinopathy that VEGF is significantly increased (P<0.01) in the retina at both the mRNA and protein levels. In this mouse model, PlGF was significantly upregulated in the retina at the protein level (P<0.01) without a corresponding change in mRNA levels. In cultured human retinal and umbilical vein endothelial cells, VEGF induced the production of PlGF protein by over 10-fold (P<0.01) in a dose-dependent manner through a post-transcriptional mechanism. The increased PlGF expression upon VEGF treatment was significantly reduced by inhibition of the protein kinase C (PKC) and MEK signaling pathways, as well as by treatment with the calcium ionophore A23187. Taken together, our findings demonstrate that VEGF can amplify its effects on endothelial cells by inducing the production of PlGF via a post-transcriptional mechanism in a PKC-dependent manner, and provide a potential link between PKC inhibition and amelioration of vascular complications in the development of angiogenic diseases.