Mice lacking the vascular endothelial growth factor-B gene (Vegfb) have smaller hearts, dysfunctional coronary vasculature, and impaired recovery from cardiac ischemia

Angiogenesis and current antiangiogenic strategies for the treatment of cancer

Angiogenesis is a complex process critical for embryonic development and for survival. It is also a critical player in many pathologic processes, most notably in neoplasia. The cell signaling pathways involved in angiogenesis have become key targets for drug design, with more than 2,500 clinical trials currently under way. This review summarizes the essential features of angiogenesis and discusses therapeutic strategies that have been applied to specific diseases known to be associated with perturbation of normal angiogenic control.

Angio-adaptation in unloaded skeletal muscle: new insights into an early and muscle type-specific dynamic process

With a remarkable plasticity, skeletal muscle adapts to an altered functional demand. Muscle angio-adaptation can either involve the growth or the regression of capillaries as respectively observed in response to endurance training or muscle unloading. Whereas the molecular mechanisms that regulate exercise-induced muscle angiogenesis have been extensively studied, understanding how muscle unloading can in contrast lead to capillary regression has received very little attention. Here we have investigated the consequences of a 9 day time course hindlimb unloading on both capillarization and expression of angio-adaptive molecules in two different rat skeletal muscles. Both soleus and plantaris muscles were atrophied similarly. In contrast, our results have shown different angio-adaptive patterns between these two muscles. Capillary regression occurred only in the soleus, a slow-twitch and oxidative postural muscle. Conversely, the level of capillarization was preserved in the plantaris, a fast-twitch and glycolytic muscle. We have also measured the time course protein expression of key pro- and anti-angiogenic signals (VEGF-A, VEGF-B, VEGF-R2, TSP-1). Our results have revealed that the angio-adaptive response to unloading was muscle-type specific, and that an integrated balance between pro- and anti-angiogenic signals plays a determinant role in regulating this process. In conclusion, we have brought new evidence that measuring the ratio between pro- and anti-angiogenic signals in order to evaluate muscle angio-adaptation was a more accurate approach than analysing the expression of molecular factors taken individually.

VEGF signaling has distinct spatiotemporal roles during heart valve development

Heart valve malformations are one of the most common types of birth defects, illustrating the complex nature of valve development. Vascular endothelial growth factor (VEGF) signaling is one pathway implicated in valve formation, however its specific spatial and temporal roles remain poorly defined. To decipher these contributions, we use two inducible dominant negative approaches in mice to disrupt VEGF signaling at different stages of embryogenesis. At an early step in valve development, VEGF signals are required for the full transformation of endocardial cells to mesenchymal cells (EMT) at the outflow tract (OFT) but not atrioventricular canal (AVC) endocardial cushions. This role likely involves signaling mediated by VEGF receptor 1 (VEGFR1), which is highly expressed in early cushion endocardium before becoming downregulated after EMT. In contrast, VEGFR2 does not exhibit robust cushion endocardium expression until after EMT is complete. At this point, VEGF signaling acts through VEGFR2 to direct the morphogenesis of the AVC cushions into mature, elongated valve leaflets. This latter role of VEGF requires the VEGF-modulating microRNA, miR-126. Thus, VEGF roles in the developing valves are dynamic, transitioning from a differentiation role directed by VEGFR1 in the OFT to a morphogenetic role through VEGFR2 primarily in the AVC-derived valves.

Vascular endothelial growth factor-B gene transfer prevents angiotensin II-induced diastolic dysfunction via proliferation and capillary dilatation in rats

AIMS

heart growth and function are angiogenesis-dependent, but little is known concerning the effects of key regulators of angiogenesis on diastolic heart failure. Here, we tested the hypothesis that local vascular endothelial growth factor-B (VEGF-B) gene therapy prevents left ventricular diastolic dysfunction.

METHODS AND RESULTS

rats were subjected to pressure overload by infusing angiotensin II (33.3 microg/kg/h) for 2 weeks using osmotic minipumps. Intramyocardial delivery of adenoviral vector expressing VEGF-B(167A) improved the angiotensin II-induced diastolic dysfunction compared with LacZ control virus. Local VEGF-B gene transfer increased the mean capillary area in the left ventricle in control and angiotensin II-infused animals, whereas the density of capillaries was not affected. Interestingly, significant increases were noted in Ki67(+) proliferating cells, expression of interleukin1β, and c-kit(+) cells in response to VEGF-B gene transfer. The increase in cardiac c-kit(+) cells was not associated with an induction of stromal cell-derived factor 1α, suggesting no mobilization of cells from bone marrow. Also, the phosphatidylinositol 3-kinase/Akt pathway was activated.

CONCLUSION

VEGF-B gene transfer resulted in prevention of the angiotensin II-induced diastolic dysfunction associated with induction of the Akt pathway, increased proliferation and number of c-kit(+) cells, as well as an increase in the capillary area in the left ventricle. VEGF-B may offer novel therapeutic possibilities for the prevention of the transition from compensated to decompensated cardiac hypertrophy and thereby for the treatment of heart failure.

Structural insights into the binding of vascular endothelial growth factor-B by VEGFR-1(D2): recognition and specificity

The formation of blood vessels (angiogenesis) is a highly orchestrated sequence of events involving crucial receptor-ligand interactions. Angiogenesis is critical for physiological processes such as development, wound healing, reproduction, tissue regeneration, and remodeling. It also plays a major role in sustaining tumor progression and chronic inflammation. Vascular endothelial growth factor (VEGF)-B, a member of the VEGF family of angiogenic growth factors, effects blood vessel formation by binding to a tyrosine kinase receptor, VEGFR-1. There is growing evidence of the important role played by VEGF-B in physiological and pathological vasculogenesis. Development of VEGF-B antagonists, which inhibit the interaction of this molecule with its cognate receptor, would be important for the treatment of pathologies associated specifically with this growth factor. In this study, we present the crystal structure of the complex of VEGF-B with domain 2 of VEGFR-1 at 2.7 A resolution. Our analysis reveals that each molecule of the ligand engages two receptor molecules using two symmetrical binding sites. Based on these interactions, we identify the receptor-binding determinants on VEGF-B and shed light on the differences in specificity towards VEGFR-1 among the different VEGF homologs.

Gene therapy for ischemic heart disease

Current pharmacologic therapy for ischemic heart disease suffers multiple limitations such as compliance issues and side effects of medications. Revascularization procedures often end with need for repeat procedures. Patients remain symptomatic despite maximal medical therapy. Gene therapy offers an attractive alternative to current pharmacologic therapies and may be beneficial in refractory disease. Gene therapy with isoforms of growth factors such as VEGF, FGF and HGF induces angiogenesis, decreases apoptosis and leads to protection in the ischemic heart. Stem cell therapy augmented with gene therapy used for myogenesis has proven to be beneficial in numerous animal models of myocardial ischemia. Gene therapy coding for antioxidants, eNOS, HSP, mitogen-activated protein kinase and numerous other anti apoptotic proteins have demonstrated significant cardioprotection in animal models. Clinical trials have demonstrated safety in humans apart from symptomatic and objective improvements in cardiac function. Current research efforts are aimed at refining various gene transfection techniques and regulation of gene expression in vivo in the heart and circulation to improve clinical outcomes in patients that suffer from ischemic heart disease. In this review article we will attempt to summarize the current state of both preclinical and clinical studies of gene therapy to combat myocardial ischemic disease. This article is part of a Special Section entitled "Special Section: Cardiovascular Gene Therapy".

Transcriptional networks characterize ventricular dysfunction after myocardial infarction: a proof-of-concept investigation

There is currently no method powerful enough to identify patients at risk of developing ventricular dysfunction after myocardial infarction (MI). We aimed to identify major mechanisms related to ventricular dysfunction to predict outcome after MI. Based on the combination of domain knowledge, protein-protein interaction networks and gene expression data, a set of potential biomarkers of ventricular dysfunction after MI was identified. Here we propose a new strategy for the prediction of ventricular dysfunction after MI based on "network activity indices" (NAI), which encode gene network-based signatures and distinguishes between prognostic classes. These models outperformed prognostic models based on standard differential expression analysis. NAI-based models reported high classification accuracy, with a maximum area under the receiver operating characteristic curve (AUC) of 0.75. Furthermore, the classification capacity of these models was validated by performing evaluations on an independent patient cohort (maximum AUC=0.75). These results suggest that transcriptional network-based biosignatures can offer both powerful and biologically-meaningful prediction models of ventricular dysfunction after MI. This research reports a new integrative strategy for identifying transcriptional responses that characterize cardiac repair and for predicting clinical outcome after MI. It can be adapted to other clinical domains, such as those constrained by small molecular datasets and limited translational knowledge. Furthermore, it may reflect clinically-meaningful synergistic effects that cannot be identified by standard analyses.

Intramyocardial VEGF-B167 gene delivery delays the progression towards congestive failure in dogs with pacing-induced dilated cardiomyopathy

RATIONALE

Vascular endothelial growth factor (VEGF)-B selectively binds VEGF receptor (VEGFR)-1, a receptor that does not mediate angiogenesis, and is emerging as a major cytoprotective factor.

OBJECTIVE

To test the hypothesis that VEGF-B exerts non-angiogenesis-related cardioprotective effects in nonischemic dilated cardiomyopathy.

METHODS AND RESULTS

AAV-9-carried VEGF-B(167) cDNA (10(12) genome copies) was injected into the myocardium of chronically instrumented dogs developing tachypacing-induced dilated cardiomyopathy. After 4 weeks of pacing, green fluorescent protein-transduced dogs (AAV-control, n=8) were in overt congestive heart failure, whereas the VEGF-B-transduced (AAV-VEGF-B, n=8) were still in a well-compensated state, with physiological arterial Po(2). Left ventricular (LV) end-diastolic pressure in AAV-VEGF-B and AAV-control was, respectively, 15.0+/-1.5 versus 26.7+/-1.8 mm Hg and LV regional fractional shortening was 9.4+/-1.6% versus 3.0+/-0.6% (all P<0.05). VEGF-B prevented LV wall thinning but did not induce cardiac hypertrophy and did not affect the density of alpha-smooth muscle actin-positive microvessels, whereas it normalized TUNEL-positive cardiomyocytes and caspase-9 and -3 activation. Consistently, activated Akt, a major negative regulator of apoptosis, was superphysiological in AAV-VEGF-B, whereas the proapoptotic intracellular mediators glycogen synthase kinase (GSK)-3beta and FoxO3a (Akt targets) were activated in AAV-control, but not in AAV-VEGF-B. Cardiac VEGFR-1 expression was reduced 4-fold in all paced dogs, suggesting that exogenous VEGF-B(167) exerted a compensatory receptor stimulation. The cytoprotective effects of VEGF-B(167) were further elucidated in cultured rat neonatal cardiomyocytes exposed to 10(-8) mol/L angiotensin II: VEGF-B(167) prevented oxidative stress, loss of mitochondrial membrane potential, and, consequently, apoptosis.

CONCLUSIONS

We determined a novel, angiogenesis-unrelated cardioprotective effect of VEGF-B(167) in nonischemic dilated cardiomyopathy, which limits apoptotic cell loss and delays the progression toward failure.

Integrated protein network and microarray analysis to identify potential biomarkers after myocardial infarction

A significant proportion of patients develop left ventricular (LV) dysfunction and heart failure (HF) after acute myocardial infarction (MI). Existing biomarkers of HF provide limited information after MI. To identify new prognostic biomarkers in MI patients, we designed an approach combining protein interaction networks and microarray analysis of blood cells. Blood samples for RNA and protein analysis were taken from 127 acute MI patients. Echocardiography was performed at one month. Assuming that angiogenesis is related to cardiac repair after MI, a protein-protein interaction network of angiogenesis was constructed and analyzed. Among the 556 proteins and 686 interactions of this network, a cluster of 53 proteins highly specialized in regulation of cell growth was identified. Of these 53 proteins, 38 were found differentially expressed by microarrays between low (< or = 40%) and high (>40%) LV ejection fraction (EF) patients (n = 32). Among these 38 genes, prediction analysis identified a set of three genes able to predict significant LV dysfunction (EF < or = 40%) with an area under the receiver operating characteristic curve (AUC) of 0.82. These three genes-vascular endothelial growth factor B, thrombospondin-1 and placental growth factor-had a stronger predictive value than brain natriuretic peptide and troponin T (AUC of 0.63). Independent validations on protein expression and quantitative PCR datasets confirmed the results. In conclusion, a new strategy is described that allows identifying new potential biomarkers. The three specific biomarkers described here remain to be validated in a larger patient population.

Vascular endothelial growth factor B controls endothelial fatty acid uptake

The vascular endothelial growth factors (VEGFs) are major angiogenic regulators and are involved in several aspects of endothelial cell physiology. However, the detailed role of VEGF-B in blood vessel function has remained unclear. Here we show that VEGF-B has an unexpected role in endothelial targeting of lipids to peripheral tissues. Dietary lipids present in circulation have to be transported through the vascular endothelium to be metabolized by tissue cells, a mechanism that is poorly understood. Bioinformatic analysis showed that Vegfb was tightly co-expressed with nuclear-encoded mitochondrial genes across a large variety of physiological conditions in mice, pointing to a role for VEGF-B in metabolism. VEGF-B specifically controlled endothelial uptake of fatty acids via transcriptional regulation of vascular fatty acid transport proteins. As a consequence, Vegfb(-/-) mice showed less uptake and accumulation of lipids in muscle, heart and brown adipose tissue, and instead shunted lipids to white adipose tissue. This regulation was mediated by VEGF receptor 1 and neuropilin 1 expressed by the endothelium. The co-expression of VEGF-B and mitochondrial proteins introduces a novel regulatory mechanism, whereby endothelial lipid uptake and mitochondrial lipid use are tightly coordinated. The involvement of VEGF-B in lipid uptake may open up the possibility for novel strategies to modulate pathological lipid accumulation in diabetes, obesity and cardiovascular diseases.

Stimulation of functional vessel growth by gene therapy

The process of growing new blood vessels through gene therapy may be difficult but is certainly possible. This review will discuss the most important factors determining the efficacy of angiogenic gene therapy.

Cardiomyocyte VEGFR-1 activation by VEGF-B induces compensatory hypertrophy and preserves cardiac function after myocardial infarction

Mounting evidence indicates that the function of members of the vascular endothelial growth factor (VEGF) family extends beyond blood vessel formation. Here, we show that the prolonged intramyocardial expression of VEGF-A(165) and VEGF-B(167) on adeno-associated virus-mediated gene delivery determined a marked improvement in cardiac function after myocardial infarction in rats, by promoting cardiac contractility, preserving viable cardiac tissue, and preventing remodeling of the left ventricle (LV) over time. Consistent with this functional outcome, animals treated with both factors showed diminished fibrosis and increased contractile myocardium, which were more pronounced after expression of the selective VEGF receptor-1 (VEGFR-1) ligand VEGF-B, in the absence of significant induction of angiogenesis. We found that cardiomyocytes expressed VEGFR-1, VEGFR-2, and neuropilin-1 and that, in particular, VEGFR-1 was specifically up-regulated in hypoxia and on exposure to oxidative stress. VEGF-B exerted powerful antiapoptotic effect in both cultured cardiomyocytes and after myocardial infarction in vivo. Finally, VEGFR-1 activation by VEGF-B was found to elicit a peculiar gene expression profile proper of the compensatory, hypertrophic response, consisting in activation of alphaMHC and repression of betaMHC and skeletal alpha-actin, and an increase in SERCA2a, RYR, PGC1alpha, and cardiac natriuretic peptide transcripts, both in cultured cardiomyocytes and in infarcted hearts. The finding that VEGFR-1 activation by VEGF-B prevents loss of cardiac mass and promotes maintenance of cardiac contractility over time has obvious therapeutic implications.

VEGF-B: a survival, or an angiogenic factor?

Despite its early discovery and high sequence homology to the other VEGF family members, the biological function of VEGF-B remained debatable for a long time, and VEGF-B has received little attention from the field thus far. Recently, we and others have found that (1) VEGF-B is a potent survival factor for different types of cells by inhibiting apoptosis via suppressing the expression of BH3-only protein and other apoptotic/cell death-related genes. (2) VEGF-B has a negligible role in inducing blood vessel growth in most organs. Instead, it is critically required for blood vessel survival. VEGF-B targeting inhibited pathological angiogenesis by abolishing blood vessel survival in different animal models. (3) Using different types of neuro-injury and neurodegenerative disease models, VEGF-B treatment protected endangered neurons from apoptosis without inducing undesired blood vessel growth or permeability. Thus, VEGF-B is the first member of the VEGF family that has a potent survival/anti-apoptotic effect, while lacking a general angiogenic activity. Our work thus advocates that the major function of VEGF-B is to act as a "survival", rather than an "angiogenic" factor and implicates a therapeutic potential of VEGF-B in treating different types of vascular and neurodegenerative diseases.

Role and therapeutic potential of VEGF in the nervous system

The development of the nervous and vascular systems constitutes primary events in the evolution of the animal kingdom; the former provides electrical stimuli and coordination, while the latter supplies oxygen and nutrients. Both systems have more in common than originally anticipated. Perhaps the most striking observation is that angiogenic factors, when deregulated, contribute to various neurological disorders, such as neurodegeneration, and might be useful for the treatment of some of these pathologies. The prototypic example of this cross-talk between nerves and vessels is the vascular endothelial growth factor or VEGF. Although originally described as a key angiogenic factor, it is now well established that VEGF also plays a crucial role in the nervous system. We describe the molecular properties of VEGF and its receptors and review the current knowledge of its different functions and therapeutic potential in the nervous system during development, health, disease and in medicine.

VEGF-B is dispensable for blood vessel growth but critical for their survival, and VEGF-B targeting inhibits pathological angiogenesis

VEGF-B, a homolog of VEGF discovered a long time ago, has not been considered an important target in antiangiogenic therapy. Instead, it has received little attention from the field. In this study, using different animal models and multiple types of vascular cells, we revealed that although VEGF-B is dispensable for blood vessel growth, it is critical for their survival. Importantly, the survival effect of VEGF-B is not only on vascular endothelial cells, but also on pericytes, smooth muscle cells, and vascular stem/progenitor cells. In vivo, VEGF-B targeting inhibited both choroidal and retinal neovascularization. Mechanistically, we found that the vascular survival effect of VEGF-B is achieved by regulating the expression of many vascular prosurvival genes via both NP-1 and VEGFR-1. Our work thus indicates that the function of VEGF-B in the vascular system is to act as a "survival," rather than an "angiogenic" factor and that VEGF-B inhibition may offer new therapeutic opportunities to treat neovascular diseases.

Positive and negative modulation of angiogenesis by VEGFR1 ligands

Vascular endothelial growth factor-A (VEGF-A) is a key target for new antiangiogenic drugs for the treatment of both malignant and nonmalignant human diseases. Vascular effects of VEGF family members are mainly mediated by VEGF receptor 2 (VEGFR2). Conversely, the function and signaling of VEGFR1, which is present on endothelial and nonendothelial cells, are poorly understood. Intriguingly, two of five members in the VEGF family--VEGF-B and placental growth factor (PlGF)--are exclusive ligands for VEGFR1 and do not interact with the other VEGFRs, VEGFR2 and VEGFR3. These VEGFR1-specific ligands may be important therapeutic targets for the treatment of cancer. This Review discusses the distinctive roles of VEGFR1 and its ligands PlGF and VEGF-B in the mediation of angiogenic signaling and considers the therapeutic potential of targeting these particular vascular factors.

Vascular endothelial growth factors in cardiovascular medicine

The discovery of vascular endothelial growth factors (VEGFs) and their receptors has considerably improved the understanding of the development and function of endothelial cells. Each member of the VEGF family appears to have a specific function: VEGF-A induces angiogenesis (i.e. growth of new blood vessels from preexisting ones), placental growth factor mediates both angiogenesis and arteriogenesis (i.e. the formation of collateral arteries from preexisting arterioles), VEGF-C and VEGF-D act mainly as lymphangiogenic factors. The study of the biology of these endothelial growth factors has allowed a major progress in the comprehension of the genesis of the vascular system and its abnormalities observed in various pathologic conditions (atherosclerosis and coronary artery disease). The role of VEGF in the atherogenic process is still unclear, but actual evidence suggests both detrimental (development of a neoangiogenetic process within the atherosclerotic plaque) and beneficial (promotion of collateral vessel formation) effects. VEGF and other angiogenic growth factors (fibroblast growth factor), although initially promising in experimental studies and in initial phase I/II clinical trials in patients with ischemic heart disease or peripheral arterial occlusive disease, have subsequently failed to show significant therapeutic improvements in controlled clinical studies. Challenges still remain about the type or the combination of angiogenic factors to be administered, the form (protein vs. gene), the route, and the duration of administration.

FLT1 and its ligands VEGFB and PlGF: drug targets for anti-angiogenic therapy?

Less than 5 years ago, it was still not clear whether anti-angiogenic drugs would prove successful in the clinic. After numerous patients with cancer or age-related macular degeneration have been treated with these drugs, they have now become part of the standard range of therapeutic tools. Despite this milestone, anti-angiogenic therapy still faces a number of clinical hurdles, such as improving efficacy, avoiding escape and resistance, and minimizing toxicity. Hopefully, other agents with complementary mechanisms, such as those that target placental growth factor, will offer novel opportunities for improved treatment.

Novel role for vascular endothelial growth factor (VEGF) receptor-1 and its ligand VEGF-B in motor neuron degeneration

Although vascular endothelial growth factor-B (VEGF-B) is a homolog of the angiogenic factor VEGF, it has only minimal angiogenic activity, raising the question of whether this factor has other (more relevant) biological properties. Intrigued by the possibility that VEGF family members affect neuronal cells, we explored whether VEGF-B might have a role in the nervous system. Here, we document that the 60 kDa VEGF-B isoform, VEGF-B(186), is a neuroprotective factor. VEGF-B(186) protected cultured primary motor neurons against degeneration. Mice lacking VEGF-B also developed a more severe form of motor neuron degeneration when intercrossed with mutant SOD1 mice. The in vitro and in vivo effects of VEGF-B(186) were dependent on the tyrosine kinase activities of its receptor, Flt1, in motor neurons. When delivered intracerebroventricularly, VEGF-B(186) prolonged the survival of mutant SOD1 rats. Compared with a similar dose of VEGF, VEGF-B(186) was safer and did not cause vessel growth or blood-brain barrier leakiness. The neuroprotective activity of VEGF-B, in combination with its negligible angiogenic/permeability activity, offers attractive opportunities for the treatment of neurodegenerative diseases.

Modulation of angiogenesis by a tetrameric tripeptide that antagonizes vascular endothelial growth factor receptor 1

Vascular endothelial growth factor receptor-1 (VEGFR-1, also known as Flt-1) is involved in complex biological processes often associated to severe pathological conditions like cancer, inflammation, and metastasis formation. Consequently, the search for antagonists of Flt-1 has recently gained a growing interest. Here we report the identification of a tetrameric tripeptide from a combinatorial peptide library built using non-natural amino acids, which binds Flt-1 and inhibits in vitro its interaction with placental growth factor (PlGF) and vascular endothelial growth factor (VEGF) A and B (IC(50) approximately 10 microm). The peptide is stable in serum for 7 days and prevents both Flt-1 phosphorylation and the capillary-like tube formation of human primary endothelial cells stimulated by PlGF or VEGF-A. Conversely, the identified peptide does not interfere in VEGF-induced VEGFR-2 activation. In vivo, this peptide inhibits VEGF-A- and PlGF-induced neoangiogenesis in the chicken embryo chorioallantoic membrane assay. In contrast, in the cornea, where avascularity is maintained by high levels of expression of the soluble form of Flt-1 receptor (sFlt-1) that prevents the VEGF-A activity, the peptide is able to stimulate corneal mouse neovascularization in physiological condition, as reported previously for others neutralizing anti-Flt-1 molecules. This tetrameric tripeptide represents a new, promising compound for therapeutic approaches in pathologies where Flt-1 activation plays a crucial role.

Crystal structure of vascular endothelial growth factor-B in complex with a neutralising antibody Fab fragment

Vascular endothelial growth factor (VEGF) B effects blood vessel formation by binding to VEGF receptor 1. To study the specifics of the biological profile of VEGF-B in both physiological and pathological angiogenesis, a neutralising anti-VEGF-B antibody (2H10) that functions by inhibiting the binding of VEGF-B to VEGF receptor 1 was developed. Here, we present the structural features of the 'highly ordered' interaction of the Fab fragment of this antibody (Fab-2H10) with VEGF-B. Two molecules of Fab-2H10 bind to symmetrical binding sites located at each pole of the VEGF-B homodimer, giving a unique U-shaped topology to the complex that has not been previously observed in the VEGF family. VEGF-B residues essential for binding to the antibody are contributed by both monomers of the cytokine. Our detailed analysis reveals that the neutralising effect of the antibody occurs by virtue of the steric hindrance of the receptor-binding interface. These findings suggest that functional complementarity between VEGF-B and 2H10 can be harnessed both in analysing the therapeutic potential of VEGF-B and as an antagonist of receptor activation.

Human mesenchymal stem cells as a stable source of VEGF-producing cells

Vascular endothelial growth factor (VEGF) is a positive regulator and plays a crucial role in angiogenesis. We demonstrate that VEGF was highly expressed in cultures of human bone marrow-derived mesenchymal stem cells (hMSCs) and the high expression level was maintained during prolonged culture periods (checked up to passage 10). We also confirmed that in vivo hMSCs engrafted into immunodeficient mice could survive and secreted human VEGF. These findings suggest that implantation of hMSCs is a practical means as a source of VEGF production and might be effective in neoangiogenesis.

Correlations of the expression of vascular endothelial growth factor B and its isoforms in hepatocellular carcinoma with clinico-pathological parameters

BACKGROUND

The vascular endothelial growth factor (VEGF) is involved in the growth of cancer cells through angiogenesis. At present the role of VEGF-B has not been clarified completely. We investigated correlations of the expression of VEGF-B and its isoforms, VEGF-B167 and VEGF-B186, by alternative splicing in hepatocellular carcinoma (HCC) with the pathological findings and prognosis.

METHODS

Forty-eight patients with HCC were investigated. We examined the mRNA expression of total VEGF-B, VEGF-B167 and VEGF-B186 in primary HCC and non-cancerous tissues using quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) analysis.

RESULTS

In 16 (33.3%) of 48 HCCs, the expression of total VEGF-B increased compared with the corresponding non-cancerous liver tissues. Regarding the isoforms, the expression of VEGF-B167 and VEGF-B186 was increased in 17 (35.4%) of 48 and 33 (68.75%) of 48 HCCs, respectively. Cases with high expression level of total VEGF-B in HCC significantly correlated with the advanced pathological stage (P < 0.018), tumor multiplicity (P < 0.033), vascular invasion (P < 0.045) and lack of capsule formation (P < 0.027). The result in VEGF-B167 was similar to total VEGF-B.

CONCLUSIONS

Our results indicated that the expression of VEGF-B is correlated with tumor growth and invasiveness in HCC. VEGF-B167 seemed to be the clinically dominant isoform.

Overexpression of vascular endothelial growth factor-B in mouse heart alters cardiac lipid metabolism and induces myocardial hypertrophy

Vascular endothelial growth factor (VEGF)-B is poorly angiogenic but prominently expressed in metabolically highly active tissues, including the heart. We produced mice expressing a cardiac-specific VEGF-B transgene via the alpha-myosin heavy chain promoter. Surprisingly, the hearts of the VEGF-B transgenic mice showed concentric cardiac hypertrophy without significant changes in heart function. The cardiac hypertrophy was attributable to an increased size of the cardiomyocytes. Blood capillary size was increased, whereas the number of blood vessels per cell nucleus remained unchanged. Despite the cardiac hypertrophy, the transgenic mice had lower heart rate and blood pressure than their littermates, and they responded similarly to angiotensin II-induced hypertension, confirming that the hypertrophy does not compromise heart function. Interestingly, the isolated transgenic hearts had less cardiomyocyte damage after ischemia. Significantly increased ceramide and decreased triglyceride levels were found in the transgenic hearts. This was associated with structural changes and eventual lysis of mitochondria, resulting in accumulation of intracellular vacuoles in cardiomyocytes and increased death of the transgenic mice, apparently because of mitochondrial lipotoxicity in the heart. These results suggest that VEGF-B regulates lipid metabolism, an unexpected function for an angiogenic growth factor.

Overexpression of vascular endothelial growth factor-B in mouse heart alters cardiac lipid metabolism and induces myocardial hypertrophy

Vascular endothelial growth factor (VEGF)-B is poorly angiogenic but prominently expressed in metabolically highly active tissues, including the heart. We produced mice expressing a cardiac-specific VEGF-B transgene via the alpha-myosin heavy chain promoter. Surprisingly, the hearts of the VEGF-B transgenic mice showed concentric cardiac hypertrophy without significant changes in heart function. The cardiac hypertrophy was attributable to an increased size of the cardiomyocytes. Blood capillary size was increased, whereas the number of blood vessels per cell nucleus remained unchanged. Despite the cardiac hypertrophy, the transgenic mice had lower heart rate and blood pressure than their littermates, and they responded similarly to angiotensin II-induced hypertension, confirming that the hypertrophy does not compromise heart function. Interestingly, the isolated transgenic hearts had less cardiomyocyte damage after ischemia. Significantly increased ceramide and decreased triglyceride levels were found in the transgenic hearts. This was associated with structural changes and eventual lysis of mitochondria, resulting in accumulation of intracellular vacuoles in cardiomyocytes and increased death of the transgenic mice, apparently because of mitochondrial lipotoxicity in the heart. These results suggest that VEGF-B regulates lipid metabolism, an unexpected function for an angiogenic growth factor.

Identification of mouse heart transcriptomic network sensitive to various heart diseases

Exploring biological systems from highly complex datasets is an important task for systems biology. The present study examined co-expression dynamics of mouse heart transcriptome by spectral graph clustering (SGC) to identify a heart transcriptomic network. SGC of microarray data produced 17 classified biological conditions (called condition spectrum, CS) and co-expression patterns by generating bi-clusters. The results showed dynamic co-expression patterns with a modular structure enriched in heart-related CS (CS-1 and -13) containing abundant heart-related microarray data. Consequently, a mouse heart transcriptomic network was constructed by clique analysis from the gene clusters exclusively present in the heart-related CS; 31 cliques were used for constructing the network. The participating genes in the network were closely associated with important cardiac functions (e. g., development, lipid and glycogen metabolisms). Online Mendelian Inheritance in Man (OMIM) database indicates that mutations of the genes in the network induced serious heart diseases. Many of the tested genes in the network showed significantly altered gene expression in an animal model of hypertrophy. The results suggest that the present approach is critical for constructing a heart-related transcriptomic network and for deducing important genes involved in the pathogenesis of various heart diseases.

Reevaluation of the role of VEGF-B suggests a restricted role in the revascularization of the ischemic myocardium

OBJECTIVE

The endogenous role of the VEGF family member vascular endothelial growth factor-B (VEGF-B) in pathological angiogenesis remains unclear.

METHODS AND RESULTS

We studied the role of VEGF-B in various models of pathological angiogenesis using mice lacking VEGF-B (VEGF-B(-/-)) or overexpressing VEGF-B(167). After occlusion of the left coronary artery, VEGF-B deficiency impaired vessel growth in the ischemic myocardium whereas, in wild-type mice, VEGF-B(167) overexpression enhanced revascularization of the infarct and ischemic border zone. By contrast, VEGF-B deficiency did not affect vessel growth in the wounded skin, hypoxic lung, ischemic retina, or ischemic limb. Moreover, VEGF-B(167) overexpression failed to enhance vascular growth in the skin or ischemic limb.

CONCLUSIONS

VEGF-B appears to have a relatively restricted angiogenic activity in the ischemic heart. These insights might offer novel therapeutic opportunities.

VEGF-B inhibits apoptosis via VEGFR-1-mediated suppression of the expression of BH3-only protein genes in mice and rats

Despite its early discovery and high sequence homology to the other VEGF family members, the biological functions of VEGF-B remain poorly understood. We revealed here a novel function for VEGF-B as a potent inhibitor of apoptosis. Using gene expression profiling of mouse primary aortic smooth muscle cells, and confirming the results by real-time PCR using mouse and rat cell lines, we showed that VEGF-B inhibited the expression of genes encoding the proapoptotic BH3-only proteins and other apoptosis- and cell death-related proteins, including p53 and members of the caspase family, via activation of VEGFR-1. Consistent with this, VEGF-B treatment rescued neurons from apoptosis in the retina and brain in mouse models of ocular neurodegenerative disorders and stroke, respectively. Interestingly, VEGF-B treatment at the dose effective for neuronal survival did not cause retinal neovascularization, suggesting that VEGF-B is the first member of the VEGF family that has a potent antiapoptotic effect while lacking a general angiogenic activity. These findings indicate that VEGF-B may potentially offer a new therapeutic option for the treatment of neurodegenerative diseases.

Myocardial hypertrophy in the absence of external stimuli is induced by angiogenesis in mice

Although studies have suggested a role for angiogenesis in determining heart size during conditions demanding enhanced cardiac performance, the role of EC mass in determining the normal organ size is poorly understood. To explore the relationship between cardiac vasculature and normal heart size, we generated a transgenic mouse with a regulatable expression of the secreted angiogenic growth factor PR39 in cardiomyocytes. A significant change in adult mouse EC mass was apparent by 3 weeks following PR39 induction. Heart weight; cardiomyocyte size; vascular density normalization; upregulation of hypertrophy markers including atrial natriuretic factor, beta-MHC, and GATA4; and activation of the Akt and MAP kinase pathways were observed at 6 weeks post-induction. Treatment of PR39-induced mice with the eNOS inhibitor L-NAME in the last 3 weeks of a 6-week stimulation period resulted in a significant suppression of heart growth and a reduction in hypertrophic marker expression. Injection of PR39 or another angiogenic growth factor, VEGF-B, into murine hearts during myocardial infarction led to induction of myocardial hypertrophy and restoration of myocardial function. Thus stimulation of vascular growth in normal adult mouse hearts leads to an increase in cardiac mass.

Functional significance of vascular endothelial growth factor receptors on gastrointestinal cancer cells

Vascular endothelial growth factor (VEGF) has been shown to be the major mediator of physiologic and pathologic angiogenesis. VEGF was initially thought to be an endothelial cell specific ligand, but recently, VEGF has been shown to mediate tumor cell function via activation of receptors on tumor cells themselves. Here, we review the expression patterns and binding profiles of the VEGF receptors and their ligands on gastrointestinal tumor cells. Furthermore, we describe the current knowledge in regards to the function of these receptors on tumor cells. Elucidating the function of VEGF receptors on tumor cells should help us to better understand the potential mechanisms of action of anti-VEGF therapies.

Transgenic mouse models of angiogenesis and lymphangiogenesis

The development of transgenic technologies in mice has allowed the study of the consequences of genetic alterations on angiogenesis and lymphangiogenesis. This review summarizes the murine models currently available for studies involving the manipulation of angiogenesis and lymphangiogenesis. Abnormal embryonic vascular development, resulting from defects in the formation of a primitive vascular plexus, has been observed in mice lacking vascular endothelial growth factor, vascular endothelial growth factor receptor-1 and -2, transforming growth factor-beta, fibronectin, or vascular endothelial cadherin. Defects in the expansion and remodeling of the embryonic vasculature occur in mice deficient in Tie-1, Tie-2, or angiopoietin-1, and in mice overexpressing neuropilin or angiopoietin-2. Impaired recruitment and investment of mural cells have been observed in mice with disruption of the genes encoding platelet-derived growth factor-B, platelet-derived growth factor-B receptor, and tissue factor. Gene-targeting experiments in mice have identified the EphB/ephrinB system as a critical and rate-limiting determinant of arteriovenous differentiation during embryonic vascular development. Vascular endothelial growth factor-C is necessary for the initial sprouting and migration of lymphatic endothelial cells from embryonic veins, and mice lacking vascular endothelial growth factor-C die prenatally, whereas vascular endothelial growth factor-D is dispensable for embryonic lymphatic development.

Early gene expression profiles during intraoperative myocardial ischemia-reperfusion in cardiac surgery

OBJECTIVE

The effects of cold cardioplegic arrest and reperfusion on human ventricular gene expression are unknown. We tested the hypothesis that intraoperative ischemia-reperfusion under conditions of blood cardioplegic arrest would induce a unique myocardial genomic profile indicative of a cardioprotective response.

METHODS

Right ventricular samples were serially acquired during surgical repair of ventricular septal defect.

RESULTS

Expression profiling revealed 3 patterns of gene expression: (1) increased expression above control levels within 1 hour of cardioplegic arrest, with further amplification during early reperfusion; (2) increased expression limited to the reperfusion phase; and (3) reduced expression during reperfusion. Functional annotation and network mapping of differentially expressed genes indicated activation of multiple signaling pathways regulated by phosphatidylinositide 3'-OH kinase convergent on cellular growth and reparative programs. Also observed was increased expression of genes regulating hemoglobin synthesis, suggesting a novel cardioprotective pathway evoked during ischemia-reperfusion.

CONCLUSION

Reversible myocardial ischemia-reperfusion during cardiac surgery is associated with an immediate genomic response that predicts a net cardioprotective phenotype.

Different networks, common growth factors: shared growth factors and receptors of the vascular and the nervous system

Growth factors and their respective receptors are key regulators during development and for homeostasis of the nervous system. In addition, changes in growth factor function, availability or downstream signaling is involved in many neuropathological disorders like Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, stroke and brain tumours. Research of the recent years revealed that some growth factors, initially discovered as neural growth factors are also affecting blood vessels [e.g. nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF)]. Likewise, vascular growth factors, such as vascular endothelial growth factor (VEGF), which was previously described as an endothelial cell specific mitogen, also affect neural cells. The discovery of shared growth factors affecting the vascular and the nervous system is of relevance for potential therapies of vascular and neurological diseases. This review aims to give an overview about the growing field of common growth factors and receptors within the two different networks.

Clinical and fundamental aspects of angiogenesis and anti-angiogenesis

Insight into the fundamental physiological mechanisms of blood vessel development and neoformation has led to the discovery of multiple angiogenic growth factors and inhibitors. To date, at least 5 angiogenesis inhibitors are readily available for clinical use, mainly in the treatment of cancers and age-related macular degeneration. More inhibitors are yet to come and the indications for their clinical use are expected to broaden. Conversely, the use of angiogenic stimulators, although initially promising in animal models and in small uncontrolled pilot studies in patients with ischaemic heart disease or peripheral arterial occlusive disease, could thus far not show any convincing therapeutic improvement. Challenges still remain as to which angiogenic factor or combination of factors should be administered and in which form (protein versus gene), and what route and duration of administration should be used. Further clinical perspective might come from the recent identification of vascular endothelial growth factor (VEGF) as a modifier of the neurodegenerative disease amyotrophic lateral sclerosis (ALS), and as a promising therapy in the treatment of ALS in preclinical animal models. This review discusses the different clinical trials of angiogenic inhibitors and stimulators, preceded by some fundamental aspects of angiogenesis, giving the clinician a brief overview of the most relevant angiogenic topics.

The prokineticin receptor-1 (GPR73) promotes cardiomyocyte survival and angiogenesis

Prokineticins are potent angiogenic factors that bind to two G protein-coupled receptors to initiate their biological effects. We hypothesize that prokineticin receptor-1 (PKR1/GPR73) signaling may contribute to cardiomyocyte survival or repair in myocardial infarction. Since we showed that prokineticin-2 and PKR1 are expressed in adult mouse heart and cardiac cells, we investigated the role of prokineticin-2 on capillary endothelial cell and cardiomyocyte function. In cultured cardiac endothelial cells, prokineticin-2 or overexpression of PKR1 induces vessel-like formation without increasing VEGF levels. In cardiomyocytes and H9c2 cells, prokineticin-2 or overexpressing PKR1 activates Akt to protect cardiomyocytes against oxidative stress. The survival and angiogenesis promoting effects of prokineticin-2 in cardiac cells were completely reversed by siRNA-PKR1, indicating PKR1 involvement. We thus, further investigated whether intramyocardial gene transfer of DNA encoding PKR1 may rescue the myocardium against myocardial infarction in mouse model. Transient PKR1 gene transfer after coronary ligation reduces mortality and preserves left ventricular function by promoting neovascularization and protecting cardiomyocytes without altering VEGF levels. In human end-stage failing heart samples, reduced PKR1 and prokineticin-2 transcripts and protein levels implicate a more important role for prokineticin-2/PKR1 signaling in heart. Our results suggest that PKR1 may represent a novel therapeutic target to limit myocardial injury following ischemic events.

Angiogenesis in cancer

New growth in the vascular network is important since the proliferation, as well as metastatic spread, of cancer cells depends on an adequate supply of oxygen and nutrients and the removal of waste products. New blood and lymphatic vessels form through processes called angiogenesis and lymphangiogenesis, respectively. Angiogenesis is regulated by both activator and inhibitor molecules. More than a dozen different proteins have been identified as angiogenic activators and inhibitors. Levels of expression of angiogenic factors reflect the aggressiveness of tumor cells. The discovery of angiogenic inhibitors should help to reduce both morbidity and mortality from carcinomas. Thousands of patients have received antiangiogenic therapy to date. Despite their theoretical efficacy, antiangiogeic treatments have not proved beneficial in terms of long-term survival. There is an urgent need for a new comprehensive treatment strategy combining antiangiogenic agents with conventional cytoreductive treatments in the control of cancer.

Vascular endothelial growth factor family of ligands and receptors: review

VEGF signaling often represents a critical rate-limiting step in physiological angiogenesis. The VEGF family comprises seven secreted glycoproteins that are designated VEGF-A, VEGF-B, VEGF-C, VEGF-D, VEGF-E, placental growth factor (PlGF) and VEGF-F. The VEGF family members bind their cognate receptors. The receptors identified so far are designated VEGFR-1, VEGFR-2, VEGFR-3 and the neuropilins (NP-1 and NP-2). We review in this article the biology of the VEGF ligands and the receptors.

Short and long-term effects of hVEGF-A(165) in Cre-activated transgenic mice

We have generated a transgenic mouse where hVEGF-A(165) expression has been silenced with loxP-STOP fragment, and we used this model to study the effects of hVEGF-A(165) over-expression in mice after systemic adenovirus mediated Cre-gene transfer. Unlike previous conventional transgenic models, this model leads to the expression of hVEGF-A(165) in only a low number of cells in the target tissues in adult mice. Levels of hVEGF-A(165) expression were moderate and morphological changes were found mainly in the liver, showing typical signs of active angiogenesis. Most mice were healthy without any major consequences up to 18 months after the activation of hVEGF-A(165) expression. However, one mouse with a high plasma hVEGF-A(165) level died spontaneously because of bleeding into abdominal cavity and having liver hemangioma, haemorrhagic paratubarian cystic lesions and spleen peliosis. Also, two mice developed malignant tumors (hepatocellular carcinoma and lung adenocarcinoma), which were not seen in control mice. We conclude that long-term uncontrolled hVEGF-A(165) expression in only a limited number of target cells in adult mice can be associated with pathological changes, including possible formation of malignant tumors and uncontrolled bleeding in target tissues. These findings have implications for the design of long-term clinical trials using hVEGF-A(165) gene and protein.

Decreased Expression of VEGF-A in Rat Experimental Autoimmune Encephalomyelitis and in Cerebrospinal Fluid Mononuclear Cells from Patients with Multiple Sclerosis

Vascular endothelial growth factor A (VEGF-A) stimulates angiogenesis, but is also pro-inflammatory and plays an important role in the development of neurological disease, where it can have both attenuating and exacerbating effects. VEGF-B, a related molecule, is highly expressed in the central nervous system and seems to be important in neurological injury. A few studies have indicated that VEGF-A may play a role in the pathogenesis of multiple sclerosis (MS), but the role of VEGF-B has not been studied. We have studied the expression of VEGF-A, -B and their receptors by mRNA in situ hybridization, immunohistochemistry and real-time PCR in spinal cord from LEW rats with experimental autoimmune encephalomyelitis (EAE) and in cerebrospinal fluid (CSF) and blood samples from MS patients. Whereas VEGF-A is downregulated in glia in EAE, the infiltrating inflammatory cells are positive for VEGF-A. Expression of VEGF-B and the VEGF receptors is unaltered. In addition, the levels of VEGF-A mRNA in mononuclear cells [corrected] in CSF are lower in MS patients compared with controls. These results demonstrate a complex regulation of VEGF-A during neuroinflammation and suggest that VEGF-B is not involved in the pathogenesis of MS.

Molecular and functional diversity of vascular endothelial growth factors

Members of the vascular endothelial growth factor (VEGF) family are crucial regulators of neovascularization and are classified as cystine knot growth factors that specifically bind cellular receptor tyrosine kinases VEGFR-1, VEGFR-2, and VEGFR-3 with high but variable affinity and selectivity. The VEGF family has recently been expanded and currently comprises seven members: VEGF-A, VEGF-B, placenta growth factor (PlGF), VEGF-C, VEGF-D, viral VEGF (also known as VEGF-E), and snake venom VEGF (also known as VEGF-F). Although all members are structurally homologous, there is molecular diversity among the subtypes, and several isoforms, such as VEGF-A, VEGF-B, and PlGF, are generated by alternative exon splicing. These splicing isoforms exhibit differing properties, particularly in binding to co-receptor neuropilins and heparin. VEGF family proteins play multiple physiological roles, such as angiogenesis and lymphangiogenesis, while exogenous members (viral and snake venom VEGFs) display activities that are unique in physiology and function. This review will highlight the molecular and functional diversity of VEGF family proteins.

Molecular pathways regulating pro-migratory effects of Hedgehog signaling

The Hedgehog proteins play a crucial role in metazoan embryo development. Constitutive activation of the pathway is associated with multiple types of cancer. Recent experimental data suggest involvement of Hedgehog signaling in vascular remodeling, germ cell migration, and axon guidance. The molecular mechanisms underlying these effects remain elusive. Here we show that yolk sac-derived endothelial cells and embryonic fibroblasts can directly respond to the Hedgehog signal by increased migration in an in vitro scratch (wound) assay. We also identify Hedgehog transcriptional target genes in these cells, many of which participate in cell migration, axon guidance, and angiogenesis processes. Inhibition of one such molecular pathway, neuropilin-flavomonooxygenase, blocks Hedgehog-induced cell migration. These findings suggest that Hedgehog signaling directly affects embryonic endothelial and fibroblast cell migration via molecules and pathways known to regulate cell migration in response to a variety of environmental cues.

Angiogenesis, vasculogenesis, and induction of healing in chronic wounds

A key central stage of wound healing requires neovascularization of the wound base granulation tissue. In the adult, neovascularization is now known to occur by both angiogenesis and vasculogenesis. Understanding the biology of these 2 processes offers promising new therapeutic options for patients who suffer from chronic, nonhealing ischemic wounds. The authors review the current literature on the processes of angiogenesis and vasculogenesis and how it relates to wound healing.

Fibroblast growth factor signals regulate a wave of Hedgehog activation that is essential for coronary vascular development

Myocardial infarction and ischemic heart disease are the leading cause of death in the industrial world. Therapies employed for treating these diseases are aimed at promoting increased blood flow to cardiac tissue. Pharmacological induction of new coronary growth has recently been explored, however, clinical trials with known proangiogenic factors have been disappointing. To identify novel therapeutic targets, we have explored signaling pathways that govern embryonic coronary development. Using a combination of genetically engineered mice and an organ culture system, we identified novel roles for fibroblast growth factor (FGF) and Hedgehog (HH) signaling in coronary vascular development. We show that FGF signals promote coronary growth indirectly by signaling to the cardiomyoblast through redundant function of Fgfr1 and Fgfr2. Myocardial FGF signaling triggers a wave of HH activation that is essential for vascular endothelial growth factor (Vegf)-A, Vegf-B, Vegf-C, and angiopoietin-2 (Ang2) expression. We demonstrate that HH is necessary for coronary vascular development and activation of HH signaling is sufficient to promote coronary growth and to rescue coronary defects due to loss of FGF signaling. These studies implicate HH signaling as an essential regulator of coronary vascular development and as a potential therapeutic target for coronary neovascularization. Consistent with this, activation of HH signaling in the adult heart leads to an increase in coronary vessel density.

VEGF receptor signalling - in control of vascular function

Vascular endothelial growth-factor receptors (VEGFRs) regulate the cardiovascular system. VEGFR1 is required for the recruitment of haematopoietic precursors and migration of monocytes and macrophages, whereas VEGFR2 and VEGFR3 are essential for the functions of vascular endothelial and lymphendothelial cells, respectively. Recent insights have shed light onto VEGFR signal transduction and the interplay between different VEGFRs and VEGF co-receptors in development, adult physiology and disease.

Vascular endothelial growth factor co-ordinates proper development of lung epithelium and vasculature

The vasculature forms an intrinsic functional component of the lung and its development must be tightly regulated and coordinated with lung epithelial morphogenesis. Vascular endothelial growth factor (VEGF) and its receptors are highly expressed in a complementary pattern in the lungs during embryonic development. VEGF is expressed by epithelium and the receptors in the surrounding mesenchyme. To determine the function of VEGF in lung formation, we inhibited its activity using a soluble receptor in lung renal capsule grafts. Inhibition of VEGF results in inhibition of vascular development and significant alteration in epithelial development. Epithelial proliferation is inhibited, sacculation is impaired, and the epithelium undergoes apoptosis. Interestingly, when VEGF is attenuated, epithelial differentiation still proceeds, as shown by acquisition of both proximal and distal markers. These data show that VEGF co-ordinates epithelial and vascular development. It is required for the development of the lung vasculature and the vasculature is necessary for epithelial proliferation and morphogenesis, but not for cell differentiation.

Crystal structure of human vascular endothelial growth factor-B: identification of amino acids important for receptor binding

The development of blood vessels (angiogenesis) is critical throughout embryogenesis and in some normal postnatal physiological processes. Pathological angiogenesis has a pivotal role in sustaining tumour growth and chronic inflammation. Vascular endothelial growth factor-B (VEGF-B) is a member of the VEGF family of growth factors that regulate blood vessel and lymphatic angiogenesis. VEGF-B is closely related to VEGF-A and placenta growth factor (PlGF), but unlike VEGF-A, which binds to two receptor tyrosine kinases VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1/KDR), VEGF-B and PlGF bind to VEGFR-1 and not VEGFR-2. There is growing evidence of a role for VEGF-B in physiological and pathological blood vessel angiogenesis. VEGF-B may provide novel therapeutic strategies for the treatment of vascular disease and be a potential therapeutic target in aberrant vessel formation. To help understand at the molecular level the differential receptor binding profile of the VEGF family of growth factors we have determined the crystal structure of human VEGF-B(10-108) at 2.48 Angstroms resolution. The overall structure is very similar to that of the previously determined cysteine-knot motif growth factors: VEGF-A, PlGF and platelet-derived growth factor-B (PDGF-B). We also present a predicted model for the association of VEGF-B with the second domain of its receptor, VEGFR-1. Based on this interaction and the present structural data of the native protein, we have identified several putative residues that could play an important role in receptor recognition and specificity.