Vascular endothelial growth factor B promotes transendothelial fatty acid transport into skeletal muscle via histone modifications during catch-up growth.

Caloric restriction (CR) followed by refeeding, a phenomenon known as catch-up growth (CUG), results in excessive lipid deposition and insulin resistance in skeletal muscle, but the underlying mechanisms remain elusive. Recent reports have suggested that vascular endothelial growth factor B (VEGF-B) controls muscle lipid accumulation by regulating endothelial fatty acid transport. Here, we found continuous activation of VEGF-B signaling and increased lipid uptake in skeletal muscle from CR to refeeding, as well as increased lipid deposition and impaired insulin sensitivity after refeeding in the skeletal muscle of CUG rodents. Inhibiting VEGF-B signaling reduced fatty acid uptake in and transport across endothelial cells. Knockdown of Vegfb in the tibialis anterior (TA) muscle of CUG mice significantly attenuated muscle lipid accumulation and ameliorated muscle insulin sensitivity by decreasing lipid uptake. Furthermore, we showed that aberrant histone methylation (H3K9me1) and acetylation (H3K14ac and H3K18ac) at the Vegfb promoter might be the main cause of persistent VEGF-B upregulation in skeletal muscle during CUG. Modifying these aberrant loci using their related enzymes [PHD finger protein 2 (PHF2) or E1A binding protein p300 (p300)] could regulate VEGF-B expression in vitro. Collectively, our findings indicate that VEGF-B can promote transendothelial lipid transport and lead to lipid overaccumulation and insulin resistance in skeletal muscle during CUG, which might be mediated by histone methylation and acetylation.

VEGF-B ablation in pancreatic ß-cells upregulates insulin expression without affecting glucose homeostasis or islet lipid uptake.

Type 2 diabetes mellitus (T2DM) affects millions of people and is linked with obesity and lipid accumulation in peripheral tissues. Increased lipid handling and lipotoxicity in insulin producing ß-cells may contribute to ß-cell dysfunction in T2DM. The vascular endothelial growth factor (VEGF)-B regulates uptake and transcytosis of long-chain fatty acids over the endothelium to tissues such as heart and skeletal muscle. Systemic inhibition of VEGF-B signaling prevents tissue lipid accumulation, improves insulin sensitivity and glucose tolerance, as well as reduces pancreatic islet triglyceride content, under T2DM conditions. To date, the role of local VEGF-B signaling in pancreatic islet physiology and in the regulation of fatty acid trans-endothelial transport in pancreatic islet is unknown. To address these questions, we have generated a mouse strain where VEGF-B is selectively depleted in ß-cells, and assessed glucose homeostasis, ß-cell function and islet lipid content under both normal and high-fat diet feeding conditions. We found that Vegfb was ubiquitously expressed throughout the pancreas, and that ß-cell Vegfb deletion resulted in increased insulin gene expression. However, glucose homeostasis and islet lipid uptake remained unaffected by ß-cell VEGF-B deficiency.

[Role of VEGF in diseases of the retina]. / Papel del factor de crecimiento del endotelio vascular en las enfermedades de la retina.

Angiogenesis is the process through which new blood vessels are formed, based on preexisting vessels, and is the paradigm of diseases such as cancer and exudative ageassociated macular degeneration (ARMD). Several proangiogenic factors have been identified, such as vascular endothelial growth factor (VEGF), especially VEGF-A, which activates endothelial cells and promotes cell proliferation, migration, and an increase in vascular permeability. VEGF is also involved in the etiopathogenesis of other retinal diseases, such as diabetic macular edema and macular edema secondary to retinal vein occlusion. Likewise, there is increasing evidence that placental growth factor (PIGF) acts recepsynergetically with VEGF in promoting these diseases. Currently, the main treatment for these diseases are the anti-VEGF drugs, aflibercept, ranibizumab and bevacizumab. These agents differ in their molecular structure and mechanism of action.

Vascular endothelial growth factor-B in physiology and disease.

Vascular endothelial growth factor-B (VEGF-B), discovered over 15 years ago, has long been seen as one of the more ambiguous members of the VEGF family. VEGF-B is produced as two isoforms: one that binds strongly to heparan sulfate in the pericellular matrix and a soluble form that can acquire binding via proteolytic processing. Both forms of VEGF-B bind to VEGF-receptor 1 (VEGFR-1) and the neuropilin-1 (NRP-1) coreceptor, which are expressed mainly in blood vascular endothelial cells. VEGF-B-deficient mice and rats are viable without any overt phenotype, and the ability of VEGF-B to induce angiogenesis in most tissues is weak. This has been a puzzle, as the related placenta growth factor (PlGF) binds to the same receptors and induces angiogenesis and arteriogenesis in a variety of tissues. However, it seems that VEGF-B is a vascular growth factor that is more tissue specific and can have trophic and metabolic effects, and its binding to VEGFR-1 shows subtle but important differences compared with that of PlGF. VEGF-B has the potential to induce coronary vessel growth and cardiac hypertrophy, which can protect the heart from ischemic damage as well as heart failure. In addition, VEGF-B is abundantly expressed in tissues with highly active energy metabolism, where it could support significant metabolic functions. VEGF-B also has a role in neuroprotection, but unlike other members of the VEGF family, it does not have a clear role in tumor progression. Here we review what is hitherto known about the functions of this growth factor in physiology and disease.

Endothelium as a gatekeeper of fatty acid transport.

The endothelium transcends all clinical disciplines and is crucial to the function of every organ system. A critical, but poorly understood, role of the endothelium is its ability to control the transport of energy supply according to organ needs. Fatty acids (FAs) in particular represent a key energy source that is utilized by a number of tissues, but utilization must be tightly regulated to avoid potentially deleterious consequences of excess accumulation, including insulin resistance. Recent studies have identified important endothelial signaling mechanisms, involving vascular endothelial growth factor-B, peroxisome proliferator-activated receptor-γ, and apelin, that mediate endothelial regulation of FA transport. In this review, we discuss the mechanisms by which these signaling pathways regulate this key endothelial function.

Vascular endothelial growth factor B prevents the shift in the ocular dominance distribution of visual cortical neurons in monocularly deprived rats.

A key model for examining the activity-dependent development of primary visual cortex (V1) involves the imbalance in activity between the two eyes induced by monocular deprivation (MD). MD early in life causes dramatic changes in the functional and structural organization of mammalian visual cortex. The molecular signals that mediate the effects of MD on the development of visual cortex are not well defined. Neurotrophic factors are important in regulating the plasticity of visual cortex, but the choice of an appropriate growth factor as well as its delivery has proven difficult. Although vascular endothelial growth factor-B (VEGF-B) is a homolog of the angiogenic factor VEGF-A, 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 has a role in the nervous system. In rats, VEGF-B infusion during monocular deprivation (MD) counteracted the normally occurring ocular dominance (OD) shift toward the non-deprived eye so that the deprived eye dominated the VEGF-B-treated cortex after MD. In particular, VEGF-B counteracted the effects of MD without causing detectable alterations in spontaneous discharge or behavior. In conclusion, the simultaneous analysis of visual cortical cell discharge and ocular dominance plasticity suggests that VEGF-B has important effects on the functional architecture of the visual cortex. Therefore, VEGF-B is a new candidate trophic challenge molecule for the visual cortex.

Low levels of vascular endothelial growth factor B predict left ventricular remodeling after acute myocardial infarction.

BACKGROUND: Left ventricular (LV) remodeling is a prognostically important development after acute myocardial infarction (AMI). We recently reported that vascular endothelial growth factor B (VEGFB) may be a potential new biomarker of LV remodeling. This potential biomarker was evaluated in the present study. METHODS AND RESULTS: Patients with AMI (n = 290) and healthy volunteers (n = 42) were included. Plasma VEGFB levels were assessed before discharge. LV remodeling was determined by echocardiography at 6 months' follow-up. Levels of VEGFB were elevated in AMI patients compared with healthy volunteers (1.5-fold; P = .001). Mean plasma levels of VEGFB were 64% higher (P < .001) in patients in whom LV end-diastolic volume (EDV) decreased during follow-up (ΔEDV ≤ 0; n = 144; reverse remodeling) compared with patients in whom ΔEDV increased (ΔEDV > 0; n = 146; remodeling). Using logistic regression models, independent relationships were found between VEGFB (odds ratio [OR] 0.8, 95% confidence interval [CI] 0.7-0.9; P = .0007) and infarct territory (OR 1.7, 95% CI 1.1-2.8; P = .02). Patients with anterior MI and low levels of VEGFB had the highest risk of remodeling. VEFGB outperformed N-terminal pro-B-type natriuretic peptide to predict LV remodeling, and low levels of VEGFB (<100 pg/mL) provided a specificity of 90%. Adding VEGFB to a clinical model involving age, sex, smoking habit, and infarct territory resulted in a net reclassification index of 11.7%. CONCLUSIONS: Plasma levels of VEGFB increase after AMI and correlate with preservation of cardiac function. Low levels of VEGFB accurately predict LV remodeling. Therefore, circulating VEGFB may have clinical utility in the identification of patients at high risk of remodeling after AMI.

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 interleukin1ß, 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.

Vascular endothelial growth factor-B acts as a coronary growth factor in transgenic rats without inducing angiogenesis, vascular leak, or inflammation.

BACKGROUND: Vascular endothelial growth factor-B (VEGF-B) binds to VEGF receptor-1 and neuropilin-1 and is abundantly expressed in the heart, skeletal muscle, and brown fat. The biological function of VEGF-B is incompletely understood. METHODS AND RESULTS: Unlike placenta growth factor, which binds to the same receptors, adeno-associated viral delivery of VEGF-B to mouse skeletal or heart muscle induced very little angiogenesis, vascular permeability, or inflammation. As previously reported for the VEGF-B(167) isoform, transgenic mice and rats expressing both isoforms of VEGF-B in the myocardium developed cardiac hypertrophy yet maintained systolic function. Deletion of the VEGF receptor-1 tyrosine kinase domain or the arterial endothelial Bmx tyrosine kinase inhibited hypertrophy, whereas loss of VEGF-B interaction with neuropilin-1 had no effect. Surprisingly, in rats, the heart-specific VEGF-B transgene induced impressive growth of the epicardial coronary vessels and their branches, with large arteries also seen deep inside the subendocardial myocardium. However, VEGF-B, unlike other VEGF family members, did not induce significant capillary angiogenesis, increased permeability, or inflammatory cell recruitment. CONCLUSIONS: VEGF-B appears to be a coronary growth factor in rats but not in mice. The signals for the VEGF-B-induced cardiac hypertrophy are mediated at least in part via the endothelium. Because cardiomyocyte damage in myocardial ischemia begins in the subendocardial myocardium, the VEGF-B-induced increased arterial supply to this area could have therapeutic potential in ischemic heart disease.

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.

Molecular diversity of VEGF-A as a regulator of its biological activity.

The vascular endothelial growth factor (VEGF) family of proteins regulates blood flow, growth, and function in both normal physiology and disease processes. VEGF-A is alternatively spliced to form multiple isoforms, in two subfamilies, that have specific, novel functions. Alternative splicing of exons 5-7 of the VEGF gene generates forms with differing bioavailability and activities, whereas alternative splice-site selection in exon 8 generates proangiogenic, termed VEGF(xxx), or antiangiogenic proteins, termed VEGF(xxx)b. Despite its name, emerging roles for VEGF isoforms on cell types other than endothelium have now been identified. Although VEGF-A has conventionally been considered to be a family of proangiogenic, propermeability vasodilators, the identification of effects on nonendothelial cells, and the discovery of the antiangiogenic subfamily of splice isoforms, has added further complexity to their regulation of microvascular function. The distally spliced antiangiogenic isoforms are expressed in normal human tissue, but downregulated in angiogenic diseases, such as cancer and proliferative retinopathy, and in developmental pathologies, such as Denys Drash syndrome and preeclampsia. Here, we examine the molecular diversity of VEGF-A as a regulator of its biological activity and compare the role of the pro- and antiangiogenic VEGF-A splice isoforms in both normal and pathophysiological processes.

Activated forms of VEGF-C and VEGF-D provide improved vascular function in skeletal muscle.

The therapeutic potential of vascular endothelial growth factor (VEGF)-C and VEGF-D in skeletal muscle has been of considerable interest as these factors have both angiogenic and lymphangiogenic activities. Previous studies have mainly used adenoviral gene delivery for short-term expression of VEGF-C and VEGF-D in pig, rabbit, and mouse skeletal muscles. Here we have used the activated mature forms of VEGF-C and VEGF-D expressed via recombinant adeno-associated virus (rAAV), which provides stable, long-lasting transgene expression in various tissues including skeletal muscle. Mouse tibialis anterior muscle was transduced with rAAV encoding human or mouse VEGF-C or VEGF-D. Two weeks later, immunohistochemical analysis showed increased numbers of both blood and lymph vessels, and Doppler ultrasound analysis indicated increased blood vessel perfusion. The lymphatic vessels further increased at the 4-week time point were functional, as shown by FITC-lectin uptake and transport. Furthermore, receptor activation and arteriogenic activity were increased by an alanine substitution mutant of human VEGF-C (C137A) having an increased dimer stability and by a chimeric CAC growth factor that contained the VEGF receptor-binding domain flanked by VEGF-C propeptides, but only the latter promoted significantly more blood vessel perfusion when compared to the other growth factors studied. We conclude that long-term expression of VEGF-C and VEGF-D in skeletal muscle results in the generation of new functional blood and lymphatic vessels. The therapeutic value of intramuscular lymph vessels in draining tissue edema and lymphedema can now be evaluated using this model system.

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.

VEGF in physiological process and thyroid disease.

Angiogenesis is a physiological process involving the growth of new vessels from pre-existing vasculature. Vascular endothelial growth factor (VEGF) is an important regulator of both benign and malignant disease processes in the thyroid gland. The VEGF family includes seven members respectively named VEGF-A, also known as VPF (vascular permeability factor), VEGF-B, VEGF-C, VEGF-D, all described in mammals, VEGF-E (found in Parapoxviridae), VEGF-F (also called svVEGF, for snake venom VEGF, found in viper venom) and PlGF (placental growth factor). Thyrocytes are able to synthesize and secrete VEGF. VEGF-A is implicated in tumour growth and metastasis via blood vessels while VEGF-C and VEGF-D, involved in lymphangiogenesis, favour metastasis to the cervical lymph nodes in papillary thyroid carcinomas. High levels of VEGF expression in thyroid tumour cells may correlate with a poorer outcome in papillary thyroid carcinomas. Because of its important role in malignant angiogenesis, VEGF is the preferential target of a new variety of therapeutic agents called angiogenesis inhibitors.

Expression and functions of the vascular endothelial growth factors and their receptors in human basophils.

Angiogenesis is a multistep complex phenomenon critical for several inflammatory and neoplastic disorders. Basophils, normally confined to peripheral blood, can infiltrate the sites of chronic inflammation. In an attempt to obtain insights into the mechanism(s) underlying human basophil chemotaxis and its role in inflammation, we have characterized the expression and function of vascular endothelial growth factors (VEGFs) and their receptors in these cells. Basophils express mRNA for three isoforms of VEGF-A (121, 165, and 189) and two isoforms of VEGF-B (167 and 186). Peripheral blood and basophils in nasal polyps contain VEGF-A localized in secretory granules. The concentration of VEGF-A in basophils was 144.4 +/- 10.8 pg/10(6) cells. Immunologic activation of basophils induced the release of VEGF-A. VEGF-A (10-500 ng/ml) induced basophil chemotaxis. Supernatants of activated basophils induced an angiogenic response in the chick embryo chorioallantoic membrane that was inhibited by an anti-VEGF-A Ab. The tyrosine kinase VEGFR-2 (VEGFR-2/KDR) mRNA was expressed in basophils. These cells also expressed mRNA for the soluble form of VEGFR-1 and neuropilin (NRP)1 and NRP2. Flow cytometric analysis indicated that basophils express epitopes recognized by mAbs against the extracellular domains of VEGFR-2, NRP1, and NRP2. Our data suggest that basophils could play a role in angiogenesis and inflammation through the expression of several forms of VEGF and their receptors.

Vascular endothelial growth factor-B (VEGFB) stimulates neurogenesis: evidence from knockout mice and growth factor administration.

Vascular endothelial growth factor-B (VEGFB) is an angiogenic and neuroprotective protein that reduces hypoxic and ischemic neuronal injury. To determine if VEGFB also regulates neurogenesis in the adult brain, we studied the effects of VEGFB administration in vitro and in vivo, as well as the effect of VEGFB gene knockout (KO) in mice, on bromodeoxyuridine (BrdU) incorporation and expression of immature neuronal markers in the subgranular zone (SGZ) of the hippocampal dentate gyrus and the forebrain subventricular zone (SVZ). Intracerebroventricular VEGFB administration increased BrdU incorporation into cells of neuronal lineage both in vitro and in vivo, and VEGFB-KO mice showed impaired neurogenesis, consistent with a neurogenesis-promoting effect of VEGFB. In addition, intraventricular administration of VEGFB restored neurogenesis to wild-type levels in VEGFB-KO mice. These results suggest a role for VEGFB in the regulation of adult neurogenesis, which could have therapeutic implications for diseases associated with central neuronal loss.

Transgenic overexpression of vascular endothelial growth factor-B isoforms by endothelial cells potentiates postnatal vessel growth in vivo and in vitro.

Vascular endothelial growth factors (VEGFs) play significant roles in endothelial growth, survival, and function, and their potential use as therapeutic agents to promote the revascularization of ischemic tissues in being avidly explored. VEGF-A has received most attention, as it is a potent stimulator of vascular growth. Results in clinical trials of VEGF-A as a therapeutic agent have fallen short of high expectations because of serious edematous side effects caused by its activity in promoting vascular permeability. VEGF-B, a related factor, binds some of the VEGF-A receptors but not to VEGF receptor 2, which is implicated in the vascular permeability promoting activity of VEGF-A. Despite little in vitro evidence to date for the ability of Vegf-B to directly promote angiogenesis, recent data indicate that it may promote postnatal vascular growth in mice, suggesting that it may have potential therapeutic application. We have specifically studied the effects of VEGF-B on vascular growth in vivo and on angiogenesis in vitro by analyzing transgenic mice in which individual isoforms (VEGFB167Tg and VEGFB186Tg) of VEGF-B are overexpressed in endothelial cells. VEGFB167Tg and VEGFB186Tg mice displayed enhanced vascular growth in the Matrigel assay in vivo and during cutaneous wound healing. In the aortic explant assay, explants from VEGFB167Tg and VEGFB186Tg mice displayed elevated vascular growth, suggesting a direct effect of VEGF-B isoforms in potentiating angiogenesis. These data support the use of VEGF-B as a therapeutic agent to promote vascular growth, in part, by potentiating angiogenesis. Furthermore, the lack of vascular permeability activity associated with either transgenic overexpression of the VEGF-B gene in endothelial cells or application of VEGF-B protein to the skin of mice in the Miles assay indicates that use of VEGF-B as a therapy should not be associated with edematous side effects.