Vascular endothelial growth factor (VEGF) is a key regulator of physiological angiogenesis during embryogenesis, skeletal growth and reproductive functions. VEGF has also been implicated in pathological angiogenesis associated with tumors, intraocular neovascular disorders and other conditions. The biological effects of VEGF are mediated by two receptor tyrosine kinases (RTKs), VEGFR-1 and VEGFR-2, which differ considerably in signaling properties. Non-signaling co-receptors also modulate VEGF RTK signaling. Currently, several VEGF inhibitors are undergoing clinical testing in several malignancies. VEGF inhibition is also being tested as a strategy for the prevention of angiogenesis, vascular leakage and visual loss in age-related macular degeneration.

The biology of VEGF and its receptors.

The establishment of a vascular supply is required for organ development and differentiation as well as for tissue repair and reproductive functions in the adult1 Neovascularization (angiogenesis) is also implicated in the pathogenesis of a number of disorders These include: proliferative retinopathies, age-related macular degeneration, tumors, rheumatoid arthritis, and psoriasis1,2 A strong correlation has been noted between density of microvessels in primary breast cancers and their nodal metastases and patient survival3 Similarly, a correlation has been reported between vascularity and invasive behavior in several other tumors4–6

The biology of vascular endothelial growth factor

ANGIOGENESIS is required for a wide variety of physiological and pathological processes1. The endothelial cell-specific mitogen vascular endothelial growth factor (VEGF)2,3 is a major mediator of pathological angiogenesis4–6. Also, the expression of VEGF and its two receptors, Flt-1 and Flk-1/KDR, is related to the formation of blood vessels in mouse and rat embryos7–10. Mice homozygous for mutations that inactivate either receptor die in utero between days 8.5 and 9.5 (refs 11,12). However, ligand(s) other than VEGF might activate such receptors13,14. To assess the role of VEGF directly, we disrupted the VEGF gene in embryonic stem cells. Here we report the unexpected finding that loss of a single VEGF allele is lethal in the mouse embryo between days 11 and 12. Angiogenesis and blood-island formation were impaired, resulting in several developmental anomalies. Furthermore, VEGF-null embryonic stem cells exhibit a dramatically reduced ability to form tumours in nude mice.

/pdf/heterozygous-embryonic-lethality-induced-by-targeted-rko74mua9o.pdf

Heterozygous embryonic lethality induced by targeted inactivation of the VEGF gene.

A recent explosion in newly discovered vascular growth factors has coincided with exploitation of powerful new genetic approaches for studying vascular development. An emerging rule is that all of these factors must be used in perfect harmony to form functional vessels. These new findings also demand re-evaluation of therapeutic efforts aimed at regulating blood vessel growth in ischaemia, cancer and other pathological settings.

Vascular-specific growth factors and blood vessel formation

Vascular endothelial growth factor (VEGF) is a highly specific mitogen for vascular endothelial cells. Five VEGF isoforms are generated as a result of alternative splicing from a single VEGF gene. These isoforms differ in their molecular mass and in biological properties such as their ability to bind to cell-surface heparan-sulfate proteoglycans. The expression of VEGF is potentiated in response to hypoxia, by activated oncogenes, and by a variety of cytokines. VEGF induces endothelial cell proliferation, promotes cell migration, and inhibits apoptosis. In vivo VEGF induces angiogenesis as well as permeabilization of blood vessels, and plays a central role in the regulation of vasculogenesis. Deregulated VEGF expression contributes to the development of solid tumors by promoting tumor angiogenesis and to the etiology of several additional diseases that are characterized by abnormal angiogenesis. Consequently, inhibition of VEGF signaling abrogates the development of a wide variety of tumors. The various VEGF forms bind to two tyrosine-kinase receptors, VEGFR-1 (flt-1) and VEGFR-2 (KDR/flk-1), which are expressed almost exclusively in endothelial cells. Endothelial cells express in addition the neuropilin-1 and neuropilin-2 coreceptors, which bind selectively to the 165 amino acid form of VEGF (VEGF165). This review focuses on recent developments that have widened considerably our understanding of the mechanisms that control VEGF production and VEGF signal transduction and on recent studies that have shed light on the mechanisms by which VEGF regulates angiogenesis.

Vascular endothelial growth factor (VEGF) and its receptors

Background Retinal ischemia induces intraocular neovascularization, which often leads to glaucoma, vitreous hemorrhage, and retinal detachment, presumably by stimulating the release of angiogenic molecules. Vascular endothelial growth factor (VEGF) is an endothelial-cell-specific angiogenic factor whose production is increased by hypoxia. Methods We measured the concentration of VEGF in 210 specimens of ocular fluid obtained from 164 patients undergoing intraocular surgery, using both radioimmunoassays and radioreceptor assays. Vitreous proliferative potential was measured with in vitro assays of the growth of retinal endothelial cells and with VEGF-neutralizing antibody. Results VEGF was detected in 69 of 136 ocular-fluid samples from patients with diabetic retinopathy, 29 of 38 samples from patients with neovascularization of the iris, and 3 of 4 samples from patients with ischemic occlusion of the central retinal vein, as compared with 2 of 31 samples from patients with no neovascular disorders (P<0.00...

https://www.nejm.org/doi/pdf/10.1056/NEJM199412013312203

Vascular Endothelial Growth Factor in Ocular Fluid of Patients with Diabetic Retinopathy and Other Retinal Disorders

Background: Vascular endothelial growth factor (VEGF) is an angiogenic protein and vasopermeability factor whose intraocular concentrations are closely correlated with active neovascularization in patients with diabetes mellitus, central retinal vein occlusion, retinopathy of prematurity, and rubeosis iridis. Objective: To determine whether hypoxia could induce expression of VEGF in retinal cells, which then promotes retinal endothelial cell proliferation. Methods: Retinal pigment epithelial cells, pericytes, and microvascular endothelial cells were exposed to hypoxic conditions in vitro, and RNA expression of VEGF was evaluated by Northern blot analysis. The VEGF-specific proliferative potential of the medium was measured by means of retinal endothelial cell growth assays and VEGF-neutralizing VEGF receptor IgG chimeric protein. Results: The VEGF RNA levels increased within 4 hours and reached elevations of threefold to 30-fold after 18 hours of hypoxia (0% to 5% oxygen, 5% carbon dioxide, 90% to 95% nitrogen) in all cell types (.01 Conclusion: Hypoxia increases VEGF expression in retinal cells, which promotes retinal endothelial cell proliferation, suggesting that VEGF plays a major role in mediating intraocular neovascularization resulting from ischemic retinal diseases.

https://jamanetwork.com/HttpHandlers/ArticlePdfHandler.ashx?journal=ophth&articleId=641436&pdfFileName=archopht_113_12_012.pdf

Hypoxic Regulation of Vascular Endothelial Growth Factor in Retinal Cells

Vascular Endothelial Growth Factor In Ocular Fluid of Patients with Diabetic Retinopathy and Other Retinal Disorders

Penetrating ocular fish-hook injuries. Surgical management and long-term visual outcome.

Morquio syndrome (mucopolysaccharidosis IV) is a hereditary lysosomal storage disease characterized by dwarfism, spondyloepiphyseal and dental abnormalities, corneal opacification, and normal intelligence. We report the light and electron microscopic features of two patients with mucopolysaccharidosis type IV A (MPS IV A). Variable degrees of mucopolysaccharide deposition were seen in tissue surveyed by light microscopy. Transmission electron microscopy demonstrated fibrillogranular and multimembranous membrane-bound inclusions distributed primarily in the cornea and trabecular meshwork, to a milder degree in the conjunctiva and sclera, and rarely in the retinal pigment epithelium. Our findings indicate that the accumulation of mucopolysaccharide in MPS IV A occurs primarily in the structures of the anterior segment.

Mami Iwamoto

Papers

Vascular Endothelial Growth Factor in Ocular Fluid of Patients with Diabetic Retinopathy and Other Retinal Disorders

Hypoxic Regulation of Vascular Endothelial Growth Factor in Retinal Cells

Vascular Endothelial Growth Factor In Ocular Fluid of Patients with Diabetic Retinopathy and Other Retinal Disorders

Penetrating ocular fish-hook injuries. Surgical management and long-term visual outcome.

Ocular histopathology and ultrastructure of Morquio syndrome (systemic mucopolysaccharidosis IV A)