Corneal avascularity is due to soluble VEGF receptor-1

Cardiovascular disease complications in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a highly variable autoimmune disease characterized by aberrant host-immune responses and chronic inflammation. Recently, a strong association between cardiovascular (CV) disease and SLE has emerged. Thus, low serum, high-density lipoprotein strongly correlated with elevated erythrocyte sedimentation rate, IL-6, TNF-alpha and the SLE disease activity index after adjusting for age, gender, race, BMI, insulin sensitivity and any concurrent drug use. In SLE, CV disease is characterized by increased VEGF, which may alter vascular hemostasis and promote neoangiogenesis. Increased low-density lipoprotein-cholesterol and proinflammatory high-density lipoprotein-cholesterol uptake by monocytes together with enhanced low-density lipoprotein-cholesterol oxidation results in the deposition of altered cholesterol forms into the vascular wall. This contributes to precocious and accelerated development of coronary artery plaques. Cholesterol-reducing drugs should be considered in the standard of care of SLE patients, especially in those with an unfavorable CV disease risk profile, which could reduce the probability of atherosclerosis progressing to CV disease or stroke in these patients.

Corneal epithelial MT1-MMP inhibits vascular endothelial cell proliferation and migration

PURPOSE

To determine the effects of corneal epithelial membrane-type 1 matrix metalloproteinase (MT1-MMP) on vascular endothelial migration and proliferation.

METHODS

We generated immortalized wild-type, MT1-MMP knockout and MT1-MMP knock-in corneal epithelial cells. Calf pulmonary arterial endothelial (CPAE) cell proliferation and Boyden chamber migration were assayed.

RESULTS

Conditioned media from MT1-MMP epithelial knockout cells significantly increased CPAE proliferation 5-bromo-2'-deoxy-uridine (BrdU) incorporation, and CPAE migration as compared with wild-type epithelial cells. Conditioned media from knock-in cells reversed the increase in CPAE proliferation, BrdU incorporation and CPAE migration. Knock-in cells transfected with mutant MT1-MMP (E240A) did not abrogate the reversal effect.

CONCLUSIONS

Corneal epithelial MT1-MMP is antiangiogenic. This antiangiogenic activity does not require the catalytic domain.

Mediators of ocular angiogenesis

Angiogenesis is the formation of new blood vessels from pre-existing vasculature. Pathologic angiogenesis in the eye can lead to severe visual impairment. In our review, we discuss the roles of both pro-angiogenic and anti-angiogenic molecular players in corneal angiogenesis, proliferative diabetic retinopathy, exudative macular degeneration and retinopathy of prematurity, highlighting novel targets that have emerged over the past decade.

Effect of subconjunctival and intraocular bevacizumab injections on corneal neovascularization in a mouse model

PURPOSE

This study sought to evaluate the efficacy of bevacizumab (Avastin), an anti-VEGF agent, in the reduction of corneal neovascularization in a rodent model, and compare between the effect of intraocular and subconjunctival injection.

METHODS

Corneal neovascularization was induced by application of a mixture of 75% silver nitrate and 25% potassium nitrate to the corneal center of the right eye of 125 mice. Immediately thereafter, 75 eyes were treated with subconjunctival, anterior chamber, or intravitreal injection of bevacizumab. The remaining mice served as a control. The groups were compared at different postoperative time points for percentage area of neovascularization evaluated by digital photos, the presence of corneal stromal vascular endothelial cells studied by immunohistochemical staining, and VEGF levels measured by real-time PCR.

RESULTS

In the untreated eyes, percentage area of neovascularization increased from 11.3 +/- 7% on day 2 to 20 +/- 8.9% on day 4, 47 +/- 25.4% on day 8, and 51 +/- 24.7% on day 10. The percentage area of neovascularization following subconjunctival injection was 7 +/- 2.9% on day 2, 15.7 +/- 6% on day 4, 32.2 +/- 15.2% on day 8, and 39.7 +/- 14.5% on day 10. The percentage area of neovascularization following anterior chamber injection was 14.4 +/- 3% on day 2, 16.5 +/- 6.3% on day 4, 26.3 +/- 6.5% on day 8, and 19.8 +/- 1.2% on day 10. The percentage area of neovascularization following intravitreal injection was 11 +/- 2.5% on day 2, 14.7 +/- 5% on day 4, 23.5 +/- 6.5% on day 8, and 24.2 +/- 14.9% on day 10.

CONCLUSIONS

Bevacizumab injections partially inhibit the growth of corneal neovascularization induced by acute chemical injury in a mouse model. The intraocular routes of injection were found to be the most effective, and the subconjunctival route of injection yielded the earliest peak response.

Alternate processing of Flt1 transcripts is directed by conserved cis-elements within an intronic region of FLT1 that reciprocally regulates splicing and polyadenylation

The vascular endothelial growth factor receptor, Flt1 is a transmembrane receptor co-expressed with an alternate transcript encoding a secreted form, sFlt1, that functions as a competitive inhibitor of Flt1. Despite shared transcription start sites and upstream regulatory elements, sFlt1 is in far greater excess of Flt1 in the human placenta. Phorbol myristic acid and dimethyloxalylglycine differentially stimulate sFlt1 compared to Flt1 expression in vascular endothelial cells and in cytotrophoblasts. An FLT1 minigene construct containing exon 13, 14 and the intervening region, recapitulates mRNA processing when transfected into COS-7, with chimeric intronic sFlt1 transcripts arising by intronic polyadenylation and other Flt1/sFlt1 transcripts by alternate splicing. Inclusion of exon 15 but not 14 had a modest stimulatory effect on the abundance of sFlt1. The intronic region containing the distal poly(A) signal sequences, when transferred to a heterologous minigene construct, inhibited splicing but only when cloned in sense orientation, consistent with the presence of a directional cis-element. Serial deletional and targeted mutational analysis of cis-elements within intron 13 identified intronic poly(A) signal sequences and adjacent cis-elements as the principal determinants of the relative ratio of intronic sFlt1 and spliced Flt1. We conclude that intronic signals reciprocally regulate splicing and polyadenylation and control sFlt1 expression.

VEGF Trap(R1R2) suppresses experimental corneal angiogenesis

PURPOSE

To determine the effect of vascular endothelial growth factor (VEGF) TrapR1R2 on bFGF-induced experimental corneal neovascularization (NV).

METHODS

Control pellets or pellets containing 80 ng bFGF were surgically implanted into wild-type C57BL/6 and VEGF-LacZ mouse corneas. The corneas were photographed, harvested, and the percentage of corneal NV was calculated. The harvested corneas were evaluated for VEGF expression. VEGF-LacZ mice received tail vein injections of an endothelial-specific lectin after pellet implantation to determine the temporal and spatial relationship between VEGF expression and corneal NV. Intraperitoneal injections of VEGF TrapR1R2 or a human IgG Fc domain control protein were administered, and bFGF pellet-induced corneal NV was evaluated.

RESULTS

NV of the corneal stroma began on day 4 and was sustained through day 21 following bFGF pellet implantation. Progression of vascular endothelial cells correlated with increased VEGF-LacZ expression. Western blot analysis showed increased VEGF expression in the corneal NV zone. Following bFGF pellet implantation, the area of corneal NV in untreated controls was 1.05+/-0.12 mm2 and 1.53+/-0.27 mm2 at days 4 and 7, respectively. This was significantly greater than that of mice treated with VEGF Trap (0.24+/-0.11 mm2 and 0.35+/-0.16 mm2 at days 4 and 7, respectively; p<0.05).

CONCLUSIONS

Corneal keratocytes express VEGF after bFGF stimulation and bFGF-induced corneal NV is blocked by intraperitoneal VEGF TrapR1R2 administration. Systemic administration of VEGF TrapR1R2 may have potential therapeutic applications in the management of corneal NV.

Autocrine VEGF signaling synergizes with EGFR in tumor cells to promote epithelial cancer development

It is established that tumor cell-derived VEGF acts on endothelial cells to promote angiogenesis and tumor growth. Here, we demonstrate that in K5-SOS-dependent mouse skin tumors, autocrine VEGF is required for tumor cell proliferation in a cell-autonomous and angiogenesis-independent manner. VEGF is upregulated in SOS-expressing tumors, and its deletion in epidermal cells delays tumorigenesis by suppressing angiogenesis and tumor cell proliferation. Epidermis-specific Flt1 deletion also impairs tumorigenesis and proliferation. Surprisingly, complete tumor inhibition occurs in the absence of VEGF in EGFR mutant mice, demonstrating that VEGFR and EGFR synergize in neoplastic cells to promote tumor growth. Mechanistically, K5-SOS upregulates VEGF, Flt1, and Neuropilin-1 in an Erk-dependent manner, thereby activating an autocrine proliferation loop, whereas EGFR prevents tumor cells from apoptosis. Moreover, Flt1 is upregulated in human SCC, and its inhibition in SCC cells impairs proliferation. Thus, in addition to regulating angiogenesis, VEGF has to be considered as a potent growth factor for epidermal tumors.

A placental growth factor variant unable to recognize vascular endothelial growth factor (VEGF) receptor-1 inhibits VEGF-dependent tumor angiogenesis via heterodimerization

Angiogenesis is one of the crucial events for cancer development and growth. Two members of the vascular endothelial growth factor (VEGF) family, VEGF-A and placental growth factor (PlGF), which are able to heterodimerize if coexpressed in the same cell, are both required for pathologic angiogenesis. We have generated a PlGF1 variant, named PlGF1-DE in which the residues Asp72 and Glu73 were substituted with Ala, which is unable to bind and activate VEGF receptor-1 but is still able to heterodimerize with VEGF. Here, we show that overexpression in tumor cells by adenoviral delivery or stable transfection of PlGF1-DE variant significantly reduces the production of VEGF homodimer via heterodimerization, determining a strong inhibition of xenograft tumor growth and neoangiogenesis, as well as significant reduction of vessel lumen and stabilization, and monocyte-macrophage infiltration. Conversely, the overexpression of PlGF1wt, also reducing the VEGF homodimer production comparably with PlGF1-DE variant through the generation of VEGF/PlGF heterodimer, does not inhibit tumor growth and vessel density compared with controls but induces increase of vessel lumen, vessel stabilization, and monocyte-macrophage infiltration. The property of PlGF and VEGF-A to generate heterodimer represents a successful strategy to inhibit VEGF-dependent angiogenesis. The PlGF1-DE variant, and not PlGF1wt as previously reported, acts as a "dominant negative" of VEGF and is a new candidate for antiangiogenic gene therapy in cancer treatment.

Novel aspects of corneal angiogenic and lymphangiogenic privilege

In this article, we provide the results of experimental studies demonstrating that corneal avascularity is an active process involving the production of anti-angiogenic factors, which counterbalance the pro-angiogenic/lymphangiogenic factors that are upregulated during wound healing. We also summarize pertinent published reports regarding corneal neovascularization (NV), corneal lymphangiogenesis and corneal angiogenic/lymphangiogenic privilege. We outline the clinical causes of corneal NV, and discuss the angiogenic proteins (VEGF and bFGF) and angiogenesis regulatory proteins. We also describe the role of matrix metalloproteinases MMP-2, -7, and MT1-MMP, anti-angiogenic factors, and lymphangiogenic regulatory proteins during corneal wound healing. Established and potential new therapies for the treatment of corneal neovascularization are also discussed.

ADAMTS9 is a cell-autonomously acting, anti-angiogenic metalloprotease expressed by microvascular endothelial cells

The metalloprotease ADAMTS9 participates in melanoblast development and is a tumor suppressor in esophageal and nasopharyngeal cancer. ADAMTS9 null mice die before gastrulation, but, ADAMTS9+/- mice were initially thought to be normal. However, when congenic with the C57Bl/6 strain, 80% of ADAMTS9+/- mice developed spontaneous corneal neovascularization. beta-Galactosidase staining enabled by a lacZ cassette targeted to the ADAMTS9 locus showed that capillary endothelial cells (ECs) in embryonic and adult tissues and in capillaries growing into heterotopic tumors expressed ADAMTS9. Heterotopic B.16-F10 melanomas elicited greater vascular induction in ADAMTS9+/- mice than in wild-type littermates, suggesting a potential inhibitory role in tumor angiogenesis. Treatment of cultured human microvascular ECs with ADAMTS9 small-interfering RNA resulted in enhanced filopodial extension, decreased cell adhesion, increased cell migration, and enhanced formation of tube-like structures on Matrigel. Conversely, overexpression of catalytically active, but not inactive, ADAMTS9 in ECs led to fewer tube-like structures, demonstrating that the proteolytic activity of ADAMTS9 was essential. However, unlike the related metalloprotease ADAMTS1, which exerts anti-angiogenic effects by cleavage of thrombospondins and sequestration of vascular endothelial growth factor165, ADAMTS9 neither cleaved thrombospondins 1 and 2, nor bound vascular endothelial growth factor165. Taken together, these data identify ADAMTS9 as a novel, constitutive, endogenous angiogenesis inhibitor that operates cell-autonomously in ECs via molecular mechanisms that are distinct from those used by ADAMTS1.

VEGFR1-mediated pericyte ablation links VEGF and PlGF to cancer-associated retinopathy

VEGF coordinates complex regulation of cellular regeneration and interactions between endothelial and perivascular cells; dysfunction of the VEGF signaling system leads to retinopathy. Here, we show that systemic delivery of VEGF and placental growth factor (PlGF) by protein implantation, tumors, and adenoviral vectors ablates pericytes from the mature retinal vasculature through the VEGF receptor 1 (VEGFR1)-mediated signaling pathway, leading to increased vascular leakage. In contrast, we demonstrate VEGF receptor 2 (VEGFR2) is primarily expressed in nonvascular photoreceptors and ganglion cells. Moreover, blockade of VEGFR1 but not VEGFR2 significantly restores pericyte saturation in mature retinal vessels. Our findings link VEGF and PlGF to cancer-associated retinopathy, reveal the molecular mechanisms of VEGFR1 ligand-mediated retinopathy, and define VEGFR1 as an important target of antiangiogenic therapy for treatment of retinopathy.

Anti-SPARC oligopeptide inhibits laser-induced CNV in mice

It is known that SPARC gates VEGF-A signal transduction towards KDR, the primary angiogenic VEGF receptor. We sought to determine whether inhibition of SPARC activity using anti-SPARC peptide could inhibit laser-induced CNV by promoting binding of VEGF-A to FLT-1. We created anti-SPARC l-peptide and retro-inverso anti-SPARC d-peptide. Anti-SPARC peptides or PBS were injected intravitreally 1day before or after laser induction. Intravitreal injection of anti-SPARC l-peptide 1day before laser induction promotes FLT-1 phosphorylation and inhibited laser-induced CNV and anti-SPARC d-peptide had no effect. Injection 1day after laser injury did not affect size of laser-induced CNV. Inhibition of SPARC activity could be complementary to existing anti-CNV therapy.

Endogenous LXA4 circuits are determinants of pathological angiogenesis in response to chronic injury

Inflammation and angiogenesis are intimately linked, and their dysregulation leads to pathological angiogenesis in human diseases. 15-lipoxygenase (15-LOX) and lipoxin A(4) receptors (ALX) constitute a LXA(4) circuit that is a key feature of inflammatory resolution. LXA(4) analogs have been shown to regulate vascular endothelial growth factor (VEGF)-A-induced angiogenic response in vitro. 15-LOX and ALX are highly expressed in the avascular and immune-privileged cornea. However, the role of this endogenous LXA(4) circuit in pathological neovascularization has not been determined. We report that suture-induced chronic injury in the cornea triggered polymorphonuclear leukocytes (PMN) infiltration, pathological neovascularization, and up-regulation of mediators of inflammatory angiogenesis, namely VEGF-A and the VEGF-3 receptor (FLT4). Up-regulation of the VEGF circuit and neovascularization correlated with selective changes in both 15-LOX (Alox15) and ALX (Fpr-rs2) expression and a temporally defined increase in basal 15-LOX activity. More importantly, genetic deletion of 15-LOX or 5-LOX, key and obligatory enzymes in the formation of LXA(4), respectively, led to exacerbated inflammatory neovascularization coincident with increased VEGF-A and FLT4 expression. Direct topical treatment with LXA(4), but not its metabolic precursor 15-hydroxyeicosatetraenoic acid, reduced expression of VEGF-A and FLT4 and inflammatory angiogenesis and rescued 15-LOX knockout mice from exacerbated angiogenesis. In summary, our findings and the prominent expression of 15-LOX and ALX in epithelial cells and macrophages place the LXA(4) circuit as an endogenous regulator of pathological angiogenesis.

Mediators of neovascularization and the hypoxic cornea

The maintenance of corneal avascularity is essential to vision. The mechanisms by which the cornea becomes vascularized in response to inflammation or hypoxic stress are beginning to be elucidated. A detailed understanding of the molecular responses of the cornea to hypoxia is critical for prevention and development of novel treatments for neovascularization in a range of disease states. Here, we have examined the current literature on the major mediators of angiogenesis, which have previously been reported during hypoxia in the cornea in order to better understand the mechanisms by which corneal angiogenesis occurs in circumstances where the available oxygen is reduced. The normal cornea produces angiogenic factors that are regulated by the production of anti-angiogenic molecules. The various cell types of the cornea respond differentially to inflammatory and hypoxic stimuli. An understanding of the factors that may predispose patients to development of corneal blood vessels may provide an opportunity to develop novel prophylactic strategies. The difficulties with extrapolating data from other cell types and animal models to the cornea are also examined.

Gene therapy for diseases of the cornea - a review

The cornea is particularly suited to gene therapy. The cornea is readily accessible, normally transparent, and is somewhat sequestrated from the general circulation and the systemic immune system. The principle of genetic therapy for the cornea is to use an appropriate vector system to transfer a gene to the cornea itself, or to the ocular environs, or systemically, so that a transgenic protein will be expressed that will modulate congenital or acquired disease. The protein may be structural such as a collagen, or functionally active such as an enzyme, cytokine or growth factor that may modulate a pathological process. Alternatively, gene expression may be silenced by the use of modalities such as antisense oligonucleotides. Interestingly, despite a very considerable amount of work in animal models, clinical translation directed to gene therapy of the human cornea has been minimal. This is in contrast to gene therapy for monogenic inherited diseases of the retina, where promising early results of clinical trials for Leber's congenital amaurosis have already been published and a number of other trials are ongoing.

Signaling "cross-talk" is integrated by transcription factors in the development of the anterior segment in the eye

Extracellular signaling "cross-talk" between tissues is an important requirement for development of many organs yet the underlying mechanisms generally remain poorly understood. The anterior segment of the eye, which is constructed from four embryonic lineages, provides a unique opportunity to genetically dissect developmental processes such as signaling "cross-talk" without fear of inducing lethality. In the current review, we summarize recent data showing that PITX2, a homeodomain transcription factor, integrates retinoic acid and canonical Wnt/beta-catenin signaling during anterior segment development. Because the requirements for retinoic acid signaling, canonical Wnt/beta-catenin signaling, and PITX2 are not unique to the eye, this newly identified pathway may have relevance elsewhere during development and in tissue homeostasis.

The Flk1-myr::mCherry mouse as a useful reporter to characterize multiple aspects of ocular blood vessel development and disease

The highly vascularized mouse eye is an excellent model system in which to elucidate the molecular genetic basis of blood vessel development and disease. However, the analysis of ocular vessel defects has traditionally been derived from fixed tissue, which fails to account for dynamic events such as blood flow and cell migration. To overcome the limitations of static analysis, tremendous advances in imaging technology and fluorescent protein reporter mouse lines now enable the direct visualization of developing cells in vivo. Here, we demonstrate that the Flk1-myr::mCherry transgenic mouse is an extremely useful live reporter with broad applicability to retinal, hyaloid, and choroid vascular research.

Lymphangiogenesis and angiogenesis: concurrence and/or dependence? Studies in inbred mouse strains

Genetic background significantly affects angiogenesis in mice. However, lymphangiogenic response to growth factors (GFs) in different strains has not been studied. We report constitutive expression of corneal lymphatics that extends beyond the limits of normal limbal vessels. In untreated corneas, the total number (P=0.006), the number above blood vessels (P=10(-8)), and the area of preexisting lymphatics (P=0.007) were significantly higher in C57BL/6 than in BALB/c mice. Normal corneas of three other strains, the nu/nu, 129E, and Black Swiss mice, showed in most parameters intermediate phenotypes. FGF-2(-/-) mice showed significantly less preexisting lymphatics than control (P=0.009), which suggests a role for this GF in lymphatic development. VEGF-A-induced corneal lymphangiogenic response was significantly higher in BALB/c mice (P=0.03), but it did not differ significantly in C57BL/6 mice, when compared to PBS-implanted control. FGFR-3 expression was higher in C57BL/6 than BALB/c mice, which suggests GF-receptor heterogeneity as a possible explanation for strain-dependent differences. The heterogeneity of preexisting lymphatic vessels in the limbal area significantly correlated with the extent of corneal lymphangiogenesis (VEGF-A: r=0.7, P=0.01; FGF-2: r=0.96, P=10(-5)) in BALB/c but not in C57BL/6 mice. Removal of conjunctival lymphatics did not affect GF-induced lymphangiogenesis. This work introduces physiological expression of lymphatics without blood vessels, which indicates that angiogenesis and lymphangiogenesis, even though intricately related, may occur independently. Furthermore, we show strain-dependence of normal and GF-induced lymphangiogenesis. These differences may affect disease development in various strains.

A systems biology perspective on sVEGFR1: its biological function, pathogenic role and therapeutic use

Angiogenesis is the growth of new capillaries from pre-existent microvasculature. A wide range of pathological conditions, from atherosclerosis to cancer, can be attributed to either excessive or deficient angiogenesis. Central to the physiological regulation of angiogenesis is the vascular endothelial growth factor (VEGF) system – its ligands and receptors (VEGFRs) are thus prime molecular targets of pro-angiogenic and anti-angiogenic therapies. Of growing interest as a prognostic marker and therapeutic target in angiogenesis-dependent diseases is soluble VEGF receptor-1 (sVEGFR1, also known as sFlt-1) – a truncated version of the cell membrane-spanning VEGFR1. For instance, it is known that sVEGFR1 is involved in the endothelial dysfunction characterizing the pregnancy disorder of pre-eclampsia, and sVEGFR1’s therapeutic potential as an anti-angiogenic agent is being evaluated in pre-clinical models of cancer. This mini review begins with an examination of the protein domain structure and biomolecular interactions of sVEGFR1 in relation to the full-length VEGFR1. A synopsis of known and inferred physiological and pathological roles of sVEGFR1 is then given, with emphasis on the utility of computational systems biology models in deciphering the molecular mechanisms by which sVEGFR1’s purported biological functions occur. Finally, we present the need for a systems biology perspective in interpreting circulating VEGF and sVEGFR1 concentrations as surrogate markers of angiogenic status in angiogenesis-dependent diseases.

Vascular endothelial growth factor receptor-1 (VEGFR-1) expression in human corneal fibroblast decreased with age

PURPOSE

Mechanisms by which fibroblast networks between stromal lamellae are laid in the corneal stroma are far from clear. We have investigated the role of vascular endothelial growth factor receptors (VEGFRs) by in vitro studies in the human corneal network formation obtained from donors whose ages ranged from 19 to 89 years.

METHODS

Corneal fibroblasts were prepared from cornea donations. The functional properties of these cells to form networks were analyzed using a semi solid matrix (substratum) of Matrigel. The presence of VEGF receptor-1 (VEGFR-1) and the functionality in these fibroblasts were investigated using immunofluorescence, molecular analysis (gene microarray, reverse transcription polymerase chain reaction [RT-PCR] and VEGFR siRNA transfections), and cell culture.

RESULTS

Corneal fibroblasts from 61 donors were classified into two groups according to whether they formed (82%) a reticulum on Matrigel or not (18%). By RT-PCR and immunofluorescence analysis, we showed that corneal fibroblasts expressed VEGFR-1 (mRNA and protein). Further, cell culture analysis revealed that only the network (reticulum) forming corneal fibroblast expressed VEGFR-1 in contrast to non network-forming fibroblasts. Use of inhibitors such as VEGFR-1 siRNA transfection or neutralizing antibody (Avastin) indicated that VEGFR-1 was essential to the formation of the corneal network in vitro.

CONCLUSIONS

The cell reticulum formation seemed to be directly related to the expression of VEGFR-1 in the corneal fibroblast, and this expression decreased with age. The decrease in VEGFR-1 expression is probably related to the diminution of autocrine functions, which may alter the overall tissular homeostasis. This may culminate in the gradual development of poor vision, which is observed in certain pathologies and in aging individuals.

Inhibitory effects of polysaccharide extract from Spirulina platensis on corneal neovascularization

PURPOSE

To assess the effects of polysaccharide extract from Spirulina platensis (PSP) on corneal neovascularization (CNV) in vivo and in vitro.

METHODS

PSP was extracted from dry powder of Spirulina platensis. Its anti-angiogenic activity was evaluated in the mouse corneal alkali burn model after topical administration of PSP four times daily for up to seven days. Corneal samples were processed for histochemical, immunohistochemical, and gene expression analyses. The effects of PSP on proliferation, migration, tube formation, and serine threonine kinase (AKT) and extracellular regulated kinase1/2 (ERK1/2) signaling levels in vascular endothelial cells were determined using 3-(4,5)-dimethylthiahiazo (-z-y1)-3, 5-di-phenytetrazoliumromide (MTT) and carboxyfluorescein succinimidyl ester (CFSE) labeling assays, wound healing assay, Matrigel tube formation assay, and western blot.

RESULTS

Topical application of PSP significantly inhibited CNV caused by alkali burn. Corneas treated with PSP showed reduced levels of platelet endothelial cell adhesion molecule (CD31) and stromal cell-derived factor 1 (SDF1) proteins, reduced levels of vascular endothelial growth factor (VEGF), matrix metalloproteinase-2 (MMP2), matrix metalloproteinase-9 (MMP9), SDF1, and tumor necrosis factor-alpha (TNF-alpha) mRNAs, and an increased level of pigment epithelium-derived factor (PEDF) mRNA. These are parameters that have all been related to CNV and/or inflammation. In human vascular endothelial cells, PSP significantly inhibited proliferation, migration, and tube formation in a dose-dependent manner. Furthermore, PSP also decreased the levels of activated AKT and ERK 1/2.

CONCLUSIONS

These data suggest that polysaccharide extract from Spirulina platensis is a potent inhibitor of CNV and that it may be of benefit in the therapy of corneal diseases involving neovascularization and inflammation.

[Topical inhibition of angiogenesis at the cornea. Safety and efficacy]

BACKGROUND

The efficacy and safety of novel topical inhibitors of corneal neovascularisation will be discussed.

METHODS

A literature review after a PUBMED search and own clinical and experimental results are presented.

RESULTS

The off-label use of Avastin eye drops and GS101 eye drops against insulin receptor substrate (IRS)-1, which have been tested in phase II trial, both seem to be relatively efficient and safe ways to inhibit progressive corneal neovascularisation. Other VEGF antagonists, such as ranibizumab and pegaptanib eye drops also inhibit corneal neovascularisation.

CONCLUSIONS

Avastin and GS101 eye drops are the first specific angiogenesis inhibitors for topical inhibition of corneal angiogenesis available for clinical use.

Alternatively spliced vascular endothelial growth factor receptor-2 is an essential endogenous inhibitor of lymphatic vessel growth

Disruption of the precise balance of positive and negative molecular regulators of blood and lymphatic vessels can lead to myriad diseases that affect one in four people worldwide. Although dozens of natural inhibitors of hemangiogenesis have been identified, an endogenous selective inhibitor of lymphatic vessels has not yet been described. We report the existence of a secreted, splice variant of vascular endothelial growth factor receptor-2 (sVegfr-2) that inhibits developmental and reparative lymphangiogenesis by blocking Vegf-c. Tissue-specific loss of sVegfr-2 in mice induced, at birth, spontaneous lymphatic invasion of the normally alymphatic cornea and hyperplasia of skin lymphatics without accompanying changes in blood vasculature. sVegfr-2 inhibited lymphangiogenesis but not hemangiogenesis induced by corneal suture injury or transplantation, enhanced corneal allograft survival, and suppressed lymphangioma cellular proliferation. Naturally occurring sVegfr-2 is a molecular uncoupler of blood and lymphatic vessels whose modulation might have a therapeutic role in lymphatic vascular malformations, transplantation, and potentially in tumor lymphangiogenesis and lymphedema.

Immunoregulation on the ocular surface: 2nd Cullen Symposium

A one-day symposium with 20 invited participants was held to review current knowledge regarding immunoregulation in the ocular surface and cornea. The program consisted of 11 lectures on various aspects of ocular and systemic immunoregulation, followed by a group discussion to formulate regulatory pathways. The ocular surface and its secondary lymphoid tissues contain numerous components of the innate and adaptive immune systems, which modulate the immune response to suppress or prevent excessive damaging immune reactions. These include factors that regulate induction of the immune response (afferent loop), as well as effector cells and soluble factors (efferent loop). The ocular surface is an immunologically active mucosal site that contains numerous mechanisms to regulate the immune response to prevent tissue destruction and vision loss.

Gene delivery to cornea

This paper reviews the strategies of in vivo gene delivery to the cornea. A number of studies have demonstrated the feasibility of targeted delivery of oligonucleotides, small interfering RNA (siRNA), plasmid DNA, and viral vectors to the corneal cells in vivo, specifically stromal keratocytes and corneal epithelial cells, via intrastromal injection, iontophoresis, electroporation, and gene gun. Intrastromal injection of plasmid DNA and adenovirus each can result in efficient transgene expression to stromal keratocytes. The introduction of foreign genes into intact corneal epithelium specifically requires more invasive procedures such as gene gun to disrupt the tight junction barrier and/or cell membranes. The combination of iontophoresis and electroporation was found to be effective in delivering siRNA but not plasmid DNA into the corneal epithelium. Nanocarriers such as polymeric micelles are promising methods of corneal gene delivery.

Reduction of circulating soluble Flt-1 alleviates preeclampsia-like symptoms in a mouse model

Preeclampsia (PE) is characterized by widespread endothelial damage with hypertension, proteinuria, glomeruloendotheliosis and elevated soluble Flt-1 (sFlt-1), a natural occurring antagonist of vascular endothelial growth factor (VEGF). Cancer patients receiving anti-VEGF therapy exhibit similar symptoms. We suggested that a decrease in circulating sFlt-1 would alleviate the symptoms associated with PE. Adenoviral (Adv) overexpression of sFlt-1 induced proteinuria, caused glomerular damage and increase in blood pressure in female Balb/c mice. Circulating level of sFlt-1 above 50 ng/ml plasma induced severe vascular damage and glomerular endotheliosis. Albumin concentration in urine was elevated up to 30-fold, compared to control AdvGFP-treated animals. The threshold of kidney damage was in the range of 20–30 ng/ml sFlt-1 in plasma (8–15 ng/ml in urine). Co-administration of AdvsFlt-1 with AdvVEGF to neutralize circulating sFlt-1 resulted in more than a 70% reduction in free sFlt-1 in plasma, more than 80% reduction in urine and rescued the damaging effect of sFlt-1 on the kidneys. This demonstrates that below a critical threshold sFlt-1 fails to elicit damage to the fenestrated endothelium and that co-expression of VEGF is able to rescue effects mediated by sFlt-1 overexpression.

Corneal transparency: genesis, maintenance and dysfunction

Optimal vision is contingent upon transparency of the cornea. Corneal neovascularization, trauma and, surgical procedures such as photorefractive keratectomy and graft rejection after penetrating keratoplasty can lead to corneal opacification. In this article we identify the underlying basis of corneal transparency and factors that compromise the integrity of the cornea. With evidence from work on animal models and clinical studies, we explore the molecular mechanisms of both corneal avascularity and its dysfunction. We also seek to review therapeutic regimens that can safely salvage and restore corneal transparency.

Subconjunctival gene delivery of the transcription factor GA-binding protein delays corneal neovascularization in a mouse model

Corneal neovascularization can reduce visual acuity. GA-binding protein (GABP) is a transcription factor that regulates the expression of target genes including vascular endothelial growth factor (VEGF) and roundabout4 (Robo4), which participate in pathologic angiogenesis. We assessed whether intraocular injection of the GABP gene affects the growth of new corneal blood vessels in a mouse ocular neovascularization model. Transfection of human GABPalpha and GABPbeta gene (GABPalpha/beta) into human conjunctival epithelial cells resulted in decreased VEGF and Robo4 expression. Three groups of mice underwent chemical and mechanical denudation of the corneal epithelium. Subsequently, two groups were administered subconjunctival injection of lipoplexes carrying plasmid DNA encoding for human GABPalpha/beta or an empty plasmid DNA at 1-week intervals. The third group served as an experimental control. In vivo delivery of human GABPalpha/beta into mouse neovascularized cornea reduced VEGF and Robo4 gene expression. Biomicroscopic examination showed that, at 1 week after one or two injections, GABPalpha/beta-treated eyes had significantly less neovascularized corneal area than did eyes treated with the empty vector. Histologic examination showed significantly less vascularized area and fewer blood vessels in the GABP-treated group at 1 week after injections. However, these angiosuppressive effects were weakened at 2 weeks after injections. Our results indicate that subconjunctival GABP gene delivery delays corneal neovascularization for up to 2 weeks in a mouse model of deliberate corneal injury.

Characterization of the corneal surface in limbal stem cell deficiency and after transplantation of cultivated limbal epithelium

PURPOSE

Transplantation of in vitro-cultivated limbal epithelium (TCLE) recently was developed to treat limbal stem cell deficiency (LSCD). The objective of this study was to characterize changes in the cornea during LSCD and on the corneal surface after TCLE.

DESIGN

Experimental study.

PARTICIPANTS AND CONTROLS

The pannus tissue excised from the corneas of 17 LSCD patients was analyzed to characterize the changes in the cornea during LSCD. Five corneal buttons obtained during perforating keratoplasty (pKP) from patients who had undergone TCLE at least 6 months before pKP were examined to assess the effect of TCLE. Six samples of healthy central cornea and 6 of bulbar conjunctiva served as control tissue.

METHODS

The expression of epithelial lineage markers (keratin [K] 3, K12, K19, and mucin 5AC) and inflammatory markers (interleukin-1alpha [IL-1alpha], IL-1beta, intercellular adhesion molecule 1 [ICAM-1], vascular cell adhesion molecule 1 [VCAM-1], and vascular endothelial growth factor [VEGF]) were analyzed using real-time polymerase chain reaction, Western blotting, and immunofluorescence in the tissue samples.

MAIN OUTCOME MEASURES

Comparison of the markers' expression patterns.

RESULTS

The expression of all markers differed in healthy cornea and conjunctiva. Expression of lineage markers was similar in pannus to conjunctiva, but not to cornea. Interleukin-1beta, ICAM-1, VCAM-1, and VEGF were increased significantly in pannus compared with the levels in healthy cornea. Interleukin-1alpha, IL-1beta, and ICAM-1 were increased compared with healthy conjunctiva. The TCLE improved vision and reduced inflammation, vascularization, and discomfort. After TCLE, the lineage markers in the excised corneal buttons showed a corneal phenotype and a significant reduction in inflammatory markers in 4 of 5 cases.

CONCLUSIONS

Limbal stem cell deficiency is characterized by ingrowth of abnormal inflamed tissue with a conjunctival phenotype. Transplantation of limbal epithelium cultivated in vitro on intact amniotic membrane restored a noninflamed ocular surface and a corneal phenotype.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Microglial VEGF receptor response is an integral chemotactic component in Alzheimer's disease pathology

We hypothesize that microglial chemotactic responses to amyloid-beta peptide (Abeta(1-42)) serve as an early and integral component of inflammatory response in Alzheimer's disease (AD) brain. This study reports a receptor for vascular endothelial growth factor (VEGF), termed VEGF-1 (Flt-1), subserves microglial chemotactic responses induced by Abeta(1-42) stimulation, in vivo and in vitro. Expression of Flt-1 was significantly increased in tissue obtained from AD patients [compared with tissue from nondemented (ND) individuals], in Abeta(1-42)-injected rat hippocampus, and in peptide-stimulated human microglia. Single and double immunohistochemical staining demonstrated marked immunoreactivity, for both Flt-1 and its ligand VEGF, in association with microglia and Abeta deposits in AD, but not ND, brain tissue. Functionally, treatment with anti-Flt-1 antibody was highly effective in inhibiting microglial mobility and chemotactic responses measured in vitro using a transwell migration assay. In vivo, transplanted enhanced green fluorescent protein (EGFP)-labeled microglia exhibited Flt-1-dependent chemotaxis induced by peptide injection with anti-Flt-1 effective in blocking migration of cells. Importantly, anti-Flt-1 reduction of microglial mobility was neuroprotective in peptide-injected hippocampus and associated with a significant increase in numbers of viable hippocampal neurons. The results of this study suggest critical functional roles for Flt-1 in mediating microglial chemotactic inflammatory responses which contribute to pathological conditions in AD brain.

A compartment model of VEGF distribution in humans in the presence of soluble VEGF receptor-1 acting as a ligand trap

Vascular endothelial growth factor (VEGF), through its activation of cell surface receptor tyrosine kinases including VEGFR1 and VEGFR2, is a vital regulator of stimulatory and inhibitory processes that keep angiogenesis--new capillary growth from existing microvasculature--at a dynamic balance in normal physiology. Soluble VEGF receptor-1 (sVEGFR1)--a naturally-occurring truncated version of VEGFR1 lacking the transmembrane and intracellular signaling domains--has been postulated to exert inhibitory effects on angiogenic signaling via two mechanisms: direct sequestration of angiogenic ligands such as VEGF; or dominant-negative heterodimerization with surface VEGFRs. In pre-clinical studies, sVEGFR1 gene and protein therapy have demonstrated efficacy in inhibiting tumor angiogenesis; while in clinical studies, sVEGFR1 has shown utility as a diagnostic or prognostic marker in a widening array of angiogenesis-dependent diseases. Here we developed a novel computational multi-tissue model for recapitulating the dynamic systemic distributions of VEGF and sVEGFR1. Model features included: physiologically-based multi-scale compartmentalization of the human body; inter-compartmental macromolecular biotransport processes (vascular permeability, lymphatic drainage); and molecularly-detailed binding interactions between the ligand isoforms VEGF(121) and VEGF(165), signaling receptors VEGFR1 and VEGFR2, non-signaling co-receptor neuropilin-1 (NRP1), as well as sVEGFR1. The model was parameterized to represent a healthy human subject, whereupon we investigated the effects of sVEGFR1 on the distribution and activation of VEGF ligands and receptors. We assessed the healthy baseline stability of circulating VEGF and sVEGFR1 levels in plasma, as well as their reliability in indicating tissue-level angiogenic signaling potential. Unexpectedly, simulated results showed that sVEGFR1 - acting as a diffusible VEGF sink alone, i.e., without sVEGFR1-VEGFR heterodimerization--did not significantly lower interstitial VEGF, nor inhibit signaling potential in tissues. Additionally, the sensitivity of plasma VEGF and sVEGFR1 to physiological fluctuations in transport rates may partially account for the heterogeneity in clinical measurements of these circulating angiogenic markers, potentially hindering their diagnostic reliability for diseases.

Corneal (lymph)angiogenesis--from bedside to bench and back: a tribute to Judah Folkman

The normal cornea, the transparent "windscreen" of the eye, is devoid of both blood and lymphatic vessels. Nevertheless, both hem- and lymphangiogenesis can occur in response to severe corneal inflammation and can lead to blindness. Judah Folkman and co-workers exceedingly used the normally avascular cornea as the in vivo model system to study the mechanisms of angiogenesis and to test activators and inhibitors of angiogenesis in the last 3 decades. Recently, the cornea also became a successful model to study especially inflammatory lymphangiogenesis. As the last step in the circle from bedside to bench and back, we now are seeing the first (usually off-label) use of specific novel angiogenesis inhibitors in the diseased and pathologically vascularized human cornea to treat sight-threatening corneal angiogenesis and to promote graft survival after corneal transplantation by inhibiting lymphangiogenesis.

Identification of ligand-induced proteolytic cleavage and ectodomain shedding of VEGFR-1/FLT1 in leukemic cancer cells

Vascular endothelial growth factor receptor-1/fms-related tyrosine kinase 1 (VEGFR-1/FLT1) is expressed as a membrane-bound receptor tyrosine kinase and as an alternatively spliced soluble protein (sVEGFR-1) containing the 1-6 IgG-like domain of its ectodomain. sVEGFR-1 is known as a naturally occurring inhibitor of angiogenesis and as a surrogate marker for cancer progression; it is also linked to pregnancy-induced hypertension called preeclampsia and to avascularity of normal cornea. It remains an open question whether alternative mRNA splicing is the only mechanism by which sVEGFR-1 is generated. In this study, we show that in leukemic cancer cells, PlGF and VEGF-A both induce tyrosine phosphorylation of VEGFR-1 and render it susceptible to ectodomain shedding, resulting in the generation of sVEGFR-1 and an intracellular cytoplasmic fragment. Activation of protein kinase C and tumor necrosis factor-alpha-converting enzyme family metalloproteases are critically required for the occurrence of sVEGFR-1. Following the removal of the ectodomain, the remnant of VEGFR-1 remains attached to the membrane, and the activity of gamma-secretase/presenilin is required for its release from the cell membrane. We propose that sVEGFR-1 produced via ectodomain shedding plays a prominent role in the VEGF receptor system by antagonizing VEGF receptor signaling by acting as a dominant-negative form and/or forming a nonsignaling dimerizing complex with VEGF receptors.

Regulation of nitric oxide signalling by thrombospondin 1: implications for anti-angiogenic therapies

In addition to long-term regulation of angiogenesis, angiogenic growth factor signalling through nitric oxide (NO) acutely controls blood flow and haemostasis. Inhibition of this pathway may account for the hypertensive and pro-thrombotic side effects of the vascular endothelial growth factor antagonists that are currently used for cancer treatment. The first identified endogenous angiogenesis inhibitor, thrombospondin 1, also controls tissue perfusion, haemostasis and radiosensitivity by antagonizing NO signalling. We examine the role of these and other emerging activities of thrombospondin 1 in cancer. Clarifying how endogenous and therapeutic angiogenesis inhibitors regulate vascular NO signalling could facilitate development of more selective inhibitors.

Analysis of soluble vascular endothelial growth factor receptor-1 secreted from cultured corneal and oral mucosal epithelial cell sheets in vitro

BACKGROUND

In clinical trials, eyes transplanted with cultured oral mucosal epithelial cell sheets have shown increased neovascularisation compared with eyes treated with cultured corneal epithelial cell sheets. As reported recently, soluble vascular endothelial growth factor receptor-1 (soluble VEGFr-1) is a main factor to maintain a corneal avascularity.

AIM

To investigate soluble VEGFr-1 of cultured corneal epithelial cells (CCE) and cultured oral mucosal epithelial cells (COE) in vitro.

METHODS

Rabbit corneal and oral mucosal epithelial cells were co-cultured with mitomycin C-treated NIH/3T3 cells on culture plates. After CCE and COE were multilayered, culture medium was replaced by basal medium and incubated. Protein secretion of soluble VEGFr-1 was assessed in conditioned medium from CCE and COE by ELISA. Angiogenic potential was examined by invasion, migration assays with human umbilical vein endothelial cells (HUVECs) in addition to recombinant soluble VEGFr-1.

RESULTS

CCE secreted a significantly higher amount of soluble VEGFr-1 than did COE. Recombinant soluble VEGFr-1 significantly suppressed HUVEC migration induced by COE, without suppression in CCE. In conclusion, these findings suggest that low protein levels of soluble VEGFr-1 may lead to corneal neovascularisation after COE sheet transplantation.

C5a, but not C3a, increases VEGF secretion in ARPE-19 human retinal pigment epithelial cells

PURPOSE

We examined the potential for the pro-inflammatory complement proteins C5a and C3a to increase VEGF expression in ARPE-19 cells.

MATERIALS AND METHODS

Expression of complement receptors in ARPE-19 cells was evaluated by RT-PCR. VEGF secretion from ARPE-19 cells treated with C5a or C3a was determined by ELISA.

RESULTS

C5a and C3a receptor, but not C5L2, were detected in human eye tissue and ARPE-19 cells. C5a, but not C3a, treatment increased VEGF secretion from ARPE-19 cells, an effect inhibited by the C5aR antagonist, NDT 9513727.

CONCLUSIONS

C5a receptor mediates increased VEGF secretion from ARPE-19 cells, suggesting a role for the C5a receptor in the pathogenesis of macular degeneration.

Systems biology of vascular endothelial growth factors

Several cytokine families have roles in the development, maintenance, and remodeling of the microcirculation. Of these, the vascular endothelial growth factor (VEGF) family is one of the best studied and one of the most complex. Five VEGF ligand genes and five cell-surface receptor genes are known in the human, and each of these may be transcribed as multiple splice isoforms to generate an extensive family of proteins, many of which are subject to further proteolytic processing. Using the VEGF family as an example, we describe the current knowledge of growth-factor expression, processing, and transport in vivo. Experimental studies and computational simulations are being used to measure and predict the activity of these molecules, and we describe avenues of research that seek to fill the remaining gaps in our understanding of VEGF family behavior.

Angiogenesis in systemic sclerosis: impaired expression of vascular endothelial growth factor receptor 1 in endothelial progenitor-derived cells under hypoxic conditions

OBJECTIVE

To assess angiogenesis and explore the expression and regulation of vascular endothelial growth factor (VEGF), VEGF receptor 1 (VEGFR-1), and VEGFR-2, the leading mediators of angiogenesis, in SSc patients and controls.

METHODS

Late-outgrowth endothelial progenitor cells (EPCs), isolated from the peripheral blood of systemic sclerosis (SSc) patients and controls, and human umbilical vein endothelial cells (HUVECs) were assessed under normal and hypoxic conditions. Genomic background was evaluated in a large case-control study (including 659 patients with SSc and 511 controls) using tag single-nucleotide polymorphisms on VEGFR1 and VEGFR2 genes.

RESULTS

EPCs from SSc patients had the phenotype of genuine endothelial cells and displayed in vitro angiogenic properties similar to those of HUVECs and control EPCs under basal conditions, as determined by flow cytometry, tube formation, and migration assay. However, after 6 hours of hypoxic exposure, EPCs from SSc patients exhibited lower induced expression of VEGFR-1 at the messenger RNA and protein levels, but similar VEGF and VEGFR-2 expression, compared with HUVECs or EPCs from healthy controls. There was no evidence of defective expression of hypoxia-inducible factor 1alpha. These results were supported by the lower serum levels of soluble VEGFR-1 found in SSc patients (n = 187) compared with healthy controls (n = 48) (mean +/- SD 163.7 +/- 98.5 versus 210.4 +/- 109.5 pg/ml; P = 0.0042). These abnormalities did not seem to be related to genomic background.

CONCLUSION

Our findings shed new light on the possible role of VEGFR-1 in the main vascular disturbances that occur in SSc and lead to more severe disease.

Measurement of angiogenic phenotype by use of two-dimensional mesenteric angiogenesis assay

Successful therapeutic angiogenesis requires an understanding of how the milieu of growth factors available combine to form a mature vascular bed. This requires a model in which multiple physiological and cell biological parameters can be identified. The adenoviral-mediated mesenteric angiogenesis assay as described here is ideal for that purpose. Adenoviruses expressing growth factors (vascular endothelial growth factor [VEGF] and angiopoietin 1 [Ang-1]) were injected into the mesenteric fat pad of adult male Wistar rats. The clear, thin, and relatively avascular mesenteric panel was used to measure increased vessel perfusion by intravital microscopy. In addition, high-powered microvessel analysis was carried out by immunostaining of features essential for the study of angiogenesis (endothelium, pericyte, smooth muscle cell area, and proliferation), allowing functional data to be obtained in conjunction with high-power microvessel ultrastructural analysis. A combination of individual growth factors resulted in a distinct vascular phenotype from either factor alone, with all treatments increasing the functional vessel area. VEGF produced shorter, narrow, highly branched, and sprouting vessels with normal pericyte coverage. Ang-1 induced broader, longer neovessels with no apparent increase in branching or sprouting. However, Ang-1-induced blood vessels displayed a significantly higher pericyte ensheathment. Combined treatment resulted in higher perfusion, larger and less-branched vessels, with normal pericyte coverage, suggesting them to be more mature. This model can be used to show that Ang-1 and VEGF use different physiological mechanisms to enhance vascularisation of relatively avascular tissue.

Genetic ablation of CD36 induces age-related corneal neovascularization

PURPOSE

Corneal avascularity is tightly regulated by a balance between angiogenic and antiangiogenic factors (angiogenic privilege). In the current study, we tested the hypothesis that the CD36+/+ antiangiogenic receptor contributes toward the maintenance of corneal avascularity.

METHODS

Corneas of CD36 wild-type (CD36) and knockout (CD36) mice aged 4, 16, 52, and 78 weeks were histologically evaluated for corneal haze and neovascularization (NV). Quantitative real-time polymerase chain reaction was performed on corneal tissue from CD36+/+ and CD36-/- mice aged 4 and 52 weeks to examine the effect of CD36 deficiency on expression of relevant angiogenic factors.

RESULTS

Corneal haze and NV were absent in CD36+/+ mice at all ages. Conversely, corneal haze and NV were evident at 52 and 78 weeks in CD36-/- mice, and the latter demonstrated a significant increase in vessel density at 52 and 78 weeks. Interestingly, compared with CD36+/+ mice, in the corneas of 52-week-old CD36-/- mice, thrombospondin-1 messenger RNA was repressed, and vascular endothelial growth factor A, c-Jun N-terminal kinase-1, and c-Jun levels were robustly upregulated.

CONCLUSIONS

CD36-/- mice develop corneal NV that increases in severity with age, thus accentuating the role of CD36 in preserving corneal avascularity.

Degradation of soluble VEGF receptor-1 by MMP-7 allows VEGF access to endothelial cells

Vascular endothelial growth factor (VEGF) signaling in endothelial cells serves a critical role in physiologic and pathologic angiogenesis. Endothelial cells secrete soluble VEGF receptor-1 (sVEGFR-1/sFlt-1), an endogenous VEGF inhibitor that sequesters VEGF and blocks its access to VEGF receptors. This raises the question of how VEGF passes through this endogenous VEGF trap to reach its membrane receptors on endothelial cells, a step required for VEGF-driven angiogenesis. Here, we show that matrix metalloproteinase-7 (MMP-7) degrades human sVEGFR-1, which increases VEGF bioavailability around the endothelial cells. Using a tube formation assay, migration assay, and coimmunoprecipitation assay with human umbilical vein endothelial cells (HUVECs), we show that the degradation of sVEGFR-1 by MMP-7 liberates the VEGF(165) isoform from sVEGFR-1. The presence of MMP-7 abrogates the inhibitory effect of sVEGFR-1 on VEGF-induced phosphorylation of VEGF receptor-2 on HUVECs. These data suggest that VEGF escapes the sequestration by endothelial sVEGFR-1 and promotes angiogenesis in the presence of MMP-7.

Abnormal epithelial homeostasis in the cornea of mice with a destrin deletion

PURPOSE

Dstn(corn1) mice lack normal destrin expression and develop corneal abnormality shortly after birth such as epithelial hyperplasia and total vascularization. Thus, the mice serve as a model for ocular surface disorders. To determine the nature of epithelial defects, we examined whether epithelial homeostasis is altered in these corneas.

METHODS

Dstn(corn1) mice were crossed with ubiquitous GFP mice to generate a double homozygous line, GFP-Dstn(corn1), and cell movements were determined by whole-mount histology and in vivo time-lapse microscopy, tracking the change of epithelial GFP patterns. Rates of cell division and the presence of label-retaining cells (LRCs) were determined by systemic bromodeoxyuridine (BrdU). Epithelial expression of keratins 8, 12, and 15, and MUC5AC were determined by whole-mount immunofluorescence.

RESULTS

Epithelial cells in an adult GFP-Dstn(corn1) cornea were generally immobile with no sign of directed movement for the entire life of the animal. These cells were not senescent because more than 70% of basal epithelial cells incorporated BrdU over a 24 h period. LRCs were widely distributed throughout a GFP-Dstn(corn1) cornea. The epithelium of a GFP-Dstn(corn1) cornea contained a mixed population of cells with a corneal and a conjunctival phenotype as judged by the expression of keratins and MUC5AC.

CONCLUSIONS

Epithelial cells of an adult GFP-Dstn(corn1) cornea are generally stationary, mitotically active, and contain LRCs, indicating that the epithelium is self-sustained, which in turn suggests that epithelial stem cells are present within the cornea. Epithelial homeostasis of adult GFP-Dstn(corn1) corneas is abnormal, mimicking that of a normal conjunctiva or a pathological, conjunctivalized cornea.