Expression of basic fibroblast growth factor mRNA in developing choroidal neovascularization

Eye on the horizon: The metabolic landscape of the RPE in aging and disease

To meet the prodigious bioenergetic demands of the photoreceptors, glucose and other nutrients must traverse the retinal pigment epithelium (RPE), a polarised monolayer of cells that lie at the interface between the outer retina and the choroid, the principal vascular layer of the eye. Recent investigations have revealed a metabolic ecosystem in the outer retina where the photoreceptors and RPE engage in a complex exchange of sugars, amino acids, and other metabolites. Perturbation of this delicate metabolic balance has been identified in the aging retina, as well as in age-related macular degeneration (AMD), the leading cause of blindness in the Western world. Also common in the aging and diseased retina are elevated levels of cytokines, oxidative stress, advanced glycation end-products, increased growth factor signalling, and biomechanical stress - all of which have been associated with metabolic dysregulation in non-retinal cell types and tissues. Herein, we outline the role of these factors in retinal homeostasis, aging, and disease. We discuss their effects on glucose, mitochondrial, lipid, and amino acid metabolism in tissues and cell types outside the retina, highlighting the signalling pathways through which they induce these changes. Lastly, we discuss promising avenues for future research investigating the roles of these pathological conditions on retinal metabolism, potentially offering novel therapeutic approaches to combat age-related retinal disease.

Choroidal Neovascular Membranes in Retinal and Choroidal Tumors: Origins, Mechanisms, and Effects

Choroidal neovascularizations are historically associated with exudative macular degeneration, nonetheless, they have been observed in nevus, melanoma, osteoma, and hemangioma involving the choroid and retina. This review aimed to elucidate the possible origins of neovascular membranes by examining in vivo and in vitro models compared to real clinical cases. Among the several potential mechanisms examined, particular attention was paid to histologic alterations and molecular cascades. Physical or biochemical resistance to vascular invasion from the choroid offered by Bruch's membrane, the role of fibroblast growth factor 2 and vascular endothelial growth factor, resident or recruited stem-like/progenitor cells, and other angiogenic promoters were taken into account. Even if the exact mechanisms are still partially obscure, experimental models are progressively enhancing our understanding of neovascularization etiology. Choroidal neovascularization (CNV) over melanoma, osteoma, and other tumors is not rare and is not contraindicative of malignancy as previously believed. In addition, CNV may represent a late complication of either benign or malignant choroidal tumors, stressing the importance of a long follow-up.

Inhibition of hypoxia-inducible factor-1 by Salidroside in an in vitro model of choroidal neovascularization

PURPOSE

As a characteristic of age-related macular degeneration (AMD), choroidal neovascularization (CNV) causes severe vision loss. The current treatment has limited efficacy. This study was to investigate effects of Salidroside against CNV and explore its underlying mechanisms.

METHODS

RF/6A cells were treated with 200 mM cobalt chloride (CoCl₂) for 6 hr to mimic hypoxic condition. Cells were then treated with Salidroside at 10, 30 and 100 µM for 24 hr. Cells treated with DMSO were used as negative control. The cell proliferation was assessed using 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium-bromid assay. The tube formation was investigated on Matrigel. The cell migration was measured by a Transwell assay. RT-qPCR was used to detect the gene expression. Immuohistochemistry and western blot were used to detect the expression of proteins.

RESULTS

Salidroside significantly inhibited the cell migration and tube formation activity of RF/6A cells under hypoxia. Moreover, Salidroside reduced the expression levels of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor-1 (HIF-1) in RF/6A cells.

CONCLUSIONS

Our data suggested that Salidroside could be a potential novel therapeutic agent against CNV.

Choriocapillaris: Fundamentals and advancements

The choriocapillaris is the innermost structure of the choroid that directly nourishes the retinal pigment epithelium and photoreceptors. This article provides an overview of its hemovasculogenesis development to achieve its final architecture as a lobular vasculature, and also summarizes the current histological and molecular knowledge about choriocapillaris and its dysfunction. After describing the existing state-of-the-art tools to image the choriocapillaris, we report the findings in the choriocapillaris encountered in the most frequent retinochoroidal diseases including vascular diseases, inflammatory diseases, myopia, pachychoroid disease spectrum disorders, and glaucoma. The final section focuses on the development of imaging technology to optimize visualization of the choriocapillaris as well as current treatments of retinochoroidal disorders that specifically target the choriocapillaris. We conclude the article with pertinent unanswered questions and future directions in research for the choriocapillaris.

Heparan Sulfate Binding Promotes Accumulation of Intravitreally Delivered Adeno-associated Viral Vectors at the Retina for Enhanced Transduction but Weakly Influences Tropism

Many adeno-associated virus (AAV) serotypes efficiently transduce the retina when delivered to the subretinal space but show limited success when delivered to the vitreous due to the inner limiting membrane (ILM). Subretinal delivery of AAV serotype 2 (AAV2) and its heparan sulfate (HS)-binding-deficient capsid led to similar expression, indicating transduction of the outer retina occurred by HS-independent mechanisms. However, intravitreal delivery of HS-ablated recombinant AAV2 (rAAV2) led to a 300-fold decrease in transduction compared to AAV2. Fluorescence in situ hybridization of AAV transgenes was used to identify differences in retinal trafficking and revealed that HS binding was responsible for AAV2 accumulation at the ILM. This mechanism was tested on human ex vivo retinas and showed similar accumulation with HS-binding AAV2 capsid only. To evaluate if HS binding could be applied to other AAV serotypes to enhance their transduction, AAV1 and AAV8 were modified to bind HS with a single-amino-acid mutation and tested in mice. Both HS-binding mutants of AAV1 and AAV8 had higher intravitreal transduction than their non-HS-binding parent capsid due to increased retinal accumulation. To understand the influence that HS binding has on tropism, chimeric AAV2 capsids with dual-glycan usage were tested intravitreally in mice. Compared to HS binding alone, these chimeric capsids displayed enhanced transduction that was correlated with a change in tropism. Taken together, these data indicate that HS binding serves to sequester AAV capsids from the vitreous to the ILM but does not influence retinal tropism. The enhanced retinal transduction of HS-binding capsids provides a rational design strategy for engineering capsids for intravitreal delivery.

IMPORTANCE

Adeno-associated virus (AAV) has become the vector of choice for viral gene transfer and has shown great promise in clinical trials. The need for development of an easy, less invasive injection route for ocular gene therapy is met by intravitreal delivery, but delivery of AAV by this route results in poor transduction outcomes. The inner limiting membrane (ILM) creates a barrier separating the vitreous and the retina. Binding of AAV to heparan sulfate proteoglycan (HSPG) at the ILM may allow the virus to traverse this barrier for better retinal transduction. We show that HSPG binding is correlated with greater accumulation and penetration of AAV in the retina. We demonstrated that this accumulation is conserved across mouse and human retinas and that the addition of HSPG binding to other AAV capsids can increase the number of vectors accumulating at the ILM without dictating tropism.

Aflibercept: a review of its use in the treatment of choroidal neovascularization due to age-related macular degeneration

Choroidal neovascularization (CNV) due to age-related macular degeneration (AMD) is an important cause of visual morbidity globally. Modern treatment strategies for neovascular AMD achieve regression of CNV by suppressing the activity of key growth factors that mediate angiogenesis. Vascular endothelial growth factor (VEGF) has been the major target of neovascular AMD therapy for almost two decades, and there have been several intravitreally-administered agents that have enabled anatomical restitution and improvement in visual function with continual dosing. Aflibercept (EYLEA(®)), initially named VEGF Trap-eye, is the most recent anti-VEGF agent to be granted US Food and Drug Administration approval for the treatment of neovascular AMD. Biologic advantages of aflibercept include its greater binding affinity for VEGF, a longer intravitreal half-life relative to other anti-VEGF agents, and the capacity to antagonize growth factors other than VEGF. This paper provides an up-to-date summary of the molecular mechanisms mediating CNV. The structural, pharmacodynamic, and pharmacokinetic advantages of aflibercept are also reviewed to rationalize the utility of this agent for treating CNV. Results of landmark clinical investigations, including VIEW 1 and 2 trials, and other important studies are then summarized and used to illustrate the efficacy of aflibercept for managing treatment-naïve CNV, recalcitrant CNV, and CNV due to polypoidal choroidal vasculopathy. Safety profile, patient tolerability, and quality of life measures related to aflibercept are also provided. The evidence provided in this paper suggests aflibercept to be a promising agent that can be used to reduce the treatment burden of neovascular AMD.

The dynamic sclera: extracellular matrix remodeling in normal ocular growth and myopia development

Myopia is a common ocular condition, characterized by excessive elongation of the ocular globe. The prevalence of myopia continues to increase, particularly among highly educated groups, now exceeding 80% in some groups. In parallel with the increased prevalence of myopia, are increases in associated blinding ocular conditions including glaucoma, retinal detachment and macular degeneration, making myopia a significant global health concern. The elongation of the eye is closely related to the biomechanical properties of the sclera, which in turn are largely dependent on the composition of the scleral extracellular matrix. Therefore an understanding of the cellular and extracellular events involved in the regulation of scleral growth and remodeling during childhood and young adulthood will provide future avenues for the treatment of myopia and its associated ocular complications.

Suppression of laser-induced choroidal neovascularization by intravitreal injection of tristetraprolin

AIM

To examine the effect of intravitreal adenoviral vector-mediated tristetraprolin (Ad-TTP) on VEGF mRNA expression in a rat model of laser-induced choroidal neovascularization.

METHODS

Ad-TTP was prepared using a commercial kit. Retinal laser-induced photocoagulation (10 spots per eye) was performed on rats in this experimental choroidal neovascularization (CNV) model. Rats were divided into four groups: control (single intravitreal injection of balanced salt solution, n=10), laser-induced CNV (photocoagulation only, n=20), laser-induced CNV plus Ad-TTP injection (photocoagulation plus a single intravitreal Ad-TTP injection, n=20) and Ad-TTP injection only (n=10). Changes in choroidal morphology were evaluated in ten rats in the laser only and the laser plus Ad-TTP groups. Two weeks after laser injury, the size of CNV was calculated by perfusion with high-molecular-weight fluorescein isothiocyanate (FITC)-dextran. VEGF mRNA expression in retina-choroid tissue from ten rats in each group was measured by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Two weeks after treatment, the area of laser-induced CNV was reduced by approximately 60% in the rats given the Ad-TTP injection compared with that in the laser-only group. There was a tendency toward decreased VEGF mRNA expression in the Ad-TTP injection groups.

CONCLUSION

A single intravitreal injection of Ad-TTP significantly suppressed CNV size in this experimental laser-induced CNV model. Ad-TTP injection also decreased VEGF mRNA expression compared with that in the laser-induced CNV group. The present study is meaningful as the first study to investigate the effect of tristetraprolin delivered via intravitreal injection.

The choroid as a sclera growth regulator

Emmetropization is a vision dependent mechanism that attempts to minimize refractive error through coordinated growth of the cornea, lens and sclera such that the axial length matches the focal length of the eye. It is generally accepted that this visually guided eye growth is controlled via a cascade of locally generated chemical events that are initiated in the retina and ultimately cause changes in scleral extracellular matrix (ECM) remodeling which lead to changes in eye size and refraction. Of much interest, therefore, are the molecular mechanisms that underpin emmetropization and visually guided ocular growth. The choroid, a highly vascularized layer located between the retina and the sclera is uniquely situated to relay retina-derived signals to the sclera to effect changes in ECM synthesis and ocular size. Studies initiated by Josh Wallman clearly demonstrate that the choroid plays an active role in emmetropization, both by modulation of its thickness to adjust the retina to the focal plane of the eye (choroidal accommodation), and well as through the release of growth factors that have the potential to regulate scleral extracellular matrix remodeling. His discoveries prompted numerous investigations on the molecular composition of the choroid and changes in gene expression associated with visually guided ocular growth. This article will review molecular and functional studies of the choroid to provide support for the hypothesis that the choroid is a source of sclera growth regulators that effect changes in ocular growth in response to visual stimuli.

Animal models of age related macular degeneration

Age related macular degeneration (AMD) is the leading cause of vision loss of those over the age of 65 in the industrialized world. The prevalence and need to develop effective treatments for AMD has lead to the development of multiple animal models. AMD is a complex and heterogeneous disease that involves the interaction of both genetic and environmental factors with the unique anatomy of the human macula. Models in mice, rats, rabbits, pigs and non-human primates have recreated many of the histological features of AMD and provided much insight into the underlying pathological mechanisms of this disease. In spite of the large number of models developed, no one model yet recapitulates all of the features of human AMD. However, these models have helped reveal the roles of chronic oxidative damage, inflammation and immune dysregulation, and lipid metabolism in the development of AMD. Models for induced choroidal neovascularization have served as the backbone for testing new therapies. This article will review the diversity of animal models that exist for AMD as well as their strengths and limitations.

Genetic association study of age-related macular degeneration in the Spanish population

PURPOSE

To investigate new genetic risk factors and replicate reported associations with advanced age-related macular degeneration (AMD) in a prospective case-control study developed with a Spanish cohort.

METHODS

Three hundred and fifty-three unrelated patients with advanced AMD (225 with atrophic AMD, 57 with neovascular AMD, and 71 with mixed AMD) and 282 age-matched controls were included. Functional and tagging SNPs in 55 candidate genes were genotyped using the SNPlex™ genotyping system. Single SNP and haplotype association analysis were performed to determine possible genetic associations; interaction effects between SNPs were also investigated.

RESULTS

In agreement with previous reports, ARMS2 and CFH genes were strongly associated with AMD in the studied Spanish population. Moreover, both loci influenced risk independently giving support to different pathways implicated in AMD pathogenesis. No evidence for association of advanced AMD with other previous reported susceptibility genes, such as CST3, CX3CR1, FBLN5, HMCN1, PON1, SOD2, TLR4, VEGF and VLDLR, was detected. However, two additional genes appear to be candidate markers for the development of advanced AMD. A variant located at the 3' UTR of the FGF2 gene (rs6820411) was highly associated with atrophic AMD, and the functional SNP rs3112831 at ABCA4 showed a marginal association with the disease.

CONCLUSION

We performed a large gene association study in advanced AMD in a Spanish population. Our findings show that CFH and ARMS2 genes seem to be the principal risk loci contributing independently to AMD in our cohort. We report new significant associations that could also influence the development of advanced AMD. These findings should be confirmed in further studies with larger cohorts.

Effects of photodynamic therapy using hematoporphyrin monomethyl ether on experimental choroidal neovascularization

Hematoporphyrin monomethyl ether (HMME) is a novel and promising second-generation porphyrin-related photosensitizer for photodynamic therapy (PDT). To study the effects of HMME PDT on choroidal neovascularization (CNV) in rats, the PDT was performed 20 min after HMME bolus injection, which was investigated prior to the PDT by fluorescence microscopy with laser-induced CNV, and delivered at an irradiance of 400, 600 and 1000 mW cm(-2) corresponding to a fluence of 36, 54, 90 J cm(-2) in PDT plan I (15 mg kg(-1) HMME). In PDT plan II (30 mg kg(-1) HMME), the laser had a constant irradiance of 600 mW cm(-2), which was delivered for 60, 90 or 150 s, to also achieve total energy doses of 36, 54 or 90 J cm(-2). CNV closure rates assessed by fluorescein angiography and histologic damage to treated areas of choroid and retina varied as a function of the dose of HMME and of the activating light energy fluence. Endothelial cell labeled by platelet/endothelial cell adhesion molecule-1 presented treated CNV lesions that were significantly reduced in size (P < 0.01). It can be concluded that PDT using HMME can effectively occlude CNV. HMME is a potentially useful photosensitizer for the reduction in CNV size of irradiated areas.

Inhibitory effects of arresten on bFGF-induced proliferation, migration, and matrix metalloproteinase-2 activation in mouse retinal endothelial cells

PURPOSE

The potential role of arresten (alpha1(IV)NC1) as an endogenous angiogenesis inhibitor in the prevention of bFGF mediated retinal angiogenesis and regulation of matrix metalloproteinase-2 activation has not been explored.

METHODS

Mouse retinal endothelial cells (MREC) were cultured on type IV collagen and treated with basic fibroblast growth factor (bFGF) alone or in the presence of arresten at concentrations ranging from 1 to 10 microg/ml. The proliferation of MRECs were evaluated using 3(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay, and bFGF stimulated endothelial cell migration was assessed using Boyden chamber. Expression of matrix metalloproteinase-2 (MMP-2) was assessed by reverse transcription polymerase chain reaction (RT-PCR) analysis using RNA isolated from MRECs. Secretion and activation of MMP-2 in arresten-treated conditioned MREC growth medium was determined by gelatin zymography and Western blotting.

RESULTS

Different doses of bFGF induced MREC proliferation was significantly inhibited upon arresten treatment (P < 0.005). The bFGF-induced migration was significantly inhibited by arresten at 1 and 10 microg/ml concentrations (P < 0.01). The bFGF stimulated expression of MMP-2 mRNA and secretion of MMP-2 in MREC was not affected and interestingly activation of MMP-2 was suppressed by arresten in a dose and time dependent manner.

CONCLUSIONS

Inhibitory effects of arresten on proliferation, migration and MMP-2 activation but not on expression and secretion of MMP-2 in MREC; this early work with arresten supports potential therapeutic action in retinal neovascularization dependent disorders.

Introduction: Understanding the role of angiogenesis and antiangiogenic agents in age-related macular degeneration

Inhibition of angiogenesis is critical in the prevention and treatment of neovascular age-related macular degeneration (AMD). Pathologic states such as hypoxia, ischemia, or inflammation may tip the balance of proangiogenic and antiangiogenic factors in favor of the formation of new blood vessels. Vascular endothelial growth factor (VEGF) is pivotal in ocular angiogenesis because it is highly selective for endothelial cells, hypoxia drives its synthesis, it diffuses to its target, and it affects multiple components of angiogenesis such as endothelial cell proliferation, survival, and migration. Basic and clinical research implicates VEGF in the pathogenesis of choroidal neovascularization (CNV), although other candidate factors involved with regulation of angiogenesis exist. Intravitreal drugs that block VEGF have revolutionized the care of patients with neovascular AMD, decreasing growth and leakage from choroidal neovascular lesions and preventing moderate and severe vision loss associated with this process.

Differences in the temporal expression of regulatory growth factors during choroidal neovascular development

Although the roles of vascular endothelial growth factor (VEGF), basic fibroblast growth factor (bFGF), and hepatocyte growth factor (HGF) in pathologic neovascularization have been well characterized in certain tissues, their particular functions and expression patterns in choroidal neovascularization (CNV) have not been clearly established. After localized laser trauma to Bruch's membrane to induce CNV development, the temporal changes in mRNA and protein expression of these 3 cytokines were documented and compared histologically to areas of immunofluorescence, the proliferation of endothelial cells, neovascular development, and temporal changes in vascular permeability. Changes in mRNA and protein levels of bFGF and HGF occurred quickly and reached peak expression within hours. This activity corresponded in time to intense and localized immunofluorescence for these cytokines within the choriocapillaris within laser lesion sites. During this same initial time period, mRNA upregulation of VEGF occurred, primarily within the neural retina and this expression corresponded to intense immunolabeling of Müller cells immediately adjacent to the lesion sites. By 3 days after lasering, increased VEGF(164) protein expression was measurable, whereas early neovascular development histologically corresponded to HGF and bFGF mRNA expansion into the developing choroidal neovascular membrane (CNVM). At 7 days, CNV expansion, maturation, and increased vascular permeability corresponded to peak VEGF mRNA and protein expression and to immunofluorescence of the CNVM. Differences also occurred in the expression of precursor and activated isoforms of these cytokines in the retinal pigment epithelium/choroid as compared to those in the retina. These molecular and immunocytochemical results suggest that bFGF and HGF may be important as initial regulators neovascularization in this CNV model; whereas VEGF may be important during later phases of angiogenesis and neovascular hyperpermeability.

Regulation of VEGF mRNA expression and protein secretion by TGF-beta2 in human retinal pigment epithelial cells

VEGF secretion by the human retinal pigment epithelium (hRPE) plays an important role in retinal and choroidal neovascularization. In this study, transforming growth factor-beta2 (TGF-beta2)-induced vascular endothelial growth factor (VEGF) gene expression was investigated in hRPE cells. Treatment of hRPE cells with TGF-beta2 for 24 and 48h as compared to 8h resulted in markedly increased VEGF secretion by fivefold and nine-fold, respectively. Induced VEGF mRNA peaked within 3h of stimulation and remained above the basal at 36h. Stimulation of VEGF expression by TGF-beta2 was blocked by cycloheximide, suggesting that de novo protein synthesis is required. Induced VEGF production was strongly inhibited by anti-inflammatory agents, dexamethasone and cyclosporin A. Despite of the weak stimulation of VEGF expression by TNF-alpha or bFGF alone, co-administration of either of these two cytokines synergized the effect of TGF-beta2 on VEGF mRNA expression and protein production. Quantitative RT-PCR revealed that the synergy was predominantly at the level of VEGF transcription. Moreover, TGF-beta2-induced RPE VEGF secretion was significantly reduced by inhibitors of mitogen-activated protein (MAP) kinase (MEK) (U0126), p38 (SB202190), c-Jun NH2-terminal kinase (JNK), Sp600125, protein tyrosine kinase (PTK) (Genistein), and phosphatidylinositol 3-kinase (PI3K) (Ly294002). Induced VEGF expression was completely abrogated by inhibitors of protein kinase C (PKC) (Ro318220), nuclear factor-kappaB (NF-kappaB) [caffeic acid phenethyl ester (CAPE)], and reactive oxygen species (ROS) [N-acetyl-cysteine (Nac) and diphenyleneiodonium (DPI)]. These results suggest that MEK, p38, JNK, PI3K, and NF-kappaB as well as multiple essential signaling intermediates, including PKC, PTK and ROS, are involved in hRPE VEGF up regulation by TGF-beta2.

ORAL ADMINISTRATION OF LUMIRACOXIB REDUCES CHOROIDAL NEOVASCULAR MEMBRANE DEVELOPMENT IN THE RAT LASER-TRAUMA MODEL

PURPOSE

To determine whether lumiracoxib, a highly selective cyclooxygenase-2 (COX-2) inhibitor that exhibits anti-inflammatory and antiangiogenic properties, can inhibit experimental choroidal neovascular membrane (CNVM) development induced by focal laser trauma in a well-characterized Brown Norway rat CNVM model.

METHODS

Over a 35-day period, 24 rats received daily oral gavage dosages of 20 mg/kg lumiracoxib in a 0.5% (w/v) suspension of sodium carboxymethylcellulose (CMC), while a control group received the 0.5% CMC suspension only. After 7 days, eight laser photocoagulation sites were placed concentrically around the optic disk to induce CNVMs. Thirty-five days later, fundus photography and fluorescein angiography (FA) were performed and eyes were processed for histopathologic analysis.

RESULTS

Masked FA grading of lesion sites revealed a small, but statistically significant difference (P<0.0001) in late stage staining intensity and leakage between the mean group scores of treated (1.4) and control (1.7) eyes. Histopathologic analysis demonstrated that the mean CNVM thickness +/- SD of 38 +/-19 microm (n=24 eyes, 175 photocoagulation sites) in the lumiracoxib-treated animals was reduced by 30% (P<0.001) compared to the CNVM mean thickness+/- SD of 54+/- 20 microm (n=24 eyes, 171 photocoagulation sites) in the control animals.

CONCLUSION

Systemic administration of the selective COX-2 inhibitor lumiracoxib results in a partial but significant reduction in CNVM development in the rat laser-trauma model and thus may be clinically beneficial as a potential inhibitor of CNVM formation in exudative age-related macular degeneration.

The fibroblast growth factor receptors, FGFR-1 and FGFR-2, mediate two independent signalling pathways in human retinal pigment epithelial cells

To examine the effects and potential implications for the expression of the two basic fibroblast growth factor (bFGF) receptors, FGFR-1 and FGFR-2, in retinal pigment epithelial (RPE) cells, bFGF-dependent changes in gene expression and RPE cell function were studied. bFGF increased L-type Ca2+ channel activity of RPE cells, which in turn resulted in an increase of vascular endothelial growth factor A (VEGF-A) secretion from RPE cells. Also, both bFGF and direct stimulation of L-type Ca2+ channels by BayK8644 increased the expression of c-fos in RPE cells, to the same extent. bFGF-induced-c-fos expression was reduced by inhibition of FGFR-1, but not by L-type Ca2+ channel inhibition, demonstrating that stimulation of FGFR-1 results in a Ca2+ channel-independent change of gene expression. In contrast, stimulation of FGFR-2 results in a Ca2+ channel-dependent stimulation of VEGF secretion. Furthermore, immunohistological investigation of neovascular tissues obtained from patients with age-related macular degeneration (AMD) revealed FGFR-1 and FGFR-2 expression in the RPE of the diseased tissue. Our findings support the hypothesis that there are two different FGFR-1- and FGFR-2-dependent pathways that modulate the role of bFGF in induction of neovascularisation in AMD.

Time-course of experimental choroidal neovascularization in Dutch-Belted rabbit: clinical and histological evaluation

In order to study the pathogenesis of choroidal neovascularization (CNV) and explore a suitable animal model for assessing anti-angiogenic agents, rabbit CNV was induced by subretinal injection of a cocktail containing endotoxin and growth-factor, incorporated in Heparin-sepharose beads. The presence and development of CNV lesions was visualized by fluorescein angiography and quantified by image analysis. The time-course of experimental CNV was evaluated clinically and histologically, with some lesions followed up to 3-years. The suitability of this model for drug evaluation was appraised by the systemic administration of dexamethasone. The experimental results suggest two subsets of CNV, primary and secondary, observed in all treated eyes. Primary CNV, defined as neovascularization extending into the subretinal space and associated with injury to Bruch's membrane at the time of injection, was visible in 100% of eyes by 2-weeks and stable by 3-months. Secondary CNV, defined as neovascularization extending into the sub RPE space away from the initial injection related injury, became visible as early as 2-weeks in some of eyes and developed in 100% of eyes by 8-months. Both primary and secondary CNV were maintained and demonstrated leakage throughout the entire observation period. Atrophy of primary retinal pigmented epithelium (RPE) cells and hyper-proliferation of secondary RPE cells were observed in tissue sections with CNV lesions. The formation and growth of primary and secondary CNV were significantly inhibited by dexamethasone. This study indicates that a reproducible and quantitative model of rabbit CNV has been established utilizing subretinal administration of endotoxin and growth-factor. Studies of the stages of experimental CNV both clinically and histologically indicated an intimate relationship between CNV, macrophages and RPE. Furthermore, the inhibition observed with dexamethasone points to the possibility of being able to evaluate effective means of pharmacological intervention.

Impact of endostatin on bFGF-induced proliferation, migration, and matrix metalloproteinase-2 expression/secretion of bovine choroidal endothelial cells

PURPOSE

To investigate the potential role of endostatin, an endogenous angiogenesis inhibitor, in the prevention of choroidal angiogenesis-related disorders.

METHODS

Bovine choroidal endothelial cells (CEC) were cultured and treated with basic fibroblast growth factor (bFGF) alone or combined with endostatin at concentrations ranging from 0.1 to 10 microg/ml. The proliferation and migration of CECs were evaluated by using 3, (4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay and modified Boyden chamber assay, respectively. For evaluating expression and secretion of matrix metalloproteinase-2 (MMP-2), CEC-conditioned media were subjected to zymography and/or Western blot analysis, and the cells were used for semiquantitative reverse transcription polymerase chain reaction (RT-PCR) analysis.

RESULTS

Endostatin did not inhibit bFGF-induced or nonstimulated CEC proliferation (p > 0.05). The bFGF-induced migration was significantly inhibited by endostatin at concentrations of 1 and 10 microg/ml (p < 0.05). The bFGF-upregulated expression of mRNA in CECs and the secretion of MMP-2 protein of CECs were both suppressed by endostatin.

CONCLUSIONS

Inhibitory effect of endostatin on expression and secretion of MMP-2 and cell migration, but not on proliferation of CECs, could respond to its therapeutic action for choroidal neovascularization-dependent disorders.

Retinal degeneration is delayed by tissue factor pathway inhibitor-2 in RCS rats and a sodium-iodate-induced model in rabbits

PURPOSE

To investigate the in vivo effects of tissue factor pathway inhibitor 2 (TFPI-2), which stimulates proliferation of retinal pigment epithelial cells, but not the proliferation of fibroblast and vascular endothelial cells in vitro, on retinal degeneration using a sodium-iodate (SI)-induced model in rabbits and Royal Collage of Surgeons (RCS) rats.

METHODS

79 microg of recombinant TFPI-2 (rTFPI-2) or vehicle alone was injected intravitreously to 18 eyes of 12 pigmented rabbits a day after 20 mg/kg of SI was intravenously administered. Retinal function was assessed 4, 7, 14, and 21 days after the injection by analysing amplitudes of the c-wave of a bright flash electroretinogram. Additionally, 10 microg of rTFPI-2 or vehicle alone was injected intravitreously to 11 eyes of RCS rats at both 3 and 4 weeks old, then the retina was examined histologically at 5 weeks old.

RESULTS

The rTFPI-2-treated eyes in rabbits showed a significantly less decrease in the relative amplitude of the c-wave than control eyes on days 4 and 7. The thickness of the outer nuclear layer was significantly thicker and the vacuole in the photoreceptor layer was less frequently observed in the rTFPI-2-treated RCS rats than the controls.

CONCLUSIONS

Intravitreal injection of TFPI-2 rescues SI-induced retinal degeneration in rabbits and naturally occurring retinal degeneration in RCS rats at least partly. These results may suggest that this compound can be utilized in the treatment of retinal degeneration.

Role of complement and complement membrane attack complex in laser-induced choroidal neovascularization

Choroidal neovascularization (CNV), or choroidal angiogenesis, is the hallmark of age-related macular degeneration and a leading cause of visual loss after age 55. The pathogenesis of new choroidal vessel formation is poorly understood. Although inflammation has been implicated in the development of CNV, the role of complement in CNV has not been explored experimentally. A reliable way to produce CNV in animals is to rupture Bruch's membrane with laser photocoagulation. A murine model of laser-induced CNV in C57BL/6 mice revealed the deposition of C3 and membrane attack complex (MAC) in the neovascular complex. CNV was inhibited by complement depletion using cobra venom factor and did not develop in C3(-/-) mice. Anti-murine C6 Abs in C57BL/6 mice inhibited MAC formation and also resulted in the inhibition of CNV. Vascular endothelial growth factor, TGF-beta2, and beta-fibroblast growth factor were elevated in C57BL/6 mice after laser-induced CNV; complement depletion resulted in a marked reduction in the level of these angiogenic factors. Thus, activation of complement, specifically the formation of MAC, is essential for the development of laser- induced choroidal angiogenesis in mice. It is possible that a similar mechanism may be involved in the pathophysiology of other angiogenesis essential diseases.

Expression of pigment epithelium derived factor and vascular endothelial growth factor in choroidal neovascular membranes and polypoidal choroidal vasculopathy

AIMS

To determine whether pigment epithelium derived factor (PEDF), a protein that inhibits angiogenesis, is expressed in human choroidal neovascular membranes (CNVMs) and in tissues from an eye with polypoidal choroidal vasculopathy (PCV). In addition, to compare the expression of PEDF with that of vascular endothelial growth factor (VEGF), a known stimulator of angiogenesis, in these tissues.

METHODS

CNVMs, associated with age related macular degeneration (AMD), angioid streaks, and PCV, were obtained during surgery. The expression of PEDF and VEGF in the excised subretinal fibrovascular membranes was determined by immunohistochemistry.

RESULTS

PEDF and VEGF were strongly expressed in the vascular endothelial cells and retinal pigment epithelial (RPE) cells in the CNVMs where numerous new vessels were prominent (clinically active CNVMs). On the other hand, immunoreactivity for PEDF and VEGF was weak in the new vessels where fibrosis was prominent (clinically quiescent CNVMs). However, the RPE cells were still positive for PEDF and VEGF. The specimens from the eye with PCV also showed strong expression of PEDF and VEGF in the vascular endothelial cells and the RPE cells.

CONCLUSION

Because PEDF is an inhibitor of ocular angiogenesis and an inhibitor of ocular cell proliferation, our results suggest that PEDF along with VEGF may modulate the formation of subfoveal fibrovascular membranes.

Squalamine lactate reduces choroidal neovascularization in a laser-injury model in the rat

PURPOSE

To determine if systemically administered squalamine lactate, a novel aminosterol with antineoplastic and antiangiogenic activity, inhibits the development of experimental choroidal neovascularization membranes (CNVMs) induced by laser trauma in a rat model.

METHODS

Twenty anesthetized male Brown-Norway rats received a series of 8 krypton red laser lesions per eye (647 nm, 0.05 second, 50 microm, 150 mW). One half the animals received an intraperitoneal injection of squalamine and the other one half received an injection of 5% dextrose in water, all performed in a masked fashion. Fundus photography and fluorescein angiography were performed at postlaser treatment days 14 and 28, and ocular tissues were processed for light microscopic examination following euthanasia of the rats on postlaser treatment day 28.

RESULTS

Although fundus photography and fluorescein angiography yielded no statistically significant quantitative differences between the two groups, histologic analysis of the lesion sites revealed a partial but statistically significant reduction of experimental CNVM development in the squalamine-treated population. In particular, the squalamine-treated eyes (n = 20) demonstrated lesions (n = 149) with a mean CNVM thickness +/- SD of 47 +/- 11 microm, as compared with the control eyes (n = 20) that had lesions (n = 142) with a mean CNVM thickness +/- SD of 63 +/- 14 microm (P < 0.001).

CONCLUSION

Systemically administered squalamine lactate partially reduced choroidal neovascular membrane development induced by laser trauma in this animal model. In conjunction with other existing and developing therapies, this agent may have a potential role in the treatment of human CNVM formation. Further study of squalamine lactate for treatment of neovascular eye disease is warranted.

Choroidal neovascular membrane inhibition in a laser treated rat model with intraocular sustained release triamcinolone acetonide microimplants

AIM

To determine if intravitreal microimplants containing triamcinolone acetonide (TAAC) inhibit experimental fibrovascular proliferation (FVP) induced by laser trauma in a rat as a model of choroidal neovascular membranes (CNVMs).

METHODS

20 anaesthetised male Brown Norway rats received a series of eight krypton red laser lesions per eye (647 nm, 0.05 s, 50 micro m, 150 mW). Three types of sterilised TAAC microimplant designs were evaluated: implant A consisting of 8.62% TAAC/20% polyvinyl alcohol (PVA) matrix (by dry weight); implant B consisting of 3.62% TAAC/20% PVA matrix; and implant C consisting of a dual 8.62% TAAC/20% PVA matrix design combined with a central core (0.5 mm) of compressed TAAC to extend the implant release time. For each animal studied, one eye received one of the three aforementioned TAAC implant designs, while the fellow eye received a control implant consisting of PVA but without TAAC. The animals were sacrificed at day 35 and ocular tissues were processed for histological analysis. Serial histological specimens were methodically assessed in a masked fashion to analyse each laser lesion for the presence or absence of FVP; maximum FVP thickness for each lesion was measured from the choriocapillaris.

RESULTS

All three types of TAAC implants inhibited FVP relative to controls in a statistically significant fashion. In the eyes that received implant A (n = 8), the mean thickness of the recovered lesions (n = 36) measured 32 (SD 22) micro m, compared to 52 (30) micro m (p <0.005) for the recovered lesions (n = 40) from the fellow control eyes. In the eyes that received implant B (n = 6), the mean thickness of the recovered lesions (n = 31) measured 28 (15) micro m, compared to 50 (29) micro m (p <0.001) for the lesions (n = 19) recovered from the fellow control eyes. In the eyes that received implant C (n = 6), the mean thickness of the recovered lesions (n = 21) measured 39 (24) micro m, compared to 65 (30) micro m (p <0.001) for the lesions (n = 39) recovered from the fellow control eyes.

CONCLUSIONS

All three of the tested TAAC microimplant designs produced potent inhibition of FVP in a rat model of CNVMs. There were no differences in inhibition of FVP between the three different types of implants evaluated. This study provides evidence that: (1) corroborates previous investigations that propose TAAC as a potential treatment for CNVMs in humans, and (2) demonstrates TAAC can be effectively delivered via long acting sustained release intraocular microimplants. It should be noted, however, that the FVP observed in this rat laser trauma may not reflect the CNVM observed in human with exudative age related macular degeneration (AMD).

Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies

Age-related macular degeneration is the principal cause of registered legal blindness among those aged over 65 in the United States, western Europe, Australia, and Japan. Despite intensive research, the precise etiology of molecular events that underlie age-related macular degeneration is poorly understood. However, investigations on parallel fronts are addressing this prevalent public health problem. Sophisticated biochemical and biophysical techniques have refined our understanding of the pathobiology of drusen, geographic atrophy, and retinal pigment epithelial detachments. Epidemiological identification of risk factors has facilitated an intelligent search for underlying mechanisms and fueled clinical investigation of behavior modification. Gene searches have not only brought us to the cusp of identifying the culpable gene loci in age-related macular degeneration, but also localized genes responsible for other macular dystrophies. Recent and ongoing investigations, often cued by tumor biology, have revealed an important role for various growth factors, particularly in the neovascular form of the condition. Transgenic and knockout studies have provided important mechanistic insights into the development of choroidal neovascularization, the principal cause of vision loss in age-related macular degeneration. This in turn has culminated in preclinical and clinical trials of directed molecular interventions.

VEGF-TRAP(R1R2) suppresses choroidal neovascularization and VEGF-induced breakdown of the blood-retinal barrier

Vascular endothelial growth factor (VEGF) plays a central role in the development of retinal neovascularization and diabetic macular edema. There is also evidence suggesting that VEGF is an important stimulator for choroidal neovascularization. In this study, we investigated the effect of a specific inhibitor of VEGF, VEGF-TRAP(R1R2), in models for these disease processes. VEGF-TRAP(R1R2) is a fusion protein, which combines ligand binding elements taken from the extracellular domains of VEGF receptors 1 and 2 fused to the Fc portion of IgG1. Subcutaneous injections or a single intravitreous injection of VEGF-TRAP(R1R2) strongly suppressed choroidal neovascularization in mice with laser-induced rupture of Bruch's membrane. Subcutaneous injection of VEGF-TRAP(R1R2) also significantly inhibited subretinal neovascularization in transgenic mice that express VEGF in photoreceptors. In two models of VEGF-induced breakdown of the blood-retinal barrier (BRB), one in which recombinant VEGF is injected into the vitreous cavity and one in which VEGF expression is induced in the retina in transgenic mice, VEGF-TRAP(R1R2) significantly reduced breakdown of the BRB. These data confirm that VEGF is a critical stimulus for the development of choroidal neovascularization and indicate that VEGF-TRAP(R1R2) may provide a new agent for consideration for treatment of patients with choroidal neovascularization and diabetic macular edema.

Absence of fibroblast growth factor 2 does not prevent tumor formation originating from the RPE

We have analysed the importance of fibroblast growth factor 2 (FGF2) in tumor development. In a transgenic mouse model (Tyrp1-Tag) tumors form in the retinal pigment epithelium (RPE), invade surrounding tissues, and metastasize to lymph node and spleen. To address whether RPE tumor formation is dependent on FGF2, we generated FGF2-deficient mice. Such mice appeared healthy and exhibited no impairment of growth or development. Tyrp1-Tag transgenic mice, which are lacking FGF2 (FGF2-/-) developed RPE tumors that metastasize to spleen and lymph nodes. Tumor growth and survival rate are identical to Tyrp1-Tag transgenic littermates expressing FGF2. Cell lines were isolated from RPE tumors of wild-type and FGF2-deficient mice. They grow in culture, are pigmented and form vascularized tumors, when injected subcutaneously into nude mice of either FGF2-/- or FGF2+/+ genetic background. Kinetics of tumor growth was identical and independent of presence of FGF2. Together, these results demonstrate that FGF2 is not essential for tumor formation of the RPE thus suggesting that tumor growth in general may not be dependent on FGF2.

Quantitative image analysis of laser-induced choroidal neovascularization in rat

Rodent models of laser-induced choroidal neovascularization (CNV) are now extensively used to identify angiogenic proteins, determine the role of specific genes with knockout mice, and evaluate the efficacy and safety of anti-angiogenic therapies. CNV is typically evaluated by fluorescein angiography or vascular endothelial cell labeling in histologic sections. The current study examined an alternative method using high molecular weight FITC-dextran (MW 2 x 10(6)) for high resolution angiography in RPE-choroid-sclera flat mounts. At 24 hr after lasering, the lesions appeared as a circular weakly fluorescent area of approximately equal diameter to the laser spot. No FITC-dextran labeled blood vessels were visible in the lesion at day 1. Three days after lasering, 47% of the lesions showed FITC-dextran labeling indicative of CNV. The incidence (71%) and extent of CNV increased by day 6, and by day 10 all lesions were vascularized, and the maximal area was attained. No significant change followed day 10, and the neovascular area remained constant through day 31. The highest rate of blood vessel growth (between 3 and 10 days after laser) correlates with the peak expression of VEGF, bFGF, and their receptors shown in previous studies. Morphologic analysis of flat mounts and histologic sections showed that the neovascular plexus in most lesions originates from deeper choroidal vessels in the center of the lesion, grows towards the neural retina, then branches circumferentially to anastamose with uninjured choriocapillaris. The microvessels in these lesions are broad and flat, similar to normal choriocapillaris. In a separate study, rats were treated daily with the angiostatic corticosteroid dexamethasone (20-500 microg kg(-1)day(-1)), and CNV was examined at day 10 in FITC-dextran labeled flat mounts and histologic sections. Dexamethasone dose-dependently inhibited CNV, and its highest dose inhibited approximately 95% of CNV labeled by FITC-dextran and resulted in lesions with no detectable Factor VIII immunostaining. High resolution angiography with FITC-dextran is reproducible and quantifiable, and it may accelerate the discovery of therapeutic agents that modulate choroidal neovascularization.

Neural and angiogenic defects in eyes of transgenic mice expressing a dominant-negative FGF receptor in the pigmented cells

Fibroblast growth factors (FGF) are multipotent cytokines with demonstrated mitogenic, neurotrophic and angiogenic properties. There is evidence that they have multiple functions during and after development of the vertebrate eye. Amongst these, the role of FGF receptor mediated signaling in the retinal pigmented epithelium (RPE) is not yet well understood. FGF-2 is produced in RPE cells and may play a role in photoreceptor development and/or survival in vivo. It may also stimulate growth of melanocytes and angiogenesis in the choroid. To address these questions, we have specifically disrupted FGF signaling by generating lines of transgenic mice expressing dominant-negative FGF receptor 1 (FGFR-1) in the pigmented cells. Histological analysis of the eyes were conducted on hemizygous and homozygous mice at different ages. In homozygotes, eye growth is strongly impaired during embryogenesis leading to massive eye degeneration seen in the early post-natal stages. In hemizygotes, the choroid is thinned and the finger-like junctions between RPE cells and photoreceptors are disrupted. Scanning electron microscopy of the choroid vasculature showed that choriocapillary density, diameter and branching are strongly affected. As mice age, they develop progressive retinal degeneration as evidenced by photoreceptor cell loss. Our results are in agreement with the hypothesis that FGF signaling in the RPE participates in photoreceptor survival in vivo. Our model provides evidence that FGF signaling is also involved in choroidal angiogenesis by a process that could relate to induction of terminal branching.

Cell injury unmasks a latent proangiogenic phenotype in mice with increased expression of FGF2 in the retina

Fibroblast growth factor-2 (FGF2) is a potent mitogen for vascular endothelial cells and exogenous administration of FGF2 stimulates angiogenesis. However, increased expression of FGF2 in the retina does not cause angiogenesis. One possible explanation is that FGF2 may not be capable of initiating angiogenesis unless it is administered in pharmacologic levels or there is coexpression of another angiogenic factor. Alternatively, there may be control mechanisms that sequester FGF2 in vivo, preventing it from manifesting its in vitro angiogenic activity. We tested the first hypothesis by crossing mice that express FGF2 in the retina with mice that express vascular endothelial growth factor (VEGF) in the retina. Surprisingly, despite comparable levels of VEGF expression, mice that expressed both FGF2 and VEGF had significantly less neovascularization than mice that expressed VEGF alone. The second hypothesis was tested by treating Rho/FGF2 transgenic mice with low-intensity laser photocoagulation that disrupts photoreceptors, but does not rupture Bruch's membrane, or intense laser that ruptures Bruch's membrane. In Rho/FGF2 transgenics, but not wild type mice, choroidal neovascularization developed in areas of low-intensity laser. Both wild type and transgenic mice developed choroidal neovascularization in areas of intense laser that ruptured Bruch's membrane, but the area of neovascularization was significantly greater in transgenics. These data suggest that increased retinal expression of FGF2 is angiogenic only when it is accompanied by cell injury that overcomes sequestration control mechanisms.

Retinal and choroidal neovascularization

The unique vascular supply of the retina, the ability to visualize the vasculature in vivo, and the ability to selectively express genes in the retina make the retina an ideal model system to study molecular mechanisms of angiogenesis. In addition, this area of investigation has great clinical significance, because retinal and choroidal neovascularization are the most common causes of severe visual loss in developed countries and new treatments are needed. As a result, interest in ocular neovascularization is rapidly growing and there has been considerable recent progress. Use of genetically engineered mice in recently developed murine models provides a means to investigate the role of individual gene products in neovascularization in two distinct vascular beds, the retinal vasculature and the choroidal vasculature. It appears that angiogenesis in different vascular beds has common themes, but also has tissue-specific aspects. This review summarizes recent progress in the field of ocular neovascularization and the prospects that it provides for the development of new treatments.

Experimental subretinal neovascularization is inhibited by adenovirus-mediated soluble VEGF/flt-1 receptor gene transfection: a role of VEGF and possible treatment for SRN in age-related macular degeneration

Accumulating evidence has shown the importance of vascular endothelial growth factor (VEGF) in chorioretinal angiogenesis. However, whether or not VEGF is indeed critical for the pathogenesis of subretinal neovascularization (SRN) in adulthood, which is a serious complication of age-related macular degeneration, has to be further investigated. We constructed an adenovirus expressing an entire ectodomain of the human VEGF receptor/flt-1 fused to Fc portion of human IgG (Adflt-ExR): this soluble receptor is secreted from Adflt-ExR-transfected cells. We studied the effect of Adflt-ExR on the formation of experimental SRN. Experimental SRN was induced by intense photocoagulation on the retina in pigmented rats and Adflt-ExR was injected into the femoral muscle. The formation of SRN assessed by fluorescein angiography was more significantly inhibited for 7 days in the Adflt-ExR-treated rats than in the control rats who received either an adenovirus vector encoding LacZ gene or balanced salt solution (BSS). The serum concentration of this soluble receptor increased for 7 days and thereafter gradually decreased. An immunohistochemical study disclosed the fibroblast cell proliferation and inflammatory cell infiltration to be reduced in the photocoagulation spot of Adflt-ExR-treated rats. VEGF plays a crucial role in the formation of SRN and VEGF soluble receptor gene transfection can inhibit SRN. This method will contribute to future gene therapy for age-related macular degeneration.

Expression of vascular endothelial growth factor and its receptor (KDR/flk-1) mRNA in experimental choroidal neovascularization

PURPOSE

Vascular endothelial growth factor (VEGF) is an angiogenic peptide that has been suggested to be important in the pathogenesis of choroidal neovascularization. We investigated the transcription of VEGF and its receptor KDR/flk-1 genes during the development of experimentally induced choroidal neovascularization.

METHODS

Rat VEGF or KDR cDNA was inserted in PGEM or pBluescript to prepare antisense or sense riboprobes. Multiple krypton laser burns were applied to the posterior pole of pigmented rat eyes according to a previously described protocol which produces choroidal neovascularization. At intervals of up to 4 weeks after photocoagulation, the eyes were removed and cut into thin sections. The sections were subjected to in situ hybridization with digoxigenin (DIG)-labeled single-strand rat VEGF and KDR cDNA riboprobes.

RESULTS

In normal adult rat retinas, VEGF and KDR mRNA expression was mainly observed in the ganglion cell and the inner nuclear layers. During the development of neovascularization, VEGF and KDR mRNAs were detected in retinal pigment epithelial-like cells, fibroblast-like cells and endothelial cells in neovascular lesions. The level of expression was strongest at 1 week after photocoagulation in lasered lesions, and decreased by 4 weeks after photocoagulation.

CONCLUSIONS

Our findings demonstrate that expression of VEGF and its receptor KDR may play a role in the formation of experimentally induced choroidal neovascularization. In this study, VEGF and its receptor were co-localized, suggesting that an autocrine and/or paracrine mechanism may be operative.

Targeted disruption of the FGF2 gene does not prevent choroidal neovascularization in a murine model

Choroidal neovascularization (CNV) is the major cause of severe visual loss in patients with age-related macular degeneration. Laser treatment is helpful for a minority of patients with CNV, and development of new treatments is hampered by a poor understanding of the molecular signals involved. Several lines of evidence have suggested that basic fibroblast growth factor (FGF2) plays a role in stimulating CNV. In this study, we tested this hypothesis using mice with targeted disruption of the FGF2 gene in a newly developed murine model of laser-induced CNV. One week after krypton laser photocoagulation in C57BL/6J mice, 34 of 60 burns (57%) showed fluorescein leakage and 13 of 16 (81%) showed histopathological evidence of CNV. At 2 weeks, CNV was detected in 9 of 10 burns (90%) in which a bubble had been observed at the time of the laser treatment. Electron microscopy showed fenestrated vessels with large lumens within choroidal neovascular lesions. Two weeks after laser-induced rupture of Bruch's membrane, 27 of 36 burns (75%) contained CNV in FGF2-deficient mice compared with 26 of 30 (87%) in wild-type control mice, a difference that is not statistically significant. This study demonstrates that FGF2 is not required for the development of CNV after laser-induced rupture of Bruch's membrane and provides a new model to investigate molecular mechanisms and anti-angiogenic therapy in CNV.

Expression of vascular endothelial growth factor and its receptor, KDR, following retinal ischemia-reperfusion injury in the rat

PURPOSE

There is considerable evidence that vascular endothelial growth factor (VEGF) mediates ocular neovascularization in retinal vascular diseases. We investigated the time-dependent changes in the expression of VEGF and its receptor KDR/ Flk in a transient retinal ischemia-reperfusion injury model.

METHODS

Transient retinal ischemia was induced by increasing the intraocular pressure in albino rats eyes for 45 min. In situ hybridization was used to identify the retinal cells synthesizing VEGF mRNA and KDR mRNA at various times following reperfusion. Immunohistochemical analysis was also carried out to detect VEGF immunoreactivity.

RESULTS

In the control, non-ischemic retinas, signals for VEGF mRNA and KDR mRNA were observed in the cells of the ganglion cell layer. Immunoreactivity to VEGF was also found in the nerve fiber layer, the ganglion cell layer, and the retinal pigment epithelial (RPE) cell layer. Immediately and 6 h after reperfusion, VEGF and KDR mRNA expression was markedly decreased, but recovered by 24 h to the levels observed in normal retinas. Immunoreactivity for VEGF was also decreased immediately and 6 h after reperfusion, and was detected in the endothelial cells of the retinal vessels after 24 h. Immunoreactivity to VEGF recovered by 48 h after reperfusion.

CONCLUSIONS

The hybridization pattern of VEGF and KDR mRNA in the ganglion cell layer strongly suggests that the ganglion cells are the major source of this growth factor. The decrease of VEGF mRNA, KDR/Flk mRNA and VEGF protein levels after ischemia and recovery after reperfusion suggest that transient hypoxia might mediate short-term down-regulation of VEGF and KDR mRNA.