氧诱导视网膜病模型中曲安奈德抑制新生血管生长的机制

目的观察氧诱导视网膜病模型(OIR)中曲安奈德(TA)对CD14+细胞聚集及VEGF表达的干预作用,初步探讨曲安奈德抑制视网膜新生血管生长的可能机制。方法清洁级C57BL/6哺乳期小鼠36只(共36个眼球),随机将其分为四组:①正常对照组(6个眼球),6只17日龄正常小鼠先行FFA眼底造影,然后每鼠随机摘取一个眼球,行眼球石蜡切片HE染色。②单纯高氧组(6个眼球),6只17日龄OIR模型小鼠处理同单纯对照组。③TA高氧组(12个眼球),12只12日龄OIR模型小鼠随机一眼注射TA 2μL,再于17日龄后行FFA眼底造影后摘除术眼,其中6个眼球行眼球石蜡切片HE染色及视网膜CD14和VEGF免疫组化染色,另6个眼球行视网膜VEGF mRNA的real-time PCR检测。④BSS高氧(12个眼球),12只12日龄OIR模型小鼠随机一眼注射BSS 2μL,余处理同TA高氧组。用t检验两两比较各组视网膜突破内界膜的内皮细胞核数,视网膜CD14与VEGF免疫组化染色的平均吸光度值(IOD/AOI),及VEGF mRNA的相对含量值(2-ΔCt×105)。结果与正常对照组相比,高氧诱导组突破视网膜内界膜的内皮细胞核数...     

TIMP-1 promotes VEGF-induced neovascularization in the retina

Proteolysis of vascular basement membranes and surrounding extracellular matrix is a critical early step in neovascularization. It requires alteration of the balance between matrix metalloproteinases (MMPs) and proteins that bind to and inactivate MMPs, tissue inhibitors of metalloproteinases (TIMPs). TIMP-1 has been demonstrated to inhibit neovascularization in chick chorioallantoic membranes. However, TIMP-1 has also been shown to either promote or inhibit cell proliferation and migration in different settings. To determine whether genetic alteration of the MMP/TIMP-1 ratio would alter retinal neovascularization, we crossed mice that express vascular endothelial growth factor (VEGF) in photoreceptors with TIMP-1-deficient mice or mice that overexpress TIMP-1. Compared to VEGF transgene-positive/TIMP-1-sufficient mice, VEGF transgene-positive/TIMP-1-deficient mice showed smaller neovascular lesions. There was also no difference between the two groups of mice in the appearance of the neovascularization by light or electron microscopy. Compound VEGF/TIMP-1 transgenic mice had increased expression of both VEGF and TIMP-1 in the retina, and had more neovascularization than mice that had increased expression of VEGF alone. These gain- and loss-of-function data suggest that alteration of the TIMP-1/MMP ratio modulates retinal neovascularization in a complex manner and not simply by altering the proteolytic activity and thereby invasiveness of endothelial cells.     

Pigment epithelium-derived factor inhibits retinal and choroidal neovascularization.

In this study, we investigated whether overexpression of pigment epithelium-derived factor (PEDF) by gene transfer can inhibit neovascularization by testing its effect in three different models of ocular neovascularization. Intravitreous injection of an adenoviral vector encoding PEDF resulted in expression of PEDF mRNA in the eye measured by RT-PCR and increased immunohistochemical staining for PEDF protein throughout the retina. In mice with laser-induced rupture of Bruch's membrane, choroidal neovascularization was significantly reduced after intravitreous injection of PEDF vector compared to injection of null vector or no injection. Subretinal injection of the PEDF vector resulted in prominent staining for PEDF in retinal pigmented epithelial cells and strong inhibition of choroidal neovascularization. In two models of retinal neovascularization (transgenic mice with increased expression of vascular endothelial growth factor (VEGF) in photoreceptors and mice with oxygen-induced ischemic retinopathy), intravitreous injection of null vector resulted in decreased neovascularization compared to no injection, but intravitreous injection of PEDF vector resulted in further inhibition of neovascularization that was statistically significant. These data suggest that sustained increased intraocular expression of PEDF by gene therapy might provide a promising approach for treatment of ocular neovascularization.     

Beta‐lapachone inhibits pathological retinal neovascularization in oxygen‐induced retinopathy via regulation of HIF‐1α

Retinal neovascularization in retinopathy of prematurity (ROP) is the most common cause of blindness for children. Despite evidence that hypoxia inducible factor (HIF)‐1α ‐VEGF axis is associated with the pathogenesis of ROP, the inhibitors of HIF‐1α have not been established as a therapeutic target in the control of ROP pathophysiology. We investigated the hypothesis that degradation of HIF‐1α as a master regulator of angiogenesis in hypoxic condition, using β‐lapachone, would confer protection against hypoxia‐induced retinopathy without affecting physiological vascular development in mice with oxygen‐induced retinopathy (OIR), an animal model of ROP. The effects of β‐lapachone were examined after intraocular injection in mice with OIR. Intraocular administration of β‐lapachone resulted in significant reduction in hypoxia‐induced retinal neovascularization without retinal toxicity or perturbation of developmental retinal angiogenesis. Our results demonstrate that HIF‐1α–mediated VEGF expression in OIR is associated with pathological neovascularization, not physiological angiogenesis. Thus, strategies blocking HIF‐1α in the developing eye in the pathological hypoxia could serve as a novel therapeutic target for ROP.     

Fatty Acid Binding Protein 4 Deficiency Protects against Oxygen-Induced Retinopathy in Mice

Retinopathy of prematurity (ROP) is a leading cause of blindness in children worldwide due to increasing survival rates of premature infants. Initial suppression, followed by increased production of the retinal vascular endothelial growth factor-A (VEGF) expression are key events that trigger the pathological neovascularization in ROP. Fatty acid binding protein 4 (FABP4) is an intracellular lipid chaperone that is induced by VEGF in a subset of endothelial cells. FABP4 exhibits a pro-angiogenic function in cultured endothelial cells and in airway microvasculature, but whether it plays a role in modulation of retinal angiogenesis is not known. We hypothesized that FABP4 deficiency could ameliorate pathological retinal vascularization and investigated this hypothesis using a well-characterized mouse model of oxygen-induced retinopathy (OIR). We found that FABP4 was not expressed in retinal vessels, but was present in resident macrophages/microglial cells and endothelial cells of the hyaloid vasculature in the immature retina. While FABP4 expression was not required for normal development of retinal vessels, FABP4 expression was upregulated and localized to neovascular tufts in OIR. FABP4^−/− mice demonstrated a significant decrease in neovessel formation as well as a significant improvement in physiological revascularization of the avascular retinal tissues. These alterations in retinal vasculature were accompanied by reduced endothelial cell proliferation, but no effect on apoptosis or macrophage/microglia recruitment. FABP4^−/− OIR samples demonstrated decreased expression of genes involved in angiogenesis, such as Placental Growth Factor, and angiopoietin 2. Collectively, our findings suggest FABP4 as a potential target of pathologic retinal angiogenesis in proliferative retinopathies.     

Antiangiogenic effects of β2 -adrenergic receptor blockade in a mouse model of oxygen-induced retinopathy

Oxygen-induced retinopathy (OIR) is a model for human retinopathy of prematurity. In mice with OIR, beta-adrenergic receptor (β-AR) blockade with propranolol has been shown to ameliorate different aspects of retinal dysfunction in response to hypoxia. In the present study, we used the OIR model to investigate the role of distinct β-ARs on retinal proangiogenic factors, pathogenic neovascularization and electroretinographic responses. Our results demonstrate that β(2) -AR blockade with ICI 118,551 decreases retinal levels of proangiogenic factors and reduces pathogenic neovascularization, whereas β(1) - and β(3) -AR antagonists do not. Determination of retinal protein kinase A activity is indicative of the fact that β-AR blockers are indeed effective at the receptor level. In addition, the specificity of ICI 118,551 on retinal angiogenesis has been demonstrated by the finding that in mouse retinal explants, β(2) -AR silencing prevents ICI 118,551 effects on hypoxia-induced vascular endothelial growth factor accumulation. In OIR mice, ICI 118,551 is effective in increasing electroretinographic responses suggesting that activation of β(2) -ARs constitutes an important part of the retinal response to hypoxia. Lastly, immunohistochemical studies demonstrate that β(2) -ARs are localized to several retinal cells, particularly to Müller cells suggesting the possibility that β(2) -ARs play a role in regulating vascular endothelial growth factor production by these cells. The present results suggest that pathogenic angiogenesis, a key change in many hypoxic/ischemic vision-threatening retinal diseases, depends at least in part on β(2) -AR activity and indicate that β(2) -AR blockade can be effective against retinal angiogenesis.     

Attenuation of retinal vascular development and neovascularization in PECAM-1-deficient mice

Platelet-endothelial cell adhesion molecule-1 (PECAM-1/CD31) is expressed on the surface of endothelial cells (EC) at high levels with important roles in angiogenesis and inflammation. However, the physiological role PECAM-1 plays during vascular development and angiogenesis remains largely unknown. Here we determined the role of PECAM-1 in the postnatal development of retinal vasculature and retinal neovascularization during oxygen-induced ischemic retinopathy (OIR) using PECAM-1-deficient (PECAM-1−/−) mice. A significant decrease in retinal vascular density was observed in PECAM-1−/− mice compared with PECAM-1+/+ mice. This was attributed to a decreased number of EC in the retinas of PECAM-1−/− mice. An increase in the rate of apoptosis was observed in retinal vessels of PECAM-1−/− mice, which was compensated, in part, by an increase in the rate of proliferation. However, the development and regression of hyaloid vasculature were not affected in the absence of PECAM-1. We did not observe a significant defect in astrocytes, the number of endothelial tip cell filopodias, and the rate of developing retinal vasculature progression in PECAM-1−/− mice. However, we observed aberrant organization of arterioles and venules, decreased secondary branching, and dilated vessels in retinal vasculature of PECAM-1−/− mice. In addition, retinal neovascularization was attenuated in PECAM-1−/− mice during OIR despite an expression of VEGF similar to that of PECAM-1+/+ mice. Mechanistically, these changes were associated with an increase in EphB4 and ephrin B2, and a decrease in eNOS, expression in retinal vasculature of PECAM-1−/− mice. These results suggest that PECAM-1 expression and its potential interactions with EphB4/ephrin B2 and eNOS are important for survival, migration, and functional organization of EC during retinal vascular development and angiogenesis.     

Sirtuin1 Over-Expression Does Not Impact Retinal Vascular and Neuronal Degeneration in a Mouse Model of Oxygen-Induced Retinopathy

Proliferative retinopathy is a leading cause of blindness, including retinopathy of prematurity (ROP) in children and diabetic retinopathy in adults. Retinopathy is characterized by an initial phase of vessel loss, leading to tissue ischemia and hypoxia, followed by sight threatening pathologic neovascularization in the second phase. Previously we found that Sirtuin1 (Sirt1), a metabolically dependent protein deacetylase, regulates vascular regeneration in a mouse model of oxygen-induced proliferative retinopathy (OIR), as neuronal depletion of Sirt1 in retina worsens retinopathy. In this study we assessed whether over-expression of Sirtuin1 in retinal neurons and vessels achieved by crossing Sirt1 over-expressing flox mice with Nestin-Cre mice or Tie2-Cre mice, respectively, may protect against retinopathy. We found that over-expression of Sirt1 in Nestin expressing retinal neurons does not impact vaso-obliteration or pathologic neovascularization in OIR, nor does it influence neuronal degeneration in OIR. Similarly, increased expression of Sirt1 in Tie2 expressing vascular endothelial cells and monocytes/macrophages does not protect retinal vessels in OIR. In addition to the genetic approaches, dietary supplement with Sirt1 activators, resveratrol or SRT1720, were fed to wild type mice with OIR. Neither treatment showed significant vaso-protective effects in retinopathy. Together these results indicate that although endogenous Sirt1 is important as a stress-induced protector in retinopathy, over-expression of Sirt1 or treatment with small molecule activators at the examined doses do not provide additional protection against retinopathy in mice. Further studies are needed to examine in depth whether increasing levels of Sirt1 may serve as a potential therapeutic approach to treat or prevent retinopathy.     

Bim is responsible for the inherent sensitivity of the developing retinal vasculature to hyperoxia

Apoptosis plays an important role in development and remodeling of vasculature during organogenesis. Coordinated branching and remodeling of the retinal vascular tree is essential for normal retinal function. Bcl-2 family members, such as bim not only influence apoptosis, but also cell adhesive and migratory properties essential during vascular development. Here we examined the impact of bim deficiency on postnatal retinal vascularization, as well as retinal neovascularization during oxygen-induced ischemic retinopathy (OIR) and laser-induced choroidal neovascularization. Loss of bim expression was associated with increased retinal vascular density in mature animals. This was mainly attributed to increased numbers of pericytes and endothelial cells. However, the initial spread of the superficial layer of retinal vasculature and, the appearance and density of the tip cells were similar in bim+/+ and bim−/− mice. In addition, hyaloid vessel regression was attenuated in the absence of bim. Furthermore, in the absence of bim retinal vessel obliteration and neovascularization did not occur during OIR. Instead, normal inner retinal vascularization proceeded independent of changes in oxygen levels. In contrast, choroidal neovascularization occurred equally well in bim+/+ and bim−/− mice. Together our data suggest bim expression may be responsible for the inherent sensitivity of the developing retinal vasculature to changes in oxygen levels, and promotes vessel obliteration in response to hyperoxia.     

Inhibition of Oxygen-Induced Ischemic Retinal Neovascularization with Adenoviral 15-Lipoxygenase-1 Gene Transfer via Up-Regulation of PPAR-γ and Down-Regulation of VEGFR-2 Expression

15-lipoxygenase-1 (15-LOX-1) plays an important role in angiogenesis, but how it works still remains a controversial subject. The aims of our study are focused on determining whether or not 15-LOX-1 inhibiting oxygen-induced ischemic retinal neovascularization (RNV) and the underlying regulatory mechanism involving of 15-LOX-1, peroxisome proliferator-activated receptor γ (PPAR-γ) and vascular endothelial growth factor receptor 2 (VEGFR-2) in oxygen-induced retinopathy (OIR). Recombinant adenoviral vectors that expressing the 15-LOX-1 gene (Ad-15-LOX-1-GFP) or the green fluorescence protein gene (Ad-GFP) were intravitreous injected into the OIR mice at postnatal day 12 (P12), the mice were sacrificed 5 days later (P17). Retinal 15-LOX-1 expression was significantly increased at both mRNA and protein levels after 15-LOX-1 gene transfer. Immunofluorescence staining of retinal sections revealed 15-LOX-1 expression was primarily in the outer plexiform layer (OPL), inner nuclear layer (INL) and ganglion cell layer (GCL) retina. Meanwhile, RNV was significantly inhibited indicated by fluorescein retinal angiography and quantification of the pre-retinal neovascular cells. The expression levels of PPAR-γ were significantly up-regulated while VEGFR-2 were significantly down-regulated both in mRNA and protein levels. Our results suggested 15-LOX-1 gene transfer inhibited RNV in OIR mouse model via up-regulation of PPAR-γ and further down-regulation of VEGFR-2 expression. This could be a potentially important regulatory mechanism involving 15-LOX-1, PPAR-γ and VEGFR-2 during RNV in OIR. In conclusion, 15-LOX-1 may be a new therapeutic target for treating neovascularization diseases.     

Anti-Angiogenic Effect of Metformin in Mouse Oxygen-Induced Retinopathy Is Mediated by Reducing Levels of the Vascular Endothelial Growth Factor Receptor Flk-1

Purpose

To evaluate the effect of metformin on vascular changes in oxygen-induced retinopathy (OIR) in mouse, and to elucidate the possible underlying mechanism.

Methods

OIR mice were treated with metformin by intraperitoneal injection from postnatal day 12 (P12) to P17 or P21. At P17 and P21, vessel formation and avascular areas were assessed using retinal flat mounts. Levels of vascular endothelial growth factor (VEGF) were measured by enzyme-linked immunosorbent assays, and the effects of metformin on VEGF-induced proliferation of human umbilical vein endothelial cells (HUVECs) were assessed. The effects of metformin on the levels of Flk1 (VEGF receptor-2) and phosphorylated Flk1 (pFlk1) were measured by Western blotting (HUVECs) and immunohistochemistry (retinal tissue).

Results

Retinal morphologic changes were analyzed between two groups (saline-treated OIR; metformin-treated OIR). Metformin treatment did not change the extent of avascular areas at P17. However, at P21, when OIR pathology was markedly improved in the saline-treated group, OIR pathology still remained in the metformin-treated OIR group. VEGF expression levels did not differ between metformin- and saline-treated OIR groups at P17 and P21, but Flk1 levels were significantly reduced in the metformin group compared with saline-treated OIR group. Moreover, metformin inhibited VEGF-induced cell proliferation and decreased levels of Flk1 and pFlk1, consistent with the interpretation that metformin inhibits vascular growth by reducing Flk1 levels.

Conclusion

Metformin exerts anti-angiogenesis effects and delays the normal vessel formation in the recovery phase of OIR in mice, likely by suppressing the levels of Flk1.     

Oxygen-induced retinopathy in mice with retinal photoreceptor cell degeneration

Aims

It is reported that retinal neovascularization seems to rarely co-exist with retinitis pigmentosa in patients and in some mouse models; however, it is not widely acknowledged as a universal phenomenon in all strains of all animal species. We aimed to further explore this phenomenon with an oxygen-induced retinopathy model in mice with retinal photoreceptor cell degeneration.

Main methods

Oxygen-induced retinopathy of colored and albino mice with rapid retinal degeneration were compared to homologous wild-type mice. The retinas were analyzed using high-molecular-weight FITC-dextran stained flat-mount preparation, hematoxylin and eosin (H&E) stained cross-sections, an immunohistochemical test for vascular endothelial growth factor (VEGF) distribution and Western blotting for VEGF expression after exposure to hyperoxia between postnatal days 17 (P17) and 21.

Key findings

Leakage and areas of non-perfusion of the retinal blood vessels were alleviated in the retinal degeneration mice. The number of preretinal vascular endothelial cell nuclei in the retinal degeneration mice was smaller than that in the homologous wild-type mice after exposure to hyperoxia (P < 0.01). The degree of oxygen-induced retinopathy was positively correlated with the VEGF expression level. However, the VEGF expression level was lower in the retinal degeneration mice.

Significance

Proliferative retinopathy occurred in mice with rapid retinal degeneration, but retinal photoreceptor cell degeneration could partially restrain the retinal neovascularization in this rapid retinal degeneration mouse model.     

Arginase 2 Deficiency Prevents Oxidative Stress and Limits Hyperoxia-Induced Retinal Vascular Degeneration

Background

Hyperoxia exposure of premature infants causes obliteration of the immature retinal microvessels, leading to a condition of proliferative vitreoretinal neovascularization termed retinopathy of prematurity (ROP). Previous work has demonstrated that the hyperoxia-induced vascular injury is mediated by dysfunction of endothelial nitric oxide synthase resulting in peroxynitrite formation. This study was undertaken to determine the involvement of the ureahydrolase enzyme arginase in this pathology.

Methods and Findings

Studies were performed using hyperoxia-treated bovine retinal endothelial cells (BRE) and mice with oxygen-induced retinopathy (OIR) as experimental models of ROP. Treatment with the specific arginase inhibitor 2(S)-amino-6-boronohexanoic acid (ABH) prevented hyperoxia-induced apoptosis of BRE cells and reduced vaso-obliteration in the OIR model. Furthermore, deletion of the arginase 2 gene protected against hyperoxia-induced vaso-obliteration, enhanced physiological vascular repair, and reduced retinal neovascularization in the OIR model. Additional deletion of one copy of arginase 1 did not improve the vascular pathology. Analyses of peroxynitrite by quantitation of its biomarker nitrotyrosine, superoxide by dihydroethidium imaging and NO formation by diaminofluoroscein imaging showed that the protective actions of arginase 2 deletion were associated with blockade of superoxide and peroxynitrite formation and normalization of NOS activity.

Conclusions

Our data demonstrate the involvement of arginase activity and arginase 2 expression in hyperoxia-induced vascular injury. Arginase 2 deletion prevents hyperoxia-induced retinal vascular injury by preventing NOS uncoupling resulting in decreased reactive oxygen species formation and increased nitric oxide bioavailability.     

Attenuation of retinal vascular development and neovascularization during oxygen-induced ischemic retinopathy in Bcl-2-/- mice

Bcl-2 is a death repressor that protects cells from apoptosis mediated by a variety of stimuli. Bcl-2 expression is regulated by both pro- and anti-angiogenic factors; thus, it may play a central role during angiogenesis. However, the role of bcl-2 in vascular development and growth of new vessels requires further delineation. In this study, we investigated the physiological role of bcl-2 in development of retinal vasculature and retinal neovascularization during oxygen-induced ischemic retinopathy (OIR). Mice deficient in bcl-2 exhibited a significant decrease in retinal vascular density compared to wild-type mice. This was attributed to a decreased number of endothelial cells and pericytes in retinas from bcl-2-/- mice. We observed, in bcl-2-/- mice, delayed development of retinal vasculature and remodeling, and a significant decrease in the number of major arteries, which branch off from near the optic nerve. Interestingly, hyaloid vessel regression, an apoptosis-dependent process, was not affected in the absence of bcl-2. The retinal vasculature of bcl-2-/- mice exhibited a similar sensitivity to hyperoxia-mediated vessel obliteration compared to wild-type mice during OIR. However, the degree of ischemia-induced retinal neovascularization was significantly reduced in bcl-2-/- mice. These results suggest that expression of bcl-2 is required for appropriate development of retinal vasculature as well as its neovascularization during OIR.     

Implication of the hypoxia response element of the Vegf promoter in mouse models of retinal and choroidal neovascularization, but not retinal vascular development

Retinal neovascularization (NV) and macular edema, resulting from blood-retinal barrier (BRB) breakdown, are major causes of visual loss in ischemic retinopathies. Choroidal NV (CNV) occurs in diseases of the retinal pigmented epithelium/Bruch's membrane complex and is another extremely prevalent cause of visual loss. We used mice in which the hypoxia response element (HRE) is deleted from the vascular endothelial growth factor (vegf) promoter (Vegf(delta/delta) mice) to explore the role of induction of VEGF through the HRE in these disease processes. Compared to wild type (Vegf+/+) mice with oxygen-induced ischemic retinopathy (OIR) in which vegf mRNA levels were increased and prominent retinal NV and BRB breakdown occurred, Vegf(delta/delta) littermates with OIR failed to increase vegf mRNA levels in the retina and had significantly less retinal NV and BRB breakdown, but showed prominent dilation of some superficial retinal vessels. Vegf(+/delta) littermates with ischemic retinopathy developed comparable retinal NV to Vegf+/+ mice, exhibited intermediate levels of BRB breakdown, and did not show vasodilation. In a mouse model of CNV, due to laser-induced rupture of Bruch's membrane, the area of CNV at Bruch's membrane rupture sites was more than tenfold greater in Vegf+/+ mice than in Vegf(delta/delta) littermates. In contrast to these dramatic differences in pathologic ocular NV, Vegf(delta/delta) mice showed subtle differences in retinal vascular development compared to Vegf+/+ mice; it was slightly delayed, but otherwise normal. These data suggest that induction of VEGF through the HRE in its promoter is critical for retinal and CNV, but not for retinal vascular development.     

Hyperoxia causes decreased expression of vascular endothelial growth factor and endothelial cell apoptosis in adult retina

Mice or humans with photoreceptor degenerations experience permeability and dropout of retinal capillaries. Loss of photoreceptors results in decreased oxygen usage and thinning of the retina with increased oxygen delivery to the inner retina. To investigate the possibility that increased tissue oxygen plays a role in the vascular damage, we exposed adult mice to hyperoxia, which also increases oxygen in the retina. After 1, 2, or 3 weeks of hyperoxia, there was a statistically significant decrease in retinal vascular density that was not reversible, and endothelial cell apoptosis was demonstrated by TUNEL staining. Mice exposed to hyperoxia and mice with photoreceptor degeneration both showed decreased expression of VEGF in the retina. After complete or near-complete degeneration of photoreceptors, there was increased expression of VEGF in RPE cells, which may explain the association of photoreceptor degeneration and neovascularization in or around the RPE. Increased expression of VEGF in photoreceptors of transgenic mice failed to prevent hyperoxia-induced retinal capillary dropout. These data suggest that increased oxygen in the retina, either by increased inspired oxygen or by photoreceptor degeneration, results in endothelial cell death and dropout of capillaries. Decreased expression of VEGF may be a contributing factor, but the situation may be more complicated for mature retinal vessels than it is for immature vessels, because VEGF replacement does not rescue mature retinal vessels, suggesting that other factors may also be involved.     

Prolonged blockade of VEGF family members does not cause identifiable damage to retinal neurons or vessels

Several ocular diseases complicated by neovascularization are being treated by repeated intraocular injections of vascular endothelial growth factor (VEGF) antagonists. While substantial benefits have been documented, there is concern that unrecognized damage may be occurring, because blockade of VEGF may damage the fenestrated vessels of the choroicapillaris and deprive retinal neurons of input from a survival factor. One report has suggested that even temporary blockade of all isoforms of VEGF-A results in significant loss of retinal ganglion cells. In this study, we utilized double transgenic mice with doxycycline-inducible expression of soluble VEGF receptor 1 coupled to an Fc fragment (sVEGFR1Fc), a potent antagonist of several VEGF family members, including VEGF-A, to test the effects of VEGF blockade in the retina. Expression of sVEGFR1Fc completely blocked VEGF-induced retinal vascular permeability and significantly suppressed the development of choroidal neovascularization at rupture sites in Bruch's membrane, but did not cause regression of established choroidal neovascularization. Mice with constant expression of sVEGFR1Fc in the retina for 7 months had normal electroretinograms and normal retinal and choroidal ultrastructure including normal fenestrations in the choroicapillaris. They also showed no significant difference from control mice in the number of ganglion cell axons in optic nerve cross sections and the retinal level of mRNA for 3 ganglion cell-specific genes. These data indicate that constant blockade of VEGF for up to 7 months has no identifiable deleterious effects on the retina or choroid and support the use of VEGF antagonists in the treatment of retinal diseases.     

PF4 antagonizes retinal neovascularization via inhibiting PRAS40 phosphorylation in a mouse model of oxygen-induced retinopathy

Retinal neovascularization (RNV) is a common pathology of blinding proliferative retinopathies. The current treatments to RNV, however, are hindered by limited efficacy, side effects, and drug resistance. A naturally-occurring cytokine in retina that is amicable to immune system and possesses robust anti-neovascular function would facilitate to overcome the hurdles. In this study, retinas from a mouse model of oxygen-induced retinopathy (OIR) underwent a protein array to screen the naturally-occurring cytokines that may antagonize RNV. Among the 62 angiogenesis-associated cytokines, platelet factor 4 (Pf4) stood out with the most prominent upregulation and statistical significance. Moreover, an intravitreal injection of mouse Pf4 demonstrated dramatic anti-vaso-obliteration and anti-neovascularization effects dose dependently in the OIR model; whereas human PF4 inhibited the proliferation, migration, and tubulogenesis of monkey retinal vascular endothelial cells treated with VEGF and TNF-α. These previously undescribed angiostatic effects of PF4 in OIR retinas and retinal vascular endothelial cells support translation of this naturally-occurring chemokine into a therapeutic modality to RNV supplementary to the anti-VEGFs. Mechanistically, a phosphorylation array and western blots indicated that downregulation of proline-rich Akt substrate of 40 kDa (Pras40) and its phosphorylation were necessary for Pf4's anti-neovascular effects in the OIR retinas. Indeed, overexpression of the wildtype Pras40 and the mutant version with deficient phosphorylation abolished and mimicked the Pf4's angiostatic effects in the OIR retinas, respectively. The similar effects were also observed in vitro. This study, for the first time, links PF4's anti-RNV function to an intracellular signaling molecule PRAS40 and its phosphorylation.     

Overexpression of miR-181a-5p inhibits retinal neovascularization through endocan and the ERK1/2 signaling pathway

Retinal neovascularization (RNV) is a common pathological feature of angiogenesis-related retinopathy. Endocan inhibition has previously been reported to suppress RNV in oxygen-induced retinopathy (OIR); however, its molecular mechanisms remain to be elucidated. Here, we investigated the role and mechanism of endocan in OIR. We established an OIR mouse model and detected aberrant endocan overexpression in OIR mouse retinas. Endocan inhibition through small interfering RNA or a neutralizing antibody inhibited vascular endothelial growth factor-induced cell survival, cell proliferation, and tube formation in human retinal endothelial cells in vitro and reduced the RNV area in vivo. Using RNA sequencing, a luciferase reporter assay, and bioinformatics analyses, we identified endocan as a microRNA-181a-5p target gene. The antiangiogenic effect of miR-181a-5p on RNV was verified by intravitreal injection, and we showed that this involved the extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) signaling pathway. Collectively, our data demonstrate that miR-181a-5p/endocan regulates retinal angiogenesis through the ERK1/2 signaling pathway and might represent an attractive therapeutic strategy for RNV.     

Interruption of Wnt Signaling in Müller Cells Ameliorates Ischemia-Induced Retinal Neovascularization

Retinal Müller cells are major producers of inflammatory and angiogenic cytokines which contribute to diabetic retinopathy (DR). Over-activation of the Wnt/β-catenin pathway has been shown to play an important pathogenic role in DR. However, the roles of Müller cell-derived Wnt/β-catenin signaling in retinal neovascularization (NV) and DR remain undefined. In the present study, mice with conditional β-catenin knockout (KO) in Müller cells were generated and subjected to oxygen-induced retinopathy (OIR) and streptozotocin (STZ)-induced diabetes. Wnt signaling was evaluated by measuring levels of β-catenin and expression of its target genes using immunoblotting. Retinal vascular permeability was measured using Evans blue as a tracer. Retinal NV was visualized by angiography and quantified by counting pre-retinal nuclei. Retinal pericyte loss was evaluated using retinal trypsin digestion. Electroretinography was performed to examine visual function. No abnormalities were detected in the β-catenin KO mice under normal conditions. In OIR, retinal levels of β-catenin and VEGF were significantly lower in the β-catenin KO mice than in littermate controls. The KO mice also had decreased retinal NV and vascular leakage in the OIR model. In the STZ-induced diabetic model, disruption of β-catenin in Müller cells attenuated over-expression of inflammatory cytokines and ameliorated pericyte dropout in the retina. These findings suggest that Wnt signaling activation in Müller cells contributes to retinal NV, vascular leakage and inflammation and represents a potential therapeutic target for DR.