Retinal and choroidal angiogenesis: a review of new targets

Inhibition of PDGF-BB reduces alkali-induced corneal neovascularization in mice

The aim of the present study was to investigate the role of platelet-derived growth factor (PDGF)-BB/PDGF receptor (R)-β signaling in an experimental murine corneal neovascularization (CrNV) model. Experimental CrNV was induced by alkali injury. The intra-corneal expression of PDGF-BB was examined using immunohistochemistry. The effect of PDGF-BB on CrNV was evaluated using immunofluorescence staining. The expression levels of PDGFR-β in human retinal endothelial cells (HRECs) under normal conditions or following cobalt chloride treatment, which induced hypoxic conditions, was assessed using reverse transcription-quantitative PCR. The effect of exogenous treatment of PDGF-BB on the proliferation, migration and tube formation of HRECs under normoxic or hypoxic conditions was evaluated in vitro using Cell Counting Kit-8, wound healing and 3D Matrigel capillary tube formation assays, respectively. The results indicated that the intra-corneal expression levels of the proteins of PDGF-BB and PDGFR-β were detectable on days 2 and 7 following alkali injury. The treatment with neutralizing anti-PDGF-BB antibody resulted in significant inhibition of CrNV. The intra-corneal expression levels of vascular endothelial growth factor A, matrix metallopeptidase (MMP)-2 and MMP-9 proteins were downregulated, while the expression levels of thrombospondin (TSP)-1, TSP-2, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-1 and ADAMTS-2 were upregulated significantly in mice treated with anti-PDGF-BB antibody. The expression levels of PDGFR-β were upregulated in HRECs under hypoxic conditions compared with those noted under normoxic conditions. Recombinant human PDGF-BB promoted the proliferation, migration and tube formation of HRECs under hypoxic conditions. The data indicated that PDGF-BB/PDGFR-β signaling was involved in CrNV and that it promoted endothelial cell proliferation, migration and tube formation. The pro-angiogenic effects of this pathway may be mediated via the induction of pro-angiogenic cytokine secretion and the suppression of anti-angiogenic cytokine secretion.

PRODUCTION AND APPLICATION OF ANGIOSTATINS FOR THE TREATMENT OF OCULAR NEOVASCULAR DISEASES

Angiostatins comprise a group of kringle-containing proteolytically-derived fragments of plasminogen/plasmin, which act as potent inhibitory mediators of endothelial cells proliferation and migration. Angiostatins are involved in modulation of vessel growth in healthy tissues and various pathological conditions associated with aberrant neovascularization. The aim of the present paper was to summarize available information, including our own experimental data, on prospects of angiostatin application for treatment of ocular neovascular diseases (OND), focusing on retinal pathologies and corneal injury. In particular, literature data on prospective and retrospective studies, clinical trials and animal models relating to the pathophysiology, investigation and management of OND are described. Special emphasis was made on the laboratory approaches of production of different angiostatin isoforms, as well as comparison of antiangiogenic capacities of native and recombinant angiostatin polypeptides. Several studies reported that angiostatins may completely abolish pathologic angiogenesis in diabetic proliferative retinopathy without affecting normal retinal vessel development and without exhibiting adverse side effects. Angiostatins have been tested as a tool for corneal antiangiogenesis target therapy in order to manage diverse ocular surface pathological conditions induced by traumas, chemical burns, previous surgery, chronic contact lens wear, autoimmune diseases, keratitis and viral infections (herpes, COVID-19), corneal graft rejection, etc. Among all known angiostatin species, isolated K5 plasminogen fragment was shown to display the most potent inhibitory activity against proliferation of endothelial cells via triggering multiple signaling pathways, which lead to cell death and resulting angiogenesis suppression. Application of adenoviral genetic construct encoding angiostatin K5 as a promising tool for OND treatment illustrates a vivid example of upcoming revolution in local gene therapy. Further comprehensive studies are necessary to elucidate the clinical potential and optimal regimes of angiostatinbased intervention modalities for treating ocular neovascularization.

The Impact of Oxidative Stress on Blood-Retinal Barrier Physiology in Age-Related Macular Degeneration

The blood retinal barrier (BRB) is a fundamental eye component, whose function is to select the flow of molecules from the blood to the retina and vice-versa, and its integrity allows the maintenance of a finely regulated microenvironment. The outer BRB, composed by the choriocapillaris, the Bruch's membrane, and the retinal pigment epithelium, undergoes structural and functional changes in age-related macular degeneration (AMD), the leading cause of blindness worldwide. BRB alterations lead to retinal dysfunction and neurodegeneration. Several risk factors have been associated with AMD onset in the past decades and oxidative stress is widely recognized as a key factor, even if the exact AMD pathophysiology has not been exactly elucidated yet. The present review describes the BRB physiology, the BRB changes occurring in AMD, the role of oxidative stress in AMD with a focus on the outer BRB structures. Moreover, we propose the use of cerium oxide nanoparticles as a new powerful anti-oxidant agent to combat AMD, based on the relevant existing data which demonstrated their beneficial effects in protecting the outer BRB in animal models of AMD.

CRISPR Technology for Ocular Angiogenesis

Among genome engineering tools, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-based approaches have been widely adopted for translational studies due to their robustness, precision, and ease of use. When delivered to diseased tissues with a viral vector such as adeno-associated virus, direct genome editing can be efficiently achieved in vivo to treat different ophthalmic conditions. While CRISPR has been actively explored as a strategy for treating inherited retinal diseases, with the first human trial recently initiated, its applications for complex, multifactorial conditions such as ocular angiogenesis has been relatively limited. Currently, neovascular retinal diseases such as retinopathy of prematurity, proliferative diabetic retinopathy, and neovascular age-related macular degeneration, which together constitute the majority of blindness in developed countries, are managed with frequent and costly injections of anti-vascular endothelial growth factor (anti-VEGF) agents that are short-lived and burdensome for patients. By contrast, CRISPR technology has the potential to suppress angiogenesis permanently, with the added benefit of targeting intracellular signals or regulatory elements, cell-specific delivery, and multiplexing to disrupt different pro-angiogenic factors simultaneously. However, the prospect of permanently suppressing physiologic pathways, the unpredictability of gene editing efficacy, and concerns for off-target effects have limited enthusiasm for these approaches. Here, we review the evolution of gene therapy and advances in adapting CRISPR platforms to suppress retinal angiogenesis. We discuss different Cas9 orthologs, delivery strategies, and different genomic targets including VEGF, VEGF receptor, and HIF-1α, as well as the advantages and disadvantages of genome editing vs. conventional gene therapies for multifactorial disease processes as compared to inherited monogenic retinal disorders. Lastly, we describe barriers that must be overcome to enable effective adoption of CRISPR-based strategies for the management of ocular angiogenesis.

Rice Bran and Vitamin B6 Suppress Pathological Neovascularization in a Murine Model of Age-Related Macular Degeneration as Novel HIF Inhibitors

Pathological neovascularization in the eye is a leading cause of blindness in all age groups from retinopathy of prematurity (ROP) in children to age-related macular degeneration (AMD) in the elderly. Inhibiting neovascularization via antivascular endothelial growth factor (VEGF) drugs has been used for the effective treatment. However, anti-VEGF therapies may cause development of chorioretinal atrophy as they affect a physiological amount of VEGF essential for retinal homeostasis. Furthermore, anti-VEGF therapies are still ineffective in some cases, especially in patients with AMD. Hypoxia-inducible factor (HIF) is a strong regulator of VEGF induction under hypoxic and other stress conditions. Our previous reports have indicated that HIF is associated with pathological retinal neovascularization in murine models of ROP and AMD, and HIF inhibition suppresses neovascularization by reducing an abnormal increase in VEGF expression. Along with this, we attempted to find novel effective HIF inhibitors from natural foods of our daily lives. Food ingredients were screened for prospective HIF inhibitors in ocular cell lines of 661W and ARPE-19, and a murine AMD model was utilized for examining suppressive effects of the ingredients on retinal neovascularization. As a result, rice bran and its component, vitamin B6 showed inhibitory effects on HIF activation and suppressed VEGF mRNA induction under a CoCl₂-induced pseudo-hypoxic condition. Dietary supplement of these significantly suppressed retinal neovascularization in the AMD model. These data suggest that rice bran could have promising therapeutic values in the management of pathological ocular neovascularization.

IGFBP‑rP1‑silencing promotes hypoxia‑induced angiogenic potential of choroidal endothelial cells via the RAF/MEK/ERK signaling pathway

Insulin-like growth factor binding protein-related protein 1 (IGFBP-rP1) has been reported to have various functions in different cellular contexts. Our previous investigation discovered that IGFBP-rP1 inhibited retinal angiogenesis in vitro and in vivo by inhibiting the pro-angiogenic effect of VEGF and downregulating VEGF expression. Recently, IGFBP-rP1 was confirmed to be downregulated in the aqueous humor of patients with neovascular age-related macular degeneration compared with controls; however, its specific role remains unknown. The present study applied the technique of gene silencing, reverse transcription-quantitative PCR, western blotting, cell viability assays, cell motility assays and tube formation assays. Chemical hypoxic conditions and choroidal endothelial (RF/6A) cells were used to explore the effect of IGFBP-rP1-silencing on the phenotype activation of RF/6A cells under hypoxic conditions and to elucidate the underlying mechanisms. siRNA achieved IGFBP-rP1-silencing in RF/6A cells without cytotoxicity. IGFBP-rP1-silencing significantly restored the viability of RF/6A cells in hypoxia and enhanced hypoxia-induced migration and capillary-like tube formation of RF/6A cells. Furthermore, IGFBP-rP1-silencing significantly upregulated the expression of B-RAF, phosphorylated (p)-MEK, p-ERK and VEGF in RF/6A cells under hypoxic conditions; however, these upregulations were inhibited by exogenous IGFBP-rP1. These data indicated that silencing IGFBP-rP1 expression in RF/6A cells effectively promoted the hypoxia-induced angiogenic potential of choroidal endothelial cells by upregulating RAF/MEK/ERK signaling pathway activation and VEGF expression.

Etanercept as a TNF-alpha inhibitor depresses experimental retinal neovascularization

PURPOSE

The formation of retinal neovascularization (RNV) is the primary pathological process underlying retinopathy of prematurity (ROP). Previous studies have shown that inflammatory factors are related to the formation of RNV. Tumor necrosis factor-α (TNF-α), as an important factor in the inflammatory response, is involved in the regulation of RNV formation. However, the mechanism through which TNF-α inhibition reduces RNV formation is not fully clarified. Therefore, the purpose of this study was to explore the effect of etanercept, an inhibitor of TNF-α, on RNV, and its possible mechanism.

METHODS

In vivo, an oxygen-induced retinopathy (OIR) mouse model was used to determine the effect of etanercept on the formation of RNV by performing immunostaining. The effect of etanercept on tumor necrosis factor receptor-associated factor 2 (TRAF2), pro-angiogenic-related factors, and pro/anti-inflammatory factors in OIR mice was assessed by real-time PCR and Western blotting. In vitro, the effect of etanercept on TNF-α-induced human retinal microvascular endothelial cell tube formation was evaluated by tube formation assays, and the potential mechanism of etanercept was explored by Western blotting.

RESULTS

In vivo, etanercept reduced the area of RNV and decreased the expression of TRAF2 in the OIR mouse model. Etanercept also suppressed the expression of several pro-angiogenic factors and regulated the pro/anti-inflammatory factors. In vitro, etanercept reduced endothelial cell tube formation by inhibiting activation of the NF-κB signaling pathway.

CONCLUSION

Etanercept can regulate pro/anti-inflammatory factors and reduce the expression of pro-angiogenic factors by inhibiting NF-κB phosphorylation, thereby reducing RNV formation.

Gene Therapy Intervention in Neovascular Eye Disease: A Recent Update

Aberrant growth of blood vessels (neovascularization) is a key feature of severe eye diseases that can cause legal blindness, including neovascular age-related macular degeneration (nAMD) and diabetic retinopathy (DR). The development of anti-vascular endothelial growth factor (VEGF) agents has revolutionized the treatment of ocular neovascularization. Novel proangiogenic targets, such as angiopoietin and platelet-derived growth factor (PDGF), are under development for patients who respond poorly to anti-VEGF therapy and to reduce adverse effects from long-term VEGF inhibition. A rapidly advancing area is gene therapy, which may provide significant therapeutic benefits. Viral vector-mediated transgene delivery provides the potential for continuous production of antiangiogenic proteins, which would avoid the need for repeated anti-VEGF injections. Gene silencing with RNA interference to target ocular angiogenesis has been investigated in clinical trials. Proof-of-concept gene therapy studies using gene-editing tools such as CRISPR-Cas have already been shown to be effective in suppressing neovascularization in animal models, highlighting the therapeutic potential of the system for treatment of aberrant ocular angiogenesis. This review provides updates on the development of anti-VEGF agents and novel antiangiogenic targets. We also summarize current gene therapy strategies already in clinical trials and those with the latest approaches utilizing CRISPR-Cas gene editing against aberrant ocular neovascularization.

Intravitreal injection of peptides PnPa11 and PnPa13, derivatives of Phoneutria nigriventer spider venom, prevents retinal damage

Background:

PnPa11 and PnPa13 are synthetic peptides derived from Phoneutria nigriventer spider venom, which display antinociceptive and neuroprotective properties. In this work, we evaluated the safety of intravitreal use and the neuroprotective effect of these peptides.

Methods:

The cytotoxicity and the antiangiogenic activity of these peptides were evaluated by the sulforhodamine-B method and chicken chorioallantoic membrane (CAM) assay, respectively. The in vivo safety was analyzed in Wistar rats that were intravitreally injected with different doses (0.50; 1.25; 2.50; 3.75 and 5.00 µg/mL) of these peptides (right eye, n = 6). The retinal function was assessed by electroretinography exams (ERG), intraocular pressure (IOP), and histological analyzes. In order to investigate the neuroprotective effect, Wistar rats received intravitreal injections (right eye, n = 6) of peptides at 1.25 µg/mL and then were exposed to blue LED light. In addition, the visual function and the retinal microstructure were verified.

Results:

Cytotoxicity analyses demonstrated that the peptides did not present any toxicity over ARPE-19 (adult retinal pigmented epithelial) cell line and the antiangiogenic study highlighted that the peptides promoted the reduction of blood vessels. The intravitreal injection did not cause major changes, neither induced any irreversible damage. In the retinal degeneration assay, the ERG records demonstrated that the prior treatment with PnPa11 and PnPa13 protected the retina from damage. Morphological analyses confirmed the ERG findings. Immunoblotting analyses revealed that PnPa11 increased Erk1/2, NR2A, and NR2B retinal expression after the light stress model, but did not cause Akt1 activation, while PnPa13 prevented Erk1/2 and Akt1 dephosphorylation.

Conclusions:

The intraocular administration of these peptides was well tolerated and presented protective activity against retinal degeneration, suggesting the potential use of these peptides as neuroprotectors in the ophthalmological field.

A Fairy Chemical Suppresses Retinal Angiogenesis as a HIF Inhibitor

Neovascular retinal degeneration is a leading cause of blindness in advanced countries. Anti-vascular endothelial growth factor (VEGF) drugs have been used for neovascular retinal diseases; however, anti-VEGF drugs may cause the development of chorioretinal atrophy in chronic therapy as they affect the physiological amount of VEGF needed for retinal homeostasis. Hypoxia-inducible factor (HIF) is a transcription factor inducing VEGF expression under hypoxic and other stress conditions. Previously, we demonstrated that HIF was involved with pathological retinal angiogenesis in murine models of oxygen-induced retinopathy (OIR), and pharmacological HIF inhibition prevented retinal neovascularization by reducing an ectopic amount of VEGF. Along with this, we attempted to find novel effective HIF inhibitors. Compounds originally isolated from mushroom-forming fungi were screened for prospective HIF inhibitors utilizing cell lines of 3T3, ARPE-19 and 661W. A murine OIR model was used to examine the anti-angiogenic effects of the compounds. As a result, 2-azahypoxanthine (AHX) showed an inhibitory effect on HIF activation and suppressed Vegf mRNA upregulation under CoCl₂-induced pseudo-hypoxic conditions. Oral administration of AHX significantly suppressed retinal neovascular tufts in the OIR model. These data suggest that AHX could be a promising anti-angiogenic agent in retinal neovascularization by inhibiting HIF activation.

Novel Programmed Cell Death as Therapeutic Targets in Age-Related Macular Degeneration?

Age-related macular degeneration (AMD) is a leading cause of severe visual loss among the elderly. AMD patients are tormented by progressive central blurring/loss of vision and have limited therapeutic options to date. Drusen accumulation causing retinal pigment epithelial (RPE) cell damage is the hallmark of AMD pathogenesis, in which oxidative stress and inflammation are the well-known molecular mechanisms. However, the underlying mechanisms of how RPE responds when exposed to drusen are still poorly understood. Programmed cell death (PCD) plays an important role in cellular responses to stress and the regulation of homeostasis and diseases. Apart from the classical apoptosis, recent studies also discovered novel PCD pathways such as pyroptosis, necroptosis, and ferroptosis, which may contribute to RPE cell death in AMD. This evidence may yield new treatment targets for AMD. In this review, we summarized and analyzed recent advances on the association between novel PCD and AMD, proposing PCD’s role as a therapeutic new target for future AMD treatment.

Development of a Recombinant Monospecific Anti-PLGF Bivalent Nanobody and Evaluation of it in Angiogenesis Modulation

During the past two decades, tumor therapy based on monoclonal antibody has been found as a confident therapeutic approach in solid tumors and hematologic malignancies. Nanobodies are the smallest fragment of an antigen-binding domain in heavy chain-only antibody originated from the Camelidae family. Accordingly, they are being recently developed rapidly as diagnostic and therapeutic agents. In this regard, targeting of angiogenic factors like Placenta growth factor (PLGF) via nanobodies show a high effectiveness. In the current study, we developed a recombinant anti-PLGF bivalent nanobody based on the affinity enhancement mutant form of anti-PLGF nanobody to suppress the angiogenesis progression. Thereafter, the bivalent nanobody (bi-Nb) was cloned and then expressed into a bacterial system. Afterward, the purity was authorized using western blot assay and the affinity was assessed using ELISA. In this regard, proliferation, 3D capillary tube formation, and migration assays were employed as functional assays. The obtained data were analyzed using t-test and P < 0.05 was considered as statistically significant. The results indicate that the bivalent nanobody could inhibit proliferation, mobility, and formation of endothelial cell capillary-like structure. Moreover, the EC50 was estimated for endothelial cell's proliferation and capillary tube's formation to be about 100 ng/ml and 65 ng/ml, respectively. Migration of MCF-7 was inhibited as about 69%, rather than the control. Accumulation of data have shown that targeting of angiogenic factors like VEGF via monoclonal antibodies or nanobodies can be useful in the suppression of tumor progression. Also, the inhibition of PLGF with monoclonal antibody indicated that it is significant in angiogenesis suppression. However, due to intrinsic properties of nanobodies, they are suggested to be used. Since the small size is rapidly removed through liver or kidney system, so it is important to use bivalent or polymeric forms for extending the half-life. Our findings indicated that the inhibition of PLGF can prevent growth and proliferation of endothelial cells and tumor cells through the bivalent nanobody. So, it is suggested as a novel therapeutic agent for angiogenesis suppression.

DS-7080a, a Selective Anti-ROBO4 Antibody, Shows Anti-Angiogenic Efficacy with Distinctly Different Profiles from Anti-VEGF Agents

Purpose

Neovascular age-related macular degeneration (nAMD) results from choroidal neovascularization (CNV) and causes severe vision loss. Intravitreal anti-vascular endothelial growth factor (VEGF) therapies have significantly improved therapeutic outcomes; however, a substantial number of patients experience disease progression. Roundabout 4 (ROBO4) has been reported to be a vascular-specific protein that stabilizes vasculature in ocular pathological angiogenesis. To explore ROBO4 targeting as a novel treatment against neovascularization, we generated a humanized anti-human ROBO4 antibody, DS-7080a, and evaluated its efficacy.

Methods

ROBO4 mRNA in human whole eye cross-sections was examined by in situ hybridization. Human umbilical vein endothelial cell (HUVEC) migration was measured in the presence of VEGF, basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF), or conditioned medium of primary human retinal pigment epithelial (HRPE) cells. CNV was induced in cynomolgus monkeys by laser irradiation. Vascular leakage was measured by fluorescein angiography, and pathological changes were determined by histology.

Results

ROBO4 mRNA was detected in choroidal vessels of nAMD patients. DS-7080a suppressed HGF- or bFGF-induced HUVEC migration in addition to that induced by VEGF. Further, HUVEC migration induced by HRPE-conditioned medium was inhibited by either DS-7080a or ranibizumab in a similar manner, and the combination of these showed further inhibition. In a laser-induced CNV monkey model, single intravitreous administration of 1.1 mg/eye of DS-7080a reduced the incidence of grade 4 leakage from 44.45% in control eyes to 1.85% (P < 0.05 by Dunnett's test).

Conclusions

Anti-ROBO4 antibody DS-7080a suppressed HUVEC migration in a distinctly different fashion from anti-VEGF agents and improved laser-induced CNV in non-human primates.

Translational Relevance

DS-7080a may be a novel treatment option for nAMD.

Novel hybrid lipid nanocapsules loaded with a therapeutic monoclonal antibody - Bevacizumab - and Triamcinolone acetonide for combined therapy in neovascular ocular pathologies

The aim of this study was to design and develop a novel hybrid formulation based on lipid nanocapsules containing bevacizumab (BVZ), an effective therapeutic antibody, on the surface and triamcinolone acetonide (TA) in the inner core (BVZ-TA-LNC) intended to improve ocular therapy. Hence, a phase inversion-insertion one step method was developed to drug loading and surface modification of lipid nanocapsules by post-insertion of a bifunctional polymer, followed by antibody coupling using "click" chemistry. The covalent bond and antibody capacity binding to its specific antigen were confirmed by thermal analysis and immunoassay, respectively. BVZ-TA-LNC presented nanometric size (102 nm), negative surface potential (-19 mV) and exhibiting 56% of TA in the lipid core. BVZ-TA-LNC tended to prevent the endothelial cell migration and significantly prevented the capillary formation induced by the vascular endothelium growth factor (VEGF). The novel hybrid system allowed the co-loading of two different therapeutic molecules and may be promising to improve the therapy of eye disorders that occur with inflammation and/or neovascularization.

Inhibition of retinal neovascularization by VEGF siRNA delivered via bioreducible lipid-like nanoparticles

PURPOSE

Previously, we have demonstrated the use of lipidoid (lipid-like) nanoparticles (e.g., "1-O16B") for gene delivery to live cells, as an alternative to viral vectors. Here, we encapsulate VEGF siRNA (siVEGF) in bioreducible lipidoid nanoparticles and examine whether these nanocomplexes can reduce intravitreal neovascularization in a rodent model of oxygen-induced retinopathy (OIR).

METHODS

Firstly, we constructed siVEGF-nanoparticles (NPs) and transfected human umbilical vein endothelial cells, which caused significantly reduced expression of VEGF, compared to exposure to siVEGF in solution. Secondly, we compared the effect of intravitreal siVEGF-NPs and an anti-VEGF drug (ranibizumab) on retinal vascular development and VEGF mRNA/protein expression in the retinas of a rat model of OIR.

RESULTS

Compared to a non-functional lipid vehicle control group, the level of VEGF mRNA and protein was significantly lower in the siVEGF-NP group (p < 0.01), but the level of VEGF mRNA was not significantly lower in the ranibizumab group. Anatomically, the number of retinal neovascular endothelial nuclei that had protruded through the internal limiting membrane and the number of areas of non-perfusion of the retina were both significantly lower in the siVEGF-NP group and the ranibizumab group than in the OIR group (p < 0.01).

CONCLUSION

Our results demonstrate that bioreducible lipidoid nanoparticles conveying VEGF siRNA can effectively inhibit retinal neovascularization in a rodent model of OIR, and reduce the expression of VEGF mRNA and protein. This novel treatment modality could have profound implications for treating retinal angiogenic diseases.

Zeb1 promotes corneal neovascularization by regulation of vascular endothelial cell proliferation

Angiogenesis is required for tissue repair; but abnormal angiogenesis or neovascularization (NV) causes diseases in the eye. The avascular status in the cornea is a prerequisite for corneal clarity and thought to be maintained by the equilibrium between proangiogenic and antiangiogenic factors that controls proliferation and migration of vascular endothelial cells (ECs) sprouting from the pericorneal plexus. VEGF is the most important intrinsic factor for angiogenesis; anti-VEGF therapies are available for treating ocular NV. However, the effectiveness of the therapies is limited because of VEGF-independent mechanism(s). We show that Zeb1 is an important factor promoting vascular EC proliferation and corneal NV; and a couple of small molecule inhibitors can evict Ctbp from the Zeb1-Ctbp complex, thereby reducing EC Zeb1 expression, proliferation, and corneal NV. We conclude that Zeb1-regulation of angiogenesis is independent of Vegf and that the ZEB1-CtBP inhibitors can be of potential therapeutic significance in treating corneal NV.

Nonexudative Macular Neovascularization - A Systematic Review of Prevalence, Natural History, and Recent Insights from OCT Angiography

PURPOSE

To review the available literature on the prevalence, incidence, natural history, and exudative conversion rates of subclinical (treatment-naïve) nonexudative macular neovascularization (MNV) in patients with age-related macular degeneration (AMD).

CLINICAL RELEVANCE

Nonexudative MNV is now known to be more prevalent in patients with AMD than initially thought and is bringing new insights into both the natural history and management of this very prevalent disease.

METHODS

We conducted a literature search on PubMed, Scopus, and Web of Science, along with a manual search, from January 2014 to June 2019. We included studies that used optical coherence tomography angiography (OCTA) as a primary diagnostic tool to evaluate subclinical (treatment-naïve), nonexudative, neovascular AMD.

RESULTS

Of the 258 screened articles, 12 were included. The prevalence of subclinical nonexudative neovascular AMD in the fellow eyes of patients with unilateral exudative AMD ranged from 6.25% to 27%. Although these lesions were not associated with a significant decrease in visual acuity, the presence of nonexudative MNV seems to be an important predictor of exudative disease. Incidence of exudation in the reviewed studies ranged from 20% to 80% (follow-up 6 months to 2 years). There is some evidence that nonexudative MNV may slow down the growth of adjacent geographic atrophy (GA). As long as exudation does not occur, it appears that subclinical nonexudative MNV is not responsible for the deterioration of visual function.

CONCLUSIONS

Nonexudative MNV is an asymptomatic condition. Although nonexudative MNV seems to be a precursor for the formation of exudative neovascular AMD, there is evidence suggesting a protective effect in slowing the progression of GA. Early detection of nonexudative MNV before exudation develops should result in better monitoring of patients who are at high risk of conversion to exudative AMD. Though no controlled clinical trial has been performed to provide definitive recommendations, the authors of the studies included in this review agree that nonexudative lesions should not be treated until symptomatic exudation develops. Moreover, the existence of a nonexudative form of neovascular AMD would suggest that the term "neovascular AMD" should be preceded by either "exudative" or "nonexudative" when describing this neovascular stage of AMD.

New frontiers and clinical implications in the pathophysiology of age-related macular degeneration

Age-related macular degeneration (AMD) involves progressive degeneration of the central retina, termed the macula, which provides high-acuity vision needed to recognize faces, drive, etc. AMD is the leading cause of blindness in the aging population. A plethora of paradigm-shifting perspectives regarding AMD's multifaceted pathophysiology is emerging. This review will endeavor to gather novel insights and attempts to identify translational implications and new areas of research. The concept of aberrant inflammation being at the center of age-related diseases, particularly AMD, is being received with increasing credence. Retinal angiogenesis, at the forefront of the neovascular complications of AMD (nAMD), is now being understood as an imbalance between trophic factors released by retinal cells secretome. Additionally, mechanisms involving oxidative stress and inflammatory complement pathways have also been identified, along with genetic and other risk factors that play a key role in AMD's onset and progression. Associations have been drawn with AMD and other degenerative deposit diseases such as Alzheimer's disease, atherosclerosis, and glomerulonephritis, which are providing further insight into this maculopathy.

The retinal tyrosine kinome of diabetic Akimba mice highlights potential for specific Src family kinase inhibition in retinal vascular disease

Although anti-VEGF therapies have radically changed clinical practice, there is still an urgent demand for novel, integrative approaches for sight-threatening retinal vascular diseases. As we hypothesize that protein tyrosine kinases are key signaling mediators in retinal vascular disease, we performed a comprehensive activity-based tyrosine kinome profiling on retinal tissue of 12-week-old Akimba mice, a translational model displaying hallmarks of early and advanced diabetic retinopathy. Western blotting was used to confirm retinal tyrosine kinase activity in Akimba mice. HUVEC tube formation and murine organotypic choroidal sprouting assays were applied to compare tyrosine kinase inhibitors with different specificity profiles. HUVEC toxicity and proliferation were evaluated using the CellTox™ Green Cytotoxicity and PrestoBlue™ Assays. Our results indicate a shift of the Akimba retinal tyrosine kinome towards a hyperactive state. Functional network analysis of significantly hyperphosphorylated peptides and upstream kinase prediction revealed a central role for Src-FAK family kinases. Western blotting confirmed hyperactivity of this signaling node in the retina of Akimba mice. We demonstrated that not only Src but also FAK family kinase inhibitors with different selectivity profiles were able to suppress angiogenesis in vitro and ex vivo. In the latter model, the novel selective Src family kinase inhibitor eCF506 was able to achieve potent reduction of angiogenesis, comparable to the less specific inhibitor Dasatinib. None of the tested compounds demonstrated acute endothelial cell toxicity. Overall, the collected findings provide the first comprehensive overview of retinal tyrosine kinome changes in the Akimba model of diabetic retinopathy and for the first time highlight Src family kinase inhibition using highly specific inhibitors as an attractive therapeutic intervention for retinal vascular pathology.

Investigating the Role of PPARβ/δ in Retinal Vascular Remodeling Using Pparβ/δ-Deficient Mice

Peroxisome proliferator-activated receptor (PPAR)β/δ is a member of the nuclear receptor superfamily of transcription factors, which plays fundamental roles in cell proliferation and differentiation, inflammation, adipogenesis, and energy homeostasis. Previous studies demonstrated a reduced choroidal neovascularization (CNV) in Pparβ/δ-deficient mice. However, PPARβ/δ's role in physiological blood vessel formation and vessel remodeling in the retina has yet to be established. Our study showed that PPARβ/δ is specifically required for disordered blood vessel formation in the retina. We further demonstrated an increased arteriovenous crossover and wider venous caliber in Pparβ/δ-haplodeficient mice. In summary, these results indicated a critical role of PPARβ/δ in pathological angiogenesis and blood vessel remodeling in the retina.

Efficacy of ranibizumab combined with photodynamic therapy on wet age-related macular degeneration

Efficacy and safety of intravitreal ranibizumab (IVR) combined with photodynamic therapy (PDT) in treating wet age-related macular degeneration (wAMD) were studied. A total of 130 eyes were collected from 130 wAMD patients treated in Affiliated to Qingdao University Yuhuangding Hospital of Yantai, of which 65 were given IVR combined with PDT (combination therapy group) and the remaining 65 were treated with simple IVR (ranibizumab group). The differences in best corrected visual acuity (BCVA), central macular thickness (CMT), intraocular pressure, choroidal neovascularization (CNV) leakage, levels of serum vascular endothelial growth factor (VEGF) and transforming growth factor-β1 (TGF-β1) as well as complication rate were compared before and after treatment between the two groups. At 1, 3, 6 and 12 months after treatment, combination therapy group had remarkably better BCVA and notably smaller CMT than ranibizumab group. Fundus fluorescein angiography (FFA) showed that the area of macular degeneration was reduced markedly after treatment in both groups, and the area in combination therapy group was evidently smaller than that in ranibizumab group at 1, 3 and 6 months after treatment. At 3 months after treatment, the levels of serum VEGF and TGF-β1 declined obviously in the two groups compared with those before treatment. The IVR combined with PDT can effectively improve the visual acuity, decrease CMT and prominently reduce the area of macular degeneration of wAMD patients, and its therapeutic effects are long-standing and tolerable for the patients, so it is worthy of clinical popularization.

Targeting connexin37 alters angiogenesis and arteriovenous differentiation in the developing mouse retina

Connexin37 (Cx37) forms intercellular channels between endothelial cells (EC), and contributes to coordinate the motor tone of vessels. We investigated the contribution of this protein during physiological angiogenesis. We show that, compared to WT littermates, mice lacking Cx37 (Cx37-/- ) featured (i) a decreased extension of the superficial vascular plexus during the first 4 days after birth; (ii) an increased vascular density at the angiogenic front at P6, due to an increase in the proliferative rate of EC and in the sprouting of the venous compartment, as well as to a somewhat displaced position of tip cells; (iii) a decreased coverage of newly formed arteries and veins by mural cells; (iv) altered ERK-dependent endothelial cells proliferation through the EphB4 signaling pathway, which is involved in the specification of veins and arteries. In vitro studies documented that, in the absence of Cx37, human venous EC (HUVEC) released less platelet-derived growth factor (PDGF) and more Angiopoietin-2, two molecules involved in the recruitment of mural cells. Treatment of mice with DAPT, an inhibitor of the Notch pathway, decreased the expression of Cx37, and partially mimicked in WT retinas, the alterations observed in Cx37-/- mice. Thus, Cx37 contributes to (i) the early angiogenesis of retina, by interacting with the Notch pathway; (ii) the growth and maturation of neo-vessels, by modulating tip, stalk, and mural cells; (iii) the regulation of arteriovenous specification, thus, representing a novel target for treatments of retina diseases.

Novel Cell-Based and Tissue Engineering Approaches for Induction of Angiogenesis as an Alternative Therapy for Diabetic Retinopathy

Diabetic retinopathy (DR) is the most frequent microvascular complication of long-term diabetes and the most common cause of blindness, increasing morbidity in the working-age population. The most effective therapies for these complications include laser photocoagulation and anti-vascular endothelial growth factor (VEGF) intravitreal injections. However, laser and anti-VEGF drugs are untenable as a final solution as they fail to address the underlying neurovascular degeneration and ischemia. Regenerative medicine may be a more promising approach, aimed at the repair of blood vessels and reversal of retinal ischemia. Stem cell therapy has introduced a novel way to reverse the underlying ischemia present in microvascular complications in diseases such as diabetes. The present review discusses current treatments, their side effects, and novel cell-based and tissue engineering approaches as a potential alternative therapeutic approach.

CD73+ extracellular vesicles inhibit angiogenesis through adenosine A2B receptor signalling

Pathological angiogenesis is a hallmark of several conditions including eye diseases, inflammatory diseases, and cancer. Stromal cells play a crucial role in regulating angiogenesis through the release of soluble factors or direct contact with endothelial cells. Here, we analysed the properties of the extracellular vesicles (EVs) released by bone marrow mesenchymal stromal cells (MSCs) and explored the possibility of using them to therapeutically target angiogenesis. We demonstrated that in response to pro-inflammatory cytokines, MSCs produce EVs that are enriched in TIMP-1, CD39 and CD73 and inhibit angiogenesis targeting both extracellular matrix remodelling and endothelial cell migration. We identified a novel anti-angiogenic mechanism based on adenosine production, triggering of A2B adenosine receptors, and induction of NOX2-dependent oxidative stress within endothelial cells. Finally, in pilot experiments, we exploited the anti-angiogenic EVs to inhibit tumour progression in vivo. Our results identify novel pathways involved in the crosstalk between endothelial and stromal cell and suggest new therapeutic strategies to target pathological angiogenesis.

Unfolded protein response (UPR) integrated signaling networks determine cell fate during hypoxia

During hypoxic conditions, cells undergo critical adaptive responses that include the up-regulation of hypoxia-inducible proteins (HIFs) and the induction of the unfolded protein response (UPR). While their induced signaling pathways have many distinct targets, there are some important connections as well. Despite the extensive studies on both of these signaling pathways, the exact mechanisms involved that determine survival versus apoptosis remain largely unexplained and therefore beyond therapeutic control. Here we discuss the complex relationship between the HIF and UPR signaling pathways and the importance of understanding how these pathways differ between normal and cancer cell models.

Cell-based approaches towards treating age-related macular degeneration

Age-related macular degeneration as one of the most common causes of worldwide vision loss needs a proper approach for treatment. Therein, cell therapy and regenerative medicine can hold a great promise to be an effective approach. Accordingly, some preclinical and clinical studies were conducted to search around the therapeutic influence of stem cells in Age-related macular degeneration models and subjects. Hereupon, the purpose of the current review is to discuss the mechanisms of age-related macular degeneration, appropriate animal models along with suitable dosage and route of stem cell administration for its treatment.

Neutralization of Bombina variegata peptide 8 suppresses retinal neovascularization in two different murine models: The oxygen-induced retinopathy model and the rhodopsin promoter/VEGF transgenic mouse model

Bombina variegata 8 (Bv8), also known as prokineticin-2 (PK-2), is a potent pro-angiogenic factor. However, its role in retinal neovascularization (RNV) remains unknown. In this study, we explored the role of Bv8 in the pathogenesis of RNV. We found that the expression of Bv8 was significantly increased in two different models of retinal neovascularization: the oxygen-induced retinopathy (OIR) mouse model and the rhodopsin promoter (rho)/VEGF transgenic mouse model. Neutralization of Bv8 by intravitreal injections of its antibody, not only inhibited retinal and subretinal neovascularization but also decreased the mRNA and protein levels of several pro-angiogenic factors. Our in vitro assay showed that recombinant human Bv8 (RhBv8) protein promoted human retinal microvascular endothelial cells (HRECs) tube-formation, cell proliferation and vascular endothelial growth factor receptor 1 (VEGFR1) and receptor 2 (VEGFR2) expression. Our findings suggest that Bv8 could be used as a novel target for the treatment of RNV-related ocular diseases.

MicroRNA-96 Promotes Vascular Repair in Oxygen-Induced Retinopathy-A Novel Uncovered Vasoprotective Function

Background and Aims

Vascular degeneration is a hallmark in the pathogenesis of oxygen-induced retinopathy (OIR). Dysregulation of microRNAs (miRNAs), key regulators of genes expressions, has been implicated in the regulation of ocular angiogenesis. However, miRNAs specific functions in impaired vascular development during OIR are poorly understood. Herein, we identified miR-96 as one of the most highly expressed miRNAs in the retina and choroid during vascular development and investigated the potential role of miR-96 on microvascular degeneration in a rat OIR model.

Methods and Results

Next generation sequencing (NGS) and qRT-PCR analysis showed that miR-96 maintain high levels of expression during ocular vascular development. Nevertheless, miR-96 was significantly downregulated in the retina and choroid of OIR rats (80% O₂ from P5 to P10) during the phase of microvascular degeneration. Similarly, human retinal microvascular endothelial cells (HRMEC) subjected to hyperoxia (80% O₂) showed a significant downregulation of miR-96 evaluated by qPCR. Interestingly, HRMEC supplemented with miR-96 regulated positively the expression of several key angiogenic factors including VEGF and ANG-2. To explore the angiogenic activity of miR-96 on HRMEC, we performed a gain/loss of function study. In a similar way to hyperoxia exposure, we observed a robust angiogenic impairment (tubulogenesis and migration) on HRMEC transfected with an antagomiR-96. Conversely, overexpression of miR-96 stimulated the angiogenic activity of HRMEC and protected against hyperoxia-induced endothelial dysfunction. Finally, we evaluated the potential vasoprotective function of miR-96 in OIR animals. Rat pups intravitreally supplemented with miR-96 mimic (1 mg/kg) displayed a significant preservation of retinal/choroidal microvessels at P10 compared to controls. This result was consistent with the maintenance of physiologic levels of VEGF and ANG-2 in the OIR retina.

Conclusion

This study demonstrates that miR-96 regulates the expression of angiogenic factors (VEGF/ANG-2) associated to the maintenance of retinal and choroidal microvasculature during physiological and pathological conditions. Intravitreal supplementation of miR-96 mimic could constitute a novel therapeutic strategy to improve vascular repair in OIR and other ischemic retinopathies.

New therapeutic targets in the treatment of age-related macular degeneration

Age-related macular degeneration and especially neovascular age-related macular degeneration is the leading cause of low vision in developed countries. Even though the introduction of anti-VEGF drugs in recent years completely changed the management of this condition, its cost, the need for repeated intravitreal injections, and loss of efficacy in the long term are still issues to deal with. Currently, a new generation of novel therapies under development is attempting to address some of these limitations. Some of the most prominent among them are new anti-VEGFs such as brolucizumab or abicipar, drugs against angiopoietin-2 receptor such as faricimab, sustained-release systems, or tyrosine kinase inhibitors. As regards dry age-related macular degeneration, neuroprotection, the complement pathway, and stem cell therapy are the most promising targets currently under investigation.

Associations of microRNAs, Angiogenesis-Regulating Factors and CFH Y402H Polymorphism-An Attempt to Search for Systemic Biomarkers in Age-Related Macular Degeneration

Age-related macular degeneration (AMD) remains the leading cause of blindness in elderly people, but the pathophysiology of this disease is still largely unknown. We investigated the systemic expression of angiogenesis-regulating growth factors and selected miRNAs known to regulate angiogenesis in AMD patients. We also focused on possible correlations of their expression with the presence of CFH Y402H or ARMS A69S risk variants. A total of 354 AMD patients and 121 controls were enrolled in this study. The levels of angiogenesis-regulating factors were analyzed in plasma samples using Luminex technology. The expression of selected miRNAs was analyzed in peripheral blood plasma using real-time qPCR. The genetic analysis was performed with an Illumina NextSeq500 system. AMD was an independent factor associated with lower levels of angiogenin (β = −0.29, p < 0.001), endostatin (β = −0.18, p < 0.001), FGF-basic (β = −0.18, p < 0.001), PlGF (β = −0.24, p < 0.001), miRNA-21-3p (β = −0.13, p = 0.01) and miRNA-155-5p (β = −0.16, p = 0.002); and with higher levels of FGF-acidic (β = 0.11, p = 0.03), miRNA-23a-3p (β = 0.17, p < 0.001), miRNA-126-5p (β = 0.13, p = 0.009), miRNA-16-5p (β = 0.40, p < 0.001), miRNA-17-3p (β = 0.13, p = 0.01), miRNA-17-5p (β = 0.17, p < 0.001), miRNA-223-3p (β = 0.15, p = 0.004), and miRNA-93 (β = 0.11, p = 0.04). The expression of analyzed miRNA molecules significantly correlated with the levels of tested angiogenesis-regulating factors and clinical parameters in AMD patients, whereas such correlations were not observed in controls. We also found an association between the CFH Y402H polymorphism and miRNA profiles, whereby TT homozygotes showed evidently higher expression of miRNA-16-5p than CC homozygotes or TC heterozygotes (p = 0.0007). Our results suggest that the balance between systemic pro- and anti-angiogenic factors and miRNAs is vital in multifactorial AMD pathogenesis.

Revascularization after angiogenesis inhibition favors new sprouting over abandoned vessel reuse

Inhibiting pathologic angiogenesis can halt disease progression, but such inhibition may offer only a temporary benefit, followed by tissue revascularization after treatment stoppage. This revascularization, however, occurs by largely unknown phenotypic changes in pathologic vessels. To investigate the dynamics of vessel reconfiguration during revascularization, we developed a model of reversible murine corneal angiogenesis permitting longitudinal examination of the same vasculature. Following 30 days of angiogenesis inhibition, two types of vascular structure were evident: partially regressed persistent vessels that were degenerate and barely functional, and fully regressed, non-functional empty basement membrane sleeves (ebms). While persistent vessels maintained a limited flow and retained collagen IV+ basement membrane, CD31+ endothelial cells (EC), and α-SMA+ pericytes, ebms were acellular and expressed only collagen IV. Upon terminating angiogenesis inhibition, transmission electron microscopy and live imaging revealed that revascularization ensued by a rapid reversal of EC degeneracy in persistent vessels, facilitating their phenotypic normalization, vasodilation, increased flow, and subsequent new angiogenic sprouting. Conversely, ebms were irreversibly sealed from the circulation by excess collagen IV deposition that inhibited EC migration and prevented their reuse. Fully and partially regressed vessels therefore have opposing roles during revascularization, where fully regressed vessels inhibit new sprouting while partially regressed persistent vessels rapidly reactivate and serve as the source of continued pathologic angiogenesis.

Phase 1 Study of OPT-302 Inhibition of Vascular Endothelial Growth Factors C and D for Neovascular Age-Related Macular Degeneration

PURPOSE

OPT-302 is a novel inhibitor of vascular endothelial growth factor (VEGF)-C and VEGF-D. A phase 1 trial assessed the safety of intravitreal OPT-302 as monotherapy or combined with ranibizumab (Lucentis; Genentech, South San Francisco, CA) in patients with neovascular age-related macular degeneration (nAMD).

DESIGN

Open-label, dose escalation followed by a randomized dose expansion.

PARTICIPANTS

Fifty-one patients with nAMD who were either treatment naïve (n = 25) or previously were treated with anti-VEGF A therapy (n = 26).

METHODS

In the dose escalation, groups of 5 patients in 4 cohorts received ascending doses of OPT-302 (0.3 mg, 1 mg, or 2 mg) in combination with ranibizumab (0.5 mg), or as monotherapy (2 mg). In the dose expansion, 31 patients were randomized (3:1) to OPT-302 (2 mg) in combination with ranibizumab (n = 23) or as monotherapy (n = 8). Participants received three intravitreal treatments of OPT-302 once every 4 weeks either with or without ranibizumab.

MAIN OUTCOME MEASURES

Safety and tolerability, OPT-302 pharmacokinetics and immunogenicity, effects on best-corrected visual acuity (BCVA), and anatomic changes.

RESULTS

Intravitreal OPT-302 with or without ranibizumab was well tolerated with low systemic exposure, no dose-limiting toxicities and no immunogenicity. In patients receiving OPT-302 monotherapy, 7 of 13 (54%) did not require rescue anti-VEGF-A therapy and the mean change in BCVA from baseline to week 12 was +5.6 letters (range, 0-18 letters). Mean BCVA gains from baseline to week 12 following combination OPT-302 with ranibizumab were +10.8 letters (95% confidence interval [CI], 4-17; n = 18) in treatment-naïve patients and +4.9 letters (95% CI, 3-7; n = 19) in previously treated patients, respectively. Corresponding reductions in mean central subfield thickness at week 12 in both groups were -119 μm (95% CI, -176 to -62 μm) and -54 μm (95% CI, -82 to -26 μm), respectively, whilst 50% of treatment-naïve patients also showed no detectable choroidal neovascularization at week 12 on fluorescein angiography.

CONCLUSIONS

Intravitreal OPT-302 inhibition of VEGF-C and -D was well tolerated, and OPT-302 combination therapy may overcome an escape mechanism to VEGF-A suppression in the management of nAMD.

Anti-angiogenic and anti-inflammatory effects of CD200-CD200R1 axis in oxygen-induced retinopathy mice model

OBJECTIVE

In this study, the expression changes and the potential effects of CD200 and its receptors during the process of retinal neovascularization (RNV) development had been detected, using a classic oxygen-induced retinopathy (OIR) mice model and CD200Fc (a CD200R1 agonist) intravitreal injection.

MATERIALS AND METHODS

7 day postnatal (P7) C57BL/6J mice were raised in hyperoxia incubators with 75±2% oxygen for 5 days, and returned to room air at P12. All animals were subdivided into three groups: normoxia control, OIR, and OIR+CD200Fc group. The mice of OIR+CD200Fc group were intravitreal injected with CD200Fc (2μg/μL, 0.5μL) at P12. Retinas and vitreous samples were harvested at P17. The expression and localization of CD200 and its receptors were analyzed by Western blot, quantitative real-time polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA), and retinal whole-mount immunofluorescence. To investigate the effects of CD200Fc treatment, vascular endothelial growth factor (VEGF)-A, platelet-derived growth factor (PDGF)-BB, pro-inflammatory cytokines, NV area, and microglial activation were detected respectively.

RESULTS

In OIR group, both protein and RNA levels of CD200 and CD200R1 were significantly up-regulated. The increased CD200 and CD200R1 were co-localized with Alex594-labeled Griffonia simplicifolia isolectin B4 (IB4) on vascular endothelial cells in NV area of OIR samples, and CD200R1 was co-expressed with ionized calcium-bind adapter molecule 1 (iba1) on microglia in OIR samples at the same time. CD200Fc intravitreal injection could significantly reduce the release of VEGF-A, PDGF-BB, and pro-inflammatory cytokines; shrink the NV area; and inhibit the activation of microglia in OIR mice.

CONCLUSION

These findings suggested that the up-regulation of CD200 and CD200R1 was closely related to RNV development, and the antiangiogenic effects of CD200Fc in OIR model might be realized by inhibition of inflammatory response and microglia activation. The results may provide a new therapeutic target for RNV diseases.

The role of sphingosine 1-phosphate receptors on retinal pigment epithelial cells barrier function and angiogenic effects

Sphingosine-1-phosphate (S1P) is a lysophospholipid mediator, promoting angiogenesis and inflammation via interactions with its receptors (S1P1-5), but the receptors and signaling pathways responsible for the progression of choroidal neovascularization (CNV) remain unknown. We investigated the roles of S1P/S1P receptors in RPE cells. ARPE-19 cells were treated with S1P dissolved in carrier proteins of albumin or apolipoprotein M (ApoM). The mRNA expression levels of interleukin-8 (IL-8), C-C motif chemokine ligand 2 (CCL2), and vascular endothelial growth factor (VEGF) were evaluated using quantitative real-time polymerase chain reaction. The protein level of hypoxia-inducible factor (HIF)-1α was assessed via enzyme-linked immunosorbent assay. HIF transcriptional activity was evaluated with a dual-reporter luciferase assay. Cellular barrier integrity was evaluated using transepithelial electrical resistance and the FITC-dextran permeability assay. The suppressive effect of an S1P antagonist on CNV progression was investigated with a laser-induced CNV model in mice. The increase in expression of IL-8, CCL2, and VEGF due to albumin-bound S1P was significantly mitigated by an S1P2 antagonist. The expression of HIF-1α significantly decreased with inhibition of S1P2 and S1P3. In addition, albumin-bound S1P disrupted the barrier integrity of retinal pigment epithelial cells via S1P2, whereas integrity was strengthened by ApoM-bound S1P. CNV lesions were significantly reduced in the mouse model with intravitreal injection of S1P2 antagonist. This study demonstrated that S1P significantly promotes angiogenesis, inflammation, and barrier integrity, which was attenuated by inhibition of S1P2 or S1P3, suggesting that regulation of S1P2 and S1P3 is a novel therapeutic target for CNV.

Human Skin-Derived Mast Cells Spontaneously Secrete Several Angiogenesis-Related Factors

Mast cells are classically recognized as cells that cause IgE-mediated allergic reactions. However, their ability to store and secrete vascular endothelial growth factor (VEGF) suggests a role in vascular development and tumorigenesis. The current study sought to determine if other angiogenesis-related factors, in addition to VEGF, were also secreted by human tissue-derived mast cells. Using proteome array analysis and ELISA, we found that human skin-derived mast cells spontaneously secrete CXCL16, DPPIV, Endothelin-1, GM-CSF, IL-8, MCP-1, Pentraxin 3, Serpin E1, Serpin F1, TIMP-1, Thrombospondin-1, and uPA. We identified three groups based on their dependency for stem cell factor (SCF), which is required for mast cell survival: Endothelin-1, GM-CSF, IL-8, MCP-1, and VEGF (dependent); Pentraxin 3, Serpin E1, Serpin F1, TIMP-1, and Thrombospondin-1 (partly dependent); and CXCL16, DPPIV, and uPA (independent). Crosslinking of FcεRI with multivalent antigen enhanced the secretion of GM-CSF, Serpin E1, IL-8, and VEGF, and induced Amphiregulin and MMP-8 expression. Interestingly, FcεRI signals inhibited the spontaneous secretion of CXCL16, Endothelin-1, Serpin F1, Thrombospondin-1, MCP-1 and Pentraxin-3. Furthermore, IL-6, which we previously showed could induce VEGF, significantly enhanced MCP-1 secretion. Overall, this study identified several angiogenesis-related proteins that, in addition to VEGF, are spontaneously secreted at high concentrations from human skin-derived mast cells. These findings provide further evidence supporting an intrinsic role for mast cells in blood vessel formation.

mTORC1 and mTORC2 are differentially engaged in the development of laser-induced CNV

Background

The mechanistic target of rapamycin (mTOR) pathway is a potential target to inhibit pathologic processes in choroidal neovascularization. However, the exact role of mTOR signaling in the development of CNV remains obscure. In this study, we assessed the role of mTORC1 and mTORC2 as well as the effect of rapamycin (sirolimus) on choroidal neovascularization (CNV) in a laser-induced mouse model.

Methods

In experiment A, we observed the natural course of CNV development and the dynamics of mTOR-related proteins during the 12 days after the laser injury. The expression of mTOR-related proteins was evaluated using Western blot (WB). Cryosections of CNV-induced mice were immunostained for the visualization of the vascular and extravascular components of the CNV. Experiment B was performed to confirm the critical period of mTOR signaling in the development of laser-induced CNV, we administered rapamycin before and/or during the active period of mTOR complexes. WB and immunofluorescence staining was performed to evaluate the mode of action and the effect of mTOR inhibition on CNV development.

Results

In experiment A, we detected high levels of p-mTOR S2448 and p-mTOR S2481 from the 5th to 12th day of laser injury. Immunofluorescence imaging of cryosections of mice sacrificed on day 7 revealed greater co-immunoreactivity of p-mTOR S2448 positive cells with CD11b and F4/80, while p-mTOR S2481 positive cells showed colocalization with CD31, α-SMA, and cytokeratin. In experiment B, rapamycin injection during the active period of mTOR signaling demonstrated near-complete inhibition of CNV lesion as well as significant induction of autophagy.

Conclusion

Our study suggests the mTOR as a critical player during CNV development in laser-induced mouse model through differentially acting with the mTORC1 and mTORC2. mTORC1 activity was high predominantly in inflammatory cells in CNV lesion, while mTORC2 activity was higher in vascular components and the RPE.

Electronic supplementary material

The online version of this article (10.1186/s12964-019-0380-0) contains supplementary material, which is available to authorized users.

c-Cbl: An Important Regulator and a Target in Angiogenesis and Tumorigenesis

Casitas B lineage lymphoma (c-Cbl) is a multifunctional protein with a ubiquitin E3 ligase activity capable of degrading diverse sets of proteins. Although previous work had focused mainly on c-Cbl mutations in humans with hematological malignancies, recent emerging evidence suggests a critical role of c-Cbl in angiogenesis and human solid organ tumors. The combination of its unique structure, modular function, and ability to channelize cues from a rich network of signaling cascades, empowers c-Cbl to assume a central role in these disease models. This review consolidates the structural and functional insights based on recent studies that highlight c-Cbl as a target with tantalizing therapeutic potential in various models of angiogenesis and tumorigenesis.

Oxidative stress upregulates Wnt signaling in human retinal microvascular endothelial cells through activation of disheveled

Abnormal retinal neovascularization associated with various retinopathies can result in irreversible vision loss. Although the mechanisms involved in this occurrence is unclear, increasing evidence suggests that aberrant Wnt signaling participates in the pathogenesis of abnormal neovascularization. Because Wnt signaling upregulation can be induced by oxidative stress through the activation of disheveled (DVL), a key molecule in the Wnt signaling pathway, we investigated whether oxidative stress can activate Wnt signaling and induce angiogenic phenotypes in human retinal microvascular endothelial cells (HRMECs). We found that increased Wnt signaling activity, as well as enhanced angiogenic phenotypes, such as tube formation and cell migration, were detected in the hydrogen peroxide-treated HRMECs. Moreover, these effects were effectively suppressed by a small-molecule Wnt inhibitor targeting the PDZ domain of DVL. Therefore, we propose that targeting abnormal Wnt signaling at the DVL level with a small-molecule inhibitor may represent a novel approach in retinal neovascularization treatment and prevention.

Experimental Evidence Behind Clinical Trial Outcomes in Retinopathy of Prematurity

Treatment of severe retinopathy of prematurity (ROP) has evolved over the last decade. This article reviews recent clinical trials and experimental evidence that supports clinical outcomes and observations, including the efficacy of anti-vascular endothelial growth factor (VEGF) agents in reducing the vascular activity of severe ROP, and the mechanisms behind recurrent stage 3 ROP and plus disease in some infants treated with anti-VEGF agents. Also discussed will be current imaging modalities that link experimental models of ROP with longitudinal human studies and which provide exciting future opportunities to enhance the understanding of pathophysiology of ROP and improve treatments. [Ophthalmic Surg Lasers Imaging Retina. 2019;50:228-234.].

Function-first ligandomics for ocular vascular research and drug target discovery

Human eyes may develop different vascular diseases with neovascularization and/or leakage, including wet age-related macular degeneration (AMD), diabetic macular edema (DME), proliferative diabetic retinopathy (PDR), retinopathy of prematurity, corneal neovascularization and intraocular tumors. A breakthrough in therapy is the advent and approval of vascular endothelial growth factor (VEGF) inhibitors. However, anti-VEGF drugs not only have limited efficacy to treat AMD, DME and PDR but also are not approved for other ocular indications. The key to addressing these unmet clinical needs is to develop novel therapies against VEGF-independent angiogenic factors or signaling pathways for alternative or combination therapy. We recently developed the first paradigm of ligandomics for global mapping of cell-wide ligands as well as disease-selective ligands. Therapies targeting disease-selective angiogenic or vascular leakage factors likely have high efficacy, minimal side effects, wide therapeutic windows and relatively low drug attrition rates. A critical challenge is how to distinguish between genuine drug targets and spurious hits identified by high-throughput ligandomics. Here we exploited the unique advantages of the eye and extracellular ligands by combining ligandomics with "function-first" and/or "therapy-first" analyses to efficiently characterize functional activity, disease selectivity, pathogenic role and therapeutic potential of identified ligands. The innovative function- or therapy-first ligandomics will systematically and reliably delineate disease-selective angiogenic or vascular leakage factors and markedly facilitate ocular vascular research and ligand-guided targeted anti-angiogenic therapy.

Anticancer activity of saponin isolated from Albizia lebbeck using various in vitro models

ETHNOPHARMACOLOGICAL RELEVANCE

Albizia lebbeck (L.) Benth. (Family: Mimosaceae) is commonly known as Sirisha in Sanskrit. The leaves and pods of A. lebbeck were claimed to be used against cancer in traditional medicine. Previous studies using bark, leaves, seeds and pods of A. lebbeck showed cytotoxic activity against hepatic, colon, larynx, cervical and breast cancer cell lines.

AIM OF THE STUDY

To evaluate the anticancer activity of saponin rich fraction of Albizia lebbeck by using various in vitro models.

MATERIALS AND METHODS

Albiziasaponins (A-E) are oleanene triterpene presents in Albizia lebbeck were used for in silico studies. In silico testing of albiziasaponins for structure based pharmacological activity prediction using PASS Online software and docking with Autodock tool and Autodock Vina revels it's anticancer and apoptogenic potential. Antiproliferative activity of saponin rich fraction of A. lebbeck was performed using MCF-7 human breast cancer cells by MTT assay methods. Anti-angiogenic property of saponin rich fraction of A. lebbeck was evaluated in in vitro shell less chick embryo cultures with different concentrations (0.1 µg/ml, 0.5 µg/ml, and 1 µg/ml) by using ImageJ software. In vitro cultured lymphocytes chromosomal aberration assay was performed to determine the physical integrity of chromosomes in cells and effect of saponin rich fraction of A. lebbeck on cell cycle. Apoptogenic potential was evaluated using Caspases-3 and Caspase-8 ELISA assay in MCF-7 cells.

RESULTS

Result of MTT assay showed IC50 of saponin rich fraction of A. lebbeck at 1 μg/ml in MCF-7 cells. Treatment with saponin rich fraction of A. lebbeck significantly (p < 0.05) reduced angiogenic parameters. Significant chromosomal aberrations (hypodiploid, hyperdiploid, ring, premature separation, Dicentric fragments, Acentric fragment, chromatid break, and chromosomal gap) were observed in saponin rich fraction of A. lebbeck treated groups. Treatment with saponin rich fraction of A. lebbeck increased levels of Caspases-3 (optical density of 0.24 at 450 nm) and Caspase-8 (optical density of 0.31 at 450 nm) as compared to staurosporine (optical density of 2.47 and 2.65 for caspases-3 and -8 respectively at 450 nm).

CONCLUSION

In our study, saponin rich fraction of A. lebbeck showed antiproliferative, antiangiogenic and apoptogenic potential using various in-vitro models. It also found to increase chromosomal aberration and thereby may affect cell cycle.

β‑elemene inhibits oxygen‑induced retinal neovascularization via promoting miR‑27a and reducing VEGF expression

The present study aimed to investigate the significant role of β-elemene in mouse models of oxygen-induced retinopathy (OIR). C57BL/6J neonatal mice were used to establish OIR models. They were divided into four groups: Normoxia, OIR, OIR control and OIR‑treated. Mice in the OIR group were exposed to 75±5% oxygen for 5 days and returned to a normal oxygen environment on postnatal day 12 (P12). The OIR treated group was intravitreally injected with 1 µl β‑elemene on P12 and subsequently returned to a normal oxygen environment for 5 days (P12‑P17). Retinas were obtained on P17. Retinal neovascularization (RNV) was detected using adenosine diphosphatase staining and analyzed by counting the nuclei of neovascular endothelial cells. Vascular endothelial growth factor (VEGF) expression was determined by reverse transcription‑quantitative polymerase chain reaction, immunohistochemistry and western blot analysis. MicroRNA (miRNA/miR) microarrays were used to screen out differentially expressed miRNAs between the OIR and β‑elemene‑treated groups. Binding the 3'‑untranslated region (UTR) of VEGF and miR‑27a was confirmed using luciferase assays. It was found that high oxygen concentrations accelerated RNV and increased the number of preretinal neovascular cells; β‑elemene treatment reduced these effects. VEGF mRNA and protein expression was higher in the OIR and OIR control groups, compared with the normoxia and OIR‑treated groups. Further, it was shown that miR‑22, miR‑181a‑1, miR‑335‑5p, miR‑669n, miR‑190b, miR‑27a and miR‑93 were upregulated in the OIR‑treated group, and downregulated in the OIR group. The prediction websites TargetScan and miRanda revealed that VEGF contained a potential miR‑27a binding site in its 3'‑untranslated region (UTR). Luciferase assays demonstrated that miR‑27a directly bound to the 3'‑UTR of VEGF. In vitro experiments demonstrated that miR‑27a inhibited VEGF expression. In addition, β‑elemene treatment upregulate miR‑27a expression in vivo and in vitro. When miR‑27a expression was depleted by miR‑27a inhibitor, the protective effect of β‑elemene on RNV was eliminated. The present study demonstrated that β‑elemene reduced RNV in mouse OIR models via miR‑27a upregulation, leading to reduced VEGF expression. This finding may contribute to the development of novel therapeutic strategies for human retinopathy.

Secretogranin III as a novel target for the therapy of choroidal neovascularization

Wet age-related macular degeneration (AMD) with choroidal neovascularization (CNV) is a leading cause of vision loss in the elderly. The advent of anti-vascular endothelial growth factor (VEGF) drugs represents a major breakthrough in wet AMD therapy but with limited efficacy to improve visual acuity. Secretogranin III (Scg3, SgIII) was recently discovered as a novel angiogenic factor with VEGF-independent mechanisms. Scg3-neutralizing monoclonal antibody (mAb) was reported to alleviate pathological retinal neovascularization in oxygen-induced retinopathy mice and retinal vascular leakage in diabetic mice with high efficacy and disease selectivity. Herein we investigated whether Scg3 is a novel angiogenic target for CNV therapy in mouse models. We found that anti-Scg3 ML49.3 mAb inhibited Scg3-induced proliferation and Src phosphorylation in human retinal microvascular endothelial cells. Intravitreal injection of Scg3-neutralizing polyclonal antibodies (pAb) or mAb significantly attenuated laser-induced CNV leakage, CNV 3D volume, lesion area and vessel density. Furthermore, subcutaneous administration of Scg3-neutralizing pAb or mAb significantly prevented Matrigel-induced CNV. The efficacy of anti-Scg3 pAb or mAb was comparable to VEGF inhibitor aflibercept. These findings suggest that Scg3 plays an important role in CNV pathogenesis and that anti-Scg3 mAb efficiently ameliorates laser- or Matrigel-induced CNV.

Bioactive lipids and pathological retinal angiogenesis

Angiogenesis, disruption of the retinal barrier, leukocyte-adhesion and oedema are cardinal signs of proliferative retinopathies that are associated with vision loss. Therefore, identifying factors that regulate these vascular dysfunctions is critical to target pathological angiogenesis. Given the conflicting role of bioactive lipids reported in the current literature, the goal of this review is to provide the reader a clear road map of what has been accomplished so far in the field with specific focus on the role of polyunsaturated fatty acids (PUFAs)-derived metabolites in proliferative retinopathies. This necessarily entails a description of the different retina cells, blood retina barriers and the role of (PUFAs)-derived metabolites in diabetic retinopathy, retinopathy of prematurity and age-related macular degeneration as the most common types of proliferative retinopathies.

Oxidative stress, autophagy and pyroptosis in the neovascularization of oxygen‑induced retinopathy in mice

Retinal neovascularization (RNV) is a principal cause of visual impairment and blindness worldwide. The present study aimed to investigate how oxidative stress, autophagy and pyroptosis alter in RNV. The oxygen‑induced retinopathy (OIR) model was established in C57BL/6J mice by exposing them to a high concentration of oxygen. RNV was clearly visible in the fundus images and was qualitatively analyzed by counting the number of neovascular endothelial cell nuclei at postnatal day 17. Subsequently, the expression of vascular endothelial growth factor (VEGF)‑A and hypoxia‑inducible factor‑1α (HIF‑1α) at the protein level were measured. Furthermore, oxidative stress was examined using dihydroethidium (DHE) staining, and NADPH oxidase (NOX) 1 and 4 in the retinas were detected using reverse transcription‑quantitative polymerase chain reaction analysis. Additionally, immunostaining of microtubule associated protein 1 light chain 3α (LC3) was performed and the expression levels of the LC3, p62, autophagy protein (Atg)5, Atg7, Atg12, Beclin1, NOD‑like receptor family pyrin domain‑containing 3 (NLRP3), caspase‑1, interleukin (IL)‑1β, pro‑caspase‑1 and pro‑IL‑1β proteins were determined using western blotting in order to detect pyroptosis and autophagic flux. Autophagosomes were also detected using transmission electron microscopy. The results revealed that VEGF‑A and HIF‑1α protein expression levels, the DHE‑positive area, and NOX1 and NOX4 mRNA expression levels were significantly increased in the OIR mice. Furthermore, increased levels of NLRP3, caspase‑1, IL‑1β, pro‑caspase‑1 and pro‑IL‑1β proteins demonstrated that pyroptosis was activated. However, an accumulation of p62 and a reduction in the levels of LC3II/I and autophagosomes indicated that autophagic flux was compromised. Therefore, elevated levels of reactive oxygen species and pyroptosis along with attenuated autophagy were demonstrated in the OIR mice. The combination of oxidative stress, pyroptosis and impaired autophagy may serve an important role in the pathophysiology of RNV and may be a potential target to prevent RNV.

The Different Facades of Retinal and Choroidal Endothelial Cells in Response to Hypoxia

Ocular angiogenic diseases, such as proliferative diabetic retinopathy and neovascular age-related macular degeneration, are associated with severe loss of vision. These pathologies originate from different vascular beds, retinal and choroidal microvasculatures, respectively. The activation of endothelial cells (EC) plays pivotal roles in angiogenesis, often triggered by oxygen deficiency. Hypoxia-inducible factors in ECs mediate the transcription of multiple angiogenic genes, including the canonical vascular endothelial growth factors. ECs show notable heterogeneity in function, structure, and disease, therefore the understanding of retinal/choroidal ECs (REC; CEC) biochemical and molecular responses to hypoxia may offer key insights into tissue-specific vascular targeting treatments. The aim of this review is to discuss the differences spanning between REC and CEC, with focus on their response to hypoxia, which could provide innovative and sustainable strategies for site specific targeting of ocular neovascularization.

A review of the multifunctionality of angiopoietin-like 4 in eye disease

Angiopoietin-like protein 4 (ANGPTL4) is a multifunctional cytokine regulating vascular permeability, angiogenesis, and inflammation. Dysregulations in these responses contribute to the pathogenesis of ischemic retinopathies such as diabetic retinopathy (DR), age-related macular degeneration (AMD), retinal vein occlusion, and sickle cell retinopathy (SCR). However, the role of ANGPTL4 in these diseases remains controversial. Here, we summarize the functional mechanisms of ANGPTL4 in several diseases. We highlight original studies that provide detailed data about the mechanisms of action for ANGPTL4, its applications as a diagnostic or prognostic biomarker, and its use as a potential therapeutic target. Taken together, the discussions in this review will help us gain a better understanding of the molecular mechanisms by which ANGPTL4 functions in eye disease and will provide directions for future research.

Effect of integrin α5β1 inhibition on SDF-l/CXCR4-mediated choroidal neovascularization

AIM

To investigate the roles of integrins in choroidal neovascularization (CNV) and their associations with the stromal cell-derived factor-1 (SDF-1)/CXCR4 axis.

METHODS

CNV lesions were induced in mice using laser photocoagulation. After CNV induction, all animals were randomly assigned to: control, SDF-1, SDF-1+age-related macular degeneration (AMD) 3100 (CXCR4 inhibitor), and SDF-1+ATN161 (integrin α5β1 inhibitor) groups; their effects on CNV progression were observed using hematoxylin eosin (HE) staining, fundus fluorescein angiography (FFA) grading and optical coherence tomography (OCT), and their effects on CXCR4/integrin α5 expression were evaluated using Western blot and double immunofluorescence staining. Hypoxia-exposed endothelial cells (ECs) were used to simulate CNV in vitro, they were treated with SDF-1, combined with CXCR4 siRNA/AMD3100 or ATN161, and expression of integrin α5, cell migration and tube formation were analyzed.

RESULTS

Integrin subunit α5 increased at 3^rd and 7^th day and decreased at 14^th day in CNV mice, with no significant change of β1-integrin. CXCR4 expression in CNV mice had persistent increase within 14d after induction. SDF-1 treatment significantly promoted the CNV progression during 3-14d. The mean CNV length in AMD3100 and ATN161 group at day 7 was 270.13 and 264.23 µm in HE images, significantly lower than the mean length in SDF-1 (345.70 µm) group. AMD3100 and ATN161 also significantly reduced thickness and leakage of CNV induced by SDF-1. Mean integrin α5 positive area in SDF-1 group reached 2.31×104 µm², significantly higher than control (1.25×104 µm²), which decreased to 1.78×104 µm² after AMD3100 treatment. About 61.36% of ECs in CNV lesions expressed α5 in SDF-1 group, which significantly decreased to 43.12% after AMD3100 treatment. In vitro, integrin α5 peaked by 6 folds after 6h of hypoxia exposure and CXCR4 gradually increased by up to 2.3 folds after 24h of hypoxia. Approximately 25.12% of ECs expressed integrin α5 after SDF-1 stimulation, which decreased to 7.2%-9.5% after si-CXCR4 or AMD3100 treatment. ATN161 exerted an inhibitory effect comparable to that of si-CXCR4 on EC migration and tube formation in the presence of SDF-1.

CONCLUSION

SDF-1/CXCR4 signaling induces integrin α5β1 expression in ECs to promote CNV.

Collective adhesion and displacement of retinal progenitor cells upon extracellular matrix substrates of transplantable biomaterials

Strategies to replace retinal photoreceptors lost to damage or disease rely upon the migration of replacement cells transplanted into sub-retinal spaces. A significant obstacle to the advancement of cell transplantation for retinal repair is the limited migration of transplanted cells into host retina. In this work, we examine the adhesion and displacement responses of retinal progenitor cells on extracellular matrix substrates found in retina as well as widely used in the design and preparation of transplantable scaffolds. The data illustrate that retinal progenitor cells exhibit unique adhesive and displacement dynamics in response to poly-l-lysine, fibronectin, laminin, hyaluronic acid, and Matrigel. These findings suggest that transplantable biomaterials can be designed to improve cell integration by incorporating extracellular matrix substrates that affect the migratory behaviors of replacement cells.