Beyond VEGF: Angiopoietin-Tie Signaling Pathway in Diabetic Retinopathy

Complications from diabetic retinopathy such as diabetic macular edema (DME) and proliferative diabetic retinopathy (PDR) constitute leading causes of preventable vision loss in working-age patients. Since vascular endothelial growth factor (VEGF) plays a major role in the pathogenesis of these complications, VEGF inhibitors have been the cornerstone of their treatment. Anti-VEGF monotherapy is an effective but burdensome treatment for DME. However, due to the intensive and burdensome treatment, most patients in routine clinical practice are undertreated, and therefore, their outcomes are compromised. Even in adequately treated patients, persistent DME is reported anywhere from 30% to 60% depending on the drug used. PDR is currently treated by anti-VEGF, panretinal photocoagulation (PRP) or a combination of both. Similarly, a number of eyes, despite these treatments, continue to progress to tractional retinal detachment and vitreous hemorrhage. Clearly there are other molecular pathways other than VEGF involved in the pathogenesis of DME and PDR. One of these pathways is the angiopoietin-Tie signaling pathway. Angiopoietin 1 (Ang1) plays a major role in maintaining vascular quiescence and stability. It acts as a molecular brake against vascular destabilization and inflammation that is usually promoted by angiopoietin 2 (Ang2). Several pathological conditions including chronic hyperglycemia lead to Ang2 upregulation. Recent regulatory approval of the bi-specific antibody, faricimab, may improve long term outcomes in DME. It targets both the Ang/Tie and VEGF pathways. The YOSEMITE and RHINE were multicenter, double-masked, randomized non-inferiority phase 3 clinical trials that compared faricimab to aflibercept in eyes with center-involved DME. At 12 months of follow-up, faricimab demonstrated non-inferior vision gains, improved anatomic outcomes and a potential for extended dosing when compared to aflibercept. The 2-year results of the YOSEMITE and RHINE trials demonstrated that the anatomic and functional results obtained at the 1 year follow-up were maintained. Short term outcomes of previously treated and treatment-naive eyes with DME that were treated with faricimab during routine clinical practice suggest a beneficial effect of faricimab over other agents. Targeting of Ang2 has been reported by several other means including VE-PTP inhibitors, integrin binding peptide and surrobodies.

SOCS3 regulates pathological retinal angiogenesis through modulating SPP1 expression in microglia and macrophages

Pathological ocular angiogenesis has long been associated with myeloid cell activation. However, the precise cellular and molecular mechanisms governing the intricate crosstalk between the immune system and vascular changes during ocular neovascularization formation remain elusive. In this study, we demonstrated that the absence of the suppressor of cytokine signaling 3 (SOCS3) in myeloid cells led to a substantial accumulation of microglia and macrophage subsets during the neovascularization process. Our single-cell RNA sequencing data analysis revealed a remarkable increase in the expression of the secreted phosphoprotein 1 (Spp1) gene within these microglia and macrophages, identifying subsets of Spp1-expressing microglia and macrophages during neovascularization formation in angiogenesis mouse models. Notably, the number of Spp1-expressing microglia and macrophages exhibited further elevation during neovascularization in mice lacking myeloid SOCS3. Moreover, our investigation unveiled the Spp1 gene as a direct transcriptional target gene of signal transducer and activator of transcription 3. Importantly, pharmaceutical activation of SOCS3 or blocking of SPP1 resulted in a significant reduction in pathological neovascularization. In conclusion, our study highlights the pivotal role of the SOCS3/STAT3/SPP1 axis in the regulation of pathological retinal angiogenesis.

METTL3-Mediated RNA m6A Modification Regulates the Angiogenic Behaviors of Retinal Endothelial Cells by Methylating MMP2 and TIE2

Purpose

N6-methyladenosine (m6A) is a commonly occurring modification of mRNAs, catalyzed by a complex containing methyltransferase like 3 (METTL3). Our research aims to explore how METTL3-dependent m6A modification affects the functions of retinal endothelial cells (RECs).

Methods

An oxygen-induced retinopathy (OIR) mouse model was established, and RECs were isolated using magnetic beads method. Human retinal microvascular endothelial cells (HRMECs) were treated with normoxia (21% O2) or hypoxia (1% O2). Dot blot assay determined m6A modification levels. Quantitative RT-PCR and Western blot detected the mRNA and protein expression levels of the target candidates, respectively. Genes were knocked down by small interfering RNA transfection. Matrigel-based angiogenesis and transwell assays evaluated the abilities of endothelial tube formation and migration, respectively. Methylated RNA immunoprecipitation-qPCR determined the levels of m6A modification in the target genes.

Results

The m6A modification levels were significantly upregulated in the retinas and RECs of OIR mice. Exposure to hypoxia significantly elevated both METTL3 expression and m6A modification levels in HRMECs. METTL3 knockdown curtailed endothelial tube formation and migration in vitro under both normoxic and hypoxic conditions. Concurrently, this knockdown in HRMECs resulted in reduced m6A modification levels of MMP2 and TIE2 transcripts, subsequently leading to a decrease in their respective protein expressions. Notably, knockdown of MMP2 and TIE2 also markedly inhibited the angiogenic activities of HRMECs.

Conclusions

METTL3-mediated m6A modification promotes the angiogenic behaviors of RECs by targeting MMP2 and TIE2, suggesting its significance in retinal angiogenesis and METTL3 as a potential therapeutic target.

The Transcription Factor RUNX1 Aggravates Hypoxia-Induced Human Retinal Microvascular Endothelial Cell Dysfunction by Negatively Regulating TFF1 Promoter

OBJECTIVE

As a retinal vaso-proliferative disorder, retinopathy of prematurity (ROP) is characterized by neovascularization and angiogenesis, causing irreversible retinal damage and even visual loss among premature infants. Trefoil factor 1 (TFF1) has been identified as a key regulator in mediating retinal angiogenesis in diabetic retinopathy. However, whether TFF1 can mediate the angiogenic process in ROP remains unknown. Here, we aimed to investigate the regulatory function of TFF1 and its underlying mechanisms in hypoxia-exposed human retinal vascular endothelial cells (HRVECs) in vitro.

METHODS

HRVECs were exposed to hypoxia condition to establish the in vitro ROP models. HRVEC viability was validated using CCK-8 assay. The migratory and angiogenic capacities of HRVECs were assessed by wound healing and tube formation assays, respectively. RT-qPCR was performed to detect gene levels. Western blotting was used to measure the protein levels of TFF1 and Runt-related transcription factor 1 (RUNX1). The binding relationship between RUNX1 to TFF1 promoter was confirmed by chromatin immunoprecipitation and luciferase reporter assays.

RESULTS

Hypoxia downregulated TFF1 expression and elevated RUNX1 expression in HRVECs. Moreover, hypoxic condition increased HRVEC viability and accelerated HRVEC migration and angiogenesis, which were antagonized by TFF1 elevation or RUNX1 knockdown. RUNX1 as a transcription factor bound to TFF1 promoter and transcriptionally repressed TFF1 expression in HRVECs. In rescue assays, overexpression of TFF1 counteracted the promotive effect of RUNX1 overexpression on the viability, migratory and angiogenic abilities of HRVECs under hypoxia.

CONCLUSIONS

RUNX1 transcriptionally suppresses TFF1 expression to aggravate hypoxia-induced HRVEC dysfunction.

The Antiangiogenic Effect and Ocular Pharmacology of Novel Modified Nonsteroidal Anti-Inflammatory Drugs in the Treatment of Oxygen-Induced Retinopathy

Purpose: To evaluate the hypothesis that 3 novel compounds, OXT-328, Q-922, and CL-717 show efficacy in the treatment of oxygen-induced retinopathy (OIR) and whether or not their route of administration is intravitreal, topical, or systemic. Methods: The OIR mouse model, characterized by an avascular area (AVA) and a neovascular area (NVA) of the retina, was used to study retinopathy of prematurity and other retinal diseases characterized by abnormal vessel growth. We measured the effect of our compounds on both the AVA and NVA in whole mounts of mouse retinal tissue. We also evaluated their ability to prevent new vessel formation in chicken chorioallantoic membranes (CAMs). Finally, we measured the in vitro uptake and biodistribution of topically applied CL-717 in human eye explants. Results: In mice with OIR, compared to controls, a single intravitreal administration of Q-922 or OXT-328 significantly reduced both AVA and NVA. CL-717 administered as eye drops over 5 days also reduced AVA and NVA, whereas OXT-328 eye drops had no effect. Q-922 given intraperitoneal (150 mg/kg/day × 5 days) reduced AVA and NVA. Remarkably, explanted human eyes bathed in CL-717 show rapid uptake and biodistribution in ocular tissues. In the chicken CAM model, all 3 compounds reduced the formation of new blood vessels by about one-third. No side effect in mice was observed, except for mild ocular surface irritation with Q-922. Conclusions: Systemic administration of Q-922 or topical administration of CL-717 holds particular promise for a simplified treatment of proliferative retinopathies without the necessity of intravitreal injections.

Genome Editing of Pik3cd Impedes Abnormal Retinal Angiogenesis

Abnormal angiogenesis is associated with myriad human diseases, including proliferative diabetic retinopathy (PDR). Signaling transduction through phosphoinositide 3-kinases (PI3Ks) plays a critical role in angiogenesis. Herein, we showed that p110δ, the catalytic subunit of PI3Kδ, was highly expressed in pathological retinal vascular endothelial cells (ECs) in a mouse model of oxygen-induced retinopathy (OIR) and in fibrovascular membranes from patients with PDR. To explore novel intervention with PI3Kδ expression, we developed a recombinant dual adeno-associated viral (rAAV) system for delivering CRISPR/Cas9 in which Streptococcus pyogenes (Sp) Cas9 expression was driven by an endothelial specific promoter of the intercellular adhesion molecule 2 (pICAM2) to edit genomic Pik3cd, the gene encoding p110δ. We then demonstrated that infection of cultured mouse vascular ECs with the dual rAAV1s of rAAV1-pICAM2-SpCas9 and rAAV1-SpGuide targeting genomic Pik3cd resulted in 80% DNA insertion/deletion in the locus of genomic Pik3cd and 70% depletion of p110δ expression. Furthermore, we showed that in the mouse model of OIR editing retinal Pik3cd with the dual rAAV1s resulted in not only a significant decrease in p110δ expression, and Akt activation, but also a dramatic reduction in pathological retinal angiogenesis. These findings reveal that Pik3cd editing is a novel approach to treating abnormal retinal angiogenesis.

Key Role of Astrocytes in Postnatal Brain and Retinal Angiogenesis

Angiogenesis is a key process in various physiological and pathological conditions in the nervous system and in the retina during postnatal life. Although an increasing number of studies have addressed the role of endothelial cells in this event, the astrocytes contribution in angiogenesis has received less attention. This review is focused on the role of astrocytes as a scaffold and in the stabilization of the new blood vessels, through different molecules release, which can modulate the angiogenesis process in the brain and in the retina. Further, differences in the astrocytes phenotype are addressed in glioblastoma, one of the most devastating types of brain cancer, in order to provide potential targets involved in the cross signaling between endothelial cells, astrocytes and glioma cells, that mediate tumor progression and pathological angiogenesis. Given the relevance of astrocytes in angiogenesis in physiological and pathological conditions, future studies are required to better understand the interrelation between endothelial and astrocyte signaling pathways during this process.

CCRL2 Modulates Physiological and Pathological Angiogenesis During Retinal Development

Chemerin is a multifunctional protein involved in the regulation of inflammation, metabolism, and tumorigenesis. It binds to three receptors, CMKLR1, GPR1 and CCRL2. CMKLR1 is a fully functional receptor mediating most of the known activities of chemerin. CCRL2 does not seem to couple to any intracellular signaling pathway and is presently considered as an atypical receptor able to present the protein to cells expressing CMKLR1. CCRL2 is expressed by many cell types including leukocyte subsets and endothelial cells, and its expression is strongly upregulated by inflammatory stimuli. We recently reported that chemerin can negatively regulate the angiogenesis process, including during the development of the vascular network in mouse retina. The role of CCRL2 in angiogenesis was unexplored so far. In the present work, we demonstrate that mice lacking CCRL2 exhibit a lower density of vessels in the developing retina and this phenotype persists in adulthood, in a CMKLR1-dependent manner. Vascular sprouting was not affected, while vessel pruning, and endothelial cell apoptosis were increased. Pathological angiogenesis was also reduced in CCRL2^-/- mice in a model of oxygen-induced retinopathy. The phenotype closely mimics that of mice overexpressing chemerin, and the concentration of chemerin was found elevated in the blood of newborn mice, when the retinal vasculature develops. CCRL2 appears therefore to regulate the distribution and concentration of chemerin in organs, regulating thereby its bioactivity.

Cellular senescence in pathologic retinal angiogenesis

Pathologic angiogenesis causes blindness in many eye diseases. Crespo-Garcia, Tsuruda, and Dejda et al. employed bioinformatics to characterize cell senescence as a primary factor in the common pathogenesis of retinopathies. They validated their findings using human and mouse retina with proliferative retinopathy. Clearance of senescent cells suppressed neovessel growth.

Age-Dependent Dysregulation of Muscle Vasculature and Blood Flow Recovery after Hindlimb Ischemia in the mdx Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD), caused by a lack of functional dystrophin, is characterized by progressive muscle degeneration. Interestingly, dystrophin is also expressed in endothelial cells (ECs), and insufficient angiogenesis has already been hypothesized to contribute to DMD pathology, however, its status in mdx mice, a model of DMD, is still not fully clear. Our study aimed to reveal angiogenesis-related alterations in skeletal muscles of mdx mice compared to wild-type (WT) counterparts. By investigating 6- and 12-week-old mice, we sought to verify if those changes are age-dependent. We utilized a broad spectrum of methods ranging from gene expression analysis, flow cytometry, and immunofluorescence imaging to determine the level of angiogenic markers and to assess muscle blood vessel abundance. Finally, we implemented the hindlimb ischemia (HLI) model, more biologically relevant in the context of functional studies evaluating angiogenesis/arteriogenesis processes. We demonstrated that both 6- and 12-week-old dystrophic mice exhibited dysregulation of several angiogenic factors, including decreased vascular endothelial growth factor A (VEGF) in different muscle types. Nonetheless, in younger, 6-week-old mdx animals, neither the abundance of CD31⁺α-SMA⁺ double-positive blood vessels nor basal blood flow and its restoration after HLI was affected. In 12-week-old mdx mice, although a higher number of CD31⁺α-SMA⁺ double-positive blood vessels and an increased percentage of skeletal muscle ECs were found, the abundance of pericytes was diminished, and blood flow was reduced. Moreover, impeded perfusion recovery after HLI associated with a blunted inflammatory and regenerative response was evident in 12-week-old dystrophic mice. Hence, our results reinforce the hypothesis of age-dependent angiogenic dysfunction in dystrophic mice. In conclusion, we suggest that older mdx mice constitute an appropriate model for preclinical studies evaluating the effectiveness of vascular-based therapies aimed at the restoration of functional angiogenesis to mitigate DMD severity.

A specific RIP3+ subpopulation of microglia promotes retinopathy through a hypoxia-triggered necroptotic mechanism

Retinopathy is the leading cause of blindness, and development of effective therapy is urgently needed. Here, we defined an unprecedented subgroup of microglia that is responsible for causing retinopathy under hypoxia. Mechanistic studies demonstrated the signaling pathway of hypoxia-induced necroptosis of retinal microglia, i.e., the hypoxia–RIP1–RIP3–MLKL signaling axis, triggered an explosive release of FGF2, which in its turn to induce retinal neovascularization. Simultaneous targeting of necroptosis–FGF2 pathway and VEGF produces synergistic effects for treating retinopathy. On the basis of our findings, we propose a concept of necroptotic microglia-induced retinal angiogenesis and highlight a combination therapy for effective treatment of retinopathy.

Retinal neovascularization is a leading cause of severe visual loss in humans, and molecular mechanisms of microglial activation-driven angiogenesis remain unknown. Using single-cell RNA sequencing, we identified a subpopulation of microglia named sMG2, which highly expressed necroptosis-related genes Rip3 and Mlkl. Genetic and pharmacological loss of function demonstrated that hypoxia-induced microglial activation committed to necroptosis through the RIP1/RIP3-mediated pathway. Specific deletion of Rip3 gene in microglia markedly decreased retinal neovascularization. Furthermore, hypoxia induced explosive release of abundant FGF2 in microglia through RIP3-mediated necroptosis. Importantly, blocking signaling components of the microglia necropotosis–FGF2 axis largely ablated retinal angiogenesis and combination therapy with simultaneously blocking VEGF produced synergistic antiangiogenic effects. Together, our data demonstrate that targeting the microglia necroptosis axis is an antiangiogenesis therapy for retinal neovascular diseases.

PPARs and Angiogenesis-Implications in Pathology

Peroxisome proliferator-activated receptors (PPARs) belong to the family of ligand-activated nuclear receptors. The PPAR family consists of three subtypes encoded by three separate genes: PPARα (NR1C1), PPARβ/δ (NR1C2), and PPARγ (NR1C3). PPARs are critical regulators of metabolism and exhibit tissue and cell type-specific expression patterns and functions. Specific PPAR ligands have been proposed as potential therapies for a variety of diseases such as metabolic syndrome, cancer, neurogenerative disorders, diabetes, cardiovascular diseases, endometriosis, and retinopathies. In this review, we focus on the knowledge of PPAR function in angiogenesis, a complex process that plays important roles in numerous pathological conditions for which therapeutic use of PPAR modulation has been suggested.

Inhibition of Pathological Retinal Neovascularization by a Small Peptide Derived from Human Tissue-Type Plasminogen Kringle 2

Retinal neovascularization is a hallmark pathological process of numerous ocular diseases which comprise the most common causes of blindness and affect millions of people from infants to the elderly. Compared to large proteins, small peptides have advantages for therapeutic application in ocular diseases, especially for retinal diseases. In this study, we investigated a small peptide derived from human tissue-type plasminogen kringle 2 (t-PA kringle 2), named TKII-12, and investigated the effect of TKII-12 on various aspects of vascular endothelial growth factor (VEGF)-induced angiogenesis in vitro and in vivo. Our results showed that TKII-12 effectively inhibited VEGF-induced human retinal microvascular endothelial cell proliferation, migration and tube formation on Matrigel dose-dependently as well as sequence-dependently. TKII-12 inhibited VEGF-induced formation of actin stress fibers and focal adhesions in vascular endothelial cells. Moreover, TKII-12 effectively inhibited retinal neovascularization in a mouse oxygen-induced retinopathy (OIR) model. Our study demonstrated that TKII-12 could effectively inhibit retinal angiogenesis in vitro and in vivo by eliminating the formation of focal adhesion complexes and the organization of actin stress fibers. TKII-12 can serve as a prototype for retinal angiogenesis inhibitory drug development.

Dlg1 activates beta-catenin signaling to regulate retinal angiogenesis and the blood-retina and blood-brain barriers

Beta-catenin (i.e., canonical Wnt) signaling controls CNS angiogenesis and the blood-brain and blood-retina barriers. To explore the role of the Discs large/membrane-associated guanylate kinase (Dlg/MAGUK) family of scaffolding proteins in beta-catenin signaling, we studied vascular endothelial cell (EC)-specific knockout of Dlg1/SAP97. EC-specific loss of Dlg1 produces a retinal vascular phenotype that closely matches the phenotype associated with reduced beta-catenin signaling, synergizes with genetically-directed reductions in beta-catenin signaling components, and can be rescued by stabilizing beta-catenin in ECs. In reporter cells with CRISPR/Cas9-mediated inactivation of Dlg1, transfection of Dlg1 enhances beta-catenin signaling ~4 fold. Surprisingly, Frizzled4, which contains a C-terminal PDZ-binding motif that can bind to Dlg1 PDZ domains, appears to function independently of Dlg1 in vivo. These data expand the repertoire of Dlg/MAGUK family functions to include a role in beta-catenin signaling, and they suggest that proteins other than Frizzled receptors interact with Dlg1 to enhance beta-catenin signaling.

MicroRNA-34a attenuates VEGF-mediated retinal angiogenesis via targeting Notch1

Pathological angiogenesis in the retina is one of the main ocular diseases closely associated with vision loss. This work investigated the roles of microRNA-34a (miR-34a) and its potential target Notch1, in retinal angiogenesis. For this we used oxygen-induced retinopathy (OIR) rats and human retinal microvascular endothelial cells (HRMECs) stimulated with vascular endothelial growth factor (VEGF). We performed hematoxylin-eosin staining, Western blot for VEGF, and immunofluorescence staining for CD31 to verify the establishment of our OIR model. We observed down-regulation of miR-34a, and up-regulation of Notch1 and Hey1 in retinas from OIR rats. We found similar results with the VEGF-stimulated HRMECs. By performing MTT assay, cell scratch assay, tube formation assay, and by detecting the expression of matrix-metalloproteinase-2 (MMP-2), MMP-9, tissue inhibitors of metalloproteinases-1 (TIMP-1), and TIMP-2, we found that transfection of miR-34a ameliorated VEGF-mediated angiogenesis of HRMECs. We further observed that siRNA-induced gene silencing of Notch1 prevented VEGF-induced angiogenesis via regulating cell proliferation, cell migration, and tube formation of HRMECs. Additionally, activation of Notch1 by transfection of Notch1 plasmid attenuated the inhibitory effects of miR-34a on tube formation, in the present of VEGF. Results from our dual-luciferase reporter gene assay suggested that miR-34a targets Notch1. In summary, our data demonstrate that miR-34a attenuates retinal angiogenesis via targeting Notch1.

Intravitreal Delivery of VEGF-A165-loaded PLGA Microparticles Reduces Retinal Vaso-Obliteration in an In Vivo Mouse Model of Retinopathy of Prematurity

PURPOSE

Retinopathy of prematurity (ROP) is a condition of abnormal retinal vascularization with reduced levels of vascular endothelial growth factor (VEGF) causing vaso-obliteration (Phase I), followed by abnormal neovascularization from increased VEGF (Phase II). We hypothesized that intravitreal pro-angiogenic VEGF-A in microparticle form would promote earlier retinal revascularization in an oxygen-induced ischemic retinopathy (OIR) mouse model.

MATERIALS AND METHODS

Wildtype mice (39) were exposed to 77% oxygen from postnatal day 7 (P7) to P12. VEGF-A₁₆₅-loaded poly(lactic-co-glycolic acid) (PLGA) (n = 15) or empty PLGA (n = 14) microparticles were fabricated using a water-in-oil-in-water double emulsion method, and injected intravitreally at P13 into mice right eyes (RE). Left eyes (LE) were untreated. At P20, after retinal fluorescein angiography, vascular parameters were quantified. Retinal VEGF levels at P13 and flatmounts at P20 were performed separately.

RESULTS

VEGF-A₁₆₅-loaded microparticles had a mean diameter of 4.2 μm. with a loading level of 8.6 weight.%. Retinal avascular area was reduced in VEGF-treated RE (39.5 ± 9.0%) compared to untreated LE (52.6 ± 6.1%, p < 0.0001) or empty microparticle-treated RE (p < 0.001) and untreated LEs (p = 0.001). Retinal arteries in VEGF-treated RE were less tortuous than untreated LE (1.08 ± 0.05 vs. 1.18 ± 0.08, p < 0.001) or empty-microparticles-treated RE (p = 0.02). Retinal arterial tortuosity was similar in the LE of VEGF and empty microparticle-treated mice (P > 0.05). Retinal vein width was similar in VEGF-treated and empty microparticle-treated RE (P > 0.9), which were each less dilated than their contralateral LE (p < 0.01). VEGF levels were higher in P13 OIR mice than RA mice (p < 0.0001). Retinal flatmounts showed vaso-obliteration and neovascularization.

CONCLUSIONS

Endogenous retinal VEGF is suppressed in OIR mice. Exogenous intravitreal VEGF-A₁₆₅-loaded microparticles in OIR mice reduced retinal vaso-obliteration and accelerated recovery from vein dilation and arterial tortuosity. This may be beneficial in preventing Phase II ROP without systemic effects.

Inhibition of retinal angiogenesis by gold nanoparticles via inducing autophagy

AIM

To investigate the effect of gold nanoparticles on retinal angiogenesis in vitro and in vivo, and to reveal the possible mechanism.

METHODS

Seed growth method was used to synthesize gold nanoparticles (GNPs). The size, zeta potential, absorption spectrum and morphology of GNPs were identified using Malvern Nano-ZS, multimode reader (BioTek synergy2) and transmission electron microscope. Cell viability was analyzed using cell counting kit-8 method and cell growth was assessed with EdU kit. Transwell chamber was used to investigate cell migration. Tube formation method was used to assess the angiogenic property in vitro. Oxygen induced retinopathy (OIR) model was used to investigate the effect of GNPs on retinal angiogenesis. Confocal microscope and Western blot were used to study the possible mechanism of GNPs inhibited angiogenesis.

RESULTS

The GNPs synthesized were uniform and well dispersed. GNPs of 10 µg/mL and 20 µg/mL were able to inhibit human umbilical vein endothelial cells proliferation (50% and 72% separately, P<0.001), migration (54% and 83% separately, P<0.001) and tube formation (52% and 90% separately, P<0.001). Further data showed that GNPs were able to improve the retinopathy in an OIR model. The possible mechanism might be that GNPs were able to induce autophagy significantly (P<0.05).

CONCLUSION

The present study suggests that GNPs are able to inhibit retinal neovascularization in vitro and in vivo. GNPs might be a potential nanomedicine for the treatment of retinal angiogenesis.

O-GlcNAc on NOTCH1 EGF repeats regulates ligand-induced Notch signaling and vascular development in mammals

The glycosyltransferase EOGT transfers O-GlcNAc to a consensus site in epidermal growth factor-like (EGF) repeats of a limited number of secreted and membrane proteins, including Notch receptors. In EOGT-deficient cells, the binding of DLL1 and DLL4, but not JAG1, canonical Notch ligands was reduced, and ligand-induced Notch signaling was impaired. Mutagenesis of O-GlcNAc sites on NOTCH1 also resulted in decreased binding of DLL4. EOGT functions were investigated in retinal angiogenesis that depends on Notch signaling. Global or endothelial cell-specific deletion of Eogt resulted in defective retinal angiogenesis, with a mild phenotype similar to that caused by reduced Notch signaling in retina. Combined deficiency of different Notch1 mutant alleles exacerbated the abnormalities in Eogt-/- retina, and Notch target gene expression was decreased in Eogt-/-endothelial cells. Thus, O-GlcNAc on EGF repeats of Notch receptors mediates ligand-induced Notch signaling required in endothelial cells for optimal vascular development.

Effects of Phenotype of Retinal Macrophages on the Features of Angiogenesis of Murine Retina

The period of forming of superficial vascular plexus during physiological retinal angiogenesis was shorter in C57Bl/6 mice. Experiments on the model of oxygen-induced retinopathy showed that avascular and vascularized zones in BALB/c mice on day 17 are smaller than in C57Bl/6 mice are by 5 and 1.5 times, respectively. The obtained results confirmed the importance of phenotype of retinal macrophages in the regulation of processes of both physiological and pathological retinal angiogenesis.

SWI/SNF chromatin-remodeling enzymes Brahma-related gene 1 (BRG1) and Brahma (BRM) are dispensable in multiple models of postnatal angiogenesis but are required for vascular integrity in infant mice

Background

Mammalian SWItch/Sucrose NonFermentable (SWI/SNF) adenosine triphosphate (ATP)‐dependent chromatin‐remodeling complexes play important roles in embryonic vascular development by modulating transcription of specific target genes. We sought to determine whether SWI/SNF complexes likewise impact postnatal physiological and pathological angiogenesis.

Methods and Results

Brahma‐related gene 1 (BRG1) and Brahma gene (BRM) are ATPases within mammalian SWI/SNF complexes and are essential for the complexes to function. Using mice with vascular‐specific mutations in Brg1 or with a global mutation in Brm, we employed 3 models to test the role of these ATPases in postnatal angiogenesis. We analyzed neonatal retinal angiogenesis, exercise‐induced angiogenesis in adult quadriceps muscles, and tumor angiogenesis in control and mutant animals. We found no evidence of defective angiogenesis in Brg1 or Brm mutants using these 3 models. Brg1/Brm double mutants likewise show no evidence of vascular defects in the neonatal retina or tumor angiogenesis models. However, 100% of Brg1/Brm‐double mutants in which Brg1 deletion is induced at postnatal day 3 (P3) die by P19 with hemorrhaging in the small intestine and heart.

Conclusions

Despite their important roles in embryonic vascular development, SWI/SNF chromatin‐remodeling complexes display a surprising lack of participation in the 3 models of postnatal angiogenesis we analyzed. However, these complexes are essential for maintaining vascular integrity in specific tissue beds before weaning. These findings highlight the temporal and spatial specificity of SWI/SNF activities in the vasculature and may indicate that other chromatin‐remodeling complexes play redundant or more essential roles during physiological and pathological postnatal vascular development.

Isoxanthohumol modulates angiogenesis and inflammation via vascular endothelial growth factor receptor, tumor necrosis factor alpha and nuclear factor kappa B pathways

Angiogenesis and inflammation are becoming distinguished players in the pathogenesis of many heterogeneous diseases, such as diabetes, cardiovascular disease, and cancer. Therefore, it is crucial to study new compounds that are able to modulate these events. Isoxanthohumol (IXN) is a polyphenol with antioxidant, anti-inflammatory, and antiangiogenic properties. The aim of this study was to evaluate the effects of IXN on blood vessel proliferation and maturation and describe underlying molecular mechanisms in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). Angiogenic profile of IXN was analyzed by retinal angiogenesis at different time points. IXN modulation of angiogenic and inflammatory signaling pathways was evaluated by Western blotting on EC and VSMC cultures. IXN inhibited by 20% sprouting angiogenesis and decreased vascular coverage by mural cells up to 39%. IXN of 10 µM also decreased inflammatory signals, namely tumor necrosis factor alpha (TNF-α) (26 and 40%) and factor nuclear kappa B (24 and 42%) in human aortic smooth muscle cells (HASMCs) and human umbilical vein endothelial cells (HUVECs). Angiogenic regulators, including vascular endothelial growth factor receptor 2 (HUVEC, 55%), angiopoietins 1 (HUVEC, 39%; HASMC, 35%), angiopoietin 2 (HUVEC, 38%), and Tie2 (HUVEC, 56%) were also inhibited by 10 µM of IXN treatments. Akt activation was reduced by 47% in HUVEC-treated cells and Erk activation was also reduced by 52 and 69% upon IXN treatment of HUVEC and HASMC. IXN seems to regulate in vivo vascular proliferation and stabilization and the EC-VSMC-inflammatory crosstalk, leaving this molecule as an interesting nutritional player for angiogenesis and inflammation-related diseases.

The effects of nepafenac and amfenac on retinal angiogenesis

PURPOSE

Nepafenac is a potent NSAID that rapidly penetrates the eye following topical ocular administration. In the eye, nepafenac is converted to amfenac, which has unique time-dependent inhibitory properties for COX-1 and COX-2. The purpose of the present study was to investigate the capacity of amfenac to inhibit discrete aspects of the angiogenic cascade in vitro, and to test the efficacy of amfenac and nepafenac in vivo, using the rat OIR model.

METHODS

Müller cells were treated with amfenac, celecoxib (COX-2), or SC-560 (COX-1), and hypoxia-induced VEGF and PGE(2) assessed. Endothelial cells were treated with amfenac, celecoxib, or SC-560, and VEGF-induced proliferation and tube formation assessed. Rat pups were subjected to OIR, received intravitreal injections of amfenac, celecoxib, or SC-560, and neovascularization (NV), prostanoid production, and VEGF assessed. Other OIR-exposed pups were treated with topical nepafenac, ketorolac, or diclofenac, and inhibition of NV assessed.

RESULTS

Amfenac treatment failed to inhibit hypoxia-induced VEGF production. Amfenac treatment significantly inhibited VEGF-induced tube formation and proliferation by EC. Amfenac treatment significantly reduced retinal prostanoid production and NV in OIR. Nepafenac treatment significantly reduced retinal NV in OIR; ketorolac and diclofenac had no effect.

CONCLUSIONS

Nepafenac and amfenac inhibit OIR more effectively than the commercially available topical and injectable NSAIDs used in this study. Our data suggests there are COX-dependent and COX-independent mechanisms by which amfenac inhibits OIR. Because it is bioavailable to the posterior segment following topical delivery, nepafenac appears to be a promising advancement in the development of therapies for neovascular eye diseases.

c-abl is required for the development of hyperoxia-induced retinopathy

The requirement for the nonreceptor tyrosine kinase c-abl in the pathogenesis of retinopathy of prematurity (ROP) was examined using the mouse model for ROP and c-abl-deficient mice. Hyperoxia-induced retinal neovascularization was observed in wild-type and heterozygous mice but animals that were homozygous null for c-abl did not develop a vasoproliferative retinopathy in response to hyperoxia. Two gene products, endothelin-1 (ET-1) and vascular endothelial growth factor (VEGF), have been implicated in the pathogenesis of ROP. The mRNA expression of ET-1 and VEGF was assessed in mice maintained in normoxia and in hyperoxia-exposed mice. ET-1 mRNA levels were unchanged in wild-type mice throughout the hyperoxia treatment, suggesting that ET-1 mRNA expression is not regulated by the increase in inspired oxygen. In wild-type mice maintained in room air, VEGF mRNA levels rose threefold from postnatal day 6 (P6) to P17. When wild-type mice were treated with the hyperoxia regimen, a fivefold decrease in VEGF mRNA expression was observed from P7 to P16. However, retinal VEGF expression in hyperoxia-treated homozygous null mice did not decrease and remained at control levels. These data suggest that c-abl is required for the hyperoxia-induced retinal neovascularization and hyperoxia-induced decrease in VEGF mRNA levels.