The Succinate Receptor SUCNR1 Resides at the Endoplasmic Reticulum and Relocates to the Plasma Membrane in Hypoxic Conditions.

The GPCR SUCNR1/GPR91 exerts proangiogenesis upon stimulation with the Krebs cycle metabolite succinate. GPCR signaling depends on the surrounding environment and intracellular localization through location bias. Here, we show by microscopy and by cell fractionation that in neurons, SUCNR1 resides at the endoplasmic reticulum (ER), while being fully functional, as shown by calcium release and the induction of the expression of the proangiogenic gene for VEGFA. ER localization was found to depend upon N-glycosylation, particularly at position N8; the nonglycosylated mutant receptor localizes at the plasma membrane shuttled by RAB11. This SUCNR1 glycosylation is physiologically regulated, so that during hypoxic conditions, SUCNR1 is deglycosylated and relocates to the plasma membrane. Downstream signal transduction of SUCNR1 was found to activate the prostaglandin synthesis pathway through direct interaction with COX-2 at the ER; pharmacologic antagonism of the PGE2 EP4 receptor (localized at the nucleus) was found to prevent VEGFA expression. Concordantly, restoring the expression of SUCNR1 in the retina of SUCNR1-null mice renormalized vascularization; this effect is markedly diminished after transfection of the plasma membrane-localized SUCNR1 N8A mutant, emphasizing that ER localization of the succinate receptor is necessary for proper vascularization. These findings uncover an unprecedented physiologic process where GPCR resides at the ER for signaling function.

Müller Cell-Localized G-Protein-Coupled Receptor 81 (Hydroxycarboxylic Acid Receptor 1) Regulates Inner Retinal Vasculature via Norrin/Wnt Pathways.

Ischemic retinopathies are characterized by a progressive microvascular degeneration followed by a postischemic aberrant neovascularization. To reinstate vascular supply and metabolic equilibrium to the ischemic tissue during ischemic retinopathies, a dysregulated production of growth factors and metabolic intermediates occurs, promoting retinal angiogenesis. Glycolysis-derived lactate, highly produced during ischemic conditions, has been associated with tumor angiogenesis and wound healing. Lactate exerts its biological effects via G-protein-coupled receptor 81 (GPR81) in several tissues; however, its physiological functions and mechanisms of action in the retina remain poorly understood. Herein, we show that GPR81, localized predominantly in Müller cells, governs deep vascular complex formation during development and in ischemic retinopathy. Lactate-stimulated GPR81 Müller cells produce numerous angiogenic factors, including Wnt ligands and particularly Norrin, which contributes significantly in triggering inner retinal blood vessel formation. Conversely, GPR81-null mice retina shows reduced inner vascular network formation associated with low levels of Norrin (and Wnt ligands). Lactate accumulation during ischemic retinopathy selectively activates GPR81-extracellular signal-regulated kinase 1/2-Norrin signaling to accelerate inner retinal vascularization in wild-type animals, but not in the retina of GPR81-null mice. Altogether, we reveal that lactate via GPR81-Norrin participates in inner vascular network development and in restoration of the vasculature in response to injury. These findings suggest a new potential therapeutic target to alleviate ischemic diseases.

Erratum: Nuclear localization of platelet-activating factor receptor controls retinal neovascularization.

[This corrects the article DOI: 10.1038/celldisc.2016.17.].

Nuclear localization of platelet-activating factor receptor controls retinal neovascularization.

Platelet-activating factor (PAF) is a pleiotropic phospholipid with proinflammatory, procoagulant and angiogenic actions on the vasculature. We and others have reported the presence of PAF receptor (Ptafr) at intracellular sites such as the nucleus. However, mechanisms of localization and physiologic functions of intracellular Ptafr remain poorly understood. We hereby identify the importance of C-terminal motif of the receptor and uncover novel roles of Rab11a GTPase and importin-5 in nuclear translocation of Ptafr in primary human retinal microvascular endothelial cells. Nuclear localization of Ptafr is independent of exogenous PAF stimulation as well as intracellular PAF biosynthesis. Moreover, nuclear Ptafr is responsible for the upregulation of unique set of growth factors, including vascular endothelial growth factor, in vitro and ex vivo. We further corroborate the intracrine PAF signaling, resulting in angiogenesis in vivo, using Ptafr antagonists with distinct plasma membrane permeability. Collectively, our findings show that nuclear Ptafr translocates in an agonist-independent manner, and distinctive functions of Ptafr based on its cellular localization point to another dimension needed for pharmacologic selectivity of drugs.

Retinal neurons curb inflammation and enhance revascularization in ischemic retinopathies via proteinase-activated receptor-2.

Ischemic retinopathies are characterized by sequential vaso-obliteration followed by abnormal intravitreal neovascularization predisposing patients to retinal detachment and blindness. Ischemic retinopathies are associated with robust inflammation that leads to generation of IL-1ß, which causes vascular degeneration and impairs retinal revascularization in part through the liberation of repulsive guidance cue semaphorin 3A (Sema3A). However, retinal revascularization begins as inflammation culminates in ischemic retinopathies. Because inflammation leads to activation of proteases involved in the formation of vasculature, we hypothesized that proteinase-activated receptor (Par)-2 (official name F2rl1) may modulate deleterious effects of IL-1ß. Par2, detected mostly in retinal ganglion cells, was up-regulated in oxygen-induced retinopathy. Surprisingly, oxygen-induced retinopathy-induced vaso-obliteration and neovascularization were unaltered in Par2 knockout mice, suggesting compensatory mechanisms. We therefore conditionally knocked down retinal Par2 with shRNA-Par2-encoded lentivirus. Par2 knockdown interfered with normal revascularization, resulting in pronounced intravitreal neovascularization; conversely, the Par2 agonist peptide (SLIGRL) accelerated normal revascularization. In vitro and in vivo exploration of mechanisms revealed that IL-1ß induced Par2 expression, which in turn down-regulated sequentially IL-1 receptor type I and Sema3A expression through Erk/Jnk-dependent processes. Collectively, our findings unveil an important mechanism by which IL-1ß regulates its own endothelial cytotoxic actions by augmenting neuronal Par2 expression to repress sequentially IL-1 receptor type I and Sema3A expression. Timely activation of Par2 may be a promising therapeutic avenue in ischemic retinopathies.

Subcellular localization of coagulation factor II receptor-like 1 in neurons governs angiogenesis.

Neurons have an important role in retinal vascular development. Here we show that the G protein-coupled receptor (GPCR) coagulation factor II receptor-like 1 (F2rl1, previously known as Par2) is abundant in retinal ganglion cells and is associated with new blood vessel formation during retinal development and in ischemic retinopathy. After stimulation, F2rl1 in retinal ganglion cells translocates from the plasma membrane to the cell nucleus using a microtubule-dependent shuttle that requires sorting nexin 11 (Snx11). At the nucleus, F2rl1 facilitates recruitment of the transcription factor Sp1 to trigger Vegfa expression and, in turn, neovascularization. In contrast, classical plasma membrane activation of F2rl1 leads to the expression of distinct genes, including Ang1, that are involved in vessel maturation. Mutant versions of F2rl1 that prevent nuclear relocalization but not plasma membrane activation interfere with Vegfa but not Ang1 expression. Complementary angiogenic factors are therefore regulated by the subcellular localization of a receptor (F2rl1) that governs angiogenesis. These findings may have implications for the selectivity of drug actions based on the subcellular distribution of their targets.

G-protein-coupled receptor 91 and succinate are key contributors in neonatal postcerebral hypoxia-ischemia recovery.

OBJECTIVE: Prompt post-hypoxia-ischemia (HI) revascularization has been suggested to improve outcome in adults and newborn subjects. Other than hypoxia-inducible factor, sensors of metabolic demand remain largely unknown. During HI, anaerobic respiration is arrested resulting in accumulation of carbohydrate metabolic intermediates. As such succinate readily increases, exerting its biological effects via a specific receptor, G-protein-coupled receptor (GPR) 91. We postulate that succinate/GPR91 enhances post-HI vascularization and reduces infarct size in a model of newborn HI brain injury. APPROACH AND RESULTS: The Rice-Vannucci model of neonatal HI was used. Succinate was measured by mass spectrometry, and microvascular density was evaluated by quantification of lectin-stained cryosection. Gene expression was evaluated by real-time polymerase chain reaction. Succinate levels rapidly increased in the penumbral region of brain infarcts. GPR91 was foremost localized not only in neurons but also in astrocytes. Microvascular density increased at 96 hours after injury in wild-type animals; it was diminished in GPR91-null mice leading to an increased infarct size. Stimulation with succinate led to an increase in growth factors implicated in angiogenesis only in wild-type mice. To explain the mode of action of succinate/GPR91, we investigated the role of prostaglandin E2-prostaglandin E receptor 4, previously proposed in neural angiogenesis. Succinate-induced vascular endothelial growth factor expression was abrogated by a cyclooxygenase inhibitor and a selective prostaglandin E receptor 4 antagonist. This antagonist also abolished succinate-induced neovascularization. CONCLUSIONS: We uncover a dominant metabolic sensor responsible for post-HI neurovascular adaptation, notably succinate/GPR91, acting via prostaglandin E2-prostaglandin E receptor 4 to govern expression of major angiogenic factors. We propose that pharmacological intervention targeting GPR91 could improve post-HI brain recovery.

Microglia and interleukin-1ß in ischemic retinopathy elicit microvascular degeneration through neuronal semaphorin-3A.

OBJECTIVE: Proinflammatory cytokines contribute to the development of retinal vasculopathies. However, the role of these factors and the mechanisms by which they elicit their effects in retina are not known. We investigated whether activated microglia during early stages of ischemic retinopathy produces excessive interleukin-1ß (IL-1ß), which elicits retinal microvascular degeneration not directly but rather by triggering the release of the proapoptotic/repulsive factor semaphorin-3A (Sema3A) from neurons. APPROACH AND RESULTS: Sprague Dawley rats subjected to retinopathy induced by hyperoxia (80% O2; O2-induced retinopathy) exhibited retinal vaso-obliteration associated with microglial activation, NLRP3 upregulation, and IL-1ß and Sema3A release; IL-1ß was mostly generated by microglia. Intraperitoneal administration of IL-1 receptor antagonists (Kineret, or rytvela [101.10]) decreased these effects and enhanced retinal revascularization; knockdown of Sema3A resulted in microvessel preservation and, conversely, administration of IL-1ß caused vaso-obliteration. In vitro, IL-1ß derived from activated primary microglial cells, cultured under hyperoxia, stimulated the release of Sema3A in retinal ganglion cells-5, which in turn induced apoptosis of microvascular endothelium; antagonism of IL-1 receptor decreased microglial activation and on retinal ganglion cells-5 abolished the release of Sema3A inhibiting ensuing endothelial cell apoptosis. IL-1ß was not directly cytotoxic to endothelial cells. CONCLUSIONS: Our findings suggest that in the early stages of O2-induced retinopathy, retinal microglia are activated to produce IL-1ß, which sustains the activation of microglia and induces microvascular injury through the release of Sema3A from adjacent neurons. Interference with IL-1 receptor or Sema3A actions preserves the microvascular bed in ischemic retinopathies and, consequently, decreases ensued pathological preretinal neovascularization.

Fatty acid receptor Gpr40 mediates neuromicrovascular degeneration induced by transarachidonic acids in rodents.

OBJECTIVE: Nitro-oxidative stress exerts a significant role in the genesis of hypoxic-ischemic (HI) brain injury. We previously reported that the ω-6 long chain fatty acids, transarachidonic acids (TAAs), which are nitrative stress-induced nonenzymatically generated arachidonic acid derivatives, trigger selective microvascular endothelial cell death in neonatal neural tissue. The primary molecular target of TAAs remains unidentified. GPR40 is a G protein-coupled receptor activated by long chain fatty acids, including ω-6; it is highly expressed in brain, but its functions in this tissue are largely unknown. We hypothesized that TAAs play a significant role in neonatal HI-induced cerebral microvascular degeneration through GPR40 activation. APPROACH AND RESULTS: Within 24 hours of a HI insult to postnatal day 7 rat pups, a cerebral infarct and a 40% decrease in cerebrovascular density was observed. These effects were associated with an increase in nitrative stress markers (3-nitrotyrosine immunoreactivity and TAA levels) and were reduced by treatment with nitric oxide synthase inhibitor. GPR40 was expressed in rat pup brain microvasculature. In vitro, in GPR40-expressing human embryonic kidney (HEK)-293 cells, [(14)C]-14E-AA (radiolabeled TAA) bound specifically, and TAA induced calcium transients, extracellular signal-regulated kinase 1/2 phosphorylation, and proapoptotic thrombospondin-1 expression. In vivo, intracerebroventricular injection of TAAs triggered thrombospondin-1 expression and cerebral microvascular degeneration in wild-type mice, but not in GPR40-null congeners. Additionally, HI-induced neurovascular degeneration and cerebral infarct were decreased in GPR40-null mice. CONCLUSIONS: GPR40 emerges as the first identified G protein-coupled receptor conveying actions of nonenzymatically generated nitro-oxidative products, specifically TAAs, and is involved in (neonatal) HI encephalopathy.

Restoration of renal function by a novel prostaglandin EP4 receptor-derived peptide in models of acute renal failure.

Acute renal failure (ARF) is a serious medical complication characterized by an abrupt and sustained decline in renal function. Despite significant advances in supportive care, there is currently no effective treatment to restore renal function. PGE(2) is a lipid hormone mediator abundantly produced in the kidney, where it acts locally to regulate renal function; several studies suggest that modulating EP(4) receptor activity could improve renal function following kidney injury. An optimized peptidomimetic ligand of EP(4) receptor, THG213.29, was tested for its efficacy to improve renal function (glomerular filtration rate, renal plasma flow, and urine output) and histological changes in a model of ARF induced by either cisplatin or renal artery occlusion in Sprague-Dawley rats. THG213.29 modulated PGE(2)-binding dissociation kinetics, indicative of an allosteric binding mode. Consistently, THG213.29 antagonized EP(4)-mediated relaxation of piglet saphenous vein rings, partially inhibited EP(4)-mediated cAMP production, but did not affect Gα(i) activation or ß-arrestin recruitment. In vivo, THG213.29 significantly improved renal function and histological changes in cisplatin- and renal artery occlusion-induced ARF models. THG213.29 increased mRNA expression of heme-oxygenase 1, Bcl2, and FGF-2 in renal cortex; correspondingly, in EP(4)-transfected HEK293 cells, THG213.29 augmented FGF-2 and abrogated EP(4)-dependent overexpression of inflammatory IL-6 and of apoptotic death domain-associated protein and BCL2-associated agonist of cell death. Our results demonstrate that THG213.29 represents a novel class of diuretic agent with noncompetitive allosteric modulator effects on EP(4) receptor, resulting in improved renal function and integrity following acute renal failure.

Role of receptor-mediated endocytosis in the antiangiogenic effects of human T lymphoblastic cell-derived microparticles.

Microparticles possess therapeutic potential regarding angiogenesis. We have demonstrated the contribution of apoptotic human CEM T lymphocyte-derived microparticles (LMPs) as inhibitors of angiogenic responses in animal models of inflammation and tumor growth. In the present study, we characterized the antivascular endothelial growth factor (VEGF) effects of LMPs on pathological angiogenesis in an animal model of oxygen-induced retinopathy and explored the role of receptor-mediated endocytosis in the effects of LMPs on human retinal endothelial cells (HRECs). LMPs dramatically inhibited cell growth of HRECs, suppressed VEGF-induced cell migration in vitro experiments, and attenuated VEGF-induced retinal vascular leakage in vivo. Intravitreal injections of fluorescently labeled LMPs revealed accumulation of LMPs in retinal tissue, with more than 60% reductions of the vascular density in retinas of rats with oxygen-induced neovascularization. LMP uptake experiments demonstrated that the interaction between LMPs and HRECs is dependent on temperature. In addition, endocytosis is partially dependent on extracellular calcium. RNAi-mediated knockdown of low-density lipoprotein receptor (LDLR) reduced the uptake of LMPs and attenuated the inhibitory effects of LMPs on VEGF-A protein expression and HRECs cell growth. Intravitreal injection of lentivirus-mediated RNA interference reduced LDLR protein expression in retina by 53% and significantly blocked the antiangiogenic effects of LMPs on pathological vascularization. In summary, the potent antiangiogenic LMPs lead to a significant reduction of pathological retinal angiogenesis through modulation of VEGF signaling, whereas LDLR-mediated endocytosis plays a partial, but pivotal, role in the uptake of LMPs in HRECs.

NK-like T cells and plasma cytokines, but not anti-viral serology, define immune fingerprints of resilience and mild disability in exceptional aging.

Exceptional aging has been defined as maintenance of physical and cognitive function beyond the median lifespan despite a history of diseases and/or concurrent subclinical conditions. Since immunity is vital to individual fitness, we examined immunologic fingerprint(s) of highly functional elders. Therefore, survivors of the Cardiovascular Health Study in Pittsburgh, Pennsylvania, USA were recruited (n = 140; mean age = 86 years) and underwent performance testing. Blood samples were collected and examined blindly for humoral factors and T cell phenotypes. Based on results of physical and cognitive performance testing, elders were classified as "impaired" or "unimpaired", accuracy of group assignment was verified by discriminant function analysis. The two groups showed distinct immune profiles as determined by factor analysis. The dominant immune signature of impaired elders consisted of interferon (IFN)-γ, interleukin (IL)-6, tumor necrosis factor-α, and T cells expressing inhibitory natural killer-related receptors (NKR) CD158a, CD158e, and NKG2A. In contrast, the dominant signature of unimpaired elders consisted of IL-5, IL-12p70, and IL-13 with co-expression of IFN-γ, IL-4, and IL-17, and T cells expressing stimulatory NKRs CD56, CD16, and NKG2D. In logistic regression models, unimpaired phenotype was predicted independently by IL-5 and by CD4(+)CD28(null)CD56(+)CD57(+) T cells. All elders had high antibody titers to common viruses including cytomegalovirus. In cellular bioassays, T cell receptor (TCR)-independent ligation of either CD56 or NKG2D elicited activation of T cells. Collectively, these data demonstrate the importance of immunological parameters in distinguishing between health phenotypes of older adults. NKR(+) T cells and cytokine upregulation indicate a unique physiologic environment in old age. Correlation of particular NKR(+) T cell subsets and IL-5 with unimpaired performance, and NKR-driven TCR-independent activation of T cells suggest novel immunopathway(s) that could be exploited to improve immunity in old age.

Ischemic neurons prevent vascular regeneration of neural tissue by secreting semaphorin 3A.

The failure of blood vessels to revascularize ischemic neural tissue represents a significant challenge for vascular biology. Examples include proliferative retinopathies (PRs) such as retinopathy of prematurity and proliferative diabetic retinopathy, which are the leading causes of blindness in children and working-age adults. PRs are characterized by initial microvascular degeneration, followed by a compensatory albeit pathologic hypervascularization mounted by the hypoxic retina attempting to reinstate metabolic equilibrium. Paradoxically, this secondary revascularization fails to grow into the most ischemic regions of the retina. Instead, the new vessels are misdirected toward the vitreous, suggesting that vasorepulsive forces operate in the avascular hypoxic retina. In the present study, we demonstrate that the neuronal guidance cue semaphorin 3A (Sema3A) is secreted by hypoxic neurons in the avascular retina in response to the proinflammatory cytokine IL-1ß. Sema3A contributes to vascular decay and later forms a chemical barrier that repels neo-vessels toward the vitreous. Conversely, silencing Sema3A expression enhances normal vascular regeneration within the ischemic retina, thereby diminishing aberrant neovascularization and preserving neuroretinal function. Overcoming the chemical barrier (Sema3A) released by ischemic neurons accelerates the vascular regeneration of neural tissues, which restores metabolic supply and improves retinal function. Our findings may be applicable to other neurovascular ischemic conditions such as stroke.

Herpes simplex virus type 1-induced FasL expression in human monocytic cells and its implications for cell death, viral replication, and immune evasion.

Herpes simplex virus type 1 (HSV-1) is a ubiquitously occurring pathogen that infects humans early in childhood. The virus persists as a latent infection in dorsal root ganglia, especially of the trigeminal nerve, and frequently becomes reactivated in humans under conditions of stress. Monocytic cells constitute an important component of the innate and adaptive immune responses. We show here for the first time that HSV-1 stimulates human FasL promoter and induces de novo expression of FasL on the surface of human monocytic cells, including monocytes and macrophages. This virus-induced FasL expression causes death of monocytic cells growing in suspension, but not in monolayers (e.g., macrophages). The addition of a broad-spectrum caspase inhibitor, as well as anti-FasL antibodies, reduced cell death but increased viral replication in the virus-infected cell cultures. We also show here for the first time that the virus-induced de novo expression of FasL on the cell surface acts as an immune evasion mechanism by causing the death of interacting human CD4+ T cells, CD8+ T cells, and natural killer (NK) cells. Our study provides novel insights on FasL expression and cell death in HSV-infected human monocytic cells and their impact on interacting immune cells.

Expansions of NK-like αßT cells with chronologic aging: novel lymphocyte effectors that compensate for functional deficits of conventional NK cells and T cells.

As the repertoire of αßT cell receptors (TCR) contracts with advancing age, there is an associated age-dependent accumulation of oligoclonal T cells expressing of a variety of receptors (NKR), normally expressed on natural killer (NK) cells. Evidences for differential regulation of expression of particular NKRs between T cells and NK cells suggest that NKR expression on T cells is physiologically programmed rather than a random event of the aging process. Experimental studies show NKRs on aged αßT cells may function either as independent receptors, and/or as costimulatory receptors to the TCR. Considering the reported deficits of conventional αßTCR-driven activation and also functional deficits of classical NK cells, NKR(+) αßT cells likely represent novel immune effectors that are capable of combining innate and adaptive functions. Inasmuch as immunity is a determinant of individual fitness, the type and density of NKRs could be important contributing factors to the wide heterogeneity of health characteristics of older adults, ranging from institutionalized frail elders who are unable to mount immune responses to functionally independent community-dwelling elders who exhibit protective immunity. Understanding the biology of NKR(+) αßT cells could lead to new avenues for age-specific intervention to improve protective immunity.

Sustained hypercapnia induces cerebral microvascular degeneration in the immature brain through induction of nitrative stress.

Hypercapnia is regularly observed in chronic lung disease, such as bronchopulmonary dysplasia in preterm infants. Hypercapnia results in increased nitric oxide synthase activity and in vitro formation of nitrates. Neural vasculature of the immature subject is particularly sensitive to nitrative stress. We investigated whether exposure to clinically relevant sustained high CO(2) causes microvascular degeneration in the newborn brain by inducing nitrative stress, and whether this microvascular degeneration has an impact on brain growth. Newborn rat pups were exposed to 10% CO(2) as inspired gas (Pa(CO(2)) = 60-70 mmHg) starting within 24 h of birth until postnatal day 7 (P7). Brains were notably collected at different time points to measure vascular density, determine brain cortical nitrite/nitrate, and trans-arachidonic acids (TAAs; products of nitration) levels as effectors of vessel damage. Chronic exposure of rat pups to high CO(2) (Pa(CO(2)) approximately 65 mmHg) induced a 20% loss in cerebrovascular density at P3 and a 15% decrease in brain mass at P7; at P30, brain mass remained lower in CO(2)-exposed animals. Within 24 h of exposure to CO(2), brain eNOS expression and production of nitrite/nitrate doubled, lipid nitration products (TAAs) increased, and protein nitration (3-nitrotyrosine immunoreactivity) was also coincidently augmented on brain microvessels (lectin positive). Intracerebroventricular injection of TAAs (10 microM) replicated cerebrovascular degeneration. Treatment of rat pups with NOS inhibitor (L-N(omega)-nitroarginine methyl ester) or a peroxynitrite decomposition catalyst (FeTPPS) prevented hypercapnia-induced microvascular degeneration and preserved brain mass. Cytotoxic effects of high CO(2) were reproduced in vitro/ex vivo on cultured endothelial cells and sprouting microvessels. In summary, hypercapnia at values frequently observed in preterm infants with chronic lung disease results in increased nitrative stress, which leads to cerebral cortical microvascular degeneration and curtails brain growth.

Proliferative retinopathies: angiogenesis that blinds.

Proliferative ischemic retinopathies such as proliferative diabetic retinopathy (PDR), retinopathy of prematurity (ROP) and those stemming from retinal vein occlusion are the leading causes of blindness in the working age and pediatric populations of industrialized countries. They present major financial burdens for health care systems and account for significant loss of productivity. These pathologies are characterized by excessive pre-retinal blood vessel growth that can ultimately lead to a fibrous scar formation and culminate in retinal detachment. This abnormal and disproportionate hyper-vascularization is a compensatory mechanism to overcome an earlier phase of microvessel degeneration and reinstate metabolic equilibrium to the hypoxic retina. To date, the treatment modalities to counter these diseases largely rely on invasive and moderately efficient surgical interventions. In this review, we discuss the current views on retinal vaso-obliteration, neovascularization and available treatments and present future strategies to tackle these diseases.