Oxygen-induced Retinopathy Mice Research Articles

Diacylglycerol kinase (DGK) inhibitor II (R59949) could suppress retinal neovascularization and protect retinal astrocytes in an oxygen-induced retinopathy model.

Hypoxia-inducible factors (HIF) play a fundamental role in retinal neovascularization (NV) induced by low oxygen tension. In the presence of oxygen, the HIF-α subunit becomes hydroxylated at specific prolyl residues by prolyl hydroxylases (PHD), which triggers HIF-α for degradation. In our present study, we examined the effect of R59949, the diacylglycerol kinase (DGK) inhibitor II, on the retinal NV and its potential mechanism in an oxygen-induced retinopathy (OIR) model. OIR model was induced by exposure of hyperoxia (75 % oxygen) to C57BL/6J mice from postnatal day 7 (P7) to P12 and then returned to room air. By intraperitoneal injection once a day (10 μg/g/day) from P12 to P17, R59949 not only effectively prevented pathologic NV but also preserved the astrocyte morphology. Furthermore, the expression of PHD-2 was upregulated and HIF-1α and vascular endothelial growth factor (VEGF) were downregulated in the retina of OIR mice following R59949 treatment. These findings suggested a potential possibility that R59949 suppressed retinal neovascular pathophysiology via PHD2/HIF-1α/VEGF pathway.

Sulodexide inhibits retinal neovascularization in a mouse model of oxygen-induced retinopathy

Sulodexide is a mixed glycosaminoglycan composed of heparin and dermatan sulfate. In this study, the anti-angiogenic effect of sulodexide was investigated using an oxygen-induced retinopathy (OIR) mouse model. The retinas of sham-injected OIR mice (P17) had a distinctive central area of nonperfusion, and this area was significantly decreased in sulodexide-injected mice. The number of neovascular tufts measured by SWIFT_NV and mean neovascular lumen number were significantly decreased in sulodexide-injected mice. Hyperbaric oxygen exposure resulted in increased levels of VEGF, MMP-2 and MMP-9, and when mice were treated with sulodexide, a dose-dependent reduction in VEGF, MMP-2 and MMP-9 levels was observed. Our results clearly demonstrate the anti-angiogenic effect of sulodexide and highlight sulodexide as a candidate supplementary substance to be used for the treatment of ocular pathologies that involve neovascularization. [BMB Reports 2014; 47(11): 637-642]

Evaluation of anti-HIF and anti-angiogenic properties of honokiol for the treatment of ocular neovascular diseases.

Pathological activation of the hypoxia-inducible-factor (HIF) pathway leading to expression of pro-angiogenic genes, such as vascular endothelial growth factor (VEGF), is the fundamental cause of neovascularization in ocular ischemic diseases and cancers. We have shown that pure honokiol inhibits the HIF pathway and hypoxia-mediated expression of pro-angiogenic genes in a number of cancer and retinal pigment epithelial (RPE) cell lines. The crude extracts, containing honokiol, from Magnolia plants have been used for thousands of years in the traditional oriental medicine for a number of health benefits. We have recently demonstrated that daily intraperitoneal injection of honokiol starting at postnatal day (P) 12 in an oxygen induced retinopathy mouse model significantly reduced retinal neovascularization at P17. Here, we evaluate the mechanism of HIF inhibition by honokiol in RPE cells. Using chromatin immunoprecipitation experiments, we demonstrate that honokiol inhibits binding of HIF to hypoxia-response elements present on VEGF promoter. We further show using a number of in vitro angiogenesis assays that, in addition to anti-HIF effect, honokiol manifests potent anti-angiogenic effect on human retinal micro vascular endothelial cells. Our results suggest that honokiol possesses potent anti-HIF and anti-angiogenic properties. These properties of honokiol make it an ideal therapeutic agent for the treatment of ocular neovascular diseases and solid tumors.

Pulmonary surfactant protein a is expressed in mouse retina by Müller cells and impacts neovascularization in oxygen-induced retinopathy.

Surfactant protein A (SP-A) up-regulates cytokine expression in lung disease of prematurity. Here we present data that for the first time characterizes SP-A expression and localization in the mouse retina and its impact on neovascularization (NV) in the mouse. Retinal SP-A was localized in wild-type (WT) mice with the cell markers glutamine synthetase (Müller cells), neurofilament-M (ganglion cells), glial acid fibrillary acid protein (astrocytes), and cluster of differentiation 31 (endothelial cells). Toll-like receptor 2 and 4 (TLR-2 and TLR-4) ligands were used to up-regulate SP-A expression in WT and myeloid differentiation primary response 88 (MyD88) protein (necessary for NFκB signaling) null mouse retinas and Müller cells, which were quantified using ELISA. Retinal SP-A was then measured in the oxygen-induced retinopathy (OIR) mouse model. The effect of SP-A on retinal NV was then studied in SP-A null (SP-A(-/-)) mice. SP-A is present at birth in the WT mouse retina and colocalizes with glutamine synthetase. TLR-2 and TLR-4 ligands increase SP-A both in the retina and in Müller cells. SP-A is increased at postnatal day 17 (P17) in WT mouse pups with OIR compared to that in controls (P = 0.02), and SP-A(-/-) mice have reduced NV compared to WT mice (P = 0.001) in the OIR model. Retinal and Müller cell SP-A is up-regulated via the NFκB pathway and up-regulated during the hypoxia phase of OIR. Absence of SP-A attenuates NV in the OIR model. Thus SP-A may be a marker of retinal inflammation during NV.

CEACAM1 confers resistance toward oxygen-induced vessel damage in a mouse model of retinopathy of prematurity.

To determine a functional role for the carcinoembryonic antigen-related cell-adhesion molecule 1 (CEACAM1) in retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR). In a 21/75/21% OIR mouse model, retinal neovascularization was compared in wild-type and CEACAM1-deficient mice. Animals were housed under normoxic conditions until postnatal day 7, followed by exposure to 75% oxygen for 5 days, and further housing under normoxic conditions. Retinal vascular anatomy, vaso-obliteration, neovascularization, and tuft formation were characterized and quantified in retinal flat-mounts from untreated mice and from experimental mice during and at different time points after exposure to high oxygen levels. The vascular network was stained with fluorescently labeled isolectin B4. Mice deficient in CEACAM1 did not present any apparent abnormalities in their postnatal retinal vascular development under normoxic housing conditions. However, after hyperoxia and under relative hypoxic conditions, retinal neovascularization and tuft formation were aggravated in the mutant. Congruently, revascularization and vessel maturation were delayed in CEACAM1-deficient mice whereas in wild-type mice, tuft regression and vascular remodeling occurred efficiently after exposure to high oxygen levels. Our report describes a functional role for CEACAM1 in retinal neovascularization in a mouse model of OIR. This is the first study demonstrating that CEACAM1 enhances vascular remodeling and tuft regression by increasing endothelial resistance to alterations in oxygen tension, thus accelerating vascular recovery after systemic hypoxia.

Therapeutic efficacy of a novel non-peptide αvβ3 integrin antagonist for pathological retinal angiogenesis in mice

αvβ3 integrin has been reported as a promising therapeutic target for angiogenesis. In the present study, we tested the antiangiogenic activity of 3-[3-(6-guanidino-1-oxoisoindolin-2-yl) propanamido]-3-(pyridin-3-yl) propanoic acid dihydrochloride (GOPPP), a novel non-peptide αvβ3 antagonist. Both human umbilical vein endothelial cells (HUVECs) and a mouse model of oxygen-induced retinopathy (OIR) were investigated separately. HUVEC adhesion, proliferation, migration, ERK1/2 and Akt phosphorylation were assessed. C57BL/6 mice were used for the studies in the OIR model. After exposure to 75% oxygen from postnatal day (PD) 7 to PD12, the mice were returned to room air, and GOPPP was intravitreally administered on PD12. Retinal neovascularization was evaluated on PD17. Hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) protein levels and ERK1/2 phosphorylation were determined by Western blot analysis of retina proteins. GOPPP significantly inhibited the pro-angiogenic effects of vitronectin on HUVECs, including adhesion, proliferation, and migration, and inhibited ERK1/2 and Akt phosphorylation. Retinal neovascularization in the OIR model was significantly suppressed by intravitreal administration of 50 ng GOPPP. The pro-angiogenic factors HIF-1α and VEGF induced by hypoxia were significantly inhibited by GOPPP in OIR mice. GOPPP administration also inhibited ERK1/2 phosphorylation in the OIR model. These results indicate that GOPPP, a novel αvβ3 integrin antagonist, may have potential for the treatment of pathological retinal angiogenesis.

Anti-Angiogenic Effects of a Mutant Endostatin: A New Prospect for Treating Retinal and Choroidal Neovascularization

PurposePathological fundus angiogenesis is a major cause of vision loss in retina diseases. Endostatin, a C-terminal fragment of collagen XVIII, is an endogenous anti-angiogenic protein. The present study aimed to investigate the in vitro and in vivo anti-angiogenic properties of two proteins: an N-terminal H1D/H3D mutant endostatin (M-ES) and a polyethylene glycol propionaldehyde (PEG) covalent M-ES (PEG-M-ES).MethodsM-ES and PEG-M-ES properties were characterized in vitro using a zinc ion binding assay and a stability test. Activity assays, including migration, proliferation, and tube formation assays, were performed with human retinal microvascular endothelial cells (HRMECs) and human umbilical vein endothelial cells (HUVECs). Mouse oxygen-induced retinopathy (OIR) and choroidal neovascularization (CNV) models were used to evaluate in vivo anti-angiogenic effects. In addition, a rabbit model was used to study the retinal pharmacokinetic profile following an intravitreal injection.ResultsThe results indicated that the H1D/H3D mutations of endostatin reduced the zinc binding capacity of M-ES and facilitated PEG covalent binding. PEG-M-ES was more stable and persisted longer in the retina compared with M-ES. The in vitro studies demonstrated that M-ES and PEG-M-ES inhibited HRMEC and HUVEC proliferation, migration, and tube formation more efficiently than ES. In vivo, a single intravitreal injection of M-ES and PEG-M-ES significantly decreased neovascularization in both the OIR and CNV animal models.ConclusionThe present study demonstrated for the first time that PEG-M-ES exhibits a long-term inhibitory effect on neovascularization in vitro and in vivo. These data suggest that PEG-M-ES may represent an innovative therapeutic strategy to prevent fundus neovascularization.

Neuropilin-1 mediates myeloid cell chemoattraction and influences retinal neuroimmune crosstalk.

Immunological activity in the CNS is largely dependent on an innate immune response and is heightened in diseases, such as diabetic retinopathy, multiple sclerosis, amyotrophic lateral sclerosis, and Alzheimer's disease. The molecular dynamics governing immune cell recruitment to sites of injury and disease in the CNS during sterile inflammation remain poorly defined. Here, we identified a subset of mononuclear phagocytes (MPs) that responds to local chemotactic cues that are conserved among central neurons, vessels, and immune cells. Patients suffering from late-stage proliferative diabetic retinopathy (PDR) had elevated vitreous semaphorin 3A (SEMA3A). Using a murine model, we found that SEMA3A acts as a potent attractant for neuropilin-1-positive (NRP-1-positive) MPs. These proangiogenic MPs were selectively recruited to sites of pathological neovascularization in response to locally produced SEMA3A as well as VEGF. NRP-1-positive MPs were essential for disease progression, as NRP-1-deficient MPs failed to enter the retina in a murine model of oxygen-induced retinopathy (OIR), a proxy for PDR. OIR mice with NRP-1-deficient MPs exhibited decreased vascular degeneration and diminished pathological preretinal neovascularization. Intravitreal administration of a NRP-1-derived trap effectively mimicked the therapeutic benefits observed in mice lacking NRP-1-expressing MPs. Our findings indicate that NRP-1 is an obligate receptor for MP chemotaxis, bridging neural ischemia to an innate immune response in neovascular retinal disease.

Characterization of Oxygen-Induced Retinopathy in Mice Carrying an Inactivating Point Mutation in the Catalytic Site of ADAM15

Retinal neovascularization is found in diseases such as macular degeneration, diabetic retinopathy, or retinopathy of prematurity and is usually caused by alterations in oxygen supply. We have previously described that mice lacking the membrane-anchored metalloproteinase ADAM15 (a Disintegrin and Metalloprotease 15) have decreased pathological neovascularization of the retina in the oxygen-induced retinopathy (OIR) model. The main purpose of the present study was to determine the contribution of the catalytic activity of ADAM15 to OIR. To address this question, we generated knock-in mice carrying an inactivating Glutamate to Alanine (E>A) point mutation in the catalytic site of ADAM15 (Adam15E>A mice) and subjected these animals to the OIR model and a heterotopic tumor model. Moreover, we used cell-based assays to determine whether ADAM15 can process cell surface receptors involved in angiogenesis. We found that pathological neovascularization in the OIR model in Adam15E>A mice was comparable to that observed in wild type mice, but tumor implantation by heterotopically injected melanoma cells was reduced. In cell-based assays, overexpressed ADAM15 could process the FGFR2iiib, but was unable to process several receptors with roles in angiogenesis. Collectively, these results suggest that the catalytic activity of ADAM15 is not crucial for its function in promoting pathological neovascularization in the mouse OIR model, most likely because of the very limited substrate repertoire of ADAM15. Instead, other noncatalytic functions of ADAM15 must be important for its role in the OIR model.

RETRACTED ARTICLE: Inhibitory effect of discoidin domain receptor 2 (DDR2) on oxygen-induced retinopathy in mice

This article, “Inhibitory effect of discoidin domain receptor 2 (DDR2) on oxygen-induced retinopathy in mice”, published OnlineFirst in Graefe's Archive for Clinical and Experimental Ophthalmology, DOI 10.1007/s00417-014-2798-9, has been retracted at the request of the Editor-in-Chief. The data in this article was used without acknowledgement or approval by the research team. The online version of this article contains the full text of the retracted article as electronic supplementary material.

Expression of netrin-1 receptors in retina of oxygen-induced retinopathy in mice.

BackgroundNetrin-1 has been reported to promote retinal neovascularization in oxygen-induced retinopathy (OIR). However, netrin-1 receptors, which may mediate netrin-1 action during retinal neovascularization, have not been characterized. In this study, we investigated netrin-1 receptor subtype expression and associated changes in the retinas of mice with OIR.MethodsC57BL/6J mice were exposed to 75±2% oxygen for 5 days and then returned to normal air to induce retinal neovascularization. Reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot were used to examine the expression of netrin-1 receptor subtypes in the mouse retinas. Double staining of netrin-1 receptor subtypes and isolectin B4 was used to determine the location of the netrin-1 receptor subtypes in the retinas. Inhibition of retinal neovascularization was achieved by UNC5B shRNA plasmid intravitreal injection. Retinal neovascularization was examined by fluorescein angiography and quantification of preretinal neovascular nuclei in retinal sections.ResultsRT-PCR results showed that, except for UNC5A, netrin-1 receptor subtypes UNC5B, UNC5C, UNC5D, DCC, neogenin, and A2b were all expressed in the retinas of OIR mice 17 days after birth. Western blots showed that only UNC5B expression was significantly increased on that day, and immunofluorescence results showed that only UNC5B and neogenin were expressed in retinal vessels. Treatment of OIR mice with the UNC5B shRNA plasmid dramatically reduced neovascular tufts and neovascular outgrowth into the inner limiting membrane.ConclusionsUNC5B may promote retinal neovascularization in OIR mice.

Aquaporin 4 is required to induce retinal angiogenesis in a mouse model of oxygen‐induced retinopathy

AbstractPurpose Aquaporin 4 (AQP4) is the most abundant water channel in the retina and participates in the formation of blood‐retinal barrier (BRB). In several retinal pathologies accompanied by BRB dysfunction the expression of AQP4 is altered. In the present study, we investigated the effects of AQP4 deletion in the vascular retinal response to hypoxia.Methods We used wild type (WT) and AQP4 knockout (KO) mice. The retinal angiogenic response to hypoxia was studied in a mouse model of oxygen‐induced retinopathy (OIR) using real time RT‐PCR, Western blot, ELISA and immunohistochemistry.Results In WT mice, retinal levels of AQP4 were increased in response to hypoxia. In OIR mice, the BRB dysfunction was more pronounced in KO than in WT mice. BRB tight junction proteins, occludin, ZO‐1 and JAM‐C, were analyzed and significant alteration was found for JAM‐C in KO mice, indicating a role for this protein in the observed dysfunctions. The formation of neovascular tufts, which are characteristic of OIR, was completely prevented in KO mice, possibly as a result of the decrease in hypoxia‐induced up‐regulation of VEGF mRNA and protein. Unexpectedly, this reduced increase in VEGF levels was paralleled by a dramatic increase in the activity of transcription factors which regulate VEGF expression indicating that in KO retinas mechanisms of VEGF transcription, such as promoter methylation, may be altered.Conclusion Together, the present results indicate a role for AQP4 in the formation of angiogenic processes in the retina and suggest that inhibiting AQP4 function may be a strategy to reduce pathologic angiogenesis in proliferative retinopathies.

Genetic deletion of β1‐ and β2‐adrenergic receptors rescues the retina from hypoxia‐induced pathologic angiogenesis

AbstractPurpose To investigate the effects of β1‐ and β2‐adrenergic receptor (AR) deletion in the vascular retinal response to hypoxia, to confirm and expand the role of β1‐ and β2‐ARs in regulating retinal angiogenesis and to get insights into the role of β3‐ARs.Methods We used wild type (WT) and β1/β2‐AR knockout (KO) mice. The retinal angiogenic response to hypoxia was studied in a mouse model of oxygen‐induced retinopathy (OIR) using real time RT‐PCR, Western blot, ELISA and immunohistochemistry.Results Our results show that β1‐ and β2‐AR deletion did not affect β3‐AR expression or norepinephrine (NE) levels. In KO mice, NE was less upregulated in response to hypoxia indicating a reduced stimulation of the β‐adrenergic system. In KO, the angiogenic response to hypoxia, including the formation of both a central avascular area and neovascular tufts, was nearly abolished while no improvements were observed in blood‐retinal barrier dysfunction typical of OIR. Unexpectedly, VEGF levels did not differ between WT and KO in spite of a recover of the angiogenic response, but a reduced activation of VEGF signaling was observed in KO, which may explain the reduced response to hypoxia. To get insights into the role of β3‐ARs, we treated OIR mice with a β3‐AR agonist, BRL37344 (2 mg/kg, s.c. injected), which resulted in an increase in VEGF levels and the formation of neovascular tufts in both WT and KO, indicating that β3‐AR stimulation may function as a proangiogenic switch.Conclusion Taken together, our results confirm the notion that β1‐ and/or β2‐ARs play a role in retinal angiogenesis and indicate that β3‐ARs may potentiate the angiogenic response in WT and sustain the angiogenic drive in KO.

Placental growth factor expression is reversed by antivascular endothelial growth factor therapy under hypoxic conditions.

Clinical trials have revealed that the antivascular endothelial growth factor (VEGF) therapies are effective in retinopathy of prematurity (ROP). But the low level of VEGF was necessary as a survival signal in healthy conditions, and endogenous placental growth factor (PIGF) is redundant for development. The purpose of this study was to elucidate the PIGF expression under hypoxia as well as the influence of anti-VEGF therapy on PIGF. CoCl2-induced hypoxic human umbilical vein endothelial cells (HUVECs) were used for an in vitro study, and oxygen-induced retinopathy (OIR) mice models were used for an in vivo study. The expression patterns of PIGF under hypoxic conditions and the influence of anti-VEGF therapy on PIGF were evaluated by quantitative reverse transcription-polymerase chain reaction (RTPCR). The retinal avascular areas and neovascularization (NV) areas of anti-VEGF, anti-PIGF and combination treatments were calculated. Retina PIGF concentration was evaluated by ELISA after treatment. The vasoactive effects of exogenous PIGF on HUVECs were investigated by proliferation and migration studies. PIGF mRNA expression was reduced by hypoxia in OIR mice, in HUVECs under hypoxia and anti-VEGF treatment. However, PIGF expression was reversed by anti-VEGF therapy in the OIR model and in HUVECs under hypoxia. Exogenous PIGF significantly inhibited HUVECs proliferation and migration under normal conditions, but it stimulated cell proliferation and migration under hypoxia. Anti-PIGF treatment was effective for neovascular tufts in OIR mice (P<0.05). The finding that PIGF expression is iatrogenically up-regulated by anti-VEGF therapy provides a consideration to combine it with anti-PIGF therapy.

Hypoxia-mediated retinal neovascularization and vascular leakage in diabetic retina is suppressed by HIF-1α destabilization by SH-1242 and SH-1280, novel hsp90 inhibitors.

In diabetic retinopathy (DR), visual deterioration is related with retinal neovascularization and vascular hyperpermeability. Anti-vascular endothelial growth factor (VEGF) agents are currently utilized to suppress retinal neovascularization and macular edema (ME); however, there are still concerns on the widespread use of them because VEGF is a trophic factor for neuronal and endothelial cells in the retina. As an alternative treatment strategy for DR, it is logical to address hypoxia-related molecules to treat DR because the retina is in relative hypoxia as DR progresses. In this study, we demonstrate that destabilization of hypoxia-inducible factor-1α (HIF-1α) by SH-1242 and SH-1280, novel heat shock protein 90 (hsp90) inhibitors, leads to suppression of hypoxia-mediated retinal neovascularization and vascular leakage in diabetic retina. In vitro experiments showed that these inhibitors inhibited hypoxia-induced upregulation of target genes of HIF-1α and further secretion of VEGF. Furthermore, these inhibitors effectively suppressed expression of target genes of HIF-1α including vegfa in the retina of oxygen-induced retinopathy (OIR) mice. Interestingly, despite hsp90 inhibition, these inhibitors do not induce definite toxicity at the level of gene expression, cellular viability, and histologic integrity. We suggest that SH-1242 and SH-1280 can be utilized in the treatment of DR, as an alternative treatment of direct VEGF inhibition. Key message: SH-1242 and SH-1280 are novel hsp90 inhibitors similar to deguelin. HIF-1α destabilization by hsp90 inhibition leads to anti-angiogenic effects. Despite hsp90 inhibition, both inhibitors do not induce definite toxicity. HIF-1α modulation can be a safer therapeutic option than direct VEGF inhibition.

Up-regulation of VEGF by retinoic acid during hyperoxia prevents retinal neovascularization and retinopathy.

Retinopathy of prematurity (ROP) is directly associated with abnormal expression of retinal vascular endothelial growth factor (VEGF) in premature neonates. This study was to investigate whether the systemic administration of retinoic acid (RA) regulates retinal VEGF expression and prevents retinal neovascularization and retinopathy in the oxygen-induced retinopathy (OIR) mouse model. C57BL/6 mice were subjected to OIR by exposure to 75% oxygen from postnatal day (P) 7 to 12 of age. RA was intraperitoneally injected daily to pups from P6 to P9. Retinal whole mount staining and image analysis, immunostaining, Western blotting, quantitative RT-PCR, TUNEL assay, and electroretinography were performed to evaluate the effects of RA on VEGF expression, retinal neovascularization, and retinal neuron functions. Systemic administration of RA in OIR mice promoted retinal VEGF mRNA and protein expression in phase I; the stabilized level of VEGF in phase I supported retinal vascular development and counteracted vaso-obliteration in OIR mice. Subsequently, the excessive generation of VEGF in phase II was attenuated; the retinal vascular leakage and apoptotic cells were significantly ameliorated. As a result, RA significantly prevented the development of hypoxia-induced retinal neovascularization and retinopathy in OIR mice and improved the functional recovery of retinal neurons downstream of photoreceptor cells as measured by focal electroretinography. Systemic administration of RA regulates retinal VEGF expression and supports retinal vascular development in OIR mouse model. We propose that systemic administration of RA to extremely low birth weight, preterm infants during oxygen therapy could potentially be an effective therapeutic approach for the prevention of ROP.

PPARα regulates mobilization and homing of endothelial progenitor cells through the HIF-1α/SDF-1 pathway.

The mechanism for the antiangiogenic activity of peroxisome proliferator-activated receptor alpha (PPARα) remains incompletely understood. Endothelial progenitor cells (EPC) are known to participate in neovascularization (NV). The purpose of this study was to investigate whether PPARα regulates EPC during retinal NV. Retinal NV was induced by oxygen-induced retinopathy (OIR). Mice with OIR were injected intraperitoneally with the PPARα agonist fenofibric acid (FA) or with adenovirus expressing PPARα (Ad-PPARα). Flow cytometry was used to quantify circulating and retinal EPC. Serum stromal cell-derived factor 1 (SDF-1) levels were measured by ELISA. Hypoxia was induced in primary human retinal capillary endothelial cells (HRCEC) and mouse brain endothelial cells (MBEC) by CoCl2. Levels of SDF-1 and hypoxia-inducible factor 1 alpha (HIF-1α) were measured by Western blotting. Fenofibric acid and overexpression of PPARα attenuated the increase of circulating and retinal EPC, correlating with suppressed retinal NV in OIR mice at P17. The PPARα knockout enhanced the OIR-induced increase of circulating and retinal EPC. Fenofibric acid decreased retinal HIF-1α and SDF-1 levels as well as serum SDF-1 levels in the OIR model. In HRCEC, PPARα inhibited HIF-1α nuclear translocation and SDF-1 overexpression induced by hypoxia. Further, MBEC from PPARα(-/-) mice showed more prominent activation of HIF-1α and overexpression of SDF-1 induced by hypoxia, compared with the wild-type (WT) MBEC. PPARα failed to block SDF-1 overexpression induced by a constitutively active mutant of HIF-1α, suggesting that regulation of SDF-1 by PPARα was through blockade of HIF-1α activation. Peroxisome proliferator-activated receptor alpha suppresses ischemia-induced EPC mobilization and homing through inhibition of the HIF-1α/SDF-1 pathway. This represents a novel molecular mechanism for PPARα's antiangiogenic effects.

Protective and antioxidant effects of PPARα in the ischemic retina.

Previous studies have demonstrated that peroxisome proliferator-activated receptor-alpha (PPARα) agonists have therapeutic effects in diabetic retinopathy, although the mechanism of action remains incompletely understood. The purpose of this study was to evaluate PPARα's protective effects in the ischemic retina, and to delineate its molecular mechanism of action. For the oxygen-induced retinopathy (OIR) model, wild-type (WT), and PPARα knockout (PPARα(-/-)) mice were exposed to 75% O₂ from postnatal day 7 (P7) to P12 and treated with the PPARα agonist fenofibric acid (Feno-FA) from P12 to P16. At P17, the effects of Feno-FA on retinal glial fibrillary acidic protein (GFAP) expression, apoptotic DNA cleavage, and TUNEL labeling were analyzed. Cultured retinal cells were exposed to CoCl₂ to induce hypoxia, and TUNEL staining and 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein dye were used to measure apoptosis and reactive oxygen species (ROS) generation. Western blotting was used to measure GFAP levels and cell signaling. Feno-FA decreased retinal apoptosis and oxidative stress in WT but not PPARα(-/-) OIR mice. Peroxisome proliferator-activated receptor-alpha knockout OIR mice showed increased retinal cell death and glial activation in comparison to WT OIR mice. Feno-FA treatment and PPARα overexpression protected cultured retinal cells from hypoxic cell death and decreased ROS levels. Nuclear hypoxia-inducible factor-α (HIF-1α) and nicotine adenine dinucleotide phosphate oxidase-4 (Nox 4) were increased in OIR retinas and downregulated by Feno-FA in WT but not in PPARα(-/-) mice. Peroxisome proliferator-activated receptor-alpha has a potent antiapoptotic effect in the ischemic retina. This protective effect may be mediated in part through downregulation of HIF-1α/Nox 4 and consequently alleviation of oxidative stress.

Fatty acid binding protein 4 deficiency protects against oxygen-induced retinopathy in mice.

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

Correspondence of retinal thinning and vasculopathy in mice with oxygen-induced retinopathy

The aberrantly vascularized peripheral retina in retinopathy of prematurity (ROP) may be associated with visual field constriction, retinal dysfunction, and abnormalities in retinal thickness which is commonly assessed by spectral domain optical coherence tomography (SDOCT). However, due to the limitation of SDOCT for peripheral retinal imaging, retinal thickness in avascular peripheral retina in ROP has not been evaluated. Oxygen induced retinopathy (OIR) in mice has features of vasculopathy similar to those in human ROP. These features occur in the posterior retina and thereby are accessible by standard imaging methods. The purpose of the current study was to determine the correspondence between abnormalities in retinal thickness and vasculopathy in neonatal OIR mice by simultaneous SDOCT imaging and fluorescein angiography (FA). Newborn mice (N = 19; C57BL/6J strain) were exposed to 77% oxygen from postnatal day 7 (P7) to P12. Age-matched control mice (N = 12) were raised in room air. FA and SDOCT were performed in mice between P17 and P19 to visualize retinal vasculature and measure retinal thickness, respectively. Retinal thickness measurements in vascular regions of interest (ROIs) of control mice, and in hypovascular and avascular ROIs of OIR mice were compared. In control mice, FA showed uniformly dense retinal capillary networks between major retinal vessels and retinal thickness of vascular ROIs was 260 ± 7 μm (N = 12). In OIR mice, FA displayed hypovascular regions with less dense and fewer capillaries and avascular regions devoid of visible capillaries. Retinal thickness measurements of hypovascular and avascular ROIs were 243 ± 21 μm and 209 ± 11 μm (N = 19), respectively. Retinal thickness in hypovascular and avascular ROIs of OIR mice was significantly lower than in vascular ROIs of control mice (p ≤ 0.01). Likewise, retinal thickness in avascular ROIs was significantly lower than in hypovascular ROIs (p < 0.001). Retinal thinning in hypovascular and avascular regions may be due to arrested retinal development and/or ischemia induced apoptosis.