Retinal and choroidal microangiopathies: therapeutic opportunities

Injectable Self-Oxygenating Cardio-Protective and Tissue Adhesive Silk-Based Hydrogel for Alleviating Ischemia After Mi Injury

Myocardial infarction (MI) is a significant cardiovascular disease that restricts blood flow, resulting in massive cell death and leading to stiff and noncontractile fibrotic scar tissue formation. Recently, sustained oxygen release in the MI area has shown regeneration ability; however, improving its therapeutic efficiency for regenerative medicine remains challenging. Here, a combinatorial strategy for cardiac repair by developing cardioprotective and oxygenating hybrid hydrogels that locally sustain the release of stromal cell-derived factor-1 alpha (SDF) and oxygen for simultaneous activation of neovascularization at the infarct area is presented. A sustained release of oxygen and SDF from injectable, mechanically robust, and tissue-adhesive silk-based hybrid hydrogels is achieved. Enhanced endothelialization under normoxia and anoxia is observed. Furthermore, there is a marked improvement in vascularization that leads to an increment in cardiomyocyte survival by ≈30% and a reduction of the fibrotic scar formation in an MI animal rodent model. Improved left ventricular systolic and diastolic functions by ≈10% and 20%, respectively, with a ≈25% higher ejection fraction on day 7 are also observed. Therefore, local delivery of therapeutic oxygenating and cardioprotective hydrogels demonstrates beneficial effects on cardiac functional recovery for reparative therapy.

Metabolomics facilitates the discovery of metabolic profiles and pathways for myopia: A systematic review

BACKGROUND

Myopia is one of the major eye disorders and the global burden is increasing rapidly. Our purpose is to systematically summarize potential metabolic biomarkers and pathways in myopia to facilitate the understanding of disease mechanisms as well as the discovery of novel therapeutic measures.

METHODS

Myopia-related metabolomics studies were searched in electronic databases of PubMed and Web of Science until June 2021. Information regarding clinical and demographic characteristics of included studies and metabolomics findings were extracted. Myopia-related metabolic pathways were analysed for differential metabolic profiles, and the quality of included studies was assessed based on the QUADOMICS tool. Pathway analyses of differential metabolites were performed using bioinformatics tools and online software such as the Metaboanalyst 5.0.

RESULTS

The myopia-related metabolomics studies included in this study consisted of seven human and two animal studies. The results of the study quality assessment showed that studies were all phase I studies and all met the evaluation criteria of 70% or more. The myopia-control serum study identified 23 differential metabolites with the Sphingolipid metabolism pathway beings enriched. The high myopia-cataract aqueous humour study identified 40 differential metabolites with the Arginine biosynthesis pathway being enriched. The high myopia-control serum study identified 43 differential metabolites and 4 pathways were significantly associated with metabolites including Citrate cycle; Alanine, aspartate and glutamate metabolism; Glyoxylate and dicarboxylate metabolism; Biosynthesis of unsaturated fatty acids (all P value < 0.05).

CONCLUSIONS

This study summarizes potential metabolic biomarkers and pathways in myopia, providing new clues to elucidate disease mechanisms.

Metabolomics and Biomarkers in Retinal and Choroidal Vascular Diseases

The retina is one of the most important structures in the eye, and the vascular health of the retina and choroid is critical to visual function. Metabolomics provides an analytical approach to endogenous small molecule metabolites in organisms, summarizes the results of “gene-environment interactions”, and is an ideal analytical tool to obtain “biomarkers” related to disease information. This study discusses the metabolic changes in neovascular diseases involving the retina and discusses the progress of the study from the perspective of metabolomics design and analysis. This study advocates a comparative strategy based on existing studies, which encompasses optimization of the performance of newly identified biomarkers and the consideration of the basis of existing studies, which facilitates quality control of newly discovered biomarkers and is recommended as an additional reference strategy for new biomarker discovery. Finally, by describing the metabolic mechanisms of retinal and choroidal neovascularization, based on the results of existing studies, this study provides potential opportunities to find new therapeutic approaches.

Comparison of Clinical Outcomes of Intravitreal Bevacizumab and Aflibercept in Type 1 Prethreshold Retinopathy of Prematurity in Posterior Zone II

Purpose

To evaluate the efficacy and safety of intravitreal injection (IVI) of bevacizumab (IVB) versus aflibercept (IVA) in premature infants with type 1 prethreshold retinopathy of prematurity (ROP) in the posterior Zone II.

Methods

The study was a multicenter, historical cohort of premature newborns diagnosed with type 1 prethreshold ROP in the posterior Zone II, treated with IVB or IVA. Demographic features, complications, and treatment outcomes were then compared between the two groups.

Results

Seventy-six patients received aflibercept (the IVA group), and 210 received bevacizumab (the IVB group). The two groups were not significantly different in terms of postmenstrual age (PMA) at the time of ROP diagnosis and other known risk factors for ROP development and progression. All eyes in both the groups responded to IVI; however, recurrence was observed in four eyes (1.9%) in the IVB group and 12 (15.8%) in the IVA group (P = 0.001). Recurrence occurred 9.1 ± 0.83 (5-12) and 15.5 ± 0.98 (12-18) weeks after primary treatment in the IVB and IVA groups, respectively (P = 0.000). In the IVA group, retinal vascularization was completed in 38.18 ± 6.5 weeks (21-48) after IVI, and it happened in 23.86 ± 9.3 weeks (13-60) in the IVB group (P = 0.009). Furthermore, vascularization reached the peripheral retina in 73.25 ± 6.5 (56-84) and 58.75 ± 8.8 (45-93) weeks, PMA in the IVA and IVB groups, respectively (P = 0.03). No acute postoperative complications were observed in the treated eyes in either group.

Conclusion

This study shows that both IVA and IVB are effective and well tolerated for the management of type 1 prethreshold ROP in the posterior Zone II; however, IVA needs a significantly longer time for vascularization completion and has a higher recurrence rate compared with IVB.

Resveratrol reduced the detrimental effects of malondialdehyde on human endothelial cells

Introduction: According to the statistics, vascular injury occurs during the onset of diabetic changes after the production of several byproducts. Many authorities have focused to find an alternative therapy for diabetic patients. In this study, we investigated the therapeutic effects of natural polyphenol like resveratrol on human endothelial cells exposed to malondialdehyde for 48 hours.

Methods: Human Umbilical Vein Endothelial Cells were randomly classified into four groups;control, malondialdehyde (2.5 mM), resveratrol (100 μM), and cells received the combined regime for 48 hours. Cell viability was determined by 3-(4, 5-dimethyl thiazol-2-yl) 2, 5-diphenyl-tetrazoliumbromide (MTT) assay. Griess reaction was performed to measure the content of Nitric oxide (NO).Apoptosis was studied by using real-time polymerase chain reaction (RT-PCR) and western blotting assays. Levels of receptor tyrosine kinases like VEGFR-1, -2, Tie-1, and -2 were analyzed by enzyme-linked immunosorbent assay(ELISA). The affinity of resveratrol and malondialdehyde to serum albumin was measured by Surface Plasmon Resonance Assay. Any changes in chromatin remodeling were detected by PCR array analysis.

Results: Resveratrol reduced cytotoxicity and NO content inside cells induced by malondialdehyde(MDA) (P < 0.05). Endothelial cell apoptosis was decreased by the reduction of pro-apoptotic factor Bax and increase of Bcl-2 following the incubation with resveratrol (P < 0.05). MDA-induced receptor tyrosine kinases increase was inhibited by resveratrol and reached near-to-normal levels (P < 0.05).Surface Plasmon Resonance revealed a higher affinity of resveratrol to albumin compared to the malondialdehyde-albumin complex. Polymerase chain reaction (PCR) array revealed the potency of resveratrol in chromatin remodeling following the treatment with malondialdehyde (P < 0.05).

Conclusion: Based on our findings, resveratrol has the potential to decrease diabetic vascular injury induced by lipid byproducts such as MDA.

YAP promotes ocular neovascularization by modifying PFKFB3-driven endothelial glycolysis

Ocular neovascularization is the leading cause of vision impairment in a variety of ocular diseases, such as age-related macular degeneration and retinopathy of prematurity. Emerging studies have suggested that the yes-associated protein (YAP), a downstream effector of the Hippo pathway, is involved in the pathological angiogenesis, but the mechanism are largely unknown. Here, we demonstrated that hypoxic treatment triggered YAP expression and nuclear translocation in human umbilical vein endothelial cells (HUVECs). YAP acted as a transcriptional co-activator working together with transcriptional enhancer activator domain 1 (TEAD1) to binds the promoter of the key glycolytic regulator 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase3 (PFKFB3), and thereby increases PFKFB3 expression. Moreover, silencing of YAP inhibited glycolysis as well as proliferation, migration, sprouting and tube formation of HUVECs under hypoxia, all of which could be reversed by enforced expression of PFKFB3. Finally, our animal study also showed that intravitreal injection of small interfering RNA of YAP or PFKFB3 dramatically suppressed the neovascular growth in mouse models of choroidal neovascularization and oxygen-induced retinopathy. These findings provide new insights into a previously unrecognized effect of YAP on endothelial glycolysis and highlight the potential of targeting YAP/PFKFB3 axis in the treatment of ocular neovascularization.

MicroRNAs in laser-induced choroidal neovascularization in mice and rats: their expression and potential therapeutic targets

Choroidal neovascularization characterizes wet age-related macular degeneration. Choroidal neovascularization formation involves a primarily angiogenic process that is combined with both inflammation and proteolysis. A primary cause of choroidal neovascularization pathogenesis is alterations in pro- and anti-angiogenic factors derived from the retinal pigment epithelium, with vascular endothelium growth factor being mainly responsible for both clinical and experimental choroidal neovascularization. MicroRNAs (miRNAs) which are short, non-coding, endogenous RNA molecules have a major role in regulating various pathological processes, including inflammation and angiogenesis. A review of recent studies with the mouse laser-induced choroidal neovascularization model has shown alterations in miRNA expression in choroidal neovascularization tissues and could be potential therapeutic targets for wet age-related macular degeneration. Upregulation of miR-505 (days 1 and 3 post-laser), miR-155 (day 14) occurred in retina; miR-342-5p (days 3 and 7), miR-126-3p (day 14) in choroid; miR-23a, miR-24, miR-27a (day 7) in retina/choroid; miR-505 (days 1 and 3) in retinal pigment epithelium/choroid; downregulation of miR-155 (days 1 and 3), miR-29a, miR-29b, miR-29c (day 5), miR-93 (day 14), miR-126 (day 14) occurred in retinal pigment epithelium/choroid. Therapies using miRNA mimics or inhibitors were found to decrease choroidal neovascularization lesions. Choroidal neovascularization development was reduced by overexpression of miR-155, miR-188-5p, miR-(5,B,7), miR-126-3p, miR-342-5p, miR-93, miR-126, miR-195a-3p, miR-24, miR-21, miR-31, miR-150, and miR-184, or suppression of miR-505, miR-126-3p, miR-155, and miR-23/27. Further studies are warranted to determine miRNA expression in mouse laser-induced choroidal neovascularization models in order to validate and extend the reported findings. Important experimental variables need to be standardized; these include the strain and age of animals, gender, number and position of laser burns to the eye, laser parameters to induce choroidal neovascularization lesions including wavelength, power, spot size, and duration.

Lipid Signaling in Ocular Neovascularization

Vasculogenesis and angiogenesis play a crucial role in embryonic development. Pathological neovascularization in ocular tissues can lead to vision-threatening vascular diseases, including proliferative diabetic retinopathy, retinal vein occlusion, retinopathy of prematurity, choroidal neovascularization, and corneal neovascularization. Neovascularization involves various cellular processes and signaling pathways and is regulated by angiogenic factors such as vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF). Modulating these circuits may represent a promising strategy to treat ocular neovascular diseases. Lipid mediators derived from membrane lipids are abundantly present in most tissues and exert a wide range of biological functions by regulating various signaling pathways. In particular, glycerophospholipids, sphingolipids, and polyunsaturated fatty acids exert potent pro-angiogenic or anti-angiogenic effects, according to the findings of numerous preclinical and clinical studies. In this review, we summarize the current knowledge regarding the regulation of ocular neovascularization by lipid mediators and their metabolites. A better understanding of the effects of lipid signaling in neovascularization may provide novel therapeutic strategies to treat ocular neovascular diseases and other human disorders.

MicroRNAs in Vascular Eye Diseases

Since the discovery of the first microRNA (miRNA) decades ago, studies of miRNA biology have expanded in many biomedical research fields, including eye research. The critical roles of miRNAs in normal development and diseases have made miRNAs useful biomarkers or molecular targets for potential therapeutics. In the eye, ocular neovascularization (NV) is a leading cause of blindness in multiple vascular eye diseases. Current anti-angiogenic therapies, such as anti-vascular endothelial growth factor (VEGF) treatment, have their limitations, indicating the need for investigating new targets. Recent studies established the roles of various miRNAs in the regulation of pathological ocular NV, suggesting miRNAs as both biomarkers and therapeutic targets in vascular eye diseases. This review summarizes the biogenesis of miRNAs, and their functions in the normal development and diseases of the eye, with a focus on clinical and experimental retinopathies in both human and animal models. Discovery of novel targets involving miRNAs in vascular eye diseases will provide insights for developing new treatments to counter ocular NV.

MicroRNA-145 Regulates Pathological Retinal Angiogenesis by Suppression of TMOD3

Pathological angiogenesis is a hallmark of various vascular diseases, including vascular eye disorders. Dysregulation of microRNAs (miRNAs), a group of small regulatory RNAs, has been implicated in the regulation of ocular neovascularization. This study investigated the specific role of microRNA-145 (miR-145) in regulating vascular endothelial cell (EC) function and pathological ocular angiogenesis in a mouse model of oxygen-induced retinopathy (OIR). Expression of miR-145 was significantly upregulated in OIR mouse retinas compared with room air controls. Treatment with synthetic miR-145 inhibitors drastically decreased levels of pathological neovascularization in OIR, without substantially affecting normal developmental angiogenesis. In cultured human retinal ECs, treatment with miR-145 mimics significantly increased the EC angiogenic function, including proliferation, migration, and tubular formation, whereas miR-145 inhibitors attenuated in vitro angiogenesis. Tropomodulin3 (TMOD3), an actin-capping protein, is a direct miR-145 target and is downregulated in OIR retinas. Treatment with miR-145 mimic led to TMOD3 inhibition, altered actin cytoskeletal architecture, and elongation of ECs. Moreover, inhibition of TMOD3 promoted EC angiogenic function and pathological neovascularization in OIR and abolished the vascular effects of miR-145 inhibitors in vitro and in vivo. Overall, our findings indicate that miR-145 is a novel regulator of TMOD3-dependent cytoskeletal architecture and pathological angiogenesis and a potential target for development of treatments for neovascular eye disorders.

Beta-blockers for prevention and treatment of retinopathy of prematurity in preterm infants

BACKGROUND

Retinopathy of prematurity (ROP) is a vision-threatening disease of preterm neonates. The use of beta-adrenergic blocking agents (beta-blockers), which modulate the vasoproliferative retinal process, may reduce the progression of ROP or even reverse established ROP.

OBJECTIVES

To determine the effect of beta-blockers on short-term structural outcomes, long-term functional outcomes, and the need for additional treatment, when used either as prophylaxis in preterm infants without ROP, stage 1 ROP (zone I), or stage 2 ROP (zone II) without plus disease or as treatment in preterm infants with at least prethreshold ROP.

SEARCH METHODS

We searched the Cochrane Neonatal Review Group Specialized Register; CENTRAL (in the Cochrane Library Issue 7, 2017); Embase (January 1974 to 7 August 2017); PubMed (January 1966 to 7 August 2017); and CINAHL (January 1982 to 7 August 2017). We checked references and cross-references and handsearched abstracts from the proceedings of the Pediatric Academic Societies Meetings.

SELECTION CRITERIA

We considered for inclusion randomised or quasi-randomised clinical trials that used beta-blockers for prevention or treatment of ROP in preterm neonates of less than 37 weeks' gestational age.

DATA COLLECTION AND ANALYSIS

We used the standard methods of Cochrane and the Cochrane Neonatal Review Group. We used the GRADE approach to assess the quality of evidence.

MAIN RESULTS

We included three randomised trials (N = 366) in this review. Two of these studies were at high risk of bias. All studies reported on prevention of ROP and compared oral propranolol with placebo or no treatment. We found no trials assessing beta-blockers in infants with established stage 2 or higher ROP with plus disease.In one trial, study medication was started after one week of life, i.e. prior to the first ROP screening. The other two trials included preterm infants if they had stage 2 or lower ROP without plus disease. Based on the GRADE assessment, we considered evidence to be of low quality for the following outcomes: rescue treatment with anti-VEGF or laser therapy; and arterial hypotension or bradycardia requiring inotropic support. Evidence was of moderate quality for the following outcomes: progression to stage 2 with plus disease; progression to stage 3 ROP; and progression to stage 4 or 5 ROP.Meta-analysis of three trials (N = 366) suggested beneficial effects of oral beta-blockers on the risk of requiring anti-VEGF agents (typical risk ratio (RR) 0.32, 95% confidence interval (CI) 0.12 to 0.86; I² = 0%; typical risk difference (RD) -0.06, 95% CI -0.10 to -0.01; I² = 75%; number needed to treat for an additional beneficial outcome (NNTB) 18, 95% CI 14 to 84) and laser therapy (typical RR 0.54, 95% CI 0.32 to 0.89; typical RD -0.09, 95% CI -0.16 to -0.02; I² = 31%; NNTB 12, 95% CI 8 to 47). Meta-analysis of two trials (N = 161) demonstrated a beneficial effect of oral beta-blockers on progression to stage 3 ROP (typical RR 0.60, 95% CI 0.37 to 0.96; I² = 0%; typical RD -0.15, 95% CI -0.28 to -0.02; I² = 73%; NNTB 7, 95% CI 5 to 67). There was no significant effect of oral beta-blockers on progression to stage 2 ROP with plus disease or to stage 4 or 5 ROP. Although meta-analysis did not indicate a significant effect of beta-blockers on arterial hypotension or bradycardia, propranolol dosage in one study was reduced by 50% in infants of less than 26 weeks' gestational age due to severe hypotension, bradycardia, and apnoea in several participants. Analyses did not indicate significant effects of beta-blockers on complications of prematurity or mortality. None of the trials reported on long-term visual impairment.

AUTHORS' CONCLUSIONS

Limited evidence of low-to-moderate quality suggests that prophylactic administration of oral beta-blockers might reduce progression towards stage 3 ROP and decrease the need for anti-VEGF agents or laser therapy. The clinical relevance of those findings is unclear as no data on long-term visual impairment were reported. Adverse events attributed to oral propranolol at a dose of 2 mg/kg/d raise concerns regarding systemic administration of this drug for prevention of ROP at the given dose. There is insufficient evidence to determine the efficacy and safety of beta-blockers for prevention of ROP due to high risk of bias in two included trials and the lack of long-term functional outcomes. We would encourage researchers to conduct large, well-designed trials to confirm or refute the role of beta-blockers for prevention and treatment of ROP in preterm infants. Trials should report on long-term visual impairment. Researchers should consider dose-finding studies of systemic beta-blockers and topical administration of beta-blockers, in order to optimise drug delivery and minimise adverse events.

Salubrinal attenuated retinal neovascularization by inhibiting CHOP-HIF1α-VEGF pathways

Retinal neovascularization (RNV) related disease is the leading cause of irreversible blindness in the world. The aim of this study is to identify whether salubrinal could attenuate RNV by inhibiting CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP)- hypoxia inducible factors 1α (HIF1α) -vascular endothelial growth factor (VEGF) pathways in both mouse retinal microvascular endothelial cells (mRMECs) and oxygen-induced retinopathy (OIR) mouse model. After being treated with salubrinal (20μmol/L) or CHOP-siRNA, mRMECs were exposed to a hypoxia environment. OIR mice were intraperitoneally injected with salubrinal (0.5 mg/kg/day) from P12 to P17. With salubrinal or CHOP-siRNA treatment, the elevated CHOP protein and mRNA levels in hypoxia-induced mRMECs were significantly decreased. HIF1α-VEGF pathways were activated under hypoxia condition, then HIF1α protein was degraded and VEGF secretion was down-regulated after salubrinal or CHOP-siRNA treatment. In OIR mice, the areas of RNV were markedly decreased with salubrinal treatment. Moreover, elevated expressions of CHOP, HIF1α and VEGF in retinas of OIR mice were all reduced after salubrinal treatment. It suggested that salubrinal attenuated RNV in mRMECs and OIR mice by inhibiting CHOP-HIF1α-VEGF pathways and could be a potential therapeutic target for hypoxia-induced retinal microangiopathy.

Animal models of ocular angiogenesis: from development to pathologies

Pathological angiogenesis in the eye is an important feature in the pathophysiology of many vision-threatening diseases, including retinopathy of prematurity, diabetic retinopathy, and age-related macular degeneration, as well as corneal diseases with abnormal angiogenesis. Development of reproducible and reliable animal models of ocular angiogenesis has advanced our understanding of both the normal development and the pathobiology of ocular neovascularization. These models have also proven to be valuable experimental tools with which to easily evaluate potential antiangiogenic therapies beyond eye research. This review summarizes the current available animal models of ocular angiogenesis. Models of retinal and choroidal angiogenesis, including oxygen-induced retinopathy, laser-induced choroidal neovascularization, and transgenic mouse models with deficient or spontaneous retinal/choroidal neovascularization, as well as models with induced corneal angiogenesis, are widely used to investigate the molecular and cellular basis of angiogenic mechanisms. Theoretical concepts and experimental protocols of these models are outlined, as well as their advantages and potential limitations, which may help researchers choose the most suitable models for their investigative work.-Liu, C.-H., Wang, Z., Sun, Y., Chen, J. Animal models of ocular angiogenesis: from development to pathologies.

Regulating the regulators of angiogenesis by CCN1 and taking it up a Notch

CCN1 is encoded by an extracellular matrix protein-gene that is essential for the proper development of the cardiovascular system and the control of angiogenesis, inflammation, progenitor cell lineage commitment and extracellular matrix protein remodeling during the adult life. High-precision genetic models of tissue-specific gene deletion demonstrated a pivotal role of CCN1 in providing positional information to angiogenic endothelial cells (ECs) during the outgrowth and maturation of nascent blood vessel sprouts, fine-controlling Notch-dependent inter-endothelial cell communications and mediating interaction with inflammatory cells. Some of these pleiotropic activities of CCN1 are unique among proteins of the extracellular matrix. Thus, CCN1 represents a model molecule for investigating and unraveling novel aspects of extracellular protein signaling in vascular development and diseases.

MicroRNA-195a-3p inhibits angiogenesis by targeting Mmp2 in murine mesenchymal stem cells

MicroRNAs (miRNAs) modulate complex physiological and pathological processes, including the regulation of angiogenesis. Our previous study reported that bone marrow-derived mesenchymal stem cells (MSCs) are recruited into choroidal neovascularization lesions. miRNA-195 is highly expressed in MSCs, but its function remains unknown. In the present study, miR-195a-3p abundance was significantly decreased in hypoxia-treated murine MSCs; on the other hand, its overexpression reduced MSC proliferation and migration while increasing the activation of anti-angiogenic factor pigment epithelium-derived factor (PEDF). We further discovered that matrix metalloproteinase 2 (Mmp2) transcript is a target of miR-195a-3p, and that silencing Mmp2 phenocopied the reduced proliferation and migration of MSCs. The therapeutic potential of miR-195a-3p as an angiogenesis inhibitor was also demonstrated in a laser-induced choroidal neovascularization mouse model. These findings collectively indicate that miR-195a-3p is a negative modulator of angiogenesis, and could be used as an angiogenesis inhibitor. Mol. Reprod. Dev. 83: 413-423, 2016. © 2016 Wiley Periodicals, Inc.

Endothelial microRNA-150 is an intrinsic suppressor of pathologic ocular neovascularization

Pathologic ocular neovascularization commonly causes blindness. It is critical to identify the factors altered in pathologically proliferating versus normally quiescent vessels to develop effective targeted therapeutics. MicroRNAs regulate both physiological and pathological angiogenesis through modulating expression of gene targets at the posttranscriptional level. However, it is not completely understood if specific microRNAs are altered in pathologic ocular blood vessels, influencing vascular eye diseases. Here we investigated the potential role of a specific microRNA, miR-150, in regulating ocular neovascularization. We found that miR-150 was highly expressed in normal quiescent retinal blood vessels and significantly suppressed in pathologic neovessels in a mouse model of oxygen-induced proliferative retinopathy. MiR-150 substantially decreased endothelial cell function including cell proliferation, migration, and tubular formation and specifically suppressed the expression of multiple angiogenic regulators, CXCR4, DLL4, and FZD4, in endothelial cells. Intravitreal injection of miR-150 mimic significantly decreased pathologic retinal neovascularization in vivo in both wild-type and miR-150 knockout mice. Loss of miR-150 significantly promoted angiogenesis in aortic rings and choroidal explants ex vivo and laser-induced choroidal neovascularization in vivo. In conclusion, miR-150 is specifically enriched in quiescent normal vessels and functions as an endothelium-specific endogenous inhibitor of pathologic ocular neovascularization.

Pericyte chemomechanics and the angiogenic switch: insights into the pathogenesis of proliferative diabetic retinopathy?

PURPOSE

To establish the regulatory roles that pericytes have in coordinating retinal endothelial cell (EC) growth and angiogenic potential.

METHODS

Pericytes were derived from donor diabetic (DHuRP) or normal (NHuRP) human retinae, and characterized using vascular markers, coculture, contraction, morphogenesis, and proliferation assays. To investigate capillary "cross-talk," pericyte-endothelial coculture growth, and connexin-43 (Cx43) expression assays were performed. Paracrine effects were examined via treating EC with pericyte-derived conditioned media (CM) in proliferation, angiogenesis, and angiocrine assays. The effects of sphingosine 1-phosphate (S1P) were assessed using receptor antagonists.

RESULTS

The DHuRP exhibit unique proliferative and morphologic properties, reflecting distinctive cytoskeletal and isoactin expression patterns. Unlike NHuRP, DHuRP are unable to sustain EC growth arrest in coculture and display reduced Cx43 expression. Further, CM from DHuRP (DPCM) markedly stimulates EC proliferation and tube formation. Treatment with S1P receptor antagonists mitigates DPCM growth-promotion in EC and S1P-mediated pericyte contraction. Angiocrine assays on normal and diabetic pericyte secretomes reveal factors involved in angiogenic control, inflammation, and metabolism.

CONCLUSIONS

Effects from the diabetic microenvironment appear sustainable in cell culture: pericytes derived from diabetic donor eyes seemingly possess a "metabolic memory" in vitro, which may be linked to original donor health status. Diabetes- and pericyte-dependent effects on EC growth and angiogenesis may reflect alterations in bioactive lipid, angiocrine, and chemomechanical signaling. Altogether, our results suggest that diabetes alters pericyte contractile phenotype and cytoskeletal signaling, which ultimately may serve as a key, initiating event required for retinal endothelial reproliferation, angiogenic activation, and the pathological neovascularization accompanying proliferative diabetic retinopathy.

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.

Endothelial TWIST1 promotes pathological ocular angiogenesis

PURPOSE

Pathological neovessel formation impacts many blinding vascular eye diseases. Identification of molecular signatures distinguishing pathological neovascularization from normal quiescent vessels is critical for developing new interventions. Twist-related protein 1 (TWIST1) is a transcription factor important in tumor and pulmonary angiogenesis. This study investigated the potential role of TWIST1 in modulating pathological ocular angiogenesis in mice.

METHODS

Twist1 expression and localization were analyzed in a mouse model of oxygen-induced retinopathy (OIR). Pathological ocular angiogenesis in Tie2-driven conditional Twist1 knockout mice were evaluated in both OIR and laser-induced choroidal neovascularization models. In addition, the effects of TWIST1 on angiogenesis and endothelial cell function were analyzed in sprouting assays of aortic rings and choroidal explants isolated from Twist1 knockout mice, and in human retinal microvascular endothelial cells treated with TWIST1 small interfering RNA (siRNA).

RESULTS

TWIST1 is highly enriched in pathological neovessels in OIR retinas. Conditional Tie2-driven depletion of Twist1 significantly suppressed pathological neovessels in OIR without impacting developmental retinal angiogenesis. In a laser-induced choroidal neovascularization model, Twist1 deficiency also resulted in significantly smaller lesions with decreased vascular leakage. In addition, loss of Twist1 significantly decreased vascular sprouting in both aortic ring and choroid explants. Knockdown of TWIST1 in endothelial cells led to dampened expression of vascular endothelial growth factor receptor 2 (VEGFR2) and decreased endothelial cell proliferation.

CONCLUSIONS

Our study suggests that TWIST1 is a novel regulator of pathologic ocular angiogenesis and may represent a new molecular target for developing potential therapeutic treatments to suppress pathological neovascularization in vascular eye diseases.

Glycobiology of ocular angiogenesis

Ocular neovascularization can affect almost all the tissues of the eye: the cornea, the iris, the retina, and the choroid. Pathological neovascularization is the underlying cause of vision loss in common ocular conditions such as diabetic retinopathy, retinopathy of prematurity and age-related macular neovascularization. Glycosylation is the most common covalent posttranslational modification of proteins in mammalian cells. A growing body of evidence demonstrates that glycosylation influences the process of angiogenesis and impacts activation, proliferation, and migration of endothelial cells as well as the interaction of angiogenic endothelial cells with other cell types necessary to form blood vessels. Recent studies have provided evidence that members of the galectin class of β-galactoside-binding proteins modulate angiogenesis by novel carbohydrate-based recognition systems involving interactions between glycans of angiogenic cell surface receptors and galectins. This review discusses the significance of glycosylation and the role of galectins in the pathogenesis of ocular neovascularization.

Suppression of retinal neovascularization by small interfering RNA targeting PGC-1α

Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) is a key coordinator of gene programs in metabolism and energy homeostasis in mammals. The aim of this study was to determine whether PGC-1α is involved in the transcriptional regulation of retinal neovascularization in oxygen-induced retinopathy (OIR). The expression of PGC-1α in the retina of mice with OIR was detected by real-time polymerase chain reaction (PCR) and western blot analysis. Mice with OIR were administered small interfering RNA (siRNA) targeting PGC-1α by intravitreal injection, and the effects of PGC-1α siRNA were confirmed by fluorescein angiography and quantification of pre-retinal neovascular nuclei in the retinal sections. PGC-1α was upregulated at both the mRNA and protein level under hypoxic conditions. Retinal neovascularization was inhibited by PGC-1α siRNA. Furthermore, PGC-1α mRNA and protein levels were also reduced by PGC-1α siRNA, which were detected by real-time PCR and western blot analysis. The downregulation of PGC-1α expression resulted in the reduction of vascular endothelial growth factor (VEGF) expression in the mice. In conclusion, siRNA targeting PGC-1α inhibits retinal neovascularization by downregulating the expression of PGC-1α and VEGF in the murine retina. Therefore, PGC-1α represents a potential therapeutic target for ischemia-induced retinal diseases and other ocular neovascular diseases.

Anti-vascular endothelial growth factor therapy for diabetic macular edema

Diabetes mellitus is a serious health problem that affects over 350 million individuals worldwide. Diabetic retinopathy (DR), which is the most common microvascular complication of diabetes, is the leading cause of new cases of blindness in working-aged adults. Diabetic macular edema (DME) is an advanced, vision-limiting complication of DR that affects nearly 30% of patients who have had diabetes for at least 20 years and is responsible for much of the vision loss due to DR. The historic standard of care for DME has been macular laser photocoagulation, which has been shown to stabilize vision and reduce the rate of further vision loss by 50%; however, macular laser leads to significant vision recovery in only 15% of treated patients. Mechanisms contributing to the microvascular damage in DR and DME include the direct toxic effects of hyperglycemia, sustained alterations in cell signaling pathways, and chronic microvascular inflammation with leukocyte-mediated injury. Chronic retinal microvascular damage results in elevation of intraocular levels of vascular endothelial growth factor A (VEGF), a potent, diffusible, endothelial-specific mitogen that mediates many important physiologic processes, including but not limited to the development and permeability of the vasculature. The identification of VEGF as an important pathophysiologic mediator of DME suggested that anti-VEGF therapy delivered to the eye might lead to improved visual outcomes in this disease. To date, four different inhibitors of VEGF, each administered by intraocular injection, have been tested in prospective, randomized phase II or phase III clinical trials in patients with DME. The results from these trials demonstrate that treatment with anti-VEGF agents results in substantially improved visual and anatomic outcomes compared with laser photocoagulation, and avoid the ocular side effects associated with laser treatment. Thus, anti-VEGF therapy has become the preferred treatment option for the management of DME in many patients.

Early histologic lesions and risk factors for recurrence of diabetic kidney disease after kidney transplantation

BACKGROUND

Recurrence of diabetic kidney disease (DKD) after diabetic kidney transplantation has been reported. The aim of this study was to determine the early histologic lesions, focusing especially on abnormal glomerular angiogenesis, and clinical risk factors of recurrent DKD after kidney transplantation.

METHODS

The authors studied 34 renal transplant recipients with diabetes and 30 without diabetes. All patients had undergone both baseline and posttransplant follow-up biopsies. Glomerular morphometric analyses of the mesangial area, the capillary number, and the capillary area were performed with a computer-assisted image analyzer, and glomerular basement membrane (GBM) thickness was evaluated by electron microscopy. The incidence of polar vasculosis as an angiogenic phenomenon was also evaluated. Clinical data including hemoglobin (Hb)A1c, blood pressure, urinary albumin excretion, and serum lipid profiles were compared with histologic parameters.

RESULTS

Together with the increased glomerular mesangial area and GBM thickness, the glomerular capillary number and area and the incidence of polar vasculosis were significantly higher in patients with diabetes. Most of these alterations were significantly associated with the mean posttransplant HbA1c levels but not with blood pressure or lipid profiles. In the multiple regression analysis, HbA1c level remained significantly associated with these histologic parameters.

CONCLUSIONS

Similar to mesangial expansion and GBM thickening, glomerular neovascularization represented by increased capillary number and area and glomerular polar vasculosis can occur as an early diabetic lesion in recurrent DKD. Posttransplant hyperglycemia is a significant risk factor predictive of the progression of recurrent DKD in kidney allografts.

Vitreous levels of proteins implicated in angiogenesis are modulated in patients with retinal or choroidal neovascularization

AIM

The aim of this study was to investigate the levels of pigment epithelium-derived factor (PEDF), angiopoietin 2, vascular endothelial growth factor (VEGF), and soluble VEGF receptor 1 (sVEGFR-1) in vitreous samples of patients suffering from age-related macular degeneration with choroidal neovascularization or from proliferative diabetic retinopathy (PDR).

METHODS

Proteins in vitreous samples of 29 patients were quantified via enzyme-linked immunosorbent assays.

RESULTS

Vitreous levels of sVEGFR-1 were significantly higher in age-related macular degeneration with choroidal neovascularization (p = 0.005) and in PDR (p = 0.003) versus controls. In analogue comparisons, PEDF was significantly decreased (p < 0.01). PDR was associated with significantly increased angiopoietin 2 and VEGF levels (p = 0.001 for both).

CONCLUSION

The vitreous in retinal or choroidal neovascularization revealed a pro-angiogenic potential indicated by decreased PEDF or increased angiopoietin 2 levels compared to controls. However, higher amounts of sVEGFR-1 were concomitant, pointing to activation of an endogenous anti-angiogenic system in the protein network.

Novel targets against retinal angiogenesis in diabetic retinopathy

Proliferative diabetic retinopathy (PDR), characterized by pathologic retinal angiogenesis, is a major cause of blindness in the USA and globally. Treatments targeting vascular endothelial growth factor (VEGF) have emerged as a beneficial part of the therapeutic armamentarium for this condition, highlighting the utility of identifying and targeting specific pathogenic molecules. There continues to be active research into the molecular players regulating retinal angiogenesis, including pro-angiogenic factors, anti-angiogenic factors, and integrins and matrix proteinases. New insights have been especially prominent regarding molecules which regulate specialized endothelial cells called tip cells, which play a lead role in endothelial sprouting. Together, these research efforts are uncovering new, important molecular regulators of retinal angiogenesis, which provide fertile areas for therapeutic exploration. This review discusses potential molecular targets, with an emphasis towards newer targets.

Role of matrix metalloproteinase-2 and -9 in the development of diabetic retinopathy

Diabetic retinopathy represents the most common causes of vision loss in patients affected by diabetes mellitus. The cause of vision loss in diabetic retinopathy is complex and remains incompletely understood. One of the earliest changes in the development of retinopathy is the accelerated apoptosis of retinal microvascular cells and the formation of acellular capillaries by unknown mechanism. Results of a recent research suggest an important role of matrix metalloproteinases (MMPs) in the development of diabetic retinopathy. MMPs are a large family of proteinases that remodel extracellular matrix components, and under pathological condition, its induction is considered as a negative regulator of cell survival; and in diabetes, latent MMPs are activated in the retina and its capillary cells, and activation of MMP-2 and -9 induces apoptosis of retinal capillary cells. This review will focus on the MMP-2 and MMP-9 in the diabetic retina with special reference to oxidative stress, mitochondria dysfunction, inflammation and angiogenesis, as well as summarizing the current information linking these proteins to pathogenesis of diabetic retinopathy.

An experimental study of VEGF induced changes in vasoactivity in pig retinal arterioles and the influence of an anti-VEGF agent

BACKGROUND

Vascular endothelial growth factor (VEGF) plays an important role in ocular physiology. Anti-VEGF agents are now used for treatment of common retinal diseases. This study characterises the vasoactive properties of VEGF in isolated perfused pig retinal arterioles under normal tone or endothelin-1 (ET-1) pre-contracted conditions and determines the influence of an anti VEGF agent on VEGF induced vasoactivity.

METHODS

An isolated perfused retinal arteriole preparation was used. The outer diameter of retinal vessels was monitored at 2 second intervals in response to VEGF and the anti VEGF agent, bevacizumab. The effect of intraluminal delivery of VEGF was determined over a wide concentration range (10(-16) to 10(-7) M) both with and without pre-contraction with ET-1 (3 x 10(-9) M). Bevacizumab (0.35 mg mL(-1)) was applied extraluminally to determine the influence of bevacizumab on VEGF induced vasoactive changes on ET-1 pre-contracted vessels.

RESULTS

In retinal arterioles with normal tone, VEGF induced a concentration dependent contraction at low concentrations, reaching 93.5% at 10(-11) M and then contraction was reduced at higher concentrations, recovering to 98.1% at 10-7 M. VEGF produced a potent concentration dependent vasodilatation in arterioles pre-contracted with ET-1. VEGF induced vasodilatation in arterioles pre-contracted with ET-1 was significantly inhibited by bevacizumab.

CONCLUSIONS

VEGF induced vasoactive changes in pig retinal arterioles are dependent on concentration and vascular tone. Bevacizumab inhibits VEGF-induced vasodilatation in pre-contracted arterioles.

Bone marrow-CNS connections: implications in the pathogenesis of diabetic retinopathy

Diabetic retinopathy is the fourth most common cause of blindness in adults. Current therapies, including anti-VEGF therapy, have partial efficacy in arresting the progression of proliferative diabetic retinopathy and diabetic macular edema. This review provides an overview of a novel, innovative approach to viewing diabetic retinopathy as the result of an inflammatory cycle that affects the bone marrow (BM) and the central and sympathetic nervous systems. Diabetes associated inflammation may be the result of BM neuropathy which skews haematopoiesis towards generation of increased inflammatory cells but also reduces production of endothelial progenitor cells responsible for maintaining healthy endothelial function and renewal. The resulting systemic inflammation further impacts the hypothalamus, promoting insulin resistance and diabetes, and initiates an inflammatory cascade that adversely impacts both macrovascular and microvascular complications, including diabetic retinopathy (DR). This review examines the idea of using anti-inflammatory agents that cross not only the blood-retinal barrier to enter the retina but also have the capability to target the central nervous system and cross the blood-brain barrier to reduce neuroinflammation. This neuroinflammation in key sympathetic centers serves to not only perpetuate BM pathology but promote insulin resistance which is characteristic of type 2 diabetic patients (T2D) but is also seen in T1D. A case series of morbidly obese T2D patients with retinopathy and neuropathy treated with minocycline, a well-tolerated antibiotic that crosses both the blood-retina and blood-brain barrier is presented. Our results indicates that minocycine shows promise for improving visual acuity, reducing pain from peripheral neuropathy, promoting weight loss and improving blood pressure control and we postulate that these observed beneficial effects are due to a reduction of chronic inflammation.

Nerve growth factor promotes endothelial progenitor cell-mediated angiogenic responses

PURPOSE

In response to ischemia, retinal neuronal cells express nerve growth factor (NGF), which can be proangiogenic. Endothelial progenitor cells (EPCs) can participate with the resident vasculature to promote angiogenesis. We postulated that NGF may stimulate CD34⁺ EPCs to convert to an angiogenic phenotype.

METHODS

Human CD34⁺ cells and human retinal endothelial cells (HRECs) were used to examine the effect of NGF on key steps associated with neovascularization. CD34⁺ cells and HRECs were stimulated with NGF (1 to 4 pM) for 24, 48, and 72 hours. Cell migration was measured using a modified Boyden chamber assay. Expression of the receptor for the cytokine stromal derived growth factor 1 (SDF-1), CXCR-4, was assessed by flow cytometry. In vitro angiogenesis was tested using a three-dimensional (3D) extracellular matrix with HRECs/CD34⁺ cell cocultures. NGF receptor activation was assessed by western analysis.

RESULTS

NGF promoted proliferation of CD34⁺ cells but not HRECs. Pretreatment of CD34⁺ cells with NGF increased CXCR-4 expression in CD34⁺ cells, resulting in enhanced migration to SDF-1 (P < 0.0001). The enhanced tubule-forming effect of NGF in HRECs was further potentiated by coculture with NGF-pretreated CD34⁺ cells (P < 0.01). The beneficial effect of NGF was blocked (P < 0.0001) by the ERK inhibitor PD98059. In both CD34⁺ and HRECs, NGF increased phosphorylation of neurotrophic tyrosine kinase receptor type 1 (TrkA) receptor by ERK1 activation (P < 0.01).

CONCLUSIONS

Our in vitro results suggest that NGF released from ischemic nerves in vivo may contribute to the "angiogenic switch" by stimulating the angiogenic behavior of CD34⁺ cells while minimally affecting resident retinal endothelial cells.

The ubiquitin-proteasome system meets angiogenesis

A strict physiological balance between endogenous proangiogenic and antiangiogenic factors controls endothelial cell functions, such that endothelial cell growth is normally restrained. However, in pathologic angiogenesis, a shift occurs in the balance of regulators, favoring endothelial growth. Much of the control of angiogenic events is instigated through hypoxia-induced VEGF expression. The ubiquitin-proteasome system (UPS) plays a central role in fine-tuning the functions of core proangiogenic proteins, including VEGF, VEGFR-2, angiogenic signaling proteins (e.g., the PLCγ1 and PI3 kinase/AKT pathways), and other non-VEGF angiogenic pathways. The emerging mechanisms by which ubiquitin modification of angiogenic proteins control angiogenesis involve both proteolytic and nonproteolytic functions. Here, I review recent advances that link the UPS to regulation of angiogenesis and highlight the potential therapeutic value of the UPS in angiogenesis-associated diseases.

γ-Secretase inhibition of murine choroidal neovascularization is associated with reduction of superoxide and proinflammatory cytokines

PURPOSE

This study aimed to determine whether upregulation of γ-secretase could inhibit laser-induced choroidal neovascularization (CNV) and if this was associated with a reduction in both oxidative stress and proinflammatory cytokines.

METHODS

γ-Secretase, or its catalytic subunit presenilin 1 (PS1), were upregulated by exposure to either pigment epithelial derived factor (PEDF) or an AAV2 vector containing a PS1 gene driven by a vascular endothelial-cadherin promoter. Retinal endothelial cells were infected with AAV2 or exposed to PEDF in the presence or absence of VEGF and in vitro angiogenesis determined. Mouse eyes either received intravitreal injection of PEDF, DAPT (a γ-secretase inhibitor) or PEDF + DAPT at the time of laser injury, or AAV2 infection 3 weeks before receiving laser burns. Lesion volume was determined 14 days post laser injury. Superoxide generation, antioxidant activity and the production of proinflammatory mediators were assessed. Knockdown of γ-secretase was achieved using siRNA.

RESULTS

γ-Secretase upregulation and PS1 overexpression suppressed VEGF-induced in vitro angiogenesis and in vivo laser-induced CNV. This was associated with a reduction in the expression of VEGF and angiogenin 1 together with reduced superoxide anion generation and an increase in MnSOD compared with untreated CNV eyes. PS1 overexpression reduced proinflammatory factors and microglial activation in eyes with CNV compared with control. siRNA inhibition of γ-secretase resulted in increased angiogenesis.

CONCLUSIONS

γ-Secretase, and in particular PS1 alone, are potent regulators of angiogenesis and this is due in part to stabilizing endogenous superoxide generation and reducing proinflammatory cytokine expression during CNV.

Reduced retinal neovascularization, vascular permeability, and apoptosis in ischemic retinopathy in the absence of prolyl hydroxylase-1 due to the prevention of hyperoxia-induced vascular obliteration

PURPOSE

Prolyl hydroxylases (PHDs) are oxygen sensors that stabilize hypoxia-inducible factors (HIFs) to induce proinflammatory, vasopermeability, and proapoptotic factors. These may be potential targets to reduce the complications of ischemic retinopathies.

METHODS

Oxygen-induced ischemic retinopathy (OIR) was generated as a model for retinopathy of prematurity (ROP) by placing 7-day-old mice in 75% oxygen for 5 days and returning them to the relative hypoxia of room air for 5 days. Neovascularization (NV) and avascular areas were assessed on retinal flat-mounts by image analysis. Blood-retinal barrier breakdown was assessed using ³H-mannitol as a tracer. Apoptosis was detected with TUNEL staining. HIF-1α and VEGF were quantified using Western blot analysis and ELISA.

RESULTS

PHD1-deficient mice demonstrated reduced hyperoxia-associated vascular obliteration during oxygen-induced ischemic retinopathy. This was associated with subsequent reduced avascularity, vascular leakage, and pathologic NV during the hypoxic phase, which could be accounted for by a reduced expression of HIF-1α and VEGF. Apoptosis in the retina was also reduced in PHD1-depleted mice after 2 days in hyperoxia.

CONCLUSIONS

PHD1 deficiency is associated with a reduction of ischemia-induced retinal NV. The regulatory mechanism in this model appears to be: PHD1 depletion prevents HIF-1α degradation in hyperoxia, which induces VEGF, thus preventing hyperoxia-related vessel loss. Without a vessel deficiency, there would not be relative hypoxia when the mice are returned to room air and there would be no need to initiate angiogenesis signaling. Blocking PHD1 may be beneficial for ischemic retinopathies and inflammatory and neurodegenerative disorders.

PPAR-gamma, Microglial Cells, and Ocular Inflammation: New Venues for Potential Therapeutic Approaches

The last decade has witnessed an increasing interest for the role played by the peroxisome proliferator-activated receptor-γ (PPAR-γ) in controlling inflammation in peripheral organs as well as in the brain. Activation of PPAR-γ has been shown to control the response of microglial cells, the main macrophage population found in brain parenchyma, and limit the inflammation. The anti-inflammatory capacity of PPAR-γ agonists has led to the hypothesis that PPAR-γ might be targeted to modulate degenerative brain diseases in which inflammation has been increasingly recognized as a significant component. Recent experimental evidence suggests that PPAR-γ agonists could be exploited to treat ocular diseases such as diabetic retinopathy, age-related macular degeneration, autoimmune uveitis, and optic neuritis where inflammation has relevant role. Additional PPAR-γ agonist beneficial effects could involve amelioration of retinal microcirculation and inhibition of neovascularization. However, PPAR-γ activation could, in some instances, aggravate the ocular pathology, for example, by increasing the synthesis of vascular endothelial growth factor, a proangiogenic factor that could trigger a vicious circle and further deteriorate retinal perfusion. The development of new in vivo and in vitro models to study ocular inflammation and how to modulate for the eye benefit will be instrumental for the search of effective therapies.

Netrin-1 overexpression in oxygen-induced retinopathy correlates with breakdown of the blood-retina barrier and retinal neovascularization

PURPOSES

Recent research has shown netrin-1 to promote neovascularization. We evaluate the expression of netrin-1 during retinal neovascularization in a murine model of oxygen-induced retinopathy.

METHODS

C57BL/6J mice were exposed to 75 ± 5% oxygen for 5 days and returned to room air to induce retinal neovascularization. Retinal neovascularization was observed by fluorescence angiography and was quantified by counting the endothelial nuclei protruding into the vitreous cavity after hematoxylin-eosin staining. RT-PCR and Western blot analyses were used to determine retinal netrin-1 mRNA and protein levels at postnatal days (PN) 13, 15 and 17.

RESULTS

In fluorescence angiograms, irregular neovascularization and fluorescein leakage were observed surrounding the unperfused areas in the hypoxic group. The hypoxic group had, on average, 50.70 ± 4.56 neovascular nuclei protruding into the vitreous body, while similar nuclei were absent in the control group. Compared to the normoxic group, there were significant increases in both retinal netrin-1 mRNA and protein levels in the hypoxic group at PN13, PN15 and PN17.

CONCLUSION

The netrin-1 level increases in murine retina under hypoxia and may be key in inducing retinal neovascularization.

Blockade of the sonic hedgehog signalling pathway inhibits choroidal neovascularization in a laser-induced rat model

Sonic hedgehog (Shh) signaling has recently been shown to be involved in the pathological angiogenesis in response to tissue hypoxia and ischemic injury. Hypoxia/ischemia is considered to play an important role in the development of choroidal neovascularization (CNV). This study was aimed to examine the effect of blockade of the Shh signaling pathway on CNV and the underlying mechanism. A total of 64 male Brown-Norway (BN) rats were used in this study. One eye of each rat underwent laser photocoagulation. The other eye served as normal control. After the laser treatment, the 64 rats were divided into four groups (n=16 in each group): Blank control group, in which no intravitreal administration was given; cyclopamine group, recombinant Shh N-terminals protein (rShh) group and phosphate-buffered saline (PBS) group, in which cyclopamine (a Shh inhibitor), rShh (a Shh activator) and PBS were intravitreally injected into the laser-treated eyes respectively every other day for a total of four intravitreal injections immediately after the laser treatment. Fourteen days after the intravitreal administration, the changes of CNV-related variables, including positive CNV lesion percentage, CNV membrane area and CNV membrane thickness, were evaluated by fluorescein angiography, indocyanine green angiography and pathological examinations. The mRNA and protein expression of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 in each group on 14 days of CNV model was detected by real-time quantitative PCR and western blot analysis, and the relationship between the Shh cascade and the HIF-1(α)-VEGF-DLL4 cascade in CNV was analyzed. The results showed that the CNV membrane area and the CNV membrane thickness were decreased by 62.5% and 41.9% in the cyclopamine group and increased by 85.7% and 64.3% in the rShh group in comparison to those in the blank control group (P<0.01 for each). There was no significant difference in the CNV membrane area and thickness between the blank control group and PBS group (P=0.102 and P=0.063, respectively). Real-time quantitative PCR revealed a 5.23-, 4.14-, 2.97-, 2.78- and 2.39-fold up-regulation of the mRNA expression of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 genes in the laser-treated eyes compared with the normal control eyes in the control group. In the cyclopamine group, the mRNA and protein expression of Gli1, HIF-1(α), VEGF and DLL4 was significantly down-regulated (P<0.05 for each) while the expression of PTCH1 showed no significant changes at the mRNA (P=0.293) and protein level (P=0.304). The mRNA expression and protein expression (P=0.001 and P=0.021, respectively) of PTCH1, Gli1, HIF-1(α), VEGF and DLL4 was significantly increased in the rShh group when compared with the control group. The expression level of these genes was related to the severity of the CNV. It was concluded that intravitreal administration of cyclopamine can effectively inhibit the formation of laser-induced experimental CNV by down-regulating the expression of the HIF-1(α)-VEGF-DLL4 cascade in CNV. The Shh signaling pathway as an upstream signaling pathway of HIF-1(α)-VEGF-DLL4 cascade is implicated in the development of experimental CNV.

A therapeutic strategy for choroidal neovascularization based on recruitment of mesenchymal stem cells to the sites of lesions

Choroidal neovascularization (CNV) is a common cause of severe and irreversible visual loss; however, the treatment of CNV has been hindered by its complex and poorly understood pathogenesis. It has been postulated that bone marrow (BM)-derived cells (BMCs) contribute to CNV, but little is known about the role of mesenchymal stem cells (MSCs) in CNV and their therapeutic potential for CNV treatment. We found that BM-derived MSCs transplanted by intravenous injection into laser-induced CNV mouse models were specifically recruited into CNV lesions, where they differentiated into multiple cell types and participated in the development of neovascularization, without stagnation in other organs. By taking advantage of this recruitment potential, engineered MSCs were used to produce the antiangiogenic pigment epithelial-derived factor (PEDF) at the CNV sites, thereby inhibiting the growth of CNVs and stimulating regressive features. Further studies indicated that the effect may be mediated, at least partly, by retinal pigment epithelial (RPE) cells, which function as important regulators for CNV development. These results suggest that MSCs contribute to CNV and could serve as delivery vehicles of antiangiogenic agents for the treatment of a range of CNV-associated diseases.

Discovery and characterization of IGFBP-mediated endocytosis in the human retinal pigment epithelial cell line ARPE-19

Insulin-like growth factor binding proteins (IGFBPs) are prime regulators of IGF-action in numerous cell types including the retinal pigment epithelium (RPE). The RPE performs several functions essential for vision, including growth factor secretion and waste removal via a phagocytic process mediated in part by vitronectin (Vn). In the course of studying the effects of IGFBPs on IGF-mediated VEGF secretion and Vn-mediated phagocytosis in the RPE cell line ARPE-19, we have discovered that these cells avidly ingest synthetic microspheres (2.0 mum diameter) coated with IGFBPs. Given the novelty of this finding and the established role for endocytosis in mediating IGFBP actions in other cell types, we have explored the potential role of candidate cell surface receptors. Moreover, we have examined the role of key IGFBP structural motifs, by comparing responses to three members of the IGFBP family (IGFBP-3, IGFBP-4 and IGFBP-5) which display overlapping variations in primary structure and glycosylation status. Coating of microspheres (FluoSpheres((R)), sulfate modified polystyrene filled with a fluorophore) was conducted at 37 degrees C for 1 h using 20 microg/mL of test protein, followed by extensive washing. Binding of proteins was confirmed using a microBCA assay. The negative control consisted of microspheres treated with 0.1% bovine serum albumin (BSA), and all test samples were post-treated with BSA in an effort to coat any remaining free protein binding sites, which might otherwise encourage non-specific interactions with the cell surface. Serum-starved cultures of ARPE-19 cells were incubated with microspheres for 24 h, using a ratio of approximately 100 microspheres per cell. Uptake of microspheres was quantified using a fluorometer and was confirmed visually by confocal fluorescence microscopy. The ARPE-19 cells displayed little affinity for BSA-treated microspheres, but avidly ingested large quantities of those pre-treated with Vn (ANOVA; p < 0.001). Strong responses were also observed towards recombinant formulations of non-glycosylated IGFBP-3, glycosylated IGFBP-3 and glycosylated IGFBP-5 (all p < 0.001), while glycosylated IGFBP-4 induced a relatively minor response (p < 0.05). The response to IGFBP-3 was unaffected in the presence of excess soluble IGFBP-3, IGF-I or Vn. Likewise, soluble IGFBP-3 did not induce uptake of BSA-treated microspheres. Antibodies to either the transferrin receptor or type 1 IGF-receptor displayed slight inhibitory effects on responses to IGFBPs and Vn. Heparin abolished responses to Vn, IGFBP-5 and non-glycosylated IGFBP-3, but only partially inhibited the response to glycosylated IGFBP-3. Our results demonstrate for the first time IGFBP-mediated endocytosis in ARPE-19 cells and suggest roles for the IGFBP-heparin-binding domain and glycosylation status. These findings have important implications for understanding the mechanisms of IGFBP actions on the RPE, and in particular suggest a role for IGFBP-endocytosis.

Inhibition of retinal neovascularization by gene transfer of small interfering RNA targeting HIF-1alpha and VEGF

Retinal neovascularization (NV) occurs in various ocular disorders including proliferative diabetic retinopathy, retinopathy of prematurity and secondary neovascular glaucoma, which often result in blindness. Vascular endothelial growth factor (VEGF) is an essential growth factor for angiogenesis, and is particularly regulated by hypoxia inducible factor-1alpha (HIF-1alpha) under hypoxic conditions. Therefore, HIF-1alpha and VEGF could provide targets for therapeutic intervention on retinal NV. In this study, we investigated the inhibitory effects of small interfering RNA (siRNA) targeting HIF-1alpha and VEGF on the expression of HIF-1alpha and VEGF in human umbilical vein endothelial cells (HUVEC) in vitro and on retinal NV in vivo. siRNA-expressing plasmids targeting human HIF-1alpha (HIF-1alpha siRNA) and human VEGF(165) (VEGF siRNA) were constructed. They were transfected and co-transfected to HUVEC and C57BL/6J mice of ischemic retinopathy model. HIF-1alpha siRNA and VEGF siRNA specifically downregulated HIF-1alpha and VEGF at both mRNA and protein levels in vitro and in vivo. Neovascular tufts and neovascular nuclei were decreased in gene therapy group compared to control hypoxia group. Co-transfection of HIF-1alpha siRNA and VEGF siRNA resulted in maximal effects on VEGF suppression in vitro and in vivo. It also manifested the maximal inhibitory effect on retinal NV. These results indicate that the application of HIF-1alpha siRNA and VEGF siRNA technology holds great potential as a novel therapeutic for retinal NV.

Inhibition of protein kinase CK2 suppresses angiogenesis and hematopoietic stem cell recruitment to retinal neovascularization sites

Ubiquitous protein kinase CK2 participates in a variety of key cellular functions. We have explored CK2 involvement in angiogenesis. As shown previously, CK2 inhibition reduced endothelial cell proliferation, survival and migration, tube formation, and secondary sprouting on Matrigel. Intraperitoneally administered CK2 inhibitors significantly reduced preretinal neovascularization in a mouse model of proliferative retinopathy. In this model, CK2 inhibitors had an additive effect with somatostatin analog, octreotide, resulting in marked dose reduction for the drug to achieve the same effect. CK2 inhibitors may thus emerge as potent future drugs aimed at inhibiting pathological angiogenesis. Immunostaining of the retina revealed predominant CK2 expression in astrocytes. In human diabetic retinas, mRNA levels of all CK2 subunits decreased, consistent with increased apoptosis. Importantly, a specific CK2 inhibitor prevented recruitment of bone marrow-derived hematopoietic stem cells to areas of retinal neovascularization. This may provide a novel mechanism of action of CK2 inhibitors on newly forming vessels.