Comprehensive gene-expression profile in murine oxygen-induced retinopathy

Development of a Semi-automated Computer-based Tool for the Quantification of Vascular Tortuosity in the Murine Retina

Purpose

The murine oxygen-induced retinopathy (OIR) model is one of the most widely used animal models of ischemic retinopathy, mimicking hallmark pathophysiology of initial vaso-obliteration (VO) resulting in ischemia that drives neovascularization (NV). In addition to NV and VO, human ischemic retinopathies, including retinopathy of prematurity (ROP), are characterized by increased vascular tortuosity. Vascular tortuosity is an indicator of disease severity, need to treat, and treatment response in ROP. Current literature investigating novel therapeutics in the OIR model often report their effects on NV and VO, and measurements of vascular tortuosity are less commonly performed. No standardized quantification of vascular tortuosity exists to date despite this metric's relevance to human disease. This proof-of-concept study aimed to apply a previously published semi-automated computer-based image analysis approach (iROP-Assist) to develop a new tool to quantify vascular tortuosity in mouse models.

Design

Experimental study.

Subjects

C57BL/6J mice subjected to the OIR model.

Methods

In a pilot study, vasculature was manually segmented on flat-mount images of OIR and normoxic (NOX) mice retinas and segmentations were analyzed with iROP-Assist to quantify vascular tortuosity metrics. In a large cohort of age-matched (postnatal day 12 [P12], P17, P25) NOX and OIR mice retinas, NV, VO, and vascular tortuosity were quantified and compared. In a third experiment, vascular tortuosity in OIR mice retinas was quantified on P17 following intravitreal injection with anti-VEGF (aflibercept) or Immunoglobulin G isotype control on P12.

Main Outcome Measures

Vascular tortuosity.

Results

Cumulative tortuosity index was the best metric produced by iROP-Assist for discriminating between OIR mice and NOX controls. Increased vascular tortuosity correlated with disease activity in OIR. Treatment of OIR mice with aflibercept rescued vascular tortuosity.

Conclusions

Vascular tortuosity is a quantifiable feature of the OIR model that correlates with disease severity and may be quickly and accurately quantified using the iROP-Assist algorithm.

Financial Disclosures

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Neurodevelopmental outcome of infants who develop necrotizing enterocolitis: The gut-brain axis

Necrotizing enterocolitis (NEC) poses a significant risk for neurodevelopmental impairment in extremely preterm infants. The gut microbiota shapes the development of the gut, immune system, and the brain; and dysbiosis drive neonatal morbidities including NEC. In this chapter, we delineate a gut-brain axis linking gut microbiota to the adverse neurological outcomes in NEC patients. We propose that in NEC, immaturity of the microbiome along with aberrant gut microbiota-driven immaturity of the gut barrier and immune system can lead to effects including systemic inflammation and circulating microbial mediators. This nexus of gut microbiota-driven systemic effects further interacts with a likewise underdeveloped blood-brain barrier to regulate neuroinflammation and neurodevelopment. Targeting deviant gut-brain axis signaling presents an opportunity to improve the neurodevelopmental outcomes of NEC patients.

Retinopathy of prematurity: contribution of inflammatory and genetic factors

Retinopathy of prematurity (ROP) is a retinal vasoproliferative disorder that represents an important cause of childhood visual impairment and blindness. Although oxidative stress has long been implicated in ROP etiology, other prenatal and perinatal factors are also involved. This review focuses on current research involving inflammation and genetic factors in the pathogenesis of ROP. Increasing evidence suggests that perinatal inflammation or infection contributes to ROP pathogenesis. Cytokines and chemokines with a fundamental role in inflammatory responses and that significantly contributing to angiogenesis are analyzed. Microglia cells, the retinal-resident macrophages, are crucial for retinal homeostasis, however, under sustained pathological stimuli release exaggerated amounts of inflammatory mediators and can promote pathological neovascularization. Current modulation of angiogenic cytokines, such as treatment with antibodies to vascular endothelial growth factor (anti-VEGF), has shown efficacy in the treatment of ocular neovascularization; however, some patients are refractory to anti-VEGF agents, suggesting that other angiogenic or anti-angiogenic cytokines need to be identified. Much evidence suggests that genetic factors contribute to the phenotypic variability of ROP. Several studies have implicated the involvement of candidate genes from different signaling pathways in the development of ROP. However, a genetic component with a major impact on ROP has not yet been discovered. Most studies have limitations and did not replicate results. Future research involving bioinformatics, genomics, and proteomics may contribute to finding more genes associated with ROP and may allow discovering better solutions in the management and treatment of ROP.

Inflammatory mediators in diabetic retinopathy: Deriving clinicopathological correlations for potential targeted therapy

The role of inflammation in diabetic retinopathy (DR) is well-established and dysregulation of a large number of inflammatory mediators is known. These include cytokines, chemokines, growth factors, mediators of proteogenesis, and pro-apoptotic molecules. This para-inflammation as a response is not directed to a particular pathogen or antigen but is rather directed toward the by-products of the diabetic milieu. The inflammatory mediators take part in cascades that result in cellular level responses like neurodegeneration, pericyte loss, leakage, capillary drop out, neovascularization, etc. There are multiple overlaps between the inflammatory pathways occurring within the diabetic retina due to a large number of mediators, their varied sources, and cross-interactions. This makes understanding the role of inflammation in clinical manifestations of DR difficult. Currently, mediator-based therapy for DR is being evaluated for interventions that target a specific step of the inflammatory cascade. We reviewed the role of inflammation in DR and derived a simplified clinicopathological correlation between the sources and stimuli of inflammation, the inflammatory mediators and pathways, and the clinical manifestations of DR. By doing so, we deliberate mediator-specific therapy for DR. The cross-interactions between inflammatory mediators and the molecular cycles influencing the inflammatory cascades are crucial challenges to such an approach. Future research should be directed to assess the feasibility of the pathology-based therapy for DR.

VEGFR1 signaling in retinal angiogenesis and microinflammation

Five vascular endothelial growth factor receptor (VEGFR) ligands (VEGF-A, -B, -C, -D, and placental growth factor [PlGF]) constitute the VEGF family. VEGF-A binds VEGF receptors 1 and 2 (VEGFR1/2), whereas VEGF-B and PlGF only bind VEGFR1. Although much research has been conducted on VEGFR2 to elucidate its key role in retinal diseases, recent efforts have shown the importance and involvement of VEGFR1 and its family of ligands in angiogenesis, vascular permeability, and microinflammatory cascades within the retina. Expression of VEGFR1 depends on the microenvironment, is differentially regulated under hypoxic and inflammatory conditions, and it has been detected in retinal and choroidal endothelial cells, pericytes, retinal and choroidal mononuclear phagocytes (including microglia), Müller cells, photoreceptor cells, and the retinal pigment epithelium. Whilst the VEGF-A decoy function of VEGFR1 is well established, consequences of its direct signaling are less clear. VEGFR1 activation can affect vascular permeability and induce macrophage and microglia production of proinflammatory and proangiogenic mediators. However the ability of the VEGFR1 ligands (VEGF-A, PlGF, and VEGF-B) to compete against each other for receptor binding and to heterodimerize complicates our understanding of the relative contribution of VEGFR1 signaling alone toward the pathologic processes seen in diabetic retinopathy, retinal vascular occlusions, retinopathy of prematurity, and age-related macular degeneration. Clinically, anti-VEGF drugs have proven transformational in these pathologies and their impact on modulation of VEGFR1 signaling is still an opportunity-rich field for further research.

Gene expression profile of the murine ischemic retina and its response to Aflibercept (VEGF-Trap)

Ischemic retinal dystrophies are leading causes of acquired vision loss. Although the dysregulated expression of the hypoxia-responsive VEGF-A is a major driver of ischemic retinopathies, implication of additional VEGF-family members in their pathogenesis has led to the development of multivalent anti-angiogenic tools. Designed as a decoy receptor for all ligands of VEGFR1 and VEGFR2, Aflibercept is a potent anti-angiogenic agent. Notwithstanding, the molecular mechanisms mediating Aflibercept's efficacy remain only partially understood. Here, we used the oxygen-induced retinopathy (OIR) mouse as a model system of pathological retinal vascularization to investigate the transcriptional response of the murine retina to hypoxia and of the OIR retina to Aflibercept. While OIR severely impaired transcriptional changes normally ensuing during retinal development, analysis of gene expression patterns hinted at alterations in leukocyte recruitment during the recovery phase of the OIR protocol. Moreover, the levels of Angiopoietin-2, a major player in the progression of diabetic retinopathy, were elevated in OIR tissues and consistently downregulated by Aflibercept. Notably, GO term, KEGG pathway enrichment, and expression dynamics analyses revealed that, beyond regulating angiogenic processes, Aflibercept also modulated inflammation and supported synaptic transmission. Altogether, our findings delineate novel mechanisms potentially underlying Aflibercept's efficacy against ischemic retinopathies.

Etanercept as a TNF-alpha inhibitor depresses experimental retinal neovascularization

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Short- and long-term impact of hyperoxia on the blood and retinal cells' transcriptome in a mouse model of oxygen-induced retinopathy

BACKGROUND

We aimed to identify global blood and retinal gene expression patterns in murine oxygen-induced retinopathy (OIR), a common model of retinopathy of prematurity, which may allow better understanding of the pathogenesis of this severe ocular prematurity complication and identification of potential blood biomarkers.

METHODS

A total of 120 C57BL/6J mice were randomly divided into an OIR group, in which 7-day-old pups were maintained in 75% oxygen for 5 days, or a control group. RNA was extracted from the whole-blood mononuclear cells and retinal cells on days 12, 17, and 28. Gene expression in the RNA samples was evaluated with mouse gene expression microarrays.

RESULTS

There were 38, 1370 and 111 genes, the expression of which differed between the OIR and control retinas on days 12, 17, and 28, respectively. Gene expression in the blood mononuclear cells was significantly altered only on day 17. Deptor and Nol4 genes showed reduced expression both in the blood and retinal cells on day 17.

CONCLUSION

There are sustained marked changes in the global pattern of gene expression in the OIR mice retinas. An altered expression of Deptor and Nol4 genes in the blood mononuclear cells requires further investigation as they may indicate retinal neovascularization.

Stanniocalcin-1 is a Modifier of Oxygen-Induced Retinopathy Severity

Purpose/Aim: Abnormal activation of signaling pathways related to angiogenesis, inflammation, and oxidative stress has been implicated in the pathophysiology of retinopathy of prematurity (ROP), a leading cause of blindness in pre-term infants. Therapies for ROP include laser and anti-vascular endothelial growth factor agents. However, these therapies have side effects, and even with adequate treatment, visual acuity can be impaired. Novel therapeutic options are needed. Stanniocalcin-1 (STC-1) is a neuroprotective protein with anti-inflammatory and anti-oxidative stress properties. Rodent models of oxygen-induced retinopathy (OIR) were selected to determine whether STC-1 plays a role in the development of OIR.Materials and methods: STC-1 gene and protein expression was first evaluated in the Sprague Dawley rat OIR model that is most similar to human ROP. OIR was then induced in wild-type and Stc-1-/- mice. Retinas were isolated and evaluated for avascular and neovascular area on retinal flat mounts. Quantification of gene expression by quantitative real-time PCR was performed. VEGF was assayed by ELISA in media obtained from induced pluripotent stem-cell-derived retinal pigment epithelial (iPS-RPE) cells following treatment with recombinant STC-1.Results: STC-1 was significantly upregulated in a rat model of OIR compared to room air controls at the gene (P < .05) and protein (P < .001) level. Stc-1-/- OIR mice showed significantly worse ROP compared to wild-type mice as assessed by avascular (20.2 ± 2.4% vs 15.2 ± 2.5%; P = .02) and neovascular area (14.3 ± 2.7% vs 8.8 ± 3.7%; P < .05). Transcript levels of vascular endothelial growth factor-A were significantly higher in Stc-1-/- OIR mice compared to wild-type controls (P = .03). STC-1 reduced VEGF production in iPS-RPE cells (P = .01).Conclusions: STC-1 plays a role in the OIR stress response and development of pathologic vascular features in rodent OIR models by regulating VEGF levels.

Oxygen-induced circRNA profiles and coregulatory networks in a retinopathy of prematurity mouse model

Retinopathy of prematurity (ROP) is a leading cause of childhood blindness. At present, the molecular mechanisms underlying ROP are still far from being clearly understood. Circular RNAs (circRNAs), a novel class of noncoding RNAs, have been reported to serve vital regulatory roles in several human diseases. However, it is still unclear how circRNAs are involved in ROP. In the present study, oxygen-induced retinopathy (OIR) murine retinal samples and paired normal tissues were chosen for high-throughput transcriptome RNA sequencing and bioinformatic analyses. As a result, a total of 236 differentially expressed circRNAs, 14 differentially expressed miRNAs, and 9,756 differentially expressed mRNAs were identified in the OIR samples. Gene ontology analysis showed that angiogenesis ranked in the top five upregulated biological processes associated with differential mRNA expression. Then, 66 co-expression pairs of circRNA-mRNA were predicted according to the mRNAs that were enriched in angiogenesis. Furthermore, coregulation prediction was separately performed to identify the differentially expressed miRNAs that targeted angiogenesis-associated circRNAs or mRNAs. Finally, nine differentially expressed circRNAs were predicted to be competing endogenous RNAs by constructing a circRNA-miRNA-mRNA network followed by reverse transcription-quantitative PCR validation. The results of the present study suggest that the identified set of circRNA transcripts and the potential regulatory mechanisms for the development of ROP are worthy of functional studies.

Identification of altered microRNAs in retinas of mice with oxygen-induced retinopathy

AIM

To identify disease-related miRNAs in retinas of mice with oxygen-induced retinopathy (OIR), and to explore their potential roles in retinal pathological neovascularization.

METHODS

The retinal miRNA expression profile in mice with OIR and room air controls at postnatal day 17 (P17) were determined through miRNA microarray analysis. Several miRNAs were significantly up- and down-regulated in retinas of mice with OIR compared to controls by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). Two databases including Targetscan7.1 and MirdbV5 were used to predict target genes that associated with those significantly altered miRNAs in retinas of mice with OIR. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were also conducted to identify possible biological functions of the target genes.

RESULTS

In comparison with room air controls, 3 and 8 miRNAs were significantly up- and down-regulated, respectively, in retinas of mice with OIR. The qRT-PCR data confirmed that mmu-miR-350-3p and mmu-miR-202-3p were significantly up-regulated, while mmu-miR-711 and mmu-miR-30c-1-3p were significantly down-regulated in mice with OIR compared to controls. GO analysis demonstrated that the identified target genes were related to functions such as cellular macromolecule metabolic process. KEGG pathway analysis showed a group of pathways, such as Wnt signaling pathway, transcriptional misregulation in cancer, Mucin type O-glycan biosynthesis, and mitogen-activated protein kinase (MAPK) signaling pathway might be involved in pathological process of retinal neovascularization.

CONCLUSION

Our findings suggest that the differentially expressed miRNAs in retinas of mice with OIR might provide potential therapeutic targets for treating retinal neovascularization.

Current concepts and techniques of vitrectomy for retinopathy of prematurity

Retinopathy of prematurity (ROP) is a leading cause of childhood blindness worldwide. ROP screening and interventions (e.g., laser ablation and anti-vascular endothelial growth factor [VEGF] therapy) at the right time can reduce disease activity and prevent retinal detachment. However, sometimes, ROP is refractory to treatment, leading to tractional retinal detachment (TRD), requiring surgical intervention, such as vitrectomy. Vitrectomy for Stage 5 ROP (total retinal detachment) is beneficial in preventing total blindness in some patients. However, it has poor anatomical and functional results. Vitrectomy (lens-sparing vitrectomy, if possible) should be performed at Stage 4A ROP (partial TRD not involving the macula) because the anatomical and functional results are much better.

Identification of different macrophage subpopulations with distinct activities in a mouse model of oxygen-induced retinopathy

The aim of the present study was to characterize the phenotypic shift, quantity and role changes in different subgroups of retinal macrophages in a mouse model of oxygen-induced retinopathy (OIR). The mRNA expression levels of macrophage M1 and M2 subgroup marker genes and polarization-associated genes were analyzed by RT-qPCR. The number of M1 and M2 macrophages in our mouse model of OIR was analyzed by flow cytometry at different time points during the progression of OIR. Immunofluorescence whole mount staining of the retinas of mice with OIR was performed at different time points to examine the influx of macrophages, as well as the morphological characteristics and roles of M1 and M2 macrophages. An increased number of macrophages was recruited during the progression of angiogenesis in the retinas of mice with OIR due to the pro-inflammatory microenvironment containing high levels of cell adhesion and leukocyte transendothelial migration molecules. RT-qPCR and flow cytometric analysis at different time points revealed a decline in the number of M1 cells from a significantly high level at post-natal day (P)13 to a relatively normal level at P21, as well as an increase in the number of M2 cells from P13 to P21 in the mice with OIR, implicating a shift of macrophage polarization towards the M2 subtype. Immunofluorescence staining suggested that the M1 cells interacted with endothelial tip cells at the vascular front, while M2 cells embraced the emerging vessels and bridged the neighboring vessel sprouts. Thus, our data indicate that macrophages play an active role in OIR by contributing to the different steps of neovascularization. Our findings indicate that tissue macrophages may be considered as a potential target for the anti-angiogenic therapy of ocular neovascularization disease.

Differentially expressed miRNAs in oxygen‑induced retinopathy newborn mouse models

The present study aimed to identify microRNAs (miRNAs) involved in regulating retinal neovascularization and retinopathy of prematurity (ROP). A total of 80 healthy C57BL/6 neonatal mice were randomly divided into the oxygen-induced retinopathy (OIR) group (n=40), in which 7-day-old mice were maintained in 75% oxygen conditions for 5 days, or the control group (n=40). Following collection of retinal tissue, retinal angiography and hematoxylin and eosin (H&E) staining were performed. Total RNA was also extracted from retinal tissue, and miRNA microarrays and reverse transcription-quantitative polymerase chain reaction (RT-qPCR) were performed to identify differentially expressed miRNAs in the two groups. Retinal angiography and H&E staining revealed damage to retinas in the OIR group. Compared with the control group, 67 miRNAs were differentially expressed in the OIR group, of which 34 were upregulated and 33 were downregulated. Of these differentially expressed miRNAs, 32 exhibited a fold change ≥2, of which 21 were upregulated and 11 were downregulated. The results of RT-qPCR for miR-130a-3p and miR-5107-5p were in accordance with those of the miRNA microarray. The newly identified miRNAs may be important in the development of ROP, and may provide a basis for future research into the mechanisms of ROP.

Interleukin-17A neutralization alleviated ocular neovascularization by promoting M2 and mitigating M1 macrophage polarization

Neovascularization (NV), as a cardinal complication of several ocular diseases, has been intensively studied, and research has shown its close association with inflammation and immune cells. In the present study, the role of interleukin-17A (IL-17A) in angiogenesis in the process of ocular NV both in vivo and in vitro was investigated. Also, a paracrine role of IL-17A was demonstrated in the crosstalk between endothelial cells and macrophages in angiogenesis. In the retinas of mice with retinopathy of prematurity, the IL-17A expression increased significantly at postnatal day 15 (P15) and P18 during retinal NV. Mice given IL-17A neutralizing antibody (NAb) developed significantly reduced choroidal NV and retinal NV. Studies on vascular endothelial growth factor (VEGF) over-expressing mice suggested that IL-17A modulated NV through the VEGF pathway. Furthermore, IL-17A deficiency shifted macrophage polarization toward an M2 phenotype during retinal NV with significantly reduced M1 cytokine expression compared with wild-type controls. In vitro assays revealed that IL-17A treated macrophage supernatant gave rise to elevated human umbilical vascular endothelial cell proliferation, tube formation and VEGF receptor 1 and receptor 2 expression. Therefore, IL-17A could potentially serve as a novel target for treating ocular NV diseases. The limitation of this study involved the potential mechanisms, such as which transcription accounted for macrophage polarization and how the subsequent cytokines were modulated when macrophages were polarized. Further studies need to be undertaken to definitively determine the extent to which IL-17A neutralizing anti-angiogenic activity depends on macrophage modulation compared with anti-VEGF treatment.

Epidermal growth factor-like domain 7 is a marker of the endothelial lineage and active angiogenesis

Epidermal growth factor-like domain 7 (Egfl7) expression in the developing embryo is largely restricted to sites of mesodermal progenitors of angioblasts/hemangioblasts and the vascular endothelium. We hypothesize that Egfl7 marks the endothelial lineage during embryonic development, and can be used to define the emergence of endothelial progenitor cells, as well as to visualize newly-forming vasculature in the embryo and during the processes of physiologic and pathologic angiogenesis in the adult. We have generated a transgenic mouse strain that expresses enhanced green fluorescent protein (eGFP) under the control of a minimal Egfl7 regulatory sequence (Egfl7:eGFP). Expression of the transgene recapitulated that of endogenous Egfl7 at sites of vasculogenesis and angiogenesis in the allantois, yolk sac, and in the embryo proper. The transgene was not expressed in the quiescent endothelium of most adult organs. However, the uterus and ovary, which undergo vascular growth and remodeling throughout the estrus cycle, expressed high levels of Egfl7:eGFP. Importantly, expression of the Egfl7:eGFP transgene was induced in adult neovasculature. We also found that increased Egfl7 expression contributed to pathologic revascularization in the mouse retina. To our knowledge, this is the first mouse model that enables monitoring of endothelial cells at sites of active vasculogenesis and angiogenesis. This model also facilitated the isolation and characterization of EGFL7(+) endothelial cell populations by fluorescence activated cell sorting (FACS). Together, our results demonstrate that the Egfl7:eGFP reporter mouse is a valuable tool that can be used to elucidate the mechanisms by which blood vessels form during development and under pathologic circumstances.

Quantification of vascular tortuosity as an early outcome measure in oxygen induced retinopathy (OIR)

Oxygen-induced retinopathy (OIR) in mice is a popular model system to study pathological angiogenesis in the retinal vasculature. The system is based on vessel depletion by exposure to hyperoxia, which results in acute retinal hypoxia upon return to room air. This hypoxia then triggers neovascularization in the remaining vessels after 5 days. Here we aimed to establish an additional and earlier experimental readout of the vascular response to hypoxia by quantifying the tortuosity of retinal arteries after 2 days. Mouse pups from three different mouse strains were exposed to hyperoxia from postnatal day (P) 7 to P12 and retinas were analysed at P12, P14 and P17. Hypoxia was assessed by staining with the hypoxia marker EF5 and by measuring Vegf mRNA by qPCR. The retinal vasculature was stained in whole mount retinas and tortuosity of radial arterioles was quantified. C57BL/6J mice were used because the vascular response at P17 is well characterised in this strain. We also used C3H/HeJ mice, which contain the retinal degeneration 1 (Rd1) mutation (Pde6b(Rd1)) and have abnormally thin retinas. These thinner, C3H/HeJ retinas do not become ischemic during the OIR model and do not develop neovascularization. They can therefore be used as a control. In addition, we included C3H/HeJ mice that lack the Rd1 mutation (C3H/He(Rd1-)), with normal thickness retinas, to control for strain differences between C57BL/6J and C3H/HeJ. Quantification of vessel tortuosity at P14 showed tortuous arteries in normal thickness retinas (C57BL/6J and C3H/He(Rd1-)) and straight arteries in the thin C3H/HeJ retinas. This correlated with hypoxia, which was severe in normal thickness retinas and mild in the thin C3H/HeJ retinas. Furthermore, at P17 the normal thickness retinas showed strong neovascularisation whereas in the thin C3H/HeJ retinas the retinal vasculature regenerated normally. In conclusion we have demonstrated that arterial tortuosity can act as an early readout for hypoxia in the OIR model before neovascularisation develops.

Next-generation sequencing analysis of gene regulation in the rat model of retinopathy of prematurity

PURPOSE

The purpose of this study was to identify the genes, biochemical signaling pathways, and biological themes involved in the pathogenesis of retinopathy of prematurity (ROP).

METHODS

Next-generation sequencing (NGS) was performed on the RNA transcriptome of rats with the Penn et al. (Pediatr Res 36:724-731, 1994) oxygen-induced retinopathy model of ROP at the height of vascular abnormality, postnatal day (P) 19, and normalized to age-matched, room-air-reared littermate controls. Eight custom-developed pathways with potential relevance to known ROP sequelae were evaluated for significant regulation in ROP: The three major Wnt signaling pathways, canonical, planar cell polarity (PCP), and Wnt/Ca(2+); two signaling pathways mediated by the Rho GTPases RhoA and Cdc42, which are, respectively, thought to intersect with canonical and non-canonical Wnt signaling; nitric oxide signaling pathways mediated by two nitric oxide synthase (NOS) enzymes, neuronal (nNOS) and endothelial (eNOS); and the retinoic acid (RA) signaling pathway. Regulation of other biological pathways and themes was detected by gene ontology using the Kyoto Encyclopedia of Genes and Genomes and the NIH's Database for Annotation, Visualization, and Integrated Discovery's GO terms databases.

RESULTS

Canonical Wnt signaling was found to be regulated, but the non-canonical PCP and Wnt/Ca(2+) pathways were not. Nitric oxide signaling, as measured by the activation of nNOS and eNOS, was also regulated, as was RA signaling. Biological themes related to protein translation (ribosomes), neural signaling, inflammation and immunity, cell cycle, and cell death were (among others) highly regulated in ROP rats.

CONCLUSIONS

These several genes and pathways identified by NGS might provide novel targets for intervention in ROP.

Annexin A2 system in human biology: cell surface and beyond

Annexin A2 (A2) is a multicompartmental, multifunctional protein that orchestrates a growing spectrum of biologic processes. At the endothelial cell surface, A2 and S100A10 (p11) form a heterotetramer, which accelerates tissue plasminogen activator-dependent activation of the fibrinolytic protease, plasmin. In antiphospholipid syndrome, anti-A2 antibodies are associated with clinical thrombosis, whereas overexpression of A2 in acute promyelocytic leukemia promotes hyperfibrinolytic bleeding. A2 is upregulated in hypoxia, and mice deficient in A2 are resistant to oxygen-induced retinal neovascularization, suggesting a role for A2 in human retinal vascular proliferation. In solid malignancies, the (A2•p11)(2) tetramer may promote cancer cell invasion, whereas in multiple myeloma A2 enables malignant plasmacyte growth and predicts prognosis. In the central nervous system, the p11 enables membrane insertion of serotonin receptors that govern mood. In the peripheral nervous system, p11 directs sodium channels to the plasma membrane, enabling pain perception. In cerebral cortex neurons, A2 stabilizes the microtubule-associated tau protein, which, when mutated, is associated with frontotemporal dementia. In inflammatory dendritic cells, A2 maintains late endosomal/lysosomal membrane integrity, thus modulating inflammasome activation and cytokine secretion in a model of aseptic arthritis. Together, these findings suggest an emerging, multifaceted role for A2 in human health and disease.

The association between histological chorioamnionitis, funisitis and neonatal outcome in women with preterm prelabor rupture of membranes

OBJECTIVE

To determine the impact of histological chorioamnionitis (HCA) and funisitis on neonatal outcome in preterm prelabor rupture of membranes (PPROM) pregnancies.

METHODS

Women with PPROM between 24 + 0 to 36 + 6 weeks of gestation, admitted to the Department of Obstetrics and Gynecology at the University Hospital Hradec Kralove in the Czech Republic, between July 2008 and October 2010, were enrolled in the study (n = 231).

RESULTS

The incidence of early-onset sepsis (EOS) differed significantly in neonates born to women with and without HCA, after adjustment for gestational age (11% versus 1%, p = 0.011). The incidence of EOS in neonates was also significantly different, after adjustment for gestational age, in cases with and without funisitis (18% versus 4%, p = 0.002). The same was also found for retinopathy of prematurity (ROP) cases with and without funisitis (23% versus 4%, p = 0.014), after adjustment for gestational age.

CONCLUSIONS

HCA and funisitis increase the risk of adverse perinatal outcome in PPROM pregnancies.

Intravitreal injection of TIMP3 or the EGFR inhibitor erlotinib offers protection from oxygen-induced retinopathy in mice

PURPOSE

Pathological neovascularization is a crucial component of proliferative retinopathies. Previous studies showed that inactivation of A disintegrin and metalloproteinase 17 (ADAM17), a membrane-anchored metalloproteinase that regulates epidermal growth factor receptor (EGFR) signaling, reduces pathological retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR). Here, we tested how genetic inactivation of a physiological ADAM17 inhibitor, the tissue inhibitor of matrix metalloproteinases-3 (TIMP3), or intravitreal injection of TIMP3 or of the EGFR inhibitor erlotinib influenced the outcome of OIR.

METHODS

Wild-type mice were subjected to OIR in a chamber with 75% oxygen for 5 days beginning at postnatal day 7 (P7). Upon removal from the oxygen chamber at P12, they received a single intravitreal injection of TIMP3, erlotinib, or control. The central avascular area and neovascular tufts were measured after 5 days in room air (21% oxygen) at P17. Moreover, OIR experiments were performed with Timp3-/- mice and littermate controls.

RESULTS

Timp3-/- mice showed greater revascularization of the central avascular area and developed equal or fewer neovascular tufts compared to littermate controls, depending on the genetic background. Wild-type mice injected with TIMP3 or erlotinib developed fewer neovascular tufts when compared to untreated littermates. Moreover, vessel regrowth into the avascular area was reduced in TIMP3-injected mice, but not in erlotinib-injected mice.

CONCLUSIONS

These studies demonstrate that TIMP3 and erlotinib inhibit pathological neovascularization in the mouse retina, most likely due to inactivation of ADAM17 and the EGFR, respectively. Thus, TIMP3 and erlotinib emerge as attractive candidate antiangiogenic compounds for prevention and treatment of proliferative retinopathies.

CCN2/CTGF regulates neovessel formation via targeting structurally conserved cystine knot motifs in multiple angiogenic regulators

Blood vessels are formed during development and tissue repair through a plethora of modifiers that coordinate efficient vessel assembly in various cellular settings. Here we used the yeast 2-hybrid approach and demonstrated a broad affinity of connective tissue growth factor (CCN2/CTGF) to C-terminal cystine knot motifs present in key angiogenic regulators Slit3, von Willebrand factor, platelet-derived growth factor-B, and VEGF-A. Biochemical characterization and histological analysis showed close association of CCN2/CTGF with these regulators in murine angiogenesis models: normal retinal development, oxygen-induced retinopathy (OIR), and Lewis lung carcinomas. CCN2/CTGF and Slit3 proteins worked in concert to promote in vitro angiogenesis and downstream Cdc42 activation. A fragment corresponding to the first three modules of CCN2/CTGF retained this broad binding ability and gained a dominant-negative function. Intravitreal injection of this mutant caused a significant reduction in vascular obliteration and retinal neovascularization vs. saline injection in the OIR model. Knocking down CCN2/CTGF expression by short-hairpin RNA or ectopic expression of this mutant greatly decreased tumorigenesis and angiogenesis. These results provided mechanistic insight into the angiogenic action of CCN2/CTGF and demonstrated the therapeutic potential of dominant-negative CCN2/CTGF mutants for antiangiogenesis.

Inflammation and diabetic retinal microvascular complications

Diabetic retinopathy (DR) is one of the most common complications of diabetes and is a leading cause of blindness in people of the working age in Western countries. A major pathology of DR is microvascular complications such as non-perfused vessels, microaneurysms, dot/blot hemorrhages, cotton-wool spots, venous beading, vascular loops, vascular leakage and neovascularization. Multiple mechanisms are involved in these alternations. This review will focus on the role of inflammation in diabetic retinal microvascular complications and discuss the potential therapies by targeting inflammation.

Role of connective tissue growth factor in the retinal vasculature during development and ischemia

PURPOSE

To investigate the function of connective tissue growth factor (CTGF), a matricellular protein of the CCN (Cyr61/CTGF/Nov) family, in retinal vasculature during development and ischemia.

METHODS

CTGF expression was determined using RT-PCR, immunohistochemistry, and transgenic mice carrying CTGF promoter-driven-GFP. CTGF antibody was intraocularly injected into neonates at postnatal day (P)2, and its effect on retinal angiogenesis was analyzed at P4. Transgenic animals expressing GFP regulated by the glial fibrillary acidic protein promoter were used for astrocyte visualization. Retinal vascular occlusion was introduced by rose Bengal and laser photocoagulation on chimeric mice that were reconstituted with GFP+ bone marrow cells. Vascular repair in response to VEGF-A and CTGF was analyzed.

RESULTS

A temporal increase in CTGF at both mRNA and protein levels was observed in the ganglion cell layer and inner nuclear layer during development. Endothelial cells and pericytes were identified as the main cellular sources of CTGF during retinal angiogenesis. CTGF stimulated the migration of astrocytes, retinal endothelial cells, and pericytes in vitro. Inhibition of CTGF by specific antibody affected vascular filopodial extension, growth of the superficial vascular plexus, and astrocyte remodeling. In adult mice, CTGF was prominently expressed in the perivascular cells of arteries. CTGF activated bone marrow-derived perivascular cells and promoted fibrovascular membrane formation in the laser-induced adult retinopathy model.

CONCLUSIONS

CTGF is expressed in vascular beds and acts on multiple cell types. It is important for vessel growth during early retinal development and promotes the fibrovascular reaction in murine retinal ischemia after laser injury.

Mediators involved in retinopathy of prematurity and emerging therapeutic targets

Retinopathy of prematurity (ROP) is a potentially blinding disease of premature infants and despite timely treatment some infants develop retinal detachment and sight loss. Current treatment utilises laser therapy which causes destruction of treated retinal tissue resulting in field loss. There is considerable research work ongoing on neovascular eye disease which is likely to result in antiangiogenic approaches that will arrest the development of ROP by specifically targeting the involved molecular mediators. Some of these new therapeutic interventions have entered clinical trials. This article reviews new information available on the molecular pathogenesis of ROP which may result in novel treatments for ROP; it does not discuss the well-known role of oxygen in the development of ROP.

Anti-inflammatory therapy for diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common complications of diabetes. This devastating disease is a leading cause of blindness in people of working age in industrialized countries and affects the daily lives of millions of people. Despite tight glycemic control, blood pressure control and lipid-lowering therapy, the number of DR patients keeps growing and therapeutic approaches are limited. Moreover, there are significant limitations and side effects associated with the current therapies. Thus, there is a great need for development of new strategies for prevention and treatment of DR. Studies have shown that DR has prominent features of chronic, subclinical inflammation. This article focuses on the role of inflammation in DR and summarizes the progress of studies of anti-inflammatory strategies for DR.

Placenta microbiology and histology and the risk for severe retinopathy of prematurity

PURPOSE

To test the hypothesis that the presence of bacteria and/or histologic inflammation in the placenta of infants born preterm is associated with an increased risk for severe retinopathy of prematurity (ROP).

METHODS

This was a prospective cohort study. Exploratory and multivariable data analyses were used, including logistic regression models with interaction terms. Main outcomes were four definitions of severe ROP: stage 3 or higher, any ROP in zone I, prethreshold/threshold, and plus disease.

RESULTS

Individually, placenta bacteria and histologic inflammation were not associated with severe ROP in univariable analyses among 1064 infants with gestational age <28 weeks or among 715 infants with gestational age <27 weeks (we excluded infants with a gestational age of 27 weeks because of the very small number of ROP cases). However, the co-occurrence of bacteria and inflammation was associated with an increased risk for ROP in zone I (odds ratio, 3.1; 95% confidence interval, 1.02-9.5). Among 339 infants with any placental bacteria, the co-occurrence of (1) inflammation and a gestational age of 23 to 24 weeks and (2) inflammation and hyperoxia were associated with prominent increases in risk for all definitions of severe ROP.

CONCLUSIONS

While antenatal exposure to infection or inflammation alone does not appear to convey risk information for severe ROP, their co-occurrence does. This finding supports the hypothesis that a fetal inflammatory response to antenatal infection might be part of the etiology of severe ROP.

Vitreous levels of angiopoietin-1 and angiopoietin-2 in eyes with retinopathy of prematurity

PURPOSE

To determine the vitreous levels of angiopoietin (Ang)-1 and Ang-2 in eyes with retinopathy of prematurity (ROP), and to determine the correlation between the 2 levels.

DESIGN

Retrospective case-control study.

METHODS

Forty-eight eyes with stage 4 ROP were studied. Six eyes with congenital cataract were used as controls. The ROP eyes were classified by the vascular activity into highly (n = 22), moderately (n = 15), and mildly (n = 11) vascular-active ROP. Eyes with highly vascular-active ROP initially received 0.5 mg of intravitreal bevacizumab (IVB) and underwent vitrectomy within 1 week. The others underwent vitrectomy without IVB. Vitreous samples were collected at the beginning of vitrectomy, and the vitreous levels of Angs were measured by enzyme-linked immunosorbent assay.

RESULTS

The mean concentrations of Ang-1 and Ang-2 were 201.9 and 7832.1 pg/mL in highly vascular-active ROP eyes, 216.1 and 7731.2 pg/mL in moderately vascular-active ROP eyes, 533.8 and 1685.9 pg/mL in mildly vascular-active ROP eyes, and 0 and 41.5 pg/mL in control eyes. The vitreous Ang-1 level was significantly higher (P < .05) in highly, moderately, and mildly vascular-active ROP eyes than in control eyes. The vitreous Ang-2 level was significantly higher (P < .05) in highly and moderately vascular-active ROP eyes than in control eyes. There was a significant negative correlation (r = -0.406; P = .040) between the Ang-1 and Ang-2 levels in moderately and mildly vascular-active ROP eyes.

CONCLUSIONS

The balance of Ang-1 and Ang-2 in the vitreous may be important in the pathogenesis of ROP.

Gene expression changes in a rat model of oxygen-induced retinopathy

PURPOSE

To identify altered patterns of retinal mRNA expression in a rat model of oxygen-induced retinopathy (OIR).

METHODS

Sprague-Dawley rats from P2 to P14 were exposed to hyperoxia (80% oxygen) to induce OIR and then returned to normoxic conditions. Control rats were sustained in room air. Retinal gene expression between the rats of OIR and the controls was compared using cDNA microarray analysis. Reverse transcriptase polymerase chain reaction (RT-PCR) was used to verify the microarray results.

RESULTS

Among a total of 12,731 cDNAs analyzed by microarray, 13 genes were strongly up- or down-regulated (>2-fold change over controls) in the OIR rats. We found a significant increase in expression of 10 genes (CaM-kinase II inhibitor; acidic nuclear phosphoprotein 32 family, member A; vascular endothelial growth factor; interferon α-inducible protein 27-like; similar to enthoprotin, epsin 4, clathrin interacting protein; nidogen [entactin]; tubulin, β5; fibrillin-1; spectrin β2; and stearoyl-coenzyme A desaturase 2) and a significant decrease in expression of 3 genes (myelin-associated oligodendrocytic basic protein, heat shock protein, and decorin) in OIR rats compared to controls.

CONCLUSIONS

We confirmed changes in expressions of various retinal genes in a rat model of OIR by microarray and RT-PCR. This study should contribute to the understanding of genetic indicators associated with OIR.

The clustering of disorders in infants born before the 28th week of gestation

AIM

To see whether disorders prevalent in infants born extremely preterm cluster.

DESIGN

Observational cohort study.

SETTING

  University-affiliated newborn intensive care nurseries.

SUBJECTS

  One thousand two hundred and twenty-three infants born before the 28th week of gestation who survived until 36 weeks postmenstrual age when the diagnosis of bronchopulmonary dysplasia (BPD) could be made.

INTERVENTIONS

  None.

MAIN OUTCOME MEASURES

  Cerebral white matter damage (an echolucent lesion, or moderate or severe ventriculomegaly on a protocol cranial ultrasound scan), BPD, retinopathy of prematurity (ROP), necrotizing enterocolitis (NEC) and early and late bacteremia.

RESULTS

After adjustment for gestational age, children who had severe NEC (Bell stage IIIb) were at increased risk of cerebral white matter damage, severe ROP (stage 3+), and severe BPD (defined as both oxygen and ventilator dependent). Children who had early bacteremia were at increased risk of late bacteremia and severe ROP. Those who had severe ROP were at increased risk of severe BPD and both early and late bacteremia.

CONCLUSIONS

  Necrotizing enterocolitis is the disorder common to most of the clusters, but we do not know if its onset occurred before the others. Organ-damage-promoting substances, however, have been found in the circulation of newborn animals with bowel inflammation, supporting the view that NEC contributes to the damage of other organs.

Gene expression microarray analysis of early oxygen-induced retinopathy in the rat

Different inbred strains of rat differ in their susceptibility to oxygen-induced retinopathy (OIR), an animal model of human retinopathy of prematurity. We examined gene expression in Sprague-Dawley (susceptible) and Fischer 344 (resistant) neonatal rats after 3 days exposure to cyclic hyperoxia or room air, using Affymetrix rat Genearrays. False discovery rate analysis was used to identify differentially regulated genes. Such genes were then ranked by fold change and submitted to the online database, DAVID. The Sprague-Dawley list returned the term "response to hypoxia," absent from the Fischer 344 output. Manual analysis indicated that many genes known to be upregulated by hypoxia-inducible factor-1alpha were downregulated by cyclic hyperoxia. Quantitative real-time RT-PCR analysis of Egln3, Bnip3, Slc16a3, and Hk2 confirmed the microarray results. We conclude that combined methodologies are required for adequate dissection of the pathophysiology of strain susceptibility to OIR in the rat. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12177-009-9041-7) contains supplementary material, which is available to authorized users.