von Hippel-Lindau protein regulates transition from the fetal to the adult circulatory system in retina

Inhibition of hypoxia-inducible factors suppresses subretinal fibrosis

Age-related macular degeneration (AMD) is a common cause of vision loss. The aggressive form of AMD is associated with ocular neovascularization and subretinal fibrosis, representing a responsive outcome against neovascularization mediated by epithelial-mesenchymal transition of retinal pigment epithelium (RPE) cells. A failure of the current treatment (anti-vascular endothelial growth factor therapy) has also been attributed to the progression of subretinal fibrosis. Hypoxia-inducible factors (HIFs) increase gene expressions to promote fibrosis and neovascularization. HIFs act as a central pathway in the pathogenesis of AMD. HIF inhibitors may suppress ocular neovascularization. Nonetheless, further investigation is required to unravel the aspects of subretinal fibrosis. In this study, we used RPE-specific HIFs or von Hippel-Lindau (VHL, a regulator of HIFs) conditional knockout (cKO) mice, along with pharmacological HIF inhibitors, to demonstrate the suppression of subretinal fibrosis. Fibrosis was suppressed by treatments of HIF inhibitors, and similar suppressive effects were detected in RPE-specific Hif1a/Hif2a- and Hif1a-cKO mice. Promotive effects were observed in RPE-specific Vhl-cKO mice, where fibrosis-mediated pathologic processes were evident. Marine products' extracts and their component taurine suppressed fibrosis as HIF inhibitors. Our study shows critical roles of HIFs in the progression of fibrosis, linking them to the potential development of therapeutics for AMD.

Reappearance of excentric persistent fetal vasculature stalk following laser treatment in a patient with type 1 retinopathy of prematurity

PURPOSE

In this report, we aim to present an unusual reappearance of hyaloidal artery remnant with atypical localization during the follow-up of an infant who underwent indirect laser photocoagulation for type 1 ROP.

METHODS

Retrospective case report.

RESULTS

We report a case of reappearance of an eccentrically located hyaloidal stalk in the macular area during the follow-up period, 2 weeks after laser photocoagulation for type 1 ROP subsequently progressed to cause foveal distortion, which is successfully removed with a lens-sparing vitrectomy.

CONCLUSIONS

To the best of our knowledge, there is no similar case in the literature. In the presence of fibrovascular proliferation extending into the vitreous, especially in premature infants, it should be kept in mind that this may be a reappearance of PFV and it may not always be located on the optic disc.

Drusen in AMD from the Perspective of Cholesterol Metabolism and Hypoxic Response

Drusen are one of the most characteristic pathologies of precursor lesion of age-related macular degeneration (AMD). Drusen comprise a yellowish white substance that accumulates typically under the retinal pigment epithelium (RPE), and their constituents are lipids, complement, amyloid, crystallin, and others. In the past, many researchers have focused on drusen and tried to elucidate the pathophysiology of AMD because they believed that disease progression from early AMD to advanced AMD might be based on drusen or drusen might cause AMD. In fact, it is well established that drusen are the hallmark of precursor lesion of AMD and a major risk factor for AMD progression mainly based on their size and number. However, the existence of advanced AMD without drusen has long been recognized. For example, polypoidal choroidal vasculopathy (PCV), which comprises the majority of AMD cases in Asians, often lacks drusen. Thus, there is the possibility that drusen might be no more than a biomarker of AMD and not a cause of AMD. Now is the time to reconsider the relationship between AMD and drusen. In this review, we focus on early AMD pathogenesis based on basic research from the perspective of cholesterol metabolism and hypoxic response in the retina, and we discuss the role of drusen.

Integrated network pharmacology and experimental validation to explore the potential pharmacological mechanism of Qihuang Granule and its main ingredients in regulating ferroptosis in AMD

BACKGROUND

Qihuang Granule (QHG) is a traditional prescription  that has exhibited potential in safeguarding against age-related maculopathy (AMD). Salvia miltiorrhiza (SM) and Fructus lycii (FL) are the main components of QHG. Ferroptosis, a newly discovered, iron-dependent, regulated cell death pathway, have been implicated in the pathogenesis of AMD. This study delves into the intricate mechanism by which SM/FL and QHG confer protection against AMD by modulating the ferroptosis pathway, employing a combination of network pharmacology and experimental validation.

METHODS

Bioactive compounds and potential targets of SM and FL were gathered from databases such as TCMSP, GeneCard, OMIM, and FerrDb, along with AMD-related genes and key genes responsible for ferroptosis regulation. Gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis and protein-protein interaction (PPI) network were performed to discover the potential mechanism. The construction of an interaction network involving AMD, ferroptosis, SM/FL potential target genes was facilitated by the STRING database and realized using Cytoscape software. Subsequent validation was accomplished through molecular docking and in vitro cell experiments.

RESULTS

Noteworthy active compounds including quercetin, tanshinone IIA, luteolin, cryptotanshinone, and hub targets such as HIF-1α, EGFR, IL6, and VEGFA were identified. KEGG enrichment unveiled the HIF-1 signalling pathway as profoundly enriched, and IL6 and VEGF were involved. The molecular docking revealed the significant active compounds with hub genes and quercetin showed good binding to HIF-1α, which is involved in inflammation and angiogenesis. Experimental results verified that both herbs and QHG could regulate key ferroptosis-related targets in the retinal pigment epithelium and inhibit the expression of HIF-1α, VEGFA, and IL-6, subsequently increase cell viability and decrease the ROS content induced by H2O2.

CONCLUSION

This study demonstrates the molecular mechanism through which SM/FL and QHG protect against AMD and emerges as a plausible mechanism underlying this protection.

Mitophagy in the retina: Viewing mitochondrial homeostasis through a new lens

Mitochondrial function is key to support metabolism and homeostasis in the retina, an organ that has one of the highest metabolic rates body-wide and is constantly exposed to photooxidative damage and external stressors. Mitophagy is the selective autophagic degradation of mitochondria within lysosomes, and can be triggered by distinct stimuli such as mitochondrial damage or hypoxia. Here, we review the importance of mitophagy in retinal physiology and pathology. In the developing retina, mitophagy is essential for metabolic reprogramming and differentiation of retina ganglion cells (RGCs). In basal conditions, mitophagy acts as a quality control mechanism, maintaining a healthy mitochondrial pool to meet cellular demands. We summarize the different autophagy- and mitophagy-deficient mouse models described in the literature, and discuss the potential role of mitophagy dysregulation in retinal diseases such as glaucoma, diabetic retinopathy, retinitis pigmentosa, and age-related macular degeneration. Finally, we provide an overview of methods used to monitor mitophagy in vitro, ex vivo, and in vivo. This review highlights the important role of mitophagy in sustaining visual function, and its potential as a putative therapeutic target for retinal and other diseases.

ARMC5 is part of an RPB1-specific ubiquitin ligase implicated in adrenal hyperplasia

ARMC5 is implicated in several pathological conditions, but its function remains unknown. We have previously identified CUL3 and RPB1 (the largest subunit of RNA polymerase II (Pol II) as potential ARMC5-interacting proteins. Here, we show that ARMC5, CUL3 and RBX1 form an active E3 ligase complex specific for RPB1. ARMC5, CUL3, and RBX1 formed an active E3 specific for RPB1. Armc5 deletion caused a significant reduction in RPB1 ubiquitination and an increase in an accumulation of RPB1, and hence an enlarged Pol II pool in normal tissues and organs. The compromised RPB1 degradation did not cause generalized Pol II stalling nor depressed transcription in the adrenal glands but did result in dysregulation of a subset of genes, with most upregulated. We found RPB1 to be highly expressed in the adrenal nodules from patients with primary bilateral macronodular adrenal hyperplasia (PBMAH) harboring germline ARMC5 mutations. Mutant ARMC5 had altered binding with RPB1. In summary, we discovered that wildtype ARMC5 was part of a novel RPB1-specific E3. ARMC5 mutations resulted in an enlarged Pol II pool, which dysregulated a subset of effector genes. Such an enlarged Pol II pool and gene dysregulation was correlated to adrenal hyperplasia in humans and KO mice.

SIRT1: Genetic Variants and Serum Levels in Age-Related Macular Degeneration

Background: The aim of this paper was to determine the frequency of SIRT1 rs3818292, rs3758391, rs7895833 single nucleotide polymorphism genotypes and SIRT1 serum levels associated with age-related macular degeneration (AMD) in the Lithuanian population. Methods: Genotyping of SIRT1 rs3818292, rs3758391 and rs7895833 was performed using RT-PCR. SIRT1 serum level was determined using the ELISA method. Results: We found that rs3818292 and rs7895833 were associated with an increased risk of developing exudative AMD. Additional sex-differentiated analysis revealed only rs7895833 was associated with an increased risk of developing exudative AMD in women after strict Bonferroni correction. The analysis also revealed that individuals carrying rs3818292, rs3758391 and rs7895833 haplotype G-T-G are associated with increased odds of exudative AMD. Still, the rare haplotypes were associated with the decreased odds of exudative AMD. After performing an analysis of serum SIRT1 levels and SIRT1 genetic variant, we found that carriers of the SIRT1 rs3818292 minor allele G had higher serum SIRT1 levels than the AA genotype. In addition, individuals carrying at least one SIRT1 rs3758391 T allele also had elevated serum SIRT1 levels compared with individuals with the wild-type CC genotype. Conclusions: Our study showed that the SIRT1 polymorphisms rs3818292 and rs7895833 and rs3818292-rs3758391-rs7895833 haplotype G-T-G could be associated with the development of exudative AMD. Also, two SNPs (rs3818292 and rs3758391) are associated with elevated SIRT1 levels.

Mapping transgene insertion sites reveals the α-Cre transgene expression in both developing retina and olfactory neurons

The Tg(Pax6-cre,GFP)^2Pgr (α-Cre) mouse is a commonly used Cre line thought to be retinal-specific. Using targeted locus amplification (TLA), we mapped the insertion site of the transgene, and defined primers useful to deduce zygosity. Further analyses revealed four tandem copies of the transgene. The insertion site mapped to clusters of vomeronasal and olfactory receptor genes. Using R26R and Ai14 Cre reporter mice, we confirmed retinal Cre activity, but also detected expression in Gα₀⁺ olfactory neurons. Most α-Cre⁺ olfactory neurons do not express Pax6, implicating the influence of neighboring regulatory elements. RT-PCR and buried food pellet test did not detect any effects of the transgene on flanking genes in the nasal mucosa and retina. Together, these data precisely map α-Cre, show that it does not affect surrounding loci, but reveal previously unanticipated transgene expression in olfactory neurons. The α-Cre mouse can be a valuable tool in both retinal and olfactory research.

The Pax6-α-Cre mouse line used in retinal studies actually contains four transgene insertion within gene clusters of olfactory and vomeronasal receptors, leading to expression in not just retinal, but also olfactory and vomeronasal sensory neurons.

Limited hyperoxia-induced proliferative retinopathy: A model of persistent retinal vascular dysfunction, preretinal fibrosis and hyaloidal vascular reprogramming for retinal rescue

Background

Retinopathy of prematurity (ROP) remains the leading cause for blindness in children. Limited hyperoxia induced proliferative retinopathy (L-HIPR) was recently introduced as a potential animal model for ROP and persistent fetal vasculature; however, the detailed pathological changes remain unclear.

Methods

To model L-HIPR, we placed C57BL/6J mice in 65% oxygen from birth to post-natal day 7 (P7). We examined eyes at intervals between P12 and P30. Retinal morphometry, thickness, and preretinal fibrosis were quantified at different time points on histological sections stained with hematoxylin and eosin (H&E) and Masson Trichrome, respectively. Vascular development, angiogenesis, inflammation, and pericyte coverage were analyzed using immunohistochemistry staining in retinal flat mounts and cross sections.

Results

In L-HIPR, the hyaloidal vessels persisted until the latest time point in this study, P30 and began to invaginate the peripheral then central retina starting at P12. Central retinal distortion was noted beginning at P17, while the peripheral retina demonstrated a trend of thinning from P12 to P30. We found that L-HIPR was associated with delayed and abnormal retinal vascular development with subsequent retinal inflammation, pericyte loss and preretinal fibrosis.

Conclusion

Our study presents a detailed analysis of the L-HIPR animal model demonstrating vitreoretinal pathologic changes, preretinal fibrosis and persistent hyaloidal vessels into adulthood. Based on our findings, we suggest that the persistence and peculiar stepwise migration of the hyaloidal vessels into the retina may provide a potential rescue mechanism for inner retinal development that deserves further study.

Markers of Hypoxia and Metabolism Correlate With Cell Differentiation in Retina and Lens Development

Recent studies have provided novel insights of co-development of the neural and vascular elements of the retina. Knowledge of these relationships are crucial to understand the impact of therapeutic measures in Retinopathy of Prematurity (ROP). ROP is imposed by therapeutic oxygen upon immature retinal blood vessels and neural cells causing delayed development and vascular regression. However, the impact of hyperoxia on developing retinal neurons is less understood because some aspects of normal development remain unknown. The metabolic changes during differentiation of retinal progenitor cells to functional neurons is one such aspect. We correlated immunomarkers of hypoxia with markers of metabolic change in developing retinal neurons during the early postnatal period in mice. The same marker proteins were studied in secondary lens fiber differentiation at postnatal day-3 (P3). Nuclear localization of the oxygen-sensitive subunits of hypoxia inducible factor, HIF-1α and HIF-2α was correlated with increasing mitochondrial content in differentiating neurons. Nuclear HIF was also correlated with AMP-dependent protein kinase (AMPK), and the AMPK phosphorylation target PPAR-gamma coactivator-1alpha (PGC-1α), the principal regulator of mitochondrial biogenesis. Expression of AMPK, PGC1α and HIF-2α in secondary fiber differentiation was visible in each profile of the lens equator. Strong nuclear localization for all markers was present at the onset of secondary fiber differentiation, and reflected changes in size, mitochondrial content, and metabolism. We speculate that the 'physiological hypoxia' that drives retinal vascular development is cell-specific and reliant upon neuronal differentiation and mitochondrial biogenesis. We suggest that the onset of differentiation increases energy consumption that is detected by AMPK. In turn AMPK increases mitochondrial biogenesis via PGC-1α. Mitochondrial oxygen consumption may then create intracellular hypoxia that activates HIF. This progression is congruent with the expression of these markers in secondary lens fiber differentiation and nuclear localization of HIF-2α. Nuclear localization of HIF-1α and HIF-2α in the postnatal retina is less defined than in the lens as it may involve the remnant of HIF expression from the embryonic period that is sustained and increased by intracellular hypoxia caused by increasing mitochondrial oxygen consumption. This the first report of the involvement of HIF-2α, AMPK and PGC-1α in lens development.

Retinal Diseases Regulated by Hypoxia-Basic and Clinical Perspectives: A Comprehensive Review

In recent years, the number of patients with age-related macular degeneration (AMD) is increasing worldwide along with increased life expectancy. Currently, the standard treatment for wet-AMD is intravitreal injection of anti-vascular endothelial growth factor (VEGF) drugs. The upstream of VEGF is hypoxia-inducible factor (HIF), a master regulator of hypoxia-responsive genes responsive to acute and chronic hypoxia. HIF activation induces various pathological pro-angiogenic gene expressions including VEGF under retinal hypoxia, ultimately leading to the development of ocular ischemic neovascular diseases. In this regard, HIF is considered as a promising therapeutic target in ocular ischemic diseases. In clinical ophthalmology, abnormal hypofluorescent areas have been detected in the late-phase of indocyanine green angiography, which are thought to be lipid deposits at the level of Bruch’s membrane to choriocapillaris in vitreoretinal diseases. These deposits may interfere with the oxygen and nutrients that should be supplied to the retinal pigment epithelium, and that HIF/VEGF is highly suspected to be expressed in the hypoxic retinal pigment epithelium, leading to neovascularization. In this review, we comprehensively summarize pathophysiology of AMD-related ocular diseases with the HIF/VEGF pathway from basic and clinic researches with recent findings.

Clinical Pathological Features and Current Animal Models of Type 3 Macular Neovascularization

Type 3 macular neovascularization (MNV3), or retinal angiomatous proliferation (RAP), is a distinct type of neovascular age-related macular degeneration (AMD), which is a leading cause of vision loss in older persons. During the past decade, systematic investigation into the clinical, multimodal imaging, and histopathological features and therapeutic outcomes has provided important new insight into this disease. These studies favor the retinal origin of MNV3 and suggest the involvement of retinal hypoxia, inflammation, von Hippel–Lindau (VHL)–hypoxia-inducible factor (HIF)–vascular endothelial growth factor (VEGF) pathway, and multiple cell types in the development and progression of MNV3. Several mouse models, including the recently built Rb/p107/Vhl triple knockout mouse model by our group, have induced many of the histological features of MNV3 and provided much insight into the underlying pathological mechanisms. These models have revealed the roles of retinal hypoxia, inflammation, lipid metabolism, VHL/HIF pathway, and retinoblastoma tumor suppressor (Rb)–E2F cell cycle pathway in the development of MNV3. This article will summarize the clinical, multimodal imaging, and pathological features of MNV3 and the diversity of animal models that exist for MNV3, as well as their strengths and limitations.

Inhibition of the HIF-1α/BNIP3 pathway has a retinal neuroprotective effect

Retinal ischemia is a leading cause of irreversible blindness worldwide. Inner retinal dysfunction including loss of retinal ganglion cells is encountered in a number of retinal ischemic disorders. We previously reported administration of two different hypoxia-inducible factor (HIF) inhibitors exerted neuroprotective effects in a murine model of retinal ischemia/reperfusion (I/R) which mimics these disorders, as inner retinal degeneration could be involved in pathological HIF induction. However, this notion needs further investigation. Therefore, in this study, we attempted to use retina-specific Hif-1α conditional knockout (cKO) mice to uncover this notion more clearly under the same condition. Hif-1α cKO mice showed inner retinal neurodegeneration to a lesser extent than control mice. Hif-1α depletion in a murine 661W retinal cell line reduced cell death under pseudohypoxic and hypoxic conditions. Among hypoxia-related genes, the expression of BCL2 19 kDa protein-interacting protein 3 (Bnip3) was substantially upregulated in the inner retinal layer after retinal I/R. In this regard, we further examined Bnip3 depletion in retinal neurons in vitro and in vivo and found the similar neuroprotective effects. Our results support the notion that the HIF-1α/BNIP3 pathway may have a critical role in inner retinal neurodegeneration, which can be linked with the development of new promising therapeutics for inner retinal ischemic disorders.

Structural and microvascular changes of the peripapillary retinal nerve fiber layer in Von Hippel-Lindau disease: an OCT and OCT angiography study

Von Hippel–Lindau (VHL) disease is an autosomal dominant genetic disease caused by VHL gene mutation. Retinal hemangioblastomas (RH) are vascularized tumors and represent the main ocular manifestation of the disease. Histopathologically, RH are composed of capillary vessels and stromal cells, the neoplastic population of the lesion. The origin of these stromal cells remains controversial, even if they are hypothesized to be glial cells. The aim of the present study was to investigate neuronal and microvascular changes of the peripapillary retinal nerve fiber layer, in which glial cells, neurons and capillaries (the radial peripapillary capillary plexus) interact. VHL patients with or without peripheral RH were enrolled and compared to healthy controls. Mean peripapillary retinal nerve fiber layer (pRNFL) thickness was measured by means of optical coherence tomography (OCT). The following vascular parameters of the radial peripapillary capillary plexus were quantified using OCT angiography: Vessel Area Density,Vessel Length Fraction, Vessel Diameter Index and Fractal Dimension. One hundred and nine eyes of 61 patients, and 56 eyes of 28 controls were consecutively studied. Mean pRNFL was significantly thinner in VHL eyes without RH versus eyes with RH and controls. Mean pRNFL thickness did not differ between VHL eyes with RH and controls. All OCTA vascular parameters were reduced in VHL eyes with or without RH versus controls, with significative difference for Vessel Diameter Index. The same OCTA parameters did not significantly differ between VHL eyes with or without RH. In VHL eyes without RH, pRNFL thinning may be the consequence of impaired perfusion of the radial peripapillary capillary plexus, while the increase of pRNFL thickness in VHL eyes with RH may depend on possible activation and proliferation of the other RNFL resident cells, the glial cells.

Single transient intraocular pressure elevations cause prolonged retinal ganglion cell dysfunction and retinal capillary abnormalities in mice

Transient intraocular pressure (IOP) elevations are likely to occur in certain forms of glaucoma and after intravitreal injections to treat various retinal diseases. However, the impact of these transient IOP elevations on the physiology of individual retinal ganglion cells (RGCs) is unknown. In this report, we explore how transient IOP elevations in mice affect RGC physiology, RGC anatomy, and retinal arteriole and capillary structure. Transient IOP elevation was induced in 12-week old wild type C57BL6J mice by injecting sodium hyaluronate into the anterior chamber. IOP was measured immediately after the injection and again 1 and 7 days later. Average peak IOP after injection was ~50 mmHg and subsequent IOPs returned to normal. RGC physiology was assessed with a multielectrode array (MEA) by calculating a spike triggered average (STA) at the same time points. RGC counts and retinal vascular structure were assessed 14 days after injection with immunohistochemistry to label RGCs and blood vessels. Transient IOP elevation caused a marked reduction of scotopic STA presence and delayed center and surround STA peak times that did not recover. Transient IOP elevation also caused a reduced photopic receptive field size and spontaneous firing rate, both of which showed some recovery with time. Transient IOP elevation also induced vascular remodeling: the number of capillary branches was decreased within the superficial and intermediate vascular plexi. RGC counts, retinal arteriole diameter, and deep capillary plexus branching were unaffected. These previously unappreciated findings suggest that transient IOP elevation may cause unrecognized and potentially long-term pathology to RGCs and associated neurovascular units which should be accounted for in clinical practice.

Molecular and Mechanical Mechanisms Regulating Ductus Arteriosus Closure in Preterm Infants

Failure of ductus arteriosus closure after preterm birth is associated with significant morbidities. Ductal closure requires and is regulated by a complex interplay of molecular and mechanical mechanisms with underlying genetic factors. In utero patency of the ductus is maintained by low oxygen tension, high levels of prostaglandins, nitric oxide and carbon monoxide. After birth, ductal closure occurs first by functional closure, followed by anatomical remodeling. High oxygen tension and decreased prostaglandin levels mediated by numerous factors including potassium channels, endothelin-1, isoprostanes lead to the contraction of the ductus. Bradykinin and corticosteroids also induce ductal constriction by attenuating the sensitivity of the ductus to PGE2. Smooth muscle cells of the ductus can sense oxygen through a mitochondrial network by the role of Rho-kinase pathway which ends up with increased intracellular calcium levels and contraction of myosin light chains. Anatomical closure of the ductus is also complex with various mechanisms such as migration and proliferation of smooth muscle cells, extracellular matrix production, endothelial cell proliferation which mediate cushion formation with the interaction of blood cells. Regulation of vessel walls is affected by retinoic acid, TGF-β1, notch signaling, hyaluronan, fibronectin, chondroitin sulfate, elastin, and vascular endothelial cell growth factor (VEGF). Formation of the platelet plug facilitates luminal remodeling by the obstruction of the constricted ductal lumen. Vasa vasorum are more pronounced in the term ductus but are less active in the preterm ductus. More than 100 genes are effective in the prostaglandin pathway or in vascular smooth muscle development and structure may affect the patency of ductus. Hemodynamic changes after birth including fluid load and flow characteristics as well as shear forces within the ductus also stimulate closure. Current pharmacological treatment for the closure of a patent ductus is based on the blockage of the prostaglandin pathway mainly through COX or POX inhibition, albeit with some limitations and side effects. Further research for new agents aiming ductal closure should focus on a clear understanding of vascular biology of the ductus.

Macular Perfusion Impairment in Von Hippel-Lindau Disease Suggests a Generalized Retinal Vessel Alteration

Background: To evaluate macular perfusion in patients with Von Hippel–Lindau (VHL) disease. Methods: VHL patients with or without peripheral retinal hemangioblastomas (RHs) were consecutively enrolled. A group of healthy subjects served as controls. Macular perfusion was analyzed by means of OCT angiography (OCTA) in the superficial vascular plexus (SVP), and in the intermediate (ICP) and deep retinal capillary (DCP) plexuses. The following OCTA parameters were measured: Vessel Area Density (VAD), Vessel Length Fraction (VLF), Vessel Diameter Index (VDI) and Fractal Dimension (FD). Results: Sixty-three VHL patients (113 eyes) and 28 healthy controls (56 eyes) were enrolled. All OCTA quantitative parameters were reduced in VHL patients vs. controls, reaching statistical significance for VAD of the SVP (0.348 ± 0.07 vs. 0.369 ± 0.06, p = 0.0368) and VDI of all plexuses (p < 0.03 for all). No significant differences were detected between eyes without or with peripheral RHs. Conclusions: Macular perfusion is reduced in VHL patients demonstrating retinal vessel changes that are independent of the presence of peripheral RHs. VHL gene mutations disrupt the hypoxia-induced (HIF)/vascular endothelium growth factors (VEGF) pathway and the Notch signaling, both essential for the normal retinal vasculogenesis and angiogenesis. Therefore, an anomalous generalized retinal vascular development may be hypothesized in VHL disease.

Power to see-Drivers of aerobic glycolysis in the mammalian retina: A review

The mammalian retina converts most glucose to lactate rather than catabolizing it completely to carbon dioxide via oxidative phosphorylation, despite the availability of oxygen. This unusual metabolism is known as aerobic glycolysis or the Warburg effect. Molecules and pathways that drive aerobic glycolysis have been identified and thoroughly studied in the context of cancer but remain relatively poorly understood in the retina. Here, we review recent research on the molecular mechanisms that underly aerobic glycolysis in the retina, focusing on key glycolytic enzymes including hexokinase 2 (HK2), pyruvate kinase M2 (PKM2) and lactate dehydrogenase A (LDHA). We also discuss the potential involvement of cell signalling and transcriptional pathways including phosphoinositide 3-kinase (PI3K) signalling, fibroblast growth factor receptor (FGFR) signalling, and hypoxia-inducible factor 1 (HIF-1), which have been implicated in driving aerobic glycolysis in the context of cancer.

Lactoferrin Has a Therapeutic Effect via HIF Inhibition in a Murine Model of Choroidal Neovascularization

Background

Lactoferrin, a type of glycoprotein, is contained in exocrine fluids such as tears, breast milk, sweat, and saliva, and is known to have anti-microbial, antioxidant, and anti-cancer effects. In the ophthalmological field, topical administration of lactoferrin has been reported to have a therapeutic effect in a murine dry eye model. Hypoxia-inducible factor (HIF) regulates various gene expressions under hypoxia, including vascular endothelial growth factor (VEGF), and is considered as an alternative target for neovascular ocular diseases such as age-related macular degeneration (AMD). We previously screened natural products and identified lactoferrin as a novel HIF inhibitor. In this study, we confirmed that lactoferrin has an HIF inhibitory effect and a therapeutic effect in a murine model of neovascular AMD.

Methods

HIF inhibitory effects of lactoferrin were evaluated using a luciferase assay and western blotting in vitro. The quantified volume of choroidal neovascularization (CNV) induced by laser irradiation was compared with oral lactoferrin administration or conditional tissue specific Hif1a knockout mice.

Results

Lactoferrin administration showed a significant HIF inhibitory effect in the retinal neuronal cells. Oral administration of lactoferrin or conditional Hif1a gene deletion significantly reduced CNV volume compared to controls.

Conclusions

Lactoferrin has a therapeutic effect in a laser CNV model by suppressing the retinal HIF activity.

Von Hippel-Lindau Disease and the Eye

Retinal hemangioblastoma (also referred to as retinal capillary hemangioma) is a benign lesion originating from the endothelial and glial components of the neurosensory retina and optic nerve head. Historically known as a manifestation of the von Hippel-Lindau (VHL) disease, it can be seen as an isolated finding or in association with some rare ocular conditions. In addition to characteristic ophthalmoscopic features, results of numerous ancillary tests including angiography, ultrasound, optical coherence tomography, and genetic tests may support the diagnosis and differentiate it from similar conditions. Because of serious life-threatening complications of VHL disease, every ocular approach to retinal hemangioblastomas should be in relationship with additional multidisciplinary diagnostic and therapeutic efforts. In addition, any patient with actual or probable diagnosis of VHL disease should be screened for ocular involvement. Unfavorable visual loss can occur early, and ocular complications of VHL range from exudative retinopathy to tractional retinal detachment, neovascular glaucoma, and phthisis bulbi. Accordingly, various treatment methods have been tested with overall acceptable responses, including photocoagulation, cryotherapy, photodynamic therapy, plaque radiotherapy, vitrectomy, and more novel intravitreal injections of anti-vascular endothelial growth factors and propranolol.

Pemafibrate Prevents Retinal Pathological Neovascularization by Increasing FGF21 Level in a Murine Oxygen-Induced Retinopathy Model

Large-scale clinical trials, such as the Fenofibrate Intervention and Event Lowering in Diabetes (FIELD) and the Action to Control Cardiovascular Risk in Diabetes (ACCORD) studies, have shown that the administration of fenofibrate, a peroxisome proliferator-activated receptor alpha (PPARα) agonist, suppresses the progression of diabetic retinopathy. In this paper, we reveal a therapeutic effect of a selective PPARα modulator (SPPARMα), pemafibrate, against pathological angiogenesis in murine models of retinopathy. Oxygen-induced retinopathy (OIR) was induced in C57BL/6J mice by exposure to 85% oxygen from postnatal day eight (P8) for 72 h. Vehicle, pemafibrate or fenofibrate was administrated by oral gavage from P12 to P16 daily. Administration of pemafibrate, but not fenofibrate, significantly reduced pathological angiogenesis in OIR. After oral pemafibrate administration, expression levels of downstream PPARα targets such as acyl-CoA oxidase 1 (Acox1), fatty acid binding protein 4 (Fabp4), and fibroblast growth factor 21 (Fgf21) were significantly increased in the liver but not in the retina. A significant increase in plasma FGF21 and reduced retinal hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor A (Vegfa) were also observed after this treatment. In an in vitro HIF-luciferase assay, a long-acting FGF21 analogue, but not pemafibrate, suppressed HIF activity. These data indicate that SPPARMα pemafibrate administration may prevent retinal pathological neovascularization by upregulating FGF21 in the liver.

Rb1/Rbl1/Vhl loss induces mouse subretinal angiomatous proliferation and hemangioblastoma

Von Hippel-Lindau (Vhl) protein inhibits hypoxia-inducible factor (Hif), yet its deletion in murine retina does not cause the extensive angiogenesis expected with Hif induction. The mechanism is unclear. Here we show that retinoblastoma tumor suppressor (Rb1) constrains expression of Hif target genes in the Vhl-/- retina. Deleting Rb1 induced extensive retinal neovascularization and autophagic ablation of photoreceptors in the Vhl-/- retina. RNA-sequencing, ChIP, and reporter assays showed Rb1 recruitment to and repression of certain Hif target genes. Activating Rb1 by deleting cyclin D1 induced a partial defect in the retinal superficial vascular plexus. Unexpectedly, removing Vhl suppressed retinoblastoma formation in murine Rb1/Rbl1-deficient retina but generated subretinal vascular growths resembling retinal angiomatous proliferation (RAP) and retinal capillary hemangioblastoma (RCH). Most stromal cells in the RAP/RCH-like lesions were Sox9+, suggesting a Müller glia origin, and expressed Lgals3, a marker of human brain hemangioblastoma. Thus, the Rb family limit Hif target gene expression in the Vhl-/- retina, and removing this inhibitory signal generates new models for RAP and RCH.

The Mechanisms Underlying the Cytotoxic Effects of Copper Via Differentiated Embryonic Chondrocyte Gene 1

Copper is an essential trace element within cells, but it also exerts cytotoxic effects through induction of reactive oxygen species (ROS) production. To determine the mechanisms underlying copper-induced ROS production, we examined the effects of copper sulfate in HeLa cells. Exposure to copper sulfate led to dose-dependent decreases in HeLa cell viability, along with increases in the subG1 and G2/M populations and corresponding decreases in the G1 population. Copper sulfate also increased the levels of apoptosis, senescence, mitochondrial dysfunction, autophagy, ROS, and the expression of several stress proteins, including ATF3, c-Fos, DEC1 (differentiated embryonic chondrocyte gene 1), p21, p53, and HIF-1α (hypoxia-inducible factor 1 alpha). The suppression of copper-induced ROS generation by the ROS scavenger N-acetyl cysteine verified copper’s functional role, while the suppression of copper’s effects by the copper chelator disulfiram, confirmed its specificity. Selective induction of HIF-1α, p53, and phosphorylated ERK proteins by copper was blocked by the knockdown of the transcription factor DEC1, suggesting copper’s effects are mediated by DEC1. In addition to HeLa cells, copper also exerted cytotoxic effects in human endometrial (HEC-1-A) and lung (A549) adenocarcinoma cells, but not in normal human kidney (HEK293) or bronchial (Beas-2B) epithelial cells. These findings shed new light on the functional roles of copper within cells.

Pharmacological HIF inhibition prevents retinal neovascularization with improved visual function in a murine oxygen-induced retinopathy model

Neovascular retinal diseases are the leading causes of blindness in advanced countries. To date, anti-VEGF (vascular endothelial growth factor) drugs are clinically effective and widely used for these diseases. However, recent animal and clinical studies reported that potent and long-term VEGF antagonism may induce chorioretinal atrophy. Thus, physiological amount of VEGF is required for the homeostasis in the retina. Hypoxia-inducible factors (HIFs) are transcription factors located upstream of VEGF. We hypothesized that ectopically stabilized HIFs induce pathological amount of VEGF involved with retinal neovascularization. Therefore, HIF inhibition could be an alternative therapeutic candidate targeting the pathological amount of VEGF while holding a physiological amount of VEGF. To test this hypothesis, topotecan and doxorubicin, HIF inhibitors with different mechanisms were administered to the murine oxygen-induced retinopathy (OIR) model. We found that both topotecan and doxorubicin significantly prevented pathological but not physiological neovascularization in OIR. Furthermore, impaired visual function observed in OIR can also be suppressed by administering topotecan. These data suggested that HIF inhibition may be effective for pathological angiogenesis and neurodegeneration of the retina.

Hif1a inactivation rescues photoreceptor degeneration induced by a chronic hypoxia-like stress

Reduced choroidal blood flow and tissue changes in the ageing human eye impair oxygen delivery to photoreceptors and the retinal pigment epithelium. As a consequence, mild but chronic hypoxia may develop and disturb cell metabolism, function and ultimately survival, potentially contributing to retinal pathologies such as age-related macular degeneration (AMD). Here, we show that several hypoxia-inducible genes were expressed at higher levels in the aged human retina suggesting increased activity of hypoxia-inducible transcription factors (HIFs) during the physiological ageing process. To model chronically elevated HIF activity and investigate ensuing consequences for photoreceptors, we generated mice lacking von Hippel Lindau (VHL) protein in rods. This activated HIF transcription factors and led to a slowly progressing retinal degeneration in the ageing mouse retina. Importantly, this process depended mainly on HIF1 with only a minor contribution of HIF2. A gene therapy approach using AAV-mediated RNA interference through an anti-Hif1a shRNA significantly mitigated the degeneration suggesting a potential intervention strategy that may be applicable to human patients.

Targeting Hif1a rescues cone degeneration and prevents subretinal neovascularization in a model of chronic hypoxia

Background

Degeneration of cone photoreceptors leads to loss of vision in patients suffering from age-related macular degeneration (AMD) and other cone dystrophies. Evidence, such as choroidal ischemia and decreased choroidal blood flow, implicates reduced tissue oxygenation in AMD pathology and suggests a role of the cellular response to hypoxia in disease onset and progression. Such a chronic hypoxic situation may promote several cellular responses including stabilization of hypoxia-inducible factors (HIFs).

Methods

To investigate the consequence of a chronic activation of the molecular response to hypoxia in cones, von Hippel Lindau protein (VHL) was specifically ablated in cones of the all-cone R91W;Nrl^-/- mouse. Retinal function and morphology was evaluated by ERG and light microscopy, while differential gene expression was tested by real-time PCR. Retinal vasculature was analyzed by immunostainings and fluorescein angiography. Two-way ANOVA with Šídák’s multiple comparison test was performed for statistical analysis.

Results

Cone-specific ablation of Vhl resulted in stabilization and activation of hypoxia-inducible factor 1A (HIF1A) which led to increased expression of genes associated with hypoxia and retinal stress. Our data demonstrate severe cone degeneration and pathologic vessel growth, features that are central to AMD pathology. Subretinal neovascularization was accompanied by vascular leakage and infiltration of microglia cells. Interestingly, we observed increased expression of tissue inhibitor of metalloproteinase 3 (Timp3) during the aging process, a gene associated with AMD and Bruch’s membrane integrity. Additional deletion of Hif1a protected cone cells, prevented pathological vessel growth and preserved vision.

Conclusions

Our data provide evidence for a HIF1A-mediated mechanism leading to pathological vessel growth and cone degeneration in response to a chronic hypoxia-like situation. Consequently, our results identify HIF1A as a potential therapeutic target to rescue hypoxia-related vision loss in patients.

Deletion of the von Hippel-Lindau Gene in Hemangioblasts Causes Hemangioblastoma-like Lesions in Murine Retina

von Hippel-Lindau (VHL) disease is an autosomal-dominant tumor predisposition syndrome characterized by the development of highly vascularized tumors and cysts. LOH of the VHL gene results in aberrant upregulation of hypoxia-inducible factors (HIF) and has been associated with tumor formation. Hemangioblastomas of the central nervous system and retina represent the most prevalent VHL-associated tumors, but no VHL animal model has reproduced retinal capillary hemangioblastomas (RCH), the hallmark lesion of ocular VHL. Here we report our work in developing a murine model of VHL-associated RCH by conditionally inactivating Vhl in a hemangioblast population using a Scl-Cre-ERT2 transgenic mouse line. In transgenic mice carrying the conditional allele and the Scl-Cre-ERT2 allele, 64% exhibited various retinal vascular anomalies following tamoxifen induction. Affected Vhl-mutant mice demonstrated retinal vascular lesions associated with prominent vasculature, anomalous capillary networks, hemorrhage, exudates, and localized fibrosis. Histologic analyses showed RCH-like lesions characterized by tortuous, dilated vasculature surrounded by "tumorlet" cell cluster and isolated foamy stromal cells, which are typically associated with RCH. Fluorescein angiography suggested increased vascular permeability of the irregular retinal vasculature and hemangioblastoma-like lesions. Vhl deletion was detected in "tumorlet" cells via microdissection. Our findings provide a phenotypic recapitulation of VHL-associated RCH in a murine model that may be useful to study RCH pathogenesis and therapeutics aimed at treating ocular VHL.Significance: This study describes a model that phenotypically recapitulates a form of retinal pathogenesis that is driven by genetic loss of the VHL tumor suppressor, providing a useful tool for its study and therapeutic intervention. Cancer Res; 78(5); 1266-74. ©2018 AACR.

Von Hippel-Lindau mutations disrupt vascular patterning and maturation via Notch

Von Hippel-Lindau (VHL) gene mutations induce neural tissue hemangioblastomas, as well as highly vascularized clear cell renal cell carcinomas (ccRCCs). Pathological vessel remodeling arises from misregulation of HIFs and VEGF, among other genes. Variation in disease penetrance has long been recognized in relation to genotype. We show Vhl mutations also disrupt Notch signaling, causing mutation-specific vascular abnormalities, e.g., type 1 (null) vs. type 2B (murine G518A representing human R167Q). In conditional mutation retina vasculature, Vhl-null mutation (i.e., UBCCreER/+Vhlfl/fl) had little effect on initial vessel branching, but it severely reduced arterial and venous branching at later stages. Interestingly, this mutation accelerated arterial maturation, as observed in retina vessel morphology and aberrant α-smooth muscle actin localization, particularly in vascular pericytes. RNA sequencing analysis identified gene expression changes within several key pathways, including Notch and smooth muscle cell contractility. Notch inhibition failed to reverse later-stage branching defects but rescued the accelerated arterialization. Retinal vessels harboring the type 2B Vhl mutation (i.e., UBCCreER/+Vhlfl/2B) displayed stage-specific changes in vessel branching and an advanced progression toward an arterial phenotype. Disrupting Notch signaling in type 2B mutants increased both artery and vein branching and restored arterial maturation toward nonmutant levels. By revealing differential effects of the null and type 2B Vhl mutations on vessel branching and maturation, these data may provide insight into the variability of VHL-associated vascular changes - particularly the heterogeneity and aggressiveness in ccRCC vessel growth - and also suggest Notch pathway targets for treating VHL syndrome.

Abscisic acid - an anti-angiogenic phytohormone that modulates the phenotypical plasticity of endothelial cells and macrophages

Abscisic acid (ABA) has shown anti-inflammatory and immunoregulatory properties in preclinical models of diabetes and inflammation. Herein, we studied the effects of ABA on angiogenesis, a strictly controlled process that, when dysregulated, leads to severe angiogenic disorders including vascular overgrowth, exudation, cellular inflammation and organ dysfunction. By using a 3D sprouting assay, we show that ABA effectively inhibits migration, growth and expansion of endothelial tubes without affecting cell viability. Analyses of the retinal vasculature in developing normoxic and hyperoxic mice challenged by oxygen toxicity reveal that exogenously administered ABA stunts the development and regeneration of blood vessels. In these models, ABA downregulates endothelial cell (EC)-specific growth and migratory genes, interferes with tip and stalk cell specification, and hinders the function of filopodial protrusions required for precise guidance of vascular sprouts. In addition, ABA skews macrophage polarization towards the M1 phenotype characterized by anti-angiogenic marker expression. In accordance with this, ABA treatment accelerates macrophage-induced programmed regression of fetal blood vessels. These findings reveal protective functions of ABA against neovascular growth through modulation of EC and macrophage plasticity, suggesting the potential utility of ABA as a treatment in vasoproliferative diseases.

Roles of Hypoxia Response in Retinal Development and Pathophysiology

The hypoxia response is a fundamental phenomenon mainly regulated by hypoxia-inducible factors (HIFs). For more than a decade, we have investigated and revealed the roles of the hypoxia response in the development, physiology, and pathophysiology of the retina by generating and utilizing cell-type-specific conditional knockout mice. To investigate the functions of genes related to the hypoxia response in cells composing the retina, we generated various mouse lines that lack HIFs and/or related genes specifically in retinal neurons, astrocytes, myeloid cells, or retinal pigment epithelium cells. We found that these genes in the different types of retinal cells contribute in various ways to the homeostasis of ocular vascular and visual function. We hypothesized that the activation of HIFs is likely involved in the development and progress of retinal diseases, and we subsequently confirmed the pathological roles of HIFs in animal models of neovascular and atrophic ocular diseases. Currently, anti-vascular endothelial growth factor (anti-VEGF) therapy is a first-line treatment widely used for neovascular retinal diseases. However, alternative or additional targets are now required because several recent large-scale clinical trials and animal studies, including our own research, have indicated that VEGF antagonism may induce retinal vascular and neuronal degeneration. We have identified and confirmed a microRNA as a candidate for an alternative target against neovascular retinal diseases, and we are now working to establish a novel HIF inhibitor for clinical use based on the disease mechanism that we identified.

Programmed mitophagy is essential for the glycolytic switch during cell differentiation

Retinal ganglion cells (RGCs) are the sole projecting neurons of the retina and their axons form the optic nerve. Here, we show that embryogenesis-associated mouse RGC differentiation depends on mitophagy, the programmed autophagic clearance of mitochondria. The elimination of mitochondria during RGC differentiation was coupled to a metabolic shift with increased lactate production and elevated expression of glycolytic enzymes at the mRNA level. Pharmacological and genetic inhibition of either mitophagy or glycolysis consistently inhibited RGC differentiation. Local hypoxia triggered expression of the mitophagy regulator BCL2/adenovirus E1B 19-kDa-interacting protein 3-like (BNIP3L, best known as NIX) at peak RGC differentiation. Retinas from NIX-deficient mice displayed increased mitochondrial mass, reduced expression of glycolytic enzymes and decreased neuronal differentiation. Similarly, we provide evidence that NIX-dependent mitophagy contributes to mitochondrial elimination during macrophage polarization towards the proinflammatory and more glycolytic M1 phenotype, but not to M2 macrophage differentiation, which primarily relies on oxidative phosphorylation. In summary, developmentally controlled mitophagy promotes a metabolic switch towards glycolysis, which in turn contributes to cellular differentiation in several distinct developmental contexts.

HIF signalling: The eyes have it

The hypoxia inducible factors (HIFs) promote changes in gene expression in response to hypoxia, and mediate key physiological responses such as angiogenesis. They play important roles in development and normal physiology, as well as in ischaemic and other pathologies. The human eye is a complex organ, with tight regulation of vascularisation and oxygen delivery, with the highly specialised retina containing both highly vascularised and avascular regions. This review, written to honour the significant contribution of Lorenz Poellinger to this field, covers the role of the HIFs in normal development of the eye, specifically the vasculature, as well as their roles in numerous retinal pathologies, including ischaemic retinopathies, and age-related macular degeneration (AMD). The characterisation of the HIFs in the eye has improved our understanding of the development, function, and numerous pathologies of the eye, and should inform future therapeutic approaches.

Sirtuins Expression and Their Role in Retinal Diseases

Sirtuins have received considerable attention since the discovery that silent information regulator 2 (Sir2) extends the lifespan of yeast. Sir2, a nicotinamide adenine dinucleotide- (NAD-) dependent histone deacetylase, serves as both a transcriptional effector and energy sensor. Oxidative stress and apoptosis are implicated in the pathogenesis of neurodegenerative eye diseases. Sirtuins confer protection against oxidative stress and retinal degeneration. In mammals, the sirtuin (SIRT) family consists of seven proteins (SIRT1–SIRT7). These vary in tissue specificity, subcellular localization, and enzymatic activity and targets. In this review, we present the current knowledge of the sirtuin family and discuss their structure, cellular location, and biological function with a primary focus on their role in different neuroophthalmic diseases including glaucoma, optic neuritis, and age-related macular degeneration. The potential role of certain therapeutic targets is also described.

Microarray gene expression analysis in ovine ductus arteriosus during fetal development and birth transition

BACKGROUND

Patent ductus arteriosus (PDA) in the newborn is the most common congenital heart anomaly and is significantly more common in preterm infants. Contemporary pharmacological treatment is effective in only 70-80% of the cases. Moreover, indomethacin or ibuprofen, which are used to close a PDA may be accompanied by serious side effects in premature infants. To explore the novel molecular pathways, which may be involved in the maturation and closure of the ductus arteriosus (DA), we used fetal and neonatal sheep to test the hypothesis that maturational development of DA is associated with significant alterations in specific mRNA expression.

METHODS

We conducted oligonucleotide microarray experiments on the isolated mRNA from DA and ascending aorta from three study groups (premature fetus-97 ± 0 d, near-term fetus-136 ± 0.8 d, and newborn lamb-12 ± 0 h). We compared the alterations in mRNA expression in DA and aorta to identify genes specifically involved in DA maturation.

RESULTS

Results demonstrate significant changes in wingless-integrin1, thrombospondin 1, receptor activator of nuclear factor-kappa B, nitric oxide synthase, and retinoic acid receptor activation signaling pathways.

CONCLUSION

We conclude that these pathways may play an important role during both development and postnatal DA closure and warrant further investigation.

Apoptosis regulates endothelial cell number and capillary vessel diameter but not vessel regression during retinal angiogenesis

The growth of hierarchical blood vessel networks occurs by angiogenesis. During this process, new vessel growth is accompanied by the removal of redundant vessel segments by selective vessel regression ('pruning') and a reduction in endothelial cell (EC) density in order to establish an efficient, hierarchical network. EC apoptosis has long been recognised for its association with angiogenesis, but its contribution to this process has remained unclear. We generated mice in which EC apoptosis was blocked by tissue-specific deletion of the apoptosis effector proteins BAK and BAX. Using the retina as a model, we found that apoptosis made a minor contribution to the efficiency of capillary regression around arteries where apoptosis was most concentrated, but was otherwise dispensable for vessel pruning. Instead, apoptosis was necessary for the removal of non-perfused vessel segments and the reduction in EC density that occurs during vessel maturation. In the absence of apoptosis, increased EC density resulted in an increase in the diameter of capillaries, but not arteries or veins. Our findings show that apoptosis does not influence the number of vessels generated during angiogenesis. Rather it removes non-perfused vessel segments and regulates EC number during vessel maturation, which has vessel-specific consequences for vessel diameter.

Developmental regression of hyaloid vasculature is triggered by neurons

Vascular development involves not only vascular growth, but also regression of transient or unnecessary vessels. Hyaloid vasculature is the temporary circulatory system in fetal eyes, which spontaneously degenerates when the retinal blood vessels start to grow. Failure of the hyaloid vessels to regress leads to disease in humans, persistent hyperplastic primary vitreous, which causes severe intraocular hemorrhage and impairs visual function. However, the mechanism underlying the endogenous program that mediates spontaneous regression of the hyaloid vessels is not well understood. In this study, we identify a robust switch triggering this program directed by neurons in mice. Marked up-regulation of vascular endothelial growth factor (VEGF) receptor 2 (VEGFR2) occurs in retinal neurons just after birth via distal-multipotent-mesodermal enhancer, a hemangioblast-specific enhancer of VEGFR2. Genetic deletion of neuronal VEGFR2 interrupts this program, resulting in massive hyaloid vessels that persist even during late postnatal days. This abnormality is caused by excessive VEGF proteins in the vitreous cavity as a result of impairment in the neuronal sequestration of VEGF. Collectively, our data indicate that neurons trigger transition from the fetal to the postnatal circulatory systems in the retina.

Development and pathological changes of neurovascular unit regulated by hypoxia response in the retina

Retina is a highly vascularized tissue with a high oxygen and metabolic demand receiving light located in the back of the eye. The development and the maintenance of the retinal vasculature are important to regulate the homeostasis in the tissue. α Subunits of hypoxia-inducible factor (HIF) are key molecules in hypoxia response inducing genes required for cell survival such as vascular endothelial growth factor under hypoxia. Neurons, glia, and vascular endothelium cells interdependently form neurovascular unit in the retina tightly regulated by hypoxia response via HIF expression. A corruption of the precise hypoxia response in the developmental or matured retinal tissue may lead congenital vascular anomalies or adult neovascular ocular diseases. To regulate hypoxia response through HIF activity would be an ideal therapeutic target for these vision-threatening eye diseases.

Neurovascular crosstalk between interneurons and capillaries is required for vision

Functional interactions between neurons, vasculature, and glia within neurovascular units are critical for maintenance of the retina and other CNS tissues. For example, the architecture of the neurosensory retina is a highly organized structure with alternating layers of neurons and blood vessels that match the metabolic demand of neuronal activity with an appropriate supply of oxygen within perfused blood. Here, using murine genetic models and cell ablation strategies, we have demonstrated that a subset of retinal interneurons, the amacrine and horizontal cells, form neurovascular units with capillaries in 2 of the 3 retinal vascular plexuses. Moreover, we determined that these cells are required for generating and maintaining the intraretinal vasculature through precise regulation of hypoxia-inducible and proangiogenic factors, and that amacrine and horizontal cell dysfunction induces alterations to the intraretinal vasculature and substantial visual deficits. These findings demonstrate that specific retinal interneurons and the intraretinal vasculature are highly interdependent, and loss of either or both elicits profound effects on photoreceptor survival and function.

The ubiquitin ligase PDZRN3 is required for vascular morphogenesis through Wnt/planar cell polarity signalling

Development and stabilization of a vascular plexus requires the coordination of multiple signalling processes. Wnt planar cell polarity (PCP) signalling is critical in vertebrates for diverse morphogenesis events, which coordinate cell orientation within a tissue-specific plane. However, its functional role in vascular morphogenesis is not well understood. Here we identify PDZRN3, an ubiquitin ligase, and report that Pdzrn3 deficiency impairs embryonic angiogenic remodelling and postnatal retinal vascular patterning, with a loss of two-dimensional polarized orientation of the intermediate retinal plexus. Using in vitro and ex vivo Pdzrn3 loss-of-function and gain-of-function experiments, we demonstrate a key role of PDZRN3 in endothelial cell directional and coordinated extension. PDZRN3 ubiquitinates Dishevelled 3 (Dvl3), to promote endocytosis of the Frizzled/Dvl3 complex, for PCP signal transduction. These results highlight the role of PDZRN3 to direct Wnt PCP signalling, and broadly implicate this pathway in the planar orientation and highly branched organization of vascular plexuses.

The human plasma membrane peripherome: visualization and analysis of interactions

A major part of membrane function is conducted by proteins, both integral and peripheral. Peripheral membrane proteins temporarily adhere to biological membranes, either to the lipid bilayer or to integral membrane proteins with noncovalent interactions. The aim of this study was to construct and analyze the interactions of the human plasma membrane peripheral proteins (peripherome hereinafter). For this purpose, we collected a dataset of peripheral proteins of the human plasma membrane. We also collected a dataset of experimentally verified interactions for these proteins. The interaction network created from this dataset has been visualized using Cytoscape. We grouped the proteins based on their subcellular location and clustered them using the MCL algorithm in order to detect functional modules. Moreover, functional and graph theory based analyses have been performed to assess biological features of the network. Interaction data with drug molecules show that ~10% of peripheral membrane proteins are targets for approved drugs, suggesting their potential implications in disease. In conclusion, we reveal novel features and properties regarding the protein-protein interaction network created by peripheral proteins of the human plasma membrane.

Genotype-phenotype correlations, and retinal function and structure in von Hippel-Lindau disease

PURPOSE

To investigate genotype-phenotype correlation and to analyze functional and structural changes in the retina of patients with von Hippel-Lindau (VHL) disease.

METHODS

Thirteen patients from four families (A, B, C and D) with known VHL disease and known mutations in the VHL gene were examined. All patients underwent clinical examination and optical coherence tomography (OCT). Full-field electroretinography (full-field ERG) was performed in twelve patients.

RESULTS

Family A, with deletion of exon 3 in the VHL gene, and family B, with the missense mutation p.R79P, exhibited type 1 VHL characterized by the absence of pheochromocytoma and a high incidence of central nervous system hemangioblastomas. One member of family B exhibited Goldenhar syndrome. A novel missense mutation (p.L198P) was identified in the VHL gene in the patient from family C. This p.L198P mutation caused a phenotype with early onset of a neuroendocrine tumor of the pancreas, bilateral pheochromocytomas, and optic nerve hemangioblastoma. Full-field ERG showed significantly prolonged implicit times of the b-wave and maximal combined a-wave in VHL patients, compared to controls. Examination of the retinal structure in all patients with VHL, using OCT, showed a significant decrease in retinal thickness in VHL patients without ocular hemangioblastomas, compared to controls.

CONCLUSIONS

Our findings support previously established genotype-phenotype correlations. However, we here describe an unusual phenotype with a novel missense mutation, p.L198P, and report the finding that VHL disease can be associated with Goldenhar syndrome. Electrophysiological and structural findings suggest that VHL disease is a progressive, neurodegenerative disease of the retina.

A direct and melanopsin-dependent fetal light response regulates mouse eye development

Vascular patterning is critical for organ function. In the eye, there is simultaneous regression of embryonic hyaloid vasculature (important to clear the optical path) and formation of the retinal vasculature (important for the high metabolic demands of retinal neurons). These events occur postnatally in the mouse. Here we have identified a light-response pathway that regulates both processes. We show that when mice are mutated in the gene (Opn4) for the atypical opsin melanopsin, or are dark-reared from late gestation, the hyaloid vessels are persistent at 8 days post-partum and the retinal vasculature overgrows. We provide evidence that these vascular anomalies are explained by a light-response pathway that suppresses retinal neuron number, limits hypoxia and, as a consequence, holds local expression of vascular endothelial growth factor (VEGFA) in check. We also show that the light response for this pathway occurs in late gestation at about embryonic day 16 and requires the photopigment in the fetus and not the mother. Measurements show that visceral cavity photon flux is probably sufficient to activate melanopsin-expressing retinal ganglion cells in the mouse fetus. These data thus show that light--the stimulus for function of the mature eye--is also critical in preparing the eye for vision by regulating retinal neuron number and initiating a series of events that ultimately pattern the ocular blood vessels.

Von Hippel-Lindau protein in the RPE is essential for normal ocular growth and vascular development

Molecular oxygen is essential for the development, growth and survival of multicellular organisms. Hypoxic microenvironments and oxygen gradients are generated physiologically during embryogenesis and organogenesis. In the eye, oxygen plays a crucial role in both physiological vascular development and common blinding diseases. The retinal pigment epithelium (RPE) is a monolayer of cells essential for normal ocular development and in the mature retina provides support for overlying photoreceptors and their vascular supply. Hypoxia at the level of the RPE is closely implicated in pathogenesis of age-related macular degeneration. Adaptive tissue responses to hypoxia are orchestrated by sophisticated oxygen sensing mechanisms. In particular, the von Hippel-Lindau tumour suppressor protein (pVhl) controls hypoxia-inducible transcription factor (HIF)-mediated adaptation. However, the role of Vhl/Hif1a in the RPE in the development of the eye and its vasculature is unknown. In this study we explored the function of Vhl and Hif1a in the developing RPE using a tissue-specific conditional-knockout approach. We found that deletion of Vhl in the RPE results in RPE apoptosis, aniridia and microphthalmia. Increased levels of Hif1a, Hif2a, Epo and Vegf are associated with a highly disorganised retinal vasculature, chorioretinal anastomoses and the persistence of embryonic vascular structures into adulthood. Additional inactivation of Hif1a in the RPE rescues the RPE morphology, aniridia, microphthalmia and anterior vasoproliferation, but does not rescue retinal vasoproliferation. These data demonstrate that Vhl-dependent regulation of Hif1a in the RPE is essential for normal RPE and iris development, ocular growth and vascular development in the anterior chamber, whereas Vhl-dependent regulation of other downstream pathways is crucial for normal development and maintenance of the retinal vasculature.

Deletion of HIF-1α partially rescues the abnormal hyaloid vascular system in Cited2 conditional knockout mouse eyes

PURPOSE

Cited2 (CBP/p300-interacting transactivators with glutamic acid (E) and aspartic acid (D)-rich tail 2) is a member of a new family of transcriptional modulators. Cited2 null embryos exhibit hyaloid hypercellularity consisting of aberrant vasculature in the eye. The purpose of the study is to address whether abnormal lenticular development is a primary defect of Cited2 deletion and whether deletion of hypoxia inducible factor (HIF)-1α or an HIF-1α target gene, vascular endothelial growth factor (VEGF), could rescue abnormal hyaloid vascular system (HVS) in Cited2 deficient adult eyes.

METHODS

Le-Cre specific Cited2 knockout (Cited2(CKO)) mice with or without deletion of HIF-1α or VEGF were generated by standard Cre-Lox methods. Eyes collected from six-eight weeks old mice were characterized by Real Time PCR and immunohistological staining.

RESULTS

Cited2(CKO) mice had smaller lenses, abnormal lens stalk formation, and failed regression of the HVS in the adult eye. The eye phenotype had features similar to persistent hyperplastic primary vitreous (PHPV), a human congenital eye disorder leading to abnormal lenticular development. Deletion of HIF-1α or VEGF in Cited2 knockout eyes partially rescued the abnormal HVS but had no effect on the smaller lens and abnormal lens stalk differentiation. Intravitreal injection of Topotecan (TPT), a compound that inhibits HIF-1α expression, partially eliminated HVS defects in Cited2(CKO) lenses.

CONCLUSIONS

Abnormal HVS is a primary defect in Cited2 knockout mice, resulting in part from dysregulated functions of HIF-1 and VEGF. The Cited2(CKO) mouse line could be used as a novel disease model for PHPV and as an in vivo model for testing potential HIF-1 inhibitors.

A role for endothelial cells in promoting the maturation of astrocytes through the apelin/APJ system in mice

Interactions between astrocytes and endothelial cells (ECs) are crucial for retinal vascular formation. Astrocytes induce migration and proliferation of ECs via their production of vascular endothelial growth factor (VEGF) and, conversely, ECs induce maturation of astrocytes possibly by the secretion of leukemia inhibitory factor (LIF). Together with the maturation of astrocytes, this finalizes angiogenesis. Thus far, the mechanisms triggering LIF production in ECs are unclear. Here we show that apelin, a ligand for the endothelial receptor APJ, induces maturation of astrocytes mediated by the production of LIF from ECs. APJ (Aplnr)- and Apln-deficient mice show delayed angiogenesis; however, aberrant overgrowth of endothelial networks with immature astrocyte overgrowth was induced. When ECs were stimulated with apelin, LIF expression was upregulated and intraocular injection of LIF into APJ-deficient mice suppressed EC and astrocyte overgrowth. These data suggest an involvement of apelin/APJ in the maturation process of retinal angiogenesis.