Special features of human retinal angiogenesis

The Effect of Perinatal High-Dose Erythropoietin on Retinal Structural and Vascular Characteristics in Children Born Preterm

PURPOSE

To study the long-term effects of perinatal high-dose recombinant human erythropoietin (rhEPO) on macular structural and vascular development in preterm children.

DESIGN

Randomized, double-blind clinical trial follow-up plus cohort study.

METHODS

Setting: Department of Ophthalmology, University Hospital Zurich, Zurich, Switzerland.

STUDY POPULATION

extremely or very preterm born children aged 7-15 years from an ongoing neuropediatric study (EpoKids). These had been previously randomized to receive either high-dose rhEPO or placebo perinatally.

INCLUSION CRITERIA

participation in the EpoKids Study, written informed consent (IC).

EXCLUSION CRITERIA

previous ocular trauma or surgery; retinal or developmental disease unrelated to prematurity. Term-born children of comparable age were enrolled as a healthy control (HC) group.

INCLUSION CRITERIA

term birth, IC.

EXCLUSION CRITERIA

any ocular or visual abnormality, high refractive error. Examiners were blinded regarding intervention status until completion of all analyses. (Participants/guardians remain blinded).

OBSERVATION PROCEDURES

Spectral-domain OCT scans (Heidelberg Spectralis system) and OCTA imaging (Zeiss PlexElite 9000) were obtained. Ophthalmological and orthoptic examinations excluded ocular comorbidities.

MAIN OUTCOME MEASURES

OCT (central retinal thickness, CRT; total macular volume, TMV), superficial plexus OCTA (foveal avascular zone, FAZ; vessel density, VD; vessel length density, VLD) parameters and foveal hypoplasia grade according to published criteria.

RESULTS

Macular vessel density parameters (VD and VLD) were significantly lower (p =0.015, CI-95: 0.01 to 0.06 and p=0.015, CI-95: 0.74 to 3.64) in the EPO group (n= 52) when compared to placebo (n=35). No other significant differences were observed between the EPO and placebo group. When comparing the intervention subgroups to HC we found six significant differences in OCT and OCTA parameters (FAZ, VD, VLD and CRT comparing HC and EPO group; FAZ and CRT when comparing HC and placebo group).

CONCLUSIONS

Early high-dose rhEPO in infants born extremely or very preterm affects macular vessel density parameters compared to placebo. Premature birth (regardless of intervention status) affects retinal structure and vascular development. Our findings on macular vascular development do not contraindicate the administration of early high-dose EPO in preterm infants. For further understanding of the role of EPO on macular development and its clinical significance, future studies are needed.

Downregulation of miR-124-3p suppresses the development of the deep retinal blood vessels by enhancing the Stat1/Ripk1 pathway in mouse retinal microglia

The study aimed to investigate the role of microRNA (miR)-124-3p in retinal angiogenesis in a mouse model. An intravitreal injection of miR-124-3p antagomir was used to knockdown the expression of miR-124-3p in the mouse retina at postnatal day (P)3. Immunofluorescent staining of both retinal frozen sections and whole retina were used to observe retinal vascular development in the P6, P9 and P12 mice, as well as the changes in retinal ganglion cells, astrocytes, Müller cells and microglia. Whole retinal RNA extracted from P9 mice was used for transcriptome sequencing. Following gene set enrichment analysis, the enriched genes caused by miR-124-3p inhibition were analyzed by immunofluorescent staining and western blot. Results indicated that deep vascular development was significantly inhibited by the activation of M1 phenotype microglia. Moreover, there were no notable effects on superficial retinal vascular development, the retinal ganglion cells, astrocytes, and Müller cells. The expression of the Stat1/Irf9/Eif2ak2/Ripk1 axis in the miR-124-3p knockdown group was significantly increased. The microglia penetrated deep into the retina and the activation of Ripk1(+) microglia significantly increased, which was accompanied by an increased level of apoptosis to inhibit the deep vascular sprout. Downregulation of miR-124-3p during the early retinal development can suppress the development of the deep retinal blood vessels by enhancing the expression level of the Stat1/Irf9/Eif2ak2/Ripk1 axis and inducing the cell apoptosis of the activation of Ripk1(+) microglia.

Congenital aniridia beyond black eyes: From phenotype and novel genetic mechanisms to innovative therapeutic approaches

Congenital PAX6-aniridia, initially characterized by the absence of the iris, has progressively been shown to be associated with other developmental ocular abnormalities and systemic features making congenital aniridia a complex syndromic disorder rather than a simple isolated disease of the iris. Moreover, foveal hypoplasia is now recognized as a more frequent feature than complete iris hypoplasia and a major visual prognosis determinant, reversing the classical clinical picture of this disease. Conversely, iris malformation is also a feature of various anterior segment dysgenesis disorders caused by PAX6-related developmental genes, adding a level of genetic complexity for accurate molecular diagnosis of aniridia. Therefore, the clinical recognition and differential genetic diagnosis of PAX6-related aniridia has been revealed to be much more challenging than initially thought, and still remains under-investigated. Here, we update specific clinical features of aniridia, with emphasis on their genotype correlations, as well as provide new knowledge regarding the PAX6 gene and its mutational spectrum, and highlight the beneficial utility of clinically implementing targeted Next-Generation Sequencing combined with Whole-Genome Sequencing to increase the genetic diagnostic yield of aniridia. We also present new molecular mechanisms underlying aniridia and aniridia-like phenotypes. Finally, we discuss the appropriate medical and surgical management of aniridic eyes, as well as innovative therapeutic options. Altogether, these combined clinical-genetic approaches will help to accelerate time to diagnosis, provide better determination of the disease prognosis and management, and confirm eligibility for future clinical trials or genetic-specific therapies.

Functional and Structural Findings in Infants Treated for Retinopathy of Prematurity Using Optical Coherence Tomography Angiography

BACKGROUND AND OBJECTIVE

To assess the foveal microvascular structure of children with retinopathy of prematurity (ROP) treated with diode laser photocoagulation using optical coherence tomography angiography (OCTA).

PATIENTS AND METHODS

OCTA was performed at a tertiary medical center in 17 children (27 eyes) aged 4 to 16 years with a history of diode laser photocoagulation treated ROP. OCTA parameters were compared with those of 12 healthy age-matched controls (23 eyes) attending the orthoptics clinic and correlated with clinical factors.

RESULTS

Compared with controls, the ROP group had a smaller foveal avascular zone area (P < .001), lower deep vascular plexus density (P < .001), lower flow density (P = .025), and greater central macular thickness (P < .001). High intraventricular hemorrhage grade correlated with smaller foveal avascular zone area (P = .008) and greater inner macular thickness (P = .047). There was no impact of gestational age, birth weight, or refractive status.

CONCLUSION

OCTA can identify significant quantifiable long-term macular microvascular and structural changes in this patient population. [Ophthalmic Surg Lasers Imaging Retina. 2022;53(4):194-201.].

Specialized endothelial tip cells guide neuroretina vascularization and blood-retina-barrier formation

Endothelial tip cells guiding tissue vascularization are primary targets for angiogenic therapies. Whether tip cells require differential signals to develop their complex branching patterns remained unknown. Here, we show that diving tip cells invading the mouse neuroretina (D-tip cells) are distinct from tip cells guiding the superficial retinal vascular plexus (S-tip cells). D-tip cells have a unique transcriptional signature, including high TGF-β signaling, and they begin to acquire blood-retina barrier properties. Endothelial deletion of TGF-β receptor I (Alk5) inhibits D-tip cell identity acquisition and deep vascular plexus formation. Loss of endothelial ALK5, but not of the canonical SMAD effectors, leads to aberrant contractile pericyte differentiation and hemorrhagic vascular malformations. Oxygen-induced retinopathy vasculature exhibits S-like tip cells, and Alk5 deletion impedes retina revascularization. Our data reveal stage-specific tip cell heterogeneity as a requirement for retinal vascular development and suggest that non-canonical-TGF-β signaling could improve retinal revascularization and neural function in ischemic retinopathy.

Environmental oxygen regulates astrocyte proliferation to guide angiogenesis during retinal development

Angiogenesis in the developing mammalian retina requires patterning cues from astrocytes. Developmental disorders of retinal vasculature, such as retinopathy of prematurity (ROP), involve arrest or mispatterning of angiogenesis. Whether these vascular pathologies involve astrocyte dysfunction remains untested. Here, we demonstrate that the major risk factor for ROP – transient neonatal exposure to excess oxygen – disrupts formation of the angiogenic astrocyte template. Exposing newborn mice to elevated oxygen (75%) suppressed astrocyte proliferation, whereas return to room air (21% oxygen) at postnatal day 4 triggered extensive proliferation, massively increasing astrocyte numbers and disturbing their spatial patterning prior to the arrival of developing vasculature. Proliferation required astrocytic HIF2α and was also stimulated by direct hypoxia (10% oxygen), suggesting that astrocyte oxygen sensing regulates the number of astrocytes produced during development. Along with astrocyte defects, return to room air also caused vascular defects reminiscent of ROP. Strikingly, these vascular phenotypes were more severe in animals that had larger numbers of excess astrocytes. Together, our findings suggest that fluctuations in environmental oxygen dysregulate molecular pathways controlling astrocyte proliferation, thereby generating excess astrocytes that interfere with retinal angiogenesis.

Highlighted Article: Oxygen regulates proliferation of immature retinal astrocytes. Perturbing this mechanism inflates astrocyte numbers, disrupts retinal angiogenesis and leads to vascular pathologies resembling retinopathy of prematurity.

Risk Calculator for Retinopathy of Prematurity Requiring Treatment

Importance: Vascular delay that occurs early in the development of retinopathy of prematurity (ROP) is a risk factor that can be compensated by ensuring a good rate of retinal vascularization to avoid ROP that requires treatment. Background: The objective of the present study was to determine the association between ROP that requires treatment and risk factors such as the extent of the temporal avascular area of the retina and the number of days of mechanical ventilation (MV). Design: Observational retrospective case-control study. Participants: Two hundred and twenty-eight premature newborns included in the screening protocol for retinopathy of prematurity. Methods: Subjects underwent retinal examination in the 4 and 6th postnatal weeks. Main Outcome Measures: The temporal avascular area was measured in disc diameters (DD), while the MV time was measured in days of treatment. Results: Patients with a longer MV time had a higher risk of treatment (R 2: 24.7, p < 0.0001; increase in risk of 8.1% for each additional day), as did those who showed greater avascular area (R 2: 24.7, p < 0.0001; increase in risk of 111% for each additional DD). An online calculator system and a table are presented for calculating the risk of ROP requiring treatment as a function of these two risk factors. Conclusions and Relevance: The temporal avascular area of the retina and MV time must be taken into account in the first examination of the newborn to predict the need for ROP treatment.

Foveal structure, function and microvascular morphology in school-age children with laser-treated retinopathy of prematurity

PURPOSE

The purpose of this retrospective case-control study was to evaluate the relationship between foveal structure, function, microvascular morphology and visual acuity in school-age children with laser-treated retinopathy of prematurity (ROP).

METHODS

Foveal structural parameters, including the central foveal thickness (CFT), inner retinal thickness (IRT) and outer retinal thickness (ORT), were measured on B-scans using an Optovue XR Avanti optical coherence tomography device. Foveal microvascular parameters, including the foveal avascular zone (FAZ), superficial capillary plexus-vessel density (SCP-VD) and deep capillary plexus-vessel density (DCP-VD), were measured on optical coherence tomography angiography with a scan size of 3 × 3. The P1 amplitudes and P1 implicit times were recorded by a multifocal electroretinogram with 61 elements.

RESULTS

Fifty-five eyes (26 eyes of school-age ROP children and 29 eyes of full-term controls) were analysed. The ROP children manifested a significantly smaller FAZ, higher SCP-VD and higher DCP-VD than the controls (p < 0.001). The CFT (p < 0.001), IRT (p < 0.001) and ORT (p = 0.001) were significantly increased in the ROP group. The P1 amplitudes in all five-ring retinal regions were significantly smaller in the ROP group (p < 0.001). Multivariable analysis indicated that best-corrected visual acuity was positively correlated with post-menstrual age (PMA) and negatively correlated with SCP-VD and CFT (R² = 0.529, p < 0.001, 0.043 and 0.020, respectively).

CONCLUSION

The foveal structure, function and microvascular morphology are affected in school-age children with laser-treated ROP. PMA, foveal structural anomalies and microvascular changes in ROP children were associated with impaired visual function.

Paracentral acute middle maculopathy and the organization of the retinal capillary plexuses

The retinal capillary vasculature serves the formidable role of supplying the metabolically active inner and middle retina. In the parafoveal region, the retinal capillary plexuses (RCP) are organized in a system of three capillary layers of varying retinal depths: the superficial capillary plexus (SCP), intermediate capillary plexus (ICP) and deep capillary plexus (DCP). While the dynamic flow through these plexuses is complex and not completely understood, current research points to a hybrid model that includes both parallel and in series components in which blood flows in a predominantly serial direction between the superficial vascular complex (SVC) and deep vascular complex (DVC). Each capillary plexus autoregulates independently, so that under most conditions the retinal vasculature supplies adequate blood flow and oxygen saturation at varying depths despite diverse environmental stressors. When the flow in the deep vascular complex (i.e. ICP and DCP) fails, an ischemic lesion referred to as Paracentral Acute Middle Maculopathy (PAMM) can be identified. PAMM is an optical coherence tomography (OCT) finding defined by the presence of a hyperreflective band at the level of the inner nuclear layer (INL) that indicates INL infarction caused by globally impaired perfusion through the retinal capillary system leading to hypoperfusion of the DVC or specifically the DCP. Patients present with an acute onset paracentral scotoma and typically experience a permanent visual defect. Lesions can be caused by a diverse set of local retinal vascular diseases and systemic disorders. PAMM is a manifestation of the retinal ischemic cascade in which the mildest forms of ischemia develop at the venular end of the DCP, i.e. perivenular PAMM, while more severe forms progress horizontally to diffusely involve the INL, and the most severe forms progress vertically to infarct the inner retina. Management is targeted toward the identification and treatment of related vasculopathic and systemic risk factors.

Nonhuman Primate Model of Oculocutaneous Albinism with TYR and OCA2 Mutations

Human visual acuity is anatomically determined by the retinal fovea. The ontogenetic development of the fovea can be seriously hindered by oculocutaneous albinism (OCA), which is characterized by a disorder of melanin synthesis. Although people of all ethnic backgrounds can be affected, no efficient treatments for OCA have been developed thus far, due partly to the lack of effective animal models. Rhesus macaques are genetically homologous to humans and, most importantly, exhibit structures of the macula and fovea that are similar to those of humans; thus, rhesus macaques present special advantages in the modeling and study of human macular and foveal diseases. In this study, we identified rhesus macaque models with clinical characteristics consistent with those of OCA patients according to observations of ocular behavior, fundus examination, and optical coherence tomography. Genomic sequencing revealed a biallelic p.L312I mutation in TYR and a homozygous p.S788L mutation in OCA2, both of which were further confirmed to affect melanin biosynthesis via in vitro assays. These rhesus macaque models of OCA will be useful animal resources for studying foveal development and for preclinical trials of new therapies for OCA.

OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF THE FOVEAL AVASCULAR ZONE IN CHILDREN WITH A HISTORY OF TREATMENT-REQUIRING RETINOPATHY OF PREMATURITY

PURPOSE

To examine the characteristics of the foveal vascular structure of patients with retinopathy of prematurity (ROP) by optical coherence tomography angiography.

METHODS

Ten patients with a history of laser photocoagulation or cryopexy treatment for Stage 3 (Zone ≥ II) ROP and 10 normal subjects (controls) were included. Foveal avascular zone, vessel density, vessel length, and vascular diameter index were measured by optical coherence tomography angiography using the 3 × 3-mm Early Treatment Diabetic Retinopathy Study (ETDRS) sectors.

RESULTS

The median foveal avascular zone values of the patients with ROP and controls were 0.103 mm and 0.260 mm, respectively (P = 0.0025). The medians of the vessel density, vessel length, and vascular diameter index of the patients with ROP were 0.218 mm/mm, 11.75 mm/mm, and 18.00 μm, respectively, in ETDRS Sector 1 and did not significantly differ from those of the controls (P = 0.940, 0.733, and 0.705, respectively). For the average of ETDRS Sectors 2 to 5, the medians of the vessel density, vessel length, and vascular diameter index for the patients with ROP were 0.347 mm/mm, 18.95 mm/mm, and 18.28 μm, respectively; vessel density and vessel length were significantly smaller than those of the controls (P = 0.002 and 0.003, respectively), but there was no significant difference in vascular diameter index (P = 0.286).

CONCLUSION

Optical coherence tomography angiography-guided foveal avascular zone was significantly smaller in patients with ROP than in controls. Our results indicate that foveal vascular development may be altered in patients with a history of treatment-requiring ROP.

Glia of the human retina

The human retina contains three types of glial cells: microglia and two types of macroglia, astrocytes and Müller cells. Macroglia provide homeostatic and metabolic support to photoreceptors and neurons required for neuronal activity. The fovea, the site of the sharpest vision which is astrocyte- and microglia-free, contains two populations of Müller glia: cells which form the Müller cell cone in the foveola and z-shaped Müller cells of the foveal walls. Both populations are characterized by morphological and functional differences. Müller cells of the foveola do not support the activity of photoreceptors and neurons, but provide the structural stability of the foveal tissue and improve the light transmission through the tissue to the photoreceptors. This article gives overviews of the glia of the human retina and the structure and function of both Müller cell types in the fovea, and describes the contributions of astrocytes and Müller cells to the ontogenetic development of the fovea.

Retinal Vasculature in Development and Diseases

The retina is one of the most metabolically active tissues in the body, consuming high levels of oxygen and nutrients. A well-organized ocular vascular system adapts to meet the metabolic requirements of the retina to ensure visual function. Pathological conditions affect growth of the blood vessels in the eye. Understanding the neuronal biological processes that govern retinal vascular development is of interest for translational researchers and clinicians to develop preventive and interventional therapeutics for vascular eye diseases that address early drivers of abnormal vascular growth. This review summarizes the current knowledge of the cellular and molecular processes governing both physiological and pathological retinal vascular development, which is dependent on the interaction among retinal cell populations, including neurons, glia, immune cells, and vascular endothelial cells. We also review animal models currently used for studying retinal vascular development.

Spectral-Domain OCT Findings of Retinal Vascular-Avascular Junction in Infants with Retinopathy of Prematurity

PURPOSE

Bedside examination of premature infants at risk for retinopathy of prematurity (ROP) is predominantly performed with ophthalmoscopic en face viewing of the retina. While postmortem retinal microstructures have been studied at the vascular-avascular junction, a critical location for pathogenesis of ROP, to date this has not been possible in vivo. Here we present bedside, non-sedated in vivo cross-sectional imaging and analysis of retinal microstructures at the vascular-avascular junction in infants with ROP using handheld spectral-domain optical coherence tomography (SDOCT).

DESIGN

Prospective observational study.

PARTICIPANTS

Eleven preterm infants consented for research imaging during ROP screening examinations.

METHODS

We imaged the vascular-avascular junction in the temporal retina using a SDOCT system (Envisu, Bioptigen Inc., NC) in 18 eyes from 11 preterm infants with zone I or II, stage 0 through 4 ROP. B-scan and en face images were analyzed and compared to historical light micrographs.

MAIN OUTCOME MEASURES

SDOCT morphology at the vascular-avascular junction.

RESULTS

Multiple bedside SDOCT findings at the vascular-avascular junction were comparable to historic light micrographs: thickened inner retinal ridge structure in stage 2 ROP was comparable to thickened vanguard and rear guard cells in micrographs; vascular tufts on the posterior retinal surface in stage 2 ROP, broad arcs of neovascularization above the retina in stage 3 ROP, and splitting of inner retinal layers into clefts on either side of neovascularization mimicked findings of historic light micrographs. A unique findings was thickening of the avascular inner retinal band adjacent to neovascularization. On SDOCT imaging over several weeks, neovascularization and retinal clefts diminished after intravitreal bevacizumab therapy.

CONCLUSIONS

Retinal morphology at the vascular-avascular junction imaged with handheld SDOCT is consistent with known histopathology, and provide the advantage of monitoring change in vivo over time. These unique findings provide new insights into preterm retinal neurovascular development in ROP.

The primate fovea: Structure, function and development

A fovea is a pitted invagination in the inner retinal tissue (fovea interna) that overlies an area of photoreceptors specialized for high acuity vision (fovea externa). Although the shape of the vertebrate fovea varies considerably among the species, there are two basic types. The retina of many predatory fish, reptilians, and birds possess one (or two) convexiclivate fovea(s), while the retina of higher primates contains a concaviclivate fovea. By refraction of the incoming light, the convexiclivate fovea may function as image enlarger, focus indicator, and movement detector. By centrifugal displacement of the inner retinal layers, which increases the transparency of the central foveal tissue (the foveola), the primate fovea interna improves the quality of the image received by the central photoreceptors. In this review, we summarize ‒ with the focus on Müller cells of the human and macaque fovea ‒ data regarding the structure of the primate fovea, discuss various aspects of the optical function of the fovea, and propose a model of foveal development. The "Müller cell cone" of the foveola comprises specialized Müller cells which do not support neuronal activity but may serve optical and structural functions. In addition to the "Müller cell cone", structural stabilization of the foveal morphology may be provided by the 'z-shaped' Müller cells of the fovea walls, via exerting tractional forces onto Henle fibers. The spatial distribution of glial fibrillary acidic protein may suggest that the foveola and the Henle fiber layer are subjects to mechanical stress. During development, the foveal pit is proposed to be formed by a vertical contraction of the centralmost Müller cells. After widening of the foveal pit likely mediated by retracting astrocytes, Henle fibers are formed by horizontal contraction of Müller cell processes in the outer plexiform layer and the centripetal displacement of photoreceptors. A better understanding of the molecular, cellular, and mechanical factors involved in the developmental morphogenesis and the structural stabilization of the fovea may help to explain the (patho-) genesis of foveal hypoplasia and macular holes.

Foveal hypoplasia and optical coherence tomographic imaging

Foveal hypoplasia is a retinal disorder in which there is a lack of full development of the morphology of the fovea. The optical coherence tomography (OCT) and functional findings are presented in relation to the underlying genetic and developmental conditions. Recent advancements of high-resolution OCT imaging have unveiled characteristics of foveal hypoplasia that were not detected by conventional imaging methods. An absence of a foveal pit does not necessarily imply poor visual acuity, and the maturation of the cone photoreceptors is important for the visual acuity. Regardless of the degree of the development of the inner retinal layers, the visual acuity can be preserved as in diseases such as Stickler syndrome that is a newly identified retinal disorder associated with foveal hypoplasia.

Quantifying three-dimensional rodent retina vascular development using optical tissue clearing and light-sheet microscopy

Retinal vasculature develops in a highly orchestrated three-dimensional (3-D) sequence. The stages of retinal vascularization are highly susceptible to oxygen perturbations. We demonstrate that optical tissue clearing of intact rat retinas and light-sheet microscopy provides rapid 3-D characterization of vascular complexity during retinal development. Compared with flat mount preparations that dissect the retina and primarily image the outermost vascular layers, intact cleared retinas imaged using light-sheet fluorescence microscopy display changes in the 3-D retinal vasculature rapidly without the need for point scanning techniques. Using a severe model of retinal vascular disruption, we demonstrate that a simple metric based on Sholl analysis captures the vascular changes observed during retinal development in 3-D. Taken together, these results provide a methodology for rapidly quantifying the 3-D development of the entire rodent retinal vasculature.

Hyperglycemia Induces Bioenergetic Changes in Adipose-Derived Stromal Cells While Their Pericytic Function Is Retained

Diabetic retinopathy (DR) is a hyperglycemia (HG)-mediated microvascular complication. In DR, the loss of pericytes and subsequently endothelial cells leads to pathologic angiogenesis in retina. Adipose-derived stromal cells (ASC) are a promising source of therapeutic cells to replace lost pericytes in DR. To date, knowledge of the influence of HG on the bioenergetics and pericytic function of ASC is negligible. Human ASC were cultured in normoglycemia medium (5 mM d-glucose) or under HG (30 mM d-glucose) and assessed. Our data showed that HG increased the level of apoptosis and reactive oxygen species production in ASC, yet their proliferation rate was not affected. HG induced alterations in mitochondrial function and morphology in ASC. HG also strongly affected the bioenergetic status of ASC in which both the maximum oxygen consumption rate and extracellular acidification rate were decreased. This was corroborated by a reduced uptake of glucose under HG. In spite of these observations, in vitro, ASC promoted the formation of vascular-like networks of human umbilical vein endothelial cells on monolayers of ASC under HG with minimally affected.

Nutrition and Vascular Supply of Retinal Ganglion Cells during Human Development

PURPOSE

To review the roles of the different vascular beds nourishing the inner retina [retinal ganglion cells (RGCs)] during normal development of the human eye, using our own tissue specimens to support our conclusions.

METHODS

An extensive search of the appropriate literature included PubMed, Google scholar, and numerous available textbooks. In addition, choroidal and retinal NADPH-diaphorase stained whole mount preparations were investigated.

RESULTS

The first critical interaction between vascular bed and RGC formation occurs in the sixth to eighth month of gestation leading to a massive reduction of RGCs mainly in the peripheral retina. The first 3 years of age are characterized by an intense growth of the eyeball to near adult size. In the adult eye, the influence of the choroid on inner retinal nutrition was determined by examining the peripheral retinal watershed zones in more detail.

CONCLUSION

This delicately balanced situation of RGC nutrition is described in the different regions of the eye, and a new graphic presentation is introduced to combine morphological measurements and clinical visual field data.

Dihydroartemisinin targets VEGFR2 via the NF-κB pathway in endothelial cells to inhibit angiogenesis

The anti-malarial agent dihydroartemisinin (DHA) has strong anti-angiogenic activity. This study aimed to investigate the molecular mechanism underlying this effect of DHA on angiogenesis. We found that DHA shows a dose-dependent inhibition of proliferation and migration of in HUVECs. DHA specifically down-regulates the mRNA and protein expression of VEGFR2 in endothelial cells. Treatment with DHA increases IκB-α protein and blocks nuclear translocation of NF-κB p65. In addition, DHA directly regulates VEGFR2 promoter activity through p65 binding motif, and decreases the binding activity of p65 and VEGFR2 promoter, suggesting defective NF-κB signaling may underlie the observed effects of DHA on VEGFR2 expression. In the presence of the NF-κB inhibitor PDTC, DHA could not further repress VEGFR2. Co-treatment with PDTC and DHA produced minimal changes compared to the effects of either drug alone in in vitro angiogenesis assays. Similar findings were found in vivo through a mouse retinal neovascularization model examining the effects of PDTC and DHA. Our data suggested that DHA inhibits angiogenesis largely through repression of the NF-κB pathway. DHA is well tolerated, and therefore may be an ideal candidate to use clinically as an angiogenesis inhibitor for cancer treatment.

Development of astrocytes in the vertebrate eye

Astrocytes represent the earliest glial population in the embryonic optic nerve, contributing critically to retinal angiogenesis and formation of brain-retinal-barrier. Despite of many developmental and clinical implications of astrocytes, answers to some of the most fundamental questions of this unique type of glial cells remain elusive. This review provides an overview of the current knowledge about the origination, proliferation, and differentiation of astrocytes, their journey from the optic nerve toward the neuroretina, and their involvement in physiological and pathological development of the visual system.

Role of the retinal vascular endothelial cell in ocular disease

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

From oxygen to erythropoietin: relevance of hypoxia for retinal development, health and disease

Photoreceptors and other cells of the retina consume large quantities of energy to efficiently convert light information into a neuronal signal understandable by the brain. The necessary energy is mainly provided by the oxygen-dependent generation of ATP in the numerous mitochondria of retinal cells. To secure the availability of sufficient oxygen for this process, the retina requires constant blood flow through the vasculature of the retina and the choroid. Inefficient supply of oxygen and nutrients, as it may occur in conditions of disturbed hemodynamics or vascular defects, results in tissue ischemia or hypoxia. This has profound consequences on retinal function and cell survival, requiring an adaptational response by cells to cope with the reduced oxygen tension. Central to this response are hypoxia inducible factors, transcription factors that accumulate under hypoxic conditions and drive the expression of a large variety of target genes involved in angiogenesis, cell survival and metabolism. Prominent among these factors are vascular endothelial growth factor and erythropoietin, which may contribute to normal angiogenesis during development, but may also cause neovascularization and vascular leakage under pathologically reduced oxygen levels. Since ischemia and hypoxia may have a role in various retinal diseases such as diabetic retinopathy and retinopathy of prematurity, studying the cellular and molecular response to reduced tissue oxygenation is of high relevance. In addition, the concept of preconditioning with ischemia or hypoxia demonstrates the capacity of the retina to activate endogenous survival mechanisms, which may protect cells against a following noxious insult. Part of these mechanisms is the local production of protective factors such as erythropoietin. Due to its plethora of effects in the retina including neuro- and vaso-protective activities, erythropoietin has gained strong interest as potential therapeutic factor for retinal degenerative diseases.