Histologic and Immunohistochemical Characterization of GA-Like Pathology in the Rat Subretinal Sodium Iodate Model

Purpose

Geographic atrophy (GA) is an advanced form of dry age-related macular degeneration with multifactorial etiology and no well-established treatment. A model recapitulating the hallmarks would serve as a key to understanding the underlying pathologic mechanisms better. In this report, we further characterized our previously reported subretinal sodium iodate model of GA.

Methods

Retinal degeneration was induced in rats (6-8 weeks old) by subretinal injections of NaIO3 as described previously. Animals were sacrificed at 3, 8 and 12 weeks after injection and eyes were fixed or cryopreserved. Some choroids were processed as flatmounts while other eyes were cryopreserved, sectioned, and immunolabeled with a panel of antibodies. Finally, some eyes were prepared for transmission electron microscopic (TEM) analysis.

Results

NaIO3 subretinal injection resulted in a well-defined focal area of retinal pigment epithelium (RPE) degeneration surrounded by viable RPE. These atrophic lesions expanded over time. RPE morphologic changes at the border consisted of hypertrophy, multilayering, and the possible development of a migrating phenotype. Immunostaining of retinal sections demonstrated external limiting membrane descent, outer retinal tubulation (ORT), and extension of Müller cells toward RPE forming a glial membrane in the subretinal space of the atrophic area. TEM findings demonstrated RPE autophagy, cellular constituents of ORT, glial membranes, basal laminar deposits, and defects in Bruch's membrane.

Conclusions

In this study, we showed pathologic features of a rodent model resembling human GA in a temporal order through histology, immunofluorescence, and TEM analysis and gained insights into the cellular and subcellular levels of the GA-like phenotypes.

Translational Relevance

Despite its acute nature, the expansion of atrophy and the GA-like border in this rat model makes it ideal for studying disease progression and provides a treatment window to test potential therapeutics for GA.

Visualization of choroidal vasculature in pigmented mouse eyes from experimental models of AMD

A variety of techniques exist to investigate retinal and choroidal vascular changes in experimental mouse models of human ocular diseases. While all have specific advantages, a method for evaluating the choroidal vasculature in pigmented mouse eyes has been more challenging especially for whole mount visualization and morphometric analysis. Here we report a simple, reliable technique involving bleaching pigment prior to immunostaining the vasculature in whole mounts of pigmented mouse choroids. Eyes from healthy adult pigmented C57BL/6J mice were used to establish the methodology. The retina and anterior segment were separated from the choroid. The choroid with retinal pigment epithelial cells (RPE) and sclera was soaked in 1% ethylenediaminetetraacetic acid (EDTA) to remove the RPE. Tissues were fixed in 2% paraformaldehyde (PFA) in phosphate-buffered saline (PBS). Choroids were subjected to melanin bleaching with 10% hydrogen peroxide (H2O2) at 55 °C for 90 min, washed in PBS and then immunostained with anti-podocalyxin antibody to label vascular endothelium followed by Cy3-AffiniPure donkey anti-goat IgG at 4 °C overnight. Images of immunostained bleached choroids were captured using a Zeiss 710 confocal microscope. In addition to control eyes, this method was used to analyze the choroids from subretinal sodium iodate (NaIO3) RPE atrophy and laser-induced choroidal neovascularization (CNV) mouse models. The H2O2 pretreatment effectively bleached the melanin, resulting in a transparent choroid. Immunolabeling with podocalyxin antibody following bleaching provided excellent visualization of choroidal vasculature in the flat perspective. In control choroids, the choriocapillaris (CC) displayed different anatomical patterns in peripapillary (PP), mid peripheral (MP) and far peripheral (FP) choroid. Morphometric analysis of the vascular area (VA) revealed that the CC was most dense in the PP region (87.4 ± 4.3% VA) and least dense in FP (79.9 ± 6.7% VA). CC diameters also varied depending on location from 11.4 ± 1.97 mm in PP to 15.1 ± 3.15 mm in FP. In the NaIO3-injected eyes, CC density was significantly reduced in the RPE atrophic regions (50.7 ± 5.8% VA in PP and 45.8 ± 6.17% VA in MP) compared to the far peripheral non-atrophic regions (82.8 ± 3.8% VA). CC diameters were significantly reduced in atrophic regions (6.35 ± 1.02 mm in PP and 6.5 ± 1.2 mm in MP) compared to non-atrophic regions (14.16 ± 2.12 mm). In the laser-induced CNV model, CNV area was 0.26 ± 0.09 mm2 and luminal diameters of CNV vessels were 4.7 ± 0.9 mm. Immunostaining on bleached choroids with anti-podocalyxin antibody provides a simple and reliable tool for visualizing normal and pathologic choroidal vasculature in pigmented mouse eyes for quantitative morphometric analysis. This method will be beneficial for examining and evaluating the effects of various treatment modalities on the choroidal vasculature in mouse models of ocular diseases such as age-related macular degeneration, and degenerative genetic diseases.

Pathologic vs. protective roles of hypoxia-inducible factor 1 in RPE and photoreceptors in wet vs. dry age-related macular degeneration

It has previously been reported that antioxidant vitamins can help reduce the risk of vision loss associated with progression to advanced age-related macular degeneration (AMD), a leading cause of visual impairment among the elderly. Nonetheless, how oxidative stress contributes to the development of choroidal neovascularization (CNV) in some AMD patients and geographic atrophy (GA) in others is poorly understood. Here, we provide evidence demonstrating that oxidative stress cooperates with hypoxia to synergistically stimulate the accumulation of hypoxia-inducible factor (HIF)-1α in the retinal pigment epithelium (RPE), resulting in increased expression of the HIF-1-dependent angiogenic mediators that promote CNV. HIF-1 inhibition blocked the expression of these angiogenic mediators and prevented CNV development in an animal model of ocular oxidative stress, demonstrating the pathological role of HIF-1 in response to oxidative stress stimulation in neovascular AMD. While human-induced pluripotent stem cell (hiPSC)-derived RPE monolayers exposed to chemical oxidants resulted in disorganization and disruption of their normal architecture, RPE cells proved remarkably resistant to oxidative stress. Conversely, equivalent doses of chemical oxidants resulted in apoptosis of hiPSC-derived retinal photoreceptors. Pharmacologic inhibition of HIF-1 in the mouse retina enhanced-while HIF-1 augmentation reduced-photoreceptor apoptosis in two mouse models for oxidative stress, consistent with a protective role for HIF-1 in photoreceptors in patients with advanced dry AMD. Collectively, these results suggest that in patients with AMD, increased expression of HIF-1α in RPE exposed to oxidative stress promotes the development of CNV, but inadequate HIF-1α expression in photoreceptors contributes to the development of GA.

Clinicopathologic Findings in Three Siblings With Geographic Atrophy

Purpose

Age-related macular degeneration (AMD) is a leading cause of blindness among the elderly worldwide. Clinical imaging and histopathologic studies are crucial to understanding disease pathology. This study combined clinical observations of three brothers with geographic atrophy (GA), followed for 20 years, with histopathologic analysis.

Methods

For two of the three brothers, clinical images were taken in 2016, 2 years prior to death. Immunohistochemistry, on both flat-mounts and cross sections, histology, and transmission electron microscopy were used to compare the choroid and retina in GA eyes to those of age-matched controls.

Results

Ulex europaeus agglutinin (UEA) lectin staining of the choroid demonstrated a significant reduction in the percent vascular area and vessel diameter. In one donor, histopathologic analysis demonstrated two separate areas with choroidal neovascularization (CNV). Reevaluation of swept-source optical coherence tomography angiography (SS-OCTA) images revealed CNV in two of the brothers. UEA lectin also revealed a significant reduction in retinal vasculature in the atrophic area. A subretinal glial membrane, composed of processes positive for glial fibrillary acidic protein and/or vimentin, occupied areas identical to those of retinal pigment epithelium (RPE) and choroidal atrophy in all three AMD donors. SS-OCTA also demonstrated presumed calcific drusen in the two donors imaged in 2016. Immunohistochemical analysis and alizarin red S staining verified calcium within drusen, which was ensheathed by glial processes.

Conclusions

This study demonstrates the importance of clinicohistopathologic correlation studies. It emphasizes the need to better understand how the symbiotic relationship between choriocapillaris and RPE, glial response, and calcified drusen impact GA progression.

Topical Ketotifen Fumarate Inhibits Choroidal Mast Cell Degranulation and Loss of Retinal Pigment Epithelial Cells in Rat Model for Geographic Atrophy

Purpose

This study evaluates whether topical ketotifen fumarate (KTF) can prevent geographic atrophy (GA)-like phenotypes in a rat model.

Methods

Pharmacokinetics (PKs) of KTF after topical administration twice daily for 5 days was analyzed in rat retina, retinal pigment epithelium (RPE)/choroid/sclera, and in plasma by an liquid chromatography tandem mass spectrometry (LC-MS/MS) method. Rats were then given hydrogel implants +/- 48/80 in the superior subconjunctival space and topically treated with 1% and 0.25% of KTF or phosphate buffer saline (PBS) twice daily. Rats were euthanized at 1, 2, 4, and 8 weeks postinjection. Choroidal mast cells (MCs) were stained with nonspecific esterase and the RPE monolayer was labeled with RPE65 and ZO-1 in whole mount choroids. Retinal and choroidal areas were determined in cryosections stained with picrosirius red. Dark-adapted electroretinogram (ERG) was also performed to evaluate retinal function.

Results

PK results showed the highest level of KTF (average 5.6 nM/mg) in the RPE/choroid/sclera in rats given topical 1% KTF. Topical 1% KTF significantly reduced choroidal MC degranulation at 1 week and 2 weeks (both P < 0.001) and RPE loss at 4 weeks (P < 0.001) as well as retinal and choroidal thinning (both P < 0.001) and reduction in ERG amplitude at 8 weeks (P < 0.05) compared to PBS. Similar results were obtained with 0.25% KTF.

Conclusions

Both 1% and 0.25% KTF eye drops effectively reduced MC degranulation, RPE loss, and retinal and choroidal thinning while preventing the decline of ERG amplitude in a GA-like rat model. These data suggest that topical KTF might be a new therapeutic drug for treating GA.

Translational Relevance

The results of this study demonstrate that topical KTF successfully reduced GA-like phenotypes in a rat model and may provide a novel therapy for GA.

βA3/A1-crystallin regulates apical polarity and EGFR endocytosis in retinal pigmented epithelial cells

The retinal pigmented epithelium (RPE) is a monolayer of multifunctional cells located at the back of the eye. High membrane turnover and polarization, including formation of actin-based apical microvilli, are essential for RPE function and retinal health. Herein, we demonstrate an important role for βA3/A1-crystallin in RPE. βA3/A1-crystallin deficiency leads to clathrin-mediated epidermal growth factor receptor (EGFR) endocytosis abnormalities and actin network disruption at the apical side that result in RPE polarity disruption and degeneration. We found that βA3/A1-crystallin binds to phosphatidylinositol transfer protein (PITPβ) and that βA3/A1-crystallin deficiency diminishes phosphatidylinositol 4,5-biphosphate (PI(4,5)P2), thus probably decreasing ezrin phosphorylation, EGFR activation, internalization, and degradation. We propose that βA3/A1-crystallin acquired its RPE function before evolving as a structural element in the lens, and that in the RPE, it modulates the PI(4,5)P2 pool through PITPβ/PLC signaling axis, coordinates EGFR activation, regulates ezrin phosphorylation and ultimately the cell polarity.

Systemic dendrimer nanotherapies for targeted suppression of choroidal inflammation and neovascularization in age-related macular degeneration

Inflammation and neovascularization are key pathological events in human age-related macular degeneration (AMD). Activated microglia/macrophages (mi/ma) and retinal pigmented epithelium (RPE) play an active role in every stage of disease progression. Systemic therapies that can target these cells and address both inflammation and neovascularization will broaden the impact of existing therapies and potentially open new avenues for early AMD where there are no viable therapies. Utilizing a clinically relevant rat model of AMD that mirrors many aspects that of human AMD pathological events, we show that systemic hydroxyl-terminated polyamidoamine dendrimer-triamcinolone acetonide conjugate (D-TA) is selectively taken up by the injured mi/ma and RPE (without the need for targeting ligands). D-TA suppresses choroidal neovascularization significantly (by >80%, >50-fold better than free drug), attenuates inflammation in the choroid and retina, by limiting macrophage infiltration in the pathological area, significantly suppressing pro-inflammatory cytokines and pro-angiogenic factors, with minimal side effects to healthy ocular tissue and other organs. In ex vivo studies on human postmortem diabetic eyes, the dendrimer is also taken up into choroidal macrophages. These results suggest that the systemic hydroxyl dendrimer-drugs can offer new avenues for therapies in treating early/dry AMD and late/neovascular AMD alone, or in combination with current anti-VEGF therapies. This hydroxyl dendrimer platform but conjugated to a different drug is undergoing clinical trials for severe COVID-19, potentially paving the way for faster clinical translation of similar compounds for ocular and retinal disorders.

βA1-crystallin regulates glucose metabolism and mitochondrial function in mouse retinal astrocytes by modulating PTP1B activity

βA3/A1-crystallin, a lens protein that is also expressed in astrocytes, is produced as βA3 and βA1-crystallin isoforms by leaky ribosomal scanning. In a previous human proteome high-throughput array, we found that βA3/A1-crystallin interacts with protein tyrosine phosphatase 1B (PTP1B), a key regulator of glucose metabolism. This prompted us to explore possible roles of βA3/A1-crystallin in metabolism of retinal astrocytes. We found that βA1-crystallin acts as an uncompetitive inhibitor of PTP1B, but βA3-crystallin does not. Loss of βA1-crystallin in astrocytes triggers metabolic abnormalities and inflammation. In CRISPR/cas9 gene-edited βA1-knockdown (KD) mice, but not in βA3-knockout (KO) mice, the streptozotocin (STZ)-induced diabetic retinopathy (DR)-like phenotype is exacerbated. Here, we have identified βA1-crystallin as a regulator of PTP1B; loss of this regulation may be a new mechanism by which astrocytes contribute to DR. Interestingly, proliferative diabetic retinopathy (PDR) patients showed reduced βA1-crystallin and higher levels of PTP1B in the vitreous humor.

Retinal Glial and Choroidal Vascular Pathology in Donors Clinically Diagnosed With Stargardt Disease

Purpose

The present study investigated retinal glia and choroidal vessels in flatmounts and sections from individuals with clinically diagnosed Stargardt disease (STGD).

Methods

Eyes from three donors clinically diagnosed with STGD were obtained through the Foundation Fighting Blindness (FFB). Genetic testing was performed to determine the disease-causing mutations. Eyes were enucleated and fixed in 4% paraformaldehyde and 0.5% glutaraldehyde. After imaging, retinas were dissected and immunostained for glial fibrillary acidic protein, vimentin, and peanut agglutin. Following RPE removal, the choroid was immunostained with Ulex europaeus agglutinin lectin. For each choroid, the area of affected vasculature, percent vascular area, and choriocapillaris luminal diameters were measured. The retina from one donor was hemisected and cryopreserved or embedded in JB-4 for cross-section analysis.

Results

Genetic testing confirmed the STGD diagnosis in donor 1, whereas a mutation in peripherin 2 was identified in donor 3. Genetic testing was not successful on donor 2. Therefore, only donor 1 can definitively be classified as having STGD. All donors had areas of RPE atrophy within the macular region, which correlated with underlying choriocapillaris loss. In addition, Müller cells formed pre- and subretinal membranes. Subretinal gliotic membranes correlated almost identically with RPE and choriocapillaris loss.

Conclusions

Despite bearing different genetic mutations, all donors demonstrated choriocapillaris loss and Müller cell membranes correlating with RPE loss. Müller cell remodeling was most extensive in the donor with the peripherin mutation, whereas choriocapillaris loss was greatest in the confirmed STGD donor. This study emphasizes the importance of genetic testing when diagnosing macular disease.

Evolution of oxidative stress, inflammation and neovascularization in the choroid and retina in a subretinal lipid induced age-related macular degeneration model

Oxidative stress, inflammation and neovascularization are the key pathological events that are implicated in human age-related macular degeneration (AMD). There are a limited number of animal models available for evaluating and developing new therapies. Most models represent late exudative or neovascular AMD (nAMD) but there is a relative paucity of models that mimic early events in AMD. The purpose of this study is to characterize the evolution of oxidative stress, inflammation, retinal degeneration and neovascularization in a rat model of AMD, created by subretinal injection of human lipid hydroperoxide (HpODE) that found in the sub-macular region in aged and AMD patients. Subretinal HpODE induced retinal pigment epithelium (RPE) and retinal degeneration resulting in loss of RPE cells, photoreceptors and retinal thinning. RPE degeneration and atrophy were detected by day 5, followed by neural tissue degeneration at day 12 with robust TUNEL positive cells. Western blot analysis confirmed an increase in pro-apoptotic Bak protein at day 12 in retinal tissues. Oxidative damage biomarkers (4-hydroxynonenal, malondialdehyde, 8-hydroxy-2'-deoxyguanosine, and nitrotyrosine) increased in retinal tissue from days 5-12. Müller glial activation was observed in the HpODE injected area at day 5 followed by its remodeling and migration in the outer retina by day 20. RT-qPCR analysis further indicated upregulation of pro-inflammatory genes (TNF-α, IL-1β and IL-6) both in retinal and RPE/choroidal tissue as early as day 2 and persisted until day 12. Upregulation of oxidative stress markers such as NADPH oxidase (NOX and DOUX family) was detected early in retinal tissue by day 2 followed by its upregulation in choroidal tissue at day 5. Neovascularization was demonstrated from day 12 to day 20 post HpODE injection in choroidal tissue. The results from this study indicate that subretinal HpODE induces advanced AMD phenotypes comprising many aspects of both dry/early and late) and neovascular/late AMD as observed in humans. Within 3 weeks via oxidative damage, upregulation of reactive oxygen species and pro-inflammatory genes, pro-apoptotic Bak and pro-angiogenic VEGF upregulation occurs leading to CNV formation. This experimental model of subretinal HpODE is an appropriate model for the study of AMD and provides an important platform for translational and basic research in developing new therapies particularly for early/dry AMD where currently no viable therapies are available.

Role of glia in optic nerve

Glial cells are critically important for maintenance of neuronal activity in the central nervous system (CNS), including the optic nerve (ON). However, the ON has several unique characteristics, such as an extremely high myelination level of retinal ganglion cell (RGC) axons throughout the length of the nerve (with virtually all fibers myelinated by 7 months of age in humans), lack of synapses and very narrow geometry. Moreover, the optic nerve head (ONH) - a region where the RGC axons exit the eye - represents an interesting area that is morphologically distinct in different species. In many cases of multiple sclerosis (demyelinating disease of the CNS) vision problems are the first manifestation of the disease, suggesting that RGCs and/or glia in the ON are more sensitive to pathological conditions than cells in other parts of the CNS. Here, we summarize current knowledge on glial organization and function in the ON, focusing on glial support of RGCs. We cover both well-established concepts on the important role of glial cells in ON health and new findings, including novel insights into mechanisms of remyelination, microglia/NG2 cell-cell interaction, astrocyte reactivity and the regulation of reactive astrogliosis by mitochondrial fragmentation in microglia.

A role for mast cells in geographic atrophy

Mast cells (MCs) are the initial responders of innate immunity and their degranulation contribute to various etiologies. While the abundance of MCs in the choroid implies their fundamental importance in the eye, little is known about the significance of MCs and their degranulation in choroid. The cause of geographic atrophy (GA), a progressive dry form of age-related macular degeneration is elusive and there is currently no therapy for this blinding disorder. Here we demonstrate in both human GA and a rat model for GA, that MC degranulation and MC-derived tryptase are central to disease progression. Retinal pigment epithelium degeneration followed by retinal and choroidal thinning, characteristic phenotypes of GA, were driven by continuous choroidal MC stimulation and activation in a slow release fashion in the rat. Genetic manipulation of MCs, pharmacological intervention targeting MC degranulation with ketotifen fumarate or inhibition of MC-derived tryptase with APC 366 prevented all of GA-like phenotypes following MC degranulation in the rat model. Our results demonstrate the fundamental role of choroidal MC involvement in GA disease etiology, and will provide new opportunities for understanding GA pathology and identifying novel therapies targeting MCs.

Modulating EGFR-MTORC1-autophagy as a potential therapy for persistent fetal vasculature (PFV) disease

Persistent fetal vasculature (PFV) is a human disease that results from failure of the fetal vasculature to regress normally. The regulatory mechanisms responsible for fetal vascular regression remain obscure, as does the underlying cause of regression failure. However, there are a few animal models that mimic the clinical manifestations of human PFV, which can be used to study different aspects of the disease. One such model is the Nuc1 rat model that arose from a spontaneous mutation in the Cryba1 (crystallin, beta 1) gene and exhibits complete failure of the hyaloid vasculature to regress. Our studies with the Nuc1 rat indicate that macroautophagy/autophagy, a process in eukaryotic cells for degrading dysfunctional components to ensure cellular homeostasis, is severely impaired in Nuc1 ocular astrocytes. Further, we show that CRYBA1 interacts with EGFR (epidermal growth factor receptor) and that loss of this interaction in Nuc1 astrocytes increases EGFR levels. Moreover, our data also show a reduction in EGFR degradation in Nuc1 astrocytes compared to control cells that leads to over-activation of the mechanistic target of rapamycin kinase complex 1 (MTORC1) pathway. The impaired EGFR-MTORC1-autophagy signaling in Nuc1 astrocytes triggers abnormal proliferation and migration. The abnormally migrating astrocytes ensheath the hyaloid artery, contributing to the pathogenesis of PFV in Nuc1, by adversely affecting the vascular remodeling processes essential to regression of the fetal vasculature. Herein, we demonstrate in vivo that gefitinib (EGFR inhibitor) can rescue the PFV phenotype in Nuc1 and may serve as a novel therapy for PFV disease by modulating the EGFR-MTORC1-autophagy pathway.

ABBREVIATIONS

ACTB: actin, beta; CCND3: cyclin 3; CDK6: cyclin-dependent kinase 6; CHQ: chloroquine; COL4A1: collagen, type IV, alpha 1; CRYBA1: crystallin, beta A1; DAPI: 4'6-diamino-2-phenylindole; EGFR: epidermal growth factor receptor; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GFAP: glial fibrillary growth factor; KDR: kinase insert domain protein receptor; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MKI67: antigen identified by monoclonal antibody Ki 67; MTORC1: mechanistic target of rapamycin kinase complex 1; PARP: poly (ADP-ribose) polymerase family; PCNA: proliferating cell nuclear antigen; PFV: persistent fetal vasculature; PHPV: persistent hyperplastic primary vitreous; RPE: retinal pigmented epithelium; RPS6: ribosomal protein S6; RPS6KB1: ribosomal protein S6 kinase, polypeptide 1; SQSTM1/p62: sequestome 1; TUBB: tubulin, beta; VCL: vinculin; VEGFA: vascular endothelial growth factor A; WT: wild type.

Choriocapillaris dropout in early age-related macular degeneration

Loss of choriocapillaris (CC) in advanced age-related macular degeneration (AMD) is well documented but changes in early AMD have not been quantified. Postmortem eyes from donors with clinically documented early AMD were examined in choroidal whole mounts to determine the area, pattern, and severity of CC loss. Choroids from postmortem human eyes without AMD (n = 7; mean age = 86.1) and from eyes with a Grade 2 clinical classification of early AMD (n = 7; mean age = 87) were immunolabeled with Ulex europaeus agglutinin (UEA) lectin-FITC to stain blood vessels. Whole mounts were imaged using confocal microscopy and image analysis was performed to determine the area of vascular changes and density of vasculature (percent vascular area, %VA). All areas evaluated had a complete RPE monolayer upon gross examination. In age-matched control eyes, the CC had broad lumens and a homogenous pattern of freely interconnecting capillaries. The mean %VA ± standard deviation in submacula of control subjects was 78.1 ± 3.25%. In eyes with early AMD, there was a significant decrease in mean %VA to 60.1 ± 10.4% (p < 0.0001). The paramacular %VA was not significantly different in eyes with or without AMD. The area of submacular choroid affected by CC dropout was 0.04 ± 0.09 mm² in control eyes. In eyes with early AMD, the mean area affected by CC dropout was significantly increased (10.4 ± 6.1 mm²; p < 0.001). In some cases, incipient neovascular buds were observed at the border of regions with CC dropout in early AMD choroids. In conclusion, UEA lectin-labeled choroidal whole mounts from donors with clinically documented early AMD has provided a unique opportunity to examine regional changes in vascular pathology associated with choriocapillaris. The study demonstrated attenuation of submacular CC in early AMD subjects but no vascular pathology was observed outside the submacular region. While the affected area in some eyes was quite extensive histologically, these changes may not be detectable clinically using standard in vivo imaging.

Neutrophils homing into the retina trigger pathology in early age-related macular degeneration

Age-related macular degeneration (AMD) is an expanding problem as longevity increases worldwide. While inflammation clearly contributes to vision loss in AMD, the mechanism remains controversial. Here we show that neutrophils are important in this inflammatory process. In the retinas of both early AMD patients and in a mouse model with an early AMD-like phenotype, we show neutrophil infiltration. Such infiltration was confirmed experimentally using ribbon-scanning confocal microscopy (RSCM) and IFNλ- activated dye labeled normal neutrophils. With neutrophils lacking lipocalin-2 (LCN-2), infiltration was greatly reduced. Further, increased levels of IFNλ in early AMD trigger neutrophil activation and LCN-2 upregulation. LCN-2 promotes inflammation by modulating integrin β1 levels to stimulate adhesion and transmigration of activated neutrophils into the retina. We show that in the mouse model, inhibiting AKT2 neutralizes IFNλ inflammatory signals, reduces LCN-2-mediated neutrophil infiltration, and reverses early AMD-like phenotype changes. Thus, AKT2 inhibitors may have therapeutic potential in early, dry AMD.

An Acute Injury Model for the Phenotypic Characteristics of Geographic Atrophy

Purpose

Geographic atrophy (GA) is the late stage of non-neovascular age-related macular degeneration. A lack of animal models for GA has hampered treatment efforts. Presented herein is a rat model for GA using subretinal injection of sodium iodate (NaIO₃).

Methods

Rats were given subretinal injections of NaIO₃ (5 μg/μL) using a pico-injector. Fundus photographs and spectral domain optical coherent tomography scans were collected at 1, 3, 7, 14, and 28 days after injection, at which time rats were euthanized and eyes were enucleated. Eyes were either cryopreserved or dissected into retinal and choroidal flatmounts. Fluorescence immunohistochemistry was performed for retinal glial fibrillary acidic protein (activated Müller cells and astrocytes) and vimentin (Müller cells), as well as peanut agglutin lectin (photoreceptors) labeling. RPE/choroids were labeled for RPE65 and CD34. Images were collected on Zeiss confocal microscopes.

Results

Fundus photos, spectral domain optical coherent tomography, and RPE65 staining revealed well-demarcated areas with focal loss of RPE and photoreceptors in NaIO₃-treated rats. At 1 day after injection, RPE cells appeared normal. By 3 days, there was patchy RPE and photoreceptor loss in the injected area. RPE and photoreceptors were completely degenerated in the injected area by 7 days. A large subretinal glial membrane occupied the degenerated area. Choriocapillaris was highly attenuated in the injected area at 14 and 28 days.

Conclusions

The rat model reported herein mimics the photoreceptor cell loss, RPE atrophy, glial membrane formation, and choriocapillaris degeneration seen in GA. This model will be valuable for developing and testing drugs and progenitor cell regenerative therapies for GA.

A Role for βA3/A1-Crystallin in Type 2 EMT of RPE Cells Occurring in Dry Age-Related Macular Degeneration

Purpose

The RPE cells have a major role in the development of dry age-related macular degeneration (AMD). We present novel evidence that βA3/A1-crystallin, encoded by the Cryba1 gene, a protein known to be important for lysosomal clearance in the RPE, also has a role in epithelial-to-mesenchymal transition (EMT) of RPE cells.

Methods

RPE from dry AMD globes, genetically engineered mice lacking Cryba1 globally or specifically in the RPE, spontaneous mutant rats (Nuc1) with a loss-of-function mutation in Cryba1, and the melanoma OCM3 cell line were used. Spatial localization of proteins was demonstrated with immunofluorescence, gene expression levels were determined by quantitative PCR (qPCR), and protein levels by Western blotting. Cell movement was evaluated using wound healing and cell migration assays. Co-immunoprecipitation was used to identify binding partners of βA3/A1-crystallin.

Results

βA3/A1-crystallin is upregulated in polarized RPE cells compared to undifferentiated cells. Loss of βA3/A1-crystallin in murine and human RPE cells resulted in upregulation of Snail and vimentin, downregulation of E-cadherin, and increased cell migration. βA3/A1-crystallin binds to cortactin, and loss of βA3/A1-crystallin resulted in increased P-cortactin^Y421. The RPE from AMD samples had increased Snail and vimentin, and decreased E-cadherin, compared to age-matched controls.

Conclusions

We introduced a novel concept of dry AMD initiation induced by lysosomal clearance defects in the RPE and subsequent attempts by RPE cells to avoid the resulting stress by undergoing EMT. We demonstrate that βA3/A1-crystallin is a potential therapeutic target for AMD through rejuvenation of lysosomal dysfunction and potentially, reversal of EMT.

Ocular Histopathology and Immunohistochemical Analysis in the Oldest Known Individual with Autosomal Dominant Vitreoretinochoroidopathy

PURPOSE

To assess the immunohistochemical and histopathological changes in a subject with Autosomal Dominant Vitreoretinochoroidopathy (ADVIRC).

DESIGN

Case study.

PARTICIPANT

Ninety two year-old Caucasian male with ADVIRC.

METHODS

The subject was documented clinically for 54 Years. The retina/choroid complex of the right eye was evaluated with cryosections stained with hematoxylin and eosin or periodic acid schiff reagent. Cryosections were also evaluated with immunofluorescence or alkaline phosphatase immunohistochemistry (IHC) using primary antibodies against bestrophin1, GFAP, PEDF, RPE65, TGFβ, VEGF, and vimentin. The left retina and choroid were evaluated as flat mounts using immunofluorescence. UEA lectin was used to stain viable vasculature.

MAIN OUTCOME MEASURES

The immunohistochemical and histopathological changes in retina and choroid from a subject with ADVIRC.

RESULTS

The subject had a heterozygous c.248G>A variant in exon 4 of the BEST1 gene. There was widespread chorioretinal degeneration and atrophy except for an island of spared RPE monolayer in the perimacula/macula OU. In this region, some photoreceptors were present, choriocapillaris was spared, and retinal pigment epithelial cells were in their normal disposition. There was a Muller cell periretinal membrane throughout much of the fundus. Bestrophin-1 was not detected or only minimally present by IHC in the ADVIRC RPE, even in the spared RPE area. Beyond the island of retained RPE monolayer on Bruch's membrane (BrMb), there was migration of RPE into the neuro-retina, often ensheathing blood vessels and producing excessive matrix within their perivascular aggregations.

CONCLUSIONS

The primary defect in ADVIRC is in RPE, the only cells in the eye that express the BEST1 gene. The dysfunctional RPE cells may go through epithelial/mesenchymal transition as they migrate from BrMb to form papillary aggregations in the neuro-retina, often ensheathing blood vessels. This may be the reason for retinal blood vessel nonperfusion. Migration of RPE from BrMb was also associated with attenuation of the choriocapillaris.

Subretinal Glial Membranes in Eyes With Geographic Atrophy

Purpose

Müller cells create the external limiting membrane (ELM) by forming junctions with photoreceptor cells. This study evaluated the relationship between focal photoreceptors and RPE loss in geographic atrophy (GA) and Müller cell extension into the subretinal space.

Methods

Human donor eyes with no retinal disease or geographic atrophy (GA) were fixed and the eye cups imaged. The retinal posterior pole was stained for glial fibrillary acidic protein (GFAP; astrocytes and activated Müller cells) and vimentin (Müller cells) while the submacular choroids were labeled with Ulex Europaeus Agglutinin lectin (blood vessels). Choroids and retinas were imaged using a Zeiss 710 confocal microscope. Additional eyes were cryopreserved or processed for transmission electron microscopy (TEM) to better visualize the Müller cells.

Results

Vimentin staining of aged control retinas (n = 4) revealed a panretinal cobblestone-like ELM. While this pattern was also observed in the GA retinas (n = 7), each also had a distinct area in which vimentin⁺ and vimentin⁺/GFAP⁺ processes created a subretinal membrane. Subretinal glial membranes closely matched areas of RPE atrophy in the gross photos. Choroidal vascular loss was also evident in these atrophic areas. Smaller glial projections were noted, which correlated with drusen in gross photos. The presence of glia in the subretinal space was confirmed by TEM and cross cross-section immunohistochemistry.

Conclusions

In eyes with GA, subretinal Müller cell membranes present in areas of RPE atrophy may be a Müller cell attempt to replace the ELM. These membranes could interfere with treatments such as stem cell therapy.

Histopathological Insights Into Choroidal Vascular Loss in Clinically Documented Cases of Age-Related Macular Degeneration

Importance

Age-related macular degeneration (AMD) is a multifactorial disease with genetic and environmental factors contributing to risk. Histopathologic changes underlying AMD are not fully understood, particularly the relationship between choriocapillaris (CC) dysfunction and phenotypic variability of this disease.

Objective

To examine histopathologic changes in the CC of eyes with clinically documented AMD.

Design, Setting, and Participants

The study was designed in 2011. Tissues were collected post mortem (2012-2016), and histopathological images were obtained from participants enrolled in AMD studies since 1988. Clinical records and images were collected from participants as standard protocol. Eyes without AMD (n = 4) and eyes with early (n = 9), intermediate (n = 5), and advanced stages of AMD (geographic atrophy, n = 5; neovascular disease, n = 13) were evaluated. Choroidal vasculature was labeled using Ulex europaeus agglutinin lectin and examined using confocal microscopy.

Main Outcomes and Measures

A standardized classification system was applied to determine AMD stage. Ocular records and images were reviewed and histopathologic analyses performed. Viability of the choroidal vasculature was analyzed for each AMD stage.

Results

All participants were white. Fourteen were male, and 16 were female. The mean age was 90.5 years among AMD patients and 88.5 years among control participants. Submacular CC dropout without retinal pigment eipthelial (RPE) loss was observed in all cases with early stages of AMD. Higher vascular area loss for each AMD stage was observed compared with control participants: 20.5% in early AMD (95% CI, 11.2%-40.2%; P < .001), 12.5% in intermediate AMD (95% CI, 2.9%-21.4%; P = .01), 39.0% loss in GA (95% CI, 32.1%-45.4%; P < .001), and 38.2% loss in neovascular disease where RPE remained intact (95% CI, 27.7%-47.9%; P < .001). Hypercellular, apparent neovascular buds were adjacent to areas of CC loss in 22.2% of eyes with early AMD and 40% of eyes with intermediate AMD.

Conclusions and Relevance

Retinal pigment epithelial atrophy preceded CC loss in geographic atrophy, but CC loss occurred in the absence of RPE atrophy in 2 of 9 eyes with early-stage AMD. Given the cross-sectional nature of this study and the small number of eyes evaluated, definitive conclusions regarding this progression cannot be determined with certainty. We speculate that neovascular buds may be a precursor to neovascular disease. Hypoxic RPE resulting from reduced blood supply might upregulate production of vascular endothelial growth factor, providing the stimulus for neovascular disease.

The amino acid transporter SLC36A4 regulates the amino acid pool in retinal pigmented epithelial cells and mediates the mechanistic target of rapamycin, complex 1 signaling

The dry (nonneovascular) form of age‐related macular degeneration (AMD), a leading cause of blindness in the elderly, has few, if any, treatment options at present. It is characterized by early accumulation of cellular waste products in the retinal pigmented epithelium (RPE); rejuvenating impaired lysosome function in RPE is a well‐justified target for treatment. It is now clear that amino acids and vacuolar‐type H⁺‐ATPase (V‐ATPase) regulate the mechanistic target of rapamycin, complex 1 (mTORC1) signaling in lysosomes. Here, we provide evidence for the first time that the amino acid transporter SLC36A4/proton‐dependent amino acid transporter (PAT4) regulates the amino acid pool in the lysosomes of RPE. In Cryba1 (gene encoding βA3/A1‐crystallin) KO (knockout) mice, where PAT4 and amino acid levels are increased in the RPE, the transcription factors EB (TFEB) and E3 (TFE3) are retained in the cytoplasm, even after 24 h of fasting. Consequently, genes in the coordinated lysosomal expression and regulation (CLEAR) network are not activated, and lysosomal function remains low. As these mice age, expression of RPE65 and lecithin retinol acyltransferase (LRAT), two vital visual cycle proteins, decreases in the RPE. A defective visual cycle would possibly slow down the regeneration of new photoreceptor outer segments (POS). Further, photoreceptor degeneration also becomes obvious during aging, reminiscent of human dry AMD disease. Electron microscopy shows basal laminar deposits in Bruch's membrane, a hallmark of development of AMD. For dry AMD patients, targeting PAT4/V‐ATPase in the lysosomes of RPE cells may be an effective means of preventing or delaying disease progression.

Albumen Transport to Bruch's Membrane and RPE by Choriocapillaris Caveolae

PURPOSE

The choriocapillaris (CC), the capillary network of the choroid, is positioned adjacent to Bruch's membrane (BM) and the RPE. The aim of this study was to clarify the mechanism(s) for transport of serum albumen from CC lumen to RPE.

METHODS

Alexa647 conjugated to BSA (BSA-A647) or PBS was administrated via the femoral vein to young and aged wild-type (WT; C57BL/6J) mice and Caveolin-1 knockout mice (Cav1(-/-)). Mice were perfused with PBS and killed at 30 minutes, 1 hour, and 4 hours after injection. Eyecups were cryopreserved, and cryosections were analyzed on a Zeiss 710 confocal microscope. Bovine serum albumin conjugated to gold nanoparticles (BSA-GNP) was administrated through the left common carotid artery. Mice were perfused with PBS and killed at 30 minutes after injection. Eyecups were embedded after fixation, and 70-nm-thick sections were analyzed on a Hitachi H7600 transmission electron microscope.

RESULTS

In eyes of WT young mice, BSA-A647 was transported to the RPE at 30 minutes and diffused to the photoreceptor layer by 1 hour. In contrast, most BSA-A647 was found in the CC in Cav1(-/-) eyes. The majority of BSA-GNP found in the CC of young WT mice was on the luminal side in caveolae at 30 minutes after injection. In aged WT mice, BSA-GNPs were found in defective tight junctions between endothelial cells and appeared trapped at the diaphragm of fenestrations.

CONCLUSIONS

Normally, CC carefully regulates transport system of BSA from lumen to BM by caveolae-mediated transcytosis; however, endothelium cells of aged control WT mice have leaky tight junctions and lacked regulated BSA transport.

Increased choroidal mast cells and their degranulation in age-related macular degeneration

BACKGROUND/AIMS

Inflammation has been implicated in age-related macular degeneration (AMD). This study investigates the association of mast cells (MCs), a resident choroidal inflammatory cell, with pathological changes in AMD.

METHODS

Human donor eyes included aged controls (n=10), clinically diagnosed with early AMD (n=8), geographic atrophy (GA, n=4) and exudative AMD (n=11). The choroids were excised and incubated for alkaline phosphatase (APase; blood vessels) and non-specific esterase activities (MCs). Degranulated (DG) and non-degranulated MCs in four areas of posterior choroid (nasal, non-macular, paramacular and submacular) were counted in flat mounts (4-6 fields/area). Choroids were subsequently embedded in JB-4 and sectioned for histological analyses.

RESULTS

The number of MCs was significantly increased in all choroidal areas in early AMD (p=0.0006) and in paramacular area in exudative AMD (139.44±55.3 cells/mm(2); p=0.0091) and GA (199.08±82.0 cells/mm(2); p=0.0019) compared with the aged controls. DG MCs were also increased in paramacular (p=0.001) and submacular choroid (p=0.02) in all forms of AMD. Areas with the greatest numbers of DG MCs had loss of choriocapillaris (CC). Sections revealed that the MCs were widely distributed in Sattler's and Haller's layer in the choroidal stroma in aged controls, whereas MCs were frequently found in close proximity with CC in GA and exudative AMD and in choroidal neovascularisation (CNV).

CONCLUSION

Increased MC numbers and degranulation were observed in all AMD choroids. These results suggest that MC degranulation may contribute to the pathogenesis of AMD: death of CC and retinal pigment epithelial and CNV formation. The proteolytic enzymes released from MC granules may result in thinning of AMD choroid.

Idiopathic preretinal glia in aging and age-related macular degeneration

During analysis of glia in wholemount aged human retinas, frequent projections onto the vitreal surface of the inner limiting membrane (ILM) were noted. The present study characterized these preretinal glial structures. The amount of glial cells on the vitreal side of the ILM was compared between eyes with age-related macular degeneration (AMD) and age-matched control eyes. Retinal wholemounts were stained for markers of retinal astrocytes and activated Müller cells (glial fibrillary acidic protein, GFAP), Müller cells (vimentin, glutamine synthetase) and microglia/hyalocytes (IBA-1). Retinal vessels were labeled with UEA lectin. Images were collected using a Zeiss LSM 710 confocal microscope. Retinas were then cryopreserved. Laminin labeling of cryosections determined the location of glial structures in relation to the ILM. All retinas investigated herein had varied amounts of preretinal glia. These glial structures were classified into three groups based on size: sprouts, blooms, and membranes. The simplest of the glial structures observed were focal sprouts of singular GFAP-positive cells or processes on the vitreal surface of the ILM. The intermediate structures observed, glial blooms, were created by multiple cells/processes exiting from a single point and extending along the vitreoretinal surface. The most extensive structures, glial membranes, consisted of compact networks of cells and processes. Preretinal glia were observed in all areas of the retina but they were most prominent over large vessels. While all glial blooms and membranes contained vimentin and GFAP-positive cells, these proteins did not always co-localize. Many areas had no preretinal GFAP but had numerous vimentin only glial sprouts. In double labeled glial sprouts, vimentin staining extended beyond that of GFAP. Hyalocytes and microglia were detected along with glial sprouts, blooms, and membranes. They did not, however, concentrate in the retina below these structures. Cross sectional analysis identified small breaks in the ILM above large retinal vessels through which glial cells exited the retina. Preretinal glial structures of varied sizes are a common occurrence in aged retinas and, in most cases, are subclinical. While all retinal glia are found in blooms, vimentin labeling suggests that Müller cells form the leading edge. All retinas investigated from eyes with active choroidal neovascularization (CNV) had extensive glial membranes on the vitreal surface of the ILM. Although these structures may be benign, they may exert traction on the retina as they spread along the vitreoretinal interface. In cases with CNV, glial cells in the vitreous could bind intravitreally injected anti-vascular endothelial growth factor. These preretinal glial structures indicate the remodeling of both astrocytes and Müller cells in aged retinas, in particular those with advanced AMD.

Increased Lipocalin-2 in the retinal pigment epithelium of Cryba1 cKO mice is associated with a chronic inflammatory response

Although chronic inflammation is believed to contribute to the pathology of age-related macular degeneration (AMD), knowledge regarding the events that elicit the change from para-inflammation to chronic inflammation in the pathogenesis of AMD is lacking. We propose here that lipocalin-2 (LCN2), a mammalian innate immunity protein that is trafficked to the lysosomes, may contribute to this process. It accumulates significantly with age in retinal pigment epithelial (RPE) cells of Cryba1 conditional knockout (cKO) mice, but not in control mice. We have recently shown that these mice, which lack βA3/A1-crystallin specifically in RPE, have defective lysosomal clearance. The age-related increase in LCN2 in the cKO mice is accompanied by increases in chemokine (C-C motif) ligand 2 (CCL2), reactive gliosis, and immune cell infiltration. LCN2 may contribute to induction of a chronic inflammatory response in this mouse model with AMD-like pathology.

Lysosomal-mediated waste clearance in retinal pigment epithelial cells is regulated by CRYBA1/βA3/A1-crystallin via V-ATPase-MTORC1 signaling

In phagocytic cells, including the retinal pigment epithelium (RPE), acidic compartments of the endolysosomal system are regulators of both phagocytosis and autophagy, thereby helping to maintain cellular homeostasis. The acidification of the endolysosomal system is modulated by a proton pump, the V-ATPase, but the mechanisms that direct the activity of the V-ATPase remain elusive. We found that in RPE cells, CRYBA1/βA3/A1-crystallin, a lens protein also expressed in RPE, is localized to lysosomes, where it regulates endolysosomal acidification by modulating the V-ATPase, thereby controlling both phagocytosis and autophagy. We demonstrated that CRYBA1 coimmunoprecipitates with the ATP6V0A1/V₀-ATPase a1 subunit. Interestingly, in mice when Cryba1 (the gene encoding both the βA3- and βA1-crystallin forms) is knocked out specifically in RPE, V-ATPase activity is decreased and lysosomal pH is elevated, while cathepsin D (CTSD) activity is decreased. Fundus photographs of these Cryba1 conditional knockout (cKO) mice showed scattered lesions by 4 months of age that increased in older mice, with accumulation of lipid-droplets as determined by immunohistochemistry. Transmission electron microscopy (TEM) of cryba1 cKO mice revealed vacuole-like structures with partially degraded cellular organelles, undigested photoreceptor outer segments and accumulation of autophagosomes. Further, following autophagy induction both in vivo and in vitro, phospho-AKT and phospho-RPTOR/Raptor decrease, while pMTOR increases in RPE cells, inhibiting autophagy and AKT-MTORC1 signaling. Impaired lysosomal clearance in the RPE of the cryba1 cKO mice also resulted in abnormalities in retinal function that increased with age, as demonstrated by electroretinography. Our findings suggest that loss of CRYBA1 causes lysosomal dysregulation leading to the impairment of both autophagy and phagocytosis.

Co-expression of endothelial and neuronal nitric oxide synthases in the developing vasculatures of the human fetal eye

BACKGROUND

Nitric oxide (NO) is a multifunctional gaseous molecule that regulates various physiological functions in both neuronal and non-neuronal cells. NO is synthesized by nitric oxide synthases (NOSs), of which three isoforms have been identified. Neuronal NOS (nNOS) and endothelial NOS (eNOS) constitutively produce low levels of NO as a cell-signaling molecule in response to an increase in intracellular calcium concentration. Recent data have revealed a predominant role of eNOS in both angiogenesis and vasculogenesis.

METHODS

The immunohistochemical localization of nNOS and eNOS was investigated during embryonic and fetal ocular vascular development from 7 to 21 weeks gestation (WG) on sections of cryopreserved tissue.

RESULTS

eNOS was confined to endothelial cells of developing vessels at all ages studied. nNOS was prominent in nuclei of vascular endothelial and smooth muscle cells in the fetal vasculature of vitreous and choriocapillaris. nNOS was also prominent in the nuclei of CXCR4(+) progenitors in the inner retina and inner neuroblastic layer.

CONCLUSIONS

These findings demonstrate co-expression of n- and eNOS isoforms in different compartments of vasoformative cells during development. Nuclear nNOS was present in vascular and nonvascular progenitors as well as endothelial cells and pericytes. This suggests that nNOS may play a role in the transcription regulatory systems in endothelial cells and pericytes during ocular hemo-vasculogenesis, vasculogenesis, and angiogenesis.

C-reactive protein and complement factor H in aged human eyes and eyes with age-related macular degeneration

BACKGROUND

There is increasing evidence that inflammation and immune-mediated processes (complement activation) play an important role in age-related macular degeneration (AMD) pathogenesis. A genetic variation in the gene encoding complement factor H (CFH) and plasma levels of C-reactive protein (CRP), a systemic marker of subclinical inflammation, have consistently been shown to be associated with an increased risk for AMD. In the present study, we examined the immunolocalisation of CRP and CFH in aged control human donor eyes (n=10; mean age 79 years) and eyes with AMD (n=18; mean age 83 years).

METHODS

Alkaline phosphatase immunohistochemistry was performed using polyclonal antibodies against CRP and CFH on cryopreserved tissue sections from disc/macular blocks. Three independent masked observers scored the reaction product (0-8).

RESULTS

In aged control eyes, the retinal pigment epithelium/Bruch's membrane/choriocapillaris (RPE/BrM/CC) complex including intercapillary septa (ICS) had the most prominent immunostaining for CRP and CFH. CRP was significantly higher than controls in BrM/CC/ICS and choroidal stroma in early and wet AMD eyes (p<0.05). In contrast, CFH was significantly lower in BrM/CC/ICS complex of AMD choroids than in controls (p<0.05). Interestingly, CRP and CFH were significantly reduced in BrM/CC/ICS complex in atrophic area of macula in geographical atrophy (p<0.05). Drusen and basal laminar deposits were intensely positive for CRP and CFH.

CONCLUSION

These immunohistochemical findings show that changes in distribution and relative levels of CRP and CFH were evident in early and late AMD eyes. This suggests that high levels of CRP and insufficient CFH at the retina/choroid interface may lead to uncontrolled complement activation with associated cell and tissue damage. This study supports the hypothesis that inflammation and immune-mediated mechanisms are involved in the pathogenesis of AMD.

Immunohistochemical localization of low density lipoprotein receptor-related protein 1 and alpha(2)-Macroglobulin in retinal and choroidal tissue of proliferative retinopathies

The immunolocalization of the low density lipoprotein receptor-related protein 1 (LRP1) and its ligand alpha 2-Macroglobulin (alpha(2)M) was examined in tissues from human donor eyes of normal, diabetic and sickle cell disease subjects. Streptavidin alkaline phosphatase immunohistochemistry was performed with a mouse anti-human LRP1 and rabbit anti-human alpha(2)M antibodies. Retinal and choroidal blood vessels were labeled with mouse anti-human CD34 antibody in adjacent tissue sections. Mean scores for immunostaining from the pathological and control eyes were statistically compared. LRP1 immunoreactivity was very weak to negative in the neural retina of normal subjects except in scattered astrocytes. LRP1 expression in diabetic eyes was detected in the internal limiting membrane (ILM), astrocytes, inner photoreceptor matrix, choriocapillaris and choroidal stroma. The ligand alpha(2)M, however, was limited mainly to blood vessel walls, some areas of the inner nuclear layer (INL), photoreceptors, RPE-Bruch's membrane-choriocapillaris complex, intercapillary septa, and choroidal stroma. In sickle cell eyes, avascular and vascular retina as well as choroidal neovascularization (CNV) were analyzed. In avascular areas, LRP1 immunoreactivity was in innermost retina (presumably ILM, astrocytes, and Muller cells) and INL as well as RPE-Bruch's membrane-choriocapillaris complex and choroidal stroma. alpha(2)M was very weak in avascular peripheral retina compared to vascularized areas and limited to stroma in choroid. In contrast, in areas with CNV, LRP1 immunoreactivity was significantly decreased in overlying retina and in RPE-Bruch's membrane and choroidal stroma compared to the controls, while alpha(2)M was elevated in RPE-Bruch's membrane near CNV compared to normal areas in sickle cell choroid. The mean scores revealed that LRP1 and alpha(2)M in neural retina were significantly elevated in astrocytes and ILM in diabetic eyes (p < or = 0.05), whereas in sickle cell eyes scores were elevated in ILM and INL (p < or = 0.05). In addition, alpha(2)M immunoreactivity was in photoreceptors in both ischemic retinopathies. In choroid, the patterns of LRP1 and alpha(2)M expression were different and not coincident. This is the first demonstration of the presence of LRP1 and alpha(2)M in human proliferative retinopathies. Elevated LRP1 expression in sickle cell neural retina and diabetic inner retina and choroid suggests that LRP1 plays an important role in ischemic neovascular diseases.

A rat model for choroidal neovascularization using subretinal lipid hydroperoxide injection

The purpose of this study was to develop and characterize a rat model of choroidal neovascularization (CNV) as occurs in age-related macular degeneration. The lipid hydroperoxide 13(S)-hydroperoxy-9Z,11E-octadecadienoic acid (HpODE) is found in submacular Bruch's membrane in aged humans and has been reported to generate neovascularization in a rabbit model. Three weeks after a single subretinal injection of 30 microg of HpODE, eyes of Sprague-Dawley rats were harvested. Follow-up fluorescein angiography was done on other animals until 5 weeks postinjection. Histological studies, immunohistochemical staining, and flatmount choroids for CNV measurements were performed. In addition, we used murine neuronal, bovine endothelial, and human ARPE19 cells for testing the in vitro effects of HpODE. CNV developed in 85.7% of HpODE-injected eyes. The neovascular areas were significantly greater in HpODE-injected eyes compared with those in control eyes (P = 0.023). The CNV had maximum dye leakage at 3 weeks, which subsided by the 5th week. Histologically, CNV extended from the choriocapillaris into the subretinal space. ED1-positive macrophages were recruited to the site. In vitro assays demonstrated that only 30 ng/ml HpODE induced cell proliferation and migration of endothelial cells. HpODE-induced CNV was highly reproducible, and its natural course seems to be ideal for evaluating therapeutic modalities. Because HpODE has been isolated from aged humans, the HpODE-induced rat model seems to be a relevant experimental model for CNV in age-related macular degeneration.

Low nitric oxide synthases (NOSs) in eyes with age-related macular degeneration (AMD)

Nitric oxide (NO) production by vascular endothelium is important in regulation of blood flow. Reduced production of NO can adversely affect blood flow and other vascular functions. We investigated the expression of three nitric oxide synthase (NOS) isoforms in retina and choroid of aged human eyes and eyes with AMD. Alkaline phosphatase immunohistochemistry was performed using antibodies against inducible (iNOS), neuronal (nNOS), and endothelial (eNOS) NOSs on cryopreserved sections from aged control donor eyes (n = 13) and eyes with AMD (n = 22). CD34 antibody was used as an endothelial cell (EC) marker. Three independent masked observers scored the intensity of the immunohistochemical reaction product. Mean scores from the aged control and AMD eyes were statistically compared. In aged control retinas, nNOS was in ganglion cells (RGCs) and neurons of both nuclear layers. In choroid, perivascular nerve fibers and retinal pigment epithelial (RPE) cells were nNOS+. eNOS and iNOS were confined to the retinal and choroidal vascular ECs. Some cells presumably melanocytes or dendritic cells in choroid were also eNOS+. In AMD eyes, nNOS was significantly lower in RGCs, neurons, retinal vessels and RPE (p < or = 0.05) compared to the aged control eyes. iNOS and eNOS showed no significant differences between aged control and AMD eyes except that there was significantly less eNOS in choroidal arteries (p = 0.006) and choroidal cells (p = 0.03) of AMD eyes. Although NO was not measured directly, these findings suggest that there is less NO produced in AMD eyes. The decrease in retinal nNOS in AMD eyes is probably related to neuronal degeneration. The decrease in nNOS and eNOS in AMD choroid could be associated with vasoconstriction and hemodynamic changes.

Reduction of endogenous angiogenesis inhibitors in Bruch's membrane of the submacular region in eyes with age-related macular degeneration

OBJECTIVES

To determine the relative levels of 3 potent inhibitors of angiogenesis (endostatin, pigment epithelium-derived factor, and thrombospondin 1) in the retinal pigment epithelium-Bruch's membrane-choriocapillaris complex in the submacular region in aged control eyes and eyes with age-related macular degeneration (AMD).

METHODS

Immunohistochemical analysis with antibodies against endostatin, pigment epithelium-derived factor, and thrombospondin 1 was performed on the macular region of aged control donor eyes (n = 8; mean age, 79.8 years) and eyes with AMD (n = 12; mean age, 83.9 years). Three independent masked observers scored the reaction product (scored from 0-7). Mean scores from the control eyes and the eyes with AMD were analyzed using 1-way analysis of variance and unpaired t test.

RESULTS

In control eyes, strong immunoreactivity of all 3 inhibitors was observed in the retinal pigment epithelium-Bruch's membrane-choriocapillaris complex. Immunoreactivity for endostatin, pigment epithelium-derived factor, and thrombospondin 1 in Bruch's membrane was significantly lower in eyes with AMD compared with aged control eyes (analysis of variance, P = .003, P = .009, and P < .001, respectively). In the choriocapillaris, a significant reduction was observed in endostatin (analysis of variance, P = .02) and thrombospondin 1 (analysis of variance, P = .005) in eyes with AMD.

CONCLUSIONS

These findings suggest that endogenous angiogenesis inhibitors in the retinal pigment epithelium-Bruch's membrane-choriocapillaris complex may provide a biochemical barrier for choroidal neovascular invasion.

CLINICAL RELEVANCE

Decreased levels of angiogenic inhibitors at the retinal pigment epithelium-Bruch's membrane-choriocapillaris complex in eyes with AMD make Bruch's membrane vulnerable to choroidal neovascularization.

Developmental basis of nanophthalmos: MFRP Is required for both prenatal ocular growth and postnatal emmetropization

BACKGROUND

Nanophthalmos is a genetic disorder characterized by very small, hyperopic eyes that are without gross structural defects. Recessive nanophthalmos is caused by severe mutations in the MFRP gene, which encodes a Frizzled-related transmembrane protein that is selectively expressed in the retinal pigment epithelium (RPE) and ciliary body.

RESULTS

For two MFRP -/- adults, we have obtained records of refraction that begin in early childhood. At the age of 6 months, one patient's eyes already had a refractive error of +12.25 D, and over the next 20 years this slowly increased to +17.50 D. Adults homozygous for null mutations in MFRP have eyes with axial lengths shorter than those of normal newborns. Furthermore, the unusually high curvature of their corneas is consistent with eyes that had been smaller than normal during late fetal development. MFRP protein was first detected at 14 weeks of gestation, when it was restricted to the posterior pole RPE. By 20 weeks gestation, MFRP expression had spread laterally, and was found throughout the RPE. MFRP protein was detected in both posterior and lateral RPE of the adult eye.

CONCLUSIONS

Embryonic function of the MFRP gene appears necessary for the eye to reach its full size at birth. Its onset of expression in the RPE during mid-gestation suggests that MFRP does not participate in early formation of the optic cup, and is consistent with a role in later growth and development of the eye. Patients without MFRP gene function exhibit no correction of refractive error during childhood, which suggests that this gene is essential for emmetropization, a complex process by which vision regulates axial growth of the eye.

The embryonic human choriocapillaris develops by hemo-vasculogenesis

The purpose of this study was to characterize normal human choroidal vascular development from 6-23 weeks gestation (WG). Markers of endothelial cells (EC) (CD34, CD31, vWf), angioblasts and EC (CD39), leukocytes (CD45), erythroblasts (epsilon chain of hemoglobin, Hb-e), proliferating cells (Ki67), and VEGFR-2 were employed. At 6-7 WG, many erythroblasts were observed within islands of precursor cells in the choriocapillaris layer and others were independent from the islands. Many erythroblasts (Hb-epsilon(+)) were also positive for EC markers and/or VEGFR-2. By 8-12 WG, most of the Hb-epsilon cells had disappeared and vascular lumens became apparent. At 14-23 WG, some EC were proliferating on the scleral side of choriocapillaris in association with forming deeper vessels. In conclusion, embryonic choriocapillaris appears to form initially by hemo-vasculogenesis (blood vessels and blood cells form simultaneously from common precursors) while angiogenesis appears to be the mode of intermediate and large choroidal vessel development in the fetus.

betaA3/A1-crystallin in astroglial cells regulates retinal vascular remodeling during development

Vascular remodeling is a complex process critical to development of the mature vascular system. Astrocytes are known to be indispensable for initial formation of the retinal vasculature; our studies with the Nuc1 rat provide novel evidence that these cells are also essential in the retinal vascular remodeling process. Nuc1 is a spontaneous mutation in the Sprague-Dawley rat originally characterized by nuclear cataracts in the heterozygote and microphthalmia in the homozygote. We report here that the Nuc1 allele results from mutation of the betaA3/A1-crystallin gene, which in the neural retina is expressed only in astrocytes. We demonstrate striking structural abnormalities in Nuc1 astrocytes with profound effects on the organization of intermediate filaments. While vessels form in the Nuc1 retina, the subsequent remodeling process required to provide a mature vascular network is deficient. Our data implicate betaA3/A1-crystallin as an important regulatory factor mediating vascular patterning and remodeling in the retina.

Localisation of SDF-1 and its receptor CXCR4 in retina and choroid of aged human eyes and in eyes with age related macular degeneration

AIM

To examine the immunolocalisation of stromal cell derived factor 1 (SDF-1) and its receptor CXCR4 in aged control human donor eyes and eyes with age related macular degeneration (AMD).

METHODS

Postmortem eyes from eight aged control donors (mean age 79.8 years) and from 12 donors with AMD (mean age 83.9 years) were cryopreserved and sectioned through the macular region. SDF-1 and CXCR4 were localised using streptavidin alkaline phosphatase immunohistochemistry and then sections were bleached. Three independent masked observers scored the immunohistochemical reaction product.

RESULTS

In aged control retinas, SDF-1 immunoreactivity was most intense in inner photoreceptor matrix (IPM). CXCR4 showed a similar pattern of immunostaining, but was more prominent in inner segments of photoreceptors. In aged control and AMD choroid, SDF-1 and CXCR4 localisations were most prominent in retinal pigment epithelial (RPE) cells and choroidal stroma. However, the intensity for SDF-1 was significantly reduced in RPE (p < 0.0001) and choroidal stroma (p < 0.05) in late AMD eyes. SDF-1 and CXCR4 immunoreactivities were weak or nearly absent in disciform scars with choroidal neovascularisation (CNV). Circulating cells, presumably leucocytes, were most intensely positive for CXCR4.

CONCLUSIONS

These results show that changes in distribution and relative levels of SDF-1/CXCR4 were not evident in early AMD. This suggests that SDF-1/CXCR4 may not contribute to the formation of CNV in AMD, in that CXCR4+ cells were not incorporated into neovascularisation. However, the examples of CNV studied were within disciform scars, so the authors cannot comment on the role of SDF-1/CXCR4 in the early stages of CNV formation.

Impaired expression of thrombospondin-1 in eyes with age related macular degeneration

AIMS

This study investigated the expression and localisation of thrombospondin-1 (TSP-1), a known anti-angiogenic extracellular matrix protein, in normal aged control human eyes and eyes with age related macular degeneration (AMD).

METHODS

Immunohistochemical analysis with mouse anti-human TSP-1 antibody and mouse anti-human CD 34 antibody, as a blood vessel marker, was performed on frozen sections from macular and peripheral blocks of aged control donor eyes (n = 12; mean age 78.8 years), and eyes with AMD (n = 12; mean age 83.9 years). Pigment in retinal pigment epithelium (RPE) and choroidal melanocytes was bleached. Three independent observers scored the immunohistochemical reaction product.

RESULTS

In the macular region, TSP-1 expression was observed intensely in Bruch's membrane and weakly in RPE basement membrane, choriocapillaris, and the wall of large choroidal blood vessels in the aged control eyes. In eyes with AMD, TSP-1 immunoreactivity was significantly lower in all structures except RPE basement membrane (p<0.01). There was significantly lower TSP-1 in the far periphery than the equator and submacular regions in all eyes. TSP-1 immunoreactivity was low in choroidal neovascularisation (CNV), but it was high and diffuse in adjacent scar tissue.

CONCLUSION

These findings suggest that decreased TSP-1 in Bruch's membrane and choroidal vessels during AMD may permit the formation of CNV.

The expression of advanced glycation endproduct receptors in rpe cells associated with basal deposits in human maculas

Basal deposits within Bruch's membrane are associated with aging and age-related macular degeneration (AMD) although the factors causing their formation are incompletely understood. Advanced glycation endproducts (AGEs) accumulate in Bruch's membrane including basal deposits and drusen with aging. One mechanism by which AGEs alter a cell's phenotype is via AGE receptors. The purpose of this study was to immunolocalize and quantify the expression of AGE receptors by RPE cells associated with basal deposits or normal Bruch's membrane that were microdissected from human maculas. Postmortem eyes from 14 aged control donors and five donors with non-neovascular AMD were cryopreserved. RPE cells associated with normal Bruch's membrane or basal deposits were laser capture microdissected. The RNA was extracted and used for RT-qPCR to quantify the expression of RAGE, AGE R1, AGE R2, and AGE R3. Streptavidin alkaline phosphatase immunohistochemistry for these receptors was also performed and sections were bleached from 14 normal and nine AMD donors. RT-qPCR showed significant upregulation of RAGE, AGE R1, and AGE R3 in RPE cells overlying basal deposits compared to cells attached to morphologically normal Bruch's membrane. Immunohistochemical analysis for RAGE, AGER1, R2, and R3 showed diffuse, light staining of RPE cells and strong choriocapillaris staining in areas of normal Bruch's membrane. In areas of basal deposits, the RPE had more intense staining for RAGE and AGER1 compared to regions of normal Bruch's membrane. These results suggest that AGE receptors could influence the formation of basal deposits during aging and AMD.

Pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in aged human choroid and eyes with age-related macular degeneration

The purpose of this study was to examine the localization and relative levels of vascular endothelial growth factor (VEGF; an angiogenic factor) and pigment epithelium-derived factor (PEDF; an antiangiogenic factor) in aged human choroid and to determine if the localization or their relative levels changed in age-related macular degeneration (AMD). Ocular tissues were obtained from eight aged control donors (age range, 75-86 years; mean age, 79.8 years) with no evidence or history of chorioretinal disease and from 12 donors diagnosed with AMD (age range, 61-105 years; mean age, 83.9 years). Tissues were cryopreserved and streptavidin alkaline phosphatase immunohistochemistry was performed with rabbit polyclonal anti-human VEGF and rabbit polyclonal anti-human PEDF antibodies. Binding of the antibodies was blocked by preincubation of the antibody with an excess of recombinant human PEDF or VEGF peptide. Choroidal blood vessels were identified with mouse anti-human CD-34 antibody in adjacent tissue sections. Three independent observers graded the immunohistochemical reaction product. The most prominent sites of VEGF and PEDF localization in aged control choroid were RPE-Bruch's membrane-choriocapillaris complex including RPE basal lamina, intercapillary septa, and choroidal stroma. There was no significant difference in immunostaining intensity and localization of VEGF and PEDF in aged control choroids. The most intense VEGF immunoreactivity was observed in leukocytes within blood vessels. AMD choroid had a similar pattern and intensity of VEGF immunostaining to that observed in aged controls. However, PEDF immunoreactivity was significantly lower in RPE cells (p=0.0073), RPE basal lamina (p=0.0141), Bruch's membrane (p<0.0001), and choroidal stroma (p=0.0161) of AMD choroids. The most intense PEDF immunoreactivity was observed in disciform scars. Drusen and basal laminar deposits (BLDs) were positive for VEGF and PEDF. In aged control subjects, VEGF and PEDF immunostaining was the most intense in RPE-Bruch's membrane-choriocapillaris complex. In AMD, PEDF was significantly lower in RPE cells, RPE basal lamina, Bruch's membrane and choroidal stroma. These data suggest that a critical balance exists between PEDF and VEGF, and PEDF may counteract the angiogenic potential of VEGF. The decrease in PEDF may disrupt the balance and be permissive for the formation of choroidal neovascularization (CNV) in AMD.

Localization of collagen XVIII and the endostatin portion of collagen XVIII in aged human control eyes and eyes with age-related macular degeneration

PURPOSE

Endostatin, a C-terminal fragment of collagen XVIII (coll XVIII) formed by proteolysis, specifically inhibits endothelial cell migration and proliferation in vitro and potently inhibits angiogenesis and tumor growth in vivo. The purpose of this study was to examine the immunolocalization of endostatin and coll XVIII in the retina and choroid of human donor tissue sections from aged control donor eyes and to determine whether the localization or relative levels are changed in age-related macular degeneration (AMD).

METHODS

Ocular tissues were obtained from six aged control donors (age range, 75-86 years; mean age, 80.5 years) without evidence or history of chorioretinal disease and from nine donors with AMD (age range, 74-105 years; mean age, 88.6 years). Tissues were cryopreserved, and streptavidin alkaline phosphatase immunohistochemistry was performed with goat anti-human and mouse anti-human endostatin antibodies and rabbit anti-mouse coll XVIII. Blood vessels were identified with mouse anti-human CD-34 antibody in adjacent sections. Pigment in RPE and choroidal melanocytes was bleached. Three independent observers scored the immunohistochemical reaction product.

RESULTS

In aged control eyes, coll XVIII and endostatin (the endostatin portion of coll XVIII) immunoreactivity was observed in large retinal blood vessels and in capillaries in some individuals, but the internal limiting membrane (ILM) had the most intense retinal immunostaining. There was no significant difference in immunoreactivity to both antibodies in retinal blood vessels in aged control eyes. In the choroid, endostatin and coll XVIII were localized to blood vessels, Bruch's membrane, and RPE basal lamina. AMD retina and choroid had a similar pattern and intensity of coll XVIII immunostaining, as observed in control eyes but reaction product was more diffuse in the choroid. Endostatin immunoreactivity was significantly higher in ILM (P = 0.037) in AMD retina and significantly lower in the choriocapillaris, Bruch's membrane, and RPE basal lamina of AMD choroids (P < 0.05) and completely negative in some areas of AMD choroids.

CONCLUSIONS

These data suggest that reduced levels of the endostatin portion of coll XVIII in Bruch's membrane, RPE basal lamina, intercapillary septa, and choriocapillaris in eyes with AMD may be permissive for choroidal neovascularization.

Expression of pigment epithelium-derived factor (PEDF) and vascular endothelial growth factor (VEGF) in sickle cell retina and choroid

Pigment epithelium-derived factor (PEDF) has been shown to be an inhibitor of angiogenesis as well as a multipotent neurotrophic factor in the mammalian eye. Changes in PEDF levels have been correlated with development of retinal neovascularization in oxygen-induced retinopathy. The purpose of this study was to determine the localization and relative level of PEDF in human retinas and choroids using immunohistochemistry and evaluate the changes in PEDF and vascular endothelial growth factor (VEGF) localization and their relation to the progression of proliferative sickle cell retinopathy. Cryopreserved tissues from eyes of normal subjects and subjects with non-proliferative or proliferative sickle cell retinopathy were used with streptavidin peroxidase immunohistochemistry. A rabbit polyclonal antibody was made against recombinant human PEDF. Binding of the antibody was blocked by preincubation of the antibody with excess human recombinant PEDF. Relative levels of immunoreactivity were scored with a seven-point grading system and by microdensitometric analysis.The most prominent sites of PEDF localization in the normal eye were the vitreous condensed at the internal limiting membrane and RPE-Bruch's membrane-choriocapillaris complex. PEDF was also prominent in choroidal stroma. There was limited immunoreactivity in some cells of the neural retinas, in blood vessels and in the interphotoreceptor matrix (IPM). There was no difference in ratio (1.47 vs. 1.44) of PEDF/VEGF or the relative levels of either growth factor in the retinal vasculatures of the control subjects and perfused area of non-proliferative sickle cell retinas. The ratio was increased in the non-perfused area of the non-proliferative sickle cell retinas (2.24). In eyes with proliferative sickle cell retinopathy, elevated PEDF and VEGF immunostaining was present in viable vessels of sea fan neovascular formations as well as feeder vessels of sea fans. The PEDF/VEGF ratio in sea fans was 1.0. Immunoreactivity for PEDF was prominent in retinal vessels in non-perfused regions and in atrophic sea fans, while VEGF immunoreactivity was weak or absent in these structures. In conclusion, PEDF and VEGF were both significantly elevated in viable sea fan formations in sickle cell disease (p<0.05) but only PEDF was present in non-viable sea fans. The highest levels of PEDF in all eyes were associated with extracellular matrices (vitreous, choroidal stroma, IPM, and walls of blood vessels). PEDF might play an important role in inhibiting angiogenesis and inducing the regression of sea fans. Progression of angiogenesis may be dependent on the ratio of PEDF/VEGF.

Corrosion cast demonstration of choroidal vasculature in normal Wistar Kyoto rat

No previous attempt has been made so to demonstrate the details of the choroid vascularization in the rat. This paper describes the choroidal vascular pattern of the normal Wistar Kyoto rat using the corrosion cast method. 6-month-old normal Wistar Kyoto rats were used. Vascular casts prepared by our previously described technique were observed with a Hitachi S-2360N scanning electron microscope. Corrosion casts of the entire choroidal vasculature showed that the ophthalmic artery branched into two main ciliary arteries: the nasal and temporal arteries, which extend forward to form the iridociliary circle. Further the inferior ciliary artery arises from the temporal ciliary artery. In the posterior eye segment these arteries form four to seven branches supplying the adjacent choriocapillaris. There are different arrangements of choriocapillaris. The larger veins formed four vortex veins, one in each quadrant, draining blood from the anterior region of the choroid or iris. Venous blood from the central region, peripapillary choroid and sometimes optic nerve head is drained by smaller veins, which run more or less directly into the posterior ciliary veins. In conclusion corrosion casts and SEM can show the details of the choroidal vascular architecture. These three-dimensional (3-D) findings of choroidal vessels of the rat are very useful for the study of choroid vascular abnormalities in various pathological conditions.

Retinal vascular changes and systemic diseases: corrosion cast demonstration

The purpose of the present study is to clarify the specific retinal vascular changes in rat models of single spontaneous or hereditary systemic diseases. We used Wistar Kyoto (WKy) rats 6 months of age as normal controls, 24-month-old Wistar Kyoto rats in studies of aging, 16-month-old spontaneously hypertensive rats (SHR), 18-month-old rats with inherited hypercholesterolemia (RICO) for arteriosclerosis, and 18-month-old Otsuka Long-Evans Tokushima Fatty (OLETF) rats for diabetes mellitus. Retinal vascular corrosion casts were made and observed with a scanning electron microscope. The retinal vessels were also examined with a transmission electron microscope. Specific changes in the retinal vessels were: narrowing and thin thread-like capillaries in aging; capillary tortuosity, irregularity and narrowing in hypertension; straightening in hypercholesterolemia; and loop formation and microaneurysms in diabetes mellitus. These specific changes in the retinal vessels in each systemic disease can be clearly and easily revealed in a three-dimensional fashion by corrosion casts followed by scanning electron microscopy.

Microvascular architecture of the rat choroid: corrosion cast study

This study presents the details of the microvasculature of the rat choroid visualized by scanning electron microscopy of vascular corrosion casts. Wistar Kyoto rats were anesthetized with intraperitoneal sodium pentobarbital. The vascular system was perfused with heparinized saline, and Mercox resin was injected into the cannulated carotid arteries. After polymerization of the resin, the vascular casts were macerated with potassium hydroxide, washed with water, and freeze dried. The casts were examined with a Hitachi S-2360N scanning electron microscope (SEM). Corrosion casts of the entire choroidal vasculature revealed that the two long posterior ciliary arteries supplied the entire uveal vasculature. In the posterior choroid, these arteries formed five to seven branches on each side supplying the adjacent choriocapillaris. No interarterial or arteriovenous anastomoses were seen. The choriocapillaris appeared as a nonhomogeneous and nonlobular monolayer capillary network, consisting of dense honeycomb and irregular patterns. There are two distinct venous systems in the rat choroid. The venous blood from the central region, peripapillary choroid, and sometimes the optic nerve head drain into the posterior ciliary vein. The venous blood from the iris, ciliary body, anterior choroid, and half of the posterior choroid drain into the vortex veins. Corrosion casts and the SEM have shown details of the choroidal vascular architecture. These three-dimensional observations indicate that the rat choroidal vasculature has different features from those of humans and other primates. Despite these interspecies differences, the establishment of a thorough baseline concept of choroidal vasculature should permit additional studies of the choroidal pathology and enable the proper interpretation of results from rat experimental models for extrapolation to humans.

Retinal vascular architecture is maintained in retinal degeneration: corrosion cast and electron microscope study

PURPOSE

To demonstrate the changes of the retinal vascular architecture in the diffusely degenerated thin retina.

METHODS

Three-week-old weanling Wistar Kyoto rats were divided randomly into two groups. One group (n = 20) was fed a vitamin E-deficient solid diet and the other group (n = 20) was fed a solid rat chow diet. Rats were maintained on their respective diets for 14 months and then killed for scanning electron microscopy of vascular corrosion casts, light and electron microscopy and biochemical determinations.

RESULTS

The serum level of vitamin E in the E-deficient rats was 1.0 +/- 0.49 microg/ml, while that in the rats fed a normal diet was 13.7 +/- 1.0 microg/ml (Student's t-test, p = 0.0001). In vitamin E-deficient rats, light microscopy showed degenerated retinas only half as thick as normal. Corrosion casts and scanning electron microscopy revealed that the retinal capillaries of the entire retina were decreased in number and scattered with localised narrowing, calibre irregularity and frequent loop formation. In the posterior pole of the retina, some capillaries clustered into small tortuous knots. However, the two-layered architecture of the capillary network in the retina was maintained. The differences in calibre of retinal capillaries between the vitamin E-deficient and normal rats were statistically significant (p < 0.0001). No remarkable abnormal changes were observed in the large retinal vessels other than arterial calibre differences (p < 0.022). No arteriovenous shunts, crossing defects or microaneurysms were seen. Transmission electron microscopy revealed complete disappearance of the photoreceptor outer and inner segments and nuclei. The retinal pigment epithelium contained lipofuscin granules and retinal capillaries with narrow lumens. The capillary endothelial cells were thickened and had scarce cytoplasmic components with vacuoles and irregularly thickened basement membranes. The capillary pericytes had vacuoles. No abnormalities were seen in the control normal rats.

CONCLUSION

These findings indicate that the decrease in retinal capillaries in vitamin E-deficient rats is secondary to retinal degeneration. It was assumed that the morphological changes in the capillary network reflected structural damage to the retinal vascular cells caused by free radicals and lipid peroxides generated by oxidation. However, even in such severe degeneration the retinal vascular architecture, including the main artery and vein and two-layer capillary networks, was maintained. This is may be because of the basic anatomical arrangement of the blood vessels.

Retinal vascular changes in rats with inherited hypercholesterolemia--corrosion cast demonstration

PURPOSE

To demonstrate specific hypercholesterolemic changes in the retinal vascular architecture.

METHODS

Corrosion casts of 12- to 18-month-old rats with inherited hypercholesterolemia (RICO) and of control Wistar Kyoto (WKy) rats were examined with a scanning electron microscope (SEM). The diameters of the retinal arteries, veins and capillaries were measured in photographs with a caliber micrometer. The capillary branches were counted in the micrographs with the use of Adobe Photoshop. The retinal capillaries were examined by transmission electron microscopy (TEM).

RESULTS

SEM examination of the vascular casts of 15-month-old RICO rats showed slight tortuosity of large vessels at the posterior pole of the retina. The precapillary arterioles branching from the major artery were longer and straighter than normal. Retinal capillary changes such as caliber irregularity and narrowing in the capillary network were more severe in 18-month-old RICO rats. The most prominent finding was marked straightening of the capillaries in the inner and outer layers of the capillary network, which looked like fine strings. Intercapillary spaces became wider, and finally capillaries looked scattered. The diameter of the retinal capillaries lumen in RICO rats was significantly narrower than that in WKy rats (p < 0.0001). The capillary branches were fewer in 18-month-old RICO rats than that in 18-month-old WKy rats (p < 0.0001). Neither local stenosis or obstruction in the arterioles and venules nor any arteriovenous crossing defect was seen in young and old RICO rats. Transmission electron microscopy of 16-month-old RICO rat retinas revealed that the capillaries in the inner and outer plexiform layers contained scarce cytoplasmic components, vacuoles in endothelial cells and basement membranes of irregular thickness. Capillary pericytes were swollen and irregular in shape, contained vacuolated mitochondria and scarce cytoplasmic components.

CONCLUSIONS

These findings indicate that the retinal capillary changes are probably related to hypercholesterolemia.

Retinal capillary changes in Otsuka Long-Evans Tokushima fatty rats (spontaneously diabetic strain). Electron-microscopic study

The Otsuka Long-Evans Tokushima fatty (OLETF) rat is a spontaneously diabetic strain with polyuria, polydipsia and mild obesity. The pathological features of OLETF rats closely resemble those of patients with non-insulin-dependent diabetes mellitus. The purpose of this study is to investigate the retinal capillary changes in the OLETF rat and to confirm the valuability of the OLETF rat as the model of diabetic retinal disease. One-month-old male OLETF rats and age- and sex-matched Long-Evans Tokushima Otsuka (LETO) controls were supplied by Otsuka Pharmaceutical Co. Ltd. (Tokushima, Japan). Body weight and blood sugar levels were measured monthly. Their eyes were enucleated 14 months after birth. Ultrathin sections were made and examined with a transmission electron microscope. According to their location, two kinds of retinal capillaries were differentiated: those in the nerve fiber layer (NFL) and those in the outer plexiform layer (OPL). The image of each capillary was transferred to a computed image analyzer, and basement membrane thickness and the ratio of the pericyte area to total capillary cross-section area were determined. Corrosion casts of retinal vessels were made and examined with scanning electron microscopy (SEM). OLETF rats gained more weight than LETO rats from the beginning, and the difference increased gradually with age. The blood sugar level of OLETF rats was higher than that of LETO rats after 5 months of age. In the retinal capillaries of 14-month-old OLETF rats, basement membranes were significantly thicker (OLETF: 209 +/- 51 nm in NFL, 132 +/- 23 nm in OPL; LETO: 118 +/- 28 nm in NFL, 79 +/- 14 nm in OPL), and the ratio of pericyte area to the capillary cross-section area was significantly lower than that of the controls (OLETF: 0.131 +/- 0.92 in NFL, 0.111 +/- 0.102 in OPL; LETO: 0.288 +/- 0.142 in NFL, 0.198 +/- 0.136 in OPL). The endothelial cell cytoplasm had degenerated. SEM examination of the vascular corrosion cast of a 14-month-old OLETF rat showed caliber irregularity, narrowing, tortuosity and loop formations of capillaries. The morphological changes in the retinal capillaries of OLETF rats were similar to those seen in diabetic patients. The OLETF rat may be a useful animal model for the study of ocular diabetic complications in humans.

Vascular architecture of degenerated retina in WBN/Kob rats: corrosion cast and electron microscopic study

The purpose of the present study is to determine the changes of vascular architecture in the degenerated retina. We used mainly corrosion casts of the retinal vasculature and scanning electron microscopy to obtain a wide three-dimensional view. WBN/Kob rats (a spontaneously diabetic strain) were used because their outer retinas degenerate and become very thin with age. In 15-month-old rats, localized constriction and irregular caliber of the capillaries were evident in the vascular casts. Two layers of capillary network in the retina were maintained, but the capillaries were decreased in number. Numerous loop formations were present in the superficial capillary networks. Neither microaneurysms nor arteriovenous shunts were seen in young and old rats. Transmission electron microscopy revealed that capillary pericytes in the inner and outer plexiform layers had thickened basement membranes and that endothelial cells had many vesicles in their cytoplasm. Thus the retinal capillary changes in WBN/Kob rats are nondiabetic but due to hereditary retinal degeneration, although the systemic and pancreatic abnormalities in this rat strain are diabetic. Even when the retina becomes very thin, two layer capillary networks remain.

Effects of cilazapril on the retinal vessels in spontaneously hypertensive rats: corrosion cast and scanning electron microscopic study

The effects of the long-term oral angiotensin-converting enzyme inhibitor, cilazapril, on retinal circulation in stroke-prone spontaneously hypertensive (SHR-SP) rats were assessed by scanning electron microscopy (SEM), corrosion casts and transmission electron microscopy (TEM). Two groups of 20 male SHR-SP rats were compared. One group was treated with 10 mg/kg/day of cilazapril from 4 to 40 weeks of age, and the other group received no treatment. A third group of male Wistar-Kyoto (WKY) rats served as age-matched controls. At regular intervals the rats were weighed, and their systolic blood pressure was measured. Cilazapril normalized systolic arterial pressure to 121+/-2.7 mm Hg (SD) in the treated SHR-SP rats. There was no significant difference in body weight between the two groups of SHR-SP. In the 40-week-old SHR-SP rats without treatment corrosion cast and SEM revealed hypertensive retinal vascular changes. In the 40-week-old SHR-SP rats treated with cilazapril, these changes were markedly decreased to the level seen in WKY rats. The differences in caliber of retinal capillaries between the treated SHR-SP and untreated SHR-SP rats were statistically significant (p<.0001). TEM in the cilazapril-treated SHR-SP rats revealed intact basement membranes (0.29+/-0.057 microm) of the endothelial cells and pericytes, but in the untreated SHR-SP rats the basement membrane was thickened (0.51+/-0.123 microm) (p<.0001) and the pericytes damaged. Our results show that the long-term administration of cilazapril decreased systolic arterial pressure to a nearly normal level and prevented hypertensive retinal vascular changes, probably by improving endothelial function. The effects of cilazapril on the retinal vasculature are described for the first time. SEM of corrosion casts is a valuable technique for showing the effects of some drugs on the vasculature easily, precisely and three-dimensionally.