\u3cem\u3eIn vivo\u3c/em\u3e Imaging of Human Cone Photoreceptor Inner Segments

Purpose. An often overlooked prerequisite to cone photoreceptor gene therapy development is residual photoreceptor structure that can be rescued. While advances in adaptive optics (AO) retinal imaging have recently enabled direct visualization of individual cone and rod photoreceptors in the living human retina, these techniques largely detect strongly directionally-backscattered (waveguided) light from normal intact photoreceptors. This represents a major limitation in using existing AO imaging to quantify structure of remnant cones in degenerating retina. Methods. Photoreceptor inner segment structure was assessed with a novel AO scanning light ophthalmoscopy (AOSLO) differential phase technique, that we termed nonconfocal split-detector, in two healthy subjects and four subjects with achromatopsia. Ex vivo preparations of five healthy donor eyes were analyzed for comparison of inner segment diameter to that measured in vivo with split-detector AOSLO. Results. Nonconfocal split-detector AOSLO reveals the photoreceptor inner segment with or without the presence of a waveguiding outer segment. The diameter of inner segments measured in vivo is in good agreement with histology. A substantial number of foveal and parafoveal cone photoreceptors with apparently intact inner segments were identified in patients with the inherited disease achromatopsia. Conclusions. The application of nonconfocal split-detector to emerging human gene therapy trials will improve the potential of therapeutic success, by identifying patients with sufficient retained photoreceptor structure to benefit the most from intervention. Additionally, split-detector imaging may be useful for studies of other retinal degenerations such as AMD, retinitis pigmentosa, and choroideremia where the outer segment is lost before the remainder of the photoreceptor cell

Lipoprotein Particles of Intraocular Origin in Human Bruch Membrane: An Unusual Lipid Profile

PURPOSE. Throughout adulthood, Bruch membrane (BrM) accumulates esterified cholesterol (EC) associated with abundant 60-to 80-nm-diameter lipoprotein-like particles (LLP), putative apolipoprotein B (apoB) lipoproteins secreted by the retinal pigment epithelium (RPE). In the present study, neutral lipid, phospholipids, and retinoid components of human BrM-LLP were assayed. METHODS. Particles isolated from paired choroids of human donors were subjected to comprehensive lipid profiling (preparative liquid chromatography [LC] gas chromatography [GC]), thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), Western blot analysis, and negative stain electron microscopy. Results were compared to plasma lipoproteins isolated from normolipemic volunteers and to conditioned medium from RPE-J cells supplemented with palmitate to induce particle synthesis and secretion. RESULTS. EC was the largest component (32.4 Ϯ 7.9 mol%) of BrM-LLP lipids. EC was 11.3-fold more abundant than triglyceride (TG), unlike large apoB lipoproteins in plasma. Of the fatty acids (FA) esterified to cholesterol, linoleate (18:2n6) was the most abundant (41.7 Ϯ 4.7 mol%). Retinyl ester (RE) was detectable at picomolar levels in BrM-LLP. Notably scarce in any BrM-LLP lipid class was the photoreceptor-abundant FA docosahexaenoate (DHA, 22:6n3). RPE-J cells synthesized apoB and numerous EC-rich spherical particles. CONCLUSIONS. BrM-LLP composition resembles plasma LDL more than it does photoreceptors. An EC-rich core is possible for newly synthesized lipoproteins as well as those processed in plasma. Abundant EC could contribute to a transport barrier in aging and lesion formation in age-related maculopathy (ARM). Analysis of BrM-LLP composition has revealed new aspects of retinal cholesterol and retinoid homeostasis. (Invest Ophthalmol Vis Sci. 2009;50:870 -877 2 Early ARM is characterized by drusen (focal extracellular debris), basal linear deposit (BlinD; a diffusely distributed drusenoid material), and altered RPE morphology and pigmentation. This disease stage has limited treatment options, including antioxidant nutritional supplements, and, in its later stages, loss of eyesight is possible. Although some gene sequence variants increase ARM risk, 3 the largest risk factor for early ARM remains advanced age. It is therefore important to understand how age-related changes in the affected tissues impel some individuals toward severe disease. Lipoproteins are naturally occurring nanoparticles composed of lipid and protein held together by noncovalent forces. Each particle is a microemulsion consisting of a surface of phospholipids (PLs), unesterified cholesterol (UC), and apolipoproteins and a core of neutral lipids, principally esterified cholesterol (EC) and triglyceride (TG). Lipoprotein classes differ in relative amount of lipids, protein/lipid ratio, and apolipoprotein species present, resulting in differences in size, density, and electrophoretic mobility. Lipoprotein classes containing apoB are chylomicrons (CM; from intestine), very-lowdensity lipoproteins (VLDL; from liver), and LDL (metabolite of VLDL). ApoB lipoproteins must be properly lipidated by their source cells in order for particle maturation and secretion to proceed. Core lipid composition reflects the availability of input FA and the substrate preferences of catalytic enzymes in upstream pathways. 10 Rather, recent evidence implicates EC as part of an apoB lipoprotein constitutively produced within the eye by the RPE and secreted into BrM, where it participates in ARM progression. Native human RPE expresses apolipoprotein mRNA transcripts, the proteins of apos B-100 and E, and notably, microsomal triglyceride transfer protein (MTP), required for apoB secretion and the product of the abetalipoproteinemia gene. 11,12 Isolated BrM-LLP segregate into the appropriate band of a density gradient but differ from plasma lipoproteins in cholesterol profile. 13 Cultured RPE secretes apoE, primarily into a high-density fraction. 14 Size and lipid composition are strongly related for apoB lipoproteins, in that particles Ͼ25 nm diameter (CM and VLDL) have TG-rich cores and smaller particles (including LDL) have EC-rich cores. 15 BrM-LLP, as large as VLDL or small CM, are expected to be TG-rich. Indeed, an early assay of BrM/choroid From the Departments of 1 Ophthalmology

Autofluorescent granules of the human retinal pigment epithelium: phenotypes, intracellular distribution, and age-related topography

PURPOSE. The human retinal pigment epithelium (RPE) accumulates granules significant for autofluorescence imaging. Knowledge of intracellular accumulation and distribution is limited. Using high-resolution microscopy techniques, we determined the total number of granules per cell, intracellular distribution, and changes related to retinal topography and age. METHODS. RPE cells from the fovea, perifovea, and near-periphery of 15 human RPE flat mounts were imaged using structured illumination microscopy (SIM) and confocal fluorescence microscopy in young (=51 years, n = 8) and older (>80 years, n = 7) donors. Using custom FIJI plugins, granules were marked with computer assistance, classified based on morphological and autofluorescence properties, and analyzed with regard to intracellular distribution, total number per cell, and granule density. RESULTS. A total of 193,096 granules in 450 RPE cell bodies were analyzed. Based on autofluorescence properties, size, and composition, the RPE granules exhibited nine different phenotypes (lipofuscin, two; melanolipofuscin, five; melanosomes, two), distinguishable by SIM. Overall, lipofuscin (low at the fovea but increases with eccentricity and age) and melanolipofuscin (equally distributed at all three locations with no age-related changes) were the major granule types. Melanosomes were under-represented due to suboptimal visualization of apical processes in flat mounts. CONCLUSIONS. Low lipofuscin and high melanolipofuscin content within foveal RPE cell bodies and abundant lipofuscin at the perifovea suggest a different genesis, plausibly related to the population of overlying photoreceptors (fovea, cones only; perifovea, highest rod density). This systematic analysis provides further insight into RPE cell and granule physiology and links granule load to cell autofluorescence, providing a subcellular basis for the interpretation of clinical fundus autofluorescence. © 2020 Association for Research in Vision and Ophthalmology Inc.. All rights reserved

Characteristics of normal human retinal pigment epithelium cells with extremes of autofluorescence or intracellular granule count

Background: Cells of the retinal pigment epithelium (RPE) accumulate different kinds of granules (lipofuscin, melanolipofuscin, melanosomes) within their cell bodies, with lipofuscin and melanolipofuscin being autofluorescent after blue light excitation. High amounts of lipofuscin granules within the RPE have been associated with the development of RPE cell death and age-related macular degeneration (AMD); however, this has not been confirmed in histology so far. Here, based on our previous dataset of RPE granule characteristics, we report the characteristics of RPE cells from human donor eyes that show either high or low numbers of intracellular granules or high or low autofluorescence (AF) intensities. Methods: RPE flatmounts of fifteen human donors were examined using high-resolution structured illumination microscopy (HR-SIM) and laser scanning microscopy (LSM). Autofluorescent granules were analyzed regarding AF phenotype and absolute number of granules. In addition, total AF intensity per cell and granule density (number of granules per cell area) were determined. For the final analysis, RPE cells with total granule number below 5th or above the 95th percentile, or a total AF intensity ± 1.5 standard deviations above or below the mean were included, and compared to the average RPE cell at the same location. Data are presented as mean ± standard deviation. Results: Within 420 RPE cells examined, 42 cells were further analyzed due to extremes regarding total granule numbers. In addition, 20 RPE cells had AF 1.5 standard deviations below, 28 RPE cells above the mean local AF intensity. Melanolipofuscin granules predominate in RPE cells with low granule content and low AF intensity. RPE cells with high granule content have nearly twice (1.8 times) as many granules as an average RPE cell. Conclusions: In normal eyes, outliers regarding autofluorescent granule load and AF intensity signals are rare among RPE cells, suggesting that granule deposition and subsequent AF follows intrinsic control mechanisms at a cellular level. The AF of a cell is related to the composition of intracellular granule types. Ongoing studies using AMD donor eyes will examine possible disease related changes in granule distribution and further put lipofuscin´s role in aging and AMD further into perspective

Quantitative Analysis of Outer Retinal Tubulation in Age-Related Macular Degeneration From Spectral-Domain Optical Coherence Tomography and Histology

Purpose: To assess outer retinal tubulation (ORT) morphology from spectral-domain optical coherence tomography (SD-OCT) volumes and donor eye histology, analyze ORT reflectivity, and estimate the number of cones surviving in ORT. Methods: In SD-OCT volumes from nine patients with advanced AMD, ORT was analyzed en face and in B-scans. The hyperreflective ORT border in cross-section was delineated and surface area calculated. Reflectivity was compared between ORT types (Closed, Open, Forming, and Branching). A flatmount retina from a donor with neovascular AMD was labeled to visualize the external limiting membrane that delimits ORT and allow measurements of cross-sectional cone area, center-to-center cone spacing, and cone density. The number of cones surviving in ORT was estimated. Results: By en face SD-OCT, ORT varies in complexity and shape. Outer retinal tubulation networks almost always contain Closed cross-sections. Spectral-domain OCT volumes containing almost exclusively Closed ORTs showed no significant direction-dependent differences in hyperreflective ORT border intensity. The surface areas of partial ORT assessed by SD-OCT volumes ranged from 0.16 to 1.76 mm2. From the flatmount retina, the average cross-sectional area of cone inner segments was 49.1 ± 7.9 μm2. The average cone spacing was 7.5 ± 0.6 μm. Outer retinal tubulation cone density was 20,351 cones/mm2. The estimated number of cones in ORT in a macula ranged from 26,399 to 186,833 cones, which is 6% to 44% of the cones present in a healthy macula. Conclusions: These first estimates for cone density and number of cones surviving in ORT suggest that ORT formation considerably distorts the photoreceptor mosaic. Results provide additional insight into the reflectivity characteristics and number of ORT cones observable in living patients by SD-OCT, as cones persist and disease progresses

Abundant Lipid and Protein Components of Drusen

Drusen are extracellular lesions characteristic of aging and age-related maculopathy, a major retinal disease of the elderly. We determined the relative proportions of lipids and proteins in drusen capped with retinal pigment epithelium (RPE) and in RPE isolated from non-macular regions of 36 human retinas with grossly normal maculas obtained <6 hr after death.Druse pellets were examined by light and electron microscopy. Component proteins were extracted using novel methods for preserved tissues, separated, subjected to tryptic digestion and LC-MS(MS)(2) analysis using an ion trap mass spectrometer, and identified with reference to databases. Lipid classes were separated using thin layer chromatography and quantified by densitometry. Major druse components were esterified cholesterol (EC), phosphatidylcholine (PC), and protein (37.5+/-13.7, 36.9+/-12.9, and 43.0+/-11.5 ng/druse, respectively). Lipid-containing particles (median diameter, 77 nm) occupied 37-44% of druse volume. Major proteins include vitronectin, complement component 9, apoE, and clusterin, previously seen in drusen, and ATP synthase subunit beta, scavenger receptor B2, and retinol dehydrogenase 5, previously seen in RPE. Drusen and RPE had similar protein profiles, with higher intensities and greater variability in drusen. C8, part of the complement membrane attack complex, was localized in drusen by immunofluorescence.At least 40% of druse content is comprised by lipids dominated by EC and PC, 2 components that are potentially accounted for by just one pathway, the secretion of lipoproteins by RPE. Manipulating genes encoding apolipoprotein pathways would be a fruitful approach to producing drusen with high EC content in laboratory animals. Therapies that directly mitigate drusen should prepare for the substantial volume of neutral lipids. The catalog of major druse proteins is nearing completion

A Case Study

OK Publisher Copyright: © 2023 American Academy of OphthalmologyPurpose: To investigate intraretinal neovascularization and microvascular anomalies by correlating in vivo multimodal imaging with corresponding ex vivo histology in a single patient. Design: A case study comprising clinical imaging from a community-based practice, and histologic analysis at a university-based research laboratory (clinicopathologic correlation). Participants: A White woman in her 90s treated with numerous intravitreal anti-VEGF injections for bilateral type 3 macular neovascularization (MNV) secondary to age-related macular degeneration (AMD). Methods: Clinical imaging comprised serial infrared reflectance, eye-tracked spectral-domain OCT, OCT angiography, and fluorescein angiography. Eye tracking, applied to the 2 preserved donor eyes, enabled the correlation of clinical imaging signatures with high-resolution histology and transmission electron microscopy. Main Outcome Measures: Histologic/ultrastructural descriptions and diameters of vessels seen in clinical imaging. Results: Six vascular lesions were histologically confirmed (type 3 MNV, n = 3; deep retinal age-related microvascular anomalies [DRAMAs], n = 3). Pyramidal (n = 2) or tangled (n = 1) morphologies of type 3 MNV originated at the deep capillary plexus (DCP) and extended posteriorly to approach without penetrating persistent basal laminar deposit. They did not enter the subretinal pigment epithelium (RPE)–basal laminar space or cross the Bruch membrane. Choroidal contributions were not found. The neovascular complexes included pericytes and nonfenestrated endothelial cells, within a collagenous sheath covered by dysmorphic RPE cells. Deep retinal age-related microvascular anomaly lesions extended posteriorly from the DCP into the Henle fiber and the outer nuclear layers without evidence of atrophy, exudation, or anti-VEGF responsiveness. Two DRAMAs lacked collagenous sheaths. External and internal diameters of type 3 MNV and DRAMA vessels were larger than comparison vessels in the index eyes and in aged normal and intermediate AMD eyes. Conclusions: Type 3 MNV vessels reflect specializations of source capillaries and persist during anti-VEGF therapy. The collagenous sheath of type 3 MNV lesions may provide structural stabilization. If so, vascular characteristics may be useful in disease monitoring in addition to fluid and flow signal detection. Further investigation with longitudinal imaging before exudation onset will help determine if DRAMAs are part of the type 3 MNV progression sequence. Financial Disclosure(s): Proprietary or commercial disclosure may be found after the references.publishersversionpublishe

Relationship Between Foveal Cone Specialization and Pit Morphology in Albinism

Purpose.Albinism is associated with disrupted foveal development, though intersubject variability is becoming appreciated. We sought to quantify this variability, and examine the relationship between foveal cone specialization and pit morphology in patients with a clinical diagnosis of albinism. Methods. We recruited 32 subjects with a clinical diagnosis of albinism. DNA was obtained from 25 subjects, and known albinism genes were analyzed for mutations. Relative inner and outer segment (IS and OS) lengthening (fovea-to-perifovea ratio) was determined from manually segmented spectral domain-optical coherence tomography (SD-OCT) B-scans. Foveal pit morphology was quantified for eight subjects from macular SD-OCT volumes. Ten subjects underwent imaging with adaptive optics scanning light ophthalmoscopy (AOSLO), and cone density was measured. Results. We found mutations in 22 of 25 subjects, including five novel mutations. All subjects lacked complete excavation of inner retinal layers at the fovea, though four subjects had foveal pits with normal diameter and/or volume. Peak cone density and OS lengthening were variable and overlapped with that observed in normal controls. A fifth hyper-reflective band was observed in the outer retina on SD-OCT in the majority of the subjects with albinism. Conclusions. Foveal cone specialization and pit morphology vary greatly in albinism. Normal cone packing was observed in the absence of a foveal pit, suggesting a pit is not required for packing to occur. The degree to which retinal anatomy correlates with genotype or visual function remains unclear, and future examination of larger patient groups will provide important insight on this issue

Cell-Type-Specific Complement Expression in the Healthy and Diseased Retina

Complement dysregulation is a feature of many retinal diseases, yet mechanistic understanding at the cellular level is limited. Given this knowledge gap about which retinal cells express complement, we performed single-cell RNA sequencing on similar to 92,000 mouse retinal cells and validated our results in five major purified retinal cell types. We found evidence for a distributed cell-type-specific complement expression across 11 cell types. Notably, Muller cells are the major contributor of complement activators c1s, c3, c4, and cfb. Retinal pigment epithelium (RPE) mainly expresses cfh and the terminal complement components, whereas cfi and cfp transcripts are most abundant in neurons. Aging enhances c1s, cfb, cfp, and cfi expression, while cfh expression decreases. Transient retinal ischemia increases complement expression in microglia, Muller cells, and RPE. In summary, we report a unique complement expression signature for murine retinal cell types suggesting a well-orchestrated regulation of local complement expression in the retinal microenvironment