Imaging maculopathy in post-mortem human eyes

Osteopontin accumulates in basal deposits of human eyes with age-related macular degeneration and may serve as a biomarker of aging

A common clinical phenotype of several neurodegenerative and systemic disorders including Alzheimer's disease and atherosclerosis is the abnormal accumulation of extracellular material, which interferes with routine cellular functions. Similarly, patients with age-related macular degeneration (AMD), the leading cause of vision loss among the aged population, present with extracellular lipid- and protein-filled basal deposits in the back of the eye. While the exact mechanism of growth and formation of these deposits is poorly understood, much has been learned from investigating their composition, providing critical insights into AMD pathogenesis, prevention, and therapeutics. We identified human osteopontin (OPN), a phosphoprotein expressed in a variety of tissues in the body, as a newly discovered component of basal deposits in AMD patients, with a distinctive punctate staining pattern. OPN expression within these lesions, which are associated with AMD disease progression, were found to co-localize with abnormal calcium deposition. Additionally, OPN puncta colocalized with an AMD risk-associated complement pathway protein, but not with apolipoprotein E or vitronectin, two other well-established basal deposit components. Mechanistically, we found that retinal pigment epithelial cells, cells vulnerable in AMD, will secrete OPN into the extracellular space, under oxidative stress conditions, supporting OPN biosynthesis locally within the outer retina. Finally, we report that OPN levels in plasma of aged (non-AMD) human donors were significantly higher than levels in young (non-AMD) donors, but were not significantly different from donors with the different clinical subtypes of AMD. Collectively, our study defines the expression pattern of OPN in the posterior pole as a function of disease, and its local expression as a potential histopathologic biomarker of AMD.

The Effect of Systemic Hyperoxia and Hypoxia on Scotopic Thresholds in People with Early and Intermediate Age-related Macular Degeneration

Purpose: Morphological retinal changes combined with functional evidence implicate hypoxia in the pathogenesis of age-related macular degeneration (AMD). However, the role of hypoxia in the scotopic threshold deficit reported in AMD has not been investigated. This study compared scotopic thresholds in participants with early and intermediate AMD recorded under conditions of systemic hypoxia, hyperoxia and normoxia. Materials and Methods: Over two sessions scotopic thresholds were measured with participants breathing 21% and 60% oxygen (n = 12 early AMD, n = 11 age-similar controls) or 21% and 14% oxygen (n = 16 early AMD, n = 20 age-similar controls). Thresholds were measured using a 'white', annular 12 degrees stimulus, using a QUEST procedure. Results: There was no statistically significant change in scotopic thresholds within the AMD or control group when breathing the hyperoxic gas mixture (60% oxygen) or the hypoxic gas mixture (14% oxygen) when compared to the normoxic condition (21% oxygen). There was also no statistically significant difference in scotopic thresholds between groups under the hyperoxic or hypoxic gas conditions. The difference between groups under the normoxic condition was not statistically significant for the hyperoxia study (p = .70), but did reach significance in the hypoxia study (p = .05). Conclusion: This study provided no evidence that breathing that breathing 14% or 60% oxygen altered scotopic thresholds in those with early AMD when compared to controls. However, the lack of elevated scotopic thresholds in the AMD group of the hyperoxia study is of note, as it is unlikely that hyperoxia would reduce thresholds which were not significantly raised at baseline, regardless of whether hypoxia was a factor in the disease pathogenesis. The findings of this study do not rule out a role for hypoxia in early AMD, but this needs to be assessed in future experiments using measures that differ significantly between people with AMD and controls.

The Utah Protocol for Postmortem Eye Phenotyping and Molecular Biochemical Analysis

Purpose

Current understanding of local disease pathophysiology in AMD is limited. Analysis of the human disease-affected tissue is most informative, as gene expression, expressed quantitative trait loci, microenvironmental, and epigenetic changes can be tissue, cell type, and location specific. Development of a novel translational treatment and prevention strategies particularly for earlier forms of AMD are needed, although access to human ocular tissue analysis is challenging. We present a standardized protocol to study rapidly processed postmortem donor eyes for molecular biochemical and genomic studies.

Methods

We partnered with the Utah Lions Eye Bank to obtain donor human eyes, blood, and vitreous, within 6 hours postmortem. Phenotypic analysis was performed using spectral-domain optical coherence tomography (SD-OCT) and color fundus photography. Macular and extramacular tissues were immediately isolated, and the neural retina and retinal pigment epithelium/choroid from each specimen were separated and preserved. Ocular disease phenotype was analyzed using clinically relevant grading criteria by a group of four ophthalmologists incorporating data from SD-OCT retinal images, fundus photographs, and medical records.

Results

The use of multimodal imaging leads to greater resolution of retinal pathology, allowing greater phenotypic rigor for both interobserver phenotype and known clinical diagnoses. Further, our analysis resulted in excellent quality RNA, which demonstrated appropriate tissue segregation.

Conclusions

The Utah protocol is a standardized methodology for analysis of disease mechanisms in AMD. It uniquely allows for simultaneous rigorous phenotypic, molecular biochemical, and genomic analysis of both systemic and local tissues. This better enables the development of disease biomarkers and therapeutic interventions.

Soft Drusen in Age-Related Macular Degeneration: Biology and Targeting Via the Oil Spill Strategies

AMD is a major cause of legal blindness in older adults approachable through multidisciplinary research involving human tissues and patients. AMD is a vascular-metabolic-inflammatory disease, in which two sets of extracellular deposits, soft drusen/basal linear deposit (BLinD) and subretinal drusenoid deposit (SDD), confer risk for end-stages of atrophy and neovascularization. Understanding how deposits form can lead to insights for new preventions and therapy. The topographic correspondence of BLinD and SDD with cones and rods, respectively, suggest newly realized exchange pathways among outer retinal cells and across Bruch's membrane and the subretinal space, in service of highly evolved, eye-specific physiology. This review focuses on soft drusen/BLinD, summarizing evidence that a major ultrastructural component is large apolipoprotein B,E-containing, cholesterol-rich lipoproteins secreted by the retinal pigment epithelium (RPE) that offload unneeded lipids of dietary and outer segment origin to create an atherosclerosis-like progression in the subRPE-basal lamina space. Clinical observations and an RPE cell culture system combine to suggest that soft drusen/BLinD form when secretions of functional RPE back up in the subRPE-basal lamina space by impaired egress across aged Bruch's membrane-choriocapillary endothelium. The soft drusen lifecycle includes growth, anterior migration of RPE atop drusen, then collapse, and atrophy. Proof-of-concept studies in humans and animal models suggest that targeting the “Oil Spill in Bruch's membrane” offers promise of treating a process in early AMD that underlies progression to both end-stages. A companion article addresses the antecedents of soft drusen within the biology of the macula.

Optimizing optical coherence tomography and histopathology correlation in retinal imaging

OBJECTIVE

To develop a methodology to correlate optical coherence tomography (OCT) images and histopathological sections from the same eye. Part 1: To determine the best fixative for optimal OCT and histopathological analysis in post-mortem eyes. Part 2: A protocol is proposed to correlate histopathological features and OCT scans from the same post-mortem eyes.

DESIGN

Experimental study.

PARTICIPANTS

Part 1: Twenty-three rabbit eyes and 14 post-mortem human eyes. Part 2: Nineteen post-mortem human eyes.

METHODS

Part 1: Six different fixatives were tested, and specimens were evaluated on 4 criteria: globe shape, structure opacification, retinal detachment, and nuclear details. Part 2: Based on the findings from Part 1, fixed human eyes were imaged using OCT. Orientation-controlled histopathological processing was performed to obtain serial tissue sections from paraffin embedded tissue, which were matched to corresponding OCT images.

RESULTS

Part 1: Of the 6 fixatives, 2% glutaraldehyde and Davidson's solution met the proposed criteria in rabbit eyes. Of these, glutaraldehyde showed similar results in human eyes and was selected for Part 2. Part 2: Using anatomical landmarks, cross-sectional histopathological sections in the same orientation as the OCT images were correlated to their corresponding OCT images. Retinal lesions such as a macular hole, an epiretinal membrane, and the presence of drusen were easily correlated, proving the reliability of our methodology. Moreover, the photoreceptor's inner/outer junction was correlated to a hyperreflective band on OCT.

CONCLUSIONS

A standardized protocol was developed to correlate OCT images and histopathological findings by generating serial cross-sections of the retina, which can be used to better understand otherwise ambiguous OCT findings.

Macromolecular markers in normal human retina and applications to human retinal disease

Macromolecular cell markers are essential for the classification and characterization of the highly complex and cellularly diverse vertebrate retina. Although a plethora of markers are described in the current literature, the immunoreactivity of these markers in normal human tissue has not been fully determined. This is problematic as they are quintessential to the characterization of morphological changes associated with human retinal disease. This review provides an overview of the macromolecular markers currently available to assess human retinal cell types. We draw on immunohistochemical studies conducted in our laboratories to describe marker immunoreactivity in human retina alongside comparative descriptions in non-human tissues. Considering the growing number of eye banks services offering healthy and diseased human retinal tissue, this review provides a point of reference for future human retina studies and highlights key species specific disease applications of some macromolecular markers.

Subducted and melanotic cells in advanced age-related macular degeneration are derived from retinal pigment epithelium

PURPOSE

To describe, illustrate, and account for two cell types plausibly derived from RPE in geographic atrophy (GA) and choroidal neovascularization (CNV) of AMD, using melanosomes, lipofuscin, and basal laminar deposit (BLamD) as anatomical markers.

METHODS

Human donor eyes with GA (n = 13) or CNV (n = 39) were histologically processed, photodocumented, and analyzed for frequencies of occurrence. We defined RPE as cells containing spindle-shaped melanosomes and RPE lipofuscin, internal to basal lamina or BLamD, if present, or Bruch's membrane if not, and RPE-derived cells as those plausibly derived from RPE and not attached to basal lamina or BLamD.

RESULTS

'Subducted' cells contain RPE melanosomes and localize to the sub-RPE space, on Bruch's membrane. Credible transitional forms from RPE cells were seen. Grades of RPE overlying 'Subducted' cells were 'Atrophic with BLamD' (32.2% vs. 37.0% of 'Subducted,' for GA and CNV eyes, respectively), 'Dissociated' (22.0% vs. 21.7%), 'Nonuniform' (22.0% vs. 23.9%), and 'Sloughed' RPE (10.2% vs. 4.3%). Found exclusively in CNV scars, 'Melanotic' cells containing spherical melanosomes were adjacent to 'Entombed' RPE with spindle-shaped and spherical melanosomes. Of subretinal 'Melanotic' cells, 40.0% associated with 'Atrophy with BLamD,' 36.8% with 'Atrophy without BLamD,' and 20.6% with 'Entombed.'

CONCLUSIONS

'Dissociated' RPE within atrophic areas may be the source of 'Subducted' cells. 'Entombed' RPE within fibrovascular and fibrocellular scars may be the source of 'Melanotic' cells. An imaging correlate for 'Subducted' cells awaits discovery; 'Melanotic' cells appear gray-black in the CNV fundus. Results provide a basis for future molecular phenotyping studies.

Aging, age-related macular degeneration, and the response-to-retention of apolipoprotein B-containing lipoproteins

The largest risk factor for age-related macular degeneration (ARMD) is advanced age. A prominent age-related change in the human retina is the accumulation of histochemically detectable neutral lipid in normal Bruch's membrane (BrM) throughout adulthood. This change has the potential to have a major impact on physiology of the retinal pigment epithelium (RPE). It occurs in the same compartment as drusen and basal linear deposit, the pathognomonic extracellular, lipid-containing lesions of ARMD. Here we present evidence from light microscopic histochemistry, ultrastructure, lipid profiling of tissues and isolated lipoproteins, and gene expression analysis that this deposition can be accounted for by esterified cholesterol-rich, apolipoprotein B-containing lipoprotein particles constitutively produced by the RPE. This work collectively allows ARMD lesion formation and its aftermath to be conceptualized as a response to the retention of a sub-endothelial apolipoprotein B lipoprotein, similar to a widely accepted model of atherosclerotic coronary artery disease (CAD) (Tabas et al., 2007). This approach provides a wide knowledge base and sophisticated clinical armamentarium that can be readily exploited for the development of new model systems and the future benefit of ARMD patients.

Developing SDOCT to assess donor human eyes prior to tissue sectioning for research

BACKGROUND

To compare spectral domain optical coherence tomography (SDOCT) cross-sectional images of human central retina obtained from donor eyes with and without age-related macular degeneration (AMD) to corresponding histopathology from light micrographs. To establish the utility of SDOCT for localizing pathology in the posterior eyecup, for identifying ocular disease in donor eyes, or for directing subsequent sectioning of retinal lesions for research.

METHODS

Seven consecutive human donor eyes were selected based on age. The eyes, with the anterior segment removed, were imaged by SDOCT with a focusing aspheric lens. Four eyes were from donors with a clinical history of AMD, and three were from age-matched donors with no history of AMD. Histopathological correlation of morphological changes detected in three eyes by SDOCT was obtained for comparison to step serial-sectioned light microscopy images of the formalin-fixed, paraffin-embedded retina. A simplified imaging setup was tested on an enucleated porcine eye for comparison.

RESULTS

AMD pathology was detected and localized in four eyes by SDOCT. The SDOCT images correlated with the histopathology observed by light microscopy in each sectioned eye. Pathologies included a subfoveal neovascular lesion with subretinal fluid, peripapillary neovascularization, epiretinal membrane, foveal cyst, choroidal folds, and drusen. Similar imaging was possible with the simplified setup.

CONCLUSIONS

SDOCT imaging identified retinal disease of the posterior eyecup in human donor eyes. Pathology detected with SDOCT was verified by light microscopy in three eyes, supporting the utility of SDOCT as a screening tool for research.