A cardinal pathological feature of age-related macular degeneration (AMD) is the deposition of extracellular material between the retinal pigment epithelium (RPE) and Bruch's membrane, pathologically described as sub-RPE deposits. Both the presence and local organization of these deposits contribute to the clinical manifestations of AMD, including localized deposits clinically recognized as drusen. The biogenesis of sub-RPE deposits remains elusive. This work explores the pathological processes of sub-RPE deposit formation.
Matrigel was injected to the subretinal space of rats to create an amorphous deposit. Tissue sections were examined by light or confocal microscopy.
In the presence of the subretinal deposit of Matrigel, RPE cells leave Bruch's membrane to migrate toward photoreceptors and then form a new layer between the deposit and photoreceptors, resulting in RPE translocation. The new RPE layer displaces the deposit to the sub-RPE location and therefore it becomes a sub-RPE deposit. The RPE mobilization requires the presence of photoreceptors. Bruch's membrane devoid of RPE attachment becomes vulnerable to invasion by new blood vessels from the choroid.
Our work supports a novel model of sub-RPE deposit formation in which excessive material first accumulates in the subretinal space, disrupting the physical contact between RPE cells and photoreceptors. To restore the contact, RPE cells migrate toward photoreceptors and form a new layer. The subretinal material is consequently displaced to the sub-RPE location and becomes sub-RPE deposit. Our data also provide evidence that the presence of sub-RPE deposit is sufficient to induce choroidal neovascularization to penetrate Bruch's membrane.
To describe the features of intraretinal retinal pigment epithelium (RPE) migration documented on a prototype spectral domain high speed, ultrahigh resolution optical coherence tomography (OCT) device in a group of patients with early to intermediate dry age-related macular degeneration (AMD). To correlate intraretinal RPE migration on OCT to RPE pigment clumping on fundus photographs.
Retrospective, non-comparative, non-interventional case series.
Fifty-five eyes of 44 patients seen at the New England Eye Center between December 2007 and June 2008 with early to intermediate dry AMD.
3D OCT scan sets from all patients were analyzed for presence of intraretinal RPE migration, defined as small discreet hyper-reflective and highly-backscattering lesions within the neurosensory retina. Fundus photographs were also analyzed to determine the presence of RPE pigment clumping, defined as black-colored, often spiculated areas of pigment clumping within the macula. OCT en face images were correlated with fundus photographs to demonstrate correspondence of intraretinal RPE migration on OCT and RPE clumping on fundus photo.
MAIN OUTCOME MEASURES
Drusen, Dry AMD, intraretinal RPE migration, RPE pigment clumping.
54.5% of eyes (61.4% of patients) demonstrated intraretinal RPE migration on OCT scans. 56.4% of the fundus photographs demonstrated RPE pigment clumping. All eyes with intraretinal RPE migration on OCT had corresponding RPE pigment clumping on fundus photographs. RPE pigment migrated most frequently into the outer nuclear layer (66.7% of eyes) and less frequently into more anterior retinal layers. Intraretinal RPE migration mainly occurred above areas of drusen (73.3% of eyes).
The appearance of intraretinal RPE migration on OCT is a common occurrence in early to intermediate dry AMD, occurring in 54.5% of eyes or 61.4% of patients. The area of intraretinal RPE migration on OCT always correlated to areas of pigment clumping on fundus photography. Conversely, all but one eye with RPE pigment clumping on fundus photography also had areas of intraretinal RPE migration on OCT. The high incidence of intraretinal RPE migration observed above areas of drusen suggests that drusen may play physical and catalytic roles in facilitating intraretinal RPE migration in dry AMD patients.
The vertebrate retina develops from the center to the periphery. In amphibians and fish the retinal margin continues to proliferate throughout life, resulting in retinal expansion. This does not happen in mammals. However, some mammalian peripheral retinal pigment epithelial (RPE) cells continue to divide, perhaps as a vestige of this mechanism. The RPE cells are adjacent to the ciliary margin, a known stem cell source. Here we test the hypothesis that peripheral RPE is fundamentally different from central RPE by challenging different regions with microscopic laser burns and charting differential responses in terms of levels of proliferation and the regions over which this proliferation occurs.
Microscopic RPE lesions were undertaken in rats at different eccentricities and the tissue stained for proliferative markers Ki67 and bromodeoxyuridine (BrdU) and the remodeling metalloproteinase marker 2 (MMP2).
All lesions produced local RPE proliferation and tissue remodeling. Significantly more mitosis resulted from peripheral than central lesions. Unexpectedly, single lesions also resulted in RPE cells proliferating across the entire retina. Their number did not increase linearly with lesion number, indicating that they may be a specific population. All lesions repaired and formed apparently normal relations with the neural retina. Repaired RPE was albino.
These results highlight regional RPE differences, revealing an enhanced peripheral repair capacity. Further, all lesions have a marked impact on both local and distant RPE cells, demonstrating a pan retinal signaling mechanism triggering proliferation across the tissue plane. The RPE cells may represent a distinct population as their number did not increase with multiple lesions. The fact that repairing cells were hypopigmented is of interest because reduced pigment is associated with enhanced proliferative capacities in the developing neural retina.
As the retinal pigment epithelium (RPE) ages, a number of structural changes occur, including loss of melanin granules, increase in the density of residual bodies, accumulation of lipofuscin, accumulation of basal deposits on or within Bruch’s membrane, formation of drusen (between the basal lamina of the RPE and the inner collagenous layer of Bruch’s membrane), thickening of Bruch’s membrane, microvilli atrophy and disorganization of the basal infoldings. Although these changes are well known, the basic mechanisms involved in them are frequently poorly understood. These age-related changes progress slowly and vary in severity in different individuals. These changes are also found in age-related macular degeneration (AMD), a late onset disease that severely impacts the RPE, but they are much more pronounced than during normal aging. However, the changes in AMD lead to severe loss of vision. Given the many supporting functions which the RPE serves for the retina, it is important to decipher the age-related changes in this epithelium in order to understand age-related changes in vision.
retinal pigment epithelium; aging; age-related macular degeneration (AMD); ocular disorders; retinal disease
Vertebrate retinal pigment epithelium (RPE) cells are derived from the multipotent optic neuroepithelium, develop in close proximity to the retina, and are indispensible for eye organogenesis and vision. Recent advances in our understanding of RPE development provide evidence for how critical signaling factors operating in dorso-ventral and distal-proximal gradients interact with key transcription factors to specify three distinct domains in the budding optic neuroepithelium: the distal future retina, the proximal future optic stalk/optic nerve, and the dorsal future RPE. Concomitantly with domain specification, the eye primordium progresses from a vesicle to a cup, RPE pigmentation extends towards the ventral side, and the future ciliary body and iris form from the margin zone between RPE and retina. While much has been learned about the molecular networks controlling RPE cell specification, key questions concerning the cell proliferative parameters in RPE and the subsequent morphogenetic events still need to be addressed in greater detail.
Mitf/Otx/Chx10/Pax6/activin/sonic; hedgehog/fibroblast; growth; factor/neuroepithelial; domain specification/evolution
After experimental retinal detachment in rabbits macrophages are a prominent feature in the subretinal space or within the retina. Two sources for these macrophages are identified. The retinal pigment epithelium (RPE) may undergo metaplasia and actively 'bud'; the evolving macrophage is then formed by a vitreal protrusion of the cytoplasm of an RPE cell which is 'nipped off' by lateral protrusions from adjacent cells. In addition, in regions of RPE proliferation, blood-borne cells were found in Bruch's membrane and among the mass of proliferated RPE cells, suggesting that blood-borne cells may pass from the choroidal circulation through Bruch's membrane and the RPE layer.
To investigate the capacity of mature retinal pigment epithelium (RPE) cells to enter the cell cycle in vivo using a range of RPE-specific and proliferative specific markers in both pigmented and albino rats.
Whole-mounted retinas of both Dark Agouti and albino rats were immunolabeled with cell cycle markers Ki67 or PCNA and double labeled with RPE cell marker RPE65 or CRALBP. The number and distribution of these cells was mapped. An additional group of Dark Agouti rats were given repeated intraperitoneal injections of Bromodeoxyuridine (BrdU )for 20 days and then sacrificed 30 days later. The retinas were then processed for BrdU detection and Otx, a RPE cell-specific marker. For comparison, human RPE tissue from a postmortem donor was also labeled for Ki67.
In both pigmentation phenotypes, a subpopulation of mature RPE cells in the periphery were positive for both cell cycle markers. These cells were negative for Caspase 3, hence were not apoptotic. Ki67-positive cells were also seen in human RPE. Further, many cells positive for BrdU were identified in similar retinal regions, confirming that RPE cells not only enter the cell cycle but also divide, albeit at a slow cell cycle rate. There was a ten fold increase in the number of RPE cells positive for cell cycle markers in albino (approximately 200 cells) compared to pigmented rats (approximately 20 cells).
Peripheral RPE cells in rats have the capacity to enter the cell cycle and complete cellular division.
Age-related macular degeneration (AMD) is a major cause of vision loss. It is associated with development of characteristic plaque-like deposits (soft drusen) in Bruch’s membrane basal to the retinal pigment epithelium (RPE). A sequence variant (Y402H) in short consensus repeat domain 7 (SCR7) of complement factor H (CFH) is associated with risk for “dry” AMD. We asked whether the eye-targeting of this disease might be related to specific interactions of CFH SCR7 with proteins expressed in the aging human RPE/choroid that could contribute to protein deposition in drusen. Yeast 2-hybrid (Y2H) screens of a retinal pigment epithelium/choroid library derived from aged donors using CFH SCR7 baits detected an interaction with EFEMP1/Fibulin 3 (Fib3), which is the locus for an inherited macular degeneration and also accumulates basal to macular RPE in AMD. The CFH/Fib3 interaction was validated by co-immunoprecipitation of native proteins. Quantitative Y2H and ELISA assays with different recombinant protein constructs both demonstrated higher affinity for Fib3 for the disease-related CFH 402H variant. Immuno-labeling revealed colocalization of CFH and Fib3 in globular deposits within cholesterol-rich domains in soft drusen in two AMD donors homozygous for CFH 402H (H/H). This pattern of labeling was quite distinct from those seen in examples of eyes with Y/Y and H/Y genotypes. The CFH 402H/Fib3 interaction could contribute to the development of pathological aggregates in soft drusen in some patients and as such might provide a target for therapeutic intervention in some forms of AMD.
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 β, 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.
Whilst data recognise both myeloid cell accumulation during choroidal neovascularisation (CNV) as well as complement activation, none of the data has presented a clear explanation for the angiogenic drive that promotes pathological angiogenesis. One possibility that is a pre-eminent drive is a specific and early conditioning and activation of the myeloid cell infiltrate. Using a laser-induced CNV murine model, we have identified that disruption of retinal pigment epithelium (RPE) and Bruch’s membrane resulted in an early recruitment of macrophages derived from monocytes and microglia, prior to angiogenesis and contemporaneous with lesional complement activation. Early recruited CD11b+ cells expressed a definitive gene signature of selective inflammatory mediators particularly a pronounced Arg-1 expression. Accumulating macrophages from retina and peripheral blood were activated at the site of injury, displaying enhanced VEGF expression, and notably prior to exaggerated VEGF expression from RPE, or earliest stages of angiogenesis. All of these initial events, including distinct VEGF + Arg-1+ myeloid cells, subsided when CNV was established and at the time RPE-VEGF expression was maximal. Depletion of inflammatory CCR2-positive monocytes confirmed origin of infiltrating monocyte Arg-1 expression, as following depletion Arg-1 signal was lost and CNV suppressed. Furthermore, our in vitro data supported a myeloid cell uptake of damaged RPE or its derivatives as a mechanism generating VEGF + Arg-1+ phenotype in vivo. Our results reveal a potential early driver initiating angiogenesis via myeloid-derived VEGF drive following uptake of damaged RPE and deliver an explanation of why CNV develops during any of the stages of macular degeneration and can be explored further for therapeutic gain.
This study showed that mouse retina and retinal pigment epithelial (RPE) cells express the heme transporters FLVCR, BCRP, and PCFT. FLVCR is localized to the apical membrane, and BCRP and PCFT are localized to the basolateral membrane in RPE cells. Hemochromatosis, a genetic disease with iron overload, is associated with upregulation of FLVCR and PCFT, but with downregulation of BCRP in retina and RPE.
FLVCR, BCRP, and PCFT/HCP-1 represent the three heme transporters identified thus far in mammalian cells, but there is very little known about their expression and regulation in the retina. In this study, the expression of these transporters in mouse retina and retinal pigment epithelium (RPE) and their regulation in the iron-overload disease hemochromatosis were examined.
The expression of FLVCR, BCRP, and PCFT in mouse retina and primary mouse RPE cells was studied by RT-PCR and immunofluorescence. Polarized localization of the transporters in RPE was studied by co-localization using a specific marker of the RPE apical membrane. Uptake of heme in primary RPE cells was determined using zinc-mesoporphyrin, a fluorescent heme analogue. The regulation of heme transporters by iron overload was studied in two genetic models of hemochromatosis (HFE-null mouse and HJV-null mouse) and in two nongenetic models of iron overload (cytomegalovirus infection and treatment with ferric ammonium citrate).
All three heme transporters were expressed in the retina and RPE. In the RPE, the expression of FLVCR was restricted to the apical membrane, and the expression of BCRP and PCFT was restricted to the basolateral membrane. In all cases of iron overload, the expression of FLVCR and PCFT was upregulated and that of BCRP was downregulated.
Hemochromatosis is associated not only with excessive accumulation of free iron in the retina and RPE but also with excessive accumulation of heme. Since heme is toxic at high levels, as is free iron, heme-induced oxidative damage may also play a role in hemochromatosis-associated retinal pathology.
A pathological study was performed on the necropsy eyes of a 59-year old-woman who had suffered for nine years from multifocal posterior uveitis. The disease had been controlled by steroid therapy with good preservation of visual function. Extensive investigation did not reveal the aetiology. On macroscopic examination numerous focal lesions with various degrees of pigmentation were observed scattered across the fundi. These lesions were studied by light and electron microscopy and immunohistochemistry. There was ongoing chorioretinal inflammation in the foci, producing destruction of Bruch's membrane, the retinal pigment epithelium (RPE), and the outer retina. The focal scars showed migration of RPE and glial cells and neovascularisation. Capillary and venule endothelial cells were swollen at the inflammatory sites. Attempts to establish a cause for this condition were unsuccessful.
Human retinal pigment epithelial (RPE) cells synthesize an extraneous splice isoform of retinal G protein-coupled receptor (RGR). In this study, we analyzed the exon-skipping variant of RGR (RGR-d) that is found in extracellular deposits. RPE-choroid tissue sections were prepared from postmortem human eyes from donors of various ages. RGR-d was analyzed in drusen and Bruch's membrane by immunohistochemical localization. Extracellular RGR-d is present in most drusen, including hard, soft, confluent and early-stage. Initial drusen formation is known to be preferentially associated with the intercapillary regions of Bruch's membrane. We corroborated this significant association of drusen, including early-stage drusen, with the intercapillary regions. The distribution of extracellular RGR-d in Bruch's membrane differs in old and young donors. In older persons, nodes of concentrated RGR-d accumulate at intercapillary loci, predominantly at the lateral edges of the capillaries of the choriocapillaris. RGR-d loci at the lateral capillary wall appear numerous in old, but not young, donors. Intensely immunostained RGR-d loci can be found at the base of early-stage drusen mounds in the older donors and may precede the formation of these drusen.
Retinal pigment epithelium; Bruch's membrane; drusen; RGR; RPE retinal G protein-coupled receptor; RGR-d; exon-skipping isoform of human RGR; choriocapillaris; extracellular deposit
Transplants of the retina are among the new strategies being used in the treatment of genetic and degenerative macular diseases. Moreover, various cell cultures are being tested to treat retinal disorders.
Literature dated from 2004 to 2011 was comprehensively examined via Medline and PubMed searches for the following terms: auto-, homo-, heterologous transplantation, retina, stem cells, cultivated cells.
Tissue and cell therapy of retinal diseases are reviewed, including full-thickness retina/retinal pigment epithelium (RPE)/choroid graft; full and partial thickness RPE/choroid complex grafts; RPE/Bruch membrane complex graft; and RPE, iris pigment epithelium and stem cell grafts. Recommendations for transplants, as well as the benefits and weaknesses of specific techniques in retina transplants, are discussed.
Auto- and allogenic transplants of a full or partial thickness retina/RPE/Bruch membrane/choroid complex represent an alternative treatment offered to patients with some macular diseases. Stem cell transplantation to reconstruct and regenerate the macula requires further biomolecular and animal research studies.
eye ball; transplantation; autologous; homologous; heterologous; retina; stem cells
In this study, the authors describe the signaling pathways of cytokine induction by 7-ketocholesterol. This chronic inflammatory pathway may be of importance to the RPE and choriocapillaris, which are in direct contact with age-related oxidized lipoprotein deposits.
7-Ketocholesterol (7KCh) accumulates in oxidized lipoprotein deposits and is known to be involved in macrophage foam cell formation and atherosclerosis. 7-KCh is present in the primate retina and is associated with oxidized lipoprotein deposits located in the choriocapillaris, Bruch's membrane, and retinal pigment epithelium (RPE). 7-KCh can also be formed in the retina as a consequence of light-induced iron release. The purpose of this study was to examine the signaling pathways involved in the 7KCh-mediated inflammatory response focusing on three cytokines, VEGF, IL-6, and IL-8
ARPE-19 cells were treated with 7KCh solubilized in hydroxypropyl-β-cyclodextrin. Cytokines were quantified by qRT-PCR (mRNA) and ELISA (protein) using commercially available products. NFκB activation was determined by IκBα mRNA induction
Treatment of ARPE-19 cells with 15 μM 7KCh markedly induced the expression of VEGF, IL-6, and IL-8. No increase in NOX-4 expression or ROS formation was detected. 7KCh induced the phosphorylation of ERK1/2 and p38MAPK, and inhibitors to these kinases markedly reduced the cytokine expression but did not affect the IκBα mRNA expression. By contrast, inhibition of PI3K and PKCζ significantly decreased the cytokine and IκBα mRNA expression. Inhibition of the IκB kinase complex essentially ablated all cytokine induction
7KCh induces cytokines via three kinase signaling pathways, AKT-PKCζ-NFκB, p38 MAPK, and ERK. The MAPK/ERK pathways seem to preferentially enhance cytokine induction downstream from NFκB activation. The results of this study suggest that 7KCh activates these pathways through interactions in the plasma membrane, but the mechanism(s) remains unknown.
We report a case of intraocular mycosis fungoides in a 48-year-old man. The patient presented with decreased visual acuity, white subretinal lesions, and vitritis. Post-mortem histopathology revealed malignant T cell infiltrates consistent with mycosis fungoides in the retina, vitreous, and between the retinal pigment epithelium (RPE) and Bruch's membrane Focal atrophy of the RPE, along with the sub-RPE infiltrates, correlated with the clinically visible fundus lesions.
Aim: To evaluate the morphology and visual function of the macula in eyes with adult onset vitelliform macular dystrophy (AVMD).
Methods: 12 eyes of six patients with AVMD were examined by ophthalmoscopy, scanning laser ophthalmoscopy (SLO), optical coherence tomography (OCT), and multifocal electroretinography (mfERGs). The macular lesions were bilateral in all patients and varied from the typical vitelliform (five eyes), faded vitelliform changes with retinal pigment epithelium (RPE) atrophy (five eyes), and a normal fovea associated with small flecks around the macula (two eyes).
Results: SLO demonstrated small abnormal bright spots in the deep retina throughout the posterior retina in all cases. OCT showed a highly reflective fusiform thickened layer at the level of the RPE and choriocapillaris in patients with a submacular yellow vitelliform lesion. A well circumscribed, optically clear space was observed beneath the retinal layer in the macular lesions with RPE atrophy. The mfERGs were significantly reduced not only in the macular area but also in the outermost ring (20–30°) of the mfERGs.
Conclusions: The submacular materials that accumulate within the RPE or subepithelial layers reported in previous histopathological studies of vitelliform lesions can be detected by OCT. In the macular lesions with RPE atrophy, the material may have disappeared leaving a subretinal or subepithelial optical clear space. These SLO and mfERG observations suggest that the morphological and functional abnormalities may not be localised just in the macular area but may be present throughout the posterior pole in eyes with AVMD.
adult onset vitelliform macular dystrophy; optical coherence tomography; ERG; scanning laser ophthalmoscope
Scanning electron microscopic observation of Bruch's membrane was performed after removal of retinal pigment epithelium (RPE) with the osmium tetroxide treatment. Eight human eyes from subjects at various ages (from newborn to 77 years old) were examined in order to investigate aging changes in Bruch's membrane. The collagen fibres of the inner collagenous zone in young eyes formed a tightly interwoven membrane, and the meshes were regular and fine. In old eyes the meshes were irregular and coarse, and deposits were observed. Deposits were embedded in the collagen fibres of the inner collagenous zone, or attached to the surface on the inner-collagenous-zone side of the basement membrane of RPE.
Aims: To report the histopathology of two specimens of polypoidal choroidal vasculopathy (PCV) obtained from two eyes of Japanese patients.
Methods: Specimens were obtained under direct visualisation during macular translocation surgery with 360 degree retinotomy. The clinical findings were correlated with the light microscopic findings of the two specimens.
Results: One specimen from a 77 year old man was the central portion of the lesion that lay under the sensory retina on the retinal pigment epithelium (RPE). The specimen was made up mainly of fibrous tissue with small, thin walled vessels. Indocyanine green angiography after surgery revealed that active leaking polypoidal element remained under the RPE. Another specimen obtained from a 62 year old man was made up of a fibrovascular membrane situated within Bruch's membrane. The part of this specimen inferior to the foveal region included a collection of dilated, thin walled blood vessels without pericytes, surrounded by macrophages that stained positive for CD68. The dilated vessels appeared to be correlated with the orange coloured polyps observed by ophthalmoscopy, the polypoidal structure seen in indocyanine green angiograms, and the pyramidal elevation with intermediate reflectivity by optical coherence tomography.
Conclusion: Polypoidal structures are located within Bruch's space. They are composed of clusters of dilated, thin walled blood vessels surrounded by macrophages and fibrin material. The positive immunohistochemical staining for vascular endothelial growth factor in the RPE and the vascular endothelial cells suggests that this fibrovascular complex is a subretinal choroidal neovascularisation.
polypoidal choroidal vasculopathy; macular translocation; histopathology
There is a mutualistic symbiotic relationship between the components of the photoreceptor/retinal pigment epithelium (RPE)/Bruch’s membrane (BrMb)/choriocapillaris (CC) complex that is lost in AMD. Which component in the photoreceptor/RPE/BrMb/CC complex is affected first appears to depend on the type of AMD. In atrophic AMD (~85–90% of cases), it appears that large confluent drusen formation and hyperpigmentation (presumably dysfunction in RPE) are the initial insult and the resorption of these drusen and loss of RPE (hypopigmentation) can be predictive for progression of geographic atrophy (GA). The death and dysfunction of photoreceptors and CC appear to be secondary events to loss in RPE.
In neovascular AMD (~10–15% of cases), the loss of choroidal vasculature may be the initial insult to the complex. Loss of CC with an intact RPE monolayer in wet AMD has been observed. This may be due to reduction in blood supply because of large vessel stenosis. Furthermore, the environment of the CC, basement membrane and intercapillary septa, is a proinflammatory milieu with accumulation of complement components as well as proinflammatory molecules like CRP during AMD. In this toxic milieu, CC die or become dysfunction making adjacent RPE hypoxic. These hypoxic cells then produce angiogenic substances like VEGF that stimulate growth of new vessels from CC, resulting in choroidal neovascularization (CNV). The loss of CC might also be a stimulus for drusen formation since the disposal system for retinal debris and exocytosed material from RPE would be limited. Ultimately, the photoreceptors die of lack of nutrients, leakage of serum components from the neovascularization, and scar formation.
Therefore, the mutualistic symbiotic relationship within the photoreceptor/RPE/BrMb/CC complex is lost in both forms of AMD. Loss of this functionally integrated relationship results in death and dysfunction of all of the components in the complex.
Aim: Selective retinal pigment epithelium (RPE) laser treatment is a new technique which selectively damages the RPE while sparing the neural retina. One difficulty is the inability to visualise the laser lesions. The aim of the study was to investigate whether fundus autofluorescence (AF) is changed because of the RPE damage, and thus might be used for treatment control. Additionally, the clinical course of patients with various macular diseases was evaluated.
Methods: 26 patients with macular diseases (diabetic maculopathy (DMP), soft drusen maculopathy (AMD), and central serous retinopathy (CSR)) were treated and followed up for at least 6 months. Treatment was performed with a train of repetitive short laser pulses (800 ns) of a frequency doubled Nd:YAG laser (parameters: 532 nm, 50 and 500 pulses at 100 and 500 Hz, retinal spot diameter 200 μm, pulse energies 75–175 μJ). AF was excited by 488 nm and detected by a barrier filter at 500 nm (HRA, Heidelberg Engineering, Germany). Patients were examined by ophthalmoscopy, fluorescein angiography, and autofluorescence measurements at various times after treatment (10 minutes, 1 hour, 1 and 6 weeks, 3, 6, and 12 months).
Results: Fluorescein angiography showed leakage from the irradiated areas for about 1 week after treatment. None of the laser lesions was ophthalmoscopically visible during treatment. Identification of the lesions was possible by AF imaging showing an intensity decay in the irradiated area in 22 out of 26 patients, predominantly in patients with CSR and AMD. Lesions could be identified 10 minutes after treatment as hypoautofluorescent spots, which were more pronounced 1 hour later. During follow up the laser spots became hyperautofluorescent. In patients with DMP some AF images were less helpful because of diffuse oedema and larger retinal thickness. In these cases ICG angiography was able to confirm therapeutic success very well. Most of the patients have had benefit from the treatment, with best results obtained for CSR patients.
Conclusion: Imaging of non-visible selective RPE laser effects can be achieved by AF measurements predominantly in patients without retinal oedema. Therefore, AF may replace invasive fluorescein angiography in many cases to verify therapeutic laser success. Selective laser treatment has the potential to improve the prognosis of macular diseases without the risk of laser scotomas.
retinal pigment epithelium; laser photocoagulation; microphotocoagulation; autofluorescence; diabetic maculopathy; drusen; central serous retinopathy
We investigated the permeation of liposomal and polymeric gene delivery systems through neural retina into retinal pigment epithelium (RPE) and determined the roles of various factors in permeation and subsequent uptake of the delivery systems by RPE. Anterior parts and vitreous of fresh bovine eyes were removed. Retina was left intact or peeled away. Complexes of ethidium monoazide (EMA)-labeled plasmid DNA and cationic carriers (polyethyleneimine, poly-L-lysine, DOTAP liposomes) were pipetted on the retina or RPE. Two hours later the neural retina was removed, if present, and the RPE cells were detached. Contaminants were removed by sucrose centrifugation, and the RPE cells were analyzed for DNA uptake by flow cytometry. Cellular uptake of FITC-dextrans (molecular weight [mw] 20 000, 500 000 and 2 000 000), FITC-poly-L-lysine (mw 20 000), FITC-labeled oligonucleotide (15-mer), and naked EMA-labeled plasmid DNA was determined after pipetting the solutions on the RPE or neural retina. Location of the fluorescent materials in the retina was visualized with fluorescence microscopy. Neural retina decreased the cellular uptake of DNA complexes by an order of magnitude, the uptake of FITC-dextrans slightly, whereas delivery of polycationic FITC-poly-L-lysine to RPE was almost completely inhibibited. Neural retina decreased the cellular uptake of FITC-oligonucleotides, while the uptake of uncomplexed plasmid was always negligible. conclusions from FACS and fluorescence microscopy were similar: delivery of polymeric and liposomal DNA complexes into RPE are limited by the neural retina. This is due to the size and positive charge of the complexes.
gene delivery; intravitreal; retina; liposome; polymer
Age-related macular degeneration (AMD) is a leading cause of blindness that
affects the central region of the retinal pigmented epithelium (RPE), choroid, and
neural retina. Initially characterized by an accumulation of sub-RPE deposits, AMD
leads to progressive retinal degeneration, and in advanced cases, irreversible
vision loss. Although genetic analysis, animal models, and cell culture systems
have yielded important insights into AMD, the molecular pathways underlying AMD's
onset and progression remain poorly delineated. We sought to better understand the
molecular underpinnings of this devastating disease by performing the first
comparative transcriptome analysis of AMD and normal human donor eyes.
RPE-choroid and retina tissue samples were obtained from a common cohort of 31
normal, 26 AMD, and 11 potential pre-AMD human donor eyes. Transcriptome profiles
were generated for macular and extramacular regions, and statistical and
bioinformatic methods were employed to identify disease-associated gene signatures
and functionally enriched protein association networks. Selected genes of high
significance were validated using an independent donor cohort.
We identified over 50 annotated genes enriched in cell-mediated immune responses
that are globally over-expressed in RPE-choroid AMD phenotypes. Using a machine
learning model and a second donor cohort, we show that the top 20 global genes are
predictive of AMD clinical diagnosis. We also discovered functionally enriched
gene sets in the RPE-choroid that delineate the advanced AMD phenotypes,
neovascular AMD and geographic atrophy. Moreover, we identified a graded increase
of transcript levels in the retina related to wound response, complement cascade,
and neurogenesis that strongly correlates with decreased levels of
phototransduction transcripts and increased AMD severity. Based on our findings,
we assembled protein-protein interactomes that highlight functional networks
likely to be involved in AMD pathogenesis.
We discovered new global biomarkers and gene expression signatures of AMD. These
results are consistent with a model whereby cell-based inflammatory responses
represent a central feature of AMD etiology, and depending on genetics,
environment, or stochastic factors, may give rise to the advanced AMD phenotypes
characterized by angiogenesis and/or cell death. Genes regulating these
immunological activities, along with numerous other genes identified here,
represent promising new targets for AMD-directed therapeutics and diagnostics.
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The retinal pigment epithelium (RPE) and underlying Bruch’s membrane undergo significant modulation during ageing. Progressive, age-related modifications of lipids and proteins by advanced glycation end products (AGEs) at this cell–substrate interface have been implicated in RPE dysfunction and the progression to age-related macular degeneration (AMD). The pathogenic nature of these adducts in Bruch’s membrane and their influence on the overlying RPE remains unclear. This study aimed to identify alterations in RPE protein expression in cells exposed to AGE-modified basement membrane (AGE-BM), to determine how this “aged” substrate impacts RPE function and to map the localisation of identified proteins in ageing retina.
Confluent ARPE-19 monolayers were cultured on AGE-BM and native, non-modified BM (BM). Following 28-day incubation, the proteome was profiled using 2-dimensional gel electrophoresis (2D), densitometry and image analysis was employed to map proteins of interest that were identified by electrospray ionisation mass spectrometry (ESI MS/MS). Immunocytochemistry was employed to localise identified proteins in ARPE-19 monolayers cultured on unmodified and AGE-BM and to analyze aged human retina.
Image analysis detected altered protein spot densities between treatment groups, and proteins of interest were identified by LC ESI MS/MS which included heat-shock proteins, cytoskeletal and metabolic regulators. Immunocytochemistry revealed deubiquitinating enzyme ubiquitin carboxyterminal hydrolase-1 (UCH-L1), which was upregulated in AGE-exposed RPE and was also localised to RPE in human retinal sections.
This study has demonstrated that AGE-modification of basement membrane alters the RPE proteome. Many proteins are changed in this ageing model, including UCHL-1, which could impact upon RPE degradative capacity. Accumulation of AGEs at Bruch”s membrane could play a significant role in age-related dysfunction of the RPE.
Bruch’s membrane; RPE; Advanced glycation endproducts; Ubiquitin carboxyterminal hydrolase-1
Retina organ cultures can be used as a valuable tool to study retina development ex vivo. Comparison between culture methods has revealed that timing the start of the culture and the presence of the retinal pigment epithelium (RPE) are critical for the development of the rods and cones, which are the two types of photoreceptors; rods can develop in the absence of the RPE, cones cannot. One of the necessary compounds produced by the RPE and essential for cone development and survival is the chromophore 11-cis retinal. Here, we further examined rod and cone development, chromophore production by the RPE, and photoreceptor signaling to the inner retina under organ culture conditions.
Retina-RPE cultures were prepared from 7-day-old C57BL/6 pups and maintained in culture for 11 days. Rod and cone structure was analyzed by immunohistochemistry, and cell-specific mRNA expression was analyzed by quantitative real-time PCR. We quantified 11-cis retinal spectrophotometrically by measuring rhodopsin. Signal transmission in the rod pathway was studied by analyzing c-fos expression in the inner retina in response to stroboscopic illumination.
In retina-RPE cultures analyzed after 11 days in culture, rod and cone numbers exhibited a similar ratio to those observed in the intact animal. Although photoreceptor outer segments were shorter when grown ex vivo, membrane proteins, such as cone opsin and transducin, were localized appropriately to the outer segment. Relative 11-cis retinal production ex vivo plateaued after 7 days in culture, resulting in approximately 30% of the in vivo level by day 11. The retinas responded to prolonged stroboscopic illumination with the normal nuclear expression of c-fos in cells in the inner retina.
Mouse retinal structure is maintained in retina–RPE organ cultures. The RPE in organ cultures produces sufficient amounts of 11-cis retinal to promote cone development and support signal transmission in the rod pathway. Organ cultures may be a powerful low-throughput screening tool to identify novel agents to promote photoreceptor cell survival and signaling.