Comparison of Mouse and Human Retinal Pigment Epithelium Gene Expression Profiles: Potential Implications for Age-Related Macular Degeneration

Background

The human retinal pigment epithelium (RPE) plays an important role in the pathogenesis of age related macular degeneration (AMD). AMD is the leading cause of blindness worldwide. There is currently no effective treatment available. Preclinical studies in AMD mouse models are essential to develop new therapeutics. This requires further in-depth knowledge of the similarities and differences between mouse and human RPE.

Methods

We performed a microarray study to identify and functionally annotate RPE specific gene expression in mouse and human RPE. We used a meticulous method to determine C57BL/6J mouse RPE signature genes, correcting for possible RNA contamination from its adjacent layers: the choroid and the photoreceptors. We compared the signature genes, gene expression profiles and functional annotations of the mouse and human RPE.

Results

We defined sets of mouse (64), human (171) and mouse–human interspecies (22) RPE signature genes. Not unexpectedly, our gene expression analysis and comparative functional annotation suggested that, in general, the mouse and human RPE are very similar. For example, we found similarities for general features, like “organ development” and “disorders related to neurological tissue”. However, detailed analysis of the molecular pathways and networks associated with RPE functions, suggested also multiple species-specific differences, some of which may be relevant for the development of AMD. For example, CFHR1, most likely the main complement regulator in AMD pathogenesis was highly expressed in human RPE, but almost absent in mouse RPE. Furthermore, functions assigned to mouse and human RPE expression profiles indicate (patho-) biological differences related to AMD, such as oxidative stress, Bruch’s membrane, immune-regulation and outer blood retina barrier.

Conclusion

These differences may be important for the development of new therapeutic strategies and translational studies in age-related macular degeneration.     

Receptor-Coupled Phosphoinositide Hydrolysis in Human Retinal Pigment Epithelium

Carbachol and histamine stimulated phosphoinositide (PPI) hydrolysis in cultured human retinal pigment epithelium (RPE), as reflected by an accumulation of 3H-inositol phosphates in the presence of 10 mM Li+. Carbachol increased PPI hydrolysis to greater than 600% of basal with an EC50 of 60 microM; stimulation was linear up to 60 min. This activation likely occurred via the M3 muscarinic cholinergic receptor based on the IC50 values for 4-diphenylacetoxy-N-methylpiperidine methiodide (0.47 nM), pirenzepine (280 nM), and 11-[[2-[(diethylamino)methyl]-1-piperidinyl]-acetyl]-5,11- dihydro-6H-pyrido[2,3-b][1,4]benzodiazepin-6-one (1.4 microM). Carbachol-mediated PPI hydrolysis was decreased by 80% in the absence of extracellular Ca2+. Histamine stimulated PPI turnover in a linear manner by 180% with an EC50 of 20 microM by the H1 histaminergic receptor. Serotonin, glutamate, norepinephrine, and dopamine were inactive. In human RPE, the resting cytoplasmic Ca2+ concentration, as determined by fura-2 fluorescence, was 138 +/- 24 nM. On the addition of carbachol, there was a 180% increase in peak intracellular Ca2+; addition of histamine increased intracellular Ca2+ by 187%. These results suggest receptor-mediated, inositol lipid hydrolysis is coupled to intracellular Ca2+ flux in human RPE.     

Cytotoxic Effects of Curcumin in Human Retinal Pigment Epithelial Cells

Backround

Curcumin from turmeric is an ingredient in curry powders. Due to its antiinflammatory, antioxidant and anticarcinogenic effects, curcumin is a promising drug for the treatment of cancer and retinal diseases. We investigated whether curcumin alters the viability and physiological properties of human retinal pigment epithelial (RPE) cells in vitro.

Methodology/Principal Findings

Cellular proliferation was investigated with a bromodeoxy-uridine immunoassay, and chemotaxis was investigated with a Boyden chamber assay. Cell viability was determined by trypan blue exclusion. Apoptosis and necrosis rates were determined with a DNA fragmentation ELISA. Gene expression was determined by real-time PCR, and secretion of VEGF and bFGF was examined with ELISA. The phosphorylation level of proteins was revealed by Western blotting. The proliferation of RPE cells was slightly increased by curcumin at 10 µM and strongly reduced by curcumin above 50 µM. Curcumin at 50 µM increased slightly the chemotaxis of the cells. Curcumin reduced the expression and secretion of VEGF under control conditions and abolished the VEGF secretion induced by PDGF and chemical hypoxia. Whereas low concentrations of curcumin stimulated the expression of bFGF and HGF, high concentrations caused downregulation of both factors. Curcumin decreased dose-dependently the viability of RPE cells via induction of early necrosis (above 10 µM) and delayed apoptosis (above 1 µM). The cytotoxic effect of curcumin involved activation of caspase-3 and calpain, intracellular calcium signaling, mitochondrial permeability, oxidative stress, increased phosphorylation of p38 MAPK and decreased phosphorylation of Akt protein.

Conclusion

It is concluded that curcumin at concentrations described to be effective in the treatment of tumor cells and in inhibiting death of retinal neurons (∼10 µM) has adverse effects on RPE cells. It is suggested that, during the intake of curcumin as concomitant therapy of cancer or in the treatment of eye diseases, retinal function should be monitored carefully.     

MicroRNA Expression Profiles of Human iPS Cells,Retinal Pigment Epithelium Derived From iPS,and Fetal Retinal Pigment Epithelium

The objective of this report is to describe the protocols for comparing the microRNA (miRNA) profiles of human induced-pluripotent stem (iPS) cells, retinal pigment epithelium (RPE) derived from human iPS cells (iPS-RPE), and fetal RPE. The protocols include collection of RNA for analysis by microarray, and the analysis of microarray data to identify miRNAs that are differentially expressed among three cell types. The methods for culture of iPS cells and fetal RPE are explained. The protocol used for differentiation of RPE from human iPS is also described. The RNA extraction technique we describe was selected to allow maximal recovery of very small RNA for use in a miRNA microarray. Finally, cellular pathway and network analysis of microarray data is explained. These techniques will facilitate the comparison of the miRNA profiles of three different cell types.     

Identification of Age-associated Proteins and Functional Alterations in Human Retinal Pigment Epithelium

Retinal pigment epithelium(RPE) has essential functions, such as nourishing and supporting the neural retina, and is of vital importance in the pathogenesis of age-related retinal degeneration. However, the exact molecular changes of RPE during aging remain poorly understood.Here, we isolated human primary RPE(h RPE) cells from 18 eye donors distributed over a wide age range(10–67 years old). A quantitative proteomic analysis was performed to analyze changes in their intracellular and secreted p...     

Autophagy and Exosomes in the Aged Retinal Pigment Epithelium: Possible Relevance to Drusen Formation and Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a major cause of loss of central vision in the elderly. The formation of drusen, an extracellular, amorphous deposit of material on Bruch''s membrane in the macula of the retina, occurs early in the course of the disease. Although some of the molecular components of drusen are known, there is no understanding of the cell biology that leads to the formation of drusen. We have previously demonstrated increased mitochondrial DNA (mtDNA) damage and decreased DNA repair enzyme capabilities in the rodent RPE/choroid with age. In this study, we found that drusen in AMD donor eyes contain markers for autophagy and exosomes. Furthermore, these markers are also found in the region of Bruch''s membrane in old mice. By in vitro modeling increased mtDNA damage induced by rotenone, an inhibitor of mitochondrial complex I, in the RPE, we found that the phagocytic activity was not altered but that there were: 1) increased autophagic markers, 2) decreased lysosomal activity, 3) increased exocytotic activity and 4) release of chemoattractants. Exosomes released by the stressed RPE are coated with complement and can bind complement factor H, mutations of which are associated with AMD. We speculate that increased autophagy and the release of intracellular proteins via exosomes by the aged RPE may contribute to the formation of drusen. Molecular and cellular changes in the old RPE may underlie susceptibility to genetic mutations that are found in AMD patients and may be associated with the pathogenesis of AMD in the elderly.     

Proteomics Characterization of Cell Membrane Blebs in Human Retinal Pigment Epithelium Cells

Age-related macular degeneration (AMD) is the leading cause of legal blindness among the elderly population in the industrialized world, affecting about 14 million people in the United States alone. Smoking is a major environmental risk factor for AMD, and hydroquinone is a major component in cigarette smoke. Hydroquinone induces the formation of cell membrane blebs in human retinal pigment epithelium (RPE). Blebs may accumulate and eventually contribute first to sub-RPE deposits and then drusen formation, which is a prominent histopathologic feature in eyes with AMD. As an attempt to better understand the mechanisms involved in early AMD, we sought to investigate the proteomic profile of RPE blebs. Isolated blebs were subjected to SDS-PAGE fractionation, and in-gel trypsin-digested peptides were analyzed by LC-MS/MS that lead to the identification of a total of 314 proteins. Identified proteins were predominantly involved in oxidative phosphorylation, cell junction, focal adhesion, cytoskeleton regulation, and immunogenic processes. Importantly basigin and matrix metalloproteinase-14, key proteins involved in extracellular matrix remodeling, were identified in RPE blebs and shown to be more prevalent in AMD patients. Altogether our findings suggest, for the first time, the potential involvement of RPE blebs in eye disease and shed light on the implication of cell-derived microvesicles in human pathology.Age-related macular degeneration (AMD)¹ is one of the most common pathologies in the retina, consisting in a chronic degenerative disorder that constitutes the leading cause of blindness in the elderly, probably affecting 14 million people in the United States. AMD is a multifactorial disease in nature in which age is the predominant risk factor, although there are also environmental factors involved. In this regard, smoking is thought to be a major environmental risk factor as supported by extensive epidemiological evidence (1–5). AMD develops in two different stages: early AMD (also referred to as dry AMD) and the late stage of AMD known as wet AMD by virtue of the extensive neovascularization taking place in the retina choroid. Although there is a fair understanding of the mechanisms involved in wet AMD, little is known about dry AMD and its transition into the most severe stage of this disorder, i.e. wet AMD (6).Early AMD targets the retinal pigment epithelium (RPE) and the Bruch membrane (BrM) in the retina. The RPE constitutes a cell monolayer that is crucial to maintain a normal photoreceptor function. In fact, RPE participates in the cycling of the visual molecules, provides nutrients to rods and cones, and is responsible for withdrawing waste debris from the outer segments of photoreceptors (7). The early stage of AMD is characterized by initial deregulation of the normal extracellular matrix (ECM) turnover leading to thickening of the BrM, sub-RPE deposit accumulation, and drusen formation (8). As mentioned earlier, cumulative evidence suggests that smoking may constitute a major risk factor for early AMD. In fact, we and others have provided evidence that hydroquinone (HQ), a major component of cigarette smoke, has the ability to deregulate the ECM (9–12). Aside from cigarette smoke, HQ is a compound of environmental relevance because of its broad presence in plastics, foodstuff, and air pollution (13, 14).Mild injuries inflected to the retina elicit a cellular response in the RPE consisting in pinching off small areas of the plasma membrane, which renders small microvesicles called blebs (15). The reason(s) behind membrane blebbing remains unknown, although it has been postulated to be an attempt to discard damaged cellular constituents by the RPE cell (8). Under prolonged injury, blebs may accumulate between the RPE and the basal lamina underneath this cell monolayer. Based on this concept, a plausible role for blebs in the pathogenesis of dry AMD has been suggested as a likely contributor to build-up of the sub-RPE deposits, which are characteristic of the early stages of this disorder (8). To date, however, RPE bleb composition and potential functions remain largely unexplored.However, membrane bleb or microvesicle production stimulated by a variety of stress has been extensively described in many different cell types (16–23). To gain a better understanding of the functional relevance of blebs in general and the pathogenic mechanism(s) involved in early AMD in particular, we sought to investigate the identity of proteins carried by human RPE blebs. Previously microvesicles from lymphocytes have been subjected to analysis leading to the identification of a number of proteins (24). In our study, we show the proteomics characterization of stress-induced blebs in RPE cells from human retina. We report identification of several proteins, some of them potentially involved in matrix metalloproteinase (MMP) activation, membrane lipid raft formation, and immunogenic processes. Interestingly RPE blebs were found to carry basigin (including highly glycosylated species) and MMP-14, which are key proteins regulating the ECM turnover and remodeling. A previous proteomics study also has revealed the presence of basigin in the blebs from malignant lymphocytes (24). In the present study, we intended to gain some insight into the functional characterization of blebs to unravel some of the biological consequences of cell membrane blebbing in disease.     

Biological Effects of Cigarette Smoke in Cultured Human Retinal Pigment Epithelial Cells

The goal of the present study was to determine whether treatment with cigarette smoke extract (CSE) induces cell loss, cellular senescence, and extracellular matrix (ECM) synthesis in primary human retinal pigment epithelial (RPE) cells. Primary cultured human RPE cells were exposed to 2, 4, 8, and 12% of CSE concentration for 24 hours. Cell loss was detected by cell viability assay. Lipid peroxidation was assessed by loss of cis-parinaric acid (PNA) fluorescence. Senescence-associated ß-galactosidase (SA-ß-Gal) activity was detected by histochemical staining. Expression of apolipoprotein J (Apo J), connective tissue growth factor (CTGF), fibronectin, and laminin were examined by real-time PCR, western blot, or ELISA experiments. The results showed that exposure of cells to 12% of CSE concentration induced cell death, while treatment of cells with 2, 4, and 8% CSE increased lipid peroxidation. Exposure to 8% of CSE markedly increased the number of SA-ß-Gal positive cells to up to 82%, and the mRNA expression of Apo J, CTGF, and fibronectin by approximately 3–4 fold. Treatment with 8% of CSE also increased the protein expression of Apo J and CTGF and the secretion of fibronectin and laminin. Thus, treatment with CSE can induce cell loss, senescent changes, and ECM synthesis in primary human RPE cells. It may be speculated that cigarette smoke could be involved in cellular events in RPE cells as seen in age-related macular degeneration.     

Infection of Human Retinal Pigment Epithelium with Chlamydia trachomatis

Purpose

Little is known about the susceptibility of posterior segment tissues, particularly the human retinal pigment epithelium (hRPE), to Chlamydia trachomatis. The purpose of the study was to investigate the possibility of infecting the hRPE with Chlamydia trachomatis, and to examine the infectivity of different Chlamydia trachomatis clinical isolates for hRPE cells and the hRPE cell response to the infection.

Methods

Cultured hRPE and McCoy cells were inoculated with eight Chlamydia trachomatis (serovar E) clinical isolates at multiplicity of infection (MOI) of 2.0 or 0.3. To detect Chlamydia trachomatis, samples were stained immunohistochemically with anti-major outer membrane protein antibodies at 24h, 48h, and 72h postinoculation (PI). The changes in the expression of signaling molecules and proteins of cytoskeleton and extracellular matrix in hRPE cells were examined immunohistochemically.

Results

All eight clinical isolates demonstrated ability to infect hRPE cells. At equal MOI of 0.3, the infectivity of Chlamydia trachomatis clinical isolates for RPE culture was found to be at least as high as that for McCoy cell culture. At 24h PI, the percentage of inclusion-containing cells varied from 1.5 ± 0.52 to 14.6 ± 3.3% in hRPE cell culture infected at MOI of 2.0 against 0.37 ± 0.34 to 8.9 ± 0.2% in McCoy cell culture infected at MOI of 0.3. Collagen type I, collagen type IV, basic fibroblast growth factor, transforming growth factor-beta and interleukin–8 expression at 48h PI were maximally increased, by 2.1-, 1.3-, 1.5-, 1.5- and 1.6-fold, respectively, in the Chlamydia trachomatis-infected compared with control hRPE cell culture specimens (P < 0.05).

Conclusions

This study, for the first time, proved the possibility of infecting hRPE cultured cells with Chlamydia trachomatis, which leads to proproliferative and proinflammatory changes in the expression of signaling molecules and extracellular matrix components.     

Neuronatin对人视网膜色素上皮细胞增殖迁移的影响

目的:研究胚胎时期表达部位广泛、丰度高,而成年后分化表达的印记基因Neuronatin(Nnat)的两种剪接形式Nnatα和Nnatβ对人视网膜色素上皮细胞(RPE)增殖、迁移的影响。方法:构建Nnatα、β两种剪接形式的表达质粒,转染RPE获得表达该基因的稳定表达细胞株;CCK-8实验检测稳定表达细胞株的增殖能力,流式细胞仪分析细胞周期,细胞划痕实验检测其迁移能力。结果:成功构建了Nnatα和Nnatβ表达质粒,并获得了Nnatα和Nnatβ基因稳定表达PRE细胞株。CCK-8实验结果显示cNNATα组与对照组相比较,增值率为23.33%(P0.05),cNNATβ组相较于对照组无显著性差异,细胞周期分析cNNATα组和cNNATβ组细胞在G2-S期的百分率分别为18.60%、11.11%,对照组细胞的为9.94%;相较于对照组,cNNATα组的细胞迁移能力显著增强,cNNATβ组的细胞迁移能力微弱增强。结论:Nnatα对RPE有一定的增殖作用,其影响主要在S期;同时,Nnatα显著促进RPE细胞的迁移能力。     

The Polarity of the Retinal Pigment Epithelium

The diversity of epithelia in the body permits a multitude of organ-specific functions. One of the foremost examples of this is the retinal pigment epithelium. Located between the photoreceptors of the retina and their principal blood supply, the choriocapillaris, the retinal pigment epithelium is critical for the survival and function of retinal photoreceptors. To serve this purpose, the retinal pigment epithelium cell has adapted the classic Golgi-to-cell-surface targeting pathways first described in such prototypic epithelial cell models as the Madin-Darby canine kidney cell, to arrive at a unique distribution of membrane and secreted proteins. More recent data suggest that the retinal pigment epithelium also takes advantage of its inherent asymmetry to augment the classical pathways of Golgi-to-cell-surface traffic. As retinal pigment epithelium transplants and gene therapy represent potential cures for retinal degenerative diseases, understanding the basis of the unique polarity properties of retinal pigment epithelium cells will be a critical issue for the development of future therapies.     

Phototoxic Action Spectrum on a Retinal Pigment Epithelium Model of Age-Related Macular Degeneration Exposed to Sunlight Normalized Conditions

Among the identified risk factors of age-related macular degeneration, sunlight is known to induce cumulative damage to the retina. A photosensitive derivative of the visual pigment, N-retinylidene-N-retinylethanolamine (A2E), may be involved in this phototoxicity. The high energy visible light between 380 nm and 500 nm (blue light) is incriminated. Our aim was to define the most toxic wavelengths in the blue-green range on an in vitro model of the disease. Primary cultures of porcine retinal pigment epithelium cells were incubated for 6 hours with different A2E concentrations and exposed for 18 hours to 10 nm illumination bands centered from 380 to 520 nm in 10 nm increments. Light irradiances were normalized with respect to the natural sunlight reaching the retina. Six hours after light exposure, cell viability, necrosis and apoptosis were assessed using the Apotox-Glo Triplex™ assay. Retinal pigment epithelium cells incubated with A2E displayed fluorescent bodies within the cytoplasm. Their absorption and emission spectra were similar to those of A2E. Exposure to 10 nm illumination bands induced a loss in cell viability with a dose dependence upon A2E concentrations. Irrespective of A2E concentration, the loss of cell viability was maximal for wavelengths from 415 to 455 nm. Cell viability decrease was correlated to an increase in cell apoptosis indicated by caspase-3/7 activities in the same spectral range. No light-elicited necrosis was measured as compared to control cells maintained in darkness. Our results defined the precise spectrum of light retinal toxicity in physiological irradiance conditions on an in vitro model of age-related macular degeneration. Surprisingly, a narrow bandwidth in blue light generated the greatest phototoxic risk to retinal pigment epithelium cells. This phototoxic spectrum may be advantageously valued in designing selective photoprotection ophthalmic filters, without disrupting essential visual and non-visual functions of the eye.     

Anti-Inflammatory Effects of Resveratrol on Human Retinal Pigment Cells and a Myopia Animal Model

Resveratrol is a key component of red wine and other grape products. Recent studies have characterized resveratrol as a polyphenol, and shown its beneficial effects on cancer, metabolism, and infection. This study aimed to obtain insights into the biological effects of resveratrol on myopia. To this end, we examined its anti-inflammatory influence on human retinal pigment epithelium cells and in a monocular form deprivation (MFD)-induced animal model of myopia. In MFD-induced myopia, resveratrol increased collagen I level and reduced the expression levels of matrix metalloproteinase (MMP)2, transforming growth factor (TGF)-β, and nuclear factor (NF)-κB expression levels. It also suppressed the levels of tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1β. Resveratrol exhibited no significant cytotoxicity in ARPE-19 cells. Downregulation of inflammatory cytokine production, and inhibition of AKT, c-Raf, Stat3, and NFκB phosphorylation were observed in ARPE-19 cells that were treated with resveratrol. In conclusion, the findings suggest that resveratrol inhibits inflammatory effects by blocking the relevant signaling pathways, to ameliorate myopia development. This may make it a natural candidate for drug development for myopia.     

Engineering,Structure and Immunogenicity of the Human Metapneumovirus F Protein in the Postfusion Conformation

Human metapneumovirus (hMPV) is a paramyxovirus that is a common cause of bronchiolitis and pneumonia in children less than five years of age. The hMPV fusion (F) glycoprotein is the primary target of neutralizing antibodies and is thus a critical vaccine antigen. To facilitate structure-based vaccine design, we stabilized the ectodomain of the hMPV F protein in the postfusion conformation and determined its structure to a resolution of 3.3 Å by X-ray crystallography. The structure resembles an elongated cone and is very similar to the postfusion F protein from the related human respiratory syncytial virus (hRSV). In contrast, significant differences were apparent with the postfusion F proteins from other paramyxoviruses, such as human parainfluenza type 3 (hPIV3) and Newcastle disease virus (NDV). The high similarity of hMPV and hRSV postfusion F in two antigenic sites targeted by neutralizing antibodies prompted us to test for antibody cross-reactivity. The widely used monoclonal antibody 101F, which binds to antigenic site IV of hRSV F, was found to cross-react with hMPV postfusion F and neutralize both hRSV and hMPV. Despite the cross-reactivity of 101F and the reported cross-reactivity of two other antibodies, 54G10 and MPE8, we found no detectable cross-reactivity in the polyclonal antibody responses raised in mice against the postfusion forms of either hMPV or hRSV F. The postfusion-stabilized hMPV F protein did, however, elicit high titers of hMPV-neutralizing activity, suggesting that it could serve as an effective subunit vaccine. Structural insights from these studies should be useful for designing novel immunogens able to induce wider cross-reactive antibody responses.     

Glucose Metabolism in Rat Retinal Pigment Epithelium

The retinal pigment epithelium (RPE) is the major transport pathway for exchange of metabolites and ions between choroidal blood supply and the neural retina. To gain insight into the mechanisms controlling glucose metabolism in RPE and its possible relationship to retinopathy, we studied the influence of different glucose concentrations on glycogen and lactate levels and CO₂ production in RPE from normal and streptozotocin-treated diabetic rats. Incubation of normal RPE in the absence of glucose caused a decrease in lactate production and glycogen content. In normal RPE, increasing glucose concentrations from 5.6 mM to 30 mM caused a four-fold increase in glucose accumulation and CO₂ yield, as well as reduction in lactate and glycogen production. In RPE from diabetic rats glucose accumulation did not increase in the presence of high glucose substrate, but it showed a four- and a seven-fold increase in CO₂ production through the mitochondrial and pentose phosphate pathways, respectively. We found high glycogen levels in RPE which can be used as an energy reserve for RPE itself and/or neural retina. Findings further show that the RPE possesses a high oxidative capacity. The large increase in glucose shunting to the pentose phosphate pathway in diabetic retina exposed to high glucose suggests a need for reducing capacity, consistent with increased oxidative stress.