Primary Retinal Pigment Epithelium Research Articles

Expression and differential regulation of HLA-G isoforms in the retinal pigment epithelial cell line, ARPE-19

The purpose of this study was to examine if HLA-G is expressed in the retinal pigment epithelium (RPE) cells of the eye. The RPE comprises the outer most layer of the retina and as such defines the interface to the blood and contributes to the immune privilege in the posterior part of the eye. One way the RPE might be regulating the immune system could be by expressing the non-classical human leukocyte antigen (HLA) molecule, HLA-G. We therefore sought to define if the RPE cell line, ARPE-19, expressed HLA-G and analyse the regulation as a response to pro-inflammatory cytokines. This was done by digital droplet PCR, measuring the gene expression of HLA-G in total RNA. The protein expression was analysed by immunohistochemistry and by immunofluorescence followed by confocal microscopy and the expression of the HLA-G isoforms was explored by fragment analysis. In the current study, we show that HLA-G is expressed by ARPE-19 cells and is upregulated as a response to pro-inflammatory cytokines. Moreover, we are the first to describe a differential regulation of the HLA-G isoforms as a direct response to stimulation. These results might indicate that HLA-G can be part of the immune privilege of the posterior part of the eye, but further experiments on primary RPE cells are needed.

Isolation, Characterization, and Establishment of Spontaneously Immortalized Cell Line HRPE-2S With Stem Cell Properties.

The retinal pigment epithelium is a monolayer of highly specialized pigmented cells located between the neural retina and the Bruch's membrane of the choroid. RPE cells play a crucial role in the maintenance and function of the underlying photoreceptors. This study introduces a spontaneously arising human retinal pigment epithelial cell line, HRPE-2S, which was isolated from primary RPE cell culture of 2 days old male donor. We characterized morphology and functional properties of the new cell line. The immortalized cell line was maintained in culture for more than 70 passages and 240 divisions. The average doubling time of the cells was approximately 22 h and got freezed at 26th passage. The cell line expressed RPE-specific markers RPE65 and cell junction protein ZO1 as an epithelial cell marker. It also expressed CHX10, PAX6, Nestin, SOX2 as stem and retinal progenitor cell markers. Ki67 as a marker of cell proliferation was expressed in all HRPE-2S cells. It represented typical epithelial cobblestone morphology and did not phenotypically change through several passages. Stem cell-like aggregations (neurospheres) were observed in SEM microscopy. The cells represented high mitotic index. They could be viable under hypoxic conditions and serum deprivation. According to functional studies, the cell line exhibited stem cell-like behaviors with particular emphasis on its self-renewal capacity. LDH isoenzymes expression pattern confirmed the same cellular source for both of the HRPE-2S cells and primary RPE cells. Characteristics of HRPE-2S cells promise it as an in vitro model for RPE stem cell-based researches. J. Cell. Physiol. 232: 2626-2640, 2017. © 2016 Wiley Periodicals, Inc.

Protective effects of fluoroquinolones on UV-induced damage of cultured ocular cell lines

Although the fluoroquinolones have strong antibacterial effects, some of them also have adverse ocular effects such as diplopia, uveitis, optic neuropathy, and retinal detachment. The purpose of this study was to determine whether low concentrations of fluoroquinolones can lessen the cytotoxic effects of ultraviolet (UV) light on different kinds of cultured ocular cells. We studied cultured human corneal endothelial cells (HCECs), a retinal ganglion cell line (RGC-5), a mouse-derived photoreceptor cell line (661W), a human adult retinal pigment epithelial cell line (ARPE-19), primary retinal cells, and primary human RPE cells. Levofloxacin, ciprofloxacin, and clinafloxacin were selected as the fluoroquinolones to test. The viabilities of the 661W, ARPE-19, and hRPE cells were assessed by Cell Counting Kit-8, and that of HCECs, 661W cells, and ARPE-19 cells by double fluorescent staining with Hoechst 33342 and propidium iodide (PI). Damage of retinal primary culture cells was assessed by immunostaining. Intracellular production of reactive oxygen species was measured in ARPE-19 cells by CM-H2DCFDA after UV light exposure. An activation of caspase by UV light in ARPE-19 cells was detected with a caspase-3/7 assay kit. UV exposure increased the number of dead cells, and the three fluoroquinolones tested suppressed this increase. Fluoroquinolones also protected the cells against the hydroxyperoxide (H2O2)-induced cell damage. Moreover, the fluoroquinolones decreased the production of reactive oxygen species and the activity of caspase-3/7, and low concentrations of fluoroquinolones reduced the oxidative stress in cultured ocular cell lines. We conclude that fluoroquinolones may have protective effects in these cells against UV exposure.

Activation of liver X receptor α protects amyloid β1-40 induced inflammatory and senescent responses in human retinal pigment epithelial cells.

To investigate whether activation of the liver X receptors (LXRs) inhibits amyloid β1-40 (Aβ1-40) induced inflammatory and senescent responses in human retinal pigment epithelial (RPE) cells. Confluent cultures of human primary RPE and ARPE-19 cells pretreated with 5μΜ of TO901317 (TO90), a synthetic agonist of LXR, or vehicle were incubated with 1μΜ of Aβ1-40 or Aβ40-1. The optimum concentrations of Aβ1-40 and TO90 were determined by cell viability assay. Pro-inflammatory cytokines IL-6, IL-8, MCP-1 were detected by real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA). Expression and localization of an aging protein p16INK4a (p16) were analyzed by western blotting and immunofluorescence. Expressions of LXRs and one of their target genes ATP-binding cassette transporter A1 (ABCA1) were examined by real-time PCR and western blotting. Phosphorylated transcription inhibition factor-κB-α (p-IκB-α) was assessed by western blotting. A negative linear relationship between the Aβ1-40 concentration and the cell viability was evident, indicating Aβ1-40 decreased ARPE-19 cell viability in a dose-dependent manner. Aβ1-40 enhanced the expression of IL-6, IL-8, MCP-1 as well as p16 in both RPE cell lines at both mRNA and protein levels, whereas TO90 counteracted the detrimental effects. TO90 upregulated the expression of LXRα and its target gene ABCA1, but it did not affect the expression of LXRβ. Meanwhile, TO90 inhibited the phosphorylation of IκB-α mediated by Aβ1-40 stimulation. Activation of the LXRα-ABCA1 axis may alleviate Aβ1-40 induced inflammatory and senescent responses in RPE cells. The beneficial effect appears associated with the inhibition of the NF-κB signaling pathway.

Bioengineered Bruch's-like extracellular matrix promotes retinal pigment epithelial differentiation

In the eye, the retinal pigment epithelium (RPE) adheres to a complex protein matrix known as Bruch's membrane (BrM). The aim of this study was to provide enriched conditions for RPE cell culture through the production of a BrM-like matrix. Our hypothesis was that a human RPE cell line would deposit an extracellular matrix (ECM) resembling BrM. The composition and structure of ECM deposited by ARPE19 cells (ARPE19-ECM) was characterized. To produce ARPE19-ECM, ARPE19 cells were cultured in the presence dextran sulphate. ARPE19-ECM was decellularized using deoxycholate and characterized by immunostaining and western blot analysis. Primary human RPE and induced pluripotent stem cells were seeded onto ARPE19-ECM or geltrex coated surfaces and examined by microscopy or RT-PCR. Culture of ARPE19 cells with dextran sulphate promoted nuclear localization of SOX2, formation of tight junctions and deposition of ECM. ARPE19 cells deposited ECM proteins found in the inner layers of BrM, including fibronectin, vitronectin, collagens IV and V as well as laminin-alpha-5, but not those found in the middle elastic layer (elastin) or the outer layers (collagen VI). ARPE19-ECM promoted pigmentation in human RPE and pluripotent stem cell cultures. Expression of RPE65 was significantly increased on ARPE19-ECM compared with geltrex in differentiating pluripotent stem cell cultures. ARPE19 cells deposit ECM with a composition and structure similar to BrM in the retina. Molecular cues present in ARPE19-ECM promote the acquisition and maintenance of the RPE phenotype. Together, these results demonstrate a simple method for generating a BrM-like surface for enriched RPE cell cultures.

Oxidative stress-mediated NFκB phosphorylation upregulates p62/SQSTM1 and promotes retinal pigmented epithelial cell survival through increased autophagy.

p62 is a scaffolding adaptor implicated in the clearance of protein aggregates by autophagy. Reactive oxygen species (ROS) can either stimulate or inhibit NFκB-mediated gene expression influencing cellular fate. We studied the effect of hydrogen peroxide (H2O2)-mediated oxidative stress and NFκB signaling on p62 expression in the retinal pigment epithelium (RPE) and investigated its role in regulation of autophagy and RPE survival against oxidative damage. Cultured human RPE cell line ARPE-19 and primary human adult and fetal RPE cells were exposed to H2O2-induced oxidative stress. The human apolipoprotein E4 targeted-replacement (APOE4) mouse model of AMD was used to study expression of p62 and other autophagy proteins in the retina. p62, NFκB p65 (total, phosphorylated, nuclear and cytoplasmic) and ATG10 expression was assessed by mRNA and protein analyses. Cellular ROS and mitochondrial superoxide were measured by CM-H2DCFDA and MitoSOX staining respectively. Mitochondrial viability was determined using MTT activity. qPCR-array system was used to investigate autophagic genes affected by p62. Nuclear and cytoplasmic levels of NFκB p65 were evaluated after cellular fractionation by Western blotting. We report that p62 is up-regulated in RPE cells under H2O2-induced oxidative stress and promotes autophagic activity. Depletion of endogenous p62 reduces autophagy by downregulation of ATG10 rendering RPE more susceptible to oxidative damage. NFκB p65 phosphorylation at Ser-536 was found to be critical for p62 upregulation in response to oxidative stress. Proteasome inhibition by H2O2 causes p62-NFκB signaling as antioxidant pre-treatment reversed p62 expression and p65 phosphorylation when RPE was challenged by H2O2 but not when by Lactacystin. p62 protein but not RNA levels are elevated in APOE4-HFC AMD mouse model, suggesting reduction of autophagic flux in disease conditions. Our findings suggest that p62 is necessary for RPE cytoprotection under oxidative stress and functions, in part, by modulating ATG10 expression. NFκB p65 activity may be a critical upstream initiator of p62 expression in RPE cells under oxidative stress.

Subretinal Pigment Epithelial Deposition of Drusen Components Including Hydroxyapatite in a Primary Cell Culture Model.

PurposeExtracellular deposits containing hydroxyapatite, lipids, proteins, and trace metals that form between the basal lamina of the RPE and the inner collagenous layer of Bruch's membrane are hallmarks of early AMD. We examined whether cultured RPE cells could produce extracellular deposits containing all of these molecular components.MethodsRetinal pigment epithelium cells isolated from freshly enucleated porcine eyes were cultured on Transwell membranes for up to 6 months. Deposit composition and structure were characterized using light, fluorescence, and electron microscopy; synchrotron x-ray diffraction and x-ray fluorescence; secondary ion mass spectroscopy; and immunohistochemistry.ResultsApparently functional primary RPE cells, when cultured on 10-μm-thick inserts with 0.4-μm-diameter pores, can produce sub-RPE deposits that contain hydroxyapatite, lipids, proteins, and trace elements, without outer segment supplementation, by 12 weeks.ConclusionsThe data suggest that sub-RPE deposit formation is initiated, and probably regulated, by the RPE, as well as the loss of permeability of the Bruch's membrane and choriocapillaris complex associated with age and early AMD. This cell culture model of early AMD lesions provides a novel system for testing new therapeutic interventions against sub-RPE deposit formation, an event occurring well in advance of the onset of vision loss.

β2–Adrenergic Receptor Antagonism Attenuates CNV Through Inhibition of VEGF and IL-6 Expression

PurposeThe role of β–adrenergic receptor (AR) signaling in neovascular ocular diseases has recently emerged. We have previously reported that intraperitoneal propranolol inhibits choroidal neovascularization (CNV) in vivo and β2-AR blockade reduces vascular endothelial growth factor (VEGF) expression in mouse retinal pigment epithelium and choroidal endothelial cells in culture. Here we tested the hypothesis that the β2-AR regulates CNV through modulation of VEGF and inflammatory cytokine expression.MethodsMice were subjected to laser burns, inducing CNV, and were treated with an intravitreal β2-AR antagonist. After 3 and 5 days, total eye interleukin-6 (IL-6) and VEGF protein levels were measured, respectively. After 14 days, CNV was measured on choroidal–scleral flatmounts. The effects of β-AR signaling on VEGF and IL-6 expression were investigated in various mouse retinal and human RPE cells by using specific β-AR agonists and antagonists.Resultsβ2–Adrenergic receptor signaling increased Vegf mRNA expression by approximately 3- to 4-fold in mouse retinal microglia and pericytes in culture. β2–Adrenergic receptor signaling upregulated IL-6 mRNA expression between 10- and 60-fold in mouse retinal microglia, pericytes, RPE, and choroidal endothelial cells in culture. Intravitreal injection of β2-AR antagonist ICI 118,551 reduced CNV by 35% and decreased IL-6 protein levels by approximately 50%. In primary human RPE cells, β2-AR activation also stimulated VEGF and IL-6 mRNA expression by 2- and 10-fold, respectively.ConclusionsAnti-VEGF therapy for CNV is highly effective; however, some patients are resistant to therapy while others undergo repeated, frequent treatments. β2–Adrenergic receptor signaling is a potential therapeutic target because of its angiogenic and inflammatory properties.

Role of Caveolin-1 for Blocking the Epithelial-Mesenchymal Transition in Proliferative Vitreoretinopathy.

Proliferative vitreoretinopathy (PVR) is one of the most severe ocular diseases. Fibrotic changes in retinal cells are considered to be involved in the pathogenesis of PVR. Epithelial-mesenchymal transition (EMT) of RPE cells is one of the main concepts in the pathogenesis of fibrovascular membranes (FVMs) in PVR. In this study, we examined the expression of Caveolin-1 in human FVMs from patients with PVR. We also examined the role of Caveolin-1 in the pathogenesis of PVR. Western blotting, real-time PCR, and immunohistochemistry were performed with human FVMs and mouse eyes with PVR. Cell migration assays were performed to evaluate the involvement of Caveolin-1 in EMT using primary human and mouse RPE cells. Caveolin-1 was expressed in human FVMs and upregulated in the mouse eyes with PVR. The alpha-smooth muscle actin (αSMA) expression and migration ability were increased in RPE cells with knockout or knockdown of Caveolin-1, whereas zonula occludens-1 (ZO-1) immunohistochemistry showed reduced morphology and expression of ZO-1. In addition, migration assays showed that Caveolin-1 reduction increased RPE cell migration abilities. These results indicated that Caveolin-1 in RPE cells prevents PVR by blocking EMT.

The nanomechanical role of melanin granules in the retinal pigment epithelium

Nanomechanical properties of cells and tissues, in particular their elasticity, play an important role in different physiological and pathological processes. Recently, we have demonstrated that melanin granules dramatically modify nanomechanical properties of melanoma cells making them very stiff and, as a result, less aggressive. Although the mechanical effect of melanin granules was demonstrated in pathological cells, it was never studied in the case of normal cells. In this work, we analyzed the impact of melanin granules on nanomechanical properties of primary retinal pigment epithelium tissue fragments isolated from porcine eyes. The obtained results clearly show that melanin granules are responsible for the exceptional nanomechanical properties of the tissue. Our findings suggest that melanin granules in the retinal pigment epithelium may play an important role in sustaining the stiffness of this single cell layer, which functions as a natural mechanical barrier separating the retina from the choroid.

MicroRNA-182 Suppresses HGF/SF-Induced Increases in Retinal Pigment Epithelial Cell Proliferation and Migration through Targeting c-Met.

As increases in hepatocyte growth factor/scatter factor (HGF/SF) induce retinal pigment epithelial (RPE) migration and proliferation into the vitreous cavity and contribute to proliferative vitreoretinopathy (PVR) development, we determined if changes in miR-182 expression affect such behavioral changes. We found that miR-182 expression was less in PVR clinical samples than in primary RPE cells whereas c-Met was upregulated. Ectopic miR-182 inhibited RPE cell proliferation, cell cycle, and migration. Bioinformatic analysis identified c-Met as a miR-182 target, which was confirmed with the luciferase reporter assay. Transfection of miR-182 into RPE cells induced c-Met downregulation, which led to reduced cell proliferation and migration through declines in p-Akt formation. MiR-182 downregulation along with c-Met upregulation in PVR tissues suggest that these two opposing effects play important roles in PVR development. As ectopic miR-182 expression suppressed RPE cell proliferation and migration, strategies to selectively upregulate miR-182 expression in a clinical setting may provide a novel option to treat this disease.

Anoctamin2 (TMEM16B) forms the Ca2+-activated Cl− channel in the retinal pigment epithelium

Chloride channels (Cl channels) play an essential role for the retinal pigment epithelium (RPE). They provide a plasma membrane conductance for Cl− important for transepithelial transport and volume regulation. Ca2+-dependent chloride channels (CaCC) in the RPE were found to adapt Cl− transport to specific needs by increasing intracellular free Ca2+. Although a variety of Cl channels have been identified in the RPE, the molecular identity of the CaCC remains controversial. Sagittal sections of mouse retina were stained against anoctamin2 (Ano2) and analyzed by confocal microscopy. Membrane currents from ARPE-19 cells and primary murine RPE cells were recorded in the whole-cell configuration of the patch-clamp technique. Expression of Ano2 was assessed via immunocytochemistry, PCR and western-blot and down-regulated via siRNA approaches. In the mouse retina, Ano2 was found in the basolateral membrane of the RPE. In primary mouse RPE cells, Ano2 was localized predominantly in the cell membrane. Ano2 mRNA and protein were also detected in rat and primate RPE as well as ARPE-19 cells. Whole-cell currents were elicited by increasing intracellular free Ca2+ via ATP application. These currents were identified as Cl− currents by their reversal potential and blocker sensitivity. Knock-down of Ano2 by siRNA decreased both the Ca2+ dependent chloride conductance and protein expression of Ano2. The biophysical and pharmacological properties of CaCC in ARPE-19 and primary mouse RPE cells resemble those described in previous publications using RPE cells from different species. The siRNA knock-down suggests that Ano2 contributes to Ca2+-dependent chloride conductance in the RPE.

Receptor MER Tyrosine Kinase Proto-oncogene (MERTK) Is Not Required for Transfer of Bis-retinoids to the Retinal Pigmented Epithelium

Accumulation of bis-retinoids in the retinal pigmented epithelium (RPE) is a hallmark of aging and retinal disorders such as Stargardt disease and age-related macular degeneration. These aberrant fluorescent condensation products, including di-retinoid-pyridinium-ethanolamine (A2E), are thought to be transferred to RPE cells primarily through phagocytosis of the photoreceptor outer segments. However, we observed by two-photon microscopy that mouse retinas incapable of phagocytosis due to a deficiency of the c-Mer proto-oncogene tyrosine kinase (Mertk) nonetheless contained fluorescent retinoid condensation material in their RPE. Primary RPE cells from Mertk-/- mice also accumulated fluorescent products in vitro Finally, quantification of A2E demonstrated the acquisition of retinal condensation products in Mertk-/- mouse RPE prior to retinal degeneration. In these mice, we identified activated microglial cells that likely were recruited to transport A2E-like condensation products to the RPE and dispose of the dying photoreceptor cells. These observations demonstrate a novel transport mechanism between photoreceptor cells and RPE that does not involve canonical Mertk-dependent phagocytosis.

The Ingenious Interactions Between Macrophages and Functionally Plastic Retinal Pigment Epithelium Cells.

The purpose of this study was to clarify the interactions between macrophages (MPs) and RPE cells in coculture systems to investigate the functional plasticity of RPE cells. Adherent peritoneal cells or murine MP cell line Raw 264.7 was cocultured with primary RPE cells taken from C57BL/6 mice, with or without lipopolysaccharide (LPS) or TNF-α stimulation. The cytokine levels of the culture supernatants (CSs) were then analyzed with the Bio-Plex murine 23-Plex Panel Assay Kit (Bio-Rad Laboratories). Monocyte chemoattractant protein-1 (MCP-1), IL-6, VEGF, and TNF-α in CS were further quantified by ELISA. The expression profiles, in cocultures, of complement-associated genes, TNF-α, and angiogenesis-associated genes were analyzed by quantitative real-time PCR. The production of MCP-1, IL-6, and VEGF was synergistically elevated when primary MPs or RAW264.7 cells and RPE cells were cocultured compared with those derived from sole cultures of MPs and RPE cells. The synergistic effect was confirmed without direct cell contact and was more prominent in the presence of LPS or TNF-α. TNF-α production by MPs was suppressed by RPE cells. Coculture of RPE cells with RAW264.7 cells increased the gene expression of C3, CFB, and VEGF genes, whereas it reduced those of complement regulatory factors CFH, CD59, clusterin, and TNF-α and antiangiogenic pigment epithelium-derived factor (PEDF). Our findings indicate the presence of ingenious interactions between MPs and RPE cells that forces the inflammation and complement activation in the vicinity of RPE cells under pathologic conditions.

Salvianolic Acid B (Sal B) Protects Retinal Pigment Epithelial Cells from Oxidative Stress-Induced Cell Death by Activating Glutaredoxin 1 (Grx1).

Protein glutathionylation, defined as the formation of protein mixed disulfides (PSSG) between cysteine residues and glutathione (GSH), can lead to cell death. Glutaredoxin 1 (Grx1) is a thiol repair enzyme which catalyzes the reduction of PSSG. Therefore, Grx1 exerts strong anti-apoptotic effects by improving the redox state, especially in times of oxidative stress. However, there is currently no compound that is identified as a Grx1 activator. In this study, we identified and characterized Salvianolic acid B (Sal B), a natural compound, as a Grx1 inducer, which potently protected retinal pigment epithelial (RPE) cells from oxidative injury. Our results showed that treatment with Sal B protected primary human RPE cells from H2O2-induced cell damage. Interestingly, we found Sal B pretreatment upregulated Grx1 expression in RPE cells in a time- and dose-dependent manner. Furthermore, NF-E2-related factor 2 (Nrf2), the key transcription factor that regulates the expression of Grx1, was activated in Sal B treated RPE cells. Further investigation showed that knockdown of Grx1 by small interfering RNA (siRNA) significantly reduced the protective effects of Sal B. We conclude that Sal B protects RPE cells against H2O2-induced cell injury through Grx1 induction by activating Nrf2 pathway, thus preventing lethal accumulation of PSSG and reversing oxidative damage.

Humanin Protects RPE Cells from Endoplasmic Reticulum Stress-Induced Apoptosis by Upregulation of Mitochondrial Glutathione.

Humanin (HN) is a small mitochondrial-encoded peptide with neuroprotective properties. We have recently shown protection of retinal pigmented epithelium (RPE) cells by HN in oxidative stress; however, the effect of HN on endoplasmic reticulum (ER) stress has not been evaluated in any cell type. Our aim here was to study the effect of HN on ER stress-induced apoptosis in RPE cells with a specific focus on ER-mitochondrial cross-talk. Dose dependent effects of ER stressors (tunicamycin (TM), brefeldin A, and thapsigargin) were studied after 12 hr of treatment in confluent primary human RPE cells with or without 12 hr of HN pretreatment (1–20 μg/mL). All three ER stressors induced RPE cell apoptosis in a dose dependent manner. HN pretreatment significantly decreased the number of apoptotic cells with all three ER stressors in a dose dependent manner. HN pretreatment similarly protected U-251 glioma cells from TM-induced apoptosis in a dose dependent manner. HN pretreatment significantly attenuated activation of caspase 3 and ER stress-specific caspase 4 induced by TM. TM treatment increased mitochondrial superoxide production, and HN co-treatment resulted in a decrease in mitochondrial superoxide compared to TM treatment alone. We further showed that depleted mitochondrial glutathione (GSH) levels induced by TM were restored with HN co-treatment. No significant changes were found for the expression of several antioxidant enzymes between TM and TM plus HN groups except for the expression of glutamylcysteine ligase catalytic subunit (GCLC), the rate limiting enzyme required for GSH biosynthesis, which is upregulated with TM and TM+HN treatment. These results demonstrate that ER stress promotes mitochondrial alterations in RPE that lead to apoptosis. We further show that HN has a protective effect against ER stress-induced apoptosis by restoring mitochondrial GSH. Thus, HN should be further evaluated for its therapeutic potential in disorders linked to ER stress.

The Role of IRE-XBP1 Pathway in Regulation of Retinal Pigment Epithelium Tight Junctions.

PurposeThe retinal pigment epithelium (RPE) tight junctions play a pivotal role in maintaining the homeostatic environment of the neural retina. Herein, we investigated the role of X-box binding protein 1 (XBP1), an endoplasmic reticulum (ER) stress-responsive transcription factor, in regulation of RPE tight junctions.MethodsHuman RPE cell line (ARPE-19) and primary primate RPE cells were used for in vitro experiments and RPE-specific XBP1 knockout (KO) mice were used for in vivo study. Endoplasmic reticulum stress was induced by a sublethal dose of thapsigargin or tunicamycin. XBP1 activation was manipulated by IRE inhibitor 4μ8C, which suppresses XBP1 mRNA splicing. The integrity of tight junctions and the involvement of calcium-dependent RhoA/Rho kinase pathway were examined.ResultsInduction of ER stress by thapsigargin, but not tunicamycin, disrupted RPE tight junctions in ARPE-19 cells. Inhibition of XBP1 activation by 4μ8C resulted in a remarkable downregulation of tight junction proteins (ZO-1 and occludin) and defects in tight junction formation in the presence or absence of ER stress inducers. Overexpression of active XBP1 partially reversed 4μ8C-induced anomalies in tight junctions. Mechanistically, XBP1 inhibition resulted in increased intracellular Ca2+ concentration, upregulation of RhoA expression, redistribution of F-actin, and tight junction damage, which was attenuated by Rho kinase inhibitor Y27632. In vivo, deletion of XBP1 in the RPE resulted in defective RPE tight junctions accompanied by increased VEGF expression.ConclusionsTaken together, these results suggest a protective role of XBP1 in maintaining RPE tight junctions possibly through regulation of calcium-dependent RhoA/Rho kinase signaling and actin cytoskeletal reorganization.

Activated monocytes resist elimination by retinal pigment epithelium and downregulate their OTX2 expression via TNF-α.

SummaryOrthodenticle homeobox 2 (OTX2) controls essential, homeostatic retinal pigment epithelial (RPE) genes in the adult. Using cocultures of human CD14+ blood monocytes (Mos) and primary porcine RPE cells and a fully humanized system using human‐induced pluripotent stem cell‐derived RPE cells, we show that activated Mos markedly inhibit RPE OTX2 expression and resist elimination in contact with the immunosuppressive RPE. Mechanistically, we demonstrate that TNF‐α, secreted from activated Mos, mediates the downregulation of OTX2 and essential RPE genes of the visual cycle among others. Our data show how subretinal, chronic inflammation and in particular TNF‐α can affect RPE function, which might contribute to the visual dysfunctions in diseases such as age‐related macular degeneration (AMD) where subretinal macrophages are observed. Our findings provide important mechanistic insights into the regulation of OTX2 under inflammatory conditions. Therapeutic restoration of OTX2 expression might help revive RPE and visual function in retinal diseases such as AMD.

Autophagy is affected by Mitf in mouse primary RPE cells

PurposeMicrophthalmia‐associated transcription factor (MITF) regulates the differentiation and development of the retinal pigment epithelium (RPE). Mice that lack functional MITF do not develop the RPE and have microphthalmia. Recent studies have involved MITF in autophagy regulation in other cell types. The purpose of this study was to examine if the Mitf gene plays a fundamental role in regulating autophagy in primary RPE cells using various mutations in the Mitf gene.MethodsPrimary RPE cells from wild type and MITF mutant mice Mitf mi‐enu122(398), Mitf Mi‐Wh/+ and Mitf Mi‐Wh/Mitf mi‐mi) were isolated by enzymatic dissociation. The levels of LC3 and MITF were measured and compared by western blot in the primary RPE cultures from wild type and mutant mice. Basal autophagy was also analysed with western blots and confocal imaging using same markers in primary RPE cells from C5BL/6J mice. Untreated cells were compared to cells treated with the mTOR inhibitor Torin1, cells incubated in starvation media and cells treated with the autophagy inhibitor, bafilomycin A1 (Baf A1).ResultsThe treatment with starvation media and Torin1 increased the levels of LC3 in RPE cells. Furthermore, both starvation and Torin1treatment resulted in reduced MITF protein levels. Cotreatment of Torin1 or starvation with Baf A1 restored the protein levels of MITF and LC3. Only the LC3II protein was detected in RPE cells from MITF mutant whereas wild type RPE cells showed both LC3I and II, suggesting that the degradation pathway of LC3 is stalled in the RPE from Mitf mutant mice.ConclusionsThis study suggests that autophagy is affected in Mitf mutant mice. This is consistent with in vitro data showing that MITF regulates expression of genes involved in autophagy.

EVER Past president lecture: lessons from the Fascinating World of Bestrophinopathies

SummaryPurposeTo describe the genotypes and phenotypes in patients with bestrophinopathies.MethodsExamples of Best vitelliform macular dystrophy will be compared with the phenotype of patients with autosomal recessive bestrophinopathy and autosomal dominant vitreoretinochoroidopathy.ResultsPhenotypes of BVMD range from asymptomatic, normal fundi in heterozygous BEST1 mutation carriers, to classic macular egg yolk‐like lesions. Biallelic BEST1 mutations cause ARB, characterized by shallow retinal detachments in the posterior pole, with hyperautofluorescent deposits in the watershed zone and superonasal to the optic disc. In addition, there are small, inner retinal, cystoid changes. Rod‐cone dystrophy (RCD) develops later. Subacute angle closure glaucoma is frequent. ADVIRC patients show a 360° peripheral hyperpigmented band, peripapillary staphylomata, RCD and microcornea. Unique mutations in one BEST1 allele cause ADVIRC. Electro‐oculography is abnormal in all bestrophinopathies first.ConclusionsBestrophinopathies are a diverse group of conditions caused by either mono‐ or biallelic mutations in BEST1. Whereas ADVIRC is very different, BVMD and ARB show considerable overlap. This suggests that a threshold of bestrophin protein production, blurring the differences between dominant or recessive mechanisms of disease, may be the main determinant of the phenotype. Abnormal EOGs indicate primary RPE involvement.