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At least 145 records · Page 8Linked to original sources
PubMed1993

Diffusible, retinal factors stimulate the barrier properties of junctional complexes in the retinal pigment epithelium.

The retinal pigment epithelium lies at the interface between the neural retina and the choriocapillaris where it forms a blood-retinal barrier. Barrier function requires a polarized distribution of plasma membrane proteins and 'tight' tight junctions. During chicken embryogenesis, these features develop gradually. Although terminal junctional complexes are established by embryonic day 4, the distribution of the Na+/K(+)-APTase is not polarized in all cells of the epithelium until embryonic day 11. Similarly, the tight junctions of early embryos are leaky, but become tight by hatching (embryonic day 21). We used primary cell culture to examine the molecular basis of this gradual induction of polarized function. Pigment epithelium harvested from embryonic day 7, and cultured on filters, formed monolayers coupled by junctional complexes. The distribution of the Na+/K(+)-ATPase was non-polarized and the tight junctions were leaky with a transepithelial electrical resistance of 20-30 omega cm2. To isolate diffusible factors that stimulate the transepithelial electrical resistance, neural retinas from embryonic day 7, 14 or 16 embryos were incubated at 37 degrees C in base medium for 6 hours. The conditioned medium was added to the apical chamber of freshly cultured pigment epithelium. The distribution of the Na+/K(+)-ATPase became basolateral, and the electrical resistance gradually increased two to three times over 6 days. The increase in electrical resistance corresponded to a decrease in the rate of [3H]inulin diffusion across the monolayer. The effectiveness of the conditioned medium increased steadily with increasing age of the neural retina. Rather than increased production of an active factor, apparently different active factors were produced at different ages.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2001

[The myc oncogene and transdifferentiation of the retinal pigment epithelium].

The retinal pigment epithelium (RPE) develops from the same sheet of neuroepithelium as the neuroretina. When infected with MC29, a v-myc expressing virus, the RPE cells can be induced to transdifferentiate and to take a neuroretinal epithelium fate. After a PCR-based differential screening from these cells we have identified three genes of interest. Qath5, a quail basic helix-loop-helix (bHLH) gene that is closely related to the Drosophila atonal, and whose expression is found in the developing neuroretina. A Chx10-related homeobox gene also expressed in the developing neuroretina and HuD, a RNA-binding protein not expressed in the RPE but expressed during neurogenesis. Beside these genes whose function is involved in regulating neuronal differentiation myc also induced a transient Mitf expression. Mitf is expressed in the entire optic cup, later restricted to the pigmented retina. Mitf is involved in the regulation of the pigmented differentiation. We conclude that v-myc can reverse the RPE to the bipotential retinal primordia.

Alpharetrovirus↗
PubMed2003

Protein database, human retinal pigment epithelium.

The retinal pigment epithelium (RPE) is a single cell layer adjacent to the rod and cone photoreceptors that plays key roles in retinal physiology and the biochemistry of vision. RPE cells were isolated from normal adult human donor eyes, subcellular fractions were prepared, and proteins were fractionated by electrophoresis. Following in-gel proteolysis, proteins were identified by peptide sequencing using liquid chromatography tandem electrospray mass spectrometry and/or by peptide mass mapping using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Preliminary analyses have identified 278 proteins and provide a starting point for building a database of the human RPE proteome.

Chromatography, Liquid↗
PubMed2006

Activation of mitogen-activated protein kinases is essential for hydrogen peroxide -induced apoptosis in retinal pigment epithelial cells.

Retinal pigment epithelial (RPE) cells are constantly exposed to oxidative injury while clearing byproducts of photoreceptor turnover, a circumstance thought to be responsible for degenerative retinal diseases. The mechanisms of hydrogen peroxide (H(2)O(2))-induced apoptosis in RPE cells are not fully understood. We studied signal transduction mechanisms of H(2)O(2)-induced apoptosis in the human RPE cell line ARPE-19. Activation of two stress kinases (JNK and p38) occurs during H(2)O(2) stimulation, and H(2)O(2)-mediated cell death was significantly reduced by their specific inhibition. Exposure to a lethal dose of H(2)O(2) elicited Bax translocation to the mitochondria and release of apoptosis-inducing factor (AIF) from the mitochondria, both of which were abolished by either JNK- or p38-specific inhibitors. Both H(2)O(2)-induced cell death and JNK/p38 phosphorylation were partially inhibited by C. difficile toxin B, inhibitor of Rho, Rac, and cdc42. Use of pull-down assays revealed that the small GTPase activated by H(2)O(2) is Rac1. This study is the first to demonstrate that H(2)O(2) induces a Rac1/JNK1/p38 signaling cascade, and that JNK and p38 activation is important for H(2)O(2)-induced apoptosis as well as AIF/Bax translocation of RPE cells.

Active Transport, Cell Nucleus↗
PubMed2001

Rat retinal progenitor cells and a retinal pigment epithelial factor.

Retinal progenitor cells were isolated from explants of neonatal rat retinas and characterized by transmission electron microscopy and reverse transcriptase-polymerase chain reaction and by their response to an isolated retinal pigment epithelial cell cell factor. The isolated progenitor cells demonstrated nuclei with abundant euchromatin typical of progenitor cells and showed the presence of nestin and opsin message. A protein ( approximately 67 kDa) isolated from conditioned media of cultured rat RPE cells promoted the survival of isolated retinal progenitor cells.

Animals↗
PubMed2001

Limited macular translocation for the management of subfoveal retinal pigment epithelial loss after submacular surgery.

PURPOSE: To report a case of subfoveal retinal pigment epithelial (retinal pigment epithelium) loss after submacular surgery managed successfully by limited macular translocation. METHODS: Case report. RESULTS: A 28-year-old woman presented with a visual acuity of 20/100 caused by subfoveal choroidal neovas-cularization secondary to ocular histoplasmosis syndrome. Submacular resection of the choroidal neovascularization was complicated by inadvertent retinal pigment epithelium loss from beneath the foveal center. She underwent limited macular translocation 5 days after the initial surgery and had successful displacement of the fovea to an area inferior to the retinal pigment epithelium defect. Her visual acuity was 20/60 4 months postoperatively. CONCLUSION: This report demonstrates the feasibility of using limited macular translocation for the management of eyes with central retinal pigment epithelium defect after submacular surgery and extends the clinical indications for limited macular translocation.

Adult↗
PubMed1980

Interrelationships between the retinal pigment epithelium and the neurosensory retina.

The role of the retinal pigment epithelium in regulating transport between the choriocapillariss and sensory retina was studied by examining the diffusion fluorescent across the intact rabbit retinal pigment epithelium and the retinal pigment epithelium damaged by intravenous injection of sodium iodate. Destruction of the tight junctions of the retinal pigment epithelium allowed free diffusion of fluorescein from the choroid into the retina. The electrical characteristics of the cat retinal pigment epithelium which play an important role in governing transport of substances across the retinal pigment epithelium were studied. The apical membrane of the cat retinal pigment epithelium resembled that of the frog in having high sensitivity to apical K+, greater sensitivity to apical Na+, and less sensitivity to apical HCO3-. The apical membrane was sensitive to oubain which produced a rapid fall in the transepithelial potential. Previous studies of the electrical properties of the retinal epithelium in cold blooded preparations are summarized with emphasis on the important interactions between the retinal pigment epithelium and sensory retina and the implications that these studies have with regard to the regulation of photoreceptor function.

Animals↗
PubMed1995

Retinal pigment epithelial repopulation in monkeys after submacular surgery.

BACKGROUND: Transplantation of retinal pigment epithelium may be a treatment for retinal diseases, such as age-related macular degeneration and hereditary macular degeneration. Before transplantation studies are undertaken, questions concerning repopulation of retinal pigment epithelial cells in situ and photoreceptor repair after submacular surgery need to be addressed. METHODS: We removed the retinal pigment epithelium from Bruch's membrane in the macaque monkey in the macula and outside the vascular arcades. This model allowed the study of in situ retinal pigment epithelium regrowth and photoreceptor repair for 9 months following débridement. RESULTS: Fluorescein angiography revealed a window defect in the area of denuded retinal pigment epithelium. Histologic studies revealed repopulated nonpigmented retinal pigment epithelial cells in the denuded areas in both the early and late periods. At 9 months, the repopulated retinal pigment epithelium was associated with repaired, normal-appearing photoreceptor outer segments. Retinal pigment epithelium regrowth was observed only if Bruch's membrane was intact. CONCLUSIONS: Repopulation of retinal pigment epithelium in the adult primate can occur rapidly and can support the repair of damaged photoreceptors following submacular surgery.

Animals↗
PubMed1995

Molecular characterization of the human gene encoding an abundant 61 kDa protein specific to the retinal pigment epithelium.

The retinal pigment epithelium (RPE) of the eye expresses an abundant 61 kDa protein (RPE65), that is developmentally regulated and tissue-specific. In our efforts toward understanding the specialized functions and development of the RPE, and the origins of inherited retinal degenerations, we have characterized the human gene encoding the 61 kDa protein. This is the first structural characterization of a gene transcribed specifically in the RPE. The gene maps to human chromosome 1p31. The sequence encoding the transcript spans over 20 kb, and is interrupted by 13 introns. A putative transcription start site lies 54 bp upstream of the initiation codon. A single transcript of approximately 2.9 kb is present in human RPE, and is not detected in other tissues. The deduced 533 amino acid sequence of the human protein is 98.7% identical to the bovine, but shows no significant similarity to any other entry in the databases. Expression of the 61 kDa protein appears to depend on the presence of environmental cues, since the corresponding transcripts are rapidly lost from RPE cells established in culture. Down regulation may occur post-transcriptionally, since AU-rich elements proposed to target RNA for rapid degradation are present throughout the 3'-untranslated region. The tissue-specific expression, high abundance, evolutionary conservation, developmental regulation, and sequence of the 3'-untranslated region suggest that the 61 kDa protein is the product of a functionally important gene whose expression is tightly regulated.

Amino Acid Sequence↗
PubMed1997

Evidence for beta 1-integrins on both apical and basal surfaces of Xenopus retinal pigment epithelium.

The retinal pigment epithelium (RPE) is a transporting epithelium with polarized membrane domains. A unique characteristic of these cells is that their apical surface does not face a lumenal space, but is directly apposed to a layer of neurons (photoreceptors) and their associated extracellular matrix. Because the interaction occurring at this site is important for retinal attachment and particle phagocytosis, an attempt was made to identify epithelial molecules which potentially could mediate cell-cell or cell-matrix adhesion. In the present report, the subcellular localization of beta 1-integrins, the main receptors for extracellular matrix ligands, has been examined within Xenopus RPE. Several previously characterized antibodies were used in this analysis including: two rabbit polyclonal antibodies directed against purified chick muscle fibronectin receptor (pAbs No. 3818 and No. 2999), and a monoclonal antibody specific for Xenopus beta 1-integrin subunit (mAb 8C8). In Western blots of whole epithelial cell extracts, each of the antibodies intensely labeled a 115 kDa band, consistent with beta 1-integrin reactivity. One of the reagents (pAb No. 3818) also weakly stained unidentified bands of 50 and 100 kDa. Pre-clearing experiments demonstrated that pAb No. 3818 and mAb 8C8 both recognize the same detergent-soluble integrin: when cell extracts were depleted of beta 1-integrin by immunoprecipitation with mAb 8C8, the 115 kDa antigen recognized by pAb No. 3818 was not observed. Consistent with their similar immunochemical reactivities, each of the antibodies produced equivalent immunocytochemical staining of many eyecup tissues, including extraocular skeletal muscle cells, scleral and choroidal fibroblasts and vascular endothelium of the choroid and neural retina. In the native RPE, and isolated sheets of epithelium, however, qualitative differences in labeling between these antibodies were evident. Analysis by confocal microscopy showed that, while all three antibodies stained the basal surface of the epithelium, pAb No. 3818 also strongly labeled the apical microvillar surface. As the adjacent photoreceptors did not cross-react with this antibody in control experiments, the apical RPE staining could not be accounted for as contamination with retinal tissues during isolation. Furthermore, when the apical cell surface was selectively biotinylated in situ, and biotinylated proteins precipitated by streptavidin-agarose, beta 1-integrin was detected by immunoblotting with both mAb 8C8 and pAb No. 3818. This domain-specific material, however, represented only a fraction of the whole cell surface integrin: substantially greater amounts of tagged molecules could be detected when isolated epithelial sheets were biotinylated, most likely representing the basal protein. Based on these results, it can be concluded that beta 1-integrin is present in both basal and apical RPE plasma membranes. Molecules present in the apical membrane may represent components of adhesion receptors responsible for retina-epithelium interactions.

Animals↗
PubMed1989

[Growth stimulating activity of heparin-binding growth factor in the neural retina for retinal pigment epithelial cells].

Retinal pigment epithelial cells (RPE cells) participate in intraocular fibrocellular proliferation in proliferative vitreoretinopathy (PVR). The initial signal for proliferation and migration of RPE cells on PVR is not clear. However, water soluble extract from neural retina has been known to stimulate RPE cells, and fibroblast growth factor had a high affinity for heparin. In this experiment, we purified heparin-binding growth factor (HBGF) from neural retina using heparin-affinity chromatography. Then we examined the growth stimulating activity of HBGF for RPE cells proliferation. RPE cells were stimulated by HBGF, on the other hand heparin non-binding component could not stimulate RPE cells. This result suggests that the grwth-stimulating activity of retinal extract on RPE cells is related to HBGF.

Cell Division↗
PubMed1997

Differentiation and transdifferentiation of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) lies between the retina and the choroid of the eye and plays a vital role in ocular metabolism. The RPE develops from the same sheet of neuroepithelium as the retina and the two derivatives become distinguished by different expression patterns of a number of transcription factors during embryonic development. As the RPE layer differentiates it expresses a set of unique molecules, many of which are restricted to certain regions of the cell. PRE cells undergo both a loss of polarity and a loss of expression of many of these cell type-specific molecules when placed in monolayer culture. The RPE of many species, including mammals, can be induced to transdifferentiate by growth factors such as basic fibroblast growth factor. Under the influence of such factors the RPE is triggered to alter expression of a wide array of molecules and to take on a retinal epithelium fate, from which differentiated retinal cell types including rod photoreceptors can be produced.

Animals↗
PubMed1995

Deletion mutants in human cytomegalovirus glycoprotein US9 are impaired in cell-cell transmission and in altering tight junctions of polarized human retinal pigment epithelial cells.

Retinal cytomegalovirus (CMV) disease is one of the major manifestations of viral pathogenesis in immunosuppressed patients with the acquired immunodeficiency syndrome (AIDS). CMV infection of the retina causes directional destruction which begins at the optic nerve head adjacent to the retinal capillaries and progresses, if untreated, to retinal detachment and blindness. Infection does not occur across the basal membrane of the retinal pigment epithelium (RPE), adjacent to the highly vascularized choroid. CMV replicates in polarized RPE cells, and progeny virions cross apical and lateral membranes of RPE cells grown on permeable filter supports, but not basal membranes. Cell-cell junctions of CMV-infected RPE cells are permeabilized, and the tight junction protein zonula occludens (ZO-1) is disassembled; progeny virions then spread to neighboring cells through the lateral cell membranes, which in polarized cells differ significantly in lipid and protein composition from the apical cell membranes. We found that CMV mutants with deletions in US9 and US8/US9 failed to spread from cell to cell, exhibiting a small-plaque phenotype in polarized RPE cells. Immunofluorescence confocal microscopy staining of ZO-1 protein revealed that RPE cells infected with CMV deletion mutants RV35, RV80, and RV61 did not exhibit altered tight junctions, in contrast to RPE cells infected with wild-type strain AD169 virus. Our findings indicate that US9, which is an accessory glycoprotein in infected foreskin fibroblasts, is required for transmission of virus across cell-cell junctions of polarized RPE cells. The relationship between US9 expression and virus transmission across cell-cell boundaries suggests that US9 may directly or indirectly permeabilize tight junction complexes of polarized RPE cells.

Cytomegalovirus↗
PubMed2000

Differential regulation of tight junction permeability during development of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) is an epithelial region of the blood-brain barrier. During embryogenesis, permeability of the barrier gradually decreases. A culture model of RPE development revealed differences in how tight junctions regulate the paracellular diffusion of ionic and nonionic solutes (Ban Y and Rizzolo LJ. Mol Vis 3: 18, 1997). To examine these differences, the permeation of ionic and nonionic monosaccharides was compared with mannitol, and the permeation of the alkali metals was compared with sodium. The order of permeation was 3-O-methlyglucose = glucosamine = mannitol > N-acetylneuraminic acid. The ratio of N-acetylneuraminic acid to mannitol permeability decreased with embryonic age of the RPE or exposure to retinal-conditioned medium. Neither the ratio nor the permeability was affected by inhibiting transcytosis. The ratio increased if tight junctions were disrupted in low-calcium medium. The permeation of cations followed the sequence cesium > rubidium > potassium = sodium > lithium and was unaffected by embryonic age or retinal-conditioned medium. These results are considered in terms of a model in which the size distribution, charge, or number of open junctional pores could be modulated. It suggests that different subpopulations of pores can be regulated independently during development.

Animals↗
PubMed2000

Regulation of glucose transporters during development of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) separates the outer retina from its blood supply. To satisfy the retina's large requirement for glucose, the RPE expresses high levels of glucose transporters. In most rat cells, the transporter GLUT3 provides a basal level of transport, but the expression of GLUT1 can be regulated. The opposite is true in chicken (P. Wagstaff, H.Y. Kang, D. Mylott, P.J. Robbins, M.K. White, Characterization of the avian GLUT1 glucose transporter: differential regulation of GLUT1 and GLUT3 in chicken embryo fibroblasts, Mol. Biol. Cell 6 (1995) 1575-1589). We examined chick RPE to determine which isoform is regulated during development, and if the neural retina regulates GLUT expression. By RT-PCR, RPE expressed GLUT1 and GLUT3, but not GLUT2. Only the level of GLUT1 increased between E5 and E18. A corresponding increase in GLUT1 protein was observed by immunoblotting. Most of the increase occurred between E14 and E18, which corresponds to the late stage of tight junction development. A culture model of development was used to examine the intermediate phase, which extends from E7 to E14. While medium conditioned by the neural retina decreased paracellular diffusion across the tight junctions, it increased diffusion through the glucose transporters. Unlike mammals, chick upregulates different isoforms in quiescent RPE and proliferating fibroblasts. Further, the upregulation of glucose transport is coordinated with the development of tight junctions in the blood-retinal barrier.

Animals↗