Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Retinal Pigments”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1999

Ectopic expression of RET results in microphthalmia and tumors in the retinal pigment epithelium.

The retinal pigment epithelium (RPE) is essential for eye development by interacting with the overlaying neuroepithelium. Regulatory sequences of the gene encoding for tyrosinase-related protein 1 (TRP-1), linked to the lacZ reporter gene, lead to strong and specific beta-galactosidase expression in the RPE. We asked how the oncogene ret would affect this epithelial cell type during mouse development. We used the TRP-1 promoter to express ret in the developing RPE, and obtained transgenic mouse lines, which showed mild to severe microphthalmia. During development, the RPE changed to a stratified epithelium with reduced or absent pigmentation from E10.5 onward. In addition, proliferation of RPE cells and tumor formation were observed from E12.5 onward. These early events prevent closure of choroid fissure and lead to microphthalmia and secondary malformations after birth. We conclude that ret transgene expression in the RPE prevents normal differentiation of this epithelial layer and induces proliferation and tumor formation. The appearance of the microphthalmic phenotype underlines the requirement of a normally developed RPE for eye development.

Animals↗
PubMed1997

Identification of a unique monocarboxylate transporter (MCT3) in retinal pigment epithelium.

The retinal pigment epithelium transports lactate between two tissue compartments, the interphotoreceptor matrix and the choriocapillaris. In this report we describe a 2.45-kb cDNA isolated from a chick cDNA RPE library that encodes a membrane protein found only in RPE cells. The deduced protein has 542 amino acids with twelve putative membrane spanning domains. The cDNA has been designated MCT3 based on its 45% identity in amino acid sequence and structural similarity with the monocarboxylate transporters MCT1 and MCT2. Stable transfectants (pCl-neo/MCT3), made in a rat thyroid epithelial cell line (FRTL-5), express MCT3 RNA. Transfectants had enhanced pyruvate uptake (used as a measure of lactate uptake) which was proton-dependent and inhibited by alpha-cyano-4-hydroxycinnamate. In summary, MCT3's unique expression in RPE cells, multiple potential phosphorylation sites, and basolateral distribution suggest that MCT3 may regulate lactate levels in the interphotoreceptor space.

Amino Acid Sequence↗
PubMed1994

Membrane polarity of the Na(+)-K+ pump in primary cultures of Xenopus retinal pigment epithelium.

The retinal pigment epithelium is a transporting epithelium that helps regulate the volume and composition of the subretinal space surrounding photoreceptor outer segments. The capacity of the RPE to actively transport Na+ and K+ between the retina and the blood supply depends on the localization of the Na+, K(+)-ATPase to the apical membrane, but in culture this polar distribution can be lost. Using primary cultures of Xenopus RPE, we examined the anatomical and functional polarity of this electrogenic pump. Confluent monolayers were established on Matrigel-coated microporous filters and cultured for 2-4 weeks in serum-free defined medium. Electrogenic pump activity at the apical and basolateral membranes was assayed by mounting the monolayer and filter in an Ussing chamber and exposing one or the other surface to ouabain while recording the apical (Vap) and basolateral (Vba) membrane potentials with an intracellular microelectrode. The addition of 0.2 mM ouabain to the apical bath caused Vap to rapidly depolarize by about 4 mV, consistent with the inhibition of a hyperpolarizing pump current at that membrane. When ouabain was added to the basal bath, however, it had no effect on Vba, suggesting the absence of a functional Na(+)-K+ pump on the basolateral membrane. To confirm these electrophysiological results, we examined the distribution of the Na+, K(+)-ATPase catalytic component using an antiserum specific for the bovine kidney alpha subunit. Antibody labeling of cultures was highly polarized, with strong reaction present on the apical microvilli, but not the basolateral cell surfaces. The findings of this study indicate that the Na(+)-K+ pump in monolayers of Xenopus RPE, as in native RPE, is located mainly in the apical membrane, providing evidence of a functionally intact transport pathway in these primary cultures.

Animals↗
PubMed1981

Extrusion of lysosomal bodies from apical mouse retinal pigment epithelium.

The retinal pigment epithelium (RPE) of 1- 24-month-old CF-1 mice was examined by both light and electron microscopy. Measurement of the area occupied by lysosomal bodies was carried out using a semiautomatic quantitative picture analyzing system (Kontron-EKO). Accumulation of lysosomal bodies in the apical RPE cytoplasm was the most characteristic feature in eyes over 12 months of age. The relative volume of lysosomal bodies to each RPE cytoplasm was maximal in 24-month-old mice RPE, approximately three times that of 3-month-old mice. Complicated lysosomal bodies and small lysosomal bodies were also observed in the dilated microvilli, in the apices of the apical RPE cytoplasm and in the subretinal spaces in eyes over 18 months of age. The passway and extrusive mechanism of lysosomal bodies are discussed.

Animals↗
PubMed2006

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 CO(2) 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 CO(2) 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 CO(2) 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.

Animals↗
PubMed1990

Identification and localization of talin in chick retinal pigment epithelial cells.

Retinal pigmented epithelial cells are adherent at their basal surface to Bruch's membrane and at their apical surface to the neural retina. We examined the expression and distribution of two proteins that are found in regions of cell-matrix interaction, talin and integrin. Talin is a 235-kDa cytoplasmic protein that has been localized to regions of cell-substrate adhesion. It binds to both integrin, a transmembrane glycoprotein complex, and to vinculin, a cytoskeletal protein. In the present study, we produced a polyclonal antibody to chicken gizzard talin. Using this antibody we showed by western blot analysis that talin is expressed by RPE cells and is found in the triton-soluble fraction. Talin was shown to co-localize with integrin and vinculin in the basal region of chick RPE cells isolated from 18-day-old chick embryos. Neither talin nor integrin was found in the apical processes or in the zonula adherens. Antibodies to vinculin showed staining both in the apical and basal regions of the RPE cells. The localization of integrin, talin and vinculin along the basal membrane suggests that this complex is important in the attachment of the RPE cells to the basement membrane. The distribution of integrin and talin was examined in primary cultures of RPE cells grown on permeable filters. In these cells, a polarized distribution of integrin and talin was not observed. This may suggest that the neural retina may be important for maintaining the differentiated state of the RPE cells.

Animals↗
PubMed1992

Polarized budding of vesicular stomatitis and influenza virus from cultured human and bovine retinal pigment epithelium.

The retinal pigment epithelium (RPE) is able to perform a variety of functions because of its high degree of plasma membrane polarity. Some aspects of this polarity such as the localization of the majority of Na-K ATPase to the apical membrane distinguish the RPE from kidney cells and most other transporting epithelia. The polarized budding of enveloped viruses such as vesicular stomatitis and influenza from the basolateral and apical membrane, respectively, has been used to study mechanisms underlying the domain-specific sorting of membrane proteins in cultured epithelial cell lines. These processes also serve as a useful index of the degree of polarization in epithelial cell cultures. Viral budding from apical and basolateral RPE membranes was used in this study to determine whether the sorting of viral envelope membrane proteins by the RPE is reversed in polarity from that of kidney cells and, if so, whether this might predict a fundamental difference in membrane protein sorting for RPE. The results clearly indicate that the polarity of viral membrane sorting and subsequent viral budding is the same in RPE as in other polarized epithelial cell lines examined to date.

Animals↗
PubMed1992

Interleukin-6 (IL-6) gene expression and secretion by cytokine-stimulated human retinal pigment epithelial cells.

Retinal and choroidal inflammatory lesions are important causes of visual loss, but the mechanisms regulating intraocular inflammation remain poorly understood. By virtue of its position at the blood-retina barrier, the retinal pigment epithelium (RPE) cells may be critical to the initiation and propagation of ocular inflammation. Previously we showed that cytokine-stimulated RPE cells produce interleukin-8, a well-defined chemotactic factor for neutrophils and lymphocytes. In this study, we found that human RPE cells stimulated by human recombinant interleukin-1-beta (rIL-1 beta) or tumor necrosis factor-alpha (rTNF-alpha) produce interleukin-6 (IL-6). Using a plasmacytoma proliferation assay, significant levels of IL-6 were found in media of RPE cells stimulated with either rIL-1 beta or rTNF-alpha for 4 hr. Progressive accumulation of IL-6 in media overlying stimulated RPE cells occurred over the subsequent 20 hr. IL-1 beta was a significantly more potent stimulator of RPE IL-6 production than TNF-alpha, RPE IL-6 production in response to each of these cytokines was also dose-dependent over a range of 20 pg to 20 ng ml-1. Specific anti IL-6 antibody, but not control immunoglobulin, neutralized RPE-derived IL-6 activity in the plasmacytoma proliferation assays. RPE IL-6 mRNA levels were detectable 1 hr after cytokine stimulation, plateaued within 8 hr in 24-hr assays, and demonstrated dose-dependent kinetics in 6 hr assays. Lipopolysaccharide failed to induce RPE IL-6 mRNA expression or RPE IL-6 production.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed2005

Critical role of the Rho-kinase pathway in TGF-beta2-dependent collagen gel contraction by retinal pigment epithelial cells.

Retinal pigment epithelial cells (RPEs) are thought to be one of the main components of fibrous membrane observed in eyes with proliferative vitreo-retinopathy. We investigated the signalling mechanisms of TGF-beta2-dependent collagen gel contraction by RPEs. An in vitro type I collagen gel contraction assay was performed to evaluate the effect of TGF-beta2 on gel contraction. The expression of alpha-smooth muscle actin (alpha-SMA) and the phosphorylation state of myosin light chain (MLC) were analyzed by Western blotting. The involvement of protein kinases such as p44/42 mitogen-activated protein kinase (MAPK), protein kinase C (PKC), p38 MAPK and phosphatidylinositol-3 kinase was investigated. The contribution of Rho-kinase and/or MLC-kinase was also evaluated using respective kinase inhibitors (Y27632, hydroxyfasudil and ML7). Additionally, RPEs were immunostained to examine whether the expression of alpha-SMA detected in our western blotting correlated to the stress fiber formation within the cells. TGF-beta2 caused time (0-5 days)-and dose (0 10 ng ml(-1))-dependent gel contraction associated with overexpression of alpha-SMA and phosphorylation of MLC (p < 0.01, respectively). PKC inhibitor (GF109203X, 5 microM) and p38 MAPK inhibitor (SB203580, 10 microM) significantly attenuated TGF-beta2-elicited gel contraction via partial downregulation of both alpha-SMA expression and MLC phosphorylation (p < 0.01, respectively). The gel contraction was prominently inhibited in the presence of Y27632 (10 microM) or hydroxyfasudil (10 microM) with strong suppression of MLC phosphorylation but had no significant effect on alpha-SMA expression. Treatment with ML7, in contrast, resulted in a marginal inhibition of MLC phosphorylation and gel contraction. Finally, pretreatment of the cells with Y27632 or hydroxyfasudil prevented the formation of stress fiber within the cells. These results indicate that TGF-beta2-dependent myofibroblastic transdifferentiation and MLC phosphorylation by RPEs involve both PKC and p38 MAPK pathways at least in part. Myofibroblastic transdifferentiation of RPEs appears to be independent of the Rho-kinase pathway, and the presence of alpha-SMA does not necessarily reflect the contractile potential of a cell. While Rho-kinase inhibitors are incapable of preventing myofibroblastic transdifferentiation itself, this pathway could be one of the critical targets of cell-mediated contraction of the tissue containing fibrillar collagens by transdifferentiated RPEs.

Actins↗
PubMed1985

A photogrammetric method to measure fluid movement across isolated frog retinal pigment epithelium.

Bullfrog retinal pigment epithelium (RPE)/choroid explants were mounted in an Ussing chamber modified so that the side bathing the choroid was completely sealed. Net fluid movement across the RPE and into or out of the sealed side of the chamber forced the tissue to assume a convex or concave shape. Photogrammetry was used to measure this tissue bowing by analyzing the displacement of the image produced on the RPE surface by an off-axis laser. Under baseline conditions, measured net fluid movements were always in the retina-to-choroid direction with a mean of 7.6 microliter cm-2 h-1. Potential artifacts from a variety of sources have been examined and shown to be insignificant.

Animals↗
PubMed1999

Analysis of the secretion pattern of monocyte chemotactic protein-1 (MCP-1) and transforming growth factor-beta 2 (TGF-beta2) by human retinal pigment epithelial cells.

Retinal pigment epithelial (RPE) cells, situated between the neurosensory retina and the vascularized choroid, form part of the blood-eye barrier and are important for homeostasis of the outer retina. These cells are able to produce a variety of cytokines which may play a role in the maintenance of the immunosuppressive milieu inside the eye and in intraocular inflammatory responses. In the present study, we investigated whether RPE cells secreted the anti-inflammatory cytokine TGF-beta2 and the proinflammatory cytokine MCP-1 in a polarized manner. Monolayers of human donor RPE cells were cultured on transwell filters. Secretion of TGF-beta2 and MCP-1 at either the apical or basal side of the RPE cell monolayers, that were not treated or stimulated with IL-1beta (200 U/ml), was analysed by ELISA. All three cell lines examined had a different TGF-beta2 secretion pattern. In two of the three donor RPE cell lines tested, TGF-beta2 secretion was polarized, but not in the same direction. TGF-beta2 secretion was not up-regulated by stimulation with IL-1beta. In contrast, IL-1beta strongly induced MCP-1 secretion preferentially into the basal compartment of all RPE monolayers tested. These data indicate that human RPE cells are able to secrete TGF-beta2 and MCP-1 in a polarized fashion. Our results suggest that MCP-1 can be secreted by RPE cells in the direction of choroidal vessels during inflammatory responses in the posterior part of the eye, which may limit damage to the neurosensory retina.

Adolescent↗
PubMed1999

Differential regulation of nitric oxide synthase-II mRNA by growth factors in rat, bovine, and human retinal pigmented epithelial cells.

Retinal pigmented epithelial cells (RPE cells) express the inducible isoform of NO synthase (NOS-II) after stimulation by cytokines and endotoxin. We have attempted to describe and compare the effect of fibroblast growth factor (FGF) and transforming growth factor beta (TGFbeta) on NOS-II mRNA level in three different cell species: rat, bovine, and human. Northern blot analysis demonstrated that, in the rat RPE cells, FGF upregulates and TGFbeta inhibits NOS-II mRNA accumulation, whereas in the bovine cells, the opposite effect appears. For the human RPE cells, RT-PCR analysis demonstrated that FGF upregulates and TGFbeta inhibits NOS-II mRNA accumulation, as in rat cells, even though the effect of TGFbeta was weaker. Thus, this study demonstrates that marked differences in growth factors regulating NOS-II occur between species, suggesting fundamental signal transduction differences at some level between rat, human, and cow.

Animals↗
PubMed1992

Post-mortem HLA tissue typing of retinal pigment epithelial cells.

Retinal pigment epithelial cells (RPE) were derived from bulbi of cornea donors and maintained in culture. The time-span between donor's death and cell cultivation ranged from 2 to 122 h. The mean numbers of hours was 25.6 (n = 130). After IFN-gamma stimulation, cells were serologically typed for class I and class II antigens. Unclear class I allospecificities were verified by one-dimensional isoelectric focusing. Data from the serological typing of lymphocytes and those of the serological and biochemical typing of RPE from the same donors were compared in 22 cases. There was a discrepancy of less than 5%, whereby either the typing on lymphocytes could not identify some specificities declared as blanks or the RPE typing had failed to clearly define a specificity. Our data show that the strategy adopted here is very successful for tissue typing post mortem, thus increasing the number of available HLA-matched corneas and consequently reducing the number of corneal graft rejections.

Adolescent↗
PubMed1990

The potentiating effects of ethanol on the blue light depolarization of the retinal pigment epithelium.

The retinal pigment epithelium (RPE) is the site of two major effects of ethanol. In humans, ethanol produces a slow damped oscillation in the steady electrical potential of the eye, which is generated primarily by the RPE. It has also been shown that ethanol potentiates the reversible, depolarizing effect of blue light on the transepithelial potential (TEP) of the isolated RPE. The present study demonstrates that in addition to the depolarizing effect of blue light on the TEP, a secondary, compensatory potential arises, which functions to maintain the TEP. The magnitude of the secondary response varies somewhat among preparations. It appears that ethanol eliminates or reduces the secondary, compensatory potential change which results in a large depolarization of the TEP when the RPE is irradiated with blue light. Microelectrode studies reveal that ethanol hyperpolarizes both the apical and basal membranes of the RPE with a greater effect noted in the apical membrane. This would account for the corneal positive potential elicited by ethanol in the human eye. Brief exposures (2-3 min) of blue light, after administration of 0.5% ethanol, results in a large (25-30 mV) depolarization of both membrane potentials as compared with 3 to 5 mV in untreated tissue. On the basis of our observations, it is hypothesized that some of the potentiating effects of ethanol in combination with other agents may result from an interference with a cellular adaptive response to impaired respiration rather than an additive effect on a common mechanism.

Animals↗
PubMed1990

Voltage-dependent currents in isolated cells of the frog retinal pigment epithelium.

1. Retinal pigment epithelial (RPE) cells were isolated enzymatically from bullfrog retinae. The patch-clamp technique was employed to investigate whole-cell currents under voltage-clamp conditions. 2. Isolated RPE cells were columnar or cuboidal in form, often with long processes protruding from the apical surface. Distinct apical and basal membrane domains were maintained for several hours following isolation. 3. The mean membrane capacitance was 62 pF. The resting potential averaged -30 mV, but it was as high as -75 mV in some cells. 4. Three voltage-dependent currents were observed: a time-independent and inwardly rectifying current and two time-dependent outwardly rectifying currents that had distinct kinetic properties. 5. Voltage pulses from a holding potential of -70 mV to potentials ranging from -30 to -120 mV produced membrane currents that were essentially time independent. The I-V relationship in this voltage range depended on the resting potential. It was usually inwardly rectifying in cells with resting potentials negative to about -50 mV, but tended to be linear in cells with more positive potentials. Three observations strongly suggested that the inwardly rectifying current is carried by K+. First, increasing the extracellular K+ concentration [( K+]) from 2 to 112 mM shifted the zero-current potential of the I-V relationship in the positive direction from an average value of -60 mV to 0 mV. Second, the addition of the K+ channel blockers Ba2+ (2 mM) or Cs+ (5 mM) to the extracellular solution inhibited a major component of the inwardly rectifying current. Finally, the reversal potential (Vr) of the Ba2(+)-sensitive current averaged -90 mV, near the K+ equilibrium potential (EK). 6. In approximately 50% of the cells, depolarizing voltage pulses to potentials more negative than -30 mV evoked an outward current that resembled the delayed rectifier present in other non-excitable cells. It activated with sigmoidal kinetics in less than 100 ms following a brief delay and then declined exponentially with a time constant of approximately 1 s. The peak chord conductance associated with this current was half-maximal at +14 mV. Several observations indicated that this outwardly rectifying current is carried primarily by K+: its Vr closely matched EK over a wide range of extracellular [K+]; it was inhibited 80% by exposure to the K+ channel blockers 4-aminopyridine (1 mM) and tetraethylammonium (20 mM); and it was abolished by intracellular dialysis with a K(+)-free solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1998

Adenylyl cyclase type 7 is the predominant isoform in the bovine retinal pigment epithelium.

The retinal pigment epithelium (RPE) fulfills important supporting tasks to maintain the visual functions of the sensorineural retina. One major signalling mechanism by which adjacent tissues impinge on the RPE is the adenylyl cyclase (AC)/cAMP pathway. In the RPE, cAMP seems to modulate unique functions such as the phagocytosis of discs shed from the rod outer segments, transport of vitamin A or the ion and fluid control in the subretinal space. We analyzed the AC expression pattern in the retina and the RPE and found AC type 7 to be almost the only isoform expressed in the RPE. We cloned AC type 7 from a cDNA library established with fresh bovine RPE, expressed this isoform in eukaryotic cells and characterized some of its properties.

Adenylyl Cyclases↗
PubMed2001

Lack of FasL expression in cultured human retinal pigment epithelial cells.

Retinal pigment epithelial (RPE) cells have been proposed to play a part in maintaining the eye as an immune privileged organ. However, our knowledge of the implicated mechanism is still sparse. Fas ligand (FasL) expression of RPE cells is generally recognized to be essential for the immune privilege of the eye, but due to contradictory published results, it is unclear whether RPE cells express this molecule. The purpose of this study was to investigate the expression of FasL in RPE cells in vitro and in vivo. Cultured human fetal and adult RPE cells were examined by flow cytometry, Western blotting, RT-PCR and RNase Protection assay for FasL expression. Additionally, sections of ocular tissue were stained for FasL by immunohistochemistry. None of the used methods indicated FasL expression in cultured fetal or adult RPE cells of various passages. However, RPE cells in vivo, as judged from tissue sections, were positive for FasL, indicating a discrepancy between RPE cells in vitro and in vivo with regard to this molecule.

Adult↗
PubMed1997

Apical sorting of influenza hemagglutinin by transcytosis in retinal pigment epithelium.

The retinal pigment epithelium is endowed with a unique distribution of certain plasma membrane proteins. Na+,K+-ATPase, for instance, is polarized to the apical surface of RPE, rather than to the basolateral surface as in most other epithelia. To study the sorting pathways of RPE cells, we used temperature sensitive mutants of influenza and vesicular stomatitis virus (VSV) to synchronize the transport of hemagglutinin (HA) and VSV G protein (VSV G) along the biosynthetic pathway of the RPE cell line RPE-J. After HA and VSV G accumulated in the trans-Golgi network of RPE-J cells kept at 20 degrees C, transfer to the permissive temperature (32 degrees C) resulted in the transport of both HA and VSV G to the basolateral plasma membrane. Later, while VSV G remained basolateral, HA progressively reversed its polarity, eventually becoming apical. Further analysis demonstrated that the reversal of HA polarity was due to transcytosis of HA from the basolateral to the apical surface of RPE-J cells. To determine whether HA followed a transcytotic route in RPE in vivo, influenza and VSV were injected into the subretinal space of rat eyes. Again, both HA and VSV G were initially observed at the basolateral surface of RPE cells. However, whereas VSV G remained there, HA progressively redistributed to the apical surface. These findings demonstrated that RPE cells use a transcytotic pathway for the targeting of at least some apical proteins to their destination.

Animals↗