Questioning photostasis

2013 ◽  
Vol 30 (4) ◽  
pp. 169-174 ◽  
Author(s):  
ALEXANDER CUNEA ◽  
RANA BEGUM ◽  
DIETER REINISCH ◽  
GLEN JEFFERY
Keyword(s):  
Statistical Analysis ◽  
Retinal Pigment Epithelium ◽  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Photoreceptor Outer Segment ◽  
Rpe Cells ◽  
Significant Difference ◽  
Environmental Lighting ◽  
Pigmentation Phenotype

AbstractPhotostasis is a phenomenon where the photoreceptor outer segment (OS) length and its rhodopsin content vary depending on environmental lighting. When light is reduced for extended periods, it is argued that OS lengthen and its rhodopsin concentration rises to increase photon capture in darker environment. Increases in OS length may occur because the retinal pigment epithelium (RPE) cells reduce OS consumption in prolonged darkness. But sample sizes in assessing changes in OS length have been small, and results highly varied with no statistical analysis ever offered. Further, animals used were often albinos, which have abnormal RPE cells. Here we keep pigmented and albino mice for 21 days in darkness and compare OS length with those in a normal 12:12 light/dark environment. We measured approximately 1300 OS but found no statistically significant difference in their lengths between light and dark groups in either pigmentation phenotype, although there was a small trend in the data favoring OS extension in the dark. Given that earlier studies were undertaken on limited samples with no statistical analysis, our data pose serious questions for the notion of mammalian photostasis in terms of significant OS plasticity.

scholarly journals Light-induced Oxidation of Photoreceptor Outer Segment Phospholipids Generates Ligands for CD36-mediated Phagocytosis by Retinal Pigment Epithelium

2006 ◽  
Vol 281 (7) ◽  
pp. 4222-4230 ◽  
Author(s):  
Mingjiang Sun ◽  
Silvia C. Finnemann ◽  
Maria Febbraio ◽  
Lian Shan ◽  
Suresh P. Annangudi ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Photoreceptor Outer Segment

scholarly journals Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-derived Factor Receptor (PEDF-R)

2021 ◽  
Author(s):  
Jeanee Bullock ◽  
Federica Polato ◽  
Mones Abu-Asab ◽  
Alexandra Bernardo-Colón ◽  
Elma Aflaki ◽  
...  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Phospholipase A2 ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Photoreceptor Outer Segment ◽  
Western Blots ◽  
Rpe Cells ◽  
Photoreceptor Outer Segments ◽  
Transmission Electron ◽  
Bromoenol Lactone

AbstractPurposeTo examine the contribution of PEDF-R to the phagocytosis process. Previously, we identified PEDF-R, the protein encoded by the PNPLA2 gene, as a phospholipase A2 in the retinal pigment epithelium (RPE). During phagocytosis, RPE cells ingest abundant phospholipids and protein in the form of photoreceptor outer segment (POS) tips, which are then hydrolyzed. The role of PEDF-R in RPE phagocytosis is not known.MethodsMice in which PNPLA2 was conditionally knocked out in the RPE were generated (cKO). Mouse RPE/choroid explants were cultured. Human ARPE-19 cells were transfected with siPNPLA2 silencing duplexes. POS were isolated from bovine retinas. The phospholipase A2 inhibitor bromoenol lactone was used. Transmission electron microscopy, immunofluorescence, lipid labeling, pulse-chase experiments, western blots, and free fatty acid and β-hydroxybutyrate assays were performed.ResultsThe RPE of the cKO mice accumulated lipids as well as more abundant and larger rhodopsin particles compared to littermate controls. Upon POS exposure, RPE explants from cKO mice released less β-hydroxybutyrate compared to controls. After POS ingestion during phagocytosis, rhodopsin degradation was stalled both in cells treated with bromoenol lactone and in PNPLA2-knocked-down cells relative to their corresponding controls. Phospholipase A2 inhibition lowered β-hydroxybutyrate release from phagocytic RPE cells. PNPLA2 knock down also resulted in a decline in fatty acids and β-hydroxybutyrate release from phagocytic RPE cells.ConclusionsPEDF-R downregulation delayed POS digestion during phagocytosis. The findings imply that efficiency of RPE phagocytosis depends on PEDF-R, thus identifying a novel contribution of this protein to POS degradation in the RPE.

Membrane turnover in rod photoreceptors: ensheathment and phagocytosis of outer segment distal tips by pseudopodia of the retinal pigment epithelium

1987 ◽  
Vol 230 (1260) ◽  
pp. 339-354 ◽  
Keyword(s):  
Retinal Pigment Epithelium ◽  
Outer Segment ◽  
Excitatory Amino Acid ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Ultrastructural Changes ◽  
Membrane Turnover ◽  
Rhodamine Phalloidin ◽  
Cytoplasmic Matrix ◽  
Rpe Cells

We have documented the ultrastructural changes that occur within the photoreceptor outer segment and the retinal pigment epithelium (rpe) during photosensitive membrane turnover. We employed an in vitro eyecup preparation from Xenopus laevis in which a large shedding event was induced by adding the excitatory amino acid l-aspartate (Green-berger & Besharse I985; J . comp . Neurol . 239. 361-372). We found that during L-aspartate-induced shedding the rpe cells formed. on their apical domains, previously undescribed processes that were directly involved in disc phagocytosis. These processes are structurally similar to processes formed by macrophages during phagocytosis and are accordingly referred to as pseudopodia. Pseudopodia were distinguishable from the apical villous process normally extended from the rpe in that they were closely applied to the surface of the outer segment, had a cytoplasmic matrix of low electron density that was devoid of most cellular organelles and were enriched in thin (7 nm diameter) filaments. Filament size, specific pseudopodial staining with the actin-specific probe rhodamine phalloidin and inhibition of pseudopod formation by cytochalasin D suggested that the thin filaments were composed of actin. Pseudopodial formation also occurs during a normal light-initiated shedding event. However, the low frequency of shedding, the asynchrony of the individual shedding events and the transient appearance of the pseudopodia prevented a full appreciation of their role during normal disc shedding. Associated with massive shedding and pseudopodial formation, there was an increased adherence between retina and rpe. During l-aspartate treatment, the apical portions of the rpe cells partitioned with the distal outer segment during retinal isolation. This effect was directly related to the development of pseudopodia and may reflect alteration of surface features of the rod outer segment (ros)-rpe interface related to phagocytosis. Our observations show that transiently forming pseudo­podia are the organelles of phagocytosis and that they may play a role in disc detachment as well.

scholarly journals Fast voltage sensitivity in retinal pigment epithelium: sodium channels and their novel role in phagocytosis

2017 ◽  
Author(s):  
Julia K. Johansson ◽  
Teemu O. Ihalainen ◽  
Heli Skottman ◽  
Soile Nymark
Keyword(s):  
Retinal Pigment Epithelium ◽  
Sodium Channels ◽  
Connexin 43 ◽  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Cell Junctions ◽  
Voltage Sensitivity ◽  
Photoreceptor Outer Segment ◽  
Junction Protein

AbstractDespite the discoveries of voltage-gated sodium channels (Nav) from a number of non-excitable cell types, the presence of Nav-mediated currents in cells of the retinal pigment epithelium (RPE) has been dismissed as a cell culture artifact. Here, we challenge this notion by demonstrating functional Nav1.4-Nav1.6 and Nav1.8 channels in human embryonic stem cell derived and mouse RPE. Importantly, we show that Navs are involved in photoreceptor outer segment phagocytosis: blocking their activity significantly reduces the efficiency of this process. Consistent with this role, Nav1.8 co-localizes with the endosomal marker Rab7 and, during phagocytosis, with opsin. Nav1.4 localizes strongly to the cell-cell junctions together with the gap junction protein Connexin 43. During phagocytosis, both are localized to the phagosomes with a concurrent decrease in the junctional localization. Our study demonstrates that Navs give the capacity of fast electrical signaling to RPE and that Navs play a novel role in photoreceptor outer segment phagocytosis.

The cytoskeletal elements of human retinal pigment epithelium: in vitro and in vivo

1988 ◽  
Vol 91 (2) ◽  
pp. 303-312
Author(s):  
N.M. McKechnie ◽  
M. Boulton ◽  
H.L. Robey ◽  
F.J. Savage ◽  
I. Grierson
Keyword(s):  
Retinal Pigment Epithelium ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Cytokeratin 18 ◽  
Rpe Cells ◽  
Human Retinal Pigment Epithelium ◽  
Cytoskeletal Elements

The cytoskeletal elements of normal (in situ) and cultured human retinal pigment epithelium (RPE) were studied by a variety of immunocytochemical techniques. Primary antibodies to vimentin and cytokeratins were used. Positive immunoreactivity for vimentin was obtained with in situ and cultured material. The pattern of reactivity obtained with antisera and monoclonals to cytokeratins was more complex. Cytokeratin immunoreactivity could be demonstrated in situ and in cultured cells. The pattern of cytokeratin expression was similar to that of simple or glandular epithelia. A monoclonal antibody that specifically recognizes cytokeratin 18 identified a population of cultured RPE cells that had particularly well-defined filamentous networks within their cytoplasm. Freshly isolated RPE was cytokeratin 18 negative by immunofluorescence, but upon culture cytokeratin 18 positive cells were identifiable. Cytokeratin 18 positive cells were identified in all RPE cultures (other than early primaries), regardless of passage number, age or sex of the donor. In post-confluent cultures cytokeratin 18 cells were identified growing over cytokeratin 18 negative cells, suggesting an association of cytokeratin 18 immunoreactivity with cell proliferation. Immunofluorescence studies of retinal scar tissue from two individuals revealed the presence of numerous cytokeratin 18 positive cells. These findings indicate that RPE cells can be identified by their cytokeratin immunoreactivity and that the overt expression of cytokeratin 18 may be associated with proliferation of human RPE both in vitro and in vivo.

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