scholarly journals Chronically shortened rod outer segments accompany photoreceptor cell death in Choroideremia

PLoS ONE ◽  
2020 ◽  
Vol 15 (11) ◽  
pp. e0242284
Author(s):  
Ingrid P. Meschede ◽  
Thomas Burgoyne ◽  
Tanya Tolmachova ◽  
Miguel C. Seabra ◽  
Clare E. Futter
Keyword(s):  
Cell Death ◽  
Membrane Trafficking ◽  
Outer Segment ◽  
Photoreceptor Cell ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Membrane Traffic ◽  
Rod Outer Segments ◽  
Rab Protein ◽  
Outer Segments

X-linked choroideremia (CHM) is a disease characterized by gradual retinal degeneration caused by loss of the Rab Escort Protein, REP1. Despite partial compensation by REP2 the disease is characterized by prenylation defects in multiple members of the Rab protein family that are master regulators of membrane traffic. Remarkably, the eye is the only organ affected in CHM patients, possibly because of the huge membrane traffic burden of the post mitotic photoreceptors, which synthesise outer segments, and the adjacent retinal pigment epithelium that degrades the spent portions each day. In this study, we aimed to identify defects in membrane traffic that might lead to photoreceptor cell death in CHM. In a heterozygous null female mouse model of CHM (Chmnull/WT), degeneration of the photoreceptor layer was clearly evident from increased numbers of TUNEL positive cells compared to age matched controls, small numbers of cells exhibiting signs of mitochondrial stress and greatly increased microglial infiltration. However, most rod photoreceptors exhibited remarkably normal morphology with well-formed outer segments and no discernible accumulation of transport vesicles in the inner segment. The major evidence of membrane trafficking defects was a shortening of rod outer segments that was evident at 2 months of age but remained constant over the period during which the cells die. A decrease in rhodopsin density found in the outer segment may underlie the outer segment shortening but does not lead to rhodopsin accumulation in the inner segment. Our data argue against defects in rhodopsin transport or outer segment renewal as triggers of cell death in CHM.

scholarly journals Phagocytosis of Retinal Rod and Cone Photoreceptors

Physiology ◽  
2010 ◽  
Vol 25 (1) ◽  
pp. 8-15 ◽  
Author(s):  
Brian M. Kevany ◽  
Krzysztof Palczewski
Keyword(s):  
Outer Segment ◽  
Photoreceptor Cell ◽  
Current Knowledge ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Photoreceptor Cells ◽  
Constant Length ◽  
Outer Segments ◽  
Retinal Rod ◽  
Rod And Cone Photoreceptors

Photoreceptor cells maintain a roughly constant length by continuously generating new outer segments from their base while simultaneously releasing mature outer segments engulfed by the retinal pigment epithelium (RPE). Thus postmitotic RPE cells phagocytose an immense amount of material over a lifetime, disposing of photoreceptor cell waste while retaining useful content. This review focuses on current knowledge of outer segment phagocytosis, discussing the steps involved along with their critical participants as well as how various perturbations in outer segment (OS) disposal can lead to retinopathies.

scholarly journals Modulating GLUT1 expression in retinal pigment epithelium decreases glucose levels in the retina: impact on photoreceptors and Müller glial cells

2019 ◽  
Vol 316 (1) ◽  
pp. C121-C133 ◽  
Author(s):  
Aditi Swarup ◽  
Ivy S. Samuels ◽  
Brent A. Bell ◽  
John Y. S. Han ◽  
Jianhai Du ◽  
...  
Keyword(s):  
Cell Death ◽  
Retinal Pigment Epithelium ◽  
Glucose Transport ◽  
Glial Cells ◽  
Photoreceptor Cell ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Conditional Knockout ◽  
Müller Glial Cells ◽  
Outer Segments

The retina is one of the most metabolically active tissues in the body and utilizes glucose to produce energy and intermediates required for daily renewal of photoreceptor cell outer segments. Glucose transporter 1 (GLUT1) facilitates glucose transport across outer blood retinal barrier (BRB) formed by the retinal pigment epithelium (RPE) and the inner BRB formed by the endothelium. We used conditional knockout mice to study the impact of reducing glucose transport across the RPE on photoreceptor and Müller glial cells. Transgenic mice expressing Cre recombinase under control of the Bestrophin1 ( Best1) promoter were bred with Glut1flox/flox mice to generate Tg-Best1-Cre:Glut1flox/flox mice ( RPEΔGlut1). The RPEΔGlut1 mice displayed a mosaic pattern of Cre expression within the RPE that allowed us to analyze mice with ~50% ( RPEΔGlut1m) recombination and mice with >70% ( RPEΔGlut1h) recombination separately. Deletion of GLUT1 from the RPE did not affect its carrier or barrier functions, indicating that the RPE utilizes other substrates to support its metabolic needs thereby sparing glucose for the outer retina. RPEΔGlut1m mice had normal retinal morphology, function, and no cell death; however, where GLUT1 was absent from a span of RPE greater than 100 µm, there was shortening of the photoreceptor cell outer segments. RPEΔGlut1h mice showed outer segment shortening, cell death of photoreceptors, and activation of Müller glial cells. The severe phenotype seen in RPEΔGlut1h mice indicates that glucose transport via the GLUT1 transporter in the RPE is required to meet the anabolic and catabolic requirements of photoreceptors and maintain Müller glial cells in a quiescent state.

CD36 participates in the phagocytosis of rod outer segments by retinal pigment epithelium

1996 ◽  
Vol 109 (2) ◽  
pp. 387-395 ◽  
Author(s):  
S.W. Ryeom ◽  
J.R. Sparrow ◽  
R.L. Silverstein
Keyword(s):  
Retinal Pigment Epithelium ◽  
Outer Segment ◽  
Retinal Pigment Epithelial ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Immunofluorescent Staining ◽  
Rod Outer Segments ◽  
Photoreceptor Outer Segments ◽  
Pigment Epithelial ◽  
Outer Segments

Mechanisms of phagocytosis are complex and incompletely understood. The retinal pigment epithelium provides an ideal system to study the specific aspects of phagocytosis since an important function of this cell is the ingestion of packets of membranous discs that are normally discarded at the apical ends of rod and cone cells during outer segment renewal. Here we provide evidence that rod outer segment phagocytosis by retinal pigment epithelium is mediated by CD36, a transmembrane glycoprotein which has been previously characterized on hematopoietic cells as a receptor for apoptotic neutrophils and oxidized low density lipoprotein. Immunocytochemical staining with monoclonal and polyclonal antibodies demonstrated CD36 expression by both human and rat retinal pigment epithelium in transverse cryostat sections of normal retina and in primary cultured cells. By western blot analysis of retinal pigment epithelial cell lysates, polyclonal and monoclonal antibodies to CD36 recognized an 88 kDa protein which comigrated with platelet CD36. Furthermore, the synthesis of CD36 mRNA by retinal pigment epithelium was confirmed by reverse transcriptase-PCR using specific CD36 oligonucleotides. The addition of CD36 antibodies to cultured retinal pigment epithelial cells reduced the binding and internalization of 125I-labeled rod outer segments by 60%. Immunofluorescence confocal microscopy confirmed that outer segment uptake was significantly diminished by an antibody to CD36. Moreover, we found that transfection of a human melanoma cell line with CD36 cDNA enabled these cells to bind and internalize isolated photoreceptor outer segments as seen by double immunofluorescent staining for surface bound and total cell-associated rod outer segments, and by measurement of cell-associated 125I-labeled rod outer segments. We conclude that the multifunctional scavenger receptor CD36 participates in the clearance of photoreceptor outer segments by retinal pigment epithelium and thus, participates in the visual process.

scholarly journals Synthesis of retinoids by human retinal epithelium and transfer to rod outer segments

1990 ◽  
Vol 268 (1) ◽  
pp. 201-206 ◽  
Author(s):  
S R Das ◽  
N Bhardwaj ◽  
P Gouras
Keyword(s):  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Primary Cultures ◽  
Progressive Increase ◽  
Retinyl Palmitate ◽  
Rod Outer Segments ◽  
Outer Segments ◽  
Retinal Epithelium ◽  
The Media

The synthesis and release of 11-cis-retinoids by primary cultures of human retinal pigment epithelium (RPE) and the transfer of these retinoids to co-incubated human rod outer segments (ROS) were studied. Monolayers of 2-3-week-old cultured RPE incorporate tritiated all-trans-retinol, esterify it to the corresponding retinyl palmitate, form 11-cis-retinol and 11-cis-retinaldehyde and release retinaldehyde into the culture medium. The ratio of 11-cis to all-trans isomers of retinol, retinyl palmitate and retinaldehyde formed in the cells along with retinaldehyde released and incorporated into the ROS progressively increases, indicating a progressive increase in the concentration of 11-cis isomer from the time it is formed in RPE cells until its transfer to ROS. Incorporation of 11-cis-retinaldehyde into the ROS is directly related to the amount of albumin present in the media, suggesting the transfer of retinoids from RPE to photoreceptor to be a protein-mediated process. Events leading to isomerization, esterification, oxidation and release of retinoids by human RPE and incorporation of retinoids into ROS can therefore be examined in vitro.

scholarly journals Kif17 phosphorylation regulates its ciliary localization and photoreceptor outer segment turnover

2018 ◽  
Author(s):  
Tylor R. Lewis ◽  
Sean R. Kundinger ◽  
Brian A. Link ◽  
Christine Insinna ◽  
Joseph C. Besharse
Keyword(s):  
Mammalian Cells ◽  
Outer Segment ◽  
Pigment Epithelium ◽  
Retinal Pigment ◽  
Consensus Sequence ◽  
Intraflagellar Transport ◽  
Photoreceptor Outer Segment ◽  
Transgenic Expression ◽  
Outer Segments ◽  
Ciliary Localization

AbstractBackgroundKIF17, a kinesin-2 motor that functions in intraflagellar transport, can regulate the onset of photoreceptor outer segment development. However, the function of KIF17 in a mature photoreceptor remains unclear. Additionally, the ciliary localization of KIF17 is regulated by a C-terminal consensus sequence (KRKK) that is immediately adjacent to a conserved residue (mouse S1029/zebrafish S815) previously shown to be phosphorylated by CaMKII. Yet, whether this phosphorylation can regulate the localization, and thus function, of KIF17 in ciliary photoreceptors remains unknown.ResultsUsing transgenic expression in both mammalian cells and zebrafish photoreceptors, we show that phospho-mimetic KIF17 has enhanced localization to cilia. Importantly, expression of phospho-mimetic KIF17 is associated with greatly enhanced turnover of the photoreceptor outer segment through disc shedding in a cell-autonomous manner, while genetic mutants of kif17 in zebrafish and mice have diminished disc shedding. Lastly, cone expression of constitutively active tCaMKII leads to a kif17-dependent increase in disc shedding.ConclusionsTaken together, our data support a model in which phosphorylation of KIF17 promotes its ciliary localization. In cone photoreceptor outer segments, this promotes disc shedding, a process essential for photoreceptor maintenance and homeostasis. While disc shedding has been predominantly studied in the context of the mechanisms underlying phagocytosis of outer segments by the retinal pigment epithelium, this work implicates photoreceptor-derived signaling in the underlying mechanisms of disc shedding.

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