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

PURPOSE: To examine the contribution of pigment epithelium-derived factor receptor (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 abun...

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Autores principales: Bullock, Jeanee, Polato, Federica, Abu-Asab, Mones, Bernardo-Colón, Alexandra, Aflaki, Elma, Agbaga, Martin-Paul, Becerra, S. Patricia
Formato: Online Artículo Texto
Lenguaje:English
Publicado: The Association for Research in Vision and Ophthalmology 2021
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7900850/
https://www.ncbi.nlm.nih.gov/pubmed/33605986
http://dx.doi.org/10.1167/iovs.62.2.30
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author Bullock, Jeanee
Polato, Federica
Abu-Asab, Mones
Bernardo-Colón, Alexandra
Aflaki, Elma
Agbaga, Martin-Paul
Becerra, S. Patricia
author_facet Bullock, Jeanee
Polato, Federica
Abu-Asab, Mones
Bernardo-Colón, Alexandra
Aflaki, Elma
Agbaga, Martin-Paul
Becerra, S. Patricia
author_sort Bullock, Jeanee
collection PubMed
description PURPOSE: To examine the contribution of pigment epithelium-derived factor receptor (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. METHODS: Mice in which PNPLA2 was conditionally knocked out (cKO) in the RPE were generated. Mouse RPE/choroid explants were cultured. Human ARPE-19 cells were transfected with siPNPLA2 silencing duplexes. POSs 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. RESULTS: The 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 knockdown also resulted in a decline in fatty acids and β-hydroxybutyrate release from phagocytic RPE cells. CONCLUSIONS: PEDF-R downregulation delayed POS digestion during phagocytosis. The findings imply that the efficiency of RPE phagocytosis depends on PEDF-R, thus identifying a novel contribution of this protein to POS degradation in the RPE.
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spelling pubmed-79008502021-03-03 Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R) Bullock, Jeanee Polato, Federica Abu-Asab, Mones Bernardo-Colón, Alexandra Aflaki, Elma Agbaga, Martin-Paul Becerra, S. Patricia Invest Ophthalmol Vis Sci Biochemistry and Molecular Biology PURPOSE: To examine the contribution of pigment epithelium-derived factor receptor (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. METHODS: Mice in which PNPLA2 was conditionally knocked out (cKO) in the RPE were generated. Mouse RPE/choroid explants were cultured. Human ARPE-19 cells were transfected with siPNPLA2 silencing duplexes. POSs 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. RESULTS: The 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 knockdown also resulted in a decline in fatty acids and β-hydroxybutyrate release from phagocytic RPE cells. CONCLUSIONS: PEDF-R downregulation delayed POS digestion during phagocytosis. The findings imply that the efficiency of RPE phagocytosis depends on PEDF-R, thus identifying a novel contribution of this protein to POS degradation in the RPE. The Association for Research in Vision and Ophthalmology 2021-02-19 /pmc/articles/PMC7900850/ /pubmed/33605986 http://dx.doi.org/10.1167/iovs.62.2.30 Text en Copyright 2021 The Authors http://creativecommons.org/licenses/by/4.0/ This work is licensed under a Creative Commons Attribution 4.0 International License.
spellingShingle Biochemistry and Molecular Biology
Bullock, Jeanee
Polato, Federica
Abu-Asab, Mones
Bernardo-Colón, Alexandra
Aflaki, Elma
Agbaga, Martin-Paul
Becerra, S. Patricia
Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title_full Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title_fullStr Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title_full_unstemmed Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title_short Degradation of Photoreceptor Outer Segments by the Retinal Pigment Epithelium Requires Pigment Epithelium-Derived Factor Receptor (PEDF-R)
title_sort degradation of photoreceptor outer segments by the retinal pigment epithelium requires pigment epithelium-derived factor receptor (pedf-r)
topic Biochemistry and Molecular Biology
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7900850/
https://www.ncbi.nlm.nih.gov/pubmed/33605986
http://dx.doi.org/10.1167/iovs.62.2.30
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