title: Phagosome maturation during endosome interaction revealed by partial rhodopsin processing in retinal pigment epithelium.
abstract: Defects in phagocytosis and degradation of photoreceptor outer segments (POS) by the retinal pigment epithelium (RPE) are associated with aging and retinal disease. The daily burst of rod outer segment (ROS) phagocytosis by the RPE provides a unique opportunity to analyse phagosome processing in vivo. In mouse retinae, phagosomes containing stacked rhodopsin-rich discs were identified by immuno-electron microscopy. Early apical phagosomes stained with antibodies against both cytoplasmic and intradiscal domains of rhodopsin. During phagosome maturation, a remarkably synchronised loss of the cytoplasmic epitope coincided with movement to the cell body and preceded phagosome-lysosome fusion and disc degradation. Loss of the intradiscal rhodopsin epitope and disc digestion occurred upon fusion with cathepsin-D-positive lysosomes. The same sequential stages of phagosome maturation were identified in cultured RPE and macrophages challenged with isolated POS. Loss of the cytoplasmic rhodopsin epitope was insensitive to pH but sensitive to protease inhibition and coincided with the interaction of phagosomes with endosomes. Thus, during pre-lysosomal maturation of ROS-containing phagosomes, limited rhodopsin processing occurs upon interaction with endosomes. This potentially provides a sensitive readout of phagosome-endosome interactions that is applicable to multiple phagocytes.
authors: Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ, UK UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK.
authors: Silène T
authors: ST
authors: Wavre-Shapton
authors: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK.
authors: Ingrid P
authors: IP
authors: Meschede
authors: Molecular Medicine Section, National Heart and Lung Institute, Imperial College London, London SW7 2AZ, UK CEDOC, Faculdade de Ciências Médicas, Universidade Nova de Lisboa, 1169-056 Lisbon, Portugal Instituto Gulbenkian de Ciência, 2780-156 Oeiras, Portugal.
authors: Miguel C
authors: MC
authors: Seabra
authors: UCL Institute of Ophthalmology, University College London, London EC1V 9EL, UK c.futter@ucl.ac.uk.
authors: Clare E
authors: CE
authors: Futter
mesh_terms: D000818:Animals; D002469:Cell Separation; D011992:Endosomes / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000378:metabolism; D008810:Mice, Inbred C57BL; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000378:metabolism*; D012243:Rhodopsin / Q000378:metabolism*
chemical_list: D012243:Rhodopsin
keywords: Phagosome; RPE; Rhodopsin