Retinal Pigment Epithelial Cells Mitigate the Effects of Complement Attack by Endocytosis of C5b-9.
Retinal pigment epithelial (RPE) cell death is a hallmark of age-related macular degeneration. The alternative pathway of complement activation is strongly implicated in RPE cell dysfunction and loss in age-related macular degeneration; therefore, it is critical that RPE cells use molecular strategies to mitigate the potentially harmful effects of complement attack. We show that the terminal complement complex C5b-9 assembles rapidly on the basal surface of cultured primary porcine RPE cells but disappears over 48 h without any discernable adverse effects on the cells. However, in the presence of the dynamin inhibitor dynasore, C5b-9 was almost completely retained at the cell surface, suggesting that, under normal circumstances, it is eliminated via the endocytic pathway. In support of this idea, we observed that C5b-9 colocalizes with the early endosome marker EEA1 and that, in the presence of protease inhibitors, it can be detected in lysosomes. Preventing the endocytosis of C5b-9 by RPE cells led to structural defects in mitochondrial morphology consistent with cell stress. We conclude that RPE cells use the endocytic pathway to prevent the accumulation of C5b-9 on the cell surface and that processing and destruction of C5b-9 by this route are essential for RPE cell survival.
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom.
Apostolos
A
Georgiannakis
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom.
Tom
T
Burgoyne
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom.
Katharina
K
Lueck
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom.
Clare
C
Futter
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom.
John
J
Greenwood
Department of Cell Biology, University College London Institute of Ophthalmology, London EC1V9EL, United Kingdom s.moss@ucl.ac.uk.
Stephen E
SE
Moss
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003167:Complement Activation / Q000276:immunology; D015938:Complement Membrane Attack Complex / Q000276:immunology*; D034281:Dynamins / Q000037:antagonists & inhibitors; D004705:Endocytosis / Q000276:immunology*; D004847:Epithelial Cells / Q000166:cytology / Q000276:immunology*; D006835:Hydrazones / Q000494:pharmacology; D008268:Macular Degeneration / Q000276:immunology / Q000473:pathology; D008928:Mitochondria / Q000473:pathology; D021381:Protein Transport / Q000276:immunology; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000276:immunology*; D013552:Swine; D033921:Vesicular Transport Proteins / Q000378:metabolism
D015938:Complement Membrane Attack Complex; D006835:Hydrazones; C511794:N'-(3,4-dihydroxybenzylidene)-3-hydroxy-2-naphthahydrazide; D033921:Vesicular Transport Proteins; C093846:early endosome antigen 1; D034281:Dynamins