title: Complement Component C5a Primes Retinal Pigment Epithelial Cells for Inflammasome Activation by Lipofuscin-mediated Photooxidative Damage.
abstract: Complement activation, oxidative damage, and activation of the NLRP3 inflammasome have been implicated in retinal pigment epithelium (RPE) pathology in age-related macular degeneration (AMD). Following priming of RPE cells, the NLRP3 inflammasome can be activated by various stimuli such as lipofuscin-mediated photooxidative damage to lysosomal membranes. We investigated whether products of complement activation are capable of providing the priming signal for inflammasome activation in RPE cells. We found that incubation of primary human RPE cells and ARPE-19 cells with complement-competent human serum resulted in up-regulation of C5a receptor, but not C3a receptor. Furthermore, human serum induced expression of pro-IL-1β and enabled IL-1β secretion in response to lipofuscin phototoxicity, thus indicating inflammasome priming. Complement heat-inactivation, C5 depletion, and C5a receptor inhibition suppressed the priming effect of human serum whereas recombinant C5a likewise induced priming. Conditioned medium of inflammasome-activated RPE cells provided an additional priming effect that was mediated by the IL-1 receptor. These results identify complement activation product C5a as a priming signal for RPE cells that allows for subsequent inflammasome activation by stimuli such as lipofuscin-mediated photooxidative damage. This molecular pathway provides a functional link between key factors of AMD pathogenesis including lipofuscin accumulation, photooxidative damage, complement activation, and RPE degeneration and may provide novel therapeutic targets in this disease.
authors.affiliation: From the Department of Ophthalmology, University of Bonn, 53127 Bonn, Germany.
authors.forename: Carolina
authors.initials: C
authors.lastname: Brandstetter
authors.affiliation: From the Department of Ophthalmology, University of Bonn, 53127 Bonn, Germany.
authors.forename: Frank G
authors.initials: FG
authors.lastname: Holz
authors.affiliation: From the Department of Ophthalmology, University of Bonn, 53127 Bonn, Germany krohne@uni-bonn.de.
authors.forename: Tim U
authors.identifier: http://orcid.org/0000-0003-2280-925X
authors.initials: TU
authors.lastname: Krohne
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D015936:Complement C5a / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology; D006801:Humans; D058847:Inflammasomes / Q000378:metabolism*; D053583:Interleukin-1beta / Q000378:metabolism; D008062:Lipofuscin / Q000378:metabolism*; D008268:Macular Degeneration / Q000378:metabolism* / Q000473:pathology; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D010084:Oxidation-Reduction; D055213:Retinal Pigment Epithelium / Q000378:metabolism* / Q000473:pathology
chemical_list: D002352:Carrier Proteins; C508585:IL1B protein, human; D058847:Inflammasomes; D053583:Interleukin-1beta; D008062:Lipofuscin; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; D015936:Complement C5a
keywords: complement system; eye; immunology; inflammasome; interleukin 1 (IL-1); oxidative stress; retinal degeneration