gms | German Medical Science

Purpose: Both phototoxic effects of lipofuscin and local inflammation in the sub-RPE space have been implicated in the progressive dysfunction and degeneration of the retinal pigment epithelium (RPE) in age-related macular degeneration (AMD). To identify a common molecular mechanism of these two phenomena we investigated the phototoxic effects of lipofuscin on lysosomal membrane stability and activity of the NALP3 inflammasome in the RPE.

Methods: Photoreceptor outer segments (POS) were modified with the lipid peroxidation products 4-hydroxynonenal (HNE) or malondialdehyde (MDA), and confluent monolayers oft the human RPE cell line ARPE-19 were incubated with the modified POS. Effects of an irradiation of the cells with blue light (wave length 455–460 nm; irradiance 0.8 mW/cm²) on lysosomal membrane permeability and cellular viability were analyzed. Activation of the NALP3 inflammasome after priming with IL-1β was measured by means of IL-1β secretion.

Results: Phagocytosis of HNE- and MDA-modified POS induced pronounced lipofuscinogenesis, and subsequent irradiation with blue light for 9 h reduced cellular viability to 17%. In contrast, control cells incubated with unmodified POS were unaffected by irradiation (viability 97%). Cytotoxicity was mediated by apoptosis. After blue light irradiation we detected a dose-dependent permeabilization of lysosomal membranes that was associated with activation of the NALP3 inflammasome and release of IL-1β Specific inhibition of caspase-1 prevented IL-1β secretion.

Conclusion: Lipofuscinogenesis induced by lipid peroxidation products renders the RPE susceptible for phototoxic destabilization of lysosomes and apoptotic cell death. Lysosomal membrane permeabilization results in activation of the NALP3 inflammasome and secretion of inflammatory cytokines. Via these mechanisms lipofuscin accumulation in the RPE may contribute to local inflammation in AMD.