N-acetylcysteine improves lysosomal function and enhances the degradation of photoreceptor outer segments in cultured RPE cells

Background: In the retinal pigment epithelium (RPE) lipofuscin granules accumulate with age in the lysosomal compartment mainly as a byproduct of constant phagocytosis of oxidized membranous discs shed from photoreceptor outer segments. Antioxidative defiency and prooxidative conditions in the RPE play a key role in the pathogenesis of RPE dysfunction and macular degenerations such as ARMD. In human RPE cell cultures we investigated the antioxidative effect of N-acetylcysteine (ACC) on lysosomal functions. Methods: Primary human RPE cell cultures were loaded with regular or oxidized human and porcine rod outer segments (ROS) and treated with ACC. Lysosomal volume and accumulation of autoflurescent material was measured using [14C] methylamine accumulation and FACS analysis. The regulation pattern of lysosomal proteins were investigated by proteome analysis. Results: ACC reduced total lysosomal volume in control, ROS and oxidized ROS fed RPE cells. After ROS incubation increased accumulation of autofluorescent material was measured. ACC treatment decreased intracellular accumulation. Furthermore, incubation with ACC leads to a general down regulation of lysosomal proteins. Conclusion: In our cell culture model of ROS fed RPE cells simulating aged RPE ACC improves lysosomal volume and metabolism. Therefore ACC may represent a new prophylactic and causal treatment option for AMD.