RESUMO
PURPOSE: To elucidate the origins of biologically active retinal lipofuscin (RLF) by examining its protein composition. METHODS: Total protein and total lipid were extracted and quantified. Proteins in this lipoprotein granule were identified by limited-scale proteomic analysis using both two-dimensional (2D) gel electrophoresis and SDS-PAGE coupled with MALDI-QqToF MSMS and automated LCMSMS, respectively. RESULTS: RLF granules were 44% protein and 50% lipid. Proteomic analyses identified 41 constituent proteins. Hydrophobic proteins and several proteins specific to photoreceptors, including rhodopsin, that have not previously been reported, were identified. Extensive protein modification, especially oxidative damage, was observed. CONCLUSIONS: Proteins identified support the model that RLF accumulates in RPE cells as a result of the buildup of undigested material from the phagocytosis of photoreceptor outer segments. Perhaps oxidative damage renders some of these proteins indigestible and thus leads to the accumulation of RLF granules.
