Proteomic and phototoxic characterization of melanolipofuscin:Correlation to disease and model for its origin

[摘要] Purpose: Melanolipofuscin (MLF) is a complex granule, exhibitingproperties of both melanosomes and lipofuscin (LF) granules, whichaccumulates in retinal pigment epithelial (RPE) cells and may contributeto the etiology of age-related macular degeneration (AMD). MLFaccumulation has been reported by Feeney-Burns to more closely reflectthe onset of AMD than the accumulation of lipofuscin. In an effort toassess the possible contribution MLF may have to the onset of AMD, weanalyzed the phototoxicity and protein composition of MLF and comparedthose results to that of LF.Methods: Specifically, we observed the accumulation of MLF in humanRPE from different decades of life, and assessed the phototoxicity ofthese granules. We also employed fluorescence spectroscopy, atomic forcemicroscopy, transmission and scanning electron microscopy and proteomicanalysis to examine the composition of MLF granules in an effort toascertain their origin.Results: Our results show that MLF granules are phototoxic and theiraccumulation more closely reflects the onset of AMD than does LFaccumulation. Our compositional analysis of MLF has shown that whilethese granules contain some similarities to LF granules, MLF issubstantially different. Of significant interest is the finding thatMLF, in contrast to LF, does not contain photoreceptor-specificproteins, suggesting that MLF may not originate from the phagocytosis ofphotoreceptor outer segments. Instead the presence of RPE- andmelanosome-specific proteins would suggest that MLF accumulates as aresult of the melanosomal autophagocytosis of RPE cells.Conclusions: Our results provide significant insight intounderstanding the formation and toxicity of MLF and suggest a possiblecontribution to the etiology of retinal diseases.

[学科分类] 生物化学/生物物理