Examining the proteins of functional retinal lipofuscin using proteomic analysis as a guide for understanding its origin.
OBJECTIVE
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.
Warburton
Sarah
S
Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.
Southwick
Katie
K
Hardman
Ryan M
RM
Secrest
Aaron M
AM
Grow
Ryan K
RK
Xin
Huijun
H
Woolley
Adam T
AT
Burton
Gregory F
GF
Thulin
Craig D
CD
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015180:Electrophoresis, Gel, Two-Dimensional; D004591:Electrophoresis, Polyacrylamide Gel; D005434:Flow Cytometry; D006801:Humans; D008062:Lipofuscin / Q000032:analysis*; D008855:Microscopy, Electron, Scanning; D016253:Microscopy, Immunoelectron; D008875:Middle Aged; D010857:Pigment Epithelium of Eye / Q000737:chemistry* / Q000648:ultrastructure; D020543:Proteome / Q000032:analysis*; D040901:Proteomics; D013050:Spectrometry, Fluorescence; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D008062:Lipofuscin; D020543:Proteome