Proteomics of the retinal pigment epithelium reveals altered protein expression at progressive stages of age-related macular degeneration

PURPOSE. Age-related macular degeneration (AMD) is characterized clinically by changes in the retinal pigment epithelium (RPE), formation of drusen between the RPE and the underlying vasculature, geographic atrophy, and choroidal neovascularization. Later clinical stages are accompanied by impaired central vision. A limited understanding of the molecular events responsible for AMD has constrained the development of effective treatments. A proteomics approach was used to investigate the underlying mechanisms of AMD and to identify proteins exhibiting significant changes in expression with disease onset and progression. METHODS. Human donor eyes were categorized into one of four progressive stages of AMD. Proteins from the RPE were resolved and quantified by two-dimensional (2-D) gel electrophoresis. Proteins exhibiting significant expression changes at different disease stages were identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry. 2-D and semiquantitative one dimensional (1-D) Western blot analyses were used to determine whether changes identified by the proteomic analysis were specific for a protein subpopulation or representative of the entire protein population. RESULTS. Proteins were identified from several critical pathways that changed at early and late disease stages, indicating potential causal mechanisms and secondary consequences of AMD, respectively. Proteins involved in protecting from stress-induced protein unfolding and aggregation, mitochondrial traf-ficking and refolding, and regulating apoptosis changed early in the disease process. Late-stage changes occurred in proteins that regulate retinoic acid and regeneration of the rhodopsin chromophore. CONCLUSIONS. These results provide the first direct evidence of AMD stage-specific changes in human RPE protein expression and provide a basis for functional investigation of AMD that may ultimately suggest new therapeutic strategies.