Mitochondrial proteomics of the retinal pigment epithelium at progressive stages of age-related macular degeneration

PURPOSE. Age-related macular degeneration (AMD) is the leading cause of vision loss in individuals over the age of 65. Histopathological changes become evident in the retinal pigment epithelium (RPE), a monolayer that provides metabolic support for the overlying photoreceptors, even at the earliest stages of AMD that precede vision loss. In a previous global RPE proteome analysis, changes were identified in the content of several mitochondrial proteins associated with AMD. In this study, the subproteome of mitochondria isolated from human donor RPE graded with the Minnesota Grading System (MGS) was analyzed. METHODS. Human donor eye bank eyes were categorized into one of four progressive stages (MGS 1-4) based on the clinical features of AMD. After dissection of the RPE, mitochondrial proteins were isolated and separated by two-dimensional gel electrophoresis based on their charge and mass. Protein spot densities were compared between the four MGS stages. Peptides from spots that changed significantly with MGS stage were extracted and analyzed by using mass spectrometry to identify the protein. RESULTS. Western blot analyses verified that mitochondria were consistently enriched between MGS stages. The densities of eight spots increased or decreased significantly as a function of MGS stage. These spots were identified as the α-, β-, and δ-ATP synthase subunits, subunit VIb of the cytochrome c oxidase complex, mitofilin, mtHsp70, and the mitochondrial translation factor Tu. CONCLUSIONS. The results are consistent with the hypothesis that mitochondrial dysfunction is associated with AMD and further suggest specific pathophysiological mechanisms involving altered mitochondrial translation, import of nuclear-encoded proteins, and ATP synthase activity.