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Eugenia Poliakov, Natalia Strunnikova, Bianca Martinez, Toral Parikh, Brian Brooks, T. Michael Redmond; Long-term multiple A2E treatment leads to melanization of ARPE19 cells. Invest. Ophthalmol. Vis. Sci. 2013;54(15):331.
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Incomplete degradation of outer segments (OS) by retinal pigment epithelium (RPE) leads to the accumulation of storage bodies containing autofluorescent lipofuscin, which consists of a mixture of lipids and the bisretinoid pyridinium salt A2E and its oxidation products, and other bisretinoids. A2E and its oxidation products are major components of lipofuscin and its accumulation is implicated in pathology of several retinal degeneration diseases (Vitelliform Macular Dystrophy, Stargardt macular dystrophy and Age-Related Macular Degeneration (AMD)). However, A2E accumulates in RPE during normal aging. In this study we developed a cell model to determine the coping mechanisms of RPE cells to A2E accumulation.
To distinguish between pathologic and normal response of RPE to A2E accumulation we used fully differentiated ARPE19 cells treated with low micromolar amounts of A2E over the course of several weeks. Then the A2E-treated ARPE19 cells were challenged with OS and compared with non-treated cells for lysosomal functions, lysosomal pH, degree of phagocytosis and melanization.
We found that fully differentiated ARPE19 cells uptake, accumulate and partially degrade A2E under dim light conditions. A2E is stored in lysosomes and leads to an increase in lysosomal pH. Upon challenge with ROS, A2E-treated ARPE-19 cells show an increase in melanin pigment. In addition, the activities of the lysosomal enzymes cathepsin D and lysosomal acid phosphatase are impaired in A2E treated cells. We found that these cells compensate by producing a melanolysosome fraction and therefore do not become impaired in OS phagocytosis.
We have developed a new ARPE19 cell model where melanization was elicited as a response to chronic accumulation of RPE’s natural toxin A2E. We found that although A2E treatment leads to lysosomal alkanization and lysosomal impairment, as has been previously reported, ARPE19 cells compensate by increased production of a special type of lysosomes - melanolysosomes.
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