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Mitra Farnoodian-Tedrick, Praveen Joseph Susaimanickam, Vladimir Khristov, Qin Wan, Karla Y Barbosa-Sabanero, Sheldon S Miller, Kapil Bharti; ABCA4 in Human Retinal Pigment Epithelium: a New Link to Stargardt Pathogenesis. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1985.
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ABCA4 is a member of the ABCA subfamily of ATP binding cassette (ABC) transporters involved in transfer of a N-retinylidene-phosphatidylethanolamine and all-trans-retinal from the lumenal to the cytosolic side of photoreceptor outer segment discs. ABCA4 mutations have been associated with different retinal degeneration diseases including Stargardt disease, cone-rod degeneration, age macular degeneration (AMD) and retinitis pigmentosa. We utilized cell surface capturing technology (CSC) to selectively identify apical and basal surface markers of polarized surface proteome of retinal pigment epithelium (RPE). Our analysis identified number of previously unreported proteins present on RPE membrane surface including ABCA4. To understand the role ABCA4 in RPE and its contribution to Stargardt disease, we developed Stargardt patient derived iPS cell-derived RPE as an in vitro disease model.
Fibroblasts from Stargardt patient and healthy donor were reprogrammed into induced pluripotent stem cells (iPSCs) using Yamanaka factors. Fully characterized iPSCs were differentiated into RPE using a developmentally guided protocol. iPSC-derived RPE were cultured on semi-permeable membranes for 6 weeks to obtain a functionally mature and polarized monolayer tissue. Cells were evaluated for RPE-specific functions including ability to digest photoreceptors outer segments, electrophysiological response and the junctional integrity. To determine the human pathogenetic sequence, lipofuscin accumulation was evaluated using photoreceptor outer segment regimen. We are generating two additional isogenic iPSC lines including CRISPR/Cas9 based ABCA4 knockout and ABCA4-ΔNBD2-GFP to confirm phenotypes observed in Stargardt patient derived iPS cell-RPE.
Stargardt patient derived iPS cell-RPE represented altered electrophysiological response and abnormal structural properties compared to the control derived iPS cell-RPE. Cells also exhibited reduced ability to digest photoreceptor outer segments, and decreased trans epithelial resistance. Stargardt patient derived iPS cell-RPE exhibited lipofuscin accumulation while exposed to photoreceptor outer segment regimen.
Our results indicate that ABCA4 plays an important role in RPE function and mutations in the ABCA4 lead to the altered function of RPE cells contributing to Stargardt disease pathogenesis.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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