July 2018
Volume 59, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2018
Localization of ABCA4 in the Retinal Pigment Epithelium and its implications for Stargardt Disease
Author Affiliations & Notes
  • Tamara Lee Lenis
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Sze Yin Ng
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Jane Hu
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Zhichun Jiang
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Marcia Lloyd
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Nicholas Esposito
    Department of Biological Sciences, Fordham University, Los Angeles, California, United States
  • Dean Bok
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Silvia C Finnemann
    Department of Biological Sciences, Fordham University, Los Angeles, California, United States
  • Gabriel H Travis
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Roxana A. Radu
    Stein Eye Institute, UCLA, Los Angeles, California, United States
    Department of Ophthalmology, David Geffen School of Medicine at UCLA, Los Angeles, California, United States
  • Footnotes
    Commercial Relationships   Tamara Lenis, None; Sze Yin Ng, None; Jane Hu, None; Zhichun Jiang, None; Marcia Lloyd, None; Nicholas Esposito, None; Dean Bok, None; Silvia Finnemann, None; Gabriel Travis, None; Roxana Radu, None
  • Footnotes
    Support  R01 EY025002 (RAR), R01 EY11713 (GHT), R01 NIH 26215 (SCF), R01 EY000331 Stein Eye Institute Core Grant for Vision Research; Unrestricted Grant from Research to Prevent Blindness, Inc. (RPB, New York); BrightFocus Foundation (RAR); Macula Vision Research Foundation (RAR, DB); Gerald Oppenheimer Family Foundation Center for the Prevention of Eye Disease (RAR)
Investigative Ophthalmology & Visual Science July 2018, Vol.59, 4502. doi:
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    • Get Citation

      Tamara Lee Lenis, Sze Yin Ng, Jane Hu, Zhichun Jiang, Marcia Lloyd, Nicholas Esposito, Dean Bok, Silvia C Finnemann, Gabriel H Travis, Roxana A. Radu; Localization of ABCA4 in the Retinal Pigment Epithelium and its implications for Stargardt Disease. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4502.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Recessive Stargardt disease (STGD1) is an inherited macular degeneration caused by mutations in ABCA4, a membrane protein thought to be exclusively expressed in photoreceptor (PR) outer-segment (OS) discs. Loss of ABCA4 results in retinal pigment epithelium (RPE) deposition of bisretinoid-lipofuscin and late-onset PR degeneration. Preliminary studies showed that ABCA4 is additionally expressed in the RPE. Here, we sought to further investigate the expression and function of ABCA4 in RPE cells.

Methods : ABCA4 transcript was identified by RNAscope in situ hybridization (ISH) assay in human donor eyes, in human fetal (hf) RPE cultured cells, and in wild-type (WT) and Abca4-/- mouse eyes. ABCA4 protein was evaluated, by immunoblotting, immuno-electron microscopy (EM), and immunofluorescence (IF) in WT and Abca4-/- mice, in Mertk-/- mice which do not phagocytose PR-OS, and in hfRPE cells which never contact PRs. ABCA4 co-localization with endo-lysosomal markers was assessed by IF in mouse and human RPE sections. ABCA4 was functionally evaluated in a transgenic (Tg) mouse line that expresses ABCA4 in the RPE, but not in retina. Ocular bisretinoids were measured by HPLC. Retinal morphology, lipofuscin and autofluorescence were assessed by light, electron, and confocal microscopy, respectively.

Results : By ISH of human and WT mouse eyes, ABCA4 mRNA was clearly visualized in both PRs and RPE. ABCA4 mRNA was also detected in hfRPE cells. Notably, ABCA4 mRNA was absent in Abca4-/- eyes. ABCA4 expression was confirmed in Mertk-/- RPE and hfRPE cells by IF. Immuno-EM detection of ABCA4 in human RPE showed an intracellular membrane distribution. By IF, ABCA4 appears to co-localize with endo-lysosomal structures in human and murine RPE. Compared to Abca4-/- mice, Tg mice with only RPE-expressed ABCA4 (on the Abca4-/- background) had less RPE bisretinoid-lipofuscin and greater PR preservation, suggesting an active role for ABCA4 in the RPE.

Conclusions : ABCA4 is expressed in the RPE within endo-lysosomal membranes, where it may serve an important role in protecting PRs. Our studies suggest that in the RPE, ABCA4 performs a similar function as in PR-OS: to facilitate recycling of retinaldehydes released from rhodopsin proteolysis, and to prevent the buildup of toxic bisretinoids. This finding introduces a novel, cell-autonomous pathway in the pathophysiology of STGD1 with significant therapeutic implications.

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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