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Camille Dejos, Heather Capel, Sharee Kuny, Yves Sauve; Dysregulation of degradation pathways in the retinal pigment epithelium of a Stargardt-like maculopathy mouse model. Invest. Ophthalmol. Vis. Sci. 2017;58(8):586.
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© ARVO (1962-2015); The Authors (2016-present)
Mechanisms triggering photoreceptor degeneration in Stargardt-like juvenile maculopathy (STGD3) still elude us. Studies in this model demonstrate defects in outer segment degradation by the underlying retinal pigment epithelial cells (RPE), prior to photoreceptor death. Following phagocytosis, phagosomes retain an apical localization and still contain undigested materials. RPE cells demonstrate vacuolization adjacent to their junction membranes. We investigated whether regulation of autophagy and expression of CLEAR genes by the transcription factor TFEB might be impaired in STGD3.
STGD3 mice (TG1-2), expressing the human mutated ELOVL4 protein in photoreceptor cells, and wild type littermates were culled at 3 months of age, before or 2 hours after light onset. Following enucleation, one eye was used to perform TFEB immunofluorescence on a RPE flatmount. Total RNA was extracted from the other eyecup (after removal of the retina) to study expression of CLEAR genes using quantitative RT-PCR.
In WT RPE flatmounts, before light onset, TFEB labeling was punctate and distributed evenly outside of the nuclei, reflecting a lysosomal association. Two hours after light exposure (at the peak of outer segment phagocytosis), TFEB labelling was preferentially associated with the nucleus, denoting activation of this transcription factor. In TG, TFEB labeling also followed a lysosomal distribution, but in addition, a nuclear distribution was evident in a subset of RPE cells, prior to light onset. TFEB distribution within RPE cells remained unchanged two hours after light exposure in TG. In addition, punctate TFEB labeling delineated the hexagonal mosaic formed by the RPE monolayer.
Our findings support that photoreceptor loss in STGD3 involves dysregulation of outer segment phagocytosis by the underlying RPE cells, with defects in autophagy and CLEAR gene activation by the transcription factor TFEB.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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