Cited by 347Autophagy in Disease and TherapyRetinal Development and DisordersRetinal Diseases and Treatments

The DOI matches its Crossref record; 69 of the 69 references it cites were found in a registry or an index; none of the 42 sources its claims cite is checked for support yet.

Noncanonical Autophagy Promotes the Visual Cycle

Open access

Abstract

SUMMARY Phagocytosis and degradation of photoreceptor outer segments (POS) by the retinal pigment epithelium (RPE) is fundamental to vision. Autophagy is also responsible for bulk degradation of cellular components but its role in POS degradation is not well understood. We report that the morning burst of RPE phagocytosis coincided with the enzymatic conversion of autophagy protein LC3 to its lipidated form. LC3 then associated with single membrane phagosomes containing engulfed POS in an Atg5 dependent manner that required Beclin1 but not the autophagy pre-initiation complex. The importance of this process was verified in mice with Atg5-deficient RPE cells that showed evidence of disrupted lysosomal processing. These mice also exhibited decreased photoreceptor responses to light stimuli and decreased chromophore levels that were restored with exogenous retinoid supplementation. These results establish that the interplay of phagocytosis and autophagy within the RPE are required for both POS degradation and the maintenance of retinoid levels to support vision.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

In the retinal pigment epithelium (RPE), phagocytosed photoreceptor outer segments (POS) recruit LC3 through a noncanonical autophagy pathway (LAP) that requires Atg5 and Beclin1 but not the autophagy pre-initiation complex. Atg5-deficient RPE mice show disrupted POS processing, reduced chromophore levels, and decreased visual function that is rescued by exogenous 9-cis retinal.

Key findings

  • RPE LC3 lipidation is cyclical: LC3-II was most abundant in RPE at 7:00 AM (1 h after lights on) and much less at 7:00 PM; Atg5ΔRPE mice lost detectable LC3-II and GFP-LC3 punctae.
  • LC3 associated with single-membrane phagosomes containing engulfed POS in an Atg5- and Beclin1-dependent manner, but silencing Fip200, Ulk1, or Atg13 did not prevent POS-induced LC3 association or LC3-II formation.
  • Atg5ΔRPE mice at 16 weeks had significantly decreased rod and cone ERG responses to brighter light stimuli, without significant outer nuclear layer nuclei loss by 24 weeks or up to 1.5 years and without significant cone photoreceptor reduction.
  • At 20 weeks, Atg5ΔRPE mice had significantly reduced 11-cis, all-trans, and 13-cis RAL compared with littermate controls, while all-trans retinyl-esters were not significantly different; intraperitoneal 9-cis RAL (0.25 mg/animal) restored rod and cone function after 24 h dark adaptation.

Methods

  • Conditional Atg5 deletion in RPE was generated by crossing BEST1(VMD2)-cre mice with Atg5flox/flox mice; Ulk1−/− and Ulk1+/− mice were also used, with littermate controls.
  • Rat RPE-J cells were differentiated with retinoic acid, fed bovine POS, and analyzed by confocal microscopy, time-lapse imaging, TEM, siRNA knockdowns, and phagocytosis assays.
  • Retinoid analysis pooled 2 eyecups from 20-week Atg5ΔRPE (n=4) and Atg5f/f (n=5) mice; ERG and other experiments used at least 3 mice per group and were repeated at least 3 times; statistics used two-tailed unpaired Student’s t test with P<0.05 and standard error bars.

Limitations

  • The paper states that the exact relationship between Atg5 function and the visual cycle is not completely understood and that further studies are required to uncover all molecular details of the coupling between phagocytosis and the visual cycle.
  • Evident from the text: the conclusions rely on mouse RPE-specific Atg5 deletion and the rat RPE-J cell line, with no human data; the mechanism by which LAP supports retinoid recovery and chromophore synthesis is not fully resolved.
  • Evident from the text: despite significant ERG deficits, no significant photoreceptor loss was detected, so the functional defect appears subtle and may involve processes beyond photoreceptor survival.

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Integrity signals

Registry

Crossref · 10.1016/j.cell.2013.06.012

Cites

69 of 69 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Verification

Claims the paper makes

0 of 42 cited sources checked · 0 supported · 0 flagged

Show all 72 claims

  • It may state two separate claims as one. 23
  • The quote only partly states this claim. 1
  • Probably not a substantial claim. 12
31 of 31
  • The paper relies on this without support.

    9-cis RAL is a functional analog of the visual chromophore 11-cis RAL.

    “Mice then received an intraperitoneal injection of 0.25 mg/animal of the 9-cis RAL, a functional analog of the visual chromophore 11-cis RAL.”
  • The paper relies on this without support.

    The RPE takes up 11-cis RAL bound to opsin and probably other forms of retinoids from the photoreceptors through daily phagocytosis.

    “Although the RPE can also take up bis-retinoids (Finnemann et al., 2002; Katz et al., 1987), 11-cis RAL bound to opsin, and probably other forms of retinoids from the photoreceptors through daily phagocytosis, little is known about how retinoid products recovered by this route affect photoreceptor function and/or survival.”
  • The paper relies on this without support.

    The relationship of autophagy to POS phagocytosis and degradation is currently unknown.

    “The relationship of autophagy to POS phagocytosis and degradation is currently unknown.”
  • The paper relies on this without support.

    9-cis RAL can substitute for 11-cis RAL to restore visual function in Atg5-deficient RPE.

    “the loss of visual function was restored by exogenous supplementation with the chromophore analog, 9-cis RAL.”
  • The paper relies on this without support.

    The visual cycle requires 11-cis RAL for phototransduction.

    “The visual cycle begins following the absorption of light by visual pigments containing 11-cis RAL, which isomerizes to the all-trans configuration.”
  • The paper relies on this without support.

    Phagocytosis of POS tips supports photoreceptor disk renewal.

    “Phagocytosis of the POS tips (left), which are shed in the early morning, supports photoreceptor disk renewal.”
6 of 6

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Metadata

Authors
Kim, J.-Y., Zhao, H., Martinez, J., Doggett, T. A., Kolesnikov, A. V., Tang, P. H., Ablonczy, Z., Chan, C.-C., Zhou, Z., Green, D. R., & Ferguson, T. A.
Affiliations
  • Washington University in St. Louis (US)
  • St. Jude Children's Research Hospital (US)
  • Medical University of South Carolina (US)
  • National Institutes of Health (US)
Corresponding author
  • Green, Douglas R.
  • Ferguson, Thomas A.
Venue
Cell
Publisher
Elsevier BV
Published
2013-07
Volume
154
Issue
2
Pages
365-376
ISSN
0092-8674 (ISSN-L)
OpenAlex
W2053670812
Cited by
347
References
68
Citations by year
2026: 11 · 2025: 18 · 2024: 26 · 2023: 30 · 2022: 30 · 2021: 33 · 2020: 39 · 2019: 24 · 2018: 30 · 2017: 21 · 2016: 22 · 2015: 27 · 2014: 33 · 2013: 3
FWCI
20.64
Type
journal article
Language
en
Update notices
erratum (2013-10-24)
Open access
Locations
  • Cell (publishedVersion)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (acceptedVersion)
  • PubMed Central (acceptedVersion)
Funders
National Institutes of Health (EY015570, AI40646, EY02687)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Cell Biology › Autophagy in Disease and Therapy
  • Health Sciences › Medicine › Ophthalmology › Retinal Development and Disorders
  • Health Sciences › Medicine › Ophthalmology › Retinal Diseases and Treatments
Keywords
non-canonical autophagy, visual cycle, retinal pigment epithelium, phagocytosis, LC3 lipidation, ATG5, Beclin-1, lysosomal processing, chromophores, retinal degeneration
MeSH terms
Beclin-1, Autophagy-Related Protein 5, Animals, Autophagy, Cattle, Lysosomes, Microtubule-Associated Proteins, Phagocytosis, Phagosomes, Retinoids, Vision, Ocular, Photoreceptor Cells, Vertebrate, Apoptosis Regulatory Proteins, Mice, Retinal Pigment Epithelium

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