mTOR-mediated dedifferentiation of the retinal pigment epithelium initiates photoreceptor degeneration in mice
Chen Zhao, … , Matthew M. LaVail, Douglas Vollrath
Chen Zhao, … , Matthew M. LaVail, Douglas Vollrath
Published December 6, 2010
Citation Information: J Clin Invest. 2011;121(1):369-383. https://doi.org/10.1172/JCI44303.
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Research Article Ophthalmology

mTOR-mediated dedifferentiation of the retinal pigment epithelium initiates photoreceptor degeneration in mice

Abstract

Retinal pigment epithelial (RPE) cell dysfunction plays a central role in various retinal degenerative diseases, but knowledge is limited regarding the pathways responsible for adult RPE stress responses in vivo. RPE mitochondrial dysfunction has been implicated in the pathogenesis of several forms of retinal degeneration. Here we have shown that postnatal ablation of RPE mitochondrial oxidative phosphorylation in mice triggers gradual epithelium dedifferentiation, typified by reduction of RPE-characteristic proteins and cellular hypertrophy. The electrical response of the retina to light decreased and photoreceptors eventually degenerated. Abnormal RPE cell behavior was associated with increased glycolysis and activation of, and dependence upon, the hepatocyte growth factor/met proto-oncogene pathway. RPE dedifferentiation and hypertrophy arose through stimulation of the AKT/mammalian target of rapamycin (AKT/mTOR) pathway. Administration of an oxidant to wild-type mice also caused RPE dedifferentiation and mTOR activation. Importantly, treatment with the mTOR inhibitor rapamycin blunted key aspects of dedifferentiation and preserved photoreceptor function for both insults. These results reveal an in vivo response of the mature RPE to diverse stressors that prolongs RPE cell survival at the expense of epithelial attributes and photoreceptor function. Our findings provide a rationale for mTOR pathway inhibition as a therapeutic strategy for retinal degenerative diseases involving RPE stress.

Authors

Chen Zhao, Douglas Yasumura, Xiyan Li, Michael Matthes, Marcia Lloyd, Gregory Nielsen, Kelly Ahern, Michael Snyder, Dean Bok, Joshua L. Dunaief, Matthew M. LaVail, Douglas Vollrath

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Figure 2

RPE dedifferentiation and hypertrophy in RPEΔMT mice.

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RPE dedifferentiation and hypertrophy in RPEΔMT mice. (A and B) RPE flat...
(A and B) RPE flat mounts stained for cre (red) and phalloidin (green) show (B) loss of cuboidal appearance in cre-reactive cells in RPEΔMT mice at 16 weeks of age. (C–F) Light microscopy reveals thickened RPE cells (D) in a 14-week-old RPEΔMT mouse. (E and F) Numerous RPE cells of RPEΔMT mice have progressively increased thickness and apical location of nuclei (arrows). (G) At 35 weeks of age, both maximum and minimum RPE thickness are significantly different between RPEΔMT mice and controls. (H–K) Electron microscopy in 22-week-old RPEΔMT mice (I and K) shows a thickened RPE cell, with apical location of nucleus, (I, arrow denotes nucleus, OS stands for outer segments) loss of microvilli (MV), (H) arrows denote MV, and (K) absent basal infoldings (BI). (L) Loss of a series of RPE-characteristic markers, with the exception of MITF, in RPE cells from RPEΔMT mice (R) versus control (C) is detected by immunoblot, and (M) confirmed by quantification of protein. (N) The percentage of BrdU reactive RPE cells at 2 days PI is significantly increased in RPEΔMT mice at 18 weeks and older. (O) However, RPEΔMT mice have a gradual loss of RPE cells over time. (P and Q) BrdU staining shows cre-expressing (P, arrows denote; insets are pictures of the same cell with higher magnification) and cre-negative RPE cells (Q, arrows) that have multiple BrdU-reactive nuclei within 1 cell boundary (denoted by ZO1) at 3 months PI. Original magnification, ×400. Error bars in G, M, N, and O represent SD from triplicates. Scale bars: 25 μm (A–F); 2 μm (H–K). *P < 0.05; §P < 0.01; #P < 0.001.