mTOR-mediated dedifferentiation of the retinal pigment epithelium initiates photoreceptor degeneration in mice
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
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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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 4

Photoreceptor degeneration correlates with RPE dedifferentiation in albino RPEΔMT mice.

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Photoreceptor degeneration correlates with RPE dedifferentiation in albi...
(A) Light micrographs of the posterior retina show a progressive regional loss of photoreceptors reflected by outer nuclear layer (ONL) thickness (black box) and correlating with RPE dedifferentiation (red boxes). Original magnification, ×630. (B) Global assessment of outer nuclear layer thickness in 36-week-old RPEΔMT mice (n = 3) and controls (n = 3). Sup., superior retina; ONH, optic nerve head; Inf., inferior retina. (C) Quantification of mean outer nuclear layer thickness and cones shows a significant loss of rod and cone photoreceptors in 36-week-old RPEΔMT mice (n = 3) compared with that in controls (n = 3, mean value of controls is defined as 100%). (D–G) Immunostaining images from the posterior ventral retinas of 22-week-old mice. Original magnification, ×200. (D and E) Costaining for lectin-PNA (green) and RPE65 (red) demonstrates (E) a striking loss of cones in RPEΔMT mice, which correlates with diminished RPE65 protein. (F and G) Immunostaining for M-opsin (green) and cre (red) shows abnormalities of red/green opsin-expressing cones, which correlate with cre-expresssing cells (G). (H) Electroretinograph demonstrates significantly reduced rod responses (scotopic a-wave and b-wave) and cone responses (photopic b-wave) in 36-week-old RPEΔMT mice (n = 3), compared with those in controls (n = 5). Verticle bars clarify the 2 groups of values used for statistical comparison. Data in H represent mean ± SEM. *P < 0.05; §P < 0.01; #P < 0.001.