Deletion of autophagy inducer RB1CC1 results in degeneration of the retinal pigment epithelium

Autophagy regulates cellular homeostasis and response to environmental stress. Within the retinal pigment epithelium (RPE) of the eye, the level of autophagy can change with both age and disease. The purpose of this study is to determine the relationship between reduced autophagy and age-related degeneration of the RPE. The gene encoding RB1CC1/FIP200 (RB1-inducible coiled-coil 1), a protein essential for induction of autophagy, was selectively knocked out in the RPE by crossing Best1-Cre mice with mice in which the Rb1cc1 gene was flanked with Lox-P sites (Rb1cc1(flox/flox)). Ex vivo and in vivo analyses, including western blot, immunohistochemistry, transmission electron microscopy, fundus photography, optical coherence tomography, fluorescein angiography, and electroretinography were performed to assess the structure and function of the retina as a function of age. Deletion of Rb1cc1 resulted in multiple autophagy defects within the RPE including decreased conversion of LC3-I to LC3-II, accumulation of autophagy-targeted precursors, and increased numbers of mitochondria. Age-dependent degeneration of the RPE occurred, with formation of atrophic patches, subretinal migration of activated microglial cells, subRPE deposition of inflammatory and oxidatively damaged proteins, subretinal drusenoid deposits, and occasional foci of choroidal neovascularization. There was secondary loss of photoreceptors overlying the degenerated RPE and reduction in the electroretinogram. These observations are consistent with a critical role of autophagy in the maintenance of normal homeostasis in the aging RPE, and indicate that disruption of autophagy leads to retinal phenotypes associated with age-related degeneration.

Dysregulated autophagy in the RPE is associated with increased susceptibility to oxidative stress and AMD

Autophagic dysregulation has been suggested in a broad range of neurodegenerative diseases including age-related macular degeneration (AMD). To test whether the autophagy pathway plays a critical role to protect retinal pigmented epithelial (RPE) cells against oxidative stress, we exposed ARPE-19 and primary cultured human RPE cells to both acute (3 and 24 h) and chronic (14 d) oxidative stress and monitored autophagy by western blot, PCR, and autophagosome counts in the presence or absence of autophagy modulators. Acute oxidative stress led to a marked increase in autophagy in the RPE, whereas autophagy was reduced under chronic oxidative stress. Upregulation of autophagy by rapamycin decreased oxidative stress-induced generation of reactive oxygen species (ROS), whereas inhibition of autophagy by 3-methyladenine (3-MA) or by knockdown of ATG7 or BECN1 increased ROS generation, exacerbated oxidative stress-induced reduction of mitochondrial activity, reduced cell viability, and increased lipofuscin. Examination of control human donor specimens and mice demonstrated an age-related increase in autophagosome numbers and expression of autophagy proteins. However, autophagy proteins, autophagosomes, and autophagy flux were significantly reduced in tissue from human donor AMD eyes and 2 animal models of AMD. In conclusion, our data confirm that autophagy plays an important role in protection of the RPE against oxidative stress and lipofuscin accumulation and that impairment of autophagy is likely to exacerbate oxidative stress and contribute to the pathogenesis of AMD.