Alu RNA Induced Rpe Cell Apoptosis Triggered By DICER Dysregulation In Geographic Atrophy

Purpose: Geographic atrophy (GA), an advanced form of age-related macular degeneration that causes blindness in millions of people worldwide, results from death of retinal pigmented epithelium (RPE) cells. We recently identified that human eyes with GA exhibit reduced levels of DICER and accumulation of cytotoxic Alu repeat RNAs. We sought to determine the relationship between these observations in the context of RPE cell viability.Methods: The effect of DICER knockdown (by antisense or Cre/LoxP ablation) on Alu RNA accumulation and on cell viability was assayed. The ability of DICER to degrade Alu was studied. The administration of Alu RNA on cell viability was assayed in human and in mouse RPE.Results: DICER knockdown in human RPE induces accumulation of Alu RNA and cell death over time. Similarly, Ad-Cre infection of RPE cells isolated from Dicerf/f mice results in accumulation of B1 and B2 (Alu-like elements) repeat RNAs. Recombinant DICER degrades Alu RNA, and overexpression of DICER prevents accumulation of Alu RNA induced by DICER knockdown in human RPE cells. Alu RNA administration induces human RPE cell cytotoxicity via caspase-3 activation, and DICER overexpression protects RPE cells from Alu RNA-induced cytotoxicity. Human or mouse RPE cell death triggered by DICER knockdown is inhibited by antisense oligonucleotides targeting Alu/B1/B2 RNA.Conclusions: These data reveal a novel cell survival function of DICER mediated via its degradation of retrotransposon transcripts and introduce the concept that Alu can cause human pathology via direct RNA toxicity.