Dicer Dysregulation Induces Cytotoxic Alu Rna Accumulation In Age-related Macular Degeneration

Abstract

 

Purpose:

 

Geographic atrophy (GA) is an important cause of vision loss in AMD. We sought to determine whether accumulation of double stranded RNA (dsRNA) in retinal pigmented epithelium (RPE) triggers cell death leading to GA, and whether perturbations in miRNA biogenesis trigger such accumulation.

 

Methods:

 

In an unbiased fashion, we isolated, amplified, and cloned dsRNA species from dsRNA-enriched preparations of RPE of normal and GA human donor eyes. We quantified levels of genes involved in miRNA biogenesis (Dicer, Drosha, Dgcr8, Ago1-4) in human GA RPE and analyzed the fundus of mice whose RPE was deficient in these genes. We tested the effect of GA-specific dsRNA on human RPE cells and in mouse eyes.

 

Results:

 

We immunolocalized dsRNA in human GA but not normal RPE. This dsRNA was identified as a family of Alu transcripts that were 40-fold higher in abundance in human GA RPE. We found a dramatic reduction of Dicer mRNA and protein in human GA RPE whereas other miRNA biogenesis enzymes were not differentially regulated. Conditional Dicer ablation induced accumulation of Alu-like elements and RPE degeneration in mice. Mice deficient in other miRNA biogenesis enzymes had normal RPE. Alu RNA induced RPE cell death in mice and in human cell culture but did not do so when cleaved by Dicer. Pharmacological targeting of Alu-like RNA rescue Dicer ablation-induced RPE degeneration in mice.

 

Conclusions:

 

Our findings reveal a novel miRNA-independent cell survival function for Dicer via cleavage of retrotransposon transcripts, introduce the new concept that Alu RNA can directly cause human pathology, and identify potential therapeutic targets for GA.

 

Keywords: age-related macular degeneration • gene/expression • signal transduction