Purpose:
DICER is critical for miRNA biogenesis. We recently identified that loss of DICER expression leads to accumulation of cytotoxic Alu repeat RNAs in the eyes of individuals with geographic atrophy, which causes blindness in millions. We sought to determine whether miRNA expression deficits contribute to death of retinal pigment epithelial (RPE) cells, whose loss is a critical step in geographic atrophy pathogenesis.
Methods:
The effect of DICER knockdown (by antisense or Cre/loxP ablation) on cell viability and miRNA expression was studied in human and mouse RPE cells with/without simultaneous knockdown of Alu or B1/B2 (mouse equivalent of Alu) RNAs. Viability of cells expressing a mutant DICER with impaired miRNA processing was studied. The effect of ablating other genes required for miRNA biogenesis/function was assessed in mouse retina.
Results:
DICER knockdown reduced cell viability and global miRNA expression in human and mouse RPE cells. Simultaneous knockdown of Alu or B1/B2 RNAs rescued cell death without rescuing miRNA expression. Expression of a miRNA-impaired DICER mutant did not lead to increased Alu RNA accumulation and did not prevent Alu-induced cytotoxicity. Conditional or germline ablation of Drosha, Ago1-4, Dgcr8, or Tarbp2 did not induce RPE degeneration in mice.
Conclusions:
RPE cell death and retinal degeneration induced by loss of DICER expression are independent of impaired miRNA expression.
Keywords: age-related macular degeneration • retinal pigment epithelium • apoptosis/cell death