Abstract
Background Oxidative stress critically underlies the neurodegenerative pathogenesis of Alzheimer's disease (AD). Depletion of Dicer1, an endoribonuclease central to microRNA maturation, also leads to neurodegeneration. We therefore hypothesized that altered Dicer1 expression may play a role in AD. Results Using immunoblotting and quantitative real-time PCR, we found that Dicer1 protein and mRNA levels were reduced in the hippocampi of animals of the AD mouse model APPswe/PSEN1dE9 compared with littermate controls. SiRNA-meditated Dicer1 knockdown induced oxidative stress, reduced mitochondrial intermembrane potential, and increased apoptosis in cultured neurons. Aβ42 exposure decreased Dicer1 and also down-regulated the oxidative stress–induced transcriptional regulator nuclear factor erythroid 2-related factor 2 (Nrf2). Conversely, Nrf2 overexpression increased Dicer1 mRNA and protein levels and reverted the Aβ42-induced Dicer1 reduction. To further investigate Dicer1 regulation, we cloned Dicer1 promoter variants harboring the Nrf2-binding site, the antioxidant response elements (ARE), into a luciferase reporter and found that simultaneous transfection of Nrf2-expressing plasmid increased luciferase expression from these promoter constructs. ChIP assays indicated that Nrf2 directly interacted with the ARE motifs in the Dicer1 promoter. Furthermore, Dicer1 overexpression in cultured neurons reverted Aβ42-induced neurite deficits. Of note, injection of Dicer1-expressing adenovirus into the hippocampus of the AD mice significantly improved spatial learning. Conclusions These findings indicate that Dicer1 expression is reduced in the AD brain and that chronic Aβ exposure decreases Dicer1 levels in neurons via Nrf2–ARE signaling. Our results uncover a significant role for Dicer1 in AD and highlight that Dicer1 expression responds to oxidative stress in the brain.
Brain Dicer1 Is Down-Regulated in a Mouse Model of Alzheimer’s Disease Via Aβ42-Induced Repression of Nuclear Factor Erythroid 2-Related Factor 2
