The microrna-mediated regulation of proteins implicated in the pathogenesis of Alzheimer's Disease

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder characterized by the post-mortem deposition of amyloid-beta (Aβ) containing neuritic plaques and tau-loaded tangles. According to the amyloid hypothesis, the generation of Aβ via the cleavage of Aβ precursor protein (APP) by β-APP site-cleaving enzyme 1 (BACE1) is a causative step in the development of AD. Therefore, targeting the production and/or clearance of Aβ peptide (by Aβ-degrading enzymes such as Neprilysin) would help understand the disorder as well as serves as therapeutic potential to treat the disorder. MicroRNA are small, noncoding RNA capable of modulating protein expression by primarily targeting their 3’UTR. Therefore, identifying miRNA which target APP, BACE1 and Neprilysin (NEP) would elucidate the complicated regulatory mechanisms involved in protein turnover and provide novel drug targets. We identified miR-20b as a modulator of APP and soluble Aβ. We also identified the target site for miR-20b’s binding on the APP 3’UTR. Further, miR-20b exerts influence on neuronal morphology, likely due to its APP reduction. We also identified miR-298 as a dual regulator of APP and BACE1 and confirmed miR-298’s targeting of both 3’UTRs. We also showed that miR-298 overexpression reduced levels of both soluble Aβ40 and Aβ42 peptides. Additionally, we identified two SNPs in proximity to the MIR298 gene, which are associated with AD-related biomarkers. Based on these results, we showed miR-298 targets a specific isoform of tau by putatively binding a non-canonical target site on the MAPT 3’UTR. Finally, the insertion of the NEP 3’UTR into a reporter vector increases reporter expression; suggesting regulatory elements targeting the 3’UTR. We subsequently identified miR-216 as reducing NEP 3’UTR-mediated luciferase activity. We also measured levels of NEP protein in various mammalian tissue – such as rodent and human fetal tissue, and subsequently showed measurable Aβ levels in correlation with NEP expression. Therefore, herein, we have identified miRNA involved in the regulation of proteins implicated in the pathogenesis of AD.