miRNA Alterations Elicit Pathways Involved in Memory Decline and Synaptic Function in the Hippocampus of Aged Tg4-42 Mice

Abstract

The transcriptome of non-coding RNA (ncRNA) species is increasingly focused in Alzheimer's disease (AD) research. NcRNAs comprise, among others, transfer RNAs, long non-coding RNAs and microRNAs (miRs), each with their own specific biological function. We used smallRNASeq to assess miR expression in the hippocampus of young (3 month old) and aged (8 month old) Tg4-42 mice, a model system for sporadic AD, as well as age-matched wildtype controls. Tg4-42 mice express N-truncated Aβ_4-42, develop age-related neuron loss, reduced neurogenesis and behavioral deficits. Our results do not only confirm known miR-AD associations in Tg4-42 mice, but more importantly pinpoint 22 additional miRs associated to the disease. Twenty-five miRs were differentially expressed in both aged Tg4-42 and aged wildtype mice while eight miRs were differentially expressed only in aged wildtype mice, and 33 only in aged Tg4-42 mice. No significant alteration in the miRNome was detected in young mice, which indicates that the changes observed in aged mice are down-stream effects of Aβ-induced pathology in the Tg4-42 mouse model for AD. Targets of those miRs were predicted using miRWalk. For miRs that were differentially expressed only in the Tg4-42 model, 128 targets could be identified, whereas 18 genes were targeted by miRs only differentially expressed in wildtype mice and 85 genes were targeted by miRs differentially expressed in both mouse models. Genes targeted by differentially expressed miRs in the Tg4-42 model were enriched for negative regulation of long-term synaptic potentiation, learning or memory, regulation of trans-synaptic signaling and modulation of chemical synaptic transmission obtained. This untargeted miR sequencing approach supports previous reports on the Tg4-42 mice as a valuable model for AD. Furthermore, it revealed miRs involved in AD, which can serve as biomarkers or therapeutic targets.

Keywords: Alzheimer; NGS; Tg4-42; miRNA transcriptome; miRNA-Seq; transgenic mouse model.

FIGURE 1

Genotyp-specific expression of miRs with significantly altered expression level during aging. Volcano plot comparison of the fold changes and values of miR expression in WT (A) and Tg4-42 (B) mice. The vertical lines correspond to 2-fold up and down, respectively, and the horizontal line represents a p-value of 0.05. (C) miRs in hippocampus of young (3 month old) and aged (8 month old) Tg4-42 and WT mice. Total number of significantly altered miR expression levels between 3 and 8 months of age n = 58; 8 in WT, 33 in Tg4-42 and 25 in both WT and Tg4-42 mice.

FIGURE 2

Box plots of significantly altered miRs in hippocampus of young (3 month old; 3m) and aged (8 month old; 8m) Tg4-42 and WT.

FIGURE 3

GO annotation analysis of predicted miR targets in Tg4-42 (A) and WT mice (B). Number of genes enriched and –log10 (P-value) for each term are displayed for the top 17 GO terms, if applicable, in molecular function, cellular component and biological process.