Upregulation of miR-181 decreases c-Fos and SIRT-1 in the hippocampus of 3xTg-AD mice.

MicroRNAs are a group of small RNAs that regulate diverse cellular processes including neuronal function. Recent studies have shown that dysregulation of specific microRNAs is critically involved in the development of Alzheimer's disease (AD). Most of these reports have focused on microRNAs implicated in alterations of amyloid-β and tau. However, studies exploring the relation between microRNAs dysregulation in AD and synaptic plasticity are scarce despite the well-known involvement of microRNAs in synaptic plasticity. Since impairments in synaptic plasticity and neuronal loss are two important features displayed in AD patients, it is feasible to hypothesize that alterations in plasticity-related microRNAs underlie AD progression. Here, levels of a small number of microRNAs implicated in normal neuronal function and/or plasticity were examined in an AD model. Twelve-month old 3xTg-AD mice with plaques and tangles presented a significant upregulation of miR-181 in the hippocampus compared to age-matched wild type mice. Increased miR-181 was not detected in pre-pathological 3xTg-AD mice. Analysis of predicted targets of miR-181 identified c-Fos and SIRT-1, proteins critically involved in memory formation. Both c-Fos and SIRT-1 levels were significantly decreased in the ventral hippocampus of twelve-month old 3xTg-AD mice. Overexpression of miR-181 in SH-SY5Y cells significantly decreased c-Fos and SIRT-1, strongly suggesting that miR-181 directly regulates the expression of these two proteins. These findings indicate a connection between miR-181 and proteins involve in synaptic plasticity and memory processing in a transgenic mouse model of AD. Our results suggest that microRNAs involved in synaptic plasticity might be an important factor that contributes to AD neuropathology.