A novel mechanism of synaptic and cognitive impairments mediated via microRNA-30b in Alzheimer's disease

Background: It is widely accepted that cognitive and memory deficits in Alzheimer's disease (AD) primarily result from synaptic failure. However, the mechanisms that underlie synaptic and cognitive dysfunction remain unclear. Methods: We utilized molecular biology techniques, electrophysiological recordings, fluorescence in situ hybridization (FISH), immuno-and Golgi-staining, chromatin immunoprecipitation (CHIP); lentivirus (LV)-based microRNA overexpression and 'sponging', and behavioral tests to assess upregulated miR-30b causing synaptic and cognitive declines in APP transgenic (TG) mice. Findings: We provide evidence that expression of miR-30b, which targets molecules important for maintaining synaptic integrity, including ephrin type-B receptor 2 (ephB2), sirtuin1 (sirt1), and glutamate ionotropic receptor AMPA type subunit 2 (GluA2), is robustly upregulated in the brains of both AD patients and APP transgenic (TG) mice, an animal model of AD, while expression of its targets is significantly downregulated. Overexpression of miR-30b in the hippocampus of normal wild-type (WT) mice impairs synaptic and cognitive functions, mimicking those seen in TG mice. Conversely, knockdown of endogenousmiR-30b in TG mice prevents synaptic and cognitive decline. We further observed that expression of miR-30b is upregulated by proinflammatory cytokines and A beta 42 through NF-kappa B signaling. Interpretation: Our results provide a previously undefined mechanism by which unregulated miR-30b causes synaptic and cognitive dysfunction in AD, suggesting that reversal of dysregulated miR-30b in the brain may prevent or slow cognitive declines in AD. Fund: This work was supported by National Institutes of Health grants R01NS076815, R01MH113535, R01AG058621, P30GM103340 Pilot Project, and by the LSUHSC School of Medicine Research Enhancement Program grant (to C.C.). (c) 2018 The Authors. Published by Elsevier B.V.