Abstract
Background: Alzheimer's disease (AD) is the most common cause of dementia; its main pathological features are neurofibrillary tangles (NFTs) consisting of hyperphosphorylated microtubule-associated protein (Tau) in the cell and extracellular beta-amyloid protein (Aβ)-based senile plaques (SP). The ubiquitin-proteasome system (UPS) is the main pathway for protein degradation in cells. Proteasome malfunction exists in AD patients and may promote the progression of the disease. USP14 is a deubiquitinating enzyme associated with the 19S proteasome. Functional inhibition of USP14 was shown to enhance proteasome proteolytic function, but no reported study has investigated the impact of genetic inhibition of USP14 on AD.Methods: Mice with heterozygous knockout of the Usp14 gene (USP14+/-) were generated and cross-bred with the APP/PS1 transgenic mice, the resultant offspring littermates were subjected to basal survival and growth analyses, and comparison of AD-like pathologies as detected with biochemical and histopathological methods and of cognitive function as assessed with the Morris water maze tests. Results:USP14 mRNA and protein levels in USP14+/- mice were decreased by ~50% compared with USP14+/+mice. The increases of total, K48 or K63 linked ubiquitinated proteins in APP/PS1 mouse brains were abolished in APP/PS1::USP14+/- mice. The increases in Aβ deposition and AD-associated phosphorylated Tau, senile plagues and neurofibrillary tangles, as well as spatial learning and memory decline induced by APP/PS1 were significantly attenuated in APP/PS1 mice. Conclusions: This study demonstrates that global knocking down USP14 protein expression by 50% is tolerable by mice and exhibits marked protection against AD-like pathologies in a widely used AD mouse model, favoring the exploration of moderate inhibition ofUSP14 as a potentially novel and viable therapy against AD.
The ubiquitin-proteasome system in Alzheimer's disease