The Proteasome Function Reporter GFPu Accumulates in Young Brains of the APPswe/PS1dE9 Alzheimer’s Disease Mouse Model
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Alzheimer’s disease (AD), the most common cause of dementia, is neuropathologically characterized by accumulation of insoluble fibrous inclusions in the brain in the form of intracellular neurofibrillary tangles and extracellular senile plaques. Perturbation of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the pathogenesis of AD. However, studies on UPS functionality with various methods and AD models have achieved non-conclusive results. To get further insight into UPS functionality in AD, we have crossed a well-documented APPswe/PS1dE9 AD mouse model with a UPS functionality reporter, GFPu, mouse expressing green fluorescence protein (GFP) fused to a constitutive degradation signal (CL-1) that facilitates its rapid turnover in conditions of a normal UPS. Our western blot results indicate that GFPu reporter protein was accumulated in the cortex and hippocampus, but not striatum in the APPswe/PS1dE9 AD mouse model at 4 weeks of age, which is confirmed by fluorescence microscopy and elevated levels of p53, an endogenous UPS substrate. In accordance with this, the levels of ubiquitinated proteins were elevated in the AD mouse model. These results suggest that UPS is either impaired or functionally insufficient in specific brain regions in the APPswe/PS1dE9 AD mouse model at a very young age, long before senile plaque formation and the onset of memory loss. These observations may shed new light on the pathogenesis of AD.
KeywordsAlzheimer disease Ubiquitin-proteasome system Proteasome function reporter GFPu Protein degradation Ubiquitinated proteins
Green fluorescence reporter for UPS functionality
Amyloid precursor protein
We would like to thank Dr. Robin Miskimins for critical reading of the manuscript, Dr. Fran Day at the Imaging Core of the University of South Dakota for help in fluorescence microscopy, and Mr. Suleman said at the histopathology core for assistance in preparation of brain sections. This work was supported by Start-up Funds from the University of South Dakota (HW).
Conflict of interest
The authors have declared no conflicts of interest.
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