β-Amyloid impairs Proteasome structure and function. Proteasome activation mitigates amyloid induced toxicity and cognitive deficits
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Background
Impaired proteasome activity is a robust and reproducible feature in Alzheimer’s disease (AD) patients and animal models. Although amyloid beta (Aβ) may inhibit proteasomes, it is unclear if this reflects direct structural interference or indirect toxicity. The proteasome controls a myriad of critical neuronal processes with its disruption potentially driving downstream AD pathology.
Methods
We examined the direct impact of distinct Aβ forms on proteasome structure, dynamics, and function by evaluating enzyme activity and morphology by atomic force microscopy (AFM) and native-gel electrophoresis. To prevent Aβ-induced impairments in vitro and in AD animal models, we used allosteric proteasome activating peptidomimetics. We characterized their interactions with proteasome by AI enhanced in silico docking.
Results
Toxic soluble Aβ42 oligomers selectively inhibit 20S and 26S proteasome activity, while monomeric and fibrillar forms and Aβ40 show minimal inhibitory effects. Morphometric analysis of AFM images suggests Aβ42 oligomers bind laterally to the 20S proteasomes, and impair proteasome dynamics by disabling gate opening, critical for catalytic activity. Oligomer-decorated proteasomes are locked in catalytically inert cycling between closed and intermediate gate conformations. Oligomeric Aβ42 also induces disassembly of the 26S complex, increasing content of free 20S cores. Importantly, we show proteasome dysfunction induced by oligomeric Aβ42 is both preventable and reversible by employing an allosteric proteasome activator TAT-DEN, promoting gate opening and restoring enzymatic activity with the full-cycle of conformational transitions in oligomers-treated proteasomes. In cellular and animal models, restoring proteasome function via TAT-DEN mitigated Aβ-induced cell death, spatial learning/memory deficits, and survival impairments, even under conditions of pre-established Aβ deficits.
Conclusions
Oligomeric Aβ42 decorates the lateral sides of the 20S proteasome restricting cycling between conformations and blocking gate opening. It also reduces the pool of 26S proteasomes necessary for the ubiquitin-dependent protein degradation. We demonstrate proteasome dysfunction can be prevented and reversed by proteasome agonist that lowers 20S affinity to oligomers and promotes allosteric gate opening. We show that proteasome activation with TAT-DEN prevents cognitive deficits in AD animal models. This suggests proteasome dysfunction is a key downstream target in AD pathology and supports proteasome activation as a therapeutic strategy to restore neuronal function in AD.
