S14G-humanin inhibits Aβ1-42 fibril formation, disaggregates preformed fibrils, and protects against Aβ-induced cytotoxicity in vitro.

The aggregation of soluble amyloid-beta (Aβ) peptide into oligomers/fibrils is one of the key pathological features in Alzheimer's disease (AD). The Aβ aggregates are considered to play a pivotal role in the pathogenesis of AD. Therefore, inhibiting Aβ aggregation and destabilizing preformed Aβ fibrils would be an attractive therapeutic target for prevention and treatment of AD. S14G-humanin (HNG), a synthetic derivative of Humanin (HN), has been shown to be a strong neuroprotective agent against various AD-related insults. Recent studies have shown that HNG can significantly improve cognitive deficits and reduce insoluble Aβ levels as well as amyloid plaque burden without affecting amyloid precursor protein processing and Aβ production in transgenic AD models. However, the potential mechanisms by which HNG reduces Aβ-related pathology in vivo remain obscure. In the present study, we found that HNG could significantly inhibit monomeric Aβ1-42 aggregation into fibrils and destabilize preformed Aβ1-42 fibrils in a concentration-dependent manner by Thioflavin T fluorescence assay. In transmission electron microscope study, we observed that HNG was effective in inhibiting Aβ1-42 fibril formation and disrupting preformed Aβ1-42 fibrils, exhibiting various types of amorphous aggregates without identifiable Aβ fibrils. Furthermore, HNG-treated monomeric or fibrillar Aβ1-42 was found to significantly reduce Aβ1-42-mediated cytotoxic effects on PC12 cells in a dose-dependent manner by MTT assay. Collectively, our results demonstrate for the first time that HNG not only inhibits Aβ1-42 fibril formation but also disaggregates preformed Aβ1-42 fibrils, which provides the novel evidence that HNG may have anti-Aβ aggregation and fibrillogenesis, and fibril-destabilizing properties. Together with previous studies, we concluded that HNG may have promising therapeutic potential as a multitarget agent for the prevention and/or treatment of AD.