Identification of walnut-derived peptide WNP-8 as a potential therapeutic agent and SIRT2 as a biomarker for cognitive deficiency: A label-free LC-MS/MS proteomics study.

Aberrant autophagic flux and epigenetic mechanisms are involved in the development of neurodegenerative diseases. However, limited studies have been conducted on the relationship between the histone acetylation-particularly sirtuin 2 (SIRT2)-and autophagy in cognitive deficiency. We investigated the effects of a walnut-derived peptide (WNP-8) on SIRT2, synaptic plasticity, and autophagy and the involvement of SIRT2 in learning and memory. Using four-dimensional label-free quantitative proteomics, we analyzed hippocampal tissue from mice treated or not treated with WNP-8 and exposed to scopolamine and identified 71 significantly differentially expressed proteins (DEPs). A pathway enrichment analysis showed that the DEPs were mostly located in the cytoplasm and involved in the negative regulation of cell proliferation and nicotinate and nicotinamide metabolism, which are associated with SIRT2. Western blotting and immunofluorescence analyses demonstrated that pretreatment with WNP-8 significantly modulated the expression of synaptic and autophagic proteins in scopolamine-treated cells in both in vivo and in vitro models (p < .05). Notably, WNP-8 significantly reversed the level and morphology of synaptic plasticity and autophagic flux in PC12 cells that overexpressed SIRT2 (p < .05). Together, our results provide evidence of a link between SIRT2, autophagy, and synaptic plasticity in neurons and novel insights into a potential predictive biomarker that could be used to prevent and delay Alzheimer's disease.