Mechanism of walnut-derived antioxidant pepetides for improving learning and memory dysfunction

Walnut residues, the byproducts of walnut oil extraction, are often regarded as waste or used as low-value feed, fertilizer, etc. However, walnut residues are rich in proteins (40-55%) and have a multitude of physiological and pharmacological properties that provide a wide range of potential applications for the generation of bioactive peptides. In this thesis work, the neuroprotective effect of walnut-derived peptides on learning and memory dysfunction was addressed. Firstly, CHAPTER 1 displays a general knowledge of the nut-derived peptides and learning and memory dysfunction, especially focus on 1) the preparation, purification, and identification methods used to study of nut-derived peptides; 2) the test of antioxidant activity in vitro and in vivo; 3) the structure-activity relationship (SAR) of antioxidant peptides; 4) the biological capacity of walnut-derived peptides; 5) the mechanisms of learning and memory. Secondly, CHAPTER 2 obtained 3 novel walnut peptides (TWLPLPR, YVLLPSPK, and KVPPLLY) with high antioxidant activity through chemical experiment ORAC, combined with PC12 cell model in vitro. Studies demonstrated that TWLPLPR, YVLLPSPK, and KVPPLLY can maintain integrity after oral administration, and then be absorbed and utilized by the body through imaging detection of mice in vivo. Then, CHAPTER 3 & 4 investigated the mechanism of walnut- derived peptides on improving learning and memory dysfunction. Specially, CHAPTER 3 revealed that walnut-derived peptides (TWLPLPR, YVLLPSPK and KVPPLLY) could ameliorate learning and memory impairment through suppressed oxidative stress via Akt/mTOR signaling pathway in Aβ25-35-induced oxidative stress in PC12 cells. Furthermore, CHAPTER 4 proved that walnut-derived peptide YVLLPSPK could mediate PINK1 to promote mitophagy and improve neuron impairment via NRF2/KEAP1/HO-1 pathway in scopolamine-induced aging mice and HT- 22 cells induced by H2O2 with the presence of inhibitor ML385. Finally, CHAPTER 5 explored the effect of walnut-derived peptide YVLLPSPK on DNA methylation. 4D-label free quantitative proteomics of mouse hippocampus showed that differential proteins were enriched in complement and coagulation cascades, oxidative phosphorylation, riboflavin metabolism, ribosome, pyrimidine metabolism and drug metabolism-other enzymes with administrated YVLLPSPK. Most importantly, the results indicated that YVLLPSPK potentially modulated DNA methylation in embryonic and neural precursor cells in creating new methylation patterns in LPS-induced THP-1 cells. This study aimed to develop new functional food, provided theoretical and methodological guidance for improving the mechanism of memory ability and its application in industrial production.