Recombinant Walnut-Derived Peptide Ameliorates d-Galactose-Induced Cognitive Deficits

Cognitive decline associated with aging and neuroinflammation has been linked to gut microbiota dysbiosis and systemic inflammation, potentially mediated through the gut-brain axis. Bioactive peptides have shown potential as therapeutic candidates for neurodegenerative and neuroinflammatory disorders. While the walnut-derived peptide EVSGPGYSPN (EV-10) has demonstrated cognitive benefits, the therapeutic potential of its recombinant form, recombinant walnut-derived peptide (rWDP), expressed and purified from an Escherichia coli system, remains to be fully characterized. In this study, behavioral assessment using the Morris water maze revealed that rWDP significantly improved spatial learning and memory in d-galactose-induced aging mice. rWDP treatment was associated with changes in gut microbiota composition, including an increase in Akkermansia muciniphila and improvements in colon mucosal integrity. Systemic inflammation appeared to be attenuated, with reduced levels of IFN-γ and VCAM-1 and normalization of G-CSF and CXCL1 levels. In the brain, rWDP was associated with reduced microglial activation and preservation of hippocampal neuronal architecture. Notably, decreased p21 expression was observed in the hippocampus and cortex. In vitro, rWDP suppressed LPS-induced nitric oxide production and attenuated the expression of proinflammatory genes in BV2 microglial cells. Metabolomic analysis suggested a restoration of neurotransmitter homeostasis following rWDP treatment, with increased levels of 5-hydroxyindoleacetic acid, kynurenine, and glutathione observed. Overall, rWDP may alleviate cognitive deficits through multifaceted pathways involving the gut-brain axis and immune modulation, warranting further mechanistic investigation.