Comparative proteomics reveals silver nanoparticles alter fatty acid metabolism and amyloid beta clearance for neuronal apoptosis in a triple cell coculture model of the blood-brain barrier

Silver nanoparticles (AgNPs) enter the central nervous system through the blood-brain barrier (BBB). AgNP exposure canincrease amyloid beta (Aβ) deposition in neuronal cells to potentially induce Alzheimer's disease (AD) progression.However, the mechanism through which AgNPs alter BBB permeability in endothelial cells and subsequently lead toAD progression remains unclear. This study investigated whether AgNPs disrupt the tight junction proteins of brainendothelial cells, and alter the proteomic metabolismof neuronal cells underlying AD progression in a triple cell coculturemodel constructed using mouse brain endothelial (bEnd.3) cells, mouse brain astrocytes (ALT), and mouse neuroblastomaneuro-2a (N2a) cells. The results showed that AgNPs accumulated in ALT and N2a cells because of the disruption of tightjunction proteins, claudin-5 and ZO-1, in bEnd.3 cells. The proteomic profiling of N2a cells after AgNP exposure identified298 differentially expressed proteins related to fatty acid metabolism. Particularly, AgNP-induced palmitic acid productionwas observed in N2a cells, which might promote Aβ generation. Moreover, AgNP exposure increased the protein expressionof amyloid precursor protein (APP) and Ab generation-related secretases, PSEN1, PSEN2, and b-site APP cleaving enzyme forAPP cleavage in ALT and N2a cells, stimulated Aβ40 and Aβ42 secretion in the culture medium, and attenuated the geneexpression of Aβ clearance-related receptors, P-gp and LRP-1, in bEnd.3 cells. Increased Aβ might further aggregate on theneuronal cell surface to enhance the secretion of inflammatory cytokines, MCP-1 and IL-6, thus inducing apoptosis in N2acells. This study suggested that AgNP exposure might cause Aβ deposition and inflammation for subsequent neuronal cellapoptosis to potentially induce AD progression.