Fig 2: Schematic illustration showing the preparation and underlying mechanism of MNPs@FMN in memory protection. A) Preparation process of biomimetic nanocarriers (MNPs@FMN). B) Schematic diagram showing the proposed mechanism of MNPs@FMN crossing the BBB to become recruited by microglia. Briefly, MNPs@FMN penetrates the BBB via binding cell surface receptors on the brain endothelial cells. Afterward, MNPs@FMN accumulates in microglia, and released FMN inhibits RFK via KMT2B, while RFK promotes the TNFR1/NF-?B signaling pathway. Ultimately, MNPs@FMN restores cognitive function by suppressing the inflammatory response.

Fig 3: Hippocampal Rfk knockdown attenuates LPS-induced cognitive impairment and inflammatory response. A) Experimental design for Rfk knockdown and FMN administration in the LPS-induced mouse model. B) Travel path tracings of mice in the Y-maze test. C) Spontaneous alterations of LPS mice treated with LV-Rfk shRNA or FMN in the Y-maze. D) Representative path tracings in each quadrant during the probe trial. E-H) The escape latency over a five-day training course (panel E), latency in the probe test (panel F), time spent in the target zone (panel G), and number of target crossings (panel H) in the Morris water maze n = 7–8. I-K) Representative blots and quantification of RFK, TNFR1, p-NF-?B, NF-?B, p-I?Ba and I?Ba expression levels in the hippocampus of LPS mice treated with LV-Rfk shRNA or FMN n = 3 per group. L) Immunofluorescence staining and quantification of Iba1-positive cells in the hippocampus of LPS mice treated with LV-Rfk shRNA or FMN. Scale bars, 40 µm. Magnified images and skeletal diagrams of Iba1-positive cells are shown to the right of each staining image. Scale bars, 10 µm n = 8–9. M,N) The mRNA expression levels of Il-1b, Il-6, Tnfa, Tmem119, Cx3cr1, Csf1r, and P2ry12 in the hippocampus of LPS mice treated with LV-Rfk shRNA or FMN n = 3 per group. Results are expressed as mean ± SEM. ** p < 0.01, *p < 0.05 versus WT; ## p < 0.01, # p < 0.05 versus LPS; && p < 0.01, & p < 0.05 versus LPS + Rfk shRNA. Statistical significance was determined using one-way ANOVA and Tukey's tests for post hoc comparisons.

Fig 4: RNA-seq analysis of MNPs@FMN treatment in the LPS-induced mouse model. A,B) Representative blots and quantification showing KMT2B and RFK expression levels in the hippocampi of LPS mice treated with NPs@FMN, MNPs, or MNPs@FMN, n = 4 per group. C) Schematic illustration of RNA-seq. D) Volcano plot showing the DEGs between the LPS and WT groups. E) KEGG pathways enriched by downregulated DEGs in the LPS compared with WT group. F) Downregulated DEGs in the LPS groups that are enriched in the “Alzheimer's disease” KEGG pathway. G) Venn diagram showing 38 DEGs that were downregulated by LPS and upregulated by MNPs@FMN. H) KEGG pathways are enriched by these 38 DEGs. I,J) KEGG and GO pathways enriched by upregulated DEGs in LPS + MNPs@FMN compared with LPS. K) Hierarchical clustering of the 38 LPS + MNPs@FMN reversed DEGs. L) The mRNA expression levels of Uqcrb, Cox8b, and Calml4 in the hippocampi of the WT, LPS, and LPS + MNPs@FMN groups. n = 3 per group. M–O) The mRNA expression levels of Uqcrb, Cox8b, and Calml4 upon treatment with different concentrations of FMN in LPS-treated BV2 cells n = 3 per group. P) The mRNA expression levels of Uqcrb, Cox8b, and Calml4 upon FMN and RFK plasmid treatment in LPS-treated BV2 cells. n = 3 per group. Results are expressed as mean ± SEM. ** p < 0.01, *p < 0.05 versus WT or Control; ## p < 0.01, # p < 0.05 versus LPS-MNPs@FMN or LPS. Statistical significance was determined using one-way ANOVA and Tukey's tests for post hoc comparisons.

Fig 5: FMN supplementation suppresses LPS-induced inflammation in BV2 cells and primary microglia. A) Schematic model of the riboflavin biosynthesis metabolic pathway. RFK, riboflavin kinase; FMN, flavin mononucleotide; FAD, flavin adenine dinucleotide. B-D) The supernatant levels of IL-1ß, IL-6, and TNF-a in LPS-treated BV2 cell cultures with different doses of FMN or FAD n = 3 per group. E–G) Representative blots and quantification of RFK, TNFR1, p-NF-?B, NF-?B, p-I?Ba, and I?Ba expression levels in LPS-treated BV2 cells with 200 µM FMN. n = 3 per group. H,I) Immunofluorescence staining and quantification of TNFR1 with the membrane dye DIL in LPS-treated BV2 cells with FMN n = 6–8. Scale bars, 20 µm. Magnified images are shown in the right columns. Scale bars, 5 µm. (J) The mRNA expression levels of Il-1b, Il-6, and Tnfa in LPS-treated primary microglia with 200 µM FMN n = 3 per group. K-M) Representative blots and quantification of RFK, TNFR1, p-NF-?B, NF-?B, p-I?Ba and I?Ba expression levels in LPS-treated primary microglia with 200 µM FMN n = 3 per group. N,O) Immunofluorescence staining and quantification of RFK with Iba1 in LPS-treated primary microglia with 200 µM FMN n = 7–9. Scale bars, 40 µm. Magnified images are shown in the right columns. Scale bars, 13 µm. Results are expressed as mean ± SEM. ** p < 0.01, *p < 0.05 versus Ctrl; ## p < 0.01, # p < 0.05 versus LPS. Statistical significance was determined using one-way ANOVA and Tukey's tests for post hoc comparisons.