Nicotinamide Mononucleotide Ameliorates Alzheimer’s Disease Symptoms through Modulation of Gut Microbiota in APP/PS1 Mice

Research Hypothesis:
NMN supplementation can alleviate AD symptoms in APP/PS1 mice by modulating gut microbiota and its metabolites, influencing brain health through the gut-brain axis.
Data Collection and Methodology:
APP/PS1 (AD) and C57BL/6 (NC) mice were divided into four groups: ADNMN, ADPBS, NCNMN, and NCPBS. Experiments included microbiota analysis (DNA extraction, sequencing, MENs, PCA, LEfSe), metabolite analysis (HPLC-MS/MS), pathological analysis (Alcian Blue staining, immunohistochemistry), ROS detection, RNA sequencing for GO and KEGG enrichment, Morris water maze test for spatial memory, ATP and mitochondrial complex I activity measurement, and Western blotting for protein expression.
Notable Findings:
1. NMN restored intestinal flora structure and composition in AD mice, increasing MEN complexity and resilience. PCA showed similarity to normal controls, and LEfSe identified reduced bacteria (Catellicoccus, Lactobacillus_aviarius, and uncultured_bacterium) levels in ADNMN.
2. After 16 weeks of NMN treatment, most metabolite changes in AD mice reversed, with Acylcarnitine 14:1, Corticosterone, and Taurine showing significant improvement. Spearman correlation analysis revealed that Bacteroides, uncultured-bacterium-c-Gammaproteobacteria, and Campylobacter were key genera affecting metabolite differences between ADNMN and ADPBS groups. In ADNMN, Bacteroides and Enterorhabdus correlated positively with LysoPI 18:0, LysoPE 12:0, and DHA methyl ester, while in ADPBS, Gemella correlated positively with LysoPG 16:0, Cer (AP) 33:2, LysoPG 18:1, and LysoPI 20:3.
3.NMN altered metabolic pathways in AD mice, promoting nervous system development and reducing abnormal immune activation. Key microbial taxa were identified, with metabolites impacting AD development.
4. NMN increased goblet cell counts in both AD and healthy mice, enhancing the mucus barrier to protect against microbial invasion. RNA-Seq analysis showed elevated expression of mucus-related genes (Clca1 and Fcgbp) in the ADNMN group. NMN also partially reversed downregulated genes in AD mice, upregulating immune and cell adhesion pathways while downregulating oxidative stress and lipid metabolism genes. In vivo imaging showed NMN reduces colon ROS, lessening oxidative stress damage in AD mice.
5. In the MWM test, ADPBS mice had worse performance than NCPBS mice during training (days 1-5). NMN improved metrics for both groups. On day 6, ADPBS mice showed cognitive impairments, but NMN helped restore their spatial memory.
6.NMN mitigated brain inflammation and oxidative stress in AD mice through pathway regulation, reducing lipids, azelaic acid metabolism, and key acids.
7. NMN restored ATP levels and mitochondrial complex I activity in AD mice's hippocampus. It also enhanced synaptic density and reversed synaptic dysfunction by increasing presynaptic and postsynaptic protein expression.