Assessment of the Association of Periodontitis and Diabetes Mellitus with Alzheimer’s Disease in a Mouse Model

The purpose of the present study was to investigate how periodontitis and diabetes mellitus (DM) are associated with Alzheimer’s disease (AD) through microRNA (miRNA) using AD model mice. The experimental period was 8 weeks. Twenty-four male knock-in mice (B6-AppNL-G-F/NL-G-F/J) were divided into four groups: control group fed a normal diet (C), DM group fed a high-fat/sucrose diet (DM), periodontitis (P) group, and DM + periodontitis (DM+P) group. Memory performance was compared using the Y-maze test. Next-generation sequencing was performed on brain samples, and fold changes in miRNA expression were calculated by comparing the DM+P and C groups. Integrated miRNA–mRNA analysis identified putative miRNA-targeted mRNAs, and protein expression of the top candidate gene was assessed. Memory function in the DM+P group was significantly lower than in the C group. Among the seven mRNAs identified by the integrated analysis, Neurod1 showed the greatest decrease in expression, and it was predicted to be regulated by miR-693-3p. Neurod1 protein expression in the hippocampus was significantly lower in the DM+P group than the C group. Our results suggest that the combined exposure to periodontitis and DM was associated with AD-like pathological changes and identified the miR-693-3p/Neurod1 pair as a candidate regulatory axis.