Changes in cognitive ability and serum microRNA levels during aging in mice.

Mild cognitive impairment (MCI) is an early stage that can result in dementia. MCI can be reversed, and diagnosis at an early stage is crucial to control the progression to dementia. Dementia is currently diagnosed based on interviews and screening tests; however, novel biomarkers must be identified to allow early MCI detection. Therefore, the present study aimed to identify novel biomarkers in the form of blood microRNAs (miRNAs/miRs) for the diagnosis of MCI or early dementia. Blood samples were collected from C57BL/6NJcl male mice at four time points, including 4-week-old (4W), 8-week-old (8W), 36-week-old (36W) and 58-week-old (58W), and serum was isolated. Body weight and blood total cholesterol levels were increased, and blood alkaline phosphatase was decreased with aging. The 8W mice exhibited the highest cognitive ability in the Morris water maze test, whereas the 58W mice demonstrated decreased cognitive ability. The serum RNA concentrations of the 4W, 8W, 36W and 58W mice demonstrated no significant differences. Furthermore, small RNA levels were detected in the serum of all mice. miRNA microarray analysis revealed a >1.5-fold increase in the serum expression of two miRNAs (miR-21a-5p and miR-92a-3p) and a >1.5-fold decrease in the serum expression of two other miRNAs (miR-6769b-5p and miR-709) in 58W mice compared with those in 8W mice. In the future, we aim to further analyze aged mice to discover novel MCI biomarkers.