Dihydromyricetin improves social isolation-induced cognitive impairments and astrocytic changes in mice

Abstract

Social isolation induces stress, anxiety, and mild cognitive impairment that could progress towards irreversible brain damage. A probable player in the mechanism of social isolation-induced anxiety is astrocytes, specialized glial cells that support proper brain function. Using a social isolation mouse model, we observed worsened cognitive and memory abilities with reductions of Object Recognition Index (ORI) in novel object recognition test and Recognition Index (RI) in novel context recognition test. Social isolation also increased astrocyte density, reduced astrocyte size with shorter branches, and reduced morphological complexity in the hippocampus. Dihydromyricetin, a flavonoid that we previously demonstrated to have anxiolytic properties, improved memory/cognition and restored astrocyte plasticity in these mice. Our study indicates astrocytic involvement in social isolation-induced cognitive impairment as well as anxiety and suggest dihydromyricetin as an early-stage intervention against anxiety, cognitive impairment, and potential permanent brain damage.

Figure 1

Cognition-related behaviors. (A) Novel object recognition. ORI = object recognition index. (B) Novel context recognition. RI = recognition index. G2 + Veh2: 2-week grouped plus 2-week grouped with vehicle treatment; G2 + D2: 2-week grouped plus 2-week grouped with DHM treatment; Iso2 + Veh2: 2-week SoIso plus 2-week SoIso with vehicle treatment; Iso2 + D2: 2-week SoIso plus 2-week SoIso with DHM administration. Bars represent mean ± SEM. Two-way ANOVA followed by multiple comparisons with Holm-Sidak method. *, P ≤ 0.05. †, P ≤ 0.05 vs Iso2 + D2.

Figure 2

Astrocyte density and size in the dentate gyrus. (A) 20X Airyscan super resolution images of single or near-single astrocytes in the dentate gyrus of mice: blue = DAPI, nucleus; red = GFAP, astrocytes. Scale bar = 200 µm. (B) Number of astrocytes per sample normalized to DG area. Data shown as mean + SEM. Two-way ANOVA with multiple comparisons, Holm-Sidak method. Astrocyte size in µm² (C) and µm³ (D). Data shown as box plot, where center line is the median, limits are the interquartile range (IQR), and whiskers are the minimum and maximum. Kruskal–Wallis one-way ANOVA on ranks with multiple comparisons, Dunn’s method. For all graphs, N = 3–4 mice analyzed per group, one section per mouse. G2 + Veh2: 2-week grouped plus 2-week grouped with vehicle treatment; G2 + D2: 2-week grouped plus 2-week grouped with DHM administration; Iso2 + Veh2: 2-week SoIso plus 2-week SoIso with vehicle treatment; Iso2 + D2: 2-week SoIso plus 2-week SoIso with DHM administration. *, P ≤ 0.05; †, P ≤ 0.05 vs Iso2 + D2; ‡, P ≤ 0.05 vs G2 + D2.

Figure 3

Astrocyte morphology in the dentate gyrus. (A) Upper: two-dimensional images of the astrocytes analyzed for morphology. Bottom: area of the DG containing the selected astrocyte. Blue = DAPI, nucleus; red = GFAP, astrocytes. Scale bar = 20 µm. (B) Three-dimensional images of astrocyte morphology. Scale bar = 20 µm. (C) Binary representation of astrocytes used for morphological complexity. Scale bar = 20 µm. (D) Quantification of morphological complexity (Sholl analysis). Two-way ANOVA with multiple comparisons, Holm-Sidak method. G2 + Veh2: 2-week grouped plus 2-week grouped with vehicle treatment; G2 + D2: 2-week grouped plus 2-week grouped with DHM administration; Iso2 + Veh2: 2-week SoIso plus 2-week SoIso with vehicle treatment; Iso2 + D2: 2-week SoIso plus 2-week SoIso with DHM administration. 5 astrocytes analyzed per mouse. N = 4 mice per group. *, P ≤ 0.05.