Figure 2.
Microglia ingest more synapses in Alzheimer’s disease compared with midlife and aged controls
(A) Confocal images of immunostaining with orthogonal views (left) and three-dimensional reconstructions of stacks (right) of midlife control, aged control, and Alzheimer’s disease showing ingestion of synapsin 1 (Syn1, green) by microglia (CD68, magenta) in human brain sections. Aβ plaques and nuclei are counterstained with Thioflavin S and DAPI, respectively, shown in blue. Only ingested Syn1 is shown in 3D Imaris reconstructions. Representative images are from BA17. Scale bars represent 5 μm.
(B) Quantification of synapsin 1 ingested by CD68-positive microglia showed significantly increased levels in AD compared with midlife (Tukey corrected post hoc test t = 3.56, p = 0.0024) and aged controls (t = 3.09, p = 0.0096). No statistical difference was seen between midlife controls and aged control (t = 0.93, p = 0.625). Data here are pooled from both BA17 and BA20/21, sample size corrected by mixed effected linear model.
(C) Statistically significant increase of synapsin 1 ingestion by microglia near Aβ plaques in AD cases (ANOVA F[1,881.57] = 20.74, p = 6.01 × 10−6).
(D) The APOE4 genotype was associated with an increase in synapsin 1 colocalization inside CD68-positive microglia (F[1,42.86] = 5.84, p = 0.02).
(E) BA17 (primary visual cortex) was associated with higher levels of synapsin 1 colocalization inside CD68-positive microglia compared with BA20/21 (inferior temporal cortex) (F[1,1973.76] = 67.82, p = 3.42 × 10−16). Statistical comparisons were made using post hoc Tukey test or ANOVA after linear mixed effects model on Tukey transformed data with case as a random effect and disease, brain region, APOE4 status, gender, and age as fixed effects. Untransformed data are presented in graphs (B)–(E). Males are represented by circles and females by triangles. Biological replicates were human brain donors: n = 10 midlife controls, 17 aged controls, AD 22 cases.