Figure 3.

Astrocytes and microglia ingestion of synapses in the absence of neuronal neurite ingestion

(A) Staining presynaptic terminals with synaptophysin, neuronal neurites with MAP2, astrocytes with GFAP, and microglia with P2Y12 reveals synaptic ingestion by astrocytes (cyan boxes, arrowheads) and microglia (magenta boxes, arrows) in the absence of MAP2 staining in control and AD brain. In AD, MAP2 positive neuronal protein can also be observed in astrocytes (cyan boxes, dotted ovals) and microglia (magenta boxes, dotted ovals). Large panels are maximum intensity projections of confocal image stacks. Insets are single sections to demonstrate colocalization. Scale bars represent 20 μm in large panels, 5 μm in insets.

(B) Quantification of synaptophysin (SyO) ingested by GFAP-positive astrocytes showed significantly increased levels in AD compared with aged controls (ANOVA after linear mixed effects model with cohort, gender, and age as fixed effects and case as a random effect F[1,13.02] = 17.38, p = 0.001).

(C) Quantification of SyO ingested by P2Y12-positive microglia showed significantly increased levels in AD compared with aged controls (ANOVA after linear mixed effects model F[1,13.007] = 4.8, p = 0.047).

(D) Quantification of SyO and MAP2 ingested by GFAP-positive astrocytes showed no significant differences between AD and aged controls (ANOVA after linear mixed effects model F[1,13.01] = 2.58, p = 0.1324).

(E) Quantification of SyO and MAP2 ingested by P2Y12-positive microglia showed no significant differences between AD and aged controls (post hoc Tukey corrected tests after linear mixed effects model F[1,12.98] = 0.08, p = 0.778). Biological replicates were human brain donors: n = 5 aged controls, AD 8 cases. Males are represented by circles and females by triangles.