Fig. 7

Trem2 KO exosomes exhibit enhanced tau seeding activity. A Western blot of tau and Alix in lysates and exosomal preparations from tau-loaded WT microglia with or without LPS/ATP stimulation. B Comparison of tau and Alix in lysates and exosomes from tau-loaded WT and Trem2 KO microglia following LPS/ATP stimulation by Western blot analysis. C ELISA measurement of tau levels in WT and Trem2 KO microglial exosomes from 3 independent cultures, 2 replicate ELISA runs per culture. D Experimental design schematic, WT and Trem2 KO microglia exposed to tau oligomers were treated (or untreated) with exosome inhibitor (GW4869), followed by exosomal induction with LPS/ATP. Purified exosomes were then assayed for tau seeding using the tau-RD FRET biosensor cell line, or injected into mouse brain for histopathological analysis. E Exosomes were purified from 1 × 10⁷ WT or Trem2 KO microglia in the absence of tau (no tau), pre-loaded with tau oligomers (+ tau) and induced with LPS/ATP, or Trem2 KO microglia pre-loaded with tau and pre-treated with 10 μM GW4869 prior to LPS/ATP release (+ tau, + exosome inhib), and applied to a tau RD reporter cell line. Tau fret signals were then visualized by fluorescence microscopy. Bar = 10 μm. F Quantification of the area of FRET-positive signals detected (μm²) per cell from representative images in (E). G Characterizing pathological effects of exosomal tau preparations in vivo. Exosomal preparations from tau-loaded or control (“no tau”) WT or Trem2 KO microglia were stereotactically injected into 5-month old WT mouse hippocampus, and stained for AT8 pathology (green) or nuclei (DAPI, blue) 21 days after injection. Bar = 50 μm. H Number of AT8-positive cells (per 2.5 × 10⁵ μm² area) were scored from 6 independently injected animals per treatment/genotype, graph represent mean ± SE. Graphs in (C), (F) and (H) depict mean ± SE. Statistical significance was determined by Student’s t-test (C), One-way ANOVA with Tukey’s multiple comparison (F, H), **p < 0.01, ***p < 0.001, ****p < 0.0001