Fig. 6. Clusterin enhances Tau seeding and toxicity in neurons.

a Workflow for TauRD aggregate seeding experiments with primary mouse neurons. DIV, days in vitro. b Representative fluorescence microscopy images of primary mouse neurons expressing TauRD-YFP (yellow) incubated with PBS, TauRD seeds or TauRD/Clu seeds (70 ng TauRD). Neurons were stained with an antibody against the neuronal marker MAP2 (red). Arrowheads indicate aggregates. Scale bar, 20 μm. c Comparison of seeding competence of TauRD (gray) and TauRD/Clu (red) seeds (70 ng TauRD) in primary mouse neurons. The fraction of neurons containing YFP-positive aggregates by fluorescence microscopy imaging was quantified. Data represent the mean ± SEM (n = at least 800 cells examined over 3 independent experiments). **p < 0.01 (p = 0.0038) by two-tailed Student’s t-test. d Viability of neurons expressing TauRD-YFP at 4 and 7 days after incubation with TauRD (black) or TauRD/Clu (red) seeds (11 ng TauRD). Data from MTT assays are normalized to the control sample incubated with PBS (100%) and represent the mean ± SEM (n = 5 independent experiments). *p < 0.05 (p = 0.034); n.s., not significant (p = 0.99) by two-way ANOVA with Sidak post hoc test. e Hypothetical model for the role of Clu (red) in amyloid seeding of Tau (brown) and α-Synuclein (α-Syn) (blue). Tau and α-Syn seeding competent species, partially produced by chaperone-mediated disaggregation, are released to the extracellular space from cells containing amyloid aggregates (gray). Clu (red) interacts with these species increasing seeding competence for Tau upon uptake by neighboring cells via the endosomal pathway. In contrast, Clu inhibits seeding for α-Syn. Tau/Clu seeds efficiently template aggregation of endogenous Tau, resulting in cytotoxicity, while α-Syn/Clu seeds are unable to template aggregation of endogenous α-Syn.