Figure 8DIV21 neurons were co-exposed to fixed concentration of Fib-Tau (0.36nM, 60min, ATTO550 labelled, red) and increasing concentrations (given in monomer-equivalent) of α-Syn fibrils [in total 5-experiments were performed with either ATTO647 labeled α-Syn (shown here in green) or unlabeled α-Syn A concentration-dependent increase in the binding and clustering of α-Syn fibrils is seen. Notably, Fib-Tau clustering dramatically increased with increasing concentrations of α-Syn DIV21 neurons were co-exposed to fixed concentration of Fib-Tau (0.36nM, 60min, ATTO550 labelled, red) and increasing Aβ (given in monomer-equivalent) of Aβ (B) fibrils [in total 5-experiments were performed with either ATTO647 labeled Aβ (shown here in green) or unlabeled Aβ fibrils]. concentration-dependent increase in the binding and clustering of Aβ fibrils is seen. Notably, Fib-Tau clustering dramatically increased with increasing concentrations of α-Syn, but not Aβ fibrils DIV21 neurons were co-exposed to fixed concentration of Fib-Tau (0.36nM, 60min, ATTO550 labelled, red) and increasing concentrations (given in monomer-equivalent) of α-Syn fibrils [in total 5-experiments were performed with either ATTO647 labeled α-Syn or unlabeled α-Syn A concentration-dependent increase in the binding and clustering of both α-Syn fibrils is seen. One-Way ANOVA with Dunnett's post-hoc test was performed to compare the different condition to the reference condition (100nM).The number of images analyzed is 27, 25, 25, 26 and 28 in (C) , from left to right. The data originate from 3 to 4 independent experiments. Data information: Box-plot represents: median, interquartile range and 10-90% distribution, Mann-Whitney-test is performed, n=40 images from 4-experiments, Scale bars, 5µm. *p<0.05, ***p<0.001; ns= not significant. DIV21 neurons were co-exposed to fixed concentration of Fib-Tau (0.36nM, 60min, ATTO550 labelled, red) and increasing concentrations (given in monomer-equivalent) of Aβ fibrils [in total 5-experiments were performed with either ATTO647 labeled Aβ or unlabeled Aβ fibrils A concentration-dependent increase in the binding and clustering of Aβ fibrils is seen. One-Way ANOVA with Dunnett's post-hoc test was performed to compare the different condition to the reference condition (100nM).The number of images analyzed is 18, 50, 50, 50, 25 in (D), from left to right. The data originate from 3 to 4 independent experiments. Data information: Box-plot represents: median, interquartile range and 10-90% distribution, Mann-Whitney-test is performed, n=40 images from 4-experiments, Scale bars, 5µm. *p<0.05, ***p<0.001; ns= not significant. Notably, Fib-Tau clustering dramatically increased with increasing concentrations of α-Syn, but not Aβ fibrils The quantification in (E) includes all 5-experiments (n = number of images analyzed, left to right: 58, 54, 50, 62, 63, 65, 43, 35, 60, 60, 60, 35; One-Way ANOVA with Dunnette's post-hoc test was performed to compare the size of Fib-Tau clusters). Data information: Box-plot represents: median, interquartile range and 10-90% distribution, Mann-Whitney-test is performed, n=40 images from 4-experiments, Scale bars, 5µm. *p<0.05, ***p<0.001; ns= not significant. A perfect co-localization between Fib-Tau and α-Syn clusters is also observed. The proportion of Fib-Tau clusters co-localizing with α-Syn fibrils increased with an increasing concentration of α-Syn fibrils reaching 60-70% overlap A weaker, concentration independent, overlap (10-20%) was observed with Aβ fibrils The quantification in (F) is derived from 3 to 4 independent experiments. The number of images analyzed is 27, 25, 25, 26, 28 for α-Syn and 18, 50, 50, 50, 25 for Aβ from left to right. One-Way ANOVA with Dunnett's post-hoc test was performed to compare the co-localization differences from 100nM concentration. Box-plot represents: median, interquartile range and 10-90% distribution. Data information: Box-plot represents: median, interquartile range and 10-90% distribution, Mann-Whitney-test is performed, n=40 images from 4-experiments, Scale bars, 5µm. *p<0.05, ***p<0.001; ns= not significant. (G-I) Primary neurons were co-exposed to Fib-Tau (0.36nM, ATTO550 labelled) and Fib-α-Syn (50nM, monomer-equivalent, unlabeled) for 60min and immunolabelled for homer (G) or α3-NKA (H). Quantification of Fib-Tau clusters co-localized with homer or α3-NKA (I). Note an increased co-localization of Fib-Tau with homer in presence of Fib-α-Syn. Data information: Box-plot represents: median, interquartile range and 10-90% distribution, Mann-Whitney-test is performed, n=40 images from 4-experiments, Scale bars, 5µm. *p<0.05, ***p<0.001; ns= not significant.