Fig. 2

Trans-synaptic spreading of α-syn aggregate pathology from DG via CA3 to the CA1 region depends on α-syn expression levels. a No aggregation is induced by injection of (i) monomeric α-syn in WT slices or (ii) S129A PFFs in α-syn KO slices. Scale bars: 20 μm. b Composite image of immunostaining for aggregated (MJF-14, green) and pS129-α-syn (11A5, red) 7 dpi in WT OHSCs, scale bar: 200 μm. Areas from DG, CA3, and CA1 regions indicated are magnified in panels i, ii, and iii. Scale bars: 20 μm. Axonal aggregates (arrows) are present in all three regions, while cell body inclusions (arrowheads) are present only in DG at 7 dpi. c Composite image of immunostaining with MJF-14 and pS129 for aggregates 7 dpi in ASO OHSCs. Scale bar: 200 μm. i, ii Extensive MJF-14- and pS129-positive aggregation and (iii) faster progression with development of cell body inclusions in the CA1 region. Scale bars: 20 μm. d Quantification of pS129-α-syn aggregate fluorescence signals in total slices from PFF-injected WT and ASO slices. Bars represent mean ± SD, n = 3. Unpaired Student’s T-test, p-value = 0.019. e Immunostaining with pS129 (11A5) and MJF-14 at CA1 region of WT slices 14 dpi of PFFs show more compacted, spherical cytoplasmic inclusions, resembling Lewy bodies. Scale bar: 5 μm. f Schematic presentation of progressive development of aggregation; from short into longer serpentine, axonal inclusions in DG regions, which spread to CA3 and CA1 regions. Cell body inclusions appear at later stages when axonal pathology is already established in the region. Images in a are illustrative of 2–3 individual experiments with 10–12 slices in total. Images in b are representative of 17 slices/6 experiments, while images in c represent 3 slices/1 experiment. For quantification in d, 3 slices were included per group