Trans-seeding of Alzheimer-related tau protein by a yeast prion

Abstract

Abnormal tau protein aggregates constitute a hallmark of Alzheimer's disease. The mechanisms underlying the initiation of tau aggregation in sporadic neurodegeneration remain unclear. Here we investigate whether a non-human prion can seed tau aggregation. Due to their structural similarity with tau aggregates, we chose Sup35NM yeast prion domain fibrils for explorative tau seedings. Upon in vitro incubation with tau monomers, Sup35NM fibrils promoted the formation of morphologically distinct tau fibril strains. In vivo, intrahippocampal inoculation of Sup35NM fibrils accentuated tau pathology in P301S tau transgenic mice. Thus, our results provide first in vivo evidence for heterotypic cross-species seeding of a neurodegenerative human prion-like protein by a yeast prion. This opens up the conceptual perspective that non-mammalian prions present in the human microbiome could be involved in the initiation of protein misfolding in neurodegenerative disorders, a mechanism for which we propose the term "trans-seeding."

Keywords: Alzheimer's disease; Sup35; neurodegeneration; prion; seeding; tau; trans-seeding; yeast.

FIGURE 1

Sup35NM seeds P301S mutant tau aggregation in vitro. A‐C, Transmission electron microscope images of negatively stained preparations of human 2N4R P301S mutant tau monomer aggregates, formed under low heparin conditions (A), and after addition of ‐5TyrSup35NM monomers (B), or Sup35NM seeds (C), at days 0, 3, and 16. Note the occurrence of corkscrew‐shaped tau fibrils at days 3 and 16 upon seeding with Sup35NM fibrils (arrows, C). Scale bar for all images: 500 nm, for all magnified insets: 100 nm

FIGURE 2

Sup35NM seeds wild‐type tau aggregation in vitro. A‐C, Transmission electron microscope images of negatively stained preparations of human 2N4R wild‐type tau monomer aggregation under low heparin conditions (A), and after addition of ‐5TyrSup35NM monomers (B), or Sup35NM seeds (C), at days 0, 3, and 16. Note the occurrence of corkscrew‐shaped tau fibrils at days 3 and 16 upon seeding with Sup35NM fibrils (arrows, C). Scale bar for all images: 500 nm, for all magnified insets: 100 nm

FIGURE 3

Re‐seedings of tau monomers by Sup35NM‐induced wild‐type tau filaments. A, B, Transmission electron microscope images of negatively stained preparations of human 2N4R wild‐type tau monomer aggregation under low heparin conditions at time points day 0 and day 3, using corkscrew‐like 2N4R wild‐type tau filaments (Generation 0 seeds) previously induced by Sup35NM seeds. This resulted in a next generation (Generation 1 [G1]) of corkscrew‐like filaments (arrow, A). Re‐seeding with G1 filaments again induced corkscrew‐like tau aggregates in G2 (arrow, B). Scale bar for all images: 500 nm, for all magnified insets: 100 nm

FIGURE 4

Sup35NM seeds tau aggregation in P301S tau transgenic mice. A‐D, Increase in AT8 immunohistochemistry (AT8) and Gallyas staining (GALL) positive neurons in the unilateral CA3 field after intrahippocampal Sup35NM fibril inoculation in P301S tau transgenic mice. AT8 and Gallyas positive neurons comparing P301S tau mice inoculated with C57BL/6 mouse brain homogenates (B6‐bh), ‐5TyrSup35NM solution, and Sup35NM fibrils (A, C; one‐way analysis of variance, followed by Tukey's test), and corresponding histology (Bregma level –2.6 mm). Comparison between non‐injected (contralateral) and injected (ipsilateral) side (B, D; paired t‐tests), and representative histological findings (Bregma level –2.4 mm). *P < .05, **P < .01, n.s. = non‐significant; indicated is the mean number of positive CA3 neurons per section ± standard deviation. For detailed quantitative data see Table S2 in supporting information

FIGURE 5

Sup35NM induces focal tau pathology. Focal tau pathology induced around hippocampal inoculation canal and ipsilateral dorsal fornix upon Sup35NM inoculation. A, B, Gallyas stains. Note the characteristic focal grain‐like tau aggregates in proximity of the hippocampal injection canal upon Sup35NM inoculation (A, arrows indicate tau pathology along the inoculation canal). Granular tau pathology develops in the ipsilateral dorsal fornix of a SUP35NM‐seeded P301S mouse (B, right; arrow), but is absent in the contralateral fornix (B, left)