Synaptic and metabolic gene expression alterations in neurons that are recipients of proteopathic tau seeds

Abstract

Recent studies suggest that misfolded tau molecules can be released, and taken up by adjacent neurons, propagating proteopathic seeds across neural systems. Yet critical to understanding whether tau propagation is relevant in pathophysiology of disease would be to learn if it alters neuronal properties. We utilized high resolution multi-color in situ hybridization technology, RNAScope, in a well-established tau transgenic animal, and found that a subset of neurons in the cortex do not appear to express the transgene, but do develop phospho-tau positive inclusions, consistent with having received tau seeds. Recipient neurons show decreases in their expression of synaptophysin, CAMKIIα, and mouse tau in both young and old animals. These results contrast with neurons that develop tau aggregates and also overexpress the transgene, which have few changes in expression of metabolic and synaptic markers. Taken together, these results strongly suggest that tau propagation impacts neuronal functional integrity.

Keywords: Alzheimer’s disease; Neurofibrillary tangles; RNA expression; Tau seeding.

Fig. 1

Cell populations analyzed in different RNAScope assays. a Table summarizing the total number analyzed for each cell population, and the number of animals, in every RNAScope assay in young and old animals. b Percentage of pyramidal neurons, interneurons and other cell types, performed in control animals and using the same method as the experimental RNAScope assays. c Percentages of each cell population in every experimental RNAScope assay, in young and old animals. d Representative images of a HsMAPT- (“recipient neuron”, left cell) and a HsMAPT + (right cell). e Consequent gray value histograms extracted from the HsMAPT channel shown in d. e1 Histogram of the HsMAPT- (“recipient neuron”) and e2 HsMAPT + neuron. Scale bar: 15 µm

Fig. 2

Transcript amount in NFT bearing neurons of young animals. a Single focal planes of neurons lacking (AT8-, blue arrowheads) or bearing NFT (AT8 + , orange arrowheads) for the total amount of mRNA (Poly(A) tail, left panel); and every gene analyzed. b Graphs summarizing the percentage of area covered with mRNAs (poly(A) tail). c Graphs summarizing the percentage of area covered with each probe targeting the genes of interest. Scale bar: 10 µm

Fig. 3

Transcript amount in NFT bearing neurons of old animals. a Single focal planes of neurons lacking (AT8-, blue arrowheads) or bearing NFT (AT8 + , orange arrowheads) for the total amount of mRNA (Poly(A) tail, left panel); and every gene analyzed. b Graphs summarizing the percentage of area covered with mRNAs (poly(A) tail). c Graphs summarizing the percentage of area covered with each probe targeting the genes of interest. Scale bar: 8 µm

Fig. 4

Transcript amount in NFT seeded neurons of young animals. a Single focal planes of seeded neurons (NFT bearing neurons lacking HsMAPT expression; HsMAPT- blue arrowheads) or NFT bearing, and not seeded, neurons (NFT bearing neurons expressing HsMAPT; HsMAPT + , orange arrowheads) for the total amount of mRNA (Poly(A) tail, left panel); and every gene analyzed. b Graphs summarizing the percentage of area covered with mRNAs (poly(A) tail). c Graphs summarizing the percentage of area covered with each probe targeting the genes of interest. Scale bar: 17 µm

Fig. 5

Transcript amount in NFT seeded neurons of old animals. a Single focal planes of seeded neurons (NFT bearing neurons lacking HsMAPT expression; HsMAPT- blue arrowheads) or NFT bearing, and not seeded, neurons (NFT bearing neurons expressing HsMAPT; HsMAPT + , orange arrowheads) for the total amount of mRNA (Poly(A) tail, left panel); and every gene analyzed. b Graphs summarizing the percentage of area covered with mRNAs (poly(A) tail). c Graphs summarizing the percentage of area covered with each probe targeting the genes of interest. Scale bar: 17 µm