Common mouse models of tauopathy reflect early but not late human disease

Abstract

Background: Mouse models that overexpress human mutant Tau (P301S and P301L) are commonly used in preclinical studies of Alzheimer's Disease (AD) and while several drugs showed therapeutic effects in these mice, they were ineffective in humans. This leads to the question to which extent the murine models reflect human Tau pathology on the molecular level.

Methods: We isolated insoluble, aggregated Tau species from two common AD mouse models during different stages of disease and characterized the modification landscape of the aggregated Tau using targeted and untargeted mass spectrometry-based proteomics. The results were compared to human AD and to human patients that suffered from early onset dementia and that carry the P301L Tau mutation.

Results: Both mouse models accumulate insoluble Tau species during disease. The Tau aggregation is driven by progressive phosphorylation within the proline rich domain and the C-terminus of the protein. This is reflective of early disease stages of human AD and of the pathology of dementia patients carrying the P301L Tau mutation. However, Tau ubiquitination and acetylation, which are important to late-stage human AD are not represented in the mouse models.

Conclusion: AD mouse models that overexpress human Tau using risk mutations are a suitable tool for testing drug candidates that aim to intervene in the early formation of insoluble Tau species promoted by increased phosphorylation of Tau.

Keywords: Alzheimer’s disease; Disease progression; Human Tau; Mouse model; P301L; P301S; Post-translational modifications; Protein aggregation; Quantitative proteomics; Tauopathy.

Fig. 1

Overview on pathological and behavioral changes of the P301S and the P301L mouse model. A Overview on the disease progression of the P301S and the P301L mouse model and the respective analyzed brain regions and time points [–18]. B Schematic overview of the sample preparation and PTM-focused proteomic workflow

Fig. 2

Quantification of insoluble and soluble Tau fractions in the P301S and the P301L model. A, B Average absolute amount of cortical insoluble (A) and soluble (B) Tau for both mouse models compared to average levels of human AD (BA39) (mean +—SD) (human data adapted from [20]). C, D Relative amount of insoluble total Tau measured in specified brain region compared to the first time point of the P301S (C) and the P301L (D) model (Significance was determined using a t-test, 5–7 replicates for each condition)

Fig. 3

PTMs in insoluble Tau occur in a sequential manner during disease progression in mouse models. A, B A summary of PTMs identified in cortical insoluble Tau at the last time point of the P301S (A) and the P301L (B) models. PTMs represented are found in $\ge$ 50% of the biological replicates. C, D A sequential addition of PTMs in the cortex during disease progression is observed with unbiased Euclidean distance hierarchical clustering of Tau PTM data (binary—presence/absence) from the P301S (C) and the P301L (D) models. PTMs used for clustering were identified in ≥ 50% of the biological replicates. Grey squares indicate the presence of a PTM. Annotated clusters represent PTMs identified at all time points (blue), PTMs appearing concomitant with tangle formation (orange), and PTMs that appear after tangle formation (magenta)

Fig. 4

Tau modification extent correlates with Tau pathology kinetics in both models and human AD. A-B Specific Tau regions and modification sites with high stoichiometry of modification are identified by unbiased data analyses. Euclidean hierarchical clustering of relative amounts of unmodified FLEX-peptide of insoluble Tau derived from the cortex of the P301S (A) and P301L model (B) shows regions with high modification extent. C Average extent of modification of FLEX-peptides per condition from insoluble Tau derived from the cortex of the P301S and P301L model ordered from N- to C-terminus. Arrows indicate regions that become highly modified when aggregates form. D-G Pearson correlation analyses are performed to study the extent of modification of specific peptides and the amount of insoluble Tau. 195–209 (D), 212–221 (E), 386–395 (F), 396–406 (G). This correlation analyses are performed for the cortex of the P301S and P301L model and the BA39 of human AD (human AD data is adapted from [20]). H-J Pearson correlation of singly phosphorylated peptides with insoluble Tau in the cortex of the P301S and P301L models. Phosphorylated peptides 195–209 (H), 212–221 (I), 396–406 (J) also show a strong association with disease

Fig. 5

Pathological insoluble Tau of human P301L patients exhibits only minimal modification (Frontal cortex, BA46). A, B Absolute amount of insoluble (A) and soluble (B) Tau from P301L patients and healthy controls. C Euclidean distance hierarchical clustering of binary PTMs data from insoluble Tau derived from P301L patients and healthy controls in comparison to the cortex in the end stage of the P301S and P301L mouse models. PTMs used for clustering were identified in ≥ 50% of the human biological replicates or were present in one of the mouse models at the last time point. Grey squares indicate the presence of a PTM. D Euclidean hierarchical clustering of relative amounts of unmodified FLEX-peptide of insoluble Tau derived from P301L patients and healthy controls in comparison to the cortex in the end stage of the P301S and P301L mouse models. E Relative amounts of unmodified FLEX-peptides from insoluble Tau derived from P301L patients and healthy controls ordered from N- to C-terminus controls in comparison to the cortex in the end stage of the P301S and P301L mouse models

Fig. 6

Comparison of the modification landscape of murine and human insoluble Tau. Insoluble Tau of the cortex of P301S and P301L mouse models shows a similar phosphorylation pattern to early stages of human AD and human P301L carriers (human AD data is adapted from [20]). Tau ubiquitination and acetylation of human late-stage AD is not represented in both mouse models. The represented modification sites are documented in table S2. Transverse lines indicate the absence of two N-terminal repeat regions in the human Tau transgene of both mouse models as both models only overexpress 0N4R Tau