Skip to main page content
Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
, 127 (5), 667-83

A Novel in Vivo Model of Tau Propagation With Rapid and Progressive Neurofibrillary Tangle Pathology: The Pattern of Spread Is Determined by Connectivity, Not Proximity

Affiliations

A Novel in Vivo Model of Tau Propagation With Rapid and Progressive Neurofibrillary Tangle Pathology: The Pattern of Spread Is Determined by Connectivity, Not Proximity

Zeshan Ahmed et al. Acta Neuropathol.

Abstract

Intracellular inclusions composed of hyperphosphorylated filamentous tau are a hallmark of Alzheimer's disease, progressive supranuclear palsy, Pick's disease and other sporadic neurodegenerative tauopathies. Recent in vitro and in vivo studies have shown that tau aggregates do not only seed further tau aggregation within neurons, but can also spread to neighbouring cells and functionally connected brain regions. This process is referred to as 'tau propagation' and may explain the stereotypic progression of tau pathology in the brains of Alzheimer's disease patients. Here, we describe a novel in vivo model of tau propagation using human P301S tau transgenic mice infused unilaterally with brain extract containing tau aggregates. Infusion-related neurofibrillary tangle pathology was first observed 2 weeks post-infusion and increased in a stereotypic, time-dependent manner. Contralateral and anterior/posterior spread of tau pathology was also evident in nuclei with strong synaptic connections (efferent and afferent) to the site of infusion, indicating that spread was dependent on synaptic connectivity rather than spatial proximity. This notion was further supported by infusion-related tau pathology in white matter tracts that interconnect these regions. The rapid and robust propagation of tau pathology in this model will be valuable for both basic research and the drug discovery process.

Figures

Fig. 1
Fig. 1
Characterisation of P301SBE-induced hippocampal tau pathology. a At 2.5 months post-infusion, PG-5 immunohistochemistry identified severe neuronal tau pathology in the hippocampus (dentate gyrus, CA3 and CA1) of mice infused with P301SBE, whereas age-matched controls infused with either WTBE or PBS showed only sparse tau pathology. Neuronal tau pathology in P301SBE mice was: (1) accompanied by neuropil threads, (2) more severe on the infused than the contralateral side and (3) Gallyas silver positive. b Quantification of PG-5-positive neurons in the infused (solid shapes) and contralateral (empty shapes) hippocampi showed significant (P < 0.05) differences between P301SBE- (red) and WTBE- (blue) or PBS- (green) infused mice; in addition, the infused and contralateral hippocampi of P301SBE mice showed a significant difference. c At this time-point, PG-5-positive tau pathology could also be detected by anti-tau antibodies AT8 (recognising tau phosphorylated at Ser202/Thr205), MC1 (conformation-dependent tau epitope) and TG3 (phosphorylation of tau at Thr231 and conformation-dependent), with staining for the latter being more restricted. Confocal microscopy showed that a small subset of neuronal inclusions was Thioflavin-S-positive with limited neuropil thread staining (white arrows); such inclusions were absent in age-matched control mice (data not shown). Statistics: Groupwise comparison, one-way ANOVA with Bonferroni’s post hoc test; ****, P < 0.0001. BE brain extract, PBS phosphate-buffered saline, WT wild type. Scale bars: a, 200 µm; b, 50 µm
Fig. 2
Fig. 2
Time-dependent progression of P301SBE-induced hippocampal tau pathology. a Representative images showing PG-5-positive tau pathology in the hippocampus (bregma −2.50) of human P301S tau transgenic mice 1 day, 2 weeks, 1 month, 2 months and 2.5 months after the infusion with P301SBE, compared to P301S tau mice 2.5 months after the infusion with WTBE/PBS. Insets show PG-5 immunohistochemistry and Gallyas silver staining in the CA1 region (performed on adjacent serial sections); those on the right show the infused side and those on the left the contralateral side. Tau pathology was absent at 1 day post-infusion, but mild infusion-related tissue damage was visible on the infused side (indicated by asterisk). From 2 weeks post-infusion, PG-5-positive tau pathology increased in a time-dependent manner on the infused side; neuronal inclusions became more strongly PG-5 positive, were associated with neuropil threads and became increasingly Gallyas silver positive. Similar pathological changes occurred on the contralateral side 1 month post-infusion, where the pathology was comparatively less severe. In contrast, tau pathology was only sparse in the infused and contralateral hippocampus of WTBE mice, even 2.5 months post-infusion. b The density of PG-5-positive neurons in the hippocampus showed an age-associated increase on the infused and contralateral sides. From 2 weeks post-infusion, the density of PG-5-positive neurons was significantly (P < 0.05) increased in the infused hippocampus of P301SBE mice when compared with WTBE/PBS-infused mice 2.5 months post-infusion; similar results were obtained on the contralateral side, but only at 2 months post-infusion. c To investigate the relative proportion of PG-5-positive, silver-negative tau inclusions (pre-tangles) versus PG-5-positive and silver-positive inclusions (NFTs), the number of Gallyas-positive neurons in the CA1 region was expressed as the percentage of the number of PG-5-positive neurons quantified in the same region, but on an adjacent serial section. At 2 weeks post-infusion, the majority of tau inclusions in P301SBE-infused mice were pre-tangles, whereas by 2.5 months both the infused and contralateral hippocampi contained predominantly NFTs. In contrast, pre-tangles predominated in PBS-infused mice, even 2.5 months post-infusion. Comparison of P301SBE and PBS groups at 2.5 months post-infusion showed a significant increase in NFTs in the former. Statistics: Groupwise comparison, one-way ANOVA with Dunnett’s post hoc test (b) and one-way ANOVA with Bonferroni’s post hoc test (c); pairwise comparison, Student’s t test (c). BE brain extract, WT wild type, d day, w weeks, m month; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Scale bars: a, 1 mm; insets, 100 µm
Fig. 2
Fig. 2
Time-dependent progression of P301SBE-induced hippocampal tau pathology. a Representative images showing PG-5-positive tau pathology in the hippocampus (bregma −2.50) of human P301S tau transgenic mice 1 day, 2 weeks, 1 month, 2 months and 2.5 months after the infusion with P301SBE, compared to P301S tau mice 2.5 months after the infusion with WTBE/PBS. Insets show PG-5 immunohistochemistry and Gallyas silver staining in the CA1 region (performed on adjacent serial sections); those on the right show the infused side and those on the left the contralateral side. Tau pathology was absent at 1 day post-infusion, but mild infusion-related tissue damage was visible on the infused side (indicated by asterisk). From 2 weeks post-infusion, PG-5-positive tau pathology increased in a time-dependent manner on the infused side; neuronal inclusions became more strongly PG-5 positive, were associated with neuropil threads and became increasingly Gallyas silver positive. Similar pathological changes occurred on the contralateral side 1 month post-infusion, where the pathology was comparatively less severe. In contrast, tau pathology was only sparse in the infused and contralateral hippocampus of WTBE mice, even 2.5 months post-infusion. b The density of PG-5-positive neurons in the hippocampus showed an age-associated increase on the infused and contralateral sides. From 2 weeks post-infusion, the density of PG-5-positive neurons was significantly (P < 0.05) increased in the infused hippocampus of P301SBE mice when compared with WTBE/PBS-infused mice 2.5 months post-infusion; similar results were obtained on the contralateral side, but only at 2 months post-infusion. c To investigate the relative proportion of PG-5-positive, silver-negative tau inclusions (pre-tangles) versus PG-5-positive and silver-positive inclusions (NFTs), the number of Gallyas-positive neurons in the CA1 region was expressed as the percentage of the number of PG-5-positive neurons quantified in the same region, but on an adjacent serial section. At 2 weeks post-infusion, the majority of tau inclusions in P301SBE-infused mice were pre-tangles, whereas by 2.5 months both the infused and contralateral hippocampi contained predominantly NFTs. In contrast, pre-tangles predominated in PBS-infused mice, even 2.5 months post-infusion. Comparison of P301SBE and PBS groups at 2.5 months post-infusion showed a significant increase in NFTs in the former. Statistics: Groupwise comparison, one-way ANOVA with Dunnett’s post hoc test (b) and one-way ANOVA with Bonferroni’s post hoc test (c); pairwise comparison, Student’s t test (c). BE brain extract, WT wild type, d day, w weeks, m month; *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. Scale bars: a, 1 mm; insets, 100 µm
Fig. 3
Fig. 3
Propagation of tau pathology to brain regions distal to the infusion site. The density of PG-5-positive neurons or the area occupied by PG-5-positive immunoreactivity (tau burden;  % area) was quantified in discrete brain regions distal to the site of infusion. This analysis was conducted in P301SBE (red) and PBS (green) mice 2.5 months post-infusion, both on the infused (solid bars) and the contralateral (checked bars) sides. Statistical analysis identified regions with significantly more tau pathology in P301SBE mice than in PBS controls. The results of this analysis are summarised in Table 3. Tau propagation was detected in numerous distal sites (ai), all of which have strong synaptic connections with the hippocampal formation. Regions not directly connected to the hippocampal formation (jl) showed no evidence of tau propagation. Representative images showing PG-5 staining in retrosplenial cortex (m), lateral septal nucleus (n) and medial/lateral mammillary nucleus (o) serve to illustrate the severity and distribution of tau pathology in P301SBE and PBS mice. RSC retrosplenial cortex, mlMN medial/lateral mammillary nucleus, suMN supramammillary nucleus, LSN lateral septal nucleus, ADthalamus anterodorsal thalamus, AVthalamus anteroventral thalamus, LGN lateral geniculate nucleus, BE brain extract, PBS phosphate-buffered saline. Scale bars: 150 µm
Fig. 4
Fig. 4
P301SBE-induced tau pathology in white matter tracts. a The fornix (red) is a white matter tract that projects from the hippocampal formation (orange) to the basal forebrain structures, including the mammillary nucleus (green), both of which contain P301SBE-induced tau pathology (Table 3; Fig. 3). Representative images of the dorsal and ventral aspects of the fornix (bregma −1.00; corresponding to the red dotted line) showed PG-5-positive dot-like structures (insets) that were more numerous in P301SBE mice than in controls. The morphology and location of these dot-like structures are compatible with tau aggregates in neuronal axons (cut in cross section; inset). Semi-quantitative scoring in the dorsal (b) and ventral fornix (c) confirmed that tau pathology was more severe (P < 0.05) on the infused side of P301SBE mice at 2 weeks (0.5 months) and 2.5 months post-infusion when compared with controls. On the contralateral side, there was an increase in tau pathology between 2 weeks and 2.5 months in P301SBE mice (significant for the ventral fornix). At both 2 weeks and 2.5 months, tau pathology was significantly more severe on the infused side of P301SBE mice compared to the contralateral side. A similar analysis of the internal capsule (d) did not identify any P301SBE-induced changes in tau pathology, although there was a mild but significant increase between 2 weeks and 2.5 months post-infusion. Statistics: Groupwise comparison, Kruskal–Wallis test with Dunn’s post hoc test; Pairwise comparison, Mann–Whitney test; ***, P < 0.001; **, P < 0.01; *, P < 0.05; #, P > 0.05 and ≤0.08 (trend). d dorsal, l lateral, v ventral, r rostal, c caudal, INF relative coronal level of the infusion site, BE brain extract, PBS, phosphate-buffered saline. Scale bars: 100 µm
Fig. 5
Fig. 5
Tau propagation is related to connectivity, and not proximity. Schematic of the mouse brain at two sagittal levels (lateral: 2.04 and 0.60) shows the structural relationship between nuclei with (red) and without (green) evidence of tau propagation. The former are synaptically connected to neurons in the hippocampus (dark red), the target of the P301SBE infusion (purple dots). Nuclei located anteriorly and ventrally are connected to the hippocampus through the fimbria–fornix (FF), which also showed evidence of tau propagation. The lateral geniculate nucleus (LG), which was proximal to the site of infusion, did not exhibit propagation and was not synaptically connected to the hippocampus, nor are nuclei associated with the striatonigral system that are interconnected through the internal capsule. This distribution suggests that tau spreads to regions synaptically connected to the infusion site and not necessarily to regions in close proximity. Only specific nuclei were analysed for evidence of tau propagation (Table 3) and the sagittal levels were selected for illustrative purposes only. Grey dotted lines indicate anterior/posterior bregma levels in which nuclei were sampled (Supplementary Fig. 1). AT anterior thalamus, CA, CA1-3, CC corpus callosum, CP caudate/putamen, DG dentate gyrus, FF fimbria/fornix, FI fimbria, GP globus pallidus, HP hippocampus, IC internal capsule, LG lateral geniculate nucleus, LSN lateral septal nucleus, MN mammillary nucleus, NAc nucleus accumbens, RSC retrosplenial cortex, Sub subiculum, VC visual cortex, VT ventral thalamus

Similar articles

See all similar articles

Cited by 125 articles

See all "Cited by" articles

References

    1. Allen B, Ingram E, Takao M, Smith MJ, Jakes R, Virdee K, Yoshida H, Holzer M, Craxton M, Emson PC, et al. Abundant tau filaments and nonapoptotic neurodegeneration in transgenic mice expressing human P301S tau protein. J Neurosci. 2002;22:9340–9351. - PMC - PubMed
    1. Andersen P. The hippocampus book. USA: Oxford University Press; 2007.
    1. Bancher C, Brunner C, Lassmann H, Budka H, Jellinger K, Wiche G, Seitelberger F, Grundke-Iqbal I, Iqbal K, Wisniewski HM. Accumulation of abnormally phosphorylated tau precedes the formation of neurofibrillary tangles in Alzheimer’s disease. Brain Res. 1989;477:90–99. doi: 10.1016/0006-8993(89)91396-6. - DOI - PubMed
    1. Braak E, Braak H, Mandelkow EM. A sequence of cytoskeleton changes related to the formation of neurofibrillary tangles and neuropil threads. Acta Neuropathol. 1994;87:554–567. doi: 10.1007/BF00293315. - DOI - PubMed
    1. Braak H, Braak E. Neuropathological stageing of Alzheimer-related changes. Acta Neuropathol. 1991;82:239–259. doi: 10.1007/BF00308809. - DOI - PubMed

Publication types

MeSH terms

LinkOut - more resources

Feedback