Thioflavin-positive tau aggregates complicating quantification of amyloid plaques in the brain of 5XFAD transgenic mouse model

Abstract

Transgenic mouse models recapitulating Alzheimer’s disease (AD) pathology are pivotal in molecular studies and drug evaluation. In transgenic models selectively expressing amyloid-β (Aβ), thioflavin S (ThS), a fluorescent dye with β-sheet binding properties, is widely employed to observe amyloid plaque accumulation. In this study, we investigated the possibility that a commonly used Aβ-expressing AD model mouse, 5XFAD, generates ThS-positive aggregates of β-sheet structures in addition to Aβ fibrils. To test this hypothesis, brain sections of male and female 5XFAD mice were double-stained with ThS and monoclonal antibodies against Aβ, tau, or α-synuclein, all of which aggregates are detected by ThS. Our results revealed that, in addition to amyloid plaques, 5XFAD mice express ThS-positive phospho-tau (p-tau) aggregates. Upon administration of a small molecule that exclusively disaggregates Aβ to 5XFAD mice for six weeks, we found that the reduction level of plaques was smaller in brain sections stained by ThS compared to an anti-Aβ antibody. Our findings implicate that the use of ThS complicates the quantification of amyloid plaques and the assessment of Aβ-targeting drugs in 5XFAD mice.

Prion-like strain effects in tauopathies

“…Due to its structural plasticity, tau possesses the tendency to change its global conformations to form protein aggregates that are energetically favorable, detergent-insoluble, protease-resistant (Novak et al 1993 ) and can be stained with amyloid dyes (e.g., Thioflavin S, Congo Red, and their derivatives) (Styren et al 2000 ; Shin et al 2021 ) (Fig. 1 b).…”

The Glial Aging & Senescence Hypothesis of Late-onset Alzheimer’s

“…Third, inhibiting microglial proliferation through smaller CSF1R inhibitor dosages was shown to inhibit senescent microglia abundance through reduced Iba1/SA--gal fluorescence in 5xFAD mice. CSF1R inhibition did not remove Iba1/SA--gal positive cells completely at 7.5 months of age; while this can be interpreted towards other factors, the 5xFAD model also features hp-tau pathology at this timepoint 145 . Thus, the remaining senescent microglia after CSF1R inhibition may have become senescent through hp-tau engulfment or endocytosis.…”

Validation of Fucoxanthin from Microalgae Phaeodactylum tricornutum for the Detection of Amyloid Burden in Transgenic Mouse Models of Alzheimer’s Disease

“…It is characterized by the cohesion of oligomers, fibrils, and plaques from monomers; therefore, specific detection substances for Aβ aggregates are used in AD diagnosis. ThS is most used to detect Aβ aggregates; however, recent studies have shown that ThS also detects tau protein aggregates in certain AD transgenic mouse brains, such as 5×FAD [6]. Therefore, additional reagents capable of specific or supportable detection of Aβ aggregates is needed.…”

“…Thioflavin S (ThS) specifically binds to the β-sheet rich structure of Aβ aggregates, leading to increased fluorescence intensity of its emission spectrum, which enables the visualization of aggregated Aβ via fluorescence microscopy [3,4]. However, ThS detects other β-sheet rich protein complexes, including tau [5,6]; therefore, new dyes that specifically validate Aβ aggregate detection are required. Aβ-specific antibodies, such as 6E10 and A11, are used to visualize Aβ aggregates via immunohistochemistry; however, these require expensive and time-consuming methods.…”