Detection of filamentous tau inclusions by the fluorescent Congo red derivative FSB [(trans,trans)-1-fluoro-2,5-bis(3-hydroxycarbonyl-4-hydroxy)styrylbenzene]

Abstract

Filamentous inclusions made of the microtubule-associated protein tau in a hyperphosphorylated state are a defining feature of a large number of human neurodegenerative diseases. Here we show that (trans,trans)-1-fluoro-2,5-bis(3-hydroxycarbonyl-4-hydroxy)styrylbenzene (FSB), a fluorescent Congo red derivative, labels tau inclusions in tissue sections from a mouse line transgenic for human P301S tau and in cases of familial frontotemporal dementia and sporadic Pick's disease. Labelling by FSB required the presence of tau filaments. More importantly, tau inclusions in the spinal cord of human P301S tau transgenic mice were labelled following a single intravenous injection of FSB. These findings indicate that FSB can be used to detect filamentous tau in vivo.

Fig. 1

Labelling of tau inclusions and β-amyloid deposits by FSB in transgenic mice. Spinal cord sections from 5 month-old mice transgenic for human P301S tau and brain sections from 8 month-old mice transgenic for human amyloid precursor protein with mutations K670M/N671L + V717F (line CRND8) were incubated with FSB at the indicated concentrations. Confocal microscopy was used to visualize the signal. Scale bar, 150 μm.

Fig. 2

FSB and anti-tau antibodies label the same structures in mice transgenic for human P301S tau. Spinal cord sections from 5 month-old transgenic mice were incubated with anti-tau antibodies BR134 (A), T14 (B), AT100 (C) and AT8 (D). Following immunohistochemistry, the sections were incubated with FSB. Confocal microscopy was used to visualize the signal. Scale bar, 60 μm.

Fig. 3

FSB labels filamentous tau: (A) Recombinant human P301S tau protein was incubated in the absence (No filaments) or the presence (filaments) of heparin and labelled with FSB. Intrinsic fluorescence was then measured. Scale bar, 300 nm. (B) Spinal cord sections from 5 month-old human P301S tau mice were incubated with 90% formic acid. Following immunohistochemistry with anti-tau antibody AT8, the sections were incubated with FSB. Scale bar, 60 μm.

Fig. 4

FSB and anti-tau antibody AT8 label the same structures in human tauopathies. (A) Frontal cortex section from a case of FTDP-17T with the P301L mutation in Tau. (B) Frontal cortex section from a case of sporadic Pick’s disease. Following immunohistochemistry, the sections were incubated with FSB. Scale bars, 60 μm.

Fig. 5

FSB labels filamentous tau inclusions in vivo. Five month-old human P301S tau transgenic mice received a single intravenous injection of 0.1% FSB. One hour (A), 2 h (B) and 4 h (C) after the injection the mice were perfused, the spinal cord sectioned and analysed by confocal microscopy. Scale bar, 150 μm. (D), Motor neurons labelled following the intravenous injection of FSB were also immunoreactive with anti-tau antibody AT8. Scale bar, 60 μm.