# Classification of tauopathies from human brain homogenates through salt‐modulated tau amplification

## TL;DR

A new method using salt-modulated RT-QuIC classifies eight types of tau-related brain diseases by analyzing tau protein aggregation patterns.

## Contribution

A heparin-free, salt-modulated RT-QuIC method that improves classification of tauopathies using fewer substrates and salt modulation.

## Key findings

- The method successfully differentiated eight tauopathies, including Alzheimer's and Pick disease.
- Salt modulation and ATR-FTIR confirmed strain-specific conformational differences in tau aggregates.
- A decision-tree workflow using fluorescence metrics refined classification of complex 4R tauopathies.

## Abstract

Tauopathies are a heterogeneous group of neurodegenerative disorders defined by abnormal aggregation of tau protein. Although cryogenic electron microscopy (cryo‐EM) has uncovered disease‐specific tau structures, translating these insights into diagnostic tools remains difficult.

We developed a heparin‐free, salt‐modulated real‐time quaking‐induced conversion (RT‐QuIC) assay using K12 and K11 tau substrates, targeting aggregation‐prone regions. This current method improves on previous methodology by minimising the number of required substrates by modulating reaction salt content in order to differentiate yet‐undistinguished tauopathy strains. Thioflavin T fluorescence kinetics and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) spectroscopy were used to classify tau aggregates from human brain homogenates.

This method differentiated eight tauopathies, including Alzheimer's disease, Pick disease, progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), argyrophilic grain disease (AGD), frontotemporal dementia with parkinsonism associated with chromosome 17 with N279K mutation (FTDP‐17 N279K), and globular glial tauopathies types II and III. Subclassification of 4R tauopathies was achieved by modulating salt conditions and analyzing aggregation profiles. FTIR confirmed preservation of conformational differences.

This salt‐modulated, heparin‐free RT‐QuIC platform enables sensitive tauopathy classification based on strain‐specific kinetics and structure. It offers a practical tool for diagnostic development, mechanistic studies, and therapeutic screening.

Heparin‐free, salt‐modulated real‐time quaking‐induced conversion (RT‐QuIC) with two tau substrates (K12 and K11) classifies eight tauopathy subtypes from human brain homogenates.Anionic cofactor modulation (sodium sulfate and citrate) plus kinetics resolves challenging 4R subtypes and separates glial globular tauopathy (GGT) type II from III.A simple decision‐tree workflow using ThT maxima, half‐time, and Hill slope discriminates Alzheimer's disease (AD) and Pick disease (PiD), and refines corticobasal degeneration (CBD)/ argyrophilic grain disease (AGD)/N279K/progressive supranuclear palsy (PSP)/GGT.Attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) of RT‐QuIC products confirms preservation of strain‐specific conformational signatures underpinning the fluorescence‐based clustering.

Heparin‐free, salt‐modulated real‐time quaking‐induced conversion (RT‐QuIC) with two tau substrates (K12 and K11) classifies eight tauopathy subtypes from human brain homogenates.

Anionic cofactor modulation (sodium sulfate and citrate) plus kinetics resolves challenging 4R subtypes and separates glial globular tauopathy (GGT) type II from III.

A simple decision‐tree workflow using ThT maxima, half‐time, and Hill slope discriminates Alzheimer's disease (AD) and Pick disease (PiD), and refines corticobasal degeneration (CBD)/ argyrophilic grain disease (AGD)/N279K/progressive supranuclear palsy (PSP)/GGT.

Attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR) of RT‐QuIC products confirms preservation of strain‐specific conformational signatures underpinning the fluorescence‐based clustering.