4-Repeat tau seeds and templating subtypes as brain and CSF biomarkers of frontotemporal lobar degeneration

Abstract

To address the need for more meaningful biomarkers of tauopathies, we have developed an ultrasensitive tau seed amplification assay (4R RT-QuIC) for the 4-repeat (4R) tau aggregates of progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), and other diseases with 4R tauopathy. The assay detected seeds in 10 6 -10 9 -fold dilutions of 4R tauopathy brain tissue but was orders of magnitude less responsive to brain with other types of tauopathy, such as from Alzheimer's disease cases. The analytical sensitivity for synthetic 4R tau fibrils was ~ 50 fM or 2 Byron Caughey,

A single ultrasensitive assay for detection and discrimination of tau aggregates of Alzheimer and Pick diseases

“…A key to success in developing RT-QuIC or other seed amplification assays is maximizing the kinetic difference between seeded and unseeded (spontaneous) polymerization of the substrate molecules. In our experience the K12CFh substrate is readily seeded but is less prone to spontaneous polymerization than the tau fragments that we have used in our previous tau RT-QuIC assays [21,23,28,29]. This feature can improve assay sensitivity and specificity, which may be crucial for detecting aggregates in accessible diagnostic specimens with relatively low tau seed concentrations.…”

“…Cysteines in the canonical tau sequences were mutated to serines (*) or alanine (★) for recombinant tau fragments used in tau RT-QuIC assays. The 3R, AD, and 4R RT-QuIC assays mentioned in this figure have been described previously [21,23,27,29] Table 1 End-point quantification of tau seeding activity in brain tissue across tau RT-QuIC assays fixed tissues were made using the stains described in [6,21]. Tissue samples in this study were collected from frontal cortex except for CTE and primary age-related tauopathy (PART) samples which were from temporal cortex.…”

“…For instance, the modified 3R tau fragment K19CFh forms fibrils when seeded with PiD brain homogenate as dilute as 10 − 9 , but not with PSP brain homogenate even at a 10 5 -fold higher concentration [27]. In contrast, the modified 4R tau fragment K18CFh amplifies 4R tau aggregates [29], and a tau fragment spanning the cross-β core of AD tau fibrils (τ306-378) selectively amplifies mixed 3R/4R tau seeds [21]. Figure 1 schematically represents the recombinant tau fragments used in different tau RT-QuIC assays.…”

“…Diseases involving tau pathology include those with preferential aggregation of 3 microtubule binding-repeat (3R), 4-repeat (4R), or both 3R and 4R (3R/4R) tau isoforms. Previously, our lab has developed tau RT-QuIC assays optimized to detect the mainly 3R aggregates of Pick disease (PiD) [27]; the 3R/4R aggregates of Alzheimer disease (AD) and chronic traumatic encephalopathy (CTE) [21]; or the 4R aggregates of progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), frontotemporal dementias associated with MAPT mutations (FTDP 17 MAPT) and others [29]. In these assays, tau seeds from crude brain homogenates or cerebrospinal fluid (CSF) are added to reaction mixtures containing purified tau fragments truncated at different points in the microtubule binding domains to help confer seeding selectivity.…”

PMCA Applications for Prion Detection in Peripheral Tissues of Patients with Variant Creutzfeldt-Jakob Disease

“…Therefore, PMCA and RT-QuIC might be exploited for detecting peripheral disease-specific biomarkers associated with these more frequent disorders. In this regard, we and others have already shown that traces of aberrantly folded α-synuclein, amyloid-β, and tau can be detected in the cerebrospinal fluid and olfactory mucosa of patients with different neurodegenerative diseases [110][111][112][113][114][115][116][117][118][119]. However, these studies are in their very early phases of development and additional studies are required before these amplification technologies can be used as robust and reliable diagnostic tools.…”