Detection of Aggregation-Competent Tau in Neuron-Derived Extracellular Vesicles

Abstract

Progressive cerebral accumulation of tau aggregates is a defining feature of Alzheimer’s disease (AD). A popular theory that seeks to explain the apparent spread of neurofibrillary tangle pathology proposes that aggregated tau is passed from neuron to neuron. Such a templated seeding process requires that the transferred tau contains the microtubule binding repeat domains that are necessary for aggregation. While it is not clear how a protein such as tau can move from cell to cell, previous reports have suggested that this may involve extracellular vesicles (EVs). Thus, measurement of tau in EVs may both provide insights on the molecular pathology of AD and facilitate biomarker development. Here, we report the use of sensitive immunoassays specific for full-length (FL) tau and mid-region tau, which we applied to analyze EVs from human induced pluripotent stem cell (iPSC)-derived neuron (iN) conditioned media, cerebrospinal fluid (CSF), and plasma. In each case, most tau was free-floating with a small component inside EVs. The majority of free-floating tau detected by the mid-region assay was not detected by our FL assays, indicating that most free-floating tau is truncated. Inside EVs, the mid-region assay also detected more tau than the FL assay, but the ratio of FL-positive to mid-region-positive tau was higher inside exosomes than in free solution. These studies demonstrate the presence of minute amounts of free-floating and exosome-contained FL tau in human biofluids. Given the potential for FL tau to aggregate, we conclude that further investigation of these pools of extracellular tau and how they change during disease is merited.

CNS-Derived Blood Exosomes as a Promising Source of Biomarkers: Opportunities and Challenges

“…The pathology of AD is characterized by the aggregation of Aβ in senile plaques and of hyperphosphorylated tau in neurofibrillary tangles. Accumulation and spread of the latter lesion in susceptible brain regions correlate with a progressive cognitive decline (Rajendran et al, 2006;Guix et al, 2018). Different roles of exosomes related to both Aβ and tau pathologies in AD have been reported in several studies.…”

Exosome Production Is Key to Neuronal Endosomal Pathway Integrity in Neurodegenerative Diseases

“…In AD, EVs have been proposed to contribute to the spread of Aβ and Aβ pathology in the brain (Rajendran et al, 2006) as well as the spread of hyper-phosphorylated pathogenic tau between neurons (Saman et al, 2012;Wang et al, 2017;Guix et al, 2018;Winston et al, 2019). We and others have shown that EVs contain full-length APP, the CTFs of APP generated through cleavage by β-secretase (βCTFs) or α-secretase (αCTFs), Aβ, and the enzymes that are responsible for these cleavage steps (Rajendran et al, 2006;Vingtdeux et al, 2007;Escrevente et al, 2008;Sharples et al, 2008;Pérez-González et al, 2012;Laulagnier et al, 2018;Miranda et al, 2018).…”

A cell-based assay for CD63-containing extracellular vesicles

“…It has been proposed that EVs modulate tumor environments to allow for tumor seeding and growth and promote angiogenesis [2][3][4][5][6][7][8]. EVs have also been implicated in the prion-like spread of neuropathogenic protein aggregates in several neurodegenerative diseases [9][10][11][12][13][14][15]. Certain viruses and bacteria such as hepatitis A virus [16], herpesvirus 6 [17], HTLV-1 [18], HIV [19,20] and uropathogenic E. coli a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 [21,22] may use the cellular pathways of EV biogenesis for extracellular release.…”