Distinct differences in prion-like seeding and aggregation between Tau protein variants provide mechanistic insights into tauopathies

Abstract

The accumulation of aberrantly aggregated microtubule-associated protein tau (MAPT) 1 defines a spectrum of tauopathies, including Alzheimer's disease. Mutations in the MAPT gene cause frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17), characterized by neuronal pathological tau inclusions in the form of neurofibrillary tangles and Pick bodies, and in some cases glial tau pathology. Increasing evidence points to the importance of prion-like seeding as a mechanism for the pathological spread in tauopathy and other neurodegenerative diseases. Herein, using a cell culture model, we examined a multitude of genetic FTDP-17 tau variants for their ability to be seeded by exogenous tau fibrils. Our findings revealed stark differences between FTDP-17 tau variants in their ability to be seeded, with variants at proline 301 and serine 320 showing robust aggregation with seeding. Similarly, we elucidated the importance of certain tau protein regions and unique residues, including the role of proline 301 in inhibiting tau aggregation. We also revealed potential barriers in cross-seeding between 3-repeat and 4-repeat tau isoforms. Overall, these differences alluded to potential mechanistic differences between wild-type and FTDP-17 tau variants, as well as different tau isoforms, in influencing tau aggregation. Furthermore, by combining two FTDP-17 tau variants (either P301L or P301S with S320F), we generated aggressive models of tauopathy that does not require exogenous seeding. These models will allow for rapid screening of potential therapeutics to alleviate tau aggregation without the need for exogenous tau fibrils. Together, these studies provide novel insights in the molecular determinants that modulate tau aggregation.Tauopathies are a spectrum of neurodegenerative diseases characterized by the presence of pathological inclusions composed of aberrantly aggregated and hyperphosphorylated microtubule-associated protein tau (MAPT). Tauopathies are pathologically and phenotypically diverse, and include Alzheimer's disease (AD), progressive supranuclear palsy, corticobasal degeneration, chronic traumatic encephalopathy, Pick's disease, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17)(1-4). Tau is abundant in neurons and expressed at lower levels in glia (1, 6, 7), and primarily stabilizes microtubules (MTs) among other diverse physiological functions (1,5,8,9). Six different isoforms of tau, ranging from 352 to 441 amino acids, are expressed in the adult human brain as a result of alternative splicing (10, 11). Differential splicing results in the inclusion or exclusion of the R2 MT-binding repeat, producing tau isoforms with either three (3R) or four (4R) repeats, respectively, and one or two N-terminal inserts (Figure 1).Over 50 mutations have been identified in the MAPT gene in families with 2,4,12 Tau Mutants and Seeding 2 disease, and patients typically experience disease onset at ~49 years of age with an average disease duration of 8.5 years (13). Certai...

Structural disorder in four-repeat Tau fibrils reveals a new mechanism for barriers to cross-seeding of Tau isoforms

“…Notably, homotypic recruitment of P301S and P301L monomers onto their respective seeds was even more efficient (Ͼ90%) and faster (t1 ⁄ 2 ϭ 5-9 min) than heterotypic recruitment of htau40 ( Fig. S2), in agreement with previous studies that suggested preferential growth of mutant over WT Tau (12,(33)(34)(35). To obtain visual confirmation for the recruitment of WT Tau onto mutant seeds, we next collected TEM images of negatively stained samples ( Fig.…”

Untangling the Prion-Like Misfolding Mechanism for Neurodegenerative Diseases

“…However, within the proposed mechanism of tau conformational-templating and seeding, the aggregation of tau monomer to tau seeds must first take place. A recent study from Strang et al, [55], indicates that specific regions within tau, play a key role in regulating aggregation and seeding. In particular, P301L and S320F tau mutants are uniquely able to aggregate with seeding when compared to WT tau, and aggregated P301L tau failed to sequester soluble WT tau into insoluble aggregates in HEK293 cells seeding model [55].…”

“…A recent study from Strang et al, [55], indicates that specific regions within tau, play a key role in regulating aggregation and seeding. In particular, P301L and S320F tau mutants are uniquely able to aggregate with seeding when compared to WT tau, and aggregated P301L tau failed to sequester soluble WT tau into insoluble aggregates in HEK293 cells seeding model [55]. Moreover, because of a lower tendency of P301L tau to aggregate in the presence of WT tau expression, it is possible that WT tau may reduce template conformation of P301L tau.…”

“…Tau is expressed in neurons and at lower levels in glia [50] and the main attributed function is to stabilize microtubules [54]. Differential splicing results in the production of tau isoforms with either three (3R) or four (4R) repeats, and one or two N-terminal inserts (reviewed in [55]). Intriguingly, certain intronic and some exonic mutations can alter the 3R/4R ratio increasing unbound tau and leading to aggregation [50][51][52][53], which by mounting evidence is thought to occur in a prion-like manner [56].…”

Utilizing minimally purified secreted rAAV for rapid and cost-effective manipulation of gene expression in the CNS

“…Organotypic BSCs were washed in PBS, fixed on their inserts with 4% paraformaldehyde for 1 h, and then stained with 0.0125% Thioflavin S as previously described [31]. In brief, a stock solution of 1% Thioflavin S (Sigma-Aldrich) in 50% EtOH in PBS was filtered through a 0.2-μm filter.…”