Amyloidogenic cross-seeding of Tau protein: Transient emergence of structural variants of fibrils

Abstract

Amyloid aggregates of Tau protein have been implicated in etiology of many neurodegenerative disorders including Alzheimer's disease (AD). When amyloid growth is induced by seeding with preformed fibrils assembled from the same protein, structural characteristics of the seed are usually imprinted in daughter generations of fibrils. This so-called conformational memory effect may be compromised when the seeding involves proteins with non-identical sequences leading to the emergence of distinct structural variants of fibrils (amyloid ‘strains’). Here, we investigate cross-seeding of full-length human Tau (FL Tau) with fibrils assembled from K18 and K18ΔK280 fragments of Tau in the presence of poly-L-glutamate (poly-Glu) as an enhancer of Tau aggregation. To study cross-seeding between Tau polypeptides and the role of the conformational memory effect in induction of Tau amyloid polymorphism, kinetic assays, transmission electron microscopy, infrared spectroscopy and limited proteolysis have been employed. The fastest fibrillization was observed for FL Tau monomers seeded with preformed K18 amyloid yielding daughter fibrils with unique trypsin digestion patterns. Morphological features of daughter FL Tau fibrils induced by K18 and K18ΔK280 seeds were reminiscent of the mother fibrils (i.e. straight paired fibrils and paired helical filaments (PHFs), respectively) but disappeared in the following generations which became similar to unpaired FL Tau amyloid fibrils formed de novo. The structural evolution observed in our study was accompanied by disappearance of the unique proteolysis profile originated from K18. Our findings may have implications for understanding molecular mechanisms of the emergence and stability of Tau amyloid strains.

Asparagine endopeptidase cleaves tau at N167 after uptake into microglia

“…The addition of pre-formed aggregate seeds furthermore resulted in an aggregation kinetics with a very short lag time (Fig. 2B), in agreement with previous studies on seeded tau aggregation (27). This suggests that small amounts of aggregates formed by the tau 168-368 fragment may cause full-length tau to form fibrils, even though the protein is normally much more conformationally stable and remains soluble.…”

In vitro generation of tau aggregates conformationally distinct from parent tau seeds of Alzheimer’s brain

“…A recent study reported that cross-seeding of tau protein lead to the emergence of structural variant of fibrils [61], again supporting the possibility that the difference in size we observed may be attributed to the mutated tau fragment tagged with eGFP. To explore this possibility, we have conducted cell-free conversion assay in which full-length recombinant tau was used as substrate.…”

Tau-Cofactor Complexes as Building Blocks of Tau Fibrils

“…This question is essential in the context of prion-like mechanisms (Sanders et al, 2014;Woerman et al, 2016), where one needs to understand the conditions required to ensure the faithful propagation of a given strain. Although cellular work has suggested that strain properties (based on proteolysis patterns and cellular localization of aggregates) can be maintained through seeding (Kaufman et al, 2016), other in vitro work suggested that properties of the seeded protein, and not the seed, dictate the structure of the obtained aggregates (Nizynski et al, 2018). Fichou and coworkers (Fichou et al, 2018a) showed that cofactor-assisted seeding achieve a mild degree of structural convergence compared to heterogeneous heparin fibrils, but without deciphering its origin.…”