The Q336H MAPT Mutation Linked to Pick's Disease Leads to Increased Binding of Tau to the Microtubule Network via Altered Conformational and Phosphorylation Effects.

Giacomo Siano,Valentina Quercioli,Mariachiara Micaelli,Arianna Scarlatti,Antonino Cattaneo,Cristina Di Primio

doi:10.3389/fnmol.2020.569395

Abstract

Tauopathies are neurodegenerative disorders characterized by Tau aggregation. Genetic studies on familial cases allowed for the discovery of mutations in the MAPT gene that increase Tau propensity to detach from microtubules and to form insoluble cytoplasmic Tau aggregates. Recently, the rare mutation Q336H has been identified to be associated with Pick’s disease (PiD) and biochemical analyses demonstrated its ability to increase the microtubules (MTs) polymerization, thus revealing an opposite character compared to other Tau mutations studied so far. Here we investigated the biophysical and molecular properties of TauQ336H in living cells by the employment of the conformational Tau biosensor CST. We found that this mutation alters Tau conformation on microtubules, stabilizes its binding to tubulin, and is associated with a paradoxical lower level of Tau phosphorylation. Moreover, we found that this mutation impacts the cytoskeletal complexity by increasing the tubulin filament length and the number of branches. However, despite these apparently non-pathological traits, we observed the formation of intracellular inclusions confirming that Q336H leads to aggregation. Our results suggest that the Tau aggregation process might be triggered by molecular mechanisms other than Tau destabilization or post-translational modifications which are likely to be detrimental to neuronal function in vivo.

Highlights

Tauopathies are a group of heterogeneous pathologies characterized by the dysfunction and aggregation of Tau protein
We have developed the CST Tau biosensor, a genetically encoded FRET sensor based on the full-length Tau fused at the N-terminus with ECFP and at the C-terminus with EYFP
By using CST, we have previously reported that Tau assumes a relaxed conformation when it is soluble into the cytoplasm, while, upon binding to tubulin, it displays a paperclip conformation with the N-and C-termini in proximity (Di Primio et al, 2017)

Summary

Introduction

Tauopathies are a group of heterogeneous pathologies characterized by the dysfunction and aggregation of Tau protein. Mutations in the MAPT gene, encoding Tau protein, are usually associated with familial disease up to now, almost 50 mutations have been identified in patients affected by different tauopathies (Strang et al, 2019). Some mutations increase Tau sensitivity to post-translational modifications, in particular the hyperphosphorylation followed by the formation of toxic amyloidogenic aggregates All these alterations lead to synaptic dysfunction and neuronal cell death (Hasegawa et al, 1998; Dayanandan et al, 1999; Goedert and Jakes, 2005; Fischer et al, 2007; Alonso et al, 2008; Wolfe, 2009; Iqbal et al, 2010; Strang et al, 2019). Tau mutations are a valuable tool to reproduce and study in vitro and in vivo the pathological mechanisms associated with Tau destabilization and aggregation

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Conclusion