Tau N-Terminal Inserts Regulate Tau Liquid-Liquid Phase Separation and Condensates Maturation in a Neuronal Cell Model.

Shifeng Xiao,Junyi Zhao,Qiuping Wu,Chengchen Wu,Qiong Liu,Qiulong Tan

doi:10.3390/ijms22189728

Shifeng Xiao, Junyi Zhao + Show 4 more

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https://doi.org/10.3390/ijms22189728

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Abstract

The microtubule-associated protein tau can undergo liquid–liquid phase separation (LLPS) to form membraneless condensates in neurons, yet the underlying molecular mechanisms and functions of tau LLPS and tau droplets remain to be elucidated. The human brain contains mainly 6 tau isoforms with different numbers of microtubule-binding repeats (3R, 4R) and N-terminal inserts (0N, 1N, 2N). However, little is known about the role of N-terminal inserts. Here we observed the dynamics of three tau isoforms with different N-terminal inserts in live neuronal cell line HT22. We validated tau LLPS in cytoplasm and found that 2N-tau forms liquid-like, hollow-shell droplets. Tau condensates became smaller in 1N-tau comparing with 2N-tau, while no obvious tau accumulated dots were shown in 0N-tau. The absence of N-terminal inserts significantly affected condensate colocalization of tau and p62. The results reveal insights into the tau LLPS assembly mechanism and functional effects of N-terminal inserts in tau.

Highlights

Liquid–liquid phase separation (LLPS) has been observed within the cells at the molecular level to allow membraneless compartmentalization and regulation of biological processes, such as gene expression, autophagic degradation, assembly of signaling clusters, formation of synaptic density signaling assemblies, asymmetric segregations of cell fate determinants, etc. [1,2,3,4] the assembly and aggregation mechanisms of the biomolecular interactions giving rise to phase separation and the functions of such biomolecular condensates are still elusive
The hypothesis has been proposed that LLPS-driven tau droplet formation may represent a common and critical mechanism as the initial step to further lead to tauopathies [7], a group of progressive neurodegenerative disorders that are pathologically defined by the presence of tau protein aggregates in the brain [9]
Our findings reveal the role of tau N-terminal inserts in tau LLPS in live neuronal cell lines, and in the context of the previously proposed hypothesis that tau droplet formation can lead to tau aggregation [7], tau N-terminal inserts may hold promise as a novel therapeutic target to intervene in tau pathological aggregation in neurodegenerative diseases

Summary

Introduction

Liquid–liquid phase separation (LLPS) has been observed within the cells at the molecular level to allow membraneless compartmentalization and regulation of biological processes, such as gene expression, autophagic degradation, assembly of signaling clusters, formation of synaptic density signaling assemblies, asymmetric segregations of cell fate determinants, etc. [1,2,3,4] the assembly and aggregation mechanisms of the biomolecular interactions giving rise to phase separation and the functions of such biomolecular condensates are still elusive. [1,2,3,4] the assembly and aggregation mechanisms of the biomolecular interactions giving rise to phase separation and the functions of such biomolecular condensates are still elusive. The intrinsically disordered microtubule-associated protein tau has been reported to efficiently undergo LLPS to form condensed liquid droplets [7], which are clearly distinct from fibrillary aggregates in neurofibrillary tangles in neurodegenerative diseases [8]. The hypothesis has been proposed that LLPS-driven tau droplet formation may represent a common and critical mechanism as the initial step to further lead to tauopathies [7], a group of progressive neurodegenerative disorders that are pathologically defined by the presence of tau protein aggregates in the brain [9].

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