β‐arrestin2 oligomers impair the clearance of pathological tau and increase tau aggregates

Abstract

Background Frontotemporal lobar degeneration (FTLD) is second only to Alzheimer’s disease as a cause of dementia, and we find the scaffolding protein β‐arrestin2 is elevated in human brains with this condition, and is responsible for accumulation of pathological tau tangles. Increased β‐arrestin2 impairs tau clearance and promotes tau aggregation by impeding the autophagy cargo carrier p62/SQSTM1. Such activity requires β‐arrestin2 in its oligomeric form, an assembly state that is not involved with receptor binding. Virus delivered gene therapy to the brain with dominant‐negative mutant β‐arrestin2s ablates pathologic tau in neurons of a mouse model of FTLD‐tau, revealing a new strategy to mitigate tauopathy by targeting β‐arrestin2 oligomerization. Method mice: Arrb2−/−, tau P301S, and WT mice were all bred in the C57BL6 background. Patients samples: Frozen frontal cortex tissue samples were obtained from the Alzheimer’s Disease Research Center at Emory University. We used samples from FTLD‐tau diagnosed patients. Primary neuronal cultures, Proximity ligation assay (PLA), Immunocytochemistry and Immunohistochemistry, Sarkosyl extraction, Generation of rAAV9 and stereotaxic injections, Electrophysiology, and Atomic force Microscopy Imaging applications were used in this study. Result β‐arrestin2 levels in brains of FTLD‐tau patients and tau P301S transgenic mice were significantly increased. β‐arrestin2 increases tau stability without altering tau mRNA levels. Furthermore, genetic reduction of β‐arrestin2 mitigates tauopathy and synaptic dysfunction in tau P301S mice. β‐arrestin2 oligomerization is required for tau stability, and β‐arrestin2 oligomers increase tau levels by inhibiting self‐association of the autophagy cargo receptor p62/SQSTM1, impeding p62 autophagy flux. Hence, reduction of oligomerized β‐arrestin2 with virus encoding β‐arrestin2 mutants acting as dominant‐negatives markedly reduced tau‐laden neurofibrillary tangles in FTLD mice in vivo. Reducing β‐arrestin2 oligomeric status represents a new strategy to alleviate tau pathology in FTLD and related tauopathies. Conclusion Based on our findings, the effects of inhibiting β‐arrestin2 oligomerization would be expected to not only inhibit the development of new tau tangles, but also to clear existing tau accumulations due to this mechanism of enhancing tau clearance. Beyond tauopathy, it is conceivable that this strategy could also prove to be beneficial in other neurodegenerative diseases bearing proteinopathies that are cleared via p62.

Slingshot homolog-1 mediates the secretion of small extracellular vesicles containing misfolded proteins by regulating autophagy cargo receptors and actin dynamics

“…Cofilin activity is increased in the brains of AD patients (Zhao et al, 2006;Kim et al, 2013) and the APP/PS1 mouse model (Woo et al, 2015b). At the same time, the autophagy-lysosome pathway is overwhelmed and impaired in AD (Lin et al, 2003;Nixon et al, 2005;Salminen et al, 2012;Hebron et al, 2014;Rea et al, 2014;Tanji et al, 2014;Feng et al, 2019;Roca-Agujetas et al, 2021a,b), which contributes to the accumulation of misfolded proteins and dysfunctional mitochondria (Ramesh Babu et al, 2008;Xu et al, 2019;Woo et al, 2020;Fang et al, 2021;Roca-Agujetas et al, 2021a,b). Meanwhile, AD pathological proteins Aβ and tau are secreted in exosomes and are propagated from cell to cell in part via exosomes (Asai et al, 2015;Sardar Sinha et al, 2018;Miyoshi et al, 2021).…”

“…This secretory pathway has been proposed to involve the fusion of autophagosomes with MVBs to form amphisomes, which are then secreted by fusion with the plasma membrane (Gordon et al, 1992;Liou et al, 1997;Fader et al, 2008;Ganesan and Cai, 2021). Interestingly, autophagy cargo receptors, such as Sqstm1/p62 and optineurin, are often found in secreted exosomes (Gudbergsson and Johnsen, 2019), while they play vital roles in the clearance of misfolded proteins such as tau in AD (Xu et al, 2019;Woo et al, 2020;Fang et al, 2021;Roca-Agujetas et al, 2021a,b). However, whether prototypic autophagy cargo receptors regulate exosome secretion is unknown.…”