Normal and Pathological Tau Uptake Mediated by M1/M3 Muscarinic Receptors Promotes Opposite Neuronal Changes.

Viktoriya Morozova,Alison Shur,Guillermo Pilar,Ali El-Hadi Makki,Abdeslem El Idrissi,Alejandra D Alonso,Leah S Cohen

doi:10.3389/fncel.2019.00403

Abstract

The microtubule associated protein tau is mainly found in the cell’s cytosol but recently it was also shown in the extracellular space. In neurodegenerative diseases, like Alzheimer’s disease (AD), pathological tau spreads from neuron to neuron enhancing neurodegeneration. Here, we show that HEK293 cells and neurons in culture uptake extracellular normal and pathological Tau. Muscarinic receptor antagonists atropine and pirenzepine block 80% this uptake. CHO cells do not express these receptors therefore cannot uptake tau, unless transfected with M1 and/or M3 receptor. These results strongly suggest that muscarinic receptors mediate this process. Uptake of normal tau in neurons enhances neuronal process formation but a pseudophosphorylated form of tau (pathological human tau, PH-Tau) disrupts them and accumulates in the somatodendritic compartment. AD hyperphosphorylated tau (AD P-Tau) has similar effects as PH-Tau on cultured neurons. Addition of either PH-Tau or AD P-tau to neuronal cultures induced microglial activation. In conclusion, uptake of extracellular tau is mediated by muscarinic receptors with opposite effects: normal tau stabilizes neurites; whereas pathological tau disrupts this process leading to neurodegeneration.

Highlights

Tau is a neuronal cytosolic microtubule associated phospho-protein whose function can be influenced by post-translational modifications
To better understand the mechanism of uptake, culture media spiked with recombinant proteins GST-tau, or GST-PH-Tau, 400 ng/mL (Supplementary Figure S1) was added to HEK293 or Chinese Hamster Ovary (CHO) cells and incubated for 4 h
Tau and PH-Tau were taken up into the HEK293 cells, but no uptake was observed in CHO cells (Figure 1A)

Summary

Introduction

Tau is a neuronal cytosolic microtubule associated phospho-protein whose function can be influenced by post-translational modifications. Soluble hyperphosphorylated tau taken from AD patients (AD P-tau) does not promote microtubule assembly. AD P-tau binds normal tau, sequestering it from interactions with tubulin and producing bundles of filaments observed by electron microscopy (Alonso et al, 1996). This suggests that differences in tau phosphorylation states could affect its conformation and subsequently alter protein-protein interactions and tau biological function. Seeding activity into self-assembled aggregates can lead to the development of neurofibrillary

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Conclusion