Clioquinol Decreases Levels of Phosphorylated, Truncated, and Oligomerized Tau Protein.

Gaoping Lin,Feiyan Zhu,Soichi Enomoto,Asako Ueno,Tadanori Hamano,Shu-Hui Yen,Tomohisa Yamaguchi,Hirohito Sasaki,Masamichi Ikawa,Yasunari Nakamoto,Kouji Hayashi,Nicholas M Kanaan,Yoshinori Endo,Rei Asano,Osamu Yamamura,Norimichi Shirafuji

doi:10.3390/ijms222112063

Abstract

The neuropathological hallmarks of Alzheimer’s disease (AD) are senile plaques (SPs), which are composed of amyloid β protein (Aβ), and neurofibrillary tangles (NFTs), which consist of highly phosphorylated tau protein. As bio-metal imbalance may be involved in the formation of NFT and SPs, metal regulation may be a direction for AD treatment. Clioquinol (CQ) is a metal-protein attenuating compound with mild chelating effects for Zn2+ and Cu2+, and CQ can not only detach metals from SPs, but also decrease amyloid aggregation in the brain. Previous studies suggested that Cu2+ induces the hyperphosphorylation of tau. However, the effects of CQ on tau were not fully explored. To examine the effects of CQ on tau metabolism, we used a human neuroblastoma cell line, M1C cells, which express wild-type tau protein (4R0N) via tetracycline-off (TetOff) induction. In a morphological study and ATP assay, up to 10 μM CQ had no effect on cell viability; however, 100 μM CQ had cytotoxic effects. CQ decreased accumulation of Cu+ in the M1C cells (39.4% of the control), and both total and phosphorylated tau protein. It also decreased the activity of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) (37.3% and 60.7% levels of the control, respectively), which are tau kinases. Of note, activation of protein phosphatase 2A (PP2A), which is a tau phosphatase, was also observed after CQ treatment. Fractionation experiments demonstrated a reduction of oligomeric tau in the tris insoluble, sarkosyl soluble fraction by CQ treatment. CQ also decreased caspase-cleaved tau, which accelerated the aggregation of tau protein. CQ activated autophagy and proteasome pathways, which are considered important for the degradation of tau protein. Although further studies are needed to elucidate the mechanisms responsible for the effects of CQ on tau, CQ may shed light on possible AD therapeutics.

Highlights

The characteristic pathological hallmarks of Alzheimer’s disease (AD) are neurofibrillary tangles (NFTs) that consist of intracellular hyperphosphorylated tau [1], and senile plaques (SPs) formed by the aggregation of extracellular amyloid β peptide (Aβ) [2]
We explored whether the metal-protein attenuating compound CQ decreased multiple forms of tau protein including phosphorylated, C-terminal truncated and oligomeric tau species in a cell culture model of tauopathy [32,33,34,35,36,37]
As the tau degradation mechanisms, CQ activated autophagy and proteasomal systems, suggesting that they play a role in reducing tau levels

Summary

Introduction

The characteristic pathological hallmarks of Alzheimer’s disease (AD) are neurofibrillary tangles (NFTs) that consist of intracellular hyperphosphorylated tau [1], and senile plaques (SPs) formed by the aggregation of extracellular amyloid β peptide (Aβ) [2]. Drugs for AD mainly consist of acetylcholine esterase inhibitors (donepezil, galantamine, and rivastigmine) [3] and N-methyl-D-aspartic acid receptor (NMDA) antagonists [4]. These drugs can alleviate the symptoms of AD, but do not reverse or stop the course of AD. Ca2+ and Mg2+ may selectively induce the formation of NFT, whereas Al3+, Cu2+, and Fe2+/Fe3+ can bind to tau as shown by in vitro study [19], and immunohistochemical study in AD and control brain [20]

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