Endo, Yoshinori

AbstractBackgroundPathological hallmarks of Alzheimer's disease (AD) are senile plaques (SPs) and neurofibrillary tangles (NFTs), which are formed from highly phosphorylated tau. Lithium chloride (LiCl) has been shown to inhibit phosphorylated tau by inhibiting glycogen synthase kinase‐3β (GSK‐3β). In addition, autophagy lysosome system (Hamano et al., Eur J Neurosci 27; 1119, 2008) and proteasome (J Neurochem 2000) are known to play an important role as tau degradation pathways. We investigated the decrease of phosphorylated tau by LiCl by using cell culture model expressing wild‐type tau via TetOff induction system.MethodsTen to 50mM of LiCl treatment (24 hours) was performed to neuroblastoma cells (M1C) expressing wild‐type tau protein (4R0N) via TetOff induction. Total and phosphorylated tau (PHF‐1) levels and autophagy activation were examined by Western blot (WB) analysis.ResultsReduction of total tau (Tau5) and phosphorylated tau (PHF‐1, and CP13) with LiCl treatment was detected by WB analysis. C‐terminal truncated tau species detected by TauC3 was decreased by LiCl, too. In addition, increase of LC3Ⅱ/I, and decrease of P62 suggesting autophagy activation was observed. Major Tau kinase GSK3β was inactivated by LiCl.ConclusionsThese results imply that LiCl may decrease the phosphorylated tau through suppression of tau phosphokinase and activation of autophagy.

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.