LiCl Attenuates Thapsigargin-Induced Tau Hyperphosphorylation by Inhibiting GSK-3 beta In Vivo and In Vitro

Abnormal hyperphosphorylation of microtubule-associated protein tau is involved in the pathogenesis of several neurodegenerative diseases, including Alzheimer's disease (AD). Endoplasmic reticulum (ER) stress is indicated to play an important role in neurodegeneration and activation of glycogen synthase kinase-3 beta (GSK-3 beta), an integral kinase in tau phosphorylation. To explore the effect of ER stress on tau phosphorylation, we treated cultured cells (HEK293 and SH-SY5Y cells) and rat brain with thapsigargin, an ER stress inducer. We found that the phosphorylation level of tau was significantly increased after thapsigargin treatment. By using a cell-free reconstitution system, we also observed that co-culture of the thapsigargin-treated ER fraction from HEK293/wt (without tau) with cytoplasm prepared from HEK293/tau induced an increased tau phosphorylation. Concurrently, activation of GSK-3 beta as evidenced by an increased phospho-GSK-3 beta at Tyr-216 and decreased phospho-GSK-3 beta at Ser-9 both in vitro and in vivo was detected. Application of lithium chloride, a GSK-3 inhibitor, could efficiently attenuate the thapsigargin-induced tau hyperphosphorylation with suppressed activation of GSK-3 beta in cell cultures and rat brains. Our data provide further evidence supporting the role of ER stress in tau hyperphosphorylation and the protective role of lithium.