Lithium chloride alters Tau phosphorylation, kinase activity, and Rho GTPase signaling in cell models

Hyperphosphorylation and intracellular aggregation of Tau are pathological hallmarks of several neurodegenerative diseases, including Alzheimer's disease (AD). Clinical trials involving protein kinase inhibitors to modulate Tau phosphorylation in AD patients have shown mixed outcomes. For clinical trials using lithium salts, this could be explained by sequestration of lithium by β-amyloid and might be circumvented by selection of lithium salts with low affinity to Aβ fibrils and oligomers, promoting improved therapeutic efficacy and positive outcomes in future clinical trials. Here, we assessed the effects of lithium chloride (LiCl), a potent inhibitor of the serine/threonine kinase GSK-3β, on Tau phosphorylation and kinase activity using two cell models: the U2OS cell line overexpressing human triple mutant Tau-tGFP and a mouse cortical neuron/BV-2 co-culture model with inflammation-induced Tau hyperphosphorylation. We show that in the co-culture model, induction of inflammation led to increased Tau phosphorylation at the assessed phosphosites. LiCl reduced Tau phosphorylation depending on the concentration and the targeted phosphosites. Proteomics data from the U2OS cell line showed that LiCl treatment led to decreased phosphorylation at most of the examined phosphosites, which was consistent with the biochemical data. Our data suggest that LiCl may affect other kinases beyond GSK-3β. Additionally, we observed changes in the phosphorylation status of several proteins belonging to different Rho GTPase cycles, known to play a role in AD pathogenesis. Taken together, our data expand the understanding of the effects of LiCl on Tau phosphosites, kinases, and other AD-relevant pathways, such as Rho GTPases.