GSK3 Activity is Decreased in The Hippocampus of Male Mice Supplemented with Low‐Dose Lithium in Drinking Water

Abstract

Sporadic Alzheimer’s disease (AD) is a neurodegenerative disease characterized by neurofibrillary tangles composed of hyperphosphorylated tau proteins and amyloid‐beta (Aβ) plaques. Together, these two histopathological detriments in the brain lead to progressive cognitive decline. Glycogen synthase kinase‐3 β (GSK3β), a kinase found abundantly in the brain, has been implicated in the development of these AD pathologies. GSK3β remains constituently active until phosphorylated at its inhibitory Ser9 residue. When active, GSK3β is capable of inducing tau hyperphosphorylation and can phosphorylate amyloid‐precursor protein (APP), influencing greater levels of Aβ peptide production. Lithium (Li), a GSK3β inhibitor, has been suggested as an AD prophylaxis. However, Li has also been associated with several dose‐dependent adverse side effects. The purpose of this study was thus to examine the effects of a prophylactic low‐dose Li supplementation on brain GSK3β signaling and activity. C57BL/6J male mice were given 10mg/kg/day Li or no Li in their drinking water for 6 weeks (n=12/group) and the prefrontal cortex (PFC) and hippocampal (HIP) tissues were collected for GSK3 activity assay and western blot analyses. Li mice had increased serum Li concentrations (p<0.0001) and decreased hippocampal GSK3 activity (p=0.06) as compared to control mice. pAkt Thr308 phosphorylation, a kinase immediately upstream of GSK3β capable of inducing inhibitory pGSK3β Ser9 phosphorylation, was increased in the PFC of Li mice compared to control mice (p<0.05). However, no differences in pGSK3β Ser9 or Tyr216, an activating residue, were observed between control and Li mice in both the PFC and HIP. Changes in GSK3 activity without changes in inhibitory Ser9 phosphorylation may suggest that a longer supplementation is needed to affect significant changes in the brain. Furthermore, these results demonstrate that the phosphorylation status of GSK3β may not always be a direct translation of its activity. This highlights the importance of measuring GSK3β activity alongside of measures of upstream kinases (i.e. PI3K/Akt signaling) and downstream targets to obtain a better indication of GSK3β’s overall activity within the brain. Overall, this initial work provides evidence that Li can inhibit hippocampal GSK3 activity and alter the phosphorylation status of upstream kinases at a low‐dose. Future work will examine Li’s potential prophylactic effects in a diseased model which better mimics AD (i.e. aged and metabolically‐distressed mice). This is important to further elucidate the efficacy of low‐dose Li in the prevention of AD pathologies. Support or Funding Information This work is supported by the Alzheimer Society of Brant, Haldimand Norfolk, Hamilton Halton and NSERC.

Lithium Content of 160 Beverages and Its Impact on Lithium Status in Drosophila melanogaster

“…Additional studies in flies providing purified Li (e.g., LiCl) should be performed to elucidate critical dietary Li concentrations sufficient to modulate Li-sensitive targets, including an inactivation of glycogen synthase kinase 3ß (Gsk3ß) [14,46]. Beside Gsk3ß, other Li sensitive targets including the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) have been identified in Drosophila melanogaster [14,47].…”