Lithium Enhances Hippocampal Glucose Metabolism in an In Vitro Mice Model of Alzheimer's Disease

Abstract

Impaired cerebral glucose metabolism is an early event that contributes to the pathogenesis of Alzheimer's disease (AD). Importantly, restoring glucose availability by pharmacological agents or genetic manipulation has been shown to protect against Aβ toxicity, ameliorate AD pathology, and increase lifespan. Lithium, a therapeutic agent widely used as a treatment for mood disorders, has been shown to attenuate AD pathology and promote glucose metabolism in skeletal muscle. However, despite its widespread use in neuropsychiatric disorders, lithium's effects on the brain have been poorly characterized. Here we evaluated the effect of lithium on glucose metabolism in hippocampal neurons from wild-type (WT) and APPSwe/PS1ΔE9 (APP/PS1) mice. Our results showed that lithium significantly stimulates glucose uptake and replenishes ATP levels by preferential oxidation of glucose through glycolysis in neurons from WT mice. This increase was also accompanied by a strong increase in glucose transporter 3 (Glut3), the major carrier responsible for glucose uptake in neurons. Similarly, using hippocampal slices from APP-PS1 mice, we demonstrate that lithium increases glucose uptake, glycolytic rate, and the ATP:ADP ratio in a process that also involves the activation of AMPK. Together, our findings indicate that lithium stimulates glucose metabolism and can act as a potential therapeutic agent in AD.

Keywords: Alzheimer’s disease; glucose; lithium; metabolism.

Figure 1

Lithium treatment promotes glucose uptake in hippocampal neurons. (A) ¹⁴C-glucose uptake kinetics curve of hippocampal cultures treated with increasing concentrations of lithium measured over 180 s. (B) ¹⁴C-glucose uptake at 180 s of (A). (C) ¹⁴C-glucose uptake competition assay. Hippocampal cultures were treated with 10-mM lithium in the absence or presence of cytochalasin B (Cyt B), cytochalasin E (Cyt E) or 2-deoxy-D-glucose (2DG). (D) Michaelis–Menten kinetics of hippocampal neurons incubated with 10-mM lithium and ¹⁴C-glucose for 30 min. Data were analyzed by nonlinear regression and the Michaelis–Menten equation was used to determine kinetic parameters V_max and K_m. Data plotted as means ± SEM (n ≥ 3 independent cell culture preparations). * p < 0.05, ** p < 0.01, and *** p < 0.001 were determined by one-way ANOVA (in (B,C)) or two-way ANOVA (in (A,D)) followed by Bonferroni’s post hoc test for multiple comparisons; ns, not significant.

Figure 2

Lithium alters hippocampal bioenergetic status. (A) Glycolytic flux of hippocampal neurons treated with 10-mM lithium in the presence or absence of sodium dichloroacetate (DCA) (B) Hexokinase activity in hippocampal neurons treated with 10-mM lithium or 2-deoxy-D-glucose (2DG). (C) Pentose phosphate flux of hippocampal neurons treated with 10-mM lithium. (D) Glucose-6-phosphate dehydrogenase (G6PDH) activity in hippocampal lysates treated with 10 mM lithium. (E) NADPH/NADP⁺ ratio of hippocampal neurons treated with 10-mM lithium. Data plotted as means ± SEM (n = 5 independent cell culture preparations). *** p < 0.001 were determined by one-way ANOVA (in (A,B)) followed by Bonferroni’s post hoc test for multiple comparisons or Student’s t-test (in (C–E)); ns, not significant.

Figure 3

Lithium increases ATP levels and triggers the activation of AMPKα. (A–C) ATP and ADP levels, and ATP:ADP ratio of hippocampal lysates treated with 10-mM lithium in the presence or absence of oligomycin. (D) AMPKα activity in hippocampal neurons treated with either 10-mM lithium or the AMPK inhibitor compound C (CC). Data plotted as means ± SEM (n = 5 independent cell culture preparations). *** p < 0.001 were determined by one-way ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 4

Lithium enhances the expression of neuronal glucose transporter 3. (A–E) mRNA levels of hexokinase (HK), phosphofructokinase-1 (PFK-1), glucose transporter 1 (Glut1), Glut3, and Cyclin D1 (relative to cyclophilin) from hippocampal lysates, measured by qPCR. Data plotted as means ± SEM (n ≥ 4 independent cell culture preparations). *** p < 0.001 was determined by Student’s t-test; ns, not significant.

Figure 5

Lithium increases glucose uptake, ATP levels and glycolytic rate in hippocampal slices from APP/PS1 mice (A) Effect of 10-mM lithium on ¹⁴C-glucose uptake in hippocampal slices co-treated with either cytochalasin B (Cyt B), cytochalasin E (Cyt E) or 2-deoxy-D-glucose (2DG). (B) glycolytic rate of hippocampal slices from APP/PS1 mice treated with 10-mM lithium in the presence or absence of sodium dichloroacetate (DCA) (C) Hexokinase activity in APP/PS1 slices treated with 10-mM lithium or 2-deoxy-D-glucose (2DG). (D–F) ATP and ADP levels, and ATP:ADP ratio in hippocampal slices treated with 10-mM lithium in the presence or absence of oligomycin. (G) AMPKα activity in hippocampal neurons treated with either 10 mM lithium or compound C (CC). Data plotted as means ± SEM (n = 5 independent cell culture preparations). * p < 0.05 and *** p < 0.001 were determined by one-way ANOVA followed by Bonferroni’s post hoc test for multiple comparisons.

Figure 6

Schematic model for the action mechanism of lithium. Once internalized, lithium results in the activation of the canonical Wnt signaling pathway, promoting AMPK activation. Both AMPK and the Wnt pathway activation can trigger the upregulation of neuronal Glut3, resulting in glucose metabolism restoration by the stimulation of glucose uptake, increased glycolysis, and elevated ATP levels. Dashed lines indicate the participation of several proteins.