Lithium Promotes Longevity through GSK3/NRF2-Dependent Hormesis

Abstract

The quest to extend healthspan via pharmacological means is becoming increasingly urgent, both from a health and economic perspective. Here we show that lithium, a drug approved for human use, promotes longevity and healthspan. We demonstrate that lithium extends lifespan in female and male Drosophila, when administered throughout adulthood or only later in life. The life-extending mechanism involves the inhibition of glycogen synthase kinase-3 (GSK-3) and activation of the transcription factor nuclear factor erythroid 2-related factor (NRF-2). Combining genetic loss of the NRF-2 repressor Kelch-like ECH-associated protein 1 (Keap1) with lithium treatment revealed that high levels of NRF-2 activation conferred stress resistance, while low levels additionally promoted longevity. The discovery of GSK-3 as a therapeutic target for aging will likely lead to more effective treatments that can modulate mammalian aging and further improve health in later life.

Keywords: GSK-3; Keap1; NRF-2; aging; dietary restriction; triglycerides; xenobiotic stress.

Graphical abstract

Figure 1

Lithium Regulated Longevity and Metabolism in Drosophila (A) Lithium extended lifespan of w^DahDrosophila females (n = 160 flies per condition) at concentrations between 1 and 25 mM (+16% and +18% median and maximum lifespan extension; p < 0.001), but resulted in a dose-dependent reduction in lifespan at concentrations between 50 and 100 mM (p < 0.001). (B) Lithium treated female w¹¹¹⁸ flies showed a significant improvement and protection against age-related locomotor decline (p < 0.01, two-way ANOVA for 10 mM). (C) Lithium extended lifespan of aged, 32-day-old female w^Dah flies at concentrations from 1 to 25 mM (30 days later than in Figure 1A): 1 mM extended median lifespan by 5% (4 days) and maximum lifespan by 13% (8 days; p < 0.05); 10 and 25 mM lithium increased median lifespan by 9% (6 days); 10 mM increased maximum lifespan by 4.5% (3.5 days); wherease 25 mM lengthened it by 8% or 6 days (p < 0.01); and 50 and 75 mM significantly shortened lifespan (p < 0.01). n = 150 flies per condition. (D) Brief treatment with lithium for 15 days early in adulthood extended lifespan of female w^Dah flies (p < 0.05 for 1 mM and p < 0.01 for 10 mM; n = 150 flies per condition). (E) Lithium induced a dose-dependent reduction in triglyceride levels. Bars represent means of six replicas of five flies per condition ± SEM. ^∗p < 0.01, ^∗∗p < 0.001. (F) Female w^Dah flies pre-treated with lithium for 15 days were subsequently sensitive to starvation in a dose-dependent manner (n = 90 flies per condition). (G) Lithium treatment significantly extended the lifespan of w¹¹¹⁸ female flies exposed to a four times higher sucrose concentration (2g/L; p < 0.001; n = 120 flies per condition). (H) The increase of triglycerides observed on a high-sucrose diet was completely blocked after 15 days of treatment with 1 mM lithium. Bars represent means of six replicas of five w¹¹¹⁸ female flies per condition ± SEM. ^∗p < 0.01.

Figure 2

Lithium Extended Lifespan beyond Dietary Restriction by Inhibiting Sgg/GSK-3 (A) Median lifespans at different lithium concentrations (0, 1, 2.5, 5, or 10 mM) are plotted for four different yeast concentrations (0.2×, 0.5×, 1.0×, and 2.0× yeast): 1–5 mM lithium extended lifespan under all dietary conditions tested. Although 10 mM lithium prolonged life at 1.0× and 2.0×, it showed no effect at 0.2× and significantly shortened lifespan at 0.5× yeast. ^∗p < 0.05, ^∗∗p < 0.01, ^∗∗∗p < 0.001, from 0 lithium; n = 160 flies per condition. Complete survival curves are shown in Figures S2A–S2D. (B) Lithium treatment for 15 days significantly increased the inhibitory phosphorylation of Sgg/GSK-3 in a dose-dependent manner. Bars represent means of triplicates of ten flies per biological repeat ± SEM, ^∗p < 0.05, ^∗∗p < 0.01. (C) Ubiquitous overexpression of wild-type sgg significantly shortened lifespan (p < 0.001) and this was partially rescued by lithium treatment at two concentrations (10 and 25 mM; p < 0.001). See Figure S2E for the interaction of sgg(S9A) and lithium treatment on lifespan. (D) Ubiquitous RNAi-mediated downregulation of sgg extended lifespan (p < 0.001) and no further extension occurred when the flies were treated with 1 or 5 mM lithium (p > 0.05), whereas 10 mM lithium treatment restored the lifespan to control levels (p > 0.05), and 25 mM was significantly toxic (p > 0.05). See Figure S2F for lifespan extension obtained with an independent RNAi line.

Figure 3

Lithium Activated a Transcriptional Response Similar to that of CncC/NRF-2 (A) Ten most significantly upregulated GO categories induced by lithium treatment of w¹¹¹⁸ female flies. See Figure S3A for downregulated GO categories. (B) Lithium treatment of w¹¹¹⁸ females flies induced a transcriptional response that significantly overlapped with that induced by cncC overexpression (p = 7.83 × 10⁻⁸) or phenobarbital treatment (p = 3.85 × 10⁻¹⁴) (Misra et al., 2011). Heatmap showing the 57 genes most significantly changed by lithium or phenobarbital treatment and overexpression of cncC. (C) Genes upregulated by lithium treatment mapped to the three phases of the xenobiotic detoxification pathway in flies. (D) Lithium treatment of w^Dah female flies upregulated Gst-D protein levels. Bars represent means of triplicates of ten flies per condition ± SEM. ^∗p < 0.05, ^∗∗p < 0.01.

Figure 4

Lithium-Induced Xenobiotic Resistance and Longevity Were Mediated by CncC (A) Ubiquitous knockdown of cncC blocked lifespan extension by lithium. (B) Pre-treatment with increasing concentrations of lithium protected against a subsequent toxic dose of lithium (500 mM; p < 0.01 for doses from 10 to 100 mM; p < 0.05 for 1 mM). (C) Ubiquitous downregulation of cncC blocked the protective effect of 10 mM lithium pre-treatment against a subsequent toxic dose and partially blocked the protective effect of 25 mM lithium pre-treatment. (D) 1 to 100 mM lithium pre-treatment protected against a 6% phenobarbital (p < 0.001 for all doses). (E) Lithium pre-treatment (for 15 days) protected against the herbicide paraquat in a dose-dependent manner (p < 0.001 for all doses, with maximal protection at 50 mM). (F) RNAi-mediated downregulation of cncC completely blocked the protective effect of lithium against phenobarbital.

Figure 5

Reduced Activity of GSK-3 Increased Resistance to Xenobiotics (A) Ubiquitous overexpression of wild-type sgg significantly (p < 0.05) reduced survival under xenobiotic stress with phenobarbital. n = 75 flies per condition. (B) Overexpression of wild-type sgg significantly reduced multidrug-resistance like protein 1 (MRP) mRNA levels (p < 0.05, paired t test), whereas non-significant trends were detected for glutathione S transferase D2 (gstD2) and cncC mRNA levels (p > 0.05). A non-significant increase of keap1 mRNA levels was observed. (C) RNAi-mediated knockdown of sgg protected against phenobarbital stress (p < 0.001). n = 75 flies per condition. (D) Knockdown of sgg increased mRNA levels of cncC, keap1 and gstD2 (p < 0.05), while a non-significant increase was observed for MRP mRNA levels.

Figure 6

Higher Activation Levels of CncC Promote Xenobiotic Resistance but Not Lifespan (A) Overexpression of keap1 did not prevent the lifespan-modulatory effects of lithium treatment. n = 150 flies per condition. (B) Schematic of the keap1 gene showing the portion deleted in the keap1^Del mutant (top) and agarose gel showing start and end of P-element disrupting keap1 coding sequence in the keap1^Del mutant (bottom). (C) Combination of heterozygous deletion of keap1 and lithium treatment showed a greater activation of CncC than on their own. Bars represent means of four replicas of five flies per repeat ± SEM. ^∗∗p < 0.01. (D) Deletion of keap1 in flies treated with lithium showed greater protection against paraquat than either treatment on its own, with maximal effects observed at 25 mM (p < 0.001). (E) The keap1 deletion protected against toxic concentrations of lithium (500 mM), and this protection was augmented with lithium pre-treatment (p < 0.01). (F) Deletion of keap1 did not extend lifespan: 1 mM lithium (p < 0.05), but not 10 mM (p > 0.05), treatment of keap1 flies resulted in a small but significant extension. n = 150 flies per condition. (G) keap1^EY5 mutant flies showed significant lifespan extension (p < 0.001), that was dose-dependently abolished (p > 0.05) by lithium, likely as a result of over-activation of CncC. n = 150 flies per condition.

Figure 7

Lithium Regulates Longevity, Metabolism, and Stress Resistance by Inhibiting GSK-3 and Activating NRF-2 (A) Summary of findings with lithium for longevity, stress resistance, starvation, and triglyceride levels. (B) Proposed model showing the mechanism by which lithium, Sgg/GSK-3, and CncC/NRF-2 act in the same pathway to modulate longevity and xenobiotic resistance.