Role of adult hippocampal neurogenesis in the antidepressant actions of lactate

Abstract

In addition to its role as a neuronal energy substrate and signaling molecule involved in synaptic plasticity and memory consolidation, recent evidence shows that lactate produces antidepressant effects in animal models. However, the mechanisms underpinning lactate's antidepressant actions remain largely unknown. In this study, we report that lactate reverses the effects of corticosterone on depressive-like behavior, as well as on the inhibition of both the survival and proliferation of new neurons in the adult hippocampus. Furthermore, the inhibition of adult hippocampal neurogenesis prevents the antidepressant-like effects of lactate. Pyruvate, the oxidized form of lactate, did not mimic the effects of lactate on adult hippocampal neurogenesis and depression-like behavior. Finally, our data suggest that conversion of lactate to pyruvate with the concomitant production of NADH is necessary for the neurogenic and antidepressant effects of lactate.

Fig. 1. Peripheral administration of lactate reverses the reduction of adult hippocampal neural progenitor cells (NPCs) proliferation and survival in the corticosterone model of depression.

a Timeline showing the experimental design for measuring NPCs proliferation. Mice received a single subcutaneous injection of corticosterone (20 mg/kg) or vehicle (2% DMSO in sesame oil) on each of 21 consecutive days. Together with corticosterone treatment, mice received intraperitoneal injections of vehicle (0.9% NaCl) or lactate (1 g/kg) daily for 21 days. On the last day of treatment, mice also received BrdU injections. b Confocal maximal projection micrographs of hippocampal sections immunostained for BrdU. Inset: higher magnification confocal micrograph of a BrdU-immunolabeled group of cells. c Analysis of NPCs proliferation. Histogram of the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. d Timeline showing the experimental design for measuring NPCs survival. BrdU administration was performed the day before the start of the treatment. Then, mice received a single subcutaneous injection of corticosterone (20 mg/kg) or vehicle (2% DMSO in sesame oil) on each of 14 consecutive days. Together with corticosterone treatment, mice received intraperitoneal injections of vehicle (0.9% NaCl) or lactate (1 g/kg) daily for 14 days. e Analysis of NPCs survival. Histogram of the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. f Analysis of adult neurogenesis in the mouse dentate gyrus. Histogram showing the number of BrdU⁺ NeuN⁺ cells per mm³. g Confocal images of cells double-labeled for BrdU (red) and NeuN (green) and counterstained with DAPI (blue) in the dentate gyrus. The right panel corresponds to a higher magnification view of the boxed region shown in the merged image. Solid arrows point to BrdU⁺ NeuN⁺ cells and thin arrows to BrdU⁺ cells. Data are the mean ± SEM. One-way ANOVA followed by Tukey post-hoc test ((c): n = 7/condition; (e): n > 10/condition; (f): n > 4/condition). *p < 0.05. NS not significant.

Fig. 2. Inhibition of adult hippocampal neurogenesis by temozolomide suppresses the antidepressant and neurogenic effects of lactate in the corticosterone model of depression.

a Timeline showing the experimental design. Mice received an intraperitoneal injection of temozolomide (TMZ) (25 mg/kg) on the first 3 days of a week for 4 consecutive weeks. On the second week of TMZ treatment, mice received a daily subcutaneous injection of vehicle or corticosterone (20 mg/kg) and an intraperitoneal injection of vehicle (NaCl 0.9%) or lactate (1 g/kg) for 21 consecutive days. On the last day of treatment, mice received BrdU injections. b Confocal maximal projection micrographs of hippocampal sections immunostained for BrdU. Inset: Higher magnification confocal micrograph of a BrdU-immunolabeled group of cells. c Analysis of neural progenitor cells (NPCs) proliferation. Histogram of the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. d Assessment of depressive-like behavior in FST. Histogram of the time spent immobile during FST. e Assessment of depressive-like behavior in TST. Histogram of the time spent immobile during TST. f Assessment of anhedonia-like behavior in the saccharin preference test. Data are the mean ± SEM. One-way ANOVA followed by Tukey post-hoc test ((c): n = 7/condition; (d): n = 8/condition; (e): n = 11/condition, (f): n = 6/condition). *p < 0.05.

Fig. 3. Lack of antidepressant and neurogenic effects of pyruvate in the corticosterone model of depression.

a Timeline showing the experimental design for measuring neural progenitor cells (NPCs) proliferation. Mice received a single subcutaneous injection of corticosterone (20 mg/kg) or vehicle (2% DMSO in sesame oil) on each of 21 consecutive days. Together with corticosterone treatment, mice received intraperitoneal injections of vehicle (0.9% NaCl) or pyruvate (1 g/kg) daily for 21 days. On the last day of treatment, mice also received BrdU injections. b Confocal maximal projection micrographs of hippocampal sections immunostained for BrdU. Inset: Higher magnification confocal micrograph of a BrdU-immunolabeled group of cells. c Analysis of NPCs proliferation. Histogram of the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. d Assessment of depressive-like behavior in FST. Histogram of the time spent immobile during FST. e Timeline showing the experimental design for measuring NPCs survival. BrdU administration was performed the day before the start of the treatment. Then, mice received a single subcutaneous injection of corticosterone (20 mg/kg) or vehicle (2% DMSO in sesame oil) on each of 14 consecutive days. Together with corticosterone treatment, mice received intraperitoneal injections of vehicle (0.9% NaCl) or pyruvate (1 g/kg) daily for 14 days. f Analysis of NPCs survival. Histogram of the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. Data are the mean ± SEM. One-way ANOVA followed by Tukey post-hoc test ((c), (d): n > 10/condition; (f): n = 4/condition). *p < 0.05.

Fig. 4. Lactate, β-hydroxybutyrate, and NADH suppress ROS production induced by corticosterone in adult hippocampal stem/progenitor cells in vitro.

Analysis of ROS production. Cultures of adult hippocampal stem/progenitor cells were treated for 48 h with corticosterone (5 μM) together with either lactate (20 mM) (a), pyruvate (20 mM) (a), β-hydroxybutyrate (20 mM) (b), acetoacetate (20 mM) (b) or NADH (100 μM) (c). Left panels: histograms of CellROX intensity per cell shown as the percentage of the vehicle. Right panels: illustrations of CellROX fluorescence (green) in stem/progenitor cells counterstained with NucBlue (Hoechst)(blue). Data are the mean ± SEM. One-way ANOVA followed by Tukey post-hoc test (n > 17/condition). *p < 0.05. NS not significant.

Fig. 5. Lactate, β-hydroxybutyrate, and NADH partially counteract the decreased proliferation of adult hippocampal stem/progenitor cells induced by corticosterone in vitro.

Analysis of stem/progenitor cell proliferation. Cultures of adult hippocampal stem/progenitor cells were treated for 48 h with corticosterone (5 μM) together with either lactate (20 mM) (a), pyruvate (20 mM) (a), β-hydroxybutyrate (20 mM) (b), acetoacetate (20 mM) (b) or NADH (100 μM) (c). Left panels: histograms of the number of BrdU⁺ cells presented as a percentage of the vehicle. Right panels: fluorescent images of stem/progenitor cells immunostained for BrdU. Data are the mean ± SEM. One-way ANOVA followed by Tukey post-hoc test (n > 16/condition). *p < 0.05.