Extremely Low-Frequency Electromagnetic Field (ELF-EMF) Increases Mitochondrial Electron Transport Chain Activities and Ameliorates Depressive Behaviors in Mice

Abstract

Compromised mitochondrial electron transport chain (ETC) activities are associated with depression in humans and rodents. However, the effects of the enhancement of mitochondrial ETC activities on depression remain elusive. We recently reported that an extremely low-frequency electromagnetic field (ELF-EMF) of as low as 10 μT induced hormetic activation of mitochondrial ETC complexes in human/mouse cultured cells and mouse livers. Chronic social defeat stress (CSDS) for 10 consecutive days caused behavioral defects mimicking depression in mice, and using an ELF-EMF for two to six weeks ameliorated them. CSDS variably decreased the mitochondrial ETC proteins in the prefrontal cortex (PFC) in 10 days, which were increased by an ELF-EMF in six weeks. CSDS had no effect on the mitochondrial oxygen consumption rate in the PFC in 10 days, but using an ELF-EMF for six weeks enhanced it. CSDS inactivated SOD2 by enhancing its acetylation and increased lipid peroxidation in the PFC. In contrast, the ELF-EMF activated the Sirt3-FoxO3a-SOD2 pathway and suppressed lipid peroxidation. Furthermore, CSDS increased markers for mitophagy, which was suppressed by the ELF-EMF in six weeks. The ELF-EMF exerted beneficial hormetic effects on mitochondrial energy production, mitochondrial antioxidation, and mitochondrial dynamics in a mouse model of depression. We envisage that an ELF-EMF is a promising therapeutic option for depression.

Keywords: extremely low-frequency electromagnetic field (ELF-EMF); major depressive disorder; mitochondrial electron transport chain; oxidative stress; social defeat stress.

Figure 1

The ELF-EMF exerted antidepressant-like behavioral effects in the CSDS mouse model of depression. (A) Experimental protocols: C57BL/6N mice were divided into four groups. CSDS was applied for 10 continuous days. CSDS-resilient mice were excluded from the following studies. CSDS-susceptible mice were individually housed in a cage with or without the ELF-EMF for six weeks. (B) Electromagnetic intensities were generated by a coil around the mouse cage. The mouse’s head was about 2 cm above the floor. (C) Immobility times in the tail suspension test two weeks after CSDS (n = 11 to 12 mice each). (D) Immobility times in the forced swim test two weeks after CSDS (n = 11 mice each). (E) Schematic of the social interaction test. (F) Time spent in the interaction zone with or without an ICR mouse and the SI ratio, which is calculated by dividing the time spent with the ICR mouse by that without the ICR mouse six weeks after CSDS (n = 14, 13, 22, and 19 mice, respectively). (C,D,F) Mean and SEM are indicated. * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001 according to one-way ANOVA, followed by Tukey’s multiple comparisons test.

Figure 2

CSDS for 10 consecutive days variably downregulated the mitochondrial electron transport chain (ETC) complex proteins in the prefrontal cortex (PFC), which were increased by the ELF-EMF for 6 weeks. Spare respiratory capacity according to the OCR remained unchanged by CSDS but was increased by using the ELF-EMF for 6 weeks. (A,C) Representative duplicated immunoblots of the PFC on the next day after CSDS. (B,D) Densitometric analysis of immunoblots. Mean and SEM are indicated (n = 5 to 6 mice each). (B) No statistical difference according to the unpaired t-test. (D) * p < 0.05 according to two-way ANOVA, followed by Šídák’s multiple comparisons test. (E) The OCR of mitochondria isolated from the cerebral cortex on the next day after CSDS. The OCR was normalized to that at Phase I. Mean and SEM are indicated (n = 10 and 12 brain hemispheres, respectively). No statistical difference by two-way repeated-measures ANOVA. (F,G) ADP-induced respiration (Phase II) (F) and spare respiratory capacity (Phase IV–Phase I) (G) of mitochondria isolated from the cerebral cortex on the next day after CSDS are normalized to the mean of the control. Mean and SEM are indicated (n = 10 and 12 brain hemispheres, respectively). No statistical difference according to the unpaired t-test. (H,J) Representative immunoblots of the PFC six weeks after CSDS. (I,K) Densitometric analysis of immunoblots. Mean and SEM are indicated (n = 6 mice each). (I) No statistical difference according to one-way ANOVA. (K) * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001 according to two-way ANOVA, followed by Tukey’s multiple comparisons test. (L) The OCR of mitochondria isolated from the cerebral cortex. The OCR was normalized to that at Phase I. Mean and SEM are indicated (n = 8 to 10 brain hemispheres each). Statistical significance was observed in CSDS + ELF-EMF compared to CSDS according to two-way repeated-measures ANOVA, followed by Dunnett’s multiple comparisons test (** p < 0.005, *** p < 0.0005, and **** p < 0.0001). (M,N) ADP-induced respiration (Phase II) (M) and spare respiratory capacity (Phase IV–Phase I) (N) of mitochondria isolated from the cerebral cortex are normalized to the mean of the control. Mean and SEM are indicated (n = 8 to 10 brain hemispheres each). * p < 0.05 and ** p < 0.01 according to one-way ANOVA, followed by Tukey’s multiple comparisons test.

Figure 3

CSDS for 10 consecutive days increased the acetylation at K68 of SOD2 and the levels of 4-HNE-modified proteins in the prefrontal cortex (PFC), which were mostly mitigated by ELF-EMF exposure for 6 weeks. (A,C,E) Representative duplicated immunoblots of the PFC on the next day after CSDS. (B,D) ** p < 0.01 according to two-way ANOVA, followed by Šídák’s multiple comparisons test. (F) * p < 0.05 according to the unpaired t-test. (G,I,K) Representative immunoblots of the PFC six weeks after CSDS. (H,J,L) Densitometric analysis of immunoblots. Mean and SEM are indicated (n = 6 mice each). (H,J) * p < 0.05 and ** p < 0.01 according to two-way ANOVA, followed by Tukey’s multiple comparisons test. (L) * p < 0.05 and ** p < 0.01 according to one-way ANOVA, followed by Tukey’s multiple comparisons test.

Figure 4

CSDS-mediated enhanced phosphorylation of DRP1 in the PFC was not changed by the ELF-EMF, whereas CSDS-mediated upregulation of mitophagy in the PFC was mitigated by the ELF-EMF six weeks after CSDS. (A,G) Representative immunoblots six weeks after CSDS. (B–F,H) Densitometric analysis of immunoblots. Mean and SEM are indicated (n = 6 mice each). (B–F) * p < 0.05, ** p < 0.01, and *** p < 0.001 according to one-way ANOVA, followed by Tukey’s multiple comparisons test. (H) * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001 according to two-way ANOVA, followed by Tukey’s multiple comparisons test.