Melatonin Alleviates Neuroinflammation and Metabolic Disorder in DSS-Induced Depression Rats

Abstract

There is a bidirectional relationship between inflammatory bowel disease (IBD) and depression/anxiety. Emerging evidences indicate that the liver may be involved in microbiota-gut-brain axis. This experiment focused on the role of melatonin in regulating the gut microbiota and explores its mechanism on dextran sulphate sodium- (DSS-) induced neuroinflammation and liver injury. Long-term DSS-treatment increased lipopolysaccharide (LPS), proinflammation cytokines IL-1β and TNF-α, and gut leak in rats, breaking blood-brain barrier and overactivated astrocytes and microglia. Ultimately, the rats showed depression-like behavior, including reduction of sucrose preference and central time in open field test and elevation of immobility time in a forced swimming test. Oral administration with melatonin alleviated neuroinflammation and depression-like behaviors. However, melatonin supplementation did not decrease the level of LPS but increase short-chain fatty acid (SCFA) production to protect DSS-induced neuroinflammation. Additionally, western blotting analysis suggested that signaling pathways farnesoid X receptor-fibroblast growth factor 15 (FXR-FGF 15) in gut and apoptosis signal-regulating kinase 1 (ASK1) in the liver overactivated in DSS-treated rats, indicating liver metabolic disorder. Supplementation with melatonin markedly inhibited the activation of these two signaling pathways and its downstream p38. As for the gut microbiota, we found that immune response- and SCFA production-related microbiota, like Lactobacillus and Clostridium significantly increased, while bile salt hydrolase activity-related microbiota, like Streptococcus and Enterococcus, significantly decreased after melatonin supplementation. These altered microbiota were consistent with the alleviation of neuroinflammation and metabolic disorder. Taken together, our findings suggest melatonin contributes to reshape gut microbiota and improves inflammatory processes in the hippocampus (HPC) and metabolic disorders in the liver of DSS rats.

Figure 1

Behavior tests after rats were treated with DSS and melatonin. (a) The development of depression induced by DSS. (b) Results of sucrose preference test. (c) Results of open field test. (d) Results of forced swimming test. (e–g) Representative motion tracks for the CON group, the DSS group, and the MT group. Data represent the mean ± SEM. ^∗p < 0.05; ^∗∗p < 0.01. CON = 7; DSS = 5; MT = 6.

Figure 2

Melatonin altered gut microbiota structure in DSS rats. (a, b) Chao1 index analysis. (c, d) Shannon index analysis. (e, f) PCA and PCoA plot analysis. Data represent the mean ± SEM. ^∗p < 0.05; ^∗∗p < 0.01. CON = 7; DSS = 5; MT = 6.

Figure 3

Melatonin improved gut microbiota in DSS rats. (a–d) Microbiota compositions in phylum level. (e–h) Microbiota compositions in family level. (i–m) Microbiota compositions in genera level. (n, o) SCFAs change when rats were treated with DSS and melatonin. Data represent the mean ± SEM. ^∗p < 0.05; ^∗∗p < 0.05. CON = 7; DSS = 5; MT = 6.

Figure 4

Melatonin-induced attenuation of hippocampal neuroinflammation in DSS rats. (a–c) Micrographs depict labeling of GFAP (green) and Iba-1 (red) in rat hippocampal slices. Nuclear staining was performed with DAPI (blue). (d) The number of cells expressing GFAP, a marker of astrocyte activation. (e) The number of cells expressing Iba1, a marker of microglia activation. (f) Hippocampal IL-1β levels of rats measured with ELISA. (g) Hippocampal zonulin levels of rats measured with ELISA. Data represent the mean ± SEM. ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001. CON = 7; DSS = 5; MT = 6.

Figure 5

Melatonin altered intestinal morphology and promoted the gut leak in DSS rats. (a) Melatonin influenced intestinal morphology. (b) The histology score of DSS and MT rats. (c) Melatonin had no significant effect to prevent LPS production in the plasma. (d–f) Effects of melatonin in regulating zonulin, IL-1β, and TNF-α in the colon. Data represent the mean ± SEM. ^∗p < 0.05; ^∗∗p < 0.01. CON = 7; DSS = 5; MT = 6.

Figure 6

Inhibition of melatonin on FXR-FGF15 and ASK1 signaling pathways in DSS rats. (a) Melatonin inhibited FXR-FGF15 signaling pathways. (b) Total ASK1, phospho-ASK1, total p38, and phospho-p38 protein levels in liver tissue were determined using immunoblotting. (c) HE staining and histology analysis of liver tissue in DSS and melatonin treatment. Data represent the mean ± SEM. ^∗p < 0.05, ^∗∗p < 0.01, and ^∗∗∗p < 0.001. CON = 7; DSS = 5; MT = 6.