Latroeggtoxin-VI improves depression by regulating the composition and function of gut microbiota in a mouse model of depression

Abstract

Introduction. Depression has become one of the mental diseases that seriously affect human health. Its mechanism is very complex, and many factors influence the condition. An imbalance of the gut microbiota is being considered as a factor that impacts the occurrence and progression of depression. Future therapies may therefore tap into this connection, treating depression through manipulation of the gut microbiome.Hypothesis/Gap Statement. Latroeggtoxin-VI (LETX-VI), a proteinaceous neurotoxin from Latrodectus tredecimguttatus eggs, was previously demonstrated to inhibit excessive inflammation and improve depression behaviours, suggesting that it might be able to regulate the balance of gut microbiota. The aim of this study was to explore the effects of LPS and LETX-VI on depressive behaviours and gut microbiota and to analyse correlations between changes in the gut microbiota and depressive behaviours.Methodology. A murine model of depression was established, and the effects of LPS and LETX-VI treatment on depressive behaviours and gut microbiota were investigated.Results. In the murine model, depressive behaviour was induced by LPS; the ratio of Firmicutes to Bacteroidetes (F/B) and the number of pro-inflammatory bacteria in the gut microbiota increased (P<0.01), while butyric acid-producing bacteria with anti-inflammatory effect decreased (P<0.05). Furthermore, the metabolic function of the gut microbiota was disrupted, and the level of virulence factors among gut microbiota was up-regulated (P<0.05). Association analysis showed that the changes in the composition and function of gut microbiota were closely related to the depression phenotype of mice, suggesting that the abnormal function of gut microbiota is linked to depression. However, when LETX-VI was applied before LPS injection, the LPS-induced changes in the gut microbiota were alleviated, and the depressive behaviour greatly improved.Conclusion. LETX-VI can prevent depressive behaviour by regulating the composition and/or function of the gut microbiota.

Keywords: depression; depression mouse model; depressive behaviour; gut microbiota; latroeggtoxin-VI.

Fig. 1.. Preparation and identification of recombinant LETX-VI. (a) LETX-VI RP-HPLC separation results, the target peak marked by * in the figure. (b) MS identification of * labelled component in (a).

Fig. 2.. LETX-VI improves depressive behaviours and alleviates LPS-induced changes in body weight. (a) Behavioural test devices. (b) Effects of intraperitoneal injection of LPS and pretreatment with LETX-VI before LPS injection on the sucrose preference. (c) Effects of intraperitoneal injection of LPS and pretreatment with LETX-VI before LPS injection on the immobility times in TST. (d) Effects of intraperitoneal injection of LPS and pretreatment with LETX-VI before LPS injection on the immobility times in FST. (e) Effects of LPS and LETX-VI on the body weight of mice. LPS, LPS group; VI_LPS, LETX-VI-LPS group. *P<0.05, **P<0.01 and ***P<0.001.

Fig. 3.. Diversity analysis of the gut microbiota in mice. (a) Venn diagram analysis of intestinal identified gut microbiota. (b) Chao index analysis of the gut microbiotas. (c) Coverage index analysis of gut microbiotas. (d) Shannon index analysis of gut microbiota. (e) Simpson index analysis of gut microbiota. (f) PCA of gut microbiota. LPS, LPS group; VI_LPS, LETX-VI-LPS group.

Fig. 4.. Composition analysis of mouse gut microbiota. (a) Column diagram of phylum-level composition of mouse gut microbiota. (b) Column diagram of the composition of mouse gut microbiota at the genus level. (c) Firmicutes/Bacteroidetes ratio of mouse gut microbiota. LPS, LPS group; VI_LPS, LETX-VI-LPS group. **P<0.01.

Fig. 5.. Analysis of differential microbiotas in the gut of differently treated mice. (a) LEfSe analysis of gut microbiota in mice. (b) LDA distribution histogram of differential gut microbiota in mice. (c) Multi-group comparison of differential bacterial genera in mouse gut microbiota. LPS, LPS group; VI_LPS, LETX-VI-LPS group. *P<0.05, **P<0.01 and ***P<0.001.

Fig. 6.. Effects of LETX-VI and LPS on gut microbiota function in mice. (a) Heat map analysis of KEGG function of gut microbiota in mice. (b) LDA score histogram of the content of the enzymes for carbohydrate metabolism in the gut microbiota of mice. (c) Multi-group comparison of the content of differential enzymes for carbohydrate metabolism in mouse gut microbiota. LPS, LPS group; VI_LPS, LETX-VI-LPS group. *P<0.05, **P<0.01 and ***P<0.001.

Fig. 7.. Effects of LETX-VI and LPS on virulence factors of gut microbiota in mice. (a) Heat map analysis of the changes in different classifications of virulence factors of gut microbiota in mice after LETX-VI and LPS treatment. (b) Heat map analysis of differential virulence factors in the gut microbiota of mice after LETX-VI and LPS treatment. LPS, LPS group; VI_LPS, LETX-VI-LPS group.

Fig. 8.. Correlation analysis between the differential virulence factors and metabolism pathway disturbance of mouse gut microbiota and the depression phenotypes. (a) RDA of the effects of different groups of virulence factors on depression phenotypes. (b) RDA of the correlation of differential virulence factors with depression phenotypes. (c) RDA of the correlation of metabolism pathway disturbance with depression phenotypes. LPS, LPS group; VI_LPS, LETX-VI-LPS group.

Fig. 9.. Correlation analysis between differential species of gut microbiota and depression phenotypes in mice. (a) Heat map analysis of the association between top 50 differential genera and depression phenotypes. (b) RDA of differential phyla and depression phenotypes. (c) The two-factor correlation analysis of differential genera and depression phenotypes. (d) LETX-VI pretreatment weakened the adverse effects of LPS on some depression-related bacterium species. LPS, LPS group; VI_LPS, LETX-VI-LPS group.