The gut microbiota regulates the depressive-type behaviors and inflammatory processes after severe burn injuries in mice

Abstract

An emerging number of studies have recently revealed the correlation between burn injuries and psychological disorders. Gut microbiota and inflammatory factors may play a vital role in this process. Nevertheless, there are few studies conducted to disclose the potential mechanism of the gut microbiota between depression and burn injuries. In this study, we constructed a burn model of C57BL/6 mice, which showed that the symptom of depression became more and more severe with the burn of mice lasted longer. Meanwhile, there are significant differences of composition of gut microbiota among mice before and after burn. Then, we tested the inflammatory factors in the brain and peripheral blood, which showed an increased expression of Iba1, VWF, TNF-α and IL-6, and a decreased expression of IL-10 in burn mice. In addition, the expression of zonula occludens-1 (ZO-1) in cecum showed a down-regulation in burn mice, which indicated impaired intestinal barrier function. Lastly, the crossing fecal microbiota transplantation (FMT) and cohousing experiment were conducted to determine the functions of cross-transplantation of fecal microbiota on the depressive-type behaviours in burned mice. According to the score of Tail suspension test (TST), the burn mice were divided into two groups: Resilient mice (no-depressed mice) and Abnormal mice (depressed mice). After abnormal mice were transplanted with fecal microbiota of resilient mice, the symptom of depression was improved, and the expression of TNF-α, IL-6 and IL-10 return to normal levels (P < 0.05). On the contrary, after resilient mice were transplanted with fecal microbiota of abnormal mice both the TST scores and inflammatory factor developed depressive-type changes. In conclusion, our study demonstrated the changes of gut microbiota and inflammatory factors in depressed burn mice and non-depressed burn mice. The gut microbiota dysbiosis could impaired intestinal barrier function and lead to neuroinflammation, and this phenomenon could be significantly mitigated by FMT.

Keywords: Burn injuries; Depressive-type behaviors; Gut microbiota; Inflammatory factors.

Fig. 1

Study flowchart.

Fig. 2

The diversity of between mice in D0 (before burn, n = 8) and D7 (after burn, n2 = 8). A&B&C shows the difference of α diversity between mice in D0 and D7 based on chao1 index, observed otus and Shannon index. D PCoA analysis based on Bray–Curtis distance between mice in D0 and D7 (P = 0.001). E NMDS analysis based on Bray–Curtis distance between mice in D0 and D7 (Stress = 0.05). F PCA analysis based on Bray–Curtis distance between mice in D0 and D7 (P = 0.001). G&H Unweighted and Weighted UniFrac UPGMA analysis between mice in D0 and D7. I Anosim analysis based on Bray–Curtis distance between mice in D0 and D7 (*** means P < 0.001).

Fig. 3

A&B the relative abundance at Phylum and Genus between mice in D0 (n = 8) and D7 (n = 8). C&D the LEfSe analysis between mice in D0 and D7. The LDA score >4 was chose as the selection criteria.

Fig. 4

The α_diversity (A&B), β_diversity (C&D), relative abundance at Phylum and Genus (E&F) and LEfSe analysis (G&H) between Abnormal mice (n = 9) and Resilient mice (n = 9). D7_Resilient means the normal mice in D7 after burn, D7_Abnormal means the depressed mice in D7 after burn.

Fig. 5

The expression of Iba1, VWF and ZO-1 between Resilient mice (n = 9) and Abnormal mice (n = 9). A the Iba1 and VWF were tested in Hippocampus tissue (brain), and the ZO-1 was tested in cecum tissue. B the quantitative analysis of immunohistochemistry in Iba1, VWF and ZO-1 (* means P < 0.05).

Fig. 6

A the results of TST and OFT between control group (n = 12) and burn mice (n = 12) in D0, D1, D7 and D14 (comparison by t-test). B&C the TST scores of Resilient mice (n = 6) and Abnormal mice (n = 6) after cross FMT. D&E the TST scores of Resilient mice and Abnormal mice after cross Cohousing. (D7: the 7th day after burn; F7: the 7th day after FMT or Cohousing).

Fig. 7

The difference of Serum inflammatory factor TNF-α (A), IL-10 (B) and IL-6 (C) of control group (n = 12), Resilient mice (n = 6) and Abnormal mice (n = 6) between D7 and F7 (*: P < 0.05; **: P < 0.01; ***: P < 0.001; Compasion by Kruskal-Wallis test).