ABSTRACT
Objective:To evaluate the relationship between intestinal microbiota heterogeneity and acquired myasthenia in septic mice.Methods:Eighty SPF healthy male C57BL/6 mice, weighing 18-20 g, aged 6-8 weeks, were included. Forty mice were selected to prepare a sepsis model by intraperitoneal injection of lipopolysaccharide (LPS) 10 mg/kg. Sepsis-sensitive mice (state of dying or even death within 24 h after developing the model) and sepsis-resistant mice (survival for 7 days and recovery) were screened. The feces from donor mice were collected to make fecal bacteria fluid. Forty mice were selected and divided into 4 groups ( n=10 each) by the random number table method: control group (C group), antibiotic group (ABX group), resistant group (Res group), and sensitive group (Sen group). Group C received no treatment. In ABX group, compound antibiotics were given by intragastric gavage once a day for 5 consecutive days. In Res group, the fecal solution from sepsis-resistant mice 150 μl was given by gavage once a day for 3 consecutive days starting from 5 days after gavage administration of compound antibiotics, and then LPS 15 mg/kg was intraperitoneally injected. In Sen group, the fecal solution from sepsis-sensitive mice was given by gavage for 3 days (using the same method as previously described in Res group) starting from 5 days after gavage administration of compound antibiotics, and then LPS 15 mg/kg was intraperitoneally injected. The severity of sepsis was assessed and scored at 24 h after developing the model. The four limb grip strength was measured after fecal bacteria transplantation and at 24 h after developing the sepsis model. The Compound Muscle Action Potential (CMAP) of the gastrocnemius was measured at 24 h after developing the sepsis model. Then blood samples were collected for determination of the levels of interleukin-1 (IL-1), IL-6 and tumor necrosis factor α (TNF-α) in serum by enzyme-linked immunosorbent assay. The tissues of anterior tibial muscle and gastrocnemius muscle were obtained for determination of the expression of muscle-specific ring finger protein 1 (MuRF-1) and muscle atrophy box F protein (MAFbx) by Western blot. The diameter and cross-sectional area of gastrocnemius muscle fibers were measured after HE staining. The feces of mice were collected at 3 days after fecal bacteria transplantation, and DNA was extracted from mouse fecal samples for 16S rDNA sequencing and untargeted metabolomics analysis. Results:Compared with C group, the score for severity of sepsis was significantly increased, the four limb grip strength was decreased after developing the sepsis model, the serum IL-6 concentration was increased, and the diameter and cross-sectional area of gastnemius muscle fibers were decreased ( P<0.05), and no statistically significant changes were found in the other parameters in Res group, and no statistically significant changes were found in the indexes mentioned above in ABX group ( P>0.05). Compared with C group and Res group, the score for severity of sepsis was significantly increased, the four limb grip strength was decreased, the latency of CMAP was prolonged, and the amplitude of CMAP was decreased, the serum concentrations of IL-1, IL-6 and TNF-α were increased, the diameter and cross-sectional area of gastrocnemius muscle fibers were decreased, and the expression of MuRF-1 and MAFbx in anterior tibial muscle was up-regulated after developing the sepsis model in Sen group ( P<0.05). 16S rDNA sequencing of intestinal flora: Compared with Sen group, no significant change was found in Chao1 index, Good-coverage index and Simpson index in Res group ( P>0.05), Shannon index was increased ( P<0.05), and no significant change was found in β diversity in Res group ( P>0.05). LDA analysis showed that f_Akkermarisiaceae, o_Verrucomicrobiales, g_Akmansia, c_Verrucomicrobiae and p_Verrucomicrobiota were significantly enriched in Sen group, and g_Enterococcus and f_Enterococcaceae were significantly enriched in Res group ( P<0.05). Nontargeted metabolic analysis: The metabolite profiles in Res group and Sen group suggested that the model was well developed (R2Y>Q2Y). Compared with Sen group, 90 metabolites was significantly up-regulated and 88 down-regulated, significantly up-regulated metabolic substances including vitamin K1, gamma-tocopherol, and taurine in Res group ( P<0.05). The differential metabolite KEGG enrichment pathway included 2-oxocarboxylic acid metabolism and ubiquinone and other terpenoid-quinone biosynthesis ( P<0.05). Conclusions:Intestinal flora heterogeneity may be involved in the pathogenesis of acquired myasthenia in septic mice.