Figure 6.

Gut microbiota-metabolite axis contributes to gut barrier dysfunction in squalene epoxidase (Sqle) transgenic (tg) mice and in germ-free mice receiving faecal microbiota transplantation (FMT) from Sqle tg mice. (A) Correlation analysis revealed that pathogenic bacteria are positively correlated with altered metabolites, including secondary bile acids. (B) Fluorescein isothiocyanate (FITC)-dextran intestinal permeability test was performed on Sqle tg mice and wild-type (WT) littermates at 3 months after tamoxifen injection, revealing that the gut barrier was impaired in Sqle tg mice. (C) Electron microscopy confirmed impaired intestinal tight junction in Sqle tg mice. (D) Western blot analysis showed that tight junction proteins Jam-c and occludin were downregulated in Sqle tg mice. (E) Muc2 messenger RNA (mRNA) was downregulated in Sqle tg mice. (F) Stool collected from Sqle tg and WT littermates was gavaged to germ-free mice aged 6 weeks. One month later, FITC-dextran was gavaged 4 hours before sacrifice to perform permeability assay. Intestinal permeability was significantly induced in germ-free mice gavaged with stool from Sqle tg mice. (G) Electron microscopy confirmed the impaired intestinal tight junction germ-free mice fed with stool from Sqle tg mice. (H) Western blot analysis showed that tight junction proteins Jam-c and occludin were downregulated in germ-free mice gavaged with stool from Sqle tg mice. (I) Germ-free mice transplanted with Sqle tg mice stool showed increased Ki-67 staining in the colon epithelium as compared with those gavaged with WT mice stool. Two-tailed Student’s t-test was used for the difference determination between two groups.