Figure 3.

Gut microbiota metabolites modulation of intestinal barrier. Intestinal barrier consists of microbial barrier, chemical barrier, physical barrier, and immune barrier. SCFAs can enhance the chemical barrier by stimulating the secretion of antimicrobial peptides, sIgA and mucins to prevent harmful bacteria. SCFAs, bile acids, and indole derivatives can enhance physical barrier via increasing tight junction proteins such as cludins, occluden-1, and occludin. The epithelial cross of SCFAs and indole derivatives can act on immune cells and lead to release of anti-inflammatory cytokines such as IL-10 and IL-22. During chronic diseases, disturbance of tights junctions can lead to destruction of physical barrier, and further lead to translocation of LPS and bacteria. This translocation triggers the activation of immune cells and lead to production of pro-inflammatory cytokines. The release of pro-inflammatory cytokines can act on local epithelial cells to worsen physical barrier or can act on extraintestinal organs to trigger other diseases.