Bile acid - "intestinal" city guard

Figure 1: The regulatory role of bile acids in the physical barrier of animal intestinal tract

The villus length, crypt depth, and tight junctions between intestinal epithelial cells are important indicators reflecting the integrity of the intestinal physical barrier. Bile acids can increase villus length and decrease crypt depth to promote normal proliferation of intestinal cells and protect the intestinal mucosa from damage or infection. At the same time, they regulate the tight junctions between intestinal epithelial cells by modulating the key enzyme - myosin light chain kinase (MLCK), thereby maintaining the integrity of the physical barrier

The growth performance and intestinal health of animals are closely related to their intestinal morphology, structure, and physical barrier integrity (Figure 1). The height of villi, depth of crypts, and their ratio are important indicators of intestinal digestion and absorption function and health status. Supplementing with BAs in the diet can increase the villus height and villus ratio of intestinal cells in animals such as piglets and mice, to protect the intestinal mucosa from damage or infection and maintain intestinal health. The BAs binding receptor FXR not only promotes normal proliferation of intestinal cells, but also inhibits abnormal development of the intestine, playing an important role in the formation and maintenance of the intestinal mucosal barrier. For example, activation of FXR can increase the height of duodenal villi in mice, expand the absorption area of the small intestine, and enhance intestinal digestion function.

The tight junctions between cells composed of ZO-1, Claudins, and Occludin proteins are the structural basis for the intestinal physical barrier to effectively block the entry of bacteria, viruses, and endotoxins. They directly act on intestinal epithelial cells and control the molecular permeability between cells. There is a close relationship between bile acids and intestinal permeability. Treatment of intestinal epithelial cells with super physiological concentrations of DCA and CDCA showed that epidermal growth factor receptor (EGFR) mediated signaling leads to downstream serine threonine dephosphorylation, dissociation of Occludin-ZO1 complex, and enhanced intestinal permeability in the cytoplasmic tail of Occludin. After administration of EGFR inhibitors, changes in intestinal permeability were reversed, indicating that bile acids can regulate tight junctions between intestinal epithelial cells through the EGFR signaling pathway, thereby affecting intestinal homeostasis. Stone bile acid also improves intestinal physical barrier integrity and promotes animal intestinal health by alleviating the decrease in ZO-1, Occludin, and Claudin-1 protein expression and distribution induced by tumor necrosis factor - α. Myosin light chain kinase (MLCK) is a key enzyme in the expression of tight junction proteins. DCA can activate MLCK to increase the expression of tight junction proteins. At the same time, taurodeoxycholic acid can reverse the decrease of tight junction proteins ZO-1 and Claudins induced by lipopolysaccharide (LPS) through the FXR/GPBAR1-MLCK pathway, improving the damage to the intestinal epithelial barrier. Certain plant extracts such as curcumin can reverse LPS induced downregulation of ZO-1 and Occludin transcription expression and alleviate acute mucosal inflammation by altering the chicken microbiome and regulating bile acid metabolism, thereby maintaining intestinal health. Early weaning of piglets can lead to intestinal mucosal atrophy and intestinal dysfunction. Exogenous supplementation of chenodeoxycholic acid can enhance the expression of genes involved in distal small intestinal mucosal protection and barrier function, such as ZO-1, promoting intestinal health in piglets. In addition, supplementing CDCA in the diet of weaned piglets can not only effectively increase the villus height/crypt depth of the ileum and jejunum, but also promote the expression of tight junction proteins such as ZO-1 and Occludin in the jejunum, enhance intestinal digestion ability, and significantly improve the final weight and average daily weight gain of weaned piglets, greatly improving production performance.

In summary, BAs have potential protective effects on the intestinal mucosal barrier, thereby maintaining the health of animal intestines.

Original text: Wang Xinyi, Yao Junhu, Zhang Xia, etc Research progress on the role and mechanism of bile acids in regulating animal intestinal health [J/OL]. Journal of Animal Husbandry and Veterinary Medicine, 1-13 [March 5, 2025] http://kns.cnki.net/kcms/detail/11.1985.S.20250106.1724.004.html.

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