Bile Acid Signaling in Inflammatory Bowel Diseases

Area of Science:

• Microbiology
• Immunology
• Gastroenterology

Background:

• Bile acids are steroids synthesized by the host liver (primary) and metabolized by gut microbes (secondary).
• These molecules act as signaling agents, interacting with bile acid-activated receptors throughout the gastrointestinal tract.
• These receptors mediate communication between the gut microbiota and the host immune system.

Purpose of the Study:

• To review how bile acids and their receptors mediate host-microbiota-immune system communication.
• To discuss alterations in bile acid metabolism during inflammatory bowel diseases (IBD).
• To explore therapeutic strategies targeting bile acid signaling for IBD treatment.

Main Methods:

• Review of existing literature on bile acid metabolism, signaling pathways, and immune interactions.
• Analysis of studies on gene-ablated mice to understand receptor functions (FXR, GPBAR1, RORγt).
• Consideration of gene-wide association studies and functional characterizations in IBD.

Main Results:

• Bile acid receptors (FXR, GPBAR1, RORγt) are crucial for maintaining intestinal immune tolerance.
• FXR and GPBAR1 are essential for a tolerogenic gut phenotype; their absence promotes inflammation.
• Oxo-bile acids inhibit RORγt, constraining pro-inflammatory Th17 cell responses.

Conclusions:

• Impaired bile acid signaling is implicated in the development of inflammatory bowel diseases (IBD).
• Targeting bile acid signaling pathways presents a potential therapeutic avenue for managing IBD.