Gut microbiota-derived tryptophan metabolite indole-3-carboxaldehyde enhances intestinal barrier function via AhR/AMPK signaling activation.

Objective: Intestinal inflammatory diseases significantly impair animal health, primarily due to compromised intestinal barrier function. Indole-3-carboxaldehyde (IAld), a key gut microbiota-derived tryptophan metabolite, exhibits protective effects against intestinal inflammatory diseases. However, the regulatory mechanism by which IAld modulates intestinal barrier function requires further investigation.

Methods: We established an intestinal epithelial cell injury model by tumor necrosis factor-alpha (TNF-α) stimulation and a mouse colitis model induced by dextran sulfate sodium (DSS) administration. Intestinal barrier function was assessed by immunoblotting, immunofluorescence, in vitro permeability assays, and histopathological analysis. Mitochondrial integrity and function were evaluated via JC-1 staining and transmission electron microscopy (TEM). Additionally, key components of the AhR/AMPK signaling pathway were analyzed via immunoblotting, immunofluorescence, and immunoprecipitation techniques.

Results: Our findings demonstrate that IAld treatment significantly enhanced tight junction (TJ) protein expression in intestinal epithelial cells and effectively attenuated TNF-α-induced intestinal barrier injury. Mechanistically, IAld activated cellular AMP-activated protein kinase (AMPK) signaling, thereby promoting autophagy, maintaining mitochondrial homeostasis, and ultimately improving intestinal barrier function. Importantly, the activation of AMPK signaling by IAld was found to be dependent on the aryl hydrocarbon receptor (AhR), as evidenced by the fact that the AhR-specific inhibitor CH-223191 abolished both IAld-induced AMPK activation and intestinal barrier integrity up-regulation. Furthermore, in vivo experiments confirmed that IAld ameliorated intestinal barrier dysfunction and mitochondrial damage in DSS-induced colitis mice, whereas pharmacological inhibition of AMPK largely abrogated these protective effects.

Conclusion: Our findings demonstrate that IAld effectively preserves intestinal barrier integrity, highlighting its potential for treating intestinal inflammatory diseases in animals or humans.