Aryl hydrocarbon receptor alleviates intestinal ischemia/reperfusion-induced epithelial barrier damage by inhibiting the 5-hydroxytryptamine-mediated complement C3 cascade.

Activation of the aryl hydrocarbon receptor (AhR) protects against intestinal epithelial barrier (IEB) dysfunction in multiple diseases, particularly during intestinal ischemia/reperfusion (II/R) injury. Studies have shown that AhR protects the epithelial barrier by regulating key functional molecules, however, the roles and mechanisms of AhR in intestinal epithelial cells (IECs) that maintain the IEB remain unclear. In this study, we found that Indole-3-carbinol (I3C) activated AhR, significantly ameliorating II/R-induced IEB damage and inflammatory responses. However, specific knockout of AhR in IECs significantly exacerbated II/R-induced histopathological damage, IEB disruption, and inflammatory response. Mechanistically, AhR deletion disrupted tryptophan metabolism, resulting in aberrant 5-hydroxytryptamine (5-HT) accumulation and hyperactivation of the complement C3 cascad, as evidenced by upregulation of C3, complement component 3a (C3a), and the C3a receptor (C3ar). In addition, pharmacological blockade of C3 activation with SB290157 trifluoroacetate (TFA), substantially reduced II/R-induced intestinal injury, reversed the loss of TJ proteins and maintained the IEB structure. More importantly, 5-HT significantly activated the NF-κB pathway, while co-treatment with an NF-κB inhibitor markedly reduced the expression of C3. These results suggest that AhR indirectly regulates the C3 cascade via the 5-HT/NF-κB axis. Taken together, this study reveals a regulatory mechanism of complement C3 in IECs, demonstrating that AhR signaling indirectly suppresses the C3 cascade via the 5-HT-NF-κB axis, thereby alleviating II/R-induced IEB damage and inflammation. Therapeutic interventions targeting the AhR-5-HT-NF-κB/C3 axis may offer novel therapeutic approaches for IEB injury.