Antagonistic TGR5 and FXR Signaling Shapes STAT1-Dependent Interferon Responses in Intestinal Epithelial Cells

Bile acids function not only as digestive metabolites but also as signaling molecules that influence mucosal immunity. However, how the bile acid receptors Takeda G-protein-coupled receptor 5 (TGR5; also known as GPBAR1) and farnesoid X receptor (FXR) coordinate intestinal epithelial interferon (IFN) responses remains incompletely understood. Here, we investigated the impact of TGR5 and FXR on IFN signaling in porcine IPEC-J2 and murine MODE-K intestinal epithelial cells. Pharmacological activation of TGR5 with INT-777 induced type I and type III IFNs together with multiple interferon-stimulated genes (ISGs), among which IFNλ3 and ISG15 showed the most prominent responses. Mechanistically, TGR5 enhanced STAT1 phosphorylation and nuclear accumulation, and both STAT1 silencing and pharmacological blockade of STAT1 phosphorylation attenuated TGR5-driven IFNλ3 and ISG15 expression. Inhibition of adenylate cyclase or protein kinase A further placed a cAMP-PKA-STAT1 axis downstream of TGR5. By contrast, activation of FXR with GW4064 suppressed poly(I:C)-induced IFNλ3 and ISG15 transcription and antagonized TGR5-mediated STAT1 activation and downstream gene expression. Confocal imaging further suggested that FXR restrains STAT1 nuclear trafficking through cytoplasmic colocalization with STAT1. Collectively, our findings identify a bile acid receptor rheostat in which TGR5 amplifies, whereas FXR dampens, epithelial IFN signaling through STAT1. This work provides a mechanistic framework for understanding how bile acid sensing may tune antiviral readiness at the intestinal mucosa.