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- Title
The Bile Acid Sensor FXR Is Required for Immune-Regulatory Activities of TLR-9 in Intestinal Inflammation.
- Authors
Renga, Barbara; Mencarelli, Andrea; Cipriani, Sabrina; D'Amore, Claudio; Carino, Adriana; Bruno, Angela; Francisci, Daniela; Zampella, Angela; Distrutti, Eleonora; Fiorucci, Stefano
- Abstract
Background: Toll like receptors (TLRs) sense the intestinal microbiota and regulate the innate immune response. A dysregulation of TLRs function participates into intestinal inflammation. Farnesoid X Receptor (FXR) is a nuclear receptor and bile acid sensor highly expressed in entero-hepatic tissues. FXR regulates lipid metabolism and innate immunity. Methodology/Principal Findings: In this study we have investigated whether FXR gene expression/function in the intestine is modulated by TLRs. We found that in human monocytes activation of membrane TLRs (i.e. TLR2, 4, 5 and 6) downregulates, while activation of intracellular TLRs (i.e. TLR3, 7, 8 and 9) upregulates the expression of FXR and its target gene SHP, small heterodimer partner. This effect was TLR9-dependent and TNFa independent. Intestinal inflammation induced in mice by TNBS downregulates the intestinal expression of FXR in a TLR9-dependent manner. Protection against TNBS colitis by CpG, a TLR-9 ligand, was lost in FXR-/- mice. In contrast, activation of FXR rescued TLR9-/- and MyD88-/- mice from colitis. A putative IRF7 response element was detected in the FXR promoter and its functional characterization revealed that IRF7 is recruited on the FXR promoter under TLR9 stimulation. Conclusions/Significance: Intestinal expression of FXR is selectively modulated by TLR9. In addition to its role in regulating type-I interferons and innate antiviral immunity, IRF-7 a TLR9-dependent factor, regulates the expression of FXR, linking microbiota-sensing receptors to host's immune and metabolic signaling.
- Subjects
TOLL-like receptors; NATURAL immunity; IMMUNE response; BILE acids; GENE expression; ANTIVIRAL agents
- Publication
PLoS ONE, 2013, Vol 8, Issue 1, p1
- ISSN
1932-6203
- Publication type
Article
- DOI
10.1371/journal.pone.0054472