Ablation of liver Fxr results in an increased colonic mucus barrier in mice

Noortje Ijssennagger; Kristel S van Rooijen; Stefanía Magnúsdóttir; José M Ramos Pittol; Ellen C L Willemsen; Marcel R de Zoete; Matthijs J D Baars; Paul B Stege; Carolina Colliva; Roberto Pellicciari; Sameh A Youssef; Alain de Bruin; Yvonne Vercoulen; Folkert Kuipers; Saskia W C van Mil

doi:10.1016/j.jhepr.2021.100344

Ablation of liver Fxr results in an increased colonic mucus barrier in mice

JHEP Rep. 2021 Aug 4;3(5):100344. doi: 10.1016/j.jhepr.2021.100344. eCollection 2021 Oct.

Authors

Noortje Ijssennagger¹, Kristel S van Rooijen¹, Stefanía Magnúsdóttir¹, José M Ramos Pittol^{1

2}, Ellen C L Willemsen¹, Marcel R de Zoete³, Matthijs J D Baars¹, Paul B Stege³, Carolina Colliva⁴, Roberto Pellicciari⁴, Sameh A Youssef⁵, Alain de Bruin^{6

7}, Yvonne Vercoulen¹, Folkert Kuipers⁶, Saskia W C van Mil¹

Affiliations

¹ Department of Molecular Cancer Research, Center for Molecular Medicine, University Medical Center Utrecht, Utrecht, The Netherlands.
² Institute of Biochemistry, University of Innsbruck, Innsbruck, Austria.
³ Department of Medical Microbiology, University Medical Center Utrecht, Utrecht, The Netherlands.
⁴ TES Pharma S.r.l., Perugia, Italy.
⁵ Non-Clinical Safety, Department of Pathology, Janssen Pharmaceutica Research and Development, Beerse, Belgium.
⁶ Departments of Pediatrics and Laboratory Medicine, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands.
⁷ Department of Biomolecular Health Sciences, Faculty of Veterinary Medicine, Utrecht University, Utrecht, the Netherlands.

Abstract

Background & aims: The interorgan crosstalk between the liver and the intestine has been the focus of intense research. Key in this crosstalk are bile acids, which are secreted from the liver into the intestine, interact with the microbiome, and upon absorption reach back to the liver. The bile acid-activated farnesoid X receptor (Fxr) is involved in the gut-to-liver axis. However, liver-to-gut communication and the roles of bile acids and Fxr remain elusive. Herein, we aim to get a better understanding of Fxr-mediated liver-to-gut communication, particularly in colon functioning.

Methods: Fxr floxed/floxed mice were crossed with cre-expressing mice to yield Fxr ablation in the intestine (Fxr-intKO), liver (Fxr-livKO), or total body (Fxr-totKO). The effects on colonic gene expression (RNA sequencing), the microbiome (16S sequencing), and mucus barrier function by ex vivo imaging were analysed.

Results: Despite relatively small changes in biliary bile acid concentration and composition, more genes were differentially expressed in the colons of Fxr-livKO mice than in those of Fxr-intKO and Fxr-totKO mice (3272, 731, and 1824, respectively). The colons of Fxr-livKO showed increased expression of antimicrobial genes, Toll-like receptors, inflammasome-related genes and genes belonging to the 'Mucin-type O-glycan biosynthesis' pathway. Fxr-livKO mice have a microbiome profile favourable for the protective capacity of the mucus barrier. The thickness of the inner sterile mucus layer was increased and colitis symptoms reduced in Fxr-livKO mice.

Conclusions: Targeting of FXR is at the forefront in the battle against metabolic diseases. We show that ablation of Fxr in the liver greatly impacts colonic gene expression and increased the colonic mucus barrier. Increasing the mucus barrier is of utmost importance to battle intestinal diseases such as inflammatory bowel disease, and we show that this might be done by antagonising FXR in the liver.

Lay summary: This study shows that the communication of the liver to the intestine is crucial for intestinal health. Bile acids are key players in this liver-to-gut communication, and when Fxr, the master regulator of bile acid homoeostasis, is ablated in the liver, colonic gene expression is largely affected, and the protective capacity of the mucus barrier is increased.

Keywords: BAs, bile acids; Colon; DSS, dextran sodium sulfate; FITC, fluorescein isothiocyanate; Farnesoid X receptor; Fgfr4, fibroblast growth factor receptor 4; Fxr, farnesoid X receptor; Fxr-intKO, intestine-specific Fxr knockout; Fxr-livKO, liver-specific Fxr knockout; Fxr-totKO, whole body Fxr knockout; GO, Gene Ontology; Gut microbiome; HID, high-iron diamine; IBD, inflammatory bowel disease; Intestine-specific Fxr-KO mouse; KEGG, Kyoto Encyclopedia of Genes and Genomes; Liver-specific Fxr-KO mouse; Liver–gut axis; Mucus layer; RT qPCR, real-time quantitative PCR; fpkm, fragments per kilobase of transcript per million mapped reads.