Follow your gut: Does AKR1D1 impact gastrointestinal health?

Dysfunction of the gut-liver axis contributes to non-alcoholic fatty liver disease (NAFLD) pathogenesis and progression. Bile acid homeostasis is disrupted in NAFLD, and this has been suggested to increase cytotoxic bile acids species in the intestine, disrupt cytoprotective intestinal bile acid signalling and drive gut dysbiosis, impairing intestinal barrier function and inducing hepatic inflammation. We have previously shown that expression of the bile acid synthesis enzyme 5β-reductase (AKR1D1) is decreased in patients with NAFLD. In this thesis, I have examined the impact of AKR1D1 deletion on intestinal barrier function and hepatic inflammation in mice. Female and male wild type (WT) and AKR1D1 knockout (KO) mice were maintained on a control diet until 12 months of age. Suggesting increased bacterial translocation, liver bacterial load was increased in AKR1D1 KO mice. Toll-like receptor 4 (TLR4) signalling was upregulated in the female mice, as was the pan-macrophage marker, F4/80, at mRNA and protein level. Suggestive of impaired barrier function, intestinal morphology of the AKR1D1 KO mice was modified, key ileal and colonic tight junction mRNA and protein levels were altered, goblet cell number and mRNA levels of key antimicrobial peptides were reduced. To examine the mechanisms that underpin these changes, caecal bile acid levels were examined. AKR1D1 KO mice had reduced total bile acid levels and altered bile acid composition, with decreased hydrophobicity and reduced farnesoid X receptor (FXR) affinity. Accordingly, RNAseq analysis revealed a decrease in the mRNA levels of key antioxidant and FXR target genes in the ileum. Although caecal microbiome analysis showed no change in total phylum bacterial counts and key markers of dysbiosis (ratio of Firmicutes to Bacteroidetes and species diversity), bacterial composition was altered suggesting that microbiota could play a role in the intestinal barrier dysfunction. To examine the role of AKR1D1 in NAFLD, AKR1D1 KO mice were challenged for 12 months with a NAFLD inducing diet (American lifestyle-induced obesity syndrome (ALIOS)). Although the ALIOS diet impaired intestinal barrier function and activated hepatic TLR4 signalling in WT mice, the deletion of AKR1D1 did not worsen the effects. In summary, AKR1D1 deletion and disruption of bile acid synthesis impairs intestinal barrier function and drives hepatic inflammation in female mice by reducing intestinal FXR signalling in the ileum and altering caecal microbiome composition. This is the first study that demonstrates the impact of disrupting bile acid synthesis on gastrointestinal health.

Grantor dc:publisher

Oxford Brookes University

Year dc:date

2021

Author dc:creator

• Arvaniti, Anastasia

Contributors dc:contributor

• Gathercole, Laura
• Tomlinson, Jeremy
• Nikolaou, Nikolaos

Statement dc:rights

• All rights reserved

Language dc:language

en

DOI dc:identifier

https://doi.org/10.24384/qkd0-8m59

OAI identifier oai:identifier

tle:7bf69063-db45-4c72-a3a7-083bf13d683d:d6bd9758-527a-46cd-bfe2-c433766e8fca:1