Gut feelings: Does AKR1D1 deletion affects intestinal bile acid composition and gastrointestinal health?
Anastasia Arvaniti, Oxford Brookes University
Gut-liver axis dysregulation is central component of metabolic disease. Bile acids (BA) are synthesised in liver and released into intestine to aid lipid absorption. BA homeostasis is disrupted in non-alcoholic fatty liver disease (NAFLD). Disruption of BA synthesis can be predicted to alter intestinal BA profile, leading to impaired gastrointestinal health via three mechanisms; increased cytotoxic BAs, gut dysbiosis and loss of cytoprotective actions of Farnesoid-X-receptor (FXR). However, a direct link between altered BA synthesis and intestinal health is yet to be confirmed.
We have shown that AKR1D1, a key enzyme in BA synthesis, is downregulated in patients with NAFLD and hypothesised that resultant disruption of BA synthesis, is a key driver in NAFLD pathogenesis. To test this, we generated an AKR1D1-/- mouse. At 52-weeks, -/-mice had intestinal damage with increased antioxidative/apoptotic markers, increased permeability and hepatic inflammation. The effects were sexually dimorphic with females been more susceptible to gastrointestinal damage, and we predict they’re driven by altered intestinal BA profile.
With this grant, I’d like to outsource the profiling of cecal BAs. The data will be used to compare BA profile of female and male -/-mice, determine cytotoxicity of BA pool and define AKR1D1’s role to FXR-driven cytoprotective effects.
I was not able to visit our collaborator’s laboratory in Switzerland to carry out mass-spectrometry (LC-MS). This Covid support grant allowed me to outsource the profiling of the cecal BAs (Creative Proteomics). The data analysis confirmed our hypothesis that AKR1D1 plays an important role in intestinal BA levels and composition. Our data revealed that total cecal BA levels were decreased following AKR1D1 deletion in both female and male animals. Composition of the BA pool was enriched with increased cytotoxic species in both sexes (e.g., lithocholic acid - LCA), but the hydrophobicity-cytotoxicity index remained in similar levels to those seen in wildtype animals. Sex dimorphic differences were observed in several BA species; as an example, levels of the primary BA chenodeoxycholic acid (CDCA) were increased in female-/-,but decreased in male-/- animals. Moreover, FXR affinity was decreased in both sexes, proposing that the observed intestinal damage is driven by the loss of the farnesoid-X-receptor- (FXR) mediated cytoprotective effects.
Grant awarded: £5,320