Abstract Background Bile acids (BAs) were suggested to have immunomodulatory properties that could influence inflammatory pathways in Inflammatory Bowel Disease (IBD). Dysregulated BA metabolism has been observed in IBD patients, further presented in our study by an analysis of IBD patients BA profiles with association to gene expression and targeted treatment of organoid models to elucidate the specific mechanisms by which BAs may affect intestinal inflammation in IBD. Methods Small intestinal organoids were grown from WT mice and an IBD mouse model with caspase-8 KO in intestinal epithelial cells (IEC). Organoids treated with primary (1°) and secondary (2°) BAs (CDCA, LCA, DCA) and BA + JAK-inhibitor (CDCA + inhibitor) were analysed thoroughly by bulk-RNA sequencing to investigate effects of BA and possible strategies to ameliorate negative effects. BA composition of serum samples from healthy controls (HC) (n=25) and IBD patients (n= 85) was quantified using LC-MS/MS and compared to bulk-RNA sequencing results of the same individuals in order to identify correlations of BA abundancy and gene expression. Results In WT organoids, CDCA treatment induced a significant upregulation of numerous genes associated with key cellular processes such as immunological, cell death but also mitochondrial. In contrast, in genetically-predisposed IBD organoids predominantly displayed gene downregulation in response to CDCA, indicating a divergent transcriptional response between WT and KO genotypes. In IBD organoids, JAK inhibition in conjunction with CDCA significantly altered the expression profile, reversing the expression of several genes that were downregulated by CDCA alone. This reversal was gene-specific and suggests a compensatory or modulatory effect of JAK inhibition on CDCA signalling in a caspase-8 deficient background. Notably, this combinatorial effect was not observed in WT organoids, where CDCA + JAK inhibitor treatment did not substantially alter gene expression compared to CDCA alone. Targeted metabolomic analysis of patient serum samples revealed two distinct bile acid profiles within the IBD cohort. In one subgroup, serum was characterized by elevated levels of the 1°BA CDCA coupled with lower concentrations of both primary and conjugated 2°BAs. In contrast, a second subgroup displayed lower CDCA levels alongside increased concentrations of secondary bile acids. These bile acid composition patterns suggest differing metabolic states within the patient cohort. Conclusion Our findings reveal significant links between BA composition, gene expression, and JAK pathway modulation, offering new insights into BA–driven gene regulatory mechanisms in both murine organoids and an IBD patient cohort. References TRR241 IBDome Consortium, TRR 241 Research Initiative, Berlin-Erlangen, Germany
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