Introduction
Bile acids serve as essential signaling molecules that regulate metabolic pathways, immune responses, and cellular proliferation through receptors such as TGR5 and S1PR2 (1). Notably, TGR5 deficiency exacerbates liver injury, while S1PR2 knockdown offers hepatoprotection (2,3).
Aims & Methods
This study examines the receptor-specific roles and interactions between TGR5 and S1PR2 in regulating cholangiocyte function under physiological and injury-related conditions. Intrahepatic biliary organoids were generated from murine liver tissue through microdissection and enzymatic dissociation, followed by morphological and phenotypic characterization. To enhance accessibility to apically expressed receptors, apical-out organoids (AOOs) were established under matrigel-free conditions using ultra-low attachment culture systems. Organoids were derived from wild-type, TGR5-knockout (TGR5⁻/⁻), S1PR2-knockout (S1PR2⁻/⁻), double-knockout (TGR5⁻/⁻S1PR2⁻/⁻), and S1PR2⁻/⁻ mice overexpressing TGR5 (S1PR2⁻/⁻/TGR5-tg). Organoids were stimulated for 6 hours with bile acids and receptor-specific agonists. Total RNA was subsequently extracted and processed for bulk RNA sequencing to evaluate global transcriptomic responses.
Results
Transcriptomic profiling revealed distinct gene expression patterns among knockout conditions compared to wild-type controls under non-stimulated conditions. Major histocompatibility complex class I (MHC-I) genes were significantly downregulated in TGR5⁻/⁻ organoids across multiple comparisons (TGR5⁻/⁻ vs. WT and double-knockout vs. WT), with consistent reductions in H2-Q1, H2-Q6, H2-Q10, H2-T5, H2-T7, and H2-T15 expression.
Conclusion
These transcriptomic findings suggest a potential immunomodulatory role for TGR5 in the regulation of MHC-I gene expression in biliary epithelial cells under basal conditions. The consistent downregulation of MHC-I–related transcripts in TGR5-deficient organoids may indicate a role for this receptor in maintaining antigen presentation capacity in cholangiocytes. While these observations point toward a possible link between bile acid signaling and hepatic immune regulation, further validation is needed to confirm the functional consequences of altered MHC-I expression and to elucidate the underlying mechanisms.
References
1. Keitel V, Stindt J, Häussinger D. Bile Acid-Activated Receptors: GPBAR1 (TGR5) and Other G Protein-Coupled Receptors. In: Fiorucci S, Distrutti E, editors. Bile Acids and Their Receptors. Cham: Springer International Publishing; 2019. p. 19-49.
2. Reich M, Deutschmann K, Sommerfeld A, Klindt C, Kluge S, Kubitz R, et al. TGR5 is essential for bile acid-dependent cholangiocyte proliferation in vivo and in vitro. Gut. 2016;65(3):487-501.
3. Wang Y, Aoki H, Yang J, Peng K, Liu R, Li X, et al. The role of sphingosine 1-phosphate receptor 2 in bile-acid-induced cholangiocyte proliferation and cholestasis-induced liver injury in mice. Hepatology. 2017;65(6):2005-18.
