Effects of taurochenodeoxycholic acid on Ca²⁺/CaM signalling mediated by the TGR5 signalling pathway

Taurochenodeoxycholic acid (TCDCA), a natural bioactive substance in animal bile, has anti-inflammatory and immunoregulatory effects. This study evaluates the effects of TCDCA on calcium/calmodulin (Ca2+/CaM) signalling mediated by G Protein Coupled Bile Acid Receptor 1 (TGR5) to provide preliminary information on the mechanism of TCDCA in immune regulation and also to benefit future research. After treatment of NR8383 and high TGR5 expression cell (TGR5-NR8383) with TCDCA (10-6 mol/L, 10-5 mol/L, and 10-4 mol/L) for 1 h, we measured TGR5 and CaM gene and protein levels by quantitative reverse transcription-polymerase chain reaction (qPCR) and western blotting, respectively. The inositol triphosphate (IP3) concentration was measured by Enzyme-linked Immunosorbent Assay (ELISA), and the Ca2+ concentration was measured by calcium fluorescent probe (Fluo-3 AM). The present study showed that the expression levels of IP3, Ca2+, and CaM in NR8383 cells were increased by TCDCA at concentrations ranging from 10-6 mol/L to 10-4 mol/L. TCDCA (10-4 mol/L) increased both the gene and protein expression of IP3and CaM through TGR5. TCDCA (10-4 mol/L or 10-5 mol/L) also increased the Ca2+ concentration via the TGR5 receptor. Our data suggest TCDCA activates Ca2+/CaM signalling via the TGR5 signalling pathway.