Bile acids regulate hepatic gluconeogenic genes and farnesoid X receptor via Gαi-protein-coupled receptors and the AKT pathway

Bile acids are important regulatory molecules that can activate specific nuclear receptors and cell signaling pathways in the liver and gastrointestinal tract. In the current study, the chronic bile fistula (CBF) rat model and primary rat hepatocytes (PRH) were used to study the regulation of gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase) and the gene encoding short heterodimeric partner (SHP) by taurocholate (TCA). The intestinal infusion of TCA into the CBF rat rapidly (1 h) activated the AKT (similar to 9-fold) and ERK1/2 (3- to 5-fold) signaling pathways, downregulated (similar to 50%, 30 min) the mRNA levels of PEPCK and G-6-Pase, and induced (14-fold in 3 h) SHP mRNA. TCA rapidly (similar to 50%, 1-2 h) downregulated PEPCK and G-6-Pase mRNA levels in PRH. The downregulation of these genes by TCA was blocked by pretreatment of PRH with pertussis toxin (PTX). In PRH, TCA plus insulin showed a significantly stronger inhibition of glucose secretion/synthesis from lactate and pyruvate than either alone. The induction of SHP mRNA in PRH was strongly blocked by inhibition of PI3 kinase or PKC zeta by specific chemical inhibitors or knockdown of PKC zeta by siRNA encoded by a recombinant lentivirus.jlr Activation of the insulin signaling pathway appears to be linked to the upregulation of farnesoid X receptor functional activity and SHP induction.-Cao, R., Z. X. Cronk, W. Zha, L. Sun, X. Wang, Y. Fang, E. Studer, H. Zhou, W. M. Pandak, P. Dent, G. Gil, and P. B. Hylemon. Bile acids regulate hepatic gluconeogenic genes and farnesoid X receptor via G alpha(i) protein coupled receptors and the AKT pathway. J. Lipid Res. 2010. 51: 2234-2244.