Conjugated Bile Acids Activate the Sphingosine–1–Phosphate Receptor 2 in Primary Rodent Hepatocytes

Abstract

Bile acids have been shown to be important regulatory molecules for cells in the liver and gastrointestinal tract. They can activate various cell signaling pathways including the extracellular regulated kinase (ERK)1/2 and AKT as well as the G-protein coupled receptor (GPCR), TGR5/M-BAR. Activation of the ERK1/2 and AKT signaling pathways by conjugated bile acids has been reported to be pertussis toxin (PTX) and dominant negative Gαi sensitive in primary rodent hepatocytes. However, the GPCRs responsible for activation of these pathways have not been identified. Screening GPCRs in the lipid activated phylogenetic family, expressed in HEK293 cells, identified sphingosine 1-phosphate receptor 2 (S1P2) as being activated by taurocholate (TCA). TCA, taurodeoxycholic acid (TDCA), tauroursodeoxycholic acid (TUDCA), glycocholic acid (GCA), glycodeoxycholic acid (GDCA), and S1P-induced activation of ERK1/2 and AKT were significantly inhibited by JTE-013, a S1P2 antagonist, in primary rat hepatocytes. JTE-013 significantly inhibited hepatic ERK1/2 and AKT activation as well as short heterodimeric partner (SHP) mRNA induction by TCA in the chronic bile fistula rat. Knock down of the expression of S1P2 by a recombinant lentivirus encoding S1P2 shRNA, markedly inhibited the activation of ERK1/2 and AKT by TCA and S1P in rat primary hepatocytes. Primary hepatocytes prepared from S1P2 knock out (S1P2−/−) mice were significantly blunted in the activation of the ERK1/2 and AKT pathways by TCA. Structural modeling of the S1P receptors indicated that only S1P2 can accommodate TCA binding. In summary, all these data support the hypothesis that conjugated bile acids activate the ERK1/2 and AKT signaling pathways primarily via S1P2 in primary rodent hepatocytes.

Consequences of bile salt biotransformations by intestinal bacteria

“…86 Both nuclear receptors and GPCRs have varying affinities for different bile acids (Table 1). In this regard, by altering the bile acid pol composition, gut bacteria have the potential to alter cellular metabolism and host physiology and metabolism of cells exposed to bile acids.…”

The roles of bile acids and sphingosine-1-phosphate signaling in the hepatobiliary diseases

“…In addition, bile acids regulate energy metabolism by activating specific nuclear receptors and G protein-coupled receptors (GPCRs) in cells of the liver and gastrointestinal tract. Those receptors include the farnesoid X receptor (FXR) (3)(4)(5), as well as other nuclear receptors (pregnane X receptor, vitamin D receptor), and GPCRs, such as TGR5 (also known as GPBAR1), muscarinic receptors 2 and 3, and sphingosine-1-phosphate receptor (S1PR)2 (6)(7)(8). Bile acids also activate cellular signaling pathways, such as c-Jun N-terminal kinase 1/2 (JNK1/2) (9).…”

“…On the other hand, secondary conjugated bile acids stimulate S1PR2 in the intestine. *These bile acids were shown to stimulate S1PR2 previously (8). GCA, glycocholic acid; GCDCA, glycochenodeoxycholic acid; TCDCA, taurochenodeoxycholic acid; GDCA, glycodeoxycholic acid; TDCA, taurodeoxycholic acid; GLCA, glycolithocholic acid; TLCA, taurolithocholic acid; GUDCA, glycoursodeoxycholic acid, TUDCA, tauroursodeoxycholic acid.…”

“…Conjugated bile acids have been demonstrated to activate ERK1/2 and AKT in a manner sensitive to pertussis toxin and dominant-negative Gi, thereby implicating GPCRs in this signaling pathway (8,41). Activation of the AKT pathway by conjugated bile acids was shown to activate glycogen synthase activity in vitro and in vivo in a Gi-dependent manner (10).…”

Intestinal transport and metabolism of bile acids

“…However, bile acids also act through other receptors including muscarinic receptors, the sphingosine-1-phosphate receptor 2, ␣ 5, ␤ 1-integrin, through signal transduction pathways such as those mediated by Jun Nterminal kinase (JNK), ERK, and Akt ( 3,(6)(7)(8), and through posttranslational interactions with proteins ( 9 ). Signaling via these diverse pathways is regulated in part by the local concentration and chemical structure of the bile acid species, which in turn is controlled by hepatic synthesis, host and microbial metabolism, and the enterohepatic circulation.…”