The bile acid membrane receptor TGR5: a valuable metabolic target

Bile acids (BAs) are amphipathic molecules that facilitate the uptake of lipids, and their levels fluctuate in the intestines as well as in the circulation depending on food intake. Besides their role in dietary lipid absorption, BAs function as signaling molecules that activate specific BA receptors and trigger downstream signaling cascades. The BA receptors and the signaling pathways they control are not only important in the regulation of BA synthesis and their metabolism, but they also regulate glucose homeostasis, lipid metabolism and energy expenditure - processes relevant in the context of the metabolic syndrome. In addition to the function of the nuclear receptor FXRα in regulating local effects of BAs in the organs of the enterohepatic axis, increasing evidence points to a crucial role of the G-protein-coupled receptor TGR5 in mediating systemic actions of BAs. Here we review the current knowledge on BA receptors, with a strong focus on the cell membrane receptor TGR5, which has emerged as a promising target for intervention in metabolic diseases.