Piperine, as a TAS2R14 agonist, stimulates secretion of glucagon-like peptide-1 in human enteroendocrine cell line Caco-2

Piperine is reported to ameliorate common metabolic diseases, however, the molecular mechanism is still unclear. In the present study, we examined whether piperine could stimulate glucagon-like peptide-1 (GLP-1) secretion in a human enteroendocrine cell line Caco-2, and explored the potential mechanisms from activation of human bitter taste receptors (TAS2Rs). It was found that TAS2R14 was highly expressed in Caco-2 cells, far more than TAS2R4 and TAS2R10. Piperine and flufenamic acid (FA, a known TAS2R14 agonist) markedly increased intracellular calcium mobilization and significantly enhanced GLP-1 secretion, accompanied by elevated proglucagon mRNA in Caco-2 cells compared with control. Moreover, piperine and FA activated TAS2R14 signaling as evidenced by the increased mRNA and protein levels of TAS2R14, and the protein expression of its downstream key molecules including phospholipase C β2 (PLCβ2) and transient receptor potential channel melastatin 5 (TRPM5). On the other hand, a G protein βγ submit inhibitor Gallein or a PLC inhibitor U73122 alleviated piperine-stimulated GLP-1 secretion in Caco-2 cells. At the meantime, a flavanone hesperetin significantly attenuated piperine and FA induced intracellular calcium mobilization and GLP-1 secretion. Further, TAS2R14 knockdown reversed piperine-triggered up-regulation of PLCβ2 and TRPM5 as well as increase in GLP-1 secretion in Caco-2 cells by using TAS2R14 shRNA transfection. In summary, our findings demonstrated that piperine promoted GLP-1 secretion from enteroendocrine cells through activation of TAS2R14 signaling. Moreover, TAS2R14 was likely a target of piperine in alleviation of metabolic diseases.