Mechanistic insights into the detection of free fatty and bile acids by ileal glucagon-like peptide-1 secreting cells

Abstract : Objectives: The aim of this study was to investigate the electrical properties of ileal Glucagon-like peptide 1 (GLP-1) secreting L-cells using murine organoid cultures and the electrophysiological and intracellular signaling pathways recruited following activation of the G aq-coupled free fatty acid receptors FFA1 and G as-coupled bile acid receptors GPBAR1. Methods: Experiments were performed using ileal organoids generated from mice transgenically expressing fluorescent reporters (Epac2camps and GCaMP3) under control of the proglucagon promoter. Electrophysiology and single cell imaging were performed on identified L-cells in organoids, and GLP-1 secretion from cultured organoids was measured by immunoassay. Results: The FFA1 ligand TAK-875 triggered L-cell electrical activity, increased intracellular calcium, and activated a depolarizing current that was blocked by the TRPC3 inhibitor Pyr3. TAK-875 triggered GLP-1 secretion was Pyr3 sensitive, suggesting that the TRPC3 channel links FFA1 activation to calcium elevation and GLP-1 release in L-cells. GPBAR1 agonist triggered PKA-dependent L-type Ca 2þ current activation and action potential firing in L-cells. The combination of TAK-875 and a GPBAR1 agonist triggered synergistic calcium elevation and GLP-1 secretory responses. Conclusions: FFA1 and GPBAR1 activation individually increased electrical activity in L-cells by recruiting pathways that include activation of TRPC3 and L-type voltage-gated Ca 2þ channels. Synergy between the pathways activated downstream of these receptors was observed both at the level of Ca 2þ elevation and GLP-1 secretion.